Download - Minesite Water Management Handbook
Minesite Water Management
Handbook
1997
Copyright © 1997 Minerals Council of Australia
Inquiries should be addressed to the publishers. Minerals Council of Australia PO Box 363, Dickson ACT 2602 Telephone: 61 262793600 Facsimile: 61 262793699 Email: [email protected]
First Edition 1997
Minesite Water Management Handbook
ISBN 0 909276 73 0
In 2008 the first edition was transcribed into electronic format, without consideration of the accuracy or currency of the content. Users should note that in some areas of the book, more recent publications (post 1997) provide updated technical information.
Every effort has been made to contact the copyright holders of material used in this book. However, where an omission has occurred, the publisher will gladly include acknowledgment in any future editions.
Disclaimer This Minesite Water Management Handbook (the Handbook) has been prepared by the Minerals Council of Australia in the interests of encouraging excellence in environmental management. However, the Minerals Council of Australia accepts no liability (including liability in negligence) and takes no responsibility for any loss or damage which a user of the Handbook or any third party may suffer or incur as a result of reliance on the Handbook and in particular for:
(a) any errors or omissions in the Handbook;
(b) any inaccuracy in the information and data on which the Handbook is based or which is contained in the Handbook;
(c) any interpretations or opinions stated in, or which may be inferred from, the Handbook.
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1. Introduction 8
2. Statutory Requirements 9
3. Planning and Principles 11
3.1 INTRODUCTION 11
3.2 THE HYDROLOGIC CYCLE AND MINESITE WATER BALANCE 11
3.3 SITE DESCRIPTION 12
3.3.1 Climate 123.3.2 Geology and Geomorphology 123.3.3 Topography 123.3.4 Catchment Characteristics 123.3.5 Site Water Requirements 123.3.6 Vegetation and Fauna Assessment 123.3.7 Aquatic Ecology 133.3.8 Heritage Values 133.3.9 Downstream and Offsite Users 133.3.10 Monitoring 13
3.4 SITE PLAN 13
3.5 MONITORING AND DATA MANAGEMENT 14
4. Water Chemistry 15
4.1 CHEMISTRY OF NATURAL WATERS 15
4.1.1 Introduction 154.1.2 Dissolved Versus Particulate and Total Constituents 154.1.3 Difference Between Organic Acid and Carbonate Water Systems 164.1.4 Load Versus Concentration 174.1.5 pH 184.1.6 Alkalinity 194.1.7 Hardness 194.1.8 Conductivity 204.1.9 Salinity 204.1.10 Solids 214.1.11 Turbidity 234.1.12 Oxygen Demand (Dissolved Oxygen, BOD and COD) 23
Contents
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C O N T E N T S
4.1.13 Anions and Cations 244.1.14 Metals (Trace Metals, Heavy Metals, Metal Speciation) 254.1.15 Nutrients 254.1.16 Oils, Greases and Hydrocarbons 264.1.17 Organics, Natural Organic Matter, Dissolved Organic Carbon 264.1.18 Colour 274.1.19 Cyanide 274.1.20 Odour and Taste 284.1.21 Radionuclides 29
4.2 BIOLOGICAL ASPECTS OF WATERS 30
4.2.1 Micro-organisms 304.2.2 Algal Blooms 314.2.3 Toxicity and Ecosystem Health 314.2.4 Factors Influencing Bioavailability and Toxicity of Contaminants 324.2.5 Bio-monitors, Bio-accumulation and Bio-amplification 32
4.3 NATURE OF WATERS 33
4.3.1 Beneficial Use 334.3.2 Assimilative Capacity 334.3.3 Receiving Waters 33
5. Water Sampling and Flow Measurement 34
5.1 INTRODUCTION 34
5.2 PRINCIPLES AND PURPOSE OF MONITORING 34
5.3 COMPLIANCE MONITORING 35
5.3.1 Ambient, Point Source and Non-point Source pollution 365.3.2 Mixing Zones 36
5.4 DATA COLLECTION - QUALITY 36
5.4.1 Monitoring Design 365.4.2 Identification of Key Monitoring Parameters 375.4.3 Initial Screening Program 375.4.4 Sampling Locations 375.4.5 Sampling Frequency 375.4.6 Sampling Techniques and Design 385.4.7 Sample Transportation 395.4.8 Sample Analysis 395.4.9 Data Management 405.4.10 Laboratory, Pilot Plant and Leach Tests 40
5.5 DATA COLLECTION - QUANTITY 40
5.5.1 Rainfall Reading 415.5.2 Flow Recording 41
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C O N T E N T S
5.6 GROUNDWATER 42
5.6.1 Groundwater Mapping 425.6.2 Testing and Monitoring 435.6.3 Groundwater Parameters 465.6.4 Prediction of Groundwater Characteristics and Responses 46
5.7 REVIEW OF MONITORING DATA 46
6. Water Supply 48
6.1 SURFACE WATER 48
6.1.1 Catchment Yield 486.1.2 Recycling of Water 49
6.2 GROUNDWATER 49
6.2.1 Sources of Supply 496.2.2 Security of Supply 49
7. Exploration 53
7.1 SURFACE WATER 53
7.1.1 Surface Water Data Collection 537.1.2 Access Tracks 547.1.3 Exploration Sites 54
8. Open Cut Mines 56
8.1 SURFACE WATER RUNOFF 56
8.1.1 Flood Mitigation 568.1.2 Methods of Flood Mitigation 578.1.3 In-Pit Drainage 598.1.4 Interception Drainage Around Pit 608.1.5 Sediment Containment 61
8.2 GROUNDWATER 62
8.2.1 Groundwater Inflow 638.2.2 Managing Groundwater Inflow 63
8.3 WATER QUALITY 65
8.3.1 Pit Water Disposal 658.3.2 Acid Drainage 658.3.3 Salinity 66
8.4 PIT CLOSURE 66
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C O N T E N T S
9. Underground Mines 68
9.1 SURFACE DRAINAGE AWAY FROM HEAD WORKS 68
9.2 GROUNDWATER INFLOW 68
9.2.1 Managing Groundwater Inflow 68
9.3 WATER QUALITY 69
9.3.1 Treatment and Disposal of Underground Mine Water 69
10. Heap Leach Processes 70
10.1 INTRODUCTION 70
10.2 PLANNING FOR HEAP LEACHING 70
10.2.1 Baseline Evaluation 7010.2.2 Rainfall Events, Acceptable Risk, Contingency Planning 7010.2.3 Baseline Groundwater Monitoring 7110.2.4 Closure Planning 71
10.3 SOLUTION CONTROL DURING OPERATIONS 72
10.3.1 Maintenance of Drain and Pond Capacity 7210.3.2 Integrity of the Pad or Liner 7210.3.3 Integrity of Piping and Valves 72
10.4 WATER MANAGEMENT ON CLOSURE 72
10.4.1 Criteria for Long-term Leachate Quality 7210.4.2 Residues and Long-term Contaminated Site Management 72
11. Waste Dumps 73
11.1 WASTE DUMP CONSTRUCTION FOR WATER MANAGEMENT 73
11.2 SURFACE WATER 73
11.2.1 Location of Waste Dumps 7311.2.2 Erosion on Waste Dumps 7311.2.3 Interception Drainage Around Waste Dumps 7411.2.4 Sediment Containment Around Waste Dumps 75
11.3 GROUNDWATER 75
11.3.1 Infiltration to Groundwater 7511.3.2 Monitoring 76
11.4 WATER QUALITY 76
11.4.1 Acid Drainage 7711.4.2 Salinity 7711.4.3 Suspended Solids 7811.4.4 Leachate and Other Constituents 78
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C O N T E N T S
12. Tailings Water Management 79
12.1 DISPOSAL METHODS 79
12.2 CHARACTERISTICS AND MANAGEMENT OF TAILINGS WATER 80
12.2.1 Nature of the Water 8012.2.2 Management 80
12.3 SEEPAGE MANAGEMENT 80
12.3.1 Seepage Control 8012.3.2 Monitoring 8112.3.3 Water Control 81
13. Mine Infrastructure 82
13.1 PROCESS PLANT 82
13.1.1 Characteristics 8213.1.2 Containment and Treatment Technologies 82
13.2 INDUSTRIAL AND WORKSHOP AREAS 83
13.2.1 Containment and Treatment Technologies 83
13.3 HAUL ROADS 84
13.3.1 Environmental Issues 8413.3.2 Surface Water Drainage 8413.3.3 Groundwater Drainage 84
References 86
Glossary 88
List of Tables
Table 2.1: Typical State and Commonwealth Legislation 9
Table 4.1: Typical Conductivity Range of Waters 20
Table 5.1: Key Planning Steps for Water Monitoring 35
Table 5.2: Selection Criteria for Establishing Sampling Sites 38
Table 5.3: Advantages and Disadvantages of Using Numerical Models 47
Table 6.1: Sources and Uses of Recycled Water 50
Table 10.1: Suggested Minimum Design Event Criteria for Heap Leach Operations 71
Table 11.1: Prevention and Remedial Strategies for Acid Drainage 78
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C O N T E N T S
List of Figures
Figure 4.1: Species of the Carbonate System as a Function of pH 17
Figure 5.1: Typical Groundwater Surface Map 42
Figure 5.2: Relationship Between Piezometric Level and Groundwater 43
Figure 5.3: Typical Piezometer Installation 44
Figure 5.4: Diagram of a Piezometer Dip Meter 45
Figure 8.1: Calculating the Lowest Cost Flood Mitigation Scheme 57
Figure 8.2: Types of Constructed Embankments 58
Figure 8.3: Conceptual Drainage Around an Open Pit 60
Figure 8.4: Idealised Pit Inflow 62
Figure 8.5: Effects of Barriers to Groundwater Flow 63
Figure 8.6: Effects of Dewatering Around a Pit 64
Figure 8.7: Channel Dewatering 64
Figure 8.8: Water Flows in Open Voids 67
Figure 11.1: The Soil Capillary Zone 75
Figure 11.2: Monitoring Network Around a Waste Rock Dump 76
Figure 12.1: Seepage Paths from a Tailings Storage Facility 81
Figure 13.1: Drainage Considerations on Haul Roads 85
Fact Sheets
Fact Sheet No. 1: Field Record Data Sheets 93
Fact Sheet No. 2: Estimation of Surface Runoff 97
Fact Sheet No. 3: Understanding Event Probability 101
Fact Sheet No. 4: Open Channel Drains 103
Fact Sheet No. 5: Construction of Small Earth Embankment Dams 105
Fact Sheet No. 6: Culvert Crossings 110
Fact Sheet No. 7: Acid Drainage 112
Fact Sheet No. 8: Erosion Control and Sediment Containment 115
Fact Sheet No. 9: Bioremediation Technology 121
Fact Sheet No. 10: Hydrological Data for Design Purposes 122
Fact Sheet No. 11: Groundwater 124
Fact Sheet No. 12: Numerical Modelling 125
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Acknowledgments
The Minesite Water Management Handbook has undergone a considerable gestation period and many
individuals have assisted in its production. It is with much appreciation that the Minerals Council of
Australia acknowledges the contributions of these people, all experts in their individual fields, who
gave freely of their time: Raj Aseervatham, Denis Brooks, Michael Cox, Geoff Day, Tom Farrell, Kurt
Hammerschmid, Gavin Murray, Pamela Ruppin, Peter Roe, Ian Wood, and Ray Woods. The comments of
many other individuals on earlier drafts were invaluable in efforts to treat such a broad range of material
as fully and accurately as possible. The Minerals Council of Australia would also like to acknowledge
the companies and organisations for whom the individuals work. All input has been most valuable.
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1. Introduction
In the course of mining and mineral processing,
landscapes are altered and soils, rock and water
are subject to physical and chemical change. These
changes must be managed to ensure that any
resulting impacts are minimised, do not jeopardise
future land and water uses, and do not breach
any regulatory requirements. Failure to manage
these impacts in an acceptable manner will result
in the mining industry finding it increasingly
difficult to obtain community and government
support for existing and future projects.
The Minesite Water Management Handbook provides
practical guidance, based on scientific principles and
leading industry practice, on how to investigate and
manage surface and groundwater during exploration,
mining and mineral processing. The information
is sourced from industry, government(s) and
research organisations, consultants and individuals
actively participating in the minerals industry.
This handbook has been prepared as a companion
document to the AMIC (now the Minerals Council
of Australia) Rehabilitation Handbook (AMIC 1990).
The handbook has been developed for those who
are not familiar with the fundamentals, processes
and requirements (both technical and legislative)
of water management for mining purposes, and for
those site personnel with limited or no experience or
training in water management from an environmental
perspective. It also provides an indication of what
the minerals industry sees as its prime objectives and
directions with regard to water management.
The handbook is divided into 13 main chapters
which include both theoretical and practical
topics relating to mine water management. The
first five chapters provide an overview of the
regulatory requirements, management planning
and principles, basic water chemistry and the
principles of sampling and flow measurement.
Chapters 6 to l3 describe the major water-related
technical issues relevant to all areas of a mining
operation. They include generic guidelines for:
• thedesign,constructionandmaintenanceof
site surface water drainage;
• issuesassociatedwitherosionandsediment
control; and
• managementandmonitoringofsurfaceand
groundwater quality:
Specific topics, for example acid drainage, are
presented as fact sheets. Both theoretical and practical
aspects of each issue are discussed. A glossary of
terms is included and, finally, a reference list which
is designed to direct the reader to a greater level
of detail than is provided in this handbook.
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2. Statutory Requirements
Environmental management of mining and
mineral processing requires consideration of
both State and Commonwealth legislation,
although most minerals industry operations
are subject only to State environmental law.
Legislation relevant to water issues within the mining
industry is passed by both State and Commonwealth
governments. These laws are usually enforced by the
relevant State Environmental Protection Authority
or Department, State Department of Mines or the
Commonwealth Department of the
Environment.
Typical State and Commonwealth environmental
legislation relevant to water management in the
Australian minerals industry is shown in Table 2.1
This legislation is frequently supported by regulations
which provide more detail on how the legislation
is to be implemented and complied with. For
example, regulations under a Clean Waters Act may
contain limits for physical, chemical and biological
parameters which cannot be exceeded in effluents.
TABLE 2.1: Typical State and Commonwealth Legislation
State Legislation Commonwealth Legislation
• MiningAct • EnvironmentProtection(SeaDumping) Act1981• EnvironmentalProtectionAct
• LocalGovernmentAct • GreatBarrierReefMarineParkAct1975
• CleanWatersAct • Petroleum(SubmergedLands)Act1967
• GroundwaterAct • ProtectionoftheSea(PreventionofPollution fromShips)Act1983• PollutionofWatersbyOilAct
• EnvironmentalProtection/Marine (SeaDumping)Act
• SeasandSubmergedLandsAct1973
• NationalParksandWildlifeConservation Act1975• MarineandHarboursAct
• Petroleum(SubmergedLands)Act • EnvironmentProtection(AlligatorRivers Region)Act1978• CoastalProtectionAct
• SoilConservationAct • EnvironmentProtection(ImpactofProposals) Act1974• DangerousGoodsAct
• RadiationControlAct • IndustrialChemicals(Notificationand Assessment)Act1989
• WorldHeritagePropertiesConservation Act1983
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S TAT U T O RY R E Q U I R E M E N T S
Most operations involving water, either supply or
disposal, will be licensed under the relevant act.
Licences are issued for a defined period, typically
one year, and have conditions attached to them.
These conditions may specify the monitoring
which is required to ensure compliance, the
limits which apply, and specific procedures
which must be followed in order to reduce
the environmental impact of the discharge.
As a minimum, every operation should ensure
that its facility fully complies with the relevant
State and Commonwealth acts, laws, regulations
and licences. Therefore, systems need to be
established and maintained to track compliance
with these statutory requirements and to
report this compliance on a regular basis.
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3. Planning and Principles
3.1 Introduction
Water respects no boundaries, and drought and
floods are events beyond our direct control.
The industry’s role in water management
is one of stewardship, not ownership, and
therefore our operating philosophy should
be based on the following concepts:
• efficientuseofwater;
• implementationofthereduce,re-use,recycle
concepts;
• avoidorminimisecontaminationof
clean streams and catchments;
• recogniseandprotectdownstreambeneficial
uses (for both surface and groundwaters); and
• onrelinquishmentoftitle,thequantityand
quality of drainage from the site should not
prejudice the productive use of the land.
Implementing these concepts requires considerable
planning, based on a clear understanding of the
project and the hydrological, geochemical and
processing regimes in which it operates. This section
sets out the principles, while subsequent sections
will provide the tools to prepare a detailed water
management plan for a site.
3.2 The Hydrologic Cycle and Minesite Water Balance
The hydrologic cycle is the primary model for the
input and output water management elements in
any site development. These elements include:
rainfall;
surface runoff;
evaporation;
groundwater flow;
seepage;
site and process water uses;
site and process water outputs;
offsite discharges; and
on-site discharges.
Assigning values to the parameters of the
hydrological cycle will identify the water
surplus or deficit nature of the site. This
process is referred to as the water balance.
The minesite water balance is a central component in
the minesite water management system. Through the
water balance, we can gain a clearer understanding
of the principal water management issues of
supply, protection, containment and discharge.
The principal data required for a
water balance include:
• determiningtheappropriatetimestep for the
flow detail being assessed (hourly, daily, monthly
or yearly); and
• definingtheinputs, demands and outputs.
The results obtained from the water balance
present data that provide definable benefits
in developing the components and systems
for effective water management.
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P L A N N I N G A N D P R I N C I P L E S
Various tools are available for the water balance
including: spreadsheets for analysis; commercial
software such as AWBM and RORB for rainfall/
runoff analysis; and customised software to
suit the circumstances of a particular site.
3.3 Site Description
Basic information about a site is necessary so that
a workable water management strategy or plan
can be developed. Many of the components and
processes in this description are required for other
site assessment purposes. However, each topic
should be considered in terms of the information
needs required to address potential water
management issues at the site. Not all topics will
need to be researched intensively for every site.
3.3.1 CLIMATE
The essential climatic parameters are rainfall
and evaporation. To a lesser extent, temperature,
relative humidity, wind speed and direction and
solar radiation are also required. Prior to resource
development, daily records generally form the
basis of data collection systems. Because long-
term historical data are central to optimising
water management studies and design, the earliest
possible installation of real-time continuous data
recording equipment is advised when a nearby
weather station is not available. Once a project
is undergoing detailed feasibility studies, climate
monitoring systems which provide more frequent
and specially targeted records may be required.
3.3.2 GEOLOGY AND GEOMORPHOLOGY
The data compiled here will assist with an
understanding of the groundwater and surface water
movement characteristics and likely responses to
mine induced changes in flow or water quality.
3.3.3 TOPOGRAPHY
A site plan showing the geographic setting, contours
and the land systems at the site is required. The
contour intervals are dependent on the level of
investigation and the type of structures - the more
advanced the project the closer the contour intervals
and the greater the accuracy. Typical values are 0.5
to 1.0 m (+/- 0.25 to 0.5 m) intervals for detailed
design and 2.5 to 5.0 m (+/- 1 to 2 m) intervals
for preliminary investigations. More detailed
survey data may be required in particular cases.
3.3.4 CATCHMENT CHARACTERISTICS
A characterisation of the site for parameters relevant
to the surface and groundwater hydrology is
essential for the planning, design and operation of
site water management systems. Storm and volume
runoff coefficients, times of concentration for
peak runoff, storage parameters, erosion potential,
sedimentation characteristics and hydraulic
coefficients such as Manning’s “n” are relevant for
surface characterisation. Hydraulic conductivity and
permeability, sub-surface water zones and aquifers
and storage and yield characteristics are typically
required for an understanding of the groundwater
system. Monitoring systems are necessary to obtain
site-specific data and to confirm calculations.
3.3.5 SITE WATER REQUIREMENTS
It is important to understand what are the site
water demands and how they may vary with
time. A dynamic water balance is frequently a
great asset in establishing and maintaining a water
management program. Short-term benefits in
reducing water use and cost should not jeopardise
future opportunities for expansion of the operation.
3.3.6 VEGETATION AND FAUNA ASSESSMENT
The purpose of this assessment is to provide
a clearer understanding of the catchment
characteristics for rainfall runoff assessments, and
to highlight sensitivities to the implementation
of the various water management strategies.
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P L A N N I N G A N D P R I N C I P L E S
3.3.7 AQUATIC ECOLOGY
The impact of the various strategies must recognise
the type and diversity of species and relevant
conservation values. Opportunities to utilise natural
systems, eg. local wetland species in water treatment
schemes can be highlighted in this assessment.
3.3.8 HERITAGE VALUES
A comprehensive assessment, listing and plan of
archaeological, heritage, historical values and the
visual character at the site will enable proper planning
and locating of water management structures.
3.3.9 DOWNSTREAM AND OFFSITE USERS
Identification of the potential offsite impacts from
the changes to the existing water patterns is required.
The operator should assess the constraints, the
target quality and quantity parameters required and
where any benefits of the mine water management
systems might pass to downstream users.
3.3.10 MONITORING
Monitoring will be required during the various
phases of mine development: baseline, feasibility,
construction, operations, decommissioning and
active rehabilitation. The monitoring systems
must be established with a view to understanding
the catchment responses to the proposed site
activity and verifying licence requirements, and
for corroborating design data. Such systems need
consistency through all phases of the project.
3.4 Site Plan
Mine water management is a long-term
process which may be simplified by:
• planningfortheenergy-efficientstorage,
transport and use of water; and
• modellingtoquantifypresent
and future water budgets.
The thoroughness of the initial planning process will
determine the ease with, and extent to which future
changes to the water budget may be accommodated.
The planning process should consider:
• identifyingthelocationsofpotentialsources
and probable yields (including surface water
yields from rainfall and groundwater);
• identifyingthelocationsofpotentialusers
of water and their likely demands;
• sizingandpositioningofdamsandotherwater
control structures to cater for local demands;
• preventingdegradationofwater
quality by identifying and separating
“clean” and “dirty” streams;
• optimisingtheflexibilityofthewatersystem
by linking components in the water circuit
(using gravity drainage where possible);
• focusingexcesswatertodown-gradient
control dams of adequate size and at key
locations to control offsite discharges;
• implementingrecyclingschemestore-
use water wherever possible; and
• implementingmonitoringsystemsto
quantify water entering the circuit, moving
within the circuit and exiting the circuit.
Frameworks of water management systems derived
in this way may be used to assess the impact of
future changes in the water budget. This may be
achieved by modelling the response of the mine
water circuit to these changes commonly referred
to as the minesite water balance. Models may be
written using computer programming languages
or developed using conventional spreadsheets.
Models should include:
• flexibilitytoalterquantitiesof
source and demand water;
• flexibilitytoalterwatertransportrates;
• flexibilitytoalterdamsizes;
• flexibilitytoaddordeletewater
transport routes; and
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P L A N N I N G A N D P R I N C I P L E S
• ‘calibration’checksagainstmonitored
quantities where appropriate.
Planning and modelling of site water budgets
will allow any imbalances between water supply
and demand at the site to be quantified and
accommodated efficiently. The quality of water may
also need to be considered in such an analysis.
The site plan must also address the final land
use and the use of the water management
infrastructure for the site after mining is finished.
This will be a constant reference for ongoing
planning of the water management systems.
Where quantitative data are collected as part of the
site description they should be compiled and stored
on an appropriate water management database
for reliable reference and review. Where possible,
qualitative data arising from this compilation
should be stored on the same database.
3.5 Monitoring and Data Management
Within the resources industry, the basic
principles of water monitoring are to:
• identifythereceivingwatersornaturalresources
which require protection from the existing or
proposed mining and processing development;
• establishwaterqualityobjectives
for these resources;
• collectandevaluatesitespecificdatasuch
as local climatic conditions, permeability of
soil and underlying bedrock, any potential
pathways for the migration of contaminants;
• prepareandimplementamonitoringprogram
for the region prior to the commencement of
mining. Collect rainfall data, background flow
and water quality data for all surface waters
(especially up and downstream of the operation),
groundwater, estuarine and coastal waters that
may be affected by the development;
• ensurethatCommonwealth,Stateandlocal
statutory requirements are observed and
incorporated into the monitoring plan;
• ensurethatsufficientdataarecollectedover
time in order to enable accurate assessment
of the physical and chemical properties of
all point source, diffuse source, industrial
and domestic wastewater streams; and
• collectrepresentativesamplesofthemedium
being measured and an adequate number
of duplicate and quality control samples.
Data management forms an important part of the
monitoring system. The following points should be
considered when designing a monitoring system:
• samplesmustbecollectedaccordingtoa
site-specific protocol, established to fulfil
the objectives of the monitoring program;
• allsamplesshouldbeanalysedusing
NATA registered methods;
• alldatacollectedusingelectronicloggers
must be validated and calibrated against
physically measured data wherever possible;
• calibrationproceduresmustbeestablished
at the earliest possible stage in a monitoring
program and the calibration of equipment
should be checked periodically;
• allwaterquantityandqualitydatashouldbe
stored in a database designed specifically for
the site’s requirements; data should be able
to be retrieved rapidly and systematically;
• waterinformationshouldbereported
regularly to site management (ie. actually
used for management purposes); and
• datashouldberegularlyreviewedand
interpreted to ensure that the beneficial
uses (eg. ecological, recreational) of regional
watercourses are protected in accordance with
appropriate guidelines for receiving water
quality in the region (eg. ANZECC 1992).
Further information on the establishment of site
monitoring programs can be obtained in EPA (1995).
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4. Water Chemistry
4.1 Chemistry of Natural Waters
4.1.1 INTRODUCTION
Water quality is a generic term and is usually
determined by the levels of various indicator
substances. These indicators are generally selected
on the basis of the type of waterbody in question
(eg. stream, estuary, groundwater, potable water) and
the water use (eg. the quality of water required for
drinking is higher than that required for recreation).
Impacts on surface and groundwater water quality
can occur during exploration, construction and
operation of mines, as well as at abandoned and
rehabilitated minesites. Uncontrolled drainage
from mines can contribute potentially harmful
materials to local waterways and may degrade
the water’s suitability for domestic, agricultural
or industrial uses, or be harmful to the ecology
of the receiving environment. Government
authorities are placing tighter controls on site
discharges and many sites throughout Australia
now operate under a zero discharge policy.
It is important to understand the characteristics
associated with the various types of water sources
and discharges likely to be encountered.
While the quality of the source or discharge at
any given site is dependent on the geochemistry,
mineralogy and geographical location of the
operation, there are general characteristics
associated with the water that may be encountered
in Australia. This section includes a general
overview of some of the common physicochemical
parameters and includes for each:
• definitionandalternatenames;
• unitsinwhichtheparameteriscommonly
measured and reported;
• sources(whatactivitycancontributeto
the levels of these parameters); and
• environmentalsignificanceofthe
parameter being determined.
However, before discussing individual
physico-chemical parameters, several terms
and concepts common to most aquatic and
geochemical parameters will be introduced.
4.1.2 DISSOLVED VERSUS PARTICULATE AND
TOTAL CONSTITUENTS
Definition
The distinction between dissolved, particulate and
total constituents is one of the most important
definitions used in water quality assessment.
An element can move between the dissolved
and particulate phase depending on physico-
chemical conditions such as temperature, pH or
the presence of some other element or compound.
This is often referred to as “partitioning”. Discharge
licences generally relate levels of a certain element
to either the dissolved, particulate or total
concentration. The following example depicts
the relationship between the three phases.
Consider a one litre bottle of a water sample
collected for the analysis of cadmium. The sample
contains both dissolved and particulate forms of
cadmium. The dissolved cadmium concentration
is the cadmium in the sample after it has been
filtered through a 0.45µm pore size filter. The
particulate cadmium in the sample is what
remains bound to the material on the filter.
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Total concentration can be determined either
directly or by calculation from the dissolved and
particulate results. It is not simply a summation
of the two concentrations as the suspended solids
concentration has to be taken into account. For
example, the dissolved cadmium concentration
was found to be 3µg/L, the particulate
concentration of cadmium was determined as
250µg/g (or mg/kg), and the suspended sediment
concentration was 6540 mg/L (0.650 g/L).
Therefore the total cadmium concentration is:
0.650(g/L) x 250 (µg/g) + 3 (µg/L) =
154.5 µg total Cd/L.
Alternatively, the total cadmium concentration
may be measured directly by digesting
(using acid) and analysing a sub-sample
of the original one litre sample.
The definition of “dissolved” using a 0.45
µm filter is purely operational and has no
direct biological rationale. Precise definitions
may be found in APHA (1994).
The classifications of total, particulate and dissolved
concentration are used widely when setting discharge
permits and water quality criteria. Generally, dissolved
criteria are more often used for the protection of
aquatic ecosystems. This is because most toxicity
data show that it is the dissolved phase of pollutants
which is bioavailable to aquatic organisms and thus
potentially toxic. Total concentration criteria are
generally used for recreation, livestock and human
health water quality criteria, given that separation
of the particulate load prior to either swimming or
drinking raw water is unlikely to occur. In addition,
the acidic nature of the human gut means that
many pollutants can remobilise into the dissolved
phase and therefore become more bioavailable.
4.1.3 DIFFERENCE BETWEEN ORGANIC ACID
AND CARBONATE WATER SYSTEMS
The main aquatic geochemical processes throughout
most of Australia's inland fresh waters are dominated
by one of two general geochemical systems. In the
context of this handbook, these will be termed:
• carbonatewater(waterinwhichthecarbonic
acid equilibrium plays the dominant role
in governing water chemistry); and
• organicacidwater(waterwithnatural
high levels of dissolved organic matter).
Waters in which the primary control is the carbonic
acid system have pH values ranging from 6 to 8.5
and electrical conductivities up to many thousands
of mS/cm. Organic acid systems generally have a pH
less than 6 and much lower electrical conductivity.
Carbonate Waters
The carbonate, or carbonic acid, system describes
water in which carbonate species in solution control
or influence aquatic geochemical processes. The
principal components of the carbonate system include
carbon dioxide (CO2), carbonic acid (H2CO3),
bicarbonate (HCO3-) and carbonate (CO3
2-)The
reactions involving these species are very important in
surface waters, groundwaters and in the atmosphere.
Carbonic acid in water can be derived from several
sources, the most important of which are:
1. the weathering of carbonate rocks via:
CaCO3 Ca2+ + CO32-
CO32- + H+ HCO3
-
and
2. uptake of CO2 from the atmosphere via:
CO2 + H2O H2CO3
H2CO3 H+ + HCO3-
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The species of the carbonate system that is present
depends on the pH of the solution (see Figure 4.1).
Below pH 6.4, carbonic acid (H2CO
3) is the dominant
species in solution whereas above pH 6.4 bicarbonate
(HCO3-) is the dominant species. The greater the
total concentration of the carbonate species, ie.
HCO3- plus CO
32-, the greater the buffering capacity
of the water, ie. the greater the ability of the water
to resist change from either acidic or basic inputs.
The amount of carbonate produced from reaction
2 is far less important than that derived from the
weathering process of rocks. Generally, carbonate
system rivers have a higher conductivity, due not to
the presence of bicarbonate but rather the co-cations
in solutions which are also weathered as a part of
the same process that liberates the bicarbonate.
Organic Acid Waters
The particular organic acids which control the
second major system of aquatic geochemical
processes occurring in Australian freshwater rivers
and streams are derived from what is loosely
termed humic and fulvic material or dissolved
organic matter (DOM). DOM is derived from
the breakdown products of organic matter and
comprises a wide range of complex molecules.
Almost all surface partitioning and adsorption
processes involving natural sediments are mediated
to some degree by organic matter of this type. Rivers
draining regions where little or no carbonate is
present, and where bedrock is resistant to weathering,
tend to have a low pH and low conductivity. Soils
developed in these areas are frequently organic-rich
because the bedrock is resistant to breakdown and
therefore contributes little mineral to the soil. As
water percolates and circulates through the organic
rich soil, cations that are present in solution (Ca, Mg,
Na, K) are exchanged for H+ in the soil organic matter.
As the H+ accumulates in solution, the pH
decreases. As the pH decreases, organic
compounds are leached from the surface litter,
into solution. Organic acids are also synthesised
by soil organisms and excreted by plant roots.
These waters also originate from areas of high
rainfall where peat deposits are common,
eg. the western highlands of Tasmania.
4.1.4 LOAD VERSUS CONCENTRATION
In determining water quality, the distinction
between load and concentration must often be
made. Concentration of the element compound
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is emphasised in systems where a threshold or
regulatory level is desirable in the receiving water,
eg. maintaining total suspended solid values below
100 mg/L, or dissolved oxygen above 9.5 mg/L.
Concentration is usually expressed in terms of
mass per unit volume, ie. µg/L, mg/L, g/L or %.
There are other situations where total load or flux
(ie. the total amount - mass or volume - of substance
per unit time) may be of more concern, eg. nutrient
loading into lakes and rivers to avoid algal blooms
or the spread of nuisance weeds and phytoplankton.
Loadings are usually expressed in terms of mass per
unit time (g/day, tonnes/year), mass per unit area (kg/
ha), or mass per unit area per unit time (kg/ha/year).
4.1.5 pH
Definition and Alternative Names
pH is an indicator of the intensity of the acidic
or basic character of a solution (APHA 1994).
Units of Measurement
pH is a dimensionless parameter and is
represented on a logarithmic scale of 1 to
14. A pH value of 1 indicates a highly acidic
solution, 7 is neutral and 14 is strongly basic,
or alkaline. The technical definition is:
pH = -1/log10
[H3O+].
Sources and Environmental Significance
One of the greatest causes or contributors to the
production of acidic water is from sulphide oxidation
of iron sulphide minerals such as pyrite (FeS2) in the
presence of oxygen (air) and water. The oxidation
reactions are bacterially mediated, primarily by
Thiobacillus ferrooxidans. Acid generating conditions
can occur in damp mine workings, in exposed waste
rock dumps, tailings dams and in washeries. Fact
Sheet No.7 discusses acid drainage in greater detail.
As the water moves through the acidic material,
oxidation of reactive sulphides occurs, generating
acidity which initially can be neutralised by
alkalinity in the groundwater. If more acid is
generated than the initial alkalinity of the water,
the alkalinity will be consumed and acid water will
result. If sufficient oxygen is present, the amount
of acidity generated is determined by the amount
of reactive sulphides in the material. In the absence
of mining, acid waters are uncommon because
dissolved oxygen in the groundwater is insufficient
to produce acidity greater than the alkalinity of
the groundwater. During mining, gaseous oxygen
is introduced as the rock is broken up, and water
movement through the system is accelerated.
The bacteria that catalyse the acidity producing
reactions thrive only under acid conditions so that,
once acidity is initiated, acid production becomes
more rapid and the problem increases rapidly.
A phenomenon only recently identified in Australia
is natural acidification of water as a result of acid
sulphate soils. These waters have developed in tidal
swamps, wetlands and estuarine environments along
coastal regions where iron rich silts and muds have
mixed with accumulated organic matter. Bacteria
thrive in these anaerobic conditions, creating pyrite.
When these soils are exposed to air, as occurs with
disturbance due to coastal development, sulphuric
acid is produced due to oxidation of the pyrite.
Potential acid sulphate soils occur in most coastal
regions from north of Sydney to Onslow in Western
Australia. Any mining development which potentially
affects such soils could also result in acid drainage.
In most natural streams where acid drainage is
not present, pH levels range between 5.5 and 8.5.
Extremes to these levels are usually the results of
high loads of natural organic acids (DOM) or high
carbonate concentrations. Another effect of mixing
acid water with receiving waters high in carbonate
is the formation of CO2 which affects the respiration
of aquatic biota. When pH values fall below 4,
most aquatic biota will be severely stressed.
In contrast to the low pH water produced by acid
rock drainage, many mineral processing facilities
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require water with an elevated pH (9 to 11) which
is normally achieved through the addition of lime.
Problems of scaling in pipes and ecosystem stress
brought about by high pH waters are no less serious
than the problems associated with low pH waters.
Treatment Options
Several approaches can be adopted to
raise or lower pH including:
• additionofanalkalioracid;
• activatedcarbonorultra-violet
irradiation to remove DOM; and
• bubblingwithCO2 to manipulate
the carbonic acid equilibrium.
4.1.6 ALKALINITY
Definition and Alternative Names
Alkalinity refers to the acid neutralising capacity
(pH buffering) of water, ie. its ability to reduce
changes in pH brought about by the addition
of an acid. The higher the alkalinity, the more
acid is required to reduce the pH. Alkalinity is
generally due to the presence of inorganic anions
including carbonate (CO32-), bicarbonate (HCO
3- )
and hydroxide (OH-); however alkalinity may
also result from the presence of borates (B4O
72- ),
phosphates (P043-) and silicates (SiO
22-).
Units of Measurement
Alkalinity is expressed in the units of:
mg of calcium carbonate per litre
of water (mg CaCO3/L).
The reported results for alkalinity are influenced by
the method of the determination and depend on
the pH end-point used in the analysis. Analytical
methods are documented in APHA (1994).
Sources and Environmental Significance
The main sources of alkalinity are the soluble
salts of the anions listed in Section 4.1.13.
Alkalinity is known to influence several
aquatic geochemical processes including:
• pHandeffectsfromaciddrainage;
• dissolvedmetalsolubilityandbioavailability
(toxicity) to aquatic organisms;
• foaming,scalingandmetallurgicalproblems;and
• dissolutionofbicarbonateandcarbonate,
causing liberation of CO2 and corrosion.
4.1.7 HARDNESS
Definition and Alternative Names
Hardness is commonly associated with a waters ability to lather or foam soap. The harder the water the more difficult it is to lather the soap. The principal components of hard water are calcium and magnesium ions (Ca2+ and Mg2+).
Total hardness is defined as the numerical sum of the calcium and magnesium concentrations, expressed as calcium carbonate. When hardness is numerically greater than the sum of carbonate and bicarbonate alkalinity, that amount of hardness equivalent to the total alkalinity is called “carbonate hardness”; the amount of hardness in excess of this is called “non-carbonate hardness”. When hardness is numerically equal to or less than the sum of the carbonate and bicarbonate alkalinity, all hardness is carbonate hardness and non-carbonate hardness is normally absent.
Units of Measurement
Hardness is reported in the same units as alkalinity, ie. mg (CaCO
3)/L.
There are two methods for determining hardness. The first is by calculation from the Ca2+ and Mg2+ concentration in solution, the other is by titration.
Hardness may range from zero to several hundred mg/L, depending on the source and any prior pre-treatment of the water.
Sources and Environmental Significance
Hardness usually occurs throu gh dissolution of minerals containing calcium, magnesium, and silica compounds, typically calcium and magnesium carbonates, sulphates, chlorides or
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nitrates. Because of the inverse solubility of
these compounds with temperature, at high
concentrations they precipitate out of solution
in, for example, boilers and hot water pipes.
There are no reported human toxicological
consequences of elevated hardness; however,
high hardness waters are generally unpalatable.
Treatment Options
Treatment options for water with high hardness
comprise mainly precipitation of the Ca2+ and
Mg2+ ions using a mixture of lime (Ca(OH)2) and
soda ash (Na2CO
3). In this process, the Ca2+ and
Mg2+ ions precipitate as CaCO3 and Mg(OH)
2.
As this process occurs at high pH, subsequent pH
adjustment may be required. This can easily be
achieved by the addition of either H2SO
4 or by the
bubbling of CO2 through the softened solution.
4.1.8 CONDUCTIVITY
Definition and Alternative Names
"Conductivity" is a measure of the ability of water
to conduct an electric current. Factors affecting
conductivity include temperature and the type,
concentration and valency of ions present
(eg. Na+, Ca2+, Cl- and SO42-).
The higher the concentration of conducting
solutes, such as salts, the higher the
conductivity (see Table 4.1).
TABLE 4.1 Typical Conductivity Range of Waters
Water Conductivity Range
(mS/m)
Freshlydistilled 0.5-2
Potablewaters 50-1500
Seawater 40000-50000
Groundwater upto50000
Units of Measurement
Conductivity is usually determined by
measuring the resistance where:
Conductivity = 1
Resistance.
The SI1 unit for conductivity is mS/m (milliSiemens
per metre); however µS/cm is still in common use,
and many conductivity instruments use the units
µmhos/cm, where 1 mS/m = 10 µmhos/cm.
Sources and Environmental Significance
Conductivity is used to monitor several
different processes, some of which include:
• determinationofamountsofionic
reagent needed in certain precipitation
and neutralisation reactions; and
• estimationoftotaldissolvedsolids(TDS)in
mg/L and salinity in a sample by multiplying
the conductivity in mS/m by an empirical factor.
For TDS this factor may vary from 0.55 to 0.90
depending on the soluble components of the
water and the temperature of the measurement.
In the absence of a site-specific relationship,
a factor of 0.68 is commonly assumed.
Similarly, an estimate (in milliequivalents
per litre) of either anions or cations can be
derived from the conductivity measurement.
4.1.9 SALINITY
Definition and Alternative Names
Salinity is an indirect measurement of the
total amount of soluble salts in solution.
These salts include sodium chloride as well
as various calcium and magnesium salts
of chlorides, sulphate and nitrates.
Units of Measurement
Salinity is generally expressed as parts
per thousand (ppt or 0/00).
1 Systéme lnternationale = International System of Units
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The only direct method of measuring absolute
salinity is to analyse the individual chemical
components. Given the time and costs associated
with individual analyses, indirect methods
such as conductivity are normally favoured.
Conductivity measurements can be made in the
field or laboratory with a meter and probe which
has temperature compensation. Total dissolved
solids is also an approximate measure of salinity
Sources and Environmental Significance
Dry land salinity is a major problem in certain areas
of Australia, caused primarily by the widespread
clearing of native vegetation. Replacement of deep-
rooted perennial native vegetation with shallow
rooted annual pastures which use much less water,
allows the water table to rise, bringing dissolved
salts to the surface where they are concentrated
by evaporation. Similarly, the storage of acid and
saline mine water in dams can pollute high quality
groundwater reserves. Hypersaline groundwater,
with salinities well in excess of seawater, is used as
process water in the goldfields of Western Australia.
Release of this water into the environment can
cause death of vegetation and land degradation.
Criteria for salinity pertaining to various
livestock, irrigation and domestic uses can be
found in ANZECC (1992) and DME (nd).
4.1.10 SOLIDS
Total solids, as the name suggests, is a measure of
all the substances associated with a water sample,
other than the water itself. It can be further refined
into its constituent parts, total dissolved solids
(TDS) and total suspended solids (TSS), ie.
TS = TDS + TSS.
Definition and Alternative Names
Another name for total solids is total residue.
TDS or filterable residue is that portion of a sample
(other than water) which passes through a filter of
pre-defined pore size. This will obviously depend
on the pore size of the filter used. For this reason,
industry has standardised on a range of filters from
various manufacturers all with a similar nominal pore
size of around 1.2µm. In Australia, perhaps the most
widely used is the Whatman glass-fibre filter GF/C
After the water sample is filtered through the GF/C
filter, the filtrate is evaporated to dryness at 1800C
and weighed; the TDS is calculated from this result.
It is important not to confuse dissolved solids,
which are filtered through the GF/C type
filters, with the dissolved component of metals.
Dissolved metals refers to that portion of the total
metals in a sample which pass through, or are
not retained on, a 0.45µm filter membrane.
TSS may also be referred to as non-filterable residue
(NFR) or suspended particulate matter (SPM).
This parameter measures the amount of solids
suspended in a water sample which can be separated
from the water and dissolved solids phase by
filtration through a filter of fixed pore size.
TSS can be related to the turbidity of a water
sample. With careful site-specific calibration, and
where the sediment source is relatively constant
and homogenous, turbidity can be used to calculate
TSS (see: Section 4.1.11). However, extreme care
must be taken in developing this relationship.
Units of Measurement
Total solids and its constituent parts are
reported as mg/L. In samples with very high
concentrations the units may be expressed as %.
Sources and Environmental Significance
The composition of total solids depends on the
geology, land use, geochemistry and the environment
of the catchment. Dissolved solids in water may result
from the dissolution of materials exposed during
mining, or from the addition of soluble chemicals
during the processing of ores. High levels of TDS
are often not suitable for potable water, mainly
due to inferior taste. In addition, waters high in
TDS are rarely suited for industrial applications.
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Suspended solids can result from erosion of
unprotected ground surfaces, from wash water,
or from stormwater mobilising solids deposited
on the ground surface as a result of mining or
processing activities. The TSS in water can affect
the operation of biological and physical wastewater
treatment processes. Samples high in TSS are also
aesthetically unsatisfactory and affect the partitioning
and distribution of various contaminants in the
aquatic system. Suspended solids reduce light
penetration through the water column, affecting
growth of aquatic flora and fauna as well as the
aesthetic appeal of the water and its subsequent
use for recreation. Under certain flow conditions,
suspended material settles out and can smother
benthic organisms and their habitats. Other problems
with sedimentation include possible disruption to
navigation. Since most pollutants can be carried by
or adsorbed onto suspended solids, tight controls
of TSS in a water management plan can also
lower the flux or total load of pollutants entering
watercourses. Adsorbed nutrients and organic matter
are also a source of nutrients for algal blooms.
Solids remain in suspension only when there
is enough force or energy (turbulence) in the
water column to keep them in suspension. Rivers
with lower gradients and lower energy enable
suspended sediments to settle out and become
benthic sediment or bed load. The effect of
increased sediment loads to a river system are
numerous. High suspended sediment loads can
effect the gills of fish leading to irritation and
lesions. When suspended sediment settles, it can
increase river bed elevation or aggradation which,
as well as affecting aquatic organisms, may also
lead to increased overbank flows and flooding.
Sedimentation in water storage can reduce the life
of a dam, or increase the costs of dredging as well
as decreasing the quality of the retained water.
Treatment Options
Prevention of dust generation through control
of processes and stockpiles, and erosion of
land through controls on clearing and prompt
revegetation, are ways of reducing solids loadings
to water. Sediment retention through the placement
of sediment traps will lead to a reduction in the
amount of sediment reaching natural watercourses.
Sediment traps upstream of a storage dam are
an effective means of prolonging the life of a
relatively small dam. Treatment of water containing
suspended sediments prior to use in a plant or
for domestic potable water may require settling,
screening, filtering or dosing with a flocculant.
4.1.11 TURBIDITY
Definition and Alternative Names
"Turbidity" is an optical measurement of the
sample’s inherent ability to scatter light. Turbidity
measurements can be affected by the particle size
of the suspended matter, its mineral content and
its respective abilities to scatter and absorb light. In
addition, fine colloidal material can have a major
effect on increasing the turbidity (light scattering)
of a sample but only have a minor effect or increase
in the concentration of total suspended solids.
Optical right angled back-scatter nephelometers are
generally used for low level turbidity measurements
while forward scattering devices, which are more
sensitive to the presence of larger particles, are
generally used for in-stream analysis systems.
Care must be taken in using optical devices,
especially in tropical regions where algae and
slime growth can rapidly affect the calibration
of these instruments. Similarly, in waters with
high suspended solids, abrasion of the optical
surface can affect calibration of the instrument.
Units of Measurement
The units of turbidity are generally reported in
nephelometric turbidity units (NTU). It is possible
to produce a calibration curve or regression curve
of turbidity versus TSS at a given site; however,
this must be repeated for each site, because of the
likely changes in the characteristics of suspended
solids between different geological regions.
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Flow rates can also affect particle size distribution and
hence the relationship between turbidity and TSS.
Sources and Environmental Significance
By world standards, Australian watercourses are quite
turbid as a result of intense rainfall and flood events,
and the erodibility of agricultural and arid soils. The
aquatic ecosystems of many Australian watercourses
have adapted to higher turbidity levels than existed
prior to white settlement, but most probably at
a cost of lower species numbers and diversity.
Turbid waters normally require some form of
treatment prior to their use as industrial or potable
water. Treatment processes used to remove turbidity
can include filtration, coagulation and settling.
4.1.12 OXYGEN DEMAND
(DISSOLVED OXYGEN, BOD AND COD)
Dissolved oxygen is a key water quality parameter
required to sustain a healthy aquatic ecosystem.
The presence of excess organic materials such
as sewage sludge can significantly add to the
oxygen demand of a system, consuming dissolved
oxygen from the water as they decompose.
Dissolved Oxygen
Definition and Alternative Names
Dissolved oxygen refers to the oxygen
molecules that are dissolved in water.
Units of Measurement
Dissolved oxygen is usually expressed in parts
per million or mg/L. For some natural systems,
% saturation is also commonly used.
Sources and Environmental Significance
For the protection of aquatic ecosystems,
ANZECC (1992) recommends that dissolved
oxygen should not normally be permitted to fall
below 6 mg/L or 80-90% saturation, this being
determined over at least one diurnal cycle.
Reduction in dissolved oxygen within natural
aquatic systems can result from inputs of
organic material to the system (eg. sewage, some
mineral processing effluents) and also from algal
blooms. Dissolved oxygen concentrations usually
decrease with increasing water temperature.
Biochemical Oxygen Demand (BOD)
Definition and Alternative Names
The BOD test is an empirical test in which
standardised laboratory procedures are used to
determine the relative oxygen demand of wastewaters,
effluents and polluted waters. It is often referred
to as the BOD5 test, referring to the biochemical
oxygen demand over a five day incubation period.
Units of Measurement
The units of BOD5 are expressed in mg/L
along with the incubation time.
Sources and Environmental Significance
The BOD test measures the oxygen consumed
by biochemical degradation of organic material
(carbonaceous demand) and the oxygen used
to oxidise inorganic material such as sulphides
and ferrous iron. It may also measure the
oxygen used to oxidise reduced forms of
nitrogen (nitrogenous demand), unless their
oxidation is prevented by an inhibitor.
If BOD5 in effluent is high, then oxygen
dependent organisms in the receiving
waters may become stressed.
Chemical Oxygen Demand (COD)
Definition and Alternative Names
The COD test is used as a measure of the oxygen
equivalent of the organic matter concentration
of a sample that is susceptible to oxidation by
a strong chemical oxidant. For samples from a
given location COD can be empirically related
to BOD, organic carbon or organic matter.
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Units of Measurement
Results are expressed in units of mg O2/L.
Sources and Environmental Significance
COD is a useful, but not commonly used, parameter
in mine water management. Its usefulness stems from
its measurement of the total oxygen demand, unlike
BOD which measures oxygen demand available to
bacteria over a five day period. As a result, COD
concentrations will normally always be higher
than BOD concentrations from the same sample.
4.1.13 ANIONS AND CATIONS
Definition
Anions are those elements with a negative charge (eg.
Cl-, OH-, HCO3-, SO
42-, CO
32-, P0
43-) as opposed
to cations which are positively charged (eg. Na+,
K+, Ca2+, Mg2+). This discussion will be restricted
to the common inorganic anions and cations.
Inorganic Anions
Common anions associated with mine water
quality management are chloride (Cl–), hydroxide
(OH–), bicarbonate (HCO3–), nitrate (NO
3–), sulphate
(SO42–), carbonate (CO
32–), and phosphate (PO
43–)·
Units of Measurement
Anions are typically reported in the units mg/L.
Values in natural and wastewaters range
from zero to several hundred mg/L.
Sources and Environmental Significance
The sources of these anions is dependent on
geology as well as prior treatment and uses of
the water. Sources of chloride are salts such as
NaCl and CaCl2 which are often present in high
concentrations in groundwater. For example, the
aquifers of the Hunter Valley of New South Wales
contain high concentrations of salt as a result of
deposition of sediments in a marine environment.
The most common source of soluble SO42– from
mine operations is from the oxidation of sulphide
minerals such as pyrite (FeS2). Phosphates (which
are present in domestic and industrial detergents)
and nitrates (from mine explosives and fertilisers
used in mine rehabilitation) can also find their
way to watercourses. If these nutrients occur in
moderate to high concentrations they can readily
stimulate the growth of algae and aquatic weeds.
Inorganic Cations
Definition
Cations are those elements with a positive charge,
such as sodium (Na+), potassium (K+), calcium (Ca2+),
and magnesium (Mg2+). These are among the most
abundant natural elements in the environment.
Units of Measurement
Cations are typically reported in the
units mg/L. Values in natural surface and
groundwaters and wastewaters range
between zero to several hundred mg/L.
Sources and Environmental Significance
The concentrations of these elements in natural
waters depends on the geology and geochemistry
of the host rock. Calcium concentrations in
water from limestone areas are typically higher
than for waters from non-calcareous areas.
High concentrations of these cations are typically
found in groundwaters and increase their hardness.
They also affect the permeability and fertility of
soils and, for this reason, their concentrations are
closely monitored in the agricultural sector.
Other sources of these cations include leachate
from waste rock and tailings dams.
The ratio of the specific major cations relative to
each other is also an important factor in considering
the implication of their respective concentrations
in either feed, process or discharge water.
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4.1.14 METALS (TRACE METALS, HEAVY
METALS, METAL SPECIATION)
Definition
Two terms are commonly used when discussing
metals in water and environmental management.
These are:
• Trace metals, which commonly refers to:
– metals at very low levels in the environment
(trace analysis); or
– trace elements
which are either essential nutrients or
serve some other necessary biochemical
function. These include zinc, iron, copper,
cobalt, sodium and potassium;
and
• Heavy metals, which are generally thought
to mean toxic metals. Strictly speaking the
term refers to metals with an atomic weight
greater than that of sodium (22.9).
Units of Measurement
The units are dependent on the metal and its
concentration. Particulate metals are usually
reported as µg/g or mg/kg. Dissolved metals are
usually expressed in terms of µg/L or parts per
billion. Other units in which metals are sometimes
reported include mol, millimol or micromol per
litre (mol/L, mmol/L, µmol/L). These units relate
to the number of molecules of the metal that are
present and are not influenced by the actual weight
of the elements of concern. This unit is most
commonly used in toxicological assessment.
Sources and Environmental Significance
In natural systems, most metals are only sparingly
soluble in water, with higher concentrations
usually associated with the particulate phase. The
amount of a metal released from its particulate
phase into solution is a function of pH, particle
geochemistry, aquatic geochemistry, hydrologic
factors, temperature, etc. Mobilisation of metals is
frequently a secondary effect of acid drainage.
The impact of a particular metal on water quality
depends not only on the type and concentration of
the metal, but also on its chemical form or speciation.
The chemical speciation of a metal (eg. whether
copper exists as Cu2+, CuCO3, Cu(OH)2, or Cu-
dissolved organic matter complexes etc.) dictates how
bioavailable it is and the extent to which it may enter
the food chain, where it may accumulate to toxic
levels. Generally, metals are most toxic in their soluble
free ionic form (species) eg. Cu2+, Ag+ etc., compared
to metals complexed with either inorganic or organic
ligands (eg. CuCO3 or Cu-DOM) or in particulate
form (associated with minerals). One exception is
mercury which is more toxic in the methyl mercury
(CH3Hg) species compared to the free (Hg2+) species.
Further information on individual metals and their
environmental Significance can be obtained from
the various ANZECC guideline documents.
4.1.15 NUTRIENTS
Definition and Alternative Names
The term "nutrient" refers collectively to elements
and compounds which are essential to sustaining
adequate biological function. The most common
nutrients which may affect the water management
of a mining operation are nitrogen and phosphorus.
There are various forms of nitrogen such as ammonia,
nitrite, nitrate, and organic nitrogen. Phosphorus
can be found in the form of orthophosphate, total
phosphorus and organically bound phosphates.
The form of the nutrient has an integral role in
its function and fate in the aquatic environment.
Biological productivity may be limited by the
availability of either nitrogen or phosphorus,
which are often referred to as the growth limiting
nutrients. Silica has also been identified as a
limiting nutrient in some aquatic systems.
Units of Measurement
The units of measurement for nutrients depend
on the form of either phosphorus or nitrogen
that is being measured. Typical expressions are
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micrograms of total phosphorus or total
nitrogen per litre (µg TP/L or µg TN/L) and
milligrams of ortho-phosphorus or nitrate
nitrogen (mg Ortho-P/L or mg NO3-N/L).
Sources and Environmental Significance
Sources of nutrients in mining operations include:
• sewageorsepticwastewater;
• nitrogenbasednutrientsfromexplosives;
• phosphorusbasednutrientsfromprocess
chemicals and industrial detergents;
• fertilisersappliedduringrehabilitationworks;
and
• degradationproductsofcyanide.
Excessive concentrations of nutrients can promote
and accelerate growth of aquatic plants and algae,
including attached and floating macrophytes and
dense suspensions of free-floating algae. These reduce
light penetration and, upon decomposition, cause
odours and loss of oxygen in the host ecosystem.
4.1.16 OILS, GREASES AND HYDROCARBONS
Definition and Alternative Names
The parameter “oil and grease” refers to a
range of chemicals which can be extracted
from a water sample into the organic solvent
trichlorotrifluoroethane. The types of compounds
collectively analysed by this method are primarily
fatty components from animal and vegetable sources
and hydrocarbons from petroleum products. While
trichlorotrifluoroethane is used to extract the group
of compounds of interest, there are three subsequent
analyses which can be conducted depending on
the make-up of the water being examined and the
likely constituents. Oil and grease determination
can also be performed on sludge samples.
If required, total petroleum hydrocarbons (TPH)
can be selectively analysed as a separate group by
a modification of the oil and grease method.
Units of Measurement
Oil and grease in water samples is commonly
expressed in mg/L. Oil and grease in solid
sludge is expressed as % of dry solids.
Hydrocarbons are also expressed in this way.
Sources and Environmental Significance
If present in high amounts, oil and grease can
reduce the efficiency of water treatment processes
by interfering with anaerobic and aerobic
biological processes. Large quantities of oil and
grease discharged in wastewater can cause surface
films and deposits and result in the staining of
riverbanks and coast lines. They can also affect
oxygen exchange, oxygen demand and palatability.
Treatment Options
Treatment options available for the reduction
of synthetic organics (fuels, oils, grease etc.)
include simple oil-water separators through to
expensive dissolved air flotation systems.
4.1.17 ORGANICS, NATURAL ORGANIC
MATTER, DISSOLVED ORGANIC CARBON
Definition and Alternative Names
The term organics refers to a broad group of chemical
parameters, some of which are used in the resource
development and mineral processing industries.
In addition to manufactured organic compounds,
there is a broad group of naturally occurring organic
compounds which play an important role in aquatic
biogeochemical processes. Collectively, these
compounds are referred to as dissolved organic matter
(DOM), natural organic matter (NOM), dissolved
organic carbon (DOC), or humic substances (HS).
Units of Measurement
For the more general definition of synthetic
organics, the units of measurement depend on
the analysis being undertaken. Most commonly,
they are reported in either mg/L or µg/L.
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Naturally derived organic material is most
commonly measured as DOC and expressed
in units of mg C/L. DOC typically represents
approximately 50% by mass of DOM.
Sources and Environmental Significance
Process reagents such as collectors, frothers
and flocculants are all synthetic organic-based
compounds. Usually, the amounts of organic
compounds used for mineral processing are small
and any residual concentrations decay rapidly.
DOM, NOM, DOC and HS refer to a generic group
of compounds which are best described as the humic
and tannin extracts of soil and plant materials which
impart the characteristic tea colour of some natural
waters. The organic compounds making up DOM are
a group of weakly acidic molecules which, in high
concentrations, are able to reduce the pH of the water.
Treatment Options
The removal of natural organic material can be
performed in many ways and is dependent on
the amount of DOC present and the amount of
water requiring treatment. Common treatment
options include adsorption onto activated
carbon, UV oxidation and ozone oxidation.
4.1.18 COLOUR
Definition and Alternative Names
The term colour can be divided into:
• True colour, ie. the colour of a sample from
which turbidity has been removed; and
• Apparent colour, which includes the colour
and turbidity of the total sample.
Apparent colour is measured on the sample prior
to any treatment (except inversion of the sample to
suspend all particulate matter) and true colour is
measured after either filtration or centrifugation.
Normally, unless otherwise stated, the term
colour refers to the measure of true colour.
Units of Measurement
Several methods exist for the analysis of colour,
varying from the simple visual comparison, to
techniques requiring sophisticated instruments
and determination of the colour wavelength of
the sample. The units of colour depend on the
method of analysis but generally correspond to
a “colour number” or code which is based on a
visual comparison of the colour of the sample to
that of a series of standards, usually made with a
platinum cobalt solution. Alternatively, the colour
can be measured by light transmittance through a
special system of photoelectric cells and light filters.
The final choice of measurement depends on the
specific water quality to be determined. Regulatory
authorities usually specify the parameters to be
determined and the specific method of analysis.
Sources and Environmental Significance
Colour may result from a number of sources
including metallic ions (iron and manganese),
dissolved organic material (humus and peat material),
plankton and weeds. Highly coloured industrial
wastes can also contribute to the colour of water.
The environmental implications of colour depend
on the element that is imparting the colour.
4.1.19 CYANIDE
Definition and Alternative Names
Cyanide (CN) is used widely throughout the
mining industry to dissolve and complex
gold and silver to separate them from the ore.
In terms of water quality management there
are three main forms or species of CN:
• totalCN-referstoallformsofCNandis
usually determined by performing an exhaustive
hot acid extraction whereby all the CN from
both liquid and solid phases are dissolved
and subsequently analysed as NaCN;
• weakaciddissociableCN(WADCN)includesonly those CN compounds that are liberated
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under weakly acidic conditions, ie. it does not
include all the CN present in the sample; and
• freeCN(CN–) and hydrogen cyanide (HCN)
are the most bioavailable forms of CN, the
abundance of which is strongly dependent
on pH. The lower the pH the greater the
proportion of the total CN that exists as HCN.
Units of Measurement
The units in which CN is expressed depends on the
form being analysed and from where it was collected.
Samples from process waters containing CN will
generally have total CN values in the mg/L range;
however, after storage or treatment the values may
realistically be in the very low µg/L range. Generally,
for process waters using CN values are reported as:
• mgtotalCN/L;
• mgWADCN/L;and
• gfreeCN/L.
Sources and Environmental Significance
While CN can be formed naturally by nitrifying
bacteria, the main source in the mining
industry is waste streams from cyanidation
processes. The mechanisms affecting the
environmental fate of CN include:
• bacterialdegradation-movementofCNthrough
soils and sediments is thought to be restricted
through biodegradation by soil organisms
and adsorption to soil particle complexes;
• atmosphericdiffusion-atneutralandacidicpH,
CN in solution occurs predominantly as HCN
gas which readily diffuses into the atmosphere;
• conversiontothiocyanate-freeCN
reacts with pyrite and pyrrhotite to form
thiocyanate, which is relatively stable and
non-toxic. Thiocyanate is also produced
as a part of the natural detoxification and
biodegradation of CN in biotic systems;
• complexformationwithmetals-CNforms
complexes with metal ions which are common
in mineral processing wastes. These complexes
are usually resistant to biological uptake and
are stable in the environment, although some
may be readily broken down to their basic
components, for example CuCN; and
• photochemicaldegradation-althoughcomplex
ions such as ferro-CN and ferri-CN are
thermodynamically stable, they can undergo
photo-reduction to form free CN in the presence
of UV light. In compacted and solid tailings
dams, this is only a problem at the surface of
the dam. Beneath the surface, away from the
UV light, the CN remains as a stable metal-CN
complexes. The conversion of CN complexes
to free CN is affected by pH, temperature,
pond geometry and the intensity of UV light
incident on the pond. The concentration of
total CN has been observed to drop from
around 60 mg/L to less than 5 mg/L in just
over 1.5 months (Smith &. Mudder, 1991).
4.1.20 ODOUR AND TASTE
Definition and Alternative Names
Both odour and taste are subjective tests which
often depend on an individual’s personal criterion to
determine the acceptability of the water or otherwise.
The tests are usually based on a comparison with
tasteless and odourless water samples. Flavour
is more objective, and can be used instead.
Documented procedures for flavour are available.
Units of Measurement
Taste and odour are generally reported as
dimensionless descriptive numbers which
relate to threshold detection limits where the
sample is compared to a standard with no, or
some definable taste or odour characteristics.
The measurements include threshold odour
number, flavour threshold number, flavour rating
assessment and flavour profile analysis number.
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Sources and Environmental Significance
Taste and odour may render the water unsuitable
for human consumption and domestic use
as well as tainting fish and other foods which
inhabit the water. There is no single compound
which causes odour. However, tests exist for
the determination of several of the prime
compounds which impart an odour in waters.
4.1.21 RADIONUCLIDES
Definition and Alternative Names
The mining and milling of ore containing uranium
may result in water and wastewater that contains
variable concentrations of radionuclides present
in the ore. The water that is retained or discharged
from an operation should, as a minimum, be
analysed for radium-226, thorium-230, lead-
210, uranium-238 and polonium-210.
Units of Measurement
The commonly used unit of measurement for
radionuclides is the becquerel (bq). For water,
the units are expressed as bq/L and for soil and
sediment the units are expressed as bq/g.
Sources and Environmental Significance
Radionuclides can be found in wastewater arising
from the mining and milling of radioactive ores.
Typical streams are:
• excessprocesswater,whichmaybe
pumped to a tailings impoundment;
• runofffromtheminepit,orestockpiles,waste
dumps, borrow areas, haul roads and plant area;
• seepagefromtheminepit,tailings
dam and evaporation ponds; and
• waterfromwatersupplyboresanddamswhich
has flowed through mineralised material.
4.2 Biological Aspects of Waters
Mining and mineral processing operations rely on
or influence the biological component of natural
or artificial systems. These systems can include:
• biologicalprocessesbeneficialtothe
operation, eg. anaerobic and aerobic
treatment ponds, artificial wetlands;
• ecosystemprotection,ie.limitingthe
physical and/or chemical parameters
associated with mine discharges to levels
suitable for ecosystem protection; and
• bio-monitoring,ie.usingaquaticorganisms
to monitor the effects and effectiveness
of water management practices.
ANZECC (1992) recommended four biological indicators to assess ecosystem condition or health. These indicators are based on the assumption that the extent to which the integrity of an ecosystem is being maintained can only be assessed when the characteristic biological communities of a region are known or, since this will rarely be the case in Australia, by comparison of the biological community at the site or sites of interest with unimpacted communities in similar habitats elsewhere in the region. Each of these indicators relies on a rigorous and statistically sound sampling scheme, which is able to distinguish between various population parameters between impacted and unimpacted sites. Of these biological indicators, two relate to biological community structure and two to community processes.
The biological indicators recommended are:
Species Richness
Measures of specific richness indicate the number of species present in a sample of organisms of given size. They differ from diversity measures which also incorporate the concept of species evenness. A decrease in richness is generally considered as an indicator of ecosystem stress.
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Since different components of an ecosystem may
respond differently to stress, it is important that all
the major biological groups (eg. macroinvertebrates,
fish) be evaluated. The ANZECC guideline
specifies that the species richness as measured
by a standardised index should not be altered.
Species Composition
ANZECC (1992) has proposed a guideline that, in
any waterbody, impacts that result in Significant
changes in species composition compared to those
in similar, local unimpacted systems should not be
permitted. It is possible, although probably unlikely,
that ecosystems could maintain species richness while
still changing markedly in species composition.
Primary Production
Primary production forms the basis of most
aquatic food chains. In any waterbody, net
primary production should not vary from the
levels encountered in similar local, unimpacted
habitats, under similar light, temperature and
nutrient loading regimes. Primary production
is known to be sensitive to light (water clarity),
temperature and nutrients, amongst other factors.
Ecosystem Function
In any waterbody, changes that vary the relative
importance of the detrital and grazing food chains
should be minimised. Production to respiration
ratios should not vary significantly from those
of similar, local, unimpacted systems.
Some ecosystems, such as large standing waterbodies,
have autochthonous primary production (produced
within the waterbody) as their major energy
source. Others, including forest streams and some
wetland systems derive most of their energy from
allocthonous detritus (produced from outside the
waterbody and is transported to where it is used).
Aquatic systems should be managed such
that the relative balance between these two
major energy pathways is maintained, and
that natural detritus-driven aquatic systems
are not converted to autochthonous primary
production driven systems, and vice versa.
Levels of Protection
Two categories of aquatic ecosystems are identified
within the national ANZECC guidelines:
• Pristine ecosystems are not subject to
human interference through discharges
or activities within the catchment. For
these ecosystems, now largely restricted
to National Parks, it is appropriate for the
existing water quality to be protected and
preserved through strict management; and
• Modified ecosystems include all those systems
subject to human interference. Some modified
ecosystems have been permanently altered
physically, for example through stream
channelisation or port construction. Others
have been changed through long-term
chemical toxicity caused by contaminated
sediment or by changed river flow regimes.
4.2.1 MICRO-ORGANISMS
Micro-organisms play an important role in natural
aquatic systems and in the treatment of wastewater.
The greatest use of microbes in wastewater treatment
is for the treatment of sewage using anaerobic and
aerobic treatment systems. Other uses of micro-
organisms relevant to the minerals industry are:
• treatmentofcyanidewastestreamsgenerated
from mining and mineral processing operations;
• treatmentofhydrocarboncontamination
arising from spillage or leaks from
storage tanks or pipes; and
• remediationofhighnutrientor
sulphate waste waters.
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4.2.2 ALGAL BLOOMS
Problem algal blooms are usually the result of a
number of factors and not generally the result of
a single person or a projects activities. A bloom is
usually an indication of widespread problems or
stress throughout the catchment, as in the case of
blue-green algal blooms along the Murray-Darling
system. While localised algal blooms can occur on a
site, they usually do not pose any great problems and
can frequently be controlled. Algal blooms are usually
short-term occurrences leading to a population
explosion and normally result from a combination of
high light penetration and water temperatures, slow
flowing or stagnant water and high concentrations
of nitrogen and phosphorous. Oxygen depletion
and the release of toxic constituents from blue-
green algae are common problems that can develop
when a bloom collapses and the algae decay.
4.2.3 TOXICITY AND ECOSYSTEM HEALTH
In general, toxicity testing involves determining
the effect of various compounds on test organisms
under set conditions. The terms LD50
and LC50
are
both acute measures of toxicity. However, toxicity
can also be measured in terms of non-lethal, chronic
parameters such as an organism’s growth rate,
fecundity changes and behavioural response changes.
An extensive listing of toxicological data has recently
been compiled within the ANZECC guidelines,
which list the types of compounds and the range
of toxicity data available. In general, toxicity
evaluation is time-consuming and very expensive.
Acute Toxicity
This term refers to a relatively short-term lethal
or other effect, usually defined as occurring
within four days for fish and macroinvertebrates
and less for smaller organisms.
Lethal dose50
(LD50
) refers to the dose of a test
compound, which kills 50% of the test population.
The time required to kill 50% of the population
is then used as an index of toxicity. Standard LC50
and LD50
tests are performed over 96 hours. The
96 hour duration is operationally defined and
has no biological or biochemical foundation. It
was established so that a test could be completed
within one working week. It refers to a specific
dose of a test compound and is usually expressed
as a concentration of the test compound per mass
of test organism body weight. Such information is
usually used to calculate and assign a safe exposure
limit or of recommended dose per person per day.
Lethal concentration50
(LC50
) is similar to the lethal
dose but refers to a concentration. Therefore,
this figure is more widely used to test aquatic
organisms such as fish and invertebrates. Often,
toxicity data are related to a time of exposure,
eg. a value of 50µg/L is not to be exceeded more
than once over any 12 month period. While such
limits do take into account accidental spillages,
they are assigned on a purely arbitrary basis and
the toxicological information in relation to this
value being exceeded is not absolute in nature.
Chronic Toxicity
This term refers to long-term toxicity as opposed
to sudden death resulting from a test compound.
Chronic toxicity is much more difficult to diagnose
and relates to longer term exposure to a specific
compound. Continued chronic exposure can
include adverse responses such as changes to
spawning, metabolism or growth rates, or appetite,
behavioural or reproductive changes. Because
chronic effects are harder to identify, minimal work
has been performed to date on the chronic effects
of most pollutants, except in the case of human
health (mercury for example). Chronic toxicity is
often more subjective than a measurement of acute
toxicity or LC50
or LD50
. However the chronic toxicity
effects of pollutants are now becoming much more
important to maintain long-term ecosystem health.
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4.2.4 FACTORS INFLUENCING
BIOAVAILABILITY AND
TOXICITY OF CONTAMINANTS
The following factors play a major role
in determining the fate of any waste
discharge to the aquatic environment.
• Carbonate equilibria and effect on metals
speciation - The presence of carbonate enables
the formation of inorganic carbonate-metal
complexes, as well as buffering pH which can
have a major effect on metal speciation.
• pH effects on speciation - The lower the pH (ie. the
more acid the water), the higher the proportion
of a dissolved metal which is bioavailable or in
the free ionic or weakly complexed state. If there
are significant quantities of particulate-bound
metals in the waterbody, a reduction in pH can
leach metals from the particles into solution and
thus alter the distribution (partitioning) of the
metal between the soluble and particulate phases.
• Effects of organic matter on complexation and
speciation - Natural organic matter in aquatic
systems can consist of large polyelectrolytic
molecules with numerous binding sites of
different polarities. Consequently, on a single
molecule, numerous sites are available for
binding metals and pesticides. The degree
to which organic carbon partitions between
the solid and solution phase also influences
pollutant partitioning. High concentrations of
dissolved organic carbon (DOC) can increase the
solubility of metals and pesticides by stabilising
and complexing these compounds into
soluble aqueous complexes. If high suspended
solids are present, DOC also binds strongly
with sediment particles, and consequently
detoxifies the adsorbed contaminant. DOC is
critical in assessing the environmental fate of
effluent containing metal and organic wastes.
• Partitioning between dissolved and particulate
species - Bioavailability is dependent on
whether a compound is associated with the
particulate phase compared to the aqueous
phase, in addition to the pH and concentration
of organic matter. The more the compound
is associated with the particulate phase, the
less bioavailable it will be. The partition
coefficient is the term which defines the ratio
of the amount of particulate bound pollutant
to the amount in the aqueous phase.
4.2.5 BIO-MONITORS, BIO-ACCUMULATION
AND BIO-AMPLIFICATION
Definitions
Bio-monitors are organisms used to determine
the extent of pollutant transport and the
extent of biological uptake of a pollutant.
Bio-accumulation refers to the increase in a
contaminant concentration within a particular
organism or group of organisms, eg. liver
of fish, egg shells of birds of prey.
Bio-amplification refers to the amplification of the
bio-accumulated contaminant through the food
web from one organism up the trophic order.
Organisms such as bivalves (mussels, oysters etc.)
are sometimes used as bio-monitors because they
filter large volumes of water and any associated
metals and organic pollutants, thus bio-concentrating
the actual levels of a pollutant within the water
column. At this stage bio- monitors can only be
used reliably as indicators of the presence of a
pollutant. Further research is required before the
significance of any relationships between bio-
monitor and ecosystem health can be established.
Whether a compound will bio-accumulate depends
on a number of physico-chemical parameters
such as the class of compound (eg. metal, organic
pesticide), its concentration, exposure frequency
and duration. Bio-accumulation also depends on
the target organism, the compound of concern and
its fate within the target organism. Many organisms
have the ability to regulate pollutant levels in certain
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parts of their body. Therefore identification
of key organs (kidney, liver, adipose or fat
tissue) are important considerations when
interpreting bio-accumulation data.
Bio-amplification is an extension of bio accumulation
where a contaminant which has been taken up by one
particular organism or trophic level is passed on to
higher order organisms - such as the case of mercury
in fish which are then consumed by humans.
4.3 Nature of Waters
This section outlines a number of additional
concepts which are pertinent to the complete
understanding of the properties of water.
4.3.1 BENEFICIAL USE
Beneficial use refers to the designated uses of a
waterbody. Examples of beneficial uses include:
• ecosystemprotection;
• recreation-swimming,fishing,aesthetics;
• domesticandpotablewater;
• livestockwatering;
• commercialfisheries;and
• irrigation.
Dischargers to waterbodies will generally be required
to identify and meet a designated beneficial use.
This may include the designation of a mixing zone.
4.3.2 ASSIMILATIVE CAPACITY
Assimilative capacity refers to a waterbody's
ability to absorb or resist changes brought about
by the addition of a particular parameter. An
example is that of buffering capacity, where high
alkalinity waters are able to assimilate additions
of low pH water with no adverse changes.
4.3.3 RECEIVING WATERS
The type of receiving water into which wastewater
is discharged is an important factor in determining
the effect and ultimate fate of discharged pollutants.
For example, the fate of metals discharged into a
freshwater lake will be different to that of an estuary
or ocean. Physical characteristics such as temperature,
flow, pH, salinity, dissolved oxygen and light
penetration determine the behaviours of a specific
pollutant in the aquatic environment. The capacity
of the receiving environment to dilute and assimilate
the effluent stream is also of primary importance.
These considerations should be evaluated prior to an
effluent stream being discharged to a receiving water.
Effluent streams of significance emanating from
mining operations include sewage treatment plants,
stormwater discharges from haul roads, waste dumps,
workshop discharges and machinery washdown
discharges containing hydrocarbons, or surfactants.
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5. Water Sampling and Flow Measurement
5.1 Introduction
Water monitoring can be a very expensive
and time consuming exercise and therefore
the monitoring plan must be well designed
before the program is implemented. Suggested
planning steps are shown in Table 5.1
In addition to these key steps, specific requirements
of the National Water Quality Management Strategy
need to be considered and the ANZECC (1992)
guideline documents also need to be reviewed.
5.2 Principles and Purpose of Monitoring
The key issues that must be addressed
before the commencement of sampling
and flow monitoring are listed below.
1. Reasons for monitoring - The objectives and
purpose of the monitoring program must be
established. Monitoring programs are usually
implemented for compliance with an operating
licence, to meet company or corporate policy
requirements, for project design input data or
for a baseline survey. Data from monitoring
will also provide valuable feedback and
corroboration of design data adopted. The
program should meet the defined objectives.
2. Trained field staff - Personnel who collect
meteorologic, hydrologic and water quality
data should be skilled in hydrography,
field flow measurement techniques and the
fundamentals of water chemistry. The increased
use of electronic field data also requires field
personnel to be skilled in the use of data
loggers, portable computers and associated
software. Standard and uniform sampling
and preservation procedures need to be used.
If this expertise is unavailable within the
organisation, consideration should be given to
using a reputable and experienced consultant.
3. Execution of the program - The type of
sample collection (eg. automatic or manual grab
sampling), frequency, number of monitoring
sites and phase (exploration, feasibility,
construction, operation, decommissioning
and after site closure) of the project should be
identified within the initial planning stage.
4. Budget - Sufficient financial resources must be
assigned to meet the objectives of the program,
or else the program needs to be modified.
Ideally, staff and financial resources allocated
to a monitoring program should complement
the scope of the program, and the sensitivity of
the local environment. In circumstances where
financial resources are limited, it is better to:
• ensurethatthesamplescollectedare
representative in both time and space;
• restrictsamplecollectiontokey
locations (including controls); and
• reviewpreviouslycollecteddatatoensure
unwarranted analyses are not requested.
Finally, when allocating and revising
financial resources, all the associated costs
need to be incorporated. Expenses that
are frequently neglected include:
• samplestoragecosts(iceforfield
storage, temporary refrigeration);
• sampletransportcoststothelaboratory;
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• consumablecosts(samplebottles,acidrinsing
of sample bottles, labels, coolers, field clothing);
• costsassociatedwithcalibratingstreamflow
data, which requires qualified personnel
manually undertaking a program
of streamflow gauging; and
• databasedevelopment,dataanalysiscosts
(eg. computer facilities and employees’
time) and implementation of an
appropriate data management system.
5.3 Compliance Monitoring
In the past, licence and discharge criteria varied
frequently between the States. Recently, a more
uniform approach has been taken with a move
towards the ANZECC Water Quality Guidelines
(1992)1, which consider both discharge limits and
receiving water quality. This document should be
reviewed in order to understand the existing national
approach to water quality management in Australia.
1 Under revision 1997-98.
TABLE 5.1: Key Planning Steps for Water Monitoring
The Key Planning Steps
1. Identify the potential receiving waters and their beneficial uses.
2. Outline the site resources (personnel, financial) which are available for the monitoring program.
3. Locate and review the presence of any existing data, environmental audits and reports.
4. Identify all Local, State and Commonwealth statutory requirements which must be met by the operation.
5. Select a reputable laboratory which can advise on sampling methodology, containers, preservation and storage, etc.
6. Using a site plan, identify the physical and chemical properties of all likely point and non-point sources of pollution, the network and the catchment partitioning.
7. Design and implement a “screening” monitoring program to identify all sources and types of contaminants (eg. suspended solids, zinc, phosphates, E. coli) from each location. The screening program should include all surface waters, groundwater, industrial and domestic discharges, receiving waters etc. Control or background sites should also be identified and sampled. This program should be undertaken during dry and wet weather periods and the results reviewed in detail to identify contaminants which should or should not be analysed for a specific location.
8. Identify all monitoring sites which require flow measuring facilities (if contaminant loadings are required for water balance data, for catchment yield characterisation and rainfall/runoff parameters). Ensure a proper program is in place for physical measurement of flows for calibration and for validation of all recorded data.
9. Design and implement a calibration, quality control and quality assurance program with appropriate control sites, blank and duplicate samples, etc., and ensure detection limits are appropriate.
10. Ensure rainfall guages (and climate stations as appropriate) are in place for catchment rainfall/runoff characterisation.
11. Implement a site-wide sampling program and review the data once they are available. Parameters that have been measured below the detection limit can be sampled less frequently.
12. Review all results against statutory requirements.
13. Design an appropriate computerised database management system so that results can be managed and retrieved with ease.
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5.3.1 AMBIENT, POINT SOURCE AND
NON-POINT SOURCE POLLUTION
Ambient concentrations generally refer to natural
or background levels of water quality parameters
within a receiving water. It is important to determine
if the background values reflect actual natural
conditions or a natural system which may have
been modified over the past two centuries.
Discharge or point source criteria refer to the
concentration of a contaminant or parameter
at the point of discharge (eg. an outfall from
a wastewater treatment plant). The criteria
may specify a mean value and a higher level
not to be exceeded at a given frequency.
Non-point source pollution refers to a diffuse
source rather than a single discharge point, eg.
unconfined stormwater runoff from a minesite,
workshop and maintenance areas. Contaminants
from diffuse sources may be measured as a
concentration (eg. Mg/L), but usually contaminant
loading data (eg. kg/ha/yr) are required and both
quality and quantity data must be collected.
5.3.2 MIXING ZONES
When assessing compliance with receiving water
quality guidelines, the “mixing zone” of the
waterbody must also be considered. This is a region
of the receiving water at which elevated levels of
a contaminant can be present due to a discharge
source, before dilution to an acceptable level.
ANZECC (1992) defines a “mixing zone” as an
explicitly defined area around an effluent discharge
where certain environmental values are not protected.
All relevant mixing zones, both within and
outside a lease area, should be clearly identified.
Monitoring programs and interpretation of
data need to consider that these areas exist.
Control strategies should ensure that the area
of a mixing zone is limited in order that the
value of the waterbody is not prejudiced.
5.4 Data Collection - Quality
The resources allocated to environmental
data collection will depend on the phase
of the mining operation (ie. exploration,
construction, operating, closure).
• Baselinestudiesandassociatedmonitoring
programs should be implemented at prospective
sites prior to the commencement of any major
earthworks or infrastructure development.
• Theresourceevaluationandfeasibilityphases
usually involve the collection of meteorological
and hydrological data, if no long-term data
exist for the local region. Long-term time series
data will improve techniques for optimising
tailings dam design, surface drainage works,
water supply and flood mitigation.
• Theconstructionphasegenerallyinvolves
expanding the monitoring program as staff
and financial resources increase. A target
monitoring program during construction
is often necessary to measure the impacts
of the construction activities. It also
allows fine tuning of initial “screening”
programs prior to full-scale operation.
• Theoperationalphasewillnormallyinvolve
frequent monitoring of all point source (eg.
sewage effluent, potable water, process and
tailings dam water), non-point source (eg.
stormwater from the plant area, landfill
leachate) and receiving water quality and
quantities (waterbodies within and adjacent
to the mine and mineral processing lease).
• Thedecommissioningphaseandtheextent
and duration of monitoring will depend on the
nature of the operation and the requirements
outlined in the mine decommissioning
plan, agreements and licences.
5.4.1 MONITORING DESIGN
Initially both a statistical evaluation of the
monitoring design and a review of the procedures
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and techniques to be adopted should be undertaken.
Once a preliminary plan is prepared, the logistics (eg.
staff and financial resources) need to be reviewed.
Development of the statistical design and validation
of the sampling program, analytical methods and
final data set need to be undertaken by personnel
with appropriate expertise. The use of blank
samples, unidentified duplicate samples and
inter-laboratory testing should be incorporated as
key components of the monitoring program.
Electronically collected hydrological data from
streams and rivers should also be validated using
appropriate statistical procedures and manual
gauging methods during low, medium and
high flow flood events. Electronically collected
rainfall data should be validated similarly.
5.4.2 IDENTIFICATION OF KEY
MONITORING PARAMETERS
The monitoring parameters selected (physical,
chemical and biological) will depend on the
ore being mined at the operation, the process
technology and chemistry, the geographical
location and the beneficial environmental uses
which need to be protected. It is important
to identify all the key monitoring parameters
early in the program in order to avoid possible
delays at some later stage of the development.
5.4.3 INITIAL SCREENING PROGRAM
Prior to commencing a full-scale monitoring program,
it is worthwhile undertaking an initial screening
survey at all potential monitoring locations within
the project area to determine which parameters are
relevant, significant and measurable above analytical
detection limits. This should be done in conjunction
with the statutory authorities concerned and the
analytical laboratory. Multi- element screening of
water samples for total and dissolved contaminants
on a selected number of samples is a cost-effective
technique to identify parameters which should be
incorporated into the site monitoring program.
Results from the initial screening program should
be compared with guideline values such as those
published by ANZECC (1992) and NHMRC (1994).
Locating best positioned flow monitoring stations,
relative to the monitoring locations required, can also
be assessed as part of the initial screening program.
5.4.4 SAMPLING LOCATIONS
The selection of suitable sampling sites within
and surrounding a mining operation should be
based on the potential for a specific area, process
or activity to have an environmental impact.
Selection criteria for sampling and
control sites are shown in Table 5.2
It should be noted that the conditions required
for an acceptable control site for biological
monitoring programs are generally more
stringent and complex than a control location
for chemical monitoring programs.
Sufficient samples should be collected to quantify
accurately the concentrations and behaviour
of a compound from the time it is discharged
through to the point where it can no longer
be detected above ambient concentrations.
5.4.5 SAMPLING FREQUENCY
The frequency interval selected for the collection
of samples for a water monitoring program
will depend on the following factors:
• statutoryandlicenceconditions
(eg. weekly, monthly);
• sizeandgeographiclocationof
the mining operation;
• distanceandeaseofaccesstosamplelocations;
• variabilityofnaturalandseasonalconditions;
• availabilityofstaffresourcestocollect
samples and process data; and
• typeofanalysis.
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5.4.6 SAMPLING TECHNIQUES AND DESIGN
There are numerous methods by which a
representative sample can be collected, with the
final technique selected primarily dependent on
the type of waterbody or waste stream requiring
assessment. It is particularly important that the
procedures used, and any changes to these, be
thoroughly documented, and all persons using
them are adequately trained in their use.
Surface Water Sampling
Sample collection of surface waters (sewage
effluent, stormwater, tailings dams, streams and
estuaries) can range from simple grab sampling
TABLE 5.2: Selection Criteria for Establishing Sampling Sites
Sample Sites Control Sites
The selection of sampling sites within and outside
the project area should reflect the:
• beneficialusesrequiringprotection;
• geographiclocationandtheareapotentially
impacted by the operation;
• thenatureoftheoperationandthetypeof
ore/minerals/metal produced;
• conditionsofthelicenceagreement;
• accesstosamplingsites(allweatherif
required); and
• budgetandanalyticalconstraints.
An overview of the "typical" monitoring sites that
should be sampled at an operation are:
• withinoradjacenttoareasofbeneficialuse;
• thedischargepointforindustrialordomestic
waste streams prior to entering receiving waters;
• monitoringofreceivingwatersupstream
and downstream of the discharge point
or property boundary, if a mixing zone
is identified in licence conditions;
• monitoringofallimpoundedwater
including tailings dams, retention
pond water, seepage ponds;
• monitoringofgroundwaterdownstream
from contaminated sites, eg. dirty water
ponds, hazardous waste sites; and
• belowtheconfluencepointofmajor
tributaries within the region.
Control sampling sites are an essential component
of any water monitoring program. The location and
number of control sites selected will depend on:
• thegeographicandtopographic
location of the operation;
• thespatialcoverageoftheproposed
monitoring program; and
• financialconstraints.
It is essential that control and
routinely monitored sites:
• areinsimilarlocations,preferably
in the same catchment;
• arenotinfluencedbypastorcurrentmining
operations or other human influences;
• havesimilargeochemicalconditions,ie.either
carbonate systems or organic systems; and
• havesimilarmeteorologicaland
hydrological conditions.
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techniques through to sophisticated automatic
samplers, which have the capacity to collect both
discrete or composite samples over a specified period.
When surface sampling techniques are to be
used the following should be considered.
• Thesamplecontainersusedmustbeappropriate
for the chemical parameter being measured
(eg. acid washed high density polyethylene
for trace metals, organic solvent rinsed glass
bottle with teflon lid for organic compounds).
• Beforefilling,rinsethesamplebottleoutthree
times with the water being collected, unless
the bottle contains a preservative. Ensure clean
hands are used as dirty hands may contaminate
the sample (eg. cigarette smoke or residual
ash will contaminate low level nutrient and
metal samples). For trace metal samples,
prevention of contamination is paramount,
and special techniques such as the use of
non-powdered latex gloves are required.
• Avoidcontaminationofthesampleand
disturbance of the waterbody being sampled.
• Excludeairfromthesamplecontainers.
• Appropriatesamplepreservationtechniques
must be implemented immediately after
sample collection (eg. filtration and addition
of AR grade HNO3 for dissolved trace metals,
temporary storage at 40C for nutrients).
Note that sample holding times vary between 3 hours
and 28 days for different parameters being analysed.
• Ensurethelaboratoryandtheanalytical
techniques used are NATA (National
Association of Testing Authorities) registered.
Variations in sampling and preservation techniques,
storage times prior to analysis and the analytical
methods chosen all contribute to incompatibility
of data. Considerable time and effort should be
allocated to ensure that the samples collected, and
the results obtained, are of a consistent high quality.
To facilitate the collection of high quality
samples and data interpretation, field log
sheets need to be completed at the time of
sample collection. Examples of field record data
sheets are presented in Fact Sheet No. 1.
The reader is strongly recommended to review
published guidelines and texts for the collection
and preservation of samples prior to designing
and implementing a monitoring program.
Examples of such documents are provided in
the references section of this handbook.
5.4.7 SAMPLE TRANSPORTATION
The remote location of most Australian mining
operations means that samples may need to
travel considerable distances to the laboratory
at which the analysis will be performed.
Water samples should be freighted in portable
“coolers” containing ice, as many parameters
require storage at 40C prior to analysis. Samples
should be placed in designated “coolers”
to allow the separation of low-level control
samples from high level effluent samples.
Some parameters (for example alkalinity) require
analysis within 3 to 24 hours of sample collection
and so, it is recommended that these analyses be
performed at the mining operation using properly
calibrated instrumentation and clean conditions.
Others, such as pH, EC and temperature should be
measured in the field. The remaining samples should
be rapidly transported to the allocated laboratory
if possible by same-day or overnight transport.
Appropriate chain-of-custody forms must also be
dispatched with the samples, clearly identifying
all sample details and the required analysis.
5.4.8 SAMPLE ANALYSIS
The selection of a laboratory is an important
decision in the design phase of the program. It is
preferable that the laboratory and the methods
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used for a specific analysis are NATA registered.
NATA registration means that the laboratory has been
inspected by personnel from the governing authority;
the analytical method has passed stringent quality
control procedures and the method has been used in
inter-laboratory quality control programs. The results
of these inter laboratory quality control programs
should be requested prior to commissioning
long-term work to a specific laboratory.
The inclusion of duplicate and blank samples
within all sample batches sent to a laboratory
is recommended. Feedback should be
provided to the laboratory to identify and
remedy problem areas in the analysis.
As a guide, the QAQC component of monitoring
and analysis should account for at least 10-15% of
the effort (and cost) of the monitoring program.
It is essential that all aspects of a QA/QC
program are discussed with the selected
laboratory once the site screening program is
complete and prior to the implementation of
a long-term site-wide monitoring program.
5.4.9 DATA MANAGEMENT
Data management is an important component of
any environmental monitoring program, as vast
amounts of data can be generated within short
periods. Data management should be incorporated
into the initial planning stages of the program in
order that the database may be used to meet the
initial objectives of the monitoring program.
The use of spreadsheets for data storage and
management is often insufficient for most long-term
environmental monitoring programs. A relational
database is more applicable due to its capacity to
store and easily process vast quantities of data.
It also has the advantage of rapidly retrieving
information for a specific purpose, such as reporting
to government authorities. In most cases, existing
hydrologic, water quality and meteorological data
which are stored in a spreadsheet or ASCII format can
be imported easily to a central relational database.
A relational database linked to a geographic
information system (GIS) provides a particularly
powerful tool for the management and interpretation
of data. For example, geographic trends, such as
downstream dilution of groundwater contaminants,
are easily identified and readily appreciated
by management when presented visually.
5.4.10 LABORATORY, PILOT
PLANT AND LEACH TESTS
In some circumstances, laboratory bench scale tests
can increase the knowledge about the behaviour
and removal of a pollutant within a treatment
plant, sedimentation dam or tailings dam.
Pilot plant and laboratory studies can often be
more closely and easily monitored than full-
scale field studies, as samples can be collected
more frequently and the time, travel and cost of
collecting samples is significantly less. Examples
include the use of leach columns to test the acid
generation potential and leachability of tailings,
waste rock and other materials stored in bulk.
Where laboratory and pilot plant tests are
conducted, it is important that findings and
conclusions based on these studies are verified
in the field under full-scale natural conditions.
5.5 Data Collection - Quantity
When considering the data measuring systems
for the volumetric water parameters such as
rainfall, evaporation, and stream flow, the specified
use of the data is the primary consideration
in selecting the appropriate recording system.
The following is an overview of appropriate
recording systems and controls for various climate
and water-related parameters and the various
circumstances when each may be utilised.
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5.5.1 RAINFALL READING
There are two methods of recording data.
• Manualrecordingofrainfallcollectors,eg.a
standard rain gauge, on a daily basis. These
data are useful for general interpretation of
rainfall trends and long-term water balance
analyses. The data can also be used to
verify automatic recording rain gauges.
• Automaticrecordingraingauges,whichhavea
calibrated tipping bucket gauge with associated
electronic data recording logger. The advantage
with the automatic system is its ability to record
the time sequencing of rainfall events. These
data are valuable for characterising the storm
intensities for an area and for the establishment
of the rainfall runoff response at the site.
An automatic recording system is relatively
inexpensive to install, with power from localised
battery or solar panels. These systems can
manually download data to a computer or can
be connected to a telemetry system for data
capture remote from the site of installation.
5.5.2 FLOW RECORDING
Flow recording in existing streams and waterways
and future waste streams or diversion works is
essential for comprehensive characterisation of
the site hydrology and water management plan.
The critical areas where flow recording
instrumentation is either required or desirable
for developing site specific characteristics are:
• atlicenseddischargelocationsfromthesite;
• atstormwaterdischargelocationsaroundthesite;
• onexistingstreamsbothupstream
and downstream of the site; and
• selectedcatchmentswhereflowmonitoring
will provide useful design data.
The selection of flow monitoring systems will depend
on the characteristics of the monitoring location.
These normally range from constructing hydraulically
rated controls in streams, pipe monitoring systems
and manually flow rating the streams. Regardless
of the type of hydraulic control structure it is
imperative that the following basic rules be followed
in establishing the flow recording system.
1. Select the monitoring location that will maximise
the reliability of data recovery for the range
of flows that will occur. This may require
construction of hydraulic control devices such
as a flume or v-notch weir. Where natural
controls are selected they must be robust.
2. Select the appropriate flow depth recording
hardware for the monitoring location.
Typical flow depth recording sensors
include pressure gauges, sonic systems,
float gauges and capacitance probes.
3. It is essential that flow monitoring stations
be rated for flow and height. This may be
undertaken using a hydraulic structure that has
a pre-determined rating relationship. Where
natural controls are used, it is critical that the
flows are rated by physically measuring the flows
through the control and relating this directly
to monitored flow heights at the station. It is
not sufficient to rate a flow monitoring station
using only theoretical and analytical hydraulic
relationships that require subjective assessments
of coefficients (eg. Mannings equation).
4. Few chances occur to collect time related data,
and therefore it is critical that both reliable
and appropriate monitoring equipment be
installed. As vital development and strategic
decisions depend upon the values recorded
at these stations, the hardware monitoring
and recording equipment must be of a high
calibre. The following questions help with
the selection of suitable instrumentation:
• Willtheequipmentbeintactand
record throughout extreme events?
• Isthesiteaccessibleduringflowperiodsfor
manual flow recording (for rating relationship)?
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• Howoftencanloggersbedownloaded
and is a telemetry system required?
• Whatisthepotentialforvandalismor
damage by animals or large trees?
• Haverainguagesbeeninstalledat
appropriate locations for characterising
the rainfall/runoff response?
• Dopersonnelresponsibleforcollecting
the data and maintaining the station
have the required levels of expertise?
5. Measured and recorded data must be
validated to ensure the data is correctly
presenting the conditions being measured.
The validation must take place as soon as
possible after it is collected and should check:
• thatthedatarecordedarerealistic;
• anymalfunctionsininstrumentrecording;and
• thecalibrationdata.
Validation processes involve processing the
raw data into physical outputs (height and
flow), checking compliance against similarly
recorded data, verifying where the data fall
within the calibration limits and scanning the
data for anomalies and unrealistic outputs.
For the installation and operation of flow
monitoring systems, reference should be made
to the Australian Standard 3778 - “Measurement
of water flow in open channels” and all its
associated sub-sections. Care must be taken
that specific requirements for the location of
the system and measuring devices are followed,
otherwise inaccurate monitoring data will result.
5.6 Groundwater
5.6.1 GROUNDWATER MAPPING
Groundwater mapping involves the identification
and location of groundwater resources. A typical
groundwater map contains contour information
representing piezometric levels. Groundwater
contours should be shown relative to an absolute
datum (eg. AHD or a suitable mine datum) rather
than relative to ground level, as the ground contours
may bear no relation to groundwater levels.
Figure 5.1 shows a typical groundwater surface map.
Groundwater flow is always from a region of high
water level or piezometric level to a region of low
water level or piezometric level (see Figure 5.1).
The following steps are required to construct a
groundwater map.
• Groundwater“borders”shouldbedetermined
(eg. rivers, lakes, oceans and significant changes
in types of soil and rock). Where practical,
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mapping should include the entire
groundwater resource as well as its borders.
• Observationboresorpiezometers(seeSection
5.6.2) should be installed in a relatively regular
grid pattern over the area of interest. Piezometers
should be located such that the difference in
water levels between adjacent piezometers is less
than the planned contour interval of the map.
• Ambientgroundwaterlevelsshouldbemeasured
at regular temporal intervals to identify
seasonal fluctuations as well as responses to
rainfall and periods of drought. Care should
be taken to gather ambient data well before
activities such as pumping are commenced.
• Interpolationpackagesavailableforcomputer
simulation of contours may be used to
generate maps from gathered data. Each map
should be a snapshot of groundwater levels
for the relevant period of monitoring.
5.6.2 TESTING AND MONITORING
Groundwater testing and monitoring is carried
out to establish water quality and changes in
quality, and water levels and changes in levels.
Testing and monitoring should be undertaken
for ambient or pre-existing groundwater reserves
to establish baseline groundwater characteristics.
Testing and monitoring subsequent to events such
as pumping, recharge and contaminant leakage can
then be used to derive groundwater parameters
related to these events. These parameters allow
calculation of quantities such as drawdown
for various pumping rates, rates of recharge or
speed and direction of contaminant flow.
Prior to establishing a groundwater testing program,
hydrogeologists and analytical laboratories
should be consulted to determine the appropriate
testing, sampling and storage methods required
for identification of individual compounds in the
groundwater. Samples may need to be gathered
and stored in non-reactive containers to ensure
that they are not contaminated. Special care may
be required for biologically active contaminants.
Groundwater levels and quality may be monitored
using piezometers. Piezometers extending into
unconfined (water table) aquifers show water
levels which represent the surrounding water
table level. Piezometers extending into confined
aquifers show water levels which represent the
pressure existing within the aquifer. When there
are strong flows within the aquifer, a component
of the measured pressure may result from inertial
forces as well as static groundwater levels.
Figure 5.2 indicates the water levels given by
piezometers in unconfined and confined aquifers.
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Piezometer Construction
A piezometer is simply an open stilling well into
which a probe may be inserted to measure water
level or quality, or from which a sample of the
groundwater can be collected. Piezometers are
primarily made of either PVC (polyvinyl chloride)
or ABS (acrylonitrile butadiene styrene).
The material chosen for piezometer construction
should have strength, rigidity, low maintenance,
resistance to galvanic and electrochemical
corrosion, resistance to abrasion, high strength-to-
weight ratios, partial flexibility and low cost.
Other considerations are:
• piezometersmaybeinstalledusingavariety
of means from hand augers to drilling rigs. In
all cases, the piezometer tube is installed after
drilling a hole of sufficient diameter and depth;
• thediameterofthepiezometeruseddependson
the type of monitoring or sampling that needs to
be carried out. The sizes of probes and sampling
devices need to be considered. It is rare to find
piezometers of less than 50 mm in diameter, and
100 mm diameter piezometers are common;
• thelengthofthepiezometerneeds
to be sufficient to measure the
maximum possible drawdown;
• whenmonitoringconfinedaquifers,thewell
may need to protrude significantly above
ground, in order to measure the standing
head of the water. However, if this protrusion
becomes impractical, the well may be capped
and a pressure transducer installed within it;
• wellsshouldbeslottedorscreenedto
facilitate a good connection to the aquifer.
Open-bottomed, unslotted wells may
be used effectively in granular soils;
• slottedwellsoftenformthecheapestalternative,
as slots may be machined by the manufacturer
or cut by hand on site. Slots should be cut
liberally (either horizontally or vertically) but
should be small enough to exclude significant
intake of soil. Porous geotextile fabrics may
be used to filter out soil particles if required;
• preventionofcontaminationiscriticalforthe
collection of water quality data; the installation
of slotted or screened casing will be important.
In these instances, a hydrogeologist should be
consulted to provide appropriate well designs;
• piezometersshouldbecappedatthe
surface, preferably with a screw-in cap for
ease of removal and re-application;
• atetherwireandconcretecollarserveto
anchor the piezometer and reduce the risk
of slippage in unconsolidated material or
accidental movement from outside impact; and
• thelipofthepiezometershouldbesurveyed
into the mine datum or Australian Height
Datum (AHD), as this is the most convenient
point of reference for manual monitoring.
Figure 5.3 shows a typical piezometer installation.
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Monitoring
Monitoring of piezometric levels may be performed
manually or remotely. Manual devices include:
• dipmeters:thesecompriseanelectrical
sensor at the end of a graduated wire. Contact
with water completes the electrical circuit
between sensor and wire, causing a tone to
be emitted (see Figure 5.4). The distance
between the sensor and the reference point
(eg. the lip of the piezometer) may be read off
the graduated wire. Dip meters are popular
because of the ease and speed of use; and
• graduatedtransparentpiezometersor
manometers (when the piezometric
level is above ground).
Remote monitoring is carried out using a sensor
installed within the piezometer. The sensor may
be connected to a central monitoring system or to
a data logger which reads, at regular intervals, the
voltage output at the sensor. The data logger may be
downloaded regularly using a portable computer,
or may have removable memory banks which can
be replaced and downloaded later. The recorded
voltages are then translated into water levels via
calibration relationships. Popular sensors include:
• pressuretransducers;
• capacitanceprobes;and
• floatlevels.
Remote monitoring carries a much higher
risk of data contamination or error. A rigorous
schedule of equipment maintenance, data
verification using manual methods, and frequent
calibration checks should be in place.
Groundwater Sampling
Testing of groundwater quality may be carried
out using in-situ methods or by the extraction
of a representative sample. A range of field
equipment exists for measuring such basic
parameters as pH and conductivity, using probes
which may be lowered into piezometers.
Groundwater samples are normally collected from
a piezometer or bore using one of two techniques:
a bailer or submersible pump. Submersible pumps
powered by a battery or generator are preferred
due to the large volumes of water that need to
be displaced from a bore prior to the collection
of a representative groundwater sample.
In addition to these two methods,
groundwater samples may also be collected
from sample valves located near above-
ground pumps on water supply bores.
When groundwater samples are to be collected,
the following should be considered:
• thepiezometerorboreneedstobepurged
prior to sample collection. This technique must
be used in order to obtain a representative
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groundwater or aquifer sample. In the absence
of extensive pumping, the sample collected
will merely represent water held in the bore
or piezometer which has been exposed to
atmospheric conditions. Extensive pumping also
reduces cross contamination of the sampling
equipment between bores. Typically, three times
the volume of water held in the piezometer or
bore needs to be removed prior to sampling;
• ifabailerisusedthenextensivebailingof
water held in the bore must be undertaken
prior to sample collection. Most bailers only
have about one litre capacity and consequently
manual bailing of a bore can be a time
consuming procedure. If sufficient funds
are available, disposable bailers should be
considered to eliminate the risk of sample
contamination between bores; and
• appropriatesamplecontainers,rinsing
procedures and preservation techniques
must be used, as for surface waters.
5.6.3 GROUNDWATER PARAMETERS
Physical and chemical parameters are of interest
when attempting to characterise and model aquifers
in order to simulate various scenarios. Groundwater
parameters are best obtained by stressing the aquifer
and observing the response induced. These stresses
are typically obtained by pumping water out of the
aquifer or pumping water into the aquifer via bores.
A large range of pump tests and analytical methods
exist for this purpose. Advice from qualified
hydrogeologists should be sought to determine:
• whichparametersareofinterest;
• cost-effectivemethodsofobtainingthisdata;and
• theapplicabilityofthesemethods
to site-specific conditions.
5.6.4 PREDICTION OF GROUNDWATER
CHARACTERISTICS AND RESPONSES
Prediction of aquifer responses to various scenarios
allows “what if ... ?” questions to be answered.
Predictive modelling may be carried out using
analytical models (simplified equations) or, more
recently, numerical models which use the technically
rigorous and complex physics of groundwater flow.
Numerical models have developed significantly
in the last two decades and their popularity
has increased. A brief discussion of the types
of numerical models is presented in Fact Sheet
No.12, and advantages and disadvantages of using
numerical models are summarised in Table 5.3.
Predictive modelling in groundwater now enjoys
widespread use and offers significant benefits
in assessing groundwater-related issues. An
increasing environmental focus in the mining
industry and the recognition of groundwater as
a fragile natural resource has seen the expanding
use of groundwater models. Models simulating
contaminant transport in groundwater and root-
zone behaviour are now widely available.
Predictive modelling should always be used with
a questioning attitude, and a rigorous process of
calibration, verification and sensitivity analysis should
be an integral part of any modelling program.
5.7 Review of Monitoring Data
For a vast majority of existing monitoring programs,
insufficient time is spent actually reviewing and
analysing the data. Regular screening of data can
detect problems in sampling and analytical techniques
as well as in hydrographic data recording systems.
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A review of the data set can establish seasonal
trends and will detect analyses that are unwarranted
(ie. those continually below the detection limit).
Sites with data that do not fluctuate to any degree
can be sampled less frequently to reduce costs.
Regular review will also forewarn management
of any impending changes which may effect
the sites ability to obtain or discharge water
or any breaches in compliance with statutory
obligations. Presentation of data in a graphical
format allows easy scanning of large numbers of
results and identification of trends in the data.
TABLE 5.3: Advantages and Disadvantages of Using Numerical Models
Primary Advantages Primary Disadvantages
• Abilitytoruncomplexandlengthy
calculations in increasingly short times
as computers evolve rapidly;
• alowleveloflabourintensity
during simulations;
• highcapacityfortestingthesensitivity
to groundwater parameters;
• thedevelopmentofincreasinglyvisualoutputs,
which allow the lay person to understand
the answers proposed by the models; and
• flexibilityinassessingarangeof
scenarios quickly and easily.
• Initiallyhighleveloflabourintensity
during setting up a numerical model;
• developmentofa‘blackbox’mentalitywhich
results in the widespread use of models without
understanding of concepts and limitations;
• atendencyamongthepublictoperceive
models as infallible and acceptance
of results as the literal truth; and
• highcapacityformisunderstandingormisuse
of models because of their complexity.
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6. Water Supply
In a country as arid as Australia, mining and mineral
processing operations will almost certainly require
a regular supply of water. Therefore, identification,
evaluation and maintenance of this supply will be
critical to the continued operations. While this topic
could demand a handbook of its own, some concepts
will be introduced in this section.
6.1 Surface Water
This section examines sources of surface water supply
around typical minesites.
6.1.1 CATCHMENT YIELD
When discussing the useful yield of surface water
within a catchment it is important to realise that it
can never be any greater than the facilities available
for storing or continuously using water. This can
include groundwater recharge, as discussed in the
next section.
The balance of processes contributing to the final
yield at a given storage facility can be represented as
Yield = Inflow - Outflow.
Inflow
The inflow into a storage may originate from any of
the following sources.
Imported water: reservoirs, irrigation schemes or major
supply pipelines are often the major source of water
for minesites in Australia.
Recycled water: most minesites in areas of water
scarcity are now recycling water from various stages
of the mine process. This is discussed in the following
section.
Direct rainfall: within shallow storages covering
large surface areas, the amount of direct rainfall may
be appreciable.
Rainfall runoff: the quantity and quality of rainfall
runoff will be dependent on the catchment area soil
type, topography and vegetation. A discussion on
estimation of rainfall runoff is given in Fact Sheet
No.2.
Groundwater seepage: during periods of rain, a
percentage of the water will seep into the ground as
infiltration. Some of this water will percolate into
groundwater stores. However, on sloping sites or
areas underlain by shallow rock, most water will flow
through the soil profile to the bedrock and percolate
out into a watercourse or cutting. This water will
continue to flow long after rain has ceased.
Mine dewatering: surface and groundwater reserves
that flow into mine workings are usually pumped
out to a suitable storage. This aspect is covered in
Sections 8 and 9.
Outflow
Outflows will result from any combination of
the following.
Releases: resulting from:
• excesswaterovertoppingstoragesandpassing
into the next catchment or off the lease;
• waterdrainedfromdarnstoallowfor
maintenance, to make room for expected inflows
or as regulated to provide water for downstream
ecosystems or users; or
• treatedwaterwhichmaybereleasedafter
sufficient residence time to remove pollutants
(eg. acidity, suspended solids, salinity).
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Evaporation: the loss of water from reservoirs
through evaporation is appreciable in many
regions of Australia. Where water supply is a
critical issue, it can be worthwhile attempting
to reduce evaporation by the use of a deeper
storage or various cover techniques. Evaporation
is also often used as a disposal method for
highly saline or otherwise polluted waters.
Water use: this will depend on the location of the
storage, the quality of the water and the scarcity
of water on the site. Other potential users of the
water must also be considered. A number of ideas
for recycling water are presented in Section 6.1.2.
Seepage: although seepage through the ground has
been identified as an inflow it is also an outflow
mechanism. Any dam is likely to lose some water
through seepage into the groundwater unless the
groundwater level is higher than the base of the
dam. In earth darns (as most minesite dams are)
seepage may also occur through the dam wall.
If considering the yield of a specific catchment, it
will be necessary to obtain specific information on
all the above processes relevant to that catchment.
Historical records of inflows and outflows will
provide invaluable information for the calculations.
The water balance method for identifying the inflows
and outflows is a useful tool for understanding how
the water supply for a minesite may be achieved
by considering all the potentially contributing
elements. The water balance allows the user to
optimise parameter values for the most desirable
outcome and to explore the probability boundaries
when variations are introduced (refer also to
Fact Sheet No.3 for probability information).
6.1.2 RECYCLING OF WATER
Most minesites promote the use of recycled
water. Recycling often occurs when water is
scarce, or the discharge of polluted waters could
be a hazard to the surrounding environment.
Even where water is freely available, it may
be more cost-effective to recycle water.
It is usually a more environmentally sound
practice to recycle lower quality water on a
minesite rather than to discharge the water and
use better quality water from clean supplies when
it is not needed. Some examples of sources and
uses of recycled water are given in Table 6.1.
6.2 Groundwater
6.2.1 SOURCES OF SUPPLY
There are two primary sources of groundwater
supply; unconfined aquifers and confined
aquifers. Perched water tables (see Fact Sheet
No. 11) are a special form of unconfined aquifer.
Unconfined aquifers may be used for water
supply via the pumping of bores. Confined
aquifers are generally under pressure and,
in some cases, may not require pumping to
extract water (eg. a flowing or artesian bore).
Individual groundwater resources tend to be
compartmentalised by geology, but are rarely truly
isolated. Despite some connection to other aquifers,
an individual groundwater resource should be
viewed as a finite body of water. Replenishment of
groundwater (or recharge) is a vital component in
assessing the long-term viability of a source of supply.
Recharge may occur through rainfall infiltration, or
from rivers and streams, or from artificial recharge
(such as pumping of surface water into aquifers).
6.2.2 SECURITY OF SUPPLY
Security of supply may be breached if the sustainable
yield is compromised when a bore is overpumped
or drawdown is quick but recovery slow. The quality
is compromised when pumping stresses lead to
dissolution of salts from the soil matrix and excessive
salinisation of the pumped water or development of
flow paths from neighbouring contaminated aquifers.
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TABLE 6.1: Sources and Uses of Recycled Water
Sources of Recyclable Water Uses for Recycled Water
Dirty mine water: surface runoff from dirty
areas, intercepted to remove suspended
solids and/or other pollutants.
Clean mine water: there will be some limitations on
the amount of water which can be intercepted from
undisturbed areas. This is to ensure that downstream
users and ecosystems are not disadvantaged.
Process water: most process plants or washeries
will use large quantities of water which is often
returned to a process water tank or dam, and
then recycled back through the process.
Tailings liquor: tailings are deposited with varying
percentages of water to allow pumping, and to
ensure proper deposition and drying. Excess water
remaining after solids have settled can be recycled
directly or after passing through a filter dam.
Washdown water: vehicle and workshop
washdown water should be passed through
a settling pond and oil separator, after which
it may be suitable for selected recycling.
“Grey” water: wastewater from showers, hand
basins, laundries and kitchens should be treated to
remove solids and can then be recycled. Chemical
dosing (eg. chlorine) may be necessary if people
will come into contact with the recycled water.
Treated effluent: package or site built treatment
plants are used to treat sewage to acceptable levels
after which it can be used for limited recycling
applications. Treated industrial effluent from
workshops may also be used for recycle water.
Dust suppression: dust control for haul roads,
conveyor belts and transfer stations, loading facilities,
dump hoppers, stockpiles (product and waste),
construction sites and working faces does not require
high quality water. Issues which may affect this are:
• suspendedsolids,whichmayblock
pumping and spraying equipment;
• viralandbacterialmicro-organisms
which, if present in fine aerosol mists,
are easily ingested by workers; and
• nutrientlevelswhichcanpromotealgal
growth and block spray equipment.
Process water: processes which involve crushing,
washing and screening are suited to using
recycled water. Co-disposal tailings will utilise
recycled water. Typical quality issues are:
• chemicalmakeupofthewater;and
• suspendedsolids.
Irrigation: rehabilitated areas, gardens and perhaps
even neighbouring properties or stock may be a very
efficient use of wastewater. Irrigation to rehabilitated
areas may result in water dependant regrowth with
shallow root systems which will struggle to survive
if irrigation ceases. Water quality issues are:
• chemical,salinityandpHextremeswhich
may adversely affect plants and/or stock;
• suspendedsolids(asfordustsuppression);
• viralandbacterialmicro-organisms.
Wetlands maintenance: during rainy periods there
will usually be enough dilution and flushing to
keep wetland systems healthy. However during dry
periods there may be a build up of pollutants from
mine dewatering or simply a shortage of water.
Quality issues are similar to those for irrigation.
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Sustainable yield is a significant parameter in water
supply. It determines the maximum flow which
may be extracted over the long term. This factor
is determined by pump testing and analysis of
drawdown. Borefields of two or more bores will
incur some penalty in the sustainable yield of each
bore because of interaction between the drawdown
from each bore. More intensive analyses are required
to identify the sustainable yields of borefields. The
sustainable yield should be identified whenever bore
water supply is considered. Expert advice should be
sought before commissioning a bore drilling program.
The quality of water pumped out of a bore may
depend on the rate of pumping exerted. The
sustainable yield of a bore should be identified
in conjunction with any deterioration in the
quality of water being pumped. The likelihood
of quality deterioration may increase with the
rate of aquifer pumping. For example, in coastal
locations seawater may migrate towards a bore
which is pumped beyond its sustainable yield.
Constant monitoring of quantity and
quality is an integral part of water supply
evaluation and maintenance.
• Quantities of pumped water should be
noted throughout the life of a bore. Flow
totalisers are a convenient and cheap method
of monitoring quantity. These show the total
volume of water pumped. When monitored
regularly and used together with a record
of pump down time, adequate information
on pump rates may be gathered.
• Aquifer drawdown should also be monitored
on a regular basis. This may be done using
adjacent observation bores and, where possible,
within the pumping bores themselves.
• Water quality monitoring should be carried out
regularly on representative samples pump from
bores. Relevant water quality standards should
be consulted, depending on the use of the
supply. These may be for potable water, ablution
water or process water. Site-specific process
water requirements should be determined
where the water is used for processing.
TABLE 6.1: Sources and Uses of Recycled Water (CONTINUED)
Sources of Recyclable Water Uses for Recycled Water
Slurry transport water: at the end of a slurry
pipeline, the slurry is dewatered, leaving large
quantities of water. The location will often be
environmentally sensitive, hence the water
would require treatment to high standards before
discharge; re-use may be a better option.
Washdown water: recycled “grey” water and treated
wash down water can be used for washdown of mine
equipment and workshop areas. Quality issues are:
• buildupsofoilordetergents;
• viralandbacterialmicro-organisms
which if present in fine aerosol mists
are easily ingested by workers.
Potable water: in very arid and remote areas it may
be viable to treat recycled water to very high levels
and use it as a potable water source. Clean and
dirty water runoff are obvious sources, but other
sources can be used. All facets of water quality
will obviously be vital if this is the intended use.
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If a licence is required for the bore or borefield,
conditions such as these are generally included
on the permit. The information gathered
usually has to be provided to the licensing
authority on renewal of the permit.
The intensity of the monitoring program
selected for water supply bores should reflect
the importance placed upon the supply.
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7. Exploration
Water is an important component in
exploration activities and therefore careful
management is necessary as in any other
aspect of mining and mineral processing.
A lack of water for process, potable and fire
protection requirements or an excess of water (eg.
high groundwater table, large aquifers, flood risks)
can determine the subsequent economic viability of
a mining project. Therefore serious consideration
must be given to water constraints during the
early exploration phases of a project. This should
include data gathering of both surface water and
groundwater resources as well as initial flood studies.
The environmental significance and sensitivity of
watercourses and other waterbodies (surface or
ground) will determine the extent of exploration and
subsequent mineral extraction allowed in any area.
This will be dictated by the relevant legislative body
(ie. Mining, Environmental and Water Resources
departments) at both State and Commonwealth level.
Water will also play a role as a resource and/or
hindrance to the actual exploration efforts. Rivers,
streams, rainfall runoff and groundwater all need to
be managed to avoid or minimise damage
during exploration.
Many exploration activities could be
considered as miniature minesite operations;
hence all sections of this handbook will be
applicable, albeit at a modified level.
7.1 Surface Water
Most exploration activities in Australia will be
in areas where minimal knowledge of ground
and surface water behaviour exists. Therefore
the collection of all possible information that
may be relevant is encouraged. At the same time,
care of the existing environment is required.
7.1.1 SURFACE WATER DATA COLLECTION
The lack of water or the possibility of serious
flooding may seriously impact the extent or timing
of an exploration program. Information on rainfall,
evaporation and stream flows in the project area is
often inadequate, and important decisions are usually
made using data extrapolated from many kilometres
away. Exploration teams can provide important data
to reduce the risk associated with these decisions.
Records should be kept of local surface water
conditions. This can include evidence of previous
flood heights through the location of debris and local
knowledge, conditions of watercourses (ie. flowing
regime, photographs), signs of erosion, and quality
of water. Monitoring water quality will also provide
valuable background information, which may form
an important part of future license conditions.
If a new deposit has high potential and continuing
exploration is likely, a remote weather station
network as well as stream gauges in all major
watercourses should be established. These
installations should measure rainfall, temperature,
wind speed and direction, evaporation and stream
flows. A few years of local climatic data between
54 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
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the time of initial exploration and the stage of
feasibility decisions will provide invaluable assistance
in the design of water supply dams, tailings dams,
evaporation ponds and any flood mitigation or
mine drainage works required (refer to Sections
5.4 and 5.5, and also Fact Sheet Nos 3 and 10).
7.1.2 ACCESS TRACKS
Exploration projects which cover a large area with
many drill holes in different locations will often
result in a “spider web” of access tracks linking
the different sites. The clearing and constant traffic
associated with such drill lines and access tracks
can lead to serious erosion and sediment problems
if precautions are not taken to minimise their
impact. The construction and rehabilitation of access
roads is dealt with in Section 6.8 of AMIC (1990),
while the following points provide guidelines for
reducing the impact of tracks on surface water.
• Minimisetheareaofdisturbancebyreducing
the number of tracks and using the same routes
(even if the journey takes slightly longer). It is
also very important that four wheel drive vehicles
remain on existing tracks whenever possible.
• Whenlocatingtracks:
– every effort should be made to minimise
clearing and other disturbance to vegetation,
especially in well vegetated areas with
easily eroded soils (eg. wet tropical areas).
Tracks should deviate around large trees;
where this is impractical, use the timber
to stabilise edges and low points;
– avoid using gullies as convenient
locations for tracks;
– locate creek crossings in naturally
rocky locations, or line sensitive or
erodible crossings with rocks;
– avoid permanently wet and boggy areas;
– install silt fences or hay bales across
watercourses where sediment from
disturbed areas will impact the
undisturbed drainage line; and
– keep tracks a reasonable distance
away from watercourses to ensure a
vegetation strip is maintained.
• Whenconstructingtracks:
– avoid using heavy earth moving
equipment to construct temporary
tracks, as this will destroy root stock;
– culverts are recommended for creeks and
streams on more permanent tracks. These
will reduce mud and keep tracks passable in
most weather. For guidelines on the design
of culverts, refer to Fact Sheet No.6;
– runoff should not be allowed to concentrate
on tracks. Flow should be shed off the road
as quickly as possible by using reasonable
crossfall (say 3%) side drains with regular
take-offs and by allowing sheet runoff to
flow uninterrupted across the track. Where
road access cuts across steep hillsides, road
stability may necessitate sloping the cross
fall into the hill slope and into a side drain,
which then discharges via a constructed
drain built at a low point under the road
or across an armoured road crossing;
– if it is necessary to cut roads greater than
2 m wide into the natural surface, then
small v-type interception drains should be
used to divert water from the batter slopes.
Generally batter slopes should be no steeper
than 2H:1V (0.75H:1V in rock); and
– any discharge points for culverts or table
drains must be protected against erosion.
• Ensurealltrackstobeusedarelocatedon
field maps and that all personnel are instructed
to use only those marked tracks. This will
reduce people’s desire to create their own
tracks and hence minimise disturbance.
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7.1.3 EXPLORATION SITES
On any given project, the area physically
disturbed will be reasonably small and control
of erosion, runoff and discharges from these
areas is relatively straight forward. Guidelines
for minimising impacts on water include:
• abufferzoneshouldbekeptbetweenthe
exploration activities and environmentally
sensitive areas. The width of this zone will
depend on the sensitivity of the area and may
range from 10 m for a non-sensitive bank
of a watercourse up to 3 000 m or greater
for an environmental conservation zone;
• aswithaccesstracks,theareaanddegreeof
clearing should be kept to a minimum;
• thedischargeofwastesintowatercourses
must be avoided. Various waste
can be handled as follows:
– fuel and oil storage tanks and dispensing areas
must be bunded and sealed. Oil absorbent
booms should be used across storm water
drainage points away from these areas;
– sewage should be treated to recognised
levels using septic systems or commercially
available package treatment plants or
contained and removed from site;
– toxic and saline wastewater must be stored
in ponds either permanently or until
treated or degraded to safe levels; and
– sludges and silt resulting from drilling
or processing operations must pass
through sumps to settle or filter out
fines before the water is discharged;
• thedownstreamorlowersideofanycleared
area should be arranged so as to intercept and
contain sediment washed down by surface
runoff or concentrated discharges. This is easily
achieved by the use of interception drains
and silt fences, hay bales, silt traps or filter
dams, as described in Fact Sheet No.8; and
• damsordiversionstowatercoursesshould
be thoroughly investigated to ensure any
adverse effects are minimal. They should also
be designed, constructed and maintained to
ensure good water management (Fact Sheet
No.5). It is important to advise the relevant
Water Resources department in any State before
undertaking such works. Dams which retain
large volumes or which could risk life and
property in the event of failure will often require
licensing and much stricter design standards.
Exploration within a watercourse or riparian
zone has the potential to severely damage the
surrounding environment and hence will require
more rigorous control than described above.
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8. Open Cut Mines
Management of surface and groundwater flows
around open cut mines is critical to safety and
the operation of the mine. This is a specialist
topic and detailed design and engineering
should be undertaken by relevant experts.
However, the environmental officer may
play an important role in tasks such as:
• providingthebasedatatodetermine
the likelihood of an event;
• routinemonitoringtoevaluatethe
performance of the control structures; and
• adviceonthebestmeansof
disposal of excess waters.
Consequently, it is important that there is close
consultation between the expert and the officer
charged with site management responsibilities.
The following section provides some basic
information to assist the environmental
officer in understanding some of the specialist
hydrological engineering issues.
8.1 Surface Water Runoff
Flooding of open cut mines can be a very real
problem if a mine is located in a valley or in the path
of a stream or a river with a significant upstream
catchment. Depending on how quickly it occurs
and how severe it is, flooding can cause a variety
of problems such as loss of life or injury, damage
to machinery and infrastructure and, far more
likely, loss of access to the pit due to water and silt
and subsequent loss of production. All of these
scenarios are highly undesirable to mine operators.
8.1.1 FLOOD MITIGATION
There are numerous factors which dictate the
type and extent of flood mitigation works best
suited to a particular site. Every mine will have a
different set of conditions; hence only the major
issues will be covered in this handbook.
Type of Flooding
Before considering any mitigation works, the
extent of flooding likely to occur naturally
should be estimated. This should include
conservative estimates of the following:
• totalvolumeofsurfacerunoffentering
the pit (Fact Sheet No.2);
• thepeakrateofflowintothispit
(Fact Sheet No.2); and
• themajordrainagepathsby
which water enters the pit.
Safety
This is the highest priority in mining and the
possibility of injury or death due directly or
indirectly to pit flooding will be the primary
determinant of flood mitigation measures.
Economics
If safety is not a deciding factor, a cost/benefit
study should be carried out. For the proposed
schemes, the capital and annual maintenance
costs should be added to the residual costs due
to annual flood damage (eg. the costs incurred
when the scheme fails). The scheme which gives
the lowest total cost will then be the most effective
solution. This approach is illustrated in Figure 8.1.
It is rarely practical to eliminate totally the risk
of flooding and hence protection of the flood
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O P E N C U T M I N E S
mitigation works against overtopping
damage should also be considered.
Pit Location
The location of the pit in relation to the catchment
will determine whether a particular scheme
is feasible, ie. a pit at the bottom of a steep
valley will have fewer alternatives than a pit
located in a wide gently sloped flood plain.
Appropriate Risk
The level of risk (of failure) associated with a
given flood mitigation scheme is linked to both
the safety and economic issues. When deciding
at what level of risk to design a scheme, an
important consideration is that a very low level of
risk (ie. failures are very rare) may lead to a lack
of contingency planning such that when a very
large flood occurs the results may be disastrous.
8.1.2 METHODS OF FLOOD MITIGATION
There are many flood mitigation methods
available to the mining engineer. Each method
has different environmental impacts and these
should be addressed as part of the design criteria.
For example, if the waterway is a valuable riverine
habitat, it may be better to build an upstream
flood control reservoir than widen the channel.
Maximising Waterway Capacity
The intent of this method is to optimise the ability of
existing rivers, streams or drainage channels to carry
flood waters away from the pit. This can be done by:
• altering cross section - increasing the cross
section size will give a greater flow capacity
Note that, if the existing waterway is prone to
erosion, the channel should be made wider
only. If the existing waterway is prone to silting
the channel should be made deeper only
(Take care that the existing system does not
incorporate both erosion at high flows and
silting at low flows.) Impacts on downstream
unaltered sections must also be assessed;
• upstream erosion protection - a reduced sediment
load can prevent clogging problems in the
lower reaches of a waterway. This can be
achieved by protecting steep sections (usually
the upper reaches) of a stream against erosion,
using methods such as drop structures,
check dams, bottom sills, vegetation and
channel armouring (Fact Sheet No.8); and
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• coarse sediment traps - another method of
reducing sediment load in flows is to create a
coarse sediment trap upstream of the area to be
protected against flooding. This can consist of
a wide shallow pond or flood plain area which
will allow the same flow to pass at a much lower
velocity, hence allowing sediment to settle. It is
important to note that sediment traps require
regular cleaning to maintain their performance.
Dykes
Constructed embankments either side of a
natural waterway can give a large increase in flow
capacity. The final capacity is determined by the
height of the embankments and their distance
apart. Where space is available it is better to
have low embankments spaced far apart. This
configuration will be cheaper, safer and result in
less erosion. For a meandering stream the dyke
system should form a band which envelopes the
stream (Figure 8.2). Upstream and downstream
impacts of these structures must be assessed.
Flood Control Reservoirs
If the catchment upstream of the pit is steep and
subject to short heavy storms, it is likely that
flooding will be short in duration and have a high
peak flow (refer Fact Sheet No.2). In this situation
a useful method of flood control is to attenuate
this peak flow (eg. temporarily hold back some of
the flood water until the peak flow downstream
has passed, and then release it at an acceptable
rate). The simplest method of achieving this is to
build a dam or basin with an open outlet at the
base to gradually release the intercepted water.
Flood Diversion
If it is feasible, the most effective way of flood
mitigation is to divert water away from the
mine. Diversion channels can direct water
to a number of different points, such as:
• samewaterwaydownstream;
• adjacentfloodplains;or
• nearbylakesorstreams.
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If a diversion method which returns flow to
the same waterway further downstream is
used, it is important to assess any backwater
effects. For example, a sudden increase in flow
downstream may cause the waterway to back up
and flood the pit from the downstream end.
8.1.3 IN-PIT DRAINAGE
All open cut mines are likely to have water entering
the pit and ponding at the lowest point. In most
cases this water will need to be removed from the pit
to avoid disruption to mining activity. The amount
of water to be dealt with will depend on the area
of the pit and access ramps (which will determine
the amount of direct rainfall), the effectiveness
of flood mitigation and pit interception drainage
schemes (refer to Sections 8.1.1 and 8.1.4) and
management of groundwater inflow (Section 8.2).
The quality of water will, in part, depend on
the residence time in the pit. Water may be
exposed to mineralised or acidic material and
become contaminated, or may contact spilled
hydrocarbons. In both cases treatment may
be necessary prior to release. Rapid disposal
of in-pit water will limit the problem.
Drains
Design criteria will need to consider:
• themainaccessrampintothepitmustbe
kept trafficable. Hence ramp side drains
should cater for high peak flows;
• drainsonthepitfloormustbekeptaway
from main traffic routes. This saves the drains
from damage by large vehicles, keeps the
pit accessible by small service vehicles (eg.
surveyors) and avoids mud on vehicles;
• wherepossible,drainsshouldbemaintained
at a slope between 1% and 3% to avoid
silting and erosion problems; and
• drainswhichcrossmajortrafficroutesshould
behardlined“swayles”(wideshallow‘v’
drains). If large flows are expected then correctly
sized culverts should be installed (refer to
Fact Sheet No.6). Inexpensive and re-useable
corrugated steel pipes (Armco culverts) are
suitable; however attention must be paid
to installation and cover requirements.
Sumps
The size and configuration of sumps will vary
to suit individual conditions. However the
following guidelines should be followed:
• forsafetyandconveniencelocate
sumps away from trafficked areas;
• incorporatethesumplocationatthemine
planning stage to ensure floor slopes
and seam slopes are accounted for;
• ifpumpingoutisused,locatethesumpto
give a suitable route for the pipeline to the
required discharge point (Section 8.3.1);
• locatethesumptogivemaximumlifebefore
pit development dictates a new location;
• duetotypicallyhighsedimentloadsinin-pit
runoff water, the sump should ideally have at
least two cells. The first cell will allow the silt to
settle or be filtered out of suspension and should
be easily cleaned by in-pit equipment; and
• thesizeofthesumpdoesnotnecessarily
need to cater for the total flow into the pit
but rather should be located such that all
water eventually drains into it (ie. once the
dewatering system catches up with the inflow).
Dewatering Options
Three commonly used methods to dewater mine pits
are pumping, shaft and tunnel, and slot drainage.
If water discharging from the pit is not retained,
the impact of variable flows and water quality on
the downstream surface water or groundwater
bodies will need to be considered. Water disposed
of in these ways may need to be monitored
continuously as its quality will be affected by the
length of contact with mineralised zones in the pit.
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8.1.4 INTERCEPTION DRAINAGE AROUND PIT
Where open cut mines do not have flooding
problems there will usually be some runoff towards
the pit from the immediate surrounding areas
(Figure 8.3). If this water enters the pit it may
be exposed to acid generating rock not present
on the surface and will also necessitate larger pit
pumps, generally causing inconvenience and
delays to in-pit operations. Therefore interception
drainage should be installed around the pit.
Interception drains should be installed as close
to the top of the pit as practicable. It is also good
practice to use these drains to separate clean water
(ie. runoff from undisturbed catchment) from dirty
water (ie. runoff from disturbed catchment). This
may require parallel drainage systems but will result
in much smaller sediment loads and in some cases
a reduction in treatment facilities (Figure 8.3).
Providing interception drainage can be difficult
if the mine is in rough terrain or located in a
valley. There are many techniques that can be
used to develop an interception scheme.
Runoff Interception Techniques
Contour drains: the simplest method is to use the
natural topography and run an open channel
drain around the pit. If the pit is at the bottom
of a natural bowl this technique is ideal. It is
usual to design these drains for a 20 Year ARI or
an ARI to suit the acceptable risk for the open
cut (refer to Fact Sheet No.3). For the design of
open channel drains refer to Fact Sheet No.4.
Gully dams: simple contour drains will not be
effective if a number of gullies run towards the pit.
In this situation it is necessary to cut off the gullies
using dams (refer to Fact Sheet No.5). These dams
should be sized such that the overflow spillway is
high enough to direct flow into an adjacent gully
which is not flowing into the pit, or into a high
level contour drain which can avoid the pit.
Flow detention basins: small scale versions of the
flood control reservoirs discussed in Section 8.1.1
can be used to detain and regulate flows as part
of an interception scheme. Where a number of
small catchments feed into a single collector drain,
detention basins can be used to delay flows from
some of the areas and hence reduce the peak flow
in that drain. If pumping is necessary as part of
the interception scheme, detention basins can be
effectively used to regulate flow to the pump. This
will reduce the required pump size. As with the
flood control reservoirs, it is important that these
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dams should self drain to ensure they are
empty when a storm occurs. The size and
design of detention basins is dependant on
the area, steepness and ground cover of the
catchment as well as the design storm (Fact
Sheet No.3) and degree of detention required.
In-pit systems: if the terrain is extremely difficult
it may be too expensive to create an effective
interception scheme. In such cases it may be possible
to use the benches of the pit as a drainage path. In
strip mines, where the pit is continually moving
forward, this is especially effective. If possible, the
back bench of the pit should be sloped towards
a deep gully where the water can be discharged
away from the pit. In some cases, however, the
only feasible direction to drain water is into the
pit. If this is necessary, careful thought should
still be given to doing it in a controlled manner so
that drainage paths remain stable and pit pumps
can cope with the inflows (Section 8.1.3).
8.1.5 SEDIMENT CONTAINMENT
The containment and control of sediment in
and around open pits is important for efficient
mine operations and is vital for the protection
of the environment surrounding the mine
(Note: for containment of sediment on and
around waste dumps refer to Section 11.2.4).
Some of the adverse effects from uncontrolled
sediment transport and deposition are:
• upstreamerosion;
• cloggingofpumpinletsandsumps;
• blockageofculverts;
• reductionofdraincapacities;
• accessproblemsforlightvehicles;
• damagetovegetation;
• lossofhabitat;and
• off-leasedischargesexceedinglicenselimits
for suspended solids and/or turbidity:
The best way to avoid these problems is to prevent
sediment from being eroded and transported.
If this is not feasible, it is then necessary to
contain the sediment in controlled locations
where it can not cause these problems.
Avoiding Erosion and Transport of Sediment
Clearing control: the most effective way to prevent
soil erosion is to not disturb the natural (stable)
ground. In open cut mining, clearing of vegetation
and stripping of topsoil and overburden is necessary
and must be carried out in advance of pit operations.
Care must be taken not to strip this area too early,
and to minimise the area actually cleared.
Effective rehabilitation: rapid rehabilitation of
disturbed mine areas will stabilise soil, and so
prevent erosion. It is advisable to direct runoff
from rehabilitated areas into the dirty water system
for some time after completion of the area, to
ensure that any sediment that is eroded can be
contained before flow is discharged offsite.
Open channel erosion control: controlling erosion in
open channels is very important for effective flood
control and interception drainage. Prevention of
scour in drains is achieved through good design and
adequate protection (refer to Fact Sheet Nos 4 and 8).
Increasing infiltration: erosion and transport of
sediment is caused by water flowing at high
velocities entraining soil particles. To prevent this
it is necessary to reduce the amount of runoff and
to slow it down. On large disturbed slopes, such
as stripped or recently rehabilitated areas, this can
be achieved by ripping along contour lines using
grader or dozer tines. This will increase infiltration
and inhibit overland flow. Important considerations
for ripping are covered in AMIC (1990).
In-pit sediment: an open pit is naturally a highly
disturbed area. Therefore as a sediment management
technique, it is best to have as much sediment
as possible in the pit where it does not have
to be controlled. Large and shallow sediment
traps upstream of pit pump-out sumps are an
effective way of achieving this (Section 8.1.3).
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Removal of Suspended Sediment
from Flowing Water
The two techniques for removing suspended
sediment from flowing water are filtration
and settlement (refer to Fact Sheet No.8).
Filtration: by passing water through a fine media or by
causing it to percolate slowly through an obstruction,
silt will be removed. For overland flow this can best
be achieved using synthetic or hay bale silt fences
for small to medium sized cleared areas, or strips of
heavy vegetation where these have not been cleared.
When planning for clearing of an area, vegetation
should be left undisturbed wherever possible. For
channel flow it is best to use rock filter dams.
Settlement: allowing water to flow into a large wide
body of water will significantly reduce the flow
velocity and will allow sediment to settle out of
suspension. These sediment ponds can be designed
to allow even the smallest sediment particles to settle.
Shallow heavily vegetated wetlands are extremely
efficient sediment traps as they both settle and
filter suspended solids. They can also be effective
in the treatment of acid drainage and heavy metal
problems. They must be designed and constructed
with care to ensure the correct level of water
and balance of vegetation are maintained.
8.2 Groundwater
8.2.1 GROUNDWATER INFLOW
Groundwater inflow to open cut mine pits
is controlled by three primary factors:
• hydraulicgradient(theslopeofthewater
table in an unconfined aquifer, or the
piezometric pressure in a confined aquifer);
• hydraulicconductivity(oftenreferredto
as permeability) of the soil or rock; and
• theareathroughwhichflowoccurs.
An idealised example of pit inflow in a homogeneous
unconfined aquifer is shown in Figure 8.4.
Visual evidence of the flow through area is given
by the existence of a “seepage face” on a pit wall.
This is characterised by a slick or wet appearance
of the soil or rock surface, and close examination
of this region may reveal trickling flow.
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Where a permeable fracture or a similar preferred
flow path exists (in a non-homogeneous aquifer),
the seepage face is often a discrete feature and
may only show up as a long, thin line rather
than a plane, as shown in Figure 8.4.
8.2.2 MANAGING GROUNDWATER INFLOW
Groundwater inflow may be accommodated in
the mine plan by restricting and/or containing
the flow, and routing it elsewhere (dewatering).
Flow Restriction
Groundwater flow may be restricted by reducing
the hydraulic conductivity and/or reducing the area
through which flow occurs. These may be achieved
by any of the following methods (Bedient et al, 1994):
• Slurry walls may be constructed perpendicular
to the direction of groundwater flow. These are
generally installed at sufficient depth to intersect
bedrock so that the aquifer is “barricaded”;
• Grout curtains are formed by injecting grout
(which may be in a liquid, slurry or emulsion
form) under pressure via grids of staggered
wells. Solidification of the grout then provides
a barrier to groundwater flow; and
• Sheet piling is applied by driving sheets
of steel into the ground until contact is
made with bedrock. Improved hydraulic
retardation is obtained by using interlocking
sheets to form a more continuous barrier.
Figure 8.5 shows, schematically, the effect
of placing a barrier to groundwater flow
Containment and Re-routing of Flow
• Dewatering is commonly carried out to lower the
watertable by pumping water out of the aquifer
and away from the mine. A series of bores or
spear points may be positioned in areas of
good hydraulic connectivity to allow pumping
at a sufficient rate to draw down the aquifer.
Drawdown of the watertable reduces the flow
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through area of groundwater near the mine pits.
Ideally, the watertable should be drawn down
below the floor of the pit so that groundwater
inflows are eliminated altogether. Figure 8.6
indicates the effect produced by dewatering.
• Channel dewatering: groundwater may also be
intercepted outside the pit if the topography,
groundwater regime and mine plan allow this.
A channel may be constructed to lower the
water table and drain the water to downstream
catchments. However, lowering of the watertable
in this manner is generally less effective because
of the reliance on steady gravity drainage. Figure
8.7 shows the method of channel dewatering.
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When groundwater flows are not highly
significant, the water is often intercepted in the
pit, collected in a sump and pumped to a retention
dam for treatment or storage as required.
Each method of managing groundwater inflows
will have different environmental impacts. These
will need to be evaluated prior to implementing
a control technology. Issues such as volume
of flows, water quality, effect on other users of
the groundwater, surface drainage systems and
receiving water bodies should be addressed.
8.3 Water Quality
8.3.1 PIT WATER DISPOSAL
Water held at the base of an open mine pit may
be derived from direct rainfall, surface runoff from
outside the pit and groundwater seepage. The
contaminants which can be present include:
• oilsandgreasesfromlightandheavymachinery;
• dissolvedandparticulatemetalsresultingfrom
the dissolution of metalliferous minerals;
• nutrientsfromexplosiveresidues;
• aciddrainage;
• suspendedsediments;and
• salts.
If acid drainage is present from the oxidation of
sulphide minerals contained in the rock within
the pit, then specific treatment and management
strategies need to be considered. Options for
the prevention and alleviation of acid drainage
problems are provided in Section 8.3.2.
Options available for the disposal of pit
water include:
• disposaltoevaporationponds;
• directorindirectuseasprocessplantwater;
• irrigationofrehabilitatedareaswithin
the minesite (eg. waste dumps);
• co-disposalwithtailingswater;and
• treatmentfollowedbydisposal
to receiving waters.
The option decided upon will depend on the quantity
and quality of the water needed to be disposed.
8.3.2 ACID DRAINAGE
Acid drainage can occur within an open pit
when sulphide bearing minerals are exposed to
air and water. The resulting low pH water can
readily dissolve heavy metals that are contained
in the orebody, overburden and waste rock.
Additional detail outlining the chemistry and
conditions favourable to the formation of acid
drainage are provided in Fact Sheet No.7.
Acid water within an open pit is a problem if the
water within the pit migrates to groundwater
via rock pores or fissures or if the water from
the pit is pumped to a storage area which
may leach or overflow to receiving waters.
It may also be an operational problem; for
example, corroding structures and pumps.
Hutchinson and Ellison (1992) identified three
generally accepted approaches to the prevention
or abatement of acid generation and leachate
migration. These measures are applicable to acid
drainage from open pits, waste rock dumps and
stockpiles and include, in order of preference:
• controloftheacidgenerationprocess;
• controlofthemigrationoftheleachate;and
• collectionandtreatmentofaciddrainage.
A combination of these three measures can
often be the most applicable solution.
While considerable research is being undertaken
on this topic, options for the prevention of acid
drainage at new mining operations and the control
and elimination of problems within existing.
open cut mines are generally limited to:
• analysesofdrillcoresamplesforawide
range of acid generation laboratory tests
prior to the commencement of mining;
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• avoidingorrestrictingtheexposureofsulphide
bearing rocks to the atmosphere. This may be
achieved by selective mining of the orebody
or modifying the overall mine plan;
• ensuringlong-termslopestabilitywithin
the open cut as deterioration can result in
the long-term exposure of fresh rock to
conditions which lead to acid generation;
• removalofthewaterasquicklyaspossible;and
• incorporatingacidneutralisingrock(eg.
limestone) in flow channels within the mine pit.
A number of standard laboratory tests may be
undertaken to determine the capacity of waste
rock or ore to generate acid and mobilise heavy
metals. Laboratory tests available include:
• acidneutralisingcapacity(ANC)-the
ability of a sample to neutralise acid
generated from sulphide oxidation;
• netacidproducingpotential(NAPP)-
the difference between the maximum
potential acidity (MPA) and ANC; and
• netacidgeneration(NAG)-adirectevaluation
without measuring the MPA and ANC separately.
Where these static tests indicate the potential for
acid drainage, it may be useful to perform kinetic (or
leach) testing. The data from both types of testing
can then be used to derive appropriate management
strategies to reduce the incidence or treat the
outcome of acid drainage. Expert advice at the testing
and planning stage can reduce the need for costly and
long-term chemical treatment of polluted discharges.
8.3.3 SALINITY
Mine pits which contain highly saline waters
require specific management strategies which
allow dewatering of the pit with minimal
environmental impact. The strategies implemented
will be dependent on the geographical location
of the mine and local climatic conditions.
In arid regions, evaporation ponds are the most
common method for the disposal of saline or
contaminated pit water. However care must
be taken to avoid discharge of the water, and
disposal of potentially contaminated bottom
sludge must also be considered. Some mines
dispose of hypersaline water to natural salt lakes,
but this technique is not favoured by regulatory
authorities. Depending on the quality of the pit
water, other techniques such as irrigation within
the release area may also be considered. Potential
impacts on vegetation would need to be reviewed
if irrigation is considered as an option. The
potential for deep well disposal may also exist.
In temperate and tropical regions, where rainfall
can equal or exceed evaporation, alternate methods
of disposal must be developed. Site specific
techniques and management practices usually
need to be implemented within these areas.
High flow conditions in surrounding rivers and
streams may also provide opportunities for discharge.
For example, in the Hunter Valley of New South
Wales saline mine waters are discharged to the Hunter
River during times of high or flood river flows when
the assimilative capacity of the river is high and the
saline water can be quickly flushed to the ocean. This
practice is now regulated by the NSW Government
through the Hunter Salinity Trading Scheme.
8.4 Pit Closure
Pit closure strategies are formulated to ensure that
protection of the water environment, both within the
site and downstream from the operation, is continued
following pit closure. Final pit geometry is dictated
by the balance of borrow and fill of earth, from the
mining operations to the rehabilitation operations.
However, water management concerns should be
addressed interactively during pit closure design.
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Open cut mine closure leaves voids which may
extend hundreds of metres below the water table.
Consequently groundwater is often a primary issue
in pit closure. An open void (see Figure 8.8) will
tend to fill with water from the adjacent groundwater
until a level of long-term equilibrium is attained.
This will impact on the surrounding equilibrium
groundwater levels. Recharge areas such
as streams or rivers may be affected by
these equilibrating processes. Surface water
drainage into the open void and evaporative
losses will form part of these processes.
Pit closure strategies should be viewed as a water
balance exercise, assessing the regional significance
as well as the local significance of the presence of the
void. Hydrological, surface water and groundwater
issues should be addressed to quantify and minimise
environmental effects of the final void on the
hydrological cycle and vegetation of the region.
In some cases, flooding of the open pit may be
desirable, especially if sulphide rock is exposed to
the atmosphere. In order to accelerate flooding,
adjacent streams may be diverted into the pit.
Such pits can also provide reliable sources of
water for stock or irrigation. However, monitoring
of the water quality will be necessary to ensure
that it does not degrade due to, for example,
acid generation from exposed sulphide rock.
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9. Underground Mines
A sudden and large flow of water into an
underground mine can have disastrous results and
minor quantities will also cause inconvenience to
personnel and machinery accessing the shaft.
The potential for this type of problem
and hence the level of preventative works
is dependant on the mine locality.
9.1 Surface Drainage Away from Head Works
The most cost-effective method to avoid water
entering a shaft or decline is to locate the shaft
away from any watercourses or flood plains.
If the general topography or the geological formation
of the ore body makes this impossible, it will be
necessary to undertake more pro-active flood
protection civil works. For a discussion of flood
mitigation and interception drainage techniques
refer to Sections 8.1.1, 8.1.2 and 8.1.4. Due to
the importance of a mine’s access shaft, flood
protection and mitigation works must be designed
to give a very low risk of failure. Where flooding
is possible the level of risk must be very carefully
analysed. If flooding may be life threatening, it
is advisable to cater for the probable maximum
flood (PMF) (refer to Fact Sheet No.2).
9.2 Groundwater Inflow
Groundwater inflows may originate from lateral
connections to local and regional groundwater
resources at working faces, vertical seepage from
roofs of underground pits and local seepage from
water bearing strata or “pockets” of groundwater.
Unplanned interception of adjacent flooded
workings, especially in coal mines, can have
disastrous consequences on workers and machinery.
Blasting and drilling operations which tap into
sources of water may result in a quick and widespread
impact of the inflow in connected working areas.
9.2.1 MANAGING GROUNDWATER INFLOW
Managing groundwater inflow in underground
mines can take many forms. Some techniques are:
• preventative,usingflowrestriction,containment
and re-routing of flow (Section 8.2.2). Bore
dewatering, in particular, provides an effective
way of reducing the effects of groundwater
inflow to the underground mine by removing
a proportion of the groundwater resource;
• contingent,allowingfortheinflowofground-
water. The confined nature of underground
mines makes the design of adequate drainage
into an adit or shaft used exclusively for
collection of groundwater (ie. a sump) essential.
Drainage to an adit which passively discharges
to the environment may prove to be a long-term
problem if acid drainage is present. Control
and treatment of such drainage streams after
mine closure is difficult and expensive;
• depressurisationattheinteriorsurfaceof
the underground working, which involves
progressively tapping into water bearing
strata to “bleed” water and hydrostatic
pressure at several points; and
• pumpingtothesurfacefromsumpsorpumping
to abandoned shafts from temporary sumps
may also be used to move volumes of water
from areas in which they are not wanted.
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In wet areas, the plugging of old shafts and
surface exploration drill holes can reduce
water inflows quite significantly
9.3 Water Quality
Water present within underground mines is
normally derived from direct infiltration of
rainfall and seepage of groundwater into the
excavation. Water extracted from underground
mine workings may be contaminated with:
• increaseddissolvedandparticulatemetals
resulting from the abrasion and dissolution of
metalliferous minerals (eg. acid drainage);
• nutrientsfromexplosiveresidues;
• highconcentrationsofsuspendedsediments;and
• oilsandgreasesfromundergroundmachinery
9.3.1 TREATMENT AND DISPOSAL
OF UNDERGROUND MINE WATER
Water extracted from underground mine pits
should be pumped to a central holding facility
where suspended sediments can settle. If possible,
the settling facilities should be underground, so
that the sediment does not become a problem on
the surface. Appropriate treatment technologies
can then be implemented for the removal of any
hydrocarbons, heavy metals or acid drainage.
If acid drainage is present within the underground
workings, then treatment of this water will
be required, as outlined in Sections 8.3.2 and
11.4.1. In addition to the water extracted for
treatment, consideration should be given to
water that may potentially escape through mine
shafts, adits and bedrock cracks and fissures.
If at all possible, clean water flowing into a mine
should be kept separate from dirty streams
and removed as quickly as possible. This will
prevent contamination of the water and reduce
the quantity which then has to be treated.
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10. Heap Leach Processes
10.1 Introduction
Management of a heap leaching operation is effectively
the management of flows: the flow of barren leach
solution to the leach pad and through the heap;
containment of the pregnant solution; removal of the
dissolved metals and recycling of the barren solution.
In order to maximise the recovery of metal values
and avoid environmental damage, catchments must
be clearly separated and all drainage systems sized to
contain the normal and abnormal flows. Inadequate
design means both a loss of the resource and
contamination of stream flows by process solutions.
The design and management of a heap leach operation
is a specialist skill. However, some traditional
operations may decide to treat low-grade material
using the principles of heap leaching. In these cases
the design of the water and solution management
systems may fall to the site engineer. The following
sections are provided to assist site personnel in
obtaining useful site specific information for the
design, operating management, decommissioning
and rehabilitation of a heap leach facility.
10.2 Planning for Heap Leaching
10.2.1 BASELINE EVALUATION
It is essential to define and isolate catchments, and
size drainage lines and ponds to ensure that clean and
contaminated flows are separated and that the drains
and containment ponds are not over-topped. The
groundwater system beneath the pads and process
ponds should be defined with regard to its hydrology
and chemistry. In the event of contamination
by process water, a proper understanding of the
underground flow conditions and water chemistry
will predict the extent and environmental significance
of any process water seepage and enable the
rapid implementation of remedial actions.
Chemical parameters to be measured should
include both the natural groundwater constituents,
process chemicals and any chemicals which might
be formed or liberated as a result of the process
chemicals interacting with the soils or rock.
10.2.2 RAINFALL EVENTS, ACCEPTABLE
RISK, CONTINGENCY PLANNING
The collection system must be designed to
accommodate the solution from both the leaching
process and storm runoff without overflow or erosion
occurring. The facility will need a water balance to
properly manage the flows and containment ponds.
Climatic factors to be considered include high
intensity rainfall and long-term wet or dry
periods. Local climatic data normally provide
the most reliable data for predicting hydrological
events. Suggested minimum design event
frequencies are presented in Table 10.1.
Design event frequencies should be determined
in conjunction with a risk analysis.
Storm design parameters must consider the
critical duration of the design event, whereas
seasonal variability is important for the design
of water supply and containment ponds
sizes. The ponds will need to contain:
• minimumoperatingvolumesto
enable the pumps to operate;
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• heapdraindownvolume;
• rinsingcycles;
• normalseasonalfluctuationsinwatervolume
(based on average climatic conditions);
• floodsurge(basedonthecritical
design event); and
• extremeeventdischargeoutletorspillway.
Contingency plans should be developed (and
preferably tested) prior to an event resulting in the
release of process solution. Useful equipment to
have on site or in daily operation may include:
• acontinuousflowmonitoronthereceiving
creek to enable estimates of dilution; and
• emergencychemicalsanddosing
equipment to neutralise overflows.
10.2.3 BASELINE GROUNDWATER MONITORING
Many materials are available to seal the heaps from
the underlying soil and for use as pond liners.
These include PVC, asphalt and clay. It should be
assumed that all ponds and heaps will potentially
leak, so a groundwater monitoring program should
be implemented to determine if there is any loss
of process solution and contamination of the
groundwater. Routine field monitoring should evaluate
changes in the water table and the water chemistry.
The geochemistry of the process solution should be
fully evaluated to determine the best indicators of
contamination. For example, with regard to a copper
heap leach operation, elevated sulphates in the
groundwater may be identified in perimeter bore hole
samples long before elevated copper concentrations.
10.2.4 CLOSURE PLANNING
The chemical characteristics of the spent leach
pile and the long-term leachate stream should
be determined during the design phase. The
characteristics will depend on the nature of the
ore, the process solutions used and the degree of
rinsing and/or chemical treatment of the heap once
active leaching has finished. It is important that
the process ponds are sized to contain the volume
of solution generated during the rinsing process.
Where heaps are constructed sequentially, experience
gained during the operation should provide the
information needed to establish closure criteria for
water quality and heap stability. Revegetation of
the heaps may be problematic due to slope angles,
chemistry and water retention of the spent ore.
Ongoing treatment of the heap leachate may be
required for some time after the last heap has ceased
active leaching and it is important that adequate
provisions are made to ensure containment of any
contaminated water during the closure phase.
TABLE 10.1: Suggested Minimum Design Event Criteria for Heap Leach Operation
Facility Type of Design Event
Access road, culverts and drainage ditches 10 year ARI to 50 year ARI flood peak
Drainage courses and ditches outside of leach pad
perimeter berm, pregnant pond and barren ponds 100 year ARI flood peak
Internal freeboard within leach pad,
pregnant and barren solution ponds
Maximum of:
• averagehydrologicalconditionsplusashort-
term, 100 year ARI storm event; and
• alongertermequivalent100yearARIevent
over a period of several months or years.
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10.3 Solution Control During Operations
10.3.1 MAINTENANCE OF DRAIN AND
POND CAPACITY
Heaps should be designed to avoid slope failure and/
or erosion of the ore and subsequent blockage of
the drains. Erosion and sedimentation within the
drains reduces the capacity for containment and
may result in overtopping of containment structures.
Testing should be undertaken on both saturated
and unsaturated heaps as the shear strength of the
material will vary with different pore water pressures.
The effects of earthquakes should not be overlooked.
10.3.2 INTEGRITY OF THE PAD OR LINER
The pad should be protected from flood flows in
the natural drainage systems by appropriately sized
berms. These should also extend around the process
solution ponds. It is recommended that the 100 year
ARI storm event be the minimum design standard.
During construction of the pad care is required to
ensure the integrity of the liner. The strength of the
liner should be commensurate with the hydraulic
pressure to be applied and the chemicals to be used.
Multiple use of a pad increases the risk of tears in
the liner and subsequent seepage. Careful inspection
is required to ensure integrity of the liner prior to
the construction of the heap. A leachate collection
system should be constructed to collect seepage.
10.3.3 INTEGRITY OF PIPING AND VALVES
All pipes containing process solution should
be located within bunds which are sized to
contain the amount of solution which would be
released should the pipe or valve fail plus any
additional flows due to rainfall within the bund
catchment. Routine inspections and leak detection
equipment should be used to identify leakages
and these should be repaired immediately to avoid
contamination of the groundwater. Preventative
maintenance rather than the repair of leaks
should be the underlying operating philosophy.
10.4 Water Management on closure
10.4.1 CRITERIA FOR LONG-TERM
LEACHATE QUALITY
The leachate discharge criteria should be developed
on the basis of the downstream beneficial uses
of the surface and groundwater flows. State
regulations (and/or catchment or river specific
environmental protection policies) and the
ANZECC (1992) guidelines for receiving water
quality will provide a basis for determining the
appropriate long-term leachate quality. These, in
conjunction with the flows and chemistry of the
leachate stream and of the receiving waterbody,
will determine the final discharge quality, and
where applicable, the size of a mixing zone.
10.4.2 RESIDUES AND LONG-TERM
CONTAMINATED SITE MANAGEMENT
All heaps should be contained as safe, stable
structures which will erode at an acceptable rate.
This rate will need to be determined through
project specific field trials as the slope angles,
particle size and length of slope will influence
the rate and extent of erosion. The use of
vegetation to control erosion may be subject to
both geochemical and physical limitations and
the early establishment of field trials should
provide the data needed to evaluate this option.
Leachate and surface runoff from the heaps
should not cause degradation of watercourses
downstream from the site through either siltation
or long- or short-term toxicity. The operation
will need to implement a monitoring program
to evaluate the success of its rehabilitation and
leachate management strategies. This will include
both surface and groundwater quality monitoring
and should include contingency plans for the
implementation of alternative control strategies
should they be required. Relinquishment of the lease
can be expected once the operation has attained an
acceptable discharge quality and stable surfaces.
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11. Waste Dumps
11.1 Waste Dump Construction for Water Management
Attention to waste dump construction with a
view to the final rehabilitation plan will minimise
erosion potential and facilitate a drainage system
that reflects the final drainage network. Accordingly,
waste dump planning and construction should
attend to the following critical matters.
11.2 Surface Water
The information provided in this section should be
read in conjunction with Section 6.1 of AMIC (1990).
The type of material to be stored in the waste dump
will determine its design and ongoing construction.
The presence of acid or other undesirable leachate-
producing waste may necessitate a capped waste
dump which will generate high volumes of surface
runoff. Alternatively, if the material is inert it may
be desirable to encourage infiltration. The types of
contaminants to be expected are discussed in Section
11.4. To ensure this contamination is minimised
and contained there are many critical design issues
for waste dumps. These are discussed below.
11.2.1 LOCATION OF WASTE DUMPS
The location of waste dumps should be planned well
in advance to cater for the expected waste volumes,
the final and intermediate design profiles, visual
and noise screening of mine operations and the
interaction with groundwater. The following surface
water issues should also be considered in the plan:
• newwastedumpsshouldbelocated
within catchments serviced by dirty water
interception and treatment facilities;
• wherepossible,naturaldrainagepathsshouldbe
maintained, and room should be left around the
base of the waste dump for interception drainage;
• wastedumpsshouldnotbeconstructed
immediately adjacent to natural or
uncontaminated watercourses. Provision must
be made for intercepting runoff, leachate and
seepage before it enters such watercourses;
• roomshouldalsobeleftforconstructionof
retention ponds, or it must be possible to
direct interception drains into existing ponds
for the removal of suspended materials and
the treatment of chemical contaminants; and
• avoidlocatingroadculvertsimmediately
downstream of waste dumps. The high sediment
load in waste dump runoff can easily cause
blockages. Where this is not possible, ensure
that sediment retention dams are located
upstream of the culverts. Culvert inlets should
be carefully designed to maximise velocities
into the culvert and outlets designed to ensure
that sediment is removed from the outfall.
11.2.2 EROSION ON WASTE DUMPS
Severe rilling on waste dump batters and the
problems associated with high sediment loads
in waste dump runoff can be reduced by proper
design and construction of the waste dump. This
should include close attention to batter slopes,
benching, armouring and drains. Apart from these
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‘geometric’designguidelines,thefollowing
points should be considered.
Capped Waste Dumps
Where acid drainage and other leachate formation
is to be minimised by capping the waste dump
with impervious clay or rock, there will be
very high volumes of runoff. It is important to
incorporate erosion control when constructing
the capping layer. This will include properly
designed drains, spillways, drop structures,
armoured batters and immediate topsoil and
grassing. It is also very important to ensure the
impervious material selected is not excessively
dispersive (clays) or soluble (weak limestone).
Encouraging Infiltration
If seepage of water into the waste dump will
not cause structural instability or contaminated
leachate and groundwater seepage, it can be very
beneficial to encourage infiltration. This will
greatly reduce runoff volumes and hence reduce
erosion. Increased infiltration can be achieved by
contour ripping of the surface, “moonscaping”
(refer to AMIC, 1990), creation of small detention
ponds or sink holes on top of the stockpile.
Erosion Control
Erosion control can be achieved through:
• effectiveandearlyrevegetationofcompleted
waste dumps or even of completed sections of
active waste dumps. This will require thorough
advance planning of final dump profiles, but in
so doing may prevent double handling of waste;
• armouringoreffectiveslopereduction
which will reduce scour. Planning of
open channels to achieve stable profiles
and slopes (ie. 0.5% - 1.0%) is also
important (refer to Fact Sheet No.4);
• reductionofslopelengthsbyconstructionof
contour banks and/or drainage benches; and
• introducingstormwaterretention
basins into the final profile to reduce
the magnitude of peak flows.
11.2.3 INTERCEPTION DRAINAGE
AROUND WASTE DUMPS
Contaminated runoff or leachate derived from waste
dumps must be intercepted and directed towards
‘dirtywater’treatmentponds.Thedegreeoftreatment
required to match the quality of natural watercourses
in the area can vary from none at all, to removal of
nearly all suspended solids and treatment for acid,
salinity, and heavy metals. Typical techniques for
runoff interception are discussed in Section 8.1.3
which, along with the following guidelines, will
ensure that the interception system works effectively.
Separation of Water Streams
To avoid excessive volumes of water entering the dirty
water treatment systems, runoff from undisturbed
catchments around the waste dump should be
kept separate from dump runoff and associated
disturbed areas. If large quantities of dust from the
waste dump settles on nearby areas, then these areas
should be included in the dirty water system.
Vegetation Filters
The retention of natural vegetation between the
waste dump and the interception drains can be
highly effective for removing sediment from runoff
and reducing contaminants in the leachate.
Drainage Design
If sediment cannot be retained on the waste
dump then it must be kept in suspension until
it reaches a designated location for sediment
removal (ie. a sediment pond). Drainage
velocities must be sufficient to keep sediment
suspended but not too fast so as to cause scour.
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11.2.4 SEDIMENT CONTAINMENT
AROUND WASTE DUMPS
Containment of sediment on the stockpile is
the ideal solution and can be maximised using
silt fences, hay bales, silt traps, filter dams,
retention basins and any other method which
will temporarily reduce runoff water velocities to
allow suspended solids to settle. A description of
these techniques is given in Fact Sheet No.8.
When de-silting ponds, sediment should be
dumped in a location where it will be exposed to
minimal surface runoff. Methods of containing the
sediment either on the waste dump or in a dirty
water system are dealt with in detail in Fact Sheet
No.8. If wetlands are used, they should only be
used to remove very fine sediment particles and a
pre-settling pond should be constructed upstream.
11.3 Groundwater
11.3.1 INFILTRATION TO GROUNDWATER
Between ground level and the top of the aquifer,
the level of saturation in the soil may vary from
zero (dry) to fully saturated (Figure 11.1).
This zone, referred to as the capillary zone,
contains water which is held under negative
(suction) pressures within the soil matrix.
Flow in the capillary zone is strongly vertical and
only weakly horizontal. Therefore water infiltrates
or percolates through this zone. Similarly, the
migration of contaminants is strongly vertical.
Flow in the capillary zone is complicated by
the strong and variable presence of air in the
soil matrix. This results in a variable hydraulic
conductivity of the soil, which, in turn, results in
variable groundwater infiltration characteristics
between ground level and the top of the aquifer.
The main factors influencing
groundwater contamination are:
• traveltimeofcontaminatedwaterfrom
the ground surface to the water table;
• thefractionofcontaminantthat
reaches the water table; and
• therateatwhichthecontaminantenters
the aquifer from the capillary zone.
Characteristic behaviour of contaminants include:
• solublecontaminantscollectnearthe
water table in a floating lens and are
then transported across the water table
where horizontal dispersion occurs;
• solventswhicharedenserthanwater
migrate downwards to the bottom of the
aquifer and are then transported by a
process of advection and diffusion; and
• residual(freephase)chemicalcontamination
in the soil matrix above the water table has the
potential to generate long-term problems.
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Control of infiltration may be achieved through:
• linersorimperviouslayersplacedbetween
the waste dump and the soil matrix
(eg. polyethylene, PVC, non-reactive
clays or soil-bentonite mixtures);
• surfacecappingtoinsulateagainstthe
infiltration, percolation and contaminant
migration via rainfall through the waste dump.
Surface capping materials may be impermeable
materials such as clay, concrete or liners; and
• adequatewastedumpdrainagetoconfine
runoff to the surface, where it may be more
easily contained and treated if required.
Attenuation of groundwater contamination
may be achieved by isolating the
groundwater near waste dumps using:
• slurrywalls(Section8.2.2);
• groutcurtains(Section8.2.2);and
• sheetpiling(Section8.2.2).
In addition, groundwater control methods
such as dewatering bores and capture trenches
(Section 8.2.2) may be used to collect water
for pumping to treatment facilities. However,
these methods should only be employed
after source control methods have failed.
11.3.2 MONITORING
Groundwater should be monitored as close as
practical to the perimeter of the waste dump
and the piezometers should extend into the
subsurface groundwater regime. Monitoring and
sampling should be carried out both upstream and
downstream of the prevailing groundwater flow
direction near the waste dump (Figure 11.2).
Monitoring and sampling should include:
• groundwaterlevelsorpiezometricheads;
• pHandsalinity;and
• chemicaland/orbiological
analyses as appropriate.
When sampling for chemical or biological
analysis, standard sampling procedures
should be used (Section 5.4).
Contaminants may react within the soil
matrix, so that groundwater monitored at the
periphery of waste dumps may not directly
reflect some characteristics of the primary
contaminant infiltrating from waste dumps.
11.4 Water Quality
Waste rock dumps may be a source of contaminants
to local streams and receiving waters. The range of
problems that occur from these structures include:
• aciddrainage;
• salinerunoff;
• suspendedsolidsrunoff;and
• heavymetalsinrunoffandleachate.
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11.4.1 ACID DRAINAGE
Acid drainage from waste rock dumps is normally
a more significant problem than that from within
open cut or underground mines. This is primarily a
result of increased surface area of exposed reactive
sulphides, higher porosity and infiltration within
waste rock dumps and the difficulty in containing
and/or treating leachate. The extent of the acid
drainage and subsequent metal solubility problems
within a waste rock pile will depend on the following
physical, chemical and biological conditions:
• physicalsizeandgeological
characteristics of the waste rock;
• thepresenceandtypeofsulphide
bearing minerals;
• theextentofrainfallinfiltration;
• thepermeabilityofthewasterock
dump to air and water;
• thepresenceofacidneutralisingrocks
within the waste rock dump; and
• thelevelofmicrobiologicalactivity,
including the presence of bacteria.
Monitoring techniques that can be used to identify
acid generation within a waste dump include:
• thepresenceof“hotspots”onthewaste
surface that are warm to the touch;
• theappearanceofsteamfromsectionsof
the dump, particularly after rain events;
• redandbrowncolouredwateraroundthe
base of the dump, red or brown colouring on
stream bottoms and banks, or the presence
of colloidal yellow precipitate in the water;
• theuseofremoteimagingtechniques,such
as thermal infra-red, to identify higher than
ambient temperatures in the dump;
• in-situtemperaturesensing;
• gassamplingwithinthepartially
saturated zone; and
• samplingandanalysisofsolubleacid
drainage products in the waste rock
and underlying geologic formation.
Specialised sampling techniques are required
when monitoring for acid drainage and
the reader is referred to Hutchinson and
Ellison (1992) for further information.
A wide range of prevention and remedial strategies
are available for acid drainage problems from waste
rock dumps. These are shown in Table 11.1
11.4.2 SALINITY
Saline runoff from waste dumps can be a common
problem at mines located within arid regions
and regions with specific high salinity geological
formations, for example, much of the Hunter and
Bowen Basin coalfields. Overburden and waste rock
that originated from within saline parent material
can have high concentrations of dissolved and
precipitated salts. Once this material is removed and
placed on waste rock dumps, rainfall infiltration
can result in highly saline runoff and leachate.
Runoff and leachate from saline waste
rock dumps should be intercepted and
directed to storage ponds for:
• evaporation;
• recyclingifsuitable;
• dilutionwithlowsalinewaterif
available and subsequent use;
• treatmentiffeasible;or
• controlleddischarge,forexampleunder
flood flows where natural dilution occurs.
The chosen option will depend largely on
the water’s suitability for use on site and the
characteristics of the receiving waterbody.
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11.4.3 SUSPENDED SOLIDS
Common techniques used to control sediment
runoff from waste dumps have been outlined
in Sections 11.2.2 and 11.2.4. Further
techniques applicable to erosion control and the
rehabilitation of waste rock dumps are provided
in Fact Sheet No.8 and AMIC (1990).
11.4.4 LEACHATE AND OTHER CONSTITUENTS
Additional contaminants that may emanate
from waste rock dumps include:
• asbestosfibresfromnaturallyoccurringminerals;
• solublecationsandanionssuchas
chlorides, sulphates and carbonates;
• heavymetalswhichmaybedissolved
by acid forming processes; and
• acidandalkalinewastestreamsfrom
naturally forming inorganic acids and
natural carbonates or alkaline silicates.
Specific treatment of these waste streams may
be required, and special disposal techniques
may be needed for sediment derived from these
materials and deposited in sedimentation dams.
TABLE 11.1: Prevention and Remedial Strategies for Acid Drainage
Control of Acid Generation
• pre-treatmenttoremoveorexcludesulphideminerals
• useofanimpermeablecovertoexcluderainfallinfiltrationandoxygen
• wastesegregationandblendingtocontrolpH
• useofbactericidestocontrolbacterialoxidationofsulphideminerals
• avoidexposingreactivemineralstoatmosphericconditionsbymodifying
the mine plan or avoid mining sections of the deposit
Control of Acid Migration
• useofcoversandsealstoexcludeinfiltration
• controlledplacementofwastetominimiseinfiltration
• interceptionanddiversionofsurfaceandgroundwater
Collection and Treatment of Acid Drainage
• useofaphysicaland/orchemicaltreatmentsystem
• useofbiologicaltreatmentsystemssuchaswetlands
Modified from Hutchinson and Ellison (1992)
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12. Tailings Water Management
All tailings disposal systems require management of
the water component in the tailings. Management
strategies are closely linked with the method of
disposal, design of containment facilities and the
potential for impacts both on and off the site.
12.1 Disposal Methods
Tailings disposal methods can be
separated into four major categories:
• saturatedtailingsmanagement,wherethe
tailings are transported and discharged as
a slurry. The saturated tailings are held in a
dedicated containment area where gravity
separation isolates a percentage of the water
from the tailings solids. As deposition of
the tailings is in a wet slurry, tailings beach
slopes are flat and, consequently, large
containment areas required. To minimise storage
requirements, the separated water should
always be recycled as much as possible;
• semidryorthickenedtailingsmanagement,
which involves discharging the tailings to a
containment area at higher solids content
than the saturated tailings management.
Depending upon the stacking characteristics
of the particles in the tailings, higher beaching
slopes are possible, with resulting smaller
containment areas for tailings and decant water;
• drystacking,whichpermitstheextraction
of most of the water before deposition. This
allows the solids to be transported into a
solids rejects dump from where they can be
taken to waste dump areas for contouring,
topsoiling and revegetating; and
• co-disposaloftailingswhichisthecombined
disposal of coarse rejects material and fine
tailings usually by combined slurry pumping.
The mixture produces a stable landform at
the point of disposal with major advantages
for rehabilitation. Significantly larger volumes
of water are required than for conventional
tailings disposal. The advantages of co-disposal
are the stable ongoing and end landform, the
reduction in area for waste disposal, the potential
for recycling most of the discharge water and
fewer environmental impacts. The technique
does require large volumes of water, and there
are greater potential seepage losses and large
recycling pumps are required to return the
water for the ongoing co-disposal process.
Co-disposal techniques are being used at coal
mines but are also applicable to metalliferous
mines where there is a rejects component that,
when combined with tailings will produce
a well graded stable in-situ landform.
In all these processes, the effectiveness of the
dewatering processes is a function of local
conditions, the type of waste solids, size distribution,
statutory requirements and economics.
It is critical for the rehabilitation of tailings facilities
that the disposal and decommissioning methods
are compatible and decided upon in the planning
stage. For example, if a tailings storage facility is
planned to be decommissioned by drying out the
surface and covering it with waste rock or other
material to encourage revegetation, disposal of the
tailings under water (sub-aqueous disposal) could
lead to poor settlement and ineffective drying of
the surface. Conversely, a facility which will be
decommissioned using a wet cover, typically used
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to inhibit acid drainage, should not be
operated with dry beaches where oxidation
of the sulphides can take place.
12.2 Characteristics and Management of Tailings Water
12.2.1 NATURE OF THE WATER
The water used to transport tailings and co-disposal
tailings or extracted during thickening of the waste
becomes contaminated during the process. In some
cases, such as in the goldfields of Western Australia,
the water itself is a risk to the environment because
of its hypersaline nature. Tailings water can be acid
or alkaline, have elevated concentrations of heavy
metals or contain concentrations of cyanide which
can have considerable environmental impacts if it
is released to the environment. It is important to
characterise the tailings water through a monitoring
program and manage the water accordingly.
In some cases, it may be necessary to treat the
water before disposal to the tailings storage
facility. Denaturing or recovery of cyanide from
gold process liquors is frequently practiced
in order to reduce costs and also to reduce
the potential environmental impacts.
12.2.2 MANAGEMENT
The following are the key elements that need to
be considered in tailings water management:
• thesensitivityofthecontainmentareato
infiltration and hence the requirements for
lining the storage area need to be evaluated;
• theabilityofthestorageareatocontain
stormwater inflows should be assessed. The
potential impact of discharges from the tailings
storage during storm events must be assessed.
This will necessitate a risk assessment (see
Fact Sheet Nos 2 and 3) with a resulting
design storm event for containment;
• diversionofdrainagefromsurrounding
catchment areas in order to reduce
inflow as much as possible;
• theneedforseparatereservoirsforwater
to be recycled eg. in co-disposal;
• recyclingoftailingsdecantwatershould
be encouraged as much as possible;
• tailingspipelinesshouldbebundedand
have collection sumps to contain spills
from leaking or ruptured pipes;
• infiltrationmonitoringsystemsare
required around the containment
site to detect contaminants escaping
from the impoundment; and
• dischargemonitoringfordisposal
systems with continuous discharge
of tailings liquor and/or solids.
12.3 Seepage Management
Seepage can occur through the walls and through
the floor of a tailings storage facility (Figure 12.1).
Infiltration through the floor of the tailings storage
facility usually decreases with time as tailings
are deposited in successive layers and form a
retardant to vertical flow. In the long-term, the
majority of tailings water seepage occurs through
the dam wall and via infiltration through the
ground surface on which the wall is built.
12.3.1 SEEPAGE CONTROL
Seepage may be controlled to some extent by
constructing the tailings facility using permeable (for
filter dam segments) and impermeable soils where
applicable. In addition, geofabric liners may be used
to increase the insulation against seepage flow.
Under-drains may be installed in the floor of the
facility before deposition of tailings in order to
collect and channel water to a collection system.
Similarly, interception drains and trenches may be
811 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
TA I L I N G S WAT E R M A N A G E M E N T
installed around the facility to collect seepage before
it can escape into the environment. In extreme cases,
impervious slurry walls and interception systems
have been installed in the preferred seepage paths to
prevent escape of potentially contaminated water into
sensitive environments downstream of the facility.
12.3.2 MONITORING
Monitoring of seepage flow through the wall
of a tailings storage facility (TSF) is readily
accomplished using piezometers to determine
the geometry of the phreatic surface (Figure
12.1). This may be translated to seepage flow
rates using standard groundwater flow theory.
It is also common practice to install piezometers
around the base of the impoundment wall in order
to detect seepage escape into shallow aquifers under
the facility. Such piezometers should be installed
in appropriate locations so as to be able to detect a
contamination front moving from the impoundment
early enough to take remedial action. Indicator
elements should be determined from a knowledge
of the chemical composition of the tailings water.
Water balance monitoring of TSFs enhances the
overall understanding of the site water circuit.
Monitoring should be carried out within the tailings
pond, in the dam wall and in any downstream
evaporation ponds. Adequate knowledge of
tailings settlement and water retention in voids,
as well as evaporation rates, are critical to
forming a water balance management scheme.
12.3.3 WATER CONTROL
Tailings water control may be implemented
using containment measures such as:
• sizingtheTSFsufficientlytoholdlargevolumes;
• constructingfilterdamstoallowselectiveseepage
of water into retention ponds or evaporation
ponds. Water extracted in this way may be more
acceptable for recycling in processing plants;
• stagingofcontainmentwallconstructionto
facilitate drainage from the co-disposal area;
• sizingandlocatingoutletstructures
to hydraulically control discharges
from the storage; and
• sizingevaporationpondstoreduce
water levels at sufficiently high rates.
The re-use of tailings water is often limited
because of specific water quality requirements
of the process. In general, the characteristics
of tailings water is process-specific, as is the
acceptability of tailings water for re-use.
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13. Mine Infrastructure
Water is essential for many aspects of a mining
operation. As well as the core function of extracting
the ore, virtually every other part of the mining
infrastructure uses water in some way. After coming
in contact with the operations, this water can pick up
contamination. It is important to be aware that this
contamination can exist, and of ways to minimise it.
Water used in these support functions needs to be
managed in the same way as other water on the site.
This section examines three main areas of an
operation where good water management
is essential. It is important to ensure that all
operators are aware of the potential environmental
impacts from failure to follow procedures,
and that they are adequately trained in the
operation of all pollution control systems.
13.1 Process Plant
Water used in a process plant is normally
confined within its designated piping and storage
facilities. It is only through washdown, pipe
ruptures, spillages and overflows from process
water tanks and dams that significant volumes
of process water can enter receiving waters.
The quality of surface runoff from the process
plant is dependent on the type of ore being
processed and the metallurgical process adopted,
eg. flotation, beneficiation, cyanide leaching.
A risk analysis and the associated contingency
plans should be undertaken at the planning
stage. Engineering solutions should be
commensurate with the level of acceptable
risk, safety hazards and environmental harm
which could result from an event.
13.1.1 CHARACTERISTICS
The process plant and associated ore stockpile area
can be a source of the following contaminants:
• suspendedsediment;
• oilsandgreases;
• processreagents;
• increaseddissolvedandparticulate
metals resulting from the dissolution
of metalliferous minerals;
• strongmineralacidsandbasessuch
as sulphuric acid and lime; and
• nutrientsfromresidualnitratesfromblasting.
13.1.2 CONTAINMENT AND
TREATMENT TECHNOLOGIES
Remedial measures and technologies available
for the containment and treatment of
contaminants from the process plant include:
• improvedhousekeepingstrategiestoidentify
the locations of spillage (eg. conveyor
transfer points) and the implementation
of appropriate remedial measures;
• bundingofallprocesschemicalstorage
areas and the interception and treatment of
all stormwater from within these areas;
• drainageofallprocessplantrunoff
to a central treatment facility (eg.
sedimentation or evaporation pond);
• provisionofquiescentconditionsinretention
ponds to enable settlement of fine grained
sediment. More rapid settling can be
achieved using a flocculent such as alum;
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• pHcorrectionusinglimedosingorother
suitable material may be necessary if the
retention pond water is acidic or incompatible
with receiving water quality; and
• interceptionandtreatmentofstormwater
runoff containing hydrocarbons through a
oil-water separation facility or alternatively,
materials contaminated with hydrocarbons
may well be suited to treatment using
Bioremediation Technology (Fact Sheet No.9).
The treatment of soluble contaminants is
dependent on the volume and quality of the waste
stream. Wastewater or contaminated runoff can
be diverted to a retention pond, tailings storage
facility or evaporation pond. Some waste streams
may require more advanced forms of treatment
such as activated carbon or ion exchange.
13.2 Industrial and Workshop Areas
The industrial area and its associated workshops
can be a frequent source of contaminants such
as lubrication oils, greases, solvents, surfactants
(water and solvent based products), suspended
solids from vehicles, atmospheric sources, spillage,
and metal shavings from lathes. Stormwater runoff
is the major transport route of these pollutants
to local watercourses and receiving waters.
13.2.1 CONTAINMENT AND
TREATMENT TECHNOLOGIES
Fuel Storage Areas
General principles for the design and
operation of storage areas include:
• bundingtotheappropriateAustralian
Standards in order to contain spillages;
• frequentinspectionofstoragetanks
and piping for corrosion and any above
ground and underground leaks;
• constructionofthefacilitiestocollectand
contain minor spillages outside the bunded
area during refuelling operations; and
• diversionofoilcontaminatedbundwater
collected during rain events through oil
interception or separation facilities.
Workshop and Truck Washdown Areas
General principles of design and
operation of these areas include:
• bettercontrolofhydrocarbons,eg.
central bulk storage and reticulation
throughout the workshop rather than
the use of 20 or 200 L drums;
• designofdispensingfacilitiesto
prevent drips and spillage;
• coveringoftheworkingareatoprevent
storm water picking up contaminants;
• installingadrainagesystemtoseparateclean
and contaminated water streams from within
and surrounding all workshop areas;
• diversionofoilcontaminatedwatertoa
separation system, which can range from simple
concrete sumps through to more sophisticated
mechanical systems such as coalescing plate
separators, skimmers and centrifugal separators;
• useofdrycleaningmethodssuchasindustrial
vacuum cleaners and absorbents rather than
water to clean floors and other surfaces;
• phasingoutofsolventsforcleaningapplications
in favour of new generation water-based
detergents, suitable for the cleaning of
hydrocarbons soiled equipment (solvents are
more difficult to treat and remove in wash
water than heavy lubricating oils); and
• moreeffectivedispensing,mixingand
use of detergents by operators, which
can also reduce consumption.
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13.3 Haul Roads
Controlled drainage from haul roads is essential
for the maintenance of the road integrity for
haul truck usage. The drainage systems have
environmental impacts in terms of both the
structures adopted and the quality of the drainage
waters collected for disposal. Both surface and
groundwater drainage issues should be addressed.
13.3.1 ENVIRONMENTAL ISSUES
Haul roads are potentially a source of contamination
in water, notably from suspended particulate
matter. Any spillage of mined material onto the
road surface is a source of these particulates
and, depending on its nature, also a source of
chemical contamination. Any pyrite present in
the ore or waste could oxidise, leading to acid
drainage and mobilisation of heavy metals.
It is important to ensure that, wherever possible,
haul roads are constructed of material which will
not lead to further environmental impacts.
There are recorded instances where materials
used in the construction of haul roads
have led to environmental contamination
along the entire length of a road.
13.3.2 SURFACE WATER DRAINAGE
The important elements in surface water
drainage on haul roads include:
• watermustbeclearedfromthepavementor
wearing surface quickly to avoid excessive
soaking of the surface base course layer and
without creating deeply incised scour paths.
Generally; maximum cross fall slopes of 3%
will facilitate both these criteria (Figure 13.1);
• sidedrainsarerequiredtocatchsurfacewater
from the pavement and runoff from cut bank
slopes. The side drains should be sized such
that the design flow depth is no higher than the
underside of the pavement top course or base
course layer. This will minimise the potential
for saturation of this layer (Figure 13.1).
It is preferable to direct drains off the
haul road at cut and fill interfaces or
otherwise down batter slopes at designated
locations via erosion protected chutes;
• ifthegradeoftheroadexceeds2-3%,erosion
protection along side drains may be required to
prevent undercutting of the pavement layers.
The erosion protection may be in the form of
lining (rocks, concrete, synthetic materials)
or barriers for inducing flatter slopes; and
• haulroaddrainagecrossingsshouldbethrough
culverts, with attention given to upstream and
downstream erosion protection. Appropriate
slopes and surface level designs are necessary
to facilitate sediment movement without
deposition and consequent culvert blockages.
13.3.3 GROUNDWATER DRAINAGE
Groundwater investigations will reveal the necessity
for any groundwater drainage systems. The primary
purpose of groundwater drainage systems associated
with haul roads is to minimise the potential for
saturation of the haul road sections and possible
failure. The environmental consequences of such
failures can extend to washouts of the road with
excessive sediment loads and destruction of the
integrity of the surface water drainage systems.
Typical groundwater protection mechanisms include:
• slottedpipesingravelbeds;
• rockfill“pipes”;
• rockfillblanketstofacilitateboththe
construction and haul road operation;
• syntheticgeotextilematerialstoseparate
layers and provide strength; and
• dewateringbymechanicalmeans
(pumps) in extreme cases.
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86 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
References
AMEEF (1996). Environmental Management in the
Australian Minerals and Energy Industries.
Ed. David Mulligan.
AMIC (1990) Mine Rehabilitation Handbook. Minerals
Council of Australia, Canberra (under revision 1997).
Anderson, M.P. & Woessner, W.W. (1992). Applied
Groundwater Modelling; Simulation of Flow and Advective
Transport. 381pp, Academic Press, New York.
ANZECC (1992). Australian Water Quality
Guidelines for Fresh and Marine Waters. Australian
& New Zealand Environment & Conservation
Council (under revision 1997-98).
APHA (1994). Standard Methods for the Examination of
Water and Wastewater. 18th Edition. Washington, USA.
AWRC (1992). Draft Guidelines for Groundwater
Protection. Australian Water Resources Council.
Bedient, P.B., Rifai, H.S. & Newell C.J. (1994).
Groundwater Contamination; Transport and
Remediation. 541pp, Prentice Hall, New Jersey.
Bureau of Meteorology (1994). The Estimation of
Probable Maximum Precipitation in Australia: Generalised
Short Duration Method. Bulletin 53, December 1994.
Australian Government Publishing Service, Canberra.
Chow, VT. (1973). Open Channel Hydraulics.
Intl. Student Ed. McGraw-Hill, Tokyo, Japan.
DEH (1995). Water Quality Sampling
Manual- For Use in Testing Compliance with the
Environmental Protection Act 1994. Department
of Environment & Heritage, Queensland.
DME (1995). Technical Guidelines for the Environmental
Management of Exploration and Mining in Queensland.
Department of Minerals & Energy, Queensland.
DME (nd). Groundwater Quality and Water
Well Maintenance. Information Sheet No. 10,
Department of Mines & Energy, South Australia.
EPA (1995). Environmental Monitoring and
Performance. One Module in a series on
Best Practice Environmental Management in
Mining. Environment Australia, Canberra.
EPA (1997) Managing Sulphidic Mine Wastes
and Acid Drainage. One module in a series of
Best Practice Environmental Management in
Mining. Environment Australia, Canberra.
Faust, S.D. & Aly, O.M. (1983). Chemistry of Water
Treatment. 723 pp, Butterworths, Boston USA.
Fetter, C.W. (1994). Applied Hydrology. 3rd. Ed.
MacMillan College Publishing Co., New York.
Haan, C.T. (1994). Design Hydrology and Sedimentology
for Small Catchments. Academic Press, USA.
Hart, B.T. (1974). A Compilation of Australian Water
Quality Criteria. AWRC Technical Paper No.7,
Australian Government Publishing Service, Canberra.
Hart, B.T. (1982). Australian Water Criteria for Heavy
Metals. AWRC Technical Paper No. 77, Australian
Government Publishing Service, Canberra.
Hutchinson, I. & Ellison, R. (1992). Mine
Waste Management: A Resource for Mining
Industry Professionals, Regulators and Consulting
Engineers. Lewis Publishers, USA.
871 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
R E F E R E N C E S
International Organisation for Standardisation
(1994). ISO Standards Compendium (Environment
- Water Quality): Volume 1 - General; Volume 2-
Chemical Methods; Volume 3 - Physical, biological and
microbiological methods. First Edition. Switzerland.
Kinori, B.Z. & Mevorach, J. (1984) Manual
of Surface Drainage Engineering, Vol II.
Stream Flow Engineering and Flood Protection.
Elsevier, Amsterdam The Netherlands.
Nelson, K. D. (1991). Design and Construction of
Small Earth Dams. Inkata Press, Melbourne.
NH&MRC (1994). Draft - Australian
Drinking Water Guidelines. National Health
& Medical Research Council, Canberra.
Pilgrim & Cordery (eds) (1987). Australian
Rainfall and Runoff. Institution of Engineers,
Australia. (This document is revised regularly)
Shaus, E.M. (1994). Hydrology in Practice.
3rd Edition. Chapman Hall.
Smith, A. & Mudder, T. (1991). The Chemistry
and Treatment of Cyanidation Wastes. Mining
Journal Books Limited, London.
Vick, S.G. (1983). Planning, Design and
Analysis of Tailings Dams. Wiley
Williams, R.E., Winter, G.V., Bloomsburg, G.L.
& Ralston, D.R. (1986). Mine Hydrology. 169pp,
Society of Mining Engineers, Colorado.
88 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Glossary
Advection The process by which solutes are transported by the motion of flowing groundwater.
Anisotropy The condition under which one or more of the hydraulic properties of an aquifer vary
according to the direction of flow.
Antecedent conditions The moisture conditions existing in a catchment at the onset of a storm.
Aquifer Rock or sediment in a formation, group of formations, or part of a formation that is
saturated and sufficiently permeable to transmit economic quantities of water to wells
and springs.
Aquifer, confined An aquifer that is overlain by a confining bed. The confining bed has a significantly
lower hydraulic conductivity than the aquifer.
Aquifer, perched A region in the unsaturated zone where the soil may be locally saturated because it
overlies a low-permeability unit.
Aquifer, unconfined An aquifer in which there are no confining beds between the zone of saturation and
the surface. There will be a water table in an unconfined aquifer. Watertable aquifer is
a synonym.
ARI - (Average The average or expected value of the period between exceedances of a given event
(eg. rainfall, discharge etc.).
This period is a randomly distributed variable.
Bailer A device used to withdraw a water sample from a small diameter well or piezometer.
A bailer typically is a piece of pipe attached to a wire and having a check valve in
the bottom.
Basecourse A layer of granular fill material constituting the uppermost structural element of a
road pavement immediately below the wearing course.
Capillary zone The zone immediately above the water table, where water is drawn upward by
capillary attraction.
Capture trench A trench which extends below the water table and into which the
groundwater drains.
Catchment The area which drains into a given stream or dam by way of natural ground slopes or
constructed drainage systems.
Clean water Surface runoff which has not picked up any solid or dissolved pollutants through
contact with disturbed or contaminated surfaces.
Recurrence Interval)
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G L O S S A RY
Co-disposal The combined disposal of tailings and coarse reject material.
d/s Down stream (eg. d/s of a dam).
Dewatering The process of removing water from a given source (eg. pit dewatering,
aquifer dewatering).
Diffusion The process by which both ionic and molecular species dissolved in water move from
areas of higher concentration to areas of lower concentration.
Dirty water Surface runoff which has picked up solid or dissolved pollutants through contact
with disturbed or polluted surfaces.
Drawdown A lowering of the water table of an unconfined aquifer or the potentiometric surface
of a confined aquifer caused by pumping of groundwater from wells.
Finite-difference model A digital computer model based upon a rectangular grid that sets the boundaries of
the model and the nodes where the model will be solved.
Finite-element model A digital ground-water-flow model where the aquifer is divided into a mesh formed
of a number of polygonal cells.
Gabion A flexible wire basket filled with stones and used to retain earth and sediment or to
control scour.
(Typical size: 1m wide x 1m high x 2m long)
Geotextile, geofabric, Any permeable synthetic textile material, fabric or net used with earth, soil, rock or
foundations as an integral part of an engineering structure. Mainly used to improve
structural and/or hydraulic properties of soil, to reinforce or stabilise embankments,
as a filter layer in drainage applications or for erosion control.
Groundwater The water contained in interconnected pores located below the water table in an
unconfined aquifer or located in a confined aquifer.
Groundwater, confined The water contained in a confined aquifer. Pore water pressure is greater than
atmospheric at the top of the confined aquifer.
Groundwater, perched The water in an isolated, saturated zone located in the zone of aeration. It is the result
of the presence of a layer of material of low hydraulic conductivity, called a perching
bed. Perched groundwater will have a perched water table.
Groundwater, The water in an aquifer where there is a water table.
Grout curtain An underground wall designed to stop ground waterflow; can be created by injecting
grout into the ground, which subsequently hardens to become impermeable.
Heterogeneous Pertaining to a substance having different characteristics in different locations.
A synonym is non-uniform.
geosynthetic material
unconfined
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Homogeneous Pertaining to a substance having identical characteristics everywhere.
A synonym is uniform.
Hydraulic conductivity A coefficient of proportionality describing the rate at which water can move through
a permeable medium. The density and kinematic viscosity of the water must be
considered in determining hydraulic conductivity.
Hydraulic gradient The change in total head with a change in distance in a given direction.
The direction is that which yields a maximum rate of decrease in head.
Hydraulic radius A measure of waterway geometry used in hydraulic calculations. The cross sectional
area of flow in a drain or pipe divided by the wetted perimeter (ie. length of wetted
surface) perpendicular to the direction of flow.
Hydrogeology The study of the interrelationships of geologic materials and processes with water,
especially groundwater.
Hydrologic cycle The circulation of water from the oceans and other waterbodies through the
atmosphere to the land and ultimately back to the ocean.
Hydrology The study of the occurrence, distribution and chemistry of all waters of the earth.
Infiltration The flow of water downward from the land surface into and through the upper
soil layers.
Isotropy The condition in which hydraulic properties of the aquifer are equal in all directions.
Laminar flow That type of flow in which the fluid particles follow paths that are smooth, straight,
and parallel to the channel walls. In laminar flow, the viscosity of the fluid damps out
turbulent motion. Contrast with turbulent flow.
Manning's coefficient (n) A dimensionless value defining the roughness of a surface (eg. pipe wall or sides
of a drain) with regards to water running across that surface. Used in hydraulic
calculations such as Mannings equation.
Manning’s equation A formula used for calculating the flow in a given waterway (eg. pipe or open
channel drain).
Model calibration The process by which the independent variables of a digital computer model are
varied in order to calibrate a dependent variable (eg. head) against a known value (eg.
water table).
Model verification The process by which a digital computer model that has been calibrated against a
steady-state condition is tested to see if it can generate a transient response, such as
the decline in the water table with pumping, that matches the known history of
the aquifer.
Numerical model A model of groundwater flow in which the aquifer is described by numerical
equations with specified values for boundary conditions that are solved on a
digital computer.
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G L O S S A RY
Phreatic surface “Free” surface of groundwater; pressures are equal to atmospheric along this surface.
Piezometer A non pumping well, generally of small diameter, that is used to measure the
elevation of the water table or potentiometric surface. A piezometer generally has a
short well screen through which water can enter.
Piezometric head Pressure head experienced by a given body of water, comprising both static levels and
inertial forces.
Piping failure Failure of an earth dam wall caused by excessive seepage of water through the
embankment.
PMF - (Probable The flood caused by runoff water from the probable maximum precipitation.
PMP - (Probable The greatest depth of precipitation for a given duration meteorologically possible for
a given size storm area at a particular location at a particular time of year.
Porosity The ratio of the volume of void spaces in a rock or sediment to the total volume of
the rock or sediment.
Recharge The process of replenishment of a water resource (recharging of aquifer, recharge
of dam).
Rational method A procedure for calculating the peak discharge from a small to medium sized
catchment, resulting from a storm of a given ARI and duration.
Reno mattress A low profile flexible wire basket filled with stones and used to control scour.
(Typical size: 2 m wide x 6 m long x 0.3 m deep)
Revetment mattress A hard surface armouring formed by using pocketed pervious fabric filled with
concrete. Used to control scour.
Rip Rap Irregular rocks of medium to large size, used for the lining of embankments, drainage
channels, dam spillways etc. for prevention of erosion.
Runoff The total amount of water flowing in a stream. It includes overland flow, return flow,
interflow and baseflow.
Sediment barriers Structures placed in a drainage channel to promote settling out of sediment until a
stable flow slope is achieved between each barrier. Used for erosion prevention.
Sediment fence / A low fence of woven geotextile designed to filter suspended solids from overland
flow, (sheetflow). Used for containment of sediment in disturbed areas.
Seepage Common term for groundwater flow, encompassing the characteristic “slow flow”
processes (see laminar flow).
Sheet piling Physical barrier applied by driving solid sheets of impermeable material into
the ground.
maximum flood)
maximum precipitation)
silt fence
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G L O S S A RY
Slurry wall An underground wall designed to stop groundwater flow; constructed by digging a
trench and backfilling it with a slurry rich in bentonite clay.
Soil matrix Skeletal structure of soil, within which “honeycombs” of pores exist.
... % Standard An earthworks term used to specify the amount of compaction effort required (or
compaction achieved) in engineered earthworks.
Surface water Water found in ponds, lakes, inland seas, streams and rivers.
Time of concentration The time required for rain falling at the farthest point of the catchment to flow to the
point at which the discharge is being calculated. Used in hydrology calculations such
as the Rational Method.
u/s Up stream (eg. u/s of a dam).
Water table The surface in an unconfined aquifer or confining bed at which the pore water
pressure is atmospheric. It can be measured by installing shallow wells extending a
few feet into the zone of saturation and then measuring the water level in those wells.
Wetlands Areas where water is over or near the ground surface for long enough each year to
maintain saturated soil conditions along with related vegetation (eg. marshes,
bogs, swamps etc.).
compaction
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Field Record Data Sheets
Sampling method
Analysis profiles
Remarks
Sampler Signature Date
Example of Sampling Report Form for Marine Waters
Site Site Code
Date Time
Latitude Longitude
Site Description
HYDROGRAPHIC CONDITIONS
Tidal Currents: Direction Approx. velocity
Time of high water Time of low water
WEATHER CONDITIONS
Wind Direction Force
Cloud cover State of sea
MODIFIED FROM IS0 STD 5667-9:1992 (E)
FA C T S H E E T N O . 1
Depth(m)
Temperature(ºC)
Salinity Dissolved Oxygen(% sat.)
Sample
Number Time
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Field Record Data Sheets
Example of Sampling Report Form for Groundwaters
Site Site Code
Date Time
PUMPING DETAILS
Height of riser/bore pipe above ground level (m)
Water level within aquifer (before pumping) (m)
Water level within aquifer (after pumping) (m)
Pumping Time
Volume Extracted (estimated)
SAMPLING DETAILS
Time: Start End of sampling
Depth of sampling
Sampling method
Sample appearance
Details of preservation techniques employed
Details of sample storage method employed/required
Remarks
Sampler Signature Date
FA C T S H E E T N O . 1
MODIFIED FROM IS0 STD 5667-11:1993 (E)
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Field Record Data Sheets
Example of Sampling Report Form for Surface Waters (LAKES, STREAMS, WATER STORAGES AND TAILINGS DAMS)
Site Site Code
Date Time
Site Description
Water Depth Volume
Time: Start End of sampling
Sampling method
DEPTH-INTEGRATED SAMPLE
Withdrawal between and m
OBSERVATIONS AT THE SAMPLING POINT
Turbidity, caused by sediment particles /plankton
Colour Odour
Water plants
Estimation of the discharge of the streams/river: (high/medium/low)
LOCAL WEATHER CONDITIONS
Air temperature
Wind force
Direction of wind
Cloudiness (%)
Remarks
Sampler Signature Date
FA C T S H E E T N O . 1
MODIFIED FROM IS0 STD 5667-4:1987 (E)
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Example of Sampling Report Form for Domestic and Industrial Wastewater
Site Site Code
Date Time
Sample method: Grab
Composite-time dependent
Equipment Used
Interval of flow between samples min or m3
Volume of grab samples mL
Sampling started Sampling ended
Preservation method
FIELD MEASUREMENTS
Remarks
Sampler Signature Date
Field Record Data Sheets FA C T S H E E T N O . 1
MODIFIED FROM IS0 STD 5667-10:1992 (E)
Test Result Unit Time
971 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
This fact sheet examines surface runoff processes
and techniques used to estimate total catchment
runoff and peak flows generated by runoff for
smalltomediumsized‘nonurbanised’catchments
(< 250 km2). Accurate estimation of these quantities
depends on a large number of site characteristics.
Hence it is not within the scope of this handbook
to give precise techniques for every region in
Australia. Instead, the general principles will
be discussed and references provided to locate
the information specific to a given region.
Runoff Processes
Losses: When rain falls on a catchment surface,
aportionofitwillbeheldbackas‘losses’before
theremaining‘excessrainfall’reportstostreams
or drainage channels as surface runoff. The losses
combine a number of rainfall and interception
mechanisms. In the early stages of a storm, much
of the rain is intercepted by trees, grass and other
plants and stored on leaves and branches etc. as
interception storage. When these stores are full,
water will reach the ground surface and commence
filling small depressions. As these fill and overflow,
large depressions begin to fill until this depression
storage is full and overland flow commences.
There are continuing losses through infiltration
into the soil which starts at a high rate if the soil
is initially dry and then rapidly decreases until
approaching a steady rate known as the infiltration
capacity of the soil. Evaporation from the vegetation
and ground surfaces will also contribute to the
losses. From this discussion it can be seen that
losses (and hence rainfall excess) are affected by
vegetation type and density, soil type and degree
of disturbance, catchment slope and the number
and efficiency of watercourses in the catchment.
Runoff types: Once losses have been absorbed
there are two major runoff routes by which water
reaches watercourses. In areas where soil is thinly
overlying an impervious or rock layer, or where the
groundwater level is very near the surface (eg. at
valley bottoms or near streams) it will not take long to
saturate the surface soil. Once this occurs, infiltration
ceases and water will flow over the surface as
saturated overland flow. Alternatively in sandy areas,
or areas of deep permeable soil overlying impervious
layers, water can rapidly flow downslope through the
soil and percolate out of the soil when it intercepts
a saturated zone. This is known as interflow and is
differentiated from groundwater flow by the speed
with which it reports to watercourses. The efficiency
of these runoff processes is again dependant on soil
types, as well as rainfall intensity, the geology of the
area, catchment slopes and groundwater levels.
Design losses: When estimating total or peak
runoff values it is necessary to estimate the losses,
as it is only the rainfall excess which contributes
to the runoff. With losses depending on so many
site specific variables it is almost impossible to
realistically model the processes. Even within a
Single small catchment there will be a large number
of sub areas responding differently due to varying
physical characteristics. To simplify matters, a
number of methods have been developed for
applying general losses across a whole catchment.
A full discussion of these methods, along with
typical loss values for regions throughout Australia
can be found in Chapter 6 of Australian Rainfall and
Runoff 1987 (AR&R). The simplest and most popular
of these methods are (refer to Figure FS 2.1):
(i) Constant fraction (proportional losses/
runoff coefficients): Loss is assumed
to be a constant fraction of the rainfall.
This can be viewed in two ways:
a) A runoff coefficient (ie. 0.7) is applied to
the rainfall. If a catchment large distinct
areas (ie. undisturbed, stockpiles, sealed
areas etc.) then a different coefficient
can be applied to sub areas; and
Estimation of Surface Runoff FA C T S H E E T N O . 2
98 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
b) If a predictable proportion of the catchment
is known to become saturated during rain
then this area can be viewed as the proportion
of the catchment contributing runoff.
(ii) Constant loss rate: If a catchment has
minimal interception or depression storage
and the infiltration into the soil is fairly
constant (ie. if the catchment is already
wet from previous antecedent rain) then a
constant loss rate matching the infiltration
capacity of the soil is a valid approach.
(iii) Initial loss - constant loss rate: In line with
the above discussion of interception losses
through vegetation and depression storage,
followed by ongoing losses due to soil
infiltration and evaporation, is the concept
of having no runoff until an initial loss is
satisfied and then having a constant loss rate
for the remaining duration of the rain.
As well as AR&R there are many other sources of
information for loss values applicable to an area:
• Consultingengineers/hydrologists;
• Stategovernmentwaterresourcesdepartments;
• Stategovernmentminingdepartments;
• Stategovernmentagriculture/primary
industries/forestry etc. departments;
• LocalLandcaregroups;and
• Localgovernmentengineers.
To obtain accurate estimates of losses it is important
to note that there is no substitute for site measured
data. A historical record of rainfall and streamflow
(or dam levels, releases and overflows) will enable
a hydrologist or engineer to develop much more
accurate versions of the above loss models.
Estimation of Surface Runoff FA C T S H E E T N O . 2
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Estimating Total Runoff
The total volume of runoff (saturated overland flow
and interflow) from a catchment is important when
examining overall site water balances or storage
capacities required for water supply dams etc. The
general procedure is to simply apply rainfall from
the period of interest (eg. a single storm, a typical
year or a long sequence of wet or dry years) to
the catchment, subtract the appropriate losses as
discussed previously and assume the excess rainfall
reports as runoff to a stream, dam or pond. (The
long-term processes of evaporation and seepage
losses from a storage area must also be taken into
account for long-period water balances.) The rainfall
data required is discussed in Fact Sheet No. 10:
Hydrological Data for Design Purposes. Computer
programs are available for applying long-term
daily rainfall records to a catchment, varying the
loss values to suit historical stream flows or dam
levels. These can be used for projecting catchment
yields into the future to examine water storage and
recycling opportunities. One such model gaining
popularity in Australia is the AWBM model.
Estimating Peak Flows
As discussed throughout this handbook,
interception drainage, erosion protection, settling
ponds and essential drainage infrastructure (eg.
culverts, spillways etc.) must all be carefully
designed to suit the expected peak flow
they are expected to experience. A confident
estimate of this flow is essential to:
a) prevent under designing drainage
infrastructure, which may result in damage
and hence disruptions to mine operations and
ongoing repair and upgrade works; and
b) avoid over designing, which is
of course uneconomical.
Detailed discussions of estimation procedures can be
found in AR&R. For typical mine catchments,
the best method to obtain a quick estimate is
the rational method which is of the form:
QY = 0.278. CY. Itc, Y . A (Eqn 5.1 AR&R)
where
• QY = Peak flow rate (m3/s) of average
recurrence interval (ARl) of Y years
• CY = Runoff coefficient (dimensionless)
for ARI of Y years
• A=Areaofcatchment(km2)
• Itc, Y = Average rainfall intensity (mm/h) for the
design duration of tc hours and ARI of Y years.
The way to use the rational method is as follows:
• firstdecideontheappropriaterisklevel,hence
selecting the average recurrence interval of
storm to be used (refer to Fact Sheet No.3);
• thedurationofstormtogivetheworstflood
is then selected. The principle here is that
the shorter the storm the higher the intensity
will be for a given ARI. However, if too short
a time is used then runoff from far reaches
of the catchment will not have had a chance
to contribute to the flow. Hence the critical
duration, known as the time of concentration
tc, is selected as the time required for the
most remote part of the catchment to begin
contributing to runoff at the point of interest.
Different methods for calculating tc are
presented in AR&R for various regions in
Australia. Most of these depend on stream
lengths and typical catchment slopes;
• determinetheaveragerainfallintensity
(mm/hour) associated with the selected ARI
and tc. Intensity; duration, and frequency
rainfall curves for the specific minesite will
be required. These can be developed using
guidelines in AR&R or can be obtained
through the Bureau of Meteorology.
Estimation of Surface Runoff FA C T S H E E T N O . 2
100 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
They will simply need the longitude and latitude
of the minesite (refer to Fact Sheet No. 10);
• calculatetherunoffcoefficientforthesiteusing
the methods defined in AR&R for each region
within Australia, or if available using values
developed for your specific area and type of land
use. (Neighbouring mines, land care groups,
soil conservation departments or universities
involved in runoff management in your area may
have previously developed such coefficients); and
• measuretheplanarea(km2) of the catchment
feeding into the point of interest, taking into
account pits, diversion drains, ridges etc.
Having obtained all the above information, it can be
used in the previous equation to give the peak flow.
Probable Maximum Flows (PMF)
When designing spillways on large dams or
examining major flood mitigation works where
lives may be at risk, it is usually wise to use the
maximum possible flow rate. This will ensure that
the given element is unlikely to ever fail. Due to
the importance of such calculations, experienced
engineers or hydrologists should be consulted
before using these flows for design purposes.
Before it is possible to calculate peak flows, it is
necessary to determine the probable maximum
precipitation for the given area. For small
areas and short-duration storms the Bureau of
Meteorology has published an upgraded method
of calculating PMP in Bulletin 53 (December 1994)
The Estimation of Probable Maximum Precipitation
in Australia: Generalised Short Duration Method.
For larger areas or long storms, the Bureau will
provide estimates of PMP for a set charge.
Once the PMP is determined, small losses are applied
to determine the rainfall excess. The losses will
be small due to the high likelihood of antecedent
rainfall. It is suggested that values of zero or slightly
below the lowest specified loss values for the area
can be used. Having determined the rainfall excess,
it is then a matter of using methods as described
above, or more complex flood routing techniques
(depending on catchment size and complexity)
to determine the probable maximum flow (PMF).
Section 13.4 of AR&R gives basic descriptions
of the techniques used in such calculations.
Estimation of Surface Runoff FA C T S H E E T N O . 2
1011 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Water management is not an exact science as rainfall is an integral part of the hydrological, and therefore the water management, cycle. Just as it is impossible to accurately predict quantities of rainfall, it is impossible to provide definitive answers to most water management questions. However, it is possible to define probabilities and risks of occurrence of particular events.
Care should be taken when communicating and interpreting probabilities and risks, and rigorous terminology should always be used. Probabilities and risks which are based on historical data carry an implicit assumption that history will repeat itself.
The following are more common risk terminologies used in water management practices. More detailed descriptions and understandings can be found in Australian Rainfall and Runoff 1987 (AR&R).
Average Recurrence Interval (ARI)
The average recurrence interval is the average interval between exceedances of that value or event when viewed in the long (ideally infinite) term.
All data above an arbitrary base value are used when ranking event values for determining the ARI. The ARI is usually expressed in years. It should be noted that, a rainfall (or flood) ARI of 100 years does not imply the event will only occur every 100 years; it is also feasible that the event will occur five times in five successive years and not occur for another 495 years. The terms “100 year return interval” and “the one-in-hundred-year-storm” falsely advocate the former interpretation.
Annual Exceedance Probability (AEP)
The annual exceedance probability is the probability of exceedance of a given event within a period of one year. It is based on data that uses only the highest event in each year of record.
The AEP is often used for the probability expressions associated with large and extreme events and some flood estimation methods. The AEP is generally expressed as a fraction or percentage.
Probability (P) of Exceedance in L Years
Probability of exceedance in L years is a descriptive risk term that relates the event exceedance probability to the design or useful life of the resource or structure. In probability terms it can be expressed as:
P = l-exp(–L/T
where T is the ARI.
Probable Maximum Precipitation (PMP)
The probable maximum precipitation refers to the greatest depth of precipitation for a given duration that is meteorologically possible for a given size storm area at a particular location at a particular time of year. The Probable Maximum Flood (PMF) has a similar definition and is related directly to the PMP (Also refer to Fact Sheet No.2.)
Due to the variable nature of the hydrological cycle, the use of risk analyses and probabilities should be encouraged in water management strategies.
Where historical data are used to determine these risks, care must be taken to include as much relevant historical data as are possible. This reduces the element of skewing in risk analyses. In this way, although absolute answers are rarely available, water management strategies may be assessed a logical and justifiable manner.
Because water management involves expressions of risk, the impacts of failure must always be assessed. Where appropriate, contingency failure strategies should be established and regularly audited and monitored.
Understanding Event Probability FA C T S H E E T N O . 3
102 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Sensitivity analyses provide means of assigning
boundaries or limits to water management scenarios
by asking “what if...?” type questions. Sensitivity
analyses should be carried out on parameters which
are thought to be important or on those which
are not very well understood, such as hydraulic
conductivity of soil, process plant water use etc.
Where hydrological analyses are used in a water
management study, it should be clearly understood
that a large proportion of the quantitative analyses
is probabilistic only. The broad assumptions and
the extent to which historical data play a part are
documented in the industry standard AR&R. This
document should be referred to when a more detailed
understanding of event probability is required.
Understanding Event Probability FA C T S H E E T N O . 3
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The basic principles behind locating and sizing an
open channel drain for normal depth flows are:
• determinethesizeofthecatchmentfeeding
into the base of the proposed section of
drain. On reasonable size catchments, it is
often worthwhile to separate the proposed
drain into sections. By doing this it may be
possible to have a smaller cross section in
the upper section of the drain which only
services the upper reaches of the catchment;
• forasuitableARI(commonly5to20yrs)
calculate the peak flow in each section of
the drain as described in Fact Sheet No.2;
• calculatetheslopeofthedrain.Ifitisnot
possible to achieve a uniform slope along the
length of the drain it should again be separated
into sections of similar average slope. (Note:
Wherever possible the slope of the drain should
be in the range of 0.5% to 1.0% or to suit local
soil conditions. This will drastically reduce the
cost of erosion control measures. It is preferable
to ‘snake’ drains down steep slopes rather than
taking the shortest possible route;) and
• havingestablishedtheflowsandslopesfor
the proposed section of drain, a cross section
size can be calculated using the Manning’s
equation (shown below) with suitable roughness
coefficients. (Note: Roughness coefficients are
determined by the type of lining there is in the
drain, ie. a smooth bare earth channel will have a
low roughness coefficient while a channel lined with
large unevenly placed rocks or dense vegetation will
have a high roughness coefficient.) A freeboard
of between 100 and 300 mm is added to the
flow depth to give the design drain depth.
Manning’s Equation:
Q = A.R2/3S1/2
n
where:
Q = Flow (m3/s)
A = Cross sectional area of flow (m2)
R = Hydraulic Radius (= A/WP)
WP = Wetted perimeter; length in m of wetted
contact between water and the channel measured
at right angles to the direction of flow
S = Slope of channel section (m/m)
n = Manning’s roughness coefficient.
Typical values of Manning’s n are:
Smooth concrete lining 0.014 - 0.018
Smooth graded earth 0.025 - 0.03
Grass cover 0.04 - 0.06
Rock lining 0.04 - 0.06
In uniform section open channels, regard for
flow and hydraulic radius should be considered
for Manning’s n (refer Chow, 1973).
Open Channel Drains FA C T S H E E T N O . 4
104 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
The best method for using this equation is to trial
different drain cross sections and flow depths
until sufficient flow capacity is achieved.
• Asaniterativeprocedurewiththeprevious
step, the type of erosion protection to be
used in the drain should be decided at this
stage. As described in Fact Sheet No.8, a
different level of protection is required as the
flow velocities increase; however the erosion
protection method will also affect the flow
velocity (Q/A) hence the need for iteration.
• Thefollowingtipsshouldbefollowed
for selecting a drain cross section:
– steep side slopes should be avoided
(2-3 H to 1 V recommended);
– the cross fall of the natural ground
will affect the actual slopes used;
– v-shape drains are recommended for minor
drains while trapezoidal shapes should be
used for large drains. The base width of a
trapezoidal drain should be sized to suit
earth moving equipment to be used;
– a contour drain should be cut into the
cross slope sufficiently to provide a
balance of cut to embankment fill; and
– embankments should be compacted to a
minimum 90% Standard Compaction.
Note: where large channels are required, expert
advice should be sought due to the potential
for backwater and downstream effects.
Open Channel Drains FA C T S H E E T N O . 4
1051 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
The intent of this fact sheet is to allow the mine
operator to build small earth dams (“farm dams”)
for minor or temporary water supply or to form
part of a diversion drainage scheme. If the dam is
an important water supply or flood mitigation tool
then input from civil engineers and hydrologists
is vital. The calculation of expected catchment
yields and flood flows are covered elsewhere in
this handbook; hence this fact sheet will cover
the selection of a dam site, dam design and
dam construction. The information in this fact
sheet is collated from the text Nelson (1991).
Selecting a Dam Site
The easiest and most efficient dams involve
constructing an earth embankment across a small
valley. These are commonly known as gully dams and
will be the focus here. Other types of small dams,
including hillside dams, turkeys nest ponds and
excavated tanks, are feasible alternatives if a suitable
gully is not available, and involve many of the same
principles to be discussed. The important points to
consider when selecting a dam site are as follows:
• minesitelicenceconditionsshouldbechecked
or local water resources authorities contacted to
ensure a dam is allowable under environmental,
water use and dam safety restrictions;
• thestoragevolumeshouldbeselected
to suit the expected catchment runoff
volumes. This will prevent excessive
earthworks or an eroded spillway;
• unlessthedamisforsedimentcapturepurposes,
the upstream (u/s) catchment should not be
excessively disturbed. If this is unavoidable,
an u/s silt trap will have to be installed and
constantly maintained (ie. emptied);
• anideal site is on a flat gradient watercourse
in a wide flat-bottomed valley immediately
upstream of a narrow gorge. Sides of the
valley must remain stable when saturated
to avoid land slips into the dam;
• thefoundations for the dam must be
sufficiently strong to support the embankment
without excessive settlement and must
be impervious to seepage. Stiff inorganic
clay is ideal while sedimentary rock can be
acceptable. Fractured igneous rock or deep
layers of sand and gravel should be avoided;
• theavailability of suitable material nearby
is vital. Available quantities will determine the
type of embankment used as illustrated in the
attached table (Figure FS 5.1). Impervious
material for embankment construction should
contain 20%-30% clay with sand, silt and some
gravel. No rocks greater than 75 mm size should
be present. As a safety factor, two to three times
the expected quantities should be available; and
• a subsurface geotechnical investigation should
be carried out on favoured sites to assess the
above factors as well as groundwater levels,
cutoff trench depths and borrow pit boundaries.
The investigation should include excavated pits
along the dam centreline, spillway and in borrow
areas followed by geotechnical testing of samples.
Dam Design
Good design of the dam and spillway is vital to ensure
a stable embankment and to prevent failure due to
erosion or excessive seepage leading to piping failure.
Piping failure results from seepage water transporting
materialoutoftheembankmentcausinga‘pipe’
which rapidly expands leading to massive failure. The
basic geometric design principles for a stable dam
are illustrated in Figure FS 5.1. The following points
should also be accounted for in the dam design.
• Cutoff excavations are used to prevent
seepage under the embankment by providing a
impervious barrier linking the embankment to
Construction of Small Earth Embankment Dams FA C T S H E E T N O . 5
106 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
impervious foundation material. It must be connected
directly to the impervious embankment material
and must be keyed into suitable foundation material
as shown in the table below. If a cutoff trench is
impractical due to excessive depths, an effective
alternative where foundations are moderately
pervious is to use a clay blanket 0.6 m thick (approx.)
extended 35 m (approx.) u/s from the embankment.
• Spillway flows must be diverted away from the
downstream (d/s) toe of the embankment to
avoid erosion. A small return wall at the spillway
may be required, as shown in the figure. If
continuous small flows are expected over the
spillway it is advisable to install a trickle pipe
or a small flow channel just below the main
spillway level. This will prevent scour erosion.
• Outlet pipes are sometimes necessary to create
a gravity supply, supply a pump, drain water
for dam maintenance, satisfy legal requirements
or to allow the dam to be used as a flood flow
detention storage. If these requirements are
not applicable it is best to avoid outlet pipes.
• Freeboard is required on dams to allow
for uncertainties in flood flow estimation,
inaccuracies in construction and wave action.
The heights shown on the figure assume
a maximum 500 mm flow depth over the
spillway. If an alternative spillway arrangement
is used, the freeboard must be altered to suit.
Dam Construction
Good control of construction methods and
material condition is vital to achieve a water
tight dam. The following construction phases
and guidelines should be adopted:
• priortocommencingconstructionofthe
dam a surveyor should identify the extent of
inundation, the embankment centre line and
batter toe lines, the spillway and borrow pits;
• ensuretheproperequipment is available.
This should include scrapers and dozers for
small embankments while larger projects will
also require graders, rollers and water carts;
• ifthedamislocatedinagullyorstream
which flows regularly it will be necessary
to dewater the site. This is best achieved
using an upstream weir and a gravity drain
which bypasses the dam. Groundwater in
trenches will need to be pumped out;
• areliablewater supply is important if
the material used in the embankment
needs conditioning (ie. addition of
water to allow proper compaction);
• theareatobeinundatedbythedamwater
must generally be cleared and grubbed. This
includes removing all trees, shrubs, rocks and
any debris. This can be modified if aquatic
habitat is to be an ancillary function of the
storage. This should be burnt or pushed
downstream of the embankment. At the same
time the area under the embankment should
be cleared and have all topsoil stripped
(100 mm minimum) and stockpiled;
Construction of Small Earth Embankment Dams FA C T S H E E T N O . 5
Suitable foundation
material (SFM)
Required penetration
depth into SFM
Width of cutoff
trench at base
Batter slopes for
excavated trench
Clay 0.6 m 2.5 m minimum 1 :1
Rock 0.3 m 0.3 m vertical
1071 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
• thecutoff excavation should then be carried
out and impervious material placed and
compacted to bring the level back up to that of
the stripped foundation. The whole foundation
area is then lightly scarified (50 mm deep) in
preparation for construction of the embankment;
• borrow pits should ideally be within the area
covered by the stored water. They should
have side slopes of 3H:1V and should be
positioned a minimum of 6 m away from the
upstream toe of the dam embankment;
• embankment construction requires control of:
– the moisture content of the embankment
material when placed must generally be within
the range 3% dry to 2% wet of optimum
moisture content. This is the moisture content
which allows the maximum density to be
achieved by the compaction equipment used;
– the loose thickness of layers placed
should not exceed 100 mm if dozers
and scrapers are used for compaction
or 200 mm for sheepsfoot rollers;
– the degree of compaction achieved should be
95% Standard Compaction or 90% Modified
Compaction. This will usually require between
four and eight passes with a sheepsfoot roller;
– batter slopes should be controlled using
a template (timber triangle with the
required horizontal and vertical length
ratios ie. 3H:1V) and spirit level;
• thespillway must be constructed absolutely
level to ensure there are no preferential
flow paths which will erode. When
cutting is complete the surface should be
topsoiled, grassed and compacted;
• outlet pipes, if required:
– must only be placed in a trench cut into
natural ground or compacted embankment.
The trench should be at least 100 mm
deeper than the pipe diameter;
– between three and six cutoff collars (1.2m x
1.2m) shall be evenly spaced along the pipe
to prevent seepage of water along the pipe;
– do not place pipes at the very base of the
dam if sediment is likely to be a problem;
– it is advisable to include a trash
rack at the inlet to the pipe;
– valves should be placed at the
discharge end or in a pit on the d/s
slope of the embankment; and
• topsoil to a depth of 100 to 150 mm
minimum and good holding grass such
as kikuyu or couch should be placed over
the entire embankment (u/s and d/s) and
spillway. This should be fertilised and
irrigated if necessary to ensure rapid growth
and hence immediate erosion prevention.
Construction of Small Earth Embankment Dams FA C T S H E E T N O . 5
Dam Element
GEOMETRIC DESIGN CRITERIA
Homogenous Zoned Dam Diaphragm Dam
HEIGHT OF DAM (m) 0-3 3-6 6-9 0-3 3-6 6-9 0-3 3-6 6-9
CREST WIDTH (m) 2.8 3.5 4 2.8 3.5 4 2.8 3.5 4
UPSTREAM BATTER SLOPE (H : V) 3:1 3:1 3.5:1 2:1 2.5:1 3:1 3:1 3:1 3.5:1
DOWNSTREAM BATTER SLOPE (H : V) 2.5:1 3:1 3:1 2:1 2.5:1 3:1 2.5:1 3:1 3:1
DIAPHRAGMTHICKNESS‘D’(m)
(Perpendicular to dam face)
0.6 0.85 1.1
FREEBOARD (m) : FETCH < 1000 m 1.0 m - Assuming 0.5 m maximum spillover depth
FETCH > 1000 m 1.5 m - Assuming 0.5 m maximum spillover depth
SETTLEMENT ALLOWANCE (mm) (Construction level above required crest level)
150 300 500 150 300 500 150 300 500
108 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Construction of Small Earth Embankment Dams FA C T S H E E T N O . 5
F I G U R E F S 5 . 1
1091 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Construction of Small Earth Embankment Dams FA C T S H E E T N O . 5
SPILLWAY DESIGN
FLOOD FLOW MINIMUM INLET WIDTH
MINIMUM OUTLET WIDTH (m) (Various Return Slopes.)
(m3/s) (m) <5% 5-10% 10-15% 15-20% 20-25%
3 5.5 6.5 10 15 18 20
6 11 13 21 30 35 40
9 16.5 19 31 44 53 60
12 22 26 41 59 70 80
15 27.5 33 52 74 87 100
CONSTRUCTION MATERIAL (in order of preference)
CODE DESCRIPTION
GC Clayey gravels
SC Clayey sands
CL Inorganic clays (Low liquid limit)
CH Inorganic clays (High liquid limit.)
GW Well graded gravels.
GP Poorly graded gravels
SW Well graded sands
SP Poorly graded sands
110 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Culverts are commonly used to provide road
crossings over drains or small creeks, and there is
a wide variety of culvert shapes and materials that
can be selected to best suit a particular application.
The correct design and installation of these culvert
crossings will prevent blocked or eroded drainage
channels as well as costly road repairs. There are
a number of areas that need to be addressed.
Flow Capacity
The first and perhaps most obvious concern is to
construct a culvert which is large enough to pass
the design flow without overtopping the road or
embankment. It is not practical to design culverts
to take all possible flows; hence the designer must
decide what risk level is acceptable for overtopping
of the road and calculate a design flow of a suitable
ARI (refer to Fact Sheet Nos 2 and 3). A culvert
installation must then be sized to pass this flow. The
hydraulics of culverts are surprisingly complex and
rely greatly on the site conditions (ie. downstream
flow depths, culvert sizes, shapes, lengths and
slopes). It is not feasible to cover all possibilities
in this handbook; however suppliers of culverts,
State government roads departments, and many
open channel hydraulics text books provide charts
for determining the flow through various culverts.
The basic controlling factors are as follows:
• inlet/outlet control: a culvert which is able
to pass water at a greater rate than is being
supplied is said to be flowing with inlet control.
If the culvert inlet geometry, flow resistance
or depth of water in the downstream channel
result in water being supplied at a greater
rate than it can flow through the culvert, it
is said to be under outlet control. When using
design charts it is important to examine both
control cases and adopt the worst case value
(ie. the highest headwater or least flow);
• headwater: the greater the level of water at the
inlet to a culvert compared to the outlet, the
greater flow it will pass. It is generally acceptable
to design culverts to flow with water up to a
level just below overtopping of the road (ie.
300 mm to 1.0 m), for the design peak flow;
• downstream depth: in contrast to the upstream
depth, the normal depth of flow immediately
downstream from the culvert should be kept as
low as possible to maximise the efficiency of the
culvert. To achieve this a deep or wide channel
is advisable downstream of the culvert; and
• inlet design: the design of the inlet can greatly
affect the flow capacity of a culvert flowing under
inlet control. Greater flow can be achieved be
shaping the approach to the culvert to funnel
flow into the culvert. If the water entering
the culvert has a high suspended solids load,
it is important to keep this water moving
through the culvert. Any ponding at the inlet
will inevitably result in the culvert becoming
blocked. To avoid this, drops or chutes can be
utilised to accelerate flow into the culvert.
Inlet/Outlet Protection
Flows forced through culverts with a high head
water will accelerate into the pipe and can discharge
at a high velocity. High levels of turbulence will also
result from water spreading out into basic channel
flow again. To ensure that this high energy flow
does not cause massive erosion at the inlet and
outlet and under scour of the pipe it is important to
provide erosion protection. This is usually achieved
with headwalls and aprons of reinforced concrete,
a concrete revetment mattress or grouted rock. At
the downstream end, rock Rip Rap is also advisable
for a further distance downstream from the apron.
The level of protection required will depend on the
outlet velocity, as described in Fact Sheet N0. 8.
Culvert Crossings FA C T S H E E T N O . 6
1111 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
This will normally form part of the
above hydraulic calculations.
Installation
Correct selection of culverts and supervised
installation is vital to ensure that heavy vehicles
passing over will not damage the culvert. Depending
on the culvert material and shape selected, there
will be varying requirements for cover (fill depth)
over the culvert and compaction requirements
around the culvert. Concrete culverts rely on their
own strength and require good foundations and
substantial cover, while corrugated steel culverts
rely on the strength of the fill around them and
hence require very good compaction in the side
zones. Numerous Australian Standards, as well as
material supplied by manufacturers, give excellent
advice on correct installation. One important factor
to note is that many mine vehicle axle loadings
will exceed standard highway values and hence
special care must be taken when selecting the
class of culvert (ie. wall thickness) required.
Culvert Crossings FA C T S H E E T N O . 6
112 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Acid drainage occurs when sulphides (usually
iron sulphides) are oxidised according to the
following, highly simplified, equation:
FeS2 + xO2 + yH2O –> Fe(OH)3 + 2H2SO4.
The process is bacterially mediated and temperature
and moisture all affect the rate and expression of
the problem. However, the neutralising capacity
of the gangue is probably the most significant
factor in reducing or preventing the formation
of acid drainage. The geochemical reactions
and indicators of sulphide oxidation and acid
generation are shown in Figure FS 7.1.
In addition to the generation of acid, the
low pH of these waters can mobilise trace
and heavy metals, resulting in the potential
for widespread contamination.
There are many techniques available to foresee if
acid drainage is likely to be a problem, including:
• chemicalprediction/materialscharacterisation
(NAPP, ANC, NAG, solution indicators);
• models(eg.forlocationofacidgenerating
material in a model of the orebody and
waste, rates of acid generation, timing of
appearance in mining schedule, predictions
and schedule of cost of treatment); and
• predictionsofecologicalimpacts.
Once acid drainage is present, opportunities
to manage it are limited to:
•preventionofthegenerationofacid:
– separate the acid producers
(for sale or entombing);
– cut off oxygen (wet or dry covers);
– pacify the mineral surface;
– solidify the waste rock or waste rock mass; and
– minimise water movement (generation
and transport of acid); and/or
• treatmentofaciddrainage:
– lime or alkali treatment of the drainage; blend
solids with alkaline material eg. limestone;
– use bacteria for sulphide precipitation;
– use plants to uptake and store
metals, eg. wetlands; and
– use concentration/recovery
process, eg. cementation.
Considerable work has been undertaken around the
world and the status and outlook for key control
technologies are summarised in Table FS 7.1.
In high rainfall environments, the volumes of
contaminated water that are generated can be
extremely difficult and costly to contain and/or treat.
This potentially ongoing, long-term cost should
be factored in to any development decision.
Acid Drainage FA C T S H E E T N O . 7
1131 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Note 1: Non ferrous metal sulphides such as CuS, PbS, NiS, ZnS are acid neutral. Sulphides such as Cu2S are acid consuming.
Note 2: Siderite (FeCO3) is not included since it has nil net neutralising capacity in an oxidising environment.
Note 3: pH of site drainage may initially increase in response to sulphide oxidation and acid neutralization reactions.
Note 4: Other precipitates such as CuCO3, MnO
2, CuSO
4 can also be observed over a wide pH range.
Note 5: Jarosite iron oxide/hydroxide equilibria is a strong pH buffer and can maintain the pH as 3 even after all pyrite has
been oxidised. Jarosite and iron oxides coat soil mineral surfaces and dominate the mineral solution chemistry.
Acid Drainage FA C T S H E E T N O . 7
ENVIRONMENTAL GEOCHEMISTRY INTERNATIONAL PTY LTD
114 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Acid Drainage FA C T S H E E T N O . 7
TABLE FS 7.1: Status and Outlook for Key Control Technologies
Technology Applicable Current status Research outlook Major limits
Chemical prediction All Inexact Good Costly
Prediction models All Incomplete Good Complex
Pre-treatment Some Beginning Good Site specific
Dry covers Many Field demonstration Very good Cost
Wet covers Many Laboratory/Field Very good Site specific
Fixation Selected Laboratory Fair Cost
Lime neutralisation All In practice Excellent Perpetual
Sludge disposal All Emerging Good Volume/
Containment
Bio-treatment Partial Laboratory/Pilot Fair Capability/
Efficiency
Metal recovery Selected Laboratory/Pilot Poor Economics
1151 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Minimising erosion and capturing sediment
contained in surface runoff is a major environmental
issue on minesites. Site discharge licences will
normally specify a suspended solids limit for
discharge offsite from a storm of a given risk level
(eg. a 5 year Average Recurrence Interval).
There are four main control options and an effective
site program will need to incorporate all of these.
• Minimising disturbance and rapid
revegetation of disturbed areas:
Mining by its very nature involves disruption
of natural vegetation and soils. This results
in a huge increase in erosion potential
and sediment transport. The impact of
such areas can be minimised by better
planning of clearing and rehabilitation to
ensure that the minimum possible area
of soil is left unprotected at any time.
• Drainage control: Water erosion is increased
when concentrated flows pass over unprotected
or steep sloping ground. A properly designed
and maintained drainage system will avoid
this occurring. The most important principles
are to divert uncontaminated drainage
away from erosion prone areas, and to
control flows by using properly constructed
drains at gentle grades as discussed in the
fact sheet concerning drainage design.
• Erosion control: The best method for controlling
erosion is to prevent its occurrence. Methods
for preventing erosion are discussed below.
• Sediment containment: In areas where erosion
prevention is not feasible it is necessary to trap
the suspended sediment before the water passes
offsite. In-stream sediment traps can be used
along the drainage path to remove the bulk
of the solids, however, constructed sediment
retentionpondsmaybenecessaryto‘polish’
the water immediately prior to discharge.
Containment methods are discussed below.
Erosion Control Methods
The prevention of erosion is achieved by protecting
soils from the erosive forces of water and/or by
controlling the flow of water to reduce erosive forces.
Large areas subject to sheet runoff
should be protected as follows.
• Contour ripping: Bare or newly revegetated
areas should be cross contoured to
slow down flows. This will also prevent
concentrated flow paths from forming.
An added benefit of this technique is the
retention of water stored in the furrows
which will aid the growth of new vegetation
and will reduce total quantities of runoff.
• Grassing as described above is the most
effective large-scale method. If moderate
slopes and suitable topsoil are provided
such that good growth occurs, this will
effectively protect soils against sheet runoff
from very heavy and intense storms.
• Surface covers: Steep slopes such as creek banks
or cut and fill batters are hard to revegetate
due to the difficulties in keeping topsoil and
seeds etc. in place. Layers of jute, geosynthetics
or mulch are very effective in protecting these
layers until the root system of the grass has
developed. These layers must be securely
fastened with pegs and the upslope layer must
overlap the top edge of the downslope layer.
Drains or gullies subject to concentrated flows
can be protected using the following techniques.
• Grassing: (reference Chow 1973) Having grass
lining in a channel will significantly retard the
flow and hence reduce the velocity and erosion
potential. Grass will also stablise the channel
consolidate the soil and check the movement of
sediment along the channel bed. The selection
Erosion Control and Sediment Containment FA C T S H E E T N O . 8
116 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
of grass should be “fine and uniformly distributed
sod-forming grasses” where the main flow occurs.
The use of bunch grasses should be avoided in
drains because they will channelise the flow creating
scour lines. Grassing can also be used successfully
in combination with rock fill to provide a very
stable and well interlocked matrix. In establishing
a grass cover in drains it is important to:
– ensure there is a mixture of fast and
slow germinating varieties to ensure
immediate and long-term protection;
– irrigation should be provided as necessary
to ensure good germination if the seed is
planted outside the wet season (usually
the ideal time to build drains);
– provide adequate protection for the seed
if flow is likely in the drain immediately
after construction. (This can be achieved
using degradable natural fibre type covers
which stabilise the surface and allow the
grass to grow up through the fabric); and
– when laying topsoil on drain batters prior
to seeding, tyne the batters parallel to the
direction of flow in the drain. This will
result in long furrows along the drain which
will both retain water and help to prevent
scour paths down the batter slopes.
• Rip rap lining: Rip rap simply refers to a lining
of large rock placed in the drain to armour the
natural ground against erosion. The rock is
sized to ensure its stability during the peak flow
conditions. Size of the rock is based on the flow
depth and velocity. Rip rap should be carefully
machine placed to ensure that a uniform
‘mattress’ofinterlockingrockisachieved.This
is very important to ensure that the rock does
not get displaced during early flows before silt
and grass fill the spaces between rocks thereby
locking them in position. The following points
should be noted when installing rip rap:
– batter slopes steeper than 2.5 H to 1.0 V will
not reliably support rip rap;
– a layer of medium-weight geofabric should
be placed under all rip rap to prevent scour
of the soil. (Due to the rough nature of rip
rap which retards the flow, there will be
much turbulence around the rocks which
can easily result in under scour beneath
the rocks making them unstable)
– a uniform grading of rock size (ie. a good
range from small to big rocks) is vital to
create a good interlocking mattress;
– if rip rap is used on steep drops it must
be carried a short distance into the flatter
sections preceding and following the drop.
• Reno mattresses/gabions: Reno mattress or
gabion lining is a form of rock lining where a
low-profile wire cage is used to hold the rock in
place. This enables the use of smaller diameter
rocks but requires more careful placement.
Mattresses are available in thicknesses of
approximately 170 mm, 250 mm, 300 mm and
500 mm. This type of protection can be used
where very high velocities or extremely turbulent
conditions are expected. This may occur on
very steep slopes (when very large rip rap is not
available or not preferred), at culvert outlets, or
at the base of drops. Reno mattresses are also
aesthetically pleasing and may provide a good
alternative to rip rap in highly visible areas.
• Concrete filled ‘revetment’ mattress:
Revetment is also a form of hard armouring,
utilising a pocketed pervious fabric with
concrete pumped through it. This creates a
solid layer moulded to the shape of the natural
ground below. Small penetrations between
the pockets allow for drainage of subsurface
water preventing any lifting pressures. As
with Reno mattresses this type of protection
can be used where very high velocities or
extremely turbulent conditions are expected.
Erosion Control and Sediment Containment FA C T S H E E T N O . 8
1171 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
This may occur on very steep slopes (when very
large rip rap is not available or not preferred),
at retention dam inlets and spillways, at culvert
outlets, or at the base of drops. With good
preparation of the base, revetment will provide
a very neat and durable protective layer.
• Bottomsills:Insmallsteepdrainswhere
continuous minor erosion is likely, bottom
sills can effectively prevent the propagation of
deep scour gullies. Concrete or gabion barriers
are set into the base of the drain such that
scouring will only occur until a stable slope
is formed between sills (see Figure FS 8.l).
• Corrugatedsteelchutes:Insituationswherean
intercept drain or a gully at the top of a cutting
must drop down a very steep slope into a drain
below running in a perpendicular direction it is
advisable to create a lined chute down the slope.
This will prevent large scour gullies forming. A
simple method of lining such chutes is to use
half round corrugated steel pipes. These should
be lapped at the ends of each pipe section with
the upstream section on top. The pipe sections
canbeheldinplacebyeitherusing‘tentpeg’
style posts or by providing a small concrete
beam down each edge. It should be noted that
steel chutes will eventually rust out and are
therefore suitable only for medium term projects.
In-stream Sediment Containment
Fast flowing surface runoff with a heavy load
of suspended solids can cause major problems
downstream by clogging culverts, blocking inlets or
causing short-circuiting through sediment retention
ponds etc. The solution is to have a number of
in-stream sediment traps along the drainage path.
• Sedimentbarriers/filterdamsplacedacross
the drainage channel with rock protection
downstream will trap heavy suspended solids
as well as providing effective scour protection.
The important feature of these barriers is that
they should be semi-impermeable to water.
This will cause water to pond behind them
and hence silt will settle out of suspension and
build up behind the barriers such that steps
are formed in the channel floor. These barriers
are positioned so that the final slope between
the toe of one step and the top of the next is
approximately 0.5%–1%. The rock downstream
protects the channel from scour at the base of
Erosion Control and Sediment Containment FA C T S H E E T N O . 8
118 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
the drops while the flow velocity between the
drops is reduced enough to prevent erosion. These
structures are effective and economical at drain
slopes up to 3%-4% and can be formed from either
timber, gabions, or graded rock (see Figure FS 8.2).
Points to keep in mind are:
– as well as being required downstream,
rock protection is required upstream of
the barriers for a short distance. This is
to prevent scour around the edge of the
barriers which may occur from the highly
turbulent water spilling over the drop;
– rock protection is also required up the
batter slopes in the vicinity of the barrier.
This will prevent side scour as the water
spills over; fabric must be placed under
the downstream rock to ensure the
underlying soil is not washed out;
– the downstream rock must be cut in, such
that the top of the rock is level with the
natural drain surface, to ensure that another
step is not induced at the end of the rock
apron; and the lowest section of the barrier
crest should be over the drain centre line
such that low flows are preferentially
directed away from the drain edges.
• Silt fences: In areas where flow is not
channelised but carries a high sediment
load it is possible to filter out the suspended
solids using a silt or sediment fence. This
may be desirable during the construction
of roads, at the base of stockpiles, or along
the length of natural watercourses which
receive sheet flow off disturbed areas. There
are many proprietary brand sediment fences
available today which only require posts to be
supplied and have their own ties and support
bands (usually marketed by suppliers of civil
products or geotextiles) (see Figure FS 8.3).
• Vegetation strips: An alternative to silt fences
for capturing silt in sheet flow is to pass the
water through heavily grassed strips. These can
ideally be placed adjacent to catch drains or
road edge drains. An advantage of a vegetation
strip is that as the sediment builds up the grass
grows up through it. Detailed information
on the design and effectiveness of vegetative
filter strips can be found in Haan (1994).
Erosion Control and Sediment Containment FA C T S H E E T N O . 8
1191 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Sediment Removal Ponds
Surface runoff with levels of suspended solids
higher than licence levels will need to be
intercepted and treated prior to discharge offsite.
• Sediment settling ponds: These are the
most common method for settling out solids.
Usually positioned immediately upstream
of a monitored discharge point they also
provide a useful location for controlling
other water pollution problems such as pH,
BOD etc. and may also be used as a storage
for recycling water. For optimum removal
of sediment these pond systems should
address the following design issues:
– the length to width ratio should
be approximately 3:1;
– the inlet and discharge point shall be
positioned to ensure the maximum flow
length between them. Baffles should be used
if necessary to prevent short circuiting. It is
beneficial to have two successive cells. The
first cell can then be free draining and hence
provide flood detention as well as capturing
the bulk of the coarse sediment. The second
cell is then a polishing and treatment pond
for sediment and other quality parameters.
Ideally the second pond should also be
drained in a controlled manner after each
runoff event, however it can be left full as a
water storage facility. The draining should
preferentially take water from the surface
of the pond near the outlet end or should
slowly discharge water through slotted
riser pipes or rock/sand filters; and
– a volume over and above that required
for efficient pond operation must be
incorporated for storage of sediment.
A mechanism for completely draining the pond, and
access into and around the pond must be provided
for periodic removal of captured sediment.
There are many methods for designing sediment
ponds. A good rule of thumb is the CALM
method as developed by the NSW Department
of Conservation and Land Management.
Erosion Control and Sediment Containment FA C T S H E E T N O . 8
120 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
• Wetlands for sediment removal: The use
of artificial wetlands to improve storm water
quality is becoming increasingly popular.
The sediment removal efficiency of wetlands
is known to be high; however in a mining
environment care must be taken that excessive
sediment loads are not imposed on the wetland
plants and that water is always available. The
design of artificial wetlands requires much care
and consideration in the following areas:
– the hydraulics of flow through
dense vegetation;
– the selection of plants. The common
approach is to use emergent macrophytes
such as reeds or bulrushes that are common
to the area. These plants are fast growing
and tolerant of high pollution loads and
some fluctuation of water levels;
– supply of water to plants, especially when
young. Wetland plants rely on a saturated
base but must not be drowned (short periods
of total inundation are tolerable); and
– spread of plants. The plants most effective
for use in wetlands are typically invasive
species that will take over existing wetland
areas if given the opportunity. Deep water
should be used to keep open ponds
clear of the plants, and great care must
be taken to prevent spreading if fragile
wetland ecosystems exist in the area.
Erosion Control and Sediment Containment FA C T S H E E T N O . 8
1211 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Bioremediation is a process which relies on
micro-organisms to break down and detoxify
organic chemicals such as hydrocarbons, and
some organo-chlorines. Carbon dioxide and
water are the final degradation products for
hydrocarbon wastes using this process.
Bioremediation has a number of applications
within the mining industry; including the
treatment of the following types of wastes:
• oilysludges;
• hydrocarboncontaminatedeffluent(eg.
heavy equipment washdown pads);
• hydrocarboncontaminatedsoils;
• specificlowvolumeoilspillages;and
• workshopandpowerstationliquidwastes.
Within Australia, bioremediation is being used
as a cost-effective alternative for the treatment
of wastewater effluent and hydrocarbon
contaminated soils. Most applications involve
theconstructionofa‘bioremediationpad’,and
implementing the process known as landfarming.
Landfarming involves the spreading of wastes
(usually about 30 cm thick) over the ground
to enhance the natural degradation process.
This procedure involves the use of soil micro-
organisms, water or effluent application, nutrients
(usually fertiliser) and oxygen (air). This technique
is highly suited to minesites in arid regions,
due to the higher degradation rates that can be
achieved with high air and soil temperatures.
Prior to commitment to this technology, the soil
and effluent stream need to be assessed by a
suitably qualified laboratory for the following:
• soiltype(particlesizeanalysis,
organic content, etc.);
• thelevelofactivityofhydrocarbondegrading
microbes (ie. C17: pristane ratio);
• thenutrientstatusofthematerialtobedegraded;
• themoisturecontent;and
• concentrationofspecifichydrocarbonfractions.
In the event that insufficient numbers or
incorrect species are present, then the waste
stream can be inoculated with microbes that
are grown within an on-site bioreactor.
Bioremediation Technology FA C T S H E E T N O . 9
Design Process Peak Flows
Hydro- graph
Analysis
Water Balance
Water Storage
Pollutant Dispersion
Tailings Storage
Wetlands Waste- water
Disposal Hydrological Data Format
Rainfall
•IntensityFrequency-
Duration curves (IFD Curves)
(see Figure FS 10.1) ✓ ✓ ✓
•Rainfallpatterns
(Hyetographs) ✓
•DailyRainfall ✓ ✓ ✓ ✓ ✓
•MonthlyandSeasonal
Rainfall ✓ ✓
•AnnualRainfall ✓ ✓
•ContinuousRainfall
(minutes) ✓
Streamflow
•ContinuousFlow ✓ ✓ ✓ ✓ ✓
•DailyFlow ✓ ✓ ✓ ✓ ✓ ✓
•MonthlyandSeasonalFlow ✓ ✓
•AnnualFlow ✓ ✓
Evaporation
•Daily ✓ ✓ ✓ ✓
•Monthly ✓ ✓
•Annual ✓ ✓
122 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
There are various formats for hydrological data
to suit both design and reporting outputs. The
reporting formats may be tabulated or graphed
with time frames to suit the receiver of the report.
Design formats will depend upon the design
process for which the data is to be utilised.
The following table presents the various
data formats and the principal design
processes for which they may be utilised.
Hydrological Data for Design Purposes FA C T S H E E T N O . 1 0
1231 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Hydrological Data for Design Purposes FA C T S H E E T N O . 1 0
124 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Groundwater is the generic term identifying water
resources which are resident in soil or rock pores
and matrices. By far the major proportion of
groundwater resides under positive pore pressures
within aquifers, but some water lies in the interstices
between ground surface and the aquifer within
the capillary zone. Aquifers are generally fully
saturated, whereas the capillary zone contains a
significant proportion of air as well as water.
Aquifers may be confined (pressurised between layers
of relatively impermeable ground or aquicludes), or
unconfined (a water table aquifer with a phreatic
or‘free’surface).Inbothcases,theflowdynamics
are similar in that flow is generated by differences in
pressure from one point to another. A perched water
table is a special type of unconfined aquifer which
may exist within another unconfined aquifer, and is
‘perched’onathinimpermeablelenssuchasclay.
Flow in aquifers is generally laminar, or seepage
flow. In some cases where preferential flow paths
may exist (eg. permeable faults and fractures in rock),
turbulent flow may be generated. Flow in aquifers
is always from a region of higher pressure or higher
potential energy to a region of lower potential energy.
Most aquifers are interconnected, and it is
very rare that a single aquifer will exist in
isolation. Connections between aquifers may
be weak or strong depending on the porous
media and the geological stratification.
The single intrinsic soil or rock parameter that
determines the characteristics of groundwater flow
is the hydraulic conductivity. This is often (and
strictly incorrectly) referred to as the permeability.
The hydraulic conductivity is a quantitative
measure of the velocity of seepage flow of water
reached whilst being generated by a unit pressure
gradient. Hydraulic conductivity may vary in space
(heterogeneous porous media) as well as in the
direction of flow (anisotropic porous media).
A homogeneous and isotropic groundwater regime
is an ideal saturation that rarely occurs in nature.
Groundwater, while recognised as a separate entity
in the hydrologic cycle, is nevertheless strongly
interactive with other components of the hydrologic
cycle such as rain, rivers, lakes and oceans. Although
the time scale of processes in groundwater is
long because of the laminar nature of flow, its
interaction with surface water components of the
hydrologic cycle should always be considered.
Groundwater FA C T S H E E T N O . 1 1
1251 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K
Numerical modelling is the process of solving the
equations describing a physical process using a
step-wise approximation. Solutions are obtained
by performing iterations (successively improved
approximations) at each step until the numerical
answer satisfies all the equations being used.
The approximation is improved by decreasing
the size of the steps, much like drawing a curve
using a series of short, straight lines. Decreasing
step size, however, increases the amount of labour.
With the rapid advances in computer processing
speed, this is becoming less of a concern.
The advantage of numerical modelling is that,
once the model is set up and established, a range
of scenarios may be investigated with relatively
little effort, and complex problems may be solved
using numerical models. Nevertheless, numerical
models should be viewed with caution as their
complexityandtheir‘blackbox’appearancemay
promote errors of judgement in their application.
Numerical models were developed in the early
1960s and are now well established tools. Finite
difference (FD) and finite element (FE) models are
currently popular. These subdivide the physical
area of interest into small fragments which are
each treated in a simplified manner. FE models
are more adaptable to complicated boundaries,
but the methods of solution are slightly more
complex than FD models. Other models which have
limited use are boundary integral and method-of-
characteristics formulations, but these presently lack
the practical applicability of FD and FE methods.
Numerical models may be applied to a wide
range of problems in hydrology, flood flow and
groundwater flow. In recent times, advances in the
understanding of contaminant transport, sediment
transport and complex boundary conditions have
resulted in a generation of problem-specific models.
Before choosing a model, its applicability to a
specific problem must be questioned in depth.
Theprocessof‘calibration’andverificationisan
integral part of numerical modelling. Because
a numerical model may operate using several
parameters describing the physical processes (eg.
frictional stresses, soil-water conductivity) a historical
event for which cause-and-effect data exists should
always be simulated. This allows the modeller to
‘tune’theparametersagainstanobservedevent.
The complexity of the model chosen should
realistically reflect the extent to which the relevant
parameters may be measured or inferred with
accuracy, as well as required accuracy of modelled
answers in a particular project. The sensitivity of
the model to prime parameters should always be
investigated and quantified. The use of models as
decision making tools often have greater value in
sensitivity analysis than in absolute predictions.
The applicability of simpler (one dimensional)
models should be investigated first before adopting
complex (eg. three dimensional) models under
the philosophy that complicated models have a
greater opportunity for errors, both judgemental
and numerical. Finally, the limitations of the
model should always be clearly understood.
Numerical Modelling FA C T S H E E T N O . 1 2
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