karoo groundwater atlas volume 2 - gwdgwd.org.za/sites/gwd.org.za/files/kgeg_karoo groundwater...

by

Karoo Groundwater Expert Group

(KGEG)

September 2013

KAROO GROUNDWATER ATLAS

VOLUME 2

Dr G. Tredoux A.S. Talma

A.C. Woodford P.N. Rosewarne

D. Visser

C. Esterhuyse

R. O’Brien

M. Goes

Prof. G. Van Tonder

Karoo Groundwater Atlas

Volume 2

by


(KGEG)

September 2013

Hydrogeologist/Peer Review RPS, Perth, Australia

[email protected]

Private Consultant Hydrogeologist/Peer Review Bloemfontein, South Africa

[email protected]

Private Consultant Hydrogeochemist/Peer Review Pretoria, South Africa

[email protected]

Private Consultant Hydrogeochemist/Peer Review Pretoria, South Africa

[email protected]

1-Hydrogeologists/2-Geochemist/3-GIS Cape Town, South Africa

[email protected] or [email protected]

P.N. Rosewarne1

M. Goes3 - R. O’Brien2

D. Visser1 - C. Esterhuyse1

A.C. Woodford Prof. G. Van Tonder Dr G. Tredoux A.S. Talma

mailto:[email protected]







Karoo Groundwater Atlas Volume 2 Page i

Executive Summary

The Karoo Basin is an arid area of South Africa occupying about one third of the country’s land surface and

comprising a thick sequence of sedimentary rocks intruded by dolerite dykes and sills. Groundwater

contained in weathered and fractured rock aquifers is an important resource for local communities for

domestic, livestock and irrigation water supply. The shallow aquifers (c.<300 m) in this Basin are relatively

well understood following decades of research and groundwater exploration, use and monitoring.

However, groundwater occurrence and characteristics in the deeper underlying Karoo formations that

contain the target shale gas beds, are largely unknown. Such information as is available is limited to sparse

data from a few deep (up to 4 692 m) hydrocarbon exploration wells from the 1960s and 70s and some

thermal springs. In support of their application for shale gas exploration licences in the Karoo Region, Shell

has therefore committed to identify, assess and manage groundwater risks so that existing and future

groundwater use will be preserved. Progress in the understanding of the groundwater systems has so far

been limited to desk-based studies of existing public domain information pending resolution by government

about granting of exploration licenses.

A Water Expert Group was convened by Shell in September 2011 comprising a group of hydrogeologists

with a combined experience of c.240 years. An inaugural workshop was held in Cape Town in October 2011

at which this group tabled hydrogeological concepts, which were debated and developed. This culminated

in the production of a comprehensive database from which a series of groundwater maps and a preliminary

3D conceptual model were derived. The work was released in February 2012 as the Karoo Groundwater

Atlas (KGA).

Further desktop studies were undertaken by an expanded group of water scientists, known as the Karoo

Groundwater Expert Group (the KGEG) who debated their ideas in a series of workshops. All work has been

rigorously peer reviewed. The results of this two-year study are contained in this Karoo Groundwater Atlas

Volume 2, and some preliminary findings/outputs are:

A general observation is that groundwater quality improves, recharge increases and water levels

become shallower from west to east, which is considered to be a function of the increase in rainfall

and percentage of sandstone and dolerite in this direction.

Analysis of logs of relevant deep SOEKOR wells showed free-flowing groundwater intersections (1-

4 L/s) in the Dwyka Group below the Great Escarpment, with TDS of up to 10 000 mg/L and

temperature of 76°C;

Development of very preliminary conceptual models based on published surface geological maps,

interpolations of SOEKOR well logs and application of basic hydrogeological principles;

Analysis of the c.20 years of water level and chemistry data from the Department of Water Affairs

(DWA) CHART borehole database. This shows no clear trends in water levels but three broad

groupings in terms of chemistry, viz, CaMg/SO4Cl, Ca/Mg(HCO3)2 and NaCl. However, the broad

scatter of water types and variations at most boreholes and wind pumps seen in the database

indicates that establishing baseline water quality ‘norms’ and assessing whether shale gas

exploration has impacted on aquifers will not be straightforward tasks;

The chemical analysis of a water sample obtained from SOEKOR well SA1/66 showed a clear

distinction between this water and the three types mentioned above. This water is a strongly NaCl

type, with relatively high concentrations of F, Br, Li and B, possibly indicating a deep, end-member

water type. However, there are uncertainties over the origin within the well profile of this water

and the effects of long-term stagnation within the capped well.

Regional artesian conditions in the parts of the Karoo Basin under consideration are postulated to

only occur between the GE and the Cape Fold Belt due to local topographic and

stratigraphic/structural characteristics.

If shale gas exploration proceeds it is envisaged that these desk study assessments will be expanded

considerably by fieldwork, collaboration with other researchers, particularly the WRC and university

research projects, to take the knowledge of Karoo aquifers and the deeper underlying Karoo formations to

new levels. This will, inter alia, assist Shell in the management of potential risks to groundwater in the Karoo

from shale gas exploration and help to preserve the integrity of aquifers. In parallel with the KGEG studies

there is an opportunity to inspire and help train a new generation of South African water scientists through

this project. To this end, the composition of the KGEG will evolve as project requirements and the

availability of suitable personnel dictate.

http://s06.static-shell.com/content/dam/shell/static/zaf/downloads/media/karoo-groundwateratlas.pdf


Karoo Groundwater Atlas Volume 2 Page ii

NOTE For clarity purposes this document should be printed on A3 paper size.

ACKNOWLEDGEMENTS The Karoo Groundwater Expert Group (KGEG) would like to acknowledge Shell Research Ltd for their role in initiating the KGEG and for sponsoring this project.

The following institutions are credited for data supplied for use in this project:

Department of Water Affairs Council for Geoscience

Water Research Commission

DISCLAIMER This is a desk-based study using information gathered by other parties. Although all care has been taken to ensure integrity and the quality of this publication and

the information herein, no responsibility is assumed by the Karoo Groundwater Expert Group or its Cooperating Partners nor the authors or their organisations for any use of data presented herein beyond its intended use as a background to Karoo hydrogeology within the study area indicated. All hypotheses put forward

are preliminary and subject to further confirmatory work.


Karoo Groundwater Atlas Volume 2 Page iii

Glossary of Terms

Aquifer: A formation, group of formations or part of a formation that contains sufficient saturated permeable material to store and transmit water, and to yield economic quantities of water to boreholes or springs.

Aquifer system: A heterogeneous body of interlayered permeable and less permeable material that acts as a water-yielding hydraulic unit covering a region.

Attributes: Geological and groundwater features that impart key hydrogeological characteristics to rock formations.

Borehole: Includes a well, excavation, or any other artificially constructed or improved groundwater cavity which can be used for the purpose of intercepting, collecting or storing water from an aquifer; observing or collecting data and information on water in an aquifer; or recharging an aquifer [from the National Water Act (Act No. 36 of 1998)].

Catchment: The area from which any rainfall will drain into the watercourse, contributing to the runoff at a particular point in a river system, synonymous with the term river basin.

Connate water: Water that has remained trapped in sedimentary formations since before their lithification.

Consideration Zone: A zone around/along key features such as boreholes and dykes wherein special consideration needs to be applied prior to carrying out any invasive activities.

Contamination: the introduction of pollutants (whether chemical substances, or energy such as noise, heat, or light) into the environment to such an extent that its effects become harmful to human health, other living organisms, or the environment.

Electrical conductivity (EC): A measurement of the ease with which water conducts electricity due to the presence of dissolved salts/ions in the water, i.e. distilled water - low EC, poor conductor of electricity, sea water - high EC and salt content indicate a good conductor of electricity.

Fault: A zone of displacement in rock formations resulting from forces of tension or compression in the earth’s crust.

Formation: A general term used to describe a sequence of rock layers.

Fracture: Cracks, joints or breaks in the rock that can enhance water movement.

Hydrogeology: The study of the properties, circulation and distribution of groundwater, in practise used interchangeably with geohydrology; but in theory hydrogeology is the study of geology from the perspective of its role and influence in hydrology, while geohydrology is the study of hydrology from the perspective of the influence on geology.

Groundwater: Water found in the subsurface in the saturated zone below the water table or piezometric surface, i.e. the water table marks the upper surface of groundwater systems.

Groundwater flow: The movement of water through openings and pore spaces in rocks below the water table, i.e. in the saturated zone. Groundwater naturally drains from higher lying areas to low lying areas such as rivers, lakes and the oceans. The rate of flow depends on the slope of the water table and the transmissivity of the aquifer materials.

Hydraulic conductivity: Measure of the ease with which water will pass through porous material; defined as the rate of flow through a cross-section of one square meter under a unit hydraulic gradient at right angles to the direction of flow (in m/d).

Lineaments: A major, linear, topographic feature of regional extent of structural or volcanic origin, most easily appreciated from remote sensing data, e.g. a fault system or dyke.

Porosity: The percentage of void space that a rock or sediment contains, which is an index of how much groundwater can be stored per volume when saturated. The effective porosity, also called the kinematic porosity, of a porous medium is defined as the ratio of the part of the pore volume where the water can circulate to the total volume of a representative sample of the medium.

Potability: Suitability of water for drinking.

Quaternary catchment: Fourth order catchment within a primary river basin catchment.

Recharge: The addition of water to the zone of saturation, either by the downward percolation of precipitation or surface water and / or the lateral migration of groundwater from adjacent aquifers.

Saturated zone: The subsurface zone below the water table where interstices are filled with water under pressure greater than that of the atmosphere.

Transmissivity: the rate at which a volume of water is transmitted through a unit width of aquifer under a unit hydraulic head (m2/d); product of the thickness and average hydraulic conductivity of an aquifer.

Unsaturated zone: That part of the geological stratum above the water table where interstices and voids contain a combination of air and water; synonymous with the zone of aeration and vadose zone.

Vulnerability: The tendency or likelihood for contaminants to reach a specified position in the groundwater system after introduction at some location above the uppermost aquifer.

Water table: The upper surface of the saturated zone of an unconfined aquifer at which pore pressure is at atmospheric pressure, the depth to which may fluctuate seasonally.

Wellfield: An area containing more than one pumping borehole that provides water to a public water supply system or single owner (e.g. a municipality).

For a detailed dictionary of groundwater terms please refer to the following DWA website:

http://www.dwa.gov.za/Groundwater/GroundwaterDictionary.aspx

http://www.dwa.gov.za/Groundwater/GroundwaterDictionary.aspx


Karoo Groundwater Atlas Volume 2 Page iv

List of Abbreviations

c.

DEADP

DEM

approximately

Department of Environmental Affairs and Development Planning

Digital Elevation Model

DRASTIC Groundwater vulnerability assessment method

DTEC Department of Tourism, Environment and Conservation (N Cape Province

DWA Department of Water Affairs (formerly the DWAF)

DWAF Department of Water Affairs and Forestry

EC electrical conductivity (mS/m)

EIA Environmental Impact Assessment

EMP Environmental Management Plan

GA General Authorisation

GE Great Escarpment

GIS Geographical Information System

AGRP Average Groundwater Resource Potential

K hydraulic conductivity

L/s litres per second

LANDSAT TM LANDSAT Thematic Mapper

m2/day square metres per day

m3/a cubic metres per annum

mamsl metres above mean sea level

MAP Mean Annual Precipitation

mbgl metres below ground level

mg/L milligrams per litre

mS/m milli-Siemens per metre

NGA National Groundwater Archives (formerly NGDB)

NGDB National Groundwater Database

NWRS National Water Resource Strategy

Q Yield (L/s)

SOEKOR Southern Oil Exploration Corporation

SRK SRK Consulting (SA) Pty Ltd

T Transmissivity (m2/day)

Tr, Tw Topography index for DRASTIC method

TDS Total dissolved solids (mg/L)

WARMS Water Authorization Registration Management System

WSA Water Services Act

WQMS Water Quality Management Services


Karoo Groundwater Atlas Volume 2 Page v

Table of Contents

1. INTRODUCTION ..................................................................................................................................... 1

1.1. Background ........................................................................................................................................... 1

1.2. Scope of Work ....................................................................................................................................... 1

2. GROUNDWATER MAPPING ................................................................................................................... 3

2.1. Attributes Map ...................................................................................................................................... 3

2.2. Vulnerability Maps ................................................................................................................................ 3

3. CONSIDERATION ZONES ...................................................................................................................... 11

4. CONCEPTUALISATIONS ........................................................................................................................ 15

4.1. Approach ............................................................................................................................................ 15

4.2. Western Karoo Example Area (Figure 4—5) ......................................................................................... 15

4.3. Central Karoo Example Area (Figure 4—6) ........................................................................................... 16

4.4. Eastern Karoo Example Area (Figure 4—7) .......................................................................................... 16

4.5. Shallow Aquifer ................................................................................................................................... 17

4.6. Deep Karoo Formations ....................................................................................................................... 17

5. CHART BOREHOLE DATA ..................................................................................................................... 25

5.1. Background ......................................................................................................................................... 25

5.2. Methodology ...................................................................................................................................... 25

5.3. Data Processing and Quality Checking ................................................................................................. 25

5.4. Water Level Analysis Results ............................................................................................................... 25

5.5. Chemistry Analysis Results .................................................................................................................. 32

6. CONCLUDING REMARKS ...................................................................................................................... 34

7. REFERENCES ........................................................................................................................................ 35

List of Tables

Table 2-1: Parameters Controlling the Vulnerability of an Aquifer................................................................. 3

Table 2-2: Ratings for Depth to Groundwater, Recharge and Slope ................................................................ 3

Table 2-3: Ratings for Soil Media .................................................................................................................. 4

Table 2-4: Lithological Ratings for Aquifer Media, Hydraulic Conductivity and Impact of the Vadose Zone .... 4

Table 3-1: Consideration Zones and Suggested Dimensions ........................................................................ 11

Table 5-1: Water Level Quality Scoring ....................................................................................................... 25

Table 5-2: Sub-Precinct Summary of Water Level Analysis Results .............................................................. 26

Table 5-3: Notes on Sample Water Level Time Series Graphs by Sub-Precinct ............................................. 27

Table 5-4: Chemical Analysis Results for a Water Sample from SOEKOR Well SA1/66 and Comparison with Dwyka and Beaufort Group Samples ........................................................................................................... 32

List of Figures

Figure 1—1: Locality Map ............................................................................................................................. 2

Figure 2—1: Composite Attributes Map Western Karoo ............................................................................... 5

Figure 2—2: Composite Attributes Maps Central Karoo ................................................................................ 6

Figure 2—3: Composite Attributes Maps Eastern Karoo ............................................................................... 7

Figure 2—4: Vulnerability Map Western Karoo ............................................................................................. 8

Figure 2—5: Vulnerability Map Central Karoo ............................................................................................... 9

Figure 2—6: Vulnerability Map Eastern Karoo ............................................................................................ 10

Figure 3—1: Consideration Zones Western Karoo ....................................................................................... 12

Figure 3—2: Consideration Zones Central Karoo ......................................................................................... 13

Figure 3—3: Consideration Zones Eastern Karoo ........................................................................................ 14

Figure 4—1: Geological Log for SOEKOR Well SA1/66 ................................................................................. 18

Figure 4—2: Geological Log for SOEKOR Well VR1/66 ................................................................................. 19

Figure 4—3: Geological Log for SOEKOR Well KL1/65.................................................................................. 19

Figure 4—4: Schematic Conceptual Hydrogeological Model for the General Study Area ............................. 20

Figure 4—5: Conceptual Hydrogeological Model: Western Karoo ............................................................... 21

Figure 4—6: Conceptual Hydrogeological Model: Central Karoo ................................................................. 22

Figure 4—7: Conceptual Hydrogeological Model: Eastern Karoo ................................................................. 23

Figure 4—8: Schematic N-S Hydrogeological Cross Section ......................................................................... 24

Figure 5—1: CHART Groundwater Level Analysis: Borehole Positions ......................................................... 28

Figure 5—2: Water Level Time Series Graph for Borehole 033062, Sub-Precinct W1................................... 29


Karoo Groundwater Atlas Volume 2 Page vi

Figure 5—3: Water Level Time Series Graph for Borehole 033085, Sub-Precinct W1 .................................. 29

Figure 5—4: Water Level Time Series Graph for Borehole 3123AC000022, Sub-Precinct C1 ........................ 29

Figure 5—5: Water Level Time Series Graph for Borehole 3222BD00075, Sub-Precinct C2.......................... 29

Figure 5—6: Water Level Time Series Graph for Borehole 029856A, Sub-Precinct C2.................................. 30

Figure 5—7: Water Level Time Series Graph for Borehole 3124DA00001, Sub-Precinct C5 ......................... 30

Figure 5—8: Water Level Time Series Graph for Borehole 3124DB00044, Sub-Precinct E1 .......................... 30

Figure 5—9: Water Level Time Series Graph for Borehole 3124BB0055, Sub-Precinct E1 ............................ 30

Figure 5—10: Water Level Time Series Graph for Borehole 3125DB00002, Sub-Precinct E2 ........................ 31

Figure 5—11: Water Level Time Series Graph for Borehole 3125BA00026, Sub-Precinct E2 ........................ 31

Figure 5—12: Water Level Time Series Graph for Borehole 3226AB00001, Sub-Precinct E3 ........................ 31

Figure 5—13: Water Level Time Series Graph for Borehole 3225DD00004, Sub-Precinct E4........................ 31

Figure 5—14: Composite Piper Diagram for the Three Precincts .................................................................. 33


Karoo Groundwater Atlas Volume 2 Page 1

1. INTRODUCTION

• Karoo groundwater background • Formation of the Karoo Groundwater Expert Group • Scope of work • Sources of information • Atlas format

1.1. Background

The Karoo Basin is an arid area of South Africa occupying about one third of the country’s land surface and comprising a thick sequence of sedimentary rocks intruded by dolerite dykes and sills. Groundwater contained in weathered and fractured rock aquifers is an important resource for local communities for domestic, livestock and irrigation water supply. The shallow aquifers (c.<300 m) in this Basin are relatively well understood following decades of research and groundwater exploration, use and monitoring. However, groundwater occurrence and characteristics in the deeper underlying Karoo formations that contain the target shale gas beds, are largely unknown. Such information as is available is limited to sparse data from a few deep (up to 4 692 m) hydrocarbon exploration wells from the 1960s and 70s and some thermal springs. In support of their application for shale gas exploration licences in the Karoo Region, Shell has therefore committed to identify, assess and manage groundwater risks so that existing and future groundwater use will be preserved. Progress in the understanding of the groundwater systems has so far been limited to desk-based studies of existing public domain information pending resolution by government about granting of exploration licenses.

A Water Expert Group was convened by Shell in September 2011 comprising a group of hydrogeologists with a combined experience of c.240 years. A workshop was held in Cape Town in October 2011 at which this group tabled concepts, which were debated and developed. This culminated in the production of a comprehensive database from which a series of groundwater maps and a 3D conceptual model were derived. The work was released in February 2012 as the Karoo Groundwater Atlas (KGA).

In 2012/13 further desktop studies were undertaken to improve on the current understanding of Karoo Aquifers by an expanded group of hydrogeologists, hydrogeochemists, known as the Karoo Groundwater Expert Group (the KGEG). The KGEG currently comprises authors listed on the cover of the Atlas. The grouping of highly experienced practitioners, with diverse Karoo experience, from differing backgrounds and affiliations is intended to reduce bias and enhance the credibility of results. This intention is founded on two precepts, namely the breadth of knowledge and experience within such a grouping and the reduced risk of bias affecting results. To further assure scientific rigour all work has been challenged by debate in workshops and peer reviewed.

The results of these further studies are presented in this update of the KGA (Volume 2). Further background information from the KGA 2012 is not included in this text and the reader is referred to the link above to understand the KGEG work more. The Shell Precincts are shown in Figure 1—1 while the full study area was extended to include the quaternary drainage catchment boundaries containing these precincts in order to provide for more natural boundaries.

1.2. Scope of Work

The latest work has centered on the following:

Holding a series of workshops where concepts and approaches were formulated and debated;

Development of groundwater attributes and vulnerability maps;

Application of the concept of Consideration Zones associated with key features;

Analysis of logs of the deep SOEKOR wells;

Development of conceptual hydrogeological models;

Analysis of the relatively long-term (c.20 years) water level and chemistry data from the Department of Water Affairs (DWA) CHART borehole database.

The main sources of information (see Section 6 References) have been the following:

The Environmental Management Plan (Golder Associates, 2011);

Published maps by the DWA e.g. 1:500 000 scale hydrogeological map series (DWA, 2001)

Published 1:250 000 scale geological map series (Geological Survey, 1991);

National Groundwater Archive (NGA) and Water Authorisation Registration Management System (WARMS) databases;

Water Research Commission (WRC) reports (Chevallier et al, 2001; Chevallier and Woodford, 1999; Dondo et al, 2010; Murray et al 2011; Steyl et al, 2012; Woodford and Chevallier, 2002);

Department of Mineral Resources report (DMR, 2012);

DWA reports (Vandoolaeghe MAC, 1980)

DWA CHART database;

Consultants reports (Vegter, 2001; Xu et al, 2002, Water Expert Group, 2012);

Southern Oil Exploration Corporation (SOEKOR), now Petro SA, hydrocarbon exploration well logs;

Groundwater Resource Assessment Phase 2 (GRA2) Project (DWA, 2005)

The outputs from the latest work are presented as follows:

Section 2: Groundwater Mapping

Section 3: Consideration Zones

Section 5: Conceptualisations

Section 6: CHART Borehole Data

Section 7: Concluding Remarks

http://s06.static-shell.com/content/dam/shell/static/zaf/downloads/media/karoo-groundwateratlas.pdf



Figure 1—1: Locality Map



2. GROUNDWATER MAPPING • Concept of groundwater attributes developed • Groundwater attributes mapping • Groundwater vulnerability mapping

Figure 1-1 provides some key background features of the Karoo Basin that occur within the Shell precincts/study area and influence the mapping and conceptualisations presented later in this document. These are, generally progressing from south to north:

The southern limit of outcrop of dolerite intrusions;

The Great Escarpment (GE);

The northerly limit of the sub-outcrop of the Cape Supergroup

Thermal springs

Specific boreholes and wells indicated are the SOEKOR wells, DWA long-term monitoring boreholes and boreholes that are known to emit methane, to show that such emissions are quite common in the Karoo Basin.

Building on the data collation and interpretation in KGA1 further assessment resulted in two types of groundwater maps were produced for the Project, namely Attributes and Vulnerability. The former is an aquifer classification methodology developed by the KGEG while the latter uses the well-known DRASTIC methodology developed by the US Environmental Protection Agency (EPA) in the 1980s. The outer boundaries of the maps have been extended out from the boundaries of the precincts to the quaternary catchment boundaries so that the influence of surrounding aquifers and groundwater users are taken into account. These maps have been produced at a small scale initially and will be expanded to progressively larger scales as more site specific data become available.

The maps are being used to assist in preliminary siting and to develop the field assessment needs of future gas exploration wells. Many technical and environmental factors will be used to determine the exact location of gas exploration well sites. From a hydrogeological perspective, aquifer potential and adequate buffer zones from known pathways and potential, receptors are important considerations being taken into account.

2.1. Attributes Map

The Attributes Map has been reported on in the KGA and is briefly revisited here. The 10 attributes (layers) listed below were decided upon by workshop participants as being of significance in characterising Karoo Aquifers. These represent characteristics that can be mapped using existing information. Recharge is incorporated into aquifer yield. The attributes recognised are:

1 Aquifer yield

2 Depth to water level

3 Groundwater quality (key indicators for the Karoo are EC, F, NO3, mostly from a potability perspective)

4 Dolerite intrusions

5 Faults

6 Folded lithologies

7 Lithology

8 Depth to main water strike

9 Depth of weathering

10 Soil type

The first four attributes made up 60 per cent of the ranking points allocated by the workshop participants. Three composite attributes maps of example areas from the western, central and eastern Shell precincts are shown in Figure 2—1, 2-2 and 2-3.

The composite maps indicate that the ranking of attributes increases from west to east, from mainly low to mainly high. This is due to aquifer yield and recharge increasing, water levels becoming shallower and groundwater electrical conductivity (EC) decreasing, as a function of a higher ratio of sandstones and dolerite intrusions and higher rainfall in an easterly direction.

2.2. Vulnerability Maps

Groundwater vulnerability is defined as the tendency or likelihood for contaminants to reach a specified position in the groundwater system after introduction at some location above the uppermost aquifer. The general concept is based on the valid assumption that the physical environment may provide some degree of protection to groundwater against impacts, especially with regard to contaminants entering the subsurface. As a result, some land areas are more vulnerable to groundwater contamination than others. The US EPA built on the protection criteria to develop the DRASTIC methodology (Aller et al, 1987) for the screening of groundwater vulnerability. The DRASTIC model uses seven environmental parameters, namely Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone and hydraulic Conductivity in order to characterise the hydrogeological setting and evaluate aquifer vulnerability.

The sources of the seven parameters controlling the DRASTIC model are discussed in Table 2-1 below.

Table 2-1: Parameters Controlling the Vulnerability of an Aquifer

Parameter Input dataset

Depth to water table (D) Groundwater levels as part of the GRA2 project where 126 263 groundwater levels from the National Groundwater Data Base (for 4,280 of these, the mean groundwater level was calculated from time-series data) were interpolated to a groundwater level on a 1 km

2 grid and re-sampled to 20 x 20 m.

Recharge (R) Recharge calculated as part of GRA2 project.

Aquifer material (A) 1:250 000 scale geological map sheets from the Council for Geoscience

Soils (S) ARC Institute for Soils, Climate and Water

Topography and slope (T) DWAF 20 m Digital Terrain Model

Impact of the vadose (unsaturated) zone (I)

Lithological data from the 1:250 000 geological maps sheets

Hydraulic conductivity (C) Lithological data from the 1:250 000 geological maps sheets

The overall DRASTIC equation is shown below:

Aquifer Vulnerability = DrDw + RrRw + ArAw + SrSw + TrTw + IrIw + CrCw

Where: R = rating and w = weighting. The ratings and weights used are presented in Table 2-2, 2-3 and 2-4. The categories are based on the DRASTIC methodology. Three composite groundwater vulnerability maps of example areas from the western, central and eastern Shell precincts are shown in Figure 2—4, 2-5 and 2-6.

Table 2-2: Ratings for Depth to Groundwater, Recharge and Slope



Depth to Groundwater Recharge Topography (slope)

Range (m) Rating Range (mm/a) Rating Range (%) Rating

0 – 1.5 10 0 – 50 1 <2 10

1.5 – 4.5 9 50 – 100 3 2 – 6 9

4.5 – 9.0 7 100 – 175 6 6 – 12 5

9.0 – 15.0 5 175 – 250 8 12 – 18 3

15.0 – 22.5 3 > 250 9 > 18 1

22.5 – 30.0 2

> 30 1

Weight 5 4 1

Table 2-3: Ratings for Soil Media

Soil Type Rating

RED-YELLOW APEDAL, FREELY DRAINED SOILS

Ae - Red, high base status, >300mm deep (no dunes) 5

Af - Red, high base status, >300mm deep (with dunes) 9

Ag - Red, high base status, <300mm deep 6

Ah - Red and yellow, high base status, usually < 15% clay 7

Ai - Yellow, high base status, usually < 15% clay 7

DUPLEX SOILS DOMINANT

Da - Red B horizons 4

Db - B horizons not red 4

Dc - In addition, one or more of: vertic, melanic, red structured horizons 3

ONE OR MORE OF VERTIC, MELANIC, RED STRUCTURED DIAGNOSTIC HORIZONS

Ea - Undifferentiated 3

GLENROSA AND/OR MISPAH FORMS (other soils may occur)

Fa - Lime rare or absent in the entire landscape 5

Fb - Lime rare or absent in upland soils but generally present in low-lying soils 5

Fc - Lime generally present in the entire landscape 5

MISCELLANEOUS LAND CLASSES

Ia - Undifferentiated deep deposits 3

Ib - Rock areas with miscellaneous soils 3

Ic - Rock with little or no soil 4

Soil Type Rating

Weighting 2

Table 2-4: Lithological Ratings for Aquifer Media, Hydraulic Conductivity and Impact of the Vadose Zone

Label Litho1 Litho2 Litho3 Aquifer Media Vadose Zone Hydraulic Conductivity

Jd DOLERITE (sills)

4 5 5

Jd DOLERITE (dykes)

4 8 8

Ksu PYROCLASTIC BRECCIA TUFF TRACHYTOID 4 9 9

Pa MUDSTONE ARENITE

2 5 5

Pc ARENITE SHALE

2 5 5

Pf SHALE

1 4 4

Pk SHALE

1 4 4

Pko ARENITE SHALE

2 5 5

Ppr SHALE

1 4 4

Ps SHALE ARENITE

2 5 5

Pt SHALE

1 4 4

Pvo SHALE

1 4 4

Pw SHALE

1 4 4

Pwa ARENITE SHALE

2 5 5

Q SEDIMENTARY SAND CALCRETE 7 9 9

Tg SILCRETE

2 3 3

T-Qk SAND LIMESTONE

10 9 9

TRm ARENITE MUDSTONE SHALE 2 5 5

TRt MUDSTONE ARENITE

2 5 5

Weight

3 5 3

For spatial distribution and analysis ArcGIS 10.1 (an Economic and Social Research Institute software product) was used. The ranges (significant types) of each parameter were established based on its impact potential. Each range was then assigned a rating. Each parameter was assigned a weighting relative to each other in order of importance. A composite of all the results was generated i.e. the groundwater vulnerability map, by using the GIS to intersect of all the parameters. It should be noted that the vulnerability indexes so produced relate mainly to impacts on the Shallow Aquifer from surface/near surface sources.



Figure 2—1: Composite Attributes Map Western Karoo



Figure 2—2: Composite Attributes Maps Central Karoo



Figure 2—3: Composite Attributes Maps Eastern Karoo



Figure 2—4: Vulnerability Map Western Karoo



Figure 2—5: Vulnerability Map Central Karoo



Figure 2—6: Vulnerability Map Eastern Karoo



3. CONSIDERATION ZONES • Concept of zones of influence developed • Proposed features for considerations zones • Proposed widths of zones of influence

Some of the groundwater attributes do not have fixed boundaries and may have zones of influence extending beyond their surface-mapped locations, e.g. dolerite intrusions. To accommodate such variation the concept of a ‘consideration zone’ was derived by the KGEG. These are 3D zones surrounding potentially sensitive features that need to be taken into account (i.e. considered) in the siting and design phase of shale gas exploration phase.

Table 3-1 presents a preliminary list of features for which consideration zones will be generated. The dimensions of the zones were agreed at a workshop in October 2011 based on experience and preliminary interpretation of the GIS. These zones will be further refined during later stages of field mapping and geophysical interpretation and used to inform management plans. Additional features that may be included are recharge areas, areas with upward groundwater flow (subject of a separate WRC-sponsored research project, K5/2254/1) and drainage channels. These will be incorporated into the more detailed and larger-scale mapping/investigation planned to be done.

Table 3-1: Consideration Zones and Suggested Dimensions

Feature Consideration Zone

(m)

Dykes 250

Other intrusions 250

Faults/fold axes 250

Production boreholes 1 000

Hot springs 1 000

Hydrothermal plugs 100

Kimberlite fissures 100



Figure 3—1: Consideration Zones Western Karoo



Figure 3—2: Consideration Zones Central Karoo



Figure 3—3: Consideration Zones Eastern Karoo



4. CONCEPTUALISATIONS • Preliminary conceptualisation using existing data • Main geological and hydrogeological features described • Shallow Aquifer and deep Karoo formations

4.1. Approach

Preliminary conceptual models have been compiled using the following main sources:

- KGEG Karoo Aquifers Atlas Vol. 1

- Groundwater Attributes Maps

- Groundwater Vulnerability Maps

- GRA2 data sets

- Geological logs of four historic SOEKOR wells occurring within the precincts and seven occurring in close proximity of the precinct boundaries

- WRC, DWA, Government task team reports on fracking and the EMP

- CGS 1:250 000 scale geological map sheets

- DWA National Groundwater Archive borehole information

These conceptualisations represent a distillation of available data as at August 2013, at desk study level and at a relatively small scale. They can be used for planning purposes but not at the site-specific level. Ground-truthing in the form of, inter alia, remote sensing, geophysics, hydrocensus, baseline sampling and exploration drilling will be used to update them.

They were developed using software (Leapfrog) which enables the construction of an ‘interactive’ 3D representation of the geology imported from the SOEKOR well logs and the other sources listed above. The 3D Leapfrog geological models are still in development and will be supplemented with the results of the ground-truthing mentioned above before release. The versions included in this section have been imported into GIS for ease of visual examination along with these notes and appears in ‘section’ format. Additional data can be incorporated as they become available and can be imported into other modelling packages such as MODFLOW, if required. Note that the vertical exaggeration for the illustrative GIS representations is x10 and so dips are apparent. Examples from the western, central and eastern Karoo, chosen to present a range of features of interest, are given in the following subsections. Some observations on deep groundwater occurrence from information gleaned from the SOEKOR logs are given in Subsection 5.2.4. There then follows some discussion on characteristics of shallow aquifers and the deeper underlying formations, with example conceptualisations and descriptions in Figure 4—4 to 4-7. The surface geology is shown in dark colour to indicate a high level of confidence as this is based on published geological maps. All formations below this are shown in light colours to indicate uncertainties and all boundaries are represented with dashed lines and question marks to further emphasise uncertainties with depth based on current information.

4.2. Western Karoo Example Area (Figure 4—5)

The main geological features are:

The example area is located above the GE and the northern-most extent of the Cape Supergroup rocks passes through its southern edge.

There is one deep SOEKOR well, QU1/65, located on the western edge of the depicted area and so the level of confidence in the deep geological succession is high in this area, decreasing to the east.

The largest dolerite sill is c. 128 m thick, with a median sill thickness of 34 m.

A thick sill underlies the Shallow Aquifer; however, the lateral continuity of such structures is uncertain and will require investigation using geophysical surveys.

Sills appear to be thicker in the Beaufort Group than in the Ecca Group.

Dolerite ring-structures are present and curvilinear ring-feeder dykes. Well QU1/66 is situated on the edge of a ring-structure and may lie within a second one. There is also another large ring-structure just to the east. (intrusion type varies within stratigraphic units)

There is an organic shale layer in the Upper Ecca which contains coal seams.

There are no kimberlite fissures or diatremes indicated in this area, although the Victoria West kimberlite province is located nearby. More detailed work will be required to clarify/confirm this. Breccia pipes could be present at depth in the Ecca and Dwyka groups, terminating against the base of the Beaufort Group, and thus not providing potential pathways to the Shallow Aquifer.

At the scale of information supplied (1:250 000) it is not possible to assess the thicknesses of specific dykes. However, the fact that they are mapped at this scale indicates that they are the most prominent in the area and can reasonably be presumed to be ≥3 m thick. There are regional north-northwest trending dykes present which are known to feed into ring-structures.

The target shale gas horizons are located between c. 1 700 m and 1 900 m depth.

The main hydrogeological features are:

The average thickness of the upper weathered zone is 25 m and underlying fractured zone is 142 m thick, giving a total Shallow Aquifer thickness of 167 m.

The groundwater attributes rating is Low over the whole area.

Groundwater vulnerability is mostly Very Low to Low, with a few small areas of High in the north-east.

Groundwater levels are mostly relatively shallow at <15 mbgl.

The regional groundwater flow direction in the Shallow Aquifer is mostly to the north.

Groundwater EC is <150 mS/m.

There are 45 boreholes and 81 wind pumps, which indicates a possibly moderate groundwater potential, as supported by the low attributes rating.

There are no large-scale groundwater abstraction centres, i.e. municipal wellfields.

There is one DWA CHART borehole located on the southwestern boundary of this area.

There are no thermal springs in the area.

As the target shale gas horizons are located between c.1 700 m to 1 900 m it is unlikely that highly saline groundwater or brine will be encountered during gas well drilling. This is supported by the fact that SOEKOR well KL1/65, located below the GE, produced groundwater with a Total Dissolved Solids (TDS) of 1 390 mg/L from a depth of 1 006 m.

With this area being located above the GE and the relatively shallow shale gas depth, it is also unlikely that the piezometric head in any deep groundwater encountered would be sufficient to cause natural outflow at the well head.



The main surface water drainage direction in the area is effected by the north- flowing Sout River, but flow is intermittent.

About 47 per cent of the area is covered by Consideration Zones according to the preliminary assessment of such zones, mainly relating to dykes, boreholes and wind pumps.

4.3. Central Karoo Example Area (Figure 4—6)


The example area is mostly located just below the GE. Apart from the northern-most edge, Cape Supergroup rocks underlie the whole area.

There are two deep SOEKOR wells, AB1/65 and KA1/66, located 54 km to the northwest and 30 km to the northeast, respectively, and therefore the level of confidence in the geological succession is therefore moderate.

There are no kimberlite fissures or diatremes indicated. Breccia pipes could be present in the Ecca and Dwyka groups, terminating against the base of the Beaufort Group. The latter will therefore not form pathways to the Shallow Aquifer.

The area is dominated by dolerite sills with some dykes in the northern and eastern areas.

The thickest dolerite sill is c. 265 m thick, with a median sill thickness of 52 m.

There are extensive coarse alluvial deposits in valleys and scree on mountain slopes in this area.

At the scale of information supplied (1:250 000) it is not possible to assess the thicknesses of specific dykes. However, the fact that they are mapped at this scale indicates that they are the most prominent in the area and can reasonably be presumed to be ≥3 m thick. Trends are mostly north and northwest

The target shale gas horizons are located below a depth of c. 1 295 m.

There is uranium mineralisation present in the Central Karoo and extensive exploration drilling has been carried out (thousands of boreholes potentially present). Feasibility studies for the development of mines have been carried out but have not gone beyond the planning stage. Exploration borehole logs from the Rystkuil area on the southern boundary of the Central Precinct have been assessed and a detailed groundwater study was carried out by members of the KGEG. A high yielding shallow aquifer occurs in this area but drilling depth was limited to c150 m and so information on the deeper formations was not obtained.


The average thickness of the upper weathered zone is c.50 m and the underlying fractured zone c.110 m, with a total Shallow Aquifer thickness of 160 m.

The groundwater attributes rating is mainly High (80 per cent of the area), dropping to Medium in the east.

Groundwater vulnerability is variable, being High to Very High in the west and Very Low to High in the east.

Groundwater levels are shallow at 5-10 mbgl in the west, deepening somewhat to 10-15 mbgl in the central and eastern areas.

The regional groundwater flow in the Shallow Aquifer is mostly from a northerly direction towards the southwest, south and southeast.

Groundwater EC data are sparse but <70 mS/m in the central area, becoming more saline to the west and east in the range 150-370 mS/m.

There are 264 boreholes and 169 wind pumps identified, which supports the high to very high attributes rating, i.e. this area has relatively good groundwater potential.

Two DWA CHART boreholes are located within this area and one on the northern boundary and water level and chemistry data from 1994 to the present will be used to determine sub-regional trends.

There are no thermal springs in this area.

There is a wellfield close to the southwestern boundary that supplies Beaufort West with municipal water and extensive water supply borehole drilling programmes have been carried out in the Beaufort West area since the mid-1970s.

With the target shale gas horizons being located from about 1 290 m it is unlikely that saline groundwater or brine will be encountered during gas well drilling. Supporting evidence for this contention comes from SOEKOR well KL1/65, located below the GE, produced groundwater with a TDS of 1 390 mg/L at a depth of 1 006 m, and the Aliwal North spring, which is postulated to originate from a depth of c.1 000 m has a TDS of c.1 200 mg/L.

This area is located below the GE and although the shale gas formations are relatively shallow recharge from the higher lying areas could generate free-flowing groundwater out of the well head. This could also arise if the Dwyka Group or Cape Supergroup rocks are penetrated, as free-flowing groundwater was encountered in some SOEKOR wells in the former and is postulated to occur in the latter.

The main surface water drainage direction is to the south, away from the GE but is non-perennial.

About 62 per cent of this example area is covered by Consideration Zones using the preliminary assessment of these zones, mainly relating to dykes, boreholes and wind pumps.

4.4. Eastern Karoo Example Area (Figure 4—7)


The example area located above the GE with the northernmost extent of the Cape Supergroup rocks passing through the middle of it.

The nearest deep SOEKOR well, WE 1/66, is located c. 160 km to the north-east and so confidence in the deep geological succession is low (there are closer boreholes but these are below the GE and thus have a differing geological profile).

There are no kimberlite fissures or diatremes indicated in this area. Breccia pipes could be present in the Ecca and Dwyka groups, terminating at the base of the Beaufort Group and thus not providing a pathway to the Shallow Aquifer.

The form of dolerite intrusion is strata-bound and lies within the zone of likely ring complexes. At depth in the Ecca rocks, dolerite intrusions are more likely to be undulating or flat sills. Based on WE1/66, the thickest sill is c. 200 m in width while the median is c. 77 m.

The boundaries of the depicted area appear to follow the outcrop of a dolerite ring structure.

Sills appear to be thicker in the Beaufort Group than in the Ecca Group.

There is an organic shale layer in the Upper Ecca, which may contain coal seams.



Dolerite outcrops at surface consist almost entirely of dykes. At the scale of information supplied (1:250 000) it is not possible to assess thicknesses of specific dykes. However, the fact that they are mapped at this scale indicates that they are the most prominent in the area and can reasonably be presumed to be ≥3 m thick.

The target shale gas horizons are located between c. 3 300 to 3 600 m depth.


The average thickness of the upper weathered zone is c.35 m and the underlying fractured zone, c.130 m, giving a total Shallow Aquifer thickness of c.165 m

The groundwater attributes rating is mostly Medium (74 per cent of the area) with areas of High in the north-east.

Groundwater vulnerability is mostly Medium to High (46 per cent of the area), and Very High in the north-east.

Groundwater levels are shallow at 5 – 10 mbgl in the central area and quite a bit deeper at >30 mbgl in the south and north.

The regional groundwater flow direction in the Shallow Aquifer is variable, being northeast in the northwest areas and easterly in the eastern areas.

Data on groundwater EC is sparse, however available data indicate ECs of <150 mS/m.

There are 38 boreholes and 200 wind pumps identified.

There are no large-scale groundwater abstraction centres, i.e. municipal wellfields.

There are no thermal springs.

With the target shale gas horizons being located from about 3 300 to 3 600 m saline groundwater or brine may be encountered during gas well drilling. SOEKOR well KL1/65, located below the GE, produced groundwater with a TDS of 10 010 mg/L from a depth of 3 184 m.

There are no perennial rivers and no significant drainage channels, and therefore there are unlikely to be alluvial aquifers present.

About 78 per cent of the area is covered by Consideration Zones according to the preliminary assessment of such zones, mainly relating to dolerite sheets, sills and dykes, as well as boreholes and wind pumps.

4.5. Shallow Aquifer

Some generalisations on the Shallow Aquifer characteristics are:

The main aquifer zone is <c.300 m in depth and is relatively well researched;

The thickness of the weathered aquifer zone varies from c.10 to 50 m. The groundwater level lies within this zone;

The thickness of the fractured aquifer zone varies from c.100 to 160 m;

Attributes rankings vary from Low (39 per cent of the area) to High (54 per cent of the area of the area);

Vulnerability rankings vary from Very Low/Low (55 per cent of the area) to High/Very High (24 per cent of the area);

Aquifer yield, recharge and quality improve and water levels get shallower from west to east;

The Shallow Aquifer provides many municipalities and communities with their sole source of water supply.

4.6. Deep Karoo Formations

Some generalisations on the deeper Karoo formations in the study area, based on published geological maps, cross-sections and literature, are as follows:

Karoo sediments thicken from north to south;

Thermal springs, e.g. Aliwal North, indicate possible groundwater circulation to c.1 000 m and possibly deeper as the groundwater is likely to cool somewhat during its upward flow;

Depth to the shale gas horizons varies from c.1 000 (W) to c.3 450m (E);

Groundwater salinity and age increases with depth due to slow movement, longer residence time (which allows for increased dissolution of constituent minerals in the host rocks, stagnation and possible incorporation of connate water);

The sediments are compartmentalised by dolerite intrusions;

There was one main relatively shorty intrusive event at c.183Ma, with the magma source being from the east (Woodford and Chevallier, 2002).

Some ‘new’ information on deep groundwater occurrence has come to light from a detailed review of the original geological logs and field notes for some of the SOEKOR wells. Direct information on groundwater occurrence, i.e. water strikes, artesian flows and quality was only recorded in wells located below the GE. This is attributed to the fact that only fracture zones that produced free-flowing water at surface were recorded because of the core drilling method employed, where the only indication of possible sub-artesian groundwater strikes would be the presence of ‘open’ fractures and/or mud losses. Regional artesian conditions in the parts of the Karoo Basin under consideration are postulated to only occur between the GE and the Cape Fold Belt due to local topographic and stratigraphic/structural characteristics. The main groundwater-related information (apart from the first bullet) is as follows, and applies only to the area below the GE:

The SOEKOR hydrocarbon exploration wells were sited on, or to intersect at depth, fold axes and ‘dome’ structures, presumably as these structures were seen as being favourable for hydrocarbon accumulation;

Water strikes were encountered, mainly in the Dwyka rocks; any shallower strikes were presumably sub-artesian and not readily identifiable. Fracture zones, faults and drilling mud losses can be taken as possible indicators of water-bearing zones;

Evidence of fractures and faults occur to c.3 500 m depth, mainly infilled with quartz and calcite;

Flows of 1 to 4 L/s were recorded at surface;

Pressure heads of 700 m and 3 307 m were measured at 674 m and 3 215 m depth, respectively;

Water temperatures ranged from 46 to 77oC;

Porosity of the sandstones varies from c.0.5 to >20 per cent;

TDS of 1 390 mg/L and 10 010 mg/L were recorded from strikes at depths of 1 016 m and 3 184 m, respectively. Groundwater at depth may be more saline to the north of the GE because of more stagnant conditions

Summary logs from SOEKOR wells SA1/66, VR1/66 and KL1/65 are shown in Figure 4—1, Figure 4—2 and Figure 4—3, respectively, which illustrates some of the features listed above. Figure 4-4 is a conceptual block model of the general study area showing very preliminary representations of possible configurations



of the main geological and hydrogeological features and types of intrusions. All boundaries are approximate and very schematic. The relative thickness and density of dolerite is only broadly shown on this scale of model but it does show where the main intrusions are likely, i.e. thick sill along the Ecca/Dwyka contact resulting in widespread hydrothermal activity, e.g. breccia plugs, predominance of laterally persistent, closely spaced, relatively thin undulating sheets or flat sills in the Ecca and discrete, thick, laterally extensive sills on the Beaufort, with ring structures in the middle Beaufort. The reader is referred to the provisional hypotheses regarding groundwater that are shown in the annotations on either side of the ‘model’. Figure 4-8 is a schematic north-south cross-section from north of Fraserburg to George, which is not to scale. It basically puts forward the hypothesis of artesian conditions below the GE and sub-artesian conditions above the GE, and the possible linkage with the Cape Supergroup to the south and possible groundwater flow paths. Annotations are provided on the schematic.

Figure 4—1: Geological Log for SOEKOR Well SA1/66



Figure 4—2: Geological Log for SOEKOR Well VR1/66

Figure 4—3: Geological Log for SOEKOR Well KL1/65



Figure 4—4: Schematic Conceptual Hydrogeological Model for the General Study Area



Figure 4—5: Conceptual Hydrogeological Model: Western Karoo



Figure 4—6: Conceptual Hydrogeological Model: Central Karoo



Figure 4—7: Conceptual Hydrogeological Model: Eastern Karoo



Figure 4—8: Schematic N-S Hydrogeological Cross Section



5. CHART BOREHOLE DATA • Assessment of historical monitoring data • Groundwater levels and chemistry from c. 20 year record • Provisional grouping of chemical types • Possible deep end-member groundwater type

5.1. Background

The Department of Water Affairs (DWA) manages a National Groundwater Information System (NGIS) that contains monitoring data from boreholes throughout South Africa, known as CHART boreholes. The water level and chemistry data for boreholes in the Shell Precincts was downloaded using the DWA CHART website tool. It subsequently underwent quality checking and review of statistical and chemical analysis. The objectives of completing this review were:

To assess historical data that extends for nearly 20 years and improve the understanding of long-term trends in Karoo groundwater;

To gain additional knowledge for the preliminary conceptual model of the region (water levels and hydrogeochemistry);

To extend the data set used for future groundwater risk assessment and management.

There are 52 field monitoring points i.e. 45 boreholes and 7 springs, which fall within or in close proximity to the Shell Precincts. Spreadsheets showing the recorded monitoring data were downloaded per annum for each of the monitoring stations. Data spans a period of approximately 20 years between 1994 and 2012. However, it is important to note that not all of the monitoring stations span the same period. Current sites are monitored bi-annually where:

1. Field measurements are undertaken of EC, pH, temperature and groundwater levels

2. Samples are collected for groundwater quality analysis

In addition, CHART groundwater level data collated from the NGA, WARMS and HYDSTRA (time series data management system) databases were downloaded in the region of the Shell Precincts at 7 422 locations, of which 220 boreholes had more than five groundwater level readings (the minimum required for time series statistical analysis).

5.2. Methodology

The main steps completed were as follows:

1. Download Data. The individual spreadsheets were downloaded from the DWA CHART website, with each spreadsheet containing a single sample, single date, analysis.

2. Gathering of background information. Background information was sought from the originator of the data to establish, where possible, information such as selection of monitoring stations, boreholes logs, borehole usage and equipment, sampling techniques.

3. Import data to database and format. Scripts were then written to collate all the data into an Access database, where the data can be stored and manipulated all at once.

4. Quality Checking. Scripts were programmed to automatically quality check the data using specific checks for, inter alia, bad data, inconsistencies, outliers, cation/anion balance calculations. This was followed up by checking of data inconsistencies by eye using time series and other graphs.

5. Water Level Frequency and Regression Analysis. Frequency analysis can be used to predict how often certain values of a variable phenomenon may occur and to assess the reliability of the prediction. It was used to give an idea of seasonal variations, cycles of periods of a number of years, etc. Regression analysis is used to detect the relation between the values of two or more variables, and to test whether the relation is statistically significant. It helped to establish links between spatial locations, as well as comparisons such as water levels to rainfall.

6. Data plots. There are a number of techniques and presentation options for analysing chemical data in order to improve comparison between samples, implement classification according to water types, assist in establishing sources of water, etc. A Piper diagram has been used to give an indication of broad water types in this atlas.

5.3. Data Processing and Quality Checking

Data were collated into appropriate tables in the database. Automated quality checks were applied to all the data as follows:

Removal of duplicate entries (based on identifier and data/time fields);

Removal of rows containing null values;

Conversion of all date/time fields to general data format, and data fields (e.g. water level) to number (double) format;

Removal of outliers (details not included herein);

Additional chemistry quality checking included calculation of the cation/anion balance.

A final quality scoring system was applied to the water level data as shown in Table 5-1.

Table 5-1: Water Level Quality Scoring

ID Quality Criteria Comments

1 Insufficient Data

<5 data entries

<1 year monitoring period

Manually observed anomalous data

Only long term average water levels shown on spatial plots, but marked in a different colour to other long term averages

Water level trends and fluctuations not calculated

2 Skewed By Pumping

Linear water level trend line showing > 1 m/yr change in water level (this corresponded to manual checks of the data in example cases, which showed a strong link between >1 m/yr change in water level trend and pumping characteristics on the data)

>5 m fluctuations in water levels between long term average monthly data

Manually observed pumping characteristics

Long term linear water level trend gradients removed from output

3 Incomplete Data not available for all months Average water level fluctuations(between

months) removed from output

4 Good All boreholes meeting exceeding criteria listed above All data fields exported for plotting

5.4. Water Level Analysis Results

The available water level data underwent statistical analysis within defined areas, whereby the Shell Precincts (Western, Central and Eastern) were further divided into sub-precincts, essentially dividing current precincts into quarters, but linked to the location of clustered boreholes data.

The main output fields are as follows:



Avg WL in metres above mean sea level (mamsl). Average water level from all water level data locations (even if only one data point available for a borehole). The CHART water level data, specified in metres below ground level (mbgl), were converted to mamsl using the 1:20 DEM topographical map of the area.

Avg Summer WL (mamsl). Average water level from all data collected between October and March. Only calculated if there is at least one data entry per month.

Avg Winter WL (mamsl). Average water level from all data collected between April and September. Only calculated if there is at least one data entry per month.

Avg Fluctuation (m). Long term monthly data was calculated. Fluctuations were then calculated as the difference in the water levels between the month with maximum water level and the month with minimum water level.

Avg WL Trend (mm/yr). Regression analysis techniques were applied to plot a linear trend line through the water level time series data, from which the trend line gradient was calculated. This gradient was then converted into a value representing mm/year movements in water level.

The results of the analysis per sub-precinct are shown in Table 5-2. The actual values of the output fields are given, along with the number of points used (count) and the statistical standard deviation (STDEV).

Table 5-2: Sub-Precinct Summary of Water Level Analysis Results

AllBHs Avg WL (mamsl)

Avg Summer WL (mamsl)

Avg Winter WL (mamsl)

Avg WL Fluctuation (m)

Avg WL Trend (mmyr)

Count Count Avg ST

DEV Count Avg

ST DEV

Count Avg ST

DEV Count Avg

ST DEV

Count Avg ST

DEV

W1 823 823 1 063 54 30 1 144 50 30 1 144 50 26 2 1 27 -197 428

W2 219 219 1 287 134 0 0 0 0

W3 132 132 1 189 67 0 0 0 0

W4 281 281 1 355 119 0 0 0 0

W5 302 302 1 367 63 0 0 0 0

W6 219 219 1 431 76 0 0 0 0

C1 550 550 1 328 62 2 1 270 10 2 1 270 10 2 1 0 5 118 716

C2 865 865 1 097 195 95 953 53 95 953 53 81 1 1 84 -208 264

C3 107 107 1 323 87 0 0 0 0

C4 109 109 1 104 232 0 0 0 0

C5 187 187 1 428 127 7 1 398 104 7 1 398 104 7 1 0 7 131 438

C6 109 109 1 385 127 0 0 0 0

E1 1194 1194 1 296 117 39 1 384 138 39 1 385 138 38 2 1 41 58 307

E2 392 392 1 430 159 41 1 491 110 41 1 492 110 28 3 1 31 88 306

E3 995 995 1 164 205 3 1 329 43 3 1 330 44 3 3 1 5 -378 394

E4 938 938 705 177 3 500 20 3 499 20 3 3 2 5 72 282

The main points to note from this table are:

The data are not evenly distributed spatially. After filtering out the single data boreholes, dubious data, and strong pumping data, only a handful of borehole clusters remain, and sub-precincts W2 to W6, C3, C4 and C6 don’t have enough data for analysis beyond average water levels

From the high numbers shown for the standard deviations, and in-depth interrogation of the data, it was found that statistical trends seem to be more locally specific and it is difficult to find generalisations that are applicable on a regional scale

The water level averages given in the ‘Avg WL (mamsl)’ column can show quite large differences to those shown in the summer and winter averages columns because only boreholes with time series data for all months in a season are used for the seasonal averages, whereas a large number of additional boreholes with very few monitoring points are included in the ‘Avg WL (mamsl)’ column

There tends to be greater water level fluctuations in the eastern precinct, compared to the central and western precincts, probably linked to a quicker response to recharge (from rainfall) events

There is a relatively strong decreasing trend in water levels in sub-precincts C3 and E3, both located close to the GE, whereas most of the other precincts indicate a fairly stable water level trend

Average water level elevations are higher in the northern precincts (W1, C5, E1 and E2) and decrease towards the coast, representing a regional flow of groundwater to the south

Some boreholes were then selected for individual water level time series analysis, based on the following criteria:

Good quality data sets;

Representative of typical trends in the region;

Located near points of interest highlighted during spatial analysis;

Proximity to features of interest;

Proximity to chemistry results of interest.

Summary notes on the time series graphs are shown in Table 5-3, followed by sample time series graphs in figures, as listed in column 2 of the table. The locations of the selected boreholes are shown on Figure 5—1. Please note that no long term time series data was available for precincts W2 to W6, C3, C4 and C6.



Table 5-3: Notes on Sample Water Level Time Series Graphs by Sub-Precinct

Sub-Precinct Graph Figure Summary Notes

W1 Figure 5—2

Figure 5—3

• Western precinct, above the GE • Decreasing trend as shown by a few boreholes in near vicinity, and possibly due to over-

abstraction in the local area • Small responses to high rainfall months are visible (approx. 0.3 m) • Some fluctuations probably linked to local pumping

C1 Figure 5—4

• Central precinct, above the GE • Long term trend in the region is fairly static • Shallow groundwater levels (within 4 m of the surface) • Small fluctuations of generally less than 0.5 m • Drawdown of just over 1 m in the second half of 1997 is probably linked to low rainfall or

some local pumping (following the dry season)

C2 Figure 5—5

Figure 5—6

• Central precinct, below the GE • Long term decreasing water level trend in the region • Some response to rainfall events is evident • Pumping characteristics are clearly visible in the water levels of borehole 029856A • Water level is generally below 10 mbgl

C5 Figure 5—7

• Central precinct, above the GE • Long term trend in the region is fairly static • Shallow groundwater levels (within 8 m of the surface) • Small fluctuations of generally less than 1 m • Small responses to rainfall events are visible • Some drawdown may be linked to local pumping

E1 Figure 5—8

Figure 5—9

• Eastern precinct, above the GE • Difficult to find data for non-pumping observation boreholes, so long term trends and

fluctuations difficult to assess • Long term trend in the region appears fairly static • Large fluctuations are linked to pumping

E2 Figure 5—10

Figure 5—11

• Eastern precinct, above the GE • Long term trend in the region is fairly static, although there is some evidence of local long

term decreases in water level • Responses to rainfall events and pumping is evident

E3 Figure 5—12

• Eastern precinct, on the GE • Long term static water levels • Fluctuations in response to rainfall events and pumping are evident

E4 Figure 5—13

• Eastern precinct, below the GE • Long term static water levels • Fluctuations in response to rainfall events and pumping are evident



Figure 5—1: CHART Groundwater Level Analysis: Borehole Positions



Figure 5—2: Water Level Time Series Graph for Borehole 033062, Sub-Precinct W1

Figure 5—3: Water Level Time Series Graph for Borehole 033085, Sub-Precinct W1

Figure 5—4: Water Level Time Series Graph for Borehole 3123AC000022, Sub-Precinct C1

Figure 5—5: Water Level Time Series Graph for Borehole 3222BD00075, Sub-Precinct C2



Figure 5—6: Water Level Time Series Graph for Borehole 029856A, Sub-Precinct C2

Figure 5—7: Water Level Time Series Graph for Borehole 3124DA00001, Sub-Precinct C5

Figure 5—8: Water Level Time Series Graph for Borehole 3124DB00044, Sub-Precinct E1

Figure 5—9: Water Level Time Series Graph for Borehole 3124BB0055, Sub-Precinct E1



Figure 5—10: Water Level Time Series Graph for Borehole 3125DB00002, Sub-Precinct E2

Figure 5—11: Water Level Time Series Graph for Borehole 3125BA00026, Sub-Precinct E2

Figure 5—12: Water Level Time Series Graph for Borehole 3226AB00001, Sub-Precinct E3

Figure 5—13: Water Level Time Series Graph for Borehole 3225DD00004, Sub-Precinct E4



5.5. Chemistry Analysis Results

In this subsection some preliminary observations are made about 527 chemical analyses from 26 boreholes in or close by the Shell precincts and from one old SOEKOR well. Figure 5—14 is a Piper plot of average chemical analyses of these boreholes. The main features of the spread of data points are:

The western area boreholes plot in two distinct groupings;

o Cl dominant, no dominant cation with TDS values >1 000 mg/L;

o HCO3 dominant, no dominant cation with TDS values <1 000 mg/L.

The central area boreholes mainly plot in the Ca/Mg Cl/SO4 and Ca/Mg(HCO3)2 fields;

The eastern area boreholes show a greater variation in composition than those in the western and central areas (possibly due in part to the larger number of boreholes in this area). The water types are generally Ca/Mg(HCO3)2, indicating recent recharge, plus some in the NaCl and NaHCO3 fields, the former possibly being influenced by some boreholes situated in the coastal zone.

A water sample was taken from SOEKOR well SA1/66, which is located below the GE. The well log is shown in Figure 4—1 and water strikes are shown in the Dwyka Group from c.2 900 to c.3 200 m and fracture zones to c.3 670 m. The TDS of the two water strikes recorded in the Dwyka Group was 6 460 mg/L and 8 745 mg/L. The water sample was analysed for macro and trace elements chemistry with selected results shown in Table 5-4 (analysis supplied by van Tonder, 2012). It must be emphasized that there is no information on the original construction, e.g. casing depth, any plugs inserted or their current physical state. The analytical results are therefore merely an indication of possible deep groundwater quality, possibly influenced by shallower groundwater and the effects of stagnation after the well had been sealed for c.40 years. However, the laboratory calculated TDS is consistent with the two readings listed above. The sample was taken from a free-flowing stream of water emanating from the piping attached to the well. Chemical analyses for water samples from two boreholes in Dwyka and Beaufort group rocks from the CHART database are included for comparison.

The water from well SA1/66 plots in a unique position as an ‘extreme’ NaCl end-member type on the Piper diagram. Notwithstanding the uncertainties about the provenance of the water sampled, its position on the Piper plot, plus the high concentrations of Br, F, B and Li, suggests (with many caveats due to the unknowns described above) some chemical characteristics that could typify deep groundwater, at least in this part of the Karoo. Further work is required on this aspect and the DWA and WRC are currently investigating the locations and accessibility of SOEKOR wells with a view to obtaining further water samples for chemical analysis. Such samples may provide further insights into deep groundwater chemical characteristics and some down-well logging probes, such as caliper, EC/temperature and camera logging (to identify fracture/inflow zones), will be required as a minimum in order to assess the likely origin of the water being sampled.

Table 5-4: Chemical Analysis Results for a Water Sample from SOEKOR Well SA1/66 and Comparison with Dwyka and Beaufort Group Samples

Determinand (concentrations in mg/L unless otherwise stated)

SA1/66

ZQMFRR1 (probably

Dwyka Group)

ZQMDPS1 (Beaufort

Group)

pH 7.83 7.79 7.85

Electrical conductivity (mS/m) 1 182 258 287

TDS 7 181 1 481 1 859

Na 2 612.5 315.0 262.0

K 1.9 12.5 4.8

Ca 150.0 91.7 211.0

Mg 51.3 65.0 91.0

Cl 3 897.1 465.4 595.0

SO4 228.1 102.4 295.0

Total Alkalinity (as CaCO3) 229 347.4 309.0

NO3 (as N) 0.54 0.84 5.1

Si 24.8 11.4 10.0

F 4.74 1.62 0.76

Fe 0.056 - -

Mn 0.3 - -

Ba 0.19 - -

B 18.55 - -

Br 3.76 - -

Zn 0.024 - -

Li 4.1 - -



Figure 5—14: Composite Piper Diagram for the Three Precincts



6. CONCLUDING REMARKS The Karoo Groundwater Atlas Volume 2 provides an update on progress made in assessing the shallow aquifers and the underlying deep formations in the southern Karoo Basin, as of August 2013. The results presented are based on a desk study only and interpretation of existing information using some GIS, 3D and statistical methodologies. Further interpretation of these data is ongoing and the hypotheses presented herein are likely to be modified as this work and the gathering of new data progresses. However, the interpretations included provide a fresh perspective and cover some aspects not previously documented in the literature and builds on the progress made in the first Karoo Groundwater Atlas publication of February 2012. The next step will be to augment this work with site-specific data from ground-truthing sources such as geophysics, borehole surveys and exploratory drilling.

It is hoped that these desk study assessments will be expanded and confidence levels improved considerably by fieldwork and collaboration with other researchers, particularly the WRC and university research projects, to take the knowledge of Karoo aquifers and the deeper underlying formations to new levels. The intention is also to share the findings widely and inspire and help train and nurture a new generation of South African water scientists.



7. REFERENCES These are not all cited in the text but some have been used in the formulation of hypotheses on which Vol. 2 is based.

Aller, L. Bennet, T. Lehr, J.H., Petty, R.J. and Hacket, G (1987), DRASTIC: A Standardized System for Evaluating Ground Water Pollution Potential Using Hydrogeologic Settings. US Env. Protection Agency, Ada, OK, EPA/600/2-87-036, 455 p.

Chevallier, L., Goedhart, M. and Woodford, A.C. (2001), The Influence of Dolerite Sill and Ring Complexes on the Occurrence of Groundwater in Karoo Fractured Aquifers: a Morpho-tectonic Approach. WRC Report No. 937/1/01. Pretoria.

Chevallier, L. and Woodford, A.C. (1999), Morpho-tectonics and Mechanism of Emplacement of the Dolerite Rings and Sills of the Western Karoo, South Africa. South African Journal of Geology. Vol. 102, No.1, p43-54.

Department of Mineral Resources (2012), Report on Investigation of Hydraulic Fracturing in the Karoo Basin of South Africa. Pretoria.

Department of Water Affairs (2011), The Groundwater Dictionary: A Comprehensive Reference of Groundwater Related Terminology.2nd Ed. Pretoria.

Department of Water Affairs and Forestry. (2006), Best Practise Guideline G3, Water Monitoring Systems for Water Resource Protection in the South African Mining Industry. Pretoria.

Department of Water Affairs (2005). National Groundwater Resource Assessment Phase 2 Unpublished Reports (series of 25). Pretoria.

Department of Water Affairs (2001), 1:500,000 Hydrogeological Map Series of South Africa. Sheets 3117, Calvinia, 3122, Beaufort West and 3126, Queenstown. Pretoria.

Department of Water Affairs. National Groundwater Archives (NGA).Pretoria.

Dondo, C., Chevallier, L., Woodford, A.C., Murray, E.C., Nhleko, L.O., Nomnganga, A. and Gqiba, D. (2010), Flow Conceptualisation, Recharge and Storativity Determination in Karoo Aquifers, with Special Emphasis on Mzimvubu – Keiskamma and Mvoti – Umzimkulu Water Management Areas in the Eastern Cape and KwaZulu-Natal Provinces of South Africa. WRC Report No. 1565/1/10. Pretoria.

Enslin, J.F., (1950): Geophysical methods of tracing and determining contacts of dolerite dykes in Karroo

sediments in connection with the siting of boreholes for water, Geol. Soc. South Africa, Trans. and Proc., Vol.

53, pp. 193-204.

Geological Survey of South Africa (1991), 1:250 000 Geological Map Series Sheets 3120 Williston, 3122 Victoria West, 3124 Middelburg, 3126 Queenstown, 3220 Sutherland, 3222 Beaufort West, 3224 Graaff Reinet and 3226 King William’s Town . Pretoria.

Golder Associates (2011), Environmental Management Plan: South Western Karoo Basin Gas Exploration Application. For submission to the Petroleum Agency of South Africa. PASA Reference No. 12/3/219. Golder Report No. 12800-10484-27. Johannesburg.

Life, D.R. (1991), Handbook of Chemistry and Physics. 72nd edn, CRC Press, Boca Baton.

Murray, R, Baker, K, Ravenscroft, P, Musekiwa, C and Dennis,R. (2011) A Groundwater Planning Toolkit for the Main Karoo Basin: Identifying and Quantifying Groundwater Development Options Incorporating the Concept of Wellfield Yields and Aquifer Firm Yields. WRC Project No. K5/1763. Pretoria.

Republic of South Africa (1998), National Water Act. Act No. 36 of 1998. Pretoria.

Steyl, G. Van Tonder, GJ, and Chevalier, L. (2012), State of the Art: Fracking for Shale Gas Exploration in South-Africa and the Impact on Water Resources. Water Research Commission report KV294/11. Pretoria.

Vandoolaeghe, M.A.C., (1980): Queenstown geohydrological investigation, Unpublished Technical Report

GH3135, Directorate : Geohydrology, Department of Water Affairs, Cape Town.

Vegter J.R. (2001), Groundwater Development in South Africa and an Introduction to the Hydrogeology of Groundwater Regions. WRC Report No. TT 134/00. Pretoria.

Water Expert Group (2012), Karoo Aquifers Atlas. Published report for Shell. Cape Town.

Woodford, A.C. and Chevallier, L. (2002) Regional characterization and mapping of Karoo Fractured Aquifer Systems – an integrated approach using a Geographical Information System and Digital Image Processing. WRC Report No. 653/1/02. Pretoria.

Woodford, A.C. and Chevallier, L. (Editors) (2002) Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs. WRC Report No. TT 179/02. Pretoria

Xu, Y. & van Tonder, G.J., (2002): Capture Zone simulation for boreholes located in Fractured Dykes using

the Linesink Concept, Water SA, Vol. 28, No.2, 5p.

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