phosphorous retention by lateritesthere is currently interest in the use of local laterite material...

Phosphorous Retention by Laterites

Laura Clayson Final year project, November 2007 Supervised by Associate Professor Carolyn Oldham (School of Environmental Systems

Engineering, University of Western Australia)

Jose Romero (GHD)

School of Environmental Systems Engineering

School of Environmental Systems Engineering Final Year Project

Phosphorous Retention by Laterites i

Abstract High nutrient loads can be detrimental to aquatic ecosystems, causing algal blooms and

associated problems. Such problems have been observed in the Swan-Canning Estuarine

System. One method of controlling nutrient concentrations is through use of permeable

reactive barriers. There is currently interest in the use of local laterite material (cracked pea

gravel) in these barriers to encourage phosphorous removal in the Swan-Canning Estuarine

System.

A combination of laboratory experiments and field data analysis were utilised to characterise

the adsorption properties of cracked pea gravel under various conditions. Investigations

examined performance under different initial phosphorous concentrations, pHs, salinities and

redox conditions. The effect of grain size was also examined. These investigations provided a

list of recommendations for use.

Laboratory investigations showed that initial phosphorous concentration, pH and salinity have

an effect upon phosphorous adsorption by laterites. In each case, subjecting laterite materials

to a broad range of conditions resulted in a maximum of 20 % difference in adsorption. In

contrast, grain size was not found to affect adsorption. Importantly, all experiments and

treatments provided a minimum of 50 % adsorption of phosphorous from the water column.

Field trials conducted by GHD on behalf of the Water Corporation of Western Australia

investigated a range of materials for both phosphorous and nitrogen reduction. Results did

show some effect upon both Filterable Reactive Phosphorous and Total Phosphorous

concentrations; however they were inconclusive in determining the relative contribution of

laterite material in causing this.

A summary is given below of the recommendations for use of cracked pea gravel in the field.

Conditions with adequate phosphorous removal were given a tick, where the greater the

number of ticks, the more appropriate the cracked pea gravel is as an adsorption agent.


Phosphorous Retention by Laterites ii

Condition Variable Low Moderate High Initial orthophosphate

concentration 0.04 mgP/L

0.40 mgP/L

4.00 mgP/L

Grain size 6-8 mm -- 10-12 mm

pH ~2

~5

~10

Salinity ~1ppt

~15 ppt

~40 ppt

Redox conditions Anaerobic -- Aerobic


Phosphorous Retention by Laterites iii

Acknowledgments I would like to acknowledge the assistance and support provided by various parties on a

professional and/or personal basis throughout the year.

Carolyn Oldham

and Jose Romero

First and foremost I would like to thank my primary supervisor,

Associate Professor Carolyn Oldham, for her guidance and

encouragement over the year. I would also like to thank my secondary

supervisor, Jose Romero from GHD, for his time and assistance.

SESE

Thank you to the staff at the School of Environmental Systems

Engineering for all of your help throughout the past year. Special

thanks to Diane Krikke for her assistance in the lab.

GHD I would like to thank Halinka Lamparski and Phoebe Mack for their

time spent answering my questions and for providing the field data.

Water Corporation Thank you to the Water Corporation of Western Australia for kindly

allowing the provision of the field data used in this dissertation.

Lifesavers

To Jakub Kielbasa, Helen Bailey, John Marion, Alycea Foo, Alison

Stubbs, Jayne Walton. Words cannot express my deepest gratitude for

the time spent by all keeping me motivated… and for occasionally

providing a (well earned???) distraction. Thank you for all the

conversations and support you provided throughout the year. I can

honestly say that I wouldn’t have gotten through the year without you!!!

Friends and Family

To my fellow SESE students and to my Floreat and DHQ friends, thank

you for your friendship and support throughout the year. Special thanks

to Dani Black and Aisha Chalmers for your support. Thanks also

Jacinta Hewett for her assistance with editing in the final stages. To my

family, thank you for the care packages and the support you have

provided over the past six years.

Miscellaneous

Thank you to those responsible for the production of the following

items: Missy Higgins, V, Red Bull, Coke, Gummi Bears. I relied on

these products for much needed energy and motivation.


Phosphorous Retention by Laterites iv

Table of contents

Abstract ...................................................................................................................................... i

Acknowledgments....................................................................................................................iii

Table of contents...................................................................................................................... iv

List of tables............................................................................................................................. vi

List of figures ..........................................................................................................................vii

Glossary.................................................................................................................................... ix

Acronyms .................................................................................................................................. x

1.0 Introduction .................................................................................................................. 1

2.0 Literature Review......................................................................................................... 2 2.1 The Swan-Canning Estuarine System........................................................................ 2 2.2 Nutrients in the Swan-Canning Estuarine System ..................................................... 6

2.2.1 Types of nutrients ............................................................................................... 6 2.2.2 Sources and pathways of phosphorous in the estuary........................................ 7 2.2.3 Phosphorous control strategies........................................................................ 10

2.3 Phosphorous retention by laterites ........................................................................... 13 2.3.1 Local studies, mechanism and capacity ........................................................... 13 2.3.2 International studies......................................................................................... 14 2.3.3 Current investigations into phosphorous retention by laterites....................... 15 2.3.4 Effect of variables on phosphorous adsorption................................................ 17

2.4 Outcomes of this project .......................................................................................... 18

3.0 Methods ....................................................................................................................... 19 3.1 Laboratory experiments............................................................................................ 19

3.1.1 Preliminary measurements and pre-treatment................................................. 19 3.1.2 General methodology for phosphorous adsorption experiments ..................... 20 3.1.3 Experiment 1 – variations in initial phosphorous concentrations ................... 23 3.1.4 Experiment 2 – variations in grain sizes.......................................................... 24 3.1.5 Experiment 3 – variations in pH ...................................................................... 24 3.1.6 Experiment 4 – variations in salinity ............................................................... 24 3.1.7 Experiment 5 – variations in redox conditions ................................................ 24

3.2 Field trials................................................................................................................. 26 3.2.1 Details of trials................................................................................................. 26 3.2.2 Raw data........................................................................................................... 27 3.2.3 Analysis of raw data......................................................................................... 28

4.0 Results ......................................................................................................................... 29

4.1 Laboratory experiments............................................................................................ 29 4.1.1 Preliminary investigations ............................................................................... 29 4.1.2 Controls............................................................................................................ 29 4.1.3 Experiment 1 – variations in initial phosphorous concentrations ................... 29 4.1.4 Experiment 2 – variations in grain sizes.......................................................... 31 4.1.5 Experiment 3 – variations in pH ...................................................................... 32 4.1.6 Experiment 4 – variations in salinity ............................................................... 33 4.1.7 Experiment 5 – variations in redox conditions ................................................ 34 4.1.8 Laboratory results in combination................................................................... 37

4.2 Field trials................................................................................................................. 38


Phosphorous Retention by Laterites v

4.2.1 Blanket trial...................................................................................................... 38 4.2.2 Curtain trial...................................................................................................... 40

5.0 Discussion of results ................................................................................................... 51 5.1 Laboratory experiments............................................................................................ 51

5.1.1 Preliminary investigations ............................................................................... 51 5.1.2 Controls............................................................................................................ 51 5.1.3 General observations for Experiments 1-5 ...................................................... 52 5.1.4 Experiment 1 – variations in initial phosphorous concentrations ................... 53 5.1.5 Experiment 2 – variations in grain size ........................................................... 54 5.1.6 Experiment 3 – variations in pH ...................................................................... 55 5.1.7 Experiment 4 – variations in salinity ............................................................... 56 5.1.8 Experiment 5 – variations in redox conditions ................................................ 57 5.1.9 Laboratory results in combination................................................................... 57

5.2 Field trials................................................................................................................. 58 5.2.1 Blanket trial...................................................................................................... 58 5.2.2 Curtain trial...................................................................................................... 59

5.3 Laboratory and field results in combination ............................................................ 64 5.4 Recommendations for use in the field...................................................................... 65

6.0 Conclusions ................................................................................................................. 67 6.1 Laboratory and field results...................................................................................... 67 6.2 Recommendations for use ........................................................................................ 67

7.0 Limitations and recommendations of project.......................................................... 68 7.1 Limitations ............................................................................................................... 68

7.1.1 Limitations of laboratory experiments ............................................................. 68 7.1.2 Limitations of field trials .................................................................................. 69

7.2 Future recommendations .......................................................................................... 69 7.2.1 Future investigations for phosphorous retention by laterites .......................... 69

8.0 References ................................................................................................................... 71

Appendices .............................................................................................................................. 77


Phosphorous Retention by Laterites vi

List of tables

Table 1. Tributaries for the Swan-Canning Estuarine System with a summary of land uses for each tributary (Adapted from Peters & Donohue 2001) ............................................................ 4

Table 2. Materials and examples of studies for phosphorous removal in reactive barriers .... 12

Table 3. Expected outcomes of the project .............................................................................. 18

Table 4. Suggested standardised procedure for phosphorous adsorption experiments............ 21

Table 5. General methodology of experiments ........................................................................ 22

Table 6. Experiments completed.............................................................................................. 23

Table 7. Dates of installation and dates for commencement of monitoring for field trials ..... 26

Table 8. Combinations of materials within groundwater curtain for each section .................. 27

Table 9. Monitored parameters in field trials........................................................................... 28

Table 10. Results of preliminary investigations....................................................................... 29

Table 11. Results for Controls 1 and 2..................................................................................... 29

Table 12. Results for Experiment 1 – variations in initial phosphorous concentrations.......... 30

Table 13. Results for Experiment 2 – variations in grain sizes................................................ 31

Table 14. Results for Experiment 3 – variations in pH............................................................ 32

Table 15. Results for Experiment 4 – variations in salinity ..................................................... 33

Table 16. Results for Experiment 5 – redox conditions........................................................... 35

Table 17. Ranges of measurements for temperature, salinity and pH for blanket trial............ 39

Table 18. Ranges of measurements for temperature, salinity and pH for curtain trial ............ 50

Table 19. Recommendations for use of cracked pea gravel in the field .................................. 65

Table 20. Summary of recommendations for use of cracked pea gravel in the field............... 67

Table 21. Limitations of laboratory experiments ..................................................................... 68

Table 22. Limitations of field trials.......................................................................................... 69

Table 23. Future recommendations.......................................................................................... 70


Phosphorous Retention by Laterites vii

List of figures

Figure 1. The Swan-Canning Estuarine System (Adapted from Thompson 2001) ................... 2

Figure 2. Tributary locations for Swan-Canning Estuarine System (Peters & Donohue 2001) 3

Figure 3. Forms of phosphorous found within a water body (ANZECC & ARMCANZ2000b; Wetzel 2001) (proportions provided by Wetzel)........................................................................ 7

Figure 4. Phosphorous adsorption index versus iron and aluminium content (Gerritse 2000) 13

Figure 5. Locations of Patterson Road Sub-branch Drain Blanket Trial and Abernathy Road Sub-branch Drain Curtain Trial (Adapted from GHD 2007b) ................................................. 16

Figure 6. Cracked pea gravel (6-12 mm), photograph by L. Clayson 11/11/2007 .................. 17

Figure 7. Vessels used for laboratory experiments .................................................................. 22

Figure 8. Results of Experiment 1 – variations in initial phosphorous concentrations............ 30

Figure 9. Results for Experiment 2 – variations in grain size (with an initial water column phosphorous concentration of 0.40 mgP/L) ............................................................................. 31

Figure 10. Results for experiment 3 - variations in pH (initial water column phosphorous concentration of 0.40 mgP/L)................................................................................................... 33

Figure 11. Results for Experiment 4 - variations in salinity (initial concentration of 0.25 mgP/L)...................................................................................................................................... 34

Figure 12. Results for Experiment 5 – variations in redox conditions..................................... 35

Figure 13. Dissolved oxygen versus phosphorous concentration in water column for aerobic samples and sealed samples opened at 1, 3 5 and 7 days......................................................... 36

Figure 14. Dissolved oxygen versus phosphorous concentration in water column for all measurements ........................................................................................................................... 36

Figure 15. Final percentage adsorption from water column for all experiments ..................... 37

Figure 16. Filterable Reactive Phosphorous concentrations for blanket trial .......................... 38

Figure 17. Total Phosphorous concentrations for blanket trial ................................................ 39

Figure 18. Dissolved Oxygen concentrations for blanket trials ............................................... 40

Figure 19. Locations of bores for Section B of curtain trial (not to scale)............................... 41

Figure 20. Difference in groundwater head between bores for Section B of curtain trial ....... 41

Figure 21. Filterable Reactive Phosphorous concentrations for Section B of curtain trial ...... 42

Figure 22. Total Phosphorous concentrations for Section B of curtain trial............................ 43

Figure 23. Location of bores for Section C of curtain trial (not to scale) ................................ 44

Figure 24. Change in head between bores in Section C of curtain trial ................................... 44

Figure 25. Filterable Reactive Phosphorous concentrations for Section C of curtain trial ...... 45

Figure 26. Total Phosphorous concentrations for Section C of curtain trial............................ 46

Figure 27. Location of bores for Extended Section of curtain trial (not to scale).................... 47

Figure 28. Head differences between bores in Extended Section of curtain trial .................... 47

Figure 29. Filterable Reactive Phosphorous concentrations for Extended Section of curtain trial ........................................................................................................................................... 48


Phosphorous Retention by Laterites viii

Figure 30. Total Phosphorous concentration for Extended Section of curtain trial ................. 49

Figure 31. Dissolved Oxygen for Section B, Section C and Extended Section Bores in curtain trial ........................................................................................................................................... 50


Phosphorous Retention by Laterites ix

Glossary Aerobic In the presence of oxygen (Department of Environment &

Climate Change NSW 2007)

Anaerobic Condition in which there is an absence of oxygen (Hemond &

Fechner-Levy 2000)

Ephemeral As in “ephemeral river” – A water course which does not have

flow occurring throughout the year (Parsons 1999)

Ligand A molecule which is bound to a metal ion to form a complex

ion (Silberberg 2000)

Ligand Exchange A reaction whereby a ligand which is bound to a metal is

replaced by another ligand (Cotton et al. 1999)

Orthophosphate A salt or ester of orthophosphoric acid (Merriam-Webster Inc

2002)

Orthophosphoric acid An acid used in fertilizers and soaps with a molecular structure

of H3PO4 (Miller et al. 2006)

Perennial As in “perennial river” - A water course which flows

throughout the year (USEPA 1993).

Trophic level A stage in the food chain. Levels may contain producers or

primary, secondary or tertiary consumers. (Houghton Mifflin

Company 2002)


Phosphorous Retention by Laterites x

Acronyms

ANZECC Australian and New Zealand Environment and Conservation Council

CPG Cracked Pea Gravel

DO Dissolved Oxygen

DP Darling Plateau

FRP Filterable Reactive Phosphorous

MSMD Mills Street Main Drain

OP Organic Phosphorous

ppm parts per million

ppt parts per thousand

RCP Rural Coastal Plain

SCES Swan Canning Estuarine System

SCP Swan Coastal Plain

SWWA South-West of Western Australia

TP Total Phosphorous

UCP Urban Coastal Plain


Phosphorous Retention by Laterites 1

1.0 Introduction High nutrient loads can be detrimental to aquatic ecosystems, and may cause algal blooms

and other serious problems. The Swan-Canning Estuarine System, located in the South-West

of Western Australia, is a natural system which has been negatively affected by nutrient

loading. One method of controlling nutrient concentrations is thorough use of permeable

reactive barriers. There is currently interest in the use of local laterite material (cracked pea

gravel) in these barriers to encourage phosphorous removal in the Swan-Canning Estuarine

System.

The following dissertation examines the phosphorous adsorption of cracked pea gravel. The

aim of the project was to determine the performance of the cracked pea gravel under a range

of conditions. Initial phosphorous concentration, grain size, pH, salinity, and redox conditions

were varied to identify the conditions most suited to the use of the material to remove

phosphorous from the water column. A combination of laboratory experiments and field data

analysis were used to produce a list of recommendations for the use of cracked pea gravel in

the field.

Chapter Two introduces the SCES and provides a summary of the phosphorous related issues

experienced within the SCES. Possible remediation actions are discussed, with particular

attention given to the use of permeable reactive barriers. A summary of investigations with

regards to phosphorous retention by laterites is then provided.

Chapter Three focuses upon the methods of the project. The rationale and methodology for

each laboratory experiment is provided. A summary of the trials from which the field data

was provided is also presented and methodology for the analysis of the raw field

measurements is discussed.

The results of the laboratory experiments and the analysis of the field data are presented in

Chapter 4 and a discussion of these data is provided in Chapter Five. Chapter Six provides a

summary of the major findings of the project while Chapter Seven summarises limitations

encountered within the project and lists some recommendations for future investigations

arising from this project.



2.0 Literature Review

2.1 The Swan-Canning Estuarine System

The Swan-Canning Estuarine System (SCES) is located in the Perth region of the South-West

of Western Australia (SWWA) extending from Fremantle to Ellen Brook, 60 km inland (see

Figure 1 below). The system has a surface area of approximately 53 km2 (Thompson 2001)

with a drainage area of approximately 121 000 km2 (Peters & Donohue 2001; Donohue et al.

2001; Smith & Turner 2001). The region is characterised by a Mediterranean climate (Bureau

of Meteorology 2007).

Figure 1. The Swan-Canning Estuarine System (Adapted from Thompson 2001)

The SCES is tidally and seasonally forced and remains in permanent contact with the Indian

Ocean at Fremantle (Linderfelt & Turner 2001; Smith & Turner 2001). Salt water intrusion



reaches as far as Guildford, 45 km upstream (Smith & Turner 2001). The estuary has dynamic

interactions between seawater, freshwater and groundwater (Linderfelt & Turner 2001).

Natural tributaries entering the SCES include the Avon River and ten additional streams

(Peters & Donohue 2001). There are also four urban drains entering the SCES (Peters &

Donohue 2001). Figure 2 details the locations of the fifteen natural and constructed

tributaries.

Figure 2. Tributary locations for Swan-Canning Estuarine System (Peters & Donohue 2001)

The drainage catchment areas of the 15 tributaries make up 99 % of the total drainage

catchment area for the SCES (Peters & Donohue 2001; Donohue et al. 2001). There are three

catchment types: the Darling Plateau, rural to semi-rural agricultural areas on the Swan



Coastal Plain (SCP) and highly urbanized areas on the SCP (Donohue et al. 2001). Land use,

catchment type and drainage areas are provided in Table 1. As a result of the Mediterranean

climate many of the streams are ephemeral, though channel areas may vary due to

groundwater interactions (Peters & Donohue 2001; Donohue et al. 2001).

Table 1. Tributaries for the Swan-Canning Estuarine System with a summary of land uses for each tributary (Adapted from Peters & Donohue 2001)

Tributary Area (km2)

Catchment type* Land Use

Bayswater Main Drain 262 UCP • Urban—high-density residential (sewered and

unsewered), commercial, areas of light industry Claise Brook Main Drain 16 UCP • Urban—medium-density residential mixed light industry,

commercial Mill Street Main Drain 12 UCP • Urban—commercial, high-density residential

South Belmont Main

Drain 10 UCP • Urban—light service industries, high-density residential

Avon River 119 035 DP • Agriculture—broad-acre grazing, animal feedlots, some high-density stocking, e.g. feedlots • Many small urban centres and townships

Bannister Creek 23 UCP • Urban—commercial, light and heavy industry

• Some residual areas

Bennett Brook 99 UCP • Urban/semi-rural—low-density residential, livestock feedlots, viticulture and horticulture

Blackadder Creek 13 DP • Urban—medium-density residential; service industries

and business zones

Canning River 163 DP • Urban—large areas of medium-density residential, heavy industry • Semi-rural—animal feedlots, horticulture, turf farms

Ellen Brook 664 RCP • Rural—agricultural, broad-acre grazing, animal feedlots, horticulture and viticulture • Several small urban townships

Helena River 161 DP • Urban/rural—low-density residential, mixed light industry, service industries

Jane Brook 135 DP

• Rural—large tracts of native forest (water-supply area), some small areas of viticulture and poultry farming • Urban—isolated small pockets of residential developments

Southern River 149 RCP • Rural—broad-acre agriculture, horticulture, poultry

• Urban –low-density residential

Susannah Brook 19 DP

• Susannah Brook 19 Rural—broad-acre agriculture, grazing, isolated forested remnants • Urban—some pockets of low-density residential

Yule Brook 53 UCP • Rural—horticulture, poultry • Urban—extensive areas of light to medium industry, large tracts of parklands

*from Donohue et. al. (2001) DP – Darling Plateau; UCP – Urban Coastal Plain; RCP – Rural Coastal Plain



The SCES is also a point of groundwater discharge from the superficial aquifer systems

located beneath the Perth metropolitan region (Linderfelt & Turner 2001; Smith & Turner

2001). There are three main groundwater systems that discharge into the estuary: the

Gnangara Mound, located to the north of the Swan River; the Cloverdale Groundwater Flow

System, located between Swan and Canning Rivers and extending east towards Darling

Scarp; and the Jandakot Mound, located in the South and discharging into Canning and lower

estuary (Thompson 2001; Donohue et al. 2001). This groundwater may enter directly into the

estuary through onshore discharge, discharge into drains releasing to the estuary, or through

off-shore discharge at the sediment bed of the estuary (Thompson 2001).

Smith and Turner (2001) indicate that on occasion flow reversal will occur; with adjacent

aquifers being recharged by river water. This results in mixing of the surface and groundwater

(Smith & Turner 2001).

Nutrient levels in the estuary and associated problems

The leaching of nutrients into a water system is a significant contributor to its environmental

degradation (Gerritse 2000). European settlement in the catchment of the SCES has resulted

in significantly increased inputs of nutrients in the local environment, in particular

phosphorous (Gerritse 2000).

Although European settlement in the Perth area commenced in the late 1820s (Taylor 2003),

Stephens and Imberger (1996) observed that the SCES had remained relatively healthy prior

to the late 20th century. By the 1990s it was apparent that nutrient loads in the system were

receiving were approaching levels that were degrading the estuary. For example, the first

recorded toxic cyanobacterial bloom in any major Swan River tributary occurred in 1994

(Thompson & Hosja 1996).

Currently, the SCP is undergoing a period of rapid urbanisation; this is particularly seen in

areas adjacent to the estuary (Peters & Donohue 2001). This development results in increased

stress on the SCES catchment through the clearing of natural vegetation and through

increased nutrient loadings (Thompson 2001).

The increase of nutrient concentrations within surface waters may result in increased growth

of aquatic plants and algae (Gerritse 1996; Weaver & Reed 1998; Hart et al. 2003; Chin

2006; ANZECC & ARMCANZ 2000b). Such excessive growth (known as an algal bloom)

may reduce light levels and dissolved oxygen (DO) concentrations, leading to the death of



seagrasses and the onset of anaerobic conditions (Weaver & Reed 1998; Chin 2006). Blooms

may be associated with issues such as: human and animal health, fish kills (Correll 1998; Hart

et al. 2003; Linderfelt & Turner 2001), shifts in the composition of species on all trophic

levels (Correll 1998), or a reduction in the aesthetic quality of river (Linderfelt & Turner

2001; Hart et al. 2003). It is therefore of great importance to lower nutrient inputs into the

SCES.

2.2 Nutrients in the Swan-Canning Estuarine System

To combat the negative effects of high nutrient levels in the estuary, an understanding of

types of nutrients, their sources and pathways into the estuary is required. This knowledge

may then be used to reduce nutrient levels entering the SCES.

2.2.1 Types of nutrients

There are 19 elements required for biological growth, referred to as nutrients (Chin 2006).

Growth rate is dictated by the availability of these nutrients (Gerritse 2000). Five nutrients are

required in large amounts: carbon, hydrogen and oxygen which are readily available and

nitrogen and phosphorous which are less abundant (Chin 2006). Nitrogen and phosphorous

are the most critical in the environment as they are generally the limiting factors for growth

(Gerritse 2000; Chin 2006). There is conflicting information in regards to the limiting nutrient

in the case of the SCES. Weaver and Reed (1998) indicate that phosphorous is considered to

be an important limiting nutrient for algal growth in the SWWA. In contrast, a study

conducted by Thompson and Hosja (1996) suggest that the SCES is nitrogen limited during

the summer.

It is therefore acknowledged that both phosphorous and nitrogen concentrations need to be

addressed within the SCES. However, as this project focuses on phosphorous retention by

laterites, the sources, pathways and remediation methods discussed below are specific to

phosphorous. By no means should nitrogen be ignored when attempting to decrease nutrient

concentrations within the SCES.

Phosphorous concentrations in the Swan-Canning Estuarine System

Phosphorous concentrations within the estuary are two to three times greater than those

measured in the 1940s (Gerritse, Wallbrink & Murray 1998). Concentrations vary seasonally,



reaching a maximum during late summer (January – March) and a minimum in late spring

(October – December) (Thompson 2001).

Concentrations of phosphorous within the SCES sediments are also higher than background

levels (Gerritse, Wallbrink & Murray 1998). This is because a substantial proportion of the

phosphorous entering the SCES is retained within the sediment (Gerritse, Wallbrink &

Murray 1998).

2.2.2 Sources and pathways of phosphorous in the estuary

Sources of phosphorous

Fertilisers and animal waste disposal are the primary sources of phosphorous in the SCES

(Peters & Donohue 2001). Once phosphorous compounds are introduced to the water system

through anthropogenic activity, they accumulate in soils and eventually reach a steady state

by leaching into water systems (Gerritse 2000) in both dissolved and particulate forms

(Correll 1998; ANZECC & ARMCANZ 2000b). Both forms contain organic and inorganic

fractions, as shown in Figure 3. The figure also provides some approximate proportions of

each fraction, provided by Wetzel (2001).

Figure 3. Forms of phosphorous found within a water body (ANZECC & ARMCANZ2000b;

Wetzel 2001) (proportions provided by Wetzel)

Once phosphorous reaches the waterways, equilibrium interactions between the sediment and

phosphorous species allow production of orthophosphate (Correll 1998). Orthophosphate is

Total Phosphorous

Inorganic Phosphorous

10 %

Organic Phosphorous

90 %

Dissolved <5 %

• Ortho-phosphates • Polyphosphates

• Small phosphate esters

Particulate>5 %

• Mineral phase of rock and soil

Dissolved27 %

• Organic colloids

Particulate 63 %

• In organisms • Detritus



the only form of phosphorous that may be taken up by bacteria, algae and plants; and these

equilibrium interactions allow a substantial proportion of the phosphorous within the system

to be taken up in this manner (Correll 1998).

Pathways of phosphorous

Both the quantity and rate of nutrient loss from a catchment depends on: the availability of the

nutrient, chemical speciation, and hydrological flow pathways, which include surface runoff

and groundwater discharge (Peters & Donohue 2001). It is therefore important to investigate

hydrological flow paths in the SCES. Generally, phosphorous may travel in three flow paths:

overland flow, deep through flow, or shallow through flow (Johnes & Hodgkinson 1998).

There are also interactions between these pathways (Johnes & Hodgkinson 1998).

Additionally, soil type determines the quantity of phosphorous that may be retained during

transport. For example, Weaver and Reed (1998) indicate that soils containing low

ammonium oxalate extractable iron are less able to retain phosphorous.

The SCES has two main hydrological flow paths (Peters & Donohue 2001) and a range of

soil types, resulting in a wide variation in phosphorous retention ability (Donohue et al.

2001). As such, the phosphorous pathways of the three catchment types (as shown in Table 1)

are distinct.

The dominant pathway for tributaries from the Darling Plateau is through stormwater flow

(Donohue et al. 2001). The clayey soils of the plateau also retain phosphorous relatively well

(Donohue et al. 2001; Peters & Donohue 2001). In contrast, the dominant flow path on the

SCP is shallow translatory flow, which discharges at the SCES or one of its tributaries

(Donohue et al. 2001). This is attributed to the high permeability and low phosphorous

retention of the sandy soils of the SCP (Donohue et al. 2001).

The SCP is also naturally nutrient deficient, requiring the use of fertilisers (Peters & Donohue

2001). This compounds the phosphorous problem, where changes in phosphorous

concentrations within the shallow aquifer are caused by variations in both the amount and the

solubility of the fertiliser applied (Donohue et al. 2001).

Early studies such as Appleyard (1993) and Gerritse et al (1998) showed low phosphorous

concentrations in the local groundwater. However, it was suggested that phosphorous from

surrounding residential areas had not yet reached the groundwater table, and could be

expected to significantly increase phosphorous concentrations in the groundwater in the future



(Gerritse, Wallbrink & Murray 1998). This theory aligns well with Peters and Donohue

(2001) who estimated that it takes one to five years for phosphorous transport through sandy

soils, though time may increase depending on the distance from source to drainage.

There are also differences between rural and urban tributaries on the SCP. Rural SCP

tributaries include both the Ellen Brook and the Southern River. Both rivers are surrounded

by highly permeable sand, so groundwater is a major contributor to flow and nutrient load

(Donohue et al. 2001). For example, the Ellen Brook consists of 70 % baseflow (Donohue et

al. 2001). Here, the major inorganic phosphorous pathway for Ellen Brook and probably also

the Southern River is saturated overland flow, which is caused by the seasonally high water

table (Donohue et al. 2001). Ellen Brook is also the dominant source of phosphorous for the

SCES (Peters & Donohue 2001) (Gerritse, Wallbrink & Murray 1998), amounting to 42 % of

the total phosphorous added to the SCES (Peters & Donohue 2001).

While phosphorous concentrations in urban drains are lower than rural SCP drainage areas

(Donohue et al. 2001), a study conducted by Peters and Donohue (2001) showed that while

volume weighted Total Phosphorous (TP) ranged from 0.03 to 0.7 mg/L for 14 tributaries

entering the estuary, all urban drains were over 0.06 mg/L (the TP guideline for lowland

rivers (ANZECC & ARMCANZ 2000a)). Banister Creek, an urban tributary, was also over

0.06 mg/L. It is noted that Ellen Brook and Southern River had the highest TP concentrations

while tributaries from the Darling Plateau had generally lower concentrations.

While urban and non-urban drains/tributaries contribute approximately the same flow, non-

urban tributaries are generally ephemeral while the urban system is perennial (Peters &

Donohue 2001). Urban drains therefore have a proportionally greater impact than other

tributaries during the summer (Peters & Donohue 2001). Linderfelt and Turner (2001)

showed that only 10 % of the total inflow into the SCES from May-October is due to

groundwater discharge; while from November to April the total inflow due to groundwater

discharge is as high as 55 %. During these low flow periods, the groundwater nutrients

contribute significantly to the loads the estuary receives and are one of the main contributors

to algal blooms (Linderfelt & Turner 2001).



2.2.3 Phosphorous control strategies

It is a common management action to reduce nutrient (including phosphorous) loads entering

the system (Ryding & Rast 1989; Hart et al. 2003; Thompson & Hosja 1996). If elimination

or sufficient reduction at the source is not possible, the control of nutrients entering the water

body may be accomplished by reducing or preventing effluent discharges or runoff from

agricultural land (Hart et al. 2003).

Specific methods of reducing phosphorous entering through surface waters include: chemical

precipitation during wastewater treatment, restriction of phosphate detergents, land use

controls, pre-reservoirs, physical/chemical treatment of entering tributaries, phosphorous

precipitating chemicals added to influent waters and filtration of water with phosphorous

removal media (Ryding & Rast 1989). This filtration method will occasionally utilise a

structure known as a permeable reactive barrier.

Groundwater phosphorous concentrations may be lowered by increasing the soil adsorption

capacity of the surface soils (Gerritse 2000); this may occur through addition of iron- and

aluminium-oxide rich soils, for example, red mud and clay (Sampson 1994). Other techniques

include: pumping, treating contaminant plumes and isolation of the contaminant source with

low permeability and covers (Blowes et al. 2000; Fetter 1999). An alternate approach is the

use of permeable reactive barriers (Blowes et al. 2000); these are placed within the flow path

of contaminated groundwater and consist of materials that remove the contaminant in

question (Blowes et al. 2000), in this case phosphorous.

Though point sources may be removed, it must be remembered that the resulting change in

concentration within the groundwater entering the water body will be substantially delayed,

even in sandy soils (Gerritse & Schofield 1989; Donohue et al. 2001). It is therefore

important to address existing groundwater contamination, even if reductions are made at the

source. Linderfelt and Turner (2001) suggest that during low flow conditions (November to

April), when groundwater contributions to the system are relatively high, this is particularly

important.

Additionally, once sources or inputs of phosphorous have been managed, recovery of the

water body is sometimes delayed due to internal cycling of phosphorous in sediments

(Gerritse 2000). Hart (2003) explains that anaerobic conditions cause the release of

phosphorous. Two reasons were given: the slow dissolution of iron oxyhydroxide complexes



that trap phosphorous within the sediment, allowing its release, and the mineralisation of

organic phosphorous (OP) in the top layer of the sediments. Addressing phosphorous within

the sediments of the water body is therefore required in conjunction with source control.

Various methods may be employed to remove or reduce the concentrations of contaminated

sediments. Reduction of sediment concentrations may be accomplished by dredging the top

few centimetres of the sediments (Gerritse 2000; Ryding & Rast 1989). This process,

however, is not sustainable so nutrient inputs also need to be decreased (Gerritse 2000). The

dredged sediments also need to be treated with chemicals such as iron or aluminium oxides

before they can be disposed of on land (Ryding & Rast 1989).

Nutrient concentrations may also be reduced using various chemical and physical means.

However, these processes are complex and also costly for large areas (Jacobs & Forstner

1999).

Reducing nutrient release from sediments is an alternative to removal or reduction of nutrients

from the sediments. This may be accomplished by capping the sediments with either

permeable or impermeable barriers (Hart et al. 2003). This is known as sub-aqueous capping

and involves the placement of a cover over the sediment, essentially sealing it and minimising

nutrient release into the water column (Hart et al. 2003; Jacobs & Forstner 1999). The cover

can act in one of two ways; an impermeable material acts as a physical barrier while a

permeable barrier allows groundwater and surface water interchange while removing

contaminants (Hart et al. 2003).

Permeable reactive barriers

As mentioned above, permeable reactive barriers can be utilised in sediment decontamination

(Hart et al. 2003; Jacobs & Forstner 1999), groundwater decontamination (Baker, Blowes &

Ptacek 1998; Blowes et al. 2000) and in-stream (Ryding & Rast 1989). Therefore, permeable

reactive barriers may be utilised for the two main pathways of phosphorous entering the

SCES (surface and subsurface flows) and also for internal cycling of phosphorous within the

SCES. Additionally, reactive barriers are low cost and require limited technology compared to

other nutrient removal techniques (Jacobs & Forstner 1999). The barriers are therefore of

particular interest.

Jacobs and Forstner (1999) describe four criteria or requirements for materials used within an

active barrier. These are: availability at low cost, active retention of contaminants, physical



and chemical stability, and sufficient hydraulic conductivity. To date, a number of materials

that meet the above criteria have been investigated for phosphorous removal. Some examples

are shown in Table 2. Of interest to the SWWA is laterite material; this is due to its relative

availability at low cost.

Table 2. Materials and examples of studies for phosphorous removal in reactive barriers

Material Examples of studies

aluminium oxide Baker, Blowes and Ptacek (1998) Ryding and Rast (1989)

bentonite Miller (2005)

calcite Hart et al. (2003)

iron/calcium oxides Baker, Blowes and Ptacek (1998)

lanthanum modified bentonite clays (e.g. Phoslock™) Akhurst, Jones and McConchie (2004)

laterite material (or cracked pea gravel)

Sekiranda and Kiwanuka (1998) Wood and McAntamney (1996) Weaver, Ritchie and Gilkes (1992)

limestone Miller (2005) Baker, Blowes and Ptacek (1998) Debnath and Mandal (1983)

red mud (bauxol, bauxite residue)

Akhurst, Jones and McConchie (2004) Sampson (1994)

silica sand Baker, Blowes and Ptacek (1998)

steel slag Miller (2005)

zeolites Jacobs and Forstner (1999) Miller (2005)

Additionally, the use of permeable reactive barriers has been studied for the removal of other

contaminants such as nitrogen (Schipper & Vojvodic-Vukovic 2000; Miller 2005), metals

(Blowes et al. 2000; Wood & McAtamney 1996; Sobha & Anish 2003; Bhattacharyya et al.

2001) and organic compounds (Fetter 1999). Some studies have also been conducted for acid

mine drainage (Wybrant, Blowes & Ptacek 1998; Johnson & Hallberg 2005). In some cases

mixtures of materials are utilised in an attempt to remove other contaminants; for example,

Wood and McAtamney (1996) investigated both phosphorous and heavy metal removal.

This project will focus on the use of laterite material as a reactive barrier. In addition, there is

a brief investigation regarding the use of laterites in combination with materials designed to

remove nitrogen.



2.3 Phosphorous retention by laterites

2.3.1 Local studies, mechanism and capacity

There is limited published information with regards to phosphorous retention by laterites in

the SWWA. The following is a summary of this research, specifically with regards to the

mechanism and capacity.

Laterites contain high proportions of iron- and aluminium- oxides (Wood & McAtamney

1996; Gerritse 2000) and it is these compounds that allow phosphorous to readily adsorb

(Peters & Donohue 2001), and be removed from the water column. The mechanism for this

phosphorous adsorption is through a process called ligand exchange (Wood & McAtamney

1996).

A ligand is a molecule which is bound to a metal ion to form a complex ion (Silberberg

2000). Ligand exchange occurs when the ligand bound to the metal ion is replaced by another

ligand (Cotton et al. 1999). In this case, the orthophosphate molecule acts as a ligand, binding

at the hydrous oxides of iron and aluminium (Wood & McAtamney 1996), replacing the

current ligands, the (hydr)oxides.

There is a strong positive correlation between iron- and aluminium- oxide content within a

soil and phosphorous adsorption (see Figure 4) (Gerritse 2000). The adsorption index is

described as “the amount of phosphate (in grams P) that is retained by one tonne of soil after

one day for a step increase in the soil solution of 1 g of P per m3” (Gerritse 2000, page 12).

Illustrated in the figure, lateritic soil in the Canning Catchment tends to have an adsorption

index of over 100 gP/m3 of soil.

Figure 4. Phosphorous adsorption index versus iron and aluminium content (Gerritse 2000)



While the above information shows a high adsorption index for lateritic soils, hydraulic

conductivity must be sufficient for use as a permeable reactive barrier. Though there is no

mention of grain size in the above study, Weaver et. al. (1992) states that many tests only

investigate soil with fractions <2 mm size. Weaver et. al. (1992) investigated the effect of

grain size and the mineralogy of the gravels on phosphorous adsorption by lateritic soils.

For this study, Weaver et. al. (1992) separated lateritic soils into two fractions (<2mm and

>2mm), and measured for phosphorous adsorption over 35 days. Weaver et. al. (1992)

concluded that adsorption decreased with increasing gravel size and that adsorption increased

with reaction time. Sorption equilibriums for various concentrations and soil:gravel mixtures

over five weeks ranged from approximately 0.4 to 1.4 mgP/g laterite (Weaver, Ritchie &

Gilkes 1992).

Weaver et. al. (1992)’s investigation into phosphorous adsorption by lateritic soils showed

that after one week the adsorbed phosphorous had not penetrated the surface of the gravel,

except for when the gravel had a crack. Here, penetration of phosphorous occurred only in the

region of the crack.

2.3.2 International studies

Phosphorous retention by laterites outside Australia has been discussed in a number of

publications. While not being directly applicable, these lateritic soils would have similar

chemical characteristics to lateritic material local to the SWWA. The following is a summary

of published information concerning phosphorous adsorption through the use of laterite

materials.

Characterisation of soils – phosphorous uptake

General phosphorous uptake for soils was investigated in India. Kothandaraman and

Hrishnamoorthy (1978) investigated phosphorous adsorption for three local soils, including

laterites, to determine phosphorous availability and phosphorous fertilising requirements for

the area. They determined that laterite material had the highest uptake of the three and that all

soils had initial fast reactions followed by slow reactions.



Use of laterite material in wetlands and polishing ponds

Laterite material was investigated for use in wetlands and polishing ponds of wastewater

treatment due to its ability to uptake phosphorous. Tests were undertaken in both Ireland

(Wood & McAtamney 1996) and Uganda (Sekiranda & Kiwanuka 1998).

In Ireland, Wood and McAtamney (1996) trialled laterite material in both laboratory

experiments and pilot scale constructed wetlands. The wetlands included panels of laterite

material placed between rows of planted beds. The results showed 80-90 % removal and

greater than 90 % removal of phosphorous for pilot scale wetlands and laboratory

investigations, respectively.

In Uganda, Sekiranda and Kiwanuda (Sekiranda & Kiwanuka 1998) investigated the use of

laterite material in constructed wetlands. Phrangmites nauritianus was rooted in laterite

material and placed in the wetlands and produced a greater removal than when the plants were

not rooted in laterite material.

2.3.3 Current investigations into phosphorous retention by laterites

There are currently investigations in the SWWA concerning phosphorous removal through

the use of laterite material in the form of cracked pea gravel (CPG). The following

information has been provided by GHD (GHD 2007a; GHD 2007b) and will be utilised and

expanded upon in detail within this report.

Currently, CPG is being trialled by GHD on behalf of the Water Corporation for phosphorous

removal at Mills Street Main Drain (MSMD). These trials are taking place at the Patterson

Road Sub-branch Drain and the Abernathy Road Sub-Branch Drain. In the near future trials

are planned for Ellen Brook (Jose Romero, GHD, pers. com. 05/04/07).



Figure 5. Locations of Patterson Road Sub-branch Drain Blanket Trial and Abernathy Road

Sub-branch Drain Curtain Trial (Adapted from GHD 2007b)

The field trials utilised laterite material in three forms of permeable reactive barriers. First, as

a blanket which overlaid the sediments at the base of the drain. Second, as a curtain to

decontaminate the groundwater prior to discharge into the drain. Third, as an in-stream

structure for removing phosphorous from surface water tributaries.

The blanket trial consists of replacing approximately 0.2 m of sediments along the 100 m

Patterson Road Sub-branch Drain with a layer of CPG. Measurements were taken from

January 2006 while the blanket was installed mid May 2006. Excavated sediments were

disposed of at an appropriate waste management facility.

The curtain trial was installed along the South-Eastern boundary of Abernathy Road Sub-

Branch Drain. The curtain is a trench alongside the drain which has been filled with various

permeable reactive materials to encourage both nitrogen and phosphorous removal. Such

materials included CPG (6-12 mm, Figure 6), VirobindTM, woodchips and sawdust and

Spearwood sand. Choices of materials and specific mixtures are detailed in Section 3.2.



Measurements of various parameters were taken from July 2005 while the five curtain

sections were installed either in December 2005 or May 2006.

Figure 6. Cracked pea gravel (6-12 mm), photograph by L. Clayson 11/11/2007

It is intended that an in-stream structure will be employed in the Ellen Brook in the near

future (Jose Romero, GHD, pers. com. 05/04/07). This trial will allow determination of

whether laterites may be used in-stream to remove phosphorous.

2.3.4 Effect of variables on phosphorous adsorption

It is apparent from studying the phosphorous adsorption mechanism that variations in some

properties or parameters of any material may cause variations in phosphorous adsorption.

These may include: initial phosphorous concentration (Nair et al. 1984); grain size (Weaver,

Ritchie & Gilkes 1992; Gerritse 2000; Kothandaraman & Krishnamoorthy 1978); the

presence of other ions, for example pH (Debnath & Mandal 1983; Sundareshwar & Morris

1999; Liu et al. 2002) and salts (Sundareshwar & Morris 1999; Liu et al. 2002); and redox

conditions (Hart et al. 2002; Gomez et al. 1999).

At present, there has been limited research specific to laterite material on the above

parameters. One notable exception is grain size (Gerritse 2000; Weaver, Ritchie & Gilkes

1992), as discussed in Section 2.3.1.



How such parameters affected phosphorous adsorption is expanded upon in later sections of

this dissertation (namely Sections 3.1 and 5.0)

2.4 Outcomes of this project

From the literature review, it is apparent that laterite material is potentially useful for use as a

permeable reactive barrier in the SWWA. However, research with regards to laterite material

is still in its preliminary stages. The aim of this project was to investigate how phosphorous

adsorption is affected by changes in various parameters.

This research project attempts to consolidate research on laterites to date, utilising a

combination of field data sourced from GHD and laboratory experiments. By addressing these

areas that two major outcomes were intended (as shown in Table 3). Laterite material was to

be characterised to determine how it would behave under different conditions; such as

phosphorous concentrations within the water column, grain sizes, pH, salinity and redox

conditions. Based on the characterisation, recommendations were to be made for laterite use

in the field.

Table 3. Expected outcomes of the project

Outcomes

1

Characterisation of laterites - behaviour in different pH, salinity and redox conditions - performance differences between laboratory and field studies

2 Recommendations as to the best use of laterites in various environmental conditions



3.0 Methods

3.1 Laboratory experiments

The laterite material utilised for laboratory experiments was CPG (6-12 mm), which was also

utilised in the curtain trial by GHD. The following sections explain the rationale and give a

brief summary of the methodology for each experiment. Full experimental data is provided in

Appendix A.

3.1.1 Preliminary measurements and pre-treatment

Rationale

Preliminary measurements of the CPG were conducted to determine whether the raw material

caused any significant changes in parameters such as phosphorous concentration, pH and

salinity in the water column when first added to an aqueous environment. This allowed the

determination of whether pre-treatment would be necessary on a large scale.

Regardless of the preliminary results, pre-treatment was conducted on the laboratory scale.

This was conducted following the methodology of Bhattacharyya et. al. (2001), who showed

that pre-treatment with a weak acid and deionised water resulted in an increased number of

positive surface charges of the material in contrast to material that was washed with tap water.

This is a reasonable assumption as tap water contains ions which may reduce the laterite

material’s capability of adsorbing the phosphorous. In effect, the acid ‘activates’ the CPG by

removing any negative ions that have absorbed onto the material. Pre-treatment therefore

produces CPG with maximum adsorption capability.

Methodology

Preliminary measurements of raw laterite material involved adding CPG and a small amount

of salt (0.1M) to deionised water. The addition of salt was to ensure for electrolyte balance

(Nair et al. 1984). Salinity, pH and phosphorous concentrations were measured.

Pre-treatment following the method of Bhattacharyya (2001) was conducted for all

experiments and consisted of rinsing in tap water, and subsequent rinsing in deionised water,

weak acid (0.1 mol/L HNO3) and again in deionised water.



3.1.2 General methodology for phosphorous adsorption experiments

Rationale

The overall aim of the phosphorous adsorption experiments was to determine how

phosphorous adsorption is affected by changes in various conditions. It was of importance to

follow a standard experiment, changing variables when required. This allowed for comparison

between each experiment.

There are a number of laboratory variables that may affect phosphorous adsorption and stop

comparisons between different laboratory results (Nair et al. 1984). Such variables include:

soil:solution ratios, ionic strength (including cationic species), equilibration period, initial

phosphorous concentration, geometry, rate and type of mixing and extent of solid:solution

separation after equilibration (Nair et al. 1984). For this reason, Nair et. al. (1984) suggested a

standardised phosphorous adsorption procedure to allow for comparison between results. This

procedure consisted of standardised list of ten parameters to maintain between trials testing

the phosphorous adsorption of soils (as listed in Table 4). Where possible, this procedure was

followed; however, some parameters were not applicable or required altering for various

reasons; Table 4 provides indication as to the procedure followed within this research project.



Table 4. Suggested standardised procedure for phosphorous adsorption experiments

Parameter Suggested procedure by Nair et. al. (1984) Adherence to suggested procedure

Weight of soil 0.5-1.0 g Too low for larger sized CPG – used 10g (following Wood & McAtamney 1996)

Soil:Solution ratio 1:25 ratio maintained by using 250 mL

solution

Extraction time 24 h NA

Electrolyte 0.01 mol/L CaCl2, un-buffered correct concentration used NaCl, as it was more appropriate

for conditions in SWWA

Initial dissolved Pinorg

concentrations 0, 6.45, 16.13, 32.26, 161.3 323 µmol/L as KH2PO4, NaH2PO4

similar concentrations compounds unavailable, replaced with

Na2HPO4. Do not expect change to modify results.

temperature 24-26 degrees Room temperature acceptable

Microbial inhibition 20g/L chloroform

Experiment is not sealed and chloroform has boiling point of 61°C. Replaced with toluene, boiling point of 110°C (Following Kothandaraman & Krishnamoorthy 1978; Duffera & Robarge 1999)

Equilibration vessel

50mL, or other size, providing at least 50 % head space 250 mL vessel, open to the atmosphere

Shaking End-over-end shaker if available Continuous shaking not available – shaken daily by hand

Separation Filter through 0.45 µm pore diameter filter (0.2 µm for clays) NA

Analysis Any procedure for determination of orthophosphate, capable of detecting >750 µmol P

HACH 3000 machine using PhosVer3 method (ascorbic acid)

Replication Duplicate equilibriums, a single analysis of orthophosphate in solution 2 replicates of each experiment

Further considerations included the initial phosphorous solution concentration. An ideal

concentration would have less than 0.04 mgP/L, the ANZECC guideline for orthophosphate

(ANZECC & ARMCANZ 2000a); however, concentrations below this are too close to the

lower limit of the HACH spectrophotometer. The initial concentration therefore used in the

experiments (except Experiments 1, where a range of concentrations were used) was ten times

greater than this at 0.4 mgP/L.



Also considered was the length of time over which the experiment was conducted. Limited

availability of reagent pillows required that experiments were tested for one week (Following

Wood & McAtamney 1996) with approximately four tests at 1, 2, 4 and 7 days.

Methodology

All laboratory experiments conducted contained the following basic components. Alterations

were made for individual experiments where appropriate.

Table 5. General methodology of experiments

Component Purpose Quantity

Laterite material phosphorous absorber 10g (6 – 12 mm)

Na2HPO4 phosphorous source 250 mL, various concentrations

NaCl electrolyte balance 0.1 mol/L

Toluene prohibits microbial activity 5 drops

Experiments were conducted in 250 mL plastic containers (Figure 7), which were left open to

the atmosphere. Each day, samples were temporarily sealed and shaken end over end to

ensure complete mixing. All treatments were conducted in duplicate. Phosphorous

concentrations were measured periodically and where necessary salinity, pH and DO

concentrations were also recorded.

Figure 7. Vessels used for laboratory experiments

Table 6 is a summary of the five experiments. Any changes to the above methodology are

addressed in the following sections (Section 3.1.3 to 3.1.7) while complete experimental

details are found in Appendix A.



Table 6. Experiments completed

Parameter to determine Number of Experiments Variable to be changed Measurements made

Preliminary experiments 1 NA phosphorous

concentration; pH; salinity

Controls 2 a. no phosphorous b. no laterite material

phosphorous concentration

1 Adsorption capacity 6

phosphorous concentration 0.125, 1.25, 12.5 mg/L 2 duplicates each


2 Optimal size 4

grain size small grains, large grains (of 6-12 mm mixture ) 2 duplicates each


3 Behaviour due to pH 6 pH ~2.5, 5.0, 8.5 2 duplicates each

phosphorous concentration; pH

4 Behaviour due to salinity 6 salinity 1, 15, 40 ppt 2 duplicates each

phosphorous concentration; salinity

5 Behaviour due to redox conditions 10

redox condition (indicated by DO content) 2 open to atmosphere, 8 sealed

phosphorous concentration; DO

3.1.3 Experiment 1 – variations in initial phosphorous concentrations

Natural water systems in the SCES generally have Filterable Reactive Phosphorous (FRP), or

orthophosphate, concentrations less than 0.1 mgP/L, though they can be as high as 0.5 mgP/L

(Peters & Donohue 2001). However, laterite material has also been trialled globally for use in

wastewater treatment ponds/wetlands (Wood & McAtamney 1996; Sekiranda & Kiwanuka

1998), where phosphate concentrations are higher than those of natural systems. For example,

Perth municipal wastewater influent concentrations are 10-15 mgP/L for TP (Water

Corporation 2003).

It was therefore of interest to investigate a broad range of concentrations. The concentrations

of orthophosphate investigated were 0.04, 0.40 and 4.00 mgP/L. These concentrations gave a

broad spectrum of conditions in which laterite material may be placed within the field. It is

noted that through use of the HACH spectrophotometer, the phosphorous measurements are

only accurate for concentrations as low as 0.02 mgP/L. This restricted the testing of any initial

concentrations less than 0.04 mgP/L though a lower concentration would also have been of

interest.



3.1.4 Experiment 2 – variations in grain sizes

Grain sizes used in the experiments ranged from 6 to 12 mm. To determine whether there was

any significant difference in adsorption between grain sizes, small or large grains were

selected manually to make up the required 10 g.

3.1.5 Experiment 3 – variations in pH

A wide range of pH conditions can occur in natural water systems (Wetzel 2001). Generally,

pH is between four and nine (Hemond & Fechner-Levy 2000). In some situations, extreme

pHs will occur. For example, acid mine lakes are known to have pHs as low as two (Hemond

& Fechner-Levy 2000; Boine et al. 1999; Kleeberg & Gruneberg 2005) and alkaline lakes

may reach pHs above ten (Hemond & Fechner-Levy 2000).

Three pHs were tested for their phosphorous uptake: 2.3, 4.6, and 10.6. pHs were chosen for

experimental reasons. The three pHs covered the broad spectrum of conditions which laterite

material may be placed in.

3.1.6 Experiment 4 – variations in salinity

The SCES, as with many other estuarine systems, contains both freshwater and seawater.

Seawater is typically 35 ppt (Loáiciga 2006). This implies that laterite material may

potentially be required for use in both fresh water and water with salinity close to that of

seawater. Low, moderate and high salinities (1, 15, 40 ppt) were also tested to investigate any

differences in phosphorous adsorption which may have occured as a result of different

salinities.

3.1.7 Experiment 5 – variations in redox conditions

In some cases, water systems may experience periods of anaerobic conditions (Hemond &

Fechner-Levy 2000). In the low oxygen environment, the microbial community begins to

utilize other oxidants (following the biological redox sequence), such as iron and sulfur

compounds (Hemond & Fechner-Levy 2000). As discussed in Section 2.3.1, the mechanism

of phosphorous retention by laterites involves iron- and aluminium- oxides forming bonds

through ligand exchange with orthophosphate (Wood & McAtamney 1996).



If this iron is used as an oxidant in these low redox conditions, it is reasonable to assume that

the mechanism for phosphorous sorption in laterite material will be reduced and in some cases

phosphorous may be released. This assumption aligns well with studies into anaerobic

conditions (Hart et al. 2003; Krom & Berner 1980; Young & Ross 2001).

There was a need to investigate whether there would be any change in phosphorous

adsorption, or indeed a release of adsorbed phosphorous in low redox conditions. To simulate

these conditions, ten reaction vessels (without toluene) were left for one week under aerobic

conditions (following the same procedure as in Experiments 1-4) to allow some phosphorous

to adsorb into the laterite.

All vessels were subsequently dosed with carbon and nitrogen sources. Carbon was in the

form of D-glucose (following Hollender et al. 2002; Sponza & Atalay 2005; Kargi & Uygur

2003) while nitrogen was in the form of ammonium chloride (following Sponza & Atalay

2005; Hollender et al. 2002). This was to encourage microbial activity to produce anaerobic

conditions. Eight vessels were then sealed while two were left open to create aerobic

conditions. At 1, 3, 5 and 7 days, two of the eight vessels were unsealed and their DO (to

determine whether redox conditions had been reached) and phosphorous concentration in the

water column tested.



3.2 Field trials

Field work was conducted by GHD on behalf of the Water Corporation. Information specific

to the field trials within this section was provided by GHD with the permission of the Water

Corporation of Perth. To date, this data is unpublished. It is noted that while all information

has been provided by GHD, some specific instances (for example figures which have been

used directly without modification) have been referenced specifically as (GHD 2007a) or

(GHD 2007b).

3.2.1 Details of trials

Installation and dates of measurements for the blankets and curtain are detailed in Table 7.

Table 7. Dates of installation and dates for commencement of monitoring for field trials

Trial Type Sections Measurements Commenced Installation Blanket -- 05/01/06 18/05/06 Curtain A & B 07/07/05 20/12/05 Curtain C, D & Extension 07/07/05 19/05/06

Blanket Trial

The blanket was installed by excavating approximately 0.2 metres of bed sediment along the

100 metre drain and immediately replacing with CPG. The CPG (<6 mm diameter) was

placed to a depth of approximately 0.2 metres. Figure B. 1, Appendix B is a blueprint of the

Patterson Road Sub-branch Drain Blanket Trial.

During low flow conditions in the summer months, the drain inlet was boarded (GHD 2007b).

This ensured that the only source of water entering the drain during this time was

groundwater which would have passed through the laterite blanket.

Curtain Trial

The curtain was 200 metres in total length and was divided into four 25 metre sections and a

fifth 100 metre extension. The curtain was 1 metre wide and approximately 3.2 metres high.

The area vertically above the curtain was backfilled to the original ground level with the

assumption that the groundwater height would not exceed the height of the curtain at any time

throughout the year. The groundwater could also flow beneath the curtain; however bores

were placed in such a way that they would only monitor water that had a flow path through



the treatment curtain. Figure B. 2, Appendix B is a blueprint of the Abernathy Road Sub-

branch Drain Curtain Trial.

The four 25 metre sections contained four different material mixtures, chosen for either their

nitrogen or phosphorous stripping capacity. The 100 metre extension was constructed using

the most promising of the original four mixtures. Table 8 details the combinations used in the

curtain and the intended function of each section.

Table 8. Combinations of materials within groundwater curtain for each section

Material

For phosphorous removal For nitrogen removal**

CPG (6-12 mm) VirobindTM Spearwood

sand Woodchips Sawdust Intended

function of section

A -- -- 70 % 30 % -- phosphorous & nitrogen removal

B 70 % -- -- -- 30 % phosphorous & nitrogen removal

C 50 % -- 50 % -- -- phosphorous removal

D -- 5 % 95 % -- -- phosphorous removal

Sect

ion

Ext* 70 % -- -- -- 30 % phosphorous & nitrogen removal

*Ext = Extension, same mixture as Section B **Nitrogen removal through biological activity – material is used as carbon source, encouraging denitrification.

3.2.2 Raw data

Field measurements from 07/07/05 to 26/04/07 were included in the analysis. Bores and

surface waters for both trials were monitored for a number of parameters, detailed in Table 9.



Table 9. Monitored parameters in field trials

Parameter Measurement

Physical Temperature, salinity, DO, total dissolved solids, conductivity, pH, oxygen reduction potential, groundwater level (bores), flow rate (surface waters)

Nitrogen Total nitrogen, total kjehldahl nitrogen, nitrate, nitrite, ammonium

Phosphorous TP, FRP

Carbon Dissolved organic carbon, total organic carbon

Anions Bicarbonate, carbonate, sulphate, chlorine Cations Sodium, potassium, magnesium, calcium

Metals Iron (total and filterable), aluminium, zinc

3.2.3 Analysis of raw data

Parameters of interest were predominantly phosphorous concentrations. Also of interest were

physical parameters such as temperature, salinity, DO, pH, groundwater levels and flow rates.

Blanket Trial

Two bores and two points in the drain (inlet and outlet) were sampled regularly at the blanket

trial. The data obtained was analysed in order to determine how the addition of the blanket or

the curtain affected phosphorous concentrations. This was achieved by plotting the TP and

FRP concentrations taken at each sample point over the study period.

Curtain Trial

Two of the four mixtures utilised CPG. A mixture of laterite material, Spearwood sand and

sawdust was used in both Section B and the Extended Section (for nitrogen and phosphorous

removal), while a mixture of Spearwood sand and CPG was used in Section C (for

phosphorous removal only).

Paired bores were installed upstream and downstream of each curtain section. Head difference

were used to determine flow direction for the sample day. It was assumed that samples taken

from the upstream bore had not passed through the curtain and samples taken from the

downstream bore had. A change in concentration (TP and FRP) could then be determined for

water flowing through each medium type.



4.0 Results


4.1.1 Preliminary investigations

It was established that the presence of CPG did not have a significant effect on salinity, pH or

phosphorous levels within the water column when placed in water. Results are shown in

Table 10.

Table 10. Results of preliminary investigations

Parameter Units Measurement salinity ppt 0.021

pH -- 6-6.5 phosphorous mgP/L 0 (below detection)

4.1.2 Controls

The two controls produced the results shown in Table 11. Results from Control 1 showed no

detectable phosphorous under experimental conditions (0.1 mol/L NaCl; toluene). Control 2

showed in the absence of CPG there was no significant change in phosphorous solution

concentration over the time period of the experiment.

Table 11. Results for Controls 1 and 2

Phosphorous concentration (mgP/L) Time

(days) Control 1 (absence of phosphorous - deionised water used)

Control 2 (absence of CPG)

0 0 0.25 1.13 0 -- 2.21 0 -- 3.92 0 -- 6.33 -- 0.724 6.63 0 --


The results for Experiment 1 are provided in Table 12, where decreases in phosphorous

concentrations within the water column are shown as a percentage of the initial concentration.

Actual phosphorous concentrations are given in the experimental section in Appendix A.

From the results it is seen that Treatment A (0.04 mgP/L) reached levels below the sensitivity



of the HACH spectrophotometer after four days. Treatments B and C did not reach zero

concentration over the period of the experiment.

Table 12. Results for Experiment 1 – variations in initial phosphorous concentrations

Water column phosphorous concentration (% of initial) Treatment A 0.04 mgP/L

Treatment B 0.40 mgP/L

Treatment C 4.00 mgP/L

Time (days)

i ii i ii i ii 0 100 100 100 100 100 100

1.13 40 52 29 20.8 40 37 2.21 16 40 24 12 30 31.44 3.92 0 0 8.5 6.4 24.8 25.6 6.63 0 0 6 6.4 20 24

Figure 8 shows the results graphically. From the figure, it is evident that replicates for

Treatments A and B varied to some extent over the first few days, though they reached

relatively consistent values from the fourth day onwards.

0

20

40

60

80

100

0 1 2 3 4 5 6 7time (days)

Pho

spho

rous

con

cent

ratio

n in

w

ater

col

umn

(% o

f ini

tial)

0.04 mgP/L (i) 0.04 mgP/L (ii) 0.40 mgP/L (i)0.40 mg/L (ii) 4.00 mgP/L (i) 4.00 mgP/L (ii)

Figure 8. Results of Experiment 1 – variations in initial phosphorous concentrations



4.1.4 Experiment 2 – variations in grain sizes

The results for Experiment 2 are shown in Table 13, where decreases in phosphorous

concentrations in the water column are given as a percentage of the initial concentration.

Actual phosphorous concentrations are provided in the experimental section in Appendix A.

The results show that both treatments resulted in similar reductions in water column

phosphorous concentration.

Table 13. Results for Experiment 2 – variations in grain sizes

Water column phosphorous concentration (% of initial) Treatment A

small grain size (6-8 mm) Treatment B

large grain size (10-12 mm) Time

(days) i ii i ii

0 100 100 100 100 0.21 84 62 57.6 54.4 0.88 76 50 43.2 43.2 1.40 65.6 40 40.4 39.2 5.04 44.4 26.8 24 25.2

7.916667 18.8 17.6 18.4 18

Figure 9 shows the results graphically. From this, it is evident that Replica i of Treatment A

showed significantly lower phosphorous removal from the water column than Treatment A

Replica ii and Treatment B replicates. However, results for both replicates of Treatment B

were similar.

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8time (days)

Phos

phor

ous

conc

entr

atio

n in

w

ater

col

umn

(% o

f ini

tial)

small grain (i) small grain (ii) large grain (i) large grain (ii)

Figure 9. Results for Experiment 2 – variations in grain size (with an initial water column phosphorous concentration of 0.40 mgP/L)




The results for Experiment 3 are shown in Table 14. Here, decreases in phosphorous

concentrations in the water column are shown as a percentage of the initial concentration.

Actual phosphorous concentrations are given in the experimental section (Appendix A). The

results show that different treatments resulted in different amounts of phosphorous

adsorptions from the water column. It can be seen that Treatment C (pH of 10.6) removed less

phosphorous from the water column than treatments at lower pHs. Treatments A and B also

removed different amounts of phosphorous from the water column, though the difference

between the values is relatively small.

pH changed significantly with the addition of laterite material, particularly at higher pH’s.

Readings at the commencement of the experiment were taken before the addition of CPG.

Table 14. Results for Experiment 3 – variations in pH


pH 2.3 Treatment B

pH 4.6 Treatment C

pH 10.6 Time

(days) Replica i Replica ii Replica i Replica ii Replica i Replica ii

0 100 100 100 100 100 100 0.42 56 57.6 57.2 56 55.6 64 1.92 61.6 38 39.6 34 54.8 56 4.08 24.8 25.2 25.6 24 42.8 41.2

7 23.6 22.4 18 17.2 30.4 31.6 pH reading 0 2.3 2.3 4.6 4.6 10.6 10.6

1.91 2.4 2.4 5.0 5.0 8.7 8.7

Figure 10 shows the results graphically. It can be seen that Replica i of Treatment A showed a

water column concentration significantly higher than that of Replica ii during measurement

on day 2, though this appears to be an outlier. Otherwise, replicate results for all treatments

are similar.



0

20

40

60

80

100

0 1 2 3 4 5 6 7time (days)

Phos

phro

us c

once

ntra

tion

in w

ater

co

lum

n (%

of i

nitia

l)

pH 2.3 (i) pH 2.3 (ii) pH 4.6 (i) pH 4.6 (ii)pH 10.6 (i) pH 10.6 (ii)

Figure 10. Results for experiment 3 - variations in pH (initial water column phosphorous

concentration of 0.40 mgP/L)


The results for Experiment 4 are shown in Table 15. Decreases in phosphorous concentrations

in the water column are given as a percentage of the initial concentration. Actual phosphorous

concentrations are presented in the experimental section (Appendix A). The results indicate

that different salinities resulted in different adsorptions, where the adsorption decreased as

salinity increased.

Table 15. Results for Experiment 4 – variations in salinity


1 ppt Treatment B

16 ppt Treatment C

42 ppt Time

(days) Replica i Replica ii Replica i Replica ii Replica i Replica ii

0 100 100 100 100 100 100 1.08 68.8 65.6 72.7 70.1 72.7 69.5 3.27 42.2 41.6 51.3 46.1 51.9 50.6 6.33 32.5 33.8 36.4 38.3 49.4 50

Salinity (ppt)

0 1.1 1.2 15.5 16.5 42.2 42.6 1.08 1.1 1.1 15.7 16 42.2 42.5 6.33 1.25 1.15 16.6 16.9 36.9 36.8



The data is presented graphically in Figure 11, below. Replicates for high and low salinities

yielded similar results, while those of 15 ppt differed during the first half of the experiment.

0

20

40

60

80

100

0 1 2 3 4 5 6 7Time (days)

Phos

phor

ous

conc

entr

atio

n in

wat

er

colu

mn

(% o

f ini

tial)

1 ppt (i) 1 ppt (ii) 15 ppt (i) 15 ppt (ii)

40 ppt (i) 40 ppt (ii)

Figure 11. Results for Experiment 4 - variations in salinity (initial concentration of 0.25 mgP/L)


The results for Experiment 5 are given in Table 16, where decreases in phosphorous

concentrations in the water column are given as a percentage of the initial concentration.

Actual phosphorous concentrations are given in the experimental section in Appendix A.

Sealed samples were resealed immediately after testing, and all samples were retested at 14

days.



Table 16. Results for Experiment 5 – redox conditions

Phosphorous concentration in water column as % of initial; (DO in mg/L) Time

(days) 1 2 3 4 5 6 7 8 9 10

0 100 100 100 100 100 100 100 100 100 100

7 26.2 32.1 24.6 28.7 31.6 26.2 27.0 28.7 24.6 27.9

-- Left Open

Left Open Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed

8 -- -- 20.5 (2.3)

20.5 (1.9) -- -- -- -- -- --

10 28.3 23.3 -- -- 27.0 (0.4)

20.49 (0.8) -- -- -- --

12 -- -- -- -- -- -- 23.8 (1.4)

21.3 (0.6) -- --

14 29.9 (3.0)

21.3 (2.8)

25.8 (0.8)

27.9 (0.2)

31.1 (0.8)

22.1 (1.1)

20.0 (1.6)

21.3 (0.9)

24.6 (0.2)

20.1 (0.5)

The results show varied phosphorous and DO concentrations, regardless of the length of time

sealed. This is particularly evident in Figure 12, a graphical representation of the phosphorous

concentration in the water column. As shown, there was no correlation between any of the

replicates, including the aerobic samples.

18

20

22

24

26

28

30

32

34

7 8 9 10 11 12 13 14

Time (days)

Pho

spho

rous

con

cent

ratio

n in

wat

er

colu

mn

(% o

f ini

tial)

Aerobic (i) Aerobic (ii) Sealed 1 day (i) Sealed 1 day (ii)Sealed 3 days (i) Sealed 3 days (ii) Sealed 5 days (i) Sealed 5 days (ii)Sealed 7 days (i) Sealed 7 days (ii)

Figure 12. Results for Experiment 5 – variations in redox conditions



Possible relationships between DO and phosphorous adsorption were investigated. Figure 13

shows DO concentrations for the sealed bottles opened at 1, 3, 5 and 7 days graphed against

percentage phosphorous adsorption while Figure 14 shows all measured data points.

15

19

23

27

31

35

0 0.5 1 1.5 2 2.5 3 3.5

Dissolved Oxygen (mg/L)

Phos

phor

ous

conc

entr

atio

n in

wat

er

colu

mn

(% o

f ini

tial)

Aerobic Sealed 1 day Sealed 3 days Sealed 5 days Sealed 7 days

Figure 13. Dissolved oxygen versus phosphorous concentration in water column for aerobic samples and sealed samples opened at 1, 3 5 and 7 days

y = 0.0662x + 23.745R2 = 0.0003

15

19

23

27

31

35

0 0.5 1 1.5 2 2.5 3 3.5

Dissolved Oxygen (mg/L)

Phos

phor

ous

conc

entr

atio

n in

wat

er

collu

mn

(% o

f ini

tial)

All results Linear (All results)

Figure 14. Dissolved oxygen versus phosphorous concentration in water column for all measurements



4.1.8 Laboratory results in combination

The final percentage adsorptions of phosphorous from the water column for all experiments

are shown in Figure 15. Adsorption values ranged from 50 % to 100 % for all experiments.

0

20

40

60

80

100

0.12

50.

125

1.25

1.25

12.5

12.5

Sm

all

Sm

all

Larg

eLa

rge

2.3

2.3

4.6

4.6

10.6

10.6 1 1 16 16 42 42

Aer

obic

Aer

obic

Sea

l 1d

Sea

l 1d

Sea

l 3d

Sea

l 3d

Sea

l 5d

Sea

l 5d

Sea

l 7d

Sea

l 7d

Initial P conc (mg/L) Grain Size pH Salinity (ppt) Redox conditions (seals initiatedafter 7 days)

P re

mov

ed fr

om th

e w

ater

col

umn

(% o

f ini

tial

conc

entr

atio

n ad

sorb

ed b

y La

teri

te m

ater

ial)

Figure 15. Final percentage adsorption from water column for all experiments



4.2 Field trials

4.2.1 Blanket trial

TP and FRP concentrations were monitored for the blanket trial. Measurements were taken at

two monitoring bores and within the drain upstream and downstream of the blanket (at the

entry and exit points of the drain). These locations are shown in Figure B. 2 (Appendix B).

The results are shown in Figure 16 and Figure 17 below while raw data is provided in

Appendix B.

Filterable Reactive Phosphorous

FRP measurements are provided in Figure 16. The bores both have higher levels of FRP than

the surface water. Surface water concentrations decreased significantly after the installation of

the blanket; though concentrations increased in later months. The ANZECC guideline of 0.04

mgP/L for FRP (ANZECC & ARMCANZ 2000a) is shown in green. The majority of the

surface water measurements were below this limit.

0.0

0.2

0.4

0.6

0.8

1.0

3/01/2006 13/04/2006 22/07/2006 30/10/2006 7/02/2007Filte

rabl

e Re

activ

e P

hosp

horo

us (m

gP/L

)

Bore 1 Bore 2 Drain Entry Drain Exit Blanket Installed ANZECC

Figure 16. Filterable Reactive Phosphorous concentrations for blanket trial

Total Phosphorous

TP concentrations are shown in Figure 17. Of the two bores, Bore 1 contained the highest

levels of TP. TP remained relatively low at the drain entry over the monitoring period. In

contrast, the exit of the drain had high concentrations prior to the installation of the blanket.

These concentrations decreased immediately after the installation of the blanket. The

ANZECC guideline of 0.065 mgP/L for TP (ANZECC & ARMCANZ 2000a) is shown in



green. A large proportion of the surface water concentrations at the entry and exit of the drain

were above this limit.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

3/01/2006 13/04/2006 22/07/2006 30/10/2006 7/02/2007

Tota

l Pho

spho

rous

(mgP

/L)

Bore 1 Bore 2 Drain Entry Drain Exit Blanket Installed ANZECC

q

Figure 17. Total Phosphorous concentrations for blanket trial

Other parameters

Table 17 contains the range of temperature, salinity and pH values that were measured at the

four sample locations for the blanket trial. Temperature ranged between approximately 9 and

30 °C and the salinity was between 0 and 1.7 ppt. pH was between 6 and 9. Surface waters

had a greater range of temperature and pH values but a smaller salinity range than those of the

bores.

Table 17. Ranges of measurements for temperature, salinity and pH for blanket trial (bold values indicate the overall minimum or maximum)

Temperature (°C) Salinity (ppt) pH Sample

Minimum Maximum Minimum Maximum Minimum Maximum Bore 1 17.7 26.0 0.40 1.47 6.20 7.12 Bore 2 18.5 27.2 1.07 1.67 6.42 7.03

Surface - Entry 10.2 28.5 0.12 0.53 5.98 8.55 Surface - Exit 9.1 30.7 0.06 0.66 5.88 8.99



Figure 18 shows the DO concentrations for each monitoring point. Bore concentrations

ranged between 0 and 5 mgP/L while surface water concentrations were generally higher,

with a maximum value of 26 mgP/L.

0

5

10

15

20

25

30

3/01/2006 14/03/2006 23/05/2006 1/08/2006 10/10/2006 19/12/2006 27/02/2007

Dis

solv

ed O

xyge

n (m

g/L)

Bore 1 Bore 2 Surface - Entry Surface - Exit

Figure 18. Dissolved Oxygen concentrations for blanket trials

4.2.2 Curtain trial

Of the four mixtures investigated in the curtain trial, two contained laterite material (or CPG)

and are discussed in detail below. The results presented in this section are in a graphical form

and raw data is provided in Appendix B.

Section B – Cracked pea gravel and Sawdust

The performance of Section B was monitored by four bores (Bores 01, 01a, 03 and 03a).

Their locations relative to the drain are shown in Figure 19. Bores 01 and 03 were the original

bores which were monitored prior to installation of the curtain. However, these bores were

damaged during construction, resulting in the eventual replacement with Bores 01a and 3a.

Data from Bores 01 and 03 between 22/07/05 and 07/04/06 and Bores 01a and 03a from

14/03/06 onwards was used.



Figure 19. Locations of bores for Section B of curtain trial (not to scale)

Bore levels

The differences between the groundwater heights for the bores on either side of the curtain are

shown in Figure 20. A positive value shows discharge into the drain and a negative value

shows recharge into the groundwater. The figure shows head differences ranging from -0.5

cm to 6 cm. With the exception of two dates prior to curtain installation (29/09/05 and

14/11/05), measurements of groundwater head indicate flow towards the drain.

-1

0

1

2

3

4

5

6

7

17/07/2005 25/10/2005 2/02/2006 13/05/2006 21/08/2006 29/11/2006 9/03/2007

∆H

ead

(cm

)

∆Head (positive = flow towards drain) ∆Head (positive = flow towards drain)

Curtain Installed

Figure 20. Difference in groundwater head between bores for Section B of curtain trial


FRP measurements for the bores are shown in Figure 21. Using the head difference as an

indication of the flow direction, the difference between downstream and upstream

concentrations was also calculated for each pair of measurements, shown in green. Since the



flow interchanges between a recharge or discharge system, the designation of upstream and

downstream bores will also interchange accordingly. As such, in some cases the green data

point shows Bore 01 minus Bore 03 while for other cases, the data point is Bore 03 minus

Bore 01. A positive value indicates an increase in FRP between the bores and a negative value

indicates a decrease in FRP between the bores.

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

17/07/2005 25/10/2005 2/02/2006 13/05/2006 21/08/2006 29/11/2006 9/03/2007

Filte

rabl

e Re

activ

e Ph

osph

orou

s (m

gP/L

)

Bore 3 Bore 3a Bore 1Bore 1a ∆FRP (positive = increase) ∆FRP (positive = increase)Curtain Installed

Figure 21. Filterable Reactive Phosphorous concentrations for Section B of curtain trial

The figure illustrates that in most instances there is a decrease in FRP concentrations between

the bores. One exception is the measurement taken on 29/09/05. This sampling day was where

the groundwater gradient indicated recharge from the drain to the groundwater, though the

difference in head was only 0.5 cm (Figure 20).

The decrease in FRP is greatest during the first half of the trial, where samples were taken

from Bore 01 and Bore 03. The concentrations of FRP decrease significantly with the

installation of new bores and this is reflected in the calculated difference between the

upstream and downstream concentrations. For example, measurement ranges for Bores 01 and

03 are approximately 0 to 0.16 mgP/L while Bores 01a and 03a have a range of

approximately 0 to 0.05 mgP/L.

Total Phosphorous



TP concentrations are shown in Figure 22. Changes in TP concentration between the bores are

shown in green and were calculated in the same manner as for FRP concentrations (above).

For the change in TP, a positive value indicates an increase in TP between the bores, while a

negative value indicates a decrease between the bores.

-0.5

-0.25

0

0.25

0.5

0.75

1

17/07/2005 25/10/2005 2/02/2006 13/05/2006 21/08/2006 29/11/2006 9/03/2007

Tota

l Pho

spho

rous

(mgP

/L)

Bore 3 Bore 3a Bore 1Bore 1a ∆TP (positive = increase) ∆TP (positive = increase)Curtain Installed

Figure 22. Total Phosphorous concentrations for Section B of curtain trial

Raw TP values range between approximately 0.1 to 0.9 mgP/L. The data shows an increase in

TP concentration between the two bores prior to installation of the curtain and decreasing

concentrations after installation. One notable exception is the sample day where the head

difference indicated flow was recharging the groundwater system (gradient of 0.5 cm).

Section C –Cracked pea gravel and Spearwood sand

Bores 09 and 12 provided data for Section C. The bores were positioned relative to the drain

as shown in Figure 23. Monitoring was only carried out on Section C immediately prior to

and during the trial period.



Figure 23. Location of bores for Section C of curtain trial (not to scale)

Bore levels

The difference between the groundwater heights is shown in Figure 24. Where there is a

positive value, discharge into the drain was occurring. A negative value indicates recharge

from the drain into the groundwater. The head differences generally ranged from 0.2 to 9 cm,

with one extreme head difference of 26 cm. Water was discharging into the drain for all but

two of the sample days (21/08/06 and 29/11/06).

-10

0

10

20

30

3/05/2006 22/06/2006 11/08/2006 30/09/2006 19/11/2006 8/01/2007 27/02/2007 18/04/2007

∆Hea

d (c

m)

∆Head (positive = flow towards drain) Curtain Installed

Figure 24. Change in head between bores in Section C of curtain trial


FRP concentrations for Bores 12 and 09 are shown in Figure 25. Following the same

procedure as for Section B, the head difference between the bores was used to determine the

flow direction, which provided the concentration differences between upstream and

downstream measurements, shown in green. Here a positive value indicates an increase and a

negative value indicates a decrease.



-0.15

-0.1

-0.05

0

0.05

0.1

0.15

3/05/2006 22/06/2006 11/08/2006 30/09/2006 19/11/2006 8/01/2007 27/02/2007 18/04/2007

Filte

rabl

e Re

activ

e Ph

osph

orou

s (m

gP/L

)

FRP Bore 12 FRP Bore 09 ∆FRP (positive = increase) Curtain Installed

Figure 25. Filterable Reactive Phosphorous concentrations for Section C of curtain trial

The figure shows FRP values ranging from approximately 0 to 0.12 mgP/L throughout the

sample period. Changes between upstream and downstream concentrations are negative, with

the notable exception of 01/03/07. This date corresponds with the date that the large head

change occurs, as shown in Figure 24.

No data point for the change in concentration is shown prior to the installation of the curtain.

This was because there were no bore water level measurements for this data point recorded in

the provided data.

Total Phosphorous

TP and the difference between upstream and downstream concentrations (calculated in the

same manner as for Section B) are plotted in Figure 26. A positive value for the change in

concentration indicates an increase while a negative value indicates a decrease.



-1

0

1

2

3

3/05/2006 22/06/2006 11/08/2006 30/09/2006 19/11/2006 8/01/2007 27/02/2007 18/04/2007

Tota

l Pho

spho

rous

(mgP

/L)

TP Bore 12 TP Bore 09 ∆TP (positive = increase) Curtian Installed

Figure 26. Total Phosphorous concentrations for Section C of curtain trial

The figure shows TP measurements ranging from approximately 0 to 2.7 mgP/L. The change

in TP as it passes through the curtain is generally positive, indicating an increase in

concentration. However, there are three data points showing a decrease (22/09/06, 29/11/06

and 11/04/07).

Again, no data point for the change in concentration is shown prior to the installation of the

curtain. This was because there were no bore water level measurements recorded prior to this

date.

Extended section – Cracked pea gravel and sawdust

Two bores provided concentrations for the Extended Section: Bore EB1 and Bore EB2. Their

locations are shown in Figure 27. Measurements for this section of curtain were only taken

immediately prior to the curtain installation.



Figure 27. Location of bores for Extended Section of curtain trial (not to scale)

Bore Levels

The head differences between the sampling bores are shown in Figure 28. Where there is a

positive value, water is discharging into the drain while a negative value indicates recharge

into the groundwater. As shown, the head differences range from approximately 0.2 to 8 cm.

Approximately half of the measurements indicate water discharging into the drain while the

remaining indicate recharge into the groundwater. Most values show a head difference of less

than 2 cm.

-4

-2

0

2

4

6

8

8/05/2006 27/06/2006 16/08/2006 5/10/2006 24/11/2006 13/01/2007 4/03/2007 23/04/2007

∆Hea

d (c

m)

∆Head (positive = flow towards drain) Curtain Installed

Figure 28. Head differences between bores in Extended Section of curtain trial


FRP concentrations for Bores EB1 and EB2 are shown in Figure 29. As with Section B, the

flow direction was determined and the change in FRP between the upstream and downstream



bore was calculated. Here a positive value indicates an increase and a negative value indicates

a decrease once it passes though the curtain.

-0.5

-0.3

-0.1

0.1

0.3

0.5

8/05/2006 27/06/2006 16/08/2006 5/10/2006 24/11/2006 13/01/2007 4/03/2007 23/04/2007

File

tera

ble

Rea

ctiv

e P

hosp

horo

us (m

gP/L

)

FRP Bore EB2 FRP Bore EB1 ∆FRP (positive = increase) Curtain Installed

Figure 29. Filterable Reactive Phosphorous concentrations for Extended Section of curtain trial

The figure shows values ranging from approximately 0 to 0.3 mgP/L. Measurements from

EB1 are consistently close to zero while measurements for EB2 vary significantly. There is no

data available for 10/05/06. The downstream and upstream differences in concentrations were

positive, with three exceptions (22/09/06, 01/03/07 and 14/03/07).


This is because there were no bore water level measurements for this data point recorded in

the provided data.

Total Phosphorous

TP and the change in concentration between the upstream and downstream bores (calculated

in the same manner as those for Section B) are plotted in Figure 30. A positive value for the

change in concentration indicates an increase, while a negative value indicates a decrease.



-2

-1

0

1

2

3

8/05/2006 27/06/2006 16/08/2006 5/10/2006 24/11/2006 13/01/2007 4/03/2007 23/04/2007

Tota

l Pho

spho

rous

(mgP

/L)

TP Bore EB2 TP Bore EB1 ∆TP (positive = increase) Curtain Installed

Figure 30. Total Phosphorous concentration for Extended Section of curtain trial

TP concentrations range between approximately 0 and 2.5 mgP/L. Similar to FRP

measurements, Bore EB1 concentrations appear to be more consistent than those of Bore

EB2. The difference between the upstream and downstream values varies widely. As stated

previously, the head difference between upstream and downstream bores was less than 2 cm

on during most sampling days.


This was because there were no bore water level measurements for this data point recorded in

the provided data.

Other parameters

Table 18 contains information on the data recorded for temperature, salinity and pH for the

blanket trial. The temperature ranged from approximately 18 to 26 °C while the salinity was

between 0.08 and 0.63 ppt. The pH ranged between approximately 4.7 and 7.7.



Table 18. Ranges of measurements for temperature, salinity and pH for curtain trial (bold values indicate the overall minimum or maximum)

Temperature (°C) Salinity (ppt) pH Location Minimum Maximum Minimum Maximum Minimum Maximum Bore 1 20.2 25.2 0.19 0.43 5.93 6.63

Bore 1a 18.9 24.8 0.10 0.40 6.03 7.08 Bore 3 20.7 25.1 0.19 0.29 6.25 6.91

Section B

Bore 3a 18.9 25.0 0.10 0.24 5.76 7.02 Bore 9 17.9 24.9 0.14 0.43 5.38 6.82 Section C Bore 12 18.7 25.8 0.14 0.63 4.69 6.79

Bore EB1 16.2 24.5 0.08 0.49 5.83 6.88 Extension Bore EB2 18.2 23.8 0.16 0.39 5.36 7.68

Figure 31 shows the DO for each bore for the sampling period. Rather than providing a range

of values, as was provided for temperature, salinity and pH, data is provided for all sampling

days as this depth of detail for DO is required for adequate analysis. DO generally ranges

between 0 and 3.5 mg/L. One exception is for Bore EB1, where it reaches just over 5 mg/L.

DO reaches 0 mg/L consistently during the last 4 monitoring days.

0

1

2

3

4

5

17/07/2005 25/10/2005 2/02/2006 13/05/2006 21/08/2006 29/11/2006 9/03/2007

Dis

solv

ed O

xyge

n (m

g/L)

Bore 1 Bore 1a Bore 3 Bore 3a Bore 9Bore 12 Bore EB1 Bore EB2

Figure 31. Dissolved Oxygen for Section B, Section C and Extended Section Bores in curtain

trial



5.0 Discussion of results


5.1.1 Preliminary investigations

The preliminary investigations established that CPG did not significantly affect salinity, pH or

phosphorous levels of the water column when placed in water. This result was expected as

CPG is used in landscaping with no detrimental effects.

5.1.2 Controls

The control tests were performed in order to determine whether any components other than

the CPG and the variable to be changed had an effect upon the concentration of phosphorous

within the water column.

The results for Control 1 indicated no detectable phosphorous concentration within the water

column when CPG was placed in deionised water with toluene and NaCl (0.1 mol/L). This

showed that the mixture containing toluene, NaCl and CPG would not affect the measurement

of phosphorous concentrations.

Control 2 results showed no significant phosphorous removal from a water column containing

toluene and 0.1 mol/L NaCl over the 7 day test period. There was no CPG present within the

control. The small decrease (0.02 mgP/L) was within the normal observed error range of the

HACH spectrometer (as discussed in Section 3.1.3). This signifies that any natural decrease in

phosphorous concentrations due to natural processes is insignificant and within the error of

the method of measurement of phosphorous. Additionally, as shown in Control 1, results from

Control 2 indicate that the presence of salt and toluene do not effect phosphorous

concentrations.

From the information above, two assumptions may be made in regards to Experiments 1 to 5

(below). First, CPG is the dominant cause of phosphorous removal from the water column.

Second, the treatments for each experiment are the only factors which may affect the

differences in rates of phosphorous removal from the water column.



5.1.3 General observations for Experiments 1-5

Observed reductions in phosphorous concentrations – shape of curve

Measurements of phosphorous concentration in the water column for Experiments 1-4 were

undertaken regularly during the seven day time period of the experiment. Experiment 5 was

not conducted in this manner as the investigation of redox conditions required initial

adsorption for 7 days with subsequent measurements in the following seven days.

Experiments 1-4 showed similar patterns in their rate of phosphorous adsorption over time. In

the initial 24 hours of the experiment, phosphorous concentrations decreased rapidly, with the

rate of adsorption decreasing in subsequent days. The results align well with observations by

Kothandaraman & Krishnamoorth (1978), who investigated phosphorous adsorption of

lateritic soil.

Investigations conducted by Weaver et. al. (1992) may also provide some insight into the

adsorption curves observed in the experiments. Weaver et. al. (1992) investigated

phosphorous adsorption of laterite gravel in SWWA, where autoradiographs of the laterite

gravel showed no penetration of phosphorous beneath the surface of the laterite gravel, except

for where cracks existed (Weaver, Ritchie & Gilkes 1992).

The rapid decrease in phosphorous concentrations observed in the initial 24 hours of the

experiment may correspond to the adsorption of the phosphorous to the surface of the laterite.

The slower decrease in concentration in the water column which followed may indicate

phosphorous is being adsorbed into the less accessible cracks in the laterite.

Interestingly, CPG appeared to have stopped adsorbing within the time period of the

experiment for two treatments. The two cases are for Experiment 3 (Treatment A: pH of 2.6)

and Experiment 4 (Treatment C: salinity of 42 ppt). This indicates that equilibrium was

reached at that particular concentration.

Variations between replicates

Also of interest were the variations between the replicates for a number of treatments in

Experiments 1, 2 and 3. Experiments 1 and 3 only showed variations between replicates over

the first three days. After this, replicates showed similar results. Experiment 2 had differences



between the two replicates of treatment A as late as day 5, though by the end of the

experiment, the two replicates had similar concentrations.

No definitive explanation can be given for these variations. One may hypothesise that these

values may be through accidental contamination of the sample during measurement

(particularly for Experiment 3, which only shows one varied data point); however it is

unlikely that this is the case for Experiments 1 and 2.

One possible cause of the differences in rates adsorption of phosphorous is the relative

accessibility between the two replicates of the iron- and aluminium- oxyhydroxides in the

CPG. The laterite grains were randomly chosen for each sample, however there may have

been some differences between surface areas and number of ‘cracks’, which would affect the

rate of adsorption (as discussed earlier in this section), though not necessarily the final

adsorption value. The small scale of the experiment (10g laterite in 250 mL solution) would

have also exacerbated this.

The small number of replicates and the relatively small scale in this case was due to the

limited availability of required chemicals and equipment. It is recommended that future

investigations utilise a greater number of replicates and/or incorporate a larger scale

experiment, which may give a greater understanding of (and the reasons for) variations in

replicates.


Percentage reductions

Subjecting CPG to treatments of differing initial phosphorous concentrations within the water

column resulted in differing adsorption. All treatments removed greater than 75 % of the

phosphorous within the water column after seven days. The greatest percentage removal was

observed for treatments with lower initial concentrations.

Treatment A is shown to have removed 100 % of the phosphorous within the water column.

Though, as discussed in Section 3.1.3, the sensitivity of the HACH spectrophotometer used to

measure the phosphorous concentrations was such that any value below 0.02 mgP/L was

within the error range. Since 0.02 mg/L is 4 % of the initial concentration for Treatment A,

we can say the percentage removal from the water column would have been at least 96 %,



though an exact value could not be measured. While the HACH spectrophotometer was

sufficient to determine general trends in phosphorous adsorption, it is recommended that

future investigations into phosphorous adsorption by laterites utilise more accurate methods

of determining phosphorous concentrations, particularly at lower concentrations.

Concentration reductions and phosphorous removal capacity

By investigating the actual change in concentration of phosphorous, one may calculate the

total volume of phosphorous adsorbed by the 10 g of CPG for Treatments A, B and C. These

were 0.01, 0.09 and 0.78 mgP/10g of CPG respectively, where the initial masses of

phosphorous within the water column were 0.01, 0.10 and 1.00 mg, respectively. This shows

that where a larger volume of phosphorous is present, adsorption at a higher rate may occur.

While adsorption capacity cannot be specifically quantified, some observations may be made.

By extrapolating the trend of the concentrations in the water column for the treatments (with

the exception of Treatment A, which was beneath measurement concentrations), it is seen that

further adsorption would occur beyond the experiment time frame, though only at low rates.

This would imply that the adsorption capacity of the CPG is greater than 0.08 mgP/g of CPG.

Also, as discussed in Section 2.3.1, investigations of laterite soil/gravel mixtures in the

SWWA show adsorption between approximately 0.4 and 1.4 mgP/g of soil over 5 weeks

(Weaver, Ritchie & Gilkes 1992). One would expect an adsorption capacity of the CPG no

greater than those of a soil:gravel mixture (Weaver, Ritchie & Gilkes 1992). Therefore, one

may suggest the short term adsorption capacity of the laterite material is somewhere between

approximately 0.08 and 1.4 mgP/g of CPG.

While practical constraints prevented further investigation into adsorption capacity, it is

recommended that future investigations into phosphorous retention by laterites include

experiments to allow determination of adsorption capacity. By using this value and the

phosphorous concentrations of the contaminated water, a lifespan of the CPG may be

determined.

5.1.5 Experiment 2 – variations in grain size

As discussed in Section 5.1.3, there were substantial differences in the concentration of

phosphorous in the water column between the replicates for Treatment A over the first five

days. There are a number of potential explanations for this unexpected result.



Interestingly, the final measurement at the conclusion of the experiment shows comparable

concentrations in the water column between Treatments with adsorption of approximately

82 %. The values for both treatments were within 1.2 % of each other, suggesting that grain

size does not effect adsorption in the long term.

This conclusion was not that which was expected when beginning the experiment. Sorption

sites for laterite gravel are only on the surface and within any cracks (Weaver, Ritchie &

Gilkes 1992). This implies that increasing the grain size would decrease the phosphorous

adsorption, as confirmed by a study by Weaver et al (1992).

However, in contrast to the study by Weaver et al (1992), cracked pea gravel was utilised for

these experiments. This would potentially increase the effective surface area of the grains,

thereby possibly making the size of the grains irrelevant. It should be noted however, that the

range of diameters tested was limited. Grain sizes used in this experiment were between a 6

and 12 mm diameter, a those were used in the GHD curtain trial (GHD 2007a). Regardless of

effective surface area, the limited differences in diameter did not give a large variation in

external surface area.

It would have been more appropriate to investigate smaller and larger grain sizes than those

tested; however these were not available. Crushing the CPG was not considered a viable

option as this would expose faces that would be of a different chemical nature than that of the

prepared faces. This would cause a different behaviour in regards to phosphorous adsorption,

skewing the results. It is recommended that future investigations should investigate a wider

range of grain sizes.


The overall reduction of phosphorous from the water column was greater than 68 % for all

treatments. The highest removal from the water column was approximately 81 % (Treatment

B, pH 4.6) followed by 77 % (Treatment A, pH 2.3). Treatment C had the highest initial pH

(10.6) but the lowest phosphorous adsorption. With the exception of one data point

(Treatment A, replica i, day 2) all replicates showed similar concentrations for each

measurement.



An investigation by Debnath & Mandal (1983) involved determination of phosphorous

retention changes for various soils when the soil was treated with lime (thereby changing the

pH). One type of soil studied was lateritic soil, where the pH was raised from approximately

5.0 to 7.0 and 7.5 (Debnath & Mandal 1983). The results showed that the amount of added

phosphorous that was bound to aluminium or iron decreased with an increasing pH (Debnath

& Mandal 1983). Liming (increasing the pH) causes colloidal hydrous oxides of iron and

aluminium to be precipitated, thereby minimising the adsorption of applied phosphorous

(Debnath & Mandal 1983).

The observed decrease in retention from Treatment B (pH 4.6) to Treatment C (pH 10.6) is

consistent with this study. However, a study by Liu et. al. (2002) on sediments contradicts

these findings. Liu et. al. (2002) found that for pH > 8, as pH increases, adsorption increases.

The explanation provided was that calcium was responsible for phosphorous adsorption at

high pHs (Liu et al. 2002). The high iron and alumninium content within the CPG may

therefore be the reason for the contradictory adsorption trend.

Liu et. al. (2002) also investigated lower pHs, showing that for pHs < 7, adsorption will

decrease with decreasing pH. In contrasts to results for higher pHs, these results are consistent

with observations for Experiment 3. Liu et. al. (2002) explains that the anion exchange rate

decreases with enhanced pH.


The treatments of varying salinity provided 50 to 67.5 % removal of phosphorous from the

water column. As salinity increased, phosphorous removal from the water column (that is,

phosphorous adsorption) decreased. These results align well with observations by Liu et. al.

(2002) and Sundareshwar & Morris (1999).

This trend is explained by investigating the number of available sorption sites. There are

significantly less sorption sites for phosphorous to bind to in a saline system (Sundareshwar &

Morris 1999) due to enhanced ionic strength and a higher rate of competition for sorption

sites (Liu et al. 2002). At high salinities, anions (such as chlorine, sulphate, hydroxide and

bromine) were in competition with the orthophosphate (Liu et al. 2002).




Low redox conditions

Unlike Experiments 1-4, Experiment 5 was designed to encourage microbial growth in order

to provide low redox conditions, indicated by the absence of oxygen. Unfortunately, the

resulting phosphorous measurements showed no statistically significant pattern. When

investigating the DO measurements for each sample, no correlation was found between the

length of time the sample bottles were sealed and DO concentration.

Unfortunately, this experiment did not produce low redox conditions as anticipated. It was

hoped that DO concentrations would reach values lower than those measured, however this

was not the case.

Trends in measured data

While the experiment did not produce the anticipated conditions, it was of interest to

investigate any possible relationships between DO and phosphorous adsorption. To do this,

the DO concentrations for the sealed bottles opened at 1, 3, 5 and 7 days were graphed against

percentage phosphorous adsorption (Figure 13, page 36). However, there was no apparent

correlation; suggesting DO in these ranges does not have an appreciable effect on

phosphorous adsorption.

To further investigate, all measured data points were plotted in this manner, regardless of

length of time sealed (Figure 14, page 36). Again, there was no correlation between

phosphorous and DO. This is illustrated by the plotted trendline, which shows an R2 value of

0.003, which indicates no correlation.

5.1.9 Laboratory results in combination

The laboratory trials showed that the minimum adsorption from the water column for CPG for

all experiments over seven days was 50 %. However, initial phosphorous concentration, pH

and salinity all affected the final percentage adsorption.

In particular, salinity appears to have the greatest effect, producing adsorptions as low as

50 % for Treatment C, the high salinity solution. Adsorption is shown to vary by a maximum

of 20 % for each treatment range. Regardless of this, the amount of adsorption is still at least



50 %. This shows that the laterite material is capable of achieving good adsorption capacity

over a large range of conditions that may be encountered in the environment.

5.2 Field trials

FRP and TP measurements for the blanket and curtain trials are discussed in the following

sections (Sections 5.2.1 and 5.2.2, respectively). Other parameters, such as pH, DO and

salinity are investigated in Section 5.3.

5.2.1 Blanket trial


The FRP measurements taken at the blanket trial site showed that the FRP concentrations

within the bores were greater than those of the surface waters. This was the case both prior to

and following the installation of the blanket. While the measurements at the bores are unlikely

to have been affected by the blanket, it could be expected that some change in FRP

concentration in the surface waters would indicate the effect of the blanket.

After installation of the blanket, a decrease in FRP was observed, however later in the trial

period concentrations increased. The cause for this result is unclear. The CPG appeared to

have no noticeable effect upon the FRP concentrations.

Total Phosphorous

When investigating the TP measurements, the bores were generally higher in concentration

than those of the surface waters. One exception was at the exit of the drain where, prior to

blanket installation, concentrations as high as 1.9 mgP/L were measured. These measurements

do not appear to vary seasonally when compared to data from previous years though a slight

increase can be seen.

As discussed in Section 2.2.2, TP consists of inorganic or organic and soluble or insoluble

components, with 90 % in the organic form (as shown in Figure 3). Since FRP measurements

for surface waters are usually less than 0.1 mgP/L, a significant proportion of the change in

TP is in response to a decrease in organic phosphorous (OP) concentration.



It cannot be definitively concluded that the decrease in phosphorous is entirely due to the

CPG. This is particularly relevant to TP, which contains a large proportion of OP. Many

biological processes may be responsible for changes in phosphorous (Wetzel 2001).

5.2.2 Curtain trial

In contrast to the blanket trials, bores were able to be placed both upstream and downstream

of the curtain containing mixtures of CPG and other materials. Comparing the measurements

of the two bores gives a better indication of the effect of the CPG than comparisons between

surface water and bores.

It must be remembered that the groundwater curtain contains different mixtures of materials

with different nutrient removal capabilities. Any results for the sections would reflect upon

the combined effect of all materials within the mixture. The relative importance of

components within the curtain for phosphorous removal is discussed where necessary.

Bore Levels

Bore levels for Section B indicated that groundwater was discharging into the drain, with two

exceptions where drain was recharging the groundwater. Similarly, bore levels for Section C

indicated discharge into the drain except for two dates, though these are not the same dates as

Section B. By contrast, the Extended Section of the curtain had approximately half of its

samples showing recharge into the groundwater from the drain.

The bore levels were utilised to determine the flow direction of the groundwater at the time

the phosphorous measurements were taken. This allowed the calculation of the difference

between upstream and downstream concentrations. It is assumed that observed flow directions

have been in place for a long enough time period to ensure that upstream samples contain

water that has not come into contact with the curtain while downstream samples contain water

that has passed though the curtain.

It must be acknowledged that these water level measurements provide a static picture of a

dynamic process, thereby not providing a complete indication of the flow regime. For

example, the static measurement does not indicate how long the flow has been moving in the

measured direction. If the above assumption is not valid for one or more data point (though

there is no way to determine this), results may be skewed. However, this assumption must be

made in order to determine the change in concentration across the curtain. One must therefore



be cautious when interpreting the results, and bear in mind the assumptions made to produce

the results.

For the most part, measurements taken at Sections B and C showed the same flow direction,

suggesting that the flow direction was reasonably consistant, discharging into the drain. In

contrast, the relatively high number of alterations between flow directions for Section C are of

some concern. There may therefore be a significant number of data points that have measured

concentrations of water that have or have not passed through the curtain, though it is assumed

that they have. This must be kept in mind when analysing the calculated changes in

concentrations, particularly in the case of the Extended Section.


Measurements in general

For all sections, the bores placed closest to the drain showed consistently lower FRP

concentrations throughout the study period. Bores furthest from the drain had more variable

concentrations, in some cases as low as the bore closer to the drain, other times much higher.

Interestingly, for the cases where flow was discharging into the drain, the corresponding

downstream concentrations did not have an increase in concentration. This may simply be due

to delays in water transport, or may show that the curtain is actively removing FRP from the

water.

Calculated changes in concentration using head differences

The FRP measurements for Sections B and C showed decreases in concentration, though there

were some exceptions. For example, Section B had one notable increase on 29/09/05, which

corresponded to the sample day on which the surface water was recharging the groundwater.

However, the corresponding head difference was only 0.5 cm, indicating that a change in flow

direction had recently or was soon to occur. This data point is therefore not reliable.

An increase in FRP also occurred in Section C on 01/03/07. This corresponds to the sample

day which had an extreme head difference. This was the only instance where Bore 09

concentration increased above approximately 0.015 mgP/L, almost doubling in value. The

relatively high head differences and change in concentration indicates that an unknown

situation not seen in the other data points may have influenced this reading.



Changes in FRP for the Extended Section of the curtain were shown to follow the

concentration of Bore EB2, the bore furthest from the drain, with three exceptions. As stated

above, this section of the curtain appeared to experience regular changes in flow direction,

making the underlying assumptions regarding upstream and downstream measurements less

reliable.

From the available data, Sections B and C do appear to have a reduction in FRP between

downstream and upstream bores. Without a more detailed knowledge of the changes in flows

experienced in the Extended Section, no conclusions may be drawn for this section; though

the materials in this section are the same as those in Section B.

Measurements prior to installation of curtain

In order to determine whether the observed reductions in FRP at Sections B and C are due to

the presence of the curtain materials, measurements must be compared to those undertaken

prior to the curtain installation. Measurements prior to curtain installation were undertaken at

Section B. Unfortunately only one measurement was undertaken at Section C prior to

installation, providing no basis for comparison. However, general trends observed at Section

B indicate what trends would have been observed at Section C had measurements been taken.

As mentioned previously, measurements at Section B were undertaken by two sets of bores,

the first set replaced once damaged. The curtain was installed between sampling points 5 and

6 of the 9 sampling points for the original bores. The data shows greater FRP concentrations

for the measurements taken at the original bores than those taken at the replacement bores.

That is, the bore closest to the drain decrease in FRP concentrations from 0 – 0.5 to 0 – 0.2

mgP/L while the bore furthest decreases from 0.07-0.16 to 0 – 0.05 mgP/L.

These decreases are subsequently reflected in FRP differences between upstream and

downstream values. Such differences in measurements imply that the two sets of bores cannot

be directly compared to each other. However, it can be seen that both prior to and following

installation of the curtain, there is a decrease in FRP concentrations between the upstream and

downstream bores. Without data which may be directly compared, one cannot determine

whether the presence of the curtain had any notable effect on the decrease in concentration of

FRP.



Total Phosphorous

Measurements in general

TP measurements for all bores were erratic for all three groundwater sections, particularly

Section B; though TP concentrations for Section B only ranged between 0.1 and 0.9 mg/L

while Section C and the Extended Section had concentrations between 0 and 2.6 mg/L.

Similar to FRP measurements at section B, the original bores show a different trend than that

of the replacement bores. While the original bores show a decreasing trend after installation,

the replacement bores give highly erratic measurements at concentrations higher than most

samples taken for the original bores. Again, it is difficult to directly compare these values,

though the general trends may be compared.

Changes in concentrations before and after curtain installation

Interestingly, the concentration differences between the upstream and downstream

measurements at Section B are positive prior to the installation of the curtain. The only

exception to this is that of the measurement taken on 29/09/05 which, as mentioned

previously, only had a head difference between the bores of 0.5 cm, casting doubt on the

validity of this data point. However, upon installation of the curtain, both the original bores

and the replacement bores provided measurements that imply a general decrease in TP

concentration across the curtain.

In contrast, measurements undertaken at Section C show most sample days have an increase

in TP concentration across the span of the curtain. Unfortunately, there is only one data point

at this section prior to the curtain installation. However, one may assume that TP followed the

same trend as measurements taken at Section B, prior to installation. That is, increasing TP.

This implies that TP follows the same general trend before and after installation of the Section

C curtain, though no direct comparisons of TP concentrations can be made.

Calculated changes in TP for the Extended Section vary widely. This may again be attributed

to the assumptions made when determining upstream and downstream bores. Therefore, these

results are not studied further.



Components of TP affected

As mentioned previously, TP contains a large proportion of OP (Section 2.2.2, Figure 3).

Observed changes in FRP are only small amounts, therefore for increases and decreases in

TP, there must be some change in the concentration of OP.

An increase in OP content of the pore water occurs for a normal, no curtain situation and also

for a curtain mixture of CPG and Spearwood sand. However, in the presence of a mixture of

CPG and sawdust, a decrease in OP occurs.

Investigation of reasons for observations

While it is difficult to determine the exact trigger of the differing trends, the presence of CPG

in both curtains shows that it is not the direct cause of the changes in OP concentrations,

though its presence in combination with other mixtures in the curtain can not be disregarded

as a possible mechanism. The known differences between the two curtain mixtures are that

Curtain B has sawdust in addition to CPG and that Curtain C has Spearwood sand in addition

to CPG.

The sawdust is used to reduce nitrogen concentrations (GHD 2007a). This is achieved through

denitrification, where the sawdust is used as a carbon source (Blowes et al. 2000; Schipper &

Vojvodic-Vukovic 2000). Denitrification will generally occur in anaerobic conditions

(Schipper & Vojvodic-Vukovic 2000; Blowes et al. 2000). It is also known that anaerobic

conditions will result in release of phosphorous from the sediment (Hart et al. 2003; Gomez et

al. 1999). However, investigations of DO concentrations for both curtains showed that while

concentrations did fluctuate between 0 and 4 mg/L, both curtains were in the same range,

implying that both systems should show the same TP trends if it is the cause of the TP

changes. Hence, anaerobic conditions do not appear to be the cause of the change in TP.

Spearwood sand has some moderate phosphorous removal capacity through sorption (Cheung

& Venkitachalam 2006) and is used in Section C to assist in removal of phosphorous. The

most notable difference between Sections B and C is microbial activity. While Section C

contains materials which work through sorption processes, Section B has sawdust which

encourages microbial activity. It is suggested that this is the most likely cause of OP

concentration decreases.



Curtain Mixtures

The curtain trial was intended to decrease nutrient concentrations entering the drain through

the use of various mixtures capable of removing phosphorous or nitrogen from the water

column through various processes. The trial therefore consisted of different mixtures of

materials. This makes it somewhat difficult to determine the relative effect of each material

upon the nutrient concentrations.

As a result, no definitive results were found for the phosphorous removal capability of the

CPG, though Section B appears to lower TP concentrations significantly. This was

unexpected, as denitrification occurs in anaerobic conditions (Schipper & Vojvodic-Vukovic

2000; Blowes et al. 2000), while phosphorous is known to be released in anaerobic conditions

(Hart et al. 2003; Gomez et al. 1999).

5.3 Laboratory and field results in combination

When deciding whether to use CPG gravel in the field, the range of conditions that the CPG

will be subjected to and whether it is appropriate to use CPG must be considered. Laboratory

results show that for a broad range of pHs, salinities and initial phosphorous concentrations,

the phosphorous adsorption will vary. However, these variations were a maximum of 20 %

across extreme ranges which would normally not be experienced within a natural

environment.

In contrast the, field trials were undertaken in a region with relatively discrete pH, salinity and

initial concentrations compared to the laboratory investigations: water concentrations reached

a maximum of 0.1 mgP/L; the salinity reached a maximum of 1.67 ppt; the pH ranged from

4.6 to 9.

Both the initial phosphorous concentration and the salinity were within concentrations which

showed the highest adsorption for that parameter. The pH ranges between the highest and

lowest adsorption, though the laboratory results only ranged by approximately 15 %.

Unlike controlled laboratory experiments, the field trials contain a number of variables which

cannot be monitored for practical or financial reasons. As a result, it is expected that

adsorption of phosphorous by CPG in the field may, while following the same trend, provide

relatively different absorbance values. Unfortunately, analysis of the provided field results



proved inconclusive for phosphorous adsorption by CPG, giving no basis for comparison of

phosphorous removal.

5.4 Recommendations for use in the field

The following table is a summary of the conditions tested within the laboratory. All

conditions which showed adequate phosphorous removal were given a tick. The greater the

number of ticks, the more appropriate the CPG is as an adsorption agent.

Table 19. Recommendations for use of cracked pea gravel in the field

Condition Variable

Low Moderate High Comments

Initial orthophosphate concentration

0.04 mgP/L

0.40 mgP/L

4.00mgP/L

Trend is from low to high concentration. Lifespan of laterite would be greatest for lower concentrations

Grain size 6-8 mm

-- 10-12 mm

Do noticeable difference. Investigations required for other grain sizes

pH ~2

~5

~10

Most appropriate for middle pHs. Competition with anions increases with increasing pH. Decrease in anion exchange rate with decreasing pH.

Salinity ~1ppt

~15 ppt

~40 ppt

Appears to have greater effect on adsorption than pH and initial phosphorous concentration) Competition with other anions increases with increasing salinity. Life span would be greatest for lower salinities.

Redox conditions

Anaerobic --

Aerobic

Laboratory tests inconclusive, however literature suggests anaerobic environments not suitable for p adsorption in many sediments (see below for more information)

Of these variables, salinity appears to have had the greatest effect upon phosphorous

adsorption, while initial phosphorous concentration and pH had moderate effect and the

measured grain sizes had no effect.

While the redox experiment did not produce redox conditions low enough to give valuable

results, this parameter has been included within the table. Low redox conditions imply no

oxygen is present (anaerobic conditions) and are, for the present, not recommended due to

arguments presented in section 2.1.7. Further investigations regarding redox conditions are

required before this may be decided definitively.



Analysis of the field data was unable to provide additional information in regards to CPG in

isolation from other nitrogen and phosphorous reducing materials. Therefore, at the present

they have had little impact upon the above recommendations for use, though future field

experiments may have a substantial contribution.



6.0 Conclusions

6.1 Laboratory and field results

Laboratory investigations showed that, pH, salinity and initial phosphorous concentration do

have an effect upon phosphorous adsorption by laterites. In each case, subjecting laterite

material (in the form of cracked pea gravel) to a broad range of values resulted in a maximum

of 20 % difference in adsorption. By contrast, grain size has no effect on adsorption.

Importantly, all experiments and their corresponding treatments provided a minimum of 50 %

adsorption of phosphorous from the water column.

Field trials conducted by GHD investigated a range mixtures of materials for both

phosphorous and nitrogen removal. While results did show some effect upon both Filterable

Reactive Phosphorous and Total Phosphorous concentrations, results were inconclusive as to

the relative contribution of laterite material in causing these changes. These results therefore

provided no basis for comparison of phosphorous removal between laboratory and field

investigations.

6.2 Recommendations for use

The following table is a summary of the recommendations for use of cracked pea gravel. All

conditions which showed adequate phosphorous removal were given a tick. The greater the

number of ticks, the more appropriate the cracked pea gravel is as an adsorption agent.

Table 20. Summary of recommendations for use of cracked pea gravel in the field

Condition Variable

Low Moderate High

Initial orthophosphate concentration

0.04 mg/L

0.40 mg/L

4.00 mg/L

Grain size 6-8 mm

-- 10-12 mm

pH ~2

~5

~10

Salinity ~1ppt

~15 ppt

~40 ppt

Redox conditions Anaerobic

-- Aerobic



7.0 Limitations and recommendations of project

7.1 Limitations

7.1.1 Limitations of laboratory experiments

The laboratory experiments presented in this dissertation were intentionally basic and few in

number due to budget and time restraints. This results in associated limitations. Such

limitations are outlined within the table below, and have been discussed where appropriate

throughout this dissertation.

Table 21. Limitations of laboratory experiments

Limitation Short Explanation

Phosphorous concentration determination

The method employed was through use of phosphorous powder pillows and HACH 3000. This restricted concentration readings to those greater than 0.02 mgP/L.

Shaking regime

Continuous shaking is recommended, daily mixing was undertaken. This may have produced concentration gradients which could limit uptake.

Number of replicates

Resource restrictions limited the number of replicates for each treatment to two. A larger number of replicates would have given a greater understanding of what was occurring during the first few days of the experiments where replicate concentrations were not in agreement. Also, error calculations for experiments would have been possible with greater than three replicates.

Scale of experiments

Bench experiments were of a relatively small scale. Larger scales may have limited differences in measured concentrations between replicates. Experiments may also be performed on whether the scale of the experiment affects the adsorption.

Regardless of these limitations, the Experiments 1-4 produced significant results. While some

of the aforementioned limitations may have produced more accurate values, also significantly

increasing the cost, the recorded results are significant in showing that CPG has significant

phosphorous adsorption capacity over a broad range of conditions.

In contrast, Experiment 5 did not produce significant results. DO measurements were made as

a proxy to redox conditions. It was assumed that no oxygen within the system signified low

redox conditions where oxidation of iron may occur. However, in order to measure the DO,

the samples had to be exposed to the atmosphere. While DO measurements were taken

immediately upon opening and care was taken to keep the samples undisturbed, this would

have affected the results to some extent, and provide misleading information as to the redox

condition.



7.1.2 Limitations of field trials

While field trials provide a greater understanding of how CPG may behave within the field,

the major limitation is in the measurement and interpretation of parameters of interest. Some

examples of such limitations encountered with the field trails are discussed where appropriate

throughout this dissertation. A summary is provided in Table 22, below. Due to the these

limitations, field data provided less conclusive results for phosphorous retention by laterites

than anticipated.

Table 22. Limitations of field trials

Limitation Short Explanation

Measurements prior to

installation

Measurements prior to installation of the blanket/curtain are essential to determine what effect the treatment has had upon the system. Unfortunately, measurements taken prior to curtain installation cannot be directly compared to those following its installation, as these bores were damaged and replaced. While general comparisons were still made, analysis was limited.

Sampling Regime

Measurements were taken on a monthly basis. However, temporal variation of concentration and flows may not be of this timescale, and may result in misinterpretation of the gathered data.

Missing data points

In some instances, sampling days do not have data points. It is assumed that this is due to miss-sampling. Missing data points resulted in a smaller number of data points for analysis.

Understanding of flow

direction

Water level measurements provide a static picture of a dynamic process. Head differences detail the flow direction for that time, but do not provide insight into the whether the flow has been constant or whether it has been interchanging directions. Flow direction is a major tool used to determine upstream and downstream concentrations for bores. It is assumed that measured gradients have been in place for a long enough time period to ensure that upstream samples contain water that has not come into contact with the curtain while downstream samples contain water that has passed though the curtain. If this underlying assumption for a sampling day is wrong, the results are skewed.

Mixtures of materials

This project is focused upon phosphorous retention by laterites. While mixtures of materials provide important information in regards to nutrient removal through any means, the addition of other materials that may effect phosphorous concentrations directly or indirectly inhibits attempts to determine the phosphorous removal capacity of the laterite material alone.

7.2 Future recommendations

7.2.1 Future investigations for phosphorous retention by laterites

The laboratory experiments and analysis of field data presented in this dissertation provided

an early contribution to the investigation of phosphorous retention by laterites. Limitations (as

discussed in Section 7.1) and time constraints have prevented further investigation into this



area. Table 23 is a summary of future investigations or recommendations that have been

briefly mentioned throughout the dissertation where appropriate.

Table 23. Future recommendations

• Improved level of accuracy in phosphorous concentration analysis (particularly at <0.04 mg/L) • More replicates (which would also allow errors to be calculated) • Investigate larger scale experiments

general experimental procedure

• Increase frequency of mixing for experiments • Investigate alternative methods of producing low redox conditions redox conditions • Utilise alternative methods of measuring low redox conditions • Investigate a wider range of grain sizes • Investigate the addition of heavy metals or other nutrients

Laboratory investigations

further bench tests which may be of interest • Investigate flowthrough situations rather than

stagnant water further analysis of current data

• Investigate and compare phosphorous reductions compared to Sections A and D (not containing CPG) • Trail CPG alone (no mixtures) Field trials

future investigations • Alter sampling regimes for field trials* *In order to gain a greater understanding of flows and concentration changes, it is important to regularly monitor the site at a small enough time scale. However, it is understood that this may not be economically viable. One suggestion would be to have periods of intense sampling where measurements are taken on a much smaller timescale. For example, a two week period of daily sampling per season may provide a better representation of the flow and concentration variations that are typical for that season.



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Appendices

Contents

Appendices .............................................................................................................................. 77 Appendix A. Laboratory experimental................................................................................. 79

Instrument specifications.................................................................................................. 79 Experimental .................................................................................................................... 79

Appendix B. Field trials ....................................................................................................... 84 Instrument specifications.................................................................................................. 84 Field trial blueprints ........................................................................................................ 84 Raw data for field experiments......................................................................................... 87

Tables

Table A. 1. Preliminary test readings....................................................................................... 79

Table A. 2. Control results ....................................................................................................... 80

Table A. 3 Experimental data for Experiment 1 ...................................................................... 81

Table A. 4. Experimental Data for Experiment 2 .................................................................... 81

Table A. 5 Experimental Data for Experiment 3 ..................................................................... 82

Table A. 6. Experimental data for Experiment 4 ..................................................................... 82

Table A. 7. Experimental data for Experiment 5 ..................................................................... 83

Table B. 1. Raw data for Bore 1, blanket trial ......................................................................... 87

Table B. 2. Raw data for Bore 2, blanket trial ......................................................................... 87

Table B. 3. Raw data for Surface Entry Point, blanket trial..................................................... 88

Table B. 4. Raw data for Surface Exit Point, blanket trial ....................................................... 88

Table B. 5. Raw data for Bore 01, curtain trial ........................................................................ 89

Table B. 6. Raw data for Bore 01a, curtain trial ...................................................................... 89


Table B. 8. Raw data for Bore 03a, curtain trial ...................................................................... 90


Table B. 10. Raw data for Bore 12, curtain trial ...................................................................... 91

Table B. 11. Raw data for Bore EB1, curtain trial ................................................................... 91

Table B. 12. Raw data for Bore EB2, curtain trial ................................................................... 92

Table B. 13. Head differences for Section B, Section C and Extended Section of curtain trial.................................................................................................................................................. 92



Figures

Figure B. 1 Patterson Road Sub-Branch Drain Blanket Trial (GHD 2007b)........................... 85

Figure B. 2 Abernathy Road Sub-Branch Drain Curtain Trail (GHD 2007a) ......................... 86



Appendix A. Laboratory experimental

Instrument specifications

Laterite material utilised was cracked pea gravel (CPG) with diameters of 6-12 mm, which

was obtained from GHD. This material is the same that was used in the curtain field trial

(GHD 2007a).

Phosphorous measurements were conducted using a HACH 3000 spectrophotometer. The

procedure followed was Method 8048 - Phosphorous, reactive (also called orthophosphate)

PhosVer 3 (Ascorbic Acid) Method (Powder Pillows); measuring 0-2.00 mgPO4/L. Results

were converted to mgP/L for consistency purposes.

PhosVer3 phosphate reagent powder pillows for a 25 mL sample were used and dilutions

were made where necessary (Experiment 1, Treatment C only). It is noted that blank solutions

ranged from 0.00 to 0.02 mg/L on the spectrophotometer. As a result, any measurements

made within this region were assumed to have a concentration of 0.00 mg/L.

pH measurements were conducted using a TPS unit probe (dual pH–mV meter; WP-80D).

Salinity readings were conducted using a TPS unit probe (pH-Conductivity-Salinity; WP-81).

DO measurements were conducted using a TPS unit probe (AQUA-DO2; dissolved oxygen –

temp. meter, version 1.0).

Experimental

Preliminary observations

10.0g CPG was placed in 250mL distilled water. Readings of pH, salinity and phosphorous

concentrations were tested. Table A. 1 shows the results. Table A. 1. Preliminary test readings

Parameter Units Measurement salinity ppt 0.021

pH -- 6-6.5 phosphorous mg/L 0 (below detection)



Pre-treatment – for all experiments

10.0 g of CPG was rinsed twice with tap water. The CPG was then rinsed twice with

deionised water and once with 0.1 mol/L HNO3. The resulting gravel was subsequently rinsed

twice with deionised water.

Controls

Control 1

10g CPG and 5 drops of toluene were placed in 250 mL of a 0.1 mol/L brine (NaCl) solution.

Samples were left open to the atmosphere at ambient temperature and shaken daily. Periodic

phosphorous tests produced the results shown in Table A. 2. Table A. 2. Control results

Phosphorous concentration (mgP/L) Time

(days) Control 1 (absence of phosphorous - deionised water used)

Control 2 (absence of CPG)

0 0 0.25 1.13 0 -- 2.21 0 -- 3.92 0 -- 6.33 -- 0.24 6.63 0 --

Control 2

5 drops of toluene were placed in a 250 mL solution of 0.25 mgP/L and 0.1 mol/L brine

(NaCl). Samples were left open to the atmosphere and shaken daily. Phosphorous tests

produced the results also shown in Table A. 2.

Experiment 1 – variations in initial phosphorous concentrations

CPG (10g each) was added to six sample bottles. 250 mL solutions containing known

phosphorous concentrations (as shown in Table A. 3) and 0.1 mol/L brine (NaCl) were added

to each bottle. Each bottle was dosed with toluene (5 drops) to suppress microbial activity and

bottles were left open at ambient temperature. Samples were shaken daily and phosphorous

concentrations were measured periodically over seven days (also shown in Table A. 3).



Table A. 3 Experimental data for Experiment 1

Treatment A Treatment B Treatment C i ii i ii i ii Phosphorous concentration

(mgP/L) 0.04 0.04 0.40 0.40 4.00 4.00

Time (days) Water column phosphorous concentration (mgP/L)

0.00 0.040 0.040 0.400 0.400 4.000 4.000 1.13 0.016 0.021 0.093 0.083 1.600 1.480 2.21 0.006 0.016 0.077 0.048 1.200 1.258 3.92 0.000 0.000 0.027 0.026 0.992 1.024 6.63 0.000 0.000 0.019 0.026 0.800 0.960

Experiment 2 – variations in grain size

CPG (10g each) of different grain sizes (as detailed in Table A. 4) was added to four sample

containers and a 250mL solution containing 0.40 mgP/L of phosphorous and 0.1 mol/L NaCl

added. Each sample was dosed with 5 drops of toluene to suppress microbial activity.

Samples were left open to the atmosphere at ambient temperature and shaken daily and

phosphorous concentrations were taken periodically over seven days (also shown in Table A.

4).

Table A. 4. Experimental Data for Experiment 2

Treatment A Treatment B i ii i ii Grain size

(from 6-12mm mixture)

Small grain (~6-8 mm)

Small grain (~6-8 mm)

Large grain (~10-12 mm)

Large grain (~10-12 mm)


0.00 0.400 0.400 0.400 0.400 0.21 0.336 0.248 0.230 0.218 0.88 0.304 0.200 0.173 0.173 1.40 0.262 0.160 0.162 0.157 5.04 0.178 0.107 0.096 0.101 7.92 0.075 0.070 0.074 0.072

Experiment 3 – variations in pH

CPG (10g each) was placed in 6 sample bottles and a 250 mL solution of phosphorous (0.40

mgP/L) and brine (0.1 mol/L) with various pH’s (shown in Table A. 5) was added.

Concentrated sodium hydroxide (NaOH) or nitric acid (HNO3) solutions were added

accordingly to produce the required pHs. Toluene (5 drops) was also added to prohibit

microbial activity and the bottles were left open to the atmosphere at room temperature. The



sample bottles were shaken daily and phosphorous concentrations and the pH were

periodically measured over seven days (as detailed in Table A. 5).

Table A. 5 Experimental Data for Experiment 3

A B C i ii i ii i ii Initial pH 2.3 2.3 4.6 4.6 10.6 10.6


0.00 0.400 0.400 0.400 0.400 0.400 0.400 0.42 0.224 0.230 0.229 0.224 0.222 0.256 1.92 0.246 0.152 0.158 0.136 0.219 0.224 4.08 0.099 0.101 0.102 0.096 0.171 0.165 7.00 0.094 0.090 0.072 0.069 0.122 0.126

pH reading 0 2.3 2.3 4.6 4.6 10.6 10.6

1.91 2.4 2.4 5.0 5.0 8.7 8.7

Experiment 4 – variations in salinity

CPG (10g each) was placed in six sample bottles each with a 250 mL solution of phosphorous

(0.25 mgP/L) and NaCl (various concentrations as detailed in Table A. 6). Toluene (5 drops)

was added to suppress microbial activity. Samples were left open to the atmosphere at room

temperature and shaken daily and phosphorous concentrations and salinity were measured

periodically over seven days (as shown in Table A. 6).

Table A. 6. Experimental data for Experiment 4

A B C Components i ii i ii i ii Salinity (ppt –

parts per thousand)

1 1 15 15 40 40

Time

(days) Water column phosphorous concentration (mgP/L)

0.00 0.246 0.246 0.246 0.246 0.246 0.246 1.08 0.170 0.162 0.179 0.173 0.179 0.171 3.27 0.104 0.102 0.126 0.114 0.128 0.125 6.33 0.080 0.083 0.090 0.094 0.122 0.123

Salinity (ppt)

0 1.1 1.2 15.5 16.5 42.2 42.6 1.08 1.1 1.1 15.7 16 42.2 42.5 6.33 1.25 1.15 16.6 16.9 36.9 36.8



Experiment 5 – variations in redox conditions

CPG (10g each) was placed in ten sample bottles, each with 250 mL solution of phosphorous

(1.22 mgPO4/L) and 0.1 mol/L NaCl. Samples were left open to the atmosphere at room

temperature and shaken daily. After seven days, phosphorous measurements were taken and a

nitrogen source (NH4Cl, 0.1gN/L) (following Sponza & Atalay 2005; Hollender et al. 2002)

and carbon source (D-glucose, 0.5 gC/L) (following Hollender et al. 2002; Sponza & Atalay

2005; Kargi & Uygur 2003) added to each sample bottle to encourage microbial activity.

Two bottles were left open while eight were sealed. All samples were shaken daily. Two

sealed containers each, were opened at 1, 3, 5 and 7 days. Upon opening, DO and

phosphorous concentrations were measured. Table A. 7 shows a summary of concentrations

and DO readings.

After being tested, all sealed containers were resealed and retested at the conclusion of the

experiment time period.

Table A. 7. Experimental data for Experiment 5

Phosphorous concentration in water column in mgP/L; (DO in mg/L) Time (days) 1 2 3 4 5 6 7 8 9 10

0.0 0.390 0.390 0.390 0.390 0.390 0.390 0.390 0.390 0.390 0.3907.0 0.102 0.123 0.096 0.112 0.123 0.102 0.106 0.112 0.096 0.109

-- Left Open

Left Open Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed

8.0 -- -- 0.080 (2.3)

0.080 (1.9) -- -- -- -- -- --

10.0 0.110 0.091 -- -- 0.110 (0.4)

0.080 (0.8) -- -- -- --

12.0 -- -- -- -- -- -- 0.093 (1.4)

0.083 (0.6) -- --

14.0 0.117 (3.0)

0.083 (2.8)

0.101 (0.8)

0.109 (0.2)

0.122 (0.8)

0.086 (1.1)

0.078 (1.6)

0.083 (0.9)

0.096 (0.2)

0.078 (0.5)



Appendix B. Field trials

Instrument specifications

In-situ measurements were taken using a multi-parameter water quality metre. Laboratory

measurements were undertaken by ALS laboratories.

Field trial blueprints

The following figures (Figure B. 1 and Figure B. 2) show the general layout of the Paterson

Road Sub-branch Drain blanket trial and the Abernathy Road Sub-branch Drain curtain trial.

Both Drains are within the MSMD system, their locations shown in Figure 5 (page 16).

Construction of the blanket occurred on 18/05/2006, while measurements were undertaken

from 05/01/2006.

Construction of sections A and B of the curtain occurred on 20/12/2005 and construction of

Sections C, D and extended section of the curtain occurred on 19/05/2006. Measurements of

nutrients and other parameters started on 07/07/2005.



Figure B. 1 Patterson Road Sub-Branch Drain Blanket Trial (GHD 2007b)



Figure B. 2 Abernathy Road Sub-Branch Drain Curtain Trail (GHD 2007a)



Raw data for field experiments

The data provided below the proportion of the data collected by GHD for the curtain and

blanket trials (GHD 2007b; GHD 2007a) which was utilised within this dissertation.

Blanket trial

Table B. 1. Raw data for Bore 1, blanket trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

28/02/06 0.87 0.840 22.59 1.47 1.14 6.71 31/03/06 0.63 0.480 23 0.8 0.44 6.2 10/04/06 0.63 0.570 22.87 1.45 0.97 6.67 11/05/06 0.6 0.540 22.48 1.41 0.38 6.7 08/06/06 0.81 0.600 20.7 0.4 3.81 6.59 13/07/06 0.99 0.260 19.8 0.97 0.96 6.33 22/08/06 0.98 0.580 17.67 0.43 5.13 6.74 26/09/06 0.78 0.590 19.28 1.18 0.28 6.82 07/11/06 0.34 0.300 20.6 -- 3.03 -- 05/12/06 0.84 0.0015 21.3 1.16 0.32 6.67 19/12/06 0.54 0.410 21.64 0.65 1.21 6.45 31/01/07 0.76 0.728 23.4 -- 1.81 6.75 15/02/07 0.94 0.884 24.29 0.46 0.11 6.55 01/03/07 0.77 0.749 25.97 1.37 1.14 7.12 14/03/07 1.1 0.828 24.22 0.47 0.29 6.7 28/03/07 0.9 0.879 23.83 0.45 2.32 6.66 11/04/07 0.9 0.908 23.94 0.41 2.24 6.56 26/04/07 0.95 0.945 23.02 0.46 1.82 6.88

Table B. 2. Raw data for Bore 2, blanket trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

28/02/06 0.26 0.180 25.65 1.67 1.87 6.6 31/03/06 0.2 0.200 25.2 1.5 0.63 6.52 10/04/06 0.23 0.130 24.62 1.65 1.71 6.7 11/05/06 0.23 0.100 23.32 1.5 1.28 6.77 08/06/06 0.34 0.075 27.15 1.48 3.81 6.91 13/07/06 0.24 0.590 20.52 1.57 1.4 6.42 22/08/06 0.39 0.280 18.48 1.36 2.43 6.68 26/09/06 0.25 0.210 19.39 1.33 0.72 6.71 07/11/06 -- -- -- -- -- -- 05/12/06 0.2 0.0015 22.78 1.37 0.91 6.64 19/12/06 0.24 0.210 22.75 1.43 1.14 6.65 31/01/07 0.22 0.187 25.8 2.34 6.76 15/02/07 0.28 0.240 26.31 1.39 1.3 6.87 01/03/07 0.23 0.182 23.62 1.07 0.48 7.03 14/03/07 0.5 0.123 26.28 1.39 0.43 6.8 28/03/07 0.26 0.149 26.11 1.44 3.13 6.7 11/04/07 0.37 0.154 25.78 1.46 1.63 6.81 26/04/07 0.21 0.196 24.68 1.28 1.24 7.02



Table B. 3. Raw data for Surface Entry Point, blanket trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

05/01/06 0.096 0.041 19.76 0.38 16.1 7.2 28/02/06 0.15 0.072 28.49 0.16 6.27 6.72 31/03/06 0.24 0.130 20.7 0.4 5.87 5.98 10/04/06 0.16 0.098 21.22 0.44 3.85 6.76 11/05/06 0.11 0.100 18.7 0.45 2.72 6.65 08/06/06 0.25 0.130 15.3 0.44 6.18 7.34 13/07/06 0.11 0.048 10.22 0.39 5.16 6.91 22/08/06 0.07 0.024 17.26 0.12 8.17 7.16 26/09/06 0.11 0.023 19.7 0.33 7.91 6.86 07/11/06 0.75 0.023 24.16 -- 26.14 8.55 05/12/06 0.38 0.0015 27.74 0.15 13.22 8.51 19/12/06 0.23 0.030 24.37 0.23 4.38 7.2 31/01/07 0.24 0.005 26.8 -- 2.98 7.45 15/02/07 0.17 0.035 24.13 0.33 4.3 7.96 01/03/07 0.22 0.085 22.68 0.43 8.01 8.23 14/03/07 0.28 0.005 21.73 0.49 1.14 7.7 28/03/07 0.2 0.033 15.98 0.53 5.14 7.67 11/04/07 0.16 0.089 18.18 0.5 0.98 7.76 26/04/07 0.13 0.064 17.66 0.13 1.29 7.05

Table B. 4. Raw data for Surface Exit Point, blanket trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

05/01/06 0.19 0.110 21.43 0.43 17.6 7.18 28/02/06 1.6 0.370 23.9 0.39 4.78 6.64 31/03/06 0.65 0.027 15.4 0.4 7.56 5.88 10/04/06 0.81 0.069 21.98 0.49 0 8.75 11/05/06 1.9 0.031 12.24 0.45 8.77 7 08/06/06 0.13 0.085 10.99 0.45 9.37 6.54 13/07/06 0.07 0.022 9.07 0.37 7.82 6.24 22/08/06 0.04 0.0015 17.15 0.06 9.37 7.73 26/09/06 0.05 0.025 19.92 0.36 12.85 6.98 07/11/06 0.098 0.033 27.11 -- 11.43 8.02 05/12/06 0.08 0.0015 28.9 0.49 16.76 8.26 19/12/06 0.29 0.080 26.48 0.48 12.14 7.59 31/01/07 0.1 0.005 30.7 14.25 8.8 15/02/07 0.06 0.016 26.35 0.5 12.5 8.99 01/03/07 0.09 0.073 23.33 0.31 8.03 8.41 14/03/07 0.42 0.005 21.45 0.6 0 7.65 28/03/07 0.31 0.016 14.33 0.66 2 7.98 11/04/07 0.3 0.118 17.78 0.44 1.18 7.5 26/04/07 0.52 0.257 16.71 0.28 1.85 7.15



Curtain trial

Table B. 5. Raw data for Bore 01, curtain trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

22/07/05 0.9 0.021 20.35 -- 0.6 6.29 24/08/05 0.72 0.016 20.8 -- 0.6 6.42 29/09/05 0.34 0.056 20.19 0.21 0 6.23 28/10/05 0.34 0.041 20.27 0.19 0.4 6.63 14/11/05 0.18 0.0015 24.2 0.43 3.5 6.09 05/01/06 0.093 0.0015 25.21 0.23 2.27 5.93 22/02/06 0.08 0.005 23.85 0.2 0.25 6.5 14/03/06 0.41 0.0015 24.85 0.23 2.13 6.27 07/04/06 0.12 0.0015 22.06 0.3 2.69 6.3

Table B. 6. Raw data for Bore 01a, curtain trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

07/04/06 0.15 0.0015 20.95 0.4 0.42 6.47 10/05/06 0.52 0.0015 20.72 0.23 0.72 6.26 07/06/06 0.29 0.0015 20.35 0.29 0.58 6.03 12/07/06 0.6 0.0015 18.89 0.2 2.25 6.34 21/08/06 0.55 0.0015 19.27 0.21 0.51 6.72 22/09/06 0.37 0.019 20.39 0.15 0.61 6.6 24/10/06 0.33 0.0015 21.7 0.23 0.57 6.17 29/11/06 0.15 0.009 22.34 0.14 1.51 6.61 19/12/06 0.5 0.005 22.39 0.1 0.26 6.35 31/01/07 0.91 0.005 24.63 0.15 1.15 6.75 15/02/07 0.24 0.005 23.74 0.14 0 7.08 01/03/07 0.45 0.005 24.81 0.16 2.48 6.8 14/03/07 0.43 0.005 24.07 0.15 2.97 6.95 28/03/07 0.4 0.005 24.04 0.15 2.58 6.85 11/04/07 0.3 0.005 23.31 0.17 1 6.71


Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

22/07/05 0.42 0.082 21.5 -- 2.6 6.46 24/08/05 0.38 0.071 21.34 -- 2.2 6.42 29/09/05 0.17 0.11 20.66 0.24 0.4 6.44 28/10/05 0.16 0.11 20.66 0.29 2.3 6.91 14/11/05 -- -- 23.08 0.28 0.3 6.4 05/01/06 0.26 0.14 25.13 0.25 1.29 6.28 22/02/06 0.26 0.16 23.24 0.22 0.25 6.54 14/03/06 0.22 0.13 23.58 0.21 2.23 6.25 07/04/06 0.19 0.096 24.1 0.19 3.37 6.7



Table B. 8. Raw data for Bore 03a, curtain trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

22/02/2006 -- -- 23.93 0.18 0.24 6.21 14/03/2006 0.27 0.026 24.22 0.23 1.68 6.13 7/04/2006 0.12 0.018 22.42 0.24 1.06 6.26

10/05/2006 0.85 0.03 21.27 0.2 0.65 6.51 7/06/2006 0.44 0.025 19.7 0.23 1.08 6.26

12/07/2006 0.67 0.036 18.89 0.16 1.68 6.32 21/08/2006 0.58 0.008 19.21 0.16 0.27 6.18 22/09/2006 0.36 0.024 20.09 0.15 0.67 6.15 24/10/2006 0.7 0.0015 21.04 0.13 0.81 6.09 29/11/2006 0.24 0.02 21.99 0.11 1.97 6.13 19/12/2006 0.57 0.03 24.67 0.1 2.87 5.76 31/01/2007 0.52 0.052 24 0.13 0.79 6.51 15/02/2007 0.54 0.041 24.12 0.12 0 6.67 1/03/2007 0.43 0.039 25.04 0.12 0 6.87

14/03/2007 0.82 0.045 24.53 0.11 2.71 7.02 28/03/2007 0.7 0.042 24.59 0.11 0.65 6.64 11/04/2007 0.36 0.034 24.02 0.13 1.98 6.72 Table B. 9. Raw data for Bore 09, curtain trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

10/05/06 0.4 0.0015 19.59 0.4 0.57 6.4 07/06/06 0.2 0.0094 19.93 0.29 0.61 6.18 12/07/06 0.02 0.011 17.91 0.43 3.16 5.38 21/08/06 0.5 0.004 19.57 0.26 1.13 6.08 22/09/06 0.29 0.11 20.38 0.21 0.44 6.58 24/10/06 0.41 0.0015 21.58 0.19 0.54 6.04 29/11/06 0.25 0.007 21.92 0.19 0.64 6.13 19/12/06 0.52 0.035 22.58 0.2 0.59 6.22 31/01/07 1 0.005 24.57 0.19 0 6.59 15/02/07 0.74 0.012 24.31 0.17 0.27 6.74 01/03/07 0.77 0.005 24.91 0.18 0.11 6.44 14/03/07 0.63 0.015 24.32 0.17 2.47 6.7 28/03/07 0.54 0.02 24.23 0.16 0.18 6.49 11/04/07 0.66 0.012 22.54 0.14 3.15 6.82




Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

10/05/06 0.77 0.012 20.77 0.63 0.66 4.98 07/06/06 0.23 0.0015 20.1 0.21 0.93 4.69 12/07/06 0.34 0.0015 18.66 0.23 3.21 5.25 21/08/06 0.47 0.0015 19.56 0.17 0.32 6.22 22/09/06 0.11 0.004 20.27 0.17 0.91 6.31 24/10/06 0.56 0.0015 21.17 0.18 0.49 6.15 29/11/06 0.93 0.007 22.14 0.17 0.58 6 19/12/06 2.61 0.013 22.77 0.2 0.78 6 31/01/07 1.01 0.005 25.23 0.18 1.97 6.33 15/02/07 0.77 0.032 24.29 0.17 0 6.35 01/03/07 1.59 0.005 25.67 0.17 1.51 6.21 14/03/07 0.94 0.005 24.76 0.17 1.1 6.58 28/03/07 0.82 0.005 24.86 0.14 0.35 6.35 11/04/07 0.42 0.014 24.1 0.17 0.47 6.79

Table B. 11. Raw data for Bore EB1, curtain trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

10/05/06 0.32 0.019 18.29 0.42 0.61 6.18 07/06/06 0.03 0.0015 18.95 0.49 0.62 5.83 12/07/06 0.27 0.0015 16.17 0.08 5.2 6.36 21/08/06 0.07 0.0015 18.9 0.36 0.31 6.39 22/09/06 0.12 0.004 19.73 0.38 2.31 6.45 24/10/06 0.07 0.0015 21.8 0.42 1.06 6.39 29/11/06 0.24 0.0015 21.17 0.27 0.69 6.3 19/12/06 0.48 0.005 22.15 0.35 0.87 6.15 31/01/07 0.51 0.005 24.46 0.35 0.87 6.6 15/02/07 0.45 0.005 22.87 0.38 0 6.61 01/03/07 0.65 0.005 23.91 0.41 0 6.63 14/03/07 0.62 0.005 23.51 0.38 0 6.88 28/03/07 0.46 0.005 23.36 0.29 2.51 6.62 11/04/07 0.41 0.005 21.97 0.22 1.7 6.83



Table B. 12. Raw data for Bore EB2, curtain trial

Date TP (mgP/L)

FRP (mgP/L)

Temperature (°C)

Salinity (ppt)

DO (mg/L) pH

10/05/06 0.4 0.051 19.88 0.28 0.54 5.92 07/06/06 0.46 0.17 19.5 0.27 0.81 5.36 12/07/06 1.4 0.0015 18.23 0.35 2.16 6.14 21/08/06 0.49 0.013 19.07 0.39 0.19 6.42 22/09/06 0.82 0.04 19.6 0.31 0.71 6.34 24/10/06 1.3 0.0015 20.48 0.28 1.09 6.24 29/11/06 0.4 0.31 21.33 0.23 1.08 6.19 19/12/06 1.38 -- 22.88 0.16 0.44 5.95 31/01/07 2.35 0.322 23.09 0.17 0.91 6.46 15/02/07 2.1 0.005 22.94 0.21 0.34 6.61 01/03/07 1.81 0.108 23.62 0.19 0 6.55 14/03/07 0.42 0.037 23.45 0.23 0 6.85 28/03/07 1.5 0.038 23.81 0.31 0 6.45 11/04/07 2.52 0.043 23.27 0.35 2 7.68

Table B. 13. Head differences for Section B, Section C and Extended Section of curtain trial

Section B Section C Extension Date Bore 03 –

Bore 01 (cm) Bore 03a –

Bore 01a (cm) Bore 12 –

Bore 09 (cm) Bore EB2 –

Bore EB1 (cm) 22/07/05 2.1 -- -- -- 24/08/05 2.1 -- -- -- 29/09/05 -0.4 -- -- -- 28/10/05 1.1 -- -- -- 14/11/05 -0.4 -- -- -- 05/01/06 3.9 -- -- -- 22/02/06 4.9 -- -- -- 14/03/06 2.9 -- -- -- 07/04/06 3.9 -- -- -- 10/05/06 -- 2.2 -- -- 07/06/06 -- 3.2 2 -1.1 12/07/06 -- 3.7 3.5 -0.1 21/08/06 -- 6.2 -8 -2.1 22/09/06 -- 6.2 5.5 6.9 24/10/06 -- 4.4 2.5 -1.3 29/11/06 -- 2.8 -3.2 -1.1 19/12/06 -- 2.6 2.3 0.6 31/01/07 -- 1.3 2.3 -0.2 15/02/07 -- 1.8 0.8 0.4 01/03/07 -- 2.8 26.8 0.1 14/03/07 -- 1.7 1.4 0.2 28/03/07 -- 0.5 0.2 -0.6 11/04/07 -- 1.3 1.7 -0.7 26/04/07 -- 3.5 4.3 2.1

phosphorous retention by lateritesthere is currently interest in the use of local laterite material...

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