SCHOOL OF NATURAL RESOURCE SCIENCES

QUEENSLAND UNIVERSITY OF TECHNOLOGY

HYDROGEOLOGY, CONCEPTUAL MODEL AND

GROUNDWATER FLOW WITHIN ALLUVIAL

AQUIFERS OF THE TENTHILL AND MA MA

CATCHMENTS, LOCKYER VALLEY,

QUEENSLAND

ANDREW SCOTT WILSON

B. App. Sc. (QUT)

SUPERVISOR: Dr Malcolm Cox

ASSOCIATE SUPERVISOR: Dr Vivienne McNeil

A thesis submitted in partial fulfilment of the requirements for the

award of the degree of Master of Applied Science

February 2005

KEY WORDS

hydrogeology, conceptual model, groundwater, alluvial aquifers,

Lockyer Valley, Queensland

ABSTRACT

The study focuses on the adjacent Tenthill and Ma Ma catchments which

converge onto the heavily cultivated alluvial plain of Lockyer Creek.

Groundwater extracted from the alluvial aquifers is the primary source of

water for intensive irrigation. Within the study the hydrogeology is

investigated, a conceptual groundwater model produced and a numerical

groundwater flow model is developed from this. The hydrochemistry and

stable isotope character of groundwater are also investigated to determine

processes such as recharge and evaporation.

Examination of bore logs confirms the Quaternary alluvium comprises a

laterally continuous gravel aquifer with an average thickness of 4.5 m,

overlain by mixed sands and clays which form a semi-confining layer with

an average thickness of 22 m. Variations in long term groundwater

hydrographs indicate the aquifer changes from confined to unconfined in

some locations as water levels drop, while bores adjacent to creek banks

display a rapid response to a flood event. Pump testing of bores screened in

the gravel produces estimates of hydraulic conductivity ranging from 50-80

m/day and storativity of 0.00166 which are both within realistic bounds for

this aquifer material.

Major ion chemistry of surface water collected during a flood is Mg-

dominated, similar to alluvial groundwater in the Tenthill catchment and the

Lockyer plain, suggesting a strong connection between surface and

groundwater in these locations. Alluvial groundwater salinity in Tenthill

catchment is typically less than 3500 µS/cm but may approach 6000µS/cm

on the Lockyer plain. By contrast Ma Ma catchment alluvial groundwater is

Na-dominated with conductivity up to 12000 µS/cm and more associated

with groundwater from the underlying sandstone bedrock. Stable isotope

analyses of alluvial groundwater from throughout both catchments and the

Lockyer plain are compared with basalt and sandstone groundwater. A

range of processes have been identified including recharge to alluvium from

basalt groundwater and evaporated surface water; and alluvial-bedrock

groundwater mixing at some locations.

Integration of the components of the study enabled the production of a

conceptual hydrogeological model of the Lockyer alluvial plain, proposing

two hydrostratigraphic units; the gravel aquifer and the overlying mixed

sand and clay which acts as a semi confining unit. Hydrochemical and stable

isotopic evidence suggests seepage from creek channels as the dominant

recharge process. A single layer groundwater flow model using

MODFLOW was developed, based on groundwater extraction data, to

represent flow in the gravel aquifer. The model was calibrated to transient

conditions with groundwater fluctuations, incorporating both drought and

flood conditions. A sensitivity analysis for each of the aquifer properties

demonstrates the model is insensitive to variations within realistic bounds

for the gravel aquifer material, however, the model is highly sensitive to

changes in the chosen boundary conditions. Predictive simulations with

several annual extraction scenarios ranging from 1.75 to 0.5 ML/ha indicate

the resulting minimum saturated aquifer thickness ranges from 0.03 to 1.4

m.

TABLE OF CONTENTS

1. INTRODUCTION 1

Background 1

Purpose and Scope of the Investigation 1

Aims and Objectives 2

2. PHYSICAL SETTING 3

Location 3

Climate 3

Geomorphology 6

Soils 6

Land Use 8

Water Use 8

3. GEOLOGICAL SETTING 10

Regional Geology 10

Geological Units of the Tenthill and Ma Ma catchments 11

Marburg Subgroup 11

Walloon Coal Measures 15

Main Range Volcanics 16

Quaternary Alluvium 16

4. HYDROGEOLOGICAL BACKGROUND 17

Occurrence of Groundwater in the Lockyer Valley 17

Types and Features of Alluvial Aquifers 17

Features of Bedrock Aquifers 19

Previous Groundwater Investigations in the Lockyer Valley 20

NRM&E Database 24

5. HYDRAULIC INVESTIGATIONS 27

Background 27

Methods 27

Hydrograph Interpretation 27

Pumping Tests 28

Results 32

Hydrograph Interpretation 32

Pumping Tests 37

Discussion of Hydraulic Investigations 37

6. HYDROCHEMISTRY AND STABLE ISOTOPES 43

Background 43

Methods 45

Water Chemistry 45

Stable Isotopes 45

Results 46

Water Chemistry 46

Stable Isotopes 55

Discussion of Hydrochemistry and Stable Isotopes 56

7. DEVELOPMENT OF GROUNDWATER MODEL 70

Introduction 70

Background 71

Conceptualisation 80

Calibration 91

Prediction 125

Discussion of Groundwater Modelling 127

8. CONCLUSION 131

9. REFERENCES 135

APPENDICES after 141

LIST OF FIGURES

Figure 1. Location of the study area in southeast Queensland.

Figure 2. Monthly rainfall recorded at Gatton from 1960-2003.

Figure 3. Monthly rainfall and evaporation recorded at Gatton for 1992-

2002.

Figure 4. Structural setting of the Laidley Sub basin in the Clarence

Moreton Basin.

Figure 5. Surficial geology of the study area .

Figure 6. Locations of 8 bores with regular water level records for 1988-

2003.

Figure 7. Hydrographs of 8 monitoring bores with regular records for 15

year period from 1988 – 2003.

Figure 8. Bore hydrographs at different distances from creeks compared

with monthly rainfall residual mass from 1988-2003.

Figure 9. Locations of 3 pumping tests conducted on alluvial bores,

Figure 10. Plot of drawdown versus log time for pumping test 1.

Figure 11. Plot of residual drawdown versus (t/t’) for pumping test 2.

Figure 12. Plot of drawdown data from Macleod (1998) for pumping test 3.

Figure 13. Daily measurements recorded by bore 516 on bank of Tenthill

Creek during flood event of early May 1996.

Figure 14. Locations of bores sampled for hydrochemistry and stable

isotopes in the study area.

Figure 15. Locations of bores sampled for hydrochemistry and stable

isotopes outside the study area.

Figure 16. Piper diagram utilising the Davies and De Wiest (1966)

classification system for identifying groundwater types.

Figure 17. Piper diagram of surface and alluvial groundwater samples 1996.

Figure 18. Schoeller diagram showing relative proportions of major ions

1996.

Figure 19. Piper diagram of alluvial groundwater samples 2003.

Figure 20. Logarithmic plot of Ca (mg/L) vs TDS (mg/L) for groundwater

samples in 2003.

Figure 21. Logarithmic plot of HCO3 (mg/L) vs conductivity (µS/cm) for

groundwater samples in 2003.

Figure 22. Stable isotope plot of all samples.

Figure 23. Detailed stable isotope plot of surface water and alluvial and

basalt groundwater in 2003.

Figure 24. Semi logarithmic plot of δ2H ‰ VSMOW vs conductivity

(µS/cm) for groundwater samples in 2003.

Figure 25. Location of model extent and the 32 bores used to define the

hydrogeological framework for the conceptual model of the Lockyer plain.

Figure 26. Cross section A-A’

Figure 27. Cross section B-B’

Figure 28. Hydrograph of bore 516 adjacent to Tenthill Creek for period

1993-1996.

Figure 29. Conceptual hydrogeological model for cross section A-A’

Figure 30. Model grid orientated at 62.68 degrees from east showing active

cells (white), inactive cells (grey) and fixed head cells (green).

Figure 31. Top of layer contours interpolated from bore logs with 1 m

interval.

Figure 32. Bottom of layer contours interpolated from bore logs with 1 m

interval.

Figure 33. Initial heads interpolated from 10 head measurements in March

1993 with 1 m contour interval.

Figure 34. Locations of Tenthill Creek (east) and Lockyer Creek (north)

and Ma Ma creek (west) in the model grid.

Figure 35. Locations of 7 recharge zones relative to observation bores.

Figure 36. Extraction cells applied to entire model grid.

Figure 37. Head time graphs of observed and calculated heads.

Figure 38. Water budget for each stress period of the model.

Figure 39. Correlation of derived recharge volumes and rainfall for each

stress period of the model.

Figure 40. Graph of RMS error vs hydraulic conductivity.

Figure 41. Graph of RMS error vs specific yield.

Figure 42. Graph of RMS error vs specific storage.

Figure 43. Head time graphs for simulation with no groundwater extraction

for entire model.

Figure 44. Head time graphs for simulation with all time variant specified

head boundaries replaced by constant head boundaries set at initial heads.

Figure 45. Head time graphs for simulation with western time variant

specified head boundary only replaced by no flow boundary.

Figure 46. Head time graphs for two layer model with derived recharge

rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall

for layer 1.

Figure 47. Graph of minimum saturated thickness of aquifer at end of stress

period 11 versus annual extraction rate applied for entire simulation.

LIST OF TABLES

Table 1. Summary of the pump test specifications, analysis methods

and estimated aquifer properties compared with literature

values for gravel.

Table 2. Stable isotope data related to EC, TDS and aquifer geology.

Table 3. Summary of aquifer geology, EC and water chemical type.

Table 4. Summary of bore logs used to define the thickness of the

gravel aquifer in the study area.

Table 5. Summary of temporal data

Table 6. Summary of groundwater extraction data adapted for the

Lockyer plain.

Table 7. Parameter variations used in the sensitivity analysis.

LIST OF APPENDICES

Appendix 1. Example of bore record from NRM&E database.

Appendix 2. Pumping test data.

Appendix 3. Hydrochemical analytical methods.

Appendix 4. Hydrochemical data.

LIST OF ABBREVIATIONS

NRM&E Natural Resources and Mines and Energy

TMMC Tenthill and Ma Ma catchments

ICP-OES Inductively Coupled Plasma Optical Emission Spectroscopy

CSIRO Commonwealth Scientific and Industrial Research

Organisation

EC Electrical Conductivity

TDS Total Dissolved Solids

VSMOW Vienna Standard Mean Ocean Water

GNIP Global Network for Isotopes in Precipitation

K Hydraulic conductivity

Ss Specific Storage

Sy Specific yield

PMWIN Processing Modflow for Windows

RMS Root Mean Square

QUT Queensland University of Technology

STATEMENT OF ORIGINAL AUTHORSHIP

The work contained in this thesis has not been previously submitted

for a degree or diploma at any other higher education institution.

To the best of my knowledge and belief, the thesis contains no

material previously published or written by another person except

where due reference is made.

Signature: Andrew Wilson

Date: 25 / 2 / 05

I

ACKNOWLEDGEMENTS

I would like to thank the following people for the ways they have

contributed to this study:

Dr Malcolm Cox: supervision, funding, good humour and giving me the opportunity to attempt this project.

Dr Vivienne McNeil: associate supervision and providing access to the

NRM&E groundwater database, maps, reports and sharing her knowledge.

Dr Miceala Preda: GIS and visualisation software “technical support”. Tim Ezzy: acting as an “unofficial associate supervisor” on this

project. Thanks mate for all our discussions of fish, cricket and the meaning of life.

John Harbison: groundwater modelling advice and hydrochemistry

advice. Tim Armstrong: assistance with pumping tests both in the field and at

uni. Peter Cochrane: assistance with locating bores in the field and use of

the NRM&E compressor for water sampling. Wathsala Kumar: assistance with laboratory work. NRM&E staff: Andrew Durick, Ashley Bleakley, Rob Ellis, Gerard

McMahon, Matthew Stenson, Mike Mikillop, Chris Strachotta for providing access to data, maps, reports and sharing their knowledge.

Thank you to the many friendly and co-operative landholders I’ve met in the

Lockyer Valley for their assistance.

Thanks to all my fellow students at QUT NRS.

Thanks to my friends for their help with both uni and non uni stuff.

I would especially like to thank my parents and my brother for their

continual support and interest in my studies.

1

1. INTRODUCTION

Background

The Lockyer Valley is an intensively irrigated agricultural region in

southeast Queensland and is of high economic significance, producing one

third of the vegetables in that state. Groundwater is the primary source of

irrigation water and is extracted from the Quaternary alluvial aquifers

situated along the Lockyer Creek drainage and its tributaries. Drilling by the

Queensland Department of Natural Resources, Mines and Energy

(NRM&E) has revealed the alluvium comprises a laterally continuous layer

of gravel overlain by mixed sands and clays. The underlying Mesozoic

sandstone bedrock aquifers are generally not used for irrigation as the

expected yield is generally much lower than the alluvium and the water

quality can be poor. The area under cultivation and the volume of

groundwater extracted from alluvium have increased substantially over the

past 60 years; of note, during drought conditions the demand for irrigation

water increases resulting in a reduction of yield from many bores and loss of

agricultural productivity.

Purpose and scope of the investigation

The focus of this study is two subcatchments in the south western Lockyer

Valley, those of Tenthill and Ma Ma. Although separate drainages for most

of their length, they converge and flow out onto the broad Lockyer alluvial

plain before discharging separately into Lockyer Creek. Both catchments

contain irrigated agriculture, however, the most intensive cultivation is on

the Lockyer plain below the convergence. Management of the valuable

groundwater resource requires an understanding of the hydrogeology of the

alluvial aquifers, the aim of this study. Hydrogeological techniques utilised

in this study include: bore hydrograph interpretation, pumping tests, and

hydrochemical and stable isotope analyses. The results of these

investigations are incorporated into a conceptual model, which is an

essential step before the development of a numerical groundwater flow

2

model. A calibrated groundwater flow model is a tool for predicting the

behaviour of this heavily exploited aquifer and can be used to test different

extraction scenarios, and provide the basis for decisions on future

groundwater management.

Aim

Establish the hydrogeology and a conceptual groundwater model of the

alluvial aquifers in the Tenthill and Ma Ma catchments and from this a

numerical groundwater flow model, as a tool for groundwater management.

Objectives

a) Define the types of aquifers and aquitards present within the Quaternary

alluvium;

b) Examine long term water level variations in the alluvial aquifer of the

Lockyer plain and their relationship to climatic conditions;

c) Determine estimates of the hydraulic properties of the alluvial aquifers by

the use of hydraulic (pump) testing;

d) Examine the hydrochemical and stable isotopic character of the alluvial

groundwater in Tenthill and Ma Ma catchments and the Lockyer plain, and

compare with bedrock groundwater;

e) Develop a conceptual hydrogeological model of the Lockyer alluvial

plain;

f) Develop a transient numerical groundwater flow model for the Lockyer

plain and determine the effects of different groundwater extraction rates on

the minimum saturated aquifer thickness.

3

2. PHYSICAL SETTING

Location

The study area comprises the Tenthill and Ma Ma catchments (TMMC),

situated in the western Lockyer Valley, south of the town of Gatton,

approximately 80 km west of Brisbane in southeast Queensland (Figure 1).

These two separate drainages rise in the Great Dividing Range to the south

and flow onto an alluvial plain before discharging separately into Lockyer

Creek. Elevations range from 400m at the headwaters of the creeks to

75masl at Gatton. The combined area of both drainages and the alluvial

plain is approximately 850 000 km2 (NRM&E GIS database).

Climate

Climatic conditions in the Lockyer Valley are subtropical and most

precipitation is received during the warmer months. The Great Dividing

Range to the south and west exerts a strong orographic effect on the local

climate, particularly during the summer when the dominant wind direction

is from the southeast. The resulting distribution of rainfall is of mean annual

precipitation of up to 1200 mm at the higher elevations compared to 720

mm at Gatton in the centre of the valley (Commonwealth Bureau of

Meteorology). The region has experienced numerous drought periods over

the last 40 years, notably during 1968-1970, 1979-1980, 1986-1987 and

1993-1995, with monthly rainfall events of 380 mm or greater occurring in

1968, 1974, 1988 and 1996 (Figure 2). Evaporation has been monitored at

the Queensland Department of Primary Industries (QDPI) Research station

at Gatton from 1992 onwards. Data for the period 1992 -2002 demonstrate

that evaporation is seasonal and may be more than twice as great in summer

than in winter (Figure 3).

5

Gatton monthly rainfall 1960-2003

0

50

100

150

200

250

300

350

400

450

500

Jan-60

Jan-62

Jan-64

Jan-66

Jan-68

Jan-70

Jan-72

Jan-74

Jan-76

Jan-78

Jan-80

Jan-82

Jan-84

Jan-86

Jan-88

Jan-90

Jan-92

Jan-94

Jan-96

Jan-98

Jan-00

Jan-02

Date

Mon

thly

rian

fall

(mm

)Jan 1968

Jan 1974

April 1988

May 1996

Figure 2. Monthly rainfall recorded at Gatton for the period 1960 – 2003,

demonstrating monthly rainfall events of 380 mm or greater occurred in

1968, 1974, 1988 and 1996.

Gatton monthly rainfall and evaporation 1992-2002

0

50

100

150

200

250

300

350

400

450

500

Jul-92

Jan-93

Jul-93

Jan-94

Jul-94

Jan-95

Jul-95

Jan-96

Jul-96

Jan-97

Jul-97

Jan-98

Jul-98

Jan-99

Jul-99

Jan-00

Jul-00

Jan-01

Jul-01

Jan-02

Jul-02

Date

Mon

thly

rain

fall

(mm

)

0

50

100

150

200

250

300

350

Mon

thly

eva

pora

tion

(mm

)

Monthly rainfallMonthly evaporation

Figure 3. Monthly rainfall compared to monthly evaporation recorded at

Gatton for period 1992 – 2002. Evaporation in summer (January) may be up

to two times the evaporation in winter (July).

6

Geomorphology

The TMMC are both major tributaries of Lockyer Creek, which is in turn a

tributary of the much larger Brisbane River drainage. The catchments are

bounded in the south by the Basaltic plateau of the Main Range Volcanics at

an elevation of approximately 400m, and to the north west and east by the

Jurassic Marburg Formation Sandstones. In the mid to upper reaches the

two drainages are separated by the quartzose sandstones of the upper

Marburg Formation which has been weathered to rounded hills with some

steep slopes. In the north the catchment is bounded by Lockyer Creek which

roughly follows the surface expression of the Triassic to Jurassic Gatton

Sandstone. This sandstone is finer grained and less resistant to erosion and

consequently forms gently rolling hills in the north. The TMMC drainage

systems evolve from a dendritic pattern at the basaltic headwaters to a trellis

pattern over the Marburg Sandstones. The numerous tributary streams

include Heifer, Lagoon, Dry Creeks in the Ma Ma drainage and Black Duck,

Blackfellow, Wonga and Deep Gully Creeks in the Tenthill drainage. These

systems display trellis style confluences with the main stream channels. In

the mid to upper reaches the creek channels are deeply incised with

extensive terrace deposits along their margins; while in the lower reaches

the channels become more meandering in nature and both drainages

converge to within 300 m of each other before flowing out onto the alluvial

plain of flat overbank deposits. Immediately before its confluence with

Lockyer Creek, Tenthill Creek follows the contact between the Quaternary

Alluvium and the Gatton Sandstone, which is exposed along the creek

channel.

Soils

Soils of the Lockyer Valley can be strongly correlated with the geological

units from which they are derived and in the study area seven different soil

types are recognised from the classification of Smith et al. (1990).

The Gatton Association as its name suggests occurs over the Gatton

Sandstone and is dominated by solodic soils of sandy loam and sand grading

7

down to heavy clay in the A horizons. The B horizon often contains calcium

carbonate and a greater proportion of exchangeable magnesium. Infiltration

of surface water is minimal and consequently runoff is large.

The Winwill Association is also named after the stratigraphic unit from

which it is derived, is characterised by soloths and solodized solonetz soils

with negligible amounts of exchangeable calcium but large amounts of

exchangeable sodium and magnesium. On the steeper slopes red podzolic

soils are more common. With all soils the A horizons are also hard setting

and impermeable resulting in high runoff.

The Ma Ma Association occurs over the Ma Ma Creek Sandstone and has a

varied composition ranging from sandy loam to sandy clay loam to sandy

clay with an abundance of exchangeable calcium throughout all the

horizons.

The Beins Mountain Association has formed on the steep slopes of the

Heifer Creek Sandstone Member. Resistant and non resistant beds of

sandstone have been weathered to produce red podzolic soils and clay soils

respectively. Red podzolic soils are characterised by fine sandy loam

grading down to silty clay loam and these upper horizons contain abundant

exchangeable calcium. The clay soils are typically dry cracking types with a

smooth ped fabric, containing abundant exchangeable calcium and

magnesium. Calcium carbonate is also present in the lower horizons.

A similar soil known as the Whitestone Association occurs on the upper

Heifer Creek Sandstone and the Walloon Coal Measures and comprises

grey, brown and red clays and red podzolic soils. Exchangeable cations

include calcium and magnesium.

Basalts typically weather to produce prairie soils of the Neumann

Association ranging from 30 to 80 cm thick, with abundant exchangeable

calcium and minor exchangeable magnesium.

The most productive soil in the Lockyer region is the Rosewood Association

of the Quaternary alluvium, comprised of prairie soils adjacent to the main

stream channels, ranging to black earths on the flat plains, with calcium the

dominant exchangeable cation.

8

Land Use

In the late 1800’s the Lockyer region supported dairy farming and extraction

of groundwater was minimal or non-existent. Clearing of the native eucalypt

forests exposed the agricultural potential of the rich soils and cultivation of

small crops began in the 1930’s and has continued with increasing intensity

to the present. Lucerne is widely cultivated in addition to numerous

vegetables including cauliflower, broccoli, cabbage, lettuce, onions and

potatoes. Cultivation is restricted to the alluvial soils along the major creek

channels and the broad alluvial plains in the central part of the valley and is

irrigation intensive. The surrounding bedrock slopes are used for stock

grazing, mainly beef cattle, or rejuvenation of native vegetation. Minor land

use includes a small vineyard at Mt Whitestone adjacent to Ma Ma Creek

and a fish farm in the upper Tenthill.

Water use

The use of groundwater for irrigation purposes began in the 1930’s, and

extraction had greatly increased in the 1950’s. Use of groundwater for

irrigation has continued to increase at a steady rate leading to shortages in

drought periods. Water is drawn primarily from the Quaternary alluvium

deposits throughout the valley. The underlying sandstone bedrock aquifers

are generally not used for irrigation as the expected yield is generally much

lower than the alluvium and the water quality can be poor in areas, up to

10000 µS/cm. In an attempt to quantify the volume of groundwater

withdrawn for irrigation NRM&E has established the central Lockyer region

as a proclaimed area and installed water meters on all irrigation bores. The

proclaimed area is defined as the broad alluvial plain extending from Gatton

east to Kentville and south along Laidley Creek almost to Mulgowie.

Beginning in the early 1990’s, automatic meters have been used to record

the volume of groundwater withdrawn and the data is read at approximately

3 monthly intervals and stored at the NRM&E Gatton office. Landholders

are charged for each ML of water used and the data obtained is utilised for

9

water resource management and planning. Stock watering and domestic

bores are not metered.

Three surface water storages have been constructed in the Lockyer Valley:

Lake Clarendon north of The University of Queensland Gatton Campus,

Lake Dyer (Bill Gunn Dam) at Laidley and Atkinson Dam at Lyons Bridge.

The purpose of the three dams is to catch and store runoff for later use as

irrigation water, at cost to landholders, or as is the case of Lake Dyer, the

dam acts as a source for releases into Laidley Creek to recharge the alluvial

aquifer. During the drought of 2001-2003 the only storage with useable

quantities of water remaining was Lake Clarendon. Numerous recharge

weirs have been constructed on many drainages in the Lockyer Valley,

including the TMMC, to retard the flow of surface water and increase

recharge through the creek channels to the alluvial aquifers.

5

3. GEOLOGICAL SETTING

Regional Geology

The Lockyer Valley is situated in the Laidley Sub-basin, which lies between

the Cecil Plains Sub-basin and the Logan Sub-basin in the broad

intracratonic Clarence Moreton Basin. The Laidley Sub-basin

unconformably overlies the Esk Trough and is separated from the Cecil

Plains Sub-basin in the west by the Gatton arch, a broad basement ridge, and

from the Logan Sub-basin in the east by the South Moreton Anticline. A

major structure, the West Ipswich Fault separates the Laidley Sub-basin and

the Esk Trough from the South D’Aguilar Block in the north east (Ingram

and Robinson 1996) (Figure 4).

Both the Permian Cressbrook Creek Group, comprising meta-sediments and

basic volcanics, and Permian to Triassic granites crop out in the north of the

valley. They are however overlain by younger units in other areas, primarily

the Jurassic Marburg sandstones. The definition of the Jurassic Marburg

Subgroup, has been the subject of many revisions (McTaggart 1963; Grimes

1968; Gray 1975; Wells et al. 1990; Wells and O’Brien 1994). Currently

this subgroup is divided into the Gatton Sandstone which outcrops both

north and south of Lockyer Creek, and the Koukandowie Formation (Wells

and O’Brien 1994), which only occurs south of Lockyer Creek, and includes

the Tenthill and Ma Ma catchments. The Marburg Subgroup is overlain by

the Jurassic Walloon Coal Measures which is in the upper part of the

stratigraphic profile of the Lockyer Valley, and has minor surface exposures

only. The ranges to the south and west of the valley are covered by Tertiary

basalt flows of the Main Range Volcanics. The incised channels in the

bedrock contain extensive deposits of Quaternary alluvial fill.

6

Geological units of the Tenthill and Ma Ma catchments

Four main geological units can be identified in the study area with the

following ages and stratigraphic positions:

Alluvium -Quaternary

Main Range Volcanics -Tertiary

Walloon Coal Measures -Jurassic

Marburg Subgroup -Jurassic

Marburg Subgroup

The units of the Marburg Subgroup, formally the Marburg Formation, have

been revised many times; a summary of the major revisions follows. The

group was first described in detail by McTaggart (1963), in a localised study

of the Mesozoic sequence of the Lockyer Marburg area. A type section was

presented in a south westerly direction from Gatton along Ma Ma Creek and

ending at Heifer Creek; this loosely followed the course of the Gatton-

Clifton Road. The formation conformably overlies the Helidon Sandstone in

the north and west and is conformably overlain by the Walloon Coal

Measures in the south. McTaggart (1963) described a lower caliche section

of the formation comprising three members: Gatton Sandstone, Tenthill

Conglomerate, Ma Ma Creek Sandstone and an upper siliceous portion

comprising a single member, the Heifer Creek Sandstone. All members dip

to the south and south-south west at an angle of 10o or less.

The Gatton Sandstone is a massive, caliche, lithic sandstone with minimal

cross bedding, rich in quartz and various lithic fragments set in argillaceous

matrix. Thickness ranges from 30 to 60 m.

The Tenthill Conglomerate, later renamed the Winwill Conglomerate to

avoid confusion with another unit in South Australia of the same name

(Gray 1975), is characterised by fossilwood clasts supported in a pale white

sandstone. Clasts are orientated horizontally suggesting torrential

7

accumulation from an outside source. The member generally outcrops on

the southern side of Lockyer Creek and is easily recognisable and mappable

due to the distinctive clasts. Thickness ranges from 30 to 45 m.

The Ma Ma Creek Sandstone Member is composed of micaceous, flaggy,

lithic sandstones, shales and siltstones. Minor fossilwood clasts are also

present however in much lower densities than the Tenthill Conglomerate,

supporting the definition of the Ma Ma Creek Sandstone as separate

member. Typical thickness is 75 m.

The coarse grained, ferruginous, siliceous Heifer Creek Sandstone Member

is easily recognisable as the steep resistant hills it forms in the Tenthill and

Ma Ma catchments. The member also includes minor shale and coal but its

high quartz content easily distinguishes it from the underlying Ma Ma Creek

Member and the overlying Walloon Coal Measures. Thickness ranges from

180 to 240 m.

This thesis will utilise the classification of McTaggart (1963) (Figure 5), as

each unit is treated as a lithologic and geomorphologic entity which

provides a level of detail suitable for identifying hydrological processes.

This approach has been utilised by previous groundwater investigations in

the Lockyer Valley (e.g. McMahon 1995; McMahon and Cox 1996).

Grimes (1968) noted that the conglomeritic bands and siliceous wood clasts

of the Winwill Conglomerate member were not continuous throughout the

Lower Marburg Formation. He suggested these bands were deposited in a

high energy environment, while the interbedded sandstones were deposited

in a much lower energy environment, adjacent to the stream channels. The

smooth upper boundary between the Winwill Conglomerate and the

overlying Ma Ma Creek Sandstone Member and the presence of some

fossilwood bands within the latter was argued as further justification for not

recognising the Winwill Conglomerate Member in that study.

10

The name Heifer Creek Sandstone Member of McTaggart (1963) was

dropped in favour of the name Upper Marburg Formation for the resistant

quartzose sandstones comprising up to 30% of the sequence interbedded

with non resistant friable sandstones, siltstones and shales (Grimes 1968).

The division of McTaggart (1963) into a lower caliche section and upper

siliceous section was rejected by Grimes (1968) on the basis of the

occurrence of calcite cement in both formations. Instead Grimes (1968)

placed emphasis on the lithic, non resistant Lower Marburg Formation

compared to the quartzose resistant Upper Marburg Formation.

Wells et al. (1990), and Wells and O’Brien (1994) presented a review of the

whole sedimentary sequence of the Clarence Moreton Basin, with a view

towards a standard lithological framework suitable for the entire basin in

both Queensland and New South Wales. Although the review comprises a

regional basin-wide study, as opposed to a localised classification of the

Lockyer Mesozoic sequence by McTaggart (1963) and Grimes (1968), it is

discussed here as it represents the most recent work on the sedimentary

units of the Lockyer Valley.

The Gatton Sandstone Member was elevated to Formation status, while the

Winwill Conglomerate Member was again omitted on the basis of it not

being a single discernable unit but rather numerous conglomeritic beds

within the Gatton Sandstone as detailed by Grimes (1968). The formation

was further subdivided into the shale and interbedded fine grained sandstone

of the Calamia Member, and the pebble to cobble sized Koreelah

Conglomerate, in the southern and western margins of the Clarence-

Moreton Basin, respectively. Neither of these two members outcrops in the

Lockyer Valley.

In place of the Upper Marburg Formation the Koukandowie Formation was

established. This new formation includes the lithic sandstones, shales and

siltstones of the Ma Ma Creek Sandstone Member, and quartzose sandstones

of the Heifer Creek Sandstone Member of McTaggart, which was also

reinstated. Due to the greater proportion of shales and siltstones it contains,

11

the Ma Ma Creek Sandstone Member was renamed the Ma Ma Creek

Member. Wells and O’Brien (1994), also identified an unnamed sandstone

member within the Ma Ma Creek Member, with a restricted exposure

between Ma Ma Creek and Murphy’s Creek in the Lockyer Valley. The

member is more quartz rich and less well sorted than the underlying

sandstones of the Ma Ma Creek member, although not as coarse grained as

the overlying Heifer Creek Sandstone Member. A low sinuosity river was

proposed as the environment of deposition with material sourced from the

New England Orogen, and cross bedding measurements were used to

suggest a direction of sediment transport to the north west. The shale and

thin sandstone beds of the Ma Ma Creek Member were proposed to be the

result of fluvial transgression into a lacustrine environment while the

additional description of elipson cross bedding in the Heifer Creek

Sandstone Member was used to support deposition within a highly sinuous

stream environment.

Walloon Coal Measures

A thin but continuous outcrop of the Mid Jurassic Walloon Coal Measures

occurs in the upper reaches of the Tenthill and Ma Ma catchments. The

lithology of the Walloon Coal Measures is varied and includes volcanolithic

sandstone, carbonaceous siltstone, shale and mudstone, bentonitic siltstone

and minor oil shale (McTaggart 1963). Economic coal occurs in the

Rosewood area near Ipswich with a thickness of up to 420 m; however in

the Lockyer Valley the maximum thickness is 60 m where the formation

outcrops from beneath the overlying basalts. The lower boundary is marked

by a change from quartzose sandstones of the Heifer Creek Sandstone

Member to volcanolithic sandstones and a generally higher proportion of

shale and siltstone. A lacustrine depositional environment with a volcanic

source area was suggested by Grimes (1968).

12

Main Range Volcanics

Tertiary age extrusives to the south and west of the Lockyer Valley can be

divided into two basaltic units, separated by a lateritic zone and are part of

the Main Range Volcanics. In the West Haldon area at the headwaters of

Ma Ma catchment, these flows consist of olivine basalts; the basalts also

contain plagioclase, clinopyroxene and up to 10% calcite at the base of the

sequence. Geochemical analyses have revealed the presence of normative

andesine, therefore the basalts have been classed as hawaiites (Dudgeon

1978). Cooling structures such as columnar jointing in basalt at Mt

Whitestone near Ma Ma village indicates an intrusive basaltic plug, with a

composition similar to the extrusives further south (Grimes 1968).

Quaternary Alluvium

The Tenthill and Ma Ma Creeks like all the other drainages in the Lockyer

Valley are flanked by Quaternary alluvium. NRM&E has drilled an

extensive network of alluvial monitoring boreholes throughout the Lockyer

Valley. Examination of borelogs reveals a typical fining upward sequence of

gravel, sandy gravel and sand, immediately overlying bedrock, proceeding

upwards to silt, sandy clay and clay towards the surface. The gravel, which

may approach cobble size, is well rounded and is sourced from the Main

Range Volcanics at the headwaters of the streams. In the central plains of

the lower Lockyer Valley sand is widespread and overlies the gravel,

however in the TMMC sand is minor and not laterally continuous; this sand

forms lenses above the gravel in the Lockyer plain. In the mid to upper

reaches of the catchments sand is typically absent. The gravel is an

extremely productive aquifer which supports the agricultural activities of the

region, while the overlying silt, sandy clay, and clay act as a semi-confining

layer. In the catchments being studied the alluvial sequence has an average

thickness of 27 m, of which the gravel has an average thickness of 4.5 m.

17

4. HYDROGEOLOGICAL BACKGROUND

Occurrence of Groundwater in the Lockyer Valley

The Lockyer Valley is a highly productive and economically important

agricultural region in southeast Queensland. The principal source of

irrigation water is groundwater drawn from the extensive Quaternary

alluvial deposits which infill the deeply incised channels in the sandstone

bedrock. Quaternary alluvium in the Lockyer Valley is typically up to 35 m

deep and is composed of gravel and minor sand with overbank deposits of

clay, sandy clay and silt. The alluvial aquifers produce the highest yields

and best quality water compared with the sandstone bedrock which is

typically too saline for irrigation purposes.

Types and Features of Alluvial Sequences

Alluvial channels may be divided into three main types: (a) bed load, (b)

mixed load and (c) suspended load (Galloway and Sharp 1998), which have

the following characteristics:

(a) bed load systems: contain both channel and channel flank deposits with

coarse sand common, and gravel common but not necessary. They are

characterized by a high width to depth ratio and low sinuosity with uniform

scour along the channel base. Within them longitudinal, traverse, lateral and

chaute bars may all occur.

(b) mixed load systems: have a much higher portion of sand, typically

between 30 and 60% sand with the channel fills flanked by crevasse splay

and levee sands. The width to depth ratio and the sinuosity are both lower

and higher respectively than bed load systems, which fosters the

development of lateral accretion structures such as point bars.

(c) suspended load systems: comprise of a fill of fine sand to silt to clay and

consequently levee and crevasse splay deposits are common. The width to

depth ratio is extremely low and the channels are highly sinuous to

anastomosing.

18

These different systems are closely related to topography and

geomorphology. In a downstream direction the channel slope, valley slope

and the channel width to depth ratio all decrease. This change is reflected by

the corresponding increase in sinuosity of a channel and decrease in grain

size of an alluvial sequence. Bed load systems therefore dominate the

steeper upper portions of a catchment, becoming mixed to suspended load

systems as the stream progresses down gradient (Galloway and Sharp 1998).

In an alluvial valley fill the deposits are bounded on two sides by bedrock

walls which typically are low permeability or impermeable. The channel is

only able to meander within the confines of the valley walls; coarse

sediment is deposited relatively quickly and dominates the fine overbank

deposits. This predominance of sand and gravel reflects a bed load system

and is of significance to groundwater as it forms the coarsest sediment

immediately above the valley floor which has the highest hydraulic

conductivity. In the deeper portions of the sequence this coarse sediment

may be locally confined by the upper stratum of floodplain deposits and

soil, while in shallower portions it may be hydraulically connected to the

stream channel (Galloway and Sharp 1998).

Groundwater flow within alluvial deposits may be parallel to the stream

channel as underflow or directly towards the stream channel as baseflow.

The criteria for distinguishing between these processes were investigated in

numerous alluvial basins by Larkin and Sharp (1992). The results

demonstrated that underflow was dominant when the channel gradient

exceeds 0.0008, the sinuosity is less than 1.3, the river penetration less than

20% of the alluvial sequence, and the width to depth ratio of the channel is

greater than 60. These criteria are most commonly met in valley fill and

mixed load to bed load systems, or in the upstream and tributary reaches of

a drainage.

Baseflow was found to dominate under the opposite conditions and is most

common in suspended load systems and in the lower reaches of a drainage.

Sinuosity of a fluvial channel acts as a hydraulic sink that fosters baseflow

19

and consequently baseflow is greatest where sinuosity is highest. Local

areas of baseflow may occur immediately adjacent to the stream channel in

otherwise underflow dominated systems. These areas can be recognized by

rapid fluctuations of groundwater level which correspond to the fluctuations

of the stream stage at the same location. Groundwater extraction through

pumping can also cause transient mixed flow conditions by inducing

localised underflow or baseflow and locally changing the dominant flow

process, however such effects are usually restricted to the area of pumping

influence.

Features of Bedrock Aquifers

Siliclastic sedimentary rocks including sandstone, siltstone and shale are

formed in all types of depositional environments such as marine, fluvial,

deltaic, lacustrine and eolian. The porosity and permeability of siliclastic

sedimentary rocks is a function of grain size and degree of sorting and is

lower than unconsolidated sediments due to cementation and compaction.

Cementation from clay minerals, carbonates, silica or iron oxides may

greatly reduce porosity by in-filling of spaces between grains. The effect of

cementation is greatest in sandstone; however a poorly sorted sandstone

may still have a porosity as high as 35%. In siltstones and shales the effect

of compaction on porosity is more apparent, with a decrease from 50-80% at

the time of deposition down to usually less than 3%. Therefore the primary

hydraulic conductivity of siliclastic rocks decreases with age.

Secondary porosity and permeability may be created by fracturing in

siliclastic rocks. When a rock at depth is uplifted to the surface it may

expand and subsequently fracture due to the decrease in pressure. This

process known as unloading produces fractures occurring within 100 m of

the surface. Tectonic activity may also create fractures however these

fractures can occur at any depth. Hydraulic conductivity along a fracture is

typically much greater than the surrounding rocks and vertical fractures

through impermeable strata may act as conduits for groundwater flow

(Fetter 1994; Singhal and Gupta 1999).

20

Previous groundwater investigations in the Lockyer Valley

A broad hydrogeological study presented by Zahawi (1975) provided a

useful overview of groundwater in the Lockyer Valley with discussion of

water chemistry variations. The dominance of sodium ions and lack of

calcium were suggested to originate from cation exchange in the clay

minerals in the sandstones. High magnesium concentrations were attributed

to the weathering of basalts in the south and west, some of which contain up

to 20% olivine. Zahawi also suggested magnesium may come from the

residue of marine transgressions during the Mesozoic. In the same report the

results of several pump tests conducted in the alluvial aquifers by the Water

Resources Commission were presented, with transmissivity varying from 75

to 1625 m2/day and storage coefficient ranging from 0.0001 to 0.074. From

over 500 boreholes drilled in the alluvium, an average aquifer thickness of

3.61 m was estimated.

Talbot and Dickson (1969) conducted a study of the salinity of surface

water and its suitability for irrigation purposes. Following this several

artificial recharge weirs were constructed throughout the Lockyer Valley in

the 1970’s to retard the flow of surface water and increase the amount of

recharge seeping through to the alluvial aquifers below the stream channels.

Lane and Zin (1980) presented an evaluation of the weir in the upper

reaches of Ma Ma Creek and estimated that, for the 3 year monitoring

period in the 1970’s, the weir contributed recharge of 195 000 ML per

annum to the Ma Ma creek alluvium.

Widespread sampling undertaken by Talbot et al. (1981) provided an

understanding of alluvial groundwater quality and the effects of the 1980

drought and significant deteoriation in water quality being observed.

Dixon (1988) examined the hydrochemistry of groundwater in the Tenthill

and Ma Ma catchments during wet and dry periods to establish the temporal

effects of rainfall. Following that study, Dixon and Chiswell (1992), used

hydrochemical sections to identify areas of saline intrusions from bedrock

21

into alluvial aquifers and also to identify areas of recharge from stream

waters. Dixon and Chiswell (1994) identified the enrichment in stable

isotopes δ2H and δ18O in samples from Ma Ma Creek alluvium as

evaporative concentration, and proposed re-circulation of irrigation water as

the cause of saline groundwater in this catchment.

For the Sandy Creek Catchment near Laidley McMahon (1995) and

McMahon and Cox (1996) examined the relationship between

hydrochemistry of saline groundwater in alluvial aquifers and that of the

underlying Jurassic sedimentary formations. Those studies demonstrated

that during periods of low stream flow, such as the 1993 – 1995 drought, the

chemistry of groundwater of the alluvial aquifers can be spatially grouped

and correlated to the underlying sandstone bedrock. The studies indicate

each bedrock unit has an influence on alluvial groundwater chemistry and

may discharge to the alluvium. Along the Sandy Creek drainage four

hydrochemical groups were identified, corresponding to the four members

of the underlying Marburg Formation. Two additional groups were

identified, one showing evidence of mixing between two of the Marburg

members, the other representing the influence of groundwater from the

adjacent Laidley Creek alluvium at the junction of the two drainages. It was

further suggested that the more resistant nature of the Winwill

Conglomerate Member may create a hydraulic barrier and reduce

groundwater flow. This hydrological barrier could result in longer residence

times and concentration of salts, which may account for the higher salinity

in waters observed immediately above the Winwill Conglomerate.

In a similar study in the Ma Ma Creek catchment (Macleod 1998), the

salinity of alluvial aquifers was attributed to contributions from the

underlying Gatton Sandstone and Ma Ma Creek Sandstone Members of the

Marburg Formation. From the identification of seven hydrochemical groups

it was determined that the lowest salinity waters were sourced from the

weathered basalts in the upper catchment. Higher salinity alluvial waters

22

were found to occur above the sandstones in the lower catchment, indicating

salinity increases down gradient.

A detailed assessment of existing water quality records for the whole

Lockyer Valley was conducted by McNeil et al. (1993), which demonstrated

that the existing monitoring network was inadequate. That study proposed

further monitoring bores and surface water stations, and stressed the

importance of a spatial distribution of sampling points. Wills and Raymount

(1996) compared the results of numerous groundwater chemical analyses

including the data of Talbot et al. (1981), with samples collected at different

times (a) 1984 following a flood, (b) 1994 during a drought, and (c) 1996

following a flood. Significant improvements in water quality were found to

occur following flood events or periods of regular rainfall.

An isotopic study of groundwater recharge to alluvial aquifers east of

Gatton was conducted using stable isotopes δ2H and δ18O and radiogenic

isotopes 3H and 14C (Dharmasiri and Morawska 1997). Emphasis was

placed on the importance of creek channels for the recharge of alluvial

aquifers, as evidenced by the similarity between the stable isotopic

composition of surface water and alluvial groundwater. Sandstone aquifers

were found to be isotopically distinct and not to contribute recharge to

alluvium; the exception is the Crowley Vale area, which received recharge

from the underlying Gatton Sandstone. The 14C ages of alluvial groundwater

from Crowley Vale ranged from modern up to 4810 years BP indicating

recharge from sandstone. In all other areas, 3H activities demonstrated that

the youngest alluvial groundwater occurred adjacent to the creek channels.

The 3H activity typically decreased with distance from the streams; these

variations suggest that infiltration from stream channels is the principal

recharge mechanism, as supported by stable isotope measurements.

The effects of irrigation on the water quality of alluvial aquifers were

investigated using the Lockyer Valley as a case study and presented by Ellis

and Dharmasiri (1998) and Ellis (1999). Investigation boreholes were

23

drilled at five sites throughout the valley and cores recovered for analyses of

pesticides, with 3H activities and stable isotope measurements also taken

from pore water from the cores. At all locations geological logs revealed a

fining upward alluvial sequence from gravel to sand to clay as described

previously. Results from 3H analyses indicate an average infiltration rate of

12 mm per year for the clay and silt layer, demonstrating the effects of

irrigation induced salinity have not yet reached the underlying gravel

aquifer. Pesticides were also absent below a certain depth further suggesting

slow infiltration.

A broad scale conceptualisation of the Upper Lockyer region including the

western and south western tributaries was undertaken by NRM&E for

estimating the storage potential and fluxes through the alluvium. The

thickness of the alluvium was calculated by subtracting the bedrock

elevations from the surface elevations obtained in NRM&E bore logs, and

the area of alluvium was divided into several large nodes with a

representative bore allocated for each node. Parameters used were hydraulic

conductivity of 20m/day, the measured hydraulic gradient between adjacent

nodes, and the cross sectional area of the alluvium at the boundary between

these nodes; these were substituted into Darcy’s Law to obtain an estimate

of the flow between different nodes. Landsat imagery was utilised to

determine the areas under irrigation including vegetables, lucerne, other

unspecified cultivation and soil ready for planting. An average value of

groundwater extraction was applied at 3.5 ML/ha for these areas; this is

based on average withdrawals in the NRM&E proclaimed area further east

and the storage curve for each node was calculated. The conceptualisation

did not consider the stratigraphy of the alluvium but rather the entire

sequence was treated as one aquifer. In addition the subdivision of the

alluvium into several large nodes each with a representative bore decreases

the accuracy of the determination of the hydraulic gradient and subsequently

the calculation of the flux down the valleys.

The first finite difference numerical groundwater flow model for the

Lockyer region was developed by Durick and Bleakley (2003).

Groundwater fluctuations in a drought and subsequent flood were simulated

24

for the proclaimed area using the software package MODFLOW (McDonald

and Harbaugh 1988). Geological logs were used to define the thickness of

the sand and gravel aquifer which occurs throughout the broad plain of the

proclaimed area. The overlying clay and sandy clay units were not included

as part of the aquifer. Water level measurements and extraction data from

the NRM&E database were input to estimate parameters including aquifer

hydraulic conductivity and specific yield, which were then used to estimate

recharge. The approach benefits from the abundance of groundwater

extraction measurements from meters installed on all irrigation bores in the

proclaimed area. As recharge was assumed to be zero during a drought

period, the drawdown around each pumping bore simulated by the model

was in effect a pump test. The numerous monitoring bores enabled the

spatial distribution of aquifer properties to be estimated. In all 53 zones of

different aquifer properties were identified with hydraulic conductivity

ranging from 1 to 250 m/day and specific yield ranging from 1 to 20%.

These aquifer properties were input to the model to estimate the magnitude

of recharge entering the aquifer from creeks during wet periods. The results

of the modelling have been used to test various scenarios for the application

rates of irrigation water.

NRM&E database

Queensland NRM&E has compiled an extensive groundwater database for

the entire state of Queensland. Records for monitoring bores typically

include, coordinates of the bore location and a strata log, as well as bore

completion details, bore elevations, water level measurements, water

chemical analyses and pump test data. Data are, however, variable and

continuous records are rare. In the case of the Lockyer Valley, extensive

water level measurements have been taken since the late 1950’s however

these are restricted to a few locations. In the TMMC the drilling of NRM&E

monitoring bores increased substantially in the early 1980’s and the area is

well represented by a network of bores with regular water level

measurements for the period 1988 to the present. In this network the longest

gap between water level measurements is 6 months, with measurements

25

typically being taken every 3 months. The network includes an auto

recorder bore where readings are taken and stored on a data logger;

measurements may be monthly or as regular as weekly for one period in the

mid 1990’s.

For manual readings the depth to water is measured with an electronic dip

meter comprising a tape with a probe at its end which emits a chime when

water is reached. All measurements are recorded relative to the top of the

steel well head, which for NRM&E monitoring bores has been surveyed to

Australian Height Datum (AHD); this is used as a reference for the depth to

water measurements. Bore completion details including length of slotted

casing and width of gravel pack are not always available; in these cases the

most common situation is assumed. Water chemical analyses have also been

conducted about every 5 years since 1985 and appear on the database.

Electrical conductivity and pH were not always measured in the field and

therefore may not be representative, particularly pH. Samples were taken in

plastic bottles and subsequently analysed in the laboratory for major cations

(sodium, potassium, magnesium and calcium) and major anions (chloride,

sulfate, bicarbonate and nitrate). As pumping test data is lacking for the

entire Lockyer region hydraulic testing was conducted during this study.

The NRM&E database uses a bore Registration Number (RN); the current

RN numbering system comprises 8 digits for NRM&E bores with the first 3

digits representing the basin number and the fourth digit representing the

sub basin number. The basin number for the Brisbane basin is 143 and the

sub basin number for the Lockyer basin is 2, therefore all government bores

in the Lockyer region start with 1432. The remaining 4 digits comprise the

bore’s identification number and in the Lockyer range from the oldest

0001to most recent 0865. For simplicity, in this thesis NRM&E bores will

be referred to by only the last 3 digits of their RN, for example, RN

14320865 will be 865.

Information from the database can be exported as either PDF file format to

be opened with Acrobat Reader, or dbf file format to be opened with

26

Microsoft Access. The PDF option allows the construction of a “bore card”

for a particular bore displaying all known information for that bore and

providing a useful overview of data, while the dbf format is fully compatible

with other data analysis software such as Microsoft Excel.

The NRM&E groundwater database was used as a partial data source for

this investigation as it offers several benefits in addition to historical

records. The database is useful for locating existing NRM&E monitoring

bores for current sampling and testing. Although the Lockyer Valley also

has hundreds of private irrigation bores which could be sampled, access

often presents a problem. NRM&E bores do not require landholder

cooperation for sampling, and as they are not equipped for irrigation

purposes, water level measurements are easy to take during pumping tests.

An additional benefit of NRM&E bores over private bores is they nearly

always contain a geological log on the database. An example of a bore

record from the NRM&E database is presented for bore 445 in Appendix 1.

27

5. HYDRAULIC INVESTIGATIONS

Background

The behaviour of the main aquifers in the catchments studied was also

investigated through hydrograph interpretation and the physical properties

were estimated through aquifer or pump testing. The Tenthill and Ma Ma

catchments contain NRM&E water level monitoring bores, the majority of

which are concentrated on the Lockyer plain where the two drainages

converge.

Methods

Hydrograph Interpretation

Precipitation data was obtained from the Commonwealth Bureau of

Meteorology for the synoptic station at the Gatton DPI. The NRM&E

database was searched for all available water level data for the study area

and exported to both pdf and MS Access files. This data was then imported

to MS Excel and used to create groundwater hydrographs for the 8

monitoring bores on the Lockyer plain with regular records, beginning in

January 1988 and continuing to January 2003, with rainfall data added for

comparison purposes.

The effects of rainfall on groundwater levels were examined by plotting

rainfall residual mass and groundwater levels against time. Rainfall residual

mass is the cumulative deviation from the mean as shown by the

relationship below:

( )MeanRainRain MOMORM −= ∑

where

RainMO = Monthly rainfall

MeanRainMO = Mean monthly rainfall

28

Pumping Tests

Pumping tests were conducted on two NRM&E monitoring bores in the

TMMC to obtain estimates of transmissivity which were then used to

estimate hydraulic conductivity. Test 1 comprised a single bore drawdown

test for a period of 90 minutes using a submersible Grundfos pump. The test

was stopped after 90 minutes as the water level had quickly reached

equilibrium under the pumping rate of 0.3 L/s, almost the Grundfos

maximum capacity. The drawdown was analysed with the Cooper Jacob

Time Drawdown Method by plotting drawdown vs log time; transmissivity

was estimated in accordance with the relationship shown below,

( )hhQT−Δ

=04

3.2π

where

T = transmissivity

Q = discharge

Δ (h0-h) = drawdown per log cycle of time

(Cooper and Jacob 1946)

The only requirements for the Cooper Jacob Time Drawdown method are

measurements of drawdown in a pumping bore and the pumping rate of the

pump. For this reason it is adaptable to NRM&E monitoring bores of 50

mm diameter which can be pumped with the Grundfos. This method was not

suitable for the numerous private bores in the study area as many are fully

enclosed and equipped for irrigation purposes.

Test 2 comprised drawdown in a private pumping bore with measurements

taken simultaneously in a NRM&E monitoring bore 13 m away over a

period of 22 hours. A pumping rate of 5 L/s was reported by the landholder;

however this rate could not be verified as all water was pumped directly to

an irrigation winch. After the pump was shut off the rise in water levels was

measured in the monitoring bore over a period of 5 hours. Data were

analysed with the Theis Recovery Method,

29

TQs

π43.2'=

'log

tt

where

s’ = residual drawdown

r = distance from pumping bore to observation bore

T = transmissivity

t and t’ = elapsed times from start and end of pumping

s’ is plotted on the logarithmic y axis and time is plotted on the x axis in the

form of (t/t’) and a line of best fit is drawn to produce a straight line from

which transmissivity can be estimated (Theis 1935).

For the Theis Recovery method the following conditions are assumed to be

valid:

1) The aquifer is confined and has an apparent infinite extent

2) The aquifer is homogeneous, isotropic and of uniform thickness over

the area influenced by pumping

3) The potentiometric surface was horizontal prior to the start of

pumping

4) All changes to the position of the potentiometric surface are due to

the effect of the pumping bore alone

5) The aquifer is compressible and water is released simultaneously

from the aquifer as the head is lowered

6) The pumping bore is fully penetrating

7) The pumping rate is constant for the duration of the test

8) The effects of water stored in the well is negligible

(Theis 1935; Fetter 1994)

The Theis Recovery method requires recovery versus time at a pumping or

observation bore, the distance from the pumping bore to the observation

bore and the pumping rate and duration. For this reason the method is

ideally suited for a test involving a private irrigation bore where drawdown

could not be measured, and a NRM&E monitoring bore where drawdown

30

could be measured, located 13 m away. Such a test is more desirable as the

drawdown in the observation bore is representative of the aquifer over the

distance between the pumping and observation bore. The distance of 13 m

between the private irrigation bore and the NRM&E monitoring bore was

considered close enough to observe drawdown and recovery at the

observation bore under the pumping rate specified by the landholder.

Test 3 comprised re-analysis of drawdown data collected at an observation

bore located 2 m from a pumping bore by McLeod (1998). A new aquifer

thickness of 4 m obtained by interpolation from nearby NRM&E geological

logs was utilised, as opposed to the aquifer thickness of 33 m used by

McLeod (1998). The data was re-analysed by plotting log drawdown versus

log time to produce an estimate of transmissivity using the Theis method

described below,

( )uWT

Qsπ4

=

where

s = drawdown

Q = discharge

W(u) = well function of u

Using the estimate of transmissivity produced, the Theis method was again

employed to determine an estimate of storativity from the observation bore

as shown below,

2

4rTutS =

where

S = storativity

T = transmissivity

u = dimensionless constant

31

t = elapsed times from start and end of pumping

r = distance from pumping bore to observation bore

(Theis 1935)

Each of the above tests produced an estimate of aquifer transmissivity which

was then combined with the aquifer thickness, obtained from geological

logs, to calculate an estimate of hydraulic conductivity as shown by the

following relationship,

bKT =

bTK =

where

T = transmissivity

b = aquifer thickness

K = hydraulic conductivity

The Cooper Jacob Time Drawdown, Theis Recovery and Theis methods

were selected as their requirements were consistent with the available

pumping test design.

32

Results

Hydrograph Interpretation

A continuous period of water level measurements exists for a network of 8

bores for a 15 year period from 1988 to 2003 (Figure 6). From Figure 7 it

can be seen that the highest water levels occurred in July 1990, while the

lowest occurred in October 1995. This trend is consistent for all monitoring

bores with regular measurements. Continued high levels during the period

1988 – 1991 coincides with a period of higher than average rainfall for these

years, and groundwater levels were maintained at a high level. From late

1992 and continuing through to late 1995 water levels in all bores declined.

The lowest point was reached in October 1995 and was alleviated by

frequent rains in the following summer.

A major flood event, 420 mm in one week, occurred in early May 1996 and

the responses of all monitoring bores to this event can be clearly seen on

Figure 7. To compare the response of bores adjacent to the creek channels

with that of bores far from the creek channels a plot of rainfall residual mass

and groundwater levels over the 15 year monitoring period was used. Figure

8 shows hydrographs of two bores adjacent to the creek channels, bore 446

and 516, and two bores some distance from the creeks, bores 490 and 462.

The bores adjacent to the creek display a good correlation between rainfall

residual mass and groundwater levels, while those far form the creeks

display a weaker correlation.

33

Figure 6. Locations of 8 bores with regular water level records for the15

year period 1988 – 2003.

34

Hydrographs of 8 bores with regular records 1988 - 2003

85

90

95

100

105

110

115

Date Dec-88 Dec-89 Dec-90 Dec-91 Dec-92 Dec-93 Dec-94 Dec-95 Dec-96 Dec-97 Dec-98 Dec-99 Dec-00 Dec-01 Dec-02

Date

Hea

d (m

asl)

446445502516490221442462

Figure 7. Hydrographs of 8 monitoring bores with regular records for 15

year period from 1988 – 2003.

35

446

-100

-50

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50

100

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250

300

350

400

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Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03

Date

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nfal

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idua

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s

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86

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asl)

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516

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Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03

Date

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s

82

84

86

88

90

92

94

96

98

100

102

104

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asl)

RRMHead

Figure 8. Hydrographs of two bores adjacent to the creek channels, bore

446 and 516, and two bores some distance from the creeks, bores 490 and

462. The bores adjacent to the creek display a good correlation between

rainfall residual mass and groundwater levels, while those far form the

creeks display a weaker correlation.

36

490

-100

-50

0

50

100

150

200

250

300

350

400

450

Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03

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idua

l Mas

s

98

100

102

104

106

108

110

112

114

116

Hea

d (m

asl)

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Figure 8. Hydrographs of two bores adjacent to the creek channels, bore

446 and 516, and two bores some distance from the creeks, bores 490 and

462. The bores adjacent to the creek display a good correlation between

rainfall residual mass and groundwater levels, while those far form the

creeks display a weaker correlation.

37

Pumping Tests

In order to gain an estimate of aquifer hydraulic properties two pump tests

were conducted and data from a previous pump test was re-analysed using a

new aquifer thickness interpolated from nearby NRM&E geological logs.

The location of each of each pump test is shown in Figure 9. Test 1

consisted of drawdown data plotted against time in accordance with the

Cooper Jacob Time Drawdown method to produce an estimate of hydraulic

conductivity as shown by Figure 10. Test 2 involved pumping for 22 hours

from a private pumping bore with measurements taken in a NRM&E

monitoring bore located 13 m away. The recovery data was plotted by the

Theis Recovery method and manually fitted to the curve to produce an

estimate of hydraulic conductivity (Figure 11). Test 3 was conducted by

Macleod (1998) involving a pumping bore and an observation bore located

2 m away. The drawdown data was re-analysed with a new aquifer thickness

of 4m and plotted by the Theis method and manually fitted to the curve to

produce an estimate of hydraulic conductivity and storativity (Figure 12).

Data for each of the tests is presented in Appendix 2.

Discussion of Hydraulic Investigations

During the above average rainfall of the years 1988 – 1991 groundwater

was maintained at a high level in part due to regular recharge but also in part

due to the reduction in groundwater extracted for irrigation, as frequent

rainfall reduces the irrigation demand. Widespread declining water levels in

the drought years from 1993 – 1995 are a function of both the lack of

rainfall and recharge occurring at the time and also the higher demand

placed on groundwater for irrigation supplies in that period. The creeks in

the Lockyer Valley did not flow between April 1993 and September 1995

(Durick and Bleakley 2003), however hydrographs of bores 446 and 516,

both adjacent to Tenthill Creek, display a strong correlation with rainfall

residual mass during that period (Figure 8). By contrast, bores 490 and 462

both located away from any of the creeks display a weaker correlation with

rainfall residual mass (Figure 8). This response suggests that recharge does

occur through the creeks even when these channels are dry. It is therefore

38

Figure 9. Locations of 3 pumping tests conducted on alluvial bores.

39

Figure 10. Plot of drawdown versus log time from single bore drawdown

test with Grundfos pump.

K = 5.89E-04 m/s or 50.88 m/day.

Figure 11. Plot of residual drawdown versus, elapsed time form start of

pumping divided by elapsed time from end of pumping.

K = 9.20E-4 m/s or 79.5 m/day.

40

Figure 12. Plot of drawdown data from Macleod (1998) manually fitted to

Theis curve.

K = 7.28E-4 m/s or 62.9 m/day S = 1.66E-3

Bore 516 May 1996 flood

0

20

40

60

80

100

120

140

29-Apr 30-Apr 1-May 2-May 3-May 4-May 5-May 6-May 7-May 8-May 9-May 10-May 11-May

Date

Dai

ly ra

infa

ll (

mm

)

90

91

92

93

94

95

96

97

98

Hea

d (

mas

l)

Figure 13. Daily measurements recorded by bore 516 on bank of Tenthill

Creek during flood event of early May 1996.

41

likely that the creek channels are an important, if not the dominant pathway

for recharging water, irrespective of whether they contain flowing or

standing water, or are totally dry and only receive brief storm runoff. Daily

measurements were recorded for bore 516 during a May 1996 flood event,

in which the groundwater level rose 4 m in 4 days, further supporting a

strong hydrological connection to the creek at this location (Figure 13).

A summary of the three pumping tests and the estimates of aquifer

properties is presented in Table 1.

Test Type Distance Duration Pumping Analysis Estimated Between Rate method hydraulic pumping and conductivity

observation

bore 1 Drawdown - 1.5 hours 0.3 L/s Cooper Jacob 50 m/day single bore Time Drawdown

2 Recovery 13 m 22 hours

drawdown 5.1 L/s Theis Recovery 80 m/day

observation

bore 5 hours recovery

3 Drawdown 2 m 1.5 hours 8.6 L/s Theis 65 m/day

observation

bore

Literature 80 to Values 800 m/day For (Fetter 1994) Gravel

Table 1. Summary of the pumping test specifications, analysis methods and

estimated aquifer properties compared with literature values for gravel.

Analysis of the single bore drawdown test data produced an estimate of

hydraulic conductivity of 50 m/day, however, this value should be treated as

a lower end value due to the low pumping rate of the Grundfos pump and its

inability to draw the aquifer down more than 0.4 m within the pumping

bore.

By contrast the 22 hour pumping test drew down the aquifer 0.55 m;

although this is less than 1.5 times the single bore test, the drawdown was

observed at a distance of 13 m away and represents the cone of depression

42

formed by the pumping bore. During the first 30 minutes of the drawdown

test when frequent measurements were being recorded an irrigation pipe

was inadverdantly closed, reducing the pumping rate. As a consequence

water levels began to rise in the observation bore, with a resulting loss of the

initial drawdown data. The data was analysed without this initial drawdown,

however, the estimates of hydraulic conductivity and storativity produced

were not realistic for gravel and were therefore discarded. The recovery

data, however, were still useful as the standing water level was taken to be

the level at which the aquifer began to drawdown again at approximately 30

minutes into the test; the first 30 minutes were then subtracted from the

total pumping duration and used as the new pumping duration when

analysing the recovery data. The estimate of hydraulic conductivity of 79

m/day produced by this method is considered realistic for a semi confined

gravel aquifer.

The third phase of the pumping tests involved re-analysis of the drawdown

data recorded by Macleod (1998) using a new aquifer thickness of 4 m

obtained from interpolation of nearby NRM&E geological logs, as opposed

to the 33 m originally used by Macleod. The drawdown was recorded at an

observation well located 2 m from the pumping bore and produced an

estimate of hydraulic conductivity of 63 m/day. As the drawdown was

observed at an observation bore it was also possible to produce an estimate

of storativity of 0.00166. This value represents the confined storage

coefficient which is equal to the specific storage divided by the aquifer

thickness. Therefore the specific storage was calculated to be:

0.00166 / 4 = 0.000415

43

6. HYDROCHEMISTRY AND STABLE ISOTOPES

Background

The major cations (sodium, potassium, calcium, magnesium) and the major

anions (chloride, bicarbonate and sulfate) typically comprise approximately

98% of all salts dissolved in groundwater. The measurement of the

concentrations of these major constituents provides a method for

determination of the dissolved mineral species present or which reactions

may be occurring within a particular aquifer. Identification of these

components and processes can then be used to propose the history of water-

rock interaction within an aquifer (e.g. Appelo and Postma 1996).

Groundwater chemistry can also provide both an indication of variations in

aquifer properties, and a record of the behaviour of groundwater within

internally variable aquifers such as alluvium. In alluvial aquifers higher

dissolved ions can be an indicator of areas of lower permeability, reflecting

longer residence times of groundwater and the associated increased

weathering reactions of the aquifer materials (Garcia et al. 2001; Acworth

and Jankowski 1993).

Stable isotopes 2H and 18O are valuable as natural tracers as they do not

decay with time nor are they removed from water by exchange process

during movement though most low temperature materials (Acheampong and

Hess 2000). Concentrations of stable isotopes are measured as the difference

or ratio between the two most abundant isotopes of an element. In the case

of the water molecule which contains hydrogen and oxygen, the isotopic

ratios are expressed as 2H/1H and 18O/16O (Mazor 1997). The ratios of a

sample are expressed as the ‰ (per mille) difference relative to a reference,

which for oxygen is shown below:

δ18O sample ‰ = [(18O/16O)sample / (18O/16O)VSMOW – 1] x 1000

44

This reference is V-SMOW – Vienna Standard Mean Ocean Water. The

VSMOW standard is a distilled seawater sample defined by the

International Atomic Energy Agency (IAEA) (Clark and Fritz 1997).

Isotopes 2H and 18O are commonly involved in phase changes, therefore

their concentrations before and after such reactions are governed by kinetic

fractionation. The most common phase changes to affect stable isotopes are

evaporation and condensation. Evaporative enrichment occurs most

efficiently by wind agitation of an evaporating surface water body or the

spray action of some irrigation systems (Gat 1981). Enrichment of liquid

water can be identified by measuring the ratios of stable isotopes δ2H and

δ18O and comparing them to the meteoric relationship of global fresh

waters.

In a landmark paper Craig (1961) identified a straight line relationship

between δ2H and δ18O abundances in natural waters suggesting that the

isotopic composition of meteoric waters behaves in a predictable fashion.

The equation of the straight line was calculated as: δ2H = 818O + 10 and

provided a best fit relationship for the bulk of the samples. Samples

excluded were those from rivers and lakes (east Africa) which were heavily

influenced by evaporation, and plotted below the best fit line with a slope of

approximately 5. Laboratory studies of free evaporation at ordinary

temperatures confirmed a slope of 5 for 2H/18O ratios as being a signature of

evaporated waters (Craig 1961).

When conducting a groundwater investigation it is beneficial to obtain local

area precipitation data, so that the relative enrichment or depletion of

groundwater samples can be identified. This is done by constructing a δ2H

and δ18O plot of local precipitation, from which can be produced a local

meteoric water line. From such a graph the position of a sample relative to

the local meteoric water line can be seen. Calculation of the slope of the

trend line of groundwater samples will enable any effects of evaporation to

be identified (Clark and Fritz 1997).

45

Methods

Water chemistry

Data existed for samples collected by NRM&E from a selection of

groundwater bores in the area, as well as surface water samples in 1996

following a flood event and have been included for comparison. Sampling

for this study was during the winter of 2003 which coincides with a

prolonged drought in the Lockyer Valley and consequently water levels

were very low. A bailer was used to extract water from groundwater bores,

and the equivalent of three volumes of the casing were removed before

sampling took place. Physico-chemical parameters (temperature, pH,

electrical conductivity and Eh) were all measured in situ at the bore using a

TPS multimeter. For each bore two water samples were taken in plastic

bottles, one pre acidified with 1 mL nitric acid to be used for cation

analysis, and one non-acidified to be used for alkalinity and anion analysis.

Turbid samples were filtered in the laboratory using 0.45 µm filter paper in

a flask attached to a vacuum pump. Cations were determined using a Varian

Liberty Inductively Coupled Plasma Optical Emission Spectrometer (ICP-

OES). Where necessary, samples were diluted to 4000 µS/cm for the ICP-

OES. Anions were determined by a Dionex Ion Chromotograph and all

samples were required to be diluted to 200 µS/cm before analysis.

Alkalinity was determined by titration with 0.1 M HCl. As the pH of all

samples was less than 8.3, phenolphthalein alkalinity was 0 and therefore

total alkalinity was reported as HCO3. All procedures were conducted at the

QUT School of Natural Resource Sciences chemical laboratory. For a

detailed description of analytical methods refer to Appendix 3.

Stable Isotopes

Selected bores were sampled for analysis of stable isotopes δ2H and δ18O.

The same bore purging techniques for water chemistry outlined above were

followed and samples were taken in 30 mL glass screw top McCartney

bottles and sealed in accordance with the procedures outlined by Clark and

46

Fritz (1997). All samples were analysed by CSIRO Land and Water Isotope

Laboratory in Adelaide, South Australia.

Results

Water chemistry

Previous investigations reported water chemistry from bores screened

within various geological formations such as sandstone units in the Lockyer

Valley and basalt at the headwaters of the drainages (Dixon and Chiswell

1992 and 1994; Macleod 1998; Cox unpublished data). These results are

discussed here and compared to the alluvial samples colleted by NRM&E

and those collected as part of this study (Figures 14 and 15).

A piper diagram is useful for representing different water types based on the

position of the major cations and anions plotted on a ternary diagram

(Figure 16). Bores within the Ma Ma Creek Sandstone sampled in 1987

yielded Na,Mg-Cl type water and plot on the right side of the Piper diagram

(Figure 17); a sample from the same bedrock unit collected in 1998 was also

Na,Mg-Cl type. NRM&E data for two bores into the Gatton sandstone just

to the east of the study area on the north bank of Lockyer Creek (Figure 15)

yielded high conductivities of 10000 µS/cm and Na-Cl type water in 1996.

To date no reported samples have been collected from the Winwill

conglomerate which overlies the Gatton Sandstone. As the composition of

sandstone groundwater has been shown to be relatively stable over both wet

and dry periods (Dixon and Chiswell 1992), it is reasonable to compare

samples collected at different times with alluvial groundwater samples. A

bore sampled from the basalt near Pilton (Figure 15) on the headwaters of

Ma Ma catchment produced Mg,Ca-HCO3 type water with conductivity of

1100 µS/cm (Cox, unpublished data).

47

Figure 14. Locations of bores sampled for water chemistry only (open

symbols) and both water chemistry and stable isotopes (closed symbols);

and their relationship to the geological units of the study area. Bedrock

bores S1 and S2 (Dixon and Chiswell 1994), GW027 (Macleod 1998) and

822 (this study) shown for reference.

49

Figure 16. Piper diagram utilising the Davies and De Wiest (1966)

classification system for identifying groundwater types. Water types based

on the dominant cations (left ternary) and anions (right ternary).

50

Groundwater bores considered in this study were sampled in either 1996,

2003 or both; locations of bores sampled in this study and their relationship

to the underlying geology are shown in Figure 14. The 1996 data include

surface water samples taken during the May 1996 flood event, July 1996

and several groundwater samples taken in November 1996. Although

Tenthill Creek was sampled by NRM&E for major ion chemistry analysis

during the 1996 flood event, it was not sampled for stable isotope analysis.

However, both major ion chemical analyses (NRM&E), and stable isotope

analyses (Dharmasiri and Morawska 1997) have been carried out on

samples from the adjacent Laidley Creek at this time. Due to the similarity

in the major ion chemistry of flood samples from Tenthill Creek and

Laidley Creek it was considered acceptable to use the Laidley chemical and

isotopic results for comparative purposes in this study. The lowest

conductivity of 250 µS/cm was recorded from surface water during the May

1996 flood event, and is dominated by magnesium, calcium and bicarbonate

(Figure 17). In July 1996 surface water conductivity had increased to 490

µS/cm.

In November 1996 conductivity of alluvial groundwater in Ma Ma

catchment was typically 4700 µS/cm while conductivity of Tenthill

groundwater was less than 1600 µS/cm. On the Lockyer alluvial plain

conductivity ranged from 1200 to 6500 µS/cm. Bore 256 in Ma Ma

catchment, a Na,Mg-Cl type, plots on the right of the Piper diagram

indicating a significant contribution by the sandstone aquifer. Groundwater

from the Tenthill catchment and Lockyer plain samples contain a greater

proportion of calcium over sodium and plot to the left of the Piper diagram

(Figure 17). The concentrations of major ions are plotted on a Schoeller

diagram (Figure 18) to show relative proportions of major ions. The plot

shows lower concentrations in surface water from May 1996 than in July

1996, however, the relative proportions of these same ions are largely

unchanged. In addition the ionic proportions of alluvial groundwater from

Tenthill catchment in November 1996 are very similar to those of both

surface water samples (Figure 18). Chemical analyses for 1996 are

presented in Appendix 4.

51

80 60 40 20 20 40 60 80

20

40

60

80 80

60

40

20

20

40

60

80

20

40

60

80

Ca Na HCO3 Cl

Mg SO4

Legend:

Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96

Figure 17. Piper diagram of surface and alluvial groundwater samples 1996,

compared with basalt and bedrock groundwater and surface water. Alluvial

groundwater from Tenthill catchment and the Lockyer plain is magnesium

dominated while the single sample from Ma Ma catchment is more strongly

associated with the sandstone bedrock aquifers.

52

Mg Ca Na+K Cl SO4 HCO30.01

0.1

1.

10.

100.

1000.Concentration (meq/l)

Legend:

Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96

Figure 18. Schoeller diagram showing relative proportions of major ions in

flooding surface water from May 1996, standing surface water from July

1996 and alluvial groundwater samples from November 1996. Higher

concentrations were observed in surface water from July 1996 than in May

1996, however, the relative proportions of major ions are unchanged and are

similar to the proportions of Tenthill alluvial groundwater. The single

sample of Ma Ma alluvial groundwater exhibits similar ionic proportions to

Ma Ma Creek Sandstone groundwater indicating some contribution from the

bedrock aquifer.

53

To augment existing water chemistry data and to provide a comparison,

twenty six bores were sampled in 2003 as part of the current study. The

sampling network comprises five from Ma Ma catchment, six from Tenthill

catchment and fifteen from the Lockyer plain. Results from each catchment

display a marked difference in salinity (as EC) and the proportions of major

cations and anions. Conductivity from Ma Ma catchment ranged from 8800

to 12900 µS/cm and water types were Na,Mg,Ca-Cl and Mg,Na,Ca-Cl

(Figure 19). In Tenthill catchment conductivity ranged from 1450 to 2640

µS/cm with Mg,Ca,Na-Cl,HCO3 water types dominating. The bore transect

B-B’ across the confluence of alluvium (Figure 14) provides a cross section

which enables comparison. The western (Ma Ma) portion of the transect

exhibits water of a similar chemical type to that found further upstream; and

the eastern (Tenthill) side of the transect is also similar to Tenthill

groundwaters further upstream, suggesting flow within incised channels.

Bores on the western side yielded conductivities ranging from 2500 to 9000

µS/cm and magnesium and sodium dominated waters; while on the eastern

side conductivities ranged from 3100 to 3750 µS/cm in magnesium and

calcium dominated waters.

All samples from the Lockyer plain display a conductivity ranging from

2300 to 6100 µS/cm with Mg>Na>Ca. The 5 bores of the Lockyer Creek

transect A-A’ (Figure 14), yield Mg,Na,Ca-Cl or Mg,Na,Ca-Cl,HCO3 type

water; the exception is bore 446 which is Mg,Ca,Na-HCO3,Cl with a lower

conductivity. Waters from the alluvial bore 447, and bore 822 in the Gatton

Sandstone, both located along Lockyer Creek are Na,Mg-HCO3 type and

plot well below all other samples on the Piper diagram (Figure 19). All

chemical analyses for 2003 are presented in Appendix 4.

Water chemical analyses of basalt groundwater were also conducted as part

of this study (Figure 15). Two groundwater samples both yielded Na-HCO3

type water. When compared with the sample from near Pilton, bicarbonate

is the dominant anion in each of these samples, however, there is some

variation in the proportions of major cations as is seen on the Piper diagram

(Figure 19).

54

80 60 40 20 20 40 60 80

20

40

60

80 80

60

40

20

20

40

60

80

20

40

60

80

Ca Na HCO3 Cl

Mg SO4

Legend:

Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96

Figure 19. Piper diagram of alluvial groundwater samples 2003, compared

with basalt and bedrock groundwater and surface water. Most alluvial

samples from the Lockyer plain display an increase in sodium from 1996. A

single alluvial sample from the Lockyer plain and a sample from the Gatton

Sandstone comprise an isolated group of Na-HCO3 type water. Two basalt

groundwater samples collected in 2003 also exhibit Na-HCO3 water types.

55

Stable Isotopes

Samples were collected from 18 of the bores sampled for water chemistry in

2003 (Figure 14). Results demonstrate a wide variation across the study area

and a general trend of enrichment. Values of δ2H range from -29.6 to -12.3

‰ relative to Vienna Standard Mean Ocean Water (VSMOW) while δ18O

ranges from -5.25 to -2.08 ‰ relative to VSMOW. Bore 502 and 822 are the

outliers being the most enriched and depleted waters respectively. The

majority of samples are within the ranges of δ2H: -24.9 ‰ and -21.7 ‰ and

δ18O: -4.28 ‰ and -3.77 ‰. Stable isotope data are presented with

conductivity, TDS and aquifer geology in Table 2.

Sample Date Aquifer EC TDS δ2Η δ18Ο Geology (µS/cm) (mg/L) VSMOW VSMOW

221 27/11/2003 Alluvium (Lockyer) 2600 1718 -24.5 -4.26 446 8/09/2003 Alluvium (Lockyer) 1443 824 -20.5 -3.95 447 20/11/2003 Alluvium (Lockyer) 4640 1421 -23.6 -4.15 490 6/09/2003 Alluvium (Lockyer) 3670 2086 -21.7 -3.77 491 8/09/2003 Alluvium (Lockyer) 6100 3404 -17.3 -3.05 502 8/09/2003 Alluvium (Lockyer) 3400 2002 -12.3 -2.08 516 8/09/2003 Alluvium (Lockyer) 5380 3688 -24.8 -4.51 P1 27/11/2003 Alluvium (Lockyer) 3040 1745 -23.1 -3.9 859 3/09/2003 Alluvium (Ma Ma) 9050 5444 -26.4 -4.49 861 10/09/2003 Alluvium (Ma Ma) 12160 7092 -21.2 -3.19 862 6/09/2003 Alluvium (Ma Ma) 12890 7673 -23.1 -3.83

55617 6/09/2003 Alluvium (Ma Ma) 8780 5416 -24.9 -4.28 477 25/08/2003 Alluvium (Tenthill) 2640 1518 -22.5 -4.11 783 3/09/2003 Alluvium (Tenthill) 3220 2350 -22.6 -3.81 784 3/09/2003 Alluvium (Tenthill) 3100 2488 -24.2 -4.08 864 6/09/2003 Alluvium (Tenthill) 1447 974 -23.3 -4.14 865 6/09/2003 Alluvium (Tenthill) 2340 1545 -23.5 -4.18 B1 20/11/2003 Basalt 720 223 -22.2 -4.49 B2 20/11/2003 Basalt 730 218 -23.4 -4.79 B3 30/03/1995 Basalt 1110 840 -21.7 -3.14 S1 1/01/1987 Ma Ma Ck Sandstone 4590 3016 -30.9 4.94 S2 1/01/1987 Ma Ma Ck Sandstone 6950 4865 -32.7 -5.06

GW027 1/07/1998 Ma Ma Ck Sandstone 14330 6767 -25.3 -4.1 822 10/09/2003 Gatton Sandstone 4930 2432 -29.6 -5.25

SW May 96 May-96 Surface water 255 164 -24 -4.4 SW July 96 Jul-96 Surface water 486 281 -20 -3.6

Table 2. Stable isotopes, EC, TDS and aquifer geology. S1 and S2 (Dixon

and Chiswell 1994), GW027 (Macleod 1998), B3 (Cox, unpublished data),

Surface water isotope measurements (Dharmasiri and Morawska 1997).

56

Discussion of Hydrochemistry and Stable Isotopes

The surface stream water for the valley may be represented by the Laidley

Creek sample collected in the May 1996 flood event. As demonstrated on

the Schoeller diagram (Figure 18) the concentrations of major ions are

higher in surface water from July 1996 than in May 1996, however the

relative proportions of these same ions are largely unchanged. The chemical

composition of the July surface water sample is also similar to the

compositions of groundwater samples collected several months later from

Tenthill catchment and the Lockyer plain. The sample from Ma Ma

catchment, however, is more associated with the sandstone waters identified

by Dixon and Chiswell (1992). These relationships suggest that the

chemical character of alluvial groundwater in Tenthill catchment and the

Lockyer plain is affected by surface water for a period of several months

after a major rainfall event. At the same time the effects of such an event are

not identifiable in Ma Ma catchment. A summary of aquifer geology and

water types is presented in Table 3.

Aquifer Location EC Chemical Geology (µS/cm) Type Alluvial Lockyer Plain 2300-6100 Mg,Na,Ca-Cl Alluvial Ma Ma catchment 5000-12000 Mg,Na,Ca-Cl Alluvial Tenthill catchment 1500-3500 Mg,Ca,Na-Cl,HCO3 Basalt Pilton 1100 Mg,Ca-HCO3 Basalt Mt Castle 700 Na-HCO3

Ma Ma Ck Sandstone Upper Tenthill, Mt Whitestone 4500-7000 Na,Mg-Cl

Gatton Sandstone UQ Gatton 10000 Na-Cl Stream (flooding) Laidley Ck 250 Ca,Mg,Na-HCO3 Stream (standing) Laidley Ck 490 Mg,Ca,Na-HCO3

Table 3. Summary of aquifer geology, electrical conductivity and water

chemical type.

The chemical composition of the alluvial groundwater has similarities to

stream flooding water of Ca,Mg,Na-HCO3,Cl type and basalt groundwater

of Mg,Ca-HCO3 type at the headwaters of Ma Ma catchment. The high

calcium in surface water from May 1996 may indicate the effects of runoff

57

from weathered basalt in the upper reaches. Basalt contains minerals with

available calcium including plagioclase and clinopyroxene. The basalts at

the headwaters of the Lockyer Valley have been shown to contain up to 10

% calcite (Dudgeon 1978), also a ready source of calcium. The total

dominance of magnesium in surface water and alluvial groundwater from

Tenthill catchment and the Lockyer plain may be from weathering and

runoff from these same basalts which contain up to 20% olivine (Zahawi

1975), or interactions between groundwater and basaltic gravel which

comprises the alluvial aquifer material. The two basalt groundwater samples

from Mt Castle contain sodium as the dominant cation and do not share the

same major cation chemistry with flooding water as does the Pilton sample

B3 (Figure 10); however their conductivity and TDS are similar to sample

B3. In addition bicarbonate is the dominant anion in all three samples.

For the 2003 samples the Ma Ma catchment alluvial groundwater was

sodium and magnesium dominated, consistent with the results of Dixon and

Chiswell (1992). In that study high conductivity, Na,Mg-Cl type water was

identified from private bores in the Ma Ma Creek Sandstone; the authors

proposed that bedrock groundwater mixes with the Ma Ma catchment

alluvial groundwater due to the small volume of this alluvial aquifer. A

comparison from the current sampling showed two alluvial bores overlying

(a) the Ma Ma Creek Sandstone had conductivities of 12000 µS/cm, and (b)

overlying the Winwill Conglomerate had conductivity 8000 and 9000

µS/cm. In the Sandy Creek catchment near Laidley, high salinity, sodium

dominated alluvial groundwater was identified directly overlying the

Winwill Conglomerate and attributed to upward flow from that unit into the

alluvium (McMahon 1995, McMahon and Cox 1996). A similar process

may be occurring in Ma Ma catchment due to the outcrop of Winwill

Conglomerate and Ma Ma Creek Sandstone which underlie the alluvium

using the classification of McTaggart (1963) (Figure 5). This could explain

the dominance of sodium and the high conductivity of many samples from

this catchment.

58

By contrast, alluvial groundwater samples from Tenthill catchment are

magnesium dominated with a conductivity less than 3500 µS/cm. The Ma

Ma Creek Sandstone bedrock unit does not appear to have a major influence

on the chemistry of alluvial groundwater in the Tenthill catchment. Samples

from the Lockyer plain are typically Mg,Na,Ca-Cl type water with

conductivity of 3000-6000 µS/cm; here the alluvium is underlain by the

Gatton Sandstone which yields Na-Cl type water with a conductivity of

10000 µS/cm. Like the Tenthill catchment the magnesium domination may

be due to the basaltic gravel of the aquifer material while the greater

proportion of sodium may be the result of upward discharge of Na-Cl type

water from the underlying Gatton Sandstone.

Relative variations of the major ions reflect the different aquifers. A

logarithmic plot of calcium vs TDS clearly separates these aquifers in the

study area by geographic location (Figure 20). Calcium is used on the y axis

as in all samples it is less abundant than sodium or magnesium and does not

create any bias when grouping the different aquifers. Chloride or

bicarbonate could be used on the x axis, however, TDS was used to

incorporate all water types regardless of their dominant anion. Ma Ma

catchment contains the highest calcium, while basalt waters contain the

least, with the Lockyer plain and Tenthill catchment of intermediate

character. A possible mixing relationship may exist between the bedrock

groundwater and Tenthill catchment alluvial water to produce the

groundwater of the Lockyer plain.

In Figure 21 a logarithmic plot of bicarbonate vs conductivity is used to

represent:

(a) recharge to alluvial and basalt aquifers,

(b) alluvial/bedrock groundwater mixing,

(c) variations in groundwater bicarbonate content.

Surface water during a flood is notably fresh and a starting point for

groundwater recharge. The fresh basalt groundwater with bicarbonate as the

dominant anion plots between flooding stream water and alluvial

groundwater; this indicates that rainfall may initially recharge the basalt first

59

100.0 1000.0 10000.010.0

100.0

1000.0Ca (mg/l)

TDS (mg/l)

Legend:

Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96

Ma Ma

Bedrock

Tenthill

Lockyer plain

Figure 20. Logarithmic plot of Ca (mg/L) vs TDS (mg/L) for groundwater

samples in 2003. A possible mixing relationship may exist between the

bedrock groundwater and Tenthill catchment alluvial water to produce the

groundwater of the Lockyer plain.

60

100.0 1000.0 10000.0 100000.0100.0

1000.0

10000.0HCO3 (mg/l)

Conductivity (µS/cm)

Legend:

Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96

Ma MaBasalt

822447

516

491

Bedrock

445

mixing

Flood water

rech

arge

to b

asal

t

recharg

e

direct

ly

to all

uvium

HCO type water3

Figure 21. Logarithmic plot of HCO3 (mg/L) vs conductivity (µS/cm) for

groundwater samples in 2003. Recharge may occur to basalt before

alluvium or directly to alluvium. The alluvial samples from Ma Ma

catchment and the most saline samples from the lower plain, bores 445, 491

and 516, may be mixing with bedrock groundwater. Bores 822 and 447

represent an isolated group of HCO3 type water. Broken line shows

chemical evolution of groundwater.

61

with subsequent discharge to the alluvium, plus direct recharge for the

alluvium. The similarity between the conductivity of bedrock groundwater

and Ma Ma catchment alluvial groundwater and the most saline alluvial

samples from the Lockyer plain, (bores 445, 491 and 516), indicates

possible mixing between alluvium and bedrock groundwater at these

locations. The HCO3 type water in the alluvial bore 447 and the Gatton

Sandstone bore 822 plot highest and isolated on Figure 21 and indicate an

external source of unidentified CO2.

Stable isotopes support the interpretation of water chemical evolution. A

plot of δ2H ‰ VSMOW versus δ18O ‰ VSMOW (Figure 22) indicates the

position of all samples relative to the Global Meteoric Water Line (Craig

1961) and the Brisbane Meteoric Water Line (GNIP 1998). Bedrock

groundwater is more depleted than both alluvial and basalt groundwater as

well as surface water; this water plots lower on Figure 22 indicating a

different recharge process and possibly a different climate at the time of

recharge. The alluvial and basalt and surface water have been plotted in

greater detail in Figure 23. It can be seen that surface water from the May

1996 flood plots to the left of the Global Meteoric Water Line and

represents “new water” and is as close to local rainfall composition as can

be determined for the study area. Samples collected following the May 1996

flood plot on an evaporation slope of 5 which is characteristic of

evaporation from standing surface water (Craig 1961, Gat 1981). Basalt

groundwater is slightly more enriched than the “new water” and may be

evaporated during recharge to the unconfined fractured basalt aquifer.

Tenthill catchment alluvial groundwater does not show any evaporation

which may be the result of regular recharge from the headwaters of this

large catchment. For Ma Ma catchment alluvial groundwater an evaporation

slope of 3.85 was calculated, while for the Lockyer plain alluvial

groundwater the slope calculated is 5.33 (Figure 23). These slopes are

similar to that calculated for standing surface water after the 1996 flood and

support recharge from evaporated surface water in creek channels as the

dominant recharge process to the alluvial aquifers. The samples of “new

62

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

-8 -6 -4 -2 0

-40

-30

-20

-10

0

Bedrock

Glo

bal M

eteor

ic W

ater

Lin

e y

= 8

x +

10 (C

raig

196

1)

Brisba

ne M

eteor

ic W

ater

Lin

e y

= 7

.7x

+ 12

.6 (G

NIP 1

996)

δ2H ‰ VSMOW

δ18O ‰ VSMOW

Figure 22. Stable isotope plot of surface water and alluvial, basalt and

bedrock groundwater with Brisbane Meteoric Water Line and Global

Meteoric Water Line shown for reference. Bedrock groundwater is more

depleted than all other samples indicating a different recharge process and

possibly a different climate at time of recharge.

63

-5 -4 -3 -2

-28

-24

-20

-16

-12

-5 -4 -3 -2

-28

-24

-20

-16

-12

-5 -4 -3 -2

-28

-24

-20

-16

-12Lockyer plain s = 5.33

Ma Ma s = 3.85

Surface water s = 5

Tenthill

δ2H ‰ VSMOW

δ18O ‰ VSMOW

-5 -4 -3 -2

-28

-24

-20

-16

-12

-5 -4 -3 -2

-28

-24

-20

-16

-12

-5 -4 -3 -2

-28

-24

-20

-16

-12

Brisba

ne M

eteor

ic W

ater

Lin

e y

= 7

.7x

+ 12

.6 (G

NIP 1

996)

"Loc

kyer

Mete

oric

Wat

er L

ine"

y

= 7.

7x +

9.9

4

Glo

bal M

eteor

ic W

ater

Lin

e y

= 8

x +

10 (C

raig

196

1)

516

"new water"

446

-5 -4 -3 -2

-28

-24

-20

-16

-12

-5 -4 -3 -2

-28

-24

-20

-16

-12

Figure 23. Detailed stable isotope plot of surface water and alluvial and

basalt groundwater with Global Meteoric Water Line and Brisbane Meteoric

Water Line shown for reference. Surface water from the May 1996 flood

plots to the left of the Global Meteoric Water Line and represents flowing

"new water". Tenthill alluvial groundwater shows no distinct trends

however alluvial groundwater from Ma Ma catchment and the Lockyer

plain plot on evaporation slopes of 3.85 and 5.33 respectively. The "new

water", bore 516 and bore 446 plot on a "Lockyer Meteoric Water Line"

which represents the initial composition of evaporated waters. Basalt

groundwater is slightly more enriched than "new water" indicating some

evaporation during recharge.

64

water”, bore 516 and bore 446 plot on a “Lockyer Meteoric Water Line”

(Figure 23) which represents the initial composition of evaporated waters.

When combined with groundwater salinity stable isotopes can be used to

further group different water types and identify hydrological processes. A

semi logarithmic plot of δ2H ‰ VSMOW versus conductivity (µS/cm) is

used to differentiate the alluvial groundwater samples into 4 groups (see

below); and confirm hydrological processes such as recharge, mixing and

evaporation (Figure 24).

Group 1: two samples from the upper reaches of Ma Ma atchment, both

being enriched with extremely high salinities of 12 000 µS/cm

Group 2: two samples from Ma Ma catchment and bore 516 from the

Lockyer plain, slightly more depleted but still with higher salinity

Group 3: all samples from Tenthill catchment and most samples from the

lower plain

Group 4: three samples from the Lockyer plain near which are the most

enriched of all samples

The May sample represents “new water” in the streams prior to evaporation,

while the July sample represents the effects of two months of evaporative

concentration of water in the creek channel. Before undergoing evaporation

the rainfall with a “new water” character is likely to recharge the basalt

aquifers of the surrounding ranges, which subsequently discharge to the

alluvium along the drainage systems. Basalt groundwater may also recharge

the sandstone aquifers.

The locations of the isotope samples relative to the underlying bedrock units

are shown in Figure 14. Samples from the upper reaches of Ma Ma

catchment which overlie the Ma Ma Creek Sandstone are both isotopically

enriched and strongly saline (Group 1, Figure 24). The locations of these

samples coincide with the areas where the alluvium is thinnest, with the

depth to bedrock ranging from 12 to 16 m, compared with a depth of 30 m

on the Lockyer plain. Despite the shallowness of the alluvial fill, these

highly saline samples do not represent bedrock mixing as they plot above

65

100 1000 10000 100000.0-35

-30

-25

-20

-15

-10

Conductivity (µS/cm)

Legend:

Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96

Bedrock

Group 1

Group 2

Group 3

Group 4

Basalt

“new water”

evap

orati

on

recharge

recharge

bedrock mixing

evaporation ofirrigation water

491

Figure 24. Semi logarithmic plot of δ2H ‰ VSMOW vs conductivity

(µS/cm) for groundwater samples in 2003 divided into 4 main groups;

enabling recharge, alluvial/bedrock mixing and evaporation of irrigation

water to be identified. Broken line indicates chemical evolution of

groundwater.

δ2H ‰ VSMOW

66

the “new water” on Figure 24; they also contain a greater portion of

evaporated recharge water.

Samples from bores further down Ma Ma catchment overlying the Winwill

Conglomerate, (bores 55617 and 859), and bore 516 from the Lockyer plain

are isotopically more depleted however their conductivity is high, 5500 –

9000 µS/cm (Group 2, Figure 24). It is possible that the Winwill

Conglomerate acts as a slow flow barrier as proposed by McMahon (1995)

and McMahon and Cox (1996); these samples have higher salinity, yet are

more isotopically depleted. The Winwill Conglomerate outcrops around the

alluvium for much of the Ma Ma catchment and may also underlie the

alluvium in the vicinity of bore 516 on the Lockyer plain; the conglomerate

does outcrop further east at UQ Gatton. Groundwater from the Winwill

conglomerate may be more isotopically depleted than that from the

alluvium, similar to the Ma Ma Creek Sandstone (Dixon and Chiswell 1994)

and the Gatton Sandstone (this study). As the clasts in the Winwill

Conglomerate have been suggested to lower its permeability and impede

flow (McMahon 1995), it is plausible that the longer residence times of

groundwater in this unit have led to more depletion of stable isotopes, while

maintaining a high salinity due to increased time for dissolution of minerals

in the conglomerate cement. The bores in Group 2 plot below “new water”

(Figure 24) and therefore contain a significant portion of bedrock water.

All samples from Tenthill catchment and the majority from the Lockyer

plain are less enriched and generally have conductivities lower than 3000

µS/cm (Group 3, Figure 24). In Tenthill catchment the portion of alluvium

sampled in this study is underlain by the Ma Ma Creek Sandstone and

groundwater was sampled from this unit during the 1987 drought (Dixon

and Chiswell 1994). The observed difference in both the isotopic character

and salinity between the alluvial and the more depleted bedrock

groundwater in that study suggests that any upward flow of groundwater

from the Ma Ma Creek Sandstone is likely to be minimal, even under

drought conditions. Therefore it is plausible that Tenthill alluvial samples in

the current study, also chemically and isotopically distinct from the

67

sandstone samples of Dixon and Chiswell (1994) and also sampled under

drought conditions reflect little if any contribution from the underlying Ma

Ma Creek Sandstone bedrock. With two exceptions all of these samples

plot above the “new water” indicating they were recharged by evaporated

surface water (Figure 24). The two samples which plot below “new water”

may represent some minor bedrock mixing but, unlike the mixed samples of

Group 2, their conductivity is much lower than the conductivity of bedrock

groundwater and they are not considered to be the result of mixing.

The three samples from the A – A’ transect near the confluence of Tenthill

and Lockyer Creeks, (bores 502, 491 and 446), have variable conductivity

but are the most isotopically enriched in the study (Group 4, Figure 24). At

this point the alluvial plain narrows into a thin channel between two bedrock

outcrops (Figure 14). All alluvial groundwater from the study area and the

entire western Lockyer Valley must flow through this narrow alluvial

channel which is located immediately north of the A – A’ transect and flow

around the town of Gatton before flowing down to the Central Lockyer. As

a comparison in the Juarez Valley of Mexico it was observed that stable

isotope enrichment increases down valley; this change suggested a

progressive re-cycling of irrigation water down the hydraulic gradient as the

dominant mechanism for increasing groundwater salinity (Fontes 1980).

The enriched waters of the A – A’ transect in the current study may

represent evaporative concentration of irrigation water from the entire

western Lockyer Valley accumulating in the lowest point and trapped in a

“bottle neck effect” before flowing down past Gatton. From the logarithmic

plot of bicarbonate vs conductivity (Figure 21) it could be speculated that

the high salinity of bore 491 was due to bedrock mixing. However Figure 24

demonstrates that bore 491 plots above July 1996 surface water and is

enriched relative to the evaporated water from the creek. On this basis the

bore water must have undergone an additional evaporative process,

probably evaporative enrichment of irrigation water. This evaporated

irrigation water subsequently remains in the upper soil layers until the next

flood flushes it into the creek channels where it enters the alluvial aquifer.

68

The semi logarithmic plot of δ2H ‰ V-SMOW vs conductivity (µS/cm)

(Figure 24) has been effective in identifying hydrological processes and

groundwater evolution typical of the Lockyer Valley. Samples from the

May 1996 flood represent “new water” with minimal modifications from the

composition of rainfall; a sample collected two months later is more

enriched in δ2H ‰ VSMOW with an increased conductivity indicating

evaporation of standing surface water has occurred in the creek channels.

Basalt groundwater exhibits an isotopic composition and salinity

intermediate to that of recharge water and alluvial groundwater, indicating

recharge to basalt and subsequent discharge to the alluvial aquifers, likely to

occur in the upper reaches of the catchments. The alluvial groundwaters also

show evidence of evaporation from standing surface water, indicating both

processes may contribute to alluvial aquifer recharge. Certain alluvial

samples from Ma Ma catchment have a salinity similar to that of bedrock

groundwater, and are more isotopically depleted than other alluvial waters;

this may be the result of mixing with depleted bedrock groundwater (Figure

24). The most enriched samples from the Lockyer plain have undergone an

additional evaporative process and represent the effects of evaporative

concentration of irrigation water which has returned to the creek channels

and re-entered the aquifer. A summary of hydrological processes occurring

within the Lockyer Valley is shown overleaf:

69

“New water” after a major rain event recharges the basalt aquifers and also

undergoes evaporation as standing water in the creek channels. Alluvial

aquifers subsequently receive recharge from both the basalt and evaporated

surface water. Basalt groundwater may also recharge the sandstone aquifers.

In Ma Ma catchment there is strong evidence of alluvial/bedrock

groundwater mixing, while on the Lockyer plain relatively more enriched

alluvial groundwater can be attributed to evaporative enrichment of

irrigation water.

New recharge from rain

Basalt groundwater

Alluvial groundwater

Sandstone groundwater

Evaporated surface water

Irrigation water

Mixed Alluvial- Sandstone

groundwater

70

7. DEVELOPMENT OF GROUNDWATER MODEL

Introduction

The purpose of the modelling effort is to develop a basic groundwater flow

model for the Lockyer alluvial plain and examine the effects of different

annual extraction rates on the minimum saturated aquifer thickness, as this

parameter is crucial to the yield of irrigation bores. Geological logs, water

level records and results of hydrochemical and stable isotope analyses have

been examined to produce a conceptual hydrogeological model, as the basis

to develop a groundwater flow model using PMWIN (Chiang and

Kinzelbach 2001) for the Lockyer plain. This region is the most intensively

cultivated portion of the study area and also contains abundant spatial data

including 32 regular bores (with geological logs), and 10 monitoring bores

with historical water level measurements. In addition water chemical

samples were collected from 15 bores and stable isotope samples from 10

bores. All of these data sources and the local terrain make it an interesting

and valuable area for groundwater modelling. The upper reaches of the two

catchments contain an uneven spread of bores separated by a distance of 2

km or greater from the bores of the Lockyer plain and were therefore not

included in the flow model. The model was calibrated to transient

conditions by head matching for the period March 1993 to November 1996,

representing a drought and subsequent flood and therefore two opposing

stresses on the aquifer. This period was also selected as it contains metered

groundwater extraction data. A sensitivity analysis indicates that the model

is insensitive to variations of aquifer properties within realistic bounds.

Predictive simulations have been performed using various annual extraction

rates for the model duration to establish the minimum saturated thickness in

the aquifer.

71

Background

A groundwater model is a physical or numerical representation of a real

world hydrogeological system. Models may be of 3 different types, (a)

Predictive: used for prediction of future conditions, (b) Interpretative: used

for studying system dynamics or organising data, and (c) Generic: used to

analyse hypothetical hydrogeological systems (Anderson and Woessner

1992). Although modelling is important for any of the above purposes, it is

only one component of a hydrogeological investigation requiring sound data

foundations and cannot stand alone. To ensure modelling consistency, best

practice guidelines for the development, revision and reporting of

groundwater flow models have been proposed (e.g. Murray-Darling Basin

Commission 2000; Middlemis et al. 2002; Merrick et al. 2002).

Groundwater modelling methodology can be divided into three components;

conceptualisation, calibration and prediction, which will be outlined below

with a focus towards the industry standard MODFLOW

Conceptualisation

A conceptual model is a pictorial representation of the groundwater flow

system incorporating all available geological and hydrogeological data into

a simplified block diagram or cross section (Anderson and Woessner 1992).

The first phase in producing a conceptual model is defining the geological

framework including the thickness, continuity, lithology and structure of

any aquifers and confining units. Data for the geological framework is

typically obtained from geological maps, bore logs, geophysics and

additional field mapping. Establishment of the geological framework then

permits the hydrological framework to be defined involving four important

steps; identifying the boundaries of the hydrological system, defining

hydrostratigraphic units, preparing a water budget and defining the flow

system.

The boundaries of a model must be identified first so that all the following

steps can proceed within their framework. Boundaries can be either natural

72

hydrogeological boundaries including the surface of the water table,

groundwater divides and impermeable contacts between different geological

units, or may need to be unnatural such as cadastral boundaries. The type of

boundary selected will depend on the modelling scope and requirements and

will affect how the boundaries are represented within MODFLOW, however

for simplicity, natural boundaries should be used wherever possible.

Defining hydrostratigraphic units is crucial in determining the number of

layers controlling groundwater flow within the system. A hydrostratigraphic

unit is comprised of geological units of similar hydrogeological properties.

Numerous geological units may be grouped together or a single formation

may be subdivided into different aquifers and aquitards. Estimates of

hydraulic conductivity and storativity from pump tests combined with water

chemical analyses are often used to identify and distinguish different

hydrostratigraphic units.

Preparation of a water budget involves the identification and quantification

of all flows in and out of the groundwater system. The mechanisms of

recharge are defined as areally distributed, preferential or seepage from

surface water bodies and their fluxes are estimated based on precipitation

data, the permeability of the aquifer or confining units or chemical and

isotopic techniques. Outflows from the system are defined as springflow,

baseflow, evapotranspiration or extraction and their fluxes are estimated by

chemical or isotopic techniques or metering in the case of extraction.

Definition of the flow system is essential to understanding groundwater

movement throughout the hydrogeological system. Water level

measurements are used to identify the dominant directions of groundwater

flow, the hydraulic gradient, locations of recharge areas, location of

discharge areas and connections between ground and surface water. As in

the water budget preparation, water chemical analyses are also employed to

qualitatively represent recharge and baseflow.

73

Calibration

The first phase involves model construction; the design and orientation of

the model grid. In the case of a finite difference grid, cells are rectangular

and may be all equally sized or some areas of the grid may be smaller or

larger. Finite difference grids may be divided into two different types: block

centred grids in which flux boundaries are always located at the margins of

the block; and mesh centred grids in which the boundary is centred on a

node. MODFLOW is a block centred grid. The size of each individual cell

should be as large as possible to minimise computational time and storage

space, yet small enough to reflect the curvature of the water table and the

hydraulic gradient, and also the effects of point stresses on the

hydrogeological system such as preferential recharge and pumping from

well nodes (Anderson and Woessner 1992). The spatial distribution and

heterogeneity of aquifer properties is also important when choosing an

appropriate grid size, with the more variable the aquifer properties, the finer

the model grid should be to express these variations. When aquifer

properties are not accurately defined or known a larger grid size should be

used. With lower resolution data on the distribution of aquifer properties a

larger grid size should be used. The orientation of the model grid is not

important in an isotropic aquifer as the hydraulic conductivity is constant in

all directions, however when an aquifer is anisotropic the model grid must

be orientated with the main axes of the hydraulic conductivity tensor and

these axes of maximum and minimum hydraulic conductivity are always

perpendicular to each other (Kresic 1997).

Four different layer types are recognised in MODFLOW as discussed

below:

Type 0: The layer is strictly confined and transmissivity of each cell remains

constant for the entire simulation.

Type 1: The layer is strictly unconfined and can only be applied for the

uppermost layer of a model.

Type 2: The layer is used when the aquifer alternates between confined and

unconfined as the simulation progresses.

74

Type 3: The layer is used when the aquifer alternates between confined and

unconfined as the simulation progresses resulting in variations in the

saturated thickness.

(Chiang and Kinzelbach 2001).

Three boundary conditions can be applied to cells in a finite difference grid

such as MODFLOW including (a) Dirichlet, (b) Neuman and (c) Cauchy.

(a) Dirichlet condition: the head at the boundary is known, examples are the

water table in an unconfined aquifer, or a river or lake in contact with an

unconfined aquifer, all under steady state conditions. Dirichlet conditions

are also used when simulating unnatural boundaries such as cadastral

boundaries of a hydrogeological system which are often defined for the

purposes of the modelling investigation. In a natural hydrogeological system

an aquifer may continue onwards past the boundary and therefore must be

accounted for by placing a fixed or specified head cell or cells, in which the

allocated head is known. All applications of Dirichlet boundaries require

some form of head measurement on or very near the boundary.

(b) Neuman condition: the flux across a boundary is known, examples

include no flow boundaries between geological units, interactions between

groundwater and surface water bodies, springflow, underflow, and seepage

from bedrock into alluvium. The simulation of Neuman Boundaries requires

the measurement or estimation of one of the above fluxes, which is often

inaccurate. The most commonly applied form of a Neuman Boundary is a

No-Flow or Impermeable Boundary, often occurring between a highly

permeable unit and a unit of much lower permeability. A difference in

hydraulic conductivity of two orders of magnitude or greater between two

adjacent units is sufficient to justify placement of a No-Flow Boundary, as

this contrast in permeability causes refraction of flow lines such that flow in

the higher conductivity layer is essentially horizontal and flow in the lower

conductivity unit is essentially vertical (Anderson and Woessner 1992;

Freeze and Witherspoon 1967; Neuman and Witherspoon 1969).

(c) Cauchy condition: the flux across the boundary is dependant on the

magnitude of the difference in head across the boundary, with the head on

one side of the boundary being input to the model and the head on the other

75

side being calculated by the model. Examples of a Cauchy Boundary

include leakage from a surface water body where the flux is dependant on

the difference in elevation between the surface water and groundwater level

and the vertical hydraulic conductivity of the boundary; and

evapotranspiration where the flux is proportional to the depth of the water

table in an unconfined aquifer. A Cauchy Boundary has the advantage over

a Neuman Boundary in that its flux can be calculated by the model if given

sufficient input data.

A groundwater model may represent either steady state or transient aquifer

conditions. In a steady state groundwater model all flows in and out of the

model are equal and there is no net change in storage, consequently no

storage terms are required in the input parameters. A steady state model may

be run for different times and the outcome will be the same as time is

irrelevant under steady state conditions. A transient groundwater model

simulates stresses on an aquifer over time and is therefore divided into stress

periods which are further divided into time steps. The number of stress

periods can be input by the user and should reflect any temporal stress on

the aquifer such as recharge or extraction.

Initial hydraulic heads must be input before running the simulation. In the

case of a steady state model the heads can be estimates or averages of all the

available data, however, for transient models the heads can be real values or

can be the result of a steady state simulation. Heads at fixed head cells must

be real values and therefore should be interpolated from the nearest

observation bore.

Aquifer parameters including hydraulic conductivity and storativity must be

input to the grid, with hydraulic conductivity required for all simulations

while storage terms are only required for transient simulations. Vertical

hydraulic conductivity is required for each layer of a multiple layer model

and in the absence of field data is typically taken to be 10% of the horizontal

hydraulic conductivity (Kresic 1997). Transmissivity may be input manually

or MODFLOW can be set to calculate the transmissivity for each iteration

76

in each cell by multiplying the hydraulic conductivity by the saturated

thickness of the cell. Specific storage must be input manually for a Type 0

(confined) or Type 2 or 3 (convertible) and MODFLOW can calculate the

confined storage coefficient for each cell by multiplying the specific storage

by the saturated thickness. For a Type 1 (unconfined) and Type 2 or 3

(convertible) layer the specific yield must be input manually.

Recharge can be simulated in MODFLOW as a flux of length per unit time

across the top of a cell which is then combined with the dimensions of the

cell to calculate a flow rate per unit time entering the cell. Recharge can be

areally distributed over the entire model grid as infiltration, or restricted to a

single cell or group of cells allowing recharge zones to be delineated. There

is also the option to allocate recharge to the top layer, as would be the case

with infiltration to an unconfined aquifer, or to any layer in a multi layer

model, regardless of its position in relation to the top layer.

Groundwater extraction is simulated by a pumping well using the well

package. A well is allocated to an individual cell where it occupies the

entire cell and draws water out of the model from that cell. A well can be

allocated in any model layer and it is assumed that the well penetrates the

entire thickness of that layer and consequently draws from the entire layer.

The pumping rate must be specified as the L3 per unit time for the pumping

well such as L3/s or L3/day (where L is the length term) and this is used by

MODFLOW to calculate the net extraction from that well.

The Time Variant Specified Head package is used at the model boundaries

or at any other place where a fixed head changes over time but the change in

head is known. For cells designated as Time Variant Specified Head, a

starting head and an end head can be allocated for a stress period, simulating

the head change in those cells during the course of that stress period.

Numerous stress periods with head changes can then be used to represent

the change in head at a fixed head cell during a transient simulation. This

feature is particularly useful for simulating unnatural boundaries such as

cadastral boundaries of a hydrogeological system which are often defined

77

for the purposes of the modelling investigation. In a natural hydrogeological

system an aquifer may continue onwards past the boundary and therefore

must be accounted for in the simulation by placing a fixed or specified head

boundary, which can be modified to a time variant specified head boundary

for transient conditions.

Model calibration is the process of modifying one or more model

parameters until the results of the simulation match the measured data.

Calibration of an inverse problem involves modifying the boundary

conditions, hydraulic properties and stresses of the model until the simulated

heads match the observed heads, typically the case with real world

hydrogeologic systems. Calibration of a forward problem involves working

from an existing set of boundary conditions, hydraulic properties and

stresses to estimate heads, which is usually the case with a theoretical

system (Anderson and Woessner 1992). In an inverse problem such as this

study, it is usual to match the head outputs of the model to the observed

heads as head measurements are likely to be the most accurate and most

readily available. A steady state calibration is performed to water levels that

represent steady state conditions such as long term mean water levels, mean

annual water levels, or mean seasonal water levels for a particular season. A

quasi steady state calibration is conducted to water levels that represent the

aquifer’s behaviour at a given point in time under certain stresses applicable

at that time. Transient calibration is performed to water levels that represent

the aquifer’s response to stresses such as recharge and extraction over time,

and consequently it is essential to have some handle on the magnitude of

these fluxes for the duration of the modelling period in order to achieve

accurate calibration.

Two methods may be employed to reduce the non uniqueness of the

calibrated solution. Firstly the model should be calibrated with parameters

that are consistent with field measured parameters, for example aquifer

properties determined from pumping tests. Secondly the model should be

calibrated to multiple distinct hydrological conditions, to demonstrate that

the parameters chosen are capable of reproducing the system behaviour

78

under different hydrological stresses. The different hydrological conditions

used can be natural such as a dry period and a wet period, or artificial such

as variable extraction (Murray Darling Basin Commission 2000).

The process whereby the user modifies one or more parameters to achieve

model calibration is commonly known as trial and error calibration and may

be extremely time consuming. Automated calibration is conducted by a

specialised code working in conjunction with MODFLOW to achieve a

solution to an inverse problem. In a direct solution unknown parameters are

treated as dependant variables and heads are treated as independent

variables. In an indirect solution the heads are used to adjust one or more of

the model parameters so that the objective function (phi) or sum of squared

residuals (difference between observed and calculated heads) is reduced as

low as is possible. When performing automated calibration it is usual to

input an initial guess for a parameter value and both an upper and lower

limit for the parameter in order to constrain the calibration process within

acceptable limits. The most common program for automated calibration

currently is PEST (Doherty et al. 1994) and has been added onto all major

MODFLOW graphical user interfaces such as PMWIN (Chiang and

Kinzelbach 2001).

Whether the calibration method is trial and error or automated, several

techniques are commonly employed to assess the calibration. To

qualitatively gauge the efficiency of the calibration, contour plots of heads

may be constructed. To quantitatively assess the calibration, the difference

between observed and calculated heads, otherwise known as residuals, may

be compared graphically and statistically. When the mean of the residuals is

reduced to as close to zero as possible and the standard deviation is reduced

as much as possible, the model is calibrated. Plots of observed and

calculated heads over time can be used to graphically compare the

differences between the two head datasets during the course of the model

simulation. The calibration should also be evaluated by a standard statistical

method such as the Root Mean Square (RMS) Error, which is the average of

79

the squared differences in measured and simulated heads, as shown by the

following formula:

( )5.0

1

21 ⎥⎦

⎤⎢⎣

⎡−= ∑

=

n

iiCO HHnRMS

where

n = number of model observations

HO = observed head for each observation

HC = calculated head for each observation

Running a calibrated model with changes to a parameter by predetermined

amounts within a realistic range can be utilised to establish the model’s

sensitivity to that parameter and is known as a sensitivity analysis. It is

essential that only one parameter is varied at a time in order to see the

effects of the changes on the solution, and that any effects be evaluated by

the same statistical methods used to evaluate the model calibration.

In order to compensate for the effects of any bias or uncertainty in the

system stresses and boundary conditions used in the model solution, the

calibrated model should be tested under a different set of stresses and

boundary conditions in order to verify the model. Such an experiment is

most easily facilitated by running the model with a different set of head,

rainfall and pumping measurements in order to determine if the same level

of calibration accuracy can be replicated with the different datasets. If

successful the model can be deemed to be verified.

Prediction

Predictions can be used to test various scenarios of how a calibrated model

will respond to different system stresses such as recharge and extraction.

Predictions are limited by the uncertainties in the calibrated solution and the

accuracy of the verification.

80

Conceptualisation

Geological Framework

The bedrock in the study area is the Triassic–Jurassic Marburg Formation,

within which incised channels contain Quaternary alluvial fill. The alluvium

/ bedrock contact was obtained from geological maps and the extent and

area of alluvium in the Lockyer plain was calculated. The examination of 32

drill logs revealed a laterally continuous layer of gravel at the base of the

sequence, overlain by clay, sandy clay and silt. The gravel is a productive

aquifer with a mean thickness of 4.47 m while the overlying deposits form a

semi confining layer. A summary of geological data is presented in Table 4

with the locations of bores displayed in Figure 25. Two cross sections, both

west-east, are displayed in Figures 26 and 27.

Based on the width of the alluvium at cross section A – A’ (Figure 26) of

3000 m and the average depth to bedrock of 28.2 m, the width to depth ratio

of the channel is 106. Similarly the width of the alluvium at cross section B

– B’ (Figure 27) is 3480 m and the average depth to bedrock is 28 m,

resulting in a width to depth ratio of the channel of 124. The average

bedrock elevation on cross section A – A’ is 82 m and cross section B – B’

is 99 m, with a difference in elevation of 17 m. The distance between two

bores in the middle of these cross sections bores 491 and 231 is 5950 m,

resulting in a channel gradient of 0.00285.

Due to the high width to depth ratios of 106 and 124 of the cross sections

and the channel gradient of 0.00285, the alluvial sequence in the study area

can be classed as underflow dominated using the classification of Larkin

and Sharpe (1992).

81

Figure 25. Location of model extent and the 32 bores used to define the

hydrogeological framework for the conceptual model of the Lockyer plain.

Bore RN Easting

(AGD 84) Northing (AGD 84)

Surface elevation (mAHD)

Depth to gravel (m)

Depth to bedrock (m)

Gravel elevation (mAHD)

Bedrock elevation (mAHD)

Gravel Thickness (m)

106054 425310 6948653 111 22.6 27.7 88.4 83.3 5.1 171 425416 6949969 111.25 19.8 27.7 91.45 83.55 7.9 173 425722 6949386 113.48 22 25 91.48 88.48 3 175 425859 6949202 114.23 25.9 32.6 88.33 81.63 6.7 176 426081 6948896 114.64 22 24.4 92.64 90.24 2.4 177 426219 6948712 113.92 19.2 24.4 94.72 89.52 5.2 220 423801 6947943 120.01 26.8 29.7 93.21 90.31 2.9 221 424271 6947886 119 24.5 31.1 94.5 87.9 6.6 222 424575 6947692 120.03 20.7 22.9 99.33 97.13 2.2 227 422068 6945886 128.5 28.3 30.8 100.2 97.7 2.5 228 422427 6945831 127.1 27.1 30.5 100 96.6 3.4 229 422899 6945759 129 22.9 28 106.1 101 5.1 231 423332 6945678 128.5 27.4 33.4 101.1 95.1 6 232 423661 6945619 126.8 19.8 25.3 107 101.5 5.5 233 424073 6945560 125.2 20.3 26.5 104.9 98.7 6.2 235 424402 6945500 124.7 18.3 23.8 106.4 100.9 5.5 426 422681 6948966 115.9 18.7 25 97.2 90.9 6.3 428 422759 6949490 116.67 17.5 21.8 99.17 94.87 4.3 440 423956 6947059 123.52 25.9 29.5 97.62 94.02 3.6 442 423403 6947209 124.54 24.3 28 100.24 96.54 3.7 445 427435 6950520 110.02 24.9 29.8 85.12 80.22 4.9 446 428044 6950846 107.68 25.6 28 82.08 79.68 2.4 462 423823 6945612 126.92 20.4 26.2 106.52 100.72 5.8 489 423888 6948882 117.01 25.5 28 91.51 89.01 2.5 490 423285 6948817 116.61 18 24.5 98.61 92.11 6.5 491 426619 6950622 110.94 21.4 27 89.54 83.94 5.6 502 425414 6950369 111.9 25.6 27.8 86.3 84.1 2.2 516 425748 6949632 113.42 25.1 27 88.32 86.42 1.9 557 426155 6950373 110 25.75 28.4 84.25 81.6 2.65 444 427221 6950995 105 15.2 19.5 89.8 85.5 4.3 447 427520 6951427 105.59 18.8 27.1 86.79 78.49 8.3 449 426341 6951297 106.04 16.1 17.9 89.94 88.14 1.8

Table 4. Summary of bore logs used to define the thickness of the gravel aquifer in the study area.

Figure 26. Cross section A-A’ showing alluvial infill into channels incised in sandstone bedrock. Bore screens shown where records exist.

Figure 27. Cross section B-B’ showing alluvial infill into channels incised in sandstone bedrock. Bore screens shown where records exist.

85

Hydrologic Framework

When the gravel is fully saturated the aquifer exhibits confined conditions

and its upper surface forms a no flow boundary with the overlying semi

confining layer. In drought conditions when the demand for irrigation water

is high the potentiometric surface of the aquifer falls below the top of the

gravel layer in some locations; the aquifer exhibits unconfined behaviour

with the water table as its upper boundary. At all times a no flow boundary

also exists between the gravel and the adjacent and underlying sandstone

bedrock.

Unnatural boundaries were allocated in three locations for the purposes of

the modelling study, in the south at the junction of the two catchments, in

the west at the confluence of Ma Ma and Lockyer Creeks, and in the north

immediately downstream of the confluence of Tenthill and Lockyer Creeks.

These boundaries were allocated in order to enclose the Lockyer plain. A

monitoring bore is situated at each of these locations and the head on the

boundary is known, enabling these boundaries to be designated as Dirichlet

(constant head) boundaries.

From the cross sections in Figure 26 and 27 two hydrostratigraphic units

were identified, the gravel aquifer and the mixed sands and clays of the semi

confining layer. All monitoring bores are screened in the gravel aquifer and

therefore water level measurements and water samples taken from these

bores are representative of the basal aquifer, not the semi confining unit and

as such represent a potentiometric surface. In addition the results of pump

tests conducted on these bores and the estimates of hydraulic properties are

also indicative of the gravel. Therefore the gravel aquifer was designated as

the single hydrostratigraphic unit. As presented in the results section, the

hydraulic conductivity values of the gravel were estimated at 63 and 79

m/day which were averaged for the conceptual model to 70 m/day; and

storativity (storage coefficient) was estimated at 0.0016 which was divided

by the aquifer thickness of 4 m to obtain the specific storage of 0.0004.

Specific yield was conceptualised as 0.24 which is suggested as the mean

value of specific yield for gravel by Morris and Johnson (1967).

86

Preparation of a water budget and definition of the flow system involves

identifying and quantifying all fluxes into and out of the hydrogeological

system. Areal recharge through the clay, sandy clay and silt was considered

unlikely due to the low permeability of these sediments and an average

infiltration rate of 12 mm/year for unsaturated sediments of the Lockyer

Valley was calculated using tritium methods (Ellis 1999). Preferential

recharge through the creek channels was considered the primary source of

recharge to the gravel aquifer. This interpretation is because bore 516

adjacent to Tenthill Creek displays a positive response to a monthly rainfall

of 100 mm or greater, indicating such a minimal amount of rainfall can have

an effect on measurements in a nearby bore (Figure 28). A flood event in

May 1996 when 400 mm of rain was received in 4 days had a dramatic

effect on this bore, with levels rising 4 m in 4 days, and continued flow in

creeks resulting from this event filled the aquifer to its pre 1993-1995

drought levels.

A surface water sample collected during the flood in May 1996 is extremely

fresh with a conductivity of 250 µS/cm, while the conductivity of a sample

collected later that year in July was 490 µS /cm. The ionic proportions of

surface water did not change from May to July, however the ionic

concentrations increased, with those of the July sample approaching the

concentrations of groundwater as indicated on the Schoeller diagram (Figure

18). The increase in salinity from May to July is likely due to evaporation,

with water standing in the creek channels after the flood event.

Ratios of stable isotopes δ2H and δ18O also support preferential recharge

through the creek channels as the dominant recharge mechanism. Infiltration

through the mixed sand and clay overlying the aquifer was quantified as 12

mm/year using tritium methods (Ellis and Dharmasiri 1998; Ellis 1999). In

the same studies, stable isotopes were also measured in pore water from drill

cores of the mixed sand and clay at 5 different sites throughout the Lockyer

Valley. The ratios of δ2H and δ18O for pore water from these cores plot on a

slope of 2.9. By contrast a plot of δ2H vs δ18O for water samples from the

87

0

50

100

150

200

250

300

350

400

450

500

Jan-93 Jan-94 Jan-95 Jan-96

Date

Mon

thly

rain

fall

(mm

)

82

84

86

88

90

92

94

96

98

100

Hea

d (m

asl)

Monthly RainfallHead

Figure 28. Hydrograph of bore 516 adjacent to Tenthill Creek for period

1993-1996, showing 100 mm is the minimum monthly rainfall needed for

positive response from groundwater.

88

gravel aquifer taken during the current study plot on a slope of 5.56 (Figure

23). A slope of between 2 and 3 is indicative of evaporation from the

unsaturated zone, while a slope of between 4 and 6 is indicative of

evaporation from a surface water body (Gat 1981).

These relationships suggest the following:

(a) Water from the unsaturated zone has undergone different evaporative

processes to that of groundwater.

(b) Infiltration through the semi confining layer is extremely low and has

minimal influence on the aquifer (Ellis and Dharmasiri 1998; Ellis 1999).

(c) Water from the gravel aquifer has undergone evaporation characteristic

of standing surface water at some stage (data from this study).

The effects of evaporative concentration from re-infiltration of spray

irrigation water can be discounted due to the extremely low infiltration rate

of the semi-confining layer. Therefore seepage of surface water from the

creek channels is the dominant recharge process.

A study of a similar alluvial system in the Logan Albert catchment (Please

et al. 1997), with a gravel and sandy gravel aquifer ranging from 1-10 m

thick overlain by a semi confining unit of mixed sands and clays ranging

from 10-20 m thick, proposed evaporation from surface water as the cause

of isotopic enrichment in groundwater. For the three sub-catchments, plots

of δ2H vs δ18O produced slopes of 6.61, 5.62 and 4.59. The most enriched

samples were found to occur in bores adjacent to the drainage channels,

suggesting that some recharge was received from evaporated surface water

bodies. In addition an increase in enrichment was observed down the flow

path providing further evidence of evaporated surface water contribution.

Like NRM&E monitoring bores, private irrigation bores are also screened in

the gravel aquifer for the best yields possible. Groundwater extraction of the

Lockyer plain has not been measured, however, in the NRM&E proclaimed

area to the east of Gatton all private irrigation bores have been installed with

automatic meters to measure the volumes of groundwater withdrawn in ML.

Data exists for this region for a 4 year period from 1993 – 1997, with meters

89

being read approximately every 3 months. The total extraction ranges from

18.9 – 70 ML/day over an area of 10800 ha (Durick and Bleakley 2003). By

contrast the Lockyer plain of this study covers an area of 1460 ha, which

can be rounded up to one eighth the size of the NRM&E proclaimed area.

Dividing the extraction rates of the NRM&E proclaimed area by eight

produces extraction rates ranging from 2.36 – 8.75 ML/day for the Lockyer

plain. As the landholders in the study area are practising the same forms of

agriculture as in the NRM&E proclaimed area, growing the same species of

crops using groundwater for irrigation, the rates from the proclaimed area

are applicable for this study on a volume per hectare basis and produce the

best estimation of data available.

Figure 29 (overleaf). Conceptual hydrogeological model for cross section

A-A’ on the Lockyer plain. Water levels are shown at the beginning of the

proposed simulation period in March 1993, at their lowest point in October

1995 and at the end of the simulation period in November 1996 following a

major flood event. Estimates of aquifer properties hydraulic conductivity

and specific storage determined from pump tests are shown for the gravel

aquifer with a literature value of 0.24 applied for specific yield. The

similarity between both the major ion chemical and stable isotopic

composition of surface water and groundwater indicates recharge from

creek channels is the dominant recharge process. This is supported by the

different stable isotopic composition of water from the mixed sand and clay

semi confining layer and the low infiltration rates for this layer presented by

Ellis and Dharmasiri (1998) and Ellis (1999). Groundwater extraction from

the gravel aquifer ranging from 2.4-8.75 ML/day was calculated for the

Lockyer plain based on data presented in Durick and Bleakley (2003).

Discharge of higher salinity groundwater may occur from the adjacent and

underlying sandstone bedrock aquifers. Arrows show fluxes.

91

Calibration

Spatial Discretisation

To represent the Lockyer plain a model grid of 50 columns x 50 rows was

selected. The grid size was selected as 200 x 200 m as this size had been

used successfully to model a similar alluvial system with a similar

resolution of geological and water level data in the NRM&E proclaimed

area. Utilising the same grid size as that study would enable useful

comparisons between these two areas for water resource planning. The grid

was angled at 62.68 deg from east so that the grid was orientated with the

main axes of the hydraulic conductivity tensor, thus all cells were

perpendicular to the flow direction (Figure 30).

Boundary Conditions

The IBOUND array in MODFLOW was used to designate the different

boundaries and their types in the model. A base map was positioned under

the model grid and used to distinguish the alluvium-bedrock contact. Grid

cells outside the alluvium coverage were all allocated a value of 0 in the

IBOUND array thus rendering these cells as inactive and creating a no flow

boundary between the alluvium and bedrock. Cells inside the area of

alluvium were all left with the default value of 1 and therefore they

remained active. The bounds of the Lockyer plain in the south, west and

north, created for the purposes of this modelling investigation, were all

allocated a value of -1, designating these cells as fixed head (Dirichlet

conditions) resulting in a total of 30 fixed head cells. This was necessary as

the aquifer continues onwards past the boundary and therefore must be

accounted for by placing fixed or specified head cells, in which the allocated

head is known (Figure 30).

Layer type

Although two hydrostratigraphic units were identified in the conceptual

model, only the gravel aquifer could be modelled, largely due to the total

absence of head data for the overlying semi confining unit, and therefore a

one layer model was chosen. As shown on previous hydrographs the

92

Figure 30. Model grid orientated at 62.68 degrees from east showing active

cells (white), inactive cells (grey) and fixed head cells (green).

93

potentiometric head of the aquifer varies over time and when the gravel is

fully saturated confined conditions prevail, while when the water level falls

below the top of the gravel unconfined conditions prevail. For this reason

alone, a type 3 layer was selected in PMWIN to represent the gravel aquifer.

A type 3 layer allows the layer to convert from confined to unconfined as

the head varies, and the transmissivity of each cell is recalculated for each

model iteration based on the hydraulic conductivity and the saturated

thickness of each cell.

Top and Bottom of Layer

The top of the aquifer, and therefore the top of the layer was taken as the top

of the gravel. The elevation of the gravel surface was obtained from 32 bore

logs and these data points were then interpolated by kriging into the model

grid (Figure 31). The bottom of the aquifer, and therefore the bottom of the

layer was taken as the contact between alluvium and the underlying

sandstone bedrock. The elevation of the bedrock was also obtained from 32

bore logs and interpolated by kriging into the model grid (Figure 32).

Time

The aquifer in the lower plain is under constant pressure from extraction,

and to truly reproduce its behaviour a transient model is required. The

period March 1993 – November 1996 was chosen for the simulation as it

represents the aquifer’s response to a 3 year drought and the associated

decline in water levels due to the increase in demand for irrigation water,

followed by a flood in May 1996 in which the aquifer was recharged

significantly. This period was also selected as it contains water level

measurements at approximately 3 monthly intervals or better, while prior to

March 1993 the preceding measurement was 6 months earlier and after

November 1996 the following measurement was 10 months later. Such long

hiatus in water level measurements greatly decrease the accuracy of the

model calibration in a hydrogeological system under constant stress. Finally

the governing variable for the selection of the period to be modelled was the

availability of extraction data for the same period from the NRM&E

proclaimed area which could be applied at the same rates per unit area for

94

Figure 31. Top of layer contours interpolated from bore logs with 1 m

interval.

Figure 32. Bottom of layer contours interpolated from bore logs with 1 m

interval.

95

this modelling study. The model period contained 16 water level

measurements and was subdivided into 15 stress periods with a

measurement at the start and end of each stress period. By trial and error a

timestep of 7 days was identified as the largest possible timestep that did not

affect the solution outcome and therefore was implemented as

recommended by Anderson and Woessner (1992). For a summary of

temporal data refer to Table 5.

Stress Period Start Finish WL Date

Length (Days) Timesteps

Cumulative (Days)

1 8/03/1993 11/05/1993 11/05/1993 64 9 64 2 12/05/1993 5/08/1993 5/08/1993 86 12 150 3 6/08/1993 24/11/1993 24/11/1993 111 16 261 4 25/11/1993 28/01/1994 28/01/1994 65 9 326 5 29/01/1994 29/03/1994 29/03/1994 60 9 386 6 30/03/1994 26/05/1994 26/05/1994 58 8 444 7 27/05/1994 21/09/1994 21/09/1994 118 17 562 8 22/09/1994 11/01/1995 11/01/1995 112 16 674 9 12/01/1995 11/04/1995 11/04/1995 90 13 763

10 12/04/1995 21/07/1995 21/07/1995 101 14 863 11 22/07/1995 17/10/1995 17/10/1995 88 12 950 12 18/10/1995 17/01/1996 17/01/1996 92 13 1042 13 18/01/1996 27/03/1996 27/03/1996 70 10 1112 14 28/03/1996 26/07/1996 26/07/1996 121 17 1233 15 27/07/1996 9/11/1996 9/11/1996 106 15 1339

Table 5. Summary of temporal data.

Initial Heads

The hydrogeological system in the study area is under constant stress from

extraction and has never been at a steady state during the period for which

water level measurements exist. Consequently a steady state calibration was

not possible and initial heads could not be sourced from the results of a

steady state simulation as is common in modelling practice. Instead the

heads measured at the beginning of the period to be modelled, 8 March

1993,were used as initial heads for the start of the simulation. The head

dataset was interpolated into the model grid using kriging (Figure 33).

96

Observation boreholes

Ten NRM&E monitoring boreholes exist in the Lockyer plain with 3

monthly or better water level measurements for the simulation period and

were utilised as data points for head matching during calibration. These 10

bores were also used in the interpolation of initial heads and time variant

specified head boundary conditions and their locations are shown in Figure

33.

Aquifer properties

Horizontal hydraulic conductivity was applied at a blanket value of 70

m/day. The specific storage was applied at a blanket value of 0.0004 to all

cells in the grid so that the confined storage coefficient was calculated by

PMWIN in each cell based on the thickness of the cell. The unconfined

storage term, specific yield was applied at a blanket value of 0.24 for the

entire grid.

Time Variant Specified Head

The cells defined as fixed head boundaries in the IBOUND array were

modified with the Time Variant Specified Head package to simulate the

change in head at these boundaries over time. The package allows the heads

at the boundary cells to be input for the start and end of each stress period.

For each stress period, the start and end set of head measurements were

interpolated using kriging from the set of 10 observation bores, and the

values at the boundary cells were allocated for the start and end of the stress

period using the Time Variant Specified Head Package.

97

Figure 33. Initial heads interpolated from 10 head measurements in March

1993 with 1 m contour interval.

Figure 34. Locations of Tenthill Creek (east) and Lockyer Creek (north)

and Ma Ma creek (west) in the model grid.

98

Recharge

Recharge was conceptualised as not areally distributed but as preferential

seepage through the creek channels. As no creeks in the study area were

gauged during the period of the model simulation the MODFLOW River

package could not be used to estimate the flux from the creeks to the

aquifer. Therefore the recharge flux was unknown and was estimated by

PEST during calibration. Hydrograph peaks and monthly rainfall indicate

recharge occurred in stress periods 2, 5, 9, 12, 13, 14 and 15; with the two

last stress periods corresponding to the May 1996 flood event and the

subsequent standing water in the creek channels for several months. Using a

base map of the drainages, Tenthill and Lockyer Creeks were digitised as

recharge cells in the model grid. Ma Ma Creek was not digitised as recharge

cells as it flows over bedrock for much of its length in the Lockyer plain

(Figure 34). The creek channels were divided into seven different recharge

zones, based on the locations of monitoring bores for increased accuracy in

estimating recharge during calibration. In total 73 cells were designated as

recharge cells (Figure 35).

Extraction

Pumping from the aquifer for irrigation was simulated by the well package.

The volumes of water extracted from the NRM&E proclaimed area have

been measured and expressed as volume per time as shown in the table

below. As the rate of groundwater extraction per unit time for the study area

is largely unknown, it was decided to apply the pumping rates of the Central

Lockyer on a volume per area basis. The Central Lockyer model constructed

by Durick and Bleakley (2003) contained 2700 active cells, excluding

boundary cells, covering an area of 10800 ha. By contrast the Lockyer plain

covers an area of 1800 ha and this model contained 478 active cells. Of

these 478 active cells 30 were time variant specified head cells, 73 were

recharge cells and 10 contained a water level observation bore, leaving 365

active cells for potential extraction. This represents an area of 1460 hectares,

which has been rounded up to one eighth the size of the proclaimed area. To

adapt the pumping rates of the NRM&E proclaimed area to the Lockyer

99

Figure 35. Locations of 7 recharge zones relative to observation bores.

Figure 36. Extraction cells applied to entire model grid excluding the 30

time variant specified head cells, the 73 recharge cells and each of the 10

cells containing an observation bore.

Table 6. Summary of extraction data.

Stress Start Finish No of Days Central Lockyer Extraction Rate m3/Day m3/Day

Period Extraction Rate divided by 8 divided by

(ML/Day) (ML/Day) 365 pumping

cells 1 8/03/1993 11/05/1993 64 70.00 8.75 8750.00 23.97 2 12/05/1993 5/08/1993 86 61.21 7.65 7651.74 20.96 3 6/08/1993 24/11/1993 111 60.29 7.54 7536.15 20.65 4 25/11/1993 28/01/1994 65 53.38 6.67 6673.08 18.28 5 29/01/1994 29/03/1994 60 46.04 5.76 5755.00 15.77 6 30/03/1994 26/05/1994 58 44.61 5.58 5576.29 15.28 7 27/05/1994 21/09/1994 118 63.62 7.95 7952.12 21.79 8 22/09/1994 11/01/1995 112 52.57 6.57 6570.76 18.00 9 12/01/1995 11/04/1995 90 30.61 3.83 3826.25 10.48

10 12/04/1995 21/07/1995 101 41.14 5.14 5142.08 14.09 11 22/07/1995 17/10/1995 88 39.30 4.91 4912.78 13.46 12 18/10/1995 17/01/1996 92 23.70 2.96 2963.04 8.12 13 18/01/1996 27/03/1996 70 18.90 2.36 2362.50 6.47 14 28/03/1996 26/07/1996 121 25.49 3.19 3186.36 8.73 15 27/07/1996 9/11/1996 106 30.31 3.79 3789.03 10.38

101

plain the extraction rates were divided by eight and converted to m3 per day

for each stress period for input to PMWIN as summarised in Table 6.

In the NRM&E proclaimed area the locations, pumping rates and pumping

durations of each irrigation bore were known with reasonable confidence,

however for the Lockyer plain this data was largely unknown. Therefore to

avoid any bias in the allocation of extraction rates to the model grid, a

blanket value of extraction was applied to all the 365 cells. The 30 time

variant specified head cells, 73 recharge cells and 10 observation bore cells

were not allocated a pumping rate as this would create errors in the

modelling calibration (Figure 36).

Calibration

The flow model was calibrated as an inverse problem with head values,

boundary conditions, aquifer properties, and extraction all input and the

model used to estimate recharge. PEST was used for calibration of recharge

fluxes in meters per day for each of the seven zones for each of the seven

stress periods when recharge occurred. PEST requires a Parval value or

initial starting value for the optimisation process and this was initially set at

10% of Gatton rainfall for each stress period designated to receive recharge.

The Parval was allowed to vary between a minimum of 1E-06 of the Parval

value and a maximum of 100% of the rainfall. The Parameter

transformation was set at log transformed which is suitable for values which

do not become negative during the optimisation process such as recharge.

Plots of observed and calculated heads for the entire model simulation

display an initial gap between the observed and model calculated heads

which may be due to numerical instability at the beginning of the

simulation, however after the first two stress periods the graphs display a

close fit and clearly correspond for the recharge event of May 1996 (Figure

37). The optimisation results from PEST produced a phi value of 4002 from

1900 observations and a correlation coefficient of 0.9650. The calibrated

recharge values were then input to the model and the model subsequently

run and using the residuals for all model observations the RMS error was

calculated as 1.61m. A water budget for each stress period in the model is

presented in Figure 38. A graph of the total rainfall for each stress period

102

446

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

445

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

502

85

90

95

100

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

516

85

90

95

100

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 37. Head time graphs of observed and calculated heads.

103

514

92949698

100102

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

220

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

221

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

442

95100105110115

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 37. Head time graphs of observed and calculated heads.

104

490

90

95

100

105

0 2 4 6 8 10 12 14 16

Stress period

Hea

d (m

asl)

CalculatedObserved

462

102104106108110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 37. Head time graphs of observed and calculated heads.

105

Period 1 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 23053.01 151.91 22901.10

CONSTANT 56309.62 460.89 55848.73 HEAD

WELLS 0 78750.15 -78750.15

RECHARGE 0 0 0

SUM 79362.63 79362.95 -0.32

Period 2 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 4203.53 2688.22 1515.32

CONSTANT 64886.35 2593.53 62292.83 HEAD

WELLS 0 91821.20 -91821.20

RECHARGE 28012.39 0 28012.39

SUM 97102.28 97102.94 -0.66

Period 3 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 22774.99 0.00 22774.99

CONSTANT 97863.61 59.87 97803.74 HEAD

WELLS 0 120578.33 -120578.33

RECHARGE 0 0 0

SUM 120638.60 120638.20 0.40

Period 4 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 12480.27 172.63 12307.64

CONSTANT 47954.20 205.61 47748.59 HEAD

WELLS 0 60057.51 -60057.51

RECHARGE 0 0 0

SUM 60434.47 60435.76 -1.28

Period 5 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 2713.64 8510.06 -5796.42

CONSTANT 35947.27 945.94 35001.33 HEAD

WELLS 0 51794.90 -51794.90

RECHARGE 22588.73 0 22588.73

SUM 61249.64 61250.90 -1.26

Figure 38. Water budget for each stress period of the model

106

Period 6 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 11818.84 129.41 11689.43

CONSTANT 33469.28 546.98 32922.31 HEAD

WELLS 0 44610.27 -44610.27

RECHARGE 0 0 0

SUM 45288.12 45286.65 1.47

Period 7 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 74342.06 0.00 74342.06

CONSTANT 63214.22 2367.97 60846.25 HEAD

WELLS 0 135185.99 -135185.99

RECHARGE 0 0 0

SUM 137556.27 137553.96 2.31

Period 8 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 72386.17 268.86 72117.31

CONSTANT 35737.71 2722.86 33014.85 HEAD

WELLS 0 105132.08 -105132.08

RECHARGE 0 0 0

SUM 108123.88 108123.80 0.08

Period 9 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 22188.45 8424.85 13763.60

CONSTANT 24225.26 1695.58 22529.69 HEAD

WELLS 0 49741.39 -49741.39

RECHARGE 13446.83 0 13446.83

SUM 59860.54 59861.81 -1.28

Period 10 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 45077.66 353.27 44724.40

CONSTANT 27814.11 549.76 27264.36 HEAD

WELLS 0 71989.11 -71989.11

RECHARGE 0 0 0

SUM 72891.78 72892.14 -0.36

Figure 38. Water budget for each stress period of the model

107

Period 11 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 42777.90 3.42 42774.48

CONSTANT 18565.88 2388.75 16177.13 HEAD

WELLS 0 58953.34 -58953.34

RECHARGE 0 0 0

SUM 61343.78 61345.51 -1.72

Period 12 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 6445.26 98307.66 -91862.40

CONSTANT 34387.35 3988.90 30398.45 HEAD

WELLS 0 38519.53 -38519.53

RECHARGE 99980.38 0 99980.38

SUM 140812.98 140816.09 -3.11

Period 13 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 4415.73 52430.46 -48014.73

CONSTANT 36113.69 3758.92 32354.77 HEAD

WELLS 0 23625.10 -23625.10

RECHARGE 39283.13 0 39283.13

SUM 79812.55 79814.48 -1.93

Period 14 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 167.39 125679.63 -125512.24

CONSTANT 72128.46 8764.07 63364.39 HEAD

WELLS 0 54168.05 -54168.05

RECHARGE 116311.75 0 116311.75

SUM 188607.60 188611.74 -4.14

Period 15 FLOW TERM IN (m3) OUT (m3)

IN-OUT (m3)

STORAGE 2033.31 49936.61 -47903.30

CONSTANT 71287.74 8474.76 62812.98 HEAD

WELLS 0 56835.29 -56835.29

RECHARGE 41924.95 0 41924.95

SUM 115246.00 115246.67 -0.67

Figure 38. Water budget for each stress period of the model

108

Correlation between rainfall (m) and calibrated recharge volume (m3) for each stress period

0

0.1

0.2

0.3

0.4

0.5

0.6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Stress period

Rai

nfal

l (m

)

0

20000

40000

60000

80000

100000

120000

140000

Rec

harg

e vo

lum

e (m

3)

Rainfall (m)Recharge Volume (m3)

Figure 39. Graph of rainfall and derived recharge volumes for each stress

period of the model.

109

with the calibrated recharge volume (Figure 39) displays a strong

correlation between these two parameters.

Sensitivity Analysis

To determine the calibrated solution’s sensitivity to the aquifer properties

hydraulic conductivity and specific yield each was varied in turn by factors

of 0.5, 0.8, 1.2, 1.5 so that all values were within realistic bounds for each

parameter. These multipliers and the resultant values are shown in Table 7

below:

Multipliers 0.5 0.8 1.2 1.5

Parameter Calibrated Value Hydraulic

Conductivity 70 35 56 84 105 Specific Yield 0.24 0.12 0.192 0.288 0.36

Table 7. Parameter variations used in the sensitivity analysis.

Specific storage was varied by an order of magnitude each way from the

calibrated value of 0.0004 in order to see a significant change. Model

simulations were then run with each parameter being varied by the above

values while the other two parameters were kept constant, culminating in a

total of 10 model runs. Graphs of RMS error versus each varied parameter

value demonstrate the relative sensitivity of the model to each parameter

change. For hydraulic conductivity the value of 70 m/day and RMS error of

1.61m for the calibrated model is by far the lowest point on the graph, and

the model is relatively insensitive to the variables of 56, 84 and 105 m/day

compared with the outlier of 35 m/day (Figure 40). For specific yield the

variables of 0.12 and 0.192 both produced a higher RMS error than the

calibrated model value of 0.24, while for the other variables RMS error

decreases as specific yield increases (Figure 41). For specific storage the

variable of 0.00004 plots slightly below the value of 0.0004 for the

calibrated model, while the other variable of 0.004 produced a much higher

RMS error (Figure 42).

110

Hydraulic Conductivity Sensitivity

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110

Hydraulic conductivity (m/day)

RM

S er

ror

Figure 40. Graph of RMS error vs hydraulic conductivity, showing the

model is highly sensitive to a decrease in hydraulic conductivity and

relatively less sensitive to increases in hydraulic conductivity.

Specific Yield Sensitivity

0

1

2

3

4

5

6

7

0.1 0.15 0.2 0.25 0.3 0.35 0.4

Specific yield

RM

S er

ror

Figure 41. Graph of RMS error vs specific yield showing model is more

sensitive to decreases in specific yield compared to increases in this

parameter which produced lower RMS errors.

111

Specific Storage Sensitivity

0

1

2

3

4

5

6

7

8

9

10

11

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032 0.0036 0.004 0.0044

Specific Storage

RM

S er

ror

Figure 42. Graph of RMS error vs specific storage showing model is

relatively insensitive to decreasing the specific storage by an order of

magnitude, yet highly sensitive to increasing the specific storage by an order

of magnitude.

112

The effects of no groundwater extraction were also tested as part of the

sensitivity analysis. Groundwater extraction from the WEL package was

turned off for the entire simulation and the model was run. All hydrographs

display higher calculated than observed heads (Figure 43) than in the

calibrated solution (Figure 37). The RMS error was 9165m, considerably

higher than in the calibrated solution.

The model’s sensitivity to the applied boundary conditions was tested in two

ways. Firstly all the time variant specified head boundary cells were

replaced by fixed head cells which remained constant for the entire model

simulation. The fixed head cells were set at the same values as those applied

for the initial hydraulic heads in those cells and the model was run.

Hydrographs of bores near the boundaries are highly influenced by the fixed

head boundaries, with higher calculated than observed heads (Figure 44),

and higher calculated heads than in the calibrated model (Figure 37). The

resulting RMS error of 6961m was also much higher. Secondly the time

variant specified head boundary cells were retained on the southern and

northern alluvial boundaries of the study area however the western

boundary was replaced with a no flow boundary. Head time graphs

demonstrate an improved correlation (Figure 45) when compared to the

previous simulation (Figure 44), and a lower RMS error of 966 m.

To investigate the influence of the semi-confining unit of mixed sands and

clays on the gravel aquifer a two layer model was constructed, covering an

area identical to that of the single layer model. Layer 1 represented the

mixed sands and clays and layer 2 the gravel aquifer. All existing

parameters were retained for layer 2, while for layer 1, the semi confining

unit, a number of assumptions were made: k = 1 m/day, Ss = 0.001, Sy =

0.01 all of which are within the range for sandy clay (Heath 1983;

Domenico 1972; Morris and Johnston 1967). Vertical hydraulic

conductivity is required for each layer of a multiple layer model. Vertical

hydraulic conductivity was taken to be 10% of the horizontal hydraulic

conductivity values listed above, in accordance with the relationship

outlined by Kresic (1997). The initial hydraulic heads were assumed to be

113

446

85

90

95

100

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

445

889092949698

0 5 10 15 20

Stress Period

Hea

d (m

asl)

CalculatedObserved

502

859095

100105

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

516

859095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 43. Head time graphs for simulation with no groundwater extraction.

114

514

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

220

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

221

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

442

95100105110115

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 43. Head time graphs for simulation with no groundwater extraction.

115

490

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

462

102104106108110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 43. Head time graphs for simulation with no groundwater extraction.

116

446

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

445

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

502

859095

100105

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

516

859095

100105

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 44. Head time graphs for simulation with all time variant specified

head boundaries replaced by constant head boundaries set at initial heads.

117

514

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

220

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

221

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

442

95100105110115

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 44. Head time graphs for simulation with all time variant specified

head boundaries replaced by constant head boundaries set at initial heads.

118

490

90

95

100

105

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

462

102104106108110112

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 44. Head time graphs for simulation with all time variant specified

head boundaries replaced by constant head boundaries set at initial heads.

119

446

88

90

92

94

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

445

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

502

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

516

85

90

95

100

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 45. Head time graphs for simulation with western time variant

specified head boundary only replaced by no flow boundary.

120

514

90

95

100

105

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

220

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

221

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

442

95100105110115

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 45. Head time graphs for simulation with western time variant

specified head boundary only replaced by no flow boundary.

121

490

90

95

100

105

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

462

102104106108110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 45. Head time graphs for simulation with western time variant

specified head boundary only replaced by no flow boundary.

122

446

88

90

92

94

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

445

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

502

8890929496

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

516

85

90

95

100

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 46. Head time graphs for two layer model with derived recharge

rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall

for layer 1.

123

514

92949698

100102

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

220

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

221

9095

100105110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

442

95100105110115

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 46. Head time graphs for two layer model with derived recharge

rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall

for layer 1.

124

490

90

95

100

105

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

462

102104106108110

0 2 4 6 8 10 12 14 16

Stress Period

Hea

d (m

asl)

CalculatedObserved

Figure 46. Head time graphs for two layer model with derived recharge

rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall

for layer 1.

125

potentiometric heads and set as the same for layer 2. Recharge was applied

as 1% of rainfall to layer 1 for each stress period when recharge was

received (Table 5), while for layer 2 the derived recharge rates from the

calibrated model were retained and applied to only layer 2 using the WEL

package. The model was run, producing higher calculated than observed

heads (Figure 46) and the resulting RMS error was 796m.

Prediction

In order to determine the safe annual extraction rate for the total model

duration of 44 months, the calibrated solution was run with 6 different

annual extraction scenarios to determine the minimum saturated thickness in

the aquifer at the end of stress period 11 in October 1995, when the water

levels were at their lowest point before the major recharge of stress periods

12, 13, 14 and 15 in 1996. The annual extraction rates were applied in ML

per ha, converted to m3 per day for input to PMWIN and applied for each

day of the 44 months of the model simulation. By trial and error it was

established that the maximum annual extraction rate before any cell goes

dry at the end of stress period 11 is 1.75 ML/ha and the minimum saturated

thickness of the aquifer is 0.029 m. The model was run with additional

annual extraction scenarios of 1.5, 1.25, 1, 0.75 and 0.5 ML/ha and the

corresponding minimum saturated thicknesses are summarised in Figure 47.

126

Minimum saturated thickness of aquifer vs annual extraction rate

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2

Annual extraction rate (ML/Ha)

Min

imum

sat

urat

ed th

ickn

ess

(m)

Figure 47. Graph of minimum saturated thickness of aquifer at end of stress

period 11 versus annual extraction rate applied for entire simulation.

Minimum saturated thickness decreases as pumping rate increases.

127

Discussion of Groundwater Modelling

In the model calibration all 10 observation bores display an initial gap

between the observed and calculated heads as shown in the head time

graphs of Figure 37. This deficit is possibly due to numerical instability at

the beginning of the simulation as the initial heads were not sourced from a

steady state simulation but rather from real head data recorded in March

1993 which is the beginning of the model period. The simulation period was

chosen to be from March 1993 to November 1996 as these years include the

aquifer’s response to a drought from 1993 to late 1995 followed by regular

rain in the summer of 1995-96, culminating in a flood event in May 1996.

The other crucial point in the nomination of the simulation period was the

availability of extraction data recorded by meters on all irrigation bores in

the NRM&E Proclaimed Area, as this data could be adapted for the Lockyer

plain. As metering of private irrigation bores does not occur in the study

area, the pumping rates utilised in the model were adapted on a volume per

unit area from the extraction records of the NRM&E proclaimed area. The

addition of meters on private irrigation bores in the study area would greatly

increase the accuracy of the extraction rates in the model. If the location and

pumping rates of all irrigation bores are known it would also permit better

determination of the spatial distribution of aquifer properties as done by

Durick and Bleakley (2003)

In the current modelling study the estimates of the aquifer properties

hydraulic conductivity and specific storage were based on two pumping

tests conducted with a pumping bore and a NRM&E monitoring bore close

enough to observe drawdown and recovery. Additional NRM&E monitoring

bores drilled close enough to private irrigation bores to be influenced by

pumping at distances of 15 m or less would enable better delineation of the

spatial distribution of aquifer properties which could be input to the model

grid as different zones.

128

Although the influence of the semi confining layer of clay, sandy clay and

silt has been shown to be minimal (Ellis and Dharmasiri 1998; Ellis 1999),

the provision of monitoring bores within this hydrostratographic unit would

allow leakage rates to the aquifer to be calculated in the long term, further

increasing the accuracy of any water resource studies. In addition, any

upward leakage from the adjacent and underlying sandstone aquifers, which

has been qualitatively shown to occur, cannot be quantified due to the total

absence of monitoring bores screened in the sandstones.

As streams in the study area were not gauged during the period of the model

simulation there is no stream stage data to compare with the calibrated

recharge volumes derived using PEST. Consequently the recharge volumes

have been compared with rainfall for each stress period of the model to find

a physical process for the varying recharge rates. A graph of rainfall (m) and

calibrated recharge volumes (m3) for each stress period in Figure 39

demonstrates a strong correlation between these two parameters and

indicates that temporal variations in rainfall throughout the model

simulation are the controlling variable on the calibrated recharge volumes.

To investigate the sensitivity of the calibrated model to variations in the

aquifer properties hydraulic conductivity and specific yield, these were both

increased and decreased by factors of 20% and 50% so that the variables

were still within realistic bounds for gravel. Specific storage was varied by

an order of magnitude each way in order to see a significant change. The

model has demonstrated relative insensitivity to increases in hydraulic

conductivity, however decreases in this parameter have resulted in a much

higher RMS error. The storage terms specific yield and specific storage

display an inverse and a direct relationship respectively with the RMS error

with the calibrated parameters sitting in the middle of the curve. It is

therefore plausible that the aquifer material has a higher specific yield of

0.36, and a lower specific storage of 0.00004 than the calibrated values.

The higher specific yield of 0.36 which produced a RMS error lower than

the calibrated value of 0.24 may suggest that the aquifer material is more

129

sandy than previously thought. A maximum of 0.46 and mean of 0.32 for

the specific yield of sand were presented by Morris and Johnson (1967).

NRM bore completion details indicate that monitoring bores are typically

screened in the gravel, irrespective of whether the gravel is overlain by a

sand lens or not at that point. For this modelling study the thickness of

gravel was taken as the thickness of the aquifer in order to produce a

conservative estimate of the water resource. If future monitoring bores are

screened in the sand, where it is present, it may be possible to model sand as

an additional hydrostratigraphic unit and to investigate the potential release

from storage of this unit.

A lower specific storage of 0.00004 is still within the bounds of specific

storage of gravel set out by Domenico (1972), however the calibrated value

of 0.0004 was obtained from a pumping test. A possible explanation may be

the short duration of the pumping test of 90 minutes in which the aquifer

was not stressed long enough which decreased the accuracy of the estimates

of the aquifer properties. However an increase in the specific storage of an

order of magnitude to 0.004 produced a much higher RMS error, indicating

this value is unrealistic for gravel.

Removing groundwater extraction from the model has produced poor

matches in the head time graphs (Figure 43) with the calculated heads much

higher than the observed heads indicting groundwater extraction is an

essential component of the water budget.

Changing the applied boundary conditions has revealed the model is highly

sensitive. All time variant specified head boundary cells were replaced with

fixed head cells set at the same values as those applied for the initial

hydraulic heads. Head time graphs, particularly of bores near the fixed head

boundaries eg. 446, 490 and 462 display higher calculated than observed

heads. This suggests these observation bores are highly influenced by the

fixed head boundaries. A much higher RMS error than that of the calibrated

solution was obtained. Similarly, retaining the time variant specified head

cells on the southern and northern alluvial boundaries yet designating the

130

western boundary as no flow has produced a worse correlation at bore 490

than in the calibrated solution, suggesting that the western time variant

specified head boundary was responsible for the near perfect head matches

at bore 490 in the calibrated solution.

The 2 layer model has produced higher calculated than observed heads at all

observation bores which is undoubtedly due to the effects of leakage from

the overlying mixed sands and clays of layer 1. It should be noted that these

results are highly influenced by the choice of parameters for layer 1 and as

there are no bores screened in this semi confining layer, no field data could

be obtained for the hydraulic properties of this layer and consequently all

values are based on mean values from literature eg Domenico (1972); Heath

(1983); Morris and Johnson (1967).

The predictive simulations were based on an annual extraction rate applied

for the entire model duration and used to demonstrate the minimum

saturated thickness of the aquifer at the end of stress period 11 in October

1995 before the recharge of stress periods 12, 13, 14 and 15 in the summer

of 1995-96. The extraction rates ranged from 1.75 ML/ha, the maximum

pumping rate before the aquifer goes dry resulting in a minimum saturated

thickness of 0.029 m, to 0.5 ML/ha resulting in a minimum saturated

thickness of 1.4 m. Scenario results were expressed as a minimum saturated

thickness as opposed to a volume of water as the saturated thickness is the

governing variable in the effectiveness of an irrigation bore and therefore

the pumping rate. Discussions with landholders indicate that yields are

severely reduced in periods of low water levels when pumps draw in air.

These minimum thicknesses are applicable only in one small area of the

model grid, yet represent the absolute worst case scenario with all other

regions of the model domain producing higher saturated thicknesses. This

conservative approach was adopted in order to produce an underestimation

as opposed to an overestimation of the groundwater resource. It must also be

noted that these predictions are only valid for the 44 month period from

March 1993 to November 1996 and that a longer pumping and head dataset

would greatly increase the accuracy of these predictions.

131

8. CONCLUSION

Hydrograph interpretation of bores screened in the gravel has demonstrated

that the alluvial aquifer in the Lockyer plain is subject to large variations in

groundwater levels, which can be directly correlated to recharge and

indirectly correlated to irrigation use. Water levels in bores adjacent to the

creek banks respond to small amounts of rainfall e.g. 100 mm/month; these

bores also display a rapid response to a flood event. Pumping tests or

aquifer tests on two boreholes screened in gravel has produced estimates of

hydraulic conductivity of 50 – 80 m/day. The higher value is considered to

be more realistic for both the duration and magnitude of the stress placed on

the aquifer and also the gravel-dominant character of the aquifer material.

Re-interpretation of a previous drawdown test (Macleod 1998) has produced

estimates of hydraulic conductivity of 63 m/day and of storativity of 0.0016,

which are considered realistic for a semi-confined gravel aquifer.

Hydrochemical analyses of samples collected under both wet and dry

conditions display little variation, however, the major ion chemistry of

surface water from the May 1996 flood is similar to alluvial groundwater

which suggests a strong connection. Ma Ma catchment alluvial groundwater

is magnesium and sodium dominated with conductivity range of 4500 to

12000 µS/cm. This groundwater is a water type very similar to bedrock

groundwater defined in previous studies (e.g. Dixon and Chiswell 1992;

Macleod 1998). Groundwater in the Tenthill catchment is magnesium

dominated with calcium as the secondary cation and typically less than 3500

µS/cm with a water type different to bedrock groundwater. Major ion

chemistry of the Lockyer alluvial plain is extremely variable, with the

magnesium domination observed in Tenthill catchment continuing down to

the plain with some areas more sodium rich. Conductivity may reach 6000

µS/cm.

Samples analysed for stable isotopes from throughout both catchments and

the Lockyer plain show a range of values depending on aquifer type and

other processes such as evaporation and mixing. Stream water from a flood

132

event (data from Dharmasiri and Morawska 1997) represents recharging

water and indicates a starting point for isotopic evolution of groundwater.

Basalt groundwater displays an isotopic composition and salinity between

new water and alluvial groundwater which indicates that precipitation may

recharge basalt first and subsequently discharge to the alluvium or may also

recharge the alluvium directly. Alluvial groundwater from Ma Ma

catchment and the Lockyer plain display slopes of sample distribution

characteristic of evaporation from standing surface water. This trend

suggests evaporated water in the creek channels is the principal source of

recharging water; however, leakage from bedrock units may account for the

relatively more depleted composition of Ma Ma catchment alluvial

groundwater.

A conceptual hydrogeological model was developed for the Lockyer plain

incorporating all the previously interpreted data. Geological logs from

NRM&E bores were examined to determine the thickness and extent of both

the gravel aquifer and the mixed sands and clays of the overlying semi-

confining unit. Bore hydrograph variations when combined with the

thickness of the gravel indicate that the aquifer changes from confined to

unconfined conditions in some locations as the water level drops. Previous

studies, for example Ellis and Dharmasiri (1998) and Ellis (1999) have

demonstrated that infiltration through the mixed sands and clays is

extremely slow; water chemical and stable isotopic investigations in this

current study suggest that recharge of evaporated surface water through the

creek channels is the dominant recharge process.

To simulate groundwater flow in the gravel aquifer a single layer model was

constructed using PMWIN and calibrated to water level fluctuations using

PEST to estimate recharge. The transient simulation period ranged from

March 1993 to November 1996 for a total of 44 months, incorporating a

drought and the associated decline in water levels followed by a wet period

and flood and the resulting rise in water levels. The sensitivity analysis

demonstrates the model is insensitive to variations in hydraulic

conductivity, specific yield and specific storage within realistic bounds for

133

the aquifer material, however, the model is highly sensitive to changes in

the chosen boundary conditions. Predictive simulations with different

annual extraction scenarios for the model duration produced a minimum

saturated aquifer thickness with a range of 0.03 m to 1.4 m.

The main findings of this study are summarised as follows:

• The Quaternary alluvium is comprised of a laterally continuous semi

confined gravel aquifer overlain by mixed sands and clays.

• Pumping tests of the gravel aquifer has produced estimates of

hydraulic conductivity of 50 – 80 m/day and storativity of 0.0016.

• Alluvial groundwater in Ma Ma catchment is Mg and Na dominated

with a conductivity ranging from 4500 – 6500 µS /cm. Alluvial

groundwater in Tenthill catchment and the Lockyer plain is Mg

dominated with Ca>Na in Tenthill catchment and Na>Ca on the

Lockyer plain. Conductivity of Tenthill alluvial groundwater ranges

from 1500 – 3500 µS/cm while the Lockyer plain ranges from 2000

– 6500 µS/cm.

• Major ion chemistry of surface water from the May 1996 flood is

similar to alluvial groundwater suggesting a strong connection.

• Stable isotope plots of alluvial groundwater from Ma Ma catchment

and the Lockyer plain display slopes characteristic of evaporation

from standing surface water, suggesting recharge from evaporated

water in creek channels is the dominant recharge process.

• Relatively more depletion in stable isotopes was observed in alluvial

groundwater from Ma Ma than in Tenthill catchment and the

Lockyer plain, indicating possible mixing with more depleted

sandstone bedrock groundwater.

134

• Transient simulations of groundwater flow using PMWIN with a

number of annual extraction scenarios have demonstrated the

resulting minimum saturated thickness of the aquifer ranges from

0.03 to 1.4 m.

135

9. REFERENCES

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groundwater system in the southern Voltaian Sedimentary Basin of

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Anderson, M. P. and Woessner, W. W. 1992. Applied Groundwater

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Appello, C. A. J. and Postma, D. 1996. Geochemistry, groundwater and

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Chiang, W.-H. Kinzelbach, W. 2001. 3D-Groundwater Modelling with

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Clark, I. D. and Fritz, P. 1997. Environmental Isotopes in Hydrogeology.

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Craig, H. 1961. Isotopic Variations in Meteoric Waters. Science 133, 1702-

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Davies, S. N. and De Wiest, R. J. M. 1966. Hydrogeology. John Wiley and

Sons, New York.

Dharmasiri, J. K. and Morawska, L. 1997. Isotope Studies on Groundwater

Recharge to Alluvial Aquifer in Gatton, Queensland. Centre for

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(Unpublished).

Dixon, W. 1988. Hydrochemistry of groundwater salinity in the S. W.

Lockyer Valley, Queensland. MSc Thesis, University of

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Dixon, W. and Chiswell, B. 1992. The use of hydrochemical sections to

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Dixon, W. and Chiswell, B. 1994. Isotopic study of alluvial groundwaters,

south-west Lockyer Valley, Queensland, Australia. Hydrological

Processes. 8, 359-367.

Doherty, J., Brebber, L., and Whyte, P. 1994. PEST Model-independent

parameter estimation. Users Manual. Watermark Numerical

Computing, Brisbane.

Domenico, P. A. 1972. Concepts and Models in Groundwater Hydrology.

McGraw-Hill, New York.

Dudgeon, M. 1978. The geology of east and west Haldon, Main Range,

South- east Queensland. Hons thesis, University of Queensland,

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Durick, A. and Bleakley, A. 2003. Central Lockyer Groundwater Model.

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Ellis, R. 1999. Water Quality Deterioration in Alluvial Aquifers. LWRRDC

Project QPI30 Final Report. Queensland Department of Natural

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Ellis, R. and Dharmasiri, J. K. 1998. Chemical and Stable Isotopic Methods

used in Investigating Groundwater Quality Deterioration in the

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Groundwater Sustainable Solutions, Melbourne, Australia 8 -13

February 1998.

Fetter, C. W. 1994. Applied Hydrogeology. Prentice Hall, New Jersey.

Fontes, J. C. 1980.Environmental Isotopes in Groundwater Hydrology, in

Fritz P. and Fontes J. C. (eds), Handbook of Environmental Isotope

Geochemistry,Volume 1. Elsevier Scientific Publishing Company,

Amsterdam – Oxford – New York.

Freeze, R. A. and Witherspoon, P. A. (1967). Theoretical analysis of

regional groundwater flow: 2. Effect of water-table configuration

and subsurface permeabllity variation. Water Resources Research. 3,

623-624.

Freeze, R. A. 1969. The mechanism of natural groundwater recharge and

discharge. 1. One-dimensional, vertical, unsteady, unsaturated flow

above a recharging or discharging ground-water flow system. Water

Resources Research. 5, 1, 153-171.

Galloway, W. E. and Sharp, J. M Jr. 1998. Hydrogeology and

characterization of fluvial aquifer systems, in G. S. Fraser and J. M.

Davis (eds), Hydrogeologic Models of Sedimentary Aquifers. SEPM

(Society for Sedimentary Geology), 91-106.

138

Garcia, M. G., Hidalgo, M. D. V., and Blesa, M. A. 2001. Geochemistry of

groundwater in the alluvial plain of Tucuman province, Argentina.

Hydrogeology Journal. 9, 597-610.

Gat, J. R. 1981. Isotope Fractionation, in J. R. Gat and R. Gonfiantini (eds),

Stable Isotope Hydrology Deuterium and Oxygen-18 in the Water

Cycle. IAEA Technical Report Series No. 210, International Atomic

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GNIP 1998. Global Network for isotopes in precipitation. International

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Gray, A. R. G. 1975. Bundamba Group - stratigraphic relationships and

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310-324.

Grimes, K. G. 1968. The geology of the Lockyer Valley area, south-east

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(Unpublished).

Heath, R. C. 1983. Basic ground-water hydrology. USGS, Water Supply

Paper 2220.

Ingram, F. T. and Robinson, V. A 1996. Petroleum Prospectivity of the

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Lane, W. B. and Zinn, P. 1980. Recharge from weir storages. Groundwater

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Larkin, R. G. and Sharpe, J. M. Jr. 1992. On the relationship between river

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Macleod, K. 1998. The groundwater resource of the Ma Ma Creek

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141

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Hydrogeological report. Record 1975/36. Department of Mines

Geological Survey of Queensland, Brisbane.

APPENDIX 1 EXAMPLE OF NRM&E DATABASE RECORD

27Page

27/09/2002DATEGROUNDWATER DATABASE

BORE CARD REPORT

BASIN 27-34-07LATITUDE MAP-SCALE

OFFICE SUB-AREA 152-15-50LONGITUDE MAP-SERIES

UG 7/2D/O FILE NO. SHIRE 427328EASTING 9342-14MAP-NOR/O FILE NO. LOT 6950342NORTHING MAP NAMEH/O FILE NO. PLAN 56ZONE PROG SECTION

ORIGINAL DESCRIPTION ACCURACY

GPS ACC

NEPRES EQUIPMENT

NCHECKED

-27.5687400101GIS LAT

152.2638107809GIS LNG

4495-TENTHILLPARISH NAME

CHURCHILLCOUNTY

ORIGINAL BORE NO

PROPERTY NAME

-BORE LINE

FIELD LOCATION

01/06/1979DATE DRILLED

POLYGON

DRILLERS NAME

RN OF BORE REPLACED

DRILL COMPANYCABLE TOOL - V DOONAN JUNE 197METHOD OF CONST.

CONFIDENTIAL

SFFACILITY TYPE

EXSTATUS

ROLES

A

A

A

A

PIPE

01/06/1979

01/06/1979

01/06/1979

01/06/1979

DATE

1

2

3

4

RECORDNUMBER

Plastic Casing (unspecified)

Perforated or Slotted Casing

Open Hole

Gravel Pack

MATERIAL DESCRIPTION

3.350

MAT SIZE(mm)

WT

SIZE DESC

50

50

203

OUTSIDEDIAM

0.00

26.40

27.40

0.00

TOP(m)

27.40

27.40

30.40

30.40

BOTTOM(m)

1

2

3

RECORDNUMBER

0.00

0.60

1.20

STRATATOP (m)

0.60

1.20

7.30

STRATABOT (m)

TOPSOIL (FILE UG 7/2)

SANDY CLAY

LOAMY SOIL

STRATA DESCRIPTION

STRATA LOG DETAILS

CASING DETAILS

LICENSE DETAILS

M

253

Gatton

REGISTRATION DETAILS

1432

T01

P15

157-GATTON

14320445REG NUMBER

**** NO RECORDS FOUND ****

DATA OWNER

PDF processed with CutePDF evaluation edition www.CutePDF.com

28Page

27/09/2002DATEGROUNDWATER DATABASE

BORE CARD REPORT

DNR

SOURCE

1

RECORDNUMBER

0.00

STRATATOP (m)

29.80

STRATABOT (m)

TENTHILL CK ALLUV

STRATA DESCRIPTION

1

REC

20.70

TOPBED(M)

29.80

BOTTOMBED(M)

BEDLITHOLOGY

DATE SWL(m)

FLOW QUALITY

SAND

GRAV

CGRY

YIELD(l/s)

CTR

UC

CONDIT

TENTHILL CK ALLUV

FORMATION NAME

4

5

6

7

8

902

RECORDNUMBER

7.30

20.70

23.70

24.90

29.80

STRATATOP (m)

20.70

23.70

24.90

29.80

30.40

STRATABOT (m)

SANDY CLAY

SAND - WB

SAND AND GRAVEL - WB

CLAYBOUND GRAVEL - WB

SANDSTONE

SWL 15.6 METRES WHEN DRILLED

STRATA DESCRIPTION

A

PIPE

10/09/1979

DATE

110.31

ELEVATION

AHD

DATUM

SVY

PRECISION

R

MEASUREMENT POINT

ELEVATION DETAILS

AQUIFER DETAILS

STRATIGRAPHY DETAILS

PUMP TEST DETAILS PART 1

PUMP TEST DETAILS PART 2

BORE CONDITION

14320445REG NUMBER

**** NO RECORDS FOUND ****

**** NO RECORDS FOUND ****

**** NO RECORDS FOUND ****

SURVEY SOURCE

29Page

27/09/2002DATEGROUNDWATER DATABASE

BORE CARD REPORT

A

A

A

A

A

A

A

A

PIPE

18/10/1979

03/03/1981

12/05/1981

05/03/1984

23/04/1985

01/03/1991

14/03/1991

30/08/2001

DATE

1

1

1

1

1

1

1

1

RD

085437

088728

089083

104932

108468

138112

138075

211631

QAN

27.00

27.00

28.00

28.00

15.00

15.00

20.00

DEPTH(m)

PU

PU

AI

AI

AI

AI

PG

RMK

GB

GB

GB

GB

GB

GB

GB

GB

SRC

4000

4400

4600

4800

4950

3600

3550

4790

COND(uS/cm)

7.5

7.5

7.5

7.4

7.6

8.2

7.8

7.9

pH

34

36

32

32

32

29

30

30

Si(mg/L)

2224.30

2407.10

2549.10

2670.22

2886.40

2235.23

2156.82

2909.79

TOTALIONS

2122.08

2260.11

2389.47

2539.57

2727.79

2065.99

1983.50

2697.58

TOTALSOLIDS

1412

1511

1645

1658

1712

1095

1107

1622

HARD

220

295

309

264

310

329

332

397

ALK

2.6

2.7

2.8

2.4

2.2

1.5

1.5

1.9

FIG. OFMERIT

2.8

2.9

2.9

3.4

3.8

4.4

4.5

4.2

SAR

0.00

0.00

0.00

RAH

A

A

A

A

A

A

A

A

PIPE18/10/1979

03/03/1981

12/05/1981

05/03/1984

23/04/1985

01/03/1991

14/03/1991

30/08/2001

DATE1

1

1

1

1

1

1

1

RD 246.0

260.0

270.0

315.0

360.0

335.0

345.0

391.3

Na 4.0

4.0

5.0

4.1

4.0

4.4

5.0

4.9

K 196.0

226.0

250.0

260.0

265.0

150.0

155.0

260.5

Ca 224.0

230.0

248.0

245.0

255.0

175.0

175.0

236.5

Mg

0.00

0.35

0.01

0.01

2.27

Mn 268.0

360.0

377.0

320.0

375.0

390.0

400.0

476.9

HCO3

0.12

0.05

0.02

0.01

0.00

Fe 0.0

0.0

0.0

0.9

1.4

5.6

2.3

3.5

CO3 1190.0

1230.0

1300.0

1400.0

1500.0

1050.0

960.0

1421.0

Cl 0.10

0.10

0.10

0.10

0.10

0.20

0.10

0.12

F 0.2

2.0

0.0

0.0

0.5

10.0

9.4

33.1

NO3 96.0

95.0

99.0

125.0

125.0

115.0

105.0

82.0

SO4

0.02

Zn

0.00

Al

0.06

B

0.00

Cu

A A A

A A A

A A A

A A A

PIPE

10/09/1979 05/11/1979 14/01/1980

07/02/1980 08/02/1980 11/02/1980

15/02/1980 15/04/1980 06/08/1980

07/11/1980 02/01/1981 05/01/1981

DATE

-15.90 -16.14 -16.22

-16.42 -16.40 -16.30

-16.19 -16.93 -17.44

-17.94 -18.08 -17.83

MEASURE(m)

R R R

R R R

R R R

R R R

N/R RMK

X

PIPE

10/09/1979

DATE

110.02

ELEVATION

AHD

DATUM

SVY

PRECISION

N

MEASUREMENT POINT

WATER LEVEL DETAILS

WATER ANALYSIS PART 2

WATER ANALYSIS PART1

PIPE DATE MEASURE(m)

N/R RMK PIPE DATE MEASURE(m)

N/R RMK

GCL

GCL

GCL

GCL

GCL

GCL

GCL

GCL

ANALYST

14320445REG NUMBER

SURVEY SOURCE

30Page

27/09/2002DATEGROUNDWATER DATABASE

BORE CARD REPORT

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A A

PIPE

07/01/1981 22/01/1981 09/02/1981

10/02/1981 11/02/1981 13/02/1981

23/02/1981 25/02/1981 27/03/1981

06/04/1981 10/04/1981 14/04/1981

14/08/1981 15/12/1981 12/03/1982

18/06/1982 13/08/1982 22/02/1983

05/05/1983 12/05/1983 15/07/1983

14/10/1983 03/02/1984 04/05/1984

06/07/1984 09/11/1984 25/01/1985

12/04/1985 28/06/1985 30/09/1985

13/12/1985 21/03/1986 18/06/1986

05/11/1986 16/01/1987 30/03/1987

03/07/1987 23/10/1987 25/11/1987

09/12/1987 08/01/1988 03/05/1988

18/05/1988 12/08/1988 21/10/1988

10/02/1989 03/05/1989 07/07/1989

26/09/1989 20/11/1989 29/01/1990

19/03/1990 31/05/1990 26/07/1990

18/09/1990 22/11/1990 31/01/1991

14/03/1991 01/05/1991 11/06/1991

09/08/1991 01/10/1991 20/01/1992

03/06/1992 19/08/1992 19/10/1992

08/03/1993 11/05/1993 04/08/1993

24/11/1993 28/01/1994 31/03/1994

26/05/1994 23/09/1994 11/01/1995

11/04/1995 21/07/1995 17/10/1995

17/01/1996 27/03/1996 26/07/1996

09/11/1996 16/01/1997 18/09/1997

01/10/1997 13/03/1998 27/03/1998

14/05/1998 01/07/1998 29/07/1998

11/09/1998 22/09/1998 09/11/1998

DATE

-17.76 -17.53 -17.31

-17.18 -17.12 -16.98

-16.38 -16.31 -16.00

-15.94 -15.86 -15.83

-15.81 -15.64 -14.87

-15.35 -15.61 -16.30

-16.38 -15.98 -14.22

-15.10 -15.10 -15.33

-15.41 -15.40 -15.45

-15.57 -15.65 -15.87

-15.80 -16.86 -16.70

-17.56 -17.80 -17.42

-17.75 -18.09 -17.46

-17.17 -16.95 -14.92

-15.15 -15.09 -15.34

-15.42 -14.87 -14.94

-15.38 -15.28 -15.28

-15.42 -14.58 -15.04

-15.26 -15.54 -15.63

-15.44 -15.94 -16.11

-16.55 -17.35 -15.85

-15.54 -15.55 -15.90

-16.65 -17.75 -18.04

-18.69 -18.46 -18.28

-18.78 -19.49 -20.20

-18.70 -19.53 -20.20

-17.27 -16.88 -15.36

-15.58 -16.00 -17.33

-17.38 -16.00 -16.33

-16.53 -16.92 -17.00

-17.00 -17.00 -17.00

MEASURE(m)

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R R

N/R RMK PIPE DATE MEASURE(m)

N/R RMK PIPE DATE MEASURE(m)

N/R RMK

14320445REG NUMBER

31Page

27/09/2002DATEGROUNDWATER DATABASE

BORE CARD REPORT

A A A

A A A

A A A

A A A

A A A

A A A

A A A

A A

PIPE

06/12/1998 08/03/1999 23/03/1999

03/06/1999 25/08/1999 08/09/1999

22/11/1999 07/12/1999 28/02/2000

02/03/2000 29/05/2000 04/09/2000

17/10/2000 04/12/2000 27/02/2001

30/05/2001 04/06/2001 29/08/2001

03/09/2001 04/12/2001 07/03/2002

16/04/2002 10/07/2002

DATE

-16.50 -15.44 -15.60

-15.68 -15.90 -15.90

-15.71 -15.86 -15.75

-15.73 -16.55 -17.00

-17.27 -17.40 -15.75

-16.02 -16.20 -16.85

-16.96 -16.65 -17.04

-17.50 -18.10

MEASURE(m)

R R R

R R R

R R R

R R R

R R R

R R R

R R R

R R

N/R RMK

A

A

A

A

A

A

A

A

PIPE

18/10/1979

03/03/1981

12/05/1981

05/03/1984

23/04/1985

01/03/1991

14/03/1991

11/04/2002

DATE DEPTH(m)

4000

4400

4600

4800

4950

3600

3550

5000

COND(uS/cm)

pH TEMP(C)

NO3(mg/L)

DO(mg/L)

Eh(mV)

PU

PU

AI

AI

AI

AI

AI

METH

GB

GB

GB

GB

GB

GB

GB

GB

SOURCE

Y 30/06/1992

WLVDETREGDET

Y 30/06/1992

STRLOG

Y 30/06/1992

PUMTES

Y 27/07/1993

FIELDQ

Y 30/06/1992

ELVDETCASING

Y 30/06/1992 Y 30/06/1992

AQUIFR

FIELD MEASUREMENTS

WIRE LINE LOG DETAILS

VALIDATION LOG - PART 1

SPECIAL WATER ANALYSIS

PIPE DATE MEASURE(m)

N/R RMK PIPE DATE MEASURE(m)

N/R RMK

14320445REG NUMBER

**** NO RECORDS FOUND ****

**** NO RECORDS FOUND ****

32Page

27/09/2002DATEGROUNDWATER DATABASE

BORE CARD REPORT

APIPE

22/03/2001DATE

1REC

Bore shield and marker post replaced.NOTES

WIRLOGWATANL

Y 30/06/1992

STRTIG

Y 28/07/1993

SAMPLE MULCND

Y 28/07/1993

GNOTESFPREADBRCOND

GENERAL NOTES

METERED USE

VALIDATION LOG - PART 2

14320445REG NUMBER

**** NO RECORDS FOUND ****

APPENDIX 2 PUMPING TEST DATA

Pumping Test 1

Drawdown vs time dataAquifer thickness = 6.1 m

Time (s) Depth to Drawdown (m)water level (m)

30 20.425 0.39560 20.43 0.490 20.436 0.406120 20.439 0.409150 20.441 0.411180 20.442 0.412210 20.442 0.412240 20.442 0.412270 20.443 0.413300 20.444 0.414330 20.445 0.415360 20.446 0.416390 20.446 0.416420 20.446 0.416450 20.446 0.416480 20.446 0.416510 20.446 0.416540 20.447 0.417570 20.447 0.417600 20.447 0.417630 20.447 0.417660 20.447 0.417690 20.447 0.417720 20.447 0.417750 20.447 0.417780 20.447 0.417810 20.447 0.417840 20.447 0.417870 20.448 0.418900 20.448 0.418960 20.45 0.421020 20.45 0.421080 20.45 0.421140 20.45 0.421200 20.451 0.4211500 20.454 0.4241800 20.456 0.4262100 20.456 0.4262400 20.458 0.4282700 20.455 0.4253000 20.457 0.4273300 20.458 0.4283600 20.459 0.4294200 20.459 0.4294800 20.46 0.435400 20.46 0.43

Pumping Test 2

Recovery vs time dataAquifer thickness = 4.2 m

Time (s) Depth to Drawdown (m)water level (m)

81000 27.745 0.5481010 27.7 0.49581020 27.69 0.48581030 27.69 0.48581040 27.69 0.48581050 27.69 0.48581060 27.69 0.48581070 27.69 0.48581080 27.69 0.48581090 27.685 0.4881100 27.685 0.4881110 27.685 0.4881120 27.682 0.47781130 27.68 0.47581140 27.68 0.47581150 27.68 0.47581170 27.682 0.47781180 27.675 0.4781210 27.67 0.46581240 27.665 0.4681270 27.665 0.4681300 27.662 0.45781330 27.66 0.45581360 27.655 0.4581390 27.655 0.4581420 27.652 0.44781450 27.645 0.4481480 27.645 0.4481510 27.643 0.43881540 27.641 0.43681570 27.64 0.43581600 27.637 0.43281630 27.635 0.4381660 27.632 0.42781690 27.63 0.42581720 27.628 0.42381750 27.628 0.42381780 27.625 0.4281810 27.62 0.41581840 27.62 0.41581870 27.618 0.41381900 27.618 0.41381960 27.613 0.40882020 27.608 0.40382080 27.605 0.482140 27.602 0.39782200 27.602 0.39782260 27.595 0.3982320 27.593 0.388

82380 27.59 0.38582440 27.59 0.38582500 27.587 0.38282560 27.582 0.37782620 27.58 0.37582680 27.58 0.37582740 27.578 0.37382800 27.575 0.3783100 27.565 0.3683400 27.55 0.34583700 27.54 0.33584000 27.525 0.3284300 27.512 0.30784960 27.5 0.29585800 27.48 0.27586400 27.47 0.26586700 27.465 0.2687000 27.46 0.25587300 27.455 0.2587600 27.45 0.24588200 27.445 0.2488500 27.44 0.23588800 27.435 0.2389100 27.435 0.2389400 27.43 0.22589700 27.425 0.2290000 27.422 0.21791800 27.405 0.294200 27.39 0.18594800 27.385 0.1895400 27.38 0.17596000 27.375 0.17

Pumping Test 3

Drawdown vs time data (Macleod 1998)Aquifer thickness = 4 m (this study)

Time (s) Depth to Drawdown (m)water level (m)

0 22 030 22.8 0.860 22.82 0.8290 22.9 0.9120 22.99 0.99150 23.02 1.02180 23.09 1.09210 23.12 1.12240 23.15 1.15270 23.18 1.18300 23.21 1.21330 23.23 1.23360 23.26 1.26390 23.29 1.29420 23.32 1.32450 23.34 1.34480 23.36 1.36510 23.38 1.38540 23.41 1.41570 23.42 1.42600 23.43 1.43630 23.45 1.45660 23.47 1.47690 23.485 1.485720 23.5 1.5750 23.52 1.52780 23.54 1.54810 23.56 1.56840 23.58 1.58870 23.6 1.6900 23.615 1.615960 23.64 1.641020 23.655 1.6551080 23.685 1.6851140 23.71 1.711200 23.74 1.741260 23.77 1.771320 23.79 1.791380 23.815 1.8151440 23.835 1.8351500 23.865 1.8651800 23.955 1.9552100 24.035 2.0352400 24.105 2.1052700 24.17 2.17

APPENDIX 3 HYDROCHEMICAL METHODS

WATER ANALYSIS

OVERVIEW OF SAMPLE COLLECTION, PRESERVATION, ANALYSIS AND RESULTS

Essential analyses carried out in situ are pH, conductivity and temperature. Redox potential (Eh) may also be determined. Before going into field it is very important that all equipment is calibrated properly and in some cases recalibration will be required every few hours while in the field. See individual procedural notes for calibration of equipment. Samples will need to be collected for the determinations that will be carried out in the Geochemistry Laboratory. The following cation and anion, determinations are required for most projects. Cations: Na+, K+, Ca++ and Mg++ (Majors) Fe, Al, Si, Cu, Mn, Pb and Sr may also be included Anions: SO42-, Cl- and Alkalinity F-, Br-, PO4

3- and NO3- may also be included

· Cations are determined by ICP-OES, refer to ‘Cation in Water by ICP-OES’ procedural

notes for sample requirement and more information on this determination. · Alkalinity is determined using a titrimetric method, refer to ‘Alkalinity in Water’ procedural

notes for more information on this determination. · The rest of the anions listed above are determined by ion chromatography, refer to ‘Anions

in Water by Ion Chromatography’ procedural notes. It is important to note if chloride concentration is high, it must be determined by titration. Ion chromatography may give low results for high chloride.

PRESERVATION and STORAGE of SAMPLES: Use the following Table 1 to determine what bottle preparation, preservation and storage requirements is required for each sample. For some determinations more than one method is possible, methods other than the usual or preferred method are listed in italics.

TABLE 1: Sampling and preservation requirements.

Determination

Container

Minimum

Sample Size mL

Preservation

Maxim

um Storage

Analysis Method

Alkalinity P 200mL Refrigerate 14d Titration Bromide P 100mL None required Ion chromatography Chloride P 100mL Refrigerate 14d Titration

Fluoride P 300mL None required 28d Ion chromatography

or ion selective electrode

Nitrate P 100mL Refrigerate 48h Ion chromatography or ion selective electrode

pH P Analyse Immediately

nil pH electrode

Phosphate G(A) 100mL Refrigerate 48h Ion chromatography or colourimetry

Sulfate P 100mL Refrigerate 28d Ion chromatography or ICP-OES or nephelometry

Turbidity P 100mL Analyse same day or store in dark for up to 24h, refrigerate

48h Nephelometry

Metals (Most cations come under this category)

P(A) 250 mL For dissolved metals filter immediately, add HNO3 to pH<2

6mths ICP-OES

For determinations not listed refrigerate and analyse as soon as possible. P = Plastic (polyethylene or equivalent) P(A) = Plastic and rinsed with 1:1 HNO3 G(A) = Glass and rinsed with 1:1 HNO3 Refrigerate = Store at <4oC nil = No storage allowed If both anion and cation analyses are to be done, two samples bottles will be required for each site: one acidified sample for cation analysis (metals) of at least 250 mLs is required and one unacidified sample of at least 500 mLs for anion analysis is required. Sample bottles may need to be acid rinsed before use (Check table 1 to see if this is required). How to acid rinse Sample Bottles: Prepare 50 mLs of 1:1 nitric acid by diluting 25mL of conc nitric acid (HNO3) in a 100 mL beaker. Transfer approximately 20 mL of 1:1 nitric acid to a bottle, shake vigorously for about 30 seconds, and transfer to the next bottle. Rinse the bottle thoroughly at least 3 times with deionised water. This operation must be performed in a fume cupboard. Do not pour dilute acid or even the rinse water down stainless steel sinks.

How to Acidify Sample: (This can be done before going into field.) Add 2 mL of concentration nitric acid (HNO3) to each cation sample bottle (This should be half your sample bottles) to give a pH <2 in the final sample. SAFETY: Transporting concentration acid involves risks. Please read risks assessment for this application before acidifying bottles. RESULTS Once all determinations are done it is important to do a cation-anion balance to check the correctness of analyses. The cation-anion balance compares the total anions to the total cations on a molecular level. To do this the results must be converted to milliequivalents per litre (me/L) by multiplying each analyte concentration (mg/L) by the conversion factor given in Table 1. The factor is equal to the number of charges associated with the ion species divided by the weight of the ion. eg for Sodium, Na+, there is one positive charge associated and it has an atomic weight of 22.99 thus me/L = mg/L x 1/22.99 = mg/L x 0.043 Once the results are in the form of me/L the percentage difference between sums of anion and cation species is calculated as follows: % Difference = 100 x [(Σ Cations - Σ Anions)/(Σ Cations + Σ Anions)] An agreement of <10% is acceptable, greater than this may require further ion determinations or examination of procedural techniques. REPORTING OF RESULTS CHECKLIST Have you: • completed all determinations required (all those it the attached table)? • taken into account any dilutions made before analyses and recalculated results? • checked results are not below the detection limit of the method? If results are less than

the detection limit report as being less than detection limit as stated in Table 1. • calculated a cation/anion balance to check the correctness of your results and reported on

accuracy of determinations? • only included significant figures in final values?

CATIONS in WATER by INDUCTIVELY COUPLED PLASMA - OPTICAL EMISSION

SPECTROSCOPY (ICP-OES) Cations commonly analysed in water samples by ICP-OES are: Major Cations: Na, K, Mg and Ca Minor Cations: Al, Si, Sr, Mn, Fe, Zn and Cu DECTECTION LIMITS: Element

Working Detection Limits

Na 0.015 – 1500 mg/L

K 0.20 – 150 mg/L

Mg 0.001 – 150 mg/L

Ca 0.0003 – 250 mg/L

Al 0.015 – 75 mg/L

Si 0.011 – 75 mg/L

Sr 0.0006 – 75 mg/L

Mn 0.003 – 7.5 mg/L

Fe 0.015 – 7.5 mg/L

Zn 0.009 – 7.5 mg/L

Cu 0.02 – 0.75 mg/L

THEORY OF OPERATION: The cation and sulfur concentrations are measured using inductively coupled plasma - optical emission spectroscopy (ICP-OES). This technique involves the water sample being aspirated into a plasma. The intensity of characteristic wavelengths emitted by the excited analyte ions in the plasma are measured by a spectrophotometer. The measured intensity is proportional to concentration, thus concentration of ions in the sample can be determined. SAMPLE PREPARATION: Little or no sample preparation is required for analysis of aqueous samples by ICP-OES except for highly turbid samples which must be filtered and samples of high conductivity which must be diluted to <4000 µS before analysis. Also, concentration of elements

determined must be within the detection limits of the ICP-OES for the results to have analytical meaning. Filter turbid samples through a 0.45 or 0.8 µm membrane filter, collect and analyse the filtrate, diluting if necessary. It is possible for cations other than those listed above to be analysed, however it may not be feasible if the selected analyte ions are present only in trace amounts ie at levels below the limits of ICP-OES detection. RESULTS All data should be within detection limits set out above. Any results out of this range should be recorded as being out of detection limits. Data out of dectection limits has no real meaning, inclusion this data in a report or thesis is completely inaccurate. Interpreting ICP-OES results print-outs: Sample Name Program File Name Date Time Element Mean Units Standard Weight/Volume Analysed Intensity Deviation Recalculated concentration element Wavelength Concentration Percent in original sample at which of element in Relative adjusting for sample element is solution Standard weight and dilution. determined Deviation The above printout shows for Sample 1 the potassium (K) concentration was measured at a wavelenth of 769.896 nm and was found to be 3.101 ppm in the original sample.

ANIONS in WATER By ION CHROMATOGRAPHY (IC)

Anions determined by this method: Cl-, SO4

2-, Fl-, Br-, NO3- and PO4

3- (NO2

- and SO32- can also be analysed but are not included in the routine analysis.)

DECTECTION LIMITS: A working range has been given below. This range is based on a combination of standard concentration range and instrument working range. Fl- 0.05 to 12 ppm Cl- 0.5 to 150 ppm SO4

2- 0.5 to 100 ppm Br- 0.05 to 12 ppm NO3

- 0.05 to 12 ppm PO4

3- 0.05 to 12 ppm THEORY OF OPERATION: The Ion Chromatographic Process: The sample is introduced in the flowing stream and carried into the anion exchange column. Ions interact with the ion exchange sites on the stationary phase in the column. Mobile phase ions (or eluent ions) compete with the sample ions for ion exchange sites on the column. Separation depends upon the different ions having different affinities for both phases. In the case of anion separations the differing affinities for stationary and mobile phases are due to the ionic charge and ion size (ionic radius) of each anion species. Once anions are separated the concentration of each species present in the sample is measured using a conductivity detector. A chromatogram displays peaks in conductivity at various retention times. Each anionic species is identified by its retention time which remains constant throughout successive runs. Stationary Phase: the column packing material containing functionalised active sites. For anion determinations the Dionex AS14 anion exchange column is used. Mobile Phase (or Eluent): The liquid flowing though the column that contains competing ion for the active sites. SAMPLE PREPARATION: Little of no sample preparation is required of analysis of aqueous sample by ion chromatography. However highly turbid samples must be filtered before analysis and sample

of high conductivity require diluting before analysis. Samples analysed must have a conductivity of less than 700 μS, if not dilution is required. Filter turbid samples through a 0.45 of 0.8 um membrane filter, collect and analyse the filtrate, diluting if necessary. REAGENTS:

Eluent: 3.5mM Na2CO3/1.0 mM NaHCO3. Prepare diluting the 100x concentrate 100 fold. Ie pipette 10 mL of 100x concentrate into a 1000 mL volumetric flask and dilute to the mark with ultra pure water. (Obtain ultra pure water from the purification unit located on the back island bench located in the Geochem lab R431.) Fill eluent bottle with this solution and sparge with argon for at least ten minutes before starting eluent pump.

Regenerant solution: Add 2.4 mL of conc H2SO4 to 1000 mL of ultra pure water and dilute further to 2000mLs. Fill regen bottle with this solution recap and allow to pressurise. After several minutes ensure regen solution is flowing through suppressor.

RESULTS: Ion chromatography is a excellent method of anion species determination in water samples. It has a extremely good precision with a %RSD of <2%. However it is important that results obtained are not taken on face value but are checked to assure data is reasonable. This is particularly important as peaks can be misnamed due to small shifts in retention time. The retention time can change due to a variety of reasons most commonly due to problems with the eluent pump, blockages and inaccurate preparation of eluent. Always check with previous days data to determine if retention times have not changed (refer to daily log, located next to instrument for this information). Also data should be with the working range of each species listed above, if not an dilution may be require before reruning samples or an alternative method of analysis may be required. In particular, high chloride data should be checked by titration as concentrations over 150-200 ppm may not be linear, giving inaccurate results. An example of a chromatogram using

ALKALINITY ACID TITRATION METHOD

DETECTION LIMIT: 0.25 ppm CaCO3 (mg/L water) APPARATUS: 250 mL conical flask, calibrated pH meter and 25 mL burette SAFETY EQUIPMENT: Laboratory coat, safety glasses. Refer to Risk Assessment/s: Hydrochloric acid (32%) - Student usage REAGENTS: 0.1N Standard HCl: SAFETY: This dilution must be carried out in a fume cupboard.

Pipette 10 mLs of conc HCl (10 M) into a 1000 mL volumetric flask and dilute to mark.

Standardisation of 0.1 N HCl: Weigh 0.7 - 0.8 g of pure sodium tetraborate by difference into a 150 mL conical

flask, dissolve in about 50 mLs of distilled water and add a few drops of methyl red indicator. Titrate the sodium tetraborate solution with the 0.1N HCl as the titrant until the colour changes to pink. Record the volume of HCl used. Carry out this procedure in triplicate. Use the following equation to calculated the normality of the acid solution.

N HCl = Weight of Na2B4O7 mg / (190.72 x Vol of Titrant (HCl) ml ) 0.02 N Standard HCl: Pipette 200 mLs of standard 0.1N HCl into a 1000 mL

volumetric flask and dilute to the mark. PROCEDURE: The alkalinity of a sample is due to the presence of hydroxide, carbonate or

bicarbonate ions. The concentration of each of these ions in a sample can be calculated once the phenolphthalein and total alkalinity have been determined.

1) Determination of phenolphthalein alkalinity or P

a) Pipette 100 mLs of sample into a 250 mL beaker. Measure the pH of the sample. If pH is less than 8.3 go on to step 2) as P=0.

b) If pH is greater than 8.3 then titrate the sample with 0.1N HCl to pH 8.3. Use a magnetic stirrer and leave pH probe in sample while titrating. Record volume of

HCl used. Calculate alkalinity due to hydroxide, P, by using Calculation (a). Go on to step 2).

2) Determination of total alkalinity or T

a) Titrate the sample to the pH 4.7 if the sample alkalinity is unknown. If known choose the appropriate total alkalinity equivalence point from the following

table. These pH values are suggested equivalence points for the corresponding alkalinity concentrations.

Alkalinity (mg/L CaCO3)

End Point pH: Total

30 4.9 150 4.6 500 4.3 Silicates, phosphates known or

suspected 4.5

Industrial waste or complex system 4.5

b) Record total volume of HCl titrated ie. include volume of titrant used in step 1 if appropriate. Calculate the Total Alkalinity, T, using calculation (b). If Total

Alkalinity, T, is less than 20 mg/L CaCO3 go to step 3). If Total Alkalinity, T, is greater than 20 mg/L CaCO3 go to step 4. 3) Determination of Total Alkalinity less the 20mg/L CaCO3 a) Pipette 100 mLs of sample into a 250 mL beaker and titrate using 0.01M HCl to

an end point in the range of 4.3 to 4.7. Record the volume and the exact pH. b) Titrate the solution further to reduce the pH exactly 0.30 pH units and record

volume. Use Calculation (c) to determine Total Alkalinity, T. 4) Determine the relationship between Hydroxide, Carbonate and Bicarbonate Alkalinity

using Table 2. NOTE: As the end point is approached make smaller additions of acid and be sure that pH

equilibrium is reached before adding more titrant. CALCULATIONS: a) P (Phenolphthalein Alkalinity) P mg/L CaCO3 = A x N x 50 000 / volume of sample where A = mL standard acid used N = normality of standard acid b) T (Total Alkalinity) T mg/L CaCO3 = A x N x 50 000 / volume of sample where A = mL standard acid used N = normality of standard acid c) Potentiometric titration of low alkalinity (<20mg/L CaCO3):

T (Total alkalinity), T mg/L CaCO3 = (2B - C) x N 50 000 / volume of sample where B = mL of titrant to first recorded pH C = total mL of titrant of reach pH 0.3 unit lower N = normality of acid TABLE 2: Calculation of alkalinity relationships:

Result of titration Hydroxide Alkalinity as CaCO3

Carbonate Alkalinity as CaCO3

Bicarbonate Alkalinity as CaCO3

P = 0 0 0 T P < 1/2T 0 2P T - 2P P >=1/2T 0 2P 0 P > 1/2T 2P-T 2(T-P) 0

P=T T 0 0 Where P = phenolphthalein alkalinity T = total alkalinity Report total alkalinity as: "The alkalinity to pH ____ = ____ mg CaCO3/L" To convert hydroxide, carbonate and bicarbonate expressed as alkalinity to concentration of their own species to be used in a mass balance multiply by the following factors. Hydroxide mg/L OH- = mg/l CaCO3 x 0.34 Carbonate mg/L CO32- = mg/L CaCO3 x 0.60 Bicarbonate mg/L HCO3- = mg/L CaCO3 x 1.22 WORKED EXAMPLE: A 100mL sample of pH 9.0 was titrated with 0.09871 M HCl to the phenolphthalein end point, pH 8.3, and the titrant volume of 2.60 mL was recorded. The sample was then titrated further to and end point of pH 4.7 and the additional titrant volume of 7.35 mL was recorded. i) Calculation of Phenolphthalein Alkalinity P = A x N x 50 000 / volume of sample = 2.6 x 0.09871 x 50 000 / 100 = 128.32 mg/L CaCO3 ii) Calculation of Total Alkalinity T = A x N x 50 000 / volume of sample

= (2.60 + 7.35) x 0.09871 x 50 000 / 100 = 491.08 mg/L CaCO3 iii) Determination of alkalinity relationship using Table 2 Where P = 128.32 mg/L CaCO3 and T = 491.08 mg/L CaCO3 since 128.32 < 1/2 of 491.08 thus P < 1/2 T

According to Table 2 alkalinity is due to the following alkali concentrations Hydroxide = 0 mg/L CaCO3 Carbonate = 2P = 2 x 128.32 = 256.64 mg/L CaCO3 Bicarbonate = T - 2P = 491.08 - (2 x 128.32) = 234.44 mg/L CaCO3 iv) Alkali concentrations expressed as species concentrations Hydroxide mg/L OH- = mg/L CaCO3 x 0.34 = 0 x 0.34 = 0 mg/L OH- Carbonate mg/L CO32- = mg/L CaCO3 x 0.60 = 256.64 x 0.60 = 153.98 mg/L CO32- Bicarbonate mg/L HCO3- = mg/L CaCO3 x 1.22 = 234.44 x 1.22 = 284.80 mg/L HCO3

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v) Finally reporting Alkalinity = 491.08 mg/L CaCO3 to pH 4.7 Hydroxide = 0 mg/L Carbonate = 153.98 mg/L Bicarbonate = 284.80 mg/L

APPENDIX 4 HYDROCHEMICAL DATA

Bore RN Date pH EC (µS/cm) Na K Mg Ca Cl SO4 HCO3220 25/10/1996 7.8 1880 150 1.8 116.8 79 334 57 549221 25/10/1996 7.8 1255 76 1.0 73.0 77 226 49 350222 14/11/1996 7.8 1730 123 0.3 139.9 45 283 71 565256 12/11/1996 7.6 4710 757 8.8 173.0 93 1230 171 755462 14/11/1996 7.5 4090 144 2.2 304.0 289 1080 82 610476 1/11/1996 7.8 1550 90 1.5 85.9 100 288 52 391477 14/11/1996 7.5 1480 88 1.7 88.4 95 246 100 390 Table A1. Chemical analyses of 490 25/10/1996 7.6 4170 213 5.7 273.8 231 1093 59 680 major constituents 1996.491 25/10/1996 7.4 6580 490 4.2 365.1 387 2039 121 651 All concentrations in mg/L.777 13/11/1996 7.8 9500 2016 14.2 146.7 86 2862 129 1119 DL: detection limit778 12/11/1996 7.4 11420 2419 14.6 177.7 99 3894 14 916783 4/11/1996 7.5 2450 144 5.5 144.6 151 559 59 560784 4/11/1996 7.8 2540 94 2.6 182.5 162 603 71 546865 25/10/1996 7.6 1530 100 1.6 83.8 96 265 62 423

SW May 96 9/05/1996 7.57 507 29 2.7 27.3 35 54 12 197SW Nov 96 28/11/1996 8.3 1470 105 3.9 75.2 78 272 67 328

Bore RN Date Al Fe Mn Zn Cu F NO3 CO3 SiO2220 25/10/1996 0.01 <DL <DL <DL 0.01 0.2 32.3 2.6 36221 25/10/1996 0.01 <DL <DL <DL <DL 0.2 4.2 1.8 35222 14/11/1996 <DL <DL <DL <DL <DL 0.2 9.7 3.0 43256 12/11/1996 <DL <DL 0.06 0.23 0.01 0.4 18.4 2.9 27462 14/11/1996 <DL <DL <DL 0.01 <DL 0.2 78.8 2.0 34476 1/11/1996 <DL <DL <DL <DL <DL 0.2 30.8 1.9 36477 14/11/1996 <DL <DL <DL 0.01 0.01 0.2 14.2 0.9 33 Table A2. Chemical analyses of 490 25/10/1996 <DL <DL <DL <DL 0.01 0.1 91.3 2.4 35 minor constituents 1996.491 25/10/1996 <DL <DL <DL 0.01 0.01 0.2 35.6 1.8 36 All concentrations in mg/L.777 13/11/1996 <DL <DL 1.44 0.02 0.01 0.2 <DL 8.2 23 DL: detection limit778 12/11/1996 <DL <DL 0.48 <DL <DL 0.2 <DL 3.0 18783 4/11/1996 <DL <DL 0.01 <DL 0.02 0.2 9.1 1.4 30784 4/11/1996 <DL <DL <DL 0.01 0.01 0.1 5.9 2.8 29865 25/10/1996 0.01 <DL <DL 0.37 0.01 0.1 24.9 1.4 39

SW May 96 9/05/1996 <DL <DL <DL <DL <DL 0.1 11.2 0.4 33SW Nov 96 28/11/1996 <DL <DL <DL <DL <DL 0.2 8.2 5.0 27

Bore RN Date pH Eh T EC Na K Mg Ca Cl SO4 HCO3(mV) ( C ) (µS/cm)

220 3/09/2003 7.33 40 20.8 2110 118 10.0 172.2 110 297 58 423221 27/11/2003 7.17 116 23 2600 100 3.6 155.0 131 431 82 740445 8/09/2003 7.04 -15 21.8 5030 367 6.1 268.0 249 1276 227 415446 8/09/2003 7.3 -101 21.7 1443 87 3.8 77.3 86 191 27 345447 20/11/2003 6.37 -70 22.7 4640 609 7.2 134.3 85 102 10 2385462 3/09/2003 7.47 85 21.9 3750 152 4.1 340.4 319 768 58 516477 25/08/2003 7.2 72 18.6 2640 128 3.1 172.1 173 428 120 412489 6/09/2003 7.17 57 22.6 3800 205 4.7 218.5 178 833 79 536490 6/09/2003 6.91 76 22.9 3670 244 6.5 250.3 205 686 56 536491 8/09/2003 7.01 46 22.2 6100 478 4.6 343.0 306 1570 236 400502 8/09/2003 7.13 -140 21.3 3400 246 10.0 249.1 176 681 111 454514 8/09/2003 7.44 8 22.9 2045 132 5.1 151.3 76 228 150 603515 8/09/2003 7.48 -87 22.3 2330 104 2.9 199.4 99 305 38 680516 8/09/2003 6.87 -165 22.8 5380 205 6.2 432.5 407 1879 127 490

55617 6/09/2003 6.95 71 23.5 8780 847 6.8 462.4 413 2565 349 619557 8/09/2003 7.44 22 15.4 2320 160 4.4 134.4 126 368 71 365783 3/09/2003 7.87 81 22.3 3220 199 11.0 319.0 424 652 63 418784 3/09/2003 7.52 38 22.3 3100 120 6.5 455.9 499 619 81 526822 10/09/2003 6.97 -67 21.5 4930 915 14.9 186.0 147 440 105 2681858 3/09/2003 7.48 -69 21.9 2490 271 8.3 158.7 120 332 24 459859 3/09/2003 7.42 83 23.1 9050 475 7.9 735.8 822 2584 84 722861 10/09/2003 6.9 106 22.2 12160 776 13.3 1039.0 649 3706 392 397862 6/09/2003 7.01 63 23 12890 1536 31.5 715.2 586 3737 223 799864 6/09/2003 7.52 109 22.3 1447 80 2.6 126.8 156 177 56 356865 6/09/2003 7.23 76 21.7 2340 138 4.6 193.8 237 361 77 448P1 27/11/2003 7.47 32 24 3040 174 2.2 193.7 62 587 45 672B1 20/11/2003 7.2 22 720 95 2.0 14.5 19 22 3 490B2 20/11/2003 7.37 22 730 107 2.5 15.2 15 17 5 535

Table A3. Chemical analyses of major constituents 2003. All concentrations in mg/L. DL: detection limit

Bore RN Date Al Fe Mn Sr Zn Cu F Br NO3220 3/09/2003 6.20 8.82 3.97 1.20 1.30 0.12 1.50 1.0 50.8221 27/11/2003 1.70 4.57 0.63 0.90 0.17 0.00 0.13 0.9 66.4445 8/09/2003 0.73 1.86 2.09 1.67 0.64 0.04 0.40 <DL 14.8446 8/09/2003 0.60 2.84 0.42 0.73 0.24 0.02 0.30 <DL 1.7447 20/11/2003 1.18 18.37 0.26 1.19 0.51 0.04 <DL <DL <DL462 3/09/2003 11.14 17.83 6.28 1.56 0.35 0.17 0.40 <DL 30.0477 25/08/2003 2.74 31.13 19.33 0.87 0.50 0.08 <DL <DL 27.3489 6/09/2003 1.48 3.93 0.66 1.59 0.16 0.04 <DL 3.2 116.0490 6/09/2003 7.24 5.15 4.15 2.55 0.27 0.04 1.20 2.8 79.2491 8/09/2003 1.62 4.40 0.67 2.42 0.07 0.02 0.40 <DL 57.6502 8/09/2003 6.63 7.24 10.57 1.17 1.31 0.06 <DL 1.1 47.3514 8/09/2003 0.76 6.39 2.77 0.49 0.27 0.02 0.25 <DL <DL515 8/09/2003 1.80 12.34 1.40 0.49 0.12 0.03 <DL 0.5 <DL516 8/09/2003 5.83 100.88 26.12 2.87 0.70 0.08 0.40 4.0 <DL

55617 6/09/2003 0.17 0.08 0.03 4.28 0.00 0.04 50.40 27.2 72.0557 8/09/2003 3.82 6.06 7.90 0.87 0.42 0.05 0.25 <DL 16.5783 3/09/2003 9.55 204.70 18.84 2.66 0.62 0.06 6.65 2.8 19.3784 3/09/2003 11.41 105.80 12.60 2.76 0.48 0.07 <DL <DL 48.3822 10/09/2003 0.09 0.15 3.89 2.91 0.70 0.01 0.40 <DL 3.6858 3/09/2003 5.05 19.58 4.24 1.51 1.20 0.05 1.75 <DL <DL859 3/09/2003 0.39 4.55 1.57 5.39 0.06 0.03 1.60 <DL <DL861 10/09/2003 0.25 0.22 1.77 6.19 0.24 0.00 3.60 6.0 102.0862 6/09/2003 13.48 5.21 18.30 8.18 0.84 0.00 <DL <DL <DL864 6/09/2003 7.60 6.15 3.91 0.80 0.40 0.06 0.15 <DL 1.2865 6/09/2003 9.46 5.56 14.30 1.40 0.44 0.08 9.00 <DL 43.8P1 27/11/2003 0.04 0.03 0.09 0.44 0.00 0.01 0.30 2.9 5.4B1 20/11/2003 0.89 3.11 0.11 0.22 0.02 0.01 <DL <DL <DLB2 20/11/2003 0.05 0.17 0.01 0.16 0.02 0.01 <DL <DL <DL

Table A4. Chemical analyses of minor constituents 2003. All concentrations in mg/L. DL: detection limit