24973985 minesite water management handbook

Minesite Water Management

Handbook

1997

Copyright © 1997 Minerals Council of Australia

Inquiries should be addressed to the publishers. Minerals Council of Australia PO Box 363, Dickson ACT 2602 Telephone: 61 262793600 Facsimile: 61 262793699 Email: [email protected]

First Edition 1997

Minesite Water Management Handbook

ISBN 0 909276 73 0

In 2008 the first edition was transcribed into electronic format, without consideration of the accuracy or currency of the content. Users should note that in some areas of the book, more recent publications (post 1997) provide updated technical information.

Every effort has been made to contact the copyright holders of material used in this book. However, where an omission has occurred, the publisher will gladly include acknowledgment in any future editions.

Disclaimer This Minesite Water Management Handbook (the Handbook) has been prepared by the Minerals Council of Australia in the interests of encouraging excellence in environmental management. However, the Minerals Council of Australia accepts no liability (including liability in negligence) and takes no responsibility for any loss or damage which a user of the Handbook or any third party may suffer or incur as a result of reliance on the Handbook and in particular for:

(a) any errors or omissions in the Handbook;

(b) any inaccuracy in the information and data on which the Handbook is based or which is contained in the Handbook;

(c) any interpretations or opinions stated in, or which may be inferred from, the Handbook.

11 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K

1. Introduction 8

2. Statutory Requirements 9

3. Planning and Principles 11

3.1 INTRODUCTION 11

3.2 THE HYDROLOGIC CYCLE AND MINESITE WATER BALANCE 11

3.3 SITE DESCRIPTION 12

3.3.1 Climate 123.3.2 Geology and Geomorphology 123.3.3 Topography 123.3.4 Catchment Characteristics 123.3.5 Site Water Requirements 123.3.6 Vegetation and Fauna Assessment 123.3.7 Aquatic Ecology 133.3.8 Heritage Values 133.3.9 Downstream and Offsite Users 133.3.10 Monitoring 13

3.4 SITE PLAN 13

3.5 MONITORING AND DATA MANAGEMENT 14

4. Water Chemistry 15

4.1 CHEMISTRY OF NATURAL WATERS 15

4.1.1 Introduction 154.1.2 Dissolved Versus Particulate and Total Constituents 154.1.3 Difference Between Organic Acid and Carbonate Water Systems 164.1.4 Load Versus Concentration 174.1.5 pH 184.1.6 Alkalinity 194.1.7 Hardness 194.1.8 Conductivity 204.1.9 Salinity 204.1.10 Solids 214.1.11 Turbidity 234.1.12 Oxygen Demand (Dissolved Oxygen, BOD and COD) 23

Contents

2 1 9 9 7 M I N E S I T E W A T E R M A N A G E M E N T H A N D B O O K

C O N T E N T S

4.1.13 Anions and Cations 244.1.14 Metals (Trace Metals, Heavy Metals, Metal Speciation) 254.1.15 Nutrients 254.1.16 Oils, Greases and Hydrocarbons 264.1.17 Organics, Natural Organic Matter, Dissolved Organic Carbon 264.1.18 Colour 274.1.19 Cyanide 274.1.20 Odour and Taste 284.1.21 Radionuclides 29

4.2 BIOLOGICAL ASPECTS OF WATERS 30

4.2.1 Micro-organisms 304.2.2 Algal Blooms 314.2.3 Toxicity and Ecosystem Health 314.2.4 Factors Influencing Bioavailability and Toxicity of Contaminants 324.2.5 Bio-monitors, Bio-accumulation and Bio-amplification 32

4.3 NATURE OF WATERS 33

4.3.1 Beneficial Use 334.3.2 Assimilative Capacity 334.3.3 Receiving Waters 33

5. Water Sampling and Flow Measurement 34

5.1 INTRODUCTION 34

5.2 PRINCIPLES AND PURPOSE OF MONITORING 34

5.3 COMPLIANCE MONITORING 35

5.3.1 Ambient, Point Source and Non-point Source pollution 365.3.2 Mixing Zones 36

5.4 DATA COLLECTION - QUALITY 36

5.4.1 Monitoring Design 365.4.2 Identification of Key Monitoring Parameters 375.4.3 Initial Screening Program 375.4.4 Sampling Locations 375.4.5 Sampling Frequency 375.4.6 Sampling Techniques and Design 385.4.7 Sample Transportation 395.4.8 Sample Analysis 395.4.9 Data Management 405.4.10 Laboratory, Pilot Plant and Leach Tests 40

5.5 DATA COLLECTION - QUANTITY 40

5.5.1 Rainfall Reading 415.5.2 Flow Recording 41


C O N T E N T S

5.6 GROUNDWATER 42

5.6.1 Groundwater Mapping 425.6.2 Testing and Monitoring 435.6.3 Groundwater Parameters 465.6.4 Prediction of Groundwater Characteristics and Responses 46

5.7 REVIEW OF MONITORING DATA 46

6. Water Supply 48

6.1 SURFACE WATER 48

6.1.1 Catchment Yield 486.1.2 Recycling of Water 49

6.2 GROUNDWATER 49

6.2.1 Sources of Supply 496.2.2 Security of Supply 49

7. Exploration 53


7.1.1 Surface Water Data Collection 537.1.2 Access Tracks 547.1.3 Exploration Sites 54

8. Open Cut Mines 56

8.1 SURFACE WATER RUNOFF 56

8.1.1 Flood Mitigation 568.1.2 Methods of Flood Mitigation 578.1.3 In-Pit Drainage 598.1.4 Interception Drainage Around Pit 608.1.5 Sediment Containment 61

8.2 GROUNDWATER 62

8.2.1 Groundwater Inflow 638.2.2 Managing Groundwater Inflow 63

8.3 WATER QUALITY 65

8.3.1 Pit Water Disposal 658.3.2 Acid Drainage 658.3.3 Salinity 66

8.4 PIT CLOSURE 66


C O N T E N T S

9. Underground Mines 68

9.1 SURFACE DRAINAGE AWAY FROM HEAD WORKS 68

9.2 GROUNDWATER INFLOW 68

9.2.1 Managing Groundwater Inflow 68


9.3.1 Treatment and Disposal of Underground Mine Water 69

10. Heap Leach Processes 70

10.1 INTRODUCTION 70

10.2 PLANNING FOR HEAP LEACHING 70

10.2.1 Baseline Evaluation 7010.2.2 Rainfall Events, Acceptable Risk, Contingency Planning 7010.2.3 Baseline Groundwater Monitoring 7110.2.4 Closure Planning 71

10.3 SOLUTION CONTROL DURING OPERATIONS 72

10.3.1 Maintenance of Drain and Pond Capacity 7210.3.2 Integrity of the Pad or Liner 7210.3.3 Integrity of Piping and Valves 72

10.4 WATER MANAGEMENT ON CLOSURE 72

10.4.1 Criteria for Long-term Leachate Quality 7210.4.2 Residues and Long-term Contaminated Site Management 72

11. Waste Dumps 73

11.1 WASTE DUMP CONSTRUCTION FOR WATER MANAGEMENT 73


11.2.1 Location of Waste Dumps 7311.2.2 Erosion on Waste Dumps 7311.2.3 Interception Drainage Around Waste Dumps 7411.2.4 Sediment Containment Around Waste Dumps 75

11.3 GROUNDWATER 75

11.3.1 Infiltration to Groundwater 7511.3.2 Monitoring 76


11.4.1 Acid Drainage 7711.4.2 Salinity 7711.4.3 Suspended Solids 7811.4.4 Leachate and Other Constituents 78


C O N T E N T S

12. Tailings Water Management 79

12.1 DISPOSAL METHODS 79

12.2 CHARACTERISTICS AND MANAGEMENT OF TAILINGS WATER 80

12.2.1 Nature of the Water 8012.2.2 Management 80

12.3 SEEPAGE MANAGEMENT 80

12.3.1 Seepage Control 8012.3.2 Monitoring 8112.3.3 Water Control 81

13. Mine Infrastructure 82

13.1 PROCESS PLANT 82

13.1.1 Characteristics 8213.1.2 Containment and Treatment Technologies 82

13.2 INDUSTRIAL AND WORKSHOP AREAS 83

13.2.1 Containment and Treatment Technologies 83

13.3 HAUL ROADS 84

13.3.1 Environmental Issues 8413.3.2 Surface Water Drainage 8413.3.3 Groundwater Drainage 84

References 86

Glossary 88

List of Tables

Table 2.1: Typical State and Commonwealth Legislation 9

Table 4.1: Typical Conductivity Range of Waters 20

Table 5.1: Key Planning Steps for Water Monitoring 35

Table 5.2: Selection Criteria for Establishing Sampling Sites 38

Table 5.3: Advantages and Disadvantages of Using Numerical Models 47

Table 6.1: Sources and Uses of Recycled Water 50

Table 10.1: Suggested Minimum Design Event Criteria for Heap Leach Operations 71

Table 11.1: Prevention and Remedial Strategies for Acid Drainage 78


C O N T E N T S

List of Figures

Figure 4.1: Species of the Carbonate System as a Function of pH 17

Figure 5.1: Typical Groundwater Surface Map 42

Figure 5.2: Relationship Between Piezometric Level and Groundwater 43

Figure 5.3: Typical Piezometer Installation 44

Figure 5.4: Diagram of a Piezometer Dip Meter 45

Figure 8.1: Calculating the Lowest Cost Flood Mitigation Scheme 57

Figure 8.2: Types of Constructed Embankments 58

Figure 8.3: Conceptual Drainage Around an Open Pit 60

Figure 8.4: Idealised Pit Inflow 62

Figure 8.5: Effects of Barriers to Groundwater Flow 63

Figure 8.6: Effects of Dewatering Around a Pit 64

Figure 8.7: Channel Dewatering 64

Figure 8.8: Water Flows in Open Voids 67

Figure 11.1: The Soil Capillary Zone 75

Figure 11.2: Monitoring Network Around a Waste Rock Dump 76

Figure 12.1: Seepage Paths from a Tailings Storage Facility 81

Figure 13.1: Drainage Considerations on Haul Roads 85

Fact Sheets

Fact Sheet No. 1: Field Record Data Sheets 93

Fact Sheet No. 2: Estimation of Surface Runoff 97

Fact Sheet No. 3: Understanding Event Probability 101

Fact Sheet No. 4: Open Channel Drains 103

Fact Sheet No. 5: Construction of Small Earth Embankment Dams 105

Fact Sheet No. 6: Culvert Crossings 110

Fact Sheet No. 7: Acid Drainage 112

Fact Sheet No. 8: Erosion Control and Sediment Containment 115

Fact Sheet No. 9: Bioremediation Technology 121

Fact Sheet No. 10: Hydrological Data for Design Purposes 122

Fact Sheet No. 11: Groundwater 124

Fact Sheet No. 12: Numerical Modelling 125


Acknowledgments

The Minesite Water Management Handbook has undergone a considerable gestation period and many

individuals have assisted in its production. It is with much appreciation that the Minerals Council of

Australia acknowledges the contributions of these people, all experts in their individual fields, who

gave freely of their time: Raj Aseervatham, Denis Brooks, Michael Cox, Geoff Day, Tom Farrell, Kurt

Hammerschmid, Gavin Murray, Pamela Ruppin, Peter Roe, Ian Wood, and Ray Woods. The comments of

many other individuals on earlier drafts were invaluable in efforts to treat such a broad range of material

as fully and accurately as possible. The Minerals Council of Australia would also like to acknowledge

the companies and organisations for whom the individuals work. All input has been most valuable.


1. Introduction

In the course of mining and mineral processing,

landscapes are altered and soils, rock and water

are subject to physical and chemical change. These

changes must be managed to ensure that any

resulting impacts are minimised, do not jeopardise

future land and water uses, and do not breach

any regulatory requirements. Failure to manage

these impacts in an acceptable manner will result

in the mining industry finding it increasingly

difficult to obtain community and government

support for existing and future projects.

The Minesite Water Management Handbook provides

practical guidance, based on scientific principles and

leading industry practice, on how to investigate and

manage surface and groundwater during exploration,

mining and mineral processing. The information

is sourced from industry, government(s) and

research organisations, consultants and individuals

actively participating in the minerals industry.

This handbook has been prepared as a companion

document to the AMIC (now the Minerals Council

of Australia) Rehabilitation Handbook (AMIC 1990).

The handbook has been developed for those who

are not familiar with the fundamentals, processes

and requirements (both technical and legislative)

of water management for mining purposes, and for

those site personnel with limited or no experience or

training in water management from an environmental

perspective. It also provides an indication of what

the minerals industry sees as its prime objectives and

directions with regard to water management.

The handbook is divided into 13 main chapters

which include both theoretical and practical

topics relating to mine water management. The

first five chapters provide an overview of the

regulatory requirements, management planning

and principles, basic water chemistry and the

principles of sampling and flow measurement.

Chapters 6 to l3 describe the major water-related

technical issues relevant to all areas of a mining

operation. They include generic guidelines for:

• thedesign,constructionandmaintenanceof

site surface water drainage;

• issuesassociatedwitherosionandsediment

control; and

• managementandmonitoringofsurfaceand

groundwater quality:

Specific topics, for example acid drainage, are

presented as fact sheets. Both theoretical and practical

aspects of each issue are discussed. A glossary of

terms is included and, finally, a reference list which

is designed to direct the reader to a greater level

of detail than is provided in this handbook.


2. Statutory Requirements

Environmental management of mining and

mineral processing requires consideration of

both State and Commonwealth legislation,

although most minerals industry operations

are subject only to State environmental law.

Legislation relevant to water issues within the mining

industry is passed by both State and Commonwealth

governments. These laws are usually enforced by the

relevant State Environmental Protection Authority

or Department, State Department of Mines or the

Commonwealth Department of the

Environment.

Typical State and Commonwealth environmental

legislation relevant to water management in the

Australian minerals industry is shown in Table 2.1

This legislation is frequently supported by regulations

which provide more detail on how the legislation

is to be implemented and complied with. For

example, regulations under a Clean Waters Act may

contain limits for physical, chemical and biological

parameters which cannot be exceeded in effluents.

TABLE 2.1: Typical State and Commonwealth Legislation

State Legislation Commonwealth Legislation

• MiningAct • EnvironmentProtection(SeaDumping) Act1981• EnvironmentalProtectionAct

• LocalGovernmentAct • GreatBarrierReefMarineParkAct1975

• CleanWatersAct • Petroleum(SubmergedLands)Act1967

• GroundwaterAct • ProtectionoftheSea(PreventionofPollution fromShips)Act1983• PollutionofWatersbyOilAct

• EnvironmentalProtection/Marine (SeaDumping)Act

• SeasandSubmergedLandsAct1973

• NationalParksandWildlifeConservation Act1975• MarineandHarboursAct

• Petroleum(SubmergedLands)Act • EnvironmentProtection(AlligatorRivers Region)Act1978• CoastalProtectionAct

• SoilConservationAct • EnvironmentProtection(ImpactofProposals) Act1974• DangerousGoodsAct

• RadiationControlAct • IndustrialChemicals(Notificationand Assessment)Act1989

• WorldHeritagePropertiesConservation Act1983


S TAT U T O RY R E Q U I R E M E N T S

Most operations involving water, either supply or

disposal, will be licensed under the relevant act.

Licences are issued for a defined period, typically

one year, and have conditions attached to them.

These conditions may specify the monitoring

which is required to ensure compliance, the

limits which apply, and specific procedures

which must be followed in order to reduce

the environmental impact of the discharge.

As a minimum, every operation should ensure

that its facility fully complies with the relevant

State and Commonwealth acts, laws, regulations

and licences. Therefore, systems need to be

established and maintained to track compliance

with these statutory requirements and to

report this compliance on a regular basis.


3. Planning and Principles

3.1 Introduction

Water respects no boundaries, and drought and

floods are events beyond our direct control.

The industry’s role in water management

is one of stewardship, not ownership, and

therefore our operating philosophy should

be based on the following concepts:

• efficientuseofwater;

• implementationofthereduce,re-use,recycle

concepts;

• avoidorminimisecontaminationof

clean streams and catchments;

• recogniseandprotectdownstreambeneficial

uses (for both surface and groundwaters); and

• onrelinquishmentoftitle,thequantityand

quality of drainage from the site should not

prejudice the productive use of the land.

Implementing these concepts requires considerable

planning, based on a clear understanding of the

project and the hydrological, geochemical and

processing regimes in which it operates. This section

sets out the principles, while subsequent sections

will provide the tools to prepare a detailed water

management plan for a site.

3.2 The Hydrologic Cycle and Minesite Water Balance

The hydrologic cycle is the primary model for the

input and output water management elements in

any site development. These elements include:

rainfall;

surface runoff;

evaporation;

groundwater flow;

seepage;

site and process water uses;

site and process water outputs;

offsite discharges; and

on-site discharges.

Assigning values to the parameters of the

hydrological cycle will identify the water

surplus or deficit nature of the site. This

process is referred to as the water balance.

The minesite water balance is a central component in

the minesite water management system. Through the

water balance, we can gain a clearer understanding

of the principal water management issues of

supply, protection, containment and discharge.

The principal data required for a

water balance include:

• determiningtheappropriatetimestep for the

flow detail being assessed (hourly, daily, monthly

or yearly); and

• definingtheinputs, demands and outputs.

The results obtained from the water balance

present data that provide definable benefits

in developing the components and systems

for effective water management.


P L A N N I N G A N D P R I N C I P L E S

Various tools are available for the water balance

including: spreadsheets for analysis; commercial

software such as AWBM and RORB for rainfall/

runoff analysis; and customised software to

suit the circumstances of a particular site.

3.3 Site Description

Basic information about a site is necessary so that

a workable water management strategy or plan

can be developed. Many of the components and

processes in this description are required for other

site assessment purposes. However, each topic

should be considered in terms of the information

needs required to address potential water

management issues at the site. Not all topics will

need to be researched intensively for every site.

3.3.1 CLIMATE

The essential climatic parameters are rainfall

and evaporation. To a lesser extent, temperature,

relative humidity, wind speed and direction and

solar radiation are also required. Prior to resource

development, daily records generally form the

basis of data collection systems. Because long-

term historical data are central to optimising

water management studies and design, the earliest

possible installation of real-time continuous data

recording equipment is advised when a nearby

weather station is not available. Once a project

is undergoing detailed feasibility studies, climate

monitoring systems which provide more frequent

and specially targeted records may be required.

3.3.2 GEOLOGY AND GEOMORPHOLOGY

The data compiled here will assist with an

understanding of the groundwater and surface water

movement characteristics and likely responses to

mine induced changes in flow or water quality.

3.3.3 TOPOGRAPHY

A site plan showing the geographic setting, contours

and the land systems at the site is required. The

contour intervals are dependent on the level of

investigation and the type of structures - the more

advanced the project the closer the contour intervals

and the greater the accuracy. Typical values are 0.5

to 1.0 m (+/- 0.25 to 0.5 m) intervals for detailed

design and 2.5 to 5.0 m (+/- 1 to 2 m) intervals

for preliminary investigations. More detailed

survey data may be required in particular cases.

3.3.4 CATCHMENT CHARACTERISTICS

A characterisation of the site for parameters relevant

to the surface and groundwater hydrology is

essential for the planning, design and operation of

site water management systems. Storm and volume

runoff coefficients, times of concentration for

peak runoff, storage parameters, erosion potential,

sedimentation characteristics and hydraulic

coefficients such as Manning’s “n” are relevant for

surface characterisation. Hydraulic conductivity and

permeability, sub-surface water zones and aquifers

and storage and yield characteristics are typically

required for an understanding of the groundwater

system. Monitoring systems are necessary to obtain

site-specific data and to confirm calculations.

3.3.5 SITE WATER REQUIREMENTS

It is important to understand what are the site

water demands and how they may vary with

time. A dynamic water balance is frequently a

great asset in establishing and maintaining a water

management program. Short-term benefits in

reducing water use and cost should not jeopardise

future opportunities for expansion of the operation.

3.3.6 VEGETATION AND FAUNA ASSESSMENT

The purpose of this assessment is to provide

a clearer understanding of the catchment

characteristics for rainfall runoff assessments, and

to highlight sensitivities to the implementation

of the various water management strategies.



3.3.7 AQUATIC ECOLOGY

The impact of the various strategies must recognise

the type and diversity of species and relevant

conservation values. Opportunities to utilise natural

systems, eg. local wetland species in water treatment

schemes can be highlighted in this assessment.

3.3.8 HERITAGE VALUES

A comprehensive assessment, listing and plan of

archaeological, heritage, historical values and the

visual character at the site will enable proper planning

and locating of water management structures.

3.3.9 DOWNSTREAM AND OFFSITE USERS

Identification of the potential offsite impacts from

the changes to the existing water patterns is required.

The operator should assess the constraints, the

target quality and quantity parameters required and

where any benefits of the mine water management

systems might pass to downstream users.

3.3.10 MONITORING

Monitoring will be required during the various

phases of mine development: baseline, feasibility,

construction, operations, decommissioning and

active rehabilitation. The monitoring systems

must be established with a view to understanding

the catchment responses to the proposed site

activity and verifying licence requirements, and

for corroborating design data. Such systems need

consistency through all phases of the project.

3.4 Site Plan

Mine water management is a long-term

process which may be simplified by:

• planningfortheenergy-efficientstorage,

transport and use of water; and

• modellingtoquantifypresent

and future water budgets.

The thoroughness of the initial planning process will

determine the ease with, and extent to which future

changes to the water budget may be accommodated.

The planning process should consider:

• identifyingthelocationsofpotentialsources

and probable yields (including surface water

yields from rainfall and groundwater);

• identifyingthelocationsofpotentialusers

of water and their likely demands;

• sizingandpositioningofdamsandotherwater

control structures to cater for local demands;

• preventingdegradationofwater

quality by identifying and separating

“clean” and “dirty” streams;

• optimisingtheflexibilityofthewatersystem

by linking components in the water circuit

(using gravity drainage where possible);

• focusingexcesswatertodown-gradient

control dams of adequate size and at key

locations to control offsite discharges;

• implementingrecyclingschemestore-

use water wherever possible; and

• implementingmonitoringsystemsto

quantify water entering the circuit, moving

within the circuit and exiting the circuit.

Frameworks of water management systems derived

in this way may be used to assess the impact of

future changes in the water budget. This may be

achieved by modelling the response of the mine

water circuit to these changes commonly referred

to as the minesite water balance. Models may be

written using computer programming languages

or developed using conventional spreadsheets.

Models should include:

• flexibilitytoalterquantitiesof

source and demand water;

• flexibilitytoalterwatertransportrates;

• flexibilitytoalterdamsizes;

• flexibilitytoaddordeletewater

transport routes; and



• ‘calibration’checksagainstmonitored

quantities where appropriate.

Planning and modelling of site water budgets

will allow any imbalances between water supply

and demand at the site to be quantified and

accommodated efficiently. The quality of water may

also need to be considered in such an analysis.

The site plan must also address the final land

use and the use of the water management

infrastructure for the site after mining is finished.

This will be a constant reference for ongoing

planning of the water management systems.

Where quantitative data are collected as part of the

site description they should be compiled and stored

on an appropriate water management database

for reliable reference and review. Where possible,

qualitative data arising from this compilation

should be stored on the same database.

3.5 Monitoring and Data Management

Within the resources industry, the basic

principles of water monitoring are to:

• identifythereceivingwatersornaturalresources

which require protection from the existing or

proposed mining and processing development;

• establishwaterqualityobjectives

for these resources;

• collectandevaluatesitespecificdatasuch

as local climatic conditions, permeability of

soil and underlying bedrock, any potential

pathways for the migration of contaminants;

• prepareandimplementamonitoringprogram

for the region prior to the commencement of

mining. Collect rainfall data, background flow

and water quality data for all surface waters

(especially up and downstream of the operation),

groundwater, estuarine and coastal waters that

may be affected by the development;

• ensurethatCommonwealth,Stateandlocal

statutory requirements are observed and

incorporated into the monitoring plan;

• ensurethatsufficientdataarecollectedover

time in order to enable accurate assessment

of the physical and chemical properties of

all point source, diffuse source, industrial

and domestic wastewater streams; and

• collectrepresentativesamplesofthemedium

being measured and an adequate number

of duplicate and quality control samples.

Data management forms an important part of the

monitoring system. The following points should be

considered when designing a monitoring system:

• samplesmustbecollectedaccordingtoa

site-specific protocol, established to fulfil

the objectives of the monitoring program;

• allsamplesshouldbeanalysedusing

NATA registered methods;

• alldatacollectedusingelectronicloggers

must be validated and calibrated against

physically measured data wherever possible;

• calibrationproceduresmustbeestablished

at the earliest possible stage in a monitoring

program and the calibration of equipment

should be checked periodically;

• allwaterquantityandqualitydatashouldbe

stored in a database designed specifically for

the site’s requirements; data should be able

to be retrieved rapidly and systematically;

• waterinformationshouldbereported

regularly to site management (ie. actually

used for management purposes); and

• datashouldberegularlyreviewedand

interpreted to ensure that the beneficial

uses (eg. ecological, recreational) of regional

watercourses are protected in accordance with

appropriate guidelines for receiving water

quality in the region (eg. ANZECC 1992).

Further information on the establishment of site

monitoring programs can be obtained in EPA (1995).


4. Water Chemistry

4.1 Chemistry of Natural Waters

4.1.1 INTRODUCTION

Water quality is a generic term and is usually

determined by the levels of various indicator

substances. These indicators are generally selected

on the basis of the type of waterbody in question

(eg. stream, estuary, groundwater, potable water) and

the water use (eg. the quality of water required for

drinking is higher than that required for recreation).

Impacts on surface and groundwater water quality

can occur during exploration, construction and

operation of mines, as well as at abandoned and

rehabilitated minesites. Uncontrolled drainage

from mines can contribute potentially harmful

materials to local waterways and may degrade

the water’s suitability for domestic, agricultural

or industrial uses, or be harmful to the ecology

of the receiving environment. Government

authorities are placing tighter controls on site

discharges and many sites throughout Australia

now operate under a zero discharge policy.

It is important to understand the characteristics

associated with the various types of water sources

and discharges likely to be encountered.

While the quality of the source or discharge at

any given site is dependent on the geochemistry,

mineralogy and geographical location of the

operation, there are general characteristics

associated with the water that may be encountered

in Australia. This section includes a general

overview of some of the common physicochemical

parameters and includes for each:

• definitionandalternatenames;

• unitsinwhichtheparameteriscommonly

measured and reported;

• sources(whatactivitycancontributeto

the levels of these parameters); and

• environmentalsignificanceofthe

parameter being determined.

However, before discussing individual

physico-chemical parameters, several terms

and concepts common to most aquatic and

geochemical parameters will be introduced.

4.1.2 DISSOLVED VERSUS PARTICULATE AND

TOTAL CONSTITUENTS

Definition

The distinction between dissolved, particulate and

total constituents is one of the most important

definitions used in water quality assessment.

An element can move between the dissolved

and particulate phase depending on physico-

chemical conditions such as temperature, pH or

the presence of some other element or compound.

This is often referred to as “partitioning”. Discharge

licences generally relate levels of a certain element

to either the dissolved, particulate or total

concentration. The following example depicts

the relationship between the three phases.

Consider a one litre bottle of a water sample

collected for the analysis of cadmium. The sample

contains both dissolved and particulate forms of

cadmium. The dissolved cadmium concentration

is the cadmium in the sample after it has been

filtered through a 0.45µm pore size filter. The

particulate cadmium in the sample is what

remains bound to the material on the filter.


WAT E R C H E M I S T RY

Total concentration can be determined either

directly or by calculation from the dissolved and

particulate results. It is not simply a summation

of the two concentrations as the suspended solids

concentration has to be taken into account. For

example, the dissolved cadmium concentration

was found to be 3µg/L, the particulate

concentration of cadmium was determined as

250µg/g (or mg/kg), and the suspended sediment

concentration was 6540 mg/L (0.650 g/L).

Therefore the total cadmium concentration is:

0.650(g/L) x 250 (µg/g) + 3 (µg/L) =

154.5 µg total Cd/L.

Alternatively, the total cadmium concentration

may be measured directly by digesting

(using acid) and analysing a sub-sample

of the original one litre sample.

The definition of “dissolved” using a 0.45

µm filter is purely operational and has no

direct biological rationale. Precise definitions

may be found in APHA (1994).

The classifications of total, particulate and dissolved

concentration are used widely when setting discharge

permits and water quality criteria. Generally, dissolved

criteria are more often used for the protection of

aquatic ecosystems. This is because most toxicity

data show that it is the dissolved phase of pollutants

which is bioavailable to aquatic organisms and thus

potentially toxic. Total concentration criteria are

generally used for recreation, livestock and human

health water quality criteria, given that separation

of the particulate load prior to either swimming or

drinking raw water is unlikely to occur. In addition,

the acidic nature of the human gut means that

many pollutants can remobilise into the dissolved

phase and therefore become more bioavailable.

4.1.3 DIFFERENCE BETWEEN ORGANIC ACID

AND CARBONATE WATER SYSTEMS

The main aquatic geochemical processes throughout

most of Australia's inland fresh waters are dominated

by one of two general geochemical systems. In the

context of this handbook, these will be termed:

• carbonatewater(waterinwhichthecarbonic

acid equilibrium plays the dominant role

in governing water chemistry); and

• organicacidwater(waterwithnatural

high levels of dissolved organic matter).

Waters in which the primary control is the carbonic

acid system have pH values ranging from 6 to 8.5

and electrical conductivities up to many thousands

of mS/cm. Organic acid systems generally have a pH

less than 6 and much lower electrical conductivity.

Carbonate Waters

The carbonate, or carbonic acid, system describes

water in which carbonate species in solution control

or influence aquatic geochemical processes. The

principal components of the carbonate system include

carbon dioxide (CO2), carbonic acid (H2CO3),

bicarbonate (HCO3-) and carbonate (CO3

2-)The

reactions involving these species are very important in

surface waters, groundwaters and in the atmosphere.

Carbonic acid in water can be derived from several

sources, the most important of which are:

1. the weathering of carbonate rocks via:

CaCO3 Ca2+ + CO32-

CO32- + H+ HCO3

-

and

2. uptake of CO2 from the atmosphere via:

CO2 + H2O H2CO3

H2CO3 H+ + HCO3-



The species of the carbonate system that is present

depends on the pH of the solution (see Figure 4.1).

Below pH 6.4, carbonic acid (H2CO

3) is the dominant

species in solution whereas above pH 6.4 bicarbonate

(HCO3-) is the dominant species. The greater the

total concentration of the carbonate species, ie.

HCO3- plus CO

32-, the greater the buffering capacity

of the water, ie. the greater the ability of the water

to resist change from either acidic or basic inputs.

The amount of carbonate produced from reaction

2 is far less important than that derived from the

weathering process of rocks. Generally, carbonate

system rivers have a higher conductivity, due not to

the presence of bicarbonate but rather the co-cations

in solutions which are also weathered as a part of

the same process that liberates the bicarbonate.

Organic Acid Waters

The particular organic acids which control the

second major system of aquatic geochemical

processes occurring in Australian freshwater rivers

and streams are derived from what is loosely

termed humic and fulvic material or dissolved

organic matter (DOM). DOM is derived from

the breakdown products of organic matter and

comprises a wide range of complex molecules.

Almost all surface partitioning and adsorption

processes involving natural sediments are mediated

to some degree by organic matter of this type. Rivers

draining regions where little or no carbonate is

present, and where bedrock is resistant to weathering,

tend to have a low pH and low conductivity. Soils

developed in these areas are frequently organic-rich

because the bedrock is resistant to breakdown and

therefore contributes little mineral to the soil. As

water percolates and circulates through the organic

rich soil, cations that are present in solution (Ca, Mg,

Na, K) are exchanged for H+ in the soil organic matter.

As the H+ accumulates in solution, the pH

decreases. As the pH decreases, organic

compounds are leached from the surface litter,

into solution. Organic acids are also synthesised

by soil organisms and excreted by plant roots.

These waters also originate from areas of high

rainfall where peat deposits are common,

eg. the western highlands of Tasmania.

4.1.4 LOAD VERSUS CONCENTRATION

In determining water quality, the distinction

between load and concentration must often be

made. Concentration of the element compound



is emphasised in systems where a threshold or

regulatory level is desirable in the receiving water,

eg. maintaining total suspended solid values below

100 mg/L, or dissolved oxygen above 9.5 mg/L.

Concentration is usually expressed in terms of

mass per unit volume, ie. µg/L, mg/L, g/L or %.

There are other situations where total load or flux

(ie. the total amount - mass or volume - of substance

per unit time) may be of more concern, eg. nutrient

loading into lakes and rivers to avoid algal blooms

or the spread of nuisance weeds and phytoplankton.

Loadings are usually expressed in terms of mass per

unit time (g/day, tonnes/year), mass per unit area (kg/

ha), or mass per unit area per unit time (kg/ha/year).

4.1.5 pH

Definition and Alternative Names

pH is an indicator of the intensity of the acidic

or basic character of a solution (APHA 1994).

Units of Measurement

pH is a dimensionless parameter and is

represented on a logarithmic scale of 1 to

14. A pH value of 1 indicates a highly acidic

solution, 7 is neutral and 14 is strongly basic,

or alkaline. The technical definition is:

pH = -1/log10

[H3O+].

Sources and Environmental Significance

One of the greatest causes or contributors to the

production of acidic water is from sulphide oxidation

of iron sulphide minerals such as pyrite (FeS2) in the

presence of oxygen (air) and water. The oxidation

reactions are bacterially mediated, primarily by

Thiobacillus ferrooxidans. Acid generating conditions

can occur in damp mine workings, in exposed waste

rock dumps, tailings dams and in washeries. Fact

Sheet No.7 discusses acid drainage in greater detail.

As the water moves through the acidic material,

oxidation of reactive sulphides occurs, generating

acidity which initially can be neutralised by

alkalinity in the groundwater. If more acid is

generated than the initial alkalinity of the water,

the alkalinity will be consumed and acid water will

result. If sufficient oxygen is present, the amount

of acidity generated is determined by the amount

of reactive sulphides in the material. In the absence

of mining, acid waters are uncommon because

dissolved oxygen in the groundwater is insufficient

to produce acidity greater than the alkalinity of

the groundwater. During mining, gaseous oxygen

is introduced as the rock is broken up, and water

movement through the system is accelerated.

The bacteria that catalyse the acidity producing

reactions thrive only under acid conditions so that,

once acidity is initiated, acid production becomes

more rapid and the problem increases rapidly.

A phenomenon only recently identified in Australia

is natural acidification of water as a result of acid

sulphate soils. These waters have developed in tidal

swamps, wetlands and estuarine environments along

coastal regions where iron rich silts and muds have

mixed with accumulated organic matter. Bacteria

thrive in these anaerobic conditions, creating pyrite.

When these soils are exposed to air, as occurs with

disturbance due to coastal development, sulphuric

acid is produced due to oxidation of the pyrite.

Potential acid sulphate soils occur in most coastal

regions from north of Sydney to Onslow in Western

Australia. Any mining development which potentially

affects such soils could also result in acid drainage.

In most natural streams where acid drainage is

not present, pH levels range between 5.5 and 8.5.

Extremes to these levels are usually the results of

high loads of natural organic acids (DOM) or high

carbonate concentrations. Another effect of mixing

acid water with receiving waters high in carbonate

is the formation of CO2 which affects the respiration

of aquatic biota. When pH values fall below 4,

most aquatic biota will be severely stressed.

In contrast to the low pH water produced by acid

rock drainage, many mineral processing facilities



require water with an elevated pH (9 to 11) which

is normally achieved through the addition of lime.

Problems of scaling in pipes and ecosystem stress

brought about by high pH waters are no less serious

than the problems associated with low pH waters.

Treatment Options

Several approaches can be adopted to

raise or lower pH including:

• additionofanalkalioracid;

• activatedcarbonorultra-violet

irradiation to remove DOM; and

• bubblingwithCO2 to manipulate

the carbonic acid equilibrium.

4.1.6 ALKALINITY


Alkalinity refers to the acid neutralising capacity

(pH buffering) of water, ie. its ability to reduce

changes in pH brought about by the addition

of an acid. The higher the alkalinity, the more

acid is required to reduce the pH. Alkalinity is

generally due to the presence of inorganic anions

including carbonate (CO32-), bicarbonate (HCO

3- )

and hydroxide (OH-); however alkalinity may

also result from the presence of borates (B4O

72- ),

phosphates (P043-) and silicates (SiO

22-).


Alkalinity is expressed in the units of:

mg of calcium carbonate per litre

of water (mg CaCO3/L).

The reported results for alkalinity are influenced by

the method of the determination and depend on

the pH end-point used in the analysis. Analytical

methods are documented in APHA (1994).


The main sources of alkalinity are the soluble

salts of the anions listed in Section 4.1.13.

Alkalinity is known to influence several

aquatic geochemical processes including:

• pHandeffectsfromaciddrainage;

• dissolvedmetalsolubilityandbioavailability

(toxicity) to aquatic organisms;

• foaming,scalingandmetallurgicalproblems;and

• dissolutionofbicarbonateandcarbonate,

causing liberation of CO2 and corrosion.

4.1.7 HARDNESS


Hardness is commonly associated with a waters ability to lather or foam soap. The harder the water the more difficult it is to lather the soap. The principal components of hard water are calcium and magnesium ions (Ca2+ and Mg2+).

Total hardness is defined as the numerical sum of the calcium and magnesium concentrations, expressed as calcium carbonate. When hardness is numerically greater than the sum of carbonate and bicarbonate alkalinity, that amount of hardness equivalent to the total alkalinity is called “carbonate hardness”; the amount of hardness in excess of this is called “non-carbonate hardness”. When hardness is numerically equal to or less than the sum of the carbonate and bicarbonate alkalinity, all hardness is carbonate hardness and non-carbonate hardness is normally absent.


Hardness is reported in the same units as alkalinity, ie. mg (CaCO

3)/L.

There are two methods for determining hardness. The first is by calculation from the Ca2+ and Mg2+ concentration in solution, the other is by titration.

Hardness may range from zero to several hundred mg/L, depending on the source and any prior pre-treatment of the water.


Hardness usually occurs throu gh dissolution of minerals containing calcium, magnesium, and silica compounds, typically calcium and magnesium carbonates, sulphates, chlorides or



nitrates. Because of the inverse solubility of

these compounds with temperature, at high

concentrations they precipitate out of solution

in, for example, boilers and hot water pipes.

There are no reported human toxicological

consequences of elevated hardness; however,

high hardness waters are generally unpalatable.

Treatment Options

Treatment options for water with high hardness

comprise mainly precipitation of the Ca2+ and

Mg2+ ions using a mixture of lime (Ca(OH)2) and

soda ash (Na2CO

3). In this process, the Ca2+ and

Mg2+ ions precipitate as CaCO3 and Mg(OH)

2.

As this process occurs at high pH, subsequent pH

adjustment may be required. This can easily be

achieved by the addition of either H2SO

4 or by the

bubbling of CO2 through the softened solution.

4.1.8 CONDUCTIVITY


"Conductivity" is a measure of the ability of water

to conduct an electric current. Factors affecting

conductivity include temperature and the type,

concentration and valency of ions present

(eg. Na+, Ca2+, Cl- and SO42-).

The higher the concentration of conducting

solutes, such as salts, the higher the

conductivity (see Table 4.1).

TABLE 4.1 Typical Conductivity Range of Waters

Water Conductivity Range

(mS/m)

Freshlydistilled 0.5-2

Potablewaters 50-1500

Seawater 40000-50000

Groundwater upto50000


Conductivity is usually determined by

measuring the resistance where:

Conductivity = 1

Resistance.

The SI1 unit for conductivity is mS/m (milliSiemens

per metre); however µS/cm is still in common use,

and many conductivity instruments use the units

µmhos/cm, where 1 mS/m = 10 µmhos/cm.


Conductivity is used to monitor several

different processes, some of which include:

• determinationofamountsofionic

reagent needed in certain precipitation

and neutralisation reactions; and

• estimationoftotaldissolvedsolids(TDS)in

mg/L and salinity in a sample by multiplying

the conductivity in mS/m by an empirical factor.

For TDS this factor may vary from 0.55 to 0.90

depending on the soluble components of the

water and the temperature of the measurement.

In the absence of a site-specific relationship,

a factor of 0.68 is commonly assumed.

Similarly, an estimate (in milliequivalents

per litre) of either anions or cations can be

derived from the conductivity measurement.

4.1.9 SALINITY


Salinity is an indirect measurement of the

total amount of soluble salts in solution.

These salts include sodium chloride as well

as various calcium and magnesium salts

of chlorides, sulphate and nitrates.


Salinity is generally expressed as parts

per thousand (ppt or 0/00).

1 Systéme lnternationale = International System of Units



The only direct method of measuring absolute

salinity is to analyse the individual chemical

components. Given the time and costs associated

with individual analyses, indirect methods

such as conductivity are normally favoured.

Conductivity measurements can be made in the

field or laboratory with a meter and probe which

has temperature compensation. Total dissolved

solids is also an approximate measure of salinity


Dry land salinity is a major problem in certain areas

of Australia, caused primarily by the widespread

clearing of native vegetation. Replacement of deep-

rooted perennial native vegetation with shallow

rooted annual pastures which use much less water,

allows the water table to rise, bringing dissolved

salts to the surface where they are concentrated

by evaporation. Similarly, the storage of acid and

saline mine water in dams can pollute high quality

groundwater reserves. Hypersaline groundwater,

with salinities well in excess of seawater, is used as

process water in the goldfields of Western Australia.

Release of this water into the environment can

cause death of vegetation and land degradation.

Criteria for salinity pertaining to various

livestock, irrigation and domestic uses can be

found in ANZECC (1992) and DME (nd).

4.1.10 SOLIDS

Total solids, as the name suggests, is a measure of

all the substances associated with a water sample,

other than the water itself. It can be further refined

into its constituent parts, total dissolved solids

(TDS) and total suspended solids (TSS), ie.

TS = TDS + TSS.


Another name for total solids is total residue.

TDS or filterable residue is that portion of a sample

(other than water) which passes through a filter of

pre-defined pore size. This will obviously depend

on the pore size of the filter used. For this reason,

industry has standardised on a range of filters from

various manufacturers all with a similar nominal pore

size of around 1.2µm. In Australia, perhaps the most

widely used is the Whatman glass-fibre filter GF/C

After the water sample is filtered through the GF/C

filter, the filtrate is evaporated to dryness at 1800C

and weighed; the TDS is calculated from this result.

It is important not to confuse dissolved solids,

which are filtered through the GF/C type

filters, with the dissolved component of metals.

Dissolved metals refers to that portion of the total

metals in a sample which pass through, or are

not retained on, a 0.45µm filter membrane.

TSS may also be referred to as non-filterable residue

(NFR) or suspended particulate matter (SPM).

This parameter measures the amount of solids

suspended in a water sample which can be separated

from the water and dissolved solids phase by

filtration through a filter of fixed pore size.

TSS can be related to the turbidity of a water

sample. With careful site-specific calibration, and

where the sediment source is relatively constant

and homogenous, turbidity can be used to calculate

TSS (see: Section 4.1.11). However, extreme care

must be taken in developing this relationship.


Total solids and its constituent parts are

reported as mg/L. In samples with very high

concentrations the units may be expressed as %.


The composition of total solids depends on the

geology, land use, geochemistry and the environment

of the catchment. Dissolved solids in water may result

from the dissolution of materials exposed during

mining, or from the addition of soluble chemicals

during the processing of ores. High levels of TDS

are often not suitable for potable water, mainly

due to inferior taste. In addition, waters high in

TDS are rarely suited for industrial applications.



Suspended solids can result from erosion of

unprotected ground surfaces, from wash water,

or from stormwater mobilising solids deposited

on the ground surface as a result of mining or

processing activities. The TSS in water can affect

the operation of biological and physical wastewater

treatment processes. Samples high in TSS are also

aesthetically unsatisfactory and affect the partitioning

and distribution of various contaminants in the

aquatic system. Suspended solids reduce light

penetration through the water column, affecting

growth of aquatic flora and fauna as well as the

aesthetic appeal of the water and its subsequent

use for recreation. Under certain flow conditions,

suspended material settles out and can smother

benthic organisms and their habitats. Other problems

with sedimentation include possible disruption to

navigation. Since most pollutants can be carried by

or adsorbed onto suspended solids, tight controls

of TSS in a water management plan can also

lower the flux or total load of pollutants entering

watercourses. Adsorbed nutrients and organic matter

are also a source of nutrients for algal blooms.

Solids remain in suspension only when there

is enough force or energy (turbulence) in the

water column to keep them in suspension. Rivers

with lower gradients and lower energy enable

suspended sediments to settle out and become

benthic sediment or bed load. The effect of

increased sediment loads to a river system are

numerous. High suspended sediment loads can

effect the gills of fish leading to irritation and

lesions. When suspended sediment settles, it can

increase river bed elevation or aggradation which,

as well as affecting aquatic organisms, may also

lead to increased overbank flows and flooding.

Sedimentation in water storage can reduce the life

of a dam, or increase the costs of dredging as well

as decreasing the quality of the retained water.

Treatment Options

Prevention of dust generation through control

of processes and stockpiles, and erosion of

land through controls on clearing and prompt

revegetation, are ways of reducing solids loadings

to water. Sediment retention through the placement

of sediment traps will lead to a reduction in the

amount of sediment reaching natural watercourses.

Sediment traps upstream of a storage dam are

an effective means of prolonging the life of a

relatively small dam. Treatment of water containing

suspended sediments prior to use in a plant or

for domestic potable water may require settling,

screening, filtering or dosing with a flocculant.

4.1.11 TURBIDITY


"Turbidity" is an optical measurement of the

sample’s inherent ability to scatter light. Turbidity

measurements can be affected by the particle size

of the suspended matter, its mineral content and

its respective abilities to scatter and absorb light. In

addition, fine colloidal material can have a major

effect on increasing the turbidity (light scattering)

of a sample but only have a minor effect or increase

in the concentration of total suspended solids.

Optical right angled back-scatter nephelometers are

generally used for low level turbidity measurements

while forward scattering devices, which are more

sensitive to the presence of larger particles, are

generally used for in-stream analysis systems.

Care must be taken in using optical devices,

especially in tropical regions where algae and

slime growth can rapidly affect the calibration

of these instruments. Similarly, in waters with

high suspended solids, abrasion of the optical

surface can affect calibration of the instrument.


The units of turbidity are generally reported in

nephelometric turbidity units (NTU). It is possible

to produce a calibration curve or regression curve

of turbidity versus TSS at a given site; however,

this must be repeated for each site, because of the

likely changes in the characteristics of suspended

solids between different geological regions.



Flow rates can also affect particle size distribution and

hence the relationship between turbidity and TSS.


By world standards, Australian watercourses are quite

turbid as a result of intense rainfall and flood events,

and the erodibility of agricultural and arid soils. The

aquatic ecosystems of many Australian watercourses

have adapted to higher turbidity levels than existed

prior to white settlement, but most probably at

a cost of lower species numbers and diversity.

Turbid waters normally require some form of

treatment prior to their use as industrial or potable

water. Treatment processes used to remove turbidity

can include filtration, coagulation and settling.

4.1.12 OXYGEN DEMAND

(DISSOLVED OXYGEN, BOD AND COD)

Dissolved oxygen is a key water quality parameter

required to sustain a healthy aquatic ecosystem.

The presence of excess organic materials such

as sewage sludge can significantly add to the

oxygen demand of a system, consuming dissolved

oxygen from the water as they decompose.

Dissolved Oxygen


Dissolved oxygen refers to the oxygen

molecules that are dissolved in water.


Dissolved oxygen is usually expressed in parts

per million or mg/L. For some natural systems,

% saturation is also commonly used.


For the protection of aquatic ecosystems,

ANZECC (1992) recommends that dissolved

oxygen should not normally be permitted to fall

below 6 mg/L or 80-90% saturation, this being

determined over at least one diurnal cycle.

Reduction in dissolved oxygen within natural

aquatic systems can result from inputs of

organic material to the system (eg. sewage, some

mineral processing effluents) and also from algal

blooms. Dissolved oxygen concentrations usually

decrease with increasing water temperature.

Biochemical Oxygen Demand (BOD)


The BOD test is an empirical test in which

standardised laboratory procedures are used to

determine the relative oxygen demand of wastewaters,

effluents and polluted waters. It is often referred

to as the BOD5 test, referring to the biochemical

oxygen demand over a five day incubation period.


The units of BOD5 are expressed in mg/L

along with the incubation time.


The BOD test measures the oxygen consumed

by biochemical degradation of organic material

(carbonaceous demand) and the oxygen used

to oxidise inorganic material such as sulphides

and ferrous iron. It may also measure the

oxygen used to oxidise reduced forms of

nitrogen (nitrogenous demand), unless their

oxidation is prevented by an inhibitor.

If BOD5 in effluent is high, then oxygen

dependent organisms in the receiving

waters may become stressed.

Chemical Oxygen Demand (COD)


The COD test is used as a measure of the oxygen

equivalent of the organic matter concentration

of a sample that is susceptible to oxidation by

a strong chemical oxidant. For samples from a

given location COD can be empirically related

to BOD, organic carbon or organic matter.




Results are expressed in units of mg O2/L.


COD is a useful, but not commonly used, parameter

in mine water management. Its usefulness stems from

its measurement of the total oxygen demand, unlike

BOD which measures oxygen demand available to

bacteria over a five day period. As a result, COD

concentrations will normally always be higher

than BOD concentrations from the same sample.

4.1.13 ANIONS AND CATIONS

Definition

Anions are those elements with a negative charge (eg.

Cl-, OH-, HCO3-, SO

42-, CO

32-, P0

43-) as opposed

to cations which are positively charged (eg. Na+,

K+, Ca2+, Mg2+). This discussion will be restricted

to the common inorganic anions and cations.

Inorganic Anions

Common anions associated with mine water

quality management are chloride (Cl–), hydroxide

(OH–), bicarbonate (HCO3–), nitrate (NO

3–), sulphate

(SO42–), carbonate (CO

32–), and phosphate (PO

43–)·


Anions are typically reported in the units mg/L.

Values in natural and wastewaters range

from zero to several hundred mg/L.


The sources of these anions is dependent on

geology as well as prior treatment and uses of

the water. Sources of chloride are salts such as

NaCl and CaCl2 which are often present in high

concentrations in groundwater. For example, the

aquifers of the Hunter Valley of New South Wales

contain high concentrations of salt as a result of

deposition of sediments in a marine environment.

The most common source of soluble SO42– from

mine operations is from the oxidation of sulphide

minerals such as pyrite (FeS2). Phosphates (which

are present in domestic and industrial detergents)

and nitrates (from mine explosives and fertilisers

used in mine rehabilitation) can also find their

way to watercourses. If these nutrients occur in

moderate to high concentrations they can readily

stimulate the growth of algae and aquatic weeds.

Inorganic Cations

Definition

Cations are those elements with a positive charge,

such as sodium (Na+), potassium (K+), calcium (Ca2+),

and magnesium (Mg2+). These are among the most

abundant natural elements in the environment.


Cations are typically reported in the

units mg/L. Values in natural surface and

groundwaters and wastewaters range

between zero to several hundred mg/L.


The concentrations of these elements in natural

waters depends on the geology and geochemistry

of the host rock. Calcium concentrations in

water from limestone areas are typically higher

than for waters from non-calcareous areas.

High concentrations of these cations are typically

found in groundwaters and increase their hardness.

They also affect the permeability and fertility of

soils and, for this reason, their concentrations are

closely monitored in the agricultural sector.

Other sources of these cations include leachate

from waste rock and tailings dams.

The ratio of the specific major cations relative to

each other is also an important factor in considering

the implication of their respective concentrations

in either feed, process or discharge water.



4.1.14 METALS (TRACE METALS, HEAVY

METALS, METAL SPECIATION)

Definition

Two terms are commonly used when discussing

metals in water and environmental management.

These are:

• Trace metals, which commonly refers to:

– metals at very low levels in the environment

(trace analysis); or

– trace elements

which are either essential nutrients or

serve some other necessary biochemical

function. These include zinc, iron, copper,

cobalt, sodium and potassium;

and

• Heavy metals, which are generally thought

to mean toxic metals. Strictly speaking the

term refers to metals with an atomic weight

greater than that of sodium (22.9).


The units are dependent on the metal and its

concentration. Particulate metals are usually

reported as µg/g or mg/kg. Dissolved metals are

usually expressed in terms of µg/L or parts per

billion. Other units in which metals are sometimes

reported include mol, millimol or micromol per

litre (mol/L, mmol/L, µmol/L). These units relate

to the number of molecules of the metal that are

present and are not influenced by the actual weight

of the elements of concern. This unit is most

commonly used in toxicological assessment.


In natural systems, most metals are only sparingly

soluble in water, with higher concentrations

usually associated with the particulate phase. The

amount of a metal released from its particulate

phase into solution is a function of pH, particle

geochemistry, aquatic geochemistry, hydrologic

factors, temperature, etc. Mobilisation of metals is

frequently a secondary effect of acid drainage.

The impact of a particular metal on water quality

depends not only on the type and concentration of

the metal, but also on its chemical form or speciation.

The chemical speciation of a metal (eg. whether

copper exists as Cu2+, CuCO3, Cu(OH)2, or Cu-

dissolved organic matter complexes etc.) dictates how

bioavailable it is and the extent to which it may enter

the food chain, where it may accumulate to toxic

levels. Generally, metals are most toxic in their soluble

free ionic form (species) eg. Cu2+, Ag+ etc., compared

to metals complexed with either inorganic or organic

ligands (eg. CuCO3 or Cu-DOM) or in particulate

form (associated with minerals). One exception is

mercury which is more toxic in the methyl mercury

(CH3Hg) species compared to the free (Hg2+) species.

Further information on individual metals and their

environmental Significance can be obtained from

the various ANZECC guideline documents.

4.1.15 NUTRIENTS


The term "nutrient" refers collectively to elements

and compounds which are essential to sustaining

adequate biological function. The most common

nutrients which may affect the water management

of a mining operation are nitrogen and phosphorus.

There are various forms of nitrogen such as ammonia,

nitrite, nitrate, and organic nitrogen. Phosphorus

can be found in the form of orthophosphate, total

phosphorus and organically bound phosphates.

The form of the nutrient has an integral role in

its function and fate in the aquatic environment.

Biological productivity may be limited by the

availability of either nitrogen or phosphorus,

which are often referred to as the growth limiting

nutrients. Silica has also been identified as a

limiting nutrient in some aquatic systems.


The units of measurement for nutrients depend

on the form of either phosphorus or nitrogen

that is being measured. Typical expressions are



micrograms of total phosphorus or total

nitrogen per litre (µg TP/L or µg TN/L) and

milligrams of ortho-phosphorus or nitrate

nitrogen (mg Ortho-P/L or mg NO3-N/L).


Sources of nutrients in mining operations include:

• sewageorsepticwastewater;

• nitrogenbasednutrientsfromexplosives;

• phosphorusbasednutrientsfromprocess

chemicals and industrial detergents;

• fertilisersappliedduringrehabilitationworks;

and

• degradationproductsofcyanide.

Excessive concentrations of nutrients can promote

and accelerate growth of aquatic plants and algae,

including attached and floating macrophytes and

dense suspensions of free-floating algae. These reduce

light penetration and, upon decomposition, cause

odours and loss of oxygen in the host ecosystem.

4.1.16 OILS, GREASES AND HYDROCARBONS


The parameter “oil and grease” refers to a

range of chemicals which can be extracted

from a water sample into the organic solvent

trichlorotrifluoroethane. The types of compounds

collectively analysed by this method are primarily

fatty components from animal and vegetable sources

and hydrocarbons from petroleum products. While

trichlorotrifluoroethane is used to extract the group

of compounds of interest, there are three subsequent

analyses which can be conducted depending on

the make-up of the water being examined and the

likely constituents. Oil and grease determination

can also be performed on sludge samples.

If required, total petroleum hydrocarbons (TPH)

can be selectively analysed as a separate group by

a modification of the oil and grease method.


Oil and grease in water samples is commonly

expressed in mg/L. Oil and grease in solid

sludge is expressed as % of dry solids.

Hydrocarbons are also expressed in this way.


If present in high amounts, oil and grease can

reduce the efficiency of water treatment processes

by interfering with anaerobic and aerobic

biological processes. Large quantities of oil and

grease discharged in wastewater can cause surface

films and deposits and result in the staining of

riverbanks and coast lines. They can also affect

oxygen exchange, oxygen demand and palatability.

Treatment Options

Treatment options available for the reduction

of synthetic organics (fuels, oils, grease etc.)

include simple oil-water separators through to

expensive dissolved air flotation systems.

4.1.17 ORGANICS, NATURAL ORGANIC

MATTER, DISSOLVED ORGANIC CARBON


The term organics refers to a broad group of chemical

parameters, some of which are used in the resource

development and mineral processing industries.

In addition to manufactured organic compounds,

there is a broad group of naturally occurring organic

compounds which play an important role in aquatic

biogeochemical processes. Collectively, these

compounds are referred to as dissolved organic matter

(DOM), natural organic matter (NOM), dissolved

organic carbon (DOC), or humic substances (HS).


For the more general definition of synthetic

organics, the units of measurement depend on

the analysis being undertaken. Most commonly,

they are reported in either mg/L or µg/L.



Naturally derived organic material is most

commonly measured as DOC and expressed

in units of mg C/L. DOC typically represents

approximately 50% by mass of DOM.


Process reagents such as collectors, frothers

and flocculants are all synthetic organic-based

compounds. Usually, the amounts of organic

compounds used for mineral processing are small

and any residual concentrations decay rapidly.

DOM, NOM, DOC and HS refer to a generic group

of compounds which are best described as the humic

and tannin extracts of soil and plant materials which

impart the characteristic tea colour of some natural

waters. The organic compounds making up DOM are

a group of weakly acidic molecules which, in high

concentrations, are able to reduce the pH of the water.

Treatment Options

The removal of natural organic material can be

performed in many ways and is dependent on

the amount of DOC present and the amount of

water requiring treatment. Common treatment

options include adsorption onto activated

carbon, UV oxidation and ozone oxidation.

4.1.18 COLOUR


The term colour can be divided into:

• True colour, ie. the colour of a sample from

which turbidity has been removed; and

• Apparent colour, which includes the colour

and turbidity of the total sample.

Apparent colour is measured on the sample prior

to any treatment (except inversion of the sample to

suspend all particulate matter) and true colour is

measured after either filtration or centrifugation.

Normally, unless otherwise stated, the term

colour refers to the measure of true colour.


Several methods exist for the analysis of colour,

varying from the simple visual comparison, to

techniques requiring sophisticated instruments

and determination of the colour wavelength of

the sample. The units of colour depend on the

method of analysis but generally correspond to

a “colour number” or code which is based on a

visual comparison of the colour of the sample to

that of a series of standards, usually made with a

platinum cobalt solution. Alternatively, the colour

can be measured by light transmittance through a

special system of photoelectric cells and light filters.

The final choice of measurement depends on the

specific water quality to be determined. Regulatory

authorities usually specify the parameters to be

determined and the specific method of analysis.


Colour may result from a number of sources

including metallic ions (iron and manganese),

dissolved organic material (humus and peat material),

plankton and weeds. Highly coloured industrial

wastes can also contribute to the colour of water.

The environmental implications of colour depend

on the element that is imparting the colour.

4.1.19 CYANIDE


Cyanide (CN) is used widely throughout the

mining industry to dissolve and complex

gold and silver to separate them from the ore.

In terms of water quality management there

are three main forms or species of CN:

• totalCN-referstoallformsofCNandis

usually determined by performing an exhaustive

hot acid extraction whereby all the CN from

both liquid and solid phases are dissolved

and subsequently analysed as NaCN;

• weakaciddissociableCN(WADCN)includesonly those CN compounds that are liberated



under weakly acidic conditions, ie. it does not

include all the CN present in the sample; and

• freeCN(CN–) and hydrogen cyanide (HCN)

are the most bioavailable forms of CN, the

abundance of which is strongly dependent

on pH. The lower the pH the greater the

proportion of the total CN that exists as HCN.


The units in which CN is expressed depends on the

form being analysed and from where it was collected.

Samples from process waters containing CN will

generally have total CN values in the mg/L range;

however, after storage or treatment the values may

realistically be in the very low µg/L range. Generally,

for process waters using CN values are reported as:

• mgtotalCN/L;

• mgWADCN/L;and

• gfreeCN/L.


While CN can be formed naturally by nitrifying

bacteria, the main source in the mining

industry is waste streams from cyanidation

processes. The mechanisms affecting the

environmental fate of CN include:

• bacterialdegradation-movementofCNthrough

soils and sediments is thought to be restricted

through biodegradation by soil organisms

and adsorption to soil particle complexes;

• atmosphericdiffusion-atneutralandacidicpH,

CN in solution occurs predominantly as HCN

gas which readily diffuses into the atmosphere;

• conversiontothiocyanate-freeCN

reacts with pyrite and pyrrhotite to form

thiocyanate, which is relatively stable and

non-toxic. Thiocyanate is also produced

as a part of the natural detoxification and

biodegradation of CN in biotic systems;

• complexformationwithmetals-CNforms

complexes with metal ions which are common

in mineral processing wastes. These complexes

are usually resistant to biological uptake and

are stable in the environment, although some

may be readily broken down to their basic

components, for example CuCN; and

• photochemicaldegradation-althoughcomplex

ions such as ferro-CN and ferri-CN are

thermodynamically stable, they can undergo

photo-reduction to form free CN in the presence

of UV light. In compacted and solid tailings

dams, this is only a problem at the surface of

the dam. Beneath the surface, away from the

UV light, the CN remains as a stable metal-CN

complexes. The conversion of CN complexes

to free CN is affected by pH, temperature,

pond geometry and the intensity of UV light

incident on the pond. The concentration of

total CN has been observed to drop from

around 60 mg/L to less than 5 mg/L in just

over 1.5 months (Smith &. Mudder, 1991).

4.1.20 ODOUR AND TASTE


Both odour and taste are subjective tests which

often depend on an individual’s personal criterion to

determine the acceptability of the water or otherwise.

The tests are usually based on a comparison with

tasteless and odourless water samples. Flavour

is more objective, and can be used instead.

Documented procedures for flavour are available.


Taste and odour are generally reported as

dimensionless descriptive numbers which

relate to threshold detection limits where the

sample is compared to a standard with no, or

some definable taste or odour characteristics.

The measurements include threshold odour

number, flavour threshold number, flavour rating

assessment and flavour profile analysis number.




Taste and odour may render the water unsuitable

for human consumption and domestic use

as well as tainting fish and other foods which

inhabit the water. There is no single compound

which causes odour. However, tests exist for

the determination of several of the prime

compounds which impart an odour in waters.

4.1.21 RADIONUCLIDES


The mining and milling of ore containing uranium

may result in water and wastewater that contains

variable concentrations of radionuclides present

in the ore. The water that is retained or discharged

from an operation should, as a minimum, be

analysed for radium-226, thorium-230, lead-

210, uranium-238 and polonium-210.


The commonly used unit of measurement for

radionuclides is the becquerel (bq). For water,

the units are expressed as bq/L and for soil and

sediment the units are expressed as bq/g.


Radionuclides can be found in wastewater arising

from the mining and milling of radioactive ores.

Typical streams are:

• excessprocesswater,whichmaybe

pumped to a tailings impoundment;

• runofffromtheminepit,orestockpiles,waste

dumps, borrow areas, haul roads and plant area;

• seepagefromtheminepit,tailings

dam and evaporation ponds; and

• waterfromwatersupplyboresanddamswhich

has flowed through mineralised material.

4.2 Biological Aspects of Waters

Mining and mineral processing operations rely on

or influence the biological component of natural

or artificial systems. These systems can include:

• biologicalprocessesbeneficialtothe

operation, eg. anaerobic and aerobic

treatment ponds, artificial wetlands;

• ecosystemprotection,ie.limitingthe

physical and/or chemical parameters

associated with mine discharges to levels

suitable for ecosystem protection; and

• bio-monitoring,ie.usingaquaticorganisms

to monitor the effects and effectiveness

of water management practices.

ANZECC (1992) recommended four biological indicators to assess ecosystem condition or health. These indicators are based on the assumption that the extent to which the integrity of an ecosystem is being maintained can only be assessed when the characteristic biological communities of a region are known or, since this will rarely be the case in Australia, by comparison of the biological community at the site or sites of interest with unimpacted communities in similar habitats elsewhere in the region. Each of these indicators relies on a rigorous and statistically sound sampling scheme, which is able to distinguish between various population parameters between impacted and unimpacted sites. Of these biological indicators, two relate to biological community structure and two to community processes.

The biological indicators recommended are:

Species Richness

Measures of specific richness indicate the number of species present in a sample of organisms of given size. They differ from diversity measures which also incorporate the concept of species evenness. A decrease in richness is generally considered as an indicator of ecosystem stress.



Since different components of an ecosystem may

respond differently to stress, it is important that all

the major biological groups (eg. macroinvertebrates,

fish) be evaluated. The ANZECC guideline

specifies that the species richness as measured

by a standardised index should not be altered.

Species Composition

ANZECC (1992) has proposed a guideline that, in

any waterbody, impacts that result in Significant

changes in species composition compared to those

in similar, local unimpacted systems should not be

permitted. It is possible, although probably unlikely,

that ecosystems could maintain species richness while

still changing markedly in species composition.

Primary Production

Primary production forms the basis of most

aquatic food chains. In any waterbody, net

primary production should not vary from the

levels encountered in similar local, unimpacted

habitats, under similar light, temperature and

nutrient loading regimes. Primary production

is known to be sensitive to light (water clarity),

temperature and nutrients, amongst other factors.

Ecosystem Function

In any waterbody, changes that vary the relative

importance of the detrital and grazing food chains

should be minimised. Production to respiration

ratios should not vary significantly from those

of similar, local, unimpacted systems.

Some ecosystems, such as large standing waterbodies,

have autochthonous primary production (produced

within the waterbody) as their major energy

source. Others, including forest streams and some

wetland systems derive most of their energy from

allocthonous detritus (produced from outside the

waterbody and is transported to where it is used).

Aquatic systems should be managed such

that the relative balance between these two

major energy pathways is maintained, and

that natural detritus-driven aquatic systems

are not converted to autochthonous primary

production driven systems, and vice versa.

Levels of Protection

Two categories of aquatic ecosystems are identified

within the national ANZECC guidelines:

• Pristine ecosystems are not subject to

human interference through discharges

or activities within the catchment. For

these ecosystems, now largely restricted

to National Parks, it is appropriate for the

existing water quality to be protected and

preserved through strict management; and

• Modified ecosystems include all those systems

subject to human interference. Some modified

ecosystems have been permanently altered

physically, for example through stream

channelisation or port construction. Others

have been changed through long-term

chemical toxicity caused by contaminated

sediment or by changed river flow regimes.

4.2.1 MICRO-ORGANISMS

Micro-organisms play an important role in natural

aquatic systems and in the treatment of wastewater.

The greatest use of microbes in wastewater treatment

is for the treatment of sewage using anaerobic and

aerobic treatment systems. Other uses of micro-

organisms relevant to the minerals industry are:

• treatmentofcyanidewastestreamsgenerated

from mining and mineral processing operations;

• treatmentofhydrocarboncontamination

arising from spillage or leaks from

storage tanks or pipes; and

• remediationofhighnutrientor

sulphate waste waters.



4.2.2 ALGAL BLOOMS

Problem algal blooms are usually the result of a

number of factors and not generally the result of

a single person or a projects activities. A bloom is

usually an indication of widespread problems or

stress throughout the catchment, as in the case of

blue-green algal blooms along the Murray-Darling

system. While localised algal blooms can occur on a

site, they usually do not pose any great problems and

can frequently be controlled. Algal blooms are usually

short-term occurrences leading to a population

explosion and normally result from a combination of

high light penetration and water temperatures, slow

flowing or stagnant water and high concentrations

of nitrogen and phosphorous. Oxygen depletion

and the release of toxic constituents from blue-

green algae are common problems that can develop

when a bloom collapses and the algae decay.

4.2.3 TOXICITY AND ECOSYSTEM HEALTH

In general, toxicity testing involves determining

the effect of various compounds on test organisms

under set conditions. The terms LD50

and LC50

are

both acute measures of toxicity. However, toxicity

can also be measured in terms of non-lethal, chronic

parameters such as an organism’s growth rate,

fecundity changes and behavioural response changes.

An extensive listing of toxicological data has recently

been compiled within the ANZECC guidelines,

which list the types of compounds and the range

of toxicity data available. In general, toxicity

evaluation is time-consuming and very expensive.

Acute Toxicity

This term refers to a relatively short-term lethal

or other effect, usually defined as occurring

within four days for fish and macroinvertebrates

and less for smaller organisms.

Lethal dose50

(LD50

) refers to the dose of a test

compound, which kills 50% of the test population.

The time required to kill 50% of the population

is then used as an index of toxicity. Standard LC50

and LD50

tests are performed over 96 hours. The

96 hour duration is operationally defined and

has no biological or biochemical foundation. It

was established so that a test could be completed

within one working week. It refers to a specific

dose of a test compound and is usually expressed

as a concentration of the test compound per mass

of test organism body weight. Such information is

usually used to calculate and assign a safe exposure

limit or of recommended dose per person per day.

Lethal concentration50

(LC50

) is similar to the lethal

dose but refers to a concentration. Therefore,

this figure is more widely used to test aquatic

organisms such as fish and invertebrates. Often,

toxicity data are related to a time of exposure,

eg. a value of 50µg/L is not to be exceeded more

than once over any 12 month period. While such

limits do take into account accidental spillages,

they are assigned on a purely arbitrary basis and

the toxicological information in relation to this

value being exceeded is not absolute in nature.

Chronic Toxicity

This term refers to long-term toxicity as opposed

to sudden death resulting from a test compound.

Chronic toxicity is much more difficult to diagnose

and relates to longer term exposure to a specific

compound. Continued chronic exposure can

include adverse responses such as changes to

spawning, metabolism or growth rates, or appetite,

behavioural or reproductive changes. Because

chronic effects are harder to identify, minimal work

has been performed to date on the chronic effects

of most pollutants, except in the case of human

health (mercury for example). Chronic toxicity is

often more subjective than a measurement of acute

toxicity or LC50

or LD50

. However the chronic toxicity

effects of pollutants are now becoming much more

important to maintain long-term ecosystem health.



4.2.4 FACTORS INFLUENCING

BIOAVAILABILITY AND

TOXICITY OF CONTAMINANTS

The following factors play a major role

in determining the fate of any waste

discharge to the aquatic environment.

• Carbonate equilibria and effect on metals

speciation - The presence of carbonate enables

the formation of inorganic carbonate-metal

complexes, as well as buffering pH which can

have a major effect on metal speciation.

• pH effects on speciation - The lower the pH (ie. the

more acid the water), the higher the proportion

of a dissolved metal which is bioavailable or in

the free ionic or weakly complexed state. If there

are significant quantities of particulate-bound

metals in the waterbody, a reduction in pH can

leach metals from the particles into solution and

thus alter the distribution (partitioning) of the

metal between the soluble and particulate phases.

• Effects of organic matter on complexation and

speciation - Natural organic matter in aquatic

systems can consist of large polyelectrolytic

molecules with numerous binding sites of

different polarities. Consequently, on a single

molecule, numerous sites are available for

binding metals and pesticides. The degree

to which organic carbon partitions between

the solid and solution phase also influences

pollutant partitioning. High concentrations of

dissolved organic carbon (DOC) can increase the

solubility of metals and pesticides by stabilising

and complexing these compounds into

soluble aqueous complexes. If high suspended

solids are present, DOC also binds strongly

with sediment particles, and consequently

detoxifies the adsorbed contaminant. DOC is

critical in assessing the environmental fate of

effluent containing metal and organic wastes.

• Partitioning between dissolved and particulate

species - Bioavailability is dependent on

whether a compound is associated with the

particulate phase compared to the aqueous

phase, in addition to the pH and concentration

of organic matter. The more the compound

is associated with the particulate phase, the

less bioavailable it will be. The partition

coefficient is the term which defines the ratio

of the amount of particulate bound pollutant

to the amount in the aqueous phase.

4.2.5 BIO-MONITORS, BIO-ACCUMULATION

AND BIO-AMPLIFICATION

Definitions

Bio-monitors are organisms used to determine

the extent of pollutant transport and the

extent of biological uptake of a pollutant.

Bio-accumulation refers to the increase in a

contaminant concentration within a particular

organism or group of organisms, eg. liver

of fish, egg shells of birds of prey.

Bio-amplification refers to the amplification of the

bio-accumulated contaminant through the food

web from one organism up the trophic order.

Organisms such as bivalves (mussels, oysters etc.)

are sometimes used as bio-monitors because they

filter large volumes of water and any associated

metals and organic pollutants, thus bio-concentrating

the actual levels of a pollutant within the water

column. At this stage bio- monitors can only be

used reliably as indicators of the presence of a

pollutant. Further research is required before the

significance of any relationships between bio-

monitor and ecosystem health can be established.

Whether a compound will bio-accumulate depends

on a number of physico-chemical parameters

such as the class of compound (eg. metal, organic

pesticide), its concentration, exposure frequency

and duration. Bio-accumulation also depends on

the target organism, the compound of concern and

its fate within the target organism. Many organisms

have the ability to regulate pollutant levels in certain



parts of their body. Therefore identification

of key organs (kidney, liver, adipose or fat

tissue) are important considerations when

interpreting bio-accumulation data.

Bio-amplification is an extension of bio accumulation

where a contaminant which has been taken up by one

particular organism or trophic level is passed on to

higher order organisms - such as the case of mercury

in fish which are then consumed by humans.

4.3 Nature of Waters

This section outlines a number of additional

concepts which are pertinent to the complete

understanding of the properties of water.

4.3.1 BENEFICIAL USE

Beneficial use refers to the designated uses of a

waterbody. Examples of beneficial uses include:

• ecosystemprotection;

• recreation-swimming,fishing,aesthetics;

• domesticandpotablewater;

• livestockwatering;

• commercialfisheries;and

• irrigation.

Dischargers to waterbodies will generally be required

to identify and meet a designated beneficial use.

This may include the designation of a mixing zone.

4.3.2 ASSIMILATIVE CAPACITY

Assimilative capacity refers to a waterbody's

ability to absorb or resist changes brought about

by the addition of a particular parameter. An

example is that of buffering capacity, where high

alkalinity waters are able to assimilate additions

of low pH water with no adverse changes.

4.3.3 RECEIVING WATERS

The type of receiving water into which wastewater

is discharged is an important factor in determining

the effect and ultimate fate of discharged pollutants.

For example, the fate of metals discharged into a

freshwater lake will be different to that of an estuary

or ocean. Physical characteristics such as temperature,

flow, pH, salinity, dissolved oxygen and light

penetration determine the behaviours of a specific

pollutant in the aquatic environment. The capacity

of the receiving environment to dilute and assimilate

the effluent stream is also of primary importance.

These considerations should be evaluated prior to an

effluent stream being discharged to a receiving water.

Effluent streams of significance emanating from

mining operations include sewage treatment plants,

stormwater discharges from haul roads, waste dumps,

workshop discharges and machinery washdown

discharges containing hydrocarbons, or surfactants.


5. Water Sampling and Flow Measurement

5.1 Introduction

Water monitoring can be a very expensive

and time consuming exercise and therefore

the monitoring plan must be well designed

before the program is implemented. Suggested

planning steps are shown in Table 5.1

In addition to these key steps, specific requirements

of the National Water Quality Management Strategy

need to be considered and the ANZECC (1992)

guideline documents also need to be reviewed.

5.2 Principles and Purpose of Monitoring

The key issues that must be addressed

before the commencement of sampling

and flow monitoring are listed below.

1. Reasons for monitoring - The objectives and

purpose of the monitoring program must be

established. Monitoring programs are usually

implemented for compliance with an operating

licence, to meet company or corporate policy

requirements, for project design input data or

for a baseline survey. Data from monitoring

will also provide valuable feedback and

corroboration of design data adopted. The

program should meet the defined objectives.

2. Trained field staff - Personnel who collect

meteorologic, hydrologic and water quality

data should be skilled in hydrography,

field flow measurement techniques and the

fundamentals of water chemistry. The increased

use of electronic field data also requires field

personnel to be skilled in the use of data

loggers, portable computers and associated

software. Standard and uniform sampling

and preservation procedures need to be used.

If this expertise is unavailable within the

organisation, consideration should be given to

using a reputable and experienced consultant.

3. Execution of the program - The type of

sample collection (eg. automatic or manual grab

sampling), frequency, number of monitoring

sites and phase (exploration, feasibility,

construction, operation, decommissioning

and after site closure) of the project should be

identified within the initial planning stage.

4. Budget - Sufficient financial resources must be

assigned to meet the objectives of the program,

or else the program needs to be modified.

Ideally, staff and financial resources allocated

to a monitoring program should complement

the scope of the program, and the sensitivity of

the local environment. In circumstances where

financial resources are limited, it is better to:

• ensurethatthesamplescollectedare

representative in both time and space;

• restrictsamplecollectiontokey

locations (including controls); and

• reviewpreviouslycollecteddatatoensure

unwarranted analyses are not requested.

Finally, when allocating and revising

financial resources, all the associated costs

need to be incorporated. Expenses that

are frequently neglected include:

• samplestoragecosts(iceforfield

storage, temporary refrigeration);

• sampletransportcoststothelaboratory;


WAT E R S A M P L I N G A N D F L O W M E A S U R E M E N T

• consumablecosts(samplebottles,acidrinsing

of sample bottles, labels, coolers, field clothing);

• costsassociatedwithcalibratingstreamflow

data, which requires qualified personnel

manually undertaking a program

of streamflow gauging; and

• databasedevelopment,dataanalysiscosts

(eg. computer facilities and employees’

time) and implementation of an

appropriate data management system.

5.3 Compliance Monitoring

In the past, licence and discharge criteria varied

frequently between the States. Recently, a more

uniform approach has been taken with a move

towards the ANZECC Water Quality Guidelines

(1992)1, which consider both discharge limits and

receiving water quality. This document should be

reviewed in order to understand the existing national

approach to water quality management in Australia.

1 Under revision 1997-98.

TABLE 5.1: Key Planning Steps for Water Monitoring

The Key Planning Steps

1. Identify the potential receiving waters and their beneficial uses.

2. Outline the site resources (personnel, financial) which are available for the monitoring program.

3. Locate and review the presence of any existing data, environmental audits and reports.

4. Identify all Local, State and Commonwealth statutory requirements which must be met by the operation.

5. Select a reputable laboratory which can advise on sampling methodology, containers, preservation and storage, etc.

6. Using a site plan, identify the physical and chemical properties of all likely point and non-point sources of pollution, the network and the catchment partitioning.

7. Design and implement a “screening” monitoring program to identify all sources and types of contaminants (eg. suspended solids, zinc, phosphates, E. coli) from each location. The screening program should include all surface waters, groundwater, industrial and domestic discharges, receiving waters etc. Control or background sites should also be identified and sampled. This program should be undertaken during dry and wet weather periods and the results reviewed in detail to identify contaminants which should or should not be analysed for a specific location.

8. Identify all monitoring sites which require flow measuring facilities (if contaminant loadings are required for water balance data, for catchment yield characterisation and rainfall/runoff parameters). Ensure a proper program is in place for physical measurement of flows for calibration and for validation of all recorded data.

9. Design and implement a calibration, quality control and quality assurance program with appropriate control sites, blank and duplicate samples, etc., and ensure detection limits are appropriate.

10. Ensure rainfall guages (and climate stations as appropriate) are in place for catchment rainfall/runoff characterisation.

11. Implement a site-wide sampling program and review the data once they are available. Parameters that have been measured below the detection limit can be sampled less frequently.

12. Review all results against statutory requirements.

13. Design an appropriate computerised database management system so that results can be managed and retrieved with ease.



5.3.1 AMBIENT, POINT SOURCE AND

NON-POINT SOURCE POLLUTION

Ambient concentrations generally refer to natural

or background levels of water quality parameters

within a receiving water. It is important to determine

if the background values reflect actual natural

conditions or a natural system which may have

been modified over the past two centuries.

Discharge or point source criteria refer to the

concentration of a contaminant or parameter

at the point of discharge (eg. an outfall from

a wastewater treatment plant). The criteria

may specify a mean value and a higher level

not to be exceeded at a given frequency.

Non-point source pollution refers to a diffuse

source rather than a single discharge point, eg.

unconfined stormwater runoff from a minesite,

workshop and maintenance areas. Contaminants

from diffuse sources may be measured as a

concentration (eg. Mg/L), but usually contaminant

loading data (eg. kg/ha/yr) are required and both

quality and quantity data must be collected.

5.3.2 MIXING ZONES

When assessing compliance with receiving water

quality guidelines, the “mixing zone” of the

waterbody must also be considered. This is a region

of the receiving water at which elevated levels of

a contaminant can be present due to a discharge

source, before dilution to an acceptable level.

ANZECC (1992) defines a “mixing zone” as an

explicitly defined area around an effluent discharge

where certain environmental values are not protected.

All relevant mixing zones, both within and

outside a lease area, should be clearly identified.

Monitoring programs and interpretation of

data need to consider that these areas exist.

Control strategies should ensure that the area

of a mixing zone is limited in order that the

value of the waterbody is not prejudiced.

5.4 Data Collection - Quality

The resources allocated to environmental

data collection will depend on the phase

of the mining operation (ie. exploration,

construction, operating, closure).

• Baselinestudiesandassociatedmonitoring

programs should be implemented at prospective

sites prior to the commencement of any major

earthworks or infrastructure development.

• Theresourceevaluationandfeasibilityphases

usually involve the collection of meteorological

and hydrological data, if no long-term data

exist for the local region. Long-term time series

data will improve techniques for optimising

tailings dam design, surface drainage works,

water supply and flood mitigation.

• Theconstructionphasegenerallyinvolves

expanding the monitoring program as staff

and financial resources increase. A target

monitoring program during construction

is often necessary to measure the impacts

of the construction activities. It also

allows fine tuning of initial “screening”

programs prior to full-scale operation.

• Theoperationalphasewillnormallyinvolve

frequent monitoring of all point source (eg.

sewage effluent, potable water, process and

tailings dam water), non-point source (eg.

stormwater from the plant area, landfill

leachate) and receiving water quality and

quantities (waterbodies within and adjacent

to the mine and mineral processing lease).

• Thedecommissioningphaseandtheextent

and duration of monitoring will depend on the

nature of the operation and the requirements

outlined in the mine decommissioning

plan, agreements and licences.

5.4.1 MONITORING DESIGN

Initially both a statistical evaluation of the

monitoring design and a review of the procedures



and techniques to be adopted should be undertaken.

Once a preliminary plan is prepared, the logistics (eg.

staff and financial resources) need to be reviewed.

Development of the statistical design and validation

of the sampling program, analytical methods and

final data set need to be undertaken by personnel

with appropriate expertise. The use of blank

samples, unidentified duplicate samples and

inter-laboratory testing should be incorporated as

key components of the monitoring program.

Electronically collected hydrological data from

streams and rivers should also be validated using

appropriate statistical procedures and manual

gauging methods during low, medium and

high flow flood events. Electronically collected

rainfall data should be validated similarly.

5.4.2 IDENTIFICATION OF KEY

MONITORING PARAMETERS

The monitoring parameters selected (physical,

chemical and biological) will depend on the

ore being mined at the operation, the process

technology and chemistry, the geographical

location and the beneficial environmental uses

which need to be protected. It is important

to identify all the key monitoring parameters

early in the program in order to avoid possible

delays at some later stage of the development.

5.4.3 INITIAL SCREENING PROGRAM

Prior to commencing a full-scale monitoring program,

it is worthwhile undertaking an initial screening

survey at all potential monitoring locations within

the project area to determine which parameters are

relevant, significant and measurable above analytical

detection limits. This should be done in conjunction

with the statutory authorities concerned and the

analytical laboratory. Multi- element screening of

water samples for total and dissolved contaminants

on a selected number of samples is a cost-effective

technique to identify parameters which should be

incorporated into the site monitoring program.

Results from the initial screening program should

be compared with guideline values such as those

published by ANZECC (1992) and NHMRC (1994).

Locating best positioned flow monitoring stations,

relative to the monitoring locations required, can also

be assessed as part of the initial screening program.

5.4.4 SAMPLING LOCATIONS

The selection of suitable sampling sites within

and surrounding a mining operation should be

based on the potential for a specific area, process

or activity to have an environmental impact.

Selection criteria for sampling and

control sites are shown in Table 5.2

It should be noted that the conditions required

for an acceptable control site for biological

monitoring programs are generally more

stringent and complex than a control location

for chemical monitoring programs.

Sufficient samples should be collected to quantify

accurately the concentrations and behaviour

of a compound from the time it is discharged

through to the point where it can no longer

be detected above ambient concentrations.

5.4.5 SAMPLING FREQUENCY

The frequency interval selected for the collection

of samples for a water monitoring program

will depend on the following factors:

• statutoryandlicenceconditions

(eg. weekly, monthly);

• sizeandgeographiclocationof

the mining operation;

• distanceandeaseofaccesstosamplelocations;

• variabilityofnaturalandseasonalconditions;

• availabilityofstaffresourcestocollect

samples and process data; and

• typeofanalysis.



5.4.6 SAMPLING TECHNIQUES AND DESIGN

There are numerous methods by which a

representative sample can be collected, with the

final technique selected primarily dependent on

the type of waterbody or waste stream requiring

assessment. It is particularly important that the

procedures used, and any changes to these, be

thoroughly documented, and all persons using

them are adequately trained in their use.

Surface Water Sampling

Sample collection of surface waters (sewage

effluent, stormwater, tailings dams, streams and

estuaries) can range from simple grab sampling

TABLE 5.2: Selection Criteria for Establishing Sampling Sites

Sample Sites Control Sites

The selection of sampling sites within and outside

the project area should reflect the:

• beneficialusesrequiringprotection;

• geographiclocationandtheareapotentially

impacted by the operation;

• thenatureoftheoperationandthetypeof

ore/minerals/metal produced;

• conditionsofthelicenceagreement;

• accesstosamplingsites(allweatherif

required); and

• budgetandanalyticalconstraints.

An overview of the "typical" monitoring sites that

should be sampled at an operation are:

• withinoradjacenttoareasofbeneficialuse;

• thedischargepointforindustrialordomestic

waste streams prior to entering receiving waters;

• monitoringofreceivingwatersupstream

and downstream of the discharge point

or property boundary, if a mixing zone

is identified in licence conditions;

• monitoringofallimpoundedwater

including tailings dams, retention

pond water, seepage ponds;

• monitoringofgroundwaterdownstream

from contaminated sites, eg. dirty water

ponds, hazardous waste sites; and

• belowtheconfluencepointofmajor

tributaries within the region.

Control sampling sites are an essential component

of any water monitoring program. The location and

number of control sites selected will depend on:

• thegeographicandtopographic

location of the operation;

• thespatialcoverageoftheproposed

monitoring program; and

• financialconstraints.

It is essential that control and

routinely monitored sites:

• areinsimilarlocations,preferably

in the same catchment;

• arenotinfluencedbypastorcurrentmining

operations or other human influences;

• havesimilargeochemicalconditions,ie.either

carbonate systems or organic systems; and

• havesimilarmeteorologicaland

hydrological conditions.



techniques through to sophisticated automatic

samplers, which have the capacity to collect both

discrete or composite samples over a specified period.

When surface sampling techniques are to be

used the following should be considered.

• Thesamplecontainersusedmustbeappropriate

for the chemical parameter being measured

(eg. acid washed high density polyethylene

for trace metals, organic solvent rinsed glass

bottle with teflon lid for organic compounds).

• Beforefilling,rinsethesamplebottleoutthree

times with the water being collected, unless

the bottle contains a preservative. Ensure clean

hands are used as dirty hands may contaminate

the sample (eg. cigarette smoke or residual

ash will contaminate low level nutrient and

metal samples). For trace metal samples,

prevention of contamination is paramount,

and special techniques such as the use of

non-powdered latex gloves are required.

• Avoidcontaminationofthesampleand

disturbance of the waterbody being sampled.

• Excludeairfromthesamplecontainers.

• Appropriatesamplepreservationtechniques

must be implemented immediately after

sample collection (eg. filtration and addition

of AR grade HNO3 for dissolved trace metals,

temporary storage at 40C for nutrients).

Note that sample holding times vary between 3 hours

and 28 days for different parameters being analysed.

• Ensurethelaboratoryandtheanalytical

techniques used are NATA (National

Association of Testing Authorities) registered.

Variations in sampling and preservation techniques,

storage times prior to analysis and the analytical

methods chosen all contribute to incompatibility

of data. Considerable time and effort should be

allocated to ensure that the samples collected, and

the results obtained, are of a consistent high quality.

To facilitate the collection of high quality

samples and data interpretation, field log

sheets need to be completed at the time of

sample collection. Examples of field record data

sheets are presented in Fact Sheet No. 1.

The reader is strongly recommended to review

published guidelines and texts for the collection

and preservation of samples prior to designing

and implementing a monitoring program.

Examples of such documents are provided in

the references section of this handbook.

5.4.7 SAMPLE TRANSPORTATION

The remote location of most Australian mining

operations means that samples may need to

travel considerable distances to the laboratory

at which the analysis will be performed.

Water samples should be freighted in portable

“coolers” containing ice, as many parameters

require storage at 40C prior to analysis. Samples

should be placed in designated “coolers”

to allow the separation of low-level control

samples from high level effluent samples.

Some parameters (for example alkalinity) require

analysis within 3 to 24 hours of sample collection

and so, it is recommended that these analyses be

performed at the mining operation using properly

calibrated instrumentation and clean conditions.

Others, such as pH, EC and temperature should be

measured in the field. The remaining samples should

be rapidly transported to the allocated laboratory

if possible by same-day or overnight transport.

Appropriate chain-of-custody forms must also be

dispatched with the samples, clearly identifying

all sample details and the required analysis.

5.4.8 SAMPLE ANALYSIS

The selection of a laboratory is an important

decision in the design phase of the program. It is

preferable that the laboratory and the methods



used for a specific analysis are NATA registered.

NATA registration means that the laboratory has been

inspected by personnel from the governing authority;

the analytical method has passed stringent quality

control procedures and the method has been used in

inter-laboratory quality control programs. The results

of these inter laboratory quality control programs

should be requested prior to commissioning

long-term work to a specific laboratory.

The inclusion of duplicate and blank samples

within all sample batches sent to a laboratory

is recommended. Feedback should be

provided to the laboratory to identify and

remedy problem areas in the analysis.

As a guide, the QAQC component of monitoring

and analysis should account for at least 10-15% of

the effort (and cost) of the monitoring program.

It is essential that all aspects of a QA/QC

program are discussed with the selected

laboratory once the site screening program is

complete and prior to the implementation of

a long-term site-wide monitoring program.

5.4.9 DATA MANAGEMENT

Data management is an important component of

any environmental monitoring program, as vast

amounts of data can be generated within short

periods. Data management should be incorporated

into the initial planning stages of the program in

order that the database may be used to meet the

initial objectives of the monitoring program.

The use of spreadsheets for data storage and

management is often insufficient for most long-term

environmental monitoring programs. A relational

database is more applicable due to its capacity to

store and easily process vast quantities of data.

It also has the advantage of rapidly retrieving

information for a specific purpose, such as reporting

to government authorities. In most cases, existing

hydrologic, water quality and meteorological data

which are stored in a spreadsheet or ASCII format can

be imported easily to a central relational database.

A relational database linked to a geographic

information system (GIS) provides a particularly

powerful tool for the management and interpretation

of data. For example, geographic trends, such as

downstream dilution of groundwater contaminants,

are easily identified and readily appreciated

by management when presented visually.

5.4.10 LABORATORY, PILOT

PLANT AND LEACH TESTS

In some circumstances, laboratory bench scale tests

can increase the knowledge about the behaviour

and removal of a pollutant within a treatment

plant, sedimentation dam or tailings dam.

Pilot plant and laboratory studies can often be

more closely and easily monitored than full-

scale field studies, as samples can be collected

more frequently and the time, travel and cost of

collecting samples is significantly less. Examples

include the use of leach columns to test the acid

generation potential and leachability of tailings,

waste rock and other materials stored in bulk.

Where laboratory and pilot plant tests are

conducted, it is important that findings and

conclusions based on these studies are verified

in the field under full-scale natural conditions.

5.5 Data Collection - Quantity

When considering the data measuring systems

for the volumetric water parameters such as

rainfall, evaporation, and stream flow, the specified

use of the data is the primary consideration

in selecting the appropriate recording system.

The following is an overview of appropriate

recording systems and controls for various climate

and water-related parameters and the various

circumstances when each may be utilised.



5.5.1 RAINFALL READING

There are two methods of recording data.

• Manualrecordingofrainfallcollectors,eg.a

standard rain gauge, on a daily basis. These

data are useful for general interpretation of

rainfall trends and long-term water balance

analyses. The data can also be used to

verify automatic recording rain gauges.

• Automaticrecordingraingauges,whichhavea

calibrated tipping bucket gauge with associated

electronic data recording logger. The advantage

with the automatic system is its ability to record

the time sequencing of rainfall events. These

data are valuable for characterising the storm

intensities for an area and for the establishment

of the rainfall runoff response at the site.

An automatic recording system is relatively

inexpensive to install, with power from localised

battery or solar panels. These systems can

manually download data to a computer or can

be connected to a telemetry system for data

capture remote from the site of installation.

5.5.2 FLOW RECORDING

Flow recording in existing streams and waterways

and future waste streams or diversion works is

essential for comprehensive characterisation of

the site hydrology and water management plan.

The critical areas where flow recording

instrumentation is either required or desirable

for developing site specific characteristics are:

• atlicenseddischargelocationsfromthesite;

• atstormwaterdischargelocationsaroundthesite;

• onexistingstreamsbothupstream

and downstream of the site; and

• selectedcatchmentswhereflowmonitoring

will provide useful design data.

The selection of flow monitoring systems will depend

on the characteristics of the monitoring location.

These normally range from constructing hydraulically

rated controls in streams, pipe monitoring systems

and manually flow rating the streams. Regardless

of the type of hydraulic control structure it is

imperative that the following basic rules be followed

in establishing the flow recording system.

1. Select the monitoring location that will maximise

the reliability of data recovery for the range

of flows that will occur. This may require

construction of hydraulic control devices such

as a flume or v-notch weir. Where natural

controls are selected they must be robust.

2. Select the appropriate flow depth recording

hardware for the monitoring location.

Typical flow depth recording sensors

include pressure gauges, sonic systems,

float gauges and capacitance probes.

3. It is essential that flow monitoring stations

be rated for flow and height. This may be

undertaken using a hydraulic structure that has

a pre-determined rating relationship. Where

natural controls are used, it is critical that the

flows are rated by physically measuring the flows

through the control and relating this directly

to monitored flow heights at the station. It is

not sufficient to rate a flow monitoring station

using only theoretical and analytical hydraulic

relationships that require subjective assessments

of coefficients (eg. Mannings equation).

4. Few chances occur to collect time related data,

and therefore it is critical that both reliable

and appropriate monitoring equipment be

installed. As vital development and strategic

decisions depend upon the values recorded

at these stations, the hardware monitoring

and recording equipment must be of a high

calibre. The following questions help with

the selection of suitable instrumentation:

• Willtheequipmentbeintactand

record throughout extreme events?

• Isthesiteaccessibleduringflowperiodsfor

manual flow recording (for rating relationship)?



• Howoftencanloggersbedownloaded

and is a telemetry system required?

• Whatisthepotentialforvandalismor

damage by animals or large trees?

• Haverainguagesbeeninstalledat

appropriate locations for characterising

the rainfall/runoff response?

• Dopersonnelresponsibleforcollecting

the data and maintaining the station

have the required levels of expertise?

5. Measured and recorded data must be

validated to ensure the data is correctly

presenting the conditions being measured.

The validation must take place as soon as

possible after it is collected and should check:

• thatthedatarecordedarerealistic;

• anymalfunctionsininstrumentrecording;and

• thecalibrationdata.

Validation processes involve processing the

raw data into physical outputs (height and

flow), checking compliance against similarly

recorded data, verifying where the data fall

within the calibration limits and scanning the

data for anomalies and unrealistic outputs.

For the installation and operation of flow

monitoring systems, reference should be made

to the Australian Standard 3778 - “Measurement

of water flow in open channels” and all its

associated sub-sections. Care must be taken

that specific requirements for the location of

the system and measuring devices are followed,

otherwise inaccurate monitoring data will result.

5.6 Groundwater

5.6.1 GROUNDWATER MAPPING

Groundwater mapping involves the identification

and location of groundwater resources. A typical

groundwater map contains contour information

representing piezometric levels. Groundwater

contours should be shown relative to an absolute

datum (eg. AHD or a suitable mine datum) rather

than relative to ground level, as the ground contours

may bear no relation to groundwater levels.

Figure 5.1 shows a typical groundwater surface map.

Groundwater flow is always from a region of high

water level or piezometric level to a region of low

water level or piezometric level (see Figure 5.1).

The following steps are required to construct a

groundwater map.

• Groundwater“borders”shouldbedetermined

(eg. rivers, lakes, oceans and significant changes

in types of soil and rock). Where practical,



mapping should include the entire

groundwater resource as well as its borders.

• Observationboresorpiezometers(seeSection

5.6.2) should be installed in a relatively regular

grid pattern over the area of interest. Piezometers

should be located such that the difference in

water levels between adjacent piezometers is less

than the planned contour interval of the map.

• Ambientgroundwaterlevelsshouldbemeasured

at regular temporal intervals to identify

seasonal fluctuations as well as responses to

rainfall and periods of drought. Care should

be taken to gather ambient data well before

activities such as pumping are commenced.

• Interpolationpackagesavailableforcomputer

simulation of contours may be used to

generate maps from gathered data. Each map

should be a snapshot of groundwater levels

for the relevant period of monitoring.

5.6.2 TESTING AND MONITORING

Groundwater testing and monitoring is carried

out to establish water quality and changes in

quality, and water levels and changes in levels.

Testing and monitoring should be undertaken

for ambient or pre-existing groundwater reserves

to establish baseline groundwater characteristics.

Testing and monitoring subsequent to events such

as pumping, recharge and contaminant leakage can

then be used to derive groundwater parameters

related to these events. These parameters allow

calculation of quantities such as drawdown

for various pumping rates, rates of recharge or

speed and direction of contaminant flow.

Prior to establishing a groundwater testing program,

hydrogeologists and analytical laboratories

should be consulted to determine the appropriate

testing, sampling and storage methods required

for identification of individual compounds in the

groundwater. Samples may need to be gathered

and stored in non-reactive containers to ensure

that they are not contaminated. Special care may

be required for biologically active contaminants.

Groundwater levels and quality may be monitored

using piezometers. Piezometers extending into

unconfined (water table) aquifers show water

levels which represent the surrounding water

table level. Piezometers extending into confined

aquifers show water levels which represent the

pressure existing within the aquifer. When there

are strong flows within the aquifer, a component

of the measured pressure may result from inertial

forces as well as static groundwater levels.

Figure 5.2 indicates the water levels given by

piezometers in unconfined and confined aquifers.



Piezometer Construction

A piezometer is simply an open stilling well into

which a probe may be inserted to measure water

level or quality, or from which a sample of the

groundwater can be collected. Piezometers are

primarily made of either PVC (polyvinyl chloride)

or ABS (acrylonitrile butadiene styrene).

The material chosen for piezometer construction

should have strength, rigidity, low maintenance,

resistance to galvanic and electrochemical

corrosion, resistance to abrasion, high strength-to-

weight ratios, partial flexibility and low cost.

Other considerations are:

• piezometersmaybeinstalledusingavariety

of means from hand augers to drilling rigs. In

all cases, the piezometer tube is installed after

drilling a hole of sufficient diameter and depth;

• thediameterofthepiezometeruseddependson

the type of monitoring or sampling that needs to

be carried out. The sizes of probes and sampling

devices need to be considered. It is rare to find

piezometers of less than 50 mm in diameter, and

100 mm diameter piezometers are common;

• thelengthofthepiezometerneeds

to be sufficient to measure the

maximum possible drawdown;

• whenmonitoringconfinedaquifers,thewell

may need to protrude significantly above

ground, in order to measure the standing

head of the water. However, if this protrusion

becomes impractical, the well may be capped

and a pressure transducer installed within it;

• wellsshouldbeslottedorscreenedto

facilitate a good connection to the aquifer.

Open-bottomed, unslotted wells may

be used effectively in granular soils;

• slottedwellsoftenformthecheapestalternative,

as slots may be machined by the manufacturer

or cut by hand on site. Slots should be cut

liberally (either horizontally or vertically) but

should be small enough to exclude significant

intake of soil. Porous geotextile fabrics may

be used to filter out soil particles if required;

• preventionofcontaminationiscriticalforthe

collection of water quality data; the installation

of slotted or screened casing will be important.

In these instances, a hydrogeologist should be

consulted to provide appropriate well designs;

• piezometersshouldbecappedatthe

surface, preferably with a screw-in cap for

ease of removal and re-application;

• atetherwireandconcretecollarserveto

anchor the piezometer and reduce the risk

of slippage in unconsolidated material or

accidental movement from outside impact; and

• thelipofthepiezometershouldbesurveyed

into the mine datum or Australian Height

Datum (AHD), as this is the most convenient

point of reference for manual monitoring.

Figure 5.3 shows a typical piezometer installation.



Monitoring

Monitoring of piezometric levels may be performed

manually or remotely. Manual devices include:

• dipmeters:thesecompriseanelectrical

sensor at the end of a graduated wire. Contact

with water completes the electrical circuit

between sensor and wire, causing a tone to

be emitted (see Figure 5.4). The distance

between the sensor and the reference point

(eg. the lip of the piezometer) may be read off

the graduated wire. Dip meters are popular

because of the ease and speed of use; and

• graduatedtransparentpiezometersor

manometers (when the piezometric

level is above ground).

Remote monitoring is carried out using a sensor

installed within the piezometer. The sensor may

be connected to a central monitoring system or to

a data logger which reads, at regular intervals, the

voltage output at the sensor. The data logger may be

downloaded regularly using a portable computer,

or may have removable memory banks which can

be replaced and downloaded later. The recorded

voltages are then translated into water levels via

calibration relationships. Popular sensors include:

• pressuretransducers;

• capacitanceprobes;and

• floatlevels.

Remote monitoring carries a much higher

risk of data contamination or error. A rigorous

schedule of equipment maintenance, data

verification using manual methods, and frequent

calibration checks should be in place.

Groundwater Sampling

Testing of groundwater quality may be carried

out using in-situ methods or by the extraction

of a representative sample. A range of field

equipment exists for measuring such basic

parameters as pH and conductivity, using probes

which may be lowered into piezometers.

Groundwater samples are normally collected from

a piezometer or bore using one of two techniques:

a bailer or submersible pump. Submersible pumps

powered by a battery or generator are preferred

due to the large volumes of water that need to

be displaced from a bore prior to the collection

of a representative groundwater sample.

In addition to these two methods,

groundwater samples may also be collected

from sample valves located near above-

ground pumps on water supply bores.

When groundwater samples are to be collected,

the following should be considered:

• thepiezometerorboreneedstobepurged

prior to sample collection. This technique must

be used in order to obtain a representative



groundwater or aquifer sample. In the absence

of extensive pumping, the sample collected

will merely represent water held in the bore

or piezometer which has been exposed to

atmospheric conditions. Extensive pumping also

reduces cross contamination of the sampling

equipment between bores. Typically, three times

the volume of water held in the piezometer or

bore needs to be removed prior to sampling;

• ifabailerisusedthenextensivebailingof

water held in the bore must be undertaken

prior to sample collection. Most bailers only

have about one litre capacity and consequently

manual bailing of a bore can be a time

consuming procedure. If sufficient funds

are available, disposable bailers should be

considered to eliminate the risk of sample

contamination between bores; and

• appropriatesamplecontainers,rinsing

procedures and preservation techniques

must be used, as for surface waters.

5.6.3 GROUNDWATER PARAMETERS

Physical and chemical parameters are of interest

when attempting to characterise and model aquifers

in order to simulate various scenarios. Groundwater

parameters are best obtained by stressing the aquifer

and observing the response induced. These stresses

are typically obtained by pumping water out of the

aquifer or pumping water into the aquifer via bores.

A large range of pump tests and analytical methods

exist for this purpose. Advice from qualified

hydrogeologists should be sought to determine:

• whichparametersareofinterest;

• cost-effectivemethodsofobtainingthisdata;and

• theapplicabilityofthesemethods

to site-specific conditions.

5.6.4 PREDICTION OF GROUNDWATER

CHARACTERISTICS AND RESPONSES

Prediction of aquifer responses to various scenarios

allows “what if ... ?” questions to be answered.

Predictive modelling may be carried out using

analytical models (simplified equations) or, more

recently, numerical models which use the technically

rigorous and complex physics of groundwater flow.

Numerical models have developed significantly

in the last two decades and their popularity

has increased. A brief discussion of the types

of numerical models is presented in Fact Sheet

No.12, and advantages and disadvantages of using

numerical models are summarised in Table 5.3.

Predictive modelling in groundwater now enjoys

widespread use and offers significant benefits

in assessing groundwater-related issues. An

increasing environmental focus in the mining

industry and the recognition of groundwater as

a fragile natural resource has seen the expanding

use of groundwater models. Models simulating

contaminant transport in groundwater and root-

zone behaviour are now widely available.

Predictive modelling should always be used with

a questioning attitude, and a rigorous process of

calibration, verification and sensitivity analysis should

be an integral part of any modelling program.

5.7 Review of Monitoring Data

For a vast majority of existing monitoring programs,

insufficient time is spent actually reviewing and

analysing the data. Regular screening of data can

detect problems in sampling and analytical techniques

as well as in hydrographic data recording systems.



A review of the data set can establish seasonal

trends and will detect analyses that are unwarranted

(ie. those continually below the detection limit).

Sites with data that do not fluctuate to any degree

can be sampled less frequently to reduce costs.

Regular review will also forewarn management

of any impending changes which may effect

the sites ability to obtain or discharge water

or any breaches in compliance with statutory

obligations. Presentation of data in a graphical

format allows easy scanning of large numbers of

results and identification of trends in the data.

TABLE 5.3: Advantages and Disadvantages of Using Numerical Models

Primary Advantages Primary Disadvantages

• Abilitytoruncomplexandlengthy

calculations in increasingly short times

as computers evolve rapidly;

• alowleveloflabourintensity

during simulations;

• highcapacityfortestingthesensitivity

to groundwater parameters;

• thedevelopmentofincreasinglyvisualoutputs,

which allow the lay person to understand

the answers proposed by the models; and

• flexibilityinassessingarangeof

scenarios quickly and easily.

• Initiallyhighleveloflabourintensity

during setting up a numerical model;

• developmentofa‘blackbox’mentalitywhich

results in the widespread use of models without

understanding of concepts and limitations;

• atendencyamongthepublictoperceive

models as infallible and acceptance

of results as the literal truth; and

• highcapacityformisunderstandingormisuse

of models because of their complexity.


6. Water Supply

In a country as arid as Australia, mining and mineral

processing operations will almost certainly require

a regular supply of water. Therefore, identification,

evaluation and maintenance of this supply will be

critical to the continued operations. While this topic

could demand a handbook of its own, some concepts

will be introduced in this section.

6.1 Surface Water

This section examines sources of surface water supply

around typical minesites.

6.1.1 CATCHMENT YIELD

When discussing the useful yield of surface water

within a catchment it is important to realise that it

can never be any greater than the facilities available

for storing or continuously using water. This can

include groundwater recharge, as discussed in the

next section.

The balance of processes contributing to the final

yield at a given storage facility can be represented as

Yield = Inflow - Outflow.

Inflow

The inflow into a storage may originate from any of

the following sources.

Imported water: reservoirs, irrigation schemes or major

supply pipelines are often the major source of water

for minesites in Australia.

Recycled water: most minesites in areas of water

scarcity are now recycling water from various stages

of the mine process. This is discussed in the following

section.

Direct rainfall: within shallow storages covering

large surface areas, the amount of direct rainfall may

be appreciable.

Rainfall runoff: the quantity and quality of rainfall

runoff will be dependent on the catchment area soil

type, topography and vegetation. A discussion on

estimation of rainfall runoff is given in Fact Sheet

No.2.

Groundwater seepage: during periods of rain, a

percentage of the water will seep into the ground as

infiltration. Some of this water will percolate into

groundwater stores. However, on sloping sites or

areas underlain by shallow rock, most water will flow

through the soil profile to the bedrock and percolate

out into a watercourse or cutting. This water will

continue to flow long after rain has ceased.

Mine dewatering: surface and groundwater reserves

that flow into mine workings are usually pumped

out to a suitable storage. This aspect is covered in

Sections 8 and 9.

Outflow

Outflows will result from any combination of

the following.

Releases: resulting from:

• excesswaterovertoppingstoragesandpassing

into the next catchment or off the lease;

• waterdrainedfromdarnstoallowfor

maintenance, to make room for expected inflows

or as regulated to provide water for downstream

ecosystems or users; or

• treatedwaterwhichmaybereleasedafter

sufficient residence time to remove pollutants

(eg. acidity, suspended solids, salinity).


WAT E R S U P P LY

Evaporation: the loss of water from reservoirs

through evaporation is appreciable in many

regions of Australia. Where water supply is a

critical issue, it can be worthwhile attempting

to reduce evaporation by the use of a deeper

storage or various cover techniques. Evaporation

is also often used as a disposal method for

highly saline or otherwise polluted waters.

Water use: this will depend on the location of the

storage, the quality of the water and the scarcity

of water on the site. Other potential users of the

water must also be considered. A number of ideas

for recycling water are presented in Section 6.1.2.

Seepage: although seepage through the ground has

been identified as an inflow it is also an outflow

mechanism. Any dam is likely to lose some water

through seepage into the groundwater unless the

groundwater level is higher than the base of the

dam. In earth darns (as most minesite dams are)

seepage may also occur through the dam wall.

If considering the yield of a specific catchment, it

will be necessary to obtain specific information on

all the above processes relevant to that catchment.

Historical records of inflows and outflows will

provide invaluable information for the calculations.

The water balance method for identifying the inflows

and outflows is a useful tool for understanding how

the water supply for a minesite may be achieved

by considering all the potentially contributing

elements. The water balance allows the user to

optimise parameter values for the most desirable

outcome and to explore the probability boundaries

when variations are introduced (refer also to

Fact Sheet No.3 for probability information).

6.1.2 RECYCLING OF WATER

Most minesites promote the use of recycled

water. Recycling often occurs when water is

scarce, or the discharge of polluted waters could

be a hazard to the surrounding environment.

Even where water is freely available, it may

be more cost-effective to recycle water.

It is usually a more environmentally sound

practice to recycle lower quality water on a

minesite rather than to discharge the water and

use better quality water from clean supplies when

it is not needed. Some examples of sources and

uses of recycled water are given in Table 6.1.

6.2 Groundwater

6.2.1 SOURCES OF SUPPLY

There are two primary sources of groundwater

supply; unconfined aquifers and confined

aquifers. Perched water tables (see Fact Sheet

No. 11) are a special form of unconfined aquifer.

Unconfined aquifers may be used for water

supply via the pumping of bores. Confined

aquifers are generally under pressure and,

in some cases, may not require pumping to

extract water (eg. a flowing or artesian bore).

Individual groundwater resources tend to be

compartmentalised by geology, but are rarely truly

isolated. Despite some connection to other aquifers,

an individual groundwater resource should be

viewed as a finite body of water. Replenishment of

groundwater (or recharge) is a vital component in

assessing the long-term viability of a source of supply.

Recharge may occur through rainfall infiltration, or

from rivers and streams, or from artificial recharge

(such as pumping of surface water into aquifers).

6.2.2 SECURITY OF SUPPLY

Security of supply may be breached if the sustainable

yield is compromised when a bore is overpumped

or drawdown is quick but recovery slow. The quality

is compromised when pumping stresses lead to

dissolution of salts from the soil matrix and excessive

salinisation of the pumped water or development of

flow paths from neighbouring contaminated aquifers.


WAT E R S U P P LY

TABLE 6.1: Sources and Uses of Recycled Water

Sources of Recyclable Water Uses for Recycled Water

Dirty mine water: surface runoff from dirty

areas, intercepted to remove suspended

solids and/or other pollutants.

Clean mine water: there will be some limitations on

the amount of water which can be intercepted from

undisturbed areas. This is to ensure that downstream

users and ecosystems are not disadvantaged.

Process water: most process plants or washeries

will use large quantities of water which is often

returned to a process water tank or dam, and

then recycled back through the process.

Tailings liquor: tailings are deposited with varying

percentages of water to allow pumping, and to

ensure proper deposition and drying. Excess water

remaining after solids have settled can be recycled

directly or after passing through a filter dam.

Washdown water: vehicle and workshop

washdown water should be passed through

a settling pond and oil separator, after which

it may be suitable for selected recycling.

“Grey” water: wastewater from showers, hand

basins, laundries and kitchens should be treated to

remove solids and can then be recycled. Chemical

dosing (eg. chlorine) may be necessary if people

will come into contact with the recycled water.

Treated effluent: package or site built treatment

plants are used to treat sewage to acceptable levels

after which it can be used for limited recycling

applications. Treated industrial effluent from

workshops may also be used for recycle water.

Dust suppression: dust control for haul roads,

conveyor belts and transfer stations, loading facilities,

dump hoppers, stockpiles (product and waste),

construction sites and working faces does not require

high quality water. Issues which may affect this are:

• suspendedsolids,whichmayblock

pumping and spraying equipment;

• viralandbacterialmicro-organisms

which, if present in fine aerosol mists,

are easily ingested by workers; and

• nutrientlevelswhichcanpromotealgal

growth and block spray equipment.

Process water: processes which involve crushing,

washing and screening are suited to using

recycled water. Co-disposal tailings will utilise

recycled water. Typical quality issues are:

• chemicalmakeupofthewater;and

• suspendedsolids.

Irrigation: rehabilitated areas, gardens and perhaps

even neighbouring properties or stock may be a very

efficient use of wastewater. Irrigation to rehabilitated

areas may result in water dependant regrowth with

shallow root systems which will struggle to survive

if irrigation ceases. Water quality issues are:

• chemical,salinityandpHextremeswhich

may adversely affect plants and/or stock;

• suspendedsolids(asfordustsuppression);

• viralandbacterialmicro-organisms.

Wetlands maintenance: during rainy periods there

will usually be enough dilution and flushing to

keep wetland systems healthy. However during dry

periods there may be a build up of pollutants from

mine dewatering or simply a shortage of water.

Quality issues are similar to those for irrigation.


WAT E R S U P P LY

Sustainable yield is a significant parameter in water

supply. It determines the maximum flow which

may be extracted over the long term. This factor

is determined by pump testing and analysis of

drawdown. Borefields of two or more bores will

incur some penalty in the sustainable yield of each

bore because of interaction between the drawdown

from each bore. More intensive analyses are required

to identify the sustainable yields of borefields. The

sustainable yield should be identified whenever bore

water supply is considered. Expert advice should be

sought before commissioning a bore drilling program.

The quality of water pumped out of a bore may

depend on the rate of pumping exerted. The

sustainable yield of a bore should be identified

in conjunction with any deterioration in the

quality of water being pumped. The likelihood

of quality deterioration may increase with the

rate of aquifer pumping. For example, in coastal

locations seawater may migrate towards a bore

which is pumped beyond its sustainable yield.

Constant monitoring of quantity and

quality is an integral part of water supply

evaluation and maintenance.

• Quantities of pumped water should be

noted throughout the life of a bore. Flow

totalisers are a convenient and cheap method

of monitoring quantity. These show the total

volume of water pumped. When monitored

regularly and used together with a record

of pump down time, adequate information

on pump rates may be gathered.

• Aquifer drawdown should also be monitored

on a regular basis. This may be done using

adjacent observation bores and, where possible,

within the pumping bores themselves.

• Water quality monitoring should be carried out

regularly on representative samples pump from

bores. Relevant water quality standards should

be consulted, depending on the use of the

supply. These may be for potable water, ablution

water or process water. Site-specific process

water requirements should be determined

where the water is used for processing.

TABLE 6.1: Sources and Uses of Recycled Water (CONTINUED)

Sources of Recyclable Water Uses for Recycled Water

Slurry transport water: at the end of a slurry

pipeline, the slurry is dewatered, leaving large

quantities of water. The location will often be

environmentally sensitive, hence the water

would require treatment to high standards before

discharge; re-use may be a better option.

Washdown water: recycled “grey” water and treated

wash down water can be used for washdown of mine

equipment and workshop areas. Quality issues are:

• buildupsofoilordetergents;

• viralandbacterialmicro-organisms

which if present in fine aerosol mists

are easily ingested by workers.

Potable water: in very arid and remote areas it may

be viable to treat recycled water to very high levels

and use it as a potable water source. Clean and

dirty water runoff are obvious sources, but other

sources can be used. All facets of water quality

will obviously be vital if this is the intended use.


WAT E R S U P P LY

If a licence is required for the bore or borefield,

conditions such as these are generally included

on the permit. The information gathered

usually has to be provided to the licensing

authority on renewal of the permit.

The intensity of the monitoring program

selected for water supply bores should reflect

the importance placed upon the supply.


7. Exploration

Water is an important component in

exploration activities and therefore careful

management is necessary as in any other

aspect of mining and mineral processing.

A lack of water for process, potable and fire

protection requirements or an excess of water (eg.

high groundwater table, large aquifers, flood risks)

can determine the subsequent economic viability of

a mining project. Therefore serious consideration

must be given to water constraints during the

early exploration phases of a project. This should

include data gathering of both surface water and

groundwater resources as well as initial flood studies.

The environmental significance and sensitivity of

watercourses and other waterbodies (surface or

ground) will determine the extent of exploration and

subsequent mineral extraction allowed in any area.

This will be dictated by the relevant legislative body

(ie. Mining, Environmental and Water Resources

departments) at both State and Commonwealth level.

Water will also play a role as a resource and/or

hindrance to the actual exploration efforts. Rivers,

streams, rainfall runoff and groundwater all need to

be managed to avoid or minimise damage

during exploration.

Many exploration activities could be

considered as miniature minesite operations;

hence all sections of this handbook will be

applicable, albeit at a modified level.

7.1 Surface Water

Most exploration activities in Australia will be

in areas where minimal knowledge of ground

and surface water behaviour exists. Therefore

the collection of all possible information that

may be relevant is encouraged. At the same time,

care of the existing environment is required.

7.1.1 SURFACE WATER DATA COLLECTION

The lack of water or the possibility of serious

flooding may seriously impact the extent or timing

of an exploration program. Information on rainfall,

evaporation and stream flows in the project area is

often inadequate, and important decisions are usually

made using data extrapolated from many kilometres

away. Exploration teams can provide important data

to reduce the risk associated with these decisions.

Records should be kept of local surface water

conditions. This can include evidence of previous

flood heights through the location of debris and local

knowledge, conditions of watercourses (ie. flowing

regime, photographs), signs of erosion, and quality

of water. Monitoring water quality will also provide

valuable background information, which may form

an important part of future license conditions.

If a new deposit has high potential and continuing

exploration is likely, a remote weather station

network as well as stream gauges in all major

watercourses should be established. These

installations should measure rainfall, temperature,

wind speed and direction, evaporation and stream

flows. A few years of local climatic data between


E X P L O R AT I O N

the time of initial exploration and the stage of

feasibility decisions will provide invaluable assistance

in the design of water supply dams, tailings dams,

evaporation ponds and any flood mitigation or

mine drainage works required (refer to Sections

5.4 and 5.5, and also Fact Sheet Nos 3 and 10).

7.1.2 ACCESS TRACKS

Exploration projects which cover a large area with

many drill holes in different locations will often

result in a “spider web” of access tracks linking

the different sites. The clearing and constant traffic

associated with such drill lines and access tracks

can lead to serious erosion and sediment problems

if precautions are not taken to minimise their

impact. The construction and rehabilitation of access

roads is dealt with in Section 6.8 of AMIC (1990),

while the following points provide guidelines for

reducing the impact of tracks on surface water.

• Minimisetheareaofdisturbancebyreducing

the number of tracks and using the same routes

(even if the journey takes slightly longer). It is

also very important that four wheel drive vehicles

remain on existing tracks whenever possible.

• Whenlocatingtracks:

– every effort should be made to minimise

clearing and other disturbance to vegetation,

especially in well vegetated areas with

easily eroded soils (eg. wet tropical areas).

Tracks should deviate around large trees;

where this is impractical, use the timber

to stabilise edges and low points;

– avoid using gullies as convenient

locations for tracks;

– locate creek crossings in naturally

rocky locations, or line sensitive or

erodible crossings with rocks;

– avoid permanently wet and boggy areas;

– install silt fences or hay bales across

watercourses where sediment from

disturbed areas will impact the

undisturbed drainage line; and

– keep tracks a reasonable distance

away from watercourses to ensure a

vegetation strip is maintained.

• Whenconstructingtracks:

– avoid using heavy earth moving

equipment to construct temporary

tracks, as this will destroy root stock;

– culverts are recommended for creeks and

streams on more permanent tracks. These

will reduce mud and keep tracks passable in

most weather. For guidelines on the design

of culverts, refer to Fact Sheet No.6;

– runoff should not be allowed to concentrate

on tracks. Flow should be shed off the road

as quickly as possible by using reasonable

crossfall (say 3%) side drains with regular

take-offs and by allowing sheet runoff to

flow uninterrupted across the track. Where

road access cuts across steep hillsides, road

stability may necessitate sloping the cross

fall into the hill slope and into a side drain,

which then discharges via a constructed

drain built at a low point under the road

or across an armoured road crossing;

– if it is necessary to cut roads greater than

2 m wide into the natural surface, then

small v-type interception drains should be

used to divert water from the batter slopes.

Generally batter slopes should be no steeper

than 2H:1V (0.75H:1V in rock); and

– any discharge points for culverts or table

drains must be protected against erosion.

• Ensurealltrackstobeusedarelocatedon

field maps and that all personnel are instructed

to use only those marked tracks. This will

reduce people’s desire to create their own

tracks and hence minimise disturbance.


E X P L O R AT I O N

7.1.3 EXPLORATION SITES

On any given project, the area physically

disturbed will be reasonably small and control

of erosion, runoff and discharges from these

areas is relatively straight forward. Guidelines

for minimising impacts on water include:

• abufferzoneshouldbekeptbetweenthe

exploration activities and environmentally

sensitive areas. The width of this zone will

depend on the sensitivity of the area and may

range from 10 m for a non-sensitive bank

of a watercourse up to 3 000 m or greater

for an environmental conservation zone;

• aswithaccesstracks,theareaanddegreeof

clearing should be kept to a minimum;

• thedischargeofwastesintowatercourses

must be avoided. Various waste

can be handled as follows:

– fuel and oil storage tanks and dispensing areas

must be bunded and sealed. Oil absorbent

booms should be used across storm water

drainage points away from these areas;

– sewage should be treated to recognised

levels using septic systems or commercially

available package treatment plants or

contained and removed from site;

– toxic and saline wastewater must be stored

in ponds either permanently or until

treated or degraded to safe levels; and

– sludges and silt resulting from drilling

or processing operations must pass

through sumps to settle or filter out

fines before the water is discharged;

• thedownstreamorlowersideofanycleared

area should be arranged so as to intercept and

contain sediment washed down by surface

runoff or concentrated discharges. This is easily

achieved by the use of interception drains

and silt fences, hay bales, silt traps or filter

dams, as described in Fact Sheet No.8; and

• damsordiversionstowatercoursesshould

be thoroughly investigated to ensure any

adverse effects are minimal. They should also

be designed, constructed and maintained to

ensure good water management (Fact Sheet

No.5). It is important to advise the relevant

Water Resources department in any State before

undertaking such works. Dams which retain

large volumes or which could risk life and

property in the event of failure will often require

licensing and much stricter design standards.

Exploration within a watercourse or riparian

zone has the potential to severely damage the

surrounding environment and hence will require

more rigorous control than described above.


8. Open Cut Mines

Management of surface and groundwater flows

around open cut mines is critical to safety and

the operation of the mine. This is a specialist

topic and detailed design and engineering

should be undertaken by relevant experts.

However, the environmental officer may

play an important role in tasks such as:

• providingthebasedatatodetermine

the likelihood of an event;

• routinemonitoringtoevaluatethe

performance of the control structures; and

• adviceonthebestmeansof

disposal of excess waters.

Consequently, it is important that there is close

consultation between the expert and the officer

charged with site management responsibilities.

The following section provides some basic

information to assist the environmental

officer in understanding some of the specialist

hydrological engineering issues.

8.1 Surface Water Runoff

Flooding of open cut mines can be a very real

problem if a mine is located in a valley or in the path

of a stream or a river with a significant upstream

catchment. Depending on how quickly it occurs

and how severe it is, flooding can cause a variety

of problems such as loss of life or injury, damage

to machinery and infrastructure and, far more

likely, loss of access to the pit due to water and silt

and subsequent loss of production. All of these

scenarios are highly undesirable to mine operators.

8.1.1 FLOOD MITIGATION

There are numerous factors which dictate the

type and extent of flood mitigation works best

suited to a particular site. Every mine will have a

different set of conditions; hence only the major

issues will be covered in this handbook.

Type of Flooding

Before considering any mitigation works, the

extent of flooding likely to occur naturally

should be estimated. This should include

conservative estimates of the following:

• totalvolumeofsurfacerunoffentering

the pit (Fact Sheet No.2);

• thepeakrateofflowintothispit

(Fact Sheet No.2); and

• themajordrainagepathsby

which water enters the pit.

Safety

This is the highest priority in mining and the

possibility of injury or death due directly or

indirectly to pit flooding will be the primary

determinant of flood mitigation measures.

Economics

If safety is not a deciding factor, a cost/benefit

study should be carried out. For the proposed

schemes, the capital and annual maintenance

costs should be added to the residual costs due

to annual flood damage (eg. the costs incurred

when the scheme fails). The scheme which gives

the lowest total cost will then be the most effective

solution. This approach is illustrated in Figure 8.1.

It is rarely practical to eliminate totally the risk

of flooding and hence protection of the flood


O P E N C U T M I N E S

mitigation works against overtopping

damage should also be considered.

Pit Location

The location of the pit in relation to the catchment

will determine whether a particular scheme

is feasible, ie. a pit at the bottom of a steep

valley will have fewer alternatives than a pit

located in a wide gently sloped flood plain.

Appropriate Risk

The level of risk (of failure) associated with a

given flood mitigation scheme is linked to both

the safety and economic issues. When deciding

at what level of risk to design a scheme, an

important consideration is that a very low level of

risk (ie. failures are very rare) may lead to a lack

of contingency planning such that when a very

large flood occurs the results may be disastrous.

8.1.2 METHODS OF FLOOD MITIGATION

There are many flood mitigation methods

available to the mining engineer. Each method

has different environmental impacts and these

should be addressed as part of the design criteria.

For example, if the waterway is a valuable riverine

habitat, it may be better to build an upstream

flood control reservoir than widen the channel.

Maximising Waterway Capacity

The intent of this method is to optimise the ability of

existing rivers, streams or drainage channels to carry

flood waters away from the pit. This can be done by:

• altering cross section - increasing the cross

section size will give a greater flow capacity

Note that, if the existing waterway is prone to

erosion, the channel should be made wider

only. If the existing waterway is prone to silting

the channel should be made deeper only

(Take care that the existing system does not

incorporate both erosion at high flows and

silting at low flows.) Impacts on downstream

unaltered sections must also be assessed;

• upstream erosion protection - a reduced sediment

load can prevent clogging problems in the

lower reaches of a waterway. This can be

achieved by protecting steep sections (usually

the upper reaches) of a stream against erosion,

using methods such as drop structures,

check dams, bottom sills, vegetation and

channel armouring (Fact Sheet No.8); and



• coarse sediment traps - another method of

reducing sediment load in flows is to create a

coarse sediment trap upstream of the area to be

protected against flooding. This can consist of

a wide shallow pond or flood plain area which

will allow the same flow to pass at a much lower

velocity, hence allowing sediment to settle. It is

important to note that sediment traps require

regular cleaning to maintain their performance.

Dykes

Constructed embankments either side of a

natural waterway can give a large increase in flow

capacity. The final capacity is determined by the

height of the embankments and their distance

apart. Where space is available it is better to

have low embankments spaced far apart. This

configuration will be cheaper, safer and result in

less erosion. For a meandering stream the dyke

system should form a band which envelopes the

stream (Figure 8.2). Upstream and downstream

impacts of these structures must be assessed.

Flood Control Reservoirs

If the catchment upstream of the pit is steep and

subject to short heavy storms, it is likely that

flooding will be short in duration and have a high

peak flow (refer Fact Sheet No.2). In this situation

a useful method of flood control is to attenuate

this peak flow (eg. temporarily hold back some of

the flood water until the peak flow downstream

has passed, and then release it at an acceptable

rate). The simplest method of achieving this is to

build a dam or basin with an open outlet at the

base to gradually release the intercepted water.

Flood Diversion

If it is feasible, the most effective way of flood

mitigation is to divert water away from the

mine. Diversion channels can direct water

to a number of different points, such as:

• samewaterwaydownstream;

• adjacentfloodplains;or

• nearbylakesorstreams.



If a diversion method which returns flow to

the same waterway further downstream is

used, it is important to assess any backwater

effects. For example, a sudden increase in flow

downstream may cause the waterway to back up

and flood the pit from the downstream end.

8.1.3 IN-PIT DRAINAGE

All open cut mines are likely to have water entering

the pit and ponding at the lowest point. In most

cases this water will need to be removed from the pit

to avoid disruption to mining activity. The amount

of water to be dealt with will depend on the area

of the pit and access ramps (which will determine

the amount of direct rainfall), the effectiveness

of flood mitigation and pit interception drainage

schemes (refer to Sections 8.1.1 and 8.1.4) and

management of groundwater inflow (Section 8.2).

The quality of water will, in part, depend on

the residence time in the pit. Water may be

exposed to mineralised or acidic material and

become contaminated, or may contact spilled

hydrocarbons. In both cases treatment may

be necessary prior to release. Rapid disposal

of in-pit water will limit the problem.

Drains

Design criteria will need to consider:

• themainaccessrampintothepitmustbe

kept trafficable. Hence ramp side drains

should cater for high peak flows;

• drainsonthepitfloormustbekeptaway

from main traffic routes. This saves the drains

from damage by large vehicles, keeps the

pit accessible by small service vehicles (eg.

surveyors) and avoids mud on vehicles;

• wherepossible,drainsshouldbemaintained

at a slope between 1% and 3% to avoid

silting and erosion problems; and

• drainswhichcrossmajortrafficroutesshould

behardlined“swayles”(wideshallow‘v’

drains). If large flows are expected then correctly

sized culverts should be installed (refer to

Fact Sheet No.6). Inexpensive and re-useable

corrugated steel pipes (Armco culverts) are

suitable; however attention must be paid

to installation and cover requirements.

Sumps

The size and configuration of sumps will vary

to suit individual conditions. However the

following guidelines should be followed:

• forsafetyandconveniencelocate

sumps away from trafficked areas;

• incorporatethesumplocationatthemine

planning stage to ensure floor slopes

and seam slopes are accounted for;

• ifpumpingoutisused,locatethesumpto

give a suitable route for the pipeline to the

required discharge point (Section 8.3.1);

• locatethesumptogivemaximumlifebefore

pit development dictates a new location;

• duetotypicallyhighsedimentloadsinin-pit

runoff water, the sump should ideally have at

least two cells. The first cell will allow the silt to

settle or be filtered out of suspension and should

be easily cleaned by in-pit equipment; and

• thesizeofthesumpdoesnotnecessarily

need to cater for the total flow into the pit

but rather should be located such that all

water eventually drains into it (ie. once the

dewatering system catches up with the inflow).

Dewatering Options

Three commonly used methods to dewater mine pits

are pumping, shaft and tunnel, and slot drainage.

If water discharging from the pit is not retained,

the impact of variable flows and water quality on

the downstream surface water or groundwater

bodies will need to be considered. Water disposed

of in these ways may need to be monitored

continuously as its quality will be affected by the

length of contact with mineralised zones in the pit.



8.1.4 INTERCEPTION DRAINAGE AROUND PIT

Where open cut mines do not have flooding

problems there will usually be some runoff towards

the pit from the immediate surrounding areas

(Figure 8.3). If this water enters the pit it may

be exposed to acid generating rock not present

on the surface and will also necessitate larger pit

pumps, generally causing inconvenience and

delays to in-pit operations. Therefore interception

drainage should be installed around the pit.

Interception drains should be installed as close

to the top of the pit as practicable. It is also good

practice to use these drains to separate clean water

(ie. runoff from undisturbed catchment) from dirty

water (ie. runoff from disturbed catchment). This

may require parallel drainage systems but will result

in much smaller sediment loads and in some cases

a reduction in treatment facilities (Figure 8.3).

Providing interception drainage can be difficult

if the mine is in rough terrain or located in a

valley. There are many techniques that can be

used to develop an interception scheme.

Runoff Interception Techniques

Contour drains: the simplest method is to use the

natural topography and run an open channel

drain around the pit. If the pit is at the bottom

of a natural bowl this technique is ideal. It is

usual to design these drains for a 20 Year ARI or

an ARI to suit the acceptable risk for the open

cut (refer to Fact Sheet No.3). For the design of

open channel drains refer to Fact Sheet No.4.

Gully dams: simple contour drains will not be

effective if a number of gullies run towards the pit.

In this situation it is necessary to cut off the gullies

using dams (refer to Fact Sheet No.5). These dams

should be sized such that the overflow spillway is

high enough to direct flow into an adjacent gully

which is not flowing into the pit, or into a high

level contour drain which can avoid the pit.

Flow detention basins: small scale versions of the

flood control reservoirs discussed in Section 8.1.1

can be used to detain and regulate flows as part

of an interception scheme. Where a number of

small catchments feed into a single collector drain,

detention basins can be used to delay flows from

some of the areas and hence reduce the peak flow

in that drain. If pumping is necessary as part of

the interception scheme, detention basins can be

effectively used to regulate flow to the pump. This

will reduce the required pump size. As with the

flood control reservoirs, it is important that these



dams should self drain to ensure they are

empty when a storm occurs. The size and

design of detention basins is dependant on

the area, steepness and ground cover of the

catchment as well as the design storm (Fact

Sheet No.3) and degree of detention required.

In-pit systems: if the terrain is extremely difficult

it may be too expensive to create an effective

interception scheme. In such cases it may be possible

to use the benches of the pit as a drainage path. In

strip mines, where the pit is continually moving

forward, this is especially effective. If possible, the

back bench of the pit should be sloped towards

a deep gully where the water can be discharged

away from the pit. In some cases, however, the

only feasible direction to drain water is into the

pit. If this is necessary, careful thought should

still be given to doing it in a controlled manner so

that drainage paths remain stable and pit pumps

can cope with the inflows (Section 8.1.3).

8.1.5 SEDIMENT CONTAINMENT

The containment and control of sediment in

and around open pits is important for efficient

mine operations and is vital for the protection

of the environment surrounding the mine

(Note: for containment of sediment on and

around waste dumps refer to Section 11.2.4).

Some of the adverse effects from uncontrolled

sediment transport and deposition are:

• upstreamerosion;

• cloggingofpumpinletsandsumps;

• blockageofculverts;

• reductionofdraincapacities;

• accessproblemsforlightvehicles;

• damagetovegetation;

• lossofhabitat;and

• off-leasedischargesexceedinglicenselimits

for suspended solids and/or turbidity:

The best way to avoid these problems is to prevent

sediment from being eroded and transported.

If this is not feasible, it is then necessary to

contain the sediment in controlled locations

where it can not cause these problems.

Avoiding Erosion and Transport of Sediment

Clearing control: the most effective way to prevent

soil erosion is to not disturb the natural (stable)

ground. In open cut mining, clearing of vegetation

and stripping of topsoil and overburden is necessary

and must be carried out in advance of pit operations.

Care must be taken not to strip this area too early,

and to minimise the area actually cleared.

Effective rehabilitation: rapid rehabilitation of

disturbed mine areas will stabilise soil, and so

prevent erosion. It is advisable to direct runoff

from rehabilitated areas into the dirty water system

for some time after completion of the area, to

ensure that any sediment that is eroded can be

contained before flow is discharged offsite.

Open channel erosion control: controlling erosion in

open channels is very important for effective flood

control and interception drainage. Prevention of

scour in drains is achieved through good design and

adequate protection (refer to Fact Sheet Nos 4 and 8).

Increasing infiltration: erosion and transport of

sediment is caused by water flowing at high

velocities entraining soil particles. To prevent this

it is necessary to reduce the amount of runoff and

to slow it down. On large disturbed slopes, such

as stripped or recently rehabilitated areas, this can

be achieved by ripping along contour lines using

grader or dozer tines. This will increase infiltration

and inhibit overland flow. Important considerations

for ripping are covered in AMIC (1990).

In-pit sediment: an open pit is naturally a highly

disturbed area. Therefore as a sediment management

technique, it is best to have as much sediment

as possible in the pit where it does not have

to be controlled. Large and shallow sediment

traps upstream of pit pump-out sumps are an

effective way of achieving this (Section 8.1.3).



Removal of Suspended Sediment

from Flowing Water

The two techniques for removing suspended

sediment from flowing water are filtration

and settlement (refer to Fact Sheet No.8).

Filtration: by passing water through a fine media or by

causing it to percolate slowly through an obstruction,

silt will be removed. For overland flow this can best

be achieved using synthetic or hay bale silt fences

for small to medium sized cleared areas, or strips of

heavy vegetation where these have not been cleared.

When planning for clearing of an area, vegetation

should be left undisturbed wherever possible. For

channel flow it is best to use rock filter dams.

Settlement: allowing water to flow into a large wide

body of water will significantly reduce the flow

velocity and will allow sediment to settle out of

suspension. These sediment ponds can be designed

to allow even the smallest sediment particles to settle.

Shallow heavily vegetated wetlands are extremely

efficient sediment traps as they both settle and

filter suspended solids. They can also be effective

in the treatment of acid drainage and heavy metal

problems. They must be designed and constructed

with care to ensure the correct level of water

and balance of vegetation are maintained.

8.2 Groundwater

8.2.1 GROUNDWATER INFLOW

Groundwater inflow to open cut mine pits

is controlled by three primary factors:

• hydraulicgradient(theslopeofthewater

table in an unconfined aquifer, or the

piezometric pressure in a confined aquifer);

• hydraulicconductivity(oftenreferredto

as permeability) of the soil or rock; and

• theareathroughwhichflowoccurs.

An idealised example of pit inflow in a homogeneous

unconfined aquifer is shown in Figure 8.4.

Visual evidence of the flow through area is given

by the existence of a “seepage face” on a pit wall.

This is characterised by a slick or wet appearance

of the soil or rock surface, and close examination

of this region may reveal trickling flow.



Where a permeable fracture or a similar preferred

flow path exists (in a non-homogeneous aquifer),

the seepage face is often a discrete feature and

may only show up as a long, thin line rather

than a plane, as shown in Figure 8.4.

8.2.2 MANAGING GROUNDWATER INFLOW

Groundwater inflow may be accommodated in

the mine plan by restricting and/or containing

the flow, and routing it elsewhere (dewatering).

Flow Restriction

Groundwater flow may be restricted by reducing

the hydraulic conductivity and/or reducing the area

through which flow occurs. These may be achieved

by any of the following methods (Bedient et al, 1994):

• Slurry walls may be constructed perpendicular

to the direction of groundwater flow. These are

generally installed at sufficient depth to intersect

bedrock so that the aquifer is “barricaded”;

• Grout curtains are formed by injecting grout

(which may be in a liquid, slurry or emulsion

form) under pressure via grids of staggered

wells. Solidification of the grout then provides

a barrier to groundwater flow; and

• Sheet piling is applied by driving sheets

of steel into the ground until contact is

made with bedrock. Improved hydraulic

retardation is obtained by using interlocking

sheets to form a more continuous barrier.

Figure 8.5 shows, schematically, the effect

of placing a barrier to groundwater flow

Containment and Re-routing of Flow

• Dewatering is commonly carried out to lower the

watertable by pumping water out of the aquifer

and away from the mine. A series of bores or

spear points may be positioned in areas of

good hydraulic connectivity to allow pumping

at a sufficient rate to draw down the aquifer.

Drawdown of the watertable reduces the flow



through area of groundwater near the mine pits.

Ideally, the watertable should be drawn down

below the floor of the pit so that groundwater

inflows are eliminated altogether. Figure 8.6

indicates the effect produced by dewatering.

• Channel dewatering: groundwater may also be

intercepted outside the pit if the topography,

groundwater regime and mine plan allow this.

A channel may be constructed to lower the

water table and drain the water to downstream

catchments. However, lowering of the watertable

in this manner is generally less effective because

of the reliance on steady gravity drainage. Figure

8.7 shows the method of channel dewatering.



When groundwater flows are not highly

significant, the water is often intercepted in the

pit, collected in a sump and pumped to a retention

dam for treatment or storage as required.

Each method of managing groundwater inflows

will have different environmental impacts. These

will need to be evaluated prior to implementing

a control technology. Issues such as volume

of flows, water quality, effect on other users of

the groundwater, surface drainage systems and

receiving water bodies should be addressed.

8.3 Water Quality

8.3.1 PIT WATER DISPOSAL

Water held at the base of an open mine pit may

be derived from direct rainfall, surface runoff from

outside the pit and groundwater seepage. The

contaminants which can be present include:

• oilsandgreasesfromlightandheavymachinery;

• dissolvedandparticulatemetalsresultingfrom

the dissolution of metalliferous minerals;

• nutrientsfromexplosiveresidues;

• aciddrainage;

• suspendedsediments;and

• salts.

If acid drainage is present from the oxidation of

sulphide minerals contained in the rock within

the pit, then specific treatment and management

strategies need to be considered. Options for

the prevention and alleviation of acid drainage

problems are provided in Section 8.3.2.

Options available for the disposal of pit

water include:

• disposaltoevaporationponds;

• directorindirectuseasprocessplantwater;

• irrigationofrehabilitatedareaswithin

the minesite (eg. waste dumps);

• co-disposalwithtailingswater;and

• treatmentfollowedbydisposal

to receiving waters.

The option decided upon will depend on the quantity

and quality of the water needed to be disposed.

8.3.2 ACID DRAINAGE

Acid drainage can occur within an open pit

when sulphide bearing minerals are exposed to

air and water. The resulting low pH water can

readily dissolve heavy metals that are contained

in the orebody, overburden and waste rock.

Additional detail outlining the chemistry and

conditions favourable to the formation of acid

drainage are provided in Fact Sheet No.7.

Acid water within an open pit is a problem if the

water within the pit migrates to groundwater

via rock pores or fissures or if the water from

the pit is pumped to a storage area which

may leach or overflow to receiving waters.

It may also be an operational problem; for

example, corroding structures and pumps.

Hutchinson and Ellison (1992) identified three

generally accepted approaches to the prevention

or abatement of acid generation and leachate

migration. These measures are applicable to acid

drainage from open pits, waste rock dumps and

stockpiles and include, in order of preference:

• controloftheacidgenerationprocess;

• controlofthemigrationoftheleachate;and

• collectionandtreatmentofaciddrainage.

A combination of these three measures can

often be the most applicable solution.

While considerable research is being undertaken

on this topic, options for the prevention of acid

drainage at new mining operations and the control

and elimination of problems within existing.

open cut mines are generally limited to:

• analysesofdrillcoresamplesforawide

range of acid generation laboratory tests

prior to the commencement of mining;



• avoidingorrestrictingtheexposureofsulphide

bearing rocks to the atmosphere. This may be

achieved by selective mining of the orebody

or modifying the overall mine plan;

• ensuringlong-termslopestabilitywithin

the open cut as deterioration can result in

the long-term exposure of fresh rock to

conditions which lead to acid generation;

• removalofthewaterasquicklyaspossible;and

• incorporatingacidneutralisingrock(eg.

limestone) in flow channels within the mine pit.

A number of standard laboratory tests may be

undertaken to determine the capacity of waste

rock or ore to generate acid and mobilise heavy

metals. Laboratory tests available include:

• acidneutralisingcapacity(ANC)-the

ability of a sample to neutralise acid

generated from sulphide oxidation;

• netacidproducingpotential(NAPP)-

the difference between the maximum

potential acidity (MPA) and ANC; and

• netacidgeneration(NAG)-adirectevaluation

without measuring the MPA and ANC separately.

Where these static tests indicate the potential for

acid drainage, it may be useful to perform kinetic (or

leach) testing. The data from both types of testing

can then be used to derive appropriate management

strategies to reduce the incidence or treat the

outcome of acid drainage. Expert advice at the testing

and planning stage can reduce the need for costly and

long-term chemical treatment of polluted discharges.

8.3.3 SALINITY

Mine pits which contain highly saline waters

require specific management strategies which

allow dewatering of the pit with minimal

environmental impact. The strategies implemented

will be dependent on the geographical location

of the mine and local climatic conditions.

In arid regions, evaporation ponds are the most

common method for the disposal of saline or

contaminated pit water. However care must

be taken to avoid discharge of the water, and

disposal of potentially contaminated bottom

sludge must also be considered. Some mines

dispose of hypersaline water to natural salt lakes,

but this technique is not favoured by regulatory

authorities. Depending on the quality of the pit

water, other techniques such as irrigation within

the release area may also be considered. Potential

impacts on vegetation would need to be reviewed

if irrigation is considered as an option. The

potential for deep well disposal may also exist.

In temperate and tropical regions, where rainfall

can equal or exceed evaporation, alternate methods

of disposal must be developed. Site specific

techniques and management practices usually

need to be implemented within these areas.

High flow conditions in surrounding rivers and

streams may also provide opportunities for discharge.

For example, in the Hunter Valley of New South

Wales saline mine waters are discharged to the Hunter

River during times of high or flood river flows when

the assimilative capacity of the river is high and the

saline water can be quickly flushed to the ocean. This

practice is now regulated by the NSW Government

through the Hunter Salinity Trading Scheme.

8.4 Pit Closure

Pit closure strategies are formulated to ensure that

protection of the water environment, both within the

site and downstream from the operation, is continued

following pit closure. Final pit geometry is dictated

by the balance of borrow and fill of earth, from the

mining operations to the rehabilitation operations.

However, water management concerns should be

addressed interactively during pit closure design.



Open cut mine closure leaves voids which may

extend hundreds of metres below the water table.

Consequently groundwater is often a primary issue

in pit closure. An open void (see Figure 8.8) will

tend to fill with water from the adjacent groundwater

until a level of long-term equilibrium is attained.

This will impact on the surrounding equilibrium

groundwater levels. Recharge areas such

as streams or rivers may be affected by

these equilibrating processes. Surface water

drainage into the open void and evaporative

losses will form part of these processes.

Pit closure strategies should be viewed as a water

balance exercise, assessing the regional significance

as well as the local significance of the presence of the

void. Hydrological, surface water and groundwater

issues should be addressed to quantify and minimise

environmental effects of the final void on the

hydrological cycle and vegetation of the region.

In some cases, flooding of the open pit may be

desirable, especially if sulphide rock is exposed to

the atmosphere. In order to accelerate flooding,

adjacent streams may be diverted into the pit.

Such pits can also provide reliable sources of

water for stock or irrigation. However, monitoring

of the water quality will be necessary to ensure

that it does not degrade due to, for example,

acid generation from exposed sulphide rock.


9. Underground Mines

A sudden and large flow of water into an

underground mine can have disastrous results and

minor quantities will also cause inconvenience to

personnel and machinery accessing the shaft.

The potential for this type of problem

and hence the level of preventative works

is dependant on the mine locality.

9.1 Surface Drainage Away from Head Works

The most cost-effective method to avoid water

entering a shaft or decline is to locate the shaft

away from any watercourses or flood plains.

If the general topography or the geological formation

of the ore body makes this impossible, it will be

necessary to undertake more pro-active flood

protection civil works. For a discussion of flood

mitigation and interception drainage techniques

refer to Sections 8.1.1, 8.1.2 and 8.1.4. Due to

the importance of a mine’s access shaft, flood

protection and mitigation works must be designed

to give a very low risk of failure. Where flooding

is possible the level of risk must be very carefully

analysed. If flooding may be life threatening, it

is advisable to cater for the probable maximum

flood (PMF) (refer to Fact Sheet No.2).

9.2 Groundwater Inflow

Groundwater inflows may originate from lateral

connections to local and regional groundwater

resources at working faces, vertical seepage from

roofs of underground pits and local seepage from

water bearing strata or “pockets” of groundwater.

Unplanned interception of adjacent flooded

workings, especially in coal mines, can have

disastrous consequences on workers and machinery.

Blasting and drilling operations which tap into

sources of water may result in a quick and widespread

impact of the inflow in connected working areas.

9.2.1 MANAGING GROUNDWATER INFLOW

Managing groundwater inflow in underground

mines can take many forms. Some techniques are:

• preventative,usingflowrestriction,containment

and re-routing of flow (Section 8.2.2). Bore

dewatering, in particular, provides an effective

way of reducing the effects of groundwater

inflow to the underground mine by removing

a proportion of the groundwater resource;

• contingent,allowingfortheinflowofground-

water. The confined nature of underground

mines makes the design of adequate drainage

into an adit or shaft used exclusively for

collection of groundwater (ie. a sump) essential.

Drainage to an adit which passively discharges

to the environment may prove to be a long-term

problem if acid drainage is present. Control

and treatment of such drainage streams after

mine closure is difficult and expensive;

• depressurisationattheinteriorsurfaceof

the underground working, which involves

progressively tapping into water bearing

strata to “bleed” water and hydrostatic

pressure at several points; and

• pumpingtothesurfacefromsumpsorpumping

to abandoned shafts from temporary sumps

may also be used to move volumes of water

from areas in which they are not wanted.


U N D E R G R O U N D M I N E S

In wet areas, the plugging of old shafts and

surface exploration drill holes can reduce

water inflows quite significantly

9.3 Water Quality

Water present within underground mines is

normally derived from direct infiltration of

rainfall and seepage of groundwater into the

excavation. Water extracted from underground

mine workings may be contaminated with:

• increaseddissolvedandparticulatemetals

resulting from the abrasion and dissolution of

metalliferous minerals (eg. acid drainage);

• nutrientsfromexplosiveresidues;

• highconcentrationsofsuspendedsediments;and

• oilsandgreasesfromundergroundmachinery

9.3.1 TREATMENT AND DISPOSAL

OF UNDERGROUND MINE WATER

Water extracted from underground mine pits

should be pumped to a central holding facility

where suspended sediments can settle. If possible,

the settling facilities should be underground, so

that the sediment does not become a problem on

the surface. Appropriate treatment technologies

can then be implemented for the removal of any

hydrocarbons, heavy metals or acid drainage.

If acid drainage is present within the underground

workings, then treatment of this water will

be required, as outlined in Sections 8.3.2 and

11.4.1. In addition to the water extracted for

treatment, consideration should be given to

water that may potentially escape through mine

shafts, adits and bedrock cracks and fissures.

If at all possible, clean water flowing into a mine

should be kept separate from dirty streams

and removed as quickly as possible. This will

prevent contamination of the water and reduce

the quantity which then has to be treated.


10. Heap Leach Processes

10.1 Introduction

Management of a heap leaching operation is effectively

the management of flows: the flow of barren leach

solution to the leach pad and through the heap;

containment of the pregnant solution; removal of the

dissolved metals and recycling of the barren solution.

In order to maximise the recovery of metal values

and avoid environmental damage, catchments must

be clearly separated and all drainage systems sized to

contain the normal and abnormal flows. Inadequate

design means both a loss of the resource and

contamination of stream flows by process solutions.

The design and management of a heap leach operation

is a specialist skill. However, some traditional

operations may decide to treat low-grade material

using the principles of heap leaching. In these cases

the design of the water and solution management

systems may fall to the site engineer. The following

sections are provided to assist site personnel in

obtaining useful site specific information for the

design, operating management, decommissioning

and rehabilitation of a heap leach facility.

10.2 Planning for Heap Leaching

10.2.1 BASELINE EVALUATION

It is essential to define and isolate catchments, and

size drainage lines and ponds to ensure that clean and

contaminated flows are separated and that the drains

and containment ponds are not over-topped. The

groundwater system beneath the pads and process

ponds should be defined with regard to its hydrology

and chemistry. In the event of contamination

by process water, a proper understanding of the

underground flow conditions and water chemistry

will predict the extent and environmental significance

of any process water seepage and enable the

rapid implementation of remedial actions.

Chemical parameters to be measured should

include both the natural groundwater constituents,

process chemicals and any chemicals which might

be formed or liberated as a result of the process

chemicals interacting with the soils or rock.

10.2.2 RAINFALL EVENTS, ACCEPTABLE

RISK, CONTINGENCY PLANNING

The collection system must be designed to

accommodate the solution from both the leaching

process and storm runoff without overflow or erosion

occurring. The facility will need a water balance to

properly manage the flows and containment ponds.

Climatic factors to be considered include high

intensity rainfall and long-term wet or dry

periods. Local climatic data normally provide

the most reliable data for predicting hydrological

events. Suggested minimum design event

frequencies are presented in Table 10.1.

Design event frequencies should be determined

in conjunction with a risk analysis.

Storm design parameters must consider the

critical duration of the design event, whereas

seasonal variability is important for the design

of water supply and containment ponds

sizes. The ponds will need to contain:

• minimumoperatingvolumesto

enable the pumps to operate;


H E A P L E A C H P R O C E S S E S

• heapdraindownvolume;

• rinsingcycles;

• normalseasonalfluctuationsinwatervolume

(based on average climatic conditions);

• floodsurge(basedonthecritical

design event); and

• extremeeventdischargeoutletorspillway.

Contingency plans should be developed (and

preferably tested) prior to an event resulting in the

release of process solution. Useful equipment to

have on site or in daily operation may include:

• acontinuousflowmonitoronthereceiving

creek to enable estimates of dilution; and

• emergencychemicalsanddosing

equipment to neutralise overflows.

10.2.3 BASELINE GROUNDWATER MONITORING

Many materials are available to seal the heaps from

the underlying soil and for use as pond liners.

These include PVC, asphalt and clay. It should be

assumed that all ponds and heaps will potentially

leak, so a groundwater monitoring program should

be implemented to determine if there is any loss

of process solution and contamination of the

groundwater. Routine field monitoring should evaluate

changes in the water table and the water chemistry.

The geochemistry of the process solution should be

fully evaluated to determine the best indicators of

contamination. For example, with regard to a copper

heap leach operation, elevated sulphates in the

groundwater may be identified in perimeter bore hole

samples long before elevated copper concentrations.

10.2.4 CLOSURE PLANNING

The chemical characteristics of the spent leach

pile and the long-term leachate stream should

be determined during the design phase. The

characteristics will depend on the nature of the

ore, the process solutions used and the degree of

rinsing and/or chemical treatment of the heap once

active leaching has finished. It is important that

the process ponds are sized to contain the volume

of solution generated during the rinsing process.

Where heaps are constructed sequentially, experience

gained during the operation should provide the

information needed to establish closure criteria for

water quality and heap stability. Revegetation of

the heaps may be problematic due to slope angles,

chemistry and water retention of the spent ore.

Ongoing treatment of the heap leachate may be

required for some time after the last heap has ceased

active leaching and it is important that adequate

provisions are made to ensure containment of any

contaminated water during the closure phase.

TABLE 10.1: Suggested Minimum Design Event Criteria for Heap Leach Operation

Facility Type of Design Event

Access road, culverts and drainage ditches 10 year ARI to 50 year ARI flood peak

Drainage courses and ditches outside of leach pad

perimeter berm, pregnant pond and barren ponds 100 year ARI flood peak

Internal freeboard within leach pad,

pregnant and barren solution ponds

Maximum of:

• averagehydrologicalconditionsplusashort-

term, 100 year ARI storm event; and

• alongertermequivalent100yearARIevent

over a period of several months or years.


H E A P L E A C H P R O C E S S E S

10.3 Solution Control During Operations

10.3.1 MAINTENANCE OF DRAIN AND

POND CAPACITY

Heaps should be designed to avoid slope failure and/

or erosion of the ore and subsequent blockage of

the drains. Erosion and sedimentation within the

drains reduces the capacity for containment and

may result in overtopping of containment structures.

Testing should be undertaken on both saturated

and unsaturated heaps as the shear strength of the

material will vary with different pore water pressures.

The effects of earthquakes should not be overlooked.

10.3.2 INTEGRITY OF THE PAD OR LINER

The pad should be protected from flood flows in

the natural drainage systems by appropriately sized

berms. These should also extend around the process

solution ponds. It is recommended that the 100 year

ARI storm event be the minimum design standard.

During construction of the pad care is required to

ensure the integrity of the liner. The strength of the

liner should be commensurate with the hydraulic

pressure to be applied and the chemicals to be used.

Multiple use of a pad increases the risk of tears in

the liner and subsequent seepage. Careful inspection

is required to ensure integrity of the liner prior to

the construction of the heap. A leachate collection

system should be constructed to collect seepage.

10.3.3 INTEGRITY OF PIPING AND VALVES

All pipes containing process solution should

be located within bunds which are sized to

contain the amount of solution which would be

released should the pipe or valve fail plus any

additional flows due to rainfall within the bund

catchment. Routine inspections and leak detection

equipment should be used to identify leakages

and these should be repaired immediately to avoid

contamination of the groundwater. Preventative

maintenance rather than the repair of leaks

should be the underlying operating philosophy.

10.4 Water Management on closure

10.4.1 CRITERIA FOR LONG-TERM

LEACHATE QUALITY

The leachate discharge criteria should be developed

on the basis of the downstream beneficial uses

of the surface and groundwater flows. State

regulations (and/or catchment or river specific

environmental protection policies) and the

ANZECC (1992) guidelines for receiving water

quality will provide a basis for determining the

appropriate long-term leachate quality. These, in

conjunction with the flows and chemistry of the

leachate stream and of the receiving waterbody,

will determine the final discharge quality, and

where applicable, the size of a mixing zone.

10.4.2 RESIDUES AND LONG-TERM

CONTAMINATED SITE MANAGEMENT

All heaps should be contained as safe, stable

structures which will erode at an acceptable rate.

This rate will need to be determined through

project specific field trials as the slope angles,

particle size and length of slope will influence

the rate and extent of erosion. The use of

vegetation to control erosion may be subject to

both geochemical and physical limitations and

the early establishment of field trials should

provide the data needed to evaluate this option.

Leachate and surface runoff from the heaps

should not cause degradation of watercourses

downstream from the site through either siltation

or long- or short-term toxicity. The operation

will need to implement a monitoring program

to evaluate the success of its rehabilitation and

leachate management strategies. This will include

both surface and groundwater quality monitoring

and should include contingency plans for the

implementation of alternative control strategies

should they be required. Relinquishment of the lease

can be expected once the operation has attained an

acceptable discharge quality and stable surfaces.


11. Waste Dumps

11.1 Waste Dump Construction for Water Management

Attention to waste dump construction with a

view to the final rehabilitation plan will minimise

erosion potential and facilitate a drainage system

that reflects the final drainage network. Accordingly,

waste dump planning and construction should

attend to the following critical matters.

11.2 Surface Water

The information provided in this section should be

read in conjunction with Section 6.1 of AMIC (1990).

The type of material to be stored in the waste dump

will determine its design and ongoing construction.

The presence of acid or other undesirable leachate-

producing waste may necessitate a capped waste

dump which will generate high volumes of surface

runoff. Alternatively, if the material is inert it may

be desirable to encourage infiltration. The types of

contaminants to be expected are discussed in Section

11.4. To ensure this contamination is minimised

and contained there are many critical design issues

for waste dumps. These are discussed below.

11.2.1 LOCATION OF WASTE DUMPS

The location of waste dumps should be planned well

in advance to cater for the expected waste volumes,

the final and intermediate design profiles, visual

and noise screening of mine operations and the

interaction with groundwater. The following surface

water issues should also be considered in the plan:

• newwastedumpsshouldbelocated

within catchments serviced by dirty water

interception and treatment facilities;

• wherepossible,naturaldrainagepathsshouldbe

maintained, and room should be left around the

base of the waste dump for interception drainage;

• wastedumpsshouldnotbeconstructed

immediately adjacent to natural or

uncontaminated watercourses. Provision must

be made for intercepting runoff, leachate and

seepage before it enters such watercourses;

• roomshouldalsobeleftforconstructionof

retention ponds, or it must be possible to

direct interception drains into existing ponds

for the removal of suspended materials and

the treatment of chemical contaminants; and

• avoidlocatingroadculvertsimmediately

downstream of waste dumps. The high sediment

load in waste dump runoff can easily cause

blockages. Where this is not possible, ensure

that sediment retention dams are located

upstream of the culverts. Culvert inlets should

be carefully designed to maximise velocities

into the culvert and outlets designed to ensure

that sediment is removed from the outfall.

11.2.2 EROSION ON WASTE DUMPS

Severe rilling on waste dump batters and the

problems associated with high sediment loads

in waste dump runoff can be reduced by proper

design and construction of the waste dump. This

should include close attention to batter slopes,

benching, armouring and drains. Apart from these


WA S T E D U M P S

‘geometric’designguidelines,thefollowing

points should be considered.

Capped Waste Dumps

Where acid drainage and other leachate formation

is to be minimised by capping the waste dump

with impervious clay or rock, there will be

very high volumes of runoff. It is important to

incorporate erosion control when constructing

the capping layer. This will include properly

designed drains, spillways, drop structures,

armoured batters and immediate topsoil and

grassing. It is also very important to ensure the

impervious material selected is not excessively

dispersive (clays) or soluble (weak limestone).

Encouraging Infiltration

If seepage of water into the waste dump will

not cause structural instability or contaminated

leachate and groundwater seepage, it can be very

beneficial to encourage infiltration. This will

greatly reduce runoff volumes and hence reduce

erosion. Increased infiltration can be achieved by

contour ripping of the surface, “moonscaping”

(refer to AMIC, 1990), creation of small detention

ponds or sink holes on top of the stockpile.

Erosion Control

Erosion control can be achieved through:

• effectiveandearlyrevegetationofcompleted

waste dumps or even of completed sections of

active waste dumps. This will require thorough

advance planning of final dump profiles, but in

so doing may prevent double handling of waste;

• armouringoreffectiveslopereduction

which will reduce scour. Planning of

open channels to achieve stable profiles

and slopes (ie. 0.5% - 1.0%) is also

important (refer to Fact Sheet No.4);

• reductionofslopelengthsbyconstructionof

contour banks and/or drainage benches; and

• introducingstormwaterretention

basins into the final profile to reduce

the magnitude of peak flows.

11.2.3 INTERCEPTION DRAINAGE

AROUND WASTE DUMPS

Contaminated runoff or leachate derived from waste

dumps must be intercepted and directed towards

‘dirtywater’treatmentponds.Thedegreeoftreatment

required to match the quality of natural watercourses

in the area can vary from none at all, to removal of

nearly all suspended solids and treatment for acid,

salinity, and heavy metals. Typical techniques for

runoff interception are discussed in Section 8.1.3

which, along with the following guidelines, will

ensure that the interception system works effectively.

Separation of Water Streams

To avoid excessive volumes of water entering the dirty

water treatment systems, runoff from undisturbed

catchments around the waste dump should be

kept separate from dump runoff and associated

disturbed areas. If large quantities of dust from the

waste dump settles on nearby areas, then these areas

should be included in the dirty water system.

Vegetation Filters

The retention of natural vegetation between the

waste dump and the interception drains can be

highly effective for removing sediment from runoff

and reducing contaminants in the leachate.

Drainage Design

If sediment cannot be retained on the waste

dump then it must be kept in suspension until

it reaches a designated location for sediment

removal (ie. a sediment pond). Drainage

velocities must be sufficient to keep sediment

suspended but not too fast so as to cause scour.


WA S T E D U M P S

11.2.4 SEDIMENT CONTAINMENT

AROUND WASTE DUMPS

Containment of sediment on the stockpile is

the ideal solution and can be maximised using

silt fences, hay bales, silt traps, filter dams,

retention basins and any other method which

will temporarily reduce runoff water velocities to

allow suspended solids to settle. A description of

these techniques is given in Fact Sheet No.8.

When de-silting ponds, sediment should be

dumped in a location where it will be exposed to

minimal surface runoff. Methods of containing the

sediment either on the waste dump or in a dirty

water system are dealt with in detail in Fact Sheet

No.8. If wetlands are used, they should only be

used to remove very fine sediment particles and a

pre-settling pond should be constructed upstream.

11.3 Groundwater

11.3.1 INFILTRATION TO GROUNDWATER

Between ground level and the top of the aquifer,

the level of saturation in the soil may vary from

zero (dry) to fully saturated (Figure 11.1).

This zone, referred to as the capillary zone,

contains water which is held under negative

(suction) pressures within the soil matrix.

Flow in the capillary zone is strongly vertical and

only weakly horizontal. Therefore water infiltrates

or percolates through this zone. Similarly, the

migration of contaminants is strongly vertical.

Flow in the capillary zone is complicated by

the strong and variable presence of air in the

soil matrix. This results in a variable hydraulic

conductivity of the soil, which, in turn, results in

variable groundwater infiltration characteristics

between ground level and the top of the aquifer.

The main factors influencing

groundwater contamination are:

• traveltimeofcontaminatedwaterfrom

the ground surface to the water table;

• thefractionofcontaminantthat

reaches the water table; and

• therateatwhichthecontaminantenters

the aquifer from the capillary zone.

Characteristic behaviour of contaminants include:

• solublecontaminantscollectnearthe

water table in a floating lens and are

then transported across the water table

where horizontal dispersion occurs;

• solventswhicharedenserthanwater

migrate downwards to the bottom of the

aquifer and are then transported by a

process of advection and diffusion; and

• residual(freephase)chemicalcontamination

in the soil matrix above the water table has the

potential to generate long-term problems.


WA S T E D U M P S

Control of infiltration may be achieved through:

• linersorimperviouslayersplacedbetween

the waste dump and the soil matrix

(eg. polyethylene, PVC, non-reactive

clays or soil-bentonite mixtures);

• surfacecappingtoinsulateagainstthe

infiltration, percolation and contaminant

migration via rainfall through the waste dump.

Surface capping materials may be impermeable

materials such as clay, concrete or liners; and

• adequatewastedumpdrainagetoconfine

runoff to the surface, where it may be more

easily contained and treated if required.

Attenuation of groundwater contamination

may be achieved by isolating the

groundwater near waste dumps using:

• slurrywalls(Section8.2.2);

• groutcurtains(Section8.2.2);and

• sheetpiling(Section8.2.2).

In addition, groundwater control methods

such as dewatering bores and capture trenches

(Section 8.2.2) may be used to collect water

for pumping to treatment facilities. However,

these methods should only be employed

after source control methods have failed.

11.3.2 MONITORING

Groundwater should be monitored as close as

practical to the perimeter of the waste dump

and the piezometers should extend into the

subsurface groundwater regime. Monitoring and

sampling should be carried out both upstream and

downstream of the prevailing groundwater flow

direction near the waste dump (Figure 11.2).

Monitoring and sampling should include:

• groundwaterlevelsorpiezometricheads;

• pHandsalinity;and

• chemicaland/orbiological

analyses as appropriate.

When sampling for chemical or biological

analysis, standard sampling procedures

should be used (Section 5.4).

Contaminants may react within the soil

matrix, so that groundwater monitored at the

periphery of waste dumps may not directly

reflect some characteristics of the primary

contaminant infiltrating from waste dumps.

11.4 Water Quality

Waste rock dumps may be a source of contaminants

to local streams and receiving waters. The range of

problems that occur from these structures include:

• aciddrainage;

• salinerunoff;

• suspendedsolidsrunoff;and

• heavymetalsinrunoffandleachate.


WA S T E D U M P S

11.4.1 ACID DRAINAGE

Acid drainage from waste rock dumps is normally

a more significant problem than that from within

open cut or underground mines. This is primarily a

result of increased surface area of exposed reactive

sulphides, higher porosity and infiltration within

waste rock dumps and the difficulty in containing

and/or treating leachate. The extent of the acid

drainage and subsequent metal solubility problems

within a waste rock pile will depend on the following

physical, chemical and biological conditions:

• physicalsizeandgeological

characteristics of the waste rock;

• thepresenceandtypeofsulphide

bearing minerals;

• theextentofrainfallinfiltration;

• thepermeabilityofthewasterock

dump to air and water;

• thepresenceofacidneutralisingrocks

within the waste rock dump; and

• thelevelofmicrobiologicalactivity,

including the presence of bacteria.

Monitoring techniques that can be used to identify

acid generation within a waste dump include:

• thepresenceof“hotspots”onthewaste

surface that are warm to the touch;

• theappearanceofsteamfromsectionsof

the dump, particularly after rain events;

• redandbrowncolouredwateraroundthe

base of the dump, red or brown colouring on

stream bottoms and banks, or the presence

of colloidal yellow precipitate in the water;

• theuseofremoteimagingtechniques,such

as thermal infra-red, to identify higher than

ambient temperatures in the dump;

• in-situtemperaturesensing;

• gassamplingwithinthepartially

saturated zone; and

• samplingandanalysisofsolubleacid

drainage products in the waste rock

and underlying geologic formation.

Specialised sampling techniques are required

when monitoring for acid drainage and

the reader is referred to Hutchinson and

Ellison (1992) for further information.

A wide range of prevention and remedial strategies

are available for acid drainage problems from waste

rock dumps. These are shown in Table 11.1

11.4.2 SALINITY

Saline runoff from waste dumps can be a common

problem at mines located within arid regions

and regions with specific high salinity geological

formations, for example, much of the Hunter and

Bowen Basin coalfields. Overburden and waste rock

that originated from within saline parent material

can have high concentrations of dissolved and

precipitated salts. Once this material is removed and

placed on waste rock dumps, rainfall infiltration

can result in highly saline runoff and leachate.

Runoff and leachate from saline waste

rock dumps should be intercepted and

directed to storage ponds for:

• evaporation;

• recyclingifsuitable;

• dilutionwithlowsalinewaterif

available and subsequent use;

• treatmentiffeasible;or

• controlleddischarge,forexampleunder

flood flows where natural dilution occurs.

The chosen option will depend largely on

the water’s suitability for use on site and the

characteristics of the receiving waterbody.


WA S T E D U M P S

11.4.3 SUSPENDED SOLIDS

Common techniques used to control sediment

runoff from waste dumps have been outlined

in Sections 11.2.2 and 11.2.4. Further

techniques applicable to erosion control and the

rehabilitation of waste rock dumps are provided

in Fact Sheet No.8 and AMIC (1990).

11.4.4 LEACHATE AND OTHER CONSTITUENTS

Additional contaminants that may emanate

from waste rock dumps include:

• asbestosfibresfromnaturallyoccurringminerals;

• solublecationsandanionssuchas

chlorides, sulphates and carbonates;

• heavymetalswhichmaybedissolved

by acid forming processes; and

• acidandalkalinewastestreamsfrom

naturally forming inorganic acids and

natural carbonates or alkaline silicates.

Specific treatment of these waste streams may

be required, and special disposal techniques

may be needed for sediment derived from these

materials and deposited in sedimentation dams.

TABLE 11.1: Prevention and Remedial Strategies for Acid Drainage

Control of Acid Generation

• pre-treatmenttoremoveorexcludesulphideminerals

• useofanimpermeablecovertoexcluderainfallinfiltrationandoxygen

• wastesegregationandblendingtocontrolpH

• useofbactericidestocontrolbacterialoxidationofsulphideminerals

• avoidexposingreactivemineralstoatmosphericconditionsbymodifying

the mine plan or avoid mining sections of the deposit

Control of Acid Migration

• useofcoversandsealstoexcludeinfiltration

• controlledplacementofwastetominimiseinfiltration

• interceptionanddiversionofsurfaceandgroundwater

Collection and Treatment of Acid Drainage

• useofaphysicaland/orchemicaltreatmentsystem

• useofbiologicaltreatmentsystemssuchaswetlands

Modified from Hutchinson and Ellison (1992)


12. Tailings Water Management

All tailings disposal systems require management of

the water component in the tailings. Management

strategies are closely linked with the method of

disposal, design of containment facilities and the

potential for impacts both on and off the site.

12.1 Disposal Methods

Tailings disposal methods can be

separated into four major categories:

• saturatedtailingsmanagement,wherethe

tailings are transported and discharged as

a slurry. The saturated tailings are held in a

dedicated containment area where gravity

separation isolates a percentage of the water

from the tailings solids. As deposition of

the tailings is in a wet slurry, tailings beach

slopes are flat and, consequently, large

containment areas required. To minimise storage

requirements, the separated water should

always be recycled as much as possible;

• semidryorthickenedtailingsmanagement,

which involves discharging the tailings to a

containment area at higher solids content

than the saturated tailings management.

Depending upon the stacking characteristics

of the particles in the tailings, higher beaching

slopes are possible, with resulting smaller

containment areas for tailings and decant water;

• drystacking,whichpermitstheextraction

of most of the water before deposition. This

allows the solids to be transported into a

solids rejects dump from where they can be

taken to waste dump areas for contouring,

topsoiling and revegetating; and

• co-disposaloftailingswhichisthecombined

disposal of coarse rejects material and fine

tailings usually by combined slurry pumping.

The mixture produces a stable landform at

the point of disposal with major advantages

for rehabilitation. Significantly larger volumes

of water are required than for conventional

tailings disposal. The advantages of co-disposal

are the stable ongoing and end landform, the

reduction in area for waste disposal, the potential

for recycling most of the discharge water and

fewer environmental impacts. The technique

does require large volumes of water, and there

are greater potential seepage losses and large

recycling pumps are required to return the

water for the ongoing co-disposal process.

Co-disposal techniques are being used at coal

mines but are also applicable to metalliferous

mines where there is a rejects component that,

when combined with tailings will produce

a well graded stable in-situ landform.

In all these processes, the effectiveness of the

dewatering processes is a function of local

conditions, the type of waste solids, size distribution,

statutory requirements and economics.

It is critical for the rehabilitation of tailings facilities

that the disposal and decommissioning methods

are compatible and decided upon in the planning

stage. For example, if a tailings storage facility is

planned to be decommissioned by drying out the

surface and covering it with waste rock or other

material to encourage revegetation, disposal of the

tailings under water (sub-aqueous disposal) could

lead to poor settlement and ineffective drying of

the surface. Conversely, a facility which will be

decommissioned using a wet cover, typically used


TA I L I N G S WAT E R M A N A G E M E N T

to inhibit acid drainage, should not be

operated with dry beaches where oxidation

of the sulphides can take place.

12.2 Characteristics and Management of Tailings Water

12.2.1 NATURE OF THE WATER

The water used to transport tailings and co-disposal

tailings or extracted during thickening of the waste

becomes contaminated during the process. In some

cases, such as in the goldfields of Western Australia,

the water itself is a risk to the environment because

of its hypersaline nature. Tailings water can be acid

or alkaline, have elevated concentrations of heavy

metals or contain concentrations of cyanide which

can have considerable environmental impacts if it

is released to the environment. It is important to

characterise the tailings water through a monitoring

program and manage the water accordingly.

In some cases, it may be necessary to treat the

water before disposal to the tailings storage

facility. Denaturing or recovery of cyanide from

gold process liquors is frequently practiced

in order to reduce costs and also to reduce

the potential environmental impacts.

12.2.2 MANAGEMENT

The following are the key elements that need to

be considered in tailings water management:

• thesensitivityofthecontainmentareato

infiltration and hence the requirements for

lining the storage area need to be evaluated;

• theabilityofthestorageareatocontain

stormwater inflows should be assessed. The

potential impact of discharges from the tailings

storage during storm events must be assessed.

This will necessitate a risk assessment (see

Fact Sheet Nos 2 and 3) with a resulting

design storm event for containment;

• diversionofdrainagefromsurrounding

catchment areas in order to reduce

inflow as much as possible;

• theneedforseparatereservoirsforwater

to be recycled eg. in co-disposal;

• recyclingoftailingsdecantwatershould

be encouraged as much as possible;

• tailingspipelinesshouldbebundedand

have collection sumps to contain spills

from leaking or ruptured pipes;

• infiltrationmonitoringsystemsare

required around the containment

site to detect contaminants escaping

from the impoundment; and

• dischargemonitoringfordisposal

systems with continuous discharge

of tailings liquor and/or solids.

12.3 Seepage Management

Seepage can occur through the walls and through

the floor of a tailings storage facility (Figure 12.1).

Infiltration through the floor of the tailings storage

facility usually decreases with time as tailings

are deposited in successive layers and form a

retardant to vertical flow. In the long-term, the

majority of tailings water seepage occurs through

the dam wall and via infiltration through the

ground surface on which the wall is built.

12.3.1 SEEPAGE CONTROL

Seepage may be controlled to some extent by

constructing the tailings facility using permeable (for

filter dam segments) and impermeable soils where

applicable. In addition, geofabric liners may be used

to increase the insulation against seepage flow.

Under-drains may be installed in the floor of the

facility before deposition of tailings in order to

collect and channel water to a collection system.

Similarly, interception drains and trenches may be


TA I L I N G S WAT E R M A N A G E M E N T

installed around the facility to collect seepage before

it can escape into the environment. In extreme cases,

impervious slurry walls and interception systems

have been installed in the preferred seepage paths to

prevent escape of potentially contaminated water into

sensitive environments downstream of the facility.

12.3.2 MONITORING

Monitoring of seepage flow through the wall

of a tailings storage facility (TSF) is readily

accomplished using piezometers to determine

the geometry of the phreatic surface (Figure

12.1). This may be translated to seepage flow

rates using standard groundwater flow theory.

It is also common practice to install piezometers

around the base of the impoundment wall in order

to detect seepage escape into shallow aquifers under

the facility. Such piezometers should be installed

in appropriate locations so as to be able to detect a

contamination front moving from the impoundment

early enough to take remedial action. Indicator

elements should be determined from a knowledge

of the chemical composition of the tailings water.

Water balance monitoring of TSFs enhances the

overall understanding of the site water circuit.

Monitoring should be carried out within the tailings

pond, in the dam wall and in any downstream

evaporation ponds. Adequate knowledge of

tailings settlement and water retention in voids,

as well as evaporation rates, are critical to

forming a water balance management scheme.

12.3.3 WATER CONTROL

Tailings water control may be implemented

using containment measures such as:

• sizingtheTSFsufficientlytoholdlargevolumes;

• constructingfilterdamstoallowselectiveseepage

of water into retention ponds or evaporation

ponds. Water extracted in this way may be more

acceptable for recycling in processing plants;

• stagingofcontainmentwallconstructionto

facilitate drainage from the co-disposal area;

• sizingandlocatingoutletstructures

to hydraulically control discharges

from the storage; and

• sizingevaporationpondstoreduce

water levels at sufficiently high rates.

The re-use of tailings water is often limited

because of specific water quality requirements

of the process. In general, the characteristics

of tailings water is process-specific, as is the

acceptability of tailings water for re-use.


13. Mine Infrastructure

Water is essential for many aspects of a mining

operation. As well as the core function of extracting

the ore, virtually every other part of the mining

infrastructure uses water in some way. After coming

in contact with the operations, this water can pick up

contamination. It is important to be aware that this

contamination can exist, and of ways to minimise it.

Water used in these support functions needs to be

managed in the same way as other water on the site.

This section examines three main areas of an

operation where good water management

is essential. It is important to ensure that all

operators are aware of the potential environmental

impacts from failure to follow procedures,

and that they are adequately trained in the

operation of all pollution control systems.

13.1 Process Plant

Water used in a process plant is normally

confined within its designated piping and storage

facilities. It is only through washdown, pipe

ruptures, spillages and overflows from process

water tanks and dams that significant volumes

of process water can enter receiving waters.

The quality of surface runoff from the process

plant is dependent on the type of ore being

processed and the metallurgical process adopted,

eg. flotation, beneficiation, cyanide leaching.

A risk analysis and the associated contingency

plans should be undertaken at the planning

stage. Engineering solutions should be

commensurate with the level of acceptable

risk, safety hazards and environmental harm

which could result from an event.

13.1.1 CHARACTERISTICS

The process plant and associated ore stockpile area

can be a source of the following contaminants:

• suspendedsediment;

• oilsandgreases;

• processreagents;

• increaseddissolvedandparticulate

metals resulting from the dissolution

of metalliferous minerals;

• strongmineralacidsandbasessuch

as sulphuric acid and lime; and

• nutrientsfromresidualnitratesfromblasting.

13.1.2 CONTAINMENT AND

TREATMENT TECHNOLOGIES

Remedial measures and technologies available

for the containment and treatment of

contaminants from the process plant include:

• improvedhousekeepingstrategiestoidentify

the locations of spillage (eg. conveyor

transfer points) and the implementation

of appropriate remedial measures;

• bundingofallprocesschemicalstorage

areas and the interception and treatment of

all stormwater from within these areas;

• drainageofallprocessplantrunoff

to a central treatment facility (eg.

sedimentation or evaporation pond);

• provisionofquiescentconditionsinretention

ponds to enable settlement of fine grained

sediment. More rapid settling can be

achieved using a flocculent such as alum;


M I N E I N F R A S T R U C T U R E

• pHcorrectionusinglimedosingorother

suitable material may be necessary if the

retention pond water is acidic or incompatible

with receiving water quality; and

• interceptionandtreatmentofstormwater

runoff containing hydrocarbons through a

oil-water separation facility or alternatively,

materials contaminated with hydrocarbons

may well be suited to treatment using

Bioremediation Technology (Fact Sheet No.9).

The treatment of soluble contaminants is

dependent on the volume and quality of the waste

stream. Wastewater or contaminated runoff can

be diverted to a retention pond, tailings storage

facility or evaporation pond. Some waste streams

may require more advanced forms of treatment

such as activated carbon or ion exchange.

13.2 Industrial and Workshop Areas

The industrial area and its associated workshops

can be a frequent source of contaminants such

as lubrication oils, greases, solvents, surfactants

(water and solvent based products), suspended

solids from vehicles, atmospheric sources, spillage,

and metal shavings from lathes. Stormwater runoff

is the major transport route of these pollutants

to local watercourses and receiving waters.

13.2.1 CONTAINMENT AND

TREATMENT TECHNOLOGIES

Fuel Storage Areas

General principles for the design and

operation of storage areas include:

• bundingtotheappropriateAustralian

Standards in order to contain spillages;

• frequentinspectionofstoragetanks

and piping for corrosion and any above

ground and underground leaks;

• constructionofthefacilitiestocollectand

contain minor spillages outside the bunded

area during refuelling operations; and

• diversionofoilcontaminatedbundwater

collected during rain events through oil

interception or separation facilities.

Workshop and Truck Washdown Areas

General principles of design and

operation of these areas include:

• bettercontrolofhydrocarbons,eg.

central bulk storage and reticulation

throughout the workshop rather than

the use of 20 or 200 L drums;

• designofdispensingfacilitiesto

prevent drips and spillage;

• coveringoftheworkingareatoprevent

storm water picking up contaminants;

• installingadrainagesystemtoseparateclean

and contaminated water streams from within

and surrounding all workshop areas;

• diversionofoilcontaminatedwatertoa

separation system, which can range from simple

concrete sumps through to more sophisticated

mechanical systems such as coalescing plate

separators, skimmers and centrifugal separators;

• useofdrycleaningmethodssuchasindustrial

vacuum cleaners and absorbents rather than

water to clean floors and other surfaces;

• phasingoutofsolventsforcleaningapplications

in favour of new generation water-based

detergents, suitable for the cleaning of

hydrocarbons soiled equipment (solvents are

more difficult to treat and remove in wash

water than heavy lubricating oils); and

• moreeffectivedispensing,mixingand

use of detergents by operators, which

can also reduce consumption.



13.3 Haul Roads

Controlled drainage from haul roads is essential

for the maintenance of the road integrity for

haul truck usage. The drainage systems have

environmental impacts in terms of both the

structures adopted and the quality of the drainage

waters collected for disposal. Both surface and

groundwater drainage issues should be addressed.

13.3.1 ENVIRONMENTAL ISSUES

Haul roads are potentially a source of contamination

in water, notably from suspended particulate

matter. Any spillage of mined material onto the

road surface is a source of these particulates

and, depending on its nature, also a source of

chemical contamination. Any pyrite present in

the ore or waste could oxidise, leading to acid

drainage and mobilisation of heavy metals.

It is important to ensure that, wherever possible,

haul roads are constructed of material which will

not lead to further environmental impacts.

There are recorded instances where materials

used in the construction of haul roads

have led to environmental contamination

along the entire length of a road.

13.3.2 SURFACE WATER DRAINAGE

The important elements in surface water

drainage on haul roads include:

• watermustbeclearedfromthepavementor

wearing surface quickly to avoid excessive

soaking of the surface base course layer and

without creating deeply incised scour paths.

Generally; maximum cross fall slopes of 3%

will facilitate both these criteria (Figure 13.1);

• sidedrainsarerequiredtocatchsurfacewater

from the pavement and runoff from cut bank

slopes. The side drains should be sized such

that the design flow depth is no higher than the

underside of the pavement top course or base

course layer. This will minimise the potential

for saturation of this layer (Figure 13.1).

It is preferable to direct drains off the

haul road at cut and fill interfaces or

otherwise down batter slopes at designated

locations via erosion protected chutes;

• ifthegradeoftheroadexceeds2-3%,erosion

protection along side drains may be required to

prevent undercutting of the pavement layers.

The erosion protection may be in the form of

lining (rocks, concrete, synthetic materials)

or barriers for inducing flatter slopes; and

• haulroaddrainagecrossingsshouldbethrough

culverts, with attention given to upstream and

downstream erosion protection. Appropriate

slopes and surface level designs are necessary

to facilitate sediment movement without

deposition and consequent culvert blockages.

13.3.3 GROUNDWATER DRAINAGE

Groundwater investigations will reveal the necessity

for any groundwater drainage systems. The primary

purpose of groundwater drainage systems associated

with haul roads is to minimise the potential for

saturation of the haul road sections and possible

failure. The environmental consequences of such

failures can extend to washouts of the road with

excessive sediment loads and destruction of the

integrity of the surface water drainage systems.

Typical groundwater protection mechanisms include:

• slottedpipesingravelbeds;

• rockfill“pipes”;

• rockfillblanketstofacilitateboththe

construction and haul road operation;

• syntheticgeotextilematerialstoseparate

layers and provide strength; and

• dewateringbymechanicalmeans

(pumps) in extreme cases.


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Small Earth Dams. Inkata Press, Melbourne.

NH&MRC (1994). Draft - Australian

Drinking Water Guidelines. National Health

& Medical Research Council, Canberra.

Pilgrim & Cordery (eds) (1987). Australian

Rainfall and Runoff. Institution of Engineers,

Australia. (This document is revised regularly)

Shaus, E.M. (1994). Hydrology in Practice.

3rd Edition. Chapman Hall.

Smith, A. & Mudder, T. (1991). The Chemistry

and Treatment of Cyanidation Wastes. Mining

Journal Books Limited, London.

Vick, S.G. (1983). Planning, Design and

Analysis of Tailings Dams. Wiley

Williams, R.E., Winter, G.V., Bloomsburg, G.L.

& Ralston, D.R. (1986). Mine Hydrology. 169pp,

Society of Mining Engineers, Colorado.


Glossary

Advection The process by which solutes are transported by the motion of flowing groundwater.

Anisotropy The condition under which one or more of the hydraulic properties of an aquifer vary

according to the direction of flow.

Antecedent conditions The moisture conditions existing in a catchment at the onset of a storm.

Aquifer Rock or sediment in a formation, group of formations, or part of a formation that is

saturated and sufficiently permeable to transmit economic quantities of water to wells

and springs.

Aquifer, confined An aquifer that is overlain by a confining bed. The confining bed has a significantly

lower hydraulic conductivity than the aquifer.

Aquifer, perched A region in the unsaturated zone where the soil may be locally saturated because it

overlies a low-permeability unit.

Aquifer, unconfined An aquifer in which there are no confining beds between the zone of saturation and

the surface. There will be a water table in an unconfined aquifer. Watertable aquifer is

a synonym.

ARI - (Average The average or expected value of the period between exceedances of a given event

(eg. rainfall, discharge etc.).

This period is a randomly distributed variable.

Bailer A device used to withdraw a water sample from a small diameter well or piezometer.

A bailer typically is a piece of pipe attached to a wire and having a check valve in

the bottom.

Basecourse A layer of granular fill material constituting the uppermost structural element of a

road pavement immediately below the wearing course.

Capillary zone The zone immediately above the water table, where water is drawn upward by

capillary attraction.

Capture trench A trench which extends below the water table and into which the

groundwater drains.

Catchment The area which drains into a given stream or dam by way of natural ground slopes or

constructed drainage systems.

Clean water Surface runoff which has not picked up any solid or dissolved pollutants through

contact with disturbed or contaminated surfaces.

Recurrence Interval)


G L O S S A RY

Co-disposal The combined disposal of tailings and coarse reject material.

d/s Down stream (eg. d/s of a dam).

Dewatering The process of removing water from a given source (eg. pit dewatering,

aquifer dewatering).

Diffusion The process by which both ionic and molecular species dissolved in water move from

areas of higher concentration to areas of lower concentration.

Dirty water Surface runoff which has picked up solid or dissolved pollutants through contact

with disturbed or polluted surfaces.

Drawdown A lowering of the water table of an unconfined aquifer or the potentiometric surface

of a confined aquifer caused by pumping of groundwater from wells.

Finite-difference model A digital computer model based upon a rectangular grid that sets the boundaries of

the model and the nodes where the model will be solved.

Finite-element model A digital ground-water-flow model where the aquifer is divided into a mesh formed

of a number of polygonal cells.

Gabion A flexible wire basket filled with stones and used to retain earth and sediment or to

control scour.

(Typical size: 1m wide x 1m high x 2m long)

Geotextile, geofabric, Any permeable synthetic textile material, fabric or net used with earth, soil, rock or

foundations as an integral part of an engineering structure. Mainly used to improve

structural and/or hydraulic properties of soil, to reinforce or stabilise embankments,

as a filter layer in drainage applications or for erosion control.

Groundwater The water contained in interconnected pores located below the water table in an

unconfined aquifer or located in a confined aquifer.

Groundwater, confined The water contained in a confined aquifer. Pore water pressure is greater than

atmospheric at the top of the confined aquifer.

Groundwater, perched The water in an isolated, saturated zone located in the zone of aeration. It is the result

of the presence of a layer of material of low hydraulic conductivity, called a perching

bed. Perched groundwater will have a perched water table.

Groundwater, The water in an aquifer where there is a water table.

Grout curtain An underground wall designed to stop ground waterflow; can be created by injecting

grout into the ground, which subsequently hardens to become impermeable.

Heterogeneous Pertaining to a substance having different characteristics in different locations.

A synonym is non-uniform.

geosynthetic material

unconfined


G L O S S A RY

Homogeneous Pertaining to a substance having identical characteristics everywhere.

A synonym is uniform.

Hydraulic conductivity A coefficient of proportionality describing the rate at which water can move through

a permeable medium. The density and kinematic viscosity of the water must be

considered in determining hydraulic conductivity.

Hydraulic gradient The change in total head with a change in distance in a given direction.

The direction is that which yields a maximum rate of decrease in head.

Hydraulic radius A measure of waterway geometry used in hydraulic calculations. The cross sectional

area of flow in a drain or pipe divided by the wetted perimeter (ie. length of wetted

surface) perpendicular to the direction of flow.

Hydrogeology The study of the interrelationships of geologic materials and processes with water,

especially groundwater.

Hydrologic cycle The circulation of water from the oceans and other waterbodies through the

atmosphere to the land and ultimately back to the ocean.

Hydrology The study of the occurrence, distribution and chemistry of all waters of the earth.

Infiltration The flow of water downward from the land surface into and through the upper

soil layers.

Isotropy The condition in which hydraulic properties of the aquifer are equal in all directions.

Laminar flow That type of flow in which the fluid particles follow paths that are smooth, straight,

and parallel to the channel walls. In laminar flow, the viscosity of the fluid damps out

turbulent motion. Contrast with turbulent flow.

Manning's coefficient (n) A dimensionless value defining the roughness of a surface (eg. pipe wall or sides

of a drain) with regards to water running across that surface. Used in hydraulic

calculations such as Mannings equation.

Manning’s equation A formula used for calculating the flow in a given waterway (eg. pipe or open

channel drain).

Model calibration The process by which the independent variables of a digital computer model are

varied in order to calibrate a dependent variable (eg. head) against a known value (eg.

water table).

Model verification The process by which a digital computer model that has been calibrated against a

steady-state condition is tested to see if it can generate a transient response, such as

the decline in the water table with pumping, that matches the known history of

the aquifer.

Numerical model A model of groundwater flow in which the aquifer is described by numerical

equations with specified values for boundary conditions that are solved on a

digital computer.


G L O S S A RY

Phreatic surface “Free” surface of groundwater; pressures are equal to atmospheric along this surface.

Piezometer A non pumping well, generally of small diameter, that is used to measure the

elevation of the water table or potentiometric surface. A piezometer generally has a

short well screen through which water can enter.

Piezometric head Pressure head experienced by a given body of water, comprising both static levels and

inertial forces.

Piping failure Failure of an earth dam wall caused by excessive seepage of water through the

embankment.

PMF - (Probable The flood caused by runoff water from the probable maximum precipitation.

PMP - (Probable The greatest depth of precipitation for a given duration meteorologically possible for

a given size storm area at a particular location at a particular time of year.

Porosity The ratio of the volume of void spaces in a rock or sediment to the total volume of

the rock or sediment.

Recharge The process of replenishment of a water resource (recharging of aquifer, recharge

of dam).

Rational method A procedure for calculating the peak discharge from a small to medium sized

catchment, resulting from a storm of a given ARI and duration.

Reno mattress A low profile flexible wire basket filled with stones and used to control scour.

(Typical size: 2 m wide x 6 m long x 0.3 m deep)

Revetment mattress A hard surface armouring formed by using pocketed pervious fabric filled with

concrete. Used to control scour.

Rip Rap Irregular rocks of medium to large size, used for the lining of embankments, drainage

channels, dam spillways etc. for prevention of erosion.

Runoff The total amount of water flowing in a stream. It includes overland flow, return flow,

interflow and baseflow.

Sediment barriers Structures placed in a drainage channel to promote settling out of sediment until a

stable flow slope is achieved between each barrier. Used for erosion prevention.

Sediment fence / A low fence of woven geotextile designed to filter suspended solids from overland

flow, (sheetflow). Used for containment of sediment in disturbed areas.

Seepage Common term for groundwater flow, encompassing the characteristic “slow flow”

processes (see laminar flow).

Sheet piling Physical barrier applied by driving solid sheets of impermeable material into

the ground.

maximum flood)

maximum precipitation)

silt fence


G L O S S A RY

Slurry wall An underground wall designed to stop groundwater flow; constructed by digging a

trench and backfilling it with a slurry rich in bentonite clay.

Soil matrix Skeletal structure of soil, within which “honeycombs” of pores exist.

... % Standard An earthworks term used to specify the amount of compaction effort required (or

compaction achieved) in engineered earthworks.

Surface water Water found in ponds, lakes, inland seas, streams and rivers.

Time of concentration The time required for rain falling at the farthest point of the catchment to flow to the

point at which the discharge is being calculated. Used in hydrology calculations such

as the Rational Method.

u/s Up stream (eg. u/s of a dam).

Water table The surface in an unconfined aquifer or confining bed at which the pore water

pressure is atmospheric. It can be measured by installing shallow wells extending a

few feet into the zone of saturation and then measuring the water level in those wells.

Wetlands Areas where water is over or near the ground surface for long enough each year to

maintain saturated soil conditions along with related vegetation (eg. marshes,

bogs, swamps etc.).

compaction


Field Record Data Sheets

Sampling method

Analysis profiles

Remarks

Sampler Signature Date

Example of Sampling Report Form for Marine Waters

Site Site Code

Date Time

Latitude Longitude

Site Description

HYDROGRAPHIC CONDITIONS

Tidal Currents: Direction Approx. velocity

Time of high water Time of low water

WEATHER CONDITIONS

Wind Direction Force

Cloud cover State of sea

MODIFIED FROM IS0 STD 5667-9:1992 (E)

FA C T S H E E T N O . 1

Depth(m)

Temperature(ºC)

Salinity Dissolved Oxygen(% sat.)

Sample

Number Time



Example of Sampling Report Form for Groundwaters

Site Site Code

Date Time

PUMPING DETAILS

Height of riser/bore pipe above ground level (m)

Water level within aquifer (before pumping) (m)

Water level within aquifer (after pumping) (m)

Pumping Time

Volume Extracted (estimated)

SAMPLING DETAILS

Time: Start End of sampling

Depth of sampling

Sampling method

Sample appearance

Details of preservation techniques employed

Details of sample storage method employed/required

Remarks






Example of Sampling Report Form for Surface Waters (LAKES, STREAMS, WATER STORAGES AND TAILINGS DAMS)

Site Site Code

Date Time

Site Description

Water Depth Volume

Time: Start End of sampling

Sampling method

DEPTH-INTEGRATED SAMPLE

Withdrawal between and m

OBSERVATIONS AT THE SAMPLING POINT

Turbidity, caused by sediment particles /plankton

Colour Odour

Water plants

Estimation of the discharge of the streams/river: (high/medium/low)

LOCAL WEATHER CONDITIONS

Air temperature

Wind force

Direction of wind

Cloudiness (%)

Remarks





Example of Sampling Report Form for Domestic and Industrial Wastewater

Site Site Code

Date Time

Sample method: Grab

Composite-time dependent

Equipment Used

Interval of flow between samples min or m3

Volume of grab samples mL

Sampling started Sampling ended

Preservation method

FIELD MEASUREMENTS

Remarks


Field Record Data Sheets FA C T S H E E T N O . 1


Test Result Unit Time


This fact sheet examines surface runoff processes

and techniques used to estimate total catchment

runoff and peak flows generated by runoff for

smalltomediumsized‘nonurbanised’catchments

(< 250 km2). Accurate estimation of these quantities

depends on a large number of site characteristics.

Hence it is not within the scope of this handbook

to give precise techniques for every region in

Australia. Instead, the general principles will

be discussed and references provided to locate

the information specific to a given region.

Runoff Processes

Losses: When rain falls on a catchment surface,

aportionofitwillbeheldbackas‘losses’before

theremaining‘excessrainfall’reportstostreams

or drainage channels as surface runoff. The losses

combine a number of rainfall and interception

mechanisms. In the early stages of a storm, much

of the rain is intercepted by trees, grass and other

plants and stored on leaves and branches etc. as

interception storage. When these stores are full,

water will reach the ground surface and commence

filling small depressions. As these fill and overflow,

large depressions begin to fill until this depression

storage is full and overland flow commences.

There are continuing losses through infiltration

into the soil which starts at a high rate if the soil

is initially dry and then rapidly decreases until

approaching a steady rate known as the infiltration

capacity of the soil. Evaporation from the vegetation

and ground surfaces will also contribute to the

losses. From this discussion it can be seen that

losses (and hence rainfall excess) are affected by

vegetation type and density, soil type and degree

of disturbance, catchment slope and the number

and efficiency of watercourses in the catchment.

Runoff types: Once losses have been absorbed

there are two major runoff routes by which water

reaches watercourses. In areas where soil is thinly

overlying an impervious or rock layer, or where the

groundwater level is very near the surface (eg. at

valley bottoms or near streams) it will not take long to

saturate the surface soil. Once this occurs, infiltration

ceases and water will flow over the surface as

saturated overland flow. Alternatively in sandy areas,

or areas of deep permeable soil overlying impervious

layers, water can rapidly flow downslope through the

soil and percolate out of the soil when it intercepts

a saturated zone. This is known as interflow and is

differentiated from groundwater flow by the speed

with which it reports to watercourses. The efficiency

of these runoff processes is again dependant on soil

types, as well as rainfall intensity, the geology of the

area, catchment slopes and groundwater levels.

Design losses: When estimating total or peak

runoff values it is necessary to estimate the losses,

as it is only the rainfall excess which contributes

to the runoff. With losses depending on so many

site specific variables it is almost impossible to

realistically model the processes. Even within a

Single small catchment there will be a large number

of sub areas responding differently due to varying

physical characteristics. To simplify matters, a

number of methods have been developed for

applying general losses across a whole catchment.

A full discussion of these methods, along with

typical loss values for regions throughout Australia

can be found in Chapter 6 of Australian Rainfall and

Runoff 1987 (AR&R). The simplest and most popular

of these methods are (refer to Figure FS 2.1):

(i) Constant fraction (proportional losses/

runoff coefficients): Loss is assumed

to be a constant fraction of the rainfall.

This can be viewed in two ways:

a) A runoff coefficient (ie. 0.7) is applied to

the rainfall. If a catchment large distinct

areas (ie. undisturbed, stockpiles, sealed

areas etc.) then a different coefficient

can be applied to sub areas; and

Estimation of Surface Runoff FA C T S H E E T N O . 2


b) If a predictable proportion of the catchment

is known to become saturated during rain

then this area can be viewed as the proportion

of the catchment contributing runoff.

(ii) Constant loss rate: If a catchment has

minimal interception or depression storage

and the infiltration into the soil is fairly

constant (ie. if the catchment is already

wet from previous antecedent rain) then a

constant loss rate matching the infiltration

capacity of the soil is a valid approach.

(iii) Initial loss - constant loss rate: In line with

the above discussion of interception losses

through vegetation and depression storage,

followed by ongoing losses due to soil

infiltration and evaporation, is the concept

of having no runoff until an initial loss is

satisfied and then having a constant loss rate

for the remaining duration of the rain.

As well as AR&R there are many other sources of

information for loss values applicable to an area:

• Consultingengineers/hydrologists;

• Stategovernmentwaterresourcesdepartments;

• Stategovernmentminingdepartments;

• Stategovernmentagriculture/primary

industries/forestry etc. departments;

• LocalLandcaregroups;and

• Localgovernmentengineers.

To obtain accurate estimates of losses it is important

to note that there is no substitute for site measured

data. A historical record of rainfall and streamflow

(or dam levels, releases and overflows) will enable

a hydrologist or engineer to develop much more

accurate versions of the above loss models.



Estimating Total Runoff

The total volume of runoff (saturated overland flow

and interflow) from a catchment is important when

examining overall site water balances or storage

capacities required for water supply dams etc. The

general procedure is to simply apply rainfall from

the period of interest (eg. a single storm, a typical

year or a long sequence of wet or dry years) to

the catchment, subtract the appropriate losses as

discussed previously and assume the excess rainfall

reports as runoff to a stream, dam or pond. (The

long-term processes of evaporation and seepage

losses from a storage area must also be taken into

account for long-period water balances.) The rainfall

data required is discussed in Fact Sheet No. 10:

Hydrological Data for Design Purposes. Computer

programs are available for applying long-term

daily rainfall records to a catchment, varying the

loss values to suit historical stream flows or dam

levels. These can be used for projecting catchment

yields into the future to examine water storage and

recycling opportunities. One such model gaining

popularity in Australia is the AWBM model.

Estimating Peak Flows

As discussed throughout this handbook,

interception drainage, erosion protection, settling

ponds and essential drainage infrastructure (eg.

culverts, spillways etc.) must all be carefully

designed to suit the expected peak flow

they are expected to experience. A confident

estimate of this flow is essential to:

a) prevent under designing drainage

infrastructure, which may result in damage

and hence disruptions to mine operations and

ongoing repair and upgrade works; and

b) avoid over designing, which is

of course uneconomical.

Detailed discussions of estimation procedures can be

found in AR&R. For typical mine catchments,

the best method to obtain a quick estimate is

the rational method which is of the form:

QY = 0.278. CY. Itc, Y . A (Eqn 5.1 AR&R)

where

• QY = Peak flow rate (m3/s) of average

recurrence interval (ARl) of Y years

• CY = Runoff coefficient (dimensionless)

for ARI of Y years

• A=Areaofcatchment(km2)

• Itc, Y = Average rainfall intensity (mm/h) for the

design duration of tc hours and ARI of Y years.

The way to use the rational method is as follows:

• firstdecideontheappropriaterisklevel,hence

selecting the average recurrence interval of

storm to be used (refer to Fact Sheet No.3);

• thedurationofstormtogivetheworstflood

is then selected. The principle here is that

the shorter the storm the higher the intensity

will be for a given ARI. However, if too short

a time is used then runoff from far reaches

of the catchment will not have had a chance

to contribute to the flow. Hence the critical

duration, known as the time of concentration

tc, is selected as the time required for the

most remote part of the catchment to begin

contributing to runoff at the point of interest.

Different methods for calculating tc are

presented in AR&R for various regions in

Australia. Most of these depend on stream

lengths and typical catchment slopes;

• determinetheaveragerainfallintensity

(mm/hour) associated with the selected ARI

and tc. Intensity; duration, and frequency

rainfall curves for the specific minesite will

be required. These can be developed using

guidelines in AR&R or can be obtained

through the Bureau of Meteorology.



They will simply need the longitude and latitude

of the minesite (refer to Fact Sheet No. 10);

• calculatetherunoffcoefficientforthesiteusing

the methods defined in AR&R for each region

within Australia, or if available using values

developed for your specific area and type of land

use. (Neighbouring mines, land care groups,

soil conservation departments or universities

involved in runoff management in your area may

have previously developed such coefficients); and

• measuretheplanarea(km2) of the catchment

feeding into the point of interest, taking into

account pits, diversion drains, ridges etc.

Having obtained all the above information, it can be

used in the previous equation to give the peak flow.

Probable Maximum Flows (PMF)

When designing spillways on large dams or

examining major flood mitigation works where

lives may be at risk, it is usually wise to use the

maximum possible flow rate. This will ensure that

the given element is unlikely to ever fail. Due to

the importance of such calculations, experienced

engineers or hydrologists should be consulted

before using these flows for design purposes.

Before it is possible to calculate peak flows, it is

necessary to determine the probable maximum

precipitation for the given area. For small

areas and short-duration storms the Bureau of

Meteorology has published an upgraded method

of calculating PMP in Bulletin 53 (December 1994)

The Estimation of Probable Maximum Precipitation

in Australia: Generalised Short Duration Method.

For larger areas or long storms, the Bureau will

provide estimates of PMP for a set charge.

Once the PMP is determined, small losses are applied

to determine the rainfall excess. The losses will

be small due to the high likelihood of antecedent

rainfall. It is suggested that values of zero or slightly

below the lowest specified loss values for the area

can be used. Having determined the rainfall excess,

it is then a matter of using methods as described

above, or more complex flood routing techniques

(depending on catchment size and complexity)

to determine the probable maximum flow (PMF).

Section 13.4 of AR&R gives basic descriptions

of the techniques used in such calculations.



Water management is not an exact science as rainfall is an integral part of the hydrological, and therefore the water management, cycle. Just as it is impossible to accurately predict quantities of rainfall, it is impossible to provide definitive answers to most water management questions. However, it is possible to define probabilities and risks of occurrence of particular events.

Care should be taken when communicating and interpreting probabilities and risks, and rigorous terminology should always be used. Probabilities and risks which are based on historical data carry an implicit assumption that history will repeat itself.

The following are more common risk terminologies used in water management practices. More detailed descriptions and understandings can be found in Australian Rainfall and Runoff 1987 (AR&R).

Average Recurrence Interval (ARI)

The average recurrence interval is the average interval between exceedances of that value or event when viewed in the long (ideally infinite) term.

All data above an arbitrary base value are used when ranking event values for determining the ARI. The ARI is usually expressed in years. It should be noted that, a rainfall (or flood) ARI of 100 years does not imply the event will only occur every 100 years; it is also feasible that the event will occur five times in five successive years and not occur for another 495 years. The terms “100 year return interval” and “the one-in-hundred-year-storm” falsely advocate the former interpretation.

Annual Exceedance Probability (AEP)

The annual exceedance probability is the probability of exceedance of a given event within a period of one year. It is based on data that uses only the highest event in each year of record.

The AEP is often used for the probability expressions associated with large and extreme events and some flood estimation methods. The AEP is generally expressed as a fraction or percentage.

Probability (P) of Exceedance in L Years

Probability of exceedance in L years is a descriptive risk term that relates the event exceedance probability to the design or useful life of the resource or structure. In probability terms it can be expressed as:

P = l-exp(–L/T

where T is the ARI.

Probable Maximum Precipitation (PMP)

The probable maximum precipitation refers to the greatest depth of precipitation for a given duration that is meteorologically possible for a given size storm area at a particular location at a particular time of year. The Probable Maximum Flood (PMF) has a similar definition and is related directly to the PMP (Also refer to Fact Sheet No.2.)

Due to the variable nature of the hydrological cycle, the use of risk analyses and probabilities should be encouraged in water management strategies.

Where historical data are used to determine these risks, care must be taken to include as much relevant historical data as are possible. This reduces the element of skewing in risk analyses. In this way, although absolute answers are rarely available, water management strategies may be assessed a logical and justifiable manner.

Because water management involves expressions of risk, the impacts of failure must always be assessed. Where appropriate, contingency failure strategies should be established and regularly audited and monitored.

Understanding Event Probability FA C T S H E E T N O . 3


Sensitivity analyses provide means of assigning

boundaries or limits to water management scenarios

by asking “what if...?” type questions. Sensitivity

analyses should be carried out on parameters which

are thought to be important or on those which

are not very well understood, such as hydraulic

conductivity of soil, process plant water use etc.

Where hydrological analyses are used in a water

management study, it should be clearly understood

that a large proportion of the quantitative analyses

is probabilistic only. The broad assumptions and

the extent to which historical data play a part are

documented in the industry standard AR&R. This

document should be referred to when a more detailed

understanding of event probability is required.

Understanding Event Probability FA C T S H E E T N O . 3


The basic principles behind locating and sizing an

open channel drain for normal depth flows are:

• determinethesizeofthecatchmentfeeding

into the base of the proposed section of

drain. On reasonable size catchments, it is

often worthwhile to separate the proposed

drain into sections. By doing this it may be

possible to have a smaller cross section in

the upper section of the drain which only

services the upper reaches of the catchment;

• forasuitableARI(commonly5to20yrs)

calculate the peak flow in each section of

the drain as described in Fact Sheet No.2;

• calculatetheslopeofthedrain.Ifitisnot

possible to achieve a uniform slope along the

length of the drain it should again be separated

into sections of similar average slope. (Note:

Wherever possible the slope of the drain should

be in the range of 0.5% to 1.0% or to suit local

soil conditions. This will drastically reduce the

cost of erosion control measures. It is preferable

to ‘snake’ drains down steep slopes rather than

taking the shortest possible route;) and

• havingestablishedtheflowsandslopesfor

the proposed section of drain, a cross section

size can be calculated using the Manning’s

equation (shown below) with suitable roughness

coefficients. (Note: Roughness coefficients are

determined by the type of lining there is in the

drain, ie. a smooth bare earth channel will have a

low roughness coefficient while a channel lined with

large unevenly placed rocks or dense vegetation will

have a high roughness coefficient.) A freeboard

of between 100 and 300 mm is added to the

flow depth to give the design drain depth.

Manning’s Equation:

Q = A.R2/3S1/2

n

where:

Q = Flow (m3/s)

A = Cross sectional area of flow (m2)

R = Hydraulic Radius (= A/WP)

WP = Wetted perimeter; length in m of wetted

contact between water and the channel measured

at right angles to the direction of flow

S = Slope of channel section (m/m)

n = Manning’s roughness coefficient.

Typical values of Manning’s n are:

Smooth concrete lining 0.014 - 0.018

Smooth graded earth 0.025 - 0.03

Grass cover 0.04 - 0.06

Rock lining 0.04 - 0.06

In uniform section open channels, regard for

flow and hydraulic radius should be considered

for Manning’s n (refer Chow, 1973).

Open Channel Drains FA C T S H E E T N O . 4


The best method for using this equation is to trial

different drain cross sections and flow depths

until sufficient flow capacity is achieved.

• Asaniterativeprocedurewiththeprevious

step, the type of erosion protection to be

used in the drain should be decided at this

stage. As described in Fact Sheet No.8, a

different level of protection is required as the

flow velocities increase; however the erosion

protection method will also affect the flow

velocity (Q/A) hence the need for iteration.

• Thefollowingtipsshouldbefollowed

for selecting a drain cross section:

– steep side slopes should be avoided

(2-3 H to 1 V recommended);

– the cross fall of the natural ground

will affect the actual slopes used;

– v-shape drains are recommended for minor

drains while trapezoidal shapes should be

used for large drains. The base width of a

trapezoidal drain should be sized to suit

earth moving equipment to be used;

– a contour drain should be cut into the

cross slope sufficiently to provide a

balance of cut to embankment fill; and

– embankments should be compacted to a

minimum 90% Standard Compaction.

Note: where large channels are required, expert

advice should be sought due to the potential

for backwater and downstream effects.

Open Channel Drains FA C T S H E E T N O . 4


The intent of this fact sheet is to allow the mine

operator to build small earth dams (“farm dams”)

for minor or temporary water supply or to form

part of a diversion drainage scheme. If the dam is

an important water supply or flood mitigation tool

then input from civil engineers and hydrologists

is vital. The calculation of expected catchment

yields and flood flows are covered elsewhere in

this handbook; hence this fact sheet will cover

the selection of a dam site, dam design and

dam construction. The information in this fact

sheet is collated from the text Nelson (1991).

Selecting a Dam Site

The easiest and most efficient dams involve

constructing an earth embankment across a small

valley. These are commonly known as gully dams and

will be the focus here. Other types of small dams,

including hillside dams, turkeys nest ponds and

excavated tanks, are feasible alternatives if a suitable

gully is not available, and involve many of the same

principles to be discussed. The important points to

consider when selecting a dam site are as follows:

• minesitelicenceconditionsshouldbechecked

or local water resources authorities contacted to

ensure a dam is allowable under environmental,

water use and dam safety restrictions;

• thestoragevolumeshouldbeselected

to suit the expected catchment runoff

volumes. This will prevent excessive

earthworks or an eroded spillway;

• unlessthedamisforsedimentcapturepurposes,

the upstream (u/s) catchment should not be

excessively disturbed. If this is unavoidable,

an u/s silt trap will have to be installed and

constantly maintained (ie. emptied);

• anideal site is on a flat gradient watercourse

in a wide flat-bottomed valley immediately

upstream of a narrow gorge. Sides of the

valley must remain stable when saturated

to avoid land slips into the dam;

• thefoundations for the dam must be

sufficiently strong to support the embankment

without excessive settlement and must

be impervious to seepage. Stiff inorganic

clay is ideal while sedimentary rock can be

acceptable. Fractured igneous rock or deep

layers of sand and gravel should be avoided;

• theavailability of suitable material nearby

is vital. Available quantities will determine the

type of embankment used as illustrated in the

attached table (Figure FS 5.1). Impervious

material for embankment construction should

contain 20%-30% clay with sand, silt and some

gravel. No rocks greater than 75 mm size should

be present. As a safety factor, two to three times

the expected quantities should be available; and

• a subsurface geotechnical investigation should

be carried out on favoured sites to assess the

above factors as well as groundwater levels,

cutoff trench depths and borrow pit boundaries.

The investigation should include excavated pits

along the dam centreline, spillway and in borrow

areas followed by geotechnical testing of samples.

Dam Design

Good design of the dam and spillway is vital to ensure

a stable embankment and to prevent failure due to

erosion or excessive seepage leading to piping failure.

Piping failure results from seepage water transporting

materialoutoftheembankmentcausinga‘pipe’

which rapidly expands leading to massive failure. The

basic geometric design principles for a stable dam

are illustrated in Figure FS 5.1. The following points

should also be accounted for in the dam design.

• Cutoff excavations are used to prevent

seepage under the embankment by providing a

impervious barrier linking the embankment to

Construction of Small Earth Embankment Dams FA C T S H E E T N O . 5


impervious foundation material. It must be connected

directly to the impervious embankment material

and must be keyed into suitable foundation material

as shown in the table below. If a cutoff trench is

impractical due to excessive depths, an effective

alternative where foundations are moderately

pervious is to use a clay blanket 0.6 m thick (approx.)

extended 35 m (approx.) u/s from the embankment.

• Spillway flows must be diverted away from the

downstream (d/s) toe of the embankment to

avoid erosion. A small return wall at the spillway

may be required, as shown in the figure. If

continuous small flows are expected over the

spillway it is advisable to install a trickle pipe

or a small flow channel just below the main

spillway level. This will prevent scour erosion.

• Outlet pipes are sometimes necessary to create

a gravity supply, supply a pump, drain water

for dam maintenance, satisfy legal requirements

or to allow the dam to be used as a flood flow

detention storage. If these requirements are

not applicable it is best to avoid outlet pipes.

• Freeboard is required on dams to allow

for uncertainties in flood flow estimation,

inaccuracies in construction and wave action.

The heights shown on the figure assume

a maximum 500 mm flow depth over the

spillway. If an alternative spillway arrangement

is used, the freeboard must be altered to suit.

Dam Construction

Good control of construction methods and

material condition is vital to achieve a water

tight dam. The following construction phases

and guidelines should be adopted:

• priortocommencingconstructionofthe

dam a surveyor should identify the extent of

inundation, the embankment centre line and

batter toe lines, the spillway and borrow pits;

• ensuretheproperequipment is available.

This should include scrapers and dozers for

small embankments while larger projects will

also require graders, rollers and water carts;

• ifthedamislocatedinagullyorstream

which flows regularly it will be necessary

to dewater the site. This is best achieved

using an upstream weir and a gravity drain

which bypasses the dam. Groundwater in

trenches will need to be pumped out;

• areliablewater supply is important if

the material used in the embankment

needs conditioning (ie. addition of

water to allow proper compaction);

• theareatobeinundatedbythedamwater

must generally be cleared and grubbed. This

includes removing all trees, shrubs, rocks and

any debris. This can be modified if aquatic

habitat is to be an ancillary function of the

storage. This should be burnt or pushed

downstream of the embankment. At the same

time the area under the embankment should

be cleared and have all topsoil stripped

(100 mm minimum) and stockpiled;


Suitable foundation

material (SFM)

Required penetration

depth into SFM

Width of cutoff

trench at base

Batter slopes for

excavated trench

Clay 0.6 m 2.5 m minimum 1 :1

Rock 0.3 m 0.3 m vertical


• thecutoff excavation should then be carried

out and impervious material placed and

compacted to bring the level back up to that of

the stripped foundation. The whole foundation

area is then lightly scarified (50 mm deep) in

preparation for construction of the embankment;

• borrow pits should ideally be within the area

covered by the stored water. They should

have side slopes of 3H:1V and should be

positioned a minimum of 6 m away from the

upstream toe of the dam embankment;

• embankment construction requires control of:

– the moisture content of the embankment

material when placed must generally be within

the range 3% dry to 2% wet of optimum

moisture content. This is the moisture content

which allows the maximum density to be

achieved by the compaction equipment used;

– the loose thickness of layers placed

should not exceed 100 mm if dozers

and scrapers are used for compaction

or 200 mm for sheepsfoot rollers;

– the degree of compaction achieved should be

95% Standard Compaction or 90% Modified

Compaction. This will usually require between

four and eight passes with a sheepsfoot roller;

– batter slopes should be controlled using

a template (timber triangle with the

required horizontal and vertical length

ratios ie. 3H:1V) and spirit level;

• thespillway must be constructed absolutely

level to ensure there are no preferential

flow paths which will erode. When

cutting is complete the surface should be

topsoiled, grassed and compacted;

• outlet pipes, if required:

– must only be placed in a trench cut into

natural ground or compacted embankment.

The trench should be at least 100 mm

deeper than the pipe diameter;

– between three and six cutoff collars (1.2m x

1.2m) shall be evenly spaced along the pipe

to prevent seepage of water along the pipe;

– do not place pipes at the very base of the

dam if sediment is likely to be a problem;

– it is advisable to include a trash

rack at the inlet to the pipe;

– valves should be placed at the

discharge end or in a pit on the d/s

slope of the embankment; and

• topsoil to a depth of 100 to 150 mm

minimum and good holding grass such

as kikuyu or couch should be placed over

the entire embankment (u/s and d/s) and

spillway. This should be fertilised and

irrigated if necessary to ensure rapid growth

and hence immediate erosion prevention.


Dam Element

GEOMETRIC DESIGN CRITERIA

Homogenous Zoned Dam Diaphragm Dam

HEIGHT OF DAM (m) 0-3 3-6 6-9 0-3 3-6 6-9 0-3 3-6 6-9

CREST WIDTH (m) 2.8 3.5 4 2.8 3.5 4 2.8 3.5 4

UPSTREAM BATTER SLOPE (H : V) 3:1 3:1 3.5:1 2:1 2.5:1 3:1 3:1 3:1 3.5:1

DOWNSTREAM BATTER SLOPE (H : V) 2.5:1 3:1 3:1 2:1 2.5:1 3:1 2.5:1 3:1 3:1

DIAPHRAGMTHICKNESS‘D’(m)

(Perpendicular to dam face)

0.6 0.85 1.1

FREEBOARD (m) : FETCH < 1000 m 1.0 m - Assuming 0.5 m maximum spillover depth

FETCH > 1000 m 1.5 m - Assuming 0.5 m maximum spillover depth

SETTLEMENT ALLOWANCE (mm) (Construction level above required crest level)

150 300 500 150 300 500 150 300 500



F I G U R E F S 5 . 1



SPILLWAY DESIGN

FLOOD FLOW MINIMUM INLET WIDTH

MINIMUM OUTLET WIDTH (m) (Various Return Slopes.)

(m3/s) (m) <5% 5-10% 10-15% 15-20% 20-25%

3 5.5 6.5 10 15 18 20

6 11 13 21 30 35 40

9 16.5 19 31 44 53 60

12 22 26 41 59 70 80

15 27.5 33 52 74 87 100

CONSTRUCTION MATERIAL (in order of preference)

CODE DESCRIPTION

GC Clayey gravels

SC Clayey sands

CL Inorganic clays (Low liquid limit)

CH Inorganic clays (High liquid limit.)

GW Well graded gravels.

GP Poorly graded gravels

SW Well graded sands

SP Poorly graded sands


Culverts are commonly used to provide road

crossings over drains or small creeks, and there is

a wide variety of culvert shapes and materials that

can be selected to best suit a particular application.

The correct design and installation of these culvert

crossings will prevent blocked or eroded drainage

channels as well as costly road repairs. There are

a number of areas that need to be addressed.

Flow Capacity

The first and perhaps most obvious concern is to

construct a culvert which is large enough to pass

the design flow without overtopping the road or

embankment. It is not practical to design culverts

to take all possible flows; hence the designer must

decide what risk level is acceptable for overtopping

of the road and calculate a design flow of a suitable

ARI (refer to Fact Sheet Nos 2 and 3). A culvert

installation must then be sized to pass this flow. The

hydraulics of culverts are surprisingly complex and

rely greatly on the site conditions (ie. downstream

flow depths, culvert sizes, shapes, lengths and

slopes). It is not feasible to cover all possibilities

in this handbook; however suppliers of culverts,

State government roads departments, and many

open channel hydraulics text books provide charts

for determining the flow through various culverts.

The basic controlling factors are as follows:

• inlet/outlet control: a culvert which is able

to pass water at a greater rate than is being

supplied is said to be flowing with inlet control.

If the culvert inlet geometry, flow resistance

or depth of water in the downstream channel

result in water being supplied at a greater

rate than it can flow through the culvert, it

is said to be under outlet control. When using

design charts it is important to examine both

control cases and adopt the worst case value

(ie. the highest headwater or least flow);

• headwater: the greater the level of water at the

inlet to a culvert compared to the outlet, the

greater flow it will pass. It is generally acceptable

to design culverts to flow with water up to a

level just below overtopping of the road (ie.

300 mm to 1.0 m), for the design peak flow;

• downstream depth: in contrast to the upstream

depth, the normal depth of flow immediately

downstream from the culvert should be kept as

low as possible to maximise the efficiency of the

culvert. To achieve this a deep or wide channel

is advisable downstream of the culvert; and

• inlet design: the design of the inlet can greatly

affect the flow capacity of a culvert flowing under

inlet control. Greater flow can be achieved be

shaping the approach to the culvert to funnel

flow into the culvert. If the water entering

the culvert has a high suspended solids load,

it is important to keep this water moving

through the culvert. Any ponding at the inlet

will inevitably result in the culvert becoming

blocked. To avoid this, drops or chutes can be

utilised to accelerate flow into the culvert.

Inlet/Outlet Protection

Flows forced through culverts with a high head

water will accelerate into the pipe and can discharge

at a high velocity. High levels of turbulence will also

result from water spreading out into basic channel

flow again. To ensure that this high energy flow

does not cause massive erosion at the inlet and

outlet and under scour of the pipe it is important to

provide erosion protection. This is usually achieved

with headwalls and aprons of reinforced concrete,

a concrete revetment mattress or grouted rock. At

the downstream end, rock Rip Rap is also advisable

for a further distance downstream from the apron.

The level of protection required will depend on the

outlet velocity, as described in Fact Sheet N0. 8.

Culvert Crossings FA C T S H E E T N O . 6


This will normally form part of the

above hydraulic calculations.

Installation

Correct selection of culverts and supervised

installation is vital to ensure that heavy vehicles

passing over will not damage the culvert. Depending

on the culvert material and shape selected, there

will be varying requirements for cover (fill depth)

over the culvert and compaction requirements

around the culvert. Concrete culverts rely on their

own strength and require good foundations and

substantial cover, while corrugated steel culverts

rely on the strength of the fill around them and

hence require very good compaction in the side

zones. Numerous Australian Standards, as well as

material supplied by manufacturers, give excellent

advice on correct installation. One important factor

to note is that many mine vehicle axle loadings

will exceed standard highway values and hence

special care must be taken when selecting the

class of culvert (ie. wall thickness) required.

Culvert Crossings FA C T S H E E T N O . 6


Acid drainage occurs when sulphides (usually

iron sulphides) are oxidised according to the

following, highly simplified, equation:

FeS2 + xO2 + yH2O –> Fe(OH)3 + 2H2SO4.

The process is bacterially mediated and temperature

and moisture all affect the rate and expression of

the problem. However, the neutralising capacity

of the gangue is probably the most significant

factor in reducing or preventing the formation

of acid drainage. The geochemical reactions

and indicators of sulphide oxidation and acid

generation are shown in Figure FS 7.1.

In addition to the generation of acid, the

low pH of these waters can mobilise trace

and heavy metals, resulting in the potential

for widespread contamination.

There are many techniques available to foresee if

acid drainage is likely to be a problem, including:

• chemicalprediction/materialscharacterisation

(NAPP, ANC, NAG, solution indicators);

• models(eg.forlocationofacidgenerating

material in a model of the orebody and

waste, rates of acid generation, timing of

appearance in mining schedule, predictions

and schedule of cost of treatment); and

• predictionsofecologicalimpacts.

Once acid drainage is present, opportunities

to manage it are limited to:

•preventionofthegenerationofacid:

– separate the acid producers

(for sale or entombing);

– cut off oxygen (wet or dry covers);

– pacify the mineral surface;

– solidify the waste rock or waste rock mass; and

– minimise water movement (generation

and transport of acid); and/or

• treatmentofaciddrainage:

– lime or alkali treatment of the drainage; blend

solids with alkaline material eg. limestone;

– use bacteria for sulphide precipitation;

– use plants to uptake and store

metals, eg. wetlands; and

– use concentration/recovery

process, eg. cementation.

Considerable work has been undertaken around the

world and the status and outlook for key control

technologies are summarised in Table FS 7.1.

In high rainfall environments, the volumes of

contaminated water that are generated can be

extremely difficult and costly to contain and/or treat.

This potentially ongoing, long-term cost should

be factored in to any development decision.

Acid Drainage FA C T S H E E T N O . 7


Note 1: Non ferrous metal sulphides such as CuS, PbS, NiS, ZnS are acid neutral. Sulphides such as Cu2S are acid consuming.

Note 2: Siderite (FeCO3) is not included since it has nil net neutralising capacity in an oxidising environment.

Note 3: pH of site drainage may initially increase in response to sulphide oxidation and acid neutralization reactions.

Note 4: Other precipitates such as CuCO3, MnO

2, CuSO

4 can also be observed over a wide pH range.

Note 5: Jarosite iron oxide/hydroxide equilibria is a strong pH buffer and can maintain the pH as 3 even after all pyrite has

been oxidised. Jarosite and iron oxides coat soil mineral surfaces and dominate the mineral solution chemistry.


ENVIRONMENTAL GEOCHEMISTRY INTERNATIONAL PTY LTD



TABLE FS 7.1: Status and Outlook for Key Control Technologies

Technology Applicable Current status Research outlook Major limits

Chemical prediction All Inexact Good Costly

Prediction models All Incomplete Good Complex

Pre-treatment Some Beginning Good Site specific

Dry covers Many Field demonstration Very good Cost

Wet covers Many Laboratory/Field Very good Site specific

Fixation Selected Laboratory Fair Cost

Lime neutralisation All In practice Excellent Perpetual

Sludge disposal All Emerging Good Volume/

Containment

Bio-treatment Partial Laboratory/Pilot Fair Capability/

Efficiency

Metal recovery Selected Laboratory/Pilot Poor Economics


Minimising erosion and capturing sediment

contained in surface runoff is a major environmental

issue on minesites. Site discharge licences will

normally specify a suspended solids limit for

discharge offsite from a storm of a given risk level

(eg. a 5 year Average Recurrence Interval).

There are four main control options and an effective

site program will need to incorporate all of these.

• Minimising disturbance and rapid

revegetation of disturbed areas:

Mining by its very nature involves disruption

of natural vegetation and soils. This results

in a huge increase in erosion potential

and sediment transport. The impact of

such areas can be minimised by better

planning of clearing and rehabilitation to

ensure that the minimum possible area

of soil is left unprotected at any time.

• Drainage control: Water erosion is increased

when concentrated flows pass over unprotected

or steep sloping ground. A properly designed

and maintained drainage system will avoid

this occurring. The most important principles

are to divert uncontaminated drainage

away from erosion prone areas, and to

control flows by using properly constructed

drains at gentle grades as discussed in the

fact sheet concerning drainage design.

• Erosion control: The best method for controlling

erosion is to prevent its occurrence. Methods

for preventing erosion are discussed below.

• Sediment containment: In areas where erosion

prevention is not feasible it is necessary to trap

the suspended sediment before the water passes

offsite. In-stream sediment traps can be used

along the drainage path to remove the bulk

of the solids, however, constructed sediment

retentionpondsmaybenecessaryto‘polish’

the water immediately prior to discharge.

Containment methods are discussed below.

Erosion Control Methods

The prevention of erosion is achieved by protecting

soils from the erosive forces of water and/or by

controlling the flow of water to reduce erosive forces.

Large areas subject to sheet runoff

should be protected as follows.

• Contour ripping: Bare or newly revegetated

areas should be cross contoured to

slow down flows. This will also prevent

concentrated flow paths from forming.

An added benefit of this technique is the

retention of water stored in the furrows

which will aid the growth of new vegetation

and will reduce total quantities of runoff.

• Grassing as described above is the most

effective large-scale method. If moderate

slopes and suitable topsoil are provided

such that good growth occurs, this will

effectively protect soils against sheet runoff

from very heavy and intense storms.

• Surface covers: Steep slopes such as creek banks

or cut and fill batters are hard to revegetate

due to the difficulties in keeping topsoil and

seeds etc. in place. Layers of jute, geosynthetics

or mulch are very effective in protecting these

layers until the root system of the grass has

developed. These layers must be securely

fastened with pegs and the upslope layer must

overlap the top edge of the downslope layer.

Drains or gullies subject to concentrated flows

can be protected using the following techniques.

• Grassing: (reference Chow 1973) Having grass

lining in a channel will significantly retard the

flow and hence reduce the velocity and erosion

potential. Grass will also stablise the channel

consolidate the soil and check the movement of

sediment along the channel bed. The selection

Erosion Control and Sediment Containment FA C T S H E E T N O . 8


of grass should be “fine and uniformly distributed

sod-forming grasses” where the main flow occurs.

The use of bunch grasses should be avoided in

drains because they will channelise the flow creating

scour lines. Grassing can also be used successfully

in combination with rock fill to provide a very

stable and well interlocked matrix. In establishing

a grass cover in drains it is important to:

– ensure there is a mixture of fast and

slow germinating varieties to ensure

immediate and long-term protection;

– irrigation should be provided as necessary

to ensure good germination if the seed is

planted outside the wet season (usually

the ideal time to build drains);

– provide adequate protection for the seed

if flow is likely in the drain immediately

after construction. (This can be achieved

using degradable natural fibre type covers

which stabilise the surface and allow the

grass to grow up through the fabric); and

– when laying topsoil on drain batters prior

to seeding, tyne the batters parallel to the

direction of flow in the drain. This will

result in long furrows along the drain which

will both retain water and help to prevent

scour paths down the batter slopes.

• Rip rap lining: Rip rap simply refers to a lining

of large rock placed in the drain to armour the

natural ground against erosion. The rock is

sized to ensure its stability during the peak flow

conditions. Size of the rock is based on the flow

depth and velocity. Rip rap should be carefully

machine placed to ensure that a uniform

‘mattress’ofinterlockingrockisachieved.This

is very important to ensure that the rock does

not get displaced during early flows before silt

and grass fill the spaces between rocks thereby

locking them in position. The following points

should be noted when installing rip rap:

– batter slopes steeper than 2.5 H to 1.0 V will

not reliably support rip rap;

– a layer of medium-weight geofabric should

be placed under all rip rap to prevent scour

of the soil. (Due to the rough nature of rip

rap which retards the flow, there will be

much turbulence around the rocks which

can easily result in under scour beneath

the rocks making them unstable)

– a uniform grading of rock size (ie. a good

range from small to big rocks) is vital to

create a good interlocking mattress;

– if rip rap is used on steep drops it must

be carried a short distance into the flatter

sections preceding and following the drop.

• Reno mattresses/gabions: Reno mattress or

gabion lining is a form of rock lining where a

low-profile wire cage is used to hold the rock in

place. This enables the use of smaller diameter

rocks but requires more careful placement.

Mattresses are available in thicknesses of

approximately 170 mm, 250 mm, 300 mm and

500 mm. This type of protection can be used

where very high velocities or extremely turbulent

conditions are expected. This may occur on

very steep slopes (when very large rip rap is not

available or not preferred), at culvert outlets, or

at the base of drops. Reno mattresses are also

aesthetically pleasing and may provide a good

alternative to rip rap in highly visible areas.

• Concrete filled ‘revetment’ mattress:

Revetment is also a form of hard armouring,

utilising a pocketed pervious fabric with

concrete pumped through it. This creates a

solid layer moulded to the shape of the natural

ground below. Small penetrations between

the pockets allow for drainage of subsurface

water preventing any lifting pressures. As

with Reno mattresses this type of protection

can be used where very high velocities or

extremely turbulent conditions are expected.



This may occur on very steep slopes (when very

large rip rap is not available or not preferred),

at retention dam inlets and spillways, at culvert

outlets, or at the base of drops. With good

preparation of the base, revetment will provide

a very neat and durable protective layer.

• Bottomsills:Insmallsteepdrainswhere

continuous minor erosion is likely, bottom

sills can effectively prevent the propagation of

deep scour gullies. Concrete or gabion barriers

are set into the base of the drain such that

scouring will only occur until a stable slope

is formed between sills (see Figure FS 8.l).

• Corrugatedsteelchutes:Insituationswherean

intercept drain or a gully at the top of a cutting

must drop down a very steep slope into a drain

below running in a perpendicular direction it is

advisable to create a lined chute down the slope.

This will prevent large scour gullies forming. A

simple method of lining such chutes is to use

half round corrugated steel pipes. These should

be lapped at the ends of each pipe section with

the upstream section on top. The pipe sections

canbeheldinplacebyeitherusing‘tentpeg’

style posts or by providing a small concrete

beam down each edge. It should be noted that

steel chutes will eventually rust out and are

therefore suitable only for medium term projects.

In-stream Sediment Containment

Fast flowing surface runoff with a heavy load

of suspended solids can cause major problems

downstream by clogging culverts, blocking inlets or

causing short-circuiting through sediment retention

ponds etc. The solution is to have a number of

in-stream sediment traps along the drainage path.

• Sedimentbarriers/filterdamsplacedacross

the drainage channel with rock protection

downstream will trap heavy suspended solids

as well as providing effective scour protection.

The important feature of these barriers is that

they should be semi-impermeable to water.

This will cause water to pond behind them

and hence silt will settle out of suspension and

build up behind the barriers such that steps

are formed in the channel floor. These barriers

are positioned so that the final slope between

the toe of one step and the top of the next is

approximately 0.5%–1%. The rock downstream

protects the channel from scour at the base of



the drops while the flow velocity between the

drops is reduced enough to prevent erosion. These

structures are effective and economical at drain

slopes up to 3%-4% and can be formed from either

timber, gabions, or graded rock (see Figure FS 8.2).

Points to keep in mind are:

– as well as being required downstream,

rock protection is required upstream of

the barriers for a short distance. This is

to prevent scour around the edge of the

barriers which may occur from the highly

turbulent water spilling over the drop;

– rock protection is also required up the

batter slopes in the vicinity of the barrier.

This will prevent side scour as the water

spills over; fabric must be placed under

the downstream rock to ensure the

underlying soil is not washed out;

– the downstream rock must be cut in, such

that the top of the rock is level with the

natural drain surface, to ensure that another

step is not induced at the end of the rock

apron; and the lowest section of the barrier

crest should be over the drain centre line

such that low flows are preferentially

directed away from the drain edges.

• Silt fences: In areas where flow is not

channelised but carries a high sediment

load it is possible to filter out the suspended

solids using a silt or sediment fence. This

may be desirable during the construction

of roads, at the base of stockpiles, or along

the length of natural watercourses which

receive sheet flow off disturbed areas. There

are many proprietary brand sediment fences

available today which only require posts to be

supplied and have their own ties and support

bands (usually marketed by suppliers of civil

products or geotextiles) (see Figure FS 8.3).

• Vegetation strips: An alternative to silt fences

for capturing silt in sheet flow is to pass the

water through heavily grassed strips. These can

ideally be placed adjacent to catch drains or

road edge drains. An advantage of a vegetation

strip is that as the sediment builds up the grass

grows up through it. Detailed information

on the design and effectiveness of vegetative

filter strips can be found in Haan (1994).



Sediment Removal Ponds

Surface runoff with levels of suspended solids

higher than licence levels will need to be

intercepted and treated prior to discharge offsite.

• Sediment settling ponds: These are the

most common method for settling out solids.

Usually positioned immediately upstream

of a monitored discharge point they also

provide a useful location for controlling

other water pollution problems such as pH,

BOD etc. and may also be used as a storage

for recycling water. For optimum removal

of sediment these pond systems should

address the following design issues:

– the length to width ratio should

be approximately 3:1;

– the inlet and discharge point shall be

positioned to ensure the maximum flow

length between them. Baffles should be used

if necessary to prevent short circuiting. It is

beneficial to have two successive cells. The

first cell can then be free draining and hence

provide flood detention as well as capturing

the bulk of the coarse sediment. The second

cell is then a polishing and treatment pond

for sediment and other quality parameters.

Ideally the second pond should also be

drained in a controlled manner after each

runoff event, however it can be left full as a

water storage facility. The draining should

preferentially take water from the surface

of the pond near the outlet end or should

slowly discharge water through slotted

riser pipes or rock/sand filters; and

– a volume over and above that required

for efficient pond operation must be

incorporated for storage of sediment.

A mechanism for completely draining the pond, and

access into and around the pond must be provided

for periodic removal of captured sediment.

There are many methods for designing sediment

ponds. A good rule of thumb is the CALM

method as developed by the NSW Department

of Conservation and Land Management.



• Wetlands for sediment removal: The use

of artificial wetlands to improve storm water

quality is becoming increasingly popular.

The sediment removal efficiency of wetlands

is known to be high; however in a mining

environment care must be taken that excessive

sediment loads are not imposed on the wetland

plants and that water is always available. The

design of artificial wetlands requires much care

and consideration in the following areas:

– the hydraulics of flow through

dense vegetation;

– the selection of plants. The common

approach is to use emergent macrophytes

such as reeds or bulrushes that are common

to the area. These plants are fast growing

and tolerant of high pollution loads and

some fluctuation of water levels;

– supply of water to plants, especially when

young. Wetland plants rely on a saturated

base but must not be drowned (short periods

of total inundation are tolerable); and

– spread of plants. The plants most effective

for use in wetlands are typically invasive

species that will take over existing wetland

areas if given the opportunity. Deep water

should be used to keep open ponds

clear of the plants, and great care must

be taken to prevent spreading if fragile

wetland ecosystems exist in the area.



Bioremediation is a process which relies on

micro-organisms to break down and detoxify

organic chemicals such as hydrocarbons, and

some organo-chlorines. Carbon dioxide and

water are the final degradation products for

hydrocarbon wastes using this process.

Bioremediation has a number of applications

within the mining industry; including the

treatment of the following types of wastes:

• oilysludges;

• hydrocarboncontaminatedeffluent(eg.

heavy equipment washdown pads);

• hydrocarboncontaminatedsoils;

• specificlowvolumeoilspillages;and

• workshopandpowerstationliquidwastes.

Within Australia, bioremediation is being used

as a cost-effective alternative for the treatment

of wastewater effluent and hydrocarbon

contaminated soils. Most applications involve

theconstructionofa‘bioremediationpad’,and

implementing the process known as landfarming.

Landfarming involves the spreading of wastes

(usually about 30 cm thick) over the ground

to enhance the natural degradation process.

This procedure involves the use of soil micro-

organisms, water or effluent application, nutrients

(usually fertiliser) and oxygen (air). This technique

is highly suited to minesites in arid regions,

due to the higher degradation rates that can be

achieved with high air and soil temperatures.

Prior to commitment to this technology, the soil

and effluent stream need to be assessed by a

suitably qualified laboratory for the following:

• soiltype(particlesizeanalysis,

organic content, etc.);

• thelevelofactivityofhydrocarbondegrading

microbes (ie. C17: pristane ratio);

• thenutrientstatusofthematerialtobedegraded;

• themoisturecontent;and

• concentrationofspecifichydrocarbonfractions.

In the event that insufficient numbers or

incorrect species are present, then the waste

stream can be inoculated with microbes that

are grown within an on-site bioreactor.

Bioremediation Technology FA C T S H E E T N O . 9

Design Process Peak Flows

Hydro- graph

Analysis

Water Balance

Water Storage

Pollutant Dispersion

Tailings Storage

Wetlands Waste- water

Disposal Hydrological Data Format

Rainfall

•IntensityFrequency-

Duration curves (IFD Curves)

(see Figure FS 10.1) ✓ ✓ ✓

•Rainfallpatterns

(Hyetographs) ✓

•DailyRainfall ✓ ✓ ✓ ✓ ✓

•MonthlyandSeasonal

Rainfall ✓ ✓

•AnnualRainfall ✓ ✓

•ContinuousRainfall

(minutes) ✓

Streamflow

•ContinuousFlow ✓ ✓ ✓ ✓ ✓

•DailyFlow ✓ ✓ ✓ ✓ ✓ ✓

•MonthlyandSeasonalFlow ✓ ✓

•AnnualFlow ✓ ✓

Evaporation

•Daily ✓ ✓ ✓ ✓

•Monthly ✓ ✓

•Annual ✓ ✓


There are various formats for hydrological data

to suit both design and reporting outputs. The

reporting formats may be tabulated or graphed

with time frames to suit the receiver of the report.

Design formats will depend upon the design

process for which the data is to be utilised.

The following table presents the various

data formats and the principal design

processes for which they may be utilised.

Hydrological Data for Design Purposes FA C T S H E E T N O . 1 0


Hydrological Data for Design Purposes FA C T S H E E T N O . 1 0


Groundwater is the generic term identifying water

resources which are resident in soil or rock pores

and matrices. By far the major proportion of

groundwater resides under positive pore pressures

within aquifers, but some water lies in the interstices

between ground surface and the aquifer within

the capillary zone. Aquifers are generally fully

saturated, whereas the capillary zone contains a

significant proportion of air as well as water.

Aquifers may be confined (pressurised between layers

of relatively impermeable ground or aquicludes), or

unconfined (a water table aquifer with a phreatic

or‘free’surface).Inbothcases,theflowdynamics

are similar in that flow is generated by differences in

pressure from one point to another. A perched water

table is a special type of unconfined aquifer which

may exist within another unconfined aquifer, and is

‘perched’onathinimpermeablelenssuchasclay.

Flow in aquifers is generally laminar, or seepage

flow. In some cases where preferential flow paths

may exist (eg. permeable faults and fractures in rock),

turbulent flow may be generated. Flow in aquifers

is always from a region of higher pressure or higher

potential energy to a region of lower potential energy.

Most aquifers are interconnected, and it is

very rare that a single aquifer will exist in

isolation. Connections between aquifers may

be weak or strong depending on the porous

media and the geological stratification.

The single intrinsic soil or rock parameter that

determines the characteristics of groundwater flow

is the hydraulic conductivity. This is often (and

strictly incorrectly) referred to as the permeability.

The hydraulic conductivity is a quantitative

measure of the velocity of seepage flow of water

reached whilst being generated by a unit pressure

gradient. Hydraulic conductivity may vary in space

(heterogeneous porous media) as well as in the

direction of flow (anisotropic porous media).

A homogeneous and isotropic groundwater regime

is an ideal saturation that rarely occurs in nature.

Groundwater, while recognised as a separate entity

in the hydrologic cycle, is nevertheless strongly

interactive with other components of the hydrologic

cycle such as rain, rivers, lakes and oceans. Although

the time scale of processes in groundwater is

long because of the laminar nature of flow, its

interaction with surface water components of the

hydrologic cycle should always be considered.

Groundwater FA C T S H E E T N O . 1 1


Numerical modelling is the process of solving the

equations describing a physical process using a

step-wise approximation. Solutions are obtained

by performing iterations (successively improved

approximations) at each step until the numerical

answer satisfies all the equations being used.

The approximation is improved by decreasing

the size of the steps, much like drawing a curve

using a series of short, straight lines. Decreasing

step size, however, increases the amount of labour.

With the rapid advances in computer processing

speed, this is becoming less of a concern.

The advantage of numerical modelling is that,

once the model is set up and established, a range

of scenarios may be investigated with relatively

little effort, and complex problems may be solved

using numerical models. Nevertheless, numerical

models should be viewed with caution as their

complexityandtheir‘blackbox’appearancemay

promote errors of judgement in their application.

Numerical models were developed in the early

1960s and are now well established tools. Finite

difference (FD) and finite element (FE) models are

currently popular. These subdivide the physical

area of interest into small fragments which are

each treated in a simplified manner. FE models

are more adaptable to complicated boundaries,

but the methods of solution are slightly more

complex than FD models. Other models which have

limited use are boundary integral and method-of-

characteristics formulations, but these presently lack

the practical applicability of FD and FE methods.

Numerical models may be applied to a wide

range of problems in hydrology, flood flow and

groundwater flow. In recent times, advances in the

understanding of contaminant transport, sediment

transport and complex boundary conditions have

resulted in a generation of problem-specific models.

Before choosing a model, its applicability to a

specific problem must be questioned in depth.

Theprocessof‘calibration’andverificationisan

integral part of numerical modelling. Because

a numerical model may operate using several

parameters describing the physical processes (eg.

frictional stresses, soil-water conductivity) a historical

event for which cause-and-effect data exists should

always be simulated. This allows the modeller to

‘tune’theparametersagainstanobservedevent.

The complexity of the model chosen should

realistically reflect the extent to which the relevant

parameters may be measured or inferred with

accuracy, as well as required accuracy of modelled

answers in a particular project. The sensitivity of

the model to prime parameters should always be

investigated and quantified. The use of models as

decision making tools often have greater value in

sensitivity analysis than in absolute predictions.

The applicability of simpler (one dimensional)

models should be investigated first before adopting

complex (eg. three dimensional) models under

the philosophy that complicated models have a

greater opportunity for errors, both judgemental

and numerical. Finally, the limitations of the

model should always be clearly understood.

Numerical Modelling FA C T S H E E T N O . 1 2

24973985 minesite water management handbook

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