Eff Guide
Eff Guide
Eff Guide
Published by:
Department of Environment and Conservation (NSW)
59–61 Goulburn Street Sydney
PO Box A290
Sydney South 1232
Phone: (02) 9995 5000 (switchboard)
Phone: 131 555 (information & publications requests)
TTY: (02) 9211 4723
Fax: (02) 9995 5999
Email: info@environment.nsw.gov.au
Website: www.environment.nsw.gov.au
Bob Debus
Minister for the Environment
Contents
Foreword ...................................................................................................................iii
Figures and Tables .............................................................................................................viii
Symbols and Abbreviations................................................................................................ix
Executive Summary ...............................................................................................................x
1. Introduction................................................................................................................1
1.1 Purpose and scope ...........................................................................................................1
Application of this Guideline....................................................................................................... 2
Related documents ........................................................................................................................ 3
1.2 Environmental performance objectives........................................................................4
1.3 Uses of effluent in irrigation...........................................................................................5
1.4 Guidance............................................................................................................................5
1.5 How this Guideline is organised...................................................................................6
1.6 Procedure checklist for establishing a system.............................................................6
Planning........................................................................................................................................... 6
Site selection.................................................................................................................................... 6
Design .............................................................................................................................................. 6
Statutory requirements ................................................................................................................. 7
Installation....................................................................................................................................... 7
Operation and maintenance......................................................................................................... 7
2. Site Considerations...................................................................................................8
2.1 Land use conflicts.............................................................................................................8
2.2 Selecting the site ...............................................................................................................8
Climate............................................................................................................................................. 8
Preliminary investigations............................................................................................................ 8
Detailed soil investigations........................................................................................................... 9
2.3 Soil properties.................................................................................................................10
Soil sodicity ................................................................................................................................... 10
Soil salinity .................................................................................................................................... 10
Saturated hydraulic conductivity.............................................................................................. 11
Available water holding capacity.............................................................................................. 11
Soil pH ........................................................................................................................................... 11
Cation exchange capacity and exchangeable cations............................................................. 11
Emerson Aggregate Test (EAT)................................................................................................. 12
Soil phosphorus adsorption ....................................................................................................... 12
2.4 Soil organic matter .........................................................................................................13
2.5 Acid sulfate soils ............................................................................................................13
2.6 Groundwater ..................................................................................................................15
Groundwater vulnerability ........................................................................................................ 15
2.7 Surface water ..................................................................................................................16
2.8 Flood potential................................................................................................................17
iv
3. Effluent Quality and Irrigation Considerations................................................18
3.1 Classification of effluent for environmental management......................................18
3.2 Organic content ..............................................................................................................20
3.3 Solids................................................................................................................................20
3.4 Nutrients..........................................................................................................................21
Nitrogen......................................................................................................................................... 21
Phosphorus ................................................................................................................................... 22
Potassium ...................................................................................................................................... 23
3.5 pH .....................................................................................................................................23
3.6 Chemical contaminants.................................................................................................23
Metals............................................................................................................................................. 24
Synthetic organic compounds.................................................................................................... 25
Herbicides ..................................................................................................................................... 26
3.7 Mineral salts....................................................................................................................26
3.8 Specific ions.....................................................................................................................28
Sodium........................................................................................................................................... 28
Chloride and chlorine.................................................................................................................. 29
Alkalinity....................................................................................................................................... 30
Bicarbonate.................................................................................................................................... 30
Boron.............................................................................................................................................. 30
Fluoride.......................................................................................................................................... 30
3.9 Oil and grease.................................................................................................................31
3.10 Treatment and disinfection ..........................................................................................31
Municipal sewage effluent ......................................................................................................... 32
Other effluent types ..................................................................................................................... 32
3.11 Other factors....................................................................................................................33
4. Design Considerations...........................................................................................34
Licensing considerations in the design process......................................................................34
Load-based licensing ..................................................................................................................34
The use of models in design ......................................................................................................35
Other design considerations....................................................................................................... 35
4.1 Calculating land area and storage requirements......................................................35
Full reuse schemes ....................................................................................................................... 35
Partial reuse schemes................................................................................................................... 36
4.2 The water balance ..........................................................................................................36
Precipitation.................................................................................................................................. 36
Effluent applied............................................................................................................................ 37
Evapotranspiration ...................................................................................................................... 37
Percolation..................................................................................................................................... 38
Runoff ............................................................................................................................................ 39
Effluent storage............................................................................................................................. 39
4.3 Nutrient loading rates ...................................................................................................40
Nitrogen balance .......................................................................................................................... 42
Phosphorus compounds ............................................................................................................. 44
Nutrient imbalances .................................................................................................................... 47
v
4.4 Salinity control and salt balances ................................................................................48
Soil salinity and plant growth.................................................................................................... 48
4.5 Organic Loading Rates..................................................................................................51
4.6 Heavy metals and persistent organic chemicals.......................................................51
Herbicides ..................................................................................................................................... 55
4.7 Models .............................................................................................................................55
The DEC model ............................................................................................................................ 57
4.8 Plant selection and land use.........................................................................................58
4.9 Erosion control................................................................................................................58
4.10 Separation distances and management of buffer zones ..........................................58
4.11 Irrigation..........................................................................................................................62
Methods......................................................................................................................................... 62
Suitable irrigation areas .............................................................................................................. 63
Irrigation scheduling ................................................................................................................... 63
Storage management................................................................................................................... 64
5. Operation and Management Considerations.....................................................65
5.1 Site management plans .................................................................................................65
5.2 Control systems..............................................................................................................66
5.3 Monitoring systems .......................................................................................................67
Frequency of sampling................................................................................................................ 68
Effluent .......................................................................................................................................... 69
Soil .................................................................................................................................................. 70
Surface waters............................................................................................................................... 72
Groundwater ................................................................................................................................ 73
Plants.............................................................................................................................................. 73
Animals.......................................................................................................................................... 74
5.4 Tailwater and stormwater runoff control ..................................................................74
Uncontaminated runoff diversion............................................................................................. 74
Contaminated runoff collection................................................................................................. 74
5.5 Site access ........................................................................................................................75
5.6 Occupational health and safety issues........................................................................76
5.7 Plant and animal health ................................................................................................76
5.8 Reporting on scheme performance .............................................................................78
5.9 Transfer of effluent to other users ...............................................................................78
6. Statutory Requirements .........................................................................................79
6.1 Environment Protection Licences................................................................................79
Background................................................................................................................................... 79
When is a licence required?........................................................................................................ 80
Assessing a licence application .................................................................................................. 81
Information to be included when applying for a licence....................................................... 82
Licence conditions........................................................................................................................ 86
6.2 Environmental offences ................................................................................................86
vi
6.3 Development consent....................................................................................................86
Part 4 of the EP&A Act................................................................................................................ 87
Integrated development assessment (IDA) ............................................................................. 87
Part 5 of the EP&A Act................................................................................................................ 87
Examples ....................................................................................................................................... 88
6.4 Other statutory requirements ......................................................................................89
Sewerage schemes managed by local government ................................................................ 89
Activities within national parks................................................................................................. 89
Threatened species....................................................................................................................... 89
Protection of drinking water supplies ...................................................................................... 90
Animals to abattoirs..................................................................................................................... 90
Pure food legislation.................................................................................................................... 91
Australian and New Zealand Joint Food Standards Code.................................................... 91
7. References and Further Reading ..........................................................................92
7.1 References........................................................................................................................92
7.2 Further reading...............................................................................................................95
Soils, site suitability and planning............................................................................................. 95
Plant water and nutrient requirements .................................................................................... 95
Sewage effluent ............................................................................................................................ 95
Other .............................................................................................................................................. 95
Glossary .................................................................................................................................97
Appendix 1: Guidelines for the Use of Reclaimed Water from
Municipal Sewage Treatment Plants...............................................105
Appendix 2: Load-based Licensing .........................................................................108
Appendix 3: Soil Texture Factors for Soil Salinity Measurement .....................109
Appendix 4: The Effluent Reuse Irrigation Model (ERIM)................................110
Model description .....................................................................................................................110
Model assumptions...................................................................................................................111
Decisions .....................................................................................................................................111
Modelling method ..................................................................................................................... 111
Model time step.......................................................................................................................... 112
Percolation................................................................................................................................... 113
Capacity independent solution method................................................................................. 113
Crop factors................................................................................................................................. 114
Rainfall runoff and terminal pond sizing............................................................................... 114
Evaporation, rainfall and the storage pond ........................................................................... 114
Discounting rainfall for tree canopy interception................................................................. 115
Discounting irrigation for spray misting................................................................................ 115
Wet weather augmented flows................................................................................................ 115
Method of characterising schemes .......................................................................................... 116
Precautionary discharges.......................................................................................................... 116
Formal model specification ...................................................................................................... 117
Appendix 5: Government Agency Roles ................................................................119
Appendix 6: Department of Environment and Conservation Offices ..............121
vii
Figures and Tables
Table 2.1: Landform requirements for effluent irrigation systems.................................13
Table 2.2: Typical soil characteristics for effluent irrigation systems.............................14
Table 3.1: Classification of effluent for environmental management ............................19
Table 3.2: Mineralisation of organic nitrogen in wastewater sludge
and effluent in soil ................................................................................................22
Table 3.3: Trigger values for metals in irrigation effluent
for long term use on all soil types (up to 100 years) .......................................25
Table 3.4: General irrigation water salinity ratings
based on electrical conductivity .........................................................................27
Figure 3.1: Relationship between SAR and EC of irrigation water
for prediction of soil structural stability............................................................29
Table 4.1: Crop factors for some crops, trees and pasture................................................37
Table 4.2: Yield and nutrient content of crops in NSW
for cultivation under irrigation with effluent...................................................41
Table 4.3: Phosphorus adsorption potential of NSW soils (1m depth)..........................47
Table 4.4: Yield reduction of crops due to soil salinity.....................................................49
Table 4.5: Yield reduction of trees due to soil salinity ......................................................50
Table 4.6: Maximum permitted topsoil concentration
for chemical contaminants ..................................................................................53
Table 4.7: Concentrations of herbicides in irrigation effluent
at which crop injury may occur..........................................................................55
Table 4.8 Sensitive receptors of effluent irrigation schemes...........................................60
Table 4.9: Recommended buffer distances to water resources and public areas.........61
Table 5.1: Recommended effluent sampling frequency...................................................70
Table 5.2: Recommended soil monitoring strategy...........................................................72
Table 6.1: Design parameters for effluent irrigation systems..........................................85
Table A1: Guidelines for treatment, disinfection and irrigation controls
for the spray application of municipal sewage effluent...............................105
Table A3: Soil texture factors for converting EC 1:5 soil-water solution
measurement to saturated extract....................................................................109
Table A5: Summary of key agency regulatory and advisory roles ..............................119
viii
Symbols and Abbreviations
ABM Australian Bureau of Meteorology
AMG Australian Map Grid
ARR Australian rainfall and runoff
ASS Acid sulfate soils
BOD biochemical oxygen demand
cfu colony-forming unit (of thermotolerant bacteria)
COD chemical oxygen demand
DA Development Application
DEC Department of Environment and Conservation
DIPNR Department of Infrastructure, Planning and Natural Resources
dS/m deciSiemens per metre
EC electrical conductivity
ECe electrical conductivity of saturated soil extract
EIS environmental impact statement
EMP environmental management plan
EPA Environment Protection Authority
ERIM effluent reuse irrigation model
h hour
ha hectare
IDA Integrated Development Assessment
HCB hexachlorobenzene
kL/d kilolitres per day
L litre
LBL Load-based licensing
LEP Local Environmental Plan
meq/L milliequivalent per litre
mg milligrams
mL millilitre
ML megalitre
NTU nephelometric turbidity unit
OC organochlorine
PCB polychlorinated biphenyl
ppm parts per million
REF review of environmental factors
REP Regional Environmental Plan
SAR sodium adsorption ratio
SEPP State Environmental Planning Policy
STP sewage treatment plant
TDS total dissolved solids
TOC total organic carbon
TSS total suspended solids
UV ultra-violet
ix
Executive Summary
The reuse of effluent by irrigation can make a significant contribution to the
integrated management of our water resources. When the water and nutrients
in effluent are beneficially utilised through irrigation some of the water
extracted from rivers can be replaced and the amount of pollutants
discharged into our waterways can be reduced. The Department of
Environment and Conservation (NSW) has adopted a policy of encouraging
the beneficial use of effluent where it is safe and practicable to do so and
where it provides the best environmental outcome.
This Guideline is educational and advisory in nature. It is not a mandatory or
regulatory tool and it does not introduce new environmental requirements.
The emphasis is on best management practices related to the management of
effluent by irrigation, to be used to design and operate effluent irrigation
systems, with the goal of reducing risks to the environment, public health and
agricultural productivity. The Guideline will assist decision-makers and
industry members in achieving the best environmental outcome for each site
at least cost.
The Guideline is not intended to provide specific guidance on every
individual industry’s detailed issues. Rather it provides an information base
to be used as a foundation for addressing issues that might arise in the range
of situations, circumstances and industries in which effluent irrigation may be
considered or underway. Industry specific guidelines or site-specific
information may need to be taken into account when applying the Guideline.
Approaches to effluent irrigation management other than those outlined in
this Guideline will always be considered on their merits provided that they
demonstrate environmental sustainability and are safe from a public health
perspective.
This Guideline has been developed through extensive consultation with
industry and government and is based on national guidelines and principles
where they are relevant.
The Guideline reflects the idea that a sustainable effluent irrigation system
will be a function of the interactions between the site, soil, agronomic system
and effluent characteristics, and diligent operational practices. These
interactions require effective management to maximise the resources available
in effluent and ensure that the environment is protected.
Selecting a suitable site is important for successfully establishing an effluent
irrigation system. The Guideline provides criteria for assessing a proposed
irrigation site, and discusses related issues important to the assessment of a
site. Landform and soil characteristics can limit the use of effluent on some
sites for example, because of the presence of soil that is poorly drained or
excessively well drained. The relationship between effluent quality and soil
characteristics that should also be considered when selecting a site are also
outlined to ensure that soil structure is not likely to be adversely affected
and/or pollution is not likely to be caused.
x
In relation to effluent quality, effluent contains valuable resources (water,
organic matter and nutrients). However, in excessive amounts these can be
detrimental to soils or plant growth. Effluent can also contain chemical
contaminants, salts and pathogens that can pose a risk to the wider
environment, public health or may cause pollution. These risks can be
minimised by applying the criteria and information provided in the Guideline
to during site selection, design and operation phases of an effluent irrigation
system.
Best management practices which optimise the use of the water, nutrients and
organic matter and reduce the potential for harm from other contaminants are
also critical. For an effluent irrigation system to be sustainable, the amount of
water, nutrients and chemicals that will be applied should be determined to
ensure that it is the optimum for the crop or cultivar, the agronomic system
employed, and site-specific factors such as climate, topography and soil.
Adjustments to the amount of effluent applied or the area over which it is
applied can then be made to ensure that irrigated plants and environments
are not stressed by water or by the organic material, nutrients or chemicals
applied.
Water and nutrient balances are used to calculate the amount of water and
nutrients that should be applied, and at what times, to meet the crop
requirements while ensuring increases in runoff and percolation are
minimised. The water balance is calculated to determine the maximum
volume of effluent that can be sustainably used. The elements to be
considered in a water balance are rainfall, evapotranspiration, runoff and
percolation. For some effluents, the loading rates of nutrients such as nitrogen
and phosphorus can limit the quantity of effluent to be used for irrigation in a
given area. In a nutrient balance the amount of the specific nutrient, (e.g.
nitrogen or phosphorus) assumed to be applied in a year is compared with
the amount taken up by the biological or physical processes of the crop-soil
system. Pre-irrigation soil nutrient status is also considered.
In some systems the amount of effluent that can be applied is limited by
potential adverse impacts of salinity, heavy metals and persistent organic
chemicals. The Guideline suggests that key components in managing these
types of limitations include designing the system to avoid any potential
impacts, and having in place management and monitoring system to correct
any emerging problems and to identify when action needs to be taken to
ensure the environmental and agronomic performance of the system.
xi
1. Introduction
Effluent irrigation is encouraged when it is safe and practicable to do so and
where it provides the best environmental outcome. The NSW Department of
Environment and Conservation (DEC) especially encourages substituting
effluent for high quality water wherever high quality water is being used for a
purpose for which effluent water would be acceptable. Where this is not
possible, or would not provide the best environmental and natural resource
outcome, effluent should be returned to the water cycle in an environmentally
and socially responsible manner.
This document covers the broad framework, principles and objectives that
should be considered when establishing an irrigation system that uses
effluent (effluent irrigation system). Development of sustainable effluent
irrigation schemes requires technical analyses of environmental interactions.
Proponents of effluent irrigation schemes are encouraged to seek out industry
specific guidelines and/or seek advice from suitably qualified personnel.
1. Introduction 1
dual reticulation systems and for most non-potable uses in urban areas with
open public access.
This Guideline does not cover:
• uses of effluent for purposes other than irrigation
• irrigation of effluent from single household on-site sewage treatment
systems (see Department of Local Government 1998)
• selection of sites for effluent storage and transport infrastructure or their
design and construction
• wastes that are classified as hazardous, Group A, Group B or Group C and
will require an environment protection licence for their generation,
storage, treatment or transport.
It is the proponent’s responsibility to assess whether their effluent falls under
the latter category. Proponents may contact DEC or refer to the Department’s
Environmental Guidelines: Assessment, Classification and Management of Liquid
and Non-Liquid Wastes (EPA 1999a).
Related documents
Other relevant guidelines, endorsed for use in NSW by the NSW Government,
should be read in conjunction with this Guideline. These include national and
NSW industry-specific guidelines developed by government agencies or
industry. Where national or industry-specific guidelines and this Guideline
give conflicting guidance on proposals to irrigate effluent, the environmental
performance objectives of this Guideline should be referred to in order to
determine whether the objectives would be achieved by the proposal.
Other documents produced by the NSW Government and other agencies,
such as the National Guidelines for Beef Cattle Feedlots in Australia (SCARM
1997); and the NSW Feedlot Manual (NSW Agriculture 1997) provide
information on the use of effluent by irrigation and should be used to provide
more industry-specific guidance where appropriate.
National guidelines are also available for some industries and provide a
framework for consistent environmental management across Australia. State
guidelines provide further detailed information to suit local environmental
and regulatory conditions.
Relevant National Water Quality Management Strategy (NWQMS) guidelines
include: Guidelines for Sewage Systems – Reclaimed Water (ARMCANZ,
ANZECC & NHMRC 2000); and Australian and New Zealand Guidelines for
Fresh and Marine Water Quality, in particular Volume 3, Primary Industries –
Rationale and Background (ANZECC & ARMCANZ 2000). See Section 7.2,
Further Reading for other industry-specific NWQMS guidelines.
1. Introduction 3
1.2 Environmental performance objectives
The following environmental performance objectives apply to the use of
effluent by irrigation.
Protection of surface waters: Effluent irrigation systems should be located,
designed, constructed and operated so that surface waters do not become
contaminated by any flow from irrigation areas, including effluent, rainfall runoff,
contaminated sub-surface flows or contaminated groundwater.
Protection of groundwater: Effluent irrigation areas and systems should be
located, designed, constructed and operated so that the current or future beneficial
uses of groundwater do not diminish as a result of contamination by the effluent or
runoff from the irrigation scheme or changing water tables.
Protection of lands: An effluent irrigation system should be ecologically
sustainable. In particular, it should maintain or improve the capacity of the land to
grow plants, and should result in no deterioration of land quality through soil
structure degradation, salinisation, waterlogging, chemical contamination or soil
erosion.
Protection of plant and animal health: Design and management of effluent
irrigation systems should not compromise the health and productivity of plants,
domestic animals, wildlife and the aquatic ecosystem. Risk management procedures
should avoid or manage the impacts of pathogenic micro-organisms, biologically
active chemicals, nutrients and oxygen depleting substances.
Prevention of public health risks: The effluent irrigation scheme should be sited,
designed, constructed and operated so as not to compromise public health. In this
regard, special consideration should be given to the provision of barriers that prevent
human exposure to pathogens and contaminants.
Resource use: Potential resources in effluent, such as water, plant nutrients and
organic matter, should be identified, and agronomic systems developed and
implemented for their effective use.
Community amenity: The effluent irrigation system should be located, designed,
constructed and operated to avoid unreasonable interference with any commercial
activity or the comfortable enjoyment of life and property off-site. In this regard,
special consideration should be given to odour, dust, insects and noise.
1.4 Guidance
This document promotes the use of best management practices in the
planning, design, construction, operation and management of effluent
irrigation systems to achieve a beneficial environmental outcome. Best
management practices are those approaches that prevent or minimise water
and soil pollution at or as close as practicable to the source. Other approaches
might be acceptable, provided that the resulting scheme is ecologically
sustainable, and satisfies the requirements of DEC or local council and other
statutory authorities.
The need for sustainability in an irrigation system is important. To this end, a
program of continuous monitoring and progressive modification might be
necessary to correct design flaws and deficiencies, and to adjust the system as
more complete information on the site becomes available, accommodating
changes in operation over time.
This document is an environmental guide; it is not a design and operations
manual. Technical and scientific problems associated with the use of effluent
can be complex and often require the integrated efforts of several disciplines
in science and engineering. Accordingly, designers and operators might need
to seek advice from specialist consultants and from government authorities
such as NSW Department of Primary Industries, NSW Department of
Infrastructure, Planning and Natural Resources, NSW Health, NSW Food
Authority, and WorkCover NSW. Advice for using effluent in tree plantations
may be obtained from the CSIRO Division of Forestry and Forest Products,
Canberra.
1. Introduction 5
1.5 How this Guideline is organised
This section sets out the broad scope, objectives and procedures for
establishing an effluent irrigation system.
Section 2 provides guidance on the site planning for an effluent irrigation
system.
Section 3 describes important characteristics of effluent when establishing
effluent irrigation systems.
Sections 4 and 5 outline design and operation considerations.
Section 6 summarises statutory requirements for an effluent irrigation
system.
Planning
a) Discuss the proposal/plans and inquire about statutory requirements with
the relevant local council or DEC regional office and other authorities as
appropriate (e.g. NSW Department of Primary Industries, NSW Department
of Infrastructure, Planning and Natural Resources (DIPNR) regional offices,
NSW Health, and WorkCover NSW). This should occur at an early stage to
ensure that all relevant issues are addressed before the design and
operational phases begin. Appendix 6 summarises the specific regulatory or
advisory information each agency can provide. Appendix 8 lists the DEC
offices.
b) Assess effluent quality (Section 3 provides information on effluent
characteristics that can have an influence on the design of an effluent reuse
scheme.)
Site selection
a) Identify a suitable site and conduct a site assessment (Section 2).
Design
a) Establish the minimum area of irrigation land needed, based on limiting
loading rates, i.e. hydraulic, nutrient, organic and chemical contaminants
(Section 4).
b) Calculate the minimum irrigation land area and wet weather storage needed
for the irrigation system (Section 4).
c) Define the operational processes to be used in effluent irrigation and
management (Section 5).
Installation
a) Install the system in accordance with the conditions of all relevant
authorities.
b) Develop a monitoring and reporting program as described in Section 5 so
that the performance of the system can be objectively assessed and adjusted
if necessary.
1
The EPA is a statutory body with specific powers under environment protection legislation. In
September 2003, the EPA became part of the Department of Environment and Conservation
(DEC).
1. Introduction 7
2. Site Considerations
When selecting a site for irrigation, it is fundamental to consider the
compatibility of surrounding land uses as well as the suitability of land for
irrigation, effluent storage and transport and other management
requirements.
Selecting a suitable site is important for successfully establishing an effluent
irrigation system that complies with the principles and guidelines set out in
this document. This section provides criteria for assessing a proposed
irrigation site, and discusses related issues important to the assessment of a
site. Effluent quality (Section 3) should also be considered when selecting a
site.
For irrigators who receive effluent on an ‘as needed’ basis (for example,
partial reuse schemes, Section 4.1) some of the site selection criteria, such as
the area of the storage facility might not apply.
See Section 7.2, Further Reading, for additional references on soils and site
suitability.
Climate
The climate of the area is a major factor in determining the type of plants that
can be grown and the amount of irrigation water that can be applied. These
aspects are discussed in more detail in Section 5.
Preliminary investigations
Taking a staged approach to site selection can reduce the costs associated with
selecting a suitable site. The first stage could be to identify how much land is
likely to be needed by undertaking a preliminary water, nutrient, organic
matter or salt balance (Section 4) using the expected effluent quantity and
quality data. (Where the area to be irrigated is predetermined, e.g. an existing
golf course, this step may not be necessary). The preferred locality should also
be selected. This will usually be land located in close proximity to an existing
2. Site considerations 9
2.3 Soil properties
Soil properties that describe soils likely to be suitable for effluent irrigation
are shown in Table 2.2. Subsoil as well as surface soil properties need to be
considered and soil properties should be characterised for the appropriate soil
horizon. Where a soil property limitation (in Table 2.2) is considered ‘slight’,
no soil amelioration is generally required. If the property limitation is
considered “moderate”, some soil amelioration or a management response is
required, for example, application of gypsum to a sodic (dispersive) soil, lime
to an acidic soil, or careful irrigation of poorly drained or excessively well
drained soil. Where a limitation is considered ‘severe’, the site may be
unsuited to irrigation of some or all potential effluent products. For example,
if a soil has a low phosphorus sorption potential, the irrigation of effluent
with high phosphorus levels is unlikely to be sustainable.
Soil sodicity
Soil sodicity refers to the amount of exchangeable sodium (Na) cations
relative to other cations in the soil and is expressed in terms of exchangeable
sodium percentage (ESP).
Dispersion of soil or a poor soil structure may be associated with sodicity.
Exchangeable sodium acts as a mechanism for weakening the bonds of soil
aggregates creating a soil with poor structure that can impede water and
plant root movement into and through the soil. The degree to which
dispersion occurs is also dependent on the soil’s clay content and mineralogy,
pH, Ca/Mg ratio, electrical conductivity (EC), organic matter content and the
presence of iron and aluminium oxides.
Australian soil scientists generally agree that soils with an ESP of greater than
5 are at risk of showing the adverse structural impacts associated with
sodicity. Effluent with an SAR (sodium adsorption ratio) of greater than 6 is
likely to raise ESP in non sodic soils, whereas effluent with a SAR of less than
3 may lower ESP in sodic soils (see also Section 4.4).
Soil salinity
Soil salinity refers to the amount of dissolved salts in the soil solution. Soil
salinity levels are usually determined by measuring the EC of a soil
suspension, which estimates the concentration of soluble salts in the soil. The
soluble salts are likely to be the cations Na+, Ca2+, and Mg2+ and the anions Cl-,
SO42- and HCO3-. Effluent and other soluble fertiliser may also contribute
other ions such as K+, NH4+ and NO3- which are also plant nutrients. Effluent
or the combined effect of effluent and fertilisers may raise soluble salt levels
to the extent that they impede plant growth and/or create salt scalds thereby
increasing the potential for soil erosion.
However, in evaluating potential impacts on soil and groundwater salinity it
is important to acknowledge the role of plant uptake in removing salt from
the soil (see also Section 4.4).
Soil pH
Soil pH is a measure of the concentration of hydrogen ions in the soil. It is
known to be related to the availability of plant macro and micro nutrients. For
most plants a pH range of between 6 and 7.5 (measured in calcium chloride)
maximises the availability of plant nutrients and hence the potential for plant
growth. Measurements of pH will vary depending on the field or laboratory
technique used. It is advisable to measure pH in calcium chloride to ensure a
consistent interpretation of results.
2. Site considerations 11
contaminant content of effluent. Addition of organic matter (which typically
has a high CEC) or the incorporation of a green manure crop (which will also
increase the soils organic matter content) may improve soils with a low CEC.
Exchangeable cations in soil include Ca2+, Mg2+, K+, Na+ (exchangeable bases),
and H+ and Al3+ (exchangeable acidity). The other cations such as manganese,
iron, copper and zinc are usually present in amounts that do not contribute
significantly to the sum of cations on the exchange complex. It is therefore
common practice to measure the concentration of the five most abundant
cations and use these to measure the effective cation exchange capacity
(ECEC).
Source: Based on Hardie and Hird (1998), NSW Agriculture, Organic Waste Recycling Unit
Notes: 1. Careful consideration should also be given to potential impacts on groundwater (see
2.6 Groundwater).
2. Sites with these properties are generally not suitable for irrigation.
3. Slopes over 12% may be acceptable provided runoff and erosion risks are identified in the
site selection process.
2. Site considerations 13
Table 2.2: Typical soil characteristics for effluent irrigation systems
Limitation
Salinity measured as electrical <2 2–4 > 43 excess salt may restrict plant
conductivity (ECe) growth
(dS/m at 0–70 cm)
Salinity measured as electrical <4 4–8 > 83 excess salt may restrict plant
conductivity (ECe) growth, potential seasonal
(dS/m at 70–100 cm) groundwater rise
Depth to top of seasonal high > 34 0.5–34 < 0.5 poor aeration, restricts plant
water table (metres) growth, risk to groundwater5
Depth to bedrock or hardpan >1 0.5–1 < 0.5 restricts plant growth, excess
(metres) runoff, waterlogging
Available water capacity > 100 < 100 6 – little plant-available water in
(AWC, mm/m) reserve, risk to groundwater
Soil pHCaCl2 (surface layer) > 6–7.5 3.57–6.0 < 3.5 reduces optimum plant
> 7.5 growth
Effective cation exchange > 15 3–158 <3 unable to hold plant nutrients
capacity (ECEC, cmol (+)/kg,
average 0–40 cm)
Source: Based on Hardie and Hird (1998), See also NSW Department of Primary Industries (2004)
Notes: 1. Sites with these properties are unlikely to be suitable for irrigation of some or all effluent products.
2. Application of gypsum or lime may be required to maintain long-term site sustainability.
3. Some high EC soils containing calcium ‘salts’ are not necessarily considered ‘severe’.
4. Where unable to excavate to 3m, local knowledge and absence of indications of water table to the
depth of sampling (1m) should be used.
5. Criteria are set primarily for assessing site suitability for plant growth. Presence of a shallow soil
water table may indicate soil conditions that favour movement of nutrients and contaminants into
groundwater. In such cases, careful consideration should be given to quality and potential impacts
on groundwater (see 2.6 Groundwater).
6. Careful irrigation scheduling and good irrigation practices will be required to maintain site
sustainability.
7. Soil pH may need to be increased to improve plant growth. Where effluent is alkaline or lime is
available, opportunities exist to raise pH. If acid sulfate soil is present, site-specific specialist
advice should be obtained.
8. Soil may become more sodic with effluent irrigation. In some cases, however, this soil property
may be ameliorated with addition of a calcium source.
9. Soils with medium to high phosphorus sorption capacity can adsorb excess phosphorus not taken
up by plants. The effectiveness of this depends not only on the sorption capacity but also, the
depth and permeability of the soil. A nutrient budget must be undertaken (see Section 4.3).
Groundwater vulnerability
Environmental impact assessment for groundwaters should be based on the
principles set out in the National Water Quality Management Strategy: Guidelines
for Groundwater Protection in Australia (ARMCANZ & ANZECC 1995) and the
NSW State Groundwater Policy.
DIPNR have published groundwater availability/vulnerability maps that
highlight areas that are at risk due to effluent irrigation. Groundwater
investigations should take into account current groundwater chemistry and
condition and the quality and quantity of the effluent to be irrigated; for
example, the quality of the irrigation water should not exacerbate rising
salinity in the watertable.
Where supporting technical advice has not been obtained, effluent should not
be applied to land where the depth to groundwater table is considered to be
less than 10 metres or where the irrigation area is located less than 1000
metres from a town water supply bore.
In areas subject to existing or potential problems, such as rising groundwater
tables or dryland salinity, or where groundwater is a direct conduit
discharging to surface waters, appropriate measures must be taken to ensure
that the effluent irrigation system does not exacerbate these problems.
The following are appropriate ways to protect groundwater from impacts of
effluent irrigation.
• Careful selection of suitable sites for irrigation.
2. Site considerations 15
• Implementation of a well-structured management plan that includes,
details of deficit irrigation scheduling, monitoring soil moisture content
and strategies to suspend irrigation when soil moisture content is high.
• Selection of areas where the presence of one or more impervious
geological strata (for example, a thick layer of compacted clay) above the
groundwater aquifer can prevent deep percolation from reaching the
aquifer.
• In the absence of protective geological strata, an adequate depth to the
normal watertable at or near the irrigation site will usually be needed for
groundwater with current or potential beneficial uses. On some
moderately permeable soils, a minimum depth of 15 metres may be
required.
On sites with identified risks to groundwater, baseline groundwater
chemistry should be established as a basis for assessing the extent of potential
impacts and to develop a monitoring program, if required. Regular
groundwater monitoring is required for effluent irrigation systems that
operate in a location where they pose a threat to groundwater.
Water quality objectives for the groundwater (i.e. water quality needed to
protect beneficial uses of groundwater) also should be considered. See also
Section 4.10 Separation Distances and Management of Buffer Zones.
2. Site considerations 17
3. Effluent Quality and Irrigation Considerations
Effluent contains valuable resources, such as organic matter and nutrients,
however, it also can contain concentrations of chemical contaminants, salts
and pathogens that are potentially detrimental to soils or plant growth
and/or pose a risk to the wider environment or public health. The
constituents of effluent are discussed in general in this section. How effluent
quality impacts on the design of irrigation systems is discussed in Section 4.
When designing a wastewater treatment system, effluent quality needed to
ensure a sustainable irrigation system will influence the effluent treatment
needed and the design and operation of the irrigation system.
Grease and oil Effluent with more than 1,500 mg/L of grease and oil must be considered high
strength and irrigation rates and practices must be managed to ensure soil and
vegetation is not damaged.
3.3 Solids
Care must be taken if effluent has high concentrations of solids (non-filtrable
residues). These may coat leaf surfaces or obstruct some types of sprinkler
nozzles. It may be necessary to reduce the concentration of solids to avoid
operational problems with any irrigation scheme.
Suspended solids can provide a substrate for other pollutants such as heavy
metal and pathogens, therefore suspended solids or turbidity are measures of
water treatment plant effectiveness when a high quality effluent is required.
High turbidity can decrease the effectiveness of disinfection involving
chlorine or ultra violet light.
Nitrogen
Nitrogen (N) can be present in organic and mineral forms, the latter including
gaseous (N2), ammonia (NH3) ammonium (NH4+), nitrate (NO3-), nitrite (NO2-)
and urea (NH2CONH2). The relative amount of each of these forms depends
on the original constitution of the wastewater, and the treatment and
stabilisation processes used.
Total nitrogen concentrations in effluent from municipal sewage treatment
plants are generally between 5 and 50 mg/L. Effluent from rural and food
processing industries may contain much higher concentrations of nitrogen
with total nitrogen in effluent from intensive animal industries likely to vary
between 50 and 750 mg/L.
Mineral forms of nitrogen are readily transformed into other mineral forms.
Some mineral forms such as nitrate, nitrite and ammonia can be taken up by
plants. Nitrate is also readily leached to groundwater. High concentrations of
nitrate make waters unsuitable for stock and domestic water supplies, or can
nourish unwanted plants and algae. N2 and NH3 can be lost to the atmosphere
in gaseous form. It is estimated that between 15% (cool climates) and 25%
(warm climates) of applied nitrogen in the form of ammonia can be lost to the
atmosphere, with up to 50% volatilised under optimal conditions (e.g. fine
spray irrigation in hot and low humidity climates), (see also the nitrogen
balance sub-section in Section 4.3, Nutrient Loading Rates).
Phosphorus
Phosphorus (P) concentrations in municipal sewage plants are between 0.5
and 10 mg/L depending on the extent of P removal processes used. Effluent
from intensive animal industries and food processing may contain much
higher levels of P. For example, total P loads in wastewater from intensive
animal industries are likely to vary between 10 and 500 mg/L.
Phosphorus contained in effluent exists in many forms but is normally
expressed as total P. The orthophosphates (H2PO4-, HPO42- and PO43-) are
Potassium
Effluent contains potassium, particularly animal effluents and effluent from
wool scouring plants. While potassium is an essential nutrient for healthy
plant growth, it contributes to the salinity of effluent and in excess can
adversely affect the uptake of other nutrients by plants, soil stability and
animal health. For example, grass tetany is a condition in dairy cattle
associated with imbalances of potassium and magnesium through ingestion
of fodder and soil. Salt balances should be determined for all proposed
effluent irrigation schemes to ensure that management processes are in place
to avoid potassium accumulation. More information on salt balances and
salinity is given in Sections 3.7 and 4.4.
Proposals to apply effluent with known high concentrations of potassium
such as wool scour effluent should also refer to ARMCANZ and ANZECC
(1999) Effluent Management Guidelines for Aqueous Wool Scouring and
Carbonising (see Further Reading).
3.5 pH
Effluent with a pH between 5 and 8.5 is generally acceptable for use in
irrigation. If the effluent is very acidic (pH less than 5), or very alkaline (pH
greater than 8.5), it may need to be neutralised before application as soil pH
affects the availability of nutrients and other elements to plants.
Metals
Although some metals are essential for plant growth, many are toxic at
elevated concentrations and their toxicity may be increased if soil is acidic.
Therefore, it is important to establish the average concentrations of metals in
irrigation effluent to avoid irreversibly contaminating the irrigation site in the
long term.
ANZECC and ARMCANZ (2000) Water Quality Guidelines (for irrigation)
identify the maximum concentrations of metals in irrigation waters
considered acceptable for continuous use. If concentrations of one or more
metals exceed these levels (based on appropriate sampling), then the
proponent must examine the potential impact of the metal on the soil and the
land management system. Calculations must be made to determine the length
of time the effluent can be applied before soil concentrations exceed guideline
limits (see Section 4.6 and cumulative concentration limit triggers in ANZECC
and ARMCANZ (2000)). The land management system must be able to
tolerate the higher levels of metal without detrimental effects.
It is important to regularly monitor the levels of metals which are risk factors
in effluent to ensure that it is managed appropriately or as a means of
reviewing estimates of the soil/plants capability of immobilising these. Soil
and plant monitoring may also be required where metal levels exceed
recommended levels for irrigation waters. Monitoring programs in these
situations will need to be tailored to evaluate the risk posed by the metal or
contaminant for the agronomic system in use. ANZECC and ARMCANZ
(2000) Water Quality Guidelines (for irrigation) should be consulted for the
context in which the criteria in Table 3.3 should be applied. Further advice is
provided in Section 5.3 Monitoring Systems.
Total concentration
Metal (mg/L) Comments
Arsenic 0.1
Beryllium 0.1
Chromium VI 0.1
Cobalt 0.05
Copper 0.2
Iron 0.2
Lead 2
Manganese 0.2
Mercury 0.002
Molybdenum 0.01
Nickel 0.2
Selenium 0.02
Source: ANZECC and ARMCANZ (2000) (Refer to any current Australian Water Quality Guidelines
as they are updated and endorsed for use in NSW).
Note: 1. Trigger values should only be used in conjunction with information on each individual
element and the potential for offsite transport of contaminants (see ANZECC &
ARMCANZ (2000) Volume 3, Section 9.2.5). See also short-term use trigger values (up to
20 years) and cumulative contaminant loading limit triggers in ANZECC and ARMCANZ
(2000), Volume 1, Table 4.2.10.
Herbicides
Herbicides are harmful to plants. Phenoxyacid herbicides, such as 2,4-D and
its derivatives, are widely used for weed control. It is therefore possible for
these compounds to be in effluent. They degrade rapidly in soil, but can
persist in effluent. Where there is a risk that herbicide is present in the
effluent, it is advisable to conduct periodic monitoring of effluent for the
presence of herbicides as these may interfere with plant growth. See further
guidance in ANZECC and ARMCANZ (2000) Volume 1, Section 4.2.8.
Source: Adapted from DNR (1997), cited in ANZECC and ARMCANZ (2000).
The term ‘total dissolved solids’ (TDS) is commonly used to express the
combined concentration of salts in mg/L. TDS in mg/L may be estimated by
measuring the electrical conductivity (EC) of the effluent, in dS/m and
multiplying by an empirical factor ranging from 550–900. Conversely, the EC
at 25oC, expressed in units of dS/m, is calculated (with an error of within
about 10%) by multiplying TDS, in mg/L, by 0.00155. When converting, the
correct conversion factor should be established by measuring both properties
at the commencement of any irrigation scheme.
See ANZECC and ARMCANZ 2000 Volume 3, Section 9.2.3 for
comprehensive information on sustainable irrigation practice in relation to the
affects of salinity.
Sodium
Sodium salts are of particular concern, as excessive sodium levels relative to
calcium and magnesium can adversely affect plant growth, soil structure and
permeability. As discussed in Section 2.3, sodicity is a condition that degrades
soil properties by making the soil more dispersible and erodible, restricting
water entry and reducing hydraulic conductivity (the ability of the soil to
conduct water). These factors also limit leaching so that salt accumulates over
long periods of time, giving rise to saline subsoils. Furthermore, a soil with
increased dispersibility becomes more susceptible to erosion by water and
wind.
Both the sodium concentration and the sodium adsorption ratio of effluent
must be determined.
Sodium adsorption ratio (SAR) is the relative proportion of sodium ions (Na+)
to both calcium ions (Ca2+) and magnesium ions (Mg2+) as shown in
Equation 1.
Water compositions that occur to the right of the equilibrium lines (in Figure
3.1) are considered satisfactory for use, provided the SAR is not so high that
severe dispersion of the surface soil water will occur following rainfall. Water
quality that falls to the left of the solid line is likely to induce degradation of
soil structure and corrective management will be required (e.g. application of
lime or gypsum). Water that falls between the lines is of marginal quality and
should be treated with caution and specifically managed with reference to soil
properties.
Soil permeability and aeration problems can occur when it is irrigated with
water that has a SAR above 6. There is evidence that these problems may
increase with an increasing ratio of magnesium to calcium. Soils with a low
cation exchange capacity will become sodic more quickly than soils with high
CECs. These latter soils may become sodic with effluent SARs of between 3
and 6. Where effluent SAR is high, calcium in the form of lime, gypsum, ash
or organic matter can be applied to the irrigated soil to counteract the
potential negative impacts on soil structure.
Alkalinity
Except when applied to soils that are strongly acidic, highly alkaline effluent
can adversely affect the availability and uptake by plants of calcium,
magnesium and some trace elements by increasing the soil pH to levels
greater than 7.5. At high pH, calcium, for example, can be precipitated as a
salt. This loss of calcium accentuates the imbalance of exchangeable ions in
favour of sodium, increasing the soils exchangeable sodium percentage (ESP).
With time, this process will have a detrimental effect on soil structure, and
will reduce the permeability of the soil.
Bicarbonate
High concentrations of bicarbonate in effluent can lead to a high concentration
of bicarbonate in the soil water where it may be concentrated through the
process of evapotranspiration. There is then an increased tendency for calcium
and magnesium to precipitate as insoluble salts. Over time, this reduction in
available calcium and magnesium will result in an increased SAR, which can
adversely affect soil structure and could cause a sodium hazard.
Boron
Boron is an essential micro-nutrient for plants, however, at high
concentrations it can be toxic (see ANZECC & ARMCANZ (2000) Volume 3,
Section 9.2.5.6). It is also likely to remain in the soil solution and move into the
groundwater because soils have a very limited capacity to absorb boron.
Fluoride
Fluoride is contained naturally in soils and in fresh water, but excess intake in
plant material or soil by grazing cattle has detrimental effects on their health.
Fluoride may be present in effluent and has the potential to bind to and
accumulate in soils irrigated with effluent over extended periods. However,
there are insufficient data from Australian soils to prescribe soil loading limits
or to determine bioavailability (ANZECC and ARMCANZ 2000). Stock health
monitoring procedures for effluent irrigation schemes should include checks
Load-based licensing
Industry groups that are included in the load-based licensing (LBL) scheme
administered by DEC and who reuse effluent can obtain a discount on the
pollutant load fee where effluent is reused in a sustainable manner. The LBL
protocol (EPA 1999b; and Appendix 2) provides background information on
the circumstances under which a fee reduction can be claimed. The design
2
The EPA is a statutory body with specific powers under environment protection legislation. In
September 2003, the EPA became part of the Department of Environment and Conservation
(DEC).
4. Design considerations 35
water balance using the calculated minimum land area and the allowable
discharge frequency, which is determined from the strength of the effluent
and any additional management practices or issues that reduces effluent
strength or impacts.
Precipitation
The rainfall data over a historical period is used. This data can be obtained in
monthly or daily format from the Bureau of Meteorology.
Evapotranspiration
This will vary throughout the year depending on temperature, humidity,
solar radiation, wind, crop type and crop growth patterns. It can be estimated
by multiplying daily or monthly evaporation values for a district by the
appropriate crop factor for the particular species of plant to be grown.
The crop factor takes into account plant productivity, and the meteorological
factors. Some crop factors are given in Table 4.1. However, as they can be
highly variable, they are a generalised guide only and will not be suitable for
all circumstances. Myers et al. (1999) includes crop factors for locations in
addition to Wagga Wagga. It is recommended that proponents consider site-
specific conditions when adopting crop factors used for water balance
determination. A useful source of information on crop water use is Doorenbos
and Pruitt (1977).
Table 4.1: Crop factors1 for some crops, trees and pasture
Crop J F M A M J J A S O N D
Lucerne .95 .90 .85 .80 .70 .55 .55 .65 .75 .85 .95 1.00
Citrus .55 .55 .55 .55 .50 .50 .50 .50 .55 .55 .55 .55
Grape-vines .60 .60 .50 .40 .25 .20 .15 .20 .25 .40 .55 .60
Deciduous orchard .75 .65 .45 .25 .15 .10 .15 .20 .30 .50 .70 .75
Pasture .70 .70 .70 .60 .50 .45 .40 .45 .55 .65 .70 .70
2
Eucalypt plantation .78 .84 .94 1.17 1.21 1.15 1.13 1.33 1.33 1.26 .99 .83
Notes: 1. Crop factors are expressed as the ratio of crop evapotranspiration to pan evaporation.
2. At Wagga Wagga – Source: Myers et al. (1999). Humidity has a profound influence on the
crop factor of eucalypts and values only suit climates similar to Wagga Wagga.
Crop factors are sometimes expressed on different bases. Some are expressed
as the ratio of crop evapotranspiration to pan evaporation while others are
expressed as the ratio of potential evapotranspiration to crop
evapotranspiration. The difference between pan evaporation and potential
evapotranspiration is known as the pan factor. Care should be taken when
4. Design considerations 37
using crop factors to ensure that the correct factor is used for the calculation
being carried out.
Percolation
Percolation is the movement of water down through the soil profile and is a
natural phenomenon after any rainfall event that exceeds the soil moisture
deficit. An irrigated site will have more percolation than a site with rainfall
only. Percolation is a process that prevents build-up of salt in the root zone.
In humid coastal and mountain areas percolation due to natural rainfall may
be sufficient to prevent salt build up, but in dry climates, a small fraction of
irrigated effluent may be all that is required to leach salts out of the root zone.
The need for deliberate percolation of effluent will also depend on the salt
tolerance of the plants and the salt concentration in the irrigation effluent.
Percolation must not simply be used as a means to dispose of effluent to the
environment as there is potential for other pollutants (e.g. nitrates) to be
leached in addition to salts.
The rate of salt accumulation depends on a number of factors including the
effluent salinity, hydraulic loading, rainfall and resulting natural leaching.
One simple method for determining the fraction of irrigation water required
to leach salts is to use the following equation:
Effluent storage
The effluent storage is also a key component of the water balance and can be
used to optimise the land area required to satisfy water demand
requirements. Section 4.7 provides information on modelling storage and land
area requirements for a sustainable water and nutrient reuse.
Full reuse
Where there is to be no effective discharges of effluent to waters, adequate
capacity to store effluent must be calculated from the water balance. The
strength of the effluent (Section 3 and Table 3.1) is used as a tool to determine
the allowable frequency of uncontrolled discharges which inevitably occur as
a result of prolonged rainfall events. As a general guide, for low strength
effluents, uncontrolled releases may be permitted in 50 percent of years. For
medium and high strength effluent, discharges may be limited to 25 and 10
percent of years respectively. It should be noted, for example, that a 60th
percentile storage requirement could be applied where the effluent is
marginally stronger than the low strength (See also Section 4.7, Models). In
some situations, either the strength of the effluent and/or the sensitivity of
the receiving environment may be such that there should be no overflows (or
less frequent overflows than those provided above as guidance) from the
storage to the environment.
Partial reuse
In a partial reuse scheme wet weather storage is considered if the daily
effluent flow rate is less than the irrigation demand during periods of peak
plant water demand, or the effluent manager wishes to only discharge
effluent under certain receiving water conditions.
The water balance can be used to calculate the monthly (or other time period)
irrigation demand. The time period with the greatest irrigation demand is
then compared with the actual effluent flow rate over the same time period. If
the flow rate is less than the plant irrigation demand then the proponent of
the scheme may choose to construct a wet weather storage to ensure that
plant growth is maintained at this critical time.
Storage construction
Advice should be sought (from DIPNR, NSW Department of Primary
Industries or professional engineering services) on techniques to build
4. Design considerations 39
effluent storages to prevent failure and leakage. Overflows should have a
properly constructed overflow point from the storage facility to ensure
control of the overflow. Where licensed, DEC may require monitoring and
reporting of overflows.
Average grain
yield (tonnes/ha Nitrogen Phosphorus Potassium
Grain Crop Area dry matter) % % %
Barley State-wide 3.5 1.8 0.4 0.69
1
Canola Central–west 2.8 4.6 (0.7) (0.7)
South–west 2.8
slopes
4. Design considerations 41
Table 4.2: Yield and nutrient content of crops in NSW for cultivation under
irrigation with effluent (continued)
Average grain
yield (tonnes/ha Nitrogen Phosphorus Potassium
Grain Crop Area/season dry matter) % % %
Barley straw State-wide 14.0 0.5 0.1 0.4
Oat straw State-wide 5.0 0.7 0.1 2.4
Lupin straw State-wide 0.5 0.6 0.05 0.9
Pea straw State-wide 0.5 1.1 0.1 1.3
Triticale Central West 6.0 0.5 0.1 0.5
South-west 6.0
Grain sorghum North-west 3.0 (1.2) (0.2) (1.2)
Central west 3.0
Riverina 3.5
Maize North-west 7.0 (0.9) (0.3) (2.2)
Central west 7.0
Riverina 9.0
Coastal 9.0
Soybean North-west 5.0 (0.8) (0.1) (0.6)
Riverina 5.0
Kikuyu Sept–Mar 20 2.6 0.3 2.8
Phalaris Mar–Nov 12 1.1 0.3 2.8
Perennial Mar–Dec 12 3.5 0.3 2.0
ryegrass
Fescue All year 14 2.4 0.4 2.1
Lucerne All year 20 3.5 0.4 2.5
White clover Sept–Feb 20 3.7 0.4 2.6
Nitrogen balance
The behaviour of nitrogen in plant-soil systems is complex and includes
additions and losses to the system as well as transformations of the forms of
nitrogen. Additions of nitrogen to the system include effluent, fertiliser and
nitrogen fixation by plants. The processes that reduce nitrogen include:
removal of harvestable plant matter from the system; volatilisation of
ammonia; and denitrification of both nitrate and nitrite to gaseous nitrogen
forms. Nitrogen can also be stored in the system, for example as residue left
on the ground or as humus in the soil.
Nitrogen inputs should be compared with nitrogen losses. A simple approach
to the nitrogen balance is to compare the total nitrogen usage of each
cultivated crop with the amount of total nitrogen available. This is a
4. Design considerations 43
Equation 5: Total available nitrogen
Ry = U/TNEy
Where:
Ry = annual effluent loading in year y in ML/ha/yr
U = annual crop uptake of nitrogen in kg/ha/yr (Table 4.2)
For irrigation systems where the nitrogen loading rate is the limiting factor,
the nitrogen removal capacity of the crop should be estimated by the nitrogen
content of its harvestable portion (see Table 4.2).
The above equation is one example of a nitrogen budget. Proponents of
effluent irrigation schemes may seek advice from suitably qualified persons
who may have different methods for estimating nitrogen balances.
For reuse schemes subject to load-based licensing, the nitrogen balance can be
a factor in fee discount calculations. Load-based licensing protocols should be
consulted for more detail on how nitrogen balance calculations are
undertaken for industry groups included in the load-based licensing scheme.
Phosphorus compounds
The capacity of an irrigation system to use nitrogen can be maintained and
restored over time since the removal of nitrogen from effluent largely
depends on biological processes. In contrast, phosphorus (P) is removed from
effluent through biological, chemical and physical processes in the soil. The
existing P sorption capacity of the soil and the P uptake by the plants to be
grown determines how much P can be introduced before the site is saturated.
Soils with a high degree of pedality (or cracking soils) or major geological
discontinuity (identified in the planning process) could act as a conduit for
phosphorus rich effluent to enter a valuable water resource. This information
4. Design considerations 45
Example of a phosphorus sustainability calculation
Assumptions:
• Phosphorus sorption capacity = 350 mg/kg
• Phosphorus sorption capacity (critical) = 117 mg/kg (for most soils, the
strength of P sorption is low to moderate, so in this example only about
one third of the P sorption capacity can be used before some leaching of P
occurs).
• Soil depth = 1 metre (m)
• Soil density = 1,300 kg/m3
• Land area for irrigation = 40 ha
• Total P in applied effluent = 8 mg/L
• Volume of effluent at 1 ML/day = 365 ML/yr
Calculations:
Total P adsorbed before leaching:
= P sorption capacity (critical) x soil density x soil depth x 40 Ha
= 117 mg/kg x 1,300 kg/m3 x 1 m x 40 Ha x 10,000 m2 /Ha x 10-
6
mg/kg
= 60,840 kg
Total orthophosphate in applied effluent per year
= 8 mg/L x 365,000,000 L
= 2,920 kg
Total P removed by crop per ha per year = 25 kg
Therefore total P removed by crop per 40 ha per year = 1,000 kg
Site irrigation period:
= (60,840 kg)/(2,920 kg/year - 1,000 kg/year)
= 31.7 years
Total P
sorption P sorption
Soil parent capacity capacity (critical)
Location material Soil classification (kg/ha) (kg/ha)
Sydney Hawkesbury Soloth 5,440 2,700
Basin sandstone
Nutrient imbalances
Effluent can supply some or all of the essential nutrients for healthy plant
growth, but these are usually not supplied in the correct ratio. It might be
necessary to diagnose nutritional disorders in soils and crops, and determine
corrective action. It may also be necessary to add fertilisers to promote plant
growth so that nutrient removal from the site is efficient. The advice of NSW
Department of Primary Industries or other professional agronomists should
be sought on this. Some crops (e.g. wine grapes) have particular nutrient
requirements at certain times of the year. For example, applying too much
fertiliser, such as nitrogen, may promote leaf growth at the expense of
flowering and fruiting.
Operators should assess which nutrients are already present in the soil before
applying effluent. In many cases, imbalances of micronutrients and metals
may be inferred by soil pH. Usually, problems of deficiency or toxicity can be
minimised if surface soils are maintained at a pH of between 6.0 and 8.0.
4. Design considerations 47
4.4 Salinity control and salt balances
Proper management is necessary to ensure that effluent irrigation does not
lead to soil degradation by increasing soil salinity.
All irrigation waters contain some salt. Salt may concentrate in the root zone if
there is insufficient drainage to take away any salt not utilised by the growing
plant. With each effluent application, the salt concentration in the root zone
may progressively increase unless leaching and drainage remove it. Without
the downward water flow of leaching and drainage, salts within the root zone
can be drawn towards the soil surface by water evaporation. Therefore, the
prime requirement for salinity control in irrigation systems is to provide
adequate leaching to prevent salt accumulation. This requires periodic
monitoring of the levels and distributions of soil salinity, particularly within
the root zone areas.
When using effluent that consistently contains more than 500 mg/L of TDS, a
higher level of salinity control to maintain a viable and lasting system is
required. More area for irrigation may be required than is calculated by water
or nutrient balance equations to compensate for the high salt concentrations.
It may also be necessary to dilute effluent to avoid damaging plants,
especially those with a low salt tolerance. The relative tolerance of plants to
saline irrigation effluent can be found in ANZECC and ARMCANZ (2000)
and other references.
Modelling the movement of salt through the soil is particularly difficult as the
interactions between irrigation and natural rainfall, plant uptake and
recycling of specific salts and the dynamics of soil salt and sodicity levels on
soil hydraulic conductivity are not precisely understood. Estimates of salt
movement are possible with commercially available modelling software that
calculate salt balances from inputs of parameters such as salt load, effluent
volumes, climatic data, proposed cropping regime, crop water use and
physical soil properties. Salt balances should be determined for all proposed
schemes to ensure that salinity is appropriately managed.
For those industry groups subject to load-based licensing, the Load Based
Licensing Protocol can be used to identify management and monitoring
conditions for salt in effluent that will attract full or partial load-based
licensing discounts as at the time of this publication. Current load-based
licensing protocols should be consulted. These tables also provide information
on where the saltiness of the effluent is a major determinant in minimum area
requirements. Available salt models should be used with caution and advice
sought on their appropriateness in the area under consideration.
Barley (grain)2 10 18
Cotton 9.6 17
Medium tolerance
Cabbage 2 7
Low tolerance
Apricot 2 3.7
4. Design considerations 49
Table 4.4: Yield reduction of crops due to soil salinity (continued)
1
Yield reduction (dS/m)
Radish 2 5.0
A = CQ / (1,000 x Lc)
Where:
A= irrigation area (ha)
C = concentration of BOD5 (mg/L)
Q= average effluent flow rate (kL/month)
Lc = critical loading rate of constituent (kg/ha/month)
4. Design considerations 51
and must not allow the irrigation area to become an officially contaminated
site.
DEC has used extensive research carried out by the former NSW Department
of Agriculture (now NSW Department of Primary Industries) to set maximum
allowable trace metal and persistent organic chemicals concentrations for
agricultural and non-agricultural soils following biosolids application in
Environmental Guidelines: Use and Disposal of Biosolids Products (EPA 1997).
These are shown in Table 4.6 and are used to determine the upper limit in
soils that are being irrigated. Further guidance on cumulative contaminant
loadings can be found in ANZECC and ARMCANZ (2000) Volume 3,
Section 9.2.5.
Cadmium is a critically important element in the animal and human food
chains. Both soils and plants can contribute significant amounts of cadmium
to those food chains. The risk of exceeding legal residue limits in edible
animal tissues is increased if soil and plant levels of zinc, molybdenum and
sulfate are low. Horses and other monogastric animals show adverse effects
with dietary intakes as low as 1 mg of cadmium per kilogram of dietary dry
matter.
Copper toxicity is a common cause of death in sheep in Australia. Dietary
levels as low as 8mg of copper per kilogram of dietary dry matter can cause
toxicity. This is most likely when soil and plant levels of molybdenum are
low. Both soils and plants can contribute significant amounts of copper.
The maximum tolerable dietary level for lead is considered to be 30 mg of
lead per kilogram of dry matter for most domestic animals. However lead
residues in some tissues may still build up at this level. Young animals absorb
more lead from the diet than adults. Ingested soil is the main source of lead.
Maximum concentration in
1
Contaminants topsoil (mg/kg)
Arsenic 20
Cadmium 1.0
2
Chromium VI 1.0
Copper 100
Lead 150
Mercury 1.0
Nickel 60
Selenium 5.0
Zinc 200
DDT/DDD/DDE 0.5
Aldrin 0.02
Dieldrin 0.02
Chlordane 0.02
Lindane 0.02
Hexachlorobenzene 0.02
3
PCBs non-detect
4. Design considerations 53
Where heavy metals or persistent organic chemicals are likely to be present,
the cumulative concentration over time should be estimated. See below for an
example calculation.
Acrolein Flood or furrow: beans 60; corn 60; cotton 80; soybeans 20; sugar-beets 60
Sprinkler: corn 60; soybeans 15; sugar-beets 15
Amitrol Lucerne 1,600; beans 1,200; carrots 1,600; corn 3,000; cotton 1,600; grains
sorghum 800
Dichlobenil Lucerne 10; corn 10; soybeans 1.0; sugar-beets 1.0–10; corn 125; beans 5
4.7 Models
An array of models have been developed for determining the storage and
land area requirements to ensure a sustainable irrigation scheme in terms of
the water, nutrient and/or salt balance. They may also facilitate the planning
and assessment of environmental impacts of the effluent irrigation system.
The models vary widely in their degree of complexity. Their primary function
is simply to assist in designing an irrigation system appropriate to a particular
site.
Water balance models are those that simulate the water cycle through plants,
animals, land, waterbodies and air. They are widely used to estimate land and
storage requirements for irrigation schemes on different soil types, with
variable agricultural enterprises and climatic conditions. Their complexity can
range from those that simply rely on monthly rainfall and evaporation to
those using complex estimates of plant water use and similarly complex
soil/water relationships.
4. Design considerations 55
Salt balance models examine changes in soil salinity over time and can predict
leaching requirements to avoid excessive salt accumulation in the root zone.
Nutrient budget models examine the fate of nutrients, particularly nitrogen
and phosphorus, when applied to the soil. They are based on knowledge of
the cycling of nutrients and their performance in the environment. Nutrient
models are widely used to estimate the application rate of nutrients and long
term management of a scheme based on the soil characteristics and
agricultural enterprise.
DEC has developed one such effluent reuse irrigation model (ERIM) based on
water balance and the strength of the applied effluent to provide guidance for
developing effluent irrigation systems. However, the DEC model (ERIM) is
not considered mandatory for use in conjunction with this guideline.
There are various computer models commercially available to plan effluent
irrigation systems and the assumptions and methods used to construct them
can vary widely. It is therefore likely that results generated by various models
can differ. Models, including ERIM, usually give at best a reasonable
approximation of likely water, nutrient, storage and irrigation area
requirements of an effluent irrigation system. In variable climates (mainly
coastal), particularly where daily-based rainfall models are used, providing
information on the extent of the rainfall variability, and on natural percolation
and runoff, would assist in demonstrating a sustainable irrigation scheme. For
high strength effluent the chance of storage overflow must be small, one year
in ten. The mix of weather conditions that combine to cause an overflow will
therefore be relatively rare and a relatively higher degree of uncertainty will
be associated with these cases. Care must be taken when modelling these
scenarios and interpreting results.
Care should therefore be taken to avoid over-reliance on models to establish
sustainable effluent irrigation systems (e.g. models may not include inorganic
fertiliser/conditioner inputs into the nutrient cycles, such as gypsum, muriate
of potash and urea). It is important to emphasise, however, that DEC or local
council will require the proponent to:
• demonstrate to the satisfaction of DEC or local council that the proposal is
sized (storage and land area), based on sound knowledge of volume of
effluent generated, natural climatic and soil conditions, and the likely
nutrient, salt, organic and chemical content of the effluent (see Sections 2
and 3)
• demonstrate that realistic assumptions have been used in any model and
that model outcomes are sustainable
• include a monitoring program so that model assumptions and outcomes
can be tested. If the scheme performs differently from model predictions
then the monitoring program is to be used to make adjustments to the
scheme design and subsequent performance.
4. Design considerations 57
Care must be taken in using the model when effluent flow rates are variable
and where a range of crop types are being irrigated from the same effluent
source. The ERIM model can be used to predict the performance of partial
reuse schemes provided the effluent volume for the scheme can be nominated
on a month by month basis.
Details relating to the construction and use of the model are at Appendix 4.
4. Design considerations 59
including the separation of uses, buffer zones and selection of appropriate
effluent treatment and irrigation systems can be designed and employed.
Natural water bodies (e.g. rivers, lakes) Water quality, aquatic ecosystems, relevant
beneficial uses
Other waters: e.g. artificial waters with beneficial uses, Water quality, ecosystems, relevant beneficial
drainage channels, small streams, intermittent streams, uses
farm dams
Domestic well used for household water Water quality and public health
Houses, schools, playing fields, public roads, public Odour, noise, Water quality (pathogens,
open space contaminants)
Environmentally sensitive areas: e.g. drinking water Water quality, ecosystems, soil and water
catchments, wetlands, stands of native vegetation nutrient status, biodiversity
When determining the size of a separation distance the nature of the buffer
zone and techniques to avoid impacts must be considered. Where a buffer
zone for a spray irrigation proposal is characterised by flat, open country
where ground cover is predominantly pasture separation distances may need
to be in the order of hundreds of metres to protect sensitive receptors. The
same irrigation scheme may require a separation distance of only tens of
metres if impact mitigation strategies such as tree and shrub planting in the
buffer zone, lower height and pressure of sprayers and larger droplet sizes are
incorporated.
Table 4.9 provides recommendations on appropriate buffer distances between
effluent irrigation sites and water resources and public areas. These can be
used where no other information is available to determine buffers or where a
proponent prefers to use these values rather than determine appropriate
buffers on a site-specific basis. Other factors such as pathogen levels should
be taken into account when establishing buffers to protect human health.
Wider buffers may be required, or narrower buffers may be allowed,
depending on site- or issue-specific factors. For example, narrower buffers
may be appropriate where high quality effluent, a low volume of effluent or
vegetated filter strips are used. Wider buffers may be necessary where there is
limiting site characteristics such as soil or slope. Proposals for narrower buffer
distances must be supported by technical advice. Due regard also must be
given to relevant planning requirements that specify buffers.
Separation
Separation distance
distance (low (medium to
strength high
Sensitive area effluent) strength) Impact of concern/comments
Other waters (e.g. artificial Site-specific Site-specific Protection of water quality for most
waters with beneficial uses, sensitive water uses of the
small streams, intermittent potentially affected waterbody.
streams, water distribution
and drainage channels,
farm dams)
Domestic well used for Site-specific 250 m Groundwater quality for domestic
household water supply human uses protected.
Town water supply bores Site-specific 1000 m Water and groundwater quality for
drinking water supply protected.
Town bores generally pump at high
rates and draw water from a large
area.
1
Where spray irrigation 50 m 50 m Avoidance of spray drift of effluent
gives rise to aerosols near containing pathogens offsite.
houses, schools, playing Buffers for odours and noise have
fields, roads, public open separate assessment criteria and
space and waterbodies these are assessed on a site-
specific basis.
Other sensitive areas (e.g. Site-specific 250 m Greater buffer distances and
waters in drinking water management may be required in
catchments, aquatic some circumstances to protect
ecosystems with high drinking water (e.g. within the
conservation value, Sydney Drinking Water Catchment
wetlands, native stands of the Sydney Catchment Authority
vegetation) would seek a buffer of 100 metres in
the absence of other evidence of a
neutral or beneficial effect on water
quality).
Notes: 1. Recommended in ARMCANZ, ANZECC and NHMRC (2000) for the spray application of
reclaimed water from sewerage systems.
4. Design considerations 61
It should be noted that separation distances are not a substitute for effective
effluent irrigation system design. The impacts of deficiencies in design, such
as soil and water degradation through the loading of soils with salts and/or
nutrients, may be delayed by the use of large buffer zones but they will not be
avoided or overcome through the use of this strategy. Separation distances
and buffer zones are the final strategy available to provide a margin of safety
to the range of impact mitigation designed throughout the system. The
quality of the effluent, the irrigation method used and the nature of the
environment within which the scheme is located will determine the size and
composition of buffer zones.
In summary, the most appropriate buffer zone will be one that complements
best effluent irrigation practices in providing a margin of safety against the
possibility of nutrient pollution, aerosol drift and human and animal health
impacts, without unnecessarily restricting the efficiency of the enterprise or
amenity of adjacent land uses. Determination of the optimal buffer zone for a
particular land use mix can only be determined following an assessment of
the effluent irrigation practices proposed and the sensitivity of the receiving
environment.
4.11 Irrigation
Methods
Irrigation methods used depend on site topography, soil type, the species of
plants to be grown, cost, effluent quality, labour availability, power
requirements and public health and environment considerations. Effluent
generally should be applied to the site by trickle, spray or drip irrigation, to
avoid over-application and unintended environmental effects that could occur
with furrow or flood irrigation systems. Use of the latter may indicate the
need for laser levelled sites.
The infiltration rate of soil is an important consideration in the type of
irrigation method used and the way it is operated. Effluent should be applied
uniformly and at a rate less then the nominal infiltration rate to avoid surface
runoff.
In drip or trickle irrigation, pressurised water is discharged through micro-
emitters. The water is dripped thereby minimising the risk of aerosols. In
spray irrigation, water is pumped through pipelines and discharged through
sprinklers that can vary from high pressure ‘big guns’ that can generate
aerosol drifts of up to 1 km, to small low pressure microsprays that minimise
the risk of aerosol drift and reduce the potential for odour. High pressure
systems should only be used for effluent which meets the pathogen reduction
criteria for use on raw human food crops given in Appendix 1, with buffer
distances determined according to the principles given in Section 4.10. High
pressure systems should not be used when weather conditions are such that
spray drift will be excessive.
Flood irrigation methods include border check, border ditch, basin, contour
bank, hillside and furrow irrigation. Flood irrigation generates little or no
Irrigation scheduling
The scheduling of irrigation is one of the most important functions of the
irrigation manager. Excessively long intervals without irrigation can lead to
water stress and crop loss. Irrigating too often can waterlog the soil and allow
excess effluent to runoff or percolate to groundwater, polluting both
groundwater and surface water. To ensure that the application site is not
overloaded, an irrigation schedule should be based on knowledge of the
water content of the soil and the water requirements of the cultivated crop.
There are direct and indirect methods available to estimate the water content
of a soil. Direct methods rely on insertion of soil moisture monitors (e.g.
neutron probes) at representative sites within the system. Indirect
measurements estimate plant evapotranspiration by taking direct
measurements of rainfall, temperature and sometimes evaporation and
converting these through recognised models into predicted
evapotranspiration for the particular crop being grown.
Generally, it is advisable to irrigate the soil to allow a 5 to 10 mm soil water
deficit. This allows for a buffer capacity in the soil should rain fall soon after
an irrigation event.
4. Design considerations 63
The design must allow for adequate resting periods between irrigation to
avoid rainfall runoff. For most plant systems a soil moisture deficit of at least
30 mm should be allowed to accrue before further irrigation takes place.
Storage management
Management of wet weather storage is an important aspect of ensuring that
the environmental impact of an irrigation system is minimised. Storage dams
must be managed to ensure that they have the capacity to store effluent
during wet weather. This means that irrigation needs to be carefully
scheduled and carried out to ensure that the maximum amount of effluent is
applied without causing undesirable impacts such as waterlogging or runoff.
Overflows from full reuse schemes will occur at the frequency used to design
the system, on average. Overflows are most likely after a prolonged period of
low evaporation, perhaps where there has been continual rain in later winter.
However, this might not always coincide with high stream flows and
therefore the in-stream dilution might not be high.
Precautionary discharges can be used to ensure that discharge occurs when
conditions will minimise environmental impacts (rather than uncontrolled
overflows as discussed in Section 4.2.) This approach is only permitted when
licence conditions expressly allow it to occur. Licence conditions will include
an in-stream trigger flow, a time horizon or lower flow limit as well as
volume and effluent quality limits. The conditions will be designed to ensure
that a higher load than would otherwise occur is not discharged.
Frequency of sampling
Frequency (how often) and intensity (number of samples) of monitoring will
depend on the type and scale of the scheme, sensitivity of the site and trends
identified in any previous monitoring.
Provided impacts are not hidden for the first few years of a scheme (as would
be the case with phosphorus), a rigorous monitoring program is
recommended during the commissioning phase of effluent reuse schemes.
The sampling frequency and number of test constituents could then be
reduced, based on satisfactory historical records and subject to negotiation
with any relevant government agency (e.g. DEC, local councils, DIPNR and
NSW Health). If performance values exceed those indicated in the design of
the effluent scheme, then sampling frequencies should be increased, and the
irrigation management program should be adjusted accordingly.
Recommendations on sampling frequency are provided below (see Table 5.1).
Soil
Soil characteristics of the application site should be established when
designing the project as described in Section 2. In addition, plant nutrient
levels in the root zone should be established.
Soil sampling should be performed or supervised by a qualified person with
knowledge of soil science (e.g. Certified Professional Soil Scientist, CPSS),
accredited by the Australian Society of Soil Science Incorporated.
Soil samples should be taken in close proximity to the initial soil sampling
locations. These initial locations are likely to be one every 2 to 20 hectares
depending on the geological complexity and the size of the proposed
irrigation site. As discussed in Section 2, an EM survey can be used to identify
these initial sampling sites.
Frequency of sampling
Surface waters
Surface waters should be analysed several times before effluent irrigation
(upstream and downstream of the effluent reuse site, if relevant), following
storms and during high flows. Thereafter, depending on the frequency of
effluent discharge and the strength of the effluent, a sampling program
should be developed as necessary to determine and manage any impacts, or
in accordance with licensing requirements for licensed premises.
Licensed premises will be required to monitor waters in accordance with
the licence or load-based licensing protocols (or propose an alternative
monitoring program approved by the load-based licensing Technical
Review Panel).
Monitoring should be conducted in a manner consistent with the sample
collection, handling and preservation principles enunciated in the current
version of Standard Methods for the Examination of Water and Wastewater
(APHA, 1998). Monitoring samples should be analysed for water pollutants
by the methods set out in the DEC’s Approved Methods for the Sampling and
Analysis of Water Pollutants in NSW (DEC 2004). Australian Guidelines for Water
Quality Monitoring and Reporting (ANZECC 2000) provides detailed
information on appropriate monitoring methods.
In general, water monitoring must provide data that is representative of the
waterbody and is able to indicate contributions of any pollutants as a result of
the scheme (compared to contributions of similar pollutants from upstream
sources).
Groundwater
Groundwater need only be monitored if it is within 10 metres of the ground
surface and/or if the existing groundwater quality is at risk from the effluent
irrigation scheme. Groundwater sampling should occur on the established
enterprises before crop planting, during the middle of the crop growth and
quarterly/yearly thereafter (see below). Where the depth is shallow or where
the soils are highly permeable, monthly monitoring may be appropriate.
Hydraulic gradients should be considered when establishing groundwater
monitoring. Monitoring any potential impacts on groundwater drinking
water supplies also may be required (see also Section 2.6, Groundwater).
Attributes to be measured in groundwaters include:
Quarterly
• groundwater height: monitor at regular intervals where the groundwater
is above 3 metres
• pH (no units)
• EC (dS/m)
Annually (site specific)
• Cations (mg/L)
• N: total and nitrate (mg/L)
• P: total and plant-available (mg/L)
Plants
Sampling of crops or pastures is good practice to determine the adequacy of
any fertiliser and irrigation program. Plant sampling may be required if
unacceptable levels of trace contaminants have been identified in the system.
Trace elements of concern should be measured at harvest, or as appropriate.
Advice should be sought from specialist agronomists or plant pathologists if
there are noticeable yield problems or unusual colourations develop on the
leaf foliage.
Stormwater runoff
The extent to which runoff from storms must be retained depends upon the
nature and magnitude of the water pollution that might result from the
discharge. Other variables include rainfall distribution and land management
practices.
With terminal systems, initial calculations should be based on collecting the
volume equivalent to 12 mm of rainfall runoff from effluent utilisation areas.
In non-sensitive locations, alternative measures such as vegetative buffers or
artificial wetlands may be used to manage the 12 mm of stormwater runoff.
The performance of vegetative buffers can be variable (see Section 4.10,
Separation distances and the management of buffer zones).
A collection system usually consists of catch drains that direct the runoff to a
terminal collection pond and a system to return the collected runoff to the
effluent storage facility and/or the irrigation supply system. In some systems,
the catch drains may need to include deep drains to collect sub-surface flows.
However deep drains should be avoided on potential acid sulfate soils.
Ideally, where a system is needed, it would be designed to collect all tailwater
and stormwater leaving the irrigation area. In practice, though, the system is
usually designed to collect the tailwater and the most contaminated “first
flush” stormwater. Provision should be made for any subsequent less
contaminated stormwater to by-pass the terminal pond via a well-vegetated
flow-way.
To function properly, terminal ponds should have sufficient length and depth
to detain the flow of runoff long enough for solids to settle out and to collect
the maximum volume of tailwater and/or stormwater runoff from the
system. If tailwater is not generated from the irrigation system itself, the
terminal pond should only be large enough to collect and store the
stormwater runoff. In a situation where the collection of tailwater and
stormwater runoff is necessary, the terminal pond should have a capacity to
retain both the volume of the effluent irrigation tailwater and the stormwater
runoff from the effluent utilisation areas.
Background
The POEO Act replaces the five media-specific pollution control Acts: Clean
Air Act 1961, Clean Waters Act 1970, Pollution Control Act 1970, Noise Control
Act 1975 and Environmental Offences and Penalties Act 1989. It also incorporates
all premises and activity based regulatory functions of the Waste Minimisation
and Management Act 1995.
The POEO Act established a system of Environment Protection Licences, to
minimise and control the impact of activities on the surrounding
environment. Under the POEO Act, the EPA is the relevant authority for an
activity whenever:
(a) the activity is listed on Schedule 1 of the POEO Act
(b) a licence to control water pollution from the activity has been granted,
or
6. Statutory requirements 79
(c) a public authority is carrying out the activity or is occupying the
premises where the activity occurs.
The licence can deal with the impact of an activity on any environmental
media in both the construction and operating phases. This means the potential
impacts of an activity on air quality (including odour), water quality, noise
pollution and/or the waste stream can all be dealt with in the one licence. The
licence is ongoing, but will be reviewed at least once every three years.
There is no longer a need to obtain separate EPA approvals and licences. A
single licence can cover both the construction phase (scheduled development
work) and the operation phase for a scheduled activity.
Non-scheduled activities
Non-scheduled activities are any activities other than those listed in the
‘Schedule of EPA-licensed activities.’ The POEO Act does not generally
require non-scheduled activities, which includes effluent irrigation, to be
licensed.
Operators of effluent irrigation schemes should be able to manage their
effluent to avoid pollution of water, i.e. in a manner that meets statutory
obligations and the environmental performance objectives set out in this
guideline. It is an offence to cause or permit any surface or groundwater
6. Statutory requirements 81
The EPA may require proponents to install measures to abate pollution. In
some cases, adoption of such measures may eliminate the need for a licence.
Description of site
• locality map, indicating catchment, Eastings, Northings, AMG Zone and
scale
• current land use
• proximity of site to dwellings and roads, water courses, other property
boundaries, urban areas, areas of natural timber and protected
environmental areas (e.g. wetlands)
• location of existing groundwater bores.
Description of climate
• precipitation analysis (average monthly distribution)
• storm intensities
• evapotranspiration (average monthly distribution)
• prevailing wind (if applicable)
• description of water balance (daily or monthly) used to estimate
maximum hydraulic loading.
Topography/landform
• ground slope and relief
• description of adjacent land
• erosion potential
• drainage features
• seasonal wet areas and springs
Soil characteristics
• type, structure, profile features, colour, texture, electrical conductivity,
cation exchange capacity, exchangeable cations, hydraulic conductivity,
nutrient levels, organic matter, phosphorus sorption capacity, salinity
levels and pH
• infiltration and percolation characteristics.
Groundwater
• depth to groundwater
• location of existing wells on the subject site and adjoining sites
• current use and ambient groundwater chemistry
• an analysis of the hydrogeological conditions under the site
• vulnerability of groundwater systems to pollution.
Surface water
• proximity
• quality and current use
• flow characteristics
• quality of aquatic ecosystems.
Cropping system
• crops/vegetation to be grown
• details of planting and harvesting cycles
• details of cropping or grazing management and practices.
Animal system
• animal species and types to be fed/grazed
• farm design and facilities for animal enterprise
• plan of production and health practices
• exposure of pets, birds and native animals.
Effluent transport
• detailed plans of effluent transport facilities
• wet weather storage facilities
6. Statutory requirements 83
• detailed plans of effluent storage facilities (including balance ponds) and
any return pumping arrangements.
Irrigation system
• type of irrigation system: spray, trickle, flood or furrow –for spray systems
detail the pressure at which effluent is discharged
• plan of irrigation system
• schematic diagram of the system controls, including pipes, pumps, valves,
timers, alarms and runoff controls
• proposed monitoring program
• analysis of risks to environment from scheme
• how monitoring program was developed in response to risk
• details of components to be monitored
• details of tests to be undertaken
• details of analysis reporting mechanisms.
width metres
Organic loading rate (as BOD5) design daily and annual rate kg/ha/day or year
Other constituents loading rates design daily and annual rate kg/ha/day or year
BOD5 mg/L
TOC mg/L
COD mg/L
grease mg/L
pH –
Storage capacity kL or ML
Note: Section 1 provides a checklist of procedures to follow when setting up an effluent irrigation system
6. Statutory requirements 85
Licence conditions
The standard conditions of a licence include emission/discharge limits and
operating conditions, as well as monitoring, reporting and compliance review
requirements.
Site-specific conditions, however, also may be determined on a case-by-case
basis, depending on the particular environmental characteristics of the
effluent irrigation system. For example, a licence may include conditions
relating to effluent quality and quantity limits.
Operators may be required to produce an annual environmental management
report to enable assessment of the performance of the irrigation scheme. The
requirements of this report will depend on the size of the effluent irrigation
system and the sensitivity of the environment in which the system is located.
6. Statutory requirements 87
3. assess the need for an EIS. Activities that are likely to significantly affect
the environment require an EIS
4. if an EIS is required, obtain Director General’s Requirements from DIPNR
for the preparation of an EIS.
Further guidance can be found in Is an EIS Required? (DUAP 1995). The
environmental guidelines, EIS: Guidelines for Irrigation of Sewage Effluent
(DUAP 1996) is also available from DIPNR.
Examples
Sewage treatment plants (STPs)
If the proponent is a private organisation, the storage or use of effluent at a
sewage treatment plant would normally require consent under the provisions
of the local environmental plan (LEP) or other environmental planning
instruments. Depending on scale, nature and location, this could be a
designated development, falling within the sewerage systems category of
Schedule 3 of the EP&A Regulation.
If the effluent is used or stored on a site not directly associated with the STP,
then the proposal needs to be characterised to determine if it is permissible
and whether development consent is required under the LEP. When
characterising a proposal, the scale, nature and location of the proposal need
to be considered.
If the proponent is a municipal council or another public authority, the
storage or use of effluent at a municipal STP may not require development
consent under the provisions of SEPP 4 – Development without Consent.
However, environmental impact assessment will proceed in accordance in
Part 5 of the EP&A Act.
SEPP 4 may not apply when the storage or use of effluent is not directly
associated with the STP. In this case, the activity should be characterised to
assess if it is permissible under the relevant environmental planning
instruments.
Threatened species
The Threatened Species Conservation Act 1995 integrates the conservation of
threatened species into the development control processes under the EP&A
Act. The Act sets out factors to be considered in deciding whether there is
likely to be a significant effect on threatened species, populations or ecological
communities and if a Species Impact Statement is required. Where there is
6. Statutory requirements 89
likely to be a significant effect, the consent authority must seek concurrence of
the Director-General of DEC. Further information may be obtained from the
local Parks Service Division offices of the Department.
Legislation that provides for the protection of all threatened fish and marine
plants came into affect on 1 July 1998. Threatened species provisions were
included as Part 7A of the Fisheries Management Act 1994. This legislation
provides for the protection, conservation and recovery of threatened species,
and makes provision for the management of threats. Further information may
be obtained from the local office of the NSW Department of Primary
Industries.
Animals to abattoirs
Federal regulations (Export Meat Orders 135 and 141) require the owner of
cattle grazed on effluent areas to seek approval from the abattoir veterinarian
before submitting the animals to any abattoir holding an export licence. The
owner would be expected to demonstrate that the risks of the animals
carrying pathogens (or chemical residues) originating from the effluent were
being adequately managed. Advice should be sought from the Animal
6. Statutory requirements 91
7. References and Further Reading
7.1 References
ANZECC 1992, Australian Water Quality Guidelines for Fresh and Marine Waters,
National Water Quality Management Strategy. Australian & New Zealand
Environment and Conservation Council, Australia.
ANZECC 2000, Australian Guidelines for Water Quality Monitoring and
Reporting. National Water Quality Management Strategy. Australian & New
Zealand Environment and Conservation Council, Australia.
ANZECC and ARMCANZ 2000, Australian and New Zealand Guidelines for
Fresh and Marine Water Quality. National Water Quality Management Strategy.
Australian & New Zealand Environment and Conservation Council, and
Agriculture and Resource Management Council of Australia and New
Zealand, Australia.
APHA 1998, Standard Methods for the Examination of Water and Wastewater.
American Public Health Association, 19th edition, Washington, DC.
ARMCANZ and ANZECC 1995, National Water Quality Management Strategy:
Guidelines for Groundwater Protection in Australia, Australia.
ARMCANZ, ANZECC and NHMRC 2000, National Water Quality Management
Strategy: Guidelines for Sewerage Systems – Use of Reclaimed Water. Agriculture
and Resource Management Council of Australia and New Zealand,
Australian & New Zealand Environment and Conservation Council and
National Health and Medical Research Council, Canberra, Australia.
DEC 2004, Approved Methods for the Sampling and Analysis of Water Pollutants in
NSW. NSW Department of Environment and Conservation, Sydney.
Department of Local Government 1998, On-site Sewage Management for Single
Households. Environment and Health Protection Guidelines. Department of
Local Government, NSW.
DLWC 1997, The NSW State Groundwater Policy – Framework document,
Department of Land and Water Conservation, Parramatta.
DLWC 1998, The NSW State Groundwater Quality Protection Policy. Department of
Land and Water Conservation, Sydney.
DLWC 2000, www.dlwc.nsw.gov.au/care/soil/salis.htm
DNR 1997, Salinity Management Handbook. Department of Natural Resources,
Brisbane.
Doorenbos, J. and Pruitt, W. O. 1977, Guidelines for predicting crop water
requirements. Food and Agriculture Organisation of the United Nations.
DUAP 1995, Is an EIS Required? NSW Department of Urban Affairs and
Planning, Sydney.
Sewage effluent
Myers, B. J., Bond, W. J., Falkiner, R. A., O’Brien, N. D., Polglase, P. J., Smith,
C. J. and Theiveyanathan, S. 1995, Effluent-Irrigated Plantations: Design and
Management. CSIRO Division of Forestry, Technical Paper No. 2.
NSW Department of Local Government, NSW Environment Protection
Authority, NSW Health and Department of Urban Affairs and Planning 1998,
Environmental and Health Protection Guidelines: On-site Sewage Management for
Single Households. NSW Department of Local Government, Sydney.
Other
ARMCANZ and ANZECC 1999
a) Effluent Management Guidelines for Intensive Piggeries.
b) Effluent Management Guidelines for Dairy Processing Plants.
c) Effluent Management Guidelines for Dairy Sheds.
d) Effluent Management Guidelines for Aqueous Wool Scouring and Carbonising.
e) Effluent Management Guidelines for Tanning and Related Industries.
f) Effluent Management Guidelines for Wineries and Distilleries. National Water
Quality Management Strategy. Agriculture and Resource Management
Glossary 97
Controlled public access: The limitation of public access to sites so as to
minimise the likelihood of direct physical contact with effluent.
Crop Factor (Kc): The proportion of potential evapotranspiration (PET)
actually transpired by the crop (Etcrop). (Etcrop = Kc x PET)
Deficit (irrigation) scheduling: Scheduling irrigation used to ensure that a
soil moisture deficit remains after each irrigation event (see also irrigation
scheduling).
Denitrification: The biological process by which nitrate is converted to
nitrogen and other gaseous end products.
Designated development: A development designated under any of the
categories listed in Schedule 3 of the Environmental Planning and Assessment
Regulation (or if designated by virtue of an environmental planning
instrument). Examples of designated developments include sewerage
systems, livestock intensive industries, livestock processing industries,
depending on scale and location.
Disinfection: Destruction of disease-causing organisms.
Effluent irrigation system: Irrigation system that uses effluent. Irrigation of
effluent is not synonymous with disposal.
Effluent: As defined in the Protection of the Environment Operations
Amendment Regulation 1999, effluent means:
(a) wastewater from sewage collection or treatment plants; or
(b) wastewater from collection or treatment systems that are ancillary to
processing industries involving livestock, agriculture, wood, paper or food,
being wastewater that is conveyed from the place of generation by means of
a pipe, canal or other conventional method used in irrigation (but not by
means of tanker or truck); or
(c) wastewater from collection or treatment systems that are ancillary to
intensive livestock, aquaculture or agricultural industries, being wastewater
that is released by means of a pipe, canal or other conventional method used
in irrigation as part of day-to-day farming operations.
Electrical conductivity (EC): A measure of the conduction of electricity
through water or a water extract (1 part soil to 5 parts water) of soil. This can
be used to determine the soluble salts content. To obtain the real soil electrical
conductivity (Effective electrical conductivity) the EC of a soil water extract is
converted by a factor which reflects the texture of the soil.
Eutrophication: Enrichment of waters with nutrients, primarily phosphorus,
causing abundant aquatic plant growth.
Evapotranspiration: The combined loss of material from a given area during a
specified period of time by evaporation from the soil or water surface and
transpiration from plants.
Glossary 99
Infiltration rate: The rate at which water can enter the soil surface. It affects
the rate at which a soil may recharge with water and because it affects the
likelihood of surface runoff and hence erosion during heavy rain or irrigation.
Irrigation: The artificial supply of water or wastewater to plants and soils to
replenish moisture lost by evapotranspiration and to grow plants. Irrigation is
not synonymous with disposal.
Irrigation corporation: A company, co-operative or corporation that manages
an irrigation scheme area and is listed on Schedules 1 or 2 of the Irrigation
Corporations Act, 1994. Irrigation corporations construct, maintain, manage
and operate drainage networks and water supply systems and services to
users in the irrigation scheme area. To carry out the business of supplying
water, the irrigation corporations must hold an irrigation corporation licence
(granted by the Governor) and operate in accordance with licence conditions.
Irrigation scheduling: The monitoring of soil moisture deficits either by
direct measurement (e.g. neutron probe) or indirectly by soil moisture
budgeting to determine the frequency and quantity of irrigation water
required. Normally used to ensure that only enough water is applied to meet
plant water requirements.
Leaching fraction: Irrigation water applied in excess of the soil water holding
capacity in order to leach salts to below the plant root zone. The fraction is
usually smaller in higher rainfall areas and larger for higher strength
effluents.
Leaching: The downward movement of a material in solution through soil.
Metasediments: Partly metamorphosed sedimentary rocks.
Micronutrients: Chemical elements such as boron, copper, zinc, iron,
manganese, molybdenum and chlorine that are necessary in only extremely
small amounts for plant growth.
Mole: The molecular weight of a substance expressed in grams.
Nitrification: Transformation of inorganic ammonium (NH4+) into nitrate
(NO3-). In treatment processes, conversion of organic nitrogen to ammoniacal
nitrogen is preceding or occurring simultaneously with nitrification.
Transformation of organic nitrogen in soil is referred to as mineralisation.
Ordovician: The second of the periods comprised in the Paleozoic era, in the
geological classification now generally used. Also, the system of strata
deposited during that period. In older literature, it was called Lower Silurian.
Orthophosphate (PO43-): A water-soluble form of phosphate found in soil
solution, and some effluents, that is taken up by plant roots.
Pan A evaporation: Evaporation is the change of water from its liquid (or
solid) phase to its vapour phase. Supply of energy (solar radiation and
transport of vapour away from the surface (i.e. winds) are two main factors
influencing evaporation for the earth's surface. A standard evaporation pan
called a Class A pan is used a basis to estimate evapotranspiration or
evaporation from open water bodies. See also evapotranspiration.
Glossary 101
Saturated hydraulic conductivity: The flow of water through soil per unit of
energy gradient. It is an important measure of the drainage capacity of the
soil.
Secondary treatment: A combination of processes used to remove
biodegradable organics and suspended solids in wastewater. It removes 85%
of BOD and suspended solids, generally by biological and chemical treatment
processes. Secondary effluent generally has BOD < 30 mg/L, TSS < 30 mg/L
but may rise to > 100 due to algal solids in lagoon or pond systems.
Siliceous: Of or pertaining to silica; containing silica, or partaking of its
nature. Containing abundant quartz.
Sodic soil: A soil containing sufficient exchangeable sodium to adversely
affect soil stability, plant growth and land use. Such a soil would typically
contain a horizon in which the amount of exchangeable sodium percentage
(ESP) would be five or more. Strongly sodic soils are those with an ESP of 15
or more. Sodic soils generally have severe surface crusting, low infiltration
and hydraulic conductivity, hard and dense subsoil, and are highly
susceptible to gully and tunnel erosion.
Sodium adsorption ratio (SAR): The measurement of sodium ions in soil or
water relative to calcium and magnesium ions.
Soil fertility: The capacity of the soil to provide adequate supplies of
nutrients in proper balance for the growth of specified plants, when growth
factors such as light, moisture and temperature are favourable.
Soloth: One of the great soil groups with recognised profile development. It is
a mildly leached soil often with a high sodium content.
Sorption strength: The sorption strength of a soil is a measure of how
strongly P is sorbed to the soil. It depends on the mineralogy and surface
characteristics of the soil.
Spray irrigation: A method of applying water or effluent.
Stormwater runoff: Runoff resulting from rainfall.
Surface irrigation system: An irrigation system using bays, borders or
furrows. This typically excludes spray, drip and sub-surface irrigation
methods.
Surfactant: A substance that alters the surface-modifying properties of
another substance, particularly water. Surfactants are used in detergents to
reduce the surface tension of water so that the water is able to penetrate
fabrics.
Suspended solids (non-filtrable residue): The solids in suspension in
wastewater that are removable by laboratory filtering, usually by a filter of
nominal pore size of about 1.2 micrometers.
Tailwater: Wastewater runoff leaving the down-slope end of an effluent
irrigation area.
Glossary 103
Water quality objective: Numerical concentration limits or other
requirements established to support and protect ambient water quality for
designated environmental values (or water uses) at a specified site, (eg.
establishing instream salinity levels needed to protect water quality used for
the irrigation of crops). Under the National Water Quality Management
Strategy they are locally established benchmarks for water quality derived
from prevailing Australian Water Quality Guidelines for Fresh and Marine
Waters.
Wet weather storage (storage): A facility for storing effluent generated when
the use of effluent for irrigation is not possible, such as when it is raining, or
when evaporation is very low.
Table A1: Guidelines for treatment, disinfection and irrigation controls for the spray application of municipal sewage effluent
Urban (non-potable)
7
Municipal with uncontrolled public Tertiary pH 6.5–8.5 pH weekly Application rates limited to protect
≤2 NTU
9
access BOD weekly groundwater quality.
and Turbidity continuous
Irrigation open spaces, parks, Salinity should be considered for
sportsgrounds, dust suppression, 10 irrigation.
5 1 mg/L Cl2 residual or equivalent level of With disinfection system, e.g. Cl2
construction sites Pathogen reduction pathogen reduction Disinfection systems daily
6
3 4 3
Thermotolerant coliforms <10 cfu/100mL Thermotolerant coliforms weekly
Municipal with controlled public access Secondary pH monthly Irrigation during times of no public
SS monthly access.
Irrigation open spaces, parks, and Application rates limited to protect
3
sportsgrounds, dust suppression, 5 3 4
Thermotolerant coliforms weekly groundwater quality. Salinity
construction sites, mines Pathogen reduction Thermotolerant coliforms <1,000 cfu/100 mL Disinfection systems daily
6
should be considered for irrigation.
Withholding period nominally 4
hours or until irrigated area is dry.
Agricultural
7
Food production Tertiary pH 6.5–8.5 pH weekly Application rates limited to protect
≤2 NTU
9
Turbidity continuous groundwater quality. Salinity
Raw human food crops in direct and should be considered.
contact with effluent e.g. via sprays, 5 10 6
irrigation of salad vegetables Pathogen reduction 1 mg/L Cl2 residual or equivalent level of Disinfection systems daily A minimum of 25 days ponding or
disinfection equivalent treatment (e.g. sand
In NSW, NSW Health does not support filtration) for helminth control.
3 4
the use of reclaimed water for spray Thermotolerant coliforms <10 cfu/100 mL 3
6 Thermotolerant coliforms weekly
irrigation of salad vegetables where <1 intestinal nematode egg or larva/L
the effluent is in contact with the edible
part of the plant.
105
106
Table A1: Guidelines for treatment, disinfection and irrigation controls for the spray application of municipal sewage effluent (cont)
Source: These requirements are based on National Water Quality Management Strategy: Guidelines for Sewage Systems — Use of Reclaimed Water (ARMCANZ,
ANZECC and NHMRC 2000).
Notes: DEC/local council will adopt the criteria set in any updated national guidelines except where NSW Health provides different requirements particular to NSW or local
conditions.
Appendix 1
Consistent with the national guidelines, it should be noted that in some cases, the Department of Environment and Conservation/local council or NSW Health may
adopt more stringent requirements than those outlined in the national document, eg. It is possible that NSW Health may apply the national guideline values as
maximum levels rather than median levels.
Intensive animal industries should check for specific animal health protection measures.
SS = suspended solids
NTU = nephelometric turbidity unit
CFU = colony-forming units
1. Effluent quality refers to its quality following treatment appropriate for a particular application and prior to mixing with receiving waters. The guideline levels apply to
the treated effluent feeding into the reticulation system, after the point of treatment and disinfection. The effluent should not degrade in quality while it is being
stored or while travelling through a reticulation system. Chlorine may need to be added as a primary or secondary disinfectant to allow for a residual disinfection.
2. Monitoring demonstrates effluent water quality at the point of supply rather than at the treatment plant. In most cases this will be the point of entry to the
reticulation system or other suitable representative sampling location.
3. Thermotolerant coliforms (see Glossary).
4. Median value. Refer to statistical treatment of data in ARMCANZ, ANZECC & NHMRC (2000) or future updates
5. Pathogen reduction beyond secondary treatment may be accomplished by disinfection (eg. chlorine) or by detention (eg. ponds or lagoons). Systems using
detention only do not provide reduction of thermotolerant coliform counts to <10 per 100 mL and are unsuitable as the sole means of pathogen reduction for high
contact uses.
6. Disinfection systems refer to chlorination, ultraviolet irradiation or other disinfection systems. Monitoring requirements may include checking chlorine residual or
operational checking of UV equipment. Monitoring frequency for pond and lagoon systems will be site-specific and dependent on factors such as detention time.
7. 90% compliance for samples.
8. Helminths controls include measures such as removal by treatment, veterinary inspection, cattle husbandry and/or a withholding period prior to grazing. For
pasture and fodder applications, other options may be used to control helminth infection in grazing animals if they are acceptable to the NSW Department of
Primary Industries.
9. Limit met prior to disinfection. 24 hour mean value. 5 NTU maximum value not to be exceeded.
10. Total Chlorine Residual after a minimum contact time of 30 minutes.
11. In NSW, NSW Health specifies that for raw food crops separated from contact with effluent by peel, the level of treatment should be the higher category of ‘Raw
food crops in direct contact with effluent.’
107
Appendix 2: Load-based Licensing
At the time of publication of this Guideline some activities are subject to the
EPA’s load-based licensing (LBL) scheme. The following information is from
the Load Calculation Protocol referred to in the Protection of the Environment
Operations (General) Regulation 1998 (the Regulation). The full Protocol sets
out those activities that are subject to LBL and the methods that must be used
to calculate assessable pollutant loads. A revised Load Calculation Protocol
may be issued from time to time and should be referred to. These revisions
are notified in the Government Gazette. Copies of the full and most recent
LBL Protocol, and relevant legislation are available from DEC’s web site at
www.environment.nsw.gov.au, or contact the Department.
Effluent irrigation schemes subject to LBL can obtain a discount on the
pollutant load fee where effluent is reused in a sustainable manner. In the
case of reuse of effluent, weighted loads are calculated by multiplying the
actual loads of each pollutant by ‘reuse discount factors’. There are different
performance criteria for achieving discounts for each pollutant. The reuse
discount factor for each pollutant is the sum of a ‘pollutant management
factor’ (0, 0.25 or 0.5) and a ‘water management factor’ (0, 0.25 or 0.5). Better
performance leads to a lower factor and thus a higher fee discount; i.e. the
best possible score is 0 + 0 = 0 (100% discount), and the least beneficial is 0.5 +
0.5 = 1 (nil discount).
If a range of discount factors applies to different portions of the effluent (e.g.
different disposal or reuse methods for parts of the total load), the load is
divided into portions, the appropriate discount factors are applied to each
portion, and then the values are summed to calculate total weighted loads of
each pollutant.
Refer to the full and most recent LBL Protocol available from DEC or the
Department’s website at www.environment.nsw.gov.au.
Table A3: Soil texture factors for converting EC 1:5 soil-water solution
measurement to saturated extract
Clay loam 9
Medium clay 7
Heavy clay 6
Appendix 3 109
Appendix 4: The Effluent Reuse Irrigation Model (ERIM)
The design of a sustainable agronomic system for the use of water, nutrients
and organic matter in effluent is central to these guidelines. This appendix
explains the basis upon which DEC’s Effluent Reuse Irrigation Model was
constructed. The following is an extract from a paper presented at a
WaterTech Conference (EPA 1996).
Model description
The Effluent Reuse Irrigation Model (ERIM) is based on historical rainfall and
evaporation data supplied by the Australian Bureau of Meteorology. The
computer implementation of the model is interactive and allows the user to
supply local data to generate design criteria for the storage and land
requirements of a sustainable irrigation system through a range of graphical
displays.
ERIM is designed to be general in that it functions in the same way regardless
of location, although site-specific parameters must be provided.
Initially, the evaporation at the selected site is adjusted by a set of crop factors
to yield evapotranspiration, which is a measure of water usage by the crop.
The crop factors depend on the site, crop grown, agricultural practice,
agronomic considerations and month of year.
The deficit of rainfall over evapotranspiration (referred to as irrigation
demand) is used to define the potential irrigation pattern, which is established
for as many years as historical data is available. A cumulative distribution of
yearly irrigation demands is used to pick a lower and upper limit on the
depth of irrigation between which a solution will be determined. By default,
the lower limit is half the lowest recorded irrigation demand and the default
upper limit is the 10% point on the cumulative distribution, but both may be
adjusted if they are unsuitable. It is extremely unlikely that a feasible solution
will exist outside these two nominated limits.
The historical rainfall and evaporation data is used to calculate the wet
weather storage that would have been used for each target irrigation depth
from the whole range identified above. The guidelines associate a level of
acceptable environmental risk of wet weather storage overflow with defined
effluent strength (low, medium or high). The storage sizes necessary to reflect
the various environmental risks are determined by counting down the
appropriate number of yearly peaks.
The computer implementation of the model will then display these given
storage sizes for the range of irrigation depths previously determined. A
subsequent graphic display shows the same relationship but plots storage size
in megalitres (or equivalent days of dry weather flow) against irrigation land
area required (in hectares).
Decisions
The major decisions and alternatives considered in constructing this model
and its computer implementation are discussed in this section.
Modelling method
Two alternatives were considered for the basis of the irrigation demand
calculation:
• Direct calculation: Australian rainfall and runoff (ARR) can be used to
estimate the total volume of rain falling on a site during a range of storm
events (Pilgrim 1987).
These figures have often been used to calculate the size of terminal ponds
protecting the downstream ecology of irrigation sites. Additionally the
yearly rain expected may also be estimated from ARR or directly from
rainfall tables. This rainfall estimate could be subtracted from average
evaporation (or evapotranspiration) to yield an irrigation demand. Such
direct calculations could be carried out for a 50 percentile, 75 percentile
and 90 percentile rainfall year to estimate irrigation depths (or land area)
and storage required. The assumed environmental risks would be set to
50%, 25% and 10% of years of wet weather storage overflow.
• Historical simulation: The alternative is to use historical rainfall and
evaporation in a simulation to determine the patterns of rainfall deficit or
irrigation demand for each year. These patterns will determine the yearly
depth of irrigation possible and requirements for wet weather storage.
In most of NSW, although the pattern of evaporation is reasonably
constant from year to year, the yearly rainfall pattern is by no means well
defined. This is exemplified by the long periods of drought and then high
intensity rain leading to floods. Two different years at a high rainfall level
(for example the 90th percentile) will almost certainly have different
Appendix 4 111
rainfall patterns throughout the year and hence different irrigation
demands. This leads to inconsistencies with the direct calculation
approach.
DEC guidelines have adopted a ‘difficult to irrigate’ concept measured by
maximum wet weather storage required during the year. This is reasoned
from a perspective of environmental protection. Such a measure translates
into risk of storage overflow with the possibility of ecological harm. This,
in turn, requires the historical simulation approach used in the DEC model
instead of direct calculation.
Percolation
A reuse water scheme should ideally not pollute either surface or
groundwaters. However, with unpredictable rain this will not always be the
case, though the scheme design should minimise such occurrences. This goal,
however, must be modified in the case of saline wastes. From a land
management perspective, undesirable changes will occur if saline water is
irrigated and all the water and nutrients are taken up by plants. The salt will
not be absorbed, and over time will accumulate in the soil. Therefore,
percolation of effluent is advisable so that introduced salts can be leached
from the root zone to promote healthy plant growth. Fortunately, salts are
very soluble, so that with minimal percolation to groundwater the salt build-
up in the root zone can be prevented.
Where the underlying groundwaters are naturally brackish, then the leaching
of salts will have little or no impact. If however, natural groundwaters have a
low salt content, then the impact caused by leaching must not be excessive to
the point where it lowers the beneficial use of the groundwater.
In the DEC model, an amount of irrigation over the monthly demand can be
applied for the purpose of salt percolation. This over-irrigation only occurs
when such percolation is not naturally supplied by rain, and in any case is
strictly limited in the computer implementation. The maximum percolation
value of up to 15 mm/month (EPA 1995) has been a considerable debating
point. Some arguments suggest that the proposed value is inadequate.
Although DEC or local council would, of course, consider any reasoned
proposal for a higher figure, the current DEC opinion is that higher values
would represent wastewater disposal, not reuse, and would increase the risk
of groundwater pollution. It should be noted here that in coastal NSW, with
high rainfall, DEC does not expect that schemes will need any irrigation-
supplied percolation.
Appendix 4 113
the substitution curve for a given environmental risk. Initially the curve is in
terms of millimetres of irrigation and so is independent of actual effluent
volumes. Doubling the effluent volume will obviously double both the land
and storage required.
For easy interpretation in the computer implementation, the values for
effluent volumes are used to re-scale the capacity independent relationship in
terms of storage volume in ML (or days of supply) versus land area.
Crop factors
The crop factors are the adjustments to evaporation to reflect actual crop
usage of water. For simplicity, the DEC model combines all the influences into
one site-specific set of monthly factors. DEC crop factors also include the ‘pan
factor’ which relates the Pan A evaporation to evaporation from a surface (i.e.
soil or crop surface). The actual crop factors to be used on any particular
scheme should be supplied at the design stage. Therefore there is no crop-
specific or site-specific values fixed by the DEC model. This was implemented
to ensure that the model is useable independent of location.
Appendix 4 115
accommodate wet weather flows to enable both use for feedlot schemes and
better estimation for STP effluent.
The wet weather flow is modelled as a linear function of rainfall between two
limits. The lower limit is set in terms of millimetres of rain before runoff (or
wet weather flow) is assumed to occur. That is, the value can be set so that
light showers will not produce wet weather flow. The upper limit is set in
terms of flow volume, and for a sewer system would represent the maximum
hydraulic flow of the pipe-work. For animal feedlots, this upper limit would
be the maximum design storm event that the scheme will be required to deal
with. The function relating rainfall to wet weather augmented flow is as
simple as possible while still being compatible with current practice using
runoff coefficients.
Precautionary discharges
Precautionary discharges can be used to ensure that discharge occurs when
conditions will minimise environmental impacts (rather than uncontrolled
overflows as discussed in Section 4.2.) This approach is only permitted when
Appendix 4 117
From the cumulative distribution of IDy identify
• G0 = ID[0%] ÷ 2 (half the lowest value) and
• GL = ID[10%] (10% point on cumulative distribution)
as lower and upper grid limits for depth of irrigation. These may be adjusted
but usually give good limits.
For all grid points define
S(g) = G0 + (GL - G0) × (g - 1) ÷ (ng - 1)
as supply levels for the range of irrigation depths
Set
• Fy,m to be the fraction of yearly flow in year y, month m. Here
yearly flow is dry weather flow plus average yearly wet
weather flow. Note that SFy,m m=1.12 may exceed 1 for years
with significant wet weather flows
• ADJy,m to be the net adjustment for rain and evaporation over the
storage area
• UDy,m to the unsatisfied irrigation demand due to lack of effluent
water
• PDy,m to precautionary discharges (mostly = 0)
then
ADDg,y,m = S(g) × Fy,m + ADJy,m - [ (IDy,m - UDy,m) + PDy,m]
is the net addition to storage for irrigation rate g in year y and month m;
Qg,y,m = ∑ADDg,j,n {j, n} = {ymin,1} .. {y,m}
is the storage volume for irrigation rate g in year y and month m;
QYg,y = max Qg,y,m defines yearly storage maximums.
Using the cumulative distributions QYg,[x], derived from QYg,y select the
value corresponding to environmental risk r% of overflow using all years.
QS(g)r = QYg,[100 - r%] is the model solution storage level given irrigation
depth g for environmental risk r%. Note for a given environmental risk r QS is
a function of irrigation depth g.
Management of all reserves and dedicated areas under the National Parks and
Wildlife Act 1974.
Planning matters:
Department of Approval of works under Local Government Act 1993 (Section 60) and provide
Energy, Utilities and for sewage being discharged, treated and supplied to any person.
Sustainability
NSW Department of Advice on: agricultural best management practices; site management and
Primary Industries assessment; soil, pasture/crop and irrigation management; animal health; and
constructing and managing effluent storage dams.
Advice on important fish and fisheries and proximity to sensitive fish habitats.
NSW Health Advice on health protection measures for effluent irrigation schemes.
Appendix 5 119
NSW Food Food hygiene and contamination.
Authority
Regulatory Authority for pollution control for irrigation schemes that are not
regulated by the EPA through a licence, i.e. most schemes on Schedule 1 of
the POEO Act.
Water Authorities Management of special or controlled areas for drinking water supplies.
Sydney Catchment Concurrence and notification roles in planning decisions affecting water quality
Authority within Sydney water supply catchment.
Contact details for regional and district DEC offices can be found at
www.environment.nsw.gov.au/about, or by calling Pollution Line on 131 555.
Appendix 6 121