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Dairy effluent: Protecting groundwater

Updated: April, 1999
Note Number: AG0841
ISSN 1329-8062
David Hopkins (Colac) and Colin Waters (Ellinbank)

This Agriculture Note is a guide to protecting groundwater from dairy effluent.

The protection of our groundwater resources is important for our nation's survival. Dairy effluent has significant levels of nitrate which has the potential to contaminate groundwater. Proper siting and construction of dairy effluent ponds and careful application of effluent to pastures and crops will help minimise nitrate contamination.

Groundwater is defined as the water beneath the surface of the earth. It is the water we find in wells, bores, springs, and which helps sustain life in surface waters such as streams and wetlands in dry periods.

It forms the main source of water supply for many towns and farms where surface water supplies are limited. For example in the south west of Victoria, Geelong, Timboon, Port Fairy, Portland (and others) all use groundwater in town water supplies. Many farms also use groundwater for their dairy water and stock supplies. In inland Australia, if not for groundwater, there would be far fewer communities. About 18% of Australia's total water use is derived from groundwater.

In the USA, half the population rely completely or partially on groundwater , and similar figures are available for Europe.

Consequently protection of this valuable resource is important for human prosperity.

Groundwater contamination

Wherever there is human activity there is potential for groundwater contamination. In agriculture, groundwater can be contaminated from point sources such as effluent ponds or diffuse sources such as pesticide and fertiliser use.

Typical examples of contamination sources are:

  • industrial effluent and manufacturing effluents
  • leaking underground storage tanks and pipelines
  • landfills and stockpiles of contaminated soil
  • intensive agricultural use of fertiliser and animal wastes and pesticides
  • septic tanks and effluent lagoons
  • mining industry wastes
  • contamination of bores and wells
  • urban stormwater

Why should I protect groundwater?

In many cases, groundwater probably assists farm productivity. This may either be directly through providing water from a bore, dam or spring, or providing stock with drinking water. Groundwater is also important where it flows into streams and lakes and assists in the protection of aquatic life.

Groundwater moves through cracks in rock and in the pore space in soils. Where these cracks are tight or the soil contains clay, groundwater travels very slowly. As a result, the impact we have on groundwater today may not become obvious for many years. There is no doubt that some of the groundwater problems we are now suffering are due to human activities undertaken decades ago. Protecting groundwater today will therefore help in protectingproductivity of our farms in years to come, as well as the livelihoods of the next generation of farmers.

Nitrate

One of the major concerns with dairy effluent is the significant levels of nutrients in particular nitrogen in the form of nitrate.

  • Nitrate leaches readily through the soil (if it is permeable) and can reach the groundwater.
  • Nitrate lasts a long time in the environment and can travel long distances once in groundwater.
  • Nitrate can adversely affect human health.
  • Nitrate may indicate other contaminants are present.

Nitrate is a health concern particularly for young infants, causing a sometimes fatal condition called methhaemoglobinaemia or "blue baby syndrome". In areas where high nitrates in water have been found such as old volcanic eruptions points (eg. around Colac, Warrnambool, and Mortlake) it is wise to have the drinking water tested if you are using bore water and have a baby under six months. Above that age babies are able to cope as well as adults.

Nitrate groundwater limits

Groundwater nitrate levels above recommended limits have been found in all regions in Victoria.

Australian and New Zealand Environment and Conservation Council (ANZECC) guidelines for drinking water specify that nitrate levels should not exceed 10 mg/l. The ANZECC guidelines for natural ecosystems indicate problems would be expected at nitrate levels at or above 0.1-0.75 mg/l.

If groundwater measuring 10 mg/l nitrate-N moves through the soil and reaches a stream then the effect on the aquatic life can be devastating. High nitrates in surface waters enable greater plant growth and if conditions are right more potentially toxic algal blooms.

Hence it is most important to keep nitrates out of the groundwater wherever possible.

Managing dairy effluent to prevent groundwater pollution

The main potential sources of groundwater pollution from dairy effluent are storage ponds and inappropriate application of effluent to land.

Storage ponds

Point sources such as effluent ponds if not properly sealed are a potential source of pollution to groundwater. Thus, a properly sealed effluent pond is imperative. A effluent pond that never fills is a sure indication that leakage to the groundwater is occurring.

So, when designing and building ponds:

  • Seal all ponds with clay or some other impermeable material.
  • Avoid sandy or gravel soils unless you have sealing materials.
  • Avoid wet sites where the groundwater is close to the surface. This situation can lead to groundwater entering the pond and effluent leaving the pond.
  • Choose a site where the groundwater table is at least 0.5 metres below the base of the pond at the wettest time of the year.
  • If it will be difficult to seal the pond, consider whether direct irrigation of effluent is a better option on your farm.

See Agriculture Note AG0424: Dairy effluent: Pond site selection.

Effluent application to land

As nitrate is long lasting in the soil and travels readily in soil water, it is important to apply it to pastures and crops at the right time and in the right quantity to minimise leaching to groundwater.

The key things to remember when applying effluents are:

  • actively growing and can utilise the nutrients. For example the end of spring and just after the autumn break.
  • Apply small quantities of effluent at a time (about 25mm or 1 megalitre per 4 ha.) so that it stays in the root zone of the pasture and can be used by the plants. Application should not exceed crop requirements.
  • If possible avoid applying effluent when the soil is saturated. If you have a direct irrigation system, irrigate the effluent as widely as possible under these conditions.
  • Avoid applying effluent to the same area year after year.
  • Avoid applying large volumes of effluent to sandy or gravely areas just because it does not run off. It will probably be moving straight to the groundwater.

For further details on application rates see Agriculture Note AG0419: Dairy effluent: Application to pastures.

Further information

If in doubt you can get further advice from your nearest DPI or EPA office.

Department of Primary Industries:

Colac - 03 5233 5500
Ellinbank - 03 5624 2222
Kyabram - 03 5852 0500
Leongatha - 03 5662 2204
Warrnambool - 03 5561 9900
DPI internet Site - www.nre.vic.gov.au

Environment Protection Authority:

Traralgon - 03 5176 1744
Wangaratta - 03 5721 7277
Bendigo - 03 5442 4393
Dandenong - 03 9794 0677
Geelong - 03 5226 4825
EPA internet site - www.epa.vic.gov.au

This publication may be of assistance to you but the State of Victoria and its officers do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.