State of the Environment

2001

Inland Waters Theme Report

Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7

Water quality and sources of pollution (continued)

Groundwater pollution

Pressure: Sources and causes of groundwater pollution [IW Indicator 3.6]

There are many well-documented cases of groundwater pollution in Australia. Experience from Europe and North America suggests that groundwater pollution in Australia will become a more serious issue in the future. Both diffuse and point sources contribute to groundwater pollution and dependent ecosystems.

Diffuse-source pollution can occur over large areas and involve widespread land-use practices or numerous small sources.

Pollutants from point sources are generally related to urban development, while diffuse sources are generally rural in nature. The most significant diffuse contaminant of groundwater in Australia is nitrates, due to their adverse affects on people, animals and the environment (SKM 2000c). The most significant point-source contaminants include underground storage tanks (hydrocarbons), septic tanks, landfills (various), intensive rural industries (nitrate), cattle and sheep dips (pesticides), manufacturing spills (pesticides, organochloride solvents), gas works (coal, tars, ash, coke) and mining-related activities (heavy metals, acid, hydrocarbons).

National (NWQMS 1995) and state guidelines for groundwater protection rely on a framework in which existing or potential beneficial uses for each groundwater resource are identified. The choice of a beneficial use classification depends on the quality of groundwater present and the potential values of the groundwater in the long term (NWQMS 1995). The following beneficial uses were recommended by the NWQMS Guidelines for Groundwater Protection in Australia (1995):

Each beneficial use category has a unique set of 'water quality criteria', which refers to a list of the critical concentrations of contaminants in the groundwater that must not be exceeded if a beneficial use is to be sustained (DLWC 1998). 'Pollution' is a specific impairment of water quality by human activity or land use change to a degree that has an adverse effect on the beneficial use of the water (Barber 2000).

Groundwater pollution in Australia (and especially diffuse pollution) is not considered a major issue by government, and therefore groundwater quality information is limited.

Nitrate pollution

The key activities that can generate or mobilise nitrates and contaminate groundwater involve human activities or human introduced sources (LWRRDC 1999).

Human activities that mobilise nitrates are:

Human introduced sources include:

The quantity of nitrates that leach into groundwater is related to the amount of nitrogen deposited on the land surface, the ability of plants to use nitrogen and the breakdown of organic nitrogen in the soil. Elevated concentrations of nitrate in groundwater destined for domestic use and stock watering are a health risk. The toxic effects of nitrate are particularly high in infants due to methaemoglobinaemia. There is also evidence that nitrate may be converted to suspected carcinogenic nitrosamines in the human digestive tract (ANZECC/AWRC 1992).

Where groundwater discharges to surface waters, nitrate can also cause nutrient enrichment. Elevated nitrate concentrations in surface waters can alter the nitrogen to phosphorus ratio, resulting in increased risk of eutrophication and algal blooms (LWRRDC 1999).

Pesticides (diffuse contaminants)

For a full discussion of pesticide use and trends see the Land Theme Report.

Groundwater contamination by pesticides is of concern where the resource is used for domestic supply or irrigation, where it contributes to baseflow of adjacent rivers, or where rising water tables are alleviated by pumping to nearby surface waters (Bauld 1994).

Other pressures

Three other diffuse pollutants are microbiological contaminants such as bacteria, fungi and protozoa; contamination by seawater intrusion; and arsenic generation. Microbiological contaminants are of concern where groundwater is used for domestic and agricultural purposes. Seawater intrusion is a significant pressure on coastal groundwater resources and was studied intensively in 1960s and 1970s. In more recent times, seawater intrusion has not been recognised as an issue, despite many coastal aquifers suffering from its effects. A case study on seawater intrusion is presented below, on the Bundaberg region in Queensland.

The drawdown of water levels (either permanently or periodically) by pumping from coastal sand-dune systems is a hazard for unreticulated domestic water users in eastern Australia as it can result in the release of arsenic from the crystal matrix of oxidised pyrite.

Underground tank contamination

Hydrocarbons are the principal constituents of petroleum and natural gas. Pollution of groundwater by hydrocarbons has been documented extensively in the US and Western Europe and to a lesser extent in Australia (Barber et al. 1990).

Case study 5: Seawater intrusion - Bundaberg, Queensland

In the 1880s, Bundaberg established itself as a major centre for growing and milling sugar cane and refining sugar. High sugar prices, favourable government policies and readily available water caused a rapid expansion of the sugar industry in the region so that Bundaberg became the largest southern source of sugar cane in Queensland. Today, the cultivation and manufacturing of sugar remain the mainstay of the region's economy.

In 1992, Bundaberg was the largest of Queensland's major irrigation areas, with 55 638 hectares being supplied with water from a combination of surface water and groundwater resources. Surface water is provided to the Bundaberg area from the Burnett, Kolan and Elliott rivers. Four major storages in the area have a combined capacity of 159 000 ML per year.

The Bundaberg Groundwater Area (BGA) occupies a coastal strip approximately 20 km wide, extending north from Theodolite Creek to the Kolan River. The aquifers consist of a series of poorly interconnected sand and gravel channels that slope gently towards the coast. These aquifers are split by an intervening clay layer into two vertical components. The Elliott Formation lies between 5 m and 35 m below sea level and is intersected by the estuaries of the Kolan, Burnett and Elliott rivers. The underlying Fairymead Formation extends to 100 m below sea level in some places.

The BGA's total annual groundwater allocation is 65 000 ML based on 1970 use levels. Based on sustainable water levels, the estimated yield is 54 500 ML. Actual water use ranges from 30 400 ML to 65 000 ML, but has exceeded the allocation in drought years - for example, 74 400 ML in 1994-95. When this happens, the salt front (where freshwater, acting like a piston, prevents underground seawater intrusion) moves inland. Water withdrawn downstream of the salt front will be contaminated.

Since 1994-95, excessive use of groundwater has been banned in the BGA. Restrictions have been set to limit use, particularly in coastal areas where saltwater intrusion is more likely. Saltwater intrusion monitoring occurs at 80 sites to determine the movement of the salt front, changes in extent, responses to changes in groundwater level, long-term trends and responses to management.

Saltwater now underlies 580 ha at Elliott Heads and 6700 ha of the Burnett Heads peninsula. Water quality in the Elliott Formation appears stable. Water quality in the Fairymead Formation deteriorated to a low in 1994 but seems to have improved slightly since restrictions were imposed.

Source: Extract from State of the Environment, Queensland 1999, Queensland Environment Protection Agency.

Spillages and leakages of petroleum products from petroleum refining facilities, storage (principally from underground storage tanks) and petrol stations can cause surface-soil and groundwater contamination. Corrosion is the primary cause for leakage of carbon steel fuel storage tanks. Although petroleum hydrocarbons are of low solubility, very low concentrations can impart objectionable tastes and odours in drinking water. Also benzene and polynuclear aromatic hydrocarbons, which are more soluble components of petrol, are known carcinogens (Barber et al. 1990).

The gas and coal industry

Wastes produced from the conversion of coal to gas have contaminated over 100 sites in Australia. Some sites have long histories, stretching back to the 19th century (Knight 1993). The dominant contaminants associated with the process of conversion are:

The main chemicals of concern include organic chemical groups, polynuclear aromatic hydrocarbons (PAH), in particular benzo(a)pyrene (BaP) which is suspected of being carcinogenic, as well as volatile aromatics and phenolics.