Turf areas are an important part of our everyday lives. Turf enhances the visual amenity of our landscape and improves our living environment. In order to maintain these turf areas at a desired quality, a variety of chemicals and equipment are used. This equipment requires regular maintenance to ensure it functions effectively. Unfortunately, the washdown of vehicles, containers and spraying equipment can impact adversely on the environment if not managed correctly.

Washdown from turf areas contains grass clippings, detergents, grease oil and other chemicals (e.g. pesticides and wetting agents). Turf washdown differs from other washdown in that it has a high organic component resulting in a high biological demand (BOD). Some chemicals in the washdown can be readily treated whilst some are quite persistent and are difficult to treat. Chemicals such as pesticides can be toxic at part per billion concentrations.

Washdown Management

Fortunately, washdown from turf sites can be easily managed. There are several factors to consider when designing a washdown facility:

• The composition and volume of wastewater;

• Characteristics of the receiving environment;

• Legislative requirements;

• Cost (installation and ongoing costs).

Washdown from turf areas often contains a large quantity of grass clippings. These pose a high organic load and can decompose and cause nutrient and odour problems. It is important to remove as much of these clippings (either before maintenance or before treatment) as they put unnecessary loads on the treatment system. Poorly designed treatment systems will require increasing maintenance to ensure filters and soakwells are not blocked by excess grass clippings.

Characteristics of receiving environment

The nature of the receiving environment will determine the final water quality criteria (and hence treatment level required) and limit disposal options. More stringent criteria apply to environmentally sensitive areas such as public drinking water source areas or in close proximity to waterways or wetlands. Sewerage service providers also set criteria on the concentration and volume of waste that can be discharged to sewer.

It is important to test washdown water and compare it to discharge criteria. This will help in determining the level of treatment required. For example, if the sewer limit for oil and grease is 50 mg/l and the washdown water is 28 mg/l, then you would not need to treat for oil and grease before discharge to sewer. Alternatively, if the washdown had a BOD of 500 mg/l and the sewer limit was 150 mg/l then the waste would require treatment to reduce the BOD.

Legislative requirements

Approval is usually required by local government to install a treatment system and this may be subject to local by-laws. In sensitive environments, there may be additional requirements specified by the environmental regulator (Department of Environmental Protection and Health Department in Western Australia).

Discharge to sewer will require approval from the sewerage service provider to ensure that treated water is of a suitable quality to be discharged to sewer.

Cost considerations

More complex systems will cost more to install and operate. It is important to consider ongoing maintenance and running costs including chemicals, electricity and disposal costs. Treatment capability should not be compromised in order to meet your budget. It may be possible to build a system up over time or look at alternative options until funds become available.

Design Principles

The basic principles for designing and operating a washdown area are:

• All washdown should be contained.

• Stormwater run-off from the area should be minimised.

• Uncontained stormwater should be kept separate from contaminated water.

• Washdown water should be collected and treated to an appropriate standard before disposal.

Treatment options

The first stage of treatment is usually some form of detention basin to assist in flow regulation. This holding pit contains flows, which are subsequently pumped out to the treatment system. Wastewater treatment systems function more effectively when there is a uniform flow through the system.

Treatment options will depend on the composition of the wastewater. Normally, washdown will firstly require solids removal to remove grass clippings and solids (sand particles etc.). This is usually achieved through a combination of a coarse screen and setting pit.

Washdown will often need to undergo biological treatment to reduce the BOD. Sources of nutrients include fertiliser applied to the turf as well as those in grass clippings. Biological filtration can take a number of forms including:

• Filter system where waste water is passed over a media containing micro-organisms which will break down the chemicals,

• Artificial wetlands that use natural processes to remove nutrients.

Biological breakdown depends on temperature and this will be influenced by climate.

Oil and grease removal relies on a physical separation process because these substances are hydrophobic and hence float on water. Techniques include triple interceptor pits, coalescing plate separators or similar.

Removal of other chemicals such as pesticides are generally not included in the treatment process due to the high cost of treatment. There are chemical and biological treatment processes that have various levels of success.

Disposal options

The disposal options available will depend on the nature of the receiving environment. It is preferential to reuse the treated washdown water on-site if this is possible.

Options for disposal of treated washdown water include:

• Recycling for future washdown. This would be appropriate where low-cost water is not readily available.

• Irrigation of turf or gardens either directly or diversion to an irrigation dam for later use.

• Discharge to sewer provider the water quality meets the requirements of the sewerage service provider.

• Local groundwater recharge by discharge to soakwell.

• Direct discharge to nearby wetlands, rivers or drains provided relevant approvals are obtained.

All these requirements will need an assessment of water quality to make sure they are suited to their intended use or disposal option. Some options require prior approval from the environmental regulator.

The washdown process will also produce a large quantity of solid wastes mainly consisting of grass clippings and soil. These solids should be collected and composted on site or dispersed over a turf area. Care should be taken with the storage and placement of this material so it is not washed into local wetlands, rivers or drains. Sometimes the solids will need to be disposed offsite and may be recycled e.g. for use in soil blends.

Oils, grease and hydrocarbons recovered by the oil separator should be collected and securely stored for recycling or disposal at an approved site. Waste disposal contractors will take this waste to an approval facility for a fee.

Consideration must be given to the environmental impact of the disposal option. For example, the risk of groundwater contamination can be high when water is drained off hardstand areas into soakwells or infiltration basins. This is because water is concentrated in a small area below the root zone of many plants and water loss by transpiration and evaporation is minimised. In addition, the hydraulic head imposed by a large volume of water in an infiltration basin acts as driving force that can push water and any dissolved contaminants quickly through the soil profile and down to the watertable.

System maintenance

A regular maintenance schedule is required to ensure a treatment facility functions in accordance with to its design. This may include cleaning of pits and grates, backwashing and addition chemicals and/or microorganisms. Some of the package treatment systems available have these features built in.

Regular testing of the quality of both washdown water and treated water should be undertaken to determine the effectiveness of the treatment system.

Education and training

One of the most important aspects of washdown management is the education and training of staff. Staff should be made aware of environmental issues and the impacts that washdown may have on the environment. Only trained staff should use equipment and operate washdown facilities.

Consequences of poor management – case studies

The importance of correct management cannot be understated. In November 1997, a spill of 600 litres of insecticide occurred at Belmont Park racecourse, situated on the banks of the Swan River. The spill was not immediately reported and was only discovered after over 4000 black bream fish were killed, representing approximately 30% of the rivers fish stock. This repeatable tragedy was due to the lack of preparedness or emergency response of racecourse staff who could have prevented the spill or at least reduced its effects. The lever to prevent the valve leaking on the 600 litre mobile tank was inadvertently left open and slowly drained into a stormwater drain near where the tank was parked. No emergency authorities were alerted and the insecticide was transported straight to the river via the drain. Similar events happen every day, fortunately of a smaller scale.

A pesticide contamination problem was detected in the Perth suburb of Dianella in 1992 when a resident reported that his garden was dying when irrigated with groundwater from his domestic bore. The groundwater was found to contain 2000 ug/L (equivalent to parts per billion) of atrazine which was killing plants in the garden (Appleyard, 1995). The groundwater also contained fenamiphos at a concentration of 1000 ug/L. At this concentration, fenamiphos could be toxic on skin contact and cause health problems.

The source of contamination was found to be pest control operator who washed down vehicles at his residence across the road from the contaminated bore. Washdown water was drained into filtration basins on the property. A groundwater remediation program was undertaken at the site, but thus was not successful, as indicated by further contamination being detected in domestic more than 300 metres downgradient of the source.

Additional investigations were carried out by the Water and Rivers Commission to determine whether the Dianella contamination problem was an isolated occurrence or a more widespread contamination problem. Investigations were carried out around five pest control depots in the Perth metropolitan area in 1995 and 1996 (Appleyard et al., 1997). A number of pesticides were detected in groundwater near washdown areas, with concentration of some pesticides exceeding ANZECC criteria for drinking water and the protection of aquatic ecosystems. Persistent organochlorine pesticides such as dieldrin, which have not been used for many years, are still being detected in groundwater. The most widely detected pesticide in groundwater was diazinon. This pesticide is not normally considered to have a high mobility in water, but its mobility is being enhanced by washdown water being discarded to infiltration basins and soakwells.

References

Appelyard, S.J., 1993, Impact of stormwater infiltration on groundwater quality, Perth metropolitan region, Western Australia. Environmental Geology, 21 pp.227-236.
Appleyard, S.J., 1995, Investigation of ground water contamination by fenamiphos and atrazine in a residential area: source and distribution of contamination. Ground Water Monitoring Review, Fall edition, pp. 110-113.
Appleyard, S.J., Manning, P. and Thorpe, P., 1997, Pest control depots as sources of groundwater contamination in Perth, Western Australia. Land Contamination and Reclamation, 5 (4), pp. 229-305.