Indicator: Discharges to Waters

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Summary

A number of accidental and illegal discharges occurred in the ACT over the reporting period due to accidents to infrastructure, and due to major storm events.

The combined effects of extended low flow conditions and isolated, extreme storms led to significant event-based discharges that had a deleterious effect with on- and off-site impacts during 2000–03.

There has been a decreasing trend in discharges to waters over the reporting period, although there can be significant variation on a month-by-month basis.

There has been a decreasing trend in discharges to waters over the reporting period, although there can be significant variation on a month-by-month basis.

What the results tell us about the ACT

Water is discharged legally into streams in the Australian Capital Territory from urban runoff (stormflow) and treated sewage effluent. These discharges have the capacity to transport pollutants as nutrients (nitrogen and phosphorus), agricultural chemicals (as fertilisers, herbicides and pesticides), and suspended solids derived from urban surfaces and industrial sites.

Although sewage treatment plants are the main point source of pollutants, high levels of treatment may mitigate impacts on the environment.

In addition to legal discharges, a number of accidental and illegal discharges have occurred in the ACT over the reporting period due to accidents to infrastructure, and to major storm events.

The combined effects of extended low flow conditions and isolated, extreme storms led to significant event-based discharges with deleterious on and off-site impacts in the ACT during 2000–03, and can be expected to continue under current climatic conditions.

Discharge of treated sewage

The total municipal discharge volumes for the 2000–03 reporting period suggest a decreasing trend in discharges to waters (Table 1),

There can be significant variation on a month-by-month basis (see the monthly data in Table 2).

Lower Molonglo

The Lower Molonglo Water Quality Control Centre (LMWQCC) treats nearly all of Canberra's sewage. Treated water from the centre is discharged to the Molonglo River just above its confluence with the Murrumbidgee River. There is significant inter-annual variability in effluent loads at this site, due to both climatic factors and the performance of the water treatment centre.

Table 1: Municipal discharges to waters, 2000–03
Year ending June 30 Discharge (gigalitres)
LMWQCC QSTP Total
2000 32.6 3.9 36.5
2001 30.3 3.9 34.2
2002 30.6 3.8 34.4
2003 28.4 2.3 30.7

Source: Environment ACT (2004) Think water, act water

Table 2. Volume of treated effluent discharged from LMWQCC per month in megalitres, 1999–2000 to 2002–03
Month 1999–2000 2000–2001 2001–2002 2002–2003
July 2579 2368 2444 2484
August 2694 2594 2545 2517
September 2754 2592 2714 2635
October 3345 2841 2569 2543
November 2542 3160 2398 2334
December 2800 2433 2370 2247
January 2731 2118 2399 2109
February 2467 2470 3015 2163
March 2746 2520 2624 2405
April 2751 2298 2516 2270
May 2471 2341 2533 2389
June 2305 2316 2420 2288

(Ray Brown, ActewAGL, pers.comm.)

Other treatment facilities

In addition to this major site, there are a number of small sewage treatment plants outside metropolitan Canberra in the ACT, including Cotter Effluent Absorption Facility (operated by ACTEW). This services the Casuarina Sands picnic area and ranger dwellings through a common effluent collection system, and discharges to a CSIRO-designed sub-surface effluent absorption facility. There are also small schemes at the Tidbinbilla Tracking Station, river picnic ground facilities at Uriarra, Tharwa, Woods Reserve, Orroral Valley, and others under the ownership of Parks and Wildlife, Forestry, and ACT Housing which service either picnic grounds or a very limited number of dwellings.

Infrastructure damage from fire

The fires of January 2003 damaged infrastructure at the LMWQCC with consequent impacts on the capacity of the plant to treat sewage; however, untreated sewage was not discharged from the site during or after the bushfires (Ray Brown, ActewAGL, pers. comm.).

Accidental discharges

A number of accidental discharges occurred during the 2000–03 reporting period, some of which impacted water quality and generated concerns for aquatic ecosystem and human health.

Approximately 2000 litres of diesel oil leaked into soils and Lake Burley Griffin in 2000 from a damaged pipe in Parliament House. In March 2001, about 120,000 litres of effluent from a damaged sewer in Jerrabomberra Creek catchment discharged into the creek, and a proportion reached Lake Burley Griffin. the lake closed as a result.

Additional concerns were raised during the reporting period due to discharge of stormwater after major rainfall events being associated with elevated nutrient, sediment and faecal coliform concentrations.

These events and the associated lake closures have drawn attention, during the reporting period, to water quality and the designated uses (particularly recreation) of urban lakes.

Given the prolonged drought conditions that are expected to continue, and the pressures exerted by increasing urbanisation, the condition of the urban lakes in relation to stormwater and accidental discharges will continue to be an issue in the immediate future.

Data sources and references

Environment ACT 2004, Think water, act water Volume 3: State of the ACT’s water resources and catchments. Australian Capital Territory, Canberra, April 2004.

Personal Comment: E-mail from Ray Brown, Manager Operations and Maintenance, Treatment Branch Water Division ActewAGL Distribution, Lower Molonglo Water Quality Control Centre, Stockdill Drive, Holt ACT 2615

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