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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