ACT State of the Environment 2007

Indicator: Discharge to waters

Summary

In response to the drought and the consequent water demand management measures, there has been a decrease in the volume of the discharge to waters in the ACT from the major point source of the Lower Molonglo Water Quality Control Centre (LMWQCC).

The quality of the discharge from the LMWQCC for the reporting period complied with the Environment Protection Authority guidelines. While this is an excellent result for the reporting period, the results discussed in the Surface water quality indicator suggest that the discharge from the LMWQCC is the single largest point source of pollutants within the ACT.

What the results tell us for the ACT

Any water that is discharged to waterways has the potential to introduce contaminates such as nutrients, chemicals and heavy metals. Water that is legally discharged to waterways includes storm water runoff from urban and agricultural lands and treated sewage from treatment plants.

In the ACT, discharges to water are mainly derived from the LMWQCC, the Territory's major sewerage plant. The LMWQCC discharges treated water to the Molonglo River, a few hundred metres upstream of the confluence with the Murrumbidgee River. The volume of water discharged from LMWQCC is summarised in Table 1.

Table 1: Monthly volumes (ML) discharged from Lower Molonglo Water Quality Control Centre 1999–2000 to 2006–07
Year Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
1999–2000 2,579 2,694 2,754 3,345 2,542 2,800 2,731 2,467 2,746 2,751 2,471 2,305 32,185
2000–01 2,368 2,594 2,592 2,841 3,160 2,433 2,118 2,470 2,520 2,298 2,341 2,316 30,051
2001–02 2,444 2,545 2,714 2,569 2,398 2,370 2,399 3,015 2,624 2,516 2,533 2,420 30,547
2002–03 2,484 2,517 2,635 2,543 2,334 2,247 2,109 2,163 2,405 2,270 2,389 2,288 28,384
2003–04 2,380 2,605 2,455 2,507 2,437 2,406 2,143 2,125 2,266 2,178 2,269 2,189 27,960
2004–05 2,185 2,377 2,342 2,373 2,429 2,337 2,192 2,106 2,236 2,191 2,255 2,269 27,292
2005–06 2,663 2,463 2,709 2,653 2,569 2,326 2,333 2,126 2,333 2,236 2,301 2,307 29,019
2006–07 2,405 2,356 2,302 2,270 2,212 2,077 2,048 2,006 2,241 2,087 2,240 2,193 26,437

Source: ActewAGL

During this reporting period, the volume of discharges to waters from the LMWQCC have declined as a result of the water availability problems stemming from the drought and consequent water demand management measures. 2006–07 saw the lowest volume of discharges during this time.

The quality of the discharge leaving the LMWQCC is summarised in Table 2. Apart from the diffuse source water quality problems associated with land use and the 2003 bushfire, the LMWQCC is the single largest point source of pollutants within the ACT. While this is the case, the LMWQCC meets the discharge standards set by the Environment Protection Authority. Not enough data were available at the time of writing to estimate the loads of this contribution, however the effect of this discharge on water quality is discussed in the Surface water quality indicator.

Table 2: Lower Molonglo Water Quality Control Centre summary of effluent water quality data June 2000 to April 2007
Parameter Unit Number of samples Mean value
Biochemical oxygen demand mg/L 2,671 <2
Chemical oxygen demand mg/L 2,670 14
Conductivity µS/cm 2,670 700
Dissolved organic carbon mg/L 14 8.2
pH 2,701 7.7
Suspended solids mg/L 2,702 <2
Temperature Deg C 2,644 21
Total dissolved solids mg/L 2,671 480
Total organic carbon mg/L 130 5.7
Turbidity NTU 342 1.7
Ammonia mg/L 2,673 0.1
Oxidised nitrogen mg/L 2,673 22
Total nitrogen mg/L 2,673 23
Orthophosphate mg/L 2,673 0.082
Soluble phosphate mg/L 29 0.099
Total phosphorus mg/L 2,673 0.15

Key: mg/L = milligrams per litre; µS/cm = microSiemens per centimeter; Deg C = degrees Celsius; NTU = nephelometric turbidity units.
Source: ActewAGL

The ACT in the Murray Darling Basin

Data presented in Surface water quality show that the quality of the water leaving the ACT is inferior to that entering the ACT. The main water quality issue identified is the discharge of salts from the LMWQCC. Recent ActewAGL estimates of the sources and fate of salts in ACT waters found that 127 tonnes per day (t/day) passed through the Murrumbidgee at Halls Crossing. Some 50 t/day of this entered the ACT through the upstream Molonglo and Murrumbidgee Rivers. Within the ACT, catchments generated some 39 t/day through natural catchment processes and land use impacts. The remainder, some 38 t/day, was derived from the Territory's human population; this load of salts is exported through the LMWQCC.

The fate of the salt once it leaves the ACT becomes an issue further down the Murrumbidgee River. Following export from the ACT the load enters the Burrinjuck Reservoir; the Territory's contribution totals some 24% of the total salts entering Burrinjuck.

While this is not regarded as a large contribution to the Murrumbidgee, the contribution can be lessened. At the time of writing, efforts were being discussed between ACTEW and the ACT Government on methods to manage the salt load exported from the LMWQCC. Efforts at the LMWQCC to reduce the total dissolved solids (Salt load) are likely to be expensive and further investigation on targeted salt reduction programs in other parts of the downstream river system may lead to more effective and efficient salt reduction outcomes. However, it is possible to effect a small reduction in salt loads entering LMWQCC from the household such as by the use of salt reduced detergents. Efforts to address both these issues should occur during the next reporting period.

Data sources and references

ActewAGL supplied information for this indicator

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