6: Development of Benchmark Levels for Water Quality

6.1 General

The water quality of Lake Burley Griffin has been extensively monitored since about 1978, by a number of organisations, including:

Water quality in the Lake and its tributaries has also been the focus of a number of research studies (including Honours, Masters and Doctoral projects), from:

Community groups, through Waterwatch ACT, have also collected water quality information on the Lake and its surrounding tributaries.

Collectively, these various efforts have provided a considerable amount of valuable information on water quality in the Lake, and have made the Lake one of the most studied lakes in Australia (Atech Group, 2002).

Consequently, it is possible to provide some good indications for benchmark water quality values within the Lake.

A summary of these benchmark values for the respective environmental values is provided below, with additional information in subsequent sections of the previous chapter:

Environmental value: Ornamental water

Environmental value: Protection of freshwater aquatic system

Environmental value: Recreational water

Environmental value: Irrigation water for parks and gardens

6.2 Methodology

The National Water Quality Management Strategy (NWQMS), which has provided the ANZECC/AMRCANZ (2000) guidelines, has suggested that communities develop their own water quality objectives in their local environment, based on a number of factors, including:

This Lake Burley Griffin WQMP generally follows the above-mentioned NWQMS procedures. However, instead of using water quality objectives (based on the 80th percentile values), this WQMP uses water quality benchmark values (which are close to, but not necessarily exactly, at the 80th percentile value for each data set).

Because the Lake has been extensively studied, it is possible to establish benchmark values for the key water quality characteristics at levels that in the past have shown no adverse effects (in terms of either ecology or human health).

This approach is suggested, as it is unlikely that the community would be interested in paying for and providing a more stringent benchmark than one that showed no adverse effects on the environment or on human health. For example, it is unlikely that the community would be willing to pay for increased phosphorus removal at the Queanbeyan Wastewater Treatment Plant (upstream of Lake Burley Griffin), if current phosphorus concentrations showed no adverse effects. Limited financial resources would then be allocated to other, more needy water quality issues (or indeed to a range of other general issues such as schools, hospitals, roads etc).

It is important to balance the above approach (using specific information on the Lake) with:

Furthermore, once a benchmark is established, it is nevertheless important to continue with its ongoing assessment (and if necessary, with its ongoing adjustment).

6.3 Turbidity and Suspended Material

The ANZECC/ARMCANZ (2000) guideline value for turbidity is 20 NTU. The corresponding value for suspended material is 25mg/L.

Other ACT water bodies have no specific turbidity standard for recreational areas, other than the requirement that the turbidity should not be objectionable. The corresponding value for aquatic habitats is 10-30 NTU (ACT Government, 2003).

The Lake often exceeds these values, particularly in the shallower areas such as East Basin. Most of this is due to wind mixing, with turbidity levels in East Basin often being well above those in the Molonglo Reach (just upstream of the Lake).

Lake Burley Griffin has always been a relatively turbid lake, but these levels have shown no adverse effects in terms of ecology or human health.

Consequently, based on past information on the Lake, it is proposed that the benchmark level for Lake Burley Griffin turbidity should be 60 NTU and 30 NTU in East Basin and West Lake respectively.

It is proposed that the benchmark suspended solids values should be 50 mg/L and 25 mg/L in East Basin and West Lake respectively.

6.4 Phosphorus

The ANZECC/ARMCANZ (2000) guideline values for total phosphorus and filterable phosphorus are 0.1 mg/L and 0.05 mg/L respectively.

The corresponding value for other ACT waters is 0.1 mg/L total phosphorus. Filterable phosphorus concentrations are not specified, as total phosphorus concentrations appear to be the more important measure in terms of lake management (ACT Government, 2003).

Consequently, a 0.1 mg/L benchmark total phosphorus value is proposed for Lake Burley Griffin.

6.5 Nitrogen

The ANZECC/ARMCANZ (2000) guideline values for total nitrogen and ammonia are 0.35mg/L and 0.1mg/L respectively.

There is no particular value for other ACT waters (ACT Government, 2003).

The Lake has higher than usual nitrogen values, but this has had no adverse effects in terms of ecology or human health. Consequently, based on past information on the Lake, it is proposed that the benchmark concentrations for total nitrogen be 1.6 mg/L in East Basin and 1.2 mg/L in West Lake.

It is proposed that for ammonia, the benchmark level should be 0.1 mg/L, which is the ANZECC/ARMCANZ (2000) trigger value.

6.6 Algae and Chlorophyll-a

Algal counts and chlorophyll-a concentrations have remained in the same general range, despite phosphorus reduction measures implemented at the Queanbeyan Wastewater Treatment Plant. However, the intensity of late summer algal blooms has generally decreased.

Based on past information on the Lake, and from other sources, it is proposed that the benchmark level for algal number should be 5,000 cells/mL. This is based on algal water quality standards for other ACT waters (ACT Government, 2003).

A benchmark value of 30 μg/L chlorophyll-a is proposed for the Lake.

6.7 Conductivity and pH

Based on monitoring information on the Lake over the past 23 years, a conductivity value of 500 μS/cm is proposed as a benchmark value.

Similarly, based on monitoring information a pH range of 6.5-9.0 is proposed for Lake Burley Griffin. This is also the same range as that specified for other ACT waters (ACT Government, 2003).

6.8 Bacteria

Bacterial counts in terms of faecal coliforms have been in the same general range, except in the late summer months, at which times they have increased.

The ANZECC/ARMCANZ (2000) faecal coliform guideline value is 150 CFU/100mL for primary contact recreation, and 1,000 CFU/100mL for secondary contact recreation. This is the same as water quality standards for other ACT waters.

These are important health based guidelines, and are proposed as the Lake Burley Griffin benchmark values for primary and secondary contact recreational activities.

Based on previous faecal coliform levels in the Lake, it is likely that additional effort and resources will be required to ensure that the Lake meets these benchmark levels. Alternatively, if these levels are exceeded, appropriate action will be required to close the Lake (or parts of the Lake) to some types of recreational activities.

However, it will also be important to establish the cause of the increase in faecal coliform levels. Possible factors include:

6.9 Metals

Trace metal concentrations have generally decreased in the Lake since abandoned mining areas upstream of the Lake were rehabilitated in the 1970s.

Consequently, trace metal concentrations in the Lake are generally not regarded as an ecological or human health problem. This is further supported by results indicating that trace metal concentrations in fish caught from the Lake are either extremely low or below detection values specified by the Australian National Food Authority.