ACT State of the Environment 2007

Indicator: Groundwater

Summary

Significant progress has been made towards understanding the ACT's groundwater resources since the last reporting period. A comprehensive monitoring system has been installed in four of the ACT's high demand catchments; the Lake Burley Griffin, Fyshwick, Woden and Woolshed Creek catchments. However, the short monitoring period and lack of rainfall has allowed only an interim assessment of the monitoring results. A full assessment is expected before the next reporting; however, for this period, the availability of data on groundwater resources is a concern. This is especially the case for groundwater quality, where only a limited dataset is available.

What the results tell us about the ACT

Groundwater is an essential resource for the ongoing health and maintenance of many ecosystems. Ecosystems depending on groundwater include surface water bodies – such as wetlands, rivers and lakes – that are connected to groundwater and many terrestrial ecosystems. Changes in groundwater quality have the potential to degrade these ecosystems causing a loss of terrestrial and aquatic species.

In addition to the environmental values, to a limited extent groundwater is used as a resource, supplying on average 300 ML per year. Its uses include water for irrigation, stock watering and other agricultural uses and industrial purposes. Importantly, the availability of groundwater for these uses depends on the quantity of the resource and its quality.

Since the last reporting period – where the lack of comprehensive groundwater data was a major concern – the ACT Government has established a program of research into the groundwater resources of the ACT to ensure groundwater is used appropriately as an alternative to mains water without being over-extracted.

Further broadening our understanding of groundwater resources, the ACT Environment Protection and Heritage Branch (TAMS) has entered into an agreement with the National Water Commission to be part of the Australian Government Water Fund for Raising National Water Standards Program. The ACT component of the program will involve the strategic assessment and management of priority/stressed groundwater catchments. The objective of the program is to better manage water resources through:

  • improving capacity to monitor, evaluate and report on water resources at the national, regional and catchment level
  • improving knowledge, information and skills needed to better manage our water resources
  • enhancing innovation for rural and urban water use efficiency.

Groundwater monitoring

The Bureau of Rural Sciences, on behalf of the ACT Government, has installed 12 groundwater bores in the high demand sub catchments of Lake Burley Griffin, Woden, Fyshwick and Woolshed Creek. The purpose of these monitoring bores is to gather information about the capacity for water to move through the aquifer (transmissivity), hydraulic conductivity, storage capacity potential, and recharge rates of the various aquifer types within these sub catchments. Pumping tests of these bores have been performed while monitoring of the aquifer recharge response to rainfall continues.

The lack of rainfall as a consequence of the drought during the first year of monitoring has limited the ability to test aquifer recharge response.   Recharge estimates based on hydrographic fluctuations in response to rainfall events have been made using the data available, but once again, due to the prevailing dryer-than-average conditions, these estimates are not representative of the full range of climatic conditions that may be expected to occur in the ACT. During the reporting period, sustainable yield estimates are considered interim until more monitoring data are acquired.  The interim annual groundwater recharge for each sub catchment ranges from 2.3% (Woden) to 3.4% (Lake Burley Griffin) of total rainfall.

Groundwater use

Introduction of a compliance program for groundwater licence holders during the reporting period resulted in an increase in both the license volume data and the extraction data for ACT groundwater.

This data showed that as well as total licensed volume, actual extraction was within the sustainable yield of groundwater in all 32 water management units. Licensing of 45 new groundwater bores during the reporting period demonstrated a significant increase in groundwater use since the previous reporting period. Most licenses were located within the inner urban Lake Burley Griffin sub catchment and the resulting extraction remained within sustainable limits.

The ability to remain within sustainable limits is particularly important given the increase in groundwater use (Table 1). The increase in groundwater use appears to be significant, although it is estimated that 7,000 megalitres of water is available for use.

Table 1: Groundwater use, 2000–06
Year Water used (megalitres)
2000 168
2001 262
2002 243
2003 249
2004 345
2005 322
2006 327

Source: Data provided by TAMS 2007

Groundwater quality

Few data that characterise groundwater quality for state of the environment reporting are available. Some bore data are available for the West Belconnen and Mugga Lane landfill sites; they provide information on the physical, chemical and bacteriological properties of groundwater, as well as water table depth. The monitoring results of the Mugga Lane site indicate no obvious chemical contaminants with no hydrocarbons, no pesticides, and very low occurrences of heavy metals; however, some water contamination as indicated by the presence of faecal coliforms. The data also indicates the groundwater at both sites has a higher than average salinity range.

Contaminated plumes associated with underground fuel storage at service stations exist at a number of locations across the ACT (see Contaminated sites). Similar to the previous reporting period, there is a need to understand the potential or actual impacts of these contaminated sites on surface waters.

Data sources and references

Territory and Municipal Services

ACT Water Reports 2003–04, 2004–05, 2005–06 and 2006–07, TAMS

Bureau of Rural Sciences 2007, Data Collection and Recharge Determination for Sub-catchments in the ACT: Lake Burley Griffin, Fyshwick, Woden and Woolshed Creek, Phase 1: Report to ACT Government

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