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Yass Water Treatment Plant

Water Quality and Capacity - Improvements

The two pressing issues that need to be resolved are the question of capacity of the Murrumbateman Water supply and the quality of both the Yass Water and Murrumbateman Water with relation to hardness.

Improvements to Murrumbateman Water Supply

The existing bore is relatively shallow at 30 metres in depth and is relatively low yielding of 3.5 litres per second for an urban water supply. There is no backup bore and the system fails to deliver peak day demand to the village. Water quality issues surround the high hardness of the water (total hardness of 380 to 430 mg/l) and the occasional elevated nitrate levels marginally above the Australian Drinking Water Guidelines of 50 mg/l.

The first task is an improvement program for Murrumbateman Water Supply is to determine whether there is a viable groundwater source. A viable source would be considered to be a groundwater source that could deliver 10 l/s and meet the Australian Drinking Water Guidelines in terms of quality. Council engaged the services of Hydroilex in 2001 to undertake a hydrogeological investigation to determine whether such a groundwater resource exists in reasonable proximity to the village of Murrumbateman.

A total of seven bores were drilled in the Murrumbateman area with indicative yields in the range of 10 to 15 l/s. Water sampling and geophysical logs of each borehole provided a comprehensive record of the sub-surface geology, fracture distribution and aquifer characteristics. The evaluation concluded:

• Significant groundwater resources were available in the region;
• Water quality is variable, but generally characterised by moderate salinity and hardness;
• The best available groundwater exists at Bore No. 7 located at the Murrumbateman Recreation Ground adjacent to the site of the existing bore;
• Water treatment will be required to improve water quality.

The Council constructed a new bore approximately 6 metres away from the existing bore.  Due to the close proximity of the existing bore, the Department of Water and Energy issued the licence stating the volume of ground water extracted from both bores shall not exceed 56 ML in any 12 month period.  The average current annual requirement is 45ML.

Council is in the process of installing a bore pump.  The new bore is expected to be fully operational by October 2008.  Stage 3 restrictions have been in place since 20 December 2007.

Despite the additional groundwater source, there is still a concern regarding the security to supply peak demand to Murrumbateman Village.  Any expansion of the village will therefore be required to secure additional water sources.

Once the dam is raised by 3 metres, around 75 to 100 ML of water can be shared to Murrumbateman Village.  There is a possibility to supply water to Murrumbateman village from Yass water system via a trunk main with inline boosting pump arrangements. An investigation of such a water supply pipeline as a medium term solution to Murrumbateman village will be undertaken.

Given the proximity of the ACT to Murrumbateman, the long term water supply from the ACT is seen as the preferred solution.

As a part of the Integrated Water Cycle Management Study, rain water tanks are considered as an additional alternative water source to Murrumbateman village.  The scenarios investigated were based on the assumption that rain water providing 48% of total internal demand.
Three scenarios were investigated:

1. Total internal water requirement of 500 litres/house/day
2. Total internal water requirement of 275 litres/house/day
3. Total internal water requirement of 390 litres/house/day

The result shows that an internal use of 240 litres/house/day could be supplied by 35 KL capacity rain water tank if connected to a roof size of 300 sq.m.

Water Hardness Improvements to Yass Water Supply

The quality of Yass water with relation to hardness fluctuates depending on the amount of rainfall and the characteristics of the River. Total hardness (measured as CaCO3) varies from as low as 50 mg/l to as high as 450 mg/l. Although hardness is not a health related issue, levels in excess of 200 mg/l are considered to represent marginal quality in terms of hardness.

A customer survey undertaken in the year 2000, identified water quality as one of the major sources of complaint within the town of Yass. In response to this survey Council engaged the services of Department of Public Works and Services (DPWS) presently known as the Department of Commerce, to identify suitable treatment processes that would reduce the hardness of the raw water to acceptable levels of between 80 and 120 mg/l.

The Department of Public Works & Services, outlined the following options for consideration by Council:

• Chemical Precipitation $ 0.9M;
• Chemical Precipitation with clarifier $ 2.3M;
• Reverse Osmosis (nanofiltration) $ 5.5M.

Bench scale jar test experimentation was undertaken to establish the effectiveness of the chemical precipitation process using hydrated lime, soda ash and carbon dioxide in conjunction with the dissolved air flotation and filtration process.

Plant trial was carried out from February to April 2004. During plant trial, hydrated lime and soda ash have been used and the results were encouraging. On completion of the water source capacity upgrade Council plans to address the water quality improvement.

Contact details
Yass Valley Council
02 62261 477 (ph)
02 6226 2598 (fax)
Council@yass.nsw.gov.au

© 2008 Yass Valley Council
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