Water Journal : Water Journal August 2012
groundwater management refereed paper technical features 90 AUGUST 2012 water Bore Construction The construction of groundwater bores to access the Deep Leads was relatively complicated, as in some cases the aquifer overlying the Deep Leads contained saline groundwater. Multiple casing in both exploration and production bores was required to seal off shallower non-potable groundwater and preserve the developed aquifer water quality. Two production bores were constructed at the Moolort Borefield and one at Stony Creek. Geophysical logging was undertaken to identify the coarser grained intervals of the Deep Lead over which to place the bore screens, and sieve analysis undertaken to size (and maximise the screen apertures). Production bores were constructed with ABS casing and wire-wound stainless steel screens. The pumphouse casing of the Moolort production bores are 300mm in diameter with 10m of 2mm aperture screens positioned some 70--80m below the surface. A further eight monitoring bores were constructed to monitor conditions in the Deep Lead and overlying aquifers. Aquifer pumping tests confirmed sustainable production flow rates in excess of 4ML/day from each bore. The Greenlock Deep Lead is not as thick as the Moolort Deep Lead, and the production bore at Stony Creek is capable of flows of 1.5 ML/day. In the order of five monitoring bores were also installed in the vicinity to monitor conditions within the Deep Lead sediments and overlying basalt, as well as potential impacts on a nearby waterway. Groundwater quality was assessed during the investigations. Water from the pumping tests undertaken at both borefields was fed directly into water supply system to avoid wastage of the resource. The groundwater salinity extracted from both the Moolort and Stony Creek borefields is around 700mg/L to 800mg/L Total Dissolved Solids. Groundwater hardness is somewhat elevated, however, significant treatment to remove other unusual constituents is not required. Assessment of Impacts Under the Water Act (1989), the Minister issued the guidelines for the groundwater licensing of urban supplies (Victorian Government 2008). The guidelines "provide that applications for groundwater licence for urban water supply may require a groundwater assessment report. The groundwater assessment report essentially describes the potential yield of groundwater resource and makes an assessment of potential risks or any adverse impacts arising from the proposed extraction of groundwater (Victorian Government, 2008). Under these guidelines, the delegated licensing authority, in this instance Goulburn- Murray Water, is empowered to: • Issue bore construction licenses; • Request a program of pumping test investigations to define the hydraulic parameters of an aquifer; • Issue short-term licences (e.g. three-year period) to enable further monitoring of extraction and assessment of extraction impacts; • Provide a means of compensating impacted, authorised users of the resource. GHD undertook pumping test investigations consistent with Australian Standards AS2368 (1990) and the Ministerial Guidelines. The pumping tests enabled the determination of aquifer hydraulic parameters (and thus the impacts of extraction), and further characterisation of the water quality under sustained extraction. An assessment of extraction impacts on neighbouring groundwater users and the environment was undertaken by GHD to satisfy the Ministerial Guidelines for licensing urban authorities. While understanding the requirement for provision of essential urban supplies, Goulburn-Murray Water also has to ensure that the rights of existing users and environmental values of the system are not compromised. Analysis of the test results indicated that impacts to existing users and the environment were deemed to be acceptable. Goulburn-Murray Water subsequently granted groundwater extraction licenses to Central Highlands Water to enable commissioning of both the Moolort and Stony Creek Borefields. Consistent with the Ministerial Guidelines, and in consultation with Goulburn-Murray Water, GHD and Central Highlands Water developed monitoring and reporting programs to assess the impacts of extraction over time. In addition, through- flow analysis was undertaken to understand the impacts down-gradient in the aquifer system, particularly under the influence of prolonged drought conditions. Central Highlands Water annually reports the results of their monitoring program to Goulburn- Murray Water as part of the extraction licensing conditions, and to confirm the longer term sustainability of the systems (both during and outside of drought periods). Conclusions The development of the Moolort and Evansford (Stony Creek) Borefields has provided Central Highlands Water with a drought-proof water supply for the City of Maryborough. With the breaking of the drought in 2010, and filling of Tullaroop (to spilling capacity) the borefields are no longer required in continuous operation. However, Central Highlands Water periodically operates the borefields to confirm the system's operation, and continues to undertake an approved groundwater-monitoring program to build upon the knowledge base of the aquifer system. Note: This paper is taken from a presentation made at the National Groundwater Conference 2010, Canberra. The Authors Tim Anderson (email: firstname.lastname@example.org) is a Principal Hydrogeologist with GHD, primarily involved in groundwater resource and environmental investigations associated with the development of water supplies, salinity studies, groundwater flow processes and surface water interactions, mine dewatering, mineral spring and contaminated groundwater. He also undertakes EPA groundwater monitoring compliance reviews. Pat Russell is Manager Water Resources, with Central Highlands Water. Brendan Cossens is Senior Water Resources Officer with Goulburn-Murray Water. David Stanley is a Principal Hydrogeologist with GHD and has over 30 years' experience in the field of geology/ hydrogeology. David has undertaken projects for Central Highlands Water and its predecessors for over 20 years. Figure 2. Moolort Borefield geological section.
Water Journal September 2012-1
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