Utilising the shut-down of Mosgiel bore field to determine broad properties in a stratified aquifer

Abstract

The Mosgiel water supply was fed by 9 production bores scattered throughout the township with a combined 3,500 m3/d rate of groundwater production in the lead up to a complete shut down from 4 October 2009 to 14 January 2010. The Mosgiel water supply derives its groundwater from the Lower Taieri groundwater system, which is a stratified to semi-confined alluvial aquifer (Rekker & Houlbrooke, 2010). The water supply bores are the predominant large water takes from the East Taieri compartment of the Lower Taieri with a consent volume limit of 1.83 million cubic metres per annum (Mm3/a) and actual consumption of 1.2 Mm3/a. The 102 day long bore field shut down resulted in a 1.8 metre rise in the level of the Otago Regional Council monitoring bore that measures level / pressure in the ‘water supply’ water bearing layer. Figure 1 shows the response in groundwater level at the nearby Harleys monitoring bore to the bore field shut down. The level response to the cessation and resumption of bore field pumping at Mosgiel has been used as a ‘super recovery & drawdown’ analysis of aquifer properties. Preliminary results using the Theis Recovery method indicate a transmissivity of 875 m2/d. This and further analysis will be explored in the full presentation.