The use of Airborne EM to investigate coastal carbonate aquifer, seawater intrusions and sustainable borefield yield at Exmouth, Western Australia

Abstract

Exmouth, a regional centre located 1260km north of Perth, Western Australia relies entirely on groundwater for its water supply. Its borefield extracts groundwater from an unconfined limestone aquifer within the Cape Range Group. Groundwater flows easterly from Cape Range into Exmouth Gulf where it discharges above a saline wedge at the base of the aquifer. The current borefield extraction has insufficient capacity to meet increased water demand from population growth and tourists during holiday periods. In 2016-2017, Water Corporation decided to investigate options for improving borefield production from the existing infrastructure. This study comprised an airborne electromagnetic (AEM) survey, a desktop review, 3D hydrogeological modelling and pumping tests. The AEM survey and new hydrogeological modelling have established a clear relationship between the extent of the saltwater interface and the location of karstic features. The AEM survey effectively mapped the saline water distribution. It identified existing bores in thicker lower salinity areas and away from the saline wedge. Twenty-four hour pumping tests of these bores were undertaken, producing flow rates much higher than the established normal production rates. Hydrogeological modelling indicated that these bores could accommodate substantial additional sustainable production. The AEM survey and study also identified bores in areas of higher conductivity and salinity where extraction rates should not be increased, or should be reduced.