In 2016, in association with WaterNSW, Golder Associates assisted in the development of two emergency groundwater borefields, Menindee Lakes and the Talyawalka floodplain, to secure short term water supply for the residents of Broken Hill, Menindee and Sunset Strip (western NSW). The borefield locations were identified as a result of hydrogeological review; targeting the shallow, sand aquifer known as the Calivil Formation for water supply.
This paper discusses data collected during the drilling and hydraulic testing of the Menindee Lake borefield; as well as a GoldSim mixing model designed as an operational tool for the Menindee Lake borefield to predict the combined water quality from 12 supply bores. Groundwater variations were identified during the installation of the borefield through field parameters and water quality samples.
As there was limited total dissolved solid (TDS) data at each bore location, the TDS data was pooled into groups of bores partly based on water quality and location. The statistical distributions of these groups were input to a GoldSim mixing model as a distribution representing the range of TDS values measured within that group. This allowed for the prediction of future TDS from the borefield using a probabilistic framework that recognises the heterogeneous nature of water quality in the Calivil Formation. A stochastic data input element was used in GoldSim with resampling set at defined trigger periods throughout a model realisation. The final TDS of the mixed solution was estimated over time depending on the number of supply wells and predicted pumping rates, showing results as a statistical distribution of water quality.
The model was successfully used to predict water quality from various pumping scenarios to meet strict water treatment requirements for potable use.