Groundwater flow and solute transport at the Mourquong saline-water disposal basin, Murray Basin, southeastern Australia

Saline groundwater and drainage effluent from irrigation are commonly stored in some 200 natural and artificial saline-water disposal basins throughout the Murray-Darling Basin of Australia. Their impact on underlying aquifers and the River Murray, one of Australia's major water supplies, is of serious concern. In one such scheme, saline groundwater is pumped into Lake Mourquong, a natural groundwater discharge complex. The disposal basin is hydrodynamically restricted by low-permeability lacustrine clays, but there are vulnerable areas in the southeast where the clay is apparently missing. The extent of vertical and lateral leakage of basin brines and the processes controlling their migration are examined using (1) analyses of chloride and stable isotopes of water (²H/¹H and ¹⁸O/¹⁶O) to infer mixing between regional groundwater and lake water, and (2) the variable-density groundwater flow and solute-transport code SUTRA. Hydrochemical results indicate that evaporated disposal water has moved at least 100 m in an easterly direction and that there is negligible movement of brines in a southerly direction towards the River Murray. The model is used to consider various management scenarios. Salt-load movement to the River Murray was highest in a "worst-case" scenario with irrigation employed between the basin and the River Murray. Present-day operating conditions lead to little, if any, direct movement of brine from the basin into the river. Electronic Publication