Hydrologic controls on groundwater salinisation, Murray Basin, Australia

Groundwater flows through a multiple aquifer system near the regional recharge area of the southern Murray Basin. Despite low topographic relief (similar to 70m elevation / 15,000 km(2)) local recharge and discharge processes control groundwater quality. Total dissolved solids (TDS) contents in the upper aquifer (similar to 30m deep) range from 650 to 105,000 mg/L over short distances (27 km). In the deepest aquifer at similar to 180m, TDS ranges from 600 to 17,000 mg/L over the same area. In this semi-arid environment, recharge of fresh water occurs along palaeo-sand ridges and infiltrates the upper aquifer (similar to 650 mg/L). However, in a nearby palaeo-river channel, groundwater in the shallow aquifer is highly saline (> 100,000 mg/L) due to evaporative concentration in salt lakes and playas. This discharge area compromises water quality throughout the entire aquifer system, and indicates that brines from salt lakes and playas may penetrate by reflux to depths of over 180m, potentially transporting salt from the surface to aquifers relatively rapidly and over short distances.