The chemistry of shallow groundwaters in the Murrumbidgee irrigation area, New South Wales

Abstract

The chemistry of shallow groundwaters in the Murrumbidgee Irrigation Area of New South Wales, Australia, is examined in terms of the degree of saturation with calcium minerals. Many water samples were found to be saturated with calcite, especially when brought into equilibrium with atmospheric CO2 pressures; gypsum saturation was found more frequently from regions having waters of high ionic strength. A thermodynamic chemical model is used to describe the effects on water 'quality', for irrigation purposes, if the groundwaters are to be reused in mixtures with irrigation supply water. A tentative classification in terms of salinity and sodium hazard is presented and a simple relationship between both hazards has been derived. A potential exists for using between 25% and 95% groundwater in mixtures with supply water for irrigation, depending on the initial salt concentration.