Groundwater quality trends related to aquitard salt storage at selected sites in the Lower Murrumbidge alluvium, Australia

摘要

The risk of declining groundwater quality due to induced leaching of salts is a major concern in the over-stressed Lower Murrumbidgee alluvial groundwater system, Australia. Significant groundwater quality decline has occurred at some sites, with TDS increasing by up to 133 mg/L/yr in the shallow Shepparton aquifer, though no TDS increases were observed in the deep Calivil aquifer. Similar hydrochemical changes were observed to uccur in the Shepparton aquifer, over 15 years, and to a lesser degree during the 1998-99 irrigation season. Preliminary mass balance modelling suggests that between 10 and 38percent of groundwater volume was due to leakage of aquitard pore waters. Mixing was associated with Nacl dissolution, and reverse ion-exchange. The potential for further leaching is substantial, given the 4.25 kg/m~2 of salt within the Upper Shepparton aquitard, which accounted for 81percent of total clay salt storage. Increased hydraulic gradient due to pumping was directly related to increased salinity in the Shepparton aquifer.