ABSTRACT
The nature and extent of well clogging at an experimental Aquifer Storage and Recovery (ASR) site in South Australia, where urban stormwater has been opportunistically injected into a confined carbonaceous aquifer was studied over four years. Mass balances of injected and extracted sediment and microorganisms were determined from flow rate, concentration and size distribution data, and the quantity of aquifer materials dissolved inferred from a geochemical mass balance model derived from a series of groundwater samples. Piezometric head response between the injection well and a nearby observation well allowed a comparison between years where injectant quantities and qualities differ. Our results reveal no significant clogging by either coliform, Pseudomonas or heterotrophic iron bacteria, but there is some clogging by injected sediment, especially where sediment concentrations are high. However, most of the clogging is believed to be offset by increased secondary porosity through calcite dissolution, which also raises the issue of rearrangement and mobilisation of residual aquifer sediments. The artificial recharge capacity at this site has been shown to be sustained over the four years, but issues related to the fate of injected sediments and the stability of the injection well remain unanswered.
