Otto, C., and Townley, L.R. (1999), Response of a dense aqeous phase contaminant plume under pumping stress, Proceedings of Contaminated Site Remediation: Challenges posed by urban and industrial contaminants, Ed. C.D. Johnston, 21-25 March 1999, Fremantle WA, 8pp.

A leaking point source has resulted in a dense plume composed mainly of ammonium sulfate, which has spread radially over an area of several square kilometres. The contaminant has accumulated in the lower 30-50% of an unconfined sandy limestone aquifer system. The main limitation of a conventional pump and treat strategy is that the efficiency of recovery decreases with time, due to downconing of the dense/freshwater interface and dilution by freshwater. A dual pump recovery (DPR) system has been developed and tested in the field to counter-balance the downconing and to enhance the efficiency of remediation operations. The principle of a DPR system is that, apart from local drawdown near a pump, groundwater flows horizontally towards a pumping bore, such that the lower recovery pump captures the dense contaminated groundwater and freshwater is captured by the upper control pump. Results are presented for DPR trials in two adjacent bores and a single bore. It is estimated that a DPR system can halve the recovery time.

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