Otto, C.J., Townley, L.R., and Watson, G.D. (1997), Two dual pump recovery tests in single bores at the Kwinana Nickel Refinery, Report to WMC Kwinana Nickel Refinery, CSIRO Division of Water Resources Consultancy Report No. 96/63, 11pp., March. [Confidential]

The concept of dual pump recovery (DPR) is simple. Conventional recovery in a layered aquifer mixes the water recovered from each layer and requires all recovered water to be treated. DPR recovers two separate types of water: contaminated water from depth which must be treated, and fresh water from near the water table which is clean enough that it can be safely recharged to the aquifer a short distance away. The preferred method of setting up a DPR recovery system is to install two pumps in the same borehole.

Recent field studies by Otto et al. (1996) demonstrated the feasibility of a fully-screened fully-penetrating DPR system near the Baldivis tailings pond, and in particular that the concentration of AMSUL in recovered groundwater can be controlled adaptively by varying the ratio of the pumping rate in the control pump, Qc, to the pumping rate in the recovery pump, Qr. The studies also showed that when DPR pumps are installed in a fully-screened bore, drawdown is minimal, and pumping rates can therefore be much higher than with conventional recovery bores, which are generally screened over a small vertical interval.

This report describes results from field trials at two bores at the Kwinana Nickel Refinery. The bore at site KNR-NRB1 is fully screened, while the bore at site KNR-NRB2 is only partially screened, over a thickness of 6 m at the bottom of the borehole. The results show conclusively that an adaptive DPR bore can be managed, by modifying the ratio Qc/Qr, so as to obtain any desired concentration from either the recovery pump or the control pump. The only potential limitation of using a partially screened borehole is the likelihood of increased drawdown for any given total pumping rate, Qr+Qc.