Otto, C.J., Townley, L.R., and Barr, A.D. (1997), Design of adaptive dual pump recovery (DPR) systems near the Baldivis tailings pond, Report to WMC Kwinana Nickel Refinery, CSIRO Land and Water Consultancy Report No. 97/30, 16pp., September. [Confidential]

WMC KNR has decided to improve the recovery of AMSUL-contaminated groundwater near the Baldivis tailings pond by installing an adaptive dual pump recovery (DPR) system. It has been proposed that four adaptive DPR bores should be used concurrently, but that several combinations of locations of DPR bores, injection bores and recharge basins will be used during the estimated 10 years of DPR operation.

Current recovery operations are based on the use of four recovery bores: P1, P2C, P4 and P6A. The main limitation of the existing bores is that the efficiency of recovery is less than optimal, due to increasing dilution by fresh water as the interface between the plume of contaminated water and overlying fresh groundwater is lowered. A dual pump recovery (DPR) system was proposed by the CSIRO Land and Water (Townley et al., 1995), and the concept has been extensively tested (Otto et al., 1995, 1996, 1997) and modelled (Townley and Barr, 1996).

The concept of dual pump recovery (DPR) is simple. Conventional recovery in a layered or stratified 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. Because the water from the control pumps can be recharged, it is possible to pump at a larger total rate at each DPR site without adversely affecting the water balance of the region. As a result, the plume is recovered more quickly. Because the water sent for treatment is not diluted by overlying fresh water, the volume of water to be treated is less, and water treatment costs are therefore reduced. At present the KNR water treatment plant has a capacity of 4000 L min-1 into the first reverse osmosis plant, which can be bypassed when the concentration of AMSUL in groundwater is too high, and then 2000 L min-1 at up to 10000 mS cm-1 into the nanofiltration/ reverse osmosis plant.