CHANGES IN DISSOLVED AND PARTICULATE COPPER FOLLOWING MIXING OF POTW EFFLUENTS WITH DELAWARE RIVER WATER

Effluents from publicly owned treatment works (POTWs) were mixed with Delaware River water at ratios of 1:1 or 1:2 effluent to Delaware Rive r water. These mixing experiments were performed at pH 6, ambient pH a nd pH 8. In all mixing experiments, copper was released from effluent particulate matter when mixing was conducted at pH 6. No copper releas e was observed for mixing at the ambient pH of the samples. At pH 8, n o copper was released when effluent from the Delcora or Camden POTWs w as mixed with Delaware River water, but copper was released for Levitt own, Philadelphia Northeast, Philadelphia Southwest and Gloucester eff luents mixed with Delaware River water. The fraction dissolved of tota l recoverable copper was evaluated statistically at pH 6, ambient pH a nd pH 8. Because there was no copper released at ambient pH of mixing, we conclude that POTWs may be overregulated on the basis of total rec overable metal concentration as required by the National Pollutant Dis charge Elimination-System (NPDES). This is due to the fact that efflue nt particulate copper, which is the majority of the total recoverable copper, does not change to dissolved copper at the ambient pH of the r iver. Receiving water quality is evaluated on the basis of dissolved c opper. (C) 1998 Elsevier Science Ltd. All rights reserved.