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LONG-TERM IMPACTS OF ORTHOPHOSPHATE TREATMENT ON COPPER LEVELS
Citation:
SCHOCK, M. R. AND A. M. SANDVIG. LONG-TERM IMPACTS OF ORTHOPHOSPHATE TREATMENT ON COPPER LEVELS. Presented at 2006 Minnesota Section of AWWA Annual Conference, Duluth, MN, September 21, 2006.
Impact/Purpose:
To inform the public
Description:
Laboratory, pilot, and field data collected support the theoretical “cupric hydroxide” copper solubility model. For the short time frames inherent in laboratory and pilot studies of copper solubility and in initial field monitoring for the LCR from Tier 1 soldered copper sites, cupric hydroxide or a very microcrystalline tenorite should be the dominant solid phase, whereas over time, the pipe will “age” and tenorite or malachite will form and predominate as the surface phase. Orthophosphate treatment will initially lower copper levels, when applied in the proper pH range. Unlike systems optimizing pH and DIC adjustment, the orthophosphate-treated systems tend to see stable copper levels, rather than the “aging” phenomenon. Given enough time (years to decades), in similar systems without orthophosphate, the copper levels will probably eventually drop to below what would be achieved with orthophosphate. Systems employing orthophosphate see rapid reductions initially, but the stabilization long-term could be difficult to overcome if there are later issues with more stringent limits on phosphate or copper levels in wastewater. Compliance monitoring required for the LCR is biased towards sites that may exhibit elevated lead levels rather than elevated copper levels. Current targeting will basically show that Cu levels will continue to decline, so the discrepancy between the copper levels covered under LCR monitoring and that in the locations with potential for highest exposure to copper will increase over time.