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TETRAVALENT LEAD: A HITHERTO UNRECOGNIZED CONTROL OF TAP WATER LEAD CONTAMINATION
Citation:
Schock*, M R., J. Swertfeger, S M. Harmon*, R. Lohmann, AND J. DeMarco. TETRAVALENT LEAD: A HITHERTO UNRECOGNIZED CONTROL OF TAP WATER LEAD CONTAMINATION. Presented at AWWA Water Quality Technology Conference, Nashville, TN, 11/11-14/2001.
Description:
Almost all of the theoretical framework underlying the control of plumbosolvency and lead release has been based on the presumption that the lead release is explicable by Pb(II) solubility, aqueous speciation, and reaction kinetics. Utilities struggling to comply with the Lead and Copper Rule use guidance on expected relationships of lead release to water quality parameters such s dissolved inorganic carbon (DIC), pH, and phosphate concentrations. Several published papers have tried to compare actual monitoring data generated under the LCR to various solubility models and have tried to ascertain and quantify apparent responses of lead levels to different treatment conditions. These studies have revealed discrepancies between theory and observation which may be related to either the diversity of nature and configuration of plumbing materaisl from site to site, and across water systems, or to divergence from the chemical theory for unknown reasons. During 1999 and 2000 Cincinnati Water Works observed considerable sensitivity of lead levels to small pH changes in the distribution system. This paper will describe the analytical procedures for the pipe and the water chemistry conditions observed in the Cincinnati Water Works distribution network. Results of an evaluation of existing chemical literature on Pb(IV) chemistry in water will be given, leading to a tentative solubility model for new treatment guidance for other water utilities.