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Impact of treatment on scale formation and lead release from aged LSLs
Citation:
Doré, E., C. Cartier, M. Edwards, Mike DeSantis, M. Schock, L. Larouche, S. Nour, AND M. Prévost. Impact of treatment on scale formation and lead release from aged LSLs. In Proceedings, AWWA Water Quality Technology Conference, Toronto, BC, CANADA, November 04 - 07, 2012. AWWA Internet, Denver, CO, 1792, (2013).
Impact/Purpose:
This study provides longer term results of partial replacements simulated using harvested lead pipes operated under typical flow conditions. Results will benefit utilities and regulatory authorities by: (1) providing scientific evidence of Pb release due to galvanic corrosion following partial LSL replacement, with associated long-term ramifications for public health, and (2) estimating the limits of common corrosion control options to mitigate it. Our results demonstrate that corrosion control may not be efficient to mitigate lead release following partial LSL replacement, and that some treatment options may actually aggravate this release in some water qualities.
Description:
Background Municipalities have been replacing the public part of lead service lines (LSLs) by copper piping, which often leaves a lead section on the private side, resulting in partial LSL replacements. Depending on water chemistry, such practices may result in galvanic and deposition corrosion, resulting in higher particulate and dissolved Pb concentrations. More information is needed on strategies to mitigate this potential long-term problem. Objectives The aims of this study were to: (1) use harvested Pb pipes to assess the efficacy of corrosion control to limit Pb release after partial LSL replacement; (2) to investigate the types of scales formed at the pipe junction under various water quality conditions. Methodology Field harvested Pb pipes (45) from the City of Montreal were assembled in a flow through (5 LPM@8 h/day) pipe rig and fed with water from its distribution system (pH 7.9, chloride:sulfate mass ratio [CSMR] of 0.9). Pipes were conditioned for a year and treated for four months. Then, partial replacements (20% of length) were simulated by adding copper piping upstream or downstream of the Pb pipe using red brass union fittings. Post-replacement results were compared to reference 300cm long Pb pipes. Four water conditions were studied: addition of OrthoP at 1 mg P/L, increase of pH to 8.3, decrease of CSMR to 0.3, and a control condition. In June 2012, a year of data will be available following partial LSL replacement. Scale samples will be taken after 10 months of treatment and analyzed by XRD to evaluate mineralogical changes. Results OrthoP was the only treatment that significantly decreased Pb release from a full lead pipe before simulating partial replacement with copper (64% for the full Pb). On average, partial replacements without OrthoP treatment resulted in a large Pb release (+451%) from a mean concentration of 31 to 170 µg/L. There was no difference between Pb-Cu and Cu-Pb, suggesting no significant deposition corrosion problems in this water four months following the partial replacement. Much higher mean Pb releases were observed after partial replacements, with 1183% higher lead (8 to 103 µg/L) for OrthoP and 719% (from 29 to 234 µg/L) for pH adjustment. A water with lower CSMR reduced this impact to only 159%. Additional tests are underway and pipe scale deposits analysis will also be performed at the Cu-Pb junction in spring 2012.
