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Importance of Pipe Deposits to Lead and Copper Rule Compliance
Schock, M., A. Cantor, S. Triantafyllidou, Mike DeSantis, AND K. Scheckel. Importance of Pipe Deposits to Lead and Copper Rule Compliance. JOURNAL OF THE AMERICAN WATER WORKS ASSOCIATION. American Water Works Association, Denver, CO, 106(7):E336-E349, (2014).
This paper combines laboratory and field data that describes the importance of pipe deposits other than lead corrosion solids in enabling regulatory compliance and controlling lead contamination of the water. Treatment for lead corrosion must include a program to limit or remove adverse pipe scale deposits. The study also shows the value of full lead service line replacement in solving lead corrosion issues.
When Madison, WI exceeded the lead Action Level in 1992, residential and off-line tests suggested that lead release into the water was more complex than a simple lead solubility mechanism. In-depth scale analyses (color/texture, mineralogical and elemental composition) of 5 excavated lead service lines (LSLs) revealed that accumulation of manganese (and iron) onto pipe walls had implications for lead corrosion, by sometimes obstructing the predominance of an insoluble and thus potentially protective plattnerite [Pb(IV) solid] scale and instead encouraging the predominance of more soluble cerussite and litharge [Pb(II) solids], and by providing a high capacity sink for lead. Manganese that accumulated from the source well water onto pipe scales (up to 9-10% by weight) served to capture, accumulate, and transport lead to consumer taps. Removing existing pipe scales using uni-directional flushing was employed concurrently with full LSL replacement to achieve Lead and Copper Rule compliance and major reduction in lead contamination and exposure.