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Peak Lead Levels and Diagnostics in Lead Service Lines Dominated by PbO2 - abstract
Citation:
Schock, M., S. Triantafyllidou, AND Mike DeSantis. Peak Lead Levels and Diagnostics in Lead Service Lines Dominated by PbO2 - abstract. Presented at AWWA Annual Conference and Exposition, Boston, MA, June 11, 2014.
Impact/Purpose:
To inform the public.
Description:
Multiple studies have presented “profiles” of water lead levels from tap to main through lead service lines (LSLs), in systems where the LSLs were coated with common Pb(II) corrosion solids. These Pb(II) solids were either actual Pb(II) minerals or Pb(II) sorbed onto other pipe scale materials (e.g. aluminum, iron, and manganese). No study has ever linked water lead profiles to known Pb(IV) (i.e., PbO2 )scales in the lead pipes, which are much less soluble than most known Pb(II) drinking water corrosion byproduct solids. With Pb(II)-controlled LSL chemistries , the peak lead levels in tap water due to the LSLs are often at least 3 to 5 times higher than the levels reported in Lead and Copper Rule sampling (LCR). Unlike profile sampling, LCR sampling captures the first liter of water only, and does not directly capture the contribution of the LSL to peak water lead levels in subsequent liters of water. Prior EPA studies of LSL corrosion included sampling of water from 2 systems having PbO2 as the dominant lead mineral. These studies also involved collection of either full water lead profiles, or targeted sampling of water in overnight standing contact with the LSLs. Detailed plumbing configuration information was collected at all sampled residences, to guide the sampling and interpretation of results. Recently, two residences in a third water system with LSLs having PbO2 scales have also been sampled, using different stagnation times and profiling protocols. Free chlorine residuals were also obtained during some of the detailed profiling events. Overall, results quantify for the first time the relatively low levels of lead released by the Pb(IV) scales, even after prolonged water stagnation of many days in one of the systems. The diverse water qualities affirm that substantial protection from plumbosolvency, equivalent to orthophosphate dosing, can be achieved in widely different hardnesses and alkalinities, if PbO2 scales form and can be maintained. Other important observations in PbO2 LSL systems include: • With all-day or longer standing times, the leaded brass plumbing device(s) can release a higher level of lead than the LSL • Levels of lead from the LSL are sometimes only slightly above levels found in the interior plumbing • A commonality across the three water systems is that their full suite of treatment processes reduce oxidant demand of the water, iron mains, or both, helping to stabilize ORP • Health studies of lead contributions from different media must consider the types of lead scales in the water system, or unreliable and misleading extrapolations can be made about relative exposure sources. This presentation will also cover implications for premise plumbing water sampling diagnoses of lead problems, possible ways to infer the presence of PbO2 scales without extensive and expensive scale analyses, and identify some key future research needs with respect to formation and maintenance of PbO2 scales.
URLs/Downloads:
http://www.awwa.org/portals/0/files/education/conferences/ace/conference-program/2014/resources/