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Impact of water quality change on corrosion scales in full and partially replaced lead service lines
Citation:
Doré, E., M. DeSantis, M. Schock, E. Deshommes, S. Nour, L. Laroche, AND M. Prevost. Impact of water quality change on corrosion scales in full and partially replaced lead service lines. Presented at AWWA Water Quality Technology Conference, Indianapolis, Indiana, November 13 - 17, 2016.
Impact/Purpose:
The presentation gives the results of lead pipe scale analyses from sites in Montreal, QE representing undisturbed lead service lines, brass valves and copper pipes and also sites where partial lead service line replacements had taken place. Partial lead service line replacement is a controversial technique necessitated by boundaries of property ownership and control, and therefore, directly relates to debates in the US about the practice for the Lead and Copper Rule revisions process.
Description:
BackgroundChanges in water qualities have been associated with an increase in lead release from full and partial lead service lines (LSLs), such as the cases of Washington D.C. or more recently of Flint (Mi). Water qualities affect the mineralogy of the scales. Furthermore, following partial LSL replacement, significant galvanic corrosion occurs and locally affects the water quality (pH) and scale formation. Furthermore, field studies and pilot studies have been shown to yield different levels of lead release for similar water qualities tested, suggesting that other factors, such as water usage patterns, could drive lead release from scales on the pipes. This study evaluates the long and short term impact of partial LSL replacement and changes to water qualities on the scale formation and lead release from LSLs.ObjectivesThe main objective is to compare scales from full and partial LSLs harvested from the field and from a pilot setup fed with water from the same distribution system and subjected to water quality changes.MethodologyLead service lines (45) harvested from the City of Montreal were installed in a flow through pilot fed with water from the distribution system (5 LPM, 8h/d, 5d/wk; pH 7.9, 0.9 chloride:sulfate mass ratio [CSMR], no Cl2, alk. 80 mg CaCO3/L). Full LSL and simulated partial LSL were tested. During 3 years, 4 water qualities were used to feed the different trains: 1) control condition, 2) reduced CSMR, 3) pH adjustment to 8.3, 4) addition of orthoP at 1 mg oPO4/L with pH adjustment to 7.9. At the end of the study, 1 mg Cl2/L was added to the lowered CSMR (2) and the pH adjustment (3) and the orthoP dosage was increased to 1.5 mg oPO4/L (4). Rigs were harvested prior to the changes made to the water quality and at the end of the study. Also, partial and full LSLs were harvested from the corresponding distribution system. Scales from both partials and full LSL were harvested from the rigs by separating the different sections based on their appearance, texture and location. Sub-samples were analysed using XRD and SEM analysis.Results Preliminary results from scales formed 38 weeks following the LSL replacement simulations revealed differences in scale formations amongst varying water qualities and pipe sequence. Rigs fed with dechlorinated tap water show distinct pH gradients between the galvanic and the background zones. Hydrocerussite and litharge are found both in field and pilot rigs. However, plumbonacrite, massicot, scrutinyite and plattnerite are only present in pipes harvested directly from the field. Laurionite, leadhillite, cerussite and calcite are found in rigs from the pilot. Cerussite is mostly present in the galvanic zones, close to the connexion to the Cu pipe. Different types of scales are present in the rigs from the pilot and from the field, suggesting that differences in the formation in the scales and therefore differences in lead realease from the pipes. The particulate Pb fraction in water samples is more important in samples from the pilot than from the field, median concentrations are 85X higher in partial LSL and 10X higher in full LSL in the pilot. Lead phosphates are present in the scales from the rigs treated with orthoP. Complete results will be obtained by the end of July 2016.Relevance to the industry Scale analysis will provide insight on the water quality changes on the potential for lead release after water quality changes and the benefits of corrosion control treatments. Coupled with the data on lead release from the rigs, this analysis will help understand differences of lead levels observed at pilot and full scale, especially in terms of particulate lead release.
URLs/Downloads:
http://www.awwa.org/conferences-education/conferences/water-quality-technology.aspx#1384489-2016-program