Classification of Chloride-to-Sulfate Mass Ratio for U.S. Groundwater With Respect to the Potential to Promote Galvanic Corrosion of Lead, 1991-2015; Water Well Data and Characteristic Values for States

Galvanic corrosion of lead in water distribution systems can occur when lead pipe or lead solder is in contact with a dissimilar metal such as copper. If the source water entering those systems has a relatively elevated chloride-to-sulfate mass ratio (CSMR), the potential for galvanic corrosion to occur is elevated (Gregory 1985; Edwards and Triantafyllidou, 2007), especially in water with low values of alkalinity (Nguyen and others, 2011). Values of CSMR were computed for untreated groundwater samples from 26,631 locations in the United States. Three levels, identified by Nguyen and others (2011), were used to classify CSMR values relative to their potential for promoting galvanic corrosion of lead. The three-level classification, defined here as the potential to promote galvanic corrosion (PPGC), was based on values of CSMR and alkalinity (Nguyen and others, 2011). The data and maps presented in this report do not indicate the occurrence of lead pipe or lead solder in distribution systems across the U.S., rather they reflect the potential of the untreated groundwater resource to promote galvanic corrosion where lead and other metals might occur in distribution systems. The data for calculating CSMR and PPGC at sites were obtained from the US Geological Survey (USGS) National Water Information System (NWIS). The data included in this report are for untreated groundwater samples obtained during the period 1991-2015. At each location, the most recent sample (during the period 1991-2015) with the necessary measurements was used to calculate CSMR and PPGC. Of the 26,631 sites, the PPGC is: high at 8%, moderate at 67%, and low at 26%. The values of PPGC at sites presented in this report can be used to identify which areas in the U.S. might be more susceptible to galvanic corrosion of lead from drinking water distribution systems and which areas may be less susceptible. A companion dataset provides characteristic values for each groundwater site. Characteristic statewide values of PPGC were computed for the fifty states and District of Columbia of the United States. The characteristic statewide values were computed using PPGC values from 26,631 untreated groundwater sites. For each state, four characteristic values were computed: proportion of sites where PPGC is low; proportion of sites where PPGC is moderate; proportion of sites where PPGC is high; and, a statewide category. The number of sites in each state is also reported. The characteristic statewide values of PPGC presented in this report can be used to identify which state(s) in the U.S. might be more susceptible to galvanic corrosion of lead from drinking water distribution systems and which state(s) may be less susceptible. Please see the individual metadata for the two datasets contained within the geodatabase for detailed descriptions of the process steps and attributes.