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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

May 19, 2016

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 groundwater samples from 27,416 locations in the United States. Three levels of concern, 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 CSMR-class, 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 it reflects 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 CSMR-class at sites were obtained from the US Geological Survey (USGS) National Water Information System (NWIS). The data included in this report are for 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 CSMR-class. Of the 27,416 sites, the CSMR-class is: high at 8%, moderate at 67%, and low at 26%. The values of CSMR-class 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 in household drinking water and which areas may be less susceptible.
Characteristic statewide values of CSMR-class were computed for the fifty states and District of Columbia of the United States. The characteristic statewide values were computed using CSMR-class values from 27,416 groundwater sites. For each state, four characteristic values were computed: proportion of sites where CSMR-class is low; proportion of sites where CSMR-class is moderate; proportion of sites where CSMR-class is high; and, a statewide category. The number of sites in each state is also reported. The characteristic statewide values of CSMR-class presented in this report can be used to identify which state(s) in the US might be more susceptible to galvanic corrosion of lead in household drinking water and which state(s) may be less susceptible.

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