Data for Assessing the Lead Solubility Potential of Untreated Groundwater of the United States

Groundwater chemistry data used for assessing the lead (Pb) solubility potential of untreated groundwater of the United States were compiled from the USGS National Water Information System (NWIS) database for groundwater sites sampled between January 1, 2000 and January 1, 2016. Two datasets were compiled: one dataset having 13,324 groundwater sites was used to assess Pb occurrence in untreated groundwater from different well types and a second dataset having 8,313 groundwater sites was used for geochemical modeling (Tables S1 and S2). In both datasets, only the most recent sample was used when multiple water-quality samples were available for a site. Samples were collected in accordance with protocols established by the USGS National Field Manual and the USGS National Water Quality Assessment (NAWQA) project. Samples for Pb, major ions, and nutrients were filtered with 0.45 micrometers capsule filters prior to analysis. Pb was screened to a common reporting level of 1 mcg/L. Non-detections and detected Pb concentrations that were at or below 1 mcg/L were recoded to 0.5 mcg/L. Non-detections of Pb above 1 mcg/L were removed from the dataset. The censoring of reporting levels mainly affected older samples that used analytical methods with higher detection levels. Table 1 includes groundwater samples from sites used for public-supply (PS), domestic (DOM), monitoring, and for other purposes, such as irrigation, stock, or industrial supply. Groundwater sites are mainly wells, but include some springs. From heretofore drinking water supply (DW) sites will be used to refer to DOM and PS sites as a group. The geochemical modeling dataset was compiled to obtain DW samples with a complete set of measured values of pH, calcium, magnesium, sodium, chloride, and sulfate. Alkalinity, fluoride (F), orthophosphate (OP), and bromide were included when available. DW sites were the primary source of data used to evaluate the solubility of Pb in untreated groundwater. Pb that was measured on the same date as the sample used for geochemical modeling was retained for statistical analysis of model output but was not included as input to the geochemical model. In addition, samples with missing alkalinity values were included when pH was at or below 5.5 and cation-anion balances were within 5%, indicating alkalinity was not a major component of the ion chemistry.