About one-third of more than 8300 wells tested across the United States had groundwater with chemical characteristics that could cause lead, if present in plumbing, to leach into tap water at levels above the U.S. Environmental Protection Agency action level, according to a new study by the U.S. Geological Survey National Water Quality Program. These characteristics are most common in groundwater in the East and Southeast.
Lead can dissolve into water if the water corrodes a lead-containing material such as lead pipes, lead solder, or brass fittings. The USGS study used measured chemical characteristics of groundwater from more than 8300 wells tapping groundwater to estimate the potential solubility of lead for each sample. Groundwater with low pH, low alkalinity, or low phosphate concentrations had the greatest lead solubility potentials.
Nationwide, about 33 percent of untreated groundwater samples had the potential to dissolve 15 micrograms per liter or more of lead, the U.S. EPA action level for lead in treated water from public drinking water supplies, and 5 percent had the potential to dissolve 300 micrograms per liter or more of lead.
The states with the greatest percentage of wells producing untreated groundwater with a high lead solubility potential (300 micrograms per liter or greater) were Maryland, New Jersey, Delaware, Tennessee, and Arkansas. Lead is a toxic metal that can be harmful to human health even at low exposure levels.
In the United States, groundwater at the wellhead is rarely a source of high lead concentrations in drinking water; rather, the source of the lead typically is somewhere in the plumbing system. Less than 1 percent of the more than 8300 untreated groundwater samples evaluated contained dissolved lead at a concentration greater than the EPA action level of 15 micrograms per liter.
NGWA has published an information brief titled Lead Presence in Well Systems detailing sources of lead and corrosion. NGWA also has a best suggested practice, Reducing Problematic Concentrations of Lead in Residential Water Well Systems, which is free to download for members and available for purchase for nonmembers.