Contaminants in Sources of Drinking Water from Public Wells

In the USGS study, water-quality conditions were assessed in untreated water from 932 public wells, and in untreated and treated water from a subset of 94 public wells. Water samples were analyzed for as many as 337 contaminants.

On May 21, 2010, the Environmental and Energy Study Institute (EESI), Water Environment Federation (WEF), and U.S. Geological Survey (USGS) held a briefing on the quality of water from public supply wells in the United States. At this briefing, the USGS National Water-Quality Assessment (NAWQA) Program released new information on the prevalence of naturally-occurring and man-made contaminants in public wells around the country. This assessment is particularly significant because more than a third of the Nation’s population depends on drinking water from public water systems that rely on groundwater pumped from public wells.

• The USGS study assessed more contaminants than any previous national study, including 44 inorganic contaminants (mostly from natural sources, except for nitrate from livestock, fertilizer, etc.) and 293 man-made organics (including pesticides, volatile organic compounds, and personal-care products). It also evaluated contaminant mixtures.
• One in five source water samples had concentrations greater than human health benchmarks. Benchmarks do not exist for 43 percent of the contaminants studied.
• Contaminants from natural sources accounted for 75 percent of the concentrations above benchmarks. The contaminants of greatest concern were radon in western and northeastern states, arsenic in western states, and pesticides and VOCs in east coast states.
• One or more pesticides or volatile organic compounds (VOCs) were found in two-thirds of the samples. Man-made contaminants were detected in most samples.
• Deeper wells that draw from confined aquifers were better protected from man-made contaminants.
• Concentrations of the most common organic contaminants were similar in source water and finished water.
• There is an information gap regarding the potential health effects of individual contaminants that do not have benchmarks and the health effects of contaminant mixtures.
• The groundwater in Modesto, California is affected by present and historical land use. Nearly 20 percent of Modesto wells have been shut down due to contaminants above Maximum Contaminant Levels (MCLs). When several wells in one area are shut down, this negatively impacts water pressure.
• Modesto is reducing the concentrations of contaminants by through well design and location, adjusted pumping times and duration, and blends with surface water resources.
• Collaborative efforts with the USGS are helpful for local water agencies who don’t have the capacity to collect data on their own.
• The Environmental Protection Agency regulates contaminants under the Safe Drinking Water Act. Ninety-three percent of the population drinking from community water systems consume water that meets the standards of this law.