In a new study, the U.S. Geological Survey (USGS) and the Centers for Disease Control and Prevention (CDC) estimate that about 2.1 million people in the United States may be getting drinking water from private wells with concentrations of arsenic that exceed EPA’s maximum contaminant level (MCL) of 10 micrograms per liter (µg/L).
By law, the federal MCL must be met only by public drinking water systems; the maintenance, testing, and treatment of private water supplies are the sole responsibility of the homeowner. The USGS/CDC study “presumes” that the high levels of arsenic are almost entirely from natural sources, primarily rocks and minerals through which the water flows.
Long-term exposure to arsenic in domestic wells may cause health-related problems, including an increased risk of cancer. Testing and, if necessary, treating the water is an effective way of reducing or eliminating the concern.
Statistical model
According to the study, about 44 million people in the lower 48 states use water from domestic wells. (The study did not include Alaska and Hawaii.) Analyzing water samples from more than 20,000 domestic wells, the researchers developed a statistical model that estimates the probability of having high arsenic in domestic wells in a specific area. The model was used in combination with information on the U.S. domestic well population to estimate the population in each county of the continental United States with potentially high concentrations of arsenic in domestic wells.
Some of the locations where it is estimated the most people have high levels of arsenic in private domestic well water include:
- Much of the West—Arizona, California, Nevada, New Mexico, Oregon, Washington
- Parts of the Northeast and Midwest—Illinois, Indiana, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, Ohio, Wisconsin
- Some of the Atlantic Southeast coastal states—Carolina, Carolina, Florida, North, South, Virginia
The researchers caution that the state and county estimates are not intended to take the place of more detailed or local information that may already be available in some areas.
Test and treat
“About 44 million people in the United States get their drinking water from private wells, yet surveys indicate many homeowners are unaware of some basic testing that should be done to help ensure safe drinking water in the home,” says the USGS/CDC study.
Arsenic can be removed from a domestic water supplies with four standard technologies—granular ferric adsorption (whole house); gran ferric single tap cartridges; anion exchange (whole house); and reverse osmosis (single tap). Installation costs range from several hundred dollars for gran ferric single tap cartridges to several thousand dollars for whole house granular ferric adsorption.
Arsenic cannot be removed from water by boiling, which can actually increase the concentration of arsenic because of evaporation. Neither can water softeners or granular-activated carbon remove arsenic from drinking water.
Information on the USGS/CDC study is here.