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USGS study found levels above federal limits in a sample of water wells
The U.S. Geological Survey (USGS) this week released a study that indicates that levels of naturally occurring arsenic and uranium exceed drinking water standards in some private drinking water wells in central and northeastern Massachusetts. State officials are working with USGS to develop resources that will help private well users determine whether their water meets federal safety standards, and provide guidance on water testing and treatment if it does not.
USGS researchers analyzed water samples from 478 private bedrock wells in 116 area cities and towns and found that 13% exceeded federal drinking water standards for arsenic, and 3% exceeded standards for uranium. Both arsenic and uranium are found naturally in some types of bedrock in the study area.
The Massachusetts Department of Environmental Protection (MassDEP) and the Massachusetts Department of Public Health (MDPH) provided funding and assistance to complete this study, and are providing health and water treatment information to health officials in each town with a higher probability of contamination from bedrock sources.
In estimating how widespread the issue is, researchers plotted the tested wells on a map showing types and extent of bedrock in the study area to relate concentrations of arsenic and uranium to bedrock type. They then plotted the remaining wells and estimated that about 5,700 of the estimated 90,000 wells in the study area may exceed the standard for arsenic, and about 3,300 may exceed the standard for uranium. Depending on rock type, the probability of exceeding a standard ranges from less than 1% to 26% for arsenic, and from less than 1% to 21% for uranium.
The federal public drinking water standard for arsenic is 10 micrograms per liter. The standard for uranium is 30 micrograms per liter. Long-term exposure to arsenic above the standards can cause darkened patches of skin on the body and has been linked to skin, bladder and lung cancer. Long-term exposure to uranium in drinking water can damage the kidneys. Based on information available on water testing results and the MDPH companion effort testing for arsenic and uranium in urine, the probability that anyone’s well poses an acute health concern is very low.
The USGS study is the first detailed look at the distributions of arsenic and uranium in 116 communities within the Massachusetts portion of the New England “arsenic belt,” a swathe of naturally occurring arsenic in bedrock stretching from Dudley to Salisbury. Bedrock wells are a significant source of groundwater in the area. USGS led the study to help site future public water supplies as demand for groundwater grows in the arsenic belt, and to inform private well owners following the recent adoption of new federal drinking water safety standards.
Although private wells are not subject to the same regulatory standards as those set for public drinking-water supplies, it is recommended for health purposes that private well owners use these standards to guide their treatment decisions.
The USGS data indicated that most of the wells in the study that exceeded the safety standards were used for drinking water without treatment. Since testing and treatment are the responsibility of private well owners, Massachusetts officials strongly recommend that the owners have their wells tested and treat their water if necessary.