The report “Assessment of Arsenic Concentrations in Domestic Well Water, by Town, in Maine, 2005–09” and maps now are posted online.

Potentially harmful arsenic levels have been found in private water wells in towns across Maine where elevated arsenic risks were not previously suspected. Arsenic levels in some private wells exceeded the federal safety standard for public drinking water by 10 to 100 times or more, according to findings recently released by the U.S. Geological Survey (USGS). The study is the largest of its kind in Maine.

“We found large differences in concentrations from well to well, even at the town level, so residents need to test their wells to know their arsenic level,” says USGS scientist Martha Nielsen, who led the study in cooperation with the Maine Center for Disease Control and Prevention (CDC). “We are working with the Maine CDC to identify towns throughout the state where elevated arsenic levels are common but have gone mostly unnoticed.”

"The USGS has been working nationwide for many years to test ground water for arsenic,” says Robert Lent, Director of the USGS Maine Water Science Center in Augusta. “Arsenic levels in this study are some of the highest we have seen in private wells,” explains Lent. “Nearly half of Maine’s population use private wells for drinking water, so this issue quite literally hits home for many people.”

“It only takes one person in a town to be an advocate and champion to encourage fellow citizens to have their wells tested. The variability in arsenic concentrations, even at the town level, shows that testing is crucial for homeowners in assessing personal risk,” notes Lent.

The Maine CDC is distributing posters and brochures to selected town offices based on the proportion of residents on private wells and information about the presence of wells with arsenic. The Maine CDC has worked in partnership with towns throughout Maine to prevent the spread of diseases.

“This mapping effort is helping us to better target our efforts to promote testing of private wells for arsenic,” says state toxicologist Andrew Smith with the Maine CDC. “Statewide only about 40 percent of private water well owners have tested for arsenic, so it is crucial that we target our resources to the highest risk areas and nearby areas where we lack data,” Smith reveals.

For this study, scientists examined data from more than 11,000 wells in 530 cities, towns and townships in Maine. Data came from water samples submitted to the Maine Health and Environmental Testing Laboratory between 2005 and 2009.

Arsenic levels ranged from less than the detection limit of 0.5 micrograms/liter (ug/L) to 3,100 ug/L. The federal safety standard for public drinking water is 10 ug/L.

Test results were summarized at the town level to produce maps showing arsenic concentrations by town where sufficient samples were collected. The maps provide a much greater spatial resolution of arsenic in private wells across the state than have previous efforts.

“This study confirmed many areas already known to have high levels of arsenic in ground water and revealed for the first time, towns that should be further investigated,” says Nielsen. “Several towns in eastern Washington and central Penobscot counties, and in the southern parts of Piscataquis and Somerset counties have elevated arsenic that is more widespread than we realized.”

Even though the study included more than 11,000 wells, this is a relatively small sample of all the private wells in Maine.

“This study shows the difficulty of predicting arsenic concentrations at the local level, and should signal to everyone with a private well that the only way to know about arsenic concentrations in their well is to have their water tested,” states Nielsen.

Most towns with more than 20 wells in the database had at least one well with arsenic levels greater than the safety standard. In a few towns, more than 50 percent of the sampled wells had arsenic levels greater than the safety standard. In considering these data, it is important to understand that the wells do not represent a random sample of the state. These data, however, provide a better indicator of potential arsenic hotspots than any other dataset.

"Geology is probably the biggest factor in the distribution of arsenic in private wells,” explains Nielsen. “But the degree of local variability means that we can't simply use bedrock type to determine all the areas in the state where it is critical that people test their wells.”

Drinking water with arsenic above safety standards has been linked to an increased risk for skin, bladder and lung cancer; to reproductive and developmental problems; diabetes; and effects on the immune system. Private water wells are not regulated under the federal Safe Drinking Water Act, and well owners typically are responsible for testing the quality of their drinking water.

Elevated arsenic levels are not limited to Maine. A recent national USGS study found arsenic concentrations above the federal drinking water standard in more than 10 percent of private wells in New England’s bedrock aquifers compared to about 7 percent of private wells nationwide.

Private well owners can contact the Maine Drinking Water Program for guidance and information about well maintenance, testing, and in-home water treatment options. Access the USGS Maine Water Science Center for more information about water in Maine. Information about water quality nationwide is found on the USGS National Water-Quality Assessment Program site.