More than half of Maine residents get their water from wells and many of those have high arsenic levels, according to a new joint federal and state report.

Among Waldo County communities, Northport had the highest percentage of domestic wells that had arsenic levels greater than that considered safe by the U.S. Environmental Protection Agency.

Those are the findings of a report issued by the U.S. Department of the Interior and the U.S. Geological Survey titled “Assessment of Arsenic Concentrations in Domestic Well Water, by Town, in Maine, 2005-09.”

The study notes that the widespread occurrence of arsenic in groundwater is a well-known public health issue in Maine. Arsenic occurs naturally in bedrock in Maine and dissolves into groundwater along bedrock fractures, the study noted. Forms of arsenic were also used during the early 1900s as a crop pesticide for apples, blueberries and potatoes.

The aim of the study, according to its authors, is to educate the public about arsenic in hopes that residents will get their wells tested and then have their water supplies treated. There are various methods to treat water with high levels of arsenic.

The EPA has linked arsenic to several forms of cancer, primarily of the bladder and skin.

All public water supplies are tested for arsenic, but there is no requirement for private wells to be tested.

The EPA has set the maximum safe level of arsenic in drinking water at 10 micrograms of arsenic per liter of water. A liter is slightly less than a quart. Thirty million micrograms equals an ounce.

Northport had the 15th-highest percentage of wells tested that had arsenic levels above the EPA recommended maximum. The study sampled water from 531 communities in Maine and from more than 11,000 individual wells. The list of those towns with the highest percentages only used communities in which 20 or more wells were sampled.

Of the 35 wells tested in Northport, 13 had arsenic levels exceeding the safe limit. Of those 13, five had levels greater than 50 micrograms per liter and two had levels above 100 micrograms per liter.

The Northport area is one of a handful of so-called “arsenic clusters” in the state, areas with occurrences of high levels of arsenic. Other clusters have been identified in the Buxton/Hollis area in southern Maine, the Waldoboro area, the greater Augusta area, the Ellsworth/Blue Hill area and the towns of Rangely (Franklin County) and Danforth (Washington County).

“Some of the clusters of wells with high concentrations of arsenic encompass several towns, and maximum arsenic concentrations are in hundreds of micrograms per liter (southern Maine, greater Augusta area, and Ellsworth/Blue Hill),” the report states. “Other clusters encompass much smaller geographic areas but have maximum arsenic concentrations in thousands of micrograms per liter (Northport and Danforth, for example).”

The town of Manchester in Kennebec County had the highest percentage, with 62 percent of the 111 wells tested having arsenic levels greater than the EPA limit.

The study also included a chart that listed communities and the median arsenic concentration per well tested. The median is the number where there is an equal number less than that level and more than that level.

The highest median arsenic level to be found in Waldo County was in the town of Northport, at 7.9 micrograms per liter. Thirty-five wells were sampled in Northport.

Islesboro, where seven wells were tested, had the second-highest median leve,l with 4.0 micrograms per liter. Belmont, where 11 wells were tested, rounded out the top three towns with a median level of 3.5 micrograms per liter.

None of the towns tested in Waldo County had a median arsenic concentration above the EPA’s maximum safe level of arsenic in drinking water (at 10 micrograms of arsenic per liter of water).

The median level of arsenic in Waldo County communities and the number of wells tested were:

• Belfast: 1.9 micrograms (42 wells tested)

• Belmont: 3.5 micrograms (11 wells tested)

• Brooks: less than 0.5 microgram (36 wells tested)

• Burnham: 1.0 microgram (eight wells tested)

• Frankfort: less than 0.5 microgram (nine wells tested)

• Freedom: less than 0.5 microgram (six wells tested)

• Islesboro: 4.0 micrograms (seven wells tested)

• Jackson: less than 0.5 microgram (12 wells tested)

• Knox: less than 0.5 microgram (16 wells tested)

• Liberty: 0.6 microgram (23 wells tested)

• Lincolnville: 2.7 micrograms (30 wells tested)

• Monroe: less than 0.5 microgram (17 wells tested)

• Montville: less than 0.5 microgram (26 wells tested)

• Morrill: 1.0 microgram (10 wells tested)

• Northport: 7.9 micrograms (35 wells tested)

• Palermo: less than 0.5 microgram (28 wells tested)

• Prospect: 1.3 micrograms (26 wells tested)

• Searsmont: 0.7 microgram (17 wells tested)

• Searsport: 0.5 microgram (15 wells tested)

• Stockton Springs: 1.0 microgram (23 wells tested)

• Swanville: 2.3 micrograms (19 wells tested)

• Thorndike: 0.7 microgram (13 wells tested)

• Troy: less than 0.5 microgram (two wells tested)

• Unity: 1.4 micrograms (26 wells tested)

• Waldo: 0.5 microgram (14 wells tested)

• Winterport: less than 0.5 microgram (41 wells tested)

In the report, the authors did note that the samples used for the study, “because they were submitted by homeowners and were not part of a random sample, may not be representative of all wells in a given area.”

Amanda Gott, the office manager for Haskell’s Water Treatment in Rockland, said that testing and treating arsenic in water is one of the big things the company does.

Gott noted that water must first be tested to determine the type and level of arsenic before an effective treatment plan can be developed. She said treatment can cost as little as $1,000 or as much as several thousand dollars. She said most of the time the cost can be between $2,000 to $3,000.

She noted that Aqua Maine Water Company has a laboratory available for the tests to be done to determine which type of arsenic is in a water supply and Haskell’s has its tests done at Aqua Maine.

For more information on water testing, visit the Health and Environmental Testing Laboratory’s Web site at maine.gov/dhhs/etl/standard.htm. For information on how to order test kits from HETL, or to find out more about private companies that test water for arsenic, visit informe.org/hetl/.

Additional reporting by Steve Fuller.