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Denis Thoet tests his well every year for bacteria.
But the West Gardiner vegetable farmer said he never thought to check for arsenic or uranium, known carcinogens.
An estimated 11 percent of Maine homes with private wells have high levels of arsenic above current health benchmarks, as many as 20 percent have elevated radon levels and an estimated 4 percent have elevated uranium levels, according to state statistics.
And while the state has a robust safety program for public water supplies, there are no regulations for these substances in private wells.
That has some of the more environmentally sensitive gardeners questioning what they're putting on their plants.
"I suppose it's a potential area to have tested for irrigation water," Thoet said. "We have a pond we do part of our irrigation from, and want to use it for more of that. It's a combination of runoff water and spring water.
"We haven't tested that for anything yet. There's usually some kind of bacteria from general runoff that's fine for irrigation water but not for human consumption."
In elevated levels, arsenic has been linked to certain types of cancers, childhood learning disabilities, heart disease and low birth rates. Uranium can affect the kidneys, according to the centers for Disease Control and Prevention.