MANCHESTER — State geologist Bob Johnston stood over a bore hole in Peter Meulendyk’s front lawn Wednesday and watched as workers retrieved cylindrical 2-inch samples of rock from 154 feet down in the earth.

Geologists are continuing to help Columbia University researchers with a five-year project to study arsenic in central Maine’s groundwater.

Johnston said researchers are looking for the source of the toxic element. The core samples retrieved from Meulendyk’s property will be shipped to the university for analysis.

He said some surprises were found.

According to a geological map of Maine, Meulendyk’s home is on top of 320-million-year-old metamorphic rock — compressed, layered sediment from the ocean bottom.

But when they drilled core samples, they found Hallowell granite.

“Hallowell granite is a younger, intrusive igneous rock,” Johnston said. “Hallowell rock came up from the (earth’s) mantle as molten.

“When you’ve got hot rock around metamorphic rock, it solidifies. When that happens, there’s a chemical reaction that could cause the arsenic.”

Robert Marvinney, director of the Maine Geological Survey, said his geologists know that arsenic comes from rocks, it’s just a matter of sorting out details.

“We’re hoping that we can determine what specific rock types are most likely to yield arsenic into ground water,” Marvinney said. “If we understand better which rock types are involved, we can understand a little better the distribution patterns throughout the state.”

Using data from more than 11,000 wells in 530 Maine municipalities, a landmark U.S. Geological Survey study released in 2010 showed three high-arsenic clusters in Maine: The southern coast, Down East and Greater Augusta.

Columbia University followed up those results and estimated 31 percent of all private wells in Greater Augusta likely contain arsenic above the federal standard of 10 parts per billion.

But the federal standard is binding on public drinking water systems, not private wells. Meanwhile, nearly half of Maine residents rely on private wells for drinking water — the highest percentage in the nation.

Using data from the Columbia study, the Kennebec Journal reported in September that as many as 15,561 Kennebec County residents are drinking from private wells that have toxic levels of arsenic, which has been linked to increased risk of skin, lung and bladder cancer; developmental problems in children; diabetes; and undesirable effects on the immune system.

Arsenic in toxic concentrations was most prevalent in Readfield and Manchester, and in a band along the western edge of the county from Winthrop and Monmouth south through Hallowell and Litchfield. Arsenic found in some private wells sampled by Columbia researchers exceeded the standard by 10 to more than 100 times.

Marvinney said one weakness in the study is that Columbia researchers never drilled core samples from the wells they sampled.

“We can only guess at the source of arsenic in these wells, although it is most likely from the bedrock,” Marvinney said. “So we are drilling at one of the well sites to get actual samples of bedrock from near the well. We can analyze the minerals in the bedrock drill core to determine the source of arsenic.”

Chris Palmer of East Coast Explorations, in Hallowell, owner of the drilling rig, said the information researchers gain from the core samples could be a real benefit to people building homes.

“When you think about it, there’s not that many unknowns in geology today,” Palmer said. “It would be great if they could solve the mystery (of where arsenic comes from) and get it out on the web so the world would know.

“If there’s a high probability of arsenic (in the bedrock),” he said. “People might want to stay away from building on that property and build somewhere else.”

Meulendyk, a pharmacist, said his family has participated in the Columbia study for past two years.

He said they knew when they built the house in 2006 that the property had high levels of arsenic, radon and uranium.

Meulendyk said he couldn’t recall what his arsenic levels were, but said he has addressed the problem with filtration.

“Whatever information they can continue to glean from this type of work is important,” he said. “I’m in health care, and that’s another reason we’re supportive of this study. Public awareness is critical.”

Mechele Cooper — 621-5663

[email protected]

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