EVANS CITY, Pa. (AP) — A woman says state environmental officials refused to do follow-up tests after their lab reported her drinking water contained chemicals, but it’s unclear where the pollutants came from.

At least 10 households in the rural Woodlands community, about 30 miles north of Pittsburgh, in western Pennsylvania, have complained that recent gas drilling impacted their water in different ways.

The Department of Environmental Protection first suggested that Janet McIntyre’s well water contained low levels of only one chemical, toluene, a paint thinner. But a review of the DEP tests by The Associated Press found in her water four other volatile organic compounds that can be associated with gas drilling.

After this story was first published, drilling firm Rex Energy Corp. provided a list that shows none of those chemicals was used at its nearby well with a procedure known as hydraulic fracturing, which involves blasting chemical-laced water deep into the ground.

That suggests that Rex may be getting blamed for problems that are not its fault, even as another mystery remains: Others in the community have complained of water that became discolored, smelled and had higher levels of minerals and solids after recent drilling.

Further complicating the situation, other companies have older wells in the same area.

Some anti-drilling activists have suggested that there are major problems in the Woodlands area, but one expert said that the low concentrations shown in the test may not be a health threat and may be unconnected to gas drilling.

Dr. Bernard Goldstein, professor emeritus at the University of Pittsburgh School of Public Health, said the lack of follow-up tests by the DEP doesn’t make sense.

“DEP cannot just simply walk away,” Goldstein said.

DEP spokesman Kevin Sunday said on Friday that the low chemical concentrations were not a health risk, and he suggested that the contamination may have come from the agency’s laboratory or from abandoned vehicles on or near the property. But Sunday didn’t answer why the DEP failed to do follow-up tests if it suspected that its own testing process was contaminated.

Sunday said the agency had conducted enough tests to make an informed, rational decision that the compounds did not come from drilling activity.

McIntyre and other residents say the water problems started about a year ago, after Rex, based in State College, drilled two wells. But a map Rex provided also shows gas wells from other companies in the area, and it noted that the people who have complained are uphill from the nearby gas wells.

Rex has been supplying drinking water to many households but has sent letters notifying them it will no longer deliver water after Feb. 29.

In a statement, Rex said that the wells of residents who have complained are from 2,100 to 4,600 feet from its drilling locations. The company noted that many other homeowners in the area haven’t raised complaints or concerns.

Rex also said there are old oil wells in the region that could impact some ground water and there were “no notable differences in water chemistry between pre- and post-drill water quality tests of the water wells in question.”

McIntyre’s water showed detectable levels of t-Butyl alcohol, acetone, chloromethane, toluene and 1, 3, 5-trimethylbenzene. Some are commonly used in households and other industry, such as toluene.

Goldstein said the multi-chemical mix is what is so unusual, since it suggests either multiple sources of contamination or an industry that uses many different chemicals.

“Where would you get such a strange mixture?” Goldstein asked, adding that if DEP’s own laboratory was even a potential source of the chemicals, the agency had the obligation to follow up.

“You’ve got to pursue the finding,” Goldstein said, since if the lab was at fault the variety of chemicals that showed up “makes no sense at all, except a really sloppy lab.”

Sunday said an independent peer review of the DEP laboratory found it to be “a well-managed, efficient and highly functional laboratory” that is “driven by a culture of customer service.”

McIntyre told the AP that she repeatedly asked a DEP field worker for follow-ups after two tests last summer showed the chemicals and elevated levels of some natural underground compounds such as barium.

“He said no,” she said, leaving her feeling that she had no one to turn to for an objective public health opinion.

She also said the chemicals didn’t show up on pre-drill water tests.

As drillers have poured into Pennsylvania to tap its vast gas reserves in the Marcellus Shale, a massive rock formation also underlying New York, Ohio and West Virginia, residents and environmentalists have raised concerns over the impact or potential impact to water supplies. Water contamination in Dimock, in northeast Pennsylvania, has riled some homeowners for months, even as others say their water is fine.

State regulators determined that Houston-based Cabot Oil & Gas Co. drilled faulty gas wells that allowed methane to escape into Dimock’s aquifer. The company paid heavy fines but denied responsibility; it has been banned from drilling in a 9-square-mile area of Dimock since April 2010.

Another Woodlands resident who complained about dramatic changes in her water over the last year said DEP staff suggested the bad smell was simply from garden slugs in her well, which is 300 feet deep.

“They just insult your intelligence. I don’t trust the DEP,” said Kim McEvoy, who lives about a mile from McIntyre.

McEvoy said she wants the U.S. Environmental Protection Agency to investigate the community. She said she’s come to that point because state environmental officials haven’t answered her questions.

“Something has happened here,” McEvoy said.