A second private drinking water well in Manorville has been found to be contaminated with high levels of a banned gasoline additive, according to environmental officials — and this time, the concentration is nearly 25 times the state limit.

Last week, Suffolk County and state environmental officials began investigating private wells after a gas-blending compound known as methyl tertiary butyl ether, or MTBE, was found in the Bennett family’s Oakwood Drive well at 110 parts per billion.

The drinking water standard is 10 parts per billion, although private wells are not required to be held to that standard.

A well at a nearby house sampled this week showed levels of the compound at 240 parts per billion, the state Department of Environmental Conservation said Tuesday.

A second test was taken at the well Tuesday, homeowner George Moretti said. The state worker “said it was very high,” Moretti said, adding that his household has stopped using the water for “domestic purposes.”

“It’s been a very quick response” by the state and county, he said. “I don’t know how to take that. I don’t know if that’s good or if it’s scary.”

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The probe was launched last week after the Bennett family paid Suffolk County in November to test the water quality in their private well — something they do every few years.

Despite having a filtration system, their initial test detected MTBE at 110 parts per billion, prompting the DEC investigation. Another test this week saw concentrations of 120 parts per billion.

“Six years ago I didn’t have any” MTBE, Clare Bennett said Tuesday. “I just want to make sure I get good water.”

DEC spokeswoman Erica Ringewald said the agency has been out to the neighborhood, plans to install a treatment system at the Bennett house and is giving bottled water to affected families.

About 25 homes are in the vicinity, and Suffolk’s Department of Health Services has sent notices about the MTBE discovery to all private well owners there.

As of Tuesday, the county had sampled wells at six properties, with results expected in a few days, the department’s spokeswoman Grace Kelly-McGovern said.

After the results are compiled, the DEC and Suffolk will develop an investigation plan into the source of the contamination that includes collecting groundwater samples, the DEC said.

“DEC is aggressively conducting an investigation to quickly identify the source and extent of the MTBE contamination and address it in order to protect the public and the environment,” Ringewald said in a statement.

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MTBE is not regulated nationally, but New York State banned its use in 2004 and set a drinking water standard that applies to public water-supply systems.

Exposure to MTBE can irritate the eyes and respiratory tract, as well as cause headaches, lightheadedness, stupor, dizziness, nausea, disorientation or confusion.

Richard Amper, executive director of the Pine Barrens Society, said the MTBE find was disturbing.

“Where did it come from and how far has it spread is a matter of conjecture,” he said. “That’s the scary part. We don’t know what’s getting into our water.”

Moretti said they are eager to know. His family bought the house in 1987 and lost it to the Manorville-Ridge fires in 2012, causing them to live in a trailer on their property for 15 months while they rebuilt.

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“Hopefully they’ll be able to track it down and tell where it’s coming from,” Moretti said. “Are they going to be able to tell how long we’ve been drinking this?”