Slots are filling quickly for a pilot study of pesticide contamination in well water at Westport and Weston homes.

Mark Cooper, director of the Westport Weston Health District, said Monday that he's already received several applications for the free program, which is limited to 10 homes in each town.

He said roughly 50 percent of Westport homes are serviced by private wells, while nearly all of Weston homes have wells.

"I anticipate we'll get 10 from each community relatively quickly," Cooper said. "I think once the public is aware of this, our 10 slots for each community are going to fill up pretty quick."

The state Department of Public Health, which will analyze the water samples taken from each well, is looking for man-made pesticides used decades ago to kill insects in soil, particularly termites.

The homes of residents who apply for the program should be built before 1980, when use of the pesticides was banned, and should have some likelihood of receiving underground treatment for termites in the past, Cooper said.

Exposure through drinking water to the pesticides could have health consequences through long-term repeated doses, Cooper said.

"These are pesticides we're looking for so if you find it, that's not a good thing," he said. "This would not be good stuff to drink ... Very low levels may not have any health consequence, but over time these things add up."

The DPH is looking specifically for dieldrin, classified as a probable human carcinogen, and chlordane, which can affect the liver and nervous and digestive systems, according to William Gerrish, director of the state agency's Office of Communications and literature provided by Gerrish.

Gerrish said in an email that the DPH also has asked the New Canaan Health Department to participate in the pilot study.

He said in the email that the DPH plans to test 20 wells in each of four or five towns and that other towns would be asked to participate in a later phase of the pilot study.

The DPH launched the pilot program for well water testing due to the discovery of pesticides in well water in Stamford about three years ago, Cooper said. "The state doesn't know how widespread the problem is. This is their way of trying to get a better handle on it," he said. "The state is not sure if that's something unique to the Stamford area."

So far, the city of Stamford has tested 944 well water samples and 15 percent have been positive for some level of dieldrin or chlordane, with 6 percent above the department's action levels, Gerrish's email says.

When the action levels are exceeded (0.03 micrograms per liter for dieldrin and 0.3 micrograms per liter for chlordane) the department recommends that a homeowner use bottled water or install a drinking water treatment system. The action levels are based on a person drinking two liters of water a day for a lifetime, according to literature provided by Gerrish.

"If a person is exposed to a chemical in their drinking water at a concentration below the Action Level, DPH considers their health risk from that exposure to be insignificant," the literature says. "At concentrations above the Action Level, exposure over many years can increase a person's risk of health effects."

Contamination in Stamford wells "seems to be scattered throughout this city, rather than being confined to only one area," Gerrish said in the email. "The source of this contamination is unknown, but may be due to widespread past termite treatment during or before the mid-1980s."

Cooper said homes in Westport and Weston would be selected on a first-come, first-served basis and that he anticipates receiving qualified applications from 10 homes in Westport and Weston in less than two weeks. He said local health officials would collect the water from wells and send it to a lab at the DPH for testing at no cost.

Homeowners would then be notified of the test results and ways to remove the pesticides if they're found in the water, Cooper said.

An activated carbon filtration system, which would cost about $1,500, could remove not only dieldrin and chlordane, but any volatile organic compounds in the water supply, Cooper said.