Pesticides at "unusual and unexpected" levels are in groundwater at and around Roberto Clemente Park in Brentwood, but the source may not be the contaminated fill dumped there, according to a county report released Monday.

Elevated levels of three pesticides banned in the late 1980s -- chlordane, dieldrin and heptachlor epoxide -- were found in test wells drilled by the Suffolk County Department of Health at and around the park.

The pesticides, in addition to high levels of manganese, ammonia and nitrates, largely were found at lower depths in the park and at higher elevations outside the park. That led county scientists to suspect the source of that pollution is something other than the contaminated debris used as fill, according to the report by the health department.

DataContaminants found in parksee alsoDocuments: Illegal dumpingsee alsoComplete coverage

The pesticide findings "are particularly rare" and "not often detected in Suffolk County groundwater," especially since they usually bind tightly to soil particles and don't easily slip into water, according to the report, which recommended an additional investigation to find the source of that contamination.

All three of the pesticides, which were found at levels above state groundwater-protection standards, are classified as probable human carcinogens, according to the U.S. Environmental Protection Agency.

But the health department's report did not rule out the possibility that the dumped fill could have partially contributed to the contamination found in the groundwater, and some contaminants found at shallower levels may have come from the fill -- such as high levels of iron, which were found directly south of the recharge basin.

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The health department also noted some caveats to the findings -- particularly that there was no baseline groundwater data collected before the dumping occurred and that only one round of data collection was performed, leaving scientists unable to study trends.

The health department drilled 13 temporary monitoring wells earlier this year to test for contaminants at the behest of the Suffolk County Legislature. Two of the wells were drilled north of the park in an area unaffected by the dumping, while two others were drilled south of the park. Groundwater in the area flows southeast.

Six men and four companies were indicted in Suffolk County in December in connection with the dumping at the park and three other sites in and around Islip Town. All have pleaded not guilty.

The health department's report, based on results from the 76 samples taken at varying depths over three months, recommends continued groundwater testing north and south of the park after the fill has been removed, but also recommends an investigation into the source of the pesticides and other contamination, and whether it could hit areas from which wells draw water for the public to consume.

The department has the authority to begin such an investigation, spokeswoman Grace Kelly-McGovern said.

Suffolk Legis. Monica R. Martinez (D-Brentwood), who sponsored the legislation directing the health department to conduct the testing, said she was gratified that the department wanted to continue monitoring the site.

"I think it's important we continue to monitor it," she said. "Right now it's all new. Who knows what the long-lasting impacts might be?"

Islip Town Supervisor Angie Carpenter said the results weren't surprising.

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"If you think about it, things like this take an awful long time to penetrate and have an adverse effect," she said. "So it isn't a terrible surprise."

She said it was "good news" that the county did not consider it likely that contaminants from the fill have invaded the groundwater.

"I am delighted to be able to go out there now and announce to our residents . . . that the county health department has found no contamination in the drinking water or groundwater from illegal dumping at Roberto Clemente Park," Carpenter said. "Whatever there might be is off-site, and I would assume that an investigation where exactly that might be would be commenced immediately."

The town is removing the estimated 50,000 tons of contaminated fill dumped in the park's soccer fields and recharge basin.

The report noted that public water supplied to residents around the Brentwood park is safe and meets all standards.

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Jeffrey Szabo, chief executive of the Suffolk County Water Authority, said his agency already tests its water for all the contaminants mentioned in the report, and that treatment methods are available to remove the contaminants from water.

Legis. Tom Cilmi (R-Bay Shore) said he hadn't been convinced the extra testing by the health department was needed, especially as the Town of Islip had done its own groundwater testing, but he was glad it occurred.

"To the extent that testing can provide the residents in Brentwood with some level of comfort and provide us with information as to the quality of the soil in that area and the contaminants that exist there, I think it's helpful," he said.

Meanwhile, groundwater testing has been completed at the dumping site at Veteran's Way in Islandia and will begin next week at the dumping site at a state-protected wetlands area in Deer Park, Kelly-McGovern said. The county is continuing to negotiate with the owner of the fourth dumping site -- a 1-acre lot at the corner of Sage Street and Islip Avenue in Central Islip -- to drill test wells there.