Thousands of cubic yards of contaminated fill at a Central Islip vacant lot tied to a dumping probe must be discarded off Long Island to protect the region's groundwater, according to state environmental officials.

Pappachan Daniel, environmental engineer for the state Department of Environmental Conservation's Long Island region, said in an Aug. 31 email that the property owner's plan to take the debris to a Melville site was "not acceptable" because contaminants in the fill exceeded standards to protect groundwater -- the region's sole source of drinking water.

"Site remediation will require removal and disposal of the materials at authorized facilities located off of Long Island," Daniel wrote.

Suffolk County prosecutors say illegal dumping occurred at the 1-acre site at the corner of Sage Street and Islip Avenue.

L-C Real Estate Group, which owns the site, had proposed to truck the debris to 110 Sand and Gravel in Melville.

An attorney for the group, Frederick Eisenbud of Ronkonkoma, said the debris isn't contaminated enough to require its total removal from the Island.

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Eisenbud said "large quantities" of the fill could meet standards to stay on Long Island, and hoped that the DEC would allow the owner to ship out only what is unacceptable.

He estimated it would cost about $65 per ton to ship the material off Long Island, compared with about $45 or less per ton for it to be trucked to a disposal site here.

"If we're not able to separate out that which exceeds protection of groundwater standards and that which does not, the client will not have the funds to carry this out," he said.

An October report by a Plainview consulting firm hired by L-C Real Estate concluded that the estimated 25,000 to 35,000 cubic yards of material "will likely" need to be taken off Long Island due to the amount of contaminants found in some of the 10 samples taken at the site.

Testing of the fill showed contaminants including hydrocarbons, pesticides and metals.

L-C Real Estate's plan is the result of its agreement with the DEC, signed in July. That order on consent required L-C Real Estate to remove all the fill or face a $500,000 penalty.

Eisenbud said a revised work plan would be submitted to DEC on Monday.

"We will try to find a way to satisfy the DEC without exceeding the financial ability of the property owner to complete the remediation," he said.

The Central Islip site is one of four under investigation by Suffolk prosecutors as part of a larger probe into dumping in and around Islip Town.

In December, six men, including Thomas Datre Jr. and his father, Islip Town GOP and Conservative Party fundraiser Thomas Datre Sr., and four companies were indicted in connection with the dumping. All have pleaded not guilty.

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L-C Real Estate was not charged with a crime as part of the dumping probe, and its attorneys say the company, whose managing member is Islip Town GOP contributor Tommy Lau, was a victim of the dumping scheme.

In March, L-C Real Estate filed a civil suit in Suffolk County Supreme Court against several of the indicted individuals and companies, among others, seeking $3 million for the cost of the cleanup.

Attorneys for those named in the suit have said the case is meritless.

Meanwhile, cleanup at the other sites where Suffolk prosecutors have said dumping has occurred are in various stages of progress.

Cleanup at Roberto Clemente Park in Brentwood, where prosecutors said an estimated 50,000 tons of contaminated fill was dumped, is on schedule and in its final stage of completion, Islip Town spokeswoman Tracey Krut said.

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Contaminated fill at a six-home development for veterans in Islandia was removed in December.

Gerard Glass, an attorney representing the owner of a parcel adjacent to a state-protected wetlands area in Deer Park where prosecutors said dumping occurred, did not immediately respond Thursday to a request for an update on the status of the site.