Debris found dumped at a horse-riding center in a Suffolk County park in August has tested positive for “acutely hazardous and hazardous substances” — with contamination at levels greater than that found in a previous dumping of materials at a Brentwood park, Suffolk’s top prosecutor said Thursday.

“Unfortunately, once again I have to announce that yet another and even more serious environmental nightmare has been discovered, and this time it is in the West Hills County Park,” Suffolk County District Attorney Thomas Spota said at a news conference at his Hauppauge offices.

Hundreds of truckloads of material containing pesticides, semi-volatile organic compounds, asbestos and metals had been dumped at the Sweet Hills Riding Center, a West Hills facility that leased about 8.5 acres of the park from the county.

Six “acutely hazardous” substances — pesticide components that have been banned since the 1980s — were found in the debris, the district attorney’s office said.

The material, which was finely pulverized, was discovered at the center at an average depth of 3.5 feet to 6 feet, Spota said.

“That entire area, the Sweet Hills Riding Center, has been severely contaminated by dumping at a magnitude unfortunately even greater than what was found at Roberto Clemente Park in Brentwood and all of the other facilities in the town of Islip and the one in the Town of Babylon,” Spota said, referencing an earlier dumping scheme in which six men and four companies were indicted in 2014.

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He said the debris found at the riding center is believed to have come from New York City.

No one has been charged in the case, and while no suspects have been publicly identified by the district attorney’s office, Spota said “we have identified a number of participants” in the dumping scheme.

“I would anticipate we will probably be identifying others,” he said. He declined to provide a timeline of when any charges may be filed.

Mark Smith, a spokesman for the riding center, issued a statement saying the center is cooperating with authorities.

“The Sweet Hills Riding Center, with a 30-year commitment to the equestrian community and families of Long Island, is continuing to cooperate in the ongoing investigation,” Smith said. “This disturbing incident occurred without our knowledge or consent.”

He declined to comment further, citing the ongoing criminal probe.

While the public-health issues from the materials are “unknown” at this point, Spota said it was a concern that the riding center — which operates a summer camp for children — was open at the same time the dumping occurred.

Spota said his office planned to contact the families of the more than 70 children who were known to have attended summer camp at the riding center.

“This area here was wide open and actively used” during the dumping, Spota said.

Dr. James Tomarken, commissioner of the Suffolk County Department of Health Services, said in a statement that his office “just received the raw data” of the soil samples taken from the park from Spota’s office on Thursday afternoon.

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The data was then forwarded to the state Health Department with a request for an expedited evaluation “to determine whether there is a risk to public health,” Tomarken said in the statement.

Paul Tonna, chairman and commissioner of the South Huntington Water District, said the dumped materials did not pose a threat to the public water supply.

It would take about 75 years for the groundwater flowing beneath the park to reach the district’s public water-supply well on Gwynne Road, which serves West Hills and lower Melville, he said.

The water district has several treatment systems in place to ensure the water is safe for human consumption, Tonna said.

“We want to assure everybody that their drinking water is 1,000 percent clean,” Tonna said in an interview Thursday. “Nobody has to worry. We are constantly monitoring and testing our water.”

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Prosecutors believe the dumping at the riding center began in October 2015 and continued through August.

Tipping fees to dispose of the materials properly at a DEC-approved facility — the closest one being in Pennsylvania — would have cost the haulers $1,500 to $5,000 per truckload, Spota said.

The scheme paved the way for those involved to “make huge profits.”

“The name of the game here is pure greed,” Spota said.

The investigation at the park began in August, after county park rangers contacted officers from the state Department of Environmental Conservation, who “immediately investigated the site,” according to an emailed statement from the DEC.

“The DEC is continuing to work in partnership with the Suffolk County District Attorney’s office to determine the next appropriate steps as this investigation moves forward,” the statement read.

The DEC did not provide further details, such as the location where the materials were processed.

Investigators took more than 100 samples of the debris in late August, after officials sealed part of the park after the discovery of processed construction material. The county closed the riding center after the investigation, and cordoned off about 15 acres of the roughly 900-acre park.

The dumping investigation was reminiscent of Suffolk authorities’ probe into dumping at Roberto Clemente Park and three other locations in and around Islip Town.

Prosecutors said thousands of tons of contaminated fill, including construction and demolition debris, was dumped at the town’s park in Brentwood, a one-acre private lot in Central Islip, a six-home development for veterans in Islandia, and a state-protected wetlands area in Deer Park on the Islip-Babylon border.

Prosecutors said that dumping was motivated by “greed,” to avoid the tipping fees to dispose of the debris legally.

Four of the men indicted — including two former town officials — and one of the companies pleaded guilty, while one of the men was found guilty of charges in connection with that probe.

Suffolk County Executive Steve Bellone, in a statement Thursday, vowed to continue the county’s efforts to “undertake all necessary precautions to protect the public and prosecute to the fullest extent those who are responsible for this.”