The state is unveiling a new $12.5 million mitigation plan for a former factory Superfund site in West Islip that is once again considered a “significant threat to the public health or environment” after additional contaminants were discovered there last year.

After years of monitoring, the state Department of Environmental Conservation in 1999 determined the former Dzus Fastener Co. at 425 Union Blvd. had been sufficiently “remediated.” But early last year, routine testing of surface water found elevated levels of cadmium in the floodplains of Willetts Creek, according to the DEC, triggering a reclassification of the site back to a “significant threat.”

“On rare occasions the long-term monitoring of a site leads to the need for further action if conditions change, as was the case at the Dzus site. This is why we maintain a site management presence at remediated sites,” the DEC said in an emailed statement.

The new plan, which will be discussed at a public meeting Wednesday in West Islip, involves removing sediment with excessive levels of cadmium and chromium and restoring the excavated area of the creek to a “stable riparian corridor,” while “wetland habitat will be restored to the maximum extent possible,” according to the DEC.

Metal fasteners were manufactured at the factory from 1937 until 2015. When the DEC began investigating the site in the 1980s, the agency found cadmium, chromium, cyanide and organic compounds in the soil and groundwater. The resurgence of cadmium contamination probably was from leaching pools that had been removed as part of site remediation and may have been stirred up by flooding from superstorm Sandy in October 2012, the DEC has said. Cadmium and cadmium compounds are carcinogenic. Breathing high levels can cause lung damage, and long-term exposure can lead to kidney disease.

The DEC said the remediation would be paid for out of the state’s Superfund program, after which the state would work to “recoup the costs” from the responsible party — Dzus Fastener, which later was renamed DFCI Solutions, Inc.

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A phone message left for Stephen Meshover, a listed manager for DFCI, was not returned.

Of concern are two West Islip schools bordering Willetts Creek that are downstream from the Dzus site. The DEC in January removed sediment from culverts by two walkways crossing Willetts Creek that lead to Beach Street Middle School and West Islip High School property.

“The district encourages the community to participate in the upcoming forum hosted by the NYSDEC as they present their proposed cleanup plan,” West Islip Superintendent of Schools Bernadette M. Burns said in a statement. “The well-being of our students and staff is our top priority and we will continue to work with environmental officials to ensure that our schools and grounds provide a safe learning environment.”

State Sen. Phil Boyle (R-Bay Shore), who has hosted previous forums on the site and plans to attend Wednesday’s meeting, said he was encouraged by the progress at the site.

“I have been assured by the Suffolk County Water Authority that our drinking water is safe and will remain unaffected by the Dzus Superfund Site contamination,” Boyle said in a statement. “It is also important to note that the community has been advised that limited exposure is not a significant concern, as this contamination is not an airborne risk. Should residents come in physical contact with any dirt or debris from the site, it is advised that they clean thoroughly.”