State environmental officials are re-evaluating nearly one-third of Long Island’s Superfund sites for possible contamination with radioactive compounds after radium concerns arose recently in Lake Success and Bethpage.

Forty-three sites associated with past defense and military work, including laboratories, metal fabricators and electronic manufacturers, will be looked at, as will 10 landfills that may have taken waste from those operations, state Department of Environmental Conservation Commissioner Basil Seggos said.

“We expect the number of sites to have any issues to be low, but we’re casting a large net so we don’t miss anything,” he said Thursday.

The agency would not release a list of the sites and landfills to be examined initially, but said there are 26 in Nassau County and 27 in Suffolk.

Operators of the 43 sites, all part of the Superfund program, were industries that may have used radioactive materials but were not previously evaluated for radioactive contamination.

“It’s something that could have been done years ago and we are doing now,” Seggos said.

The probe will start with an examination of site histories and documents, though additional testing or samples could be ordered.

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Recent radium detections have brought renewed attention to possible radioactive contamination in, and related to, waste sites.

Nassau and Suffolk counties have 154 Superfund sites that are classified either as representing a significant threat to public health or where the cleanup work has been finished but still is monitored.

“I’m disappointed, but not surprised we’re finding radiologicals,” said Paul Granger, superintendent of the Port Washington Water District and New York chairman of the Water Utility Council for the nonprofit trade group American Water Works Association. “As you get more information you find more and more surprises. It almost tells me that both the state and federal Superfund programs need to take a step back and look at the fundamentals.”

The DEC plans to expand the effort to evaluate sites for radiological contamination statewide, Seggos said. The Island, which gets its drinking water from a complex network of underground aquifers, is where the effort is starting.

“Our primary objective in Long Island, as far as we’re concerned, is to protect the sole source aquifer,” the commissioner said.

On June 30, the DEC ordered Lockheed Martin to test monitoring wells and stop excavation work at a former military gyrocompass manufacturing plant in Lake Success after soil removed from the 94-acre parcel tested positive for radium.

Ten days earlier, DEC had ordered Northrop Grumman to provide more information about use of radioactive compounds at a Superfund site in Bethpage where the Navy and the defense contractor researched, tested and manufactured aviation and space exploration equipment from the 1930s to the 1990s. The site is subject to several Superfund cleanup programs to remove soil contamination and treat groundwater plumes.

Also that month, monitoring wells at Bethpage High School — across from a park under Superfund cleanup related to Navy and Northrop Grumman operations — detected elevated levels of radium. In addition, Newsday revealed that Northrop Grumman had reported to the DEC in October 2016 that the company, which earlier operated as Grumman Aerospace Corp., had used three dozen radioactive materials at its Bethpage facilities.

The Long Island Water Conference, a coalition of 50 water industry and business groups, supported the investigation, said chairman Stan Carey, who is the Massapequa Water District’s superintendent.

“Any information is helpful,” Carey said. “It’ll help us water suppliers identify sources of contamination.”

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In its heyday, Grumman, which stopped manufacturing operations in 1996, employed thousands of people and produced planes used in World War II and the Korean War. Many companies sprang up to supply and support Grumman operations.

“We were a manufacturing community for decades,” said Rich Humann, president and CEO of H2M, a Melville engineering firm representing water suppliers. “The likelihood is they’re going to find things.”

He said other companies probably used compounds similar to those in Grumman’s operations, but on a smaller scale.

“The challenges have always been there,” Humann said. “It’s just that the state in the past hasn’t maybe pursued it like they are now.”

The U.S. Geological Survey has never done a study of radiological materials in Long Island’s aquifers. A regional survey of North Atlantic coastal states released in 2015 said that radium can be found when naturally occurring uranium and thorium degrade.

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Naturally occurring radium concentrations increase as acidity decreases in water, said Stephen Terracciano, associate director of the USGS New York Water Science Center in Coram.

The Bethpage Water District closed down a well in 2013 because radium levels were above what the water supplier was seeing in its other facilities. Earlier this year, after the monitoring wells on the high school grounds detected radium, the district and elected officials pressed for more investigation as to the source.

Acidity levels are higher near Bethpage, so “that would lead you to believe [the radium] is coming from a Superfund site” and not naturally occurring, Carey said.