Over the years that Grumman Aerospace Corp. operated a manufacturing and research facility in Bethpage, the defense contractor handled radium, tritium, polonium, uranium and other radioactive isotopes, according to a document filed with state environmental officials that was obtained by Newsday.

Included in a footnote of the same document — submitted to the state by Northrop Grumman, the current incarnation of the company — is mention of a 1996 incident in which a federal government employee working at one of the company’s buildings in Bethpage was implicated in an unsuccessful plot to poison local officials with radium.

Newsday articles from the time reported that the employee was found to have given radium to a UFO conspiracy-theorist who wanted to use it on Suffolk County officials and take over the local Republican Party.

State Department of Environmental Conservation officials, who have previously said there was no evidence of radioactive materials used at the site, say they are now seeking more information from Northrop Grumman.

“I haven’t believed or trusted a single thing that I’ve seen or heard from the company,” DEC Commissioner Basil Seggos said Thursday. “It’s my job to fact-check absolutely everything.”

Seggos joined DEC in 2015 and in early 2016 ordered the company to provide a detailed and comprehensive report about use of radioactive materials at the site after Bethpage Water District said it believed levels of radium in a well were exceeding drinking water standards.

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Northrop Grumman replied in October with a nine-page report, which is the document obtained by Newsday under the state Freedom of Information Law.

DEC officials said this week they notified Northrop Grumman that they want to see the documents the company had examined for the report.

And in a statement Thursday evening, the agency said it was “analyzing information regarding activities” at a building on the Grumman property “and is mobilizing to conduct additional sampling at the site.”

The Northrop Grumman report has not been released publicly, angering the Bethpage Water District.

“The state has a history of not being forthcoming with the districts,” said Rich Humann, president and CEO of H2M, a Melville engineering firm retained by several water suppliers, including the Bethpage Water District.

Humann said DEC has been more responsive lately but it should not rely on Northrop Grumman to do testing or analysis. “The state needs to find its independence and commit . . . time and money to do their own investigation. Stop leaving it up to the community to find things under the rug.”

The Northrop Grumman report, which covers1960-2015, said there was no evidence that material used on-site would be contributing to radium detections.

It lists more than three dozen radiological materials used in research and testing activities, and says records show radioactive materials were disposed of in appropriate off-site facilities.

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Also, luminescent dials and switches once installed in aircraft at Grumman were manufactured at a separate, off-site location, the report maintains.

In the attempted radium-poisoning episode, the report notes that no definitive source of the radium was ever established.

“In general, the use, handling and disposal of radiological materials at the site during the documented period were consistent with contemporaneous industry standards,” the report said.

It mentions use of radioactive materials, but not many specific activities or buildings.

“I can’t say for sure or not what we got from them was the complete picture,” Seggos said, adding later, “It is an awfully thin report.”

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Northrop Grumman did not respond to questions about the document.

Earlier this month, shallow groundwater monitoring wells at nearby Bethpage High School detected levels of radium above drinking water standards, prompting DEC to seek additional testing. The school is served by the Bethpage Water District, and no one on campus would have been exposed, state officials said.

Recent scans of ballfields and soils at the school did not detect elevated levels of radioactivity, but the wells have not been retested, Seggos said earlier this week.

The wells were installed by the district two years ago because the school is across the street from a property that was once part of the Grumman complex, which is undergoing an intense groundwater remediation program.

Concerned residents point out that radium levels above what is typical for the area have also been found at a water-district well about two miles south and another well in between.

“It’s just screaming for a real investigation,” said James P. Rigano a Melville environmental attorney who is serving as a spokesman for the residents. “What we have is completely inadequate.”

The release of the Northrop Grumman report is the latest chapter in a decadeslong story that began in the late 1930s and 1940s, when the Navy and Grumman set up manufacturing, research and testing facilities on a more than 600-acre plot in Bethpage.

The facility turned out Hellcat, Tigercat, Albatross and other planes that helped turn the tide during World War II and the Korean War. It was also home to the Apollo moon lander.

But that legacy came with contaminated soils and groundwater. Wells on Grumman property were tainted by the late 1940s, volatile organic chemicals had been found in water by the 1970s, and in 1983 the state added the site to its hazardous waste Superfund list. Several cleanup plans are in place, primarily focused on volatile organic chemicals.

Radium surfaced as a possible issue in 2013, when the Bethpage Water District shut down a drinking water well off Sophia Street where it detected elevated levels of the element.

At the time, a state DEC spokeswoman told Newsday in a statement: “We have no information that radioactive substances were ever used at the Grumman or Navy sites.”

But a confidential report compiled by contractors for Northrop Grumman in 2000 to assess environmental areas of concern and potential liabilities said there was a lab in one building at the site “in which various types of metals were tested with different types of radiation (alpha, beta, and gamma),” according to a document released by a DEC remediation official two years ago to a resident and given to Newsday.

That report also details the history of that structure — plant 26, the roughly 61,000-square-foot facility built in 1960 and expanded over the decades. It once served as company headquarters, but also had research labs and a Department of Defense “black room” that required security clearance to enter.

State officials said Grumman at one point had a radiological license from the state Department of Labor.

Norman J. Kleiman, director of master’s degree programs in radiological sciences and toxicology at Columbia University’s Mailman School of Public Health, reviewed Northrop Grumman’s report and said it was consistent with materials that would have been used during the era.

The state could take samples in plant 26 and use a Geiger counter to measure ionizing radiation. In addition to sampling water for radium, the DEC should also test for uranium and thorium, which can decay into radium, and radon, which is found in water and air and is a breakdown product of radium, he said.

“The simple and most direct path is to go test, go sample,” Kleiman said.

After the radium levels at the school were revealed, Sen. Chuck Schumer (D-N.Y.) sent letters to Northrop Grumman and the Navy demanding they make all relevant documents about use of radioactive materials public.

Northrop Grumman responded, saying that it shared Schumer’s concern for the Bethpage community and mentioned its report filed with the DEC.

“The investigation did not identify any releases of radioactive materials,” the June 15 response stated.

The Navy this week said it would not respond to questions about use of radioactive materials until it had answered Schumer’s letter.

Schumer reiterated his call for more information Thursday.

“Northrop Grumman’s response does not fully answer the question we all have: at any point in time, were any radioactive materials ever used, stored, or disposed of at this site?,” he said in a statement. “That is why I am asking again — directly — for Northrop Grumman to fully answer my question, and I am doubling down on my demand that the Navy answer the same question.”