A study is being launched to investigate how to contain and clean up groundwater contamination emanating from former U.S. Navy and Northrop Grumman manufacturing sites in Bethpage, state officials announced Friday.

Department of Environmental Conservation Commissioner Basil Seggos, at a news conference at Farmingdale State College, said the engineering analysis will involve water testing, fieldwork and computer modeling. It also will look at how to reuse or dispose of treated water.

Contamination from the site has spread over decades and covers an area 2 miles wide and 3 miles long. It mostly consists of the solvent trichloroethylene, or TCE, which the U.S. Environmental Protection Agency lists as carcinogenic.

It is the largest such contamination in the state, and local officials have said drinking water supplies for 250,000 people are at risk.

“We need to stop the plume from reaching any other water districts,” Seggos said after he and state Health Commissioner Dr. Howard A. Zucker met for a roundtable discussion with local politicians and water suppliers.

Between the late 1930s and 1996, the Navy and what now is Northrop Grumman occupied more than 600 acres in Bethpage for manufacturing, testing and researching aircraft and equipment to serve NASA’s space exploration efforts. Contamination was discovered in the 1940s.

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The site was put on the state Superfund list in 1983, and there are a number of cleanup plans in place to address both shallow and deep plumes, as well as hot spots of contamination. Wells as far south as Levittown are affected.

Local officials have said cleaning up the toxic chemicals has taken far too long.

Superintendents from the Bethpage and Massapequa water districts welcomed the fresh look. “The DEC is being very aggressive, so that’s good,” Bethpage Water District Superintendent Mike Boufis said.

Long Island and its nearly 3 million residents rely on an complex series of underground aquifers as the sole source of drinking water. Contaminated sites have come under increased scrutiny in the past year.

Gov. Andrew M. Cuomo, in a statement to Newsday, said he directed state agencies to aggressively move toward finding a way to contain the plumes.

“We must do everything in our power to address the contamination of the Grumman plume and hold the polluters accountable for their actions,” Cuomo said.

In August, the DEC released a report by engineering firm HDR Inc. that said fully containing and removing the contamination could cost between $268 million and $587 million and would require treatment for up to 100 years. That study cost $150,000 and was required by 2014 legislation filed by Sen. Kemp Hannon (R-Garden City) and then-Assem. Joseph Saladino, who now is Oyster Bay Town supervisor.

HDR will do the new study, using state Superfund money. The firm will take a deeper look at the plumes, including what to do with discharge and whether removing water will cause saltwater intrusion and other factors, said Martin Brand, DEC’s remediation and materials management deputy commissioner.

“What we want to come out of this is a plan of action,” Brand said.

The cost of the analysis is not yet known. Results should be released for public comment before the end of the year, Brand said.

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At the roundtable, officials also discussed 1,4-dioxane, a probable carcinogen that was found throughout Long Island’s water supply in trace amounts as part of an national survey mandated by the EPA.

EPA has not set a drinking water standard, and Cuomo and others last week urged the agency to do so. Zucker reiterated that call and said the state would take action to set its own specific regulation if the EPA did not act within three months.

“It’s just encouraging to see all levels of government come together to plan to protect our drinking water,” said Adrienne Esposito, executive director of the Citizens Campaign for the Environment, a not-for-profit in Farmingdale.