NEWBURGH — As Silver Stream pours down a dam and rushes over rocks toward Moodna Creek and, eventually, the Hudson River, it carries the chemical that closed a drinking water supply and led to Stewart Air National Guard Base’s designation as a state Superfund site.

For months state officials have negotiated with the Department of Defense on a cleanup plan for perfluorooctane sulfonate, the toxic chemical whose discharge from Recreation Pond, a detention basin at the base, into Silver Stream shut down the City of Newburgh’s Washington Lake.

An investigation is to begin this spring at the base, but it will involve confirming the release of the chemical into the environment, something state investigators have already confirmed.

The state Department of Environmental Conservation and the environmental group Riverkeeper say the DoD could be moving faster to address the contamination’s impact, including stopping the continued discharge of tainted water into the stream.

Minimizing the environmental impact while a cleanup plan is crafted and implemented has been one of DEC’s ongoing demands, said Martin Brand, deputy commissioner for remediation and materials management for the DEC.

“The DoD and ANG continue to drag their feet and have refused to conduct a robust investigation that will quickly lead to remedial action, even though the evidence is clear that contamination in Recreation Pond and other areas is emanating from the base,” Brand said.

In May, Newburgh stopped drawing drinking water from Washington Lake because of high levels of PFOS. Researchers have linked the chemical to kidney and testicular cancers, high cholesterol and low infant birth weight. Newburgh stopped diverting water from Silver Stream into Washington Lake in June.

In August the state determined that the contamination stemmed from the use of aviation firefighting foams at Stewart and declared the base a Superfund site.

One water sample, taken from where the pond discharges into Silver Stream, showed 5,900 parts per trillion of PFOS, about 84 times the level at which the Environmental Protection Agency recommends action.

The military is preparing to submit to the DEC a work plan for a more in-depth probe to confirm the release of PFOS into the environment, Casarez said. Those results will be ready by this fall, she said.

Unclear is whether the plan will include interim measures to stop the flow of PFOS-tainted water.

“There is no sense in waiting for the results of this new investigation when you can identify an interim remedial measure and take action now that will have real environmental and public health benefit,” Brand said.

In October, amid concerns that the unused Washington Lake posed a flooding hazard, a contractor hired and paid for by the state began using a portable system to pull water from the lake, remove the PFOS and release it into Silver Stream.

The environmental group Riverkeeper has been demanding that DoD employ the same system for Recreation Pond.

“We want to apply that remedy as close to the source as possible, so that the water flowing off the base is not contaminating all the streams down from it,” said Dan Shapley, director of Riverkeeper’s water quality program. “They need to get on that now, rather than wait a year to gather the same information that’s essentially already been gathered.”