New environmental testing of property on Arsenal Street in Watertown, Massachusetts once used by the Department of Defense to store nuclear waste indicates the land is more contaminated with PCBs than previously believed.

Consultants for the US Army Corps of Engineers, which is overseeing the cleanup of the site across Greenough Boulevard from the Charles River, told town officials last week that tests done in July and August found higher levels of polychlorinated biphenyls than prior tests had shown.

"That surprised us," said David E. Heislein, project manager for MACTEC, a consulting firm.

Heislein said the contamination appears to be confined largely to the soil surface. Officials said that may make it easier to eventually remove the polluted dirt and convert the site to parkland.

But the need for further testing will yet again delay plans to clean up the nearly 12-acre parcel, known as the General Services Administration property, and transfer it to the state Department of Conservation and Recreation. The Corps had initially set a September 2006 deadline for the handover.

The MACTEC study was commissioned after an evaluation completed in 2007 by another consultant hired by the state recreation department found levels of contaminants in different locations and in higher concentrations than the Corps had documented. Those results put an abrupt halt to efforts to transfer the property last fall.

The 2007 study found PCB levels ranging from 2 to 43 parts per million. The latest testing by MACTEC found levels ranging from .06 to 361 parts per million, said Ellen Iorio, project manager for the Corps.

To meet state safety standards for passive recreational use, the soil can contain PCB levels at or below 3 parts per million, said Joanne Dearden of the state Department of Environmental Protection. PCBs pose a public health risk because they are a known carcinogen, she said.

Once federal funding is secured, MACTEC intends to return to the site next spring for more tests to better outline the area of PCB contamination and to make sure it has not entered wetlands on the property. Though there were some slight variations from the state's results in the amount of heavy metals found in the soil, the firm doesn't believe it requires more testing, said Heislein.

Determining the extent of the property's contamination has been a slow-moving process that began in 1989.

From the 1920s to the late 1960s, the property was used by the US Army to store materials and burn depleted uranium in connection with the once-active Watertown Arsenal. The General Services Administration took over the site in 1968, using it for storage and leasing part of the property to the State Police for a firing range.

The US Nuclear Regulatory Commission deemed the property safe from radioactive refuse in 2003.

The meeting with local officials did not address a major local concern, the presence of four vacant buildings on the property that officials would like to see demolished.

Marylouise McDermott, chairwoman of the Conservation Commission, insisted the 1920s-era lease between the Metropolitan District Commission and the federal government stipulated that the property be returned to the state in its original condition, without the buildings that were added later. "I'm willing to pursue that," she said.

Testing and removing four abandoned buildings on the property, which contain lead paint and asbestos, will not be part of the Corps cleanup, Iorio said.

The Department of Defense program under which the current work is being conducted precludes work to any part of the site except the land, she said.

"I think we all share this sense that this could go on forever," said Jonathan Hecht, a member of the Town Council.

Iorio conceded the project has moved "at a snail's pace" and blamed budget shortfalls and government bureaucracy for the piecemeal progress.

But Councilor Susan Falkoff, who has spent nearly two decades working on Arsenal-related cleanups in town, said she's not worried.

"It's more important that it be cleaned thoroughly than quickly."