Encouraging discussions after a June 7 Medfield Board of Selectmen meeting have turned to a more critical analysis over restoration plans of the former Medfield State Hospital site.

The State Hospital Environmental Review Committee (SHERC) met Wednesday night and discussed the Massachusetts Division of Capital Asset Management's (DCAM) proposal to move forward with the clean up of oil and other waste on the site.

Although town officials were happy with the progress of DCAM to eventually clean up the 2.2 acre construction and demolition (C&D) land site — more than about the size of two soccer fields — behind the Medfield State Hospital and in the Charles River, committee members now question the report they received by the state agency.

"It may not be as thorough … as it could be," said John Thompson, chair of SHERC.

The 100-plus-year-old hospital remains home to numerous facilities that were completely shut down in 2003, including a power plant area, greenhouse, and laundry buildings. Attention now is focused on how the area can be cleaned of any environmental impacts and be safe for public use.

Debris in the form of concrete, brick, asphalt, metal, glass, coal fragments, ash and other materials exists on the 2.2 acre C&D site and lies along the southern bank of the Charles River, according to documents. Dumping of debris over time and the general position of the river eroded the bank to a steep slope. DCAM has developed plans to remove the debris and stabilize the riverbank using layered material, giving it a stable slope.

Thompson said analyses of the river itself determined heavy oil underground, covering an area of "about a large living room," or 800 square feet — presumably left behind by the old power plant — exists near the site and is pushing closer to an aquifer. This impact, and the oil's possible "bubbling" up toward the river's surface, potentially makes the water unsafe for human consumption and recreation.

DCAM has developed plans to remedy the issue by using an "impermeable amendment material," such as using a product called AquaBlok. According to documents, a combination of product, sand and other materials would contain the oil at the site.

Rather than containing the oil, "why doesn't DCAM physically remove it?" Thompson asks, questioning why the agency is pushing to work on the river bank first, rather than moving the oil and other volatile organic compounds, or VOCs.

"Common sense is saying the simplest answer is the best," he said. "We're fighting a battle for the public."

Concern that oil continues to leak into the river from the 2.2 acre site adds insult to injury, but there is a sense of confusion between SHERC and DCAM regarding how the oil — contamination under the river and contamination under the land site — is related to each other.

"It's not clear to me that the two are separate," said Bill Massaro, a Medfield resident who owns property next to the hospital. "Why would you go ahead with cleaning up the river when you still have the source possibly from the C&D area [remaining]?"

Town Administrator Michael Sullivan said it was mentioned at a previous meeting that an expansive dig up of the river probably would be opposed by the Army Corp of Engineers and the Charles River Watershed Association because it would do more damage than what's already occurring.

DCAM will have the opportunity to respond to SHERC's comments on July 6 and there will be a public meeting slated for July 14.

"At the end of the day, it's a place that the public can use and enjoy - unrestricted," Thompson said.