Dresden Board Hears TCE Update
Officials: Toxic Plume In Ground Is Trapped
Hanover — The primary concern Dresden School Board members raised Monday night about vapor from a carcinogenic solvent detected in the soil beneath the Richmond Middle School property is whether the plume is stationary or still on the move.
The presence of the vapor, the result of decades-old chemical spills at the military research laboratory across the street, was confirmed this summer.
“Right now we do not know how long those vapors have been there,” School Board member Anne Day said. “They could have been there for decades, or they could be because of a recent migration.”
Last week, school administrators learned that there are no detectable levels of trichloroethylene inside the school, but TCE vapor was found below the ground on the middle school property at depths of 10, 25, 50 and 75 feet. Officials with the Army Corps of Engineers have assured school administrators that the soil contamination does not pose a health threat.
Darrell Moore, the Army Corps of Engineers’ project manager for the cleanup at the Cold Regions Research and Engineering Lab on Route 10, was at last night’s meeting, along with Larry Cain, a risk assessor for the Army Corps of Engineers, to answer the School Board’s questions.
Day went on to ask Moore if additional soil borings would confirm that the vapor is moving.
Moore used the word “static” to describe the plume and said he doesn’t think the vapor is still migrating. Moore said last night that additional boring samples might be taken from the middle school property to help identify the edges of the plume and determine how far the TCE has traveled.
Cain stressed to board members that the air inside their school is clean.
“The important thing to remember is that although we are detecting it at the sub surface, it’s not getting into the school,” Cain said. “The air quality is actually remarkably good. Usually you see fuel vapors, but this school doesn’t even have that. There are very low levels of urban chemicals.”
Even so, officials said last week that the air at the middle school will be tested quarterly for TCE during the upcoming year to confirm that the building is safe.
Trichloroethylene was used at CRREL as a liquid solvent, and there were two significant spills in 1970. In March, the laboratory’s neighbors — Richmond Middle School, residents of housing owned by Dartmouth College and two nearby businesses — were informed that the Army Corps of Engineers was concerned that soil vapor had migrated off the Army lab’s campus. Army officials worried that the carcinogenic vapor could be entering buildings through cracks in foundations, which has occurred at CRREL.
However, the latest round of testing, which occurred earlier this month, showed that TCE isn’t in the air inside the middle school, but it is beneath the ground. Further testing is planned for other buildings in the area.
Attendance at Monday night’s meeting was sparse, with only 10 people in the audience, most of them military and school officials.
Jim Miles Blencowe, the one community member in the audience, said he was satisfied with the conversation and has no major concerns about the contamination.
“I just wanted to be informed,” said Miles Blencowe, who has a daughter entering the seventh grade at the middle school.
Miles Blencowe lives on Dresden Road, which runs next to the middle school, and he said the soil borings that showed a presence of TCE underneath the school property were not an immediate concern.
“It’s quite far down and as it rises it becomes diluted,” Miles Blencowe said after the meeting. “I think it’s reassuring that they’ll continue to test. It’ll be long-term.”
Moore said last week that the Army is planning a pilot program on the CRREL site to remove the vapor from the ground. The extraction method would be similar to a vacuum, trapping the air so it could be treated. That pilot program will be in place by the end of the year, and if it works, it could be used to try to extract the contaminated soil vapor at the middle school.
Other extraction methods have been attempted in the past, but those methods were done at a depth of 35 feet or less, Moore said Monday night. The top 50 feet of soil is made up of very fine sands and silt and is very tight, however, and those prior extraction attempts were unsuccessful. This time, the pilot extraction method will be focused at depths of 50 to 75 feet, and Moore said he’s hopeful that it will be more effective.
Across the street at CRREL, the Army has installed a sub-slab depressurization system, but Bert Davis, the director of the Army lab, said that system isn’t working. Depressurization systems are designed to release harmful vapor beneath a building into the ambient air to prevent it from entering and becoming trapped inside a building.
The pilot depressurization system at the Army lab wasn’t as effective as planned, Davis said, because the soil directly underneath the slab was “too tight.”
Instead, workers at the Army lab have begun to excavate soil and replace it with gravel that would allow the vapor to dissipate, Moore said.
A plastic seal will be placed under the slab that will act as a vacuum to pull the vapor away from the building.
A letter sent out to Richmond Middle School parents last week said administrators are “exploring the merits” of installing sub-slab depressurization systems at the middle school if the indoor air does become contaminated.
However, Moore said last week that the school does not currently need such a system, and if the system were installed, it would have to be funded through the school district’s budget.
“I would never get approval to put in a sub-slab depressurization system with tax dollars with that low of levels,” Moore said in an interview last week.
Sarah Brubeck can be reached at firstname.lastname@example.org or 603-727-3223.