Coal tar clean-up plans to be finalized
June 16, 2010
The Board of Selectmen expects to receive a letter from the Department of Environmental Services within the next month that will state their course of remedial action on the Lower Liberty Hill site.
After the letter is received, Dunn said the selectmen will discuss DES's preliminary plans proposed to tackle the coal-tar removal on Liberty Hill, a concern that dates back to 2004, and a history that dates back decades prior, when the area was first contaminated with industrial waste.
A presentation will be held and open to the public and their comments, and then a final decision will be made to tackle the potentially hazardous problems within the site.
The decision should be finalized and go into action within the year.
The DES has considered two Remedial Actions Alternatives, including 100 percent coal tar removal (RAA1) for about $16 million, which the selectmen favor, and 80 percent coal tar removal (RAA5a), which the DES has suggested as their course of action in prior months.
This 80 percent coal tar removal plan has been estimated to cost about $10.9 million and would encompass containing the remaining 20 percent of tar with a slurry wall and under an impermeable cap to prevent the infiltration of precipitation into the contained area. Tar impacted soil and saturated soil would be excavated below three feet, and limited ground water pumping would be installed. Off-site soil would be treated with thermal desorption to remove contaminants.
The 80 percent removal plans appear to be more cost-effective, although the selectmen, along with residents of Liberty Hill, have said they won't feel at ease until 100 percent of the contaminants are removed, even if it means spending more for the sake of the surrounding waters, and for the health of the community.
During prior studies, coal tar has been found in soil and groundwater adjacent to the site, including 69, 77, 83, and 37 Liberty Hill Road, (and was purchased by the National Grid).
Well water has been tested and is deemed acceptable, although groundwater and soil in the southern part of the site has tested positive for contaminants, a toxic by-product, which has become a primary concern over the years.
A small groundwater seep was also detected at the site adjacent to Jewett Brook, and was filled with gravel in 2008. The DES had requested that the National Grid further determine the initial impacts to this site, which appeared to be limited but still remain a potential concern.