The Carlisle Mosquito Online

Friday, July 14, 2000

News

Town's hazardous waste sites are reexamined

At the selectmen's meeting on June 27, Chris Mariano of ENSR provided an update on the status of the department of public works' hazardous waste site, where a diesel tank was removed in September 1998, and 300 tons of soil were subsequently taken out. Last year, ENSR suggested microbe injections to deal with the residual pollution in groundwater which was showing petroleum compounds, as high as 2,400 parts per billion (ppb). The microbe injections began in October 1999 and have continued monthly. Recent testing indicates the injections have been successful, lowering the levels of petroleum compounds to 130 ppb. The injection program, which cost $45,000, will continue throughout August. The microbes are natural organisms that die off once their food source, the petroleum compounds, is gone.

Impressed by these results, selectman Vivian Chaput queried whether the same method could be applied to the problem with town center wells. Mariano indicated this would not be a good application, as the problem there is too widespread. Keeping microbe levels sufficiently high would be expensive and complicated, he explained. Also, microbes are less effective in treating methyl tertiary butyl ether (MTBE) than they are in breaking down other petroleum compounds.

Talk then turned to the police station site. "Recent tests have shown no MTBE, and benzene and naphthalene at very low levels," reported Mariano. He recommended classifying the site as a "Class C" hazardous waste site; one where natural attenuation rather than active removal is the best solution. The site would continue to be monitored and reevaluated at a minimum of every five years. A pump installed to speed the dispersion of pollutants has not been working recently, but appears not to have been doing much good anyway.

Selectmen chair Michael Fitzgerald was concerned with the public perception. "I'm not convinced that spending $1,000 [to fix the pump] is inappropriate if it shows our continued commitment to the site." Selectman Doug Stevenson wondered if closing out a site which still showed some levels over the standard might set a bad precedent.

It was decided to wait for a recommendation from the water quality subcommittee before acting.


2000 The Carlisle Mosquito