The Carlisle Mosquito Online

Friday, June 2, 2000


Water quality committee recaps steps taken to address MTBE

On May 23, the selectmen had the opportunity to hear Mike Holland of the water quality subcommittee present a history of the problem with methyl tertiary butyl ether (MTBE) in the town center water supply.

The subcommittee was formed in 1996 by the board of health in response to a lack of action by the state Department of Environmental Protection (DEP) on water concerns related to leakage from gas tanks at the former Daisy's Gas Station. In 1997, on February 1, February 22 and April 5, the subcommittee sampled wells in the center and found three with MTBE levels over the allowable limit of 70 parts per billion. The wells were located at 11 East Street, 46 Lowell Street, and 13-15 Lowell Street. About ten more wells were found to have MTBE at lower levels. The results were sent to homeowners and to the DEP. In mid-1997, 21E,Inc., the Daisys' licensed site professional, was required to test wells in the center. The water quality subcommittee retested wells with the lower MTBE levels in February 1998. From June 1997 through the fall 1999, 21E, Inc. has tested six wells, three with MTBE above the allowable limit and three others below, at intervals prescribed by the DEP. In December 1998, the gas tanks were removed and a final test confirmed that their removal had not negatively impacted the situation.

Recently, the DEP announced that they will oversee clean-up of the site, due to dissatisfaction with the way it's been managed by the Daisy family. Holland pointed out that he believes the situation regarding MTBE has stabilized, with no great fluctuations or changes in some time. Now that the tanks are gone, the only source of MTBE is the residual in the soil. The subcommittee will analyze the flow patterns of water in the center to get a better picture of what's going on. Holland encouraged anyone with a concern to participate in the testing of wells to take place on June 11.

Water quality member Tony Mariano then offered information on how a clean-up might proceed. Claiming that "MTBE is unique," Mariano explained it does not adhere to soil and is very difficult to remove from water. In addition, it doesn't naturally degrade, so "it's not going to go away anytime soon." The good news is that it is very unlikely to increase, as the source has been removed, and wells of concern can be fitted with carbon filters which are effective in removing MTBE. Mariano pointed out the levels in Carlisle "are not a threat to health, but a nuisance," explaining that the 70 ppb limitation was adopted because the smell and taste is detectable at that level. "Experiments on animals have shown toxicity only at levels hundreds of times the 70 ppb level." Mariano then summarized, "The DEP is involved, it won't get worse, but it won't go away soon."

Although several center residents were present, they were quiet when question time came. Pointing out that New York recently lowered their acceptable level for MTBE to 10 ppb, selectman John Ballantine questioned whether the DEP resisted lowering its 70 ppb guideline to avoid becoming involved in even more sites. Holland scoffed at the 10 ppb guideline, pointing out that you could get greater exposure filling your car.

Mariano then explained that the DEP is currently holding a "bid walk" at which not only price, but the extraction method, for the Carlisle site will be proposed. He suggested the method might involve digging out the contaminated soil to the water level or using vapor extraction to reduce levels in the water table.

In response to another question, Mariano promised to publish the result.

2000 The Carlisle Mosquito