NINE YEARS LATER: THE PERSISTENCE OF MTBE IN GROUNDWATER IN WINDHAM, MAINE

The gasoline additive MtBE has become one of the most commonly detected contaminants in groundwater nationwide and has been a pollutant of concern in the state of Maine. In 1998 the Maine Department of Human Services conducted a statewide survey of groundwater wells and MtBE was detected in 16% of private and public wells tested. These findings resulted in the state regulatory agencies deciding to opt out of the reformulated gasoline (RFG) program in 1999. Subsequently, the average concentration of MtBE in gasoline dropped from ~15% to 2% by volume to protect water resources. In order to test the effect of this policy on water quality, groundwater samples were analyzed over a period of nine years (1998-2006) from 19 wells distributed across a sand and gravel aquifer in Windham, Maine. MtBE continues to occur in detectable concentrations in 30% of the study wells despite Maine's decision to opt out of the RFG program in 1999. Detectable MtBE concentrations in 2006 ranged from 0.4 to 3.3 µg/L; well below safe drinking water limits. Although recently detected concentrations are lower than in previous years for several wells, some trends are ambiguous (concentrations rise and fall between sampling dates). This study confirms MtBE's temporal and spatial persistence in the environment. Reducing MtBE concentrations in gasoline may not be sufficient to eliminate its occurrence from groundwater.