Levels of a gasoline additive contaminating wells near Fallston have declined significantly since a treatment system was installed at an Exxon service station in the area, the Maryland Department of the Environment reported yesterday.
"These figures indicate that actions taken at the gas station in recent weeks are proving beneficial," said Jonas Jacobson, deputy secretary of the department.
State officials believe the station at Routes 152 and 165 is part of the problem, though other possible sources are being investigated.
Methyl tertiary butyl ether (MTBE) levels in groundwater beneath the gas station have fallen significantly since Exxon Mobil Corp. installed a vapor recovery system June 17, state officials said. Last month, when the wells were first tested, a reading of 26,000 parts per billion was recorded beneath the station's fuel tanks. Since the treatment began, readings have fallen to 97.3 parts per billion.
MTBE is added to gasoline to reduce air pollution. It helps fuel burn more cleanly but has proven a troublesome groundwater contaminant.
State officials have asked Exxon Mobil to perform an enhanced leak detection test at the gas station next week. The test -- which will take three to seven days to complete -- will check for previously unidentified leaks in the fuel system.
In recent weeks, 233 wells have been sampled, most testing below the state action level of 20 parts per billion. Seventy homes in Orchard Lakes are being tested this week.
Since the leak was discovered, residents have used bottled water for drinking and cooking, and some have had filtration systems installed at company expense.