State officials told a group of Hampstead area residents last night that they are still unsure how their wells became contaminated by a toxic gasoline additive.
Herbert Meade, chief of oil control for the Maryland Department of the Environment, told about 40 people at the Hampstead Town Hall that officials have investigated four possible sources for the methyl tertiary butyl ether, or MTBE, in their wells.
Investigators have checked a Shell Jiffy Mart service station in town and three residences, including one where they discovered a leaking underground gas tank. "None of these have been proven or disproven," Meade said.
MTBE has been detected in the wells of three dozen homes, and 10 had concentrations above the state's "action level."
MTBE is added to gasoline to make it burn more cleanly and to reduce air pollution. The addition of an oxygenating chemical such as MTBE or ethanol has been required by the Environmental Protection Agency since the early 1990s in metropolitan areas like Baltimore that have smog in the summer.
The chemical has shown up in wells after leaking out of underground fuel storage tanks at service stations and other businesses. MDE officials say it has tainted more than 600 wells statewide, primarily in Cecil, Harford, Carroll, Anne Arundel and Baltimore counties.
Laboratory tests have found that MTBE can cause cancer in rats at high doses, but its health effects when consumed at low levels in drinking water are unknown.
The state advises residents to filter their water or to drink bottled water when MTBE reaches 20 parts per billion or greater - the point at which some people can smell or taste the additive in their water.
Meade assured residents the levels being detected in their wells were too low to harm their health, and it was undetectable from the tap in homes with filtration systems.
The state has supplied filtration systems to eight of the homes, and is installing another one next week. A 10th is being supplied by a landlord.
State officials have said they will maintain the $3,000 filtration systems at public expense until the source of the contamination is pinpointed.
Not all residents were reassured by Meade's comments.
"I have a 4-month-old and a 3-year-old in the house," said Christopher Adamcik. "If there's something potentially bad, I want it out of there completely."
Hampstead officials offered to provide municipal water to the affected neighborhood, which is just east of the town limits, if those residents petition to be annexed.
"The only way the town can provide water is through annexation," said Town Manager Ken Decker.
MTBE was discovered in the Hillcrest Avenue area east of Hampstead in September 2003, after a tenant in an apartment building complained of a gasoline odor in the water.
Sampling of the wells detected MTBE at 40 to 290 parts per billion.
Prompted largely by an outcry over MTBE contamination in the Fallston area of Harford County, where many wells have shown traces of the chemical, MDE proposed emergency regulations aimed at curtailing leaks from underground storage tanks. The rules, which took effect yesterday, require new tanks to be fitted with double-walled piping and automatic leak sensors. Tank owners also are required to monitor their wells and the groundwater around their tanks for contamination.
Some service station owners have complained that the cost of complying with the rules could drive them out of business, while some Fallston area residents said that the only way to prevent more contamination would be to ban MTBE's use in gasoline, as some other states have.