7-Eleven Inc. is responsible for the leak of a gasoline additive that threatened Aberdeen's water supply, according to the Maryland Department of the Environment.
The source of methyl tertiary butyl ether, or MTBE, discovered in Aberdeen's wells two years ago was the 7-Eleven store on South Philadelphia Road, just across the highway from the city's well field, state officials said.
The state's investigation found a crushed vent line in the gas station's underground tanks. Tanks are vented to allow fumes to escape into the air, where they dissipate. The damaged line "dead-ended into the ground," said Chuck Gates, MDE spokesman.
The MTBE migrated under Philadelphia Road and contaminated city wells, officials said.
The city shut down three wells in August 2004 and created a system to aerate its water. It has been pumping 500 gallons a minute from one of its largest wells into the atmosphere since March. The MTBE in the well water evaporates in the mist sprayed into the air, officials said.
"We are basically sucking MTBE out of the ground," said city manager Douglas R. Miller. "It is a costly operation that is depleting our water resources. But it has worked, and we will probably continue it for the rest of the year."
Recent tests show how well the city's aeration system is working, officials said.
Contamination levels at a containment pond at the well field are negligible, Miller said. The city will seek compensation for its water and cleanup costs, said Mayor S. Fred Simmons, but the city has no clear estimate of the costs yet.
"We are looking for actual costs, not punitive ones," Simmons said. "The plume from the station came across Route 40 and damaged our wells. The company better offer our costs up, or we will sue. We have done the remediation job for them, and there is no more leakage."
The town can use the state as a witness in any potential lawsuit, Gates said.
Cynthia Baker, spokeswoman for 7-Eleven Inc., headquartered in Dallas, said the company is unaware of the recent communication between the city and MDE.
"We have worked closely with the city on this issue and hope to continue that working relationship into the future," Baker said.
Aberdeen's Department of Public Works supplies 1.7 million gallons a day to about 14,000 people from several sources, including the wells.
In April 2004, the city reported to the MDE that one of its wells was pumping water with MTBE levels of 60 to 80 parts per billion. The state investigates MTBE contamination above 20 ppb and advises private homeowners to filter their water or use bottled water when it exceeds that level.
MTBE, a gasoline additive that spreads readily through groundwater, has caused cancer in laboratory animals.
The highest level of MTBE - 110,000 parts per billion - was detected beneath the gas station's underground fuel tanks two years ago. No gas leaked from the station's double-walled tanks, officials said.
The company has since replaced the line and cleaned the site. Most recent MTBE levels at the station were 6,600 ppb. Remediation is continuing, officials said.