As many as 17 potential fuel vapor leaks have been found at an Exxon service station that state officials believe is a prime suspect in contaminating at least 127 Fallston-area wells with a noxious gasoline additive.
Spokespeople for the Maryland Department of the Environment and ExxonMobil Corp. sparred yesterday over the significance of the leaks detected by a contractor for the oil company.
MDE spokesman Jeffrey Welsh said preliminary testing late last week of the Upper Crossroads Exxon at Routes 152 and 165 in Harford County identified leaks in the station's gasoline storage tanks, piping and equipment.
Betsy Eaton, ExxonMobil's spokeswoman, characterized the leaks as minor ones that could not have contaminated the groundwater with methyl tertiary butyl ether, or MTBE.
But Welsh said state regulators believe it's possible that one or more of those leaks may have contributed to the widespread groundwater contamination
MTBE is added to gasoline to help it burn more cleanly, but it dissolves easily in water and, through leaking fuel tanks, has contaminated hundreds of wells in Maryland. Its health effects in drinking water are largely unknown, but it can be tasted or smelled at very low levels, making the water unpalatable.
MDE officials have said for weeks that they suspect the station, where MTBE has been detected in well water off and on since 1991, is one of the sources -- if not the main source -- of the MTBE that has tainted residential and commercial wells within a half-mile of the station.
"Until the testing is done, we won't know if this is the main source of the problem," said Welsh. Later, he added, "We believe that they are part of the problem."
The leaks, which were detected by pumping helium into the station's fuel storage system, were repaired before even more sensitive testing began Sunday. That's when Praxair Services Inc. of Tucson, Ariz., injected a tracer chemical into the station's fuel system and began monitoring for seepage into the ground around the tanks and piping.
Exxon's Eaton said the leaks detected with helium are in areas of the fuel system where any gasoline or vapor seepage "are least likely to have gotten into the soil." Among the leaks found with helium were cracks, pinholes or loose gaskets in the equipment that siphons gasoline from the underground storage tanks to gas pumps used by motorists. Those devices sit inside spill basins, which may not capture vapor leaks.
"They have no idea the size of these leaks, these helium leaks," Eaton said of the testing contractor. "It's too early for them to come to any kind of conclusions." She also noted that the fuel tanks were pressurized during the helium test, which may have forced leaks where none had existed before.
The chemical tracer testing, far more sensitive than the standard leak tests required by Maryland environmental regulators, has yet to detect any vapor leaks into the ground, Eaton said, but testing continues. She said it was premature to draw conclusions about the station's culpability for the groundwater contamination until the contractor finishes its work and submits a written report.
Meanwhile, the oil company's spokeswoman acknowledged that some of the water filtration systems supplied to homeowners with tainted wells were defective.
The defects, in nine of 80 carbon filtration systems installed at ExxonMobil's expense, were caught during a routine series of tests conducted before residents were cleared to resume using their water, said Eaton. The oil company fired the contractor that installed the defective systems after learning of the problem Monday, she said.
None of the tests showed levels of MTBE higher than the state's threshold for drinking water of 20 parts per billion, she said.
"Should this have happened? No," Eaton said. "Will we fix it? Absolutely."
Health officials have tried to allay fears about MTBE, saying the levels found in Fallston wells are probably not high enough to do any harm.