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Fuel drips at gas stations may add up to big problem, study says

Research indicates gasoline can seep through concrete, probably in vapor form, said Markus Hilpert, associate research professor at Johns Hopkins Bloomberg School of Public Health.

Little things can become a big deal, especially if they happen over and over again. A recently published study suggests that may be true of the many small spills that occur when motorists refuel their vehicles at service stations.

Maybe no more than a few drops of gasoline fall to the pavement during any one fill-up as a fuel nozzle is returned to the pump. But Markus Hilpert and Patrick N. Breysse, researchers with the Johns Hopkins Bloomberg School of Public Health, figure those drips could add up over the years to significant contamination of soil and groundwater at a busy service station near a residential area.


Hilpert and Breysse, faculty members in the Department of Environmental Health Sciences, developed a mathematical model to simulate what happens to the gasoline routinely dribbled out while refueling.

In their study, published online in the Journal of Contaminant Hydrology, they estimate that roughly 1,500 liters of gas are spilled at a typical gas station over a decade, where as many as 10,000 vehicles refuel in a month. At the newer mega-stations that have been built in recent years, the fuel loss — and impacts — could be even greater over time, they suggest.


"We need to take a closer look at this problem," said Hilpert, lead author of the study.

Over the years, there have been some headline-grabbing fuel leaks and spills, including the contamination of dozens of household wells in the Jacksonville community of northern Baltimore County by a 25,000-gallon leak under an ExxonMobil station there. Under pressure from government regulators and the threat of lawsuits, gas station owners have taken steps to prevent such leaks and spills.

But Hilpert and Breysse say these tiny spills also deserve scrutiny, even if they might seem too small to worry about individually. Gasoline that drips out of the nozzle during refueling can be washed off the concrete pad by rainfall, they note. What doesn't wash away or evaporate into the air can soak into the pavement around the pumps, and over time it may infiltrate down into the ground. Research indicates gasoline can seep through concrete, probably in vapor form, Hilpert said.

"Concrete is not a barrier — it's not impermeable," he said.

State officials haven't reviewed the study but say Maryland's regulations on gas stations are among the most stringent in the nation, stricter than federal requirements. Jay Apperson, spokesman for the Department of the Environment, said the state requires groundwater monitoring in certain high-risk areas that officials believe are likely to pick up contamination of the type the study projects.

"MDE is confident that the regulatory scheme is protecting water supplies," Apperson said.

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Kirk McCauley, government affairs director for the WMDA Service Station and Automotive Repair Association, notes that stations today are highly regulated, subject to reporting and testing requirements and inspections.

"The good news is that dispensing equipment and tank technology is evolving constantly," McCauley said, "and station owners go to great extremes to comply with environmental regulations while continuing to provide food and fuel to Maryland's motoring public."


"There is no hard evidence that groundwater is contaminated due to chronic spills," Hilpert acknowledged. Their study only modeled the impacts, he said, and did not make any field measurements.

But it, along with some other research, suggests the issue deserves a closer look, he said. A 2002 study in North Carolina, for instance, did find higher levels of gasoline components — including benzene, a carcinogen, and toluene, which is also toxic — in stormwater sampled near service stations or in groundwater discharged from a former leaking underground storage tank.

And spill-prevention technology is not fail-safe, Hilpert contended. He recalled how, during a recent fill-up of his own vehicle, the fuel pump's automatic shut-off device failed to work, and "gas just gushed out."

Hopkins researchers have approached state regulators about making a closer study of the issue at selected service stations, Apperson said. State officials are weighing the proposal.