At gas stations, certain things are just unavoidable—the acrid smell in the air, the unclean bathrooms, the Slim Jims on display by the cash register. And, of course, the stains on the concrete from where people have spilled gasoline. Often, in the act of pumping gas from the underground storage tanks beneath a gas station to a car, a few dribbling drops will sneak out and land on the ground.

But a new study published in the Journal of Contaminant Hydrology suggests that those little drips pile up, and could leach out into the environment around the gas station, polluting air, water, and soil.

Previous research has found a correlation between urbanization and higher amounts of gasoline in groundwater, but has attributed the link to leaks from underground storage tanks. Markus Hilpert, lead author of the new study and senior scientist at the Johns Hopkins University School of Public Health, thinks that the correlation could also be explained by the cumulative effect of these small surface-level spills.

Your typical gas station is built on a concrete pad that is intended to keep gasoline from polluting the ground below. That pad is usually about six to eight inches thick, Hilpert says.

“Concrete is not really impermeable,” he says. “It’s almost impermeable—if you look at water puddles on concrete after it rains, they stay around for a very long time, but a small amount of the water gets through.”