If you’ve ever pumped your own gas, you probably know that no matter how careful you are, it’s nearly impossible not to drip a drop or two of gasoline onto the ground in the process. But while a couple of small drops might seem harmless, researchers from the Department of Environmental Health Sciences at the Bloomberg School of Public Health have found that those little drips can add up to a major public health hazard over time.
While most studies of the environmental impact of gas stations have focused on the problems associated with large-scale leaks from underground tanks, few have examined the impact of small-scale, routine spillage of the kind caused by consumers every day.
"Gas station owners have worked very hard to prevent gasoline from leaking out of underground storage tanks,” says study leader Markus Hilpert, PhD, a senior scientist in the Department of Environmental Health Sciences in the Johns Hopkins Bloomberg School of Public Health. “But our research shows we should also be paying attention to the small spills that routinely occur when you refill your vehicle's tank.”
Using a combination of mathematical modeling and experimental techniques, Hilpert and his co-investigator Patrick N. Breysse, PhD, found that the concrete pads underneath the pumps at gas stations can accumulate significant amounts of gasoline. And rather than staying within the porous concrete pads, the gasoline can eventually penetrate the concrete and leech into the underlying soil and eventually find its way into the groundwater, leading to significant risks to public health.
“Even the smallest gasoline spills can have a lasting impact.”
Markus Hilpert, PhD, senior scientist in the Department of Environmental Health Sciences
“Even if only a small percentage reaches the ground, this could be problematic because gasoline contains harmful chemicals including benzene, a known human carcinogen,” Hilpert says.
Hilpert and Breysse were able to estimate the amount of gasoline that could potentially reach the ground by modeling the behavior of gasoline droplets that had been spilled on concrete. Contrary to the conventional wisdom that says that those small droplets instantly evaporate, their model found that if the droplets remain on the surface for a few minutes or longer, a significant amount penetrates into the porous concrete without a trace.
“When gasoline spills onto concrete, the droplet will eventually disappear from the surface. If no stain is left behind, there has been a belief that no gasoline infiltrated the pavement, and all of it evaporated,” Hilpert says. “According to our laboratory-based research and supported by our mathematical model, this assumption is incorrect. Our experiments suggest that even the smallest gasoline spills can have a lasting impact.”
In their study published on September 19, 2014 in the Journal of Contaminant Hydrology, Halpert and Breysse stress the urgency of further study into the topic of soil and groundwater contamination from routine spills, especially because of the trend towards larger and larger gas stations – often built in or near residential areas—with more and more pumps that offer more opportunities for chronic spillage.
“Chronic gasoline spills could well become significant public health issues since the gas station industry is currently trending away from small-scale service stations that typically dispense around 100,000 gallons per month to high-volume retailers that dispense more than 10 times this amount, " warns Breysse.
“In a perfect world, it would be ideal to avoid chronic spills,” adds Hilpert. “However, if these spills do occur, it is also important to prevent rainwater from flowing over the concrete pads underneath the pumps. Otherwise, storm runoff gets contaminated with benzene and other harmful chemicals and can infiltrate into adjacent soil patches or form storm water that may end up in natural bodies of water.”
More information can be found at “Infiltration and Evaporation of Small Hydrocarbon Spills at Gas Stations”.