Infiltration and evaporation of small hydrocarbon spills at gas stations

Small gasoline spills frequently occur at gasoline dispensing stations. We have developed amathematical model to estimate both the amount of gasoline that infiltrates into the concreteunderneath the dispensing stations and the amount of gasoline that evaporates into the typicallyturbulent atmosphere. Our model shows that the fraction of infiltrated gasoline can exceed thefraction that evaporates from the sessile droplets. Infiltrated gasoline then evaporates and isslowly released to the atmosphere via slow diffusive transport in pores. Tentative experimentsshow that our theoretical approach captures observed experimental trends. Predictions based onindependently estimated model parameters roughly describe the experimental data, except forthe very slow vapor release at the end of Stage II evaporation. Our study suggests that, over thelifespan of a gas station, concrete pads underneath gas dispensing stations accumulate significanta mounts of gasoline,which could eventually break through into underlying soil and groundwater.Our model also shows that lifetimes of spilled gasoline droplets on concrete surfaces are on theorder of minutes or longer. Therefore contamination can be carried away by foot traffic orprecipitation runoff. Regulations and guidelines typically do not address subsurface and surfacecontaminations due to chronic small gasoline spills, even though these spills could result in nonnegligiblehuman exposure to toxic and carcinogenic gasoline compounds.