Gas stations chronically release gasoline vapor to the environment that contains the carcinogen benzene. However, there is no method for estimating setbacks for a gas station depending on an acceptable excess cancer risk due to the benzene emissions, sales volume, benzene content of the emissions, and inhalation dose, without performing an air dispersion simulation for each scenario.
We developed a new modeling framework, in which only one air dispersion simulation is performed for a reference gas station. Then, a new scaling law is used to estimate cancer risks and setbacks for different gas station characteristics and exposure scenarios.
Our new scaling law allows estimating cancer risk vs. distance as a function of an acceptable excess cancer risk, total benzene emission rate, and frequency of exposure. Setbacks can also be determined from this scaling law or graphically from a design chart. Calculated setbacks differ only slightly from those determined from air dispersion simulations. Different emission control technologies substantially affect calculated setbacks.
We developed a framework that allows policy makers to examine easily how setbacks depend on regulatable measures such as emission control and acceptable cancer risk as well as on exposure characteristics. The framework also allows incorporating a safety factor to account for increased emissions. While this study was conducted in the context of US gas stations, our framework can be applied world-wide.