API PUBL 4498-1989

Methods have been devised and demonstrated to characterize liquid gasoline releases to the environment during vehicle refueling at service stations. These methods have been employed in a limited study of the release characteristics of contemporary refueling equipment at well-maintained Stage II facilities in the District of Columbia, and at comparable conventional facilities in the Baltimore metropolitan area. Within the limitations of the study, results show that 33 percent and 37 percent of all refueling events at stage II and conventional facilities, respectively, are completed without liquid release. When release occurs, it most commonly consists of a very small amount (= 0.1 grams) which almost entirely can be described as drips. Larger releases (> 0.1 grams), when they occur, are more frequent at Stage II facilities. Moreover, when release is expressed in terms of the amount of fuel dispensed, the resultant emission factor is significantly larger at Stage II facilities. The statistical significance of this conclusion depends upon the larger average amount of fuel dispensed per refueling event at conventional facilities. This, in turn, is due at least partially to the characteristics of the dispensing equipment which results in the practice of topping-off at conventional facilities. In any case, topping-off has a statistically significant impact on increasing the volume of fuel released from both Stage II and conventional dispensing systems.