A method for determining in-use efficiency of stage II vapor recovery systems

Abstract

A practical methodology has been developed to evaluate the in-use efficiency of Stage II vapor recovery systems. While the theoretical efficiency of these vapor recovery systems may be measured in chamber studies, their true effectiveness can only be assessed in the field under normal operating conditions. VOC concentrations during automobile refueling were measured at a gasoline station with conventional pumps and a station equipped with a Stage II vapor recovery system. A dual VOC sampling train was developed in order to minimize measurement variability caused by environmental conditions. The results showed a significant difference between VOC emissions during refueling at the Stage II and conventional gasoline stations investigated. The estimated efficiency per refueling of the vapor recovery system at the Stage II station, relative to the conventional station, was between 81% and 93%. Although gasoline spills during refueling have been documented as greater as typical Stage II stations as compared to conventional stations, the presented results indicate the magnitude of these spills is insufficient to substantially undermine the overall efficacy of these vapor recovery systems.