A METHOD FOR DETERMINING IN-USE EFFICIENCY OF STAGE-II VAPOR RECOVERY-SYSTEMS

A practical methodology has been developed to evaluate the in-use effi ciency of Stage II vapor recovery systems. While the theoretical effic iency of these vapor recovery systems may be measured in chamber studi es, their true effectiveness can only be assessed in the field under n ormal operating conditions. VOC concentrations during automobile refue ling were measured at a gasoline station with conventional pumps and a station equipped with a Stage II vapor recovery system. A dual VOC sa mpling train was developed in order to minimize measurement variabilit y 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, r elative to the conventional station, was between 81% and 93%. Although gasoline spills during refueling have been documented as greater at t ypical Stage II stations as compared to conventional stations, the pre sented results indicate the magnitude of these spills is insufficient to substantially undermine the overall efficacy of these vapor recover y systems.