U.S. EPA has proposed an amendment to 40 CFR Parts 63, Subpart CC and Subpart UUU that requires all petroleum refineries to deploy passive time-integrated benzene samplers at the fenceline (where fenceline is equivalent to the facility property line) of their facility to alert them of fugitive emissions from leaks of Subpart CC and UUU process equipment. The proposed amendment also requires the operation of an on-site meteorological monitoring system in conjunction with the fenceline benzene monitoring. U.S. EPA proposed the use of 12 to 24 passive samplers placed at 15 to 30 degree intervals along the perimeter of each refinery, depending on the size and shape of the property. Ideally, for a small refinery (< 750 acres), samplers would be placed at 30 degree intervals for a total of 12 samplers. For a medium-sized refinery (750 to 1,500 acres) a total of 18 samplers would be deployed at 20 degree intervals, and for a large refinery (> 1,500 acres), samplers would be distributed at 15 degree intervals for a total of 24 samplers. An extra sampling location may be required when there is an emission sources located close to the fenceline/property line. A sampling event would consist of 14 days.