STI is working with multiple gas refineries to perform fenceline monitoring of refinery emissions to address Federal regulations. The fenceline monitoring portion of the regulation is intended to ensure that hazardous air pollutant emissions from refineries are controlled, with specific control actions required if fenceline concentrations exceed a specified level. Measurements include 14-day benzene passive samples collected every 2,000 feet around refinery fencelines. STI performed pilot fenceline sampling at multiple refineries for up to a year to better understand benzene concentrations in advance of the official sampling.