Air emissions impact measurements at a perchloroethene remediation site
As part of an U.S. EPA time critical removal action, an air monitoring system was established to measure real-time impacts of perchloroethene (PCE) on the surrounding areas. The soils and groundwater beneath the site (located in West Fargo, North Dakota) were treated using in situ heating of soil and groundwater, with the produced vapors collected using conventional vapor extraction. In order to control the risks associated with air toxics emissions from the remedial activities, an air pathway analyses was conducted, and air monitoring and emissions mitigation were developed on a site specific basis. Because concentrations to be measured were expected to be low Pneumatic Focusing Gas Chromatography (PFGC) was used to allow direct air sample injection gas chromatography while increasing the sensitivity to levels found in sample concentrating techniques. Over three thousand determinations were made during the 1 year remediation, started in January 2005. In addition to real-time measurements of indoor levels of PCE (and other compounds) in the remedial process building and contiguous residential basement, the resulting controlled vapor extraction emission stack concentrations were modeled to ambient impact concentrations by incorporating real-time site meteorological measurements. These modeled results were used to determine impacts to downwind ambient locations over the course of the project. Real time data at these areas proved to be a great benefit for understanding the impacts from the remedial actions, and mitigation measures were implemented based on the monitoring data results.