2009 Issue

26 A LONGWITH ACTIVE TREATMENT OF groundwa- ter in many areas on and around the base, Hill AFB engineers manage an indoor air sampling program focused on monitoring and mitigating human exposure to chemicals as- sociated with groundwater contamination. Beginning in 2002, Hill AFB began sampling the air inside off-base residences to see if chemicals from the groundwater, originating on the base, have evaporated and moved up into homes. To date, more than 5,500 samples have been col- lected in more than 1,700 homes. The base has a long history of industrial operations, including: aircraft, missile, vehicle, and railroad engine maintenance and repair (i.e., metal plating, degreasing, paint stripping, painting, sounding, and other operations). These industrial operations usedor generated numerous chemicals and wastes, including chlorinated and non-chlorinated solvents, degreasers, fuels and other hydrocarbons, acids, bases, andmetals. The historic use and disposal of these chemicals and their associated waste products has resulted in several large areas of contaminated groundwater migrating from the base to surrounding communi- ties (Figure 1). The primary chemical of concern at clean- up sites around the base is trichloroethene or TCE, a degreasing solvent widely used into the 1970s. Most of the off-base areas affected by the contamination are residential and although the groundwater isn’t typically used by residents or municipalities, the chemicals can evaporate easily and move up through the soil and into overlying buildings. This process, referred to as vapor intrusion, has become a significant concern for the base, as well as clean-up sites throughout the country, and presents many challenges to Hill AFB engineers. Figure 2 provides a conceptual view of how vapors from contaminated ground- water can get into homes. Hill AFB established an indoor air sampling program to deal with the potential problems posed by the chemical vapors, and decided early on to sample directly in homes. The alternative to indoor air sampling, used by many sites around Air Sampling in Homes Dealing with Vapor Intrusion at Hill Air Force Base JARROD D. CASE, P.E. AND KYLE A. GORDER, P.E., HILL AIR FORCE BASE Engineers in the Hill Air Force Base (AFB) Environmental Restoration Program are responsible for managing the cleanup of sites where historical disposal of chemicals has resulted in soil and groundwater contamination. One of the biggest challenges faced by the program is the number of homes potentially affected. As part of its annual sampling efforts, the base sends out more than 2,600 letters each fall to residents asking them to participate in the air sampling program. Sampling requires the placement of a canister in the home for 24 hours (Figure 3). The canister is essentially a vacuum, and slowly draws in air over time. Once completed, the canisters are closed and sent to a laboratory for analysis. Working with the U.S. Environmental Protection Agency (EPA) and the Utah Department of Environmental Quality, Hill AFB has established action levels for each of the chemicals it tests for. The action levels represent the lowest level at which the base recommends taking action to fix the problem. For homes with detections of chemicals above Figure 1: Areas of Shallow Underground Contamination at Hill AFB, UT. the country, includes collectingmultiple soil vapor samples beneath homes. Conducting extensive soil vapor sampling in residential areas can be intrusive to residents and their properties, and if vapors are detected in the soil, sampling would still be required in the home. The direct indoor air sampling approach was chosen to address the base’s primary concern: Are residents being ex- posed to vapors from Hill AFB-contamination?