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Residential Vapor Intrusion Evaluation: Long Duration Passive Sampling v. Short Duration Active Sampling

Sampling indoor air for potential vapor-intrusion impacts using current standard 24-hour sample collection methods may not adequately account for temporal variability and detect contamination best represented by long-term sampling periods. Henry Schuver of the U.S. Environmental Protection Agency Office of Solid Waste stated at the September 2007 Air & Waste Management Association vapor-intrusion conference that the US EPA may consider recommending longer-term vapor sampling to achieve more accurate time-weighted-average detections. In November 2007, indoor air at four residences was sampled to measure trichloroethene (TCE) concentrations over short- and long-duration intervals. A carefully designed investigation was conducted consisting of triplicate samplers for three different investigatory methods: dedicated 6-liter Summa canisters (US EPA Method TO-15), pump/sorbent tubes (US EPA Method TO-17), and passive diffusion samplers (MDHS 80). The first two methods collected samples simultaneously for a 24-hour period, and the third method collected samples for two weeks. Data collected using Methods TO-15 (canisters) and TO-17 (tubes) provided reliable short duration TCE concentrations that agree with prior 24-hour sampling events in each of the residences; however, the passive diffusion samplers may provide a more representative time-weighted measurement. The ratio of measured TCE concentrations between the canisters and tubes are consistent with previous results and as much as 28.0 μg/m3 were measured. A comparison of the sampling procedures, and findings of the three methods used in this study will be presented.