Risk characterization of vapor intrusion in former manufactured gas plant sites

Soil vapor intrusion (SVI) has recently garnered much interest as a potential exposure route for occupants of properties overlying and surrounding former Manufactured Gas Plants (MGPs). This investigation evaluates SVI at 10 commercial buildings and 26 single family and multi-family residential properties overlying and/or adjacent to three former MGPs. SVI was evaluated in three categories according to thickness of the vadose zones: no vadose zone; 0-6 feet thick, and 6-25 feet thick. Indoor and outdoor air, and soil vapor samples were analyzed for volatile organic compounds (VOCs). Comparative risks were evaluated based on maximum and mean concentrations for benzene, toluene, ethylbenzene, and xylenes relative to background levels. All calculated Hazard Indices were less than 1 or were comparable to mean and maximum background levels. Cancer risks for exposure to benzene ranged from 9.75 × 10−6 to 4.52 × 10−4. Comparative background cancer risk from benzene exposure not related to former MGP sites ranged from 9.9 × 10−6 to 3.59 × 10−3. The results did not identify evidence of MGP-related soil vapor intrusion from any of the 36 sites. No increased public health risks were associated with occupied residential or commercial properties overlying or surrounding MGPs.