Evaluation of Subsurface Utilities and Indoor Air Environments As Migration Pathways and Points of Exposure In a RBCA Site Assessmnt

摘要

In has been recognized that indoor air quality can be a significant contributor to total human exposure to particulate and volatile organic compounds from multiple sources in the home. Indoor air quality has often been overlooked in subsurface investigations, since many State regulatory programs have been driven historically by impacts to groundwater and soil rather than by public health risk. As States move towards adoption of riskk-based ocrrective action (RBCA) programs, there has been more of a focus on the equal footing with soil and water. Although numerical cleanup criteria for soil and groundwater may be established, air criteria may be lacking unless a SState has implemented a RBCA program. As the RBCA proces is adopted, indoor air pathway ave become a primary driver of the risk assessment process particularly in urban areas. In the case of gasoline, benzene is usually the chemical of concern (COC) for the indoor air pathway. This is due to benzene's regulation as a carcinogen and resulting risk based residential inhalation concentrations of 0.3 to 3 ug/m~3, depending on State specific acceptable risk levels. Evaluation of benzene in air is cmplicated by ambient concentrations in outdoor air of 1 to 4 ug/m~3 and indoor air concentrations ranging from 5 to 10 ug/m~3. Methyl tertiary butyl ether (MTBE) is not a significant driver of the indoor air pathway using the USEPA IRIS inhalation reference concentration of 3,000 ug/m~3. The odor threshold for MTBE in air is lower than this health based criteria. Establishment of background levels for COCs is an important component of an evaluation of air quality in indoor environments or subsurface utilities. Subsurface utilities are not discussed in the ASTM RBCA guide (E-1739-95) but need tobe evaluated during site assessment as potential migration pathways for chemicals of concern and as potential points of exposure. Air sampling results of indoor air environments. subsurface utilities and other benzene, toluene, ethlybenzene and xylene (BTEX) sources are presented fromthe established at levels higher than residential indoor air environments since utilities are confined spaces and exposures. if any, are of limited duration. A practical process for systematically evaluating subsurface utilities and indoor air pathways is presented which includes soil gas and other aie sampling mapping, and fate and transport modeling.