A Comparison of Surface Emission Flux Chamber Measurements to Modeled Emissions from Subsurface Contamination

摘要

Analytical models (a series of screening equations) are commonly used to determine if volatile contaminants in subsurface soils and groundwater may be migrating into buildings and exposing people to adverse health risks. Specifically, the screening equations are used to estimate the contaminant concentrations in indoor air resulting from volatilization of contaminants from subsurface soils and groundwater. These estimated indoor air contaminant concentrations are compared to acceptable indoor air concentrations to determine if adverse risks to people may exist. The screening equations are conservative due to uncertainties in modeling volatile contaminants partitioning from subsurface soil and groundwater, diffusing through the vadose zone, and migrating into buildings1. Because of this conservatism, the equations often indicate that an unacceptable risk exists to people living or working in buildings overlying subsurface contamination. In order to determine if actual contaminant vapor migration is occurring, surface emission flux chambers can be used to measure volatile contaminants emanating from the subsurface. These measured values can be used to more accurately evaluate risk. This paper presents case studies of two leaking underground storage tank sites in Utah. Subsurface investigations were performed at both sites and site-specific data was used in the screening equations. The screening equations were used to determine if people living or working in buildings overlying the subsurface contamination may be exposed to unacceptable risks. The screening equations indicated that benzene may be migrating from subsurface contaminated soil and groundwater to the ground surface and that an adverse risk to building inhabitants may exist. Subsequent surface emission flux chamber testing, however, indicated that benzene was not migrating from the subsurface contamination to the ground surface.