Sensitivity analysis of a soil leachability model for petroleum fate and transport in the vadose zone

摘要

Risk-based assessment methods are commonly used at petroleum-contaminated sites. In South Carolina, the Soil leachability Model (SLM) is used to calculate site-specific target levels (SSTLs) for soils that may leach contaminants to groundwater. The SLM is a series of analytical equations that is based upon the Green and Ampt equation to predict infiltration rates and accounts for equilibrium partitioning and first-order biodegradation of the contaminant as it travels to groundwater. To reduce costs, many soil property inputs to the model are estimated using regression equations that relate textural classification to these physical properties. It was not known what effect errors in these inputs might have on the SSTLs computed with the SLM. Thus, a sensitivity analysis was performed to determine the influence of parameter variability on benzene and naphthalene SSTLs computed for three soil types and two groundwater depths. The results of this study indicate that SSTLs computed with the SLM are very sensitive to organic carbon content and biodegradation half-lives for sand, loam, and clay, saturated hydraulic conductivity for loam and clay and most soil input parameters for clay. Overestimation of organic carbon content or underestimation of biodegradation half-lives in sand, loam or clay, or underestimation of the saturated hydraulic conductivity in loam or clay can result in SSTLs that are orders of magnitude too large, and therefore, potentially unconservative.