Calculation of soil cleanup criteria for volatile organic compounds as controlled by the soil‐to‐groundwater pathway: Comparison of four unsaturated soil zone leaching models

Four computer models that predict leaching of chemicals in the unsaturated soil zone were used to calculate example soil cleanup criteria for volatile organic compounds, using a hypothetical environmental scenario. The criteria were calculated so that allowable groundwater concentrations for the chemicals were not exceeded. The models used were the Pesticide Root Zone Model (PRZM) and the Seasonal Soil Compartment Model (SESOIL) from the U.S. Environmental Protection Agency, the Sanitary Landfill Model (SLM1) from Oregon State University, and the Integrated Moisture and Aqueous Contaminant Transport model (IMPACT) under development for the State of New Jersey. The hypothetical scenario assumed a water table depth of 10 ft, a contaminated zone from 0 to 4 ft, and sandy loam soil properties. Transport times to groundwater were similar for all four models. The calculated soil criteria for many chemicals using the four models agreed to within an order of magnitude. In a few instances, SLM1 and PRZM predicted much lower cleanup criteria than the other two models because volatilization losses were not modeled. Calculated criteria were often quite low when degradation was assumed to be zero. When estimated degradation rates were employed, criteria were sometimes considerably higher.