Project Summary (1995-2000)

Processes affecting the uptake of chlorinated, volatile organic compounds (CVOCs) under variable moisture conditions in soils are being investigated in this project. Parameters are being estimated that characterize the uptake as a function of moisture content and the principal physical and chemical parameters of the CVOC. Intermediate-scale soil column and sandbox experiments are addressing fundamental issues related to the fate and transport of organic contaminants in the vadose zone using a range of matrix materials, organic compounds, and flow conditions in both one- and two-dimensional systems. Previously developed, highly efficient numerical models for simulating water flow and transport of reactive contaminants in multi-dimensional porous media are being modified to include flow and transport of VOCs in both gas and aqueous phases. More importantly, the models are being modified to incorporate an iterative co-conditional approach to address practical field sampling issues and uncertainties in prediction of the fate and transport of VOCs in the vadose zone. This approach provides a practical means of addressing the issues of physical and chemical heterogeneities and the resulting effects on VOCs. This tool will be valuable to scientists and engineers for designing monitoring programs and to aid regulatory agencies to assess the risks associated with VOC contamination in the vadose zone.