APPLICATION OF VLEACH TO VADOSE ZONE TRANSPORT OF VOCS AT AN ARIZONA SUPERFUND SITE

Cleanup standards for volatile organic compounds in thick vadose zones can be based on indirect risk (transport to ground water) when contam ination is below depths of significant direct risk. At one Arizona Sup erfund site, a one-dimensional vadose zone transport model (VLEACH) wa s used to estimate the continued transport of VOCs from the vadose zon e to ground water. VLEACH is a relatively simple and readily available model that proved useful for estimating indirect risk from VOCs in th e vadose zone at this site. The estimates of total soil concentrations used as initial conditions for VLEACH incorporated a variety of data from the site. Soil gas concentrations were found to be more useful th an soil matrix data for estimating total soil concentrations at this a rid-zone site. A simple mixing cell model was used with the VLEACH-der ived mass loading estimates from the vadose zone over time to estimate the resulting changes in ground water concentrations. For this site, the results of the linked VLEACH/mixing cell simulations indicate it i s likely that the federal MCL for TCE will be exceeded in underlying g round water if remedial action on the vadose zone is not pursued.