A study of vadose zone transport model VLEACH

Application of vadose zone transport models has been hampered by lack of mo del validation. Difficulties to validate vadose zone models using field dat a not only come from model assumptions that are uncertain to the subsurface transport processes but also from the uncertainties associated with soil c ontaminants' release time and quantity, soil sampling, sample transport, an d analytical procedures. This article first conducts a test of a popularly used vadose zone transport VLEACH by comparing model results with a set of laboratory soil column infiltration and volatilization study data. The comp arison shows a close agreement between the VLEACH model results and the lab oratory data. Second, the sorption coefficient K-d calculated in VLEACH is compared with field data. The comparison indicates that VLEACH may overesti mate the mass leached from soil to groundwater. The article also discusses the selection of the model simulation timestep, the vertical dimension incr ement, the Courant criterion, and the lower boundary condition using the se nsitivity analysis method based on a case study of soil remediation for tri chloroethylene. The procedures presented in this paper are important to pra ctical model application and modification. This level of work should be rou tinely conducted for any new or modified version of vadose zone models.