Dissolution of TCE and TCA Pools in Saturated Subsurface Systems

The factors affecting the dissolution kinetics of 1,1,2-trichloroethene (TCE) and 1,1,2-trichloroethane (TCA) pools in saturated porous media were investigated, using an experimental aquifer and a pool formation method specially developed for dense nonaqueous-phase liquids (DNAPLs). Under conditions of steady and uniform flow, the dissolved DNAPL concentrations decreased with increasing vertical distance from the pool resulting in steep concentration gradients. The concentration gradient increased with increasing ground-water velocity. The vertical extent (thickness) of the dissolved plume increased with increasing distance along the pool and decreasing ground-water velocity. In all cases, measured concentrations were a small fraction of the respective DNAPL solubility. A two-dimensional steady-state transport model successfully predicted the TCA experimental data, but the prediction for TCE was rather poor. This was attributed to heterogeneities in the TCE pool. Depending on ground-water velocity and DNAPL solubility, pool removal times by pumping were determined to be between 0.4 and five years, which is an extremely long period for the small volumes (200 mL) of DNAPL considered.