3-D SIMULATION OF SOIL VAPOR EXTRACTION IN A DEEP UNSATURATED ZONE

Material Disposal Area L (MDA L) is an inactive liquid-waste disposal site operated from 1973 to 1985 located within the boundary of Los Alamos National Laboratory (LANL). A subsurface vapor plume of volatile organic compounds (VOCs) extends to depths of greater than 100 m in the vadose zone, and site remediation is recommended to reduce possible future impacts to groundwater. Soil vapor extraction (SVE) using two SVE wells was conducted at the site as an interim remediation measure. Over the past 18 months, we have monitored the changes in both the effluent and the subsurface plume over time. We see an overall reduction of concentrations with time in both the SVE effluent and many of the surrounding monitoring wells, changes in the molar concentration ratios of extracted gas, and a 60% decrease in total plume mass. SVE effluent concentration data for the most prevalent VOC contaminant found in the vapor plume (1,1,1 TCA) were compared to those predicted by a previously calibrated 3-D multiphase numerical model of the site. The west side effluent data and model curves matched well, but the east side curves require recalibration of the subsurface permeability. The newly calibrated simulations are then used to explore rebound data and constrain leakage rates from subsurface waste containers.