Subsurface Venting of Vapors Emanating from Hydrocarbon Product on Ground Water

The results of an API‐sponsored pilot‐scale subsurface venting system study are presented. The purpose of this study was to evaluate the effectiveness of forced venting techniques in controlling and removing hydrocarbon vapors from a subsurface formation. Both qualitative and quantitative sampling and analytical procedures were developed to measure hydrocarbon vapors extracted from the soil. Vapor recovery and equivalent liquid product recovery rates were measured at each test cell evacuation rate. Two identical test cells were installed. Each cell contained 16 vapor monitoring probes spaced at distances from 4 to 44 feet from a vapor extraction (vacuum) well. Each cell was also configured with two air inlet wells to allow atmospheric air to enter the subsurface formation. The vapor monitoring probes were installed at three discrete elevations above the capillary zone. In situ vapor samples were obtained periodically from these probes to measure changes in vapor concentration and composition while extracting vapors from the vacuum well at three different flow rates (18.5 scfm, 22.5 scfm and 39.8 scfm). In situ vapor samples were analyzed using a portable gas chromatograph to quantify and speciate the vapors. Vacuum levels were also measured at each vapor sampling probe and at the vacuum well. The soil venting techniques evaluated during this study offer an alternative approach for controlling and eliminating spilled or leaked hydrocarbons from sand or gravel formations of high porosity and moderate permeability. These techniques may also be used to augment conventional liquid recovery methods. The data collected during this study will be useful in optimizing subsurface venting systems for removing and controlling hydrocarbon vapors in soil. Study results indicate pulsed venting techniques may offer a cost‐effective means of controlling or eliminating hydrocarbon vapors in soil.