HR: 12:00h
AN: H22A-07    [Abstracts]
TI: Transport of Carbon Tetrachloride in a Fractured Vadose Zone due to Atmospheric Pressure Fluctuations, Diffusion, and Vapor Density
AU: * McCray, J E
EM: jmccray@mines.edu
AF: Environmental Science and Engineering Division, Hydrologic Science and Engineering Program, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401
AU: Downs, W
EM: downsw@et.byu.edu
AF: Brigham Young Univ., Department of Civil and Environmental Engineering, Provo, UT 84602
AU: Falta, R W
EM: faltar@clemson.edu
AF: Dept. Geological Science, Clemson University, Clemson, SC 29634
AU: Housley, T
EM: houslt@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, INEEL, Idaho Falls, ID 83415
AB: DNAPL sources of carbon tetrachloride (CT) vapors are of interest at the Radioactive Waste Management Complex (RWMC) at the Idaho National Engineering and Environmental Laboratory (INEEL). The site is underlain by thick fractured basalt that includes sedimentary interbeds, each are a few meters thick. Daily atmospheric pressure fluctuations serve as driving forces for CT vapor transport in the subsurface. Other important transport processes for vapor movement include gas-phase diffusion and density-driven transport. The objective of this research is to investigate the influence and relative importance of these processes on gaseous transport of CT. Gas pressure and vapor concentration measurements were conducted at various depths in two wells. A numerical multiphase flow model (TOUGH2), calibrated to field pressure data, is used to conduct sensitivity analyses to elucidate the importance of the different transport mechanisms. Results show that the basalt is highly permeable to vertical air flow. The pressure dampening occurs mainly in the sedimentary interbeds. Model-calibrated permeability values for the interbeds are similar to those obtained in a study by the U.S. Geological Survey for shallow sediments, and an order of magnitude higher than column-scale values obtained by previous studies conducted by INEEL scientists. The transport simulations indicate that considering the effect of barometric pressure changes is critical to simulating transport of pollutants in the vadose zone above the DNAPL source. Predicted concentrations can be orders of magnitude smaller than actual concentrations if the effect is not considered. Below the DNAPL vapor source, accounting for density and diffusion alone would yield acceptable results provided that a 20% error in concentrations are acceptable, and that simulating concentrations trends (and not actual concentrations) is the primary goal.
DE: 1055 Organic and biogenic geochemistry
DE: 1832 Groundwater transport
DE: 1846 Model calibration (3333)
DE: 1865 Soils (0486)
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: Fall Meeting 2005