Field measurements of soil air permeability at the Chemical Waste Landfill

摘要

The disposal of liquid organic solvents in unlined pits at the Sandia National Laboratories Chemical Waste Landfill (CWL) has created an organic solvent vapor plume in the subsurface soils. The groundwater, at a depth of 485 feet below ground surface, shows contamination by the vapor plume. The primary strategy to remove the volatile organic constituents from the soil include methods based on vacuum vapor extraction technologies. These technologies utilize the physical process of inducing air flow through the soils, into an extraction well, and to the surface for collection and/or treatment. The ability of the soils to be ventilated by a vacuum vapor extraction system is primarily dependent on the permeability of the soil. However, soil stratigraphic layers can have different permeabilities due to the differences in soil texture (percentages of sand, silt, and clay) and soil structure (bulk density and pore size distribution). These differences can create local soil horizons that are preferentially ventilated. The less ventilated zones will prolong the removal of vapor phase contaminants. This will increase the time needed to reach the remediation cleanup levels. Air permeability estimates at sequential depth horizons would provide valuable design input for segmented well screen completion zones that may improve removal efficiency of vacuum vapor extraction systems. Soil permeability characterization can be accomplished in many ways including laboratory tests, field scale tests, and reference to analogous soil texture properties. The work presented here represents an evaluation of soil permeability test methods at selected locations of the CWL.