Assessment of the potential for natural attenuation of chlorinated solvents in contaminated groundwater in the Texas High Plains

Reese Air Force Base (RAFB), now known as Reese Center is located in the Southern High Plains region of west Texas in Lubbock County. In 1987, concentrations of chlorinated solvents, especially trichloroethene (TCE), were found to be out of compliance with the federal limits. Significant concentrations of perchloroethene (PCE) were also present on site. Pump and treat technologies, which consist of extracting contaminated groundwater and treating it on the surface, have been the traditionally considered technology when significant levels of groundwater contamination exist. Natural attenuation (NA), also called "mtrinsic remediation" has recently been recognized as a potential method for treatment of contaminated groundwater. NA of contaminants includes sorption to soil particles, dilution, dispersion, volatilization, biochemical stabilization, radioactive decay and biodegradation in soils and groundwater. If NA is found to be a viable option at Reese AFB, it can replace the presently employed pump and treat technique and result in monetary gains.

A study was conducted to estimate the potential for NA of the TCE present in the Ogallala aquifer at the Reese Air Force Base. Initial assessment of the site showed the existence of three distmct TCE plumes, two on-site and the third off-site. Initial site assessment revealed that one of the plumes exhibited signs of NA. This area is present on-site and consists mostly of the area near the Picnic Lake. A detailed examination of this area was conducted. Plume maps were drawn for the study area using SURFER to study the variation of PCE, TCE, cis-dichloroethene (cis-DCE), and dissolved oxygen (DO) concentrations from 1996 to 1998 (Only data available). These plume maps were then analyzed to study the potential for NA occurring at the site. Data analysis for the study area shows the presence of a large TCE and cis-DCE plume. The TCE plume is located up-gradient and to the northwest of the cis-DCE plume. Data analysis and modeling was used to determme whether the cis-DCE plume is a result of the TCE plume located up-gradient to it. In addition, modeling was used to back track the movement of the TCE plume and locate its possible source as well as assess the future potential of the plume movement.