Purpose:

The Department of Defense (DoD) has many sites with chlorinated solvent groundwater contamination. There are concerns about groundwater plumes discharging into wetland environments at some of these sites. Traditional cleanup technologies are costly and may cause damage to sensitive wetland ecosystems since chlorinated solvents tend to be relatively resistant to degradation within most natural aquifer systems. However, substantial beneficial transformation can occur within the highly reducing environment of wetland sediments - - a development that suggests that natural attenuation may be a viable, cost-effective remediation option for discharges in wetlands. The purpose of this project is to demonstrate methodologies for the assessment of natural attenuation of chlorinated solvent-contaminated groundwater plumes discharging into wetland environments.

Description:

Natural attenuation comprises all processes which can reduce contaminant exposure concentrations. In most aquifers, trichloroethylene and other chlorinated solvents tend to be relatively resistant to degradation, leading to the development of long, chlorinated solvent plumes which reach surface water discharge points, such as wetlands. Conditions conducive to transformation reactions (biotic and abiotic) tend to exist in the reduced organic-rich wetland sediment prior to discharge to the surface water; thus substantial natural attenuation can occur. The organic-rich sediment zones of wetlands are relatively thin compared to the thickness of most aquifers, requiring a high resolution groundwater sampling framework to assess natural attenuation. The key sampling strategy of this project is the use of multilevel piezometer transects. Sampling and analysis will focus on redox zonation and chlorinated solvent and degradation product concentrations. In this demonstration, natural attenuation will be evaluated at three DoD chlorinated solvent discharge wetland sites. Working with regulators and the Air Force Center for Environmental Excellence, a protocol for the assessment of natural attenuation as a remedial option at discharge wetlands will be developed.

Benefits:

Scientifically defensible and cost-effective demonstrations of chlorinated solvent natural attenuation at discharge wetland sites will provide DoD with a low-cost remedial alternative at sites where traditional cleanup technologies are either expensive or threaten sensitive wetland ecosystems. (Project Completed - 2007)

Contact:

Mr. Chris Antworth
U.S. Air Force Research Laboratory/MLQR
139 Barnes Drive, Suite 2
Tyndall AFB, FL 32403-5323
Telephone: (850) 283-6026
Fax: (850) 283-6090
E-mail: chris.antworth@tyndall.af.mil