title: Natural attenuation of chlorinated solvents at Area 6, Dover Air Force Base: groundwater biogeochemistry.
abstract: Monitored natural attenuation (MNA) has recently emerged as a viable groundwater remediation technology in the United States. Area 6 at Dover Air Force Base (Dover, DE) was chosen as a test site to examine the potential for MNA of tetrachloroethene (PCE) and trichloroethene (TCE) in groundwater and aquifer sediments. A "lines of evidence" approach was used to document the occurrence of natural attenuation. Chlorinated hydrocarbon and biogeochemical data were used to develop a site-specific conceptual model where both anaerobic and aerobic biological processes are responsible for the destruction of PCE, TCE, and daughter metabolites. An examination of groundwater biogeochemical data showed a region of depleted dissolved oxygen with elevated dissolved methane and hydrogen concentrations. Reductive dechlorination likely dominated in the anaerobic portion of the aquifer where PCE and TCE levels were observed to decrease with a simultaneous increase in cis-1,2-dichloroethene (cis-DCE), vinyl chloride (VC), ethene, and dissolved chloride. Near the anaerobic/ aerobic interface, concentrations of cis-DCE and VC decreased to below detection limits, presumably due to aerobic biotransformation processes. Therefore, the contaminant and daughter product plumes present at the site appear to have been naturally atteuated by a combination of active anaerobic and aerobic biotransformation processes.
authors.affiliation: Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, MI 48674, USA. mewitt@dow.com
authors.forename: Michael E
authors.initials: ME
authors.lastname: Witt
authors.forename: Gary M
authors.initials: GM
authors.lastname: Klecka
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Lutz
authors.forename: Tom A
authors.initials: TA
authors.lastname: Ei
authors.forename: Nancy R
authors.initials: NR
authors.lastname: Grosso
authors.forename: Francis H
authors.initials: FH
authors.lastname: Chapelle
mesh_terms: D001420:Bacteria, Aerobic; D001421:Bacteria, Anaerobic; D017606:Chlorine Compounds / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D003691:Delaware; D004784:Environmental Monitoring; D055593:Geological Phenomena; D005844:Geology; D006843:Hydrocarbons, Chlorinated / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D012989:Soil Pollutants / Q000032:analysis* / Q000378:metabolism; D012997:Solvents / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D014873:Water Pollutants / Q000032:analysis* / Q000378:metabolism
chemical_list: D017606:Chlorine Compounds; D006843:Hydrocarbons, Chlorinated; D012989:Soil Pollutants; D012997:Solvents; D014873:Water Pollutants