We investigated the distribution and activity of chloroethene-degrading microorganisms and associated functional genes during reductive dehalogenation of tetrachloroethene to ethene in a laboratory continuousflow column. Using real-time PCR, we quantified "Dehalococcoides" species 16S rRNA and chloroethenereductive dehalogenase (RDase) genes (pceA, tceA, vcrA, and bvcA) in nucleic acid extracts from different sections of the column. Dehalococcoides 16S rRNA gene copies were highest at the inflow port [(3.6 ؎ 0.6) ؋ 10 6 (mean ؎ standard deviation) per gram soil] where the electron donor and acceptor were introduced into the column. The highest transcript numbers for tceA, vcrA, and bvcA were detected 5 to 10 cm from the column inflow. bvcA was the most highly expressed of all RDase genes and the only vinyl chloride reductase-encoding transcript detectable close to the column outflow. Interestingly, no expression of pceA was detected in the column, despite the presence of the genes in the microbial community throughout the column. By comparing the 16S rRNA gene copy numbers to the sum of all four RDase genes, we found that 50% of the Dehalococcoides population in the first part of the column did not contain either one of the known chloroethene RDase genes. Analysis of 16S rRNA gene clone libraries from both ends of the flow column revealed a microbial community dominated by members of Firmicutes and Actinobacteria. Higher clone sequence diversity was observed near the column outflow. The results presented have implications for our understanding of the ecophysiology of reductively dehalogenating Dehalococcoides spp. and their role in bioremediation of chloroethenes.Tetrachloroethene (PCE) and trichloroethene (TCE) are the most-abundant groundwater contaminants in the United States (32). In situ bioremediation is a promising technology for the removal of these chlorinated solvents from contaminated aquifers (6,23,29). Of particular interest for bioremediation are microorganisms of the genus "Dehalococcoides" (1,7,10,11,13,15,31). In addition to other recalcitrant chloroorganic pollutants, Dehalococcoides spp. reductively dechlorinate PCE, TCE, cis-dichloroethene (cDCE), and vinyl chloride (VC) to ethene. While some microbial species other than Dehalococcoides spp. degrade chlorinated solvents, reductive dechlorination of PCE past cDCE has been linked exclusively to members of the genus Dehalococcoides (11,31,36,45).The reduction of chloroethenes by Dehalococcoides spp. is mediated by reductive dehalogenase (RDase) enzymes. While many RDase genes have been identified, only a few have been characterized for their function. Known RDase genes involved in chloroethene reduction are pceA, encoding PCE reductases from Dehalococcoides ethenogenes strain 195 (DET0318; GenBank accession no. NC_002936) (28) and Dehalococcoides sp. strain CBDB1 (cbdB_A1588; GenBank accession no. NC_007356) (8); tceA, encoding TCE reductases from D. ethenogenes strain 195 (DET0079; GenBank accession no. NC_002936) (27) and Dehalococcoides sp. s...

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. REPORT DATE NOV 20062. REPORT TYPE ER-99165e. TASK NUMBER 5f. WORK UNIT NUMBER PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Oregon State University Department of Civil, Construction, and Environmental Engineering Corvallis, OR 97331 8. PERFORMING ORGANIZATION REPORT NUMBER SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) Environmental Security Technology Certification Program 901 North Stuart Street, #303 Arlington, VA 22203 SPONSOR/MONITOR'S ACRONYM(S) ESTCP SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited SUPPLEMENTARY NOTESThe original document contains color images. 14 EXECUTIVE SUMMARYNonaqueous phase liquids (NAPL), including chlorinated solvents, aromatic hydrocarbons, and other volatile organic chemicals (VOC), are common contaminants at Department of Defense (DoD) and other federal and non-federal sites. Residual or pooled NAPL contamination provides a long-term source of contamination as it slowly dissolves into groundwater. A major obstacle preventing cost-effective soil and groundwater cleanup at many DoD sites is the current inability to accurately and inexpensively locate and quantify NAPL contamination. This final report describes the use of naturally occurring radon-222 (Rn) as a partitioning tracer for locating and quantifying NAPL contamination in the subsurface and for monitoring changes in NAPL quantities resulting from remediation activities.Radon-222 possesses unique physical properties that make it a useful "natural" partitioning tracer for detecting and quantifying NAPL. Rn is produced in the subsurface by the continuous decay of naturally occurring radium-226. In the absence of NAPL contamination, the aqueous Rn concentration quickly reaches a site-specific equilibrium value determined by the mineralogy and porosity of the geologic formation. In the presence of NAPL, however, the Rn concentration is substantially reduced due to partitioning of Rn into the organic NAPL phase. Moreover, the reduction in Rn concentration of groundwater in contact with a NAPL phase is quantitatively correlated with the quantity of NAPL present, as described by simple equilibrium models. Thus, the method is based on measu...

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