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RELATIONSHIP BETWEEN DEHALOCOCCOIDES DNA AND DECHLORINATION RATES AT FIELD SITES
Citation:
Lu, X., J T. Wilson*, AND D H. Kampbell*. RELATIONSHIP BETWEEN DEHALOCOCCOIDES DNA AND DECHLORINATION RATES AT FIELD SITES. Presented at 4th Int'l. Conf, Monterey, CA, May 24 - 27, 2004.
Impact/Purpose:
To inform the public.
Description:
Chlorinated ethenes are common contaminants in groundwater. To date, Dehalococcoides species are the only known organisms capable of completely dechlorinating all chlorinated ethenes to non-toxic ethene. Studies in the laboratory have shown a good correlation between Dehalococcoides DNA and complete dechlorination. The rate of complete dechlorination in the field is important for an evaluation of natural attenuation. However, the relationship between the rate of dechlorination rates in the field and the presence of absence of Dehalococcoides species has not been established. The objective of this research is to investigate the relationship between Dehalococcoides DNA and dechlorination rates of chlorinated ethenes at field scale.
Several sites contaminated with chlorinated ethenes undergoing natural attenuation were selected across the United States. At each site, groundwater samples were collected from monitoring wells upgradient of the plume, in the source zone of the plume, and in the plume downgradient of the source. Dehalococcoides DNA in the groundwater samples were analyzed by SiREM laboratory using its patented Gene-TracTM Test. The groundwater samples were also analyzed for a series of monitored natural attenuation parameters including chlorinated ethenes, ethene, ethane, methane, dissolved hydrogen, etc. EXCEL and BIOCHLOR software were respectively used to calculate the concentration vs. time decay rate constants (kpoint) for a point and the concentration vs. distance decay rate constant ( ) for a plume. Reductive dechlorination screening scores were calculated based on the obtained parameters. The decay rate constants were determined to be dechlorination rates for those with high reductive dechlorination screening scores and with increase or detection of dechlorination products. Statistical method was used to evaluate the relationship between Dehalococcoides DNA and dechlorination rates.
The kpoint was calculated based on the available historical data. The studied samples were classified into two groups according to the presence or absence of Dehalococcoides DNA. For each chlorinated ethene, a comparison of mean kpoint value between the two groups was conducted using student T test. The results showed that for both TCE and cis-DCE there were no significant differences in the mean kpoint values between the two groups. However, the mean kpoint value for VC in the presence of Dehalococcoides DNA was significantly higher than that in the absence of Dehalococcoides DNA (P=0.08, alpha=0.1). The was calculated based on the recent data along the centreline of a plume. Although only a few of the studied sites were determined to be undergoing dechlorination process along the plumes, good relationships were found to exist between the Dehalococcoides DNA intensities and the dechlorination rates for TCE, cis-1,2-DCE and VC. Results from this research provide a novel approach in characterizing solvent plume and evaluation of natural attenuation in the field.