Relationship between geochemical parameters and the occurrence of Dehalococcoides DNA in contaminated aquifers

Abstract

Strains of Dehalococcoides are the only microbes known that can completely dechlorinate PCE, TCE, cis‐DCE, and vinyl chloride to ethylene. Either naturally occurring strains or bioaugmentation cultures of Dehalococcoides are widely used for in situ bioremediation of contaminated groundwater. Naturally occurring strains have an important role in natural attenuation of PCE, TCE, cis‐DCE, and vinyl chloride in groundwater. This study evaluated the relationship between selected biogeochemical parameters and the presence of Dehalococcoides DNA in field‐scale plumes. A total of 81 monitoring wells were sampled from 15 groundwater plumes at 10 locations across the United States (one sample per monitoring well). The presence of Dehalococcoides DNA was determined with an assay based on the polymerase chain reaction (PCR) using DNA primers targeting the 16S rRNA gene of Dehalococcoides. The groundwater samples were also analyzed for concentrations of O2, NO3−1 plus NO2−1 − N, CH4, H2, Fe (II), SO4−2, TOC, Cl−1, and benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and for alkalinity, ORP, electrical conductivity, pH, and temperature. Dehalococcoides DNA was unequivocally detected in 26 wells, most of which exhibited methanogenic conditions. A two‐sample Kolmogorov‐Smirnov test was used to compare the distribution of each parameter in water where Dehalococcoides DNA was present to the distribution where Dehalococcoides DNA was absent. The only parameters for which the distributions were different at 95% confidence were NO3−1 plus NO2−1 − N, CH4, and ORP. Using these three statistically significant geochemical parameters as descriptors, a predictive model for the presence of Dehalococcoides DNA was developed using logistic regression with a binary response. Under conditions where data of direct biochemical assay are not available a calculated probability could be used to properly calibrate computer models of natural attenuation.