Performance assessment of enhanced bioremediation of DNAPLs using innovative techniques

Recent interest in applying enhanced in situ bioremediation (ISB) at field sites containing chlorinated solvent DNAPLs has resulted in a need to understand how best to design, monitor, predict, and optimize performance of this technology. A field pilot study began in July 2005 at the Fort Lewis East Gate Disposal Yard to demonstrate enhanced mass transfer of trichloroethene (TCE) from the DNAPL phase to the aqueous phase during and after high and low concentration whey powder injections. In addition to assessing enhanced mass transfer, the efficacy of a suite of innovative diagnostic tools was evaluated as performance metrics for ISB including 3-D vertical monitoring, stable carbon isotope analysis, fluxmeter assessment, and molecular characterization using terminal restriction fragment length polymorphism (T-RFLP), quantitative polymerase chain reaction (QPCR), and fluorescence in situ hybridization (FISH). Collectively, these data were used to assess the mechanisms for contaminant dissolution and degradation, to assess the interactions between symbiotic and competitive populations within the microbial community, and to predict how these interactions affect ISB performance.
Contaminant mass destruction was evaluated using groundwater monitoring in three dimensions and using fluxmeter analysis. These data illustrated dramatic increases in contaminant mass loading in groundwater during the high concentration (factor of 3-16) whey powder injections, but not during the low concentration (factor of 0.8-1.5) whey powder injections. Compound-specific stable carbon isotope analysis, which measures the shifts in the ratio of ¹³C to ¹²C during biological transformation of contaminants illustrated efficient biological degradation despite substantial loss of mass in groundwater once vinyl chloride and ethene were produced. These tools can be used to optimize the contaminant mass loading to the aqueous phase, where it is efficiently degraded, thereby increasing the effectiveness of bioremediation in residual source zones.
The characterization of the 16S rDNA and rRNA community at this site was performed to elucidate population dynamics pertinent to contaminant degradation performance. T-RFLP community profiling; QPCR for Dehalococcoides spp. including the 16S rRNA gene and functional genes tceA, vcrA, and bvcA; and FISH using probes specific to Dehalococcoides spp. and methanogenic populations were used to track microbial community changes in response to biostimulation and bioaugmentation. In all cases, the correlation between community structure and overall bioremediation performance is being evaluated in order to determine if population shifts can be correlated to more efficient reductive dechlorination as measured based upon 3-D sampling and isotopic fractionation to predict and optimize bioremediation performance.