CH2M HILL has been involved in the application of this technology at several sites over the past few years. This paper summarizes the results of the application of enhanced reductive dechlorination at eight of these sites.
The groundwater at the sites included in this evaluation contained chlorinated solvents and their breakdown products, such as PCE, TCE, DCE, and Vinyl Chloride. Groundwater at one of the sites contained pentachlorophenol and other chlorinated phenols. The groundwater concentrations at the sites ranged from the 100s of parts per billion to more than 10,000 parts per billion. Some of the tests were perform in what was likely a DNAPL source area, and the others
were in the dissolved plume. The aquifer materials at the sites varied from primarily sand, to silty sand, to clay interbedded with sand and gravel. The projects involved pilot studies at six of the sites, a laboratory microcosm study for one site, and full-scale application at one site. Two different electron donors were used at these sites. Hydrogen Release Compound (HRCTM) was used at five of the sites, and vegetable oil was used at the other three sites.
Data that will be presented from these sites include the estimated area of influence around the injection points, the estimated distribution of the electron donors in the subsurface, the estimated longevity of the electron donors, the production of fatty acids from the electron donors, the production of daughter products from the chlorinated compounds, and the trends in the reduction of the original chlorinated compounds. One of the primary lessons learned from these sites is the importance of effective injection and distribution of the electron donors. Even in what was thought to be a relatively homogeneous soil, evenly distributing the electron donor was a challenge. Another challenge that was encountered at these sites was in the interpretation of the data. As a result of the heterogeneity of the subsurface conditions, it was difficult to locate the monitoring wells in ideal locations to understand both the hydrogeology and microbiology of the process. In all, this compilation of data provides a broad snapshot of enhanced reductive dehalogenation progress at a range of sites, which can be a valuable reference that may assist others in evaluating the potential for applying enhanced reductive dehalogenation at their sites.