BIOAUGMENTATION FOR TCE REMEDIATION IN FRACTURED BEDROCK

Retention of bacteria in fractured bedrock can be a challenge for bioaugmentation. The relatively low surface area in the aquifer compared to porous media sites may not retain a high enough density of bacteria for effective remediation. Recirculation can be used to retain bacteria within the area of concern, but the cost and infrastructure associated with this strategy can be prohibitive at some sites. A site with TCE contaminated groundwater in fractured bedrock in New Jersey was treated with a combination of emulsified oil substrates and KB-1 bacteria. The working hypothesis is that the hydrophobic oil partitions to coat the surface of the fractures and helps to retain the hydrophobic bacteria at the surface of the fractures. Long term monitoring suggests that the oil/bacteria coating on the fractures prevents further diffusion from the sandstone/shale bedrock.

The former Naval Air Warfare Center in West Trenton, NJ has had a pump and treat system operating since 1997; the concentration of TCE in groundwater pumped to the treatment system has not decreased substantially from 1998 to the present. The test plot has an areal extent of approximately 9,000 ft2, is up to 115 ft deep and has concentrations of TCE ranging from 265 to 23,400 µg/L TCE. The test area is bounded by four wells that were used as well pairs for injection and extraction to distribute the amendments. The distances between wells in the test plot were up to 240 feet apart, but a 2% solution of EOS® was readily distributed along the flow path between the well pairs. Injections of bacteria and electron donor occurred in July 2005; post injection monitoring indicated that TCE concentrations decreased rapidly with the subsequent production and degradation of daughter products resulting in the innocuous product ethene. The concentration of TCE is below detection at all wells within the test plot as the concentration of Dehalococcoides sp. has continued to increase since injection. One of the goals of this pilot study is to evaluate the longevity of the EOS® as a source of electron donor in this environment; currently two of the wells in the test plot have TOC concentrations that have decreased below 50 ppm. The lack of rebound of TCE suggests that the hypothesized EOS®/KB-1coating of the fractures may be degrading any TCE diffusing from the matrix.