Direct-Push Injection and Circulation Biobarrier to Remediate a TCE Groundwater Plume

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ABSTRACT: The goal of this study was to determine if direct-push drilling methods combined with a circulation system could be used to establish a passive biobarrier in a very transmissive aquifer to treat tricholoroethene (TCE). The Site is located in central Indiana, where historic use of TCE has impacted an unconfined aquifer. A plume consisting primarily of TCE has migrated from west to east across the Site toward a regionally significant river. The plume is approximately 1,100 feet wide, 6,300 feet long, and up to 50 feet deep. The horizontal groundwater flow velocity is estimated to be 2.0 to 5.0 feet/day. Site geochemical and volatile organic compound (VOC) data did not indicate the natural attenuation of TCE. A bench test indicated that bioaugmentation could be successfully applied at the site. Direct push injection of emulsified vegetable oil with 5% lactate was applied at 14 drive points in the upgradient portion of a circulation cell. Very positive results were observed within weeks suggesting that the combination of direct injection and circulation accelerated the establishment of the biobarrier. Halorespiring bacteria have been quantified in the circulation area using Real-Time Polymerase Chain Reaction (PCR) techniques. Recent VOC, geochemical and microbial data indicate that the biobarrier continues to persist in the circulation zone more than six months since system shut-down. Based on these results the Indiana DEM approved the work plan for full-scale implementation of biobarriers at the Site.

INTRODUCTION
Site Description. The Site is located in the New Castle Till Plains and Drainage Ways physiographic region of Indiana (Gray, 2000). Historic use of TCE at a manufacturing plant has impacted an unconfined aquifer. The aquifer is part of a north-south trending glacial outwash channel. The outwash deposits are composed of coarse-grained sands and gravel with occasional interbeds of silty sand and silt that generally coarsen toward the center of the channel. The bedrock surface is located at depths ranging from 30 feet near the western margin of the channel to greater than 120 feet near the center. A plume consisting primarily of TCE has migrated from west to east across the Site toward a regionally significant river located at the center of the outwash channel. The plume is approximately 1,100 feet wide, 6,300 feet long, and up to 50 feet deep.

The properties of the aquifer were characterized by grain size distributions, an eighthour pump test and a sodium bromide tracer test. The specific yield was estimated to be 0.28, and the hydraulic conductivity was calculated to be 204 ft/day. Non-pumping and pumping groundwater flow velocities in the circulation area were approximately 2 and 5 feet per day, respectively.

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