Enhanced Bioremediation of High Contaminant Concentrations in Source Residual Area (PDF)
Although enhanced bioremediation has proven to be effective at many sites, typically it has been applied to relatively low contaminant concentrations and in relatively permeable media. The project site described herein is an application that potentially extends the practical limits of in situ bioremediation applications. An active eyewear manufacturing facility located in Western NY was found to be contaminated with 1,1,1-Trichloroethane (TCA) with groundwater concentrations as high as 400-500 mg/l in the source residue area. The facility entered into a Voluntary Cleanup Agreement (VCA) with New York State and was required to investigate site conditions and remediate the site. Site investigations were completed in April 2000. Site soils consist of a very dense till comprised primarily of clayey silts with some sand. Due to facility constraints, many typical remedies such as soil vapor extraction, excavation, or soil heating, could not be applied. Enhanced bioremediation was evaluated through microcosm studies and concluded that site conditions were conducive for enhanced bioremediation. Site conditions necessitated different injection scenarios at various locations of the site, comprised of varying injection grid patterns. The most significant field limitation is the need to penetrate the dense tills to accomplish effective substrate delivery from 11.6m (38 ft) bgs to approximately 1.6m (5 ft) bgs with effective loading of bioremediation substrate (HRC used as a lactate slow-release agent). Because of the depth of injection and the density of the site soils, an innovative injection/drilling program was designed. While HRC is typically introduced to the subsurface via direct-push methods, direct-push alone was found to be inadequate for site conditions. The injection design consists of a combination air rotary and direct-push method with tooling modified to allow for rotary pilot holes followed by direct push injection.