Recommended CitationLee, L. S., X. Zhai, and J. Lee. INDOT Guidance Document for In-Situ Soil Flushing. Publication FHWA/IN/JTRP-2006/28-2. Joint Transportation Research Program, Indiana Department of Transportation and Purdue University, West Lafayette, Indiana, 2007. doi: 10.5703/1288284314230.
Many of the Indiana Department of Transportation (INDOT) sites are contaminated with aromatic hydrocarbons and chlorinated solvents; these contaminants often occur in the form of light non-aqueous phase liquids (LNAPLs) or dense non-aqueous phase liquids (DNAPLs). Considerable effort has recently been focused on developing in-situ technologies for removing or destroying NAPL source zones, and several potentially viable methods have emerged including cosolvent-enhanced source zone removal. Most recently, site-specific remedial designs involving a combination of in-situ methods (often referred to as a treatment train) have been proposed for which data are still sparse. The primary goal of the laboratory experiments is to assess the utility and effectiveness of a biofriendly cosolvent ethyl lactate for source zone flushing through enhanced dissolution mechanisms followed by assessing enhanced biological removal of contaminant residuals by cosolvent residuals. Ethyl lactate residuals after source zone remediation can serve as a substrate for indigenous microorganisms to induce anaerobic conditions and enhance in-situ reductive dehalogenation, but whether or not this process would further facilitate complete mineralization or if it too would stall at undesirable metabolites is unknown. Results from these lab evaluations involving batch tests and one-dimensional (1-D) and two-dimensional (2-D) flow systems will contribute to assessing the value of this treatment train approach for relevant INDOT sites and to developing an effective strategy for using this approach under field conditions. Ethyl lactate was found to be very efficient in recovering DNAPL mass in source zone. The residual amount of EL not only poses no harm to indigenous microbial population in a DNAPL contaminated site, but also serves as electron donor to promote the microbial dehalogenation of chlorinated contaminants, such as perchloroethene (PCE) and trichloroethylene (TCE) in the down gradient plume. Therefore, the flushing agent, EL, can be left behind at low concentrations to facilitate biodegradation in the plume. The soils used were from INDOT sites selected based on input from INDOT staff regarding amenability to future site remediation via the proposed treatment train. Site selection and assessment required travel by senior personnel to evaluate the nature and extent of contamination and by research assistants to collect soil samples for laboratory experiments.
In-situ enhanced dissolution, remediation, source zone, NAPLs, perchloroethene, toluene, enhanced microbial dehalogenation
Joint Transportation Research Program
West Lafayette, IN
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