Electrokinetic-Enhanced Bioremediation of Chlorinated Solvents in Denmark

Like other industrialized nations, chlorinated solvents were used abundantly in Sweden for manufacturing, degreasing and dry cleaning industries during the 20th century. Annual consumption of chlorinated solvents in Sweden during the 1970s was on the order of 20,000 tons. Today, Sweden consumes approximately 1,000 tons of chlorinated solvents annually.

The many decades of chlorinated solvent use has resulted in soil and groundwater contamination at thousands of sites across Sweden. At many of these sites, a significant quantity of chlorinated solvents is present in the subsurface as a dense nonaqueous phase liquid (DNAPL) that, left untreated, will continue to contaminate groundwater supplies for decades to come. There is growing recognition in Sweden of the need to remediate chlorinated solvent DNAPL sites; however, many Swedish consulting hydrogeologists and engineers lack direct experience with remediation of DNAPLs. The Swedish Environmental Protection Agency (Naturvårdsverket) has recognized the importance of investing in technical capacity building to improve the ability of Swedish practitioners to clean up chlorinated solvent sites. As a first step in the capacity-building process, Naturvårdsverket selected a team of chlorinated solvent remediation experts consisting of Geosyntec Consultants (Geosyntec), SWECO VIAK (Sweden), and COWI A/S (Denmark) to write a detailed technical guidance manual entitled Chlorinated Solvents – Identification and Evaluation of Remediation Technologies (Naturvårdsverket Report 5663). The document was funded as part of Naturvårdsverket’s Hållbar Sanering (Sustainable Remediation) program.

Geosyntec applied its expertise with DNAPL remediation technologies and American regulatory programs to lead the project team in the development of a systematic protocol for evaluating and selecting one or more remediation technologies for a given site. This protocol consists of five steps: (i) development of remedial action objectives (i.e., identify the purpose of remediation); (ii) development of general response actions (e.g., institutional controls, physical containment, or mass removal); (iii) preliminary screening to identify a broad list of feasible and appropriate remedial alternatives; (iv) detailed technology evaluation to identify a focused short list of remedial alternatives; and (v) assembly and detailed evaluation of site-specific remedial alternatives. Geosyntec prepared detailed technical fact sheets for a variety of chlorinated solvent remediation technologies, including excavation, pump-and-treat, air sparging/soil vapor extraction, multi-phase extraction, in situ flushing, in situ thermal remediation, in situ bioremediation, in situ chemical oxidation, in situ metal-catalyzed reduction, and phytoremediation. Each fact sheet includes information regarding technology treatment mechanisms, applicability to varying geologic terrains, applicability to plumes and source zones, design criteria, and costs. Geosyntec also prepared presentation materials for an associated training course on chlorinated solvent remediation for Swedish regulators and consultants.

Geosyntec led the development of a first-of-its-kind, user-friendly technical manual and training course to assist Swedish regulators, consultants, and industry in selecting technologies for remediation of sites impacted with chlorinated solvent DNAPL. The document is available on the Naturvårdsverket website.