Objective: The objective of this project was to promote the development of alternative landfill closure designs and management strategies for Department of Defense (DoD) landfills that can reduce the time required for stabilization of the landfilled wastes and enhance the long-term natural attenuation of chlorinated solvent leachate plumes. A literature review was completed to determine how alternative landfill closure designs and management strategies can impact the natural attenuation and long-term risk of solvent plumes. Historical geochemical data for leachate-contaminated groundwater at a variety of DoD landfill sites also were evaluated to determine typical geochemical characteristics. Various leachate-control, recirculation, and landfill-cover options were evaluated for their potential use under different climatic and hydrogeologic scenarios. Results: Three decision trees were developed to assist DoD remedial project managers in the selection of an appropriate remedial strategy for chlorinated-solvent-contaminated landfills. These decision trees guide the user through the following remedy selection steps: (1) landfill screening, (2) detailed remedial alternatives assessment, and (3) landfill cover designs. The landfill screening decision tree assists the user in determining if engineered remediation of chlorinated solvents in groundwater is required or if cleanup goals can be met with natural attenuation. The remedial alternatives decision tree guides the selection of an appropriate remedial alternative when risk or time considerations dictate a more aggressive approach and indicates the conditions under which operation of the landfill as a bioreactor, with collection and recirculation of leachate-contaminated groundwater, is an appropriate alternative. The landfill cover decision tree facilitates selection of an appropriate cover for solvent-contaminated landfills. Benefits: The 'enhanced-leaching' theory of landfill treatment could move the waste industry toward more permanent and efficient waste-management solutions including greater reliance on evapotranspiration (ET) landfill covers using natural vegetation and greater emphasis on natural attenuation. At some landfills, surface infiltration may accelerate leaching of the source and reduce the time required for biological stabilization of the landfilled waste. Recirculation of landfill leachate also could accelerate the source-leaching process and promote reductive dechlorination within a closed-loop in-situ bioreactor. ET covers can generally be installed and maintained for 50 percent of the cost of conventional RCRA covers. Additional cost savings are possible when landfill leachate is allowed to migrate and attenuate naturally or is recirculated in the landfill. Leachate collection and treatment systems can cost $200,000 to $400,000 per year to operate and must be operated indefinitely at most landfills. Leachate recirculation techniques may be able to both contain and destroy chlorinated solvents and reduce long-term operation and maintenance costs. Implications: By tailoring landfill closure requirements to site-specific natural attenuation requirements, relatively low-cost cover designs could be selected for many chlorinated-solvent-contaminated landfills. These cover designs could reduce the time required for a solvent plume to stabilize and degrade, thereby reducing the long-term risk posed by the site. More rapid stabilization of wastes also will reduce long-term monitoring costs because most regulatory agencies require rigorous post-closure monitoring activities as long as wastes pose a potential threat to water quality. References: - Hicks, J., Downy, D., Pohland, F., and McCray, J. Final Report for the Impact of Landfill Closure Designs on Long-Term Natural Attenuation of Chlorinated Hydrocarbons. Parsons Corporation, University of Pittsburgh, and Colorado School of Mines, March 2002.
Contacts: Technical Contacts: Doug Downey or John Hicks
Parsons Engineering Science, Inc.
1700 Broadway, Suite 900
Denver, CO 80290
Telephone: (303) 831-8100
Fax: (303) 831-8208
E-mail: doug.downey@parsons.com, john.hicks@parsons.com DoD Liaison Officer: Dr. Andrea Leeson
ESTCP Program Office
901 North Stuart Street, Suite 303
Arlington, VA 22203
Telephone: (703) 696-2118
Fax: (703) 696-2114
E-mail: Andrea.Leeson@osd.mil
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