Field-Scale Assessment of Evapotranspirative Methane Oxidation Caps for Sustainable Management of MSW Landfills in Sub-Humid Climates
Investigators: Michigan State University
Conventional caps include geomembrane and compacted clay components. The long-term performance of compacted clay is concerning due to cracks that develop in compacted clays when subjected to freeze/thaw cycles. The use of geomembrane when post-closure care period has ended is problematic because potential erosion of the soil layers above the geomembrane can expose the geomembrane. Once the geomembrane is exposed to the sun light, its life is expected to shrink significantly. In addition, the capital cost of construction and maintenance of conventional caps is relatively high. Such capital cost savings can be several million dollars for a typical mid-size landfill! Hence, alternative caps have been evolving during the last 15 years. However, such cap
designs have been more commonly explored and used at arid and semi-arid sites located to the west of the Mississippi river including the most recent Alternative Cap Assessment Program (ACAP) that was carried out by the U.S. EPA. However, in sub-humid climates, typically located the mid-western and eastern U.S., we have relatively less data on field-scale performance of alternative caps designed as ETMO caps. The modeling carried out by the PI indicates that such alternative caps could be equally effective in sub-humid climates when the equivalency is tied with the sustainability of the landfill. Hence, the proposed project can have economical and environmental impact on several hundred landfill sites in the U.S. where the total financial impacts across the country could reach several billion dollars! Financial savings associated with earthen alternative caps and sustainability due to environmental and end-use factors is the major motivation of the proposed project.
The proposed project activities include construction, instrumentation, monitoring, and modeling/assessment of two field-scale (100 ft by 50 ft) earthen cap test sections proposed at the Woodland Meadows Landfill located in Detroit, Michigan. These test sections are designed as evapotranspirative methane oxidation (ETMO) caps. The key long-term objectives of the proposed project are to: (1) quantify and model the percolation or drainage from earthen caps made of native soils for sub-humid (east of the Mississippi river) and colder climates and assess implications for leachate production; (2) quantify and model the methane oxidation capacity of the caps for various soils types; (3) assess the effect of diversity and density of biota on physical changes (e.g., freeze/thaw cracking) in the cap and implications on gas and water flow and hence sustainability of the cap after the post-closure care period; and (4) evaluate the effect of the lysimeter boundary on the percolation projections and implications of this method for permitting such caps. The two test sections will be constructed on an active landfill which is operated by Waste Management. The soils used for the test sections are native glacial tills and are geologically identical to many sites located to the east-northeast of the Mississippi river. Hence, this site will represent typical climatic and soil conditions at several hundred landfill sites where alternative caps have not been evaluated. Hence, when combined with the existing data from EPAâ€™s ACAP sites, this project will have implications for multiple sites.
Mijares, R. and Khire, M. (2012), “Field Data and Numerical Modeling of Water Balance of Lysimeters vs Actual Earthen Cap,” Journal of Geotechnical & Geoenvironmental Engineering, American Society of Civil Engineers, accepted (in press), scheduled for Print in August.
Khire, M. and Saravanathiiban, D. (2012), “Centrifuge Testing of Unsaturated Hydraulic Properties of Municipal Solid Waste,” ASCE Geotechnical Special Publication No. 225: State of the Art and Practice in Geotechnical Engineering, Reston, VA.
Mijares, R. G. and Khire, M. (2010), “Soil water characteristic curves of compacted clay subjected to multiple wetting and drying cycles.” ASCE Geotechnical Special Publication No. 199: Advances in Analysis, Modeling and Design, Reston, VA., pp. 400-409.
Khire, M. and Mijares, R. G. (2010), “Effect of geocomposite drainage layer on water balance of earthen cap lysimeters.” Proceedings 2010 Global Waste Management Symposium, San Antonio, TX, Oct. 3-6.
Mijares, R. G., Khire, M., and Johnson, T. (2010). “Lysimeters versus actual earthen caps: Numerical assessment of soil water storage.” ASCE Geotechnical Special Publication No. 199: Advances in Analysis, Modeling and Design, Reston, VA., pp. 2849-2858.