U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Evapotranspiration Covers

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Application • Other Case Studies

Alternative Landfill Covers Project Profiles

Information about proposed, tested, or installed projects of alternative landfill covers are captured in this web site. The alternative landfill covers presented involve design concepts that manipulate water balance principles to minimize the infiltration of water to the waste.

Analysis and Design of Evapotranspirative Cover for Hazardous Waste Landfill.
Zornberg, J.G., L. LaFountain, and J.A. Caldwell. Journal of Geotechnical and Geoenvironmental Engineering 129(5):427-438(2003)

A site-specific unsaturated flow investigation was undertaken for the design of an evapotranspirative (ET) cover system at the Operating Industries, Inc. (OII) Superfund landfill in southern California. This cover system constitutes the first ET cover approved by the US Environmental Protection Agency for construction at a Superfund site. Percolation control in an ET cover system relies on the storage of moisture within the cover soils during the rainy season and on the subsequent release of the stored moisture by evapotranspiration during the dry season. The site-specific sensitivity evaluation shows that percolation response to design parameters such as rooting depth, cover thickness, and saturated hydraulic conductivity is highly nonlinear. This facilitated selection of the design parameters in the final cover. The analyses also provide insight into the effect of irrigation, increased natural precipitation, and initial moisture content of the cover soils. Unsaturated flow analyses performed for closure design at the OII site show that an ET cover is feasible for a wide range of conditions. Equivalence demonstration procedures using site-specific weather conditions and soil-specific hydraulic properties were developed to evaluate compliance of the proposed alternative cover with the prescriptive system. A laboratory testing program, implemented to determine the hydraulic characteristics of candidate borrow soils, indicated that placement conditions do not affect significantly the moisture retention properties of the compacted soils.

Evaluating Capping Alternatives for an Arctic Landfill.
Hinds, C., J. LeMay, and K. Stricklan. Cold Regions Engineering 2002: Cold Regions Impacts on Transportation and Infrastructure. ASCE, Reston, VA, ISBN: 0784406219, 2002

This paper presents an evaluation of capping alternatives for an 18.2 hectare landfill located in Barrow, Alaska. When closure planning for the Barrow Landfill began, excavation and removal or treatment of wastes was included in the initial evaluation of potential closure options. However, due to Barrow's remote location and the high costs of waste excavation, transportation, and/or incineration, capping was identified as the most cost-effective closure method. Three general types of caps were evaluated in a comparative analysis, including a freezeback cap, silt cap, and a composite soil/geomembrane cap. A numerical selection process introduced by Peggs and Thiel was used for rating and selecting a specific geomembrane. Cold weather shear testing results for Linear Low Density Polyethylene (LLDPE) and Polypropylene (PP) are presented. Based on the evaluation process and the cold weather testing of geomembrane samples, the recommended capping alternative was a buried PP geomembrane.

Fort Carson Finishes Alternative Landfill Cap for Landfill 5.
Defense Environmental Programs Annual Report to Congress: Fiscal Year 2005 -- Success Stories. Apr 2006

Fort Carson has successfully completed construction of an evapotranspiration (ET) cap for a World War II-era landfill. This cap was custom-designed for 15 of the 20 acres of Landfill 5, which is located at the northeastern end of the installation. The remaining five acres were covered with a conventional landfill cap to convert the site into a motor pool parking lot. The ET cap design was approved in March 2000, and it is the first RCRA Subtitle C-alternative cap in the state of Colorado. The ET cap consists of a four-foot-thick clay loam texture soil planted with a combination of warm and cool season native grasses. The ET cap relies on soil water storage, the establishment of vegetation, and soil water loss through ET to restrict deep drainage into potential ground-water sources. The ET cap at Fort Carson Landfill 5 uses approximately 500 tons of biosolids (sewage sludge) from the Fort Carson wastewater treatment plant as a soil amendment. The use of biosolids allows the installation to avoid $90,000 for landfill tipping fees. The installation will save approximately $50,000 to $60,000 a year in such fees hereafter, provided that biosolids are used. This material is added to the cap material primarily to increase the amount of organic matter and aid in water retention. The biosolids will promote vegetative growth within the cap and provide a good plant community for the cap surface. Future landfill caps on Fort Carson will also incorporate biosolids as filler in the cap material. An ET cover costs approximately 75% less to install and maintain than conventional multilayer clay, soil, and membrane caps because it requires only a grading layer and a natural material layer (the ET layer). Fort Carson saves approximately $100,000 per acre when the costs for purchases of clay materials are evaluated. Forty-seven acres on the installation are receiving ET covers, yielding total potential savings of $4,700,000 from the use of this innovative technology at Fort Carson.

A Seven-Year Water Balance Study of an Evapotranspiration Landfill Cover Varying in Slope for Semiarid Regions.
Nyhan, J.W. Vadose Zone Journal 4(3):466-480(2005)

The goal of radioactive and hazardous waste disposal in shallow landfills is to reduce risk to human health and to the environment by isolating contaminants until they no longer pose a hazard. To achieve this for a semiarid region, we studied a landfill cover containing a gravel layer, an evapotranspiration (ET) cover, in the field for 7 yr. We measured total water balance at 6-h intervals for this landfill cover design in four 1.0- by 10.0-m plots with downhill slopes of 5, 10, 15, and 25%. During the 7 yr of the field study, runoff accounted for 1.4 to 3.8% of the precipitation losses on these unvegetated landfill cover designs, whereas similar values for evaporation ranged from 88 to 95%. Evaporation usually increased with increases in slope in our field plots; for example, the ET Cover at slopes of 5 and 15% displayed 274 and 296 cm of evaporation, respectively. Interflow and seepage usually decreased with increasing slope; for example, as slope increased from 10 to 25%, interflow decreased from 18.4 to 8.8 cm. Seepage consisted of up to 1.7% of the precipitation on the ET cover, showing a maximum value of 5.3 cm on the ET cover with the slope of 5%.

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