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 • Research

Articles on this page document research studies that tested the effectiveness of different ET cover types and methods. The studies include both comparisons between cover types and tests of covers under different climate and environmental conditions.

Assessing the Performance of a Cold Region Evapotranspiration Landfill Cover Using Lysimetry and Electrical Resistivity Tomography.
Schnabel, W.E., J. Munk, T. Abichou, D. Barnes, W. Lee, and B. Pape.
International Journal of Phytoremediation 14(1):61-75(2012)

To evaluate the efficacy of a cold-region ET landfill cover against a conventional compacted clay landfill cover, two pilot-scale covers were constructed in side-by-side basin lysimeters (20m x 10m x 2m) at a site in Anchorage, Alaska. Percolation of moisture from the bottom of each lysimeter was monitored and compared between 30 April 2005 and 16 May 2006. As part of the project, ERT was utilized to measure and map soil moisture in ET lysimeter cross sections. Based on performance, ERT is proposed as a reliable tool for assessing the function of field-scale ET covers in the absence of drainage measurement devices.

The Effectiveness of Two Capillary Barriers on a 10% Slope. Stormont, J.C.
Geotechnical and Geological Engineering 14(4):243-267(1996)

Capillary barriers, consisting of fine-over-coarse soil layers, are being considered as an alternative cover component for waste-disposal facilities, especially in dry climates. Infiltrating water is removed from the fine layer by evaporation or transpiration, or percolation into the coarse layer (failure). If the fine-coarse interface is sloped, water in the fine layer can also drain laterally under unsaturated conditions. The effectiveness of two capillary barriers in laterally diverting water was tested. The barriers were 7 m long and 1.2 m thick, built on a 10% slope. One had a homogeneous fine layer, while the fine layer of the other was layered to increase its ability to divert water laterally. The barriers were first subjected to constant infiltration (10 mm/day) followed by exposure to ambient climatic conditions. The layered capillary barrier was successful in laterally diverting water near the interface and did not permit any water to enter the coarse layer. In contrast, the homogeneous capillary barrier failed over its entire length. These results indicate that a significant lateral diversion capacity can be designed into capillary barriers, greatly increasing their effectiveness.

Evaluation of Using Municipal Solid Waste Compost in Landfill Closure Caps in Arid Areas.
Elshorbagy, W.A. and A.M.O. Mohamed. Waste Management 20(7):499-507(2000)

Covering systems of landfills involve partial or complete isolation of waste materials from the surrounding environment. Available materials and management practices in arid areas may not be adequate to fulfill the requirements of the current regulations. As an alternative to compacted clay-based barriers, this study investigates the performance of a native soil available in arid areas blended with municipal solid waste compost as an infiltration barrier layer in landfill closure cap design. Tests to determine different physical properties of the produced mixture were conducted and the optimum blend of minimum hydraulic conductivity was selected. The effect of organic decomposition and thermal fluctuation prevailing in the arid environment upon the changes in hydraulic conductivity was evaluated experimentally. The developed mixture of 60% compost and 40% native soil was found to have a hydraulic conductivity 4.0 to 6.0 x 10(9) m/s. Other tests were conducted to examine the effect of organic decomposition and thermal fluctuations upon the hydraulic conductivity. From the hydraulic performance viewpoint, it was concluded that the developed mixture is an alternative. Some precautions are still needed in that case to eliminate the potential emission of gases from the cover material, anticipated settlement during the active stage of biological degradation, and the increased possibilities of deterioration related to burrowing animals.

Hydrologic Behavior of Two Engineered Barriers Following Extreme Wetting.
Porro, I. Journal of Environmental Quality 30:655-667(2001)

Many engineered barriers are expected to function for hundreds of years or longer. Over the course of time, it is likely that some barriers will experience infiltration to the point of breakthrough. This study compares the recovery from breakthrough of two storage´┐Żevapotranspiration type engineered barriers. Replicates of test plots comprising thick soil and capillary´┐Żbiobarrier covers were wetted to breakthrough in 1997. Test plots were kept cleared of vegetation to maximize hydrologic stress during recovery. Following cessation of drainage resulting from the wetting irrigations, water storage levels in all plots were at elevated levels compared with pre-irrigation levels. As a result, infiltration of melting snow during the subsequent spring overloaded the storage capacity and produced drainage in all plots. Relatively rapid melting of accumulated snowfall produced the most significant infiltration events each year during the study. Capillary barriers yielded less total drainage than thick soil barriers. By limiting drainage, capillary barriers increased water storage in the upper portions of the test plots, which led to increased evaporation from the capillary barrier plots compared with thick soil plots. Increased evaporation in the capillary barrier plots allowed more water to infiltrate in the second season following the wetting tests without triggering drainage. All thick soil plots again yielded drainage in the second season. Within two years of intentionally induced breakthrough, evaporation alone (without transpiration) restored the capability of the capillary barrier covers to function as intended, although water storage in these covers remained at elevated levels.

Using Fiber Optics to Detect Moisture Intrusion Into a Landfill Cap Consisting of a Vegetative Soil Barrier.
Weiss, J.D. Journal of the Air and Waste Management Association 53(9):1130-1148(2003)

The intrusion of moisture into landfills can pose a health hazard because of the possibility that the moisture will carry harmful substances into the groundwater. Early detection of moisture anywhere within these landfills is essential if corrective action is to be taken well before an occurrence of this kind. This paper presents the results of a field-scale simulation test of the use of fiber optics to detect the presence of moisture within landfill covers, using a detection method based on the thermal response of soils as a function of their moisture content. By sending electrical current through an embedded stainless-steel tube, soils of varying moisture content were heated and time-dependent temperature measurements were obtained with a fiber-optic distributed temperature sensor system. The optical fiber itself lay within the tube, but its temperature was a function of how rapidly heat was conducted into the surrounding medium. The results of this experiment, which are in agreement with those obtained using more traditional "point" sampling and laboratory analysis, are presented along with the strengths and limitations of the thermal-response method of detecting moisture.

Vegetation Cover Analysis of Hazardous Waste Sites in Utah and Arizona Using Hyperspectral Remote Sensing
Im, J., J.R. Jensen, R.R. Jensen, J. Gladden, J. Waugh, and M. Serrato.
Remote Sensing 4(2):327-353(2011)

The specific objectives of this study were to (1) estimate leaf-area-index (LAI) of the vegetation using three different methods (i.e., vegetation indices, red-edge positioning, and machine-learning regression trees) and (2) map the vegetation cover using machine-learning decision trees based on either the scaled reflectance data or mixture-tuned matched filtering-derived metrics and vegetation indices. Inputs were gathered from HyMap airborne data collected over DOE uranium-processing sites near Monticello, UT, and Monument Valley, AZ. Mixed grass and shrub species grow on an engineered disposal cell cover at the Monticello site. Shrub species are dominant in the phytoremediation plantings at the Monument Valley site. Results suggest that hyperspectral imagery can be useful for characterizing biophysical characteristics (LAI) and vegetation cover on capped hazardous waste sites; however, the vegetation mapping likely would benefit from the use of hyperspectral data of higher spatial resolution owing to the small size of many of the vegetation patches (<1 m) found on the sites.

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