Matching soil types with vegetation and climate is integral in creating alternative landfill covers that are sustainable for very long periods of time.

The Desert Research Institute (DRI) recently completed a unique project to design landfill covers for future use on Edwards Air Force Base (EAFB) located near Lancaster, California. This research was conducted to assist EAFB under the sponsorship of the Air Force Flight Test Center, Environmental Management and Restoration Division, with involvement from the Sacramento District of the U.S. Army Corp of Engineers. This was a collaborative DRI project with faculty representing two research centers supporting the work, including the Center for Arid Lands and Environmental Remediation (CALEM) and Center for Environmental Remediation and Monitoring (CERM). Michael Young, project director and co-principal investigator, and Bill Albright, co-principal investigator, were joined with Walter Zachritz, David Shafer, Karl Pohlmann, Mary Cablik, Stephen Zitzer, and Eric McDonald in bringing the project to fruition.

The project focused on developing a technical approach for designing evapotranspiration (ET) covers. ET covers rely on evapotranspiration processes (plant uptake and soil evaporation) to reduce percolation of water into waste material. Conversely, prescriptive covers rely on engineered, low-permeability layers for shedding water away from the waste material. DRI's research in the arid southwestern United States has shown that ET covers can protect the underlying waste, sometimes much better than some prescriptive covers, at substantially lower costs.

A landfill final cover must perform several functions, most notably containing waste and waste byproducts and preventing infiltration of rainfall. However, a consistent design methodology has not existed that allows engineers and regulators to easily negotiate the permitting processes for site closures. To this end, DRI researchers used knowledge of site soils, plants, and numerical simulation to thoroughly analyze design parameters. The numerical simulation, known as Monte Carlo modeling, can be used to evaluate the effects of changing design parameters on deep infiltration, also known as flux. Modeling results were coupled with cost factors to compare alternatives. In the future, these methods may provide a template to support regulatory permitting activities for land managers at other large, multi-site installations.