Design and installation of the ACAP field facilities was completed in November 2000. Test facilities were constructed at 12 sites throughout the United States. EPA plans to operate the network until 2005, with ongoing data collection and maintenance operations. This report summarizes activities through fiscal year 2002.

This report reviews current data collection efforts and numerical modeling capabilities for cover designs. Existing data collection efforts were evaluated for possible inclusion in the program. Currently used models were evaluated for features that are appropriate to the evaluation of alternative cover designs. The results of these reviews and evaluations are discussed.

This study compares the hydrologic performance of alternative covers over a range of climates, soil types, and vegetation types. The first section of the paper briefly reviews underlying concepts and experience with both conventional and alternative cover designs. The greater part of the paper, a comparison of alternative covers tested in different climatic settings, is based entirely on water balance data from large scale lysimeters or test sections constructed under ACAP. The last section draws conclusions from the ACAP comparisons, and then recommends follow-up work on near-term processes that can change cover performance, an approach for projecting long-term performance, and an approach to improve the sustainability of existing conventional covers.

This peer-reviewed study represents a snapshot in the evolution of final covers ~5 to 10 years after construction. The data indicate that engineering properties of cover soils change while in service and that long-term engineering properties should be used as input to models employed for performance assessments. The findings demonstrate that covers should be monitored to ensure that they are functioning as intended. This report includes an update on the results of the ACAP demonstration, which evaluated the performance of 27 different final cover profiles.

A 4-year field study was conducted to assess the ability of landfill covers to control percolation into the waste. Performance of one conventional cover was compared to that of two ET tree covers, using large (7 x 14 m) lined lysimeters at the Leon County Solid Waste management facility in Tallahassee, FL. ET tree covers vegetated with cottonwood or eucalyptus performed well in the North Florida climate as an alternative to a conventional cover with a geosynthetic clay liner.

Landfill covers are critical to waste containment, yet field performance of specific cover designs has not been well documented and seldom been compared in side-by-side testing. A study was conducted to assess the ability of landfill final covers to control percolation into underlying waste. Conventional covers employing resistive barriers as well as alternative covers relying on water-storage principles were monitored in large (10 x 20 m), instrumented drainage lysimeters over a range of climates at 11 field sites in the United States. The data collected support conclusions from other studies that detailed, site-specific design procedures are very important for successful performance of alternative landfill covers.

This study dealt with characterizing the hydrologic properties of cover soils in ACAP. Soil samples collected from 10 ACAP test sites were tested to determine their saturated hydraulic conductivity, soil water characteristic curve, physical properties, and index properties. A primary objective was to understand how the hydrologic properties of alternative cover soils (i.e., saturated hydraulic conductivity, ks, and the van Genuchten parameters a and n) are related to index and physical properties. A secondary objective was to develop functional relationships between index and hydrologic properties, which are commonly known as pedotransfer functions (PTFs). PTFs for ks, a, and n were developed using stepwise regression and the index, physical, and hydrologic properties that were measured. These PTFs were compared with other PTFs from the literature. Analysis of the PTFs from the literature showed that none predicted ks, a, and n accurately. For some of the PTFs, no apparent relationship exists between the predicted and measured hydrologic properties. The poor predictive capability of these PTFs is attributed to differences between engineered fill soils used for alternative covers and the natural, agricultural, or manufactured soils that form the basis of the PTFs in the literature. Better predictions were obtained from the PTFs developed in this study, but the predictions made with these PTFs also are not particularly accurate. Thus, the existing PTFs, including those developed in this study, do not appear to be a viable surrogate for material testing.