EVALUATION OF FINAL COVER PERFORMANCE: FIELD DATA FROM THE ALTERNATIVE COVER ASSESMENT PROGRAM (ACAP)

Field tests of final covers are described that are being conducted as part of a five-year study referred to as the Alternative Cover Assessment Program (ACAP). Data are being collected from 24 final cover test sections located at eleven sites in seven states. Climates ranging from arid to humid/subtropical are represented. Percolation rates less than 1 mm/yr are currently being transmitted by all covers located in semi-arid or arid climates. The mean percolation rates for the covers in semi-arid climates are as follows: (i) conventional covers with composite barriers - 0.09 mm/yr; (ii) monolithic barriers - 0.16 mm/yr, and (iii) capillary barriers - 0.36 mm/yr. Percolation rates for the covers located in humid regions currently are higher than anticipated, and vary significantly from site-to-site for all cover types except conventional covers with composite barriers. For humid regions, the percolation rates range between 12.2 and 128 mm/yr for the alternative covers, between 3.1 and 315 mm/yr for the conventional covers with clay barriers, and between 1.0 and 7.1 mm/yr for the conventional covers with composite barriers. Tentative recommendations regarding equivalent percolation rates for conventional covers have been made based on the data. The recommended equivalent percolation rates for covers with composite barriers are 1 mm/yr for semi-arid and arid climates and 5 mm/yr for humid climates. These recommendations are based on the relatively short data record collected to date, and may change as more data are collected during the study. Recommendations for equivalent percolation rates for conventional covers with clay barriers have not yet been formulated due to insufficient data.