Case Study of a Full-Scale Evapotranspiration Cover

The design, construction, and performance analyses of a 6.1 ha evapotranspiration (ET) landfill cover at the semiarid U.S. Army Fort Carson site, near Colorado Springs, Colo. are presented. Initial water-balance model simulations, using literature reported soil hydraulic data, aided selection of borrow-source soil type(s) that resulted in predictions of negligible annual drainage (<= 1 mm/year). Final construction design was based on refined water-balance simulations using laboratory determined soil hydraulic values from borrow area natural soil horizons that were described with USDA soil classification methods. Cover design components included a 122 cm thick clay loam (USDA), compaction <= 80% of the standard Proctor maximum dry density (dry bulk density similar to 1.3 Mg/m(3)), erosion control measures, top soil amended with biosolids, and seeding with native grasses. Favorable hydrologic performance for a 5 year period was documented by lysimeter-measured and Richards'-based calculations of annual drainage that were all < 0.4 mm/year. Water potential data suggest that ET removed water that infiltrated the cover and contributed to a persistent driving force for upward flow and removal of water from below the base of the cover.