Hydrologic Comparison of Prescriptive and Water Balance Covers

Abstract

The objective of this study is to compare the hydrology of prescriptive and water balance cover designs for Larimer County Landfill in Colorado via hydrologic models parameterized from laboratory-measured testing of undisturbed and remolded landfill soils. A prescriptive cover is designed to limit percolation into underlying waste via a low-permeability layer, whereas a water balance cover is designed to limit percolation via storing infiltrated precipitation and subsequently releasing the water through evaporation and transpiration. Soil characteristics and engineering properties were determined for an existing prescriptive closure cover and two borrow areas. Hydrologic modeling was completed using commercially available software to predict percolation through the prescriptive and water balance covers. The wettest 10 consecutive years on record with a complete meteorological data set (1992–2001) were selected for the analysis. Predicted percolation through a prescriptive cover was <0.1 mm/year, and evaporation was the main mechanism for removing water from the cover profile. Predicted percolation in the water balance cover models ranged from 4.9 to 13.2 mm/year depending on borrow area soil, cover thickness, and vegetation parameters. Transpiration was the main mechanism for removing water from the water balance cover models.