Evaluation of alternative cover systems using GIS

Geographic Information Systems (GIS) can be used to determine and display t he depths of native soil covers required for waste containment sites. Readi ly available data for the State of New Mexico are used in a GIS environment to determine the required depth of two separate cover systems. The depth o f an evapotranspirative (ET) soil cover is determined using the available w ater capacity of the soil and the amount of dormant precipitation. The thic kness of a capillary barrier cover system is determined using unsaturated h ydraulic parameters, the amount of dormant precipitation, and an iterative numerical model. A difference map showing the savings using a capillary bar rier instead of an ET cover is then created. The use of a capillary barrier in areas with fine-grained soils can decrease the necessary soil cover thi ckness by 90 cm of soil. The computed cover thicknesses compare well with t hose determined using Hydrologic Evaluation of Landfill Performance (HELP) (Schroeder et al., 1994), a model commonly used in New Mexico to determine if alternative cover systems can meet the required performance criteria.