"EPA/600-S2-88-048." At head of title: Project summary. "Dec. 1988."

"Federal regulations stipulate that landfill cover technology ensure the long-term stability and integrity of a hazardous waste landfill system. Specific guidance for achieving compliance with these regulations requires cover designs that manage the water balance on the landfill site. Special attention must be given to the design of the soil profile and the establishment of a stable vegetative cover in order to minimize erosion of the surface soils and the percolation of water into the waste. Recommendations for a specific landfill must be based on a combination of field and laboratory data, and computer modeling of water balance to assess specific design scenarios. The purpose of this study was to investigate the utility of two hydrologic models (CREAMS and HELP) for assisting in the process of designing landfill cover systems that are stable and free of maintenance requirements. The process of parameterizing and using simple hydrologic models is outlined. Examples of modeling potential and actual sites are presented. Results of the modeling study suggest that, overall, CREAMS performs more satisfactorily than HELP in accurately predicting the soil water storage in the soil profile although more detailed calibration of HELP will probably improve model performance. While relative estimates of runoff, deep percolation and evapotranspiration are very useful for comparing different cover designs, absolute quantitative estimates of these values are subject to considerable error. Choice of values for soil parameters requires more experience and more detailed data than is indicated by the documentation for either model. Data to support choice of vegetation parameter values are largely unobtainable, especially for the native plant species which will inevitably invade a landfill site. Successional processes that lead to such invasions are discussed, and it is concluded that establishment of a vegetative community consisting of a mix of native plant species would result in a vegetative cover that is the most stable and most efficient in removing water from the soil profile."