SUITABILITY OF HYDROLOGIC EVALUATION OF LANDFILL PERFORMANCE (HELP) MODEL OF THE US ENVIRONMENTAL-PROTECTION-AGENCY FOR THE SIMULATION OF THE WATER-BALANCE OF LANDFILL COVER SYSTEMS

Cover systems are widely used to safeguard landfills and contaminated sites. The evaluation of the water balance is crucial for the design o f landfill covers. The Hydrologic Evaluation of Landfill Performance ( HELP) model of the US Environmental Protection Agency was developed fo r this purpose. This paper discusses some limitations of version 2 of this model and some operational difficulties for the use of this model in Germany, which has been developed for the United States. The model results are tested against field data of the water balance, measured on test fields on the Georgswerder landfill in Hamburg. Theoretically, HELP considers gravitational forces as driving forces of water flow o nly. Therefore capillary barriers cannot be simulated. Furthermore, th e formation of and the flow through macropores are not considered, a m ain critical process that the diminishes the effectiveness of compacte d soil liners. In the output comparison, the matching of measured and simulated data is quite good for lateral drainage, but failed for surf ace runoff and liner leakage through compacted soil liners. A further validation study is planned for HELP version 3 using a broader range o f test field data.