The HELP model is a quasi-two-dimensional, deterministic, water-routing model for determining water balances. The HELP versions,1, 2, and 3 were developed by the U.S. Army Engineer Waterways Experiment Station (WES), Vicksbury, M.S. for the U.S. E.P.A.Risk Reduction Engineering Laboratory, Cincinnati, OH, in response to needs in the RCRA and the CEERLA (Superfund). The primary purpose of the model is to assist in the comparison of landfill design alternatives as judged by their water balances.
Version 1 of the HELP model incorporated a lateral subsurface drainage model and improved unsaturated drainage and liner leakage models into the HSSWDS (Hydrologic Simulation Model for Estimating Percolation at Solid Waste Disposal Sites), this provided a simulation of the entire landfill including leachate collection and liner systems.
In Version 2, a synthetic weather generator developed by the USDA was added to the model to yield values of precipitation, temperature and solar radiation. This replaced the use of normal mean monthly temperature and solar radiation values and improved the modeling of snow and evapotranspiration. Modeling of unsaturated hydraulic conductivity and flow and lateral drainage computations were improved.
In Version 3, the number of layers that can be modeled has been increased. The default soil / material texture list has been expanded to contain additional waste materials, geomembranes, geosynthetic drainage nets and compacted soils and permits the use of a user-built library of soil textures. Computations of leachate recirculation and groundwater drainage into the landfill were added. It also accounts for leakage through geomembranes due to manufacturing and installation defects and by vapor diffusion through the liner. The estimation of runoff from the surface of the landfill has been improved to account for large landfill surface slopes and slope lengths. The snowmelt model has been replaced with an energy-based model; the evapotranspiration model has been replaced incorporating wind and humidity effects as well as long wave radiation losses. Frozen soil model was added to improve infiltration and runoff predictions in cold regions. The unsaturated vertical drainage model has also been improved to aid in storage computations.