Hydrologic Evaluation of Landfill Performance (HELP)

The model accepts weather, soil, and design data and uses solution techniques that account for the effects of surface storage, snowmelt, frozen soil, runoff, infiltration, evapotranspiration, vegetative growth, soil moisture storage, lateral subsurface drainage, leachate recirculation, unsaturated vertical drainage, and leakage through soil, geomembrane, or composite liners.

• Climate data requirements: General evapotranspiration data and daily values of precipitation, temperature, and solar radiation. The HELP model has a default evapotranspiration database for 183 U.S. cities, containing data for latitude, evaporative zone depths, leaf area indices, growing season, average wind speed, and average quarterly relative humidities. A default precipitation database is included, containing 5 years of daily values for 102 cities throughout the United States. The model also has a synthetic weather generator with coefficients for 139 cities for daily precipitation data generation and for 183 cities for daily temperature and solar radiation data generation. The user interface also contains a number of utility routines to import weather data from other databases.
  
  
• Soil data requirements: Porosity, field capacity, wilting point, initial moisture content, and saturated hydraulic conductivity of up to 20 layers of materials. The model contains a default soil database of characteristics for 42 types of materials (soils, waste, and geosynthetics). Design data requirements include the AMC-II runoff curve number for the site, a description of the vegetation, a description of the function of each layer of material, the thickness of each layer, the slope at the base of each drainage layer, the spacing between drainage collectors in each drain system, a description of leakage potential of each geomembrane liner, and a description of the leachate recirculation, if used. As evident by the data requirements, the model permits an evaluation of detailed designs and a sensitivity analysis of design components and climatological variables.

Landfill systems including various combinations of vegetation, cover soils, waste cells, lateral drain layers, low permeability barrier soils, and synthetic geomembrane liners may be modeled. The program facilitates rapid estimation of the daily, monthly, annual, and average annual amounts of runoff, evapotranspiration, drainage, leachate collection, and liner leakage that may result from the operation of a wide variety of landfill designs. The model applies to open, partially closed, and fully closed sites and serves designers and permit writers.

The primary purpose of the model is to assist in the comparison of design alternatives as judged by their water balances. The model is sufficiently sophisticated to consider all of the principal design parameters including vegetation, soil types, geosynthetic materials, initial moisture conditions, thicknesses, slopes, and drain spacing as well as climate effects.

The HELP model was developed at the U.S. Army Engineer Waterways Experiment Station under a cooperative agreement with the U.S. Environmental Protection Agency (EPA) to support RCRA and Superfund programs. Use of the HELP model is recommended by the EPA and required by most states for evaluating closure designs of hazardous and nonhazardous waste management facilities. More than 2,000 private engineering offices in more than a dozen countries, and greater than 200 offices of federal, state, and municipal governmental agencies, use the model for design evaluation and regulatory permitting actions. The model is also used for training and continuing research at more than 50 universities.