On the new Hydrologic Evaluation of Landfill Performance (HELP) model version 4 for the water balance simulation of landfill liner systems

23 years after the last original US HELP version 3.07, in 2020 Environmental Protection Agency released a new version, called 4. With this Excel-based model has arrived modern Windows world. However, itself remains 3.07. The papers deals with experiences of author using 4 and compares simulation results four versions (HELP 4.0.1, DOS 3.07 3.95 D included D) for two applications. First, RCRA example 3 (US) customary units 30 synthetically generated weather data Nashville, TN. Second, water balance test field F1 on landfill Georgswerder Hamburg, Germany, 1988 to 1995 metric units. user interface is easy use; however, it more restrictive than necessary not usable outside USA without having files import. average annual totals all tested are close together. Differences occur probably due computer numeric because 4.0.1 neglects day leap years. computing times factor about 50 larger D. Despite reasonable criticism that may be made, valuable tool those who aware its limitations merits enhancements match current state art.