The Hydrologic Evaluation of Landfill Performance (HELP) Model for the simulation of the water balance of landfill liner systems

The HELP Model

The "Hydrologic Evaluation of Landfill Performance" (HELP) model was developed since 1982 by Dr. Paul Schroeder (U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi) and several contributors for the U.S. Environmental Protection Agency (EPA). HELP version 1 was released in 1984, version 2 in 1988 and version 3 in 1994 (Schroeder et al. 1994a,b), current original version (March 2006) is HELP 3.07. The HELP model is a "quasi-two-dimensional" layer model for estimating the water balance of open and closed landfills and especially of liner systems. Primary purpose is the comparison of design alternatives as jugded by the water balance under the climate of the particular site. HELP models several hydrologic processes using an one-day time step. Vertical and lateral processes are combined, but a two-dimensional flow actually is not modeled (quasi-two-dimensional). As input data HELP requires daily values of precipitation, air temperature and solar radiation of at least 1 and up to 100 complete calendar years, parameters to calculate evapotranspiration, data of soil and material properties, and data of the layer design and the site. The only vegetation considered are grasses, alternatively the soil may be bare. The layer profile must be constant during a simulation run. (In HELP 3.80 D soil and material properties and the vegetation parameters can be changed in a simulation run, and the estimation of the evapotranspiration of shrubs and trees is more realistic).

For HELP version 3 (Schroeder et al. 1994a,b) an extensive validation study under German climate was performed and the model was adapted for usage in Germany (Berger 1998). In the validation study limitations of HELP and several, partly severe errors were shown, conclusions for the user were drawn and approaches for an enhancement and further investigations needed were pointed out (see Berger 2000, 2002).

In a working group of the German Society for Geotechnics which accompanied the validation study the so called GDA-recommendation E 2-30 "Modeling the water balance of surface cover systems for landfills" (only in German) was written that deals especially with recommendations for the usage of HELP in Germany. Furthermore, the working group developed the GDA-recommendations E 2-31 and E 2-32 dealing with the design of top soil layers and the vegetation.

On September 8th, 2000 the working group and the Institute of Soil Science organized the symposium "Water balance of surface cover systems for landfills and contaminated sites" to discuss the GDA-recommendations E 2-30, E 2-31 and E 2-32. The symposium proceedings were released in the Hamburger Bodenkundliche Arbeiten (only in German).

Based on the results of the validation study and further investigations in the following years the enhanced (German) HELP versions 3.50 D (2001), 3.55 D (2002) and HELP 3.80 D (2004) were developed. In these versions errors were corrected, the model was enhanced, the user interface was completely reprogrammed and the documentation was revised.

Enhanced (German) HELP version

In the German enhancement HELP-D (current version HELP 3.80 D, Berger & Schroeder 2004; released May 2004) errors found in the validation study were corrected and some of the submodels were enhanced or replaced (actual evapotranspiration, vegetative growth and decay, frozen soil, unsaturated/saturated vertical flow in vertical percolation layers). Furthermore, HELP 3.80 D allows the user to change vegetation and soil properties in a simulation run to simulate the aging of a landfill profile e.g. the succession of the vegetation or the deterioration of lateral drainage layers due to clogging or of mineral liners due to desiccation and shrinkage.

The user interface was completely reprogrammed and some functionality was added. The user interface and the program output are in English, online help and most documents in German. For an easy postprocessing of the simulation results HELP 3.80 D outputs the daily, monthly and yearly simulation results as tables in separate output files. Soil textures and weather input options of HELP 3.07 are available. Like the current original version HELP 3.07, HELP 3.80 D is a DOS program. However, the simulation module of HELP 3.80 D requires Windows (9x or above).

The enhancements in more detail (see also Berger 2002, and the supplement to the Engineering Documentation):

• The user interface was completely reprogrammed and some functionality was added (e. g. to support a simple project management; new function keys for spreadsheet editing; clipboard; tilde in file names to allow DOS 8.3 file names; systematic file IO error checking). However, the look and feel is like in HELP 3.07.
• Since version 3.50 D HELP supports a simple project management. The HELP installation directory and the working directory of a project may (and should) be different. The simulation control files can be named and stored for later reuse.
• HELP 3.80 D outputs the daily, monthly and yearly simulation results as tables in separate output files. The daily output no longer occurs in the standard output file.

• The HELP source code of the simulation routines (HELP3O.FOR) was revised from a software technical point of view.
• Two implementation errors in the submodel of unsaturated/saturated flow in vertical percolation layers were fixed.
• The lowest water content for unsaturated vertical flow in the evaporative zone was set to field capacity.
• A systematic error that occurs in some designs with drainage nets directly above the uppermost liner does no longer occur in HELP 3.55 D due to the changing of the lowest water content for vertical flow. This error leads to a drastic underestimation of evapotranspiration.
• The frozen soil submodel was pragmatically enhanced (shorter periods with frozen soil for Germany, freezing and thawing of the soil for just one segment per day), leading to a more realistic estimation of surface runoff and a better time distribution of lateral drainage in the drainage layer below the topsoil.
• The submodels of evapotranspiration and vegetative growth and decay were enhanced:
  • The interception submodel was replaced by an adapted empirical model of von Hoyningen-Huene. This model was developed for several crops and includes an interception storage.
  • Some errors in the soil evaporation submodel were fixed leading to a more realistic relation between soil evaporation and transpiration and a more realistic influence of the vegetation on evaporatranspiration.
  • The implementation of the vegetative growth and decay model was completed and the decrease of plant growth due to short air (aeration stress) was added from the model EPIC. In HELP 3.80 D the vegetative decay model was corrected and enhanced.
• Subsurface inflow into layers is no longer allowed in some cases that lead to invalid water balance results. In HELP 3.80 D the summary output is correct also if monthly and yearly output were not selected.
• HELP 3.80 D allows the user to change vegetation and soil properties in a simulation run to simulate the aging of a landfill profile. However, these processes are actually not modeled, and the layer (type) sequence must be constant. The user can input up to 10 sets of evapotranspiration and/or soil and design data per simulation run.

More information on the German HELP version is only available in German.

Order of HELP-D

HELP 3.80 D is available for a price of EUR 119.- including shipping inside of Europe and the German sales tax (add EUR 17.85 for shipping outside of Europe including the German sales tax); please contact Dr. Klaus Berger, Institute of Soil Science (Order for a price of EUR 119.- (inside Europe) / EUR 136.85 (outside Europe)).

HELP support

The author offers support for registered users of the German HELP version and collects application experiences (e. g. unexpected results, errors ...).

References

• Berger, K., 1998: Validierung und Anpassung des Simulationsmodells HELP zur Berechnung des Wasserhaushalts von Deponien für deutsche Verhältnisse. Umweltbundesamt, Fachgebiet III 3.6 (PT AWAS des BMBF), Berlin, 569 pp. (in German, out of print)
• Berger, K., 2000: Validation of the Hydrologic Evaluation of Landfill Performance (HELP) Model for Simulating the Water Balance of Cover Systems. Environmental Geology 39 (11), pp. 1261-1274 (Article in pdf format online available at Springer-Verlag)
• Berger, K., 2002: Potential and Limitations of Applying HELP Model for Surface Covers. Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management, Vol. 6, No. 3, July 2002, pp. 192-203
• Berger, K. & P.R. Schroeder, 2004: Das Hydrologic Evaluation of Landfill Performance (HELP) Modell. Benutzerhandbuch für die deutsche Version 3. Unter Mitarbeit von N.M. Aziz, C.M. Lloyd, P.A. Zappi. 4., überarb. Aufl. für HELP 3.80 D (4th, revised edition for HELP 3.80 D). Institut für Bodenkunde der Universität Hamburg (Institute of Soil Science, University of Hamburg, 117 pp.)
  (CD, including HELP program and four electronic documents in pdf format, three documents are in German, one in English; HELP user interface and program output are in English, online help in German; soil textures and weather input options of HELP 3.07 are available.)
  Berger, K., 2004: The Hydrologic Evaluation of Landfill Performance (HELP) Model. Engineering Documentation for HELP 3.80 D - Enhancements Compared to HELP 3.07 -. Institute of Soil Science, University of Hamburg, 10 pp.
• GDA-Empfehlung E 2-30, 2003: Modellierung des Wasserhaushalts der Oberflächenabdichtungssysteme von Deponien. Current version (in German)
• Melchior, S., K. Berger, B. Vielhaber & G. Miehlich, 1994: Multilayered Landfill Covers: Field Data on the Water Balance and Liner Performance. In: Gee, G.W. & N.R. Wing (Ed.): In-Situ Remediation: Scientific Basis for Current and Future Technologies. Thirty-Third Hanford Symposium on Health and the Environment, November 7-11, 1994, Pasco, Washington, U.S.A., Part 1, pp. 411-425
• Schroeder, P.R. et al., 1994: The Hydrologic Evaluation of Landfill Performance (HELP) Model. 2 Volumes: User's Guide for Version 3; Engineering Documentation for Version 3; EPA/600/R-94/168a,b; US Environmental Protection Agency, Cincinnati, Ohio (free download from the WES website)