United States Environmental Protection Agency Environmental Research Laboratory Athens GA 30605-2720 Research and Development EPA/600/SR-93/082 June 1993 Project Summary A Subtitle D Landfill Application Manual for the Multimedia Exposure Assessment Model (MULTIMED) Susan Sharp-Hansen, Constance Travers, Paul Hummel, and Terry Allison The MULTIMED computer model simulates the transport and transfor- mation of contaminants released from a hazardous waste disposal facility into the multimedia environment. This re- port is an application manual for the use of MULTIMED In modeling Subtitle D land disposal facilities (as described in the Resource Conservation and Re- covery Act). For Subtitle D facilities, only the flow and transport components of MULTIMED are used in simulating leachate movement through the unsat- urated zone and transport in the satu- rated zone. A preprocessor guides the user In the creation of a correct Sub- title D input file by restricting certain options and parameters and by setting appropriate defaults. Instruction is pro- vided for inexperienced as well as ex- perienced model users who seek to study or design waste disposal facili- ties. This Project Summary was devel- oped by EPA's Environmental Research Laboratory, Athens, GA, to announce key findings of the research that Is fully documented In a separate report of the same title (see Project Report ordering Information at back). Overview The Multimedia Exposure Assessment Model (MULTIMED) simulates the move- ment of contaminants leaching from a waste disposal facility. The model in- cludes two options for simulating leachate flux. Either the infiltration rate to the un- saturated or saturated zone can be speci- fied directly or a landfill module can be used to estimate the infiltration rate. The landfill module is one-dimensional and steady-state, and simulates the effect of precipitation, runoff, infiltration, evapo- transpiration, barrier layers (which can include flexible membrane liners), and lateral drainage. To enhance the user-friendly nature of the model, separate interactive preprocess- ing and postprocessing software have been developed for use in creating and editing input and in plotting model output. The pre- and postprocessors, PREMED and POSTMED, have not been integrated with MULTIMED because of the size limi- tations of personal computers. Therefore, after using the preprocessor to create or modify input, the model is run in batch mode. Afterwards, the postprocessor can be used to produce plots of the Monte Carlo output or plots of concentration ver- sus time for transient output. Subtitle D Applications Some restrictions apply in the applica- tion of MULTIMED to Subtitle D facilities. These restrictions were made in an effort to develop a conservative approach for simulating leachate migration. First, only saturated and unsaturated modules may be used. Second, only steady-state or transport simulations are allowed. Third, no decay of the source term is allowed; the concentration of contaminants enter- ing the aquifer system must be constant in time. Fourth, the receptor must be lo- cated directly downgradient from the facil- ity so that it intercepts the center of the contaminant plume. Fifth, the contaminant concentration must be calculated at the top of the aquifer. Thus, MULTIMED can be applied at many Subtitle D land disposal facility sites to simulate the transport of contaminants from the source, through the saturated and unsaturated zones, to a receptor well. When MULTIMED is used in conjunction with a separate source model, such as y6 Printed on Recycled Paper ------- HELP, it can be used in a variety of appli- cations. These applications include (1) development and comparison of the ef- fects of different facility designs on ground- water quality, (2) prediction of the results of different types of "failure" of the landfill, and (3) prediction of the fate of the con- taminants in the subsurface if leachate migration into the groundwater below an existing waste disposal facility occurs. MULTIMED is not appropriate for all sites, however. Care should be taken to assure that the model is used appropriately. MULTIMED can be used in the design process to demonstrate that a particular configuration will adequately prevent con- taminant concentrations in groundwater from exceeding health-based thresholds. In other words, MULTIMED combined with a source model can be used to demon- strate that either a landfill design or the specific hydrogeologic conditions present at a site will prevent the migration of sig- nificant quantities from the landfill. In applying MULTIMED at a Subtitle D Facility, the user must (1) collect site-specific hydrogeologic data, (2) deter- mine the contaminant to be simulated and the active modules in MULTIMED and the point of compliance, (3) propose a landfill design and determine the corresponding infiltration rate, (4) run MULTIMED and calculate the dilution attenuation factor, and (5) determine whether the design is acceptable based on the resulting dilution attenuation factor. This application manual for the MULTIMED model and pre- and postprocessors, PREMED and POSTMED, is designed to be used by inexperienced as well as experienced users. Instructions are suggested for two types of inexperi- enced users—the "hands-on, learn-as-you- go" user and the "read the document first" user. An experienced user is defined as one who is already familiar with the basic capabilities and operational aspects of PREMED, MULTIMED, and POSTMED, and wants to use the programs to perform simulations. Obtaining MULTIMED Software The MULTIMED computer code may be obtained by sending a request to Model Distribution Coordinator, Center for Exposure Assessment Modeling, En- vironmental Research Laboratory, U.S. Environmental Protection Agency, Ath- ens GA 30605-2720. Please include ei- ther five 5.25-in (double-sided, double density, DS/DD 360KB) diskettes or two 3.5-in (double-sided, high-density, DS/HD 1.44MB, error free) diskettes. The MULTIMED code will be copied to your diskettes and returned to you. Model documentation is also available by send- ing two 3.5-in diskettes (DS/HD). A hard copy of the documentation is available from the National Technical Information Service (see box below). Susan Sharp-Hansen, Constance Travers and Paul Hummel are with AQUA TERRA Consultants, Mountain View, CA; Terry Allison is with Computer Sci- ences Corporation, Athens, GA. Gerard F. Laniak is the EPA Project Officer (see below). The complete report, entitled "A Subtitle D Landfill Application Manual for the Multimedia Exposure Assessment Model (MULTIMED)," (Order No. PB93- 185536; Cost: $36.50), will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Environmental Research Laboratory U.S. Environmental Protection Agency Athens, GA 30605-2720 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-93/082 ------- |