PNNL-SA-32276
Written by: John P. McDonald

Prepared for the U.S. Department of Energy

Pacific Northwest National Laboratory
Operated by the U.S. Department of Energy
By Battelle



Requirements for the MEPAS Surface Water (Non-Tidal River) Transport Module

1.0 Introduction

This document describes the requirements for the Multimedia Environmental Pollutant Assessment System (MEPAS) surface water transport module. The module is specifically designed for inclusion in the Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES), which is a platform that allows the linking of various multimedia modules into complete source/transport/exposure assessment systems (Whelan et al. 1997). These requirements can be used by oftware engineers and testers to ensure this module meets the needs of the clients and users.

2.0 Purpose of the MEPAS Surface Water Transport Module

The purpose of the MEPAS surface water transport module is to simulate the migration and fate of chemical and radionuclide constituents through non-tidal rivers. Input to the module consists of time-varying contaminant mass fluxes entering the river, the physical characteristics of the river itself, and the constituent properties. Output consists of time-varying, contaminant aqueous concentrations at a point location along the same shoreline from which the contaminant entered the river. Currently, contaminant mass fluxes entering the river can originate from contaminated soil via overland runoff, discharge of a groundwater plume from an aquifer, or direct discharge into the river itself. The river’s physical characteristics are entered through a module user interface (MUI), and constituent properties are obtained from a constituent properties database. Contaminant aqueous concentrations can be used as input to an exposure module. The surface water transport module is designed to allow for linking to subsequent media (e.g., another river section or a wetland), should these features become a requirement for a later version of FRAMES. In addition, the output contaminant aqueous concentrations can also serve as the endpoint of the simulation.

3.0 Summary of Requirements for the MEPAS Surface Water Transport Module

This section provides an overall summary of the requirements for the MEPAS surface water transport module. Detailed input, output, and scientific requirements are described in Sections 4, 5 and 6 respectively.

The MEPAS surface water transport module will

  1. simulate contaminant migration for both chemicals and radionuclides through non-tidal rivers and provide output consisting of instantaneous, time-varying, contaminant aqueous concentrations at a point location along the same shoreline from which contaminants entered the river
  2. have no limits on the number of constituents considered in a scenario
  3. have no restrictions on the number of point locations along the river shoreline at which concentrations are computed
  4. operate under Windows 95 and have a user-friendly MUI with a standard Windows look and feel.
  5. meet the module specifications for FRAMES (described in Whelan et al. 1997).
4.0 Input Requirements for the MEPAS Surface Water Transport Module

Data needed to simulate contaminant migration through a non-tidal river is obtained from three sources. The boundary conditions (i.e., time-varying, contaminant mass fluxes entering the river and source dimensions) are obtained from the previous module (i.e., source term or aquifer), the river’s physical characteristics are obtained from the user through the MUI, and constituent chemical properties are obtained from a chemical property database. The boundary conditions are communicated to the module through the Water Flux File (WFF). The river’s physical characteristics are communicated from the MUI to the model through the Global Input Data (GID) file. The GID file is also used to store the chemical property data. The specifications for the WFF and GID file are described in Whelan et al. (1997).

There are some general requirements associated with the MUI, which are

  1. The MUI will operate in Windows 95 and will have a standard Windows look and feel.
  2. The MUI will have on-line help in an HTML format that provides users with an easy-to-understand description of all input parameters required by the MUI.
  3. The MUI will provide users with a choice of units for all input parameters having dimensions associated with them.
  4. The MUI will include a reference feature in which the source of the specified value for each input item can be referenced if the user desires.
  5. The MUI will show the range of values allowed for each input data item, when the cursor is positioned on that item, as a scrolling message at the bottom of the screen. When an out-of-range value is entered in a field, the MUI will indicate this by a red background in the input field and a scrolling error message in addition to the allowed range message. Data input values within range are shown with a green field background.
  6. The MUI will display the module version number, obtained from the module description (DES) file, in an "About" menu.
The following data are obtained from the WFF by the MEPAS surface water transport module. Those items listed as required are needed by the module to perform its computations. Other items are read in along with the required data. Because the WFF is a sequential text file, the module will read through unneeded data:
  1. time-varying, instantaneous, contaminant mass fluxes entering the river (required)
  2. width and height of the vertical rectangular area (i.e., a vertical plane along the river shoreline) through which contaminant enters the river (only the width is required)
  3. distance from the water table (or river surface) to the top of the rectangular area
  4. natural recharge rate
  5. time-varying, instantaneous water flux entering the river
The following data are obtained from the MUI and are needed by the MEPAS surface water transport module to perform its computations:
  1. river width
  2. river depth (i.e., thickness of water column)
  3. river flow velocity
  4. longitudinal travel distance (i.e., x-coordinate) from the center of the source to the point at which contaminant aqueous concentrations are computed
  5. river discharge at the receptor location.
The MEPAS surface water transport module obtains the following data from the chemical property portion of the GID file:
  1. CASID
  2. degradation/decay half-life
  3. decay chain (for radionuclides)
  4. solubility limit.
5.0 Output Requirements for the MEPAS Surface Water Transport Module

The MEPAS surface water transport module is required to output its results to a Water Concentration File (WCF) for contaminant aqueous concentration results. The module also is required to produce a list file (*.WLS file) that documents the data actually read in by the model and provide a summary of intermediate calculation results (e.g., decay constant and lateral dispersion coefficient) and the simulation results (peak concentration and time of peak).

The data output to the WCF for contaminant aqueous concentration results includes instantaneous, time-varying, contaminant aqueous concentrations for each receptor location along the shoreline.

6.0 Scientific Requirements for the MEPAS Surface Water Transport Module

This section lists the scientific requirements for the MEPAS surface water transport module. The primary scientific requirements are

  1. obey the Law of Mass Conservation
  2. simulate advection in one dimension
  3. simulate dispersion in one dimension (lateral or y-direction)
  4. account for the decay of radionuclides, and be able to handle the degradation of chemicals
  5. account for the ingrowth of progeny resulting from degradation/decay, and be able to handle decay chains with up to 9 members (i.e., one parent and eight progeny)
  6. compute contaminant aqueous concentrations at the river (downgradient)boundary
  7. consider the effect that inflowing tributary or groundwater (or the withdrawl of clean water from the river) between the source and receptor has on receptor concentrations.
The implementation of these requirements, in the form of mathematical formulations, is documented in Whelan et al. (1996).

7.0 References

Whelan, G., J. P. McDonald, and C. Sato. 1996. Multimedia Environmental Pollutant Assessment System (MEPAS): Groundwater Pathway Formulations. PNNL-10907, Pacific Northwest National Laboratory, Richland, Washington.

Whelan G., K. J. Castleton, J. W. Buck, G. M. Gelston, B. L. Hoopes, M. A. Pelton, D. L. Strenge, and R. N. Kickert. 1997. Concepts of a Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES). PNNL-11748, Pacific Northwest National Laboratory, Richland, Washington.