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

This section provides an overall summary of the requirements for 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. Detailed input, output, and scientific requirements are described in the sections that follow.

The MEPAS Surface Water Transport Module will

• G1 - 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
• G2 - have no limits on the number of constituents considered in a scenario
• G3 - have no restrictions on the number of point locations along the river shoreline at which concentrations are computed
• G4 - operate under Windows 95, 98, 2000, NT, ME, and XP and have a user-friendly MUI with a standard Windows look and feel.
• G5 - meet the module specifications for the Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES), described in Whelan et al. 1997 (PNNL-11748).

Input Requirements of the MEPAS Surface Water Transport Module

Data needed to simulate contaminant migration through a non-tidal river is obtained from three sources. The previous module (i.e., source term or aquifer) provides the boundary conditions (i.e., time-varying, contaminant mass fluxes entering the river and source dimensions), which are communicated to the module through the Water Flux File (WFF). The user through the module user interface (MUI) provides the river's physical characteristics, which are communicated from the MUI to the model through the Global Input Data (GID) file. A chemical property database provides the constituent chemical properties. The specifications for the WFF and GID file are described in Whelan et al. 1997 (PNNL-11748).

General requirements associated with the MUI are

• M1 - The MUI will operate in Windows 95, 98, 2000, NT, ME, and XP and will have a standard Windows look and feel.
• M2 - The MUI will have online help in an HTML format that provides users with an easy-to-understand description of all input parameters required by the MUI.
• M3 - The MUI will provide users with a choice of units for all input parameters having dimensions associated with them.
• M4 - The MUI will include a reference feature in which the source of the specified value for each input item can be referenced if desired.
• M5 - 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 indicated by a green field background.
• M6 - The MUI will display the module version number, obtained from the module description (DES) file, in an "About" menu.

The MEPAS Surface Water Transport Module obtains the following data from the WFF. 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:

• time-varying, instantaneous, contaminant mass fluxes entering the river (required)
• width and height of the vertical rectangular area (i.e., a vertical plane along the river shoreline) through which contaminants enter the river (only the width is required)
• distance from the water table (or river surface) to the top of the rectangular area
• natural recharge rate
• time-varying, instantaneous water flux entering the river.

• river width
• river depth (i.e., thickness of water column)
• river flow velocity
• longitudinal travel distance (i.e., x-coordinate) from the center of the source to the point at which contaminant aqueous concentrations are computed
• river discharge at the receptor location.

• CASID
• degradation/decay half-life
• decay chain (for radionuclides)
• solubility limit.

Output Requirements of the MEPAS Surface Water Transport Module

The MEPAS Surface Water Transport Module has the following output requirements:

• O1 - provide its results to a Water Concentration File (WCF) for contaminant aqueous concentration results
• O2 - produce a list file (*.WLS file) that documents the data actually read in by the model and summarizes intermediate calculation results (e.g., decay constant and lateral dispersion coefficient) and the simulation results (peak concentration and time of peak).

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

Scientific Requirements of the MEPAS Surface Water Transport Module

The primary scientific requirements are

• S1 - obey the Law of Mass Conservation
• S2 - simulate advection in one dimension
• S3 - simulate dispersion in one dimension (lateral or y-direction)
• S4 - account for the decay of radionuclides and be able to handle the degradation of chemicals
• S5 - account for the ingrowth of progeny resulting from degradation/decay and be able to handle decay chains with up to nine members (i.e., one parent and eight progeny)
• S6 - compute contaminant aqueous concentrations at the river (downgradient) boundary
• S7 - consider the effect of inflowing tributary or groundwater (or the withdrawl of clean water from the river) between the source and receptor on receptor concentrations.

The implementation of these requirements, in the form of mathematical formulations, is documented in Whelan et al. 1996 (PNNL-10907).  

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