Toxic Transport Options

The toxic transport parameters and options are set using the form shown in Figure 1. The number of toxics included in the simulation are displayed in the top frame titled Major Settings. This can be changed by the user, but since boundary and initial conditions are predicated on the number of toxics, changing this value resets many of the toxics inputs. Therefore, this should only be changed when the user is prepared to reset all the initial and boundary conditions. A special case here is if the user sets the number to 0; then the toxics inputs are skipped for that project from that time forward.

To enable the simulation of toxics the Compute Toxics checkbox must be checked, and simulate toxics under the Active Modules tab must have been selected (ISTRAN(5) = 1). Each toxic type has many of its own settings so the user must first select the toxic to be edited/entered by using the drop down list in the upper left corner of the Toxic Transport Parameters frame. Once a toxic has been selected all the appropriate information is displayed on the form. The Toxic Name field is only used by EFDC_Explorer for labeling and information.

The series of tabs allow the user to define the toxics parameters in detail. In the Partition Coefficients tab the user should select the sorption model to be implemented from the radial buttons available, which include: Simple Kd; DOC and fraction of organic carbon x TSS (POC); DOC and POC; and fraction of organic carbon x TSS only. The contents of the grid (i.e., field) will change based on the partitioning model selected. The partitioning factors and the concentration factors units must be consistent. Typical units for the toxic concentrations are mg/kg or μg/kg.

Figure 1  Toxic Transport Options.

The Initial Conditions Options tab is shown in Figure 2. The initial conditions option for all toxics is set here for: constant water column and bed; spatially varying water column (requires TOXW.INP file); spatially varying bed conditions (requires in TOXB.INP file); and spatially varying for both bed conditions and water column (requires both TOXW.INP and TOXB.INP).  If a constant water column initial condition is being used then the text box under Water Column Constant IC frame is available. If a spatially varying water column is used then this option is greyed out. In the case when the spatially varying water column options are being used, the user should use the Assign button under Initial Conditions on the main form to set the varying water column values. 

Figure 2  Initial Condition Options - Toxic Transport Options.

The DOC & POC Assignments tab is shown in Figure 3. The Water Column DOC may be set to constant or vary spatially, in which latter case the user should use the DOCW.INP file to assign the constant time – spatially varying DOC. If the Sediment Bed DOC is set to be spatial varying, then the user must use the DOCB.INP file to assign the constant time – spatially varying DOC.

In the case of the Water Column POC, if set to Spatial Varying POC the user should use the POCW.INP file to assign the constant time – spatially varying POC. The spatially varying POC with fPOC option uses WC Seds and fPOC (Seds). The spatially varying POC/fPOC option uses WSeds and spatially varying fPOC from the FPOCW.INP file.

For the Sediment Bed POC, if set to Spatial Varying POC the user should use the POCB.INP file to assign the constant time – spatially varying POC. The spatially varying POC with fPOC option uses the bed sediments and fPOC (bed). The spatially varying POC/fPOC option uses WCSeds and spatially varying fPOC from the FPOCB.INP file. The Functional Specification of POC option means the user must modify the EFDC subroutine SETFPOCB to set POC in the bed.

Figure 3  DOC & POC Assignments - Toxic Transport Options.

The Loss Terms & Diffusion tab is shown in figure 4. Here the use sets the loss terms and diffusion coefficients for each of the toxic classes defined.

Figure 4  Loss Terms & Diffusion - Toxic Transport Options.