11.6. Seepage Component to Pit

MINEDW provides functions to compute pit seepage and visualize seepage locations. Pit seepage is recorded in an .SEP file, including seepage during mining operations and pit-lake formation. Seepage is recorded for each time step at each node forming the open pit. The “Seepage Component to Pit” function and .SEP file compute seepage by geological unit or other user-specified divisions. This output can be plotted or used in geochemical modeling for pit-lake chemistry predictions. The “Pit Flux” plot item and .SEP file visualize locations and relative magnitude of seepage at any time step after mining starts. This output assesses future dewatering needs and optimum locations for in-pit dewatering solutions. The following sections explain the “Seepage Component to Pit” function and “Flux” plot item.

11.6.1. Calculating Seepage to the Pit

The “Seepage Component to Pit” function computes total pit seepage and contributions from each geologic unit through time.

To compute seepage to the pit:

1. Click “Results” → “Seepage Component to Pit” on the Main Menu

2. Select the .SEP file from the folder where MINEDW was executed

3. Choose “Geological Units” to determine seepage rate from each geologic unit

4. Click the button at the bottom right to define output name and location

5. Enter a filename in the “Save Pit Flow File” dialog and click “Save”

6. Click “OK” to create the seepage file

Figure 11.7 The “Seepage Component to Pit“ dialog box

Figure 11.8 The “Save Pit Flow File“ dialog box

Import the created file to Excel or other graphing software to plot total seepage versus time (see Figure 11.9) and seepage from each geologic unit through time (see Figure 11.10).

Figure 11.9 Total seepage to the pit through time

Figure 11.10 Seepage rate from each geologic unit through time

11.6.2. Visualizing Seepage and Drains

As previously mentioned, it is possible to visualize the location where seepage to the pit is occurring, as shown in Figure 11.11. To do this, expand the “Post Processing” item under the “List” tab in the “Control Panel” Pane. Add a “Flux” plot item to the View Pane by double-clicking it. On the “Attributes” tab for the “Flux” plot item, select “+” next to the “File” attribute. In the “Select Flux File” dialog box that opens, change the type of file to “Seepage Flux Files (mdw_output.SEP)” using the drop-down list next to “Files of Type.” Now navigate to the location where the model was executed and select the file ending in .SEP. The nodes where seepage to the pit occurred are visible as colored squares. The colors indicate the magnitude of seepage occurring at the node forming part of the open pit. The size and color ramp can be modified on the attributes tab of the “Flux” plot item.

Figure 11.11 Visualizing seepage locations within the open pit

The “Flux” plot item can also be used to visualize the magnitude of flow through “Drain” boundary conditions. Seepage nodes that form the pit shell are considered drains and are automatically created when a mine plan is created (Mining Plan). “Drains,” in contrast, are created by the user and can be used to simulate sinks such as underground excavation, sub-horizontal drains, and sumps. The workflow for visualizing “Drains” is similar to the workflow for seepage, with one exception: instead of choosing “mdw_output.SEP,” select the “mdw_output.DRN” option if it is not already selected, then navigate to the .DRN file and select it. Flow through user-created drains is displayed in the View Pane. The size and color of the drain nodes can be altered using the “Contour” and “Point” attributes.