2016-01-27_HYDROLOGY - M1979059 ‎(2)‎

• Permit No: M1979059
• IBM Index Class Name: HYDROLOGY
• Doc Date: 1/27/2016
• Doc Name: Groundwater Modeling Report
• From: Weiland, Inc.
• To: DRMS
• Email Name: MAC
• Media Type: D
• Archive: No

2.5. INFILTRATION/SEDIMENT POND
The water produced during mining will be conveyed to the infiltration/sediment
pond, designated as Lake #5 in the model. This lake will not be connected to the
river via a pipe or sump. The infiltration pond will be cleaned and dredged as
needed to maintain the hydraulic connection with the sand and gravel aquifer.
2.6. ALLUVIAL WELLS
The model simulates two alluvial wells adjacent to Lake #5 using the WELL
Package in MODFLOW. These wells serve two purposes. They induce infiltration
of water from Lake #5 into the sand and gravel aquifer so that the lake does not
spill. The well water is pumped to the Big Thompson Ponds to replenish losses
caused by pit dewatering and maintain historic water levels
2.7. MODEL BOUNDARY CONDITIONS
The principle boundary conditions were prescribed heads at perimeter cells of
the model domain, and surveyed surface water elevations of the Big Thompson
River (measured June, 2003).
2.8. MODEL CALIBRATION AND STEADY STATE SIMULATION
The model was calibrated to simulate existing conditions. Calibration was
performed by varying the values for constant head boundary cells. This process
was repeated until the water levels from the model output matched the measured
heads to within about 10 percent of observed heads in both observation wells
and the surface water elevations of the lakes in the model (all surveyed in June
2003). The constant head boundary was selected as the calibration "variable
parameter" due to the fact that the hydraulic conductivity value is a required
office of the state engineer.
Table 1 summarizes the calibration of the model to 14 observation wells
measured by WI. The mean absolute difference (MAD) between measured and
simulated water levels is 1.1 feet and the root mean square (RMS) of the
differences is 1.36 feet. These MAD and RMS values represent 10 and 12.5
percent respectively of the total range water levels in our observation wells (10.9
feet).
Table 2 summarizes the calibration of the model to the 7 pond water surface
elevations (WSEL's) that were surveyed along with the edge of river elevations.
The mean absolute difference (MAD) between measured and simulated pond
WSEL's is 1.0 feet and the root mean square (RMS) of the differences is 1.2 feet.
These MAD and RMS values represent 8.5 and 10.1 percent respectively of the
total range of surface water elevations (11.8 feet)
Flying W Pit
Groundwater Modeling Report Revised June 28, 2005
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