PERMFILE121316

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 39 MINE INFLOW ESTIMATES
• Media Type: D
• Archive: No

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Getty Task 2 Page 14 March 1, 19 g3
4.0 FIODEL CALIBRATION
Prior to simulating [he mine development and estimating inflows to the
mine, it was necessary to calibrate the model. Calibration consists of
selecting values of parameters so that the computer output matches some
historical record of squifer performance. Since historical data is
discontinuous and sketchy for most of the basin, it was assumed that the
system was nt steady-state for calibration purposes. It was necessary,
therefore, to select pa tame teas so that the Lead distribution calculated by
the model was similar to that presented oa Figure 1. Obviously, physical
parameters, such as aquiclude locations, cannot be modified. Ia general, the
hydrologic properties of the aquifer, storativity, permeability, and
recharge/discharge rates, are adjusted so that the desired head distribution
is maintained for long simnlatioa periods.
As the above indicates, calibration is essentially an optimization
problem of selecting the spatial distribution of three variables. To simplify
the calibration process, it was assumed that the storativity of the aquifer is
uniform. is space and equsl to 0.0001 for eonf ined conditions cad 0.01 for
Waco of ined eond itioas. A value of 0.0001 for the eo of iced storage caef fic feat
is near the average of the values obtained from aquifer tests conducted in the
Tweatymile Park Basin. An apparent specific yield of 0.01 is near the low cad
of values tabulated by Morris Wad Johnson (1967) for siltstoaes and fine
sandstones. Using these assumptions, the model was calibrated by imposing
constant head boundaries is those grids representing recharge/discharge areas
end adjusting the permeabilities to obtain the desired output heed
distribution. Upon reaching a satisfactory calibrati oa, the amounts of
recharge or discharge were calculated and the constant Lead grids were changed
to discharge/recharge boundaries for the subsequent calculations.
The Tweatym ile Park basin was overlain with a system of 2000 feet by 2000
feet grids. The grid system consists of 26 rows and 27 columns or a total of
702 nodes. The grid system is presented oa Figure 3. All grids outside the
aquifer boundary ere coded as impermeable boundary grids. Although the method
of calibration is a trial and error procedure, the measured pe rmeabil ities
(see Table 1) provide some guidance as to the spatial distribution of
permeability.