REP08636

• Permit No: M1993041
• IBM Index Class Name: Report
• Doc Name: APPENDIX B MODFLOW COMPUTER MODEL DATA
• Media Type: D
• Archive: No

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of 16 gpm (a recharge rate of 16 gpm equates to
approximately 15 inches of water per year over a pond area
of 2 acres) to 300 gpm.
~oncentual Scenario
Assuming a value of 10'5 cm/s for K, and upon review of water budget
information, the pond in the reclaimed area should experience an
average net loss of about 10 gpm annually (about 2040 cubic feat
per day.
Since the remainder of the area of the reclaimed pit is much larger
than the pond and the fill material will have a relatively high K,
the pond will recieve constant recharge for a considerable time. If
the net outflow of the system through the pond (acting as a sink)
continues to be greater than the net inflow, groundwater levels in
the reclaimed area will begin to drop. However, the water levels
in the reclaimed pit will not drop below the bottom of the pond and
will probably be maintained at some intermediate level (i.e.
between the original water table surface and the level of the pond
bottom, an assumed range pf about 15 feet). The post reclamation
groundwater surface would be such that gradients would become
steepest near the northern boundary of the reclaimed mine area
while gradients in the central and southern pertions of the pit
would flatten. Groundwater levels in the southern portion of the
pit may become slightly elevated due to the large contrast in K
near the southern reclaimed pit boundary. If the pond acts as a
sink, the groundwater system within the majority of the reclaimed
area (especially around the pond) may always be somewhat depressed
when compared to the regional flow system.
Numerical $imulation
In order to lend support to the conceptual modeling analysis, a
highly preliminary generalized numerical simulation was conducted
using the 3-dimensional model MoDFLOW (Mcdonald fi Harbaugh (1984).
The model consists of a variable-spaced one layer grid with 29 rows
and 17 columns. A copy of the model grid is included as attachment
2. The cells of the northern grid boundary were set as constant
heads while all other cells were set as active. The reclaimed area
was treated as an unconfined aquifer with a variably saturated
thickness of about 100 feet. The preliminary steady state numerical
simulation assumes that the K of the bedrock material immediately
surrounding the reclaimed pit is equal to .03 ft/d (10'5 cm/s).
The pond area which was incorporated into the simulation is located
5