5.0 PROGRAM VERIFICATION
As stated at the end of Section 2.0, the "model" is
taken to include the conceptual hydrogeologic model, its
mathematical formulation and the computer program written
to solve the equations.    The computer program is further
described in Section 7.0.  This section presents the veri-
fication tests employed to insure that the equations are
properly solved by the computer program. This verification
process consists of a series of simulations which can be
checked by hand calculations.
The two processes modeled by the program are; (1) the
change in the groundwater table and (2) the transport of
seepage in the groundwater.     The change in groundwater
heads through time is simulated in the program by a finite
difference algorithm.   Verification of this algorithm is
provided by simulating simple drawdown and recharge cases
which can be checked by hand computations.    The drawdown
case is an infinite, homogeneous, isotropic, unconfined
aquifer   with   a   saturated    thickness  of    100 feet
(K=85 feet/day, S=0.05) from    which  2000 gpm  is  being
pumped.  Figure 5.1 shows the idealized aquifer, the simu-
lated solution and the hand calculated solution using the
Boulton method(8).    The simulated solution shows about
2 feet excess drawdown over the hand computed solution
50 feet from the well but the solutions match at 200 ft.
and beyond.   This difference is due to the discretization
of time and space of the finite difference solution.      A
grid spacing of 50 feet and an initial timestep of
0.001 days (increasing by a factor of 1.25 each cycle) was
used in the modeled analysis.    Closer grid spacing would
improve the match closer to the well. The recharge case is
an infinite, homogeneous, isotropic, unconfined aquifer
with   an   initial   saturated   thickness   of   100 feet
(K=0.5 feet/day, n=0.07) with infiltration being induced at

Golder Associates

786085

March, 1982

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