PERMFILE62071

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 35 Backfill Hydrology Evaluation
• Media Type: D
• Archive: No

• upper area
The rapid r
period also
of expected
the rest of
is transmitted to the down-dip areas fairly rapidly.
~sponse of the Pond F Spring to the 1986 snowmelt
supports this contention. Calculations may be made
storage charges during the snowmelt period and during
the year (Appendix II B).
We may assume that almost all the annual recharge to the eastern
backfill of about 3 inches occurs during the snowmelt period of
approximately 2 months. As indicated earlier, this recharge rate
over the eastern backfill area would amount to 1.5 x 10'ft~of
recharge (Appendix II A). Discharge during this period is
estimated to peak at about 2000gpm and averages about IOOOgpm.
For the two month period this would amount to 1.16 x 10' ft3of
discharge. For the given area of recharge, this rate of dis-
charge would be equivalent to about 2.5 inches during this
period. The excess of about 3.4 x 106ft'would go into ground-
water storage. Discharge for the latter part of the year when
no significant recharge is occurring is derived almost entirely
from storage. For a ten month period the average discharge from
storage would be expected to be about 58gpm. This is very close
to observed discharge rates.
The overall water balance for the eastern backfill groundwater
system appears to be good. This tends to support the conceptual
model of the groundwater flow system and various estimates of
• parameters used in the calculation.
FLOW NET. ANALYSIS
A flow net analysis was performed to evaluate whether the
conceptual model of the groundwater system could account for the
observed discharges given reasonable estimates of the various
parameters involved in the flow calculation (Appendix II C).
Although water level data for the backfill is limited, it is
reasonable to assume that groundwater flow follows the structural
dip of the underlying aquitard. The potentiometric map (Figure
5) was constructed based on elevations of discharge points and
water levels in spoil wells and also on the assumption that the
potentiometric surface essentially follows the structure of the
underlying bedrock. The map indicates that the hydraulic
gradient towards the discharge areas is about 0.08. This
gradient will increase to about 0.09 during the snowmelt recharge
period. The width of the eastern backfill area (perpendicular to
the predominant flow direction) is about 8000 feet. The satu-
rated thickness of backfill material ranges from about 100 feet
at the discharge area to close to zero about 3000 feet updip from
the discharge area. Permeability for the backfill material has
been estimated to range from 10'" to 10"5 ft/sec. The flow rate
through the backfill may be estimated from the equation;
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