2011-09-28_PERMIT FILE - C1982056A ‎(7)‎

• Permit No: C1982056A
• IBM Index Class Name: Permit File
• Doc Date: 9/28/2011
• Section_Exhibit Name: 2.04 Environmental Resources
• Media Type: D
• Archive: Yes

Pumped well data from Exhibit 9A indicates that the Wadge Overburden has an average permeability ranging from
0.01 to 0.1 ft/day, which is consistent with the low - yields observed in monitoring wells. The vertical permeability
of the confining units for the Wadge Overburden averages 0,1 ft/day, which is indicative of effective confinement
• and relative isolation from other ground water aquifers. Storage coefficient values calculated from pump tests
average 1.7 x104, which is within the normal range for a low- porosity, confined, artesian aquifer.
The recharge capacity of the Wadge overburden aquifer was calculated in the Eckman Park permit application
using the flow -net analysis method of Walton (1962) to be 50,OOQ gpd/sq. mi., equivalent to about 0.1 foot per
year. Calculation of aquifer recharge capacity was based'on the undisturbed overburden aquifer in the Eckman
Park area, where the potentiometric gradient is relatively steep in comparison to other portions of the ground water
basin. One factor that was not considered in this analysis is that much, of the overburden in this area is not
saturated and that the steep gradient is more a reflection of the structural dip of the lithologic units. Since there is a
direct relationship between the steepness of the potentiometric gradient and the actual aquifer recharge rate, the
resulting figure is considered to be a considerable overestimation of the actual recharge capacity over the entire
Wadge overburden aquifer.
A more reliable estimate of the recharge to the Wadge overburden aquifer may be based on the assumption that
recharge is approximately equal to calculated rates of total ground water flow in the Wadge overburden towards
the center of the Twenty rile Park Basin, which may be calculated from standard flow -net analysis. The flow -net
analysis was performed between the potentiometric contour elevations of 6,700 and 6,900 feet as shown on Map
13, Twentymile Park Hydrology. The average hydraulic gradient in this area is approximately 2 percent and the
width of the flow path perpendicular to flow, based on the 6,800 foot contour, is approximately 25,000 feet. An
average permeability for the Wadge overburden is about 0.3 gpd/sq.-ft. (0.04 ft/day), and an average thickness of
the aquifer is 75 feet. The standard flow -net analysis equation is:
Q = KhIL
where:
Q =Flow rate (gpd)
K = Permeability (gpd/sq. ft.)
H = Aquifer thickness (ft.)
I = Hydraulic gradient
L = Width of flow path perpendicular to flow (ft)
Substituting the above values into this equation yields an average flow rate of about 11,000 gpd (0.02 cfs).
Regional uplift of the Twentymile Park Basin during Pleistocene times has resulted in numerous northwest
trending fault zones, which displace the lithologic units. The major fault zones within the permit and adjacent area
are shown on the Twentymile Park Hydrology Map (Map 13). Field studies in which water levels in well adjacent
to fault zones were monitored during pump tests indicate that the faults tend to act as barriers to lateral ground
water movement. The potentiometric levels on either side of the fault zones reflect the vertical displacement of the
lithologic units. The restriction of ground water flow across fault zones tends to influence movement in a direction
parallel to the strike of the faults.
The storage characteristics of the Wadge overburden aquifer were evaluated in Permit 79 -177 (Pages 779 -51 and
779 -52). Using an equation developed by Lohman (1972) for storage capacity under typical hydrostatic pressure
conditions, the total storage capacity of the Wadge overburden aquifer over the entire area of the Twentymile Park
ground water basin was calculated to be 708,000 acre -feet.
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PR06 -07 2.04 -26 11/07/06