2015-08-18_PERMIT FILE - C1982056A ‎(4)‎

• Permit No: C1982056A
• IBM Index Class Name: Permit File
• Doc Date: 8/18/2015
• Section_Exhibit Name: 2.04 Environmental Resources
• Media Type: D
• Archive: Yes

monitoring variations in water levels and flows in adjacent observation wells with continuous water level and
discharge recorders.
Characteristics of the Wadge Overburden determined for specific monitoring wells in the permit and adjacent area are
summarized in Exhibit 9D, Aquifer Test Data. The highest permeability values for the Wadge Overburden (0.3 and
0.6 ft/day) are calculated from observation well data (Wells 006- 82 -74A and 74C), and may reflect effects of using
radial -flow theory in a fracture -flow situation. Unless the observation wells are in good communication with the
major fractures providing flow to the pumped well, then less drawdown in the observation well will occur and
overestimates of permeability from the data will result. Pumped well data are often better indicators of average
formation permeability in fracture- dominated systems.
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
x10 -4, 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 50,000 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 Twentymile 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 wells 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.
TR13 -83 2.04 -26 11/03/14