Nevada Water Science Center


Aquifer Tests

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Groundwater Specialist
Phone: (775) 887-7664
Email:pgardner@usgs.gov

 

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Nevada Test Site, UE-25 J-11

Primary Investigator: Robert Graves

Well Data

USGS Site ID
Local Name Altitude Uppermost
Opening
Lowermost
Opening
Primary Aquifer Transmissivity
(ft2/d)
364706116170601 UE-25 J-11 3442.8 1077 1300 VOLCANIC ROCKS 2400

 

Aquifer Tests

All Aquifer Test Files (zip)

UE-25 J-11

Aquifer Test (pdf) || Groundwater levels (NWISweb)

Introduction

Numerous aquifer tests have been conducted in and around the Nevada Test Site. Many of these tests have been completed in a fractured rock medium. Methods used to analyze these aquifer tests have included the Theis and Cooper-Jacob solutions. Although both methods are used to estimate aquifer characteristics in fracture media, the results may be qualified because both methods were developed for porous rock media. Recently, GeoTrans Inc., working in cooperation with the U.S. Department of Energy (DOE), evaluated time/drawdown data collected in wells drilled for DOE in the Oasis Valley area (ER-EC wells, completed in fractured volcanic rock) using a fractured-rock, double-porosity model (Moench, 1984). Based on this evaluation, it was thought that analyzing aquifer-test results from these wells with a dual-porosity solution would yield a better transmissivity estimate in these wells. Subsequently, individuals from GeoTrans Inc. identified approximately 62 wells in the vicinity of the Nevada Test Site with aquifer test data that could potentially be reevaluated with a fractured-rock, double-porosity model. Transmissivity estimates from these aquifer tests will support ground-water flow models being developed for DOE.

The U.S. Geological Survey (USGS) proposed to DOE to work in cooperation with GeoTrans Inc. to review these aquifer tests for the availability of aquifer-test data that might be suitable for reevaluation. Well UE-25 J-11 was one of the wells selected by the USGS for reevaluation. Transmissivity in well UE-25 J-11 has been estimated to be 3,700 ft2/d by Winograd and Thordarson (1975, p. C35, figure 22) from an aquifer test conducted on December 18, 1958. The aquifer-test data from this test were reanalyzed using the Cooper-Jacob solution (Cooper and Jacob, 1946) and Moench's dual-porosity spherical-shaped block and slab-shaped block solutions (Moench, 1984). Transmissivity estimates from each solution were compared.

Test Description

Well UE-25 J-11 is located in Area 25 of the Nevada Test Site (fig. 1). On December 18, 1958, at 3:46 pm (Pacific Standard Time, PST) the USGS began a single-well aquifer test on well UE-25 J-11 which lasted approximately 218 minutes (pump off at 7:25 pm, PST, on December 18, 1958) (USGS Project File). Average discharge during the test was 133 gallons per minute.

Winograd and Thordarson (1975, p. 35, figure 22) reported that prior to the December 18, 1958, test, a 72 hour step drawdown test had been conducted on well UE-25 J-11. The well was allowed to recover for 367 minutes following the step drawdown test and prior to the December 18, 1958, test. During the last 100 minutes of recovery, change in the well was only 0.20 feet. No adjustments to the drawdown data due to barometric, tidal, or temperature effects were made.

Test Site

Well UE-25 J-11 is located at 36° 47' 06" N.; 116° 17' 06" W., in Area 25 of the Nevada Test Site (fig. 1).

 

Location of well UE-25 J-11 on the Nevada Test Site
Figure 1. Location of well UE-25 J-11 on the Nevada Test Site.

 

Construction

Well UE-25 J-11 is a production well for water supply on the Nevada Test Site (Boucher, 1994, p. 1). The well was drilled to a depth of 1,330 feet. Drill start date was June 4, 1957, and completion date July 19, 1957. The borehole was completed from 0 – 1,327 feet with a 12-1/8 inch diameter casing. The casing is perforated from 1,077 to 1,300 feet below land surface (Boucher, 1994, p. 5).

 

Construction of well UE-25 J-11
Figure 2. Construction of well UE-25 J-11.

 

Hydrogeologic Characteristics

Savard (2001, p. 68) reported well UE-25 J-11 produces water from the basalt of Kiwi Mesa and from the welded-tuff aquifer, located within the Topopah Spring Tuff of the Paintbrush group. Belcher and Elliott (2001, Appendix A: Hydraulic-Properties Database, worksheet LFU) reported well UE-25 J-11 to be completed in vesicular basalt and welded ash-flow tuff of the basalt of Jackass Flats and Topopah Spring Tuff.

Cooper-Jacob Analysis

The Cooper-Jacob method (Cooper and Jacob, 1946), commonly referred to as the straight-line method, is a simplification of the Theis (1935) solution for flow to a fully penetrating well in a confined aquifer. Using the Cooper-Jacob method, a transmissivity was estimated to be 2,400 ft2/d by fitting a straight line to late-time drawdown data (fig. 3). Lohman (1979, p. 22) states that the Cooper-Jacob method is only valid when the well function of u is less than or equal to 0.01 (u = r2 S/4 T t, where r = distance to observation well, S = aquifer storage, T = aquifer transmissivity and t = time of pumpage). Assuming an r of 1 foot and S of 0.001, the criteria of a value of u less than or equal to 0.01 was met after the first second of pumping.

 

Measured, straight-line approximation, case (1) simulated, and case (2) simulated drawdowns for December 18, 1958, aquifer test conducted at well UE-25 J-11
Figure 3. Measured, straight-line approximation, case (1) simulated, and case (2) simulated drawdowns for December 18, 1958, aquifer test conducted at well UE-25 J-11.

 

Moench Analysis

General assumptions about aquifer geometry and hydraulic properties are similar for the Theis and Moench solutions. Common assumptions for both solutions are that aquifers are laterally infinite, have homogeneous and isotropic transmissivities, and are bounded by impermeable confining units. Production and observation wells are assumed to be fully penetrating so that all flow is horizontal. Transmissivity (T) and storage (S) are the same parameters in both solutions.

The Theis and Moench solutions differ in how the release of water from storage is simulated. Water is supplied from aquifer and water compressibility in the Theis solution, which is defined by a single parameter (S). Fractures and blocks of unfractured matrix provide two sources of water in the Moench solution. The first source is from fractures, which contribute water from aquifer and water compressibility in direct proportion to drawdown as defined by a single storage term (S). The second source of water is from the blocks of unfractured matrix that can release water at highly variable rates because the blocks are simulated as one-dimensional aquifers. The blocks of unfractured matrix are characterized by four parameters; slab thickness (2b'), (b' in table 2), fracture skin (Sf), matrix hydraulic conductivity (K'), and matrix specific storage (Ss') (fig. 4). The fracture network also can be conceptualized as spheres instead of slabs in the Moench solution where 2b' defines sphere diameter instead of slab thickness.

 

Schematic diagrams of Theis and Moench aquifers
Figure 4. Schematic diagrams of Theis and Moench aquifers.

 

The range of hydraulic properties that is expected for matrix blocks or slabs is dependent on how the dual-porosity system is conceptualized. Fracture intervals in welded tuffs that are predominantly vertical and recur in intervals of 10 ft or less suggest a spherical approximation of matrix blocks is reasonable. Matrix permeability would be similar to estimates from cores and would have a relatively limited range of expected values if the dual-porosity system were pictured as spheres. Flow logging and packer testing in wells at the Nevada Test Site suggest volcanic interbeds that recur in intervals of 100 to 1,000 ft are the primary permeable zones. This would suggest that the dual-porosity system could be conceptualized as slabs of 100 to 1,000 ft thick. Matrix permeability in the slab conceptualization could be much greater than estimates from cores because the ‘matrix’ also would be fractured, albeit less well connected than the interbeds.

Multiple conceptualizations of the dual-porosity system around well UE-25 J-11 were tested to determine the uniqueness of hydraulic property estimates. Hydraulic properties were estimated by minimizing the sum-of-squares difference between simulated and observed drawdowns after the first 20 minutes of pumping. Drawdowns from the first 20 minutes of pumping were not used because wellbore storage greatly affected these measurements.

Aquifer geometry was specified and all hydraulic properties except for transmissivity were constrained to reasonable ranges (table 2). Matrix blocks were assumed to have 10-ft diameters for the spherical solutions. Matrix blocks were assumed to have 500-ft thickness for the slab solutions. Matrix specific storage coefficients were limited to range from 10-7 to 10-5 ft-1. Matrix hydraulic conductivities were limited to range from 10-5 to 0.1 ft/d. The skin terms Sf and Sw were estimated, but were constrained to range from 0 to 100.

Estimates of S, b', Sf, K', and Ss' were not unique (table 2). Final estimates of the parameters that were estimated were highly dependent on initial estimates, except for transmissivity. Case 1 and Case 2 had RMS errors of 0.08 to 0.13 ft, respectively, which spans the range of RMS errors for all cases that were tested (table 2). Simulated drawdowns from all cases described the observed drawdowns equally well (fig. 3). Although some simulated drawdowns differed significantly for times later than when measurements existed.

 

Table 1. Parameter estimates and fitting error for multiple Moench solutions to the observed drawdowns in well UE-25 J-11.

Parameter estimates and fitting error for multiple Moench solutions to the observed drawdowns in well UE-25 J-11

 

Conclusions

Transmissivity could be reasonable estimated around well UE-25 J-11 with either Cooper-Jacob or a Moench solution from aquifer-test results. Estimates of transmissivity determined for this report using the Cooper-Jacob solution were not significantly different from those determined by the Moench solution. The best estimate of transmissivity is considered to be 2,400 ft2/d, but reasonable matches using the Moench solution between simulated and measured drawdowns were observed for transmissivity estimates that ranged from 600 to 2,700 ft2/d. Because of the short duration of testing, the best estimate of transmissivity will be biased above the actual value if the test was of insufficient duration to reach the final limb of a dual-porosity response.

Final estimates of parameters b', S, Ss, K', Ss', and Sf were dependent on initial estimates and could not be estimated uniquely. Estimates of matrix hydraulic conductivity (K') and fracture skin (Sf) could range over more than four orders of magnitude for models that matched the observed drawdowns equally well.

 

 

 

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