Nevada Water Science Center


Aquifer Tests

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

 

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Nevada Water Science Center
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Carson City, NV 89701

 

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Wells ER-EC-15 main upper zone, ER-EC-15 main intermediate zone, ER-EC-15 main lower zone

Primary Investigators: Keith Halford and Steve Reiner

Well Data

USGS Site ID
Local Name Altitude Uppermost
Opening
Lowermost
Opening
Primary Aquifer Transmissivity
(ft2/d)
371110116310501 ER-EC-15 main upper zone 5365 1393 1739 VOLCANIC ROCKS 3200
371110116310501 ER-EC-15 main lower zone 5365 2157 2408 VOLCANIC ROCKS 40
371110116310501 ER-EC-15 main intermediate zone 5365 2807 3122 VOLCANIC ROCKS <20

 

Aquifer Test

All Aquifer Test Files (zip)

ER-EC-15 main upper zone, ER-EC-15 main intermediate zone, and ER-EC-15 main lower zone


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

 

Three aquifer tests were conducted by Navarro-Intera, LLC (N-I) in wells ER-EC-15 main upper zone, ER-EC-15 main intermediate zone, and ER-EC-15 main lower zone at Pahute Mesa on the Nevada National Security Site (NNSS) in southern Nevada (Figure 1). The three wells are three completions isolated with packers in a single wellbore. Transmissivities of Upper Paintbrush/Benham, Tiva Canyon, and Topopah Spring aquifers within the central Bench area were estimated independently because interference was not observed between wells in the ER-EC-15 well cluster site which includes the main well and three other wells: shallow, intermediate and deep (Table 1; appendix 1). Well ER-EC-15 main upper zone was pumped intermittently for purposes of well development and to perform a constant-rate pumping test between September 19, 2013 and October 29, 2013. Well ER-EC-15 main intermediate zone was pumped erratically between December 31, 2013 and January 8, 2014, because of excessive drawdowns in the pumping zone—the specific capacity was less than 0.1 gallons per minute (gal/min) per foot. Well ER-EC-15 main lower zone was pumped for purposes of well development and to perform a constant-rate pumping test between January 22, 2014 and February 18, 2014. Hydraulic properties estimated from aquifer tests in wells ER-EC-15 main upper zone, ER-EC-15 main intermediate zone, and ER-EC-15 main lower zone can be used to constrain estimates of radionuclide transport through volcanic rocks beneath Pahute Mesa, NNSS.

Figure 1.—Well construction, lithology, and location of ER-EC-15 well cluster,
Pahute Mesa, Nevada National Security Site and vicinity. (Observation and background
wells were monitored, but not used in this interpretation.)

Table 1.—Well location and construction data for analyzed wells in ER-EC-15 cluster,
Pahute Mesa, Nevada National Security Site.

 

Site and Geology

The aquifer tests occurred beneath Pahute Mesa in the northwest corner of NNSS where transport of radionuclides is a concern (Laczniak and others, 1996). The three wells that were monitored during aquifer testing at Pahute Mesa are completed in Tertiary volcanic rocks. The volcanic rocks of Pahute Mesa are dominated by lavas and tuffs of rhyolitic composition (Laczniak and others, 1996). Geologic structures at Pahute Mesa include normal faults with surface exposure and buried structural zones and caldera margins. The ER-EC-15 well cluster is located in the Bench area (Figure 1). Well ER-EC-15 main penetrates about 1,300 ft of unsaturated rock, and 2,000 ft of saturated rock where water enters from Upper Paintbrush, Tiva Canyon, and Topopah Spring aquifers (Figure 2). The lithologies of major water-producing hydrostratigraphic units in the aquifer-test area are stoney lavas, vitrophyric lavas, and moderately welded, ash-flow tuff (U.S. Department of Energy, 2011).

 

 

Figure 2.—Lithology, alteration, hydrogeology, and well completion at ER-EC-15 well cluster Pahute Mesa, Nevada National Security Site.

 

Pumping and Water-Level Changes

Well ER-EC-15 main has upper, intermediate, and lower screened intervals that were isolated with packers (Figure 2). The upper, intermediate, and lower screens of well ER-EC-15 main are coincident with the open intervals of wells ER-EC-15 shallow, intermediate, and deep, respectively. Upper, intermediate, and lower screens of well ER-EC-15 main primarily produce water from Upper Paintbrush, Tiva Canyon, and Topopah Spring aquifers, respectively.


Water-levels were measured in wells ER-EC-15 shallow, ER-EC-15 intermediate, and ER-EC-15 deep during development and testing of ER-EC-15 main upper, intermediate, and lower zones. Drawdowns in all wells were estimated by subtracting water levels prior to pumping from measured water levels. Environmental fluctuations (atmospheric loading and earth tides) during the tests were assumed minimal and were not accounted for in the drawdown calculation. Water-level changes from pumping were not observed in wells that were not screened adjacent to the pumping zone.


Approximately 1.6 million gallons were withdrawn from ER-EC-15 main upper zone for well development prior to the constant-rate pumping test. The constant-rate test lasted about 181 hours from 10/21/2013 to 10/29/2013. Discharge during the constant-rate test averaged 124 gal/min with a total groundwater withdrawal of about 1.3 million gallons. Total withdrawal during the period of well development and testing was about 2.9 million gallons (Figure 3). Maximum drawdown in well ER-EC-15 shallow, adjacent to the pumping well, during the constant-rate test was about 90 ft (Figure 3).

 

Figure 3.—Pumping from ER-EC-15 main upper zone during well development and aquifer
testing, September-October, 2013.

 

Less than 0.02 million gallons were withdrawn from ER-EC-15 main intermediate zone for well development and testing between 12/31/2013 to 1/10/2014. Step and constant-rate pumping tests were not conducted in this zone because it was not possible to maintain the low discharge rates (less than 10 gal/min) without pumping water levels falling below the pump intake. Water was pumped cyclically during 6 days of development (Figure 4). Each cycle consisted of pumping 500 gallons of water during a 40-minute period, water levels declining 150 ft in well ER-EC-15 intermediate, and recovering 60 minutes after pumping ceased.

 

Figure 4.—Pumping from ER-EC-15 main intermediate zone during well development and aquifer
testing, December 2013-January 2014.



Approximately 0.52 million gallons were withdrawn from ER-EC-15 main lower zone during well development and the constant-rate test pumping test. The constant-rate test lasted about 145 hours and was conducted from 2/12/2014 to 2/18/2014 (Figure 5). Discharge during the constant-rate test averaged 20 gal/min with a total groundwater withdrawal of about 0.2 million gallons.

 

Figure 5.—Pumping from ER-EC-15 main lower zone during well development and aquifer testing, January-February, 2014.

 

Analysis

Transmissivities of Upper Paintbrush/Benham, Tiva Canyon, and Topopah Spring aquifers (Figure 2; Table 2) were estimated independently because pumping effects were not observed in wells at the ER-EC-15 well cluster that were not adjacent to the pumping intervals associated with these aquifers. Drawdowns from pumping wells ER-EC-15 main upper zone and ER-EC-15 main lower zone were interpreted with the Cooper-Jacob method (Cooper and Jacob, 1946). Drawdowns from pumping well ER-EC-15 main intermediate zone was interpreted with superimposed Theis functions (Halford and others, 2012) because pumping rates varied continuously.

 

Table 2.—Transmissivity and hydraulic conductivity estimates at ER-EC-15 well cluster.

 

Based on late-time data, the estimated transmissivity from ER-EC-15 main upper zone aquifer test was 3,200 ft2/d (Figure 6). Transmissivity near the pumping well was about 100 ft2/d based on drawdowns during the first hour of pumping. More permeable material was encountered after the first hour of pumping which caused the semi-log slope to decline more than 30 times (Figure 6). The more permeable material could be attributed to the underlying Benham aquifer, lateral changes in the Upper Paintbrush, or both.

 

Figure 6.—Drawdowns and straight-line approximations during the constant-rate aquifer test of well ER-EC-15 main upper zone.

 

The estimated transmissivity from ER-EC-15 main lower zone aquifer test was 40 ft2/d (Figure 7). All of the transmissivity was attributed to the Topopah Spring aquifer because the semi-log drawdown curve was minimally deflected by leakage from adjacent units.

 

Figure 7.—Drawdowns and straight-line approximations during the constant-rate aquifer test of well ER-EC-15 main lower zone.

 

The estimated transmissivity from ER-EC-15 main intermediate zone test was less than 20 ft2/d. Water-level changes were simulated with superimposed Theis functions (Halford and others, 2012) and fit to three pumping and recovery cycles during well development (Figure 8). Water levels were modeled with superimposed Theis functions because steady periods of pumping did not occur and recovery periods were affected by return flow from the pumping column. Return flow was suspected because after each 8-hr period of development water-levels rose 3 to 20 ft higher than prior to a development period (Figure 4).

 

Flow from the aquifer to the well differed greatly from measured discharges at the surface because of wellbore storage effects. Wellbore storage was 1.35 gal/ft for the annular space between pipes of 5 and 7 5/8 inch diameters. Wellbore storage comprised about 200 gallons of the 500 gallons discharged at the surface during each pumping cycle. Flow from the aquifer was estimated by calculating changes in wellbore storage from measured water-level changes and subtracting wellbore storage rates from surface discharge rates (Figure 8).  Water-level changes were simulated with estimated flows from the aquifer.

 

Transmissivity of the Tiva Canyon aquifer is reported as less than 20 ft2/d because of uncertainties in flow from aquifer to the well. Simulated water-level changes fluctuate 100 ft which is less than 70 percent of the observed range of fluctuations (Figure 8). This suggests that transmissivity should be less than the estimate of 20 ft2/d. Further refinement was not pursued because estimated flow from aquifer to the well cannot be refined further.

 

Figure 8.—Measured water-level changes, simulated water-level changes, measured discharge at surface, and flow from aquifer during development of well ER-EC-15 main intermediate zone.

 

References

Cooper, H.H., and Jacob, C.E.. 1946. A generalized graphical method for evaluating formation constants and summarizing well field history. American Geophysical Union Transactions v. 27, pp. 526-534.

Halford, K.J., Fenelon, J.M., Reiner, S.R., and Sweetkind, D.S., 2011, Estimates of drawdowns from ER-20-7 and ER-20-8 main upper zone multi-well aquifer tests and simultaneous numerical analysis of four recent aquifer tests to estimate hydraulic properties on Pahute Mesa, Nevada National Security Site: U.S. Geological Survey Aquifer-Test Package, available at ‘Nevada Water Science Center Aquifer Tests’ webpage, accessed February 9, 2012, at http://nevada.usgs.gov/water/aquifertests/index.htm

Halford, K., Garcia, C.A., Fenelon, J., and Mirus, B., 2012, Advanced methods for modeling water-levels and estimating drawdowns with SeriesSEE, an Excel add-In, U.S. Geological Survey Techniques and Methods 4–F4, 28 p.
http://pubs.usgs.gov//tm/tm4-F4/

Laczniak, R.J., Cole, J.C., Sawyer, D.A., and Trudeau, D.A., 1996, Summary of hydrogeologic controls on ground-water flow at the Nevada Test Site: U.S. Geological Survey Water-Resources Investigations Report 96-4109, 59 p.
http://pubs.er.usgs.gov/publication/wri964109

Spechler, Rick M., and Halford, Keith J., 2001, Hydrogeology, Water Quality, and Simulated Effects of Ground-Water Withdrawals from the Floridan Aquifer System, Seminole County and Vicinity, Florida: Water-Resources Investigations Report 01-4182, 116 p.
ttp://fl.water.usgs.gov/Abstracts/wri01_4182_spechler.html

Theis, C.V., 1935, The relation between the lowering of the piezometric surface and the rate and duration of discharge of a well using groundwater storage: American Geophysical Union Transactions, v. 16, pp. 519-524.

U.S. Department of Energy, 2011, Completion Report for Well ER-EC-15 Corrective Action Units 101 and 102: Central and Western Pahute Mesa: U.S. Department of Energy Report DOE/NV--1449.

 

Appendix A. Construction diagram well cluster ER-EC-15

As-built diagram of the well completion for well cluster ER-EC-15 which includes the wells ER-EC-15 main, ER-EC-15 deep, ER-EC-15 intermediate, and ER-EC-15 shallow (U.S. Department of Energy, 2011).

Appendix is shown in the aquifer test PDF.

 

 

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