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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USGS
Nevada Water Science Center
2730 N. Deer Run Rd.
Carson City, NV 89701

 

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ER-4-1 m1

Primary Investigator:

Well Data

USGS Site ID
Local Name Altitude (ft) Uppermost
Opening (ft)
Lowermost
Opening (ft)
Primary Aquifer Transmissivity
(ft2/d)
370625116030001 ER-4-1 m1 4158 2812 3035 CARBONATE ROCKS 56

 

Aquifer Test

All Aquifer Test Files (zip)

ER-4-1 m1

Aquifer Test (pdf)

Introduction

This memorandum documents the analysis of the ER-4-1 m1 multiple-well aquifer test in Yucca Flat at the Nevada National Security Site (NNSS). Goals of the analysis were to estimate the transmissivity of the lower carbonate aquifer (LCA) at well ER-4-1 m1 and to estimate drawdowns in observation wells from a multiple-well aquifer test in well ER-4-1 m1. The drawdowns estimated at observations wells documented in this text are not used to interpret hydraulic properties, but can be used to calibrate numerical groundwater-flow models..

The ER-4-1 m1 multiple-well aquifer test of the LCA was conducted by a private contractor, Navarro, from January 13, 2017 to February 17, 2017. The LCA is a regional carbonate aquifer that extends from Yucca Flat to groundwater discharge areas downgradient of the NNSS boundary. Borehole ER-4-1 is within the central corridor of underground nuclear testing in Yucca Flat.

A network of 27 pumping, observation, and background wells in Rainier Mesa, Yucca Flat, and Frenchman Flat were instrumented with pressure transducers by Navarro and the U.S. Geological Survey (USGS). Water levels were monitored continuously for potential drawdowns related to well development and aquifer testing in well ER-4-1 m1. About 1.7 million gallons of groundwater was withdrawn from the LCA in well ER-4-1 m1 during well development and testing.

Drawdowns were estimated at 17 observation wells using water-level models as described by Halford and others (2012). Water-level models were used because of the potential for drawdowns to be masked by environmental water-level fluctuations. Drawdown was detected in six wells: ER-6-1-2 m, ER-7-1, U-3cn 5, UE-7nS, UE-10j, and WW-2. Drawdown was not detected in 11 wells: ER-2-1 m, ER-2-2, ER-3-1-2, ER-5-3-2, ER-6-2, TW-7, TW-D, UE-1h, UE-1q, UE-1r, and WW-A. Hydrographs including estimated drawdowns, synthetic water levels from water-level models, measured water levels and residual (measured minus synthetic water levels) in the 17 observation wells as well as pumping rate time series are shown in Appendix A. The water-level models, aquifer test analysis, and supporting datasets are provided in Appendix B.

 

Location of ER-4-1 m1 pumping well and network of observation and background wells instrumented during aquifer testing.

Figure 1. Location of ER-4-1 m1 pumping well and network of observation and background wells instrumented during aquifer testing. Hydrostratigraphic unit definitions from Prothro and others (2009).

 

Table 1. Well location and construction data for pumping, observation, and background wells monitored during well ER-4-1 m1 development and testing, Nevada National Security Site.

[Well Name refers to the name of the well in the National Water Information System (NWIS) database, where the bold part of the name is shown on Figure 1 and used in the text of this document. Latitude and Longitude are in decimal degrees and referenced to North American Datum of 1983 (NAD 83); Ground surface altitude is the altitude of the well in feet above National Geodetic Vertical Datum of 1929 (NGVD 29); Depth to static water level is the water-level depth in the well in feet below ground surface (ft bgs); Top of open interval and Bottom of open interval correspond to the depth of the top and bottom of the open interval (interval can include well screen and gravel pack and/or open hole)].

 

Well Name Site Identifier Latitude Longitude Ground
surface
altitude,
ft
Depth
to static
water level,
ft bgs
Top of
open
interval,
ft bgs
Bottom
of open
interval,
ft bgs
Pumping Well
ER- 4-1 m1 370625116030001 37.1069 -116.0500 4,158 1,769 2,812 3,035
Observation Wells
ER- 2-1 main (shallow) 370725116033901 37.1253 -116.0628 4,216 1,725 1,642 2,177
ER- 2-2 o2 370831116035001 37.1419 -116.0639 4,273 2,410a 2,008 3,457
ER- 3-1-2 (shallow) 370116115561302 37.0192 -115.9367 4,407 2,014 2,208 2,310
ER- 3-3 p1 370349116021904 37.0636 -116.0386 4,054 1,667 2,630 3,193
ER- 3-3 p2 370349116021905 37.0636 -116.0386 4,054 1,653 2,203 2,507
ER- 3-3 p3 370349116021906 37.0636 -116.0386 4,054 1,444 118 1,940
ER- 4-1 p1 370625116030002 37.1069 -116.0500 4,158 1,052 118 2,375
ER- 5-3-2 365223115561801 36.8731 -115.9392 3,335 945 4,674 5,683
ER- 6-1-2 main 365901115593501 36.9839 -115.9939 3,935 1,544 1,775 3,200
ER- 6-2 365740116043501 36.9611 -116.0772 4,231 1,780 1,746 3,430
ER- 7-1 370424115594301 37.0733 -115.9961 4,246 2,394 1,775 2,500
TW- 7 370353116020201 37.0650 -116.0339 4,058 1,646 41 2,272
TW- D 370418116044501 37.0744 -116.0758 4,150 1,723 1,700 1,950
U - 3cn 5 370320116012001 37.0594 -116.0233 4,009 1,619 2,832 3,030
UE- 1h 370005116040301 37.0014 -116.0683 3,995 1,552 2,134 3,358
UE- 1q (2600 ft) 370337116033002 37.0603 -116.0592 4,081 1,655 2,459 2,600
UE- 1r WW 370142116033301 37.0283 -116.0592 4,042 1,616 2,319 4,182
UE- 4t 2 (1564-1754 ft) 370556116025406 37.0989 -116.0483 4,141 868 1,564 1,754
UE- 7nS 370556116000901 37.0986 -116.0033 4,367 1,968 1,707 2,205
UE-10j (2232-2297 ft) 371108116045303 37.1856 -116.0825 4,574 2,156 2,232 2,297
WW- 2(3422 ft) 370958116051512 37.1661 -116.0886 4,470 2,052 2,700 3,422
WW- A (1870 ft) 370142116021101 37.0369 -116.0372 4,006 1,599 1,555 1,870
Background Wells
ER- 8-1 (recompleted) 371248116032102 37.2133 -116.0567 4,820 2,293 1,947 2,863
ER-12-1 (1641-1846 ft) 371106116110401 37.1847 -116.1850 5,817 1,519 1,641 1,846
TW- 3 364830115512601 36.8083 -115.8581 3,484 1,104 165 1,860
TW- F (3400 ft) 364534116065902 36.7594 -116.1175 4,143 1,734 3,142 3,392

aEstimated steady-state water level at well ER-2-2 o2. Available water levels for this well are nonstatic.

Hydrogeology

Yucca Flat is underlain by three types of aquifers: alluvial, volcanic, and carbonate rock. The alluvial aquifers are underlain by a thick sequence of volcanic aquifers and confining units. Alluvial and volcanic aquifers contribute limited flow to the underlying carbonate aquifer because of a volcanic confining unit that acts as a flow barrier (Winograd and Thordarson, 1975).

Alluvial deposits form thin, localized aquifer systems in the Yucca Flat basin. Alluvial aquifers comprise poorly sorted gravels and sands derived from Tertiary volcanic and Paleozoic sedimentary rocks (Slate and others, 1999). Alluvial deposits increase in thickness from the margins to the center of the basin (Bechtel Nevada, 2006), and are unsaturated throughout most of Yucca Flat. However, alluvial aquifers have saturated thicknesses of up to 2,000 ft in areas along the central corridor of Yucca Flat (Fenelon and others, 2012). Observation well WW-A is the only well screened in the alluvial aquifer (Figure 1). Borehole ER-4-1 intersects 620 ft of unsaturated alluvial deposits (see well completion diagram in Appendix B).

Volcanic rocks form localized and regionally extensive aquifer systems throughout Yucca Flat. The majority of volcanic rocks were erupted during the Miocene from within the southwestern Nevada volcanic field (Winograd and Thordarson, 1975), which is located to the north and west in the Pahute Mesa-Oasis Valley and Alkali Flat-Furnace Creek Ranch groundwater basins (Figure 1). Regionally extensive volcanic aquifers comprise moderately to densely welded ash-flow tuffs. Localized volcanic aquifers comprise fractured vitric ash-fall tuffs and rhyolitic lava flows. Volcanic aquifers typically have saturated thicknesses of less than 500 ft (Fenelon and others, 2012). Observation wells TW-7, ER-3-3 p2, and ER-3-3 p3 are screened in volcanic aquifers (Figure 1).

A thick, regionally extensive volcanic confining unit forms a hydraulic barrier between the volcanic aquifers and underlying carbonate aquifer throughout most of the Yucca Flat basin. The volcanic confining unit comprises nonwelded ash-flow tuff, bedded tuff, and reworked tuffaceous sediments that are commonly zeolitized (Winograd and Thordarson, 1975). The saturated thickness of the volcanic confining unit typically ranges between 500 and 2,000 ft (Fenelon and others, 2012). The volcanic confining unit is absent in the western part of Yucca Flat, where volcanic aquifers directly overlie the lower carbonate aquifer. Wells ER-2-1 m, ER-4-1 p1, and UE-4t 2 are screened in the tuff confining unit.

Carbonate aquifers form localized and regionally extensive aquifer systems. The LCA3 is a localized carbonate aquifer in parts of Rainier Mesa and central Yucca Flat (Figure 1). The regional lower carbonate aquifer (LCA) occurs throughout Yucca Flat and large areas of southern Nevada. The LCA comprises a thick sequence of Paleozoic limestones and dolostones, and has a saturated thickness of more than 15,000 ft in some areas. Pumping well ER-4-1 m1 is open to 223 ft of the LCA (see well completion diagram in Appendix B), and the majority of observation wells are screened in the LCA (Figure 1).

Data Collection

Data were collected before, during, and after well development and aquifer testing. Continuously measured data include water levels, water temperature, and barometric pressure at the pumping, observation, and background wells (Table 1), and pumping rates in the pumping well. Water levels and temperature were measured using an INW PT12 pressure transducer, which has a pressure accuracy of + 0.05% of the pressure range. INW PT12 pressure transducers installed in distant observation wells and background wells had a pressure range of 0 to 30 psia, whereas pressure transducers installed in the pumping well and observation wells at borehole ER-4-1 had a pressure range of 0 to 2000 psia (accuracy of about 2.36 ft). The INW PT12 pressure transducer also has a temperature range of 0° to 55°C (32° to 131°F) with a temperature accuracy of + 0.5°C. Barometric pressure was measured using a PTB110 barometer, which has an accuracy of + 0.3 hPa at 20°C (68°F). A CR1000 Campbell Scientific datalogger was used to measure and record water levels, water temperature, and barometric pressure every 10 minutes or if a water-level change greater than 0.05 psi occurred. The Foxboro 8002A series flowmeter, which has a flow rate range of 13 to 250 gal/min and a flow rate accuracy of 0.029%, was used to measure pumping rates.

Water levels were analyzed for drawdown at 17 observation wells (Table 2). These wells are screened across a range of hydrostratigraphic units, and exist in opposing azimuthal quadrants from the pumping well (Figure 1). The horizontal distance between pumping and observation wells ranged from less than 1 to 17.2 miles (0.5 to 91,076 feet) (Table 2). The selection of observation wells analyzed for drawdown was sufficient to understand hydraulic connections between ER-4-1, screened in the LCA, and observation wells screened in the LCA, alluvial aquifer, and volcanic aquifer.

Water levels in observation wells ER-3-3 p1, ER-3-3 p2, ER-3-3 p3, ER-4-1 p1, and UE-4t 2 were not used in the drawdown analysis. Continuous water-level data in p1, p2 and p3 within borehole ER-3-3 have a two-month data gap (November-January) immediately prior to well development and aquifer testing, which precluded drawdown estimates in these wells. Water levels in well ER-4-1 p1 currently are recovering following well construction, and are not representative of hydrologic conditions in the aquifer system. Continuous water-level data in well UE-4t 2 had an anomalous rising trend during well development and testing that is not representative of hydrologic conditions in the aquifer system. The rising trend is formation equilibration as water in the wellbore equilibrates to low-transmissivity air-fall and bedded tuffs in the open interval of the well due to nearby nuclear testing (Halford and others, 2005; Elliott and Fenelon, 2010). Other wells screened in the tuff confining unit, such as wells ER-2-1 m, have equilibrated to the formation and water levels are representative of aquifer conditions.

The constant-rate aquifer test of well ER-4-1 m1 lasted about 243 hours and was conducted from 2/07/2017 09:34 to 2/17/2017 12:07 (Table 3). The discharge rate during the constant rate test averaged 71 gal/min with a total groundwater withdrawal of more than 1 million gallons. An additional 0.7 million gallons were pumped from ER-4-1 m1 for purposes of testing the pump function, well development and step-drawdown testing between 1/13/2017 and 2/06/2017, prior to the constant-rate test. Therefore, total withdrawal during well development and testing was 1.7 million gallons. Well development and aquifer testing of well ER-4-1 m1 are summarized in Table 3, and shown in Figure 2. Raw pumping data and a simplified pumping schedule are in the CleanData directory of Appendix B. All pumping is included in drawdown analyses where drawdown is estimated using water-level models.

 

Table 2. Distance and bearing of observation wells from pumping well ER-4-1 m1 during multiple-well aquifer testing, January-February 2017.

[Well name: name of well in USGS National Water Information System database, where bold part of name is used in text of this document;
Horizontal distance from pumping well: horizontal distance, in feet, from pumping well ER-4-1 m1;
Bearing relative to pumping well: true bearing, in degrees (referenced to 0°N), from pumping well ER-4-1 m1 to observation well.
Analyzed for drawdown?: Observation wells analyzed for drawdown or not analyzed for drawdown are denoted with a "Yes" or "No", respectively.]



Well Name Horizontal distance from
pumping well, in feet
Bearing relative to pumping well Analyzed for drawdown?
ER- 2-1 main (shallow) 7,642 331° Yes
ER- 2-2 o2 13,367 342° Yes
ER- 3-1-2 (shallow) 45,976 134° Yes
ER- 3-3 p1 16,119 168° No
ER- 3-3 p2 16,119 168° No
ER- 3-3 p3 16,119 168° No
ER-4-1 p1 0.5 270° No
ER- 5-3-2 91,076 159° Yes
ER- 6-1-2 main 47,689 160° Yes
ER- 6-2 53,673 188° Yes
ER- 7-1 19,915 128° Yes
TW- 7 15,974 163° Yes
TW- D 14,024 212° Yes
U - 3cn 5 18,958 156° Yes
UE- 1h 38,792 188° Yes
UE- 1q (2600 ft) 17,195 189° Yes
UE- 1r WW 28,738 185° Yes
UE- 4t 2 (1564-1754 ft) 2,972 171° No
UE- 7nS 13,940 103° Yes
UE-10j (2232-2297 ft) 30,140 342° Yes
WW- 2 (3422 ft) 24,298 333° Yes
WW- A (1870 ft) 25,750 172° Yes

 

Table 3. General pumping schedule of well ER-4-1 m1 during well development and aquifer testing in Yucca Flat, January-February, 2017.

[Start date/time and End date/time: Start and end date and time (Pacific Standard Time) of pumping from Navarro daily well development and testing reports.
Pumping duration: Time, in minutes, that pump was turned on.
Discharge rate: Approximate discharge, to the nearest gallons per minute, of the pumping well between the start and end time. Value estimated from Navarro daily well development and testing reports. Hyphens indicate a range of pumping rates during step-drawdown testing.
Total discharge: Approximate discharge, to the nearest gallon, of the pumping well between the start and end time. Value based upon data collected from in-line flowmeter.]



Start date/time End date/time Aquifer-test description Pumping duration Discharge rate Total discharge
01/13/2017 14:22 01/13/2017 14:24 Pump function test 2 17 25
01/17/2017 09:30 01/17/2017 09:49 Well development 19 31 580
01/17/2017 11:07 01/17/2017 11:25 Well development 18 35 635
01/17/2017 12:40 01/17/2017 15:32 Well development 172 37 6,055
01/18/2017 11:42 01/19/2017 09:31 Step drawdown test 589 50-70-42-30 42,349
01/19/2017 10:47 01/19/2017 14:54 Step drawdown test 367 40-50-59-67 12,850
01/19/2017 15:02 01/19/2017 15:06 Step drawdown test 4 61 206
01/19/2017 15:47 01/20/2017 09:01 Step drawdown test 1,094 50 50,649
01/20/2017 09:46 01/20/2017 09:55 Step drawdown test 9 50-24-40 202
01/20/2017 10:07 01/20/2017 10:19 Step drawdown test 12 50-23 276
01/20/2017 11:44 01/20/2017 14:09 Step drawdown test 265 50-95-48-110-48-70 7,482
01/20/2017 14:37 01/21/2017 09:35 Step drawdown test 1,198 57 65,239
01/21/2017 11:11 01/21/2017 11:40 Step drawdown test 29 84-50 1,563
01/21/2017 11:53 01/22/2017 08:15 Step drawdown test 1,222 49-30-55-78-55 65,028
01/22/2017 09:13 01/23/2017 09:16 Step drawdown test 1,443 50-70-90-45 73,507
01/23/2017 10:17 01/24/2017 07:13 Step drawdown test 1,256 50-70-90-45 65,168
01/24/2017 08:56 01/24/2017 12:43 Step drawdown test 227 50-70-50-70-50 11,734
01/25/2017 10:43 01/26/2017 07:54 Step drawdown test 1,330 50-70 87,372
01/26/2017 08:53 01/26/2017 09:56 Step drawdown test 63 48-37-27-65-49 2,961
01/26/2017 10:28 01/26/2017 10:36 Step drawdown test 8 50-27-50 285
01/26/2017 11:56 01/27/2017 07:53 Step drawdown test 1,197 46-65-50-70 77,204
01/27/2017 09:00 01/27/2017 15:20 Step drawdown test 500 60-70-90-80-90 28,991
02/01/2017 10:43 02/01/2017 14:08 Step drawdown test 325 50-70-90-50-65-90 12,575
02/01/2017 14:39 02/02/2017 07:57 Step drawdown test 1,038 90-50-70-90-80 85,050
02/06/2017 10:08 02/06/2017 10:28 Step drawdown test 20 80-39 1,066
02/06/2017 11:33 02/06/2017 11:46 Step drawdown test 13 39-73-40-74 718
02/06/2017 13:12 02/06/2017 14:38 Step drawdown test 86 70-39-71 4,796
02/07/2017 09:34 02/17/2017 12:07 Constant-rate test 14,553 71 1,027,594
Water levels in and (B) flow rate and cumulative discharge from well ER-4-1 m1 during pump function testing

Figure 2. (A) Water levels in and (B) flow rate and cumulative discharge from well ER-4-1 m1 during pump function testing, well development, step-drawdown testing and aquifer testing January 13-February 17, 2017. Pumping Data were binned into 204 pumping steps for use in the Theis transform model.

Drawdown Estimation Using Water-Level Models

Drawdowns from pumping well ER-4-1 m1 were estimated in observation wells using a water-level modelling approach described by Halford and others (2012). Water-level modeling was used to estimate drawdown because environmental (non-pumping) water-level fluctuations of more than 0.2 ft masked drawdown from pumping in observation wells. Drawdown was differentiated from environmental fluctuations by fitting measured water levels to a synthetic water-level curve. The synthetic curve is the sum of simulated environmental water-level fluctuations and the pumping signal.

Environmental water-level fluctuations were simulated using time series of barometric pressure, earth and gravity tides, and water levels from background wells ER-8-1, ER-12-1, TW-3, and TW-F. The background wells are assumed to be close enough to observations wells to be affected by similar environmental fluctuations, yet distant enough to be unaffected by pumping from aquifer testing. Water levels from background wells were critical because they were affected by tidal potential-rock interaction, barometric pressure, and seasonal or long-term climatic trends. These effects also are assumed present in the observation wells.

Responses from pumping well ER-4-1 m1 were modeled with a Theis transform of the pumping signal, where multiple pumping rates were simulated by superimposing multiple Theis (1935) solutions. Theis transforms serve as simple transform functions, where step-wise pumping records are translated into approximate water-level responses. Numerical experiments have confirmed that superimposed Theis transforms closely approximate water-level responses through hydrogeologically complex aquifers (Garcia and others, 2013).

Synthetic water levels were fit to measured water levels by minimizing the Root-Mean-Square (RMS) error of differences between synthetic and measured water levels (Halford and others, 2012). Amplitude and phase were adjusted in each time series used to simulate environmental water-level fluctuations (barometric pressure, water levels in background wells, and earth and gravity tides). Transmissivity and the storage coefficient were adjusted in the Theis transform model.

Synthetic water levels in the water-level models represented summed time series of earth tides, gravity tides, barometric pressure, recharge responses, and pumping responses. Earth and gravity tides were computed functions based on well-established theoretical equations (Harrison, 1971). Barometric pressure typically was measured at the well being analyzed and/or at the background well. Pumping responses were simulated with Theis transforms that used 204 simplified pumping steps in ER-4-1 m1 (Figure 2). These simplified steps were sufficient to calculate the pumping response in observation wells with Theis transforms. Total withdrawal during the period of well development and testing was 1.7 million gallons.

Drawdown estimates are the summation of Theis transforms minus residual differences between synthetic and measured water levels (Halford and others, 2012). The summation of all Theis transforms is the direct estimate of the pumping signal. Residuals represent all unexplained water-level fluctuations. These fluctuations primarily are random during non-pumping periods, but can contain unexplained components of the pumping signal during pumping periods.

Drawdown detection was classified as detected or not detected (Table 4) based on the signal-to-noise ratio. Signal and noise are defined herein as the maximum drawdown occurring in an observation well during an aquifer test and the RMS error, respectively. Drawdown was classified as detected where the signal-to-noise ratio was greater than or equal to 10 and recovery was observed. Drawdown was classified as not detected where the signal-to-noise ratio was less than or equal to 5, indicating drawdown (if any) could not be reliably differentiated from the noise. Drawdown would have been classified as ambiguous if the signal-to-noise ratio was between 6 and 9; however, computed signal-to-noise ratios did not occur in this range and no drawdowns were classified as ambiguous.

 

Table 4. Estimated drawdowns in observation wells from the ER-4-1 m1 aquifer test in Yucca Flat, January, 2017-February, 2017.

[Estimated maximum drawdown: Maximum drawdown was estimated by matching measured water levels in the observation well to a synthetic curve of non-pumping (environmental) and pumping responses. NA indicates results not available.
RMS error: Root-mean-square error between measured and synthetic water levels in water-level model.
Signal-to-noise ratio: ratio of estimated maximum drawdown (signal) to RMS error (noise).
Drawdown detection: Drawdown detection is classified as not detected, detected, or not analyzed (NA). Drawdown is not detected where the signal-to-noise ratio is ≤5, indicating drawdown cannot be reliably differentiated from the noise in the dataset. Drawdown is detected definitively where the signal-to-noise ratio is ≥10 and correlation between environmental fluctuations and pumping signals is unlikely.]



Well name Estimated maximum drawdown (feet) RMS
Error (feet)
Signal-to-noise
ratio
Drawdown detection
ER- 2-1 main (shallow) < 0.03 0.013 2 Not detected
ER- 2-2 o2 < 0.02 0.007 3 Not detected
ER- 3-1-2 (shallow) < 0.02 0.006 3 Not detected
ER- 3-3 p1 a NA NA NA NA
ER- 3-3 p2 a NA NA NA NA
ER- 3-3 p3 a NA NA NA NA
ER- 4-1 p1 b NA NA NA NA
ER- 5-3-2 < 0.02 0.008 3 Not detected
ER- 6-1-2 main 0.06 0.002 30 Detected
ER- 6-2 < 0.02 0.004 5 Not detected
ER- 7-1 0.06 0.003 20 Detected
TW- 7 < 0.01 0.004 3 Not detected
TW- D < 0.02 0.004 5 Not detected
U - 3cn 5 0.13 0.006 22 Detected
UE- 1h < 0.01 0.004 3 Not detected
UE- 1q (2600 ft) < 0.01 0.002 5 Not detected
UE- 1r WW < 0.02 0.006 3 Not detected
UE- 4t 2 (1564-1754 ft) c NA NA NA NA
UE- 7nS 0.08 0.002 40 Detected
UE-10j (2232-2297 ft) 0.04 0.002 20 Detected
WW- 2 (3422 ft) 0.02 0.002 10 Detected
WW- A (1870 ft) < 0.01 0.002 5 Not detected

a Water levels have a two-month data gap (November-January) prior to well development and aquifer testing, which precluded drawdown estimates in these wells.

b Water levels not used in drawdown analysis because levels were recovering following well construction and are not representative of hydrologic conditions in the aquifer system.

c Water levels not used in drawdown analysis because data show an anomalous rising trend during well development and testing that is not representative of hydrologic conditions in the aquifer system.

Estimated Drawdowns

Water levels were modeled from October 30, 2016 to April 1, 2017 to estimate drawdowns at 17 observation wells monitored before, during, and after the aquifer test. Synthetic water levels matched measured water levels with RMS errors between 0.002 and 0.013 ft in observation wells. Estimated drawdowns were classified as either detected or not detected (Table 4).

Estimated drawdown analysis results are shown in Figure 3. Drawdowns were detected in 6 wells: ER-6-1-2 m, ER-7-1, U-3cn 5, UE-7nS, UE-10j, and WW-2. Drawdowns were not detected in 11 wells: ER-2-1 m, ER-2-2, ER-3-1-2, ER-5-3-2, ER-6-2, TW-7, TW-D, UE-1h, UE-1q, UE-1r, and WW-A. Hydrographs showing estimated drawdowns in all observation wells are provided in Appendix A. Worksheets showing fitting parameters, measured and synthetic water levels, and drawdown estimates for analyzed wells in Table 4 are in individual Microsoft Excel workbooks in the WLM directory of Appendix B.

estimated drawdown results for observation wells from the ER-4-1 m1 aquifer test in Yucca Flat, January, 2017-February, 2017

Figure 3. Estimated drawdown results for observation wells from the ER-4-1 m1 aquifer test in Yucca Flat, January, 2017-February, 2017.

Aquifer Test Analysis

Estimated transmissivity of the LCA differs near and far from borehole ER-4-1. Drawdowns in the pumping well ER-4-1 m1 were interpreted using the Cooper-Jacob method (Cooper and Jacob, 1946). The period of analysis for estimating transmissivity spans the 10-day constant-rate aquifer test from February 7-17, 2017. On the semi-log drawdown-time plot (Figure 4), a break in slope occurs about 6 hours into the constant-rate test (25,000 gallons pumped). The estimated early-time transmissivity of the LCA is 250 ft2/d, which is representative of LCA transmissivity near borehole ER-4-1. The estimated late-time (1,000,000 gallons pumped) transmissivity of the LCA is 56 ft2/d, which is representative of LCA transmissivity farther from borehole ER-4-1. This result is counter-intuitive to estimated drawdown results. Estimated drawdowns were detected up to 9 miles from the pumping well at observation well ER-6-1-2 (Table 4), suggesting that the LCA transmissivity is high farther from borehole ER-4-1. The cause of the low estimated late-time transmissivity of the LCA is unknown.

Semi-log drawdown-time plot and straight-line approximations for estimating early-time or near-field (250 ft<sup>2</sup>/d) and late-time or far-field (56 ft<sup>2</sup>/d) transmissivity at well ER-4-1 m1 during the constant-rate aquifer test, February 7-17, 2017

Figure 4. Semi-log drawdown-time plot and straight-line approximations for estimating early-time or near-field (250 ft2/d) and late-time or far-field (56 ft2/d) transmissivity at well ER-4-1 m1 during the constant-rate aquifer test, February 7-17, 2017.

REFERENCES

Bechtel Nevada, 2006, A hydrostratigraphic model and alternatives for the groundwater flow and contaminant transport model of Corrective Action Unit 97-Yucca Flat-Climax Mine, Lincoln and Nye Counties, Nevada: U.S. Department of Energy Report DOE/NV/11718-1119, 288 p.

Cooper, H.H. and C.E. Jacob, 1946. A generalized graphical method for evaluating formation constants and summarizing well field history, Am. Geophys. Union Trans., vol. 27, pp. 526-534.

Elliott, P.E., and Fenelon, J.M., 2010, Database of groundwater levels and hydrograph descriptions for the Nevada Test Site area, Nye County, Nevada (version 7.0, October 2016): U.S. Geological Survey Data Series 533, 16 p.

Fenelon, J.M., Sweetkind, D.S., Elliott, P.E., and Laczniak, R.J., 2012, Conceptualization of the Predevelopment Groundwater Flow System and Transient Water-Level Responses in Yucca Flat, Nevada National Security Site, Nevada: U.S. Geological Survey Scientific Investigations Report 2012-5196, 72 p.

Garcia, C.A., Halford, K.J., and Fenelon, J.M., 2013, Detecting drawdowns masked by environmental stresses with water-level models, Groundwater, 51: 322 - 332.

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, (ver. 1.1, July, 2016): U.S. Geological Survey Techniques and Methods 4-F4, 28 p.

Harrison, J.C., 1971, New computer programs for the calculation of earth tides: Cooperative Institute for Research in Environmental Sciences, National Oceanic and Atmospheric Administration/University of Colorado.

Prothro, L.B., Drellack, S. L., and Mercadante, J.M., 2009, A Hydrostratigraphic System for Modeling Groundwater Flow and Radionuclide Migration at the Corrective Action Unit Scale, Nevada Test Site and Surrounding Areas, Clark, Lincoln, and Nye Counties, Nevada: National Security Technologies, LLC., Las Vegas, Nevada, 145 p.

Slate, J.L, Berry, M.E., Rowley, P.D., Fridrich, C.J., Morgan, K.S., Workman, J.B., Young, O.D., Dixon, G.L., Wil¬liams, V.S., McKee, E.H., Ponce, D.A., Hildenbrand, T.G., Swadley, W.C., Lundstrom, S.C., Ekren, E.B., Warren, R.G., Cole, J.C., Fleck, R.J., Lanphere, M.A., Sawyer, D.A., Minor, S.A., Grunwald, D.J., Laczniak, R.J., Menges, C.M., Yount, J.C., and Jayko, A.S., 1999, Digital geologic map of the Nevada Test Site and vicinity, Nye, Lincoln, and Clark Counties, Nevada, and Inyo County, California: U.S. Geological Survey Open-File Report 99-554A, 53 p., 1 pl., scale 1:120,000, accessed June 2011 at http://pubs.usgs.gov/of/1999/ofr-99-0554/.

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Appendix A. Estimated Drawdowns in Observation Wells

Appendix A contains hydrographs showing estimated drawdown analysis results of 17 observation wells monitored during the ER-4-1 m1 aquifer test. Hydrographs compare measured and synthetic water-level change, and show residuals, estimated drawdown, and groundwater withdrawals during aquifer testing at well ER-4-1 m1. Hydrographs presented for the 17 observation wells have estimated drawdowns classified as either detected or not detected, where the detection classification is provided on each hydrograph.

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

Graph of groundwater withdrawals

 

Appendix B. Water-Level Models, Slug Test Analysis, and Supporting Datasets

The water-level models, aquifer test analysis, and supporting datasets are in the compressed (zip) file, AppendixB_ER-4-1m1_AQtestPackage_2017. The zip file contains four directories: (1) AquiferTest; (2) CleanData; (3) WellCompletionDiagram; and (4) WLM.

The AquiferTest directory contains a macro-enabled Microsoft© Excel workbook that was used to estimate the transmissivity of the lower carbonate aquifer at ER-4-1. The DATA worksheet contains input data: continuous water-level data (in feet above the pressure transducer); and computed water-level change (drawdown). The COMPUTATION worksheet contains formulas used to compute aquifer hydraulic conductivity and transmissivity using the Cooper and Jacob (1946) method. The DEFAULT PROPERTIES and SETTINGS worksheet contains a reference table of extreme and likely ranges of hydraulic conductivity for different aquifer materials. The OUTPUT worksheet is used to input well construction information for computing hydraulic properties. The OUTPUT worksheet also shows a semi-log drawdown-time plot for the Cooper-Jacob analysis of the ER-4-1 m1 aquifer test.

The CleanData directory contains cleaned up time-series data used to estimate drawdowns and aquifer transmissivity. Time series data include observation-, pumping-, and background-well water levels and barometric pressure for 26 wells, and pumping rates for ER-4-1 m1. Raw data (not provided) for all wells, except ER-12-1, were obtained from Navarro. For each of the observation and background wells, a Microsoft© Excel workbook contains hourly averages of water level and barometric pressure data. Bad values (values equal to 99999 or 0) were removed from the raw time-series data prior to averaging.

The WellCompletionDiagram directory contains a Portable Document File (PDF) showing the well completion of borehole ER-4-1. Well completion diagram was obtained from Navarro (written communication, 2017).

The WLM directory contains 17 water-level models (macro-enabled Microsoft© Excel workbooks) used to estimate drawdowns at 17 observation wells during aquifer testing at well ER-4-1 m1. Water-level models were generated using a Microsoft© Excel add-in, SeriesSEE (Halford and others, 2012). Each Microsoft Excel workbook has three worksheets: DATA, Series, and WLmodel. The DATA worksheet contains the time-series data used in the water-level model. Data include time series of water levels from the observation well and background well(s), barometric pressure at the observation well, and pumping data. The Series worksheet contains the time series used in the water-level model. Time series include moving averages of background water levels and barometric pressure, Theis transforms of pumping in well ER-4-1 m1, and time series of gravity tides (in microgals) and solid Earth tides (dry dilation in ppb). Measured, synthetic, residuals, and estimated drawdown time series also are included in this worksheet. The WLmodel worksheet shows the parameters used in the water-level model, a plot of measured versus synthetic water levels and residuals, and the overall RMS error.

 

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