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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Double Spring

Primary Investigator: Kip Allander

Well Data

USGS Site ID
Local Name Altitude Uppermost
Opening
Lowermost
Opening
Primary Aquifer Transmissivity
(ft2/d)
385755118412701 Double Springs 4064 50 ALLUVIAL FILL 10000

 

Aquifer Test

All Aquifer Test Files (zip)

Double Spring

Aquifer Test (pdf)

Introduction

Walker Lake has been declining at a rate of about 1.6 feet per year since 1917 resulting in total dissolved solids concentrations increasing to the point where the lakes fishery and ecosystem health are being threatened. Uncertainties in the water budget in the Lower Walker River Basin led the U.S. Geological Survey in cooperation with the U.S. Bureau of Reclamation to undertake a study to revise the water budget of Walker Lake. The study was initiated in 2004 and a revised water budget is scheduled to be published in 2009.

Developing a better understanding of the ground–water system in the Lower Walker River Basin is a critical component of this study. To understand how ground-water interacts with Walker Lake it is necessary to understand ground-water levels and aquifer properties in the alluvial aquifers adjacent to Walker Lake. It is planned to conduct a series of aquifer tests in the alluvial aquifers of the Lower Walker River Basin. Planned tests are 1) slug tests of monitor wells installed as part of this study, 2) analysis of historic slug test data (1979) on monitor wells installed on the Hawthorne Army Ammunition Depot, 3) a multiple well aquifer test on the Walker River Indian Reservation, and 4) a single well aquifer test on the Double Springs flowing well. This aquifer test analysis documents the methods, data, analysis, and results of the single well aquifer test on the Double Springs flowing well.

An aquifer test was performed on the Double Springs flowing well in the Lower Walker River Basin on April 28th and 29th, 2008 (Figure 1; site identification number 385755118412701). The local aquifer is an alluvial aquifer system with material originating from stream and lake alluvial processes.

Location of Double Springs well, seismic lines, and cross-section in the Lower Walker River Basin
Figure 1. Location of Double Springs well, seismic lines, and cross-section in the Lower Walker River Basin.

 

Site

The Double Springs well is an open-cased free-flowing well located approximately 6 miles east of Schurz (Figure 1) and is nearby to the naturally flowing Double Springs. The well was discharging freely at about 39 gpm on April 28th, 2008. The water flows from a split in the open top of the casing and spills out into a leaky trough (Figure 2). The water ponds up around the well and then flows a short distance to spread out over the corner of a nearby playa. The discharge from this well combined with the natural discharge from the nearby spring provides for a few acres of saltgrass and water and habitat for local wildlife and cattle.

Construction of the Double Springs well was in September of 1948 by the US Indian Service (now known as US Bureau of Indian Affairs) and was for stock water use (see drillers report in Appendix A). Figure 3 shows a conceptualized diagram of the well construction for Double Springs Well. The borehole was augured using a cable tool rig and was 7.1 inches in diameter by a total depth of 102 feet. A 7.1 inch steel casing with no perforations was installed down to 50 feet. The remainder of the depth of the hole is assumed to have been left open. According to the drillers report in Appendix A, there are two primary aquifer layers, each confined by a substantial thickness of clay. The first aquifer encountered by the driller was 17 feet of gravel and was beneath a 16 foot layer of clay that started at the surface. The quality of this aquifer was documented as bad artesian water and the well was not screened in this interval. The second aquifer was 26 plus feet of gravel starting at 76 feet below land surface and was confined by 24 feet of hard pan (?) and 19 feet of clay. On January 23 2007, the well was sounded at about 47 feet when using a down-hole camera to image the bottom of the well. The video collected from the bottom of the well showed coarse grained sand upwelling due to flow entering the well through the sediments at the bottom (Video 1). The video also showed a mixture of well rounded sand and gravel at the bottom of the well. When the camera was brought to the surface, a sample of the sand from the bottom of the well came up with it and was noted as being very well rounded, smooth, and coarse (~1 mm diameter) quartz, similar to a coarse beach sand. The bottom 55 feet of the hole has filled in, but because of the observation of upwelling coarse sand in combination with the substantial discharge, it is assumed that the 24 feet of open hole in the hard pan had stayed open and has filled in with highly permeable sand and gravel. The source of water to this well is assumed to be from the chief gravel aquifer that starts at 76 feet below land surface.

The actual depth of the transmissive gravel layer that is responsible for the relatively high discharge from the Double Springs well is unknown. However, the total depth of alluvium was estimated using seismic refraction in the vicinity of this well. Seismic refraction surveys along 3 transects were conducted during September 2006 (Figure 1). The average depth of basin fill below line 4, which is about 0.3 miles west of Double Springs, is approximately 1,600 feet. The estimated minimum depth of basin fill below lines 1 and 3 are approximately 700 and 600 feet respectively. In lines 1 and 3, an intermediate layer with an acoustic velocity between that of basin fill and bedrock was detected. This layer is interpreted as being tighter and less permeable than the slower velocity layer above it.

Photograph of Double Springs Flowing Well. View is to the northeast on April 29th, 2008 by Lindsay R. Burt
Figure 2. Photograph of Double Springs Flowing Well. View is to the northeast on April 29th, 2008 by Lindsay R. Burt.

 

Conceptualized diagram of the well construction for Double Springs Well
Figure 3. Conceptualized diagram of the well construction for Double Springs Well>

 

Procedure

The aquifer at the Double Springs well was tested by measuring the head response to repeated opening and closing of the discharge valve on the packer device. To accomplish this, a special device was constructed from large diameter PVC to seal over the outside of the open casing that allowed for the discharge of the well to be controlled while using a pressure transducer to measure pressure inside. For the purposes of this test and this analysis, this device is being called the packer device. The packer device, as well as all important measurements related to computation of head, is shown in Figure 4. A vented Greenspan PS2100 pressure transducer with pressure range of 0 to 2.5 meters was used to measure head pressure every two seconds inside of the packer device. Discharge from the packer device was measured on the first day using a ThermoFisher Scientific DCT7088 acoustic flowmeter with a logging interval of every minute. On the second day, the flowmeter malfunctioned so discharge from the packer device was measured using a calibrated bucket and stopwatch.

Upon arrival at the site, natural flow discharging from the open casing was measured using a stopwatch and a 5.4 gallon bucket (volumetric method). The packer device was then placed over the open well casing with the discharge valve left open. The inner-tube seal of the packer device was then inflated to the point where there was no flow leakage between the packer and well casing. The flowmeter was attached to the PVC discharge line in front of the riser to record the flow rate from the packer device (Figure 4). A riser was used to ensure that the water completely filled the discharge pipe at the location of the flowmeter, which is a requirement for acoustic flowmeters. Two volumetric measurements of flow were collected from the riser discharge to verify the accuracy of the flowmeter. A series of four tests of variable durations were then performed by simply turning the flow on and off for the well. The data was reviewed that evening and it was determined that another test was desired in which discharge would be shutoff over a longer period of time to allow head pressure to equilibrate longer. So the test was repeated the next day on April 29th, 2008.

On April 29th, 2008, all of the same procedures were followed except: flow was not measured out of the open casing, and discharge was measured only using the volumetric method and was directly from the discharge pipe from the packer device without the riser (Figure 4). This was due to the flowmeter no longer functioning. Additionally, during the afternoon portion of the test, a major windstorm made for difficult working conditions and resulted in poor quality volumetric measurements and noisy pressure transducer readings.

The data was looked at in more detail once returning to the office. A summary of this data is shown in Figure 5. The following corrections and procedures were applied to the data: Flowmeter data on the first day was adjusted, a two-second interval of discharge data was created for both days, and pressure data on the second day was smoothed.

The quality of the flowmeter measured discharge data on the first day of testing was fair but the magnitude needed to be adjusted. The variability of the flowmeter measurements was small but the overall magnitude did not compare very well with the volumetric measured discharge. This was due to the flowmeter not being calibrated by the rental company before being sent to us, which would have been a substantial additional cost to the rental. The flowmeter discharge record was adjusted so that it would agree with volumetric measured discharge by using a simple linear relation between the volumetric discharge and flowmeter discharge (Qflowmeter.0428 worksheet in doublsprings.xls workbook; appendix B).

Flowmeter discharge data was only recorded every minute while pressure data was recorded every two seconds. To get a two-second time interval discharge record for the corrected flowmeter data, a discharge record was synthesized using the pressure data as a surrogate. This was done by developing a simple relation between corrected one-minute flowmeter data and associated pressure data and applying that relation to the two-second pressure data record to get the synthetic discharge record (QvsP.0428 worksheet in doublesprings.xls workbook; appendix B). The resulting synthesized discharge data is shown in Figure 5.

A synthetic two-second discharge dataset was also developed for the second day of testing (Figure 5). This was done using similar methodology as on the first day data except the relation was developed between volumetric discharge data and pressure data instead of using flowmeter data (QvsP.0429 worksheet in doublesprings.xls workbook; appendix B).

The noisy pressure data from day two was smoothed by applying a simple 1-minute moving average (Figure 5). The aquifer test data was analyzed in the office using a spreadsheet developed by Keith Halford (Halford, written communication, May 23, 2008) which was based on principles from Theis (1935). The analysis focused on fitting the recovery curve on the second day after the well discharge was shut off (Table 1; DoubleSprings_StepTHEIS.xls workbook in appendix B) after accounting for the different stresses on the first day.

 

Instrumentation for Double Springs Flowing Well test
Figure 4. Instrumentation for Double Springs Flowing Well test.

 

Summary of aquifer test data collected on April 28 and 29, 2008
Figure 5. Summary of aquifer test data collected on April 28 and 29, 2008.

 

Table1. Results for Double Springs Well aquifer test (SiteID 385755118412701) on April 29, 2008.
Results for Double Springs Well aquifer test (SiteID 385755118412701) on April 29, 2008

 

Hydraulic Property Estimates

Transmissivity for the Double Springs well was 10,000 ft2/d using Theis analysis (Table 1). The source of water to the Double Springs well, as inferred from the drillers report and down-hole video, is from a sand and gravel layer. The total depth of the sand and gravel is unknown. The depth of saturated basin fill at this location is estimated at about 1,600 feet. This results in estimated hydraulic conductivity of about 6 ft/d. It is assumed, based on drillers reports from other wells drilled in the area, and from the geologic history and depositional environment of the area, the basin fill in this area is alternating between fairly permeable sands and gravels and low permeability clays.

 

 

 

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