Nevada Water Science Center


Aquifer Tests

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Tracy Segment: Tahoe-Reno Commercial Center Test, TRCC–1

Primary Investigator:

Well Data

USGS Site ID
Local Name Altitude (ft) Uppermost
Opening (ft)
Lowermost
Opening (ft)
Primary Aquifer Transmissivity
(ft2/d)
TRCC1 76 327 VOLCANIC ROCK 4600

 

Aquifer Test

All Aquifer Test Files (zip)

Tracy Segment, TRCC1

Aquifer Test (pdf)

Introduction

A proposed quasi-municipal supply well, TRCC–1, for the Tahoe–Reno Commercial Center in the Tracy Segment Hydrographic Area was completed in a volcanic-rock aquifer (39°33’57” N, 119°32’55” W). Well TRCC–1 was pumped at an average rate of 321 gallons per minute (gpm) from 12/14/06 through 12/24/06 as part of a 10–day constant–discharge test. Water–level data were collected at pumping well TRCC–1, observation well MW–1 (39°33’58” N, 119°32’39” W), and observation well TRCC–2 (NWIS Site ID: 393447119312302; 39°34’46.96” N, 119°31’22.97” W) for the duration of the test and during a 5–day recovery period so that transmissivity and storage coefficient of the volcanic rock aquifer could be estimated. The constant–rate aquifer test was conducted by Eco–Logic Inc. (D. Bugenig, personal communication, March 28, 2014; Bugenig, et al., 2007).

 

Site Description

Pumping well TRCC–1 is a 12–inch diameter well that was completed in a 12.75–inch diameter borehole (fig. 1). Drillers logs report that well TRCC–1 penetrates alternating intervals of clay, sand, and gravel to 68 feet below land surface (bls), and fractured volcanic rock to the total depth of 350 feet bls. The well was screened in volcanic rock from 76–327 feet bls, and a gravel pack was installed from 0–350 feet bls. The water level was about 1.7 feet above land surface. The aquifer is assumed to be confined in the volcanic rock and unconfined in the overlying alluvial fill.

Observation well MW–1 is described as located approximately 1,200 feet from TRCC–1 (Bugenig, et al., 2007). Little information is provided for MW–1 other than the approximate distance from TRCC–1. A query of the Nevada Division of Water Resources well log database revealed a record of plugging of a 6–inch well drilled to 321 feet at the described location, 1,217 feet East of TRCC–1. Recorded water levels from the plugging report match measured water levels in MW–1 prior to the aquifer test. No drillers report or other well–construction details are provided.

Observation well TRCC–2 is located approximately 8,500 feet from TRCC–1. TRCC–2 is a 10–inch well that was completed in a 17.5–inch borehole. Drillers logs report that well TRCC–2 penetrates alternating clay, gravel and boulders to 180 feet bls, and fractured volcanic rock to the total depth of 527 feet bls. Well TRCC–2 was gravel packed and screened in similar volcanic rock as the production well. An image well was used in this aquifer test evaluation at radial distance of 3,650 feet from pumping well to account for a nearby river boundary at radial distance 1,825 feet from the pumping well (fig. 1).

 

Location TRCC-1 aquifer test site, wells, and location of simulated Truckee River recharge boundary.
Figure 1. Location TRCC–1 aquifer test site, wells, and location of simulated Truckee River recharge boundary.

 

 

Table 1. Wells, coordinates, radial distances, and completion intervals at the TRCC–1 site.
Wells, coordinates, radial distances, and completion intervals at the TRCC-1 site.

 

Test Description

The aquifer test commenced when well TRCC–1 began pumping at 09:30, 12/14/06 and continued for 10 days until 09:00, 12/24/06. Discharge ranged from 305–375 gpm during the test (fig. 2). Pumping was briefly halted at 05:50, 12/18/06 due to mechanical issues with the pump and was restarted at 10:35, 12/18/06. Discharge water was routed to an ephemeral stream channel roughly 500 feet from well TRCC–1. Once pumping had ceased, water levels were allowed to recover for an additional 5 days. During the test and recovery period water levels in wells MW–1 and TRCC–2 were monitored at 1–minute intervals.

Aquifer Test Analysis

Transmissivity and storage coefficient were estimated from the constant-discharge test by analyzing water-level drawdown and recovery in observation wells MW–1 and TRCC–2 with a Theis solution and image well theory. An Excel spreadsheet program was used to analyze the data (Halford and Kuniansky, 2012). Excessive drawdown was observed in pumping well TRCC–1 (specific capacity = 2.3 gpm/ft), so these data were not included in the analysis. Given the large distance between the pumping well TRCC–1 and observation well TRCC–2, the measured pumping response in well TRCC–2 was small and mostly obscured by natural water–level fluctuations likely due to barometric pressure fluctuations and earth tides (fig. 3). Local barometric pressure data were not available during the pumping test period, so no attempt was made to correct these variations. A decrease in the slope of drawdown vs. time beginning at approximately two hours suggests that drawdowns in observation well MW–1 were affected by leakage of water through unconsolidated fluvial sediments adjacent to the Truckee River. Unconsolidated sediments along the Truckee River corridor were assumed to be more transmissive than the underlying volcanic–rock aquifer (fig. 1). Leakage of Truckee–River water from overlying unconsolidated sediments into the volcanic-rock aquifer was assumed to provide an effectively infinite source of water. Image well position and estimates of hydraulic properties were assessed by minimizing equally weighted residuals between simulated and measured drawdowns in both observation wells MW–1 and TRCC–2, simultaneously. Simulations of drawdown and recovery for observation wells MW–1 and TRCC–2 (fig. 3) matched the measured data within 1 ft (RMSE = 0.2 ft). The estimated position of the leaky boundary generally corresponded with extension of the centerline of the Truckee River. The transmissivity estimate for the volcanic-rock aquifer at the TRCC-1 site was 4,600 ft2/d, and the estimated storage coefficient was 0.0002. Drawdown and recovery estimated with identical aquifer properties but without a leaky boundary matched late–time measured values poorly due to the departure in slope of measured drawdown beginning at approximately two hours. Root mean square error for the simulated drawdown without a leaky boundary was more than an order of magnitude greater than for the simulation with the leaky boundary (RMSE = 2.1 and 0.2 ft, respectively).

 

Pumping rate for TRCC-1 in gallons per minute (gpm).
Figure 2. Pumping rate for TRCC–1 in gallons per minute (gpm).

 

Simulated and measured drawdown and recovery in (A) observation well MW-1 and (B) observation well TRCC-2.
Figure 3. Simulated and measured drawdown and recovery in (A) observation well MW–1 and (B) observation well TRCC–2.

 

Refererences

Bugenig, D.C., M. Hanneman, and T.H. Butler, 2007. Evidence in Support of Water Rights Application 69594, 69595, and 69596, Washoe County, NV. Unpublished report prepared by ECOLOGIC Engineering for the Nevada Division of Water Resources. Dated Feb. 2, 2007.

Halford, K.J. and E.L. Kuniansky, 2002. Documentation of spreadsheets for analysis of aquifer–test and slug–test data. U.S. Geological Survey Open–File Report 02–197, 51 p.

 

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