Nevada Water Science Center


Aquifer Tests

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

 

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Nevada Water Science Center
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Tracy Segment: Tahoe-Reno Commercial Center Test, TRCC–3

Primary Investigator:

Well Data

USGS Site ID
Local Name Altitude (ft) Uppermost
Opening (ft)
Lowermost
Opening (ft)
Primary Aquifer Transmissivity
(ft2/d)
393446119311701 TRCC3 403 637 VOLCANIC ROCK 4000

 

Aquifer Test

All Aquifer Test Files (zip)

Tracy Segment, TRCC2

Aquifer Test (pdf)

Introduction

A proposed quasi–municipal supply well, TRCC–3 (NWIS Site ID: 393446119311701; 39°34’46” N, 119°31’17” W), for the Tahoe–Reno Commercial Center in the Tracy Segment Hydrographic Area was completed in a volcanic–rock aquifer. Well TRCC–3 was pumped at an average rate of 984 gpm from 11/12/06 through 11/18/06 as part of a 6–day constant–discharge test. Water–level data were collected both at well TRCC–3 and at 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–3 is located 472 feet from TRCC–2 (fig. 1) and was monitored during the aquifer test. Well TRCC–3 is a 12–inch production well completed in a 17.5–inch borehole. Drillers logs describe clay and rocks to 128 feet bls, underlain by andesite and basalt to 638 feet bls. Fracture zones were noted at 230, 430, 520, and 550 feet bls. The well was screened from 403–637 feet bls, and a gravel pack was installed from 54–637 feet bls. The aquifer is assumed to be confined in the volcanic rock unit and unconfined in overlying alluvial fill. Depth to water was about 171 feet bls. Observation well 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 below land surface (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.

 

Location TRCC-3 aquifer test site, wells, and location of simulated Truckee River recharge boundary.
Figure 1. Location TRCC-3 aquifer test site, wells, and location of simulated Truckee River recharge boundary.

 

 

Table 1. Wells, coordinates, radial distances, and completion intervals at the TRCC–3 site.
Wells, coordinates, radial distances, and completion intervals at the TRCC-3 site.

 

Test Description

The aquifer test commenced when well TRCC–3 began pumping at 09:30, 11/12/06 and continued for 6 days until 04:37, 11/18/14. Discharge was reported as 984 gpm for the duration of the test. Discharge water was routed to an ephemeral stream channel roughly 1500 feet from well TRCC–3. Once pumping had ceased, water levels were allowed to recover for an additional 3 days in TRCC–3 and an additional 9 days in TRCC–2. Water levels in pumping well TRCC–3 and observation well TRCC–2 were monitored at varying and 1–minute intervals, respectively, during the test and recovery period.

Aquifer Test Analysis

Transmissivity and storage coefficient were estimated from the constant–discharge test by analyzing water–level drawdown and recovery in pumping well TRCC–3 and observation well TRCC–2 with a Theis solution and image well theory. An Excel spreadsheet program was used to analyze the data (Halford and Kuniansky, 2012). A decrease in the slope of drawdown vs. time in observation well TRCC–2 beginning at approximately one day suggests that drawdown was affected by leakage of water through unconfined 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 estimated by minimizing equally weighted residuals between simulated and measured observations. Recovery data for observation well TRCC–2 showed evidence of transducer drift and were not used to fit estimates for hydraulic properties (fig. 2B). Simulations of drawdown and recovery for pumping well TRCC–3 and simulations of drawdown for observation well TRCC–2 (fig. 2) matched measured values reasonably well (RMSE = 5.3 and 0.4 ft, respectively). The estimated position of the leaky boundary was generally consistent with the boundary of the unconsolidated sediments along the Truckee River. Transmissivity and storage coefficients estimated for the volcanic–rock aquifer from drawdown and recovery data were 4,000 ft2/d and 0.002, respectively. Drawdown and recovery estimated with identical aquifer properties but without a leaky boundary matched late–time measured values for TRCC–3 and TRCC–2 worse than with a leaky boundary. Root mean square error for the simulated drawdowns and recoveries with the leaky boundary for both TRCC–3 and TRCC–2 were less than for the simulations without a leaky boundary.

 

Simulated and measured drawdown and residual drawdown in (A) pumping well TRCC-3 and (B) observation well TRCC-2.
Figure 2. Simulated and measured drawdown and residual drawdown in (A) pumping well TRCC–3 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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