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Aquifer Tests

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Tracy Segment, Storey County, Nevada: Tahoe-Reno Industrial Center Test, TRIC-4

Primary Investigator: Carl Thodal

Well Data

USGS Site ID
Local Name Altitude Uppermost
Opening
Lowermost
Opening
Primary Aquifer Transmissivity
(ft2/d)
393310119330101 TRIC4_P-1 4360 120 440 VOLCANIC ROCKS 400

Aquifer Test

All Aquifer Test Files (zip)

Tahoe-Reno Industrial Center Test, TRIC-4

Aquifer Test (pdf) || Related Publication: Scientific Investigations Report 2006-5010

Introduction

A proposed public supply well, TRIC4_P-1, for the Tahoe-Reno Industrial Center was completed in a volcanic-rock aquifer (39°33'10" N, 119°33'01" W). Well TRIC4_P-1 was pumped at an average rate of 510 gpm from 4/05/02 through 4/07/02 so transmissivity and storage coefficient of the volcanic rock aquifer could be estimated. This constant-rate aquifer test was conducted by Eco-Logic Inc. Additional data from observation well MW-2 was recorded by the USGS.

Location of TRIC-4 aquifer test site, wells, location of analytical approximation of the Truckee River Figure 1.— Location of TRIC-4 aquifer test site, wells, location of analytical approximation of the Truckee River.

 

Site and Test Description

The production well TRIC4_P-1 is a 12-inch well that was completed in an 18-in borehole. Well TRIC4_P-1 penetrates sand, gravel and volcanic rock from 0 to 99 ft below land surface and volcanic rock and clay from 99 to 441 ft below land surface. A gravel pack was installed from 100 to 441 ft below land surface and cement grout was installed from 0 to 100 ft below land surface. Depth to water is about 95 ft below land surface at the site. The aquifer was assumed to be confined near the production well and unconfined in the alluvial fill of the Truckee River. The edge of the alluvial fill is near the 1310-m contour (fig. 1). Two observation wells at distances of 220 and 1,250 ft from the production well (table 1, fig. 1) were monitored. Observation well MW-1 was gravel-packed and screened in similar volcanic rock as the production well. Observation well MW-2 was gravel-packed and screened in volcanic rock near alluvial fill of the Truckee River.

Wells, coordinates, radial distances, and completion intervals of wells at the TRIC-4 site Table 1. Wells, coordinates, radial distances, and completion intervals of wells at the TRIC-4 site.

 

The aquifer test started when well TRIC4_P-1 began pumping at 10:15, 4/05/02. Initial discharge was 600 gpm. Discharges declined to 570 gpm after 3 hours of pumping and declined to 500 gpm after 1 day. Discharge remained about 500 gpm for the remainder of the test and averaged 510 gpm over the 72-hour test. Discharge water was routed into a local drain and away from the aquifer test site. Water levels were monitored at intervals of 1 minute at the beginning of the test and at hourly intervals at the end of the test.

Aquifer Test Analysis

Transmissivity and storage coefficient were estimated by analyzing aquifer test results with Theis solutions and image well theory. Drawdowns in well MW-2 were affected by leakage from the Truckee River, which was assumed an infinite source of water (fig. 2). Leakage from the Truckee River was simulated with an injecting image well (fig. 1). The position of the leaky boundary was estimated because the contact between alluvium and volcanic rock was irregular and unknown relative to the straight-line approximation. Transmissivity, storage coefficient, and leaky boundary position were estimated by minimizing differences between simulated and measured drawdowns. Simulated drawdowns matched measured drawdowns within about 1 ft overall (fig. 2). Recovery data was not used because the uncertainty of recovery estimates was greater than drawdown estimates during the pumping period. Transmissivity and storage coefficient for the TRIC-4 site were estimated to be 400 ft2/d and 0.0003, respectively. A Cooper-Jacob analysis could not be applied to the production wells because drawdown was 530 ft and discharge was allowed to decline from 600 to 500 gpm during the test (fig. 3).

Simulated and measured drawdowns in observation wells MW-1 and MW-2Figure 2. Simulated and measured drawdowns in observation wells MW-1 and MW-2.

Discharge and drawdown in production well, TRIC4_P-1, from 10:15, 4/05/02 to 22:15, 4/07/0 Figure 3. Discharge and drawdown in production well, TRIC4_P-1, from 10:15, 4/05/02 to 22:15, 4/07/02.

 

 

 

 

 

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