Nevada Water Science Center


Aquifer Tests

Contact Information

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

 

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

 

Nevada Water Science Center
Information

Home Page Surface Water Groundwater Water Quality Research Contact Us

 

 

Tracy Segment, Storey County, Nevada: Tahoe-Reno Industrial Center Test, TRIC-3

Primary Investigator: Carl Thodal

Well Data

USGS Site ID
Local Name Altitude Uppermost
Opening
Lowermost
Opening
Primary Aquifer Transmissivity
(ft2/d)
393313119275501 W36-Center 4438.9 140 440 VOLCANIC ROCKS 10000

 

Aquifer Test

All Aquifer Test Files (zip)

Tahoe-Reno Industrial Center Test, TRIC-3 well

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

Introduction

A proposed public supply well, W36-Center, for the Tahoe-Reno Industrial Center was completed in a volcanic-rock aquifer (39°33'18" N, 119°27'58" W). Well W36-Center was pumped at 375 gpm from 4/25/01 through 4/28/01 so the transmissivity and storage coefficient of the volcanic-rock aquifer could be estimated. This constant-rate aquifer test was conducted by Eco-Logic Inc. and additional data from observation wells W36-West, OBS-4, and coyote were recorded by the USGS.

 

Location of TRIC-3 aquifer test site

Figure 1. Location of TRIC-3 aquifer test site.

 

Site and Test Description

The production well W36-Center is a 10-inch well that was completed in a 15-in borehole. Well W36-Center penetrates sand and rock from 0 to 34 ft below land surface and volcanic rock and clay from 34 to 566 ft below land surface. A gravel pack was installed from 100 to 566 ft below land surface and cement grout was installed from 0 to 100 ft below land surface. Depth to water is about 220 ft below land surface at the site and the aquifer is unconfined.

Five observation wells that ranged from 43 to 4,800 ft from the production well (table 1, fig. 2) were monitored. Observation wells W36-West, W36-North, and W36-South were located within 50 ft of the production well, W36-Center (fig. 2). OBS-4 and coyote wells were located 3,200 and 4,800 ft from the production well, respectively. All observation wells were gravel-packed and screened in similar volcanic rock and depths as the production well.

 

Table 1. Coordinates and radial distances of wells at the TRIC-3 site.
Coordinates and radial distances of wells at the TRIC-3 site

 

Map location of production and observation wells used in the TRIC-3 aquifer test
Figure 2. Map location of production and observation wells used in the TRIC-3 aquifer test.

 

The aquifer test started when well W36-Center began pumping at 09:45, 04/25/01. A constant discharge of 375 gpm was maintained for 72 hours. 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 specific yield were estimated by analyzing aquifer test results with a Theis solution. Changes in saturated thickness were assumed to have minimal effect on transmissivity because drawdowns in the nearest observation wells were less than 10 ft relative to a saturated thickness of more than 250 ft. Unconfined, porous media interpretation of fractured volcanic rocks also seemed questionable because drawdowns appeared to be affected by heterogeneities near the pumping well. Permeable fractures likely remained saturated fully and transmissivity would not be affected by water-level changes.

Hydraulic properties were estimated by visually fitting drawdown differences. Measured drawdown responses were non-ideal so analytical solutions of laterally homogeneous aquifers could not simulate observed responses well. Minimization of equally weighted residuals between simulated and measured observations failed because of model inadequacies. Simulated and measured drawdowns matched well at the distant observation well OBS-4 and the log-slopes of drawdown change between hours 24 and 72 were matched in the nearby observation wells (fig. 3). Recovery data was not used because the uncertainty of recovery estimates was greater than drawdown estimates during the pumping period. Drawdown slopes were analyzed instead of drawdowns because timing offsets between drawdowns in observation wells cannot be explained with lateral anisotropy. The greatest timing offset exists between wells W36-North and W36-West. This timing offset cannot be explained by lateral anisotropy because radial distances to the pumping well are similar (table 1) and the angular separation between the observation wells is nearly 180 degrees (fig. 2).

The timing offsets were interpreted as a measure of aquifer heterogeneity. Well W36-North was drilled into a set of fractures that were better connected with the production well than the fractures that intersect well W36-West. These differences affected early-time drawdowns in the nearby observation wells and suggest that a representative volume of aquifer has a length scale of more than 100 ft. Effects of local aquifer heterogeneity were assumed to dissipate with distance as the volume of aquifer affected by pumping increased. Drawdowns in well OBS-4 were interpreted as a porous media response because several representative volumes of aquifer might exist in the 3,200 ft between the production well and OBS-4.

Transmissivity and specific yield for the TRIC-3 site were estimated to be 10,000 ft2/d and 0.01, respectively. Simulated and measured drawdowns compared favorably after the first 12 hours of pumping (fig. 4). A Cooper-Jacob transmissivity estimate of 8,000 ft2/d from drawdowns in the pumping well, W36-Center differed little from the best estimate.

 

Simulated and measured drawdown differences from about 15 minutes after pumping began in well W36-Center
Figure 3. Simulated and measured drawdown differences from about 15 minutes after pumping began in well W36-Center.

 

Simulated and measured drawdowns in observation wells
Figure 4. Simulated and measured drawdowns in observation wells.

 

 

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://nevada.usgs.gov/barcass/index.htm
Page Contact Information: Nevada Water Science Center Web Team
Page Last Modified: September 29, 2009 -->