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

 

 

Tahoe Nearshore Study

Primary Investigator: David Smith

 

Well Data

USGS Site ID
Local Name Altitude Uppermost
Opening
Lowermost
Opening
Primary Aquifer Hydraulic
Conductivity
(ft/d)
390744120091910 NS1-1 6226.1 4.53 4.86 Alluvial-fill 4
390743120091920 NS1-2 6224.83 1.57 1.9 Alluvial-fill 80
390743120091930 NS1-3 6223.45 1.36 1.69 Alluvial-fill 90
390746120091710 NS2-1 6225.2 1.87 2.2 Alluvial-fill 11
390746120091720 NS2-2 6224.75 0.91 1.23 Alluvial-fill 50
390746120091730 NS2-3 6223.82 0.79 1.12 Alluvial-fill 50
390751120091110 NS3-1 6225.4 1.48 1.8 Alluvial-fill 1.1
390751120091120 NS3-2 6224.61 1.05 1.38 Alluvial-fill 10
390750120091130 NS3-3 6223.55 0.79 1.12 Alluvial-fill 0.7
390808120090610 NS4-1 6225.19 1.2 1.53 Alluvial-fill 80
390808120090620 NS4-2 6224.72 1.34 1.67 Alluvial-fill 3
390808120090630 NS4-3 6223.41 1.1 1.43 Alluvial-fill 70
390809120090710 NS5-1 6225.38 0.92 1.25 Alluvial-fill 11
390809120090720 NS5-2 6225.12 0.94 1.26 Alluvial-fill 20
390809120090730 NS5-3 6223.59 0.59 0.92 Alluvial-fill 30
390809120090740 NS5-4 6222.8 0.62 0.95 Alluvial-fill 40
390810120090740 NS6-1 6225.38 1.67 2 Alluvial-fill 0.4
390810120090710 NS6-2 6224.88 1.17 1.5 Alluvial-fill 3
390810120090720 NS6-3 6223.93 1.43 1.76 Alluvial-fill 1.1
390810120090730 NS6-4 6223.29 0.98 1.31 Alluvial-fill 50

 

Aquifer Test

All Aquifer Test Files (zip) || Aquifer Test (pdf)

 

Introduction

Excessive attached algae growing along nearshore areas of Lake Tahoe is seen as a nuisance and negatively impacts the recreational value of the lake. Attached algal biomass data collected from the nearshore of Lake Tahoe exhibit increasing trends over the last decade. However, the mechanisms that have caused these changes are not well understood.

To improve the understanding of surface-water and groundwater interactions along the nearshore of Lake Tahoe, the U.S. Geological Survey installed and monitored six piezometer transects from October, 2015 to July, 2016 (fig. 1). As part of the investigation, the hydraulic conductivity of the nearshore sediments were determined by aquifer slug tests on 7/8/2016 to further interpret hydraulic gradient data. This report documents the methods, data, analysis, and results of aquifer tests from the monitored piezometers as part of this nearshore study of Lake Tahoe.

Study Area

Lake Tahoe is a 191 square-mile subalpine lake in the eastern Sierra Nevada mountain range (fig. 1). The lake has exceptional water clarity and approximately 72 miles of shoreline that is popular for tourism. The study transects were located near the mouth of Ward Creek and north along the shoreline of Lake Tahoe (fig. 1). Nearshore sediments consist of andesitic and basaltic cobbles to boulders within an unconsolidated matrix of coarse sand with silt and (or) clay. Well-sorted sands and fine silt deposits were observed below cobbles and boulders during the piezometer installation. Loeb and Goldman (1979) estimated an average aquifer transmissivity of 3,300 ft2/day in the alluvial-fill aquifer of the Ward Creek watershed. The average thickness of the aquifer was estimated based on seismic refraction (Loeb and Goldman, 1979) to be 112 ft, with a maximum of 200 ft near the Lake Tahoe shore zone.

Fig. 1. Location of piezometers and aquifer test sites near Ward Creek, Placer County, California.

Sites and Test Descriptions

The study consisted of 20 shallow, 1-inch polyvinyl chloride (PVC) piezometers driven into the nearshore lake sediments (fig. 1). All piezometers were manually driven into the nearshore with a pilot rod and drive point tips. Piezometer site identifier numbers, locations, and design information are available in table 1. Piezometers were manually perforated 0.16 ft (5 cm) above the bottom of the casing with a screen interval of approximately 0.32 ft (10 cm). Piezometers were cleared of fine sediment prior to performing slug tests and had good contact with surrounding material. Piezometers were completed between 0.59 and 4.86 ft below land surface (bls). All piezometers were developed after their construction with a peristaltic pump.

Table 1. Piezometer site ID, coordinates, construction data, and aquifer description Lake Tahoe, Placer County, California.

 

Site name USGS site ID Latitude (NAD83) Longitude (NAD83) Land surface altitude (ft) Upper most opening (ft) Lowermost opening (ft) Primary aquifer
NS1-1 390744120091910 39.128781 -120.15533 6226.10 4.53 4.86 Alluvial-fill
NS1-2 390743120091920 39.128758 -120.1553 6224.83 1.57 1.90 Alluvial-fill
NS1-3 390743120091930 39.128742 -120.15526 6223.45 1.36 1.69 Alluvial-fill
NS2-1 390746120091710 39.129489 -120.15473 6225.20 1.87 2.20 Alluvial-fill
NS2-2 390746120091720 39.129453 -120.15465 6224.75 0.91 1.23 Alluvial-fill
NS2-3 390746120091730 39.129419 -120.15458 6223.82 0.79 1.12 Alluvial-fill
NS3-1 390751120091110 39.130900 -120.15319 6225.40 1.48 1.80 Alluvial-fill
NS3-2 390751120091120 39.130856 -120.15314 6224.61 1.05 1.38 Alluvial-fill
NS3-3 390750120091130 39.130811 -120.15308 6223.55 0.79 1.12 Alluvial-fill
NS4-1 390808120090610 39.135442 -120.15185 6225.19 1.20 1.53 Alluvial-fill
NS4-2 390808120090620 39.135447 -120.15179 6224.72 1.34 1.67 Alluvial-fill
NS4-3 390808120090630 39.135456 -120.15170 6223.41 1.10 1.43 Alluvial-fill
NS5-1 390809120090710 39.135708 -120.1519 6225.38 0.92 1.25 Alluvial-fill
NS5-2 390809120090720 39.135717 -120.15185 6225.12 0.94 1.26 Alluvial-fill
NS5-3 390809120090730 39.135739 -120.15175 6223.59 0.59 0.92 Alluvial-fill
NS5-4 390809120090740 39.135747 -120.15170 6222.80 0.62 0.95 Alluvial-fill
NS6-1 390810120090740 39.136014 -120.15204 6225.38 1.67 2.00 Alluvial-fill
NS6-2 390810120090710 39.136025 -120.15193 6224.88 1.17 1.50 Alluvial-fill
NS6-3 390810120090720 39.136033 -120.15183 6223.93 1.43 1.76 Alluvial-fill
NS6-4 390810120090730 39.136036 -120.15174 6223.29 0.98 1.31 Alluvial-fill

Procedures

Slug tests were performed by rapidly pouring a known volume of water into the piezometer and measuring the water-level response using pressure transducers set to record every second. Single or multiple liquid slug tests were performed in the piezometers based on the time of recovery. The near instantaneous rise and subsequent fall of the water-level in response to the poured slugs were recorded and analyzed as a falling head test using the Bouwer and Rice method as described by Halford and Kuniansky (2002).

Aquifer Test Analysis

The computed hydraulic conductivity (K) and for the alluvial-fill material ranged between 0.4 and 90 feet/day, with an arithmetic mean of 29 ft/day (table 2). This estimate is approximately 1.8 times greater than the average estimate of 16 ft/day reported of Loeb and Goldman (1979). Water-level measurements and slug analysis of test data are available in figures 2-7.

Table 2. Aquifer test results for the nearshore sediment of Lake Tahoe, Placer County, California.

 

Site name USGS site ID Number of slugs Hydraulic Conductivity (ft/day)
NS1-1 390744120091910 2 4
NS1-2 390743120091920 2 80
NS1-3 390743120091930 2 90
NS2-1 390746120091710 2 11
NS2-2 390746120091720 2 50
NS2-3 390746120091730 2 50
NS3-1 390751120091110 1 1.1
NS3-2 390751120091120 2 10
NS3-3 390750120091130 1 0.7
NS4-1 390808120090610 2 80
NS4-2 390808120090620 2 3
NS4-3 390808120090630 2 70
NS5-1 390809120090710 2 11
NS5-2 390809120090720 2 20
NS5-3 390809120090730 2 30
NS5-4 390809120090740 2 40
NS6-1 390810120090740 1 0.4
NS6-2 390810120090710 1 3
NS6-3 390810120090720 1 1.1
NS6-4 390810120090730 2 50

References

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

Loeb, S.L. and Goldman, C.R., 1979, Water and nutrient transport via groundwater from Ward Valley into Lake Tahoe, Limnology and Oceanography, v. 26(6), p. 1146-1154.

Water-level measurements from the pumping tests

Water-level measurements from the pumping tests

Water-level measurements from the pumping tests

Water-level measurements from the pumping tests

Water-level measurements from the pumping tests

Water-level measurements from the pumping tests

 

 

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
Page Contact Information: Nevada Water Science Center Web Team