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Aquifer Test Procedures for Aquifer Test Procedures for Determining Hydrologic Determining Hydrologic
PropertiesProperties
Dr. Michael StrobelDeputy State Director
USGS Nevada Water Science CenterEXHIBIT G– WATER RESOURCESMeeting Date: 03-22-06Document consists of 28 slides.Entire Exhibit Provided
Purposes of Aquifer Tests• Measure the change, with time, in water levels
as a result of withdrawals through wells• Determine the transmissivity and storage
coefficient of the aquifer• Determine characteristics of confining layers• Determine well efficiency and optimum pumping
rates• Determine boundary conditions (natural) and
potential well interference
Types of Aquifer Tests
• Slug• Single-well• Multiple-wells
– Time-Drawdown Analysis– Distance-Drawdown Analysis
From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground-water resources: U.S. Geological Survey Circular 1186, 79 p.
From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground-water resources: U.S. Geological Survey Circular 1186, 79 p.
From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground-water resources: U.S. Geological Survey Circular 1186, 79 p.
From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground-water resources: U.S. Geological Survey Circular 1186, 79 p.
Slug Test
• The rapid addition or removal of a known volume from a well stresses the aquifer.
• The hydraulic conductivity (K) estimate is related to the rate of recovery with various corrections for well construction and geometry.
TIME
Area of influence from slug test
Static water levelWater level in well at time t
0.01
0.10
1.00
00:00 00:43 01:26 02:10 02:53
TIME, Minute:Second
y/y 0
K = 10 feet per day
23 32
23
38
38
23
26
26
32
Wells in an aquifer with K values from slug tests
23 32
23
38
38
23
26
26
32
Contoured areas of similar K values for an aquifer
Confining layer
Confined aquifer
Unconfined aquifer
Q
Original potentiometric surface
Potentiometric surfaceat time t
h0-h
Unconfined aquifer
Q
Original water table
Water level at time th0-h
Confining layer
Confined aquifer
Unconfined aquifer
Q
Original potentiometric surface
Potentiometric surfaceat time t
h0-h
Unconfined aquifer
Q
Original water table
Water level at time th0-h
Hantush-Jacob Analysis
10
1
0.1 1010.10.010.0010.00010.00001
TIME, IN DAYS
“MEASURED”HANTUSH-JACOB
PERIOD MATCHEDT = 39,000 ft2/dKZ/b’ = 0.0008 1/dS = 4 x 10-5
10 MINUTESDR
AW
DO
WN
, IN
FEE
T
Type curves for analysis of leaky confined aquifers
Need for long-term aquifer tests
• Stresses the system over a long period of time (weeks, months, years) to see how it reacts and when near-equilibrium is reached
• Provides good analytical approach to obtaining K and storage values over large areas
• Water from storage may account for most water during early parts of tests. Effects (drawdown) may be delayed.
Concerns with long-term aquifer tests
• Discharge of water (depending on pumping rates and length of test)
• Cost• Effects on aquifer• Representation of other parts of aquifer
and other basins
