Groundwater Flow to Wells

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Groundwater Flow to Wells
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• I. Overview
• A. Water well uses
• 1. Extraction
• 2. Injection

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• I. Overview
• A. Water well uses
• B. Terms
• 1. Cone of depression
• 2. Drawdown
• 3. Unsteady Flow

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• I. Overview
• A. Water well uses
• B. Terms
• C. Goals
• 1. Compute dh/dt given knowledge
• of the properties of the aquifer
• 2. Determine the properties of the aquifer based
  on the rate of dh/dt.

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• I. Overview
• A. Water well uses
• B. Terms
• C. Goals
• D. General Assumptions

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• General Assumptions

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• General Assumptions (continued)

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• I. Overview
• A. Water well uses
• B. Terms
• C. Goals
• D. General Assumptions
• E. Radial Flow

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• II. Theis Method

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• II. Theis Method
• A. Additional Assumptions
• The aquifer is confined on the top and bottom
• There is no source of recharge to the aquifer
• The aquifer is compressible, and water is
  released instantaneously
• from the aquifer as the hydraulic head is
  lowered.
• The well is pumped at a constant rate.

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• II. Theis Method
• A. Additional Assumptions
• B. The Equations

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• II. Theis Method
• A. Additional Assumptions
• B. The Equations

s ho -ht
ho -ht Q wu 4pT
u r2S 4Tt
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THEIS CURVE
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• II. Theis Method
• C. Examples (with known values)

A well is located in an aquifer with a hydraulic
conductivity of 15 m/d, storativity is 0.005,
aquifer thickness is 20 m, and the pumping of the
water well is occurring at a rate of 2725 m3/d.
What is the drawdown at a distance of 7 m from
the well after 1 day of pumping?
ho -ht Q wu 4pT
u r2S 4Tt
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• II. Theis Method
• A. Additional Assumptions
• B. The Equations
• C. Examples (with known values)
• D. Examples (with unknown values)

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THEIS CURVE
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DRAWDOWN DATA
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Problem A well in a confined aquifer was pumped
at a rate of 42,400 ft3/d for 500 minutes. The
aquifer is 48 ft. thick. Time drawdown data from
an observation well located 824 ft away yields
the following data (see previous slide of
drawdown data). Find T, K, and S.
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• III. Jacob Straight Line Method
• A. Overview
• B. Conditions
• C. The Equation
• D. Example

T 2.3Q 4p?h
S 2.25Tt0 r2
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• III. Jacob Straight Line Method
• D. Example

T 2.3Q 4p?h
S 2.25Tt0 r2
Problem A well in a confined aquifer was pumped
at a rate of 42,400 ft3/d for 500 minutes. The
aquifer is 48 ft. thick. Time drawdown data from
an observation well located 824 ft away yields
the following data (see previous slide of
drawdown data). Find T, K, and S.
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IV. Distance Drawdown Method A. Overview B.
Equations C. Example
T 2.3Q 2p?h
S 2.25Tt r02
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IV. Distance Drawdown Method C. Example
T 2.3Q 2p?h
S 2.25Tt r02
A well is pumping 77,000 ft3/d, and has
observational wells located 10, 40, 150, 300, and
400 ft away from the pumping well. After 0.14
days of pumping, the Following drawdowns were
observed in the observation wells (see
graph). Determine T (ft2/d) and S of the aquifer.
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• Hzorslev Method
• (Slug or Bail Test)

K r2ln(L/R) 2Lt0.37
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Hzorslev Method
Time since    
injection h h/ho
0 0.88 1.000
1 0.6 0.682
2 0.38 0.432
3 0.21 0.239
4 0.12 0.136
5 0.06 0.068
6 0.04 0.045
7 0.02 0.023
8 0.01 0.011
9 0 0.000
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Hzorslev Method
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• Hzorslev Method
• (Slug or Bail Test)

K r2ln(L/R) 2Lt0.37
A slug test is performed by lowering a metal
cylinder into a piezometer that is screened in
coarse sand. The inside of the bore hole has a
radius of 0.500 ft, and the inside radius of the
piezometer is 0.083 ft. The screened section of
the well is 10 ft. The well recovery data is
shown via tables and the respective graph.
Determine the Hydraulic Conductivity of the
aquifer.
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• VI. Intersecting Pumping Cones and Well
  Interference
• General Example

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• Bounded Aquifers
• 1. Impermeable boundary

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• Bounded Aquifers
• 1. Constant Head boundary

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• VII. Recovery of Pumping Wells
• Purpose
• Example

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• VII. Recovery of Pumping Wells

Time(min) Elevation (ft)
0 520
0.2 520.2
0.4 520.3
0.8 520.6
1 521
2 522
3 523
4 524
5 525
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• VII. Recovery of Pumping Wells

1 ft3 7.48 gallons
Time(min) Elevation (ft)
0 520
0.2 520.2
0.4 520.3
0.8 520.6
1 521
2 522
3 523
4 524
5 525