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

Groundwater Flow to Wells

I. Overview

A. Water well uses

1. Extraction

2. Injection

I. Overview

A. Water well uses

B. Terms

1. Cone of depression

2. Drawdown

3. Unsteady Flow

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.

I. Overview

A. Water well uses

B. Terms

C. Goals

D. General Assumptions

General Assumptions

General Assumptions (continued)

I. Overview

A. Water well uses

B. Terms

C. Goals

D. General Assumptions

E. Radial Flow

II. Theis Method

II. Theis Method

A. Additional AssumptionsThe 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.

II. Theis Method

A. Additional Assumptions

B. The Equations

II. Theis Method

A. Additional Assumptions

B. The Equations

ho -ht = Q* * wu

4πT

u = r2*S

4Tt

s = ho -ht

THEIS CURVE

II. Theis Method

C. Examples (with known values)

A well is located in an aquifer with a hydraulic conductivity of 15 m/d, storativityis 0.005, aquifer thickness is 20 m, and the pumping of the water well is occurringat a rate of 2725 m3/d. What is the drawdown at a distance of 7 m from the wellafter 1 day of pumping?

ho -ht = Q* * wu

4πT

u = r2*S

4Tt

II. Theis Method

A. Additional Assumptions

B. The Equations

C. Examples (with known values)

D. Examples (with unknown values)

THEIS CURVE

DRAWDOWN DATA

Problem: A well in a confined aquifer was pumped at a rate of 42,400 ft3/dfor 500 minutes. The aquifer is 48 ft. thick. Time drawdown data from an observation well located 824 ft away yields the following data (see previousslide of drawdown data).

Find T, K, and S.

III. Jacob Straight Line Method

A. Overview

B. Conditions

C. The Equation

D. Example

T = 2.3Q

4πΔh

S = 2.25T*t0

r2

III. Jacob Straight Line Method

D. Example

T = 2.3Q

4πΔh

S = 2.25T*t0

r2

Problem: A well in a confined aquifer was pumped at a rate of 42,400 ft3/dfor 500 minutes. The aquifer is 48 ft. thick. Time drawdown data from an observation well located 824 ft away yields the following data (see previousslide of drawdown data).

Find T, K, and S.

IV. Distance Drawdown MethodA. OverviewB. EquationsC. Example

T = 2.3Q

2πΔh

S = 2.25T*t

r02

Distance Drawdown Method

0

2

4

6

8

10

12

14

16

1 10 100 1000

Distance (ft)

Dra

wd

ow

n (

ft)

IV. Distance Drawdown MethodC. Example

T = 2.3Q

2πΔh

S = 2.25T*t

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.

Distance Drawdown Method

0

2

4

6

8

10

12

14

16

1 10 100 1000

Distance (ft)

Dra

wd

ow

n (

ft)

V. Hzorslev Method(Slug or Bail Test)

K = r2*ln(L/R)

2Lt0.37

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

Hzorslev Method

0.01

0.1

1

0 1 2 3 4 5 6 7 8 9 10

Time (s)

h/h

oHzorslev Method

V. Hzorslev Method(Slug or Bail Test)

K = r2*ln(L/R)

2Lt0.37

A slug test is performed by lowering a metal cylinder into a piezometer that isscreened in coarse sand. The inside of the bore hole has a radius of 0.500 ft, andthe inside radius of the piezometer is 0.083 ft. The screened section of the well is10 ft. The well recovery data is shown via tables and the respective graph. Determine the Hydraulic Conductivity of the aquifer.

0.01

0.1

1

0 1 2 3 4 5 6 7 8 9 10

Time (s)

h/h

o

VI. Intersecting Pumping Cones and Well Interference

A. General Example

A. Bounded Aquifers

1. Impermeable boundary

A. Bounded Aquifers

1. Constant Head boundary

VII. Recovery of Pumping Wells

A.Purpose

B.Example

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

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

1 ft3 = 7.48 gallons