Groundwater Hydraulics: Aquifer testing

Question 1

True or False
The Theis solution for transient radial confined flow is derived under the assumption that the aquifer is homogeneous and isotropic.

Answer 1

True

Question 2

In the Theis solution, the Boltzmann variable u is defined as u = r^2S/4Tt, where S is ________, T is _________, r is radius, and t is _____.

Answer 2

storativity, transmissibility, time after pumping starts

Question 3

Which variable represents the drawdown in the Theis solution for transient radial flow in a confined aquifer?
A) T
B) S
C) s

Answer 3

C) s

Question 4

What is the Jacob late time approximation used for in groundwater studies?

Answer 4

The Jacob late time approximation is used to estimate the drawdown s at large times after pumping has started, simplifying the Theis solution using the natural logarithm and the exponential integral.

Question 5

True or False
The Theis solution assumes no recharge and an infinite aquifer extent.

Answer 5

True

Question 6

The equation s = Q_wW(u_{r,t})/4πT indicates that the drawdown s is directly proportional to the pumping rate Q_w and inversely proportional to _______.

Answer 6

transmissivity T

Question 7

Under what condition is the Jacob late time approximation considered valid?
A) When 1/u_{r,t} > 10
B) When u_{r,t} > 10
C) When 1/u_{r,t} < 0.1

Answer 7

A) When 1/u_{r,t} > 10

Question 8

True or False
The Theis solution can be adapted for large times to model unconfined aquifers by replacing storativity S with specific yield S_y.

Answer 8

True

Question 9

What is the significance of the exponential integral in the context of the Theis solution?

Answer 9

The exponential integral is used in the Jacob late time approximation to estimate the drawdown in aquifers at large times after pumping has begun, based on the rate at which the well function declines.

Question 10

The equation
s ≈ Q_w/4πT*[ln(1/(u_{r,t}))-0.5772] uses a constant known as _______, which is associated with the exponential integral.

Answer 10

Euler’s constant (approximated as -0.5772)

Question 11

What are key assumptions for Theis solution?

Answer 11

• Darcy’s Law
• Homogeneous and isotropic aquifer
• No recharge
• Constant pumping rate
• Confined aquifer
• Infinitesimal well
• Uniform initial condition

Question 12

When also can Theis solution be used?

Answer 12

For large times, this can also be used for unconfined
aquifers with S now equal to the specific yield, S_y.

Question 13

True or False
A pumping test is conducted to observe the recovery of an aquifer after it has been pumped.

Answer 13

False (It is conducted to monitor the aquifer’s response to pumping, not its recovery)

Question 14

During a pumping test, drawdown is often monitored using a _______.

Answer 14

pressure transducer

Question 15

What is the purpose of using Jacob’s large time approximation in a pumping test?
A) To calculate the initial water level in the well
B) To rearrange the drawdown equation to facilitate linear regression analysis
C) To estimate the maximum water extraction rate

Answer 15

B) To rearrange the drawdown equation to facilitate linear regression analysis

Question 16

What is a step drawdown test and why is it performed?

Answer 16

A step drawdown test involves pumping a well at progressively increasing flow rates until a quasi-steady state is reached at each level. It’s performed to determine the well’s performance, including its efficiency and the characteristics of well and formation losses.

Question 17

True or False
In step drawdown tests, each increase in flow rate leads to a proportional increase in head loss.

Answer 17

False (The head loss increases non-linearly due to inertial and turbulent energy losses)

Question 18

Formation loss in a pumping test refers to the energy loss of the _______ that is required to pump the water up to the original water level.

Answer 18

formation

Question 19

Well loss during a pumping test is attributed to:
A) Decreased velocity of water due to finer aquifer materials
B) Linear flow patterns near the well
C) Convergences in streamlines leading to increased velocity and turbulence near the well

Answer 19

C) Convergences in streamlines leading to increased velocity and turbulence near the well

Question 20

True or False
The formula s_w = AQ_w + BQ_w^n represents the total drawdown in a well, where AQ_w accounts for well loss and BQ_w^n for formation loss.

Answer 20

False (AQ_w represents formation loss and BQ_w^n represents well loss)

Question 21

How does the method of images apply to pumping tests near hydrological boundaries?

Answer 21

The method of images simulates imaginary wells to replace real hydrological boundaries, allowing the application of radial flow equations as if the aquifer were infinite, thereby simplifying analysis and extending the practical application of the test results.

Question 22

The non-linear component of the drawdown equation, BQ_w^n increases as the _______ increases during a pumping test.

Answer 22

flow rate

Question 23

How can loss be described when the flow through an aquifer is laminar?

Answer 23

Linear

Question 24

What does QSS stand for?

Answer 24

quasi-steady
state