ASBOG - Association of State Boards of Geology Hydrogeology Questions and Answers

Question 1

A hydrogeologist needs to calculate the specific discharge (Darcy flux) through a uniform, saturated sand aquifer.
The hydraulic conductivity (K) is 50 m/day, the hydraulic gradient (i) is 0.002, and the effective porosity (ne) is 0.25.
The cross-sectional area (A) perpendicular to flow is 100 m².
What is the specific discharge (q)?

Accepted Answer

0.1 m/day

Answer

10 m³/day

Answer

0.4 m/day

Answer

100 m/day

Question 2

Which of the following best distinguishes Transmissivity (T) from Hydraulic Conductivity (K) in an aquifer?

Accepted Answer

Transmissivity represents the ability of the entire saturated thickness of an aquifer to transmit water, while Hydraulic Conductivity is an intrinsic property of the porous material per unit area.

Answer

Transmissivity is a property of the fluid, while Hydraulic Conductivity is a property of the porous medium.

Answer

Transmissivity is a dimensionless coefficient, while Hydraulic Conductivity has units of length per time.

Answer

Transmissivity is only applicable to unconfined aquifers, whereas Hydraulic Conductivity applies to both confined and unconfined aquifers.

Question 3

A contaminant plume is migrating through a sandy aquifer. Geochemical testing reveals that the contaminant strongly sorbs to organic carbon on the sand grains. This sorption process will primarily result in which of the following transport phenomena?

Accepted Answer

Retardation of the contaminant front

Answer

Increased advection

Answer

Enhanced dispersion

Answer

Accelerated diffusion

Question 4

A pumping test is conducted in a homogeneous, isotropic, confined aquifer of infinite areal extent. When drawdown data from an observation well is plotted against the logarithm of time on a semi-log graph, what is the expected shape of the data curve after the initial effects of wellbore storage have dissipated?

Accepted Answer

A straight line with a positive slope

Answer

A horizontal line indicating equilibrium

Answer

A bell-shaped curve peaking at mid-time

Answer

An exponentially decreasing curve

Question 5

A well is drilled into a saturated geologic formation that is overlain by a low-permeability clay layer (an aquitard). The static water level in the well rises to an elevation significantly above the top of the saturated formation. This condition is characteristic of which type of aquifer?

Accepted Answer

A confined (artesian) aquifer

Answer

A perched aquifer

Answer

An unconfined aquifer

Answer

A leaky unconfined aquifer

Question 6

The Theis non-equilibrium equation is a fundamental tool for analyzing pumping test data. Which of the following is a key assumption required for the valid application of this method?

Accepted Answer

The aquifer is homogeneous, isotropic, and of infinite areal extent.

Answer

The aquifer is unconfined with delayed gravity drainage.

Answer

The pumping rate varies logarithmically with time.

Answer

Recharge from a nearby river is induced by pumping.