CPG Environmental Geology & Hydrogeology 2

Question 1

The Cooper-Jacob straight-line approximation of the Theis equation is generally considered valid when the well function argument u is:

Accepted Answer

Less than about 0.01

Answer

Cooper-Jacob truncates the Theis series, which is accurate only when u = r²S/4Tt is small (commonly < 0.01).

Question 2

Which range of storativity values is most typical of a confined aquifer?

Accepted Answer

0.00001 to 0.001

Answer

Confined aquifers release water by elastic compression and expansion, giving storativity on the order of 10^-5 to 10^-3.

Question 3

In a monitoring well screened across the water table, the measured LNAPL thickness is typically:

Accepted Answer

Greater than the actual mobile LNAPL thickness in the formation

Answer

LNAPL depresses the water level in the well, so apparent well thickness usually exceeds true formation thickness, especially in fine-grained soils.

Question 4

A solute has Kd = 0.5 mL/g in an aquifer with bulk density 1.6 g/cm³ and porosity 0.30. What is the approximate retardation factor?

Accepted Answer

3.7

Answer

R = 1 + (ρb/n)Kd = 1 + (1.6/0.30)(0.5) ≈ 3.7.

Question 5

On a coastal island, the fresh groundwater head is 2 m above sea level. Using the Ghyben-Herzberg relation, the freshwater-saltwater interface is about how deep below sea level?

Accepted Answer

80 m

Answer

Ghyben-Herzberg gives an interface depth about 40 times the freshwater head above sea level, so 40 × 2 = 80 m.

CPG - Certified Professional Geologist Practice Test

CPG - Certified Professional Geologist Practice Test

CPG Environmental Geology & Hydrogeology 2