ASBOG - Association of State Boards of Geology Hydrogeology Questions and Answers 2

Question 1

What is the difference between specific yield and specific retention of an aquifer material?

Accepted Answer

Specific yield is the water released under gravity; specific retention is the water held against gravity by capillary forces; they sum to total porosity

Answer

Specific yield (Sy) is the volume of water that drains by gravity per unit volume of aquifer material; specific retention (Sr) is the water retained against gravity; together they equal total porosity (n = Sy + Sr).

Question 2

What is the cone of depression in a pumping well, and what factors control its size and shape?

Accepted Answer

A funnel-shaped zone of decreased hydraulic head that develops around a pumping well, controlled by pumping rate, hydraulic conductivity, and storativity

Answer

The cone of depression is the axisymmetric drawdown pattern around a pumping well; its size (radius and depth) is controlled by pumping rate, aquifer hydraulic conductivity and transmissivity, storativity, and duration of pumping.

Question 3

In a slug test, what is being measured, and what aquifer parameter is typically derived?

Accepted Answer

The water level response to a sudden change in water level in a well; aquifer hydraulic conductivity (K) using Hvorslev or Bouwer-Rice methods

Answer

A slug test measures the rate at which water level recovers in a well after a rapid water level displacement (slug insertion or removal), and the recovery curve is analyzed to determine hydraulic conductivity of the surrounding aquifer material.

Question 4

What is the safe yield (sustainable yield) of an aquifer, and why is it a controversial concept?

Accepted Answer

The maximum long-term extraction rate at which the aquifer can produce water without causing unacceptable negative impacts, including depletion, land subsidence, and reduced baseflow to streams

Answer

Safe yield is the maximum sustainable pumping rate that avoids unacceptable impacts; it is controversial because defining 'unacceptable' impacts (stream depletion, subsidence, water quality changes) involves value judgments and varies by stakeholder.

Question 5

What is the primary difference between a gaining stream and a losing stream with respect to groundwater?

Accepted Answer

In a gaining stream, groundwater discharges into the stream channel; in a losing stream, streamflow recharges the groundwater system

Answer

A gaining (effluent) stream receives groundwater baseflow when the water table is above the stream stage; a losing (influent) stream loses water to the aquifer when the stream stage is above the water table.

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Hydrogeology Questions and Answers 2