NGWA EVALUATION EXAM 2025 QUESTIONS AND
ANSWERS RATED A+
Explain the difference between rotary "table drive" and "top head drive". - ✔✔A rotary
table drive rotates the drill string from the rig floor using a Kelly and requires more time
to add pipe sections during drilling. A top head drive rotates the drill string from the top,
allowing for continuous drilling and faster operations without the need for a Kelly.
✔✔What purpose does the drilling fluid serve in rotary drilling? - ✔✔1. Cools and
lubricates the drill bit
2. Removes cuttings from the wellbore by carrying them to the surface
3. Stabilizes the wellbore walls
4. Maintains downhole pressure to prevent blowouts or formation fluid influx.
5. It also helps in suspending cuttings when circulation is paused.
✔✔Define water table. - ✔✔The water table is the upper level of groundwater in an
aquifer where the soil or rock is fully saturated with water. It separates the unsaturated
zone above from the saturated zone below.
✔✔How do you determine the static water pressure? - ✔✔Static water pressure is
determined by measuring the height of the water column above the point of
measurement in the well. It is calculated using the formula.
Pressure (psi) = Height of water column (ft) × 0.433.
✔✔Define aquifer. - ✔✔An aquifer is a geological formation of permeable rock, sand, or
gravel that can store and transmit groundwater, providing a source of water for wells
and springs.
✔✔What is an artesian well? - ✔✔An artesian well is a type of well where groundwater
is under pressure, causing water to rise to the surface naturally without the need for
pumping. This occurs when the well taps into a confined aquifer.
✔✔What is the difference between confined and unconfined aquifers? - ✔✔A confined
aquifer is trapped between two impermeable layers of rock or clay, creating pressure
that can cause water to rise in a well.
An unconfined aquifer has no confining layer above it, so its water level is influenced
directly by the surface and atmospheric pressure.
✔✔Permeability refers to what quality in a water bearing formation? - ✔✔Permeability
refers to the ability of a water-bearing formation to transmit water through its pores or
fractures, allowing groundwater to flow through the material.
✔✔How fast does ground water move in the following formation?
, - Sand and gravel?
- Sandstone?
- Non-porous rock? - ✔✔Sand and Gravel: Groundwater moves relatively quickly,
typically ranging from 1 to 100 feet per day.
Sandstone: Groundwater moves more slowly, usually between 0.01 to 1 foot per day.
Non-Porous Rock: Groundwater movement is extremely slow or negligible, often less
than 0.001 feet per day.
✔✔Explain how ground water formations could be recharged. Define infiltration. -
✔✔Groundwater formations are recharged through the process of precipitation, where
rain or snowmelt infiltrates the ground, moving through the soil and permeable layers
until it reaches the water table. Recharge can also occur from surface water bodies like
rivers, lakes, or artificial recharge methods.
Infiltration is the process by which water on the surface enters the soil and moves
downward into the subsurface, contributing to groundwater recharge.
✔✔How is precipitation measured? What amount of precipitation becomes ground
water? - ✔✔Precipitation is measured using devices like rain gauges, which collect and
measure the amount of rain, snow, or other forms of moisture over a set period. The
amount of precipitation that becomes groundwater varies but is typically around 10% to
20%, depending on factors such as soil type, vegetation, slope, and climate conditions.
✔✔How can you determine the storage measure of aquifers? - ✔✔The storage
measure of aquifers is determined by calculating the specific yield (the volume of water
that drains from the aquifer under gravity) and the specific retention (the volume of
water retained by the aquifer). These are combined with the aquifer's total area and
thickness to estimate the total volume of water the aquifer can store.
4o
✔✔Transmissivity or transmissibility of aquifers refers to what features? -
✔✔Transmissivity (or transmissibility) of aquifers refers to the ability of the aquifer to
transmit water through its entire saturated thickness. It is the product of the permeability
of the aquifer material and its thickness, indicating how much water can flow horizontally
through a unit width of the aquifer.
✔✔Briefly explain the hydrogeologic cycle. - ✔✔The hydrogeologic cycle (or water
cycle) describes the continuous movement of water on, above, and below the Earth's
surface. It includes processes like evaporation, condensation, precipitation, infiltration,
and runoff, where water circulates between the atmosphere, land, and groundwater
systems.
ANSWERS RATED A+
Explain the difference between rotary "table drive" and "top head drive". - ✔✔A rotary
table drive rotates the drill string from the rig floor using a Kelly and requires more time
to add pipe sections during drilling. A top head drive rotates the drill string from the top,
allowing for continuous drilling and faster operations without the need for a Kelly.
✔✔What purpose does the drilling fluid serve in rotary drilling? - ✔✔1. Cools and
lubricates the drill bit
2. Removes cuttings from the wellbore by carrying them to the surface
3. Stabilizes the wellbore walls
4. Maintains downhole pressure to prevent blowouts or formation fluid influx.
5. It also helps in suspending cuttings when circulation is paused.
✔✔Define water table. - ✔✔The water table is the upper level of groundwater in an
aquifer where the soil or rock is fully saturated with water. It separates the unsaturated
zone above from the saturated zone below.
✔✔How do you determine the static water pressure? - ✔✔Static water pressure is
determined by measuring the height of the water column above the point of
measurement in the well. It is calculated using the formula.
Pressure (psi) = Height of water column (ft) × 0.433.
✔✔Define aquifer. - ✔✔An aquifer is a geological formation of permeable rock, sand, or
gravel that can store and transmit groundwater, providing a source of water for wells
and springs.
✔✔What is an artesian well? - ✔✔An artesian well is a type of well where groundwater
is under pressure, causing water to rise to the surface naturally without the need for
pumping. This occurs when the well taps into a confined aquifer.
✔✔What is the difference between confined and unconfined aquifers? - ✔✔A confined
aquifer is trapped between two impermeable layers of rock or clay, creating pressure
that can cause water to rise in a well.
An unconfined aquifer has no confining layer above it, so its water level is influenced
directly by the surface and atmospheric pressure.
✔✔Permeability refers to what quality in a water bearing formation? - ✔✔Permeability
refers to the ability of a water-bearing formation to transmit water through its pores or
fractures, allowing groundwater to flow through the material.
✔✔How fast does ground water move in the following formation?
, - Sand and gravel?
- Sandstone?
- Non-porous rock? - ✔✔Sand and Gravel: Groundwater moves relatively quickly,
typically ranging from 1 to 100 feet per day.
Sandstone: Groundwater moves more slowly, usually between 0.01 to 1 foot per day.
Non-Porous Rock: Groundwater movement is extremely slow or negligible, often less
than 0.001 feet per day.
✔✔Explain how ground water formations could be recharged. Define infiltration. -
✔✔Groundwater formations are recharged through the process of precipitation, where
rain or snowmelt infiltrates the ground, moving through the soil and permeable layers
until it reaches the water table. Recharge can also occur from surface water bodies like
rivers, lakes, or artificial recharge methods.
Infiltration is the process by which water on the surface enters the soil and moves
downward into the subsurface, contributing to groundwater recharge.
✔✔How is precipitation measured? What amount of precipitation becomes ground
water? - ✔✔Precipitation is measured using devices like rain gauges, which collect and
measure the amount of rain, snow, or other forms of moisture over a set period. The
amount of precipitation that becomes groundwater varies but is typically around 10% to
20%, depending on factors such as soil type, vegetation, slope, and climate conditions.
✔✔How can you determine the storage measure of aquifers? - ✔✔The storage
measure of aquifers is determined by calculating the specific yield (the volume of water
that drains from the aquifer under gravity) and the specific retention (the volume of
water retained by the aquifer). These are combined with the aquifer's total area and
thickness to estimate the total volume of water the aquifer can store.
4o
✔✔Transmissivity or transmissibility of aquifers refers to what features? -
✔✔Transmissivity (or transmissibility) of aquifers refers to the ability of the aquifer to
transmit water through its entire saturated thickness. It is the product of the permeability
of the aquifer material and its thickness, indicating how much water can flow horizontally
through a unit width of the aquifer.
✔✔Briefly explain the hydrogeologic cycle. - ✔✔The hydrogeologic cycle (or water
cycle) describes the continuous movement of water on, above, and below the Earth's
surface. It includes processes like evaporation, condensation, precipitation, infiltration,
and runoff, where water circulates between the atmosphere, land, and groundwater
systems.
