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MN Well Driller practice questions

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Question 1Water Well Construction and Drilling Practice

In Minnesota, a well's annular space must be sealed with grout primarily to prevent which of the following?

  1. Thermal expansion of the well casing during pumping
  2. Loss of pump efficiency caused by drawdown
  3. Surface and shallow groundwater from moving down the annulus alongside the casing Correct answer.
  4. Corrosion of the submersible pump motor windings

Explanation

Grout creates a continuous hydraulic seal in the annular space so that contaminated surface water and shallow groundwater cannot travel down along the outside of the casing into the producing aquifer. Without that seal, the well acts as a direct conduit between the land surface and the water supply.

Question 2Water Well Construction and Drilling Practice

Which drilling method advances a borehole by repeatedly lifting and dropping a heavy bit on a cable?

  1. Rotary air drilling
  2. Auger drilling
  3. Cable tool drilling Correct answer.
  4. Jetted drilling

Explanation

Cable tool rigs break and loosen formation with a heavy bit suspended on a wire line, then remove cuttings with a bailer. This percussive action is distinct from the rotating bits used in rotary methods.

Question 3Water Well Construction and Drilling Practice

What is the main purpose of a sanitary well seal at the top of a well casing?

  1. To keep surface water, insects, and debris out of the well while securing the drop pipe Correct answer.
  2. To measure the static water level during pumping
  3. To increase the pumping rate by venting the casing
  4. To anchor the pump to the aquifer formation

Explanation

A sanitary seal closes the top of the casing around the pump piping and wiring so that surface contamination, vermin, and debris cannot enter the well. It also mechanically supports the drop pipe and pump assembly.

Question 4Water Well Construction and Drilling Practice

Well casing in Minnesota must extend above the ground surface or floor of the pit to provide which protection?

  1. A mounting point for the pressure tank
  2. A minimum height above grade to keep surface water from entering the well Correct answer.
  3. A sight glass for observing pumping water levels
  4. A vent opening for gas escape from the aquifer

Explanation

Casing is required to terminate a specified height above finished grade so that runoff and ponded surface water cannot flow over the top into the well. This above-grade termination works together with the sanitary seal and grout to protect the water supply.

Question 5Water Well Construction and Drilling Practice

Which term describes the undisturbed water level in a well when the pump has been off long enough to stabilize?

  1. Total dynamic head
  2. Static water level Correct answer.
  3. Pumping water level
  4. Drawdown

Explanation

Static water level is the stabilized, non-pumping level in the well, reflecting the natural potentiometric surface of the aquifer at that location. It is the reference point from which drawdown is measured.

Question 6Water Well Construction and Drilling Practice

A well is completed in a confined sand and gravel aquifer. Which casing feature allows water to enter the well from that formation?

  1. A screened or perforated interval set across the producing zone Correct answer.
  2. A solid drive shoe at the bottom of the casing
  3. A pitless adapter below the frost line
  4. A check valve on the discharge line

Explanation

Water enters a screened or perforated well through openings placed across the producing formation, while the rest of the casing remains solid to exclude other materials. The screen also holds back formation sand and gravel.

Question 7Water Well Construction and Drilling Practice

Which practice best protects a newly drilled well from contamination during completion?

  1. Disinfecting the well and pumping equipment with a chlorine solution before placing the well into service Correct answer.
  2. Backfilling the annulus with drill cuttings to save grout
  3. Flushing the well only with water from the drill pit
  4. Leaving the casing open at the top until the pump is installed

Explanation

Disinfection with a chlorine solution is a standard completion step that reduces bacteria introduced during drilling and equipment installation. It is done after the well is constructed and developed, and the chlorinated water is then purged.

Question 8Water Well Construction and Drilling Practice

What does well development accomplish after drilling is finished?

  1. It permanently lowers the static water level
  2. It removes drilling fluid and fine material from the formation near the borehole to improve yield and water quality Correct answer.
  3. It compresses the gravel pack to reduce its permeability
  4. It increases the casing diameter to allow a larger pump

Explanation

Development draws fines and residual drilling fluids out of the near-well formation and gravel pack so that the well produces clear water at higher specific capacity. Common methods include surging, bailing, and jetting.

Question 9Water Well Construction and Drilling Practice

A well has a static water level of 40 feet and a pumping water level of 65 feet. What is the drawdown?

  1. 105 feet
  2. 40 feet
  3. 25 feet Correct answer.
  4. 65 feet

Explanation

Drawdown is the difference between the static water level and the pumping water level, so 65 minus 40 equals 25 feet. It represents how far pumping has lowered the water in the well.

Question 10Water Well Construction and Drilling Practice

A driller must set casing through 30 feet of unconsolidated sand overlying bedrock. Which completion approach is most appropriate?

  1. Set no casing and rely on the sand to stand open
  2. Set a screen only at the surface to filter runoff
  3. Set casing to bedrock, grout the annulus, and complete the well as an open borehole in the rock Correct answer.
  4. Complete the well entirely in the sand with no grout

Explanation

Casing through the unconsolidated material and seating it into bedrock isolates the sand and gives a stable hole in rock. Grouting the annulus seals off the shallow material so it cannot enter the well.

Question 11Water Well Construction and Drilling Practice

During rotary drilling with mud, the driller notices a sudden large loss of drilling fluid returns. What is the most likely interpretation?

  1. The casing has been properly grouted
  2. The mud pump is running at the correct rate
  3. The bit has worn down and needs replacement
  4. The borehole has intersected a highly permeable or fractured zone that is taking the fluid Correct answer.

Explanation

Lost circulation occurs when drilling fluid escapes into a permeable, cavernous, or fractured formation instead of returning up the annulus. The driller must adjust mud properties or placement before the hole destabilizes.

Question 12Water Well Construction and Drilling Practice

Why is a gravel pack placed around a well screen in a fine sand aquifer?

  1. To seal the screen from the producing formation
  2. To increase the velocity of water entering the well
  3. To chemically treat the water for hardness
  4. To filter formation sand while allowing water to flow freely into the screen Correct answer.

Explanation

A properly sized gravel pack holds back fine formation material and prevents it from plugging the screen or entering the pump. It is selected so formation fines pass while the gravel remains stable.

Question 13Water Well Construction and Drilling Practice

What is the function of a pitless adapter in a Minnesota well installation?

  1. It grouts the annular space during completion
  2. It measures the flow rate delivered to the pressure tank
  3. It provides a below-frost-line connection between the drop pipe and the service line through the casing Correct answer.
  4. It disinfects the water as it leaves the well

Explanation

A pitless adapter lets the service line exit the casing below the frost line, avoiding a buried pit and keeping the well head sealed. This protects the discharge line from freezing and maintains sanitary construction.

Question 14Water Well Construction and Drilling Practice

A driller is choosing between a 4-inch and a 6-inch casing for a domestic well with a required pump setting of 150 feet. What is the primary reason to select the larger casing?

  1. It reduces the required grout volume
  2. It eliminates the need for a sanitary seal
  3. It guarantees a higher aquifer yield
  4. It allows a larger pump and provides more clearance for the pump and drop pipe Correct answer.

Explanation

Casing diameter must accommodate the pump, drop pipe, wiring, and any clearance needed for installation and service. A larger casing allows a larger pump and easier maintenance but does not change aquifer yield.

Question 15Water Well Construction and Drilling Practice

Which condition most strongly indicates that a well screen slot size should be reduced?

  1. Significant sand production observed in the discharge water Correct answer.
  2. A decrease in the depth to bedrock
  3. Rising static water level in the well
  4. An increase in the grout volume used

Explanation

Sand in the produced water means the screen or gravel pack is passing formation material, so a smaller slot or finer pack may be needed to stabilize the formation. Continued sand production can damage pumps and fill the well.

Question 16Water Well Construction and Drilling Practice

What is the purpose of a well casing vent in a sealed well head?

  1. To release chlorine gas during disinfection
  2. To equalize air pressure in the casing as the water level changes Correct answer.
  3. To provide access for the pump installer
  4. To allow surface water to drain into the well

Explanation

A properly screened vent equalizes pressure in the casing as the water level moves, preventing pressure or vacuum that could damage the seal or affect pump operation. The vent must be designed to exclude water, insects, and debris.

Question 17Water Well Construction and Drilling Practice

A well produces clear water at 20 gpm with 30 feet of drawdown. After several years, the same pumping rate produces 55 feet of drawdown. What is the most likely cause?

  1. Increasing head loss from screen or gravel-pack plugging, or declining aquifer performance Correct answer.
  2. A decrease in the pump's power consumption
  3. An increase in the static water level
  4. Improper disinfection of the well

Explanation

Rising drawdown at a constant pumping rate means the well is losing specific capacity, often from plugging of the screen or gravel pack by fines, mineral scale, or biofouling. It can also reflect a regional decline in the aquifer.

Question 18Water Well Construction and Drilling Practice

Which drilling fluid property is most important for carrying cuttings out of a borehole?

  1. Electrical conductivity
  2. Chloride concentration
  3. Viscosity and gel strength Correct answer.
  4. Color and turbidity

Explanation

Viscosity and gel strength determine whether the mud can suspend and transport cuttings up the annulus and then release them at the surface. Mud that is too thin drops cuttings, while mud that is too thick can cause lost circulation.

Question 19Water Well Construction and Drilling Practice

A well is to be grouted with a neat cement slurry. Which placement method best ensures a continuous seal?

  1. Pouring dry cement from the surface into the annulus
  2. Dumping grout into the borehole before setting casing
  3. Backfilling with drill cuttings after casing is set
  4. Pumping grout from the bottom of the annular space upward through a tremie pipe Correct answer.

Explanation

Tremie placement from the bottom up displaces drilling fluid and fills the annulus continuously, avoiding voids and bridging. Surface pouring and pre-placement methods can leave gaps or mix grout with borehole fluid.

Question 20Water Well Construction and Drilling Practice

What does a driller mean by the specific capacity of a well?

  1. The pumping rate divided by the drawdown at that rate Correct answer.
  2. The pump horsepower divided by the discharge head
  3. The static water level divided by the aquifer thickness
  4. The total depth of the well divided by its casing diameter

Explanation

Specific capacity is expressed in gallons per minute per foot of drawdown and is a standard indicator of well efficiency. A declining value over time signals plugging or other loss of performance.

Question 21Water Well Construction and Drilling Practice

A driller encounters a large boulder at 60 feet while advancing a borehole with a mud rotary rig. Which response is most appropriate?

  1. Abandon the borehole without attempting to pass the obstruction
  2. Increase pump pressure to maximum and force the bit through
  3. Reduce weight on bit and rotation, and use a bit or tool suited to hard obstructions before continuing Correct answer.
  4. Switch to backfilling the hole with gravel

Explanation

Hard obstructions require controlled drilling parameters and the right tooling, such as a tricone or button bit, to avoid damaging the string or drifting the hole. Forcing the bit at maximum pressure risks equipment failure and hole deviation.

Question 22Water Well Construction and Drilling Practice

A domestic well is completed with 50 feet of grout in the annulus, but the driller proposes to place the grout only from the surface to 20 feet to save material. What is the principal risk of this shortcut?

  1. The casing will become buoyant and float out of the hole
  2. The static water level will rise above the ground surface
  3. The well will produce too much water for the pump
  4. An unsealed interval remains that can allow shallow contamination to move down the annulus Correct answer.

Explanation

Grout must extend over the full required interval to form a continuous barrier; stopping short leaves a permeable channel where shallow water can descend alongside the casing. The seal must be complete to be effective.

Question 23Water Well Construction and Drilling Practice

A well completed in a fractured granite aquifer shows a high initial yield that drops sharply within months of use. Which explanation is most consistent with this behavior?

  1. The well screen slots were too large
  2. The casing diameter was too small for the pump
  3. The producing fractures are limited and may be dewatered or plugged, so the initial yield was not sustainable Correct answer.
  4. The grout seal was placed too deep

Explanation

Fractured-rock wells produce from discrete fractures whose storage is limited; a high early yield can decline as the fractures drain or as mineral and biological plugging develops. Sustainable yield must be evaluated with a pumping test rather than the initial drill yield.

Question 24Water Well Construction and Drilling Practice

A driller plans to use a bentonite-based drilling mud in a well that will be completed with a gravel pack. Which practice best protects the gravel pack and screen from mud damage?

  1. Flush the screen with the drilling mud after installation
  2. Leave the mud in place so the gravel pack can settle through it
  3. Add more bentonite to thin the mud before completion
  4. Develop the well thoroughly to remove mud cake and residual bentonite before final completion Correct answer.

Explanation

Bentonite residue and filter cake can plug the screen and gravel pack, reducing yield and specific capacity. Thorough development, often with dispersants and surging or jetting, removes the residue before the well is placed in service.

Question 25Water Well Construction and Drilling Practice

A well has 8-inch casing set to 120 feet and a pump set at 110 feet. The static level is 30 feet and the pumping level stabilizes at 70 feet at 15 gpm. What is the specific capacity?

  1. 0.5 gpm per foot of drawdown
  2. 15 gpm per foot of drawdown
  3. 0.375 gpm per foot of drawdown Correct answer.
  4. 2.67 gpm per foot of drawdown

Explanation

Drawdown is 70 minus 30, or 40 feet. Dividing the pumping rate of 15 gpm by 40 feet of drawdown gives 0.375 gpm per foot, which is the specific capacity.

Question 26Water Well Construction and Drilling Practice

Which type of drilling rig is most commonly used for deep, large-diameter water wells in unconsolidated glacial deposits?

  1. Mud rotary rig Correct answer.
  2. Auger rig
  3. Cable tool rig
  4. Air rotary rig

Explanation

Mud rotary rigs circulate drilling fluid to remove cuttings and stabilize the borehole, making them suitable for deep, large-diameter wells in unconsolidated formations. Cable tool rigs are slower and typically used for shallow or boulder-prone holes, air rotary is limited by water influx, and auger rigs are restricted to shallow depths.

Question 27Water Well Construction and Drilling Practice

What is the primary purpose of casing in a water well?

  1. To increase the well yield
  2. To provide a pathway for the pump cable
  3. To filter sand from the produced water
  4. To prevent borehole collapse and protect the well from contamination Correct answer.

Explanation

Casing maintains the borehole opening and seals off unstable formations and potential contamination sources. Yield is determined by the aquifer and screen design, filtration is typically done by a screen or gravel pack, and pump cable support is a secondary function.

Question 28Water Well Construction and Drilling Practice

What does the term 'static water level' refer to in a well?

  1. The level of water in the well when the pump has been off and the water has stabilized Correct answer.
  2. The level of water in the well immediately after drilling is completed
  3. The level of water in the well during a pumping test
  4. The level of water in the well when the pump is running at full capacity

Explanation

Static water level is the stabilized water level in a well when no pumping is occurring and the water has reached equilibrium with the aquifer. Pumping water level, by contrast, is measured during pumping.

Question 29Water Well Construction and Drilling Practice

What is the purpose of a well screen in a water well completed in a sand aquifer?

  1. To measure the water level
  2. To allow water to enter the well while preventing formation sand from entering Correct answer.
  3. To inject grout into the annulus
  4. To support the casing string

Explanation

A well screen is designed with openings that permit water to flow into the well while blocking most formation particles. It does not support casing, measure water levels, or serve as a grout injection point.

Question 30Water Well Construction and Drilling Practice

Which type of pump is most commonly used for deep domestic water wells?

  1. Centrifugal pump
  2. Shallow well jet pump
  3. Piston pump
  4. Submersible pump Correct answer.

Explanation

Submersible pumps are placed downhole and can lift water from deep settings efficiently. Shallow well jet pumps are limited to about 25 feet of lift, centrifugal pumps are typically surface-mounted, and piston pumps are used in specialized or shallow applications.

Question 31Water Well Construction and Drilling Practice

What is the purpose of grouting the annular space between the casing and the borehole wall?

  1. To provide structural support for the pump
  2. To lubricate the casing during installation
  3. To seal the annulus and prevent contamination from entering the well Correct answer.
  4. To increase the well yield

Explanation

Grout forms a hydraulic seal that prevents surface water and shallow groundwater from migrating down the annulus and contaminating the well. It does not lubricate casing, increase yield, or support the pump.

Question 32Water Well Construction and Drilling Practice

What is the primary function of a pitless adapter in a well installation?

  1. To support the weight of the pump and drop pipe
  2. To provide a watertight connection through the casing below the frost line Correct answer.
  3. To allow air to enter the well for proper pump operation
  4. To measure the water level in the well

Explanation

A pitless adapter connects the well's drop pipe to the service line through the casing below the frost line, providing a sanitary and frost-free connection. It does not support the pump, admit air, or measure water level.

Question 33Water Well Construction and Drilling Practice

A driller is using a mud rotary rig and observes that the drilling fluid returns have decreased significantly. What is the most likely cause?

  1. The cuttings are too small
  2. The mud pump is running too fast
  3. The borehole has penetrated a highly permeable zone and is losing fluid Correct answer.
  4. The mud viscosity is too high

Explanation

A sudden loss of returns often indicates that the borehole has encountered a permeable formation, such as a sand or gravel layer or a fracture, allowing fluid to escape into the formation. Increasing pump speed or viscosity would not solve the loss and could worsen it.

Question 34Water Well Construction and Drilling Practice

A well is completed with a 6-inch diameter casing to a depth of 200 feet. The static water level is 50 feet, and the pumping water level is 80 feet. What is the drawdown?

  1. 50 feet
  2. 130 feet
  3. 30 feet Correct answer.
  4. 80 feet

Explanation

Drawdown is the difference between the static water level and the pumping water level. Here, 80 feet minus 50 feet equals 30 feet.

Question 35Water Well Construction and Drilling Practice

Which method is best for developing a well completed in a fine sand aquifer to remove drilling mud and fines?

  1. Air lifting
  2. Overpumping at a high rate
  3. Backwashing with a high-pressure jet
  4. Surging with a surge block Correct answer.

Explanation

Surging with a surge block creates a hydraulic action that loosens and removes fines and mud from the gravel pack and screen without causing formation damage. Overpumping can cause sand production and may not effectively clean the entire screen, air lifting is more suited to rock wells, and high-pressure jetting can damage the screen.

Question 36Water Well Construction and Drilling Practice

A driller is setting casing through a 40-foot layer of unconsolidated sand and gravel to reach a confined aquifer below. Which casing material is most commonly used for this application?

  1. PVC plastic Correct answer.
  2. Steel
  3. Fiberglass
  4. Concrete

Explanation

PVC casing is widely used in domestic water wells because it is durable, corrosion-resistant, and cost-effective for typical depths and loads. Steel is used in deeper or larger wells, concrete is rarely used for small-diameter wells, and fiberglass is used in specialized applications.

Question 37Water Well Construction and Drilling Practice

What is the primary purpose of a well development process after drilling?

  1. To disinfect the well with chlorine
  2. To remove drilling fluids and fines from the borehole and surrounding formation Correct answer.
  3. To increase the well yield by fracturing the formation
  4. To measure the specific capacity of the well

Explanation

Well development removes drilling mud, cuttings, and fine particles from the screen and gravel pack, improving hydraulic connection with the aquifer. It does not intentionally fracture the formation, disinfect (that is a separate step), or measure specific capacity.

Question 38Water Well Construction and Drilling Practice

A well is drilled to 150 feet in a sandstone aquifer. The driller plans to install a 20-foot screen at the bottom. What is the recommended placement of the grout seal?

  1. From the top of the screen to land surface
  2. From the top of the gravel pack to land surface Correct answer.
  3. Only in the upper 20 feet of the annulus
  4. From the bottom of the casing to land surface

Explanation

The grout seal should extend from the top of the gravel pack (or the top of the screen if no gravel pack) to land surface to prevent contamination. Grouting from the top of the screen would leave the gravel pack unsealed, and grouting only the upper 20 feet would not provide a continuous seal.

Question 39Water Well Construction and Drilling Practice

Which factor most directly determines the slot size of a well screen in a sand aquifer?

  1. The pumping rate of the well
  2. The diameter of the casing
  3. The grain size distribution of the aquifer material Correct answer.
  4. The depth of the static water level

Explanation

Screen slot size is selected based on the grain size distribution of the formation to retain a high percentage of sand while allowing water to flow. Pumping rate, casing diameter, and water level do not directly dictate slot size.

Question 40Water Well Construction and Drilling Practice

A driller is using a cable tool rig to drill through a boulder formation. Which technique is most appropriate for advancing the borehole?

  1. Switching to a tricone bit
  2. Using a heavier string and a chisel bit to break the boulder Correct answer.
  3. Reducing the stroke rate to avoid damage
  4. Increasing the drilling fluid viscosity

Explanation

Cable tool rigs break rock by impact; a heavier string and a chisel bit provide the force needed to fracture boulders. Increasing fluid viscosity is not effective for breaking rock, tricone bits are used with rotary rigs, and reducing stroke rate would slow progress.

Question 41Water Well Construction and Drilling Practice

What is the purpose of a sanitary well seal at the top of a well casing?

  1. To prevent surface water and contaminants from entering the well Correct answer.
  2. To measure the water level
  3. To allow air to escape from the well
  4. To support the pump drop pipe

Explanation

A sanitary well seal provides a watertight and vermin-proof closure at the top of the casing, preventing contamination from entering. It may include a vent, but its primary purpose is sealing.

Question 42Water Well Construction and Drilling Practice

A well has a static water level of 60 feet and a pumping water level of 90 feet at a pumping rate of 15 gpm. What is the specific capacity?

  1. 2 gpm/ft
  2. 30 gpm/ft
  3. 0.5 gpm/ft Correct answer.
  4. 6 gpm/ft

Explanation

Specific capacity is pumping rate divided by drawdown. Drawdown is 90 ft minus 60 ft = 30 ft. 15 gpm / 30 ft = 0.5 gpm/ft.

Question 43Water Well Construction and Drilling Practice

Which drilling method is most suitable for drilling a well in a consolidated rock formation with minimal water inflow?

  1. Mud rotary
  2. Cable tool
  3. Auger
  4. Air rotary Correct answer.

Explanation

Air rotary drilling is effective in consolidated rock because the air clears cuttings and the hole is stable, and it avoids the need for drilling mud that could plug fractures. Mud rotary is also used but may reduce fracture permeability, auger is for unconsolidated materials, and cable tool is slower.

Question 44Water Well Construction and Drilling Practice

A well is completed with a gravel pack. Which factor is most important in selecting the gravel pack material?

  1. The angularity of the grains
  2. The grain size relative to the aquifer sand Correct answer.
  3. The color of the gravel
  4. The cost per ton

Explanation

The gravel pack grain size must be chosen to retain the formation sand while allowing water to flow freely, typically based on a size ratio to the aquifer material. Color, cost, and angularity are secondary considerations.

Question 45Water Well Construction and Drilling Practice

What is the primary purpose of a pump test on a newly completed well?

  1. To develop the well
  2. To measure the water quality
  3. To disinfect the well
  4. To determine the well's yield and drawdown characteristics Correct answer.

Explanation

A pump test measures pumping rate, drawdown, and recovery to evaluate well performance and specific capacity. Disinfection and development are separate procedures, and water quality is determined by laboratory analysis.

Question 46Water Well Construction and Drilling Practice

A driller is installing a submersible pump in a well with a static water level at 80 feet and a pumping water level at 120 feet. The pump should be set at least 10 feet below the pumping water level. What is the minimum pump setting depth?

  1. 90 feet
  2. 120 feet
  3. 130 feet Correct answer.
  4. 80 feet

Explanation

The pump must be set below the pumping water level to avoid cavitation. Adding the 10-foot safety margin to the pumping level of 120 feet gives 130 feet.

Question 47Water Well Construction and Drilling Practice

Which condition would most likely cause a well to produce sand along with water?

  1. Pump set too deep
  2. Grout seal improperly placed
  3. Casing diameter too small
  4. Screen slot size too large for the formation Correct answer.

Explanation

If the screen openings are larger than the formation particles, sand can pass through and be produced with the water. Grout issues affect contamination, casing diameter affects capacity, and pump depth affects drawdown but not sand production directly.

Question 48Water Well Construction and Drilling Practice

A well in a fractured granite aquifer has an initial yield of 50 gpm, but after six months the yield drops to 10 gpm. What is the most likely cause?

  1. The fractures are clogged with mineral deposits or fine sediment Correct answer.
  2. The static water level has risen
  3. The pump impellers are worn
  4. The well screen is plugged

Explanation

In fractured rock wells, fractures can become clogged with mineral precipitates or fine particles, reducing yield over time. Pump wear would affect pressure but not necessarily yield, a rising water level would increase yield, and granite wells typically do not have screens.

Question 49Water Well Construction and Drilling Practice

A driller is using bentonite-based drilling mud and plans to install a gravel pack. Which practice is most important to ensure the gravel pack functions properly?

  1. Use a higher density mud to prevent cave-in
  2. Increase the mud viscosity before completion
  3. Add sand to the mud to improve filter cake
  4. Remove the mud cake and bentonite residue from the borehole wall before placing the gravel pack Correct answer.

Explanation

Bentonite residue and mud cake can clog the gravel pack and reduce its permeability, so the borehole should be cleaned and the mud removed before gravel packing. Increasing viscosity or density would worsen clogging, and adding sand is not a standard practice.

Question 50Water Well Construction and Drilling Practice

A well has 8-inch casing set to 120 feet, with a pump set at 110 feet. The static water level is 30 feet, and the pumping water level is 70 feet. What is the drawdown, and what is the specific capacity if the pumping rate is 20 gpm?

  1. Drawdown 30 ft; specific capacity 0.67 gpm/ft
  2. Drawdown 40 ft; specific capacity 2 gpm/ft
  3. Drawdown 70 ft; specific capacity 0.29 gpm/ft
  4. Drawdown 40 ft; specific capacity 0.5 gpm/ft Correct answer.

Explanation

Drawdown is 70 ft - 30 ft = 40 ft. Specific capacity is 20 gpm / 40 ft = 0.5 gpm/ft.