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MD Well Driller practice questions

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Question 1Water Supply and Well Construction

When grouting the annular space of a well with a neat cement slurry, which property most directly controls whether the slurry can be pumped without bridging?

  1. The color of the cement powder after mixing
  2. The length of the casing string above ground
  3. The thread type used on the casing couplings
  4. The slurry's water-to-cement ratio and resulting viscosity Correct answer.

Explanation

Pumpability of a cement grout depends primarily on its water-to-cement ratio, which sets viscosity, density, and set time. A slurry that is too thick bridges and refuses to flow up the annulus, while an overly thin one may settle and leave voids. Density and viscosity are the practical field checks a driller uses before pumping.

Question 2Water Supply and Well Construction

A well is completed in a confined sand aquifer where the static water level rises to 4 m above the top of the screen. What does this indicate about the aquifer?

  1. The aquifer is unconfined and dewatered
  2. The screen is plugged with fine sediment
  3. The aquifer is under artesian (confined) pressure Correct answer.
  4. The well is drawing air through the vent

Explanation

When the static water level stands above the top of a confined aquifer, the aquifer is under artesian pressure and the well is artesian. The rise is caused by confinement between low-permeability layers, not by pumping effects. A plugged screen or air entry would show as drawdown or turbulence, not a static rise.

Question 3Water Supply and Well Construction

Which casing material is normally selected for a municipal supply well where the water is aggressive, low in pH, and high in chloride?

  1. Concrete casing
  2. Thermoplastic (PVC) casing Correct answer.
  3. Ductile iron casing
  4. Galvanized steel casing

Explanation

Aggressive, low-pH, high-chloride water attacks ferrous and cementitious materials, so a corrosion-resistant thermoplastic such as PVC is commonly selected. Galvanized steel loses its zinc coating quickly in such water, and ductile iron and concrete are also vulnerable to chloride and acid attack. Material selection must match the water chemistry over the design life of the well.

Question 4Water Supply and Well Construction

A driller installs a well screen with an opening size much larger than the formation's d50 grain size. What is the most likely consequence?

  1. Reduced entrance velocity and improved well efficiency
  2. Excessive sand production and possible formation collapse around the screen Correct answer.
  3. Higher screen strength and longer service life
  4. Increased static water level in the well

Explanation

A screen opening substantially larger than the formation grain size allows sand to pass into the well, causing sand production, pump wear, and possible settling or collapse of the formation. Proper screen sizing is based on the grain-size distribution, often with a filter pack. Screen strength and entrance velocity are secondary concerns compared with retaining the formation.

Question 5Water Supply and Well Construction

During well development by surging, what is the primary purpose of the surging action?

  1. To compact the gravel pack into a solid impermeable mass
  2. To draw fine material from the formation into the well for removal Correct answer.
  3. To increase the cement bond around the casing
  4. To sterilize the screen and gravel pack

Explanation

Surging reverses flow through the screen, loosening fines and drawing them into the well so they can be removed, which increases permeability near the borehole. The goal is a clean, stable filter, not a compacted impermeable pack. Disinfection is a separate step performed after development.

Question 6Water Supply and Well Construction

What is the main function of a sanitary seal in a drilled water well?

  1. To prevent surface water and shallow contamination from entering the annulus Correct answer.
  2. To filter sediment from the produced water
  3. To support the weight of the casing string
  4. To increase the well's specific capacity

Explanation

The sanitary seal, typically a grout or bentonite plug near the surface, blocks the annular pathway that would otherwise let surface water and shallow contaminated water travel down along the casing. It is a barrier against contamination, not a structural or filtration element. Proper placement and continuity of the seal are critical to well integrity.

Question 7Water Supply and Well Construction

Which parameter is normally measured to determine the static water level in a newly completed well before pumping begins?

  1. The depth to water from a surveyed reference point on the casing Correct answer.
  2. The turbidity of the produced water
  3. The pumping rate during the test
  4. The discharge pressure at the pump

Explanation

Static water level is the depth to water measured from a fixed, surveyed reference point, such as the top of casing, when the well is at rest. This baseline is needed to calculate drawdown and specific capacity. Pumping rate, discharge pressure, and turbidity are dynamic or quality measurements, not the static level.

Question 8Water Supply and Well Construction

A gravel pack is placed around a well screen in a fine sand aquifer. What is its principal purpose?

  1. To raise the pumping water level in the well
  2. To stabilize the formation and reduce sand entry while maintaining flow Correct answer.
  3. To seal the annulus against vertical water movement
  4. To increase the collapse strength of the casing

Explanation

A properly graded gravel pack acts as a filter that holds back formation fines while allowing water to flow freely to the screen. It also supports the borehole wall in unstable formations. Sealing is done by grout or bentonite, and the pack does not strengthen the casing or raise water levels.

Question 9Water Supply and Well Construction

A well produces 15 L/s with a drawdown of 3 m after stabilization. What is the specific capacity?

  1. 18 L/s per m of drawdown
  2. 45 L/s per m of drawdown
  3. 5 L/s per m of drawdown Correct answer.
  4. 0.2 L/s per m of drawdown

Explanation

Specific capacity is discharge divided by drawdown, so 15 L/s divided by 3 m equals 5 L/s per metre. It expresses how much water the well yields for each metre of water-level decline. Multiplying or inverting the values gives the wrong units and magnitude.

Question 10Water Supply and Well Construction

A driller must set casing through a 12 m interval of running sand that collapses as the hole is drilled. Which construction approach best addresses this condition?

  1. Drill the full hole first and set casing after reaching total depth
  2. Use a larger bit and rely on the mud cake to hold the sand
  3. Drive or advance casing concurrently with drilling through the collapsing interval Correct answer.
  4. Pump clear water to wash the sand back during drilling

Explanation

Running sand collapses into an open hole, so casing must be advanced with the drilling to support the interval as it is penetrated. Drilling the full hole first would allow the sand to fill the borehole before casing can be set. Clear water washing removes the material and worsens the collapse.

Question 11Water Supply and Well Construction

A well is pumped at a constant rate and the drawdown curve is plotted on semi-log paper. The early steep portion of the curve steepens further after several hours. What does this most likely indicate?

  1. The onset of artesian conditions
  2. An increase in the aquifer's transmissivity
  3. A measurement error in the discharge rate
  4. Well loss or a low-permeability boundary affecting the well Correct answer.

Explanation

A steepening or upward break in the drawdown curve during a constant-rate test commonly reflects well loss, a nearby low-permeability boundary, or interference rather than a change in aquifer storage. Transmissivity does not increase during pumping. Artesian conditions are a pre-existing aquifer state, not a mid-test change.

Question 12Water Supply and Well Construction

What is the correct sequence for completing a screened well in a sand aquifer?

  1. Drill, set casing and screen, place gravel pack, develop, disinfect, test pump Correct answer.
  2. Drill, place gravel pack, set screen, test pump, develop, disinfect
  3. Drill, disinfect, set screen, develop, place gravel pack, test pump
  4. Drill, develop, set screen, disinfect, place gravel pack, test pump

Explanation

The screen and casing are installed first, then the gravel pack is placed around the screen, followed by development to remove fines, disinfection, and finally test pumping to verify yield. Developing before the pack is in place or disinfecting before development would leave fines and contamination in the well. Test pumping is the acceptance step at the end.

Question 13Water Supply and Well Construction

A well in a limestone aquifer shows a sudden loss of drilling fluid and very rapid penetration. What does this most likely indicate?

  1. The bit has become dull
  2. The mud weight is too high for the formation
  3. The casing has parted downhole
  4. A solution channel or cavern has been intersected Correct answer.

Explanation

Sudden fluid loss combined with a rapid penetration rate in limestone is characteristic of intersecting a solution opening or cavern. The fluid escapes into the void and the bit drops through the cavity. A dull bit slows penetration, and casing problems are unrelated to drilling-fluid loss during drilling.

Question 14Water Supply and Well Construction

Which factor most strongly determines the required wall thickness of steel casing in a deep supply well?

  1. The type of pump starter used
  2. The color coding of the pipe mill
  3. The pumping water level during the first hour
  4. The collapse and tensile loads expected over the design life Correct answer.

Explanation

Casing wall thickness is selected to resist the collapse pressure from outside loads and the tensile load of the suspended string, with a design safety factor. These loads grow with depth and with grout and formation pressures. Paint coding, short-term water levels, and electrical equipment do not govern structural design.

Question 15Water Supply and Well Construction

A well is disinfected with a chlorine solution. Which practice is correct before the well is returned to service?

  1. Add chlorine continuously to maintain a permanent residual in the aquifer
  2. Disinfect only the pump, not the casing and screen
  3. Flush immediately so no chlorine enters the distribution system
  4. Allow adequate contact time, then flush until residual chlorine is at an acceptable level Correct answer.

Explanation

Disinfection requires a specified chlorine concentration and contact time so the biocide can act on the casing, screen, and pump. After contact, the well is flushed until the residual chlorine falls to an acceptable level before sampling or service. Continuous dosing of the aquifer or disinfecting only the pump does not achieve proper well disinfection.

Question 16Water Supply and Well Construction

A well's pumping water level stabilizes quickly but the specific capacity is much lower than nearby wells of the same depth. Which explanation is most consistent with these observations?

  1. A higher elevation of the pump setting
  2. A change in the barometric pressure
  3. A regional decline in the aquifer water table
  4. High well loss from a poorly developed or undersized screen interval Correct answer.

Explanation

Rapid stabilization with unusually low specific capacity points to well loss rather than aquifer limitation, often from inadequate development, an undersized screen, or a damaged gravel pack. Regional water-table decline would affect the static level and neighboring wells similarly. Barometric pressure and pump setting depth do not explain a localized capacity deficit.

Question 17Water Supply and Well Construction

When mixing bentonite grout for an annular seal, why is the mix often designed to be relatively dense and low in free water?

  1. To limit shrinkage and settling so the seal stays continuous Correct answer.
  2. To increase the pumping pressure needed for placement
  3. To speed up the set of the cement fraction
  4. To reduce the cost of the grout per cubic metre

Explanation

A dense, low-free-water bentonite grout resists settling, syneresis, and shrinkage, keeping the annular seal continuous and bonded to the formation. Excess water produces a weaker, more permeable seal that can bridge or leave voids. Placement pressure and cost are secondary considerations compared with seal integrity.

Question 18Water Supply and Well Construction

A driller observes that the water level in a well rises and falls slightly in phase with changes in atmospheric pressure. What is the best interpretation?

  1. The well is open to a confined aquifer and responds barometrically Correct answer.
  2. The aquifer is being recharged by a nearby river
  3. The well is leaking surface water through the seal
  4. The pump is cycling on and off

Explanation

Wells completed in confined aquifers respond to barometric pressure changes because the aquifer and the well are isolated from the atmosphere by the confining layer. The water level moves inversely with atmospheric pressure. Surface leakage, pump cycling, and river recharge would produce different timing and patterns.

Question 19Water Supply and Well Construction

Which condition would most likely require a larger screen open area than normal for a given yield?

  1. A high-capacity well where entrance velocity must be kept low Correct answer.
  2. A well with a very short screen interval
  3. A shallow well with a low pumping rate
  4. A well completed in a thick clay layer

Explanation

Screen open area is chosen so that entrance velocity stays below the value that would mobilize fines or cause excessive head loss. High-capacity wells therefore need more open area, often achieved with longer screens or larger slot area. Low yield, clay formations, and short screen intervals do not drive a need for greater open area.

Question 20Water Supply and Well Construction

A well is to be completed in a fractured crystalline rock aquifer. Which completion approach is generally most appropriate?

  1. A fully slotted screen through the entire rock interval
  2. An open borehole intersecting the water-bearing fractures, with casing through the overburden Correct answer.
  3. A concrete liner sealed at the top only
  4. A continuous gravel pack from surface to total depth

Explanation

In crystalline rock, groundwater flows through discrete fractures, so an open borehole that intersects the productive fractures is standard, with casing and seal through the overburden to protect the hole. Gravel packing the entire rock interval or fully slotted screening is unnecessary and can block fractures. A liner sealed only at the top does not provide a proper sanitary seal.

Question 21Water Supply and Well Construction

A well test shows that drawdown increases disproportionately as pumping rate is increased, while the static level is unchanged. Which interpretation is best supported?

  1. The static water level measurement is wrong
  2. The aquifer transmissivity has decreased
  3. Well loss is significant and grows with the square of discharge Correct answer.
  4. The screen has become more permeable

Explanation

Well loss is turbulent and increases approximately with the square of discharge, so step tests show disproportionately larger drawdown at higher rates while static level stays the same. Aquifer transmissivity is a fixed property, and the static level is measured independently of pumping. Increased screen permeability would reduce, not increase, well loss.

Question 22Water Supply and Well Construction

A driller plans a well near a pumping well that has been operating for years. What effect should be expected on the new well's pumping water level?

  1. No change because each well has its own cone of depression
  2. A permanent rise in the aquifer's transmissivity
  3. Additional drawdown from interference between the two wells Correct answer.
  4. A higher static water level due to shared recharge

Explanation

Overlapping cones of depression cause interference, so the new well experiences additional drawdown beyond its own pumping effect. The static level is not raised by a neighboring pumping well, and cones of depression do overlap rather than remain separate. Transmissivity is an aquifer property and does not change.

Question 23Water Supply and Well Construction

A deep well is grouted with a cement slurry whose density is much higher than the drilling fluid it displaces. What is the main risk if the annulus is not sealed at the bottom during placement?

  1. The grout will set too slowly to be effective
  2. The heavier grout may channel or bypass the drilling fluid, leaving voids Correct answer.
  3. The drilling fluid will become denser than the grout
  4. The casing will float out of the hole

Explanation

Density differences drive the grout to seek the easiest path, and without a bottom seal or proper displacement the grout can channel through the lighter drilling fluid. That leaves ungrouted pockets that compromise the seal. Grout set time and drilling-fluid density are separate issues, and casing flotation is not a realistic risk here.

Question 24Water Supply and Well Construction

A well in a coastal aquifer shows chloride concentrations rising steadily over months of pumping. Which mechanism best explains this trend?

  1. Dissolution of the gravel pack
  2. Upconing or lateral intrusion of saline water drawn toward the well Correct answer.
  3. Corrosion of the casing releasing chloride
  4. Increased recharge from rainfall

Explanation

Sustained pumping in a coastal aquifer lowers freshwater heads and can draw saline water upward (upconing) or laterally toward the well, raising chloride over time. Casing corrosion and gravel-pack dissolution do not release chloride at the observed scale. Increased rainfall recharge would dilute, not raise, chloride.

Question 25Water Supply and Well Construction

During a constant-rate pumping test, the observation well shows a delayed response compared with the pumped well. What does this most likely reflect?

  1. A higher pumping rate in the pumped well
  2. An error in the observation well's depth
  3. The absence of a confining layer
  4. The storage coefficient and distance between the wells Correct answer.

Explanation

The time lag between pumping and observation responses depends on aquifer storativity and the distance between the wells, as described by transient flow theory. A higher pumping rate changes the magnitude of drawdown but not the fundamental lag relationship. Observation-well depth and confinement alter the response but are not the explanation for a lag.

Question 26Water Supply and Well Construction

Which casing material is most commonly specified for a municipal supply well where the groundwater has high chloride and low pH?

  1. Thermoplastic (uPVC) casing Correct answer.
  2. Type 304 stainless steel
  3. Galvanized steel casing
  4. Low-carbon steel casing

Explanation

Thermoplastic casing such as uPVC is resistant to chlorides and to mildly acidic water and is widely used where corrosion of steel is a concern. It is inert to galvanic attack and does not require cathodic protection. Steel and galvanized options remain vulnerable to chloride-driven corrosion and pitting.

Question 27Water Supply and Well Construction

In a drilled well, what is the primary purpose of the annular space between the borehole wall and the casing?

  1. To provide a pathway for air-lift development
  2. To allow the casing to be rotated during installation
  3. To be filled with grout or filter material that seals and stabilizes the well Correct answer.
  4. To store surplus drilling fluid for later reuse

Explanation

The annulus is the space that receives the grout seal, filter pack, or both, which isolate aquifers and hold the formation in place. Leaving it open would permit cross-connection between water-bearing zones and surface contamination. The annulus is not a storage or installation device.

Question 28Water Supply and Well Construction

A driller must choose a drilling method for a deep, large-diameter well in hard, stable bedrock. Which method is generally the most suitable?

  1. Hand augering
  2. Direct rotary drilling with mud
  3. Cable-tool (percussion) drilling
  4. Reverse-circulation rotary drilling Correct answer.

Explanation

Reverse-circulation rotary drilling moves large volumes of cuttings and is efficient for large-diameter holes in stable rock. It offers good penetration rates and hole cleaning at depth. The other methods are either slow, limited in diameter, or unsuitable for deep rock.

Question 29Water Supply and Well Construction

Which well screen slot size is most appropriate for a uniform sand with a grain-size distribution where the 50 percent passing size (D50) is 0.5 mm?

  1. Slot size equal to the largest grain in the sample
  2. Slot size approximately 2 to 3 times D50 Correct answer.
  3. Slot size about half of D50
  4. Slot size approximately equal to D50

Explanation

For a naturally developed screen in uniform sand, the slot opening is set to retain most of the formation while allowing fines to be removed during development. A common rule is about 2 to 3 times the D50 for uniform material. Slots equal to or smaller than D50 would plug rapidly, and slots equal to the largest grain would pass the formation.

Question 30Water Supply and Well Construction

What is the standard purpose of a bentonite or cement grout seal placed above the well screen or filter pack?

  1. To reduce the weight of the casing string
  2. To provide a source of alkalinity to the pumped water
  3. To increase well yield by restricting flow
  4. To prevent vertical movement of water and contaminants along the annulus Correct answer.

Explanation

The annular seal blocks the vertical pathway between aquifers and between the surface and the well, which is essential for protecting water quality. It also stabilizes the casing. It does not increase yield or alter water chemistry intentionally.

Question 31Water Supply and Well Construction

A well is developed after screen installation. Which result best indicates that development has been effective?

  1. The pumping water level rises above the static level
  2. The pumped water remains turbid throughout the test
  3. The specific capacity increases and the water clears as fines are removed Correct answer.
  4. The static water level drops permanently

Explanation

Effective development removes drilling fines and loose material from the filter pack and near-well formation, which improves flow and clears the water. Specific capacity typically improves as a result. Turbidity persisting and declining water levels indicate problems rather than success.

Question 32Water Supply and Well Construction

Which document typically specifies the required casing diameter, screen interval, and grout depth for a new public water-supply well?

  1. The driller's daily log
  2. The pump manufacturer's curve
  3. The water-quality laboratory report
  4. The well construction permit and approved design drawings Correct answer.

Explanation

The permit and approved design drawings define the required construction details that the driller must follow. These are the controlling documents for inspection and compliance. Daily logs record what happened, and equipment or lab documents serve different purposes.

Question 33Water Supply and Well Construction

Which casing diameter is generally selected for a well that must accommodate a submersible pump and still provide adequate clearance for flow and future maintenance?

  1. Any diameter, since clearance does not affect performance
  2. Half the pump outside diameter
  3. Exactly the pump outside diameter
  4. At least 2 inches (about 50 mm) larger than the pump outside diameter Correct answer.

Explanation

A clearance of at least about 2 inches around the pump allows the pump to be installed and removed and provides space for cooling flow. Too little clearance risks binding and overheating. Casing smaller than the pump is impossible to use.

Question 34Water Supply and Well Construction

A driller is completing a well in a sand aquifer and must choose between a natural-pack and an artificial gravel-pack design. Which condition most favors a gravel pack?

  1. A fine, uniform sand with a small D50 Correct answer.
  2. A hard limestone with solution openings
  3. A fractured granite with negligible fines
  4. A well-cemented sandstone with stable walls

Explanation

A fine, uniform sand is prone to sand entry and requires a gravel pack whose grains are sized to retain the formation. The pack allows a coarser screen slot while still controlling sand. Stable or fractured formations generally do not need an artificial pack.

Question 35Water Supply and Well Construction

A well is to be completed with a 200 mm diameter casing to a depth of 120 m. The driller plans to grout the annulus from the bottom of the seal to the surface. Which practice best ensures a continuous seal?

  1. Pour dry cement from the surface and let it settle
  2. Place grout only in the top 5 m of the annulus
  3. Mix grout with drilling fluid and circulate it once
  4. Pump grout through a tremie pipe from the bottom upward Correct answer.

Explanation

Tremie placement from the bottom up displaces the drilling fluid and prevents voids or dilution of the grout. This method produces a continuous, competent seal. Surface pouring and top-only placement leave gaps and are not acceptable.

Question 36Water Supply and Well Construction

A well in a confined aquifer has a static water level 15 m below ground and a pumping water level 40 m below ground at a steady yield. What is the drawdown?

  1. 40 m
  2. 15 m
  3. 55 m
  4. 25 m Correct answer.

Explanation

Drawdown is the difference between the static water level and the pumping water level. Here 40 m minus 15 m equals 25 m. The other values either represent a single level or the sum of both.

Question 37Water Supply and Well Construction

A driller must case a well through an unconsolidated gravel layer overlying a clay confining bed. Which casing configuration is most appropriate to prevent the gravel from collapsing into the well?

  1. Casing stopped above the gravel layer
  2. Open-hole completion through the gravel
  3. A blind casing with no screen
  4. A screened interval across the gravel with a filter pack Correct answer.

Explanation

A screen with a properly sized filter pack holds back the unconsolidated gravel while allowing water to enter. An open hole in such material would collapse. Blind casing and stopping above the layer would prevent water entry from the target zone.

Question 38Water Supply and Well Construction

Which test is performed to verify that the annular seal of a new well is competent before the well is placed in service?

  1. A sand-content test of the pumped water
  2. A water-level recovery test
  3. A dye or tracer test in the annulus Correct answer.
  4. A pump performance test

Explanation

A tracer or dye introduced into the annulus can reveal whether water migrates along the seal into the well or another zone. This directly tests seal integrity. Pump, recovery, and sand tests assess other aspects of well performance.

Question 39Water Supply and Well Construction

A well is pumped at a constant rate and the pumping water level continues to decline slowly without stabilizing over several days. Which condition is the most likely explanation?

  1. There is leakage from an adjacent aquifer or boundary recharge Correct answer.
  2. The well has reached a true steady state
  3. The aquifer is infinite and confined with no boundaries
  4. The pump is drawing air because the intake is above the water level

Explanation

Continued slow decline during constant-rate pumping can indicate a boundary effect or leakage from an adjacent source rather than true steady state. In a truly confined, infinite aquifer, drawdown approaches a stable rate of change on a semi-log plot. A pump drawing air would cause erratic yield rather than a steady decline.

Question 40Water Supply and Well Construction

What is the main reason for installing a packer or a bentonite plug below a screen interval during well completion?

  1. To reduce the cost of the casing string
  2. To increase the open area of the screen
  3. To support the weight of the pump column
  4. To isolate the screened zone from lower water-bearing zones Correct answer.

Explanation

A packer or plug isolates the completed interval so that water and contaminants from other zones cannot enter the well. This protects water quality and allows testing of the target zone. It does not change screen open area or support the pump.

Question 41Water Supply and Well Construction

A driller observes that the water level in a well rises when the pump is shut off and stabilizes at a level higher than the pumping level. What does this indicate?

  1. The aquifer is being dewatered permanently
  2. The water level is recovering toward the static level Correct answer.
  3. The well is losing water to the formation
  4. The pump is operating above its rated capacity

Explanation

After pumping stops, water flows back into the well and the level rises toward the static level, a normal recovery response. This behavior demonstrates that the aquifer is transmitting water to the well. It does not indicate permanent dewatering or loss to the formation.

Question 42Water Supply and Well Construction

Which factor most directly controls the required length of the screened interval in a confined aquifer well?

  1. The color of the formation samples
  2. The thickness of the aquifer and the desired yield Correct answer.
  3. The depth of the static water level alone
  4. The diameter of the pump column

Explanation

Screen length is set to match the aquifer thickness and to provide enough open area for the design yield at an acceptable entrance velocity. Aquifer thickness and target yield are the controlling design inputs. Sample color and pump column diameter do not determine screen length.

Question 43Water Supply and Well Construction

A well is completed in a sandstone aquifer with a natural pack. Which development method is generally preferred to remove drilling mud from the formation without damaging the screen?

  1. Adding acid to dissolve the sandstone
  2. Overpumping at a very high rate for a short time
  3. Surge blocking with a plunger and simultaneous pumping Correct answer.
  4. Backwashing with compressed air at maximum pressure

Explanation

Surge blocking with a plunger, combined with pumping, loosens and removes mud and fines without excessive stress on the screen. Overpumping can draw in formation sand, and acid or high-pressure air can damage the well. Controlled surging is the standard approach.

Question 44Water Supply and Well Construction

A well produces water with a noticeable sand content after completion. Which action is the most appropriate first step?

  1. Add chlorine to the well to settle the sand
  2. Increase the pumping rate to flush the sand out
  3. Install a larger pump to maintain yield
  4. Reduce the pumping rate and evaluate the screen and pack design Correct answer.

Explanation

Sand entry usually indicates an undersized screen slot, an inadequate filter pack, or overpumping. Reducing the rate and reviewing the completion design addresses the cause. Increasing the rate or pump size would worsen sand production, and chlorine does not settle sand.

Question 45Water Supply and Well Construction

A driller is planning a well near a property boundary and must ensure the casing is set deep enough to seal off a shallow, contaminated aquifer. Which design element is most critical?

  1. The depth of the annular seal below the contaminated zone Correct answer.
  2. The length of the pump column
  3. The color of the casing
  4. The size of the pump motor

Explanation

The annular seal must extend below the contaminated zone so that the shallow water cannot migrate down the annulus into the producing aquifer. Seal depth is the critical barrier element. Casing color, motor size, and column length do not control contaminant migration.

Question 46Water Supply and Well Construction

A well is to be grouted in a borehole where the drilling fluid has a much lower density than the cement slurry. Which problem is most likely during placement?

  1. The cement will float above the drilling fluid and leave a gap
  2. The drilling fluid will harden and block the tremie
  3. The cement may channel through the lighter fluid and fail to form a continuous seal Correct answer.
  4. The cement will set too slowly to be useful

Explanation

A dense slurry can channel through lighter drilling fluid, leaving pockets of fluid and an incomplete seal. Proper tremie placement and displacement control are needed to avoid this. Density contrast does not make cement float or block the tremie.

Question 47Water Supply and Well Construction

A well in a coastal aquifer shows a gradual rise in chloride concentration over several months of pumping. Which mechanism best explains this trend?

  1. Corrosion of the steel casing releasing chloride
  2. Bacterial growth in the screen
  3. Upward migration of saline water caused by drawdown Correct answer.
  4. Dissolution of chloride from the grout seal

Explanation

Heavy pumping lowers the freshwater head and can draw saline water upward or inward from adjacent saline zones, a process often called upconing or intrusion. The gradual trend matches this mechanism. Casing corrosion and grout do not release chloride in this pattern, and bacteria do not produce chloride.

Question 48Water Supply and Well Construction

A driller must decide whether to use a natural pack or a gravel pack for a well in a poorly sorted sand with a wide range of grain sizes. Which consideration is most important?

  1. The depth of the static water level
  2. The diameter of the pump motor
  3. The uniformity coefficient and the fines content of the formation Correct answer.
  4. The color of the sand samples

Explanation

Poorly sorted sand with a wide range of grain sizes is difficult to retain with a natural pack, so a gravel pack sized to the formation is often needed. The uniformity coefficient and fines content guide the pack and slot design. Color, static level, and motor size do not drive this choice.

Question 49Water Supply and Well Construction

A well has been completed with a screen and gravel pack, and the driller must verify that the pack is properly placed around the entire screen. Which method is most appropriate?

  1. Logging the annulus with a density or gamma tool Correct answer.
  2. Lowering a weighted tape to feel the pack surface
  3. Measuring the pump discharge rate
  4. Testing the water for chlorine residual

Explanation

A density or gamma log through the annulus can detect the top of the gravel pack and reveal voids or bridging. This provides a direct check on pack placement. Discharge rate, a weighted tape, and chlorine residual do not confirm pack continuity.

Question 50Water Supply and Well Construction

A driller is completing a well in a karst limestone aquifer where a large solution opening is encountered. Which completion approach best protects the well and maintains yield?

  1. A continuous screen across the entire opening
  2. A blind casing sealed below the opening
  3. Open-hole completion with casing set into rock above the opening Correct answer.
  4. A gravel pack filling the entire opening

Explanation

In stable karst rock, open-hole completion below the casing shoe is common because the rock stands without support and the opening provides high yield. Casing is set into competent rock above the opening to seal the annulus. Screening or packing a large solution opening is generally unnecessary and can reduce yield.