NGWA Certified Well Driller (CWD) — Questions and Answers

Question 1: During a pumping test, the cone of depression expands outward until it reaches:

The unsaturated zone
The bedrock surface
A recharge boundary or equilibrium (Correct answer)
The water table

Correct answer: A recharge boundary or equilibrium

The cone of depression expands until inflow from recharge or hydraulic boundaries equals the pumping rate, achieving steady-state conditions.

Question 2: Eye protection for drilling crews must meet which standard for impact resistance?

OSHA 1910.132
NFPA 70E
ANSI Z87.1 (Correct answer)
ASTM F1506

Correct answer: ANSI Z87.1

ANSI Z87.1 is the American National Standard for Occupational and Educational Personal Eye and Face Protection Devices, specifying impact resistance requirements.

Question 3: Acid treatment of a water well is most effective for which type of fouling?

Iron bacteria colonies
Calcium carbonate and mineral scale deposits (Correct answer)
Organic matter buildup
Sand infiltration

Correct answer: Calcium carbonate and mineral scale deposits

Acid treatment (typically hydrochloric or muriatic acid) is most effective at dissolving calcium carbonate and mineral scale deposits that block well screens and the surrounding formation.

Question 4: Which document legally defines the scope of work, payment terms, and liability for a well drilling project?

Drilling log
Well completion report
Written contract or work order (Correct answer)
Permit application

Correct answer: Written contract or work order

A written contract or work order is the legally binding document that specifies the scope of work, pricing, payment schedule, warranties, and liability allocation between the driller and client.

Question 5: A water sample from a newly completed well shows total coliform bacteria present. What does this finding most likely indicate?

Possible surface water intrusion or inadequate sanitary seal (Correct answer)
High dissolved iron concentration
The pump is too large for the well
Normal background levels for groundwater

Correct answer: Possible surface water intrusion or inadequate sanitary seal

Coliform bacteria in groundwater typically indicates a pathway for surface contamination, such as a failed grouting seal, improper well casing, or nearby sources of biological contamination.

Question 6: Which process recharges groundwater?

Condensation
Infiltration (Correct answer)
Photosynthesis
Evaporation

Correct answer: Infiltration

Groundwater recharge primarily occurs through the process of infiltration. This is when surface water, originating from precipitation like rain or snowmelt, seeps downwards through the soil and rock layers. This infiltrating water eventually reaches the water table, replenishing the aquifer and maintaining groundwater levels.

Question 7: What is porosity?

The color of a rock.
The amount of open space in rock or soil (Correct answer)
The ability of water to pass through rock.
The weight of the rock.

Correct answer: The amount of open space in rock or soil

Porosity refers to the amount of open space, or void space, within a rock or soil material. These interconnected or isolated pores can hold water or air. A material with high porosity can store a large volume of water, which is a fundamental characteristic for an effective aquifer, though permeability is also crucial for water extraction.

Question 8: When should a well driller notify a client of a potential cost overrun during drilling?

Notification is not required if drilling is progressing
When the overrun exceeds 50% of the original contract value
As soon as unforeseen conditions are encountered, before significant additional costs are incurred (Correct answer)
Only after project completion when the final invoice is prepared

Correct answer: As soon as unforeseen conditions are encountered, before significant additional costs are incurred

Professional and ethical practice requires notifying the client immediately when unforeseen conditions are encountered so the owner can make informed decisions before significant additional costs accumulate.

Question 9: The primary purpose of a lien waiver signed by a well drilling subcontractor is to:

Authorize additional drilling depth
Transfer equipment ownership
Document water quality test results
Release the property owner's land from potential mechanic's liens after payment is received (Correct answer)

Correct answer: Release the property owner's land from potential mechanic's liens after payment is received

A lien waiver is a document signed by the contractor/subcontractor confirming they have received payment and waiving their right to file a mechanic's lien against the owner's property for that portion of work.

Question 10: What does confined aquifer mean?

An aquifer with no water.
An aquifer under pressure between impermeable layers (Correct answer)
A dry rock formation.
An aquifer located near a volcano.

Correct answer: An aquifer under pressure between impermeable layers

A confined aquifer is an aquifer that is situated beneath a relatively impermeable layer of rock or sediment, known as an aquiclude or confining layer. This overlying layer restricts the vertical movement of water, causing the water within the aquifer to be under pressure. Consequently, the water level in a well drilled into a confined aquifer will rise above the top of the aquifer itself, often resulting in artesian conditions.

Question 11: During a pump test, 'recovery data' refers to:

Water level measurements taken after pumping stops to track aquifer recharge (Correct answer)
The pumping rate needed to recover target yield
Pump efficiency rating after rehabilitation
Chemical concentration recovery after treatment

Correct answer: Water level measurements taken after pumping stops to track aquifer recharge

Recovery data are water level measurements recorded after pumping ceases, tracking how quickly the aquifer refills the well — this data helps determine aquifer transmissivity using the Theis recovery method.

Question 12: What is permeability?

Ability to conduct electricity.
Ability to absorb sound.
Ability to reflect sunlight.
Ability to allow water to pass through (Correct answer)

Correct answer: Ability to allow water to pass through

Permeability is a measure of a material's ability to allow fluids, specifically water, to pass through it. A highly permeable material, such as sand or gravel, allows water to flow easily, which is essential for an aquifer to yield water to wells. While porosity indicates the amount of space, permeability describes how well those spaces are connected to permit water movement.

Question 13: A change order in a well drilling contract is used to:

Replace the drilling permit after expiration
Document the final well completion for the state
Transfer the contract to a subcontractor
Modify the original scope, schedule, or price due to unforeseen conditions or client requests (Correct answer)

Correct answer: Modify the original scope, schedule, or price due to unforeseen conditions or client requests

A change order formally documents and authorizes modifications to the original contract scope, timeline, or cost when unforeseen site conditions or client-requested changes arise during the project.

Question 14: What is the main advantage of reverse-circulation (RC) rotary drilling over direct-circulation rotary?

RC returns cuttings up the inside of the drill pipe, reducing cross-contamination (Correct answer)
RC allows faster bit changes without tripping the string
RC uses less horsepower for the same depth
RC eliminates the need for drilling fluid entirely

Correct answer: RC returns cuttings up the inside of the drill pipe, reducing cross-contamination

In reverse circulation, fluid flows down the annulus and cuttings are returned inside the drill pipe, providing uncontaminated samples and high annular velocity.

Question 15: What is the primary purpose of drilling fluid (mud) in rotary drilling?

To lubricate and cool the bit, remove cuttings, and stabilize the borehole (Correct answer)
To chemically treat groundwater before sampling
To seal off artesian pressure zones permanently
To dissolve rock formations and speed penetration

Correct answer: To lubricate and cool the bit, remove cuttings, and stabilize the borehole

Drilling fluid simultaneously cools and lubricates the bit, carries cuttings to the surface, and supports borehole walls to prevent collapse.

Question 16: A well driller's warranty on a new well installation typically covers:

Any future decline in water yield due to drought
Workmanship defects and materials for a specified period, but not aquifer yield changes (Correct answer)
Government-mandated water quality standards permanently
All pump maintenance for the life of the well

Correct answer: Workmanship defects and materials for a specified period, but not aquifer yield changes

A standard well driller's warranty covers defects in workmanship and materials for a defined period (commonly 1 year), but cannot guarantee aquifer yield since that depends on hydrogeologic conditions outside the driller's control.

Question 17: Why is it necessary to develop a well after drilling?

To install the pump.
To improve well efficiency and water quality (Correct answer)
To deepen the borehole.
To test the water temperature.

Correct answer: To improve well efficiency and water quality

Well development is a process performed after drilling to remove fine sediments, drilling fluids, and other debris from the borehole and the surrounding aquifer. This process improves the hydraulic connection between the well and the aquifer, increasing the well's yield and efficiency, and enhancing the quality of the water produced by reducing turbidity and sediment.

Question 18: The specific capacity of a well is defined as:

Static water level minus pumping water level
Total gallons pumped per day
Drawdown divided by pumping rate
Pumping rate divided by drawdown (Correct answer)

Correct answer: Pumping rate divided by drawdown

Specific capacity is the pumping rate (gpm) divided by the drawdown (ft), expressing how many gallons per minute the well yields per foot of drawdown.

Question 19: What is the purpose of a casing vent on a completed water well?

To introduce chlorine or other disinfectants into the well during shock treatment
To equalize pressure and prevent vacuum formation inside the casing during pumping (Correct answer)
To measure static and pumping water levels using a pressure transducer
To allow periodic water quality sampling directly from within the casing

Correct answer: To equalize pressure and prevent vacuum formation inside the casing during pumping

A casing vent allows air to enter the casing as the water level drops during pumping, preventing negative pressure that could cause casing collapse or draw contaminants through pipe joints.

Question 20: Which action should a driller take FIRST upon observing a rapid increase in the drilling fluid return flow rate (flowback) without increasing pump output?

Increase rotary speed to drill past the zone quickly
Add heavy mud material to increase fluid weight
Shut down the rig and notify the state geological survey
Close the blowout preventer and assess for formation fluid influx (Correct answer)

Correct answer: Close the blowout preventer and assess for formation fluid influx

An unexpected increase in return flow rate is a 'kick' indicator, suggesting formation fluid is entering the wellbore; the immediate response is to close the BOP and control the well.

Question 21: Which report element is legally required on a well completion report in most U.S. states?

Brand of drilling fluid used
Drilling contractor's profit margin
Name of the well owner's spouse
Driller's license number and signature (Correct answer)

Correct answer: Driller's license number and signature

Most state well completion report regulations require the licensed driller's number and signature to verify that work was performed by a qualified, licensed professional.

Question 22: Which material is most commonly approved for sealing the annular space around a well casing?

Sand and gravel mixture
Crushed limestone aggregate
Epoxy resin compound
Bentonite clay or neat cement grout (Correct answer)

Correct answer: Bentonite clay or neat cement grout

Bentonite and neat cement are standard-approved annular sealants because both achieve very low hydraulic conductivity, creating an effective barrier against contaminant migration.

Question 23: Which indicator best signals that a submersible pump is wearing out rather than the well declining?

Water pressure fluctuates with weather
Decreasing static water level
Sand in the water
Pump amp draw increases while yield decreases (Correct answer)

Correct answer: Pump amp draw increases while yield decreases

Increasing amp draw combined with decreasing yield indicates pump impeller wear, as a worn pump draws more current to overcome internal bypass while producing less water.

Question 24: Before lowering rehabilitation tools into a well, the driller should always:

Remove the pump and measure the casing ID and depth to obstructions (Correct answer)
Run the pump at full capacity for 1 hour
Shock chlorinate the well first
Notify the EPA regional office

Correct answer: Remove the pump and measure the casing ID and depth to obstructions

Before any rehabilitation work, the driller must pull the pump and measure the casing inside diameter and depth to any obstructions to ensure tools will fit and not become stuck.

Question 25: What does a Maximum Contaminant Level Goal (MCLG) represent?

The level at which no known adverse health effects occur (Correct answer)
The detection threshold of a contaminant
The legally enforceable limit for a contaminant
The treatment technique required for removal

Correct answer: The level at which no known adverse health effects occur

MCLGs are non-enforceable public health goals set at the level at which no known or anticipated adverse effects on health occur.

Question 26: A client insists on skipping well disinfection after drilling to save money. The CWD should:

Skip it but document the client's request in writing
Charge for disinfection regardless and omit it from the log
Explain that disinfection is required by code and refuse to skip it (Correct answer)
Comply with the client's wishes since they own the well

Correct answer: Explain that disinfection is required by code and refuse to skip it

Well disinfection is typically required by regulation after drilling; the driller must explain this requirement and cannot waive a regulatory mandate based on client preference.

Question 27: What is the minimum waiting period after shock chlorination before a well can be returned to domestic service according to standard US practice?

1 hour
12 hours
At least 24 hours, plus a clear bacteriological test (Correct answer)
72 hours regardless of test results

Correct answer: At least 24 hours, plus a clear bacteriological test

Standard practice requires waiting at least 24 hours for the chlorine to dissipate and then passing a clear bacteriological test (absent for total coliform and E. coli) before returning the well to service.

Question 28: For tax purposes, a well drilling company's heavy equipment is typically depreciated using which method under US tax law?

MACRS (Modified Accelerated Cost Recovery System) with Section 179 expensing options (Correct answer)
Market value appraisal annually
Straight-line depreciation only
First-in, first-out (FIFO) method

Correct answer: MACRS (Modified Accelerated Cost Recovery System) with Section 179 expensing options

Under US tax law, business equipment is depreciated using MACRS, which allows accelerated depreciation over defined asset class lives, and Section 179 allows immediate expensing of qualifying equipment purchases.

Question 29: What is the primary reason shale acts as a confining unit for aquifers?

Chemical reactivity with groundwater
Very low hydraulic conductivity due to fine grain size and high clay content (Correct answer)
High silica content
High secondary fracture porosity

Correct answer: Very low hydraulic conductivity due to fine grain size and high clay content

Shale's extremely fine clay particles pack tightly together, resulting in very low permeability that restricts vertical groundwater movement between aquifer units.

Question 30: When decontaminating drilling equipment after working in a petroleum-contaminated aquifer, the most important reason is to:

Meet equipment manufacturer warranty requirements
Prevent corrosion of drill steel
Avoid cross-contaminating an unaffected well site (Correct answer)
Reduce drilling fluid pH

Correct answer: Avoid cross-contaminating an unaffected well site

Decontamination prevents transferring contaminants from an affected site to clean formations at the next drilling location, protecting groundwater quality.

NGWA Certified Well Driller (CWD)

The NGWA Certified Well Driller (CWD) certification validates professional competency in water well drilling, covering well construction, geology, groundwater hydrology, well maintenance, business operations, and professional standards. Candidates must pass the general drilling exam plus at least one specialized drilling exam with a score of 70% or better.

Questions

35 min

Time Limit

70%

To Pass

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