NGWA Certified Well Driller (CWD) — Questions and Answers

Question 1: Hydraulic head in a groundwater system is the sum of:

Specific yield and storativity
Velocity head and gravity
Pressure head and elevation head (Correct answer)
Porosity and permeability

Correct answer: Pressure head and elevation head

Hydraulic head (h) = pressure head (p/ρg) + elevation head (z), representing the total mechanical energy per unit weight of groundwater.

Question 2: Acid treatment of a water well is most effective for which type of fouling?

Organic matter buildup
Iron bacteria colonies
Calcium carbonate and mineral scale deposits (Correct answer)
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 3: What is the primary reason shale acts as a confining unit for aquifers?

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

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 4: Which casing material is most appropriate for deep, high-pressure water wells where significant structural loads are anticipated?

Fiberglass-reinforced plastic
Schedule 40 PVC
Carbon steel (Correct answer)
Copper alloy

Correct answer: Carbon steel

Carbon steel casing is used for deep or high-pressure wells because its tensile and compressive strength far exceeds that of thermoplastic materials.

Question 5: What is the primary function of a gravel pack (filter pack) installed around a well screen?

To stabilize the borehole formation and filter fine particles from entering the well (Correct answer)
To reduce overall well construction costs
To increase hydrostatic pressure in the aquifer zone
To prevent chemical contamination migrating from the surface

Correct answer: To stabilize the borehole formation and filter fine particles from entering the well

A gravel pack stabilizes fine aquifer materials around the screen and acts as a granular filter that passes water while blocking sand and silt.

Question 6: What differentiates quality assurance from quality control in CWD?

QA is only for manufacturing
QC is always more important
QA prevents defects through processes; QC detects defects in outputs (Correct answer)
They are the same

Correct answer: QA prevents defects through processes; QC detects defects in outputs

QA is proactive and process-oriented (preventing defects). QC is reactive and product-oriented (detecting defects).

Question 7: What is the minimum waiting period after shock chlorination before a well can be returned to domestic service according to standard US practice?

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

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 8: What does the specific yield of an unconfined aquifer represent?

The total porosity of the aquifer material
The rate of vertical recharge
The pumping rate of a well
The volume of water released per unit drop in hydraulic head per unit area (Correct answer)

Correct answer: The volume of water released per unit drop in hydraulic head per unit area

Specific yield is the volume of water that drains by gravity from a unit volume of aquifer material per unit decline in the water table.

Question 9: What term describes the pressure surface to which water in a confined aquifer will rise in a tightly cased well?

Saturated zone
Water table
Capillary fringe
Piezometric surface (Correct answer)

Correct answer: Piezometric surface

The piezometric (potentiometric) surface represents the hydraulic head in a confined aquifer and is the level to which water rises under artesian pressure.

Question 10: 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)
Straight-line depreciation only
First-in, first-out (FIFO) method
Market value appraisal annually

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 11: What is a KPI in CWD quality management?

A decorative element
A personal opinion metric
A measurable value showing how effectively objectives are achieved (Correct answer)
A financial instrument

Correct answer: A measurable value showing how effectively objectives are achieved

KPIs are quantifiable measurements tied to objectives, providing actionable data about performance.

Question 12: When should a well driller notify a client of a potential cost overrun during drilling?

Notification is not required if drilling is progressing
As soon as unforeseen conditions are encountered, before significant additional costs are incurred (Correct answer)
When the overrun exceeds 50% of the original contract value
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 13: What is a near-miss report in CWD practice?

Documentation of an event that could have caused harm but did not (Correct answer)
A project near deadline
A near break-even report
An employee near target

Correct answer: Documentation of an event that could have caused harm but did not

Near-miss reports document events where harm almost occurred, providing data to prevent future incidents.

Question 14: When bidding a well drilling project on a time-and-materials basis, the contractor's risk compared to a lump-sum bid is:

The same regardless of formation conditions
Higher due to fixed overhead recovery
Higher, because unknown formations may increase costs
Lower, because actual costs plus markup are reimbursed (Correct answer)

Correct answer: Lower, because actual costs plus markup are reimbursed

In a time-and-materials contract, the contractor is reimbursed for actual costs plus an agreed markup, so unexpected formation difficulties are passed to the owner, reducing the contractor's financial risk.

Question 15: Before lowering rehabilitation tools into a well, the driller should always:

Notify the EPA regional office
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

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 16: Which safety measure is essential when operating drilling equipment?

Using equipment without manuals.
Wearing appropriate personal protective equipment (PPE) (Correct answer)
Working alone for faster results.
Avoiding protective gear for flexibility.

Correct answer: Wearing appropriate personal protective equipment (PPE)

Operating drilling equipment involves significant hazards, including heavy machinery, rotating parts, and potential exposure to dust and chemicals. Wearing appropriate Personal Protective Equipment (PPE), such as hard hats, safety glasses, hearing protection, gloves, and steel-toed boots, is essential to protect workers from injuries and ensure a safe working environment, minimizing risks on the job site.

Question 17: What is the function of a drilling rig’s mud pump?

To control rig speed.
To circulate drilling fluid through the system (Correct answer)
To power the drill bit.
To supply air to the compressor.

Correct answer: To circulate drilling fluid through the system

The mud pump is a critical component of a drilling rig, responsible for circulating the drilling fluid (mud) through the drill string, out through the drill bit, and back up the annulus to the surface. This continuous circulation is essential for cooling the bit, removing cuttings from the borehole, and stabilizing the wellbore walls.

Question 18: During a pump test, 'recovery data' refers to:

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

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

To provide a pathway for monitoring groundwater temperature
To prevent borehole collapse and protect the water supply from contamination (Correct answer)
To increase water flow rates by compressing surrounding formations
To reduce construction costs by minimizing excavation volume

Correct answer: To prevent borehole collapse and protect the water supply from contamination

Well casing maintains borehole integrity, prevents collapse, and seals out surface water and contaminants from reaching the aquifer.

Question 20: A driller's 'mobilization cost' in a bid refers to:

Labor cost per foot of drilling
Cost of drilling permits
Expense of moving equipment to and setting up at the job site (Correct answer)
Disposal cost for drill cuttings

Correct answer: Expense of moving equipment to and setting up at the job site

Mobilization cost covers the expense of transporting the drilling rig and equipment to the job site and setting it up, which is typically a fixed charge separate from per-foot drilling costs.

Question 21: Why is testing for coliform bacteria important in water wells?

They prevent algae growth.
They reduce metal corrosion.
They indicate possible contamination by pathogens (Correct answer)
They improve water taste.

Correct answer: They indicate possible contamination by pathogens

Testing for coliform bacteria is crucial because their presence indicates that disease-causing organisms (pathogens) might also be present in the water. While coliforms themselves are usually harmless, they are found in the feces of warm-blooded animals. Therefore, their detection suggests a pathway for fecal contamination into the well, posing a potential health risk.

Question 22: Which geologic process is responsible for creating the primary porosity in sandstone aquifers?

Tectonic fracturing
Depositional pore spaces between grains (Correct answer)
Dissolution by acidic water
Volcanic vesicle formation

Correct answer: Depositional pore spaces between grains

Primary porosity in sandstone results from the spaces between sand grains that were preserved during original sediment deposition and cementation.

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

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

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

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

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 25: Which hazard classification applies to a drilling site located within a 100-year floodplain?

Moderate risk — only affects surface equipment
High risk — well construction standards must address flood inundation (Correct answer)
Low risk — floods rarely occur
No special classification required

Correct answer: High risk — well construction standards must address flood inundation

Drilling in a 100-year floodplain is high-risk because floodwaters can inundate and contaminate a newly constructed well, requiring elevated wellhead designs.

Question 26: Workers' compensation insurance is required in most US states for well drilling companies because:

It insures drilling equipment against damage
It protects clients from driller negligence
It covers employee medical costs and lost wages for job-related injuries without requiring fault (Correct answer)
It is optional coverage for companies with fewer than 5 employees in all states

Correct answer: It covers employee medical costs and lost wages for job-related injuries without requiring fault

Workers' compensation provides mandatory no-fault coverage for employees injured on the job, paying medical expenses and lost wages regardless of who caused the injury, as required by most state laws.

Question 27: When drilling within 50 feet of a public road, the PRIMARY risk management measure is:

Notifying the county assessor's office
Painting all equipment in bright colors
Posting the driller's license at the road edge
Establishing a traffic control plan with barriers, flaggers, and signage (Correct answer)

Correct answer: Establishing a traffic control plan with barriers, flaggers, and signage

A formal traffic control plan using cones, barriers, flaggers, and warning signs protects both workers and passing motorists from collision hazards.

Question 28: What is the purpose of a casing in well drilling?

To filter the water before pumping.
To line the borehole and prevent collapse (Correct answer)
To increase water pressure.
To reduce drilling time.

Correct answer: To line the borehole and prevent collapse

Casing is a large-diameter pipe inserted into a drilled well. Its main purpose is to line the borehole, preventing the surrounding earth and rock from collapsing into the well. It also isolates different water-bearing zones, preventing contamination from surface water or undesirable aquifers, ensuring the structural integrity and water quality of the well.

Question 29: When a well screen is corroded beyond rehabilitation, the recommended remedy is:

Increase pump setting depth
Add chlorine annually
Install a whole-house filter only
Install a liner or sleeve, or construct a replacement well (Correct answer)

Correct answer: Install a liner or sleeve, or construct a replacement well

A corroded well screen that cannot be rehabilitated requires either installing a well liner/sleeve to bypass the damaged section or constructing a new replacement well.

Question 30: What is the primary concern with upconing in a coastal aquifer?

Loss of artesian pressure
Subsidence of the land surface
Vertical recharge being blocked
Upward movement of the freshwater-saltwater interface toward a pumping well (Correct answer)

Correct answer: Upward movement of the freshwater-saltwater interface toward a pumping well

Upconing occurs when pumping draws the denser saltwater interface upward beneath a well, potentially leading to saltwater intrusion and well contamination.

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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These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

Sources & references

Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy

groundwaterweek.com — Exam dates, registration deadline, exam information · verified Oct 2026
ngwa.org — Fees, exam format, passing score, score release, test dates, time limit, test delivery, retake policy, eligibility · verified Oct 2026
test-takers.psiexams.com — Retake fee · verified Oct 2026