100+ Free NGWA CWD Practice Questions

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Which drilling method uses a weighted bit that is alternately raised and dropped to break formation rock by percussive action?

Mud rotary drilling

Cable tool drilling

Air rotary drilling

Reverse circulation drilling

to track

2026 Statistics

Key Facts: NGWA CWD Exam

70%

Passing Score

35/50 questions each exam

2 exams

Required

General + Specialized

$150

Total Exam Fee

$75 per exam × 2

24 months

Experience Required

NGWA eligibility

7 CEPs

Annual Renewal

NGWA recertification

1970

Program Established

NGWA

The NGWA Certified Well Driller (CWD) is a national voluntary credential issued since 1970. Candidates must pass two 50-question PSI exams (general drilling + one specialized method) at 70% or better within 12 months. Each exam costs $75 ($150 total). Eligibility requires age 20+ and 24 months of full-time drilling experience. Annual renewal requires 7 continuing education points (CEPs) by December 31 each year.

Sample NGWA CWD Practice Questions

Try these sample questions to test your NGWA CWD exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Which drilling method uses a weighted bit that is alternately raised and dropped to break formation rock by percussive action?

A.Mud rotary drilling

B.Cable tool drilling

C.Air rotary drilling

D.Reverse circulation drilling

Explanation: Cable tool drilling (also called percussion or spudder drilling) uses a heavy drill string that is repeatedly lifted and dropped to crush and pulverize formation material. The resulting cuttings are removed periodically with a bailer. It is one of the oldest and most reliable well construction methods.

2In mud rotary drilling, what is the primary purpose of drilling fluid (mud)?

A.To lubricate the drill pipe threads

B.To cool the surface pump only

C.To remove cuttings, cool the bit, and stabilize the borehole wall

D.To chemically dissolve formation materials ahead of the bit

Explanation: Drilling fluid serves three simultaneous functions: it carries drill cuttings up the annulus to the surface (hole cleaning), cools and lubricates the bit, and exerts hydrostatic pressure on the borehole wall to prevent collapse and fluid influx. All three functions must work together for safe, efficient drilling.

3Bentonite is commonly added to drilling mud primarily to:

A.Increase the pH of the mud above 11

B.Increase viscosity and build a filter cake on the borehole wall

C.Reduce the sand content of returns

D.Lower the density of the mud below water

Explanation: Bentonite (sodium montmorillonite clay) swells in water and increases viscosity, improving the mud's ability to suspend and transport cuttings. It also platelets out against the borehole wall to form a low-permeability filter cake that stabilizes the formation and reduces fluid loss.

4A Marsh funnel viscosity reading of 38 seconds for a quart of mud is measured. The base freshwater standard is 26 seconds. This reading indicates the mud is:

A.Thinner than water

B.At the acceptable minimum for water-well drilling

C.More viscous than water, indicating bentonite or polymer is building viscosity

D.Too thin to transport cuttings and requires immediate thinning

Explanation: The Marsh funnel measures how long it takes one quart of mud to flow through the funnel. Pure water flows in about 26 seconds; higher readings indicate greater viscosity from suspended solids or polymer. A reading of 38 seconds is a normal working viscosity for many water-well applications, confirming that bentonite or polymer is adequately building viscosity.

5What does the uniformity coefficient (Cu) of an aquifer sand sample represent?

A.The ratio of the D60 grain size to the D10 grain size from a sieve analysis

B.The percentage of fine grains passing the No. 200 sieve

C.The ratio of the slot size to the grain diameter

D.The permeability of the gravel pack in darcies

Explanation: The uniformity coefficient is Cu = D60/D10, where D60 is the sieve size passing 60% of the sample and D10 is the effective size passing 10%. A Cu of 2 or less indicates a well-sorted, uniform sand. High Cu values indicate poorly sorted material and affect screen slot size and gravel-pack design decisions.

6For a naturally developed water well in a fine, uniform sand with D10 = 0.15 mm, the recommended slot size for the well screen is typically:

A.Equal to D10 (0.15 mm / slot 6)

B.Equal to D50 of the aquifer sand

C.40–50% of the D50 grain size

D.Larger than the D90 grain size to maximize open area

Explanation: For naturally developed wells in uniform sands (Cu ≤ 2), slot size is commonly selected at 40–50% of the D50 grain size. This allows the finer fraction to be developed out while the coarser grains form a natural gravel pack around the screen, achieving high efficiency without excessive sand pumping.

7When grouting a well annulus with neat cement, the minimum acceptable grout thickness required by ANSI/NGWA-01 around the casing is:

A.0.5 inch

B.1.5 inches

C.3 inches

D.6 inches

Explanation: ANSI/NGWA-01 specifies that annular grout must completely fill the space between the casing and borehole wall and be at least 3 inches thick (76 mm) to provide an effective sanitary seal. This thickness prevents preferential pathways for surface contaminants to migrate along the casing.

8Which casing material specification is specifically designed for steel water-well casing that must meet dimensional and tensile requirements for water-well use?

A.ASTM A53 (standard pipe specification)

B.ASTM A589 (well casing pipe)

C.PVC SDR-21

D.ASTM A36 (structural steel)

Explanation: ASTM A589 is the specification specifically written for steel water-well casing, covering dimensions, tolerances, and mechanical properties appropriate for the well environment. ASTM A53 covers general-purpose steel pipe and may be used in some states, but A589 is purpose-built for water wells.

9PVC SDR-17 casing has a higher pressure rating than PVC SDR-21 because:

A.SDR-17 uses a larger outside diameter

B.SDR-17 has a thicker wall relative to outside diameter (lower SDR = thicker wall)

C.SDR-21 uses schedule 40 fittings that reduce strength

D.SDR-17 is always schedule 80 PVC

Explanation: SDR (Standard Dimension Ratio) equals outside diameter divided by wall thickness. A lower SDR means a proportionally thicker wall, which results in a higher pressure rating. SDR-17 has a thicker wall than SDR-21 of the same diameter, making it suitable for deeper wells with greater column pressure.

10During well development by surging, the primary mechanism that improves well efficiency is:

A.Chemically dissolving iron deposits from the screen slots

B.Creating alternating inward and outward flow to rearrange formation grains and remove fines near the screen

C.Applying high chlorine concentration to the formation

D.Increasing the water level to create a positive artesian head

Explanation: Surging works by moving a surge block or bailer rapidly up and down in the casing, creating alternating positive and negative pressure surges. The alternating flow rearranges the gravel pack, dislodges bridged fines from the formation face, and removes drilling fluid residues, ultimately increasing the hydraulic connection between aquifer and well.

About the NGWA CWD Exam

Earn the NGWA Certified Well Driller (CWD) credential by passing two 50-question exams on well drilling, hydrogeology, casing, development, and safety.

Questions

50 scored questions

Time Limit

1 hour per exam

Passing Score

70%

Exam Fee

$150 total (PSI Services)

NGWA CWD Exam Content Outline

~30%

Drilling Methods

Mud rotary, air rotary, cable tool, reverse circulation, drilling fluid properties

~25%

Well Construction & Materials

Casing, screen design, gravel pack, grouting, ANSI/NGWA-01, NSF/ANSI 60

~20%

Hydrogeology & Well Hydraulics

Aquifer types, transmissivity, drawdown, specific capacity, well efficiency

~15%

Well Development & Water Quality

Surging, jetting, airlifting, chlorination, water sampling, turbidity

~10%

Site & Job Safety

OSHA 29 CFR 1926 fall protection, confined space, H2S, HazCom, derrick safety

How to Pass the NGWA CWD Exam

What You Need to Know

Passing score: 70%
Exam length: 50 questions
Time limit: 1 hour per exam
Exam fee: $150 total

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

NGWA CWD Study Tips from Top Performers

1Master the five Marsh funnel and mud balance readings — viscosity and density questions appear frequently

2Know ANSI/NGWA-01 requirements: 12-inch casing height, 3-inch grout thickness, grout to surface

3Memorize the gravel pack sizing rule: 4–6x the aquifer formation D50 grain size

4Practice drawdown and specific capacity calculations — these are straightforward math questions

5Review OSHA 29 CFR 1926 Subpart M fall protection thresholds (6-foot trigger height)

Frequently Asked Questions

What is the NGWA CWD certification?

The NGWA Certified Well Driller (CWD) is a voluntary national credential issued by the National Ground Water Association since 1970. It demonstrates that a well driller meets professional experience standards and has passed written exams covering drilling methods, well construction, hydrogeology, development, and safety. It is separate from — and does not replace — individual state well-driller licenses.

How many exams are required for the NGWA CWD?

Two exams are required: the General Drilling exam plus one specialized drilling exam (cable tool, air rotary, mud rotary, reverse circulation, jetting/driving, or augering/monitoring). Each exam is 50 questions, has a 1-hour time limit, and requires a passing score of 70% (35 correct). Both exams must be passed within a 12-month period.

What are the eligibility requirements for the NGWA CWD exam?

Applicants must be at least 20 years old and have a minimum of 24 consecutive months of full-time well drilling experience. They must provide two professional references from outside their current employer, sign an agreement form, and submit a current-year affidavit. No formal college degree is required.

How much does the NGWA CWD exam cost?

Each exam costs $75, so the two required exams total $150. This fee is the same regardless of NGWA membership status, though NGWA membership may provide discounts on study materials and recertification.

Where is the NGWA CWD exam administered?

Exams are administered by PSI Services at more than 400 test centers nationwide. Candidates schedule online at test-takers.psiexams.com/ngwa or by calling (855) 579-4642. Remote (online proctored) testing is not currently offered.

How do I renew my NGWA CWD certification?

CWD recertification requires completing 7 continuing education points (CEPs) annually by December 31 each year. CEPs can be earned through conference attendance, workshops, webinars (1 point per hour), safety training (max 3 per year), writing articles, and other NGWA-approved activities. A renewal affidavit and fee are also required.

Does the NGWA CWD replace my state well-driller license?

No. The NGWA CWD is a voluntary national credential that supplements, but does not replace, state-required well-driller licenses. Most states have their own licensing requirements with separate exams, fees, and continuing education requirements. You need both if operating in a state with mandatory licensing.

What topics are covered on the NGWA CWD general drilling exam?

The general exam covers site mobilization, well construction principles, well components (casing, screen, gravel pack), well development, well rehabilitation, decommissioning, pumping systems, and job-site safety. The specialized exam (e.g., mud rotary) adds drilling fluid properties (viscosity, density, sand content), borehole stability, and method-specific techniques.