NGWA GENERAL DRILLING EXAM 2026 — 200
MCQs| | questions , answers & rationales
Study Tips:**
- Focus on **OSHA regulations** (29 CFR 1926/1910) — heavily tested
- Know **EPA MCLs** for nitrate (10 mg/L), lead (15 μg/L), arsenic (10 μg/L), fluoride (4
mg/L)
- Understand **grouting requirements** (minimum 1-inch annular seal, 24-hour cure)
- Master **well development techniques** and **hydrogeologic terms**
- Memorize **safety standards** — confined spaces, silica, trenching, lockout/tagout
---
**1.** What is the primary purpose of a conductor casing in a water well?
- A. To support the pump
- B. To prevent surface contamination and stabilize the upper hole
- **(Correct answer: B)** — **Rationale: Conductor casing is installed at the surface to prevent
caving of loose surface materials, protect against contamination, and provide a stable
foundation for subsequent drilling operations.**
- C. To act as a screen for water entry
- D. To measure static water level
---
**2.** In rotary drilling, what function does drilling mud serve?
- A. Only cools the bit
,- **(Correct answer: D)** — **Rationale: Drilling mud cools and lubricates the bit, carries
cuttings to the surface, stabilizes the borehole wall, and provides hydrostatic pressure to
prevent blowouts.**
- B. Only carries cuttings to the surface
- C. Only stabilizes the borehole wall
- D. All of the above
---
**3.** What is the minimum recommended grout seal thickness for a water well in most state
regulations?
- A. 0.5 inches
- B. 1 inch
- **(Correct answer: B)** — **Rationale: Most state well construction codes require a
minimum 1-inch annular grout seal between the casing and the borehole wall to ensure proper
sealing against contamination.**
- C. 3 inches
- D. 6 inches
---
**4.** Which drilling method is most suitable for unconsolidated sand and gravel aquifers?
- A. Cable tool drilling
- **(Correct answer: B)** — **Rationale: Reverse circulation rotary drilling is highly effective in
unconsolidated formations like sand and gravel because it efficiently removes cuttings and
stabilizes the borehole.**
- B. Reverse circulation rotary drilling
- C. Air rotary drilling
,- D. Percussion drilling only
---
**5.** What does the term "static water level" refer to?
- A. Water level during pumping
- B. Water level after 24 hours of pumping
- **(Correct answer: C)** — **Rationale: Static water level is the equilibrium water level in a
well when no pumping is occurring and the water has recovered from any previous
disturbance.**
- C. Water level in a non-pumping well under equilibrium conditions
- D. The deepest water level ever recorded
---
**6.** What is the primary advantage of using stainless steel well screens?
- A. Lower cost
- B. Easier installation
- **(Correct answer: C)** — **Rationale: Stainless steel screens offer superior corrosion
resistance compared to carbon steel or PVC, making them ideal for wells with corrosive water
chemistry.**
- C. Corrosion resistance
- D. Lighter weight
---
**7.** What is the proper sequence for well development?
, - A. Install pump, then develop
- B. Develop before installing the permanent pump
- **(Correct answer: B)** — **Rationale: Well development should be completed before
installing the permanent pump to remove drilling residues, improve hydraulic efficiency, and
maximize yield.**
- C. Develop only if the yield is low
- D. Development is optional
---
**8.** What is the maximum allowable concentration of coliform bacteria in a potable water
well?
- A. 10 CFU/100mL
- B. 5 CFU/100mL
- **(Correct answer: C)** — **Rationale: EPA drinking water standards require zero total
coliform bacteria per 100mL; any presence indicates potential contamination requiring
immediate action.**
- C. 0 CFU/100mL (zero tolerance)
- D. 1 CFU/100mL
---
**9.** In air rotary drilling, what is the purpose of the "blooper"?
- A. To increase air pressure
- **(Correct answer: B)** — **Rationale: The blooper (or discharge line) directs exhausted air
and cuttings away from the drill rig and operator, improving safety and visibility at the drilling
site.**
- B. To direct cuttings and exhaust air away from the rig
MCQs| | questions , answers & rationales
Study Tips:**
- Focus on **OSHA regulations** (29 CFR 1926/1910) — heavily tested
- Know **EPA MCLs** for nitrate (10 mg/L), lead (15 μg/L), arsenic (10 μg/L), fluoride (4
mg/L)
- Understand **grouting requirements** (minimum 1-inch annular seal, 24-hour cure)
- Master **well development techniques** and **hydrogeologic terms**
- Memorize **safety standards** — confined spaces, silica, trenching, lockout/tagout
---
**1.** What is the primary purpose of a conductor casing in a water well?
- A. To support the pump
- B. To prevent surface contamination and stabilize the upper hole
- **(Correct answer: B)** — **Rationale: Conductor casing is installed at the surface to prevent
caving of loose surface materials, protect against contamination, and provide a stable
foundation for subsequent drilling operations.**
- C. To act as a screen for water entry
- D. To measure static water level
---
**2.** In rotary drilling, what function does drilling mud serve?
- A. Only cools the bit
,- **(Correct answer: D)** — **Rationale: Drilling mud cools and lubricates the bit, carries
cuttings to the surface, stabilizes the borehole wall, and provides hydrostatic pressure to
prevent blowouts.**
- B. Only carries cuttings to the surface
- C. Only stabilizes the borehole wall
- D. All of the above
---
**3.** What is the minimum recommended grout seal thickness for a water well in most state
regulations?
- A. 0.5 inches
- B. 1 inch
- **(Correct answer: B)** — **Rationale: Most state well construction codes require a
minimum 1-inch annular grout seal between the casing and the borehole wall to ensure proper
sealing against contamination.**
- C. 3 inches
- D. 6 inches
---
**4.** Which drilling method is most suitable for unconsolidated sand and gravel aquifers?
- A. Cable tool drilling
- **(Correct answer: B)** — **Rationale: Reverse circulation rotary drilling is highly effective in
unconsolidated formations like sand and gravel because it efficiently removes cuttings and
stabilizes the borehole.**
- B. Reverse circulation rotary drilling
- C. Air rotary drilling
,- D. Percussion drilling only
---
**5.** What does the term "static water level" refer to?
- A. Water level during pumping
- B. Water level after 24 hours of pumping
- **(Correct answer: C)** — **Rationale: Static water level is the equilibrium water level in a
well when no pumping is occurring and the water has recovered from any previous
disturbance.**
- C. Water level in a non-pumping well under equilibrium conditions
- D. The deepest water level ever recorded
---
**6.** What is the primary advantage of using stainless steel well screens?
- A. Lower cost
- B. Easier installation
- **(Correct answer: C)** — **Rationale: Stainless steel screens offer superior corrosion
resistance compared to carbon steel or PVC, making them ideal for wells with corrosive water
chemistry.**
- C. Corrosion resistance
- D. Lighter weight
---
**7.** What is the proper sequence for well development?
, - A. Install pump, then develop
- B. Develop before installing the permanent pump
- **(Correct answer: B)** — **Rationale: Well development should be completed before
installing the permanent pump to remove drilling residues, improve hydraulic efficiency, and
maximize yield.**
- C. Develop only if the yield is low
- D. Development is optional
---
**8.** What is the maximum allowable concentration of coliform bacteria in a potable water
well?
- A. 10 CFU/100mL
- B. 5 CFU/100mL
- **(Correct answer: C)** — **Rationale: EPA drinking water standards require zero total
coliform bacteria per 100mL; any presence indicates potential contamination requiring
immediate action.**
- C. 0 CFU/100mL (zero tolerance)
- D. 1 CFU/100mL
---
**9.** In air rotary drilling, what is the purpose of the "blooper"?
- A. To increase air pressure
- **(Correct answer: B)** — **Rationale: The blooper (or discharge line) directs exhausted air
and cuttings away from the drill rig and operator, improving safety and visibility at the drilling
site.**
- B. To direct cuttings and exhaust air away from the rig
