NGWA Water Systems Certification Exam
(Exam L – >100 GPM) 2026 Practice
Questions & Answers | Verified Solutions,
Pump Systems, Well Design & Groundwater
Operations Study Guide
• This practice guide contains 200 rigorous multiple-choice questions mirroring the
NGWA Water Systems Certification Exam (Exam L – >100 GPM), covering pump
systems, well design, groundwater operations, water quality, and regulatory
compliance.
• Use this material by working through each question independently before
checking the bolded correct answer and detailed EXPERT RATIONALE below it to
reinforce understanding and exam readiness.
1. What is the primary purpose of a well casing in a water well system?
A. To filter sediment from the water
B. To prevent surface water contamination and provide structural support
C. To increase the yield of the well
D. To reduce pumping costs
E. To measure the static water level
✓ B. To prevent surface water contamination and provide structural support
EXPERT RATIONALE: The well casing serves two critical functions — it prevents
surface water and shallow groundwater contaminants from entering the well, and it
provides structural integrity to keep the borehole open. It is not designed to filter
sediment, increase yield, reduce costs, or measure water levels.
2. A pump that operates at 500 GPM against a total dynamic head of 150 feet
has a water horsepower (WHP) of approximately:
A. 12.5 HP
,B. 17.0 HP
C. 19.2 HP
D. 28.6 HP
E. 32.1 HP
✓ C. 19.2 HP
EXPERT RATIONALE: Water horsepower is calculated using the formula WHP =
(GPM × TDH) / 3,960. Substituting: (500 × 150) / 3,960 = 75,,960 ≈ 19.2 HP.
This formula is fundamental to pump system design and must be memorized for
the exam.
3. What does the term "specific capacity" of a well describe?
A. The total depth of the well
B. The volume of water stored in the casing
C. The yield of the well per unit of drawdown
D. The horsepower required to pump the well
E. The static water level above the pump intake
✓ C. The yield of the well per unit of drawdown
EXPERT RATIONALE: Specific capacity is expressed as GPM per foot of drawdown
and is a key indicator of well performance. It allows operators to compare wells and
assess whether a well is declining in performance over time. It is not related to
depth, stored volume, horsepower, or static level alone.
4. Which of the following best defines "total dynamic head" (TDH)?
A. The vertical distance from ground surface to the water table
B. The sum of static head, friction losses, and velocity head in a pumping system
C. The pressure at the pump discharge only
,D. The drawdown measured during a pump test
E. The elevation difference between the pump and discharge point
✓ B. The sum of static head, friction losses, and velocity head in a pumping
system
EXPERT RATIONALE: TDH represents the total work the pump must perform and
includes static lift (elevation difference), friction head losses in pipes and fittings,
and velocity head. Understanding TDH is essential when selecting pumps and
calculating energy requirements for systems >100 GPM.
5. What is the recommended minimum well casing diameter for a pump
system producing more than 100 GPM?
A. 4 inches
B. 6 inches
C. 8 inches
D. 10 inches
E. 12 inches
✓ C. 8 inches
EXPERT RATIONALE: For wells producing more than 100 GPM, NGWA guidelines
generally recommend a minimum nominal casing diameter of 8 inches to
accommodate the pump and allow adequate annular clearance for the pump
motor, cable, and drop pipe without causing excessive friction losses or pump
overheating.
6. During a step-drawdown test, what information is primarily obtained?
A. The aquifer transmissivity and storage coefficient
B. The well loss and aquifer loss components to determine well efficiency
C. The static water level before pumping begins
, D. The pump motor efficiency at various loads
E. The chemical quality of the groundwater
✓ B. The well loss and aquifer loss components to determine well efficiency
EXPERT RATIONALE: A step-drawdown test pumps the well at progressively
increasing rates to separate well losses (caused by turbulence near the well screen)
from aquifer losses (caused by laminar flow through the formation). This allows
calculation of well efficiency, which is critical in high-yield systems >100 GPM.
7. Which type of pump is most commonly used in high-capacity water wells
exceeding 100 GPM?
A. Centrifugal surface pump
B. Jet pump
C. Submersible turbine pump
D. Piston pump
E. Diaphragm pump
✓ C. Submersible turbine pump
EXPERT RATIONALE: Vertical turbine submersible pumps are the industry standard
for high-capacity wells. They are efficient, can be staged to achieve high heads, and
are designed to operate submerged in the well casing. Jet and piston pumps are
typically limited to low-yield residential applications.
8. What is the function of a pitless adapter in a well system?
A. To connect the pump to the motor
B. To allow the discharge pipe to pass through the casing below the frost line
without disturbing the sanitary seal
C. To protect the pump from sand infiltration
(Exam L – >100 GPM) 2026 Practice
Questions & Answers | Verified Solutions,
Pump Systems, Well Design & Groundwater
Operations Study Guide
• This practice guide contains 200 rigorous multiple-choice questions mirroring the
NGWA Water Systems Certification Exam (Exam L – >100 GPM), covering pump
systems, well design, groundwater operations, water quality, and regulatory
compliance.
• Use this material by working through each question independently before
checking the bolded correct answer and detailed EXPERT RATIONALE below it to
reinforce understanding and exam readiness.
1. What is the primary purpose of a well casing in a water well system?
A. To filter sediment from the water
B. To prevent surface water contamination and provide structural support
C. To increase the yield of the well
D. To reduce pumping costs
E. To measure the static water level
✓ B. To prevent surface water contamination and provide structural support
EXPERT RATIONALE: The well casing serves two critical functions — it prevents
surface water and shallow groundwater contaminants from entering the well, and it
provides structural integrity to keep the borehole open. It is not designed to filter
sediment, increase yield, reduce costs, or measure water levels.
2. A pump that operates at 500 GPM against a total dynamic head of 150 feet
has a water horsepower (WHP) of approximately:
A. 12.5 HP
,B. 17.0 HP
C. 19.2 HP
D. 28.6 HP
E. 32.1 HP
✓ C. 19.2 HP
EXPERT RATIONALE: Water horsepower is calculated using the formula WHP =
(GPM × TDH) / 3,960. Substituting: (500 × 150) / 3,960 = 75,,960 ≈ 19.2 HP.
This formula is fundamental to pump system design and must be memorized for
the exam.
3. What does the term "specific capacity" of a well describe?
A. The total depth of the well
B. The volume of water stored in the casing
C. The yield of the well per unit of drawdown
D. The horsepower required to pump the well
E. The static water level above the pump intake
✓ C. The yield of the well per unit of drawdown
EXPERT RATIONALE: Specific capacity is expressed as GPM per foot of drawdown
and is a key indicator of well performance. It allows operators to compare wells and
assess whether a well is declining in performance over time. It is not related to
depth, stored volume, horsepower, or static level alone.
4. Which of the following best defines "total dynamic head" (TDH)?
A. The vertical distance from ground surface to the water table
B. The sum of static head, friction losses, and velocity head in a pumping system
C. The pressure at the pump discharge only
,D. The drawdown measured during a pump test
E. The elevation difference between the pump and discharge point
✓ B. The sum of static head, friction losses, and velocity head in a pumping
system
EXPERT RATIONALE: TDH represents the total work the pump must perform and
includes static lift (elevation difference), friction head losses in pipes and fittings,
and velocity head. Understanding TDH is essential when selecting pumps and
calculating energy requirements for systems >100 GPM.
5. What is the recommended minimum well casing diameter for a pump
system producing more than 100 GPM?
A. 4 inches
B. 6 inches
C. 8 inches
D. 10 inches
E. 12 inches
✓ C. 8 inches
EXPERT RATIONALE: For wells producing more than 100 GPM, NGWA guidelines
generally recommend a minimum nominal casing diameter of 8 inches to
accommodate the pump and allow adequate annular clearance for the pump
motor, cable, and drop pipe without causing excessive friction losses or pump
overheating.
6. During a step-drawdown test, what information is primarily obtained?
A. The aquifer transmissivity and storage coefficient
B. The well loss and aquifer loss components to determine well efficiency
C. The static water level before pumping begins
, D. The pump motor efficiency at various loads
E. The chemical quality of the groundwater
✓ B. The well loss and aquifer loss components to determine well efficiency
EXPERT RATIONALE: A step-drawdown test pumps the well at progressively
increasing rates to separate well losses (caused by turbulence near the well screen)
from aquifer losses (caused by laminar flow through the formation). This allows
calculation of well efficiency, which is critical in high-yield systems >100 GPM.
7. Which type of pump is most commonly used in high-capacity water wells
exceeding 100 GPM?
A. Centrifugal surface pump
B. Jet pump
C. Submersible turbine pump
D. Piston pump
E. Diaphragm pump
✓ C. Submersible turbine pump
EXPERT RATIONALE: Vertical turbine submersible pumps are the industry standard
for high-capacity wells. They are efficient, can be staged to achieve high heads, and
are designed to operate submerged in the well casing. Jet and piston pumps are
typically limited to low-yield residential applications.
8. What is the function of a pitless adapter in a well system?
A. To connect the pump to the motor
B. To allow the discharge pipe to pass through the casing below the frost line
without disturbing the sanitary seal
C. To protect the pump from sand infiltration
