North Carolina Wastewater Collection System
Operator — Grade IV Certification Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
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1. The primary purpose of a wastewater collection system is to
A. Prevent sewer gas formation
B. Transport wastewater to a treatment facility
C. Eliminate all stormwater infiltration
D. Reduce water consumption
Answer: B
Rationale: Collection systems are designed mainly to convey
wastewater for treatment.
2. A trunk sewer is best described as
A. The smallest pipe in the system
B. A pipe that receives flow from multiple mains
C. A force main leading to a pump
D. A private service lateral
Answer: B
Rationale: Trunk sewers carry combined flows from smaller pipes.
3. The minimum desirable velocity to prevent solids deposition in
gravity sewers is
A. 0.5 fps
B. 1.0 fps
, C. 2.0 fps
D. 3.5 fps
Answer: C
Rationale: About 2.0 fps maintains scouring and prevents settling.
4. Hydrogen sulfide generation is most likely during
A. High-velocity flow
B. Aerobic conditions
C. Septic conditions
D. Cold water infiltration
Answer: C
Rationale: H₂S forms in anaerobic, septic environments.
5. A drop manhole is used when
A. Invert elevations of connecting sewers differ significantly
B. Flow is too slow
C. Removing debris from the line
D. Installing force mains
Answer: A
Rationale: Drop manholes allow vertical drops without high
turbulence.
6. The recommended minimum distance between sewer lines and
potable water lines is mainly to
A. Prevent pipe corrosion
B. Reduce hydraulic losses
C. Protect water quality from contamination
D. Increase construction efficiency
Answer: C
, Rationale: Separation prevents cross-contamination should leaks
occur.
7. The purpose of an air release valve on a force main is to
A. Inject chlorine
B. Dissolve gases
C. Remove trapped air pockets
D. Reduce pipe vibrations
Answer: C
Rationale: Air pockets restrict flow and increase head loss.
8. In a wastewater collection system, I/I refers to
A. Infiltration and inflow
B. Influent and interception
C. Industrial and institutional discharge
D. Internal inspection
Answer: A
Rationale: I/I represents unwanted groundwater or stormwater
intrusion.
9. A sewer line sag that holds standing water is called a
A. Drop
B. Offset
C. Belly
D. Culvert
Answer: C
Rationale: A belly forms from improper slope or settlement.
10. Sewer gases are most dangerous because they may
A. Cause rapid corrosion of PVC
B. Displace oxygen and be toxic or explosive
Operator — Grade IV Certification Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. The primary purpose of a wastewater collection system is to
A. Prevent sewer gas formation
B. Transport wastewater to a treatment facility
C. Eliminate all stormwater infiltration
D. Reduce water consumption
Answer: B
Rationale: Collection systems are designed mainly to convey
wastewater for treatment.
2. A trunk sewer is best described as
A. The smallest pipe in the system
B. A pipe that receives flow from multiple mains
C. A force main leading to a pump
D. A private service lateral
Answer: B
Rationale: Trunk sewers carry combined flows from smaller pipes.
3. The minimum desirable velocity to prevent solids deposition in
gravity sewers is
A. 0.5 fps
B. 1.0 fps
, C. 2.0 fps
D. 3.5 fps
Answer: C
Rationale: About 2.0 fps maintains scouring and prevents settling.
4. Hydrogen sulfide generation is most likely during
A. High-velocity flow
B. Aerobic conditions
C. Septic conditions
D. Cold water infiltration
Answer: C
Rationale: H₂S forms in anaerobic, septic environments.
5. A drop manhole is used when
A. Invert elevations of connecting sewers differ significantly
B. Flow is too slow
C. Removing debris from the line
D. Installing force mains
Answer: A
Rationale: Drop manholes allow vertical drops without high
turbulence.
6. The recommended minimum distance between sewer lines and
potable water lines is mainly to
A. Prevent pipe corrosion
B. Reduce hydraulic losses
C. Protect water quality from contamination
D. Increase construction efficiency
Answer: C
, Rationale: Separation prevents cross-contamination should leaks
occur.
7. The purpose of an air release valve on a force main is to
A. Inject chlorine
B. Dissolve gases
C. Remove trapped air pockets
D. Reduce pipe vibrations
Answer: C
Rationale: Air pockets restrict flow and increase head loss.
8. In a wastewater collection system, I/I refers to
A. Infiltration and inflow
B. Influent and interception
C. Industrial and institutional discharge
D. Internal inspection
Answer: A
Rationale: I/I represents unwanted groundwater or stormwater
intrusion.
9. A sewer line sag that holds standing water is called a
A. Drop
B. Offset
C. Belly
D. Culvert
Answer: C
Rationale: A belly forms from improper slope or settlement.
10. Sewer gases are most dangerous because they may
A. Cause rapid corrosion of PVC
B. Displace oxygen and be toxic or explosive
