North Carolina Wastewater Collection System
Operator — Grade III Certification Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a wastewater collection system?
A. Transport drinking water to customers
B. Remove grit from wastewater
C. Collect and convey wastewater to a treatment facility
D. Store wastewater during peak flows
Answer: C
The main function is to move wastewater from its source to a
treatment plant.
2. A manhole drop connection is typically used when pipe elevation
differences exceed:
A. 1 foot
B. 2 feet
C. 3 feet
D. 5 feet
Answer: C
Drop connections reduce turbulence and structural stress when
elevations change significantly.
,3. The minimum recommended velocity in gravity sewers to prevent
solids deposition is:
A. 0.5 fps
B. 1.0 fps
C. 2.0 fps
D. 3.5 fps
Answer: C
A velocity of at least 2 fps helps keep solids in suspension.
4. Sewer lines are usually designed to flow at:
A. 0–10% full
B. 25–50% full
C. 50–75% full
D. 80–100% full
Answer: C
Designing sewers to run half to three-quarters full provides
capacity and ventilation.
5. The primary cause of sewer odors is the formation of:
A. Carbon dioxide
B. Hydrogen sulfide
C. Nitrogen gas
D. Methane
Answer: B
H₂S produces the characteristic “rotten egg” smell and can be
corrosive.
6. Hydrogen sulfide becomes dangerous to life at concentrations
above:
A. 5 ppm
, B. 10 ppm
C. 50 ppm
D. 100 ppm
Answer: D
High levels can cause rapid unconsciousness and death.
7. A manhole typically consists of a cone section, barrel, bench, and:
A. Weir
B. Invert
C. Lagoon
D. Vault
Answer: B
The invert directs flow through the manhole.
8. What is the most accurate method for locating sewer lines?
A. Surface observation
B. GPS alone
C. As-built drawings
D. Televised inspection with locating equipment
Answer: D
TV inspection paired with a locator gives precise alignment and
depth.
9. Which device prevents backflow into a building sewer?
A. Bar screen
B. Backwater valve
C. Force main
D. Aeration valve
Answer: B
Backwater valves stop reverse flow from surcharged systems.
Operator — Grade III Certification Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a wastewater collection system?
A. Transport drinking water to customers
B. Remove grit from wastewater
C. Collect and convey wastewater to a treatment facility
D. Store wastewater during peak flows
Answer: C
The main function is to move wastewater from its source to a
treatment plant.
2. A manhole drop connection is typically used when pipe elevation
differences exceed:
A. 1 foot
B. 2 feet
C. 3 feet
D. 5 feet
Answer: C
Drop connections reduce turbulence and structural stress when
elevations change significantly.
,3. The minimum recommended velocity in gravity sewers to prevent
solids deposition is:
A. 0.5 fps
B. 1.0 fps
C. 2.0 fps
D. 3.5 fps
Answer: C
A velocity of at least 2 fps helps keep solids in suspension.
4. Sewer lines are usually designed to flow at:
A. 0–10% full
B. 25–50% full
C. 50–75% full
D. 80–100% full
Answer: C
Designing sewers to run half to three-quarters full provides
capacity and ventilation.
5. The primary cause of sewer odors is the formation of:
A. Carbon dioxide
B. Hydrogen sulfide
C. Nitrogen gas
D. Methane
Answer: B
H₂S produces the characteristic “rotten egg” smell and can be
corrosive.
6. Hydrogen sulfide becomes dangerous to life at concentrations
above:
A. 5 ppm
, B. 10 ppm
C. 50 ppm
D. 100 ppm
Answer: D
High levels can cause rapid unconsciousness and death.
7. A manhole typically consists of a cone section, barrel, bench, and:
A. Weir
B. Invert
C. Lagoon
D. Vault
Answer: B
The invert directs flow through the manhole.
8. What is the most accurate method for locating sewer lines?
A. Surface observation
B. GPS alone
C. As-built drawings
D. Televised inspection with locating equipment
Answer: D
TV inspection paired with a locator gives precise alignment and
depth.
9. Which device prevents backflow into a building sewer?
A. Bar screen
B. Backwater valve
C. Force main
D. Aeration valve
Answer: B
Backwater valves stop reverse flow from surcharged systems.
