CWEA COLLECTIONS SYSTEM MAINTENANCE GRADE 3 |
VERIFIED EXAM PRACTICE QUESTIONS WITH CORRECT
ANSWERS & DETAILED RATIONALES | COMPLETE STUDY AND
CERTIFICATION PREPARATION GUIDE FOR WASTEWATER EXAM
CWEA Collections System Maintenance Grade 3
Advanced Practice
1. In a gravity sewer with a 0.4% slope and partially full flow, which
condition most directly increases the risk of septicity?
A. Increased velocity above 3 fps
B. Laminar flow conditions
C. Long detention time with low dissolved oxygen
D. Excessive turbulence at drop manholes
Answer: C
Rationale: Septicity develops under anaerobic conditions caused by long
detention times and depleted dissolved oxygen. Hydrogen sulfide formation
occurs when sulfate-reducing bacteria metabolize organics in low-oxygen
environments.
2. The primary structural failure mechanism in vitrified clay pipe (VCP)
installed before 1970 is typically:
A. Crown corrosion
B. Root intrusion at joints
C. UV degradation
D. Longitudinal splitting due to pressure
Answer: B
Rationale: Older VCP systems commonly used mortar joints, which
deteriorate over time, allowing root intrusion. VCP itself is chemically
resistant but vulnerable at joints.
,3. According to confined space regulations under Occupational Safety and
Health Administration (OSHA), a permit-required confined space must
have:
A. Continuous ventilation
B. Two entry attendants
C. A written entry permit system
D. A fixed gas detection system
Answer: C
Rationale: OSHA 29 CFR 1910.146 requires a written permit system for
permit-required confined spaces. Continuous ventilation and fixed detection
may be required based on hazard evaluation, but are not universally
mandated.
4. The Manning equation is primarily used to calculate:
A. Pump horsepower
B. Friction loss in force mains
C. Open channel flow velocity
D. Air release valve sizing
Answer: C
Rationale: Manning’s equation estimates velocity and discharge in open
channel flow conditions such as gravity sewers.
5. A force main experiences recurring air binding at high points. The most
effective corrective measure is:
A. Increasing pump speed
B. Installing combination air/vacuum release valves
C. Lowering pump wet well setpoints
D. Increasing pipe diameter
Answer: B
Rationale: Combination air/vacuum valves release accumulated air during
operation and admit air during draining to prevent vacuum collapse.
6. Which inspection technology provides internal structural condition
assessment without excavation?
A. Smoke testing
B. Dye testing
,C. CCTV inspection
D. Manhole vacuum testing
Answer: C
Rationale: Closed-circuit television (CCTV) inspection provides visual
documentation of structural defects, infiltration, and blockages inside
pipelines.
7. A grease blockage most commonly forms in which section of a collection
system?
A. High-velocity trunk lines
B. Near food service lateral connections
C. Downstream of lift stations
D. At force main discharge
Answer: B
Rationale: Fats, oils, and grease (FOG) accumulate near commercial food
establishments, especially where flow slows and temperatures decrease.
8. The minimum self-cleansing velocity generally accepted for sanitary
sewers is:
A. 0.5 fps
B. 1.0 fps
C. 2.0 fps
D. 5.0 fps
Answer: C
Rationale: A velocity of approximately 2.0 feet per second helps prevent solids
deposition in gravity sewers.
9. Hydrogen sulfide corrosion primarily affects which portion of a concrete
pipe?
A. Invert
B. Springline
C. Crown
D. Barrel exterior
, Answer: C
Rationale: H₂S gas rises and oxidizes to sulfuric acid at the crown, causing
accelerated corrosion in that region.
10. When conducting a smoke test, smoke emerging from roof vents
typically indicates:
A. Illegal storm connections
B. Proper plumbing venting
C. Cross-connections with potable water
D. Cracked mains
Answer: B
Rationale: Smoke exiting roof vents confirms proper connection between the
building sewer and vent stack.
11. The most critical factor in pump selection for a lift station is:
A. Color of impeller coating
B. Total dynamic head (TDH)
C. Wet well diameter
D. Pump casing thickness
Answer: B
Rationale: Total Dynamic Head (TDH) determines the energy required to
move wastewater through the system, influencing pump sizing.
12. Inflow differs from infiltration because inflow:
A. Occurs only during dry weather
B. Enters through defective pipe joints
C. Is typically storm-related surface water
D. Comes from groundwater
Answer: C
Rationale: Inflow is rapid entry of stormwater from surface sources such as
roof drains or yard drains, unlike groundwater infiltration.
13. A sag (belly) in a gravity sewer primarily results in:
A. Excessive velocity
B. Increased turbulence
VERIFIED EXAM PRACTICE QUESTIONS WITH CORRECT
ANSWERS & DETAILED RATIONALES | COMPLETE STUDY AND
CERTIFICATION PREPARATION GUIDE FOR WASTEWATER EXAM
CWEA Collections System Maintenance Grade 3
Advanced Practice
1. In a gravity sewer with a 0.4% slope and partially full flow, which
condition most directly increases the risk of septicity?
A. Increased velocity above 3 fps
B. Laminar flow conditions
C. Long detention time with low dissolved oxygen
D. Excessive turbulence at drop manholes
Answer: C
Rationale: Septicity develops under anaerobic conditions caused by long
detention times and depleted dissolved oxygen. Hydrogen sulfide formation
occurs when sulfate-reducing bacteria metabolize organics in low-oxygen
environments.
2. The primary structural failure mechanism in vitrified clay pipe (VCP)
installed before 1970 is typically:
A. Crown corrosion
B. Root intrusion at joints
C. UV degradation
D. Longitudinal splitting due to pressure
Answer: B
Rationale: Older VCP systems commonly used mortar joints, which
deteriorate over time, allowing root intrusion. VCP itself is chemically
resistant but vulnerable at joints.
,3. According to confined space regulations under Occupational Safety and
Health Administration (OSHA), a permit-required confined space must
have:
A. Continuous ventilation
B. Two entry attendants
C. A written entry permit system
D. A fixed gas detection system
Answer: C
Rationale: OSHA 29 CFR 1910.146 requires a written permit system for
permit-required confined spaces. Continuous ventilation and fixed detection
may be required based on hazard evaluation, but are not universally
mandated.
4. The Manning equation is primarily used to calculate:
A. Pump horsepower
B. Friction loss in force mains
C. Open channel flow velocity
D. Air release valve sizing
Answer: C
Rationale: Manning’s equation estimates velocity and discharge in open
channel flow conditions such as gravity sewers.
5. A force main experiences recurring air binding at high points. The most
effective corrective measure is:
A. Increasing pump speed
B. Installing combination air/vacuum release valves
C. Lowering pump wet well setpoints
D. Increasing pipe diameter
Answer: B
Rationale: Combination air/vacuum valves release accumulated air during
operation and admit air during draining to prevent vacuum collapse.
6. Which inspection technology provides internal structural condition
assessment without excavation?
A. Smoke testing
B. Dye testing
,C. CCTV inspection
D. Manhole vacuum testing
Answer: C
Rationale: Closed-circuit television (CCTV) inspection provides visual
documentation of structural defects, infiltration, and blockages inside
pipelines.
7. A grease blockage most commonly forms in which section of a collection
system?
A. High-velocity trunk lines
B. Near food service lateral connections
C. Downstream of lift stations
D. At force main discharge
Answer: B
Rationale: Fats, oils, and grease (FOG) accumulate near commercial food
establishments, especially where flow slows and temperatures decrease.
8. The minimum self-cleansing velocity generally accepted for sanitary
sewers is:
A. 0.5 fps
B. 1.0 fps
C. 2.0 fps
D. 5.0 fps
Answer: C
Rationale: A velocity of approximately 2.0 feet per second helps prevent solids
deposition in gravity sewers.
9. Hydrogen sulfide corrosion primarily affects which portion of a concrete
pipe?
A. Invert
B. Springline
C. Crown
D. Barrel exterior
, Answer: C
Rationale: H₂S gas rises and oxidizes to sulfuric acid at the crown, causing
accelerated corrosion in that region.
10. When conducting a smoke test, smoke emerging from roof vents
typically indicates:
A. Illegal storm connections
B. Proper plumbing venting
C. Cross-connections with potable water
D. Cracked mains
Answer: B
Rationale: Smoke exiting roof vents confirms proper connection between the
building sewer and vent stack.
11. The most critical factor in pump selection for a lift station is:
A. Color of impeller coating
B. Total dynamic head (TDH)
C. Wet well diameter
D. Pump casing thickness
Answer: B
Rationale: Total Dynamic Head (TDH) determines the energy required to
move wastewater through the system, influencing pump sizing.
12. Inflow differs from infiltration because inflow:
A. Occurs only during dry weather
B. Enters through defective pipe joints
C. Is typically storm-related surface water
D. Comes from groundwater
Answer: C
Rationale: Inflow is rapid entry of stormwater from surface sources such as
roof drains or yard drains, unlike groundwater infiltration.
13. A sag (belly) in a gravity sewer primarily results in:
A. Excessive velocity
B. Increased turbulence
