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CWEA Collection Systems Maintenance – 100 Practice Questions with Answers and
Rationales
This study guide covers the core knowledge, skills, and abilities (KSAs) tested across CWEA
Collection System Maintenance certification grades (Grades 1–4). Questions address system
operations, maintenance, safety, inspection, math, and regulations.
Section 1: Collection System Operations & Maintenance (Questions 1–20)
1. What is the primary purpose of a wastewater collection system?
A. To treat wastewater before discharge
B. To convey wastewater from its source to a treatment plant
C. To store wastewater during heavy rainfall
D. To filter solids from wastewater
Correct Answer: B
Rationale: The collection system (sewers, manholes, lift stations) conveys wastewater from
homes, businesses, and industries to a treatment plant. Treatment occurs at the plant, not in
the collection system. Storage and filtration are not primary purposes.
2. Which of the following is the most common cause of sanitary sewer overflows (SSOs)?
A. Treatment plant power failure
B. Grease and debris blockages
C. Excessive rainfall only
D. Chemical spills
Correct Answer: B
Rationale: Grease buildup, roots, rags, and debris are the most common causes of blockages
leading to SSOs. While rainfall can cause infiltration and inflow issues, blockages are the
primary cause.
3. What is the minimum recommended velocity in a gravity sewer line during peak dry
weather flow?
A. 1.0 foot per second
B. 2.0 feet per second
C. 3.5 feet per second
D. 5.0 feet per second
Correct Answer: B
Rationale: A minimum velocity of 2.0 feet per second is recommended to keep solids
suspended and prevent deposition. Velocities below 2 fps allow solids to settle, leading to
blockages.
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4. When sewer line grades are too flat, an odor problem is likely to result. What is the
most likely cause?
A. Decreased velocity allows decomposable solids to settle
B. Decreased treatment time in the lines
C. Increased treatment time of inorganic solids
D. Decomposable solids remain suspended
Correct Answer: A
Rationale: Flat grades reduce flow velocity, allowing decomposable solids to settle. These
settled solids create anaerobic conditions and produce hydrogen sulfide odors.
5. A sewer line is designed to flow full at a velocity of 2.0 ft/s. If the pipe diameter is
doubled while maintaining the same slope and roughness, what is the approximate new
full-flow velocity?
A. 1.0 ft/s
B. 2.0 ft/s
C. 3.2 ft/s
D. 4.0 ft/s
Correct Answer: C
Rationale: Using Manning's equation for full pipe flow, velocity is proportional to D^(2/3)
when slope and roughness are constant. Doubling the diameter increases velocity by a factor
of 2^(2/3) ≈ 1.587. Therefore, 2.0 ft/s × 1.587 ≈ 3.17 ft/s.
6. A downstream manhole has a higher invert elevation than an upstream manhole. This
condition is called:
A. Backwater effect
B. Negative grade or backgrade
C. Drop manhole
D. Flow transition
Correct Answer: B
Rationale: Negative grade (backgrade) occurs when the pipe slopes upward instead of
downward, causing flow to back up. A drop manhole intentionally drops flow vertically.
7. What is the primary purpose of a drop manhole in a steep sewer alignment?
A. To increase flow velocity at the connection point
B. To dissipate energy and prevent erosion at the outlet
C. To provide additional storage volume during peak flows
D. To allow flow direction changes without turbulence
Correct Answer: B
Rationale: Drop manholes reduce the velocity of flow entering the downstream sewer by
allowing sewage to fall vertically, preventing scour and damage to the pipe invert.
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8. A collection system technician notices sewage backing up into a residential basement
during dry weather. Which condition most directly explains this occurrence?
A. Infiltration from groundwater entering through cracked pipes
B. Inflow from roof drains connected to the sanitary sewer
C. A blockage or restriction downstream in the sewer main
D. Excessive velocity causing pipe erosion
Correct Answer: C
Rationale: Dry-weather backups indicate a flow restriction rather than rain-dependent
inflow or infiltration. A downstream blockage causes sewage to surcharge and seek the
lowest available relief point.
9. During a routine inspection, a technician observes a manhole cover vibrating during dry
weather. What is the most likely explanation?
A. High groundwater causing infiltration
B. Turbulent flow or surcharging in the sewer
C. Thermal expansion of the cover
D. Vandalism or loosened bolts
Correct Answer: B
Rationale: Cover vibration during dry weather typically indicates hydraulic turbulence or
surcharging beneath the cover, often caused by a downstream restriction or excessive flow.
10. Which of the following is the best indicator that a sewer main is experiencing
surcharging?
A. Increased hydrogen sulfide odor at the manhole
B. Sewage backing up into low-lying basements
C. Flow velocity measured higher than design velocity
D. Manhole covers vibrate during dry weather
Correct Answer: B
Rationale: Surcharging raises the water surface above the pipe crown, causing backups into
low areas. Odors or vibration can occur for other reasons.
11. What are the basic elements of a safety program?
A. Accident investigation, injury frequency rates, safety policy statement
B. Injury frequency rates, safety policy statement, safety training
C. Lost time accident statistics, injury frequency rates, accident investigation
D. Safety policy statement, safety training, accident investigation
Correct Answer: D
Rationale: The fundamental elements of an effective safety program are a written safety
policy statement, ongoing safety training, and thorough accident investigation procedures.
CWEA Collection Systems Maintenance – 100 Practice Questions with Answers and
Rationales
This study guide covers the core knowledge, skills, and abilities (KSAs) tested across CWEA
Collection System Maintenance certification grades (Grades 1–4). Questions address system
operations, maintenance, safety, inspection, math, and regulations.
Section 1: Collection System Operations & Maintenance (Questions 1–20)
1. What is the primary purpose of a wastewater collection system?
A. To treat wastewater before discharge
B. To convey wastewater from its source to a treatment plant
C. To store wastewater during heavy rainfall
D. To filter solids from wastewater
Correct Answer: B
Rationale: The collection system (sewers, manholes, lift stations) conveys wastewater from
homes, businesses, and industries to a treatment plant. Treatment occurs at the plant, not in
the collection system. Storage and filtration are not primary purposes.
2. Which of the following is the most common cause of sanitary sewer overflows (SSOs)?
A. Treatment plant power failure
B. Grease and debris blockages
C. Excessive rainfall only
D. Chemical spills
Correct Answer: B
Rationale: Grease buildup, roots, rags, and debris are the most common causes of blockages
leading to SSOs. While rainfall can cause infiltration and inflow issues, blockages are the
primary cause.
3. What is the minimum recommended velocity in a gravity sewer line during peak dry
weather flow?
A. 1.0 foot per second
B. 2.0 feet per second
C. 3.5 feet per second
D. 5.0 feet per second
Correct Answer: B
Rationale: A minimum velocity of 2.0 feet per second is recommended to keep solids
suspended and prevent deposition. Velocities below 2 fps allow solids to settle, leading to
blockages.
,2
4. When sewer line grades are too flat, an odor problem is likely to result. What is the
most likely cause?
A. Decreased velocity allows decomposable solids to settle
B. Decreased treatment time in the lines
C. Increased treatment time of inorganic solids
D. Decomposable solids remain suspended
Correct Answer: A
Rationale: Flat grades reduce flow velocity, allowing decomposable solids to settle. These
settled solids create anaerobic conditions and produce hydrogen sulfide odors.
5. A sewer line is designed to flow full at a velocity of 2.0 ft/s. If the pipe diameter is
doubled while maintaining the same slope and roughness, what is the approximate new
full-flow velocity?
A. 1.0 ft/s
B. 2.0 ft/s
C. 3.2 ft/s
D. 4.0 ft/s
Correct Answer: C
Rationale: Using Manning's equation for full pipe flow, velocity is proportional to D^(2/3)
when slope and roughness are constant. Doubling the diameter increases velocity by a factor
of 2^(2/3) ≈ 1.587. Therefore, 2.0 ft/s × 1.587 ≈ 3.17 ft/s.
6. A downstream manhole has a higher invert elevation than an upstream manhole. This
condition is called:
A. Backwater effect
B. Negative grade or backgrade
C. Drop manhole
D. Flow transition
Correct Answer: B
Rationale: Negative grade (backgrade) occurs when the pipe slopes upward instead of
downward, causing flow to back up. A drop manhole intentionally drops flow vertically.
7. What is the primary purpose of a drop manhole in a steep sewer alignment?
A. To increase flow velocity at the connection point
B. To dissipate energy and prevent erosion at the outlet
C. To provide additional storage volume during peak flows
D. To allow flow direction changes without turbulence
Correct Answer: B
Rationale: Drop manholes reduce the velocity of flow entering the downstream sewer by
allowing sewage to fall vertically, preventing scour and damage to the pipe invert.
, 3
8. A collection system technician notices sewage backing up into a residential basement
during dry weather. Which condition most directly explains this occurrence?
A. Infiltration from groundwater entering through cracked pipes
B. Inflow from roof drains connected to the sanitary sewer
C. A blockage or restriction downstream in the sewer main
D. Excessive velocity causing pipe erosion
Correct Answer: C
Rationale: Dry-weather backups indicate a flow restriction rather than rain-dependent
inflow or infiltration. A downstream blockage causes sewage to surcharge and seek the
lowest available relief point.
9. During a routine inspection, a technician observes a manhole cover vibrating during dry
weather. What is the most likely explanation?
A. High groundwater causing infiltration
B. Turbulent flow or surcharging in the sewer
C. Thermal expansion of the cover
D. Vandalism or loosened bolts
Correct Answer: B
Rationale: Cover vibration during dry weather typically indicates hydraulic turbulence or
surcharging beneath the cover, often caused by a downstream restriction or excessive flow.
10. Which of the following is the best indicator that a sewer main is experiencing
surcharging?
A. Increased hydrogen sulfide odor at the manhole
B. Sewage backing up into low-lying basements
C. Flow velocity measured higher than design velocity
D. Manhole covers vibrate during dry weather
Correct Answer: B
Rationale: Surcharging raises the water surface above the pipe crown, causing backups into
low areas. Odors or vibration can occur for other reasons.
11. What are the basic elements of a safety program?
A. Accident investigation, injury frequency rates, safety policy statement
B. Injury frequency rates, safety policy statement, safety training
C. Lost time accident statistics, injury frequency rates, accident investigation
D. Safety policy statement, safety training, accident investigation
Correct Answer: D
Rationale: The fundamental elements of an effective safety program are a written safety
policy statement, ongoing safety training, and thorough accident investigation procedures.
