CWEA Collections System Maintenance
Certification Exam | Grades 1-4 with Questions
and Answers (2026/2027
DOMAIN: COLLECTION SYSTEM OPERATION & MAINTENANCE (25%)
Q1. What is the minimum recommended velocity in a gravity sewer system during peak
dry weather flow to prevent solids deposition?
A. 1.0 feet per second (fps)
B. 2.0 feet per second (fps)
C. 3.0 feet per second (fps)
D. 4.0 feet per second (fps)
Correct Answer: B
Rationale: B. [CORRECT] The minimum recommended velocity (self-cleansing velocity)
in gravity sewers is 2.0 fps to prevent solids accumulation and sedimentation. A is
incorrect; 1.0 fps is too low and allows sand/grit deposition. C and D are incorrect; while
higher velocities are acceptable, 2.0 fps is the minimum standard per CWEA and Ten
States Standards.
Q2. Which of the following is the primary cause of hydrogen sulfide (H₂S) generation in
collection systems?
,A. Excessive flow velocity
B. Anaerobic conditions with sulfate-reducing bacteria in the presence of sulfates
C. High dissolved oxygen levels
D. Alkaline pH
Correct Answer: B
Rationale: B. [CORRECT] H₂S is produced by sulfate-reducing bacteria (Desulfovibrio)
under anaerobic conditions when organic matter and sulfates are present. This leads to
odor complaints and corrosion of concrete and metal (crown corrosion). A is incorrect;
high velocity increases oxygen transfer, reducing anaerobic conditions. C is incorrect;
high DO (>2 mg/L) prevents H₂S formation. D is incorrect; while pH affects H₂S
speciation (H₂S gas vs. HS⁻ ion), the primary cause is anaerobic biological activity.
Q3. [FOG MANAGEMENT] Fats, oils, and grease (FOG) in collection systems primarily
cause which of the following problems?
A. Increased flow velocity
B. Blockages and sanitary sewer overflows (SSOs)
C. Increased dissolved oxygen
D. Improved pump efficiency
Correct Answer: B
Rationale: B. [CORRECT] FOG accumulates on pipe walls and in pump stations,
congealing into blockages that reduce capacity and cause backups/SSOs. FOG can also
coat surfaces, preventing oxygen transfer. A is incorrect; FOG reduces effective pipe
,diameter, decreasing velocity. C is incorrect; FOG can create anaerobic conditions. D is
incorrect; FOG damages pumps and clogs impellers.
Q4. [FOG MANAGEMENT] Which of the following is the most effective method for
controlling FOG at the source?
A. Increasing pipe diameter in restaurant districts
B. Grease interceptor (trap) installation and maintenance at food service
establishments
C. Chemical addition of enzymes to the collection system
D. Increasing pump station capacity
Correct Answer: B
Rationale: B. [CORRECT] Source control through grease interceptors (traps) with proper
sizing, installation, and maintenance (regular pumping) is the most effective FOG
management strategy. A is incorrect; larger pipes allow FOG accumulation and are not a
control strategy. C is incorrect; enzymes may liquefy grease temporarily but often
re-congeal downstream. D is incorrect; this addresses capacity, not FOG source control.
Q5. [I&I IDENTIFICATION] Which of the following is a common indicator of infiltration
and inflow (I&I) in a collection system?
A. Increased dry weather flow
B. High flows during wet weather that exceed normal patterns
C. Decreased pump station run times
, D. Low turbidity in the effluent
Correct Answer: B
Rationale: B. [CORRECT] I&I is characterized by flow increases during and after wet
weather (rainfall) that significantly exceed normal dry weather patterns, often measured
as flow per capita or peaking factors. A is incorrect; dry weather flow should be
relatively stable; I&I is wet weather related. C is incorrect; I&I increases pump run times.
D is incorrect; I&I typically increases turbidity from soil infiltration.
Q6. [I&I IDENTIFICATION] Which method is most effective for identifying private lateral
connections contributing to I&I?
A. Smoke testing
B. Dye testing
C. CCTV inspection of the main line only
D. Manhole cover removal
Correct Answer: A
Rationale: A. [CORRECT] Smoke testing involves forcing non-toxic smoke into the sewer
system and observing where it exits, revealing illegal connections (roof drains,
downspouts, yard drains) and broken laterals that contribute to I&I. B is incorrect; dye
testing confirms specific connections but is less efficient for area-wide surveys. C is
incorrect; CCTV of main lines misses private lateral defects. D is incorrect; this only
reveals surface water inflow at manholes, not lateral connections.
Certification Exam | Grades 1-4 with Questions
and Answers (2026/2027
DOMAIN: COLLECTION SYSTEM OPERATION & MAINTENANCE (25%)
Q1. What is the minimum recommended velocity in a gravity sewer system during peak
dry weather flow to prevent solids deposition?
A. 1.0 feet per second (fps)
B. 2.0 feet per second (fps)
C. 3.0 feet per second (fps)
D. 4.0 feet per second (fps)
Correct Answer: B
Rationale: B. [CORRECT] The minimum recommended velocity (self-cleansing velocity)
in gravity sewers is 2.0 fps to prevent solids accumulation and sedimentation. A is
incorrect; 1.0 fps is too low and allows sand/grit deposition. C and D are incorrect; while
higher velocities are acceptable, 2.0 fps is the minimum standard per CWEA and Ten
States Standards.
Q2. Which of the following is the primary cause of hydrogen sulfide (H₂S) generation in
collection systems?
,A. Excessive flow velocity
B. Anaerobic conditions with sulfate-reducing bacteria in the presence of sulfates
C. High dissolved oxygen levels
D. Alkaline pH
Correct Answer: B
Rationale: B. [CORRECT] H₂S is produced by sulfate-reducing bacteria (Desulfovibrio)
under anaerobic conditions when organic matter and sulfates are present. This leads to
odor complaints and corrosion of concrete and metal (crown corrosion). A is incorrect;
high velocity increases oxygen transfer, reducing anaerobic conditions. C is incorrect;
high DO (>2 mg/L) prevents H₂S formation. D is incorrect; while pH affects H₂S
speciation (H₂S gas vs. HS⁻ ion), the primary cause is anaerobic biological activity.
Q3. [FOG MANAGEMENT] Fats, oils, and grease (FOG) in collection systems primarily
cause which of the following problems?
A. Increased flow velocity
B. Blockages and sanitary sewer overflows (SSOs)
C. Increased dissolved oxygen
D. Improved pump efficiency
Correct Answer: B
Rationale: B. [CORRECT] FOG accumulates on pipe walls and in pump stations,
congealing into blockages that reduce capacity and cause backups/SSOs. FOG can also
coat surfaces, preventing oxygen transfer. A is incorrect; FOG reduces effective pipe
,diameter, decreasing velocity. C is incorrect; FOG can create anaerobic conditions. D is
incorrect; FOG damages pumps and clogs impellers.
Q4. [FOG MANAGEMENT] Which of the following is the most effective method for
controlling FOG at the source?
A. Increasing pipe diameter in restaurant districts
B. Grease interceptor (trap) installation and maintenance at food service
establishments
C. Chemical addition of enzymes to the collection system
D. Increasing pump station capacity
Correct Answer: B
Rationale: B. [CORRECT] Source control through grease interceptors (traps) with proper
sizing, installation, and maintenance (regular pumping) is the most effective FOG
management strategy. A is incorrect; larger pipes allow FOG accumulation and are not a
control strategy. C is incorrect; enzymes may liquefy grease temporarily but often
re-congeal downstream. D is incorrect; this addresses capacity, not FOG source control.
Q5. [I&I IDENTIFICATION] Which of the following is a common indicator of infiltration
and inflow (I&I) in a collection system?
A. Increased dry weather flow
B. High flows during wet weather that exceed normal patterns
C. Decreased pump station run times
, D. Low turbidity in the effluent
Correct Answer: B
Rationale: B. [CORRECT] I&I is characterized by flow increases during and after wet
weather (rainfall) that significantly exceed normal dry weather patterns, often measured
as flow per capita or peaking factors. A is incorrect; dry weather flow should be
relatively stable; I&I is wet weather related. C is incorrect; I&I increases pump run times.
D is incorrect; I&I typically increases turbidity from soil infiltration.
Q6. [I&I IDENTIFICATION] Which method is most effective for identifying private lateral
connections contributing to I&I?
A. Smoke testing
B. Dye testing
C. CCTV inspection of the main line only
D. Manhole cover removal
Correct Answer: A
Rationale: A. [CORRECT] Smoke testing involves forcing non-toxic smoke into the sewer
system and observing where it exits, revealing illegal connections (roof drains,
downspouts, yard drains) and broken laterals that contribute to I&I. B is incorrect; dye
testing confirms specific connections but is less efficient for area-wide surveys. C is
incorrect; CCTV of main lines misses private lateral defects. D is incorrect; this only
reveals surface water inflow at manholes, not lateral connections.
