California Wastewater Treatment Operator
Grade II Practice Exam 2026
Exam Blueprint: Based on Title 23, CCR, Section 3701, the Grade II exam tests knowledge of preliminary,
primary, and secondary treatment, disinfection, sludge handling, sampling, process control, and safety .
Section 1: Preliminary & Primary Treatment (Questions 1-15)
1. What is the primary purpose of the preliminary treatment process?
A. To remove dissolved organic matter
B. To remove large solids, debris, and grit
C. To disinfect the wastewater
D. To break down biological solids
Correct Answer: B
Rationale: Preliminary treatment (screens and grit chambers) is designed to protect downstream
equipment (pumps, valves) by removing large debris, rags, and heavy inorganic materials like sand and
gravel that could cause clogs or excessive wear .
2. A manually cleaned bar screen should be set at an angle of approximately:
A. 15 degrees from vertical
B. 30 degrees from vertical
C. 45 degrees from vertical
D. 60 degrees from vertical
,Correct Answer: B
Rationale: Manually cleaned screens are typically installed at a 30-degree angle from the vertical to
increase the screen's surface area and make raking easier .
3. What is the primary function of a grit channel?
A. To remove floating fats and oils
B. To remove settleable organic solids
C. To remove heavy, inorganic materials like sand and eggshells
D. To add oxygen to the wastewater
Correct Answer: C
Rationale: Grit chambers are designed to reduce the velocity of the wastewater so that heavy inorganic
particles settle out, while most organic particles remain suspended and are carried forward for
treatment .
4. The main purpose of primary treatment (primary sedimentation) is to remove:
A. Colloidal solids
B. Dissolved solids
C. Substances that readily settle or float
D. Pathogenic bacteria
Correct Answer: C
Rationale: Primary clarifiers are designed to reduce the load on secondary treatment by removing
floatable scum and settleable solids (sludge) through quiescent settling .
5. What should be the first operational adjustment if you notice sludge rising in the primary clarifier
due to septicity?
A. Increase the clarifier flow rate
B. Remove the sludge more frequently
C. Increase the recycle rate from the secondary clarifier
D. Add chlorine to the clarifier influent
Correct Answer: B
Rationale: Rising sludge in a primary clarifier is often caused by sludge remaining in the tank too long
(septic conditions), leading to gas formation. Increasing the sludge removal frequency prevents this .
6. Scum collected from the surface of a primary clarifier typically consists of:
A. Heavy grit and sand
B. Fats, oils, grease, and floating debris
C. Dense biological floc
D. Dissolved nutrients
, Correct Answer: B
Rationale: Scum is lighter than water and floats. It is composed of materials like fats, oils, grease,
plastics, and other floatable matter removed from the wastewater surface.
7. A headworks facility includes all the following EXCEPT:
A. Bar screens
B. Grit removers
C. Primary sludge pumps
D. Comminutors
Correct Answer: C
Rationale: Headworks refers to the initial stage of treatment (preliminary). Sludge pumps are associated
with the primary clarifiers or sludge handling, which come after headworks.
8. If a comminutor is jammed, what is the first step an operator should take?
A. Reach in and clear the debris by hand
B. Lock out and tag out the equipment before attempting to clear it
C. Increase the flow to push the debris through
D. Reverse the direction of the cutters
Correct Answer: B
Rationale: Safety is paramount. Lockout/Tagout (LOTO) procedures must be followed to ensure the
equipment cannot be energized while an operator is clearing a jam, preventing severe injury .
9. The typical detention time in a primary clarifier for domestic wastewater is:
A. 30 minutes to 1 hour
B. 1.5 to 2.5 hours
C. 6 to 8 hours
D. 24 hours
Correct Answer: B
Rationale: Primary clarifiers are designed for relatively short detention times (usually 1.5 to 2.5 hours) to
allow for effective settling of solids without the wastewater becoming septic.
10. A high weir overflow rate in a primary clarifier can cause:
A. Improved effluent quality
B. Solids carryover to the next treatment unit
C. Increased settling of grit
D. Better scum removal
Correct Answer: B
Rationale: If the flow over the weirs is too high (high overflow rate), the upward velocity can pull lighter
solids over the weirs and into the effluent, negatively impacting downstream processes.
Grade II Practice Exam 2026
Exam Blueprint: Based on Title 23, CCR, Section 3701, the Grade II exam tests knowledge of preliminary,
primary, and secondary treatment, disinfection, sludge handling, sampling, process control, and safety .
Section 1: Preliminary & Primary Treatment (Questions 1-15)
1. What is the primary purpose of the preliminary treatment process?
A. To remove dissolved organic matter
B. To remove large solids, debris, and grit
C. To disinfect the wastewater
D. To break down biological solids
Correct Answer: B
Rationale: Preliminary treatment (screens and grit chambers) is designed to protect downstream
equipment (pumps, valves) by removing large debris, rags, and heavy inorganic materials like sand and
gravel that could cause clogs or excessive wear .
2. A manually cleaned bar screen should be set at an angle of approximately:
A. 15 degrees from vertical
B. 30 degrees from vertical
C. 45 degrees from vertical
D. 60 degrees from vertical
,Correct Answer: B
Rationale: Manually cleaned screens are typically installed at a 30-degree angle from the vertical to
increase the screen's surface area and make raking easier .
3. What is the primary function of a grit channel?
A. To remove floating fats and oils
B. To remove settleable organic solids
C. To remove heavy, inorganic materials like sand and eggshells
D. To add oxygen to the wastewater
Correct Answer: C
Rationale: Grit chambers are designed to reduce the velocity of the wastewater so that heavy inorganic
particles settle out, while most organic particles remain suspended and are carried forward for
treatment .
4. The main purpose of primary treatment (primary sedimentation) is to remove:
A. Colloidal solids
B. Dissolved solids
C. Substances that readily settle or float
D. Pathogenic bacteria
Correct Answer: C
Rationale: Primary clarifiers are designed to reduce the load on secondary treatment by removing
floatable scum and settleable solids (sludge) through quiescent settling .
5. What should be the first operational adjustment if you notice sludge rising in the primary clarifier
due to septicity?
A. Increase the clarifier flow rate
B. Remove the sludge more frequently
C. Increase the recycle rate from the secondary clarifier
D. Add chlorine to the clarifier influent
Correct Answer: B
Rationale: Rising sludge in a primary clarifier is often caused by sludge remaining in the tank too long
(septic conditions), leading to gas formation. Increasing the sludge removal frequency prevents this .
6. Scum collected from the surface of a primary clarifier typically consists of:
A. Heavy grit and sand
B. Fats, oils, grease, and floating debris
C. Dense biological floc
D. Dissolved nutrients
, Correct Answer: B
Rationale: Scum is lighter than water and floats. It is composed of materials like fats, oils, grease,
plastics, and other floatable matter removed from the wastewater surface.
7. A headworks facility includes all the following EXCEPT:
A. Bar screens
B. Grit removers
C. Primary sludge pumps
D. Comminutors
Correct Answer: C
Rationale: Headworks refers to the initial stage of treatment (preliminary). Sludge pumps are associated
with the primary clarifiers or sludge handling, which come after headworks.
8. If a comminutor is jammed, what is the first step an operator should take?
A. Reach in and clear the debris by hand
B. Lock out and tag out the equipment before attempting to clear it
C. Increase the flow to push the debris through
D. Reverse the direction of the cutters
Correct Answer: B
Rationale: Safety is paramount. Lockout/Tagout (LOTO) procedures must be followed to ensure the
equipment cannot be energized while an operator is clearing a jam, preventing severe injury .
9. The typical detention time in a primary clarifier for domestic wastewater is:
A. 30 minutes to 1 hour
B. 1.5 to 2.5 hours
C. 6 to 8 hours
D. 24 hours
Correct Answer: B
Rationale: Primary clarifiers are designed for relatively short detention times (usually 1.5 to 2.5 hours) to
allow for effective settling of solids without the wastewater becoming septic.
10. A high weir overflow rate in a primary clarifier can cause:
A. Improved effluent quality
B. Solids carryover to the next treatment unit
C. Increased settling of grit
D. Better scum removal
Correct Answer: B
Rationale: If the flow over the weirs is too high (high overflow rate), the upward velocity can pull lighter
solids over the weirs and into the effluent, negatively impacting downstream processes.
