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ABC Water Treatment Operator Class II Exam
ACTUAL QUESTIONS AND ANSWERS LATEST
UPDATE THIS YEAR
ABC Water Treatment Operator Class II Exam
Based on the official ABC "Need-to-Know" criteria, the Water Treatment Operator Class II exam covers
five core domains: Treatment Process Monitoring, Evaluation, and Adjustment (30
questions), Equipment Operation (25 questions), Equipment Evaluation & Maintenance (20
questions), Laboratory Analysis (15 questions), and Security, Safety & Administrative Procedures (10
questions).
Questions range from Recall (27% of exam) to Application (47%) to Analysis (26%), meaning you must
not only know facts but also perform calculations and troubleshoot real plant scenarios.
PART 2: 150 SCENARIO-BASED QUESTIONS & RATIONALES
Question 1
You notice the settled floc in your sedimentation basin is very small and not settling properly. Lab results
show raw water temperature is 5°C and pH is 6.2. What is the most likely cause?
A) High pH reducing coagulation efficiency
B) Cold water increasing water viscosity, slowing floc formation
C) Excessive mixing in the flocculation basin
D) Low turbidity requiring no treatment
Answer: B
Rationale: Cold water increases viscosity, which slows the rate of floc formation and settling. Alum
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coagulation is optimal near neutral pH (6.5–7.5); pH 6.2 is slightly low but the temperature is the primary
issue here.
Question 2
A conventional sedimentation basin has a detention time of 3 hours. The plant flow is 2 MGD. What is
the required basin volume in gallons?
A) 150,000 gal
B) 200,000 gal
C) 250,000 gal
D) 300,000 gal
Answer: C
*Rationale: Volume = Flow × Time = (2,000,000 gal/day) × (3 hr) × (1 day/24 hr) = 250,000 gal.*
Question 3
Your rapid sand filter operates at 4 gpm/ft². After 48 hours, the head loss reaches 8 feet and turbidity
breakthrough begins. What action should you take?
A) Increase the filtration rate to 6 gpm/ft²
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B) Backwash the filter immediately
C) Add more coagulant to the influent
D) Reduce the flow to 2 gpm/ft² until the end of the shift
Answer: B
Rationale: Maximum head loss is typically 8–10 ft for rapid filters. Turbidity breakthrough indicates the
filter is exhausted and must be backwashed to restore performance.
Question 4
Which coagulant is most likely to depress the pH of the treated water significantly?
A) Sodium aluminate
B) Ferric sulfate
C) Calcium hydroxide
D) Bentonite clay
Answer: B
Rationale: Ferric sulfate hydrolyzes to form acid, consuming alkalinity and lowering pH. Sodium
aluminate and lime raise pH, while bentonite is a coagulant aid.
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Question 5
Your plant uses alum coagulation followed by sedimentation. The influent water has moderate turbidity
but very low alkalinity (20 mg/L as CaCO₃). What is the primary concern?
A) The floc will be too large and settle too quickly
B) The coagulant will depress pH below the optimal range due to insufficient buffering
C) The water will become too hard
D) Alum will not dissolve at low alkalinity
Answer: B
Rationale: Alum consumes alkalinity during hydrolysis. With low alkalinity, pH can drop below 6.0,
impairing coagulation. Addition of lime or caustic soda may be needed.
Question 6
Tapered flocculation refers to:
A) Using three identical mixers at maximum speed
B) Gradually increasing mixing intensity from inlet to outlet
C) Gradually decreasing mixing intensity from inlet to outlet
D) Intermittent mixing followed by sedimentation
ABC Water Treatment Operator Class II Exam
ACTUAL QUESTIONS AND ANSWERS LATEST
UPDATE THIS YEAR
ABC Water Treatment Operator Class II Exam
Based on the official ABC "Need-to-Know" criteria, the Water Treatment Operator Class II exam covers
five core domains: Treatment Process Monitoring, Evaluation, and Adjustment (30
questions), Equipment Operation (25 questions), Equipment Evaluation & Maintenance (20
questions), Laboratory Analysis (15 questions), and Security, Safety & Administrative Procedures (10
questions).
Questions range from Recall (27% of exam) to Application (47%) to Analysis (26%), meaning you must
not only know facts but also perform calculations and troubleshoot real plant scenarios.
PART 2: 150 SCENARIO-BASED QUESTIONS & RATIONALES
Question 1
You notice the settled floc in your sedimentation basin is very small and not settling properly. Lab results
show raw water temperature is 5°C and pH is 6.2. What is the most likely cause?
A) High pH reducing coagulation efficiency
B) Cold water increasing water viscosity, slowing floc formation
C) Excessive mixing in the flocculation basin
D) Low turbidity requiring no treatment
Answer: B
Rationale: Cold water increases viscosity, which slows the rate of floc formation and settling. Alum
, Page 2 of 158
coagulation is optimal near neutral pH (6.5–7.5); pH 6.2 is slightly low but the temperature is the primary
issue here.
Question 2
A conventional sedimentation basin has a detention time of 3 hours. The plant flow is 2 MGD. What is
the required basin volume in gallons?
A) 150,000 gal
B) 200,000 gal
C) 250,000 gal
D) 300,000 gal
Answer: C
*Rationale: Volume = Flow × Time = (2,000,000 gal/day) × (3 hr) × (1 day/24 hr) = 250,000 gal.*
Question 3
Your rapid sand filter operates at 4 gpm/ft². After 48 hours, the head loss reaches 8 feet and turbidity
breakthrough begins. What action should you take?
A) Increase the filtration rate to 6 gpm/ft²
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B) Backwash the filter immediately
C) Add more coagulant to the influent
D) Reduce the flow to 2 gpm/ft² until the end of the shift
Answer: B
Rationale: Maximum head loss is typically 8–10 ft for rapid filters. Turbidity breakthrough indicates the
filter is exhausted and must be backwashed to restore performance.
Question 4
Which coagulant is most likely to depress the pH of the treated water significantly?
A) Sodium aluminate
B) Ferric sulfate
C) Calcium hydroxide
D) Bentonite clay
Answer: B
Rationale: Ferric sulfate hydrolyzes to form acid, consuming alkalinity and lowering pH. Sodium
aluminate and lime raise pH, while bentonite is a coagulant aid.
, Page 4 of 158
Question 5
Your plant uses alum coagulation followed by sedimentation. The influent water has moderate turbidity
but very low alkalinity (20 mg/L as CaCO₃). What is the primary concern?
A) The floc will be too large and settle too quickly
B) The coagulant will depress pH below the optimal range due to insufficient buffering
C) The water will become too hard
D) Alum will not dissolve at low alkalinity
Answer: B
Rationale: Alum consumes alkalinity during hydrolysis. With low alkalinity, pH can drop below 6.0,
impairing coagulation. Addition of lime or caustic soda may be needed.
Question 6
Tapered flocculation refers to:
A) Using three identical mixers at maximum speed
B) Gradually increasing mixing intensity from inlet to outlet
C) Gradually decreasing mixing intensity from inlet to outlet
D) Intermittent mixing followed by sedimentation
