FDEP WATER TREATMENT CLASS C OPERATOR CERTIFICATION
EXAM
200 QUESTIONS WITH VERIFIED ANSWERS & DETAILED
RATIONALES
2026-2027 | COMPREHENSIVE PREPARATION GUIDE
Question 1
What is the typical detention time range for a sedimentation basin in a
conventional water treatment plant?
A. 1-2 hours
B. 4-8 hours
C. 30-60 minutes
D. 2-4 hours
● D. 2-4 hours
RATIONALE: Sedimentation basins in conventional water treatment
typically have detention times ranging from 2 to 4 hours. This allows
sufficient time for floc particles to settle out of suspension by gravity.
Longer detention times may be needed for colder water or lighter
particles, while shorter times may be sufficient for denser flocs. Option
A (1-2 hours) is too short for effective sedimentation, Option B (4-8
hours) is excessive and more typical of storage reservoirs, and Option C
(30-60 minutes) is insufficient for proper settling.
,Question 2
Which chemical is commonly used for corrosion control in water
distribution systems?
A. Sodium hydroxide
B. Chlorine dioxide
C. Zinc orthophosphate
D. Aluminum sulfate
● C. Zinc orthophosphate
RATIONALE: Zinc orthophosphate is commonly used for corrosion
control in water distribution systems. It works by forming a protective
film on the interior surfaces of pipes, reducing the leaching of lead,
copper, and iron into the water. Option A (Sodium hydroxide) is used for
pH adjustment, Option B (Chlorine dioxide) is a disinfectant, and Option
D (Aluminum sulfate) is a coagulant.
Question 3
A centrifuge pump has a suction pressure of 5 psi and a discharge
pressure of 45 psi. What is the total dynamic head in feet? (Assume 1
psi = 2.31 feet)
A. 46.2 feet
B. 92.4 feet
C. 115.5 feet
D. 69.3 feet
● B. 92.4 feet
,RATIONALE: Total Dynamic Head = (Discharge Pressure - Suction
Pressure) × 2.31. TDH = (45 - 5) × 2.31 = 40 × 2.31 = 92.4 feet. Option A
(46.2 feet) would be the result of using only 20 psi difference, Option C
(115.5 feet) uses 50 psi incorrectly, and Option D (69.3 feet) uses 30 psi
difference.
Question 4
What is the maximum contaminant level (MCL) for total
trihalomethanes (TTHMs) in drinking water under the Safe Drinking
Water Act?
A. 0.010 mg/L
B. 0.005 mg/L
C. 0.080 mg/L
D. 0.100 mg/L
● C. 0.080 mg/L
RATIONALE: The MCL for total trihalomethanes (TTHMs) is 0.080 mg/L
(80 ppb). TTHMs are disinfection byproducts formed when chlorine
reacts with organic matter in water. Option A (0.010 mg/L) is the MCL
for arsenic, Option B (0.005 mg/L) is the MCL for lead, and Option D
(0.100 mg/L) is the maximum contaminant level goal (MCLG) for
TTHMs, not the enforceable MCL.
Question 5
Which type of filter uses a layer of anthracite coal over a layer of sand
and is commonly used in water treatment?
, A. Slow sand filter
B. Rapid sand filter
C. Dual-media filter
D. Membrane filter
● C. Dual-media filter
RATIONALE: A dual-media filter uses anthracite coal (lighter, larger
particles) over sand (heavier, smaller particles). This arrangement allows
for deeper penetration of particles and longer filter runs compared to
single-media filters. Option A (Slow sand filter) uses biological
processes, Option B (Rapid sand filter) uses only sand, and Option D
(Membrane filter) uses synthetic membranes.
Question 6
What is the purpose of lime softening in water treatment?
A. To remove dissolved organic compounds
B. To remove hardness minerals (calcium and magnesium)
C. To disinfect water and kill pathogens
D. To adjust pH by adding acid
● B. To remove hardness minerals (calcium and magnesium)
RATIONALE: Lime softening is a process that uses calcium hydroxide
(lime) to precipitate calcium carbonate and magnesium hydroxide,
thereby removing hardness from water. This reduces scaling in pipes
and improves soap efficiency. Option A describes oxidation processes,
Option C describes disinfection, and Option D incorrectly describes pH
adjustment with acid.
EXAM
200 QUESTIONS WITH VERIFIED ANSWERS & DETAILED
RATIONALES
2026-2027 | COMPREHENSIVE PREPARATION GUIDE
Question 1
What is the typical detention time range for a sedimentation basin in a
conventional water treatment plant?
A. 1-2 hours
B. 4-8 hours
C. 30-60 minutes
D. 2-4 hours
● D. 2-4 hours
RATIONALE: Sedimentation basins in conventional water treatment
typically have detention times ranging from 2 to 4 hours. This allows
sufficient time for floc particles to settle out of suspension by gravity.
Longer detention times may be needed for colder water or lighter
particles, while shorter times may be sufficient for denser flocs. Option
A (1-2 hours) is too short for effective sedimentation, Option B (4-8
hours) is excessive and more typical of storage reservoirs, and Option C
(30-60 minutes) is insufficient for proper settling.
,Question 2
Which chemical is commonly used for corrosion control in water
distribution systems?
A. Sodium hydroxide
B. Chlorine dioxide
C. Zinc orthophosphate
D. Aluminum sulfate
● C. Zinc orthophosphate
RATIONALE: Zinc orthophosphate is commonly used for corrosion
control in water distribution systems. It works by forming a protective
film on the interior surfaces of pipes, reducing the leaching of lead,
copper, and iron into the water. Option A (Sodium hydroxide) is used for
pH adjustment, Option B (Chlorine dioxide) is a disinfectant, and Option
D (Aluminum sulfate) is a coagulant.
Question 3
A centrifuge pump has a suction pressure of 5 psi and a discharge
pressure of 45 psi. What is the total dynamic head in feet? (Assume 1
psi = 2.31 feet)
A. 46.2 feet
B. 92.4 feet
C. 115.5 feet
D. 69.3 feet
● B. 92.4 feet
,RATIONALE: Total Dynamic Head = (Discharge Pressure - Suction
Pressure) × 2.31. TDH = (45 - 5) × 2.31 = 40 × 2.31 = 92.4 feet. Option A
(46.2 feet) would be the result of using only 20 psi difference, Option C
(115.5 feet) uses 50 psi incorrectly, and Option D (69.3 feet) uses 30 psi
difference.
Question 4
What is the maximum contaminant level (MCL) for total
trihalomethanes (TTHMs) in drinking water under the Safe Drinking
Water Act?
A. 0.010 mg/L
B. 0.005 mg/L
C. 0.080 mg/L
D. 0.100 mg/L
● C. 0.080 mg/L
RATIONALE: The MCL for total trihalomethanes (TTHMs) is 0.080 mg/L
(80 ppb). TTHMs are disinfection byproducts formed when chlorine
reacts with organic matter in water. Option A (0.010 mg/L) is the MCL
for arsenic, Option B (0.005 mg/L) is the MCL for lead, and Option D
(0.100 mg/L) is the maximum contaminant level goal (MCLG) for
TTHMs, not the enforceable MCL.
Question 5
Which type of filter uses a layer of anthracite coal over a layer of sand
and is commonly used in water treatment?
, A. Slow sand filter
B. Rapid sand filter
C. Dual-media filter
D. Membrane filter
● C. Dual-media filter
RATIONALE: A dual-media filter uses anthracite coal (lighter, larger
particles) over sand (heavier, smaller particles). This arrangement allows
for deeper penetration of particles and longer filter runs compared to
single-media filters. Option A (Slow sand filter) uses biological
processes, Option B (Rapid sand filter) uses only sand, and Option D
(Membrane filter) uses synthetic membranes.
Question 6
What is the purpose of lime softening in water treatment?
A. To remove dissolved organic compounds
B. To remove hardness minerals (calcium and magnesium)
C. To disinfect water and kill pathogens
D. To adjust pH by adding acid
● B. To remove hardness minerals (calcium and magnesium)
RATIONALE: Lime softening is a process that uses calcium hydroxide
(lime) to precipitate calcium carbonate and magnesium hydroxide,
thereby removing hardness from water. This reduces scaling in pipes
and improves soap efficiency. Option A describes oxidation processes,
Option C describes disinfection, and Option D incorrectly describes pH
adjustment with acid.
