Class C Practice Exam Questions And

Surface Water Treatment Operator Class C Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following is the primary purpose of coagulation in water

treatment?

• Disinfection
• Floc formation
• Sediment removal
• pH adjustment

Rationale: Coagulation is used to destabilize particles and promote

the formation of larger flocs that can be removed by sedimentation or filtration. 1 / 4

• What is the most common coagulant used in surface water treatment?
• Sodium hypochlorite
• Aluminum sulfate (alum)
• Calcium carbonate
• Ferric chloride

Rationale: Aluminum sulfate, commonly called alum, is widely used

due to its effectiveness and cost-efficiency.

• What is the main purpose of sedimentation in water treatment?
• Filtration
• Removal of settled solids
• Disinfection
• pH adjustment

Rationale: Sedimentation allows flocculated particles to settle out of

water before filtration, reducing the load on filters.

• Which water quality parameter is most important to monitor after

coagulation?

• pH
• Turbidity
• Hardness
• Chlorine residual

Rationale: Turbidity is monitored to ensure that coagulation and

flocculation effectively remove particles. 2 / 4

• What type of filter media is commonly used in slow sand filters?
• Activated carbon
• Anthracite
• Sand
• Gravel

Rationale: Slow sand filters primarily use a uniform layer of sand to

remove particles through physical straining and biological activity.

• Which process is primarily responsible for removing pathogens in slow

sand filtration?

• Coagulation
• Biological layer (schmutzdecke)
• Sedimentation
• Chlorination

Rationale: The schmutzdecke is a biological layer that removes

pathogens through predation, adsorption, and natural die-off.

• What is the typical detention time for slow sand filters?
• 5–10 minutes
• 15–30 minutes
• 12–24 hours
• 48–72 hours

Rationale: Slow sand filters require long detention times to allow

biological activity and physical filtration to effectively remove contaminants. 3 / 4

• Which water treatment process is most effective for removing iron

and manganese?

• Coagulation
• Sedimentation
• Oxidation followed by filtration
• Reverse osmosis

Rationale: Iron and manganese are oxidized to insoluble forms and

then removed by filtration.

• What is the primary purpose of disinfection in water treatment?
• Reduce turbidity
• Destroy pathogenic microorganisms
• Remove hardness
• Adjust pH

Rationale: Disinfection aims to inactivate or destroy disease-causing

microorganisms to protect public health.

• Which disinfectant provides a residual effect in the distribution

system?

• Ozone
• UV light
• Chlorine
• Chloramine (without residual adjustment)

Rationale: Chlorine maintains a residual throughout the distribution

system to prevent microbial regrowth.

• / 4