Arizona AZ L-84 Water
Treatment Contractor Practice
Exam | Questions, Verified
Answers & Detailed
Rationales | Complete
Contractor License Exam Prep
Study Guide | Updated 2026
1. What is the primary purpose of coagulation in a
conventional water treatment plant?
A. To disinfect the water
B. To destabilize suspended and colloidal particles
C. To increase water hardness
D. To remove dissolved oxygen
Correct answer: To destabilize suspended and colloidal
particles
Rationale: Coagulation neutralizes or destabilizes the
electrical charges that keep fine particles suspended,
allowing them to come together during subsequent
flocculation and sedimentation.
2. Which chemical is commonly used as a coagulant in
drinking-water treatment?
A. Sodium chloride
B. Aluminum sulfate
C. Calcium carbonate
D. Sodium bicarbonate
Correct answer: Aluminum sulfate
,Rationale: Aluminum sulfate, commonly called alum, is a
widely used coagulant. It reacts in water to form
aluminum hydroxide floc that helps capture suspended
particles.
3. What is the primary purpose of flocculation?
A. Rapidly mix disinfectant into the water
B. Allow destabilized particles to form larger particles
C. Remove dissolved salts
D. Lower the water temperature
Correct answer: Allow destabilized particles to form
larger particles
Rationale: Flocculation uses gentle mixing to encourage
small destabilized particles to collide and form larger,
heavier flocs that can settle or be filtered.
4. What is the main purpose of sedimentation?
A. Remove settleable suspended solids
B. Increase alkalinity
C. Add fluoride
D. Oxidize organic compounds
Correct answer: Remove settleable suspended solids
Rationale: Sedimentation reduces the solids load on
downstream filters by allowing heavier floc and other
settleable particles to settle out under relatively
quiescent conditions.
5. What is turbidity a measurement of?
A. Water temperature
B. Water pressure
C. Cloudiness caused by suspended particles
D. Total dissolved oxygen
,Correct answer: Cloudiness caused by suspended
particles
Rationale: Turbidity indicates the scattering of light by
suspended and colloidal material in water and is
commonly measured in NTU, or nephelometric turbidity
units.
6. What is the purpose of a rapid-mix basin?
A. Provide long-term water storage
B. Quickly and uniformly distribute treatment chemicals
C. Allow sludge to settle
D. Remove hardness
Correct answer: Quickly and uniformly distribute
treatment chemicals
Rationale: Rapid mixing provides intense agitation so
coagulants and other chemicals are dispersed
throughout the water before flocculation begins.
7. What is jar testing primarily used to determine?
A. Pipe pressure
B. Optimum chemical treatment conditions
C. Pump horsepower
D. Filter media depth
Correct answer: Optimum chemical treatment conditions
Rationale: A jar test can be used to evaluate coagulant
type, dose, pH, polymer use, and mixing conditions
under controlled conditions before adjusting full-scale
treatment.
8. What does pH measure?
, A. The concentration of suspended solids
B. The acidity or alkalinity of water
C. The chlorine demand
D. The water flow rate
Correct answer: The acidity or alkalinity of water
Rationale: pH expresses hydrogen-ion activity on a
logarithmic scale. A pH below 7 is acidic, 7 is neutral at
standard conditions, and above 7 is alkaline.
9. Why is alkalinity important during coagulation?
A. It provides buffering capacity for chemical reactions
B. It eliminates all bacteria
C. It directly measures turbidity
D. It determines pump speed
Correct answer: It provides buffering capacity for
chemical reactions
Rationale: Many coagulants consume alkalinity as they
hydrolyze. Insufficient alkalinity can cause an
undesirable pH reduction and impair treatment
performance.
10. What is the primary purpose of filtration in a
conventional treatment process?
A. Remove remaining suspended particles and microorganisms
B. Increase hardness
C. Add alkalinity
D. Increase water temperature
Correct answer: Remove remaining suspended particles
and microorganisms
Rationale: Filtration removes particles that remain after
coagulation and sedimentation and can also contribute
Treatment Contractor Practice
Exam | Questions, Verified
Answers & Detailed
Rationales | Complete
Contractor License Exam Prep
Study Guide | Updated 2026
1. What is the primary purpose of coagulation in a
conventional water treatment plant?
A. To disinfect the water
B. To destabilize suspended and colloidal particles
C. To increase water hardness
D. To remove dissolved oxygen
Correct answer: To destabilize suspended and colloidal
particles
Rationale: Coagulation neutralizes or destabilizes the
electrical charges that keep fine particles suspended,
allowing them to come together during subsequent
flocculation and sedimentation.
2. Which chemical is commonly used as a coagulant in
drinking-water treatment?
A. Sodium chloride
B. Aluminum sulfate
C. Calcium carbonate
D. Sodium bicarbonate
Correct answer: Aluminum sulfate
,Rationale: Aluminum sulfate, commonly called alum, is a
widely used coagulant. It reacts in water to form
aluminum hydroxide floc that helps capture suspended
particles.
3. What is the primary purpose of flocculation?
A. Rapidly mix disinfectant into the water
B. Allow destabilized particles to form larger particles
C. Remove dissolved salts
D. Lower the water temperature
Correct answer: Allow destabilized particles to form
larger particles
Rationale: Flocculation uses gentle mixing to encourage
small destabilized particles to collide and form larger,
heavier flocs that can settle or be filtered.
4. What is the main purpose of sedimentation?
A. Remove settleable suspended solids
B. Increase alkalinity
C. Add fluoride
D. Oxidize organic compounds
Correct answer: Remove settleable suspended solids
Rationale: Sedimentation reduces the solids load on
downstream filters by allowing heavier floc and other
settleable particles to settle out under relatively
quiescent conditions.
5. What is turbidity a measurement of?
A. Water temperature
B. Water pressure
C. Cloudiness caused by suspended particles
D. Total dissolved oxygen
,Correct answer: Cloudiness caused by suspended
particles
Rationale: Turbidity indicates the scattering of light by
suspended and colloidal material in water and is
commonly measured in NTU, or nephelometric turbidity
units.
6. What is the purpose of a rapid-mix basin?
A. Provide long-term water storage
B. Quickly and uniformly distribute treatment chemicals
C. Allow sludge to settle
D. Remove hardness
Correct answer: Quickly and uniformly distribute
treatment chemicals
Rationale: Rapid mixing provides intense agitation so
coagulants and other chemicals are dispersed
throughout the water before flocculation begins.
7. What is jar testing primarily used to determine?
A. Pipe pressure
B. Optimum chemical treatment conditions
C. Pump horsepower
D. Filter media depth
Correct answer: Optimum chemical treatment conditions
Rationale: A jar test can be used to evaluate coagulant
type, dose, pH, polymer use, and mixing conditions
under controlled conditions before adjusting full-scale
treatment.
8. What does pH measure?
, A. The concentration of suspended solids
B. The acidity or alkalinity of water
C. The chlorine demand
D. The water flow rate
Correct answer: The acidity or alkalinity of water
Rationale: pH expresses hydrogen-ion activity on a
logarithmic scale. A pH below 7 is acidic, 7 is neutral at
standard conditions, and above 7 is alkaline.
9. Why is alkalinity important during coagulation?
A. It provides buffering capacity for chemical reactions
B. It eliminates all bacteria
C. It directly measures turbidity
D. It determines pump speed
Correct answer: It provides buffering capacity for
chemical reactions
Rationale: Many coagulants consume alkalinity as they
hydrolyze. Insufficient alkalinity can cause an
undesirable pH reduction and impair treatment
performance.
10. What is the primary purpose of filtration in a
conventional treatment process?
A. Remove remaining suspended particles and microorganisms
B. Increase hardness
C. Add alkalinity
D. Increase water temperature
Correct answer: Remove remaining suspended particles
and microorganisms
Rationale: Filtration removes particles that remain after
coagulation and sedimentation and can also contribute
