SWRCB - Water Treatment Operator Certification
Examination Grade III Exam Practice Questions
And Correct Answers (Verified Answers) Plus
Rationale Q&A Instant Download Pdf. - Complete
99 Verified Q&A with Answers & Rationales for
Exam Prep
Q1
A surface water treatment plant using conventional coagulation, flocculation, sedimentation, and filtration
experiences periodic filter breakthrough despite optimal coagulant dose. Jar tests indicate good floc
formation. Which of the following is the most likely cause?
A. Insufficient chlorine residual in the filter influent
B. Filter media stratification or improper backwash
C. Excessive filter aid polymer addition
D. Low pH in the coagulation basin
Answer: B
Rationale: Filter breakthrough with good floc formation often stems from media issues such as
stratification, mudballs, or inadequate backwash, which allow particles to pass. Chlorine residual (A)
affects disinfection, not filtration. Excessive polymer (C) typically improves filtration but may cause other
issues. Low pH (D) would affect coagulation, not filter performance directly.
Q2
A water system using free chlorine must achieve 3-log inactivation of Giardia at a pH of 7.5 and 10°C. The
required CT value is 150 mg-min/L. If the residual chlorine concentration is 1.5 mg/L, what is the minimum
contact time required?
A. 50 minutes
B. 75 minutes
C. 100 minutes
D. 150 minutes
Answer: C
Rationale: CT = concentration × time. Rearranging, time = CT / concentration = .5 = 100 minutes.
Options A, B, and D are incorrect because they do not match the calculated value.
,Q3
A treatment plant uses ozone for primary disinfection and chloramine for secondary disinfection. Which of
the following best explains why chloramine rather than free chlorine is used in the distribution system?
A. Chloramine provides a higher oxidation potential than free chlorine.
B. Chloramine is more effective against viruses than free chlorine.
C. Chloramine produces fewer regulated disinfection byproducts.
D. Chloramine is less stable and dissipates quickly, reducing taste and odor.
Answer: C
Rationale: Chloramine is used because it forms fewer trihalomethanes and haloacetic acids compared to
free chlorine. Option A is false; chloramine is a weaker oxidant. Option B is false; free chlorine is more
effective against viruses. Option D is false; chloramine is more stable, which helps maintain residual.
Q4
A groundwater source has high levels of iron and manganese. The plant uses aeration followed by
filtration. If the pH of the water after aeration is 7.2, what is the most likely impact on manganese removal?
A. Manganese removal will be optimal because aeration oxidizes both iron and manganese.
B. Manganese removal will be poor because manganese requires a higher pH for effective oxidation.
C. Manganese removal will be enhanced because iron acts as a coagulant aid.
D. Manganese removal will be unaffected because manganese is removed by physical filtration alone.
Answer: B
Rationale: Manganese oxidation by aeration is slow below pH 9.5; at pH 7.2, removal is inadequate. Iron
oxidizes readily at pH >7.0. Option A is incorrect because aeration alone does not effectively oxidize
manganese at this pH. Option C is incorrect; iron does not significantly aid manganese removal. Option D
is incorrect; manganese requires oxidation before filtration.
Q5
A distribution system experiences a sudden drop in pressure due to a main break. According to the
SWRCB, which of the following is the most appropriate immediate action?
A. Issue a boil water notice for the entire system.
B. Increase chlorine residual to 2.0 mg/L throughout the system.
C. Isolate the affected area and perform a sanitary survey.
D. Flush the system and collect bacteriological samples.
Answer: C
Rationale: The first step is to isolate the break to prevent contamination and then conduct a sanitary
survey to assess risk. A boil water notice (A) may be issued later if contamination is confirmed. Increasing
chlorine (B) may be part of response but not immediate. Flushing and sampling (D) are done after isolation
and survey.
,Q6
A treatment plant uses granular activated carbon (GAC) for removal of synthetic organic compounds
(SOCs). The bed depth is 10 feet, and the empty bed contact time (EBCT) is 10 minutes. If the flow rate is
increased by 25%, what is the new EBCT?
A. 7.5 minutes
B. 8.0 minutes
C. 10.0 minutes
D. 12.5 minutes
Answer: B
Rationale: EBCT = bed volume / flow rate. If flow increases by 25%, EBCT decreases proportionally: 10
min / 1.25 = 8.0 minutes. Options A, C, and D do not reflect the inverse relationship.
Q7
Which of the following best describes the role of a surge tank in a water treatment plant?
A. To provide storage for filter backwash water
B. To dampen pressure surges and prevent water hammer
C. To aerate water for iron and manganese removal
D. To mix coagulants rapidly with raw water
Answer: B
Rationale: A surge tank mitigates hydraulic transients and water hammer by absorbing pressure
fluctuations. Option A refers to backwash storage. Option C is an aerator. Option D is a rapid mix basin.
Q8
A water sample has a total alkalinity of 120 mg/L as CaCO3 and a pH of 8.5. The calcium hardness is 150
mg/L as CaCO3. What is the approximate carbonate hardness?
A. 120 mg/L as CaCO3
B. 150 mg/L as CaCO3
C. 30 mg/L as CaCO3
D. 270 mg/L as CaCO3
Answer: A
Rationale: Carbonate hardness is the lesser of total alkalinity and calcium hardness. Since alkalinity
(120) < hardness (150), carbonate hardness = 120 mg/L as CaCO3. Options B, C, and D are incorrect
because they do not follow this rule.
, Q9
A plant uses ultraviolet (UV) disinfection. The UV dose is calculated as 40 mJ/cm². If the UV intensity is
20 mW/cm², what is the required exposure time?
A. 0.5 seconds
B. 2 seconds
C. 20 seconds
D. 800 seconds
Answer: B
Rationale: UV dose (mJ/cm²) = intensity (mW/cm²) × time (s). Rearranging, time = dose / intensity = 40 /
20 = 2 seconds. Options A, C, and D are incorrect calculations.
Q10
A treatment plant is experiencing high turbidity in the finished water due to a failure in the coagulation
process. Which of the following is the most appropriate immediate corrective action?
A. Increase the filter backwash frequency
B. Switch to a different coagulant
C. Optimize coagulant dose and pH through jar testing
D. Add powdered activated carbon to the filter influent
Answer: C
Rationale: The root cause is coagulation failure; optimizing dose and pH via jar testing addresses the
issue. Increasing backwash (A) treats symptoms, not cause. Switching coagulant (B) may be a long-term
solution but not immediate. Adding PAC (D) targets organics, not turbidity.
Examination Grade III Exam Practice Questions
And Correct Answers (Verified Answers) Plus
Rationale Q&A Instant Download Pdf. - Complete
99 Verified Q&A with Answers & Rationales for
Exam Prep
Q1
A surface water treatment plant using conventional coagulation, flocculation, sedimentation, and filtration
experiences periodic filter breakthrough despite optimal coagulant dose. Jar tests indicate good floc
formation. Which of the following is the most likely cause?
A. Insufficient chlorine residual in the filter influent
B. Filter media stratification or improper backwash
C. Excessive filter aid polymer addition
D. Low pH in the coagulation basin
Answer: B
Rationale: Filter breakthrough with good floc formation often stems from media issues such as
stratification, mudballs, or inadequate backwash, which allow particles to pass. Chlorine residual (A)
affects disinfection, not filtration. Excessive polymer (C) typically improves filtration but may cause other
issues. Low pH (D) would affect coagulation, not filter performance directly.
Q2
A water system using free chlorine must achieve 3-log inactivation of Giardia at a pH of 7.5 and 10°C. The
required CT value is 150 mg-min/L. If the residual chlorine concentration is 1.5 mg/L, what is the minimum
contact time required?
A. 50 minutes
B. 75 minutes
C. 100 minutes
D. 150 minutes
Answer: C
Rationale: CT = concentration × time. Rearranging, time = CT / concentration = .5 = 100 minutes.
Options A, B, and D are incorrect because they do not match the calculated value.
,Q3
A treatment plant uses ozone for primary disinfection and chloramine for secondary disinfection. Which of
the following best explains why chloramine rather than free chlorine is used in the distribution system?
A. Chloramine provides a higher oxidation potential than free chlorine.
B. Chloramine is more effective against viruses than free chlorine.
C. Chloramine produces fewer regulated disinfection byproducts.
D. Chloramine is less stable and dissipates quickly, reducing taste and odor.
Answer: C
Rationale: Chloramine is used because it forms fewer trihalomethanes and haloacetic acids compared to
free chlorine. Option A is false; chloramine is a weaker oxidant. Option B is false; free chlorine is more
effective against viruses. Option D is false; chloramine is more stable, which helps maintain residual.
Q4
A groundwater source has high levels of iron and manganese. The plant uses aeration followed by
filtration. If the pH of the water after aeration is 7.2, what is the most likely impact on manganese removal?
A. Manganese removal will be optimal because aeration oxidizes both iron and manganese.
B. Manganese removal will be poor because manganese requires a higher pH for effective oxidation.
C. Manganese removal will be enhanced because iron acts as a coagulant aid.
D. Manganese removal will be unaffected because manganese is removed by physical filtration alone.
Answer: B
Rationale: Manganese oxidation by aeration is slow below pH 9.5; at pH 7.2, removal is inadequate. Iron
oxidizes readily at pH >7.0. Option A is incorrect because aeration alone does not effectively oxidize
manganese at this pH. Option C is incorrect; iron does not significantly aid manganese removal. Option D
is incorrect; manganese requires oxidation before filtration.
Q5
A distribution system experiences a sudden drop in pressure due to a main break. According to the
SWRCB, which of the following is the most appropriate immediate action?
A. Issue a boil water notice for the entire system.
B. Increase chlorine residual to 2.0 mg/L throughout the system.
C. Isolate the affected area and perform a sanitary survey.
D. Flush the system and collect bacteriological samples.
Answer: C
Rationale: The first step is to isolate the break to prevent contamination and then conduct a sanitary
survey to assess risk. A boil water notice (A) may be issued later if contamination is confirmed. Increasing
chlorine (B) may be part of response but not immediate. Flushing and sampling (D) are done after isolation
and survey.
,Q6
A treatment plant uses granular activated carbon (GAC) for removal of synthetic organic compounds
(SOCs). The bed depth is 10 feet, and the empty bed contact time (EBCT) is 10 minutes. If the flow rate is
increased by 25%, what is the new EBCT?
A. 7.5 minutes
B. 8.0 minutes
C. 10.0 minutes
D. 12.5 minutes
Answer: B
Rationale: EBCT = bed volume / flow rate. If flow increases by 25%, EBCT decreases proportionally: 10
min / 1.25 = 8.0 minutes. Options A, C, and D do not reflect the inverse relationship.
Q7
Which of the following best describes the role of a surge tank in a water treatment plant?
A. To provide storage for filter backwash water
B. To dampen pressure surges and prevent water hammer
C. To aerate water for iron and manganese removal
D. To mix coagulants rapidly with raw water
Answer: B
Rationale: A surge tank mitigates hydraulic transients and water hammer by absorbing pressure
fluctuations. Option A refers to backwash storage. Option C is an aerator. Option D is a rapid mix basin.
Q8
A water sample has a total alkalinity of 120 mg/L as CaCO3 and a pH of 8.5. The calcium hardness is 150
mg/L as CaCO3. What is the approximate carbonate hardness?
A. 120 mg/L as CaCO3
B. 150 mg/L as CaCO3
C. 30 mg/L as CaCO3
D. 270 mg/L as CaCO3
Answer: A
Rationale: Carbonate hardness is the lesser of total alkalinity and calcium hardness. Since alkalinity
(120) < hardness (150), carbonate hardness = 120 mg/L as CaCO3. Options B, C, and D are incorrect
because they do not follow this rule.
, Q9
A plant uses ultraviolet (UV) disinfection. The UV dose is calculated as 40 mJ/cm². If the UV intensity is
20 mW/cm², what is the required exposure time?
A. 0.5 seconds
B. 2 seconds
C. 20 seconds
D. 800 seconds
Answer: B
Rationale: UV dose (mJ/cm²) = intensity (mW/cm²) × time (s). Rearranging, time = dose / intensity = 40 /
20 = 2 seconds. Options A, C, and D are incorrect calculations.
Q10
A treatment plant is experiencing high turbidity in the finished water due to a failure in the coagulation
process. Which of the following is the most appropriate immediate corrective action?
A. Increase the filter backwash frequency
B. Switch to a different coagulant
C. Optimize coagulant dose and pH through jar testing
D. Add powdered activated carbon to the filter influent
Answer: C
Rationale: The root cause is coagulation failure; optimizing dose and pH via jar testing addresses the
issue. Increasing backwash (A) treats symptoms, not cause. Switching coagulant (B) may be a long-term
solution but not immediate. Adding PAC (D) targets organics, not turbidity.
