MARYLAND WATER TREATMENT
PLANT OPERATOR CLASS 2
CERTIFICATION EXAM
QUESTIONS AND CORRECT
MARYLAND WATER TREATMENT PLANT OPERATOR CLASS
2 | Comprehensive Examination
MARYLAND WATER TREATMENT PLANT OPERATOR
CLASS 2 CERTIFICATION EXAM QUESTIONS AND
CORRECT ANSWERS WITH RATIONALES.pdf 1 actual
INTRODUCTION
This document is an important and very helpful preparation
resource for MARYLAND WATER TREATMENT PLANT
OPERATOR CLASS 2 CERTIFICATION EXAM
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALES.pdf 1. Every item uses a focused exam stem,
four response options, a keyed response, and a clear rationale,
making it easier to understand the subject, spot distractors, and
build real exam confidence.
Page 1
, Question 1
A conventional surface water plant feeding a distribution system with a 4-log
virus inactivation requirement uses free chlorine. If the filtered water has pH
7.8, temperature 5°C, and the target CT for 4-log virus inactivation is 6
mg-min/L, what is the minimum required chlorine residual (mg/L) if the
effective contact time (T10) is 30 minutes?
A. 0.10 mg/L
B. 0.20 mg/L
C. 0.30 mg/L
D. 0.40 mg/L
Correct Answer: B - 0.20 mg/L
RATIONALE
CT = residual × T10, so residual = CT/T10 = 6 ÷ 30 = 0.20 mg/L. The
pH and temperature values are already embedded in the tabulated CT
requirement, so no additional correction is applied here. Distractors
reflect common division errors or misreading the CT value.
Question 2
A jar test on a low-turbidity, high-alkalinity surface water shows that
increasing alum dose beyond 30 mg/L produces no further turbidity reduction
and slightly raises finished-water pH drop. What is the most technically sound
interpretation?
A. The water is underdosed and requires a coagulant aid such as a
polymer to reach optimum.
B. The system has reached the coagulant demand plateau; additional alum
only consumes alkalinity without benefit.
C. The pH is too high for alum and should be lowered with sulfuric acid
before coagulation.
D. The turbidity is too low for alum and a cationic polymer alone should
replace it.
Page 2
,Correct Answer: B - The system has reached the coagulant
demand plateau; additional alum only consumes alkalinity
without benefit.
RATIONALE
Once turbidity removal plateaus while pH continues to drop, the
coagulant demand has been satisfied and excess alum only lowers
alkalinity. Additional coagulant or pH adjustment would not improve
removal at this point. This reflects the classical coagulant demand
curve behavior.
Question 3
A rapid sand filter is operating at 4 gpm/ft² with a head loss of 8 ft after 20
hours. The filter media is 30 inches of anthracite over 12 inches of sand. Which
operational action best addresses premature head loss without sacrificing
effluent quality?
A. Increase backwash rate to 20 gpm/ft² for 10 minutes.
B. Reduce the filtration rate to 2 gpm/ft² to extend the run.
C. Perform a surface wash or air scour prior to backwash to remove
surface blinding.
D. Add a polymer filter aid continuously to the influent.
Correct Answer: C - Perform a surface wash or air scour prior to
backwash to remove surface blinding.
RATIONALE
Premature head loss in a dual-media filter is often caused by surface
blinding from accumulated floc. Air scour or surface wash before
backwash breaks up this layer and restores filter performance. Simply
increasing backwash rate or reducing rate does not address the
underlying blinding.
Page 3
, Question 4
A distribution system sample shows a heterotrophic plate count (HPC) of 450
CFU/mL and a free chlorine residual of 0.1 mg/L at a dead-end main. Which
corrective action is most appropriate under Maryland regulations?
A. Flush the dead-end main and increase chlorine residual to at least 0.2
mg/L.
B. Immediately issue a boil-water advisory for the entire system.
C. Replace the main because HPC exceedance indicates pipe corrosion.
D. Switch to chloramine disinfection to reduce HPC.
Correct Answer: A - Flush the dead-end main and increase
chlorine residual to at least 0.2 mg/L.
RATIONALE
Elevated HPC with low residual at a dead-end indicates stagnation and
loss of disinfectant residual. Flushing and restoring residual to 0.2
mg/L is the standard corrective action. HPC alone does not trigger a
boil-water advisory or main replacement.
Question 5
A lime-soda softening plant treats water with 200 mg/L as CaCO3 total
hardness, 150 mg/L calcium hardness, and 50 mg/L magnesium hardness. If
the plant targets 80 mg/L finished hardness, what is the theoretical lime dose
(mg/L as CaCO3) required for calcium removal alone?
A. 70 mg/L
B. 120 mg/L
C. 150 mg/L
D. 200 mg/L
Correct Answer: A - 70 mg/L
Page 4
PLANT OPERATOR CLASS 2
CERTIFICATION EXAM
QUESTIONS AND CORRECT
MARYLAND WATER TREATMENT PLANT OPERATOR CLASS
2 | Comprehensive Examination
MARYLAND WATER TREATMENT PLANT OPERATOR
CLASS 2 CERTIFICATION EXAM QUESTIONS AND
CORRECT ANSWERS WITH RATIONALES.pdf 1 actual
INTRODUCTION
This document is an important and very helpful preparation
resource for MARYLAND WATER TREATMENT PLANT
OPERATOR CLASS 2 CERTIFICATION EXAM
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALES.pdf 1. Every item uses a focused exam stem,
four response options, a keyed response, and a clear rationale,
making it easier to understand the subject, spot distractors, and
build real exam confidence.
Page 1
, Question 1
A conventional surface water plant feeding a distribution system with a 4-log
virus inactivation requirement uses free chlorine. If the filtered water has pH
7.8, temperature 5°C, and the target CT for 4-log virus inactivation is 6
mg-min/L, what is the minimum required chlorine residual (mg/L) if the
effective contact time (T10) is 30 minutes?
A. 0.10 mg/L
B. 0.20 mg/L
C. 0.30 mg/L
D. 0.40 mg/L
Correct Answer: B - 0.20 mg/L
RATIONALE
CT = residual × T10, so residual = CT/T10 = 6 ÷ 30 = 0.20 mg/L. The
pH and temperature values are already embedded in the tabulated CT
requirement, so no additional correction is applied here. Distractors
reflect common division errors or misreading the CT value.
Question 2
A jar test on a low-turbidity, high-alkalinity surface water shows that
increasing alum dose beyond 30 mg/L produces no further turbidity reduction
and slightly raises finished-water pH drop. What is the most technically sound
interpretation?
A. The water is underdosed and requires a coagulant aid such as a
polymer to reach optimum.
B. The system has reached the coagulant demand plateau; additional alum
only consumes alkalinity without benefit.
C. The pH is too high for alum and should be lowered with sulfuric acid
before coagulation.
D. The turbidity is too low for alum and a cationic polymer alone should
replace it.
Page 2
,Correct Answer: B - The system has reached the coagulant
demand plateau; additional alum only consumes alkalinity
without benefit.
RATIONALE
Once turbidity removal plateaus while pH continues to drop, the
coagulant demand has been satisfied and excess alum only lowers
alkalinity. Additional coagulant or pH adjustment would not improve
removal at this point. This reflects the classical coagulant demand
curve behavior.
Question 3
A rapid sand filter is operating at 4 gpm/ft² with a head loss of 8 ft after 20
hours. The filter media is 30 inches of anthracite over 12 inches of sand. Which
operational action best addresses premature head loss without sacrificing
effluent quality?
A. Increase backwash rate to 20 gpm/ft² for 10 minutes.
B. Reduce the filtration rate to 2 gpm/ft² to extend the run.
C. Perform a surface wash or air scour prior to backwash to remove
surface blinding.
D. Add a polymer filter aid continuously to the influent.
Correct Answer: C - Perform a surface wash or air scour prior to
backwash to remove surface blinding.
RATIONALE
Premature head loss in a dual-media filter is often caused by surface
blinding from accumulated floc. Air scour or surface wash before
backwash breaks up this layer and restores filter performance. Simply
increasing backwash rate or reducing rate does not address the
underlying blinding.
Page 3
, Question 4
A distribution system sample shows a heterotrophic plate count (HPC) of 450
CFU/mL and a free chlorine residual of 0.1 mg/L at a dead-end main. Which
corrective action is most appropriate under Maryland regulations?
A. Flush the dead-end main and increase chlorine residual to at least 0.2
mg/L.
B. Immediately issue a boil-water advisory for the entire system.
C. Replace the main because HPC exceedance indicates pipe corrosion.
D. Switch to chloramine disinfection to reduce HPC.
Correct Answer: A - Flush the dead-end main and increase
chlorine residual to at least 0.2 mg/L.
RATIONALE
Elevated HPC with low residual at a dead-end indicates stagnation and
loss of disinfectant residual. Flushing and restoring residual to 0.2
mg/L is the standard corrective action. HPC alone does not trigger a
boil-water advisory or main replacement.
Question 5
A lime-soda softening plant treats water with 200 mg/L as CaCO3 total
hardness, 150 mg/L calcium hardness, and 50 mg/L magnesium hardness. If
the plant targets 80 mg/L finished hardness, what is the theoretical lime dose
(mg/L as CaCO3) required for calcium removal alone?
A. 70 mg/L
B. 120 mg/L
C. 150 mg/L
D. 200 mg/L
Correct Answer: A - 70 mg/L
Page 4
