MARYLAND WATER TREATMENT
PLANT OPERATOR CLASS 4
CERTIFICATION EXAM
QUESTIONS AND CORRECT
MARYLAND WATER TREATMENT PLANT OPERATOR CLASS
4 | Comprehensive Examination
MARYLAND WATER TREATMENT PLANT OPERATOR
CLASS 4 CERTIFICATION EXAM QUESTIONS AND
CORRECT ANSWERS.pdf actual exam preparation
INTRODUCTION
This document is an important and very helpful preparation
resource for MARYLAND WATER TREATMENT PLANT
OPERATOR CLASS 4 CERTIFICATION EXAM
QUESTIONS AND CORRECT ANSWERS.pdf. 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 surface water plant uses alum coagulation at pH 6.5. Jar tests show optimal
turbidity removal at 25 mg/L alum, but plant filters experience premature
headloss breakthrough. Which adjustment best addresses this without
compromising NOM removal?
A. Increase alum dose to 35 mg/L to sweep floc.
B. Lower pH to 5.8 to improve charge neutralization.
C. Add a cationic polymer as a flocculant aid and reduce alum to 20
mg/L.
D. Switch to ferric chloride at 15 mg/L without pH adjustment.
Correct Answer: C - Add a cationic polymer as a flocculant aid
and reduce alum to 20 mg/L.
RATIONALE
Premature headloss with optimal turbidity removal suggests excessive
floc volume or poor floc strength. Adding a cationic polymer enhances
floc density and reduces alum demand, lowering sludge production
and headloss while maintaining NOM removal. Increasing alum or
lowering pH would worsen headloss, and switching to ferric chloride
without pH adjustment may not match existing optimal conditions.
Question 2
A conventional plant treats 10 MGD with a sedimentation basin overflow rate
of 800 gpd/ft². If flow increases to 12 MGD, what is the new overflow rate and
its impact on particle removal?
A. 960 gpd/ft²; removal efficiency increases due to higher velocity.
B. 960 gpd/ft²; removal efficiency decreases for particles with settling
velocity < 960 gpd/ft².
C. 800 gpd/ft²; removal efficiency unchanged because surface area is
constant.
D. 1200 gpd/ft²; removal efficiency increases due to greater driving
Page 2
, force.
Correct Answer: B - 960 gpd/ft²; removal efficiency decreases for
particles with settling velocity < 960 gpd/ft².
RATIONALE
Overflow rate = flow / surface area. Original area = 10,000,
= 12,500 ft². New rate = 12,000,,500 = 960 gpd/ft². Higher
overflow rate reduces removal of particles with settling velocity less
than the new overflow rate, as per Stokes' law and ideal settling
theory.
Question 3
A filter run terminates after 18 hours due to turbidity breakthrough. Backwash
data show media loss and mudballs. Which combination of actions best
restores filter performance?
A. Increase backwash rate to 20 gpm/ft² and extend duration to 15
minutes.
B. Perform air scour followed by low-rate backwash with surface wash,
and inspect media depth.
C. Reduce coagulant dose to decrease floc loading on filters.
D. Add anthracite to the filter bed without removing existing media.
Correct Answer: B - Perform air scour followed by low-rate
backwash with surface wash, and inspect media depth.
RATIONALE
Mudballs and media loss indicate inadequate cleaning and media
degradation. Air scour with surface wash and low-rate backwash
effectively removes floc without losing media. Inspecting media depth
ensures proper bed integrity. Increasing backwash rate may worsen
media loss; reducing coagulant may cause poor removal; adding
media without removal is improper.
Page 3
, Question 4
A groundwater plant uses free chlorine for disinfection at pH 7.2, 10°C, with a
CT requirement of 20 mg-min/L for 3-log Giardia inactivation. If chlorine
residual is 1.2 mg/L and contact time is 15 minutes, what is the CT value and
compliance status?
A. 18 mg-min/L; non-compliant, need longer contact time.
B. 18 mg-min/L; compliant because temperature adjustment reduces
requirement.
C. 20 mg-min/L; compliant exactly at requirement.
D. 24 mg-min/L; compliant with margin.
Correct Answer: A - 18 mg-min/L; non-compliant, need longer
contact time.
RATIONALE
CT = residual × contact time = 1.2 mg/L × 15 min = 18 mg-min/L.
Since 18 < 20, the system is non-compliant. Temperature and pH
affect CT tables, but the calculated CT is below the required 20
mg-min/L for the given conditions.
Question 5
Under Maryland COMAR 26.04.01, a community water system exceeds the
lead action level. Which public education requirement must be met within 60
days of the end of the monitoring period?
A. Deliver public education materials to all bill-paying customers within
60 days.
B. Provide public education to all customers within 60 days, including
posters, pamphlets, and press releases.
C. Issue a Tier 1 public notice within 24 hours.
D. Replace all lead service lines within 60 days.
Correct Answer: B - Provide public education to all customers
within 60 days, including posters, pamphlets, and press releases.
Page 4
PLANT OPERATOR CLASS 4
CERTIFICATION EXAM
QUESTIONS AND CORRECT
MARYLAND WATER TREATMENT PLANT OPERATOR CLASS
4 | Comprehensive Examination
MARYLAND WATER TREATMENT PLANT OPERATOR
CLASS 4 CERTIFICATION EXAM QUESTIONS AND
CORRECT ANSWERS.pdf actual exam preparation
INTRODUCTION
This document is an important and very helpful preparation
resource for MARYLAND WATER TREATMENT PLANT
OPERATOR CLASS 4 CERTIFICATION EXAM
QUESTIONS AND CORRECT ANSWERS.pdf. 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 surface water plant uses alum coagulation at pH 6.5. Jar tests show optimal
turbidity removal at 25 mg/L alum, but plant filters experience premature
headloss breakthrough. Which adjustment best addresses this without
compromising NOM removal?
A. Increase alum dose to 35 mg/L to sweep floc.
B. Lower pH to 5.8 to improve charge neutralization.
C. Add a cationic polymer as a flocculant aid and reduce alum to 20
mg/L.
D. Switch to ferric chloride at 15 mg/L without pH adjustment.
Correct Answer: C - Add a cationic polymer as a flocculant aid
and reduce alum to 20 mg/L.
RATIONALE
Premature headloss with optimal turbidity removal suggests excessive
floc volume or poor floc strength. Adding a cationic polymer enhances
floc density and reduces alum demand, lowering sludge production
and headloss while maintaining NOM removal. Increasing alum or
lowering pH would worsen headloss, and switching to ferric chloride
without pH adjustment may not match existing optimal conditions.
Question 2
A conventional plant treats 10 MGD with a sedimentation basin overflow rate
of 800 gpd/ft². If flow increases to 12 MGD, what is the new overflow rate and
its impact on particle removal?
A. 960 gpd/ft²; removal efficiency increases due to higher velocity.
B. 960 gpd/ft²; removal efficiency decreases for particles with settling
velocity < 960 gpd/ft².
C. 800 gpd/ft²; removal efficiency unchanged because surface area is
constant.
D. 1200 gpd/ft²; removal efficiency increases due to greater driving
Page 2
, force.
Correct Answer: B - 960 gpd/ft²; removal efficiency decreases for
particles with settling velocity < 960 gpd/ft².
RATIONALE
Overflow rate = flow / surface area. Original area = 10,000,
= 12,500 ft². New rate = 12,000,,500 = 960 gpd/ft². Higher
overflow rate reduces removal of particles with settling velocity less
than the new overflow rate, as per Stokes' law and ideal settling
theory.
Question 3
A filter run terminates after 18 hours due to turbidity breakthrough. Backwash
data show media loss and mudballs. Which combination of actions best
restores filter performance?
A. Increase backwash rate to 20 gpm/ft² and extend duration to 15
minutes.
B. Perform air scour followed by low-rate backwash with surface wash,
and inspect media depth.
C. Reduce coagulant dose to decrease floc loading on filters.
D. Add anthracite to the filter bed without removing existing media.
Correct Answer: B - Perform air scour followed by low-rate
backwash with surface wash, and inspect media depth.
RATIONALE
Mudballs and media loss indicate inadequate cleaning and media
degradation. Air scour with surface wash and low-rate backwash
effectively removes floc without losing media. Inspecting media depth
ensures proper bed integrity. Increasing backwash rate may worsen
media loss; reducing coagulant may cause poor removal; adding
media without removal is improper.
Page 3
, Question 4
A groundwater plant uses free chlorine for disinfection at pH 7.2, 10°C, with a
CT requirement of 20 mg-min/L for 3-log Giardia inactivation. If chlorine
residual is 1.2 mg/L and contact time is 15 minutes, what is the CT value and
compliance status?
A. 18 mg-min/L; non-compliant, need longer contact time.
B. 18 mg-min/L; compliant because temperature adjustment reduces
requirement.
C. 20 mg-min/L; compliant exactly at requirement.
D. 24 mg-min/L; compliant with margin.
Correct Answer: A - 18 mg-min/L; non-compliant, need longer
contact time.
RATIONALE
CT = residual × contact time = 1.2 mg/L × 15 min = 18 mg-min/L.
Since 18 < 20, the system is non-compliant. Temperature and pH
affect CT tables, but the calculated CT is below the required 20
mg-min/L for the given conditions.
Question 5
Under Maryland COMAR 26.04.01, a community water system exceeds the
lead action level. Which public education requirement must be met within 60
days of the end of the monitoring period?
A. Deliver public education materials to all bill-paying customers within
60 days.
B. Provide public education to all customers within 60 days, including
posters, pamphlets, and press releases.
C. Issue a Tier 1 public notice within 24 hours.
D. Replace all lead service lines within 60 days.
Correct Answer: B - Provide public education to all customers
within 60 days, including posters, pamphlets, and press releases.
Page 4
