Maryland Water Distribution Systems
Operator Certification Exam | Verified
Questions
Maryland Water Distribution Systems Operator Certification Exam |
Comprehensive Examination
Maryland Water Distribution Systems Operator Certification
Exam actual exam preparation document with verified
questions, complete answers, and focused rationales for
INTRODUCTION
This document is an important and very helpful preparation
resource for Maryland Water Distribution Systems Operator
Certification Exam. 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 water distribution system experiences a sudden pressure drop from 65 psi to
20 psi in a residential area. The SCADA system shows no pump failures or
valve closures. Which of the following is the most likely cause?
A. A major water main break downstream of the pressure sensor
B. A closed isolation valve upstream of the pressure sensor
C. A malfunctioning pressure-reducing valve (PRV) at a nearby
commercial building
D. Increased water demand due to a large firefighting operation
Correct Answer: A - A major water main break downstream of
the pressure sensor
RATIONALE
A sudden pressure drop without pump or valve changes typically
indicates a major main break causing significant water loss and
reduced pressure. A closed valve upstream would cause low pressure
but is less likely to be sudden without SCADA indication. A
malfunctioning PRV affects only local pressure, and firefighting
demand would be gradual and localized.
Question 2
Under the Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR), a
community water system must comply with the locational running annual
average (LRAA) for TTHM. If quarterly TTHM results at a monitoring
location are 60, 80, 70, and 90 µg/L, what is the LRAA and does it exceed the
MCL?
A. 75 µg/L; does not exceed the 80 µg/L MCL
B. 75 µg/L; exceeds the 80 µg/L MCL
C. 80 µg/L; exceeds the 80 µg/L MCL
D. 70 µg/L; does not exceed the 80 µg/L MCL
Correct Answer: A - 75 µg/L; does not exceed the 80 µg/L MCL
Page 2
, RATIONALE
The LRAA is the average of the last four quarterly results at a
location: (60+80+70+90)/4 = 75 µg/L. The MCL for TTHM is 80
µg/L, so 75 µg/L does not exceed the MCL. Options B and C
incorrectly calculate or interpret the average, and D uses an incorrect
average.
Question 3
A distribution system has a cross-connection between a potable water line and
a fire sprinkler system containing antifreeze. Which type of backflow
prevention assembly is most appropriate to protect the potable water supply?
A. Double check valve assembly (DCVA)
B. Reduced pressure zone (RPZ) assembly
C. Pressure vacuum breaker (PVB)
D. Atmospheric vacuum breaker (AVB)
Correct Answer: B - Reduced pressure zone (RPZ) assembly
RATIONALE
An RPZ assembly provides the highest level of protection against both
backpressure and backsiphonage and is required for high-hazard
cross-connections such as antifreeze in fire sprinkler systems. DCVAs
are for low-hazard, PVBs and AVBs are for backsiphonage only and
cannot protect against backpressure.
Question 4
A pump is operating at 1750 rpm and delivers 500 gpm at 100 ft TDH. If the
speed is increased to 3500 rpm, what will be the new flow rate and TDH,
assuming no change in efficiency?
A. 1000 gpm and 200 ft
B. 1000 gpm and 400 ft
C. 2000 gpm and 400 ft
D. 250 gpm and 50 ft
Page 3
, Correct Answer: B - 1000 gpm and 400 ft
RATIONALE
According to the affinity laws, flow varies directly with speed (Q2 =
Q1 × (N2/N1)), so 500 × (3500/1750) = 1000 gpm. TDH varies with
the square of speed (H2 = H1 × (N2/N1)^2), so 100 × (2)^2 = 400 ft.
Option A incorrectly squares only the flow, C doubles both
incorrectly, and D halves both.
Question 5
A water storage tank has a high water level alarm at 2:00 AM. The SCADA
system shows the tank inlet valve is open and the tank level is rising despite
normal system pressure. Which of the following is the most likely cause?
A. A pressure-reducing valve (PRV) failure causing excessive pressure
into the tank
B. A malfunctioning altitude valve allowing continuous filling
C. A pump check valve failure causing backflow into the tank
D. A telemetry error falsely indicating a high level
Correct Answer: B - A malfunctioning altitude valve allowing
continuous filling
RATIONALE
An altitude valve controls tank filling and should close when the tank
reaches the set level. If it fails open, the tank continues to fill,
triggering a high-level alarm. A PRV failure would affect system
pressure, not tank filling directly. Check valve failure would cause
backflow, not continuous filling from the inlet.
Page 4
Operator Certification Exam | Verified
Questions
Maryland Water Distribution Systems Operator Certification Exam |
Comprehensive Examination
Maryland Water Distribution Systems Operator Certification
Exam actual exam preparation document with verified
questions, complete answers, and focused rationales for
INTRODUCTION
This document is an important and very helpful preparation
resource for Maryland Water Distribution Systems Operator
Certification Exam. 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 water distribution system experiences a sudden pressure drop from 65 psi to
20 psi in a residential area. The SCADA system shows no pump failures or
valve closures. Which of the following is the most likely cause?
A. A major water main break downstream of the pressure sensor
B. A closed isolation valve upstream of the pressure sensor
C. A malfunctioning pressure-reducing valve (PRV) at a nearby
commercial building
D. Increased water demand due to a large firefighting operation
Correct Answer: A - A major water main break downstream of
the pressure sensor
RATIONALE
A sudden pressure drop without pump or valve changes typically
indicates a major main break causing significant water loss and
reduced pressure. A closed valve upstream would cause low pressure
but is less likely to be sudden without SCADA indication. A
malfunctioning PRV affects only local pressure, and firefighting
demand would be gradual and localized.
Question 2
Under the Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR), a
community water system must comply with the locational running annual
average (LRAA) for TTHM. If quarterly TTHM results at a monitoring
location are 60, 80, 70, and 90 µg/L, what is the LRAA and does it exceed the
MCL?
A. 75 µg/L; does not exceed the 80 µg/L MCL
B. 75 µg/L; exceeds the 80 µg/L MCL
C. 80 µg/L; exceeds the 80 µg/L MCL
D. 70 µg/L; does not exceed the 80 µg/L MCL
Correct Answer: A - 75 µg/L; does not exceed the 80 µg/L MCL
Page 2
, RATIONALE
The LRAA is the average of the last four quarterly results at a
location: (60+80+70+90)/4 = 75 µg/L. The MCL for TTHM is 80
µg/L, so 75 µg/L does not exceed the MCL. Options B and C
incorrectly calculate or interpret the average, and D uses an incorrect
average.
Question 3
A distribution system has a cross-connection between a potable water line and
a fire sprinkler system containing antifreeze. Which type of backflow
prevention assembly is most appropriate to protect the potable water supply?
A. Double check valve assembly (DCVA)
B. Reduced pressure zone (RPZ) assembly
C. Pressure vacuum breaker (PVB)
D. Atmospheric vacuum breaker (AVB)
Correct Answer: B - Reduced pressure zone (RPZ) assembly
RATIONALE
An RPZ assembly provides the highest level of protection against both
backpressure and backsiphonage and is required for high-hazard
cross-connections such as antifreeze in fire sprinkler systems. DCVAs
are for low-hazard, PVBs and AVBs are for backsiphonage only and
cannot protect against backpressure.
Question 4
A pump is operating at 1750 rpm and delivers 500 gpm at 100 ft TDH. If the
speed is increased to 3500 rpm, what will be the new flow rate and TDH,
assuming no change in efficiency?
A. 1000 gpm and 200 ft
B. 1000 gpm and 400 ft
C. 2000 gpm and 400 ft
D. 250 gpm and 50 ft
Page 3
, Correct Answer: B - 1000 gpm and 400 ft
RATIONALE
According to the affinity laws, flow varies directly with speed (Q2 =
Q1 × (N2/N1)), so 500 × (3500/1750) = 1000 gpm. TDH varies with
the square of speed (H2 = H1 × (N2/N1)^2), so 100 × (2)^2 = 400 ft.
Option A incorrectly squares only the flow, C doubles both
incorrectly, and D halves both.
Question 5
A water storage tank has a high water level alarm at 2:00 AM. The SCADA
system shows the tank inlet valve is open and the tank level is rising despite
normal system pressure. Which of the following is the most likely cause?
A. A pressure-reducing valve (PRV) failure causing excessive pressure
into the tank
B. A malfunctioning altitude valve allowing continuous filling
C. A pump check valve failure causing backflow into the tank
D. A telemetry error falsely indicating a high level
Correct Answer: B - A malfunctioning altitude valve allowing
continuous filling
RATIONALE
An altitude valve controls tank filling and should close when the tank
reaches the set level. If it fails open, the tank continues to fill,
triggering a high-level alarm. A PRV failure would affect system
pressure, not tank filling directly. Check valve failure would cause
backflow, not continuous filling from the inlet.
Page 4
