COLLECTION SYSTEM MAINTENANCE
GRADE 4 EXAM
,Question 1:
A Collection System Supervisor is troubleshooting a major wastewater lift station
experiencing reduced discharge flow despite pumps running at maximum RPM. Pressure
gauges at the pump discharge read significantly higher than design head pressure. What
is the most probable cause of this condition?
A) Low wet well liquid elevation
B) Partial blockage or closed valve in the force main discharge line
C) Impeller slippage due to a sheared shaft key
D) Air binding or cavitation in the suction eye
Answer: B - Partial blockage or closed valve in the force main discharge line
Rationale: High discharge pressure coupled with reduced flow indicates high system
dynamic head, typically caused by a downstream restriction, partially closed valve, or
severe grease/solids buildup in the force main.
Question 2:
Which physical process occurs when net positive suction head available (NPSHA) drops
below net positive suction head required (NPSHR), causing micro-implosions on pump
impellers?
A) Vortexing, resulting in air entrapment in the volute
B) Thermal expansion of the mechanical seal faces
C) Water hammer, causing fatigue failure of the check valve stem
D) Cavitation, leading to severe pitting and erosion of the pump impeller
Answer: D - Cavitation, leading to severe pitting and erosion of the pump impeller
Rationale: Cavitation occurs when localized pressure falls below vapor pressure, forming
vapor bubbles that implode violently against the impeller surface, causing pitting,
vibration, and distinct popping/gravel noises.
,Question 3:
An electrician is inspecting a Variable Frequency Drive (VFD) controlling a 100 HP
submersible pump. The VFD trips repeatedly on 'Overcurrent' during sudden acceleration
under heavy rain inflow. Which parameter adjustment is most appropriate?
A) Bypass the motor overload relay
B) Increase the input line voltage setting
C) Decrease the carrier frequency below 1 kHz
D) Increase the acceleration ramp time
Answer: D - Increase the acceleration ramp time
Rationale: Increasing the acceleration ramp time slows down the rate of speed change,
reducing inrush current and preventing VFD overcurrent trips when bringing heavy
wastewater pumps up to operating speed.
Question 4:
Under NFPA 70E guidelines, what is required before opening energized electrical
enclosures operating at 480 volts?
A) Use aluminum ladder stands for grounding
B) Disconnect the main ground conductor
C) Obtain a hot work permit signed by the municipal mayor
D) Wear appropriate Category-rated Arc Flash Personal Protective Equipment (PPE)
and verify boundary limits
Answer: D - Wear appropriate Category-rated Arc Flash Personal Protective Equipment
(PPE) and verify boundary limits
Rationale: Working near exposed energized parts operating at 480V requires Arc Flash
PPE appropriate for the calculated risk category, established approach boundaries, and
qualified personnel authorization.
, Question 5:
A collection crew is preparing to execute a Cured-in-Place Pipe (CIPP) lining project on a
24-inch trunk sewer line. Prior to resin inversion, what key field step is critical to prevent
liner failure or irregular wall thickness?
A) Application of petroleum lubricant along the host pipe invert
B) Filling the host pipe with water to equalize external hydrostatic pressure
C) Sandblasting the outer casing of the wet well
D) Complete high-pressure jet cleaning and CCTV inspection to remove debris and
measure exact internal dimensions
Answer: D - Complete high-pressure jet cleaning and CCTV inspection to remove debris
and measure exact internal dimensions
Rationale: Thorough cleaning and pre-lining CCTV inspection are essential to clear roots,
scale, and heavy solids and to verify pipe ovality and exact internal diameter before liner
wet-out and inversion.
Question 6:
Under NASSCO PACP coding standards, what code and severity level represent a
complete 360-degree break/fracture with soil visible?
A) Structural Defect Grade 5 (Severe / Imminent Failure)
B) Non-reportable cosmetic observation
C) Operational Maintenance Code Grade 1 (Minor)
D) Construction Feature Code Grade 2
Answer: A - Structural Defect Grade 5 (Severe / Imminent Failure)
Rationale: A 360-degree fracture or structural break with soil visible or displacement
represents a Grade 5 (highest severity) structural defect under NASSCO PACP criteria
requiring priority intervention.
GRADE 4 EXAM
,Question 1:
A Collection System Supervisor is troubleshooting a major wastewater lift station
experiencing reduced discharge flow despite pumps running at maximum RPM. Pressure
gauges at the pump discharge read significantly higher than design head pressure. What
is the most probable cause of this condition?
A) Low wet well liquid elevation
B) Partial blockage or closed valve in the force main discharge line
C) Impeller slippage due to a sheared shaft key
D) Air binding or cavitation in the suction eye
Answer: B - Partial blockage or closed valve in the force main discharge line
Rationale: High discharge pressure coupled with reduced flow indicates high system
dynamic head, typically caused by a downstream restriction, partially closed valve, or
severe grease/solids buildup in the force main.
Question 2:
Which physical process occurs when net positive suction head available (NPSHA) drops
below net positive suction head required (NPSHR), causing micro-implosions on pump
impellers?
A) Vortexing, resulting in air entrapment in the volute
B) Thermal expansion of the mechanical seal faces
C) Water hammer, causing fatigue failure of the check valve stem
D) Cavitation, leading to severe pitting and erosion of the pump impeller
Answer: D - Cavitation, leading to severe pitting and erosion of the pump impeller
Rationale: Cavitation occurs when localized pressure falls below vapor pressure, forming
vapor bubbles that implode violently against the impeller surface, causing pitting,
vibration, and distinct popping/gravel noises.
,Question 3:
An electrician is inspecting a Variable Frequency Drive (VFD) controlling a 100 HP
submersible pump. The VFD trips repeatedly on 'Overcurrent' during sudden acceleration
under heavy rain inflow. Which parameter adjustment is most appropriate?
A) Bypass the motor overload relay
B) Increase the input line voltage setting
C) Decrease the carrier frequency below 1 kHz
D) Increase the acceleration ramp time
Answer: D - Increase the acceleration ramp time
Rationale: Increasing the acceleration ramp time slows down the rate of speed change,
reducing inrush current and preventing VFD overcurrent trips when bringing heavy
wastewater pumps up to operating speed.
Question 4:
Under NFPA 70E guidelines, what is required before opening energized electrical
enclosures operating at 480 volts?
A) Use aluminum ladder stands for grounding
B) Disconnect the main ground conductor
C) Obtain a hot work permit signed by the municipal mayor
D) Wear appropriate Category-rated Arc Flash Personal Protective Equipment (PPE)
and verify boundary limits
Answer: D - Wear appropriate Category-rated Arc Flash Personal Protective Equipment
(PPE) and verify boundary limits
Rationale: Working near exposed energized parts operating at 480V requires Arc Flash
PPE appropriate for the calculated risk category, established approach boundaries, and
qualified personnel authorization.
, Question 5:
A collection crew is preparing to execute a Cured-in-Place Pipe (CIPP) lining project on a
24-inch trunk sewer line. Prior to resin inversion, what key field step is critical to prevent
liner failure or irregular wall thickness?
A) Application of petroleum lubricant along the host pipe invert
B) Filling the host pipe with water to equalize external hydrostatic pressure
C) Sandblasting the outer casing of the wet well
D) Complete high-pressure jet cleaning and CCTV inspection to remove debris and
measure exact internal dimensions
Answer: D - Complete high-pressure jet cleaning and CCTV inspection to remove debris
and measure exact internal dimensions
Rationale: Thorough cleaning and pre-lining CCTV inspection are essential to clear roots,
scale, and heavy solids and to verify pipe ovality and exact internal diameter before liner
wet-out and inversion.
Question 6:
Under NASSCO PACP coding standards, what code and severity level represent a
complete 360-degree break/fracture with soil visible?
A) Structural Defect Grade 5 (Severe / Imminent Failure)
B) Non-reportable cosmetic observation
C) Operational Maintenance Code Grade 1 (Minor)
D) Construction Feature Code Grade 2
Answer: A - Structural Defect Grade 5 (Severe / Imminent Failure)
Rationale: A 360-degree fracture or structural break with soil visible or displacement
represents a Grade 5 (highest severity) structural defect under NASSCO PACP criteria
requiring priority intervention.
