ABC Wastewater Collection Level 3 Exam — 230 Practice Questions

ABC Wastewater Collection Level 3 Exam —
230 Practice Questions
Topics Covered: Hydraulics, Collection System O&M, Pumping Systems, Safety, Confined
Space, Trenchless Technology, Flow Monitoring, Pretreatment, System Design, Maintenance
Management, Emergency Response, Regulations & Math Calculations




SECTION 1: Hydraulics & Flow Principles
1. What is the hydraulic gradient in a gravity sewer system?

 A) The slope of the pipe divided by its diameter
 B) The slope of the energy grade line, representing head loss per unit length
 C) The velocity of flow at the pipe centerline
 D) The ratio of full-flow capacity to actual flow

(Correct Answer: B) Rationale: The hydraulic gradient describes the rate of energy loss along
a pipeline — in gravity sewers, it corresponds to the slope of the water surface under pressure-
free conditions.



2. Manning's equation is used to calculate:

 A) Pump horsepower requirements
 B) Flow velocity and discharge in open channels and gravity sewers
 C) Force main pressure losses
 D) Dissolved oxygen levels in wastewater

(Correct Answer: B) Rationale: Manning's equation (V = (1.486/n) × R^(2/3) × S^(1/2))
relates velocity to pipe roughness, hydraulic radius, and slope for gravity flow calculations.



3. In Manning's equation, "n" represents:

 A) Pipe diameter in inches
 B) The roughness coefficient of the pipe material
 C) The number of pipes in a collection system
 D) Flow rate in MGD

,(Correct Answer: B) Rationale: "n" is the Manning's roughness coefficient — a dimensionless
value that varies by pipe material (e.g., PVC ≈ 0.010, concrete ≈ 0.013).



4. A sewer pipe flowing at d/D = 0.8 (80% full) is:

 A) Operating at maximum velocity
 B) Operating near peak capacity — flow is approximately 92% of full-flow capacity
 C) At risk of surcharging immediately
 D) Operating below design capacity and should be upsized

(Correct Answer: B) Rationale: Due to hydraulic properties of circular pipes, maximum flow
occurs at approximately d/D = 0.94, and d/D = 0.8 represents about 92% of full-flow discharge.



5. Self-cleansing velocity in a gravity sewer is generally considered to be:

 A) 0.5 fps
 B) 1.0 fps
 C) 2.0 fps minimum
 D) 5.0 fps

(Correct Answer: C) Rationale: A minimum velocity of 2.0 fps (feet per second) is needed to
keep solids in suspension and prevent sediment buildup in sanitary sewers.



6. What is the hydraulic radius (R) of a circular pipe flowing full?

 A) D/2
 B) D/4
 C) πD²/4
 D) D

(Correct Answer: B) Rationale: Hydraulic radius = Area / Wetted Perimeter. For a full circle:
(πD²/4) / (πD) = D/4.



7. Surcharging in a sewer system occurs when:

 A) Flow velocity exceeds 8 fps
 B) The hydraulic grade line rises above the pipe crown, filling the pipe under pressure
 C) Pump stations run dry

,  D) Sediment accumulates to 50% of pipe depth

(Correct Answer: B) Rationale: When inflow exceeds pipe capacity, the HGL rises above the
pipe soffit (crown) and the pipe flows under pressure — surcharging — which can cause
backups or overflows.



8. What does the term "d/D ratio" represent?

 A) Pipe diameter to design capacity ratio
 B) Actual depth of flow divided by the internal pipe diameter
 C) Downstream flow divided by upstream design flow
 D) Daily flow divided by design flow

(Correct Answer: B) Rationale: d/D is the ratio of actual water depth to full pipe diameter —
used to determine partial flow conditions from hydraulic elements charts.



9. Hazen-Williams equation is primarily used for:

 A) Open channel (gravity) flow calculations
 B) Pressure flow calculations in force mains
 C) Calculating pump efficiency
 D) Determining infiltration rates

(Correct Answer: B) Rationale: The Hazen-Williams equation calculates head loss in pressure
pipes (force mains), relating flow, pipe diameter, and the C coefficient of pipe smoothness.



10. What happens to flow velocity in a sewer pipe as pipe slope increases?

 A) Velocity decreases
 B) Velocity remains constant
 C) Velocity increases
 D) Velocity is unaffected — only flow rate changes

(Correct Answer: C) Rationale: From Manning's equation, velocity is proportional to S^(1/2)
(square root of slope) — steeper slopes produce higher velocities.



11. Which of the following best describes "infiltration" in a wastewater collection system?

,  A) Wastewater entering a storm drain
 B) Groundwater entering the sewer through cracks, joints, or defects
 C) Wastewater exfiltrating through pipe walls
 D) Stormwater entering through manholes

(Correct Answer: B) Rationale: Infiltration is the entry of groundwater into a sewer — it
increases flows and treatment costs without contributing waste load.



12. "Inflow" differs from "infiltration" in that inflow:

 A) Enters through soil percolation
 B) Enters directly and quickly during storm events through improper connections,
manholes, and catch basins
 C) Only occurs in force mains
 D) Reduces flow in the collection system

(Correct Answer: B) Rationale: Inflow enters the system rapidly (during rain events) through
direct connections; infiltration enters slowly through structural defects. Together they are called
I/I.



13. A flow of 1 MGD is equivalent to how many gallons per minute (gpm)?

 A) 448 gpm
 B) 694 gpm
 C) 1,000 gpm
 D) 1,440 gpm

(Correct Answer: B) Rationale: 1 MGD = 1,000,000 gal/day ÷ 1,440 min/day = 694 gpm.



14. The Chezy formula relates flow velocity to:

 A) Pipe roughness and Reynolds number
 B) Hydraulic radius and hydraulic slope
 C) Pipe diameter and flow depth
 D) Pump head and efficiency

(Correct Answer: B) Rationale: Chezy's formula V = C√(RS) relates velocity to the Chezy
coefficient (C), hydraulic radius (R), and slope (S).