CPWM Utility Systems 3 — Questions and Answers
Question 1: What is the MINIMUM residual chlorine level the EPA recommends maintaining at the ends of a potable water distribution system?
- 0.01 mg/L
- 0.2 mg/L (Correct answer)
- 1.0 mg/L
- 2.0 mg/L
Correct answer: 0.2 mg/L
The EPA recommends a minimum residual disinfectant concentration of 0.2 mg/L at all points in the distribution system to prevent microbial regrowth.
Question 2: A public works manager is evaluating natural gas distribution system leaks. Which instrument is MOST appropriate for detecting methane in soil?
- Combustible gas indicator (CGI) (Correct answer)
- Dissolved oxygen meter
- pH meter
- Turbidimeter
Correct answer: Combustible gas indicator (CGI)
A combustible gas indicator (CGI) detects the presence and concentration of flammable gases like methane, making it the standard tool for natural gas leak surveys.
Question 3: Secondary wastewater treatment primarily removes which type of pollutant?
- Heavy metals and toxics
- Biological oxygen demand (BOD) through biological processes (Correct answer)
- Dissolved minerals and salts
- Pathogens through UV disinfection
Correct answer: Biological oxygen demand (BOD) through biological processes
Secondary treatment uses biological processes (activated sludge, trickling filters) to decompose dissolved and suspended organic matter, significantly reducing BOD.
Question 4: Which condition is MOST likely to cause water hammer in a distribution system?
- Slow valve opening over 10 minutes
- Rapid pump shutdown or valve closure (Correct answer)
- Low pressure in the distribution main
- High temperature of the water supply
Correct answer: Rapid pump shutdown or valve closure
Water hammer occurs when flow is suddenly stopped or reversed, creating pressure surges that can damage pipes, valves, and equipment.
Question 5: Under OSHA's confined space regulations, a manhole in a sanitary sewer system is MOST likely classified as a:
- Non-permit required confined space
- Permit-required confined space (Correct answer)
- Restricted access utility vault
- Limited entry work zone
Correct answer: Permit-required confined space
Sewer manholes contain potential serious hazards including toxic gases (H₂S), oxygen deficiency, and engulfment risk, requiring a written permit for entry.
Question 6: In a water distribution system, what is the purpose of an air relief valve installed at a high point in the pipeline?
- To increase water pressure at elevated locations
- To release trapped air that could impede flow and cause pressure fluctuations (Correct answer)
- To prevent backflow into the supply main
- To reduce water velocity at pipeline bends
Correct answer: To release trapped air that could impede flow and cause pressure fluctuations
Air pockets at high points restrict flow and cause pressure problems; air relief valves automatically expel this trapped air to maintain efficient hydraulic conditions.
Question 7: Which wastewater treatment process is specifically designed to remove nitrogen and phosphorus?
- Primary clarification
- Grit removal
- Tertiary/advanced nutrient removal (Correct answer)
- Screening and comminution
Correct answer: Tertiary/advanced nutrient removal
Tertiary or advanced treatment processes, including biological nutrient removal (BNR) and chemical precipitation, are specifically designed to reduce nitrogen and phosphorus levels.
CPWM Utility Systems 3
What is the MINIMUM residual chlorine level the EPA recommends maintaining at the ends of a potable water distribution system?