Disinfection
What is the minimum chlorine residual required in the distribution system, and why keep a residual?
A. 2.0 mg/L,
B. 0.2 mg/L
C. 0.02 mg/L
D. 0.002 mg/L
B. 0.2 mg/L
What causes red or brown water complaints in a system?
A. Iron, Fe and Manganese, Mn
B. Calcium, Ca and Magnesium, Mg
C. Trihalomethanes and Haloacetic Acids
D. Chlorine
A. Iron, Fe and Manganese, Mn
Which of the following best describes a cross connection?
A) A pipe that carries wastewater only
B) A physical connection between potable and non-potable water sources
C) A meter installed backwards
D) A valve that fails in the closed position
B) A physical connection between potable and non-potable water sources
What type of valve is commonly used for isolation in distribution systems?
A. Gate
B. Butterfly
C. Globe
D. Ball
A. Gate
What does PPE stand for?
A) Pressurized Pipe Equipment
B) Personal Protective Equipment
C) Public Protection Enforcement
D) Pipe Pressure Evaluation
B) Personal Protective Equipment
Name two common disinfection by-products (DBPs) when organics and chlorine react.
A. Total Trihalomethanes/ Haloacetic Acids
B. Free and Total Chlorine
C. Chlorite and Chlorate
D. Monochloramine and Dichloramine
A. Total Trihalomethanes/ Haloacetic Acids
What is the most common cause of taste and odor complaints in a distribution system during summer?
A) Chlorine gas leaks
B) Algal/biofilm growth and chlorine levels
C) Low hardness
D) Excessive alkalinity
B) Algal/biofilm growth and chlorine levels
During hydrant flushing, system pressure in a neighborhood drops to 15 psi. A nearby industrial facility has a cross connection with a chemical rinse tank. Which event is most likely to occur?
A) Backpressure will push water into the distribution system
B) Backsiphonage will draw contaminants into the distribution system
C) The hydrant will prevent any cross connection hazard
D) No effect – pressure drop does not create hazards
B) Backsiphonage will draw contaminants into the distribution system
A distribution system has repeated low chlorine residuals at dead-end mains despite high feed at the plant. What is the best corrective action?
A) Increase clearwell detention time
B) Initiate a flushing program
C) Switch to chloramines
D) Replace customer meters
B) Initiate a flushing program ✅
What is the minimum safe oxygen concentration for confined space entry?
A) 16.0%
B) 17.5%
C) 19.5%
D) 21.5%
C) 19.5%
What chemical is most commonly used for routine disinfection in distribution systems?
A. Ozone
B. Sodium Hypochlorite or Chlorine gas
C. Bromide
D. Iodine
B. Sodium Hypochlorite or Chlorine gas
Name an indicator used to check for possible contamination in the distribution.
A. Turbidity
B. Cryptosporidium
C. Total Coliforms
D. pH
C. Total Coliforms
Which device protects against both backpressure and backsiphonage in high risk hazardous conditions ?
A) Double check valve assembly
B) Reduced Pressure Zone (RPZ) assembly
C) Device isnt needed
D) Pressure relief valve
B) Reduced Pressure Zone (RPZ) assembly
A 12-inch water main needs to be shut down. Why must valves be closed slowly?
A) To prevent loss of chlorine residual
B) To conserve electricity
C) To prevent water hammer and surges
D) To avoid operator fatigue
C) To prevent water hammer and surges
Which meter type is typically used for large commercial or industrial customers?
A) Turbine meter
B) Compound meter only
C) Positive displacement meter
D) Venturi meter
A) Turbine meter
What is the primary purpose of chloramination compared to free chlorination?
A. Cost
B. Longer lasting residual with fewer disinfection by-products
C. Chloramines are a stronger disinfectant
D. Free chlorine causes too many T&O
B. Longer lasting residual with fewer disinfection by-products
A sample shows low pH, low alkalinity, and elevated lead levels. What is the most likely cause?
A) Excessive chlorine residual
B) Corrosive water dissolving lead plumbing
C) Too much lime stabilization
D) Biofilm growth in dead-end mains
B) Corrosive water dissolving lead plumbing
Which physical backflow prevention device provides the highest level of protection against high hazard cross-connections?
A) Double check valve assembly
B) Air gap
C) Atmospheric vacuum breaker
D) Pressure reducing valve
B) Air gap
Operators notice a sudden pressure drop in a section of the distribution system. Customers report muddy water. What is the most likely cause?
A) Meter malfunction
B) Water main break
C) Valve partially closed
D) Pump cavitation
B) Water main break ✅
A compound meter in a commercial building is under-registering low flows but accurately measures high flows. Which component is most likely malfunctioning?
A) Strainer
B) Positive displacement chamber
C) Turbine element
D) Mainline valve
B) Positive displacement chamber
Which factor has the greatest effect on chlorine disinfection efficiency?
A) Temperature
B) Alkalinity
C) Hardness
D) Pump efficiency
A) Temperature
Which condition will most likely increase the formation of trihalomethanes (THMs)?
A) High temperature, long detention time, high organic matter
B) Low pH, low temperature, low organic matter
C) High hardness, high alkalinity, low chlorine dose
D) Short detention time, high pressure, low turbidity
A) High temperature, long detention time, high organic matter ✅
A reduced pressure zone (RPZ) backflow preventer is tested and shows a relief valve not opening when the pressure drops. What does this indicate?
A) The check valves are working properly
B) The assembly has failed and must be repaired
C) The device is functioning normally
D) The supply line is oversized
B) The assembly has failed and must be repaired
A new subdivision experiences air in the lines and frequent customer complaints of “spitting faucets.” What is the best corrective action?
A) Install additional air release valves
B) Increase chlorine dosage
C) Flush hydrants daily
D) Replace small-diameter mains
A) Install additional air release valves ✅
Workers smell rotten eggs while opening a manhole. What gas is this, and what should they do?
A) Methane; continue working with caution
B) Hydrogen sulfide; evacuate and ventilate before entry ✅
C) Carbon dioxide; wear a dust mask
D) Chlorine gas; use eye protection only
B) Hydrogen sulfide; evacuate and ventilate before entry