Water Distribution & Storage Systems Flashcards
7 cards from real WTO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Water Distribution & Storage Systems flashcards as text
When disinfecting a newly installed water main per AWWA C651, what is the minimum chlorine residual required at the end of a 24-hour contact period?
Answer: 50 mg/L
AWWA C651 requires a minimum free chlorine residual of 10 mg/L (some versions specify 25–50 mg/L initial dose) after 24 hours to ensure adequate disinfection; the flush-to-potable standard after testing is ≤ system residual.
Cathodic protection systems are installed on buried metallic water mains to:
Answer: Reduce electrochemical corrosion of the pipe exterior
Cathodic protection applies a small electrical current or sacrificial anode to counteract the electrochemical reactions that corrode buried metal pipe.
What does a negative pressure (sub-atmospheric) condition in a distribution main primarily risk?
Answer: Intrusion of groundwater or contaminants into the main
When pressure drops below atmospheric, surrounding groundwater or soil contaminants can be drawn into the main through cracks, joints, or service connections.
A distribution pump station that experiences frequent short-cycling (pump starts and stops rapidly) most likely has:
Answer: An undersized or waterlogged hydropneumatic pressure tank
Short-cycling occurs when the pressure tank lacks adequate air cushion, causing the pump to reach cut-off pressure almost immediately after starting.
The primary reason for maintaining a minimum system pressure of 20 psi during normal operation is:
Answer: To prevent backflow and contamination intrusion into the mains
A minimum residual pressure of 20 psi prevents the negative pressure events that could allow contaminants to enter the distribution system.
Tuberculation inside an unlined cast iron water main is caused by:
Answer: Biological and chemical oxidation forming iron oxide nodules
Tuberculation is the formation of rust mounds (iron hydroxide nodules) inside unlined cast iron pipe due to corrosion, which reduces flow capacity and can harbor bacteria.
When a distribution system zone is isolated by closing valves for repair, operators should first:
Answer: Notify affected customers and verify isolation before work begins
Customer notification and valve position verification ensures the correct section is isolated, work is safe to begin, and affected parties are informed.