AWWA AWWA Water Distribution Systems 3 — Questions and Answers
Question 1: What is the primary purpose of a hydropneumatic tank in a small water distribution system?
- To store large volumes of treated water
- To maintain system pressure between pump cycles (Correct answer)
- To remove air from the distribution main
- To regulate chlorine residual
Correct answer: To maintain system pressure between pump cycles
A hydropneumatic tank uses compressed air to maintain system pressure between pump cycles, preventing rapid pump cycling and pressure fluctuations.
Question 2: According to AWWA C651, what is the standard chlorine concentration and contact time used for disinfecting a new water main before placing it in service?
- 10 mg/L for 12 hours
- 25 mg/L for 24 hours
- 50 mg/L for 24 hours (Correct answer)
- 100 mg/L for 48 hours
Correct answer: 50 mg/L for 24 hours
AWWA C651 specifies a minimum chlorine concentration of 50 mg/L with a 24-hour contact time as one accepted method for disinfecting new water mains.
Question 3: What does a distribution system water loss audit based on AWWA M36 methodology primarily calculate?
- Chemical treatment efficiency
- Non-revenue water volumes and infrastructure leakage index (Correct answer)
- Pump energy consumption
- Service connection meter accuracy
Correct answer: Non-revenue water volumes and infrastructure leakage index
The AWWA M36 water audit methodology calculates non-revenue water (NRW) components and the infrastructure leakage index (ILI) to benchmark system performance.
Question 4: Which AWWA standard addresses the design and construction of elevated water storage tanks?
- AWWA D100 (Correct answer)
- AWWA C510
- AWWA C651
- AWWA M11
Correct answer: AWWA D100
AWWA D100 covers welded carbon steel tanks for water storage, including elevated tanks, ground storage, and standpipes.
Question 5: In a water distribution system, what is the primary function of an air/vacuum release valve installed at pipeline high points?
- To release excess chlorine gas
- To expel trapped air and admit air during draining to prevent pipeline damage (Correct answer)
- To regulate pressure surges from pump starts
- To allow water sampling access
Correct answer: To expel trapped air and admit air during draining to prevent pipeline damage
Air/vacuum release valves at high points expel trapped air that reduces hydraulic capacity and admit air during pipe draining to prevent vacuum collapse.
Question 6: What is the recommended minimum operating pressure in a water distribution system under normal demand conditions per AWWA guidelines?
- 10 psi
- 20 psi
- 35 psi (Correct answer)
- 60 psi
Correct answer: 35 psi
AWWA guidelines recommend a minimum operating pressure of 35 psi under normal demand conditions to ensure adequate service at customer taps.
AWWA AWWA Water Distribution Systems 3
What is the primary purpose of a hydropneumatic tank in a small water distribution system?