AWWA AWWA Water Distribution Systems 2 — Questions and Answers
Question 1: What is the recommended minimum cover depth for water mains in frost-prone regions of the US per AWWA guidelines?
- 12 inches
- 24 inches
- 48 inches
- Cover depth varies by local frost depth (Correct answer)
Correct answer: Cover depth varies by local frost depth
AWWA guidance specifies that cover depth must be sufficient to protect against local frost penetration, which varies by geographic region.
Question 2: Which AWWA standard governs polyvinyl chloride (PVC) pressure pipe for water distribution?
- AWWA C900 (Correct answer)
- AWWA C151
- AWWA C200
- AWWA C301
Correct answer: AWWA C900
AWWA C900 covers PVC pressure pipe and fabricated fittings used in water distribution systems with nominal diameters from 4 to 60 inches.
Question 3: What is the purpose of a pressure zone in a water distribution system?
- To increase disinfectant dosage
- To isolate areas with different hydraulic grade lines and maintain acceptable pressures (Correct answer)
- To separate potable and non-potable water
- To reduce pipe corrosion rates
Correct answer: To isolate areas with different hydraulic grade lines and maintain acceptable pressures
Pressure zones are established to keep system pressures within acceptable limits across varying elevations, using pressure-reducing valves or separate pumping.
Question 4: Per AWWA M31 (Distribution System Requirements for Fire Protection), what minimum static residual pressure is typically recommended during fire-flow events?
- 5 psi
- 20 psi (Correct answer)
- 40 psi
- 60 psi
Correct answer: 20 psi
AWWA M31 recommends maintaining a minimum residual pressure of 20 psi at any point in the system during design fire-flow conditions.
Question 5: What does a C-factor represent in the Hazen-Williams hydraulic formula used in distribution system modeling?
- Chemical dosage coefficient
- Pipe roughness/friction coefficient (Correct answer)
- Chlorine residual decay constant
- Corrosion protection index
Correct answer: Pipe roughness/friction coefficient
The Hazen-Williams C-factor is a roughness coefficient reflecting the smoothness of a pipe's interior; higher values indicate smoother pipes with less friction loss.
Question 6: Which device is installed on a water service connection to prevent backflow of potentially contaminated water into the distribution system?
- Pressure regulator
- Check meter
- Backflow preventer (Correct answer)
- Curb stop
Correct answer: Backflow preventer
A backflow preventer (e.g., reduced pressure zone assembly) is required at service connections where cross-connection hazards exist to protect the distribution system.
AWWA AWWA Water Distribution Systems 2
What is the recommended minimum cover depth for water mains in frost-prone regions of the US per AWWA guidelines?