October 2009, Vol. 21, No.10
Test Your Knowledge of Collection Systems Maintenance
Multiple Choice Questions:
What bacterium is responsible for hydrogen sulfide gas production in sewer lines?
Why is hydrogen sulfide production in concrete sewer mains problematic?
A. Hydrogen sulfide binds irreversibly to the pipe interior, causing scale buildup.
B. Hydrogen sulfide combines with oxygen and is converted to sulfuric acid, which attacks the crowns of concrete pipes.
C. Extremely low concentrations of hydrogen sulfide are toxic to other, more beneficial microorganisms in the collection system.
D. Hydrogen sulfide causes iron precipitation.
For smaller diameter sewer pipe, manholes should be installed at regular intervals along gravity sewer lines. What should be the maximum distance between manholes to ensure that cleaning equipment can reach the entire length of pipe between manholes?
A. 100 ft.
B. 200 ft.
C. 400 ft.
D. 1000 ft.
If flow velocities in the collection system exceed 10 ft/s, which of the following problems may occur?
A. Buildup of hydrogen sulfide.
B. Deposition of material on the pipe wall.
C. Erosion of the sewer line.
Uncoated aluminum should not come into direct contact with concrete. If it does, what will happen?
B. Corrosion of the aluminum.
C. Accumulation of hydrogen sulfide crystals at the contact point.
D. Localized softening of the concrete due to a chemical reaction.
What parameters define velocity?
A. Flow divided by cross-sectional area.
B. Cross-sectional area divided by flow.
C. Cross-sectional area divided by pipe volume.
D. Flow divided by pipe volume.
To prevent solids from settling in the pipe, flow velocities should be kept at or above what minimum velocity?
A. 1.0 ft/s.
B. 2.0 ft/s
C. 4.0 ft/s
D. 8.0 ft/s
When should scouring velocities be reached or exceeded?
A. At average daily flow.
B. Throughout the day.
C. Only during storm events.
D. During peak flows.
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Questions developed by Sidney Innerebner, owner of Indigo Water Group (Littleton. Colo.), and reviewed by the Association of Boards of Certification (Ames, Iowa) Validation and Examination Committee.
California State University–Sacramento (1996). Operation and Maintenance of Wastewater Collection Systems, A Field Study Program, Volume 1, Fifth Edition. Sacramento, Calif.: California State University.
Lindeburg, Michael R. (2003). Environmental Engineering Reference Manual for the PE Exam, Second Edition. Belmont, Calif.: Professional Publications Inc.