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May 2009, Vol. 21, No.5
Certification Quiz
Test Your Knowledge of Stormwater
Multiple Choice Questions:
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Which set lists the three types of collection systems?
A. Irrigation, sanitary, and stormwater.
B. Combined, sanitary, and open ditch.
C. Combined, sanitary, and stormwater.
D. Drinking water, open ditch, and stormwater.
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What term is used to describe groundwater that seeps into the collection system through defective or cracked pipes, manhole walls, and joints?
A. Inflow.
B. Infiltration.
C. Seepage.
D. Inflow and filtration.
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What term is used to describe water that enters the collection system from sources such as foundation drains, holes in manhole covers, surface runoff, and cross connections between sanitary and storm sewers?
A. Inflow.
B. Infiltration.
C. Seepage.
D. Inflow and filtration.
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Why are many collection systems designed to convey flows by gravity?
A. Pumping wastewater is costly and requires more maintenance than gravity lines.
B. The wastewater treatment plant is always at the lowest point in the system.
C. Gravity lines stay cleaner longer than force mains.
D. Most pipe materials can’t be pressurized.
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When infiltration occurs it should be limited to how much?
A. 50 gal/d•mi•in.
B. 100 gal/d•mi•in.
C. 300 gal/d•mi•in.
D. 500 gal/d•mi•in.
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What should be the maximum velocity of wastewater in a sanitary collection system?
A. 1 ft/s.
B. 2 ft/s.
C. 5 ft/s.
D. 10 ft/s.
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What type of flow are collection systems designed for?
A. Certification Quiz
B. Average day.
C. Maximum day.
D. Maximum month.
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Calculate the peak hour flow rate, given the following information.
Population | 50,000 |
Wastewater generated per capita | 85 gal/d |
Inflow and infiltration per capita | 10 gal/d |
Ratio of average daily to maximum daily flows | 2.5:1 |
A. 4.75 mgd.
B. 11.9 mgd
C. 15 ft3/s.
D. 37.5 ft3/s.
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.
Answer Key:
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1. c.
2. b.
3. a.
4. a.
5. d. Modern piping materials and practices can improve upon the worst allowable level of 500 gal/d•mi•in. and easily reduce infiltration to less than 200 gal/d•mi•in.
6. d. Flow velocity greater than 10 ft/s leads to excessive turbulence at junctions and erosion of the line.
7. a.
8. b. Peak flow = average daily flow × peaking factor. First find average daily flow, using per capita wastewater rates. Total flow per capita = wastewater per capita + inflow and infiltration per capita = 85 + 10 = 95 gal/d. Average daily flow = total flow per capita × population = 95 gal/person•d × 50,000 persons = 4.75 mgd. Peak flow = average daily flow × peaking factor = 4.75 mgd × 2.5 = 11.875 mgd.
References:
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, Sacramento.
Lindeburg, Michael R. (2003). Environmental Engineering Reference Manual for the PE Exam, Second Edition. Belmont, Calif.: Professional Publications Inc.