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40 questions from the water and wastewater operator practice test.
10 questions, graded as you go, with the reason for every answer. No sign-up.
A circular clarifier is 40 ft in diameter with a water depth of 16 ft. What is its volume in gallons? Use area = 0.785 × D² and 7.48 gal/ft³.
Answer in gal.
150320 gal
Surface area = 0.785 × 40² = 0.785 × 1,600 = 1,256 ft². Volume = 1,256 × 16 = 20,096 ft³. Gallons = 20,096 × 7.48 = 150,318 gal, about 150,320 gal.
Reference: Cylinder volume: V = 0.785 × D² × depth; 7.48 gal/ft³
A stream gauge shows 3.0 cfs flowing into a raw water intake. What is this flow in gpm? (1 ft³ = 7.48 gal)
Answer in gpm.
1346.4 gpm
3.0 ft³/s × 7.48 gal/ft³ = 22.44 gal/s. 22.44 gal/s × 60 s/min = 1,346.4 gpm. (Shortcut: 1 cfs = 448.8 gpm.)
Reference: Flow conversion: 1 cfs = 7.48 gal/s = 448.8 gpm
A wastewater plant's influent flow is 4.0 MGD. What is the flow in cubic feet per second? (1 ft³ = 7.48 gal; 86,400 s/day)
Answer in cfs.
6.19 cfs
4,000,000 gal/day ÷ 7.48 gal/ft³ = 534,759 ft³/day. 534,759 ÷ 86,400 s/day = 6.19 cfs. (Shortcut: 1 MGD = 1.547 cfs, so 4.0 × 1.547 = 6.19 cfs.)
Reference: Flow conversion: 1 MGD = 1.547 cfs