WTO Math 3 — Questions and Answers
Question 1: A filter has a surface area of 400 ft² and a flow rate of 1,600 gpm. What is the filtration rate in gpm/ft²?
- 4 gpm/ft² (Correct answer)
- 5 gpm/ft²
- 3 gpm/ft²
- 6 gpm/ft²
Correct answer: 4 gpm/ft²
Filtration rate = 1,600 gpm ÷ 400 ft² = 4 gpm/ft².
Question 2: A settling basin is 60 ft long, 20 ft wide, and 10 ft deep. What is its volume in gallons?
- 89,760 gal (Correct answer)
- 79,680 gal
- 99,840 gal
- 69,600 gal
Correct answer: 89,760 gal
Volume = 60 × 20 × 10 = 12,000 ft³ × 7.48 = 89,760 gallons.
Question 3: The plant flow is 4.2 MGD. Express this flow in gallons per minute (gpm).
- 2,917 gpm (Correct answer)
- 3,150 gpm
- 2,500 gpm
- 3,400 gpm
Correct answer: 2,917 gpm
4.2 × 1,000,000 ÷ 1,440 min/day = 2,917 gpm.
Question 4: A 10% sodium hypochlorite solution is needed to deliver 6 lbs of chlorine. How many gallons of solution are required?
- 7.19 gal (Correct answer)
- 8.34 gal
- 6.00 gal
- 9.50 gal
Correct answer: 7.19 gal
6 lbs ÷ (0.10 × 8.34 lb/gal) = 6 ÷ 0.834 = 7.19 gallons.
Question 5: A pump runs 14 hours per day and delivers 350 gpm. How many million gallons does it deliver in 30 days?
- 8.82 MGD (Correct answer)
- 8.40 MGD
- 9.24 MGD
- 7.98 MGD
Correct answer: 8.82 MGD
350 × 14 × 60 × 30 = 8,820,000 gal = 8.82 MG total.
Question 6: A water sample has a turbidity of 0.8 NTU before filtration and 0.04 NTU after. What is the percent removal?
- 95% (Correct answer)
- 90%
- 85%
- 80%
Correct answer: 95%
% removal = (0.8 − 0.04) ÷ 0.8 × 100 = 95%.
Question 7: The detention time in a contact chamber is required to be at least 30 minutes at a flow of 5 MGD. What minimum volume (in gallons) is needed?
- 104,167 gal (Correct answer)
- 150,000 gal
- 83,333 gal
- 208,333 gal
Correct answer: 104,167 gal
Flow = 5,000,000 ÷ 1,440 = 3,472 gpm; volume = 3,472 × 30 = 104,167 gal.
WTO Math 3
A filter has a surface area of 400 ft² and a flow rate of 1,600 gpm.
What is the filtration rate in gpm/ft²?