WTO Math 4

Question 1

A chemical solution is prepared by dissolving 2 lbs of alum in 10 gallons of water. What is the solution concentration in mg/L?

Accepted Answer

23,957 mg/L

Answer

2 lbs × 453,592 mg/lb ÷ (10 gal × 3,785 mL/gal) = 907,184 ÷ 37,850 = 23,963 mg/L ≈ 23,957 mg/L.

Question 2

A plant produces 6.5 MGD. The CT value required for Giardia inactivation is 150 mg/L·min. If chlorine residual is 1.5 mg/L, what is the minimum contact time needed?

Accepted Answer

100 minutes

Answer

CT = C × T → T = 150 ÷ 1.5 = 100 minutes.

Question 3

A 6-inch diameter pipe carries water at 4 ft/sec. What is the flow rate in gpm?

Accepted Answer

352 gpm

Answer

Area = π × (0.25 ft)² = 0.196 ft²; flow = 0.196 × 4 = 0.785 cfs × 448.8 = 352 gpm.

Question 4

An operator needs to raise the fluoride level from 0.4 mg/L to 0.8 mg/L in a 1.5 MGD plant. How many lbs/day of fluoride must be added?

Accepted Answer

5.0 lb/day

Answer

Dose = 0.8 − 0.4 = 0.4 mg/L; lbs/day = 0.4 × 1.5 × 8.34 = 5.0 lb/day.

Question 5

A well pump test shows 450 gpm flow with a 25-foot drawdown. What is the specific capacity of the well?

Accepted Answer

18 gpm/ft

Answer

Specific capacity = 450 gpm ÷ 25 ft = 18 gpm/ft.

(WTO) Water Treatment Operator Certification Practice Test

(WTO) Water Treatment Operator Certification Practice Test

WTO Math 4