1. A water storage tank is 35 feet in diameter and 65 feet high. WIth no water entering the tank, the water level dropped 14 feet in 5 hours. Find the average flow for water leaving the tank in gallons per minute.

2. If two pumps transfer 120 gpm each how long will it take (in hours and minutes) to fill a tank 50 feet long, 20 feet wide and 8 feet deep?

3. What is the average detention time in a basin given the following information: diameter is 65 feet depth is 12 feet, influent flow is 700 gpm.

4. A settling basin that is 60 feet long, 15 feet wide, and 12 feet deep is used to treat a flow of 2.4 mgd. What is the detention time?

5. A water main feeds a subdivision with a main of 500 feet long and 12 inches in diameter. The pipe delivers 30 cfm. When flushing to remove sediment, how long should they flush to achieve 2 pipe volumes?

Answers:

1. Time, hrs = (Volume, cuft) / (Flow, gph)

Volume = 0.785 X D,ft X D,ft X H,ft OR 3.14 X R,ft X R,ft X H,ft (Radius is 1/2 Diameter)

0.785 X 35 ft X 35 ft X 14 ft = 13,462.75 cuft

13,462.75 cuft X 7.48 gal/cuft = 100,701 gal

5 hrs = (100,701 gal) / (flow, gal) OR (100,701 gal) / (5 hrs) = 20,140 gal/hr

(20,140 gal/hr) / (60 min/hr) = 336 gpm

2. Detention time = (Volume) / (Flow)

Volume = Length, ft X Width, ft X Depth, ft = 50 ft X 20 ft X 8 ft

8000 cuft X 7.48 gal/cuft = 59,840 gal

(59,840 gal) / (120 gpm + 120 gpm) = 249 min

(249 min) / (60 min/hr) = 4.15 min or 4 hrs, 9 min

3. Detention time = (Volume) / (Flow)

0.785 X D, ft X D, ft X H, ft OR 3.14 X R, ft X R, ft X H, ft (Radius is 1/2 diameter)

0.785 X 65 ft X 65 ft X 12 ft = 39,799.5 cuft

39,799.5 cuft X 7.48 gal/cuft = 297,700 gal

700 gpm X 60 min/hr = 42,000 gph

(297,700 gal) / (42,000 gph) = 7.09 hrs or 7 hrs, 5 min

4. Detention time = (Volume) / (Flow)

60 ft X 15 ft X 12 ft = 10,800 cuft

10,800 cuft X 7.48 gal/cuft = 80,784 gal

(2,400,000 gpd) / (1440 min/day) = 1,666.67 gpm

(80,784 gal) / (1,666.67 gpm) = 48 min

5. Time = (Volume) / (Flow)

0.785 X 1 ft X 1 ft X 500 ft = 392.5 cuft

392.5 cuft X 2 = 785 cuft

(785 cuft) / (30 cfm) = 26 min