Civil Engineering PE

Answer: C - The total volume of the grit chamber is 2,079 ft³ when required to handle an average flow of 3 million gallons per day (mgd), with a peak flow ratio of 2.5 and a detention time of 3 minutes.

Solution:

Volume of grit chamber = (peak flow) x (detention time)

Where peak flow = (average flow) x (peak flow ratio)

= (3 mgd) x (2.5)

= 7.5 mgd

Given, 1 mgd = 1.54 ft³/sec

Where detention time = (3 min) x (60 sec/min) = 180 sec

Volume = (7.5 mgd() x (1.54 ft³/sec) x (180 sec)

= 2,079 ft³