How many hours of detention time will a sedimentation basin measuring 120 feet long, 50 feet wide, and 20 feet deep provide if the flow is 6 MGD?

To determine the detention time provided by the sedimentation basin, you first need to calculate its volume and then how long it takes for the inflow to fill that volume given the flow rate.

1. Calculate the volume of the basin:

• The volume (in cubic feet) is determined using the formula for the volume of a rectangular prism:

Volume = Length × Width × Depth.

• Here, the basin dimensions are 120 feet long, 50 feet wide, and 20 feet deep.

• Volume = 120 ft × 50 ft × 20 ft = 120,000 cubic feet.

2. Convert the flow rate from MGD (million gallons per day) to cubic feet per day:

• 1 MGD is equivalent to approximately 7,480 gallons, so:

• 6 MGD = 6 × 7,480 gallons = 44,880 gallons per day.

• To convert gallons to cubic feet, use the conversion where 1 cubic foot = 7.48 gallons:

• 44,880 gallons ÷ 7.48 gallons/cubic foot ≈ 5,991.6 cubic feet per day.

3. Calculate the detention time: