What is the width of each sedimentation tank?

• A. 30 ft
• B. 50 ft
• C. 70 ft
• D. 40 ft

Answer: (D)

Sedimentation tanks are sized to give enough surface area so water can move slowly and particles have time to settle. The key relationship is that the flow rate across the basin is related to the surface area and the velocity of the water; you want a surface area large enough to keep velocity low and provide adequate detention time for settling. In typical plant designs used for these practice questions, a width of about 40 ft provides the right balance: it yields sufficient surface area when paired with a practical basin length, while still fitting comfortably within the plant layout and leaving room for internal features like baffles and weirs. A width of 40 ft thus supports the needed hydraulic conditions for effective sedimentation, making it the correct choice.