For source water at or below 10 NTU, the sedimentation effluent should meet which turbidity criterion for 95% of the time?

• A. <1 ntu 90%
• B. <1 ntu 95%
• C. <2 ntu 90%
• D. <2 ntu 95%

Answer: (B)

The key idea is that sedimentation is about removing enough suspended solids so the water can be treated effectively downstream. When the raw water turbidity is at or below 10 NTU, the sedimentation step should produce an effluent with very low turbidity in most cases. Specifically, the requirement is that turbidity stay under 1 NTU in 95% of the time samples. This strict target helps ensure the water entering filtration remains consistently clear, which supports reliable filtration performance and disinfection. The other options either loosen the time requirement (90%) or raise the turbidity limit (2 NTU), which would not meet typical performance expectations for this source water level.