For each day of discharge from a qualifying event, the absolute minimum number of pH or turbidity effluent samples is

• A. Two
• B. Three
• C. Four
• D. Five

Answer: (B)

When discharging from a qualifying storm event, you need multiple samples to get a reliable picture of how the effluent behaves over the course of the discharge. The minimum you must collect for pH or turbidity on that discharge day is three samples. This helps capture variability in the water quality that can occur as flow changes, sediment loads shift, and chemical conditions evolve during the storm event.

Taking three samples allows you to calculate a representative average and to observe any shifts in pH or turbidity that might indicate a potential permit exceedance. Relying on a single sample could miss extreme values or fail to reflect the overall impact of the discharge, which could lead to incorrect conclusions about compliance.

While you could collect more than three if needed or if the permit requires it, three is the absolute minimum per discharge day to ensure a reasonable and representative assessment.