Storm water samples for visual assessments should be collected within how many minutes of the discharge start?

Collecting stormwater samples for visual assessments within 30 minutes of the discharge start is crucial for accurately reflecting the initial quality and characteristics of the runoff. This timeframe is important because it allows operators to observe the immediate effects of the rainfall or runoff event, which can significantly change as the storm continues. Early samples are more likely to capture pollutants that are quickly washed off surfaces during the first flush of the stormwater event, providing valuable data for compliance and assessment purposes.

Waiting longer, such as 45 or 60 minutes, may result in altered sample quality due to dilution, sediment settling, or changes in water chemistry that occur as the storm progresses. Collecting samples too late might fail to capture peak pollutant concentrations typically seen in the initial runoff. Hence, the practice of collecting samples within 30 minutes effectively balances the need for timely data collection while ensuring relevant and accurate assessments of stormwater discharges.