Bureau of Water
Agricultural and Dams Permitting Division
2600 Bull Street
Columbia, SC 29201
South Carolina Department of Health and Environmental Control NPDES General Permit for Storm Water Discharges Associated with Industrial Activities (except construction), Permit No. SCR000000, effective October 1, 2016 thru September 30, 2021
6.1.3 Measurable Storm Events
a. All required monitoring must be performed on a storm event that results in an actual discharge from your site ("measurable storm event") that follows the preceding measurable storm event by at least 72 hours (three 24-hour days). In the case of snowmelt, the monitoring must be performed at a time when a measurable discharge occurs at your site.
b. For each monitoring event, except snowmelt monitoring, you must identify the date and duration (in hours) of the rainfall event, rainfall total (in inches) for that rainfall event, and time (in days) since the previous measurable storm event or, alternatively, the absence of measurable precipitation in the 72 hours (three 24-hour days) preceding the monitoring event. For snowmelt monitoring, you must identify the dates of the snowfall and of the sampling event.
6.1.4 Sample Type
You must take a minimum of one grab sample from a discharge resulting from a measurable storm event as described in Part 6.1.3. Samples must be collected within the first 30 minutes of initial discharge from a measurable storm event. If it is not possible to collect the sample within the first 30 minutes of initial discharge from a measurable storm event, the sample must be collected as soon as practicable after the first 30 minutes, and documentation must be kept with the SWPPP explaining why it was not possible to take samples within the first 30 minutes initial discharge. In the case of snowmelt, samples must be taken during a period with a measurable discharge.
Magnitude: results in actual discharge
Interval Between Storms: at least 72 hours