Water Quality Division MC-148
Texas Commission on Environmental Quality
PO Box 13087
Austin TX 78711-3087
General Permit to General Permit to Discharge Under the Texas Pollutant Discharge Elimination System TPDES General Permit No TXR050000, effective August 14, 2016 thru August 13, 2021
Section D. General Monitoring and Records Requirements
1. Qualifying Storm Events
(a) Monitoring, sampling, examinations, and inspections of storm water discharges that are required as a provision of this general permit must be conducted on discharges from a measurable storm event that results in an actual discharge from the site, and that follows the preceding measurable storm event by at least 72 hours (3 days). The 72-hour storm interval does not apply if the permittee is able to document that less than a 72-hour (3-day) interval is representative for local qualifying storm events during the sampling period. In the case of snowmelt, the monitoring must be performed at a time when a measurable discharge occurs at the site.
(b) A facility that has retention ponds as BMPs will not always have a discharge from the pond(s) immediately following a qualifying storm event. If any storm events occurred prior to discharge from the outfall, regardless of the time period between the last storm event and the discharge, the permittee may consider the discharge to be the result of the previous qualifying storm event.
(c) The permittee shall maintain a rain gauge on-site to determine when a qualifying storm event occurs. The rain gauge must be monitored a minimum of once per week, and once per day during storm events. Records of the date and rainfall total must be retained on-site or made readily available for review. Rain gauge monitoring and recordkeeping may be temporarily suspended during a given monitoring period if a qualifying storm event has occurred and the required sampling and analyses or visual observations have been performed.
Magnitude: results in actual discharge
Interval Between Storms: at least 72 hours