Your 30-day countdown: CGP & IGP rainy season checklist

What does the Oct 1 – Apr 30 rainy season mean for you?

While rain can fall at any time, California regulators officially define the rainy season as running from October 1st through April 30th. This is the critical window when state and regional inspectors are on high alert, and it is the period when the bulk of your mandatory stormwater sampling must occur. If your site controls fail during this window, you risk severe fines and project delays.

Construction General Permit (CGP) prep

If you are managing an active construction site, your compliance rhythm is about to speed up. Before the first drop falls, you need to:

• Confirm your Risk Level: Know exactly what tier your project falls under, as this dictates your testing and reporting frequency.
• Update your REAPs: If your site is Risk Level 2 or Risk Level 3, ensure your Rain Event Action Plans (REAPs) are drafted, updated, and ready to deploy before the storms hit.
• Inspect and restock your BMPs: Walk your site today. You need to repair any torn silt fences, replace clogged drain inlet filters, and verify you have enough plastic sheeting on hand to cover your active dirt stockpiles before a rain event.

Industrial General Permit (IGP) prep

Industrial facilities operate on a different rhythm, focused heavily on grabbing clean samples during specific rain events.

• Confirm your SWPPP is current: Ensure your Stormwater Pollution Prevention Plan (SWPPP) reflects any recent changes to your facility's layout or operations.
• Prep your sampling kits and staff: You need to have the correct sample bottles and field pH testing supplies fully stocked and ready. More importantly, ensure your staff is trained to identify a Qualifying Storm Event (QSE) and knows exactly how to pull the samples.
• Check your NAL history: Review your past lab results for Numeric Action Level (NAL) exceedances. If you have a history of high pollutant numbers, you may trigger Level 1 or Level 2 Exceedance Response Actions (ERAs), which carry strict legal requirements.

📱 Screenshot this simple readiness checklist

For Construction (CGP):[ ] Risk Level confirmed[ ] REAPs drafted for Level 2/3 sites[ ] Silt fences and wattles repaired[ ] Drain inlet protection cleaned/replaced[ ] Covers and sheeting staged for stockpiles

For Industrial (IGP):[ ] SWPPP reviewed and updated[ ] Sampling bottles and pH strips stocked[ ] Staff trained on QSE sampling protocols[ ] NAL history reviewed for ERA status

Need a hand getting ready?

You have a business to run, and scrambling to prep for a storm shouldn't be your full-time job. Whether you need a quick review of your SWPPP or want us to handle the physical Best Management Practices (BMPs) out in the field, WE know water.

👉 Contact our team today to schedule a pre-season readiness audit, and let's make sure your site is fully protected before October 1st.

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