Rainy-Season SWPPP Inspections in California: Weekly, Pre-Storm, During-Storm and Post-Storm Requirements

The rains are coming, and with them the busiest stretch of the year for anyone holding Construction General Permit (CGP) coverage. California's water year starts October 1, and on average 75 percent of the state's annual precipitation falls from November through March, according to the Department of Water Resources. Each forecast storm in that window can trigger inspections and, on Risk Level 2 and 3 sites and Risk Type 2 and 3 linear projects, sampling.

The State Water Resources Control Board's Qualifying Precipitation Event Guidance for the 2022 CGP (Order WQ 2022-0057-DWQ), last updated May 5, 2025, is still listed first under Announcements on its Construction Stormwater Program page. It explains how to read a National Weather Service forecast to decide whether a storm is a QPE. And with Annual Reports filed in SMARTS, the Water Board's reporting system, by September 1, this winter's records will feed next year's report.

How often are SWPPP inspections required on a California construction site?

Under the 2022 CGP, all risk levels perform weekly, pre-, during- and post-QPE inspections, and a Qualified SWPPP Practitioner (QSP) must also inspect the site once every calendar month. The State Water Board's FAQ lists both as changes from the 2009 permit. The project's Qualified SWPPP Developer (QSD), who prepares and updates the SWPPP, may do any QSP task.

Some sites follow different rules:

• Projects in the Lake Tahoe Hydrologic Unit are covered by the Lahontan Regional Water Board's own construction permit (Order R6T-2016-0010), not the statewide CGP.
• Risk Type 1 linear underground and overhead projects do not need post-QPE inspections.
• When all construction will stop for 30 days or more, the discharger can request inactive status through a Change of Information in SMARTS. Once the Regional Water Board approves it, sampling can be suspended, and a QSP or trained delegate inspects at least once every calendar month and before each forecast QPE.

A QPE inspection also counts as that week's weekly inspection. The site's QSD owes visits too, including one between August and October and one between January and March each year.

What is a qualifying precipitation event (QPE) under the Construction General Permit?

A QPE is any weather pattern forecast to have a 50 percent or greater probability of precipitation and a quantitative precipitation forecast of 0.5 inch or more within 24 hours. Both conditions must be met. The forecast, not the rain that actually falls, triggers the pre-storm and during-storm inspections.

Water Board staff recommend the National Weather Service (NWS) Weather Table. Set it to 7 days and 6-hour intervals, enter the site's latitude and longitude, and bookmark the permanent link. Then:

1. Find the first 6-hour block with a 50 percent or greater probability of precipitation.
2. Add the forecast precipitation for that block and the next three.
3. If the 24-hour total is 0.5 inch or more, it is a QPE.
4. The QPE continues through each following 24-hour period forecast to get 0.25 inch or more. Probability does not matter for the extension.

Snow counts, as liquid equivalent. If you rely on a vendor's QPE alerts, you must verify they use NWS data and the permit's definition.

How far ahead of a storm must the pre-QPE inspection be done?

A QSP must complete the pre-QPE inspection within 72 hours before the QPE starts, or up to 120 hours ahead when the NWS has an extended forecast (more than three days).

Inspections around a qualifying precipitation event (QPE)

Illustrative diagram — not to scale

1. 1Before: a QSP inspects within 72 hours before the QPE starts, or up to 120 hours ahead with an extended NWS forecast.
2. 2During: a QSP or trained delegate inspects at least once in each 24-hour period of the QPE.
3. 3After: a QSP or trained delegate inspects within 96 hours after the QPE if the on-site rain gauge recorded 0.5 inch or more.

Before the storm

The QSP:

• Checks drainage areas for leaks, spills or uncontrolled pollutant sources.
• Confirms best management practices (BMPs) are installed as the SWPPP requires.
• Checks storage and containment areas for leaks and spare capacity.
• Follows up on earlier deficiencies.

During the storm

During the storm, the QSP or a trained delegate inspects at least once in every 24-hour period of the QPE. Risk Level 2 and 3 sites (and Risk Type 2 and 3 linear projects) also take one sample from each discharge location (each representative sample location for linear projects) in every 24-hour period of the QPE when there is active discharge.

After the storm

Afterward, a post-QPE inspection is due within 96 hours if the on-site rain gauge recorded 0.5 inch or more. It asks whether the BMPs worked, which need repair, and whether the SWPPP needs more. Risk Type 1 linear underground and overhead projects are exempt.

Repairs

Who can perform SWPPP inspections: a QSP or a trained delegate?

The monthly and pre-QPE inspections belong to the QSP, and a QSD can do anything a QSP can. Weekly, during-QPE and post-QPE inspections, and sampling, can go to a trained delegate.

A trained delegate can be construction staff often on site, such as a superintendent, foreman or contractor, or a stormwater professional not yet QSP-certified. With the discharger's authorization, the QSP delegates and provides foundational and site-specific training under the CGP Training Team's guidelines.

Each delegate's name, email and phone number must be in a training log uploaded to SMARTS before they start. Delegates report problems to the QSP within 24 hours, and the QSP reviews their work.

Is a Rain Event Action Plan (REAP) still required under the 2022 CGP?

No. The 2022 CGP removed the Rain Event Action Plan used under the 2009 permit. The State Water Board's Fact Sheet says the permit replaces it with:

• QSD involvement over the life of the project.
• More inspections and visual observations.
• Stronger requirements to document and carry out corrective actions.

Separately, the permit requires erosion control BMPs (other than sprayed products) to be available on site or nearby year-round, with trained people able to deploy them under the QSP's direction. The pre-QPE inspection is where the QSP confirms the site is ready before each forecast QPE.

What should I do if the forecast changes and an inspection is missed?

Forecasts change. The guidance advises checking them often whenever rain is predicted, and it covers these cases:

• The QPE drops out of the forecast. The QPE inspections and sampling are no longer required. A pre-QPE inspection already done can count as the monthly or weekly inspection.
• A smaller storm is upgraded to a QPE. Do the pre-QPE inspection if time allows. If not, record it as missed, explain that the earlier forecast showed no QPE, and note the forecast dates. The during-QPE inspection still applies (and so does sampling, where the site's risk level requires it), and so does the post-QPE inspection if the on-site gauge measures 0.5 inch or more over the QPE.
• The storm moves earlier. A completed pre-QPE inspection still counts, and the other inspections move up.
• The storm moves later. If the pre-QPE inspection now falls outside the 120-hour window, do a new one, or document the miss with reference to the forecasts.
• Two storms arrive back to back. One pre-QPE inspection covers both if it falls within 120 hours before the start of each. A QSP's during- or post-QPE inspection for the first storm can serve as the pre-QPE inspection for the second, and the first storm's post-QPE inspection can be met by any QPE inspection for the second storm done within 96 hours after the first ends.

In every case, the saved NWS forecasts are your evidence. Keep them with each inspection report.

What should a SWPPP inspection report include?

Your own form or a template from a group such as the California Stormwater Quality Association (CASQA) is fine if it records the permit's minimum items, and completed checklists stay with the SWPPP:

• Inspection type, date and time.
• Weather, including QPE start, duration and end, and rainfall from the on-site gauge, read at every inspection, even in dry weather.
• Stage of construction, work done since the last inspection, and approximate exposed area.
• BMPs inspected, deficiencies, and any signs of pollutants in discharges or stored water.
• Corrective actions, SWPPP changes and dates, and photos of problem areas.
• The inspector's name, title and any certification.

Do local wet-season grading rules apply on top of the CGP?

Often, yes. The State and Regional Water Boards enforce the CGP, but cities and counties enforce their own stormwater and grading ordinances, which typically require an erosion and sediment control plan sheet for projects with a grading permit.

Many agencies add wet-season rules, and they vary widely.

If winter work means your permit needs an updated erosion and sediment control plan or revised grading plans, start that review now.

What this means for your project

Before the first storm:

• Confirm your QSP, and that every delegate is trained and listed in the SMARTS training log.
• Bookmark the NWS Weather Table for your site and check it daily when rain is in the seven-day outlook.
• Stage erosion and sediment control materials where crews can reach them.
• Make sure the rain gauge works, save each forecast with its report, and log any missed inspection.
• Check your grading schedule against local wet-season rules.

We prepare stormwater pollution prevention plans (SWPPPs) and provide SWPPP inspections in California. See our stormwater and erosion control services, or contact us to talk through your site.