What is the rain trigger for SWPPP inspections in California?

In California, an inspection is triggered by QPE forecast: ≥50% chance and ≥0.5" in 24h.

State Compliance Reference

California SWPPP Compliance

Quick Facts for California

Authority: State Water Resources Control Board (SWRCB) (CA)
Permit: Construction General Permit (2022 CGP)
Inspection Schedule: Weekly + pre-, during-, and post-QPE
Rain Trigger: QPE forecast: ≥50% chance and ≥0.5" in 24h

View Official Permit Calculate Fine Risk

This page is a field reference, not legal advice. Confirm the current permit, local requirements, and project-specific conditions with State Water Resources Control Board (SWRCB) before relying on a deadline or inspection schedule.Official sources last reviewed: 2026-09-12

Regulation Overview

Permitting Authority

State Water Resources Control Board (SWRCB)

Official Permit

Construction General Permit (2022 CGP)

Inspection Frequency

Weekly + pre-, during-, and post-QPE

Rain Event Trigger

QPE forecast: ≥50% chance and ≥0.5" in 24h

Check Missed Events

State vs. Federal (EPA)
Varies

Forecast-Based QPE Inspections

California's QPE definition starts with both a probability-of-precipitation and quantitative-forecast threshold, then applies separate pre-, during-, and post-event inspection windows.

Inspection Requirements for California

Construction projects that disturb one or more acres—or smaller sites that are part of a larger common plan—commonly require stormwater permit coverage in California. Eligibility, exemptions, local approvals, and project-specific conditions vary, so confirm coverage under the Construction General Permit (2022 CGP) before construction begins.

Operational Insight

This schedule combines recurring and event-driven duties. Record rainfall or discharge events independently from the weekly calendar and document why each event did or did not trigger an inspection.

Specific State Nuance

All risk levels have weekly and qualifying precipitation event (QPE) visual inspections. The pre-QPE inspection is generally due within 72 hours before the event, during-QPE inspections every 24 hours, and a post-QPE inspection within 96 hours when actual accumulation reaches 0.5 inch or more. Confirm project-specific TMDL and monitoring requirements in SMARTS.