# Air Plan Approval; California; State Implementation Plan Revision for Chico, Modesto and Stockton Carbon Monoxide Maintenance Areas
> **Rule** · Final rule. · Published 2025-09-05 · Effective 2025-10-06 · 90 FR 42829
## Document
- **Document number:** 2025-17061
- **Category:** air-emissions
- **Federal Register citation:** 90 FR 42829
- **CFR reference:** 40 CFR 52
- **Publication date:** 2025-09-05
- **Effective date:** 2025-10-06
- **State:** CA
- **EPA docket:** EPA-R09-OAR-2024-0473
## Abstract

The Environmental Protection Agency (EPA) is taking final action to approve a revision to the California state implementation plan (SIP) that removes carbon monoxide (CO) contingency measures and monitoring requirements from the maintenance plan for three CO maintenance areas: Chico Urbanized Area, Modesto Urbanized Area, and Stockton Urbanized Area. We are approving the revision under the Clean Air Act (CAA or "Act").

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2025/09/05/2025-17061/air-plan-approval-california-state-implementation-plan-revision-for-chico-modesto-and-stockton)
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