The San Luis Obispo County Planning Commission has approved a $54 million expansion of the Machado Wastewater Treatment Facility in San Miguel—the plant’s first major upgrade in over 25 years. The two-phase project will increase treatment capacity from 200,000 to 500,000 gallons per day to accommodate regional growth and regulatory compliance.
Phase 1 will expand capacity to 325,000 gallons per day, while Phase 2 will bring it to 500,000 gallons. The upgraded facility will shift from a pond system to a Membrane Bio Reactor (MBR) process, allowing for the production of recycled water for non-potable uses such as irrigation.
The project includes redevelopment of approximately 39 acres, with new influent and effluent holding ponds, percolation beds, a maintenance building, permanent operations building, and upgraded electrical and control infrastructure.
Construction is expected to begin in early 2026, pending approval of a grant agreement with the California State Water Resources Control Board. Approximately $23 million in construction funding is anticipated from the Clean Water State Revolving Fund (CWSRF), with the possibility of additional support. The project is expected to take one to two years to complete.
The upgrade is intended to support current and future development in San Miguel, including several proposed housing projects, and address ongoing compliance issues related to salt and nitrogen levels in treated water.