Pasadena and South Pasadena Advance Arroyo Seco Water Reuse Project with Regional Environmental Impact

A transformative environmental initiative is moving forward in the cities of Pasadena and South Pasadena, where a joint public works effort is laying the groundwork for the Arroyo Seco Water Reuse Project, a regional stormwater management venture with significant environmental and public benefit implications. According to a recently filed Notice of Preparation (NOP) by the City of Pasadena, an Environmental Impact Report (EIR) is now underway, setting the stage for formal environmental review and a public scoping meeting as part of California Environmental Quality Act (CEQA) requirements.

The project spans two separate but closely linked open space-zoned sites—San Rafael and San Pascual—situated along the concrete-lined Arroyo Seco Channel, which flows through Pasadena, South Pasadena, and Los Angeles. Together, the sites encompass approximately 3.7 acres of land immediately adjacent to the flood control channel, with infrastructure connecting both locations through a watershed-based treatment plan. At its core, the project aims to construct two regional-scale water quality facilities—stormwater capture and treatment wetlands—capable of filtering runoff from a 5,005-acre drainage area within the Upper Los Angeles River Watershed. According to the NOP, the San Rafael site (1.5 acres) will serve as the first stage of runoff diversion from San Rafael Creek, providing pretreatment and partial infiltration. Remaining flows will be treated further downstream at the 2.2-acre San Pascual site, located just 850 feet away, prior to being returned to the Arroyo Seco Channel.

Beyond its primary water management role, the project includes a host of public-facing and ecological enhancements. Informational signage, native landscaping, and reclaimed-material hardscape elements—including stone-faced concrete walls and log seating—are designed to promote educational outreach and community engagement. Trail network expansions across both sites will improve pedestrian access and strengthen connections through the Lower Arroyo Seco corridor. The off-site component of the project, located within a secured maintenance yard at the Arroyo Seco Golf Course in South Pasadena, will feature a water harvester system intended for non-potable irrigation reuse. Collectively, the system is expected to generate an average annual water supply benefit of 320 acre-feet, with approximately 258 acre-feet allocated to groundwater recharge and an additional 30 acre-feet reserved for on-site reuse—thereby easing pressure on local potable water sources.

Environmental regulators have spotlighted the Arroyo Seco Channel as a high-priority water body, citing routine exceedances of bacteria thresholds. The Los Angeles Regional Water Quality Control Board previously designated the San Rafael Creek outfall as a significant contributor to bacterial loading in the river system, prompting increased regulatory scrutiny and compliance mandates. This project is positioned as a response to those requirements, while also offering broader benefits such as increased habitat connectivity, native species reintroduction, and enhanced recreational access.

City staff have conducted a preliminary review and identified multiple areas that may warrant detailed environmental analysis in the forthcoming EIR. Potentially significant topics include aesthetics, air quality, biological resources, cultural and tribal cultural resources, hydrology, greenhouse gas emissions, and wildfire risk, among others. Meanwhile, impacts related to population and housing, public services (excluding parks), transportation, and utility systems are currently anticipated to be less than significant. With climate resilience, water quality, and urban ecology high on the policy agenda, the Arroyo Seco Water Reuse Project reportedly represents a strategic investment in the long-term sustainability of the Los Angeles River watershed.