The El Cerrito Green Streets Pilot Project consisted of installing a series of stormwater treatment rain garden cells at two locations along San Pablo Avenue in the City of El Cerrito. The project also included water quality monitoring, community outreach, and technology transfer to local governments.

The purpose of this pilot project was not only to directly improve localized water quality, but also to promote the public’s awareness of stormwater pollution, and expand local governments’ existing stormwater management toolbox to include green infrastructure approaches. The scope consisted of rain garden construction, water quality monitoring, development of outreach materials and interpretive signage, and training of City maintenance staff.

Construction started in March 2010 and was completed in July 2010. Two years of post-construction wet weather monitoring was conducted at one rain garden cell to gage proper functioning and quantify pollutant removal effectiveness. The first year of monitoring was observational, the second year included influent and effluent sampling during four storm events. These samples were analyzed to quantify the pollutant removal efficiencies of the rain gardens for: PCBs, pyrethroids, suspended sediments, mercury, and copper.

Outreach activities of the project occurred throughout the planning, construction and monitoring phases of the project. Many of the outreach materials developed for the project, such as the video podcasts, interpretive signage, and educational pamphlets will continue to provide useful information about the art and science of green streets. Some of these are available on the Estuary Partnership website at www.sfestuary.org. A half-day training session in the field provided all City maintenance staff with an understanding of the purpose, design, and function of rain gardens, as well as basic inspection and maintenance procedures.

The rain gardens were constructed in the late spring/early summer of 2010, retrofitting about 750 linear feet of sidewalk. Curb cuts direct flows from the adjacent street and sidewalk into depressed vegetated treatment cells underlain with amended soils. The bio-retention cells of the rain gardens filter pollutants before the stormwater is discharged via under-drains plumbed to existing storm drain pipes that discharge to either Baxter Creek or Cerrito Creek, both of which flow to the San Francisco Bay.

The two sites have an estimated treatment volume area of 20,700 cubic feet. Visual observations indicate the rain gardens are functioning properly. The water quality monitoring results showed that the study rain garden cell is successful in reducing pollutant concentrations for most pollutants analyzed. The one exception was mercury which showed 6 mixed results from the samples collected. More monitoring is needed to understand how dissolved mercury may be better treated using these systems.

The robust outreach program associated with the project successfully engaged multiple target audiences. More than 50 local stakeholders such as adjacent property owners, residents, and commercial business were reached through direct mailings. The project webpage on the Estuary Partnerships website has received nearly 600 hits. The three video podcasts, available on YouTube have gotten about 1,400 views since they were posted. Interpretive signage at the two rain garden facilities continues to educate passers-by.

The City maintenance staff continues to upkeep the gardens using techniques reviewed at the training session. The plants are thriving, adding a lush quality to the streetscaping. Additional technology transfer includes the transmittal of the projects final report and water quality monitoring technical memo to the Countywide Clean Water Programs around the Bay Area.