Supervisors approve Rainbow nutrient reduction and street improvement project

The San Diego County Board of Supervisors approved a project whose primary objective is to reduce nutrient discharge into Rainbow Creek, and which will also provide flood control benefits and street improvements to some Rainbow roads.

The supervisors' 5-0 vote June 9 authorized the director of the county's Department of Purchasing and Contracting to take the necessary actions to advertise and award a contract for the Rainbow Water Quality Improvement Project, designated the director of the county's Department of Public Works as the county officer responsible for administering the contract, appropriated $9,000,000 for the project, and adopted an environmental Mitigated Negative Declaration and a Mitigation Monitoring and Reporting Program.

The Rainbow Creek subwatershed covers approximately 7,000 acres in Rainbow Valley. Approximately 5% of that total acreage is currently being used by 37 nurseries and greenhouses which use fertilizer and irrigation water. Runoff from septic leach fields also flows into Rainbow Creek.

Excessive nitrogen and phosphorus levels in Rainbow Creek caused the Regional Water Quality Control Board to establish total maximum daily load contaminant levels in 2006. In 2013, the RWQCB issued a municipal separate stormwater sewer system permit to the county which has an enforceable TMDL reduction for Rainbow Creek. The deadline for final compliance with those maximum load levels is Dec. 31, 2021.

The county evaluated the best way to reduce nutrients and also sought to identify how to fund the project. Rainbow Creek is within the Santa Margarita watershed, so the best management practices were also incorporated into the Water Quality Improvement Plan for the Santa Margarita Watershed which was finalized in 2018.

The project will install approximately 3,400 linear feet of subsurface wetlands channels. Adjacent road runoff will be conveyed through those channels which will deliver the water – minus whatever will be used for the vegetation or soil – to collection pipes and then to the discharge system at Rainbow Creek. The work will also include replacing other drainage channels to convey adjacent road runoff, and the county took the opportunity to add road and pedestrian safety improvements.

Capital improvements will take place along Huffstatler Street by Second Street, Huffstatler Street south of Fifth Street, Fifth Street between Huffstatler Street and Rainbow Valley Boulevard, Rainbow Valley Boulevard from Chica Road to Rainbow Creek Road, and the northern part of Rainbow Valley Boulevard.

Some modifications to driveways will be necessary near Fifth Street and Huffstatler Street, on Rainbow Valley Boulevard between Chica Road and Rainbow Creek Road, and along the 800-foot northern Rainbow Valley Boulevard segment.

Traffic improvements to the intersection of Chica Road and Rainbow Valley Boulevard will include widening for some segments and turn radius modification.

Pedestrian improvements will be made at the intersection of Huffstatler Street and Fifth Street. Ramps meeting Americans with Disabilities Act standards will be added on both the east side and the west side of Huffstatler Street.

The planned improvements to the north side of Fifth Street include an 8 foot wide shoulder. A decomposed granite pathway on the south side of Fifth Street will be installed to avoid impacts to an existing facility while enhancing pedestrian safety near Rainbow Park and Vallecitos Elementary School.

A concrete sidewalk 5 feet wide will be installed between the west end of Rainbow Park and Huffstatler Street and will meet Americans with Disabilities Act standards including curb ramps meeting ADA standards. Approximately 500 linear feet of sidewalks along with curbs and gutters will be installed, which will reduce ponded areas in the roadway and divert surface flows to the new treatment areas. The sidewalk will be on the south side only while drainage will be implemented on the north side of Fifth Street.

In addition to filtering runoff the increased depth of the channels will increase the water volume capacity. The work will also include lining the subsurface channels, geotechnical studies, and groundwater testing.

The $9,000,000 estimated cost includes a 10% contingency. A prior-year balance in the general fund will be used for the expense.

On March 17, the Rainbow Community Planning Group voted 9-0 to recommend approval of the project. Notices in both English and Spanish will be provided to the community prior to construction. Traffic control measures will be in place during construction.

Most of the construction will be within public right-of-way, and temporary construction easements will be obtained prior to the award of the contract. The work is expected to begin in fall 2021 and be complete during summer 2022. After the completion of the construction, DPW will maintain the road and channel facilities, which will be inspected one to two times a month.