San Dieguito Freshwater Runoff
Treatment Ponds

$550,017 State Grant Received

The State Water Resources Control Board has awarded a grant of $550,017 to the San Dieguito River Park for the creation of the Freshwater Runoff Treatment Ponds proposed in the Park Master Plan for the San Dieguito Coastal Area.   Region 9 of the Regional Water Quality Control Board will administer the grant.

Project Location

In San Diego, east of I-5, south of Via de la Valle, at the terminus of San Andres Road.

Project Description

This project includes the construction of a series of four connected water treatment ponds to clean a five-acre site that is impacted by poor quality runoff and construction of an 1,100 foot long segment of the multi-use “Coast to Crest Trail” through the treatment ponds on top of an existing maintenance service road.   The ponds would be constructed predominantly through the natural drainage course by flowing over the weir in the first basin.   The low, most polluted flows, would pass consecutively through the other three basins in series before returning to the natural drainage course.   The existing telephone company maintenance road in this area would be raised above the water table, and flows coming from the north would be directed underneath.   The project would also remove invasive species and replant with native vegetation; install water quality control devices including a trash rack, sediment trap, and oily wastewater separator; and install weirs, culverts and other piping necessary to make the ponds function hydrologically.

Purpose

The subject area is inundated with substantial urban runoff from a 313 acre residential watershed that is funneled via a culvert under a shopping center into the project site.   It has been roughly estimated that a residential watershed of that size in San Diego will produce 5,453,712 cubic feet of stormwater each year, and twice that amount, or 10,907,424 cubic feet of urban runoff, each year.   Left untreated, the runoff would go directly into the newly restored wetlands, introducing sediment, oily water, chemicals and invasive species. This project will capture and treat that water before it is introduced into the estuarine system.

Goals, Objectives and Outcomes

• provide water quality benefits by filtering out sediment, nutrients, heavy metals, and oily substances;
• provide habitat and wildlife benefits by removing invasive species, filtering out new invasive plant propagules and replanting native plants.
• provide ecosystem benefits by reducing the flow of freshwater into the tidal salt marsh system,
• provide recreational benefits by eliminating the muddy condition at the location of the maintenance service road so that it can be used as a public use trail.  
• provide educational benefits via an interpretive signage program about the watershed and water quality functions served by natural wetlands.  
• serve as a model for other areas impacted by non-point source pollution to use, especially in areas such as this one where it is not practical to eliminate the polluted water source.   Not only will the method proposed by this project effectively reduce the problems, but it is a natural approach that allows the watershed to cleanse itself in a cost-effective and aesthetic way.

Project Timeline

Construction will begin in September 2007 and finish in July 2008

• Remove invasive plants: 9/15/07-10/15/07.
• Grade site to form treatment basins and berms: 10/15/07-12/15/07
• Install water quality control devices: 11/15/07-12/15/07
• Install weir and culverts: 11/15/07-1/15/08
• Surface maintenance road/trail, install railing: 1/15/08-2/15/08
• Replant with wetland and native plant species: 2/15/08-4/15/08
• Install interpretive signage: 4/15/08-7/15/08

For "before" photos of the project site (in pdf), click here.

For a grading plan of the proposed treatment ponds (in pdf), click here.

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