Road pavement can contribute to excess stormwater runoff and increased levels of pollutants in waterways. When green infrastructure is introduced, it can reduce storm water runoff and improve water quality. San Diego County’s Green Streets program incorporates numerous green infrastructure design elements including tree wells, biofiltration rain gardens, rock gardens and permeable pavement.

WSP USA worked with San Diego County to develop the Green Streets technical guidance document and standard drawing details, which assist developers and county staff in understanding what is expected, what may be permitted, and what can be approved for redevelopment or retrofitting of existing paved roads, streets or alleys.

“The overall project is noteworthy in that it provides guidelines that can be used to assist the public, planners, engineers and construction contractors. The document includes over 50 standard engineering drawing details and specifications which provide a streamlined permitting approach, and reduce the need for special review of green infrastructure project components,” said Matt Moore, who served as project manager for WSP.

The guidelines established permitting provisions that created “priority development project exemptions” for road projects when they are redeveloped or retrofitted, based on criteria established by the Environmental Protection Agency (EPA) in its Green Streets municipal handbook, Managing Wet Weather with Green Infrastructure.

Green Streets create the opportunity to transform a potentially significant storm water and pollutant source into an innovative treatment system.

“Green infrastructure, unlike traditional ‘gray’ infrastructure approaches to storm water management, provides multiple benefits to communities,” Moore said. “Planting more trees and landscaping in public spaces cleans the air, cools the land, provides more habitat for wildlife, adds green maintenance jobs, increases property values and promotes a better, healthier quality of life for San Diego County residents and visitors.”

Established as an outreach tool, the guidelines serve as a companion to the county’s Best Management Practice (BMP) Design Manual, and is used by developers and engineers throughout the county. One capital improvement project that has implemented these guidelines is the $20 million widening and improvement of Cole Grade Road that is targeting completion in 2020. WSP reviewed the green infrastructure plans for part of the project on behalf of the county.

“Green Streets design criteria lay out general definitions, general policy and landscape design criteria for green infrastructure strategies,” Moore said. “It includes construction details that can be referenced in improvement plans, and a suggested maintenance schedule that includes a list with tasks, frequency, and time of year for initial, routine, and as-needed maintenance for each strategy.”

Green Streets specifications also include detailed construction material and installation requirements for strategies, including aggregates, geosynthetics, underdrains, permeable pavement, engineered soil media, mulch, overflow risers, check dams and tree grates.

“Green infrastructure has the added benefit of promoting water conservation with low water use and drought tolerant plants, and improving groundwater supplies through infiltration.” Moore said.

One challenge to overcome during preparation of the guidelines, standard drawings, and specifications was to reach consensus on conflicting requirements of various county stakeholder groups, including design, construction and maintenance issues.

This challenge was turned into an opportunity to create consensus, buy-in and ownership. The documents were reviewed and consensus was reached through seven meetings with county departments and divisions; external outreach presentations to organizations including Associated General Contractors, Construction Management Association of America, and the local Land Development Industry Group; presentations at an American Public Works Association luncheon; and a workshop on BMPs for public works projects at the 2014 California Stormwater Quality Association conference.

The green infrastructure guidelines were recognized with the Outstanding Innovation in Green Planning & Design Award, presented by the San Diego County Chapter of the Association of Environmental Professionals in 2016.

Since its completion, the document continues to evolve and has received ongoing updates and refinement to keep it current with Green Street standard specifications. San Diego County enlisted WSP to also prepare a similar guidance document for its green parking lots design.

The guidelines have become a template for similar green infrastructure programs. Moore said that other agencies in Southern California have expressed interest in working with WSP to develop similar Green Infrastructure Guidelines specific to their region.

“This was one of the most notable projects that I have worked on,” Moore said. “It gave me a unique opportunity to assist in the production of documents and standards that reach a wide audience in Southern California and have daily practical application and usefulness. The process of achieving buy-in from multiple decision-makers was as rewarding as creation of the final document,” Moore said.

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