Stormwater Retention Credit Framework/Alternative Compliance Strategies

Stormwater Retention Credit Framework/Alternative Compliance Project
Lead Agency County of San Diego
Status 50% Complete
Project Budget $441,176
$441,176 SMC Member Agencies (8)
Technical Leads Eric Stein, SCCWRP
Matt Yeager, Independent Consultant
Key Words: water quality equivalency, regional LID, offsite mitigation

The project focus is to develop model program guidance for Permittees and other stakeholders to facilitate implementation of approvable “alternative compliance” options (Options) for Priority Development Projects (PDPs)[1] where applicable. The project will also apply and test the model guidance by developing a model Alternative Compliance Program (ACP) for the Fletcher Basin and Legacy Campus Plan areas in Orange County.

This is a joint project being conducted by the San Diego and Orange County Stormwater Programs.  The project has two primary tasks, each with multiple subtasks, which are as follows:

1.0      Water Quality Equivalency (WQE) Guidance Development

  • Background research o Review available literature regarding options in California and elsewhere
  • Stakeholder participation to establish policy and technical advisory groups to engage watershed stakeholders
    • Conduct workshops to develop key project needs and review water quality equivalency objectives
  • Equivalency determination of work with participating jurisdictions to develop currency values for equivalency objectives
    • Develop a consistent set of water quality equivalency standards for each option
  • Develop equivalency guidance document o Advisory group review

2.0     Application and Testing of Water Quality Equivalency Guidance

The application and testing project phase includes two pilot projects to test methodologies, examine potential benefits or impacts, and perform effectiveness assessments. The two pilot project locations are:

Fletcher Basin: Using a detailed case study approach, the project will apply quantitative metrics, including the WQE Guidance methodology, to

  • evaluate and compare the water quality,
  • evaluate local potable water supply augmentation,
  • assess ecological, species and habitat, and property value-related benefits of installing selected combinations of the four types of LID BMPs, and
  • assess site-by-site benefits on selected parcels presumed to be classified as PDP sites in the Fletcher Basin subwatershed.

The Project will quantify the benefits expected from the development and operation of a single regional stormwater retention basin retrofitted to accept urban stormwater runoff. The Fletcher Basin retrofit analysis will examine the opportunities and challenges of individual site-by-site LID BMP implementation versus larger scale, multi-jurisdictional cooperative stormwater capture projects, including identification of key water rights issues.

Legacy Campus Plan Project (Legacy CPP): This project task will conduct a case study benefit and cost analysis for the Legacy CPP, located within the City of Orange. The Legacy CPP consists of an approximately 25-acre site that will be developed for commercial (medical) and residential uses by integrating existing and new building areas, and includes opportunities for regional stormwater capture within areas near and adjacent to Santiago Creek (which is outside of the Legacy CPP contributing area). The Legacy CPP will examine opportunities and challenges for public-private partnerships in stormwater management. Through evaluation of the Legacy CPP, the proposed SMC project can determine the optimum mixture of on-site and regional stormwater BMPs that can be installed and maintained for the least cost while providing maximum benefits.

The results of the Fletcher Basin and Legacy CPP benefit cost analyses will be combined with existing information on engineering feasibility of LID BMP use in Orange County to establish a model in-lieu program framework and recommended fee structure, including the quantitative basis for appropriate in-lieu fees. Within such a framework, PDPs in the applicable areas could comply with the requirement to manage 100% of the Design Storm runoff by funding off-site or alternative LID/retention/stormwater treatment BMPs at a level deemed equivalent to managing the Design Storm obligation on-site.

To support alternative compliance program options that meets MS4 permit obligations, the proposed project will identify and analyze the institutional (contractual and legal) agreements necessary for implementing Options including regional BMP development, green street development, water quality credit trading, and in lieu fees. By combining the economic, regulatory, institutional/ legal, and technical feasibility issues that need to be addressed in order to establish an alternative compliance program, the proposed project will serve as a model approach for watershed-based LID BMP implementation and optimization in Orange County. The work products will help decision makers to optimize the location, benefits, and costs of installing LID BMP-type stormwater management facilities in Orange County, while maintaining compliance with MS4 permit requirements and providing flexibility to project designers and developers.

5.2.1    Project Status Update

San Diego County has completed a draft of their water quality equivalency (WQE) program document; the draft is currently under review. The document includes detailed procedures for determining equivalency for offsite mitigation for both water quality and hydromodification. This includes information on both sizing and location of alternative compliance BMPs. The document focuses primarily on infiltration and retention based BMPs and has some preliminary guidelines for flow through BMPs. However, lack of data on performance of flow-through BMPs limits the specificity that can currently be provided. The document also includes preliminary discussions of floodplain and stream restoration as alternative compliance; however, the details for these options are to be refined through a future phase of the work. San Diego County expects that the draft water quality equivalency document to be out for review the first week in 2015. A public workshop was held on July 28, 2015, with comments due on August 18, 2015. The goal was to submit the guidance document to the San Diego Regional Board by September 15, 2015.

As the next step, Orange County will apply the approach developed by San Diego County to an actual project at Fletcher Basin within the City of Orange to see how well the approach adapts to sites with different environmental and physical constraints.

5.2.2    Project Related Publications

No project related publications were prepared during the 2014-2015 reporting term.

[1] PDPs are defined according to the San Diego Regional Municipal Permit (ORDER NO. R9-2013-0001) at Section E.3.b.