Orange County, California Model Water Quality Credit Trading Program Development

Water Quality Credit Trading Program Development Update

Program Development Background. Starting in 2010, CICWQ has collaborated with Orange County Public Works to implement its post construction stormwater MS4 permit requirements for new and redevelopment projects, providing engineering and economic analysis support.

This work has resulted in several publications and numerous presentations highlighting key findings and recommendations. In 2017, CICWQ prepared a comprehensive engineering case study analysis of two regional stormwater capture projects in Orange County which could potentially generate water quality credits for use in meeting MS4 permit compliance requirements. And, CICWQ produced a comprehensive benefit-cost analysis of the two projects.

The Program Today. Starting in late 2018 and continuing to the current time, CICWQ and Orange County Public Works are collaborating on a watershed-scale demonstration and research project to develop a water quality credit trading program for north Orange County, within the jurisdiction of the Santa Ana Regional Water Quality Control Board.

The Program, which is nearly developed and is entering the case-study demonstration phase, uses a regional approach to collect and manage storm water runoff, and may provide storm water permit compliance flexibility for private and public funded new and re-development projects. CICWQ is part of a large, technical and engineering team of engineers, scientists, and economists. Work is scheduled to be completed by the end of 2022.

DRAFT Water Quality Credit Trading Program for North Orange County

The North Orange County Water Quality Credit & Trading Program establishes a framework for alternative compliance to satisfy the structural Best Management Plan (BMP) requirements of the New and Redevelopment Program required by the Santa Ana Regional Water Quality Control Board Municipal Separate Storm Sewer System (MS4) permit.

The primary intent of the program is to provide a mechanism to enable the construction of regional stormwater capture projects providing expedited stormwater capture capacity and water quality and watershed improvement. Credits are generated in the program through stormwater capture projects with one cubic foot of stormwater captured generating one credit for use in the program. The program was created and is administered by the County of Orange.

The following are the goals of the program:
• Provide measurable, expedited water quality and watershed improvement in existing urban areas

• Provide an alternative and innovative funding source for watershed improvement projects

• Meet water quality regulations more efficiently and effectively and faster

• Build sustainable, integrated, and multi-benefit watershed improvement projects

• Reduce the burden on municipalities and private development related to distributed BMPs

• Incentivize projects that capture stormwater as an alternative water supply

Securing funding for stormwater capture and watershed improvement projects is the primary barrier to achieving stormwater capture and water quality and watershed improvement and therefore alternative and innovative funding sources are needed and are a primary driver for the program. The Program is at its core an alternative and innovative funding program to enable expedited construction of stormwater capture and watershed improvement projects in north Orange County.

The North Orange County Water Quality Credit & Trading Program provides an alternative to a distributed BMP approach and its associated burdens and constraints. It does this by enabling a regional, centralized approach to stormwater capture which will focus efforts and resources on ensuring that all the steps for regional stormwater capture projects are implemented correctly, thus reducing the burden on the development community, municipalities, and the Regional Board.

The North Orange County Water Quality Credit & Trading Program document includes a regulatory framework based on both the current MS4 permit and the SARWQCB’s 4th Public Release of the Draft 5th Term MS4 Permit for Orange County. The eligibility requirements for participation in the program include the credit program trading areas, specifications for credit generators, credit adjustments when credits are generated, specifications for credit users, and credit generation and use scenarios.

Administration of the program by the County of Orange includes review, approval, verification, and inspection of credit generation facilities; a credit bank and tracking of credits; timing of credit use; transfer of ownership of credit generation facilities; enforcement, program audits; reporting, and integration of the credit program with other County programs. The financial elements of the program include cost of credits, credit value and credit price, operation and maintenance costs, and credit transactions, and credit generator project reimbursements.

Engineering Case Study Proof of Concept

Approach

An engineering case study, proof of concept approach was used to support developing a model procedure to construct an urban stormwater runoff retention (infiltration) facility which generates water quality credits. Calculations necessary to size and design a retention facility to manage runoff from the 23-acre Legacy Campus Plan Project site and 241-acre tributary drainage area was performed using the Orange County Model Water Quality Management Plan and Technical Guidance Document standards.

Management Facility Evaluation

Four types of best management practices (BMPs) were evaluated to generate water quality credits: biofiltration, infiltration trench, infiltration basin, and subsurface retention. Infiltration basins use the least amount of surface area to manage runoff compared to infiltration trenches, biotreatment with underdrain, and subsurface retention. However, using surface-based BMPs to create water quality credits is constrained because tributary area runoff in urban areas is conveyed using underground storm drains. The elevation at which runoff arrives at a given project location may be deeper than that which could be conveyed feasibly to a surfacebased BMP. Therefore, subsurface retention BMPs, which infiltrate stormwater runoff directly into the ground, are a feasible type of system which can accept tributary area runoff (which generates water quality credits).

Urban Runoff Routing

An existing 84-inch diameter storm drain installed along a major arterial street adjacent to the Campus Legacy Plan Project delivers runoff to the subsurface infiltration facility. To direct runoff to the infiltration facility, a diversion and pretreatment structure is required. The diversion structure would be installed within the existing storm drain right of way at a depth below ground surface between 10.5 and 20 feet, and continuous deflection separation (CDS) for runoff pretreatment installed at a suitable location before the subsurface infiltration system inlet.