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Bacteria Load Reduction: Qualifying the Effect of 20 Years of Program Implementation and Adaptive Management in South Orange County
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Over the last 20 years, MS4 Permittees in South Orange County have developed and implemented jurisdictional and regional programs to reduce bacteria loads and protect beach and creek water quality.

During this time, the San Diego Region Twenty Beaches and Creeks Bacteria TMDL was adopted, multiple iterations of watershed plans have been developed and implemented, and dry weather TMDL compliance deadlines have come due. In support of dry weather TMDL compliance demonstrations, the Permittees recently conducted a detailed retrospective analysis of progress achieved, relying primarily on monitored outfall, stream, and beach conditions. The results of this analysis provide a comprehensive and data-driven look into the long-term progress that is possible in both beaches and creeks through targeted combinations of non-structural and structural strategies.

This presentation will focus on the foundational elements of program implementation, including jurisdictional and watershed strategies, agency collaborations, monitoring and assessment programs, and adaptive management that contributed to more than 90% dry weather bacteria load reduction across much of South Orange County. Additionally, we will focus on the datasets and statistical methods that made it possible to quantify this progress rigorously. Key topics are outlined below.

Strategy implementation. The Permittees have implemented a range of strategies aimed specifically at bacteria load reduction, including non-structural source controls, such as outreach, education, inspections, water efficiency incentives, site design and other practices, and structural BMPs such as distributed low impact development, regional treatment facilities, and low flow diversions. Implementation has been augmented by close partnerships with water and sanitation districts that span water use efficiency, resource recovery, sanitary sewer management, and recycled water management.

Adaptive management. The prioritization of these strategies has been informed by jurisdictional illicit discharge programs, inspection programs, and targeted monitoring programs. Via a combination of BMP tracking, outfall monitoring, BMP monitoring, and receiving water monitoring, the effectiveness of controls has been evaluated, supporting the iterative process of improving existing strategies and adding new strategies.

Progress quantification. Long-term monitoring programs have provided valuable data to support progress quantification. Analyses of outfall, receiving water, and BMP monitoring data between the TMDL baseline (2002) and current period have quantified the combined effect of structural and non-structural BMPs. These analyses support the hypothesis that the diffuse array of non-structural controls applied across the landscape have had similar or greater effects in reducing bacteria loads than the more discrete structural BMPs.

This presentation will offer lessons learned about strategy effectiveness, monitoring program design, and other keys to achieving a quantifiable, resilient, and successful program.

Publication Summary

  • Geosyntec Authors: Aaron Poresky
  • All Authors: Cindy Rivers, Aaron Poresky
  • Title: Bacteria Load Reduction: Qualifying the Effect of 20 Years of Program Implementation and Adaptive Management in South Orange County
  • Event or Publication: CASQA 2021
  • Practice Areas: Water and Natural Resources
  • Citation: Geosyntec practitioners will present at California Stormwater Quality Association Virtual Annual Conference on October 26-27, 2021.
  • Date: Tuesday, Oct. 26 at 3:00-3:25 p.m. PST
  • Location: California
  • Publication Type: Platform Presentation