Development of a Model On-Site Retention LID BMP Alternative Compliance Program in the Santa Ana River Watershed, California
Implementing Low Impact Development (LID) Best Management Practices (BMPs) at the watershed scale may accelerate achievement of water quality regulatory criteria (e.g. TMDL compliance) as compared to site-by-site application of LID BMPs at new and redevelopment projects. In addition, it is generally believed, but requires testing, that multi-benefit projects may provide at least equal or greater overall environmental benefit compared to project-scale (site-by-site) implementation of LID BMP stormwater retention requirements.
This presentation describes the method development and case study evaluation process used to determine the range and of environmental benefits achieved through implementation of LID BMPs at relevant project development scales in Orange County, California, and discusses the application of equivalency calculations to the LID BMP alternative compliance process. The presentation will highlight the analytical process and quantitative results derived through in-depth examination of two development scenarios within Orange County: i) a comparison of site-by-site LID BMP implementation in the 1,000-acre + Fletcher Basin watershed versus retrofit of a regional retention basin serving the entire watershed, and ii) a 65-acre mixed use, urban redevelopment project in the City of Orange, adjacent to Santiago Creek. The economic benefit-cost analysis includes estimation of the value of the water captured under different LID BMP retention scenarios, and the cost for treatment of the pollutants removed from urban stormwater relative to the benefits realized of: increasing water supplies via groundwater augmentation, removing pollutants, changing infrastructure costs, and creating such environmental benefits as urban greening, wildlife habitat generation, greenhouse gas reduction, and energy efficiency. Case study results of using equivalency calculations for determining alternative compliance will be presented.
The data discussed supports the creation of a model framework for a retention credit system or an in-lieu program that will enable project proponents to support regional and sub-regional scale projects in-lieu of on-site retention when infeasibility of on-site retention is demonstrated or off-site retention is preferred (because of equal or better environmental benefits and outcomes determined through a watershed management planning process).