Sustainability Rating of Stormwater BMPs
The County of San Diego (County) developed a comparative assessment of stormwater best management practices (BMPs) using a sustainable return on investment (SROI) study to identify benefits and impacts. This talk will present the results of the SROI study that encompassed a quantitative and qualitative evaluation of potential project costs, social outcomes, environmental performance, and monetized benefits of 21 stormwater BMP categories.
The Qualitative assessment was conducted based on the Institute for Sustainable Infrastructure (ISI) Envision™ rating system, which evaluates the BMP projects under 60 sustainability criteria in the categories of Quality of Life, Leadership, Resource Allocation, National World, and Climate and Risk.
The Envision™ rating system was applied to various stormwater BMP to develop a decision support tool that the County can use to incorporate sustainability criteria in stormwater project selection analyses. The wide range of BMPs includes green streets, hydrodynamic separators, bioinfiltration, extended detention basins, stream rehabilitation, groundwater injection, and others. Since these BMPs were not part of any existing projects, assumptions and rating criteria were developed for each stormwater BMP. This approach gives us a sense of a) how the stormwater BMPs compare to each other in terms of sustainability, and b) how the County could increase performance for projects that may seek Envision™ sustainability certification. BMP characteristics that differentiate the ratings include vegetation, structural/constructed elements, relationship to transportation infrastructure, and operation/maintenance requirements.
The study also included a quantitative assessment of the BMPs based on the BCE tool to evaluate life cycle costs, including monetized social and environmental "co-benefits". The BCE analysis is built on existing cost estimates of structural BMPs that compare their life cycle costs with estimated pollution reductions, and adds the estimated monetized impact of environmental and social costs or values.
This presentation provides a framework to use the Envision™ rating and BCE assessment to identify BMPs that may be most cost effectively and sustainably implemented in the County, providing social, environmental, and financial benefits to the community.