Development of Municipal Separate Storm Sewer System (MS4) Numeric Limits for Constituents of Concern and Evaluation of Proprietary Best Management Practices (BMPs) for the City of San Diego, CA

Abstract

As National Pollutant Discharge Elimination System (NPDES) permits continue to request more prescriptive conditions for controlling pollutants from municipal stormwater discharges, municipalities and local agencies are forced to develop methods to evaluate the effectiveness of various treatment schemes suggested by engineers for both private development and public improvement projects. The City of San Diego has developed a methodology to evaluate effectiveness levels that may be achievable by today’s manufactured Stormwater Treatment Control Best Management Practices (BMPs). The method included a large-scale data collection of treatment study data from proprietary BMP manufacturers, the International BMP Database, and Caltrans (The California Department of Transportation). Using the collected data, each treatment system was evaluated on a constituent basis using methods proposed by the ASCE Task Committee on Guidelines of Manufactured Stormwater BMPs and the professional judgment of the project investigators. The result was the development of both numeric criterion for ranking of proprietary BMP products into high, medium, or low treatment effectiveness categories for constituents of concern, and a consistent process for evaluating each system against that criterion. Unfortunately, only nine of 25 potential constituents of concern had enough test data to substantiate development of numeric treatment effectiveness ratings. This implies that much work continues to be required to clearly substantiate the use of many manufactured products that are currently available to treat constituents for which there is currently no defensible data. BACKGROUND