An Integrated Watershed Approach to TMDLs – Case Study of Chollas Creek TMDL Implementation Process

Urbanized watersheds often possess multiple water quality issues. The approach to total maximum daily loads (TMDLs) is however often implemented on a pollutant specific basis. This creates challenges in implementing pollutant reduction measures that may address the current targeted constituents, but may not be effective for future water quality issues. This may result in expenditures of funds on capital projects that will require future retro-fitting. The City of San Diego is working with the Regional Water Quality Control Board and stakeholders in developing an integrated watershed TMDL implementation approach that more cost effectively addresses the multiple constituent issues in the watersheds within the City's jurisdiction. This watershed TMDL approach is being used for the Chollas Creek dissolved metals TMDL Implementation Plan. Although the current TMDL focuses on dissolved metals, the Implementation Plan addresses anticipated load reduction requirements for bacteria and emerging issues such as trash and synthetic pyrethroid pesticides. By taking an integrated watershed approach the best management practices will be designed to address these multiple constituents. The advantage of this approach is more cost effective use of public funds that will avoid future retro-fits. This integrated approach, however, also requires a longer time frame to implement because the most cost effective solutions may not yet be proven. The integrated approach developed for the Chollas Creek watershed is a tiered and phased approach that emphasizes source control and pollutant reduction BMPs, low impact development (LID) techniques and pilot treatment projects in the initial phase, and then a ramping up of the more capital intensive projects that have shown to be cost effective during the first phase.The presentation includes a summary of the integrated watershed approach based on the case study of the Chollas Creek Watershed TMDL Implementation Plan process. Highlighted is the approach to the watershed-based BMP implementation strategy using an integrated and phased approach. This strategy employs an integrated approach by considering current and anticipated pollutants of concern and establishes geographic and source-based priorities to maximize efficiencies. The BMP implementation strategy is also phased to allow for assessment of the effectiveness of less costly source control, pollution prevention and runoff reduction BMPs prior to implementing more costly and land intensive treatment BMPs. The strategy also includes achieving multiple benefits by addressing deferred maintenance, enhancing community value, and implementing sustainable solutions that require less energy and re-use of storm water.