On February 10, 2010, the San Diego Regional Water Quality Control Board (“San Diego Water Board”) adopted indicator bacteria Total Maximum Daily Loads (TMDLs) for impaired beaches and creeks in the San Diego Region. This includes TMDLs for over nine and a half miles of Orange County beaches, the entire length of Aliso Creek and the lower mile of San Juan Creek. A map of the affected areas is provided below.
The Beaches and Creeks TMDLs define the allowable indicator bacteria loads from the stormdrain system that will still allow attainment of water quality standards. The modeled reductions required to meet these loads in south Orange County range from 73-99% during dry weather to 91-100% during wet weather depending on the location and indicator bacteria species. A 22% wet weather allowable exceedance frequency of TMDL number target is also included in the TMDLs to account for natural sources of bacteria. Compliance with the TMDLs must occur by April 4, 2021 with a possible extension to April 4, 2031 for wet weather load reductions.
Indicator bacteria can come from a variety of sources throughout the watershed including pet waste, trash, sewage spills, septic tanks, animal manure fertilizers, and natural sources such as bird and wildlife feces and decaying plant material. During wet weather, storm runoff picks up the bacteria and associated pathogens off of the land and deposits them into recreation waters through the municipal separate storm sewer system (MS4). During dry weather groundwater seepage and nuisance flows from urban land use activities such as car washing, sidewalk washing, and lawn over-irrigation provide transport through the MS4.
The impaired beaches and creeks addressed in the Beaches and Creeks TMDLs are based upon the 2002 Clean Water Act Section 303(d) list developed using water quality data collected prior to 2002. Since 2002 water quality at many south Orange County beaches has significantly improved. This is due in part to Best Management Practices (BMPs) implemented by the County, cities, non-governmental organizations, and the public in an effort to reduce bacteria and associated pathogens. These efforts have included but not limited to diversion structures, stormdrain inlet filters, treatment facilities (Dana Point Salt Creek Ozone Treatment Plant), wetlands (Wood Canyon Emergent Wetland Project), irrigation controllers, beach cleanups, the use of pet waste bags, and public outreach and education efforts.
Achieving the bacteria TMDL targets will not be easy and it is anticipated that future reductions plans will require a multitude of similar efforts. As a first step, watershed Bacteria Load Reduction Plans (BLRPs) or Comprehensive Load Reduction Plans targeting all watershed pollutants of impairment are being developed outlining the BMPs needed to meet TMDL targets and special studies to identify sources of indicator bacteria in the watershed.