Beach and Bay Program

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• Cross-Border Sewage Impacts and ddPCR Beach Water Quality Testing Information

  On May 5, 2022, San Diego County (County) became the first Federal and State approved coastal county in the nation to begin using a new droplet digital polymerase chain reaction (ddPCR) testing method that offers more rapid results to inform the public of the water quality conditions within the same day, and test for fecal indicator bacteria DNA, which is more precise and protective of public health. 

  State health standards use fecal indicator bacteria as a way of checking water quality, as these bacteria are scientifically known to indicate the presence of other bacteria or viruses that could make members of the public sick with illnesses such as gastroenteritis, respiratory disease, fever, rashes, paralysis, meningitis, infections in bloodstream, or diarrhea. The County tests waters of public beaches or bays for microbiological contaminants and to inform the public when a beach is closed, posted under advisory, or may pose public health risks. At beaches in the south county, where the community is disproportionately impacted by cross border sewage flows from Mexico and the Tijuana River Valley, samples are taken every day.

  In the first month of implementation, ddPCR test results have determined levels of bacteria in the water that exceed State health standards at beaches in the south county. These conditions have resulted in increased water contact closures in May, with Imperial Beach locations being under closure 25 of 31 days (compared to zero days in May 2021 and 11 days in May 2020), Silver Strand closed for 16 of 31 days (compared to zero days in May 2021 and two days in May 2020) and Coronado shoreline closed for 11 of 31 days (compared to zero days in May 2020 and 2021).  

  It was anticipated that by using a more precise ddPCR method that amplifies DNA in water samples to measure fecal indicator bacteria, there could be increased impacts, such as advisories and warnings, to south county beaches affected by cross border sewage flows. We communicated this possibility with our stakeholders as the method went through the approval process. The new ddPCR testing is working. It is providing us with more detailed, higher quality data on what is happening in our beach waters and providing us with the opportunity to better inform the community to protect their health and prevent potential risks of illness. We are not seeing increased closures occurring in other communities outside of the south county, even though we are utilizing the new ddPCR testing method to test beach waters for the 70 miles of San Diego county’s coastline.

  Years of thorough research, study, and side-by-side testing were conducted by federal, state, regional, and local agencies to be able to use the new ddPCR testing method. After this rigorous evaluation, determinations of Enterococcus bacteria contamination thresholds (health standards) equivalent to the existing culture based live bacteria growth method were established and agreed upon by federal, state and local agencies. Findings were published in peer reviewed journals, evaluated by public and environmental health professionals, and guided by a technical advisory group of researchers, scientists, and academic experts in the field, ultimately resulting in U.S. Environmental Protection Agency and State authorizations for the County to use the ddPCR method.

  The agreed upon health standards for the new ddPCR method are what the County is using to make beach management decisions, such as when to issue an advisory or closure. State law requires local health officers to issue advisories when ocean or bay water sample results exceed State health standards due to high bacteria levels. State law also requires local health officers to issue closures in the event of a known untreated sewage release adjacent to a public beach or a sewage release that is known to have reached the recreational waters.

  It is our goal to ensure that San Diego County residents have daily access to safe and healthy beaches. In doing so, it is important to address the root cause of the problem and the sources that are contaminating the beach waters. Additional funding, advocacy, and actions to prevent cross border sewage flows, and greater elevation of the public health crisis in the Tijuana River Valley are important factors that should be addressed to end these systemic issues.

  The County has received concerns from stakeholders and members of the community regarding the new testing method and recent increases in water contact closures. Concerns regarding what qualifies as a closure related to Enterococcus bacteria contamination thresholds approved by the US Environmental Protection Agency and CA Department of Public Health, would need to be discussed with these federal and state agencies to ensure protection of public health and may require changes to State laws or regulations

• EPA Approval to Implement Beach Water Quality Rapid Detection Method for Recreational Beaches in San Diego County

  EPA Letter: Approval to Implement ddPCR for Beach Water Quality Rapid Detection Method for Recreational Beaches in San Diego County (pdf) (October 6, 2020)