Using Microbial Source Tracking Tools to Support Public Health Decision Making: Evaluating Beach Water Quality Following Emergency Disposal of Post-Fire Debris Flow Sediment
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Following the Thomas Fire and subsequent Montecito debris flow in January of 2018, emergency actions were taken by the County of Santa Barbara (County) to remove mud and sediments from roads, creeks, and debris basins.

A portion of the material removed from roads and creeks was transported to Goleta Beach approximately 13 miles east of Montecito for disposal. Following the completion of disposal, surf zone water quality monitoring of indicator bacteria (Enterococcus, E. coli, and Total Coliform) remained elevated compared to State standards for several months. Due to the unknown presence of human waste in materials and the potential for elevated public health risks due to pathogens associated with human waste in the surf zone following disposal, the County closed the surf zone to water contact recreation throughout this period.

In May 2018, a study was conducted by Geosyntec Consultants to 1) determine if sands and remaining sediments at the beach were causing or contributing to surf zone bacteria exceedances, 2) identify the spatial extent of elevated bacteria levels in the surf zone and beach sands, and 3) determine if human waste was contributing to bacteria exceedances. Sand and surf zone samples were collected at five locations across the beach on four consecutive days. Samples were analyzed for indicator bacteria and a DNA marker specific to human waste (HF183). Combined with results from ongoing AB411 fecal indicator bacteria monitoring by the County, previous DNA marker sampling at the beach by Geosyntec and a local university (establishing pre-disposal conditions), and human DNA marker and pathogen analysis performed by a local university during and immediately following the disposal, these results showed that although indicator bacteria were elevated across the surf zone due to sands and sediments, human waste was not a significant source of contamination and therefore there was not elevated health risk through water contact recreation. Data analysis also showed that surf zone bacteria concentrations were steadily improving over time after the completion of emergency disposal actions.

This information supported the County in its decision to reopen the beach to water contact recreation in July 2018 after surf zone bacteria levels had dropped below State standards in consecutive samples. And when subsequent bacteria monitoring results were intermittently above the State standard, beach warnings were posted rather than a full closure, based on established procedures for beach posting in non-sewage impacted waters. Additional emergency actions for disposal of debris basin sediments in the Montecito area were conducted at Goleta Beach in February of 2019. Sampling and analysis of debris basin materials, beach sands, and surf zone waters were again conducted to confirm that debris basin sediments did not contain human waste contamination and that sediment disposal did not result in an increased illness risk for water contact recreation in the surf zone.

This presentation will highlight the unique use of microbial source tracking analysis to support County beach management decisions during emergency actions. Results and project conclusions will be discussed and the potential use of these tools for other similar applications will be explored. The audience will be invited to participate through a Q&A session on the utility of these tools for other example applications. This presentation is directly related to the conference's theme as it incorporates leading science and technology to assess the health of a recreational water under a unique water quality challenge.

Publication Summary

  • Geosyntec Authors: Jared Ervin, Brandon Steets
  • All Authors: Jared Ervin, Brandon Steets
  • Title: 2019 CASQA Annual Conference
  • Event or Publication: Event
  • Practice Areas: Watershed and Water Quality Studies and Modeling, Sediment Assessment and Remediation
  • Citation: Geosyntec will make substantial technical contributions at the California Stormwater Quality Association (CASQA) Annual Conference at the Monterey Conference Center in Monterey, California on October 7-9, 2019.
  • Date: October 7-9, 2019.
  • Location: Monterey, California
  • Publication Type: Platform Presentation