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Factors Influencing the Distribution of Fecal Bacteria in Stormwater in the City of San Diego

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Bacteria advisories are often issued in San Diego after a major storm event because of the gastrointestinal diseases associated with high fecal bacteria counts. Fecal coliform bacteria and enterococcus are two fecal indicator bacteria that are monitored throughout the City of San Diego (City) and are often found to be of exceedance of the total maximum daily load (TMDL), a measure of nonpoint-source pollution level. To better address this exceedance, we studied what factors are influencing the distribution of fecal bacteria within the City. We delineated watershed areas from the digital elevation model of San Diego that lead to each monitored outfall in FY17. We standardized the outfall values to watershed area and compared them to the weighted averages of physical and social conditions within each watershed. While there was no significant correlation between bacteria counts and the physical condition of the watersheds, there were trends suggesting higher bacteria counts to be associated with higher populations, lower population densities, and larger drainage areas. Additionally, large counts of enterococcus were found in drainage areas with large Hispanic population (r = 0.608, p-value = 0.002), while small counts of fecal coliform were seen in drainage areas with large white populations (r = -0.429, p-value = 0.036). Fecal bacteria concentrations appeared to be related to both physical and social factors, which will help jurisdictions target their water quality improvement initiatives in vulnerable areas.

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Factors Influencing the Distribution of Fecal Bacteria in Stormwater in the City of San Diego

Bacteria advisories are often issued in San Diego after a major storm event because of the gastrointestinal diseases associated with high fecal bacteria counts. Fecal coliform bacteria and enterococcus are two fecal indicator bacteria that are monitored throughout the City of San Diego (City) and are often found to be of exceedance of the total maximum daily load (TMDL), a measure of nonpoint-source pollution level. To better address this exceedance, we studied what factors are influencing the distribution of fecal bacteria within the City. We delineated watershed areas from the digital elevation model of San Diego that lead to each monitored outfall in FY17. We standardized the outfall values to watershed area and compared them to the weighted averages of physical and social conditions within each watershed. While there was no significant correlation between bacteria counts and the physical condition of the watersheds, there were trends suggesting higher bacteria counts to be associated with higher populations, lower population densities, and larger drainage areas. Additionally, large counts of enterococcus were found in drainage areas with large Hispanic population (r = 0.608, p-value = 0.002), while small counts of fecal coliform were seen in drainage areas with large white populations (r = -0.429, p-value = 0.036). Fecal bacteria concentrations appeared to be related to both physical and social factors, which will help jurisdictions target their water quality improvement initiatives in vulnerable areas.