Temporal and spatial patterns for surf zone bacteria before and after disinfection of the orange county sanitation district effluent

Data from pre- and post-disinfection fecal indicator bacteria (FIB) samples from final effluent, an offshore ocean outfall, and surf zone stations off Huntington Beach, CA were compared. Analysis of the results from these data sets confirmed that the ocean outfall was not the FIB source responsible for the postings and closures of local beaches that have occurred each summer since 1999. While FIB counts in the final effluent and offshore showed several order of magnitude reductions after disinfection, there were no significant reductions at the nearby surf zone stations. Additionally, the FIB spectral patterns suggest different sources. The dominant fortnightly cycle suggested that the source was related to the wetting and draining of the land from large spring tide tidal excursions.