Sources & Mitigation Study
SOURCES AND MITIGATION OF WATER QUALITY IMPAIRMENT
Introduction and Report Overview
IN AVALON BAY, CATALINA ISLAND, CALIFORNIA
The City of Avalon, located on Catalina Island, is a recreational destination for boaters, fisherman, divers, beach goers, and other ocean oriented visitors. In 1999 the County of Los Angeles began testing Avalon Bay for fecal indicator bacteria in accordance with AB 411. These test results frequently exceeded California single-sample standards for fecal indicator bacteria in coastal bathing waters, and as a result beaches in Avalon have been frequently posted as unfit for swimming.
In response to these test results, a series of studies and mitigations efforts were undertaken:
a) In 2000, Ms. Alison Davis in Jed Fuhrman’s laboratory at USC was hired to conduct a microbial source tracking study, to determine if there was evidence of human fecal pollution in Avalon Bay. This study, which was very small in scope, found no evidence of human viruses in Avalon Bay. Based on the results of this study, the City concluded that the fecal indicator bacteria problem in Avalon Bay was due to fecal material produced by birds, in particular pigeons. Accordingly, the City focused on controlling bird populations in and around the City
b) In 2001, the City received a $500,000 grant from the State of California’s Clean Beaches Initiative to further investigate the water quality problem in Avalon Bay, and pursue mitigation measures. This grant had three goals: 1) to determine the sources of fecal indicator bacteria in the Bay, 2) to conduct further microbial source tracking studies, and 3) to characterize circulation in Avalon Bay. These studies, which were conducted by Professors Stanley Grant (UCI), Burt Jones (USC), and Jed Fuhrman (USC) between September and November 2001, concluded that:
i. Fecal indicator bacteria in Avalon Bay appear to originate from several land-side sources, including bird and animal fecal droppings, broken plumbing under wharf structures, run-off from street wash down activities, and contaminated shallow groundwater.
ii. Within Avalon Bay, fecal indicator bacteria concentrations are highest in ankle depth water along the shoreline. Fecal indicator bacteria concentrations in the water and sediment are generally below detectable levels a very short distance (<10 m) bayward of the shoreline.
iii. Microbial indicators of human fecal pollution (including the human-specific bacteria Bacteroides/Provetella and human enterovirus) were detected at several locations in Avalon Bay and in groundwater sampling pits, suggesting that human sewage may contribute to water quality impairment of Avalon Bay.
iv. The rates of advection and turbulent diffusion within Avalon Bay (ca. 1 to 6 cm/s and 1 m2/s, respectively) is sufficient to disperse contaminants introduced to the Bay within an hour or so, provided that the source of contamination is not continuous.
v. A significant fraction of the water in Avalon Bay is exchanged with the ocean over a single tide cycle.
vi. The region of the Bay impacted by the storm drain (near the beach site called “Channel”) does not appear to have a circulation problem. Within one hour, pollutants released into this area of the Bay are transported 80 to 100 m into the Bay and diluted by a factor of 100 or more.
Based on these study results, the City implemented the following mitigation measures:
a) Sewer mains and manholes in the first three blocks from the waterfront were slip-lined and sealed; this effort was completed in May, 2002.
b) Bird control measures were intensified; this ongoing effort was initiated in 2001.
c) Plumbing under the wharfs was repaired and a regular twice per year inspection program initiated.
d) Street wash down procedures were modified to prevent run-off.
e) Sewer laterals in the first three blocks from the waterfront were repaired and sealed; this effort was initiated in May 2005 and completed in November 2005.