Kinnetic Laboratories, Inc

Scope Of Work

TINNER CABRILLO BEACH BACTERIAL TMDL COMPLIANCE
Inner Cabrillo Beach, located along the San Pedro shoreline inside the breakwater of the Port of Los Angeles, is a historic sheltered urban beach in use since the early 1900s. Exceedances of fecal indicator bacteria (FIB) criteria have been common at the beach for a long time, in excess of new Total Maximum Daily Load (TMDL) requirements, and an order of magnitude greater than at other sheltered beaches.

Bacterial source studies identified old sanitary and storm drainage systems that were replaced or repaired along with diversions of dry weather and first flush (0.25 inch rain) wet weather stormwater discharges. Despite these improvements, FIB exceedances continued at a high frequency. However, Harbor waters are generally clean except for a few days after significant rain events, thus dry weather bacterial sources were local to the beach. Water circulation is slow with a diurnal wind driven, two layer system that moves surface water offshore and bottom water towards shore. Fine sediments and organic particulate materials associated with the eelgrass beds in the swim area at – 1 ft MLLW were implicated in the FIB exceedances. Early genetic ribotyping results generally reflected observed sources at the beach including birds, feral cats, raccoons, etc. with human sewage estimated to be about 10-12 percent of the total.

Additional corrective actions implemented included plugging of an old abandoned sewage outfall, beach sand replacement to prevent ponding, and a rock groin removal to improve circulation. After completion of these corrective actions, FIB exceedances continued to occur during dry weather at high frequencies. However, new genetic biomarker data (live Bacteroidales genetic markers) clearly demonstrated that there was no longer evidence of human sources contributing to the observed violations.

Since City/Port discharges regulated under the Clean Water Act apparently have been eliminated, the DNA biomarker results raise a dilemma. The possibility exists for a natural source exclusion as provided for in the Harbor bacterial TMDL action, but this would be an application to a heavily used urban beach. Artificial circulation enhancement is complicated by the particulate nature of FIB contamination and the natural, wind driven bottom layer flow toward the beach. Major issues include conflicts between beneficial uses of essential marine habitat with recreational uses with at least partial eelgrass removal being a possible action.