Human fecal contamination sources identified at Inner Cabrillo Beach during QMRA study

Posted April 28, 2017

A SCCWRP-led effort to use a health risk modeling approach known as Quantitative Microbial Risk Assessment (QMRA) at Inner Cabrillo Beach in Los Angeles County has turned up evidence that microbial contamination at the beach is largely from human sources.

The conclusion, which was reached by the project’s advisory committee in February, means that the QMRA analysis cannot move forward until repairs are made to sanitary sewer infrastructure in the area. The QMRA risk modeling approach is designed for use only at sites where microbial contamination sources are not predominantly human; human contaminant sources are much more likely to contain pathogens that can make humans sick.

After reviewing the water-quality data at Inner Cabrillo, the committee determined that the frequency of detectable levels of a genetic marker for human fecal material was too high to proceed with the QMRA. During a subsequent examination of the sanitary sewer infrastructure at the beach, the Port of Los Angeles identified numerous potential issues that could be contributing to the beach’s elevated contamination levels. Repairs are expected to take at least one year.

In the interim, SCCWRP and the Port of Los Angeles will conduct studies in the harbor area surrounding the beach to determine whether a wastewater plume from a nearby treatment facility on Terminal Island may also be a source of human fecal material to the beach.

Inner Cabrillo is a popular swimming spot in the Los Angeles Harbor area where fecal indicator bacteria concentrations frequently exceed water-quality guidelines. More than $20 million has been spent to reduce contamination levels, but bacterial concentrations continue to exceed objectives; the beach has a TMDL (total maximum daily load) for fecal bacteria.

The QMRA can resume after all possible sources of human contamination to the beach have been abated or characterized as minimal.

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