Human Fecal Contamination of San Pedro Creek
PCR (polymerase chain reaction) tests for specific genetic sequences. We used PCR to distinguish between bacteria from the guts of various warm-blooded animals.
This graph of PCR data shows human fecal contamination of San Pedro Creek. A genetic marker of a human gut bacterium, HF183, was detected in creek samples taken over the past year.
At the mouth of the creek, the amount of HF183 was 30 to 40 times the human health risk threshold (brown bars on 4/13/26 and 4/21/26). At two sites upstream of the mouth, Peralta Bridge and Adobe Sanchez, HF183 was 3 to10 times the human health risk threshold (yellow and green bars, 1/5/26 to 5/18/26).
The results suggest some kind of leakage from sanitary sewers near the mouth of the creek, or another unknown source (brown bars).
Lesser but still significant contamination was detected at the Peralta Bridge and Adobe Sanchez sampling sites (yellow and green bars), but not further upstream at the Linda Mar Blvd bridge site (red bars).
This correlates with the location of Orangeburg sewer laterals shown below. Orangeburg sewer laterals, made of a soft mixture of tar, were used as a cost-saving measure in the 1950s, and are known to be leaky. Unrepaired sewer mains in this area may also contribute to the contamination.
Areas with Know Orangeburg Laterals Identified by City Staff
Tests for other species such as dogs, ruminants (deer), avian species, and horses did not yield consistent results of the magnitude that HF183 did. The fact that human feces is much more of a health risk than other warm-blooded animal feces, leads us to focus on human PCR testing next year. We will try to narrow down the locations of leakage by sampling more sites along the creek, and storm sewer outfalls into the creek. more information on Orangeburg pipe see: https://en.wikipedia.org/wiki/Orangeburg_pipe
For more information on the use of PCR testing to determine the ricks the presence of the HF183 see the attached paper “Simulated gastrointestinal risk from recreational exposure to Southern California stormwater and relationship to human-associated Bacteroidales marker HF183 click on the icon below:
Click on Icon above to download the PDF