San Clemente study links pigeon droppings, street flows to pier bacteria, finds measurable improvement after abatement

SAN CLEMENTE, Calif. — A multi‑year source‑tracking study of bacteria near the San Clemente Pier found elevated indicator bacteria in sand and at pipe outfalls driven largely by bird roosting and landscape/drainage flows, researchers told the Coastal Advisory Committee on April 3.

The study, presented by Ted Von Dittner of WSP and introduced by Nikki Beach, environmental program analyst for San Clemente, used conventional culture tests and faster molecular genetic markers to identify likely sources. "Did this result in measurable improvements? The answer is yes," Von Dittner said, citing reductions in surf‑zone bacteria and changes in public health postings.

The study began in 2018 after Heal the Bay and Orange County Health Care Agency monitoring showed the pier as a hot spot. City staff and outside consultants formed a stakeholder advisory committee and conducted repeated watershed walks, CCTV inspections of drains and sewers, sand sampling, and microbial source tracking that targeted human, bird and dog genetic markers.

Why it matters: state rules set numeric bacteria targets with an enforcement deadline of April 4, 2021, for dry‑weather conditions; failure to meet those targets can trigger regulatory enforcement or lawsuits. The committee was told the study was explicitly designed to identify and reduce sources so the city would meet those targets and avoid enforcement.

Key findings and actions - Sand under and above the high tide line contained some of the highest concentrations of indicator bacteria; samples of visible pigeon droppings returned the highest values in sand tests. That led the team to prioritize bird roosting as a major contributor. - Genetic marker testing detected human markers in a subset of samples but, after targeted inspections and repairs (including sewer CCTV and lateral repairs), the team concluded human sewage was not a continuing major source for the pier bowl watershed. Von Dittner stated the city’s source‑abatement actions produced measurable drops in human marker counts at monitored storm drains. - The city installed pigeon‑deterrent netting under the restaurant/restaurant‑pier area after other measures provided limited benefit. Von Dittner displayed before‑and‑after sampling showing fewer beach postings and lower geometric‑mean exceedances after the nets were installed. He said the number of beach postings fell from just under 20 days per year to fewer than five, and independent assessments by Heal the Bay upgraded the pier area to an A grade by 2022. - Investigations also documented nonsewer sources: leaking trash trucks, restaurant floor drains discharging to streets, and irrigation/landscape runoff. Staff worked with a restaurant to fix an improper drain connection and tracked trash‑truck discharges as part of the abatement work.

Methods and caveats The team used culture‑based fecal indicator bacteria (slower tests, historically used for regulatory decisions) and molecular microbial source tracking (DNA markers such as human‑specific markers) that return results in hours and can be source‑specific. Von Dittner and Beach emphasized limitations: genetic markers can detect free DNA from treated or recycled water (a so‑called false positive) even if no viable pathogens are present. The presentation described chemical sample pretreatment methods and complementary tracers (e.g., sucralose) used during investigation to distinguish live sewage from noninfectious DNA.

Next steps and regulatory context Speakers said the study provides a model approach for other local beaches and for addressing an upcoming wet‑weather numeric target (a separate regulatory requirement with a later deadline). The committee was told that fully complying with wet‑weather numeric targets could require major infrastructure (large capture and disinfection tanks) and that the San Clemente approach — targeted, lower‑cost source abatement across the watershed — is a desirable alternative when it reduces measured bacteria.

The full technical report and appendices are posted on the city's Clean Ocean Program and Water Quality Programs webpages and were linked in the meeting packet, Nikki Beach said. "If you need help finding it, just let me know," she added.

Reported speakers and attributions in this article are limited to those who spoke during the presentation and Q&A: Ted Von Dittner (WSP), Nikki Beach (San Clemente environmental program analyst) and Chair Susan Ambrose. The report and presentation materials were prepared by WSP and San Clemente staff.