BACKGROUND
Distinguishing anthropogenic fecal pollutant inputs to streams is currently one of the most pressing environmental challenges for urban water managers. Although stormwater enters urban waterways from municipal separate storm sewer systems (MS4s) rather than from combined sewer systems (CSSs), streams and rivers in Southern California often exceed water quality targets for fecal indicator bacteria, and human pathogens have been detected during wet weather conditions. Pathogenic microorganisms and other pollutants may be introduced to streams from both surface and subsurface sources, including sanitary sewer overflows, sewer exfiltration, leaky septic tanks, illegal discharges, illicit storm sewer connections, and runoff from waste associated with homeless encampments. However, the relative importance of different sources is not yet well understood for many urban watersheds, including the San Diego River watershed.
OUR WORK
SDSU researchers from the Department of Civil, Construction, and Environmental Engineering's WIRLab, Safe WaTER Lab, and Disturbance Hydrology Lab, the School of Public Health, and the School of Public Affairs teamed up with the San Diego River Park Foundation and water managers in the region to intensively study the sources of microbial pollutant inputs during storm events and during dry weather. We quantified microbial source tracking (MST) markers, including Escherichia coli, enterococci, bacteroides (HF183), Campylobacter jejuni, pepper mottle mild virus, norovirus, and Hepatitis A virus, and chemical markers such as caffeine and sucralose in water and soils to evaluate pollutant inputs to the San Diego River and its tributaries from two main sources: 1) untreated wastewater (derived from sewer exfiltration or sanitary sewer overflows) and 2) fecal waste associated with homeless encampments. The study was conducted from January 2018 to March 2019 and focused on the two hydrologic years following the Hepatitis A outbreak in San Diego, which included cases among the unsheltered population in San Diego. The MST and chemical markers used can help distinguish human-associated fecal pollution from general fecal pollution (which can also originate from other warm-blooded animals, such as dogs, cats, and birds). The high temporal resolution of the storm sampling, combined with multiple lines of evidence from conservative tracers and optical spectroscopy, further allowed our team to tease apart untreated wastewater sources from open defecation sources of fecal pollution.
OUR TEAM
Investigators:
- Natalie Mladenov (WIRLab), Matthew Verbyla (Safe WaTER Lab), Alicia Kinoshita (Disturbance Hydrology Lab), Rick Gersberg (School of Public Health), Tom Zink (Soil Ecology and Restoration Group)
- Jose Calderon: Evaluation of microbial source tracking markers for human-associated fecal contamination to a river from non-point sources
- Mireille Garcia: Influence of homeless encampment waste on surface water quality during dry weather
- Federick Pinongcos: Anthropogenic sources of contamination in the San Diego River during storm events
- Mia Gil: Persistence of bacteria and viruses in soils contaminated with wastewater
OUR FINDINGS
Key highlights from our collaborative study:
The findings from this collaborative study are available here:
- Homeless encampments did not have a significant influence on microbial pollution of surface waters during dry weather.
- There was microbial contamination of soils at homeless encampment sites, even after site cleanup.
- Wastewater-spiked soils (simulating sewer exfiltration and sanitary sewer overflows) continued to be a source of E. coli, enterococci, bacteroides (HF183), and pepper mottle mild virus even after 4 months.
- Caffeine and HF183 are found in high concentrations in untreated wastewater and almost undetectable in simulated stormwater runoff from soil with open defecation.
- Microbial and chemical markers revealed that untreated wastewater is likely to be the main source of San Diego River pollution during storm events.
The findings from this collaborative study are available here:
Funding provided by: California State Water Resources Control Board, Region 9, the San Diego River Conservancy, San Diego State University Division of Graduate Affairs, Office of Council member Scott Sherman (District 7) of the City of San Diego, Office of Council member Lori Zapf (District 2) of the City of San Diego, William E. Leonhard Jr. Endowment.