Chemical and Microbial Markers for Discriminating Sanitary Sewer Contamination in Coastal, Urban Streams

Abstract

Water quality benchmarks for fecal indicator bacteria (FIB) are often exceeded in many urban streams in southern California. Possible sources of elevated stream FIB concentrations within urban areas include sanitary sewer exfiltration, sanitary sewer overflows (SSOs), illegal discharges, and human or animal fecal material on the ground surface. Teasing apart the different sources remains a challenge, especially when untreated wastewater and runoff from open defecation sites both contain human fecal material. To distinguish the various sources of microbial contamination in an urban stream, temporal trends in biological and chemical markers of anthropogenic contamination were evaluated in the San Diego River and its tributaries during storm events in two consecutive hydrologic years. Temporal trends in FIB, HF183, pepper mild mottle virus (PMMoV), caffeine, sucralose, chloride, bromide, specific ultraviolet absorbance, and fluorescence index indicated that untreated wastewater flushed from the vadose zone was the main source of microbial pollution to the San Diego River, while open defecation near homeless encampments in the river margins was not a major source. We demonstrated that the combined use of caffeine/sucralose ratios and HF183 and PMMoV holds promise for identifying sewage inputs to surface waters. These findings highlight the need for maintenance and repair of aging sewer infrastructure.

Geospatial Variability of Fluorescent Dissolved Organic Matter in Urban Watersheds: Relationships with Land Cover and Wastewater Infrastructure

“…Other studies have employed these two CECs as wastewater indicators. For example, similar sucralose (e.g., 590–3,360 ng L –1 ) and caffeine (e.g., 40–1,650 ng L –1 ) levels were reported in the San Diego River watershed, and their presence was attributed to sanitary sewer leaks and overflows . The wastewater-impacted Simeo and San Leonardo Rivers in Italy contained 32–1032 ng L –1 sucralose and 24–4,478 ng L –1 caffeine .…”

“…For example, similar sucralose (e.g., 590−3,360 ng L −1 ) and caffeine (e.g., 40−1,650 ng L −1 ) levels were reported in the San Diego River watershed, and their presence was attributed to sanitary sewer leaks and overflows. 11 The wastewater-impacted Simeo and San Leonardo Rivers in Italy contained 32−1032 ng L −1 sucralose and 24−4,478 ng L −1 caffeine. 55 However, the CEC levels were lower than those reported in Florida, where up to 35,666 ng L −1 sucralose and 30,293 ng L −1 caffeine were measured in surface water and groundwater impacted by wastewater effluent and septic systems, respectively.…”

“…To differentiate DOM sources, some have adopted parallel factor analysis (PARAFAC) of excitation–emission matrices (EEMs) to identify unique components that can be collectively used to model the fluorescence signatures of environmental samples . Using EEM-PARAFAC, previous studies have evaluated the composition of fluorescent DOM (FDOM) in aquatic environments influenced by agriculture, forests, wastewater effluent, sewer leaks, − and septic systems…”

Water, sanitation, and hygiene access among people who inject drugs in Tijuana and San Diego in 2020–2021: a cross-sectional study

“…In the case of the Tijuana River, the lack of capacity in the wastewater treatment system contributes to untreated wastewater discharges, especially during rain events, which has been described as the most important source of human contamination [22,37,38]. Similarly, in the San Diego River, researchers found chemical markers indicating that high levels of fecal contamination during storm events are primarily from leaky sewers and not open defecation [39].…”

Ratio of HF183 to PMMoV in Sewage and Its Change When Exposed to Different Temperatures and Sunlight Conditions

“…4,5 The use of ratios of human-associated source tracking markers with contrasting levels of persistence, such as caffeine and sucralose, or HF183 and PMMoV, may help distinguish the sources and age of human-associated fecal pollution in surface waters. 6,7 Therefore, studying the ratio of HF183/ PMMoV and the change in this ratio under specific environmental conditions might help identify the approximate "age" or "freshness" of human fecal pollution.…”