No Smoking Gun? How Do We Address Chronic but Low-Level Fecal Contamination? (A Case Study)
Fecal indicator bacteria (FIBs) are commonly measured to assess surface water quality and are proxies for fecal contamination in local watersheds, but they cannot specify the source of fecal pollution. At many regions, total maximum daily load (TMDL) criteria have also been developed, but in many cases the implementation plans do not distinguish among sources of FIBs. Various researches have reported that FIBs can originate from both human and non-human sources such as human waste, pet waste, wildlife and decaying vegetation. They can also sustain and even regrow in natural environment such as street gutter, stream sediment and sand grains for extended period of time given appropriate environmental factors (sunlight, moisture, temperature etc). Among various types of FIB sources at coastal urban watersheds, untreated human waste, which mostly likely contains potential harmful pathogens, has the greatest potential to cause gastrointestinal (GI) problems or other illness to people recreating at downstream water bodies (e.g. beach/bay). FIBs generated in the environment, on contract, are unlikely to pose such high health risks. To truly help protecting the recreational beneficial use of waterbodies, it has been widely acknowledged that, management resources, which are always limited, should be focused on controlling human waste to the extent possible. While eliminating all FIBs could potentially help lower the risk of illness, it can be an impractical or impossible task in many region.
Extensive source tracking efforts have been conducted in southern California over the past decades, lessons were learned and being learned at different watersheds. Numerous toolboxes were developed to help watershed managers to investigate and manage FIBs sources generated from human waste. Among all the toolboxes, HF183 marker has become one of the popular tools to supplement FIB monitoring to indicate possible presence of human waste due to its higher specificity to human waste than to FIB. When high level of HF183 is detected, it often serves as a valid trigger for an extensive source tracking effort to locate human waste upstream. When the detection is ubiquitous, chronic but low level, not only locating a “smoking gun” for next step investigation is challenging, prioritizing extensive investment in infrastructure repairment may also be a hard-sell. However, consistent positive results for human waste markers, even at low concentrations, likely signal a sustained input to the storm drain and it should not be neglected. This study will present a unique case under this scenario:
The Southern California Bight 13” Regional Monitoring Program samples were collected at multiple coastal streams in wet and dry weather to understand the magnitude and extent of human contamination in coastal urban watersheds. Among 16 sites, Costa Mesa Channel (CMC), a small tributary to Newport Bay where an existing bacteria TMDL is developed, had the second-highest HF183 detection frequency in dry weather. Its frequent detection of HF183 prompted a source investigation to confirm the presence of human source and determine areas of concern. This study will summarize the source investigative effort under a high frequency, low level detection scenario and its unique challenges. It will utilize a tiered strategy and a variety of tool boxes (e.g. visual observation, GIS, stakeholder interview, monitoring, CCTV) to help generating potential hypothesis, investigate potential sources that are known to the industry but infrequently studied (e.g. private lateral root intrusion etc.), evaluate the route of transport of such sources and discuss a number of feasible options that can be implemented to manage human waste under this scenario.