Pathogens and Fecal Indicators in Stormwater

Pathogens, fecal-indicator bacteria (FIB), and viruses carried by urban stormwater runoff are among the leading causes of water body impairment in the United States. The goal of this special collection was to advance the state of knowledge in this field by bringing together the latest research and advances in the state of the practice on pathogens and fecal indicators in urban stormwater. Despite the importance of this topic, few researchers are working in this area, possibly due to the logistical difficulties and expense involved in carrying out stormwater pathogen and fecal-indicator studies. Research needs identified by the guest editors included:

In 2014, the Urban Water Resources Research Council of the ASCE Environmental and Water Resources Institute (EWRI) completed Pathogens in Urban Stormwater Systems as a technical resource for stormwater managers and local governments in complying with federal Clean Water Act requirements regarding elevated fecal indicators in urban runoff (Clary et al. 2014). Clary et al. (2022) revisited the eight applied research and policy needs identified in the 2014 EWRI report as a forum paper for the special collection to promote dialogue on the topic. The authors note that since the EWRI report was published, there is still no clear path to FIB standards attainment for stormwater managers. There are several areas where progress has been made, such as the use of host-specific DNA markers to identify sources of bacteria. However, these methods are only accessible to communities with available budgets to apply these tools. Many of the research gaps identified in the 2014 report remain largely unfilled, such as the need for rigorous FIB performance studies for nonstructural BMPs, including catch basin and storm drain cleaning and outreach-, education-, and enforcement-based programs. The authors note that there is still a pressing need for “a national policy-level dialogue regarding regulatory options that are protective of human health, while recognizing practical economic constraints facing local governments.” ASCE forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The authors of this paper invite readers to share their successes, challenges, and perspectives on ongoing research needs.

McKee and Cruz (2021) provide a state-of-the-art review of microbial and viral pathogen indicators of fecal contamination. The paper is a useful overview for stormwater managers, researchers, and students seeking an understanding of the methods used to assess health risks from recreational exposures to freshwater contaminated with fecal matter. The authors provide a historical overview of traditional methods and track how the science has evolved in recent decades. Methods discussed include culture-based methods for enumerating Escherichia coli (E. coli), enterococci, and Clostridium perfringens (C. perfringens), microbial source tracking using quantitative polymerase chain reaction (qPCR), and metabarcoding using high-throughput sequencing. A comprehensive discussion of viral indicators is provided, including use of the gut-associated bacteriophage crAssphage, which has been recently discovered in human fecal microbiomes, and plant-based pathogens that are present in human feces, such as pepper mild mottled virus and tobacco mosaic virus. The authors also review several meta-analyses comparing the presence of fecal indicators with health outcomes from freshwater recreational exposures. A number of research gaps are identified, including determining pathogen recovery efficiencies using different concentration and extraction methods, investigation of fate and transport of microbial source tracking markers, fecal indicators and pathogens, and additional studies to understand health risks due to exposure to fecal contamination from different sources.

Green infrastructure approaches, such as bioretention systems and bioswales, have demonstrated variable performance in mitigating fecal contamination. Hayes et al. (2023) investigated the performance of four green infrastructure systems in mitigating E. coli from a roadside site in Virginia: bioretention, bioswale, a grass channel, and a compost-amended grass channel. Although prior studies have investigated FIB mitigation from green infrastructure using discrete grab samples, this study used flow-weighted composite sampling for 12–19 events over 2 years to allow concentration and load reduction calculations for different seasons. The authors also investigated various water quality and environmental factors that affect FIB export from green infrastructure, including precipitation, antecedent dry conditions, temperature, and concentrations of suspended solids, total dissolved nitrogen, dissolved organic carbon, and chloride. Bioretention effectively reduced both concentrations and loadings of FIB, while the swales increased E. coli concentrations but had little effect on mass load. Geometric mean outflow FIB concentrations were greater than USEPA recreational water quality criteria and were positively correlated with average daily temperature and dissolved organic carbon concentrations. The results confirm the need for robust sampling programs to understand the fate of FIB in green infrastructure systems.

Chlorinated wastewater effluent is commonly used in Florida and other regions of the country for landscape irrigation and mixes with runoff during storm events. Applications of stormwater runoff chlorination include disinfection of combined sewer overflows and stormwater reuse applications. Although chlorine demand models have been developed for drinking water source waters and wastewater, there is a lack of information on chlorine demand kinetics for urban runoff. Dickenson and Sansalone (2022) developed a chlorine demand model for urban runoff that incorporates a parallel second-order demand model for the dissolved chemical oxygen demand (${\mathrm{COD}}_d$) and a second-order potential driving model for different functional particulate matter size fractions (suspended, settleable, sediment). The model was calibrated and validated using data from completely mixed batch reactor chlorine demand studies using runoff from a parking lot in Gainesville, Florida. Experiments were designed to elucidate chlorine demand kinetics of ${\mathrm{COD}}_d$ and size fractionated particulate matter in runoff collected from different storm events. The results showed that there is significant chlorine demand for different particulate matter fractions, with the greatest demand from sediment particulate matters, which had the highest organic content.

The Journal of Sustainable Water in the Built Environment aims to disseminate research findings, challenges, and opportunities on water issues throughout the developed landscape, including issues related to pathogens and fecal indicators in stormwater. The journal is a natural fit for this special collection addressing issues of identification and quantification of pathogens and fecal indicators, risk assessment, BMP performance, and policy issues. We encourage future submissions on this topic to this journal. Further related research work may be added to the special collection later.

We thank our authors for their outstanding contributions to this special collection and the reviewers for all their hard work helping to improve the quality of the published articles.