Environmental and Water Resources Institute (EWRI)

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Pathogens in Urban Stormwater Systems Prepared by Urban Water Resources Research Council


The single most frequent cause of water quality impairment in the U.S. is elevated fecal indicator bacteria (FIB) (EPA 2014). FIB-related impairments can have significant and costly implications for local governments, businesses, and watershed stakeholders due to beach closures and total maximum daily load (TMDL) compliance and implementation requirements to address these impairments. TMDLs and associated municipal separate storm sewer system (MS4) NPDES permit requirements for FIB load reductions pose unique challenges relative to TMDLs for chemical constituents. FIB are living organisms that occur naturally in the environment and whose sources can move freely throughout watersheds and storm drain systems, even when anthropogenic sources of FIB are controlled. Furthermore, FIB are generally not a direct cause of human health impacts; instead, they are easy-to-measure surrogate parameters that are intended to infer that fecal wastes and associated pathogens may be present. Nonetheless, FIB are currently considered to be the best available practical alternative to monitoring for multiple pathogens associated with human and animal wastes. Although the human health risk associated with exposure to waters impacted by untreated or poorly treated human sewage is well documented, the health risk from recreational exposure to elevated FIB in urban runoff-impacted receiving waters is less well known. 

The state of the art and practice in modeling transport and fate of FIB (and pathogens) involves significant uncertainty, more so than traditional water quality constituents. This uncertainty carries forward into evaluation of FIB management strategies, development of appropriate wasteload and load allocations for TMDLs, and regulatory decisions. Nonetheless, MS4 owners/operators are often assigned wasteload allocations in urban FIB TMDLs and may face significant wasteload reduction requirements, which are enforceable through MS4 discharge permits. Although management and correction of human sources of FIB (e.g., leaking sanitary infrastructure, illicit connections, dumpster drainage) to storm sewer systems can reduce FIB loads posing human health risk, many MS4s will need to reduce FIB from other sources as well to meet wasteload reduction targets. Identifying the sources of FIB and their relative contributions can be complex and costly. Load reductions are difficult, especially for the natural, non-human FIB sources, for multiple reasons (e.g., ubiquitous nature of FIB, current limits of technology related to urban stormwater controls, magnitude of reductions targeted). For these and other reasons, there are real questions regarding the attainability of FIB water quality standards in urban watersheds and in MS4 discharges. Depending on the sources of FIB affecting a particular receiving water and the manner in which MS4 permit compliance is assessed, dry weather standards may be attainable in some cases, but consistently attaining standards under wet weather conditions may be infeasible. 

To support MS4 permit holders and watershed stakeholders in developing realistic goals and effective strategies for addressing pathogens in urban stormwater systems, this report consolidates information on many facets of FIB impairments, providing information on the following topics: 

  • Basic background related to regulatory context, pathogens in receiving waters and the use of FIB as surrogates for pathogens. Pathogens in Urban Stormwater Systems August 2014 UWRRC Technical Committee Report Page xviii 
  • Sources of pathogens in the urban environment. 
  • Transport and fate issues, along with the factors affecting survival of pathogens and FIB. Although an evaluation of models for FIB is beyond the scope of this report, understanding of transport and fate issues affects the ability of water resources scientists and engineers to develop models for FIB. 
  • Approaches for monitoring, source tracking and evaluating FIB and pathogen data, including a discussion of challenges associated with these activities. 
  • Source controls and treatment strategies, including expected effectiveness, data gaps and practical constraints related to source controls, structural stormwater controls, and disinfection. 
  • Case studies illustrating challenges and approaches to implementing and complying with FIB TMDL requirements in urban areas. 
  • Conclusions and recommendations for additional applied research needs related to pathogens in urban stormwater systems and complying with FIB and/or pathogen TMDLs.
Click here for the full report

About EWRI

Created in 1999, the Environmental & Water Resources Institute (EWRI) is a civil engineering specialty institute of the American Society of Civil Engineers (ASCE), the country's oldest national engineering society. EWRI services are designed to complement ASCE's traditional civil engineering base and to attract new categories of members (non-civil engineer allied professionals) who seek to enhance their professional and technical development. The Pittsburgh Chapter of the EWRI was initiated in 2000.

EWRI was formed in keeping with the Strategic Plan of ASCE to provide improved and comprehensive products and services to a variety of engineering teams working in technical, educational, and professional areas. Former ASCE Technical Division enrollees (Environmental Engineering, Water Resources Engineering, Water Resources Planning and Management - as well as the Water and Environmental Standards Council), form EWRI's 20,000 person membership base. The former Divisions and Council have a long and successful record of performance. EWRI expands on the strong core of products and services originated by these members.

The vision for the EWRI is to be a recognized worldwide leader within ASCE for the integration of the technical expertise and public policy into the planning, design, construction and operation of environmentally sound and sustainable infrastructure impacting air, land, and water resources. To accomplish this vision, EWRI is committed to:

  • A diverse and empowered membership
  • Excellence in products and services
  • Collaborative partnerships
  • Innovative programs and solutions

The mission of the EWRI is to provide for the technical, educational and professional needs of its members; promotes the sustainable use, conservation, and protection of natural resources; and promotes human well-being by:

  • Advancing the knowledge and improving the understanding of relevant sciences
  • Improving the practice of engineering
  • Partnering with national and international organizations
  • Providing public policy input to governmental decision-makers

The Pittsburgh Section EWRI plans and conducts activities to retain current members and encourage member participation. Typically the EWRI conducts 3 to 4 dinner meetings and one day-long seminar each year. Dates for these events will be published in the ASCE Section newsletter and will be posted on the Section website.

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Please contact EWRI Chair

Nur H. Orak

626 Cochrans Mill Rd
Pittsburgh, PA 1523


Chair: Nur H. Orak

Past Chair: Gregory Scott

Vice Chair: Christina Urbanczyk

Treasurer: Ben Briston

Secretary: John V. Stullken


As part of the ASCE Pittsburgh Section Strategic Planning the EWRI has set the a goal to increase work with the Pittsburgh Chapter Sustainability Committee to promote the Envision Sustainable Infrastructure Rating System during the 2015-2018 period. Read more here

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