How can you meet the challenges of the wet weather bacteria dilemma?

The Clean Water Act (CWA) mandates that surface waters of the United States should be of sufficient quality to be fishable and swimmable. In this blog, we will focus on the swimmable aspect of the CWA, more broadly described as any recreational activity involving water contact. What are the big challenges in meeting the regulations and making waters swimmable?

Let’s start with a discussion on the most common water quality impairment nationally: fecal indicator bacteria (FIB), E. coli or Enterococcus, and increased gastrointestinal illness (GI) risk from ingestion of water during water contact recreation. Improving water quality to reduce GI risk to swimmers from fecal contamination is the driver for many pollutant control projects and the goal of watershed managers nationwide.

FIB in watersheds originates from a range of hosts including human and non-human animals, and even naturalized colonies that can grow outside of an animal host. Even when considering fecal contamination of human origin (the most likely to cause GI in swimmers), the range of sources to target is widespread including:

• combined sewer overflows (CSOs)
• sanitary sewer overflows (SSOs)
• leaking sewers
• failing septic systems
• leaching from trash
• illicit discharges, and
• open defecation.

Once the source is identified, we turn our attention to controlling the bacteria. These “bacteria control plans” take many different forms, such as long-term control plans (LTCPs) to reduce CSOs, non-point source reduction plans (e.g., Nine Key Element Plans), and a range of Total Maximum Daily Load (TMDL) stormwater implementation plans. Generally, bacteria control plans are required by regulatory authorities to address CSOs/SSOs and in some cases, permitted municipal separate storm sewer systems (MS4s).

That brings us to the second challenge. Bacteria in watersheds are ubiquitous, and studies have shown that it’s economically and technically infeasible to meet recreational water standards for many impaired waters, especially in areas affected by wet weather. After decades of plan development and implementation, fecal bacteria impairments remain widespread. For most bacteria impaired waters in urban regions, there remains a massive implementation gap during wet weather conditions.

Given this dilemma, we provide several insights into the science and policy surrounding fecal bacteria impairment to help take stock and offer a path forward that is both technically feasible and protects public health in recreational waters.

Key areas of scientific uncertainty

• Indicator bacteria do not directly assess pathogen risk. Fecal contamination from different organisms pose widely varying GI illness risk to swimmers. FIB help us monitor general water quality conditions more extensively, but do not directly measure GI illness risk.
• Overvaluing outcomes from quantitative microbial risk analysis (QMRA). Scientists have thoroughly investigated the amount of human associated fecal contamination (measured as gene copies of the Bacteroides HF183 marker) that can be ingested within an acceptable risk level for GI when swimming. Researchers continue to lower gene copy density thresholds of HF183 representative of GI illness risk levels in recreational water quality criteria (32 illnesses per 1000 swimmers). Science may evolve further to suggest the most appropriate level of human fecal contamination to address GI risk is close to zero.
• Microbial source tracking (MST) and other tracers cannot pinpoint sources. Source tracking methods are not able to paint a comprehensive understanding (pie chart) of general FIB sources in downstream water samples. This makes it difficult to estimate downstream bacteria indicator load reduction that may be realized by targeting and eliminating the most pathogenic sources.
• Effectiveness assessment tools are not geared to parse targeted sources. Measuring fecal bacteria load reduction from source control programs requires use of more costly and less widely available advanced tools to parse sources and evaluate the effectiveness of practices targeting the most pathogenic human and controllable animal sources. These metrics differ from general FIB and may include using host-specific genetic tracers (Bacteroides HF183 marker) or actual pathogenic viruses (e.g. norovirus) or bacteria (e.g. Shigella).

Gaps between policy and implementation feasibility

• Implementing retrofit stormwater controls is expensive. For MS4s, nearly all wet weather runoff volume would need to be captured and treated to provide typically greater than 95 percent reductions in bacteria from urban stormwater sources. Given the ubiquity of general FIB sources in urban stormwater, widespread retrofits will be needed, and construction costs for such retrofits can exceed $1 billion for even a small city. Citywide retrofits could take multiple decades to implement given the large number of projects to address the spatially diffuse nature of urban stormwater. As controls are deployed, annual operations and maintenance needs are likely to rise to levels that are infeasible for most public works departments in the nation. The Water Environment Federation conducts a biannual national MS4 Needs Assessment survey, of which reductions in bacteria load is one element. In 2022, the survey results were used to estimate an annual funding gap of $6.2 billion per year nationally.
• FIB sources during wet weather conditions are difficult to pinpoint and reduce. Wet weather flow can follow many paths, so determining specific origins of fecal indicator pollution is challenging. Investigative studies may successfully identify a source category (i.e. septic or sewer systems, agricultural runoff, etc.) but resource intensive investigation is needed to pinpoint the exact location for corrective actions for source elimination.
• NPDES permits for MS4 inhibit use of one water approach in watershed management. Some NPDES permits narrowly focus on downstream water quality, thereby overlooking competing interests in watershed management. For example, an MS4 permit may prioritize retaining runoff in the watershed but that could reduce runoff volume downstream and negatively impact habitat, water supply uses, and in some cases, receiving water quality.

Sensible path forward

So yes, there are plenty of challenges, but none of them preclude progress. Recreation on the water is an important goal of the Clean Water Act, and there is a way forward to restore recreational uses. Given the varying pathogenicity of different sources of fecal bacteria load, watershed management that focuses on elimination human and other more pathogenic sources (e.g. cows) is likely to be more beneficial to protecting downstream recreational use than widespread deployment of regional structural drainage system retrofits. Non-structural source controls can be implemented at a watershed scale far more quickly than structural retrofits. Where non-structural measures are not effective, bacteria/microbial source tracking and enhanced illicit discharge detection and elimination (IDDE) programs can identify locations where neighborhood scale structural retrofits can be deployed strategically to address hot spots.

New regulations related to fecal bacteria at the federal and state levels should focus on source control and provide for a long-term implementation-based path to compliance in NPDES permits. This approach in bacteria TMDL development supports an implementation approach involving integrated planning, whereby all watershed stakeholders collaborate to prioritize more pathogenic fecal bacteria sources for investigation and deployment of control measures. One example is the recently completed Massachusetts statewide bacteria TMDL that does not specify hard compliance deadlines, thus facilitating an iterative, adaptive, watershed management approach to facilitate source investigation and action over the long term.

Where does this leave us? Dischargers should not wait for TMDLs to be incorporated into NPDES permits or consent orders to take action to address controllable sources of fecal bacteria in watersheds. Regulatory agencies should consider scientific uncertainties and feasibility constraints in developing policy. Even with evolving challenges, varying regulations and scientific uncertainty, watershed managers can use tools to identify and control the most important pollutant sources to help make waters swimmable. Are you facing this challenge in your waters? Contact us to explore options (Steve Wolosoff and Sierra Wallace).