Given the one-size-fits-all federal criterion for establishing acceptable bacteria levels, it's not surprising that so many streams and rivers are designated as impaired (see table).
Most streams have higher flow velocities than lakes, which prevents pollutants from settling. In streams dominated by wastewater effluent, the lower settling rate, combined with elevated nutrient levels, contributes to regrowth of bacteria and higher pollutant densities.
But does “impairment” indicate an actual health hazard?
The criterion of no more than 126 colonies of E. coli per 100 milliliters of fresh water assumes swimmers will be dunking their heads under water and inadvertently ingesting water in the process, an unlikely scenario for many urban waterways. Even so, managers may have to comply with discharge reduction requirements stipulating that they reduce E. coli levels in stormwater discharges to achieve instream bacteria levels safe for head immersion swimming. In some extreme situations, they may have to reduce levels at the end of each stormwater pipe.
Because stormwater runoff typically contains high levels of bacteria, permittees may face severe challenges as they attempt to meet potentially unachievable instream water quality goals for bacteria.
If your department finds itself in this position, consider:
Re-examining and refining the “impaired” waterway's recreational use designation. The regulatory agency's “use” designation sets the surface water quality goal for watershed protection and permitting.
If the agency and local stakeholders are comfortable refining the use from head-immersion swimming to solely boating, the instream water quality goal may be adjusted because wading, bank fishing, and boating have lower rates of water ingestion compared to swimming.
States could use the E. coli criterion of 126 colonies/milliliter for swimming as a default value and increase it for other, lower-exposure activities, based on the ratio between the volume of water ingested during swimming (about 100 milliliters) and the volume of water ingested during the other activities.
To alter the water quality goal in this manner, stakeholders will need to conduct a “use attainability analysis” to demonstrate the existing and attainable use of a surface water body and establish a consensus regarding the level of human recreational uses to be protected.
This approach is particularly effective for urban streams that don't provide opportunities for swimming. If, for example, the stream has never been and isn't used for swimming, it's possible to designate it for a boating use, which would relax the E. coli criterion.
By working with residents who know their watersheds intimately, you can seek consensus on what constitutes the most appropriate use for a given stream and set water quality goals accordingly.
Conduct a “microbial risk assessment” to adjust the applicable criteria. A spreadsheet analysis of exposure values, organism lifecycles, and disease transmission models can be used to estimate the risks of human exposure. Such an approach could provide criteria acceptable to stakeholders, assuming they concur with the assessment's input variables, assumptions, and methods.
By working with all stakeholders, you can craft achievable quality goals that protect the environment without busting your budget.
- Bacteria in the Bayous: Reduce discharge loads by refining instream standards