Last March, the Texas Commission on Environmental Quality proposed that bacteria discharges in urban runoff to waters around Houston be reduced by 100%.
While committed to providing a healthy environment, stormwater managers expressed concern about the magnitude of the proposed reductions from wet-weather sources. Houston's Department of Public Works and Engineering urged the commission to review the proposed reductions, while Harris County and the Harris County Flood Control District suggested they might not be achievable given Houston's semi-tropical climate and frequent rain.
Like stormwater managers across the country, these public employees are struggling to reconcile a common dilemma: Urban creek restoration plans, known as total maximum daily loads (TMDLs), must achieve bacteria levels “safe” for swimming that were based on studies of large lakes—not creeks or streams. Because bacteria levels in urban runoff generally are elevated, discharge reductions can be large and challenging to achieve.
These infrastructure managers are working with state regulators to ensure that local instream standards and discharge reduction requirements are as realistic as possible. Their experience highlights the need to assess the technical issues underpinning federally mandated stream standards and to ensure that proposed discharge reductions address genuine water quality concerns.
Setting the Standards
In urban waterways, bacteria can come from many sources: storm-water runoff, illicit discharges, wildlife, leaking septic systems, sanitary sewer overflows, stream sediments, wastewater effluent, topsoil, and leaking sanitary sewer systems. Some contribute pollutants during dry weather and some during wet weather. Wet-weather sources of bacteria are particularly challenging to control.
The EPA's recommended freshwater criterion for bacteria, published in 1986, is based on studies conducted in freshwater lakes with designated swimming areas. From 1979 to 1982 the studies were performed during dry weather near wastewater treatment plant discharges. Because the study sites didn't directly receive stormwater runoff, the results don't reflect conditions in streams, rivers, or urban waterways. Yet these studies underpin the EPA's national water quality standard recommendation that state regulatory agencies use to establish safe levels in all fresh waters.
The studies assessed the concentration of three indicator organisms—fecal coliform, Enterococci, and Escherichia coli (E. coli)—to determine the organism most associated with illness. While the indicator organisms don't cause illness, they indicate the presence of fecal matter that could contain pathogens. The EPA measured concentrations of these organisms and obtained illness rates experienced by swimmers and nonswimmers on specific days. Armed with these data sets, EPA researchers used regression analysis to correlate indicator concentrations with illness rates.
Because the correlation between illness rates and E. coli levels was the highest, the EPA selected it as the indicator to be used to establish the water quality criterion for bacteria in waters designated for “contact recreation”—that is, swimming. After selecting an “acceptable” risk level of eight illnesses per 1000 swimmers, the agency established a freshwater criterion requiring that the geometric mean density of E. coli not exceed 126 colonies per 100 milliliters of fresh water.
Most of the time, the flows in Buffalo Bayou and White Oak Bayou, urban streams in the western portion of the Houston metropolitan area, consist of treated waste-water effluent. While many people use the trails along these bayous for biking and jogging, few swim in these waters.
Following the “fishable-swimmable” goal of the Clean Water Act, the Texas Commission on Environmental Quality designated the bayous for head immersion swimming, which requires the water to attain the criterion of 126 colonies per 100 milliliters of fresh water. Due to various factors, the bayous exceed this acceptable bacteria level. After concluding that stormwater conveyance systems were a major source of the bacteria, the commission proposed that stormwater dischargers reduce loads by 100% as part of its bacteria TMDL for these waters.
At press time, the commission was revising that recommendation based in part on comments from local utility managers. Although committed to improving water quality in the bayous, they were concerned about the appropriateness of the underlying surface water quality standard and the feasibility of implementing the large bacteria discharge reduction requirements.
In comments submitted to the commission in March 2007, Houston's Department of Public Works and Engineering pointed out that E. coli only indicates the presence of fecal contamination, and that the organism doesn't directly measure the presence of pathogens. The department noted that the “science, existing technology, economic feasibility, and social acceptability of potential measures [to reduce bacteria loads] need to be established.”
Harris County and Harris County Flood Control District managers expressed similar concerns and asked the commission to move forward with their planned review and revision of the applicable surface water quality standards to ensure that the applicable standards are appropriate. They suggested that swimming may not be an attainable or existing use in all portions of the bayous, pointing out that “streams in which full head immersion cannot occur because of low flow conditions are held to the same rigorous standards as a bathing beach.”
Finally, they pointed out that rather than directly indicating an actual human health risk from a microscopic pathogen, E. coli only indirectly indicates whether a stream's water threatens human health because it only indicates the possible presence of fecal matter from warm-blooded mammals, which may or may not contain human pathogens.
Like their colleagues nationwide, these managers want to move forward with actions to reduce bacteria loads from controllable sources, particularly those from human sources, and improve their communities' surface water quality. But they, like others around the country, would like instream standards to be examined and possibly refined on a concurrent path.
— Bloom is a stormwater compliance group manager in the Houston office of environmental consulting firm PBS&J.
Bacteria is the second-leading cause of water body impairment nationwide. For more information, visit the "Article Links" page.
Walking the Tightrope How to cope with discharge requirements that apply lake-specific criteria to streams and rivers.