USGS Ohio Water Science Center
Beach Monitoring FAQ
How do agencies determine recreational water
quality at beaches? How do agencies determine recreational water quality at beaches? Typically, local or state agencies collect a water sample at the beach, four or five weekdays each week, throughout the recreational season (Memorial Day through Labor Day). Sometimes, more than one bottle is collected to best represent the water quality at a particular beach. The samples are brought to the laboratory and analyzed within 6 hours of collection. Membrane filtration or enzyme-substrate most-probable number methods are the most commonly used analytical methods. Using these methods, it takes 18-24 to obtain results. Membrane filtration – link to modified mTEC Enzyme-substrate most-probable number – link to Colilert
Why is E. coli used
to assess recreational water quality? Because of its association with pathogens and because it is comparatively easy to grow in the laboratory, E. coli is the basis for Ohio recreational water-quality standards. E. coli is the basis for freshwater recreational standards in other states; enterococci, another type of bacterial indicator, is used in standards for marine waters. There are several varieties of pathogenic E. coli and hundreds of varieties of harmless E. coli. One variety of E. coli that is pathogenic and relatively rare has been associated with undercooked ground beef—E. coli 0157:H7.
Is there a “pathogen
problem” at Ohio beaches? Are people getting sick? Swimming in polluted water can make you sick (Natural Resources Defense Council, 2006). Epidemiological studies in the United States have consistently found an association between gastrointestinal illness and exposure to contaminated recreational waters; however, the potential for other types of infections is not completely understood (USEPA, 1999).
What are the sources of
pathogens at Ohio beaches?
How would use of the
predictive models differ from the current way of assessing swimming safety? In USGS studies, we found that models yield more correct responses and better predict exceedance of the recreational water-quality standard than using the previous day’s E. coli concentration.
How did you collect the
data needed for developing the models?
How well do the models
work? Although there is some uncertainty with using the models, the amount of uncertainty is quantified so that beach managers and the public can make informed decisions. We use the concept of a threshold. Probabilities equal to or above the threshold would indicate to the beach manager that E. coli concentrations are most likely above the bathing-water standard. Probabilities below the threshold would indicate that E. coli concentrations are most likely below the standard. In other words, our models can work like a weather forecast. If there was a 70 percent chance of rain, would you go to a picnic? A 20 percent chance of rain? Similarly, if there was a 70 percent chance that the standard will be exceeded, would you swim in the water? And again, because models provide an assessment of recreational water quality within an hour, they are better than the old methods that take 18-24 hours to complete. At Huntington, we tested the model developed from six years of data (2000-05) using data collected during the recreational season of 2006. The model correctly predicted recreational water quality 80 percent of the time and worked better than the current method (using the previous day’s E. coli).
Why was the USGS involved
in this research? The USGS did not do this research alone. Agencies that cooperated with us were the Ohio Water Development Authority, Northeast Ohio Regional Sewer District, Cuyahoga County Board of Health, Cuyahoga County Sanitary Engineers, the Ohio Lake Erie Office, Ohio Department of Health, Ashtabula Township Park Commission, University of Toledo, Cities of Toledo and Oregon, and Toledo Metropolitan Area Council of Governments.
Is anyone else doing the
same kind of research? Are other predictive tools being investigated?
Will this research
continue? Does USEPA allow the use of models for posting beach advisories? USEPA states that a monitoring program is essential to any beach-management program and recommends that the current E. coli laboratory method be used for assessing ambient waters and for making decisions concerning the protection of human health (USEPA 2002, p. 4-17). However, USEPA also states that modeling tools may be used to supplement, not replace, monitoring. Modeling tools can provide conservative estimates when there is a lag time between sampling the water quality and obtaining results. If models are properly developed and applied, they can be used in making beach advisory or closing decisions (USEPA 2002, p. 4-22).
How can we identify
sources of contamination at beaches? Identifying the spatial distribution of bacterial indicator concentrations, such as E. coli, helps to identify fecal contaminant “hot spots.” Sampling along the shoreline to the beach can show if E. coli is coming from a point along the shoreline further away from the beach or from the beach itself. Determining weather patterns that cause elevated E. coli concentrations can also help identify sources; for example, winds from a certain direction can be traced back to potential source areas. Sampling shallow ground water in the beach area can also help to understand if beach sands serve as a reservoir of E. coli and pathogens. More sophisticated and expensive microbial source tracking (MST) techniques can then be applied to specific areas.
Whom can I contact if I’m
concerned about swimming at a particular Ohio beach? Information on Ohio Department of Health’s bathing beach monitoring program can be found at http://www.odh.state.oh.us/odhPrograms/eh/bbeach/beachmon.aspx REFERENCES Natural Resources Defense Council, 2006, Testing the Waters VIII: New York, 349 p., available at http://www.nrdc.org/water/oceans/ttw/titinx.asp U.S. Environmental Protection Agency, 2002, National beach guidance and required performance criteria for grants: Washington, D.C., EPA-823-B-02-004. U.S. Environmental Protection Agency, 1999, EPA action plan for beaches and recreational waters: Washington, D.C., Office of Water, EPA-600-R-98-079. |