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Improved Monitoring Methods

LakeviewThe United States Environmental Protection Agency (USEPA) requires states to monitor coastal waters for the protection of recreational users as a part of the Beaches Environmental Assessment and Coastal Health Act of 2000 (U.S. Congress 2000). States are required to incorporate criteria developed by USEPA in a previous epidemiological study into state water-quality standards (U.S. Environmental Protection Agency, 1986). In that study, concentrations of Escherichia coli (E. coli) and enterococci were found to have statistically significant relations with the number of swimming-associated gastrointestinal illnesses at freshwater beaches; enterococci was significantly related to gastrointestinal illnesses at marine beaches. The USEPA published new recreational water-quality criteria in December 2012 (U.S. Environmental Protection Agency, 2012a). In Ohio, a water-quality advisory at a beach is issued if the concentration of E. coli exceeds the single-sample standard of 235 colony forming per 100 milliliters (CFU/100 mL).

Beach samplingSampling methods
Currently at beaches in Ohio, water samples are typically collected weekday mornings during the recreational season (Memorial Day – Labor Day) and analyzed for concentrations of E. coli.  Collect samples in the area used for swimming at 2-3 ft water depths, maintaining consistency in water depth throughout the sampling period.  The sample is taken 12-18 inches below the water surface using the hand-dip method.  Avoid contaminating the water sample with material kicked up from the bottom while sampling.  At some beaches, multiple samples may be needed to adequately represent overall water quality conditions. Compositing multiple samples on an equal-volume basis may provide results that are as accurate as those obtained by averaging analyses from multiple points.

EdgewaterCompositing samples
In a study done in cooperation with the Northeast Ohio Regional Sewer District (NEORSD), the USGS compared results from composited samples to those obtained by averaging individual results from multiple-point samples.  Samples were collected at 2 or 3 locations at each of three Lake Erie beaches from May through September 2005.  In the laboratory, multiple-point samples from each beach were used to form a composite sample. Each point sample was shaken and 100-mL aliquots were removed from each point sample to combine into a composite bottle.  Individual point samples and composite samples were analyzed for E. coli by use of the modified mTEC method.

No statistically significant differences in E. coli concentrations were found between multiple-point and composite samples; similar assessments of recreational water quality were determined by each method (Bertke, 2007).

Bertke, E.E., 2007, Composite analysis for Escherichia coli at coastal beaches: Journal of Great Lakes Research, v. 33, no. 2, p. 335-341.

Rapid analytical methods
Two rapid analytical methods have been used on samples from beaches by the USGS OWSC—a surface recognition method, immunomagnetic separation/adenosine triphosphate (IMS/ATP), and a molecular method, quantitative polymerase chain reaction (QPCR). Learn more about rapid methods. The U.S. Environmental Protection Agency (USEPA) developed new recreational water quality criteria and beach action values (BAVs) (U.S. EPA, 2012) for both coastal and non-coastal waters that include a rapid analytical method (Method 1611), quantitative polymerase chain reaction (qPCR) for Enterococcus spp., along with culture methods for Escherichia coli and enterococci.