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Thirteen percent of all beachwater samples collected at beaches along the Great Lakes shoreline in 2008 exceeded the federal Environmental Assessment and Coastal Health (BEACH) Act’s maximum E. coli standard for freshwater beaches (235 colony-forming units of E. coli per 100 milliliters of water), says a report issued by the Natural Resource Defense Council (NRDC) on July 29.
So far this season, Mr. Caneva said there has been “a really low amount” of beach closures …
For the 2008 beach season, the highest percent exceedances among the Great Lakes states were in New York and Ohio (19%), followed by Indiana (18%), Illinois (15%), Wisconsin (14%), Pennsylvania (9%), Michigan (6%), and Minnesota (5%).
Three Evanston beaches were among the ten beaches in Illinois with the highest incidence rates of E. coli: South Boulevard Beach (32%), Dempster/Greenwood Street Beach (19%), and Lee Street Beach 18%). Northwestern University‘s beach was also included in the top ten.
The incidence rates at the other Evanston beaches were as follows: the dog beach (15%), Clark Street Beach (11%), and Lighthouse Beach (9%).
The City of Evanston takes water samples at each of its beches twice a day, once in the morning and once in the afternoon, and it obtains test results back on the samples within 18 hours, which is the quickest turnaround time possible, said Carl Caneva of the City’s health department. He said beaches are closed for swimming if bacteria levels exceed 235 colony-forming units of E. coli per 100 milliliters of water.
In 2008, Evanston beaches were closed 84 times due to excessive bacteria counts, according to NRDC’s report: South Boulevard (19 times), Dempster/Greenwood (16 times), Lee (13 times), Clark (13 times), Lighthouse (12 times), and the dog beach (11 times).
So far this season, Mr. Caneva said there has been “a really low amount” of beach closures – a total of 13 closures for all beaches combined. He said temperatures this year have been lower than last year, which may be a factor.
Mr. Caneva said the City is moving toward using a predictive model in deciding whether to close beaches, rather than waiting 18 hours for water samples to be tested. The City is using a Great Lakes sanitary survey to record on a daily basis data, such as air temperature, wind direction and speeds, debris on the beach and other factors. At the end of the year, staff will analyze the data to determine if there is a pattern of conditions that exists when beaches were closed during the year. The City may use that data in a predictive model to decide whether to close a beach.
The NRDC report says beach authorities in Illinois, Indiana, Ohio and Wisconsin are successfully using predictive models at some of their beaches to make real-time beach closing decisions based on easily measured environmental parameters, such as wind direction, water temperature and turbidity, and currents. One predictive model, SwimCast, correctly predicts E. coli concentrations above the maximum rate 85 percent of the time, says the report.
The City already allows beaches to be closed based on some judgment factors. The City’s Recreation Division may close swimming areas following a heavy rainfall or known incident that may have contaminated the water. Beaches are closed for swimming for 24 hours after the locks in Wilmette are opened after a large storm.
Mr. Caneva said the City’s Parks and Recreation Department does a great job raking and maintaining the sand at the beaches, which helps prevent low patches in the sand where bacteria may thrive if pools of water form. The City will determine if other steps may be taken to help reduce E. coli levels as part of its review of the data collected in the Great Lakes sanitary survey.