Rainfall and its associated storm water runoff have been associated with transportof many pollutants into beach water. Fecal material, from a variety of animals (humans,pets, livestock, and wildlife), can wash into beach water following rainfall and result inmicrobial contamination of the beach. Many locales around the world issue pre-emptivebeach closures associated with rainfall. This study looked at eight beaches located inDoor County, Wisconsin, on Lake Michigan to determine the impact of rainfall on E. coliconcentrations in beach water. Water samples were collected from beach water andstorm water discharge pipes during rainfall events of 5 mm in the previous 24 hours. Sixof the eight beaches showed a significant association between rainfall and elevated beachwater E. coli concentrations. The duration of the impact of rainfall on beach water E. coliconcentrations was variable (immediate to 12 hours). Amount of rainfall in the daysprevious to the sampling did not have significant impact on the E. coli concentrationsmeasured in beach water. Presence of storm water conveyance pipes adjacent to thebeach did not have a uniform impact on beach water E. coli concentrations. This studysuggests that each beach needs to be examined on its own with regard to rain impacts onE coli concentrations in beach water.
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IMPACT OF RAINFALL ON ESCHERICHIA COLI CONCENTRATIONS AT BEACHES IN DOOR COUNTY, WISCONSIN