INVESTIGATION OF THE GROUND WATER QUALITY OF SOUTH BASS ISLAND, OTTAWA COUNTY, OHIO

During the summer of 2004, an outbreak of gastrointestinal illness was identified by the Ottawa County Health Department on South Bass Island, Ohio, a popular resort community. The Director of the Ohio Department of Health (ODH) initiated an investigation that involved multiple federal, state and local partners including the Ottawa County Health Department, the Ohio EPA, the Ohio Department of Agriculture, and the Centers for Disease Control and Prevention (CDC) including the National Center for Infectious Diseases, Foodborne and Diarrheal Diseases Branch, and the National Center for Environmental Health Branch. As part of that investigation, ODH conducted a study of the ground water quality of the island. Ground water sampling of private and public water supply wells was conducted by ODH, CDC and Ohio EPA. A preliminary report has been issued by ODH summarizing the investigation results, recommendations and actions to date. The investigation identified widespread ground water contamination with multiple pathogenic agents as the mostly likely source of the illnesses. This conclusion resulted from an epidemiological study of over 1,400 ill persons who fit the case definition, testing and assessment of many public and private water and wastewater treatment systems, and a study of the geologic and hydrogeologic conditions and ground water quality of the island. GIS analysis of data assisted in identifying contaminated areas, and implementation of subsequent public health interventions. The hydrogeology of the island is characterized by two aquifer systems that are karst limestone/dolomite formations with extensive cave features, solution fractures, and thin to absent soil cover. Hydrogeologic data suggests a hydraulic connection between the aquifers and Lake Erie. Drinking water supplies on the island are from public supplies using both surface and ground water sources, and private supplies using ground water wells. Wastewater treatment on the island is a combination of public systems utilizing typical waste treatment processes for larger systems, and private household systems using on-site treatment and/or discharging systems. Comprehensive land use planning and management, alternative water supplies, and sewage treatment to address sources of contamination on the island have been recommended.