Total Maximum Daily Load for Indicator Bacteria, Cedar River Watershed, 2010

(2010) Total Maximum Daily Load for Indicator Bacteria, Cedar River Watershed, 2010. Natural Resources, Department of

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Abstract

The Federal Clean Water Act (CWA) requires a Total Maximum Daily Load (TMDL) be developed for waters that are identified in Category 5 of Iowa’s 2006 Integrated Report (303d list) as impaired by a pollutant. Eight segments of the Cedar River and one segment of Shell Rock River were identified as having their Primary Contact Recreation Class A1 (Class A1) use impaired by the bacteria indicator Escherichia coli (E. coli). TMDLs were determined for the nine segments. The purpose of these TMDLs is to calculate the maximum allowable pathogen loads for the impaired segments within the Cedar River Watershed that will allow the river to meet Iowa water quality standards (WQS). Based on a review of the flow and water quality data available throughout the watershed, it was determined that bacterial concentrations were primarily a function of flow. U. S. Environmental Protection Agency (EPA) recommends using a flow variable expression for the TMDL when critical conditions are associated with precipitation/runoff events and sources include multiple-source types (EPA, 2007a). Thus, a flow-variable daily load was selected to represent these TMDLs.