Coordinating Interstate Listing Decisions for the Ohio River

The Ohio River is 981 miles long and borders six states (Illinois, Indiana, Kentucky, Ohio, Pennsylvania and West Virginia), and three US EPA regions (III, IV, and V). The Ohio River Valley Water Sanitation Commission (ORSANCO) is an interstate agency that conducts all of the water quality and biological monitoring on behalf of the Ohio River main stem states. Through a workgroup of state agencies, ORSANCO coordinates development of a 305b Report which the states then use in their 303d listing of waters requiring total maximum daily loads. The goal is to achieve consistency in listing of Ohio River waters between the states. Interstate consistency in 303d listing is important for a number of reasons, but among them is providing a consistent message to the public, and coordinated TMDLs completed on an interstate basis. ORSANCO was not able to achieve interstate consistency in 305b impairment decisions for the aquatic life and fish consumption uses, and states' resulting 303(d) lists are inconsistent for the Ohio River, theoretically leading to one state completing a TMDL for iron or mercury without the adjacent or downstream state doing so. In turn, this could lead to inequitable waste load allocations and effluent limitations for discharges. The primary causes for inconsistencies are the states' approaches to impairment decisions. Some states employ the “independent application” approach while others use the “weight of evidence” approach. The paper discusses the issues in depth.