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A Total Maximum Daily Load (TMDL) for polychlorinated biphenyls (PCBs) is required by a federal consent agreement to be completed for a section of the Ohio River by September 30, 2002. The TMDL study area encompasses a drainage area of approximately 56,000 square miles, and includes
portions of three states and two regions (Regions III and V) of the United States Environmental Protection Agency (USEPA). The impaired segment of the Ohio River begins at the border between Pennsylvania and West Virginia, and extends for 277 miles along the border between West Virginia and
Ohio. While the TMDL must be written to meet West Virginia's water quality standards due to the state's 303(d) listing of the Ohio River as impaired by PCBs for fish consumption, the implications to Ohio and Pennsylvania must also be considered. Due to these interstate issues, USEPA
requested that the Ohio River Valley Water Sanitation Commission (ORSANCO), an interstate basin commission for the Ohio River Valley, develop this TMDL. The TMDL development process included 1) characterizing the extent and severity of the water quality impairment, and to quantify current
loadings throughout the study area including tributary inputs, 2) compiling an inventory of potential sources, and when possible, quantify source loadings including those of a non-point source nature, 3) defining the load reductions necessary to meet the applicable water quality standards,
4) assigning load allocations to the pollutant sources, and 5) providing recommendations for future actions to address the contamination. ORSANCO conducted an extensive multimedia sampling effort in order to collect the data necessary for the TMDL development. Ultra low-level instream concentrations
were measured using an innovative sampling technique known as high-volume water sampling. The data generated from this method provided a direct measurement of the current conditions for the Ohio River and its tributaries, and established the load reductions necessary to meet the applicable
water quality standards. The data revealed that while some tributaries that enter the Ohio River within the TMDL segment contribute sizeable PCB loads, the most significant load entering the TMDL segment comes from the Pennsylvania stretch of the Ohio River, which enters the segment at the
upstream boundary. Necessary load reductions for the Ohio River ranged from 96.6% at the lower end of the study area, to 99.0% at the upstream boundary of the TMDL segment. Load allocations to the eight major tributaries within the study area call for for reductions ranging from
84.1% on the Little Kanawha River in West Virginia, to 99.6% on the Beaver River in Pennsylvania. A large-scale bottom sediment survey that included sampling at 83 locations over 317 miles of the Ohio River and its tributaries was conducted to characterize PCB levels in sediments
and to identify hot spots of contamination. The sampling revealed river-wide, low-level contamination, along with several areas with elevated PCB concentrations. The widespread contamination suggests that resuspension of sediments may contribute significant loads to the water column during
periods of higher flow conditions. Discovery of the hot spot contamination may lead to the identification of specific localized sources. Ambient air monitoring data was also collected to support the TMDL development effort. The data were used to provide a gross estimate of the potential
loadings to the Ohio River from atmospheric deposition. These estimates did not include deposition to the entire watershed, but were limited to only that which is directly deposited to the river's surface area. Based on this analysis, direct deposition to the Ohio River may contribute
over 40 percent of the allowable load for some segments of the river. Additional study is necessary to better characterize loadings from deposition, and to identify specific sources.
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