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Development of a Total Maximum Daily Load for Dioxin for the Ohio River

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In 1997, the U.S. Environmental Protection Agency, Region 3, entered into a Federal Consent Order to complete a Total Maximum Daily Load (TMDL) for dioxin for the Ohio River by September, 2000. The Ohio River Valley Water Sanitation Commission is completing the monitoring, modeling and load analysis on behalf of Region 3. Allocations are not covered in this report, however interstate allocations may be coordinated through the Commission's TMDL Work Group in the future.

TMDLs are required for waters not meeting applicable water quality standards after application of best practicable control technology. A TMDL must be designed to meet water quality standards, which is 0.013 pg/L for the Ohio River for 2,3,7,8-TCDD (dioxin). TMDLs must include load and wasteload allocations, which are not included in this report. TMDLs must consider background conditions, which are accounted for through the utilization of the dioxin sample data. TMDLs must consider critical conditions and seasonality, which can be accounted for by utilizing a high flow critical condition when developing. The flow associated with a one-year flood is selected as the critical condition for which total maximum daily loads are calculated.

Based on West Virginia's 1998 303(d) list, a dioxin TMDL is to be completed for the Ohio River segment from Ohio River Mile (ORM) 237.5 to ORM 317. “High Volume” dioxin sampling, a collection technique that effectively concentrates 1000 liters (L) into a single sample in order to achieve necessary detection levels, was conducted within the TMDL segment during 1997-1998. Multiple samples were collected over the period at various flows. The data are used to estimate TMDL segment boundary loads and to verify water quality modeling results. The SYMTOX 4 water quality model was utilized to determine dioxin loads at various river flows. The model was run at three flows: seven day-ten year low flow, harmonic mean flow, and a one-year flood high flow. These flow regimes compare with flows at which monitoring data were collected. Modeling results cannot be reliably verified at flows substantially above a one-year flood.

The highest dioxin concentrations and loads in the Ohio River occur immediately downstream of the Kanawha River at ORM 266. Based on sampling results, Ohio River dioxin concentrations increase with increasing flow. At the one-year flood, modeled dioxin concentrations and loads at ORM 266 are 0.13 pg/L and 83,700 ug/day, respectively. The stream criterion and resulting load that would not cause water quality standards violations at the one-year flood flow condition are 0.013 p/L and 8500 ug/L, respectively. Thus, Ohio River loads would need to be reduced by ninety percent to meet water quality standards at the one-year flood. It is anticipated that loadings would be greater at higher flows.

There is no net increase of dioxin within the TMDL segment, thus all important sources are located upstream of the TMDL segment. At high flow, fifty-five percent of the dioxin load originates from the Kanawha Basin, and the remaining forty-five percent from the Ohio Basin upstream of ORM 264. While several contaminated sites have been identified in the Kanawha Basin, no dioxin loads to surface waters within or upstream of the TMDL segment have been identified. Ohio River dioxin loads at high flow are approximately one thousand times greater than at low flow. Potential high flow-related sources include runoff from contaminated land sites and resuspension of contaminated bed sediments. Atmospheric deposition was eliminated as a source within the TMDL segment based on results of limited sampling, however it could be a source upstream of the TMDL segment. Results of an upper-Ohio River dioxin survey suggest the possibility of sources upstream of ORM 20 and between ORM 129 and 175.

Potential dioxin sources upstream of the TMDL segment must be identified and quantified if allocations are to be effective in achieving water quality standards. As part of that process, loads from resuspension of contaminated bed sediments should be quantified. A monitoring plan to identify and quantify sources in the upper-Ohio River is presented and will be completed during 2000-01 under the Ohio River Watershed Pollutant reduction Program.
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Document Type: Research Article

Publication date: 2000-01-01

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