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Case Study: Six Fecal Coliform TMDLs in the Blackwater River Watershed, Franklin County, Virginia

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 349-354 in Total Maximum Daily Load (TMDL) Environmental Regulations: Proceedings of the March 11-13, 2002 Conference, (Fort Worth, Texas, USA)  701P0102.(doi:10.13031/2013.7580)
Authors:   Byron Petrauskas, James Kern, Phillip McClellan
Keywords:   TMDL, Fecal Coliform, Modeling, Public Participation, Monitoring, Geometric Mean Standard, Environment, Pathogens, Water Quality, Watershed

MapTech, Inc. was contracted by the Virginia Department of Conservation and Recreation (VADCR) to develop TMDLs for six fecal-coliform impaired waters in the Blackwater River watershed, Franklin County, Virginia. Critical to the successful development and public acceptance of the TMDLs, were adequate data, public input, an ongoing monitoring effort, and an understanding of the implications of the geometric mean standard. This was a unique case, in which data were plentiful (i.e. land use, hydrologic, and water quality records). The data availability allowed for detailed modeling of the watershed and effective calibration/validation. Public input, through public meetings and focus groups, improved model development and public perception of the modeling effort. The monitoring effort, which has continued during implementation plan development, was also crucial in gaining public confidence. Direct deposition of fecal matter from human, livestock, and wildlife sources during low flow conditions was found to be the critical condition, which drove the allocation process. In Virginia, fecal-coliform TMDL modeling is geared toward meeting the 30-day geometric mean standard of 200 cfu/100 ml. In determining the critical condition and subsequent allocation scenarios, it was important to consider the impact of the geometric mean standard on modeling. Additionally, the impact of using daily average modeled output vs. instantaneous modeled output to calculate the 30-day geometric mean was assessed. It can be shown mathematically that use of daily averages will bias the geometric mean upward. This case study shows clearly the importance of adequate data, public input, water quality monitoring, and a thorough understanding of state standards in developing a TMDL that is implementable and accepted by the public.

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