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Fecal Coliform TMDL for Big Otter River, Virginia: A Case Study

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

Citation:  Pp. 367-376 in Total Maximum Daily Load (TMDL) Environmental Regulations: Proceedings of the March 11-13, 2002 Conference, (Fort Worth, Texas, USA)  701P0102.(doi:10.13031/2013.7582)
Authors:   K. M. Brannan, S. Mostaghimi, T. A. Dillaha, C. D. Heatwole, M. L. Wolfe, M. Al-Smadi, S. Shah, and J. Miller
Keywords:   Watershed, Water Quality, Nonpoint Pollution, Pathogens

Fecal coliform TMDL plans for five impaired segments were developed in the 388 square mile Big Otter River (BOR) basin in Virginia. These stream segments are Sheep Creek, Elk Creek, Machine Creek, Little Otter River, which are tributaries of the BOR, and the most downstream segment of the BOR.

The fecal coliform sources in the BOR basin were human/residential, livestock, and wildlife. Human/residential sources of fecal coliform included failing septic systems, straight-pipes, pets, combined sewage overflows in the City of Bedford, permitted point source discharges, and biosolids applications. Livestock sources included beef cattle, dairy cattle, horse, and sheep. Wildlife sources included deer, raccoon, muskrat, beaver, and wildfowl. The sources were quantified and used in a watershed model to develop a TMDL plan. The watershed model used was HSPF.

The modeling was conducted in phases to develop the TMDL plan for the BOR basin. Separate model simulations were made for the eight watersheds that made up the entire BOR basin. The simulated outflows of both water and fecal coliform from the upstream watersheds were used as inflows for the simulations of the downstream watersheds. When developing TMDL plans for downstream watersheds, the simulated outflow including source reductions of the respective TMDL plans of upstream watersheds were used.

The TMDL plans included several source reduction scenarios that met the water quality standard for fecal coliform. The water quality standard used to develop the TMDL plans states that the 30-day geometric mean of fecal coliform should not exceed 190 cfu /100 ml, which includes a 5% margin of safety. Some common source reductions were required in all five plans including almost complete exclusion of cattle from the streams of BOR basin and reductions in wildlife contributions. Also, some reductions in upstream watersheds that did not have impairments were required. Most of the reductions are achievable using agricultural and urban Best Management Practices, but other reductions, such as those from wildlife, may be difficult to achieve. The development of these and other fecal coliform TMDL plans have led to several actions by the Commonwealth of Virginia to improve the TMDL process, such as the use of bacterial source tracking to verify wildlife contributions, along with a reassessment of water quality standards and the use classification of water bodies.

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