Reproduced from Journal of Environmental Quality. Published by ASA, CSSA, and SSSA. All copyrights reserved. Development of Bacteria and Benthic Total Maximum Daily Loads: A Case Study, Linville Creek, Virginia Brian L. Benham,* Kevin M. Brannan, Gene Yagow, Rebecca W. Zeckoski, Theo A. Dillaha, Saied Mostaghimi, and Jeff W. Wynn ABSTRACT quality in approximately 22.5% of the state’s free-flow- ing streams and rivers for which sufficient data were Two total maximum daily load (TMDL) studies were performed available to assess at least some designated uses. Of the for Linville Creek in Rockingham County, Virginia, to address bacte- approximately 31 076 km (19 310 miles) assessed, some rial and benthic impairments. The TMDL program is an integrated watershed management approach required by the Clean Water Act. 18 129 km (11 265 miles) of streams and rivers were This paper describes the procedures used by the Center for TMDL classified as impaired and require a TMDL. and Watershed Studies at Virginia Tech to develop the Linville Creek A TMDL is a quantitative representation of all the TMDLs and discusses the key lessons learned from and the ramifica- contributions of a particular pollutant to a water body tions of the procedures used in these and other similar TMDL studies. and is defined as: The bacterial impairment TMDL was developed using the Hydrologi- cal Simulation Program—Fortran (HSPF). Fecal coliform loads were TMDL =WLAs +LAs + MOS [1] estimated through an intensive source characterization process. The where WLA (waste load allocations) represents the benthic impairment TMDL was developed using the Generalized sum of all point loadings, the LA (load allocations) Watershed Loading Function (GWLF) model and the reference wa- represents the sum of all nonpoint-source loadings, and tershed approach. The bacterial TMDL allocation scenario requires MOS represents a margin of safety. The sum of these a 100% reduction in cattle manure direct-deposits to the stream, a 96% reduction in nonpoint-source loadings to the land surface, and terms constitutes the TMDL and represents the loading a 95% reduction in wildlife direct-deposits to the stream. Sediment of the constituent of interest that the water body can was identified as the primary benthic stressor. The TMDL allocation assimilate without violating the applicable state water scenario for the benthic impairment requires an overall reduction of quality standard. For the USEPA to approve a TMDL, 12.3% of the existing sediment loads. Despite the many drawbacks all major point and nonpoint sources of the offending associated with using watershed-scale models like HSPF and GWLF pollutant must be identified and quantified. Developing to develop TMDLs, the detailed watershed and pollutant-source char- a TMDL often involves a study that first identifies the acterization required to use these and similar models creates informa- sources of the pollutants causing water quality impair- tion that stakeholders need to select appropriate corrective measures ments, quantifies the pollutant contribution from each to address the cause of the water quality impairment when implement- source (or source category in the case of nonpoint- ing the TMDL. source pollution), and determines the pollutant reduc- tion from each source required to meet applicable state water quality standards. Hydrologic and water quality T he total maximum daily load (TMDL) program models are often used to develop the necessary TMDL is a watershed management approach required by pollutant reduction scenarios. the Clean Water Act that integrates watershed planning Researchers affiliated with the Center for TMDL and with water quality assessment and protection. Water Watershed Studies (hereafter the Center) and in the bodies in violation of state water quality standards are Biological Systems Engineering Department at Virginia referred to as “impaired.” According to the USEPA, over Tech were contracted by the Virginia Department of 40% of assessed waters in the United States do not Environmental Quality (VADEQ) to develop TMDLs meet water quality standards and thus are impaired. This for Linville Creek for violations of the Bacteria and amounts to over 20 000 individual river segments, lakes, General Standard for Aquatic Life (benthic) impair- and estuaries and includes approximately 480 000 km ments (Mostaghimi et al., 2003). The researchers used of rivers and shorelines and approximately 2 million ha two modeling tools to develop the two TMDLs for Lin- of lakes, polluted mostly by sediments, excess nutrients, ville Creek in Rockingham County, VA: the Hydrologi- and harmful microorganisms (USEPA, 2004). Under the cal Simulation Program—Fortran (HSPF) was used for Clean Water Act, pollutant-specific TMDLs are required the bacteria impairment TMDL, and the Generalized for impaired water bodies. Virginia’s 2004 305b report Watershed Loading Function (GWLF) model was used (Virginia Department of Environmental Quality, 2004a) for the benthic impairment TMDL. The objective of presented the results of the assessment of the water this paper is to describe the processes used to develop the Linville Creek TMDLs as a case study and communi- Virginia Tech, Biological Systems Engineering (0303), Blacksburg, cate some of the key lessons learned from these and VA 24061. Received 7 Nov. 2004. *Corresponding author (benham@ other similar TMDL studies conducted by the Center. vt.edu). Abbreviations: GWLF, Generalized Watershed Loading Function; Published in J. Environ. Qual. 34:1860–1872 (2005). Technical Reports: Surface Water Quality HSPF, Hydrological Simulation Program—Fortran; LA, load alloca- tion; MOS, margin of safety; RBP II, Rapid Bioassessment Protocol doi:10.2134/jeq2004.0414  ASA, CSSA, SSSA II; TMDL, total maximum daily load; VADEQ, Virginia Department of Environmental Quality; WLA, waste load allocation. 677 S. Segoe Rd., Madison, WI 53711 USA 1860 Published online September 8, 2005