METALS AND pH TMDL DEVELOPMENT FOR THE TYGART VALLEY RIVER WATERSHED, WEST VIRGINIA
Abstract:Impairments resulting from acid mine drainage (AMD) affect nearly 500 waterbodies in West Virginia. Fifty-one of these waterbodies are located in the Tygart Valley River Watershed and are listed on the West Virginia 303(d) list due to metals and/or pH impairments. EPA Region 3, with the support of West Virginia Department Environmental Protection (WVDEP) and Tetra Tech, Inc. developed TMDLs for all impaired waterbodies in the watershed on March 30, 2001 to meet the requirements of a 1997 consent decree. The effort involved development of an innovative assessment and modeling technique to address a variety of case-specific requirements related to water quality criteria, water use designations, source pollution conveyance methods, and permitting.
The Tygart Valley River is located in northeastern West Virginia and flows in a northern direction, eventually emptying into the Monongahela River at Fairmont, West Virginia. The watershed drains approximately 1,362 square miles with forest and agricultural as the predominant land uses. Much of the watershed contains active surface and deep mining operations and virtually all of the coal fields in the watershed contain abandoned coal mines. AMD from both active and abandoned mining activities contribute significant amounts of acidity that produce low pH and high metals concentrations in the receiving waterbodies.
The modeling approach involved application of the Mining Data Analysis System (MDAS) to simulate in-stream flow and water quality conditions (based on point and nonpoint source contributions) throughout the watershed for an extended time period. The listed segments had various water use designations that require specific acute and chronic numeric criteria. Many of the listed segments were also small nested tributaries, consequently, the watershed was segmented into 1,007 smaller hydrologic units. The watershed modeling process involved the compilation of meteorological, land use, stream and land use-specific hydrology and pollutant data; hydrologic and water quality calibration; and generation of nonpoint source and in-stream flows and pollutant loadings. To account for the multiple mining related sources, additional land use categories that are specific to AMD were represented as nonpoint sources (e.g. high walls, disturbed land, and abandoned mines). Over 300 permitted mining discharges, in multiple phases of reclamation (exhibiting various water quality conditions) were represented as point sources that simulated characteristics of precipitation driven discharges. Given the many nested impaired watersheds, upstream loading contributions had a cascading effect as allocations were assigned to sources in a up-stream to down-stream fashion. In addition, WVDEP provided guidance to produce TMDL results that will support future permit development. Final TMDL allocations, which included both implicit and explicit margins of safety, were assigned to more than 1,000 subwatersheds and over 80 individual mining facilities and resulted in the development of over 150 individual TMDLs for the watershed.
The existing MDAS model for the Tygart provides a basis for permit analyses and make future adjustments. This ultimately can support future re-mining and growth issues as they arise.
Document Type: Research Article
Publication date: 2002-01-01
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