An Approach to Evaluating TMDLs to Support Permitted Discharges, Regulatory Agencies, and other Stakeholders

In November 2006 the South Carolina Department of Health and Environmental Control (SCDHEC) announced that a Watershed Analysis Risk Management Framework (WARMF) model application in the Catawba River Basin was available for public review. The model was developed by SCDHEC in response to impaired phosphorus conditions in Fishing Creek Reservoir, Cedar Creek Reservoir, and Lake Wateree which were identified in the 1998 South Carolina 303(d) List of Impaired Waters. The intended purpose of the WARMF model was to serve as the basis for future Total Maximum Daily Load (TMDL) development for phosphorus in the three aforementioned waterbodies. The modeling effort was extensive and included numerous point sources, nonpoint sources, calibration locations, multiple aquatic environments (small streams, large streams, and reservoirs), and complex environmental processes. On behalf of a consortium of industrial and municipal dischargers, URS reviewed the draft model to identify issues that may need to be addressed in order to produce a scientifically defensible TMDL capable of achieving the desired water quality goals. This paper offers a guide for groups affected by TMDLs or involved in reviewing related water quality modeling studies by describing the approach taken to review the WARMF application. Key topics covered include model documentation, model structure, model calibration and uncertainty, and loading analysis. Potential benefits of conducting a critical review are also discussed.