Anchor QEA developed a number of total maximum daily load (TMDL) assessments for the South Carolina Department of Health and Environmental Control (SCDHEC) and U.S. Environmental Protection Agency Region 4 for the coastal region of South Carolina.  SCDHEC currently classifies approximately 571,010 acres of estuarine and riverine habitat suitable for the cultivation and harvesting of molluscan shellfish.  The most economically important shellfish-producing area along the northern coast of South Carolina is the Murrell’s Inlet Estuary.  Several water quality stations within this saltwater, tidally-influenced system and the nearby Litchfield-Pawley’s Island Estuary are classified as Restricted, indicating that shellfish harvesting for direct marketing is not allowed due to unpredictable fluctuations in fecal coliform levels.

The TMDLs focused on mitigating fecal coliform sources to the impaired estuaries.  Anchor QEA employed a weight-of-evidence approach to assess the importance of the various point and nonpoint sources of fecal coliform bacteria to in-stream levels measured within each of the impaired waterbodies.  Relationships between in-stream fecal coliform levels and salinity and precipitation, as well as the lack of major point sources of fecal coliform pollution within the watershed, indicated that stormwater runoff from nonpoint sources were the primary contributors to fecal coliform contamination.  Fecal coliform loadings in the freshwater runoff from nonpoint source areas were quantified through the development of one-dimensional models for each impaired system.  The models were constructed on the principles of conservation of mass, and included computations of freshwater and tidally-influenced flows, and bacterial fate and transport.  Once calibrated, the models were used to develop the TMDLs for each impaired waterbody and to guide the development of TMDL implementation plans.