With the passage of the Clean Water Act, progress has been made in reducing water pollution from point sources, but more needs to be done. Nonpoint source controls will also typically be required to solve existing water quality problems and mitigate threats to designated uses. This is particularly evident in developing TMDLs (total maximum daily loads) for large, complex aquatic ecosystems that are impaired by legacy pollutants, such as PCBs. LimnoTech scientists helped state, regional, and federal agencies to better understand and manage PCBs in two important estuaries and a Great Lake.
The Delaware and Potomac River estuaries and Lake Ontario have all been listed as impaired due to PCB levels in the tissues of resident fish species. Both point and nonpoint sources, including legacy sediment contamination, atmospheric depositions, and other PCB sources outside the regulatory domain, appear to be contributing to the current fish contamination. Court mandates and administrative agreements required the development of TMDLs under extremely challenging circumstances.
LimnoTech conducted data assessments, reviewed monitoring plans, and developed PCB water quality models for the tidal fresh and estuarine portions of the Delaware, Anacostia, and Potomac Rivers, and the Niagara River – Lake Ontario system. LimnoTech worked in close collaboration with the U.S. EPA, two regional agencies, six states, and the District of Columbia. The calibrated models were used to conduct load reduction scenarios to determine the external PCB loads that could enter the systems and still meet the applicable TMDL targets.
The PCB models developed by LimnoTech were judged scientifically credible by external peer review, satisfied all regulatory requirements, and met all court-ordered and administrative deadlines.
The Potomac and Anacostia PCB TMDL is highlighted as a case study in USEPA’s recent Handbook for Developing Watershed TMDLs.