A Modeling Framework for Determination of Total Maximum Daily Loads to the Grand Calumet Watershed, Indiana

All segments of the Grand Calumet River/Indiana Harbor Canal (GCR/IHC) are identified as being impaired by one or more chemicals, including PCBs, Pesticides, Mercury, Cyanide, Lead, Oil and Grease, Copper, Ammonia as Nitrogen, Dissolved Oxygen and Chlorides. As such, the State of Indiana is required to develop TMDLs for each Water Quality Limited Segment. The determination of TMDLs for the GCR/IHC is complicated by the hydraulics of the system and multiple loading sources, including sediments, groundwater, combined sewer overflows (CSOs), and industrial and municipal point sources. To provide for establishing the TMDLs and to aid in the analysis of potential action alternatives, mathematical models were developed. Modeling was required first to estimate discharges and loadings from groundwater and CSOs. Models were also developed for the hydrodynamics and water quality of the GCR/IHC to relate loads to in-steam concentrations. The hydrologic, hydrodynamic and quality models were applied to the continuous period of January 1995 to September 1998. Once the models were considered to reasonably predict observed concentrations for this period, strategies were developed for their implementation. Four strategies were developed for the implementation of the models in the determination of TMDLs and the screening of action alternatives. For selected legacy pollutants, such as PCBs and pesticides, the determination of the TMDLs could potentially be reduced to a simple loading/dilution analysis. For other chemicals, the dynamic models were used to develop steady-state system response matrices for selected critical conditions that may provide for the rapid determination of TMDLs and/or screening of action alternatives. For action alternatives resulting in changes of flows and loads, the dynamic models, for both hydrodynamics and water quality, could be run to steady-state for the selected critical conditions. Finally, the dynamic model could be run over the four-year period of application in the final analysis of selected action alternatives to determine the magnitude and frequency of resulting concentrations.