An Integrated Modeling Approach to Support the Development of a CSO Long-Term Control Plan

The New York City Department of Environmental Protection is currently developing Long-Term Control Plans (LTCP) following the Demonstration Approach for more than a dozen waterbodies that receive Combined Sewer Overflow (CSO) discharges. The assessment of CSO controls for this LTCP program incorporates the use of three modeling frameworks: InfoWorks, the Estuarine Coastal and Ocean Model (ECOM), and Row-Column AESOP (RCA). The receiving water quality modeling has indicated that the controlling loss mechanism for bacteria can vary by waterbody. Loss mechanisms can include transport, die-off, settling, and solar radiation inactivation. Another important finding from the model is that while CSOs are often the largest source of bacteria to the receiving water, they are often not the most important factor to achieving a criterion based on a geometric mean concentration. Overall, an integrated modeling approach has helped optimize the CSO controls that will be applied in each LTCP.