ALCOSAN’s Water Quality Modeling Approach

Allegheny County Sanitary Authority (ALCOSAN), based in Pittsburgh, Pennsylvania, is actively executing its Clean Water Plan (CWP) to manage sewage overflows in rivers and tributaries, in compliance with a Federal Consent Decree. This involves utilizing an 11,000+ node PCSWMM hydrologic and hydraulic (H&H) model for sewage overflow control projects, encompassing source control, green infrastructure, and deep tunnels. To assess the water quality (WQ) improvement impact and ensure compliance with WQ standards, a comprehensive WQ model of the receiving waters has been developed. The presentation focuses on ALCOSAN's WQ model, a key component of the CWP. Originally developed in 2010 using EPA's SWMM and the Corps of Engineers' RMA-2/RMA-4 models, the model underwent substantial upgrades in 2023. Separate models for various streams and rivers were combined into a single systemwide model. The SWMM segment for tributary streams was calibrated for E. coli, and the main rivers model migrated to EPA's Environmental Fluid Dynamics Code (EFDC), also calibrated for E. coli. Covering 280 miles, the model simulates hydrology, river hydraulics, bacteria loading, and temperature-dependent decay. Calibration results show a strong fit to observed data, supporting its suitability for simulating typical year scenarios. Upcoming (2024-2028) WQ data collection will further validate the WQ model. The presentation delves into the WQ model outcomes and assesses the anticipated WQ benefits of the CWP.

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