Development of a System to Maintain Satisfactory Dissolved Oxygen Levels in Gowanus Canal, New York City

As part of its CSO Long-Term Control Plan (LTCP) effort, the New York City Department of Environmental Protection (NYCDEP) has developed a plan to improve dissolved oxygen (DO) and water quality in Gowanus Canal, a 30-m wide, 2,400-m long enclosed tidal basin that is adversely impacted by combined sewer overflows (CSOs) and urban runoff. However, construction of Plan elements will necessitate shutting down the “Flushing Tunnel,” an existing engineered system that now supports DO levels by enhancing circulation in the Canal. During the 26-month shut-down period, DO in the Canal would fall to unacceptable levels. After assessing various remediation alternatives, NYCDEP developed an interim plan involving use of a centralized oxygen-transfer system whereby Canal water is withdrawn, oxygenated, and returned via a diffuser system. Analyses show that this system should maintain satisfactory oxygen levels throughout the length of the Canal while minimizing the possibility of other waterquality problems.