AWWA ACE58234

The New Croton Aqueduct (NCA), built in the late 1800s/early 1900s, conveys raw water by gravity from upstate reservoirs over a distance of about 23 miles, ultimately reaching the Jerome Park Reservoir in the north Bronx. Downstream of this point, the NCA is pressurized and conveys treated water approximately eight miles to the 135th Street Gate House in Manhattan. Most of the Aqueduct lies below the local water table. Fifty-two structures (e.g., shafts, gate houses) penetrate the Aqueduct; many of these serve as access points. The New York City Department of Environmental Protection (NYCDEP) has been mandated to construct a Water Treatment Plant (WTP) to filter Croton system water, and two possible sites are under consideration. If the WTP is located in lower Westchester County, a portion of the gravity section of the NCA (downstream of the WTP) will be used to convey treated water to the Bronx and Manhattan Low Level Service. Additional protection against infiltration of contaminants into the Aqueduct downstream of the WTP may be required to protect the treated water. To address this concern, NYCDEP and its team of engineers conducted a comprehensive study to assess the potential sources of contamination to the New Croton Aqueduct, identifying hazardous materials sources, mechanisms whereby contaminants may be transported into the Aqueduct (such as through groundwater infiltration), and location of the most vulnerable sections of the Aqueduct. Following this assessment and completion of a pollution source inventory by type and location, the team developed a plan for protecting the Aqueduct from these contaminants. The plan included the following elements: recommendations for improving Aqueduct integrity and minimizing infiltration of contaminants; implementing a more rigorous water quality monitoring program; and, performing regular inspections of the treated water portion of the Aqueduct. The City is in the process of implementing the New Croton Aqueduct Plan, in preparation for construction of the Croton Water Treatment Plant. The City will also implement a rigorous inspection program to monitor Aqueduct status and conditions after the treatment plant has been placed in service. Includes figures.