Although New York's Catskill and Delaware water supplies are known for their excellent water quality, and has been granted avoidance of the need for filtration, concerns over heightened development in the watershed, coupled with increased vigilance over Cryptosporidium- and Giardia-related illness following outbreaks in other parts of the US and EPA’s Long Term 2 Enhanced Surface Water Treatment Rule, prompted the New York City Department of Environmental Protection (NYCDEP) to initiate the design and construction of a 2,020-mgd Ultraviolet (UV) Disinfection Facility in Westchester County. Hazen and Sawyer, in joint venture, undertook pilot testing, planning, environmental assessment, design, permitting and construction services for the innovative Catskill-Delaware Ultraviolet Disinfection Facility.
In a UV disinfection reactor, UV light inactivates microorganisms by causing photochemical damage to nucleic acids. Study results determined that it is feasible to use UV light for the disinfection of the Cat-Del water supplies to meet current and anticipated regulations.
To inform design, we built a validation facility to test the UV disinfection unit’s ability to meet the treatment, headloss, and power consumption goals, while also enabling competitive procurement of UV units.
Testing established the design criteria and validated the disinfection capability of the 60-mgd UV unit to be used in the facility.
The disinfection study and the environmental impact study for the Catskill-Delaware UV Disinfection Facility each received top honors from NY-ACE in the Engineering Excellence Competition.
Upon completion, the Catskill-Delaware facility will be the largest drinking water ultraviolet disinfection installation in the world.
The UV disinfection facility will have a smaller footprint and lower energy needs than a filtration plant of the same capacity, saving New York City more than $1.5 billion in construction costs and $25 million/year in operation costs.
The design incorporates inlet structures, screening, dedicated flow meters, UV reactors, and flow control valves.
Also included in the designs were hydrogenerators to recover energy from the available head in the system.
The design required planning for integration of the new facilities into the existing hydraulic grade of an operating system without interruption of the water supply to the City of New York.
A rendering of the Catskill-Delaware UV Facility, slated for completion in 2012.
While NYCDEP initially was granted a Filtration Avoidance Determination (FAD) in 1993, relieving the City from having to filter the Catskill and Delaware supplies, the FAD did require that the City plan for filtration in the future if the water supply were to change. However, the FAD does not exempt the City from needing to provide a form of disinfection that targets Cryptosporidium as required by the EPA’s Long Term Enhanced Surface Water Treatment Rule. By evaluating the effectiveness of UV disinfection against inactivating Cryptosporidium and Giardia, Hazen and Sawyer helped ensure that the City would not have to construct a filtration plant in order to maintain a safe and reliable water supply. The design and construction of the UV facility was then integrated into the FAD, which currently extends through 2017.
Hazen and Sawyer’s conceptual design for the facility evaluated both low-pressure high-output (LPHO), and medium-pressure UV units. LPHO was ultimately selected and we developed an approach that achieved testing to validate the unit’s effectiveness to meet the treatment, headloss, and power consumption goals, while at the same time providing for competitive procurement of UV units. The design was then customized around the selected equipment and required planning for integration of the new facilities, as well as potential future filtration facilities, into the existing hydraulic grade of a completely gravity fed system, all without interruption of the water supply to NYC.
As part of the JV team, the firm completed final design for the facility and is currently providing construction related engineering services, with construction set to be completed in 2012. Once constructed, this facility will have the landmark designation as the world’s largest for treating municipal drinking water.
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