Review of the New York City Watershed Protection Program (2020) / Chapter Skim
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3 New York City's Water Supply System: Past, Present, and Future
3 New York City's Water Supply System: Past, Present, and Future
Pages 53-90
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From page 53... ...
Each has a dam and spillway controlling its outflow. "Controlled" further applies to controlled access and controlled use, to protect the drinking water supply.
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From page 54... ...
54 Review of the New York City Watershed Protection Program FIGURE 3-1 New York City's surface water supply system. Figure in color at https://www.nap.edu/ catalog/25851/.
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From page 55... ...
1926 Schoharie Reservoir is completed. 1927 Board of Water Supply submits a plan for development of upper portion of the Rondout watershed and tributaries of the Delaware River within New York State.
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From page 56... ...
Because of the pressing need for a dependable water supply, and the lopsided balance of power between New York City and isolated rural communities, the Croton system's construction was the City's first use of eminent domain, including condemnation of properties and relocation of residents. This was an extraordinary step in the young republic where few, if any, tests of the Fifth Amendment to the Bill of Rights ("… nor shall private property be taken for public use, without just compensation")
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From page 57... ...
The complete Croton System is shown in Figure 3-2. With the construction of additional dams and the addition of chlorine disinfection, the Croton System was completed in 1911 and today provides roughly 10 percent of the City's water supply.
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From page 58... ...
Concurrently, the State legislature passed the state Public Health Law of 1905, allowing the City to regulate land use in the upstate watershed to protect City drinking water and providing the City eminent domain to acquire land needed for the water supply. This legislation also authorized the State Department of Health (DOH)
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From page 59... ...
The Bureau of Water Supply includes three groups responsible for the operation of the system. Source Water Operations, with 279 full-time equivalent (FTE)
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From page 60... ...
60 FIGURE 3-3 Schematic and flow from the Croton, Catskill, and Delaware systems. Figure in color at https://www.nap.edu/catalog/25851/.
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From page 61... ...
Compared to typical run-of-the river intake drinking water supplies, New York City's water supply is larger and more complex, with multiple interconnections among diverse components of the supply that allow for considerable operational flexibility. NYC DEP uses a sophisticated model (the Operations Support Tool)
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From page 62... ...
Surface water flows from the Ashokan Reservoir via the 75-mile long Catskill Aqueduct, which travels through the Croton Watershed to the Kensico Reservoir in Westchester County. The combined detention time and flow configuration of the Catskill reservoirs and Kensico is generally sufficient to remove turbidity to below drinking water standards (with the exception being during and after large storms)
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From page 63... ...
This bypass is generally initiated when wind creates shoreline erosion and raises turbidity within Kensico Reservoir, which could degrade the quality of water coming from the Catskill and Delaware aqueducts. Upon leaving Kensico, the flow enters the UV plant, from which it flows by gravity to Hillview Reservoir.
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From page 64... ...
Second, newly renovated stop shutters in the Catskill Aqueduct allow system operators to drastically reduce flows from the Catskill system into the City's supply without affecting the delivery of water to communities that draw from the aqueduct above Kensico Reservoir. Third, both the Catskill and Delaware aqueducts can bypass West Branch and Kensico reservoirs, the so-called float mode, if local conditions might impair water quality in those reservoirs.
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From page 65... ...
Tropical Storm Irene delivered an estimated 12-16 inches of rain in 12 hours to the Schoharie basin and up to 10 inches of precipitation throughout the region on August 28, 2011. Within 24 hours of the storm, NYC DEP began adding alum to the Catskill Aqueduct, and they adjusted diversions to maintain acceptable water quality in Kensico Reservoir.
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From page 66... ...
Water Demand The NYC water supply service area includes 8.5 million City residents and nearly 1 million residents of Westchester, Putnam, Orange and Ulster counties. Demand for water has declined more than 30 percent since 1990 (Figure 3-5)
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From page 67... ...
The City's current demand management plan (NYC DEP, 2018) includes six strategies to reduce water usage systemwide including programs that address municipal water efficiency, residential water efficiency, nonresidential water efficiency, water distribution system optimization, water supply shortage management, and upstate wholesale customer demand management.
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From page 68... ...
REGULATORY FRAMEWORK FOR FILTRATION AVOIDANCE The primary driver of NYC's Watershed Protection Program is the federal Safe Drinking Water Act's Surface Water Treatment Rule, which governs the conditions under which NYC's water system can continue its status as an unfiltered supply. In addition, elements of the Watershed Protection Program related to managing water quality within the reservoirs and streams are affected by the provisions of the federal Clean Water Act (CWA)
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From page 69... ...
Low levels of source water turbidity; 3. Adequate watershed protection and control; 4.
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From page 70... ...
The public water system must demonstrate through ownership or written agreements with landowners in the watershed, or a combination of both, that it controls all human activities which may have an adverse effect on the microbi ological quality of the source water. The system must submit an annual report to the State that identifies any special concerns about the watershed and how they are being handled; describes activities in the watershed that affect water quality; and projects what adverse activities are expected to occur in the future and describes how the public water system intends to address them.
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From page 71... ...
Unfiltered surface water supplies must implement disinfection adequate to inactivate 99.99 percent of enteric viruses, 99.9 percent of Giardia, and with the promulgation of the Long-Term 2 Enhanced SWTR (LT2) , 99 percent of Cryptosporidium.6 LT2 also added the requirement that two separate primary disinfectant processes be used, each capable of providing the full required inactivation for at least one of the target organisms.
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From page 72... ...
Revisions to the Surface Water Treatment Rule. Since 1989 when EPA issued the SWTR, there have been three major revisions, none of which substantially altered the watershed control-related conditions for filtration avoidance.
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From page 73... ...
, promulgated in 2000, established standards similar to those of the IESWTR for smaller systems. Finally, the Long Term 2 Enhanced Surface Water Treatment Rule (LT2)
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From page 74... ...
Water Quality Standards The CWA establishes the basic structure for regulating the quality of surface waters of the United States. States must designate beneficial uses for all surface waters (e.g., recreational uses; protection and propagation of fish, shellfish, and wildlife; drinking water supply)
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From page 75... ...
should be made consistent with that apportionment. Some waterbodies within the NYC water supply watershed have been identified as not meeting water quality standards.
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From page 76... ...
. No Phase I permittees exist in the watershed for NYC's drinking water supply.
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From page 77... ...
NYC DEP's OST is now used to manage water forecasted to be available and to inform reservoir release decisions. State and Local Regulations That Affect the NYC Water Supply Operational aspects of the NYC water system also are regulated by the NYS DEC, in part through their water supply permit program.
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From page 78... ...
Meeting these needs will require substantial investment in rehabilitating or repairing the Delaware and Catskill aqueducts, providing a redundant connection between the Kensico Reservoir and the Eastview UV plant, covering Hillview Reservoir, and extensive work on dams and intakes in the reservoir system. The public is constantly exposed to potentially confusing messages about water quality.
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From page 79... ...
This new tunnel will provide additional conveyance of 2.6 BGD between Kensico Reservoir and the UV facility. The project also will include rehabilitation and enlargement of a 100-year-old intake structure at Kensico Reservoir, shoreline improvement of Kensico Reservoir, construction of an interconnecting structure for the Town of Mount Pleasant water supply, upgrades to the chemical feed systems at Kensico Reservoir, and construction of a connection chamber at the UV disinfection facility.
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From page 80... ...
These factors may not be FAD or filtration issues per se, but they are important to the larger issues of water supply operation. In addition to regulatory trends, advances in laboratory methods and continued public attention to any water-related potential risk raise issues of how to maintain public confidence in the safety of drinking water.
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From page 81... ...
EPA continues to examine DBP national occurrence and potential health risks, most recently by including additional haloacetic acids in the current UCMR. NYC DEP meets all current DBP regulations and has undertaken studies of source water quality and disinfection levels to evaluate the potential for DBP production and to consider reservoir operating procedures to manage DBP production.
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From page 82... ...
Thoughts about the likely design of a filtration system for the NYC water supply follow. The most likely design for a NYC filtration plant would be to use granular media.
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From page 83... ...
, the number of filters required would be 105 at the higher design filtration velocity and 175 at the lower value. BOX 3-1 Filtration 101 Filtration has been a standard treatment process for preparing drinking water from surface water supplies for more than 100 years.
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From page 84... ...
can lead to the detachment of previously captured particles; such detached particles or flocs of particles can be recaptured in deeper portions of the fil ter or, ultimately, be discharged out of the filter. If either the head loss gets too high or the effluent water quality (typically measured as turbidity)
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From page 85... ...
This response is required by the SWTR in some cases but is also common in cases of actual or feared pathogen contamination of a drinking water supply. Here a boil-water order is used as a surrogate consequence for a major drinking water quality failure.
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From page 86... ...
A great reduction in source water quality reliability or a great lowering of the relative costs of filtration would be needed to make filtration of New York City's water supply economically desirable, balancing benefits and costs. Although great reductions in filtration costs seem unlikely (e.g., new technologies)
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From page 87... ...
Systems with poorer source water quality would have a higher ∆Pf line. For a given water supply system, there is only one line.
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From page 88... ...
Expediting the project to cover the Hillview Reservoir would further strengthen the water supply system by protecting water immediately after disinfection. Hillview Reservoir should be covered expeditiously, and in advance of the current timeline for doing so.
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From page 89... ...
2019. City of New York agrees to settle federal complaint by covering the Hillview Reservoir to prevent contamination of the city's drinking water supply.
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From page 90... ...
2017. New York City Water Supply System Reference Guide.
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