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NYC Filtration Plant for Delaware and Catskill Systems

NYC Filtration Plant for Delaware and Catskill Systems. Filtration avoidance criteria Alternatives to Filtration? Where should the plant(s) be located? Multiple plants or one plant? Treatment steps at different locations? Design flow Treatment scheme Backwash water.

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NYC Filtration Plant for Delaware and Catskill Systems

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  1. NYC Filtration Plant for Delaware and Catskill Systems • Filtration avoidance criteria • Alternatives to Filtration? • Where should the plant(s) be located? • Multiple plants or one plant? • Treatment steps at different locations? • Design flow • Treatment scheme • Backwash water

  2. SDWA Turbidity Loophole • At no time can turbidity go above 5 nephelolometric turbidity units (NTU) • Systems that filter must ensure that the turbidity go no higher than 1 NTU (0.5 NTU for conventional or direct filtration) in at least 95% of the daily samples for any two consecutive months • Delaware-Catskill turbidity range was ________ with an average of 1.06 NTU in 2000 • NYC claims the MCL of 5 NTU is for a monthly average 0.5-10.0

  3. § 141.71 Criteria for avoiding filtration. • The turbidity level cannot exceed 5 NTU (measured as specified in § 141.74 (a)(4) and (b)(2)) in representative samples of the source water immediately prior to the first or only point of disinfectant application unless: (i) the State determines that any such event was caused by circumstances that were unusual and unpredictable; and (ii) as a result of any such event, there have not been more than two events in the past 12 months the system served water to the public, or more than five events in the past 120 months the system served water to the public, in which the turbidity level exceeded 5 NTU. An ‘‘event’’ is a series of consecutive days during which at least one turbidity measurement each day exceeds 5 NTU.

  4. Limited Alternative To Filtration • States may allow unfiltered water systems with surface water sources to use treatment other than filtration • In order to qualify for alternative treatment, a water system must have an __________, ____________ watershed in consolidated ownership and have control over access to and activities in the watershed • The alternative treatment must ensure _________ removal or inactivation efficiencies of pathogenic organisms than would be achieved by the combination of filtration and chlorine disinfection required by section 1412 (b)(7)(C). [1412(b)(7)(C)] Sec. 106 undeveloped uninhabited greater

  5. § 141.71 Criteria for avoiding filtration • The public water system must demonstrate through ownership and/or written agreements with landowners within the watershed that it can control all human activities which may have an adverse impact on the micro-biological quality of the source water. The public water 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 expects to address them.

  6. Where Should Plant(s) Be Located? • ______________________________________________________________________ • ___________________________________ • ___________________________________ • ___________________________________ Between last watershed reservoir (Kensico) anddistribution reservoir (Hillview) Near tunnel On hydraulic grade line! (No pumps) Commercial/Industrial area (not residential)

  7. Design Flow for New Filtration Plant • Max day ever was 94 m3/s in 1975 • Future growth? • Conservation? • Croton system is separate • Proposed filtration plant for 12.7 m3/s • Ability to shut down Croton system? • Catskill/Delaware plant • Expert Panel 48.3 m3/s • NYCDEP (Debra Thomas 10/27/97) 83 m3/s

  8. Croton Plant • The construction costs of the water filtration plant, with a design capacity of 290 million gallons per day (mgd), and the related facilities, is estimated at $660 million. • Annual operations and maintenance costs are projected to be $11 million. • The plant will use state-of-the-art disinfection and filtration processes including dissolved air flotation for the removal of solids, ozonation for primary disinfection, and biologically active carbon filtration.

  9. Maximum Daily Flow 90.0 80.0 70.0 60.0 50.0 Maximum daily demand (m3/s) Catskill/Delaware 40.0 30.0 Croton 20.0 10.0 0.0 1978 1980 1982 1984 1986 1988 1990 1992 1994 year

  10. Treatment Plant Options for NYC • NYC’s water is high quality (<2 NTU) • Low particle concentration means that ___________ ______ aren’t necessary • Three options for WTP with high quality surface waters • Direct Filtration (most likely option for NYC) • Contact Filtration • Ultraviolet disinfection sedimentation basins

  11. Direct Filtration Raw water Filtration Screening sludge sludge Alum Polymers Rapid Mix Disinfection Cl2 Flocculation Storage Distribution

  12. Contact Filtration Raw water Filtration Screening sludge sludge Alum Polymers Rapid Mix Disinfection Cl2 Storage Distribution

  13. Size of Major Unit Processes Unit Process Parameter Range Flocculation  10-30 min Sedimentation Q/As 0.67 m/hr Filtration Va2.5 - 37 m/hr Los Angeles - _______ NYC considering 15 - 30 m/hr (likely 25 m/hr) 37 m/hr

  14. U FB B Backwash Requirements Total filter bed area Useable production (or area) Production used forbackwash Filter beds off line to be backwashed AT = AU + AFB + AB

  15. Area of Filter Beds in Useable Production (U) • Plant Design Flow • 83 m3/s • Area required without backwash (Va = 25 m/hr) • Backwash requirements? • 10 minutes at 50 m/hr once every 12 hours • assume 30 minute downtime for backwash • The useable filter bed area must be increased by 5 – 10% to meet backwash requirements 36.4 ha site ha=10,000 m2

  16. Backwash Water Disposal Options • Backwash water production • Approximately 3% of useable production! • Not recycled because of potential concentration of pathogens • Solids production • particles present in raw water (0.1-10 mg/L) • coagulant (5 - 50 mg/L) • Disposal options

  17. Area of Flocculation Tanks • Hydraulic retention time of 10-30 minutes • Los Angeles uses 8 minutes • Typical depth of 5 meters • Area required for flocculation will be similar to that required for filtration • Contact filtration would eliminate the need for flocculation tanks

  18. Summary • NYC Catskill/Delaware WTP (if built) will be either direct or contact filtration • The WTP will be constructed somewhere between Kensico and Hillview Reservoirs • The WTP will be designed to handle recent peak daily flows: future demand will need to be restricted to current levels • The WTP will cost several billion dollars • In the meantime, NYC will build an ultraviolet disinfection plant.

  19. Supply Aqueducts and Tunnels Catskill Aqueduct Shandaken Tunnel Delaware Aqueduct Neversink Tunnel East Delaware tunnel West Delaware tunnel

  20. Catskill Aqueduct Delaware Aqueduct Kensico to Hillview

  21. Possible Filtration Plant Site Kensico

  22. Possible Filtration Plant Site 90 acre site 36.4 ha ha=10,000 m2 Close to Catskill and Delaware Aqueducts 1 km

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