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Water Treatment for NYC

Water Treatment for NYC. Croton Schematic. 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

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Water Treatment for NYC

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  1. Water Treatment for NYC Croton Schematic

  2. 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

  3. Safe Drinking Water Act Turbidity Loophole • At no time can turbidity (cloudiness of water) go above 5 nephelolometric turbidity units (NTU) • Systems that filter must ensure that the turbidity never exceed 1 NTU, and must not exceed 0.3 NTU in 95% of daily samples in any month

  4. NYC DEP Data Interpretation • As of 2001 NYC only reports monthly average turbidity • “The MCL for turbidity is the monthly average rounded off to the nearest whole number” • “Data presented are range and averages of monthly averages”

  5. 141.71Criteria 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.

  6. 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

  7. 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. § 141.71 Criteria for Avoiding Filtration

  8. Pro Con Should NYC have to Filter?

  9. 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. To treat Delaware Catskill water

  10. Croton Treatment Scheme

  11. Croton Plant

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

  13. Design Flow for Water Treatment 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 designed for 83 m3/s

  14. 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

  15. 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 • Contact Filtration • Ultraviolet disinfection (selected by NYC) sedimentation basins

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

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

  18. UV Disinfection • Kills pathogens • Does not reduce turbidity • May be approved as an alternative to filtration for NYC Catskill/Delaware water supply • Costs much less than a filtration plant

  19. 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 - _______ 37 m/hr

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

  21. 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

  22. Backwash Water Disposal Options • Backwash water production • Approximately 3% of useable production! • Often not recycled because of potential concentration of pathogens • Will be recycled at the Croton filtration plant • Solids production • particles present in raw water (0.1-10 mg/L) • coagulant (5 - 50 mg/L) • Disposal options

  23. 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

  24. Summary • NYC is designing an ultraviolet disinfection plant (with 2009 target for operation) • The WTP will be constructed somewhere between Kensico and Hillview Reservoirs • The WTP will be designed to handle recent peak daily flows

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

  26. Catskill Aqueduct Delaware Aqueduct Kensico to Hillview

  27. Possible Water Treatment Plant Site Kensico

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

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