Catskill Aqueduct Pressurization

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NYWEA 2008 Watershed Conference
Pressurizing the Catskill Aqueduct to Increase
NYCs Water System Reliability
September 17, 2008
Roopesh Joshi, Hazen and Sawyer
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Cat-Del Water Supply System
Project Background

• Cat/Del system supplies approximately 90 of New
  York Citys water supply

Project Site
Kensico Eastview Section of Catskill Aqueduct
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Project Background

• UV Facility to be designed and constructed in
  lieu of starting final design of a 2,000-mgd
  Water Filtration Plant

• UV Facility to be located on City property at
  Eastview

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Schematic of Flow to and from UV Facility

• Pressurization of a segment of the Catskill
  Aqueduct needed for aqueduct to service UV
  Facility at Eastview

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Pressurization of the Catskill Aqueductas Raw
Water Supply to Eastview

• Eliminates the need for pumping to the UV
  Facility if using Catskill Aqueduct for raw water
  supply

• Increases reliability of raw water supply to
  Eastview by providing a second conduit

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Pressurization

• Goal Determine the rehabilitation measures
  needed for pressurization of Catskill Aqueduct
  from Kensico Reservoir to the Eastview Site to
  convey raw water to the UV Facility
• Lower Effluent Chamber (LEC) currently controls
  flow, operates on Kensico HGL Elev. 355
• Aqueduct currently operates under free-surface
  gravity flow conditions, Elev. 311
• UV Facility requires raw water at Kensico HGL,
  Elev. 355

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2004 Aqueduct Inspections

• Aqueduct inspected from Upper Effluent Chamber
  (UEC) to Catskill Connection Chamber (CCC)
• Length 12,443 feet
• Structures also inspected, where possible

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Aqueduct Sections Inspected

• Dike Grade Tunnel (1,165 feet)
• Kensico Cut-and-Cover (CC) Tunnel (2,176 feet)
• Kensico Grade Tunnel (1,515 feet)
• Kensico Steel Pipe Siphon (1,612 feet) center
  pipe only
• Eastview CC (99 feet)
• Eastview Grade Tunnel (5,456 feet between
  Eastview CC and Elmsford North CC)
• Includes brick-lined section
• Elmsford North CC (176 feet)
• Kensico (Catskill) Venturi Meter (could not be
  dewatered for inspection)

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Existing Aqueduct Conditions - Summary

• Sections of Aqueduct between Kensico Reservoir
  and Eastview in good condition.
• Samples of concrete lining extracted during
  coring indicate structurally sound concrete.
• Concrete reinforcement in circular reinforced
  concrete sections in good condition and free of
  rust.
• Ultrasonic measurements indicate competent lining
  or minor deterioration.
• Majority of deficiencies found at locations of
  groundwater infiltration. Results of GPR and
  ultrasonic testing indicate presence of voids and
  cavities behind the liner in these locations.

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Aqueduct Pressurization

• Rehabilitation
• Aqueduct Sections

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Rehabilitation Options

• All options considered both operating (primarily
  exfiltration)
• and dewatered (infiltration) aqueduct conditions
  in
• determining type and extent of rehabilitation
  work
• Option A Watertight Tunnel no leakage allowed
  in any section (1 gpm/ft dia/mi)
• Option B Reduced Leakage no leakage allowed to
  surface, reduced leakage in sections where
  aqueduct HGL is below ground surface

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Rehabilitation Options (Continued)

• Option C Minimum Rehabilitation required for
• pressurization no leakage allowed to surface
• For any section of aqueduct, rehabilitation cost
  is
• proportional to the work required. From Option A
  
• most costly, to Option C least costly
• Option A Watertight Tunnel
• Option B Reduced Leakage
• Option C Minimum Rehabilitation

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Aqueduct RehabilitationGrouting Program for
Base Case and Drift Tunnel Alternatives

• Purpose
• Fill voids
• Achieve good contact between lining and
  surrounding media
• Consolidate the ground
• Cut off water infiltration and exfiltration

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Contact Grouting

• Options A and B

Option C
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Materials Evaluated for Aqueduct Rehabilitation

• Strengthening
• Waterproofing
• Corrosion Proofing

• Strengthening through the addition of 2-inch
  to 12-inch shotcrete lining with or without
  reinforcement.
• Waterproofing through the use of an internal
  membrane concrete admixture.

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Replacement of Brick Lining in the Eastview Grade
Tunnel

• For Options A, B and C
• Replace brick lining with new reinforced concrete
  section apply waterproofing

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Aqueduct Pressurization

• Rehabilitation
• Existing Structures

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Rehabilitation of Existing Structures

• Floor elevation of existing structures is
  approximately 330 feet too low for
  pressurization to 355 feet.
• Structures must be modified to withstand the
  increased hydraulic grade.
• Existing Screen Chamber
• Currently undersized for anticipated flows and
  operates below future HGL of 355.
• Remove equipment within existing Screen Chamber.
• Screening for Catskill Aqueduct to be replaced by
  new Screen Chamber sized for increased flows to
  over 1,000 mgd.

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Rehabilitation of StructuresExisting Screen
Chamber

• Aqueduct will pass through this structure as a
  17-foot diameter pressure conduit partially
  demolish four piers in flow path

• Balance of structure will be backfilled between
  new pressure conduit and chamber walls
• Access into aqueduct through modified structure
  will be provided

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New Structures

• Screen Chamber
• Screening of Catskill Aqueduct flow from Kensico
  Reservoir
• Sized for anticipated flows of over 1,000 mgd
• Bypass Chamber
• Provides the connection point along the Catskill
  Aqueduct for transmitting raw water to the new UV
  Facility at the Eastview Site.
• Bypass Chamber is the point up to which the
  aqueduct will be pressurized.
• Drift Tunnel
• Connects the Bypass Chamber to the new UV
  Facility at the Eastview Site through a new 17-ft
  diameter rock tunnel.

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New Screen Chamber - Plan

• Construct between LEC and abandoned Catskill
  Aerators

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New Screen Chamber - Plan

• Build structure off-line (while aqueduct is
  active)

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New Screen Chamber - Plan

• Connect structure, and plug unused aqueduct
  section during shutdown

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New Bypass Chamber

• Construct BC adjacent to existing Aqueduct,
  off-line
• During an Aqueduct shutdown, make connections to
  and from BC, and bulkhead aqueduct directing flow
  through BC

Catskill Aqueduct
To Hillview
From Kensico
Air Gap
To UV Facility
Bypass Chamber
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Bypass Chamber and Drift Tunnel Alternatives

• Location depends on selected conveyance route
• Maximum aqueduct capacity is different for each
  Drift Tunnel alternative.

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Bypass Chamber for Drift Tunnel 1 - Section
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Bypass Chamber for Drift Tunnel 3 - Section
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Aqueduct Pressurization

• Costs

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Recommendation
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Recommended Plan Catskill Aqueduct
Pressurization

• Recommended Plan Provides the Greatest Hydraulic
  Capacity at the Least Cost
• Rehabilitation Option C (Minimum
  Rehabilitation)
• Drift Tunnel Alternative 1
• New 1,000 mgd Screen Chamber
• Modifications to existing structures

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Overall Schedule for Recommended Alternative
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Acknowledgements

• Mike Broder, Hazen and Sawyer
• Rich Peters, Hazen and Sawyer
• David Tanzi, CDM
• Leszek Glodkowski, Jenny Engineering
• Paul Smith, New York City DEP

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Questions?
REHABILITATION
Catskill Aqueduct
In association with
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Leakage Analysis of Ex-filtration
Aqueduct Rehabilitation

• Based on Dr. Ronald E. Heuers review, there is
  no calculable expected seepage outflow after
  conducting Option C.

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Updated Construction Costs for Recommended
Alternative
Summary of Recommended Alternative