long-term cso control plan for north dorchester bay and ...annual cso volume has been reduced...
TRANSCRIPT
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Massachusetts Water Resources Authority
Frederick A. LaskeyExecutive Director
Long-Term CSO Control Plan for North Dorchester Bay and
the Reserved Channel
March 8, 2004
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How Sewer Separation Works
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How CSOs Work: Dry Weather
CSO Outfall
Headworks
To Deer Island
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How CSOs Work: During Heavy Rains
Headworks
To Deer Island
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MWRA’s CSO Communities
• Boston, Cambridge, Chelsea and Somerville have combined sewer systems that connect toMWRA's sewer system
• Boston Harbor, the Charles, the Mystic and the Neponset Rivers are subject to overflows of combined stormwater and sewage during heavy rains
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The CSO Problem
• In 1985, the service area had:
– 84 combined sewer outfalls
– Thousands of overflows per year
– Over 3 billion gallons of CSO discharges
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Status Of CSO Control Nation-Wide
• 772 CSO communities
• 32% have submitted documentation on Nine Minimum ControlsMWRA
• 19% have approved long-term control plansMWRA
• 17% have initiated implementation of long-term control plans or other CSO facility plans
MWRA
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Annual CSO Volume Has Been Reduced Dramatically
Untreated Treated
0
0.5
1
1.5
2
2.5
3
3.5
1988 1992 2003 2008
Bill
ions
of G
allo
ns• Annual CSO volumes have already been reduced by over 2.5 billion
gallons
• By 2008, 95% of the remaining CSO flows will be treated
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Court-approved plan
$0
$100
$200
$300
$400
$500
$600
$700
$800
$900
$1,000
Conceptual Plan (Dec 1994)
Facilities Plan/EIR (Aug 1997)
FY04-06 CIP Current Estimate withPotential Additional
Costs
Mill
ions
$406 M
$481 M
$645 M
Risk of cost increases -$200-300M
CSO Project Costs
Does not include overall system improvements (e.g. Deer Island)
Court-approved plan
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South Boston Beaches
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South Boston Beaches
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North Dorchester Bay: Existing Conditions
• Seven CSO outfalls discharge to North Dorchester Bay
• During a typical year, each outfall activates between one (BOS085) and 21 times (BOS081) per year and discharge a total of approximately 8 million gallons of CSO flow into North Dorchester Bay
• Discharges are caused both by constraints in the interceptor system and the capacity of the Columbus Park Headworks
• Rain events occur 108 times per year discharging approximately 144 million gallons of separate stormwater through these outfalls
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North Dorchester Bay/Reserved Channel: Existing System
Columbus ParkHeadworks
076078
079079 080
081
082
083084085
086
087
BMD to DITP
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CSO Control Plan Reassessment
• Reassessment initially examined 160 alternatives and identified 58 potential locations for siting CSO facilities
• North Dorchester Bay control alternatives were narrowed to interceptor relief and a storage tunnel, with sewer separation recommended for Reserved Channel
• Ultimately focused on four key objectives:– Increasing storage capacity to virtually eliminate CSO discharges
without a massive pump station– Modifying design to accept some stormwater without compromising
CSO control– Minimizing impacts during construction– Minimizing siting issues
• These objectives are met by a large diameter storage tunnel mined with a tunnel boring machine
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Columbus ParkHeadworks
076078
079
080
081
082
083084085
086
087
BMD to DITP10-mgd
Pump Station
Odor ControlFacility
17-Foot Soft Ground Tunnel: 25-Year CSO Control
17-foot, soft ground storage tunnel with pump-out at Conley Terminal
Odor control facility at State Police Barracks
Virtual elimination of CSOs to North Dorchester Bay
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Columbus ParkHeadworks
076078
079
080
081
082
083084085
086
087
BMD to DITP10-mgd
Pump Station
Odor ControlFacility
StormwaterGates
Operable Gates: 25-Year CSO Control and Up To 1-Year Stormwater Control
Gates open and tunnel accepts stormwater
No CSO or stormwater discharges to North Dorchester Bay
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Columbus ParkHeadworks
076078
079
080
081
082
083084085
086
087
BMD to DITP10-mgd
Pump Station
Odor ControlFacility
StormwaterGates
Enlarged Morrissey Boulevard Storm Drain: 25-Year CSO Control and Up To 5-Year Stormwater Control
BOS087 stormwater is redirected to an enlarged stormwater drain along Morrissey Boulevard and discharged to South Dorchester Bay
5-year level of stormwater control for North Dorchester Bay
EnlargedStorm Drain
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BOS087 Stormwater Tributary Area
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Pleasure Bay
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Columbus ParkHeadworks
076078
079
080
081
082
083084085
086
087
BMD to DITP10-mgd
Pump Station
Odor ControlFacility
StormwaterGates
Pleasure Bay Stormwater
Pleasure Bay outfalls redirected to BOS080 for discharge to Reserved Channel
EnlargedStorm Drain
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Columbus ParkHeadworks
076078
079
080
081
082
083084085
086
087
BMD to DITP10-mgd
Pump Station
Odor ControlFacility
StormwaterGates
EnlargedStorm Drain
Separate ~ 355-acre area between Reserved Channel and East 4th Street
Reduce frequency of CSO discharges from 37 to 3 in a typical year
Reduce CSO discharge volume from 41 mg to 1.4 mg in a typical year
Reserved Channel Sewer Separation
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Performance Summary
• North Dorchester Bay: 25-year level of CSO control and 5-year level of separate stormwater control
• Pleasure Bay: Eliminate stormwater discharges
• Reserved Channel: Reduce CSO discharges from 37 to 3 in a typical year
• South Dorchester Bay: Roughly 15% increase in stormwaterdischarges in a typical year
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Recommended Plan
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Pump Station Location
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Pump Station Elevation View
3,360 square foot building, 56 ft. x 60 ft.
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Comparison of Pump Station Sizes
• The proposed footprint is one-fifth the size of the previous plan
• The proposed building volume is one-tenth the size of the previous plan
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Pump Station Proximity to Residences
-1000’-
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Proposed 20-Inch Dewatering Force Main
Farragut Street to East 5th Street to N Street
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Odor Control Facility Location
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Odor Control Facility Elevation View
2,900 square foot building, 45 ft. x 64 ft.
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Comparable MWRA Facility
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How Odor Control Works
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Tunnel Construction Methods
• Tunnel will be constructed using a soft-ground tunnel boring machine (TBM) designed and built specifically for this project
• Tunnel construction would proceed 24 hours per day
• As the tunnel is mined, a pre-cast, segmental concrete lining will be installed behind the TBM
• Construction of the tunnel will be performed from a mining shaftlocated near the entrance of Conley Terminal
• Upon completion, the TBM will be removed through a receiving shaft located behind the State Police barracks
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Dropshaft Locations
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Example of Dropshaft at End of N Street
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Example of Diversion Structure Construction at Dropshaft
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Truck Route for Mining Operation and Pump Station Construction
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Conceptual Construction Timeline
North Dorchester Bay
May-05
Nov-05
May-06
Nov-06
May-07
Nov-07
May-08
Nov-08
May-09
Nov-09
May-10
Nov-10
May-11
Design
Bid/Award Construction
Mobilization/Mining Shaft
Mine & Line Tunnel
Complete Pump Station & Odor Control Bldg.
Reserved Channel
Mar-05
Aug-05
Mar-06
Aug-06
Mar-07
Aug-07
Mar-08
Aug-08
Mar-09
Aug-09
Mar-10
Aug-10
Mar-11
Design
Bid/Award Construction
Construction
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Projected Costs
(in 2004 dollars)
Storage Tunnel $186 million
Stormwater Gates $2 million
Morrissey Boulevard Storm Drain $18 million
Pleasure Bay Stormwater Diversion $3 million
Reserved Channel sewer separation $48 million
Estimated cost of recommended plan $257 million
Total program cost with inflationbut not site acquisition costs $285 million
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North Dorchester Bay CSO and Stormwater Discharges Over an Typical 5-Year Period
531
1
105
00
100
200
300
400
500
600
Now Recommended Plan
Day
s
Stormwater CSO
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Conclusion
• Highest level of control of any Boston Harbor beaches
• Eliminate CSO discharges – no human waste on the beaches
• Reduce volume of stormwater discharges to North Dorchester Bay by over 96% and eliminate stormwater discharges to Pleasure Bay
• Reduce CSO discharges to Reserved Channel from 37 to 3 in a typical year
• No large permanent facilities
• Build tunnel with a tunnel boring machine to minimize construction impacts
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Next Steps
• The MWRA Board of Directors will be asked to approve the submittal to MEPA by March 31, 2004 of Supplemental Facilities Plan and Environmental Impact Report
• A 60-day comment period will follow for public and agency review
• In the meantime, DEP and EPA conduct their review of the project’s compliance with the Clean Water Act and national and state CSO policies
• MWRA will continue coordination with interested parties and hold an additional public meeting in May
• Once MEPA review is successfully completed, MWRA will renegotiate design and construction schedules with Court Parties for incorporation into Federal Court Order
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