South Boston CSO Reassessment

Transcription

1 South Boston CSO Reassessment Wastewater Advisory Committee November 1,

2 South Boston CSO System South Boston Interceptor North Branch Reserved Channel Boston Main Drain Tunnel Columbus Park Headworks Pleasure Bay Carson Beach South Boston Interceptor South Branch South Boston Interceptor Main Trunk North Dorchester Bay

3 Recommended Plan

4 Reassessment and MEPA Process Phase I Update Baseline Conditions (System Flows and WQ) Identify and Screen a Full Range of Control Options Identify and Evaluate Site Options Phase II Detailed Evaluation of Shortlisted Control Alternatives Select a New Recommended CSO Control Plan Submit SEIR for MEPA Review and Public Comment Public Participation/Consensus Building Throughout

5 Reassessment Goal Recommend an implementable CSO control plan for the beaches and Reserved Channel that: is acceptable to the public meets meets State and National CSO control policy requirements and complies with WQ standards is acceptable to the Federal Court is approved by MWRA Board

6 Four Control Options N. Dorch. Bay: Interceptor Relief Res.. Channel: Sewer Separation N. Dorch. Bay: Storage Conduit Res.. Channel: Sewer Separation N. Dorch. Bay: Storage with Phased NDB Separation Res. Channel: Sewer Separation N. Dorch. Bay: CSO Relocation (Previous Plan) Res.. Channel: Tunnel Storage (Previous Plan)

7 Option 1 NDB Interceptor Relief with RC Sewer Separation Fort Point Channel Lower Inner Harbor BOS080 Separation Reserved Channel BOS076 BOS079 BOS078 BOS080 Pleasure Bay BOS076 to BOS079 Separation BOS081 BOS085 BOS084 BOS083 BOS082 SBI South Branch Relief BOS086 Est. Cost BOS087 N. Dorch. Bay Res. Chan. North Dorchester Bay $100M No CSO Discharge in Typical Year no Change in SW CSO Discharges in Typical Year

8 Option 2 NDB Storage Conduit with RC Sewer Separation Fort Point Channel G Lower Inner Harbor BOS076 BOS078 BOS079 E Reserved Channel BOS080 F D Pleasure Bay Reserved Channel Separation BOS084 BOS082 BOS081 Storage Conduit B A BOS085 BOS083 BOS086 Est. Cost BOS087 NDB RC North Dorchester Bay $130-$230M No CSO Discharge in Typ yr or up to 5 yr Storm No SW Discharge in Typ yr or up to 5 yr Storm Untreated CSO Discharges in Typical Year

9 Option 3 - NDB Storage Conduit and Phased Sewer Separation With RC Sewer Separation Reserved Channel Separation Fort Point Channel G Lower Inner Harbor Phased Separation of BOS081 to BOS087 BOS076 BOS078 BOS079 E Reserved Channel BOS080 D F Pleasure Bay B A BOS085 BOS086 BOS087 BOS084 Est. Cost NDB RC BOS083 BOS082 BOS081 With Storage : Storage Conduit $190 to $270 Million North CSO Dorchester Discharge Bay in Typ yr or up to 5 yr Storm No SW Discharge in Typ yr or up to 5 yr Storm With Storage and Separation: No CSO Discharge in Typ yr or up to 25 yr Storm 2 SW discharges in Typical Year 3 Untreated CSO Discharges in Typical Year

10 Option 4 -NDB CSO Relocation/ RC Consolidation (Previous Plan) Fort Point Channel G Lower Inner Harbor BOS076 BOS078 BOS079 E Reserved Channel BOS080 F Pleasure Bay BOS085 BOS086 BOS087 BOS081 BOS084 BOS082 BOS083 Est. Cost North Dorchester Bay N. Dorch. Bay Relocation/ Consolidation Conduit $ M CSO Elimination 5-yr SW Control A Res. Chan. 5-yr Untreated CSO Control

11 Cost/Performance of CSO Control Options for 5-Year Period 600 $330M $350 # Discharges in 5-Year Period $0 540 $100M $130M $230M $210M $310M $270M $220M 0* 1 No Action Option 1 Option 2a Option 2b Option 3 Option 4 $300 $250 $200 $150 $100 $50 Project Cost ($millions) CSO SW Cost (High) Cost (Low)

12 Minimum Site Size Requirements Facility 600 MGD CSO Facility with Concurrent Mining Shaft 600 MGD CSO Facility with Phased Mining Shaft Approximate Site Requirements Permanent Facility 3 acres 3 acres Facility and Construction 10 acres 6 acres Mining Shaft Only 0.25 acres 4 acres 10 MGD Dewatering Facility 0.5 acres 4 acres Tunnel Odor Control Facility 0.5 acres 0.75 acres

13 Summary of Potential Sites after Initial Screening Set aside by screening criteria Carried per MEPA/EPA requirement Fits up to 600 MGD CSO Facility with Concurrent Mining Shaft Fits up to 600 MGD CSO Facility with Phased Mining Shaft Fits up to 10 MGD Dewatering Facility Fits Tunnel Odor Control Facility

14 Next Steps Complete WQ Sampling Program (November 02) Complete Phase I Evaluations (December 02) Cost/Performance Initial Look at Water Quality Impacts Start Detailed Siting Evaluations Short list of potential sites and technologies/levels of control Initiate Phase II of Reassessment (January 03) Site-specific layouts of alternatives Detailed Evaluation Based on Identified Criteria Complete Phase II Evaluations (Spring 03) File SEIR with Revised Recommended Plan

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17 Initial Site Screening Criteria Based on Land Use Actively Utilized Park/Recreation Areas Residences Located within 500 Feet Future Plans Historical/Archaeological

18 South Boston CSO Reassessment Will Follow MEPA Process April 2001 Notice of Project Change Presented Proposed Scope of Work Reassessment Will Result in a Supplemental Environmental Impact Report (SEIR)

19 Summary of Alternatives Screening Process 165: Initial Number of Alternatives 67: Remaining Alts after Initial Screening, Comparing Similar Alts 41: Remaining Alts after Combining N. Dorch. Bay and Res. Chan. Alts as Appropriate 4: Major CSO Control Options, based on Inspection of Remaining 41 Alternatives

20 Site Screening Criteria Based on Size/Configuration After applying land use criteria: - Sites too small to construct a facility - Sites with a configuration precluding construction of a facility