TOWN OF BELMONT WINNS BROOK SEWER OVERFLOW MITIGATON

TOWN OF BELMONT WINN’S BROOK SEWER OVERFLOW MITIGATON Presentation to the BOARD OF SELECTMAN December 7, 2009 Fay, Spofford & Thorndike

Presentation Objectives • • Project background Causes of sewer overflows Conceptual design and modeling Final Design Opinion of probable construction cost Funding Schedule Fay, Spofford & Thorndike

Winn’s Brook Area • Low lying area in Northeast Belmont • Close proximity to MWRA connection on Flanders Road • 85% of Belmont tributary to Flanders Road • Extensive upstream sewer system • Two different sewer subsystems Fay, Spofford & Thorndike

The Problem Periodic sanitary sewer overflows and backups into basements of homes in the Winn’s Brook Area Fay, Spofford & Thorndike

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Reported Backups Dates Number October 1996 29 Rainfall (inches) 10 June 1998 42 8 March 2001 32 7 May 2006 11 12 Fay, Spofford & Thorndike

Increased Hydraulic Grade Line Creates Sewer Backups HGL

Causes of an Increased Hydraulic Grade Line (HGL) • System Capacity Constraints • Infiltration/Inflow in Belmont – 2007 Flow Monitoring Program • Elevated downstream HGL – Flanders Road Connection to the MWRA Fay, Spofford & Thorndike

Project Timeline • 2005 – Geographical Information System (GIS) – Info. Works Sewer Model • Used by Cambridge & MWRA • 2006 – Winn’s Brook Area Study • 2007 – State (SRF) Loan Application • 2009 – Final Design Fay, Spofford & Thorndike

Solution Constraints • No transference of the problem to Cambridge or significant increase in flow to MWRA interceptor • No transference of problem within Belmont • Continued I/I reduction will be required – 2009 Sewer System Evaluation Survey Fay, Spofford & Thorndike

Mitigation Concepts • Increase sewer capacity • Flow diversion • Storage • Isolation and Pumping • I/I Removal • 13 Mitigation Alternatives Modeled Fay, Spofford & Thorndike

Collaboration with the City of Cambridge • Cambridge integrated Belmont’s model into the complete downstream system model • Key in refining the selected Alternative • NO ADVERSE IMPACT TO CAMBRIDGE • NO INCREASED CSO RELEASE (MWRA) Fay, Spofford & Thorndike

Selected Alternative No. 12 • Isolate Winn’s Book Area during elevated HGL conditions – New sewers and diversion structures – Divert flow to an off-line pumping station • Divert upstream flow – Dean Street – Leonard Street & Alexander Ave. • In-line storage conduit (Dean St) – Restricted discharge • 15% Townwide I/I reduction Fay, Spofford & Thorndike

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Predicted Impact at Key Manholes Outside Winn’s Brook Area (MH rim to HGL) Hamilton Baker Oliver Channing Baseline (May 2006) 0. 07 0. 23 0. 25 0. 37 Alt. 12 (15 % I/I red) 0. 10 0. 23 0. 34 0. 10 Fay, Spofford & Thorndike

Flanders Road Predicted Discharge May 2006 Mother’s Day Storm Peak Discharge MGD Baseline 16. 53 24 -Hour Volume MG 15. 34 Alternative 12 16. 84 14. 90 Difference 1. 98% -2. 84% Fay, Spofford & Thorndike

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Opinion of Probable Construction Cost - Contract 3 Base Bid Winn’s Brook Sewer Overflow Mitigation Facilities $6. 6 Million Additive Alternates Townwide I/I Removal $1. 4 Million TOTAL $8. 0 Million Fay, Spofford & Thorndike

Project Funding • $11. 6 M State Revolving Loan (SRF) – ARRA “Shovel Ready” Projects • Contract 1 – Wellington Brook Area Sewer and Storm Drain Improvements • Contract 2 – Stony Brook Road and Woodbine Road Pump Station Replacement • Contract 3 – Winn’s Brook Area Sewer Overflow Mitigation Fay, Spofford & Thorndike

Winn’s Brook – Contract 3 Construction Schedule 11/25/2009 - Advertised for Bid 12/21/2009 - Bids Received 01/15/2010 - Contract Execution 02/01/2010 - Notice to Proceed 07/31/2011 - Construction Complete (18 months) Fay, Spofford & Thorndike

Questions? Justin Gould, P. E. Fay, Spofford & Thorndike