Fay, Spofford & Thorndike TOWN OF BELMONT WINN’S BROOK SEWER OVERFLOW MITIGATON Presentation to...

Fay, Spofford & Thorndike

TOWN OF BELMONT

WINN’S BROOK SEWER OVERFLOW MITIGATON

Presentation to the

BOARD OF SELECTMAN

December 7, 2009


Presentation Objectives

• Project background

• Causes of sewer overflows

• Conceptual design and modeling

• Final Design

• Opinion of probable construction cost

• Funding

• Schedule


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


The Problem

Periodic sanitary sewer overflows and backups into basements of

homes in the Winn’s Brook Area


Reported Backups

Dates Number Rainfall (inches)

October 1996 29 10

June 1998 42 8

March 2001 32 7

May 2006 11 12

Increased Hydraulic Grade Line Creates Sewer Backups

HGL


Causes of an IncreasedHydraulic Grade Line (HGL)

• System Capacity Constraints

• Infiltration/Inflow in Belmont– 2007 Flow Monitoring Program

• Elevated downstream HGL– Flanders Road Connection to the MWRA


Project Timeline

• 2005 – Geographical Information System (GIS)

– InfoWorks Sewer Model• Used by Cambridge & MWRA

• 2006 – Winn’s Brook Area Study

• 2007 – State (SRF) Loan Application

• 2009 – Final Design


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


Mitigation Concepts

• Increase sewer capacity

• Flow diversion

• Storage

• Isolation and Pumping

• I/I Removal

• 13 Mitigation Alternatives Modeled


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)


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


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


Flanders RoadPredicted Discharge

May 2006

Mother’s Day Storm

Peak Discharge

MGD

24-Hour Volume

MG

Baseline 16.53 15.34

Alternative 12 16.84 14.90

Difference 1.98% -2.84%


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


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


Winn’s Brook – Contract 3Construction 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)

Questions?

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

Fay, Spofford & Thorndike TOWN OF BELMONT WINN’S BROOK SEWER OVERFLOW MITIGATON Presentation to...

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