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Breaching the Mahar Regional School Dam Presentation to Ralph C. Mahar Regional School Committee GZA GeoEnvironmental, Inc. February 9, 2011

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Presentation Outline Introductions Derek Schipper, P.E. and Greg Hunt GZA GeoEnvironmental, Inc., Norwood, MA Existing Site Information Project Background Summary of Dam Breach Feasibility Study Proposed Dam Breach Design Permitting & Construction Preliminary Cost Estimate Timeline Example Project Questions

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Existing Site

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Existing Dam Pond / Impoundment Dam Spillway & Low- level Outlet with Culvert through Dam Concrete Core Wall Around Spillway

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Dam Information Mahar Regional School Dam: Dam Size: Small Hazard Rating: Significant Condition: Poor Main Deficiencies: Growth of trees throughout dam Erosion on top of dam and near waterline Embankment seepage

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Project Background 1950s: Dam constructed 1960: Dam repaired following spillway damage 2005: New MA Dam Safety Regulations go into effect 2008: DCR Office of Dam Safety (DCR/ODS) ordered that dam be inspected by professional engineer July 2009: GZA performed Phase I Inspection/ Evaluation of Dam; found dam to be in Poor condition Sept. 2009: School District ordered by DCR/ODS to repair, breach, or remove dam by March 11, 2011and continue to have dam inspected every 6 months.

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Project Background (Cont.) 2009 present: GZA has performed three 6-month inspections, dam found to be in similar condition 2010: School Committee approves plan to address condition of dam through dam removal/breach 2010: GZA prepares Dam Breach Feasibility Study to evaluate potential dam breach

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Dam Breach Feasibility Study GZA Scope of Work: Extension request from DCR/ODS (11/30/2012 New Date) Field Work Site Survey, Wetland Resource Evaluation, Sediment Analysis Technical Analysis Hydrologic & Hydraulic Modeling, Conceptual Breach Design Permitting Investigation Estimate of project impacts and required local, state, and federal permits Cost Estimate & Funding Sources Cost estimate to perform dam breach & potential grants

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Existing Site

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Proposed Conditions Conceptual Design Restored Wetland & Upland Vegetation Remove Existing spillway/culvert. Excavated Breach Channel. Partial Removal of Core Wall Restored Gulf Brook Stream Channel

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Proposed Conditions Conceptual Design Restored Gulf Brook Stream Channel Excavated Section of Dam for Breach Channel Concrete Core Wall to Remain Below Ground Stone Erosion Protection Grassed Slopes

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Permitting & Construction Environmental Permitting: Numerous Local, State, and Federal permits required to work in wetland resource areas Permit process will likely lasts 9 months 1 year Final Design and Specifications: Prepare final design plans and specifications suitable for contractor bidding and construction Construction: Once Final Design is complete and permits are in place, work awarded to Contractor to perform breach work Construction to take about 4 weeks

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Preliminary Cost Estimate Permitting & Final Design Engineering $ 85,000 Construction Work$ 170,000 Construction Contingency (25%)$ 43,000 Construction Engineering (5 weeks)$ 35,000 Total Estimated Cost$ 333,000

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Preliminary Timeline Spring 2011: Submit Environmental Permitting Summer 2011: Final Engineering Design & Specifications Spring 2012: Award Construction Contract Summer 2012: Perform Dam Breach Work Fall 2012 - 2013: Revegetation Monitoring & Maintenance by Contractor Note: Under current timeline, dam breach work must be completed by November 30, 2012, and Six-Month Follow-Up Inspections of Dam must continue until work is completed.

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Questions?

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Before Dam Breach One Year After Dam Breach Example Project: Champlin Pond Dam Breach

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Champlin Upper Pond Dam Removal Construction

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From Left Abutment April, 2005

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From Left Abutment September, 2005

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From Left Abutment November, 2005

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From Left Abutment August, 2006

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Mouth of Channel November, 2005

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Mouth of Channel June, 2006

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From Right Abutment September, 2006

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Discussion/ Questions.