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

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

Existing Site

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

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

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.

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

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

Existing Site

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

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

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

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

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 : 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.

Questions?

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

Champlin Upper Pond Dam Removal Construction

From Left Abutment – April, 2005

From Left Abutment – September, 2005

From Left Abutment – November, 2005

From Left Abutment – August, 2006

Mouth of Channel – November, 2005

Mouth of Channel – June, 2006

From Right Abutment – September, 2006

Discussion/ Questions….