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 Dam Spillway & Low-level Outlet with Culvert through Dam Concrete Core Wall Around Spillway Pond / Impoundment Dam
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
Proposed Conditions – Conceptual Design Remove Existing spillway/culvert. Excavated Breach Channel. Partial Removal of Core Wall Restored Gulf Brook Stream Channel Restored Wetland & Upland Vegetation
Proposed Conditions – Conceptual Design Restored Gulf Brook Stream Channel Excavated Section of Dam for Breach Channel Grassed Slopes Concrete Core Wall to Remain Below Ground Stone Erosion Protection
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 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.
Example Project: Champlin Pond Dam Breach Before Dam Breach One Year After Dam Breach