Fawn Lake Dredging Project ~ Update on July 15, 2020

 

Fawn Lake from Springs Road

The long-awaited Fawn Lake dredging project is scheduled to start in mid-July. The Town has contracted with Dredgit Corp. to dredge the pond and to reconstruct the outlet dam at Springs Road.

The work includes hydraulic wet dredging of the bottom sediments to restore the lake to approximately 8-feet deep. The material is pumped from the dredge barge to a dewatering system. Once the material is dried, it will be transported to a residuals holding area and then hauled off-site to a nearby compost facility for eventual reuse as loam.

The neighborhood impacts will be noise and trucks. We anticipate 8-10 truck trips (out and back) per day on Sweetwater Avenue. Work hours will be 7 am to 7 pm, seven days a week.

Due to social distancing requirements, please do not approach the Dredgit personnel with questions. We urge you to check the project information, previous reports, construction plans, and proposed work schedule. If you have additional questions, please contact the Bedford Department of Public Works at (781) 918-4256. Thank you for your cooperation throughout this project.

PROJECT OVERVIEW 

Dredgit will utilize a small, portable dredge to hydraulically remove material from Fawn Lake. The slurry from the lake will be pumped to a parallel array of multiple, high-capacity, big-bowl centrifuges for dewatering. The paint-filter-dry material will then be trucked to a local disposal facility. The dam restoration and rehabilitation activities will proceed concurrently with the dredging and dewatering operations.

OPERATIONAL PLAN 

Phase I Mobilization – Initial Site Prep

Commencing on Tuesday, July 21, approximately four (4) days (based on working 12-hours/day, 7-days/week) to prepare the material laydown holding area, including:

    • Installation of approximately 60 CY of gravel to level out the area
    • Installation of wood mats

Phase II Mobilization – Equipment Set-up

Approximately four (4) days to receive, install, and set up the dredging, dewatering, and material handling equipment, including:

    • The centrifuge array and automated polymer injection system—together with their attendant tanks, manifolds, pumps, and piping
    • Connecting the 500 kW power plant
    • A 6-inch hydraulic dredge and aquatic weed harvester placed in Fawn Lake
    • A 6-inch HDPE dredge effluent pipeline installed from Fawn Lake to the dewatering area
    • A second 6-inch HDPE return water pipeline installed and routed from the dewatering area back to Fawn Lake
    • Installation of a silt curtain in Fawn Lake to control TSS
    • Installation of approximately 700’ of temporary chain link security fencing

Phase III Mobilization – Final Site Prep

Approximately four (4) days to finish the material laydown holding area, including:

    • Installation of concrete blocks around the laydown area to contain the dewatered material
    • Installation of approximately 300’ of silt fence
    • Placement of traffic barriers and pedestrian crossing

Dredging/Dewatering Operations

Approximately 110 days to complete dredging, dewatering, transportation, and disposal, including:

    • To aid the dredging operations, the weed harvester will first remove aquatic vegetation from Fawn Lake and deposit the harvested weeds on the ramp for drying and disposal
    • Dredge slurry from Fawn Lake will be pumped to the dewatering area
    • A pre-screening system using a scalping shaker will remove trash and debris from the slurry and dump it onto a belt conveyor for transport to the material laydown holding area
    • From there, the effluent passes through a series of hydrocyclones that will remove coarse sand which is also placed on a belt conveyor for transport to the material laydown holding area
    • The effluent is then dosed with polymer (Aspen A7620) using our automated injection system and fed into one of two big-bowl centrifuges (polymer makedown water will be drawn from Fawn Lake)
    • The dewatered, paint-filter-dry ‘cake’ from the centrifuge is transported via belt conveyors to the material laydown holding area for staging in preparation for trucking and disposal
    • The clear effluent water from the centrifuges is returned to Fawn Lake via HDPE pipeline that is placed behind a silt curtain
    • Newton Trucking Company will transport the material in 25 CY end-dump trailers to the City of Lexington’s Composting Facility

Dam Restoration & Rehabilitation

We have identified one subcontractor to do the piling work (Bay State Area Contractors) and are evaluating other subcontractors for the remaining activities (dirt/rock work, drain & gate valve, beaver deceiver, temporary cofferdam, etc.). If we are not able to find acceptable subcontractors, we will perform this work ourselves. In either event, all restoration and rehabilitation activities will proceed concurrently with the dredging and dewatering and will be completed before the conclusion of dredging and dewatering

Demobilization & Site Restoration

Approximately ten (10) days to demobilize from the site, including:

    • Tearing down the material laydown holding area, traffic barriers, pedestrian crossing, and security fence
    • Retrieving the dredge, weed harvester, silt fence, and HDPE pipelines
    • Rigging down the centrifuge array, automated polymer injection system, and conveyor systems, together with their attendant tanks, manifolds, pumps, and piping
    • Prepping and loading all equipment for transport
    • Returning all rented equipment
    • Planting grass and restoring the job site as per the project specifications

Project Dates

Assuming a start date of July 21 and a duration of approximately 132 days, we expect to finish the project and be demobilized by November 30,

EquipmentThe following is a list of all equipment to be used on this project

  1. Company-Owned Equipment:
    • 6-inch Cutterhead Hydraulic Dredge
    • Aquatic Weed Harvester
    • Work Boat
    • 6-inch HDPE Pipeline, Fittings & Floats
    • Water Pump for Polymer Makedown
    • (2) 30×120 High-Capacity, Big-Bowl Centrifuges (complete with stands, VFDs and PD Pumps)
    • Automated Polymer Injection Unit and Supporting Equipment
    • Tool Trailer (Hand Tools, Safety/HSE Equipment, Spill Response, and Containment Supplies)
    • (2) Belt Conveyors (for transporting trash, debris, sand, and centrifuge cake to the material laydown holding area)
    • 20’ Conex Trailer
  1. Locally Rented/Sourced Equipment:
    • Crane w/Operator (mobilization/demobilization)
    • Front-End Loader (3CY bucket)
    • 500 kW Generator for Centrifuge Array
    • Frac / Mix Tanks
    • Forklift (10K#)
    • Rubber Track Skid Steer
    • Mini Excavator
    • Temporary Security Fencing & Traffic Barriers
    • Desander Pump
    • Roll-Off Poly Tanks

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