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TP-1 AND TP-2 FINAL GRADING AND COVER SYSTEM PLACEMENT (CSP)

TASK WORK PLAN

APPENDIX D

PHASE II NON-TIME-CRITICAL REMOVAL ACTION ELIZABETH MINE SUPERFUND SITE

SOUTH STRAFFORD, VERMONT

REVISION NO.: 02

DATE: June 2, 2011

DOCUMENT TRACKING NO.: 83601.CSP.02

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TP-1 and TP-2 Final Grading and Cover System Placement Task Work Plan Table of Contents i

TP-1 AND TP-2 FINAL GRADING AND COVER SYSTEM PLACEMENT TASK WORK PLAN



TABLE OF CONTENTS

Section Description Page No.

1.0 PLAN IDENTIFICATION AND APPROVALS 1

2.0 INTRODUCTION 2 2.1 Plan References 2

2.1.1 Program Work Plan 2 2.1.2 Project Documents 2

2.2 TP-1 and TP-2 Final Grading and Cover System Placement Overview 2

3.0 GENERAL CONSTRUCTION SEQUENCE AND APPROACH FOR FINAL GRADING AND

COVER SYSTEM PLACEMENT ACTIVITIES 3

3.1 Equipment Mobilization/Demobilization 3 3.2 Erosion and Sediment Controls 4

3.2.1 Dust Control 4 3.2.2 Borrow Stockpiles 5 3.2.3 Tailing Stockpiles 5 3.2.4 Tailing Subgrade 5

3.3 Staging Areas 5 3.4 Access/Haul Road Improvements and Temporary Crossings 6

3.4.1 Access/Haul Road Improvements 6 3.4.2 Temporary Crossings 6

3.5 Construction Layout, Site Control, and As-Built Survey 7 3.5.1 Construction Layout and Site Control 7 3.5.2 As-Built Surveys 7

3.5.2.1 Subgrade As-Built Surveys 7 3.5.2.2 Final Grade As-Built Surveys 7

3.6 Final Grading to Establish Subgrade 8 3.7 Subgrade Preparation and Verification 8

3.7.1 Compaction and Proof Rolling 8 3.7.2 Layout and Excavation of Cover System Drainage Features 9 3.7.3 Anchor Trench Excavation and Backfill 9 3.7.4 Verification of Subgrade Elevations 9

3.8 Protection of Tailing Subgrade and Stockpiles 9 3.9 Visual Inspection of Subgrade and Approval 10 3.10 Delivery and Storage of Geosynthetics 10 3.11 Placement of Geosynthetics 10 3.12 Construction of Toe Details 11 3.13 Placement of Vegetative Support Soil 11 3.14 Installation of Cover System Drainage Features 12 3.15 Placement of Topsoil and Seeding 12 3.16 Installation of Surface Downcomers and Surface Swales 13

USACE Contract No. W912WJ-11-D-0006 Elizabeth Mine Superfund Site, Document Tracking No.: 83601.CSP.02 South Strafford, Vermont

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TP-1 and TP-2 Final Grading and Cover System Placement Task Work Plan Table of Contents ii




TABLE OF CONTENTS


3.17 Construction of Permanent Access Roads 13

4.0 2011 FINAL GRADING AND COVER SYSTEM PLACEMENT ACTIVITIES 13 4.1 TP-1A CSP Activities 13

4.1.1 Layout of TP-1A Cover System Area 14 4.1.2 Stripping Topsoil 14 4.1.3 Final Grading to Establish Subgrade 14 4.1.4 Subgrade Preparation 15

4.1.4.1 Compaction and Proof Rolling 15 4.1.4.2 Layout and Excavation of Side Slope Collector Pipe Trenches 15 4.1.4.3 Anchor Trench Excavation and Backfill 15

4.1.5 Protection of Tailing Subgrade and Stockpiles 15 4.1.6 Placement of Geosynthetics 16 4.1.7 Construction of Toe Details A & B 16 4.1.8 Placement of VSS 17 4.1.9 Installation of Cover System Drainage Features 17 4.1.10 Placement of Topsoil and Seeding 17 4.1.11 Installation of Surface Downcomer and Surface Swales 17 4.1.12 Placement of Permanent and Temporary Erosion Control Matting 18 4.1.13 Construction of Permanent Access Roads 18

4.2 TP-2B CSP Activities 18 4.2.1 Layout of TP-2B Cover System Area 18 4.2.2 Stripping Topsoil 18 4.2.3 Final Grading to Establish Subgrade 18 4.2.4 Subgrade Preparation 19

4.2.4.1 Compaction and Proof Rolling 19 4.2.4.2 Layout and Excavation of Cover System Drainage Features 19 4.2.4.3 Anchor Trench Excavation and Backfill 19

4.2.5 Protection of Tailing Subgrade 20 4.2.6 Placement of Geosynthetics 20 4.2.7 Construction of Toe Detail D and the TP-1/TP-2 Toe Detail 20 4.2.8 Placement of VSS 21 4.2.9 Installation of Cover System Drainage Features 21 4.2.10 Placement of Topsoil and Seeding 21 4.2.11 Construction of Permanent Access Road 22

4.3 2011 Construction Season Closeout 22 4.3.1 Stockpile Stabilization 22 4.3.2 Stabilization of Disturbed Areas Outside Limits of Cover System 22 4.3.3 Construction Access/Haul Roads 22 4.3.4 Erosion and Sediment Controls for Winter Shutdown 22


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TP-1 and TP-2 Final Grading and Cover System Placement Task Work Plan Table of Contents iii




TABLE OF CONTENTS


5.0 2012-2013 FINAL GRADING AND COVER SYSTEM PLACEMENT ACTIVITIES 23 5.1 TP-2A CSP Activities 23

5.1.1 Layout of TP-2A Cover System Area 23 5.1.2 Stripping Topsoil 23 5.1.3 Final Grading to Establish Subgrade 23 5.1.4 Subgrade Preparation 24


5.1.5 Protection of Tailing Subgrade and Stockpiles 24 5.1.6 Placement of Geosynthetics 24 5.1.7 Construction of Toe Details D, E, and F 25 5.1.8 Placement of VSS 25 5.1.9 Installation of Cover System Drainage Features 26 5.1.10 Placement of Topsoil and Seeding 26 5.1.11 Construction of Permanent Access Road 27

5.2 TP-1B CSP Activities 27 5.2.1 Layout of TP-1B Cover System Area 27 5.2.2 Stripping Topsoil 27 5.2.3 Final Grading to Establish Subgrade 27 5.2.4 Subgrade Preparation 28


5.2.5 Protection of Tailing Subgrade 28 5.2.6 Placement of Geosynthetics 28 5.2.7 Construction of Toe Detail C 29 5.2.8 Placement of VSS 29 5.2.9 Installation of Cover System Drainage Features 29 5.2.10 Placement of Topsoil and Seeding 30

5.3 2012-2013 Construction Season Closeout 30 5.3.1 Stockpile Stabilization 30 5.3.2 Stabilization of Disturbed Areas Outside Limits of Cover System 30 5.3.3 Construction Access/Haul Roads 30 5.3.4 Erosion and Sediment Controls for Winter Shutdown 30

6.0 GREEN AND SUSTAINABLE INITIATIVES 30


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TABLE OF CONTENTS


LIST OF FIGURES

Figure D2-1 TP-1 and TP-2 Final Grading and Cover System Placement 2011 Project Schedule

Figure D3-1 Temporary Crossing Location Plan

Figure D4-1 2011 Subgrade Cut/Fill Plan

Figure D5-1 Overall Subgrade Cut/Fill Plan

LIST OF CHARTS

Chart D2-1 TP-1 and TP-2 Final Grading and Cover System Placement Organization Chart

LIST OF APPENDIX

Appendix D2-1 Construction Drawings and Details

Appendix D2-2 Supplementary Conditions and Modified Technical Specifications


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TP-1 and TP-2 Final Grading and Cover System Placement Task Work Plan List of Acronyms i




LIST OF ACRONYMS

APP Accident Prevention Plan

AMD Acid Mine Drainage

BMP Best Management Practices

BRW Borrow Management Task Work Plan

CQC Contractor Quality Control

CSP TP-1 and TP-2 Final Grading and Cover System Placement

cy cubic yards

DGC drainage geocomposite

ft feet

GPS Global Positioning Software

H horizontal

HDPE high density polyethylene

lf linear feet

LGP low ground pressure

Nobis Nobis Engineering, Inc.

Northwoods Northwoods Excavating

NTCRA Non-Time-Critical Removal Action

PM Project Manager

PWP Program Work Plan

QAPP Quality Assurance Project Plan

QCS Site Quality Control Supervisor

SOW Statement of Work

SS Site Superintendent

TP-1 Tailing Pile 1

TP-2 Tailing Pile 2

TWP Task Work Plan

URS URS Corporation

USACE U.S. Army Corps of Engineers, New England District


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V

TP-1 and TP-2 Final Grading and Cover System Placement Task Work Plan List of Acronyms ii

USEPA United States Environmental Protection Agency

vertical

VSS vegetative support soil

VTAOT Vermont Agency of Transportation

VT DEC The State of Vermont Agency of Natural Resources Department of Environmental Conservation

Weston Weston Solutions, Inc.

WTS Water Treatment System

WWII Area World War II Infrastructure Area


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1.0

TP-1 and TP-2 Final Grading and Cover System Placement Task Work Plan Page 1




PLAN IDENTIFICATION AND APPROVALS

Project Title: Phase II Non-Time Critical Removal Action Elizabeth Mine Superfund Site

Project Location: South Strafford, Vermont

Contract No.: W912WJ-11-D-0006

Task Order No.: 0001

Nobis Project No.: 83601

Prepared By: Brett Kay

Submittal Date: 06/02/2011

Revision No.: 02

June 2, 2011 Date

APPROVALS:

_____________________________________________ Peter W. Delano, P.E., Program Manager

_____________________________________________ Andrew J. Boeckeler, P.G., Project Manager

_____________________________________________ Patrick McNabb, P.E., Lead Engineer

_____________________________________________ Brett Kay, Project Engineer

June 2, 2011 Date

June 2, 2011 Date

June 2, 2011 Date


2.0 INTRODUCTION

This Task Work Plan (TWP) was prepared by Nobis Engineering, Inc. (Nobis) to describe the work approach for the TP-1 and TP-2 Final Grading and Cover System Placement (CSP) associated with the Phase II Non-Time-Critical Removal Actions (NTCRA) at the Elizabeth Mine Site (Site) located in South Strafford, Vermont. Nobis prepared this Plan for the U.S. Environmental Protection Agency (USEPA) under contract to U.S. Army Corps of Engineers New England District (USACE) through Remedial Action Contract No. W912WJ-11-D-0006, Task Order 0001. This Task Work Plan has been developed based on the August 2, 2010 Statement of Work (SOW) issued by the USACE.

2.1 Plan References

2.1.1 Program Work Plan

Refer to the Program Work Plan (PWP) (Nobis, 2011a), prepared by Nobis, for descriptions of the overall project organization, general work approach for the performance of completing the Phase II NTCRA, and the history of response actions and investigations at the Site.

2.1.2 Project Documents

Work associated with the CSP TWP will be conducted in general accordance with the PWP and the stand-alone Accident Prevention Plan (APP) (Nobis, 2011b), Construction Quality Control (CQC) Plan (Nobis, 2011c), and the Quality Assurance Project Plan (QAPP) (Nobis, 2011d) documents prepared by Nobis. This work will also be conducted in accordance with the design plans and technical specifications titled “NTCRA Closure, Elizabeth Mine, Strafford, Vermont” dated November 2010, prepared by URS Corporation (URS), and subsequent modifications/revisions to the plans and specifications prepared by Nobis and approved by USACE including, but not limited to, the Construction Drawings, and Supplementary Conditions and Modified Technical Specifications included in Appendices D2-1 and D2-2, respectively. For the purpose of this TWP the term “Project Documents” includes each of the documents and plans noted above.

2.2 TP-1 and TP-2 Final Grading and Cover System Placement Overview

Final grading and placement of the infiltration barrier cover system over Tailing Pile 1 (TP-1) and Tailing Pile 2 (TP-2) are two major components of the Phase II NTCRA at the Elizabeth Mine Site. Final grading is necessary to stabilize TP-1 and TP-2, create positive drainage away from TP-1 and TP-2, and establish a suitable subgrade for placement of the infiltration barrier cover system. Final grading activities will include the relocation/consolidation of tailing mine waste and waste rock from various locations throughout the Site. The installation of the infiltration barrier cover system over TP-1 and TP-2 will reduce the volume of acid mine drainage (AMD) discharging from the toe of TP-1. The infiltration barrier cover system consists of a 60-mil geomembrane, a drainage geocomposite (DGC), an 18 to 24-inch thick vegetation support soil (VSS) layer, and a 6-inch thick topsoil layer.

Other significant cover system components include the side slope collector pipes, top slope drainage pipes, toe of slope transitions (toe details), stormwater collection and drainage swales, temporary haul roads, and permanent access roads.

Final grading and cover system placement activities in TP-1 and TP-2 will begin in May 2011. The cover system will encompass approximately 44 acres at completion. USEPA and USACE


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have identified the north and west slopes of TP-1, and the TP-3 waste rock stockpile located on TP-2 as the most critical areas for closure. Based on this information, Nobis sub-divided TP-1 and TP-2 area into four areas: TP-1A, TP-1B, TP-2A, and TP-2B, to establish a construction schedule where the more critical areas will be addressed, to the extent practical, during the 2011 construction season. The limits of each of the four areas are shown on the Construction Drawings included in Appendix D2-1 and are described as follows:

• TP-1A includes the north and west slopes of TP-1 and the area within 45 feet of the top of the north and west slopes, encompassing approximately 10.2 acres;

• TP-1B includes the flatter southern and central portion of TP-1, encompassing approximately 14.8 acres;

• TP-2A includes the southern portion of TP-2, encompassing approximately 7.9 acres; and,

• TP-2B includes the TP-3 waste rock stockpile and the northern portion of TP-2, encompassing approximately 11.2 acres.

The overall objective for 2011 is to complete final grading and cover system placement activities in TP-1A and TP-2B. The remaining areas, TP-1B and TP-2A will be completed in 2012-2013, or as approved by USACE. A schedule for the 2011 activity is included as Figure D2-1. Chart D2-1 contains an organization chart of the staff and subcontractors for the CSP work.

3.0 GENERAL CONSTRUCTION SEQUENCE AND APPROACH FOR FINAL GRADING AND COVER SYSTEM PLACEMENT ACTIVITIES

This Section provides an outline of the general construction sequence to be used during the TP-1 and TP-2 final grading and cover system placement activities. The general approaches and methodology described in this Section will be applied globally throughout the duration of work for the final grading and cover system placement activities. Detailed information regarding the work activities associated with each of the four areas is summarized in Sections 4.0 and 5.0 of this TWP.

The quantities, depths, and volumes provided in this TWP are approximate and subject to change prior to and/or during construction. The volumes provided are “neat” volumes that do not include fluff factors typically associated with excavated and stockpiled soil materials. Changes will be coordinated with USACE prior to and during construction.

3.1 Equipment Mobilization/Demobilization

The majority of heavy equipment necessary for the final grading and waste relocation activities to be conducted in 2011 was mobilized to the Site in March 2011, prior to the roads being posted. The mobilization of additional heavy equipment required for final grading and waste relocation, and/or the placement of the cover system, will be scheduled and phased, to the extent possible, to minimize the impact of truck traffic on Town roads and the general public. Various additional pieces of heavy equipment that may be mobilized include, but are not limited to, articulated dump trucks, low ground pressure (LGP) track mounted dump trucks, an off-road articulated water truck, track mounted bulldozers (dozers), track mounted excavators, wheeled front end loaders, vibratory rollers, lulls/forklifts, and vibratory screener. As specified in Section 7.1 of the PWP, Nobis will coordinate with USACE prior to mobilization of additional heavy equipment.


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Nobis anticipates the majority of the heavy equipment will be demobilized at the end of November 2011, prior to Winter Shutdown. Heavy equipment remaining on-site following Winter Shutdown may be demobilized throughout the winter months, as necessary for routine maintenance. Demobilization of heavy equipment will be coordinated with USACE.

Mobilization of heavy equipment for 2012-2013 final grading and cover system placement activities will be coordinated with USACE in accordance with Section 7.1 of the PWP.

3.2 Erosion and Sediment Controls

Erosion and sediment control measures will be implemented prior to the start of construction activities in 2011 and 2012-2013 to minimize impacts to water quality as a result of construction activities, and to prevent erosion and the migration of sediment from the controlled work zones. Additional information regarding the erosion and sediment control Best Management Practices (BMPs) is provided in Section 7.0 of the PWP. The BMP design criteria and construction specifications are taken from The Vermont Standards & Specifications for Erosion Prevention & Sediment Control (VT DEC, 2006).

Erosion and sediment control measures anticipated for the TP-1 and TP-2 final grading and cover system placement activities include, but are not limited to, silt fence, water bars, stone check dams, limestone check dams, temporary swales, soil berms, mulching, matting, and fiber rolls. Generally, silt fence will be installed down gradient of controlled work zones and around the perimeter of stockpile areas to divert stormwater to focused outlet areas. Filtering devices, such as stone check dams, limestone check dams, and fiber rolls, will be installed at the outlet areas to remove silt and sediment from stormwater runoff prior to discharge to perimeter diversion channels and/or other areas outside the controlled work zones. The approximate location of the anticipated erosion and sediment control measures are shown on the Construction Drawings included in Appendix D2-1. Erosion and sediment control inspection forms will be prepared in accordance with the PWP. The forms are included in Appendix F of the PWP.

Site erosion control measures may be modified based on site conditions during the progression of work and field conditions. It is anticipated there will be minimal impact from erosion and sediment migration in the vicinity of and within the defined/controlled work zones associated with each of the four areas. Erosion control measures shall be maintained in good condition until project completion at which time disturbed areas will be fully restored and stabilized with vegetation or by other means. During construction, the erosion control measures will be inspected daily and deficiencies will be corrected immediately. Additional erosion control materials shall be on-site for emergency and routine replacement and maintenance.

Areas of the Site disturbed during CSP activities in 2011 will be stabilized prior to Winter Shutdown in November 2011 and 2012. A Winter Shutdown Plan will be developed and submitted to USACE for review and approval prior to Winter Shutdown in 2011 and 2012.

3.2.1 Dust Control

A water truck will be used throughout final grading and cover system placement activities, as needed, to minimize air borne dust. The water truck will be equipped with a water dissipation bar for the application of water on haul roads and other open work areas. The water truck will also be equipped with a pressurized gun/cannon to allow stockpiles and other in accessible


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exposed work areas to be wetted, as needed. Additional water trucks will be mobilized to the site, if needed, during construction.

3.2.2 Borrow Stockpiles

Inactive stockpiles of native till and common borrow will be stabilized with a combination of mulching, matting, and seeding.

3.2.3 Tailing Stockpiles

Tailing stockpiles generated from subgrade preparation will be covered with topsoil and seeded, or covered with temporary scrim (reinforced temporary polyethylene cover) to minimize potential contact with stormwater. Refer to Section 3.8 for additional information.

3.2.4 Tailing Subgrade

Exposed tailing subgrade will be covered with temporary scrim to minimize potential contact with stormwater. Refer to Section 3.8 for additional information.

3.3 Staging Areas

Team subcontractor Northwoods Excavating (Northwoods), the site work subcontractor, will continue to utilize the existing equipment staging area located west of TP-2 for the storage of heavy equipment and materials. This staging area was utilized through the end of the 2010 construction season, so minimal site preparation is anticipated in this area prior to the start of work. Nobis and Northwoods will conduct an inspection of the staging prior to initiating work in the spring of 2011 and 2012-2013, and deficiencies will be repaired.

Prior to the start of final grading and waste relocation activities in 2011, staging areas will be established for the delivery and storage of imported stone materials and for stockpiling stripped topsoil and excess tailing fill generated during final grading activities. The staging areas for the delivery and storage/stockpiling of imported stone material, stripped topsoil, and excess tailing fill will be located in the northeast corner of TP-1. Nobis anticipated the imported stone material and stripped topsoil stockpile areas will be 125 feet (ft) by 125 ft, and the excess tailing stockpile areas will be approximately 300 ft by 300 ft. Staging areas will be constructed a minimum of 60 ft from the top of the north and west slopes of TP-1, to allow the construction of the permanent access roads. Refer to the Construction Drawings included in Appendix D2-1 for the approximate location of the staging areas referenced above.

A staging area for the delivery and storage of the geosynthetics will be constructed prior to mobilization of the geosynthetics subcontractor. The staging area for the delivery and storage of the geosynthetics is anticipated to be approximately 200 ft by 200 ft, and will be located in the northwest corner of TP-1.

Staging areas will be constructed using existing gravel materials and native soils, to the extent practical, to establish a stable working surface. The typical section depth of throughout each staging area will vary depending on the suitability of the subgrade soils below each area. The finished surface of the staging areas will be graded to promote positive drainage away from the staging area. Routine inspections, maintenance, and repairs of the staging areas will be conducted throughout the duration of the work to sustain a safe and suitable working surface.


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Construction of additional staging areas in 2011 and 2012 is anticipated as final grading and cover system placement activities progress. The location of additional staging areas will be determined in the field during construction. Nobis will coordinate with USACE prior to implementation of additional staging areas.

3.4 Access/Haul Road Improvements and Temporary Crossings

3.4.1 Access/Haul Road Improvements

Prior to the start of final grading and waste relocation activities in 2011 and 2012-2013, existing access/haul roads on-site will be repaired and/or improved to establish safe hauling routes for construction vehicles. Access/Haul roads will be constructed and maintained in accordance with Section 7.8 of the PWP. Nobis anticipates repairs and/or improvements to the following haul roads on-site:

• West side haul road prior to the start of final grading activities in 2011; and,

• TP-1 haul roads prior to the start of final grading activities in 2011.

The construction of additional temporary access/haul roads may be necessary throughout the duration of work in 2011 and 2012-2013. Nobis will coordinate with USACE prior to the construction of additional haul roads.

3.4.2 Temporary Crossings

Temporary crossings will be constructed along the east and west diversion channels to provide access to the four areas of the cover system. The temporary crossing along the west diversion channel will be constructed using woven geotextile and 7-inch minus rip rap. Culverts consisting of 24-inch diameter high density polyethylene (HDPE) pipe will be installed between the woven geotextile and 7-inch minus rip rap as necessary to handle flows in the west side diversion channel. The temporary crossing will be constructed from the southern end of the west side diversion channel to approximately 920 ft north. The woven geotextile will be installed over the existing rip rap in the west side diversion channel and 7-inch minus rip rap will be installed over the woven geotextile until a suitable, level, stable, and safe crossing is constructed from the southern end of the channel to the north limit approximately 920 ft away. Temporary crossings along the east diversion channel will be constructed of woven geotextile, 7-inch minus rip rap, and 48-inch diameter pipe, or temporary bridges will be used to span the diversion channel. Due to the presence of Copperas Brook flowing through the east side diversion channel, rip rap and pipe crossings at these locations will require a minimum 48-inch diameter pipe HDPE, or a pipe(s) with an equivalent flow capacity. This pipe size matches the diameter of the nearest downstream and upstream culvert crossings. The woven geotextile, rip rap, and pipe crossing along the east side diversion channel will be installed to minimize impacts on the flow in the channel. If the temporary bridge method is used, flow through the east diversion channel will not be affected by the temporary bridge structures. The location of the temporary crossings for each area will be coordinated with and agreed upon by USACE in the field prior to the start final grading activities in each area. Nobis anticipates constructing temporary crossings at the following locations:

• Up to 920 ft of temporary crossing (temporarily fill in channel) at the west side diversion channel in 2011 for access to the west slope of TP-1A;

• Up to two crossings at the east side diversion channel in 2011 for access to the south slopes of TP-2B;


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• Up to two crossings at the east side diversion channel in 2012-2013 for access to TP-1B; and,

• Up to two crossings at the east side diversion channel in 2012-2013 for access to the southern portion of TP-2A.

Refer to Figure D3-1 for the approximate location of the temporary crossings.

Temporary crossings will be maintained throughout the duration of work in each area. The crossings will be removed following the completion of work in each area. The 7-inch minus rip rap and HDPE pipes will be stockpiled on-site for reuse at future crossings and other portions of work. The woven geotextile will be removed and disposed of accordingly. The diversion channels will be restored to preconstruction condition following removal of the temporary crossings.

3.5 Construction Layout, Site Control, and As-Built Survey

3.5.1 Construction Layout and Site Control

Northwoods has extensive survey experience on the Site including construction layout, as-built surveys, and overall site survey control. Northwoods will utilize a combination of advanced global positioning software (GPS) and traditional total station survey instruments to conduct preconstruction cover system layout, verification of subgrade elevations, utility (cover system pipes) layout, and maintain continuous site survey control throughout the duration of construction activities. Northwoods will layout and monitor the extents of each component of the final grading and cover system activities including, but not limited to, the limits of the cover system, subgrade elevation, anchor trenches, toe details, side slope collector pipes, top slope drainage pipes, surface swales, VSS layer, and topsoil layer. The Site Superintendent (SS) and the Site Quality Control Supervisor (QCS) will review survey layout prior to the start of final grading and cover system activities, and monitor progress of the work, in accordance with the requirements outlined in the Project Documents.

3.5.2 As-Built Surveys

3.5.2.1 Subgrade As-Built Surveys

An independent third-party surveyor, licensed in the state of Vermont, will be hired by Northwoods to conduct as-built surveys of each subgrade area prior to placement of geosynthetics. Nobis anticipates the third-party surveyor will be mobilized to the Site when sections of subgrade in active work areas are prepared for placement of the geosynthetics. The surveyor will prepare and produce stamped as-built survey plans of each subgrade area. Nobis will conduct a review of the as-built survey plans to confirm work is in accordance with the acceptable tolerances described in the Project Documents. Nobis may perform an independent survey to confirm grades and locations of components as deemed necessary by the Project Manager (PM). The as-built survey plans will be submitted to USACE following Nobis’ review. Additional information regarding as-built survey requirements is provided in the Project Documents.

3.5.2.2 Final Grade As-Built Surveys

The third-party surveyor will be mobilized at the end of each construction season to conduct an as-built survey of final grades established during the active year. The surveyor will prepare and


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produce a stamped as-built plan showing the final grades in the areas of work completed each year. Nobis will conduct a review of the as-built survey plans to confirm work is in accordance with the acceptable tolerances described in the Project Documents. The as-built survey plans will be submitted to USACE following Nobis’ review.

3.6 Final Grading to Establish Subgrade

Final grading of tailing waste and/or waste rock will be performed to the approximate subgrade elevations provided on the Construction Drawings included in Appendix D2-1. Modifications to the grades and/or grading plans may be necessary and performed to adjust to field conditions, as approved by USACE. Excavation and cuts will be conducted using a combination of excavators, dozers, front end loaders, articulated dump trucks, and tracked dump trucks. Excavation activities within the four cap areas described in Section 2.2 will be limited to smaller sections, to the extent practical, to minimize the area of exposed tailing. Areas where waste rock is encountered at, or within the 6-inches below, subgrade elevations may require over-excavation, to allow for the placement of a 6-inch thick tailing cushion layer. Areas where no waste rock is encountered at subgrade elevations, only tailing waste is encountered, will not require over-excavation prior to subgrade preparation.

Fill areas will be backfilled with excess tailing waste and waste rock as needed to establish subgrade elevations, and in accordance with the Project Documents. Excess waste rock generated during cuts to subgrade will be used as fill in deeper fill areas within the same areas, to the extent practical. Waste rock fill will be placed to avoid nesting of rock and the potential for voids. Excess tailing fill will be used to backfill around larger diameter rocks. Cuts to fill, and general fills, using tailing waste and waste rock will be compacted throughout the duration of the fill process, as required by the Project Documents.

Cuts to fill will be the preferred method for handling and placing excess tailing fill and waste rock, as this minimizes the number of times materials are handled, but cuts to stockpiles are anticipated at various times throughout final grading activities. Excess tailing that cannot be transported and deposited as fill within another active work area will be transported to established tailing stockpile areas. The tailing stockpile areas will be constructed, managed, and maintained in accordance with the BMPs described in the PWP, Sections 3.2 and 3.3 above, with typical side slopes of 3 horizontal (H) to 1 vertical (V), to the extent practical. Slopes greater than 3H:1V may be constructed on active stockpiles not anticipated to remain in place following completion of work in an active area. Refer to Section 3.8 below for information regarding the protection of tailing subgrade and stockpiles.

3.7 Subgrade Preparation and Verification

3.7.1 Compaction and Proof Rolling

General procedures and requirements for the compaction and proof rolling of tailing/waste rock fill and subgrade, respectively, to be applied throughout the CSP work activities are described in the Project Documents. Cut areas will be proof rolled when subgrade elevations are established over a section of the active work area. Fill areas will be compacted, per the Project Documents, during placement of tailing lifts until subgrade elevation is established. Visible protrusions greater than ½-inch will be removed and the area will be re-rolled in accordance with the Project Documents.


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3.7.2 Layout and Excavation of Cover System Drainage Features

Layout of cover system drainage features requiring excavation including, but not limited to, side slope collector pipes, down comers, and surface swales will be conducted following subgrade preparation in the work area. Refer to the Construction Drawings included in Appendix D2-1 for the approximate location of these features and typical details for excavation.

Excavation of the cover system drainage features will be conducted following review of the layout by the QCS, SS, and Northwoods. Excavation of the features will be advanced from discharge/low points to high points, to the extent practical, to minimize the potential for trapping stormwater runoff should a rain event occur prior to completion of the excavation activities. Generally, an excavator, articulated dump trucks, and track mounted dump trucks will be used to excavate these features and transport the excess tailing material to the stockpile area. The bottom (flat area) of trenches and other drainage features will be compacted with multiple passes of vibratory plate compactor. The side slopes of the trenches and other drainage features, inaccessible to a vibratory plate compactor and/or roller, will be compacted using the excavator bucket. Disturbed areas of the subgrade outside the limit of the cover system drainage feature will be regraded and proof rolled as needed to establish a subgrade suitable for placement of the geomembrane, and in accordance with the Project Documents.

3.7.3 Anchor Trench Excavation and Backfill

The extents of anchor trenches required within an active work area will be laid out by Northwoods, and reviewed and approved in accordance with the Project Documents prior to the start of the anchor trench excavation activities. Anchor trench excavation will be conducted parallel to the top of slope, and along interim tie in locations around the perimeter of the cover system areas. Anchor trenches will consist of a 2 ft wide (minimum) by 2 ft deep (minimum) excavation. Typical details are provided in the Construction Drawings included in Appendix D2-1. Anchor trenches will be excavated just prior to the installation of the geomembrane, to minimize the potential for flooding of the trench with stormwater.

Anchor trenches will be backfilled with tailing, native till, common borrow, or other approved materials immediately following installation of geomembrane in each active work area.

3.7.4 Verification of Subgrade Elevations

Following completion of subgrade preparation within an active work area, including the excavation of cover system drainage features, the third-party surveyor will be mobilized to conduct an as-built survey of the subgrade surface. Refer to Section 3.5.2 above for additional information.

3.8 Protection of Tailing Subgrade and Stockpiles

Exposed tailing subgrade will be covered with temporary reinforced polyethylene cover (scrim) to minimize the potential for stormwater contact with the tailing waste. The scrim will be placed over the subgrade as approved by USACE and as needed based on the weather forecast. During subgrade preparation activities, such as stripping topsoil, cuts/fills to subgrade, and excavation of cover system drainage features, scrim will be removed as needed to continue work in an active area, and reinstalled at the end of the day unless approved otherwise by USACE. The edges of the sheets shall be overlapped a minimum of 18-inches or sewn together so the entire area of the prepared surface is covered/protected. Sand bags, or other approved ballast type systems, will be placed on and around the temporary scrim covers, as needed, to


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hold them in place until the geomembrane installation is complete. Stormwater runoff from the scrim will be managed using stone check dams to limit the velocity. Nobis will review the stormwater management measures in place for the scrim runoff during construction and modify them as needed. Modifications to the stormwater management measures will be coordinated with USACE.

Excess tailing stockpiles will be covered with temporary scrim, or salvaged topsoil from TP-1A. Similar to the exposed tailing subgrade, tailing stockpiles will be covered at the end of each work day, unless otherwise approved by USACE. Temporary scrim covers will be maintained over active tailing stockpiles until all the tailing material has been used as fill and the stockpile is gone. Salvaged topsoil will be used as a temporary cover for tailing stockpiles to remain in place at the end of the 2011 construction season. The topsoil layer will be installed a minimum of 6-inches thick over the entire stockpile. Lime will be applied over the topsoil, in accordance with the PWP, and the stockpile will be seeded to establish vegetation. The use of salvaged topsoil as a temporary cover will be conducted following approval by USACE.

3.9 Visual Inspection of Subgrade and Approval

Prior to the placement of geosynthetics in an active work area, the temporary scrim covers will be removed and the subgrade surface will be inspected in accordance with the Project Documents. Improvements to the subgrade will be conducted as needed until the area is approved for placement of the geomembrane by all parties listed in the Project Documents.

3.10 Delivery and Storage of Geosynthetics

Geosynthetics, including the 60-mil geomembrane and DGC, delivered to the Site will be unloaded by the geosynthetics subcontractor and stored in the geosynthetics staging area established in the northwest corner of TP-1. Nobis anticipates the geosynthetic materials for the 2011 construction season will be delivered to the Site starting in late June 2011. The geosynthetics subcontractor will be responsible for the overall handling and storage the geosynthetics in accordance with the Project Documents. Nobis will review the materials delivered to confirm applicable requirements of the Project Documents are met.

Other geosynthetics needed for the project include non-woven geotextiles. The non-woven geotextiles will be used as cushion and separation materials. The non-woven geotextiles will be supplied by Northwoods.

Nobis does not anticipate the geosynthetics for the 2012-2013 cover system activities will be delivered to the Site in 2011. The geosynthetics staging area constructed in 2011 will be used to the extent practical in 2012-2013, but an additional geosynthetic staging area will need to be constructed as final grading and cover system activities progress in 2012-2013. The location of the future geosynthetic staging area will be coordinated with USACE prior to the start of final grading and cover system placement activities in 2012-2013.

3.11 Placement of Geosynthetics

Placement of the cover system geosynthetics will start with the 60-mil geomembrane. The geomembrane placement will commence following approval of the subgrade in an active work area. Approval of the subgrade includes, but is not limited to, the visual inspection by the QCS, verification of subgrade elevations on the as-built survey, and written acceptance by the geosynthetic subcontractor. The geomembrane will be placed on the approved subgrade from the top of slope down. The geomembrane will be anchored at the top of slope by the anchor


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trench described in Section 3.7.3. Following placement, welding, and seaming of the geomembrane, testing will be conducted in accordance with the requirements of the Project Documents.

Placement of the DGC over the geomembrane will begin once an area of geomembrane has been tested and accepted in accordance with the Project Documents. Placement of the DGC will also be conducted from the top of slope to the bottom. The DGC will be joined in accordance with the Project Documents. The geomembrane and DGC will be extended past the limit of the cover system as noted on the Construction Drawings, and as approved by USACE in the field.

Installation of geomembrane boots around existing monitoring wells and toe drain cleanouts (to remain in place) will be conducted by the geosynthetic subcontractor during placement of the geomembrane. Refer to the Construction Drawings for additional information on pipe penetrations and seals.

3.12 Construction of Toe Details

Construction of toe details will be initiated following placement, testing, and acceptance of the geomembrane and DGC layers in an active work area. Generally, a 12 to18-inch thick cushion layer of 1-1/2-inch stone will be installed over the DGC and geomembrane extended beyond the limit of the cover system. The stone layer will be installed along the entire length of the active work area. The 1-1/2-inch stone will be transported to the toe of slope areas in articulated dump trucks or track mounted dump trucks. Articulated dump trucks will not drive over the DGC and geomembrane during construction of the toe details, unless a minimum 48-inch thick layer of stone and rip rap is in place. LGP track mounted dump trucks, exerting a loaded ground pressure of 8 psi or less, will not drive over the DGC and geomembrane until the full depth layer (12-inches +/-) of 1-1/2-inch stone has been spread along the toe. The stone cushion layer will be spread with a LGP bulldozer or LGP excavator depending on the width of the overall toe detail. A 12 to 36-inch thick layer of 7-inch minus rip rap will be placed over the stone cushion layer at each toe of slope detail. The means and methods used to place the 7-minus rip rap layer will be similar to those used to install the crushed stone cushion layer in each active work area. The toe of slope details are shown on the Construction Drawings included in Appendix D2-1.

3.13 Placement of Vegetative Support Soil

Placement of the VSS layer will be conducted vertically from the toe of slope to the top, to the extent practical. The VSS layer will be placed in one lift. TP-1A will have a 24-inch thick layer of VSS and all other areas of the cover system will have an 18-inch thick layer. VSS material will consist of screened native till from the existing stockpiles on-site, and screened common borrow excavated from on-site borrow sources. VSS materials will be screened to a 4-inch minus maximum diameter material. Articulated dump trucks, and/or track mounted dump trucks will be used to transport the VSS to the toe of slope. VSS material will be dumped on the DGC at the toe of slope and LGP bulldozers will be used to spread the VSS up the slope. Transported VSS will be dumped on the VSS layer once the full depth is established. VSS material will be spread up the slopes to the limit of the cover system drainage features. Placement of the VSS layer will resume following construction of the cover system drainage features. Stopping, turning, and other hard maneuvers over the cover system will be avoided to the extent practical.


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In areas of limited access Nobis anticipates constructing a 48-inch thick layer (minimum) (SES, 2011c) of VSS approximately 12 to 14 ft wide along the toe of slope to provide additional access to active work areas and to promote productivity. Articulated dump trucks will not travel over the cover system until a 48-inch thick layer (minimum) of VSS has been established. Articulated dump trucks will be allowed to travel over the cover system once the 48-inch thick layer has been established, but articulated dump trucks will not be allowed to conduct sharp/hard turning maneuvers (causing rutting) over the cover system regardless of the VSS and/or rock thickness. Additional information regarding the placement of the VSS layer is specified in the Project Documents.

LGP track mounted dump trucks, exerting a loaded ground pressure of 8 psi or less (Nobis, 2011e), will be used to transport and deliver VSS over the cover system within active work areas once the full depth VSS layer has been placed. LGP track mounted dump trucks will not travel over the cover system until the full depth VSS layer has been installed in the area of travel. At locations where LGP vehicles will be turning over the geosynthetic cover system, a layer of VSS and/or rock with a minimum total thickness of 48-inches will be placed, compacted, and maintained while such turning activity is occurring (Nobis, 2011f).

3.14 Installation of Cover System Drainage Features

Installation of cover system drainage features in the cover system areas will be accomplished simultaneously with the placement of the VSS in active work areas. Cover system drainage features include side slope collector pipes, downcomer pipes, surface swales with stone center, and top slope drainage pipes. The cover system drainage features will be installed from the low point to the high point, to the extent practical. Northwoods will begin installation of the 8-ounce non-woven geotextile and HDPE pipe following acceptance of the geosynthetics in an active work area. The geotextile and HDPE pipe will be installed manually, so only construction worker foot traffic will be on top of the DGC. Once the full depth VSS layer has been installed up to the location of a cover system drainage feature, Northwoods will use LGP track mounted dump trucks and a small LGP excavator to install the 1-1/2-inch stone component(s) of the cover system drainage feature as shown on the Construction Drawing included in Appendix D2-1. The LGP excavator and LGP track mounted dump truck will only travel over portions of the cover system where the full depth VSS layer has been installed. The geotextile will be wrapped around the stone and HDPE pipe, and the area will be covered with VSS or rip rap as shown on the Construction Drawings.

3.15 Placement of Topsoil and Seeding

Placement of the 6-inch thick topsoil layer over the VSS will be initiated as soon as possible after a section of the active work area has been covered with the full depth VSS layer and inspected by the QCS. The topsoil layer will be spread from the bottom of the slope up, to the extent practical. Northwoods will use articulated dump trucks and track mounted dump trucks to transport topsoil to the toe of slope in active work areas. The topsoil will be dumped on the VSS layer at the toe of slope and LGP bulldozers will be used to spread the topsoil up the slope. Stopping, turning, and other hard maneuvers over the cover system will be avoided to the extent practical. The QCS will review the depth of the topsoil layer in accordance with the Project Documents. Prior to seeding, all slope areas will be tracked by a LGP bulldozer to create horizontal grooves in the topsoil layer parallel to the toe of slope, to assist with the stabilization of the slope. The intent of the grooves is to minimize the stormwater runoff velocities and hold the seed in place. Seeding will be conducted following installation of surface downcomers and surface swales, refer to Section 3.16 below. Seeding will occur in accordance


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with the Supplementary Conditions and Modified Technical Specifications included in Appendix D2-2, once the slopes have been tracked.

3.16 Installation of Surface Downcomers and Surface Swales

Installation of surface downcomers will be conducted simultaneously with the placement of topsoil in an active work area. The surface downcomers shall be constructed in accordance with the construction detail titled “Downcomer Pipe with Surface Swale” as shown on the Construction Drawings. A layer of 60-mil geomembrane and 8 ounce non-woven geotextile will be installed over the stone wrapped in fabric previously installed during the downcomer pipe installation, as noted in Section 3.14. LGP track mounted dump trucks and a LGP excavator will be used to transport and install 7-inch minus rip rap over the non-woven geotextile. Surface downcomers will be installed from low point to high point. Surface swales will be constructed of topsoil, and will be installed following the placement of the entire 6-inch thick topsoil layer in an active work area. Surface Swales shall be constructed in accordance with the construction detail titled “Side Slope Collector Pipe with Surface Swale” as shown on the Construction Drawings. LGP track mounted dump trucks and LGP excavators will be used to transport and install the surface swales. The swales will be constructed from low point to high point, to the extent practical. Stopping, turning, and other hard maneuvers over the cover system will be avoided to the extent practical. The QCS will review the construction of surface swales in accordance with the Project Documents. Following the completion of seeding operations, permanent erosion control matting will be installed throughout the extents of the surface swale, as shown on the Construction Drawings.

3.17 Construction of Permanent Access Roads

Permanent access roads will be constructed over the VSS layer, as shown on the Construction Drawings. The permanent access roads will be approximately 12 ft wide, at the surface, and will be constructed of a 12-inch thick layer of Vermont Agency of Transportation (VTAOT) Specification 704.04 gravel, or approved equivalent, and a 4-inch thick layer of VTAOT Specification 704.12 gravel, or approved equivalent. LGP track mounted dump trucks and LGP bulldozers will be used to place the 12-inch thick gravel layer approximately 14 feet wide, in one continuous lift. The 4-inch thick gravel layer will be placed over the 12-inch layer in one continuous lift as well. Transitions from the edge of the gravel roads to the VSS layer will be constructed of VSS and sloped at 2H:1V, to the extent practical. Topsoil will be placed over the VSS in transition areas.

4.0 2011 FINAL GRADING AND COVER SYSTEM PLACEMENT ACTIVITIES

4.1 TP-1A CSP Activities

Final grading and cover system placement activities in TP-1A will be conducted in accordance with the general sequence and approaches described in Section 3.0 above. TP-1A final grading activities are anticipated to begin in May 2011 with the goal of finishing cover system placement activities in September 2011. Results of laboratory testing conducted by Nobis using tailing subgrade soil, specified geosynthetic layers, and VSS from on-site sources indicated the original final design slopes for TP-1A (3H:1V) would not meet the factor of safety required by the design. The tests indicated that shallower 4H:1V slopes would meet the required factor of safety. Based on this information, the north and west slopes will be stabilized by cutting the existing slopes back to a shallower 4H:1V (+/-) (SES, 2011a). Cut and fill activities will be conducted in accordance with the Project Documents.


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4.1.1 Layout of TP-1A Cover System Area

Northwoods will layout the extents of the TP-1A cover system in early May 2011. The extents will be reviewed in accordance with the Project Documents prior to the start of final grading and cover system placement activities.

4.1.2 Stripping Topsoil

Existing topsoil and vegetative cover (grass) from the north and west slopes of TP-1A will be stripped and transported to the topsoil stockpile staging area previously established in the northeast corner of TP-1. The topsoil will be stripped in a manner to avoid mixing with the underlying tailing waste, to the extent practical, for reuse as temporary cover soil. Topsoil mixed with tailing waste during the stripping process will be transported to the tailing stockpile area also located in the northeast corner of TP-1. Nobis anticipates removing approximately 8,100 cubic yards (cy) of topsoil from TP-1A. Refer to the Construction Drawings for the location of the stockpile areas. The stockpile and staging area will be managed in accordance with the BMPs described in the PWP and Sections 3.2 and 3.3 above. The side slopes of the topsoil stockpile will be managed at 2H:1V, to the extent practical.

Stripping activities will be advance in three sections: the north slope area, the northwest corner, and the west slope area. The current sequencing plan calls for stripping and final grading activities will start in the northeast corner of TP-1A, and will be advanced west. The final sequence plan will be determined in the field prior to the start of work, and changes will be approved by USACE.

4.1.3 Final Grading to Establish Subgrade

The most up-to-date cut/fill volume analysis for TP-1A result in approximately 59,000 cy of cut, 21,500 cy of fill, with a net cut of approximately 37,500 cy. The net cut is a result of the existing slopes ranging from 3.5H:1V to 2H:1V being laid back to a more stable 4H:1V (+/-). Excavation/cutting of tailing waste will be advanced to the approximate subgrade elevations provided on the Construction Drawings included in Appendix D2-1. The approximate 21,500 cy of fill needed to establish subgrade elevations will be generated from the cuts in this area. Waste rock is not anticipated to be encountered in TP-1A. The area of TP-1A with the most significant fills is between the top of the slopes and the southern and eastern limits of the area. As a result, tailing will be generally relocated from the slope to the current flat area of TP-1.

The cut/fill volume analysis provided above includes the cuts and fills necessary outside the limits of TP-1A to tie into the existing grades at the end of the 2011 construction season. The cut/fills outside the limits of TP-1A will be graded at a maximum slope of 3H:1V to the extent practical. Tailing subgrade outside the limit of TP-1A will be covered with excess salvaged topsoil, or native till material.

Nobis anticipates using the excess tailing waste, approximately 37,500 cy, generated during final grading activities in TP-1A to be used as a combination of fill and subgrade cushion layer below the geomembrane in the other areas. Approximately 22,400 cy of the excess tailing waste may be used as fill material in TP-2B as TP-1A will be constructed simultaneously.

The remaining 15,100 cy of excess fill from TP-1A will be stockpiled for future use in 2012-2013. Approximately 6,500 cy of tailing waste may be used as fill in TP-2A, and the remaining volume, approximately 8,600 cy, may be used as fill in TP-1B.


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Excess tailing from TP-1A not placed as fill in either TP-1A or TP-2B will be transported to the tailing stockpile staging area previously constructed in the northeast corner of TP-1, or an additional staging area to be established in the within the limits of TP-2B. The excess tailing stockpiles will be constructed and managed in accordance with the BMPs described in the PWP, Sections 3.2 and 3.3 above. Active tailing stockpiles will be covered with scrim on a nightly basis, or as approved by USACE.

4.1.4 Subgrade Preparation

4.1.4.1 Compaction and Proof Rolling

General procedures and requirements for compaction and proof rolling to be applied throughout the CSP activities are describe in the Section 3.0 above and in the Project Documents. For TP-1A, the tailing subgrade on the north and west slopes will be established by excavation/cutting activities, so these areas will be proof rolled once subgrade elevations are established. Fill areas at the top of the slopes will be compacted during placement of tailing fill until subgrade elevations are established.

4.1.4.2 Layout and Excavation of Side Slope Collector Pipe Trenches

The original URS design allowed maximum 100 ft spacing between the side slope collector pipes on the north and west slopes. Regrading the north and slopes back to a shallower 4H:1V finished grade resulted in increased slope lengths throughout TP-1A. The maximum slope length associated with the 4H:1V slopes is approximately 240 lf, in the northwest corner of TP-1A. Nobis conducted a series of tests on the DGC and VSS, compared them to the design parameters assumed in the URS design. Based on the results of the tests, the maximum spacing of the side slope collector pipes has been increased to 115 lf (SES, 2011b). As a result, approximately 2,100 lf of side slope collector pipe and down comer trench will be excavated throughout the north and west slopes of TP-1A.

Northwoods will layout the extents of the side slope collector pipe and down comer trenches once subgrade elevations have been established in TP-1A. The extents of the trenches will be reviewed and approved by the QCS prior to excavation.

4.1.4.3 Anchor Trench Excavation and Backfill

Approximately 1,895 lf of anchor trench excavation will be conducted along perimeter of TP-1A. Approximately, 1,745 lf of the anchor trench will be constructed in accordance with the “Top Slope Anchor with Road” detail shown on the Construction Drawings. The remaining 150 lf of anchor trench will be excavated along the southern end of the west slope. The anchor trench in this area is required to anchor the geomembrane at the extents of TP-1A and the 2011 work. Coordination between Northwoods, Nobis, and the geosynthetic subcontractor will be essential for the excavation and backfilling of the anchor trenches.

4.1.5 Protection of Tailing Subgrade and Stockpiles

Tailing subgrade and excess tailing stockpiles generated from final grading activities in TP-1A will be protected in accordance with the general procedures outlined in Section 3.0 above. The temporary scrim along the north slope of TP-1A will be draped over the toe of slope and terminated on the grass of the TP-1 buttress. The temporary scrim along the west slope of TP-1A will be extended to the west side diversion channel.


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4.1.6 Placement of Geosynthetics

The 60-mil geomembrane and DGC may be installed in up to three sections over the approved subgrade in TP-1A. Nobis anticipates the north slope area will be covered first, followed by the northwest corner, and the west slope, respectively. The sequencing may be modified following the selection of the geosynthetics subcontractor, and/or based on site conditions, to optimize the installation of materials. Installation of the geosynthetics will be conducted in accordance with the requirements of the Supplementary Conditions and Modified Technical Specifications included in Appendix D2-2, and as described in Section 3.0. Testing of the geosynthetics will be as described in the Project Documents. The geomembrane and DGC installed over the north slope will be extended to within approximately 2 ft of the face of the TP-1 buttress. The geomembrane and DGC will be terminated in the anchor trench at the limit of TP-1A along the upgradient and western perimeter.

The original URS Toe Detail A for the west slope included a geomembrane flap, perforated pipe, and the DGC being wrapped around the perforated pipe (similar to the north slope). This detail was modified by Nobis during the design review phase to eliminate the geomembrane flap, pipe, and DGC wrapping around the pipe. The revision was justified because runoff from west slope will be discharged directly into the existing rip rap lined west side diversion channel, so it was unnecessary to collect the runoff in a pipe only to discharge it to the same location. The revised Toe Detail A shows the geosynthetics (geomembrane and DGC) along the west slope being extended to the limits of the existing diversion channel, or as approved by USACE. The distance between the limit of the cover system and the diversion channel ranges from approximately 6 to10 ft along the length of the slope.

Nobis anticipates the installation of the geosynthetics over the subgrade in TP-1A will start in July 2011 and will be completed by the end of August 2011.

4.1.7 Construction of Toe Details A & B

Two different toe details will be constructed during the closure activities in TP-1A. Approximately 1,530 lf of Toe Detail B will be constructed along the north slope, and approximately 710 lf of Toe Detail A will be constructed along the west slope. Toe Detail B may be installed from east to west along the north slope. A 10-inch diameter perforated HDPE pipe will be installed over the DGC at the toe of slope along the north slope prior to the placement of the stone cushion layer. An 18-inch thick layer of 1-1/2-inch stone will be placed as the cushion layer over the DGC and pipe along the entire length of the north slope. A 36-inch (+/-) layer of 7-inch minus rip rap will be installed over the stone.

Toe Detail A will be constructed from south to north along the west slope, to the extent practical. Access along the west slope is limited because the geosynthetics will be extended out to the west side diversion channel. Therefore, up to three temporary crossings will be constructed in this area, as noted in Section 3.0. The crossings will be used during the installation of the toe details and placement of the VSS and topsoil layers. The stone cushion layer installed over the geosynthetics at Toe Detail A along the west slope will consist of a 12-inch thick layer of 1-1/2-inch stone. The stone will be covered with a 12 to 14-inch thick layer of 7-inch minus rip rap.


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4.1.8 Placement of VSS

The VSS layer will be installed in one 24-inch thick lift from the toe of slopes to the top over the north and west slopes of TP-1A. The 24-inch thick lift of VSS will be continued over the top of the slope to the western and northern limits of the permanent access roads, as shown on the Construction Drawings. The VSS layer under, south, and east of the permanent access road will be 18-inches thick. Refer to the “Top Slope Anchor with Road” detail on the Construction Drawings for additional information. Due to the limited access to the toe of the west slope of TP-1A a thickened section of VSS may be constructed along the toe of slope as described in Section 3.13. The anticipated source of VSS for TP-1A is the East Side Borrow Source Area, located east of Jeep Road on-site. Approximately 33,000 cy of screened 4-inch minus VSS will be placed over the geosynthetics throughout TP-1A. Placement of the VSS layer will be conducted in accordance with Section 3.0 and the requirements of the Project Documents.

4.1.9 Installation of Cover System Drainage Features

Cover system drainage features in TP-1A consist of side slope collector pipes and down comer pipes on the north and west slopes. Approximately 1,700 lf of side slope collector pipes will be installed and approximately 350 lf of down comers will be installed. The side slope collector pipe section will consist of 8-inch diameter perforated HDPE pipe surrounded by 1-1/2-inch stone and wrapped in 8 ounce non-woven geotextile. The down comer pipes will consist of 10-inch diameter solid wall HDPE pipe, with the typical section matching that of the side slope collector pipe. The down comer pipes will discharge onto rip rap aprons outside the limit of the cover system. Finger style rodent screens will be installed in the outlet ends of the down comer pipes, and end caps will be installed in the upgradient ends of the side slope collector pipes. HDPE pipe, fittings, and reducers will be used, as necessary, to connect the side slope collector pipes to the down comer pipes. The installation of the cover system drainage features in TP-1A will be conducted as described above in Section 3.0.

4.1.10 Placement of Topsoil and Seeding

Placement of the 6-inch thick topsoil layer will be conducted in accordance with the general procedures described above in Section 3.0. Approximately 8,300 cy of topsoil will be placed over the VSS in TP-1A. The anticipated sources of topsoil are the previously manufactured topsoil stockpile and the existing off-site east topsoil stockpile located on-site. Nobis anticipates topsoil placement will be conducted in August 2011, with seeding activities planned immediately following installation of the surface downcomers and swales described below. The goal is to have a healthy stand of vegetation by the end of September 2011.

4.1.11 Installation of Surface Downcomer and Surface Swales

Construction of the surface downcomer will be conducted simultaneously with topsoil placement, and construction of the surface swales will follow placement of the 6-inch thick topsoil layer throughout TP-1A. Construction will be conducted in accordance with the general procedures described above in Section 3.0. Approximately 210 lf of surface downcomer and 975 lf of surface swale will be constructed in TP-1A, as shown on the Construction Drawings. Approximately 550 cy of topsoil will be used to construct the surface swales. The anticipated sources of topsoil are the previously manufactured topsoil stockpile and the existing off-site east topsoil stockpile located on-site.


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4.1.12 Placement of Permanent and Temporary Erosion Control Matting

Permanent erosion control matting will be placed throughout the surface swale immediately following seeding. Approximately 23,400 sf of permanent erosion control matting will be installed to the extents shown on the Construction Drawings. Placement of temporary erosion control matting throughout the remaining slope areas of TP-1A will follow seeding operations if a healthy stand of vegetation is not established by the end of September 2011. If needed, approximately 357,000 sf of temporary erosion control matting will be placed on the slopes of TP-1A. Erosion control matting will be installed in accordance with the manufacturer’s specifications.

4.1.13 Construction of Permanent Access Roads

Construction of the permanent access roads in TP-1A will be conducted simultaneously with the placement of topsoil. Approximately 1,700 lf of access road will be installed in TP-1A. The access road will be constructed from southwest to northeast, and as described in Sections 3.0.

4.2 TP-2B CSP Activities

Final grading and cover system placement activities in TP-2B will be conducted in accordance with the general sequence and approaches described in Section 3.0 above. Final grading activities in TP-2B are anticipated to begin in June 2011 and cover system placement activities will be completed by the end of October 2011. Overall, TP-2B is a net fill as described in Section 4.2.1 below. Waste rock and tailing waste are expected to be encountered during cutting activities. TP-2B will be regraded to establish approximate 6% slopes throughout the southern and eastern portions of the area, and 7.5H:1V (+/-) in the northern section of the area. All cut and fill activities will be conducted in accordance with the Project Documents.

4.2.1 Layout of TP-2B Cover System Area

Northwoods will layout the extents of the TP-2B cover system area in late May 2011. The extents will be reviewed in accordance with the Project Documents prior to the start of final grading and cover system placement activities.

4.2.2 Stripping Topsoil

There is no topsoil over the existing waste rock and tailing stockpiles in TP-2B.

4.2.3 Final Grading to Establish Subgrade

The most up-to-date cut/fill volume analysis for TP-2B results in approximately 42,400 cy of cut, 64,800 cy of fill, with a net fill of approximately 22,400 cy. The majority of the cut in TP-2B will consist of the removal of the top layers of the TP-3 waste rock stockpile located in the northwest corner of TP-2B, as shown on Figure D4-1. Cuts in this area range from 2 ft to 18 ft. Waste rock material encountered during excavation activities is anticipated to range in size from small cobbles to 3ft by 3ft diameter rocks. The larger diameter rocks encountered during excavation activities will be relocated and placed to the north and northeast of the significant cut areas, to the extent practical, as these areas encompass the deeper fill areas. Waste rock will be backfilled as deep as practical within TP-2B. Excess tailing will be used to backfill around the waste rock material and to establish a 6-inch thick cushion layer below the subgrade elevations.


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The additional fill required, approximately 22,400 cy, to establish subgrade elevations in TP-2B will come from the excess tailing waste generated from TP-1A final grading activities. Final grading activities in TP-1A and TP-2B will be conducted simultaneously, to the extent practical, so cuts to fill are anticipated to minimize handling of the materials. The majority of this fill will be placed and compacted on the south facing slope of TP-2B.

The cut/fill volume analysis provided above includes the cuts and fills necessary outside the limits of TP-2B to tie into the existing grades at the end of the 2011 construction season. The cut/fills outside the limits of TP-2B will be graded at a maximum slope of 3H:1V, to the extent practical. Tailing and waste rock subgrade outside the limit of TP-2B will be covered with excess salvaged topsoil, or native till material, and seeded prior to the completion of work in TP-2B.

4.2.4 Subgrade Preparation

4.2.4.1 Compaction and Proof Rolling

The subgrade in the northwest portion of TP-2B is anticipated to be established by excavation/cutting to subgrade elevations, then removing additional waste rock and backfilling as needed to establish a 6-inch tailing cushion layer. Fill areas elsewhere in TP-2B will be compacted during placement of tailing fill and waste rock, until subgrade elevations are established. A 6-inch thick (minimum) tailing cushion will be installed throughout the TP-2B subgrade area. Overall, the general sequence and approaches outlined in Section 3.0 will be applied to the compaction and proof rolling activities in TP-2B.

4.2.4.2 Layout and Excavation of Cover System Drainage Features

The cover system drainage features in TP-2B will consist of top slope drainage pipe, surface swales with stone center, and the TP-1/TP-2 Toe Detail.

Each of these details has been modified from the original URS design for constructability reasons. Refer to the Construction Drawings for typical details of each of the drainage features listed above.

Of the three cover system drainage features to be constructed in TP-2B, only one requires layout during subgrade preparation. Northwoods will layout the extents of the TP-1/TP-2 Toe Detail once subgrade elevations are established. The extents will be reviewed by the QCS in accordance with the Project Documents.

Approximately 1,400 lf of the TP-1/TP-2 Toe Detail will be excavated in the northern portion of TP-2B. Following excavation, the extents of the TP-1/TP-2 Toe Detail established in the subgrade, and other areas of the subgrade disturbed during excavation activities, will be proof rolled.

4.2.4.3 Anchor Trench Excavation and Backfill

Approximately 2,325 lf of anchor trench excavation will be conducted during the TP-2B cover system placement activities. Approximately, 640 lf of the anchor trench will be constructed in accordance with the “Top Slope Anchor without Road” detail shown on the Construction Drawings. The remaining 1,685 lf of anchor trench will be excavated around the northern and western perimeter of TP-2B to anchor the geomembrane at the extents of the 2011 work.


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Coordination between Northwoods, Nobis, and the geosynthetic subcontractor will be essential for the excavation and backfilling of the anchor trenches.

4.2.5 Protection of Tailing Subgrade

The native tailing and tailing cushion subgrade layer throughout TP-2B will be protected in accordance with the general procedures outlined in Section 3.0.

4.2.6 Placement of Geosynthetics

The 60-mil geomembrane and DGC will be installed in up to two sections over the approved subgrade in TP-2B. The geomembrane and DGC will be installed from the top of slope to the bottom. The subgrade elevations in TP-2B create a crest from west to east through the approximate center of the area, so the geosynthetics will be installed heading north and south from the crest. The geomembrane will be anchored along the top of the crest from east to west, and around the western and northern extents of the TP-2B cover system area. The geomembrane and DGC over the southern portion of the area will be extended past the limit of the cover system as needed to tie into the existing east side diversion channel, or as approved by USACE. The DGC will be terminated at the top of the anchor trench around the western and northern limits of the cover system area.

Toe Detail D has been modified in the same manner as Toe Detail A described in Section 4.1.6 above, with the geomembrane flap and drainage pipe removed, and the DGC being extended to the limits of the geomembrane.

Nobis anticipates the installation of the geosynthetics in TP-2B will start in the middle of August 2011 and will be completed by the middle of September 2011.

4.2.7 Construction of Toe Detail D and the TP-1/TP-2 Toe Detail

Approximately 1,190 lf of Toe Detail D will be constructed outside the southern limit of TP-2B. Toe Detail D will be constructed from west to east, to the extent practical. Access to southern limit of the cover system area is limited because the geosynthetics will be extended out to the east side diversion channel. Therefore, up to two temporary crossings will be constructed in this area, as noted in Section 3.0. The crossings will be used during the installation of the toe details and placement of the VSS and topsoil layers. The stone cushion layer installed over the geosynthetics at the toe of slope will consist of a 12-inch thick layer of 1-1/2-inch stone. The stone will be covered with a 12 to 14-inch thick layer of 7-inch minus rip rap. The general sequence and approaches outlined in Section 3.0 will be applied to the construction of this detail.

The TP-1/TP-2 Toe Detail will be constructed along the low point in the northern portion of TP-2B. Refer to the Construction Drawings for the location of the TP-1/TP-2 Toe Detail and a typical construction detail. The detail will be constructed from the outlet at the east side diversion channel, to the western extent of the detail approximately 1,370 lf away. The 8-ounce non-woven geotextile and 8-inch diameter perforated HDPE pipe will be installed by hand over the DGC in the swale/low point. Placement of the 12-inch thick 1-1/2-inch stone cushion layer will follow installation of the drainage pipe. An 8-ounce non-woven geotextile will be installed over the stone layer. A layer of 60-mil geomembrane liner will be installed over the geotextile. The 60-mil geomembrane liner will be covered with 8-ounce non-woven geotextile. The 7-inch minus rip rap layer will be installed over the geotextile.


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4.2.8 Placement of VSS

The VSS layer will be installed in one continuous 18-inch thick lift over the DGC in TP-2B. The anticipated source of VSS for TP-2B is the existing unscreened native till stockpile located west of Jeep Road on-site. Approximately 27,000 cy of screened 4-inch minus VSS will be placed throughout TP-2B. VSS will be placed from the toe of slope to the top, so Northwoods will be placing the VSS from the north and south. Due to the limited access to the toe of the south facing slope of TP-2B a thickened section of VSS may be constructed along the toe of slope as described in Section 3.13. Placement of the VSS layer will be conducted in accordance with the general sequence and approaches described in Section 3.0, and the Project Documents.

4.2.9 Installation of Cover System Drainage Features

Cover system drainage features in TP-2B consist of the top slope drainage pipes and the surface swales with stone center. Northwoods will layout the extents of both cover system drainage features prior to the start of VSS placement. The QCS will review the extents of the cover system drainage features as marked out by Northwoods. Following approval of the layout, an 8-ounce non-woven geotextile and 4-inch diameter perforated HDPE pipe will be installed by hand over the DGC. The pipes will be sloped to drain with a minimum slope of 1%. The top slope drainage pipes will be tie into the perforated HDPE pipe under the TP-1/TP-2 Toe detail as shown on the Construction Drawings. The drainage pipe will be backfilled with approximately 12-inches of 1-1/2-inch stone once the down gradient slope areas have been covered with 18-inches of VSS and LGP tracked vehicles can travel over the cover system. Following placement of the stone, the section will be covered/wrapped by the geotextile, and VSS will be spread over the top of the geotextile. Refer to the Construction Drawings for a typical detail of this cover system drainage feature. Approximately 2,745 lf of top slope drainage pipe will be installed over the cover system in TP-2B. The maximum design spacing of 150 ft between top slope drainage pipes will be maintained.

Approximately 275 ft of surface swale with stone center will be constructed along the western portion of the cover system. The surface swale will be constructed following placement of the full depth VSS layer on either side of the swale. The surface swale will consist of an 8-inch diameter perforated HDPE pipe being installed by hand over 8-ounce non-woven geotextile. The pipe and geotextile will be covered with a 12-inch thick layer of 1-1/2-inch stone. A second layer of 8-ounce non-woven geotextile will be installed over the stone layer. The geotextile will be covered by a layer of 60-mil geomembrane to keep surface water separate from water in the cover system, to the extent practical. The 60-mil geomembrane pieces will be shingled to allow flow without being undermined. The geomembrane will be covered with a layer of 8-ounce non-woven geotextile, then backfilled with a 12 to 14-inch layer of 7-minus rip rap to match adjacent finished grades following topsoil placement.

Finger style rodent screens will be installed in the outlet ends of the pipes, and end caps will be installed in the upgradient ends of the drainage pipes. HDPE pipe fittings and reducers will be used, as necessary, to connect the various pipes. The installation of the cover system drainage features in TP-2B will be conducted as described above in Section 3.0.

4.2.10 Placement of Topsoil and Seeding

Placement of the 6-inch thick topsoil layer will be conducted in accordance with the general procedures described in Section 3.0. Approximately 9,100 cy of topsoil will be placed in TP-2B. The anticipated sources of topsoil are the existing off-site east and west topsoil stockpiles located on-site. Topsoil placement will be conducted in late September/early October 2011, with


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seeding activities planned immediately following. The goal is to have some vegetation established by the end of October 2011.

Due to the variability in the actual date of seeding, and the weather conditions in late September and early October, Nobis will evaluate whether or not additional stabilization measures are needed in TP-2B prior to the end of the 2011 construction season, anticipated to be late in November.

4.2.11 Construction of Permanent Access Road

Construction of the permanent access roads in TP-2B will be conducted simultaneously with the placement of topsoil. Approximately 430 lf of access road will be installed in TP-2B. The access road will be constructed from west to east, and as described in Section 3.0.

4.3 2011 Construction Season Closeout

As noted in Section 3.2, A Winter Shutdown Plan will be developed and submitted to USACE for review and approval prior to Winter Shutdown in 2011 and 2012.

4.3.1 Stockpile Stabilization

The excess tailing stockpile from TP-1A will be covered with salvaged topsoil from the slopes of TP-1A. The stockpile will be seeded no later than the end of August, so that a healthy stand of vegetation is established prior to Winter Shutdown. Erosion control measures described in the sections above will be maintained and/or replaced as needed prior to Winter Shutdown. Nobis will coordinate with USACE, as needed, to implement additional erosion control measures.

Stockpiles of VSS, topsoil, and other soil materials will be stabilized in accordance with the BMPs described in the PWP.

4.3.2 Stabilization of Disturbed Areas Outside Limits of Cover System

Disturbed areas of the Site outside the limits of the cover system will be stabilized with native till, common borrow, and/or topsoil. These areas will be seeded as early as possible following disturbance. Areas not seeded prior to the end of September, or not stabilized by vegetation prior to the end of October, will be stabilize with mulch, matting, or wood chips as approved by USACE.

4.3.3 Construction Access/Haul Roads

Routine maintenance and repair of on-site access/haul roads will be conducted prior to Winter Shutdown in November 2011. Installation of additional water bars, and/or other erosion control measures will be conducted, as