Excavation Depth Techniques Study

Excavation Depth Techniques Study

Prepared for the U.S. Department of Energy Assistant Secretary for Environmental Management

Contractor for the U.S. Department of Energy under Contract DE-AC06-08RL 14788

Plateau Remediation Company

P.O. Box 1600 Richland, Washington 99352

Approved for Public Release; Further Dissemination Unlimited

SGW-50712

Revision 0

SGW-50712 Revision 0


Date Published

September 2011

Prepared for the U.S. Department of Energy Assistant Secretary for Environmental Management

Contractor for the U.S. Department of Energy under Contract DE-AC06-08RL 14788

P.O. Box 1600 Richland, Washington

oved for Public Release; Further Dissemination Unlimited

TRADEMARK DISCLAIMER Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors.

This report has been reproduced from the best available copy.

Printed in the United States of America

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Contents

1 Introduction ....................................................................................................................................... 1

Appendix

A Excavation Depth Techniques Study ............................................................................................ A-i

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1 Introduction

Fluor Hanford, Inc. contracted Garry Struthers Associates, Inc. (GSAI) to review excavation and mining techniques that are efficient, safe, cost effective, protective of human health and the environment, and applicable to remediation of deep vadose zone contamination at two generic liquid waste disposal sites on the Central Plateau at the Hanford Site: a large crib and a reverse well.

The final report prepared by GSAI, Excavation Depth Techniques Study, is provided as Appendix A in this report. The final report includes the specific objectives for the review, detailed information on the applicable excavation techniques, the conclusions of the study, and recommendations.

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Appendix A


FINAL REPORT Excavation Depth Techniques Study

Professional Support Services Basic Ordering Agreement (PSSBOA) 28297

Task Order Release 3

PREPARED FOR

FLUOR HANFORD, INC.

RICHLAND, WASHINGTON

July 6, 2007

Prepared by GARRY STRUTHERS ASSOCIATES, INC.

3150 Richards Road, Suite 200 Bellevue, WA 98005

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Prepared by

GARRY STRUTHERS ASSOCIATES, INC. 3150 Richards Road, Suite 200

Bellevue, WA 98005

FINAL REPORT


for

Fluor Hanford, Inc., Richland, Washington

Professional Support Services Basic Ordering Agreement (PSSBOA) 28297

Task Order Release 3

July 6, 2007

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CONTENTS

EXECUTIVE SUMMARY ............................................................................................................ ES-1

1. INTRODUCTION AND BACKGROUND.................................................................................. 1-1 1.1 Task Goal and Objectives................................................................................................. 1-1 1.2 Background ...................................................................................................................... 1-2

1.2.1 Large Crib................................................................................................................. 1-2 1.2.2 Reverse Well ............................................................................................................ 1-2 1.2.3 Geology .................................................................................................................... 1-3 1.2.4 Meteorology ............................................................................................................. 1-3 1.2.5 Contaminant Profiles ................................................................................................ 1-3 1.2.6 Applicable Federal, State, and Fluor Requirements ................................................. 1-3

2. ASSUMPTIONS ..................................................................................................................... 2-1

3. EVALUATION FACTORS...................................................................................................... 3-1 3.1 Safety................................................................................................................................ 3-1 3.2 Protection of Human Health and the Environment .......................................................... 3-2 3.3 Minimization of Soil Material Removed.......................................................................... 3-2 3.4 Realistic Maximum Depth................................................................................................ 3-3 3.5 Cost-Effectiveness............................................................................................................ 3-3

4. EXCAVATION SUPPORT SYSTEMS...................................................................................... 4-1 4.1 Sloping and Benching ...................................................................................................... 4-1 4.2 Shoring and Shielding Systems ........................................................................................ 4-1

4.2.1 Walls......................................................................................................................... 4-3 4.2.2 Piles .......................................................................................................................... 4-6 4.2.3 Shafts ...................................................................................................................... 4-11

4.3 Ground Improvement ..................................................................................................... 4-14 4.3.1 Jet Grouting ............................................................................................................ 4-14 4.3.2 Permeation Grouting .............................................................................................. 4-14

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4.3.3 Chemical Grouting ................................................................................................. 4-15 4.3.4 Ground Freezing..................................................................................................... 4-15 4.3.5 Soil Nailing............................................................................................................. 4-15

5. RESULTS OF VENDOR SURVEYS......................................................................................... 5-1

6. EXCAVATION TECHNIQUES APPLICABLE TO LARGE CRIB............................................. 6-1 6.1 Surface Mining ................................................................................................................. 6-1 6.2 Excavation Using a Structural Diaphragm Wall Soil Support System............................. 6-2

6.2.1 Scenario 1 – Excavation to 20 ft below Crib Bottom............................................... 6-5 6.2.2 Scenario 2 – Excavation to 220 ft Below Crib Bottom ............................................ 6-6 6.2.3 Scenario 3 – Excavation to 220 ft below Crib Bottom With In-Situ Cast

Cement/Bentonite as Backfill Material .................................................................... 6-7 6.3 Excavation Using Large Diameter Access Shafts ............................................................ 6-7

6.3.1 Scenario 1-Use of Reinforced Concrete Circular Slurry Wall ................................. 6-7 6.3.2 Scenario 2-Straight Line Grid Orientation ............................................................... 6-8 6.3.3 Scenario 3 – Packed Sphere Orientation ................................................................ 6-11

6.4 Sequential Excavation Depths Using Benching and Vertical Soil Supports .................. 6-11 6.5 Top Down Excavation Using Soil Nails and Internal Brace System ............................. 6-13

7. EXCAVATION TECHNIQUES APPLICABLE TO REVERSE WELL ....................................... 7-1 7.1 Use of Auger Rig.............................................................................................................. 7-1 7.2 Use of Hydraulic Casing Oscillator and Hammer Grab ................................................... 7-1 7.3 Use of Circular Structural Diaphragm Wall Vs. Casing................................................... 7-3 7.4 Sequential Excavation to 200 ft BGS Using Corrugated Metal Pipe for Borehole

Stabilization As Proposed by Anderson Drilling ............................................................. 7-3

8. PRELIMINARY COST ESTIMATES....................................................................................... 8-5

9. CONCLUSIONS..................................................................................................................... 9-1

10. RECOMMENDATIONS........................................................................................................ 10-1

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APPENDICES

Appendix A (Map of Hanford Site and Area Designations)

Appendix B (Vadose Zone Stratigraphy)

Appendix C (216-B-46) Crib Contaminant Distribution Model of Contaminants of Potential Concern)

Appendix D (General Concepts of Contaminant Distribution Beneath 200 Area Disposal Facilities)

TABLES

Table 1. Summary Information Derived from Contacts Listed in Table 2.................................. 5-1

Table 2. List of Specialty Geotechnical Contractors................................................................... 5-2

FIGURES

Figure 1. Operation Layout of a Hydrofraise (Courtesy of Soletanche Bachy) .......................... 4-4

Figure 2. Installation of Diaphragm Wall (Courtesy of Land Transport Authority of Singapore) ..................................................................................................................................... 4-5

Figure 3. Illustration of Construction of Secant Pile Wall (Courtesy of Land Transportation Authority of Singapore)........................................................................................................ 4-7

Figure 4. Photo of Soldier Pile with Wood Laggings (Courtesy of University of California, Davis) ................................................................................................................................... 4-8

Figure 5. Illustration of Construction of Contiguous Bored Pile Wall (Courtesy of Land Transport Authority of Singapore) ....................................................................................... 4-8

Figure 6. Illustration of Installation of Sheet Pile Wall (Courtesy of Land Transport Authority of Singapore) ............................................................................................................................ 4-9

Figure 7. Illustration of Deep Soil Mixing Process (Courtesy of Hayward Baker, Inc.) .......... 4-10

Figure 8. Illustration of Drilled Shaft Construction Using Casing (Courtesy of Federal Highway Administration) .................................................................................................................. 4-11

Figure 9. Illustration of Drilled Shaft Using Slurry to Stablilize Caving Soils (Courtesy of Federal Highway Administation) ....................................................................................... 4-12

Figure 10. Illustration of Augered Shaft in Competent Soil (Courtesy of Federal Highway Administration) .................................................................................................................. 4-12

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Figure 11. Photo of Leffer Oscillator Driving Casing into the Ground (Courtesy of Leffer GmbH)................................................................................................................................ 4-13

Figure 12. Illustration of Jet Grouting (Courtesy of Hayward Baker, Inc.) .............................. 4-14

Figure 13. Soil Nailing Process (Courtesy of Hayward Baker) ................................................ 4-16

Figure 14. Excavation to 20 Feet Below Crib Bottom ................................................................ 6-3

Figure 15. Excavation to 220 Feet Below Crib Bottom .............................................................. 6-4

Figure 16. Excavation to 220 Feet Below Crib Bottom with In-Situ Cost/Bentonite as Rockfill Material ................................................................................................................................ 6-9

Figure 17. Excavation Using Large Diameter Access Shaft – Straight Line Grid Orientation . 6-10

Figure 18. Excavation Using Large Diameter Access Shaft – Packed Sphere Orientation....... 6-12

Figure 19a. Top Down Excavation Using Soil Nails and Internal Brace System ..................... 6-14

Figure 19b. Top Down Excavation Using Soil Nails and Internal Brace System..................... 6-15

Figure 19c. Top Down Excavation Using Soil Nails and Internal Brace System ..................... 6-16

Figure 20. Reverse Well Excavation Profile ............................................................................... 7-2

Figure 21. Stepped Excavation Using Large Diameter Shafts (Corrugated Metal Pipe) ............ 7-4

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ABBREVIATIONS AND ACRONYMS

ALARA As Low As Reasonably Achievable

ARAR Applicable, Relevant and Appropriate Regulations

bgs Below Ground Surface

CERCLA Comprehensive Environmental Response, Compensation and Liability Act

CFR Code of Federal Regulations

COC Chemicals of Concern

CSM Cement Soil Mixing

DOE U.S. Department of Energy

EPA U.S. Environmental Protection Agency

ERDF Environmental Restoration Disposal Facility

FH Fluor Hanford, Inc.

ft feet

GSAI Garry Struthers Associates, Inc.

GPS Global Positioning System

kN load capacity

LLW Low-Level Waste

mm millimeter

MSHA Mine Safety and Health Act

NPL National Priorities List of Superfund Sites

OSHA Occupational Safety and Health Act

PSSBOA Professional Support Services Basic Ordering Agreement

RCRA Resource Conservation and Recovery Act

RI/FS Remedial Investigation and Feasibility Study

TBC To Be Considered

TSD Treatment, Storage and Disposal Units or Facilities

WADOE Washington Department of Ecology

yd yard

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GLOSSARY

bentonite – a high swelling clay material consisting chemically of hydrated sodium calcium aluminium magnesium silicate hydroxide, (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O., known as Montmorillonite, in combination with 10 to 20 per cent various mineral impurities such as feldspars, calcite, silica, gypsum, etc. Montmorillonite swells with the addition of water.

Berliner Wall – a type of retaining wall system known as soldier piles and lagging walls that is constructed of steel piles and timber laggings. The soldier piles are embedded typically at regular intervals of 6 ft to 12 ft vertically. Excavations are conducted in small stages and timber laggings are then installed between the steel piles.

bucket chain excavators – a continuous excavation machine capable of removing up to 12,000 cubic meters (15,686 cubic yards) of material per hour. BCE’s are used most often in coal mining.

casing – A steel shell used to construct the drilled shaft. The casing can help advance the hole, and supports the sides of the hole. Casing may be permanent or temporary.

clam buckets - A bucket-like device attached to the crane and lowered into the trench. The bucket (clamshell) is lowered in the open position, the bucket closes to grab the soil, and the bucket is lifted to the surface, opened, and the excavated materials dropped into the waiting truck.

cross bracing – Diagonal members between two opposite walls or columns to provide additional structural support from horizontal forces.

diaphragm panels – This is a section of trench that is excavated where construction of a diaphragm wall begins. Panels are usually 8 to 20 feet long, with widths varying from 2 to 5 feet.

diaphragm walls - Diaphragm walls are constructed using the slurry trench technique which involves excavating a narrow trench that is kept full of an engineered fluid or slurry. The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse. Cast-in-place diaphragm walls are usually formed with concrete tremied under bentonite slurry. The slurry is displaced and recovered/reused in the process. Various types of excavation equipment can be used depending on project conditions, including hydraulic excavators and kelly-mounted or cable-hung clam buckets. Depths in excess 150 feet are possible. (The Hydrofraise, a highly specialized excavation tool, can reach depths of 500 feet.) Once the excavation of a panel is complete, a steel reinforcement cage is placed in the center of the panel. Concrete is poured in one continuous operation through one or more tremie pipes that extend to the bottom of the trench. The tremie pipes are extracted as the concrete rises; however, the discharge end of the tremie pipe always remains embedded in the fresh concrete. The slurry that is displaced by the concrete is saved and reused for subsequent panel excavations. As the concrete sets, the end pipes are withdrawn. Similarly, secondary panels are constructed between the primary panels to create a continuous wall. The finished wall may be cantilever or require anchors or props for lateral support.

dragline excavator – This heavy equipment consists of a large bucket that is suspended from a boom (a large truss-like structure) with wire ropes. The bucket is maneuvered by means of a

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number of ropes and chains. The hoistrope, powered by large diesel or electric motors, supports the bucket and hoist-coupler assembly from the boom. The dragrope is used to draw the bucket assembly horizontally.

ground improvement - involves drilling several holes and injecting concrete into the ground. The result will be an underground block of hardened soil and concrete.

heavy duty excavator- This is a heavy piece of equipment used in the construction industry that consists of a backhoe and cab mounted on a pivot ( a rotating platform) atop an undercarriage with tracks or wheel. Excavators come in a wide variety of sizes in terms of excavator weight and bucket size.

high slump concrete - High slump or "flowing" concrete mixes are economical ready mix products that allow maximum flowability without sacrificing strength. This is accomplished by adding water at the jobsite. These high slump, high strength properties are attained through the use of high range water reducing admixtures (superplasticizers). These mixes feature high slumps (8" - 11") without segregation or sacrificing strength. High slump concrete provides faster and easier placement. hollow stem continuous flight auger – This is a machine used to form contiguous bored piles by screwing a continuous auger into the ground to the required depth. Concrete is then pumped under pressure through the hollow stem of the auger to the bottom of the bore. Once pumping starts, the auger is progressively withdrawn bringing soils with it to the surface.

Hydrofraise – A drilling machine mounted on a heavy crawler crane and powered by three down-the-hole motors with reverse mud circulation. The Hydrofraise has a heavy metal frame which serves as a guide. The frame has two cutter drums equipped with tungsten carbide-tipped cutters which rotate in opposite directions in order to break up the soils. A pump placed immediately above the drums evacuates the loosened soil which is carried to the surface by the drilling mud.

Hydromill - A crane-mounted excavator with rotating wheels used to excavate a slot/trench for the slurry wall panels. The wheels mix the soil with slurry and the mixture is pumped to the surface.

Jet grouting - With the jet grouting process, a drill hole is placed in the ground. A drill rod equipped with jet nozzles injects high-pressure water, air, and cement into the ground as the drill rod is rotated and raised. The high-pressure materials cut/loosen a circular column of soil, which mixes with the cement and forms a column of soil/cement material with increased strength and lower permeability.

Kelly bar – This is a shaft of steel which transmits the torque and downward force from the rig to the drilling tool. Most kelly bars are square in cross section, but do not have to be. Kelly bars start off as a set length but can be telescoped to drill at greater depths. The kelly bar passes through a rotary table that is turned by a power unit.

Lagging – Material that is placed between soldier piles to retain the excavated face and to transfer the lateral pressures to the piles.

mechanical augers – A drill method for boring into the ground and moving material or liquid by means of a rotating helical flighting. The material is moved along the axis of rotation.

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mechanical clamshell – Type of mechanical grab device with two or more jaws, used to pick things up or to capture things.

mechanical grabs – This is type of material handling equipment relying on mechanical systems to control the lifts.

method water – amount of water used in the slurry mixture

oscillators – a machine that is used in advancing the casing into the ground through the process of oscillation during the construction of a drilled shaft or a large diameter access shaft.

permeation grouting - a ground treatment method in which grout is injected into a porous medium without disturbing its original structure. In geotechnical engineering, this usually refers to the process of filling the pores and joints in a soil and/or rock deposit to change its geotechnical properties.

reinforcing cages – Material that is placed in a diaphragm panel after completion of excavation to provide structural support to the concrete poured in the panel.

reverse circulation - the course of drilling fluid downward through the annulus and upward through the drill stem, in contrast to normal circulation in which the course is downward through the drill stem and upward through the annulus. The entire drilling assembly from the swivel to the bit; composed of the kelly, drill pipe, and drill collars, used to rotate the bit and to carry the mud or circulating fluid to the bit.

rotary drilling rigs - A drilling rig is a machine which creates holes (usually called boreholes) and/or shafts in the ground. Rotary drilling is a method in which a hole is drilled by a rotating bit to which a downward force is applied. The bit is fastened to and rotated by the drill stem, which also provides a passageway through which the drilling fluid is circulated. Additional joints of drill pipe are added as drilling progresses.

secant pile walls - Secant piles are two piles (vertical holes filled with concrete) placed side by side. One pile cuts into the second pile (overlapping), so the two are in direct contact with each other. The overlapping section is the "secant." Secant piles can be placed in a series, each cut into the adjacent pile, forming a wall. The walls can be made in a circular or rectangular pattern and hold back the soil when the inside is excavated.

sequential depth excavation – Process by which the targeted depth of excavation is achieved through a sequence of intermediate activities of installing vertical support system, excavation to a shallower depth, creating a bench to the next vertical support system and area to be excavated. The operation is manifested like a telescope, and involves removal of soil material beyond targeted amounts if a straight vertical excavation of the contaminated soil column were conducted.

sheet piling - Sheet piling is a form of driven piling using thin interlocking sheets of steel to obtain a continuous barrier in the ground. The main application of steel sheet piles is in retaining walls and cofferdams erected to enable permanent works to proceed.

slurry wall - A dense mixture made up of bentonite clay and water. It is used to fill holes (shafts, building slurry walls, tunnels, etc.) to prevent collapse.

soil mix walls – This is a top down soil treatment involving in-situ mechanical mixing of soil with cementitious material (slurry or dry powder reagent binder) using a hollow stem mix tool. Sets of 1 to 3 shafts with mixing tools, up to 8-feet in diameter, are used to mix soft and loose

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soils to depths of 100 feet. The hollow stem is used as a conduit to pump grout and mix the soil as the tool advances and/or withdraws, resulting in a column of treated soil.

soil nailing - Soil nailing is a stabilization method of reinforcing existing soil by installing threaded steel bars into slopes or cuts as construction proceeds from top down. Grouted bars are installed to create a stable mass of soil, which is the first step in building a solid wall. The nailing process creates a single block of earth able to hold-back its overburden.

soldier pile - Soldier piles, also know as king piles or Berlin walls, are constructed of wide flange steel H sections spaced about 2 to 3 m apart and are driven prior to excavation. As the excavation proceeds, horizontal timber sheeting (lagging) is inserted behind the H pile flanges.

spoils - Dirt or rock that has been removed from its original location, destroying the composition of the soil in the process, as with strip-mining or dredging.

stop-end pipes – Material that is placed vertically at each end of the primary panel of a diaphragm to form joints for adjacent secondary panels.

surface miner machines – These are large and extremely high capacity equipment for extracting, crushing, and loading material in one continuous process. These machines are primarily used in the mining and aggregates industry.

tangent pile wall - Tangent pile walls are formed by constructing reinforced concrete piles flush to each other. The piles are reinforced with either steel rebar or with steel beams and are constructed by either drilling under mud or augering. Tangent piles do not overlap unlike secant piles.

tremied concrete - An excavation is created and held open with a slurry (clay/water mix). A "tremie" pipe (open pipe) is lowered to the bottom of the excavation. Concrete is placed into the pipe and allowed to drop through the pipe to the bottom of the excavation. The concrete begins to form a pile at the bottom, displacing the slurry out of the excavation. The pipe (tremie pipe) is raised slowly allowing the excavation to be filled with concrete.

unconsolidated soils – loose and unstratified soils

wales – Horizontal members that are used to provide support across a wall section.

wheel loader - A loader, also called a front loader, front end loader or shovel, is a type of tractor, usually wheeled, that uses a wide square tilting bucket on the end of movable arms to lift and move material

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EXECUTIVE SUMMARY

Under Professional Support Services Basic Ordering Agreement (PSSBOA) 28297, Task Order Release 3, Fluor Hanford, Inc. tasked Garry Struthers Associates, Inc. (GSAI) to review excavation and mining techniques that are efficient, safe, cost-effective, and protective of human health and the environment, and are applicable to remediation of two generic liquid waste disposal sites; i.e., large crib and reverse well at the 200 Areas of the Hanford Site. These disposal sites allowed for contaminants to penetrate deeply below the ground surface. In some cases, the contamination has reached the groundwater level, nearly 300 feet below ground surface. There is potential for the necessity for removal of contaminated soil at depths well below ground level, possibly to groundwater.

Specific objectives assigned to this task include:

• Identify applicable excavation and mining techniques and methods available for deep excavation of contaminated soils at large crib sites and reverse well sites. Excavation includes removal of soil, temporary stockpiling for testing, and evaluation for ultimate disposal.

• Provide a description of excavation and mining techniques and equipment types that might be applicable to the two generic liquid waste disposal sites.

• Evaluate techniques for approximations of time required for removal of unit volumes of soil.

• Evaluate realistic maximum depth (or depth as a function of area) for excavations that are efficient, safe, cost-effective, and protective of human health for the removal of unit volumes of soil. Determination of appropriate depth would depend upon the relative significance of these factors.

• Identify measures to minimize amount of soil material removed and to be taken to ensure safety of excavation methods and protection of human health and the environment.

For the purposes of this study, it is assumed that the soil type in the generic disposal sites is a mixture of sand, gravel, and silt with either sand or gravel predominant, dependent on the depth and location. For a final remedial design involving deep excavation at these sites, soil borings will be required for design of specific earth retention systems to be used at these sites in conjunction with deep excavation. Tests for the structural properties of the soil will also need to be conducted to provide necessary basis for design of any proposed earth retention system.

GSAI focused on the following questions in reviewing deep excavation techniques for removal of contaminants at a large crib and reverse well disposal site:

• How can deep excavation in this type of soil be conducted in a safe, cost effective manner, and be protective of human health and the environment?

• What is the methodology of excavation that will minimize the amount of soil material to be removed? What is a realistic depth for excavation?

During the review, the following factors were considered to assist in answering the questions and to determine highly promising techniques that should be explored in greater engineering detail

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than the scope of this Study allows: 1) safety; 2) protection of human health and the environment; 3) minimization of soil material removed; 4) maximum realistic depth; 5) cost effectiveness.

Factors involved in designing a protective system include excavation method, soil classification, depth of cut, water content of soil, changes due to weather and climate, and other operations in the vicinity. Depending on the excavation technique, the geology surrounding the cribs and reverse wells may require some combination of sloping and benching systems, ground treatment, and support/shield systems. Since excavations will be greater than 20 feet, the design of sloping and benching systems, or design of support systems, shield systems, and other protective systems must be approved by a registered professional engineer. As a case in point, the Hanford Site geology may not be conducive to the sinking of vertical shafts without appropriate casing or other appropriate soil supporting measures.

In reviewing excavation techniques, the following study criteria were kept in mind to determine viable approaches for removal of the radioactive contaminated soil within the large crib and reverse well:

• To enhance personnel safety and avoid placing personnel and equipment in the excavation, this review focuses on techniques where removal of the contaminated soil material can be done externally. Specific supporting systems to keep the walls stable and movement of the soil around the excavation at a minimum are still required. A stable working platform around the excavation must also be addressed.

• To protect the public health and environment, this review focuses on techniques to excavate a smaller area within the larger footprint of the excavation at a time. Thus, at any one time, a smaller, more controllable excavation area is created, contaminated material removed and transported, and excavation backfilled before another excavation takes place.

• To maximize efficiency in order to minimize cost, this review focuses on techniques employed by specialty contractors to save clients both time and money on projects.

The study found the following excavation techniques applicable to large crib disposal sites: excavation using a structural diaphragm wall soil support system, excavation using large diameter access shafts, and sequential excavation depths using benching and vertical soil supports such as soldier piles with timber laggings or soil nailing with bracing supports. Details are presented in the report.

The study found that the following excavation techniques applicable to reverse well disposal site: use of vibratory hammer equipment or use of hydraulic casing oscillator to drop casing around the reverse well and use of auger rig or hammer grab equipment to extract the pipe and clean out the contaminated soil material. A reinforced circular diaphragm wall can also be used to isolate the reverse well and then hammer grabs can be employed to remove the pipe and contaminated soil material. Similarly, top down excavation with preliminary ground improvement and using sequential installation of corrugated metal casing to advance the excavation work is another technique for remediation of reverse well disposal site. Details are presented in the report.

In consideration of the factors of safety, protection of human health and the environment, minimization of soil material removed, maximum realistic depth, and cost effectiveness, GSAI’s primary conclusion from the study is that deep excavation techniques depends upon the geology and the specific soil retention system designed. Construction of excavation support systems that would allow for excavation activities to be conducted without having to place personnel and equipment in the hole offers the safest method for deep excavations at large crib and reverse well

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disposal sites at the 200 Areas of the Hanford Site. These systems need further evaluation during detailed analysis of remedial alternatives for these sites. The following conclusions are presented in the report:

• Deep excavations at the proposed depth of 250 to 280 ft require properly engineered, structurally sound vertical support systems

• Design of specific excavation support system must be done by a registered professional engineer

• Specific soil conditions at large crib and reverse well sites must be well known

• Structural diaphragm walls and large diameter access shafts offer the best method of excavation support system

• Use of vibratory hammer or oscillator/rotator machine for advancing casing is applicable to reverse well remediation

• Large, heavy equipment are required to install vertical support systems and conduct deep excavations

• Vast amount of materials such as cement/bentonite slurry mix, water, reinforcement bars (cages) are required for structural diaphragm walls

• Sequential depth excavation will generate soil material beyond targeted volumes

• Ground improvement techniques such as grouting can be used to improve stability of working platforms

• Specialty geotechnical contractors will be required to design and construct excavation support system

• Budgetary estimates are enormous

GSAI recommends the following:

• Obtain site specific geotechnical data on large crib and reverse well disposal sites • Perform a screening evaluation of deep excavation along with other remedial alternatives

being considered for the large crib and reverse well in accordance with RI/FS broad criteria of effectiveness, implementability and cost

• Use of structural diaphragm wall and large access shaft as a primary means of conducting the deep excavation without placement of personnel and equipment in the hole

• Use of specifically designed soil retention system to perform top down sequential excavation by placement of personnel and equipment in the hole

If the alternative of deep excavation is selected for detailed analysis, GSAI recommends the following:

• Installation of test shafts to determine feasibility of large access diameter shafts as a means of performing deep excavation

• Evaluation of disposal of radioactively contaminated slurry mixture • Evaluation of treatment of wet cuttings resulting from diaphragm wall excavation prior to

disposal at ERDF

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• Evaluation of left in place casing or walls as conduits for residual contaminant transport between surrounding soils and subsurface infrastructures.

If deep excavation is selected as a remedy for remediation of the large crib and reverse well disposal sites, GSAI recommends the following:

• Preparation of Scope of Work for Design and Construction of Appropriate Soil Retention System for Deep Excavation

• Preparation of Scope of Work for Deep Excavation Activities

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1. INTRODUCTION AND BACKGROUND

1.1 Task Goal and Objectives As a result of former waste disposal practices at the Hanford Site during production of plutonium from the mid-1940s to the late 1980s to support national defense, high volumes of contaminants were discharged to more than 800 waste sites on the Central Plateau (also known as the 200 Area), including cribs, reverse wells, ponds, trenches and burial grounds. Some of these contaminants present a risk to the underlying groundwater and the nearby Columbia River. Other contaminants present are not mobile enough to be considered groundwater concerns, but are present in sufficient quantities to present a potential hazard to human health and the environment. The 200 Area National Priorities List (NPL) Site includes a total of 24 operable units in the 200 East, 200 West and surrounding areas. A map of the Hanford Site and area designations is included in Appendix A

Under Professional Support Services Basic Ordering Agreement (PSSBOA) 28297, Task Order Release 3, Fluor Hanford, Inc. tasked Garry Struthers Associates, Inc. (GSAI) to review excavation and mining techniques applicable to remediation of two generic waste disposal sites; i.e., large crib and reverse well that are efficient, safe, cost-effective, and protective of human health and the environment. These disposal sites allowed for contaminants to penetrate deeply below the ground surface. In some cases, the contamination has reached the groundwater level, nearly 300 feet below ground surface. There is potential for the necessity for removal of contaminated soil at depths well below ground level, possibly to groundwater.

Specific objectives assigned to this task include:

• Identify applicable excavation and mining techniques and methods available for deep excavation of contaminated soils at large crib sites and reverse well sites. Excavation includes removal of soil, temporary stockpiling for testing, and evaluation for ultimate disposal.

• Provide a description of excavation and mining techniques and equipment types that might be applicable to the two generic liquid waste disposal sites.

• Evaluate techniques for approximations of time required for removal of unit volumes of soil.

• Evaluate realistic maximum depth (or depth as a function of area) for excavations that are efficient, safe, cost-effective, and protective of human health for the removal of unit volumes of soil. Determination of appropriate depth would depend upon the relative significance of these factors.

• Identify measures to minimize amount of soil material removed and to be taken to ensure safety of excavation methods and protection of human health and the environment.

1.2 Background Descriptions of a large crib and a reverse well are provided in this section. Information on the geology of the 200 Area, meteorological conditions, contaminant profiles, and applicable Federal, State, and Fluor Hanford Requirements are also presented in this section.

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1.2.1 Large Crib The as-constructed crib dimensions are 50 feet x 160 feet at crib bottom, with a side slope of 1.5 horizontal to 1.0 vertical, with the crib bottom 30 feet below ground surface. The groundwater is approximately 250 feet below the surface. The contaminated soil to be removed is the entire crib area at crib bottom, from: a) crib bottom to 20 feet below the crib bottom; or b) crib bottom to groundwater level.

Radionuclide contamination is expected to occur in zones of decreasing contamination from the surface to the groundwater. The primary radionuclide of concern would be expected to be Cesium 137. The near surface zone, assumed to comprise the area up to 30 feet below the crib bottom, will require (1) a single layer of personnel protection, (2) respirators, (3) dust abatement (probably performed using a water spray approximately 15% of the time), (4) dosimetry, and (5) bioassay. The next lower zone of contamination is assumed to comprise an additional 30 feet, or 60 feet below the crib bottom, and contain reduced levels of radionuclide contamination. However, these contamination levels are still sufficient to require a single layer of personnel protection and dust abatement, but would not require respiratory protection. The lowest zone, from 60 feet below the crib bottom to groundwater, is assumed to be low enough in radionuclide contamination to be performed in standard work clothing, but still require periodic radiation surveys.

Cribs were designed to receive low to moderate volume waste streams with generally higher levels of radionuclides resulting from direct contact with process chemistry. Some cribs also received very high volumes of liquid discharges (>100 million gallons). Cribs were also constructed to receive steam condensates at continuously operating separations plants where coil failures and significant releases were possible. Cribs included liquid dispersion structures were made of wood, concrete beams, cinder blocks, and/or steel plates. The cribs were filled with gravel, coarse gravel/cobble fill, crushed rock or combinations of these materials to increase the porosities. Cribs vary in sizes. Small cribs are 10 to 20 ft in diameter and 10 to 12 ft deep. The largest cribs have bottom dimensions of 1,400 ft to 1,500 ft long, 10 ft wide and 10 to 15 ft deep. Most cribs are smaller, with an average length of 200 to 500 ft, widths of 10 to 20 ft, and 15 to 35 ft deep. Cribs were normally buried beneath a 15 to 20-ft thick soil cover.

1.2.2 Reverse Well The reverse well consists of steel piping 0.5 feet in diameter and 75 feet in depth. Discharge occurred between 55 feet and 75 feet below ground surface. The contaminated soil to be removed is a soil column 10 feet in diameter located at a point 55 feet below ground surface to the groundwater level.

The entire contaminated zone from 55 feet below ground surface to groundwater is assumed contaminated sufficiently to require a single layer of personnel protection. No respirators are required. Dust abatement is required to the extent the removal technique elevates airborne soil particulate levels.

Reverse wells received smaller quantities of wastes from waste streams considered to be more contaminated than crib waste. These structures were used to place the waste deeper into the soil column.

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1.2.3 Geology The geology of the 200 Area vadose zone at the Hanford Site generally consists of sand and gravel (70 to 80%), silt (10 to 20%) and clay (<1 to 10%). The vadose zone beneath the 200 Areas ranges in thickness from approximately 180 ft beneath the former U Pond in the 200 West Area to approximately 341 ft in the southern portion of the 200 East Area to 160 ft along the western part of the 200 North Area. The vadose zone thins from the 200 Areas north to only 1 ft thick near West Lake. Sediments in the vadose zone consist primarily of the Hanford formation, Plio-Pleistocene unit/early Palouse soil, and Ringold Formation. Appendix B provides a description of each of these formations and their respective subdivisions.

1.2.4 Meteorology Meteorological conditions (precipitation, wind direction and speed, extreme temperatures) are major controlling factors during excavation activities at the Hanford Site. Summary information for the period 1945 through 2004 is abstracted from the Hanford Site Climatological Data (“Hanford Site Climatological Summary 2004 with Historical Data”, May 2005, Pacific Northwest National Laboratory). The annual average precipitation is 7.96 inches. The annual average wind speed is 7 mph out of the southwest. The annual temperature is 53.5 °F with an annual maximum temperature of 107 °F and an annual minimum temperature of 3 °F. The average monthly temperatures are: Jan 31.1 °F, Feb 37.7 °F, Mar 45.4 °F, Apr 52.9 °F, May 61.8 °F, Jun 69.4 °F, Jul 76.6 °F, Aug 75.1°F, Sep 66.2 °F, Oct 53.1°F, Nov 40.1°F, and Dec 32.4 °F.

1.2.5 Contaminant Profiles For purposes of this Study, the figure in Appendix C referred to as “Figure 2-11. “Contaminant Distribution Model of Contaminants of Potential Concern” (216-B-46 Crib) serves as the model for conceptual design, geologic cross-section and soil contamination profiles. A Generalized Physical Conceptual Model of Contaminant Distribution within the crib’s cross-sectional area is included in this document as Appendix D.

1.2.6 Applicable Federal, State, and Fluor Requirements At the Hanford Site, a common regulatory framework is established that integrates the RCRA, CERCLA, Federal Facility Regulations, and Hanford Federal Facility Agreement and Consent Order (Tri-Party Agreement) (Ecology et al. 1994) requirements into one standard approach for cleanup activities. Potential Federal applicable, relevant, and appropriate regulations (ARARs) and To Be Considered (TBC) regulations are stipulated in Table 4-1 of the document “200 Areas Remedial Investigation/Feasibility Study Implementation Plan – Environmental Restoration Program,” DOE/RL-98-28, Rev. 0, April 1999. Potential State ARARs and TBC regulations are listed in Table 4-2 of the same document. Implementation of any excavation technique must be protective of public health and the environment as warranted by these regulations.

Section 2.1 B of Fluor Hanford Special Provision for On site Services (SP-5, Rev. 6 12/29/2003), as well as Fluor Hanford’s Practice and Procedure documents, HNF-PRAC-30489 (October 27, 2006) and HNF-PRO-090 (May 11, 2006), pertaining to excavating, trenching, and shoring, and 29 Code of Federal Regulations, Part 1926, Subpart P, “Excavations” were reviewed to ensure requirements were addressed in the review of excavation depth techniques. Potential hazards associated with each excavation depth technique are identified and analyzed. Appropriate controls are incorporated into the overall evaluation of the excavation support system and removal process.

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The current study is clearly Remediation/Restoration-based and not Mineral/Beneficiation-based. However, since the study also evaluated surface mining techniques as a potential excavation method, Mine Safety and Health Act (MSHA) regulations were also reviewed. The applicable provisions of 30 CFR Parts 1-199 (Mineral Resources, Mine Safety and Health Administration, Department of Labor), 30 CFR 700-955 (Office of Surface Mining Reclamation and Enforcement, Department of the Interior), and Washington State Mining and Quarrying Safety and Health Act of 1999 were reviewed and are included by reference in this study.

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2. ASSUMPTIONS

For the purposes of this study, it is assumed that the soil type in the generic disposal sites is a mixture of sand, gravel, and silt with either sand or gravel predominant, dependent on the depth and location. There may be presence of cemented formations at the generic sites. For a selected remedy involving deep excavation at these sites, soil borings will be required for design of specific earth retention systems to be used at these sites in conjunction with deep excavation. Tests for the structural properties of the soil will also need to be conducted to provide necessary basis for design of any proposed earth retention system.

Contaminants are restricted within the confines of the given boundaries of the large crib and reverse well. Plume chasing was not within the scope of the study.

There are no structures and utilities nearby the generic disposal sites that would be affected by the deep excavation or impact excavation activities.

It is assumed that access and haul roads within the Hanford site have the capacity to bear the heavy loads expected from transport and movement of heavy equipment and materials to and from the sites to be remediated.

Single handling of removed soil is preferable. All soil removed may be routinely field-screened to determine the level of radioactive contamination. Levels are assumed to be readily manageable. Production might be affected by this requirement for periodic soil confirmation sampling and analysis. This study recognizes that requirement as a probability, but it is not included within the current scope of work.

Contaminated soil (dry condition) will be transported and disposed at the Environmental Restoration Disposal Facility (ERDF) located between the 200 East and 200 West areas on Hanford’s central plateau. Slightly contaminated soil might be used for shielding and mixing during remediation activities as recognized in the document titled, “Overview of DOE Nationwide and Hanford Site Management Programs and Initiatives”. Non-contaminated soil (<15 mrem/yr of radionuclide above background and/or <10-6 carcinogenic rate)(Ecology & EPA) would be stockpiled away from the excavation and ultimately used for backfill.

Additional acceptable backfill material is assumed to be available from within the Hanford Site. Some of this material may come from ERDF disposal cells being constructed to meet needed disposal capacity.

Modified level D with respiratory protection and dosimeters may be the required level of protection during excavation. Dust abatement will be conducted as needed. The level of personal protective equipment will be adjusted depending upon physical, chemical, and radiological hazards. Physical restraints will be necessary for anyone working on the surface near an open excavation. It is preferable that no one enters any deep excavation during the remediation process. To do so will trigger a number of necessary health, safety and engineering controls.

Excavation methods and techniques adhere to the applicable Federal, State, and Fluor Hanford Requirements described in Section 1.2.6 of this Report. It is assumed that all regulatory issues will be resolved through a final Record of Decision prior to implementation of a particular excavation technique or combination of techniques.

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Wind and water are driving forces for contaminant spread. Therefore, any excavation method that involves open expanses of soil surface area, or use of water within the soil column does require careful consideration and should be tested prior to committing to that specific procedure.

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3. EVALUATION FACTORS

GSAI focused on the following questions in reviewing deep excavation techniques for removal of contaminants at a large crib and reverse well disposal site:

• How can deep excavation in this type of soil be conducted in a safe, cost effective manner, and be protective of human health and the environment?

• What is the methodology of excavation that will minimize the amount of soil material to be removed? What is a realistic depth for excavation?

During the review, the following factors were considered to assist in answering the above questions and to determine highly promising techniques that should be explored in greater engineering detail than the scope of this study allows: Safety; Protection of Human Health and the Environment; Minimization of Soil Material Removed; Realistic Maximum Depth; and Cost Effectiveness.

3.1 Safety GSAI considered the establishment of a safe working environment as the primary evaluation factor. GSAI evaluated conducting the excavations without placing personnel and equipment within the hole. A sequence of operations creating structurally bounded excavation cells down to the required depth below ground surface was evaluated and is presented in this study.

Alternatively, GSAI also evaluated excavation techniques where it is necessary to place personnel and equipment within the excavation. Ground improvement and vertical soil support systems were reviewed and applicable systems for the soil type involved with the disposal sites are presented in this study.

For construction activities involving excavation, the work environment must be provided with an adequate protective system to protect employees from slides or cave-ins. This is required by OSHA and its applicable regulations are promulgated in 29 CFR 1926, “Safety and Health Regulations for Construction”, Subpart P, “Excavations”. Protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied or transmitted to the system. The requirements for protective systems include the design of sloping and benching systems, design of support systems, shield systems, and other protective systems, materials and equipment used for protective systems that are free from damage and defects, and proper installation and removal of members of support systems.

OSHA “fall protection” is mandatory where workers are exposed to potential fall hazards from heights of six feet or more. Insurance industry risk evaluators believe “four-foot maximum potential falls” may become the regulated standard. MSHA generally follows OSHA regulations. MSHA regulations concerning the requirement for safety harness use when working near an open excavation shaft should be followed during construction and remediation activities. [Ref.: Fall Protection Systems, Inc. offers low-cost fall protection systems. MSHA’s Approval and Certification Center can be reached at 304/547-0400].

Although remediation of the large crib and reverse well are not mining projects, awareness of MSHA regulations pertinent to the Pit and Quarry Aggregates Industry may be a prudent course of action e.g., 30 CFR Part 46 “Training of Miners Engaged in Shell Dredging at Sand and

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Gravel Surface Mines”, Sec 46.11 “Site Specific Hazard Awareness Training”, Safety and Health Standards Sec. 56.3130 “Wall, Bank and Slope Stability”, Sec. 56.3131 “Pit or Quarry Perimeter”. In places where persons work or travel in performing their assigned tasks, loose or unconsolidated material shall be sloped to the angle of repose or striped back for at least 10 feet from the top of the pit or quarry wall”, Sec.3(h)(1) of the Mine Act (30 U.S.C. 811,825) “The road appurtenant to an area of land from which minerals are extracted is a mine.” [Ref.: <www.msha.gov>].

A discussion of the Excavation Support System is presented in Section 4. Due to the radioactive nature of the contamination in the soil, excavations may be opened for a relatively longer period of time to accommodate testing requirements and personnel protection limitations. The engineering design of the excavation support system must also account for safe access, perimeter protection, egress, ventilation, lighting, and potential groundwater control when and where it is considered appropriate and necessary.

3.2 Protection of Human Health and the Environment Like any promising remedial alternative, deep excavation techniques would be analyzed against the nine CERCLA evaluation criteria with one of these criteria being overall protection of human health and the environment. Exposure of personnel working in and handling radioactively contaminated soil, as with any radiation source, can be minimized through shielding, distancing from radiation source, and time of exposure to radiation source. Although levels of radiation are manageable at these generic disposal sites, this study focuses on excavation techniques that would reflect the ALARA concept. ALARA stands for “As Low As Reasonably Achievable”. One of the primary aims of the ALARA concept is to reduce the dose incurred by an occupational worker. Another equally important ALARA goal is to minimize radiation/radioactivity releases to the environment.

According to the 200 Areas RI/FS (DOE/RL-98-28), “current fate and transport models do not adequately quantify the chemical and geochemical interactions influencing the distribution of contaminants in the soil column.” Therefore, when reviewing the various excavation methods and barrier techniques that must be incorporated into any remediation scenario cited in this study, the potential environmental impact that the “method water” might have on mobilizing the in-place waste constituents must be kept in mind. Any cleanup/remediation method should begin at the minimally-contaminated perimeter and work inward towards the zone of greatest contamination.

Excavation operations typically generate dust. Dust abatement measures must control wind dispersal and transport of radioactive contaminated soil particles. This study considered the potential for each excavation technique reviewed to generate dust.

GSAI also considered the time consuming processes of decontaminating personnel and equipment, and the likely excavation techniques that would minimize the efforts involved with this process.

3.3 Minimization of Soil Material Removed The minimal amounts of soil material to be removed were estimated for the large crib and reverse well excavations. The as-constructed crib dimensions are 50 feet x 160 feet at crib bottom (30 feet below ground surface) with a side slope of 1.5H to 1V. The calculated in place volume of contaminated material located in the upper 30-foot portion of this crib is more than 22,389 cubic yards. It is understood that Hanford Plant forces would be responsible for the removal of shallow material and the crib structure. The calculated in-place volume of material located at crib bottom

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to 20 feet below crib bottom is approximately 5,926 cubic yards. The calculated in-place volume of contaminated material located at crib bottom to 220 feet below crib bottom is approximately 65,185 cubic yards.

The reverse well consists of a 6-inch diameter carbon steel pipe sunk to a depth of 75 feet. The contaminated soil to be removed is a soil column 10 feet in diameter from 55 feet below ground surface to the groundwater level located at a depth of 280 feet. The total volume of soil displaced by the pipe (if it is intact) is minimal or about 0.5 cubic yard. The volume of overburden that must be removed to reach the affected soil (following the extraction of the pipe) is 160 cubic yards. The calculated in-place volume of contaminated soil located in a 10-foot diameter column at 55 to 280 feet below ground surface is 655 cubic yards.

3.4 Realistic Maximum Depth Geology, technical and financial resources will determine whether or not maximum depth is realistically achievable.

The Shaft Sinkers Group in South Africa claims to have mastered the art of rapid, safe sinking through every type of rock strata. Their experience includes concurrent vertical shaft sinking and lining, creating single lifts well over 8,000 feet, ”mucking” rates exceeding 200 tons per hour, and sinking rates of more than 656 feet per month. The deepest shaft is 11,748 feet. The widest is shaft is 62 feet in diameter. [Ref.: www.shaftsinkers.co.za/]

The unconsolidated, non-cemented, fluvial soils on the Hanford Plant site are not conducive to the sinking of vertical shafts whout appropriate casing or other appropriate soil supporting measures. An example of appropriate casing is derived from the Malcolm Drilling Company of Kent, Washington who claims capabilities of excavating large-diameter (to 10 feet) caissons to well over 200 feet deep. Casing can be pulled down as the cut is made through sands and gravels (alluvium). An example of other appropriate soil supporting measures is derived from South Korea, where a 5.6-ft thick x 246-ft deep cylindrical slurry wall greater than 262-ft inside diameter holds back soil and water without an anchor or internal bracing system. And, within the State of Washington, near Enumclaw, at Mud Mountain Dam is the world’s deepest slurry wall (about 400 ft). Soletanche Bachy with 60 years of experience constructed this barrier.

From a technical point-of-view, it is feasible to reach the depths required by this study.

3.5 Cost-Effectiveness This term is obviously a relative term. Overall cost-effectiveness in this case must be balanced in terms of (1) the time required for approval of the excavation method, (2) the number of sites to be remediated to determine capital cost sharing, (3) the life-cycle and maintenance of equipment used, (4) standby costs for weather-related incidents, sampling and analysis, equipment failure, and crew shortages, (5) direct and in-direct operating costs, (6) volume throughput and elapsed time, (7) mobilization/demobilization charges, (8) impacts to safety, human health and the environment, and (9) the costs of restoration and long-term monitoring (if required).

For purposes of this study, vendor sources were requested to provide budgetary estimates for excavation of affected soils and the placement of barriers.

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4. EXCAVATION SUPPORT SYSTEMS

Factors involved in designing a protective system are excavation method, soil classification, depth of cut, water content of soil, changes due to weather and climate, and other operations in the vicinity. Depending on the excavation technique, the geology surrounding the cribs and reverse wells may require some combination of sloping and benching systems, ground treatment, and support/shield systems. Since excavations will be greater than 20 feet in depth, the design of sloping and benching systems, or design of support systems, shield systems, and other protective systems must be approved by a registered professional engineer. As mentioned previously in Section 3.4, the Hanford Site geology is not conducive to the sinking of vertical shafts without appropriate casing or other appropriate soil supporting measures.

4.1 Sloping and Benching For the purposes of this study, the slope requirement is 1.5 Horizontal (H):1 Vertical (V) in accordance with Fluor Hanford excavation safety requirements.

Sloping and benching would be more applicable to the large crib disposal site. The method involves cutting back the excavation walls at such an angle to ensure there is little chance of collapse. The practicality of employing this method, however, is questionable due to depth of excavation involved and the large volume of soil material that would have to be cut back from the walls to reduce the “angle of repose” and chance of collapse. For a slope requirement of (1.5H:1V), involving a 250 ft deep excavation and a 160 ft x 50 ft floor area, approximately 2,539,352 total in-place cubic yards would have to be removed. For excavating the upper 30-foot section of the crib (22,389 in-place cubic yards), the sloping and benching method may be the logical method of choice by Hanford Plant forces. To continue excavating deeper, however, the slope and benching method is untenable. Unnecessary time and resources would be expended. Tremendous quantities of overburden will be created concomitant with the destruction of a vast amount of surface topography. The mixing of contaminated soils with clean soils is inevitable – complicated even more by the erosion and probable dispersion potential of the wind blowing across the huge open excavation. The volume produced by continuing to excavate deeper would result in approximately 2,516,963 cubic yards of in-place soil being removed. This volume is nearly 38 times greater than the volume of targeted affected soil. Constructability is a given, but keeping the contaminated soil segregated from the non-contaminated soil and out of the wind-blown air is not.

4.2 Shoring and Shielding Systems The installation of vertical soil supports is evaluated as an alternative to sloping and benching to minimize the amount of soil removed during excavation of the large crib. The viability of the installation of walls (slurry trench and structural diaphragm walls), piles (contiguous bored pile, secant or tangent pile, vertical soldier piles and horizontal lagging, also known as “Berlin Wall”, and steel sheet pile), and shafts were reviewed for applicability to possible deep excavation remedial option for large crib and reverse well disposal sites at the 200 Area of the Hanford site.

One of the study’s specific objectives is to identify measures to minimize the amount of soil removed and to ensure the safety of excavation methods, and protection of human health and the environment. To meet this objective, excavation support systems must be considered to minimize the excavation area and to keep the sides of the excavations stable. Additionally, the excavation

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support system must also ensure that movements will not cause damage to nearby structures or to utilities in the surrounding ground. It has been assumed that this is not a factor where the cribs and reverse wells are located.

Because of the wide area and potential great depth involved with the excavations of the disposal sites considered in this study, a registered professional engineer must design the appropriate shoring and shielding, or soil retention system. Having a registered professional engineer with specialized technical knowledge and experience with soil retention systems perform the design is evident from the research done by David J. Bentler for his doctoral dissertation on Finite Analysis of Deep Excavation. Dr. Bentler characterized performance of deep excavation support systems as related to both stability and deformation. He stated that “the task of predicting the performance of deep excavation is challenging, because many factors influence the performance of deep excavations. Soil conditions, groundwater conditions, and the stiffness of the support system are three factors that are always important, and experience shows that construction details and quality of workmanship can be equally as important in particular cases.” Dr. Bentler cited and summarized the important lessons learned from previous reviews of deep excavations and are listed as follows:

• Soil type is a key factor in deep excavation performance

• Prompt support installation is critical for minimizing movements

• Pre-stressing supports is effective for minimizing movements

• Deep excavation dewatering is often a significant source of settlement

• Construction sequencing is an important factor in the performance of deep excavation

• Workmanship is an important factor in the performance of deep excavation

• “Minor” construction details can be important factors in the performance of deep excavations

• Temperature changes need to be considered in braced excavations

• Support spacing is an important factor in the performance of deep excavations

• Large initial lateral soil stresses can adversely affect deep excavations

• Wall type can be an important factor in deep excavation performance

• Movements caused by auxiliary construction activities can be significant

For excavation of large crib disposal sites, the list of available methods reviewed for vertical soil support includes:

• Diaphragm walls that are constructed with reinforced concrete in situ

• Contiguous bored piling

• Secant or tangent piling

• Vertical soldiers and horizontal laggings

• Sheet piling

These methods are discussed in Sections 4.2.1 and 4.2.2.

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For excavation of reverse well disposal sites, the shaft construction method is the most viable technique. This method is discussed in Section 4.2.3.

Ground improvement techniques that are employed to stabilize the sides of an excavation and/or to strengthen the perimeter of the area surrounding the excavation are described in Section 4.3.

4.2.1 Walls Barrier walls can now be constructed by many different techniques, each offering particular advantages. Many of these techniques are making it possible to attain much greater depths. A geotechnical engineer will probably determine that some form of reinforced deep containment wall be constructed around the perimeter of the crib to prevent caving during the excavation of soils from the crib. Construction will be costly. The best geometric shape for a deep excavation wall is the cylinder. Vertical support of the cylindrical wall is achieved by constructing the wall to at least 10 feet below the floor of the proposed excavation. Horizontal support is achieved by virtue of hoop-compression stresses on the cylindrical wall. [Ref.: Cylindrical Diaphragm Wall Movement During Deep Excavation for In-ground LNG Storage Tank in Coastal Area, by Prof. Dong-Soo Kim, International Journal of Offshore and Polar Engineering Vol. 13, No.4, December 2003 (ISSN 1053-5381)]

4.2.1.1 Slurry Trench Wall Slurry wall construction is the excavation below grade through stabilizing slurry which supports the excavation walls and prevents caving and water intrusion and the replacement of slurry with purpose-designed backfill. Cut off (barrier) and diaphragm (structural) walls are two types of slurry walls. Slurry excavation support is provided by hydraulic pressure of the heavyweight slurry acting against the impermeable filter cake established on the trench walls. [Ref. Hayward Baker Geotechnical Construction]

An advantage of self-hardening slurries is that there is no separate backfilling operation. The slurry can be prepared in a remote area and pumped to the trench. This minimizes the number of workers in the exclusion zone. The panel method of construction is advantageous when working in unstable soils or near structures. The cost of self-hardening slurry walls ranges from $10-20 per vertical foot for a nominal two-feet-wide barrier and depths <100 feet (see Table 1, Section 5). [Ref.: New Technologies for Subsurface Barrier Wall Construction by Robert D Mutch, Jr., et al, National Academy of Sciences]

Slurry wall technology hinges on specialized equipment for excavating slurry trenches. The simplest type of trenching equipment is the mechanical clamshell attached on a Kelly bar. Individual contractors have developed their own specialized trenching equipment like hydraulic clamshells, hydrofraise or hydromills. Figure 1 shows the operational layout of a Hydrofraise made by Soletanche Bachy. The weight of the Hydrofraise ranges from 25 to 60 tons, while the crawler and power pack weigh a total of 70 to 160 tons. Equipment surcharge loads and other vertical pressures must be considered along with the lateral earth pressure during the design of the slurry wall.

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Figure 1. Operation Layout of a Hydrofraise (Courtesy of Soletanche Bachy)

4.2.1.2 Diaphragm (Structural) Walls The diaphragm wall technique is a tried-and-true construction method (see Table 1, Section 5). The term “diaphragm walls” refers to the final condition when the slurry is replaced by tremied concrete that acts as a structural system either for temporary excavation support or as part of the permanent structure. The continuous diaphragm wall is a structure formed and cast (in one continuous operation) in a slurry trench. The trench is initially supported by either bentonite or polymer-based slurries. The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse. As the excavation advances, more slurry is added to the trench until the excavation is complete. [Ref.: Deep Excavation LLC and Diaphragmwall.com]. Figure 2 illustrates the construction of a structural diaphragm wall.

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Figure 2. Installation of Diaphragm Wall (Courtesy of Land Transport Authority of Singapore)

Deep trench excavation is typically performed beneath a cover of trench-stabilizing slurry. Rather than forming a continuous wall, discrete diaphragm panels are formed. Since the wall is constructed in relatively small sections, there is considerably less danger of collapse in unconsolidated soils. As before, the slurry may be replaced by tremied concrete and a reinforcement structure may be lowered into the slurry-filled trench. Stop-end pipes are typically inserted vertically at each end of the primary panel and the mixture is allowed to setup. A second panel is constructed at a predetermined distance from the first panel and end stops are inserted vertically. The mixture is allowed to setup and the end stops of panels 1 and 2 are removed. Then a third panel is constructed between panels 1 and 2. The concrete mix from panel 3 flows into the end stop voids left behind in panels 1 and 2. Additional panels are constructed and tied into one another until the diaphragm wall is complete. The rate of concreting ranges from 80 to 120 cubic yards/hr.

Panels are usually 8 to 20 feet long and 2 to 5 feet wide. The excavation rate for smaller 2-foot wide trench is 10-13 cy/hr. The excavation rate by heavier equipment in a non-rock environment is 20 cy/hr. Budget price for a concrete slurry wall would be between $80/sf to $150/sf. [Ref.: Correspondence from Exec. V.P. Laurent Lefebvre of Soletanche Bachy].

The slurry that is displaced by the concrete is saved and reused for subsequent panel excavations. Alternatively, there are many varieties of self-hardening slurries that can be tailored to specific site conditions and design objectives. The site condition of greatest importance is the porous soil and the impact that “method water” might have on the potential migration of contaminants-of-concern (COCs). The cost of self-hardening slurry walls is typically in the range of $135-278/cy (see Table 1, Section 5). [Ref.: Skanska.com; Diaphragmwall.com; Deep Excavation LLC; and New Technologies for Subsurface Barrier Wall Construction, Robert D. Mutch, Jr., et al, National Academy of Sciences, 2007]

Various types of excavation equipment can be used to reach great depths depending on project conditions, including hydraulic excavators and Kelly-mounted or cable-hung clam buckets. Depths in excess of 450 feet are possible. The Hydrofraise, a highly specialized excavation tool, can reach depths of 500 feet.

Excavation accuracy may be enhanced by state-of-practice machine control that combines a global positioning system (GPS) with 3D site plans. A programmed excavation plan using Management Software such as Forefront Construction Suite, or Heavy Job could result in (1) a

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o • INSTALLATION OF RETAINING WALL • • - DIAPHRAGM WALL

•.-----------" ---

----... --... ~---.......... _ -t-"'----~ ... -.. _.. ... _.,,_.., _ _,_,,_., __ -------. ... ~----. 04 :::-:-::-:::=== .. ____ ., .... _,..,. __ .. " _ ____ .., ... .....,. ...... __ ................ ___ ..._ ______ , __ ,...,_,, .. ,_,,.., ___ _ _ ..,.,.. ___ ..,_...,,.._

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linear perimeter wall, (2) a circular perimeter wall, or (3) a monolithic structure resulting from a series of engineered panels accurately placed to fill the entire void of the excavated crib or reverse well – where all job information is aggregated; where everyone can look at daily results and what adjustments may need to be implemented. Project Management Software can manage all documents (including changes and digital photos) relating to a project and have them in one place. Machine Control Systems can cost $100K or more – Management Software Systems can range in price from $4K to 20K (see Table 1, Section 5).

During excavation, the cuttings are mixed with the slurry material. The cuttings must be brought to the surface and separated from the slurry by filtration. The slurry is then returned to the trench. As it applies to the generic disposal sites, the slurry would get contaminated due to mixing with radioactive contaminated soil.

The cuttings will have to be dried prior to disposal at ERDF. Similarly, transport and disposal of the slurry mixture will need to be addressed. When possible and practical, excavated soil should be deposited directly into trucks for immediate removal from the working area in order to maintain a clean site and minimize the risk of excessive loading adjacent to the wall of the excavation that might precipitate a collapse in the excavation. [Ref.: Diaphragmwall.com and Skanska.com].

For installation of a structural diaphragm wall around the generic large crib with a perimeter 420 ft long; 5 ft wide trench; and 250 ft deep:, approximately 19,450 cubic yards would be excavated, At the higher excavation rate of 20 cubic yards per hour, this would take 972 hours or 24 weeks assuming a 40 hour work week. At an average rate of 100 cubic yards per hour of concrete, another 194 hours or 5 weeks would be added. Budgetary price for a concrete slurry wall would range from $8,400,000 to $15,750,000. The native material within the limits of the diaphragm wall would also need to be excavated. Techniques for excavation of the contaminated soil material are presented in Section 6.

4.2.2 Piles The following types of piles are more likely to be used in a sequential process whereby a bigger area encompassing the footprint of the large crib disposal site would be bounded by these systems installed to a shallower depth, excavation performed, and then another area bounded and excavated until the required depth and footprint of the large crib has been achieved and removed. These support systems would form something like a telescopic boundary to the desired depth excavating layers of both contaminated and uncontaminated soil as the excavation progress top to bottom. Unlike the diaphragm walls, these vertical support systems are constructed at shallower depths ranging from 75ft to 150 ft.

4.2.2.1 Secant and Tangent Piles Secant walls are a form of top down construction used for environmental remediation and soil retention. Figure 3 illustrates how a secant (tangent pile) is constructed.

Secant pile walls are constructed of intersecting concrete piles measuring 1.6 to 3 feet in diameter and 95 feet in depth as a maximum. Primary piles constructed of a weak concrete mix are installed first. Secondary piles constructed of a strong concrete mix are installed between and overlapping the primary piles. In a tangent pile wall, there is no pile overlap as the piles are constructed flush to each other. The average production rate of 490 – 820 feet of secant concrete piles per day makes it one of the most economical solutions for retaining walls. This option is

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suitable where the retained soil is usually firm to stiff (not generally granular). [Ref.: Deep Excavation LLC and Forasol SA]

Figure 3. Illustration of Construction of Secant Pile Wall (Courtesy of Land Transportation Authority of Singapore)

Budgetary unit cost ranges from $65 to $75 per square foot for secant piles [Ref. Remedial Construction Services, L], and $60-$100 per square foot for tangent piles [Ref. City of Seattle].

4.2.2.2 Soldier Pile and Lagging Walls This method is also commonly known as the “Berlin Wall” when steel piles and timber lagging is used. Figure 4 shows a photo of completed soldier pile with timber lagging, corner bracing, and pile tiebacks.

Soldier piles are typically constructed at vertical intervals of 6 – 12 feet. Alternatively, reinforced concrete panels rather than timber lagging can be utilized for more permanent conditions. The lagging bridges and retains soil across piles and transfers the lateral load to the soldier pile system that is embedded beneath the excavation grade. Excavating is conducted in small stages followed by the installation of lagging and backfilling/compacting the void space behind the lagging. When compared to other retaining walls, they are very easy and fast to construct, and the least expensive system to construct. The end result is a structure that is not as stiff as other retaining systems. Fluvial material is subject to caving into the shaft and settling at the surface during installation of lagging placed by workers within the excavation. [Ref.: Deep Excavation LLC]

Budgetary cost estimate for a soldier pile and tieback-timber lagging is $55-$140 per square foot [City of Seattle].

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~--... __ ,,,__,. ____ ..,. _..,._~---P'I---• _ _. _______ .. __ ------------------ .. ----------------··-----.. _,..,._""' __ -------·-----·---··---·------·------·--·--·-------------

---------·-·----------·-_ ________ ..,_

-------·---

... -<I-


Figure 4. Photo of Soldier Pile with Wood Laggings (Courtesy of University of California, Davis)

4.2.2.3 Contiguous Bored Piles Contiguous bored pile walls are constructed to the required depth using hollow stem continuous flight auger or rotary drilling rigs. Figure 5 shows an illustration of how a contiguous bored pile is constructed.

Figure 5. Illustration of Construction of Contiguous Bored Pile Wall (Courtesy of Land Transport Authority of Singapore)

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__ , .. ____ ....,. ____ _ -•-"1 ___ .., __ .. -----·----------------___ .. ________ _ ---------··-----· .. --.. -----------·-----_ .. __ ,. ____ ., __ ----·-------·--_,. __ ,. ________ _.

-------

--------·-·-----------•---------... -_ .. ______ , __ _ -~-


Small gaps exist between adjacent piles. The size of the spacing is determined by the nature of the soils. After the drilling equipment reaches the designed depth, a high slump concrete is then pumped through the hollow stem. While the concrete is being pumped, the auger is withdrawn at a controlled rate, removing the soil, and forming a shaft of fluid concrete extending to ground level. A reinforcing cage is then inserted into the fluid concrete. Reinforcing cages with lengths up to 12 meters are common; greater lengths can be installed with the assistance of cage vibrators. Pile diameters range from 300mm to 1200mm, and depths to 30 meters or more are possible giving load capacities up to 7500 kN. {Ref. Cementation Foundations, Skanska}

The principal disadvantages of contiguous pile walls are the limitations of depth, gaps between piles, and the risk of groundwater ingress between piles. These disadvantages are overcome by the secant and tangent piles.

4.2.2.4 Sheet Piles

Sheet piling is a form of driven piling using thin interlocking sheets of steel to obtain a continuous row of interlocking vertical segments that form essentially a straight wall that is capable of acting integrally. Figure 6 shows an illustration of installation of sheet pile wall.

Figure 6. Illustration of Installation of Sheet Pile Wall (Courtesy of Land Transport Authority of Singapore)

Hot-rolled, heavy-gauge steel sheet piling has advantages over other available products

including concrete, vinyl, and fiberglass-reinforced polymers for deep-excavation

applications. There are two primary types of steel sheet pile wall structures: cantilevered and anchored. Walers are commonly used in conjunction with tiebacks to construct anchored sheet pile walls. Tiebacks are typically installed as either ground anchors or

anchor rods secured to deadmen. The design of sheet pile walls involves the evaluation of loads imposed by soil, water, surcharging, and other externally applied forces. The analysis of a sheet pile wall includes a determination of the required depth of embedment, sizing of any anchorage systems, and verification that the actual flexural stresses do not exceed the allowable. Safety factors are typically included in the determination of the minimum embedment depth. [Ref. D. Matthew Stuart, “Project-Specific Steel Sheet Piling Applications”]

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::=---== =..:,.:::-:..:= . _. .. .., __ _ --"""...u

.. -= .......

---·-· - .. _ ... _,._ 1-

.. _,. _____ --_ ___ ., ___ _ ---

--.... , ___ , ... __ ...,_ .. _ _,_lllf, ____ .,. __

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--~•-·--· ... --------------.,..._

------------_ __ "" ______ _ -----·------------•----.-----

". ...


Budgetary cost estimates for sheet piling can range from $11-$13 per square foot if the piles are removed and salvaged; $16-$24 per square foot if the sheet piles are permanent [Ref City of Seattle].

4.2.2.5 Soil Mix Walls Soil mixing has been used for many temporary and permanent deep excavation projects including the Central Artery project in Boston. Mechanical soil mixing is performed using single or multiple shafts of augers and mixing paddles. Figure 7 shows an illustration of the Deep Soil Mixing Process. The auger is slowly rotated into the ground while cement slurry is pumped through the hollow stem of the shaft(s). Spoils consisting of cement slurry and soil particles are continuously ejected from the boring cavity as the injected slurry displaces soil cuttings. A circular retaining structure using deep soil mixing is more economical when compared with other shoring systems. A recently constructed circular retaining structure was formed by nine rows of 1.8-foot diameter deep soil-mixed columns (mini-piles). The diameter of the circular excavation is >138 feet and the depth is >33 feet. Due to its low tensile strength, this system usually requires a very thick wall cross-section and is generally impractical for use as a retaining structure for very deep excavations. [Ref.: Case History of Deep Mixing Soil Stabilization for Boston Central Artery by T.D. O’Rourke and A.J. McGinn, Civil Engineering Database, and Application of Circular Retaining Structure in Shoring Deep Soft Clay Excavation by A.G. Li, et al, Civil Engineering Database, and Deep Excavation LLC]

Figure 7. Illustration of Deep Soil Mixing Process (Courtesy of Hayward Baker, Inc.)

A new cement soil mixing (CSM) method can largely replace the more conventional single or multiple auger methods of soil mixing or jet grouting. The cutter tool is similar to a cutter used in diaphragm walls or cut-off walls and is operated with a Kelly mounted on a drill rig. With this system much deeper walls can be installed and even hard soil layers can be penetrated. The fraise or hydromill excavation system is described in the section above titled Diaphragm Walls. Deep soil mixing (to 100 feet) falls within the range of $6-12 per vertical square foot. [New Technologies for Subsurface Barrier Wall Construction, Robert D. Mutch, Jr., et al, National Academy of Sciences, 2007]

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Deep Soil Mixing


4.2.3 Shafts Using casing or slurry in drilled shafts (see Figures 8 and 9) is another method of providing vertical support systems to perform deep excavations. To use this method in pattern drilling for the large crib disposal site or the reverse well disposal site, a geotechnical engineer will probably determine casing or slurry will be required to prevent caving of site soils during the excavation process. The casing will be costly. Installation of casing segments will slow the excavation process – and removal of casing segments from a shaft of this depth during the backfilling process will be challenging, if not impractical (see Table 1, Section 5). Oscillators (see Figure 11 for photo of Leffer hydraulic casing oscillator) or vibratory hammers are used together with casing to construct the shaft. Clean out of the shaft can be done with hammer grabs or mechanical augers/buckets. At the generic large crib and reverse well disposal sites, the “positioning of the rebar cage” and “placement of concrete” shown in Figures 8 and 9 are eliminated, by backfilling the shafts with clean material available at the Hanford site.

Open shafts have traditionally been excavated by mechanical grabs suspended from cranes as shown in Figure 10, but this method would apply to excavation in geological settings with competent (stable and cohesive) soils.

Bentonite slurry may again be used as a method of soil support. In the reverse circulation process, slurry is used for both soil retention and as a means of transporting the excavated soil cuttings. [Ref.: “Deep Excavations; A Practical Manual” by Malcolm Puller]. Disposal of contaminated slurry and “drying out” moisture laden cuttings to be disposed at ERDF will need to be taken into account in the use of this method.

Figure 8. Illustration of Drilled Shaft Construction Using Casing (Courtesy of Federal Highway Administration)

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P -ce


Figure 9. Illustration of Drilled Shaft Using Slurry to Stablilize Caving Soils (Courtesy of Federal Highway Administation)

Figure 10. Illustration of Augered Shaft in Competent Soil (Courtesy of Federal Highway Administration)

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Figure 11. Photo of Leffer Oscillator Driving Casing into the Ground (Courtesy of Leffer GmbH)

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4.3 Ground Improvement Ground improvement techniques were evaluated for potential application to the crib excavation. These techniques included grouting, soil nailing, reinforced soil slopes, and other techniques that could be applied to prevent slides or cave-ins during excavation of a large crib.

4.3.1 Jet Grouting Jet grouting is a top-down soil treatment used to create in situ, cemented soil formations (see Figure 12). The method uses pressurized fluids to segregate and remove some of the soil particles. These are then replaced with a soil/cement mixture that can provide high strength and low permeability.

Figure 12. Illustration of Jet Grouting (Courtesy of Hayward Baker, Inc.)

Jet grouting involves rotating high-pressure fluid jets, activated while withdrawing grouting rods from predrilled borings, to form cylindrical columns. Jet grouted walls can be constructed by overlapping these cylindrical columns. High pressure jet grouting is used to construct thin-diaphragm walls. The practical depth limit is 150 feet. Coarse-grained material can be the cause of defects in a thin wall. The cost of a nominal three-foot-wide barrier wall constructed by jet grouting is in the ranges of $15-30 per vertical square foot. [New Technologies for Subsurface Barrier Wall Construction, Robert D. Mutch, Jr., et al, National Academy of Sciences, 2007]

4.3.2 Permeation Grouting Permeation grouting is the injection of cement or chemical grouts into predominantly granular soils from the original ground surface. Grouts may include resins, silicates/emulsions, bentonite cement, and cement although most work is done with cement-based grout. The grout is injected

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Jet Grouting

l


into the soil through pipes that have been strategically placed to define the zone of soil to be treated. [Moore & Taber Soil Grouting and Ground Improvement Specialists]

4.3.3 Chemical Grouting According to Moore & Taber (Soil grouting and Ground Improvement Specialists), chemical grouting is a ground treatment method for soils with a relatively low-viscosity grout. The chemical grout materials are used to improve the strength of granular soils. There are many types of chemical grouts, each having different strength, cost, viscosity, toxicity and durability. The most common type of grout is based on gellation of sodium silicate by one of a wide variety of hardeners. Polyurethane and acrylate grouts make up most of the rest of the materials in common use.

4.3.4 Ground Freezing Freezing (refrigeration) is used to achieve temporary ground stability or control of groundwater in soft soils or excavations below the groundwater table, or to achieve stability in permafrost regions where thawing must be prevented. Ground freezing methods are temporarily utilized to aid in the construction of permanent wall systems. [Ref.: RKK-SoilFreeze Technologies,LLC]

The DOE has undertaken a pilot scale study of ground freezing at its Oak Ridge, Tennessee site (Peters, 1994). The test site is approximately 60’ x 60’ x 28’ deep. It consists of a double ring of inclined and vertical freeze pipes to form a V-shaped bathtub ring within which is a 750-gallon steel tank. [Demonstration of Ground Freezing for Radioactive/Hazardous Waste Disposal (pp. 103-111) in Proceedings of the 33rd Hanford Symposium on Health and Remediation: Scientific Basis for Current and Future Technologies, Pasco, Washington, Tallard, G.R. 1992].

4.3.5 Soil Nailing Caltrans has extensively used soil nailing technology for excavation support and reinforcement of steep slopes and vertical walls for over a decade. Soil nailing is a “top-down construction process that consists of a soil slope excavated to a vertical, or near-vertical orientation internally supported by closely spaced steel reinforcing bars fully grouted in place. Caltrans has found that the use of conventional soil nail systems for slope stabilization and excavation support poses difficulties when ground conditions are subject to caving. This situation happens for granular soils such as silty sand (sugar sand) or cobbles and boulders. [U.S. Department of Transportation Federal Highway Administration, “Current Research Program” Top Down Construction Techniques (Caltrans – Evaluation of Hollow Bar Soil Nail Systems for Excavation Reinforcement)]. Figure 13 shows an illustration of the soil nailing process.

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Figure 13. Soil Nailing Process (Courtesy of Hayward Baker)

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5. RESULTS OF VENDOR SURVEYS

Table 1 provides information on Excavation Techniques, Description, Estimated Production Rates, Equipment Needed, Equipment Availability, Equipment Operators, Equipment Contamination Considerations, Additional Resources, Environmental Considerations, Safety Considerations, and Costs. Information was derived from contacting a number of specialty geotechnical contractors and other auxiliary service contractors listed in Table 2.

Table 1. Summary Information Derived from Contacts Listed in Table 2.

EXCAVATION/MINING TECHNIQUES

DESCRIPTION PRODUCTION RATE EQUIPMENT NEEDED AND AVAILABILITY

EQUIPMENT OPERATORS EQUIPMENT CONTAMINATION

ADDITIONAL RESOURCES ENVIRONMENTAL CONSIDERATIONS

SAFETY CONSIDERATIONS COSTS

The diaphragm wall technique is a tried-and-true construction method. Reinforced concrete circular diaphragm walls can be considered self-stable. Excavation accuracy is accomplished by combining GPS data with 3D Site Plans to control the excavator. The clamshell bucket is equipped with automatic read-out for verticality in two directions (longitudinal and transverse) and rotation. The hydromill is equipped with automatic read-out for verticality in two directions (longitudinal and transverse). Koden is part of a rigorous quality control plan implemented in order to verify panel verticality and alignment. _______________________ Open excavation with wall shoring, soil nails, bracing, reinforcing mat & concrete.

Deep trench excavation is typically performed by the use of clamshell buckets or hydromills operating beneath a cover of trench-stabilizing slurry. When solidified, the slurry forms a near perfect vertical panel. A programmed excavation plan could result in (1) a linear perimeter wall, (2) a circular perimeter wall, or (3) a monolithic structure resulting from a series of engineered panels (barrettes) accurately placed to fill the entire void of the excavated crib or reverse well. _______________________ A top-down construction method of shoring & internal bracing in 5-foot lifts.

Excavation per hour 8–10 cubic meters (10-13 cubic yards) Larger excavator to 15 cubic meters/hr (20 cubic yards/hr). Slurry production is to be commensurate with the rate of excavation. Rate of Concreting: 80-120 cubic yards per hour _______________________ Estimated to be over several months.

Technology hinges on specialized equipment for excavating in this type of sand/gravel mix. The excavation proceeds via a machine-controlled, hydraulically operated purpose-built grab supported by an appropriately sized hydraulic base crane. The trench is supported during excavation by a slurry mix that is produced on site in a batch plant. The batch plant will aid in the post-excavation solidification of the slurry. Equipment is available from Anderson, Bencor, Malcolm Drilling, or SOLETANCHE BACHY Co. _______________________ Standard backhoes and spoils buckets, concrete mixers and gunite machines. Available.

Anderson Drilling a Keller Co 10303 Channel Road Lakeside, CA 92040 Dennis Poland, Dir. B.D. 619-443-3891 [email protected] SOLETANCHE BACHY Co. Laurent Lefebvre, Exec. V.P. 305-715-2080 [email protected] Case Foundation Co. 1325 W. Lake Street Roselle, IL 60172 Nicolas Willig-Friedrich, Mgr 630-924-3151 [email protected] Malcolm Drilling Co. 8701 S. 102 Street Kent, WA 98031 Mike Pollock 253-395-3300 [email protected]

Should this technique prove its usefulness to the tasks at hand, this equipment may very well serve out its useful lifecycle on site. Surficial decontamination may then be all that is required prior to moving it to another location on the reservation. _______________________ Same as above

Client provided site services such as health and safety, sampling, radiation monitoring, site security, surveying, transportation and disposal of low-level waste spoils, transportation and reuse of slightly contaminated soils for shielding and mixing during remediation activities and clean backfill if required. _______________________ Same as above.

Excavation is under the cover of a slurry that reduces cave-ins (minimizes the over-all amount of spoils requiring transportation and disposal), minimizes releases of fugitive dusts, and potential exposures to source contaminants. It minimizes impacts from weather, minimizes waste handling steps, maximizes the potential for classifying and separating spoils, and minimizes the quantity of waste designated to ERDF. _______________________ Minimizes the amount of “method water” used and spoils generated. Dust.

A stable base/platform is required for 70-160 ton crane & 25-60 ton grab. Ground conditions are subject to caving. Structural stiffness of cured panels will reduce soil movements and adjacent settlements during soil extraction. The excavation foot-print is kept relatively small. Unobstructed working space on site is maximized. The number of people onsite is minimized. Excavated soil should be deposited directly into trucks for immediate removal from the work area to maintain a clean site and to minimize the risk of excessive loading adjacent to the wall of the excavation. No workers in the excavation. _______________________ Deep open pit excavation with men and equipment inside for long periods of time. Dust.

Crane Mobilization $100K Operating Expense (slurry) Decontamination (Hanford) Slurry Plant $25-50/sf <100’ $80-150/sf>100’ Vol. Extraction Cost (incl.) LLW Disposal $100/cy ERDF Machine Control $100K (+) Management Software $4- 20K Demobilization $65K _______________________ Open excavation with shoring & internal bracing $11.2MM Mobilization $225K Engineering $80K

Use of Large Access Shaft; i.e., Large-diameter to 18’ caissons to 300’ deep. Casing can be pulled down as the cut is made through sands and gravels (alluvium)

A direct boring of a 10-ft diameter shaft to a depth of 280 feet utilizing a hydraulic casing oscillator & hydraulic clam shell. _______________________ A staged telescopic shaft diameter and surrounding ground improvement for deep ground stability, and limit lateral migration of contam-inants during large shaft excavation.

Excavation rates of 57-77 cubic meters (75-100 cubic yards)/hr are reported for large caisson rigs and 10-13 cubic yards/hr for hydraulic clam shells.

Leffer VRM 3050 (10’) hydraulic casing oscillator capable of drilling well over 200’ deep and pulls the casing down as it cuts. A hydraulic clam shell removes spoils. _______________________ Equipment is available from Anderson Drilling Co., Case Foundation Co., and Malcolm Drilling Co.

Same as described above. Should this technique prove its usefulness to the tasks at hand, this equipment may very well serve out its useful lifecycle on site. Surficial decontamination may then be all that is required prior to moving it to another location on the reservation.

Client provided site services such as health and safety, sampling, radiation monitoring, site security, surveying, transportation and disposal of low-level waste spoils, transportation and reuse of slightly contaminated soils for shielding and mixing during remediation activities and clean backfill if required.

Auger excavation is open and subject to release of fugitive dusts. The spoils are scattered in the process of auger-flight clearing resulting in handling spoils twice. Excavation with a grab-hammer or a caisson bit may take place under cover of slurry.

A stable base/platform is required for a track-mounted crane. The risk of creating such a large open excavation in this type of soil may be unacceptable. By fully casing the hole, it causes less over-break, creates a cleaner pile and a safer work environment. The oscillator significantly reduces worker accidental access into the excavation.

Equip. Mobilization <$100K Operating Expense (Included) Decontamination (Hanford) Vol. Extraction Cost $300- 330/cy LLW Disposal $100/cy ERDF Backfill/Compaction (TBD) _______________________ Test Shaft $150K Excavate/backfill $2.3MM Mobilization $250K

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The following specialty (geotechnical) contractors and equipment manufacturers and suppliers were contacted for this study:

Table 2. List of Specialty Geotechnical Contractors

Company Specialty Location Person Contacted

Telephone Number

E-Mail

TAKRAF GmbH

Manufactures and supplies large volume

and bulk materials handling

equipment and systems for

mining applications

throughout the world

Denver, CO Frank Papp 303-770-8161/Fax:

303-770-6307

[email protected]

Rowand Machineries

Dealership and rental

outlet for John Deere and

Hitachi heavy duty

machinery

Pasco, WA Ray Shepherd

509-547-8813 [email protected]

Anderson Drilling

Specializes in drilled shaft foundations,

earth retention solutions,

large diameter access shafts,

and contaminated soil removals

San Diego, CA

Dennis Poland


Remedial Construction Services, LP

Specializes in slurry wall

construction, diaphragm

wall construction, soil mixing or modification,

and jet grouting

Houston, TX. Joseph S. Lewis, Jr.


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DBM Contractors,

Inc.

Specialty geotechnical

contractor offering

design/build solutions for

earth retention,

drilled foundation

support, slope stabilization,

ground improvement and seismic

retrofit/rehabilitation

Federal Way, WA

Robert A. Carnevale


Case Foundation Company

Specializes in the following

foundation techniques:

drilled shafts (caissons), structural diaphragm

walls, piling systems, and

retention systems

Roselle, Illinois

Nicolas Willig-

Friedrich

630-924-3151/Fax:

630-529-2995

nawillig@casefoundation. com

Malcolm Drilling Co.,

Inc.

Specializes in the design and construction

of foundation, underpinning,

and earth retaining systems.

MDCI has one of the largest

and most up to date

equipment inventories in

the world.

Kent, WA Michael Pollock

253-395-3300/Fax:

253-395-3312

[email protected]

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Superior Industries

Conveyor Systems

Morris, MN Kirby Cline 800-321-1558/Fax:

320-589-3892

[email protected]

Valley Equipment Company

Conveyor System

Salem, OR Roger Jensen 503-364-4491/Fax:

503-581-1082

[email protected]

J.R. Hayes & Sons, Inc.

Conveyor Systems;

Geotechnical Construction

Maple Valley, WA

Greg Burton 425-392-5722/Fax:

425-392-9902

[email protected]

Champion Equipment Sales, LLC

Leffer Oscillator and Grab Hammer

Sales Representative

Salt Lake City, UT

Steve Wilson 801-288-8919 [email protected]

Nicholson Construction

Deep Excavations

and Diaphragm

Walls

Equipment Manufacture

Salt Lake City, UT

Los Angeles, CA

Mascot, TN

Paul Krumm

Laurent Lefebvre

Paddy Cochrane

801-322-3111

305-715-2080

865-933-8962

[email protected]

[email protected]

[email protected]

Subsurface Constructors

Deep Excavations

St. Louis, MO

Jeff Morgan 314-421-2460 [email protected]

Lampson International

Heavy Crane Manufacture

Kennewick, WA

Bill Lampson 509-586-0411 [email protected]

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6. EXCAVATION TECHNIQUES APPLICABLE TO LARGE CRIB

For the large crib, a 50 ft x 160 ft area that is 30 feet below the ground surface is the starting point of deep excavation. Hanford plant forces will remove the material and the crib structure itself from ground surface to 30 feet below ground surface where the crib bottom is located. The contaminated soil to be removed is the entire crib area (50 ft x 160 ft) from crib bottom to 20 feet below the crib bottom (50 feet below ground surface) or crib bottom to groundwater level (30 ft to 250 ft below ground surface).

In reviewing excavation techniques, the following study criteria were kept in mind to determine viable approaches for removal of the radioactive contaminated soil within the large crib and reverse well:

• To enhance personnel safety and avoid placing personnel and equipment in the excavation, this review focuses on techniques where removal of the contaminated soil material can be done externally. Specific methods to keep the walls stable and movement of the soil around the excavation at a minimum are still required. A stable working platform around the excavation must also be addressed.

• To protect the public health and environment, this review focuses on techniques to excavate a smaller area within the larger footprint of the excavation at a time. Thus, at any one time a smaller, more controllable excavation area is created, contaminated material removed and transported, and excavation backfilled before another excavation takes place.

• To maximize efficiency in order to minimize cost, this review focuses on techniques employed by specialty contractors to save clients both time and money on projects.

6.1 Surface Mining Surface mining is one technique that was reviewed for the large crib excavation. The use of commercially available heavy equipment or custom designed and manufactured specialty equipment was evaluated.

Commercially available heavy equipment such as a dragline excavator, dozer, large shovel, heavy duty excavator, and large haul trucks can be used to maximize production and transport of the excavated soi from the crib site. This method is appropriate for excavation work from the surface to a maximum depth of 20 feet bgs with the sides of the excavation being sloped back when the excavation is at 5 ft bgs and continuing as the excavation progresses from 5 ft bgs to 20 ft bgs. A minimum production rate of 1,000 cubic yards/day should easily be expected with minimal pieces of equipment such as two heavy duty excavators and a wheel loader deployed. Current monthly rental rates for the following equipment as provided by Rowand Machineries, Richland, WA are:

• John Deere 850D heavy duty (40-80 metric ton) excavator with a 8-9 yd bucket - $18,500 • Hitachi 1200-5D with a 13 yd bucket - $29,500 • John Deere 844J 7-yd wheel loader - $12,500 • 40 Ton Rock Trucks - $14,500

More aggressive techniques could be employed such as the use of the surface miners and bucket chain excavators. According to TAKRAF GmBH (Torgauer Strasse 336, D-04347 Leipzig,

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Germany), the company manufactures crawler-mounted bucket chain excavators that range in capacity up to 10,000 cubic meters/hr (13,079 cubic yards/hr), with a digging depth up to 40 meters (approximately 130 ft). TAKRAF also designs and manufactures surface miners that cover a total capacity range from 120 to 4,000 metric tones per hour (approximately 132 to 4,408 tons/hour) run-of-mine product. Applying this rate for the removal of the sand/gravel material within the large crib, assuming an average density of 100 lbs/cubic ft, the surface miner can extract the total capacity range of 2,640 cubic feet/hr to 88,160 cubic feet/hr (98 cubic yards/hr to 3,265 cubic yards/hr).

The cost of these machines is enormous. According to Mr. Frank Papp, Sales Representative for TAKRAF based in Denver, CO, the price for a bucket wheel excavator is $7.5 million (includes design and supply cost) and $1.5 million for site assembly. Delivery of this machine will take 16 months. Site installation duration will take 5 months. For a bucket chain excavator, price is $12 million for design and supply and approximately $1.9 million for site assembly. Delivery will take 18 months. Site installation duration will take 6 months. Mr. Papp indicated that a surface miner is not practical from a cost point of view. Buyer is responsible for the operation of the equipment.

Dust control is imperative with the use of any of this equipment. The equipment will have to be decontaminated prior to transport to another disposal site or demobilized from the site. Specialized operator training would be needed for operation of some of the equipment. Maintenance contracts need to be in place to service or repair specialized equipment.

6.2 Excavation Using a Structural Diaphragm Wall Soil Support System Remediation Concept – Remove contaminated material from individual cells (formed by a grid of interconnecting diaphragm wall panels) through the use of a hydraulic grab. A 50 x 160-foot perimeter diaphragm wall is installed from a point beginning at 30-feet below ground surface (the bottom of the crib) to (1) a depth of 30 feet (60 feet below ground surface), or (2) a depth of 230 feet (260 feet below ground surface). In order to keep personnel out of the excavation and in recognition of the geological conditions, the space within the perimeter wall must be cross-braced with diaphragm wall panels. Just as the perimeter wall, the cross-braces are constructed 10 feet deeper than the actual excavation depth of each cell to counter ground movement forces. A sketch of this conceptual model is included as Figure 14 and Figure 15 for the excavation to 20 feet and 220 feet below crib bottom, respectively.

In this study, the excavation effort begins at 30 feet below ground surface and extends to (1) a depth of 20 feet, or (2) a depth of 220 feet. Therefore, it is assumed that Hanford forces will remove the entire crib structure and prepare a sloped ramp (not to exceed 6 degrees) for possibly heavy tracked equipment to enter the excavation created by the removal of the crib. The 1.5 to 1.0 slope of the excavated crib will meet the regulatory requirement for sloping to the edge of a vertical excavation. From a constructability point-of-view, this excavation scenario is complicated by the fact that it begins in a depression 30-feet below grade and on top of

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Figure 14. Excavation to 20 Feet Below Crib Bottom

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V= h [(fh) x (A 1 +B 1 +2h) + A 1 xB 1] 27

V= 30 [(-½x30) x (160+50+2x30) + (160x50)] = 22 ,389 cy 27

Section Line----t-+--

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30' Deep

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CROSS-SECTIONAL 160' VIEW A1

27 ft3/yd3 ---= 5,926 yd Cross-Section Line

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Figure 15. Excavation to 220 Feet Below Crib Bottom

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contaminated soils. Without strategically placed snow fences, this depression will likely be impacted by fallout from blowing winds. For equipment and personnel to remain off the contaminated crib bottom foot-print, the sloped banks would need to be cut back substantially, or the excavated crib structure would need to be backfilled with clean site soils before the actual remediation effort could be initiated. These costs are not part of this study.

6.2.1 Scenario 1 – Excavation to 20 ft below Crib Bottom In scenario 1, heavy equipment will not be required, nor is reinforcement of the proposed 3-foot thick network of diaphragm (slurry) walls expected to be required. Placement of the outer boundary wall within the 50 x 160-foot perimeter of the excavation plan will minimize the amount of soil excavated. The construction sequence of the perimeter wall might begin with the construction of the two long walls (160 feet long by 30 feet deep by 3 feet thick). Technically, these two long walls could be constructed continuously or as a series of inter-connected panel walls. The construction sequence might then continue by keying two end and five equally spaced cross-bracing diaphragm (slurry) walls into the opposing long walls. This configuration would create six cells of approximately 23 x 44 feet in size. By following a carefully controlled plan of excavating and backfilling along the entire length of the properly cured 44-foot wall, the surface of the wall will never be completely exposed to invite structural failure. A registered professional engineer will have to determine if the 44-foot wall can standup to partial open exposure during excavation and closely following backfill operations.

The total quantity of in-place soil displaced by constructing the diaphragm (slurry) walls in scenario 1 is 2,094 cubic yards. The amount of over-excavated cement/bentonite wall derived from keying the cross-bracing walls into the two long walls is 70 cubic yards. The total in-place material removed to create six cells for excavation is 2,164 cubic yards. Assuming a fluff-factor of 1.2 when in-place material is converted to excavated material, approximately 2,600 cubic yards of material will need to be transported to EDRF. For budgetary purposes, the excavation and slurry wall construction will cost $300-600K (based upon estimates equivalent to $135-$278/cy). The tipping fee at EDRF will cost $260K (based upon a $100/cy fee and 2,600 cubic yards). It is assumed that the soil will be handled once, and that Hanford Forces will provide transportation and support functions.

The total quantity of in-place soil to be excavated from the six 23 x 44-foot cells to a depth of 20 feet is about 4,500 cubic yards. Assuming a fluff-factor of 1.2 when in-place material is converted to excavated material, approximately 5,400 cubic yards of material will need to be transported to EDRF. For budgetary purposes, the excavation of these six cells will cost $810K (based upon estimates equivalent to $150/cy). The tipping fee at EDRF will cost $540K (based upon a $100/cy fee and 5,400 cubic yards). It is assumed that the soil will be handled once and that Hanford Forces will provide transportation, clean backfill, and all necessary support services.

In summary, the minimum quantity of in-place contaminated soil to be removed from this scenario is estimated to be 5,926 cubic yards. Because of the geology, excavation support walls are deemed to be necessary. To secure these walls requires that additional material be removed. The project total results in 6,664 cubic yards of in-place soil actually requiring excavation, or 738 cubic yards more than the targeted minimum of 5,926 cubic yards. The project total tipping fees are estimated to be nearly $800K. Construction of the excavation support walls is estimated to cost $300-600K and excavation of soil from within the six cells is estimated to cost $810K. The budgetary estimate for completing this project is $1.1-$1.4MM. The estimated machine run-time required to complete this effort is 2 to 3 months. This proposed approach meets the evaluation criteria set forth for this study.

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6.2.2 Scenario 2 – Excavation to 220 ft Below Crib Bottom In scenario 2, heavy equipment will be required. Reinforcement of the proposed 3-foot thick network of diaphragm walls is expected to be required. Placement of the outer boundary wall within the 50 x 160-foot perimeter of the excavation plan will minimize the amount of soil excavated. The construction sequence of the perimeter wall might begin with the construction of the two long walls (160 feet long by 230 feet deep by 3 feet thick). Technically, these two long walls could be constructed from a series of inter-connected diaphragm panel walls. The construction sequence might then continue by keying two end and five equally spaced cross-bracing diaphragm walls into the opposing long walls. Because of the depth of excavation in this scenario, a third long-wall may be constructed at the mid-line between the two outer long walls and keyed into the two end walls. This conceptual model will result in the formation of 12 individual excavation cells measuring 23 feet long by 20.5 feet wide by 230 feet deep from the bottom of the crib. The natural forces exerting against these walls (having no well-placed series of wales for horizontal support) – when opened to the excavation depth of 220 feet – may require strengthening of the panels by the addition of more cement and/or the addition of expensive support structures to be placed within the walls during their construction. This cost will have to be determined on an as-needed basis by the engineer chosen to implement this scenario.

The total quantity of in-place soil displaced by constructing the diaphragm walls in scenario 2 is 20,394 cubic yards. The amount of over-excavated cement/bentonite wall derived from keying the cross-bracing walls into the two long walls and a third long wall keyed into the end walls is 281 cubic yards. The total in-place material removed to create 12 cells for excavation is 20,675 cubic yards. Assuming a fluff-factor of 1.2 when in-place material is converted to excavated material, approximately 24,810 cubic yards of material will need to be transported to EDRF. For budgetary purposes, the excavation and diaphragm wall construction will cost $6.9MM (based upon the higher estimate of $135-278/cy). The tipping fee at EDRF will cost $2.48MM (based upon a $100/cy fee and 24,810 cubic yards). It is assumed that the soil will be handled once, and that Hanford Forces will provide transportation and support functions.

The total quantity of in-place soil to be excavated from the twelve 23 x 20.5-foot cells to a depth of 220 feet is about 46,102 cubic yards. Assuming a “fluff-factor” of 1.2 when in-place material is converted to excavated material, approximately 55,323 cubic yards of material will need to be transported to EDRF. For budgetary purposes, the excavation of these twelve cells will cost $8.30MM (based upon estimates equivalent to $150/cy). The tipping fee at EDRF will cost $5.53MM (based upon a $100/cy fee and a volume of 55,323 cubic yards). It is assumed that the soil will be handled once and that Hanford Forces will provide transportation, clean backfill, and all necessary support services.

In summary, the minimum quantity of in-place contaminated soil to be removed from this scenario is estimated to be 65,185 cubic yards. Because of the geology, excavation support walls are deemed to be necessary. To secure these walls requires that additional material be removed. The project total results in 66,496 cubic yards of in-place soil actually requiring excavation, or 1,311 cubic yards more than the targeted minimum of 65,185 cubic yards. The project total tipping fees are estimated to be just over $8MM. Construction of the excavation support walls (without reinforcement) is estimated to cost $6.9MM and excavation of soil from within the 12 cells is estimated to cost $8.30MM. The budgetary estimate for completing this project is $23.2MM. The estimated machine run-time required to complete this effort is nearly 18 months assuming an excavation rate of 20 cubic yards per hour. This proposed approach meets the evaluation criteria set forth for this study, with costs requiring further evaluation.

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6.2.3 Scenario 3 – Excavation to 220 ft below Crib Bottom With In-Situ Cast Cement/Bentonite as Backfill Material Remediation Concept – Replace excavated contaminated soil with in-situ cast cement/bentonite panels, rather than clean soil from the site. Contaminated material is first removed through the use of a hydraulic grab operating in a trench (ca. 3 feet wide and up to 23 feet long by 220 feet deep) beneath a cover of slurry. The purpose of the slurry is to support the walls of the trench during excavation. The slurry would also serve as a dust suppressant during the excavation process. Upon completion of the trench, the in-place slurry would be amended and allowed to set-up in the trench void as a solidified panel of cement/bentonite mix. The process is continued until the designated area beneath the crib bottom is completely excavated and replaced by tightly placed solidified panels. A sketch of this conceptual model is included as Figure 16.

From a constructablility point-of-view, this ‘surgical-type’ extraction scenario minimizes the complexities of huge open-pit excavations. Also minimized are cave-ins, potential losses of heavy equipment, impacts to the environment, over-excavating into uncontaminated areas, and the need for huge volumes of clean backfill. No requirement for internal structural support is anticipated with this technique. This method would, however, proceed more accurately and faster with the added support of gps/machine-controlled equipment and a slurry plant. The combined costs of extraction/panel construction may very well exceed other remediation scenarios described within this study.

In summary, the minimum quantity of in-place contaminated soil to be removed from this scenario is estimated to be 65,185 cubic yards. Because of the expected accuracy of this technique, no more and no less than 65,185 cubic yards will be excavated. The project tipping fees are estimated to be $7.8MM. Excavation and panel construction costs based upon the estimate of $278 per cubic yard (without reinforcement) are estimated to cost $18MM. The budgetary estimate for completing this project is $25.8MM. The estimated machine run-time required to complete this effort is 18 months based on an excavation rate of 20 cubic yards per hour. This proposed approach meets the evaluation criteria set forth for this study, with costs requiring further evaluation.

6.3 Excavation Using Large Diameter Access Shafts

6.3.1 Scenario 1-Use of Reinforced Concrete Circular Slurry Wall Remediation Concept – Construct a 160 ft diameter shaft with a 5 ft thick reinforced concrete circular slurry wall to a depth of 280 ft below ground surface. Excavation inside the shaft could be done after slurry wall installation, as the reinforced concrete wall would ensure the surrounding soil retention. Excavation can be done using combination of crane and clamshell or hammer grab equipment. At greater depths, personnel and equipment may need to be placed in the hole to conduct excavations. Removal of contaminated soil material out of the hole may rely heavily on use of crane lifting muck boxes or “ERDF cans” out of the hole. Egress platforms ventilation, lighting and other safety measures will have to be incorporated into the design and construction of the shaft.

Mr. Nicolas Willig-Friedrich, Slurry Division Manager at Case Foundation Company provided a preliminary budgetary estimate and schedule for installing this type of slurry for the large crib and reverse well. He estimated $26,000,000 for the slurry wall construction and 27 weeks to complete on a 24/5 schedule involving the use of 2 hydro cutter rigs. The Mobilization and demobilization cost of the rig is $750,000 per rig. It would take 4 weeks for mobilization and 3

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weeks for demobilization. This proposed approach meets the evaluation criteria set forth for this study, with costs requiring further evaluation.

6.3.2 Scenario 2-Straight Line Grid Orientation Remediation Concept – Remove contaminated material through the use of a caisson drill rig, a hydraulic grab removing material from within sunken caisson casing, or a combination of both. In this straight-line grid orientation, 80 (10-foot diameter) and 98 (4-foot diameter) caissons are utilized. Of the total volume of soil to be remediated (65,185 cubic yards) 51,200 cubic yards are derived from the 10-foot diameter shafts and 9,996 cubic yards are derived from the 4-foot diameter shafts. One-half of 38 (4-foot diameter) shafts extend beyond the 50 x 160-foot perimeter. Therefore, the contaminated material is under-excavated by 65,185 – 51,200 – (9,996 – 1,938) cubic yards = 5,927 cubic yards. Over-excavated material (beyond the predetermined excavation boundary is equivalent to 1,938 cubic yards. A sketch of this conceptual model is included as Figure 17.

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Figure 16. Excavation to 220 Feet Below Crib Bottom with In-Situ Cast Cement/Bentonite as Backfill Material

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A j, Section

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Diaphragm Wall Panels (80) 3' - Thick x 20' - Wide x 220' - Deep

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Figure 17. Excavation Using Large Diameter Access Shaft – Straight Line Grid Orientation

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From a constructability point-of-view this straight-line grid orientation may be doable with gps/machine-controlled equipment. The overall exercise of pushing and pulling so much precisely-oriented casing, and the facts that there would be nearly 2,000 cubic yards of out-of-boundary soils removed and nearly 6,000 cubic yards of contaminated material remaining at the end of this very lengthly exercise probably deters it from further consideration. This proposed approach does not meet the evaluation criteria set forth for this study. Therefore, no budgetary cost estimates or time frames are included.

6.3.3 Scenario 3 – Packed Sphere Orientation Remediation Concept - Remove contaminated material through the use of a caisson drill rig, a hydraulic grab removing material from within sunken caisson casing, or a combination of both. In this packed-sphere orientation, 86 (10-foot diameter) and 18 (6-foot diameter) caissons are utilized. Of the total volume of soil to be remediated (65,185 cubic yards) 55,400 cubic yards are derived from the 10-foot diameter shafts and 4,140 cubic yards are derived from the 6-foot diameter shafts. Therefore, the contaminated material is under-excavated by 65,185 – 55,400 – 4,140 cubic yards = 5,645 cubic yards. A sketch of this conceptual model is included as Figure18.

From a constructability point-of-view this packed-sphere orientation would not require nearly as many borings. However, this orientation is more difficult to follow than a straight-line grid pattern. And, like the method above this one involves pushing and pulling of a great number of precisely oriented casing. Like the method above, this one leaves a considerable amount of under-excavated contaminated soil behind. This proposed approach does not meet the evaluation criteria set forth for this study. Therefore, no budgetary cost estimates or time frames are included.

6.4 Sequential Excavation Depths Using Benching and Vertical Soil Supports When the alternative method is to place personnel and equipment within the excavation, adequate sloping or a combination of benching and use of vertical soil support systems must be in place to ensure a safe working environment. The latter technique is proposed for use to conduct deep excavation of a large crib to reduce the amount of soil to be removed, especially if a lower angle of repose is necessary depending upon the structural properties of the soil. The use of a soldier pile with timber lagging is the most economical in comparison to a secant or tangent pile or a structured diaphragm wall. Maintaining a distance of 10 ft between piles, the large crib of interest to this study will require 246 soldier piles around the first 75 ft of excavation; 136 soldier piles around the second 75 ft of excavation with a 113 ft wide bench between the first and second excavation, and 46 soldier piles with another 113 ft wide bench between the second and third and final 75 ft deep excavation. Tiebacks will be installed every 10 ft of excavation or as designed by a registered professional engineer. Installation of walers (horizontal beams across the face of the laggings between piles) at appropriate locations along the wall system will also be left to the design engineer. Benches may also need to be grouted to lend stability.

Removal of soil material will initially be done with the use of a clamshell, dragline excavator, large shovel, heavy duty excavator, or combination of this equipment. Excavated material is placed directly on dump trucks that are routed through an inspection and testing station prior to

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Figure 18. Excavation Using Large Diameter Access Shaft – Packed Sphere Orientation

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transport and disposal of the material at ERDF. Heavy duty wheel loaders can also be used to load stockpiled material into dump trucks. Ramps will be constructed to provide access into and out of excavation area. Conveyor system will be installed for easier loading of dump trucks. The size and power rating of the conveyor system will depend upon desired hourly production rates.

This proposed approach does not completely meet the evaluation criteria for the study as it entails removal of larger volumes of soil material than targeted amounts.

6.5 Top Down Excavation Using Soil Nails and Internal Brace System This remediation concept is proposed by Anderson Drilling. The shoring wall would advance like any other, top down in 5-foot lifts. Figures 19a through 19c shows an illustration of this concept. Five (5) ft deep excavations would be performed. A row of nails is installed at an angle of 15 degrees below the horizontal. The nails are then tied together in a “mat” to provide reinforcement for the vertical wall. Concrete is sprayed onto the reinforcing mat. Internal bracing would also be installed at the designed intervals as the excavation advances in depth. The operation would continue until the desired depth is achieved. This proposed approach does not completely meet the evaluation criteria for the study as it entails removal of larger volumes of material than targeted amounts.

At some depth, cranes would be used to “bucket” concrete down to a hopper in the pit to assist in the concrete placement. The excavation portion would also require the use of cranes, buckets, and small equipment in the pit to remove the soil.

This method is estimated to cost $11.5MM including provision and installation of temporary shoring, engineering and mobilization. Project duration is anticipated to be several months.

This proposed approach does not completely meet the evaluation criteria for the study as it entails removal of larger volumes of soil material than targeted amounts.

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Figure 19a. Top Down Excavation Using Soil Nails and Internal Brace System

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Figure 19b. Top Down Excavation Using Soil Nails and Internal Brace System

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7. EXCAVATION TECHNIQUES APPLICABLE TO REVERSE WELL

Large diameter auger excavators such as those used for installation of large diameter access shafts, drilled shaft foundations, and earth retention systems are evaluated for the remediation of the reverse well site. Removal of the reverse well casing is evaluated as an element of this technique.

For the reverse well, the contaminated soil to be removed is a soil column 10 feet in diameter from 55 feet below ground surface to the groundwater level (280 feet below ground surface). The 6-inch steel piping (0.5 feet in diameter and 75 feet in depth) within the reverse well also needs to be removed. This may need to be pulled before excavation procedures are initiated. A sketch of the reverse well excavation profile is in Figure 20.

7.1 Use of Auger Rig Remediation Concept – Advance casing through column of contaminated soil material through use of a vibratory hammer. Remove material inside casing with auger rig supplemented by use of bucket or barrel to clean out the hole. Pull the soil-support casing as the excavation is being back-filled with clean native soil.

In this study, the excavation effort begins at the ground surface and extends to 280 feet below ground surface. From a constructability point of view, it makes sense to have a 10-foot diameter caisson drill rig complete all of the work (at one time) from ground surface to 280 feet below ground surface instead of breaking up the work where Hanford plant forces would do the first 55 ft and the remaining depth to be done by others. By properly pushing/pulling casing, cave-ins should be prevented. With the great depths involved, it is likely that difficulties will be encountered in advancing and retrieving the casing,

In summary, the calculated quantity of in-place contaminated soil to be removed from this scenario is estimated to be about 815 cubic yards. Because of the expected accuracy of this technique, no more and no less than 815 cubic yards will be excavated. The project tipping fees are estimated to be $81.5K. Excavation and casing construction costs based upon the estimate of $330 per cubic yard (with casing) is estimated to cost $270K excluding mobilization and demobilization costs. The budgetary estimate for completing this project is $350K excluding mobilization and demobilization costs. The estimated machine run-time required to complete this effort is 5 days to include installation of casing and removal of contaminated soil. This proposed approach meets the evaluation criteria set forth for this study except that excavation depth may be limited by the advancement of the casing. Recovery of the casing at a realistic depth is also a factor.

7.2 Use of Hydraulic Casing Oscillator and Hammer Grab Remediation Concept – Instead of using a combination of a vibratory hammer to push down on the casing and augering the hole to remove the contaminated material, an oscillator is used to pull down a 10 ft diameter casing down the column of contaminated soil. A hammer grab in conjunction with a heavy duty crane is used to clean out the large diameter hole as the casing progresses to the required depth. This method has been used in the construction of large diameter concrete shafts for foundation projects.

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Figure 20. Reverse Well Excavation Profile

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Overburden

V= m2 h

27 = 3.14 X (5ft)2 x 55 ft

27 ff/yd3

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Contaminated Soil

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In this study, the excavation effort begins at the ground surface and extends to 280 feet below ground surface. From a constructability point of view, it makes sense to have a 10-foot diameter caisson drill rig complete all of the work (at one time) from ground surface to 280 feet below ground surface instead of breaking up the work where Hanford plant forces would do the first 55 ft and the remaining depth to be done by others. By properly pushing/pulling casing, cave-ins should be prevented. As with the vibratory hammer, it is likely that similar difficulties in advancing and retrieving the casing will be encountered with the oscillator. Costs should also be comparable.

In summary, the calculated quantity of in-place contaminated soil to be removed from this scenario is estimated to be 815 cubic yards. Because of the expected accuracy of this technique, no more and no less than 815 cubic yards will be excavated. The project tipping fees are estimated to be $81.5K. Excavation and casing construction costs based upon the estimate of $330 per cubic yard (with casing) is estimated to cost $270K. The budgetary estimate for completing this project is $350K. The estimated machine run-time required to complete this effort is 5 days. This proposed approach meets the evaluation criteria set forth for this study.

7.3 Use of Circular Structural Diaphragm Wall vs. Casing Remediation Concept – Construct a 2 ft thick reinforced concrete circular slurry wall, 10 ft in diameter, to a depth of 300 ft below ground surface surrounding the reverse well. Excavation inside the wall could be done after slurry wall installation, as the reinforced concrete wall would ensure the surrounding soil retention. Excavation can be done using combination of crane and clamshell or hammer grab equipment. Excavated material can be placed directly in awaiting dump trucks for transport and disposal to ERDF. This proposed approach meets the evaluation criteria for the study.

7.4 Sequential Excavation to 200 ft BGS Using Corrugated Metal Pipe for Borehole Stabilization As Proposed by Anderson Drilling Remediation Concept – Verify construction methodology under existing ground conditions through a test shaft program. Improve the ground around large diameter shaft excavation by grouting highly permeable zones of strata along the perimeter of the intended excavation and to the depth of excavation. Excavate, furnish and install a series of corrugated liner casings. These liners are several feet larger in diameter than the finished shaft dimensions. The purpose of the liner system is to provide shaft stability and safety in the upper portion of the large diameter excavation. Each liner will be installed and grouted into place. The excavation for each liner will be several feet larger than the liner itself allowing for a suitable annulus space for grouting. Excavation will be performed by the “wet method” including the use of a dry vinyl polymer additive to water as the drill fluid. The initial shaft excavation is proposed to be approximately 20 ft diameter x 20 ft in depth with an 18 ft x 20 ft corrugated lines. The borehole will then be advanced at 17-ft diameter to approximately 50 ft in depth. A secondary liner 15 ft diameter x 35 ft in length will be grouted in place. The 14-ft diameter borehole will be advanced to approximately 100 ft in depth. A third liner, 12 ft diameter x 55 ft in length will be installed and grouted in place. Open hole excavation of the shaft will continue to the achievable depth of 190 ft to 200 ft. Excavation will be backfilled using lean grout to within 10 ft of the existing ground surface. Clean fill will be placed in the upper 10 ft of ground surface. All corrugated liners will remain in place. Project duration is anticipated to require 9-11 weeks. Figure 21 shows a profile of this remediation concept. The estimated cost for this technique is $2.7MM including a test shaft program, excavation and backfill, and mobilization. This proposed approach does not completely meet the evaluation criteria for the study as it involves removal of larger volumes of soil material than target amounts.

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Figure 21. Stepped Excavation Using Large Diameter Shafts (Corrugated Metal Pipe)

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8. PRELIMINARY COST ESTIMATES

This section summarizes the unit prices provided by vendors contacted, and data available from City of Seattle. This information could be used to derive preliminary cost estimates for the following soil retention systems:

• Cement/bentonite slurry wall

– $26/ft2 with a number of exclusions (RECON)

• Structural Diaphragm Wall

– $80-$150/ft2 (Nicholson Construction Co.)

– $8.4M - $15.8M for CSW around large crib (160 ft x 50 ft x 250 ft deep)

– $85-$105/ft2 (RECON)

• Reinforced Concrete Circular Slurry Wall

– $27M for large crib and reverse well (excludes disposal of all spoils and bentonite) (Case Foundation)

• Soil Nailing with Internal Brace System

– $11.5 M for large crib (includes engineering and mobilization) (Anderson Drilling)

• Secant Pile

– $65-$75/ft2 (RECON)

• Tangent Pile

– $60-$100/ft2 (City of Seattle)

• Soldier Pile & Tieback-Timber Lagging

– $55-$140/ft2 (City of Seattle)

• Sheet Pile

– $11-$13/ft2 (removed/salvaged) (City of Seattle)

– $16-$24/ft2 (permanent) (City of Seattle)

• Soil Mixing

– $6-$12/ft2 (Robert D. Mutch, Jr., “New Technologies for Subsurface Barrier Wall Construction,” National Academy of Sciences)

• Jet Grouting

– $15-$30/ft2 (Robert D. Mutch, Jr., “New Technologies for Subsurface Barrier Wall Construction,” National Academy of Sciences)

• 10 ft diameter x 200 ft deep drilled shaft

– Anderson Drilling: $2.7M (includes test shaft program, excavate & backfill, mobilization)

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9. CONCLUSIONS

In consideration of the evaluation factors of safety, protection of human health and the environment, minimization of soil material removed, maximum realistic depth and cost-effectiveness, GSAI concludes from the study that:

• Deep excavations to the proposed depths of 250 ft to 280 ft at large crib and reverse well disposal sites at the 200 Areas of the Hanford site require properly engineered, structurally sound vertical soil support systems. Some case histories reviewed reveal that the technology exists whereby great depths can be achieved. In South Africa, concurrent vertical shaft sinking and lining, creating single lifts well over 8,000 feet, was conducted by the Shaft Sinkers Group. In South Korea, a 5.6-ft thick x 246-ft deep cylindrical slurry wall greater than 262-ft inside diameter holds back soil and water without additional bracing. In the State of Washington, Soletanche Bachy installed the world’s deepest slurry wall (about 400 ft deep) in the repair of Mud Mountain Dam at Enumclaw.

• Design of a specific excavation support system must be done by a registered professional

engineer as required by OSHA regulations and FH requirements. Top down sequential excavations can be conducted by placement of personnel and equipment in the hole, but appropriate soil retention systems and benching are necessary to provide a safe working environment. Amount of soil removed will exceed targeted volumes.

• Specific soil conditions at large crib and reverse well disposal sites must be well known.

The structural properties of the soil must be determined to provide information for the feasibility and design of the excavation support system. Installation of excavation support systems reduces the amount of soil material to be removed in comparison to slope excavations.

• Based upon the configuration of the crib excavation, the crib contents and the physical

structure of the crib can most economically be removed by conventional equipment. The excavation would proceed out from the footprint of the crib base at a slope equivalent to 1.5-foot horizontal and 1.0-foot vertical. A bucket wheel excavator used in surface mining would not be a practical substitute for conventional equipment to increase production rates, as these machines are extremely heavy and large, and specially designed and fabricated for their specific use. They can only be employed to a certain depth as their size and weight would pose challenges in getting them out of deep excavations. These machines are expensive and have long lead times for production and require assembly on site. Buyer provides its own trained operators.

• Structural diaphragm walls and large diameter access shafts offer the best method of

excavation support system for the large crib and reverse well disposal sites without placing personnel and equipment in the hole to conduct the excavation activities. A structural diaphragm wall may be rectangular or circular in shape. The former may require internal struts and anchors to support the diaphragm walls. The geometry of the circular configuration lends itself to a self supporting structure without requiring any bracing.

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• Use of slurry for soil retention and prevention of cave-ins during excavation poses material handling issues. The material must be dried for disposal at ERDF. Slurry may become irradiated due to mixing with radioactive contaminated soil, and would also require disposal as a radioactive waste.

• Use of a vibratory hammer or oscillator machine to advance large diameter steel casing

around reverse well and then using a hammer grab machine to extract the 6-inch diameter steel pipe and a combination of auger rig and buckets or barrels to remove radioactively contaminated soil material is a technique that could be applied for remediation of the reverse well disposal site.

• Large, heavy machinery are required to conduct deep excavations. For installation of the

structural diaphragm walls and large diameter access shafts, equipment such as hydrofraise, hydromill, or mechanical clamshell, oscillator, rotator, 200 ton crawler crane, vibratory hammer, auger rig, hammer grab or clamshell, and 40-ton dump trucks are typically used. Haul routes and access roads at the Hanford Site must be able to handle transport of these machines on the site. Stable working platforms at the site must be prepared to accommodate surcharge loads and vibrations from these machines.

• Vast amounts of materials such as cement/bentonite slurry mix, reinforcement bars, and

up to a million gallons of water are required for construction of structural diaphragm walls. A desanding plant on site will be needed in order to separate soil cuttings from removed slurry. Large number of steel casing segments is required for installation of the deep large diameter access shafts.

• Use of jet grouting cylinders may offer a cleaner alternative to the structural diaphragm

walls, but its application to support deep excavations is limited. Similarly, piles such as soldier piles with horizontal timber laggings, secant and tangent piles, contiguous bored piles, and sheet piles are limited. In the building construction industry, excavation to depths of 100 ft to 150 ft, using these soil retention systems, have been completed depending upon soil conditions.

• Ground improvement techniques can be used in conjunction with vertical soil support

systems to improve the stability of working platforms.

• Egress, ventilation, lighting, and perimeter fencing must also be included in the design of the excavation support system. Dust generation and spread of contamination must be controlled during installation of excavation support system and conduct of excavation activities. The interface between surrounding soils and walls or casings may act as a channel for residual contamination transport and would need to be considered in the remediation design.

• Budgetary estimates are enormous for installation of excavation support systems for deep

excavation. Operational costs would be as high considering labor, heavy equipment rental or purchase, monitoring, testing, inspections, decontamination, transport and disposal. Production will be affected by meteorological conditions and the requirement to control spread of radiological contamination. Transport trucks will need to be inspected prior to leaving site for ERDF.

• Specialty geotechnical contractors will be required to design and construct excavation support systems. Excavation activities will also be performed by specialty contractors

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who will need to be certified and trained in the safety, security, and environmental protection requirements of the Hanford site.

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10. RECOMMENDATIONS

GSAI recommends the following:

• Obtain site specific geotechnical data on large crib and reverse well disposal sites • Perform a screening evaluation of deep excavation along with other remedial alternatives

being considered for the large crib and reverse well in accordance with RI/FS broad criteria of effectiveness, implementability and cost

• Use of structural diaphragm wall and large access shaft as a primary means of conducting the deep excavation without placement of personnel and equipment in the hole

• Use of specifically designed soil retention system to perform top down sequential excavation by placement of personnel and equipment in the hole

If the alternative of deep excavation is selected for detailed analysis, GSAI recommends the following:

• Installation of test shafts to determine feasibility of large access diameter shafts as a means of performing deep excavation

• Evaluation of disposal of radioactively contaminated slurry mixture • Evaluation of treatment of wet cuttings resulting from diaphragm wall excavation prior to

disposal at ERDF • Evaluation of left in place casing or walls as conduits for residual contaminant transport

between surrounding soils and subsurface infrastructures. If deep excavation is selected as a remedy for remediation of the large crib and reverse well disposal sites, GSAI recommends the following:

• Preparation of Scope of Work for Design and Construction of Appropriate Soil Retention System for Deep Excavation

• Preparation of Scope of Work for Deep Excavation Activities

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Final Report-Excavation Depth Techniques Study July 6, 2007

APPENDIX A (MAP OF HANFORD SITE AND AREA DESIGNATIONS)

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Figure 1-1. Hanford Site and Area Designation~.

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APPENDIX B (VADOSE ZONE STRATIGRAPHY)

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studies and depend largely on soil texture and. the type and density of vegetation. A narural recharge map

based on disaibutions of soil and vegetation types is shown in Figure F-4. Recharge from precipitation is

higher in the coarse-textured soils with little or no vegetation, as are found in the 200 Areas (Hartman and

Dresel I 998). Historically, the volume of natural recharge was expected to be significantly lower than the

volume of recharge conaibuted by artificial sources throughout the 200 Areas. Graham et al. ( 1981)

estimate that historical artificial recharge froin liquid waste disposal in the 200 Areas exceeded all natural

recharge on the Hanford Site by a factor of 10 (DOE-RL 1997b).

With the cessation of artificial recharge in the 200 Areas, the downward flux of moisture in the vadose

zone to groundwater has decreased underlying liquid disposal sites and is expected to continue to

decrease with time. The maximum flux of moisture occurred when plant operations were active, creating

many localized areas of saturation/near saturation in the soil column beneath liquid disposal waste sites.

When waste sites cease operating, the moisture flux continues to be significant for a period of time

because of gravity drainage of the sarurated/near-saturated soil column. When unsaturated conditions are

reached, moisrure flux becomes increasingly less significant because unsa!UrJlted hydraulic conductivity

decreases with decreasing moisture content. The decrease in artificial recharge in the 200-Areas is

reflected in the water table, which continues to decrease in elevation throughout the 200 Areas. In the

absence of artificial recharge, the potential for recharge from precipitation becomes more important as a

downward driving force for remaining vadose zone contamination (DOE-RL 1997b).

The unconfined aquifer underlying the 200 Areas may also receive natural recharge from two additional

sources. Rainfall and run-off from the higher bordering elevations to the west of the site recharge the

unconfined aquifer up gradient of the 200 Areas. Also, in areas of upward gradients, the unconfined

aquifer may be recharged with water from the under lying confined aquifer system. The direction of the

vertical gradients may change as waste water disposal practices change (DOE-RL 1993b).

Water that infiltrates the vadose zone may leach contaminants from both liquid and solid waste disposal

sites and transport them to groundwater. Recharge thus represents a potential long-term mechanism for

contaminant migration.

F4.0 V ADOSE ZONE HYDROGEOLOGY

The vadose zone beneath the 200 Areas ranges in thickness from approximately 55 m (180 ft) beneath the

former U Pond in the 200 West Area to approximately I 04 m (34 l ft) in the southern portion of the

200 East Area to 49 m (160 ft) along the western part of the 200 North Area. The vadose zone thins from

the 200 Areas north to 0.3 m ( I ft) near West Lake. Sediments in the vadose zone consist primarily of the

Hanford formation, Plio-Ph:istocene unit/early Palouse soil, and Ringold Formation, as illustrated in a

generalized east-west cross-section through the Hanford Site (Figure F-5). Variable surface topography

and the variable elevation of the water table in the underlying uppermost aquifer causes this observed

variation in vadose zone thickness. Other important features of the vadose zone include basalt of the

Columbia River Basalt Group projecting above the water table north of the 200 East Area, elastic dikes

occumng in the Hanford formation, and windblown sand and silt deposits at the surface.

Both the Ringold and Hanford formations have been subdivided into different units and facies based on

rock type and depositional environment. Detailed stratigraphic sections for the 200 West and 200 East

Areas are presented in Figure F-6. Location-specific cross-sections that provide examples of the

variability in thickness and continuity of different sedimentary units and facies are presented in

Figures F-7 through F-10. Structure and isopach maps of the principal geologic units that make up the

vadose zone are included in Connelly et al. (1992a, 1992b).

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Although sediments of the Hanford and Ringold formations are present beneath the 200 West, 200 East,

and 200 North Areas, the vadose zones at these three locations differ significantly. The Plio-Pleistocene

Unit/early Palouse soil, which has a relatively low permeability that impacts the migration ofliquid and

vapor, is found only underlying the 200 West Area. The groundwater table occurs within the less

conductive Ringold Formation in the 200 West Area and primarily within the Hanford formation in the

200 East and 200 North Areas (Figure F-11).

Calcium carbontate (CaC01) content is typically less than 1 % in the Ringold Formation Unit E, less than

I% in the upper Ringold Unit, as much as 10% in the Plio-Pleistocene Unit/early Palouse soil, and less

than 2% in the Hanford formation.

The following subsections provide a brief description of the units, in descending order, that make up the

vadose zone in the 200 Areas.

F4.l SURFICIAL DEPOSITS

Holocene-aged deposits in the 200 Areas are dominated by eolian sheets of sand that form a thin veneer

across the 200 Areas except in localized areas where they have been removed by human activity.

Surficial deposits consist of very fine- to medium-grained sand to occasionally silty sand and are

generally less than 3 m thick. Silty deposits (<I m thick) have also been documented at waste

management facilities (e.g., ponds and ditches) where fine-grained windblown material has settled out

through standing water over many years.

F4.2 HANFORD FORMATION

The Hanford fonnation (informal designation) consists of uncemented gravels, sands, and silts deposited

by Pleistocene cataclysmic flood waters. As discussed by Lindsey et al. ( 1991 ). these cataclysmic flood

deposits are divided into three facies: gravel-dominated, sand-dominated, and silt-dominated. Based on

the distribution of these facies, the Hanford formation is divided locally into three informal stratigraphic

sequences. These sequences are designated as the upper gravel, sand, and lower gravel sequences.

However, because of the variability of the Hanford formation sediments, contacts between these

sequences are sometimes difficult to distinguish, especially where the sand sequence is missing and the

upper gravel directly overlies the lower gravel. Although the Hanford formation as a whole is continuous

throughout the vadose zone in the 200 Areas, none of these individual stratigraphic sequences is

continuous across the 200 Areas: all three sequences display marked changes in thickness and continuity

and are lithologically heterogenous (Figures F-8 though F-10).

F4.2.l Upper Gravel Sequence of the Hanford Formation

The upper gravel sequence consists of interstratified gravel, sand, and lesser silt. Gravel-dominated

deposits generally dominate the sequence. This coarse-grained upper gravel sequence is distinguished by

a coarse-grained sand to a boulder gravel that displays massive bedding, plane to low angle bedding, and

large-scale cross bedding in outcrop. The matrix is commonly lacking in the gravels, giving them an

open-framework texture. The thickness of this coarse-grained sequence is 70 m (230 ft) at the northeast

comer of the 200 North Area and thins to zero near the southern border of the 200 East Area. Within the

200 West Area: the thickness of the upper coarse unit ranges from Oto 45 m (0 to 148 ft). The contact

between the coarse-grained sequence and underlying strata is generally sharp.

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F4.2.i Sand Sequence of the Hanford Formation

The sand sequence of the Hanford formation in the 200 Areas is thick, but locally discontinuous. The

sequence is O to 90 m (0 to 295 ft) thick in the central portion of the 200 East Area and O to 32 m (0 to

105 ft) thick in the 200 West Area. To the north, the sand sequence occurs only in the ancient flood

channel along the eastern border of the 200 North Area, where it is up to 15 m (50 ft) thick. It is absent

elsewhere in the 200 North Area. The sand sequence generally thickens to the south. The sequence is

missing in the central part of the 200 West Area as a result of erosional scouring during the cataclysmic

flooding events. This erosional scour is elongated in a north-south direction (Connelly et al. 1992b). The

sand sequence consists predominantly of silt, silty sand, and sand with interbedded coarser sands.

F4.2.3 Lower Gravel Sequence of the Hanford Formation

The lower gravel sequence is dominated by deposits typical of the gravel-dominated facies. Local

intercalated sandy beds typical of the sand-dominated facies are also found. In the 200 West Area this

sequence is missing. It is found throughout most of the 200 East Acea at a thickness ranging from O to

44 m (0 to 135 ft). However, it is absent in the east-central portion of the 200 East Area. In the

200 North Area, the lower gravel sequence is up to 23 m (75 ft) thick in the ancient flood channel along

the eastern border. Where this unit is overlain directly by the upper gravel sequence, it is not possible to

distinguish between the two. Where it is overlain by the sand sequence, the contact between the sand and

lower gravel sequences is interpreted to be at the top of the first thick gravelly interval (6 m [20 ft] or

greater in thickness) encountered below the sand-dominated strata of the sand sequence.

F4.3 PLIO-PLEISTOCENE/EARLY PALOUSE SOILS

The Plio-Pleistocene/early Palouse soils are missing from the 200 East and 200 North Areas. The early

Palouse soil is largely restricted to the vicinity of the 200 West Area The unit is differentiated from the

overlying Hanford slackwater deposits by (1) greater calcium carbonate content, (2) cohesive structure in

core samples, (3) uniform fine-grained texrure, and (4) high natural-gamma response. It is distinguished

from the underlying Plio-Pleistocene unit by the high natural-gamma response and lower calcium

carbonate content. The loess-like sediments of the early Palouse are uncemented. The unit pinches out

near the southern, eastern, and northern boundaries of the 200 West Area. Boreholes located west of the

200 West Area, however, do encounter the unit. Due to the fine-grained nature of the soil, this unit is also

an impediment to downward migration of water and contaminants.

Like the early Palouse soil, the Plio-Pleistocene unit is restricted to the vicinity of the 200 West Area,

pinching out to the northern, eastern, and southern boundaries of the area. It represents a highly

weathered surface that developed on the surface of the Ringold Formation. 1n the 200 West Area, the

calcrete facies dominates and is locally referred to as the "caliche layer." The differentiating features of

this unit are (1) high degree ofcementation, (2) presence of roots and animal bores in cores, and (3) white

color. This unit is an impediment to vertical migration of water and vapor due to the high degree of

cementation. The thickness is very irregular, and there may be erosional windows through the unit.

F4.4 RINGOLD FORMATION

The Ringold Formation is an interstratified sequence of unconsolidated clay, silt, sand, and

gravel-to-cobble gravel deposited by the ancestral Columbia River. The Ringold Formation forms the

lower part of the vadose zone throughout the 200 West Area and south of the 200 East Area. The Ringold

Formation generally occurs completely in the saturated zone in and north of the 200 East Area, although

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relatively small isolated pockets of Ringold occur within the 200 East Area vadose zone. In the

200 Areas, these elastic sediments, from youngest to oldest, consist of four major facies:

overbank-dominated deposits of the Upper Ringold; fluvial gravels of Unit E; paleosol and lacustrine

muds of the lower mud sequence; and fluvial gravels of Unit A. Ringold Units B, C, and Dare not

present in the 200 Areas with the exception of localized occurrences of fluvial gravel of Unit C in the

200 East Area.

F4.4.l Upper Ringold Unit

The upper Ringold unit is missing in the 200 East and 200 North Areas and is discontinuous across the

200 West Area because of post-Ringold erosion. The upper unit in the 200 West Area consists of silty

overbank deposits and flu vial sands. 11lis unit is recognized by ( 1) abundance of well-sorted sand,

(2) light color, and (3) variable natural-gamma response. It is found only in the west, north, and central

portions of the 200 West Area. It dips to the south-southwest.

F4.4.2 Unit E of the Ringold Formation

Unit E is the uppermost unit of the Ringold Formation in the 200 East and 200 North Areas. It is

dominantly composed of fluvial gravel, but strata typical of the fluvial sand and overbank facies may be

encountered locally. The unit is recognized by ( l) coarse texture, (2) high proportion of quartzite and

granitic clasts, (3) relatively low calcium carbonate content, (4) partial consolidation, and (S) relatively

low natural gamma response. In the 200 West Area, the gravels of Unit E generally thin from

north-northwest to east-southeast while the surface dips toward the east-southeast (Figure F-5). Gravels

of Unit E occur in the southwest comer of the 200 North Area, at a thickness up to 5 m ( 16 ft), and in the

southwest comer of the 200 East Area, at a thickness up to 35 m {ll5 ft). From the 200 North and East

Areas, Unit E thickens to the south-southwest. Unit Eis the only part of the Ringold Formation identified

within the 200 North Area.

F4.4.3 Lower Mud Sequence of the Ringold Formation

The overbank and lacustrine deposits of the lower mud sequence occur beneath the gravels of Unit E.

The lower mud sequence generally thickens and dips to the west and to the southeast away from the

200 East Area (Figure F-5). The unit appears in the vadose zone as small isolated pockets in the center of

the 200 East Area, underneath B Pond and between 8 Pond and Gable Mountain (Figure F-11). In the

200 West Area, it forms the aquitard at the base of the unconfined aquifer and is not a part of the vadose

zone.

F4.4.4 Unit A of the Ringold Formation

In the 200 East Area, the tluvial gravels and sands of Unit A generally thicken and dip to the south

(Connelly et al. 1992a). This unit rises above the water table in a small isolated pockets near the western

and eastern boundaries of the 200 East Area and south of Gable Mountain (Figure F-11). Unit A is below

the unconfined aquifer and therefore is not part of the vadose zone in the 200 West Area.

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F4.5 COLU1\IIBIA RIVER BASALT GROUP

The Elephant Mountain Member is the uppermost basalt unit (i.e., bedrock) in the 200 Areas. Except for

a small area north of the 200 East Area boundary wh.ere it has been eroded away, the Elephant Mountain

Member is laterally continuous throughout the 200 Areas. The Elephant Mountain Member is 21 to 30. m

thick and thins to the north. Where the Elephant Mountain Member is absent, the Pomona Member forms

the uppermost basalt unit. Areas of basalt project above the water table north of the 200 East Area

(Figure F-11 ).

F4.6 CLASTIC DIKES

Clastic dikes are common structures that occur in many of the geologic units in the Pasco Basin and

vicinity. One subset, elastic injection dikes, are fissures filled with sand, silt, clay, and minor coarser

debris. Many dikes occur as near-vertical tabular bodies filled with multiple layers of unconsolidated

sediments. The margins of most dikes and internal layers within dikes are separated by thin clay/silt

linings (Fecht et al. 1998).

Clastic dikes range in continuous venical extent from less than 30 cm to more than 55 m (Fecht et al.

1998). The deepest known occurrence of a elastic dike below ground surface is greater than 75 m (246 ft)

in the 200 West Area; the total vet1ical extent of this elastic injection dike is not known (Fecht et al.

1998). In cross section, elastic dikes range in width from less than 1 mm to over 2 m (Fecht et al. 1998).

Attitudes of the dikes range from venical to horizontal, with near-vertical dikes being more common.

Material filling the dikes is locally derived and ranges in size from mud to gravel. Distribution and

hydraulic properties of the dikes are not well known. Clastic dikes occur in the Hanford formation in

both the 200 West and 200 East Areas. They are most common in the finer grained sand sequence and

are rare in the open-framework gravel. Clastic dikes do occur in the Ringold Formation sediments

elsewhere, but their occurrences are rare. Clastic dikes can be both preferential pathways for water and

vapor and a barrier to water and vapor flow.

F4.7 WATER Ai'ID VAPOR FLOW THROUGH THE VADOSE ZONE

The flow of water, vapor, or other fluids through the vadose zone to the water table depends in complex

ways on properties of both the soil and the migrating fluid. The flux is a function of the hydraulic

conductivity and the hydraulic gradient. If the migrating fluid includes dissolved contaminants, the

contaminants will also be rransponed through the vadose zone unless they are retained as a result of

interaction with the soil.

The hydraulic conductivity has dimensions of velocity (e.g., m/day or ft/day) and describes the capability

of sediments to transmit water, vapor, or other fluids through the soil. It generally has high values for

coarser grained sediments such as sand and gravel and lower values for finer grained sediments such as

silt and clay. In addition to hydraulic conductivity, subsurface flow is controlled by:

• Thickness, lateral distribution, and dip of the sediments

• Moisture retention capacity of the sediments

• Fluid density

• Porosity, grain size, and orientation of the sediments

• Permeability of the sediments to water, air, or other fluids

• Amount of natural and artificial recharge

• Degree of saturation of the vadose zone pore spaces.

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The hydraulic gradient can be defined as the difference in hydraulic head (pressure and elevation bead)

between two locations in the subsurface divided by the distance between the two locations. Because both

the head and the distance have units oflength ( e.g., m or ft), the hydraulic gradient is usually

dimensionless.

The distribution of contaminants within the vadose zone is a function of the concentration of the

contaminants at the source and the physical and chemical interactions of the contaminants with the

sediments through which they migrate. The degree to which contaminants interact with sediments

depends on the properties of the particular contaminant ( e.g., volatility, solubility), the geochemical

properties of the sediments (e.g., calcium carbonate content, organic content, clay content), and the

physical properties described above. The distribution coefficient (K.i) for a particular contaminant

describes the likelihood that the contaminant will partition to the soil matrix rather than to the migrating

liquid. A high K.i indicates that the contaminant will tend to be retained on the soil particles, whereas a

low K.:t indicates that the contaminant will tend to remain dissolved in the water. The retardation factor

for a particular contaminant describes how much its travel time is lengthened, compared to that of water,

as a result of its retention on soil particles.

The mobility of each contaminant is determined by its K.i, and each contaminant will have a specific K.t

for a particular sediment type. In general, the K.i is dependent on the amount of fine-grained material in

the sediment. The more fine-grained the material, the higher the K.i and the greater the capacity of the

soil to retain moisture and contaminants. In the 200 West Area, the Plio-Pleistocene/early Palouse soils ·

will have higher K.i values than the Hanford or Ringold sands, which will have higher K.t values than the

Hanford or Ringold gravels. Further discussions on the mobility of contaminants are provided in

Section 3.3.

Perched water zones form when moisture moving downward through the vadose zone accumulates on top

oflow-penneability soil lenses, highly cemented horizons, or above the contact between a fine-grained

horizon and an underlying coarse-grained horizon as a result of the capillary barrier effect The

Plio-Pleistocene/early Palouse soil unit is the most significant aquitard in the 200 West Area above the

water table and is a major component controlling the accumulation of perched water where effluent was

discharged. The Ringold lower mud sequence also represents a potential perching layer. Up to 2.1 m

(7 ft) of perched water has been found above the lower mud sequence in the vicinity of the 2 l 6-B-3C

Pond lobe in the 200 East Area.

Wastewater discharges since 1943 have contributed to the rise in the water table elevation underlying the

200 Areas and have created local groundwater mounds, most notably under U Pond in the 200 West Area

and under B Pond in the 200 East Area. In the 200 West Area, water levels have declined over 6 m

(20 ft) since 1984 because of reduced discharges to the cribs and unlined trenches; in the 200 East Area,

the water table elevation has been declining since 1988 because wastewater discharges to disposal

facilities in the 200 East Area and B Pond were reduced (Hanman and Dresel 1998). A continued

decrease in the water table elevations and concomitant increase in the thickness of the vadoze zones

underlying the 200 Areas is expected.

The thickness, lateral distribution, and dip of the sediments in the vadose zone in the 200 Areas were

discussed in the previous sections. Structure and isopach maps of those sediments are provided in

Connelly et al. (1992a, 1992b). The lateral continuity and structural orientation of the sediments

determine the spatial distribution of hydraulic properties.

The major driving force to move contaminants from the vadose zone to the water table is both artificial

and natural recharge. Artificial recharge in the 200 Areas varied widely from small intermittent volumes

applied to cribs to thousands of gallons per day at the ditches and ponds. Since 1995, most artificial

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recharge in the 200 Areas has ceased, and the principal driving force today is natural recharge, which

averages approximately 100 mm/yr ( 4 in./yr) in the 200 Areas.

In the vadose zone, the pressure head is negative under unsaturated conditions. This reflects the fact that

water in. the unsarurated zone is held in the soil pores under negative pressure by surface-tension forces.

If the volume of water in the vadose zone equals the volume that can be retained by surface tension forces

( defined as the field capacity of the soil), no water will be available to migrate. However, as additional

water is added to the vadose zone, for example by recharge, it will continue to migrate vertically under

the force of gravity. Analyzing water flow in the vadose zone is complicated because both water content

and hydraulic conductivity are nonlinear functions of pressure head. As the water content increases, the

surface tension holding the water in the pore space decreases, and the water flux increases. Therefore, to

analyze flow in the vadose zone, the moisture-retention capacity of the soil must be evaluated by

measuring water content as a function of pressure head. The relationship between water content and

pressure head is typically displayed graphically on a moisture retention curve. If either the saturated

hydraulic conductivity or the unsaturated hydraulic conductivity at a specified water content is known, the

moisture-retention curve C3.!1 be used to generate the unsaturated hydraulic conductivity as a function of

moisture content (typically displayed graphically as a curve). Khaleel and Freeman (1995) and Connelly

et al. (1992a, 1992b) have cataloged the moisture retention curves as well as the saturated hydraulic

conductivity collected for the 200 Areas soils. Knowing the unsarurated hydraulic conductivity allows

the travel time for water in the vadose zone to be calculated for various conditions.

Unsaturated hydraulic conductivities may vary by several orders of magnitude depending on moisrure

content. Moisture content measurements in the 200 Area vadose zone have historically ranged widely

from I% to saruration (perched water) from liquid disposal activities, but typically range from 2% to 10%

under ambient conditions. Connelly et al. (1992a, 1992b) summarized hydraulic conductivity

measurements made for 200 Area soils under various moisture contents. For Hanford formation samples

taken in the 200 East Area, vadose zone hydraulic conductivity values at saturation range from about I O..s

to 10 em's, with many of the values falling in the I 0·5 to 10·3 em's range. However, under unsaturated

conditions at a 10% moisture content, hydraulic conductivity values range from about 10·16 to 10·' emfs,

with many of the values fall ing in the I 0·10 to 10·5 rn/s range. Unsaturated hydraulic conductivity values

for Ringold Unit A p:avel samples ranged from less than I 0·19 to 10·10 em's at moisture contents near 10%

and from 10·1 10 10· em's at saturation moisture contents of 39% and 57%, respectively. Ringold lower

mud samples had unsaturated hydraulic conductivities ranging from less than 10·11 at a 10% moisture

content to approximately 10·9 at saturation (57%) (DOE-RL 1997b).

A detailed description for using moisture-retention and hydraulic conductivity curves to calculate travel

times through the vadose zone for steady-state natural recharge conditions is provided in Appendix C of

DOE-RL ( 1996a). The following steps can be used to calculate the time for dissolved contaminants to

travel from a liquid waste site to groundwater (this does not include the rever.;e well sites or liquids other

than water):

l. Use existing geologic maps to determine the lithology at the waste site and establish the thickness

of each geologic unit.

2. Use the estimated natural recharge rate and the existing moisrure retention curves appropriate for

the geologic unit to calculate a steady-state moisture content.

3. Use the moisture content to calculate travel time for water through the geologic unit.

4. Sum the travel times through the different geologic units encountered.

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5. Apply a contaminant-specific retardation factor for each contaminant based on its distribution

coefficient and the density of the soils to obtain the travel time for each contaminant at the waste

site to reach groundwater.

6. For a radionuclide, apply the specific half-life to estimate the percentage of concentration

remaining by the time the radionuclide arrives at groundwater.

Using this methodology, the travel time for dissolved contaminants to reach the groundwater can be

estimated and the potential impact to the groundwater can be evaluated.

FS.0 SURF ACE WATER HYDROLOGY OF THE 200 AREAS

Primary surface water features associated with the Hanford Site are the Columbia and Yakima Rivers.

The 200 Areas are not on a designated flood plain of the Columbia River based on probable maximum

flood data presented by Skaggs and Walters (1981). Calculations indicate that the probable maximum

flood of the Columbia River would result in a flood wave crest to an elevation of 125 m (410 ft) above

ms!. A flood to this elevation would inundate portions of the 100 and 300 Areas along the Columbia

River, but would not be expected to affect more central portions of the Hanford Site including the

200 Areas (DOE-RL 1993b, 1993c).

Cold Creek and its tributary, Dry Creek, are ephemeral streams on the Hanford Site that are within the

Yakima River drainage system. A probable maximum flood (storm frequency of 500 to 1,000 years)

associated with the Cold Creek and Dry Creek drainages southwest of the 200 West Area would inundate

approximately the southwestern quarter of the 200 West Area, but not the 200 East or 200 North Areas.

Based on this result, Skaggs and Walters (1981) stated that flood protection would be required to an

elevation of about 197 m (645 fi) above ms! through the part of the Cold Creek Valley in the vicinity of

the 200 West Area (DOE-RL 1993b, 1993c).

The 216-N-8 Pond (West Lake), 0.8 km (0.5 mi) east of200 North Area, is the only natural lake within

the Hanford Site and the only naturally occurring surface water body within the vicinity of the 200 Areas.

Artificial surface water bodies such as wastewater ponds, cribs, and ditches associated with nuclear fuel

reprocessing and waste disposal activities have also been present in the 200 Areas during the last

5? years, and a few are still active.

Before waste water disposal began at the Hanford Site, West Lake was an intermittent seasonal pond

located in a natural basin at tht: base of Gable Mountain. After the introduction of large quantities of

water to the 216-A-25 Pond l Gable Mountain Pond) 1.2 km to the southwest in 1957, the water table in

the area was elevated sufficiently to provide year-round water to West Lake (DOE-RL 1993a,.l 993c).

West Lake is less than I m (3 ft) deep and extends over approximately 40,000 m2 (10 acres) (DOE 1988).

Bodies of standing water such as ponds ar~ accessible to migratory waterfowl, creating a potential

pathway for the dispersion of contaminants (Neitzel 1997). As the ponds dry up, exposed contaminated

soil can be transported by wind. West Lake is vegetated with riparian plant species.

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Figure F-5. Generalized Hanford Site Geologic Cross-Section (from Hartman and Dresel 1998).

Location of Cross-Section Shown in Figure F-11.

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APPENDIX C (216-B-46) CRIB CONTAMINANT DISTRIBUTION MODEL OF CONTAMINANTS

OF POTENTIAL CONCERN)

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Figure 2-1 l. 216-B-46 Crib Contaminant Distribution Model of Contaminants of Potential Concern.

Jlt•Ul· • fitlU)H

""

216- B- •6 CRIB

SOIL CONTAMINATION

.,...,,OIIOIOtw.,i.o,. CIIA'ofl•OCWlll:41(0 S(O,lllf((

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D 0-18 fT

NllRAl[ 60 3-135 mg/kg

PHOSPHA T[ U - 3 0 mg/kg

STRONTIUM-90 0 6 -2.9 pCi/g

SlJLF AT[ 268- 4 77 mg/•g

RADIUM- 226 < 1 0 pCi/g

V,77,l 18 -49 Fl

~ ANTIMONY-125 22.7-50.4 pCi/g

C(SIUM-137 !>0.1-J64,000 pCi/9

COBAl.f-60 0.685 pCi/9

CYANIDE 3.2-7.1 mg/kg

PHOSPHATE 14-42 mg/kg

NIIRAI[ 316 - 4840 mg/kg

NIIRll[ 2.8- 12.2 mg/kg

PLUTONIUM-238 0.115-6.9 4 pCi/g

PLUTONIUM-239 < 1.0 pCi/9

PLUlONIUU-239/240 3.53- 227 pCi/g

RADIUM- 226 0 872 -2.44 pCi/9

SOOIUM I 590- 4 390 mg/kg

SfRONllUM-90 2.6-353000 pCi/g

SULFATE 26•-1080 mg/kg

T(CHNETIUM- 99 90- 120 pCi/g

TRITIUM 21-53 pCi/g

T01AL URANIUM 4. 1- 35.3 mg/kg

u.s D(PARlMENT or ENERGY DOE flELO orncc. RICHLAND

IIANf'ORO [ UVIRONM(NfAL R(STOA:ATION PROCRAU

D

•9-190 fT

COllALl -60 1.24 - • 03 pCi/9

CYANIC[ 1.5 mg/kg

NITRAI[ 2220-54 70 mg/kg

RAOIUM-226 < 1.01 pCi/g

SODIUM 1370-2• 10 mg/kg

STRONllUM-90 < 1.0 pCi/g

SULfAT[ 362-822 mg/kg

T[CHN[TIUM-99 65- 160 pCi/g

TOTAL URANIUM 2.4 mg/kg

>190 fl

BISMUTH 31.3 mg/kg

COBALT-90 1.•5-1.65 pCi/g

CYANIDE 1.2 mg/kg

NITRATE 3760-3710 mg/kg

S001UM 2750 mg/kg SULf A 1( 722 mg/kg

l(C>tN[TIUM-99 100- 140 pC1/g:l.

- _j RLS DATA I_ C[SIUM-137

? • UNC[RlAINTY

216-8-46 CRIB CONTAMINANT

DISTRIBUTION MODEL


APPENDIX D (GENERAL CONCEPTS OF CONTAMINANT DISTRIBUTION BENEATH 200

AREA DISPOSAL FACILITIES)

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Figure 3-2. General Concepts of Contaminant Distribution Beneath 2~0 Area Disposal Facilities.

Root Zone

Vadose Zone

Aquifer

Waste Disposal ,r-_____ .-A-___ _

I ' Reverse

Well

Groundwater Flow

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