Remediation Management Issues and Soil Waste Minimization

International Atomic Energy Agency

Technical meeting on the

Disposal of Large Volume of Radioactive Waste

25-28 November 2013 Vienna International Centre

Case Study: Remediation Management Issues and Soil Waste Minimization

Lisa A. Durham Argonne National Laboratory

Soil and groundwater contamination are physically linked, but often programmatically separated

Unresolved disputes in end state assumptions among stakeholders complicate successful project completions

A Number of Management Themes Arise in the Environmental

Remediation Planning

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Contaminated Soil

Plant Foods

Soil Ingestion

Infiltration

Leaching Surface Water Groundwater

Drinking Water

A Number of Environmental Remediation Management

Themes… (cont.) - Remediation

Unexpected “surprises” during remediation consistently drive up project costs and cause project schedule delays

Contractual mechanism issues, a mismatch between contract types and project needs result in poorly performing clean-ups

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Long-duration projects suffer from staff retention, poor maintenance of data, and corporate knowledge loss

Need for defining closure requirements as early in the process as possible – during the remediation to keep work efficient

A Number of Environmental Remediation Management

Themes… (cont.) – Site Closure

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Experience Has Demonstrated Soil Remediation is Filled with

Uncertainty

Removed contaminated soil volumes are often greater than those estimated during the characterization/design phase

- Subsurface contaminated soil – often significant heterogeneity

Complicates:

- Program planning

- Implementation of the remedial action

Soil waste minimization an extremely important cost driver and waste management issue (e.g., volume of soils that require treatment or disposal)

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Characterization During Soil Excavation Remediation -

Segregation in Open Land Area

Soil Excavation – Removal of impacted soils as part of the remediation process

Soil Segregation – A method of separating soils with radioactivity

concentrations greater than the release acceptance criteria from soils with concentrations less than the release acceptance criteria

n

–with radioactivity greater than unrestricted release as part of site decommissioning

In Situ Soil Segregation – segregation that occurs “in place” of origin Ex Situ Soil Segregation – segregation that occurs “out of place” or moved from the place of origin

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Why is Soil Segregation Important?

Excavated soils determined to exceed the release acceptance criteria are generally transported to an off-site facility for disposal

Transportation and off-site disposal of soils are the largest cost elements of

a soils remediation effort costing ~ $200 to > $1,000 per U.S. ton (0.9 metric ton) of soil

A method to reduce the volume of waste requiring off-site shipment and

disposal that can dramatically reduce the overall project costs throughout the remediation lifecycle

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Pre-Excavation Data Sets Result

in Soil Remediation Uncertainty

Available information

– Historical descriptions, aerial photography

– Lab data, field screening data

Large data sets, but often

spatially limited

Incomplete picture

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In Situ Soil Segregation Method – Radionuclides

Systematic gross gamma activity walkover surveys, logged with a global positioning system (GPS) as excavation proceeds

Determine a gross gamma activity threshold based on the release acceptance criteria

Soils are excavated in 30 cm lifts

Soil sampling of excavation areas – walls or slopes and excavation floor

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Gross Activity Gamma Walkover Surveys Document Soil

Status During the Remediation

Survey data from a NaI detector combined with global positioning system (GPS) are loaded into GIS system for analysis

Data used to:

– Provide documentation of the contamination status of soils exposed by the excavation

– Determine current excavation footprints as the excavation proceeds with depth

and

– Provide documentation for the in-situ segregation of the soils below the cleanup criteria

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In Situ Soil Segregation Confirmed by Soil Sampling

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Additional Characterization - Biased Subsurface Sampling

Provides Information Outside of the Excavation

Scan and sample a subsurface soil bore

Scan and sample soil from a test pit

Provide additional data for in situ segregating soil outside or adjacent to the excavation area

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Subsurface Soil Contamination is a Complicating Factor for

In Situ Soil Segregation

Contaminated subsurface soil buried or overlain by clean backfill due to re-grading and construction activities

Contaminated soil surrounding

subsurface infrastructure (pipes)

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Ex Situ Soil Segregation Method

Soils are excavated in lifts

Excavated soil is segregated during removal based on characterization results (gross gamma activity surveys and sampling) as excavation proceeds

Gross gamma activity threshold(s) are determined based on the release acceptance criteria

Soils excavated for ex situ soil segregation are transported to an evaluation area or pad for confirmatory sampling

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Surveying Ex Situ Segregated Soils

Soils are transported to a pad and mechanically spread out in a 30 cm layer for scanning

A gamma walkover survey is performed on the layer of soil

Based on the results of the gamma walkover survey, soil may be classified as contaminated and removed for off-site disposal/or biased samples might be collected for further determination

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Systematic Sampling Ex Situ Segregated Soils

Soil samples are collected and analyzed to demonstrate compliance

Samples collected for laboratory analyses are based on a pre-determined soil volume density

Number of samples generally based on the contaminants of concern

The soil is staged to await the results from laboratory analysis

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“Automatic” Soil Segregation Technology

AMEC’s Orion ScanSortSM Soil Segregation System

– 100% gamma spectroscopy of all soils passing under detectors via conveyors

– System interprets spectroscopy data to determine whether volume of soil exceeds specified Diversion Control Setpoints

– Soil automatically sorted into stockpiles of greater than or less than the release acceptance criteria

– Evaluation of Diversion Control Setpoints over a volume of soil is determined from the derivation of the dose based cleanup criteria

– After processing, confirmatory off-site laboratory samples required

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“Automatic Soil” Segregation Process

Detector

Assembly Feed Stockpile

Oversize Discharge

Soil Sorting System

Control Center

Above-Criteria Stockpile

Below-Criteria Stockpile

Screening Trommel

Sorting Conveyor

Conveyors

Feed

Hopper

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Soil Segregator System Images

Loading soil into segregator system Processed soil exiting system

Survey conveyor with detectors

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Excavating soil at the Site Loading dump trucks for transfer to stockpiles

“Automatic Soil” Segregation Process

Considerations

The Orion Scan Sort System requires a significant volume of throughput soil to be cost effective

Tendency for the remediation to become a “block excavation” resulting in combining soils from the clean cut back walls and clean soil layers with soils above the release criteria

Large stock piles of soil – dust control

Equating the system’s Diversion Control Setpoints, a concentration per volume to an acceptance criteria, a concentration per area

Material must be sufficiently flowable

– Wet, sticky clay soils and large debris pose difficulties

– Extra time to allow soils to dry prior to processing

– Extra equipment to screen and break up soils and other debris

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Planning for Soil Waste Minimization: Comparison of

In Situ and Ex Situ Soil Segregation

In Situ Advantages ‒ Minimal soil handling ‒ A parcel of land for ex situ surveys, sampling, and stockpiling is not required

In Situ Disadvantages ‒ Difficult when the contaminated soil is buried or overlain by clean soil ‒ Possible tendency to excavate or remove the soil below the acceptance criteria

Ex Situ Advantages ‒ Cost-effective process for removing unimpacted soils overlying contaminated

soil lenses ‒ Soils determined to be clean can be used as backfill minimizing the expense of

offsite backfill materials

Ex Situ Disadvantages ‒ Significant amount of soil handling i.e., soil from the excavation to a soil pile,

from the soil pile to an evaluation/staging area, often the soils are stockpile awaiting offsite sample results

‒ Additional dust-control measures are generally required

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Soil Segregation Method Considerations

Applicability of these technologies to site constituents – methods depend on being able to measure gamma emitting radionuclides

– Radium-226, cesium-137, uranium-238 and thorium-232 are easily and directly measurable by gamma spectroscopy

– Thorium-230 and other uranium isotopes are NOT easily measurable by

gamma spectroscopy – At times there may be a strong correlation between a measurable

radionuclide (e.g., Ra-226) so able to use as surrogate for other constituents

– Chemical contaminants are complicated, surrogate needed or increased soil sampling required

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Throughout the Remediation Life Cycle

Soil Segregation Can Minimize Waste Volumes

Soil segregation methods achieve cost savings due to significantly less soil requiring transport and disposal

Clean segregated soils can be used to backfill the excavations reducing the costs of buying and testing clean fill

Segregation methods as part of the remediation promote environmental stewardship and sustainability

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