case study: in situ and ex situ soil segregation€¦ · · 2015-10-19in situ and ex situ soil...

April 2012 | Argonne National Laboratory, USA

Case Study:In Situ and Ex Situ Soil SegregationLisa DurhamEnvironmental Science DivisionApril 26, 2012


IDN and ENVIRONET Training Course

Soil Excavation and Soil Segregation in Open Land AreaSoil Excavation – Removing soil impacted with radioactivity concentrations

greater than the release acceptance criteria as part of site decommissioning

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

In–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 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

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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 Soils are excavated in lifts Logged, systematic gross gamma activity walkovers as excavation

proceeds Determine a gross gamma activity threshold based on the release

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

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Relationship Between Gamma Walkover Data and Cleanup Guideline

0

0.2

0.4

0.6

0.8

1

10K-16K 16K-20K 20K +

counts per minute (x 1000)

frac

tion

of s

ampl

es >

40

pCi/g

Th-

230

4/126

12/1634/40

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Gross Activity Gamma Walkover Surveys Document Soil Status Survey data from a NaI detector

combined with global positioning system 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 excavated 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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Discretionary, Biased Subsurface Sampling Provides Information Outside of the Excavation

Biased sampling from a subsurface soil bore

Biased sampling 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 Overlain by Clean Soil Is A Complicating Factors 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 walkovers 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 Segregation Soils

Soils are transported to a pad and mechanically spread to a one foot (30 cm) thickness

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.

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Systematic Sampling Ex Situ Segregation SoilsSamples for laboratory analyses are collected based on a pre-determined soil volume density (after the gamma walkover survey)

Example 1: Linde SiteTwenty cubic yards of “clean” soils are spread into 1-foot (30-cm) lifts in segregation bins on a pad. A composite sample is collected from 6 bins (120 cubic yards). The soil is staged into 120 cubic yard windrows to await the results from off-site analysis.

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Systematic Sampling Ex Situ Segregation Soils

Example 2: Shallow Land Disposal AreaSoils are sampled at a density equivalent to a MARSSIM Class 1 unit.

‒ Assume a 2,000 m2 area and a 15 cm sampling depth – the volume of ex situ soil is 306 m3 or 400 yd3

‒ For in situ Class 1 units the sample density is one per 100 m2 area or 20 samples, volume of soil per sample is 15 m3 or 20 yd3

244 yd3 pile13 samples~19 yd3 per sample

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“Automatic” Soil Segregation TechnologyMACTEC’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 waste acceptance criteria

– After processing, confirmatory off-site laboratory samples required

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“Automatic Soil” Segregation Process

DetectorAssemblyFeed

Stockpile

Oversize Discharge

Soil Sorting SystemControl Center

Above-CriteriaStockpile

Below-CriteriaStockpile

ScreeningTrommel

Sorting Conveyor

Conveyors

FeedHopper

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Painesville Site Remediation Images

Excavating soil at the Painesville SiteApplying dust control agent to stockpiles

Loading dump trucks for transfer to stockpiles 17



Painesville Site Soil Segregator Images

Loading soil into segregator system

Processed soil exiting system

Survey conveyor with detectors

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“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

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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 Considerations

Applicability of these technologies to site constituents – All 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) and acceptance criteria, so able to use as surrogate for other constituents

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Conclusions Soil segregation methods are successful at minimizing amount of soils from

radioactively contaminated sites requiring offsite disposal

Costs savings due to significantly less soil requiring transport and disposal, and reuse of below-criteria soil to fill excavations

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

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case study: in situ and ex situ soil segregation€¦ · · 2015-10-19in situ and ex situ soil...

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