Case Study:
In Situ and Ex Situ Soil
Segregation
Lisa Durham
Environmental Science Division
April 26, 2012
April 2012 | Argonne National Laboratory, USA
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Soil Excavation and Soil Segregation in Open Land Area
Soil 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
In Situ Soil Segregation –
–with radioactivity
greater
unrestricted
release as part of site
segregation
that occurs
“in than
place”
of
decommissioning
origin
Ex Situ Soil Segregation –
segregation that occurs “out of place”
or moved from the place of origin
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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Relationship Between Gamma Walkover Data and Cleanup
Guideline
1
fraction of samples
> 40 pCi/g Th-230
34/40
12/16
0.8
0.6
0.4
0.2
4/126
0
10K-16K
16K-20K
20K +
counts per minute (x 1000)
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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In Situ Soil Segregation Confirmed by Soil Sampling
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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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)
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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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.
April 2012 | Argonne National Laboratory, USA
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Systematic Sampling Ex Situ Segregation Soils
Samples for laboratory analyses are collected based on a predetermined soil volume density (after the gamma walkover survey)
Example 1: Linde Site
Twenty 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.
April 2012 | Argonne National Laboratory, USA
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Systematic Sampling Ex Situ Segregation Soils
Example 2: Shallow Land Disposal Area
Soils 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 pile
13 samples
~19 yd3 per sample
April 2012 | Argonne National Laboratory, USA
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“Automatic” Soil Segregation Technology
MACTEC’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
April 2012 | Argonne National Laboratory, USA
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“Automatic Soil” Segregation Process
Feed
Hopper
Soil Sorting System
Control Center
Above-Criteria
Stockpile
Conveyors
Detector
Assembly
Feed
Stockpile
Sorting
Conveyor
Screening
Trommel
Oversize
Discharge
April 2012 | Argonne National Laboratory, USA
Below-Criteria
Stockpile
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Painesville Site Remediation Images
Excavating soil at the Painesville Site
Applying dust control agent to stockpiles
Loading dump trucks for transfer to stockpiles
April 2012 | Argonne National Laboratory, USA
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Painesville Site Soil Segregator Images
Loading soil into segregator system
Survey conveyor with detectors
Processed soil exiting system
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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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
April 2012 | Argonne National Laboratory, USA
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