An Innovative 3-Dimensional Model to Develop and Implement Soil Clean-up Criteria

Jeffrey W. LivelyAmec Foster Wheeler

IAEA Technical Meeting| June 13-17, 2016 | Vienna, Austria

Compliance Paradigm vs. Project Reality

• Derivation of concentration-based remedial

action limits assume that contaminants are

optimally and continuously available for

exposure.

• Contaminants are rarely optimally or

continuously available for exposure.

Compliance Paradigm vs. Project Reality

• Risk assessments commonly assume that

contaminants are homogeneously

distributed in the soil column.

• Contaminants are rarely homogeneously

distributed in the soil column.

Compliance Paradigm vs. Project Reality

• Compliance measurement strategies

commonly adopt point-by-point tabular

comparisons against single-point

compliance thresholds.

• True exposure risk is a combination of:

►Contaminant Severity [Concentration]

►Contaminant Significance [Volume]

►Probability of Encountering [Position].

The Solution

3-D Subsurface Soil Model

3-Dimensional Mathematical Model

• Respects traditional application of risk-derived cleanup standards for soils

• Accounts for spatial and volumetric contributors to risk• Provides less restrictive remediation targets in favor of

rigorous and satisfying assessments of contaminant distribution

Model Architecture

12

65

4

3

1. The subsurface soil remedial goal is based on the

assumption the contaminant [in the subsurface] may be

excavated some day and brought to the surface where

exposure occurs.

2. Mixing of the contaminant [in subsurface soil layers] will

occur during excavation.

3. Subsurface soil remedial goals and mixing volumes

should be based on an acceptable site-specific risk

assessment.”

Concepts / Criteria

Compliance is assessed using core sampling of the impacted soil column

4. Number of cores is determined in order to achieve statistically significant results

5. Samples are collected from core segments homogenized over a soil thickness that is consistent with the assumptions made in the risk assessment

6. Core hole grid spacing should be adjusted (condensed), if necessary, to account for the likely presence of locally significant elevated volumes/concentrations of contaminants.

Concepts / Criteria

Traditional 2-Dimensional Sample Array

3-Dimensional Sample Array

Criterion #1

The subsurface soil remedial goal is based on the assumption the contaminant [in the subsurface] may be excavated some day and brought to the surface where exposure occurs.

Conceptual Geometry Transformation Associated with Excavation

Conceptual Geometry Transformation Associated with Excavation

Conceptual Geometry Transformation Associated with Excavation

Conceptual Geometry Transformation Associated with Excavation

Conceptual Geometry Transformation Associated with Excavation

Criterion #2

Mixing of the contaminant [in subsurface soil layers] will occur during excavation.

X Y

X

X

X

Y

Y

Y

X

YFactorMixing =

Mixing Factors

Subsurface soil remedial goals and mixing volumes should be based on an acceptable site-specific risk assessment.”

Criterion #3

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0 100 200

Vo

lum

e F

ac

tor

Volume (m3)

Volume Factor Curvefor a Single Contaminant

( ) ( )SurfaceScalingSubsurface RGkRG *=

( ) ( )MixVolScaling kkk *=

Calculating Remedial Goalsfor the Subsurface

A Solution in Continuum

Criterion #4

The number of cores is determined in order to achieve statistically significant results

Parameters of Statistical Test

LBGR)-(DCGL

= /sσ

σ∆

)0.5 - p 4(Sign

) Z + Z( = N

2

2

-1-1 βα

Cores Distributed on Regular Gridn = Statistically Significant Number

Samples are collected from core segments homogenized over a soil thickness that is consistent with the assumptions made in the risk assessment.

It is not acceptable to average contaminant concentrations over an arbitrary soil thickness

Criterion #5

Vertical Demarcation of the Soil Column

• First Order Demarcation

• Second Order Demarcation

Criterion #6

Core hole grid spacing should be adjusted (condensed), if necessary, to account for the likely presence of locally significant elevated volumes/concentrations of contaminants.

Adjusting Corehole Frequency

4

8

5

21

Consider the following example

Identify an Upper

Percentile Concentration

e.g., 90th Percentile

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 100 200

Co

nc

en

tra

tio

n

[pp

m]

Volume (m3)

Volume Factor Curvefor a Single Contaminant

The upper percentile

concentration estimate

is 40 ppmA concentration of

40 ppm intersects

the Volume Factor

curve at a volume

of 50 m3

Demonstrating Compliance w/ Subsurface Remedial Goals

Compliance Metrics

RG-W: The survey unit wide area

average.

RG-LAA: The 3-dimensional local area

average.

RG-EMC: The maximum permissible

mean concentration in a single

sample grid volume

RG-W

RG-Local Area Average (LAA)

A

2

A

1

B

2

RG-Local Area Average (LAA)

A

3

A

2

B

2

B

3

B

3

B

2

C

2

C

3

B

2

B

1

C

1

C

2

A

2

A

1

B

1

B

2

A

3

A

2

A

1

B

1

B

2

B

3

C

1

C

2

C

3

RG-Local Area Average (LAA)

A

1

B

2

A

1

B

2

RG-EMC

The elevated measurement comparison (EMC) compliance metric considers the volumetric average in a single cell.

It is a simple point-by-point comparison.

Mathematical Model &Calculations

Thank You!