© Sanborn, Head & Associates, Inc.
PFAS in Soil: Considering Leaching to Groundwater
NEWMOA Webinar July 29, 2020
Harrison Roakes, PE
© Sanborn, Head & Associates, Inc.†
Outline Fundamentals and background Leaching‐based screening values Anthropogenic background Screening approaches
The focus of this presentation is on PFOA and PFOS. PFAS, including precursors to PFOA and PFOS, have
widely ranging chemistries and properties.
2
© Sanborn, Head & Associates, Inc.†
Soil is a key media for many releases3
Soil
Groundwater
© Sanborn, Head & Associates, Inc.†
Soil is a key media for many releases4
Soil
Groundwater
Soil‐GW ratio
© Sanborn, Head & Associates, Inc.†
Soil is a key media for many releases5
1. Anderson, Adamson, and Stroo. (2019). Journal of Contaminant Hydrology, 220 59‐65: https://doi.org/10.1016/j.jconhyd.2018.11.011
Soil
Groundwater
U.S. Air Force sites histogram of Soil‐GW Ratios1
324 AFFF sites Source‐zone soil and GW 8 orders of magnitude
variation
© Sanborn, Head & Associates, Inc.†
Leaching Models6
Dilution/Attenuation
LeachingLeaching Model
Aquifer Model
Groundwater
Soil
Leachate
© Sanborn, Head & Associates, Inc.†
Leaching Models7
Dilution/Attenuation
LeachingLeaching Model
Aquifer Model
Groundwater
Soil
LeachateCommon model inputs Hydrogeology Release assumptions
© Sanborn, Head & Associates, Inc.†
USEPA Soil Screening Level8
*Simplified by assuming nonionizing compound. Details: https://semspub.epa.gov/work/HQ/175232.pdf
Dilution/Attenuation
Leaching𝒅
Groundwater
Soil
LeachateVariables Chemical‐specific Kd
Henry’s Law H′ Water‐filled soil porosity Dry soil bulk density Dilution/attenuation factor
© Sanborn, Head & Associates, Inc.†
PFOA Chemical Structure
Fluorocarbon tail Hydrophobic Lipophobic
9
Throughout the presentation, PFOA molecules are illustrated. These illustrations are not to scale, and numerous other details are not shown, including counterions, water molecules, and solids molecules.
Functional group Hydrophilic High solubility Low volatility
FF F F F
F F F F F F F
F FF
O
O(–)
AirWater
Ionic skeletal and 3D models
Branched isomer models
Surfactant
FF F F FF F F O
O(–)
F F FF F F F
© Sanborn, Head & Associates, Inc.†
General Phase Partitioning10
constant for known or assumed conditions
AirSolid Liquid
Simplified model Three soil phases Described with partition coefficients Steady‐state, equilibrium
© Sanborn, Head & Associates, Inc.†
PFOA/PFOS Phase Partitioning11
1. Li, Oliver, and Kookana. (2018). Science of the Total Environment, 628‐629 110‐120: https://doi.org/10.1016/j.scitotenv.2018.01.167
Surfactant behavior
(at higher conc.)
AirSolid Liquid
Electrostatic interactions
Hydrophobic sorption
Li et al. (2018)1
Not just Kd = Koc × foc
© Sanborn, Head & Associates, Inc.†
PFOA/PFOS Phase Partitioning12
1. Brusseau, Yan, Van Glubt, Wang, Chen, Lyu, Dungan, Carroll, Holguin. (2019). Water Research, 148 41‐50: https://doi.org/10.1016/j.watres.2018.10.0352. Guo, Zeng, and Brusseau. (2020). Water Resources Research, 57: https://doi.org/10.1029/2019WR026667
AirWater
AirSolid Liquid
LiquidAir
Brusseau et al. (2019)1 and Guo et al. (2020)2 >80% total retention Greater retention in sand vs. finer‐grains
Dr. Linda Abriola SERDP/ESTCP air‐water and NAPL‐water interface
partitioning presentation:https://www.youtube.com/user/SE
RDPESTCP
© Sanborn, Head & Associates, Inc.†
Key Factors: Soil and water chem, e.g. Organic carbon Co‐contaminants pH & surface charge Major ions
PFOA/PFOS concentration Previous conditions
PFOA/PFOS Phase Partitioning13
For more information, see ITRC PFAS Technical and Regulatory Guidance Document:https://pfas‐1.itrcweb.org/5‐environmental‐fate‐and‐transport‐processes/#5_2
nonlinear
hysteresis
Not to scale
© Sanborn, Head & Associates, Inc.†
Field Conditions Phase Partitioning Hydraulics Microscale Macroscale
Kinetics/mass transfer
Field conditions: Approach equilibrium Complex/variable Heterogeneous Cannot replicate in a lab
Delicate Disturbed by sampling
14
© Sanborn, Head & Associates, Inc.†
Soil Screening Value Calculation15
Dilution/Attenuation
Groundwater
Soil
Leaching
Leachate
Soil Screening Value
Leaching
Dilution/attenuation
Target GW value
© Sanborn, Head & Associates, Inc.†
GW and Soil Leaching Values16
1. “GW Values” and “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.2. “GW Values” and “Soil to GW Protection Values” were paired based on the availability of data. The soil values were not necessarily developed based on protecting against the indicated GW values.
10
100
1,000
10,000
100,000
1,000,000
10,000,000
ng/L
or n
g/kg
PFOAGW
PFOASoil
PFOSGW
PFOSSoil
USEPA RSLdirect contact‐based values
© Sanborn, Head & Associates, Inc.†
GW and Soil Leaching Values17
1. “GW Values” and “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.2. “GW Values” and “Soil to GW Protection Values” were paired based on the availability of data. The soil values were not necessarily developed based on protecting against the indicated GW values.
10
100
1,000
10,000
100,000
1,000,000
10,000,000
ng/L
or n
g/kg
PFOAGW
PFOASoil
PFOSGW
PFOSSoil
USEPA RSLdirect contact‐based values
USEPA RSL leaching calculation
Soil‐GW ratio = 0.95
Ratio = 0.43
© Sanborn, Head & Associates, Inc.†
10
100
1,000
10,000
100,000
ng/L
or n
g/kg
PFOSGW
PFOSSoil
USEPA RSL Equation
Equation
Equation
Model
Lab detection limits
Background
Detect triggers SPLP
0.1
1.0
10.0
100.0
1,000.0
Soil-
GW
Rat
io (L
/kg)
PFOSSoil-GW Ratios
Soil Leaching Basis
PFOS Soil Leaching Soil‐GW Ratios18
1. “GW Values” and “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.2. “GW Values” and “Soil to GW Protection Values” were paired based on the availability of data. The soil values were not necessarily developed based on protecting against the indicated GW values.
© Sanborn, Head & Associates, Inc.†
10
100
1,000
10,000
100,000
ng/L
or n
g/kg
PFOSGW
PFOSSoil
USEPA RSL Equation
Equation
Equation
Model
Lab detection limits
Background
Detect triggers SPLP
0.1
1.0
10.0
100.0
1,000.0
Soil-
GW
Rat
io (L
/kg)
PFOSSoil-GW Ratios
Soil Leaching Basis
PFOS Soil Leaching Soil‐GW Ratios19
1. “GW Values” and “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.2. “GW Values” and “Soil to GW Protection Values” were paired based on the availability of data. The soil values were not necessarily developed based on protecting against the indicated GW values.
© Sanborn, Head & Associates, Inc.†
10
100
1,000
10,000
100,000
ng/L
or n
g/kg
PFOSGW
PFOSSoil
USEPA RSL Equation
Equation
Equation
Model
Lab detection limits
Background
Detect triggers SPLP
0.1
1.0
10.0
100.0
1,000.0
Soil-
GW
Rat
io (L
/kg)
PFOSSoil-GW Ratios
Soil Leaching Basis
PFOS Soil Leaching Soil‐GW Ratios20
1. “GW Values” and “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.2. “GW Values” and “Soil to GW Protection Values” were paired based on the availability of data. The soil values were not necessarily developed based on protecting against the indicated GW values.
© Sanborn, Head & Associates, Inc.†
10
100
1,000
10,000
100,000
ng/L
or n
g/kg
PFOSGW
PFOSSoil
USEPA RSL Equation
Equation
Equation
Model
Lab detection limits
Background
Detect triggers SPLP
0.1
1.0
10.0
100.0
1,000.0
Soil-
GW
Rat
io (L
/kg)
PFOSSoil-GW Ratios
Soil Leaching Basis
PFOS Soil Leaching Soil‐GW Ratios21
1. “GW Values” and “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.2. “GW Values” and “Soil to GW Protection Values” were paired based on the availability of data. The soil values were not necessarily developed based on protecting against the indicated GW values.
© Sanborn, Head & Associates, Inc.†
10
100
1,000
10,000
100,000
ng/L
or n
g/kg
PFOSGW
PFOSSoil
USEPA RSL Equation
Equation
Equation
Model
Lab detection limits
Background
Detect triggers SPLP
0.1
1.0
10.0
100.0
1,000.0
Soil-
GW
Rat
io (L
/kg)
PFOSSoil-GW Ratios
Soil Leaching Basis
PFOS Soil Leaching Soil‐GW Ratios22
1. “GW Values” and “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.2. “GW Values” and “Soil to GW Protection Values” were paired based on the availability of data. The soil values were not necessarily developed based on protecting against the indicated GW values.
© Sanborn, Head & Associates, Inc.†
10
100
1,000
10,000
0 2 4 6 8 10
ng/L or n
g/kg PFO
A
Time (years)
Initial soil concentration = 1,000 ppt PFOA
Initial leachate concentration ~ 2,300 ppt PFOA
relatively fast leaching may lead to rapid depletion of PFAS in soil
Depletion Model Check23
Basic model assumptions include: 1st-order, USEPA RSL leaching; complete mixing, steady-state hydraulics; 0.5 meters of soil, 0.18 meters per year infiltration
© Sanborn, Head & Associates, Inc.†
PFAS in Background Vermont Shallow Soils24
Source, University of Vermont and Sanborn Head: https://anrweb.vt.gov/PubDocs/DEC/PFOA/Soil‐Background/PFAS‐Background‐Vermont‐Shallow‐Soils‐03‐24‐19.pdf
66 locations, 0‐6” depth
Parks, grass areas, forests
13 PFCAs & 4 PFSAs
ΣPFAS (ng/kg) >5,000 [n = 8]2,000‐5,000 [n = 23]1,000‐2,000 [n = 25<1,000 [n = 10]
© Sanborn, Head & Associates, Inc.†
370
685
1,300
3,580
10
100
1,000
10,000
100,000
ng/k
g
PFOSVT Data
PFOAVT Data
PFOSScreening Values
PFOAScreening Values
median
95th percentile
median
95th percentile
Soil Leaching Values & VT Background25
1. The intent of this aggregate comparison is to contextualize the regulatory and guidance values. The individual data in this study were not collected for comparison to regulatory or guidance values and should not be used for that purpose. 2. “Soil to GW Protection Values” were largely obtained from the ITRC fact sheet spreadsheet updated June 2020 (https://pfas-1.itrcweb.org/fact-sheets/). Some proposed or draft values, which may be on-hold or now replaced with updated values, are also included.
© Sanborn, Head & Associates, Inc.†
Common Tools Rely on Key Assumptions and Interpretation
26
Empirical Theoretical
Simple
Complex Site Data
Soil data
Paired Soil / GW data
Lab Tests Models
Generic
GW data
Single‐point leaching
© Sanborn, Head & Associates, Inc.†
Lab Tests
Single‐point leaching
Consider Empirical and Complex Tools27
Empirical Theoretical
Simple
Complex Site Data
Soil data
Paired Soil / GW data
Models
Generic
GW data
High res.
In‐situ testing(e.g., lysimeter) Column
testing
Kinetic andisotherm studies
Site Specific
© Sanborn, Head & Associates, Inc.†
Lab Tests
Build Multiple Lines of Evidence28
Empirical Theoretical
Simple
Complex Site Data
Soil data
Paired Soil / GW data
Models
Generic
GW data
High res.
In‐situ testing(e.g., lysimeter) Column
testing
Site Specific
Single‐point leaching
Kinetic andisotherm studies
© Sanborn, Head & Associates, Inc.†
Soil Analysis Methods29
Soil sample
Solids analysis
SPLP Column testing
Lysimeter
Three phases: Air, Water, Solids
© Sanborn, Head & Associates, Inc.†
Soil Analysis Methods30
Soil sample
Solids analysis
SPLP Column testing
Lysimeter
Solvent extraction
High lab RLs
Three phases: Air, Water, Solids
© Sanborn, Head & Associates, Inc.†
Soil Analysis Methods31
Soil sample
Solids analysis
SPLP Column testing
Lysimeter
Water extraction
High liquid‐solid ratio
Three phases: Air, Water, Solids
Solvent extraction
High lab RLs
© Sanborn, Head & Associates, Inc.†
Solvent extraction
High lab RLs
Soil Analysis Methods32
Soil sample
Solids analysis
SPLP Column testing
Lysimeter
Water extraction
High liquid‐solid ratio
May customize conditions
Lower liquid‐solid ratio
Three phases: Air, Water, Solids
© Sanborn, Head & Associates, Inc.†
May customize conditions
Lower liquid‐solid ratio
Soil Analysis Methods33
Soil sample
Solids analysis
SPLP Column testing
Lysimeter
Water extraction
High liquid‐solid ratio
Vadose zone liquids
Near field conditions
Three phases: Air, Water, Solids
Solvent extraction
High lab RLs
© Sanborn, Head & Associates, Inc.†
PFOA Atmospheric Deposition Case Study34
Column testing and photographs by XDD Environmental, LLC.
1
10
100
1,000
10,000
Soil NearbyGW
Column SPLP
ng/L or n
g/kg
NDs
ND
~0.2 L/kg ~20 L/kg
© Sanborn, Head & Associates, Inc.†
1
10
100
1,000
10,000
Soil NearbyGW
Column SPLP
ng/L or n
g/kg
NDs
ND
PFOA Atmospheric Deposition Case Study35
Column testing and photographs by XDD Environmental, LLC. ~0.2 L/kg ~20 L/kg
© Sanborn, Head & Associates, Inc.†
1
10
100
1,000
10,000
Soil NearbyGW
Column SPLP
ng/L or n
g/kg
NDs
ND
PFOA Atmospheric Deposition Case Study36
Column testing and photographs by XDD Environmental, LLC. ~0.2 L/kg ~20 L/kg
© Sanborn, Head & Associates, Inc.†
1
10
100
1,000
10,000
Soil NearbyGW
Column SPLP
ng/L or n
g/kg
NDs
ND
PFOA Atmospheric Deposition Case Study37
Column testing and photographs by XDD Environmental, LLC. ~0.2 L/kg ~20 L/kg
© Sanborn, Head & Associates, Inc.†
1
10
100
1,000
10,000
Soil NearbyGW
Column SPLP
ng/L or n
g/kg
NDs
ND
PFOA Atmospheric Deposition Case Study38
Column testing and photographs by XDD Environmental, LLC. ~0.2 L/kg ~20 L/kg
© Sanborn, Head & Associates, Inc.†
1
10
100
1,000
10,000
Soil NearbyGW
Column SPLP
ng/L or n
g/kg
NDs
ND
PFOA Atmospheric Deposition Case Study39
Column testing and photographs by XDD Environmental, LLC. ~0.2 L/kg ~20 L/kg
© Sanborn, Head & Associates, Inc.†
Normalized to Soil Dry Weight40
1
10
100
1,000
10,000
Soil SPLP Column
ng/kg
NDs
ND
0
1,000
2,000
3,000
4,000
Soil SPLP Column
ng/kg
NDs
ND
© Sanborn, Head & Associates, Inc.†
SummaryLeaching Wide‐ranging field data Default models not built for PFOA/PFOSLeaching‐Based Screening Values Typically lower than direct contact‐based values Variety of methods and large range of valuesAnthropogenic Background PFOA and PFOS present in many background soils Lower leaching‐based screening values at or below VT
background Background leaching values not knownScreening Approaches Underlying assumptions for interpretation are important Consider more empirical and complex tools Multiple lines of evidence
41
[ Boston, MA | Burlington, VT | Concord, NH | Denver, CO | Philadelphia, PA | Westford, MA ]
†This presenta on may contain copyrighted material. Typically, cita ons are provided for informa on purposes for informa on and data used from third parties. This educational presentation is a summary overview and does not replace professional judgment. Please contact the authors prior to any use, copying, or distributing of the materials.
Questions and Comments Appreciated!
42
Thank you to collaborators, including:ITRC TeamSteve Zemba, PhD, PEChip Crocetti, PhD, PGRuss Abell, PG, LSPWenyu Zhu, PhDAppala Raju Badireddy, PhDScott Crawford, PELaurel Crawford
[email protected] 603.415.6156M 207.337.3662
Harrison Roakes, PE