pfas in soil: considering leaching to groundwater · throughout the presentation, pfoa molecules...

© 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


Soil is a key media for many releases3

Soil

Groundwater



Soil

Groundwater

Soil‐GW ratio



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


Leaching Models6

Dilution/Attenuation

LeachingLeaching Model

Aquifer Model

Groundwater

Soil

Leachate


Leaching Models7


LeachingLeaching Model

Aquifer Model

Groundwater

Soil

LeachateCommon model inputs Hydrogeology Release assumptions


USEPA Soil Screening Level8

*Simplified by assuming nonionizing compound. Details: https://semspub.epa.gov/work/HQ/175232.pdf


Leaching𝒅

Groundwater

Soil

LeachateVariables Chemical‐specific Kd

Henry’s Law H′ Water‐filled soil porosity Dry soil bulk density Dilution/attenuation factor


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


General Phase Partitioning10

constant for known or assumed conditions

AirSolid Liquid

Simplified model Three soil phases Described with partition coefficients Steady‐state, equilibrium


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



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


Key Factors: Soil and water chem, e.g. Organic carbon Co‐contaminants pH & surface charge Major ions

PFOA/PFOS concentration Previous conditions


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


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


Soil Screening Value Calculation15


Groundwater

Soil

Leaching

Leachate

Soil Screening Value

Leaching

Dilution/attenuation

Target GW value


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


GW and Soil Leaching Values17


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


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



10

100

1,000

10,000

100,000

ng/L

or n

g/kg

PFOSGW

PFOSSoil

USEPA RSL Equation

Equation

Equation

Model


Background


0.1

1.0

10.0

100.0

1,000.0

Soil-

GW

Rat

io (L

/kg)

PFOSSoil-GW Ratios

Soil Leaching Basis




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


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]


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.


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


Lab Tests


Consider Empirical and Complex Tools27


Simple

Complex Site Data

Soil data


Models

Generic

GW data

High res.

In‐situ testing(e.g., lysimeter) Column

testing

Kinetic andisotherm studies

Site Specific


Lab Tests

Build Multiple Lines of Evidence28


Simple

Complex Site Data

Soil data


Models

Generic

GW data

High res.

In‐situ testing(e.g., lysimeter) Column

testing

Site Specific


Kinetic andisotherm studies


Soil Analysis Methods29

Soil sample

Solids analysis

SPLP Column testing

Lysimeter

Three phases: Air, Water, Solids



Soil sample

Solids analysis

SPLP Column testing

Lysimeter

Solvent extraction

High lab RLs




Soil sample

Solids analysis

SPLP Column testing

Lysimeter

Water extraction

High liquid‐solid ratio


Solvent extraction

High lab RLs


Solvent extraction

High lab RLs


Soil sample

Solids analysis

SPLP Column testing

Lysimeter

Water extraction


May customize conditions

Lower liquid‐solid ratio



May customize conditions

Lower liquid‐solid ratio


Soil sample

Solids analysis

SPLP Column testing

Lysimeter

Water extraction


Vadose zone liquids

Near field conditions


Solvent extraction

High lab RLs


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


1

10

100

1,000

10,000

Soil NearbyGW

Column SPLP

ng/L or n

g/kg

NDs

ND


Column testing and photographs by XDD Environmental, LLC. ~0.2 L/kg ~20 L/kg


1

10

100

1,000

10,000

Soil NearbyGW

Column SPLP

ng/L or n

g/kg

NDs

ND




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


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

pfas in soil: considering leaching to groundwater · throughout the presentation, pfoa molecules...

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