Monitoring Sediment Cap Pore Water and Water Column PAH Concentrations Using Passive Sampling Methods

Courtney Thomas, PhDHDC SETAC Meeting ~ October 7, 2015

Passive Sampling for Cap Performance Assessment

Bulk Sediment Concentrations Poorly correlated with mobility, toxicity & bioavailability

Estimate mobile & available COC w/ Equilibrium Partitioning Theory? Partitioning site specific due to

Large variations in organic matter quality for HOCs (“black carbon”) Redox and other chemical issues for metals and metalloids

Demonstration of in situ SPME PDMS methods for monitoring remediation efforts

Modified Henry Sampler

PDMS sorbent fiberSelective for non-polar compounds≤ ng/L detection with 1 cm resolution

Cap Layer

Contaminated Sediment

Water Column

Large shielded sampler- 36” Small unshielded sampler- 14”

10 µm PDMS210 µm core

West Branch of the Grand Calumet River & Roxana Marsh

COCs: PAHs, PCBs, pesticides & metals Remediation Activities: Sediment removal (~235,000 cu. yds in WBGCR

and ~150,000 cu. yds in Roxana Marsh) & capping with sand-organophilic clay/gravel

Monitoring Activities: SPME porewater/surface water sampling & sediment cores (EPA)

“…appears picturesque, but the river sediment is highly contaminated.” (USEPA, 2009)

Objectives

Define baseline for subsequent cap monitoring ~ May/June 2012 Sampling Event

Establish cap “health” & effectiveness ~ Oct 2013 & Sept 2014 Sampling Event

Approaches Identify general distribution of PAHs Establish the extent of intermixing through the WBGCR sediment cap Identify exceedance of surface water quality comparative screening

criteria at any location with special attention to the near surface (0-4” and 4-8”) porewater concentration

Expected Profiles

0 20 40 60 80 100 1200

10

20

30

40

50

60

70

80

90

Concentration (ng/L)

Dep

th f

rom

Sur

face

(cm

)

Capping layer

“Snapshot in time”

Clean cap layer (low concentrations), sharp increase in concentration below the cap layer

Loc 9: Defined Cap Layer

Cap Boundary Measurements provided by USEPA

0 5000 10000 15000 200000

20

40

60

80

100

Baseline20132014Gravel Layer Lower BoundarySand Layer Lower Boundary

ΣLPAHs (ng/L)

Dep

th (

cm) 0 2000

40006000

800010000

12000

14000

020406080

100

Baseline20132014Gravel Layer Lower BoundarySand Layer Lower Boundary

ΣHPAHs (ng/L)

Dep

th (

cm)

Loc 13: Highest Observed Concentration Levels (NAPL Present)

0 100 200 300 400 500 6000

20

40

60

80

100Baseline20132014Gravel Layer Lower BoundarySand Layer Lower Boundary

Benzo(a)anthracene Concentration (ng/L)

Dep

th (

cm)

0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000

20

40

60

80

100Baseline20132014Gravel Layer Lower Boundary

Anthracene Concentration (ng/L)

Dep

th (

cm)

0 20 40 60 80 100 120 1400

20

40

60

80

100Baseline20132014Gravel Layer Lower BoundarySand Layer Lower Boundary

Benzo(a)pyrene Concentration (ng/L)

Dep

th (

cm)

Expected Cap Thicknesses: 6” (15 cm) Organophilic Clay12” (30 cm) Sand

Actual Cap Thickness:0.3” (0.8 cm) Organophilic Clay1.8” (4.6 cm) Sand10.2” (26 cm) Gravel

Loc 19: Surface Recontamination

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100Baseline20132014Gravel Layer Lower Boundary

Benzo(a)anthracene Concentration (ng/L)

Dep

th (

cm)

0 100 200 300 400 500 6000

20

40

60

80

100Baseline20132014Gravel Layer Lower BoundarySand Layer Lower Boundary

Anthracene Concentration (ng/L)

Dep

th (

cm)

0 2 4 6 8 10 12 14 16 18 200

20

40

60

80

100Baseline20132014Gravel Layer Lower BoundarySand Layer Lower Boundary

Benzo(a)pyrene Concentration (ng/L)

Dep

th (

cm)

WBGCR

determined from comparison of bulk solid PAH concentrations from sediment cores and SPME PDMS concentrations

Black line represents calculated from (Baker et al., 1997) and from cap design (Haley & Aldrich, 2009)

SIDENOTE!

EqP could lead to misrepresentation of risk….underestimates in the cap layer…overestimates in the native sediment layer…better to directly assess porewater concentrations with passive sampler

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 80

1

2

3

4

5

6

7

8

9

10 LTM 1

LTM 2

LTM 3

LTM 4

LTM 5

LTM 6

LTM 7

LTM 8

LTM 9

LTM 10

LTM 11

logKow (L/L)

logK

d (L

/kg)

Top Cap Layer

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 80

1

2

3

4

5

6

7

8

9

10 LTM 2LTM 3LTM 4LTM 5LTM 6LTM 7LTM 8LTM 9LTM 10LTM 11

logKow (L/L)

logK

d (L

/kg)

Native Sediment Layer

11

You can’t have one without the other…

Fred Astaire & Ginger RogersBen & Jerry

Bacon & Eggs

Dolce & GabbanaHolmes & Watson

Ken & BarbieLennon & McCartney

Mickey & Minnie

Passive Samplers & PRCsSalt & Pepper

Snoopy & Charlie Brown Thunder & Lightening

12

Modeling Contaminant Uptake

𝐶𝑡=7𝑑𝑎𝑦𝑠 𝑣𝐶𝑡=30𝑑𝑎𝑦𝑠

𝐶1060 /1000 μ𝑚𝑣𝐶230 /210 μ𝑚

𝑃𝑅𝐶𝑠RD = β

Internal Resistance ModelDual Resistance Model

External Resistance Model

𝑓 𝑠𝑠=[1− exp( 𝑹𝑫𝑡𝐿2 𝐾 𝑓𝑤

2 )erfc( √𝑹𝑫 𝑡𝐿𝐾 𝑓𝑤

)]Absolute Porewater Concentrations

Comparable to Environmental Criteria

Magnitude of Diffusive Flux

=

Or for highly hydrophobic contaminants,

PRC results

COMPARISON TO DIFFUSION ONLY

Processes augmenting molecular diffusion processes at play

100000 1000000 10000000 1000000000.01

0.1

1

10 PRC Data

RD: Best Fit

RD: Diffusion Approx. 1

RD: Diffusion Approx. 2

Kow

RfD

eff

(m2/

d)

0.01

0.1

1

10

100

WBGCR

Kow

RfD

eff

(m2

/d)

EH – Eagle Harbor (tidal)CC – Chattanooga Creek (stagnant)

COMPARISON TOOTHER SITES

0 0.01 0.02 0.03 0.04 0.050

5

10

15

20

25

30

35

103050

Concentration (ng/L)

Dis

tanc

e fr

om u

nder

lyin

g se

d-im

ent (

cm)

Modeling LTM 13

Parameter BAPCo,cap (ng/L) 0Co,sediment (ng/L) 45zcap (cm) 31Cap: Rf (-) 50Cap: Deff (cm2/yr) 5,900Sed: Rf (-) 10,500Sed: Deff (cm2/yr) 27

gravel

sand

clay

Modeled using CapAn, a multi-layer porous media transport model (from Shen and Reible, 2014)

0 0.01 0.02 0.03 0.04 0.050

10

20

30

40

50

Concentration over time (years)

103050

Concentration (ng/L)

Dep

th f

rom

und

erly

ing

sedi

men

t (c

m)

Modeling LTM 13: If Cap had met design…

sand

clay

• Organophilic clay reduces flux substantially

Key Points

Porewater concentration▫ More sensitive indicator of migration in caps than bulk sediment concentration

Sensitive indicator of in-situ mixing processes▫ Can also indicate performance of in-situ treatment▫ Correlates with contaminant availability and bioaccumulation

Polymer sorbents▫ Effective measures of in-situ porewater concentrations

No assumptions of or 100% availability▫ Tradeoff between detection limits and time to equilibrium for different sorbents

With Passive Samplers ▫ Provide a more holistic view of fate and transport ▫ Better chemodynamic model → Better assessment of risk → Better management of

risk

Acknowledgements

WBGCR Team: Paul Schroeder (USACE) Karl Gustavson, Marc Mills, Amy

Mucha, & Heather Williams (USEPA)

Danny Reible (TTU)

Thank you for your attention!

References noted in presentation

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