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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