Danny Reible, University of Texas bl f Research supported by EPA, - - PowerPoint PPT Presentation

bl f Danny Reible, University of Texas Research supported by EPA, DOD‐ESTCP/SERDP, NIH & Industrial Sources

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PhD Chemical Engineering Caltech

Long range transport of atmospheric pollutants

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3

4500 3500 4000 4500

Anacostia River

Anacostia River PAHs/PCBs

2500 3000

ip (ppb)

1000 1500 2000 Ct/fli 500 1000 500 1000 1500 2000 2500 3000 3500 500 1000 1500 2000 2500 3000 3500 Csed/foc (ppb)

4

14000

y = 1.15x R² = 0 83

10000 12000

Anacostia River PAHs

R = 0.83

6000 8000

lip (ppb)

2000 4000

Ct/fl

2000 2000 4000 6000 8000 10000

K C (ppb)

5

KowCpw (ppb)

7.5 8

t

C BCF =

6 6.5 7 BCF

lipid pw

BCF f C =

5 5.5 6 log B

Freshwater oligochaetes PAHs and PCBs Anacostia River sediments

4 4.5 4 5 6 7 8

Anacostia River sediments R2= 0.93

log K ow

In sediments and in deposit-feeding organism (porewater not route of exposure) 6

PAH B(b)F B(k)F B P i M li t

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PAH Tissue Correlation with Pore Water Concentration (0-7 cm)

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PAH Tissue Correlation with TOC NormalizedSediment Concentration

PAHs – B(b)F, B(k)F, BaP in Muscalista

R² = 0.8723

10 15 20 25 30

entration (ug/kg)

R² = 0.2703

10 15 20 25 30

entration (ug/kg)

5 10 0.0 1.0 2.0 3.0 4.0

Tissue Conce Pore Water Concentration (ng/L)

5 10 5000 10000 15000 20000 25000 30000

Tissue Conce Sediment Concentration (ng/g)

Single correlation with porewater concentrations works well for all three compounds Single correlation with porewater concentrations works well for all three compounds

lk d l f l d f

Bulk sediment concentration is less useful as indicator of

exposure‐risk i b d

Porewater concentration is better indicator

(even for active benthic uptake by ingestion)

Growing ability to measure porewater with solid phase

micro extraction (SPME) and other passive approaches

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Field deployable SPME, capable of measuring porewater with vertical resolution

Extraction/centrifugation – stability? accuracy? Direct in‐situ measurement (PE POM SPME) Direct in situ measurement (PE, POM, SPME) Solid phase microextraction (SPME)

Sorbent polymer PDMS (poly‐dimethylsiloxane) So be t po y e S (po y d et y s o a e) 30 µm fiber on 110 µm core (13.6 µL PDMS/m of fiber) 10 µm on 230 µm core (7 µL /m) 30 µm on 1 mm core (94 µL /m)

ng/L detection with 1 cm resolution Profiling field deployable system May require 7‐30 days to equilibrate

x

PCB SPME POM PE** Air Bridge Extracted Extracted Predicted Congener (UT) pg/L (EERC) pg/L (MIT) pg/L (MIT) pg/L Porewater Raw pg/L Porewater TOC corr. pg/L*** Porewater Kd=Kocfoc pg/L

101 902 <915 230 602 5260 2400 6480 101 902 <915 230 602 5260 2400 6480 87 125 124 NR NR NR NR 788 110 320 492 410 433 2850 1800 2340 95 880* 1460 330 667 3300 1900 8400 151 303 101 130 365 4820 670 5680 153 347 416 NR NR NR NR 5440 153 347 416 NR NR NR NR 5440 141 134 133 NR NR NR NR 1670 138 352 <2090 79 626 16300 5200 4910 * 6 8 6 6

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149 750* 650 130 1180 15600 6200 9470 132 350* 408 720 866 20000 6100 12100

Avoids concerns about contaminant dynamics

y associated with porewater extraction

Provides in‐situ profile with up to 1 cm vertical

p p resolution depending on detection limits

Profiles provide rate/mechanism information

20 40 60 80 100

Concentration

p /

Disadvantages

Deployment time

Depth

2 4 6 8

Advection Bioturbation

Deployment time Analytical requirements Complexity

10 12 14

Diffusion

p y Volatile Losses

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d l

Monitored Natural Recovery

Part of all remedies May be an integral part of active remediation remediation

Dredging

Need to recognize impacts and limitations limitations Triggers a variety of onshore activities

Capping

Clean sediment/sand layer over Clean sediment/sand layer over contaminated sediment Can be rapidly implemented with minimal impact N d t l t t ti Need to assess long‐term protectiveness

Reduce risk by:

Stabilizing sediments Stabilizing sediments Physically isolating sediment contaminants Reducing contaminant flux to benthos and water column

Sand surprisingly effective

for strongly solid associated contaminants

“Active caps” for other

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situations

M t l ft ff ti l t i d b ti l

Metals often effectively contained by a conventional cap AVS vs. SEM‐ Capping will enhance reducing conditions

SEM

>

AVS

‐1 10 20 30 40

Salt Zn2+(ppb)

Metals will not be toxic M2+ + FeS(s) → MS(s) + Fe2+

1 2 3 Depth (cm)

SEM

<

AVS

Divalent metals may be

3 4 5 6 Sediment D

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Divalent metals may be toxic

7 8

Conceptual Model

Pre-Cap Post-Cap

F OOH O2 O2 O2 FeOOH FeOOH FeOOH SO4

2-

Methyl mercury

SO4

2-

Methyl mercury

Mobility and toxicity generally not redox sensitive Degradation is redox sensitive

g

Hydrocarbon degradation facilitated aerobically Chlorinated organics reductively dechlorinate but many g y y sediment contaminants refractory

Dynamics controlled by sorption in cap and

y y p p groundwater upwelling

Substantial groundwater upwelling of organics or potentially mobile NAPL most common reasons to consider active caps

Permeability Control

Discourage upwelling through contaminated sediment b di i d fl by diverting groundwater flow

Contaminant Migration Control

Sl t i t i ti t i ll th h Slow contaminant migration, typically through sorption related retardation

Contaminant Degradation Aid Contaminant Degradation Aid

Less well developed, contaminant specific but designed to encourage contaminant fate processes

NAPL present ‐ Organoclays

Capacity of O(1 g NAPL/g organoclay) Placement within a laminated mat for residual NAPL or to allow replacement if capacity exceeded Placement in bulk for significant NAPL volumes Placement in bulk for significant NAPL volumes Multiple organoclay layers or organoclay/activated carbon layer for both NAPL and dissolved contaminant control

l d l d b

Dissolved contaminants only ‐ Activated carbon

Placement in mat may be necessary to allow easy placement Placement as amendment also possible Placement as amendment also possible Activated carbon more subject to fouling than organoclay

– Expect bioavailability reduction proportional to – Expect bioavailability reduction proportional to porewater concentration (inversely proportional to partition coefficient, Kd) – Equivalent sand cap thickness – diffusion/dispersion q p p dominated (u<<1 cm/day)

~

active

d active eff active active

K R L L L R K =

sand

ff sand d

R K

~ 10-4 Koc 0.01Koc focKoc ~ 100Koc Log Kd ~ 1-10Koc

f

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foc ~ 0.01‐0.05

b i k h h It’s about risk, not whether a contaminant is present Benthic community is critical indicator of risk and transport transport Porewater may be better indicator than bulk sediment There are risks associated with both action and inaction There are risks associated with both action and inaction As with other media, containment can be effective

Inorganic contaminants often “self‐contained” Inorganic contaminants often self contained Organic contaminant containment can be enhanced with sorbents

Organoclay – NAPL, fouling environments Activated Carbon – Dissolved organic contaminants

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