Danny Reible, University of Texas Research supported by EPA, DOD ESTCP/SERDP, NIH & Industrial Sources 1
PhD Chemical Engineering Caltech Long range transport of atmospheric pollutants 2
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4500 4000 3500 3000 Anacostia River Anacostia River PAHs/PCBs ip (ppb) Ct/fli 2500 2000 1500 1000 500 0 0 500 1000 1500 2000 2500 3000 3500 C sed /f oc (ppb) 4
14000 C t /f lip (ppb) 12000 10000 8000 6000 4000 Anacostia River PAHs y = 1.15x R² = 083 0.83 2000 0 0 2000 4000 6000 8000 10000 K ow C pw (ppb) 5
log BCF 8 7.5 7 6.5 6 5.5 5 4.5 4 BCF = f C t lipid C pw Freshwater oligochaetes PAHs and PCBs Anacostia River sediments R 2 = 0.93 4 5 6 7 8 log K ow In sediments and in deposit-feeding organism (porewater not route of exposure) 6
PAHs B(b)F, B(k)F, BaP in Muscalista Tissue Conce entration (ug/kg) 35 30 25 20 15 10 5 0 PAH Tissue Correlation with Pore Water Concentration (0-7 cm) R² = 0.8723 0.0 1.0 2.0 3.0 4.0 Pore Water Concentration (ng/l) Tissue Conce entration (ug/kg) 35 30 25 20 15 10 5 0 PAH Tissue Correlation with TOC NormalizedSediment Concentration R² = 0.2703 0 5000 10000 15000 20000 25000 30000 Sediment Concentration (ng/g) Single correlation with porewater concentrations works well for all three compounds
Bulk sediment concentration is less useful as indicator of exposure risk 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 Field deployable SPME, capable of measuring porewater with vertical resolution 8
Extraction/centrifugation stability? accuracy? Direct in situ measurement (PE, POM, SPME) Solid phase microextraction (SPME) Sorbent polymerpdms (poly dimethylsiloxane) ys o 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) (EERC) (MIT) (MIT) Porewater pg/l pg/l pg/l pg/l Raw pg/l Porewater TOC corr. pg/l*** Porewater Kd=Kocfoc pg/l 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 141 134 133 NR NR NR NR 1670 138 352 <2090 79 626 16300 5200 4910 149 750* 650 130 1180 15600 6200 9470 132 350* 408 720 866 20000 6100 12100 10
Avoids concerns about contaminant dynamics associated with porewater extraction Provides in situ profile with up to 1 cm vertical resolution depending on detection limits Profiles provide rate/mechanism information Disadvantages Deployment time Analytical requirements Complexity Volatile Losses Depth 0 2 4 6 8 10 12 14 0 20 40 60 80 100 Concentration Advection Bioturbation Diffusion 11
Monitored Natural Recovery Part of all remedies May be an integral part of active remediation Dredging Need to recognize impacts and limitations Triggers a variety of onshore activities Capping Clean sediment/sand layer over contaminated sediment Can be rapidly implemented with minimal impact Need to assess long term protectiveness ti
Reduce risk by: 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 situations 13
Mtl Metals often effectively contained ti by a conventional cap AVS vs. SEM Capping will enhance reducing conditions Sediment Depth (cm) 1 0 1 2 3 4 5 Salt Zn 2+ (ppb) 0 10 20 30 40 AVS > SEM Metals will not be toxic M 2+ + FeS (s) MS (s) + Fe 2+ AVS < SEM 6 7 8 Divalent metals may be toxic 14
Conceptual Model Pre-Cap Post-Cap O 2 FeOOH O 2 O 2 FeOOH FeOOH Methyl mercury SO 2- Methyl SO mercury 2-4 4
Mobility and toxicity generally not redox sensitive Degradation is redox sensitive Hydrocarbon degradation facilitated aerobically Chlorinated organics reductively dechlorinate but many sediment contaminants refractory Dynamics controlled by sorption in cap and 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 by diverting i groundwater flow Contaminant Migration Control Slow contaminant t migration, typically through h sorption related retardation 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 Multiple organoclay layers or organoclay/activated carbon layer for both NAPL and dissolved contaminant control Dissolved contaminants only Activated carbon Placement in mat may be necessary to allow easy placement Placement as amendment also possible Activated carbon more subject to fouling than organoclay
Expect bioavailability reduction proportional to porewater concentration (inversely proportional to partition coefficient, K d ) Equivalent sand cap thickness diffusion/dispersion dominated (u<<1 cm/day) R L = L L dactive ~ active eff active R active sand K K d sand Log K d ~10-4 K oc 0.01K oc f oc K oc ~1-10K oc ~100K oc f oc ~ 0.01 0.05 19
It s about risk, iknot whether h a contaminant is present Benthic community is critical indicator of risk and transport Porewater may be better indicator than bulk sediment There are risks associated with both action and inaction As with other media, containment can be effective Inorganic contaminants often self contained Organic contaminant containment can be enhanced with sorbents Organoclay NAPL, fouling environments Activated Carbon Dissolved organic contaminants 20