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

Danny Reible, University of Texas bl f 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 4500 Anacostia River 4000 Anacostia River 3500 PAHs/PCBs 3000 ip (ppb) 2500 C t /f li 2000 1500 1000 1000 500 0 0 0 500 500 1000 1000 1500 1500 2000 2000 2500 2500 3000 3000 3500 3500 C sed /f oc (ppb) 4

14000 12000 Anacostia River PAHs y = 1.15x 10000 R² = 0 83 R = 0.83 lip (ppb) 8000 6000 C t /f l 4000 2000 2000 0 0 2000 4000 6000 8000 10000 K ow C pw (ppb ) (ppb ) K C 5

8 7.5 C BCF = = t BCF 7 f C lipid pw 6.5 BCF log B 6 6 5.5 Freshwater oligochaetes PAHs and PCBs 5 Anacostia River sediments Anacostia River sediments 4.5 R 2 = 0.93 4 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 PAH B(b)F B(k)F B P i M li t PAH Tissue Correlation with Pore Water PAH Tissue Correlation with TOC Concentration (0-7 cm) NormalizedSediment Concentration 35 35 R² = 0.8723 entration (ug/kg) 30 entration (ug/kg) 30 25 25 20 20 15 15 R² = 0.2703 10 10 10 10 Tissue Conce Tissue Conce 5 5 0 0 0.0 1.0 2.0 3.0 4.0 0 5000 10000 15000 20000 25000 30000 Pore Water Concentration (ng/L) 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

� Bulk sediment concentration is less useful as indicator of lk d l f l d f exposure ‐ risk � Porewater concentration is better indicator i b d ( 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) � 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 µ m core (13.6 µ L PDMS/m of fiber) � 10 µ m on 230 µ m core (7 µ L /m) � 30 µ m on 1 mm core (94 µ L /m) � ng/L detection with 1 cm resolution � Profiling field deployable system x � May require 7 ‐ 30 days to equilibrate

PCB SPME POM PE** Air Bridge Extracted Extracted Predicted Congener (UT) (EERC) (MIT) (MIT) Porewater Porewater Porewater pg/L pg/L pg/L pg/L Raw pg/L TOC corr. Kd=Kocfoc pg/L*** pg/L 101 101 902 902 <915 <915 230 230 602 602 5260 5260 2400 2400 6480 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 153 153 347 347 416 416 NR NR NR NR NR NR NR NR 5440 5440 141 134 133 NR NR NR NR 1670 138 352 <2090 79 626 16300 5200 4910 149 750* * 6 650 130 1180 8 15600 6 6 6200 9470 132 350* 408 720 866 20000 6100 12100 10

� 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 p / Depth Concentration � Disadvantages 0 20 40 60 80 100 0 � Deployment time Deployment time 2 Advection � Analytical requirements 4 6 Bioturbation � Complexity p y 8 10 Diffusion � Volatile Losses 12 11 14

� Monitored Natural Recovery d l � 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 � Need to assess long ‐ term protectiveness N d t l t t ti

� 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 situations 13

� Metals often effectively contained by a conventional cap M t l ft ff ti l t i d b ti l � AVS vs. SEM ‐ Capping will enhance reducing conditions Salt Zn 2+ (ppb) > 0 10 20 30 40 AVS SEM ‐ 1 0 Metals will not be toxic 1 Depth (cm) M 2+ + FeS (s) → MS (s) + Fe 2+ 2 3 3 Sediment D < AVS SEM 4 5 6 Divalent metals may be Divalent metals may be 7 toxic 14 8

Conceptual Model Pre-Cap Post-Cap O 2 F OOH FeOOH O 2 O 2 FeOOH FeOOH Methyl mercury Methyl mercury 2- SO 4 2- SO 4

� 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 by diverting groundwater flow i d fl � Contaminant Migration Control � Slow contaminant migration, typically through Sl t i t i ti t i ll th h 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 � Dissolved contaminants only ‐ Activated carbon l d l d b � 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, K d ) – Equivalent sand cap thickness – diffusion/dispersion q p p dominated (u<<1 cm/day) K R = d L L L active active ~ R R K K eff ff active active sand d sand ~ 10 -4 K oc Log K d 0.01K oc f oc K oc ~ 1-10K oc ~ 100K oc f f oc ~ 0.01 ‐ 0.05 19

� It’s about risk, not whether a contaminant is present b i k h h � 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 20