Innovations in Sediment Assessment and Remediation

Transcription

1 Innovations in Sediment Assessment and Remediation Danny Reible, PhD PE BCEE NAE Donovan Maddox Distinguished Engineering Chair Texas Tech University Kappe Lecture

2 Protecting public health and the environment by: Recognizing leadership and excellence through Board Certification of Environmental Engineers and Scientists (BCEE) Providing professional development opportunities for students, engineers, and scientists The Kappe Lecture Series was inaugurated by the Academy in 1989 to share the knowledge of today's practitioners with tomorrow's environmental engineers and scientists.

3 Contaminated Sediments Industrial and municipal effluents managed effectively At least for historical sediment contaminants (metals and hydrophobic organics) Concerns about perfluorinated compounds, pharmaceuticals, pesticides/herbicides Current contaminant concerns often not sediment contaminants Stormwater increasingly managed effectively Remains a source of sediment recontamination in some areas Slowing or reversing remedial efforts Legacy of strongly solid-associated refractory contaminants in sediments now pose substantial risk to bodies of water Polyaromatic hydrocarbons (PAHs) Polychlorinated biphenyls and dioxins (PCBs) Metals

4 Risk-based Decision-Making Risk relates to exposures to contaminants above acceptable levels. 0 Total PCBs (mg/kg) Remediation should be designed to eliminate or reduce those exposures. Exposures are dictated by surface sediments contaminants buried below the biologically-active zone are not available to organisms. Disrupting sediment beds to remove buried contaminants can expose organisms to otherwise inaccessible contaminants. However, removal of deeply buried contaminants may thwart future exposure and transport during severe events. Sample midpoint depth (cm) Cs-137 (pci/g) PCB profiles and Cs-137 dating Location in the Kalamazoo River

5 Stormwater can create new problems Amphipod Survival in Ex-situ Bioassay 100 P01 P08 P11 P17 10 Percent Survival (%) Cumuative Rainfall (in) 0 NT= Not Tested NT Jul-15 Oct-15 Feb-16 Oct-15 + Trap Material Trap Material Only 0 Increasing toxicity from non-toxic summer condition as storm season progressed, particularly at stations closest to creek mouth Addition of sediment trap material to surface of cores collected in October 2015 were more toxic than without the trap material Trap material was highly toxic at Stations P17 and P11, those closest to creek mouth

6 Managing Risks What are the options? Monitored Natural Recovery Depends upon effective monitoring Dredging Potentially effective but subject to resuspension/residuals Current targets are mass and volume oriented- needs refocusing on risk reduction Capping and In-Situ Treatment Effective/Efficient/Sustainable Bulk solid measures not directly applicable Depends upon effective monitoring and effective long-term stability

7 Performance of Remedial Alternatives Relative Risk Natural Recovery Dredging Capping Capping with breach Treatment Time, yrs

8 Dredging Limitations All dredges resuspend sediment All dredging operations leave residual contamination Increased resuspension and residual During debris removal and if significant debris present With hardpan or bedrock Poor operational controls Dredging most cost-effective If disposal onsite or as fill available Without local disposal, additional costs Dewatering Water treatment Transportation Disposal

9 In situ management requires process understanding Sediments- a perfect storm of chemistry, physics and biology O 2 H 2 O 3+ Fe 2+ Fe 2 SO 4 HS CH 2 O + CH 4 Aerobic Iron Reduction Sulfate Reduction Methanogenesis 11

10 Indicators of Exposure and Risk Bulk Sediment Concentration Relatively easy to measure Good indicator of contaminant mass Confusing indicator of risk Largely irrelevant to capping and insitu treatment Interstitial Water Concentration (Porewater) Indicator of mobility and availability Does not indicate route of exposure 14

11 Porewater Contaminants Mobile and Available Does not imply porewater only exposure 15

12 So How to Measure Porewater? Challenge Concentration very low for hydrophobic contaminants (O(1ng/L) or less) Approach Expose sorbents to porewater, concentrate in situ and analyze sorbent Inorganic Species - Diffusion gradient thin film (DGT) nonequilibrium devices Chelating resin (infinite sink) uptake controlled by thin diffusion gel uptake Organic Species - Polymer sorbent (PDMS,PE, POM) equilibrium devices Partitioning proportional to porewater concentration Low detection limit = Long equilibrium times

13 Measurement of Bioavailable Hg Direct porewater extraction and analysis Sediment Core Expression Passive Samplers DGTs Davison & Zhang Lancaster, UK Based on Fick s 1st Law of Diffusion- Measures flux Hg into the sampler Advantages Less invasive Time averaged pore-water concentration Higher depth resolution ~ 1cm Potential ability to measure bioavailable relevant Hg Biota Hg transformation/ accumulation? DGT porewater Hg

14 Can DGT effectively measure biological relevant Hg? 1.5 % Agarose Diffusive Gel HgCl 2 HgS clusters FeOOH HgS 2 H - Hg(HS) 2 0 HgS 0 Dissolved < 1 nm [Hg(II)] pw OM Colloidal Decreasing Methylation potential Increasing DGT relevance OM Particulate > 0.2 µm FeS R = k(thg )( φ )( RR) MeHg pw bio Can DGT measure this? Reduction rate of dominant e - acceptor (e.g., SRB)

15 Do DGTs uptake coarse particulate Hg? Expt. Parameters Uptake time: 6h THg: 1ppb Particulate Hg: Hg(II) nm thiolated silica Results Particulate noncolloidal forms Hg forms (200 to 450 nm) are unlikely to pass though DGT. Represents the upper bound in particle size for Hg that is accessible by DGT. Hg-S- DGT?? Control Expt. Uptake

16 Size Fractionated Partition Coefficients Suwannee River NOM, exposed to Hg then size fractionated by ultrafiltration % of Hg BrCl spike retentate filtrate 3-10 kda kda kda >100 kda apparent logkd (L/kg-C) Plot of Hg distribution in different size fractions of SRNOM. Loss/BrCl spike are recorded as filtrate for Kd calculation Plot of apparent log Kd values for each NOM size fraction assuming loss and BrCl spike is filtrate

17 D/Do Size fraction estimated curves Buffle (2007) DD = 2.84 xx 10 5 MM ww 1/3 D/Do DOC (mg-c)/hg (µg-hg) Unfractionated Predicted Curve Unfractionated SRNOM DGT Results

18 Bank leaching during drainage NA NA ft 2 ft

19 River Flow during Sampling 2015

20 Increased THg release during drainage Location 5 Constitution Park -5 0 Baseline Flow Location 5 07_20 Location 5 10_15 depth (cm) 5 10 Drainage Flow c(thg,dgt) (ng/l)

21 DGTs DGTs can measure contaminants that are freely dissolved or associated with molecular size complexes Generally exclude particle associated contaminants greater than nm in size Likely not biologically relevant? May provide better indication of biologically relevant contaminants Limited scientific data to support this hypothesis at this time Likely much better than traditional 0.45 µm filtered sample

22 Organics Passive Sampling Polymer Sorbents Polyethylene (PE) Sheets (planar geometry)- High volume, good surface area to volume ratio, moderate internal diffusion rates, marginal insitu feasibility PDMS Polyoxymethylene (POM) Molded thermoplastic, planar geometry - High volume, fair surface area to volume ratio, slow internal diffusion rates, marginal insitu feasibility Polydimethylsiloxane (PDMS) Thin annular coating on glass fibers- Moderate volume, good surface area to volume ratio, high internal diffusion rates, good insitu feasibility Goal- Equilibrium with porewater CC pppppppp KK PPPPPPPP CC ww Similar sorption (POM~PE>PDMS) PDMS Coating

23 Bioaccumulation Predicted by PDMS Measured Porewater Concentration C / f K C t l ow pw

24 Challenges- Variable Detection Limits Conventional Detection Limit

25 Challenges- Kinetics of Uptake Performance Reference Compounds (PRCs) typically deuterated or C-13 substituted form of target compound C pw C C C = = K f K C PDMS PDMS PRC (0) PDMS w ss PDMS w PRC 1.2 Organism Kinetics vs Passive Sampler Kinetics 1.0 C/C Sample Retrieval Time/days Phen PCB 101 B[a]P B[a]P uptake (Illyodrilus) PRC- dfla

26 Modeling Kinetics for other Compounds Simple model External resistances often control 1-D, diffusion model Parameters RD (Rectangular) or α (Cylindrical) C w Rectangular Coordinates (POM/PE) RDt RDt Mt ( ) = KswC0( V/ A) 1 exp erfc 2 2 ( V / A) K f ( V / A) K f k s Cylindrical Coordinates (PDMS) M = 1 1 M t 2β 1 a 1 + β e a +β 2τ erfc 1 + β τ 1 β a a e 1 a β 2τ erfc 1 β τ a (1) Where α = K pwa RπL o 2, β = α 1 or 1 α j, τ = td α α 2 RL o α - ratio of sorption on polymer to displaced sediment

27 PDMS PRC Model Cylindrical geometry more rapid approach to equilibrium

28 Field measurement of kinetics D x cm eff 6 2 ~ / sec R~ K ow

29 Reversible Sorption Cases PRC behave as expected Reversible Sorption fss τ Linear sorption Competitive Sorption PRC/Target Equal Concentrations PRC(0.01ug/L) PCB(0.01ug/L)

30 Problematic PRC Cases Fixed_PRC_Non-competitive_Equilibrium fss PRC f ss <Target PRC f ss > Target τ Non-linear sorption Non-competitive Sorption PRC/Target Different Concentrations PRC(0.01ug/L) Target(0.01ug/L) Target(0.0001ug/L)

31 General f ss Behavior from PRCs 2.5 CPCB = 0.01ug/L 2 fssprc/fsspcb W = KC N N=0.4 N=0.7 N=1 0.5 N= CPRC/CPCB

32 In-Situ Management Approaches to Reduce Mobility and Availability Amendment addition directly to sediments Sorbing or reactive amendments Conventional (sand/sediment) capping Thin layer capping Sand or other inert material Amended thin layer Amended isolation capping Sorbing amendments Active management approaches (e.g. redox control systems)

33 Potential Active Cap/Treatment Materials Demonstrated Clays for permeability control Activated Carbon or other carbon sequestration agent Organoclays for NAPL control & some dissolved control Significant swelling and permeability reduction with NAPL Clay and sequestration agent mixtures Phosphate additives for metals Rock phosphate (i.e. apatite) demonstrated Iron Sulfide for Hg and MeHg control Siderite (FeCO3) for ph control Zero valent iron Oxygen or hydrogen release compounds/technologies Biopolymers Electrochemical controls on redox conditions Speculative

34 Model CapSim Widely used tool to model sediment-water exchange and design sediment remedies Processes Advection, diffusion, dispersion, reaction, sorption Multiple reactive species, linked reactions, arbitrary order Linear & non-linear sorption and sorption kinetics Bioturbation, Deposition, Consolidation Multiple sediment layers and mixtures Used to model performance of Hunter s Point AC treatment AC mixing due to bioturbation Kinetics of sorption onto AC Used to explore PRC and contaminant behavior during passive sampling

35 Flux near surface for PCB 52-1cm/day upwelling Existing Condition (Natural Attenuation) 350 Flux (µg/m 2 /yr) cm sand cap 1cm OC mat In-situ OC cm OC amended sand cap In-situ AC 30cm AC amended sand cap & 1cm AC mat Time (years)

36 SPME Stations (flags) & As-Built Cores (circles) SPMEs Deployed 6/2012 & 9/2013 Roxana Marsh Grand Calumet River, Hammond, IN 41

37 Depth cm b SUM cpah Location 15 Concentration ng/l Concentration ng/l Depth cm SUM cpah Location 18 Depth cm SUM cpah Location 20 Concentration ng/l SUM cpah Location 19 Depth cm Concentration ng/l Depth cm SUM cpah Location 21 Concentration ng/l Concentration ng/l Depth cm SUM cpah Location 16 Depth cm SUM cpah Location 17 Concentration ng/l SPME Plots Sum cpah Scale ng/l 42

38 Hunter s Point Shipyard

39 Comparison of Pre and Post Cpw 8 mos 60-75% reduction 14 mos 90% reduction

40 Summary Growing emphasis on in situ remedies that emphasize reducing contaminant mobility and availability Growing use of porewater to measure mobile and available fraction and assess remedy performance using passive sampling Passive sampling shows activated carbon placement and reworking into sediment to be effective as a cap or in situ treatment Passive sampling poses challenges in its interpretation and use Slows its transition to routine use to monitor sediments and remedies

41 Understanding the processes influencing contaminant fate and behavior Assessing the resulting exposure and risks Implementing appropriate remedies

42 Acknowledgements Current Funding DoD SERDP/ESTCP Department of Homeland Security US Navy Maddox Research Foundation National Science Foundation Chevron DuPont Alcoa ExxonMobil Electric Power Research Institute Tierra Solutions Haley & Aldrich TetraTech Cabot State of Oregon Canadian Ministry of Environment and Climate Change Department of Homeland Security Critical Infrastructure Resilience Institute

43 Live Long and Prosper