In Situ Bioremediation of Persistent Organic Compounds and Heavy Metals and Groundwater Modeling Techniques for Karst and Fractured Rock Settings

Transcription

1 In Situ Bioremediation of Persistent Organic Compounds and Heavy Metals and Groundwater Modeling Techniques for Karst and Fractured Rock Settings Karst Conference, Shepherdstown WV, September 15, 2009 J. Mueller, PhD J. Moreno, PHG A. Seech, PhD

2 EHC for Treatment of VOCs in Groundwater EHC integrates in situ biological and chemical reduction (ISCR) 15 years technology development experience DARAMEND (Grace Bioremediation) Iron PRBs (EnviroMetal Technologies Inc.) Balances acidity (VFAs) and ph increase (ZVI) to prevent acidification of groundwater Very long life from 36 to 72 months Usually emplaced in slurry form via direct push injection, hydraulic / pneumatic fracturing 2

3 Substrate Composition EHC is composed of: Controlled-release, food grade, complex carbon Micro-scale zero valent iron (10-50 µm) Major, minor, and micronutrients Food grade organic binding agent 3

4 EHC Treatment Mechanisms VFAs, Nutrients Ferrous iron Reactive precipitates Low redox Controlled ph Solid Particle Bacteria 4

5 Significantly Lowered Redox (Eh) Potential = ISCR Eh Potential (mv) Redox potentials of -600 mv to -800 mv Thermodynamics of reductive decomposition become favorable -600 Control Treatment Time (days) ZVI or Carbon Only EHC Buffering capacity US Patents W.R. Grace & Company / Adventus 5

6 Dehalogenation Rates Increase as Eh Decreases CCl 4 dehalogenation rates Ti (III) Eh Live Autoclaved Abiotic Citrate (mv) (mm) Reference: anaerobic sludge study; Olivas et al. ET&C (2002) 21:

7 Benefits of Using EHC Health and Safety Minimal Methane Production Predictable Performance Constructability No Mobilization of Contaminants Accelerated Site Closure without relying on sorption / sequestration ISCR No accumulation of Dead-End Intermediates. No VC or DCE from TCE or PCE No CM, DCM or CF from CT No DNT from TNT Wide Applicability: chlorinated solvents, Freons, pesticides, perchlorate, metals, and explosives; Longevity with no Rebound Complete Technology Buffering Capacity Facilitates Natural Attenuation Processes Simultaneous Immobilization of Heavy Metals 7

8 EHC Installation Methods Direct Placement: Trenching Excavations Deep soil mixing Socks Injection Methods: Direct injection Well injections (EHC-A) Hydraulic fracturing Pneumatic fracturing Jetting 8

9 EHC Installation Methods Direct Placement Placement at bottom of excavation to treat standing groundwater. Installation of EHC PRB 9

10 EHC Conceptual Designs Source Area/ Hotspot Treatment Injection PRB for Plume Control Plume Treatment - Dosing: 0.15 to 1% wt/wt - Spacing: 5 to 15 ft (DPT) - Dosing: 0.4 to 1% wt/wt - Spacing: 5 to 10 ft (DPT) - Dosing: 0.05 to 0.2% wt/wt - Line Spacing: 100 ft / 1 year gw travel distance 10

11 Half Lives vs. Time Half Life (hours) 10,000 1, Time Varying Half Lives in PRB Carbon Tetrachloride Chloroform PCE TCE cis 1,2 DCE trans 1,2 DCE 1,1 DCE VC Time (days) 11

12 CASE STUDY: Treatment of PCE 12

13 EHC -M controlled-release carbon with sulfide, nutrients & micro-scale ZVI Encourages the precipitation and adsorption of dissolved metals. Contains controlled release carbon, ZVI and sulfate. Different metals require different conditions some metals precipitate in contact with ZVI only, other require a source of sulphur and/or low redox. EHC-M Arsenic precipitates as Iron Arsenic Sulfide. Low redox/zvi Chromium(6+) precipitates as Chromium(3+). 13

14 Metal Immobilization Processes in EHC-M Treatment Zone Cost-effective, permanent removal of heavy metals by generation of stable mineral precipitates 14

15 Irreversible and No Rebound: Influence of Oxygen and Acid on Precipitated Arsenic Column: 13 cm long and 5 cm Ø, Flow rate = 50 ml/d, Residence time = 2 days 2500 Effluent As Concentration ( g/l) Control Column Effluent 1%EHC-M Column Effluent Eh>>0 Eh>>0 ph=4 As in influent As-free influent Eh>>0 ph= Total Time of Test (days) 15

16 Long-Term Column Test for As Treatment Solid As Speciation As fraction content (mg/kg) Adsorbed/exchangeable Amorphous Fe Oxyhydroxide Crystalline Fe Oxide Sulphides and Organics Residual (Silicates) Total As Influent Part Middle Part Effluent Part Control Column Toatal As (mg/kg) 16

17 Summary of Treatment Performance Location Compounds Treated Baseline Conc. (µg/l) Post Treatment Conc. (µg/l) Removal Efficiency Washington, USA Chromium(VI) 165 <5 >97% TCE 6.1 <0.5 >92% Copper % Ontario, Canada Cobalt % Nickel % Sao Paulo, Brazil Lead 306 <10 >97% 17

18 EHC-M Case Study Initial Low TCE Concentration 18

19 EHC-O Buffered source of controlled-release oxygen and inorganic nutrients Stimulation of aerobic biodegradation through controlled-release oxygen and nutrient delivery. For organic constituents amendable to aerobic biodegradation processes: - Petroleum Hydrocarbons - Light PAHs - BTEX Significant cost savings realized through the use of EHC-O due to its higher oxygen release rate and lower price. 19

20 Oxygen Releasing Compounds Cost Efficiency Comparison Number of lbs of O 2 released per dollar of cost Allows for higher safety factors to address any unexpected oxygen demand EHC-O Calcium-peroxide based Magnesium-peroxide based Days 20

21 Installation Methods Injection methods (direct injection, fracturing ) Open excavations Socks or canisters for well applications 21

22 EHC-O O-SOX Stainless Steel Canisters (re-useable) O-SOX (single-use) Available for 2, 4, and 6 wells in length segments of 3 ft Link together to achieve target depth Estimated longevity of 3 to 6 months 22

23 In Situ Treatment of PVOCs Application of 0.1% EHC-O by dry soil mass Injection of 20% slurry via direct injection Product cost of US$0.50 per ft 3, or $13.50 per yd 3 Source: LUST Site, Kenosha, WI Lead Consultant - STS Consultants, Ltd. Concentration (ppb) Before injection Benzene MTBE Ethyl Benzene Xylenes Naphthalene 1,2,4-Trimethylbenzene 1,3,5-Trimethylbenzene Toluene ND One month after injection ND Four months after injection 23

24 DARAMEND Technology Applications Aerobic wood treatment chemicals (PAHs & PCP) manufactured gas plant PAHs phthalates Cycled Anaerobic/Aerobic chlorinated pesticides and herbicides organic explosives 0.1 to 3% w/w chlorinated solvents 24

25 O 2N Hydrocarbon-Impacted Soil Microstructure mineral particle clay/organic matter agglomerate bacterial cells O 2 N CH CH 3 NO NO 2 NO NO 2 hydrocarbon molecules adsorbed on soil binding sites CH CH 3 NO NO 2 NO NO 2 O 2 N CH CH 3 NO NO 2 O 2 N NO NO 2 CH CH 3 NO NO 2 NO NO 2 O 2 N CH CH 3 NO NO 2 NO NO 2 clay platelets organic matter micropore 25

26 Reductive Daramend Bioremediation mineral particle CH 3 O 2 N NO 2 NO 2 clay/organic matter agglomerate bacterial cells O 2 N CH 3 NO 2 NO 2 contaminant desorbs from binding site on soil and diffuses to DARAMEND particle surface O 2 N CH 3 NO 2 NO 2 multi-valent metal particle clay platelets water film organic matter CH 3 O 2 N NO 2 NO 2 O 2 N CH 3 micropore hydrated DARAMEND particle colonized by native soil bacteria NO 2 NO 2

27 U.S. EPA SITE Report Evaluated and validated treatment claims Demonstrated monitoring protocol Concluded that treatment resulted in 95% reduction in chlorinated phenols, 92% reduction in total PAHs and elimination of toxicity as measured by seed germination and earthworm mortality EPA/540/R-95/

28 Treatment of TNT & RDX at NWS Yorktown, VA 100,000 10,000 TNT RDX ppm 1, Initial Treatment Cycles (100 days total) Note: 1 Treatment Cycle = 0.5% DARAMEND tilled into soil; irrigated; then incubated for 7 days 28

29 Underlying Technologies (1) Sub-Aqueous Capping AquaBlok is a patented, composite-aggregate technology comprised of a central core, clay, and polymers. EPA-audited results* show that AquaBlok : Is physically stable in riverine environments Was better able to control groundwater seepage than sand-capped sediments Positively-influenced benthic flora and fauna (more data being collected). *Revised Month 18 Data Report for SITE Demonstration of the AquaBlok Sediment Capping Technology at the Anacostia River, Washington, D.C 29

30 AquaBlok Active Cap Water column AquaBlok + TM Active Cap Impacted Sediment predominant direction of ground water flow 30

31 AquaBlok and Reactive Gates AquaBlok TM & Reactive Gates Water column Impacted Sediment Impacted ground water predominant direction of ground water flow 31

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33 Why Use a Model? Cost-effective solutions Predict benefits & risks Define uncertainty Reduce remediation costs Remedial design optimization & risk management Design parameters Time to cleanup Natural attenuation Contingency plans Allocation of costs Shutdown criteria Monitoring design optimization & justification Conceptualization, animation, interpretation of site data Environmental impact, natural resources damage Liability estimation, litigation support 33

34 Example Conceptual Model 34

35 Models for Karst and Fractured Sites Water Supply Model, AZ Natural Resource Damages, NJ Underground gold mine EIS, WA 35

36 Water Supply Model, AZ 36

37 Fracture - Block Model Simulated and Observed Drawdown at OW Layer Model Base Case 1-Layer Model - Fracture and Block Observed Drawdown 7-Layer Model Base Case (with Ss = 5.7E-7 1/ft) Time (days) 37

38 Source Above Fractured Bedrock 38

39 Aquifer Pumping Test Observed 1 ft drawdown 39

40 Discretization and Topography Ridge at 5600 ft 250 ft UZ in summer Base of mine at 4500 ft Base of model at 1600 ft 23 square miles 20 layers 409,332 nodes and 768,500 three-dimensional elements 40

41 Mine cross section Gold Bowl 4,000 ft mine 41 Decreasing K 41

42 Proposed mine tunnels and adits 42

43 Residual Water-Level Change springs 43

44 Conclusions Detailed predictions of seasonal and annual variations in stream baseflow Drought smaller impact, delayed recovery Low recharge sensitivity show flow impacts +/- 30% and duration of impacts +/- 2 years Supported evaluation of mitigation measures EIS finalized Mine under construction 44