1. Permeable Reactive Barriers for Inorganic Contaminants and Treatment of Acid Rock Drainage USEPA Scientist - to - Scientist Meeting Las Vegas, Nevada June 14 - 15, 2000 Robert W., Ph.D. U.S. EPA, National Risk Management Research Laboratory, Ada, Oklahoma

2. What? A Permeable Reactive Barrier (PRB):  A permeable zone creating a reactive treatment area oriented to intercept and remediate a contaminant plume  Removes contaminants from groundwater flow system by physical, chemical, or biological processes

3. Why Use a PRB?  Treatment occurs in the subsurface  Treatment is passive  Lower costs than conventional methods  Allows full economic use of a property  Robust  Monitoring can be focused

4. PERMEABLE REACTIVE BARRIERS (PRBs)

5. Permeable Reactive Barriers for In-Situ Remediation of Inorganic Contaminants Task 1061 Inhouse Project - PRB for Cr and TCE - Elizabeth City Full-Scale PRB for a mixed waste plume. Task 1061 Inhouse Project - PRB for Cr and TCE - Elizabeth City Full-Scale PRB for a mixed waste plume. WA SF - 1 - 4 - PRB for Nitrate and Arsenic Contaminated Groud Water WA SF - 1 - 4 - PRB for Nitrate and Arsenic Contaminated Groud Water Task 5851 Inhouse Project - PRB Strategies and Performance Monitoring for Remediation of Inorganic Contaminants Task 5851 Inhouse Project - PRB Strategies and Performance Monitoring for Remediation of Inorganic Contaminants

6. Elizabeth City PRB Site United States Coast Guard Support Center Elizabeth City, North Carolina North Carolina Elizabeth City Vicinity Map 0 STATUTE MILES 1234 Nixonton TCE / Chromium Plume Site United States Coast Guard Support Center, Elizabeth City Weeksville Hospital Elizabeth City U.S.C.G. Support Center, Elizabeth City Pasquotank River 17 156 20 158 343 168 34 17 N

7. Elizabeth City Site Plan View Fe Fence Hanging Iron Wall Full Scale Demonstration Approximate extent of chromium contamination in shallow groundwater, dashed where inferred Approximate location of former chromic acid tank TCE Plume Axis MW 13 MW52 MW 48 MW 38 MW 18 Approximate Scale in Feet 30’20’ 10’030’ Asphalt Pavement 12 2 1 8 105 11 9 4 3 Pasquotank River N I T E D S T A T E S C O A S T G U A R D 1790 RX core location Multi-layer sampler Compliance monitoring well LEGEND N MW46 MW35D MW47 MW51 MW50 MW49

8. USEPA - USCG Full-Scale Demonstration Results First site to use continuous wall design First site to use continuous wall design  more cost effective than funnel & gate  more efficient at plume capture After 4 years continues to meet remedial objectives (MCL’s) After 4 years continues to meet remedial objectives (MCL’s) No evidence of decrease in performance No evidence of decrease in performance First wall to remediate both chlorinated solvents and chromium First wall to remediate both chlorinated solvents and chromium

9. US EPA - USCG Full-Scale Demonstration Results (cont) Most intensively monitored PRB in the world Most intensively monitored PRB in the world Continues to serve as foundation for follow-on research efforts Continues to serve as foundation for follow-on research efforts Final Report completed Sep 1999 available from CERI, Kerr lab,internet @ www.epa.gov/ada/kerrcenter.html Final Report completed Sep 1999 available from CERI, Kerr lab,internet @ www.epa.gov/ada/kerrcenter.html

10. PRB’s for Nitrate - Project Status Work on nitrate complete Work on nitrate complete Work on arsenic to continue Work on arsenic to continue  column tests  other reactive media  more basic studies to explore surface reactions

11. Objectives - PRB’s for Nitrate To evaluate nitrate reduction kinetics in zero-valent iron media To evaluate nitrate reduction kinetics in zero-valent iron media To study nitrate transformation in organic compost media To study nitrate transformation in organic compost media To evaluate the potential use of iron and organic compost as permeable reactive barrier materials for in situ remediation of nitrate in groundwater To evaluate the potential use of iron and organic compost as permeable reactive barrier materials for in situ remediation of nitrate in groundwater To derive mechanisms of nitrate degradation To derive mechanisms of nitrate degradation

12. Conclusions - PRB’s for Nitrate Nitrate removal via biological denitrification in compost was more rapid than abiotic reduction in the zero-valent iron media Nitrate removal via biological denitrification in compost was more rapid than abiotic reduction in the zero-valent iron media Nitrate reduction and transformation in compost media was predominantly a biotic process Nitrate reduction and transformation in compost media was predominantly a biotic process Zero-valent iron may be useful for in situ remediation of nitrate in groundwater only when the denitrification conditions are not favorable Zero-valent iron may be useful for in situ remediation of nitrate in groundwater only when the denitrification conditions are not favorable Technology transfer interest Technology transfer interest

13. Objectives - PRB’s for Arsenic To evaluate removal kinetics of arsenate and arsenite in the zero-valent iron media and iron oxides media To evaluate removal kinetics of arsenate and arsenite in the zero-valent iron media and iron oxides media To evaluate the potential use of iron and iron oxides as permeable reactive barrier materials for in situ arsenic remediation in groundwater To evaluate the potential use of iron and iron oxides as permeable reactive barrier materials for in situ arsenic remediation in groundwater To derive mechanisms of arsenic interaction with the permeable reactive barrier media To derive mechanisms of arsenic interaction with the permeable reactive barrier media

14. Anion Effect on As Removal by Fe o Sulfate at 0.001 M did not affect arsenate removal by Peerless Fe o compared to 0.01 M NaCl Sulfate at 0.001 M did not affect arsenate removal by Peerless Fe o compared to 0.01 M NaCl Phosphate at 0.001 M significantly reduced the rate of arsenate removal by Peerless Fe o compared to 0.01 M NaCl Phosphate at 0.001 M significantly reduced the rate of arsenate removal by Peerless Fe o compared to 0.01 M NaCl Other anions that may affect As removal are being tested including nitrate, carbonate, borate, molybdate, and chromate. Both As(V) and As(III) will be tested further. Other anions that may affect As removal are being tested including nitrate, carbonate, borate, molybdate, and chromate. Both As(V) and As(III) will be tested further.

15. Removal of As by Metal Oxides Removal of As by Metal Oxides On a mass basis, goethite was the most effective sorbent On a mass basis, goethite was the most effective sorbent All the added As(III) in the birnessite suspension was oxidized to As(V) that resulted in the almost identical sorption envelopes for both added As(V) and As(III) All the added As(III) in the birnessite suspension was oxidized to As(V) that resulted in the almost identical sorption envelopes for both added As(V) and As(III) As(III) was oxidized significantly to As(V) in the magnetite and hematite suspensions at pH > 6. Minor amounts of manganese dioxide present in the Fe oxides might be responsible for the oxidation As(III) was oxidized significantly to As(V) in the magnetite and hematite suspensions at pH > 6. Minor amounts of manganese dioxide present in the Fe oxides might be responsible for the oxidation

16. Conclusions - PRB’s for Arsenic All the zero-valent iron samples and iron oxides showed effective removal of both As(V) and As(III) from water All the zero-valent iron samples and iron oxides showed effective removal of both As(V) and As(III) from water Surface adsorption was likely the major process of As removal (at least initially) Surface adsorption was likely the major process of As removal (at least initially) Arsenic redox reactions seem occur at the surface of iron and iron oxides following adsorption Arsenic redox reactions seem occur at the surface of iron and iron oxides following adsorption Phosphate inhibited As sorption with sulfate showing no effect Phosphate inhibited As sorption with sulfate showing no effect Field testing initiated in April, 2000 Field testing initiated in April, 2000

17. PRB Strategies and Performance Monitoring for Remediation of Inorganic Contaminants Task 5851 (Wilkin, Puls) Sub tasks: Sub tasks:  Long-term performance monitoring  AMD strategies  Remediation of As-contaminated GW

18. Objectives: AMD Strategies Evaluate metal removal rate and neutralization rate of AMD using: Evaluate metal removal rate and neutralization rate of AMD using:  Fe° mixtures w/ Clinoptilolite (natural zeolite) Clinoptilolite (natural zeolite) Ca sulfide, compost Ca sulfide, compost Carbonate Carbonate Steel slag Steel slag Evaluate metal uptake mechanisms Evaluate metal uptake mechanisms

19. Status Batch and Column studies in progress Batch and Column studies in progress Synthetic AMD solution Synthetic AMD solution  pH 2.3, Fe, Al, As, Cu, Cd, Zn, Pb, Co, Ni  Connelly Iron, Fisher Iron  Zero-valent iron is useful for in situ remediation of AMD but other components required for iron removal  Sorption to both Fe metal/Fe-O coatings and “free” precipitates

20. Summary NRMRL/SPRD Research on PRB’s Leader in PRB research, development, training and technology transfer Leader in PRB research, development, training and technology transfer InHouse research focus has been on inorganic contaminants InHouse research focus has been on inorganic contaminants Mining problems naturally fit under SPRD-led NRMRL Ecosystem Restoration Program Mining problems naturally fit under SPRD-led NRMRL Ecosystem Restoration Program PRB’s likely component of large-scale remedial measures for mine wastes PRB’s likely component of large-scale remedial measures for mine wastes

21. PRB Strategies and Performance Monitoring for Remediation of Inorganic Contaminants Task 5851 (Wilkin, Puls) Sub tasks: Long-term performance monitoring AMD strategies Remediation of As-contaminated GW

22. Objectives: AMD Strategies Evaluate metal removal rate and neutralization rate of AMD using: Evaluate metal removal rate and neutralization rate of AMD using:  Fe° mixtures w/ Clinoptilolite (natural zeolite) Clinoptilolite (natural zeolite) Ca sulfide, compost Ca sulfide, compost Carbonate Carbonate Steel slag Steel slag Evalaute metal uptake mechanisms Evalaute metal uptake mechanisms

23. Status Batch and Column studies in progress Batch and Column studies in progress Synthetic AMD solution Synthetic AMD solution  pH 2.3, Fe, Al, As, Cu, Cd, Zn, Pb, Co, Ni  Connelly Iron, Fisher Iron  Zero-valent iron is useful for in-situ remediation of AMD but other components required for iron removal  Sorption to both Fe metal/Fe-O coatings and “free” precipitates  Secondary ppt problem

24. Application of an Organic-Based Sulfate-Reducing Permeable Reactive Wall for Treatment of Acid Rock Drainage David Blowes, Ph.D., (University of Waterloo, Waterloo, Canada EPA/ITRC/RTDF Permeable Reactive Barrier Short Course 1EPA

25. Acid Mine Drainage and Sulfate Reduction

26. Wall Reactions of Interest SO 4 2- + 2CH 2 O H 2 S + 2HCO 3 - SO 4 2- + 2CH 2 O  H 2 S + 2HCO 3 - Me 2+ + H 2 S MeS (s) + 2H + Me 2+ + H 2 S  MeS (s) + 2H +

27. Nickel Rim Site, Canada Sulfate2000 - 4000 mg/L Sulfate2000 - 4000 mg/L Iron200 - 1200 mg/L Iron200 - 1200 mg/L pHslightly acidic (pH < 6) pHslightly acidic (pH < 6) Alkalinityc. 50 mg/L Alkalinityc. 50 mg/L Reactive mixturecompost, limestone Reactive mixturecompost, limestone

28. Results: Nickel Rim Site, Canada The reactive wall is removing >95% of the dissolved iron The reactive wall is removing >95% of the dissolved iron Water exiting the wall has changed from acid producing to acid consuming Water exiting the wall has changed from acid producing to acid consuming Sulfate significantly reduced Sulfate significantly reduced

29. Cost: Nickel Rim Site, Canada Size15 x 8 (4 + 4) x 4 m Size15 x 8 (4 + 4) x 4 m Materials$15,400 Materials$15,400 Installation$15,500 Installation$15,500 Site Restoration$1,300 Site Restoration$1,300 Total$32,200 (Cdn$) Total$32,200 (Cdn$)