1. Two Union Square - 601 Union Street, Suite 601 Seattle, WA 98101-2341 (206) 292-2078 www.floydsnider.com Field testing and modeling of in situ groundwater arsenic remediation through iron sulfide precipitation near Tacoma, Washington Brett Beaulieu and Samantha Ewing

2. Overview Arsenic cleanup at B&L Woodwaste Site Pilot injection, two application rates of EHC-M Modeling pyrite precipitation and oxidative dissolution

3. 2009 GSA Annual Meeting, Portland OR B&L Woodwaste Site

4. Cleanup Goals Physically contain source Treat leading plume edge in situ Remediate plume remainder Study area 100 ft Groundwater Flow direction Wetlands Landfill

5. 2009 GSA Annual Meeting, Portland OR Shallow Alluvial Sand Aquifer Groundwater Flow direction Study area Wetlands Landfill Groundwater arsenic plume

6. 2009 GSA Annual Meeting, Portland OR Goals of current study Add to limited reductive precipitation field data Arsenic remediation pilot: Effectiveness and time required Dosage Permeable reactive barrier (PRB) Pyrite as arsenic sink Pyrite stability, pH in oxic groundwater

7. 2009 GSA Annual Meeting, Portland OR Methods Pilot injection of EHC-M Commercial product (Adventus) Slurry: carbon, zerovalent iron, sulfate Groundwater monitoring Kinetic reaction path modeling (Geochemist’s Workbench) pyrite precipitation oxidative dissolution

8. Methods: Pilot Study 2009 GSA Annual Meeting, Portland OR Groundwater monitoring 5 events/6 months Total and dissolved As, Fe Sulfate/sulfide Dissolved organic carbon (DOC) Redox-sensitive metals pH, ORP, DO, T Treated depth: 12 – 22 feet below ground Two injection zones: 0.6% soil weight 0.2% soil weight 0.2%0.6% PD-105PD-106 PD-122

9. 2009 GSA Annual Meeting, Portland OR Methods: Pilot Injection

10. 2009 GSA Annual Meeting, Portland OR

11. Methods: Pilot Injection 2009 GSA Annual Meeting, Portland OR

12. Methods: Pilot Injection 2009 GSA Annual Meeting, Portland OR

13. Baseline : Total As, Feb. As concentrations over time

14. 2009 GSA Annual Meeting, Portland OR Results: Total As, March As concentrations over time

15. 2009 GSA Annual Meeting, Portland OR Results: Total As, April As concentrations over time

16. 2009 GSA Annual Meeting, Portland OR Results: Total As, May As concentrations over time

17. 2009 GSA Annual Meeting, Portland OR Results: Total As, August As concentrations over time

18. 2009 GSA Annual Meeting, Portland OR Results: Arsenic removal Arsenic removal plot Injection PD-105 (0.2%) PD-122 (between treatment zones) PD-106 (0.6%)

19. Results: Dissolved Iron 2009 GSA Annual Meeting, Portland OR PD-105 (0.2%) PD-106 (0.6%) Injection

20. Results: Sulfate 2009 GSA Annual Meeting, Portland OR Injection PD-105 (0.2%) PD-106 (0.6%)

21. Results: Pyrite oxidative dissolution 2009 GSA Annual Meeting, Portland OR Dissolution rates ~10 -10 mol/sec 20% dissolved in 30-day experiment 83% dissolved in 1-year experiment/100% in 5-year

22. Results: pH and pyrite dissolution 2009 GSA Annual Meeting, Portland OR pH decreases to below 5 in 1-year, 5- year experiment

23. Conclusions EHC-M treatment at 0.2% soil weight removed 67% As in 5-m pilot Treatment at 0.6% (10% pore space) may hinder flux and treatment Pyrite a realistic sink for injection PRB application of EHC-M Pyrite and pH stable during short- to medium-term oxic events 2009 GSA Annual Meeting, Portland OR

24. Full-scale treatment: Dec 2009 2009 GSA Annual Meeting, Portland OR