Two Union Square Union Street, Suite 601 Seattle, WA (206) Field testing and modeling of in situ groundwater arsenic remediation through iron sulfide precipitation near Tacoma, Washington Brett Beaulieu and Samantha Ewing

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

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

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

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

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

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

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

2009 GSA Annual Meeting, Portland OR Methods: Pilot Injection

2009 GSA Annual Meeting, Portland OR

Methods: Pilot Injection 2009 GSA Annual Meeting, Portland OR

Methods: Pilot Injection 2009 GSA Annual Meeting, Portland OR

Baseline : Total As, Feb. As concentrations over time

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

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

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

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

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%)

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

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

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

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

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

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