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Field testing and modeling of in situ groundwater arsenic remediation through iron sulfide precipitation

near Tacoma, WashingtonBrett Beaulieu and Samantha Ewing

Overview

Arsenic cleanup at B&L Woodwaste SitePilot injection, two application rates of EHC-MModeling pyrite precipitation and oxidative dissolution

2009 GSA Annual Meeting, Portland OR

B&L Woodwaste Site

CleanupGoals

Physically contain sourceTreat leading plume edge in situRemediate 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

WetlandsLandfill

Groundwater arsenic plume

2009 GSA Annual Meeting, Portland OR

Goals of current study

Add to limited reductive precipitation field dataArsenic remediation pilot:

Effectiveness and time requiredDosagePermeable reactive barrier (PRB)Pyrite as arsenic sink Pyrite stability, pH in oxic groundwater

2009 GSA Annual Meeting, Portland OR

Methods

Pilot injection of EHC-MCommercial product (Adventus)Slurry: carbon, zerovalent iron, sulfateGroundwater monitoring

Kinetic reaction path modeling (Geochemist’s Workbench)

pyrite precipitation oxidative dissolution

Methods: Pilot Study

2009 GSA Annual Meeting, Portland OR

Groundwater monitoring5 events/6 monthsTotal and dissolved As, Fe Sulfate/sulfideDissolved organic carbon (DOC)Redox-sensitive metalspH, ORP, DO, T

Treated depth:12 – 22 feet below ground

Two injection zones:0.6% soil weight0.2% soil weight

0.2% 0.6%

PD-105 PD-106

PD-122

2009 GSA Annual Meeting, Portland OR

Methods: Pilot Injection

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

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 plotInjection

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 ~10-10 mol/sec 20% dissolved in 30-day experiment83% 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 treatmentPyrite a realistic sink for injection PRB application of EHC-MPyrite and pH stable during short- to medium-term oxic events

2009 GSA Annual Meeting, Portland OR

Full-scale treatment: Dec 2009

2009 GSA Annual Meeting, Portland OR