1. B-055, in: T.C. Fox and H.V. Rectanus (Chairs). Remediation of Chlorinated and Recalcitrant Compounds—2012.
Eighth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2012).
ISBN 978-0-9819730-5-0, ©2012 Battelle Memorial Institute, Columbus, OH, www.battelle.org/chlorcon.
Predicting the Operational Life of Zero-Valent Iron during
ISCR-Enhanced Bioremediation of TCE DNAPL
James Peale (jpeale@maulfoster.com) and Erik Bakkom
(Maul Foster & Alongi, Inc., Portland, Oregon, USA)
Jim Mueller, Josephine Molin, and Andrzej Przepiora
(Adventus Americas Inc., Freeport, IL, USA)
Background/Objectives. Groundwater at an active manufacturing facility on an 80-acre
site in Portland, Oregon, was impacted by TCE and its degradation products. Operations
at the facility began in 1980, and included the use of TCE from approximately 1980 to
1989. TCE and/or TCE-containing wastewater were released to the subsurface in the
early 1980s, roughly between 1980 and 1984. In 2006, concentrations of TCE and cis-
1,2-dichloroethene (DCE) in the primary release area ranged as high as 592,000 and
90,000 µg/L (respectively) at depths ranging from approximately 50 to 110 ft below
ground surface (bgs). Although not observed during drilling or groundwater sampling,
the presence of TCE DNAPL was inferred by concentrations approaching 50% of the
aqueous solubility limit.
Approach/Activities. Based upon bench and field pilot studies, ISCR-enhanced
bioremediation was selected for primary source area treatment and implemented in early
2009. Implementation consisted of an approximately 150 foot-long permeable reactive
barrier (PRB) consisting of EHC® and KB-1®, installed at depths ranging from approx-
imately 40 to 112 ft bgs using direct-push technology. Groundwater data were collected
from 23 performance monitoring wells located upgradient, within, and downgradient of
the PRB. Early data confirmed the success of the approach, with 99.99% TCE mass
removal less than a year following completion, with many wells below the USEPA MCL
(5 µg/L).
Results/Lessons Learned. While the performance data indicated successful remediation
of TCE DNAPL, residual concentrations of degradation products (primarily cis-1,2-DCE
and vinyl chloride) prompted questions regarding the long-term stability of the zero-
valent iron (ZVI) component of the EHC material. The primary mechanism resulting in
reduced effectiveness of ZVI is consumption of iron by processes such as corrosion,
reduction of chlorinated VOCs, reduction of nitrate, and reduction of sulfate. Pre-
injection groundwater concentration data were used to estimate the aggregate rate of ZVI
consumption based on the total amount of ZVI injected, with a predicted operational life
of the ZVI ranging from 14-60 years. Subsequent performance data (including iron,
dissolved oxygen, nitrate, sulfate, and CVOC) will be used to further evaluate the
predicted operational life. Modeling will be completed using publically available iron
corrosion/consumption calculations and geochemical models. These data and calculations
will be presented and compared to available data from other sites.

2. PREDICTING THE OPERATIONAL LIFE
OF ZERO-VALENT IRON DURING
ISCR-ENHANCED BIOREMEDIATION
OF TCE AND TCE DNAPL
James G.D. Peale, RG
Erik I. Bakkom, PE
(Maul Foster & Alongi Inc.)
Josephine Molin
Jim Mueller
Andrzej Przepiora
(FMC Environmental Solutions/Adventus)
May 2012

3.  Site Overview
 Technology Summary
 Problem Statement
 Analysis
 Results
 Summary
 Implications
TOPICS

4.  Former MGP waste site redeveloped for
manufacturing in 1970s
 80+ acres adjacent to Portland Harbor NPL site
 TCE or TCE+wastewater released from a recycling
system (1980-1985)
 Impacts from release discovered in 2002
 Source Zone
 Impacts from about 15-34 m bgs
 TCE up to 592,000 ug/L (DNAPL levels)
 No TCE DNAPL observed
 Cis-1,2-DCE up to 90,800 ug/L
 Very little VC (< 100 ug/L)
Site Overview

5. Site Overview

6. Technology Summary
 EHC
 Powdered blend of zero-valent iron (ZVI) and
hydrophilic organic carbon
 Creates strongly reducing conditions in groundwater
for in situ chemical reduction (ISCR)
 ISCR results in abiotic dechlorination and supports
anaerobic bacteria
 KB-1
 Anaerobic consortium of dechlorinating bacteria
 Includes dehalococcoides sp.
 Requires ORP < -75 mV

7. Technology Summary
 EHC+KB-1 Full-Scale Implementation
 46 m x 21 m x 3 m PRB – Source area only
 Injected from ~12 – 34 m bgs
 Supplemental upgradient areas
 200+ injection points
 ~269,400 kg EHC
 1,831 L KB-1
 Direct-push drilling
 23 Performance Monitoring Wells
 Group 1 – Upgradient or within injection zone
 Group 2 – Downgradient of injection zone

8. Technology Summary

9. Technology Summary

10. Technology Summary
 Insert TCE normalized plot?
 Subset of wells with pre-injection TCE > 11,000 ug/L
y = 0.1145e-0.011x
R² = 0.5859
y = 0.0352e-0.007x
R² = 0.4188
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
0 100 200 300 400 500 600 700 800 900
C/C0(ug/L)
Time Following Injection (d)
TCE DNAPL Predicted TCE DNAPL Not Predicted Predicted Wells Not Predicted Wells

11. Problem Statement
 Remedial action objective is 11,000 ug/L
 Threshold indicator for TCE DNAPL
 Achieved in less than 12 months
 Mean TCE 3 ug/L
 Declining cDCE
 Abiotic products confirm ZVI performance
 Dhc counts 107 – 108
 Question: how long can this continue?
 Will we see rebound?

12. Problem Statement
 How long can we rely on ZVI for residual
CVOCs?
 ZVI Consumers
 Corrosion by water
 Oxidation by CVOCs
 Oxidation by sulfate
 Wide range for longevity in experience
and literature
 15 years for granular ZVI
 7 years for micro-scale ZVI
 20-750 years (Henderson et al., 2007)

13. Problem Statement
y = -18.852x + 764496
R² = 0.9788
Predicts ZVI Exhaustion in 16 yrs
y = -1.5096x + 65608
R² = 0.4784
Predict ZVI Exhaustion in 201 yrs
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
12/18/2008 7/6/2009 1/22/2010 8/10/2010 2/26/2011 9/14/2011 4/1/2012
DissolvedFe(Kg)
Date
Rate 1 Rate 2 Linear Trend Linear Trend

14. Analysis
 Literature rates applied using t0 data
 10 – 20 yrs
 Bulk mass estimates (time-dependent)
 3D kriging of total mass of Fe over time
 10 – 200 yrs based on regression
 Geochemical modeling – PHREEQC
 Step 1: Inverse to simulate measured
chemistry assuming batch system
 Step 2: 1-D transport model to model flowing
system

15. Analysis - Geochemistry
 Data from well WS-32-76
 Geochemical trends
 Highest concentrations of iron (dissolved and
total)
 TOC and CaCO3 indicative of carbon
fermentation from the emplaced EHC
 “Worst case” – highest EHC consumption
indicated or inferred

16. Analysis - Geochemistry
Data from well WS-32-76

17. Analysis – Input Parameters
 Input parameters used in geochemical and
transport model

18. Background conditions (∑Fe=1.3E-3 M,
∑C=1.1E-2 M, and ∑S=4.3E-3 M); Fe(OH)2(a),
amakinite [Fe(OH)2], pyrite (FeS2] and
siderite [FeCO3] were assumed as
equilibrium mineral phases.
Analysis - Geochemistry
5 months after EHC injections
(∑Fe=6.5E-2 M, ∑C=7.2E-2 M, and
∑S=4.3E-3 M). Methane generation
was suppressed for equilibrium
calculations.

19. Analysis - Model
 Good fits for model

20. Results
 Difference between Fe(t) and Fe(d) indicates
precipitation
 Siderite (supersaturation); Fe-sulfides?
 Observed Fe controlled by:
 DNAPL/CVOC reduction
 Methanogenesis, sulfate reduction
 Requires carbon fermentation
 “Early” ZVI corrosion rate ~ 19 mmol/kgZVI/day
 Higher than expected; worst-case data set
 Predicts consumption of ZVI in injection + 10 years
 Useful?

21. Results – Rate Comparison
Data Method
Rate
(mmol/kgZVI/day)
ZVI Longevity
(yrs) Comment
EVS Mass
Rate 1 Regression/Slope 3.07 16
May overestimate and be
less useful for decision
making
EVS Mass
Rate 2 Regression/Slope 0.24 201
WS32-Early 1-D PHREEQC 19 3 Conservatively fast; based
on “worst-case” data
WS32-Late 1-D PHREEQC 6.3 8
t0 Data Adventus TN Rates 2.3 21
Assumed constant rate and
site-specific “t0” data
EVS Mass of
Fe
Long-term rate based
on 12.5 : 1 Ratio using
WS32-Early as Rate 1 1.5 32
Incorporates changing rate
and bulk Fe data to reflect
actual conditions and
incorporate variability

22. Summary
 Literature range sets boundaries
 20 – 750 yrs (latter less useful)
 Developing data set
 Regression provides simple tool for prediction
 Dual rates observed and should be considered
 Early consumption followed by equilibrium
 Modeling is promising approach
 Estimates match lower range of regression
 Can provide conservative (short) predictions to
improve site planning/closure

23. Implications
 Micro-scale ZVI is extremely durable
 Data fit well with other observations
 Similarity to presumed P&T timeframes (30 yrs)
 How do we manage long-term?
 Is monitoring required to demonstrate complete
exhaustion?
 How can we extend confidence of this long-term
remedy to support site closure?

24. Acknowledgements/Questions
 Thank you.
 FMC Environmental Solutions / Adventus
 Questions?