(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.
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
Site Overview Technology Summary Problem Statement Analysis Results Summary Implications
TOPICS
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
Site Overview
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
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
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
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
Analysis - Geochemistry
Data from well WS-32-76
Analysis – Input Parameters
Input parameters used in geochemical and transport model
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.
Analysis - Model
Good fits for model
Results
Difference between Fe(t) and Fe(d) indicates precipitation Siderite (supersaturation); Fe-sulfides?
