ISCO of DNAPLs: Applicability Based on 2-Dimensional Transport Studies of DNAPL Entrapment and Oxidant Delivery Techniques
Michelle Crimi, Colorado School of Mines, Golden, CO 

The Permanganate Soil Oxidant Demand: A Critical Parameter For ISCO Remediation
Philip A. Vella, Carus Chemical Company, LaSalle, IL

Oxidation of TNT, HMX, and RDX by Iron-Chelate Activated Persulfate
George E. Hoag, Hoag Environmental Systems, LLC, Storrs, CT

Persulfate Oxidation of TCE at Ambient Temperature: Kinetics and Influence of Radical Scavengers
Chenju Liang, National Chung Hsing University, Taichung, Taiwan

Field Scale Comparison of Activated Persulfate and Modified Fenton's Reagent for Treatment of Chlorinated Benzene Compounds
Brant Smith, Xpert Design and Diagnostics, LLC (XDD), Stratham, NH

Modified Fenton’s Reagent Used for Saturated Zone Remediation, former Naval Air Station, Alameda Point, California

Anthony Searls, Shaw Environmental, Inc., 1045 Jadwin Avenue, Suite C, Richland, WA, 99352, Tel: 509-946-2062, Fax: 509-943-8554, Email: Tony.Searls@shawgrp.com
Tim Eilber, In-Situ Oxidative Technologies Inc. (ISOTEC), Denver, CO, Tel: 303-843-9079, Fax: 303-931-3957, Email: teilber@insituoxidation.com
Daniel Shafer, Shaw Environmental, Inc., 1326 North Market Blvd., Sacramento, CA, 95834, Tel: 916-928-3300, Fax: 916-565-4373, Email: Daniel.Shafer@shawgrp.com
Glenna Clark, U.S. Navy, 1230 Columbia Street, San Diego, CA, 92101, Tel: 619-532-0954, Fax: 619-532-0983, Email: clarkgm@efdsw.navfac.navy.mil
Stan Haskins, In-Situ Oxidative Technologies Inc. (ISOTEC), Denver, CO, Tel: 303-843-9079, Fax: 303-931-3957, Email: shaskins@insituoxidation.com

In-situ chemical oxidation (ISCO) using modified Fenton’s chemistry has been gaining recent acceptance due to the fact that this technology not only destroys dissolved-phase contaminants in groundwater, but also desorbs contaminants from the soil matrix so that supplementary chemical oxidation may destroy these desorbed contaminants. Modified Fenton’s reagents include hydrogen peroxide (12 to 17 weight percent) and a proprietary chelated iron catalyst, combined under neutral pH reaction conditions.  Shaw initially performed a series of bench-scale tests using various in-situ oxidation reagents (sodium persulfate, potassium permanganate, ozone, hydrogen peroxide, and Fenton’s reagent [hydrogen peroxide and ferrous iron]) for varying lithologies and depths at the former the effectiveness of the technologies.  Based on the results, Fenton’s reagent was chosen as the preferred oxidant for ISCO pilot testing.  In-Situ Oxidative Technologies, Inc. (ISOTEC) teamed with Shaw to implement an ISCO remediation program. 

The program included an initial series of pilot tests at several Installation Restoration (IR) sites to evaluate the field application of the technology and to refine the application process.  This phase was followed by implementation of full-scale removal actions at several of the successful IR sites.  The contaminants of concern (COCs) at these sites were a mixture of chlorinated solvents and fuel-related products (mainly chlorobenzene, chloroethane, and chloroethene isomers).  Injection of reagents was accomplished using both conventional injection wells and direct-push drilling technology.  This paper will focus on one of the IR sites where a full-scale removal action was implemented.  At this site, over 300 temporary direct-push injection points were advanced to treat an effective area of approximately 4 acres underlain with chlorobenzene isomer contamination.  Following three separate injection events, spanning a six-month period, the two main COCs 1,2-dichlorobenzene and 1,4-dichlorobenzene were reduced approximately 98% and 94%, respectively, to near or below the State Maximum Contaminant Level. 

ISCO of DNAPLs: Applicability Based on 2-Dimensional Transport Studies of DNAPL Entrapment and Oxidant Delivery Techniques

Michelle Crimi, Environmental Science and Engineering Division, Colorado School of Mines (CSM), 1500 Illinois Street, Golden, CO  80401, Tel: 303.384.2382, Fax: 303.273.3413, Email: mcrimi@mines.edu
Sarah Seitz, Aquifer Solutions, 3081 Bergen Park Drive, Suite 140, Evergreen, Colorado, Tel: 303.679.3143, Email: sseitz@aquifersolutions.com
James Kopp, Environmental Science and Engineering Division, Colorado School of Mines (CSM), 1500 Illinois Street, Golden, CO  80401, Email: jkopp@mines.edu
Jeffrey Heiderscheidt, Environmental Science and Engineering Division, Colorado School of Mines (CSM), 1500 Illinois Street, Golden, CO  80401, Tel: 303.384.2095, Fax: 303.273.3413, Email: jheiders@mines.edu
Jason Sahl, Environmental Science and Engineering Division, Colorado School of Mines (CSM), 1500 Illinois Street, Golden, CO  80401, Tel: 303.384.2095, Fax: 303.273.3413, Email: jsahl@mines.edu
Pamela Dugan, Environmental Science and Engineering Division, Colorado School of Mines (CSM), 1500 Illinois Street, Golden, CO  80401, Tel: 303.384.2095, Fax: 303.273.3413, Email: pdugan@mines.edu
Ben Petri, Environmental Science and Engineering Division, Colorado School of Mines (CSM), 1500 Illinois Street, Golden, CO  80401, Tel: 303.384.2095, Fax: 303.273.3413, Email: bpetri@mines.edu
Robert L. Siegrist, Environmental Science and Engineering Division, Colorado School of Mines (CSM), 1500 Illinois Street, Golden, CO  80401, Tel: 303.384.2158, Fax: 303.273.3413, Email: siegrist@mines.edu

In situ chemical oxidation (ISCO) is a rapidly emerging technology for remediation of organic contaminants at hazardous waste sites in the U.S. and abroad.  While much is known about oxidative destruction of aqueous phase contaminants, there are important knowledge gaps with respect to ISCO for remediation of dense non-aqueous phase liquid (DNAPL) contaminants.  DNAPLs present a particular challenge due to their low solubility and high density, which can result in release of the contaminant to ground water above regulatory limits over extensive time frames. Successful application of ISCO at DNAPL sites requires comprehensive understanding of the conditions that will impact subsurface oxidant delivery and transport to the point of reaction, and of the conditions that will affect the rate and extent of the subsequent reactions. 

Current research at the Colorado School of Mines is examining the reaction and transport processes that impact the efficiency and effectiveness of ISCO of DNAPLs.  One experimental system this research employs is a two-dimensional, flow-through cell to assess oxidation effects as a function of representative porous media structures, DNAPL mass levels and entrapment architectures, and oxidant type and delivery techniques. Twelve experimental runs are planned (7 completed to date) to evaluate the impacts of these experimental conditions.  ISCO effects are represented by (1) treatment-induced changes in DNAPL mass transfer, (2) contaminant distribution in the transport cell, (3) contaminant plume mass flux, (4) oxidant consumption, (5) % DNAPL destroyed, and (6) changes in system geochemistry (e.g., byproducts, solids, pH, ionic content, etc.).  The measurements to determine these effects are made with respect to space and time. 

Results of these experimental studies will provide the basis for future guidance on ISCO of DNAPLs so that it can be selected as a preferred remedy when appropriate, and be implemented to reliably achieve risk-based cleanup or other performance objectives. 

The Permanganate Soil Oxidant Demand: A Critical Parameter For ISCO Remediation

Kelly A. Frasco, Carus Chemical Company, 1500 Eighth St., LaSalle, IL  61301, Tel: 815-224-6852, Fax: 815-224-6869, Email: kelly.frasco@caruschem.com
Dr. Michael W. Osborne, Carus Chemical Company, 1500 Eighth St., LaSalle, IL  61301, Tel: 815-224-6852, Fax: 815 224 6869, Email: mike.osborne@caruschem.com 
Dr. Philip A. Vella, Carus Chemical Company, 1500 Eighth St., LaSalle, IL  61301, Tel: 815-224-6852, Fax: 815-224-6869, Email: phil.vella@caruschem.com

The key design parameter to consider when applying ISCO is the background permanganate soil oxidant demand (PSOD) of the treatment zone.   The PSOD is the degree to which naturally occurring materials in the soil matrix will compete with the target contamination for oxidizing reagent.  When estimating the dosage of oxidant reagent required to treat the target contaminant, it is critical that all potential oxidant demands including reduced soil minerals and natural organic matter (NOM) are considered.  A high SOD can increase the use of an oxidizing agent that the method becomes cost-prohibitive relative to alternate technologies.  Without consideration of all these potential oxidant demands in the application design process, the required amount of oxidant delivered may be underestimated and ISCO could be ineffective.

This paper will describe two emerging procedures for determining the PSOD at a potential remediation site.  The first method (PSOD-T1) is a preliminary screening tool (2 day test) that is rapid and inexpensive to perform.  It is intended to provide general information on the amount of permanganate (potassium or sodium) that could be consumed by natural materials (organic and inorganic) and any contaminates of concern (COC) in soils at a potential remediation site. Its value is in providing a first pass evaluation on the potential application of permanganate technology (e.g. is it economically viable).  This procedure provides level I screening information.  It is not intended to be exclusively used to obtain specific engineering data required for full-scale implementation.

The second procedure, PSOD-T2 (7 day test), is a more detailed procedure intended to provide additional site information.  The PSOD-T2 provides comprehensive site data including a more extensive sampling methodology, increased reaction data points and the ability to obtain reaction kinetics.  Data generated from the PSOD-T2 procedure can provide a predictive demand curve allowing the determination of longer demand values.  It can also provide the rate constant and half-life information on the SOD of the soil that can then be related to the expected half-life for the site contaminant of concern.  An example of this is shown below for TCE. 

Figure 2.  PSOD-T2 vs. COC Half Life

As shown, application of permanganate at concentrations shown in the red zone would react with the soil components in preference to the TCE.  As the permanganate concentration increases (green zone) the permanganate will react more readily with TCE than the natural occurring soil components.  Therefore, based on a kinetic analysis of the PSOD-2 results for this soil and the COC primarily comprised of TCE, a minimum permanganate concentration of 4 ppm needs to be maintained to effectively react with TCE.      

Oxidation of TNT, HMX and RDX by Iron-Chelate Activated Persulfate

George E. Hoag, Ph.D, Hoag Environmental, Systems, LLC, P.O. Box 275, Storrs, CT  06268, Tel: 860-429-3798, Fax: 860-429-0437, Email: georgehoag@earthlink.net
Scott A. Waisner, M.S., U.S. Army Engineer Research and Development Center, 3909 Halls Ferry Rd., Vicksburg, MS 39180-6199, Tel: 601-634-2286,            Fax: 601-634-4844, Email: Scott.A.Waisner@erdc.usace.army.mil

Destruction of organic compounds by direct or by free-radical-based activated persulfate (S₂O₈^2-) oxidations is gaining interest as an in situ chemical oxidation technology.  Persulfate oxidation is generally conducted under heat-, photo-, acid-, base- or metal-activated conditions because oxidation rates can be greatly accelerated, resulting from the formation of a variety free radical species.  In this work we demonstrate the efficacy of using activated persulfate to destroy energetic compounds.  Destruction of the compounds 2,4,6-Trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and their degradation products were investigated in aqueous and soil slurry batch reactors at 20^oC.  In this paper we compare the kinetics of parent compound removal to mineralization using Fe-EDTA as the activator. Mass balances using ¹⁴C-labeled parent compounds and by-products, solids and trapped CO₂ enabled an analysis of the extent of mineralization achieved under various initial conditions.  Because of the high persulfate and sulfate concentrations present in the experimental systems, numerous modifications of normally routine analytical methods were necessary to enable analysis and mass balancing of carbon and nitrogen species, as well as other products of oxidation including the Fe-chelate.

Persulfate Oxidation of TCE at Ambient Temperature: Kinetics and Influence of Radical Scavengers

Chenju Liang, D.Eng., Dept. of Environmental Engineering, National Chung Hsing University, 250 Kuo-Kuang Rd., Taichung, Taiwan, Tel: 886-4-22856610, Fax: 886-4-22862587, Email: Cliang@dragon.nchu.edu.tw
Clifford J. Bruell, Ph.D., Dept. of Civil & Environmental Engineering, University of Massachusetts Lowell, One University Ave., Lowell, MA 01854, Tel: 978-934-2284, Fax: 978-934-3052, Email: Clifford_Bruell@uml.edu
Nihar Mohanty, Massachusetts Dept. of Environmental Protection, Bureau of Resource Protection, One Winter Street, Boston, MA 02108, Tel: 617-654 6515, Fax: 617-292 5850, Email: Nihar.Mohanty@state.ma.us
Paul F. Killian, Ph.D., Ambient Engineering, Inc., 100 Main Street, Concord, MA 01742, Tel: 888-262-6232, Fax: 978-369-8380, Email: pkillian@ambient-engineering.com
Tzu-Shin Wang, Dept. of Environmental Engineering, National Chung Hsing University, 250 Kuo-Kuang Rd., Taichung, Taiwan, Tel: 886-4-22856610, Fax: 886-4-22862587, Email: prinssin@gmail.com

Field Scale Comparison of Activated Persulfate and Modified Fenton's Reagent for Treatment of Chlorinated Benzene Compounds

Brant Smith, Ph.D, P.E., Xpert Design and Diagnostics, LLC, 22 Marin Way, Unit 3, Stratham, NH 03885, Tel: 603-778-1100, Fax: 603-778-2121, Email: Smith@xdd-llc.com
Scott C. Crawford, Xpert Design and Diagnostics, LLC, 22 Marin Way, Unit 3, Stratham, NH 03885, Tel: 603-778-1100, Fax: 603-778-2121, Email: Crawford@xdd-llc.com
Ian T. Osgerby, Ph.D, P.E, U.S. Army Corps of Engineers, New England, 696 Virginia Road, Concord, MA 01742-2751, Tel: 978-318-8631, Fax: 978-318-8663, Email:  Ian.T.Osgerby@nae02.usace.army.mil
Scott E. Acone, P.E., U.S. Army Corps of Engineers, New England, 696 Virginia Road, Concord, MA 01742-2751, Tel: 978-318-8162, Fax: 978-318-8064, Email:  Scott.E.Acone@nae02.usace.army.mil
Andrew J. Boeckeler, P.G., Nobis Engineering, Inc., 18 Chenell Drive, Concord, NH  03301, Tel: 603-224-2507, Fax: 603-224-2507, Email: ABoeckeler@nobisengineering.com
Stefanie A. Getchell, P.G., Nobis Engineering, Inc., 18 Chenell Drive, Concord, NH  03301, Tel: 603-224-2507, Fax: 603-224-2507, Email: SGetchell@nobisengineering.com

A field scale pilot demonstration comparing the in situ chemical oxidation technologies (ISCO) modified Fenton’s reagent and activated persulfate was performed in November 2004 at the Eastland Woolen Mills Superfund site (site) in Corinna, Maine.  Each ISCO application was designed to treat chlorinated benzene compounds present as residual DNAPL contamination.  The site is managed by the U.S. Army Corps of Engineers for the U.S. EPA with Nobis Engineering (Concord, NH) as the primary contractor and Xpert Design and Diagnostics, LLC (XDD, Stratham, NH) as the ISCO specialist.

Modified Fenton’s reagent is based on the decomposition of hydrogen peroxide in the presence of iron that results in the formation of:  1) the hydroxyl radical, a powerful and relatively non-selective oxidant, 2) superoxide, a reductant and nucleophile, and 3) hydroperoxide, a nucleophile.  Activated persulfate is based on the decomposition of persulfate in a reaction with Fe (II) which forms the sulfate free radical, a powerful oxidant.

Modified Fenton’s reagent and activated persulfate were applied in two separate test areas (each area consisting of two injection wells at approximately 20 foot on center spacing).  The modified Fenton’s reagent area was further divided into two test areas with different geochemical conditions; i.e., one injection well was treated with acid and one injection well was left at natural pH conditions prior to peroxide injection.  A relatively large volume of acid (one pore volume of up to 11% sulfuric acid) was required to adjust the pH to the optimal range (i.e., <3.0), indicating a fairly high aquifer buffering capacity.  This confirmed prior bench testing which had indicated that this system was buffered at approximately pH 6.2, presumably due to the presence of significant amounts of carbonate minerals in the soils.  Both injection wells in the modified Fenton’s test area were then treated with one pore volume of 10 percent hydrogen peroxide.  In each instance hydrogen peroxide was applied without catalyst as the bench test indicated that there was sufficient naturally occurring catalyst.  Within the activated persulfate test area, one pore volume of approximately 130 g/L sodium persulfate solution was applied to the activated persulfate area.  The persulfate solution was activated using a catalyst solution of Fe (II) and citric acid.

A comparison of baseline and 60-day post-treatment sample results indicated that the application of hydrogen peroxide had minimal effectiveness or was effective for a limited radius of influence (ROI).  Chlorobenzene groundwater concentrations in the injection wells decreased by up to 40 percent.  However, chlorobenzene concentrations in groundwater sampled from multiple monitoring wells within 10 feet of the injection wells showed little change in comparison to the baseline results. Post-treatment soil samples in this area exhibited little change or increases in chlorobenzene concentrations.  Field parameters collected during the application indicated the distribution of dissolved oxygen over the entire 10 ft ROI; however, significant concentrations of peroxide were not observed in the same monitoring wells.

Conversely, the concentration of chlorinated benzenes in soil and groundwater was observed to significantly decrease in the persulfate area.  The post-treatment soil data indicated approximately 50 percent to 80 percent of chlorinated benzenes were degraded with a ratio of 8 lbs of persulfate per lb of contaminant degraded.  Several monitoring locations in the persulfate area also exhibited groundwater concentration decreases of greater than 80 percent.  A few monitoring locations in close proximity to the most contaminated area did exhibit increases in groundwater concentrations, but this was likely the result of displacement of highly impacted pore water from the DNAPL impacted areas.

Both Fenton’s reagent and activated persulfate are viable ISCO technologies that have been successfully applied to several sites.  The results of these pilot tests underscore the importance of site specific characteristics when applying ISCO technologies. This side by side demonstration clearly indicated that activated persulfate was the more effective technology for this particular site.  The greater stability of the persulfate in the subsurface likely resulted in better distribution of the oxidant as compared to peroxide.  Furthermore, if the buffering capacity observed in the bench test is due to carbonates, as suspected, the results suggest that the sulfate free radical may not be as limited in carbonate systems as the hydroxyl radical.  This is significant since it is well known that the hydroxyl radical is scavenged by carbonates and as a result modified Fenton’s reagent is often not applied in systems containing significant amounts of carbonate minerals.

As a result of these pilot tests activated persulfate was recommended and selected for use in the full scale application.

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