United States
Environmental Protection
Agency
Office of Research and
Development
Washington DC 20460
EPA/540/R-97/509
May 1999
vvEPA
DOE
Sandia National
Laboratories In Situ
Electrokinetic Extraction
Technology
Innovative Technology
Evaluation Report
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
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EPA/540/R-97/509
May 1999
Sandia National Laboratories
In Situ Electrokinetic Extraction
Technology
Innovative Technology Evaluation Report
National Risk Management Research Laboratory
Office of Research and Devefopment
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
Printed on Recycled Paper
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Notice
The information in this document has been funded by the U. S. Environmental Protection Agency (EPA) under Contract No.
68-C5-0037 to Tetra Tech EM Inc. It has been subjected to the Agency's peer and administrative reviews and has been
approved for publication as an EPA document. Mention of trade names or commercial products does not constitute an
endorsement or recommendation for use.
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Foreword
The U. S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation's land, air, and water
resources. .Under a mandate of national environmental laws, the Agency strives to formulate and implement actions leading to
a compatible balance between human activities and the ability of natural systems to nurture life. To meet this mandate, EPA's
research program is providing data and technical support for solving environmental problems today and building a science
knowledge base necessary to manage our ecological resources wisely, understand hdw pollutants affect our health, and prevent
or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for investigation of technological and manage-
ment approaches for reducing risks from threats to human health and the environment. The focus of the Laboratory's research
program is on methods for the prevention and control of pollution to air, land, watpr and subsurface resources; protection of
water quality in public water systems; remediation of contaminated sites and groundwater; and prevention and control of
indoor air pollution. The goal of this research effort is to catalyze development! and implementation of innovative, cost-
effective environmental technologies; develop scientific and engineering information needed by EPA to support regulatory and
policy decisions; and provide technical support and information transfer to ensure effective implementation of environmental
regulations and strategies.
This publication has been produced as part of the! Laboratory's strategic long-term research plan. It is published and made
available by EPA's Office of Research and Development to assist the user community and to link researchers with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
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Abstract
This report evaluates an in situ electrokinetic extraction system's ability to remove hexavalent chromium in the form of
chromate ions from soil under unsaturated conditions. Specifically, this report discusses performance and economic data from
a Superfund Innovative Technology Evaluation (SITE) demonstration of an In Situ Electrokinetic Extraction (ISEE) system
developed by Sandia National Laboratories (SNL).
The ISEE system demonstrated combines electrokinetic and lysimeter technologies. The lysimeter technology hydraulically
and electrically creates a continuum between fluid in the anode casings (anolyte) and soil pore water, thereby enabling
extraction of the chromate ions in the anolyte while the anolyte is held in the electrode casing through application of a vacuum.
This feature allowed removal of chromate from unsaturated soil during the demonstration without significantly altering the soil
moisture content.
The ISEE system developed by SNL was demonstrated at the U.S. Department of Energy SNL Chemical Waste Landfill
(CWL) site's Unlined Chromic Acid Pit (UCAP) in Albuquerque, New Mexico, from May 15 to November 24, 1996. The
system was housed in two buildings: a control trailer and a temporary structure. The electrode system of the ISEE system
consisted of an anode row oriented east to west and four rows of cathodes parallel to the anode row, two rows to the north and
two rows to the south of the anode row. The entire system was operated for a total of 2,727 hours during 13 tests performed
in six phases. The first 12 tests were performed to determine the preferred operating conditions for Test 13, which consisted
of system performance testing under SNL's preferred operating conditions for the SITE demonstration.
Approximately 520 grams (g) of hexavalent chromium was removed during the demonstration. Overall hexavalent chromium
removal rates varied from 0.074 gram per hour (g/hour) during Test 1 to 0.338 g/hour during Test 5. Overall hexavalent
chromium removal efficiencies varied from 0.0359 gram per kilowatt-hour (g/kW-h) during Test 7 to 0.136 g/kW-h during
Test 13. More than 50 percent of the postdemonstration soil samples exceeded the toxicity characteristic leaching procedure
(TCLP) limit of 5 milligrams per liter (mg/L) for total chromium. The soil TCLP leachate concentrations that were above the
TCLP limit ranged from 6 to 67 mg/L. Downtime during system operation ranged from 0 percent during Test 11 to 66 percent
during Test 1. Over the entire demonstration, the ISEE system was on line 64 percent of the time.
Economic data indicate that the costs for treating 16 cubic yards (yd3) of hexavalent chromium-contaminated soil with the ISEE
system configuration used during Test 13 are about $1,400 per yd3 for 200 g of hexavalent chromium removed.
The ISEE technology developed by SNL is applicable for treating unsaturated soil contaminated with hexavalent chromium.
According to SNL, this technology can be modified to treat saturated contaminated soil and to remove contaminants dissolved
in pore water other than chromate. A full-scale, commercial system has not yet been developed. SNL maintains that a full-
scale system would be significantly be improved over the system tested during the demonstration. Therefore, further
performance and cost analyses should be performed on a full-scale system.
iv
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Contents
Notice ii
Foreword iii
Abstract iv
Acronyms, Abbreviations, and Symbols ix
Conversion Factors xi
Acknowledgments xii
Executive Summary .' 1
1 Introduction 7
1.1 Brief Description of SITE Program and Reports .' 7
1.1.1 Purpose, History, and Goals of the SITE Program ' 7
1.1.2 Documentation of SITE Demonstration Results 8
1.2 Purpose and Organization of the ITER 8
1.3 Background Information on the Demonstration of the SNLISEE System under
the SITE Program 9
1.4 Technology Description j 9
1.4.1 Process Chemistry .: 9
1.4.1.1 Electromigration 10
1.4.1.2 Electroosmosis 11
1.4.2 SNL ISEE System 12
1.4.2.1 Electrode System 12
1.4.2.2 Water Control System : 16
1.4.2.3 Vacuum Control System „ 17
1.4.2.4 Power Supply System 17
1.4.2.5 Monitoring System 18
1.4.2.6 Ancillary Equipment 19
1.4.3 Innovative Features of the Technology .; 19
1.5 Applicable Wastes 20
1.6 Key Contacts .; 20
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Contents (continued)
2 Technology Effectiveness and Application Analysis 22
2.1 Overview of ISEE System SITE Demonstration 22
2.1.1 Project Objectives 22
2.1.2 Demonstration Approach 23
2.1.3 Sampling and Analytical Procedures 23
2.2 SITE Demonstration Results 25
2.2.1 Removal of Hexavalent Chromium from Site Soil 26
2.2.2 Compliance with TCLP Regulatory Criterion for Total Chromium 33
2.2.3 Removal of Trivalent Chromium from Site Soil 33
2.2.4 Operating Problems 33
2.3 Factors Affecting Performance 33
2.3.1 Waste Characteristics 33
2.3.2 Operating Parameters 37
2.3.3 Maintenance Requirements 38
2.4 Site Characteristics and Support Requirements 38
2.4.1 Site Access, Area, and Preparation Requirements 38
2.4.2 Climate Requirements 38
2.4.3 Utility and Supply Requirements 38
2.4.4 Support System Requirements 38
2.4.5 Personnel Requirements 39
2.5 Material Handling Requirements 39
2.6 Technology Limitations ; 38
2.7 Potential Regulatory Requirements 39
2.7.1 Comprehensive Environmental Response, Compensation, and Liability Act 39
2.7.2 Resource Conservation and Recovery Act 41
2.7.3 Clean Air Act 42
2.7.4 Toxic Substances Control Act 42
2.7.5 Atomic Energy Act and Resource Conservation and Recovery Act 42
2.7.6 Occupational Safety and Health Administration Requirements 43
2.8 State and Community Acceptance 43
3 Economic Analysis 44
3.1 Introduction 44
3.2 Issues and Assumptions 44
3.3 Basis for Economic Analysis 45
VI
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Contents (continued)
3.3.1 Site and Facility Preparation Costs 49
3.3.2 Permitting and Regulatory Costs 49
3.3.3 Equipment Costs , . 49
3.3.4 Startup and Fixed Costs 50
3.3.5 Labor Costs ., 50
3.3.6 Supplies and Consumables Costs 50
3.3.7 Utilities Costs 50
3.3.8 Effluent Treatment and Disposal Costs 50
3.3.9 Residuals and Waste Shipping, Handling, and Transport Costs 51
3.3.10 Analytical Costs j 51
3.3.11 Facility Modification, Repair, and Replacement Costs 51
3.3.12 Site Restoration Costs 51
3.4 Conclusions 51
4 Technology Status 52
5 References •. 54
Appendix
Vendor's Claims for the Technology • 55
Figures
1-1 Electrokinetic Phenomena in a Soil Pore 10
1-2 ISEE System Schematic Diagram 13
1-3 ISEE System Electrode Layout 14
1-4 Anode/Cathode and Cold Finger Cathode Construction Cross Sections 15
2-1 Hexavalent Chromium Removal Efficiency Per Electrode for Test 13 28
2-2 Hexavalent Chromium Removal Rate Per Electrode for Test 13 29
2-3 Spatial Distribution of Hexavalent Chromium Concentrations In Soil 30
2-4 Spatial Distribution of TCLP Leachable, Chromium Concentrations in Soil 34
2-5 Spatial Distribution of Total Chromium Concentrations in Soil 35
VII
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Tables
ES-lSuperfund Feasibility Evaluation Criteria for the ISEE Technology 5
1-1 Correlation Between Superfund Feasibility Evaluation Criteria and ITER Sections 8
1-2 Monitoring System Parameters 18
1-3 Comparison of In Situ Treatment Technologies for Metals-Contaminated Soil 21
2-1 Test Matrix for SNL ISEE System Demonstration 24
2-2 SNL ISEE System Preferred Operating Conditions 25
2-3 SNL ISEE System Performance Data 27
2-4 Statistical Summary of Hexavalent and Total Chromium Analytical Results 32
2-5 System Shutdown Information : 37
2-6 Summary of Applicable Regulations 40
3-1 Estimated Costs for Treatment Using the SNL ISEE System 46
3-2 Estimated Cost Percentages for Treatment Using the SNL ISEE System 48
VII!
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Acronyms, Abbreviations, and Symbols
AAA Abbreviated analytical approach
AEA Atomic Energy Act
amp Ampere
ARAR Applicable or relevant and appropriate requirement
bgs Below ground surface
CAA Clean Air Act
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act of 1980
CFR Code of Federal Regulations
CWL Chemical waste landfill •;
DC Direct current .
DOE U.S. Department of Energy
EPA U.S. Environmental Protection Agency
g Gram
g/hour Gram per hour
g/kW-h Gram per kilowatt-hour ;
ICP Inductively coupled plasma
ISEE In situ electrokinetic extraction
ITER Innovative technology evaluation report
kW Kilowatt :
kW-h Kilowatt-hour
LDR Land Disposal Restriction
L/min Liter per minute
mg/kg Milligram per kilogram
mg/L Milligram per liter
m/s Meter per second
mW-s Square meter per volt-second
N-s/m2 Newton-second per square meter
N/V2 Newton per square volt
NCP National Oil and Hazardous Substances Contingency Plan
NPDES National Pollutant Discharge Elimination System
NRMRL National Risk Management Research Laboratory
IX
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Acronyms, Abbreviations, and Symbols (continued)
NSPS New Source Performance Standard
O&M Operation and maintenance
ORD Office of Research and Development
OSHA Occupational Safety and Health Administration
OSWER Office of Solid Waste and Emergency Response
PCB Polychlorinated biphenyl
PPE Personal protective equipment
ppm Part per million
psi Pound per square inch
PVC Polyvinyl chloride
QA Quality assurance
QC Quality control
QAPP Quality assurance project plan
Quanterra Quanterra Environmental Services, Inc.
RCRA Resource Conservation and Recovery Act of 1976
SAP Sampling and analysis plan
SITE Superfund Innovative Technology Evaluation
SNL Sandia National Laboratories
TCLP Toxicity characteristic leaching procedure
TER Technology evaluation report
TSCA Toxic Substances Control Act
UCAP Unlined chromic acid pit
V Volt
V/m Volt per meter
VOC Volatile organic compound
yd3 Cubic yard
ug/L Microgram per liter
> Greater than
< Less than
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Conversion Factors
To Convert From
To
Multiply By
Length
Area:
Volume:
inch
foot
mile
square foot
acre
gallon
cubic foot
centimeter
meter
kilometer
square meter
square meter
liter
cubic meter
2.54
0.305
1.61
0.0929
4,047
3.78
0.0283
Mass:
pound
kilogram
0.454
Energy:
kilowatt-hour
megajoule
3.60
Power:
kilowatt
horsepower
1.34
Temperature: (°Fahrenheit - 32) °Celsius
0.556
XI
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Acknowledgments
This report was prepared under the direction and coordination of Mr. Randy Parker, U.S. Environmental Protection Agency
(EPA) Superfund Innovative Technology Evaluation (SITE) program project manager of the National Risk Management
Research Laboratory (NRMRL) in Cincinnati, Ohio. Contributors and reviewers for this report were Sam Hayes and Ed Earth
of EPA NRMRL, Cincinnati, Ohio; and Dr. Eric Lindgren of Sandia National Laboratories, Albuquerque, New Mexico. This
report was prepared for EPA's SITE program by Dr. Kirankumar Topudurti, Ms. Cristina Radu, Mr. Shin Ahn, and Ms. Linda
Hunter of Terra Tech EM Inc.
XI!
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Executive Summary
The electrokinetic extraction technology is a treatment
process that facilitates the in situ extraction of metals from
' unsaturated and saturated soil. The In Situ Electrokinetic
Extraction (ISEE) system developed by Sandia National
Laboratories (SNL) focused on the remediation of
hexavalent chromium-contaminated soil under unsaturated
conditions (optimal moisture content in the range 10 to 12
percent by weight, representing approximately 25 percent
saturation). The SNL ISEE system was accepted into the
Superfund Innovative Technology Evaluation (SITE)
Demonstration program in Summer* 1994 and was
demonstrated at the U.S. Department of Energy (DOE)
SNL Chemical Waste Landfill (CWL) site's Unlined
Chromic Acid Pit (UCAP) in Albuquerque, New Mexico,
from May 15 to November 24, 1996. This demonstration
was funded by DOE's Office of Science and Technology
through the Subsurface Contamination Focus Area. The
ISEE system was independently evaluated under the SITE
program.
The purpose of this innovative technology evaluation
report (ITER) is to present information that will assist
Superfund decision-makers in evaluating the ISEE system
developed by SNL for application to a particular
hazardous waste site cleanup. The report provides an
introduction to the SITE program and ISEE system
technology (Section 1), analyzes the .technology's
effectiveness and applications (Section 2), analyzes the
economics of using the ISEE system to treat soil
contaminated with hexavalent chromium in the form of
chromate (Section 3), summarizes the technology's status
(Section 4), and presents a list of references used to
prepare the ITER (Section 5). Vendor's claims for the
ISEE system are presented in the appendix.
This executive summary briefly describes the ISEE
technology and system, provides an overview of the SITE
demonstration of the technology, summarizes the SITE
demonstration results, discusses the economics of using
the ISEE system to treat soil contaminated with hexavalent
chromium in the form of chromate, and discusses the
Superfund feasibility evaluation criteria for the ISEE
system.
Technology and System Description
The ISEE system developed by SNL applied electrokinetic
technology to unsaturated soil to remove hexavalent
chromium. The application of current to the soil-water
system results in the following: (1) ionic species in the soil
pore water migrate to the oppositely charged electrode (a
phenomenon '. called electromigration), (2) charged
particles in the soil pore water migrate to the oppositely
charged electrode (a phenomenon called electrophoresis),
(3) bulk water; moves toward the cathode (a phenomenon
called electrobsmosis), and (4) electrolysis reactions
occur at the 'electrodes. The combination of these
phenomena results in the movement of ionic contaminants
toward the electrodes. The direction and rate of movement
will depend on the charge of the ions (both in terms of
magnitude an
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The operation of the ISEE system was regulated by a water
control system, a vacuum control system, a power supply
system, a monitoring system, and ancillary equipment.
The anodes and cathodes used at UCAP were designed to
combine electrokinetic and lysimeter technologies. This
combination was necessary to allow the operation of the
system under unsaturated soil conditions. Lysimeter
technology hydraulically and electrically creates a
continuum between the anolyte and the pore water,
thereby enabling the extraction of the chromate ions in the
anolyte while the anolyte is held in the electrode casings
through the application of a vacuum. This feature allowed
the removal of chromate from unsaturated soil during the
demonstration without significantly altering the soil
moisture content.
The ISEE technology developed by SNL is applicable for
treating unsaturated soil contaminated with hexavalent
chromium. According to SNL, this technology can be
modified to treat saturated contaminated soil and to
remove contaminants dissolved in pore water besides
chromate. Because other anions will compete with the
targeted contaminant ions to be removed, it is necessary to
determine the electrical conductivity of soil pore water and
the target ion concentration to determine the applicability
of the ISEE technology.
Overview of the SNL ISEE System SITE
Demonstration
The ISEE system SITE demonstration took place at the
UCAP, which is part of the CWL site located within
Technical Area III at SNL. The UCAP is a rectangular pit
measuring about 15 by 45 feet and is 10 feet deep. The
areal extent and depth of the area targeted by the
demonstration was selected based on the highest results of
water soluble chromium concentrations from sampling
performed during previous investigations. During the
demonstration, the system was operated for a period of
2,727 hours between May 15 and November 24, 1996.
The primary objective of the technology demonstration
was to estimate the amount of hexavalent chromium
removed from soil by the ISEE system because the ISEE
system is primarily designed to remove hexavalent
chromium. To accomplish this objective, SNL collected
and analyzed anolyte samples for hexavalent chromium at
its field laboratory throughout the demonstration period.
An independent check of field analytical data was
provided by EPA through split sample analysis at an off-
site laboratory. Field analytical data were subsequently
deemed adequate to estimate the amount of hexavalent
chromium removed from soil by the ISEE system.
Predemonstration and postdemonstration soil samples
collected by EPA were analyzed for hexavalent chromium
to verify the hexavalent chromium removal estimate based
on anolyte sample analyses.
The secondary objectives of the technology demonstration
were to determine whether treated soil meets the toxicity
characteristic leaching procedure (TCLP) regulatory
criterion for total chromium and to evaluate the ISEE
system's ability to remove trivalent chromium from site
soil.
To conduct the demonstration, SNL was required to meet
the conditions of the New Mexico Environmental
Department's Resource Conservation and Recovery Act
(RCRA) Research, Development, and Demonstration
permit for the ISEE system. Predemonstration testing
results indicated that some of the soil in the demonstration
area is hazardous (EPA waste code D007) because
chromium concentrations exceeded the TCLP criterion for
chromium. Therefore, the permit required that SNL
perform postdemonstration TCLP testing to determine the
impact of the ISEE system on soil known to be
contaminated. SNL therefore collected a large number of
treated soil samples for total chromium analysis after
extraction using TCLP.
Because incidental removal of trivalent chromium will
likely be accomplished by the ISEE system, evaluation of
trivalent chromium removal was a secondary project
objective of this project. To accomplish this objective, the
predemonstration and postdemonstration soil samples
collected for hexavalent chromium analysis were also
analyzed for total chromium so that the trivalent
chromium concentrations could be calculated as the
difference between the total and hexavalent chromium
concentrations.
During the SITE demonstration, 13 tests were performed
during six phases. The test areas ranged from 36 to 72
square feet, and contaminated soil from 8 to 14 feet bgs
was treated. The first 12 tests were conducted so that SNL
could determine the preferred operating conditions for
Test 13 and to facilitate the migration of hexavalent
chromium toward the central portion of the test area. Test
13 consisted of system performance testing under SNL's
preferred operating conditions for the SITE demonstration.
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Three sampling events occurred during the ISEE system
SITE demonstration: one of predemonstration soil, one of
anolyte (electrolyte from the anodes), and one of
postdemonstration soil. SNL collected predemonstration
soil samples from various depth in boreholes within and
near the test areas using a 1 -inch-diameter by 24-inch-long
Geoprobe® Large Bore Sampler. SNL extracted a portion
of each sample with water and analyzed the extract for
chromium. Additional sample portions were sent to an
off-site laboratory in order to have these soil samples
extracted using TCLP and the extracts analyzed, for total
chromium. EPA used SNL's archived soil samples to
determine total and hexavalent chromium concentrations
in the predemonstration soil.
During operation of the ISEE system, SNL collected
anolyte samples daily and analyzed them for hexavalent
chromium to determine removal rates. To verify these
results, EPA obtained anolyte samples from all four
operating anodes daily for 8 days. These samples were all
sent to Quanterra for analysis for hexavalent chromium.
The relative percent differences between the SNL and
Quanterra results varied from 0 to 20 percent indicating
that SNL's field hexavalent chromium analyses were
acceptable.
After the demonstration, EPA collected soil samples using
the Geoprobe® from locations near (within 1 foof: laterally
and 2 inches vertically) the predemonstration sampling
locations and sent these samples to an off-site laboratory
for the same sort of preparation and analyses for
hexavalent chromium and total chromium conducted
during predemonstration sampling. SNL collected a
separate series of Geoprobe® samples and sent them to an
off-site laboratory for TCLP extraction and total
chromium analysis.
SITE Demonstration Results
Key findings of the ISEE system SITE demonstration are
listed below.
• Approximately 520 grams (g) of hexavalent
chromium were removed during the entire
demonstration. Overall hexavalent chromium
removal rates varied from 0.074 gram per hour (g/
hour) during Test 1 to 0.338 g/hour during Test 5.
Overall hexavalent chromium removal efficiencies
varied from 0.0359 gram per kilowatt-hour (g/kW-h)
during Test 7 to 0.136 g/kW-h during Test 13.
The total mass of hexavalent chromium extracted by
the ISEE system should have been verified by
calculating the difference between hexavalent
chromiuin mass in treated soil before and after the
demonstration. However, soil results for hexavalent
chromium exhibited a high spatial variability
resulting; from (l)the nonhomogeneous distribution
of chrofnate concentrations in soil before the
demonstration and (2) the fact that the demonstration
was terminated before chromate removal was
completed. In addition, limited data appear to indicate
that contaminants had likely migrated from areas
outside of and near the treatment area. Thus, a
determination of the mass of hexavalent chromium
removed: based on soil sampling results was not
possible.:
Of the 43 predemonstration soil samples analyzed by
TCLP, 18 exceeded the TCLP limit of 5 milligrams
per liter (mg/L) of total chromium at concentrations
ranging from 5.6 to 103 mg/L, with a median
concentration of 15.4 mg/L. Postdemonstration
results indicate that 18 out of 3 5 soil samples exceeded
the TCIiP regulatory criterion for chromium at
concentrations ranging from 6 to 67 mg/L, with a
median concentration of 20.4 mg/L.
Trivalent chromium concentrations were to be
determined by calculating the difference between total
and hexavalent chromium concentrations. In general,
the ratio; of trivalent chromium to total chromium
ranged from 7.6 to 94.9 percent in the predemonstration
samples , and from 27.6 to 99.6 percent in the
postdemonstration samples. This large variability
precluded the calculation of trivalent chromium
concentrations as originally intended because it would
have further increased the data variability. Therefore,
no conclusion was drawn regarding the ISEE system's
ability to; remove trivalent chromium.
i
The entire system was operated for a total of 2,727
hours during 13 tests performed in six phases. The
first 12 tests were performed to determine the
preferred operating conditions for Test 13. Test 13
consisted of system performance testing under SNL's
preferred operating conditions for the SITE
demonstration.
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Economics
Based on information provided by SNL and the results and
experiences gained from the SITE demonstration, an
economic analysis was performed to examine 12 separate
cost categories for using the ISEE technology to remediate
hexavalent chromium-contaminated, unsaturated soils.
According to SNL, a full-scale commercial system design
would significantly differ from the system operated during
the demonstration. In addition, the developer has not
completed a full-scale design of a commercial ISEE
system. Therefore, it is not possible to prepare a cost
estimate for a full-scale ISEE system. Because SNL states
that the full-scale treatment system design will be
significantly improved based on the performance of the
system used during the demonstration, the treatment cost
of a full-scale system will also differ from the treatment
cost of the system operated during the demonstration.
When the technology is ready for commercialization.,
further economic analysis should be performed.
Treatment costs were determined for the ISEE system
configuration used during Test 13 (SNL's preferred
operating conditions) to treat 16 cubic yards (yd3) of soil
and remove 200 g of hexavalent chromium (the
approximate mass of hexavalent chromium removed
during Test 13). Because the treatment volume is only 16
ydj and the ISEE system configuration used during Test 13
is currently at the pilot-scale level, the cost per yd3 of
treated soil is very high; the estimated treatment costs are
about $1,400 per yd3 for 200 g of hexavalent chromium
removed. If SNL is able to further optimize the ISEE
system configuration so that hexavalent chromium
removal rate increases from that calculated for Test 13,
treatment time and costs will be lower. As mentioned
above, costs from economic analysis of a full-scale ISEE
system would be more indicative of costs of a commercial-
scale ISEE system.
Super-fund Feasibility Evaluation Criteria for the
ISEE System
Table ES-1 briefly discusses the Superfund feasibility
evaluation criteria for the ISEE system to assist Superfund
decision-makers considering the technology for
remediation of contaminated groundwater or soil at
hazardous waste sites.
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Table ES-1. Superfimd Feasibility Evaluation Criteria for the ISEE Technology
Criterion
Discussion
Overall Protection of
Human Health and the
Environment
The ISEE technology is expected to protect human health by lowering the
concentration of hexavalent chromium in soil under unsaturated conditions.
According to the developer, the technology can also treat soil contaminated
with other heavy metals under both saturated and unsaturated conditions, but
this capability was not evaluated during the SITE demonstration.
Overall reduction of human health risk should be evaluated on a site-specific
basis because VOCs could be stripped from soil during treatment and increase
VOC soil vapor concentrations and VOC migration in the soil. Also, the system
effluent (anolyte) contains hexavalent chromium and therefore needs to be
characterized and handled and disposed of as hazardous waste.
The technology protects the environment by curtailing migration of hexavalent
chromium in soil.
Protection of the environment at and beyon'd the point of anolyte extraction
depends on how the anolyte is handled and disposed of. Protection of the
environment also depends on the extent of VOC emissions.
Compliance with
Applicable or Relevant
and Appropriate
Requirements (ARAR)
According to the developer, the technology has the potential to comply with
existing federal, state, and local ARARs (for example, TCLP limits) for several
inorganic contaminants (for example, chromium). However, about 51 percent
of the postdemonstration samples did not meet the chromium TCLP limit of 5
mg/L.
Long-Term
Effectiveness and
Permanence
Reduction of Toxicity,
Mobility, or Volume
Through Treatment
Human health risk can be reduced to acceptable levels by treating soil to a 1 x
10"6 excess lifetime cancer risk level. The time needed to achieve cleanup goals
depends primarily on contaminated soil characteristics.
The treatment achieved is permanent because contaminants are contained in
the anolyte, which is extracted from the soil for disposal.
Periodic review of treatment system performance is needed because application
of the technology to contaminated soil at hazardous waste sites is new.
The technology reduces the volume and mobility of contaminants in soil
because contaminants are contained in the Anolyte, which is extracted from the
soil for disposal, :
The technology can effectively control soil contaminant migration because
contaminants are contained in the anolyte, Vvhich is extracted from the soil for
disposal. !
Short-Term
Effectiveness
About 51 percent of postdemonstration samples did not meet the chromium
TCLP limit of 5 mg/L. This failure may be because the developer did not have
the state permit required to carry out the demonstration for a longer period of
time. '
Implementability
The technology is still in the development stage. No commercial system is
currently available from SNL.
• State and local permits must be obtained to: operate the ISEE system.
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Table ES-1. Supcrfund Feasibility Evaluation Criteria for the ISEE Technology (continued)
Criterion
Discussion
Cost
Treatment costs vary significantly depending on the size of the treatment
system used, contaminant characteristics and concentrations, cleanup goals,
the volume of contaminated soil to be treated, and the length of treatment.
Economic data indicate that soil remediation costs are very high, perhaps
because the system demonstrated at UCAP was not of commercial scale and
requires significant improvements.
State Acceptance
This criterion is generally addressed in the record of decision. State acceptance
of the technology will likely depend on (1) expected residual contaminant in
soil, (2) how the anolyte is handled and disposed of, and (3) the steps taken to
reduce the potential for VOC migration.
Community Acceptance
This criterion is generally addressed in the record of decision after community
responses have been received during the public comment period. Because
communities are not expected to be exposed to harmful levels of fugitive
emissions, the level of community acceptance of the technology is expected to
be moderate.
-------
Section 1
Introduction
This section briefly describes the Superfund Innovative
Technology Evaluation (SITE) program and SITE reports;
states the purpose and organization of this innovative
technology evaluation report (ITER); provides background
information on the demonstration of the Sandia National
Laboratories (SNL) In Situ Electrokinetic Extraction
(ISEE) system under the SITE program; describes the
ISEE technology; identifies wastes to which this
technology can be applied; and provides a list of key
contacts for information about the system and SITE
demonstration.
1.1 Brief Description of SITE Program
and Reports
This section provides information about the purpose,
history, and goals of the SITE program and about reports
that document SITE demonstration results.
1.1.1 Purpose, History, and Goals of the
SITE Program
The primary purpose of the SITE program is to advance
the developmenfand demonstration, and thereby establish
the commercial availability, of innovative treatment
technologies applicable to Superfund and other hazardous
waste sites. The SITE program was established by the
U.S. Environmental Protection Agency (EPA) Office of
Solid Waste and Emergency Response (OSWER) and
Office of Research and Development (ORD) in response
to the Superfund Amendments and Reauthorization Act of
1986 (SARA), which recognized the need for an
alternative or innovative treatment technology research
and demonstration program. The SITE program is
administered by ORD's National Risk Management
Research Laboratory (NRMRL). The overall goal of the
SITE program is to research, evaluate, test, develop, and
demonstrate alternative or innovative treatment
technologies that can be used in response actions to
achieve long-term protection of human health and welfare
and the environment.
This ITER wks prepared under the SITE Demonstration
program. The objective of the Demonstration program is
to provide reliable performance and cost data on
innovative technologies so that potential users can assess a
given technology's suitability for specific site cleanups.
To produce useful and reliable data, demonstrations are
conducted at actual hazardous waste sitos or 'under
conditions that closely simulate actual waste site
conditions. ,
Data collected during the demonstration are used to assess
the performance of the technology, the potential need for
pretreatment and post-treatment processing of the treated
waste, the types of wastes and media that can be treated by
the technology, potential treatment system operating
problems, and approximate capital and operating costs.
Demonstration data can also provide insight into a
technology's i long-term operation and maintenance
(O&M) costs and long-term application risks.
Under each1 SITE demonstration, a technology's
performance in treating an individual waste at a particular
site is evaluated. Successful demonstration of a
technology at i one site does not ensure its success at other
sites. Data obtained from the demonstration may require
extrapolation to estimate a range of operating conditions
over which the technology performs satisfactorily. Also,
any extrapolation of demonstration data should be based
on other information about the technology, such as case
study information.
Implementation of the SITE program is a significant,
ongoing effort involving ORD, OSWER, various EPA
regions, and private business concerns, including
technology developers and parties responsible for site
-------
remediation. The technology selection process and the
Demonstration program together provide a means to
perform objective and carefully controlled testing of field-
ready technologies. Innovative technologies chosen for a
SITE demonstration must be pilot- or full-scale
applications and must offer some advantage over existing
technologies. Mobile technologies are of particular
interest.
1.1.2 Documentation of SITE
Demonstration Results
The results of each SITE demonstration are usually
reported in four documents: the demonstration bulletin,
technology capsule, technology evaluation report (TER),
and ITER.
The demonstration bulletin provides a two-page
description of the technology and project history,
notification that the demonstration was completed, and
highlights of the demonstration results. The technology
capsule provides a brief description of the project and an
overview of the demonstration results and conclusions.
The purpose of the Technology Evaluation Report (TER)
is to consolidate all information and records acquired
during the demonstration. It contains both a narrative
portion and tables that summarize data. The narrative
portion discusses predemonstration, demonstration, and
postdemonstration activities, any deviations from the
sampling and analysis plan (SAP) during these activities,
and the impact of such deviations, if applicable. The tables
summarize quality assurance and quality control (QA/QC)
data and data quality objectives. The TER is not formally
published by EPA. Instead, a copy is retained by the EPA
project manager as a reference for responding to public
inquiries and for recordkeeping purposes. The purpose
and organization of the ITER are discussed below.
1.2 Purpose and Organization of
the ITER
Information presented in the ITER is intended to assist
Superfund decision-makers in evaluating specific
technologies for a particular cleanup situation. Such
evaluations typically involve the nine remedial technology
feasibility evaluation criteria, which are listed in Table 1-
1 along with the sections of the ITER where information
related to each criterion is discussed. The ITER represents
a critical step in the development and commercialization
of a treatment technology. The report discusses the
effectiveness and applicability of the ISEE system and
Table 1-1. Correlation Between Superfund Feasibility Evaluation Criteria and ITER Sections
Evaluation Criterion8
ITER Section
Overall protection of human health and the
environment
Compliance with ARARs"
Long-term effectiveness and permanence
Reduction of toxicity, mobility, or volume through
treatment
Short-term effectiveness
Implementability
Cost
State acceptance
Community acceptance
2.2.1 through 2.2.3
2.2.2 and 2.7
1.4 and 2.2.1
2.2.1 and 2.2.2
2.2.1 through 2.2.3
1.4, 2.2, 2.3, and 2.4
3.0
2.8
2.8
Note:
Source: EPA 1988
ARAR = Applicable or relevant and appropriate requirement
-------
analyzes costs associated with its application. The
system's effectiveness is evaluated based on data
collected during the SITE demonstration and from other
case studies. The applicability of the system is discussed
in terms of waste and site characteristics that could affect
technology performance, material handling requirements,
technology limitations, and other factors.
This ITER consists of five sections, including this
introduction. These sections and their contents are
summarized below.
• Section 1, Introduction, presents a brief description of
the SITE program and reports, the purpose and
organization of the ITER, background information
about the ISEE system demonstration under the SITE
program, a technology description, applicable wastes
that can be treated, and key contacts for information
about the ISEE system and SITE demonstration.
• Section 2, Technology Effectiveness and Application
Analysis, presents an overview of the SNL ISEE
system SITE demonstration, SITE demonstration
results, factors affecting ISEE system performance,
site characteristics and support requirements, material
handling requirements, technology limitations,
potential regulatory requirements, and state and
community acceptance.
• Section 3, Economic Analysis, discusses estimated
costs, issues and assumptions, and the basis for the
economic analysis.
• Section 4, Technology Status, discusses the
developmental status of the ISEE system.
• Section 5, References, lists references used to prepare
this ITER.
In addition to these sections, this ITER has an appendix,
Vendor's Claims for the Technology.
1.3 Background Information on the
Demonstration of the SNL ISEE
System Under the SITE Program
The SNL ISEE system was accepted into the SITE
Demonstration program in Summer 1994. The ISEE
system was demonstrated at the U.S. Department of
Energy (DOE) SNL Chemical Waste Landfill (CWL)
site's Unlined Chromic Acid Pit (UCAP) in Albuquerque,
New Mexico^ from May 15 to November 24, 1996. This
demonstration was funded by DOE's Office of Science
and Technology through the Subsurface Contamination
Focus Area. The ISEE system was independently
evaluated under the SITE program.
1.4 Technology Description
This section describes the ISEE process chemistry, ISEE
treatment system, and innovative features of the
technology. ]
1.4.1 Process Chemistry
The ISEE technology is a treatment process that facilitates
the in situ extraction of metals from unsaturated and
saturated soil. The electrokinetic removal system
developed by SNL focused on the remediation of
hexavalent chromium-contaminated soil under unsaturated
conditions (moisture content as low as 7 percent by
weight, representing approximately 25 percent saturation
in laboratory studies) (Lindgren and others 1991).
I
The application of electrokinetics to various types of
unsaturated soils, including clays and sands, has been
studied by numerous investigators. Electrokinetic
systems apply low-level direct current (DC) on the order
of milliamperes per square centimeter between electrodes,
thus establishing an electrical potential on the order of
volts per centimeter across the electrodes. Electrokinetic
systems are effective as long as the pore water in the soil
can maintain the electrical potential between the
electrodes (Lindgren and others 1991).
The application of the current to the soil-water system
under saturated or unsaturated conditions results in the
following: (1) ionic species in the soil pore water migrate
to the oppositely charged electrode (a phenomenon called
electromigration), (2) charged particles in the soil pore
water migrate to the oppositely charged electrode (a
phenomenon called electrophoresis), (3) bulk water
moves toward the cathode (a phenomenon called
electroosmosis), and (4) electrolysis reactions occur at the
electrodes (Hunter 1981). Figure 1-1 is a diagram of these
phenomena. The combination of these phenomena results
in the movement of ionic contaminants toward the
electrodes. The direction and rate of movement will
depend on the charge of the ions (both in terms of
magnitude and polarity), the degree to which the ions
-------
Hydroxyl Ion
Soil Particle
Hydrogen Ion
®@ © © ©
Charged
< Particle
Cathode
Electrical
Double
layer
Soil Particle
Figure 1-1. Electrokinetic phenomena in a soil pore.
adsorb to the soil particles, and the magnitude of the
electroosmosis flow velocity. Contaminants arriving at
the electrodes can be removed by extracting the pore water
near the electrodes, electroplating or adsorbing
contaminants onto the electrodes, precipitating and
ooprecipitating contaminants at the electrodes, or
complexing the contaminants with ion-exchange resins
(Mattson and Lindgren 1993).
The two most important transport mechanisms in
electrokinetic remediation are electromigration and
electroosmosis. Previous testing does not prove that
electrophoresis is an efficient transport mechanism
because the flow of colloid particles requires large pore
spaces and the colloid particles are likely to become
mechanically lodged in the pore space and taken out of
suspension. On the other hand, electromigration and
electroosmosis follow the potential gradient and are
independent of pore size. Electromigration and
electroosmosis are briefly discussed below.
1.4.1.1 Electromigration
Electromigration represents the transport of ionic species
in pore fluid across the soil mass under the influence of an
electric field. These ionic species may include anions such
as CrO4% HAsO4% SeO4% and carbonate complexes of
uranium and cations such as Cr3^ Na+, Fe2+, and Fe3+.
The electromigration velocity of an ion in a dilute solution
is a function of the electrical ionic mobility of a species
(the ionic transport rate under the voltage gradient). A
tortuosity term can be incorporated into the general ionic
transport equation to account for the nonlinear path of ion
travel in a soil matrix (Shapiro 1990). Equation 1-1
presents a modified version of the general ionic transport
equation, which is specific for movement under a voltage
gradient.
dV
(i-i)
10
-------
where:
dV/dx =
electromigration velocity (meter per
second [m/s])
electric ionic mobility (square meter per
volt-second [m2 /V-s])
tortuosity (dimensionless)
voltage gradient (volt per meter [V/m])
1.4.1.2 Electroosmosis
Most clay minerals have a negatively charged surface
mainly resulting from imperfections in the mineral lattices
developing during formation. The excess negative charge
on the soil surface results in the attraction and cluster of
excess cations to this surface, and the neutrality of charge
in the pore water is maintained by the respective anionic or
cationic concentrations of species away from the soil
surface. When an electric field is established across the
soil mass, soil pore water cations close to the soil surface
move toward the cathode. The movement of these cations
and any water molecules closely associated with these
species will result in pore water flow in the same direction.
This pore water flow is due to the voltage gradient and is
called electroosmosis. Generally, a wider zone of excess
cations, also known as the diffuse electrical double layer,
results in more electroosmotic flow. The double layer is
defined by the zeta potential, which is the electrostatic
potential on an imaginary surface near the soil particles.
This surface is defined by zero shear, meaning that water
particles on this surface are stationary. The zeta potential
depends on the magnitude of the charge density on the soil
surface, ionic strength of the pore water, valence of the
cation, pH, and permittivity (the ratio of electric flux
density produced by an electric field in water to that
produced in vacuum by the same field) of the pore water.
To account for the tortuosity of ion transport in the soil
pore, the Helmholtz-Smoluchowski equation (Hunter
1981), which describes the transport of water in an
electrical field, can be extended to porous media as
presented in Equation 1-2.
dV
VT2 dx
(1-2)
where:
e
c
electroosmotic velocity (m/s)
fluid permittivity (Newton-per square
volt [N/V2])
zeta potential (V)
v =
T =
dV/dx =
fluid viscosity (Newton-second per
square meter [N-s/m2])
tortuosity (dimensionless)
voltage gradient (V/m)
In general, electromigration is the dominant transport
mechanism for ions in typical soils. As shown in Figure 1-
1, the charge of the ion determines the electromigration
direction in an electric field, either toward the cathode if
the ion is positively charged or toward the anode if the ion
is negatively charged. However, because of a negative
zeta potential (the electrostatic potential on an imaginary
surface near the soil particles) of soil particles,
surrounding jvater has a net positive charge; therefore, the
electroosmosis or bulk water flow is toward the cathode.
Therefore, when a contaminant is anionic, electromigration
of the contaminant ion is counter to the direction of the
electroosmotic water flux. For a cationic contaminant,
electromigration and electroosmotic transport are in the
same direction.
By applying, electric current to soil, electrolysis of pore
water occurs, producing an acid (H+) at the anode and a
base (OH~) at the cathode, which could significantly
affects the chemistry of the soil system during treatment.
If no pH conditioning is used at the electrodes, soil could
have a net acidic characteristic at steady state conditions
because the hydrogen ion has double the mobility of the
hydroxyl ions.
A secondary: effect of current application to soil during
remediation is an increase in temperature because some of
the electrical energy will be transformed into thermal
energy. This heating may affect the remediation process,
depending on whether the electrokinetic system is
operated under constant current or constant voltage
conditions. Under constant current conditions, an increase
in pore water temperature will not affect the velocity of
electromigration; however, electroosmotic velocity will
decrease by 0.4 percent per degree Celsius. Under
constant voltage conditions, each degree increase in
temperature will increase the electromigration velocity by
3.4 percent and the electroosmotic velocity by 2.1 percent,
and the increase in temperature will decrease the viscosity
of water, thereby also increasing the electroosmotic
velocity. The increase in transport mechanism velocity
with elevated temperatures results in reduction of the time
required for'; remediation (Mattson and Lindgren 1994;
EPA 1997). System operation under constant voltage
conditions is:therefore preferred.
11
-------
Methodologies are not well established for evaluating a
site for electrokinetic remediation or for predicting the
associated cleanup level, remediation time, and cost. The
design problem can be addressed in two stages. First, an
estimate of the total amount of electric current required
must be made. This estimate will depend not only on the
contaminant mass to be removed but also on the efficiency
of current usage (in grams of chromium removed per
ampere-hour) or the transference number, which itself
depends primarily on the chemical nature of the
contamination. Second, a determination must be made of
how the current will be applied over a given time period
(which will determine the grams of chromium removed
per kilowatt-hour). This determination requires additional
physical information about the site, such as the
contaminant plume geometry, soil resistivity, and
expected temperature changes. This information, coupled
with the electrode layout, determines the voltage and
electrical power requirements.
1.4.2 SNL ISEE System
The ISEE system developed by SNL applies electrokinetic
technology to unsaturated soil. The SITE demonstration
of the system took place at the UCAP in Technical Area III
at SNL and targeted the removal of chromate (CrO4")from
an area of chromium-contaminated soil that underlies the
pit. The UCAP measures about 15 by 45 feet and is 10 feet
deep (SNL 1994).
The ISEE system used for the demonstration was housed
in two buildings: a control trailer and a temporary
structure. The control trailer contained the control panels,
the power supply, and the data logging system. The
temporary structure protected electrokinetic technology
equipment and personnel and maintained the operational
exclusion zone required during ISEE system operation.
The ISEE system used for the demonstration shown in
Figure 1-2 consisted of anodes, cathodes, and cold finger
cathodes that made up the electrode system. Because
cathodes were used only during the first phase of the
demonstration, they are not shown in Figure 1-2. The
operation of the ISEE system was regulated by four units:
a water control system, a vacuum control system, a power
supply system, a monitoring system, and ancillary
equipment. Each of these systems is discussed in detail
below.
1.4.2.1 Electrode System
Figure 1-3 shows the electrode layout of the ISEE system
used during the SITE demonstration. The system
consisted of an anode row oriented east to west and four
rows of cathodes parallel to the anode row, two rows north
and two rows south of the anode row. Two types of
cathodes were used during the SITE demonstration:
cathodes similar to the anodes, which will be referred to as
"cathodes," and simple design cathodes, which will be
referred to as "cold finger cathodes" (identified as "CF" if
they are standalone or "CFC" if they are adjacent to
cathode casings). The treatment zone was determined by
the active portion of these electrodes and extended from 8
to 14 feet below ground surface (bgs). The electrode
system's anodes and cathodes and cold finger cathodes are
discussed below.
Anodes and Cathodes
The anodes (Al through A5) and cathodes (C6 through
CIO) used at UCAP were designed to combine
electrokinetic and lysimeter technologies. This
combination was necessary to allow the operation of the
system under unsaturated soil conditions. Lysimeter
technology hydraulically and electrically creates a
continuum between the anolyte and the pore water,
thereby enabling the extraction of the chromate ions in the
anolyte while the anolyte is held under tension in the
electrode casings through the application of a vacuum.
Anodes and cathodes were installed in 6-inch-diameter
boreholes (see Figure 1-4C). Boreholes were generally
drilled to 20 feet bgs. An approximately 4-inch-thick dry
bentonite plug was installed on top of the borehole sluff,
and cuttings were added to bring the borehole bottom to 15
feet bgs. The bottom of the borehole was sealed with
bentonite. The electrodes were lowered in the borehole
and suspended from the ground surface. A watery slurry
of clean native soil was added to the borehole until at least
6 inches above the top of the ceramic part of the electrode
casing. The annular space above was filled with native soil
cuttings to 1 foot bgs. Finally, a bentonite plug was
installed to approximately 2 inches bgs and covered to the
ground surface with native soil. After installation was
complete, a vacuum was applied to each electrode to
remove excess water from the slurry.
The anodes and cathodes consisted of two main
components: the electrode casing and the internal
12
-------
El
era
e
Mf
*t>
>-*
&
•12 feet
cr.
Anode Water Control System
-------
CFC1
o-
CF1 C
'NT5
CF6
T3
NT9
'NTI
•
Tl
CFC3
-o
T21
CF3
CFC4
-o
NTS • • T4 and T6
T5« CF4,
T7
•NT2
CFC5
-O
n
) CF5
A5 "NT6
OCFIO
Ocio
LEGEND
C6 - Cathode 6
Al - Anode 1
CF1 - Cold finger cathode 1
CFC1 - Cold finger at cathode 1
Tl - Temperature probe 1
NTI - Neutron hydroprobe access station 1
\f A - Test 13 zone of influence
NOTE
The area displayed measures 12 by 12 feet.
Each square measures 3 by 3 feet.
T16
'NTIO
Figure 1-3. ISEE system electrode layout.
-------
PVC—»
Flange
PVC
Couple I
U
PVC Sump-
10-inch-
Diameter
«-PVC Cover
)<«-PVCTop E
-Male Adapter
2 inches
inch-Diameter
PVC Pipe
i-PVC
Couple
3.5-inch-
Diameter
Ceramic
Casing Passive
Voltage
Probe
PVC Couple
J> From Power
Supply
Cooling
Water
In
_Water
Level
Drive
Electrode
H«— Temperature
Probe
PVC Cap
A) Anode/Cathode
Casing
B) Anode/Cathode
Internal Assembly
and Associated
Exterior
Monitoring
Equipment
Ground Surface
Bentonite
Native Soil
-6-inch-
Diameter
Borehole
Native Soil
Slurry Mix
Bentonite
Borehole
Sluff
C) Anode/Cathode
Borehole
Backfill
-*• Cooling Water Out
0.75-inch-Diameter
PVC Pipe
0.375-inch-Diameter
Polyethylene Tubing
for Chilling Water
0.5-inch-Diameter
Copper Pipe
— PVC Couple
Water Flow
Direction
11—0.5-inch-Diameter
I Copper Pipe
|«— Powdered
Copper
Copper Cap
D) Cold Finger
Cathode
Figure 1-4, Anode/cathode and cold finger cathode construction cross sections.
-------
assembly. Figure 1-4A illustrates the electrode casing
assembly. The electrode casing consisted of two parts: the
bottom 6 feet (located from 8 to 14 feet bgs) was
constructed of a porous ceramic material, and the top part
(extending from the ground surface to 8 feet bgs) was
constructed of 3-inch-diameter polyvinyl chloride (PVC)
pipe. The top part of the electrode casing was
impermeable and nonconductive. The ceramic material
had a pore size of 3 microns, resulting in bubbling
pressures of 19 to 28 pounds per square inch (psi). High
bubbling pressure material was an important factor in the
construction of the electrodes. Depending on the
magnitude of the vacuum applied to the electrode casing
and the pore water tension in soil immediately adjacent to
the electrode casing, the pore water could enter the
electrode casing or water present in the casing could be
transferred to the soil. This innovative feature of the
electrodes was derived from lysimeter technology. The
design overcame the difficulty of soil drying near the
anodes, thus allowing operation of the electrokinetic
process in unsaturated soil for much longer periods than if
simple electrodes were implanted in direct contact with the
soil. Soil drying occurs when electric current is applied to
soil between the electrodes, thus causing water flow by
electroosmosis, usually to the cathode. The SNL ISEE
system design allowed soil moisture to be replenished
through the electrode casing.
The ceramic of the anode casings was treated with a
surfactant to alter the negative zeta potential of the
ceramic, thereby preventing electroosmotic movement of
water out of the anodes. After the surface was washed with
a 0.1-molar solution of hydrochloric acid, a 0.01-molar
solution of hexadecyltrimethylammonium bromide was
purged through the ceramic to form a layer that changed
the effective charge of the surface from negative to
positive.
The internal assembly of the anodes and cathodes
consisted of a drive electrode (see Figure 1-4B)
constructed of iridium-coated titanium for the anodes and
of copper for the cathodes. The drive electrodes were
connected to the power supply system by insulated wire
rated for 600 V DC. Control and monitoring systems also
located inside the electrode casing discussed in the
following sections.
Cold Finger Cathodes
The purpose of the cold finger cathodes was twofold: (1) to
function as active bare electrodes to increase the voltage
gradient and (2) to function as heat exchangers in case soil
temperatures become excessive. As shown in Figure 1-3,
16 cold finger cathodes were used during the SITE
demonstration of the ISEE system (cold fingers CFC2,
CF2, CF7, and CFC7 were not energized during the
demonstration and do not appear in this figure).
Originally, cold finger cathodes CF1 through CF10 were
constructed of 5-foot-long, 0.75-inch-diameter copper
piping. The bottom of the pipe was capped with a copper
cap, and the top end was fitted into a 0.75-inch-diameter,
schedule 40 PVC pipe extending to the ground surface. An
insulated copper wire was soldered to the pipe and was
brought to the ground surface. After September 24, 1996,
to prepare for the final demonstration test, cold finger
cathodes CF1, CF3 through CF6 and CF8 through CF10
were refurbished. The refurbished design (see Figure 1-
4D) consisted of 0.5-inch-diameter copper pipe extending
to the ground surface. This pipe was enclosed by the 0.75-
inch-diameter PVC piping described above and filled with
powdered copper. Inside of the 0.5-inch-diameter copper
piping, a 0.375-inch-diarneter polyethylene tubing was
used to recycle cold water to maintain the cold finger
cathode at a low temperature.
All cold finger cathodes were installed in holes drilled
using the Geoprobe® rig. The diameter of the holes was
1.5 inches, and the depth of installation ranged from 12.5
to 13.6 feet bgs. These holes were filled with soil slurry to
above the metallic part of the electrode. The cold finger
cathodes were installed immediately after soil slurry was
poured into the holes, and remaining space in the hole was
backfilled with native materials. The top of the hole was
plugged with bentonite.
The construction of cold finger cathodes CFC1 through
CFC5 was simple. These cathodes were 6.67 feet long and
constructed of 1-inch-diameter copper pipe. The
conductive part of the electrode was connected to the
bottom of 0.75-inch-diameter PVC piping extending to the
ground surface.
1.4.2.2 Water Control System
Anode and cathode casings were filled with water to about
6 inches above the fitting between the ceramic material
and the PVC pipe. The water control system consisted of
the water circulation system and the pH control system,
which are described below.
16
-------
Water Circulation System
The purposes of the water circulation system were to (1)
monitor the chemical condition of water in the electrode
casings, (2) cool water in the electrode casings, (3) provide
means to sample and remove water from the casings, (4)
provide means to regulate water pH, (5) mix anolyte in the
electrode casings, and (6) add potable water (influent) to
the anode and cathode casings to compensate for the
extraction of effluent.
The water circulation system was powered by bladder
pumps located in each electrode casing (see Figure 1-2).
The screen portion of the pump was located in the
electrode casing sump. Because the bladder pumps
operated in a subatmospheric pressure environment
because of vacuum applied to the head space of the
electrode, a liquid ring vacuum pump and an air
compressor were used to activate the pumps. The
recirculation flow rate was about 4 liters per minute (L/
min).
Anode and cathode effluent was collected in 55-gallon,
closed-top polypropylene drums. Catholyte was extracted
only from the cathodes and not from the cold finger
cathodes. At 3 0-minute intervals, the effluent controller in
the control trailer sent a signal to the air-operated, three-
way-solenoid valve, and recycle flow was redirected to the
drums instead being returned to the electrode casings. The
three-way valve was deactivated after a preset amount of
water measured by the effluent sensor was extracted from
the system. Under normal operating conditions, the
amount of water extracted from the system varied from 0.1
to 0.5 liter per 30 minutes.
The water level in the electrode casings was maintained
within a 6-inch interval above the PVC couple joining the
ceramic and PVC casing sections using reed-type float
switches.
pH Control System
The pH of water in the ISEE system had to be maintained
to ensure proper system operation. High pH values could
result in the precipitation of metals and hinder
contaminant transport and removal. To minimize these
effects, the required pH range for the anolyte was.5.5 to 11,
with an ideal pH of 8.8. The pH range for the catholyte was
3 to 11, with an ideal pH of 5.5.
The pH of pore water in the treatment area was likely to be
influenced by the hydrogen and hydroxyl ions produced at
the electrodes from electrolysis. Consequently, the pH of
the recycled iwater was closely monitored .and controlled
for each electrode using sensors, transmitters, and
controllers. The pH controller regulated the operation of a
chemical fefed pump located on top of a 55-gallon
polyethylene drum containing buffer fluid. A 10 percent
sodium hydroxide solution was used to control the anolyte
pH, and a 20 percent acetic acid solution was used to
control catholyte pH.
1.4.2.3 Vacuum Control System
As stated earlier in this section, the SNL ISEE system uses
lysimeter technology to control the amount of water
delivered to the unsaturated zone. An air compressor
provided the Compressed air necessary for the operation of
the vacuum pumps (see Figure 1-2). Compressed air was
driven through a series of Venturis within the vacuum
pumps, causing additional air to be drawn through the
venturi system. An added feature of the system was the
ability to purge hydrogen gas produced by electrolysis
from electrode casing headspace thus eliminating the
danger of explosion.
Vacuum in the cathode casings was created by three
vacuum ejector pumps installed in parallel. Vacuum in the
anode casings was created using four vacuum ejector
pumps installed in parallel. Rather than directly regulating
the vacuum applied to the electrodes, vacuum regulators
allowed air to enter the electrodes and dilute oxygen and
hydrogen gasps in the electrode headspace. The regulators
were generally maintained at a vacuum of 14 inches of
mercury for both the anodes and cathodes.
The minimum air purge necessary to maintain hydrogen at
the lower explosive limit in the anode casings was
estimated to b,e 3.3 L/min. The system alarm was set to 3.5
L/min for added safety, and the purge rate was set for 8 L/
min to ensure,that the hydrogen level was maintained well
below the explosive limit. Air was also purged through the
cathode casings at 2 L/min to dilute oxygen produced by
electrolysis, i
1.4.2.4 Power Supply System
The ISEE system electrodes were energized using four 10
kilowatt (kW) power supply units. Each unit was capable
17
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of a maximum output of 16 amperes (amp) at 600 V DC.
Each unit was operated independently under constant
voltage conditions.
The power units were located in the control trailer, and
electric current was delivered to the electrodes by
underground cables protected by 3-inch-diameter electrical
conduits. Both parallel-and independent-type connections
were equipped with a main manual disconnector that cut
off power while the system was not in operation. The
current delivered to each electrode was limited to 15 amps
by an in-line fuse and was monitored using an isolated
current transmitter by measuring the voltage drop across a
20 amp per 100 millivolt shunt. Transmitter output was
processed to determine the current, which was displayed
on a control panel and recorded by a data logger.
1.4.2.5 Monitoring System
The operating parameters of the ISEE system were
displayed on the control panel and recorded by a data
logger. Table 1-2 summarizes monitoring system
parameters. The parameters monitored were measured at
1-minute intervals, averaged and were recorded over 60-
minute intervals. The monitoring system could shut down
the ISEE system and send a problem-specific coded
message by cellular telephone to two operators if any
monitored parameters were out of preset tolerance limits.
In addition, when the system was energized, access to the
exclusion zone was not permitted. Thus, entrance to the
temporary structure was monitored using a simple switch
to ensure that the entry door to the temporary structure was
closed. Also, effluent barrels and their secondary
containment were equipped with overflow switches that
could signal system shutdown.
The shutdown system could cut off the power to the
electrodes, close influent water valves, de-energize
influent and effluent solenoids, and discontinue the
pumping of pH control solutions. Depending on the type
of alarm that triggered the shutdown, recycle of electrode
water through the recycle board could also be terminated.
Table 1-2. Monitoring System Parameters
Parameter Measured
Support System
Automatic Shutdown Limit
Air purge rate
Vacuum level
Electrode casing water
level
Recycle flow
Influent and effluent rates
Conductivity
Recycle flow temperature
PH
Soil temperature
Voltage in soil
Vacuum control
system
Vacuum control
system
Water control
system
Water control
system
Water control
system
Water control
system
Water control
system
Water control
system
Ancillary equipment
Ancillary equipment
Below 3.5 L/min for cathodes only
Below 1.47 psi
More than 6 inches above or below the
water level control floats
No recycle flow
None
None
Above 60°C
For cathodes less than 3 and greater
than 11, and for anodes less than 5.5
and greater than 11
Above 60°C
Step potential of 10V
18
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1.4.2.6 Ancillary Equipment
To monitor and control the operation of the ISEE system,
SNL installed ancillary equipment that provided
information on the state of system operation or that
provided access to the treated media to influence local soil
conditions (such as devices that altered soil moisture
content). Ancillary equipment included soil moisture
content control devices, neutron hydroprobe and radio
imaging probe tubes, temperature probes, and passive
voltage probes. This equipment is discussed below.
Soil Moisture Content Control Devices
Unsaturated soil conditions were maintained at the
demonstration site throughout the operation of the ISEE
system. Soil moisture control infiltration wells were
installed to add water to the soil, if desired. Infiltration
wells increased soil moisture content. Fourteen wells
were used prior to the operation of the system under SNL's
preferred operating conditions to add moisture to soil.
These wells were constructed of 0.5-inch-diameter PVC
piping 11 to 13 feet long. Approximately 20 slots were
made in the bottom 9 to 12 inches of the PVC pipe, and the
bottom of the pipe was sealed with a PVC plug. These
wells were installed in 1.5-inch-diameter boreholes drilled
using the Geoprobe® rig. The annular space was filled
with 10/20 silica sand in the area of the screen interval and
with dry, granular bentonite above this interval.
Neutron Hydroprobe and Radio Imaging Probe
Tubes
Neutron hydroprobe measurements of soil moisture
content were taken on a weekly basis using 10 access tubes
(see Figure 1-3). Most of the tubes were installed to 39 to
41 feet bgs, and one tube was installed to 31 feet bgs. The
tubes were installed in 7-inch-diameter boreholes drilled
using a hollow stem auger. The annular space was filled
using drill cuttings, and the holes were plugged at the top
with dry bentonite. The tubes were constructed of 2.5-
inch-diameter, threaded PVC piping. The diameter was
selected to allow access of radio imaging probes used to
determine vertical conductivity profiles of soil beneath the
UCAP.
Temperature Probes
A total of 32 temperature probes were installed at the
demonstration site (see Figure 1-2). The temperature
probes were located generally at 11 feet bgs in the
treatment zone. Sixteen of the probes (not shown in Figure
1-3) were installed on electrode casings at the PVC couple
between the two ceramic pieces that make up the electrode
casings and 16 were installed between the electrodes as
shown in Figure 1-3.
Passive Voltage Probes
Passive voltage probes were used to generate data needed
to prepare electrical potential maps of the demonstration
site. Twenty passive voltage probes were located on the
electrode casings, and another 12 were installed
throughout tfte demonstration site. These probes consisted
of 50-mesh stainless steel screen squares with an area of
about 2 square inches attached to insulated wires that
reached the ground surface. The pieces of mesh were
attached to 0.75-inch-diameter PVC pipe at a depth of
about 10 feet bgs. Probes were installed using the
Geoprobe® rig.
1.4.3 Innovative Features of the
Technology
Metals-contaminated soil can be treated either in situ or ex
situ. Common methods for treating soil in situ include
stabilization/solidification and vitrification. Promising
results were 'obtained during testing of other innovative
treatment technologies such as soil flushing. The most
common ex situ treatment technology is soil washing.
Treatment of soil hi situ using electrical separation/
electrokinetic removal under saturated soil conditions has
been tested by several vendors. However, the ISEE system
designed by SNL focuses on the remediation of
unsaturated soil instead of saturated soil.
The innovative feature of the ISEE system is that lysimeter
technology is used in the construction of the anodes and
cathodes toi hydraulically and electrically create a
continuum between the electrolyte and the pore water.
The electrode fluid is held inside the electrode by an
applied vacuum, keeping the fluid from saturating soil.
This feature allowed the removal of chromate from
unsaturated soil during the demonstration without
significantly altering the soil moisture content. The
vacuum control system maintains the vacuum in the anode
electrode, which creates the pressure gradient between the
anode's porous ceramic casing and the surrounding soil
necessary to hydraulically control water movement
between the anode casing and the soil.
19
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The ISEE system developed by SNL presents the
advantage that the structure, volume, and makeup of
treated soils are not significantly affected by the
application of the technology as is the case with
remediation by stabilization/solidification, vitrification,
or chemical treatment. The moisture content of the soil is
maintained at levels below saturation, which is not the case
with soil flushing or chemical treatment because these
technologies use water as the transport medium for
treatment additives. Table 1-3 compares several in situ
treatment options for soil contaminated with heavy metals.
1.5 Applicable Wastes
The ISEE technology developed by SNL is applicable for
treating unsaturated soil contaminated with hexavalent
chromium. According to SNL, this technology can be
modified to treat saturated contaminated soil and to
remove contaminants dissolved in pore water besides
chromate. Because other anions will compete with the
targeted contaminant ions to be removed, it is necessary to
determine the electrical conductivity of soil pore water and
the target ion concentration to determine the applicability
of the ISEE technology.
1.6 Key Contacts
Additional information about the ISEE system and the
SITE program can be obtained from the following sources:
SNL ISEE System
Dr. Eric R. Lindgren
Sandia National Laboratories
Dept.6621,MS0719
P.O. Box 5800
Albuquerque, NM 87185-0719
Telephone No.: (505) 844-3820
Fax No.: (505) 844-0543
E-mail Address: erlmdg@sandia.gov
The SITE Program
Mr. Randy Parker
Office of Research and Development
U.S. Environmental Protection Agency
26 West Martin Luther King Drive
Cincinnati, OH 45268
Telephone No.: (513) 569-7271
Fax No.: (513) 569-7571
E-mail address: parker.randy@epamail.epa.gov
Information on the SITE program is available through the
following on-line information clearinghouse: the Vendor
Information System for Innovative Treatment Technologies
(VISITT) (Hotline: 800-245-4505) database contains
information on 154 technologies offered by 97 developers.
Technical reports may be obtained by contacting U. S.
EPA/NSCEP, P. O. Box 42419, Cincinnati, Ohio 45242-
2419, or by calling 800-490-9198.
20
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Table 1-3. Comparison of In Situ Treatment Technologies for Metals-Contaminated Soili
Technology
Advantage
Disadvantage
SNL In Situ Electrokinetic
Extraction System
Stabilization/Solidification
Vitrification
Soil Flushing
Maintain unsaturated soil
conditions; soil makeup not
significantly affected
Applicable to wide range of
soils because of flexibility in
design of appropriate
additives and use of a large
variety of mixing techniques;
some organic compounds
can be incorporated in the
solidified matrix; relatively
low cost
Applicable to complex
wastes (combination of
metals and organics, .
including mixed wastes); also
applicable to
nonhomogeneous soils
containing buried containers
(however, under some
conditions, metal objects
could short-circuit the current
path); relatively moderate
cost
Applicable to soils containing
organic and inorganic
wastes; relatively low cost
Currently tested for the removal of
chrornate from unsaturated soil only;
requires disposal of liquid waste
containing hexavalent chromium as
hazardous waste; volatile organic
comppunds (VOC) may be stripped
from soil and increase soil vapor
concentrations and contaminant
migration; relatively high cost; no
commercial-scale system available
Long-term reliability not well known;
considerably increases volume of
waste; leachate from curing process
may need to be collected and disposed
of as hazardous waste
High soil moisture content limits
applicability; off-gases (VOCs,
combustion gases, and steam) need to
be collected; presence of buried
materials could start underground fire;
soil characteristics dramatically changed
by application of the technology;
decrease in volume of soil
Not applicable to soil with low
permeability; migration of contaminants
to deeper zones possible from
increased mobility if no controls exist
(for example, a clay layer); soil moisture
content increases; requires treatment of
water recovered after flushing
21
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Section 2
Technology Effectiveness and Application Analysis
Tilts section addresses the effectiveness and applicability
of the ISEE system designed by SNL for treating
unsaturated soil contaminated with hexavalent chromium
in the form of chromate. Vendor claims regarding the
effectiveness and applicability of the ISEE system are
included in the appendix. The evaluation of the ISEE
system's effectiveness and potential applicability is based
mainly on the demonstration results presented in this
section. This section provides an overview of the ISEE
system SITE demonstration and discusses SITE
demonstration results, factors affecting performance, site
characteristics and support requirements, material
handling requirements, technology limitations, potential
regulatory requirements, and state and community
acceptance.
2.1 Overview of ISEE System SITE
Demonstration
The ISEE system SITE demonstration took place at the
UCAP, which is part of the CWL site located within
Technical Area III at SNL. The UCAP is a rectangular pit
measuring about 15 by 45 feet and is 10 feet deep. The
areal extent and depth of the area targeted by the
demonstration was selected based on the highest results of
water soluble chromium concentrations from sampling
performed during previous investigations (SNL 1994).
During the demonstration, the system was operated for a
period of 2,127 hours between May 15 and November 24,
1997. The area of the demonstration ranged from 36 to
72 square feet and targeted contaminated soil located
between 8 and 14 feet bgs. The configuration of ISEE
system electrodes is presented in Figure 1-3.
The CWL site was used by SNL for chemical disposal
from 1962 to 1985. During this time, chemicals were
separated by type and disposed of in separate trenches.
Over 4,290 gallons of chromic sulfuric acid solution was
disposed in the UCAP (SNL 1997). During
predemonstration sampling activities, a few soil samples
exhibited high moisture content and pieces of glass plastic
were present in the samples, suggesting that the
Geoprobe® sampler penetrated chemical disposal
containers that have maintained their integrity.
Project objectives, the SITE demonstration approach, and
sampling and analytical procedures are discussed below.
2.1.1 Project Objectives
Project objectives were developed based on EPA's
understanding of the SNL ISEE technology, SITE
demonstration program goals, and input from the
technology developer and the State of New Mexico. The
SITE demonstration had one primary objective and two
secondary objectives. The primary objective was
considered critical for the technology evaluation.
Secondary objectives involved collection of additional
data that were useful but not critical to the technology
evaluation. The primary objective of the technology
demonstration was to estimate the amount of hexavalent
chromium removed from soil by the ISEE system because
the ISEE system is primarily designed to remove
hexavalent chromium. To accomplish this objective, SNL
collected and analyzed anolyte samples for hexavalent
chromium at its field laboratory throughout the
demonstration period. An independent check of field
analytical data was provided by EPA through split sample
analysis at an off-site laboratory. Field analytical data
were subsequently deemed adequate to estimate the
amount of hexavalent chromium removed from soil by the
ISEE system. Predemonstration and postdemonstration
soil samples collected by EPA were analyzed for
hexavalent chromium to verify the hexavalent chromium
removal estimate based on anolyte sample analysis.
22
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The secondary objectives of the technology demonstration
were to determine whether treated soil meets the toxicity
characteristic leaching procedure (TCLP) regulatory
criterion for chromium and to evaluate the ISEE system's
ability to remove trivalent chromium from site soil.
To conduct the demonstration, SNL was required to meet
the conditions of the New Mexico Environmental
Department's Resource Conservation and Recovery Act
(RCRA) Research, Development, and Demonstration
permit for the ISEE system. Predemonstration testing
results indicated that some of the soil in the demonstration
area is hazardous (EPA waste code D007) because
chromium concentrations exceeded the TCLP criterion for
chromium. Therefore, the permit required that SNL
perform postdemonstration TCLP testing to determine the
impact of the ISEE system on soil known to be
contaminated. SNL therefore collected a large number of
treated soil samples for total chromium analysis after
extraction using TCLP.
Because incidental removal of trivalent chromium will
likely be accomplished by the ISEE system, evaluation of
trivalent chromium removal was a secondary project
objective of this project. To accomplish this objective, the
predemonstration and postdemonstration soil samples
collected for hexavalent chromium analysis were also
analyzed for total chromium so that the trivalent
chromium concentrations could be calculated as the
difference between the total and hexavalent chromium
concentrations.
2.1.2 Demonstration Approach
The ISEE system SITE demonstration system operation
and test plan is detailed in SNL's demonstration plan (SNL
1997). This section summarizes SNL's demonstration
plan. During the SITE demonstration, 13 tests were
performed during six phases. The test areas ranged from
36 to 72 square feet, and contaminated soil from 8 to 14
feet bgs was treated. The first 12 tests were conducted so
that SNL could determine the preferred operating
conditions for Test 13 and to facilitate the migration of
hexavalent chromium toward the central portion of the test
area. Test 13 consisted of system performance testing
under SNL's preferred operating conditions for the SITE
demonstration. Table 2-1 summarizes key conditions
during the 13 tests.
During Phase 1, six tests were conducted in the southern
half of the test grid between the anode row and C6 through
CIO. During these tests, SNL identified inefficient
electrodes (A2 and C7) and adjusted the electrical current,
electrical power level, and anolyte extraction rate.
During Phase 2, three tests were conducted in the northern
half of the test grid between the anode row and CFC1
through CFC5. During these tests, SNL used the less
expensive cold finger cathodes; adjusted the electrical
current, electrical power level, and anolyte extraction rate;
and operated the infiltration wells to facilitate hexavalent
chromium migration toward the middle portion of the test
grid. ;
During Phase 3, one test was conducted in the southern
portion of the northern half of the test grid between the
anode row and CF1 through CF5. SNL set the operating
conditions for this test based on results from Phases 1 and
2. :
During Phase 4, one test was conducted in the southern
half of the test grid between the anode row and CFC6
through CFC10. This test was intended to be a replicate of
Test 6 during Phase 1 and was conducted to fill
information gaps identified for Test 6.
During Phase 5, one test was conducted in the northern
portion of the southern half of the test grid between the
anode row and CF6 through CF10. SNL set the operating
conditions for this test based on results from Phases 1, 2,
and 3. i
During Phase 6, one definitive test was conducted in the
middle portion of the test grid between CF1 through CF5
and CF6 through CF 10. SNL set the operating conditions
for this test based on results from Phases 1, 2, 3, and 5.
SNL identified Phase 6 (Test 13) conditions as the ISEE
system's preferred operating conditions. Operating
conditions during Test 13 are summarized in Table 2-2.
SNL operated the ISEE system at the preferred conditions
to evaluate system performance and treatment costs.
2.1.3 Sampling and Analytical
Procedures
Three sampling events occurred during the ISEE system
SITE demonstration: predemonstration soil sampling,
anolyte (electrolyte from the anodes) sampling during the
23
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Table 2-1. Test Matrix for SNLISEE System Demonstration
to
Phase Test Area
1 Southern Half Anode Row and C6
through C10
2 Northern Half Anode Row and CFC1
through CFC5
3 Southern Portion of Northern Half
Anode Row and CF1 through CF5
4 Southern Half Anode Row and CFC6
through CFC10
5 Northern Portion of Southern Half
Anode Row and CF6 through CF10
6 Middle Portion (CF1 through CF5 and
CF6 through CF10)
Test
No.
1
2
3
4
5
6
7
8
g
10
11
12
13
Anodes Used
A1,A2,A3,A4, and AS
A1,A3,A4,andA5
A1, A3, A4, andAS
A1, A3, A4, andAS
A1, A3, A4, andAS
A1,A3,A4,andA5
A1, A3, A4, andAS
A1, A3, A4, andAS
A1.A3, A4, andAS
A1, A3, A4, andAS
A1.A3, A4,andA5
A1, A3, A4, andAS
A1, A3, A4, andAS
Average Current1
Cathodes Used (amp)
C6, C7, C8, C9, and C10
C6, C7, C8, C9, C10
C6, C8, C9, and C10
C6, C8, C9, and C10
C6, C8, C9, and C10
C6, C8, C9, and C10
CFC1.CFC3, CFC4, and
CFC5
CFC1.CFC3, CFC4, and
CFC5
CFC1.CFC3, CFC4, and
CFC5
CF1.CF3, CF4, andCFS
CFC6, C8, CFC9, and CFC10
CF6, CF8, CF9, andCF10
CF1, CF3 through CF6, and
CF8 through CF10
19.45±1.68
21.09±2.07
20.08±1.41
34.25±6.98
42.15±2.38
41.07±2.55
29.27±3.48
20.94±2.10
20.79±1.21
30.31 ±3.78
33.49±1.87
39.31 ±3.64
35.92±4.71
Average Power1
(kW)
1.30±0.11
1.68±0.18
1.77±0.15
4.65±0.94
5.76±0.30
4.56±0.31
4.14±0.56
1.90±0.21
1.87±0.11
2.70±0.36
2.38±0.15
2.86±0.29
2.10±0.31
Average Anoly te
Extraction Rate11 Test Duration
(L/hour) (hour)
0.440±0.075
0.870*0.542
0.879±0.633
2.026±0.904
3.54
3.957±0.924
3.404±0.263
0.376±0.103
0.723±0.554
0.510±0.046
0.50
0.848±0.693
0.662±0.394
106
368
283
244
34
181
75
89
333
176
20
111
707
Notes:
amp = Ampere
kW = Kilowatt
L/hour = Liter per hour
a Average ± standard deviation of hourly readings for all anodes used in the test
b Average ± standard deviation of daily readings for all anodes used in the test; only average presented when fewer than three values
available
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Table 2-2. SNLISEE System Preferred Operating Conditions
Average
Average
Average
(L/hour)
Oper
Parameter A1 A3
Current (A) 9.9 7.3
Power (kW) 0.40 0.50
Effluent Extraction Rate 0.25 0.25
ating Conditions
A4 A5
8.2 10.3
0.54 0.67
0.20 0.22
demonstration, and postdemonstration soil sampling.
From December 1995 through February 1996, SNL
collected predemonstration soil samples from various
depth in boreholes within and near the test areas using a 1 -
inch-diameter by 24-inch-long Geoprobe® Large Bore
Sampler. SNL extracted a portion of each sample with
water and analyzed the extract for chromium. Additional
sample portions were sent to the Quanterra Environmental
Services, Inc. (Quanterra), laboratory in Arvada,
Colorado. Quanterra extracted these soil samples by
TCLP, SW-846 Method 1311, and analyzed the extracts
for total chromium by inductively coupled plasma (ICP)
analysis using SW-846 Method 601OA. TCLP extract
results are included in Appendix A of the TER.
In July 1996, EPA selected certain of these soil samples for
Quanterra analysis to provide information on the
concentrations of total chromium and of hexavalent
chromium throughout the test area. More samples from
more contaminated areas as determined by SNL's TCLP
results were selected because these areas are of major
concern. To maximize extraction of hexavalent
chromium, Quanterra dried these soil samples and ground
them in a ceramic-lined ring and puck mill until the
samples could pass through a No. 42 mesh sieve. A
preliminary study found that use of an ordinary steel ring
mill to grind samples resulted in unacceptable
contamination of the samples with chromium derived
from mill material. "Grinder blanks," clean sand
subjected to the pretreatment and analysis, and "sand
blanks," sand sent directly for analysis, were analyzed to
monitor for such problems.
Quanterra prepared portions of the sieved soil samples by
acid digestion using SW-846 Method 3050A and analyzed
them for total chromium using SW-846 Method 6010A.
Quanterra also prepared other portions of the sieved soil
samples by alkaline digestion using SW-846
Method 3 060A. These alkaline-digested samples were
analyzed for hexavalent chromium by colorimetry using
SW-846 Method 7196A. These analyses were
accompanied by analysis of the usual QC samples (method
blanks, matrix spikes, blank spikes, duplicates, and so on)
to ensure that results were acceptable for use in meeting
project objectives. The results of these QC analyses are
included in Appendix B of the TER.
During operation of the ISEE system, SNL collected
anolyte saniples daily and analyzed them for hexavalent
chromium to determine removal. To verify these results,
EPA obtain'ed anolyte samples from all four operating
anodes daily for 8 days. These samples were all sent to
Quanterra for analysis for hexavalent chromium by SW-
846 Method 7196A. The relative percent differences
between the |SNL and Quanterra results varied from 0 to 20
percent
After the demonstration, EPA collected soil samples using
the Geoprobe® from locations near (within 1 foot laterally
and 2 inches vertically) from the sampling locations and
sent these samples to Quanterra for the same sort of
preparation and analyses for hexavalent chromium and
total chromium conducted during predemonstration
sampling. SNL collected a separate series of Geoprobe®
samples and sent them to Quanterra for TCLP extraction
and chromium analysis. All Quanterra and corresponding
SNL results are included in Appendix A of the TER.
2.2 SITE Demonstration Results
This section summarizes ISEE system SITE demonstration
results and discusses its effectiveness in removing
chromate from contaminated soil. This section is
organized according to the project objectives stated in
Section 2.1.1. Estimated treatment costs are discussed in
Section 3.0. .
25
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2.2.1 Removal of Hexavalent Chromium
from Site Soil
The primary objective of the ISEE system SITE
demonstration was to estimate the amount of hexavalent
chromium removed from soil by the system. The mass of
hexavalent chromium removed was to be determined from
the amount of hexavalent chromium in the anolyte. In
general, SNL performed daily sampling and analysis of
the anolyte throughout the demonstration. For each test,
SNL anolyte results were used to determine the total
amount of hexayalent chromium removed and the
system's overall removal rate and removal efficiency.
These results are summarized in Table 2-3.
As mentioned before, 13 tests were performed in six
phases during the demonstration. The first 12 tests,
performed between May 15 and October 18, 1996, were
used by SNL to determine the system's preferred
operating conditions. Test 13 was performed between
October 21 and November 24,1996, to determine system
performance and operating costs.
Approximately 520 grams (g) of hexavalent chromium
were removed during the entire demonstration. Overall
hexavalent chromium removal rates varied from 0.074
gram per hour (g/hour) during Test 1 to 0.338 g/hour
during Test 5. Overall hexavalent chromium removal
efficiencies varied from 0.03 59 gram per kilowatt-hour (g/
kW-h) during Test 7 to 0.136 g/kW-h during Test 13.
Downtime during system operation ranged from 0 percent
during Test 11 to 66 percent during Test 1.
Test 13 results showed increased efficiency of hexavalent
chromium removal compared to previous test results. The
system configuration during Test 13 was representative of
the configuration of a full-scale remediation system, with
cold finger cathodes placed symmetrically outward from a
central anode row. Consequently, a more detailed analysis
was performed for Test 13 to determine the hexavalent
chromium removal efficiency and rate of each electrode in
addition to overall system performance. The data set used
for this analysis was culled from Test 13 data to eliminate
data points not representative of the system performance.
For example, data points not representative of steady-state
operation of the system, such as during the pumping out of
electrode effluent, were eliminated, as were data points
measured within 6 hours or less because the system was
shut off for some reason and had to be restarted after
servicing. The hexavalent chromium removal efficiency
of each electrode is shown in Figure 2-1, and the
hexavalent chromium removal rate of each electrode is
shown in Figure 2-2.
After data outliers were eliminated, the average
hexavalent chromium removal efficiency for anode 4 was
approximately 0.189 g/kW-h, which is considerably
higher than the average removal efficiencies for the other
three anodes (anodes 1,3, and 5), which ranged from about
0.087 to about 0.111 g/kW-h. Hexavalent chromium
removal rates were low for anodes 1 and 3 (0.040 and
0.057 g/hour, respectively) and higher for anodes 4 and 5
(0.110 and 0.079 g/hour respectively).
Verification of the total mass of hexavalent chromium
extracted by the ISEE system was supposed to be provided
by the difference between average hexavalent chromium
concentrations in soil before and after the demonstration.
Figure 2-3 presents the spatial distribution of hexavalent
chromium concentrations at the 2-foot depth intervals
characterized by the samples collected before and after the
demonstration. These results can be summarized as
follows:
• Predemonstration samples contained hexavalent
chromium concentrations ranging from below the
detection limit of 0.4 milligram per kilogram (mg/kg)
to 6,890 mg/kg.
• Postdemonstration samples contained hexavalent
chromium concentrations from below the detection
limit of 0.4 mg/kg to 4,730 mg/kg.
• Of the 48 locations sampled both before and after the
demonstration, 21 locations contained
postdemonstration hexavalent chromium concen-
trations that exceeded predemonstration
concentrations.
Predemonstration and postdemonstration hexavalent
chromium concentrations in soil and their distributions
were not suitable for any method of calculation of the total
mass of hexavalent chromium in soil. A statistical
summary of analytical results for hexavalent and total
chromium is presented in Table 2-4. No trend was
identified in the removal of hexavalent chromium from
soil. In many cases, the standard derivation exceeded
average concentrations. Soil results for hexavalent
chromium possibly exhibited high spatial variability
resulting from (l)the nonhomogeneous distribution of
chromate concentrations in soil before the demonstration
26
-------
Table 2-3. SNLISEE System Performance Data
to
Phase
Ho.
1
2
3
4
5
6
Notes:
Test Average Power Energy Applied Hexavalent
Test Duration Applied to the to the System Chromium Mass
No. (hour) System (kW) (kW-h) Removed (g)b
1 106/312
2 368/695
3 283/618
4 244/410
5 34/64"
6 181/206
7 75/9CT
8 89/92a
9 333/511
10 176/222
11 20/20"
12 111/163
13 707/831
a 1.30
a 1.68
1.77
4.65
5.76
4.56
4.14
1.90
1.87
2.70
2.38
a 2.86
2.10
138.1
619.9
490.6
1,143.4
195.7
821.2
310.5
168.8
622.1
477.0
50.1
317.5
1,494.3
g = Gram
g/hour = Gram per hour
g/kW-h= Gram per kilowatt-hour
kW = Kilowatt
kW-h = Kilowatt-hour
a Time period for which the system was operational/total test duration
b Hexavalent chromium mass removed was estimated by multiplying the
7.84
35.73
22.54
56.02
11.49
38.24
11.14
9.01
58.66
35.97
4.71
25.45
203.73
volume of ana
Hexavalent
Hexavalent Chromium Chromium Removal
Removal Rate (g/hour) Efficiency (g/kW-h)
0.074
0.097
0.079
0.230
0.338
0.211
0.149
0.101
0.176
0.204
0.236
0.229
0.288
lyte extracted with the concentration
0.0568
0.0576
0.0459
0.0490
0.0584
0.0466
0.0359
0.0534
0.0940
0.0754
0.0940
0.0809
0.136
of hexavalent
chromium in the analyte. During the entire demonstration, 520.73 g of hexavalent chromium was removed from soil.
-------
Anode 1
0.4
0.3
re
§
0.1.
• •
0 100 200 300 400 500 600 700
Time (hour)
Anode 3
0.4
•*? 0.3
IS
0) 0.1
• « •»
« »»
0 100 200 300 400 500 600 700
Time (hour)
0.4 ,
0,3
1
Anode 4*
0 100 200 300 XOO 500 600 700
Time (hour)
Anode 5
J? 0.3
I
s
r
a 0.2
I
ra
g
| ft1
« «
100 200 300 400 500 800 700
Time (hour)
*Note: Anode 4 had a removal efficiency of 0.584 g/kW-h at 628 hours.
Figure 2-1. Hexavalent chromium removal efficiency per electrode for Test 13.
28
-------
Removal Rate (g/hour)
Removal Rate (g/hour)
ffi
E.
o
£'
I
§
D.
(D
O
C
•
•
3
O
Q.
(D
o
c
•
4.
O
a
(D
Removal Rate (g/hour)
Removal Rate (g/hour)
H
(D
O
C
^_
o
o
"O
§
LJ
O
O
.b.
O
O
U1
o
a\
o
o
•Nl
o
o
OJ
*
•
4
•
•
•
4
4
4 *
4
4
4
4
4
4
4
* 4
U
O
M
O
O
w
o
^ °
0 m *
9- - §
fl> 3-
0, g
O- g
o
o\
o
o
VJ
o
o
CO
o *
•
•
^
4
4
4 *
4
4
4
4
4
4
4
4
4
4
* * 4
O
Q.
(D
W
-------
PREDEMONSTRATION
POSTDEMONSTRATION
6 FEET BGS
8FEETBGS
10 FEET BGS
12 FEET BGS
15
w10
5
0
145 •
6.4
»
0 5 10 15 20
FEET
15
5
0
44
1.2
•
510
,56 «
*
521
'157
0.4U
•
0.4U
•
47
2,120
«
0 5 10 15 20
FEET
15
E-<10
5 '
' 0
0.81
1,110 250
•
429
* •
2,590
0732
S.320
•662
0.65
•
6,890
514
«
3 5 10 15 20
FEET
20
15
5 '
0
50.9
2.2
409
452
• 1,050
502
1,290
A.
577
127
0 5 10 15 20
FEET
20
15
1
H 10
H,
fi"
n
2.3
1 2.0
,22
7.8 •
1,2
0.8
•
3.2
-
0 5 10 15 20
FEET
20
•J5
]
t_ 10
s'
9
I54 78.1
43.3
12
1^330
69.8 5"
154
•214
0.4U
•
0.4U
•
302
597
•
|
0 5 10 15 20
FEET
15
5 '
47.6
1,070 662
•
1.290
1,030
•
293
• 2,620
3,570
•2,700
1.8
•
4,730
•
1,060
533
•
0 5 10 15 20
FEET
1
U«
94.2
174 2^520
142
2J9
•
53.7
• 2,270
> 1,830
1.3
•
992
259
159
•
0 5 10 15 20
FEET
Location from which both predemonstration and postdemonstration samples collected.
A Location from which only predemonstration sample collected.
• Location from which only postdemonstration sample collected.
Coordinates (0,0) correspond to location of cathode C6.
U = Analyte not detected, value presented is detection limit.
All results in milligrams per kilogram (mg/kg).
Figure 2-3. Spatial distribution of haxavalent chromium concentrations in soil.
30
-------
PREDEMONSTRATION
POSTDEMONSTRATTON
14 FEET BGS
16 FEET BGS
18 FEET BGS
20 FEET BGS
20 .
15 .
fr-10.
5 .
0.
1,940
«
311
•
0 5 10 ' 15 20
FEET
20
15
B510 '
5
0
C
2,140.
229
512
5,290
A
764
63.6
738
76.4
5 10 15 20
FEET
15 .
ta10
5 '.
0 .
> 1,650
358.
135
497
28.3
*
0 5 10 15 20
FEET
in
15 .
is10 •
5 .
0 .
861.
55.7
32.9
0 5 10 15 20
FEET
m
15 .
I
H10 .
5 !
0 |
1 268
10.4
1
390
447
•
322
•4,340
1,410
11.1
1.7
•
64
. »
25.5
46.4
•
0 5 10 15 20
FEET
•>n
15 .
I
t-10 .
*'
0 .
1 156
154.8
74.4'
203
•
961
111
25.7
•
26.8
507
•
0 5 10 15 20
' FEET
in
15 .
1
E-.10 .
5 !
0 i
1 56.5
215
2.5.
3.7
96.9
5.9
39.6
2.9
53.6
*
!
i
0 5 10 15 20 i
FEET
in
15 .
H 10 .
* «'
0 |
15.4
80.2
2.9
44.2
2.1
35.9
5.5
8.8
i
0. 5 10 15 20 "
FEET
* Location from which both predemonstration and postdemonstration samples collected.
A Location from which only predemonstration sample collected.
• Location from which only postdemonstration sample collected.
Coordinates (0,0) correspond to location of cathode C6.
U = Analyte not detected, value presented is detection limit.
All results in milligi'ams per kilogram (mg/kg).
Figure 2-3. Spatial distribution of hexavalent chromium concentrations in soil (continued).
31
-------
Table 2-4. Statistical Summary of Hexavalent and Total Chromium Analytical Results
Sampling Depth
Parameter
6 feet bgs
8 feet bgs
10 feet bgs
12 feet bgs
Hexavalent Chromium
Number of Data Points
Average Concentration
(mg/kg)
Standard Deviation
(mg/kg)
Total Chromium
Number of Data Points
Average Concentration
(mg/kg)
Standard Deviation
(mg/kg)
Pretest Posttest Pretest Posttest Pretest Posttest Pretest Posttest
2 7 11 14 11 13 9 12
5.63 371 216 1,682 1,508 496 726
7.63 620 359 2,326 1,458 438 940
7 11 14 11 13 9 12
81.6 1,202 1,843 5,105 6,149 1,319 1,898
64.5 1,596 1,566 7,686 4,825 1,140 1,733
Sampling Depth
Parameter
Hexavalent Chromium
Number of Data Points
Average Concentration
(mg/kg)
Standard Deviation
(mg/kg)
Total Chromium
Number of Data Points
Average Concentration
(mg/kg)
Standard Deviation
(mg/kg)
14 feet bgs
Pretest Posttest
2 12
611
1,238
2 12
1,860
3,651
16 feet bgs
Pretest
8
1,227
1,772
8
2,865
4,016
Posttest
9
236
310
9
564
877
18 feet bgs
Pretest
5
534
651
5
1,201
1,582
Posttest
9
53.0
69.0
9
138
193
20 feet bgs .
Pretest Posttest
3 8
24.4
27.5
3 8
65.4
78.3
Notes:
Not calculated because data points insufficient to represent treatment area
32
-------
and (2) the fact that the demonstration was terminated
before chromate removal was completed. In 'addition,
limited data appear to indicate that contaminants had
likely migrated from areas outside of and near the
treatment area (see Figure 2-3). Thus, a determination of
the mass of hexavalent chromium removed based on soil
sampling results was not possible. Total chromium results
are summarized and discussed in Section 2.2.3.
2.2.2 Compliance with TCLP Regulatory
Criterion for Total Chromium
In order to meet the RCRA Research, Development, and
Demonstration permit for the ISEE system (see Section
2.1.1), SNL collected predemonstration and
postdemonstration soil samples and analyzed them for
total chromium in TCLP leachate. Figure 2-4 presents the
spatial distribution of TCLP chromium results for soil
samples collected before and after the demonstration
about 8 to 14 feet bgs. The results shown in Figure 2-4
represent 2-foot depth interval from the referenced depth.
For example, the 12 feet bgs sample corresponds to soil
from 12 to 14 feet bgs.
As shown in Figure 2-4, of the 43 predemonstration soil
samples analyzed by TCLP, 18 exceeded the TCLP limit
of 5 milligrams per liter (mg/L) of total chromium at
concentrations ranging from 5.6 to 103 mg/L, with a
median concentration of 15.4 mg/L. Postdemonstration
results indicate that 18 out of 35 soil samples exceeded the
TCLP regulatory criterion for chromium at concentrations
ranging from 6 to 67 mg/L, with a median concentration of
20.4 mg/L.
2.2.3 Removal of Trivalent Chromium
from Site Soil
Trivalent chromium concentrations were to be determined
by calculating the difference between total and .hexavalent
chromium concentrations. Figure 2-5 presents the spatial
distribution of total chromium concentrations in
predemonstration and postdemonstration soil samples. A
statistical summary of total chromium concentrations in
soil samples is presented in Table 2-4. Total chromium
sampling results can be summarized as follows:
• Predemonstration samples contained total chromium
concentrations ranging from 7.7 to 26,800 mg/kg.
• Postdemonstration samples contained total chromium
concentrations ranging from 8.2 to 16,200 mg/kg.
•. Of the 48 locations sampled both before and after the
demonstration, 31 locations contained
postdem'onstration trivalent chromium concentrations
that exceeded predemonstration concentrations.
In general, the ratio of trivalent to total chromium
concentrations ranged from 7.6 to 94.9 percent in
predemonstration samples and from 27.6 to 99.6 percent in
postdemonstration samples. This large variability
precluded the calculation of the trivalent chromium mass
removed as 'Originally intended because it would have
further increased the data uncertainty. The increase in
total chromium concentrations at certain locations after
the demonstration could have resulted from the migration
of chromium in the treatment area in addition to the
inherent variabilities of the test areas. Therefore, no
conclusion was drawn regarding the ISEE system's ability
to remove trivalent chromium.
2.2.4 Operating Problems
The ISEE system's operation was observed during the
demonstration, and the problems and their resolutions
were recorded by SNL personnel. The demonstration
lasted over approximately 4,230 hours.
The system was not operable for 36 percent of the time.
Table 2-5 presents the reasons for the shutdowns and the
percentages ;of shutdown times relative to the entire
duration of the demonstration. In addition, the system was
not energized for 3 percent of the tune (approximately 140
hours) to perform anolyte sampling and soil moisture
measurements using the neutron hydroprobe.
2.3 Factors Affecting Performance
Factors affecting performance of the ISEE system include
(1) waste characteristics, (2) operating parameters, and (3)
maintenance requirements. These factors are discussed
below.
2.3.1 Waste Characteristics
The ISEE system is applicable to treatment of soil
contaminated with hexavalent chromium under unsaturated
33
-------
PREDEMONSTRATION
POSTDEMONSTRATION
8FEETBGS
10FEETBGS
12 FEET BGS
15
,
10
S
5
0
1U
1U A
, 0.64 A '
0.37J
1U
A
9.2
13
A3.3U
19.7
• 3
0.49!
0.5U
A
2.5
A
3.1
0 5 10 15
FEET
15
.
10
fc
IS
5
0.5U
20.8 A3
0.5U
A
5.6 •
49.3
#17.8
35.5
•1.7
0.5U
A
103
A
0.007J
5.6 27.4
-A
5 10
FEET
15
15
10
,0.5U
0.52 • 1.8
6
0.5U
0.5U
A
7.1
8.6
20.8
A
7.9
6.1 1
A •
0.5U
A
19.5
A
5 10
FEET
15
15
10
I
H
5
0.92
0.072
1 0.99 •
1
0.078J
^
1.1
3.8
•
0.24J
B
21
29.9
•
0 5 10 15
FEET
15
10
1
h<
S
5
I
n
6
19.7
6.6
115.2 B <
0.6
0.017J
4,
12
9.4
57.2
•1.2 II
0.35J
I
4.9
40.6
62.4
"
0 5 10 15
FEET
15
10
1
W
'
5
n
32.8
14
•
43.9
13.8 •
3.6
II
8,9
1.9
67
0.01 U
0.052J
22.2
0 5 10 15
FEET
Bold number indicates that total chromium concentration exceeded TCLP limit of 5 mg/L
*. Location from which both predemonstration and postdemonstration samples collected.
A Location from which only predemonstration samples collected.
' • Location from which only postdemonstration samples collected.
All results presented in milligrams per liter (mg/L)
Coordinates (0,0) correspond to the location of cathode C6.
Figure 2-4. Spatial distribution of TCLP teachable chromium concentrations in soil.
34
-------
PREDEMONSTRATION
POSTDEMONSTRATION
6 FEET BGS
8 FEET BGS
10 FEET BGS
12 FEET BGS
20
15
t«10 .
E
g
5 .
0 .
259*
125
*
0 5 10 15 20
FEET
•m
15 .
H10 .
5 .
0 ,
i
256
11.8J
•
IZ580
620 I-6*0
«
891
>658
7.7
•
1,150
•
678
5,717
•
0 5 10 15 20
FEET
15 .
(-ID
5 !
0 .
8.81
4,540 824
1,920
8,440
• 3,450
6,550
11.1
26,800
2,3601
"
0 5 10 ' 15 20
FEET
,n
15 .
f-,10 .
s'.
0 ,
•184
4
28.2
1,470
2,990 9"
> 1,060
3,060
A
1,840
242
0 5 10 15 20
FEET
?"
15
H^O .
's\
0 |
I 21
147
132
58 »
8.2
•
ISO
•
125
0 5 10 15 20
FEET
pn
i
15
1 I
H^n
u< !
«'
l
0 ,
I344
3,020 982
I •
2,030
32.2
4/80
»
657
• 685
1,350
1.700
8.6
•
3,720
2,280
4,520
0 5 10 15 20
FEET
?n
15 .
H10 '
5 !
0 1
408
8,340^1,58
5,270
4,470
•
1,760
"•8,790
13,000
> 8,330
12.7
•
16,200
•
5,420
6,350
0 5 10 15 20
FEET
•m
\
15 .
|
H 10 .
is!
'0 ,
660
433 3,480
•
i
1,590
1,390
•
.273
• 3,970
•5,470
11.3
•
3,250
1,450
801
•
0 5 10 15 20
FEET
Location from which both predemonsfration and ppstdemonstration samples collected.
Location from which only predemonstration sample collected.
Location from which only postdemonstration sample collected.
All results in milligrams per kilogram (rag/kg)
Coordinates (0,0) correspond to location of cathode C6.
Figure 2-5. Spatial distribution of total chromium concentrations in soil.
35
-------
PREDEMONSTRATION
POSTDEMONSTRATION
14 FEET BGS
16FEETBGS
18 FEET BGS
20 FEET BGS
20
15 .
(-10 .
1
'*t
S ,
0 .
3.320
»
845
•
0 5 10 15 20
FEET
20
15 ,
[-.10 .
k
5 ,
285
•
1,340
11,900
A.
2,010
5.240
123
•
1,810
»
189
»
0 5 10 15 20
FEET
20
15
(-.10 .
5 !
0
(
3,9201
146
1,100
•792
48.6
J 5 10 15 20
FEET
20
15 .
10
5
0
62.1
• 1,7401
67.6
0 5 10 15 20
FEET
20
15
I
H10
B
s'
0 |
11,230
138.3
1
1,330
710
1,1*0
12,700
»
4,660
147.4
28
•
151
•
78.7
181
0 5 10 15 20
FEET
20
15
1
H10 .
1
I1
0
1223
79.1
240
»
2,640
203
•195
64.2
•
74.1
1,360
*
0 5 10 15 20
FEET'
20
15
1
t_,10
il
5 '
n ,
1 84. 1
•600
15.8
'I9
22.2
•11.8
72.6,
17.6
279
•
0 5 10 15 20
FEET •
20
15
'
ts
iS
i
135.3
1252
15.2
J
75.3
.10.3
58.2
"
43.5
33.5
5 10 15 20
FEET
* Location from which both predemonstration and postdemonstration samples collected.
A Location from which only predemonstration sample collected.
• Location from which only postdemonstration sample collected.
All results in milligrams per liter (mg/kg).
Coordinates (0,0) correspond to location of cathode C6.
Figure 2-5. Spatial distribution of total chromium concentrations in soil (continued).
36
-------
Table 2-5. System Shutdown Information
Reason for System Shutdown
Intentional shutdown to perform maintenance and modifications to the system
Problems related to electrode water (such as bladder pumps, float switches, and
chiller leakage) ,
Power supply failures and problems •
pH control system problems
Data logger problems ;
Total
Percent of System
Shutdown Time
21
7
4
2
2
36
conditions as demonstrated at the UCAP. According to
SNL, the ISEE system is also applicable to treatment of
soil contaminated with anionic, heavy metals if the metal
anions are water soluble. Water soluble anions such as
CrO4=, HAsO4=, and SeO4= are potential target
contaminants for the ISEE system.
The system has no absolute lower concentration limit to
which it can treat contaminants unless the system's
contaminant removal efficiency indicates otherwise;
therefore, the system's contaminant removal efficiency
needs to be determined on a site-by-site basis (Tetra Tech
1997). According to SNL, the technology is applicable to
any type of soil except gravel. Buried metal objects,
however, can short circuit the path of electric current
through the soil (Tetra Tech 1997).
The presence of dissolved VOCs in general in the pore
water does not affect system performance. However, the
application of electric current may transport dissolved
VOCs through electroosmosis toward the cathode, where
they could enter the cathode casing. In the casing, vacuum
applied would strip VOCs from the solution. These
emissions need to be collected and treated as necessary.
According to SNL, during the early stages of
demonstration, air monitoring done at the cathode casing
did not show the presence of VOCs above 150 parts per
billion. However, the VOC levels significantly increased
in the soil vapor when the soil temperature was about 50
°C. The use of cold finger cathodes that do not have an
exhaust eliminated VOC emissions to atmosphere.
2.3.2 Operating Parameters
Operating parameters can be varied during the treatment
process to achieve desired contaminant removal and
treatment goals. Limited experimental data are currently
available to define the behavior of the ISEE system used to
remediate contaminated soils under unsaturated conditions.
Experimental data are critical because soil electrochemistry
is complex and because of the nonlinear interdependence
of the parameters.
Laboratory testing was performed by SNL to evaluate the
influence of soil moisture on the efficiency of
electrokinetic technology applied to unsaturated soils
under constant current conditions. Experimental results
on UCAP soil show that near saturation, electromigration
velocity increases as soil moisture content decreases.
However, at lower moisture content, the nonlinear effect
of tortuosity dominates and the electromigration velocity
decreases sharply as moisture content decreases. Also, for
the UCAP soil, experiments show that electromigration
and thus remediation ceases at a moisture content of 3.5
percent by weight because of the loss of pore water
connectivity (Lindgren and others 1991). The minimum
moisture content required for the operation of the
electrokinetic technology needs to be determined on a site-
by-site basis.
A secondary factor that affects the performance of an
electrokinetic extraction system is soil temperature.
Thermal effects on saturated soil were studied at the
laboratory scale. If the system is operated under constant
current conditions, pore water temperature will increase,
thereby slightly decreasing electroosmotic velocity but
not affecting electromigration velocity (Mattson and
Lindgren 1994). However, under constant voltage
conditions, increased soil temperature will increase
electromigration velocity, which could result in reduced
remediation times (Mattson and Lindgren 1994; Krause
and Tarman 1995). However, during the SITE
37
-------
demonstration of the ISEE system, the tests performed did
not directly target the evaluation of the system's
performance based on the variation of operating
parameters. Consequently, operating parameter effects
were confounded and could not be dissociated.
2.3.3 Maintenance Requirements
Maintenance of a full-scale ISEE system is estimated to
require 8 hours weekly. This estimate is based on the
assumption that the design of parts of the system that
caused frequent shutdowns during the SITE demonstration,
such as bladders and float switches, would be modified to
eliminate problems.
2.4 Site Characteristics and Support
Requirements
Site-specific factors can impact the application of the
ISEE system. These factors should therefore be
considered before the system is selected for remediation of
a specific site. Site-specific factors addressed in this
section include site access, area, and preparation
requirements; climate requirements; utility and supply
requirements; support system requirements; and personnel
requirements.
2.4.1 Site Access, Area, and Preparation
Requirements
The site must be prepared for the mobilization, O&M, and
demobilization of the equipment. Access roads are
necessary for equipment transport. The site must be
accessible to equipment necessary to install electrodes and
ancillary equipment, such as Geoprobe® and drill rigs.
The air space in the equipment installation area must be
clear of obstacles (such as overhead wires).
In addition to the treatment area and corresponding
exclusion zone, enough space should be available to
accommodate the control trailer, hazardous waste storage
area, water tanks, and supply storage. This additional area
is estimated to require 8,800 square feet.
2.4.2 Climate Requirements
The demonstration took place hi Albuquerque, New
Mexico, a semi-arid region. The average winter
temperature is about 50 °F (10 °C), and freezing
conditions occur mainly during the night. A temporary
structure was installed during the demonstration to protect
the ISEE system and personnel from the weather and also
to provide an exclusion zone when electrodes were
energized. The data logger, control panels, and analytical
equipment were housed in the control trailer.
If the ISEE system is used outdoors hi a cold climate,
provisions should be made for insulating exposed portions
of the water control system to prevent freezing. In
addition, equipment such as chillers should be designed
for outdoor use.
2.4.3 Utility and Supply Requirements
i i i
The ISEE system demonstrated at UCAP was powered by
four 10-kW power supply units. The units were capable of
operating independently or in parallel. When connected in
parallel, the maximum output was 64 amps at 600 V DC.
According to SNL, a three-phase, 230-V, 150-kW power
supply is necessary to operate a full-scale ISEE system.
Water is also necessary to operate the system. SNL
estimates that for a full-scale system of 30 electrodes, a
quantity of 3 60 L of water per day is required. Water could
be obtained from a permanent source of potable water or
stored in water tanks on site. In addition, water for
decontamination activities is required as needed.
The monitoring system requires connection to a telephone
line or cellular telephone to download data to an off-site
computer and to transmit signals that the system has been
shut down to maintenance personnel.
2.4.4 Support System Requirements
Several surveys are required to determine if the site is
appropriate for electrokinetic treatment. Electromagnetic
and magnetic surveys are necessary to determine if large
metallic objects are buried in soil. These objects could
short circuit the current in the soil, thus significantly
decreasing the efficiency of the remediation process. Soil
conductivity and soil moisture are also critical to
application of the electrokinetic technology; therefore,
surveys to determine these parameters for soil to be treated
are also required.
Also, remediation progresses, anolyte containing chromate
is removed. This effluent stream is a hazardous waste and
needs to be handled, stored, and disposed of in accordance
with applicable regulations.
38
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2.4.5 Personnel Requirements
Based on the design of the ISEE system, which can
transmit system information off site, no personnel are
required to be present on site for system operation. The
system is equipped with a CR7 data logger that monitors
system parameters and can shut down the system (such as
by cutting off power to the electrodes and terminating the
water supply). The data logger consequently sends a
coded signal to the system operator that identifies the
problem. Technical service personnel should be available
on an as-needed basis to remediate any problems.
Periodic visits to the site are necessary for activities such
as collection of anolyte samples, replacement of full
effluent barrels, addition of sodium hydroxide to the pH
control barrels, and soil moisture measurement using
neutron hydroprobes. The involvement of a chemist or
technician is also periodically required for chromate
analysis of anolyte samples collected. According to the
vendor, maintenance and routine sampling and analysis
activities for a full-scale system should require the on-site
presence of a technician for 8 hours a week.
Before operating the ISEE system at a hazardous waste
site, the technician should have completed training
requirements under the Occupational Safety arid Health
Act (OSHA) outlined in Title 29 of the Code of Federal
Regulations (40 CFR), Part 1910.120, which covers
hazardous waste operations and emergency response. The
operator should also participate in a medical monitoring
program as specified by OSHA.
2.5 Material Handling Requirements
The only waste stream produced during the remediation of
soil using the SNL ISEE system is effluent containing
chromate extracted from the anode casings, which is a
hazardous waste. In addition, decontamination activities
(such as decontamination of the Geoprobe®) could also
produce hazardous wastes. If the ISEE system is applied
to soil that contains VOCs, VOCs would be stripped from
the soil matrix because of heating that occurs when current
is passed through the soil. Treatment area should be
monitored for VOC air emissions to evaluate If special
controls are needed.
In addition, a site plan is required to provide for personnel
protection and special handling measures. Wastes need to
be appropriately stored until sampling results indicate
their acceptability for disposal or release to a treatment
facility.
2.6 Technology Limitations
Prior to implementing electrokinetic remediation at a
specific site, field and laboratory screening tests should be
conducted to determine if the site is amenable to this
technology. Field conductivity surveys are necessary to
determine the soil's electrical conductivity. Also, buried
metallic objects and utility lines could short circuit the
current path,; thereby influencing the voltage gradient and
affecting the contaminant extraction rate. Electromagnetic
surveys should be conducted to determine the presence of
buried metallic objects.
In addition, if VOCs are present in soil undergoing
electrokinetic treatment, the VOCs may be stripped from
the soil to significantly increase the soil vapor VOC
concentrations that would result in significant VOC
migration from the treatment area, if soil temperature
exceeds 50 PC. Special measures therefore need to be
taken to contain and control VOC emissions.
2.7 Potential Regulatory Requirements
This section discusses regulatory requirements relevant to
use of the ISEE system at Superfund RCRA corrective
action sites. Regulations applicable to implementation of
this system depend on site-specific remediation logistics
and the type of contaminated soil being treated; therefore,
this section presents a general overview of the types of
federal regulations that may apply under various
conditions. State requirements should also be considered,
but because these requirements vary from state to state,
they are not discussed in detail in this section. Table 2-6
summarizes ;the regulations discussed below. These
regulations include the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA);
RCRA; the Clean Air Act (CAA); Toxic Substances
Control Act'(TSCA); Atomic Energy Act (AEA) and
RCRA for mixed wastes; and OSHA requirements.
2.7.1 Comprehensive Environmental
Response, Compensation, and
Liability Act
CERCLA authorizes the federal government to respond to
releases or potential releases of any hazardous substance
into the environment, as well as to releases of pollutants or
39
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Table 2-6. Summary of Applicable Regulations
Act or Authority Applicability
Application to SNLISEE System
Citation
CERCLA
Superfund sites
RCRA
Superfund and
RCRA sites
CAA
Air emissions
from stationary
and mobile
sources
TSCA
Poiychlorinated
biphenyl (PCB)
contamination
AEA and RCRA Mixed wastes
OSHA
Requirements
All remedial
actions
This program authorizes and
regulates the cleanup of
environmental contamination. It
applies to all CERCLA site cleanups
and requires that other
environmental laws be considered
as appropriate to protect human
health and the environment.
RCRA defines and regulates the
treatment, storage, and disposal of
hazardous wastes. RCRA also
regulates corrective action at
generator and treatment, storage, or
disposal facilities. The ISEE
treatment residual (anolyte) contains
hexavalent chromium and should be
characterized and disposed of as a
RCRA hazardous waste.
If VOC emissions occur or
hazardous air pollutants are of
concern, these standards may be
applicable to ensure that air pollution
is not associated with the use of this
technology. State air program
requirements should also be
considered.
If PCB-contaminated wastes are
treated, TSCA requirements should
be considered to determine waste
disposal requirements. RCRA also
regulates solid wastes containing
PCBs.
AEA and RCRA requirements apply
to the treatment, storage, or disposal
of mixed wastes containing both
hazardous and radioactive
components. OSWER and DOE
directives provide guidance that
address mixed wastes.
OSHA regulates on-site construction
activities and the health and safety of
workers at hazardous waste sites.
Installation and operation of the
system at Superfund or RCRA sites
must meet OSHA requirements.
40 CFR, Part 300
40 CFR, Parts 260
through 270
40 CFR, Parts 50 and 70
40 CFR, Part 761
AEA (10 CFR) and RCRA
(see above)
29 CFR, Parts 1900
through 1926
40
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contaminants that may present an imminent or significant
danger to public health and welfare or the environment.
As part of the requirements of CERCLA, EPA has
prepared the National Oil and Hazardous Substances
Contingency Plan (NCP) for hazardous substance
response. The NCP is codified in 40 CFR, Pait 300, and
delineates the methods and criteria used to determine the
appropriate extent of removal and cleanup of hazardous
waste contamination.
The Superfund Amendments and Reauthorization Act
(SARA) amended CERCLA and directed EPA to do the
following:
• Use remedial alternatives that permanently and
significantly reduce the volume, toxicity, or mobility
of hazardous substances, pollutants, or contaminants
• Select remedial actions that protect human health and
the environment, are cost-effective, and involve
permanent solutions and alternative treatment or
resource recovery technologies to the maximum
extent possible
• Avoid off-site transport and disposal of untreated
hazardous substances or contaminated materials when
practicable treatment technologies exist (Section
In general, two types of responses are possible under
CERCLA: removal and remedial actions. The SNL ISEE
system is likely to be part of a CERCLA remedial action.
Nine general criteria that must be addressed by CERCLA
remedial actions are listed in Table ES-1 of the Executive
Summary.
On-site remedial actions must comply with federal and
more stringent state ARARs. ARARs are determined on a
site-by-site basis and may be waived under six conditions:
(1) the action is an interim measure and the ARA.R will be
met upon remedial action completion, (2) compliance
with the ARAR would pose a greater risk to human health
and the environment than noncompliance, (3) it is
technically impractical to meet the ARAR, (4) the
standard of performance of an ARAR can be met by an
equivalent method, (5) a state ARAR has not been
consistently applied elsewhere, and (6) ARAR compliance
would not provide a balance between the protection
achieved at a particular site and demands on Superfund for
other sites. These waiver options apply only to Superfund
actions taken on site, and justification for the waiver must
be clearly demonstrated.
CERCLA requires identification and consideration of
environmental laws that are ARARs applicable to site
remediation before implementation of a remedial
technology at a Superfund site. Additional regulations
pertinent to use of the ISEE system are discussed below.
No direct water discharges are generated by the ISEE
treatment process; therefore, only regulations addressing
anolyte characterization and disposal, potential fugitive
air emissions from VOCs stripped from soil, and
additional considerations are discussed below.
2.7.2 Resource Conservation and
Recovery Act
RCRA, an amendment to the Solid Waste Disposal Act,
was passed in 1976 to address the problem of how to safely
dispose of the enormous volume of municipal and
industrial solid wastes generated annually. RCRA
specifically addressed the identification and management
of hazardous wastes. The Hazardous and Solid Waste
Amendments of 1984 greatly expanded the scope and
requirements of RCRA.
The presence of RCRA-defined hazardous waste
determines whether RCRA regulations apply to the SNL
ISEE system. If soil or anode effluent are determined to be
hazardous waste as defined by RCRA, all RCRA
requirements regarding the management and disposal of
hazardous wastes will need to be addressed. RCRA
regulations define hazardous wastes and regulate their
transport, treatment, storage, and disposal. Wastes
defined as hazardous under RCRA include characteristic
and listed wastes. Criteria for identifying characteristic
hazardous wastes are included in 40 CFR, Part 261,
Subpart C. Listed wastes from nonspecific and specific
industrial sources, off-specification products, spill
cleanups, and other industrial sources are discussed in 40
CFR, Part 26.1, Subpart D.
Treatment, storage, or disposal of hazardous waste
typically requires issuance of a RCRA Part B treatment,
storage, or disposal permit. At Superfund sites, the on-site
treatment, storage, or disposal of hazardous waste must
meet the substantive requirements of a treatment, storage,
or disposal permit. RCRA administrative requirements
(such as reporting and recordkeeping), however, are not
applicable to on-site actions.
41
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A Uniform Hazardous Waste Manifest or its state
counterpart must accompany off-site shipment of
hazardous waste, and transport must comply with U.S.
Department of Transportation hazardous waste packaging,
labeling, and transportation regulations. The receiving
treatment, storage, or disposal facility must be permitted
and in compliance with RCRA standards.
RCRA federal land disposal restrictions (LDR) in 40 C.FR,
Part 268, preclude the land disposal of hazardous waste
that fails to meet stipulated technology or treatment
standards. In situ treatment of media contaminated with
hazardous waste does not trigger LDRs for soil or
groundwater remaining in place. Consequently, soil
treated in situ by the ISEE system does not have to meet
LDRs but may have to meet other criteria in order to
remain in place. Soil or groundwater removed and treated
must meet LDRs prior to replacement. For the anolyte,
this requirement means that treatment must reduce the
concentrations of contaminants that make the anolyte
hazardous and all other LDR-triggering contaminants to
levels specified in 40 CFR, Part 268, before the anolyte can
be land disposed. The technology or treatment standards
applicable to residuals produced by the SNL ISEE system
are determined by the type and characteristics of
hazardous waste present in the soil being remediated. In
some cases, variances from LDRs can be obtained from
EPA.
Requirements for corrective action at RCRA-regulated
facilities are provided in 40 CFR, Part 264, Subparts F
(promulgated) and S (proposed). These subparts also
generally apply to remediation at Superfund sites.
Subparts F and S include requirements for initiating and
conducting RCRA corrective actions, remediating
groundwater, and ensuring that corrective actions comply
with other environmental regulations. Subpart S also
details conditions under which particular RCRA
requirements can be waived for temporary treatment units
operating at corrective action sites. Thus, RCRA
mandates requirements similar to CERCLA and as
proposed allows treatment units such as the ISEE system
to operate without the full set of permits.
2.7.3 Clean Air Act
The CAA as amended in 1990 regulates stationary and
mobile sources of air emissions. CAA regulations are
generally implemented through combined federal, state,
and local programs. The CAA requires that treatment,
storage, and disposal facilities comply with primary and
secondary ambient air quality standards. Air emissions
from the ISEE system may result from VOCs from the
vacuum exhaust system and fugitive emissions such as
drilling activities related to system installation (VOC or
dust emissions), periodic sampling efforts, and the staging
and storing of contaminated drill cuttings. VOC emission
control equipment should be provided to reduce
emissions, if the ISEE system is applied to soils that
contain VOCs. Soil moisture should be managed during
system installation to prevent or minimize impacts from
fugitive emissions. State air quality standards may require
additional measures to prevent fugitive emissions.
2.7.4 Toxic Substances Control Act
The disposal of PCBs is regulated under Section 6(e) of
TSCA. PCB treatment and disposal regulations are
described in 40 CFR, Part 761. Materials containing PCBs
at concentrations of 50 to 500 parts per million (ppm) can
either be disposed of in TSCA-permitted landfills or
destroyed by incineration at a TSCA-approved incinerator;
at PCB concentrations exceeding 500 ppm, the material
must be incinerated.
Sites where spills of PCBs have occurred after May 4,
1987, must be addressed under the PCB spill cleanup
policy in 40 CFR Part 761, Subpart G. This policy applies
to spills of materials containing 50 ppm or more of PCBs
and establishes cleanup protocols for addressing such
releases based on the volume and concentration of the
spilled material. PCBs were not anticipated to be present
at the demonstration site; therefore, no analysis for PCBS
was performed.
2.7.5 Atomic Energy Act and Resource
Conservation and Recovery Act
As defined by the AEA and RCRA, mixed waste contains
both radioactive and hazardous components. Such waste
is subject to the requirements of both the AEA and RCRA;
however, when application of both AEA and RCRA
regulations results in a situation inconsistent with the AEA
(for example, an increased likelihood of radioactive
exposure), AEA requirements supersede RCRA
requirements (EPA 1988). Use of the ISEE system at sites
with radioactive contamination might involve treatment or
generation of mixed waste.
42
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OSWER, in conjunction with the Nuclear Regulatory
Commission, has issued several directives to assist in the
identification, treatment, and disposal of low-level
radioactive mixed waste. Various OSWER directives
include guidance on defining, identifying, and disposing
of commercial, mixed, low-level radioactive and
hazardous wastes (EPA 1987). If the ISEE system is used
to treat low-level mixed waste, these directives should be
considered. If high-level mixed waste or transuranic
mixed waste is treated, internal DOE orders should be
considered when developing a protective remedy (DOE
1988b).
2.7.6 Occupational Safety and Health
Administration Requirements
OSHA regulations in 29 CFR, Parts 1900 through 1926,
are designed to protect worker health and safety. Both
Superfund and RCRA corrective actions must meet OSHA
requirements, particularly Part 1910.120, "Hazardous
Waste Operations and Emergency Response." Part 1926,
"Safety and Health Regulations for Construction," applies
to any on-site construction activities. For example,
electric utility hookups for the ISEE system must comply
with Part 1926, Subpart K, "Electrical." Product
chemicals such as NaOH used with the ISEE system must
be managed in accordance with OSHA requirements (for
example, Part 1926, Subpart D, "Occupational Health and
Environmental Controls," and Subpart H, "Materials
Handling, Storage, and Disposal"). More stringent state or
local requirements must also be met, if applicable. In
addition, health and safety plans for site remediations
should address chemicals of concern and include
monitoring practices to ensure that worker health and
safety are maintained.
2.8 State and Community Acceptance
Because few applications of the SNL ISEE system have
been attempted beyond the bench- or pilot-scale, limited
information is available to assess state and community
acceptance of the system. The fact that the ISEE system
allows in situ remediation of contaminated soils should
improve the potential for community acceptance because
excavation of contaminated soil often releases volatile
contaminants. Although some contaminants may be
released during electrode and ancillary equipment
installation, the potential for emissions during drilling is
substantially lower than during excavation. State
• acceptance of the technology may involve consideration
of performance data from applications such as the SITE
demonstration and results from on-site, pilot-scale studies
using the actual wastes to be treated during later, full-scale
remediation.:
43
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Section 3
Economic Analysis
3.1 Introduction
The primary purpose of this economic analysis is to
provide a cost estimate (not including profit) for using the
SNLISEE system to commercially remediate unsaturated
soils contaminated with hexavalent chromium. This
analysis is based on the assumptions and costs provided by
SNL and on the results and experiences gained from the
SITE demonstration conducted over a 6-month period at
SNL's UCAP. During the SITE demonstration, 13 tests
were performed during six phases. The first 12 tests were
conducted so that SNL could determine preferred ISEE
system operating conditions for Test 13 and to facilitate
the migration of hexavalent chromium toward the central
portion of the test area. Therefore, this cost estimate is
based on the preferred operating conditions documented
during Test 13. Test 13 targeted a central portion of the
demonstration area, utilizing four anodes and eight cold
finger cathodes.
Economic calculations were performed for the SITE
demonstration Test 13 treatment area, treatment depth,
and operating parameters. SNL anticipates that the cost
for operating the small-scale ISEE system used during
Test 13 will be significantly higher than the cost for
operating a full-scale, commercialized ISEE system. SNL
states that a full-scale, commercialized system would be
designed with significant improvements over the system
operated during the demonstration. However, SNL has
not yet completed the design. Therefore, it is not possible
to prepare a cost estimate for operating the full-scale ISEE
system. When the technology is ready for
commercialization, further economic analysis should be
performed to obtain the costs of operating the system
during a site remediation.
A number of factors affect the cost of treatment. These
include, but are not limited to, treatment area, treatment
depth, initial contaminant concentration, final target
contaminant concentration, soil characteristics, online
percentage of system operation, hexavalent chromium
removal rate, and hexavalent chromium removal
efficiency. This economic analysis assumes that the SNL
ISEE system will remediate unsaturated soils with the
same characteristics as soil at the UCAP site.
During Test 13 of the SITE demonstration, the ISEE
system treated a volume of approximately 16 cubic yards
(yd3) of soil contaminated with hexavalent chromium.
This volume is based on the assumption that the effective
treatment depth is 6 feet, the treatment area width is 6 feet,
and the treatment area length is 12 feet. During Test 13,
soil was treated for over 700 hours from October 21 to
November 24, 1996. SITE demonstration results are
presented in Section 2 of this report.
Treatment costs were estimated for using the Test 13 ISEE
system configuration to treat 16 yd3 of soil and remove 200
g of hexavalent chromium (the approximate mass of
hexavalent chromium removed during Test 13).
Estimated treatment costs, issues and assumptions, and the
basis for the economic analysis are discussed below.
3.2 Issues and Assumptions
The cost estimates presented in this economic analysis are
representative of charges typically assessed to the client by
the vendor but do not include profit. In general,
assumptions are based on information provided by the
developer and on observations during this and other SITE
evaluation projects.
Many actual or potential costs are not included as part of
this cost estimate. They were omitted because site-
specific engineering designs that are beyond the scope of
44
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this SITE project would be required. Also, certain
functions were assumed to be the obligation of the
responsible party or site owner and therefore are not
included. These costs are site-specific. Thus, calculations
are left to the reader so that relevant information may be
obtained for specific cases. Whenever possible,
applicable information is provided on these costs so that
the reader can independently complete the calculations
required to calculate relevant economic data.
Other important assumptions regarding operating
conditions and task responsibilities that could significantly
alter the cost estimate are discussed below.
• The site has been adequately characterized during
previous investigations.
• Treatability studies or pilot-scale studies have already
been performed.
• The site has suitable access roads.
• The site has electrical supply lines, telephone lines or
cellular telephone service, and potable water.
• Hexavalent chromium is being removed from
unsaturated soil similar to UCAP soil.
• Based on Test 13 results, the ISEE system will on
average remove hexavalent chromium at a rate of 0.29
g/hour, with an overall removal efficiency of 0.14 g of
hexavalent chromium per kW-h.
• Based on information from the developer, the online
percentage will be 85 percent for the ISEE system.
• Based on the hexavalent chromium removal rate
measured during Test 13 and an online percentage of
85 percent, the treatment time for the ISEE system is
approximately 5 weeks to remove 200 g of hexavalent
chromium.
• Based on information from the developer, the
combined total operating and maintenance labor time
during on-site treatment is 8 hours/week.
• Based on information from the developer, 80 hours of
labor will be required for startup of the ISEE system.
3.3 Basis for Economic Analysis
To compare the cost effectiveness technologies evaluated
under the SITE program, EPA breaks down costs into the
following 12 categories (Evans 1993):
• Site and facility preparation costs
• Permitting and regulatory costs
• Equipment costs
• Startup and fixed costs
• Labor costs
• Supplies and consumables costs
• Utilities costs
• Effluent treatment and disposal costs
• Residuals and waste shipping, handling, and transport
costs
• Analytical costs
• Facility modification, repair, and replacement costs
• Site restoration costs
These 12 cost categories reflect typical cleanup activities
encountered at Superfund sites. Each of these cost
categories is.defined and discussed below and form the
basis for the detailed estimated costs presented in Tables
3-1 and 3-2. Table 3-1 provides a detailed breakdown by
cost category. Table 3-2 lists each category's cost as a
percent of the total cost. Costs assumed to be the
obligation of the responsible party or site owner are
omitted from this cost estimate and are indicated by a line
(—) in Tables 3-1 and 3-2. Categories with no associated
costs are indicated by a zero (0) in Tables 3-1 and 3-2.
Costs presented in this report are order-of-magnitude
estimates as defined by the American Association of Cost
Engineers, with an expected accuracy within +50 percent
and -30 percent; however, because this technology is new,
the actual range may be wider. The 12 cost categories
examined and assumptions made are also described in
detail below.
45
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Table 3-1. Estimated Costs for Treatment Using the SNL ISEE System
Total Treatment Volume
Mass of Hexavalent Chromium Removed
Treatment Time
Cost Categories
16yd3
200 g
5 weeks
$/yd3
Site and Facility Preparation Costs
Site design and layout
Survey and site investigations
Legal searches
Access rights and roads
Preparation for support facilities
Auxiliary buildings
Transportation of waste feed
Technology-specific requirements
Total Site and Facility Preparation Costs
Permitting and Regulatory Costs
Permits
System monitoring requirements
Development of monitoring and analytical protocols
Total Permitting and Regulatory Costs
Equipment Costs
Annualized purchased equipment cost
Equipment rental/lease
Total Equipment Costs
Startup and Fixed Costs
System installation
Startup labor
Equipment mobilization
Insurance and taxes
Initiation of monitoring programs
Contingency
Total Startup and Fixed Costs
Labor Costs
Operation
Total Labor Costs
Supplies and Consumables Costs
Anode casings
Cathode casings
Plumbing
PPE
Sodium hydroxide
Total Supplies and Consumables Costs
Utilities Costs
Electricity
Water
Total Utilities Costs
188
188
48
25
73
312
250
94
656
125
125
0
0
0
2
7
9
10
<1
10
46
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Table 3-1. Estimated Costs for Treatment Using the SNLISEE System (continued)
Total Treatment Volume
Mass of Hexavalent Chromium Removed
Treatment Time
Cost Categories
16yd3
200 g
5 weeks
$/yd3
Effluent Treatment and Disposal Costs
On-site facility costs
Off-site facility costs
-anode effluent 46
-cathode effluent ' 0
Total Effluent Treatment and Disposal Costs 46
Residuals and Waste Shipping, Handling and Transport Costs
Drill cuttings §8
PPE and small equipment 16
Total Residuals and Waste Shipping, Handling and Transport Costs 114
Analytical Costs
Operations (for developer's purposes) 6
Environmental monitoring (regulatO'iy)
Total Analytical Costs 6
Facility Modification, Repair, and Replacement Costs
Design adjustments 0
Routine maintenance (materials and labor)a 0
Equipment replacement 0
Total Facility Modification, Repair, and Replacement Costs" 0
Site Restoration Costs
Site cleanup and restoration
- Technology specific 141
Permanent storage
Total Site Restoration Costs 141
TOTAL OPERATING COSTS"
1,368
(1,400)
Notes:
9
PPE
yd3
= Gram
= Personal protective equipment
= Cubic yard
= Cost omitted because assumed to be responsible party or site owner obligation
= Less than
Maintenance labor is included under operating labor costs.
Total operating costs rounded off nearest $100.
47
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Table 3-2. Estimated Cost Percentages for Treatment Using the SNLISEE System
Total Treatment Volume
Mass of Hexavalent Chromium Removed
Treatment Time
Costs Units
Site Facility Preparation Costs
Permitting and Regulatory Costs
Equipment Costs
Startup and Fixed Costs
Labor Costs
Supplies and Consumables Costs
Utilities Costs
Effluent Treatment and Disposal Costs
Residuals Shipping, Handling, and Transport Costs
Analytical Costs
Facility Modifications, Repair, and Replacement Costs
Site Restoration Costs
Total Costs ($/yd3)
Notes:
g = Gram
yd3 = Cubic yard
16yd3
200 g
4 weeks
($/yd3)
188
—
73
656
125
9
10
46
114
6
Oa
141
1,368
.
13.7%
—
5.3%
47.9%
9.1%
0.6%
0.7%
3.4%
8.3%
0.4%
Oa%
10.3%
Cost omitted because assumed to be responsible party or site owner obligation
Maintenance labor is included under operating labor costs.
48
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3.3.1 Site and Facility Preparation Costs
For the purposes of these cost calculations, "site" refers to
the location of the contaminated area. It is assumed that
preliminary site preparation will be performed by the
responsible party or site owner. The amount of
preliminary site preparation required depends OKI the site.
Site preparation responsibilities include assessment of site
design and layout, surveys and site investigations, legal
searches, securing of access rights and construction of
access roads, preparation of support and decontamination
facilities, construction of fixed auxiliary buildings, and
transportation of waste feed. Because these costs are site-
specific, they are not included as part of the site
preparation costs in this estimate.
The cost estimate assumes that the site has been
characterized during previous investigations; therefore,
characterization data are available to document the
electrical conductivity of soil pore water, contain.inant ion
concentrations in the pore water,-hydraulic conductivity,
soil moisture content, subsurface conditions regarding any
metallic objects, soil mineralogy, and the presence of
VOCs in soil.
For these cost calculations, only technology-specific site
preparation costs are included. These costs are limited to
costs for connecting utilities to the ISEE system. It is
assumed that the site has electrical supply lines, telephone
lines (or a cellular telephone service), and potable water.
The developer estimates the cost for utilities connection to
be $3,000.
3.3.2 Permitting and Regulatory Costs
Permitting and regulatory costs are generally the
obligation of the responsible party or site owner. These
costs may include actual permit costs, system monitoring
requirements, development of monitoring and analytical
protocols, and health and safety monitoring. Permitting
and regulatory costs can vary greatly because they are site-
and waste-specific. No permitting costs are included in
this analysis. Depending on the treatment site, these costs
can be a significant factor because permitting can be
expensive and time consuming.
3.3.3 Equipment Costs
Equipment costs include purchased and rented equipment.
Purchased equipment costs are presented as annualized
costs and are prorated based on the amount of time the
equipment is used for the project. The annualized
purchased equipment cost is calculated based on a 15-year
equipment life and a 6 percent annual interest rate. The
annualized equipment cost is based on the writeoff of the
total initial capital equipment cost and scrap value
(assumed tq be zero) using the following equation
(Douglas 1988; Peters 1980):
Capital recovery = (V - V )
S
(3-1)
where:
V
Vs
n
i
cost of the original equipment
salvage value of equipment
equipment life
annual interest rate
Purchased equipment for the ISEE technology includes
four anodes, eight cold finger cathodes, a water control
system, a vacuum control system, a power supply system,
and a monitoring system. This cost estimate assumes that
ISEE system used during Test 13 requires one vacuum
pump, one air compressor, two chillers, four controllers
(one for each anode), one rectifier, electrode cabling, one
skid loader, and one hurricane sampler. The developer
estimates the total capital cost of the ISEE system used
during Test 13 to be $78,400. This cost was used to
calculate the prorated annualized purchased equipment
cost based on. treatment time for the ISEE system. Based
on the hexavalent chromium removal rate measured
during Test 13 and an online percentage of 85 percent, the
treatment time for the ISEE system is approximately 5
weeks to remove 200 g of hexavalent chromium.
Rented equipment includes a trailer at a rate of $200 per
month based on a 30-day month. This cost estimate
assumes that a trailer will be rented for 2 months for
removing 200 g of hexavalent chromium.
If the ISEE system is applied to soils that contain VOCs,
the VOCs would be stripped from the soil matrix and VOC
monitoring equipment would be required. This
requirement would result in increased costs for purchased
equipment and increased costs for VOC migration control
and monitoring (depending on the VOC migration control
equipment selected).
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3.3.4 Startup and Fixed Costs
For these cost calculations, startup and fixed costs include
system installation (costs) estimated by the developer to
be $5,000; startup labor costs estimated by the developer
to be 80 hours at a rate of $50 per hour; and equipment
mobilization costs estimated by the developer to be
$1,500. System installation includes costs (including
labor) for installing the anodes, the cold finger cathodes,
plumbing, and all other aboveground ISEE system
equipment. Startup labor includes shakedown testing of
the ISEE system. Mobilization costs assume that all of the
ISEE equipment (including the control trailer) can be
mobilized to the site for $1.50 per mile for 1,000 miles.
This cost estimate assumes that treatability studies or
pilot-scale studies have already been performed.
Technology-specific site preparation costs are discussed
in Section 3.4.1.
No insurance and taxes, initiation of monitoring programs,
or contingency costs are included because the demonstration
system is not designed to be a commercial system. Often,
insurance and taxes can be estimated to be 10 percent of
the total annual purchased equipment costs. Also,
depending on the site and location of the ISEE system,
local authorities may impose specific guidelines for
monitoring programs. The stringency and frequency of
monitoring required may have significant impact on
project costs. Contingency costs are often equal to the cost
of insurance and taxes. Contingency costs allow for
unforeseen or unpredictable cost conditions, such as
Strikes, storms, floods, and price variations (Peters 1980;
Garrett 1989).
3.3.5 Labor Costs
Hourly labor rates for ISEE system operation are
estimated at $50 per hour and include base salary, benefits,
overhead, and general and administrative expenses. For
this cost estimate, operating labor is assumed to consist of
one worker for 8 hours per week during treatment.
Operating labor includes time for general maintenance of
the ISEE system. In addition, operating labor includes
time for activities such as collection of anode effluent
samples, replacement of full effluent barrels, addition of
sodium hydroxide to the pH control barrels, soil moisture
content measurement using neutron hydroprobes, and
field analysis of hexavalent chromium in anode effluent
samples.
3.3.6 Supplies and Consumables Costs
Supplies costs are limited to personal protective
equipment (PPE), anode casings, cathode casings, and
plumbing supplies. The cost of PPE is estimated at $5 per
week. SNL does not expect to replace the anode casings,
the cathode casings, or the plumbing while operating the
ISEE system for removing 200 g of hexavalent chromium
because of short duration of treatment.
Consumables costs are limited to sodium hydroxide. It is
assumed that sodium hydroxide volume requirements are
based on observations made by the developer during Test
13 of the SITE demonstration (65 g of sodium hydroxide
per hour at a cost of $2 per kilogram of sodium hydroxide).
3.3.7 Utilities Costs
Utilities required are limited to electricity and water for the
electrodes, chillers, and control equipment. Costs for a
telephone line for remote access to the data logger are not
included because they are assumed to be the obligation of
the responsible party or site owner. The volume of water
required is estimated to be 6 gallons per day based on the
average volume of effluent collected during Test 13.
Water rates are assumed to be $0.20 per 1,000 gallons.
Electricity for the electrodes is based on the 0.14 g/kW-h
hexavalent chromium removal efficiency calculated for
Test 13. Based on information provided by the developer,
electricity for the chillers is estimated to equal the
electricity required for the electrodes, and electricity for
the control equipment is estimated to be one-quarter of the
electricity required for the electrodes. Electricity costs are
based on an assumed removal efficiency of 85 percent and
electricity rates of $0.05/kW-h.
3.3.8 Effluent Treatment and Disposal
Costs
Anode effluent requires effluent treatment and disposal.
For this cost estimate, it is assumed that the effluent
disposal cost (including transportation) is $185 per 55-
gallon drum. Effluent volumes generated are based on the
average volume of anode effluent generated during Test
13 (approximately 6 gallons per day).
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3.3.9 Residuals and Waste Shipping,
Handling, and Transport Costs
It is assumed that the only residuals or solid wastes
generated from use of the ISEE system will be drill
cuttings and used PPE and small equipment. The disposal
cost (including transportation) for solid waste is estimated
at $260 per 55-gallon drum. If the solid waste is not
classified as hexavalent chromium-contaminated, the
disposal cost may be less. For this cost estimate, it is
estimated that six 55-gallon drums of drill cuttings and one
55-gallon drum of used PPE and small equipment will be
generated for removing 200 g of hexavalent chromium.
3.3.10 Analytical Costs
Only spot checks executed at the developer's discretion (to
estimate hexavalent chromium concentrations in the
anolyte and to verify that the ISEE system is functioning
properly) are included in this cost estimate. The client may
elect or may be required by local authorities to initiate a
planned sampling and analytical program at the client's
expense. The cost for the developer's spot checks is
estimated at $5 per sample for field analysis. For the
purposes of this cost estimate, it is assumed that one
sample per week per anode will be field analyzed. Labor
costs for collection of samples, field analysis of samples,
and evaluation of field data are included under labor costs.
The analytical costs associated with environmental
monitoring are not included in this estimate because
monitoring programs are not typically initiated by the
developer. Local authorities may, however, impose
specific sampling and monitoring requirements; therefore
analytical costs could contribute significantly to the cost of
the project.
3.3.11 Facility Modification, Repair, and
Replacement Costs
System maintenance costs are assumed to consist of
maintenance labor and materials. Maintenance costs are
limited to supplies and labor. Maintenance supplies are
included under supplies and consumables costs.
Maintenance labor costs are included as operating labor
under labor costs. As stated above, the developer plans to
significantly redesign the ISEE technology for full-scale
remediation. Therefore, no facility modification costs are
included for the ISEE demonstration system used for this
cost estimate. Future cost analysis of the commercialized
ISEE system should include site modification costs, and
these costs would be more indicative of site modification
costs for the ISEE system.
3.3.72 Site Restoration Costs
Site restoration requirements vary depending on the future
use of the site and are assumed to be the obligation of the
responsible party or site owner. Therefore, the only site
restoration costs included are for technology-specific site
restoration, including demobilization of ISEE system
equipment and grouting the electrode boreholes. The
developer estimates thattechnology-specific site restoration
costs will be limited $1,500 for demobilizing the ISEE
system equipment and $750 for grouting the boreholes.
3.4 Conclusions
Because the treatment volume is only 16 yd3 and the ISEE
system configuration used during Test 13 is currently at
the pilot-scale level, the cost per yd3 of treated soil is very
high; the estimated treatment costs are about $1,400 per
yd3 for 200 g of hexavalent chromium removed. If SNL is
able to further optimize the ISEE system configuration so
that hexavalent chromium removal rate increases from
that calculated for Test 13, treatment time and costs will be
lower. As mentioned above, costs from economic analysis
of a full-scale ISEE system would be more indicative of
costs of a commercial-scale ISEE system.
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Section 4
Technology Status
The SNLISEE system SITE demonstration has shown that
in situ remediation of chromate-contaminated, unsaturated
sandy soil at the field scale is possible. Vendor claims for
the ISEE system technology are discussed in the appendix.
Chromate ions were transported electrically through soil
to anodes and then extracted to the soil surface.
Furthermore, the ISEE system controlled water addition
so that the net addition of water to soil was negligible
during the demonstration.
The SNL ISEE system electrode lysimeters can treat soil
having virtually any moisture content. Previous
electrokinetic treatment methods are confined to saturated
soil and clay near saturation. The ISEE system's porous
ceramic casings contain contaminants in electrolyte fluid
that can be pumped out and disposed of. Unlike traditional
electrokinetic extraction systems that use groundwater
wells, the ISEE system's lysimeter system controls the
amount of water pumped out of the electrodes.
Presently, the ISEE system demonstrated at UCAP is
housed in a portable semitrailer. This trailer houses the
electrode controls, power supply system, and data
collection system, the trailer can also serve as a portable
laboratory for on-site analyses. Up to 10 electrode pairs
can be powered using the configuration used during the
SITE demonstration.
Data obtained from this demonstration allowed SNL to
develop a three-phase, sequential approach to evaluate a
potential site for electrokinetic remediation. During Phase
I, SNL will collect existing information and perform a
preliminary assessment of the applicability of electrokinetic
remediation to a site. If the site looks promising, Phase 2
will be conducted to further evaluate site soil and
contaminants and to provide additional information for
Phase 3. Phase 3 consists of design of the remediation
system and calculation of the total costs of remediation.
Site information pertinent to electrokinetic remediation
includes the following:
General information
• Contaminated area size and depth
• Utilities layout
• Depth to groundwater
• Soil type and moisture content profile
Chemical information
• Contaminant type
« Contaminant concentrations and distribution
• Pore water electrical conductivity
• Soil buffering capacity
• Sorption isotherm contours
• Concentration of other ions and their distribution
Other information
• Electrical conductivity distribution
• Electrical conductivity functionality with respect to
moisture content
• Zeta potential measurements
• Surface geophysical surveys
Phase 2 would involve a bench-scale feasibility study to
evaluate potential cleanup levels. Soil collected from the
proposed site would be placed in electrokinetic plexiglass
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cells with an electrode at each end. A constant current
would be applied to each cell, and periodic measurements
would be taken to evaluate contaminant movement as a
function of applied current (in amperes) per hour. Overall
removal efficiency and residual contaminant concentrations
would then be calculated. Additional testing would also be
conducted during Phase 2, such as chemical and electrical
analysis of soil, if this information was not obtained during
Phase 1.
During Phase 3, full-scale system design would be
performed, and parameters such as electrode spacing,
length of time for remediation, expected power
requirements, and total cost of remediation could be
determined.
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Section 5
References
Douglas, J.M. 1988. Conceptual Design of Chemical
Processes. McGraw Hill, Inc. New York, New York.
Evans, G.M. 1993. "Estimating Innovative Technology
Costs for the SITE Program." Journal of Air Waste
Management. Volume 40, Number 7.
Garrett, D.E. 1989. Chemical Engineering Economics.
Van Nostrand Reinhold. New York, New York.
Hunter, R.J. 1981. Zeta Potential in Colloid Science.
Academic Press. London.
Krause,T.R.andB.Tarman. 1995. "PreliminaryResults
from the Investigation of Thermal Effects in
Electrokinetic Soil Remediation." American Chemical
Society Proceedings. Presented at Emerging
Technologies in Hazardous Waste Management V
Conference. September 27 through 29.
Lindgren, E D., and others. 1991. "Electrokinetic
Remediation of Contaminated Soil." Presented at the
Environmental Restoration '91 Conference Pasco,
Washington. September 8 through 10.
Mattson,E.D., and R.E. Lindgren. 1994. "Electrokinetics:
An Innovative Technology for In-Situ Remediation of
Heavy Metals." Presented at the Eight National
Outdoor Action and Symposium. May 23 through 25.
Mattson.E.D., and R.E. Lindgren. 1993. "Electrokinetic
Extraction of Chromate from Unsaturated Soils."
Presented at Emerging Technologies in Hazardous
Waste Management V. September 27 through 29.
Peters, M.S. 1980. Plant Design and Economics for
Chemical Engineers. Third Edition. McGraw Hill,
Inc. New York, New York.
SandiaNational Laboratories (SNL). 1994. "Superfund
Innovative Treatment Technology Evaluation
Demonstration Proposal for In Situ Electrokinetic
Extraction [ISEE] System." EPA Proposal No. 14.
June 30.
SNL. 1997. "Electrokinetic Demonstration at the
Unlined Chromic Acid Pit." SAND97-2592, October
1997.
Shapiro, A. J. Dissertation Submitted to the Massachusetts
Institute of Technology. 1990
Tetra Tech EM Inc. 1997. Interview Regarding
Additional Information for the ISEE System
Technology Evaluation Report. Between Cristina
Radu, Environmental Engineer, and Earl Mattson,
Hydrogeologist, Sat-Unsat, Inc. June 11.
U.S. Department of Energy (DOE). 1988a. DOE SNL.
1995. RCRA Research, Development and
Demonstration Permit No. NM5 890110518-RDD3
for ISEE System Demonstration. Permit Attachment
G. July.
DOE. 1988b. Radioactive Waste Management Order.
DOE Order 5820.2A. September
U.S. Environmental Protection Agency (EPA). 1987.
Joint EPA-Nuclear Regulatory Agency Guidance on
Mixed Low-Level Radioactive and Hazardous Waste.
Office of Solid Waste and Emergency Response
(OSWER) Directives 9480.00-14 (June 29), 9432.00-
2 (January 8), and 9487.00-8. August.
EPA. 1988a. CERCLA Compliance -with Other
Environmental Laws: Interim Final. OSWER. EPA/
540/G-89/006. August.
EPA. 1997. "In Situ Electrokinetic Excavation System.
SNL. Technology Evaluation Report. Draft."
September.
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Appendix A
Vendor's Claimsfor the Technology
The Superfund Innovative Technology Evaluation (SITE)
demonstration of the In Situ Electrokinetic Extraction
(ISEE) system developed by SandiaNational Laboratories
(SNL) confirms that electrokinetic extraction is a viable in
situ remediation alternative for the removal of heavy
metals from unsaturated soils. Electric current is applied
to soil to be remediated, thereby causing soluble rnetals to
migrate to an electrode where they are removed using the
patented SNL technology. Advantages and innovative
features of the ISEE system and the status of the
electrokinetic technology are discussed below.
Advantages and Innovative Features
Advantages and innovative features of the ISEE system
are as follows:
• Works in soil with low moisture content and effective
in sandy and clayey soils
• Contaminant removed from unsaturated soil
• No net water addition to soil
• Soil remediated to less than toxicity characteristic
leaching procedure (TCLP) limits
• Compatible with biodegradation remediation systems
• Can be used as a contaminant barrier under landfills
• Remaining soil not sterile when remediation
completed
Electrokinetic Technology Status
Although electrokinetics was discovered by Reuss in
1809, it was not until the mid-1980s that the idea to
remediate soil using electrokinetic technology appeared.
Since 1985, numerous laboratory studies and small-scale
tests have been conducted to further characterize
electrokinetics. This emerging technology has the
potential for removing heavy metals, radionuclides, and
many organic species dissolved in pore water from
contaminated soil. Presently, large field-scale
demonstrations of electrokinetic technologies are being
conducted in the United States.
Removal of many inorganic contaminants by electrokinetic
remediation in saturated or near saturated soils has been
documented in literature. Metal cations such as copper,
zinc, chromium, iron, cobalt, nickel, arsenic, cadmium,
lead, mercury, and uranium ions, as well as anions such as
chloride, cyanide, nitrate, and sulfate, have been
successfully removed from soil using electrokinetics.
Although the focus of electrokinetics has been on
inorganic contamination, organic contaminants such as
polynuclear aromatic hydrocarbons have been also
removed (EPRI1994). No theoretical or technical reasons
are documented to indicate that organic and inorganic
contaminants cannot be removed using electrokinetic
technology on unsaturated soils.
Recently, bench-scale studies of the use of citrate to
remove uranium from unsaturated soils were conducted
(SNL 1997). In unsaturated soil, uranium normally exists
primarily as a; cation in the +6 state as UO2+2 because of
prevailing oxidation conditions. In this oxidation state, the
cation will readily sorb to soil. During the bench-scale
studies, citrate was injected at the cathode electrode
casing. The citrate electromigrated across the test cell and
chemically interacted with the uranium cations to form the
anionic complex (UO2Citrate)-2. This complex continued
electromigration to the anode. The uranium complex was
then extracted; from soil through the electrode casings of
the ISEE system.
It is important to note that the system evaluated during this
SITE demonstration is an SNL research prototype system
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and not a system that would be used for actual remediation.
The SNLISEE system used for electrokinetic remediation
during the demonstration monitors many parameters
necessary to evaluate electrokinetics. To conduct an
actual remediation project, SNL's current research efforts
have developed a low-maintenance extraction system that
can operate unsupervised for long periods of time. This
new system is to be implemented simply through initial
setup, periodic inspection of system operation, and final
dismantlement and removal of system equipment. Cost of
remediation using the new system will be dramatically
reduced because of the passive nature of its operation.
This SITE demonstration shows that electrokinetics is
applicable to unsaturated sandy soil. Contaminants can be
transported through soil pore water and collected and
removed at the electrodes. By utilizing surfactants or
complexents, electrokinetic remediation can be applied to
many contaminants besides heavy metals.
References
Electric Power Research Institute (EPRI). 1994.
Proceedings: EPRI Workshop on In Situ
Electrochemical Soil and Water Remediation. Palo
Alto, California. February 28 through March 1.
Sandia National Laboratories (SNL). 1997.
"Electrokinetic Removal of Uranium from
Contaminated, Unsaturated Soils." Albuquerque,
New Mexico. SAND97-01220. January.
56
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