United States
Environmental Protection
Agency
Office of Emergency and
Remedial Response
Washington, DC 20460
EPA/540/R-92/016a
August 1992
Superfund
&EPA Guide for Conducting
Treatability Studies Under
CERCLA Solvent
Extraction
Interim Guidance
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EPA/540/R-92/016a
August 1992
GUIDE FOR CONDUCTING
TREATABILITY STUDIES UNDER CERCLA:
SOLVENT EXTRACTION
INTERIM GUIDANCE
U.S. Environmental Agency
Risk Reduction Engineering Laboratory
Office of Research and Development
Cincinnati, Ohio 45268
and
Office of Emergency and Remedial Response
Office of Solid Waste and Emergency Response
Washington, D.C. 20460
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DISCLAIMER
The information in this document has been funded wholly or
in part by the U.S. Environmental Protection Agency (EPA)
under contract No. 68-C8-0062, Work Assignment 3-23, to
Science Applications International Corporation (SAIC). It has
been subjected to the Agency's peer and administrative
reviews and it has been approved for publication as an EPA
document. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
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FOREWORD
Today's rapidly developing and changing technologies and
industrial products and practices frequently carry with them
the increased generation of materials that, if improperly dealt
with, can threaten both public health and the environment.
The U.S. Environmental Protection Agency 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 support and nurture life.
These laws direct the EPA to perform research to define
our environmental problems, measure the impacts, and
search for solutions.
The Risk Reduction Engineering Laboratory is responsible
for planning, implementing, and managing research,
development, and demonstration programs to provide an
authoritative, defensible engineering basis in support of the
policies, programs, and regulations of the EPA with respect
to drinking water, wastewater, pesticides, toxic substances,
solid and hazardous wastes, and Superfund-related activities.
This publication is one of the products of that research and
provides a vital communication link between the researcher
and the user community.
The primary purpose of this guide is to provide standard
guidance for designing and implementing a solvent extraction
treatability study in support of remedy selection.
Additionally, it describes a three-tiered approach, that
consists of 1) remedy screening, 2) remedy selection, and 3)
remedy design, to solvent extraction treatability testing. It
also presents a guide for conducting treatability studies in a
systematic and stepwise fashion for determination of the
effectiveness of solvent extraction (in conjunction with other
treatment technologies) in remediating a CERCLA site. The
intended audience for this guide comprises Remedial Project
Managers (RPMs), On-Scene Coordinators (OSCs),
Potentially Responsible Parties (PRPs), consultants,
contractors, and technology vendors.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
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ABSTRACT
Systematically conducted, well-documented treatability studies are
an important component of the remedial investigation/feasibility
study (RI/FS) process and the remedial design/remedial action
(RD/RA) process under the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA). These
studies provide valuable site-specific data necessary to aid in the
selection and implementation of the remedy. This manual focuses on
solvent extraction treatability studies conducted in support of
remedy selection prior to developing the Record of Decision.
This manual presents a standard guide for designing and
implementing a solvent extraction remedy selection treatability study.
The manual describes and discusses the applicability and limitations
of solvent extraction technologies, and defines the prescreening and
field measurement data needed to determine if treatability testing is
required. It also presents an overview of the process of conducting
treatability tests and the applicability of tiered treatability testing for
evaluating solvent extraction technologies. The specific goals for
each tier of testing are defined and performance levels are presented,
which should be met at the remedy screening and remedy selection
levels before additional tests are conducted at the next tier. The
elements of a treatability study work plan are also defined with
detailed discussions on the design and execution of the remedy
screening and remedy selection treatability studies.
The manual is not intended to serve as a substitute for
communication with experts or regulators nor as the sole basis for
the selection of solvent extraction as a particular remediation
technology. Solvent extraction must be used in conjunction with
other treatment technologies since it generates residuals. This
manual is designed to be used in conjunction with the Guide for
Conducting Treatability Studies Under CERCLA (Interim Final).(27)
The intended audience for this guide comprises Remedial Project
Managers (RPMs), On-Scene Coordinators (OSCs), Potentially
Responsible Parties (PRPs), consultants, contractors, and
technology vendors.
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TABLE OF CONTENTS
Section Page
DISCLAIMER ii
FOREWORD 111
ABSTRACT iv
FIGURES vi
TABLES vii
ACKNOWLEDGMENTS vm
1. Introduction 1
1.1 Background 1
1.2 Purpose and Scope 1
1.3 Intended Audience 1
1.4 Use of This Guide 1
2. Technology Description and Preliminary Screening 3
2.1 Technology Description 3
2.2 Preliminary Screening and Technology Limitations 9
3. The Use of Treatability Studies in Remedy Evaluation 13
3.1 Process of Treatability Testing in Selecting a Remedy 13
3.2 Application of Treatability Tests 13
4. Treatability Study Work Plan 19
4.1 Test Goals 19
4.2 Experimental Design 20
4.3 Equipment and Materials 24
4.4 Sampling and Analysis 25
4.5 Data Analysis and Interpretation 26
4.6 Reports 26
4.7 Schedule 27
4.8 Management and Staffing 27
4.9 Budget 28
5. Sampling and Analysis Plan 31
5.1 Field Sampling Plan 31
5.2 Quality Assurance Project Plan 31
6. Treatability Data Interpretation 35
6.1 Technology Evaluation 35
6.2 Estimation of Costs 36
7. References 39
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FIGURES
Number Page
2-1 General Schematic of a Standard Solvent Extraction Process 5
2-2 General Schematic of a Near-Critical Fluid/Liquefied Gas
Solvent Extraction Process 7
2-3 General Schematic of a CST Solvent Extraction Process 8
3-1 Flow Diagram of the Tiered Approach 14
3-2 TheRoleof Treatability Studies in the RI/FS and RD/RA Process 15
4-1 Example of Pass-by-Pass PCB Concentration Plot 27
4-2 Example Project Schedule For a Solvent Extraction Treatability Study Program 28
4-3 Example Organizational Chart 29
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TABLES
Number Page
2-1 Major Site Characterization Tests 10
4-1 Suggested Organization of Solvent Extraction Treatability Study Work Plan 19
4-2 Major Cost Elements Associated with Remedy Selection Solvent Extraction Studies 29
5-1 Suggested Organization of Sampling and Analysis Plan 32
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ACKNOWLEDGMENTS
This guide was prepared for the U.S. Environmental Protection
Agency, Office of Research and Development (ORD), Risk
Reduction Engineering Laboratory (RREL), Cincinnati, Ohio, by
Science Applications International Corporation (SAIC), under
Contract No. 68-C8-0062. Mr. Mark Meckes served as the
EPA Technical Project Monitor. Mr. Jim Rawe was SAIC's
Work Assignment Manager. The primary authors for this guide
were Mr. Jim Rawe and Mr. George Wahl of SAIC. The
project team included Mr. Tom Wagner and Mr. Joseph Tillman
of SAIC. Dr. Charles Eckert of the Georgia Institute of
Technology and Mr. John Moses of CF Technologies served as
technical experts. Mr. Clyde Dial served as SAIC's Senior
Reviewer. The authors are especially grateful to Mr. David
Smith and Mrs. Esperanza Renard of EPA, RREL, who
contributed significantly by serving as technical consultants
during the development of this document.
The following Agency and Contractor personnel have
contributed their time and comments by participating in the
technical workshop and/or peer reviewing the draft document:
William McGovern CF Systems
Steve Schwartz Versar
Jean Paquin Sanivan Group
Avijit Dasgupta ABB Environmental
Saeed Darian Nukem Development
Lanny Weimer Resources Conservation
Company
Barry Rugg ART International
Monique Punt Environmental Canada
C. Judson King University of California,
Berkeley
G Bradley Hunter Tennesse Valley Authority
John Napier Martin Marietta
Rodney Hodgson Hazen Research Group
Alan Cash Terra-Kleen
Scott Engle PRC Environmental
Andre Zownir U.S. EPA, ERT
Jane Downing U.S. EPA, Region I
The document was also reviewed by the Office of Waste
Programs Enforcement and the Technology Innovation Office.
We sincerely hope we have not overlooked anyone who
participated in the development of this guide.
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SECTION 1
INTRODUCTION
1.1 BACKGROUND
Section 121 (b) of the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) mandates EPA to
select remedies that "utilize permanent solutions and
alternative treatment technologies or resource recovery
technologies to the maximum extent practicable" and to prefer
remedial actions in which treatment that "permanently and
significantly reduces the volume, toxicity, or mobility of
hazardous substances, pollutants, and contaminants is a
principal element." Treatability studies provide data to support
treatment technology selection and remedy implementation. If
treatability studies are used, they should be performed as soon
as it is evident that insufficient information is available to
ensure the quality of the decision. Conducting treatability
studies early in the remedial investigation/feasibility study
(RI/FS) process reduces uncertainties associated with
selecting the remedy and provides a sound basis for the
Record of Decision (ROD). EPA Regional planning should
factor in the time and resources required for these studies.
Treatability studies conducted during the RI/F S phase indicate
whether the technology can meet the cleanup goals for the
site, whereas treatability studies conducted during the
remedial design/remedial action (RD/RA) phase establish
design and operating parameters for optimization of
technology performance. Although the purpose and scope of
these studies differ, they complement one another since
information obtained in support of remedy selection may also
be used to support the remedy design.1-38-1
This document refers to three levels or tiers of treatability
studies: remedy screening, remedy selection, and remedy
design. Three tiers of treatability studies are also defined in the
Guide for Conducting Treatability Studies Under CERCLA,
InterimFinal,1-27-1 hereinafter referred to as the "generic guide".
The generic guide refers to the three treatability study tiers,
based largely on the scale of test equipment, as laboratory
screening, bench-scale testing, and pilot-scale testing.
Laboratory screening is typically used to screen potential
remedial technologies and is equivalent to remedy screening.
Bench-scale testing is typically used for remedy selection;
however it may fall short of providing enough information for
remedy selection. Bench-scale studies can, in some cases,
provide enough information for full-scale design. Pilot- scale
studies are normally used for remedial design, but may be
required for remedy selection in some cases. Because of
the overlap between these tiers, and because of differences in
the applicability of each tier to different technologies, the
functional description of treatability study tiers (i.e., remedy
screening, remedy selection, and remedy design) has been
chosen for this document.
Some or all of the treatability study levels may be needed on
a case-by-case basis. The time and cost necessary to perform
the testing are balanced against the improved confidence in
the selection of treatment alternatives. These decisions are
based on the quantity and quality of data available and on
other factors (e.g., state and community acceptance of the
remedy, additional site data and experience with the
technology). The need for each level of treatability testing
required are management decisions. Section 3 discusses using
treatability studies in remedy evaluation in greater detail.
1.2 PURPOSE AND SCOPE
This guide helps ensure a reliable and consistent approach in
evaluating whether solvent extraction should be considered
for site remediation. This guide discusses the remedy
screening and remedy selection levels of treatability testing.
Remedy screening studies provide a quick and relatively
inexpensive indication of whether solvent extraction is a
potentially viable remedial technology. The remedy selection
treatability test provides data to help determine if reductions
in contaminant volumes will allow cost-effective treatment to
meet site cleanup goals. Remedy selection studies also provide
a preliminary estimate of the cost and performance data
necessary to design either a remedy design study or a fullscale
solvent extraction system. While solvent extraction
technology may be applicable to inorganic contaminants in
some instances, the primary use of solvent extraction, and
therefore the focus of this guide, concerns the treatment of
organic contaminants.
In general, remedy design studies will also be required to
optimize full-scale system design. Presumably, before remedy
design studies are conducted, it has already been decided that
solvent extraction is an economically and technically viable
treatment alternative with remedy selection testing. Remedy
design is not discussed in this guidance document.
1.3 INTENDED AUDIENCE
This document is intended for use by Remedial Project
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Managers (RPMs), On-Scene Coordinators (OSCs), Potentially
Responsible Parties (PRPs), consultants, contractors, and
technology vendors. Each has different roles in conducting
treatability studies under CERCLA. Specific responsibilities for
each can be found in the generic guide.1-27-1
1.4 USE OF THIS GUIDE
This guide is organized into seven sections and reflects the
basic information required to perform treatability studies
during the RI/FS process. Section 1 is an introduction which
provides background information on the role of the guide and
outlines its intended audience. Section 2 describes different
solvent extraction processes currently available and discusses
how to conduct a preliminary screening to determine if solvent
extraction is a potentially viable remediation technology.
Section 3 provides an overview of the different levels of
treatability testing and discusses how to determine the need
for treatability studies. Section 4 provides an overview of the
remedy screening and remedy selection treatability studies,
describes the contents of a typical work plan, and discusses
the major issues to consider when conducting a treatability
study. Section 5 discusses sampling and analysis and quality
assurance proj ect plans. Section 6 explains how to interpret the
data produced from treatability studies and how to determine
if further remedy
design testing is justified. Section 7 lists the references.
This guide is one of a series of guidance documents being
developed by EPA. This guide, along with guides being
developed for other technologies, is a companion document to
the generic guide.(2?:) In an effort to avoid redundancy,
supporting information in the generic guide and other readily
available guidance documents is not repeated in this
document.
The document is not intended to serve as a substitute for
communication with regulators and/or experts in the field of
solvent extraction. This document should never be the sole
basis for the selection of solvent extraction as a remediation
technology or the exclusion of solvent extraction from
consideration.
As treatability study experience is gained, EPA anticipates
further comment and possible revisions to the document. For
this reason, EPA encourages constructive comments from
outside sources. Direct written comments to:
Mr. Michael Gruenfeld
U.S. Environmental Protection Agency
Release Control Branch
Risk Reduction Engineering Laboratory
2890 Woodbridge Ave.
Building 10, 2nd Floor
Edison, NJ 08837
(908)321-6625
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SECTION 2
TECHNOLOGY DESCRIPTION AND
PRELIMINARY SCREENING
This section presents a description of various full-scale
solvent extraction technologies and a discussion of the
information necessary for prescreening the technology before
committing to a treatability test program. Subsection 2.1
describes several types of full-scale solvent extraction
systems. For the purpose of this document, full-scale is
defined as any system which can process greater than one ton
per hour and may include some pilot-scale systems. The
quality of the data provided by vendors on specific processes
has not been determined. Subsection 2.2 discusses the
literature and database searches required, the technical
assistance available, and the review of field data required to
prescreen these technologies. Technology limitations are also
reviewed in this subsection.
2.1 TECHNOLOGY DESCRIPTION
Solvent extraction is a separation technology which uses a
fluid to remove hazardous contaminants from excavated soils,
sludges, and sediments and/or contaminated groundwater and
surface water. Solvents used are normally organic based fluids
not aqueous as is the case with soil washing systems. The
solvent is chosen such that the contaminants have a higher
affinity for the solvent than for the contaminated material.
Solvent extraction does not destroy contaminants; it
concentrates them so that they can be recycled or destroyed
more cost effectively. When contaminants are not recycled,
solvent extraction must be combined with other technologies
in a treatment train to destroy the separated, concentrated
contaminants. Although solvent extraction has limited
application as a treatment technology for inorganic
contaminants, this document is focused on extraction of
organic contaminants. Nevertheless, solvent extraction may
affect inorganic contaminants even when the process is
designed to treat organic contaminants.
Solvent extraction processes can be divided into three general
types based upon the type of solvent used: standard solvents,
near-critical fluids/liquefied gases, and critical solution
temperature (CST) solvents. Each of these process types is
discussed in the following subsections. Standard solvent
processes (subsection 2.1.2) use alkanes, alcohols, ketones, or
similar liquid solvents typically used at ambient pressure.
Near-critical fluid/liquefied gas processes (subsection 2.1.3)
use butane, isobutane, propane, carbon dioxide (CO2) or similar
gases
which have been liquefied under pressure at or near ambient
temperature. Systems involving CST solvents (subsection
2.1.4) use the unique solubility properties of those compounds
to extract contaminants at one temperature where the solvent
and water are miscible and then separate the concentrated
contaminants from the water fraction at another temperature.
Solvent is then removed from the contaminants by
evaporation. Pretreatment and post-treatment are frequently
required for solvent extraction systems. Subsections 2.1.1 and
2.1.5 present a general discussion of various pretreatment and
post-treatment needs, respectively.
Solvent extraction shows promise for treating a variety of
organic contaminants commonly found at CERCLA sites. The
technology has been used as a full-scale remedy at two
CERCLA sites: (1) the Treban PCB site in Tulsa, OK and(2) the
General Refining site in Garden City, GA. During fiscal year
1989, solvent extraction was selected in combination with other
technologies for remediation of five Superfund sites having
soils and sediments contaminated with polychlorinated
biphenyls (PCBs), polynucleararomatic hydrocarbons (PAHs),
pentachlorophenol (PCP), and other organic compounds.
These sites are Norwood PCBs, MA; O'Conner, ME; Pinette's
Salvage Yard, ME; Ewan Property, NJ; and United Creosoting,
TX(29)
Information on the technology applicability, the latest
performance data, the status of the technology, and sources
for further information is provided in one of a series of
engineering bulletins being prepared by EPA Risk Reduction
Engineering Laboratory (RREL) in Cincinnati, Ohio.1-25'
2.1.1 Pretreatment
The preparation of feed materials prior to treatment is an
important factor in all extraction processes. The purpose of
pretreatment is to ensure that the material is in a
physical/chemical condition suitable to the characteristics of
the treatment process. Pretreatment strategies depend on
whether the feed is primarily solids or liquids. Pretreatment
involves physical processing and, in some cases, chemical
conditioning after the contaminated materials have been
removed from their original location.
Since solvent extraction is an ex situ treatment, contaminated
soils and sediments must be either excavated
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or dredged. Contaminated liquid wastes, including pumpable
sludges, are removed and transported using pumps.
Pretreatment forsolid feed material typically involves physical
unit operations, such as solid-liquid separation, mixing,
screening, wet classification, floatation, and size reduction.
These operations are selected and used to optimize
performance, protect equipment from damage by debris, and/or
maximize the types of equipment which can be utilized.
Solid-liquid separation improves the performance of processes
using solvents which are hampered by the presence of water.
Reducing moisture content can also be accomplished with
excavation and air drying of the soil. For continuous
processes, mixing with solvent or other liquid may be
necessary in order to produce a pumpable slurry. Screening
prevents larger debris and rocks from damaging process
equipment. Batch processes, unlike most continuous
processes, can tolerate coarse solids without damage to
equipment. Wet classification and floatation are alternative
separation techniques to screening. Size reduction aids
extraction by breaking large particles into smaller ones and
increasing exposed surface area. This results in higher
extraction efficiencies and shorter treatment times. Too much
size reduction or an over abundance of fines can cause
problems with phase separation of the solvent and treated
solids. The decision to use any of these pretreatment
operations would depend on the waste characteristics,
operating condition (batch versus continuous), and extraction
process being used.
For liquid feed material, pretreatment may involve some type
of solids removal. This can be accomplished by such methods
as filtering, screening, or settling. Depending upon the type of
solvent extraction system used, the addition of solvent or
water may be needed to make sludges more pumpable.
The use of chemical conditioning agents varies widely and is
highly dependent upon treatment equipment,
materials-of-construction, natural buffering capacity of the
matrix, and chemical properties of the pollutants of concern.
Common chemical processes include pH adjustment and
chelating agent addition to influence the partitioning of
constituents between phases. To protect process equipment
and possibly avoid solvent degradation, pH adjustments may
be needed.
2.1.2 Standard Solvent Extraction
Processes
In standard solvent extraction processes, solvents such as
alkanes, alcohols, or ketones are used to remove contaminants
fromexcavated soils, sludges, and sediments. Some processes
may be applicable to liquid media. The solvents are mixed with
the contaminated media (solids, liquids, or both) at essentially
standard temperature and pressure. Figure 2-1 is a general
schematic of atypical standard solvent extraction process. The
system maybe operated in either a batch or continuous mode
and consists of four steps: (1) extraction, (2) separation, (3)
desorption, and (4) solvent recovery.
In the first step, solvent extraction (1), contaminants are
extracted from the contaminated media. In this step, the
solvent is mixed with the contaminated media for a
specified period of time. The contact time and type of solvent
used are contaminant-specific and are typically chosen during
treatability studies.
After the appropriate mix time the mixture is allowed to phase
separate in the second step, separation (2). This step may not
be required. If a solid and liquid phase are formed, the liquid
phase is decanted. A soil/sediment phase, which may contain
some residual solvent, will be formed if a solid matrix or sludge
is being treated. Regardless of the type of solid being treated,
a liquid phase containing the solvent, any extracted
contaminants, and fine materials will form.
Process water or moisture from the feed either remains in the
solid phase or is transported to the solvent phase depending
on the process used. In some processes, excess water may be
deleterious.
Water is typically removed from the decontaminated phase
before the material enters the third step, desorption (3).
Residual solvent is removed from the soil/sediment phase by
vapor or steam stripping or by indirect heating with hot inert
gases and/or steam in the desorption unit. Removed solvent
is sent to the extractor. Decontaminated soil/sediment is
returned to the site or sent offsite for disposal. Post-treatment
of residual solids is addressed in subsection 2.1.5 of this
document.
In the final step, solvent recovery (4), solvent is recovered in
a distillation system, combined with recovered solvent from
step 3, and recycled to the extractor. Still bottoms, which
contain concentrated contaminants, are removed from the
distillation unit periodically for final treatment or reuse as raw
material if of sufficient quality.
While a number of vendors are using systems similar to the
sy stem described above, there are also variations. Examples of
these variations are evident in the extraction processes
described within this section.
A New York University research team, funded by EPA,
developed the Low Energy Extraction Process (LEEPsm) to
extract PCBs and other hydrophobic (immiscible in water)
organic contaminants from soil, sediment, and sludge. ART
International (formerly Applied Remediation Technology) has
commercialized the LEEP™ technology. Excess water is
separated from soils and sediments by filtration if required.
Hydrophobic contaminants are removed using a hydrophilic
solvent contacted in a counter-current leaching unit. The
hydrophilic leaching solvent is able to penetrate and remove
the water film, which can interfere with the solvent extraction
process, from the surface of wet soils and sediments. The
water-solvent mixture containing the contaminant is then
extracted with a hydrophobic solvent in a countercurrent,
liquid-liquid extractor. The contaminant-free hydrophilic
leaching solvent is recycled by distillation. Relatively small
amounts of energy are used because the selected hydrophilics
boil at relatively low temperatures with low latent heat values.
Contaminants are concentrated in the hydrophobic solvent
which will require additional treatment. Contaminants in the
water fromthe initial solid-water separation step are adsorbed
onto a small portion of the cleaned soil. Contaminated soils
from the adsorption step are added to the primary feed stream
and processed through the solvent extraction system for
decontamination.1-6'
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r
Solvent Make-up
Contaminated Media
(pretreatment may -|
be necessary)
Solvent
with Organic
Contaminants
Solvent
Recovery
(Distillation)
(4)
Clean Solvent
Concentrated
Contaminants
Decontaminated
Solids plus
Residual Solvent
Desorption
(Raffinate
Stripping)
(3)
Clean Solvent
Decontaminated
Solids
Figure 2-1. General schematic of a standard solvent extraction process.
Nukem Development (formerly ENSR), Houston, Texas, is
developing a mobile solvent extraction process to
decontaminate soils and sludges without significant
pretreatment of the soil/sludge. No addition or removal of
water is required. A chemical agent is added with the solvent
to neutralize the effects of the moisture present in the
soil/sludge. The soil/sludge is mixed with the reagent and
solvent and then fed through a series of three to five extraction
stages countercurrent to the solvent. The mixture is stripped
of residual solvent and transferred to a tank for separation of
water from soils.1-13-1
The Sanivan Group, now GET Environmental Services and part
of Consolidated Environmental Technologies, has developed
two processes. One is a transportable modular solvent
extraction process called Extraksor™. This batch system
involves several steps. In the first step, solid material is loaded
into the extraction vessel where it is washed with fresh
solvent. Soil-solvent contact is enhanced by slowly rotating
the vessel on its axis. After the soil is decontaminated, the
solvent is removed and transferred to a storage tank. The
contaminated solvents are continuously regenerated by
distillation, and the concentrated contaminants are collected
in drums for offsite disposal/treatment/15^33' In the next step,
residual solvent in the decontaminated soil is driven off by
recirculating hot inert gas within the extraction vessel. The
second process is a mobile solvent extraction process called
Decontaksolv4™. It uses an autoclave in a vapor degreasing
mode to decontaminate rocks, debris, equipment, and
miscellaneous materials found in contaminated sites. The
extraction fluid used in this second process is also regenerated
by distillation(8).
Terra-Kleen has commercialized the Soil Restoration Unit, a
mobile solvent extraction process. The process is
designed for use with a selection of 14 non-toxic solvents. The
solvent or solvent combination chosen is governed by the
contaminants to be extracted from the soil or debris. The
process is typically operated at elevated temperatures. The soil
is mixed with the solvent in a counter-current method. The
collected solvent is distilled for reuse, while the clean
soil/solvent slurry is sent to a drying chamber for removal of
the solvent.(20)(21)
A laboratory-scale solvent extraction process was used by the
Emergencies Engineering Division (BED) of Environment
Canada in a joint project with the Groundwater and Soil
Remediation Program (GASRep) to compare the effectiveness
of two solvents: hexane and natural gas condensate. This
batch process had a mixing chamber where contaminated soil
and solvent were contacted and allowed to settle. During the
comparison, free liquid was decanted. The post-mix slurry was
centrifuged, resulting in another decanted liquid stream and a
decontaminated moist soil stream. The two decanted liquid
streams and make-up solvent were mixed together and distilled
to concentrate the contaminants in the bottoms and to recover
solvent. The moist soil was dried to remove residual solvent
which was sent to the distillation column.1-17-1
Martin Marietta's Soilex process was the result of an effort to
remediate PCB-contaminated soil at the Department of
Energy's Y-12 plant in Oak Ridge, Tennessee. The pilot plant
was operated and evaluated using a 50/50 mixture of kerosene
and water. Three extraction stages were used, with soil and
water added to the first stage and clean kerosene added to the
third stage. The soil-water phase was transferred by gravity
from the first to the second stage and then on to the third
stage, while kerosene was
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transferred by pump countercurrently. Air-driven mixers provided
agitation. Kerosene extracted the PCB and oil contaminants in the
soil while the water served to break up soil particles. After mixing,
the solvent was decanted. The decanted solvent from the first stage,
contaminated with PCB and oil, was sent to a packed column
distillation system. The processed soil from the third stage,
saturated with a significant amount of solvent, was removed from
the process.1-19-1
Ph0nix Milj0, Denmark has developed the Soil Regeneration Plant, a
10 ton/hour transportable solvent extraction process. This process
consists of a combined liquid extraction and steam stripping process
operating in a closed loop. A series of screw conveyors is used to
transfer the contaminated soil through the process. Contaminants
are removed from soil in a countercurrent extraction process. A
drainage screw separates the soil from the extraction liquid. The
extraction liquid is distilled to remove contaminants and is then
recycled. The soil is steam heated to remove residual contaminants
before exiting the process.1-16'
The Carver-Greenfield Process has been designed by Dehy dro-Tech
Corporation, East Hanover, NJ to separate materials into their
constituent solid, oil (including oil-soluble substances), and water
phases. It is intended mainly for soils; and sludges contaminated
with oil-soluble hazardous compounds. The technology uses afood-
grade carrier oil to extract the oil-soluble contaminants. Pretreatment
is necessary to achieve particle sizes of less than 1/4 inch. The
carrieroil, with a boiling point of 400 degrees Fahrenheit, is typically
mixed with waste sludge or soil, and the mixture is placed in an
evaporation system to remove any water. The oil serves to fluidize
the mix and maintain a low slurry viscosity to ensure efficient heat
transfer, allowing virtually all of the water to evaporate. Oil-soluble
contaminants are extracted from the waste by the carrier oil. Volatile
compounds present in the waste are also stripped in this step and
condensed with the carrier oil or water. After the water is evaporated
from the mixture, the resulting dried slurry is sent to a centrifuging
section that removes most of the carrier oil and contaminants from
the solids. After centrifuging, residual carrier oil is removed from the
solids by a process known as "hydroextraction". The carrier oil is
recovered by evaporation and steam stripping. The hazardous
constituents are removed from the carrier oil by distillation. This
stream can be incinerated or reclaimed. In some cases, heavy metals
in the solids will be complexed with hydrocarbons and will also be
extracted by the carrier oil.
2.1.3 Near-Critical Fluid/Liquefied Gas
Solvent Extraction Processes
Near-critical fluid/liquefied gas extraction is similar to standard
solvent extraction. The difference is that the solvent is near its
thermodynamic critical point (the temperature and pressure at which
the liquid and vapor phases of the solvent in equilibrium with each
other become identical, forming one phase). As a fluid approaches
its critical point it increasingly exhibits the diffusivity and viscosity
characteristics of a gas, while continuing to exhibit the solvent
characteristics of a liquid. Thus a solvent near its critical point can
effectively penetrate a soil matrix with rapid mass transfer and
remove pollutants. Near-critical fluid/liquefied gas extraction
processes generally operate at elevated pressure. Processes have
been designed to handle either solids or liquids. Figure 2-2 is a
general schematic of a typical near-critical fluid/liquefied gas
extraction process, which is a continuous cycle
consisting of four steps: (1) extraction, (2) separation, (3)
desorption, and (4) solvent recovery .(14)
Contaminated media is pretreated (see subsection 2.1.1),
transferred into an extraction vessel, and mechanically
mbed with solvent (1). Vigorous mixing is required to
thoroughly disperse the hydrophobic solvent into the
contaminated media. The extraction step can involve one
or more extraction stages where solvent and feed move
in countercurrent directions.
The separation step (2) is the part of the process where
the separation of the two phases, decontaminated media
and contaminated solvent, occurs. The decontaminated
media settles to the bottom, and consists of the treated
liquid and material fines as well as residual solvent which
is vaporized and separated from the treated materials in
the desorption step (3). The decontaminated media are
subsequently discharged. The vaporized residual
solvent is compressed and recycled back to step 1.
The contaminated solvent, which contains the organic
contaminants, rises to the top of the separation chamber.
The mixture flows to the solvent recovery step (4) where
a combination of reduced pressure and additional heat
vaporize the solvent and separate it from the organic
contaminants. The contaminants are subsequently
discharged, and the solvent is recompressed and cycled
back to the extraction step.1-23-1
Examples of this type of extraction are the proprietary
processes of CF Systems. CF Systems designs include
a liquid propane/butane solvent process for treatment of
soils and sludges and a liquefied carbon dioxide (CO2)
gas process for treatment of wastewater. Waste sludges
to be treated are pumped as slurries while soils are
loaded directly into the extractor. Their liquid
propane/butane process consists of a multi-stage mixer
settler arrangement. The liquefied CO2 process has one
multi-stage extraction tower.(23)
Sierra Environmental Services, Inc. intends to market a
liquid/liquid extraction process using liquid butane as
the solvent. This process was developed under
sponsorship by the Emergencies Engineering Division of
Environmental Canada. Tests in both a small, single-
stage, bench-scale unit (capacity approximately 0.75 L
and a continuous, counterflow pilot-plant with four
actual mixing stages (80 to 100 mL/min. water: 15 to 25
mL/min. butane) have been completed. During this work,
a total of 25 different organic pollutants were tested,
either singly or in combination with water.(1)
The near-critical fluid/liquefied gas extraction solvents
discussed thus far are sometimes referred to as near
critical liquids (NCL). Bench scale studies have also
investigated the use of super critical fluids (SCFs). These
SCFs are fluids heated and pressurized beyond their
critical temperatures and critical pressures. Three SCF
approaches are being examined. The first is a two-step
process in which an adsorbent such as activated carbon
is
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Clean Solvent
Contaminated Media
(pretreatment may _|
be necessary)
Extraction
(D
Separation
(2)
Decontaminated
Media plus
Residual Solvent
Contaminated
Solvent
Solvent
Recovery
(4)
t
Clean
solvent
Desorption
(3)
= Compressor/Pump
T
Concentrated
Contaminants
Clean Solvent
Decontaminated
Media
Solvent Make-up
J
I
Figure 2-2. General schematic of a near-critical fluid/liquified gas solvent extraction process.
used to concentrate organic contaminates and is then
regenerated by extraction with a SCF. The second approach
involves the use of supercritical water to simultaneously
extract contaminants and oxidize them with the addition of air
or pure oxygen. The third approach uses nontoxic SCFs such
as CO2, hydrocarbons, and freons to remove organic
contaminants from water.1-10-1
2.1.4 Critical Solution Temperature
(CST) Processes
CST processes use extraction solvents in which solubility
characteristics can be enhanced by changing the fluid's
temperature. For the purpose of this document, CST solvents
include those binary (liquid-liquid) systems which exhibit an
upper critical solution temperature (sometimes referred to as
upper consolute temperature), a lower critical solution
temperature (sometimes referred to as lower consolute
temperature), or both. For such systems, mutual solubilities of
the two liquids increase while approaching the CST. At or
beyond the CST the two liquids are completely miscible in
each other. Additional information on CST solvents can be
obtained from textbooks on liquid-liquid equilibria.1-5-"-9-1 Figure
2-3 is a general schematic of a typical lower CST solvent
extraction process. The process consists of four steps: (1)
extraction, (2) separation, (3) desorption, and (4) solvent
recovery. Step 4 is complex and involves many unit operations.
During the first step, pretreated contaminated media (soil or
sludge) enters the extractor (1) and is contacted with a CST
solvent which is cooled or heated until complete miscibility in
water is exhibited. The water and contaminants within the
soil/sludge dissolve into the
cooled or heated CST solvent, forming a homogeneous liquid.
Since only one liquid layer is formed, the solids can be easily
removed from the slurry by physical means such as filtering,
settling, and/or centrifuging in the second step, separation
(2)09)
In the third step, desorption (3), residual solvent is recovered
from the solids. This is normally accomplished by drying the
solids with direct heat and condensing the solvent vapor
driven off. Solvent vapor from the dryer is combined with
solvent vapor from the strippers discussed in step 4.
Solvent recovery (4) is the fourth process step. The
temperature of the liquid portion from the extraction step (the
solids were previously removed) is modified so that the
solvent is immiscible in water. Depending on the type of
solvent used, the temperature may be raised or lowered to form
a binary liquid system. The contaminated solvent-water
mixture separates into two distinct layers in the decanter. One
layer containing mostly solvent along with the extracted
contaminants, the other containing mostly water. The solvent
fraction is steam stripped to recover a solvent-water mixture or
azeotrope and a concentrated contaminant product. The water
fraction is steam stripped also, yielding a solvent-water mixture
or azeotrope and a treated water product. The recovered
solvent fractions are combined, condensed, and decanted
once more, if required. Solvent from this final decanting is used
in the extraction process again. Water from this final decanting
is recycled to the water fraction steam stripper.
Resources Conservation Company (RCC) has a patented CST
extraction process called B.E.S.T.™ which uses triethylamine
as the extraction solvent. Solvent and water
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cooled. It is similar to the generalized description with the
exception that a second extraction step takes place with the
solids from the first centrifuge. Feed pretreatment, consisting
of pH adjustment, is needed in order to keep the aliphatic
amine solvent stable.(28)(39:)
2.1.5 Post-Treatment
Solvent extraction is not a stand-alone technology. Typically,
the concentrated contaminants, the fine soils (silts and clays),
and any separated water are subject to further specific
treatment and disposal techniques, as appropriate, to complete
the cleanup. Sidestreams generated during treatment, such as
spent solvent, spent activated carbon, air emissions, etc., must
also be treated. Solvent extraction systems are generally
designed to operate without air emissions, Nevertheless,
volatile air emissions requiring treatment could occur during
waste reparation. The EPA document entitled " Technology
Screening Guide for Treatment of CERCLA Soils and Sludes"
contains a description of potential treatment technologies
which may be used as post-treatments for residual solids.(36)
The concentrated contaminants, which are usually the residual
fromsolvent recovery, may or may not meet the specifications
required for disposal, recycle, or reuse. If
not, further treatment with another technology is necessary.
Treated soil or sludge will, at minimum, have traces of
extraction solvent present. If little or no effort is made to
recover and recycle the extraction solvent during processing,
the amount of residual extraction solvent could be significant.
Typically, extraction solvents used in commercially available
systems either volatilize quickly or are biodegradable. Ambient
air monitoring can be employed to determine if the volatilizing
solvents present a problem. Depending on the system, clean
soil and solids from treated sludge or sediments may need
dewatering in order to form a dry solid and a separate water
stream. Even though solvent extraction systems designed for
organic contaminant removal may have some effect on metals
or other inorganic contaminants, such metals or other
inorganics are frequently not extracted, and their presence may
indicate the need for additional treatment of the cleaned solids
by another technique. Some inorganics may be removed in the
fine silt fraction which is removed with the sill bottoms.
Therefore, further treatment of the total waste volume may not
be necessary.
Residual water from decantation, dewatering or stripping is
normally treated using standard wastewater treatment
Contaminated
Media (pro-
treatment may~
be necessary)
Solvent plus
Residual Water
Decontaminated
Sol'xisplus
Residual Solvent \
Solvent
> Solvent Make-up
Figure 2-3. General schematic of a CST solvent extraction process.
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practices. Sludges generated during water treatment may need
subsequent treatment.
conferences and publications on specific technical areas. The
contact is Dan Powell (703) 308-8827.
2.2 PRELIMINARY SCREENING AND
TECHNOLOGY LIMITATIONS
The determination of the need for and the appropriate level of
treatability studies is dependent on available literature, expert
technical judgment, and site-specific factors. The first two
elements—the literature search and expert consultation—are
critical factors in determining if adequate data are available or
whether a treatability study is needed to provide those data.
2.2.1 Literature/Database Review
Several reports and electronic databases exist which should be
consulted to assist in planning and conducting treatability
studies and tohelp prescreen solvent extraction for use at a
specific site. Existing reports include:
• Guide for Conducting Treatability Studies Under
CERCLA, Interim Final. U.S. Environmental Protection
Agency, Office of Research and Development and Office
of Emergency and Remedial Response, Washington, D.C.
EPA/540/2-89/058, December 1989.
• Guidance for Conducting Remedial Investigations and
Feasibility Studies Under CERCLA, Intenm Final. U.S.
Environmental Protection Agency, Office of Emergency
and Remedial Response, Washington, D.C.
EPA/540/G-89/004, October 1988.
• Superfund Treatability Clearinghouse Abstracts. U.S.
Environmental Protection Agency, Office of Emergency
and Remedial Response, Washington, D.C.
EPA/540/2-89/001, March 1989.
• The Superfund Innovative Technology Evaluation
Program: Technology Profiles. U.S. Environmental
Protection Agency, Office of Solid Waste and Emergency
Response and Office of Research and Development,
Washington, D.C. EPA/540/5-89/003, November 1988.
Summary of Treatment Technology Effectiveness for
Contaminated Soil. U.S. Environmental Protection
Agency, Office of Emergency and Remedial Response,
Washington, D.C. EPA/540/8-89/053, 1989.
• Technology Screening Guide for Treatment of CERCLA
Soils and Sludges. U.S. Environmental Protection Agency.
EPA/540/2-88/004, September 1988.
Currently, the Risk Reduction Engineering Laboratory (RREL)
in Cincinnati is expanding the RREL Treatability Data Base.
This expanded database will contain data from soil treatability
studies. A repository for the treatability study reports will be
maintained at RREL in Cincinnati. The contact for this
database is Glenn Shaul (513) 569-7408.
The Office of Solid Waste and Emergency Response (O S WER)
maintains the Cleanup Information (CLU-IN) Bulletin Board
System for communicating ideas, disseminating information,
and serving as a gateway for other OSW electronic databases.
Currently, the CLU-IN Bulletin Board has eight different
components, including news and mail services, and
ORD headquarters maintains the Alternative Treatment
Technology Information Center (ATTIC), which is a
compendium of information from many available data bases.
Data relevant to the use of treatment technologies in
Superfund actions are collected and stored in ATTIC. ATTIC
searches other information systems and databases and
integrates the information into a response. It also includes a
pointer system that refers the user to individual experts in
EPA. The system currently encompasses technical summaries
for SITE program abstracts, treatment technology
demonstration projects, industrial project results, and
international program data. Contact the ATTIC System
Operator at (301) 670-6294, access the database from a modem
by calling (301) 670-3808, or call the EPA contact at (408)
321-4380.
Finally, the RREL Technical Support Branch is supporting a
variety of treatability-related activities, including development
of this guide and other technology-specific guidance
documents, preparation of engineering bulletins, and
compilation of a list of vendors who perform treatability
studies.
2.2.2 Technical Assistance
Technical assistance can be obtained from the Technical
Support Project (TSP) team which is made up of a number of
Technical Support Centers. It is a joint service of OSWER,
ORD, and the Regions. The TSP offers direct site-specific
technical assistance to OSCs and RPMs and develops
technology workshops, issue papers, and other information for
Regional staff. The TSP:
• Reviews contractor work plans, evaluates remedial
alternatives, reviews RI/FS, assists in selection and
design of final remedy
• Offers modeling assistance and data analysis and
interpretation
• Assists in developing and evaluating sampling plans
• Conducts field studies (soil gas, hydrogeology, site
characterization)
• Develops technical workshops and training, issue papers
ongroundwater topics and generic protocols
• Assists in performance of treatability studies.
As part of the TSP, the Engineering Technical Support Center
(ETSC) provides technical information and advice related to
treatability studies. The ETSC is sponsored by OSWER but
operated by RREL. The Center handles site-specific
remediation engineering problems. Access to this support
Center must be obtained through the EPA project manager.
RREL offers expertise in contaminant source control
structures; materials handling and decontamination; treatment
of soils, sludges and sediments; and treatment of aqueous and
organic liquids. The following are examples of the technical
assistance that can be obtained
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TABLE 2-1. Major Site Characterization Tests
Parameter
Chemical
Organics
Total organic carbon
(TOC)
or
Total recoverable
petroleum hydrocarbon
Physical
Grain size analysis/
particle size distribution
Moisture content
Bulk density
or
Specific gravity
Description of Test
Varied
Combustion
Infrared
Spectrophotometer
Sieve screening using a
variety of screen sizes
Drying oven at 110- C In
situ, nuclear method
Drive cylinder method
Hydrometer
Pycnometer
Pycnometer
Method
Varied (see SW-
846 or other
appropriate
methods)
Method 9060
Method 418.1
ASTM D422
ASTM D2216
ASTMD3017
ASTM D2937
ASTM D 1556
ASTM D891A
ASTMD891B
ASTM D854
Purpose and Comments Application of Data
To determine concentration of Remedy screening
target or interfering
constituents, pretreatment
needs, extraction medium.
To determine the presence of Remedy selection
organic matter, adsorption
characteristics of soil.
To determine the presence of Remedy selection
organic matter, adsorption
characteristics of soil.
To determine volume Remedy screening
reduction potential,
pretreatment needs,
solid/liquid separability.
To determine pretreatment Remedy selection
needs. Water may impede
some extraction processes.
To determine throughput Remedy screening
capacity in terms of yd3 or
tons per hour.
To determine throughput Remedy screening
capacity in terms of yd3 or
tons per hour.
Ref.
37
37
30
3
3
3
3
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through the ETSC:
• Review of the treatability aspects of RI/F S
• Review of RI/FS treatability study Work Plans and final
reports
• Oversight of RI/FS treatability studies
• Definition of alternative remedies
• Assistance with studies of innovative technologies
• Assistance in full-scale design and start-up.
For further information on the TSP, contact:
Risk Reduction Engineering Laboratory,
Cincinnati, OH
Contact: Ben Blaney
(513)569-7406
2.2.3 Prescreening Characteristics
Prescreening activities for the solvent extraction treatability
testing include interpreting any available site-related field
measurement data. The purpose of prescreening is to gain
enough information to eliminate from further consideration
technolo gies which have little chance of achieving the cleanup
goals.
Table 2-1 lists major site characterization parameters that may
be measured or available before designing treatability tests.
The "Application of Data" column indicates the tier in which
the data is initially used. The most important prescreening
parameters are the contaminant profile and concentration of
contaminants. Tests for total organic carbon (TOC) and total
recoverable petroleum hydrocarbons give an estimate of
equilibrium partitioning and contaminant transport between
soil and water and may be useful when applying results to
other sites with different organic carbon values. Particles size
distribution and moisture content are useful for evaluating
materials handling and pretreatment processes. Bulk density
or specific gravity is important for estimating throughput
capacity.
Data on other, less important parameters such as pH,
temperature, chemical oxygen demand (COD), and contaminant
toxicity may also be collected and analyzed. The matrix pH is
especially important to processes which utilize aliphatic
amines. This is because the aliphatic amines cannot exist in
solvent form at pH lower than 10.(28) Feed temperature affects
the near-critical fluid/liquefied gas process because below
6O F, hydrates may form and inhibit extraction.1-23-1 Moisture
content is necessary to convert from wet-weight based
analytical results to dry-weight based results to facilitate the
calculation of the material balance and to determine the extent
of water removal or addition required. Chemical oxygen
demand (COD) is a measure of the oxygen required to fully
oxidize all organic materials present. The Toxicity
Characteristic Leaching Procedure (TCLP) test determines the
impact of the treatment on leachability of organic and
inorganic contaminants which will affect the final disposal of
the wastes. Some parameters may or may not be applicable to
specific types of solvent extraction processes.
If contamination exists in different soil strata or in different
media, a characterization profile should be developed for
each soil type or media. Available chemical and physical data
(including contaminant concentration averages and ranges)
and the volumes of the contaminated soil requiring treatment
should be identified. For "hot spots", separate
characterizations should be done so they can be properly
addressed in the treatability tests. Solvent extraction may be
applicable to some parts of a site, but not to other parts.
Characterization test results should be broadly representative
of the contaminant profile of the site. Grab samples taken from
the site ground surface may represent only a small percentage
of the contaminated soils requiring remediation.
Contaminant characteristics such as those listed below may be
important for the design of remedy screening studies and
related residuals treatment systems.
• Composition
• Vapor pressure
• Solubility in specified solvent(s)
• Henry's Law constant
• Partition coefficient
• Boiling point
Matrix characteristics such as the bulk density of solids or the
specific gravity and viscosity of sludges and liquids may also
be important for the design of treatability studies (e.g.,
separation, transfer, and mixing techniques).
The need for a treatability study is determined near the
beginning of the RI/FS when a literature survey of remedial
technologies is performed. Remedial technologies are
identified based on compatibility with the type of
contaminants present at the site, the waste media (soil, water,
etc.), and the anticipated cleanup objectives. Remedial
technologies are prescreened. for effectiveness,
implementability, and cost. The prescreening is done using
available technical literature, databases, and manufacturer's
information. Based upon this initial technology prescreening,
solvent extraction may be one of several candidate remedial
technologies selected for further investigation or eliminated
during the remedial investigation /feasibility study. See the
generic guide for more specific details on screening of
treatment technologies and on determining the need and type
of treatability tests which may be required for evaluating
treatment technology alternatives.1-27-1
2.2.4 Solvent Extraction Limitations
Solvent extraction limitations may be defined as characteristics
that hinder cost-effective treatment of the contaminated media
with specific processes. The limitation may be due to the
contaminant (incompatibility with the selected solvents or
complex mix of contaminants), the process, or the media.
Several extraction stages may be required in some cases to
meet the site cleanup goals. Difficulties may be encountered in
recycling spent solvents. Hydrophobic and hydrophilic
contaminants may be difficult to extract with the same solvent.
The contaminated media might require substantial
pretreatment.
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Complex mixtures of contaminants in the waste media, such as
a mixture of metals, non-volatile organics, semivolatile
organics, etc., may make the design or selection of a suitable
solvent extraction system that will remove all the different
types of contaminants difficult. Organically bound metals can
co- extract with the target organic pollutants and restrict
disposal and recycle options. The presence of emulsifiers and
detergents can adversely affect the extraction performance by
competing with the extraction solvent for retention of the
organic pollutants. Emulsifiers and detergents can also lead to
foaming, which hinders separation and settling characteristics
and reduces material throughput.1-2^ Methods are available for
breaking foams and emulsions, and these have often been
used to facilitate extraction processes. Sequential extraction
steps, using different vents, may be needed. Frequent changes
in the contaminant type and concentration in the feed material
can disrupt the efficiency of the process. To accommodate
such changes in the feed, modifications to the solvent mix and
the operating settings may be required. Alternatively,
additional feedstock preparation steps may be necessary. High
moisture content can interfere with the efficiency of some
solvents (i.e. methanol), limiting the application of certain
solvent extraction processes.
Advantages and disadvantages exist between the various
types of solvent extraction processes described in this section.
The primary differences include the following: ability to handle
fines or high clay content, ability to handle a wide variety of
organic contaminants, the ease of phase separation after
extraction, and the energy requirements.
The presence of fines or high clay content may present
problems with standard solvent extraction processes. If the
contaminants are adsorbed strongly to the waste matrix, the
solvent may not be able to remove them. Standard solvent
processes are able to use numerous solvents and
combinations of solvents and therefore can be used for many
different organic contaminants. Phase separation after
extraction can be poor at times and may
require mechanical devices such as centrifuges or filters. The
energy requirements for separation are usually small for
standard solvent processes.
Near-critical fluid/liquefied gas processes are generally better
able to deal with fines or high clay content than other solvent
types because of the low viscosity and density of the solvent
which allows penetration into the clay, and may facilitate
solvent/solids separation. Although a large number of near-
critical fluid and liquefied gas solvents have been tested,
practical, environmental applications have been limited to a
few solvents, with or without cosolvents. The primary use of
near-critical fluid/liquefied gas processes has been to extract
oily contaminants and solvents such as chlorinated
hydrocarbons and ketones. The primary limitation which is
unique to near-critical fluid/liquefied gas processes is that,
because the solvents tend to be nonpolar, very polar organics
and high molecular-weight contaminants may be difficult to
extract. Phase separation after extraction for near-critical
fluid/liquefied gas processes is excellent. Once the pressure is
reduced, the density difference between the solvent and
extracted waste is very high. The energy requirements are
typically low for the near-critical fluid gas solvent processes.
The energy requirements for these processes can be
substantially less than for super-critical fluid processes.
The ability of CST solvent processes to handle fines or high
clay content may be somewhat superior to that of standard
solvent processes. This is because of the ease of phase
separation normally experienced with CST solvents. CST
solvent processes have limited choices for solvents which can
be practically applied, and therefore may not be applicable to
some contaminants. The ease of phase separation probably is
somewhere in between that of standard solvent and
near-criticalfluid/liquefied gasprocesses. Energy requirements
are normally higher than with standard solvent processes
because of the need for both refrigeration and heating of the
solvent.
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SECTION 3
THE USE OF TREATABILITY STUDIES
IN REMEDY EVALUATION
This section presents an overview of the use of treatability
tests in confirming the selection of solvent extraction as the
technology remedy under CERCL A. It also provides a decision
tree that defines the tiered approach to the overall treatability
study program with examples of the application of treatability
studies to the RI/FS andremedy selection process. Subsection
3.1 presents an overview of the general process of conducting
treatability tests. Subsection 3.2 defines the tiered approach to
conducting treatability studies and the applicability of each
tier of testing, based on the information obtained, to assess,
evaluate, and confirm solvent extraction technology as the
selected remedy.
3.1 PROCESS OF TREATABILITY
TESTING IN SELECTING A
REMEDY
Treatability studies should be performed in a systematic
fashion to ensure that the data generated can support the
remedy evaluation process. This section describes a general
approach that should be followed by RPMs, PRPs, and
contractors during all levels of treatability testing. This
approach includes:
• Establishing data quality objectives
• Selecting a contracting mechanism
• Issuing the Work Assignment
• Preparing the Work Plan
• Preparing the Sampling and Analysis Plan
• Preparing the Health and Safety Plan
• Conducting community relations activities
• Complying with regulatory requirements
• Executing the study
• Analyzing and interpreting the data
• Reporting the results.
These elements are described in detail in the generic guide.(27)
That document gives information applicable to all treatability
studies. It also presents information specific to remedy
screening, remedy selection testing, and remedy design
testing.
Treatability studies for a particular site will often entail multiple
tiers of testing. Duplication of effort can be avoided by
recognizing this possibility in the early planning phases of the
project. The Work Assignment, Work Plan, and other
supporting documents should include all anticipated activities.
There are three levels or tiers of treatability studies: remedy
screening, remedy selection, and remedy design. Some or all of
the levels may be needed on a case-by-case basis. The need
for and the level of treatability testing required are
management decisions in which the time and cost necessary
to perform the testing are balanced against the risks inherent
in the decision (e.g., selection of an inappropriate treatment
alternative). These decisions are based on the quantity and
quality of data available and on other decision factors (e.g.,
state and community acceptance of the remedy and new site
data). The flow diagram for the tiered approach in Figure 3-1
traces the stepwise review of study data and the decision
points and factors to be considered.
Technologies generally are evaluated first at the remedy
screening level and progress through the remedy selection to
the remedy design tier. A technology may enter the selection
process, however, at whatever level is appropriate based on
available data on the technology and site-specific factors. For
example, a technology that has been successfully applied at a
site with similar conditions and contaminants may not require
remedy screening to determine whether it has the potential to
work. Rather, it may go directly to remedy selection testing to
verify that performance standards can be met. Treatability
studies, at some level, will normally be needed even if previous
studies or actual implementation have encompassed similar
site-specific conditions to assure that the site target cleanup
goals are going to be achieved. Figure 3-2 shows the
relationship of the three levels of treatability study to each
other and to the RI/FS process.
3.2 APPLICATION OF
TREATABILITY TESTS
Before conducting treatability studies, the objectives of each
tier of testing must be established. Solvent extraction
treatability study objectives are based upon the specific needs
of the RI/F S. There are nine evaluation criteria specified in the
document, Guidance for Conducting Remedial Investigations
and Feasibility Studies Under
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Remedial Investigation/
Feasibility Study (RI/FS)
Identification
of Alternatives
Record of
Decision
(ROD)
Remedy
Selection
Remedial Design/
Remedial Action -
(RD/RA)
Scoping
— the -
RI/FS
Literature
Screening
and
Treatability
Study Scoping
Site
Characterization
and Technology
Screening
REMEDY
SCREENING
to Determine
Technology Feasibility
Evaluation
of Alternatives
REMEDY SELECTION
to Develop Performance
and Cost Data
Implementation
of Remedy
REMEDY DESIGN
to Develop Scale-Up, Design,
and Detailed Cost Data
Figure 3-2. The role of treatability studies in the RI/FS and RD/RA process.
CERCLA (Interim Final);(26) the treatability studies provide data
for up to seven of these criteria. These seven criteria are:
• Overall protection of human health and environment
• Compliance with applicable or relevant and appropriate
requirements (ARARs)
• Reduction of toxicity, mobility, or volume through
treatment
Short-term effectiveness
• Implementability
• Long-term effectiveness and permanence
Cost.
The first four of these evaluation criteria deal with the degree
of contaminant reduction achieved by the solvent extraction
process. What will be the remaining contaminant
concentrations? Will the residual contaminant levels be
sufficiently low to meet the established ARARs and the
risk-based contaminant cleanup levels? What are the
contaminant concentration and physical and chemical
differences between the untreated and the treated solids
fractions (e.g., has contaminant toxicity, mobility, and volume
been reduced)? The fourth criterion, short-term effectiveness,
also addresses the effects of the treatment technology
during construction and implementation of a remedy. This
evaluation is concerned not only with contaminant
concentration and toxicity, but also with the potential for
exposure to solvents or solvent vapors which may be harmful.
The implementability assessment evaluates the technical and
administrative feasibility of the technology and the availability
of required goods and services. The following questions must
be answered in order to address the implementability of
solvent extraction:
• Will solvent residuals in soil and water make residuals
treatment and disposal difficult?
• What are the characteristics and the volume of the
residuals that will be produced?
• Are the process equipment and solvent readily available?
• Can the solvent be economically recovered and recycled?
• What are the necessary pretreatment steps (specific to the
process equipment and solvent)?
• Will the solvent extraction system chemicals react with
the solutes?
Normally, the required equipment and extracting solvents are
available. However, alterations to process design may be
necessary on a site-by-site basis to accommodate
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different media and contaminants. Contaminants can be treated
onsite with mobile or portable units (modular components
constructed onsite) or removed to an off site facility. Residuals
from the solvent extraction process require additional
treatment. The implementability assessment must include these
additional treatments. The ability to recover and recycle
solvents is generally critical to the implementability of solvent
extraction.
Long-term effectiveness assesses how effective treatment
technologies are in maintaining protection of human health
and the environment after response obj ectives have been met.
The magnitude of any residual risk and the adequacy and
reliability of controls must be evaluated. Residual risk, as
applied to solvent extraction, assesses the risks associated
with the treatment residuals at the conclusion of all remedial
activities. Analysis of residual risk from sidestream and other
treatment train processes should be included in this step. An
evaluation of the reliability of treatment process controls
assesses the adequacy and suitability of any long-term
controls (such as site access restrictions and deed limitations
on land use) that are necessary to manage treatment residuals
at the site. Such assessments are usually beyond the scope of
a remedy selection treatability study, but may be addressed
conceptually based on remedy selection results. Performance
goals must consider the existing site contaminant levels and
relative cleanup goals for soils, sludges, and wateratthe site.
In previous years, cleanup goals often reflected background
site conditions. Attaining background cleanup levels through
treatment has proved impractical in many situations. The
present trend is toward the development of site-specific
cleanup target levels that are risk-based rather than
background-based.
The final EPA evaluation criterion which can specifically be
addressed during a treatability study is cost. The solvent
extraction process transfers contaminants to and concentrates
them in the solvent The solvent is typically reclaimed, leaving
behind a concentrated waste in the still bottoms. The disposal
and/or treatment cost for concentrated waste is less than that
for unconcentrated waste. Normally, the treated solid and/or
liquid phase has a low contaminant concentration. Because the
contaminant concentration is low, further treatment may not be
necessary and disposal costs are small. Air emissions are
typically minor. The cost savings, in terms of disposal and/or
treatment, realized by separating and concentrating
contaminants and by reducing the contaminant concentration
in the solid and/or liquid phase should cover the cost of
treatment by solvent extraction.
Remedy selection treatability studies can provide data to
estimate the following important cost factors:
• The volume and characteristics of residual wastewater
and sludge which require treatment or disposal.
• The degree to which process modifications can enhance
the efficiency of the process.
• The degree to which the solvent and/or contaminant can
be recovered and recycled.
• The solvent-to-feed ratio.
factors provide information about the costs of
downstream treatments by determining the amount and
character of the contaminated residuals. The last four
factors help estimate the costs of equipment, supplies,
and utilities directly associated with the specific solvent
extraction system.
Treatability tests do not directly relate to the final two criteria,
state and community acceptance, because these criteria reflect
the apparent preferences or concerns about alternative
technologies of the state and the community. A viable
remediation technology may be eliminated for consideration if
the state or community objects to its use. However, treatability
studies may provide data that can address state and
community concerns and in some cases change their
preferences.
3.2.1 Remedy Screening
Remedy screening is the first level of testing. It is used to
establish the ability of a technology to treat a waste. These
studies are generally low cost (e.g., < $30,000) and usually
require one or more days to complete the testing. Additional
time must be allowed for project planning, chemical analyses,
interpretation of test data, and report writing. Only limited
quality control is required for remedy screening studies. They
yield data indicating a technology's potential to meet
performance goals. Remedy screening tests can identify
operating standards for investigation during remedy selection
orremedy design testing. They generate little, if any, design or
cost data and should not be used as the sole basis for
selection of a remedy.
Solvent extraction remedy screening treatability studies are
occasionally skipped, if there is enough information about the
physical and chemical characteristics of contaminant and
media to allow an expert to evaluate the potential success of
solvent extraction at a site. In such cases, remedy selection
tests are normally the firstlevel of treatability study executed.
When remedy screening studies are performed, certain steps,
such as solvent recovery, may be skipped if they are based on
existing technology. When performed, remedy screening tests
are performed in laboratory-scale extraction equipment. These
tests are generic and can be performed at any laboratory with
the proper equipment and qualified personnel.
3.2.2 Remedy Selection
Remedy selection testing is the second level of testing.
Remedy selection tests identify the technology's performance
for a site. These studies generally have a moderate cost (e.g.,
$20,000 to $120,000) and require several months or more to
plan, obtain samples, and execute. Remedy selection tests
yield data that verify that the technology can meet expected
cleanup goals, provide information in support of the detailed
analysis of alternatives (i.e., seven of the nine evaluation
criteria), and give indications of optimal operating conditions.
The remedy selection tier of solvent extraction testing consists
of either bench-scale tests and/or pilot tests. Typically, these
tests are vendor-specific. Sufficient experimental controls are
needed such that a quantitative
The number of extraction stages necessary. The first two
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material balance can be achieved. The key question to be
answered during remedy selection testing is whether the
treated media will meet the cleanup goals for the site. The exact
removal efficiency or acceptable residual contaminant level
specified as the goal for the remedy selection test is
site-specific. Typically, a remedy design study would follow a
successful remedy selection study.
3.2.3 Remedy Design
Remedy design testing is the third level of testing. In this tier,
pilot tests provide quantitative performance, cost, and design
information for remediating an operable unit. This testing also
produces the remaining data required to optimize performance.
These studies are of moderate to high cost (e.g., $100,000 to
$500,000) and require several months to complete the testing.
As with the other tiers, planning, analysis, and report writing
will add to the duration of the study. For complex sites (e.g.,
sites with different types or concentrations of contaminants in
different media such as soil, sludges, and water), longer testing
periods may be required, and costs can be higher. Remedy
design tests yield data that verify performance to a higher
degree than the remedy selection and provide detailed design
information. They are performed during the remedy design of
a site cleanup after the ROD and
evaluation of alternatives.
Remedy design tests usually consist of bringing a mobile
treatment unit onto the site, or constructing a small-scale unit
for non-mobile technologies. Permit waivers may be available
for offsite treatability studies under certain conditions. For
most materials, a permit exclusion is available provided the
quantity of material being sent offsite is 4,000 kg or less. The
obj ective of this tier of testing is to confirm the cleanup levels
and treatment times specified in the Work Plan (see subsection
4.1.1). This is best achieved by operating a field unit under
conditions similar to those expected in the full-scale
remediation project.
Data obtained from the remedy design tests are used to:
• Design the full-scale unit
• Confirm the feasibility of solvent extraction based on
target cleanup goals
• Refine Cleanup time estimates
• Refine cost predictions
Given the lack of full-scale experience with solvent extraction,
remedy design testing will generally be necessary before
full-scale implementation.
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SECTION 4
TREATABILITY STUDY WORK PLAN
Section 4 of this document is written assuming that a Remedial
Project Manager is requesting treatability studies through a
work assignment/work plan mechanism. Although the
discussion focuses on this mechanism, it would also apply to
situations where other contracting mechanisms are used.
This chapter focuses on specific elements of the Work Plan for
solvent extraction treatability studies. These include test
objectives, experimental design and procedures, equipment
and materials, reports, schedule, management and staffing, and
budget. These elements are described in subsections 4.1
through 4.9. Complementing the above subsections are section
5, Sampling and Analysis Plan and Quality Assurance Project
Plan, and section 6, Treatability Data Interpretation, which
address the sampling data analysis elements of the Work Plan
in greater detail. Table 4-1 lists all of the Work Plan elements.
Table 4-1. Suggested Organization of Solvent
Extraction Treatability Study Work Plan
No.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Work Plan Elements
Projected Description
Remedial Technology Description
Test Goals
Experimental Design and
Procedures
Equipment and Materials
Sampling and Analysis
Data Management
Data Analysis and Interpretation
Health and Safety
Residuals Management
Community Relations
Reports
Schedule
Management and Staffing
Budget
Sub-
section
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
Carefully planned treatability studies are necessary to ensure
that the data generated are useful for evaluating the validity or
performance of a technology. The Work Plan, prepared by the
contractor when the Work Assignment is in place, sets forth
the contractor's proposed technical approach for completing
the tasks outlined in the Work Assignment. It assigns
responsibilities and establishes the project schedule and
costs. The Work Plan must be approved by the RPM before
initiating subsequent tasks. For more information on each of
these sections, refer to the generic guide.1-27-1
4.1 TEST GOALS
Setting goals for the treatability study is critical to the ultimate
utility of the data generated. Obj ectives must be defined before
starting the treatability study. Each tier of the treatability study
needs performance goals appropriate to that tier. For example,
remedy selection tests are used to answer the questions, "Will
solvent extraction reduce contaminant concentrations to meet
cleanup goals?" and "Can the concentrated contaminant be
treated or reclaimed in a cost-effective manner?" A
contaminant reduction of approximately 90 to 99 percent
indicates that the technology may be able to meet cleanup
goals and should be considered for the ROD.
The ideal technology performance goals are the cleanup
criteria forthe site. For several reasons, such as ongoing waste
analysis and ARARs determination, cleanup criteria are
sometimes not finalized until the ROD is signed, long after
treatability studies must be initiated. Nevertheless, treatability
study goals need to be established before the study is
performed so that the success of the treatability study can be
assessed. In many instances, this may entail an educated
guess as to what the final cleanup levels may be. In the
absence of set cleanup levels, the RPM can estimate
performance goals for the treatability studies based on the first
four criteria listed at the beginning of subsection 3.2. Previous
treatability study results may provide the basis for an estimate
of the treatability study goals when site cleanup goals have
not been set.
4.1.1 Remedy Screening Goals
Generally, the prescreening will be sufficient to determine the
applicability of solvent extraction as the remedy or as a
segment of the treatment train for a particular site. If the
contaminants of concern include organics, then solvent
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extraction can be considered a potential means of
concentrating the organics. If the contaminants of concern do
not include organics, then the solvent extraction processes
referred to in this guide would not generally be applicable.
Remedy screening tests might be appropriate in an unusual
sample such as a matrix which has not previously been
extracted (e.g., peat or organic debris). Remedy screening may
also be needed when a wide variety of contaminants are
present in the matrix.
An example of the goal for those remedy screening tests would
be to show that the chosen fluid is compatible with and will
extract contaminants up to the clean up level if known or a
sufficient percentage (e.g., 50 to 70 percent) to warrant further
treatability studies to optimize the process. The remedy
screening treatability study goals must be determined on a
site-specific basis.
Achieving the goals at this tier should merely indicate that
solvent extraction has at least a limited chance of success and
that further studies will be useful. Occasionally, such
information is available based on the type of contaminants and
media present at the site and the availability of a compatible
solvent at low cost. When such information is available,
experts in solvent extraction technology can often assess the
potential applicability of solvent extraction without performing
remedy screening.
Example 1 describes a hypothetical site and a series of
laboratory extraction tests that were used to evaluate the
potential of solvent extraction for site remediation. The
example illustrates how to decide whether the remedy selection
treatability studies using solvent extraction should be
performed.
4.1.2 Remedy Selection Treatability
Study Goals
The main objectives of this tier of testing are to:
• Measure the final contaminant concentration in and the
percentage of contaminant removal from the soil, sludge,
or water through solubilization in the chosen solvent(s).
• Produce the design information required for the next level
of testing, should the remedy selection evaluation
indicate remedy design studies are warranted.
• Provide cost estimates for full-scale remediation.
The actual goal for removal efficiency must be based on site-
and process-specific characteristics. The specified removal
efficiency must meet site cleanup goals, if available. A typical
removal efficiency of 90 to 99 percent maybe established for
the remedy selection tier depending on the specifics of the site
and the established cleanup goals.
Example 2 illustrates the goalof aremedy selection treatability
study at the Superfund site introduced in Example 1. In this
example, the remedy selection treatability studies show that
site cleanup goals can be met. Solvent extraction is chosen as
the selected remedy in the ROD.
4.2 EXPERIMENTAL DESIGN
4.2.1 Remedy Screening Tier
Screening tests can be rapidly performed in onsite or offsite
laboratories using standard laboratory glassware or specially
designed laboratory-scale extractors to evaluate the potential
performance of solvent extraction as an alternative technology.
Careful planning of experimental design and procedures is
required to produce adequate treatability study data. The
experimental design must identify the critical parameters and
determine the number of replicate tests necessary.
When assessing the need for laboratory extraction tests, the
investigator should use available knowledge of the site and
any preliminary analytical data on the type and concentration
of contaminants present. In general, the physical properties of
solid and liquid media are important to the success of solvent
extraction. Viscosity is critical to processes which require a
pumpable feed material. Specific gravity affects phase
separation. Particle size and pore space can influence the
solvent's ability to extract the contaminants from the soil.
Contaminant characteristics to examine during remedy
screening include solubility in various solvents. Vapor
pressure and Henry's law constants are useful for evaluating
solvent recovery methods. Properties of organic contaminants
are generally easier to evaluate than those of inorganic
contaminants. Inorganics, such as heavy metals, can exist in
many compounds (e.g., oxides, hydroxides, nitrates,
phosphates, chlorides, sulfates, and other more complex
mineralized forms) which can greatly alter their solubilities.
Inorganic leaching agents may be applicable for metal
separation and removal/45 Metal analyses typically provide
only total metal concentrations. More detailed analyses to
determine specific anions and cations present may be
warranted.
At this level of testing the experimental design does not have
to be vendor-specific. A recommended remedy screening test
for contaminated soils is as follows:
• Both a hotspot sample and a "representative" ornear
average sample of approximately 5 kg (see subsection
4.4.1) are placed in individual containers with a solvent at
a soil-to-solvent ratio of approximately 1:5.
• Each container is thoroughly agitated for 2 hours using a
rotary shaker or other device.
• After settling, each soil/solvent mixture is centrifuged.
• The solvent is decanted and sampled from each container.
• The soil from each container is centrifuged again, vacuum
filtered, and sampled.
• Analyses of each decant and residual are performed.
A second option is using a soxhlet extraction for remedy
screening. If a soxhlet is used, less than 1 kg of sample is
required. In any case, remedy screening tests are generally run
at ambient conditions with selected solvents from a
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Example 1. Remedy Screening
BACKGROUND
A site which had been used for disposal of oily wastes for over 40 years was in the RI/FS stage of
remediation. The wastes were stored in piles, pits, and lagoons. Data from the Rl showed that
throughout the site there was contamination with significant levels of semivolatile organic compounds
(SVOCS). The concentration and composition of volatiles and metals varied considerably, as did the
physical consistency of the solids and sludges. Samples also showed scattered, low concentrations
of PCB's. Total oil and grease varied from 3 to 25 percent. Solids were apparently catalyst fines,
clay, and carbon from refinery wastes; metals and carbon from used oil; and soil.
Because of the high levels of SVOCs, the material appeared to be a good candidate for solvent
extraction. However, since no data was available on the extraction of waste mixtures of a similar
composition and consistency a screening study was recommended.
TESTING
The remedy screening study was recommended by the contractor to demonstrate the potential
effectiveness for extracting the mix of oils and PCBs from sludge, and the semivolatiles from soil and
fine solids. The project manager agreed to the testing. Two samples were selected for testing.
These samples represented the extremes in the moisture content and physical characteristics of the
soil. The first sample was a sludge from an area where PCBs had been detected. This sample
contained primarily coarse soil particles. The other sample was from a "dry" pile containing a large
percentage of fine soils. Approximately 200 grams of each sample was extracted with liquefied
propane in a bench-scale extractor equipped with a magnetically driven mixer. In each case the
sample was extracted in "4-stages" with a 2:1 solvent:feed ratio (by weight). This was done by
placing the sample in the extractor, filling the extractor with propane, mixing for 10 minutes, settling,
decanting off the propane solution, refilling with clean propane, and repeating the above cycle for
four extractions.
The sludge, which contained about 40 percent water, was air dried and analyzed. The initial oil and
grease content was approximately 25 percent. Oil and grease were reduced by about 96 percent
and PCB's were non detectable in the solid residue. The extracted oil was also analyzed for heating
value and PCB content. The heating value was 14,000 BTU/lb and the PCB's were 30 parts per
million (ppm).
The "dry" pile sample was also extracted with propane in a bench scale batch extractor. The solids
appeared to be a clay filter cake containing about 18 percent oil. After extraction the residual oil on
the solids was approximately 0.4 percent, or a 98 percent reduction.
Solvent extraction was recommended for the follow up work. Since the screening study results were
favorable, the need for a remedy selection treatability study was debated. However, since the site
characteristics varied so greatly, it was decided to undertake a remedy selection study to test the
solvent extraction process with a variety of contaminant/matrix mixes. The extracted oil sample was
given to a rerefiner to evaluate the potential to reclaim the recovered oil.
generic list. The test should be run using a hy drophilic solvent
and then the residual solids from the first extraction should be
subjected to a second extraction with a hydrophobic solvent.
Hy drophilic solvents include acetone, methanol, and dioxane.
Hydrophobic solvents include hexane and kerosene. CST
solvents, such as triethylamine, can be either hy drophilic or
hydrophobic depending on the temperature; however, such
solvents are not generally used for remedy screening. The
concentration of the contaminants of concern in the received
soil, each solvent, and the treated soil is determined.
When performing the remedy screening test, observe whether
an emulsion forms, either at the top or the bottom of the
container. Determine the settling time, settling rate, and depth
of the solids. The rate and the relative volume of the settling
material will provide some indication of the potential for solids
separation. Removal efficiency can be estimated by analyzing
the separated solids for selected indicator contaminants of
concern. The removal efficiency goals for remedy screening
should not
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Example 2. Remedy Selection
BACKGROUND
The site discussed in Example 1 was recommended for additional remedy selection studies due to
the variety of site matrix characteristics. The solvent extraction process had demonstrated its ability
to remove a substantial percentage (>96 percent) of contaminant from two different media. However,
the ability of the process to handle all of the solids and sludges in combination with oils and other
contaminants in one processing system required verification. This opportunity was also used to
demonstrate the technology onsite at the pilot scale, and to collect remedy design data.
TESTING
A total of 12 samples representing the different matrices and contaminants was taken. Each of the
12 samples was individually extracted. Then a number of composites were made between sludges
and dry solids in an attempt to simulate a homogeneous feed which could be maintained during the
remediation by blending feed sources. These composites were extracted and used to test various
processing parameters and to test the process at a larger scale.
Each of the twelve samples was extracted at the vendor's laboratory in the same type of bench-scale
extraction equipment used in the screening tests. This required approximately 200 grams of each
sample. The same basic test was run on each sample, that is "4-stages" with a 2:1 solvent:feed ratio
(by weight). The total oil and grease was measured an each sample before and after extraction.
Next, three composites, each amounting to several gallons of sample, were made. Each composite
had approximately the same ratio of liquids:solids, 70:30. The composites each included four
different samples. Water was added to one sample to "liquefy" the sludge. Then in the same
bench-scale extraction system, a series of tests was run on the composite to determine: likely
operating conditions, the ability of the process to routinely meet cleanup goals, and approximate
cleanup processing costs.
The extraction process variables which were tested included: solvent - pure propane and two
different propane-butane blends; temperature - two temperatures, 65«F and 100* F, each at
sufficient pressure to maintain the solvent completely liquefied; and solvent to feed ratio -1:1,2:1,
and 4:1 on a weight basis. Since the samples were viscous, high intensity mixing was used in all
tests. The total oil and grease, water, and solids was measured on each sample before and after
extraction in the vendor's laboratory. Solid, water, and oil material balances were calculated for each
test, with a quality assurance goal of 90 percent closure on each component.
be as stringent as those for remedy selection. Goals will, in
general, be site-and contaminant-specific. If the cleanup level
(if known) is attained or a significant removal efficiency (e.g.
> 50 to 70 percent) is achieved for a given site during remedy
screening, then solvent extraction can be viewed favorably
and more detailed laboratory and bench tests must be
conducted.
To reduce analytical costs during the remedy screening tier, a
condensed list of known contaminants should be selected as
indicators of performance. The selection of indicator analyses
to track during remedy screening testing should be based on
the following guidelines;
1) Select one or two contaminants that are most toxic or most
prevalent.
2) Select indicator compounds to represent other chemical
groups if they are present in the soil (i.e., volatile and
semi-volatile organics, chlorinated and nonchlorinated
species, etc.).
3) If polychlorinated biphenyls (PCBs) and dioxins are
known to be present, select PCBs as indicators in the
tests and analyze forthem in the solids fraction. (A TSCA
R&D permit is required for treatability studies on materials
which contain greater than 50 parts per million (ppm) of
PCBs.)
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Example 2. (continued)
Finally, approximately 50 gallons of each of the three composites were prepared onsite. This
material was then extracted in a small portable pilot plant system brought to the contaminated site.
The pilot plant included most of the operations which are in the full-scale system. However, it can be
operated and brought to steady-state conditions using much smaller sample volumes than the
full-scale system. The pilot-plant extractor is a multi-stage continuous countercurrent mixer settler,
and includes a solvent recovery system. The mixer volume is approximately 20 gallons; at a 2:1
solvent:feed ratio by weight (4:1 by volume) there are approximately 4 gallons of sludge in the mixer
at any one time. Thus the 50-gallon sample is sufficient for reaching and maintaining steady state
for the bulk of the extraction time.
Each of the 50 gallon composites was extracted in this pilot plant in approximately 2 hours of
continuous operation. Samples were taken from the feed and at the discharge of each extraction
stage every 15 minutes during the test. In addition, after the first 8 gallons of extraction residue (two
extractor volumes) were removed, the remaining residue was collected and composited for sampling
and analysis. The extracted oil was also collected and composited for performance testing and
analysis. The samples taken every 15 minutes were analyzed for oil and grease content to
determine the length of time required to reach steady state, and to ensure that steady state was
maintained. These sample analyses were also used to determine extraction stage efficiencies and in
the calculation of the oil material balances. Three samples were taken from the composite extraction
residue and sent to an independent test laboratory for analysis of total petroleum hydrocarbons,
volatile, acid and base/neutral extractable and semivolatile organic compounds, and PCBs. After
sampling and analysis, the three oil extract samples collected from each of the large-scale
composite extraction tests were composited and rerefined to determine the potential for oil recycle.
RESULTS
The results of the study indicated that with proper pretreatment, primarily blending, all of the waste
matrices present could be extracted well below the target cleanup goals which had been tentatively
set. Pretreatment was required to make all of the feed material approximately the same ratioof solids
to liquids. This was accomplished in testing by blending the dry wastes with the sludges; alternatively
it could be accomplished by slurrying the dry wastes and partially drying the sludges.
The 12 samples tested showed oil extraction varying from 92 to 99 percent. The process tests
showed that extraction in excess of 99 percent could be routinely achieved with a heavier solvent
mixture and higher solvent-to-feed ratios than that used in the screening tests. The multiple samples
and analyses run during the continuous extraction as well as the material balances met the quality
assurance goals.
The data collected was used to determine the ability to consistently meet projected cleanup goals, to
complete a preliminary process design for the cleanup, and to estimate the cleanup cost.
It is usually not cost-effective to analyze for all contaminants 4.2.2 Remedy Selection Tier
at this level of testing. Check for other contaminants later in
the solids or water fraction from remedy selection tests. Once This series of tests may use the same equipment as the remedy
guidelines 1 through 3 have remedy screening tier or may screening tier or may require additional equipment. The tests
require additional been applied, solvent(s) should be selected are run under more controlled conditions than the remedy
which are likely to extract the contaminants to be measured. screening tests. The removal efficiency is measured under
variable extraction conditions
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which can include the addition of several solvents or an
entrainer; sequential extraction; heated solvents; pH
adjustment; and use of supercritical or near-critical conditions.
More precision is used in weighing, mixing, and phase
separation. There is an associated increase in QA/QC costs.
Wet soils and sediments may require dewatering before
treatment. Chemical analyses are frequently performed on the
solvent fraction as well as on the cleaned solids fraction. The
impact of process variables on extraction efficiency is
quantified. This series of tests is considerably more costly
than remedy screening tests, so only samples showing
promise in the remedy screening phase should be carried
forward into the remedy selection tier. The objective of the
remedy selection solvent extraction design is to meet the goals
discussed in subsection 4.1.2.
Bench-scale testing is usually sufficient for this tier, but there
are instances where additional pilot-scale testing is warranted.
If foaming problems occurred during remedy screening or
bench-scale testing, pilot-scale testing should be used to
solve any problems before full-scale remediation. Pilot-scale
testing may be necessary in order to obtain community
acceptance. A pilot-scale or short-term run with full-scale
equipment maybe used for large sites in order to better define
cost estimates for complete remediation.
A series of tests should be designed to provide information on
the technical capability of solvent extraction to meet cleanup
goals, as well as the cost of meeting the goals. The initial tests
would typically consist of a few quick screening extractions
similar to the one discussed in subsection 4.2.1 to determine
the type of solvent system to be used, and to detect any
unusual behavior or difficulties in the process. This would be
followed by tests in which extraction variables such as
solvent-to-feed ratio, extraction mixing intensity and time,
number of stages, pH, temperature, and pressure would be
examined. In order to optimize the field operating conditions,
several test samples may be required for each variable. To hold
down analytical costs, inexpensive screening analysis, such as
only measuring initial and final TOC or TPH, could be used to
indicate a relative percent removal. Only the final extraction
test samples, running close to anticipated field processing
conditions would be given full analyses. The full analyses are
needed to verify the results of inexpensive screening analyses.
In addition, the need or utility of pretreatment and
posttreatment would be evaluated, and if appropriate, tested.
The process data and analysis of samples should be of
sufficient quality to allow estimates to be made of the cost of
extraction as a function of cleanup level. The cost of pre- and
post-treatment should also be evaluated along with the value
or liabilities associated with the products of extraction.
Several factors must be considered in the design of solvent
extraction treatability studies. A remedy selection test design
should be geared to the type of system expected to be used in
the field (i.e., standard solvents, critical fluids/liquefied gases,
or CST solvents). Bench-scale testing does not have to be
vendor- specific, but pilot-scale testing does. Solvent-to-feed
ratios should be planned using the results from the laboratory
screening tests, if they were performed. In general,
solvent-to-feed ratios of 2:1 to 5:1 will be sufficient to perform
remedy selection tests. VWWWWW xhe solvent and solids
should be mixed for a minimum of 10 minutes and a maximum
of 30 minutes. The solvent-to-feed ratio and mix times
presented here are rules of thumb to be used if no other
information is available.
Normally, only the solids fraction which has been cleaned and
separated needs to be analyzed for contaminants. Contaminant
concentration in the solvent may be determined periodically
(e.g., 10 percent of the samples) to make an approximate
material balance determination. Complete separation of the
solids fraction from the solvent is necessary for accurate
material balance calculations. Concentration measurements
should be taken after each cycle orbatch, or at timed intervals
for continuous processes, so as to eventually be able to
calculate the cost of removal versus the contaminant removal
efficiency.
Initially, the solids fraction should be analyzed only for
indicator contaminants. If the removal of the indicator
contaminants confirm that the technology has the potential to
meet cleanup standards at the site, additional analyses should
be performed. Both the solvent fraction and the solids fraction
must be analyzed for all contaminants if a complete material
balance is desired. If any water is removed during the process,
it should also be analyzed. A quantitative balance for volatile
components may not be practical at this tier because of the
cost of determining losses to the air.
The decision on whether to perform remedy selection testing
on hot spots or composite samples is difficult and must be
made on a site-by-site basis. Hot spot areas should be factored
into the test plan if they represent a significant portion of the
waste site. However, it is more practical to test the specific
waste matrix that will be fed to the full-scale system over the
bulk of its operating life. If the character of soils or sediments
changes radically (e.g., from clay to sand) over the depth of
contamination, then tests should be designed to separately
study system performance on each soil type. Sample size for
this tier of testing depends on the size of the test equipment
and the number of test samples. Additional guidance on soil
sampling techniques and theory can be found in Soil Sampling
Quality Assurance User's Guide1-34-1 and Methods for
Evaluating the Attainment of Cleanup Standards.1-31-1
4.3 EQUIPMENT AND MATERIALS
The Work Plan should specify the equipment and materials
needed for the treatability test. For example, the size and type
of glassware or containers to be used during the test should
be specified. Standard laboratory methods normally dictate the
types of sampling containers which can be used with various
contaminant groups. The RPM should consult such methods
for the appropriate containers to be used for the treatability
studies.1-37-1 Normally, glass containers should be used.
Stainless steel can also be used with most contaminants. Care
should be taken when using various plastic containers and
fittings. Such materials will absorb many contaminants and can
also leach plasticizer chemicals, such as phthalate, into the
contaminant matrix. Appropriate methods for preserving
samples and specified holding times for those samples should
be used.
The following equipment is recommended for remedy
screening solvent extraction tests:
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Basic Equipment
• Standard laboratory extraction equipment (e.g., soxhlet,
separatory funnel, etc.) or specialized solvent extraction
equipment (e.g., high-pressure systems for critical fluids)
• Top loading balance
• Timer
• Sample jars
• Filter or centrifuge
• Vacuum pump
• Magnetic stirrer
Typically, the equipment used in remedy selection tests is
similar to that of remedy screening in the case of bench-scale
testing and vendor-specific in the case of pilot-scale testing.
4.4 SAMPLING AND ANALYSIS
The Work Plan should describe the procedures to be used in
field and treatability study sampling. The procedures to be
used will be site-specific.
4.4.1 Field Sampling
A sampling plan should be developed which directs the
collection of representative samples from the site for the
treatability test. The sampling plan is site-specific. It describes
the number, location, and volume of samples.Heterogeneous
soils and sediments, variations in the contaminant
concentration profile, and different contaminants in different
locations in the site will complicate sampling efforts. If the
objective of the remedy screening or remedy selection
treatability tier study is to investigate the performance of
solvent extraction at the highest contaminant concentration,
the sample collection must be conducted at a "hot spot". This
will require conducting a preliminary site sampling program to
identify the locations of highest contaminant concentration.
(This information is generated early in the RI process). If the
types of contaminants vary throughout the site and
contaminants are located in several media, extensive sampling
may be required. If solvent extraction is being considered only
for certain areas of the site, the sampling program may be
simplified by concentrating on those areas.
If the objective of the remedy selection study is to investigate
the use of the technology for a more homogenous waste
(sludge, water, or homogeneous soil), an "average" sample for
the entire site must be obtained. This will required
statistically-based program of mapping the site and selecting
sampling locations that represent the variety of waste
characteristics and contaminant concentrations present. The
selection of sampling locations should be based on
knowledge of the site. Information from previous soil and
water samples, soil gas analysis using field instrumentation,
obvious odors, or residues are examples of information which
can be used to specify sample locations.
Chapter 9 of Test Methods for Evaluating Solid Waste (37)
presents a detailed discussion of representative samples and
statistical sampling methods. Additional sources of
information on field sampling procedures can be found in
Samplers and Sampling Procedures for Hazardous Waste
Streams (November 1987), Annual Book of ASTM
Standards/3' NIOSH Manual of Analytical Methods (February,
1984),(22) and the EPA publications Soil Sampling Qualify
Assurance User's Guide^34' and Methods for Evaluating the
Attainment of Cleanup Standards.(31) These documents should
be consulted to plan effective sampling programs for either
simple or complex sites.
The method of sample collection is site-specific. For example,
drill rigs or hand augers can be used to collect samples,
depending on the depth of the sample required and the soil
characteristics. If the target contaminants are volatile, care
should be taken if samples are composited to minimize the loss
of volatile compounds. Retaining composite samples on ice is
a good method of minimizing the loss of volatile compounds.
Compositing is usually appropriate forsoils containing
non-volatile constituents. A discussion of the field sampling
plan is given in subsection 5.1 of this document.
4.4.2 Waste Analysis
Subsection 2.2.3 detailed the physical data that are useful in
characterizing the contaminants during the prescreening step.
The key for successful solvent extraction treatability studies
is to properly select the solvent based on the initial
prescreening and additional contaminant characterizations.
Important matrix characteristics include the pH of solids and
liquids, soil particle size, soil pore size, soil moisture content,
and the viscosity of liquids and sludges. The pH is important
in determining the compatibility of solvents with different
contaminants. The speciation of metal compounds may also be
affected by soil pH. Particle size and pore size information can
be used to select process designs and/or solvents for
treatment of solids or sludges. The soil moisture content is an
important consideration for materials handling and dewatering
processes.
Standard analyses for contaminants at Superfund sites should
identify the contaminants of concern. It is important to
determine contaminant solubility in various solvents to give an
indication of potential solvents for testing. Volatility will be an
important consideration for materials handling. If high
concentrations of volatiles are present, pretreatment (e.g.,
using soil vapor extraction) or collection and treatment of air
emissions may be required. Metal speciation will be an
important consideration in determining metal solubility.
However, complete analyses for metal species using x-ray
diffraction is quite expensive. Typically, less costly methods
are used to determine the primary anions and cations present.
The spatial distribution and variations in the concentrations of
contaminants will be important for the design of treatability
studies. Complex mixtures of contaminants may be difficult to
treat economically. A number of extraction stages and solvents
may be required to successfully remove many contaminants.
The cost of such a system may be prohibitive. Changes in
contaminant
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composition can cause dramatic changes in removal
efficiencies.
4.4.3 Process Control Sampling and
Analysis
For any solvent extraction system, the operating conditions
within the extractor are monitored and controlled to ensure
efficient extraction is taking place. Temperature and pressure
in the extractor are measured. The devices used for these
measurements include thermocouple and pressure-sensing
units which provide direct read-out capabilities and/or may be
tied to a recorder or computer controlled system. Feed flow,
solvent flow, and solvent-to-feed ratio are also monitored to
verify operating conditions. Feed data such as pH,
temperature, and viscosity also may be useful. Operating
conditions of auxiliary equipment such as coolers, heaters,
dryers, compressors, and pumps are routinely monitored.
4.4.4 Treatment Product Sampling
and Analysis
Solvent extraction is not a stand-alone process (see
subsection 2.1.1). It generates residuals which must be further
treated and disposed of properly. The primary residual is the
concentrated contaminants which are typically removed as the
still bottoms during solvent recovery. Because the nature of
solvent extraction equipment and processes varies greatly
between vendors, remedy design testing is frequently
necessary to evaluate the type, quantity, and properties of
residuals. The remedy design treatability testing tier will not be
discussed in detail in this document.
The treated solids, still bottoms, and each of the other various
waste streams (water, spent solvent, and oversize fraction)
should be analyzed for the contaminants identified in the
original soil analyses. In many cases, indicator contaminants,
which are representative of a larger group of contaminants, can
be analyzed in place of a full scan. Caution must be exercised
in using indicator contaminants since solvent extraction
efficiencies can vary from one contaminant to another. The
process efficiency may be either understated or overstated
when analyzing for indicator compounds.
If several solvent extraction studies are run to test the effects
of operating parameters on removal efficiency, samples of each
test should be taken of each test before and after solvent
extraction. Typically, these tests are run in triplicate.
4.4.5 Sampling and Analysis Plan
(SAP) and Quality Assurance
Project Plan (QAPjP)
A SAP is required for all field activities conducted during the
RI/FS. The SAP consists of the Field Sampling Plan and the
QAPjP. This section of the Work Plan describes how the RI/F S
SAP is modified to address field sampling, waste
characterization, and sampling activities supporting
treatability studies. It describes the samples to be collected
and specifies the level of QA/QC required. See Section 5 of
this document for additional information on the SAP.
4.5 DATA ANALYSIS AND
INTERPRETATION
The Work Plan should discuss the techniques to be used in
analyzing and interpreting the data. The objective of data
analysis and interpretation is to provide sufficient information
to the RPM and EPA management to assess the feasibility of
solvent extraction as an alternative technology. After remedy
selection testing is complete, the decision must be made
whether to proceed to the remedy design testing tier, to a
full-scale solvent extraction remediation, or to rule out solvent
extraction as an alternative. The data analysis and
interpretation are a critical part of the remedy selection
process.
Chemical analysis of the contaminants present and
interpretation of data generated in the solvent extraction
process apply to all three tiers of the solvent extraction
treatability study. The analysis of process test variables is
limited to remedy selection and remedy design studies.
The primary goal of the remedy selection solvent extraction
treatability testing is to determine how well the treatment
removes the contaminant(s). System performance is affected
by process design variables, including solvent-to-solids ratio,
number of extraction stages, type of mechanical agitation used,
agitated contact time, extraction temperature and pressure,
systempH, and solvents sequence if more than one solvent is
used. Often, two or more of these variables may affect the
results. The concentration of the target contaminant versus
the number of extraction stages is commonly graphed to
determine number of stages required. Graphs such as these are
intended to show general trends. The trends may not be
consistent on a pass-by-pass basis. The plot on Figure 4-1 is
an example of when concentration appears to increase (passes
4 and 10), These inconsistencies are related to cross
contamination within system hardware or limited analytical
precision and accuracy .(23) Statistical analysis of the data can
be performed using standard techniques to differentiate
sources of change and interactions between these sources.
Fora detailed discussion of the analysis of variance (ANOVA)
techniques, and other statistical methods refer to the
document entitled Statistical Analysis of GroundwaterData at
RCRA Facilities (Interim Final)(35) and Lentner and Bishop.(12)
4.6 REPORTS
The last step of the treatability study is reporting the results.
The Work Plan discusses the organization and content of
interim and final reports. Complete, accurate reporting is
critical, because decisions about implementability will be partly
based upon the outcome of the study. The RPM may not
require formal reports at each treatability study tier. Interim
reports should be prepared after each tier. Project briefings
should be made to interested parties to determine the need and
scope of the next tier of testing. To facilitate the reporting of
results and comparisons between treatment alternatives, a
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suggested table of contents is presented in the generic
guide/27' At the completion of the study, a formal report is
always required.
Vendors may be reluctant to provide information about the
nature of proprietary solvent(s). Nevertheless, this information
is necessary for measuring contaminants in the solvent or
assessing the risk associated with residuals containing
solvent. RPMs should consider including a separate section,
possibly as an attachment, for any confidential business
information.
OERR requires that a copy of all treatability study reports be
submitted to the Agency's Superfund Treatability Database
repository. One copy of each treatability study report must be
sent to:
Glenn Shaul
MS 445
U. S. Environmental Protection Agency
Superfund Treatability Database
ORD/RREL
26 West Martin Luther King Dr.
Cincinnati, Ohio 45268
4.7 SCHEDULE
The Work Plan includes a schedule for completing the
treatability study. The schedule gives the anticipated starting
date and ending date for each of the tasks described in the
work plan and shows how the various tasks interface. The
time span for each task accounts for the time required to obtain
the Work Plan, subcontractor, and other approvals (e.g.,
disposal approval from a commercial TSDF); sample
procurement time, if necessary; analytical
turnaround time; and review and comment period for reports
and other project deliverables. Some slack time also should be
built into the schedule to accommodate unexpected delays
(e.g., bad weather, equipment downtime) without affecting the
project completion date. The schedule is usually displayed in
the form of a bar chart (Figure 4-2). If the study involves
multiple tiers of testing, all tiers should be shown on one
schedule. Careful planning before the start of the tests is
essential. Depending on the review and approval process,
planning can take up to several months.
Setup of the laboratory and procurement of necessary
equipment and lab supplies for treatability studies may take a
month. Depending on how rapidly laboratory results can be
provided, analytical results can be available in less than 30
days. Shorter analytical turnaround time can be requested, but
this will normally double the costs. Compounds such as
pesticides and PCBs may require longer turnaround times due
to the extractions and analyses involved. Depending on the
objectives, the duration of treatability tests may be longer.
Interpretation of the results and final report writing may take
up to 4 months, but this is highly dependent on the review
process. Remedy screening typically takes 3 to 4 months to
complete treatability testing and results reporting. It is not
unusual for the remedy selection phase to take 11 or 12 months
before treatability testing and results reporting can be
completed.
4.8 MANAGEMENT AND STAFFING
The Work Plan discusses the management and staffing of
350
fc
300-
250-
200-
150-
100-
50-
0
0
4 6
Extraction Pass No.
10
Figure 4-1. Example of pass-by-pass PCB concentration plot.
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the remedy selection treatability study. The Work Plan
specifically identifies the personnel responsible for executing
the treatability study by name and qualifications. Generally,
the following is an example of the types of expertise needed for
the completion of the treatability study:
• Project Manager (Work Assignment Manager)
• QA Manager
• Chemist
• Chemical Engineer
• Lab Technician
Responsibility for various aspects of the project is typically
shown in an organizational chart such as the one in Figure 4-3.
4.9 BUDGET
The Work Plan discusses the budget for completion of the
remedy selection treatability study. Testing costs for remedy
selection depend on a variety of factors. Table 4-2 provides a
list of potential maj or cost estimate components for this tier or
mosttests, the largest single expense is the analytical program.
Sites where the soil and sediment types, contaminant types,
and contaminant concentration vary widely will usually require
more
Months From Project Start
Activity Description
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Data Review
S/C, SAP, HSP, CRP Prep
Remedy Screening
Laboratory Test(s)
Data Analysis
Remedy Selection Test
Bench-Scale Tests
Data Analysis
Pilot-Scale Test
Data Analysis
Final Report
Remedy
Screening
Rernedy Selection
Site Remediation
and RI/FS
Schedule Overview
I I
emedial Investigation - Solvent Extraction
I I. I I
Feasibility Study - All Technologies
Figure 4-2. Example project schedule for a solvent extraction treatability study program.
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samples than sites where the soil and contamination is more
homogeneous. It is not unusual for the sampling, analysis, and
QA activities to represent 50 percent of the total treatability
study cost. In general, the costs for analyzing organics are
more expensive than for metals. Actual costs will vary
according to individual laboratories, required turnaround
times, volume discounts, and any customized testing.
Table 4-2. Major Cost Elements Associated with
Remedy Selection Solvent Extraction Studies
Cost Element
Cost Range
(thousands of $)
Initial Data Review
Work Plan Preparation
Field Sample Collection
Field Sample Chemical Analysis
Laboratory
1 -
1 -
1 -
4 -
4 -
10
05
10
25
25
Setup/Materials/Testing
Treatability Test Chemical
Analysis
Data
Presentation/Report/Remediation
Cost Estimate
4 - 20
5 - 25
Sampling costs will be influenced by the contaminant types
and depth of contamination found in the soil, sludge, or
sediment. The health and safety considerations during
sampling activities are more extensive when certain
contaminants, e.g., volatile organics, are present. Level B
personal protective equipment (PPE) rather than Level D PPE
can increase the cost component an order of magnitude.
Sampling equipment for surface samples is much less
complicated than equipment for deep samples. Depending on
the number of samples and tests specified, residuals
management (e.g., contaminated solvent and water) will require
proper treatment and/or disposal. Treatment and disposal of
the residuals as hazardous wastes increases costs
significantly.
Other factors to consider include report preparation and the
availability of vital equipment and laboratory supplies.
Generally, an initial draft of the report undergoes internal
review prior to the final draft. Depending on the process, final
report preparation can be time-consuming as well as costly.
Procurement of specialized testing equipment (e.g.,
bench-scale pressurized system) and laboratory supplies (e.g.,
reagents and glassware) will also increase the costs.
Typical costs for remedy selection tests are estimated to be
from $20,000 to $120,000. The cost of remedy screening, with
its associated lack of replication and detailed testing, is
approximately 25 percent of these costs. These estimates are
highly dependent on the factors discussed above. Not
included in these costs are the cost of governmental
procurement procedures, including soliciting for bids,
awarding contracts, etc.
TOTAL COST RANGE
20 - 120
LAB TECHNICIANS
• Execute Treatability
Studies
• Execute sample
collections and analysis
CONTRACT WORK
ASSIGNMENT MANAGER
• Report to EPA Remedial
Project Manager
« Supervise Overall Project
QAMAN
• Oversee Qt
Assurance
• Prepare ap
sections of
Work Plan
CHEMICAL ENGINEER
• Oversee Treatability
Study execution
• Oversee sample
collection
• Prepare applicable
sections of Report and
Work Plan
ACER
lality
3rogram
Dlicable
Report and
CHEMIST
• Oversee sample
collection and analysis
• Prepare applicable
section of Report and
Work Plan
Figure 4-3. Example organizational chart.
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SECTION 5
SAMPLING AND ANALYSIS PLAN
The Sampling and Analysis Plan (SAP) consists of two
parts-the Field Sampling Plan (FSP) and the Quality
Assurance Project Plan (QAPjP). The purpose of this section
is to identify the contents of and aid in the preparation of
these plans. The RI/FS requires a SAP for all field activities.
The SAP ensures that samples obtained for characterization
and testing are representative and that the quality of the
analytical data generated is known and appropriate. The SAP
addresses field sampling, waste characterization, and sampling
and analysis of the treated wastes and residuals from the
testing apparatus or treatment unit. The SAP is usually
prepared after Work Plan approval.
5.1 FIELD SAMPLING PLAN
The FSP component of the SAP describes the sampling
objectives; the type, location and number of samples to be
collected; the sample numbering system; the equipment and
procedures for collecting the samples; the sample
chain-of-custody procedures; and the required packaging,
labeling and shipping procedures.
Field samples are taken to provide baseline contaminant
concentrations and contaminated material for treatability
studies. The sampling objectives must be consistent with the
treatability test objectives.
The primary objectives of remedy selection treatability studies
are to evaluate the extent to which specific chemicals are
removed from soils, sediments, sludges or water. The primary
objectives for collecting samples to be used in remedy
selection treatability testing include:
• Acquisition of samples representative of conditions
typical of the entire site or defined areas within the site.
Because a mass balance is required for this evaluation,
statistically designed field sampling plans may be
required. However, professional judgment regarding
thesampling locations may be exercised to select
sampling sites that are typical of the area (pit, lagoon,
etc.) or to appear to have above average concentrations
of contaminants in the area being considered for the
treatability test. This may be difficult because reliable
site characterization data may not be available early in
the remedial investigation.
• Acquisition of sufficient sample volumes necessary for
testing, analysis, and quality assurance and quality
control. For remedy screening, about 5 kg will be
required. During remedy selection, the amount of
sample will depend on the size of the test and the
number of test samples.
From these two primary objectives, more specific objectives
are developed. When developing the more detailed obj ectives,
consider the following types of questions:
• Should samples be composited to provide better
reproducibility for the treatability test? This question,
including the type of compositing, is addressed in
subsection 4.4.1.
• Is there adequate data to determine sampling locations
indicative of the more contaminated areas of the site?
Have soil gas surveys been conducted? Contaminants
may be widespread or isolated in small areas (hot spots).
Contaminants may be mixed with other contaminants in
one location and appear alone in others. Concentration
profiles may vary significantly with depth.
• Are the soils homogeneous or heterogeneous? Soil types
can vary across a site and will vary with depth.
Depending on professional judgement, contaminated
samples for various soil types may have to be taken to
conduct treatability tests.
• Are contaminants present in sediments, sludges, or
water? Different sampling methods must be used for these
media.
• Is sampling of a "worst-case" scenario warranted?
Assessment of this question must be made on a site-
by-site basis. Hot spots and contaminants in different
media may be difficult to treat. These should be factored
into the test plan if they represent a significant portion of
the waste site.
After identifying the sampling objectives, an appropriate
sampling strategy is described. Specific items that should be
briefly discussed and included are listed in Table 5-1.
5.2 QUALITY ASSURANCE PROJECT
PLAN
The QAPjP consists of eleven sections. Since many of these
sections are generic and applicable to any QAPjP and are
covered in available documents,(24)(32) this guide will discuss
only those aspects of the QAPjP that are affected by the
treatability testing of solvent extraction.
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Table 5-1. Suggested Organization of Sampling
and Analysis Plan
Field Sampling Plan
1.
2.
3.
4.
5.
Site Background
Sampling Objectives
Sample Location and Frequency
-Selection
-Media Type
-Sampling Strategy
-Location Map
Sample Designation
-Recording Procedures
Sample Equipment and Procedures
-Equipment
-Calibration
-Sampling Procedures
Sample Handling and Analysis
-Preservation and Holding Times
-Chain-of-Custody
-Transportation
Quality Assurance Project Plan
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Project Description
-Test Goals
-Critical Variables
-Test Matrix
-Project Organization and Responsibilities
QA Objectives
-Precision, Accuracy, Completeness
-Method Detection Limits
Sampling Procedures and Sample Custody
Analytical Procedures and Calibration
Data Reduction, Validation, and Reporting
Internal QC Checks
Performance and System Audits
Calculation of Data Quality Indicators
Corrective Action
QC Reports to Management
References
5.2.1 Experimental Description
Section 1 of the QAPjP must include an experimental project
description that clearly defines the experimental design, the
experimental sequence of events, each type of critical
measurement to be made, each type of matrix (experimental
setup) to be sampled, and each type of system to be
monitored. This section may reference Section 4 of the Work
Plan. All details of the experimental design not finalized in the
Work Plan should be defined in this section.
Items in this section include, but are not limited to the
following:
• Number of samples (areas or locations) to be studied
• Identification of treatment conditions (variables) to be
studied for each sample
• Target compounds for each sample
• Number of replicates per treatment condition
• Criteria for technology retention or rejection for each
type of remedy selection test.
The Project Description clearly defines and distinguishes the
critical measurements from other observations and system
conditions (e.g., process controls, operating parameters, etc.)
routinely monitored. Critical measurements are those
measurements, data gathering, or data generating activities
that directly impact the technical objectives of a project. At a
minimum, the determination of the target compound (identified
above) in the initial and treated solid samples will be critical
measurements for remedy selection tests. Concentrations of
target compounds in all fractions and the amount of solvent
recovered will be critical measurements for remedy design
tests.
5.2.2 Quality Assurance Objectives
Section 2 lists the QA objectives for each critical measurement
and sample matrix defined in Section 1. These objectives are
presented in terms of the six data quality indicators: precision,
accuracy, completeness, representativeness, comparability,
and, where applicable, method detection limit.
5.2.3 Sampling Procedures
The procedure used to obtain field samples for the treatability
study are described in the FSP. They need not be repeated in
this section, but should he incorporated by reference.
Section 3 of the QAPjP contains a description of a credible
plan for subsampling the material delivered to the laboratory
for the treatability study. The methods for aliquoting the
material for determination of chemical and physical
characteristics such as bulk density or specific gravity,
moisture content, contaminant concentration, etc. must be
described.
5.2.4 Analytical Procedures and
Calibration
Section 4 describes or references appropriate analytical
methods and standard operating procedures for the analytical
method for each critical measurement made. In addition, the
calibration procedures and frequency of calibration are
discussed or referenced for each analytical system, instrument,
device, or technique for each critical measurement.
The methods for analyzing the treatability study samples are
the same as those for chemical characterization of field
samples. Table 2-1 presents suitable analytical methods.
Preference is given to methods in "Test Methods for
Evaluating Solid Waste", SW-846,3rd. Ed., November 1986.(37)
Other standard methods may be used, as appropriate.(2-"-3)i:30)
Methods other than gas chromatography/mass spectroscopy
(GC/MS) techniques are
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recommended to conserve costs, when possible, at the remedy
screening level.
5.2.5 Data Reduction, Validation and
Reporting
Section 5 includes, for each critical measurement and each
sample matrix, specific presentation of the requirements for
data reduction, validation and reporting. Aspects of these
requirements are covered in subsections 4.5,4.6, and 6.1 of this
guide.
5.2.6 Quality Control Reports
Section 10 describes the QA/QC information that will be
included in the final project report. As a minimum, reports
include:
• Changes to the QA Project Plan
• Limitations or constraints on the applicability of the
data
• The status of QA/QC programs, accomplishments, and
corrective actions
• Results of technical systems and performance
evaluation QC audits
• Assessments of data quality in terms of precision,
accuracy, completeness, method detection limits,
representativeness, and comparability.
The final report contains all the QA/QC information to support
the credibility of the data and the validity of the conclusions.
This information may be presented in an Appendix to the
report. Additional information on data quality objectives1-24-1
and preparation of QAPjPs(32) is available in EPA guidance
documents.
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SECTION 6
TREATABILITY DATA INTERPRETATION
Proper evaluation of the potential of solvent extraction for
remediating a site must compare the test results (described in
subsection 4.5) to the test goals (described in subsection 4.1)
for each tier. The evaluation is interpreted in relation to seven
of the nine RI/FS evaluation criteria, as appropriate. The
remedy screening tier establishes the general applicability of
the technology. The remedy selection tier demonstrates the
applicability of the technology to a specific site. The remedy
design tier provides information in support of the evaluation
criteria. The test objectives are based on established cleanup
goals or other performance-based specifications (such as
removal efficiency). Solvent extraction testing must consider
the technology as part of a treatment train.
Subsection 4.6 of this guide discusses the need for the
preparation of interim and final reports and refers to a
suggested format. In addition to the raw and summary data for
the treatability study and associated QC, the treatability report
should describe what the results mean and how to use them in
the feasibility study in both screening and selection of
alternatives. The report must evaluate the performance of the
technology and give an estimate of the costs of final
remediation with the technology.
6.1 TECHNOLOGY EVALUATION
Remedy screening treatability studies typically consist of
simple laboratory tests. The contaminant concentration in the
solids fraction, or water before extraction, is compared to the
contaminant concentration in the same fraction after extraction.
A removal of approximately 50 to 70 percent of the
contaminants during the test indicates additional treatability
studie s are warranted. Contaminant concentrations can also be
determined for wastewater and solvent fractions. These
additional analyses add to the cost of the treatability test and
may not be needed. Before and after concentrations can
normally be based on duplicate samples at each time period.
The mean values are compared to assess the success of the
study. A number of statistical texts are available if more
information is needed. KK11^12)
Remedy screening tests can sometimes be skipped when
information about the contaminant solubilities in the selected
solvent is sufficient to decide whether remedy selection
studies will be useful. This information should be solvent- and
contaminant-specific and may or may not be applicable to
other sites. Expert assistance is needed for evaluation of data
for a site. Example 3 demonstrates a prescreening evaluation
and the decision to bypass a remedy screening test.
The remainder of this section discusses the interpretation of
data from remedy selection treatability studies. Subsections 4.1
and 4.2 of this guide discuss the goals and design of remedy
selection treatability studies, respectively. Typically,
contaminant concentrations in the contaminated matrix before
and after solvent extraction are measured in triplicate. A
reduction in the mean concentration to cleanup levels, if
known, or by approximately 90 to 99 percent indicates solvent
extraction is potentially useful in site remediation. A higher QA
level is required with this tier of testing. A number of other
factors must be evaluated before deciding to proceed to
remedy design studies.
In scaling the cost and performance estimates from remedy
selection testing to full-scale solvent extraction systems, the
parameters for consideration are:
• Performance capabilities of the solvent extraction
process including design parameters
• Residualcontaminants and contaminant concentrations
in the solids fraction
• Contaminants and contaminant concentrations in the
used solvent, in the fine soils, and in the concentrated
contaminant product
• Risk analysis evaluation for worker and community
protection
• Quantity of oversized screenable material
• Amount of contaminated water generated in dewatering
and distillation processes.
The design parameters for the solvent extraction process
include material throughput and optimum solvent usage in
gallons per dry ton of solids or gallon of water. It is important
to estimate the volume and physical and chemical
characteristics of each fraction to design treatment systems
and estimate disposal costs. The ability to cost-effectively
recover used solvent is also important for cost and
performance estimates. Removal efficiency, measured as a
function of the number of extraction stages, canbe used to
determine the number of stages required to reach cleanup
levels.
The final concentration of contaminants in the recovered
(clean) solids fraction, in the solvents, in solvent distillation
bottoms, and in water fractions are important to evaluating the
feasibility of solvent extraction. The selection of technologies
to treat the solvent or solvent still bottoms
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and water fraction from soil/sludges depends upon the types
and concentrations of contaminants present. The amount of
volume reduction achieved in terms of contaminated media is
also important to the selection of solvent extraction as a
potential remediation technology.
Contamination in excavated soils and sediments can pose
safety concerns for workers and community. Worker
protection may be required during soil excavation. The need
for such protection is a site-specific decision. Health and
safety plans should be prepared and a risk analysis conducted
for the site.
The quantity of large rocks, debris and other oversize
screenable material that must be removed is an important
measurement. While this is not a "laboratory" measurement, it
is important to determine which treatment method is most
suitable for preparing the bulk soil or sediment for entry into
the solvent extraction process, i.e., screening to remove large
rocks, stumps, debris, and washing or crushing of oversize
materials, etc. The quantity and degree of contamination of
water is important for design of ultimate treatment systems.
The water could be the media to be treated or could be
associated with a soil/sludge media.
6.2 ESTIMATION OF COSTS
Accurate cost estimates for full-scale remediation are crucial to
the feasibility study process and the subsequent detailed
analysis of alternatives. Comparisons of various technologies
must be based on the most complete and accurate estimates
available. Remedy screening treatability studies cannot
provide this type of information. However, preliminary cost
estimates for full-scale remediation may be made from remedy
selection data. Such estimates may be good enough for
comparisons to other technologies at the same tier oftesting.
On this basis, the estimates can form the basis of the ROD.
Pilot-
scale tests yield more accurate estimates of full-scale
performance and costs. This is especially true since solvent
extraction will form only one component of a treatment train. If
the results of remedy selection treatability testing indicate that
solvent extraction can be effective, consideration may be given
to pilot-scale testing. The cost for pretreatment of media and
post-treatment of contaminated solids, still bottoms, and /or
water from the solvent extraction process must also be
evaluated.
6.2.1 Solvent Extraction Pilot-Scale
Cost Estimates
Pilot-scale tests can be used to obtain a preliminary cost
estimate for full-scale remediation. Bench-scale does not give
information on all major cost estimate components in a
full-scale solvent extraction operation. The major cost estimate
components which can be determined based on pilot-scale
results and site characterization data are as follows:
• Analytical
• Excavation
• Material handling and transport
• Pretreatment
• Treatment cost and throughput
• Treatment and/or disposal of residuals.
6.2.2 Actual Full-Scale Solvent
Extraction Cost Estimates
Full-scale solvent extraction cost estimates will be solvent-and
site-specific. As of Spring 1991 only six sources of portable
soil/sludge extraction units were identified:
Example 3. Decision to Bypass Remedy Screening
A harbor sediment was being considered for solvent extraction. The sediment was contaminated with medium
to high levels of PCBs. The sediment samples had a consistency similar to many sludges which had been
extracted in previous studies. Although the concentration of PCBs was the highest that had been observed in
any of the RIs involving solvent extraction, treatability studies had been performed on samples with the same
order of magnitude of PCB contamination.
The technology vendor and resident solvent extraction expert were confident that the remedy screening study
could be passed over, and the remedy selection study started immediately to identify the level of removal
which could be expected in the remedy design and the remediation. The RPM agreed, and the remedy
selection study was designed and implemented.
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CF System's process
RCC'sB.E.S.T.™ process
ART's LEEP™ process
Nukem Development's process
Sanivan Group's Extraksol™
Terra Kleen's Soil Restoration Unit
Dehydro-Tech's
Carver-Greenfield Process
Approximate feed capacity1
0.2 tons/hour2
3 tons /hour3
1 ton/hour
ND4
1 ton/hour
2 tons/hour
ND4
1 May vary depending upon feed material and contaminant
concentration
2 Modular system may be used to increase capacity
3 110 Ib/day pilot unit also available
4 Process feed capacity not determined
Cost estimates for full-scale solvent extraction range from
$90 to $800/ton.(23)(28) These estimates were provided by
various vendors. It was not possible to determine from the
estimates the extent of pre-or post-treatment associated with
the costs, the operating parameters of their equipment, or the
target cleanup levels required at the associated sites.
Cost estimates with one commercial-size system were
determined using a base case (880,000 tons of sediment
containing 850 ppm of PCB) to a hot spot case (63,000 tons of
sediments containing 10,000 ppm of PCB). The base case cost
estimate with pre- and post-treatment was $ 148/ton using two
250-ton/day capacity units in parallel. The hot spot case cost
estimate was $447/ton using a 100-ton/day capacity system
consisting of two modules in series, with each module
containing extraction and solvent recovery units in series.
Another vendor reported cost estimates of $90/ton using a
200-ton/day facility. The cost for using a smaller facility
treating 30 tons/day increased to $280/ton. These projected
costs are based on the use of 25 ydVday modules. Foranother
site, the vendor used operational experience to estimate that
the cost of operating a 30-ton/day module could range from
$150to$800/ton.
General factors affecting full-scale cleanup cost for solvent
extraction are, the contaminants of concern, the required
cleanup levels at the site, and the specific type of equipment
selected for use. Specific factors affecting costs include the
number of cycles for continuous processes, the number of
extraction stages for batch processes, the size of the site, the
initial concentration of contaminant(s), the type of soil, the
amount of oversized materials, the type of foreign materials in
the soil (metal nuts and bolts, building debris, etc.), the
distance to the site, requirements for further treatment of
residuals, insurance required, and bonding required. The
disposal options for process waste streams and laboratory
requirements for process sample analysis will also affect costs.
Potential cost factors such as field change orders issued will
be undetermined until remediation has been initiated.
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SECTION 7
REFERENCES
7.
9.
10.
11.
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