Section 121(b) of 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 remedy selection and implementation. They should be performed as
soon as it becomes evident that the available information is insufficient to ensure the quality of the decision. Conducting treatability
studies early in the remedial investigation/feasibility study (RI/FS) process should reduce uncertainties associated with selecting the
remedy and should provide a sound basis for the Record of Decision (ROD). Regional planning should factor in the time and resources
required for these studies.
This fact sheet provides a summary of information to facilitate the planning and execution of soil vapor extraction (SVE) remedy
screening and remedy selection treatability studies in support of the RI/FS and the remedial design/remedial action (RD/RA) processes.
Detailed information on designing and implementing remedy screening and remedy selection treatability studies for SVE is provided in
the "Guide for Conducting Treatability Studies Under CERCLA: Soil Vapor Extraction," Interim Guidance, EPA/540/2-91/019A, September
1991.
United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
EPA/540/2-91/019B
September 1991
Guide for Conducting Treatability
*	Studies under CERCLA:
Soil Vapor Extraction
Office of Emergency and Remedial Response
Hazardous Site Control Division OS-220
QUICK REFERENCE FACT SHEET
INTRODUCTION
There are three levels or tiers of treatability studies: remedy
screening, remedy selection, and remedy design. The "Guide for
Conducting Treatability Studies Under CERCLA: Soil Vapor
Extraction" discusses all three levels of treatability studies.
Remedy screening studies provide a quick and relatively
inexpensive indication of whether SVE is a potentially viable
remedial technology. Remedy selection studies provide data that
permit evaluation of SVE's ability to meet expected site cleanup
goals and provide information in support of the detailed analysis of
the alternative (i.e., seven of the nine evaluation criteria specified
in the EPA's RI/FS Interim Final Guidance Document,
OSWER-9335.301). Remedy selection tests generally have
moderate costs and may require weeks to months to complete.
Remedy design testing provides quantitative performance, cost,
and design information for remediating the operable unit. Remedy
design studies are of moderate to high costs and may require
months to complete.
TECHNOLOGY DESCRIPTION AND
PRELIMINARY SCREENING
Technology Description
The SVE process is an in situ technique for the removal of
volatile organic compounds (VOCs), and some semivolatile
organic compounds (SVOCs), from the vadose zone. The vadose
zone is the subsurface soil zone located between the surface soil
and the top of the water table. SVE is used with other
technologies in a treatment train since it transfers contaminants
from soil to air and water wastestreams.
Figure 1 is a generalized schematic diagram of an SVE
system. SVE treatment is conducted as follows. Vapor extraction
wells or vents (1) are installed in the contaminated zone. As air is
removed from the soil, ambient air is injected (2) or is drawn into
the subsurface at locations around the contaminated site. When
ambient air passes through the soil, contaminants are volatilized
and removed. Entrained liquids are separated (3)
from the contaminated air stream and the liquids
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are treated (6) to remove contaminants. The contaminated gas Is
drawn through a blower (4), treated (5), and discharged to the
atmosphere.
As of fiscal year 1991 (FY 91), SVE has been selected as
the remedial technology, or a component thereof, for over 30 sites.
SVE was chosen as a component of the ROD at 10 sites in 1988,
and 17 sites in 1989. SVE has had widespread use in cleaning up
spills and leaks of hydrocarbons and other volatile organics at
non-Superfund sites.
Prescreening Characteristics
The determination of the need for and the appropriate tier of
treatability study required is dependent on the literature
information available on the technology, expert technical judgment,
and site-specific factors. The first two elements - the literature
search and expert consultation - are critical factors of the
prescreening phase in determining whether adequate data are
available or whether a treatability study is needed.
Information on the technology applicability, the latest
performance data, the status of the technology, and sources for
further information are provided in one of a series of engineering
bulletins being prepared by the EPA Risk Reduction Engineering
Laboratory in Cincinnati, Ohio.
A literature search should be performed to determine the
physical and chemical properties of the contaminants of interest.
In conjunction with the site conditions and soil properties,
contaminant properties will dictate whether SVE is feasible. SVE
is most effective at removing compounds which have high vapor
pressure and which exhibit significant volatility at ambient
temperatures in contaminated soil. Low molecular weight, volatile
compounds are most easily removed by SVE. Trichloroethene,
trichloroethane, tetrachloroethene, and many gasoline
constituents have been effectively removed by SVE. Compounds
which are less suitable for removal include less volatile
contaminants such as trichlorobenzene, heavy petroleum fuels,
and extremely water-soluble volatiles such as acetone.
The soil characteristics of the site have a significant effect on
the applicability of SVE. The air permeability of the contaminated
soils controls the rate at which air can be drawn through the soil
by the applied vacuum. The soil moisture content or degree of
saturation is also important. It is usually easier to extract VOCs
from drier soils due to the greater availability of pore area, which
permits higher air-flow rates. However, extremely dry soils may
tenaciously hold VOCs, which are more easily desorbed when
water competes with them for adsorption sites. This phenomenon,
which may be important in the southwestern states, favors a
certain quantity of moisture to prevent sorption of contaminants.
Soils with high clay or humic content generally provide
high adsorption potential for VOCs, thus leading to higher
residual levels of adsorbed contaminants in these matrices.
Clayey or silty soils, however, may be effectively ventilated
by the usual levels of vacuum developed in an SVE system,
he success of SVE in these soils may depend on the
presence of more permeable strata (as would be expected
in alluvial settings) or on relatively low moisture contents in
Clean Air
Vacuum
Blower
Process Residual
Extracted
Vapor
Vapor-
Liquid
Separator
Extraction
Well
Clean Water,
Process Residual
Air Vent or
Injection Well
Air Vent or
Injection Well
Impermeable Cap (7)
Ground Surface
Contaminated
Vadose
Zona
Water Table —
Figure 1. Generic Soil Vapor Extraction System.
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the finer grained soils. Soil and ambient temperatures affect the
performance of an SVE system primarily because they influence
contaminant vapor pressure. At lower temperatures the potential
for contaminant volatilization decreases.
the treatability studies and when applying the technology.
THE USE OF TREATABILITY STUDIES IN
REMEDY EVALUATION
Prescreening of SVE examines the field data for types of
contaminant, concentration of the contaminant, and soil
temperature to determine contaminant vapor pressure. If the
vapor pressure of the contaminants of concern is below 0.5 mm
of Hg, SVE is considered to be generally unsuitable. If the vapor
pressure at the temperature of the soil is above 0.5 mm of Hg,
treatability testing should be conducted.
Technology Limitations
Limitations of the SVE technology are those
charactedstics of the contaminants, soil, and site that hinder the
extraction of the contaminants from the unsaturated soil. Low
vapor pressure of the contaminants and low air permeability of
the soil are the two most important factors that limit SVE
technology.
Uncertainty appears to limit SVE as well as other in situ
technologies. Areas of uncertainty include lack of precise
information on site heterogeneities and contaminant location,
inability to predict cleanup times, and doubt in some cases
whether cleanup goals can be achieved (e.g., operation in
fractured bedrock or at sites with very low cleanup targets).
These areas of uncertainty must be recognized when conducting
Treatability studies should be performed in a systematic
fashion to ensure that the data generated can support the
remedy evaluation process. The results of these studies must
be combined with other data to fully evaluate the technology.
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 are management-based
decisions in which the time and cost of 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 or new site data).
Technologies may be evaluated first at the remedy
screening level and progress through the remedy selection to
the remedy design level. A technology may enter, however, at
whatever level is appropriate based on experience with the
technology and contaminants of concern and site-specific
factors. Figure 2 shows the relationship of three levels of
treatability study to each other and to the RI/FS process.
Remedial Investigation/
Feasibility Study (RI/FS)
Identification
of Alternatives
Scoping
- the -
RI/FS
Literature
Screening
and
Treatability
Study Scoping
Site
Characterization
and Technology
Screening
REMEDY
SCREENING
to Determine
Technology Feasibility
Record of
Decision
(ROD)
Remedy
Selection
Remedial Design/
Remedial Action -
(RD/RA)
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 2. The Role of Treatability Studies in the RI/FS and RD/RA Process.
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Remedy Screening
Remedy screening, the first tier of testing, is used to
screen the ability of a technology to treat a contaminated soil
using simple column tests. These studies are generally low cost
(e.g., $10,000 to $50,000) and usually require days to complete.
This tier is frequently skipped for evaluation of SVE technology.
Remedy Selection
Remedy selection, the second tier of testing, Is used to
evaluatethe technology's performance on a contaminant-specific
basis for an operable unit. These studies generally have
moderate costs (e.g., $30,000 to $100,000 for SVE) and may
require weeks to months to complete. They yield data that verify
the technology's ability to meet expected cleanup goals and
provide Information in support of the detailed analysis of
alternatives in the CERCLA Feasibility Study (FS). Column tests
are run until an end-point is achieved. Treatability studies may
be supplemented with field air permeability tests and
mathematical modeling during the remedy selection phase. The
combination of column tests, field air permeability tests, and
mathematical modeling provide quantitative and qualitative
performance information for the evaluation of SVE, as well as
some cost and design information. However, due to the high
degree of uncertainty associated with implementation of SVE,
pilot-scale testing is often appropriate to support the remedy
selection phase.
Column tests establish whether SVE can potentially meet
expected target concentrations for a given site. They can also
provide information on the contaminant distribution functions
(partition functions) for use with certain mathematical models.
Column tests do not, however, give reliable air permeability data.
They do not permit the determination of whether mass transfer
limitations will occur in the field application of SVE. The duration
and cost of column testing for SVE depend primarily on the soil
characteristics, the contaminants, the analyses being
performed, and the number of replicates required for adequate
testing. Most remedy selection column testing can be performed
within 3 to 7 weeks at a cost between $30,000 and $50,000.
Air permeability tests should be conducted at the site after
the column tests show that SVE can meet the expected target
concentrations. Air permeability tests provide information on the
air permeability of the different geological soil formations in the
vadose zone at the site. Air permeability data can be used
during the initial design to determine the radius of influence of
vapor extraction wells, expected air-flow rates, moisture removal
rates, and initial contaminant flow rates (when the effluent gas
is analyzed). The air permeability tests cost about $1,500 to
$2,500 per well. Total costs may run from $10,000 to $50,000.
They are normally performed within a time range of 2 to 5 days.
Mathematical modeling can be used to provide rough
estimates of the cleanup times required to achieve contaminant
reductions to the target goals. These predictions are
needed to evaluate health risks associated with short-term
effectiveness and to estimate the total cost of the remediation.
Mathematical modeling can also provide sensitivity analyses for
critical variables such as air permeability, radius of influence,
and vacuum applied. To be most effective, the modeling should
use field-measured data on contaminant concentrations, air
permeability, location of contaminants, soil porosity, soil
moisture content, and soil temperature. Partition coefficients are
obtained from column test measurements. The above field and
column test data are the input variables to the model.
Pilot-scale testing for remedy selection is required for sites
that have contamination in the bedrock, and complex sites that
are very heterogeneous. Sites that contain pools of NAPL may
also require pilot-scale testing. Pilot-scale tests determine
whether sufficient air flow can be achieved in the zones of
contamination to produce adequate cleanup rates. Pilot-scale
data can also be used to determine the radius of influence of the
vapor extraction wells, moisture-removal rates, and contaminant
flow rates.
For complete characterization of the SVE process, the
mathematical model must simulate both the flow field in the soil
and the behavior of the contaminants within the soil matrix. In
general, mathematical models provide a lower bound estimate
of the time required to remediate a site using SVE. Therefore,
lengthy cleanup time predictions from a model must be
seriously considered as an indicator for discontinuing treatability
assessments of SVE.
Remedy Design
Remedy design is the third tier of testing. It is used to
provide quantitative performance, cost, and design information
for remediating an operable unit. This level of testing also can
produce data required to optimize performance. These studies
are of moderate to high cost (e.g., $50,000 to $250,000 for SVE)
and may require months to complete. They yield data that verify
performance to a higher degree than remedy selection tests and
provide detailed design information. Generally, remedy design
would be performed by a vendor after the ROD.
TREATABILITY STUDY WORK PLAN
Carefully planned treatability studies are necessary to
ensure that the data generated are useful for evaluating the
validity or performance of the technology. The Work Plan sets
forth the contractor's proposed technical approach to the tasks
outlined in the RPM's Work Assignment. It also assigns
responsibilities, establishes the project schedule, and estimates
costs. The Work Plan must be approved by the RPM before
work begins. A suggested organization of the SVE treatability
study Work Plan is provided in the "Guide for Conducting
Treatability Studies Under CERCLA: Soil Vapor Extraction."
Test Goals
The overall SVE treatability study objectives must meet the
specific needs of the RI/FS. There are nine evaluation
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criteria specified in the EPA's RI/FS Interim Final Guidance
Document (OSWER-9335:301). Treatability studies can provide
data upon which seven of these criteria may be evaluated.
Treatability study goals are the specific cleanup standards
or removal rates designed to meet the test objectives. Setting
goals for the treatability study is critical to the ultimate
usefulness of its results. These goals must be well defined
before the study is performed. Each tier or phase of the
treatability study program requires appropriate performance
goals. For example, column tests could answer the question,"
Will SVE reduce contaminants to the required concentrations?"
The remedy selection column tests measure whether the
process could reduce contamination to below the anticipated
performance criteria specified in the ROD. This would indicate
that the process has potential applicability at the site and further
testing is warranted. Bench-scale column tests are used for
remedy screening. Remedy screening goals should simply
require that the contaminant of interest shows a greater than 80
percent reduction in concentration in soil. The goal is to show
SVE has the potential to work at the site. Normally, sufficient
information exists about soil conditions and contaminant
volatility so that remedy screening tests will not be necessary.
Column tests for remedy selection can determine if
ultimate cleanup levels can be met. When SVE is the primary
treatment technology, the suggested cleanup goals are set by
the ARARs.
Field air permeability tests are conducted during remedy
selection. A field air permeability of greater than 1010 cm2 (0.01
darcies) appears to be the lower feasibility limit for site air
permeability. If the permeability is lower, the technology may not
be feasible.
Pilot-scale testing frequently is used during remedy
selection. Pilot-scale or field venting tests usually encompass
the operation of a mobile SVE treatment unit onsite for a period
of 1 to 2 months. For more complex sites (e.g., sites with
different types of contaminants in separate areas or with varying
geological structures), the test rig may need to be moved around
the site and much longer overall testing periods may be
required. The goal of pilot-scale testing is to confirm that the
cleanup levels and treatment times estimated for site
remediation are achievable. This goal is accomplished by
checking for diffusion control or problems due to the site
conditions.
Experimental Design
Careful planning of experimental design and procedures is
required to produce adequate treatability study data. The
experimental design must identity the critical parameters and
determine the number of replicate tests necessary. System
design, test procedures, and test equipment will vary among
vendors. The information presented in this section provides an
overview of the test equipment and procedures as they relate to
each type of test.
Properly designed column tests for remedy selection
determine the practical cleanup limits of the contaminated soil
and the partition coefficient for use with mathematical modeling.
The key design variables for SVE column tests are contaminant
concentrations and air-flow rates. Composite samples of soil
should be prepared for the column tests. Compositing reduces
the variability in contaminant concentration, providing more
accurate soil concentration data before and after the column
testing. Some volatiles will be lost during compositing. Samples
should be collected from the zone of maximum contaminant
concentrations. They should also be collected from areas of the
site that have different types of VOCs or low-boiling
semivolatiles. For these purposes, a sufficient number of split
spoon samples should be taken from each area of concern to
provide enough material for five column tests and for analytical
testing for the contaminants of interest. Shelby tube samples
should also be taken for moisture, density, and porosity
measurements of each contaminated geological structure. Since
air-flow rates vary within the zone of influence of a vapor
extraction well, column tests should be run at a minimum of two
air-flow rates. A total of four tests, conducted at the higher flow
rates, may be required to determine the maximum cleanup level.
Onsite air permeability tests should be performed on each
geological formation identified during the site characterization.
The tests should be performed in areas of high contaminant
concentrations and in areas of lower contamination where
contaminants with different properties have been found. Figure
3 shows a typical air permeability test. A vapor extraction probe
or extraction well is connected to a vacuum pump. Piezometric
probes measure soil pressure levels at various horizontal and
vertical distances from the extraction point. Contaminant
concentrations may be measured with a portable gas
chromatograph (GC).
Since mathematical modeling of SVE requires special
expertise, modeling experts should be consulted for technical
assistance in applying mathematical models. Improper use of
mathematical models can lead to incorrect conclusions.
Pilot-scale tests conducted during remedy selection
determine whether sufficient air flow can be attained in the
zones of contamination to produce adequate cleanup rates. The
design should incorporate the available field data, including air
permeability measurements, and the locations and
concentrations of contaminants. Mathematical modeling may
supplement the above data. The piiot-scale unit typically
consists of an extraction well, and three or more probes or
monitoring wells to measure soil pressures at various depths
and distances from the extraction point. An air injection well
may also be used to examine the effect of air injection. An
impermeable cap may be installed to prevent water infiltration
and to increase the radius of influence. If pilot studies are used
for remedy selection, the same system can be used for remedy
design studies.
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 RI/FS requires a SAP for all field
activities. The SAP ensures that samples obtained for
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Soil Gas
Sampling/
Pressure
Monitoring
Probes
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The methods for analyzing the treatability study samples
are the same as those for chemical characterization of field
samples. Preference is given to methods in "Test Methods for
Evaluating Solid Waste, SW-846, 3rd.Ed.," November 1986.
Other standard methods may be used, as appropriate. Methods
other than GC/MS techniques are recommended to conserve
costs when possible.
TREATABILITY DATA INTERPRETATION
To properly evaluate SVE as a remediation alternative, the
data collected during remedy screening and remedy selection
phases must be compared to the test goals and other criteria
that were established before the tests were conducted. Figure
4 is a flowchart for evaluating SVE as a potential remedy. It
presents a framework of the decision-making process that is
based on the comparison between the goals and test results. It
also includes considerations of contaminant
volatility, ability to get air-flow to the contaminant, and predicted
cleanup times.
TECHNICAL ASSISTANCE
Literature information and consultation with experts are
critical factors in determining the need for and ensuring the
usefulness of treatability studies. A reference list of sources on
treatability studies is provided in the "Guide for Conducting
Treatability Studies Under CERCLA: Soil Vapor Extraction."
It is recommended that a Technical Advisory Committee
(TAC) be used. This committee includes experts on the
technology who provide technical support from the scoping
phase of the treatability study through data evaluation. Members
of the TAC may include representatives from EPA (Region
and/or ORD), other Federal Agencies, States, and consulting
firms.
< 0.5 mm Hg
Massive Clay
8o!T ^ ^ Soj,Typ#
>10 mm Hg /EVaiu#tie>n
Alternatives
k a Air permeability
Other soils
> 0.5 mm Hg and
<10 mm Hg
<0.5 mm Hg
a10mm Hg
Predicted
time > required
Goals not met
>0.5 mm Hg and
<10 mm Hg
Remedy
Selection
Pilot Test
Math
Modeling
Goals met
<80%Reduction'/ ™un
ecrMn \	x
Screen \ ^ X Screening
Column
Test
>80% Reduction* &
cleanup targets met
Predicted times
> 2 years and
< required time
> 80% Reduction
cleanup targets not met
k >10"10 cm2 and
k <10^ cm2
Predated
time >
required
Cleanup targets
Cleanup targets / ^un>\ met and estimated
_ , not met / Remedy x kdO^ cm2
Screen \ """ / Selection
0ut '^ Column
Tests
Math
Modeling
Eliminate.
k >10* cm2
Permeability
Tests
k <10*10 cm*
Cleanup targets met and
estimated k >10** cm2
Predicted
time <
Predicted time
2 years
required
Eliminate
FS
Evaluation of
Alternatives
' Reduction in soil gas concentration
Figure 4. Flow Chart for Evaluating the Feasibility of Soil Vapor Extraction.
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7
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Figure 4. Flow Chart for Evaluating the Feasibility of Soil Vapor Extraction.
OSWER/ORD operate the Technical Support Project (TSP)
that provides assistance in the planning, performance, and/or
review of treatability studies. For further information on
treatability study support or the TSP, please contact:
Groundwater Fate and Transport Technical Support
Center
Robert S. Kerr Environmental Research
Laboratory (RSKERL), Ada, OK
Contact: Don Draper
FTS 743-2200 or (405) 332-8800
Engineering Technical Support Center
Risk Reduction Engineering Laboratory (RREL),
Cincinnati, OH
Contact: Ben Blaney
FTS 684-7406 or (513) 569-7406
FOR FURTHER INFORMATION
In addition to the contacts identified above, the appropriate
Regional Coordinator for each Region located in the Hazardous
Site Control Division/Office of Emergency and Remedial
Response, or the CERCLA Enforcement Division/Office of
Waste Programs Enforcement should be contacted for
additional information or assistance.
ACKNOWLEDGMENTS
The fact sheet and the corresponding guidance document
were 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) and Foster
Wheeler Enviresponse, Inc. (FWEI), under Contract No.
68C8-0061. Mr. Dave Smith served as the EPA Technical
Project Monitor. Mr. Jim Rawe and Mr. Seymour Rosenthal were
SAIC's and FWEI's Work Assignment Managers, respectively.
These documents were authored by Dr. James Stumbar of
FWEI and Mr. Jim Rawe of SAIC. The authors are especially
grateful to Mr. Chi-Yuan Fan of EPA, RREL, who contributed
significantly by serving as a technical consultant during the
development of this document.
Many other Agency and independent reviewers have
contributed their time and comments by participating in the
expert review meetings and for peer reviewing the guidance
document.
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/540/2-91/019B
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