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                                         Soil
Purpose
    Section 121(b) of the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA), man-
dates the U.S. Environmental Protection Agency (EPA) to
select remedies that "utilize permanent solutions and alter-
native treatment technologies or resource recovery tech-
nologies to the maximum extent practical" and  to prefer
remedial actions in which treatment "permanently and sig-
nificantly reduces the volume, toxicity, or mobility of hazard-
ous substances, pollutants, and contaminants as a principal
element."  The Engineering Bulletins  are a series of docu-
ments that summarize the latest information available on
selected treatment and site remediation technologies and
related issues. They provide summaries of and references
for the latest information to help remedial project managers,
on-scene coordinators, contractors, and other site cleanup
managers understand the type of data and site characteris-
tics needed to evaluate a technology or technologies for
potential applicability to their Superfund or other hazardous
waste site. Those documents that describe individual treat-
ment technologies focus on remedial  investigation scoping
needs.  Addenda will be issued periodically to update the
original bulletins.

Abstract
    Pesticide contamination includes  a wide variety of com-
pounds and may result from manufacturing improper stor-
age, handling, disposal; or agricultural processes.  It can
occur in soil and can lead to secondary contamination of
groundwater. Remediation of pesticide-contaminated soils
can be a complicated process, as  most pesticides are
mixtures of different compounds rather than pure pesticide.
The remedial manager is faced  with  the task of selecting
remedial options that will meet established cleanup levels.
There are three principal options for dealing with pesticide
contamination:   containment/immobilization, destruction,
and separation/concentration. This  bulletin focuses on soils
and current or soon-to-be available separation/concentra-
tion pesticide remediation technologies.  The information
presented is condensed from the technical resource docu-
ment "Contaminants and Remedial  Options at  Pesticide
Sites" [1] and other available literature. Technologies that
                       have not produced performance data are not included nor
                       are water, sludge, or sediment treatment technologies. The
                       resource document contains site-specific  information on
                       pesticide contamination and the  remediation techniques
                       used.


                       Background
                           Pesticides, as defined by the U.S. Federal Environmen-
                       tal Pesticide Control Act, are "...any substance or mixture of
                       substances intended for preventing, destroying, repelling,
                       or mitigating any insect, rodent, nematode, fungus, weed or
                       any other form of terrestrial or aquatic plant, animal life, or
                       virus, bacteria or other microorganism which the Adminis-
                       trator declares a pest" [2].  Pesticides include insecticides,
                       fungicides, herbicides, acaricides, nematocides and roden-
                       ticides as well as any substance or mixture of substances
                       intended for use as a plant regulator, defoliant or desiccant.
                       Pesticides  do not include such substances as fertilizers or
                       veterinary medicines [1]. The EPA has developed extensive
                       data on specific pesticide products and wastes through the
                       pesticide registration program and site investigation [3,4,5].

                           Pesticide wastes are generally complex chemical mix-
                       tures and not pure pesticides. These mixtures can include
                       solvents, carriers and other components that will have a
                       direct effect on toxicity, mobility, transport and treatment.

                           The resource document categorizes  pesticides  into
                       four waste groups based on available treatment technolo-
                       gies [1]. The four waste group categories are:

                           WG01 - Inorganic pesticides
                           WG02 - Halogenated water insoluble organics
                           WG03 - Halogenated sparingly water soluble organics
                           and organo-linked compounds
                           WG04 -  Nonhalogenated organics and organo-linked
                           compounds.

                           Table  1  details the four pesticide  waste groups  and
                       gives examples of commonly  found  pesticides.  These
                       groups are subdivided further to show the chemical class or
                         indicate references
                                                                                       Printed on Recycled Paper

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Tablo 1.  Pesticide Chemical Waste Groups." [1,6]
Postlckle Chemical
Waste Group
WQ01 - Inorganics
WG02 - Halogenated water
insoluble organics
WG03- Halogenated
sparingly water soluble
organics and organo-
linkod compounds
WG04 - Nonhalogenated
organics and organo-linked
compounds
Family

Organochlorine/
DDT analog
DDT analog
uyciodiene
Hexachlorocyclohexane
Toxaphene
Nitrated aromatics
Nitrated aliphatics
Alkylmercaptan
Carboxamide
Triazine
Halogenated phenol
Halogenated volatile
aliphatics

Aryloxyalkanoic acid
Phosphorothioate
Dinitroaniline
Unsaturated aliphatics
Thiourea
Alkaloids
Carbamates
Phosphonates
Phosphorothioates
•The Bulletin covers only the technologies in bold. Discussions
Example
Lead arsenate
Sodium fluoride
Zinc phosphide
ODD
DDE
DDT
Methoxychlor
Alarm
Chlordane
Dieldrin
Endosulfan
Endrine
Heptachlor
a-BHC
/3-BHC
7- BHC (lindane)
Toxaphene
Pentachloro-
nitrobenzene
Chloropicrin
Captan
Alachlor
Pronamide
Cyanazine
Pentachlorophenol
(PGP)
Dibromochloropropane
(DBCP)
Ethylene dibromide
(EDB)
Methyl bromide
2,4-D
2,4,5-TP (silvex)
Methyl parathion
Trifluralin
Acrolein
Ethylene oxide
Ethylene thiourea (ETU)
Allethrin
Rotenone
Aldicarb
Benomyl
Carbaryl
Diazinon
Glyphosate
Dimethoate
Marathion
Parathion
Phorate
on the other technologies can
Applicable Soil Treatment
Technologies
Chemical oxidation
Soil flushing
Stabilization/Solidification
Soil washing
Incineration
Bioremediation
Dehalogenation/Hydrodehalo-
genation
Hydrolysis/Neutralization
Ultra high temperature processes
Soil flushing
Soil washing
Thermal desorption
Steam extraction
Solvent extraction
Supercritical CO2 extraction
Adsorption
Filtration
Chemical reduction
Chemical oxidation
Radio frequency heating
Incineration
Bioremediation
Dehalogenation/Hydrodehalo-
genation
Hydrolysis/Neutralization
Ultra high temperature processes
Soil flushing
Soil washing
Soil vapor extraction
Thermal desorption
Steam extraction
Solvent extraction
Supercritical CO2 extraction
Chemical oxidation
Adsorption
Filtration
Chemical reduction
Radio frequency heating
Incineration
Bioremediation
Hydrolysis/Neutralization
Ultra high temperature processes
Soil flushing
Soil washing
Thermal desorption
Steam extraction
Solvent extraction
Supercritical CO2 extraction
Chemical oxidation
Adsorption
Filtration
Chemical reduction
be found in the resource document.
         Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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family each pesticide belongs to according to their molecu-
lar structure or key functional group. Applicable treatment
technologies for each waste group are also provided.  Ref-
erences to pesticides and pesticide wastes in this document
use the above waste group categories.

    Most pesticides readily adsorb on soils because of their
high adsorption capacity.  In fact, adsorption of pesticides
on the soil surface is a dominant factorthat affects the extent
of the site contamination. As a rule, when applied properly,
pesticides migrate  slowly.  Concentrated pesticide from a
spill or leak,  however, can move more quickly into the
subsurface, especially if the pesticide is in aqueous phase
or under the influence of percolating water [1 ]. Mechanisms
of pesticide fate and transport that affect the extent of site
contamination include:
    Adsorption on soils
    Biodegradation
    Volatilization
    Downward migration
    Lateral migration
    Photolysis.

    Selecting a remedial strategy includes considering the
individual contaminant's  toxicity, persistence, migration
pathways and rate of transport from a site. The wide range
of physical and chemical properties of pesticides also influ-
ence the selection of an appropriate remedial technology or
combination of technologies (known as a treatment train).  It
is important to gain  information specific to the pesticide(s)
present  in  order to  effectively  identify  the treatment
technology(ies) that is most applicable and cost effective.

Separation/Concentration Options
    Treatment technologies or control options for pesti-
cides fall into three categories: containment/immobilization,
destruction and separation/concentration.  This document
addresses the separation/concentration options.

    Separation/concentration technologies primarily serve
to separate contaminants from soils, thereby concentrating
the waste stream and reducing the amount of material that
must be treated. These technologies are mainly used as a
pretreatment step,  since no destruction or reduction of
toxicity is attained.

    Separation/concentration technologies can be classi-
fied as follows:

•   In situ technologies
    -   Soil flushing
    -   Soil vapor extraction (SVE)
    -   Steam extraction
    -   Radio frequency (RF) heating
•   Ex situ technologies (excavated soils)
    -   Thermal desorption
    -   Soil washing
    -   Solvent extraction
    -   Supercritical CO2 extraction.
    The decision to select and implement these techniques
rests primarily on the action levels established for the site.
Key issues for these technologies  are the management,
treatment and disposal options  for the process extract
phase.  While not discussed in this bulletin,  regulatory
compliance and disposal criteria for extract-phase materials
must be addressed.

    Separation/concentration technologies can potentially
be applied to pesticide wastes in all four waste groups. Soil
flushing, SVE and steam extraction technologies have lim-
ited applicability to pesticide-contaminated soils, thus these
separation/concentration technologies are not discussed in
this document.   In this bulletin, the following separation/
concentration technologies most applicable to pesticide-
contaminated soils are discussed:

-   Radio frequency heating
-   Thermal desorption
-   Soil washing
-   Solvent extraction
-   Supercritical carbon dioxide (CO2) extraction.

    For each separation/concentration option presented,
the following items are discussed:
    Process description
    Data needs for technology implementation
    Technology performance in treating pesticides in soils
    Process residuals (if available)
    Site-specific regulatory requirements or goals (if avail-
    able).

Radio Frequency Heating
    Radio frequency (RF) heating is an in situsofi treatment
process that uses electromagnetic energy in the radio fre-
quency band to heat soil rapidly.  During this process, the
contaminants are vaporized and/or boiled out  along with
water vapor formed by the  boiling action of  native soil
moisture.  The gases and vapors formed upon heating the
soil are recovered and treated on  site. This combination of
vaporization, boiling, and steam  stripping has been  used
effectively in removing aldrin, dieldrin, endrin, isodrin (WG02)
and other pesticides that typically volatilize in the tempera-
ture range of 80°C to 300°C, such as volatile aliphatics
(WG03). This technology offers three distinct advantages:

•   the contaminated materials do not need to be exca-
    vated;
•   the contaminants  are removed from the soil as vapors
    and can be subsequently trapped and treated in a vapor
    treatment  system (process equipment may be trailer
    mounted and mobile);
•   the presence of other contaminants such as jet fuel,
    polychlorinated biphenyls (PCBs), creosote, petroleum
    hydrocarbons, does not limit the treatment effective-
    ness of the process [7,8,9].

Process Description
    The RF soil decontamination process heats a defined
volume of soil  in situ to temperatures of 80°C to 300°C by
Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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means of an electrode array inserted in bore holes drilled
Into the soil. The process uses electromagnetic energy in
the frequency range of 2 to 13 megahertz to achieve high
soil temperatures. The actual frequency depends upon the
volume and depth of the  treated soil and the dielectric
properties of the soil.

    The electrodes, spaced evenly apart in the soil, are 2 to
15 ft long. The soil between the electrodes is heated by the
RF energy during treatment. Some of the electrodes are
perforated to serve as vapor collection lines which are
manifolded to a vapor treatment system [7,8,9].


Data Needs for Technology
Implementation
    The  data  needs for RF heating are presented in
Table 2.
                               Performance

                                  A field pilot demonstration of this technology was con-
                               ducted at the Rocky  Mountain Arsenal.  The  pesticide-
                               contaminated soil was a mixture of clay and sand to a depth
                               of 12 feet and gravely sand to a  17-ft depth. The results are
                               summarized in Table 3.  The initial concentrations shown
                               are the average of 36 samples at depths of 7 to 17 ft. The
                               final contaminant concentrations shown are averages in the
                               200-250°C, 250-300°C, and  >300°C temperature  ranges.
                               The contaminant removal percentage was greater than 98
                               percent.

                                  The preliminary cleanup goals, set by EPA and state
                               agencies, were developed on a risk-based assessment of
                               10-6 biological worker exposure.  Table 4 shows the final
                               pesticide concentrations in treated soil for each of the three
                               treatment temperature ranges, with the associated cleanup
                               goal for each pesticide.  The data indicate that the best
    Table 2.  Data Needs for Radio Frequency Heating. [7,8]
                 Data Needs
                                       Possible Effects
      Type of soil

      Presence of metal drums or metallic
      debris
      Type of contaminants(s)
      Soil moisture content

      Row rate and depth of groundwater
      table
              Low permeability soils increase costs and decrease contaminant recovery;
              dielectric properties of soil determine RF power requirement
              Disrupts current flow; may interfere with electode placement

              Requires supplementation with other treatment methods if nonvolatile
              contaminants (boiling points >300°C), heavy metals, or inorganic salts are
              present
              High moisture content increases energy requirements and impacts removal
              efficiency of organic contaminants
              Presence of fast moving groundwater in heated zone acts as an energy sink
              and negatively impacts process cost; may require diversion of water from
              heated zone by slurry walls, etc.
    Table 3.   Results of Radio Frequency Heating Pilot Test Program at Rocky Mountain Arsenal Over All Temperature
              Ranges Tested". [7]
           Pesticide
Initial  Concentration  (ppm) Final Concentration  (ppm/   Percent Removal
Aldrin
DIeldrin
Endrin
Isodrin
1100
490
630
2000
11.3
3.2
2.8
33
99.0
99.3
99.6
98.4
      a200-250°C, 250-300°C, and >300°C
   Table 4.  Rnal Concentrations of Compounds versus Soil Temperature in Radio Frequency Test at Rocky Mountain
            Arsenal [9].
Pesticide
Aldrin
DIeldrin
Endrin
Isodrin
200-250°C
Concentration
(mg/kg)
0.97(±1.0)a
0.59 (±0.35)
1.7 (±2.0)
1.3 (NA)b
250-300°C
Concentration
(mg/kg)
31 (±40)
8.0 (±8.0)
5.6 (±5.3)
48 (±62)
>300°C
Concentration
(mg/kg)
1.8 (±3.1)
1.0 (±1.5)
1.1 (±1.5)
49 (±90)
Preliminary
Remediation Goal
(mg/kg)
0.56
0.40
17
3.6
     "Values in parentheses represent the standard deviation of the concentration given
     bNA s Not available
        Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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overall treatment was achieved in soils heated to between
200 and 250°C. In this temperature range removal of both
endrin and isodrin met the cleanup criteria [9].


Process Residuals
    The vapors and gases collected by the second step of
the process require treatment, combustion and/or scrubbing
to remove acid gases.  The condensed liquids  from the
collection phase are separated into aqueous and organic
fractions.  The aqueous phase is treated using activated
carbon and filtration.  The organic  phase is collected for
destruction at an approved facility [7,8,9].

Thermal Desorption
    Thermal desorption is an innovative ex situ technology
which includes a broad range of processes using thermal
energy (e.g., heated air, infrared volatilization,  laser-in-
duced desorption, etc.) to remove volatile and semivolatile
organic and inorganic compounds from contaminated soil.

    Thermal desorption is applicable to pesticide waste
from waste groups WG02, WG03, and WG04. Toxicity is not
affected by thermal desorption; the toxic compounds are
removed from the soil for further treatment or disposal [1].


Process Description

    Thermal desorption is used to desorb low, medium and
high boiling-point organic pesticides.   Front-end material
handling steps such as excavation, dewatering and/or dredg-
ing are performed. High soil moisture content may require
greater energy usage, but it may also enhance volatilization
                 by producing steam within the media. The desorption units
                 typically require at least 20 to 30 percent solids by weight.
                 Some units can accept only 10 percent total organic carbon
                 loading by weight.

                     The media enters the desorber unit and is heated to
                 temperatures between 95 and 540°C. A temperature above
                 150°C may be required to effectively desorb medium-to-
                 high boiling point organic pesticides. The vapors generated
                 from the process can be destroyed/oxidized in  an after-
                 burner. The afterburners operate in excess of 870°C and
                 have a fluid residence time sufficient to achieve a destruc-
                 tion efficiency  greater than 99.99 percent.

                     The efficiency of thermal desorption is primarily depen-
                 dent on the bed temperature and residence time in the unit.
                 Residence time determines the soil treatment temperature
                 for a given airflow rate. The resulting air and soil  tempera-
                 tures affect the rate and degree of contaminant desorption.
                 A temperature differential of approximately 95°C higher
                 than the boiling point of a pesticide is required to achieve
                 complete desorption  and to overcome  the intrinsic heat
                 transfer resistances present in the medium  [1,11].


                 Data Needs  for Technology
                 Implementation
                     The data needs are presented in Table 5.


                 Performance
                     Thermal desorption technology has  been used in sev-
                 eral remedial actions including three Superfund sites.  The
                 Low Temperature  Thermal  Aeration (LTTA)  System is a
   Table 5. Data Needs for Thermal Desorption. [12,13,14]
                Data Needs
                         Possible Effects
    Moisture content

    Particle size distribution


    Total solids content
    PH

    Contaminant concentrations

    Presence of metals or inorganics
    Volatile metals
    Total chlorine
    Total petroleum hydrocarbons

    Vapor pressure

    Boiling point

    Adsorptive properties of contaminant
High moisture content (>20%) increases energy requirement; dewatering or
pretreatment may be required
Oversize (>1-1.5 in.) particles may require size reduction or screening;
presence of fine silt or clay may generate fugitive dust loading for air
pollution control equipment
Usually a minimum of 20-30% solids is required
Very high (>11) or low (<5) soil pH may result in corrosion of system
components
Total organic bonding is limited to approximately 10%; higher organic
bonding may result in incomplete processing
Are not likely to be treated effectively
May concentrate in off-gas and require additional treatment
May affect volatilization of some metals
High concentrations may require a thermal oxidizer or afterburner and a
quench tower for cooling
Affects removal effectiveness; high contaminant vapor pressure increases
removal efficiency and requires less energy for contaminant removal
Affects process temperature and removal effectiveness; low boiling point
reduces energy requirements for contaminant removal
Affects amount of energy required to desorb contaminant from soil particles
Engineering Bulletin: Separation/Concentration Technology Alternatives lor the Remediation of Pesticide-Contaminated Soil

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remedial system developed by Canonie Environmental Ser-
vices Corporation. The LTTA System thermally desorbs
organic compounds from contaminated soil without heating
the soil to combustion temperatures. The system performs
three main operations:  soil treatment, emissions control
and process water treatment. LTTA systems can treat a
wide variety of soils having different moisture and contami-
nant concentrations, and can remove pesticides from soil to
below br near analytical detection limits [11].

    The LTTA System was used in a full-scale Superfund
Innovative Technology Evaluation  (SITE) demonstration
conducted at an  abandoned pesticide  mixing  facility in
western Arizona.   The facility stored and mixed several
pesticides including toxaphene, DDT, ODD, and DDE. The
Arizona pesticide site was remediated under supervision of
the slate by voluntary action of the potentially responsible
party.  All treated soils at the site were required to contain
                         less than 5 mg/kg total pesticide after one pass through the
                         LTTA system, as stated in the remedial action plan.  An
                         estimated 51,000 tons of contaminated soil required treat-
                         ment.  Sliding scale cleanup criteria were established,
                         shown in Table 6, with a maximum allowable concentration
                         of 1.09 mg/kg of toxaphene with no DDT/DDD/DDE (com-
                         bined) at one end, and a maximum allowable concentration
                         of 3.53 mg/kg DDT/DDD/DDE with no toxaphene at the
                         other end. Treated soils met the specific cleanup criteria if
                         90 percent of the treated soil fell within the cleanup criteria
                         on a daily basis.

                             The LTTA SITE demonstration consisted of three sepa-
                         rate runs, each requiring about 8 hr to complete. Based on
                         site characterization data of the contaminant distribution,
                         the soil was treated to a depth of 2 ft. This soil was primarily
                         clay-like in nature (40 percent fines).
   Table 6.  Sliding Scale Cleanup Criteria Concentrations for Pesticides During the LTTA™ SITE Demonstration of
            Thermal Desorption [14].
    DDT/DDD/DDE (mq/kg)    0.00
         0.01
          0.83
          1.00
         2.00
         3.00
                                                         3.36
                   3.52
    Toxaphene  (mg/kg)
1.09
1.087
0.83
0.78
0.47
0.16
                                                         0.05
                                                          0.00
   Table 7.   Pesticide Concentrations and Removal Efficiencies in LTTA™ SITE Demonstration of Thermal Desorption
             Technology. [14]
Pesticide
Toxaphene
DDT
ODD
DDE
Cone.
Range in
Feed Soil,
mg/kg
4.5 to 47
1.2 to 54
0.027 to 0.86
3.7 to 15
Average3 Concentration.
Run 1
Feed
Soil
27.5
24.1
0.34
7.1
Treated
Soil
<0.017
<0.001
<0.0003
1.1
Run 2
Feed
Soil
16.5
22.8
0.12
8.3
Treated
Soil
0.017
0.001
<0.0003
0.97
, mg/kg
Run 3
Feed
Soil
10.8
9.3
0.2
5.1
Treated
Soil
<0.025
0.002
<0.001
0.28
Removal, %
Run 1
>99.9
>99.9
>99.9
90.2
Run 2
>99.9
99.9
>99.7
88.4
Run 3
>99.8
99.9
>99.8
93.3
    •"Average of four composite samples for each feed or treated soil value
    Demonstration results, shown in Table 7, indicate toxa-
phene, DDT, ODD,  and DDE removals in excess of 99
percent for each of the three runs. The remedial cleanup
criteria were met during each of the runs [11,14].

    Williams Environmental  Services  (WILLIAMS) com-
pleted  a  treatability study using the WILLIAMS thermal
dosorption system for a removal action at a former pesticide
formulation site (T H Agriculture and Nutrition Company) in
Albany, GA.  The removal action, which included treatment
of approximately 3,000 tons of soil contaminated with over
1,000 mg/kg total pesticides, was overseen by EPA and the
Georgia Department of Natural Resources Environmental
Protection Division.  Treatability study results showed that
at a soil  treatment temperature of 500°F, total pesticide
                         removal ranged from 86 to 93 percent;  when operated at a
                         treatment temperature of 700°F, pesticide removal was
                         more than 99 percent. At 700°F, the total pesticide concen-
                         tration was reduced from about 200 mg/kg to less than 0.003
                         mg/kg [15].


                         Process Residuals
                             This innovative technology produces the following three
                         residual streams:

                         •   Decontaminated soil, sludge or sediment
                         •   Scrubber water from the air pollution control system
                         •   Off-gas emissions from the air pollution control system
                             [1]-
        Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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    The decontaminated media may be reclaimed after
analysis.  The  scrubber water can be treated  onsite or
discharged to a publicly-owned treatment works (POTW).
Off-gas emissions may require additional air pollution con-
trol before being released through a stack [1].

Soil Washing
    Soil washing is an innovative ex situ technology which
uses an aqueous solution to decontaminate soils.  Contami-
nant removal or volume  reduction is achieved by one or
more of the following mechanisms: 1) the contaminants are
suspended or dissolved in the wash solution,  2) the con-
taminants are concentrated by segregating the most con-
taminated fraction from the bulk of  the  soil  using size-
separation techniques or 3) the contaminants are concen-
trated  by segregating dense, paniculate  contaminants
through  the use of  density-separation techniques
[16,17,18,19,20,21].  Each of the four pesticide chemical
waste groups (Table 1) can potentially be treated using the
soil washing technology [1].


Process Description
    Soil washing systems consist of specific unit operations
(subsystems) that are tailored to accommodate the site
conditions and soil characteristics. In general, soil washing
systems consist of three types of subsystems:

•   feedstock preparation
•   soil washing
•   residuals treatment.

    Feedstock preparation includes excavation, transpor-
tation of the soil to the soil-washing staging area, removal of
debris  and separation of the soil into different particle-size
or density fractions.   Typical post-excavation operations
                  include screening, crushing and attrition scrubbing.  The
                  purpose of feedstock preparation is to segregate the soil
                  components into fractions based on contamination levels.
                  Minimally contaminated soils, requiring little or no treat-
                  ment, can be returned to the site  as  backfill,  but highly
                  contaminated fractions require more aggressive treatment.
                  Reducing the volume of soil passing through the remainder
                  of the system increases the cost-effectiveness of the tech-
                  nology [16,17,18,19,20,21].

                      Soil washing unit operations tend to fall into two catego-
                  ries: physical separation of the soil matrix into different
                  particle-size or density fractions, and chemical separation
                  of the contaminants from the soil matrix. Organic contami-
                  nants such as pesticides are often concentrated in the fines
                  (e.g., clays and silt). Physical separation of this fraction
                  using unit operations  such as flotation,  gravity settling,
                  hydrocloning, washing and rinsing achieves further volume
                  reduction [16,17,18,19,20,21]. Chemical separation trans-
                  fers the contaminant from the soil matrix to  the aqueous-
                  phase wash solution.   Chemical separation can be en-
                  hanced by optimizing process conditions.  Increased wash
                  or rinse temperature, addition of surfactant and pH adjust-
                  ment may enhance pesticide  removal [16,17,18,19,20,21].

                      Residuals treatment subsystems include unit opera-
                  tions that treat  process water, air emissions and highly
                  contaminated fractions of the soil, such as the fines. The
                  unit operations typically include biological, chemical or ther-
                  mal oxidation units for destruction of residual contamina-
                  tion, as well as adsorption processes to further concentrate
                  the contaminants.
                  Data Needs for Technology
                  Implementation
                      Data needs for soil washing are presented in Table 8.
   Table 8.  Data Needs for Soil Washing. [21,22]
                Data Needs
                         Possible  Effects
    Particle size distribution


    Soil type


    Complex waste mixtures

    Wash solution

    Metal content

    Organic content

    Partition coefficient

    pH, buffering capacity
Affects efficiency of removal from wash liquid; particles >2 inches in diameter
require pretreatment for oversized particles; particles <0.063 mm in diameter
are difficult to wash
Affects pretreatment and transfer requirements; high clay and silt levels
make it difficult to remove contaminants because of their strong adsorption to
the particles
Increases difficulty in formulating suitable washing fluid; solubility of different
contaminants may vary
Presence of surfactants or other reagents in wash solution may cause
difficulties in wastewater and sludge treatment/disposal
Concentrations and species affect selection of wash fluid, mobility of metals,
and post-treatment
Concentration and species affect selection of wash fluid, contaminant
mobility and post-treatment
High coefficient requires excessive volumes of wash fluid since contaminant
is tightly bound
Can affect pretreatment requirements, wash fluid selection, and choice of
materials of construction for equipment
Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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Performance
    Soil washing is an innovative technology available for
full-scale implementation. It has been used as a remediation
technology at several Superfund sites [23].  A pilot-scale
soil-washing treatability study was conducted on pesticide-
contaminated soil  at the Sand Creek  Superfund site in
Commerce City, CO.  The treatability study consisted of 23
individual runs conducted under varying process condi-
tions. The process variables tested included:

•   depth of soil excavation
•   surfactant type and concentration
*   wash water temperature
•   pH
•   number of washes
•   liquid-to-solids ratio.

    Table 9 provides a summary of the treatability study
results.  Experimental conditions and results of the indi-
vidual runs are shown in Table 10.

    Control runs using only ambient-temperature munici-
pal water without surfactants addition demonstrated re-
moval of 76 to 81 percent dieldrin  and  67 to 81 percent
heptachlor from the coarse soil fraction.  Results indicate
that surfactant addition  had a positive influence on pesti-
cide removal [24,25].
   Table 9. Summary of Sand Creek Superfund Site Soil Washing Treatability Study Results [24].
Soil Fraction
Feed
Treated Coarse
Treated Rnes
Concentration (mg/kg)
Dieldrin Heptachlor
2.7 to 27 8 to 460
0.0 to 6.8 1.4 to 50
0.0 to 37 4.4 to 340
Removal (%)
Dieldrin Heptachlor
NAa MA
-44 to 91 17 to 99
-131 to 86 -100 to 97
    BNA « Not applicable
   Table 10.  Sand Creek Superfund Site Soil Washing Treatability Study Results'[24].
Test Conditions
Run #
1
2
11
12
6
7
23
3
8
9
10
17
4
5
18
18A
19
19A
20
20A'
21
22
13
14
15
16
Surfactant Temp.
none
none
none
none
0.4A
LOA
LOA
0.4S
LOS
LOS
0.4S
0.4S
0.4T
0.5T
LOT
LOT
L5T
L5T
LOT
LOT
1.0M
LOM
LOS
LOT
LOT
LOS
ambient
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
pH Soil Depth
(feet)
7
10
10
7
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
7
10
10
10
10
10
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
0-1
1-3
1-3
0-5
0-5
Liq./ Soil
Ratio
6:1
6:1
(9:1)
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
6:1
(9:1)
(9:1)
6:1
6:1
6:1
6:1
6:1
6:1
Heptachlor
(mg/kg)
Feed
Soil
220
87
150
170
180
230
230
100
200
270
260
22
220
220
120
120
250
250
64
64
460
210
63
120
8
12
Treated
Soil
50
29
37
34
26
25
15
24
36
28
34
12
27
30
16
18
16
20
12
14
16
22
19
1.8
2.0
<1.6
Dieldrin
(mg/kg)
Feed
Soil
19
16
24
23
17
18
18
19
17
27
25
2.8
18
20
13
16
18
18
19
19
20
17
9.7
17
2.7
3.4
Treated
Soil
4.6
2.4
4.5
4.5
6.8
2.9
5.6
2.0
4.4
3.9
4.9
1.5
5.0
5.0
1.7
1.8
3.2
2.0
1.9
1.6
2.6
3.8
1.9
2.2
<1.6
<1.6
    A s Adsee; S = SDS; T = Tergitol;  M = SDS/Tergitol mix
        Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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    The site cleanup criteria, established in the Record of
Decision (ROD) by EPA Region VIII, were 0.55 mg/kg for
heptachlor and 0.15  mg/kg for dieldrin.  The analytical
detection limits, 1.6 mg/kg for both contaminants, were not
low enough to determine if these action levels were met [25].
This was due to matrix interferences.

    Bench-scale soil-washing tests conducted at the FMC
Fresno Superfund site demonstrated that contaminant re-
duction for any size fraction greater than 200 mesh is most
influenced by  the number and types of washes used. A
single wash removed about 77 percent of the dieldrin from
soil, but three  washes using a surfactant removed 99 per-
cent [26]. Additional studies at the FMC site were performed
using a froth flotation wash.  Data indicate that this surfac-
tant-assisted wash procedure removed an average of 80 to
85 percent of the organochloropesticides (WG02 and WG03)
in one wash cycle; 92 to 99 percent removal was achieved
with a triple wash. Froth flotation washing removed 81 to 85
percent of the organo-phosphorus pesticides with one wash
cycle [26].

    High percentages of clay, silt, and humic content may
have a negative effect on contaminant removal and overall
volume reduction.  This is because pesticides bind chemi-
cally or. physically more readily to clay and silt  particles.
Media with high cation exchange capacity also bind some
organic and organo-metallic pesticides that may be difficult
to separate using this technology [17,27,28].


Process Residuals
    Residuals from the aforementioned process units may
include oversize  rocks, debris, and coarse material, air
emissions, wastewater, and contaminated sludges or fines.
Oversize fractions are often minimally  contaminated and
can  be returned  as  backfill to the site  with little or no
treatment.  Debris that is porous in nature, such as wood,
roots, and vegetation, may be highly  contaminated and
require off-site disposal.  Treatment units for pesticide-
laden system wastewater include carbon adsorption, chemi-
cal or photochemical oxidation, or biological oxidation. Con-
taminated fines resulting from the soil washing subsystem
can be treated either on or off site by processes such as
biological or chemical oxidation, incineration or solidifica-
tion/stabilization in conjunction with land disposal
[16,17,18,19,20,21].

Solvent Extraction
    Solvent extraction is an innovative technology that uses
organic solvents to extract organic contaminants from soils.
Solvent extraction is mainly applicable to the decontamina-
tion of soils containing volatile and nonvolatile hydrophobia
organics, such as pesticides.  This technology achieves
volume reduction by concentrating the pesticides into an
extract phase, from which the contaminants can be recov-
ered, further concentrated or disposed.

    There are  two broad categories of processes:  conven-
tional solvent  extraction and supercritical fluid extraction.
Conventional solvent extraction uses organic solvents to
selectively  extract the contaminants.  This process may
need to be repeated several times to extract the contami-
nant to a certain concentration level.  The solvent itself can
be treated and recycled.  Supercritical fluid extraction uses
a highly compressed gas (e.g., carbon dioxide) above its
critical temperature to perform the extraction.  This highly
compressed gaseous fluid can be especially useful in re-
moving contaminants  from interstitial spaces of  the ma-
trix[1,30].   Supercritical  CO2 extraction is presented in a
separate section.  Solvent extraction technology potentially
can be used for treatment of pesticides from waste groups
WG02, WG03, and WG04 [29,30,31].


Process Description
    This process achieves volume reduction by concentrat-
ing the pesticide  into an  extract phase. Solvent extraction
typically consists of three types of subsystems:

•   feedstock preparation
•   extraction
•   residuals treatment/solvent recovery.

    As with soil washing, solvent extraction feedstock prepa-
ration typically includes excavation, followed by screening
operations to segregate the soil by size into highly contami-
nated fines and minimally contaminated coarser soil frac-
tions.  This initial volume reduction can reduce the amount
of soil that must be extracted, reducing the overall treatment
cost. Some commercially available units treat the entire soil
mass without initial volume reduction. If the soil is  very wet
(e.g.,  >70 percent moisture content), a dewatering unit  is
used to remove excess moisture before the extraction pro-
cess [20,27,29,31,32,33].

    During the soil extraction process, pesticide-contami-
nated soil is mixed with  an appropriate solvent in a tank-
based continuous countercurrent extraction. The extraction
process may require several passes to reduce the solid-
phase pesticide contamination to the desired level.  After
extraction, the solvent extract is pumped to a sedimentation
tank for removal of soil fines [20,27,29,31,32].

    A suitable solvent should:

    have high selectivity for the contaminant(s)
    have high saturation solubility for the contaminant(s)
    be immiscible in the feed material
    be stable
    be nonreactive and noninterfering with other soil-matrix
    components
•   have favorable density, viscosity and interstitial tension
    properties
•   have a sufficiently  different boiling point from the
    contaminant(s) to allow post-treatment separation
    [29,34,35].

    Residuals treatment subsystems  include unit opera-
tions for air emission control, decontamination of the extrac-
tion solvent to allow solvent recycle and removal of residual
solvent from the treated  soil [20,27,29,31,32,33].
Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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Data Needs for Technology
Implementation
    Data needs and possible effects for this technology are
presented In Table 11.


Performance
    The Sanivan Group developed the Extraksol™ solvent
extraction process which was used to treat PGP-contami-
nated soil for the purpose of system  development and
demonstration of capabilities.  A proprietary solvent was
used In the  1-ton-per-hour pilot-scale unit.  The process
efficiency, presented in Table 12, was greater than 90
percent and greater than 99.7 percent, respectively, in two
tests conducted on contaminated porous gravel.  In addi-
tion, low post-treatment POP concentrations were achieved
(<0,82 mg/kg and <0.21 mg/kg). In a test on POP-contami-
nated porous stones, the removal efficiency was lower, at 50
percent [32].

    A bench-scale study using the B.E.S.T.™ process mar-
keted by Resource Conservation Company (RCC) demon-
strated a 99 percent removal efficiency for a number of
pesticides !n waste groups WG02 and WG03. Data from this
                                                   study is presented in Table 13. Data from other bench-scale
                                                   tests using this process indicate chlordane removal efficien-
                                                   cies greater than 99 percent [1].


                                                   Process Residuals
                                                       Residuals include oversize materials, spent solvent,
                                                   gaseous solvent emissions and treated soil. Oversize soil
                                                   fractions can be returned to the site as backfill if sufficiently
                                                   clean. To improve process economics, the solvent extract
                                                   is generally recovered and recycled back to the extraction
                                                   process.  The mode of solvent recovery depends on the
                                                   physical and chemical properties of the extract (solvent and
                                                   contaminant). For pesticide  extraction operations, distilla-
                                                   tion or evaporation can be used to recover a volatile solvent
                                                   from the less volatile contaminant.  I n some cases, a second
                                                   extraction with an aqueous solution may be the method of
                                                   primary solvent recovery.

                                                      The extracted soil may need treatment to remove ex-
                                                   cess residual solvent. Dewatering (e.g., centrifugation), air
                                                   or steam stripping, vacuum  extraction, or biological treat-
                                                   ment can be used to remove residual  solvent from the soil.
                                                   Gaseous emissions from system operations must be treated
                                                   before release [20,27,29,31,32,33].
   Table 11.  Data Needs for Solvent Extraction. [36]
                Data Needs
                                                          Possible  Effects
    Complexity of waste mixture
    Particle size
    PH
    Contaminant size

    Temperature

    Metals

    Organically bound metals

    Detergents/emulsifiers

    Soli permeability

    Solvent characteristics
    Solvent extraction capacity
    Soil moisture content
                                 Affects solvent selection
                                 Oversize particles may require size reduction pretreatment
                                 Must be in a range compatible with extracting solvent
                                 Affects solvent selection and process efficiency; solvent extraction is least
                                 effective for very high molecular weight and very hydrophilic organics
                                 May impact solubility of contaminants in extraction solvent - this affects
                                 extraction efficiency
                                 Strong reaction may occur during treatment process because of caustic
                                 additions
                                 May be extracted along with organic pollutants and cause disposal/recycling
                                 difficulties
                                 May retain organic contaminants and reduce effectiveness of process; may
                                 cause foaming, which hinders settling and separation characteristics
                                 Affects solvent-contaminant contact; low permeability soils may require
                                 additional contact time for effective treatment
                                 May impact treatment process if nonbiodegradable, toxic, or nonvolatile
                                 Affects mass of contaminant that can be solubulized in the solvent
                                 Affects solvent-contaminant contact; soils containing more than 30 percent
                                 moisture may need to be dewatered before treatment	
   Table 12. PCP Removal Obtained in 1 Ton/Hour Extraksol™ Pilot-Scale Solvent Extraction Unit. [32]
      Type of Waste     Type of Solvent3
    "proprietary
                                       Initial PCP Cone.
                                            (mg/kg)
Final PCP Cone.
    (mg/kg)
Removal (%)
porous gravel
porous gravel
porous gravel
#2
#2
#2
8.2
81.4
38.5
<0.82
<0.21
19.5
>90
>99.7
50
 70
Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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    Table 13. Pesticide Removal in Bench-Scale Study Using B.E.S.T.™ Solvent Extraction Process. [37]
Analyte
p,p'-DDT
p,p'-DDE
p,p'-DDD
Endosulfan-l
Endosulfan-ll
Endrin
Dieldrin
Toxaphene
BHC-Beta
BHC-Gamma (Lindane)
Pentachlorophenol
Feedstock (ppm)
500
84
190
250
140
140
37
2,600
<30
<30
150
Product Solids (ppm)
0.2
0.5
0.05
<0.02
<0.02
0.02
<0.02
0.9
<0.13
<0.07
1.9
Removal Efficiency (%
99.96
99.40
99.97
>99.99
>99.99
99.99
>99.95
99.97
98.7
Supercritical CO2 Extraction
    Supercritical CO2 (SCO2) extraction is a type of solvent
extraction that exploits some unique properties of
supercritical fluids.  Many gases, including CO2, exhibit
enhanced solvent properties when compressed at condi-
tions above their critical temperature (the temperature above
which the gas cannot exist in the liquid state, regardless of
pressure). Supercritical carbon dioxide forms when CO2 is
heated and compressed above 31 °C and 1078 psi. In the
supercritical state, the CO2 is not a liquid, although it exhibits
liquid-like densities and  displays much better solubilizing
properties and mass transport characteristics than subcriti-
cal, gaseous CO2. Because the supercritical fluid remains
in the gaseous state, it can penetrate spaces within contami-
nated soil much more readily than liquid solvents [29,30].
Several other gases such as ethylene, ethane, propane and
dichlorodifluoromethanol (Soivent-12) have been tested in
addition to CO2 for treatment applications of supercritical
fluid extractions[29].


Process Description
    SCO2 extraction systems consist of an extraction vessel
that can  be operated at elevated temperatures and  pres-
sure.  Carbon dioxide from a liquified bulk supply is piped to
a storage vessel where it is compressed to the  desired
operating pressure. The pressurized CO2 is then heated to
the system operating temperature and piped to the extrac-
tion vessel containing the contaminated  soil.  After the
extraction process, contaminated supercritical CO2 is piped
to a separation vessel, where  the pressure is rapidly re-
duced, causing SCO2 to undergo phase transformation to
gaseous  subcritical CO2.  At lower temperatures and pres-
                 sure, the dissolved organic contaminants precipitate in the
                 bottom of the separation vessel. Uncontaminated, gaseous
                 CO2 is piped to the storage vessel for recycling, while the
                 extracted organics are collected for disposal [29,30].


                 Data Needs for Technology
                 Implementation
                     Data needs for supercritical CO2 extraction are pre-
                 sented in Table 14.


                 Performance
                     Supercritical fluid extraction processes have been used
                 extensively in various applications such as decaffeinating
                 coffee and extracting cholesterol from eggs, drugs from
                 plants, and nicotine from tobacco [6]. The full-scale appli-
                 cation of supercritical fluid extraction to the remediation of
                 contaminated soils is in its infancy.  Bench-scale SCO2
                 studies  on pesticide-contaminated soil suggest that full-
                 scale  implementations will be successful [6,38]. A pilot-
                 scale supercritical fluid system that successfully remediated
                 PCB-contaminated sediment using  a  mixture of propane
                 and butane as the extracting solvent was demonstrated by
                 CF Systems Corporation under the SITE Program [39].

                     The efficiency and choice of operating conditions of
                 SCO2 extraction systems for performing pesticide-contami-
                 nated site  soil remediations will most likely depend on the
                 specific  contaminants present.  Several sets of conditions
                 (e.g.,  temperature and pressure combinations) may  be
                 needed  to extract soils contaminated with more than one
                 pesticide [6,29,30,38].
    Table 14. Data Needs for Supercritical CO. Extraction [6,29,38]
                 Data Needs
                         Possible Effects
     Complexity of waste mixture

     Contaminant polarity

     Soil permeability
Affects temperature and pressure combinations required for effective
treatment
Extractive efficiency of polar pesticides may increase with the addition of an
enhancer, such as methanol or acetone
Affects solvent-contaminant contact; low permeability soils may require
additional contact time for effective treatment
Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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 Process Residuals
    Residuals Include treated soils, recyclable CO2 gas,
 and liquid- or solid-phase pesticide contaminants. Decon-
 taminated soils can be backfilled on site. The recondensed,
 separated pesticide contaminants can be stabilized and
 disposed of In a RCRA-permitted landfill. The CO2 gas can
 be recycled to the extraction process [6,29,30,38].

 Comparison of Option Costs,
 Advantages and Limitations

 Costs
    Figure 1 presents the cost ranges for the technologies
 discussed in this document; Table 15 lists critical factors
 affecting the cost ranges for the technologies discussed.
 Other remedial alternatives discussed in the primary refer-
 ence document, Contaminants and Remedial Options at
 Pesticide Sites, are included for comparison. This informa-
 tion should be used as a guide only. Specific cost estimates
 should be generated for each site based on specific needs
 and circumstances. These costs include capital operations
 and maintenance (O&M) costs.

 Advantages and  Limitations
    Tables 16 and 17 present generalized advantages and
 limitations, respectively, of the treatment technologies dis-
cussed. Other remedial options discussed in the primary
reference are included for comparison purposes.  Limita-
tions specific to a technology or site application are not
addressed.
EPA Contact

    Technology-specific questions regarding remedial op-
tions at pesticide sites may be directed to:

    Richard N. Koustas
    U.S. Environmental Protection Agency
    Risk Reduction Engineering Lab
    2890 Woodbridge Avenue (MS 106)
    Edison, N.J.  08837
    Phone: (908) 906-6898
    FAX: (908) 906-6990
    E-mail: Koustas.Richard@ EPAMAIL.EPA.GOV

Acknowledgements
    This bulletin was prepared for the U.S. Environmental
Protection Agency, Office of Research and Development,
National  Risk Management Research Laboratory, Edison,
NJ by IT Corporation under Contract No. 68-C2-0108. The
primary reference document, "Contaminants and Remedial
Options at  Pesticide Sites" [1], was prepared  by  Roy F.
Weston,  Inc. Mr. Richard Koustas served  as the  EPA
Technical Project Monitor. This bulletin was authored by
Ms. Ida Bennett, Mr. Gregory McGraw and Ms. Jennifer
Platt of IT Corporation.

    Mr. Gregory McGraw served as Task Manager and Mr.
Thomas Janszen of IT Corporation contributed his time and
comments by participating in the review meetings and/or
peer reviewing the document.
           Remediation Technologies
                                                            Cost($/ton)
                                        100   200   300    400    500   600    700    800   900   1000
     Separation/Concentration Options

               Radio Frequency Heating

                   Thermal Desorption

                        Soil Washing

                    Solvent Extraction

     Containment/Immobilization Options
               Stabilization/Solidification

                    Vitrification (In-Situ)

     Destruction Options
                         Incineration

           Ultra High Temperature Process

                    Chemical Oxidation

          DohatogonaltoaHydrodehalogenalion

                Hydrolysis/Neutralization

                       Bloremediation
     *No cost estimates for supercritical CO2 extraction are available
     blndmirat!on and vitrification costs are per cubic yard
     "Cost estimates ware obtained from the references provided and through contact with technology vendors


   Rgure 1. Available Estimated Cost Ranges for Pesticide-Contaminated Soil Remediation Technologies"'1"'0. [1,40,41]
 12     Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

-------
Table 15.  Factors Affecting Cost Ranges for Technology
          Alternatives for Remediating Pesticide-Con-
          taminated Soil.
  technology for which) cost Incurred increased because of this factor
Table 16.  Advantages for Technology Alternatives for
          Remediating Pesticide-Contaminated Soil.
                                                                        Advantages
                                                                Proven ability to reduce high concentrations to
                                                                clean-up goals
                                                                Destroys or detoxifies pesticides
                                                                Can be Implemented in-silu
                                                                Concentrates pesticides, reducing disposal costs
                                                                Effective on some Inorganic co-contaminants
                                                               0 technology for which a specific advantage Is applicable

                                                               Table 17.  Limitations for Technology Alternatives for
                                                                         Remediating Pesticide-Contaminated Soil.
                                                                High moisture content adversely affects treatment
                                                                Pesticides must be destroyed by another process
                                                                Produces residuals/off gases requiring treatment
                                                                and/or disposal
                                                                Sensitive to median particle size, pH and/or media
                                                                characteristics
                                                                Sensitive to co-contaminants
                         aaaaaaanaaaaa
                                                               • technology for which a specific limitation Is applicable
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2.  Federal Insecticide, Fungicide, and Rodenticide Act,
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                                                      13

-------
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24. URS Consultants, Inc., and Hazra Environmental Ser-
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25. Frederick, R.M. and S. Krishnamurthy. 1994.  Soil
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        Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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37. D.A. Austin. 1988. The B.E.S.T. Process - An Innova-
    tive and Demonstrated Process for Treating Hazardous
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38. Dooley, K.M., R. Gambrell, and F.C. Knopf. 1988.
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Engineering Bulletin: Separation/Concentration Technology Alternatives for the Remediation of Pesticide-Contaminated Soil

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