600283100
              MOBILE SYSTEM FOR EXTRACTING
               SPILLED HAZARDOUS MATERIALS
                  FROM EXCAVATED SOILS
                           by

                     Robert  Scholz
                   Joseph Milanowski
                      Rexnord Inc.
               Milwaukee, Wisconsin 53214
               Contract Number 68-03-2696
                    Project Officer
                    John E.  Brugger
        Oil  and  Hazardous Materials Spills  Branch
       Solid and Hazardous  Waste Research Division
Municipal Environmental Research Laboratory (Cincinnati)
                Edison, New Jersey 08837
       MUNICIPAL  ENVIRONMENTAL  RESEARCH  LABORATORY
           OFFICE OF RESEARCH AND DEVELOPMENT
          U.S. ENVIRONMENTAL PROTECTION AGENCY
                 CINCINNATI, OHIO 45268

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                                DISCLAIMER

The information in this document has been funded wholly or in part by the
United States Environmental Protection Agency under Contract No. 68-03-2696
to Rexnord Inc.  It has been subject to the Agency's peer and administrative
review, 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

The U.S. Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people.  Noxious air, foul  water, and spoiled
land are tragic testimonies to the deterioration of our natural environment.
The complexity of that environment and the interplay of its components
require a concentrated and integrated attack on the problem.

Research and development is that necessary first step in problem solution;
it involves defining the problem, measuring its impact, and searching for
solutions.  The Municipal Environmental Research Laboratory develops new
and improved technology and systems to prevent, treat,  and manage wastewater
and solid and hazardous waste pollutant discharges from municipal and com-
munity sources, to preserve and treat public drinking water supplies, and
to minimize the adverse economic, social, health, and aesthetic effects of
pollution.  This publication is one of the products of that research and
provides a most vital communications link between the researcher and the
user community.

This report describes the laboratory feasibility investigations and the
design and construction of a full-scale, mobile system for treating
excavated, contaminated soils at a field site by sieving, disintegrating
the soil matrix, and cleansing the soil of hazardous chemicals.  The system
is expected to take its place among other emerging methods such as in situ
treatment or incineration, for treatment of contaminated soils at the
actual site of a release under a wide variety of circumstances.
                                  Francis T- Mayo
                                  Director
                                  Municipal Environmental Research Laboratory
                                        iii

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                                  ABSTRACT

Laboratory tests were carried out with three different pollutants (phenol,
arsenic trioxide, and polychlorinated biphenyls [PCB's])  and two soils of
different character (gravel/sand/siIt/clay soil and organic loam topsoil)
to evaluate a technique for the scrubbing or cleansing of soils conta-
minated with hazardous materials.  The results of the tests were used in
the design and construction of a full-scale system for field evaluation in
cleaning excavated contaminated soils.  The system employs two major soil
scrubbing components: a newly designed water-knife, screen stripper, and
soaking unit for breaking up soil lumps and stripping chemicals from larger
particles (<2.5 cm but>2mm in diameter); and a countercurrent chemical
extractor for washing the smaller particles (<2 mm)that pass through the
screens.  The complete soils scrubbing system also requires the use of a
wastewater treatment system to permit recycling of the washing fluids and
an air cleaner when gases are evolved.  The projected processing rate of
the complete system is 2.3 to 3.8 m^/hour [3-5 yd^/hr).  (Treatment
ratesrange from  11.5-13.5 m3/hr (15-18 yd3/hr) when only the water-
knife unit is needed.)  Treatment residues consist of skimmings from froth
flotation, a mixture of washed gravel, sand, and organic detritus
discharged from the knife-screen unit, fine particles from the extractor,
the spent washing fluids, exhausted carbon, and the other treatment
products (floes, sediments).

A potentially limiting constraint on the treatability of soils is their
clay content, since clays generally are good adsorbers and the particles
may not be so effectively scrubbed as are sands.  In particular, clay lumps
that are only surface contaminated should be removed before full
disintegration is accomplished (since the uncontaminated particles could
then function as adsorbents and lower the efficiency of the cleansing).
Contaminant-saturated consolidated clay lumps, upon disintegration, will
release pollutants, however.  Most inorganic compounds, almost all water
soluble or readily oxidizable organic chemicals, and some partly
miscible-in-water organics can be treated with water or water plus an
additive.

During limited laboratory extraction tests, phenol was very efficiently
removed from both organic and inorganic soils, whereas PCB and arsenic
oxide clung more tenaciously to the soils and were released far less
readily into the washing fluids.  Until acceptable limits of residual
concentrations in the washed soil are agreed upon, the utility of the soil
washer in a particular situation cannot be assessed.  Laboratory tests did
show that soil scrubbing vastly speeds up the release of chemicals from
soils, compared with the much slower rate that occurs under natural
leaching conditions.

                                      1v

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A full-scale soil scrubber has been constructed  and  tested  and  is  ready for
further demonstration.  The cleansed soil can be  returned to  the  site  from
which the contaminated soil was excavated.

This report was submitted in fulfillment of Contract  No. 68-03-2696  by
Rexnord, Inc. under the sponsorship of the U.S.  Environmental Protection
Agency.  This report covers the period December  1976  to April 1982,
and work was completed as of November 1982.
                                     iv

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                                   CONTENTS
Foreword	   ill
Abstract	    i v
Fi gures	    vi
Tables	   vii
   1.  Introduction	     1
   2.  Conclusions	    10
   3.  Recommendations	    11
   4   Selection of Scrubbing Methods, Soils, and Chemicals for
       Testing	    12
   5.  Preliminary Laboratory Testing Program and Results	    26
   6.  Implications of the Preliminary Laboratory Testing Program
       on System Design and Soil Treatment	    62
   7.  Design and Construction	    68
References	    82

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                                    FIGURES
Number                                                                   Page
  1.  Schematic of soil scrubbing operations	
  2.  Schematic of the water knife used for chemical stripping and
      1 ump breakdown	   14
  3.  Schematic of counter-current chemical extraction system with
      two extractions	   15
  4.  Schematic of hydrocyclone solids/liquid separator	   17
  5.  Inorganic soil for laboratory experiments	   23
  6.  Organic soil for laboratory experiments	:	   24
  7.  Schematic of water knife testing apparatus	   28
  8.  Rotary screen and water kn ife	   29
  9.  Typical soil breakdown data for preliminary water knife testing...   30
 10.  Laboratory froth flotation testing apparatus	   32
 11.  Laboratory hydrocyclone testing apparatus	   35
 12.  Loss on ign/ition (LOI) and adsorption of phenol versus soil
      gradation ,for an organic soil	   48
 13.  Soil and solvent movement during shaker tests with solvent recycle   55
 14.  Soil phenol reduction as a function of number of extractions
      using two different extraction methods	   61
 15.  Process flow scheme for soil scrubber	   69
 16.  Fully constructed rotary drum screen scrubber	   72
 17.  Soil loading and metering system	   73
 18.  Soak zone description	   74
 19.  EPA Froth Flotation Unit (beach cleaner) modified as a
      counter-current chemical extractor for soil scrubbing	   76
 20.  Process flow chart of counter-current chemical extraction system..   77
 21.  Cost per volume treated for scrubbing phenol from soil	   81
                                      vi

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                                    TABLES

Number                                                                   Page

  1.  Properties of Soils Selected for Preliminary Laboratory Tests	  25

  2.  Summary of Hydrocyclone Testing Results	  37

  3.  Hydrocyclone Test Results for Solids Removal from Overflow	  39

  4.  Comparison of Preliminary Settling Test Results with Hydrocyclone
      Overflow Total Solids Concentration	  40

  5.  Beaker Settling Test Results	  41

  6.  Column Dosing Test Results for Phenol	  44

  7.  Distribution of Phenol on Organic and Inorganic Soils by
      Particle Size	  45

  8.  Distribution of Arsenic on Organic and Inorganic Soils by
      Particle Size	  46

  9.  Water Knife Test and Submerged Washing Results for Soil
      Particles in the Size Range of 2mm to 12.7mm	  51

 10.  Phenol Distribution in Soil Samples Used for Water Knife and
      Submerged Washing Tests	  52

 11.  Single Extraction Test Results	  56

 12.  Summary of Phenol Extraction Efficiency for Counter-Current
      Extractions	  59
                                    vii

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                                   SECTION 1

                                  INTRODUCTION

NEED FOR NEW TECHNOLOGY

The leaching of hazardous materials from  contaminated  soils  into  groundwater
is recognized as a potential threat to the  nation's  drinking water
supplies.  Such situations occur  as the result of  accidental  spills  of
hazardous substances and as releases from the many uncontrolled hazardous
waste disposal sites now known to exist throughout the country.   Current
corrective technology is largely  limited  to the excavation and transfer of
such soils to suitably sealed or  lined landfills where uncontrolled  leaching
cannot occur.

Onsite treatment can often be a more cost-effective  solution to the  problem,
and avoids the need for transporting hazardus wastes.   Research projects
have demonstrated, for example, that contaminated  soils  can  be isolated by
grouting, slurry-wall trenching,  installation of steel  piling, etc.,  and
then subjected to in-situ leaching for treatment.  The effectiveness  of such
processes is limited by, among other factors, the  permeability of the soil
in its undisturbed state.

An alternative process is desirable for those situations  in  which soil
permeability or other factors prevent effective cleanup  by in-situ
leaching.  This proposed technology, the  subject of  the  current effort,
consists of excavation onsite, above-ground treatment  of  the contaminated
soil, and return of the treated soil to its original site.   Excavation of
the soil from its natural state opens a number of  options for improved
separation of contaminants through better mixing and the  ability  to  use
different solvents.  Such cleanups can also be carried out more quickly than
they could with the in situ leaching of a more or  less compact natural
soil.  An integrated engineered approach  also makes  it possible,  or  more
convenient, to incorporate the controls needed for air emissions  and/or
treatment of the contaminated wastewaters generated  by the process.

In passing, one may note that, once a soil  is excavated,  cleanup  is  not
restricted to the washing approach described herein.   Washing with organic
solvents, processing with fluids  at or above their critical  points,  wet air
oxidation, incineration, and other flushing and/or disintegrative processes
may be applicable.  The prospective costs associated with each approach must
be based on a specific situation; it is not realistic  to  assume that  there
is any universal "best" approach  in terms of either  cost  or  effectiveness.

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The purpose of this project was to carry out appropriate laboratory studies
and then design and construct a system capable of treating a wide range of
excavated contaminated soils.  Ideally, the resulting system will be useful
for the correction of long-standing contamination problems (waste disposal
sites), as well as for emergency cleanup of spills.

SELECTION OF WASHING FLUIDS

A variety of washing fluids can be used to cleanse contaminated soil,
depending on the nature and properties of the chemicals to be removed
and of the soils themselves.  An effective treatment fluid or solvent must
have these characteristics:

   1. Favorable separation coefficient for extraction.
   2. Low volatility under ambient conditions.
   3. Low toxicity.
   4. Safety and ease of handling in a field situation.
   5. Recoverability.

Desirable Characteristics of Fluids

Favorable Separation Coefficient—The contaminant must be soluble in the
solvent and the solvent itself easily separated from the soil.  The higher
the solubility of the contaminant in the fluid, the lower the volumes
required for extraction.  The solvent should be effective for a large number
of contaminants and a wide variety of mixed hazardous substances.
                                    '
Low Volatility—The solvent should not be extremely volatile, especially
under ambient conditions, nor should it be flammable.  Excessive volatility
could result in significant solvent losses into the air and in causing
hazardous situations for operating personnel.

Low Toxicity—The contaminant to be scrubbed from the soil poses a potential
exposure hazard to treatment system operators, especially during those steps
of the process that are intended to reconcentrate the contaminants, e.g., in
the processing of spent extraction fluids.  A treatment fluid should not
subject treatment operators to unnecessary, additional hazards.  The
quantity of treatment fluid in the treatment system at any one time will
probably be many times greater than the amount of contaminant.  The exposure
hazards from contaminants and treatment fluids will chiefly consist of skin
and eye contact diseases and inhalation effects.

Safety and Ease of Handling—When a mobile system incorporates potential
ignition sources such as an internal combustion engine generator and an
electrical power system, special equipment design and operational procedures
are required to minimize the potential for fire and explosion in the
presence of flammable and/or explosive mixtures, contaminants, or treatment
fluids.  The transport and handling of such fluids is of equivalent concern.

Recoverability—The spent treatment fluids must be recoverable in a
field-oriented treatment system so that cleaned fluids can be recycled and
ultimately disposed of in an uncontaminated form.

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Types of Cleaning Fluid

Assuming that most contaminants can be classified  as either  organic  or
inorganic, three basic solvent systems can be  identified:

   1.  Water only.
   2.  Water plus an additive.
   3.  Organic compounds  (neat or as mixtures).

When the system uses water or water plus an additive, most  inorganic
compounds, almost all water soluble or oxidizable  organics,  and  some par-
tially miscible-in-water organics can be treated.  The  important  steps
involve obtaining good contact (high mixing energy) between  the  soil  and
water and using the optimized amount of additive.  These  additives may
include:

   1.  Acids to improve removals of metal salts and oxides.
   2.  Bases to enhance safety and removel for cyanide  compounds, solubilize
       phenolics, etc.
   3.  Oxidants to aid in organic and reducing agent treatment.
   4.  Surface active agents to increase solubility of  organics  in the
       water phase.

Organic solvents allow more effective removal of organic  contaminants,
which action is a crucial consideration for compounds that have  low  water
solubility.  However, handling these materials in  a field situation  can be
extremely difficult.  Most are volatile and many are flammable.   An  organic
solvent such as hexane or Freon may not be effective for  all  contaminants,
or may extract humectic components and harmless organics  from the soil and
lead to a fouling problem with washing fluids and  components.  Organic
solvent mixtures present special problems in recovery and reuse.  Finally,
adapting field equipment for use with an organic solvent  is,  at  best,
extremely difficult and costly.  The advantage of  using organic  solvents to
remove certain organic contaminants did not appear to outweigh the
significant disadvantages of organic solvents for  a system of the size and
cost contemplated.  For these reasons, this project concentrated  on  the
development of soil washing technology that employs water plus an additive
as a washing fluid.

When the unit is constrained to use water+additive washing fluids, the
removal effectiveness for organic contaminants may be poor.   Soil washing
with water is most efficient for compounds with a  high  water  solubility and
a greater affinity for the water than the soil.  This situation makes the
soil scrubber most efficient with short-chain organic compounds,  other
organics with a relatively high water solubility,  and inorganics  that are
rather soluble in water.  The inorganic removal efficiency may decrease in
those instances where the compound has a strong affinity  for  the  soil compo-
nents, especially, clays.  This phenomenon may be  critical for pollutants
that are chemically sorbed onto certain soil types.

Acceptable discharge levels will determine whether on site soil washing is
an appropriate treatment method for any particular contaminant.   The "clean"

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soil contaminant levels will certainly vary with the chemical  involved.
For example, treatment of'an alcohol to a parts-per-million  level may  be
acceptable while pesticide by-products may require treatment to  the  low
parts-per-billion range before environmentally safe discharge  of the soil.
When evaluating the potential usefulness of a washing process, these levels
of cleanliness must be defined beforehand.  It may also be practical to
scrub the soil to a contaminant concentration level that will  reduce the
grade of landfill required for disposal, i.e., from a hazardous  landfill  to
a sanitary landfill.

Care must also be taken to avoid compounding problems when scrubbing soil.
Transfer of contaminant to the water phase and subsequent water  treatment
will often result in a solid waste for eventual disposal.  The residual may
be spent carbon or a treatment sludge and the volumes involved may be  quite
large.  Problems and costs associated with disposal of these residues
should not exceed those that would have been encountered when  handling the
contaminated soil alone.

CONCEPTUAL APPROACH TO SOIL SCRUBBING

A review of available literature on soil systems, soil/chemical  inter-
actions, and treatment procedures produced little directly applicable
information.  It was necessary to rely on the past experience  in soil
handling and treatability of the project team and on common  sense in order
to establish reasonable limitations and to identify the potential
applicability of a particular technique.

A simplified schematic of the basic operations involved in soil  scrubbing
is shown in Figure 1.  The first step in soil washing involves excavation
of contaminated soil, which can be accomplished using various  types of
construction machinery and earth-moving equipment.  The removed  soil must
be reduced in size and the sofl structure or "fabric" disintegrated to
allow effective contact between the solvent and soil particles.

This type of pre-conditioning requires mechanical action on  a  wide variety
of soil types.  After size reduction, the appropriately conditioned soil  is
then ready for actual treatment in the scrubber.

The treatment action involves two mechanisms:

   1.  Physical stripping of that portion of the contaminant that is not
       tightly bound to the soil particles.  The contaminant may have
       filled void spaces and be physically trapped in the soil  system.
       Removal can be effectively accomplished by stripping the  contaminant
       from the soil, possibly by using high pressure fluid rinsing.

   2.  Extraction of the tightly bound contaminant from the  soil into  a
       solvent.  This step allows transfer of the contaminant  into a phase
       more easily handled using conventional treatment processes.  The
       extraction efficiency may be increased by applying a countercurrent
       approach and solvent use can be optimized if solvent treatment  and
       recycle are utilized.

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The soil scrubbing approach is quite simple; however, there  are  significant
difficulties involved in applying these concepts to complex  situations of
soil contamination.  Soil types vary considerably both  in their  physical
characteristics and attraction for different contaminants.

SOIL TREATABILITY POTENTIAL

The varied geologic history throughout the United States has resulted  in
complex combinations of near-surface soils, as exhibited by  their wide
range of chemical constituents, gradations, and organic content.  These
variables affect the soil treatability potential.

The treatability potential of any soil can be considered a combination of
its physical handling and sorption/desorption characteristics.   For
example, it may be technically feasible to desorb a particular contaminant
from a clay soil, but the mechanical effort and energy  required  to disinte-
grate the clay to a particle size that allows the contaminant to be
desorbed efficiently may result in low cost-effectiveness and low
treatability potential.

The wide variety of qualities encountered in the soil systems can adversely
affect the processing equipment.  Major difficulties or limitations can
result from:

   1.  The gradation of the soil particles, primarily the predominance of
       large objects such as rocks or boulders.  Large  rocks, boulders,
       tree roots, and branches cannot be easily broken down by  conven-
       tional size reduction equipment; they should, therefore,  be
       presorted and disposed of separately.

   2.  The clay content of the soil, primarily as related to large zones of
       clay or cohesive materials.  The cohesive and plastic nature of most
       clays, combined with their very small particle size,  makes it
       difficult to rapidly break them down into treatable sizes.  Most
       conventional size reduction systems are designed to handle only a
       certain maximum percentage of clay within a soil structure.  Clays
       can be broken down by freezing or drying combined with impact or
       crushing techniques.  However, these methods are energy intensive
       and, in general, are not very practical for high volume materials
       handling systems.  Note that the plasticity of the clay results in a
       low permeability so that the potential impact of a contaminant  spill
       on clay is much less than on a sand or gravel soil, unless the  clay
       is finely divided and dispersed (large surface-to-volume  ratio).

       The percentage of clay will directly affect the  rate  of soil treat-
       ment both at the pre-treatment stage and during  the chemical
       treatment phase itself.  Although this limitation of  clay within a
       soil system is significant, throughout most of the United States,
       use of the scrubber unit is feasible and adaptable.

   3.  The root system typically developed in a thick topsoil can foul many
       mechanical systems designed to break down soil into more  easily

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               handled sizes.   Roots tend to be flexible and resilient, and wind
               around  most rotation devices.  A common example which is understood
^,«,             by gardeners is the way in which roots tend to wind around the shaft
               of a rototiller.  Large tree roots or branches are also difficult to
               process with conventional  soil handling systems because of their
               bulk and resistance to breakdown.

        Desorption Characteristics

        The  soil/chemical  interactions that affect sorption/desorption are
        complex.   The  desorption of a contaminant from a soil is related to, though
        not  necessarily a  direct function of, the sorptive ability.  Adsorption
        onto a  soil surface is a phenomenon based upon physico-chemical equilibrium
        conditions between the contaminant, soil water, and soil itself.  The
        solubility of  the  contaminant in  water and the reactions between the
        contaminant and the soil components determine the equilibrium that is
        established.

        Researchers have evaluated attenuation or adsorption of contaminants in
        soils rather than  contaminant desorption (much work has been done on
      •  modeling  dispersion/diffusion of  pesticides in soil).  Although the
        sorption/desorption relationship  is not well-established, the generalities
        and  methods of adsorption may be  appropriate for a basic understanding of
        desorption. The existing research does suggest the following unquantified
        relationship:

             A =  f(C,  pH,  Or,  Co,  t).  The  definition  of  the parameters  follow.
*w»
        "A"  is  the attenuation of a given contaminant by the soil in question,
        expressed as percent removed from solution.  Attenuation is proportional to
        five parameters, the first being  the clay factor "C".  The clay factor, in
        turn, is  a function of four, interrelated factors:

           1.  clay content of the total  soil volume
           2.  type of clay mineral in the soil
           3.  exchange capacity of the clay
           4   specific surface area of the clay.

        The  directly proportional functional relationship between attenuation and
        increasing clay content implies an inverse relationship between attenuation
        and  an  increasing  content of granular material  in the soil.

        The  term  "pH"  refers to the pH of the soil/contaminant environment.  This
        includes  both  the  contaminant waste stream and the natural soil pH condi-
        tions.  The attenuation is affected by the pH of the leaching solution and
        is  a function  of the specific contaminant and the retention mechanism
        involved  in its removal from solution.

        "Or" is the organic content of the soil.  The organic content is most
        important when evaluating organic contaminants that tend to readily adsorb
        onto organic matter in the soil.   Whether the organic matter is in the form
•—      of  living roots or dead decaying  material may be important because of the
W      differences in structure and composition.

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"Co" is the contaminant concentration factor.  At low levels, the concen-
tration of the waste stream may influence the attenuating mechanism
operative in the soil system.  However, the situation is somewhat different
at high contaminant concentrations.  The soil, in many cases, may be
incapable of attenuating the applied dosage even when all of the factors
needed are present, simply because it does not have the required surface
area or sufficient exchange capacity.

The term "t" is a time factor.  Attenuation is directly related to the
contact time between the contaminant and the soil, all other conditions
being constant.  The attenuation achieved during a given contact time
should be proportional to the permeability of the soil.  The permeability
of the soil is directly related to its grain-size distribution, which ties
in with its mineralogical composition.

Soil contamination situations can be grouped into two types as differ-
entiated by a time factor:  immediate problems and long-term situations.  A
spill occurrence is a problem which, when responded to immediately,
involves only a short contact time between soil and contaminant.  Long-term
situations of soil contamination, on the other hand, result from initially
untreated spills or from improper chemical waste disposal practices.

The contaminant contact time defines the rate at which equilibrium will be
established.  For spill situations in which the contaminant can be
relatively quickly contained or removed, the soil/chemical interactions may
be minimal.  Conversely, in a long-term situation where leachate slowly
leaks from a landfill, the soil/chemical equilibrium reactions may be well-
defined and established.

The time effects are most prevalent in cohesive or clay-like soils.  Since
the permeability and flow rate are low in a clay or silt structure, the
contaminant will require a longer time to contact the soil and to be
adsorbed onto the soil surface.  With time, the amount adsorbed will
increase and the subsequent time for desorption may also increase.  In a
sand or gravel soil, on the other hand, a spill will flow almost
immediately through the soil structure, contacting the soil surface and
moving quickly onward.  In this latter situation, the effects of time are
less significant.

PROJECT OBJECTIVES

The purpose of this project was to develop and construct a mobile system
for demonstration of the extraction of hazardous materials from spill-
contaminated soils.  The goals of the soil-scrubbing system are threefold:

   1.  To clean contaminated soil sufficiently to make it suitable for
       redepositing into the place from which it was removed

   2.  To separate hazardous materials from the extracting fluids to the
       extent that the fluid is non-contaminated
                                      8

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   3.  To recover the hazardous material in such a form that  it can  be
       handled, reprocessed, and/or disposed of by environmentally
       acceptable methods.

This project did not explore technology for breakdown of  large soil  lumps
in any detail.  Rather, the assumed inlet situation was free-flowing  soil
which an entry screen would restrict to 2.5-cm  (1.0-in.)  particles or
smaller.  The project did not address the spent washing fluid treatment
system, which will probably consist of a physical/chemical treatment  system
such as EPA possesses and has already demonstrated for field  use  (14).
Cleaning of the air contaminants generated by the process was not
addressed, except to provide containment of these emissions with
connections for ducting to an appropriate air cleaner.  The primary
emphasis of this project was on the scrubber itself, specifically on  those
components that permit soil particles to be effectively washed through
physical and chemical reactions.

Prior to design and construction, alternative approaches  were evaluated and
selected approaches were tested on a laboratory scale.  This  report dis-
cusses those evaluations and their influence on the ultimate  construction
of the components for demonstration.

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                                  SECTION 2

                                 CONCLUSIONS
The following conclusions can be drawn from the work carried out during
this program and the knowledge gained during that effort:

   1.  Spill-contaminated soils can be excavated and treated onsite,  using
extraction with water or aqueous solutions for many pollutants frequently
encountered in such situations.

   2.  A system capable of decontaminating 2.3 to 3.8 m3/hr (3-5 yd3/hr) of
soil has been designed and constructed and is now available for field
testing by the U.S. Environmental Protection Agency (EPA).  If finer  (<2mm)
are absent or do not require treatment, the processing rate (water-knife
drum screen unit) is 11.5-13.5 m3/hr (15-18 yd3/hr).

   3.  Water knives function as a compact and economical means of  achieving
effective contact between contaminated soil particles and extractant.

   4.  Countercurrent extraction is effective in removing certain  adsorbed
contaminants from soils and, for the size of equipment needed, hydro-
cyclones are the preferred devices for separating the extracted solids from
the extractant.

   5.  Laboratory experiments demonstrate that soil characteristics
(particle size, distribution, organic content, pH, ion-exchange properties,
etc.) are very important factors in the removal of contaminants.

   6.  In addition to the percent-contaminant removed, the allowable  level
of pollutant remaining in the soil is an important consideration in
determining when adequate decontamination has been achieved, since the
final concentration affects the options available for disposal of  the
residual solids.
                                      10

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                                  SECTION 3


                               RECOMMENDATIONS
Based on the observations made during this investigation,  several
suggestions are offered for future work.

   1.  Laboratory screening tests should be performed on a wider  range  of
typical compounds and mixtures encountered in hazardous substance  spill  and
release situations to ensure that high levels of decontamination  can  be
achieved with this process.  Conversely, lab tests should  be  performed
before the complete system is field-mobilized.

   2.  The results of this study apply primarily to spill  situations.
Contaminated soils found at waste disposal sites may exhibit  different
extraction characteristics because of the extended soil/contaminant contact
time and of weathering and in situ reactions.  Studies are needed  to
establish whether and to what extent such changes affect the
decontamination process.

   3.  Other extractant solutions and solvents should be explored  to  learn
whether the efficiency of the process can be improved without damaging  the
equipment or increasing the hazards to which the workers may  be exposed.

   4.  A wider range of soils should be examined to determine what changes
in the system are practical to better cleanse soils with characteristics
(e.g., greater cohesiveness and adsorptive properties of clay- or  silt-rich
soils) that differ significantly from those of the soils already  tested,
and to evaluate the tendency of disintegrated clay (clay particles) to
function as adsorbents.
                                      11

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                                   SECTION 4

                        SELECTION OF SCRUBBING METHODS,
                        SOILS,  AND CHEMICALS  FOR  TESTING

 As the first stage in the development of a soil scrubber, it was necessary
 to make preliminary scrubbing equipment choices and to experiment with
.these methods on a laboratory scale using selected chemicals and soils.

 Physical Stripping

 The first step in the processing train involves physical stripping of
 contaminants that are not physically or chemically adsorbed on the soil
 particles.  Since a significant amount of contaminant could be entrained  in
 soil void spaces, this effort may result in high treatment efficiencies.
 However, since pretreatment devices would probably not be capable of fully
 breaking down soil lumps, a secondary objective for this equipment involves
 further size reduction below 2.5 cm (1.0 in.) in diameter.

 Both contaminant stripping and lump breaking require a relatively high
 level of energy input for the greatest efficiency.  Several systems were
 evaluated and all but one were eliminated from further consideration.
 Commercially available rotary scrubbers were eliminated because the action
 of the slowly rotating cylinder was not considered sufficiently energetic
 to perform stripping and lump breakdown.  The log washer, generally used  in
 the aggregate industry for washing clay and silt from sand or gravel, was
 also evaluated.  The device is basically an inclined rotating screw
 conveyor with internal beater paddles that increase the cleaning action.
 Unfortunately, the rotational speed of the arms is quite low, which reduces
 the unit's effectiveness in breaking down clay lumps.  In addition, the
 equipment requires large volumes of water for proper operation, a condition
 that could significantly impact its ultimate usefulness in the field.

 The attrition scrubber uses high energy scrubbing forces applied by a dual
 propeller mixer.  The pitches of the two blades are opposed, which causes a
 substantial amount of mixing turbulence.  An attrition scrubber is intended
 for use on sand-size particles and may not be suitable for breaking down
 clay lumps.  Efficient use of this device requires feed concentrations of
 70-percent solids, which is a difficult constraint to meet in a natural
 soil system contaminated with chemicals.  Wet soil can foul the unit and
 cause serious operational difficulties.  A large amount of gravel in the
 soil will cause undue wear and vibration on the equipment.  Also considered
 but rejected were: horizontal vibrating screens, fixed blade mixers,
 concrete mixers, aggregate scrubbers, ball mills, jaw crushers, hammermills
 and non-clog hammermills (1).

                                       12

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Another high energy system uses water knives to create a powerful fluid
stream for contaminant stripping and lump breakdown.  The water knives are
small, flat-blade nozzles that function by creating a high velocity stream
of water in the shape of a long narrow line (Figure 2).  Washing  is
performed by directing the nozzle stream at a moving layer of material.
The relative motion between nozzle and material can be achieved by:

   1.  Moving the material past a stationary nozzle on a conveying
       mechanism.
   2.  Moving the nozzle over the top of a stationary layer of material.
   3.  Moving the material on a conveyor and moving the nozzle over the
       material.

The knife-like hydraulic action is achieved by a combination of the force
and thinness of the water stream.  The washing is instantaneous.  The
contact of the knife with the material can be so gentle that it can clean
peaches, or it can be so "sharp" that it will strip scale layers  from
steel.  In the soils scrubbing application, the water knife seemed capable
of both lump breakdown and scrubbing.  The volumes of water and pressures
needed for proper nozzle operation can be estimated from design parameters;
however, the actual effectiveness of the scrubbing technique for  treatment
must be determined from laboratory testing.

Extraction and Separation

Small soil particles will most likely be more affected by chemically bound
contaminants than large particles.  As a result, the physical stripping
process alone may not be effective for treatment of small particles, and an
additional step may be necessary.  Chemical extraction in a counter-
current mode was chosen as a treatment method.  This process is carried out
in a series of extraction steps in which the contaminated soils are given
sufficient time to contact solvents of increasing purity.  A schematic of a
simple system incorporating/two extraction steps is shown in Figure 3.  The
purpose of countercurrent extraction is to maximize the concentration
gradient between the soil and the solvent while minimizing the volume of
solvent required through solvent reuse.  Therefore, the flow of soils from
step to step is opposite to the flow of solvents, thus the name counter-
current.

Besides the extraction tanks, the countercurrent extraction system also
requires solid/liquid separators after each extraction step.  Various units
may be applicable, including centrifuges, belt presses, vacuum filters,
filter presses, and hydrocyclones.  A gravity separation procedure could
also be used between extraction stages but is likely to be inefficient,
time consuming and, therefore, impractical.  Centrifuges and filters are
often limited by solids loading and are extremely expensive, very large,
and often difficult to operate.  They do perform efficient separations;
however, they are not suitable for multiple separations in a mobile unit.
                                      13

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The hydrocyclone, on the other hand, is less efficient but has  a  high
capacity and relatively low cost.  It utilizes fluid pressure energy to
create centrifugal fluid motion, permitting separation or classification of
suspended solids.  It is also capable of separating fluids of different
specific gravities.  A sketch of a commercially available hydrocyclone is
shown in Figure 4.  Feed slurries enter a tangential inlet at the top of
the device, then spiral their way around the cylindrical walls  proceeding
downward.  Centrifugal separation occurs during the period of spiral ing and
those materials having a higher specific gravity migrate toward the outer
walls.  When the spiral flow reaches the lower part of the cyclone it
undergoes a direction change and begins to spiral upward toward the
outlet.  The result is a spiral within a spiral.  The materials along the
outer wall of the cyclone do not participate in this inner spiral action
but, rather, continue downward where they are discharged either
continuously or intermittently from the bottom of the cyclone.  The solids
concentration in the outlet streams vary with, among other things, influent
solids type and concentration, particle size, specific gravity, and fluid
viscosity.  Hydrocyclones do "lose" some fine solids in the overflow.  The
amount of material discharged in this manner and- its impact on  treatment
efficiency requires definition by lab testing.  Mixing and chemical contact
of particles with the solvent are enhanced by the action of the
hydrocyclone.

CHEMICAL SELECTION

Once the preliminary scrubbing equipment choices were made, it  was necessary
to choose contaminants and solvents to be used in the preliminary laboratory
testing.

Contaminant Choices

Four major criteria were addressed to select contaminants for preliminary
laboratory testing.  These criteria are that the selected chemicals should
be:

   1.  representative of a wide range of contaminants that could  impact
       soils systems.

   2.  classified as hazardous and presenting a high risk of spillage.

   3.  involved preferentially in existing soil-contamination problems,
       which could be partially or completely alleviated by successful soil
       scrubbing.

   4.  chosen to span the range of difficulty of removal.

On the basis of the above contaminant-selection criteria, the following
three contaminants were selected for preliminary laboratory testing:
                                      16

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INFLOW
 INFLOW
                              TOP VIEW
                               OVERFLOW
                              UNDERFLOW
                             SIDE VIEW
                                              APEX DISCHARGE
                                                CLAMP VALVE
     Figure 4. Schematic of hydrocyclone solids/liquid separator.
                                 17

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   Water soluble organic - phenol.
   Water insoluble organic - polychlorinated biphenyls  (PCBs).
   Relatively insoluble inorganic - arsenic oxide.

Phenol

The selection of phenol as a soil contaminant for the  laboratory  testing  is
well-justified.  This chemical is one of the few water-soluble organic
compounds that meets the majority of the selection criteria.  Phenol  is a
very hazardous substance that is highly toxic to humans when  ingested or
absorbed through skin.  Fatal doses as low as 1 g have  been reported;
however, the average fatal dose is 15 g (2).  The drinking water  standard
for phenol (to avoid taste and odor problems) is 0.001  mg/1.  This
substance is also extremely dangerous to the aquatic environment.  The
provisional water quality standard for the protection  of fish species is
0.01 mg/1.  The critical concentration for fish toxicity is 0.1 mg/1,
although there are species that can tolerate much higher concentrations (3).

Phenol is ranked extremely high in a ranking system which is  used to define
potential risks from hazardous materials spills (4).   In terms of the total
quantity of hazardous chemicals shipped by various means, phenol  is ranked
46 (of 257).  When ranked according to the overall risk (degree of hazard
and possibility of spillage) of spills of soluble hazardous chemicals,
phenol ranks first.  During a 2.5-year period from January 1971 to June
1973, approximately 293,000 L (77,410 gal) of phenol were spilled in 19
reported incidents.  Six additional incidents of spills occurred; however,
the quantity spilled was not reported.  Three spills resulting from train
derailments accounted for 85.3 percent of the total volume spilled during
this period (5).  These characteristics justify the choice of phenol for
testing.

Polychlorinated Biphenyls (PCB)

The major reasons for the selection of PCB as a contaminant for the
laboratory testing are the existing soil contamination  problems with this
material and the hazardous nature of the substance.  Unlike many other
hazardous chemicals, the probability of spills of PCB  during  transport
are currently quite small since the sale, production,  and shipment of PCB
was drastically reduced since mid-1971.  The majority  of all  the PCBs
manufactured during 45 years of production are still in use,  however,
primarily in electrical transformers and capacitors, heat transfer systems,
and hydraulic systems.  When this material is replaced, it is transported
to storage and disposal sites.  Fortunately, due to stringent government
regulation, accidental spills are becoming less frequent; however, there  is
a significant portion of the total PCB production that  remains in the
environment (air, water, soil, and sediments).  Also,  a large fraction of
this material  is present in dumps and landfills (6).   The existence of
specific problem areas, such as Chatham County, North  Carolina, and other
smaller areas throughout the country, provide the justification for
laboratory testing of PCBs.
                                      18

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        There is little dispute as to the hazardous nature of PCBs.  Although it
        does not exhibit acute toxicity (toxic effects from high level, short-term
w-     exposure) it does accumulate in many biological species exhibiting chronic
        toxicity even at very low concentrations.  The chronic or long-term effects
        of PCB exposure are similar to the chronic effects of DDT exposure.  The
        extremely stable nature of PCBs and their persistence in the environment
        make this problem much more serious than that encountered with DDT.  Unlike
        DDT, the quantity of PCB present in the environment has not decreased
        greatly since the initiation of regulations on the production and disposal
        of these materials (6).

        PCBs also meet the other selection criteria for an experimental soil
        contaminant.  This chemical represents a unique group in that it is
        extremely insoluble and heavier than water.  Solubilities of PCB range from
        0.24 mg/1 for Aroclor 1242 (primarily two, three, or four substituted
        chlorine atoms) to 0.0027 mg/1  for Aroclor 1260 (primarily five, six, and
        seven substituted chlorine atoms) (6).  Therefore, the laboratory approach
        for testing the feasibility of removing PCB with a soil scrubbing system
        with water as the solvent had to examine additives such as surfactants to
        increase PCB solubility.  As a result of the extremely low solubilities and
        the lack of information on how to remove PCB that is bound to organic
        materials within the soil, this material indisputably meets the "difficulty"
        selection criterion.  PCB also represents an extremely persistent group of
        chemicals.  Its stable nature is one of several properties that made it
        ideal for use as dielectric and heat transfer fluids.  The ability to
        degrade PCB has been demonstrated in some microbial species, however, the
        rate at which degradation proceeds is extremely slow.  PCB is among the
        most persistent of all potential organic soil contaminants.

        Arsenic

        The inclusion of arsenic compounds as soil contaminants for the laboratory
        testing is to provide information on the feasibility of removing hazardous
        inorganic materials from soils with a scrubbing system.  Arsenic belongs to
        the chemical group V-A.  This group includes typical non-metals (nitrogen
        and phosphorus), a typical metal (bismuth), and elements that are often
        referred to as metalloids (arsenic and antimony).  Arsenic generally
        exhibits chemical properties intermediate to the extremes exhibited by
        other members of this group.  Arsenic compounds occur in many forms
        including halides (e.g., AsCl3, AsFs), arsenites (e.g., AS03 =),
        arsenides (e.g., Zn3As2, MgaAsz), sulfides (e.g., As2S3),
        oxides (e.g., As20a, As205), and oxygen acids (e.g., HaAsOs) (7).  Two
        common oxidation states of arsenic in solution are As(III) and As(V).  The
        ionic forms and solubility of arsenic present in solutions are highly
        dependent on oxidation potential (Eh) and pH.  Other ions in solution and
        minerals associated with soil solids influence the solubility and ionic
        form of As.

        Arsenic trioxide (As20s) is the most important arsenic compound in
        terms of manufacturing technology and is utilized to produce nearly all
        other arsenic compounds.  These compounds include insecticides, weed

w                                           19

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   killers,  rodent  poisons,  sheep  dip,  wood preservatives, Pharmaceuticals,
   and hide  preservatives.   The  oxide  is  also used in the production processes
   for commercial and  ornamental glass,  Paris Green,  and enamels (7,8).
   Although  there are  a  large  variety  of  arsenic  compounds that could be
   utilized  as  potential  soil  contaminants  for the laboratory testing, arsenic
   trioxide  was the most  desirable because  of its widespread use.

   Nearly  all compounds  containing arsenic  are extremely toxic to many animal
   and plant species.  This  is verified  by  the fact that a large number of
   arsenic compounds are  used  in an assortment of pesticides and herbicides
   (7,8).  Also, the potential hazard  posed by arsenic compounds in general
   has been  evaluated  through  rankings  in terms of the total quantity of
   materials shipped and  the overall risk from a  spill.  Of the 257 hazardous
   chemicals considered,  arsenic compounds  ranked only 221 in the annual
   quantity  shipped.   However, when ranked  according  to the potential risk
   from  spills  in aquatic systems, arsenic  compounds  have an intermediate
   ranking of 98 (1).  There have  also  been several occurrences of soil
p  contamination problems with arsenic  compounds, although these occurrences
5 "  are not well-publicized  in  comparison  with other contamination problems
   such  as those with  PCB.

tj  Solvents

   Several classes  of  additives  were considered:

      Acids.
      Bases.
      Polar  organics (short  chain  alcohols).
      Oxidizing agents.
      Reducing  agents.
      Surfactants.

   Two major considerations  for  the selection of  additives were cost and
   associated hazards.   Extraction of  contaminants with an extremely high or
   low pH  solvent would  require  large  quantities  of additives.  Also, the
   "clean" soil may not  be  suitable for  return to the spill  site without
   additional treatment.   Likewise, additives formulated with extremely toxic
   components could not  be  selected.

   Solvent for  Phenol
   Since  phenol  is a  fairly  soluble  organic  (8.2  percent @ 15°C) and is also
   quite  polar,  proposed  solvent  conditions  included  water alone (neutral  pH),
   water  in  a pH range  from  1.0 to  12.0,  methyl alcohol  and water,  and two
   aqueous surfactants.

   Methyl alcohol was selected as an additive  to  water  since phenol  is very
   soluble in alcohols.   Two  surfactants  (Tween 80  and  MYRJ 52 from ICI Inc.)
   were selected for  testing  since  these  materials  are  manufactured for the
   purpose of increasing  the  solubility of organics in  water by forming an
   emulsion.

                                         20

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Solvents for Arsenic

As discussed previously,  the  solubility  of  arsenic  ions  in a soil/water
system is  influenced by oxidation  potential,  pH,  other  ions in solution,
and materials  associated  with soil  solids.  Therefore,  a range in solvent
pH, an oxidizing  agent  (sodium hypochlorite),  and a reducing agent (sodium
bisulfite) were selected  for  laboratory  testing.  At low Eh (oxygen
depleted soils).  As(III)  is the primary  form  of  arsenic  in natural soils
and the solubility  is primarily a  function  of pH.  Below a pH of 8,
cationic forms of As(III)  predominate, e.g.,  AsO+l.  Various anionic
species (^AsOJ1"2)  are present at  pH  values above 9.0.   Arsenic (III)
oxide (As203) was selected as the  soil contaminant; therefore, a range
of solvent pH was considered  a viable means of extracting the arsenic  from
soil.  Arsenic can  be present in a  wide  range  of  oxidation states (-3  to
+5), so both a strong oxidizing agent and a strong  reducing agent added to
water were selected as solvents for laboratory extraction testing.

Solvents for PCBs

In a review of available  literature,  only one  solvent additive was
identified as  increasing  the  solubility  of PCB in water,  namely, a
commercially available surfactant called Tween 80.

The solubility of PCB in  water varies depending on  the  number of chlorine
atoms in the mixture.  For example,  the  solubility  of monochlorobiphenyls
range from 1.2 to 5.9 mg/1 at 2QQC, while the  solubility of the
decachlorobiphenyl  is 0.015 mg/1.   The solubility of the decachlorobiphenyl
in a 0.1 percent  Tween 80  solution  is 5.9 mg/1 and  exceeds 10 mg/1 in  a 1.0
percent Tween 80  solution.

On the basis of this information, only water  and  water  plus Tween 80 were
selected for laboratory testing.

SOIL SELECTION

Two representative  soils with differing  adsorption  capabilities, as well  as
somewhat variable physical handling  potentials, were selected for the
laboratory experiments.  Since a variety of chemicals were to be evaluated,
the broadest range of adsorption potential in  terms of organic content was
desired.  Thus, an organic soil and  a non-organic soil were selected.

The nature of the soil  structure was  also important in the selection of
soil types to be  evaluated.   A soil mass may contain  a wide variety of
gravels, sands, and clays.  The range and proportion  of  soil  types exhibit
varying degrees of cohesion between soil particles.   The  amount of energy
required to reduce the soil mass to treatable  sizes is a  function  of the
cohesiveness of the soil.  A  granular sand and gravel soil,  being
non-cohesive, can be readily  separated by sieving or  light crushing
forces.   Silt and clay, because of  their cohesive nature,  require  much more
energy for size reduction.  Both the  organic topsoil  sample and inorganic
gravel,  clay, and silt mixture chosen for testing exhibit  cohesive, as well
as non-cohesive,  tendencies.

                                      21

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Soil Descriptions

Sand with Gravel, Silt and Clay—A naturally occurring sandy material from
the Pioneer Pit in Kenosha, Wisconsin was selected as a representative
non-organic soil.  The clay and silt content was sufficient to  provide  some
cohesive clay lumps, although the material would generally be defined as
cohesionless (Figure 5).

Organic Topsoil~The organic soil was manufactured topsoil, produced by the
Liesener Topsoil Company of Jackson, Wisconsin.  It consisted of moist  peat
and humus, with little sand.  The organic content was 18.4 percent.  This
material represents a rich, friable, agriculturally excellent topsoil
(Figure 6).

Physical and Chemical Characteristics

The physical and chemical characteristics of both soils were evaluated.
Physical testing included specific gravity, organic content, unit dry
weight, permeability, and gradation.  These tests were useful in defining
the soils and in establishing correlations with other soil types.  Table 1
summarizes the properties of the selected soils.
                                      22

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                                                                  T
Figure 5. Inorganic soil for laboratory experiments,
                         23

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Figure 6.  Organic Soil for laboratory experiments.
                        24

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                  TABLE  1.   PROPERTIES OF SOILS SELECTED FOR
                         PRELIMINARY LABORATORY TESTS
             Parameter
Topsoil
Sand with gravel,
  silt, and clay
Physical characteristics

Specific gravity, g/cm3
Organic content, %

Natural conditions:
  Moist density, g/cm3
  Water content, %

Laboratory proctor density:
  Standard method, pcf*
  Modified method, pcf
  Optimum water content, %

Permeability:
  Falling head at natural
   density condition, cm/sec

Atterberg limits:
  Liquid limit
  Plastic limit
  Plasticity index

Gradation:
  Percent passing, %
  3/4" sieve, 19.1 mm
  No. 4 sieve, 4.76 mm
  No. 40 sieve, 0.420 mm
  No. 200 sieve, 0.074 mm

Chemical characteristics
  Cation exchange capacity,
   MEQ/100 g
  PH
  Conductivity, umho/cm
  Alkalinity, % CaCOs by weight
2.21
18.40
0.74
93.40
1.00

48.70



1.8 x 10-6
74
None
Non-plastic
100.0
100.0
82.5
56.0
26.0
6.9
860.0
0.61
   2.65
    1%
   2.07
   4.20
   2.23
   7.20
   7.4 x 10-7
   Non-plastic
   Non-plastic
   Non-plastic
   100.0
   60.3
   22.5
   14.9
   2.3
   7.9
   400.0
   5.28
*pcf = pounds per cubic foot.
                                     25

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                                 SECTION 5

             PRELIMINARY  LABORATORY TESTING PROGRAM AND RESULTS

INTRODUCTION

Once the preliminary scrubbing equipment selection and the choices of
chemicals and soils for laboratory testing had been made, the  actual
testing began.  The preliminary laboratory testing program had three
objectives, namely to:

   1.  define critical operating variables for potential scrubbing
       components.

   2.  develop laboratory procedures that could be used  to predict
       scrubbing efficiency.

   3.  test three hazardous chemicals representing a wide range of
       characteristics and potential for being removed by soil  scrubbing
       methods.

The laboratory testing was divided into two main parts.  First, equipment
testing was performed to establish certain scrubbing system
configurations and operating variables.  The actual chemical extraction
tests were then performed and incorporated much of the information
obtained in the equipment testing.

EQUIPMENT TESTING

Prior to beginning the chemical extraction testing, some preliminary
equipment testing was needed to define important operating variables for
potential scrubbing components.  The equipment evaluations centered on
three components:

   1.  Water-knife size reduction and stripping apparatus.
   2.  Froth-flotation mixing and contact unit.
   3.  Hydrocyclone liquid-solids separator.

Water Knife Experiments

Testing of the water knives involved determining an effective  contact
configuration and operational mode including nozzle type and size and
water flow-rate and pressure.  Initial tests were done with a  local
subsoil containing large amounts of clay lumps.  No chemical contaminants
were introduced in this phase of the testing.


                                     26

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        Contact  Configuration—Several  different configurations were tested to
        determine  which  one allowed the most effective stripping and lump
w      breaking.   Initial  tests used the water knives to scour soils laying on a
        moving,  impervious  belt.  Little lump breaking was accomplished since the
        high  pressure water from the knife propelled the lumps away from the water
        stream before any breaking up action could take place.  Supporting the
        soils on a screen and even using a secondary screen to sandwich the soil to
        hold  it  immobile did not improve the results.  It was concluded that the,
        water knife could not function  as a lump breaker unless the movement of the
        lumps was  constrained so that they could not move away from the knives.
        After some discussion of the problem, a tilted, rotary screen was selected
        as  a device which could provide the necessary constraint.  A schematic of
        the water  knife  and rotary screen assembly is presented in Figure 7 and a
        photograph of the rotary screen is shown in Figure 8.  A U.S. Sieve No. 10
        screen  (2-mm mesh openings) was selected to retain as much coarse material
        as  possible in the  basket for stripping while allowing the fine soil pass-
        through  to be transported to the extraction process.  This screen choice
        represented the  smallest mesh that would probably not be subject to
        plugging problems.

        Operational Mode—Various operational modes were tested using about 2.7 Kg
        (6.0  Ib) batches of the local subsoil.  The soil was placed into the rotary
        screen and physically stripped  for different time periods at a rotational
        speed of•about 20 rpm.  At various time intervals, residual soil weights
        were  recorded and observations  were made.

        The first  tests  were performed  at a water  flow rate of 4.5 1/min (1.2 gpm)
***•*"••      and a water pressure of 4.9 Kg/cm2 (70 psi).  The tilted orientation of
        the rotary screen caused the soil to remain in a small pile near the bottom
        of  the screen.  Slow rotation of the screen (10 - 20 rpm) continuously
        turned the soil  mass over to permit the knives to contact more of the
        soil.  In  addition, the water knife was moved up and down across the soil
        pile  so  that it  scoured the entire area of the pile approximately 20 times
        per minute.  As  the flow from the water knife contacted the soil, a violent
        scouring action  occurred and much of the loose soil was forced through the
        screen rapidly.   Figure 9 shows that the rapid initial breakdown of the
        soil  reduced the retained volume of the soil by two-thirds during the first
        two minutes of operation.  After this time, the soil reduction rate began
        to  diminish and  all that remained in the rotary screen was a small  amount
        of  gravel  and grayish clay lumps.  Effective breakdown of these clay lumps
        by  the water knives continued,  but more slowly.  A soaking step was found
        to  be helpful  in softening the  lumps for easier and faster disintegration.

        It  was concluded from the preliminary lab  tests that three cycles are
        needed for best  performance of  the water knives on the 2-mm screen:
                                             27

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Figure 8.  Rotary screen and water knife.
                  29

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   1.  A primary cycle using high pressure fluid recycled from  the
       collection sump.  During this period, small  soil  particles and  soil
       lumps that can be broken down to less than 2 mm  pass  through  the
       screen.

   2.  A secondary cycle composed of soaking and of stripping with water
       knives and spray nozzles.

   3.  A rinse cycle using clean water at low pressure  as a  last step
       before discharge of the retained sand and gravel.

Froth Flotation Unit Testing

One alternative piece of equipment for use as a mixer/contactor during
chemical extraction was the available EPA froth flotation unit  (13).   To
determine the feasibility of utilizing the existing mobile froth flotation
unit as part of the scrubbing system a laboratory size  froth flotation unit
was obtained from EPA for use in the testing (Figure  10).  Prior to  actual
chemical extraction testing, preliminary mechanical tests were  performed  to:

   1.  Familiarize test personnel with the operation  of the  unit.

   2.  Determine the range of unit speed and air flow settings  for adequate
       mixing action.

   3.  Determine the range of solids concentrations that can be kept in
       suspension with the unit.

   4.  Qualitatively evaluate the froth flotation unit  for use  as a  mixing
       cell in countercurrent extraction.

The mixing action of the unit was first observed using  water alone.  The
pattern of mixing was observed through the Pyrex mixing cell.   Different
mixing speeds and air flow settings were tested, and  it was  quite apparent
that the parameters were interrelated.  Speeds of 1200  to 3100  rpm were
tested.  When the air flow was too low at a particular  mixing speed, the
mixing was very turbulent.  Increasing the air flow to  a certain point
resulted in a very smooth mixing action.  Once the  point of  smooth mixing
was achieved, increases in air flow had little effect on mixing action.   As
the froth mixing speed was increased, the air flow  necessary to obtain
smooth mixing action also increased.

Testing continued using the organic and sand/clay soils with solids  con-
centrations in the range of 10 to 30 percent.  The  results indicated that,
as solids concentrations were increased, higher mixing  speeds were required
to achieve smooth mixing conditions.  Tests conducted at similar concentra-
tions indicated that the same speed and air flow settings were  required for
                                      31

-------
Figure 10.  Laboratory froth flotation testing apparatus,
                          32

-------
'***'
both soils.  An air flow of 470 ml/min was  sufficient  to  maintain  a smooth
mixing action up to an operating  speed of 2400 rpm  during all  of the tests.
The quantity of froth produced was  generally minimal.

For the organic soil, the best mixing actions were  obtained  with the opera-
tional parameters at the following  levels:

                     Optimum         Optimum
                      speed          air  flow
Percent solids _ (rpm) _ (ml/min) _ Comments _

      11.5          1800 - 2100        470           Little  change in mixing
                                                     when air  flow increased
                                                     to 640  ml/min.

      19.1          1900-2100        470           When speed  increased
                                                     to 2400 rpm,  air flow
                                                     needed  to be  increased
                                                     to 580  ml/min to main-
                                                     tain smooth mixing
                                                     action.

These results indicate that there were few  changes  necessary to  maintain
adequate mixing in this range of  solids  concentrations.   The relationship
between air flow and mixing speed observed  during the  testing  with water
was also observed when the speed  was increased above the  optimum to 2400
Test results for the sand/clay mixture  are  summarized  as  follows:

                      Speed         Air  Flow
Percent solids	(rpm)	    (ml/min)	Comments	

      18.4          1900-2100         470           Air  flow of 600 - 640
                                                     ml/min required when
                                                     speed  increased to
                                                     2400 rpm.

      31.0          2700 - 3100         580-610       Some difficulty in
                                                     keeping all  particles
                                                     in suspension—required
                                                     balanced adjustment  of
                                                     speed  and  air flow
                                                     settings.

Solids concentrations higher than 30  percent were  tested  with this soil and
the froth flotation unit provided an  adequate mixing action.  However, flow
settings seemed more critical and required  some  adjustments to  ensure
smooth mixing action at high solids concentrations.

Basically, these results indicate that  the  froth flotation  unit provides
sufficient mixing action during chemical extraction of soil  particles less
than 2 mm in size.  Adequate mixing was  achieved at solids  concentrations
up to 30 percent when proper rotational  speed and  air  flow  were maintained.

                                      33

-------
Hydrocyclone Testing

Preliminary equipment evaluations had  identified  the  hydrocyclone  as  a  good
candidate for separating the soil particles from  the  solvent  after the
extraction steps.  In the laboratory testing  program,  the  efficiency  of
this separation method had to be established  for  the  soil  types  of
interest.  After contact with manufacturers,  it was determined that
accurate and comparable results could  not be  obtained  from a  small
laboratory-sized unit.  The principal  problem was the  small size of the
apex discharge, scarcely larger than the maximum  size  of the  particles  in
the hydrocyclone feed water (less than 2 mm particles).

Therefore, a full size system, which operated at  a flow rate  up  to 227
1/min (60 gpm) and a pressure drop of  1.4 Kg/cm2  (20  psi), was obtained
for test from Krebs Engineers.  According to  the  manufacturer's
specifications, the unit could make a  particle separation  around 20 - 25 u
on a silt/sand mixture with a specific gravity of 2.6.  The actual
separation efficiency—including the amount of solids  entrained  in the
overflow and the percent solids concentration in  the  underflow—had to  be
established prior to the chemical extraction  testing.  This set  of tests
was limited to soil and water with no  chemical contaminant introduced into
the system.

Equipment Setup—A large tank and mixer was utilized  to mix the  soil
(particles less than 2 mm) and water initially and to  receive both the
underflow and overflow from the hydrocyclone  (Figure  11).   This  setup was
required to minimize tank capacity requirements since  the  hydrocyclone  was
operated at inflow rates ranging from  95 to 189 1/min  (25  to  50  gpm).  A
large tank mixer was utilized to keep  the soil in suspension  in  the holding
tank and a 7.6-cm (3-in.) submersible  pump was utilized to feed  the
hydrocyclone.

The underflow contained the concentrated soil particles whereas  the
overflow contained only the fine particles, which  could not be separated
with this hydrocyclone.  The apex was  a rubber tube that delivered the
underflow.  The flow ratio of underflow to overflow and the underflow
solids concentration could be varied with a hose  clamp on  the apex.

Test Conditions—Three variables were  identified  for  the laboratory testing
of the hydrocyclone, namely:

   1.  Inflow rate or pressure drop (interrelated variables)
   2.  Inflow solids concentration
   3.  Apex setting.

Inflow rates at pump pressures of 0.70, 1.40, 1.80 Kg/cm2  (10, 20  and 25
psi) were evaluated in the tests.  The flow rates associated  with  these
pressure drops varied on the basis of  soil type and inflow concentration.
Two soil concentrations were utilized  for each soil type.   The organic  soil
                                      34

-------
Figure 11.  Laboratory hydrocyclone testing apparatus.
                       35

-------
was tested at concentrations of approximately 5  and  10  percent  dry  weight
while the inorganic soil was tested at 2.5 and 5  percent  solids.  A maximum
inflow solids concentration of 10 percent was suggested by  Krebs  En-
gineers.  Krebs Engineers recommended that the appearance of  the  underflow
after it discharged from the apex should be cone-shaped rather  than
rope-like.  Underflow "roping" results from excessive tightening  of the
hose clamp on the apex.  Two extremes of the apex  setting were  evaluated
during the testing:

   1.  An open setting where no pressure was applied to the apex  with  the
       hose clamp.

   2.  A closed setting where the underflow was  still cone-shaped but  any
       additional tightening of the hose clamp results  in solids  roping.

For each set of test conditions (3 pressure drops  x  2 soil  types  x  2 soil
concentrations x 2 apex settings = 24 tests), samples of  the  inflow, under-
flow, and overflow were collected and analyzed for total  solids.  Overflow
and underflow rates were also measured for each  test condition.

The results indicate that the least sensitive parameters were pressure drop
and inflow rate.  The following trends were observed with increasing
pressure drop or inflow:

   1.  Underflow, as a percentage of the total flow, decreased.
   2.  The percentage of the inflow solids in the  underflow decreased.
   3.  The underflow solids concentration decreased.

Although these trends were consistent, the differences observed as  a
function of pressure drop did not have a significant impact upon  test
results.  Therefore, the data have been summarized by averaging results at
the three flow rates.

Table 2 contains the summarized data from the hydrocyclone  tests.   For the
organic soil, the percentage of the total flow as  underflow ranged  from 4.9
to 18.5 percent and the percentage of the inflow  solids concentrated in the
underflow ranged from 49.6 to 74.3 percent.  Tests conducted  with the  open
apex setting had the highest proportion of inflow  solids  (63.4  and  74.3
percent) as underflow; however, higher solids concentrations  were obtained
in the underflow with the closed apex setting.

The inorganic soil results showed similar trends  as  the organic soil;
however, the hydrocyclone was generally more effective  in concentrating
solids in the underflow in these tests.  The percentage of  total  inflow
solids in the underflow ranged from 67.6 to 82.3  percent.   Underflow solids
concentrations were more than two times higher with  the apex  closed rather
than open.

Particle-size gradation testing was performed for  both the  inflow and  under-
flow for the inorganic and organic soils.  Combined  sieve and hydrometer
tests were conducted.  Testing indicated that the  fine fractions  were
removed from the organic soils in the particle size  range of  5  to 300  u.

                                      36

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                            37

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The majority of change was  in the  10 to 200 jj range.   The  hydrocyclone  had
no effect on the removal of clay-size particles,  namely, those  smaller  than
5 ju.  For the inorganic soil, the  particle size gradation  removed  in  the
underflow contained a higher percentage of fine particles  than  the  inflow.
The fractions of particle gradation removed were  in the range of 5  to
1000 >i, especially noticeable in the 10 to 100 ju  range.  This observation
implies that the hydrocyclone removed the coarser  fraction from the
inorganic silty, fine-to-medium sand soil as expected.

Additional hydrocyclone testing was conducted to  determine whether  the
overflow solids could be effectively removed by an additional hydrocyclone.
Tests were conducted with organic  soil overflow with  a concentration  of
about 1.7 percent solids and inorganic soil overflow  with  a concentration
of about 1.5 percent solids.  Table 3 lists the results from these  tests.
The majority of the tests were conducted with the  apex setting  open since
the purpose of the tests was to optimize total removal of  solids.   The
results indicated that approximately 25 percent of the solids in the
organic overflow and 20 percent of the solids in  the  inorganic  overflow
could be removed as underflow.  However, the concentration of these
underflows was only between 2.0 and 3.8 percent,  which indicates that the
same hydrocyclone is not an effective means of concentrating the fine soil
particles in the underflow.  Underflow concentrations  as high as 9.0
percent solids were obtained with  the closed apex  setting,  but  due  to the
low rate of underflow with this setting, only 6.5  percent  of the inflow
solids were removed as underflow.  These results  show  that the  same model
hydrocyclone cannot be used to clarify the spent  solvent used for
extraction of contaminants from soil.

Hydrocyclone Simulation Testing

To accomplish a laboratory scale evaluation of the proposed counter-
current extraction scheme for the  removal of contaminants  from  fine soil
particles (less than about 2 mm in diameter), it  was  necessary  to develop  a
bench technique to approximate the solids removal  achieved with the hydro-
cyclone.  A hydrocyclone could not be used for the chemical  testing since
the smallest unit readily available for this testing  operated through a
flow range of 95 - 189 1/min (25 to 50 gpm), much  higher than can be
efficiently utilized in the lab scale study.  Scale down using  a smaller
hydrocyclone would not be representative of separations obtained in the
larger hydrocyclone.  Since the 95 - 189 1/min (25 -  50 gpm) flow range was
anticipated to be utilized in the  full-scale scrubber  unit,  simulation  of
this device should give the most valuable results.

Settling tests were tried as a method for simulating  solids removal with
the hydrocyclone.  Initially, samples of the inflow used for the hydro-
cyclone tests were mixed, poured into a graduated  cylinder, and allowed to
settle for specified periods of time.  Results from the hydrocyclone
testing were used to define the relative proportions  of underflow and
overflow for a given soil type and concentration,  and  the  solids
concentrations observed in the overflow and underflow  were utilized for
comparison purposes.  Preliminary  tests were conducted assuming both  an

                                      38

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open and closed apex setting with the organic soil.  With  a  5-percent
organic soil inflow and closed apex condition, the underflow volume
averaged approximately 5 percent of the total volume for the three flow
rates tested with the hydrocyclone.  Therefore, after the  specified
settling time for the simulation tests, 95 percent of the  total  sample
volume in the graduated cylinder was removed using a vacuum  trap.  This
liquid was considered overflow and analyzed for total solids.  When
simulating the open apex setting, approximately 85 percent of  the total
sample volume was assumed to be overflow, as determined from the
hydrocyclone tests.

Results of the preliminary tests are presented in Table 4.   The  overflow
concentrations were utilized for comparison because of difficulties
associated with obtaining a representative sample for total  solids analysis
of the sludge (underflow) in the bottom of the graduated cylinder.   All of
the overflow concentrations from the settled samples were  close  to those
obtained from the hydrocyclone.  The overflow concentrations for the open
apex setting simulation were lower than those for the closed setting since
only 85 percent (rather than 95 percent for the closed setting)  of the
total sample volume was considered overflow.  The results  from the
hydrocyclone testing indicate that the overflow concentrations are not
affected significantly by the apex setting.

          TABLE 4.  COMPARISON OF PRELIMINARY SETTLING TEST  RESULTS
            WITH HYDROCYCLONE OVERFLOW TOTAL SOLIDS CONCENTRATION
Soil type
Organic



Apex
setting
Open
Open
Closed
Closed
Settling time,
minutes
5
20
5
20
Overflow concentration, %
Settled
2.76
2.08
2.85
2.42
Hydrocyclone
2.36
2.36
2.32
2.32
These results indicate that settling was a useful technique for  simulating
the solids separation achieved with a hydrocyclone.  However, the settling
technique and times had to be modified so that these could be used  in con-
junction with countercurrent extraction testing.  Additional settling tests
were conducted with both the organic and inorganic soils but a large beaker
was used for settling the samples which allowed easy removal of  the settled
solids (underflow).  A closed apex setting was assumed for all of the
beaker settling tests; and inflow samples, from the hydrocyclone testing,
were retained and utilized for these tests.  Table 5 lists the overflow
concentrations obtained with the settling tests and from the hydrocyclone.
The results indicate that short settling times are sufficient to achieve
the desired overflow concentration.  With the organic soil, a 10-minute
settling time provided excellent results for the 5-percent solution,
                                      40

-------
however, the results indicate that a 5-minute time may be required for the
10-percent solution.  With the inorganic soil, the 5-minute settling time
provides a good comparison to the hydrocyclone results for both soil
concentrations.

The results of the settling tests indicate that, for the soils being tested,
settling is a feasible technique for approximating solids removal with the
hydrocyclone.  The purpose of these tests is not to exactly duplicate the
hydrocyclone, but to provide a technique for determining the effects of
incompleted soil/solvent separation on the countercurrent extraction system.

                    TABLE  5.   BEAKER  SETTLING TEST  RESULTS
                 Mixed
             concentration    Settling time     Overflow concentration  (%)
Soil type
Organic



Inorganic



(%)
5.0
5.0
10.0
10.0
2.5
2.5
5.0
5.0
( mi n . )
10
20 •
10
20
5
10
5
10
Settled
2.31
1.99
2.66
2.43
0.80
0.64
1.77
1.52
Hydrocyclone
2.32
2.32
3.69
3.69
0.77
0.77
1.67
1.67
CHEMICAL TESTING

Once/many of the mechanical operating parameters were established, chemical
testing began.  The testing involved several different steps designed to
establish test conditions and treatment efficiencies:

   1.  Column dosing studies, to define the amounts of contaminant to be
       added to the soil for subsequent laboratory tests.

   2.  Contaminant distribution tests, to determine the distribution of
       contaminants according to particle size.

   3.  Water-knife stripping/soaking tests for particles greater than 2 mm,
       to determine the ability of this process to strip contaminants from
       large particles.

   4.  Extraction tests for particles less than 2 mm, to determine the
       ability of the countercurrent chemical extraction process to extract
       chemicals from the soils.
                                      41

-------
Analytical Techniques

Accepted analytical procedures were utilized for all parameters involved.
The specific methods were chosen to provide accurate results with a minimum
amount of analytical time.  A colorimetric procedure was utilized to
quantitate for phenol in order to save analytical time.  Although the
procedure was straightforward for water samples, soil analysis involved a
multiple extraction of phenol into water.  The water used in the soil
extractions was analyzed and the results summed to obtain the total
quantity of phenol in the soil sample.  A 2-g sample of soil contaminated
with phenol was mixed with 500 ml of clean water and shaken for 15
minutes.  The liquid/solid separation was accomplished by centrifuging and
the liquid was analyzed for phenol.  The soil was resuspended in 500 ml of
clean water and the process repeated until the concentration measured in
the extract was insignificant compared to the initial concentration.  The
final result was reported as a summation of the phenol analyzed in each
fraction (mg/kg dry soil).

Arsenic analyses were conducted utilizing atomic absorption flame tech-
niques as presented in several sources (9, 10).  Soil samples for arsenic
analysis were digested with a mixture of hydrochloric and nitric acids.
PCB samples were analyzed by a gas chromatography-electron capture detector
(11).  Hexane was utilized to extract PCB from soil samples for analysis.
Standard cleanup procedures were utilized in the analysis.

Column Dosing Studies

The purpose of these tests was to define the amounts of contaminant to be
added to the soil for the subsequent laboratory tests.  The approach
involved simulating a spill condition as much as possible.  The liquid
contaminants were applied to the surface of the soil columns and the fluid
was allowed to drain for 24 hours.  In this way, the time factor associated
with a spill event was simulated since the contaminant (i.e., pollutant)
was primarily retained in the void volume of the soil with less being
sorbed on the particles themselves.

Test Methods—A Plexiglas (8.9-cm (3.5-in.) diameter x 15.2-cm (6.0-in.)
high) column was packed with soil using a range of soil moisture conditions
and dry bulk densities, which simulated natural conditions.  A stock
solution of contaminant at a volume equal to the soil void volume for the
given soil condition was poured onto the column.  After 24 hours, the
volume of the liquid passing through the column was measured and analyzed
for contaminant concentration.  The quantity of contaminant entrained by
the soil was calculated on a dry soil weight basis.  These tests were
conducted for both the organic and inorganic soil types.

Stock solutions of contaminant were chosen to simulate conditions expected
during a spill.  Since technical grade phenol is often shipped as a liquid
having a purity of 87 percent, this concentration was used.  Arsenic
trioxide formed a saturated, aqueous solution (9600 mg/1) within 24 hours,
thus simulating the dissolution of solid arsenic oxide after a rainfall.
                                     42

-------
The PCB concentration occurring during a spill could vary  significantly
depending upon the situation.  A value of about 75,000 mg/1 was  used  for
PCB testing.

Column Dosing Results—Phenol was the first of the contaminants  tested.
Each soil type was dosed under three conditions,  namely, concentration of
cantaminant, soil water content, and dry bulk soil density.   The conditions
represent a wide range of natural situations, including high  and low  soil
densities and water contents.  Table 6 summarizes the results.   For both
soil types, the intermediate dry bulk density and lowest water content
(tests 2 and 5) resulted in the largest entrainment of phenol.   These
dosing conditions were then utilized for all further laboratory  tests with
phenol since they represented worst case conditions.  These worst case soil
conditions were then used for the dosing studies  performed on both arsenic
oxide and PCB.  The dosing rates determined from  these tests  are as follows:

                             Arsenic oxide                 PCB
           Soil type        mg As/gm dry soil'    mq PCB/gm dry  soil

            Inorganic              0.75                    3.0
            Organic                5.00                  25.6

Contaminant Distribution Tests

These tests were conducted to determine the distribution of the  sorbed
contaminants according to soil particle size.  Only soils  contaminated with
phenol and arsenic oxide were used because of hazards associated with
excessive handling of soils highly contaminated with PCB.

Test Methods—The methodology for the distribution tests differed for
phenol and arsenic because the more volatile phenol could  be  lost during
drying.  For phenol, the tests were performed by  separating dry  soil
fractions using a sonic sieving device and then contacting the fractions
with phenol stock solution.  In order to assure contact of the phenol and
the soil fraction, a sample of the fraction was placed on  filter paper and
then phenol solution was poured over the fraction.  It remained  in contact
with the soil for 18 hours.  The soil fractions were then  rinsed with water
to remove phenol from the void volume and analyzed.  For arsenic,
contaminated soil from the column tests was dried at 60QC, size  fractions
were separated with the sonic sieving device, and the fractions  were  then
analyzed.

Contaminant Distribution Results—Tables 7 and 8  list the  results of  the
distribution tests for phenol and arsenic, respectively.   The results are
presented in two ways:

   1.  Actual contaminant (phenol or arsenic) concentration per  unit  weight
       (kg) of dry soil.
   2.  Percent of total soil contaminant in each  size fraction.

Differences of less than 20 percent were found when the fractionated  phenol
values were summed and compared to the total amount measured  on  the non-
                                      43

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fractionated sample  (Table 7)  (viz.,  ((208100-166774)7(208100))xlOO  = +20%
((1250-1471)/(1250))xlOO = -18%).  This recovery was  quite  high  considering
the natural soil variations and the difficulty of  phenol  analyses  on
soils.  The comparisons were even better  in the case  of  arsenic  (Table 8)
(viz., ((806-783.8)/(806))xlOO = +3%  and  ((200-178.5)/(200))xlOO = +11%).

Phenol Distribution—The results for  the  phenol distribution  tests onto
organic soils indicate that approximately 90 percent  of  the phenol was
sorbed by the larger particle sizes (0.595 to 2 mm).   It  was  hypothesized
that this result was caused by a high  organic content in  these  larger size
fractions.  To further evaluate this,  the organic  content or  loss  on
ignition  (LOI) test was performed on  the  organic soil.   Samples  were heated
to 5500C for four hours and then reweighed (ASTM Test Designation
D-2974).  The differing organic content in the coarse and fine  fractions
was then apparent.  When the LOI values and'phenol adsorption for  different
size ranges are presented on the same  graph (Figure 12),  it can  be seen
that a direct relationship exists for  size ranges  between 0.9 mm (U.S.
sieve No. 20) and 0.25 mm (U.S. sieve  No. 60).  This  result suggests that
woody fiber in the sample sorbed large amounts of  phenol.  For  particles
smaller than 0.25 mm, a direct relationship between the  organic  content and
phenol sorption was not observed.

The absence of a direct correlation between organic content and  phenol
uptake in the fine fraction (<0.25 mm) indicates chemical,  as well as
physical, difference between the coarse and the finely divided  organic
fractions.  The organic fines  are most probably composed of  the
decomposition products resulting from  microbiological  attack  on  plant
tissue.  These products are commonly  termed "humic" or "fulvic"  acids and
are characterized by large surface-to-mass ratios  and an  absence of
internal structure.  The particles are generally the  size of  clay
minerals.  By contrast, the woody fibers  still retain much  of the  open
structure and porosity of the original plant material.   The high phenol
sorption  in the coarse organic fraction appears to result from  the
penetration by the phenol into the woody  fibers and retention in the
internal  pore spaces.  Conversely, the finely divided organics  seem  to
adsorb in a manner similar to clay slurries.  The  net result  implies that
phenol uptake in organic soils may be  directly related to the degree of
decomposition of the organic materials.   Removal of phenol  from  the
internal  pore spaces of woody fibers will probably require  soaking.   Since
the phenol appears to have been absorbed  by the woody fibers, a  wash of the
particle surfaces would probably be only  partially effective.   The
conclusion that phenol sorption in organic soils is controlled  by  the
penetration into internal pore spaces  of  woody fibers also  suggests  that
phenol adsorption would be very sensitive to water content  of the  fibers.
If the internal pore spaces were occupied by water at the time  of  phenol
application, very little sorption would be anticipated immediately.   Since
either dry or wet conditions may exist in natural  soils,  the  amount  of
phenol sorption onto larger soil particles at a specific  spill  site  cannot
be easily predicted.

Inorganic soil fractions up to 12.7 mm were evaluated to  determine phenol
adsorption (Table 7, Inorganic).  Similar calculations were made with these

                                      47

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data as had been made with the data from the organic soil  tests so the
results could be compared.  The results indicate that in the particle size
range less than 2 mm, approximately 60 percent of the phenol was sorbed by
particles less than 0.105 mm (viz., (840/471)xlOO = 57%).

The coarse sand and fine gravel material (2 to 12.70 mm) sorbed about three
times more phenol on a weight basis than the soil fraction less than
0.105 mm.  This result was unexpected because the small  particles have a
much higher external surface area per unit weight than the gravel.
However, the dry, limestone-type gravel found in this soil has a greater
total surface area than that calculated solely on the basis of average
particle-size diameter.  The limestone has a high internal surface area
because of pores within the particle itself.  These internal pores greatly
increase the surface area exposed to phenol in the dosing tests and this
condition can account for the higher sorption found during the testing.  It
should be noted that this sorption was increased because only dry soil was
used in the testing.  The natural water content of the soil would have
filled some of these internal pore spaces and, therefore, decreased the
amount of available surface area for chemical adsorption.

Arsenic Distribution—Arsenic distribution on the organic soil (Table 8)
indicated that nearly 78 percent of the arsenic was associated with soil
particles ranging from 0.595 to 2 mm.  The results are similar to those
obtained in the phenol testing and can possibly be explained by the
retention of arsenic within the pore spaces of the woody fiber present in
these size fractions.  The smaller soil fractions sorbed approximately the
same amount of arsenic per unit weight but contributed differently to the
total based on the weight of that soil fraction present in the sample.
This is the same trend observed with phenol indicating again that the
surface area is not the only phenomenon controlling adsorption.

With the inorganic soil, the smallest size fraction (less than 0.105 mm)
had the highest arsenic concentration (420 mg As/kg).  When weighted
according to soil particle size distribution, this fraction contained
approximately 22 percent of the arsenic.  The fraction between 0.354 and
1.00 mm contained about 40 percent of the arsenic.  However, this result
can be explained by recognizing that this size fraction represented 45
percent of the total soil being tested.  The higher sorption onto smaller
particle sizes is more consistent with expected results, although it is not
consistent with the sorption found with phenol.  The difference could be
caused by the difference in testing methods.  For phenol testing, the
individual soil fractions were exposed to the phenol and then analyzed.
For arsenic, the entire soil mixture was exposed, then fractionated and
analyzed.  The tech- nique used for phenol would encourage sorption onto
the large particles since there was no other sorption media available.
Conversely, placing the arsenic onto mixed soils would allow preferential
sorption to high external surface area particles of small  size and less
sorption to internal pores of the gravel.
                                     49

-------
Water-Knife Stripping/Soaking Tests

The basic equipment operating methodology was established  in  previous
testing.  These results indicated that the water-knife  apparatus  was
effective in breaking down clay  lumps when a sequence of soaking  and water-
knife stripping was used.

Chemical tests were then required to establish the  efficiency of  the water
knives in stripping contaminants from large soil  particles  (>2 mm).  Pre-
liminary chemical testing indicated that the submerged  (soaking)  cycle  was
also important for effective removal of contaminants sorbed to larger
particles.

Test Methods—A 1000-g sample of contaminated soil  was  placed into the
rotary screen and stripped by the water knife with  clean water for one
minute.  This allowed removal of contaminated soil  particles  that were  less
than 2 mm in size and also stripped any contaminant present in the void
volumes.  The percent-removals for treatment-efficiency calculations were
based on the amount of contaminant sorbed to the  large  soil particles
measured at this point in the testing.  The bucket  containing the larger
than 2 mm soil particles was then submerged in rinse water  for time periods
that varied from 15 to 120 minutes.  The screen was rotated while it was
submerged to encourage solvent/soil contact.  Samples were  collected at
various intervals, rinsed, and analyzed.  After 120 minutes,  the  entire
contents of the bucket were rinsed with a low pressure  nozzle for one
minute, and samples were collected.

Water Knife/Submerged Washing Test Results--Water-knife test  results for
soils contaminated with phenol,  arsenic oxide, and  PCB  are  presented in
Table 9.  The percent-removals were calculated after the water knife had
stripped the contaminant from between the void spaces and  removed particles
less than 2 mm.  Therefore, the  results represent actual treatment of the
sorbed materials on the particles greater than 2  mm.

Treatment using water-knives and submerged washing  was  most efficient for
phenol (Table 10).  The removals were highest for the inorganic soil since
almost 98 percent of the phenol was removed from  the soil  after a 15-min
submergence time.  Neither arsenic nor PCB was stripped with  the  same ef-
fectiveness even after a 120-min submergence.  Removals of  phenol from  the
organic soil were lower, probably because of the  stronger  affinity of the
organic soil for the organic phenol.  This trend  is not apparent  in the
arsenic results, which is as expected since arsenic oxide  is  an inorganic
contaminant.

Residual amounts after varying submergence times  do indicate  continuing
removal with time; however, the  amount of contaminant removed per unit  time
becomes less and less.  This indicates a decreasing benefit with  time and
has an impact on the final design considerations.   The  usefulness of the
final low velocity rinse is seen when the residual  concentrations at 120
minutes are compared.  The final rinse water appears to remove or replace
contaminants retained in the washing water that remains entrained in the
void volume. A much cleaner product results from  the final  rinsing.

                                      50

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           TABLE 10.  PHENOL DISTRIBUTION  IN  SOIL  SAMPLES  USED  FOR
                   WATER KNIFE  AND SUBMERGED WASHING TESTS.
Soil type
Inorganic
Organic
Phenol
concentration,
units
mg/kga
mg/sample
mg/kga
mg/sample
Soil fractions
Complete
soil
48,300
42,700
452,200
254,410
<2 mm
710
626
196,240
110,400
>2 mm
10,770
9,520
18,210
10,250
Soil void
spaces
36,820
32,554
237,750
133,760
a Values listed are mg of phenol  in a given soil fraction  per  kg  of
    complete or non-fractionated  dry soil.


Final concentrations of contaminants in the soils varied significantly.
Treatment of the phenol-contaminated inorganic soil  resulted in the  best
removals and almost the lowest, post-treatment contaminant  concentrations.

Concentrations in the organic  soils were much higher,  however; the mass of
soil involved was considerably less.  Only five  percent of the organic soil
was within the size range of 2 to 12.7 mm treated by the water-knife.

Approximately 50 percent of the arsenic was removed  during this processing
step for both soil types.  Residual arsenic concentrations for the in-
organic soils were an order of magnitude less than those on the organic
soil, because of the higher initial dosages onto organics  and  the strong
sorption of arsenic oxide to the wood chips and  vermiculite present  in the
organic soil.  Residual arsenic concentrations were  not significantly
changed after 30 min of submergence.

PCB treatment removals were the poorest among all the  chemicals tested.
The initial concentration was  low (only 14 mg/kg) and  resultant residual
concentrations of approximately 10 mg/kg resulted in only  28 percent
removal.  The residual concentrations were the lowest  for  all  the chemicals
tested.  Because of the previously noted trend of even less effective
treatment for organic soils, especially with phenol, additional testing of
PCB removal on this substrate was judged to be unnecessary.

When evaluating these results, it should be emphasized that the water knife/
submerged washing process is performing two functions:

   1.  Removal of entrained contaminant and separation of  contaminated soil
       particles less than 2 mm from larger soil particles.

   2.  Removal of contaminant sorbed on the soil particles greater than
       2 mm.
                                      52

-------
Removal efficiencies presented  in Table 9  address  only  the  latter  functions.
If the removals had been calculated based  on  amounts  of contaminant  present
on the total mass of soil, the  percentages would have been  much  higher
because of the relatively high  amount of entrained contaminant.   Using this
overall calculation approach would not have allowed as  effective a
comparison of actual treatment  efficiency  among contaminant types.  How-
ever, the benefits of the water-knife apparatus as a  separation  device
should not be overlooked.  Entrained contaminant is transferred  from the
soil to the water phase using the water-knife.  The amounts involved can
range from 50 to 75 percent of  the contaminant present, which  immediately
results in a high removal and meets certain goals  of  the scrubber.  Fine
soil particles are separated in this step, which also "removes"  the
contaminant from the surfaces of the larger particles.   These  processing
benefits are crucial to the operation of the  unit, although they are not
readily apparent when one evaluates only percent removals.

Removal of Entrained Chemicals—The importance of  the removal  of the
contaminant present in the void spaces and sorbed  to  particles less  than
2 mm is further illustrated when the distribution  of  phenol onto the two
soil types is further evaluated (Table 10).   This  relationship in  Table 10
was calculated using the results of the fractionation tests and  the  amount
of phenol dosed onto the soil (see Table 7).

It can be seen in Table 10 that, for both  soil types, most  of  the  phenol
was entrained in the void spaces.  Although a greater percentage of  phenol
was entrained in the void spaces of the inorganic  soil  than in the organic
soil, 76.2 percent ((36820/48300)x!00) versus 52.6 percent
((237750/452200)xlOO), the entrained quantity of phenol in  the organic soil
was six times greater than (237750/36820)  in  the inorganic  soil.  Since
these calculations are based on maximum sorption conditions from the
fractionation tests, actual amounts entrained may  be  even higher.  Large
particles (greater than 2 mm) in the organic  soil  contained a  large
fraction of the phenol (22.3 percent) while this same size  fraction
contained only four percent of  the phenol  in  the inorganic  soil.  This is
due to the fact that there only was a small fraction  of large  particles
(5.7 percent of the total) present in the  organic  soil.

CHEMICAL EXTRACTION TESTS

These tests involved contaminant extraction from small  soil particles
(<2 mm) using a water plus additive solvent system to:

   1.  Determine the most effective solvent for each  contaminant.
   2.  Establish potential removals of each contaminant using  a
       countercurrent extraction system.

Two types of tests were run:  single extraction tests for solvent  screening
to establish single step removal efficiencies, and multiple extraction
tests to measure the improvements that sequential  extractions  offer  on
removal efficiency and solvent  usage.


                                      53

-------
Test Methods

For single extraction  tests,  a  Barrel!  shaker  with  a 500-ml  flask was
utilized to mix the contaminated  soil  and  solvent  (total  volume of 200 ml
and dry soil solids concentration  of  2.5 to  5.0  percent)  for three hours.
The mixture was separated by  centrifugation  and  the solvent  analyzed for
contaminant.

The procedure for multiple  extractions  was  identical  to that for the
single-step extraction tests  except that the contaminated soil  was
extracted four times instead  of once  and each  aliquot of  solvent was
recycled in a four-step countercurrent  direction (Figure  13).   The final or
fourth extraction step for  the  soil was accomplished  with clean solvent
while the first extraction  step used  the most  contaminated soil and solvent
indicative of a countercurrent  system operating  at  steady-state conditions.

The multiple extraction tests were further expanded to simulate the con-
taminant removal attainable with  a full-scale  soil  scrubber  chemical ex-
traction system.  Procedures  for  these  tests were similar to those used for
the four-step extraction tests; however, the froth  flotation unit was used
as the mixing cell and settling was used to  simulate  the  soil/solvent
separation of a hydrocyclone.   The volume of the soil/solvent mixture used
in these tests was three liters.

Extraction Test Results

Single Extractions—The results of the  single  step  solvent extractions
using different solvent systems are summarized in Table 11.   Solvents
included water only and water plus additives that appeared suitable for the
particular contaminant.  In these  tests the  emphasis  was  placed on removal
into the solvent and no additional rinsing of  the soil  was performed.  It
was the purpose of these tests  to  provide a  maximum removal  into the
solvent by maintaining the  complete mix for  three hours.   The
solvent-to-soil ratio was high  so  that  solubility limitations were not
encountered and good contact  between  solids  and  fluid could  be  maintained.

Phenol—Removals of phenol  from inorganic soils  into  the  solvent phase were
most effective.  Removals with  all of the solvent types were very high and
the best extraction occurred with  the  inorganic  soil  using water as the
solvent.  Because of possible experimental errors,  the differences among
solvents for this soil  system were probably  not  significant. The inherent
advantages of using water alone in a  soil system (e.g., cost, operational
simplicity, lower corrosion potential)  make  this the  preferred  solvent.

Phenol  removals from the organic soil were not so high  but large quantities
of phenol  were also extracted into all  of the  solvents  tested.   In this
soil, the most effective solvent system was  water with  sodium hydroxide
added to maintain a pH of 11.   However, the  handling  difficulties
associated with this rather alkaline  solvent system could be a  major
disadvantage.  Water alone, with a removal efficiency not significantly
less than the alkaline solvent, would probably be a suitable choice for the
organic soils also.
                                      54

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TABLE 11.   SINGLE  EXTRACTION TEST RESULTS



Contaminant
Phenol*







Phenol b







Arsenicc





Arsenicd





PCS*

PCS*


•Initial soil
^Initial soil
cinitial soil
^Initial soil
•Initial soil
'Initial soil



Soil type Solvent type
Inorganic Water + HgSOa
Water + H2S04
Hater + HjSO*
Water + NaOH
5* MeOH
IX Tween 30
1* MYRJ 52
Water
Organic Water + HjSOa
Water + H2S04
Water + H2S04
Water + NaOH
5X MeOH
IX Tween 80
IX NYRJ 52
Water
Inorganic Water + HjSOa
Water + NaOH
Water + NaOH
7.5X NaHSO*
5. OX NaCl
Water
Organic Water + HgSQ*
Water + NaOH
Water + NaOH
7.5X NaHSQi
5. OX NaOCl
Water
Inorganic 0.1X Tween 30
1 .OX Tween 80
water
Organic 0.1X Tween 30
l.OX Tween 80
Mater
dose was 48.3 mg phenol /g dry inorganic
dose was 452.3 mg phenol /g dry organic s
dose was 0.75 mg As/g dry inorganic soil
dose was 5.0 mg As/g dry organic soil.
dose was 3.0 mg PC8/g dry inorganic soil
dose was 25.6 mg PC8/g dry organic soil.


Initial
PH
1.0
3.0
5.0
11.0
6.7
6.4
6.3
6.9
1.0
3.0
5.0
11.0
7.1
7.1
7.1
7.1
1.0
10.0
12.0



1.0
10.0
12.0








soil.
oil.
Supernatant
contaminant
concentration,
nKj/1
1,120
1,100
,100
,060
,100
,120
,180
,190
16,300
18.000
18,600
20,000
18,600
16,200
15,300
17,600
32
16
18
23
22
16
425
310
405
405
285
375
61
110
72
850
366
418



Percent
removal
92.8
91.1
91.1
87.8
91.1
92.8
97.8
98.6
72.1
79.6
82.3
38.4
82.3
71.6
67.7
77.8
85.3
42.7
48.0
61.3
58.7
42.7
85.0
62.0
81.0
81.0
57.0
75.0
20.8
37.5
24.6
20.8
33.8
48.3

Soil residual
contaminant
concentration,
mq/g
3.48
4.30
4.30
5.39
4.30
3.48
1.06
0.68
126.2
92.3
80.1
52.5
92.3
128.5
146.1
100.4
0.11
0.43
0.39
0.29
0.31
0.43
0.75
1.90
0.95
0.95
2.15
1.25
2.38
1.38
2.66
20.3
19.5
13.2

                                   56

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Arsenic—The maximum removal of arsenic  into the  solvent  phase was  less
efficient than for phenol when inorganic soils were  extracted  (85.3 percent
as compared to 98.6 percent) but  approached the extraction  efficiency of
phenol on the organic soils  (85 percent  as compared  to  88.4 percent).

Arsenic removal from organic soils was significantly affected  by  the type
of solvent used; water with  sulfuric  acid appeared to be  the best solvent
(85-percent removal at pH 1.0) whereas water alone or water plus  NaOH
removed less than half of the arsenic.   When acid is used as a solvent in
the full scale system, the equipment  used for chemical  extraction must be
constructed with suitable corrosion-resistant materials.  Care is also
required in the handling and use  of the  acid.  When  acid  is not used,  the
next best solvent for the inorganic soils is the  sodium bisulfate (7.5
percent NaHS04) with a 61.3-percent removal.

With the organic soils, the  differences  among solvents  were not so
dramatic; and water alone, as well as water plus  NaOH or  NaHS04,  produced
results almost as good as the water plus sulfuric acid.

Another concern with the arsenic  results was the  low concentrations of this
material measured in the solvent.  The solubility of arsenic in the solvents
tested is many times higher  than  the  levels obtained during any of  the ex-
traction tests.  This result implies, at best, the need for large volumes
of clean solvent—and possibly longer contact times  to  better  approach
equilibrium—to reduce residual soil  concentrations  to  lower levels.   The
result also raises questions about the extent of  further  reduction  in  soil
arsenic levels with multiple extractions.  With lower residual soil
concentrations, solvent volume requirements may be even higher.   It was
also significant that the concentrations measured in the  different  solvents
did not vary greatly.   These relatively small differences  are important,
however, when comparing extraction efficiency by  solvent  type.  Because  of
the relatively small amount  of arsenic in the soil system,  the measured
differences in solvent concentrations do result in large  differences  in
removal efficiencies.

Problems occurred with the analysis of arsenic contaminated soils,  particu-
larly for the inorganic soils.  A strongly acidic solution  was required  to
obtain total digestion and reproducible  results.  Digestion of soils  was
attempted with nitric acid alone, mixed  nitric and hydrochloric acids, and
nitric acid with hydrogen peroxide.

Use of an extracting mixture of nitric and hydrochloric acid and
quantitation by atomic absorption spectroscopy yielded  reproducible arsenic
analyses.  However, the difficulties  in  analyses and the  requirement  for
such a rigorous digestion illustrate  the potential difficulties associated
with complete removal of arsenic  into a more moderate solvent system,  which
could be used in the soil scrubber.   Even a mixture  of  water and  acid  at
pH 1, which gave the best comparative removal, does  not provide the optimal
type of extractant that is needed for complete arsenic  removal.
                                      57

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PCB--PCB removal into the three solvent-types tested was quite low.   A
maximum removal of 48 percent was noted for the inorganic soil.   It  should
be observed that the PCB concentration in the supernatant greatly exceeded
the solubility of PCB in any of the solvent mixtures.  This indicates that
the shaker tests were actually performing a physical separation  rather than
a purely solvent extraction.  PCB that had been entrained in the soil was
removed and actually formed a third phase, which was noted by the
laboratory analyst.  Because the procedure used in the laboratory testing
does not provide the longer times necessary for soil/chemical bonding, the
test results are difficult to apply to remedial-action type situations,
which are probably those situations for which scrubbing of PCB from  soils
is most needed.  In those situations, much of the entrained PCBs would be
gone and the remaining contaminant would be more tightly bound to the soil
itself.  Depending upon the type of soil and many other factors, the
remaining PCB concentration may be either high or low.  Lab-scale treatment
of PCB in a remedial-action-type situation would have to be modified to
accurately predict the impact of the critical time factor-on removal
efficiencies.

Multiple Extractions—Phenol was selected for establishment and
demonstration of the efficiency of multiple extractions and its  effect on
solvent usage.  Arsenic was not used for the demonstration because it
appeared that further extractions would probably not.be effective in
reducing the soil arsenic levels substantially because of the small  amount
of contaminant that the solvent was able to remove in a single extraction
and the awareness of the tight bonding of the arsenic to the soil, as shown
by the difficulty in removing arsenic from the soil by acids for analysis.
PCB was not used for the demonstration because of its low efficiencies of
initial removal.  Its hazards also detracted from using it for this  initial
demonstration.

The first test run with phenol was a quick check to demonstrate  the  po-
tential for solvent reuse.  Two aliquots of soil were contaminated with
phenol and extracted; the same volume of water was used for each extraction.
In one experiment, an aliquot of soil (# S-l) was washed twice with  clean
water (# W-0) and the washings (# W-l and W-2) were saved.  In the second
experiment, a fresh aquilot of soil (# S-2) was first washed with used wash
water (# W-2) from the second washing of the first aliquot of soil (# S-l)
then rewashed with clean water (# W-0).  The results indicate that used
solvent could remove nearly as much phenol from contaminated soil as clean
solvent, so solubility limitations did not impede removals in this case.
The more detailed four-step, countercurrent extraction tests were then
conducted.

The results show that, for phenol, multiple extractions were far more
effective than a single extraction in removing the chemical from the soil
(Table 12).  Multiple extractions continued to remove phenol at  high
efficiencies so that after the fourth extraction the percent of  initial
phenol retained by the soil had been reduced to a small fraction of  a
percent.  A log-normal plot of retained phenol versus number of  extractions
indicates that the efficiency of extraction had not yet diminished sig-
nificantly after four extractions and that further extractions could be

                                      58

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-------
      expected  to further  reduce  the phenol  content  from  the  soil  (Figure  14).
W
      Reduction in soil  phenol  resulted  in  a residual  soil  product  concentration
      of about  30 mg/Kg  after four  extractions  using the  shaker  test  and
      centrifugation.

      The phenol  present in  the solvent  increased  progressively  with  the number
      of extractions,  however,  the  majority of  the phenol was removed in the
      first stage by contacting the contaminated soil  with  previously used
      solvent.   The incremental increases  in phenol  concentration were much lower
      in the subsequent  soil  extractions.   Fresh solvent  was  used  in  the last
      (4th) extraction.

      When these  results were further evaluated, it  was determined  that the re-
      moval of  phenol  after  three extractions with recycled solvent was
      equivalent  to the  removal provided by two clean water extractions.   Four
      extractions provided even better removals than two  clean water  extractions
      with half the water  requirement.

      The use of  froth flotation  and settling as an  extraction apparatus to estab-
      lish the  impact  of incomplete soil/solvent separation as would  occur with
      the use of  hydrocyclones resulted  in  a similar trend  of reduction of
      chemical  level in  the  soil, but with  somewhat  less  efficiency.   Removals
      were more efficient  from inorganic soils  than  from  organic soils, as the
      previous  single  extraction  test data  had  predicted  (Table  11).
 ft**
 W   However,  the final concentrations  of  phenol  in the  soil products are much
      different for the  two  soil  types (79  mg/Kg for the  inorganic  soil and 2560
      mg/Kg for the organic  soil) due to three  factors:

         1.  The  organic soil was dosed  with approximately  ten times  more  phenol
      per gram  of dry  soil than the inorganic soil.

         2.  The  concentration of dry soil  in the  froth unit  for the  organic soil
      was 10 percent versus  5 percent for  the inorganic;  therefore, there  was
      less solvent per gram  of dry  organic  soil.

         3.  The  organic soil retained the  phenol  more tightly because of  the
      nature of the soil.

      An additional factor that should be  considered in examining the results is
      the loss  of a portion  of the  soil  in  the  overflow  (simulated).   For  the
      inorganic soil,  approximately 25 to  30 percent of the soil dry  weight was
      lost in the simulated  overflow during the four-step extraction  process.
      Losses of up to  40 percent  were observed  in  the overflow during the  organic
      soil extractions.   Although settling  was  utilized to  simulate soil/solvent
      separation, these  soil-loss values should be indicative of the  expected
      soil loss when hydrocyclones  are actually used in separation/processing.

                                            60

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       100 (T
  -4
  M

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  r^t
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  a:
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        10
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       0.1
      0.01
FROTH FLOTATION  AtlD SETTLING



O = ORGANIC  SOIL



E = INORGANIC  SOIL


SHAKER AND CENTRIFUGATION



A= INORGANIC  SOIL
                             EXTRACTION NUMBER
Figure 14.  Soil phenol reduction as a function of  number  of  extractions

                  using two different extraction methods.
                                   61

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                                  SECTION 6

              IMPLICATIONS OF THE PRELIMINARY LABORATORY TESTING
                 PROGRAM  ON  SYSTEM DESIGN AND  SOIL  TREATMENT
INTRODUCTION
The information obtained from the preliminary evaluation  and  the  laboratory
testing allowed an initial evaluation of the soil  scrubbing concept  and
provided a basis for the design.  Since initial  laboratory testing was
limited to three different chemicals, broad generalizations regarding the
scrubber's range of application were difficult  to  establish.   Instead,  the
results were considered indicators of the  effectiveness  and usefulness  of
soil scrubbing on the particular chemicals tested  and  the classes they
represent.  The same concept holds true when extrapolating the impact of
different soil types on the scrubber unit.  Implications  on system design
based on the equipment review and the laboratory testing  are  presented
below, followed by implications from the chemical  testing.

IMPLICATIONS FROM EQUIPMENT TESTING

Water-Knife Stripping

Physical stripping of both free contaminant and that bound to soil
particles using a water-knife system was found  to  be effective.   Breaking
down small, cohesive, clay lumps can be accomplished using water  knives in
conjunction with a soaking cycle.

The most effective configuration was found to be an internally water-knife
washed rotary screen unit which passed particles less  than 2  mm in size and
provided the action to flush (strip) contaminating chemicals  from the
particles greater than 2 mm in diameter that were  retained in the screen
chamber.  This system allowed the retained soil  to be  confined in a  pocket
so that the force of the water knives could be  fully utilized. A
three-step operation, which included an initial  stripping with the water
knives to remove fines and entrained contaminant,  a submergence  step for
lump softening and treatment, and a final  rinse, was found to be
effective.  Recycle of water for the first high pressure  stripping appeared
desirable to reduce water requirements in  the system.  The final  rinse
utilized a lower pressure, clean water stream to remove  contaminated water
from the soil surfaces.

Froth-Flotation Mixing and Contact

The froth-flotation system provided smooth, efficient  mixing  using a com-
bined mechanical- and air-mix system.  The two  mechanisms were interrelated
with optimum settings established by soil  type  and solids concentrations.

                                      62

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Solutions containing 30-(or greater) percent solids were effectively mixed
with this system.  The amount of froth generated in clean soils was
minimal.  The process limitations of applying froth flotation to the
scrubbing system, however, include the added difficulty that would be
encountered in controlling emissions from volatile contaminants and the
possible foaming problems when surfactants are used as additives for
chemical extraction.

Hydrocyclone Liquid/Solids Separation

Hydrocyclone testing also had a direct impact on the scrubber evaluation.
The equipment operation was quite simple, and only a manual apex adjustment
was needed to control solids concentrations in the underflow.

With a closed or tight apex setting, the solids concentration in the
underflow ranged from approximately 30 to 50 percent.  This concentration
should be acceptable for discharge of cleaned soils, possibly with some
auxiliary drainage on sand beds.

Mounting hydrocyclones above the mixing tanks of the modified oily beach
sand cleaner was no problem and the units are capable of operation over a
relatively wide flow range.  Another advantage is that changes in the flow
rate do not have adverse impacts on the solids concentration in the
underflow.  The major disadvantage of the hydrocyclone is the amount of
solids that is entrained in the overflow of the unit.  Solid recoveries of
70 percent were measured; however, 30 percent of the solids passed out of
the system with the overflow.  The solids concentrations in the stream
ranged from 0.7 to 3.7 percent.  Treatment of this stream with a similarly
sized hydrocyclone was ineffective.  It is likely that an additional, more
efficient hydrocyclone or that chemically assisted gravity separation will
be needed prior to any additional treatment for solvent recycle.

IMPLICATIONS FROM CHEMICAL TESTING

The results of the different tests performed during the preliminary
laboratory studies had an impact on the design and operation of the soil
scrubber.  An evaluation of their effects are presented in the following
section.

The chemical test results were somewhat inconclusive since a defined system
endpoint has not been established for the chemicals tested.  The most
effective treatment, in terms of percent removed, was found for phenol.
Neither arsenic oxide nor PCB was scrubbed with as high a removal
efficiency.  In all cases, the residual soil concentrations were reduced;
but, without established, acceptable concentration limits, the results are
difficult to evaluate.

Contaminant Distribution

Varying sorption with particle sizes was expected; however, the results
obtained during the testing were not so straightforward as anticipated.
The larger soil particles in both the organic and inorganic soil sorbed a
greater fraction of contaminant than would be predicted based on nominal
                                      63

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surface  area.  This  result  can  be  partly explained  by the open structure of
the coarse, woody fibers  in  the organic  soil  and  by the dryness and pore
structure of the limestone  gravel  in  the inorganic  soil.

On the basis of these experiments  it  does  not appear fully justified to
assume that small particles  will adsorb  more  contaminant  per unit weight
than large particles.  A  number of variables  besides particle size appear
to impact how much contaminant  sorbs  to  a  particular soil  including:

   1.  initial moisture content of the soil
   2.  internal structure of the soil  particle
   3.  nature of the soil material
   4.  manner in which the  contaminant contacts the soil
   5.  duration of contact  time between  contaminant and soil.

It is difficult to predict  soil/chemical  interactions,  which emphasized the
need to make the soil scrubber  as  flexible as possible.

Effectively treating soils  by concentrating on a  predetermined soil
fraction is also difficult.   With  the  extreme variations  of soil  gradation
and of chemical sorption  to  different  soil  materials,  an  inflexible
approach would significantly limit the scrubber's effectiveness and
usefulness.

Contaminant distribution  information,  nonetheless,  is  still  very useful
because the data may be applied to estimate the overall scrubber
effectiveness when the contaminant sorption by particle size and the
particle size distribution of the  soil are known.   Both large rocks and
boulders and extremely fine  clays  will escape treatment because of system
limitations.  Knowing the fractional  distribution of particles between
these two limits permits  calculation  of  a  theoretical  system efficiency.

Water-Knife Stripping

The submergence step, which  has been  found to be  necessary for both
softening lumps and cleansing of the  larger particles,  was studied.   A
submergance time of 15 min  provided good removal  without  greatly slowing
down the processing rate.  However, the  differences in  soil  and contaminant
types emphasize the need  for flexibility  in system  operation.  The three-
step approach, i.e., initial  stripping,  soaking,  and rinsing, was
effective; however, the final rinse prior  to  discharge  had to be performed
with low-velocity spray jets  for the most  efficient removal  of the
contaminant.

Chemical  Extraction

The single solvent extraction tests provided  a way  to  compare solvents  and
to establish preliminary  removal efficiency ranges  for  soil  treatment.   The
contaminant tested that had  the best results  in these  tests  (phenol) was
further tested in a multiple  extraction  scheme, which  simulated the
four-step extraction system  proposed for the  prototype  soil  scrubber.
Multiple extractions resulted in continued, efficient  removal  of  phenol
from soil to low residual values.   In these tests,  solvent reuse  in  a
countercurrent scheme was shown to be an effective  approach.

                                      64

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      Other Considerations for Chemical Treatment
W
      Residual Soil Contaminant Levels—A second and possibly more critical
      factor that must be further addressed involves the residual contaminant
      levels remaining in soil after treatment.  This factor is of particular
      importance when one evaluates the preliminary laboratory results.
      Acceptable soil concentration limits are not always available, so it is
      difficult to determine whether the treatment has been "successful."
      Calculation of percent-removal is one way to begin the evaluation, but
      these numbers can be misleading since different initial amounts of material
      were used.  Therefore, it was necessary to reassess the results from a
      slightly different point of view.

      It became apparent that the soil scrubber system itself might be able to
      establish an acceptable upper limit of residual contaminant concentrations
      in the soil.  Since the scrubber is designed to remove materials into a
      water solvent under forced conditions, the residual remaining on the soil
      should have limited mobility in the natural environment.  It is expected
      that the material left sorbed to the soil after the sequential extractions
      will be very tightly held and have minimal environmental impact.  The
      release of the chemical may continue but at a rate so extremely low that
      there is no significant environmental danger.  If concern still remains
      regarding the impact of a specific chemical, disposal to a sanitary
      landfill or other site with more controlled access may be an acceptable
      compromise.

""*«*   The post-processing disposal option concept can be further evaluated by
      considering the three chemicals tested in the laboratory study.  Phenol
      removals after step extraction were high (>99 percent for both organic and
      inorganic soils) with lower residual concentrations on the inorganic soil.
      These results were anticipated because of the organic-chemical-to-organic-
      soil attractions.  Since the phenol was not so effectively desorbed from
      the organic soil, or from the inorganic soil  it is apparently not so
      mobile, i.e., it is more tightly held.  This observation appears to confirm
      the hypothesis that the chemical that is removable is scrubbed and that
      which remains may be quite tightly bound to the soil.  Using this concept,
      the natural attenuation or treatment capacity of the soil then works in
      favor of the treatment approach rather than against it.

      The same concept is more graphically illustrated when considering the other
      two chemicals tested, arsenic oxide and PCB.  Arsenic has a strong affinity
      for the fine inorganic soil particles, probably due to an ion exchange type
      mechanism.  It is also held quite tightly to the organic soil.  The
      relatively high residual concentrations of arsenic after treatment and the
      relatively low arsenic concentrations in the solvent confirm the strength
      of the soil/arsenic attraction.  Another indication of this interaction can
      be found when considering the rigorous analytical procedure needed for total
      arsenic analyses.  The soil sample was completely digested in a mixture of
      nitric and hydrochloric acid before a consistent arsenic measurement could
      be obtained.  If arsenic is so difficult to remove during analysis, it is
 ****   not likely to be mobile in the natural environment.  Studies of the natural
Nw   attenuation properties of soils tend to confirm this result.

                                            65

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Multiple extractions of soil contaminated with arsenic have not been run;
but it is expected that, unlike phenol, the extraction efficiency will
decrease substantially with each successive extraction.  The probable
effect will be that, after only a few extractions, very little additional
arsenic will be drawn into the solvent and further treatment by soil
scrubbing will be marginally useful in effectively reducing soil  arsenic
levels.  If additional arsenic cannot be forced out of the soil by rigorous
stripping and extraction, it should be quite immobile in the natural
environment.

Treatment of PCB using the scrubber approach provides the most difficult
challenge for effective treatment.  These materials have an extremely
limited water solubility and a strong affinity for soils.  Laboratory tests
indicated that some PCB was removed into the water phase but much of what
was being processed remained in the soil.  However, the initial sorbed
amounts of PCB were quite low since the lab approach, simulating  a spill
situation, allowed only a 24-hour contact time between contaminant and
soil.  Use of higher initial levels of sorbed PCB may show better percent-
removals.

Considering the hypothesis that soil treated with multiple extractions  to
the point such that no further removal would have only a minimum  impact on
the environment, application of soil scrubbing to PCB-contamination
problems may be promising.  Available disposal methods for PCB-materials
are limited to landfilling in specially approved sites, incineration,
and—possibly--some novel processes.  Treatment with the soil scrubber
prior to disposal may allow relaxation of some of the originally  applicable
restrictions.  It may be possible to scrub the soil and then dispose of the
residuals in a sanitary1 landfill or in a less-than-totally-secure toxic and
hazardous site.  If the concept of repeated scrubbing to reach a  stable
soil residual is accepted, the usefulness of the soil scrubber could be
almost unlimited.

FURTHER LABORATORY TESTING

Two types of soil contamination exist that can be handled by the  soil
scrubbing system.  The first is a spill situation that involves an
immediate response to a freshly spilled chemical-onto-soil system.  In  this
situation, a large amount of contaminant may be physically entrained and
only a small fraction actually sorbed to the soil.  The goal is then to
promptly remove the contaminant into the water phase and replace  the soil
at the site.  The second type of soil/chemical problem is already existing
contamination arising from improper chemical disposal.  Usually this
situation is a longer term problem so that a much larger portion  of the
contaminant is tightly sorbed to the soil.  The goal in this instance is
also removal of the contaminant.  However, it may be acceptable to mainly
remove the mobile fraction and then dispose of the residual soil  in less
rigorously designed landfills.

The laboratory work concentrated mainly on the more immediate situations
and has been used to preliminarily evaluate the treatment of different
chemicals and soil types.  Using this approach, treatment was found to  be
most effective for phenol, a water soluble organic compound.
                                      66

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Neither arsenic nor PCB were as effectively treated when  considering  percent
removals.  From a removal efficiency  standpoint,  the  soil  scrubbing  system
will probably be most useful for chemicals that have  a  higher  water
solubility and a lower affinity for soil  than  PCB's or  arsenicals.

To confirm this result, some additional testing using chemicals  with  a
higher potential for effective treatment  should be undertaken.   Possible
candidates include certain  aromatics  and  heterocyclics, medium chain  length
organics, and metals (copper, nickel, cadmium, zinc)  in cationic states.
The program requires an abbreviated version of the preliminary testing
performed to date.  The same two soil types can be dosed  in  a  manner  to
simulate spill conditions.  Then, a water-knife test  program can be
undertaken using a set submergence time of 15  or  30 minutes.  Finally, the
extraction tests can be performed to  select solvents  and,  when  appropriate,
to evaluate countercurrent  extraction.  The data  obtained  from these  tests
should give a broader indication of the potential range of application of
the scrubber for spill and  release (remedial)  situations.

Another approach to consider involves further  investigation  of the concept
of stabilizing the contaminant level  in the soil  by scrubbing.   To
accomplish this, the laboratory approach  should be modified  somewhat.
Existing contaminated soil  samples (rather than newly dosed  samples)  should
be utilized in the testing  so that the impact  of  time on  soil  sorption can
be evaluated.  Since both PCB and arsenic oxide represent  existing soil
contamination problems, either or both of these contaminants could be
tested.  Once samples are obtained, an initial analysis of the  contaminant
concentration should be made.  Then,  samples with a range  of contaminant
amounts can be tested.  Some preliminary  soil  characterization  will  also be
needed.  Typical soil testing for particle size,  organic  and water content,
and Atterburg limits would  be needed  to broadly establish  soil  types.

The actual tests would be similar to  those performed  during  the  preliminary
laboratory study.  A water-knife test, using the  three-stage treatment
approach, is the first step.  Then, material less than  2 mm  can  be tested
for extraction effectiveness.  PCB solvents screened  can  include water and
water plus Tween 80 or other detergents/surfactants.  If arsenic is
evaluated, then redox solvents may be most promising.   The extractions can
be performed using successive amounts of  solvent  until  a constant
concentration in the solvent is achieved.  Then the treated  soil  can  be
exposed to the extraction procedure (EP)  specified under the Resource
Conservation and Recovery Act (RCRA).

When the extract from the EP does not contain  contaminants in  concentra-
tions more than 100 times the primary drinking water  standard,  the soil  may
possibly be classified as non-hazardous.  In a full-scale  system, disposal
to a sanitary landfill or even replacement at  the site may then  be
acceptable, depending upon  the situation.

When EP is an acceptable indicator of the soil's  contaminant level,  this
measurement  will provide a criterion from which  to judge  the  effectiveness
of soil scrubbing.  Therefore, further evaluation including  the  EP
procedure would be extremely valuable in  assessing the  feasibility of  the
soils-scrubbing concept for any type  of soil/chemical contamination.

                                      67

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                                  SECTION  7

                           DESIGN AND CONSTRUCTION

INTRODUCTION

Upon completion of the laboratory experiments,  the treatment  sequence for
the mobile soil scrubber was finalized.  Following is  a  description  of the
flow scheme and a discussion of some of the major  design  considerations.
Photographs of the fully constructed prototype  soil  scrubber  components are
included within the text.

PROCESS FLOW SCHEME

The sequence of operations for the soil scrubber  is  as follows  (Figure 15).
Contaminated soil is deposited into a feeder through a screen that
separates oversize material  (>2.5 cm).  The feeder introduces the  soil at a
uniform rate into the drum screen scrubber where  water knives break  down
soil lumps and mechanically  strip chemicals from  the soil.  Following
initial stripping with recycled wash spray, soil  particles  greater than
2 mm, which are retained within the drum by the screen,  enter the  soaking
and final rinse zones of the drum before being  discharged from  the far end
of the drum and returned to  the site of the excavation or otherwise
disposed of.  Soil particles of this size  dewater  relatively  easily,  and
further dewatering beyond that which occurs at  the outlet screen of  the
drum screen scrubber is probably not required.

Particles less than 2 mm, which were not retained  within  the  drum  by the
screen, form a slurry with the washing fluids,  which thickens in the bottom
of the wash-spray-collector  troughs.  This slurry  is continuously  withdrawn
from the troughs and pumped  to the countercurrent  chemical  extractor for
further treatment.  In the extractor, the  soil  is  processed in  a four-step
continuous sequence wherein  the soil is contacted  by washing  fluid of
increasing purity.  The concentration gradient  between the  chemically con-
taminated soil and the washing fluid forms the  primary driving  force for
transfer of contaminants into the washing  fluid.   Within  each of the batch
chambers of the extractor, the soil/washing-fluid  slurry  is well-mixed by a
froth-flotation technique, which employs both mechanical  mixing and  fine
bubble aeration to achieve good contact between soil and  washing fluid.
Hydrocyclones are employed between the four stages to  partially/
sequentially separate the soil from the washing fluid.  There is also a
hydroclyclone in the solids  discharge line at the  output  of the treatment
system.  Unlike the drum-screen scrubber,  the product  of  the  countercurrent
chemical extractor retains a portion of the final  rinse  water as it  exits
the underflow of the last hydrocyclone.  A drying  bed  may be  necessary
before redepositing this portion of the soil at the  site, depending  on the
                                      68

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characteristics of the site and the method for reintroducing the soil.

Likewise, spent washing fluids are also discharged through a hydrocyclone
(the overflow of the hydrocyclone in the effluent of the first washing
step).  Since the hydrocyclone is not fully efficient in removing
particles, some of the very fine particles (especially clay) are carried
into the spent washing fluid stream.  These particles must subsequently be
removed by chemical treatment, clarification, and/or filtration prior to
introducing the spent washing fluids to carbon adsorption columns or other
polishing units where the extracted chemicals are removed before the
washing fluid is recycled.

The froth-flotation method of providing intimate contact between soil
particles and washing fluids results in the production of a froth, which is
skimmed from the top of each of the four extraction chambers.  This froth
is a treatment residual that must be ultimately disposed of, along with the
fines separated from the spent washing fluid.

Froth-flotation can also result in the sparging of volatile chemicals from
the wash water.  The air discharge from the froth-flotation units, as well
as that from the drum screen scrubber (the drum is not a forced-air system
but can produce fugitive air emissions), is collected and processed, when
necessary, before discharge through a stack.

WATER-KNIFE DRUM SCREEN DESIGN AND OPERATION

Preliminary, small-scale testing during the first phase of this project has
shown that thin, intense jets of water from water knives are capable of
effectively breaking up even compacted clay lumps, especially when the
spraying cycle is combined with a soaking step.  Stripping can be
effectively accomplished at a water jet pressure of 4.2 kg/cm2 (60 psi),
a low enough pressure to permit direct recycle of stripping fluids without
undue problems with nozzle clogging.  Tests showed that effective use of
water knives also required that the material being stripped be constrained
to remain beneath the water knives.  Laboratory work demonstrated that  the
necessary constraint was achieved when the soil was rotated within a
drum-like screen.

Mobility Requirements

Initially, efforts were made to procure a commercially available,
modifiable rotary screen, that could be converted to accomodate stripping,
soaking, and rinsing.  Standard trommel screens are expensive and did not
meet the design requirements.  Extensive modifications would have been
required to meet the process objectives.  The decision was then made to
design a rotary screen specifically tailored to accommodate the stripping,
soaking, and rinsing processes.

Since it is advantageous to process as much soil per hour as possible,  the
largest, practical size drum-screen is desirable.  However, since most
states limit semi-trailer size to 13.7-m (45-ft) long, 2.4-m (8-ft) wide,


                                      70

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and 4-m  (13.5-ft) high,  the  proposed  trailer-borne  drum-screen  scrubber had
to fit within that size  envelope  for  transport  without  special  permits.
When allowance  in the width  is made for  sprockets,  hoods,  drive unit,  and
piping, the maximum allowable drum shell  diameter  is  about 1.4-m (4.5-ft).
The drum-screen unit was  thus designed for  over-the-road  transport  without
special hauling permits.

After considering various means for transporting  and  mounting  the unit, it
was concluded that the best  choice was a  skid-mounted unit designed for
transport on a  drop-deck  trailer  with removal and  placement on  ground  level
during operation.  The overall dimensions are:  9.8-m (32-ft)  long, 2.4-m
(7-ft, 10-in.)  wide, and  2.4-m (8-ft) high.  The  empty  weight  is 6,340 kg
(14,000 Ib).

Drum Feeding

The loading system consists  of a  hydraulically  lifted bucket,  a feed
hopper, and a soil metering  paddle wheel  (Figure  16 and 17).   Workers  load
the bucket with a tractor-mounted front-end  loader  and  rake the soil
through a coarse bar screen  (ca.  7.5  cm  (3  in.))  on the hopper  that screens
out oversize material.   Retained  materials  can  be washed  while  still on the
screen using a  hose sprayer, and  then removed for final  disposal.  Soil and
liquid passing  through the coarse screen  fall onto  a  second bar screen (2.5
cm (1 in.)) where there  is additional spraying  and  removal  of  chunks too
large to drop into the skip  hopper.   The  skip hopper  method permits the
feeding of soils with any fraction of liquid content, from dry  materials to
slurries.  When the bucket contains a sufficient  quantity of material, the
operator elevates the bucket above the feed  hopper  and  dumps it
hydraulically.  This action  allows precise  control  of the  dumping rate.
The feeding of  the hopper is thus under control to  prevent overfilling and
spillage or clogging.  The metering paddle  wheel  in the feed hopper throat
turns at 4 rpm  when metering the  maximum  feed rate  of 13.8 m3/hr (18
yd3/hr).  (The  variable  speed, paddle-wheel-drive motor permits metering
lesser quantities of soil at lower feed rates.)

Drum Screen Construction

Once inside the drum, the soil moves  in a controlled  fashion from the  feed
end to the discharge end through  a combination  of drum  inclination  and
rotational speed.  The duration of the three cycles of  stripping, soaking,
and rinsing is  established by the length of  drum  devoted  to each process.

The rotating drum screen soil scrubber unit  itself  is 6.4-m (21  ft) long
and 1.4-m (54-in.) in diameter (Figures 17  and  18).  The  initial  spray zone
is a 1.2-m-(4-ft)  length of reinforced screen  HYCOR  Contra-Shear™ that
can be backwashed.  The  next (soaking) section  is 4.6-m (15-ft)  long and
terminates in a baffle having a 0.56-m (22-in.) diameter  opening through
which the soil  and water pass to  the  rinse  zone,  which  is  0.6-m (2-ft) long
and is similar  in construction to the initial spray zone.   Both screened
zones are equipped with water-knife nozzles.  The initial  spray zone is
fitted with 15  internal  knife spray nozzles  (13 gpm @ 60  psi)  and 6
external screen backwash knife elements  (10.6 gpm @ 40  psi).  The soak zone

                                      71

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       A.  Drun  cross  section
        B. Drun  Isonetric

Figure 18.  Soak zone description.





              74

-------
         has one wide  angle  sprayer  (24  gpm @  40  psi).   There are eight 3CK>
W      full-cone spray-pattern  nozzles (10 gpm  @  40  psi)  in the final screen rinse
         section,  (1 gpm  = 3.785  L/m;  1  psi  =  6.9 kN/m2),  some of which can be
         adjusted for  screen  backwashing.

         Once inside the  first  screened  section  (initial  spray zone)  of the drum,
         the soil is subjected  to water-knife  stripping  with  recycled water.
         Preliminary tests showed that the  minimum  stripping  time in  this  section
         should be one minute;  however,  because of  uncertainties  about the
         cohesiveness  of  the  soil to be  scrubbed, the  initial stripping was
         lengthened to four minutes.

         The soil then is flushed for  15 min by a countercurrent  flow of water in
         the soaking zone.  A baffle separates the  soaking  zone from  the final
         (rinse) zone.  The effective  baffle height is determined by  drum  pitch
         angle and soil thickness.  For  a 3-degree  pitch  of the soil  scrubber and a
         design soil thickness  of 22-cm  (8.6-in.) at the  end  of the soaking zone, a
         baffle height of 41-cm (16-in.) is  required.  A  channel  of water  is  formed
         by the soil boundary and the  drum  wall.  Soil tumbles into this
         free-flowing  reservoir to be  cleansed by flushing  and tumbling.  Flights
         are located at the end of the soak  zone  to lift  the  soil over the baffle
         into the rinse zone.

         Lower pressure,  clean  water sprays  are utilized  to rinse the soil for two
         minutes in the final screened section of the  drum.  Clean soil tumbles from
 "—      the drum into the discharge chute  for collection,  possible drying, and
W      replacement at the site.

         Drum-Screen Capacity

         Another design-limiting  factor  is  the capacity  of  the EPA-ORD mobile
         physical-chemical treatment system (activated carbon treatment trailer
         (14)), which  is  utilized to treat  washing  fluids  for reuse.   The  nominal
         processing capacity  of the basic granular  activated  carbon unit is 6.3
         L/sec (100 gpm)  but  can  be increased  six-fold with lowered residence
         times.  Floe-settle  and  sand- anthracite filtration  processing is part of
         the treatment process.   For many of the  soil  compositions and conditions
         that will be  encountered, such  a rate of wash fluid  recycle  permits  a
         processing rate  of 2.3 to 3.8 m3/hr (3 to  5 yd3/hr).  However, when  the
         soil contains a  large  amount  of free  flowing  granular solids (e.g.,  material
         from railroad of highway beds), much  higher treatment rates, perhaps as great
         as 13.8 m3/hr (18 yd3/hr), are  feasible.

         COUNTERCURRENT CHEMICAL  EXTRACTION  UNIT

         The principal elements of the semi-batch,  countercurrent chemical extractor
         for soils consist of well-mixed contact  tanks and  soil/washing-fluid
         separators (Figures  19 and 20). A  simplified schematic  of a countercurrent
         chemical extractor is  shown in  Figure 20.   A  soil  slurry containing  about
         10 percent solids is fed and  moves  through the  system in a forward
         direction (from  extraction tank 1  to  tank  4)  [left to right  in Figure 20].
w
                                               75

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Fresh water is introduced  at  the  opposite  end  of  the  system  (extraction
tank 4).  The function of  tank 4  is to  rinse residual  contaminant  and
chemical additives from  the soils  before the last  solid/liquid  separation
(hydrocyclone 4) and final discharge.   Fluid flow  through  the  system is in
a reverse direction to the flow of soils (i.e., from  extraction tank 4 to
1).  Chemical additives  may be injected during extraction  steps 2,  3, and
4.  Following solid/liquid separation  (hydrocyclone 1)  after the first
extraction, the spent washing fluids are removed  for  treatment  and  recycle.

Contact Tanks

To be effective, the extraction tanks must provide thorough  contact between
the soil and the solvent.  Mixing  enhances this contact and  is, therefore,
crucial to proper extraction.  Two types of contact tanks  were  considered
for the soil scrubber:   a  propeller-mixed  tank and the  existing EPA mobile
froth flotation unit (oily beach  sand cleaner) (Gumtz,  1972).   The  latter
alternative was chosen (Figure 19).  Advantages of the  EPA-ORD  froth-"
flotation unit are the good mixing potential of the combined pneumatic/
mechanical mixing system and the  use of a  skimming mechanism for removing
floating materials and foam.  The  drawbacks include greater  difficulty in
control of volatile substances and possible foaming problems when
surfactants are used as  additives.

Required modifications to  the EPA-ORD mobile unit  included changing inlet
and outlet configurations, mounting hydrocyclones  and  pumps, coating the
tanks to provide chemical  resistance, emplacing baffles to reduce fluid
short-circuiting, and installing  an air contaminant enclosure.   The tanks
are about 1.7-m (5-ft) high (including  sloping bottom), 1.7-m  (5-ft) long,
and 2-m (6-ft) wide.  The  modifications are complete;  the  converted
countercurrent chemical  extraction unit is shown  in Figure 19.   (The unit
can easily be reconfigured to serve its original  function  as a  beach sand
cleaner; indeed, the sand  hopper  (Figure 20, far  left)  is  not  used  in the
soil scrubbing system but  has not  been  removed.)

System Flow Equalization

A special feature has been incorporated into the  system to eliminate
problems from non-uniformity  in pump flows.  Without  this  feature  (unless
all of the pumps are perfectly matched  in  flow),  the  fluid levels  in the
tanks would not remain constant and excessive  effort  to adjust  valves
manually would be necessary unless complex servo  instrumentation was
provided.  Flow equalization  is accomplished by allowing a small amount of
fluid to overflow from each tank  back to the previous  tank,  i.e., from
right to left in Figure  20.

Solid/Liquid Separation

The preliminary evaluation indicated that  hydrocyclones were quite
acceptable for the solid/liquid separation step.   The  hydrocyclones are
rubber lined and are all the  same  size, but do have various  size vortex
finders and apex valves  to accommodate  the conditions  that exist at each
extraction tank.  When necessary,  vortex finders  can  be changed in  the
field.

                                      78

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Washing Fluid Recycle

Washing fluid recycling  is  essential  to  reduce  operating  costs  and to make
the soil scrubbing concept  economically  feasible.   The  spent  washing fluid
from the countercurrent  chemical  extraction  system  is cleaned (treated)  and
returned to the system.   Note  that  cleaned washing  fluid  is also needed  for
the nozzles of the water-knife  drum-screen scrubber.  The state-of-the-art
of treatment of contaminated water  is  quite  advanced; mobile  units are
already available for these situations.   The use of the existing EPA mobile
physical/chemical treatment unit  with  the soil  scrubber system  is one
suitable way of achieving washing fluid  recycle capability.

Treatment Residuals

In addition to the debris removed by  the initial screening, the  residuals
from the soil scrubbing  system  consist of spent carbon  in the washing fluid
recycle system, soil fines  carried  out of the soil  scrubber with the spent
washing fluids, floe-settle and filtration wastes,  and  foam and  skimmings
from the froth-flotation  tanks.

Emissions of air contaminants  from  the soil-scrubbing processes  are
controllable using enclosures  and ventilation,  followed by air  scrubbing or
other forms of air cleaning.   Some, but  limited, fugitive emissions can  be
expected during soil excavation and feed to  the system.  Personal
protection to prevent inhalation  hazards, as well as skin and eye contact,
is required for all system  operators.

TREATMENT COSTS

For comparative purposes, the  costs for  scrubbing soil  with different
levels of phenol contamination  have been  estimated  and  are presented in
Figure 21.  Higher dollar requirements at elevated  levels of  phenol
correlate primarily with the additional  expense associated with  the
cleaning and recycling of washing fluids.

The estimated costs include those for: fuel  for the diesel-powered
generators that furnish  energy  to operate the systems,  two operators for
each process, front-end  loader  rental, chemical additives, and  activated
carbon.  The estimated costs do not include  those for:  startup  and
shutdown, disposal of treatment residuals, maintenance  and repair,
depreciation, clean water supply, freight, and  shipping.

SUMMARY

A mobile system for treating excavated,  contaminated soils at a  field site
by sieving the soil,   disintegrating the  soil matrix, and cleansing the
soil is ready for shakedown, evaluation,  and demonstration.   The system  is
expected to take its place  among  other emerging methods such  as  in  situ
treatment or incineration,  for  treatment  of  contaminated  soils  at  the
actual site of a hazardous  substance spill or release under a wide variety
of circumstances.

                                      79

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Laboratory work shows that non-aqueous  (organic) solvent soil-washing
systems have special advantages in processing soils contaminated with
highly water-insoluble hazardous substances but that significant design  and
engineering problems must be overcome to make such systems economically
attractive.
                                     80

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         100
          7'j
      ee.
      UJ
      Q.
      a
         25
                   LXPLCTED
                   OPERAiING
                   RANGE
 r~ MAXIMUM
  \ SYSTEM
   \ CAPACITY


i   i  i i  mi
                                 l  I I i in
I   i
                    PHENOL CONTAMINATION, PPM
                                                  1000
Figure  21.  Cost per volume treated for  scrubbing phenol  from soil,
                                    81

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                                  REFERENCES

 1.    Huibregtse, K. R. and Kastman, K. H., "Construction and Preliminary
       Testing of a System to Protect Groundwaters from Hazardous Spills",
       Proc. of 1980 National Conference on Control of Hazardous Material
       Spills, Copyright Vanderbilt U., Nashville, Tennessee 37232,
       pp. 77-81.

 2.    The Merck Index, Merck and Co., Inc., Rahway, New Jersey, 1976.

 3.    Ottinger, R. S., et al , Recommended Methods of Reduction, Neutraliza
       tion, Recovery or Disposal of Hazardous Material, Volume II -
       Toxicologic Summary, U.S. EPA 670/2-75-053-6, U.S. Environmental
       Protection Agency, Cincinnati, Ohio, 1973.

 4.    Dawson, G. W., et al , Control of Spillage of Hazardous Polluting
       Substances, Federal Water Quality Administration, U.S. Department of
       the Interior, Washington, D.C., 1970, 89 pp.

 5.    Rockwell International, Environmental Services, Invitation to
       Propose, EPA-8, In-Situ Treatment of Hazardous Spills in
       Watercourses, Request for Proposal, March 9, 1979.

 6.    PCBs in the United States, Industrial Use and Environmental
       Distribution, PB-252-012, National Technical Information Service,
       U.S. Environmental Protection Agency, Cincinnati, Ohio, 1976.

 7.    Gould, E. S., Inorganic Reactions and Structure, Henry Holt and
       Company, New York, 1955.

 8.    The Encyclopedia of Chemical Technology, Van Nost, Rand & Reinhold
       Co., N.Y., 1966.

 9.    Standard Methods for the Examination of Water and Wastewater,
       American Public Health Association, American Water Works Associa-
       tion, Water Pollution Control Federation, Washington, D. C., 1976.

10.    Methods for Chemical Analysis of Water and Wastes, U.S. EPA
       600/4-79-020, U. S. Environmental Protection Agency, Cincinnati,
       Ohio, 1979.

11.    Bellar, T. A., and J. J. Lichtenberg, Methods for Benzidine,
       Chlorinated Organic Compounds, Pentachlorphenol and Pesticides in
       Water and Wastewater, Interim report, U.S. Environmental Protection
       Agency, Cincinnati, Ohio, 1978.
                                      82

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12.    Public Law 96-510.  "Comprehensive Environmental  Response,
       Compensation, and Liability Act of 1980".

13.    Gumtz, G.D., 1972.  Restoration of Beaches Contaminated by Oil.
       EPA-R2-72-045 (September, 1972).

14.    Gupta, M.K., 1976.  Development of a Mobile Treatment System for
       Handling Spilled Hazardous Materials. EPA-600/2-76-109.
                                      83

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                                   TECHNICAL REPORT DATA
                            (I'lcase read Instructions on the reverse before cr»ni>lctin/>/
 1. REPORT NO.
 4. TITLE AND SUBTITLE
   MOBILE  SYSTEM  FOR EXTRACTING SPILLED
   HAZARDOUS MATERIALS FROM EXCAVATED SOILS
7. AUTHOR(S)
   Robert Scholz  and Joseph Milanowski
9. PERFORMING ORGANIZATION NAME AND ADDRESS
   Rexnord,  Inc.
   5103 W.  Beloit  Road
   Milwaukee,  Wisconsin 53214
 12. SPONSORING AGENCY NAME AND ADDRESS
   Municipal  Environmental Research Laboratory—Cin.,OH
   Office of  Research  and Development
   U.S.  Environmental  Protection Agency
   Cincinnati,  Ohio  45268
                                                           3. RECIPIENT'S ACCESSION-NO.



                                                           5. REPORT DATE
             6. PERFORMING ORGANIZATION CODE
                                                           8. PERFORMING ORGANIZATION REPORT NO
             10. PROGRAM ELEMENT NO.

                        TEJY1A
             11. CONTRACT/GRANT NO.
                68-03-2696
                                                           13. TYPE OF REPORT AND PERIOD COVERED
                Final 12/76-4/82
             14. SPONSORING AGENCY CODE
                EPA/600/14
15. SUPPLEMENTARY NOTES
   Project  Officer:  John Brugger (201) 321-6634
     Laboratory tests were conducted with three  separate pollutants (phenol, arsenic
   trioxide,  and polychlorinated biphenyls  (PCB's))  and two soils of widely different
   characteristics  (sand/gravel/silt/clay and  organic  loam) to evaluate techniques  for
   cleansing  soil contaminated with released or  spilled hazardous materials.  The tests
   show  that  scrubbing of excavated soil on site is  an efficient approach for freeing
   soils of certain  contaminants but that the  effectiveness depends on the washing  fluid
   (water  + additives) and on the soil composition  and particle size distribution.  Base
   on the  test  results, a full-scale, field-use  system was designed, engineered,
   fabricated,  assembled, and briefly tested;  the unit is now ready for field
   demonstrations.   The system includes two major soil scrubbing components:  a water-
   knife stripping  and soaking unit of novel design  for disintegrating the soil fabric
   (matrix) and solubilizing the contaminant from the  larger particles (>2 mm) and an
   existing,  but re-engineered, four-stage  countercurrent extractor for freeing the
   contaminants from smaller particles «2 mm). The  complete system requires auxiliary
   equipment, such  as the EPA-ORD physical/chemical  treatment trailer, to process the
   wastewater for recycling; under some circumstances, provision must be made to confine
   and treat  released gases and mists.  The processing rate of the complete system  is
   2.3 to  3.8 m3/hr  (4 to 5 yd3/hr), though the  water-knife unit (used alone) can
   process 11.5 to  13.5 m3/hr (15 to 18 yd3/hr).
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              I'.IDFNTIFIERS/OPFN ENDED TERMS
                                                                           COSATI Held/Group
 3. DISTRIBUTION STATEMENT


     RELEASE  TO PUBLIC
19
                           ?1 NO OF PAGES
                                              2O SFCURITY CLASS (This r>af!<'I
                                                 UNCLASSIFIED
EPA Form 2220-1 (9-73)
                                            84

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