United States        Office of Emergency and    EPA/540/2-90/011
             Environmental Protection    Remedial Response      October 1990
             Agency           Washington, DC 20460


             Superfund
oEPA       Subsurface
             Contamination
             Reference Guide

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                                  NOTICE
Development of this document was funded by the United States Environmental
Protection Agency in part under Contract No. 68-C8-0058 to Dynamac Corporation.
It has been subjected to the Agency's review process and approved for publication
as an EPA document.

The policies and procedures set out in this document are intended solely for the
guidance of response personnel. They are not intended, nor can they be relied
upon, to create any rights, substantive or procedural, enforceable by any party in
litigation with the United States.  The Agency reserves the right to act at variance
with these policies and procedures and to change them at any time without public
notice.

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                                   EPA/540/2-90/011
                                     October 1990
SUBSURFACE CONTAMINATION
       REFERENCE GUIDE
   Office of Emergency and Remedial Response
     U.S. Environmental Protection Agency
          Washington, DC 20460
                                    Printed on Recycled Paper

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                                CONTENTS








1.     Introduction  	    1-1



2.     Subsurface Remedial Technologies	    2-1



      2.1    Pump and Treat	    2-1



            2.1.1  Continuous Pumping	    2-1



            2.1.2  Pulsed Pumping	    2-2



            2.1.3  Reinjection	    2-3



      2.2   Soil Vacuum Extraction	    2-3



            2.2.1  In-Situ Steam Extraction	    2-4



      2.3   Soil Flushing	    2-4



            2.3.1  Chemical Extraction	    2-5



      2.4   Containment	    2-5



      2.5    Bioremediation	    2-6



      2.6   In-Situ Vitrification	    2-7



      2.7   Treatment Combinations	    2-7



3.     Contaminant Properties Affecting Subsurface Transport and Fate	    3-1



4.     Table References	    4-1

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                                  Chapter 1
                              INTRODUCTION
      Ground water contamination is a significant concern at approximately 70% of
the Superfund sites. The difficulties associated with cleaning up contaminated
ground water are becoming more and more evident as experience with this problem
increases. A recent study of 19 ground water extraction systems (U.S. EPA, 1989,
EPA/540/2-89/054) indicated several factors that can limit the effectiveness of the
traditional pump-and-treat remediation systems and also identified possible
enhancements than may improve the performance of these systems. Many of the
factors limiting performance are a result of interactions between the contaminants
and the subsurface environments and can be tied to particular contaminant
properties (e.g., solubility,  density) and/or the nature of the subsurface (e.g., low
permeability, fractures).

      As a result of the referenced study several recommendations were made
including a recommendation to collect more detailed data on the vertical stratigraphy
of the subsurface, the vertical variations in contaminant concentration, and the
proportion of contaminant  sorbed to the soil in the saturated zone. To the  extent
possible potential limitations should be recognized even before the investigation
begins; i.e. during scoping, to better focus remedial investigation/feasibility study (Rl/
FS) efforts.

      This guide was developed to provide a source of information pertaining to
important fate and transport properties for a variety of contaminants commonly  found
in ground water at Superfund sites. This information may help to focus site
investigation efforts and identify early-on potential remediation strategies.
Knowledge pertaining to the magnitude of these properties can  be used to help to
project whether contaminants will sorb significantly to soils, dissolve and move  with
ground water flow, migrate downward as a separate phase, or float on the water
table. Potential remedial technologies have been identified for various combinations
of contaminant types and hydrogeological environments.

      Information pertaining to contaminant fate and transport properties have been
presented in tabular form and provided as separately published charts for easy
reference.

      This document was prepared as a task of the Subsurface Remediation
Information Center located at the U.S. EPA Robert S. Kerr Environmental Research
Laboratory (RSKERL), Ada, Oklahoma.  Questions pertaining to the information
contained in this document should be addressed to John E. Matthews at RSKERL-
Ada (405/332-8800).
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                                 Chapter 2
                 SUBSURFACE REMEDIAL TECHNOLOGIES
      Subsurface remedial technologies which may be applicable at Super-fund
sites are described below.  These descriptions are intended as guidance for use in
conjunction with the tabular data presented in separately published charts that are
provided with this document (Tables 1 and 2, EPA/540/2-90/011a; Table 3, EPA/
540/2-90/011b).
2.1   PUMP AND TREAT

      2.1.1  Continuous Pumping

      Pump and treat remediation technology is applicable to the saturated zone
and refers to the extraction of contaminated ground water from the subsurface and
subsequent treatment of the extracted ground water at the surface.  Extraction of
contaminated ground water is accomplished through the use of extraction (pumping)
wells which are completed at specified locations and depths to optimize contaminant
recovery.  Determination of the locations and depths of extraction wells requires
prior delineation of the contaminant plume and knowledge of the aquifer properties.
Injection wells may be installed to enhance contaminant recovery by flushing
contaminants toward extraction wells.

      Pump and treat technology is best suited for managing mobile chemicals (i.e.,
'°9 KOC or '°9 Kow values less tnan 3-0 ar|d 3.5, respectively) residing in relatively
permeable and homogeneous hydrogeologic settings.  Factors which must be
considered and may limit the ability of pump and treat remediation treatment to
achieve cleanup concentrations in the ground water include: 1) the presence of
chemicals with relatively high K^ or K^ values (e.g. log K^ > 3.0 or log K^ > 3.5),
2) aquifers exhibiting low permeability properties (e.g., < 10"6 cm/s),  3) highly
heterogeneous hydrogeologic settings (e.g. highly stratified aquifers with multiple
layers of coarse and fine textured material), and 4) the presence of spatially
discontinuous or inaccessible dense non-aqueous phase liquid (DNAPL).

      Pump and treat technology may, in many cases, be used to aid in  the removal
of light non-aqueous phase liquid (LNAPL) and/or DNAPL which may be  present.
Recovery of LNAPL  residing as free product on the surface of the water table, for
example, can be facilitated by using pumping  wells to create cones of depression.
DNAPL residing as large pools in topographical lows at the bottom of aquifers can
be recovered by pumping from wells screened over the thickness of the pools.  In
cases where recovery is not feasible (e.g., DNAPL resides in fractures or is present

                                     2-1

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as spatially discontinuous free product within an aquifer), alternative measures such
as physical containment (e.g. cement-bentonite walls) should be considered.

      Pumping technology may also be used as a means of containing or
controlling contaminant plumes. This is accomplished through control of hydraulic
gradients by selectively locating pumping wells in the area of the plume. Control of
hydraulic gradients should be considered in conjunction with physical containment
options.

      The surface treatment of extracted ground water will vary depending on the
contaminants present. Typical actions include air stripping, activated carbon
adsorption and biological treatment.  In some cases, treated ground water may be
amended with nutrients and oxygen and reinjected into the subsurface to aid in
stimulating biodegradative processes.

      Pump and treat remediation technology generally will play an important role
in ground water cleanup.  For information regarding applicability of pump and treat
technology and its modifications, contact Randall R. Ross at the RSKERL-Ada (405-
332-8800).
2.1.2 Pulsed Pumping

      Pulsed pumping is a modification of standard pump and treat technology
which involves regular or periodic cessation of pumping activities to optimize ground
water cleanup.  Pulsed pumping may be necessary or more cost-effective in cases
where extraction wells can not sustain yields (e.g., in bedrock and unconsolidated
deposits of low permeability), where desorption and/or dissolution of contaminants in
the subsurface is relatively slow, or where hydraulic conductivity heterogeneity is
high.  Pulsed pumping may be appropriate for:  1) low yield consolidated and
unconsolidated deposits; 2) relatively homogeneous hydrogeologic settings
containing contaminants with log K^ values between  2.0 and 4.0 (or log K^ values
between 2.5 and 4.5); 3) heterogeneous formations consisting of alternating high
and low permeability layers and containing contaminants with log K^. and log K^
values less than 3.0 and 3.5, respectively; and 4) hydrogeological settings
containing low to moderately soluble residual non-aqueous phase liquid (NAPL).

      A potential concern associated with  implementation of pulsed pumping is the
uncontrolled migration of the contaminant plume during non-pumping phases.
Nearby water supply wells or irrigation systems may significantly impact the behavior
of the contaminant plume during non-pumping phases and thereby create a
potentially more serious contamination scenario.
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2.1.3 Reinjection

      Reinfection, which often is used in combination with pump and treat or pulsed
pumping, generally refers to injection of treated ground water back into the
subsurface.  Reinjection may be accomplished through the use of injection wells or
other means such as infiltration galleries. Reinjected ground water can be used to
help remove contaminants residing in the unsaturated zone by forcing these
contaminants towards extraction wells.   Reinjection also may be used in the
stimulation of biodegradative processes  in the saturated zone, thereby enhancing
cleanup of the saturated zone. In such cases, the injectate is amended with
nutrients and an oxygen source. In special cases, the injectate may be amended
with surfactants or other compounds (i.e. chemical extraction) to facilitate removal of
adsorbed and residual organics in the unsaturated and/or saturated zones.
2.2   SOIL VACUUM EXTRACTION

      Vacuum extraction technology involves the enhanced removal of chemicals in
the subsurface through application of a vacuum.  The applied vacuum enhances
volatilization of compounds from soil and pore water.  The technology is particularly
applicable to relatively volatile organic compounds (Henry's Law Constant > 10/3
atm-m3/mole) residing in the unsaturated zone.  The technology also is applicable
for removal of volatile light non-aqueous phase liquids (LNAPLs) floating on the
water table or entrained in the capillary fringe.  The process involves installation of
vacuum extraction wells at strategic locations and depths.  The spacing of extraction
wells is dependent on soil properties such as permeability and porosity. The
technology is applicable to most soil types although removal efficiency will generally
decrease with decreasing soil permeability and increasing subsurface stratigraphy
(heterogeneity).

      Vapors released from the subsurface as a result of the vacuum extraction
process may be captured and then processed through a liquid-vapor separator. The
separated volatile organic vapor fraction may be treated with activated carbon or
other means.

      Vacuum extraction also can serve a dual purpose by enhancing removal of
subsurface organic contaminants through stimulation of aerobic biodegradative
processes.  This is accomplished by ensuring a constant and ample supply of
oxygen for use by indigenous subsurface microbial populations.

      Vacuum extraction also may be used in conjunction with in-situ steam
extraction (see description below).   Steam extraction may enhance the recovery of
organic chemicals, including NAPL's, from the vadose zone.
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      Vacuum extraction is a proven remedial technology which is being
increasingly applied at Superfund sites.  For further information regarding the
applicability of vacuum extraction contact Dominic DiGiulio at the RSKERL-Ada
(405-332-8800).
2.2.1  In-Situ Steam Extraction

      In-situ steam extraction facilitates the removal of moderately volatile (103 >
v.p. > 1040 mm Hg) residual organics, including NAPLs, from the vadose zone.
Steam extraction technology utilizes injection of pressured steam to the
contaminated horizon to thermally enhance the evaporative rate of the contaminant
and its subsequent removal.  Injection of steam also can be expected to enhance
removal of residual NAPL's in the unsaturated zone by decreasing their viscosities.
Steam extraction is an emerging technology that appears promising, particularly if
used in conjunction with vacuum extraction.
2.3   SOIL FLUSHING

      Soil flushing technology involves the use of extractant solvents to remove
organic and/or inorganic contaminants from soils in the subsurface.  Extractant
solvents may include water, water-surfactant mixtures, acids, bases, chelating
agents, oxidizing agents and reducing agents.  The extractants used, however,
should be limited to those which exhibit low toxicity and will not otherwise adversely
impact the subsurface environment.  Proper control measures must be exercised to
prevent migration of extractant-contaminant mixtures from the vadose zone into
ground water.

      In-situ soil flushing can be applicable to those compounds residing in the
vadose zone which are not amenable to removal by vacuum extraction. These
compounds may include semi-volatile organics, cyanide salts, and metals (e.g.,
selenium, arsenic, and hexavalent chromium).  Applications are limited to soils with
adequate permeability (k > 10'5 cm/s) and a reasonable degree of homogeneity.
For semi-volatile organics amenable to biodegradation, bioremediation in concert
with in-situ vacuum extraction (or alternative air circulation technology) will likely be a
better choice.

       The effectiveness of soil flushing relative to other vadose zone remedial
technologies is not clear.  Due to the potential environmental impact of in-situ soil
flushing, the technology should only be used in situations where other remediation
technologies of lower potential environmental impact are not appropriate.
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      Soil flushing has been used at some Superfund sites although the level of its
success is not clear.  For information regarding the applicability of soil flushing,
contact John Brugger at the EPA Risk Reduction Engineering Laboratory, Edison NJ
(201-321-6634).
2.3.1  Chemical Extraction

      Chemical extraction as used in this document refers to a specialized form of
soil flushing that applies only to the saturated zone.  This technology involves the
use of extractant solvents to enhance desorption or solubilizatton of contaminants in
the saturated zone in conjunction with pump and treat operations. Extracted ground
water is amended with solvents and/or other chemicals then reinjected at  strategic
locations into the aquifer.   The extractants used are similar to those used in soil
flushing in the vadose zone.  Chemical extraction is most applicable in cases where
contaminants are not easily mobilized or removed with water alone, i.e., strongly
sorbed to aquifer solids or present  as residual saturation.  Caution should be
exercised when using chemical extraction methods, however,  because of the
potential adverse impact introduced chemicals may have on the subsurface
environment.
2.4   CONTAINMENT

      Containment technologies are used to isolate contaminated areas in the
subsurface from the surrounding uncontaminated environment. Containment
usually involves installation of an impermeable barrier around, or a cap over, the
affected area.  The barrier may take the form of a slurry wall (e.g. soil-bentonite wall
or cement-bentonite wall), a grout curtain, or sheet piling cut-offs.  In the saturated
zone, these barriers must be tied into an impermeable layer at the base of the
aquifer. Containment, although not considered a remediation technology, warrants
consideration in concert with remedial technologies or as an interim measure  while
remediation technologies can be considered.  Spatially discontinuous DNAPL
residing within an aquifer, for example, may be an appropriate scenario for
considering containment. The selection of the barrier material must take into
account the compatibility of the material with the contaminant(s) in question.
Containment also may include installation of a cap over the contaminated area to
impede infiltration of water into that area.

      Another method of controlling contaminant migration is hydraulic containment.
Hydraulic containment involves retardation of movement of a ground water
contaminant plume by using pumping wells to control hydraulic gradients.  Hydraulic
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containment may be used early in a site investigation to prevent plume expansion
while a more detailed characterization is completed.

       For information regarding the applicability of containment technologies,
contact Dr. Walter Grube at the EPA Risk Reduction Engineering Laboratory,
Cincinnati, OH (513-569-7798).
2.5   BIOREMEDIATION

      Bioremediation technologies involve enhancing biodegradation of
contaminants in the saturated and unsaturated zones of the subsurface environment
through the artificial stimulation of indigenous soil and ground water microbial
populations.  Natural biodegradative processes are enhanced by optimizing
conditions necessary for subsurface microbes to grow and complete metabolic
pathways.  Bioremediation is applicable only for treating organic contaminants.
Bioremediation should only be considered in conjunction with source control.

      Bioremediation for subsurface contamination often can be carried out in situ.
The successful execution of an in-situ bioremediation program will depend upon:  1)
amenability of the organic compound(s) to biodegradation,  2) permeability and
heterogenic properties of the subsurface regime, 3) ability of the delivered oxygen
and nutrients to reach the contaminated area, and 4) other factors such as
temperature and pH.

      In situ bioremediation in the saturated zone can be applied as a specialized
form of pump and treat.  Extracted ground water from the contaminated zone is
treated at the surface, amended with nutrients and oxygen, and then reinjected into
the subsurface at strategic locations.  Difficulties may arise in the dissemination of
oxygen and nutrients in low permeability or highly heterogeneous regimes. Some
states may not allow reinjection of treated ground water; therefore, amendments
must be delivered to the injection  point in clean water.

      In situ bioremediation in the unsaturated (vadose) zone can be applied as a
specialized form of soil vacuum extraction.  The air circulation induced by soil
vacuum extraction ensures an ample supply of oxygen to the indigenous microbial
population. Other vadose zone in situ bioremediation systems use infiltration
galleries or injection wells for delivery of oxygen and nutrients.

      Bioremediation is a promising technology for vadose zone soils and
contaminated ground waters. For further information regarding the applicability of
bioremediation, contact John E. Matthews, Scott G. Huling or John T. Wilson at the
RSKERL-Ada (405-332-8800).
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2.6   IN-SITU VITRIFICATION

      In-situ vitrification (ISV) transforms contaminated soil into an inert glass-like
mass that is highly resistant to weathering and leaching. The technique employs
electrodes and a high amperage current to heat surrounding soil from 1600°C to
2000 °C.  When operating temperatures are reached a molten mass of
contaminated soil is created.  As the mass expands it assimilates nonvolatile
compounds into its structure and destroys volatile organic compounds by pyrolysis.
The technology is generally more applicable at sites having soils contaminated with
metals or organic chemicals exhibiting high K^ or K^ values.

      In-situ vitrification is a proven technology which has been implemented  at
selected sites. For further information regarding the applicability of in-situ
vitrification, contact Teri Shearer at the EPA Risk Reduction Engineering
Laboratory, Cincinnati, OH  (513-569-7949).
2.7   TREATMENT COMBINATIONS

      Often it will be necessary to implement a combination of treatment
technologies to effectively remediate or control subsurface contamination.   An
example of such a combination is pump and treat with in-situ bioremediation or
chemical extraction. One of these combinations may be appropriate at sites where
contaminants are strongly adsorbed within the aquifer, and pump and treat alone is
expected to have limited success.  In-situ bioremediation or chemical extraction
could facilitate removal of the strongly sorbed contaminants, thereby enhancing the
overall remediation effort. In general, in-situ bioremediation or chemical extraction
would be most effective after initial recovery efforts using pump and treat alone have
been completed.

      Another useful treatment combination involves pump and treat and
containment.  This combination may be of interest in cases where DNAPL is
distributed in a spatially discontinuous manner within the aquifer.  Because DNAPL
recovery in such a case would be very difficult, the only recourse might be to control
and/or contain the contamination. Pump and treat would initially be used to draw in
or reduce the size of the aqueous phase contaminant plume generated by the
DNAPL.  Physical containment would then be used to isolate the DNAPL source
area.

      An additional treatment combination which may be of interest is aquifer
dewatering using  pump and treat followed by soil vacuum extraction.  This
combination of technologies may be of use in cases where an aquifer is
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contaminated with volatile organics and dewatering portions of the aquifer is
feasible.  Pumping would be used to dewater a portion of the aquifer so that
vacuum extraction could be applied to enhance volatilization and biodegradation of
the volatile organics contaminants in the dewatered zone.

      Combinations involving more than two treatment technologies also should be
considered in efforts to optimize cleanup of subsurface contamination.
                                     2-8

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                                Chapters
                 CONTAMINANT PROPERTIES AFFECTING
                  SUBSURFACE TRANSPORT AND FATE
      The following is a description of some important properties which may play an
important role in the transport and fate of contaminants in the subsurface.  These
descriptions are intended to provide guidance for using the tabular information
presented in the separately published charts accompanying this document.
Melting Point - The melting point of a compound provides an indication of the
      physical state of a pure compound at field temperatures.  Compounds with
      melting points above 30°C, for example, would be expected to be immobile in
      pure form. Such compounds would be  of primary concern when in the
      dissolved phase, either in water or other solvent. Compounds with melting
      points lower than 30°C may be present as mobile non-aqueous phase liquid.

Water Solubility - Water solubility governs the extent to which a contaminant will
      partition into the aqueous phase. More soluble contaminants would be
      expected to migrate further in the subsurface than less soluble compounds.
      The greater the water solubility of a compound, the greater will be the
      tendency for that compound to migrate with the aqueous advective flow
      component. Contaminants with higher water solubilities are more amenable
      to removal from the saturated zone by pump and treat technology. These
      same compounds, however, are more likely to migrate through the vadose
      zone to ground water.

Vapor Pressure - The vapor pressure of a compound provides an indication  of the
      extent to which the compound will volatilize. The tendency of a compound to
      volatilize will rise proportionately with  its vapor pressure.  Compounds  with
      higher vapor pressures are more amenable to treatment with vacuum
      extraction technologies.  For comparative purposes, the vapor pressure of
      water at 20°C is 17.5 mm Hg.

Henry's Law Constant - Henry's Law Constant provides an indication of the extent
      to which a compound will volatilize from an aqueous solution.  Henry's Law
      Constant is directly  proportional to the vapor pressure of the compound and
      inversely proportional to the water solubility of the compound. The greater
      the Henry's Law Constant of a compound, the greater will be the tendency of
      the compound to volatilize from aqueous solution. Compounds with higher
      Henry's Law Constants are more amenable to treatment with vacuum
      extraction technologies.

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Density - The density of a compound indicates whether the compound is heavier or
      lighter than water.  (The density of water is approximately 1.0 g/cc). Liquid
      compounds with densities greater than 1.0 g/cc and of only limited water
      solubility (i.e. DNAPLs), may migrate vertically under the influence of gravity.
      DNAPLs may eventually gravitate to the bottom or other region of an aquifer
      where an impermeable layer is encountered. Compounds with limited water
      solubility and with densities less than 1.0 g/cc will tend to float on the water
      table.
Dynamic Viscosity - Dynamic viscosity provides an indication of the ease with
      which a compound (in its pure form) will flow.  The mobility of the compound
      in pure form is inversely proportional to its dynamic viscosity. The dynamic
      viscosity of water is approximately 1.0 centipoise (cp).

Kinematic Viscosity - The kinematic viscosity of a compound takes into account
      the density of the compound and provides an indication of the ease with
      which the compound (in its pure form) will percolate through the subsurface.
      The lower the kinematic viscosity of a compound, the greater will be its
      tendency to migrate in a downward direction. Kinematic viscosity is of
      particular importance with regard to the movement of DNAPLs in aquifers.
      The lower the kinematic viscosity of a DNAPL, the greater will be the ease
      with which the DNAPL will move downwards and penetrate the finer grained
      layers in the subsurface. The kinematic viscosity of water is approximately
      1.0 centistokes (cs).

Octanol/Water Partition Coefficient (Kow) - The octanol/water partition  coefficient is
      a measure of the extent to which a contaminant partitions between octanol
      and water.  It is the ratio of the concentration of the compound in octanol to
      the concentration of the compound in water. The K^ provides an indication of
      the extent to which a compound will adsorb to a soil or an aquifer solid,
      particularly organic material.  The greater the K^ value of a compound, the
      greater will be its tendency to be adsorbed in the subsurface.

Organic Carbon Partition Coefficient (K^) - The organic carbon partition
      coefficient is the ratio of the amount of chemical adsorbed per unit weight of
      organic carbon in the soil to the concentration of the chemical in solution at
      equilibrium. The K  is similar to the K .
Biodegradability Potential - The biodegradability potential of a compound is
      important in determining the feasibility of using bioremediation as a treatment
      technology. The greater the biodegradability of a compound, the greater will
      be the susceptibility of the compound to a bioremediation process. Only
      aerobic biodegradability is addressed in this document.

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                          TABLE REFERENCES
1Arthur D. Little, Inc. 1985. The Installation Restoration Program Toxicology Guide.
      Arthur D. Little, Inc., Acorn Park, Cambridge, MA. vols. 1, 2, 3, 4.

nabak, H.H., S.A. Quave, C.I. Mashni, and E.F. Earth. 1981.  Biodegradability
      Studies with Organic Priority Pollutant Compounds. J. Water Poll. Control
      Fed. (53)10:150
      3-1518.

3USGS. 1989. Properties and Hazards of 108 Selected Substances. US Geological
      Survey, Open-File Report 89-491.

4USEPA. 1988. Soil Transport and Fate Database. Prepared by the Dept. of Civil
      and Environ. Engr., Utah St. Univ., Logan, UT for the R.S. Kerr Environmental
      Research Laboratory, Ada, OK, US Environmental Protection Agency.

5Sax, I., R. Lewis, Sr. 1987. Hawley's Condensed Chemical  Dictionary. Van
      Nostrand Reinhold Co., New York.

6USDOE. 1986. Chemical Information Profile of Selected Hazardous Organic
      Chemicals. Oak Ridge National Laboratory, US Dept. of  Energy. DOE No. 40-
      1583-85.

7Verschueren, K. 1983. Handbook of Environmental Data on Organic Chemicals.
      Van Nostrand Reinhold Co., New York, 2nd. ed.

8Mackay, D., W.Y. Shiu. 1981. A Critical Review of Henry's Constants for Chemicals
      of Environmental Interest. Jour. Phys. Chem. Ref. Data,  (10)4:1175-1199.

9USEPA. 1989. Draft Guidance on Selecting Remedies for Superfund Sites with
      PCB Contamination. Remedial Operations and Guidance Branch, Hazardous
      Site Control Div., Office of Solid Waste and Emergency Response.
      Unpublished Report.

10Sax, N. 1968. Dangerous Properties of Industrial Materials. Van   Nostrand
      Reinhold Co., New York, 3rd. ed.

11USEPA. 1986. Superfund Public Health Evaluation Manual. Office of Emergency
      and Remedial Response, Office of Solid Waste and Emergency Response,
      USEPA 540/1-86/060.
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12EPRI. 1988. Chemical Data for Predicting the Fate of Organic Compounds in
      Water. Prepared by Tetra Tech, Inc. for the Electric Power Research Institute.
      EPRI EA-5818, Vol 2, Project 2879-2.

13USEPA. 1990. Basics of Pump-and Treat Ground-Water Remediation Technology.
      Prepared by GeoTrans, Inc. for the US Environmental Protection Agency.
      USEPA/600/8-90/003.

14USEPA. 1990. WERL Treatability Data Base/Superfund Treatability Data Base.
      Water Engineering Research Laboratory, US Environmental Protection
      Agency, Cincinnati, Ohio.

15Roy W.R. and R.A. Griffin. 1985. Mobility of Organic Solvents in Water-Saturated
      Soil Materials. Springer-Verlag, New York. Environ. Geol. Water Sci. 7(4):241-
      247.

16USEPA. 1990. Drinking Water Regulations and Health Advisories. Office of
      Drinking Water,  US Environmental Protection Agency. Unpublished Report.

17CIS. 1990. Information System for Hazardous Organics in Water. On-line Data
      Service. Chemical Information System, Baltimore, Maryland.
                                     4-2
                                             U.S. GOVERNMENT PRINTING OFFICE: 1991—548-187/20530

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 EPA/540/2-90/011 a
       Subsurface
     Remediation
        Guidance
      Tables
These Tables are intended as apreliminary guidance in identifyingpotential
contaminant behavior patterns and potential remedial technologies at
S uperf und sites. Descriptions of the remedial technologies and contaminant
properties identified in Table 2 are providedin the accompanying document
entitled "Subsurface Contamination Reference Guide." Contaminant-
specific values for properties identified in Table 2 are provided in Table 3.

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                                                             EPA/54Q/2«9Q/011a
                     Table 1.   Contaminants  Commonly Found at Superfund  Sites
Liquid Solvents

Carbon Trtrachtorife
Chlorobenzene
Chkxtofbnn
Cis-l,2-dichloroethylene (d)
1,1-DicWoroethane (a)
1,2-Dkshloroethane
1,1-Dichloroethylene
l^-Dichloroprop«ns (a)
Efliylene Dibromide (g)
Metfiylene Chloride
l,lA2-Tetrachloroethane
Tetrachloroethylene
Trans-l,2-dichloToeiJiykne (d)
1,1,1-TricWoroethane
1,1,2-Trichloroethane
Trichloroethylene

Gates

Chloroethane
Vinyl Chloride
Noa-Halogenated Volatile Oraanks

KetontslFurans

Methyl Ethyl Ketone
4-Me%l-2-P«itaiiDr»
Tetrahydrofuran

Aromatics

Benzene (g)
Ethyl Benzene (g)
Styrene
Toluene (g)
m-Xylene (g)
p-Xytenefe)
  Tnofyanlgg

  Arsenic (As)
  Cadmium (Cd)
  Chromium (Cr)
  Cyanide (CN)
  Lead(Pb)
  Mercray (Hg)
  Selenium (Se)
  ton(Fe)*
Haktygnated Semlvolatllo Oraank-g

PCBt (b)

Aroclorl242
ArocloTl254
Aroclorl260

PtOicidts

Chlordane
DDD
DDE
DDT
Dieldrin

Chlorinated Benzenes

1,2-DichlOTobenzene
1,4-Dichlorobenzene

Chlorinated Phenols

Pentachlorophenol (w)
2,3,4,6-Tetrachlorophenol
FAHs (e)

Acen«phthene
Anthracene
Benzo(a)anthracene
Benzo(a)pyTene
Benzo(b)£IuoTanthene
Benzo(ghi)perylene
Benzo
-------
Table 2. Property Ratings of Chemical Classes Commonly Found at Superftind Sites (from lable 1) and
                                           Applicable Technologies for In-Situ Treatment
     Chemical
       Cits*
 Melting        Water         Vapor      Henry'sL«w      Density      Dynamk    Kinematic      Log       Log       Aerobic
  Point        Solubility       Pressure       Constant                  Vtocostty     Viscosity       K^       K^    BlodegradabllKy
          tMl Volttflg Organ Ire
     Liquid SotMMf
                             low
     GUM                    low

   Nonhalnenated Volatile Oranic;
     Kttotuilfuriuu
     Aromatic!
                             low
                             low
                high
                high
Haktgentted SwnlvoUtlle Organ Ire*

   PCBt                     tow



                           high
                                          low
                                         moderate
     Chlorinated Bnaam
     ChloriMtedPhenoli
low/moderate     moderate


moderaWhigh     moderate
  high


  high



  high


  high





  low


  low


moderate


  low11
                                       moderate/high
high
                                                                   moderate
                                          high
                                                                   moderate
             high
                                                                                 tow
                                                                                 low
                                                                                 tow
                                                                                 high
                    Ijjw/modenue low/moderate
                                                                                              NA
                                                                                              low
                                                                                                         NA
                                                                                                       moderate
                                                                                                                    tow
                                                                                                                    low
                                                                                                                               tow
                                                                                                                               low
                                                                                            moderate    moderate/high    moderate    moderate
                                                                 low/moderate      low/high
                                                                    high


                                                                    low"
   Non-Hatoyenated SemivoJatilfi Organlca

     PAHi                  moderate/hifti   to^moderate
             high


             high




             high
ND


NA


high


NA




NA
ND


NA


high


NA




NA
                                                                                          high       high
                                                high
                                                                                                    high
     Non-Chlorinated PhtHob     moderate
                                          high
                                low    law/moderate
                                       high/NA     high/NA
                                                                                          high
                                                                                                                    tow
                                                                         high
                                                          tow
                                                                                                                                          ND
                                                                                                                                          ND
                                                                     high
                                                                                                                                          low
                                                                                                               low
                                                                                                                moderate    moderate      high


                                                                                                                  high       high11        high?
                                                                                                              moderate
                                                                     high
  Tnnryanlcs

     St,At,CNCr(Vl)
                                           For detailed information on subsurface transport and fate behavior for these chemicals, see Table 3.

-------
 EPA/540/2-90/011 a
Table 2, Property Ratings of Chemical Classes
                           Applicable Technologies
  Found at Superfund Sites (from Table 1)
In-Situ Treatment  (Continued)
Chemical Potential
Class Subsurface
Mobility
Mflloftfnfi'tfi'i vn'a^f£_j2cRjmiif^
liquid Solvents' moderate/Msil
Gases high
Nonhak»f*enated Volatile OrgMliGS
Ketoneslfuramf high
Aromalits moderate
Halogenated Semlvolatlle Orpanlrs"
PCBs low
Pesticides low
Chlorinated Benzenes moderate
Chlorinated Pttenolt low
Non-Halogepated Semivo)a^}e Qrgfln.|c^
PAHs low
Non-Chlorinated Phenols high
Inorganics
Se,As,CNCr(VI) high**
Hg,Pb,Cd,Cr(Ill) low**
Uraconsolldated Deposits "
(Vsdose Zone)
Homogeneous ' Heterogeneous !
SVE (1)
SF(5)
SVE(l)
SVEB(5)
SF (5)
SVE (1)
SF (5)
SF3(5)
ISV (5)
SF3(5)
ISV (5)
SVEB(5)
SF(5)
SF(5)
SVE B (5)
SVE fl (5)
SF3(5)
SF(5)
SVEB(5)

SF(5)
ISV (5)
ISV (5)
SF3(10)
SVE (5)
SF(5)
SVE(5)
SVEB(5)
SF (5)
SVE (5)
SF(5)
ISV (5)
SF3(5)
ISV (5)
SF3(5)
SVE B(5)
SF(5)
SF(5)
SVE B (10)
SVE B (10)
SF3(10)
SF(10)
SVE B (10)

ISV (5)
SF(5)
ISV (5)
SF3(10)
Unconsotidated Deposits "
(Saturated Zone)
Homogeneous ' Heterogeneous ]
P&T + ISB(1)
P&T(1)
PAT(l)
P&T (1)
P&T + ISB(1)
P&T (5)
P&T + CE"(5)
P&T (10)
P&T + CE * (5)
P&T (10)
P&T + ISB (1)
P&T (5)
P&T + ISB (1)
P&T (5)
PAT + CE^S)
P&T + ISB (5)
P&T + ISB (1)
P&T(1)

P&T(1)
P&T (5)
P&T + CE4(5)
P&T + ISB (5)
P&T (5)
P&T (5)
P&T (5)
P&T + ISB (5)
P&T (5)
P&T + CE"(10)
P&T (10)
P&T + CE4(10)
P&T (10)
P&T + ISB (5)
P&T (5)
P&T + ISB (5)
P&T (10)
P&T + CE4(10)
P&T + ISB (10)
P&T + ISB (5)
P&T (5)

P&T (5)
P&T (10)
P&T + CE4(10)
Consolidated Deposits
(Saturated Zone)
Fractured Ksrst
Bedrock Bedrock
P&T (10)
P&T (10)
P&T (10)
P&T (10)
P&T (10)
P&T (10)
P&T (10)
P&T (10)
P&T (10)
P&T (10)

P&T (10)
P&T (10)
P&T (5)
P&T (5)
P&T (5)
P&T (5)
P&T (10)
P&T (10)
P&T (5)
P&T (10)
P&T (10)
P&T (5)

P&T (5)
P&T (10)

-------
          Property Ratings of Chemical Classes Commonly Found at Superftind Sites (from Table 1) and
                                      Applicable Technologies for In-Situ Treatment  (Continued)
                                                  ' i  i   I
                                                                                 I'1'  !J
                                                                                 M  '   i
                                             ,*«•* I  *>  CO*tttt
                                                            VtoKBity    Vbcostty   1   sf
                                                  (g/cc)     (centipobe) 9 (c««tt»fc*M)  >
                                                                                                                 H
JUxr
Moderate
High
>13.00
£100.00

>100.00
                                >1.00E+00
>1.00E-03
Sl.OOE+00
>1.00E-K»     >1.00B-03
                                                                       =1
                                                                       >t*
^0,6
25.4
^0.8

>0.8
2:25
              Ap{riie« to ofg«nic ccmpotaidi only
                                                                                                                         moderate
                            NA
                                           few htvctmoderatt rating; ice TiUe 3 for ct»7ipo«aidipccificviiiae»
                                           rating for the gweo property; tee TaUe 3 for compound specific values
                                          No data found or *v«ilible
                                           (LNAPL), often floating OB fee water t^)k
                                                            '  jeowray of DNAPL fisom fl» jatnraiod zone wiH be difficullif ibeDNAPLU
                                          ip«tiaUydi»cominuoui within the aquifer

                                          : Se, A«, Hg, Pb, «nd C2* may be prctentin volatile foraw i*id» enhance dwirmofatlity;ieeT«ae3for
                                           SeeT»He3

-------
                                  EPA/540/2-90/011a
                                  Table 2 (Continued)
                                                                    iTfe-jjaL.'-^
                            H-Stu Vitrificukxi
                            ScflFlurfiing      :
                           > :Soil Vacuum Bxtr»cli»
         C5)
        (Lty

-Kefia* to uncertainty in rettoring:
»ott%roia»d wmertohe»lth^)««d cr
MCL kvelj, asiuming no NAKU
B
                                                        i Jn.sto bktfanedialfon»volve»fl«eetaiartcenKM'(rf
       Jaoi^sses ftrM%fefl» addition of amendments sach a» oxygen arKyornutrieats

       iUnoonsolidated deposits refer to gravel, sand, siltorclay or any combination thereof. Deposits fionsisting:5>rimirily
       *of ^^cifesy a« difficult to remediate and excavattoao* contasimient mi^ be the only applicable resriedisloptkiiis
                iJat fee application of soil vacuum extraction will parity or primarily be for puipose* of stimuUting
        ibiodegradative processes

        Refers to a^bsiirfaceregune in wHA^ vari*biHty inhydrailiccoiKiiictivity is lcsslhtnc^ord«

        fefians, to tsubsarface j^inw m which flie hydraulic omdw^vitywiiMn the treatment zone varies by nrore than one
        «iderofnwgnitude. A h«erose*»!0^s5**a^>»'*J^»n^^MS'e"^ baity of co^^      That technology should
        tecojBMewdwiae«Hai
-------
EPA/540/2-90/011 b
     Subsurface  Remediation
               Guidance  Table
                   Table 3 provides contaminant-specific values for properties identified in
                   Table 2. References are listed in the accompanying document entitled
                   "Subsurface Contamination Reference Guide."
     A  -
     $  -
     c
     0"  -
     M: -
     N. -
     T  -
iia -
nd -
      significant degradation with gradual adaption
      slow to moderate Activity, concomitant with significant rate of volatilization
      very slow bio^graiatiye activity, with long adaption period needed
      significant degradation with rapid adaption
      not signMcanUy degraded under die conditions of the test method
      rjotlgiMe^^
      slgnMcantdegrSaSon with gradual adaption Mowedbydeadaptiveptocere in subsequent subcultures (toxicity)
     (a) -' may be compohejit of antiknock fluids iyJded to fee! oils; remedial treatment may require considwation of
           Cd^Sfitaerit in bit phase
     (t>) -  cohstituenl m some oils, greases, dielectric liquids, and thermostatic fluids; remedial treatment may require
           consideration of constituent in oil phase
     (c) -  calculated
     (d) -  miytepfesentrndyeorlacquersolutions;remedM^
     (e)  -  constituent of crude oil fractions (including fuel oils and motor oils) and/or coal tar fractions (including creosote);
           creosote may be present as DNAPL; remedial treatment may require consideration of constituent in oil phase
     (!) -                                                           ...,,.
     (g) -  constl(jierit¥ fiiel oils 
-------
EFA/540/2-90/Oljb_
           TSble 3.  Properties of Contaminants Commonly Found at Superfund Sites
Chemical


Melting
Point
CO
Water t
Solubility
(mg/1)
Vapor t
Pressure
(mmHg)
Henry's Law t
Constant
(atm-nrVmol)
Density t

(g/cc)
Dynamic t
Viscosity
(cp)
Kinematic t
Viscosity
(cs)
Log
K

Log
K«

Aerobic
Biodegrad-
ability
MCLPi

W)
Halopenated Volatile Organics
Liquid Solvents
Carbon Tetrachloride
Chlorobenzene
Chloroform
Cis-l,2-dichloroelhylene (d)
1,1-Dichloroethane (a)
1 5-Dichloroethane
1 , 1 -Dichloroethylene
1,2-DichloTopfopane (a)
Ethylene Dibromide (g)
Methylene Chloride
1,155-Tetradiloroethane
Tetrachloroethylene
Trans-l,2-clichloroethylene (d)
1,1,1-Trichloroethane
1,15-Trichloroethane
Trichloroefhylene
Gases
Chloroethane (b.p. 125 C)
Vinyl Chloride (b.p. -13.9 C)

- 23 PI
- 45 PI
- 64 i*
- 81 PI
- 97.4 PI
- 35.4 PI
-1225 P1
- 90 P1
9.9?Pi
- 97 PI
- 43 PI
- 22.7 P1
- 50 PI
- 32 PI
- 36 PI
- 87 P1

-1383 PI
-157 PI

8 E+02 w
4.9 E+02 PI
852 E+03 PI
35 E+03 I"
55 E+03 P=
8.69 E+03 W
4 E+02PJ
2.7 E+03PI
3.4 E+03PJ
132E+04P1
Z9 E+03 I"
15 E+02P1
63 E+03 PI
95 E+02PI
45 E+03 PI
1 E+03 «i

5.7 E+03 m
1.1 E+03 W

9.13 E+01 P'
8.8 E+OOi'i
1.6 E+02 t»
2 E+02*P>
1.82 E+02 PI
637 E+01 W
5 E+02 W
3.95 E+01 "I
1.1 E+01 PI
35 E+02 W
4.9 E+00")
1.4 E+01 W
Z65 E+02 ®
1 E+02 W
1.88 E+01 ra
5.87 E+01 W

1 E+03 PI
2.3 E+03 "I

2 E-02 m
3.46 E-03 *M
3.75 E-03 *™
75 E-03 *"
5.7 E-03 *ra
1.1 E-03 *™
154E-01 *ra
3.6 E-03 *ra
3.18 E-04 "I
257 E-03 *P'
5 E-04 *P>
257 E-02 *™
6.6 E-03 *™
2.76 E-03 *PI
1.17 E-03 «"i
8.92 E-03 *™

1.1 E-02 PI
6.95 E-01 PI

15947 w
1.106 Pi
1.485 PI
1584 PJ
1.175 PJ
1553 PI
1514 PI
1.158 Pi
2.172 PI
1325 PI
1.600 P)
1.625 PI
1557 w
1325 "I
1.4436 "I
1.462 PI

0.9414 oc [i]
0.9121 "^

0.965 PI
0.756 PI
0563 ra
0.467 m
0377 I«
0.84 P'
033 Pi
0.84 Pi
1.676 2K"i
0.43 w
1.77 Pi
0.89 PI
0.404 ra
0.858 m
0.119 ra
0570 ™

• na
na

0.605 »
0.683 *>
0379 «
0364*"
0321 «
0.67 «
057 »
0.72 «
0.79 ra
0324 «
1.10 *"
054 «
0321 &>
0.647 ^
0.824 <"
0390 «

na
na

Z83PI
Z84PI
1.97 Pi
1.86 PI
1.79 m
1.48 P'
Z13 PI
2.02 PI
1.76 P'
1.25 PI
239 W
3.14 W
Z09P1
Z49"
Z17'«
Z42 m

1.43 PI
0.60 w

2.64 ra
25 ra
L64™
15 i"
1.48 m
1.15 ra
1.81 ra
1.71 'n
1.45 ra
0.94 ra
234i«
2.82 PI
1.77 ra
2.18 ra
1.75 M
Z10 PI

1.17 m
0.91 PI

DPI
D5.A10 B
A ra
B ra
A "
B ra
A B
A ™
nd
D B
N B
A ra
B B
C[2I
1-1
C ra
A *™

nd
nd

5 (f)
100 (p)
nd
70 (p)
nd
5 (f)
7 (f)
5 )
0.05 
3.15 I"

0.65 P«
138 »"]
nd

1.81 ra
2.83 ra
nd
2.41 ra
Z84 ra
Z84 PI


nd
•nd
«d

-,) ra
D5.A10PS
nd
D PI
nd
nd
nd

nd
nd
nd

5 (f)
700 (p)
nd
2000 (p)
10000 (p)
10000 (p)
10000 (p)


-------
EPA/540/2-90/011 b   Table 3. Properties of Contaminants Commonly Found at Superfund Sites (Continued)
Chemical


Melting
Point
CC)
Water t
Solubility
(reg/1)
Vapor "*•
Pressure
(mm Hg)
Henry's Law t
Constant
(atm-m3/moi)
Density t

(g/cc)
Dynamic t
Viscosity
(cp)
Kinematic *
Viscosity
(cs)
Log
K

Log
K

Aerobic
Blodegrad-
abllity
MCL1"1

(Mg/1)
palngenated Semivnlatile Oreanics
PCBs (b)
Aroclor 1242
Aroclor 1254
Aroclor 1260
Pesticides
Chlordane
ODD
DDE
DDT
Dieldrin
Chlorinated Benzenes
1 ,2-Dichlorobenzene
1 ,4-Dichlorobenzene
Chlorinated Phenols
Pentachlorophenol (w)
2,3,4, 6-Tetiachlorophenol

-19 i"
10 I"
nd

106 "i
112 PI
88.4 m
108 I7!
176.5 PI

-17 PI
53 PI

190 PI
69.5 PI

4.5 E-01""
1.2 E-02 "i
2.7 E-03 "i

5.6 E-02*"'
i.eoE-oi^p!
4.0 E-02 P1
3.1 E-03 '"
1.86 E-01 ""

1 E+02 1"
8 E+01 I"

1.4 E+01 "1
1.00 E+03 *"'!

4.06 E-04*"i
7.71 E-05*l»l
4.05 £-05*1"

1 E-05 "i
1 E-06 ^"'l
6.40 E-06 "1
1.5 E-07 "i
1.78 E-07 "i

9.6 E-01 "i
6 E-01 '"

1.1 E-04 "I
nd

3.4 E-04 "i
2.8 E-04 "1
3.4 E-04 I"

2.2 E-04 *"'
7.96 E-06 '"'1
1.9 E-04 *")
2.8 E-05 *»i
9.7 E-06 *«

1.88 E-03 *"!
1.58 E-03 *"i

2.8 E-06 "i
nd

1385 "1
1538'W
L44X.C,,,

1.6 *i"
1.385 "i
nd
0.985 "i
1.75 01

1.306 "1
1.2475 "i

1 .978 W
1.839 *l'l

nd
nd
nd

1.104 I"
na
na
na
na

1.302 "1
1.258 I"

na
na

nd
nd
nd

0.69 "'
na
na
na
na

0.997 <=>
1.008 ">

na
na

5.58 "i
6.03 M
7.15 K

5.48 "i
5.56 »i
5.69 »!
6.36 "1
5.34 "i

3.38 "i
3.39 "I

5.12 '"
4.1 nil

5 "i
nd
nd

4.58 '"
538 "i
5.41 "I
5.48 "i
3.23 "'i

3.06 "i
3.07 '"

4.80 "i
2.0 '"1

N pi
N pi
N pi

N p'
M pi
M PI
M pi
N m

T P)
T ra

A pi
nd

nd
nd
nd

2 (P)
nd
nd
nd
nd

600 (p)
750 (f)

nd
nd
Non-Halogenated Semivolatile Oreanics
PAHs (e)
Acenaphthene
Anthracene
Benzo(a)anthracene
Benzo(a)pyTene
Benzo(b)fluoranthene
Benzo(ghi)perylene
Benzo(k)fluoranthene
Chrysene
Dibenz(a,h)anthracene
Fluoranthene
Fluorene
Indeno(l,2,3-cd)pyrene
2-Methyl naphthalene
Naphthalene
Phenanthrene
Pyrene
Non-Chlorinated Phenols
Phenol
2,4-Dimethylphenol (e)
2,4-Dinitrophenol
m-Cresol (e)
o-Cresol (e)
p-Cresol (e)

92.5 P)
216.3 Pl
167 I'l
179 Pi
167 "1
278 I'1'
217 ™
254 PI
266.5 Pi
107 Pl
116.7 i"i
163 ™
34.58 "I
80.2 "i
100 Pl
150 Pi

41 Pl
26 PI
112 Pi
12 PI
31 Pi
34.8 PI

3.88E+00*!"
7.5 E-02 *'i
1.4 E-02 *<1B
3.8 E-03 «'«
1.4 E-02 «"i
2.6 E-04 *CT
4 JO E-03 «"'
6 E-03 *PI
2.5 E-03 "m
2.65 E-01 *'*
1.90E+00*™
5 JO E-04 «'"
2.54 E+01 *™
3.1 E+01 *"2'
l.lSE+OO'll
1.48 E-01 *'"

8.4 E+04 i"
6.2 E+03 *']i
6 E+03 *»>
2.35 E+04 PI
3.1 E+04
3.94 E-05 «"!
1.05 E-06 *'"i
7J3 E-08 *l"l
6.5 E-06 *»«l
7.65 E-05 *i'i
6.95 E-08 *»'!
5.06 E-02 *w
1.27 E-03 *">
3.98 E-05 «l«
1.20 E-05 *<"

7.80 E-07 w
2.5 E-06 *('l
6.45 E-10 "'i
3.8 E-05 «"2>
4.7 E-05 *"2i
3.5 E-04 «l«]

1.225 W
1.25 "'I
1.174 1°'
nd
nd
nd
nd
1.274 PI
1.252 ™
1.252 I'2'
1.203 "2i
nd
1.0058 1")
1.162 "J]
0.9800 1'2'
1.271 l"!

1.0576"c"i
1.036 Pl
1.68 w
1.038 PI
1.0273"2!
1.0347 PI

na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na

3.02 5Ki'i
na
na
21 I'Ji
na
na

na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na

3.87 
-------
                                                           EP A/540/2-90/011 b
Table 3.   Properties of Contaminants Commonly Found at  Superfund Sites


                                                              (Continued)
             CHEMICAL
                                                                                                                               MCL
             Inorganics

             arsenic (As)
            cadmium (Cd)
            chromium (Or)
            cyanide (CN)
             iron (Fe)
            lead (Pb)
            mercury (Hg)
             selenium (Se)
May occur in more than one oxidation state in subsurface. Arsenate form (AsO^) will dominate under oxidizing        nd
conditions. More toxic and mobile arsenite form (AsO3~) may dominate under increasingly reducing and acidic
conditions. Volatile alkylated-As compoundsmay form under reducing conditions. Volatile arsine (AsH,) may
form under highly reducing conditions. Adsorption of arsenate and arsenite forms will generally increase with
decreasing pH.

Occurs only in divalent form in aqueous solutions (e.g. Cd2*, CdCl*, CdSO4°). Cd2* tends to be dominant species.      5 (p)
Adsorption behavior correlates with cation exchange capacity (CEC) of soil and aquifer material. Adsorption/
precipitation increases with increasing pH with most Cd precipitating out at pH>6.

May occur in more than one oxidation state in subsurface. Trivalent form (Cr Iff) is dominant under pH and redox    100 (p)
conditions generally present in subsurface. Cr III may be converted to highly mobile and toxic hexavalent form
(Cr VI) under oxidizing conditions. Cr ID is readily adsorbed in the subsurface while Cr VI is not

Cyanide ion (CN') predominates in aqueous solution only at pH>9. Hydrogen cyanide (HCN) predominates at    200 (t)
pH<9. HCN is volatile (v.p. 741 mm Hg at 25C) and toxic. CN' behaves similar to halide ions and tends to complex
with iron. Undissolved cyanide salts may be present in vadose zone.

May occur in more than one oxidation state in the subsurface. Ferrous form (Fe2*) is most soluble and mobile, and    300 (f)
dominates under reducing conditions. Under oxidizing conditions, ferrous form is converted to ferric form (Fe3*).
Ferric form is less soluble, less mobile, and will tend to precipitate. Compounds and metals complexed to iron may
be removed from solution through the precipitation process. Conversely, compounds and metals adsorbed to kon
in the subsurface may be increasingly mobilized under increasingly reduced conditions. Precipitated iron may
hinder treatment processes such as in-situ bioremediation and air stripping.

Dominant species in aqueous solution are Pb5* under acidic conditions and Pb2*- carbonate complexes under        5 (p)
alkaline conditions. Adsorption behavior correlates with cation exchange capacity (CEC) of soil and aquifer
material. Adsorption/precipitation increases with increasing pH with most Pb precipitating out at pH>6. Volatile
alkylated-Pb compounds may be present or may form under reducing conditions.

May occur in more than one oxidation state. May occur in subsurface in mercuric form (Hg2*), mercurous form      2 (p)
(Hg/*X elemental form (Hg°), and in alkylated form (e.g. methyl and ethyl mercury). Hgj2* and Hg2* are more
stable under oxidizing conditions and are strongly adsorbed by soils. Hg* and alkylated forms are more stable under
reducing conditions. Conversion to alkylated forms may occur under reducing conditions. Hg* and alkylated-
Hg forms are volatile, toxic, and may not be as strongly adsorbed by soils.

May occur in more than one oxidation state in subsurface. Selenate form (SeO^') will dominate under oxidizing     50 (p)
conditions. Selenite form (SeO,2) will dominate under increasingly reducing conditions. Selenide form (Se2') may
dominate under highly reducing conditions. Selenate and selenite are more soluble and mobile forms. Adsorption
of selenate and selenite will generally increase with decreasing pH. Volatile alkyiated-Se compounds may form
under reducing conditions.

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