Hazard Ranking System Issue Analysis:
 Subsurface Geochemical Retardation
                MITRE

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Hazard  Ranking System Issue  Analysis:
  Subsurface Geochemical Retardation
                   Dr. Dash Sayala
                    Dr. Fred Price
                    November 1987
                     MTR-86W171
                       SPONSOR:
                U.S. Environmental Protection Agency
                     CONTRACT NO.:
                      EPA-68-01-7054
                   The MITRE Corporation
                    Civil Systems Division
                     7525 Colshire Drive
                   McLean, Virginia 22102-3481

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  Department Approval:
                      ^
                      V
                         < 7  '
MITRE Project Approval: .-  x ^
                             il

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                              ABSTRACT
     This report presents an analysis of the feasibility of
addressing geochemical retardation processes in the EPA Hazard
Ranking System.  Seven processes are examined and one, sorption, is
identified as providing the most reasonable indicator of the
potential for subsurface media to retard the migration of hazardous
substances.  It is proposed that the sorptive capacity of rocks and
sediments be estimated on the basis of their sum total clay and
organic carbon content and that this estimate be used to refine
evaluations of hazardous waste sites.

     Several options are presented for EPA consideration with regard
to ranking sorptive capacity, measuring migration path lengths, and
characterizing relative retardation potential at sites.  Suggestions
are made for incorporating this relative retardation potential into
the current MRS.  The data requirements for these options are
discussed.

Suggested Keywords:  Geochemical processes, Retardation potential,
Sorbents, Sorptive capacity, Subsurface migration path, Hazardous
waste/substance, Hazard Ranking System.
                                 iii

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                          ACKNOWLEDGEMENT
     The authors wish to thank Dr. Lawrence M. Kushner whose
critical review and constructive suggestions have helped the
authors refine the report.  Thanks are also due to Kris Barrett,
Nancy Cichowicz, and Robert Gerstein for their peer review and
suggestions.
                                 iv

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                          TABLE OF CONTENTS

                                                                 Page
LIST OF FIGURES                                                  vii
LIST OF TABLES                                                  viii

1.0  INTRODUCTION                                                  1

1.1  Background                                                    1
1.2  Issue Description                                             3
1.3  Objectives                                                    5
1.4  Approach                                                      5
1.5  Organization of the Report                                    5

2.0  APPROPRIATENESS OF CONSIDERING GEOCHEMICAL PROCESSES          7

3.0  EVALUATION OF GEOCHEMICAL PROCESSES FOR THE HRS              11

3.1  Description of Geochemical Processes                         13

     3.1.1  Adsorption                                            13
     3.1.2  Ion-Exchange                                          15
     3.1.3  Hydrolysis                                            17
     3.1.4  Dissolution and Precipitation                         18
     3.1.5  Redox Reactions                                       20
     3.1.6  Acid-Base Reactions                                   22
     3.1.7  Complexation                                          23

3.2  Selection of Geochemical Processes for Site Screening        25

4.0  ESTIMATION OF SORPTIVE CAPACITY OF ROCKS AND SEDIMENTS       29

4.1  Model for Sorptive Capacity Estimation                       30

5.0  APPLICATION OF SORPTIVE CAPACITY TO RANKING OF HAZARDOUS     35
     WASTE SITES

5.1  Ranking of Sorptive Capacities of Rocks and Sediments        37
     by Sorbent Contents

     5.1.1  Ordinal Scale                                         37
     5.1.2  Proportional Scale                                    39

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                    TABLE OF CONTENTS  (Concluded)


                                                                 Page

5.2  Migration Paths                                              41

5.3  Characterization of Migration Path for Sorptive              44
     Potential

5.4  Examination of Various Options for Ranking of Retardation    47
     Potential

5.5  Data Needs and Sources                                       49

     5.5.1  Data Needs                                            49
     5.5.2  Data Sources                                          49

5.6  Suggestions for Incorporation of a Retardation Potential     51
     Factor into the HRS Ground Water Route Score

6.0  LIMITATIONS                                                  55

7.0  CONCLUSIONS                                                  59

8.0  REFERENCES                                                   61

9.0  SUGGESTED READINGS                                           71

APPENDIX A--SORPTIVE CAPACITY ESTIMATION DATA                     73
                                 vi

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                           LIST OF FIGURES

Figure Number                                                    Page

     1          Illustration of the Retardation/Attenuation        8
                of a Hazardous Substance by Various Processes
                in the Subsurface

     2          Geochemical Processes; Example of Water-Rock-     10
                Pollutant Interactions in the Subsurface

     3          Schematic Cross Section Showing Three             42
                Alternative Migration Paths for Evaluation
                of Retardation Potential
                                 vii

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                           LIST OF TABLES

Table Number                                                     Page

     1          Ranges of Clay and Organic Carbon Contents         31
                of Six Common Groups of Rocks and Their
                Equivalent Sediments

     2          Range of Options for Ranking Sorptive             36
                Capacities, Selecting Migration Path
                and Characterizing Migration Path for
                Retardation Potential

     3          Relative Retardation Potentials  (and Their        38
                Factor Value)  of Groups of Rocks and Their
                Equivalent Sediments According to the  Range
                of Total Sorbent  Contents—Ordinal Scale

     4          Groups of Rocks and Equivalent Sediments          40
                Ordered by Their Average Total Sorbents—
                Proportional Scale

     5          Example of Numerical Factor Values for the        46
                Thickness-Weighted Average Sorbent Contents
                                viii

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1.0  INTRODUCTION




1.1  Background




     The Comprehensive Environmental Response, Compensation, and




Liability Act of 1980 (CERCLA) (PL 96-510) requires the President to




identify national priorities for remedial action among releases or




threatened releases of hazardous substances.  These releases are to




be identified based on criteria promulgated in the National




Contingency Plan (NCP).  On July 16, 1982, EPA promulgated the




Hazard Ranking System (HRS) as Appendix A to the NCP (40 CFR 300;




47 FR 31180).  The HRS comprises the criteria required under CERCLA




and is used by EPA to estimate the relative potential hazard posed




by releases or threatened releases of hazardous substances.




     The HRS is a means for applying uniform technical judgment




regarding the potential hazards presented by a release relative to




other releases.  The HRS is used in identifying releases as national




priorities for further investigation and possible remedial action by




assigning numerical values (according to prescribed guidelines) to




factors that characterize the potential of any given release to




cause harm.  The values are manipulated mathematically to yield a




single score that is designed to indicate the potential hazard posed




by each release relative to other releases.  This score is one of




the criteria used by EPA in determining whether the release should




be placed on the National Priorities List (NPL).

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     During the original NCP rulemaking process and the subsequent

application of the HRS to specific releases, a number of technical

issues have been raised regarding the HRS.  These issues concern the

desire for modifications to the HRS to further improve its

capability to estimate the relative potential hazard of releases.

The issues include:

     •  Review of other existing ranking systems suitable for
        ranking hazardous waste sites for the NPL.

     •  Feasibility of considering ground water flow direction and
        distance, as well as defining "aquifer of concern," in
        determining potentially affected targets.

     •  Development of a human food chain exposure evaluation
        methodology.

     •  Development of a potential for air release factor category
        in the HRS air pathway.

     •  Review of the adequacy of the target distance specified in
        the air pathway.

     •  Feasibility of considering the accumulation of hazardous
        substances in indoor environments.

     •  Feasibility of developing factors to account for
        environmental attenuation of hazardous substances in ground
        and surface water.

     •  Feasibility of developing a more discriminating toxicity
        factor.

     •  Refinement of the definition of "significance" as it relates
        to observed releases.

     •  Suitability of the current HRS default value for an unknown
        waste quantity.

     •  Feasibility of determining and using hazardous substance
        concentration data.

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     •  Feasibility of evaluating waste quantity on a hazardous
        constituent basis.

     •  Review of the adequacy of the target distance specified in
        the surface water pathway.

     •  Development of a sensitive environment evaluation
        methodology.

     •  Feasibility of revising the containment factors to increase
        discrimination among facilities.

     •  Review of the potential for future changes in laboratory
        detection limits to affect the types of sites considered for
        the NPL.

     Each technical issue is the subject of one or more separate but

related reports.  These reports, although providing background,

analysis, conclusions, and recommendations regarding the technical

issue, will not directly affect the MRS.  Rather, these reports will

be used by an EPA working group that will assess and integrate the

results and prepare recommendations to EPA management regarding

future changes to the HRS.  Any changes will then be proposed in

Federal notice and comment rulemaking as formal changes to the NCP.

The following section describes the specific issue that is the

subject of this report.

1.2  Issue Description

     EPA has received public comments concerning the lack of

consideration in the HRS of geochemical processes that may retard

the migration and attenuate the concentration of hazardous

substances (organic and inorganic) released from hazardous waste

sites.

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     Currently, the HRS ground water route uses selected retardation/

attenuation* parameters (or Indicators).  These Include permeability

(as a measure of vertical retardation) under the route characteristics

category and persistence (as a measure of blodegradability) under the

waste characteristics category.  These parameters address physical and

biological processes, respectively.  By not considering geochemlcal

effects while addressing permeability, the HRS Implicitly assumes that

hazardous substances released from a site will migrate to, and In, an

aquifer of concern with the same velocity as the transporting solutions

and/or ground water.  However, concern has been expressed by some

commenters that without consideration of geochemlcal processes, the HRS

Inadequately reflects the relative threat posed by sites.  The public

comments received by EPA suggest that geochemlcal process related para-

meters should be Introduced Into the HRS to more realistically assess

the likelihood of released substances reaching target populations.

     This report examines the geochemlcal processes that can affect the

fate of organic and Inorganic hazardous substances In the subsurface.

It also assesses the practicality of Introducing geochemlcal retarda-

tion parameters Into the HRS and suggests appropriate revisions to the

current HRS.  These revisions should Increase Its ability to
^Retardation Is the Immobilization of a hazardous substance while
 attenuation Is the reduction In the concentration of hazardous
 substances.  Since retardation and attenuation generally complement
 each other, the term retardation will be used In this document to
 Indicate retardation/attenuation.

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discriminate among sites on the basis of their relative potential

for hazardous substances to reach target populations.

1.3  Objectives

     The objectives of this study are:

     •  To assess whether it is feasible and practical to
        incorporate geochemical processes related to hazardous
        substance retardation in the evaluation of the ground water
        route.

     •  To develop methodologies to evaluate the relative potential
        for the subsurface environment to retard the migration of
        hazardous substances.

     •  To develop options for incorporating the appropriate
        geochemical parameter(s) into a site ranking scheme.

1.4  Approach

     In order to achieve these objectives, the following approach

was followed:

     •  Review published literature pertinent to geochemical processes.

     •  Review reports on remedial investigation and technology
        assessments for remedial action.

     •  Identify potentially important geochemical process(es) for
        retardation and assess their suitability for potential use in
        a site screening scheme.

     •  Develop methods and options for incorporating geochemical
        retardation into a site scoring scheme.

     •  Document the findings.

1.5  Organization of the Report

     The main portion of this report summarizes information on

geochemical processes and related parameters and evaluates their

importance and utility for the purpose of ranking the relative

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potential hazard of hazardous waste sites.  This material is




presented in six major sections.




     Section 2 explains why it is appropriate to consider




geochemical processes for subsurface site evaluation.  Section 3




briefly describes the important geochemical processes that control




the fate of hazardous substances in the subsurface.  It  also




identifies those geochemical  process(es)  and parameter(s) that are




most useful for evaluation of the  retardation potential  in  the




subsurface environment  between a site  and the target populations.




Section 4 explains  the  basis  and techniques of  estimating the




sorptive capacity of  rocks and sediments  for ranking the retardation




potential.  In  Section  5, options  for  ranking the sorptive




capacities of rocks and sediments, for selecting subsurface




migration path  lengths,  and  for characterizing  the retardation




potential of a  migration path are  presented.  Needs for  and sources




of data for evaluating  the retardation potential of a subsurface




geomedia are also presented  in Section 5, along with suggestions for




incorporating a retardation  potential  factor into the HRS ground




water.  Section 6 discusses  the limitations of  the methods  presented




for evaluating  the  subsurface retardation potential.  Section 7




presents the conclusions of this study.

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2.0  APPROPRIATENESS OF CONSIDERING GEOCHEMICAL PROCESSES

     Reliable and meaningful assessment of the relative hazard posed

by hazardous waste sites to target populations via subsurface*

migration requires estimation of the potential of subsurface

geologic media (geomedia) to retard hazardous substances released

from a site.

     The overall subsurface retardation potential is the result of a

variety of physical, biological and chemical processes.  Generally,

retardation is affected by a group of processes at a given site

which depend on the specific subsurface characteristics of the area

and the types of hazardous substances that are present.  The

relative contribution of the physical, biological and geochemical

processes to the retardation further depends on site-specific

circumstances.  Conceptually, it is the combination of all active

processes in the subsurface that can reduce the amount and

concentration of hazardous substances as they migrate from a site to

A target (see Figure 1).  This report addresses the major

geochemical processes, which include adsorption, ion-exchange,

hydrolysis and complexation.

     Geochemical processes include physical and chemical inter-

actions between geologic media and their environment.  Biological

interactions are not included under geochemical processes.
*The subsurface as used in this report includes both saturated and
 unssturated zones.

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00
                                                                                                Top Soil Zone
                                                                                                                      Potable
                                                                                                                     Waterwell
                                                      Sorption +
                                                      Filtration +
                                                  Biodegradatbn +
                                                Dilution + Hydrolysis +
                                                    Precipitation
                                                    Dilution + Degradation + Sorption + Hydrolysis + Complexation +
                                                                 Filtration + Diffusion + Precipitation
                                                                                          Target
                                                                                     (C2)t2
                              Legend
Q0
                                     - Rock/Sediment Types

                                     - Hazardous Substance Amount at the Release Point (QQ > QI }

                                     - Hazardous Substance Amount at the Aquifer Entry Point
                                     - Initial Concentration of a Hazardous Substance (C0>C1 >C2)
                                     - Concentration of a Hazardous Substance at the Aquifer Entry Point
                                     - Concentration of a Hazardous Substance at a Target
                                     - Initial Time of Release
                                     - Time After Migration Through Unsaturated Zone
                                     -  Time After Migration, in Saturated Zone, to a Target
                                                                                          SAXSSSF"*

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Geochemical processes such as water-rock, water-pollutant, and




pollutant-rock interactions are ubiquitous when hazardous substances




are released from a site and migrate in the subsurface (see




Figure 2).  These interactions can play a significant role in




determining the fate of hazardous substances migrating in the




subsurface.  The literature pertinent to the migration of hazardous




substances is replete with data indicating that geochemical




processes can significantly retard the migration and attenuate the




concentration of both organic and inorganic substances (for




examples, see Nowak, 1980a and 1980b; Roberts et al., 1982).




     The literature cited throughout this report provides evidence




that geochemical processes can result in significant retardation




effects.  Therefore, it is appropriate to consider these effects for




incorporation into a site ranking scheme.

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     Calcite
   Precipitates
                 REDUCING
                                                                                  OXIDIZING
^
  reas
  N
                             y
                             V
                                    Pyrrte
       pH Increases
                  H2S
            Bacterial Reduction
                of Sulfate
     ?
  H2,CO2.CH4,NH3
    Ethyl Alcohol
Acetic and Succinic Acid
>
                                                  U0?+  U020H+
                                                   ^     ^
                     * Eh Decreases
    Fermentation of
   Organic Materials
                   Sorption
                     by
     Clays -i- Organic Matter + Fe Oxides/Hydroxides
                                                                Pyrite Oxidized by
                                                                 Ferric Sulfate
                                                       Ferrous Sulfate and Sulfuric Acid
                                                               V
                                                                *Eh Increases
                                                                       'i
                                                                                           02
                                                                      Bacterial oxidation to
                                                                        Fernc Sulfate
                                              Uranium and Vanadium
                                              Oxidized and Mobilized
                                                    u 6+
                                                         "
                                                                                  j
                                                                                 I
                                                                                  T
                                                                      Hydrolysis to
                                                               Sulfuric Acid and Ferric Hydroxide
                     Uranium Reduced
                         Stable
                          U4+
                                                                pH Decreases
                                 Vanadium Reduced
                                    Stable V3+
  * Eh is the measure of the ability of chemical environment to gain or loose electrons.
  * pH is the measure of the acidity or alkalinity of a chemical environment/liquid substance.
                                             FIGURE 2
GEOCHEMICAL PROCESSES;  EXAMPLE OF WATER-ROCK-POLLUTANT INTERACTIONS
                                     IN THE SUBSURFACE

               (This Figure Shows  The Fate Of Uranium And  Vanadium When Migrating
                In Oxidizing  Ground  Water And Subsequently Encountering Reducing
                Conditions Along The Flow Path. This Model  Is Used To Explain The
                  Subsurface Migration/Deposition Of  Uranium By Ground Water.)
                                   (Modified  After  Rackley, 1972.)
                                                 10

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3.0  EVALUATION OF GEOCHEMICAL PROCESSES FOR THE HRS




     Geochemical processes which can affect the fate of hazardous




substances in the subsurface include adsorption, ion-exchange,




hydrolysis, dissolution and precipitation, reduction-oxidation




(redox), acid-base reactions and complexation.  Any combination of




these processes can operate in a given subsurface environment




depending on the geochemical and hydrologic conditions, and can




affect, to various degrees, the migration of hazardous substances in




the unsaturated and saturated zones.




     Prior to a discussion of these processes, it should be noted




that there are different types of hazardous substance releases.




These types of release may have an influence on geochemical




processes and thus affect their retardation along the migration path.




     Types of hazardous substance releases include, both single- and




multiple-point releases.  Such releases have been observed during




EPA remedial investigation studies of sites with contaminated ground




water.  These releases may be either continuous or discontinuous




depending on conditions such as influx of water for leachate




generation, leachability of the disposed waste, and adequacy of




waste containment.  In comparison to the volume of both geologic




materials and ground water within the migration medium, the volume




of leachate generated from the waste is usually small.  If the




volume of leachate generated and released from a site is small in




comparison to the volume of the migration path, then there is a high
                                 11

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probability that small volumes of released hazardous substances can

be retarded in the subsurface.  If the total amount of hazardous

substances in the leachate exceeds the retardation or retaining

capacity of a medium, then migration through the medium becomes much

more likely.

     Hazardous substance migration can be  divided  into  three major

types.  The three types of migration in  ground  water  are:

     •  Miscible migration:   migration of  substances  dissolved  in
        water.

     •  Immiscible migration:   migration of substances  not dissolved
        in water.

     •  Facilitated  migration:   migration  of substances aided by
        water  suspended materials.

The  first two  depend on  the  solubilities of the hazardous substances

along  the subsurface migration  path;  the third  refers to situations

in which migration  is aided  by  the  presence of  water  suspended  solids

such as colloids, clays and  organic matter, that carry  the hazardous

substances.   The rate at which  migration occurs in a  heterogeneous

subsurface system is governed by geochemical interactions along the

migration path, including pollutant-water-rock  interactions.

Chemical reactions leading to transformation or degradation are

faster and more effective with  the miscible substances  than

immiscible ones (Stumm and Morgan, 1981).   Generally, those

substances that migrate as immiscible forms  or with the aid of

suspensates (particulates) are more prone to retardation by sorption,

without chemical degradation or  transformation,  than are their


                                 12

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miscible counterparts  (Tinsley, 1979; Stumm and Morgan, 1981; and




Morrill et al., 1982).




3.1  Description of Geochemical Processes




     A brief description of the major geochemical processes is given




in the following sections.  The geochemical processes described in




the following sections occur in the unsaturated and saturate zones of




the subsurface migration path.




     3.1.1  Adsorption




     Adsorption is a retardation mechanism arising from the physical-




chemical interaction of hazardous substances with the surfaces of




charged mineral constituents or organic matter in the subsurface




medium.  This interaction reduces the mobility of the substances




relative to the ground water flow.  Adsorption of the substances onto




solid surfaces takes place as a result of electrostatic forces, by




weak Van Der Waals interaction, or by covalent bonding.  It occurs on




all surfaces (including water suspended particles) where the necessary




bonding conditions are present.  Laboratory experiments conducted by




Kinniburgh and Jackson (1981), Rao and Davidson (1980), and others




indicate that adsorption of inorganic and organic substances takes




place rapidly, within a matter of minutes.  Generally, adsorption




refers to an equilibrium distribution of a substance between a solid




phase and a solution phase (mobile phase).  For a fixed quantity of




migrating chemical species, the dissolved concentration of the




species decreases as the degree of adsorption increases.
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     Although adsorption is an important process for the retardation




of hazardous substances in the subsurface, under conditions of either




high or low pH, desorption can temporarily release the absorbed




substances.  However, desorption is slower than adsorption (Helling




and Dragun, 1981) and, generally, the extreme pH conditions that




promote desorption are not common in ground waters.  Among several




absorption-desorption studies, the studies by DiToro and Horzempa




(1982) and by others mentioned in Hague (1980), Marking and Kimberle




(1979), and Mayer and Hamelink (1977) conclude that persistent




organic substances (e.g., DDT, PCB) tend to strongly sorb to




absorbents present in a migration media.  They further conclude that




a significant portion of the absorbed concentration is extremely




difficult to desorb.




     Adsorption in the subsurface is promoted by the presence of




sorbents, such as clays, organic matter (organic carbon), Fe-Mn-Al




oxides/hydroxides, zeolites, and sulfides.  In addition, adsorption




tends to increase as the surface area of the solid matrix increases




(i.e., as grain size decreases) and as the ionic strength or




electrolytic concentration of the ground water increases (Mortensen,




1959; Hurle and Freed, 1972; Chiou et al., 1979; Lyman et al., 1982;




and Stuart, 1983).  Based on the works of Schwarzenbach and Westall




(1981), Means et al. (1980); and Karickhoff et al.  (1979),  the




adsorption of organic substances by sediments increases as  the




organic carbon (organic matter) content and the surface area (i.e.,
                                 14

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silt/clay-size fraction) of the sediments increase.  Similarly,




studies of sedimentary uranium deposits indicate that uranium and




associated inorganic elements, such as vanadium, selenium, lead, and




zinc are concentrated through adsorption onto clays and organic




matter found within fine-grained sedimentary rocks (Sayala, 1983;




Wayland and Sayala, 1983; Leventhal and Santos, 1981; and




Schmidt-Collerus, 1979).




     Two important observations can be made about the adsorption




process.  Namely, that (1) adsorption occurs under a wide range of




physical and chemical conditions, and (2) adsorption can affect a




variety of both organic and inorganic substances.  These observations




are discussed by several researchers, including Rao et al. (1986),




Siegrist et al. (1986), Panter et al. (1985), and Karickhoff et al.




(1979).




     3.1.2  Ion-Exchange




     Ion-exchange refers to the exchange of bound ions in the solid




matrix of a geomedium with mobile ions in the aqueous phase.   The




bonding involved, being ionic, is strong.  Ion-exchange differs from




adsorption in that the latter is strictly a surface phenomenon,




whereas the former can involve penetration of ions or molecules into




the crystal structure of the solid to replace existing ions.   The




single term, sorption, is commonly used to refer to the combination




of ion-exchange and adsorption processes.
                                 15

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     The naturally-occurring materials that exhibit ion-exchange




capacity are generally the same as those noted for their absorptive




capacities, i.e., clays, organic matter, Fe-Mn-Al oxides/hydroxides,




zeolites, and sulfides.  The ion-exchange capacity of these geologic




materials is commonly expressed in terms of their cation-exchange




capacity, or CEC.  Generally; the CEC of organic material in a




geomedium is about 200 milliequivalents per 100 grams; whereas, those




of clays range from 8 to 150 meq/100 gm depending on the type of




clays  (Brady, 1974).  The CEC of hydrous oxides is generally lower




than 8 meq/100 gm.  As a result, a medium with large amounts of clays




and organic matter will commonly have high ion-exchange capacities




and can be effective in retarding the subsurface migration of both




organic and inorganic substances.




     Cation exchangers are also known to exchange their cations for




polar  organic compounds.  For example, McAttee (1959 and 1963) found




that organic compounds containing amines and carbonyl groups are




exchanged for the cations in clays.  Studies by Fripiat et al.




(1962), Stuart (1983), and JRB Associates (1984) indicate similar




instances of the exchange of organic compounds for the cations of




clays.  This exchange and its effect on retardation of hazardous




substances can be influenced by the nature and amount of exchangeable




agents and the ionic strength of ground water.
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     3.1.3  Hydrolysis




     The reaction of a chemical compound or a metal ion with water is




called hydrolysis.  The process may be expressed as:




          R1OOOR2 + H20           RiCOOH + R2OH




            Cu+2 + H20            CuOHf + H+




Decomposition of inorganic compounds by hydrolysis is an important




process in ground water, sometimes causing relatively insoluble




compounds to form.  Similarly, decomposition of some organic




compounds by hydrolysis can transform some toxic compounds to less




toxic constituents or less toxic compounds into more toxic forms.




Metal ions, such as copper, lead, zinc, and cadmium, can be




transformed in ground water into their hydroxides (or hydrous




oxides) and then be retarded by sorption.  Generally, the hydrolysis




of metal ions is dependent on their hydropotentials; that is, the




ratio of their charge to their ionic radius (Siegel, 1974).




     It is difficult to generalize about the relative rate of




hydrolysis of organic compounds in ground water since that rate is




dependent on pH and the structural nature of the compound (Mabey and




Mill, 1978; Cherry et al., 1984; Kaplin and Likhovidova, 1984; and




Tinsley, 1979).  The relationship between hydrolysis rate and pH




depends on specific acid-base catalytic process constants.  At a




fixed pH, the half-life (T-,/?) of an organic compound due to




hydrolysis is independent of its concentration (Tinsley, 1979); i.e.,
                                 17

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            Tl/2 = °-693/Kh

        where K,  = Hydrolysis constant

     The half-lives of organic compounds in the subsurface might be

a useful measure of their persistence with regard to hydrolysis.

However, estimation of the hydrolysis potential of a migration

medium is not possible without spacial and temporal data such as the

Eh,* pH and hydrochemistry (i.e., water composition) of the ground

water and the nature of hazardous substances and their solubilities

in the water.  Site specific ground water data are difficult to

obtain and may be variable and unreliable.  The spacial and temporal

data need in situ (i.e., subsurface) water sample collection and

analyses that are costly and time consuming.  Further, field

techniques used for Eh/pH measurements are not well excepted.

     3.1.4  Dissolution and Precipitation

     When ground water interacts with a soil matrix containing

hazardous substances, dissolution (solubilization) and/or

precipitation of the hazardous substances may occur.  A detailed

discussion of the processes of dissolution and precipitation is

given by Garrels and Christ (1965), Krauskopf (1967), and Stumm and

Morgan (1981).  The kinetics of these processes are controlled by a

variety of migration media characteristics including pH, Eh,

hydrochemistry, velocity of the ground water, and the geochemistry
*Eh is the measure of the ability of an environment to supply
 electrons to an oxidizing agent, or to take up electrons from a
 reducing agent (i.e., electromotive potential).
                                 18

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of the solid matrix along flow paths.  The kinetics of dissolution




and precipitation, in turn, influence the retardation of hazardous




substances.




     The characteristics of the hazardous substances, including the




solubilities of many inorganic and organic substances, can also




influence their retardation.  Generally, the solubilities of these




substances are reduced in high ionic-strength ground water.   In




supersaturated solutions, the hazardous substances may precipitate.




     Dissolution and precipitation reactions are usually slower than




reactions involving dissolved species only, although it is difficult




to generalize about their rates.  The dissolution-related reactions




modify the chemical characteristics (e.g., change the valence or




charge) of hazardous substances and may aid in sorption-related




retardation.  However, reactions leading to dissolution and




precipitation are slower than sorption and, therefore, may have less




impact on retardation, particularly in relatively fast-moving ground




water.




     The Eh, pH and ionic strength of ground water, the geochemistry




of sediments and rocks, and the nature and solubilities of hazardous




substances are important factors in determining the probable




occurrence of dissolution and precipitation.  However, it is




difficult to estimate the dissolution and precipitation potential




along a migration pathway because spatial and temporal data on the




Eh, pH and ionic strength of the ground water along the path are
                                 19

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needed and such data are not easily and accurately measured or




reliably predicted (Plummer et al., 1983; Rubin, 1983; Lindberg and




Runnells, 1984; and Holm et al., 1986).




     3.1.5  Redox Reactions




     Redox reactions are those in which the valence or oxidation




states of ions or neutral species in ground water are altered,




indicating a gain (reduction) or loss  (oxidation) of electrons.




Redox reactions can result in decomposition, dissolution or




precipitation  of a hazardous substance.  The Eh of the ground water




system is a measure of the tendency for redox reactions to occur.




Eh and pH control the solubility of certain hazardous substances




and, therefore, influence their migration or retardation.  A good




review of redox reactions is given by  Stumm and Morgan (1981).




     Degradation and precipitation as  a result of redox reactions




are more likely to occur with inorganic than organic substances




(Utah State University and Arthur D. Little, Inc., 1984).




Generally, under oxidizing acidic conditions, copper, lead, nickel,




and uranium, for example, are mobile;  whereas, under reducing




alkaline conditions, the mobility of these inorganics is hampered




and they may precipitate.  In contrast arsenic, chromium, mercury,




molybdenum, and selenium are mobile under oxidizing alkaline




conditions and immobile under reducing acidic conditions.




     Among the organic compounds, phenols,  aldehydes,  aromatic




amines,  and certain organic sulfur compounds are more  prone to
                                 20

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oxidation-related degradation than are the alcohols, nitro- and




alkyl-substituted aromatics, unsaturated alkyl groups and aliphatic




ketones, acids, esters, and amines (JRB Associates, 1982).




Halogenated hydrocarbons, saturated aliphatic compounds, benzene and




chlorinated insecticides are less affected by oxidation reactions.




PCBs, chlorinated compounds, kepone, atrazine, and others are prone




to reduction-related degradation (Sweeney, 1981).




     In ground water, the species that promote oxidation are




fluorine, hydroxide, oxygen, hydrogen peroxide, perhydroxyl,




hypochlorous acid, and chlorine (Rice, 1981).  Those that promote




reduction are sulfides, organic matter, ammonia, methane, and




reducing bacteria (Sayala, 1983; Kobayashi and Rittman, 1982; Stumm




and Morgan, 1981).  Generally, the absence of dissolved oxygen and




presence of dissolved organic carbon (DOC) confer reducing or




anaerobic conditions on ground water.  Approximately 4 milligrams




per liter of DOC is apparently sufficient to produce, locally, a




reducing environment in ground water (Langmuir, 1972).




     Although redox reactions may promote the retardation of




hazardous substances in the subsurface, the extent to which these




reactions are likely to occur and result in retardation cannot be




easily or reliably estimated (Plummer et al., 1983; Rubin, 1983; and




Lindberg and Runnells, 1984).  As noted previously, spatial and




temporal rock/sediment and water chemical data (e.g., Eh and pH) are
                                 21

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needed to accurately assess the potential of a medium to retard




hazardous substances through redox reactions.




     3.1.6  Acid-Base Reactions




     Acid-base reactions comprise an important category of geochem-




ical processes, as some wastes deposited at hazardous waste sites




may be acidic or basic.  When very acidic or  basic wastes are




released into a geomedium,  and subsequently  into an  aquifer,




reactions such as dissolution, hydrolysis, and precipitation can




occur or there can be  changes in  the permeability of the geologic




media.  Hence, hazardous  substances may be chemically altered and




mobilized or  their movement may be retarded.  Along  the subsurface




migration path the pH  of  waters containing hazardous substances can




become gradually neutral  due to natural buffers such as carbonates,




sulfates, silicates, or ammonia,  or the mixing of ground waters of




differing compositions.   A pH near 7  (neutral) generally favors




precipitation of hazardous substances  and, therefore, retardation.




The fate of acidic hazardous substances in terms of  buffering is




explained by Haji-Djafari  et al.  (1979) and  Highland et al. (1981).




Nigrini (1971) demonstrated that  subsurface waters with low pH can




carry metals in solution.   Horsnail and Elliot (1971), from their




study of molybdenum and copper in acidic ground waters in Canada,




concluded that acidic conditions facilitate the mobility of copper,




but retard the mobility of molybdenum.   In remedial  technology




assessment studies by the Utah State  University and  Arthur  D.
                                 22

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Little, Inc. (1984), pH control Is suggested to remedy the inorganic




substance problem of a local ground water system.




     Although acid-base reactions can aid in the retardation of




primarily inorganic substances, prediction of their occurrence is




complex, and estimation of the retardation capacity of a geologic




medium that may result from acid-base reactions is unreliable (Stumm




and Morgan, 1981, and Plummer et al., 1983).




     Hydrochemical data which was systematically collected along the




subsurface migration path would be required to estimate the effect




of acid-base reactions on the hazardous substance migration and,




even then, the estimate would be uncertain.  The detailed hydro-




chemical information needed to assess the affect of acid-base




reactions on retardation is not currently available from a CERCLA




site inspection.  Furthermore, a reliable method for predicting




acid-base conditions in the subsurfaces is not known to exist.




     3.1.7  Complexation




     In aqueous solutions, metal ions can combine with anionic or




neutral species to form ionic or neutral complexes.  This process is




called complexation.  The major complexing anions or inorganic




ligands in ground water are carbonate, chloride, sulfate, phosphate,




hydroxide, and, in some cases, fluoride, nitrate and ammonia.  The




major neutral species or organic ligands are organic acids (such as




the amino acids and fatty acids), polysaccharides, and aliphatic and




aromatic compounds.  Whether a hazardous substance released to a
                                 23

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subsurface system exists in a complex molecular or ionic form depends




on site-specific water-rock and water-pollutant interactions.  The




various forms or chemical species in ground water exhibit differing




sorption, precipitation and mobility characteristics.  A compre-




hensive treatise on aqueous complexes and complexation is given by




Ringbom (1963), Stumm  (1967), Morel and Morgan  (1972), Langmuir




(1979), Stumm and Morgan  (1981), and Singer  (1982).




     Complexation, in  some cases, may solubilize  and hence mobilize




hazardous substances;  in  other  cases, it may result  in  insoluble




compounds (and  colloids)  and, therefore, promote  hazardous substance




retardation.  The metals  are particularly prone to formation of a




variety of complex species in aqueous media  (Stumm and Morgan,




1981).  Long-chain organic complexes  (polymers) have low solubility




in ground water; hence their retardation is  provided mainly  by




filtration and  sorption.  Generally, the nature and  fate of  the




complexes are determined  by the chemical nature of the  ground water




and the geochemistry of the migration medium.   In cases where




organic and inorganic  substances in leachates  are mixed, the




tendency is for formation of insoluble organometal polymers  whose




mobility is retarded.




     Through the use of chemical equilibrium models, it is possible




to predict the complex form in which a given inorganic metal ion is




likely to be found.  These models include the REDEQL model of Morel




and Morgan (1972); the SOB1NEQ model of Kharaka and Barnes (1973)•
                                 24

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the MINEQL model of Westall et al.  (1976); the WATSPEC model of




Wigley (1977); the WATEQ2 model of  Ball and Jenne (1979); and the




GEOCHEM model of Mattigod and Sposlto (1979).  These models require




spatial and temporal hydrochemical  data, including equilibrium-based




redox potential data to accurately  predict metal complexation and




precipitation.  Also, their use is  limited to the prediction of




complexation and precipitation of inorganic substances.  No suitable




models have been identified as currently available for organic




substances.




     Generally, complexation occurs slowly, and may not result in




retardation when ground water velocity is high.  Furthermore, it is




difficult to estimate a generalized complexation-aided-retardation




capacity of a migration medium, since the process promotes the




retardation of some hazardous substances and increases the mobility




of others given similar subsurface  conditions.  Finally, because the




models used to predict complexation are equilibrium-based models, it




is not clear how applicable they would be to nonequilibrium




conditions frequently found in nature.




3.2  Selection of Geochemical Processes for Site Screening




     The preceding sections described seven geochemical processes




that play a major role in the natural retardation of released




hazardous substances.  The first step in evaluating the role of




these geochemical processes would be to obtain site-specific




information about the Eh, pH and ionic strength of ground water, the
                                 25

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geochemistry of sediments and rocks, and the nature and solubilities

of hazardous substances.  These data are rarely available during the

current evaluation of CERCLA sites.  Furthermore, as discussed

above, comprehensive evaluation of the partial or combined effect of

these processes is beyond present modeling capability, even if it

were feasible to obtain all data necessary to characterize them

adequately at a site and along the migration path.

     If geochemical retardation effects are to be  considered in the

evaluation of the relative hazard of sites, then a method must be

employed which makes use of the limited and generalized  information

expected to  be available at from CERCLA site inspections.  One

method, which is described in Section 4.1, is to concentrate on the

sorption process  (adsorption plus ion-exchange)  in evaluating the

relative potential of subsurface media to retard released hazardous

substances.

     The reasons for selecting sorption are:

     •  Its  generality, as compared to other competing retardation
        processes, regarding the types of hazardous substances
        (organic and inorganic) and the wide range  of geochemical
        conditions under which it will occur.

     •  The  possibility that the sorptive capacity  of various rocks
        and  sediments can be represented, if only qualitatively, by
        easily obtainable geological information.   (This topic is
        discussed more fully in Section 4.)

     •  Sorption promotes retardation but unlike other geochemical
        processes it rarely promotes increased mobility.

     In contrast, each of the other types  of geochemical  processes

tends to be limited to specific  types  of hazardous  substances and


                                26

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chemical conditions under which they are operative.  Additionally,

processes such as complexation, redox and acid-base reactions,

dissolution, and precipitation promote not only retardation but also

migration.  Thus, any credible prediction of the effect of other

types of geochemical processes at a site requires more detailed

information than is generally available or obtained from CERCLA site

inspections.  Further, there are no reliable techniques to obtain

and model hydrochemical data (such as Eh, pH and ionic strength)

along a subsurface migration path in order to predict retardation of

hazardous substances.

     Additional support for the selection of sorption is provided by

the following:

     1.  The research literature consistently alludes to the
         importance of sorption in the retardation of both organic
         and inorganic substances.  For example, Siegrist et al.
         (1986) stress the importance of sorption for remedial
         action in their study of sorption systems for treating and
         disposing of municipal wastewaters.  Ward et al. (1985)
         conclude that sorption of trace organic compounds by
         organic matter in a geomedium is a primary geochemical
         mechanism for determining the fate of an organic
         substance.  A modeling study of a creosote site in Conroe,
         Texas by Bedient et al. (1984) indicates good agreement
         between absorption-related retardation of organic compounds
         and the amount of organic matter in the migration media,
         the explanation lying in the sorptive capacity of the
         organic matter.  From their sorption study of subsurface
         samples, Banerjee et al. (1985) conclude that total organic
         carbon content of geologic samples is a reasonably good
         predictor of sorption of organic compounds.  From their
         study of tidal marsh soils at a municipal landfill site in
         New York, Panter et al. (1985) conclude that organic matter
         and clays are effective in sorption-related retardation of
         halogenated organic substances.  Based on evaluation of the
         potential for ground water contamination from geothermal
         fluid releases, Summers et al. (1980) indicate the
                                 27

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    Importance of sorption in the retardation of various
    metals.   From their open literature review (more than 70
    published articles),  Steelman and Ecker (1984)  conclude
    that sorption is a primary mechanism for retardation of
    organic compounds.  In research related to nuclear waste
    repositories, sorption is regarded as one of the viable
    mechanisms for radionuclide retardation in natural geomedia
    and in engineered backfill barriers (Nowak, 1980, 1980a,
    I980b; Pigford et al., 1980; Serne and Relyea, 1981; and
    Moody, 1982).  A good summary on sorption of organic and
    inorganic substances is given by JRB Associates (1984) and
    Rai et al. (1984) respectively.

2.  Studies of uranium deposits in sedimentary rocks of
    different geologic ages indicate that sorption by organic
    matter and clays is one of the most important processes
    leading to concentration of uranium and associated metals
    in such deposits  (Sayala and Ward, 1983; Wayland and
    Sayala, 1983; Schmidt-Coilerus, 1979; and Leventhal and
    Santos, 1981).  These results strongly suggest that clays
    and organic matter can retard inorganics for a long time
    unless the sorptive system is drastically disturbed.

3.  Although other geochemical processes that have been
    discussed are not suitable for direct use in a site ranking
    scheme, they generally enhance sorption by controlling the
    type of ionic compounds (ion-specification), providing ions
    (through dissolution) for sorption sites, and creating net
    surface charges for sorption  (see Rai et al., 1984).
                            28

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4.0  ESTIMATION OF SORPTIVE CAPACITY OF ROCKS AND SEDIMENTS




     Quantification of the potential of subsurface media to retard




hazardous substances by sorption requires extensive (in both time




and space) data on a number of physical and chemical properties of




hazardous substances, rocks, sediments, and ground water along the




migration path.  For example, knowledge of the mineral composition,




grain size, particle surface area, and thicknesses of the different




geologic layers that are encountered by the migrating hazardous




substances is required.  Knowledge of geochemical parameters such as




the ionic strength and pH of the ground water is also necessary.




However, even if the data were available, models to quantify the




sorptive capacity are beyond the present state-of-the-art.




     If sorption effects are to be used as a basis for predicting




the retardation of hazardous substances in a site-screening




evaluation scheme, then a simple model is necessary.  This model




should provide a basis for qualitatively estimating the sorptive




capacities of rocks and sediments and ranking the overall sorptive




or retardation potential of the subsurface migration path.  The




theoretical basis for the model should be sound, and the level of




detail should be consistent with that of other factors in the site




evaluation scheme.  The model and ranking schemes described in the




following sections meet all the above mentioned criteria.
                                 29

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4.1  Model for Sorptive Capacity Estimation

     The model developed here assigns relative sorptive capacities

to various types of rocks and unconsolidated sediments based on

their  total clay plus  organic carbon content.  Organic carbon is

used as a measure  of organic matter or  carbonaceous materials.

There  are two main reasons why  total clay plus organic carbon

content have been  selected as an indication of the sorptive

capacities of rocks and  sediments.  They are:

      (a)  The inherent sorptive capacity of clays and organic
          matter found in rocks and sediments is much greater
          for a wide variety  of organic and inorganic
          substances than are those of  the other sorbents  (see
          Brady, 1974; Fuller,  1980; Rai et al., 1984; Panter
          et al.,  1985;  and Siegrist et al., 1986).  Increasing
          amounts  of these  two  sorbents in a geomedium, in
          general, increases  the medium's ability to sorb
          hazardous substances  (see Griffin and Shimp, 1978;
          Karickhoff et  al.,  1979; Karickhoff, 1984; Means
          et al.,  1980;  Hassett et al., 1980; Schwarzenbach and
          Westall, 1981; Stuart, 1983;  and JRB Associates,
          1984).

      (b)  Clays and organic carbon commonly occur together in
          rocks and sediments,  and the  range of their
          concentrations in different types of rocks and
          sediments is well known.

     Generally, fine-grained  sedimentary rocks contain more clays

and organic carbon than  their coarse-grained counterparts.  Igneous

rocks  do not contain any organic carbon, while some metamorphic

rocks  contain small amounts.  However,  both types of rocks usually

contain small amounts  of clays, generally as great  as five percent

(see Table 1 and Williams et al.,  1954  and Huang, 1962).   Available

data on the organic carbon and clay contents  of consolidated  rocks
                                 30

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                               TABLE 1

   RANGES  OF  CLAY AND ORGANIC CARBON CONTENTS  OF SIX COMMON GROUPS
              OF ROCKS AND THEIR EQUIVALENT SEDIMENTS1
                                              Organic
	Rock Type	Sediments	Carbon (%)    Clays (%)

Coal Seams                 Peat, muck, &       58-80         3-14
                           organic-rich
                           sediments

Claystones, Mudstones,     Clayey, muddy      0.4-10        37-81
Shales & Siltstones^       & silty sediments
Sandstones
Carbonates^
Metamorphic Rocks
Igneous Rocks
Sandy sediments
Limey sediments
Talus,4
clean sand,
clean gravel

0.01-0.5
0.2-0.51
0.0-0.17
Or\
• U
8-32
1-10
1-10
1_ c
J
1Source data in Tables A-l, A-2, and A-3 in Appendix A.

^Tar sands with 4 to 10 percent organic carbon and oil shales with
 about 5 to 10 percent organic carbon can be included in this
 category.

^Argillaceous carbonates mixed with claystones and mudstones
 generally have higher clay contents than those indicated.

4Talus is composed of rock fragments of variable sizes and shapes
 and usually contains very little clay (usually less than 6 percent)
 and organic carbon (usually less than 0.18 percent) (Richard, 1986).
 Therefore, talus is considered equivalent to metamorphic rocks in
 terms of its total clay and organic carbon content.
                                 31

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and unconsolidated sediments are presented in Appendix A (Tables




A-l, A-2, and A-3).  The clay and organic carbon contents of




unconsolidated sediments are generally the same as those noted for




their consolidated counterparts  (i.e., rocks).




     The ranges of clay and organic carbon contents for six common




groups of rocks and their equivalent sediments are drawn from the




data presented in Appendix A.  These ranges are given in Table 1.




From the table, one can infer that coal seams and their equivalent




sediments have the highest relative capacity for sorption while




igneous and metamorphic rocks, have the lowest capacity for




sorption.  The increase of sorptive capacity with increasing clay




and organic carbon contents is shown for a variety of inorganic and




organic substances in Appendix A (Table A-4 and Figures A-l, A-2,




A-3, and A-4).




     The values given in Table A-4 of Appendix A are a measure of




adsorption by total clays plus organic carbon and do not represent




total sorption.  However, these  values shed some light on the




combined sorptive capacity of clay and organic carbon contents.  The




inorganics, with few exceptions, generally show that sorption




increases with increasing contents of clays and organic carbon.




However, there is no single quantitative relationship between




sorbent content and amount of hazardous substances sorbed for all




inorganic substances.  Some substances are sorbed more than others




by about the same amounts of sorbents  (see Table A-4  and  Figures A-l
                                 32

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through A-4 in Appendix A).   Similar behavior is also shown for the




examples of organic substances.  These data are by no means




extensive or totally conclusive.  However, they do suggest that




increasing contents of clays plus organic carbon increases the




sorptive capacity of a geomedium, and therefore, its ability to




retard various hazardous substances by sorption.
                                 33

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5.0  APPLICATION OF SORPTIVE CAPACITY TO RANKING OF HAZARDOUS WASTE
     SITES

     In the previous section, data were shown that suggest a

generalized proportionality between the clay plus organic carbon

contents of rocks and sediments and their sorptive capacities for a

variety of hazardous substances (see Appendix A).  This section deals

with questions such as how to rank the relative sorptive capacities

of various rocks and sediments, how to estimate and rank the

subsurface sorptive or retardation potential, and finally, how to

incorporate the retardation potential factor value into a site

ranking scheme.

     A variety of options are available for estimating the sorptive

capacities of rocks and sediments and ranking the sorption-related

retardation potential of a subsurface migration path.  These options

result from combinations of choices regarding:  (1) the means for

ranking the sorptive capacities of different types of rocks and

sediments; (2) the specific subsurface migration path considered; and

(3) the means for characterizing the sorptive or retardation

potential of the selected subsurface migration path.  Table 2

illustrates the range of options available.  In the following

sections, each option is discussed.  Then, feasible combinations are

discussed along with their advantages and disadvantages.  The types

of data required by each option and possible sources of the data are

also discussed.  Finally, suggestions regarding incorporation of the
                                 35

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                                                 TABLE 2

                  RANGE OF OPTIONS FOR RANKING SORPTIVE CAPACITIES, SELECTING MIGRATION
                    PATH AND CHARACTERIZING MIGRATION PATH FOR RETARDATION POTENTIAL*
        Ranking of Sorptive
      Capacities of Rocks and
   Sediments by Sorbent Contents
  Migration Paths
      Characterization of
         Migration Path
   for Retardation Potential
       Ordinal scale:  using the
       ranges of total clay plus
       organic carbon contents

       Proportional scale:   using
       the averages of total clay
       plus organic carbon contents
u>
The total migration
path:  both total vertical
migration path and
horizontal migration
path, including aquifer,
from point of deposition
to point of exposure

The total vertical
migration path, including
the aquifer of concern
                                           The vertical migration
                                           path above the aquifer
                                           of concern
1.  Characterization by
    considering the most
    sorptive layer; i.e.,
    the layer with greatest
    sorbent content along
    the migration path
    of concern

2.  Characterization by
    considering the thickest
    layer along the migration
    path

3.  Characterization by
    thickness-weighted
    averages of the sorptive
    capacities of geomedium
    layers along the
    migration path

4.  Characterization by
    arithmetic mean of
    sorptive capacities of
    geomedium layers along
    the migration path
   *0rder  of  presentation represents sequence,  not order of preference,

-------
resulting retardation potential factors into a site ranking scheme

are made.

5.1  Ranking of Sorptive Capacities of Rocks and Sediments by Sorbent
     Contents

     Two scales have been developed for ranking sorptive capacities

using the data on clay plus organic carbon contents (sorbent content)

of rocks and sediments.  These are:

     •  An ordinal scale that uses the ranges of sorbent content.

     •  A proportional scale that uses the averages of sorbent content.

     5.1.1  Ordinal Scale

     The ordinal scale simply ranks the sorptive capacities of

different types of rocks and sediments according to the ranges of

their clay and organic carbon content.  For this ranking scheme, it

is estimated that rocks and sediments with high sorbent content have

a correspondingly higher retardation potential than those with

medium and low ranges (see Table 3).  Thus, ordinal values are

assigned to the different groups of rocks and sediments, and these

values are intended to suggest the rank order of the retardation

potential of those rocks and sediments.  For the purposes of

retardation potential factor scoring, rocks and their equivalent

sediments are divided into three broad groups as follows:

     1.   The first group is composed of coal seams, claystones,
         mudstones, shales and siltstones, and their equivalent
         unconsolidated sediments such as peat, muck and organic-
         rich soils, and clayey, muddy, and silty soils.  Based on
         Table 1, these rocks and sediments contain the greatest
         percent of sorbents (37 to 94 percent) when compared to the
         two other groups.


                                 37

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                               TABLE 3

     RELATIVE RETARDATION POTENTIALS (AND THEIR FACTOR VALUE) OF
      GROUPS OF ROCKS AND THEIR EQUIVALENT SEDIMENTS ACCORDING
       TO THE RANGE OF TOTAL SORBENT CONTENTS1—ORDINAL SCALE
    Rock Type
    Sediments
Relative
Retardation
Potential
Assigned
Factor
Value3
Coal seams, claystones
mudstones, shales and
siltstones^
Peat, muck and
organic-rich
sediments, clayey,
muddy, and silty
sediments
  High
  Low
Sandstones
Carbonate, Metamorphic
and Igneous Rocks
Sandy sediments
Limey sediments
gravels Talus
clean sands,
clean gravel
Medium Medium
Low High
-'-Ranges are given in the text and in Table 1.

^Tar sands and oil shales are included.

^Relative values for the purpose of illustration.
                                 38

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     2.  The second group is composed of sandstones and sandy
         soils.  These generally contain from about 8 to 32 percent
         clays and organic carbon.

     3.  The third group is composed of carbonate, metamorphic and
         igneous rocks, and limey soils and talus.  The clay and
         organic carbon content of these rocks and sediments is
         generally below 10 percent.

     Since Group 1 rocks and sediments have the highest values for

percent clays and organic carbon, it is expected that Group 1 rocks

and sediments have a higher potential for retardation of hazardous

substances than those of Groups 2 and 3.  Group 3 rocks and

sediments have a lower potential for retardation.

     5.1.2  Proportional Scale

     The proportional scale, shown in Table 4, is based on the

mid-point of the average clay plus organic carbon content of various

rocks and sediments.  For the purpose of rating the relative

retardation potential, the commonly occurring rocks and their

equivalent sediments are divided into five groups according to their

average total sorbent contents.  The relative magnitude of these

averages are intended to reflect semi-quantitatively the relative

sorptive capacities.  Thus, for example, coal seams and their

equivalent sediments, containing an average clay and organic carbon

content of 77 percent, are presumed to have a sorptive capacity

about 26 times greater than that of metamorphic and igneous rocks

which have an average sorbent content of 3 percent.

     While a proportional scale confers advantages not possible with

an ordinal scale, the precise quantitative relationship implied in
                                 39

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                                 TABLE 4

        GROUPS  OF ROCKS  AND EQUIVALENT SEDIMENTS  ORDERED BY THEIR
               AVERAGE TOTAL SORBENTS—PROPORTIONAL SCALE
      Rock Type
   Sediments
Average Total Sorbentsl
  (Percent Clays Plus
Percent Organic Carbon)
Coal seams
Peat, muck, and
organic-rich
sediments
•^-Mid-point value of the ranges given in Table 1.

^Tar sands and oil shales are included.
           77
Claystones, muds tones,
shales and siltstones^
Sandstones
Carbonates
Metamorphic and
Igneous Rocks
Clayey, muddy and
silty sediments
Sandy sediments
Limey sediments,
gravels
Talus, clean sands,
clean gravels
64
20
6
3
                                 40

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Table 4 between the average clay plus organic carbon content and




sorptive capacity (and, therefore, retardation potential) of rock and




sediment groups has no experimental or empirical foundation.  This




relationship, as mentioned in Section 4, is based on the premise that




sorptive capacity increases with an increase in clay plus organic




carbon content.




5.2  Migration Paths




     In order to evaluate the potential for retardation of hazardous




substances, the length of the subsurface migration path associated




with a site must be defined.  Three possible migration paths, which




are shown in Figure 3, are evaluated.  These are:




     Path A;  This path considers the entire migration distance from




point of deposition to point of exposure; i.e., the total vertical and




horizontal migration paths, including the depth of an aquifer of




concern.  This path extends from the lowest point of waste disposal to




the nearest target well.  Since hazardous substances can migrate




vertically to an aquifer of concern and horizontally within an aquifer




to the nearest target, it is prudent to evaluate the entire migration




path for retardation potential.




     Path B;  This path considers the total vertical distance from the




lowest point of waste disposal to the bottom of an aquifer of




concern.  This path does not consider the retardation potential of the




horizontal migration path in an aquifer.
                                 41

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                                         Top Soil
        Path-B •
    Aquifer
                         	WjJterJ^abJe.
                                                            Target Well
                                                                   Rock/Sediment Type 1
                                         t
                   Path-C
Path-A
                                  FIGURE 3
SCHEMATIC CROSS SECTION SHOWING THREE ALTERNATIVE MIGRATION  PATHS FOR
                    EVALUATION OF  RETARDATION POTENTIAL

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     Path C;  In this case, only the vertical distance to the upper




surface of an aquifer of concern is considered.  This option does




not consider the retardation potential of a migration path (either




vertically or horizontally) in an aquifer.  This path definition




conforms to the one used for evaluating "permeability of the




unsaturated zone," in the current HRS ground water route




characteristics category.




     Although any of the three migration path lengths could be




selected to evaluate the subsurface retardation potential of the




subsurface migration path, the HRS as currently designed excludes




consideration of hazardous substance migration in an aquifer of




concern (either vertical or horizontal).  By considering only the




vertical migration path to an aquifer of concern, the present HRS




attempts to assess the probability that released hazardous




substances will reach that aquifer.  In order to assess the




probability that hazardous substances will reach a given target, a




site ranking scheme should also consider the migration path in the




aquifer, as this can comprise a major portion of the entire




subsurface path.  Thus, the migration path length to include in a




site ranking scheme for the evaluation of subsurface retardation




potential depends upon the intended objectives of the ranking scheme




and the type of data available for characterising the sorptive




capacity along the migration path.
                                 43

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5.3   Characterization  of Migration Path  for  Sorptive Potential

      Once  the length of a migration  path is  defined, a means  of

characterizing  that path for  its sorptive potential must be

established  in  order to complete the evaluation of the subsurface

retardation  potential.  For this purpose, four methods of migration

path  characterization  are proposed.  These are:

      •   Method  1;  Characterization  by considering only the most
         sorptive geomedium layer (the layer  with the greatest sorbent
         content) along the migration path.

      •   Method  2;  Characterization  by considering only the thickest
         geomedium layer along the migration  path.

      •   Method  3;  Characterization  by a thickness-weighted average
         sorptive capacity (sorbent content)  of geomedium layers along
         the  migration  path.

      •   Method  4;  Characterization  by the arithmetic mean of the
         sorptive capacities (sorbent contents) of geomedium layers
         along the migration path.

      Method  1

      Under this method the most sorptive layer along the migration

path  is  selected to characterize the retardation potential of the

subsurface.  This layer should have  a specified minimum thickness in

order to be  considered in site evaluation.   A minimum thickness of

6 feet is suggested for naturally occurring  rock/sediment layers

because  it is twice the thickness of artificially created

barrier-clay layers (liners)  generally considered for remediation of

a hazardous waste migration problem  (Otte, 1986).
                                 44

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     Method 2

     This method would characterize the retardation potential of the

migration path by considering the thickest layer along the path.  No

minimum thickness is imposed by this method.  As in the case of

Method 1, the sorptive potential of the path would be characterized

by only a single layer.

     Method 3

     This method uses the thickness-weighted average sorptive

capacity of geomedium layers along the migration path to evaluate the

subsurface retardation potential.  The following is a step-by-step

methodology for calculating the thickness-weighted average sorptive

capacity along the subsurface migration path:

     •  Collect the data on type (i) and thickness (t) of the "n"
        number of rock and sediment layers along the migration path.

     •  Calculate the total length (L) of the migration path.

     •  Identify, from Table 4, the average total sorbent (percent
        clay + percent organic carbon) contents (TSC) of rock and
        sediment layers along the migration path.

     •  Calculate the thickness-weighted average sorbent content
        (TWASC) of the media along the migration path using the formula:


                     £         t.
             TWASC = 2-  (TSC x :pi)
                     i=l        L
     •  Assign a factor value to the site according to the assigned
        retardation potential factor values given in Table 5.

     Method 4

     This method characterizes the retardation potential of the

migration path by the arithmetic mean of the average total sorbent
                                 45

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                               TABLE  5

             EXAMPLE OF NUMERICAL FACTOR VALUES FOR THE
             THICKNESS-WEIGHTED AVERAGE  SORBENT CONTENTS
Thickness-Weighted
Average Sorbent
Content (%)
60
60 to 40
39 to 20
20
Relative
Retardation
Potential
Highest
Medium High
Medium Low
Lowest
Assigned
Factor
Value1
Lowest
Medium Low
Medium High
Highest
^Values presented for purposes of illustration only.
                                 46

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content of rock and sediment layers along the path.   The arithmetic

mean of the sorbent content (AMSC) is calculated using the formula:

                               1   n
                        AMSC = -   £  TSCi
                               n  i=l
where n, i and TSC. are the same as those defined under Method 3

above.  The site could be assigned retardation potential factor

values in the same manner as in Method 3.

5.4  Examination of Various Options for Ranking of Retardation
     Potential

     In this section, possible options for ranking the subsurface

retardation potential of a migration path are examined.  The options

are based on applicable combinations of choices with respect to

scales for ranking sorbent capacities, length of migration path, and

means for characterizing migration path retardation potential.

     Options Using the Ordinal Scale

     If the ordinal scale is used for ranking sorptive capacities,

then ranking of the retardation potential of a migration path is

necessarily limited to Method 1 or 2, that is, site evaluation by

the most sorptive or the thickest geomedium layer along a migration

path (see Section 5.3).  It is not possible to use Method 3 or 4

because ordinal rankings cannot be averaged meaningfully.  The use

of Method 1 or 2 simply suggests that the layer selected has higher

retardation potential than the other layers.  Consideration of the

layer with the greatest sorbent content infers that retardation of

migrating hazardous substances will occur, most effectively, by
                                 47

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sorption in that layer.  This assumption is similar to that




currently made in the HRS for evaluation of the permeability of the




unsaturated zone.  Alternatively, consideration of the thickest




sorptive layer assumes that most hazardous substances are sorbed and




retarded during the course of longer migration, i.e., with longer




residence time, in that layer.




      Options Using the Proportional Scale




      If the proportional scale is used, then ranking of the




retardation potential of a migration path can use any of the methods




described in Section 5.3 although its greatest potential would be




realized in Methods 3 and 4.  Evaluation of the retardation




potential of a migration path based on the thickness-weighted




average is expected to give the best estimate of the subsurface




sorptive potential because this method reflects the total sorptive




capacities of rock and sediment layers along the entire migration




path.  Undoubtedly, this evaluation would be more meaningful if the




quantitative relationship between sorbent contents and the capacity




to sorb various hazardous substances were well understood.  However,




the proportional scale provides a basis for obtaining a "relative




average" retardation potential of media along a migration path when




the thickness of different rock and sediment layers along that path




are known.




     The retardation potential of a migration path based on the




arithmetic mean of total sorbent contents is a qualitative estimate
                                 48

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of the overall subsurface sorption-related retardation potential.

By not considering the thicknesses of geologic layers, this

methodology provides only a partial sorptive capacity of the

subsurface.  However, estimation of the retardation potential based

on the arithmetic mean should be used only when data on thicknesses

of various geomedium layers along the migration path are not

available.

5.5  Data Needs and Sources

     The data required for evaluating the sorptive capacity of media

along a migration path and the sources of these data, along with

their logistics, are discussed in this section.

     5.5.1  Data Needs

     The data needed for evaluating the sorptive capacity of a

migration path are as follows:

     •  Length of the migration path.

     •  Type of rock or sediment in each layer along the path.

     •  Thicknesses of rock and/or sediment layers, as measured
        along the path.

     5.5.2  Data Sources

     The required data can be obtained from at least four possible

sources which, if available, can be obtained at little or no

additional cost to the site inspection program.  One source is

regional and local stratigraphic reports and publications prepared

by Federal and State agencies, and by universities.  These data are

usually as good as established regional or local stratigraphic


                                 49

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layers.   Often, the well-established stratigraphic layers and marker




beds  of a regional stratigraphic sequence are used, in combination




with  limited local data, to establish a local stratigraphic




sequence.  The collection of such stratigraphic data involves no




major additional costs to the site inspection program.




      A second source of local data is well logs (descriptive and




geophysical) from wells located in the vicinity of a site.  The




source of these wells would include private or municipal water




wells, and shallow exploration/production wells from industry or




government.  Frequently, these well logs will include a lithologic




description of rock/sediment layers along with their apparent




thicknesses.




      A third source of information is data gathered by the




Department of Transportation or State Highway Departments in




preparation for bridge building, overpass construction or general




roadway work.  This may include road cuts, boring logs and cross




sections.  The availability and quality of this information is




variable, and probably confined to shallow depths.




     A fourth data source which can be used for evaluating sorptive




capacity  of a media is monitoring wells and soil borings taken at




the site  as a part of the site inspection or monitoring program.




This site-specific information is valuable but will vary in quality




and quantity, depending on the site.
                                 50

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5.6  Suggestions for Incorporation of a Retardation Potential Factor
     into the HRS Ground Water Route Score

     A retardation potential factor, such as that described in

Section 5.3 and 5.4, can be incorporated either into the route

characteristics or waste characteristics category of the current HRS

ground water route.  The route characteristics category is a

reasonable location for a retardation potential factor because it

could improve the capability of that category to assess the

probability that hazardous substances will migrate to an aquifer.

Alternatively, incorporation of a retardation potential factor into

the waste characteristics category is also reasonable because it may

improve the assessment of the nature of a hazardous substance

released within an aquifer of concern, prior to reaching a target.

     The retardation potential factor could be incorporated into the

HRS route characteristics category in either of two ways:

     •  As an additive factor with the current permeability factor;
        i.e.,

        Total Route Characteristics Score = [depth to aquifer of
        concern factor value] + [net precipitation factor value] +
        [retardation potential factor value] + [permeability factor
        value] + [physical state factor value].

     •  As a multiplicative factor with the permeability factor value,
        i.e.,

        Total Route Characteristics Score = [depth to aquifer of
        concern factor value] 4- [net precipitation factor value] +
        [(permeability factor value) x (retardation factor value/
        maximum retardation factor value)] + [physical state factor
        value].
                                  51

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     Incorporating the retardation potential factor value as an

additive factor may require adjusting the maximum score for route

characteristics, whereas incorporating it as a multiplicative factor

(ranging between zero and one) with the current permeability factor

will not.  In the current HRS, permeability of the unsaturated zone

is used as an indicator of the rate at which hazardous substances

migrate from a site to an aquifer of concern.  This assumes that

hazardous substances migrate at the same rate as transporting

solutions and/or ground water.  However, in reality this may not be

the case.  Therefore, it may be more realistic to adjust the

permeability factor value by multiplying it by a retardation factor

value (ratio).

     Under the waste characteristic factor category, the retardation

potential could be incorporated as an additive factor:

     Total Waste Characteristics Score = [toxicity/persistence
     factor value] + [hazardous waste quantity factor value] +
     [retardation potential factor value].

     Currently; toxicity/persistence and hazardous waste quantity

are used in the waste characteristics factor category to evaluate

the nature of the substances that might be released to an aquifer.

Along with biodegradation which is now used to evaluate persistence,

retardation potential can be used as an additional factor to

evaluate the total waste characteristics category.  This is a viable

approach since it is the retardation potential of the migration

path, in combination with other factors, that affects the
                                 52

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concentration of released hazardous substances prior to reaching a




target.




     Note that if the route characteristics factors are meant to




evaluate the vertical migration path from the point of deposition to




the aquifer, then the retardation potential factor should reflect




only the sorptive capacity of that part of the migration path.  In




such case, the retardation potential of that portion of the




migration path which occurs in the aquifer could be incorporated




separately into the waste characteristics factor category as an




additive factor as shown above.
                                 53

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6.0  LIMITATIONS




     This section discusses the possible limitations of and concerns




with the approach described in Section 5 for incorporating a




geochemical retardation factor in the HRS.  This approach involves




an estimation of the potential of subsurface media to retard various




hazardous substances.  A simple, but practical method has been




described to estimate the sorptive capacities of rocks and sediments




in terms of the sum of their clay and organic carbon content.  Four




limitations are discussed, along with a series of general concerns.




     The first limitation of this approach is that while the clay




and organic carbon content are the major contributors to the




sorptive capacity of a rock or sediment, they may not represent the




total sorptive capacity.  This is due to the possible presence of




other sorbent components, such as Fe-Mn-Al oxides/hydroxides and




sulfides.  Unfortunately, unlike the clay and organic carbon




content, the average quantity of these sorbents in a variety of




rocks and sediments is unknown.  However, since clays and organic




carbon, unlike other sorbents, can occur together and sorb a wide




variety of hazardous substances, they are usd for estimating the




total sorptive capacities of rocks and sediments.




     Second, the organic carbon contents of each rock/sediment type




in Tables A-l and A-2 exhibit a range of values.  This may be due  to




different sample collection techniques and natural variability of




organic matter in rocks and sediments.  Samples collected from
                                 55

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outcrops are subject to oxidation which will alter the organic




matter content while core samples are subject to thermal alteration




which can affect the organic carbon content.  The organic carbon




content of rocks and sediments could vary spacially depending on the




environments in which they are deposited.




     Variations in clay contents of each rock/sediment type is




evident from Tables A-3 and A-4.  Variations in clay contents can




also be due to sample collection techniques and natural variability




of clay contents in rocks and sediments.  It is possible that both




organic carbon and clay contents of each rock/sediment type could




vary spacially at a site and among sites.  However, by the use of




the average total sorbents (carbon and clay contents, see Table 4),




the effect of sorbent variability on the estimation of subsurface




retardation potential is minimized.  The average total sorbent




values in Table 4 account for the variability mentioned above since




these values are derived from the diverse sample data summarized in




Table 1.




     Third, the effect of geologic structure (such as faults,




fractures, joints, and fissures) on sorptive capacity is not




considered.  Such effects depend on the type of rock and the nature




of the structures present.  However, the presence of geologic




structure in rocks does not necessarily mean open, pipe-like




conduits, except in karst terrane or in some igneous and metamorphic




rocks where joining is prevalent.  Generally, the structural gaps or
                                 56

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spaces in most sedimentary rocks and in some igneous and metamorphic




rocks are filled with a fine to clay-size matrix, derived from the




crushed wall—rock.  In some instances, these spaces are sealed by




reprecipitation and/or recrystallization of filled rock-matrix




(Lahee, 1961; Koch and Vogel, 1980; Birnbaum and Radlick, 1982; and




Babcock, 1982).  Therefore, in most sedimentary environments, and in




some igneous and metamorphic environments, structure is not expected




to circumvent the sorptive capacity intrinsic to the rock or sediment




itself.  Clearly, in those settings where geologic structure controls




the migration paths (such as in some karst terrane), sorption may not




be an effective hazardous substance retardation mechanism.  In the




context of site screening, however, sorptive capacity adequately




addresses the potential of most subsurface media to retard pollutants.




     Fourth, data are not available to substantiate a quantitative




relationship between the sum of clay and organic carbon content and




sorptive capacity of a rock or sediment.  However, the preponderance




of the data available in the literature indicates that an increase in




the sum of clay and organic carbon content results in an increase in




the sorption of hazardous substances (see Table A-5; Figures A-l to




A-4).  In the absence of carefully developed experimental data on




sorption of a variety of hazardous substances by different rocks and




sediments, the relationship between the sorbent content and sorption




appears to be reasonable in establishing a relative sense of sorptive




capacity.
                                 57

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     In addition to limitations to the approach previously described,




there are some general concerns with this approach.  Adding a geochem-




ical retardation potential factor to the HRS will generally reduce the




score of the sites being evaluated relative to the current HRS.




Without consideration of retardation that may occur in the subsurface,




the current HRS implies that hazardous substances migrate at the same




velocity as ground water and that there is no change in their concen-




tration after they are released.  This is a worst-case approach with




respect to hazardous substance.  Thus, incorporation of retardation




potential provides a more realistic assessment of the likelihood that




released hazardous substances will reach a target.  It is clear,




however, that the methodologies offered here for evaluating the




subsurface sorption-related retardation potential of a migration path




involve simplification of the actual situation in subsurface




migration.  Undoubtedly, the use of a single generalized parameter




(sorption) to represent retardation potential results in limitations




with respect to the accuracy of the value assigned to the retardation




potential.  However, the degree of simplification does not detract




from the purpose of the methodology which is to evaluate the




subsurface geochemical retardation potential.  In general, a more




complicated evaluation scheme might require a more sophisticated




treatment of subsurface geochemistry, but additional or more detailed




site-specific data would not by itself result in an improved




evaluation.  Rather, advances in the state-of-the-art of modeling




complex geochemical processes are also needed.




                                 58

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7.0  CONCLUSIONS




     Assessment of the relative hazard posed by hazardous waste




sites via subsurface migration can be improved by evaluating the




potential of subsurface media to retard and/or attenuate released




hazardous substances.  The most practical way to incorporate




geochemical retardation into a site evaluation scheme is by




estimating the sorptive capacity of a migration path.  The clay and




organic carbon contents of rocks and sediments is the most useful




indicator of the sorption-related retardation potential of geologic




media along a subsurface migration path.




     Among the methodologies developed to evaluate retardation




potential, the method utilizing the proportional ranking scale and




the thickness-weighted average sorptive capacity is conceptually




attractive.  Given that stratigraphic information is routinely




collected for each site, little additional information, such as




thicknesses according to rock/sediment type is required to evaluate




the geochemical retardation potential of subsurface geologic media.




     It appears to be both appropriate and feasible to include a




geochemical retardation potential factor in the HRS.  Incorporation




of the retardation potential will conceptually further improve the




capability of the HRS to discriminate among hazardous waste sites.
                                 59

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Book Company, New York, p. 159.

Lahee, F. H., 1961.  Field Geology, 6th Edition, McGraw-Hill Book
Company, New York, pp. 222-261.

Langmuir, D., 1972.  "Controls on the Amounts of Pollutants in
Subsurface Waters," In Earth and Mineral Sciences, Vol. 42, pp. 9-13.

Langmuir, D., 1979.  "Techniques of Estimating Thermodynamic
Properties for Some Aqueous Complexes of Geochemical Interest,"
in Chemical Modeling in Aqueous Systems;  Specification, Sorption,
Solubility, and Kinetics (Jenne, E.A., ed.).  ACS Symposium Series 93,
pp. 353-388.

Leventhal, J. S. and E. S. Santos, 1981.  "Relative Importance of
Organic Carbon and Sulfide Sulfur in a Wyoming Roll-Type Uranium
Deposit," U.S. Geological Survey Open-File Report 81-580, p. 14.
                                 64

-------
Lindberg, R. D., and D. D. Runnells, 1984.   "Ground Water Redox
Reactions:  An Analysis of Equilibrium State Applied to Eh
Measurements and Geochemical Modeling," in Science, Vol. 225,
pp. 925-927.

Lyman, W. J., W. F. Reehl, and  D. H. Rosenblatt, 1982.  Handbook of
Chemical Property Estimation Methods;  Environmental Behavior of
Organic Compounds,  McGraw-Hill Book Company, New York.

Mabey, W. and T. Mill, 1978.  "Critical Review of Hydrolysis of
Organic Compounds in Water Under Environmental Conditions," in
J. Phys. Chem,  Ref. Data 7, pp. 383-415.

Marking, L. L., and R. A. Kimberle  (eds.), 1979.  "Aquatic
Toxicology-Proc. Second Annual  Symposium on Aquatic Toxicology,"
ASTM STP 667; ASTM, Philadelphia, PA.

Mattigod, S. V. and G. Sposito, 1979.  "Chemical Modeling of Trace
Metal Equilibrium in Contaminated Soil Solutions Using Computer
Program GEOCHEM," in Chemical Modeling in Aqueous Systems;
Specification,  Sorption, Solubility, and Kinetics (E. A. Jeanne,
ed.).  ACS Symposium Series 93, pp. 837-856.

Mayer, F. L. and J. L. Hamelink (eds.), 1977.  "Aquatic Toxicology
and Hazard Evaluation," Proc. First Annual Symposium on Aquatic
Toxicology, ASTM STP 634; ASTM, Philadelphia, PA.

McAttee, J. L., Jr., 1959.  "Inorganic-organic Cation Exchange on
Montmorillonite," in Am. Miner., 44, pp. 1230-1236.

McAttee, J. L., Jr., 1963.  "Organic Cation-exchange on
Montmorillonite as Observed by  Ultraviolet Analysis," in Clays and
Clay Miner., 10, pp. 153-162.

Means, J. C., S. G. Wood, and W. L. Banwart, 1980.  "Sorption of
Polynuclear Aromatic Hydrocarbons by Sediments and Soils," in
Environ. Sci. Technol., 14, pp. 1524-1528.

Moody, J. B., 1982.  "Radionuclide Migration/Retardation:  Research
and Development Technology Status Report," Office of Nuclear Waste
Isolation, Battelle Memorial Institute, Columbus, OH, ONWI-321, p. 71.

Morel, F. and J. J. Morgan, 1972.   "A Numerical Method for Computing
Equilibria in Aqueous Chemical  Systems," in Env. Sci. Technol., 6,
pp. 58-67.
                                 65

-------
Morrlll, L. A., B. C. Mahilum, and S. H. Mohiuddin, 1982.   "Organic
Compounds in Soils," in Sorption, Degradation and Persistence, Ann
Arbor Science Publishers, Ann Arbor, MI, p. 279.

Mortensen, J. L., 1959.  "Adsorption of Hydrolyzed Polyacrylonitrite
on Kaolinite, II.  Effect of Solution Electrolytes," in  Soil
Science.  Soc. Am. Proc., 23, pp. 199-202.

Nigrini, A., 1971.  "Investigation Into the Transport and Deposition
of Copper, Lead, and Zinc in the Surficial Environment (Abstr.),"
Geochemical Exploration (Boyle, tech. ed.), Sp. Vol. II, Canadian
Institute of Mining and Metallurgy, p. 235.

Nowak, E. J., 1980.  "Radionuclide Sorption and Migration Studies of
Getters for Backfill Barriers," Sandia National Laboratories Report
SAND 79-110, p. 54.

Nowak, E. J., 1980a.  "The Backfill Barrier as a Component  in a
Multiple Barrier Nuclear Waste Isolation System," Sandia National
Laboratories Report SAND 79-1109, March 1980.

Nowak, E. J., 1980b.  "The Backfill as an Engineered Barrier for
Nuclear Waste Management," in Scientific Basis for Nuclear  Waste
Management, Vol. 2.  C.J. Northrup, ed., Plenum Press, New  York.

Otte, L., 1986.  Personal communication, U.S. Environmental
Protection Agency, Office of Solid Waste.

Panter, S. E., R. Barbour, and A. Tagliacozzo, 1985.  "Physical and
Chemical Attenuation Properties of Tidal Marsh Soils at  Three
Municipal Landfill Sites," in Proceedings of International  Conference
on New Frontiers for Hazardous Waste Management, September  15-18,
1985, Pittsburgh, PA.  U.S. Environmental Protection Agency,
EPA/600/9-85/025, pp. 57-63.

Philippi, G. T., 1965.  "On the Depth, Time and Mechanism of
Petroleum Generation," in Geochem. Cosmochim. Acta, 29,  pp. 1021-1049,

Pigford, T. H., P. L. Chambre, M. Albert, M. Foglia, M.  Horrada,
F. Iwamoto, T. Kanki, D. Leung, S. Masuda, S. Muraoka, and  D. Ting,
1980.  "Migration of Radionuclides Through Sorbing Media, Analytical
Solutions-II," Lawrence Berkeley Laboratory, University  of
California, Berkeley Report LBL-11616, UC-70, Vol. 1, p. 65.

Plummer, L. N., D. L. Parkhurst, and D. C. Thorstenson,  1983.
Development of Reaction Models for Ground-Water Systems:  Geochem.
et Cosmochim. Acta, Vol. 47, pp. 665-686.
                                 66

-------
Rackley, R. I., 1972.  "Environment of Wyoming Tertiary Uranium
Deposits," Am. Assoc. Petrol. Geol. Bull., Vol. 56, No. 4, p. 755.

Radian Corporation, 1980.   "Trace Metals and Stationary Conventional
Combustion Processes:  Volume 1, Technical Report," U.S. Environmental
Protection Agency Report EPA-600/7-80-155a, p. 101.

Rai, D., J. M. Zachara, A.  P. Schwab, R. L. Schmidt, D. C. Girvin,
and J. E. Rogers, 1984.  "Chemical Attenuation Rates, Coefficients,
and Constants in Leachate Migration, Volume 1:  A Critical Review,"
Report EA-3356, prepared by Battelle Pacific Northwest Laboratories,
Electric Power Research Institute, Palo Alto, CA.

Rao, P. S. C. and J. M. Davidson, 1980.  "Estimation of Pesticide
Retention and Transformation Parameters Required in Non-Point Source
Pollution Models," in Environmental Impact of Non-Point Source
Pollution, M. R. Overcash and J. M. Davidson, eds., Ann Arbor Science
Publishing Inc., Ann Arbor, MI, pp. 23-67.

Rao, P. S. C., P. NKedi-Kizza, and J. M. Davidson, 1986.  "Abiotic
Processes Affecting the Transport of Organic Pollutants In Soil," in
Land Treatment—A Hazardous Waste Management Alternative, R. C. Loehr
and J. F. Malina, Jr., eds., Water Res. Symposium, No. 13, pp. 63-72.

Rice, R. G., 1981.  "Ozone  for the Treatment of Hazardous Materials,"
Water-1980, Symposium Series, American Institute of Chemical
Engineers, 209(77), pp. 79-107.

Richard, A., 1986.  Personal communication, U.S. Soil Conservation
Service.

Ringbom, A. , 1963.  Complexation in Analytical Chemistry,
Interscience Publishers, New York.

Roberts, P. V., M. Reinhard, and A. J. Valocchi, 1982.  "Movement of
Organic Contaminants in Groundwater:  Implications for Water Supply,"
Journal of the American Water Works Association, 74:408-413.

Ronov, A. B., 1958.  "Organic Carbon in Sedimentary Rocks (In
Relation to Presence of Petroleum)," Geochemistry, Vol. 5, p. 510.

Rubin, J., 1983.  "Transport of reacting solutes in porous media:
Relation between mathematical nature of problems formulation and
chemical nature of reactions," in Water Resources Research, Vol. 19,
No. 5, pp. 1231-1252.
                                 67

-------
Sayala, D. , 1983.  "Geochemical Studies," in Multidlsclpllnary
Studies of Uranium Deposits in the Red Desert, Wyoming, U.S.
Department of Energy Open-File Report, GJBX-1(83), pp. 79-104.

Sayala, D. and D. L. Ward, 1983.  "Multidisciplinary Studies of a
Uranium Deposit in the San Juan Basin, NM," U.S. Department of Energy
Open-File Report, GJBX-2(83), p. 227.

Schmidt-Collerus, J. J., 1979.  "Investigation of the Relationship
Between Organic Matter and Uranium Deposits," U.S. Department of
Energy Open-File Report, GJBX-130(79), p. 281.

Schwarzenbach, R. P. and J. Westall, 1981.  "Transport of Nonpolar
Organic Compounds from Surface Water to Ground Water—Laboratory
Sorption  Studies," Environ. Sci. Technol., 15(11), pp. 1360-1367.

Serne, R. J. and J. F. Relyea, 1981.  "The Status of Radionuclide
Sorption—Desorption Studies," performed by the WRIT Program,
PNL-SA-9787, Battelle Pacific Laboratory, Richland, WA.

Siegel, F. R., 1974.  Applied Geochemistry, John Wiley and Sons
Publishers, New York, NY, p. 353.

Siegrist, R. L., D. L. Anderson, and D. L. Hargett, 1986.  "Large
Soil Absorption Systems for Wastewaters from Multiple-Home
Development," Water Engineering Research Laboratory, Cincinnati, OH,
U.S. Environmental Protection Agency, EPA/600/S2-86/023, p. 2.

Singer, P. C., 1982.  "Trace Metals and Metal-Organic Interactions in
Natural Waters," Ann Arbor Science Publishers Inc., Ann Arbor, MI,
p. 350.

Steelman, B. L. and R. M. Ecker, 1984.  "Organic Contamination of
Groundwater—An Open Literature Review," PNL-SA-12709, Battelle
Pacific Laboratory, Richland, WA.

Stuart, J. D., 1983.  "Organics Transported Through Selected Geologic
Media:  Assessment of Organics Transported Away from Industrial Waste
Disposal  Sites," Institute of Water Resources, The University of
Connecticut, PB83-224246, p. 20.

Stumm, W., 1967.  "Metal Ions in Aqueous Solutions," in Principles
and Applications of Water Chemistry (Faust and Hunter, eds.), John
Wiley Publishers, New York, NY.

Stumm, W. and J. J. Morgan, 1981.  Aquatic Chemistry,  Wiley
Publishers, New York, p. 583.
                                 68

-------
Summers, K., S. Gherini, and C. Chen, 1980.   "Methodology  to  Evaluate
the Potential for Ground Water Contamination  from Geothermal  Fluid
Releases."  TetraTech, Incorporated, prepared for U.S.  Environmental
Protection Agency, (EPA-600/7-80-117), U.S. Environmental  Protection
Agency, Industrial Environmental Research Laboratory,  Cincinnati, OH.

Sweeney, K., 1981.   "Reductive Treatment of Industrial  Wastewaters:
I—Process and Description and II—Process Application," in Water
1980, (G. F. Bennett, ed.), American Institute of Chemical Engineers
Symposium, Series 209 (77), pp. 67-78.

Teodorovich, G. I.,  1958.  "Study of Sedimentary Rocks,"
Gostoptekhizdat, Moscow, p. 572.

Tinsley, I. J., 1979.  Chemical Concepts in Pollutant Behavior.
John Wiley and Sons  Publishers, New York, NY.

Tissot, B. P. and D. H. Welte, 1984.  Petroleum Formation  and
Occurrence,  Springer-Verlag Publishers, New  York, NY,  p.  648.

Tomlinson, G., D. Gray, and M. Neuworth, 1984.  "Effect of Coal Rank
on Direct Coal Liquefaction Processes:  Solvent Refined Coal  (SRC)-II
Process Experiment," Sandia National Laboratories Report SAND-1984.

Utah State University and Arthur D. Little, Inc., 1984.  "Review of
In-Place Treatment Techniques for Contaminated Surface  Soils," U.S.
Environmental Protection Agency Report EPA-540/2-84-003a,  Vol. 1,
p. 163.

Vassoevich, N. B., I. V. Visotskiy, A. N. Guseva, and V. B. Olenin,
1967.  "Hydrocarbons in the Sedimentary Mantle of the Earth,"
Proceedings of the 7th World Petrology Congress, 2, pp. 37-45.

Ward, C. R., 1977.   "Mineral Matter in the Springfield-Harrisburg
(No. 5) Coal Member  in tne Illinois Basin," Illinois State Geological
Survey, Circular 498, p. 35.

Ward, C. H., M. B. Thomson, P. B. Bedient, and M. D. Lee,  1985.
"Transport and Fate  Processes in the Subsurface:  Special  Report,"
National Center for  Groundwater Research, Rice University,
Houston, TX, May 21, p. 33.

Wayland, T. and D. Sayala, 1983.  "Multidisciplinary Studies  of
Uranium Deposits in  the Red Desert, Wyoming," U.S. Department of
Energy Open-File Report, GJBX-K83), p. 395.
                                  69

-------
Westall, J. C., J. L. Zachary, and F. M. M. Morel, 1976.  "MINEQL:
Computer Program for the Calculation of Chemical Equilibrium
Composition of Aqueous Systems," Tech. Note 18, Department of Civil
Engineering, MIT, Cambridge, MA, p. 91.

Wigley, T. M. L., 1977.  "WATSPEC:  A Computer Program for
Determining the Equilibrium Specification of Aqueous Solutions,"
Brit. Geomorph. Res. Group, Technical Bulletin 20, p. 48.

Williams, H., F. J. Turner, and C. M. Gilbert, 1954.  Petrography,
W.H. Freeman and Company, San Francisco, CA, p. 403.
                                 70

-------
9.0  SUGGESTED READINGS

Anderson, M. A., and A. J. Rubin, 1981.  Adsorption  of Inorganics at
Solid-Liquid Interfaces, Ann Arbor Science Publishers, Ann Arbor, MI,
p. 357.

Lindsay, W. L. , 1979.  Chemical Equilibria in Soils, Wiley-
Interscience Publication, New York, NY, p. 423.

Manahan, S. E., 1977.  Environmental Chemistry, Willard Grant Press,
Boston, MA, p. 527.

Morrill, L. A., B. C. Mahilum, and S. H. Mohiuddin,  1982.  "Organic
Compounds in Soils," in Sorption, Degradation and Persistence, Ann
Arbor  Science Publishers, Ann Arbor, MI, p. 279.

Rai, D., J. M. Zachara, A. P. Schwab, R. L. Schmidt, D. C. Girvin,
and J. E. Rogers, 1984.  "Chemical Attenuation Rates, Coefficients,
and Constants in Leachate Migration," Electric Power Research
Institute (Palo Alto, CA) Report EA-3356, Vol. 1.

Siegel, F. R., 1974.  Applied Geochemistry, Wiley-Interscience
Publication, New York, NY, p. 345.

Stumm, W. and J. J. Morgan, 1981.  Aquatic Chemistry,
Wiley-Interscience Publication, New York, NY, p. 767.

Tinsley, I. J., 1979.  Chemical Concepts in Pollutant Behavior,
Wiley-Interscience Publication, New York, NY, p. 257.

Utah State University and Arthur D. Little, Inc., 1984.  "Review of
In-Place Treatment Techniques for Contaminated Surface Soils," U.S.
Environmental Protection Agency Report EPA-540/2-84-003a, p. 163.

Ward,  C. H., W. Giger, and P. L. McCarty, 1986.  Ground Water
Quality, Wiley-Interscience Publication, New York, NY, p. 533.
                                  71

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                             APPENDIX A




                  SORPTIVE  CAPACITY ESTIMATION DATA






     This appendix contains a collection of tables and figures




presenting data useful in estimating the sorptive capacity of various




consolidated rocks and unconsolidated sediments defined in terms of




organic carbon and clay content.
                                 73

-------
                                 TABLE  A-l

               ORGANIC  CARBON  CONTENT OF ROCKS  AND SEDIMENTS
Rock/
Sediment Type
Clay Stones
(or Clays)
Shales
Siltstones
Carbonate Rocks
Sandstones
Shales
Siltstones
Carbonate Rocks
Shales + Siltstones
Calcareous Shales
Carbonate Rocks
Petroliferous
Shales
Carbonate Rocks
Sandstones
Non-Petroliferous
Shales
Carbonate Rocks
Sandstones
Number of
Samples Analyzed



About 1,200
(200 formations
in 60 basins -US A)

Over 1,000
(USSR)
418 (Europe)
97 (Europe)
118 (Europe)

No Data (USSR)


1,105 (Composite



Average
Percent
Organic
Carbon
3.4

1.7
1.43
0.23
0.04
.90
.45
0.20
2.16
1.90
0.67

1.40
0.51
0.42
Samples* -
0.40
0.16
0.18
Source
Hunt (1963 and 1961)

Hunt (1963 and 1961)
Hunt (1963 and 1961)
Hunt (1963 and 1961)
Hunt (1963 and 1961)
Vassoevich et al. (1967)
Vassoevich et al. (1967)
Vassoevich et al. (1967)
(In Tissot & Welte, 1984)
(In Tissot & Welte, 1984)
(In Tissot & Welte, 1984)

Ronov (1958)
Ronov (1958)
Ronov (1958)
USSR)
Ronov (1958)
Ronov (1958)
Ronov (1958)
*A composite sample is made by combining the samples from different parts
 of the same rock.

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                                 TABLE  A-2




          ORGANIC CARBON  CONTENTS OF ROCKS  AND SEDIMENTS  (RANGES)
Rock/
Sediment Type
Petroleum Reservoir Rocks
Limestones
Sandstones
Non-Reservoir Rocks
Limestones
Dolomites
Gray Shales
Black Shales
Calcareous Shales
Coals
Western U.S. Coals
Illinois Basin Coals
Appalachian Coals
Recent Sediments
Red beds
Peats
Metamorphic Rocks
Slates; Argillites
Sandstones
Siltstones + Shale +
Clays tones + Muds tones*
Sandstones
Shales + Siltstones +
Claystones*
Number of
Samples
Analyzed
(USA)
2
2
(USA)
3
3
5
3
5
29
110
22
Percent
Organic
Carbon
0.27; 0.51
0.52; 0.76
0.20-0.43
0.11-0.25
0.87-1.75
2.10-8.8
1.4-10.0
58-74
62-80
63-80
(USA)
4 About 0.1
No Data About 37.0
(USA)
2

840 Samples
(Red Desert
Basin, Wyoming)

5,578 Samples
(San Juan Basin
New Mexico)
0.17; 0.16
0.05-0.2
0.64-10.0
0.01-0.5
0.4-10.0
Source
Hunt (1979)
Hunt (1979)
Hunt (1979)
Hunt (1979)
Hunt (1979)
Hunt (1979)
Hunt (1979)
Radian Corp. (1980)
Radian Corp. (1980)
Radian Corp. (1980)
Hunt (1979)
Phillippi (1965)
Hunt (1979)
Sayala (1983)
Sayala (1983)
Sayala (1983)
Sayala (1983)
*Interbedded.
                                  75

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                                 TABLE A-3

                 AVERAGE CLAY CONTENTS OF ROCKS/SEDIMENTS
      Rock/
  Sediment Type
   Number of
Samples Analyzed
Average
Percent
 Clay
Content
Source
Arenites  (Medium
  to Coarse Grained
  Sandstones)

Graywackes (Fine
  to Medium Grained
  Sandstones)
     186                  9    Wayland & Sayala  (1983)
(Red Desert Basin, WY)
      68                 32    Wayland & Sayala (1983)
(Red Desert Basin, WY)
Siltstones

Mudstones

Claystones

Triassic Arenites
Sub Graywackes

(Red

(Red

(Red


8

Desert
40

Desert
32

Desert
2
35

Basin,

Basin,

Basin,

WY)

WY)

WY)
(USA)
(USA)
37

69

81

8
9
Wayland

Wayland

Wayland

&

&

&

(In Huang
(In Huang
Sayala

Sayala

Sayala

, 1962)
, 1962)
(1983)

(1983)

(1983)



  (Most Common
  Sandstones of
  Different Ages)

Graywackes
  (Sandstones of
  Different Ages)

Graywackes
Argillaceous
Carbonates

Carbonates
      14 (USA)
      10
(Palo Duro Basin, TX)
(Gibson Dome, UT)

      11
(Gibson Dome, UT)
  25    (In Huang, 1962)
        Fukui & Davault (1985)
                         24    Fukui (1982)
   1    Fukui (1982), Fukui &
        Allen (1982)
                                   76

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                                 TABLE A-4

                      RANGE OF CLAY CONTENT OF ROCKS
  Rock Type
   Number of
Samples Analyzed
  Percent
   Clay
  Content
Source
Fossiliferous
Carbonates

Clayey Dolomites
(Argillaceous)

Dolomites
(Non-Argillaceous)

Clayey Limestones
(Argillaceous)

Slightly Clayey
Dolomitic Limestone

Slightly Clayey
Limestone

Limestones
(Non-Argillaceous)

Dolomitic Limestones
(Non-Argillaceous)

Coals
    No Data (USA)     0.2-1.0    Barrett (1964)
    No Data (USSR)      3-10.0   Teodorovich (1958)
    No Data (USSR)


    No Data (USSR)


    No Data (USSR)


    No Data (USSR)


    No Data (USSR)


    No Data (USSR)


      43 (USA)
   0-5.0    Teodorovich (1958)
10.0-30.0   Teodorovich (1958)
 5.0-10.0   Teodorovich (1958)
 5.0-10.0   Teodorovich (1958)
   0-5.0    Teodorovich (1958)
   0-5.0    Teodorovich (1958)
   3-14     Ward (1977); Harvey
            et al.  (1983);
            Tomlinson et al.
            (1984)
                                   77

-------
                        TABLE A-5

EXAMPLES OF INCREASE IN SORPTIVE CAPACITY WITH INCREASING
      CLAY  PLUS  ORGANIC  CARBON  CONTENT FOR DIFFERENT
            INORGANIC AND  ORGANIC POLLUTANTS


Metal
Arsenic



Boron






Cadmium






Lead




Inorganics

Percent Sorbents
(Clay + Organic
Carbon)
47.1
25.3
17.3
11.0
65.4
59.2
58.0
28.4
22.4
26.0
5.6
53.1
31.0
29.1
22.9
22.0
18.0
6.3
32.5
25.35
21.0
10.7
5.8
(Source: Rai et

J-CEC
(meq/lOOgm)
___
	
	
__
31.0
58.0
35.2
18.5
18.0
16.2
7.8
14.4
21.0
5.1
11.1
10.3
11.5
4.0
18.2
12.2
10.4
6.96
3.8
al., 1984)
2 Estimated Value of
Retention Capacity or
Langmiur Adsorption
Maximum (umol/gm)
4.47
3.55
3.60
3.31
14.1
8.8
3.13
1.5
2.91
0.73
0.41
11.5
10.0
0.8
6.0
10.5
4.1
1.0
23.0
16.5
11.5
7.0
8.5
                           78

-------
                        TABLE A-5 (Continued)
               Inorganics (Source:  Rai et al., 1984a)
Metal
Percent Sorbents
(Clay + Organic
    Carbon)
              2 Estimated Value of
                Retention Capacity or
   •HlEC         Langmiur Adsorption
(meq/lOOgm)      Maximum (umol/gm)
Selenium
   19.3
   18.2
   18.0
   10.0
    9.2
  16.0
  13.7
  12.3
  10.0
  10.4
16.5
 8.5
18.0
10.0
 2.5
Zinc
   50.0
             32,
             25.
             22,
             21.0
             14.5
             14.4
             10.7
               9.2
                     18.2
                     12.2
                     15.1
                     10.4
                     10.9
                      9.3
                      7.0
                      4.3
                     24.0
                     49.0
                     31.5
                     10.6
                     24.0
                     31.8
                     36.4
                     16.5
                     14.5
                                  79

-------
TABLE A-5 (Continued)


Organic
Compound
Endrin


Diazinon



Trifluraline



Terbacil



Silvex


Pharate




2,4-D Amine


Organics (Source:
Percent Sorbents
(Clay + Organic
Carbon)
58
15
9
7
58
15
9
7
42
23
16
4
42
23
16
4
48
18
13
37
28
24
9
8
42
16
4
JRB Associates, 1984)
2 Estimated Freundlich
Adsorption Constant - K
(ug/gm)
11,115
660
222
90
325
5
20
7
2.73
1.6
0.5
0.2
2.5
0.4
0.4
0.1
162
42
34
75
14
9
5
2
4.62
0.65
0.76
         80

-------
                        TABLE A-5 (Concluded)


Organic
Compound
lerbufos




Chlorpyrifos






Carbon Tetra-
chloride

Trichloro-
ethylene

Phenol





Organics (Source:
Percent Sorbents
(Clay + Organic
Carbon)
37
28
24
9
8
58
28
24
15
9
8
7
100
36
34
100
36
34
64
59
54
30
18
4
JRB Associates, 1984)
2 Estimated Freundlich
Adsorption Constant - K
(ug/gm)
50.8
20.5
7.9
10.6
3.1
7,095
389
147
102
37
24
13
1.75
1.18
0.62
70.0
1.6
3.9
19.4
22.7
10.5
11.0
2.5
0.2
J-CEC—Cation Exchange Capacity.
2Both the Langmiur Adsorption maximum and Freundlich Adsorption
 constant are used as measures of adsorption.  For a detailed
 explanation of their use, see Rai et al. (1984) and JRB Associates
 (1984).
                                 81

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(fl
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Sorbents (clay
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100


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70


60



50
40

30

20

10

0

LEG
» B
r — — O~~ L
— 0 — c
— A— z
~ — d— s

B« -•- A
, — w
• F

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PV^X ,''' A A
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inc
elenium

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       10   20   30   40   50
            Retention Capacity or Langmiur Adsorption Maximum (nmol/gm)
Based on data from Rai et al. (1984).
                           FIGURE A-1
    RELATIONSHIP BETWEEN SORBENT CONTENT AND RETENTION
      CAPACITY/ADSORPTION MAXIMUM FOR SELECTED METALS
                                82

-------
  100 -
s.
                   I
I
         10        30   40
              CECmeq/100gm
    50
         60
     Based on data from Rai et al. (1984)

                             FIGURE A-2
        RELATIONSHIP BETWEEN SORBENT CONTENT AND CATION
              EXCHANGE CAPACITY FOR SELECTED METALS
                                 83

-------
  100
•p  70
.a  60
   50
5"
5.
u
§
c  30

Q-
   20


   10


    0
                                                                   11.1151
     _ Trifiuraline
       I
                                                  Q 162
               Pharate
      11 Terbacil /
      *J      ^
                               f Silvex
          1      1     1      1     1    1     1
                                                              Endrin  ^,
                                                             -.*.--"
                                           _.090 ----- '•122
                                                  1     1     1  >  1 >  1  >l
                                                                        ^
     0     10    20    30    40    50  70   80   90 M60   170   230

                     Estimated Freundlich Adsorption Constant (ug/gm)


     Based on data from JRB Associates (1984).
                                                                330  66011,120
                                    FIGURE A-3
          RELATIONSHIP BETWEEN SORBENT CONTENT AND ADSORPTION
                 CONSTANT FOR SELECTED ORGANIC COMPOUNDS

-------
100
§
o  60
i
?
1
$
C  •30
8
Pe
 20
 10
             A*
             f\

             "
f
 5
 e\f

 I


 I

 /

 I



' 'o
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         I/
       I  / °  '


     ?/ /

      M/
                                        TCE
                                                                 7,095
                       — ^ — — O -- lerbufos
                                                       O147
                                                               ^389
                                             O 102
                           Cn|orpyrifos
                         i
                                      i
                                                     i
                                                          +r
                                                       i
                                                                1
1
          10    20    30    40    50    60   70  100  110 '140  150 380  390


                      Estimated Freundlich Adsorption Constant (ug/gm)
                                                                      7,100
   Based on data from JRB Associates (1984).
                                  FIGURE A-4

        RELATIONSHIP BETWEEN SORBENT CONTENT AND ADSORPTION

               CONSTANT FOR SELECTED ORGANIC COMPOUNDS
                                    85

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