IMPACT OF HIGH CHEMICAL CONTAMINANT
CONCENTRATIONS ON TERRESTRIAL AND AQUATIC
ECOSYSTEMS: A STATE-OF-THE-ART REVIEW
by
Louis J. Thibodeaux
Duane C. Wolf
Martha Davis
University of Arkansas
Fayetteville, AR 72701
Cooperative Agreement No. CR810480
Project Officer
George W. Bailey
Environmental Research Laboratory
Athens, GA 30613
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GA 30613
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DISCLAIMER
Although the research described in this report has been funded wholly
or in part by the United States Environmental Protection Agency through
Cooperative Agreement No. CR810480 to the University of Arkansas, it has
not been subjected to the Agency'-s peer and policy review and therefore
does not necessarily reflect the views of the Agency and no official
endorsement whould be inferred. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use by the
U.S. Environmental Protection Agency.
n
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FOREWORD
Environmental protection efforts are increasingly directed towards
preventing adverse health and ecological effects associated with specific
compounds of natural or human origin. As part of this Laboratory's research
on the occurrence, movement, transformation, and control of environmental
contaminants, the impact of pollutants or other materials in soil and water
is examined and environmental factors that affect water quality are assessed.
Environmental exposure to chemicals will increase as the demand for
these materials increases in response to population growth. Better informa-
tion about the nature of these materials and their mixtures will allow more
accurate prediction of the behavior of these potentially hazardous substances
in ecosystems and the development of better procedures for handling them.
This report reviews research on the environmental consequences of high
chemical concentrations in terrestrial and aquatic ecosystems and recommends
additional studies that would provide data to better evaluate and manage
contaminated systems.
William T. Donaldson
Acting Director
Environmental Research Laboratory
Athens, Georgia
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PREFACE
This review is designed to report the present state of our
knowledge on the impact of high concentrations of contaminants in
terrestrial and aquatic ecosystems, to extrapolate that knowledge to
hypothetic but plausible circumstances, and to suggest the gaps which
exist in information needed to control potentially hazardous
situations. This work was funded by the Environmental Protection
Agency through the U.S.EPA Environmental Research Laboratory, Athens,
Georgia.
The literature review here describes the present state of
research which has contributed to knowledge about areas of high chemi-
cal contamination and the impact of contamination on physical, chemi-
cal, and biological properties of terrestrial and aquatic ecosystems.
This information is then used in Section 3 to establish scenarios of
hypothetical cases of contamination. From gaps found in data provided
by the literature extrapolated against these scenarios, we proposed
research recommendations in Section 4 to help us remedy deficiencies
in the state of our knowledge. This report and further work based
upon these recommendations should prove beneficial in society's
efforts to deal with the control, treatment, and disposal of hazardous
wastes in our environment.
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ABSTRACT
The state-of-the-art of available methods for predicting the effects
of high chemical concentrations on the properties, processes, functions,
cycles, and responses of terrestrial and aquatic ecosystems was reviewed.
Environmental problems associated with high chemical concentrations can occur
in soil and water at landfills; landfarms; spill sites; and abandoned chemical
production, chemical use, chemical storage, and chemical disposal sites.
Considerable information is available on effects of trace chemical
contaminants, such as pesticides, polychlorinated biphenyls, chlorinated
hydrocarbons, and metal ions,in the respective ecosystems. Predictive
techniques are becoming available to describe transport and transformation
of such contaminants and, thus, their fate and distribution in certain com-
ponents of the environment. High chemical contaminant concentrations are
levels of application that are more easily expressed as percentage (i.e.,
5% or greater) and cause major physical, chemical, or biological changes
in the soil and water.
Present predictive methods and models that trace transport and trans-
formation of chemical species are based on "natural" soil and water proper-
ties such as density, porosity, infiltration, permeability, viscosity,
hydrophobicity, and diffusivity. When the chemical contaminant is present
in high concentrations, then the assumption of "natural" soil and water
properties is suspect. The major goal of this project was to assess the
research needs that will address chemical contaminants present in high
concentrations in terrestrial and aquatic ecosystems.
This report was submitted in fulfillment of Cooperative Agreement
No. CR810480 by the University of Arkansas under the sponsorship of the
U.S. Environmental Protection Agency. This report covers the period
September 13, 1982, to September 13, 1983, and work was completed as of
September 13, 1983.
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CONTENTS
Chapter Page
FOREWORD iii
PREFACE iv
ABSTRACT v
LIST OF FIGURES vii
LIST OF TABLES viii
ACKNOWLEDGEMENTS 1x
CONCLUSIONS x
1.0 INTRODUCTION 1
1.1 System Definition 3
1.2 Scope of Study 3
1.3 Research Approach 6
2.0 LITERATURE REVIEW 10
2.1 Chemical Properties 10
2.1.1 Organic 10
2.1.2 Inorganic 21
2.2 Terrestrial Ecosystems 23
2.2.1 Transport processes 24
2.2.2 Transformation processes 28
2.3 Aquatic Ecosystems 39
2.3.1 Transport processes 39
2.3.2 Transformation processes 43
3.0 SCENARIO OF HYPOTHETICAL CONTAMINANT CASES 44
3.1 Terrestrial Ecosystems 45
3.1.1 Binary solvent system 46
3.1.2 Tertiary solvent system 56
3.2 Aquatic Ecosystems 64
3.2.1 Binary solvent system 64
3.2.2 Tertiary solvent system 71
4.0 RESEARCH RECOMMENDATIONS 72
4.1 Transport Processes 73
4.1.1 Transport processes in saturated soils 73
4.1.2 Transport processes in unsaturated
soils 76
4.1.3 Transport processes on the fluid side
of earthen interfaces 77
4.2 Equilibrium Processes 78
4.2.1 Air-soil sorption processes 78
4.2.2 Water-soil sorption processes 81
4.3 Other Physico-Chemical Processes 83
4.4 Transformation Processes 85
5.0 SUMMARY 90
6.0 REFERENCES 93
7.0 GLOSSARY 105
8.0 APPENDIX 109
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LIST OF FIGURES
Figure Page
1-1. Matrix of chemical properties, transport and trans-
formation processes, and soil and sediment proper-
ties which could influence the behavior of hazardous
wastes 7
2-1. Three zones of sorption of chemicals onto soil from
a leaky landfill 18
2-2. Five locations in the aquatic environment where chemical
transport processes are important 40
3-1. EDC migration from a landfill 49
3-2. Benzene-phenol mixture migration from a landfill. ... 57
3-3. Creosote mixture in a streambed 65
Vll
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LIST OF TABLES
Table Page
3-1 Physical and chemical properties of scenario sub-
stances 47
vm
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ACKNOWLEDGEMENTS
The authors wish to acknowledge the assistance of Ms. Nancy
Miller and Ms. Anita Surin in the organization, literature search, and
preparation of this report. They are also indebted to Mrs. Corinne
Colpitts and Mr. Steve Dew for their help in conducting the computer
search of the literature and to Ms. Connie Douthit for processing the
manuscript.
IX
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CONCLUSIONS
Practical experience has demonstrated that high concentrations of
chemical contaminants can have a very serious impact on terrestrial
and aquatic ecosystems. The purpose of this report was to summarize
the literature available on the environmental consequences of high
concentrations of chemical contaminants in the soil, sediment, and
aquatic environments. Scenarios of hypothetical contaminant cases in
terrestrial and aquatic ecosystems for both binary and tertiary
solvent systems indicated a very serious lack of information appli-
cable to the cases. The vast majority of previous research has been
conducted in aqueous systems at low chemical concentrations, and this
is not the situation in a high concentration system.
The high chemical concentrations could vastly alter the transport
and transformation processes, pathways, and kinetics because of their
influence on the chemical, physical, and microbiological properties of
the soil, sediment, and aquatic ecosystems.
Specific research topics in order of priority were proposed to
reduce informational gaps which exist in our understanding of the
impact of high concentrations of chemical contaminants on the environ-
ment. The research recommendations should help us to understand
better the transport and transformation processes and, thus, be better
able to deal with chemical contaminants in the environment.
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1.0 INTRODUCTION
The impact of contamination of the environment by hazardous wastes
at places such as Times Beach in Missouri and Love Canal in New York
has received extensive popular press coverage (Fine, 1980; Sun, 1983).
Public awareness of hazardous wastes has been greatly increased in
recent years by such incidents, and the magnitude of the problem is
increasing. The Office of Technology Assessment has estimated that
the annual production of hazardous wastes in the United States
approaches 250 x 10^ metric tons (Norman, 1983). Much of the waste
is relatively low hazard material such as fly ash from coal-burning
power plants; however, the U.S. Environmental Protection Agency regu-
lates disposal of approximately 40 x 106 metric tons per year of
hazardous wastes of which some 80 percent is disposed of on land
(Norman, 1983). In some instances contaminants enter the groundwater
and pose human health hazards, and remedial actions are sometimes not
feasible (Pye and Patrick, 1983).
The purposes of this report are to provide a state-of-the-art
review of the impact of high chemical contaminant concentrations on
terrestrial and aquatic ecosystems, to define informational gaps, and
to develop research recommendations which provide data to better
evaluate and manage contaminated systems.
The purpose of this project is to assess the state-of-the-art of
available methods for predicting the effects of high concentrations of
chemical contaminant on the properties, processes, functions, cycles,
and responses of terrestrial and aquatic ecosystems. The safety,
health, and welfare of the public and the environment in general can
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be enhanced by increased knowledge of the behavior of these soil-
water-chemical mixtures. As our increasing use and demand for chemi-
cals interact with increasing population, encounters of the biota with
those mixtures will multiply dramatically. Knowledge of the nature of
these mixtures will enhance our ability to reduce the risk of exposure
to toxic/hazardous substances by allowing more accurate prediction of
behavior in the ecosystem and by supplying information which will
assist in the design of treatment, storage, and/or disposal facilities
(an aid to permit writers).
In this report, the terms hazardous waste, toxic substance, and
chemical contaminant will be used according to the following
defini tions:
hazardous waste - dangerous discards generated from our highly
industrialized, technologically based society; refers to any
waste or combination of wastes that present or pose potential
dangers to human health and safety or to living organisms in our
environment; such wastes are lethal, non-degradable or may be
biologically magnified, capable of promoting detrimental cumula-
tive effects as well as short-term hazards; toxic chemicals,
flammable, radioactive, explosive or biological in nature and
take the form of solids, sludges, gases or liquids.
toxic substance - a poison; a substance that through its chemical
action usually kills, injures, or impairs an organism.
chemical contaminant - a chemical substance that makes (water or
soil) inferior or impure by admixture, makes unfit for use by the
introduction of unwholesome or undesirable elements or compounds.
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The results of this study will a) establish the magnitude of the
problems associated with high chemical concentrations in uncontrolled
sites, b) reveal the information gaps that exist concerning the beha-
vior of the mixtures, and c) develop a set of recommendations for
research needs.
1.1 System Definition
In this report high chemical concentration in the environment is
taken to mean a level of single or joint chemical content in a phase
(i.e., air, water, or soil) that constitutes >_ 5 % (wt), or >_ 50,000
ppm (wt) of the mixture. This is not an arbitrary definition for
several reasons. At the 5% level, the volume basis of the con-
centration should include the quantity of the contaminant present or
significant error results (Thibodeaux, 1979). At the 5% level, basic
properties of the natural phases (i.e., air, water, and soil) begin to
be influenced significantly by the presence of the foreign substance.
For example, transport coefficients can not be assumed to be constant
and independent of concentration at this level. High chemical con-
centrations occur in both the soil and/or water and involve environ-
mental problems that include landfills, landfarms, and spill sites as
well as abandoned and active chemical production, use, storage, and
disposal sites.
1.2 Scope of Study
Present predictive methods and models that trace the movement,
bioconcentration; partitioning; transport; and microbial, chemical, and
photochemical degradation rates of chemical species are based upon
"natural" soil and water properties such as density, porosity,
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infiltration, permeability, viscosity, hydrophobicity, and diffusion.
When the chemical contaminant is present in high concentrations, then
the assumption of "natural" soil and water properties is suspect.
The following are some problem areas involving high chemical
concentrations:
a. Landfills and chemical dumps.
A current definition of a landfill is a land disposal site
employing an engineered method for disposing of solid waste on land in
a manner that minimizes environmental hazards by spreading the solid
waste in thin layers, compacting the solid waste to the smallest prac-
tical volume, and applying cover material at the end of each operating
day. Methods have been developed to modify this conventional sanitary
landfill to make it acceptable to receive hazardous materials. Taken
together, these modifications result in a "chemical waste landfill."
In general terms, such operations hope to provide complete long-term
protection for the quality of surface and subsurface waters from
hazardous wastes deposited therein and against hazards to public
health and the environment.
The current problems involving high concentrations of hazardous
waste from such land disposal sites are not overly concerned with the
present generation of well-sited and well-constructed chemical waste
landfills. However, the placement of bulk liquids, organic sludges,
and organic solids do give cause for problems in operation that can
involve high chemical concentrations in leachate and vapors. The
majority of problems involve the past practices of co-disposal of che-
mical wastes in municipal solid waste landfills, the mixing of chemi-
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cal wastes (including liquids) with garbage to form a non-flowing
landfill "solid," the placement of sludges capable of creating a
hydraulic head in landfill cells, and other expedient means for
disposing of chemical wastes. In the latter category the most common
is the chemical dump which involves the placement of solids and
liquids on the ground, in natural depressions, and in hastily dug pits
totally insufficient for their containment. Abandoned dump or storage
sites also fall into the latter category.
b. Landfarms, contaminated land, and spill sites.
Surface soils have received quantities of waste of high chemical
concentration applied to the surface and/or incorporated into the
soil. Landfarming or landspreading is an operation involving the
placement of sludges and aqueous wastes upon the soil surface.
Spreading and frequent plowing plus the addition of nutrients for the
active microbial culture are operating procedures. Contaminated land
results from normal chemical processing operations and involves high
levels of chemicals on or near the soil surface. This land contains
substances which, when present in sufficient concentration, are likely
to cause harm, directly or indirectly to man. Much of this land is on
former industrial sites which were developed and left in a con-
taminated condition as a result of industrial processes. A recent
international conference has highlighted the problems and reclamation
operations involving contaminated land (Essex, 1983). The accidental
spill of solids and liquids during rail and road transport also
results in contaminated soil and high chemical concentrations.
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c. Aquatic releases and spills.
High chemical concentrations can also become associated with the
aquatic environment. Episodic spills of large quantities of sinker
chemicals in river systems result in the bottom sediment being highly
contaminated such as an incidence involving chloroform spilled into
the Mississippi River (Thibodeaux, 1977). Long term releases such as
the kepone (decachloroocta-hydro-l,3,4-metheno-2H-cyclobuta[cd]-pen-
talene-2-one) contamination of the James River (Orndorff and Colwell,
1980), and PCB's in the Hudson River (Horn et al., 1979) highlight
this mode of contamination which results in high concentrations in the
sediment.
1.3 Research Approach
The state-of-the-art review of the effects of high chemical con-
taminant concentration on terrestrial and aquatic ecosystems entailed
the following activities:
1. The development of a matrix to systematize other research
activities and assure that all variables were considered. The
matrix (Fig. 1-1) consisted of soil and sediment properties, che-
mical properties, and various process variables. The matrix
covered those factors which will influence the behavior of high
concentrations of chemical contaminants in landfills, landfarms,
spill sites, and in abandoned chemical production, use, storage,
and disposal sites. A similar approach was used by Phillips and
Nathwani (1977) to assess the land disposal of industrial wastes.
2. A literature search (national and international in scope)
profile was formulated and included both computer and manual
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Processes
1. Transport
a. Diffusion
b. Permeability
c. Flow
2. Transformation
a. Biotic
b. Abiotic
Soil and Sediment Properties
1. Percent Organic Matter
2. Percent Clay
3. Cation Exchange Capacity
4. pH
5. Redox Potential
6. Surface Area
7. Percent Pore Space
8. Clay Mineralogy
9. Microbial Population
Figure 1-1
Matrix of chemical properties, transport and transformation processes,
and soil and sediment properties which could influence the behavior of
chemical wastes.
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searches. Due to the current degree of high activity in the area
of hazardous materials and the lag-time between abstracting and
entry into computerized data bases, it was desirable to use
manual search of journals, proceedings, and personal contacts
originating within the last year to supplement the computer
searches. It was assumed that all materials from 1981 and
earlier had been abstracted and were available in the computer
data bases.
The computer literature search was performed in conjunction
with data bases available to the University of Arkansas Mullins
Library and included: NTIS, AGRICOLA, BIOSIS PREVIEWS, CHEMICAL
ABSTRACTS, SCISEARCH, ENVIROLINE, POLLUTION ABSTRACTS,
ENVIRONMENTAL BIBLIOGRAPHY, WATER RESOURCES ABSTRACTS, and
AQUALINE.
The computer search procedure included: a) the selection of
key words based on the matrix, b) the use of Boolean logic to
construct an ordering of the words, c) on-line search, d)
typewriter output of titles, authors, and reference source
details, e) review of titles by the Principal Investigators, and
f) print out of selected abstracts. Based upon the content of
the abstract, a copy of each pertinent journal article was
studied.
3. A scenario analysis of hypothetical contaminant cases
was also performed. One was a binary solvent system and the
other a tertiary solvent system. The purpose of the scenario
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analysis was to assess the impact of these waste solvents on soil
and/or water properties/parameters such as acidity, hydrophobi-
city, thixotrophy, diffusivity, sorption, ion-exchange, porosity,
permeability, biological activity, transformation reactions
(chemical and biochemical) and their kinetics, volatilization,
and mass transport processes (both mass flow and diffusion). The
result of this exercise highlighted the extent to which the pre-
sent state of knowledge in bacteriology, chemistry, engineering,
physics, and soil science allows predictions involving the above
property/parameters of the affected soil and water.
4. Based upon the results of the literature search and sce-
nario analysis outcome, information gaps were identified.
5. Based upon the information gaps, a set of priority recom-
mendations for needed future research (both field and laboratory)
was developed.
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2.0 LITERATURE REVIEW
This section summarizes the information available in the
published literature that addresses the respective properties, pro-
cesses, and transformations, with respect to high chemical con-
centrations in aquatic and terrestrial ecosystems. The literature on
the subject is concerned mainly with trace contaminants in the
environment; however, reference to that body of information will be
covered only to the extent that it can be applied to high con-
centration situations.
2.1 Chemical Properties
2.1.1. Organic
a. Solubility. There is an abundance of data on the solubi-
lity of individual, pure organic chemicals in water at 25 C.
This information is usually available in chemistry-related hand-
books and in numerous other compiled sources (Dean, 1979; Reid et
al., 1977; Perry and Chilton, 1973). The availability of data on
the aqueous solubility of individual chemicals from mixtures of
two or more components is lacking. The general effects and pre-
dictability of total organic content and dissolved salts of
aqueous solutions on the solubility of individual chemicals are
also lacking. This lack of information has important consequen-
ces with respect to leachates from landfills. The work by Chou
et al. (1981) highlighted the effect of landfill leachates and
dissolved salt content on the solubility of hexachlorocyclopent-
adiene. Some sources (e.g. Reid, Prausnitz, and Sherwood, 1977)
describe physical chemistry techniques and compare various
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algorithms of estimating solubilities of aqueous and non-aqueous
mixtures. These techniques are in part based upon functional
groups and chemical structure, i.e. structure activity rela-
tionships.
On the topics of liquid-liquid equilibria, partially
miscible liquids, and solubilities of solids in liquids, the
authors conclude that thermodynamics provides only a coarse but
reliable framework. In many specific cases, the required infor-
mation must be derived from basic physical and chemical theories
and tested by laboratory research. The variety of mixtures
encountered in the chemical industry is extremely large, and the
set of reliable experimental data on mutual solubilities in
aqueous and non-aqueous systems is extremely small in comparison
(Perry and Chilton, 1973).
The disposal of liquid and solid wastes often results in mix-
tures consisting of two or more phases. The phases are typically
aqueous and organic phases. Experimentally, under ordinary tem-
peratures and pressures it is relatively simple to obtain the
compositions of two coexisting liquid phases; as a result, the
technical literature is rich in experimental results for a
variety of binary and tertiary systems near 25 C and near
atmospheric pressure. King (1969) outlines procedures for the
Nernst's distribution law (i.e., partition coefficient approach)
for non-reacting, association, dissociation, and chemical reac-
tion systems. The emphasis is on the distribution of a substance
between two phases (i.e., binary solvent). The Chemical
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Engineer's Handbook (Perry and Chilton, 1973) contains a selected
list of ternary systems that contains approximately 300" entries.
These data are for high chemical concentrations. For example,
there is an entry for the ternary system water-acetic acid-
benzene. This system contains an aqueous phase with acetic acid
and benzene in solution and an organic phase of acid and benzene
with water in solution. The section entitled "Phase
Equilibriums" should be consulted in Section 15 - Liquid
Extraction of the Handbook (Perry and Chilton, 1973) as an entry
to the literature for binary, ternary, quaternary, and other
multicomponent systems.
Finding applicable equilibrium solubility data for a par-
ticular waste mixture is highly unlikely; however, data on close-
ly related systems may be located, which are useful along with
established thermodynamic methods (Reid, Prausnitz, and Sherwood,
1977).
b. Vapor pressure. An abundance of data and methods is
available concerning vapor pressures of chemicals in the pure
state. These data cover the range of low and high concentrations
with respect to the air-phase and are available in raw form or
correlated by the Clausius-Claperyon or Antoine equations.
Lang's Handbook (Dean, 1979) is a typical source of such data.
Chemicals that exist in high concentrations in terrestrial
and aquatic ecosystems are typically in an impure state. Most
frequently, the chemical exists as a component of a mixture
either with other chemicals or with water, soil, sludge, or a
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combination of these phases. A complete review of vapor pressure
information must include each mixture system separately.
The practice of collecting and disposing organic liquid
wastes has resulted in the creation of mixtures. Mixing of simi-
lar and not so similar organic solvents, paint sludges, tank and
still bottoms, semi-solid sludges, and other wastes is a means of
consolidation and reducing storage capacity requirements.
Fortunately, such mixtures are not unlike natural fossil hydro-
carbon fluids, coal derived fluids, and mixed reaction products
of the chemical process industries. The multicomponent nature
and gas-liquid equilibrium relationships of such mixtures have
been studied extensively over the past 60 years so that a con-
siderable body of knowledge exists by which to predict individual
partial pressures of specific chemical species in the mixture.
Literature cited in Chapter 8 of The Properties of Gases and
Liquids by Reid, Prausnitz, and Sherwood (1977) is representative
of that literature.
The vapor pressure of organic chemical species dissolved in
water is normally handled by a Henry's constant, particularly for
dilute solutions. Phase Equilibrium in Mixtures by King (1969)
presents information on this subject and cites applicable litera-
ture. Recent work has been aimed at verifying Henry's constant
calculation techniques for miscible and immiscible dilute binary
mixtures (Warner et al., 1980). Lack of data and model testing
is apparent for vapor pressures with high chemical concentrations
that result when water resides in contact with a multicomponent
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liquid phase. A specific example for consideration would be the
prediction of the partial pressures of benzene, furfural, carbon-
tetrachloride, and a PCB above an aqueous solution which had been
in contact with an organic phase consisting of equal portions of
each chemical.
Several operations in the disposal of organic chemicals
involve the intimate contact with the soil. For this system par-
tial pressures of individual species are important. Disposal
operations involve the dumping of organic chemicals into land-
fills and the placement and subsequent spreading of organic
sludges, oily sludges, or wastewater treatment sludges onto land
in the so-called land treatment operations. Other events of
importance are the accidental spills of organic liquids and
solids onto soil or terrestrial ecosystems and the placement of
pesticides on or under the soil surface for agricultural pest
control.
In all these situations soil water plays an important role.
It appears that if sufficient soil water is present and dilute
solutions exist, then Henry's constant can be used to obtain par-
tial pressures for solution concentrations up to the solubility
limit. Spencer, Farmer, and Jury (1982) in a recent review
observed that the vapor pressures of lindane, DDT, and triflura-
lin dropped to very low values when the water content was
decreased below that equivalent to approximately 1 molecular
layer presumably by adsorption due to an increased competitive
advantage. Significant differences in vapor density (or
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pressure) occur for dieldrin when soil water is reduced from
3.94% to 2.1%.
This occurrence and the observations that the vapor emission
rate from soils increases dramatically under certain conditions
of soil moisture suggest that our knowledge of the equilibrium
physical chemistry processes of dilute chemical soil mixtures in
the range of unsaturated to "bone-dry" soil water conditions is
lacking. Cupitt (1980) used the Brunauer, Emmett, and Teller
(BET) modified Langmuir adsorption theory to estimate the vapor
pressures of toxic chemicals adsorbed onto "bone-dry" aerosols.
He gives no data to support the validity of the BET model.
Bailey and White (1970) suggest that the same model can be used
for pesticides on soils. However, the work of Jurinak and Volman
(1957) on ethylene dibromide adsorption on dry soils suggests
that this approach is reasonable for high concentration systems.
Various sludges generated by industrial operations and
wastewater treatment operations contain waste materials that are
potentially hazardous. Three general types of organic sludges or
organic matter can be identified: 1) natural organic matter pro-
duced from normal soil processes such as biological decay products
from biomass material consisting of grass, leaves, agricultural
residues, and other organic material; 2) bio-sludges produced
from microbial cultures of wastewater treatment plants such as
activated sludge, anaerobic digesters, primary filtration, and
others; and 3) oily/chemical sludges from petroleum, petrochemi-
cal, or organic chemical manufacturing operations which include
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sources such as American Petroleum Institute (API) oil separa-
tors, tank bottoms, and still bottoms.
Partial pressures of selected chemicals from some of the
chemical process sludges may be estimated by conventional tech-
niques used in process design as outlined by Perry and Chilton
(1973)- A simplified verson of this design was employed by
Thibodeaux and Hwang (1982) in modeling the air emission from a
petroleum landfarming operation. The vapor pressure of the vola-
tile species "dissolved" in the oily sludge can be estimated with
Raoult's law. Raoult's law applies well if solute and solvent
have no heat of mixing and no volume change on mixing. These
"ideal solution" rules are likely valid for cases such as benzene
in API sludge or in still bottom sludges; however, these specific
equilibrium systems have little support data. For vapor
pressures of volatiles above bio-sludges and natural organic
matter "solvents," no studies have been found.
c. Chemical Partition Coefficient between Soil and Water
(i.e., Kp, Kow, Koc)
The partition coefficient, Kp, for trace chemicals between
earthen solids, either soil or sediment, is defined as the ratio
at equilibrium of the concentration on the solid to the con-
centration in water. In soils and sediments the adsorption of
aromatic hydrocarbons and chlorinated hydrocarbons as expressed
by Kp is directly related to the organic carbon content of the
adsorbent. In such systems, it is convenient to use the term Koc
which is simply Kp divided by the organic carbon content of the
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adsorbent. The Koc has also been shown to be closely correlated
to the octanol/water distribution coefficient or Kow for several
compounds (Karickhoff et al., 1979; Chiou, Porter, and
Schmedding, 1983). A similar conclusion was reached by Brown and
Flagg (1981) in their study of nine chloro-^-triazine and
dinitroaniline compounds.
The partition coefficient will likely need to be generalized
to include high chemical concentrations. It is unlikely that a
simple ratio will suffice. The present generation of useful
correlations covers a very narrow range of conditions that
include organic chemicals in surface soils which have con-
siderable organic matter content. These correlations are
typified by the recent work of Chiou, Porter, and Schmedding
(1983).
The spectrum of research scenarios for the adsorption (or
solution) of chemicals onto (or into) soil systems needs to be
broadened. The work of Anderson, Brown, and Green (1982) on the
influence of adsorbed organic fluids on the change in permeabi-
lity of clay soils highlights this need. Fig. 2-1 depicts a
leaky landfill and shows three zones where the sorption of chemi-
cals onto soil may be quite different. The zones are zone-1,
leachate plume; zone-2, groundwater and leachate interaction; and
zone-3, trace containment.
The first zone is characterized by high chemical con-
centrations and possibly additional liquid phases that overwhelm
the subsoil adsorption capacity for the leaching constituents.
17
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Wind Direction
Contaminant Boundary
Layer Region
Unsaturated
Sub-soil
Groundwater
Flow
Groundwater Surface
Mixing Zone
Low Permeability
Layer
Figure 2-1
Three zones of sorption of chemicals onto soil
from a leaky landfill.
18
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For a given subsoil system the information currently available
in the literature does not allow one to estimate the quantity of
chemical adsorbed without performing simulation experiments.
Adsorption is largely based upon the organic matter content of
the soil, which may not exist for subsoil systems, or if it does,
the high chemical concentration overwhelms the "solution" or
solvent capacity of the organic matter. Recent research work
involving the sorption of pesticides in the presence of co-
solvents such as water-methanol and water acetone, in subsurface
environments appears to be a realistic approach in extending the
retardation factor concept to include such high concentration
mixtures (Rao et al., 1983).
It is also possible that certain classes of organic chemi-
cals such as phenolic compounds may undergo polymerization reac-
tions as described by Wang et al. (1978a) and result in the
formation of humic-like materials which have properties similar
to soil organic matter (Martin et al., 1972). Should this occur,
it would be possible to develop a synthetic soil horizon with
increased "organic matter" levels which would more nearly
approach the description of an A rather than a B horizon. This
could result in increased adsorption of the chemical compound.
The second zone is characterized by a dilution process that
occurs as the leachate plume meets and mixes with the passing
groundwater stream. Two liquid phases may continue to exist in
zone-2. Zone-3 is characterized by a secondary leachate plume
that is created as the groundwater picks up and transports
19
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constituents from zone-2 to points farther afield.
Spill sites and contaminated land introduce scenarios of
high chemical concentrations related to sorption onto surface
soils. Freeze and Cherry (1979) present the stages of migration
of oil seeping from a surface source and define a residual oil
saturation. This parameter is defined as a stable stage when an
oil spill on a soil surface is held in a relatively immobile
state in the pore spaces. Experiments in our laboratory
(Altenbaumer et al., 1982) with the organic liquids, propanol,
acetone, ethylene glycol, crude oil, and motor oil suggested that
surface tension was the most important independent variable
affecting the residual saturation. Residual saturation is the
volume of liquid immobilized divided by the initial soil pore
volume. Values ranged from 0.33 to 0.75, indicating that 33% to
75% of the available soil void volume was occupied by the
liquids. The residual saturation for water was 0.26 for this
soil which had 1.42% organic matter.
The above range of soil contaminant conditions, trace con-
taminants to concentrated leachates to pure fluids, is the state
of many important hazardous substance problems for which adsorp-
tion equilibrium information is almost totally lacking. A
comprehensive approach including theory and experiments along the
lines of Dexter and Pavlou (1978) seems to be an appropriate
first step. Incorporated into this approach are functional
groups and chemical structure parameters which must be included
in any comprehensive approach due to the varied nature of the
20
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organic chemicals involved.
2.1.2 Inorganic
When a metal ion is introduced into an environment such as a
waste disposal site, it can undergo numerous chemical and bioche-
mical reactions. Only a few of the basic reactions will be pre-
sented in the following discussion, and cadmium will be used as a
typical example of an inorganic, heavy metal, hazardous waste
material.
Cadmium may exist as inorganic aqua complexes and the diva-
lent cation, Cd+2, in aqueous solution. It may also be adsorbed
onto the clay or organic matter exchange complex which is impor-
tant in reducing or preventing leaching of the metal. Cadmium
may also exist in numerous other soluble inorganic and organic
forms and in insoluble forms which are discussed in greater
detail in the following section.
a. Solubility product. At high concentrations when the activity
of an inorganic ion such as cadmium exceeds the solubility pro-
duct of a given solid phase, then precipitation will occur. The
solid phase will tend to buffer the concentration of the ion in
solution. The situation is further complicated by the fact that
attainment of equilibrium is not instantaneous and the solid pha-
ses are not pure, but vary in composition (Lindsay, 1972). In a
pure system of a divalent cation and hydroxide anions, one
possible equi1ibrium would involve
M(OH)2-^ — M+2 + 20H-
(solid)
-------
The solubility product constant, Ksp, is given as Ksp = [M+2]
[OH~]2. In a cadmium system, the Ksp for OH~, C03~2, S~2, and
P04-3 systems is 10'13, 10'14, 10~28, 1(T32, respectively (Lisk,
1972). The data represent aqueous systems of the respective ions
and do not involve any mixed ionic or non-aqueous systems which
might be typical of hazardous disposal sites.
b. Chelates or Complexes. In addition to the various ionic spe-
cies which may be present in an environmental system, generally a
number of soluble metal chelates or complexes will also exist.
The soluble organometallie chelates are important because they
increase the solubility and, thus, the mobility and bioavailabi-
lity of the metal. Norvell (1972) presented stability diagrams
which compared the Cd+2 chelating ability of 11 common chelating
agents in soil solution. The results indicated that DTPA was the
most effective chelating agent at pH _> 7. At pH values typical
of acid subsoils, none of the materials were effective chelating
agents. In soil, sediment, or aquatic systems, the fulvic and
humic acids are the naturally occurring chelating agents. In
disposal sites, a complex mixture of organic compounds could be
available for chelate formation, and subsequent movement in a
nonaqueous environment could be a potential problem.
Chelation of trace metals such as cadmium is dependent upon
the amount and type of organic compounds in the system, but metal
ion speciation also depends upon the amounts of inorganic ligands
such as phosphate and carbonate. Sposito and Mattigod (1979)
developed a computer program called GEOCHEM to calculate trace
22
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metal equilibria and the system has been valuable in assessing
trace metal chemical reactions which occur in soil and water
systems.
Avnimelech and Raveh (1982) reported that chelates were not
adsorbed by soil, nor were they degraded under anaerobic con-
ditions. These authors further pointed out the serious problem
that could result if direct drainage of anaerobic leachates from
a waste disposal site into a water system were to occur.
c. Biomethylation. Methylation of toxic metals by
microorganisms plays a significant role in metal transport, and
it may serve as a detoxification mechanism for the microbial
population (Saxena and Howard, 1977). Methylcobalamin has been
shown to transfer the methyl group to mercury which results in
ci
formation of monomethyl and dimethyl mercury in soils and sedi-
ments. Methylation also increases toxicity and/or the transpor-
tability. Due to solubility and volatility, the methylated
materials are highly mobile in the environment. Other metals
which are subject to methylation are arsenic, selenium,
tellurium, lead, tin, and possibly cadmium.
2.2 Terrestrial Ecosystems
The literature review in this section covers occurrences of high
chemical concentrations and their influence on processes near the air-
soil interface and in the soil and subsoil layers down into the water
table zone.
23
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2.2.1. Transport processes
a. Saturated Soils. Wallace (1982) reviewed groundwater
models with emphasis on application to the petroleum industry.
He concludes that solute (contaminant) transport models are in an
early stage of development compared to flow models; consequently,
the use of transport models is more limited. For the movement of
many wastes, the cause-effect relationships, especially those
involving physical-chemical behavior, are only partially
understood. In theory some complex reactions (e.g., oxidation-
reduction and precipitation-dissolution) can be addressed; in
practice chemical reactions are either ignored or approximated by
very simple equations. Some of the technical difficulties still
to be overcome relate to situations where quality and quantity of
flow cannot be handled separately. Where relatively high con-
taminant concentrations affect the flow pattern, e.g., where
density differences affect the movement and mixing of the ground-
water flow, coupling of the flow and quality models must occur
(see Fig. 2-1).
Results of a recent symposium and workshop focusing on
hazardous waste management also highlighted the lack of infor-
mation on contaminant dispersion in ground-water systems (Worm,
Dantin, and Seals, 1981). There is a problem in using conven-
tional computation techniques to predict the directions of
motions of contaminants into the aquifer through spills or injec-
tion. The motion of dispersion is due to changes in the relative
viscosity of the liquids, density of the liquids, adsorptive pro-
24
-------
cesses within the liquid, and refractive properties of the
aquifer material. The interrelationship of the fields" of motion
upon one another are not presently known.
Anderson, Brown, and Green (1982) demonstrated in the
laboratory that organic fluids can substantially increase the
permeability of compacted clay soils. Chemicals selected repre-
sent four classes of organic fluids and include acetic acid, ani-
line, methanol, acetone, ethylene glycol, heptane, and xylene.
Clays included montmorillonite, illite, and kaolinite. Results of
this work indicate the need to test premeability of prospective
clay liners using the high chemical concentration of leachate to
which they will be exposed.
b. Unsaturated Soils and Vadose Zones. The transport of
chemicals of high concentration in the vapor phase has received
some consideration. Applications involve mathematical models and
have been concerned with the movement of such substances from
landfills and landfarms. The work of Alzaydi et al. (1978),
McOmber et al. (1982), and Moore et al. (1979) is mainly concerned
with the methane-air mixtures between 5% and 15% with respect to
explosion hazards in construction facilities near landfills. Gas
generated in landfills exhibits high concentrations and total
pressures just greater than atmospheric. Thus, small total
pressure gradients and high partial pressure gradients exist.
Combined transport mechanisms must be used because diffusional
and pressure flows are competitive. Thibodeaux (1981) and
Thibodeaux, Springer, and Riley (1982) developed models for the
25
-------
vapor phase transport of benzene, chloroform, vinyl chloride and
Aroclor 1248 from a landfill cell to the soil surface^ Three of
the chemicals are at extremely high concentrations. Three
transport mechanisms were identified as being important - dif-
fusion, bio-gas purge, and barometric pressure pumping (e.g. the
movement of soil gas by changes in atmospheric pressure) - in
moving the hazardous vapors to the soil surface. The verifica-
tion of important aspects of this model is presently underway
(Springer and Thibodeaux, 1982).
The accidental spill of organic chemicals onto soil surfaces
or the placement of waste-containing volatile chemicals onto soil
surfaces for so-called "land treatment" operations creates
situations involving complex transport mechanisms. Thibodeaux
and Hwang (1982) present an oversimplified model for the emission
of chemical vapors from high concentration sources at the soil
surface. This model neglects soil-water gradients, thermal gra-
dients, and capillary gradients. The lack of consideration of
these gradients may severely limit the utility of the model to
real-world applications.
The transport of radioactive waste constituents in unsa-
turated zones was considered by Winograd (1981). He makes
reference to the fact that conclusions reached apply equally to
chemical toxic wastes in trenches. The idea of waste storage in
these zones has received only peripheral attention to date for
several reasons: the paucity of hydrogeologic, soil physics,
geochemical, tectonic, and other data for the unsaturated zone
26
-------
where indeed few direct measurements of the flux of vadose water
have ever been attempted at depths of a few meters, and the
uncertainty on how retardation factors, yet to be measured for
unsaturated flow conditions, will compare with those reported for
saturated flow.
c. Air Boundary Layer above Soil. For chemicals that
exist in pure form or as constituents of a solid or liquid waste
mixture on the soil surface, the transport through the successive
boundary layers (i.e., sub-layer, buffer zone, and turbulent
zone) provides the only resistance for volatile transport to the
air. Information on the transport of high chemical concentra-
tions in the air boundary layer is undergoing investigation
from the point of view of the catastrophic release, spread, and
dispersion of cryogenic gases such as liquified natural gas and
liquified petroleum gas (Havens, 1982). This work involves dense
clouds formed by cold gases. Very little information in the
literature is associated with ambient ground sources such as che-
micals from solid waste dumps and liquid pools. The modeling
work by Springer (1979) with hydrazine spilled on airport runways
involves high chemical concentrations; however, conditions of
dispersion were chosen that overlook the effect of the presence
of a dense gas on stability and the need for wind to transport
and disperse the dense chemical vapor. A recent work by
Thibodeaux and Scott (1984) alluded to the problem areas with
transport rate prediction in the air boundary layer even for
trace contaminants. In the field, environmental transport pro-
27
-------
cess are complicated by the coexistence of mechanical and thermal
turbulence. Due to these physical effects, field-observed mass-
transfer coefficients will display a high degree of apparent ran-
dom fluctuations. The verification of the combined
mechanical/thermal model under field conditions presents a for-
midable task. Once verification has been performed for bare soil
and short grass conditions, the effects of crop canopy must be
addressed.
2.2.2 Transformation processes
Transformation processes involve the conversion of the parent
compound to any different chemical compound(s). The processes may
result in the complete degradation of the parent compound to such end
products as carbon dioxide, water, and inorganic halide ions in the
case of certain chlorinated organic compounds. The transformation
could result in the production of large molecular weight polymers for
certain reactive phenolic materials or a series of daughter products
present in different proportions. Numerous other fates could result
depending upon the material in question, the environmental conditions,
and a host of other parameters.
In this discussion, transformation processes will be treated as
biotic, which involves a biological system, or abiotic, which is
strictly a physical or chemical reaction. In certain situations one
of the processes may be dominant and, therefore, is the major degrada-
tion pathway. However, it should not be overlooked that in many real
world situations, the two processes may work in concert to determine
the ultimate fate of many chemical materials.
28
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a. Biotic transformations
Microbial degradation is an extremely important process in
the transformation of numerous organic chemicals. The bacteria,
actinomycetes, and fungi in soil, water, and sediment are the
decomposers of many organic materials. Environmental conditions
such as optimum temperature, pH, moisture, aeration, inorganic
nutrient levels, concentration of the organic material, and the
population level of the microbial community all influence the
rate of degradation for many organic chemicals. In general,
maximum degradation will occur at neutral pH values, temperatures
in the 30 C range, soil moisture levels of 0.25 to 0.35 bars,
aerobic conditions, adequate levels of N, P, and S, and con-
centrations of the organic substrate below levels toxic to the
microorganisms. For aromatic compounds, the general degradation
pathway has been summarized by Pal et al. (1977) and involves (i)
oxidation of side chains, (ii) fission of the benzene ring, and
(iii) metabolism of short chain acids to yield carbon dioxide,
water, energy, and microbial biomass.
There are many exceptions to the general guidelines, and in
most cases each chemical or mixture of chemicals must be con-
sidered on a case-by-case basis. As would be expected, the half-
lives of many of the organic materials of interest have been
shown to range from a few hours to many years in the environ-
ment.
Recently, Edgehill and Finn (1983) demonstrated that the
direct inoculation of acclimated pentachlorophenol-utilizing
-------
Arthrobacter cells to a contaminated soil increased the disap-
pearance of the chemical by a factor of 10. The half-life of
pentachlorophenol was reduced from 14 days to approximately 1 day
in both laboratory and field studies. The data also indicated
the importance of mixing the soil during inoculation to increase
the overall efficiency of degradation in the field study.
Raymond et al. (1976) also noted the importance of mixing the
soil in their study of oil degradation in soil. Such mixing
would be possible in surface application of hazardous wastes, but
in a landfill environment, a lack of mixing would result in
decreased degradation rates.
The influence of concentration of organic chemicals on their
biodegradation rate has numerous implications. Much of the
degradation research conducted on pesticides has been at levels
of 1 to 10 kg/ha rates. Boethling and Alexander (1979) concluded
that laboratory tests of decomposition at concentrations other
than what was found in the natural system may not be valid and
they showed that low concentrations may be important in limiting
biodegradation in natural waters. At the other end of the con-
centration spectrum, extremely high levels of organic and inorga-
nic chemicals are antimicrobial (Buddin, 1914) and degradation
can proceed only when the level decreases to some level tolerated
by the microbial population which degrades the material in
question.
In reviewing the effects of pesticides on microorganisms in
soil and water, Parr (1974) noted that high concentrations of
30
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chlorinated hydrocarbon insecticides could exert an inhibitory
influence on the soil microbial population. In general, the
inhibitory influence was eventually overcome and the microbial
population and activity returned to pretreatment levels. Martin
(1972) conducted extensive research on the impact of soil fungi-
cides and fumigants on soil microorganisms. Since fungicides and
fumigants are applied to the soil as antimicrobial agents, a dra-
matic impact on the microbial population is not unexpected.
Using the fumigants chloropicrin, carbon disulfide, and D-D
(dichloropropene-dichloropropane mixture), Martin (1972) reported
that there was a dramatic initial reduction in microbial numbers
which was followed by a large proliferation of microbes. He
noted that the greater the initial reduction in microbial num-
bers, the greater the subsequent peak in population. With time
periods of several months, the population returned to a level
comparable to the untreated soil. He also stated that the
nitrifying bacteria were especially sensitive to the soil fumi-
gants.
The influence of high rates of 20 pesticides on microbial
numbers and activity was reported by Stojanovic et al. (1972).
Soil amended with a pesticide rate of 11.2 metric tons/ha exhi-
bited a reduction in bacterial and fungal numbers following 56
days of incubation for such compounds as dieldrin and DDT. Ou et
al. (1978) evaluated the response of the soil microbial popula-
tion to high 2,4-D (2,4-dichlorophenoxyacetic acid) applications.
In a sandy loam soil amended with 20,000 ppm 2,4-D, the fungal,
31
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actinomycete, and bacterial populations were significantly
decreased over an 11-week study.
Recent work by Paris et al. (1981) has demonstrated the
second-order kinetics aspect of three pesticides which undergo
hydrolytic degradation. Using natural waters and low pesticide
concentrations, the researchers showed that the degradation rate
was proportional to both bacterial and xenobiotic concentrations.
It is also possible that the microbial population will alter
a given chemical such as DDT and yet the responsible microbes do
not increase in number nor is the compound utilized at a rate
sufficient to sustain microbial growth. In other words, the
microorganisms grow on one substrate while degrading a second
material. Such a degradation scheme has been termed cometabolism
and may be extremely important as the first step in degradation of
recalcitrant molecules (Alexander, 1981).
As one specific example, let us consider the microbial degra-
dation of the compound phenol. Early research by Buddin (1914)
showed that phenol concentrations of 0.94% to 9.4% (weight basis)
in soil "kept the soil life in an inactive condition" during a
75-day incubation study. At concentrations of _< 0.09%, the soil
bacterial population exhibited substantial increases in response
to the added carbon. Varga and Neujahr (1970) isolated phenol
degrading microorganisms from soil and indicated that aerobic
degradation proceeded by formation of catechol. In the presence
of oxygen, the catechol ring was cleaved to yield either suc-
cinate plus acetate or pyruvate plus acetaldehyde. In either
32
-------
case the materials readily enter established metabolic pathways
in the microbes and are used as carbon and energy sources.
Under strictly anaerobic conditions, phenol is biodegraded to
methane and carbon dioxide with 70% of the carbon converted to
gas during a 29-day study (Healy and Young, 1979). In recent
studies, Scott et al. (1982 and 1983) reported that as the phenol
concentration increased from 10~5 to 10~2 M, the lag phase
increased from _< 5 h to >^ 23 h. These results demonstrate the
antimicrobial properties of phenol. At concentrations of 10~9 to
10~6 M_ phenol, the half-life was from 2.3 to 3.7 h in two soils
studied, an indication of the relative ease of degradation at
sub-toxic concentrations.
Fannin et al. (1981) showed increased phenol degradation when
the bacterial inoculant was increased, and they reported a signi-
ficant influence on phenol degradation related to the type of
growth medium used. At high phenol concentrations, the addition
of supplemental nitrogen, phosphorus, and sulfur would be
expected to enhance the assimilative capacity of the soil, but
little work has been conducted on the topic (Overcash and Pal,
1979).
One case where the biotic-abiotic transformations appear to
overlap is that of bioconcentration. A limited number of studies
have shown that microorganisms in soil could serve as an active
sorption site of organic chemicals and can concentrate the chemi-
cals. Grimes and Morrison (1975) investigated the biocon-
centration of chlorinated hydrocarbon insecticides by thirteen
33
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soil bacteria. They observed bioaccumulation of various insec-
ticides with all the bacteria studied, and found that the degree
of bioconcentration was inversely proportional to the water solu-
bilities of the insecticides. Once sorption had occurred, the
insecticides were not easily desorbed from the bacterial cells.
They suggested that the pesticides were sorbed into the lipid
material of cells, and that desorption may not occur even after
cells died and lysed.
Paris et al. (1977) conducted bioconcentration studies of
toxaphene by soil microorganisms. They observed that cultures of
autoclaved fungi, bacteria, and algae sorbed just as much
toxaphene as viable cells of the same treatments and, thus,
suggested that bioconcentration is not an active process.
Percich and Lockwood (1978) found that mycelia of six living
actinomycete species accumulated between 900 to 4,300 yg
atrazine/g dry mycelium. Autoclaved mycelia sorbed 100 yg
atrazine/g dry mycelium during the same time. Greater variabi-
lity was observed with fungi. Living fungal mycelia bioac-
cumulated between 20 to 6,600 yg atrazine/g dry mycelium.
b. Abiotic transformations
Adsorption plays a pivotal role determining the fate of many
organic and inorganic materials in the environment (Weber and
Weed, 1974). As the given hazardous material is partitioned
between the solid and liquid, solid and gaseous, or liquid and
gaseous phases, the specific concentration available for degrada-
tion or transport is determined. As with microbial degradation,
34
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a vast amount of literature has been published related to pesti-
cide adsorption by soils and sediments in aqueous systems, but
far fewer data are available which relate to high concentrations.
Also, as was the case with microbial degradation of pesticides,
the adsorption literature was developed from the perspective of
low concentrations of organic materials in aqueous systems.
LaFleur (1973) studied the adsorption of the herbicide fluome-
turon (3-(m-trifluoromethylphenyl)l,l-dimethylurea) by soil in
solvent systems of water, ethanol, acetonitrile, dichloromethane,
and n-hexane. He noted that adsorption of fluometuron by a Cecil
B2t soil (subsoil with a clay texture) in a dichloromethane
system was linear over the concentration range of 10 to 10,000
mol/kg. As the number of adsorption sites became limiting, the
partitioning exhibited a curvilinear response. Thus, adsorption
at lower concentrations could be described by Freundlich
isotherms, but adsorption at higher concentrations was best
described by Langmuir isotherms.
Parathion adsorption by clays and lake sediments was
increased by addition of the nonionic organic dye, rhodamine B,
decreased by addition of phenol, or not influenced by methylene
blue addition (Wang et al., 1972). This was one of the few stu-
dies to use a multicomponent solution in the adsorption system.
Mills and Biggar (1969) also conducted early studies in nona-
queous systems using BHC (1,2,3,4,5,6-hexachlorocyclohexane).
They used a Ca-Staten peaty muck to study adsorption of BHC from
both aqueous and hexane solutions. The Freundlich K values at 20
35
-------
C were 330 and 0.8 for the aqueous and hexane solvents, respec-
tively. It should be noted that, in using organic sofvent systems
which extract soil organic matter, it is likely that the amount
of adsorption could be altered as well as the mechanism of
adsorption.
Limited work has been conducted in nonaqueous systems, but it
has shown that adsorption in organic solvent - soil or sediment
systems is not comparable to pesticide adsorption at low con-
centrations. However, factors such as percent clay, cation
exchange capacity, and organic matter levels appear to play
important roles in adsorption.
A second abiotic transformation is chemical degradation which
may include such reactions as hydrolysis, oxidation, and reduc-
tion. Under defined conditions, each of the three reactions have
been demonstrated.
Armstrong and Konrad (1974) have reviewed nonbiological
degradation of pesticides and noted that considerable evidence
has been published to show that sorption-catalyzed chemical
hydrolysis plays a major role in degradation of the chloro-j^-
triazines. Sorption catalyzed hydrolysis has also been shown to
be important in degradation of organophosphate insecticides.
Walker and Stojanovic (1973) reported that malathion (S_-(l,2-
dicarbethoxyethyl) -0_-(Kdimethyldi thiophosphate) was susceptible
to chemical degradation. The degradation was greatest in a clay
soil, and hydrolysis was most rapid in the alkaline pH range.
Another herbicide, dalapon or 2,2-dichloropropionate, was shown
36
-------
to undergo hydrolysis in aqueous solution to yield pyruvate and
hydrochloric acid. At a dalapon concentration of 2.4 M_, the
hydrolysis resulted in a 5.4% loss of the parent compound after
14 days at 23 C (Tanaka and Wien, 1973).
Trifluralin (a, a,a-trif luoro-2,6-dinitro-N,N,dipropyl-p-
toluidine) degradation has been shown to be a reduction reaction
which was accelerated by anaerobic conditions (Parr and Smith,
1973). Subsequent research by Willis et al. (1974) showed that
maximum trifluralin degradation in soil occurred only when the Eh
decreased below a critical range between +150 and +50 mV.
Another example of a reduction reaction in soil was reported
by Wahid et al. (1980). The insecticide parathion (0_,_0-di ethyl
0^,£ nitrophenyl phosphorothioate) was shown to be reduced to ami-
noparathion in as little as 5 sec in prereduced soils. The
reduction appeared to be mediated by heat-labile substances,
possibly enzymes, produced by soil anaerobisis.
The third abiotic transformation process which has been
described is photodegradation which involves chemical reactions
resulting from electromagnetic radiation. In general, only che-
mical compounds which absorb the sun's UV radiation above 285 nm
are expected to undergo photodecomposition (Armstrong and Konard,
1974). In the case of soils, only materials applied to or which
are transported to the soil surface are expected to be subject to
photodecomposition and such reactions have been demonstrated for
numerous pesticides and have been reviewed by Plimmer (1970).
One specific example for monuron (3-(£-chlorophenyl)-l,l-dimethyl-
37
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urea) was reported by Crosby and Tang (1969). They show that
photodecomposition of monuron in an aqueous system exposed to
sunlight followed a stepwise photo-oxidation and demethylation of
the N^methyl groups, hydroxylation of the aromatic portion of the
molecule, and subsequent polymerization. Crosby and Wong (1977)
studied the photodegradation of TCDD (2,3,7,8-tetrachlorodibenzo-
£-dioxin) on inert surfaces, plants, and soils. They reported
almost total disappearance of TCDD when exposed to 6 h of natural
sunlight if the dioxin was dissolved in a light-transmitting film
and an organic hydrogen-donor such as a solvent was present.
These results could have important implications related to photo-
degradation of chemical contaminants in binary solvent systems on
soil surfaces.
An additional abiotic transformation process which has been
studied involves catalytic polymerization of phenolic compounds
on clay surfaces. Wang et al. (1978a, 1978b) tested three clay
minerals and solutions of various phenolic compounds and
demonstrated that oxidative polymerization occurred which
resulted in the formation of dark colored organomineral
complexes. The catalytic activity was in the order illite (2:2)
> montmorillonite (2:1) > kaolinite (1:1) and was also related to
the Fe and Al content of the materials tested. The polymeric
material resembled soil humic and fulvic acid with regard to
several chemical properties. Subsequent work showed that, as the
pH of the phenolic solution was increased to 8.5 in the presence
of illite, the polymerization rate increased due to increased
38
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free radical formation and greater autooxidation. Solomon et al.
(1968) also reported the role of clay minerals in oxidation by
showing that benzidine was changed to benzidine blue at aluminum
atoms exposed at the edges of the clay. Pinnavaia et al. (1974)
used the mineral hectorite and the aromatic compound toluene to
demonstrate the formation of a toluene radical cation and sub-
sequent polymer formation.
2.3 Aquatic Ecosystems
2.3.1. Transport processes
The literature does not contain very much information on the
study of transport processes in aquatic ecosystems wititi emphasis
on high chemical concentrations. Incidences related to trans-
portation accidents and inadvertent releases from manufacturing
sites account for the placement of high concentrations of
lighter-than-water (floaters) and heavier-than-water (sinkers)
chemical substances in aquatic ecosystems. Specifically, some of
these incidences are oil slicks on river and lakes fram tanker
accidents, bottom contamination involving chloroform from a river
barge accident, bottom contamination involving carbon tetra-
chloride from an inadvertent episodic release to a river, and
bottom contamination involving creosote waste discharged con-
tinuously over a long period of time. Fig. 2-2 depicts five
locations in the aquatic environment where chemical transport
processes are important. The labeled locations are a) bottom
sediment, b) bottom water, c) water column, d) surface water, and
e) boundary layer.
39
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Wind Direction
Contaminant
Boundary Layer
Surface
Water
AIR
Bottom Sediment
Figure 2-2
Five locations in the aquatic environment where
transport processes are important.
40
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Very little is known about transport in the stream-bed sedi-
ment region. This zone of the aquatic ecosystem is the recipient
of wastes of high chemical concentration, particularly near and
on manufacturing sites. Sinker chemicals, those with a density
greater than water, enter streams and go immediately to the bot-
tom. Once on the bottom a pool, consisting of a separate phase,
forms in the low depression. Under such conditions, an apparent
physical inflow of an organic chemical substance into the porous
bottom sediment can occur because of the increased static gra-
dient of the dense chemical, attraction for the natural organic
material in the bed sediment, and coverage by the natural sedi-
ment transport processes. A specific case is the downward per-
culation of ethylene dichloride from a plant site stream bed to a
position 50 feet below the surface. No technical information is
available to describe the transport mechanisms of chemicals
involved in such occurrences. Ashworth (1982) performed some
laboratory simulation experiments with carbon tetrachloride on
sand, coarse gravel, and compacted mud. No penetration was
observed in the sand, but some did occur in the gravel and in the
mud.
Some aspects of the behavior and transport of chemicals on
the stream bed surface have been studied and reported.
Thibodeaux (1977) and Christy and Thibodeaux (1982) reported on
studies of the spill of soluble, high density, immiscible chemi-
cals on water. Qualitative aspects of the behavior of this class
of sinker chemicals was studied in aquatic system simulators.
41
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Mechanisms observed were jet break-up, rapid settling of pure
chemical droplets through the water column, and coalescence into
globs and pools on the bottom. Quantitative aspects, including
the bottom water transport coefficient in model flowing streams,
were measured and correlated to stream parameters of water velo-
city, water depth, sand wave depth and sand grain size
(Thibodeaux, Chang, and Lewis, 1980). The important physical
parameters for transport rates in the bottom water of unstra-
tified lakes and surface impoundments are wind speed, water
depth, and water fetch (i.e. the distance wind travels over
water) (Thibodeaux and Becker, 1982). Wafers of pure benzoic
acid placed on the bottom surface were used to measure transport
rates.
Theoretically, high chemical concentration layers, made up of
an aqueous solution or made of a pure organic phase of density
near unity, can form near the thermocline of lakes or the pyc-
nocline in the ocean. Sewage and industrial effluents have been
observed in stratified waterbodies occupying positions in the
water column near the pycnocline. Information relating to chemi-
cal transport processes of such layers was not found.
Oil and "floater" chemical slicks on the surface of water is
a well-documented phenomena, and there is much information in the
literature concerning spreading, dispersion, and transport pro-
cesses. In some respects the air boundary layer above the sur-
face of water is not unlike that above the soil. This is
particularly true under low wind conditions when wave action is
42
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at a minimum. The work by Havens (1982) involving the catastro-
pic release, spread, and dispersion of cryogenic gases also
involves the air boundary layer above water. This work and
related ongoing research by the U.S. Coast Guard and the British
Coast Guard research organizations comprise the literature
available on this condition (Havens, 1982).
2.3.2 Transformation processes
Many of the biotic and abiotic transformation processes
applicable to an aquatic ecosystem have been previously discussed
in section 2.2.2. However, the sediment with the highly reducing
conditions below the water-sediment interface presents a dif-
ferent environment where aerobic degradation will not occur, and
thus, the degradation rate will generally be much slower.
43
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3.0 SCENARIO OF HYPOTHETICAL CONTAMINANT CASES
A scenario analysis of two hypothetical contaminant cases was
undertaken. One involved a binary solvent system (aqueous and non-
polar organic) and the other a tertiary solvent system. Each of these
solvent systems was applied to a terrestrial and an aquatic high che-
mical concentration contamination scenario, respectively.
Given that the systems are known, the purpose of the scenario
analysis is to assess the impact of these solvents on such soil and/or
water properties/parameters as acidity, hydrophobicity, thixotrophy,
diffusivity, sorption, ion-exchange, porosity, permeability, biologi-
cal activity, transformation reactions (chemical and biochemical), and
their kinetics, volatilization, and mass-transport processes (both
mass flow and diffusion). The result of this exercise will highlight
to what extent the present state of knowledge in bacteriology, che-
mistry, engineering, physics, and soil science allows prediction of
the above property/parameter/process of the affected soil and water.
This project appears to collect data to substantiate the obvious.
Concentrations of chemicals in the range to be investigated will cer-
tainly have catastrophic effects on the characteristics of any eco-
system. The relevant questions are how can such concentrations be
kept from spreading to other ecosystems and how can they be best
controlled within or dispelled from the ecosystem. Although this
project will contribute very little toward that goal, a prerequisite to
successful disposal of hazardous wastes is to assess the state-of-the-
art of general knowledge about chemicals in the environment, par-
ticularly from the point of view of predictability in the ecosystems.
44
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True predictability, based on first principles, implies that we
understand and can quantify all the relevant properties/parameters/
processes. Questions of whether to spread, clean-up, or leave in-
place, can then be addressed, and results of the simulation models can
be applied with confidence. In this light, a scenario analysis can
give some indication of the capability for prediction.
3.1 Terrestrial Ecosystems
Scenario: Metal drums of organic liquids were placed in a sani-
tary landfill approximately 20 years ago. The waste was co-disposed
with municipal waste consisting mostly of waste paper and other cellu-
losic material. The cell was constructed in such a way that the waste
was buried under 6 m of overfill (subsoil) and other wastes. The
landfill was capped with 50 cm of clay and 50 cm of surface soil.
Evidence has accumulated to indicate that the waste has been released
from the drums and exists as free liquid in the cell. Some rainwater
has entered the cell so that a two-phase liquid system is assumed to
exist in the bottom of the cell. The bottom of the cell is 5 m above
groundwater.
This terrestrial ecosystem contamination scenario provides the
framework for considering the fate of chemicals moving upward to the
atmosphere, downward to the groundwater, and in the lateral direction.
The hypothetic binary solvent system consists of water and 1,2-dichlo-
roethane. The tertiary solvent system consists of water, benzene, and
phenol.
45
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3.1.1. Binary solvent system
The fate of 1,2-dichloroethane (EDO in the environment wii.h
respect to conditions of low concentrations has been addresse.-J
(Callahan, 1979). As is typical of current fate analyses, the
specific topics of interest are photolysis, oxidation, reduction,
hydrolysis, volatilization, sorption, bioaccumulation, and
biodegradation. The implied scenario in these conventional fate
studies calls for extremely dilute solutions with the source of
chemical contaminant located some distance removed from the !~
site (i.e., far-field). In contrast, the present scenario
for high concentrations with the source of chemical contaminant
located at or very near the study site (i.e., near-field). TabU
3-1 lists pertinent physical/chemical properties of EDC and otic.'!
substances.
A study of the properties of pure EDC indicates that, viien
is released from the metal drum, the pure liquid, with specific
gravity of 1.253, will have a tendency to percolate downward,
Gravitational acceleration will force the liquid through the
other (porous) waste materials and onto the bottom of the land-
fill cell. If water has accumulated in the bottom section, 3DC
will continue to move down and eventually come to a temporary
halt. The continual arrival of EDC from the corroding drur^. wi'i
form a pool of nearly pure liquid in the lower portions of Ihe
cell and under the water layer.
The migration downward does not stop here but continue-.
Being 25.3% heavier than water the apparent "hydraulic" hev) c?n
46
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Table 3-1. Physical and chemical properties of scenario substances
(Callahan, 1979; Dean, 1979; Perry and Chilton, 1973).
1,2-dichloro- naphtha- penta-
benzene ethane phenol lene chlorophenol
Formula C^s 02^012 Cs^ON CigHg CsClsOH
Molecular weight 78.12 98.98 94.11 128.16 66.35
Melting point ( C) 5.5 -35.4 40.9 80.6 190.0
Boiling point ( C) 80.1 83.5 182.0 218.0 10.0
Vapor pressure
(torr) at T C
95.2/25 61/20 0.529/20 0.0492/20 0.00011/20
Solubility in water,
(mg/L) at T C 1780/25 8690/20 93,000/25 34.4/25 14/20
Log (octanol/water)
partition coeffi-
cient
1.48
1.46
3.37
5.01
State at 15 C and
1 atm. liquid liquid
solid/ solid solid
liquid
Specific gravity
at T C 0.879/20 1.253/20 1.058/41 1.145/20 1.98/15
Liquid surface
tension, (N/m) at
T C 0.0289/20 0.0322/20 0.0365/55 0.02/80
Liquid water
interfacial tension
(N/m) at T C 0.035/20 0.03/25 0.02/42 0.05/80
Latent heat of vapor-
ization, (J/kg) 3.94E5 3.2E5 3.0E5
3.38E5
47
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force fluid through the liner (if it exists) and into the vadose
zone of the subsoil. The EDC will enter the groundwater and
continue to move until it encounters a rock formation or strata
with very low permeability. At this point coalescence again
occurs and pure pockets of EDC form on top of these strata.
Figure 3-1 maps the gross features of the downward percolation of
EDC.
a. Chemical properties and concentrations
Solubility - Mutual solubilities (e.g., EDC in water and
water in EDC) can likely be obtained from the literature.
Models are available to estimate mutual solubilities as a
function of temperature.
Vapor pressure - The vapor pressure of EDC has been measured
and models are available to estimate the vapor pressure as a
function of temperature.
Sorption on cellulosic material - As EDC percolates through
the waste in the lower cell, it will be sorbed by the cellu-
lose in such materials as the waste paper and vegetable cut-
tings. Neither the extent of this sorption in g EDC/g
cellulose nor the vapor pressure of EDC in the resulting mix-
ture can be estimated at present.
b. Soil properties
Porosity - The soil porosity that results after a wave of
pure EDC has passed cannot be estimated at this time. It is
possible that EDC may change the porosity of the soil matrix.
A general indication could be made if the extent of sorption
48
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Wind Direction
Z.one-1
Zone-2
Cap liner
Surface soil
EDC drum disposal cell
Vapor transport pathway
Pure EDC percolation pathway
Partition between cells
Solid waste, garbage cell
\
Standing water level in cell
Pool of pure EDC
Landfill under-liner
Un-saturated sub-soil zone
Groundwater level
Pockets of pure EDC
Saturated sub-soil zone
Top of very low
permeability formation
Figure 3-1
EDC migration from a landfill.
49
-------
were known.
Sorption - The normal partition coefficient is not applicable
where a surface soil or subsoil is exposed to a pure fluid
phase such as EDC. The traditional partition coefficient is
defined as the concentration of contaminant on the soil
divided by its concentration in the soil-water. In this case
there is no soil-water but instead there is pure EDC. A few
measurements of sorption on soils with pure substances have
been made. Jurinak and Volman (1957) sorbed ethylene dibro-
mide onto soil from the vapor phase and reported a value of
up to 0.12 g/100 g. Sims and Overcash (1983) report values
for the adsorption of benzene on smectite (Wyoming
montmorillonite) as a function of organophillie cation and
water content. Competition between water and the aromatic
molecules has the most obvious effect on the adsorption of
benzene. Benzene adsorbed (no water) ranged fom 13.8 to 22.6
g/100 g. No general principles are available, other than to
assume a Langmuir adsorption and compute the quantity for one
monolayer coverage based on knowing the surface area.
Ion-exchange - not applicable.
Solvation - The possible alteration of the clay fractions of
the soil due to irreversible sorption of EDC at interlayers
of crystal structure is not predictable at this time.
Organic matter - Since the EDC is in contact with soil
material that is either a subsoil (B horizon) or parent
material (C horizon) the amount of organic matter solubilized
50
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would be low since the level of soil organic matter is low.
However, it would be expected that a portion of the organic
material in the codisposed waste could be extracted and,
moving with the EDC, could facilitate mobility of metal che-
lates if they were present in the waste.
Microbial Population - The high EDC concentration would most
likely result in the death of the limited microbial popula-
tion present in the lower part of the landfill. The micro-
bial population normally present in the subsoil would be very
low. Only when the concentration decreased to subtoxic
levels would the microbial population be expected to
reestablish following introduction of microbes from non-
fumigated areas.
c. Transport properties
Diffusivity - Molecular diffusion is an important
transport process for EDC in the air and liquid filled spaces
of the landfill. Molecular diffusivity estimation techniques
of chemical species in gas and liquid mixtures are well deve-
loped, particularly for substances with low molecular weight
(Reid, Prausnitz, and Sherwood, 1977). Reliable estimates
involving large complex molecules such as dieldrin (1,2,3,4,
10,10-hexachloro-exo-6,7-epoxy-l,4,4a,5,6,7,8,8a-octa-hydro-
l,4-endo-exo-5,8-dimethanonaphthalene). heptachlor (1,4,5,6,
7,8,8-heptahcloro-3a,4,7,7a-tetrahydro-4,7-methanoindene),
2,3,7,8-TCDD, and others are crudely developed and untested.
A recent field study by Glotfelty, Taylor and Zoller (1983)
51
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points out the uncertainty of molecular properties on dif-
fusivity and dispersion into the atmosphere. For EDC in both
the gas-filled pore spaces and the liquid-filled (i.e.,
water, EDC mixture) pore spaces, the current estimating
methods should yield reliable .values.
Permeability - The permeability of landfill generated liquids
through soil liners is receiving considerable research atten-
tion (Acar et al., 1984; Brown and Anderson, 1980). The per-
meability of soils to chemical vapors is receiving very
little attention (Springer and Thibodeaux, 1982). The per-
meability of soil to pure EDC, EDC-water mixture, and EDC
vapor is unknown, and no methods are available to obtain an
estimate.
Capillary rise - Liquids are forced to the soil surface or
nearer to the soil surface by capillary rise. A granular
material (sand or grit with acceptably low silt content) is
necessary to allow the drainage of the overlying soil and
also to reduce to an acceptable level the capillary movement
of water-soluble pollutants up the soil column (Cairney,
1982). The role of capillary rise in moving EDC to the sur-
face cannot be assessed at this time.
Viscosity - The viscosity is an important transport property
due to the dependence of permeability on fluid viscosity.
There are reliable methods for estimating viscosities of mix-
tures such as EDC and water.
Model Concepts - The models currently proposed for the pre-
52
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diction of transport of pollutants are inadequate jfor high
chemical concentration situations because they were developed
for situations where the pollutant is present in con-
centrations in the ppm or ppb range. This includes transport
in both the fluid-water phase and the vapor-air phases. The
current models arise from studies with dilute solutions. For
water-diluted pollutant transport it is possible to piggy-
back the pollutant model on the hydraulic (Darcy's law)
aquifer model because the presence of the pollutant inter-
feres insignificantly with hydraulics. The retardation fac-
tor approach (Letey and Farmer, 1974), another feature of
dilute solutions models, is completely inadequate if a pure
organic phase is present in the aquifer. The reliability of
present-day models to predict the fate of EDC in zone 7 of
Fig. 3-1 is extremely poor. Vapor phase transport models for
zones 1, 2, 3, and 6 are also at a very crude state of deve-
lopment. Current models are inadequate for making reliable
predictions of the movement of EDC from the landfill source
to the air or water ecosystems.
d. Transformation processes
Microbial degradation of the EDC and the remaining cellu-
losic material in the landfill would most likely be an extre-
mely slow process. In the landfill environment anaerobic
conditions would result in fermentation metabolic pathways
which are well defined for such materials as cellulose.
However, a deficiency of nitrogen, phosphorus, and sulfur
53
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would drastically reduce microbial activity and, thereby
retard degradation. Other factors which would inhibit cellu-
lose decomposition would include low soil temperatures, acid
pH levels, and an inherently low microbial population.
Van Engers (1978) studied the anaerobic mineralization of
an organic leachate from a waste disposal site in Holland.
He reported that highly reduced conditions existed under the
disposal site where redox potentials were less than -120 mV.
The low redox values were conducive to anaerobic microbial
activity, and he demonstrated that both sulfate reduction and
methane production occurred with the quantity of methane plus
carbon dioxide produced equal to 10 yl/g wet soil/h in a
laboratory experiment.
The presence of high levels of EDC would most likely
result in an antimicrobial influence and thus eliminate the
already highly stressed microbial population. As the con-
centration of EDC decreased to subtoxic levels by the various
transport avenues, the population could be reestablished, but
activity levels would be very low. In general, the microbes
will utilize the most available carbon substrate first which
should translate as a preferential utilization of cellulose
within the limits of nutrient deficiency and other stresses
imposed. No data were located which were directly applicable
to the given circumstances.
Bioconcentration would not be expected to be of signifi-
cance in the system.
54
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Abiotic transformations in the system are even more dif-
ficult to predict. Sorption on the cellulosic waste would be
an important consideration, but data are not currently
available to allow assessment of its magnitude. Adsorption
related to soil organic matter or cation exchange would not
be expected to be significant. Chemical degradation for a
stable compound like EDC would not be expected; however, no
data are available to support such a statement. Sorption-
catalyzed hydrolysis of atrazine in an acid environment has
been demonstrated to be very important (Armstrong and Konrad,
1974). Hydrolysis of 2,2-dichloropropionate at high con-
centrations has also been shown to occur (Tanaka and Wien,
1973).
With the current information, it is not possible to eva-
luate the importance of photodegradation of the EDC vapor
over the landfill. Polymerization reactions would be un-
likely.
In general terms, transformation reactions would be very
limited in the hypothesized environment. However, the basis
for such a statement is mainly supposition, and few data are
available which are directly applicable to the case in point.
The vast majority of the decomposition studies conducted have
been under conditions to optimize microbial activity, and the
system defined here represents the other end of the spectrum.
55
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3.1.2. Tertiary solvent system
It will be assumed that benzene and phenol are present in the
bottom of the landfill cell in proportions of 5% benzene, 5% phe-
nol and 90% (weight) water. A study of the properties of the
chemicals in Table 3-1 suggests a behavior pattern different from
that of EDC. Although a two-phase system, consisting of organic
and aqueous, will likely exist, the organic phase will float
since the combined density will be less than unity. Fig. 3-2
shows the expected migration pathways.
The organic liquid mixture percolates through zone 2 and 3
and halts at the standing water level in zone 4. As long as
water is present in the bottom of the cell to float the organic
phase it will not contact the liner. Water moving through will
dissolve some of the benzene and phenol from the organic layer.
This leachate can then move through the bottom liner and toward
the groundwater. Once arriving at the groundwater, a floating,
low density leachate plume will form and ride atop the ground-
water aquifer. Other transport processes are occurring and will
be considered in detail below.
a. Chemical properties and concentrations
Solubility - Mutual solubilities of the three component
system in the aqueous and organic phases can likely be esti-
mated using existing methods. The maximum concentrations of
benzene and phenol in the zone 4 water will be roughly
approximated by the solubilities in Table 3-1.
Vapor pressure - The partial pressures of benzene and phenol
56
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Wind Direction
Air
Zone-1
Zone-2
Zone-3
Zone-4
Zone-5
Zone-6
Zone-7
Cap liner
Surface soil
Drum disposal cell
Vapor transport pathway
Chemical percolation pathway
Solid waste, garbage cell
Floating "pool" of organic chemical
Standing water level
Landfill under-liner
Leachate pathway
Un-saturated sub-soil zone
Groundwater level
Floating leachate plume
Top of very low
permeability formation
Figure 3-2
Benzene-phenol mixture migration from a landfill.
57
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associated with the organic and aqueous phases can likely be
estimated using existing methods. The partial pressures of
the two organics can roughly be approximated by Raoult's law,
although better procedures using activity coefficients are
readily available.
Sorption on cellulosic material - As the organic phase per-
colates through other landfill materials, fractions will be
sorbed. Just as with EDC in the binary solvent, a "trail" of
contaminated waste solid/eellulosic material will be left
behind as the benzene/phenol mixture moves downward from
cell-to-cell. The extent and nature of this sorption process
and the residual vapor pressures cannot be estimated at pre-
sent.
Porosity - The soil porosity that results after a wave of
a benzene/phenol mixture has passed cannot be estimated at
this time. A general indication could be made if the extent
of sorption were known.
Sorption - The normal partition coefficient is not applicable
where a surface soil or subsoil is exposed to a pure fluid
phase. The traditional partition coefficient is defined as
the concentration of the pollutant on the soil divided by its
concentration in the soil-water. A few measurements of sorp-
tion on soils with pure substances have been made. Jurinak
and Volman (1957) sorbed ethylene dibromide onto soil from
the vapor phase and reported a value of up to 0.12 g/100 g.
Sims and Overcash (1983) report values for the adsorption of
58
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benzene on smectite (Wyoming montmorillonite) as a function
of organophillic cation and water content. Competition bet-
ween water and the aromatic molecules has the most obvious
effect on the adsorption of benzene. Benzene adsorbed (no
water) ranged fom 13.8 to 22.6 g/100 g. No general prin-
ciples are available, other than to assume a Langmuir adsorp-
tion and compute the quantity for one monolayer coverage
based on knowing the surface area.
It should be noted that benzene sorption on organo-
modified surfaces due to the presence of the organophillic
cations may be similar to sorption on organic matter.
Ion-exchange - not applicable.
Solvation - The possible alteration of the clay fractions of
the soil due to irreversible sorption of the organic com-
pounds at interlayers of crystal structure is not predictable
at this time.
Organic Matter - Since the benzene/phenol is in contact with
soil material that is either a subsoil (B horizon) or parent
material (C horizon), the amount of organic matter solubi-
lized would be low since the level of soil organic matter is
low. However, it would be expected that a portion of organic
material in the codisposed waste could be extracted and,
moving with the organic material, could facilitate mobility of
metal chelates if they were present in the waste.
Microbial Population - The high organic chemical con-
centration would most likely result in the death of the
59
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limited microbial population present in the lower .part of the
landfill. Only when the concentration decreased to subtoxic
levels would the microbial population be expected to
reestablish following introduction of microbes from non-
fumigated areas.
c. Transport properties
Diffusivity - Molecular diffusion is an important
transport process for benzene/phenol in the air and liquid
filled spaces of the landfill. Molecular diffusivity estima-
tion techniques of chemical species in gas and liquid mix-
tures are well developed, particularly for substances with low
molecular weight. Reliable estimates involving large complex
molecules such as dieldrin, heptachlor, 2,3,7,8-TCDD, and
others are crudely developed and untested. A recent field
study by Glotfelty, Taylor and Zoller (1983) points out the
uncertainty of molecular properties on diffusivity and
dispersion into the atmosphere. For benzene/phenol in both
the gas-filled pore spaces and the liquid-filled (i.e.,
water, mixture) pore spaces, the current estimating methods
should yield reliable values.
Permeability - The area of permeability of landfill generated
liquids is receiving considerable research attention. The
permeability of soils to chemical vapors is receiving very
little attention (Springer and Thibodeaux, 1982). The per-
meability of soil to the benzene/phenol mixture, benzene/
phenol-water mixture, and benzene/phenol vapor is unknown and
60
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no methods are available to obtain an estimate.
Capillary rise - Liquids are forced to the soil surface or
nearer to the soil surface by capillary rise. A granular
material (sand or grit with acceptably low silt content) is
necessary to allow the drainage of the overlying soil and
also to reduce to an acceptable level the capillary movement
of water-soluble pollutants up the soil column (Cairney,
1982). The role of capillary rise in moving the
benzene/phenol mixture to the surface cannot be assessed at
this time.
Viscosity - The viscosity is an important transport property
due to the dependence of permeability on fluid viscosity.
There are reliable methods for estimating viscosities of mix-
tures such as benzene/phenol and water.
Model Concepts - The models currently proposed for the pre-
diction of transport of pollutants are inadequate for high
chemical concentration situations because they were developed
for situations where the pollutant is present in con-
centrations in the ppm or ppb range. This includes
transport in both the fluid-water phase and the vapor-air
phases. The current models arise from studies with dilute
solutions. For water-diluted pollutant transport it is
possible to piggy-back the pollutant model on the hydraulic
(Darcy's law) aquifer model because the presence of the
pollutant interferes insignificantly with hydraulics. The
retardation factor approach, another feature of dilute solu-
61
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tions models, is completely inadequate if a pure organic
phase is present in the aquifer. The reliability of present-
day models to predict the fate of the benzene/phenol mixture
in zone 7 of Fig. 3-2 is extremely poor. Vapor phase
transport models for zones 1, 2, 3, and 6 are also at a very
crude state of development. Current models are adequate for
making reliable predictions of the movement of benzene/phenol
mixture from the landfill source to the air or water eco-
systems.
c. Transport properties
Model concepts - In general the same comments apply as made
for the binary solvent. For this particular scenario the
current generation of groundwater pollutant transport models
cannot handle: a) in situ leaching of components from the
floating organic layer atop the standing water in zone 4; b)
the dispersion and displacement behavior of the floating
leachate plume that rides atop groundwater in zone 7.
tf
d. Transformation processes
Microbial degradation of phenol at high concentrations
would not occur because phenol is a potent antimicrobial
agent (Buddin, 1914). As the concentration decreased to
levels suitable for microbial activity, degradation under
anaerobic conditions could occur given suitable environmental
conditions and microbial population levels to result in the
formation of methane (Healy and Young, 1979). If aerobic
conditions existed at low phenol concentrations, degradation
62
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would be rapid (Scott et al., 1983).
Benzene degradation would be limited by the lack of oxy-
gen which would be necessary for the initial hydroxylation
reaction and, thus, given the additional environmental
stresses, would most likely be resistant to degradation.
Cellulose would most likely be the preferred substrate by
any microbial population that did become established as was
the case in the previous situation. Bioconcentration would
not be an important factor.
Sorption of phenol has been studied at levels of 10"^ M_
by Scott et al. (1982) and was shown to be very low and
related to organic matter levels in soil. However, soil
adsorption would not be expected to play a major role in
retention of phenol nor benzene.
If the phenol or benzene was oxidized to catechol under
partially aerobic conditions, then it is possible that clay
surface catalyzed polymerization of the material would occur
(Wang et al., 1978a, 1978b). The polymerization would result
in the formation of a dark colored complex material which
would have some properties similar to soil organic matter and
would be resistant to further degradation.
Other abiotic transformations would be expected to be
limited in importance. Again, it should be stated that few
data exist which apply directly to the defined system, but
the above represents a plausible scenario of events all of
which need further research data to validate.
63
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3.2 Aquatic Ecosystems
Scenario: Due to the existence and operation of a creosote plant
over a 20-year period, a nearby stream has received excessive waste
sludge discharges. It appears that the streambed sediment for
approximately 16 kilometers (10 miles) downstream is heavily con-
taminated with creosote sludge. Levels of up to 15% creosote have
been measured in the bottom sediment. The stream has a very slow rate
of flow (South Louisiana bayou) and the layer of contaminated sediment
is roughly 20 cm deep. Creosote odors can be detected coming from the
surface of the water at times of atmospheric inversions and low wind
speed. Creosote is an oily liquid obtained from the destructive
distillation of wood-tar. It will be assumed that the make-up of the
waste is 5% naphthalene (NPH), 5% pentachlorophenol (PCP) and 5% of
mixed organic material with properties similar to those of NPH and
PCP- Fig. 3-3 shows general features of the contamination scenario.
This aquatic ecosystem contamination scenario provides the frame-
work for considering the movement of chemicals upward to and through
the water column to the atmosphere and downward to the groundwater.
The binary solvent system will consist of water and naphthalene. The
tertiary solvent system will consist of water, naphthalene, and pen-
tachlorophenol .
3.2.1. Binary solvent system
The summary of fate data for NPH with respect to conditions
of low concentrations has been addressed (Callahan, 1979).
As is typical of current fate analysis, the specific topics of
interest are photolysis, oxidation, hydrolysis, volatilization,
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AIR
—*^.
WATER
Pathway by Movement on
Participate Matter
CTl
c_n
SEDIMENT
Air-Water Interface
Water Column
NPH & POP Pathways from
Bottom Sediment to Air
Sediment-Water Interface
Containment Layer
Pathway to Groundwater
Figure 3-3
Creosote Mixture in a Streambed.
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sorption, bioaccumulation, and biodegradation. The implied sce-
nario in these conventional fate studies calls for extremely
dilute solutions and far-field existence of the chemical. In
contrast, the present scenario calls for high concentrations and
near-field existence. Table 3-1 lists pertinent
physical/chemical properties of NPH and PCP-
A review of the properties of NPH in Table 3-1 suggests some
behavioral aspects. Naphthalene is a solid at the stream bottom-
sediment temperature, and due to its density it will not float to
the surface in bulk but will remain in place. The solubility in
water is low but finite so that dissolution is a likely mode for
transport from the sediment. Fig. 3-3 indicates that, once NPH
leaves the sediment, it can enter the water column and then the
air, and it can also enter the groundwater.
a. Chemical properties and concentration
Solubility - Mutual solubilities (e.g., NPH in water and
water in NPH) can likely be obtained according to the litera-
ture. Models are available to estimate the solubility of
pure NPH in water as a function of temperature.
Vapor pressure - The vapor pressure of NPH has been measured,
and models are available to estimate the vapor pressure as a
function of temperature.
Sorption on sediment material - Naphthalene readily adsorbs
onto the sediment. Its association here is likely with the
clay organic matter fines. The dilute solution calculated
Koc is 600 which suggests the sediment will attract and hold
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a sizable fraction of NPH compared to the pore-water. Since
correlations for Koc are typically related to solubility,
molecular weight, and melting point and are based upon data
obtained under dilute solution conditions, it is doubtful
that such correlations are applicable to sediment which con-
tains 50,000 mg/kg of NPH and another 50,000 mg/kg of other
organic material. Since pure NPH is present, the use of a
Koc is highly doubtful.
b. Water and sediment properties
Porosity - The effect of 50,000 mg/kg of NPH upon the
porosity of the natural bottom sediment is unknown. In
effect, this is 5% of the mass of the on-bottom material so
that it is a dominant constituent.
Sorption - see sorption on sediment material section in part
a. above.
Ion-exchange - Its role in this situation is likely not impor-
tant.
Solvation - Since NPH is a solid, it is unlikely that com-
ponents of the soil will be affected. The solubility of NPH
in pore-water is fairly low, and no effect from NPH is
expected at this low level, but the NPH is 5% of the sediment
phase and much uncertainty exists on solvation processes.
c. Transport properties
Diffusivity - Molecular diffusion is an important
transport process for NPH in the air, water, and liquid-
filled pore spaces of the bottom sediment. Current available
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estimating techniques should be reliable for the molecular
diffusivity of NPH in air and water. For exceptions see sec-
tion 3.1.1c.
Permeability - The gross features of permeability in bottom
sediment is fairly well understood. This statement is more
applicable to lake ecosystems than to river ecosystems mainly
because of the lack of a substantial water movement in the
lake and the uniformity of the sediment. The spatial
variation in the permeability of the various upper layers in
river bottom sediment is unknown for the most part. The bulk
of the NPH is located in these upper layers. Due to sediment
transport and bottom sand-wave forms, the upper layers of
bottom sediment can enjoy a relatively high trickle-flow of
water. Lower layers are more fully protected from the action
of the flowing water and are usually more dense. Since per-
meability controls water movement in this region its impor-
tance with respect to chemical transport is dominant in
particular for high concentrations of chemical in this
region. At this time it is not possible to estimate the per-
meability of the NPH-contaminated sediment layer.
Viscosity - The viscosity of water may be affected slightly
by the presence of NPH in solution. This is not thought to
be an important consideration.
Transport phenomena in sediment - Diffusion transport of ions
and some small organic molecules in ocean bottom sediment has
received considerable attention. It appears that the pheno-
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mena of hindered diffusion, as described by the retardation
factor, is applicable to transport of organics such as NPH in
bottom sediment provided the solution is dilute. Whether or
not the retardation factor approach is appropriate at high
concentrations is a question that needs to be investigated.
The question, as pointed out in previous sections, revolves
around the appropriate model concepts for adsorption onto the
sediment phase.
The transport phenomena in the upper sediment layer are
complicated because the process is not entirely controlled by
diffusion. This layer is highly permeable, and significant
water flow occurs so that convective transport is present.
The relative roles of both convective and diffusive transport
in the upper layers of sediment in river ecosystems is in a
crude state of development. There is no clear means of esti-
mating NPH transport out of the 20-cm contaminated layer.
Transport phenomena in the water column - As the chemical
leaves the sediment in the upward direction, it does so by
dissolution and by bed scour processes. The dissolution
involves molecular transport through the water-side boundary
layer followed by transport through the water column (both
stratified and non-stratified conditions) and then through
the air-water interface. A few studies have been conducted
on chemical transport in these various zones but none with
high chemical concentrations. Transport across the air-water
interface region seems to be well understood, and many data
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and models are available to quantify these transport parame-
ters. The scour-settling-resuspension transport processes
seem to be in a very crude state of development. Measurement
has been attempted, but the level of development is very low.
Detailed observations and studies involving high chemical
concentrations are needed. High chemical concentrations,
particular chemicals with high solubility, can cause strati-
fication of a water column (not unlike thermal stratification
of lakes) that can inhibit transport. There is no infor-
mation on this aspect in aquatic ecosystems. In summary, the
transport phenomena of NPH from the sediment water interface
upward in the water column are not understood to such an
extent that reliable predictions can be made.
Transport phenomena to groundwater - In general the phenomena
involved here are identical to those in transport to ground-
water covered in section 3.1.I.e. Since the solubility of
NPH is essentially in the dilute range, prediction of the
rate of movement downward can be performed within the range
of reliability of existing groundwater transport models
(Enfield et al., 1980).
d. Transformation processes
Microbial degradation of NPH under aerobic conditions
proceeds by hydroxylation and subsequent ring cleavage. As
in the previous examples, high NPH concentration and limiting
conditions for microbial activity would suggest a slow degra-
dation rate of the material.
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3.2.2 Tertiary solvent system
This system consists of water, naphthalene, and pentachloro-
phenol. A study of the properties of the chemicals in Table 3-1
suggests no behavior grossly different from those of the binary
solvent system.
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4.0 RESEARCH RECOMMENDATIONS
The preceding section makes obvious informational gaps that exist
in our understanding of the impact of high concentrations of hazardous
wastes on the environment. The vast majority of earlier research was
conducted in aqueous systems at low chemical concentrations, and the
present work is concerned with high chemical concentrations in systems
that include non-aqueous conditions.
At a given point in time and space, we can, for the most part,
determine how much concentration of a substance is initially deposited
into a terrestrial or an aquatic medium. The gaps in present-day data
occur in relation to our knowledge of transport through the medium and
throughout the ecosystem and transformation processes that alter the
original substance. Understanding transport and transformation is
complexed by the myriad variables which can exist in the medium and
the ecosystem and by differences in the contaminants which can result
from mixed deposits where multiple contaminants may interact. The
impact of high waste concentrations on transport and transformation
processes relate to 1) physical properties of the porous medium, 2)
chemical properties of the porous medium, and 3) microbiological pro-
perties of the system.
Consequently, our research recommendations are proposed to bridge
the gaps in information to date and to compile data on which to base
calculations, predictions, and more specific research investigations
in the future. The following recommendations are categorized under 1)
transport processes in saturated soils, unsaturated soils, the fluid
side of earthen interfaces; 2) equilibrium processes in air-soil sorp-
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tion or water-soil sorption; 3) other physico-chemical processes; and
4) transformation by microbial degradation, abiotic reactions, pho-
tochemical processes, and behavior of organometallic complexes. These
categories provide the order for the discussions which follow on
research recommendations. The order of priority for those recommen-
dations can be found in the Section 5.0, Summary, page 90.
4.1 Transport Processes
4.1.1 Transport processes in saturated soils
Research Recommendations
"Laboratory simulation of leachate migration processes for high
chemical concentrations
°Model reformulation based upon the observed mechanisms to account
for the density stratification and the presence of two phases
Many features of chemical transport processes in saturated
(with water) soil below landfills and hazardous waste sites are
poorly understood. The scenario in this report was based upon
field observations at a number of landfills and abandoned waste
sites and delineated three saturated zones: zone 1-leachate
plume, zone 2-groundwater and leachate interaction, and zone
3-trace contaminant. Zone 1 is characterized by high chemical
concentrations, and possibly additional liquid phases, that
essentially overwhelm the subsoil adsorption capacity for the
leaching constituents. Zone 2 is characterized by a dilution
process that occurs as the leachate plume meets and mixes with
the groundwater. Two liquid phases may continue to exist in zone
2. Zone 3 is characterized by a secondary leachate plume that is
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created as the groundwater picks up and transports constituents
from zone 2 to points farther afield. With data and transport
models presently available, it is possible to make fate predic-
tions about specific chemical contaminants only for the trace
contaminant conditions described in zone 3. We must be able to
make similar fate predictions about high concentrations.
Investigations need to be undertaken to explore the general
behavior of flow and disperson of high concentration wastes in
subsoils and in porous media. If these wastes are organic
chemical-waste mixtures, they may have a bulk density greater or
less than that of water. The leachate may be made up of two pha-
ses, an organic solvent phase and an aqueous phase. These phases
may co-exist in both zones 1 and 2. Results of field studies
suggest that an organic layer "floats" on the top of the aqueous
phase in the groundwater aquifer. The present generation of pre-
dictive models that purport to quantify the flow and dispersion
of chemical contaminants in groundwater cannot handle the above
described density gradient and separate phase conditions. Our
needs, then, include: first, laboratory simulation of the
leachate migration process for high chemical concentrations to
explore the qualitative features of the process and second, model
reformulation based upon the observed mechanisms to account for
the density stratification and the presence of two phases.
Some specific investigations are needed to explore the effect
of high chemical concentrations on the transport processes.
Specifically, how does density stratification or density dif-
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ferences affect the natural diffusive/dispersive processes in
porous media? Model concepts need be developed to relate the
simultaneous flow of two liquid phases in a porous media and the
interphase chemical transfer process. Are the conventional
models that result in the retardation concept appropriate for
zones 1 and 2, or are the "fixed-bed breakthrough" theory of
adsorption and ion-exchange unit operations more appropriate?
In many respects, the bottom sediment of lakes and rivers is
similar to saturated soils. Investigations of transport in this
portion of the aquatic ecosystem have been made and are still
under way; however, they have not dealt specifically with high
chemical concentrations. Results of episodic spills or long term
releases of hazardous chemicals can result in extreme con-
tamination of bottom sediment. Layers of sediment, called "hot
spots," are created. These deposits may be buried by fresher
sediment creating a highly contaminated layer which can exist for
long periods and slowly release its toxic constituents to the
overlying water. In-sediment transport processes in both
quiescent and flowing water need to be investigated by use of
pilot-scale laboratory simulators. These simulators are to be of
such dimensions that they contain the major natural influences
that exist in the specific environment.
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4.1.2. Transport processes in unsaturated soils
Research Recommendations
°The effective diffusion coefficient for the gas phase and the
liquid phase in unsaturated porous media
°The convection processes in the liquid phase as driven both by
the evaporation of water at the soil surface and the capillary
forces from liquid waste buried below the surface
°The convection processes in the gas phase as driven by internal
gas generation (i.e., bio-gas), atmospheric pressure pumping, and
water evaporation beneath the surface
"Temperature gradients with associated energy flux rates within
the top 30 to 50 cm of the surface
The conditions of unsaturated soils present an altogether
different system that in many ways is much more complex than that
of the saturated soils. Unsaturated conditions occur in both
surface and subsurface soils, resulting in the presence of a
gaseous phase. Important problems with regard to high con-
centrations of hazardous chemicals described in the body of the
report include landfills, landfarms, and contaminated land. The
latter has resulted mainly from decommissioned industrial sites.
Studies of some transport processes concerned with movement
of trace contaminants in this terrestrial ecosystem have been
made. There are virtually no studies available that address high
chemical concentrations in the soil environment. Studies, both
experimental and model development, of chemical transport mechan-
isms in unsaturated soils should involve laboratory investiga-
tions and simulations with the goal of isolating and quantifying
the specific transport mechanisms. Based upon the quantitative and
qualitative observations, appropriate mathematical models should
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be proposed and verified based upon the equations of change. Due
to the complexity of the transport processes, this work will
undoubtedly involve specific chemicals in the waste and the water
for each of the fluid phases with use of the multicomponent con-
tinuity equation, plus the equations of momentum and energy.
4.1.3. Transport processes on the fluid side of earthen interfaces
Research Recommendations
°The evaporation process, both natural convection and forced
(i.e., wind enhanced) convection, of chemicals that exist in pure
and mixed states on the surface of soil
°The mechanism and kinetics of dissolution of chemicals that exist
in pure and mixed states on the surface of bottom sediments of
lakes, rivers, and estuaries
°The deposition and re-entrainment of particles containing hazar-
dous chemical constituents in the presence of fluid flow to cover
both air and water regions above earthen surfaces
The fluid side of earthen interfaces is taken to mean the air
boundary layer above soil surfaces and the water boundary layer
above a bottom sediment surface.
Many aspects of chemical transport involving fluids near
interfaces are very well understood and numerous models exist for
obtaining reliable estimates of appropriate coefficients to quan-
tify flux rates. This work typically reflects highly idealized,
homogeneous, and regular interface regions. A lesser amount of
work has been done which involves some of the more important
complexities presented by the natural interfaces above soil and
bottom sediment. The items recommended for research require
additional investigations which should include high chemical con-
77
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centration conditions.
4.2 Equilibrium Processes
4.2.1. Air-soil sorption processes
Research Recommendations
°Equilibrium sorption on "air-dry" soils, including polar and non-
polar species in single, binary, and tertiary mixtures
"Equilibrium sorption on moist soils concerning the behavior of
equilibrium isotherms for water contents between "air-dry" and
ca. 10% water (5 bars)
°The role of cellulose-type material in the soil, disposed with
organic chemicals
°The physico-chemical nature of organic material at the waste
disposal site
A comprehensive investigation of the equilibrium behavior of
volatile chemicals on soil and subsoil systems needs to be per-
formed. As was pointed out in the body of the report and in the
scenario analysis, our understanding of the mechanisms of par-
titioning of volatile chemical species between the soil phase and
the air phase is incomplete. Only the condition of low chemical
concentrations in soils with water content of approximately 5% or
higher is fairly well understood and quantifiable. It appears
that, if the chemical concentration is low and if there is suf-
ficient moisture, Henry's law applies and then an analytical
relationship between chemical concentration (or partial pressure)
in the soil-pore air and chemical concentration on the soil can
be produced. However, even in this case few data exist for
polar and nonpolar volatile organics.
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Equilibrium sorption on "air-dry" soils: Single, binary, and
tertiary mixtures should be studied and should include both polar
and nonpolar species. The roles of the soil organic matter, clay
content, clay type, temperature, inert gases (e.g., air, methane,
and carbon dioxide) on sorption with "air-dry" soils need to be
elucidated. Some evidence suggests that the partial vapor
pressure of a chemical is reduced significantly if no soil water
is present. This is particularly important for quantifying the
appropriate partial pressure for so-called surface-applied chemi-
cals since the top few millimeters of the soil surface can become
essentially "air-dry" during some time intervals. It has been
suggested that the BET (i.e., Brunauer, Emmett, and Teller)
adsorption theory is applicable and should be considered as the
model for interpreting the data.
Equilibrium sorption on moist soils: Water will most likely
be present on soils, but not always present in sufficient quan-
tities to form one or more mono-molecular layers on the soil sur-
face. Consequently, the investigations should concern the nature
of behavior of the equilibrium isotherms for the range of water
contents between "air-dry" and approximately 10% water (5 bars),
when the water molecules tend to compete for adsorption sites.
Studies should involve polar and nonpolar substances and include
the effect of soil organic matter, surface area, clay content,
clay type, temperature, and inert gases. Ideally, mathematical
models based upon equilibrium mechanisms should be produced as a
means of extending the data and extrapolating them to other che-
micals and soils.
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The role of cellulose-type material incorporated in soil:
Codisposal in the past has involved the mixing of volatile solid
and liquid organic chemicals with domestic garbage, waste paper,
hay, and other refuse in landfills as a means of "immobilizing"
the waste. Investigations of the effect of such high con-
centrations of cellulose (i.e., 25 to 50%) type organic matter on
the vapor pressure reduction need be performed.
Characterization of the physico-chemical nature of organic
material (soil organic matter and various sludges) at the waste
disposal site: Hazardous chemicals in high concentrations can be
associated with three different types of soil organic matter: 1)
natural organic matter produced from decayed biomass such as
plant and animal debris, 2) bio-sludges produced from microbial
cultures of wastewater treatment plants (e.g., activated sludge,
anaerobic digesters), and 3) oil sludges from petroleum,
petrochemical, or organic chemical manufacturing operations. Are
these types of soil organic matter similar enough to be treated
as a single parameter with respect to equilibrium considerations,
or are they different in their sorptive properties, surface area,
chemical structure, average molecular weight, and other influen-
cial features? Raoult's law has been proposed as an equilibrium
model for estimating chemical vapor pressures of volatile hydro-
carbons in oily sludges. Is this an appropriate approach, and
under what conditions can it be extended to the other types of
soil organic matter and used for chlorinated substances such as
PCB's?
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4.2.2. Water-soil sorption processes
Research Recommendations
"Equilibrium sorption on soil and bottom sediment of single orga-
nic species, both polar and nonpolar, in the high chemical con-
centration range or at the solubility limit of the chemical. The
appropriateness of various isotherm model formulations needs to be
evaluated.
"Equilibrium sorption on soil of multicomponent organic mixtures
with the combined concentration of all species at high con-
centrations in the presence and absence of organic matter.
°Equilibrium sorption of high concentration of metals on soil and
sediment.
A comprehensive investigation needs to be performed on the
equilibrium partitioning of organic molecules, metal ions, and
metal complex ions between soil and water. The kinetics of the
partitioning process must also be studied. Much material is
available in the literature on nonpolar organics at low con-
centrations, and algorithms have been published that allow one to
predict reliable values of Kp (partition coefficients) based
upon parameters such as chemical solubility, chemical melting
point, and soil organic matter content. This approach, which is
applicable to chemicals in both terrestrial and aquatic eco-
systems, needs to be extended to cover a higher range of organic
chemical concentrations, multicomponent chemical mixtures, metal
ions, and complexes.
Studies of equilibrium sorption on soil and bottom sediment
of single organic species, both polar and nonpolar, need to be
extended to the high chemical concentration range or to the solu-
bility limit of the chemical. If the chemical is infinitely
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soluble, then a 5% solution is a reasonable upper boundary for
investigation. If a separate phase forms prior to this limit,
then investigations of concentrations up to the solubility are
appropriate. Does the presence of the soil affect the ultimate
solubility?
Most studies performed to date have been with surface soils
which have relatively high organic matter content. Data on
single component partition coefficients for subsoils need to be
generated with the goal of obtaining an analytical expression
that relates the partition coefficient to the chemical solubi-
lity, melting point, clay content, clay type, temperature, and
other influences. Development of the appropriate correlations
should be based upon sound physical chemistry concepts concerning
the nature of chemical bonds and attraction forces for water and
chemical molecules on the soil surfaces.
Studies need to be made on equilibrium sorption on soil of
multicomponent organic mixtures with the sum total concentration
of all species in the high concentration range. How does the
presence of a high concentration of cyclohexane affect the par-
tition coefficient of PCB? The prediction of key chemical con-
centrations in leachate plumes containing several organic
chemicals moving through subsoils cannot be performed at present
because of the lack of data and clear concepts of the physico-
chemical adsorption processes involving multicomponent leachates
at high total chemical concentration in subsurface soils.
Theoretical approaches such as proposed by Dexter and Pavlou
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(1978) and Rao et al. (1983) seem appropriate as a starting
point.
Studies of equilibrium sorption of high concentrations of
various species of metals on soil need to be made. Metals can be
present as ions, as complex ions, and in molecular form. What is
needed is an algorithm based upon physical chemistry processes
supported by data relating the partitioning of metal species be-
tween the pore water and the adjoining soil surface. Some of the
factors of likely importance are valence of the ion, size of the
ion, hydrodynamic radius, ion-exchange capacity of the soil
(cationic or anionic), surface area, clay type, clay content,
temperature, organic matter, and pH. These studies need to cover
the entire concentration range and include the effects of the
presence of organic compounds in the leachate.
4.3 Other Physico-Chemical Processes
Research Recommendations
"Measurement of alterations in chemical and physical properties
created in artificial or unnatural mixtures and their influence
on transport processes through a medium and an ecosystem
The presence of high chemical concentrations in aquatic and
terrestrial ecosystems will undoubtedly alter the basic structure and
properties of these natural environments to a greater or lesser
extent. Much of the work that has been done with respect to transport
and other processes in soil and sediment systems has been with the
systems very near to the natural state. Where high chemical con-
centrations occur at disposal sites, treatment sites, abandoned sites,
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or other locations, the presence of the foreign substance amounts to a
considerable fraction of the sediment or soil and, therefore, can
impart different or changed properties. In effect, we need to know
more about the nature of these artificial and unnatural mixtures that
are created.
These investigations will undoubtedly involve the re-creation of
contamination events under controlled laboratory conditions with the
subsequent measurement of properties and parameters related to
transport processes in particular. The following is a list of impor-
tant properties and parameters:
1. Residual saturation: the volume of soil or porous material
necessary to immobilize a quantity of liquid spilled or otherwise
placed on soil.
2. Porosity: the fraction of void space occupied by gases and
fluids (air, water, organic matter, chemicals) in porous media of
soils and bottom sediment.
3. Permeability: the ability of the porous media to transmit fluids
under pressure; applies to both gases and liquids in soil and
to liquids in bottom sediment.
4. Capillary rise: the ability of soil particles to become wetted
by the fluids and sustain a height of fluid due the interfacial
tension.
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5. Reactive effects: alterations of the soil or sediment that occur
due to irreversible adsorption or otherwise incorporation of
waste into the particles, producing significant physical! and che-
mical transformations which destroy or significantly alter the
basic material. An example is the complete destruction of some
clays by the presence of high organic chemical concentrations.
4.4 Transformation Processes
Research Recommendations
"Assessment of microbial degradation under stress conditions (e.g.
high chemical concentrations, oxygen-limited environment)
"Abiotic transformation of chemicals at high concentrations and
the effect of altered environmental conditions on these" abiotic
processes
"Photochemical transformations (degradation and polymerization) of
organic chemicals at high concentrations in various nonaqueous
solvents
"Transformation of organometallic complexes in sedimenti and soil
Numerous studies have been reported which deal with the trans-
formations of organic chemicals in the environment. ITI general,
most studies have been related to the microbial degradation of
various pesticides. Incubation studies have been conducted under
aerobic conditions, neutral pH values, optimum temperature regimes,
and at low pesticide concentrations. In other words,: conditions
have been selected to maximize microbial degradation irates.
However, conditions which exist in a hazardous waste landfill are
not conducive to maximizing the degradation rate of most
materials. Future research efforts need to be directed toward
providing data which would allow a better assessment7of microbial
degradation processes under stress conditions.
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An additional area of research which needs to be explored
involves abiotic transformations of chemicals. At high con-
centrations, what chemical degradation reactions occur and what
are the rates of transformation? Most pesticide studies have
been conducted at low concentrations and many of the compounds
are very complex in structure and reactivity.
A third research effort needs to be oriented towards addi-
tional studies of photochemical transformation of hazardous chem-
icals in soil and on the surface of aqueous systems. As before,
many previous studies have used pesticides which may and may not
be comparable to most hazardous organics. Neither will an
aqueous system be appropriate. How will an organic solvent
system influence photodecomposition of high concentrations of
chemicals on the soil or water surface?
Microbial degradation of high concentrations of hazardous
organic chemicals in an oxygen-limited environment: The micro-
bial degradation rate of various organic compounds under anaero-
bic conditions would be expected to be much slower than under
aerobic conditions especially for aromatic chemicals whose rapid
degradation largely depends upon the presence of molecular oxy-
gen.
Subsoil and sediment conditions of limited oxygen, low
organic matter levels, high clay content, very low nitrogen
levels, low microbial populations, and reduced temperatures would
all act to limit the microbial degradation rate of organic chemi-
cals. The biotic transformation rate of representative organic
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chemicals under "non-optimal" conditions needs to be quantitated.
The influence of parameters such as oxygen levels, nitrogen addi-
tion rates, and microbial inoculation on the degradation rates
should be evaluated.
Many chemicals at low concentrations are degraded rapidly
under optimal conditions, but degradation at high concentrations
has not been investigated. High concentrations of such chemicals
as phenol and chloroform are toxic to microorganisms, and thus,
the degradation rates would most likely be concentration depen-
dent and should be measured under various environmental con-
ditions. It would also be desirable to measure the levels of
various metabolites which may be formed. Information of the type
proposed is needed for use in development and testing of mathema-
tical models.
Abiotic transformations of high concentrations of hazardous
organic chemicals in sediment and subsoil environments: Abiotic
or chemical transformations of several pesticides have been shown
to occur, but much less information is available on hazardous
organic chemicals. In subsoil and sediment environments, the
higher clay levels and resulting larger surface area compared to
surface soil could facilitate a greater rate of abiotic transfor-
mation. Higher chemical concentration and the presence of poten-
tially catalytic inorganic ions may also facilitate chemical
reactions.
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Because of the uniqueness of the environments, future studies
need to be conducted to evaluate the influence of pH, Eh, clay
content and type, surface area, temperature, moisture, various
amounts and types of metal ions, organic chemical concentration,
and type of organic chemical on the rate of abiotic chemical
transformation. Specific abiotic transformations which are of
concern include hydrolysis, polymerization, oxidation, and reduc-
tion reactions. Test methods should be developed for the various
reactions, and the data should be incorporated into predictive
models.
Photochemical transformation of hazardous organic chemicals:
Before an organic chemical will undergo photochemical alteration,
the chemical must absorb ultraviolet radiation. Thus, the chemi-
cals to be investigated will most likely be surface applied to
the soil. Photochemical degradation has been shown to be an
important mechanism of pesticide dissipation, but data are far
more limited for hazardous organic chemicals. Studies need to be
conducted to evaluate the influence of radiation frequency and
intensity on photochemical transformations of high concentrations
of mixtures of organic chemicals in various nonaqueous solvents.
Degradation as well as polymerization reaction kinetics need to
be evaluated.
Transformation of organometallic complexes in sediment and
soil: The codisposal of heavy metals and organic chemicals may
lead to the formation of various organometallic chelates or
complexes. Such chelates or complexes may facilitate the
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transport of hazardous materials to a greater degree than
expected and most likely have altered degradation charac-
teristics. Studies need to be conducted to evaluate the kinetics
of formation of various heavy metal organic chelates and/or
complexes under conditions similar to landfills and sediments.
The biotic and abiotic transformations of such chelates should be
investigated under anaerobic conditions. Transport of chelates
is also an important characteristic and appropriate sorption and
transport studies should be conducted.
89
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5.0 SUMMARY
There is considerable information available on the effects of
trace chemical contaminants, such as pesticides, PCB's, chlorinated
hydrocarbons, and metal ions in the respective ecosystems. Predictive
techniques are becoming available to describe the transport and trans-
formation of such contaminants and, thus, their fate and distribution
in certain components of the environment. High chemical contaminant
concentrations are those levels of application which a) are more
easily expressed as a percentage (i.e., 5% or greater), and b) cause
major characteristic (i.e., physical, chemical, or biological) changes
in the soi1 or water.
Present predictive methods and models that trace the transport and
transformation of chemical species are based upon "natural" soil and
water properties such as density, porosity, infiltration, permeability,
viscosity, hydrophobicity, and diffusivity. When the chemical con-
taminant is present in high concentrations, then the assumption of
"natural" soil and water properties is very suspect. The major goal
of this project was to assess the research needs that will address
chemical contaminants present in high concentrations in terrestrial
and aquatic ecosystems.
The twelve most important research areas in priority order are
Priority
1 °Assessment of microbial degradation rates and microbial acti-
vity under stress conditions in soil and water (e.g. high
chemical contaminant concentrations and limited oxygen,
limited nutrients, and/or limited microbial populations.)
90
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2 °Abiotic transformations of chemicals at high concentrations
and the effect of altered environmental conditions on these
abiotic processes.
3 "Equilibrium sorption on soil and bottom sediment of single
organic species, both polar and nonpolar, in the high chemi-
cal concentration range or at the solubility limit of the
chemical. The appropriateness of various isotherm model for-
mulations needs to be evaluated.
4 "Equilibrium sorption on soil of multicomponent organic mix-
tures with the combined concentration of all species at high
concentrations in the presence and absence of organic matter.
5 "Formation, transformation, and transport of organometallic
chelates and complexes in soil and sediment. The studies
should also include equilibrium sorption of high con-
centrations of metals.
6 "Laboratory simulation of leachate migration processes (e.g.,
density stratification and two-phase flow) for high chemical
concentrations. Model reformulation based upon the observed
mechanisms to account for density stratification and the
presence of two phases.
7 "Vapor equilibrium sorption on "air-dry" soils, including
polar and nonpolar species in single, binary, and tertiary
mixtures.
8 "Vapor equilibrium sorption on moist soils concerning the
behavior of equilibrium isotherms for water contents between
"air-dry" and ca. 10% water (5 bars).
91
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9 "Transport processes in unsaturated soils including effective
gas and liquid phase diffusivities, convection processes due
to water and gas movement, processes driven by capillary for-
ces, and temperature gradients.
10 °The deposition and re-entrainment of particles containing
hazardous chemical constituents in the presence of fluid flow
to cover both air and water regions above earthen surfaces.
11 °Develop solubility data for aqueous-organic liquids charac-
teristic of high chemical concentrations appropriate to che-
mical waste landfill leachate and test existing solution
models for validation purposes.
12 °Develop vapor pressure data for chemical waste and organic
sludge (e.g., cellulose, biological, petroleum-petrochem) mix-
tures of high chemical concentration and test existing mix-
ture models for validation purposes.
92
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7.0 GLOSSARY
Glossary of terms used in the report.
advection - The process of conveyance of an atmospheric property
solely by the mass motion of the atmosphere. Also applied to aqueous
systems.
aerobic - Having molecular oxygen as a part of the environment.
*air-dry - The state of dryness (of a soil) at equilibrium with the
moisture content in the surrounding atmosphere. The actual moisture
content will depend upon the relative humidity and the temperature of
the surrounding atmosphere.
anaerobic - The absence of molecular oxygen or occurring in the
absence of molecular oxygen (as a biochemical process).
binary mixture - A liquid containing two substances that are miscible.
biogas - Gas, usually methane and carbon dioxide, formed during anaero-
bic decomposition of organic wastes.
bottom sediment - Sediment located at the bottom of a waterbody.
*cation-exchange capacity (CEC) - The sum of exchangeable cations that
a soil, soil constituent, or other material can adsorb at a specific
pH. It is usually expressed in milliequivalents per 100 grams of
exchanger.
chemical contaminant - a chemical substance that makes (water or soil)
inferior or impure by admixture, makes unfit for use by the introduc-
tion of unwholesome or undesirable elements or compounds.
codisposal - The process of mixing of municipal waste and industrial
waste at the same time and place, usually in a landfill.
contaminated land - Land containing mixtures of chemicals originating
from previous manufacturing operations on the site.
convection - Conveyance of a substance in which the fluid as a whole
is moving.
creosote - A colorless or yellowish oily liquid containing a mixture
of phenolic compounds obtained by distillation of coal tar.
diffusivity - The weight of a material, in grams, diffusing across an
area of 1 square centimeter by molecular processes in one second in a
unit concentration gradient.
*Specific terms relating to soil science are taken from the Glossary
of Soil Science Terms_, 1979, Soil Science Society of America, Madison,
1STsconsi~nT
105
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dispersion - The combined movement of a substance by molecular and
turbulent processes in a fluid attributed to a concentration gradient,
similar to molecular diffusion.
dispersivity - Similar to a dispersion coefficient.
dry soil - Soil void of free water.
dump site - Any site onto which waste has been placed.
hazardous waste - dangerous discards generated from our highly
industrialized, technologically based society; refers to any waste or
combination of wastes that presents or poses potential dangers to human
health and safety or to living organisms in our environment; such
wastes are lethal, non-degradable or may be biologically magnified,
capable of promoting detrimental cumulative effects as well as short-
term hazards; toxic chemicals, flammable, radioactive, explosive, or
biological in nature and take the form of solids, sludges, gases or
liquids.
*humic acid - The dark-colored fraction of the soil humus which can be
extracted with dilute alkali and is precipitated by acidification to
pH 1-2. Exchange acidity at pH 7 usually varies from 200 to 400
meq/100 g.
immiscible - Pertaining to liquids that will not mix with each other.
land treatment - Operation of sludge or liquid waste degradation by
spreading and incorporating into surface soil to promote biological
activity.
landfarming - See land treatment.
landfill - Disposal of solid waste by burying in layers of earth in
low ground.
landfill cell - A portion of a landfill partitioned off to contain a
waste of a specific type or quantity.
mass flow - The mass of a fluid in motion which crosses a given area
in a unit time.
miscible - Referring to liquids that are mutually soluble, that is,
they will dissolve in each other.
mixture - A portion of matter consisting of two or more components in
varying proportions that retain their own properties.
municipal sludge - See sewage sludge.
partial pressure - The pressure that would be exerted by one component
of a mixture of gases if it were present alone in a container.
106
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permeability - The ability of a membrane or other material to permit a
substance to pass through it. The capacity of a porous rock, soil, or
sediment for transmitting a fluid without damage to the structure of
the medium.
petroleum sludge - Viscous liquids, semi-solids and solids with high
water content from refinery operations usually still bottoms, tank
bottoms, API separator, and filter media.
pH, soil - The negative logarithm of the hydrogen-ion activity of a
soil. The degree of acidity (or alkalinity) of a soil as determined
by means of a glass, quinhydrone, or other suitable electrode or indi-
cator at a specified moisture content or soil-water ratio, and
expressed in terms of the pH scale.
phase - Portion of a physical system (liquid, gas, solid) that is
homogeneous throughout, has definable boundaries and can be separated
physically from other phases.
porosity - The fraction as a percent of the total volume occupied by
minute channels or open spaces.
retardation factor - The ratio of water velocity to the velocity of
trace chemical dissolved in water as they move together through a
porous formation.
saturated soil - Soil with all pore spaces occupied with water.
sewage sludge - A semiliquid waste with a solid concentration in
excess of 2500 parts per million, obtained from the purification of
municipal sewage.
sludge - Residue left after acid treatment of petroleum oils. Any
semi sol id waste from a chemical process.
*soil - The unconsolidated mineral matter on the surface of the earth
that has been subjected to and influenced by genetic and environmental
factors of: parent material, climate (including moisture and tem-
perature effects), macro- and microorganisms, and topography, all
acting over a period of time and producing a product-soil-that differs
from the material from which it is derived in many physical, chemical,
biological and morphological properties, and characteristics.
*soil organic matter - The organic fraction of the soil. Includes
plant, animal, and microbial residues, fresh and at all stages of
decomposition, and the relatively resistant soil humus.
soil water - Moisture in the soil.
solubility - The ability of a substance to form a solution with
another substance.
solvent - That part of a solution that is present in the largest
amount, or the compound that is normally liquid in the pure state (as
for solutions of solids or gases in liquids).
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subsoil - Soil underlying surface soil.
surface applied - An act of placing a chemical substance on'the sur-
face of the soil.
surface impoundment - A basin position on the ground without a cover
containing liquid and/or solid waste.
surface soil - See soil.
tertiary mixture - A liquid containing three substances that are
miscible.
toxic substance - a poison; a substance that through its chemical
action usually kills, injures, or impairs an organism.
transport process - The conveyance of substances from point-to-point
in space due primarily to gradients of intensive properties.
two-phase flow - The simultaneous movement of gas and liquid through a
conduit, usually in the same direction.
unsaturated soil - Soil with pore spaces containing water and air or
other gases.
vapor density - Concentration of a gas in a mixture based upon its
partial or vapor pressure.
vapor pressure - For a liquid or solid, the pressure of the vapor in
equilibrium with the liquid or solid.
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