PB87-170551
Injection of Hazardous
Wastes into Deep Wells
State-of-the-Art Report
National Inst, for Petroleum and Energy Research
Bartlesville, OK
Prepared for
Robert S. Kerr Environmental Research Lab
Ada, OK
Feb 87
U.S. DEPARTMENT OF COMMERCE
National Technical Information Sorvico
NTIS
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EPA/600/8-37/01
February 1987
State-of-the-Art Report
INJECTION OF HAZARDOUS. WASTES INTO OEEP WELLS
by
Arden Strycker and A. Gene Collins
Interagency Agreement No. DW89931947-01-0
Prepared for
The U.S. Department of Energy
and
The U.S. Environmental Protection Agency
by
National Institute for Petroleum and Energy Research
P.O. Box 2128, Bartlesvi1le, Oklahoma 74005
DOE Project Officer
Alex Crawley
U.S. Department of Energy
Bartlesville, OK 74005
.EPA Project Officer
Lowell E. Leach
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada, OK 74820
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OK 74820
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1. HEPORT NO. ] 2
EPA/600/8-87/013 j
3 REClP'ENT'S ACCESSION NO
P32 7 ; 7 i) - - • *,
4. TITLE ANO SUBTITLE
STATE-OF-THE-ART REPORT:
INJECTION OF HAZARDOUS WASTES INTO DEE? WELLS
5 REPORT OATf
February 1987
6. PERFORMING ORGANIZATION COOE
7. AUTHORISI
Arden Strycker and A. Gene Collins
8. PERFORMING ORGANIZATION R E pO R T NO
9. PERFORMING ORGANIZATION NAME ANO AOC R ESS
I IT Research Institute
National Institute for Petroleum and Energy Research
P.O. Box 2128
Bartlesville, OK 74005
10 PROGRAM ELEMENT NO
CBPC1A
1 1. CONTRACT/GRANT NO
IAG DW89931947-01-0
12. SPONSORING AGENCY NAME ANO ADORESS
Robert S. Kerr Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, OK 74820
13. TYPE OF REPORT ANO ?EBlOO COVERED
Final
14. SPONSORING AGENCY COOE
EPA-600/15
is. supplementary notes
Project Officer: Lowell E. Leach, FTS 743-2333
TECHNICAL REPORT DATA
'Please reaa Insirucnons on me reverse ot/ore completing
16. ABSTRACT
About 11 percent of all hazardous wastes are presently disposed of by injection
wells into deep subsurface environments. There are approximately 250 of these
Class I wells in the United States and to date their record of performance has been
good.
Provisions of the Resource Conservation and Recovery Act (RCRA) require that
by 1988 the U.S. Environmental Protection Agency (EPA) must show that the disposal
of specified hazardous wastes is safe to the environment and human health, or deep-
well injection practices must be discontinued. As a result, knowing the long-
term fate of these wastes in the injection zone becomes important. The literature
survey conducted in this work shows that some information is available on nearly
all of the potential chemical and biological transformation processes of hazardous
wastes. This survey indicates that many, factors affect the ultimate fate of
injected wastes and that additional research is needed in all areas of abiotic and
biotic waste interactions before definitive explanations can be given on their
long-term fate.
17.
KEY WOROS AND OOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFlERS/OPEN ENOEO TERMS C. COSATI Field/Group
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
J1. NO. OP PAGES
64
30. SECURITY CLASS (Tliu pagtl
IINfil ft^TFTFQ
22. PRICE
BPA Form 2230-1 (*•». 4-77) *R«viOUI IOition 11 oiiolitc
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DISCLAIMER
The i information in this document has been funded wholly or in part by
the United States Environmental Protection Agency under interagency agree-
ment number DW89931947-01-0 to the National Institute for Petroleum
Energy Research, 3artlesvi 1 le, Oklahoma. It has been subjected to the
Agency's peer and administrative review, and it has been approved for
publication as an EPA document.
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FOREWORD
The U.S. Environmental Protection Agency was established to coordindate
administration of the major Federal programs designed to protect the quality
of our environment.
An important part of the Agency's effort involves the search for
information about environmental problems, management techniques and new
technologies through which optimum use of the Nation's land and water resources
can be assured and the threat pollution poses to the welfare of the American
people can be minimized.
EPA's Office of Research and Development conducts this search through a
nationwide network of research facilities.
As one of the facilities, the Robert S. Kerr Environmental Research
Laboratory is the Agency's center of expertise for investigation of the soil
and subsurface environment. Personnel at the laboratory are responsible for
management of research programs to: (a) determine the fate, transport and
transformation rates of pollutants in the soil, the unsaturated zone and the
saturated zones of the subsurface environment including zones for deep-well
injection of hazardous wastes; (b) define the processes to be used in char-
acterizing the soil and subsurface environment as a receptor of pollutants;
(c) develop techniques for predicting the effect of pollutants on ground
water, soil, deep well injection zones and indigenous • organisms; and (d)
define and demonstrate the applicability and limitations of using natural
processes, indigenous to the soil and subsurface environment, for the pro-
tection of this resource.
Provisions of the Resource Conservation and Recovery Act (RCRA) require
that by 1988 the Environmental Protection Agency (EPA) show that the disposal
of specific wastes is safe to human health and the environment, or the practice
of deep-well injection of hazardous wastes must be discontinued.
This report contributes to that knowledge which is essential in order
for EPA to establish and enforce pollution control standards which are
reasonable, cost effective and provide adequate environmental protection for
the American public.
Clinton W. Hall
Director
Robert S. Kerr Environmental
Research Laboratory
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ABSTRACT
About 11 percent of all hazardous wastes are disposed of by injection
wells into deep subsurface environments. Some 250 of these Class I wells
are in the United States, and their record of performance is good.
Provisions of the Resource Conservation and Recovery Act (RCRA) require
that by 1988 the Environmental Protection Agency (EPA) show that the disposal
of specified wastes is safe to human health and the environment, or the
practice of deep-well injection of hazardous wastes must be discontinued. As
a result, knowing the long-term fate of these wastes in the injection zone
becomes important.
A survey of the literature performed in this work shows that some
information is available on nearly all of the potential chemical and
biological tranformation processes of hazardous wastes. This survey also
indicates that additional research is needed in all areas of abiotic and
biotic waste interactions before definitive explanations can be given on
their long-term fate.
Usually, the first experimental test conducted is the fluid-fluid
compatibility test of the waste with the formation fluids. However, research
results show that this simple test is not always adequate for determining
the interaction of injected wastes with the subsurface environment.
Many factors affect the ultimate fate of injected wastes. These factors
include pH-ch of the waste and reservoir fluids, brine concentration of the
waste fluids, clay type and amount in the reservoir, presence or absence of
Iron oxides, presence or absence of organic complexing agents, molecular
characteristics of organic materials, and other factors that determine if
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the environment is anaerobic or aerobic. All of these factors are inter-
related, and any mixing of different types of hazardous wastes in the reservoir
further complicates the situation, making it difficult to predict exactly
what occurs after the injection of wastes and their ultimate fate. Relevant
research conducted to date concerning this problem has been limited and is
not sufficient to address adequately the problem of predicting the ultimate
fate of injected wastes.
This report is submitted in partial fulfillment of Contract Number
0W89931947-01-0 under the sponsorship of the U.S. Environmental Protection
Agency through an interagency agreement between the U.S. Department of Energy
and the U.S. Environmental Protection Agency. This report covers the contract
period from May 1, 1986, to December 15, 1986, and the work was completed as
of December 15, 1986.
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TABLE OF CONTENTS
Page
i i i
i v
Tables vii
vi i i
]
g Non-Organic Hazardous Wastes 7
of Injection Fluids with Reservoir Fluids 8
tal Complexes on Their Mobility 13
esses of Hazardous Wastes 16
ies of Listed Metals 21
21
22
(VI) 22
24
24
24
27
27
s Used for Prediction of Fate 27
g Organic Hazardous Wastes . . . . ' 29
datlon 31
ocesses 32
Organic Hazardous Wastes 36
Organic Hazardous Wastes 36
al Degradation 38
42
rlorida 42
orth Carolina 43
orida (American Cyanamid) 45
orida (Monsanto) 46
46
48
48
48
49
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ILLUSTRATIONS
£££i
1. Distribution of molecular and ionic species of divalent
cadmium at different pH values 23
2. Distribution of molecular and ionic species of divalent
lead at different pH values 25
3. Distribution of molecular and ionic species of divalent
mercury at different pH values 26
TABLE
1. Summary of results from survey conducted by EPA in 1983 4
v1i
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ACKNOWLEDGEMENTS
This work was supported by the U.S. Environmenta1 Protection Agency (EPA)
(Contract/IAG DW89931947-01-0) and the U.S. Department of Energy (DOE) through
an interagency agreement between EPA and OOE. The support and advice of
Lowell E. Leach, EPA Project Officer, and Alex Crawley, DOE Technical Project
Officer, were instrumental in guiding the work to a conclusion. The informa-
tion given by the Steering Committee members, Jerry Thornhill, George Keeler,
Oack Keeley, Steve Schmelling, and Harv Piwoni, Robert S. Kerr Environmental
Research Laboratory, U.S. Environmental Protection Agency; and Min K. Tham,
Paul Stapp, and Michael P. Madden, NIPER, was helpful and greatly appreci-
ated. Other NIPER employees who provided information and assistance were
Michael Crocker and Partha Sarathi.
v111
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INTRODUCTION
The Environmental Protection Agency (EPA) estimates that Class I wells are
used for the disposal of about 11 percent of all 1iquid hazardous wastes
produced annually in this country. This corresponds to about 11.5 billion
gallons of hazardous wastes that are injected into seme 250 Class I wells.1
Although these wells are located in sedimentary oasins throughout this
country, most of them are in the Great Lakes region and along the Gulf Coast.
The literature survey discussed in this report was initiated to determine
what knowledge is available in the literature concerning ultimate fate of
injected hazardous wastes. The discussion in this report is limited to the
hazardous wastes listed in the Hazardous Wastes and Solids Amendments of
1984. This report also limits "ultimate fate" to a time reasonably determined
by laboratory and field pilot techniques now available. Since knowledge of
the Interactions of complex waste mixtures 1s limited, much of the discussion
relates to particular chemicals or chemical groups. Laboratory work and field
*
observations are discussed. 8ecause of the limited research conducted
specifically for deep-well formations, literature resorts that address the
interaction of wastes by any method that has useful applications to deep-well
formations were considered 1n the survey.
Increased concern of the fate of wastes after disposal has led to changes
1n chemical processes.2 Indeed, under the Resource Conservation and Recovery
Act (RCRA), the EPA 1s required to make some decision concerning the safety of
underground injection of hazardous wastes by August 8, 1988. Although a study
prepared for the Underground Injection Practices Council (UIPC) showed that to
date only a few malfunctions have resulted 1n contamination of water
supplies,3 future practices will have to ensure that no additional
contaminations will occur.
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The Hazardous and Solid Waste Amendments (HSWA) of 1984, section 3004
subsections f and g, direct EPA to undergo a 45-month review of underground
injection and to prohibit underground injection of certain wastes "if it may
reasonably be determined that disposal may not be protective of human health
and the environment for as long as the waste remains hazardous." The deter-
mination of what constitutes potential risk to human health or the environment
is totally at the discretion of EPA. Additionally, EPA may apply any restric-
tions it considers necessary to ensure the safety of the disposal practices.
If the safety of underground injection cannot be demonstrated by August 1988,
disposal of hazardous wastes by this method will be prohibited by law.
The wastes referred to in the stated amendments include liquid wastes
having any of the following properties and characteristics:
(a) Free cyanides > 1,000 mg/1
(b) The following metals or compounds of metals: arsenic > 500 mg/1,
cadmium > 100 mg/1, chromium (VI) > 500 mg/1, lead > 500 mg/1,
mercury > 20 mg/1, nickel > 134 mg/1, selenium > 100 mg/1, and
thorium > 130 mg/1
(c) A pH < 2.0
(d) Polychlorinated biphenyls > 50 ppm
(e) Halogenated organic compounds > 1000 ppm
(f) D1oxIn-containing hazardous wastes numbered as follows:
F020-product1on wastes of tr1- and tetrachlorophenols and
intermediates
F02l-product1on wastes of pentachlorophenol and intermediates
F022-product1on wastes from tetra-, penta-, and hexachlorobenzenes
F023-product1on wastes from equipment used for the manufacture of
tri- and tetrachlorophenols
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FOOl-tetrachloroethylene, trichloroethylene, methylene chloride,
1,1,1-trichloroethane, carbon tetrachloride, and chlorinated
fluorocarbons used in degreasing
F002-methylene chloride, tetrachloroethylene, trichloroethylene,
1,1,1-trichloroethane, chlorobenzene, 1,1,2-trichloro-l,2,2-tri-
fluoroethane, o-dichlorobenzene, and fluorotrichlorometbane
F003-xylene, acetone, ethyl acetate, ethyl benzene, ethyl ether,
methyl isobutyl ketone, n-butyl alcohol, cyclohexanone, and
methanol
F004-cresols, cresylic acid, and nitrobenzene
F005-toluene, methyl ethyl ketone, carbon disulfide, isobutanol, and
pyridine
In 1983 the EPA surveyed 108 active hazardous waste wells for the type and
amount of wastes injected.1 The results of that survey (TABLE 1) show that
most of the wastes categorized as hazardous contain either acid solutions or
organic materials. The volume of water injected with these wastes was 6.2
billion gallons, or about 96 percent of the total volume injected; therefore,
the amount of material considered hazardous is a relatively small portion of
the total. The total percent of wastes injected (as listed in TABLE 1) is
slightly greater than 100 percent due to some overlays in the categories;
I.e., organic wastes and acid wastes.
A survey completed for the Chemical Manufactures' Association (CMA)
investigated the wells and reservoirs used for disposing wastes such as those
just listed.* From this study, a "typical" Injection well might be described
as having the following characteristics. The well is 3,925 ft deep with an
injection zone greater than 200 ft thick. The injection zone 1s composed of
sandstone/sand/sllt, and the confining zone 1s composed of clay/shale silt.
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TABLE 1. - Summary of results from EPA 1983 survey
Waste type Percent of total gallons
Inorganic or organic solutions
pH < 2.0
20.3
Arsenic, barium, cadmium, chromium,
lead, mercury, nickel
0.7
Organic
17.4
Selenium, cyanides
0.04
Other inorganics (non-hazardous)
52.0
Other (unknown)
9.9
The median wellhead pressure and injection flow are 285 psig and 150
gal/min." Most of the facilities treat the wastes before injection. Common
pretreatment practices include solids removal, equalization, and pH
adjustment. About 96 percent of the total volume injected is water. Annular
fluid and Injection pressures are monitored continuously in most cases.
Subsection g (HSWA) does contain a provision absent from
subsection f, that specifies that a method of disposal may
not be determined to be protective of human health and the
environment unless upon application by an interested person,
1t has been demonstrated to the administrator, to a reasonable
degree of certainty, that there will be no migration of
hazardous constituents from the disposal unit orsinject1on
zone for as long as the wastes remain hazardous.
Two general ways of satisfying this condition exist: 1) by showing that
the wastes will never migrate out of the Injection zone, or 2) by showing that
the wastes become non-hazardous before they migrate to areas outside the
injection zone.
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Injection of hazardous wastes can be considered safe if the first condi-
tion is met. However, there are at least five ways a waste material may
migrate and contaminate potable ground water:0
• Wastes may escape through the well bore into an underground source of
drinking water (USDW) because of insufficient casing or failure of
the injection well casing due to corrosion, excessive injection
pressure, etc.
• Wastes may escape vertically outside of the well casing from the
injection zone into a USDW aquifer.
• Wastes may escape vertically from the injection zone through confin-
ing beds that are Inadequate because of high primary permeability,
solution channels, joints, faults, or induced fractures.
• Wastes may escape vertically from the injection zone through nearby
wells that are Improperly cemented or plugged or that have insuf-
ficient or leaky casing.
• Wastes may contaminate USDW directly by lateral travel of the
Injected waste water from a region of saline water to a region of
fresh water in the same aquifer.
The likelihood that any of these migration patterns will occur can be
reduced greatly with proper design, construction, maintenance, good reservoir
characterization, and monitoring of underground Injection well practices.
Demonstrating the fate of Injected wastes requires a knowledge of the
behavior of each waste after it enters the subsurface environment. The
interaction of a particular waste with other Injected wastes, with reservoir
fluids, and with reservoir solid materials, such as clays, silicates, and
carbonates must be known. Unfortunately, hazardous wastes are complex
mixtures of materials, and their combination with other mixed waste streams
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increases the potential number of interactions factorial1y. Furthermore,
since subsurface environments often take many years to reach chemical and
biological equilibrium, predicting exactly what will nappen a pr.cr, may be
nearly impossible. For example, some toxic metals may adsorb onto clays as
they are injected, making the migrating fluids immediately non-hazarcous.
This adsorption process does not guarantee that some waste injected into the
reservoir in the future might lead to desorption of the same metals, thus
rendering the fluids hazardous again.
The methodology for assessing fate generally is thought of as a
description of all major chemical and biological pathways for movement or
transformation of a chemical. This description includes that of concentration
as a function of time for the original chemical and all subsequent products
from transformation processes. Therefore, the chemical and biological
interactions with the subsurface environment must be outlined to determine the
fate of Injected hazardous wastes and to decide when these wastes are no
longer hazardous to satisfy the legislation using the second condition.
The first section following the introduction of ttrs report discusses wMt
is known about non-organic hazardous materials. Such major processes as
neutralization, hydrolysis, 1on exchange, precipitation, complexatlon, and
adsorption are Included 1n the discussion. As might be expected, organic
materials not considered 1n the above 11st of hazardous wastes may strongly
influence these processes and will be discussed as appropriate. Also, since
the behavior of some non-organic materials 1s more easily quantified than
organic materials, mathematical models were developed to help describe and
predict their behavior. A short discussion of these models 1s also included.
The second section discusses what 1s known about hazardous organic
materials. Such processes as thermal degradation, adsorption, oxidation,
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reduction, hydrolysis, and microbial degradation are included in this
discussion. Microbial degradation actually is a general term for many
biological processes and will be discussed at some length.
Finally, the third section discusses several field case studies. This
section is pertinent, since it deals with complex waste streams and integrates
information presented in the previous two sections. Unfortunately, the
literature available on case histories is limited.
PROCESSES INVOLVING NON-ORGANIC HAZARDOUS WASTES
One notable characteristic of most non-organic hazardous wastes, such as
lead, cadmium, and chromium, is that they never go away. The only ways such
materials can be rendered non-hazardous are by dilution, by isolation, and in
some cases by changes in oxidation state. Therefore, waste treatment methods
such as incineration are Ineffective because the metal salts are not degraded
by burning. Thus, deep-well injection is potentially useful if these
hazardous materials remain isolated, or at least disperse to a residual con-
centration that is no longer harmful to human health or the environment.
The most likely reactions or transformations for non-organic hazardous
wastes include precipitation, adsorption/desorption, ion exchange, hydrolysis,
complexation, oxidation/reduction, acid/base reaction, and mineral dis-
solution. As mentioned in the introduction, the percent of total wastes
injected that contain toxic metals is small (< 1.0 percent). These Include
arsenic, barium, cadmium, chromium, lead, mercury, nickel, and selenium. Most
of the non-organic wastes injected are classified as non-hazardous and contain
various alkali metal salts, such as lithium, sodium, and potassium. The
presence and concentration of these non-ha2ardous metals are important con-
siderations when evaluating the fate of hazardous wastes. Their effects will
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be discussed in more detail in subsequent subsections. The particular
materials addressed as hazardous under this section include free metal and
associated salts of arsenic, cadmium, chromium (VI), lead, mercury, nickel,
selenium, thorium, inorganic salts of cyanide, and any solution with a pH
lower than 2.0 derived from mineral acids.
The literature covered in this report indicates that the properties of
non-organic materials in subsurface environments are more easily quantified,
since the total possible reaction products available to any particular hazar-
dous compound is finite and is limited by combinations of other materials
found in the injection zone. Contrasting this definable situation is the
study of organic materials, where the possible number of products are much
more difficult to limit. However, the injection of non-organic wastes in
subsurface environments appears to be more easily quantifiable, and the
introduction of many different chemicals simultaneously or in succession
rapidly increases the complexity.
Compatibility of Injection FluH< with Reservoir Fluids
Subsurface reservoir fluids have equilibrated with reservoir minerals and
clays during geologic time. All of the minerals, rocks, hydrocarbons, gases,
etc. are interrelated and contribute to the final stable solute/solvent matrix
that exists 1n the reservoir. On the other hand, waste solutions considered
for deep-well Injection were generated 1n a different environment and have
attained a thermodynamic equilibrium under different circumstances. Con-
sequently, upon injection into the formation, adjustments must occur before a
new solute/solution equilibrium is reached. Some Injected wastes result in
Immediate precipitation of solids from solution and potentially may plug the
formation from further injection. Other wastes may result in less immediate
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problems but still may reduce the life of the injection well significantly.
Thus, injection well operators usually conduct laboratory tests on injected
hazardous wastes and native reservoir fluids to determine their compatibility.
Methods of testing for compatibility have been described.7"'0 Generally,
the two fluids are simply mixed together and allowed to stand for some time.
The formation of precipitate usually is an indicator of fluid-fluid incom-
patibility; however, some caution must be exercised.7"10 The solutions should
be kept at the temperatures and pressures of the reservoir; synthetic
solutions are not as reliable as native reservoir fluids for accurate results;
and sufficient time (hours to days) for incubation should be allowed. True
thermodynamic equilibrium may not be achieved very quickly for some systems.
Reactions of injected and interstitial fluids that can produce precipi-
tates in deep-well injection were discussed by Warner11"13 and include:
• Precipitation of alkaline earth metals, such as calcium, barium,
strontium and magnesium as Insoluble carbonates, sulfates, ortho-
phosphates, fluorides, and hydroxides
• Precipitation of other metals such as Iron, aluminum, cadmium, zinc,
manganese, and chromium as Insoluble carbonates, bicarbonates, hy-
droxides, orthophosphates, and sulfides
• Precipitation of oxidation/reduction reaction products, such as
hydrogen sulfide with chromium (VI).
Warner conducted Some laboratory studies of these processes using a sand-
pack model.11 Some theoretical development accompanied the laboratory work as
a means of evaluating the results. Warner's results showed that the amount of
mixing between different fluids that occurred was dependent upon hydrodynamic
dispersion processes. Once this dispersive property of the porous medium was
characterized, the amount of chemical reaction could be accurately predicted.
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Warner11 also found that the type of precipitate that was produced also
determined the degree of permeability reduction that resulted. For example,
ferric hydroxide appreciably blocked the flow of fluids through a porous
matrix, but barium sulfate and calcium sulfate did not. Ferric hydroxide is
gelatinous in nature while barium sulfate and calcium sulfate are finely
crystalline. The type of precipitate seemed to determine the effectiveness of
blocking in the porous matrix.
One method of preventing injection wells from becoming plugged due to
incompatible waters has been the injection of a buffer zone of nonreactive
water. Warner showed in his laboratory model that a sufficiently sized buffer
would effectively prevent a precipitation problem.11
Barnes13 also points out that if the pH values of the two solutions are
different, problems may result. For example, even though injected and
Interstitual fluids may be saturated with carbonate, having a different pH or
calcium activities will make the solutions incompatible. The reason pH is so
Important is that ion concentrations are linear functions of the fluid
proportions, but the equilibrium constants are not. Above pH 10, calcium,
barium, strontium, magnesium, and Iron will form gelatinous hydroxide
precipitates. Lower pH solutions containing blcarbonates, will convert to
carbonates if the pH 1s raised, and precipitates of iron, calcium, and
magnesium carbonates may result. Many scale Indices have been developed to
predict potential precipitation problems.1" However, these are not discussed
here, other than to note that they exist.
An example of Incompatible fluids was documented for the Arbuckle
formation.15 The reactions of chromates and phosphates In the waste stream
with barium sulfate, hydrogen sulfide, and soluble Iron formed precipitates
that eventually plugged the well.16
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Grubbs et al.17 presented a good literature review of studies investi-
gating incompatibility of injected fluids with reservoir fluids. Many of the
studies showed that incompatible fluids can form precipitates that reduce the
permeability of a porous matrix. Grubbs et al. also studied the injection
of liquid wastes with typical reservoir fluids and how incompatibility
affected core plugs. Reduction of permeability and pcosity was demonstrated
and was shown to be greater at the input end of the cores. Temperature was
found to be a more important variable than pressure when considering the
conditions of a formation. Grubbs et al.l? showed that while certain low pH
solutions initially may leach some formation minerals, the solutions may also
result in the precipitation of other minerals and actually reduce the
permeability rather than increase it.
Another example of mixed fluid reactions studied by Ragone et al.18
illustrated the complexity of predicting compatibilities. A particular
recharge well 1n New York was studied u^ing standard analyses of injected and
native fluids from the Injection well and observation wells. They observed a
nearly 10-fold increase of ferrous ion concentration at the fluid interfaces
over that of either the Injected fluid or the native fluids. The most likely
source of this Increased Iron concentration was thought to be from the pyrite
in the Magothy aquifer. It was thought that the Injected fluids changed the
underground environment from a reducing to an oxidizing one. Under an
oxidizing environment, pyrite becomes thermodynamlcally unstable and releases
ferrous, sulfate, and hydronlum 1ons as shown:
FeS2 + 8H20 > Fe2+ + 2S0*" + 16H~ + 14e"
The produced acids are eventually neutralized, and the produced ferrous
ions start to precipitate as ferric hydroxide 1n the presence of oxygen until
a stable system is reached. This chemistry is further complicated by solution
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pH, Eh, the presence of Fe3+ , partial 02 pressure, presence of organics,
etc. While it is not expected that all waste injection processes result in
increased solubilities of iron, it does illustrate that the non-hazardous
components, oxygen in this case, of a hazardous waste can have important
influences on the overall chemistry and potential fate of hazardous wastes.
Hower et al.19 discussed in some detail the potential interactions
involved with incompatible injected fluids. Low concentrations of salts can
lead to migration of clays. This has been demonstrated in the laboratory and
in the field. High pH solutions tended to dissolve silica and release fines
that would migrate and plug the pores, resulting in permeability damage to the
formation. Additional formation damage may occur as the dissolved silica
reprecipitates in another section of the reservoir.20-21 Alternatively, low
pH solutions may lead to silica gels or the dissolution of some clays and
carbonate (either matrix or cements). All of these problems are not as
evident in carbonate formations. However, later deposition of materials with
changes in pH may also be a problem in carbonate formations.
The study of compatible and Incompatible fluids with reservoir fluids was
extensive in the past. Although brief, this discussion Illustrates that what
appears at first to be a simple test of compatibility—simply mix the fluids
together 1n a test tube and allow 1t to sit—1s Inadequate to treat the many
complexities that often occur. Examples of apparently Incompatible fluids
causing little trouble 1n the field and apparently compatible fluids plugging
the injection wells were noted and further Illustrate the inadequacy of this
simple test.
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Effects of Metal Complexes on Their Mobility
For non-organic hazardous wastes, toxicity is a function of solubility,
and solubility determines "he relative mobility of these materials in the
reservoir. The more soluble the metal, the greater the rate of transport and
the greater the magnitude cf toxicity. Simple solution properties such as pH
and Eh affect solubility, and these effects were discussed briefly with
respect to certain materials.
However, the presence cf other organic chemicals that may form complexes
with these metals can also increase the solubility and, thus, are important
when considering their fate.22"21* For example, such chelating agents as
nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (OTPA), and
ethylenediaminetetraacetic acid (EDTA) are used in waste processing of
radioactive wastes because they are effective 1n carrying these wastes away
from the waste source.22 Unfortunately, these same chelating agents may also
enhance the mobility of the radioactive metals in the underground
environment. The solubility of most metals are much higher when in the form
of metal-organic complexes. To avoid the problem of waste migration, waste
disposal includes a pretreatment to destroy the chelating agents prior to
entering the formation.
Other organic chemicals can also have limited abilities to coordinate with
metals. Such naturally occurring chemicals as aliphatic acids, aromatic
acids, alcohols, aldehydes, ketones, amines, aromatic hydrocarbons, esters,
ethers, and phenols can all partially complex with metal compounds and
Increase their solubility.'2 Since, mobility 1s important in estimating
potential health hazards, the presence of these compounds must be considered.
One of the most common aliphatic acids found 1n oilfield waters is acetic
acid. A study covering 95 formation water samples in California and Texas
13
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found that the presence or absence of acetate anions was dependent upon the
zone from which the samples were taken.25 Most of the acetate ions were found
in zone 2 (temperature range of 80°-200° C). At temperatures greater than
200° C, very little was found. The authors claimed that thermal
decarboxylation was probably the mechanism of acetate degradation.26 Very few
aliphatic acids were found in zone 1 (temperatures lower than 80° C) as
well.22 The authors explained the absence of acetate ions in this zone as an
example of microbial degradation by methanogenic bacteria.2' Dilution by
mixing with other waters was also thought to contribute.
Although the degradation of organic materials under anaerobic conditions
has not been extensively studied, some work has been done. Novak and Ramish27
discussed anaerobic degradation as a multi-step process in which complex
compounds are broken down by certain facultative bacteria, and the resulting
short-chain acid anions' are broken down by methanogenic bacteria. Other
mechanisms have also been proposed, but will not be discussed further (see
reference 22 and references therein).
A study of adsorption/desorption properties of uranium, cobalt, strontium,
and cesium showed that chelating agents that enhance the solubility of these
metals in water do not necessarily decrease adsorption.'3 These organic
compounds are known to enhance the solubility of metals, but 1n the presence
of clays the enhanced solubilities were not always predictable. Cobalt was
found to be less strongly adsorbed when these materials were present.
However, strontium and cesium were not affected, and uranium was more strongly
adsorbed. The authors suggested that the uranium/acid complex may have a
greater tendency to adsorb to the clay surface than the individual metal,
because of additional electrostatic and molecular dlpole attractive forces
from the complex.
14
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Other evidence supports the idea that the presence of chelating agents do
2 $
not always have obvious results. Champlin discussed the various energies
associated with complexing agents, ion exchange processes, and adsorption
processes. Some of the values showed that the energies associated with
chelating agents were approximately of the same magnitude as those of
cation-silicate interactions. Thus, slight differences in conditions may have
major impact on the overall results.
Complexities are encountered when the concentrations of the metals are
considered.23 For example, when ferric ion is in low concentrations, natural
organics such as humic acids form true solutions due to metal-organic
complexes. However, at higher ferric ion concentrations, colloidal
suspensions are formed from the same humic acids. Metal complexed compounds
may have reduced intermolecular repulsion forces in the complexed molecule.
As a result, the organic material would recoil and become less hydrated in the
solution since all of the polar sites are taken up by the metal. Such a
particle then would remain suspended or precipitate depending upon the
particle size. Variations 1n pH will further complicate the chemistry since
all of these reactions are affected by the solution pH.
Additional complexity is introduced when bacteria are considered. Not
only can bacteria degrade the organic components of metal/organic complexed
particles, but bacteria may also convert some non-complex1ng materials into
complexlng agents.2* A conceivable situation might include the Injection of a
hazardous waste into a well containing certain non-hazardous materials that
support such a bacteria. The production of bacterial wastes capable of
enhancing the solubility of certain metals would increase the potential hazard
by Increasing the mobility of toxic metals. Alternatively, the same bacterial
15
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wastes may increase the adsorption of the metals due to the enhanced adsorp-
tion properties observed for some metal/organic complexes.
Even though non-organic hazardous wastes are considered in this section,
note that the presence or absence of certain organic chemicals is important in
determining the fate of non-organic hazardous wastes. The identity and
concentrations of naturally occurring organic compounds capable of forming
coordination bonds with metals should be determined before injection. Also,
the identity and quantity of organic compounds injected either simultaneously
or in succession with metal wastes should be determined, even though the
organic portion may not be considered as hazardous waste. Additionally, the
presence of bacteria capable of generating completing materials should not be
ruled out. Each injection system should be considered in detail to determine
the relative importance of metal-organic chemical interactions.
Sorption Processes of Hazardous Wastes
Although reactions between hazardous wastes and silica, dolomite, etc.,
are relatively straightforward and reactions between waste and reservoir
fluids can often be easily characterized, the interactions between waste
materials and formation clays have been difficult to characterize. Obvious
interactions such as clay swelling and clay particle migration are possible
with any injected fluid. In secondary and/or tertiary petroleum recovery
operations, petroleum engineers usually avoid Injecting alkaline solutions and
sometimes all aqueous solutions when water-sensitive clays are present.
Damage to the clays can result in drastically reduced permeabilities, and
often specialized products that stabilize clays are used in treating fluids to
prevent damage to reservoirs.
16
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The adsorption of organic and non-organic materials varies, depending upon
the amount and type of clay present in the formation because different clays
have different surface areas and charge densities. Since clays possess an
overall negative charge, cations such as moderately soluble metal wastes are
attracted to these clays.29 The more soluble ions previously attached to the
clays may resolubilize when other less soluble ions replace them cn the clay
2 9
surface. This process is termed ion exchange. Some of the metals
associated with the clay may bond so tightly that they may be considered
immobile or permanently adsorbed. Heavy metals are particularly susceptible
to this behavior.
Clays can become saturated with a particular ion when all of the sites are
filled and no further adsorption would result for that ion. Not only is this
saturation level dependent upon the amount and type of clay present, it is
also dependent upon whether iron and manganese oxides are present. Such
oxides tend to provide good surface properties for adsorption.
Clays are typically composed of alternating layers of tetrahedral silicon
oxide and octahedral aluminum oxide; however, occasionally the silicon or
aluminum 1ons are replaced with other ions having lower oxidation states,
which results 1n a net negative charge.10"31 Since the degree of charge is
highly dependent upon the conditions of the clay deposit, this exchange of
ions 1s not uniform throughout the clay or between different clays, and
explains why different clays behave differently.
Adsorption of water between these layers of clay crystals leads to
swelling of the clay. Originally, the layers of clay crystals tend to stack
over each other to bring the positive and negative charged faces close to-
gether and neutralize some of the negative charge of the material.7 If a low
salinity solution or a high pH solution contacts these layers, water molecules
17
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start to adsorb and separate the layers from each other. These realigned
crystal layers usually will not return to the original state, even if higher
salinity solutions are again added to the clays.
Carl Veley32 describes the adsorption process in more detail. The clay
particle is pictured as being negatively charged as already exDlained.
Exchangeable cations are attracted to this concentration of negative charge,
but because of electrostatic repulsion these cations try to avoid each
other. Veley describes the area near the negative charge of the clay as a
tiny atmosphere that is most dense near the surface, becoming more diffuse at
farther distances. If the solution is highly saline, there are many ions to
counteract the repulsive forces between 'atmospheres' around the clay. Thus,
the 'atmospheres' will be stable and ion exchange rates will be slow.
However, if the surrounding solution has low salinity, the atmospheres will
need to become more diffuse to avoid the repulsive forces of the cations.
These less dense atmospheres will then lead to a loosening of the clay
structure—swelling and migration.
Different cations also pack differently to form different density atmos-
pheres around the clays. Veley32 Illustrated this point with a sandstone core
containing some clay. The core was first treated with 3 percent calcium
chloride followed by delonized water. The delonized water led to a less dense
cation structure, but the calcium 1on was attracted strongly enough to prevent
migration of fines. When the same core was treated with 3 percent sodium
chloride (replaced calcium with sodium) followed by delonized water, the core
plugged. The sodium did not bind as strongly to the clay, and when the core
was treated with delonized water the 'sodium atmospheres' were not densely
packed enough to maintain the clay structure.
18
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Polyvalent metal ions bind even more strongly to the clays. The metal
first hydrates to some generali2ed form as described below.
M(H,0)^+ XZ"
After hydration, the metal begins to hydrolyze and form multiple assoc-
iations with other metals, such as :he generalized form described below.
(Mx(0H)y(H10)N|U
When these complex polynuclear ions associate with the clay particles, a
very tight structure around the clay crystal is formed. Months or years may
be required before true equilibrium is reached between all of these different
metal associations.
A core test similar to the one previously described was conducted. First,
the core was treated with one of these hydrolyzable metals. The core was then
treated with three subsequent solutions in order: delonized water, 3 percent
sodium chloride solution, and deionized water. In contrast to the previous
experiment, little reduction 1n permeability was observed. Unlike the calcium
ions, the polynuclear 1ons were bound very tightly to the clay and were not
replaced by sodium when treated with the sodium chloride solution.
This strong adsorption behavior may be very useful for certain hazardous
wastes. If these wastes underwent such strong adsorption to the clays, the
clays would be protected from swelling and fines migration and the well would
be protected from being plugged prematurely. Also, the wastes would be
isolated from man's environment, since the wastes are rendered immobile by
permanent adsorption 1n the injection zone.
L9
-------
However, another situation needs to be considered. Suppose adsorbed metal
ions were attached to very smalt particles of clays. [f the clay particles
remain unattached to the silica matrix of the reservoir, the metal would still
2 8
be capable of migrating as a metal-clay particle. Champlin did an extensive
study of the forces affecting adsorption and ion exchange processes with clay
particles and metal ions and found that this mechanism of mobility can be very
important.
Champlin divided the particle forces into two types: physical forces and
chemical forces. Physical forces include the interactions between the
suspended particles, the interaction between the suspended particles and the
grains of the sand bed, and the interaction between the suspended particles
and the earth itself in the form of gravitational effects. Accordingly, the
particles may aggregate, adsorb onto rock surfaces, or drop out of the
suspension, depending upon which of these forces predominate. Alternatively,
a pseudo-equllibrium may be attained if the energies of these forces are not
great enough to overcome the mean thermal energy of the system.
To study these physical forces, Champlin conducted flow experiments
through cores and measured the ion and particle concentrations throughout.28
He found that when the salinity of the effluent was low, both the ions and
particles were strongly retained by the sand in the core. When the salinity
of the water was high, both the 1ons and suspended particles passed through
the core and were not retained by the sand. Most importantly, Isotoplc
labeling led him to further postulate that when the ions and particles passed
through the core, the ions were still attached to the migrating particles.
Thus, a mechanism was proposed where salinity affected the attractive forces
between the suspended particles and the sand grains. The physical and
20
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chemical forces of the metal ions were sufficiently strong to remain attached
to the clay particles.
Certainly, clays provide a surface capable of attracting certain
non-organic hazardous wastes. The adsorption of these wastes onto the clays
in the injection zone is desirable, since the mobile fluids *cuid be rendered
less hazardous, and the clays may be protected from additional swelling and
migration. Of course, the adsorption of materials is not desirable when such
processes result in the plugging of the well. Predicting how much waste will
be adsorbed, how long the waste will remain immobile, and under what circum-
stances the waste will be desorbed is difficult.
Known Properties of Listed Metals
Arsenic
In general, arsenic cations are more mobile under anaerobic conditions
than aerobic conditions. Arsenic cations are more mobile than selenium,
cadmium, and lead under anaerobic conditions when the pH is neutral to
alkaline.33 Some microorganisms are capable of converting As(0H)3 to As(CH3)3
under anaerobic conditions.33
Certain forms of arsenic are known to react with limestone to produce
carbon dioxide. These Include As203, (CH3)2As02H, and Mg3(As03)2. Certain
forms are known to react with granite to hydrolyre the potash feldspar
minerals. These include As203, Ca3(AsOu)2, {CH3)2As02H, CaHAsG3, KAs02,
Na2HAsQ„, and Na3As03. Certain forms of arsenic are also known to adsorb on
shales with varying amounts of clay. These include As203, Ca3(AsO,J2,
CaHAs03, PbHAsO„, Pb(As02)2, Mg3(As03)2, MnHAsOu, KAs02, Na2HAsO^,
Na3As03, and Zn(As02)2. All of this information can be found in reference 36.
21
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Cadmium
The solubility of cadmium is less than that of some other metals, but more
than that of lead. Figure 1 illustrates relative solubilities as a function
of pH and cadmium species.33 Figure 1 shows that at higher pH values,
mixtures of hydroxides in various concentrations will exist.33-36
The presence of oxides and hydrous oxides of iron have been observed to
increase adsorption properties of cadmium.37 A threshold of the amount
adsorbed exists and is dependent upon solution Eh and pH.
Some forms of cadmium are known to react with limestone to produce carbon
dioxide. These include CdC12* CdF2, and CdSO^. Certain forms are known to
adsorb to certain shales containing varying amounts of clays. These include
CdCl2, CdF2, and CdSO„.36
In the presence of hydrogen sulfide, cadmium will precipitate as cadmium
sulfide.
Chromium (VI)
A striking characteristic of chromium is its mobility. In neutral to
alkaline conditions, chromium is more mobile than most of the other metals
listed. Under oxidizing conditions (aerobic) in soils, chromium will form
insoluble precipitates with resident biological materials.33
The oxidation state of the chromium 1s also important. For example,
chromium (III) can adsorb strongly in acid solutions and precipitate at pH
values above 6 (as hydroxide, carbonate, or sulfide). Chromium (VI) does
neither of these things.33
As with cadmium, chromium (VI) can adsorb onto oxides and hydrous oxides
, , 3 7
of iron.
22
-------
Cd (OH >4
0.9
0.8 -
0.7
T 0.6
0.5
% 0.4
0.3
0.2
0.0
2
0
-10
6
-4
6
log [OH]
1 1,1,1 ¦ I i 1
4 6 8 10 12 14
pH
FIGURE 1. Distribution of molecular and Ionic species of
divalent cadmium at different pH values33.
23
-------
Lead
Lead is not very mobile under most subsurface conditions. That suggests
that solubilities are lower and tendencies toward adsorption are higher tnan
for most of the other metals listed.33 Typical precipitates of lead include
Pb(0H)2, PbC03, and Pb5(P0„)30H.31,-35 Figure 2 illustrates the effects of pH
and lead ion species on the solubilities of lead in solution.33 The presence
of scdium chloride does increase the solubility somewhat.36
Mercury
The major problem with mercury in soil environments is the volatility of
mono and methyl mercury compounds.36 However, the hazards presented by
volatility in deep-well injection systems are unknown. Figure 3 shows the
affect of pH and ionic form on the solubility of mercury.13 As with some of
the other metals, mercury compounds strongly adsorb to iron oxides if present.
One of the unique properties of mercury compounds is the ability of a
bacteria, Methanobacterium omelianskii, to convert inorganic mercury compounds
to methyl mercury.33 Methyl mercury is considered more toxic and more
volatile than the inorganic counterparts. Whether or not this occurs in
injection zones for deep-well systems is unknown.
Nickel
As with some of the other metals, nickel compounds adsorb strongly in the
presence of Iron and manganese oxides. Nickel 1s not very soluble in the
presence of carbonates, hydroxides, or sulfides.33 Salts of nickel that are
soluble Include nickel acetate, chloride, nitrate, and sulfate.36 Nickel
oxides also may be solubilized in strong acia; however, as strong acids are
neutralized in the reservoir, these oxides may then precipitate out.
24
-------
PbOH
0.9
0.8
0.7
0.6
2 0.5
< 0.4
0.3
0.2
0.1
0.0
0
2
-12
-10
6
4
8
log [OH]
1 i I . I i I i I i I , I
2 4 6 8 10 12 14
PH
FIGURE 2. Distribution of molecular and ionic species of
divalent lead at different pH values33
25
-------
0.9
0.8
Hg OH
0.7
0.6
2 0.5
O
O 0.4
<
cr
^ 0.3
0.2
0.0
-14
-12
-10
8
-6
log [OH]
I . I . i-i.i
0 2 4 6 8
PH
FIGURE 3. Distribution of molecular and 1on1c species of
divalent mercury at different pH values .
26
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Nickel carbonyl is also very toxic and when concentrated, potentially
explosive. Nickel carbonyl is not decomposed in dilute acid or basic
solutions but will produce cabon monoxide and nickel metal when heated.37
Selenium
As with some of the other metals, some selenium compounds adsorb more
strongly in the pressure of iron oxides.3a Selenium dioxide is readily
3 9
soluble in water and forms selenous acid in aqueous solutions. Common forms
of selenium include H2Se, Se2Cl2, SeCK, Se03, Se03, H2SeG3, H2SeOu, CaSe03,
BaSe03, Se205 and K2SSeG3. Many of these compounds can be reduced to produce
selenium metal when exposed to organic matters in the subsurface
environment/0
Thorium
Thorium salts are not very soluble in neutral pH natural waters. Those
salts of thorium that are soluble are those of sulfates, chlorides, and some
sulfides. However, as the solution becomes basic, these salts are converted
to the hydroxide, Th(0H)„, and precipitate out/0 It is interesting that the
effect of temperature on the solubility of thorium sulfides depends upon the
hydrate being tested. For example, ThS2*9H20 increases in solubility with
increasing temperatures, while ThS2*4H20 decreases in solubility."*0 The more
common hydrate is ThS2*8Ha0.
Other known salts of thorium Include BaThOj, (NHw)2Th(N03)6, Th3(PO^),»,
Th(HP0J2, ThP207, ThS2, Th(S0„)2, ThO, and Th02.
MATHEMATICAL MODELS USEO FOR PREDICTION OF FATE
Several research projects have concentrated on the modeling of some of the
processes just discussed. Schechter et al."1 present a good review of some
models in the areas of aqueous geochemistry and solution chemistry. If a
27
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particular situation can be defined as containing specified components,
equilibrium constants can be approximated and the overall results predicted.
Certain thermodynamic parameters are known for many of the materials of
interest and provide a reasonable base from which to start. The report by
Schechter et a 1. ^ * provides a more detailed discussion of these modeling
systems. Some of the more popular models discussed include: WATEQF, SOIMNEQ,
PHREQE, EQ3/EQ6, PATHI, MINEQL, MINEQLI-STANFORD, PHASEQl/FLOW, and RE0EQL/;
Roberts et al/3 present a good review on some mathematical models for
simulating the transport of wastes in an underground aquifer. These models
attempt to predict the advection, dispersion, and sorption behavior of non-
degradable organic solutes. Actual field cases were examined and compared
with theoretical and laboratory results. The study showed that adsorption
processes could be predicted with some accuracy; however, they found it
necessary to measure the advective and dispersive properties in the under-
ground environment. Theoretical and laboratory studies were not sufficient to
predict the behavior in the field accurately.
Mills et al."" present a summary of five models that can be used to
predict contamination in ground water. These models calculate contaminant
concentrations as a function of time for a given set of conditions. Two
models are radial one-dimens1onal, one model 1s cartesian one-dimensional, and
two models are cartesian two-dimensional. Such parameters as boundary
conditions, aquifer dimensions, d1spers1v1ty coefficients, porosity, initial
contaminant concentrations, and retardation factors are needed as input to
these models.
Kayser and Collins"5 present a summary of some of the models relevant to
ground water contamination from enhanced oil recovery (EOR) or other fluids.
The four types of models discussed include the groundwater flow model, solute
28
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transport model, heat transport model, and deformation model. Each of these
/node! types is based on different dependent variables and is particularly
useful for answering different types of questions.
The intent of this section was primarily to indicate that if certain
processes are well defined, they can be usefully modeled. Suci models allow
researchers to predict the fate of certain chemicals for a given situation. As
shown already, many non-organic hazardous waste materials con:ain compounds
that have been extensively studied in the laboratory. The existence of this
knowledge is the reason development of mathematical models has been possible;
however, as previously stated, the underground environment contains additional
variables that have not been studied extensively. Thus, the degree of
uncertainty in fate prediction by these methods is still large, and correct
answers still must be obtained from tracer and pilot tests in the field.
PROCESSES INVOLVING ORGANIC HAZARDOUS WASTES
Unlike that of non-organic hazardous materials, the organic hazardous
wastes can be made non-hazardous by molecular transformations of the com-
pounds. Such processes as ion exchange, oxidation, reduction, hydrolysis,
cyclization, and biological transformations are all possible means of
rendering the wastes non-hazardous. Alternatively, these same processes can
lead to increased toxicity for certain wastes. Because the number of
potential products 1s almost Infinite, assessing the "ultimate fate" of these
wastes is even more difficult than for the non-organic hazardous wastes. For
example, the conclusions of one study*5 for the Injection of organic wastes at
Wilmington, NC, suggested that all of the following chemical and biological
processes occurred:
29
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• dissolution of carbonate minerals by organic acids and production of
carbon dioxide
• dissolution and complexation of iron derived from sesquioxide coat-
ings on granular materials in the aquifer by organic acids
• reprecipitation of complexed dissolved iron during waste neutral-
ization
• coprecipitation of phthaiic acid complexed with iron during iron
precipi tat ion
• methane gas production from microbial degradation
• microbial reduction of sulfates to sulfides
• reduction of ferric ion to ferrous ion from Eh and pH changes due to
microbial waste degradation
• retention of organic waste acids by adsorption and ion exchange onto
the injection-zone mineral constituents
• formation of ferric hydroxide, ferric carbonate, terephthallc acid as
precipitates, and carbon dioxide which led to the plugging of the
wells
The report by Callahan et al.*7 gives a good summary of the expected fate
for 129 non-organic and organic hazardous waste compounds. Although this
report addresses the aquatic environment and not deep-well Injection zones,
the information provides a good beginning.
Whether the environment 1s aerobic or anaerobic determines what
blodegradation processes will predominate. The types of organisms that
dominate under aerobic conditions do not dominate under anaerobic
conditions. Since some wastes are degraded more easily by aerobes and others
are degraded more easily by anaerobes, the prevailing conditions will
determine which wastes will be degraded. Furthermore, waste solutions
30
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introduced into the subsurface environment may change a predominately aerobic
environment to an anaerobic environment. Jackson et al.*8 summarize the
expected probability of transformation for some organic compounds under
different conditions. For example, chlorobenzenes are likely to degrade
under aerobic conditions but not under anaerobic conditions. Conversely,
carbon tetrachloride is not likely to degrade under aerobic conditions but is
likely to degrade under methanogenic and denitrification anaerobic conditions.
A brief discussion of the various processes of degradation available to
organic wastes will be presented in this section. The details of the
discussions are shorter than the corresponding discussions for non-organic
materials because (1) hardly any definitive work has been done and (2) the
number of possible interactions is much greater than that of non-organic
materials, making definitive fate predictions more difficult to determine.
Thermal Degradation
Such processes as oxidation, reduction, hydrolysis, adsorption, and
microbiological degradation are common methods of transformation for organic
hazardous wastes. Other transformation processes that are initiated thermally
are possible and should be considered here as thermal degradation. These
processes wight Include pyrolysls, condensation reactions, cyclization,
1ntra-molecular rearrangements, etc. However, most of these processes are
dependent upon either very high temperatures or the presence of other
chemicals.
The reservoir temperatures and pressures commonly existing in the
injection zones of the hazardous waste Injection wells are normally too low
for Initiating high-temperature reactions. However, 1f the right chemicals
(not necessarily the hazardous chemicals listed) contact some of the hazardous
31
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wastes, these other processes listed in the first paragraph are possible. For
example, phenols can react with formaldehyde to form phenolic resins. The
number and type of these chemical interactions are limitless. Because the
actual chemical reactions are dependent upon the presence of other specific
chemicals, each reservoir and waste composition should be evaluated
individually to determine what reactions and reaction products are likely.
Adsorption Processes
Adsorption is a major mechanism of fluid-solid interactions that affect
the mobility of organic wastes. Adsorption has been found to be dependent
upon the particular clays present. That is, montmorillonite and vermiculite
have very high adsorption capacities, while kaolinite has a very low adsorp-
tion capacity. IlUte and chlorite are intermediate in their ability to
adsorb."9 These properties have been attributed to the available surface area
for the respective clays.
Many factors influence the degree of adsorption of various chemicals.
Sorce of these factors Include chemical shape and configuration, acidity, water
solubility, charge distribution, polarity, molecular size, and polar-
Izability."9 Most organic compounds that adsorb on clay materials have
contributions from all of these properties. Thus, predicting the degree of
adsorption according to relative acidity may lead to incorrect predictions if
resonance stabilization 1s not considered.1*9 Molecular shape may Increase or
decrease the adsorption energies of any particular compound, even though the
other chemical properties may be very similar. All of these listed properties
have been demonstrated to be important and are found to be interdependent.
Another factor that influences adsorption is temperature. Since
adsorption processes are generally exothermic and desorption processes are
32
-------
generally endothermic, an increase in temperature would normally reduce
^ 2
adsorption.processes. However, a number of exceptions have been found. The
pesticide EPTC is an example.
The mechanism of adsorption may occur by one of several different
mechanisms for organic chemicals. These mechanisms include ion exchange,
protonation at the silicate surface, protonation in the solution phase with
subsequent adsorption by ion exchange, and protonation by reaction with the
disassociated protons from residual water present on the surface or in
coordination with the exchangeable cation."5 The most easily adsorbed organic
compound by ion exchange is that of the cation. The process is much the same
as that which occurs for inorganic materials and is well documented."9 Other
methods of adsorption include chemical adsorption via Van der Waals forces,
hydrogen bonding, and coordination with metals.
Several specific studies were conducted with pentachlorophenol.50-51
These studies explained how pentachlorophenol was adsorbed via a combination
of 1on exchange and Van der Waals forces. The study also was careful to show
the pH dependencies of the process. For example, in acidic solutions
pentachlorophenol was found to decrease in concentration by precipitation, but
at pH values greater than 5 the drop of concentration in the presence of clay
was due to adsorption, not precipitation.
The affect of temperature on adsorption of pentachlorophenol was contrary
to expectations. For four different clay samples, adsorption of penta-
chlorophenol was greater at higher temperatures (33° C) than at lower
temperatures. Admittedly the temperatures were not indicative of deep-well
environments, and no one has determined whether this trend would continue with
even higher temperatures.50
33
-------
As expected, an increase in concentration of other salts in the solution
corresponds to a decrease in the amount of adsorption of pentachloro-
phenol.50 This observation supports an ion exchange mechanism for the
adsorption process and compares similarly to the results obtained for
non-organic materials.
Mortland52 also discusses some of the mechanisms by which organic chem-
icals are adsorbed. These include the replacement of metals with cationic
molecules, replacement of metals by neutral molecules that are protonated to
become cationic, ion exchange with polyvalent metals attached to the clay,
coordination with metal cations, and by hydrogen bonding. Many of these
mechanisms have been studied and demonstrated using such techniques as
adsorption isotherms, calorimetry, X-ray diffraction, UV-visible spectroscopy,
electron spin resonance spectroscopy, and infrared spectroscopy.
Once adsorbed, other processes may take place that lead to degradation of
the adsorbed materials. For example, microorganisms may concentrate at the
solid surface and metabolize the organic wastes. The organic compounds may
undergo other chemical reactions 1f the clays or minerals attached to the
clays can catalytically initiate other such reactions. McAullffe and
Coleman53 have demonstrated this process to occur with hydrolysis of esters.
Other examples also are discussed by Mortland.52
The adsorption of trlchloroethylene and pentachlorophenol on several
Missouri soils was discussed by O'Conner et al.5" Trlchloroethylene was not
found to adsorb as readily as pentachlorophenol. Both were found to adsorb
less as the pH was increased.
Rogers and McFarlane55 studied the adsorption of carbon tetrachloride,
ethylene dlbromide, and chloroform on montmorillonite clay. The adsorption of
the materials tested depended upon the conditions and materials tested. For
34
-------
example, neither carbon tetrachloride or chloroform adsorbed onto calcium
saturated clay, but chloroform showed 17 percent sorption on aluminum satur-
ated clay. The mechanism for this difference was not understood.
Sorption studies of some chlorinated benzenes were discussed by
Scfiarzenbach and Giger.36 They found that for typical concentrations in the
natural environment, a linear sorption isotherm could be used. As organic
carbon increased, adsorption also increased.
Haque et al.57 briefly discussed adsorption processes in soil. Adsorption
processes are dependent upon factors such as structural characteristics of the
molecule, organic content of the soil, pH of the medium, particle size, ion
exchange capacity, and temperature.
The Freundlich isotherm often is used to evaluate adsorption of chemical
compounds:
x/ra = KCn
x—amount of chemical adsqrbed
n—mass of soil
C—equilibrium concentration of the chemical
K—constant describing extent of adsorption
n—constant describing the nature of adsorption
Generally, as the solubility of the adsorbate decreases, adsorption increases,
and as organic content of soil Increases, adsorption Increases. However,
ionic compounds or compounds capable of becoming Ionic do not necessarily
follow the Freundllch Isotherm concept. Of course, these studies refer to
soil. The usefulness of the Freundllch Isotherm concept for adsorption in
deep-well injection 2ones was not discussed.
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Oxidation of Organic Hazardous Wastes
Another process by which certain hazardous organic wastes can be
transformed into other compounds is by oxidation reactions. Such compounds as
phenols, aromatic amines, olefins, dienes, alkyl sulfides, and eneamines are
particularly susceptible.58 The exact species of different oxygen radicals
present in aqueous and soil environments that initiate the oxidation process
may include such oxy-radicals as HO*, RO*, and 02, depending upon the
environmental conditions. The potential importance of this process at typical
injection well conditions to hazardous waste injection has not been
evaluated. However, if certain hazardous wastes containing chromium (VI) are
co-injected either simultaneously or sequentially with organic wastes, the
oxidation process most certainly will be important. Chromium (VI) can be an
excellent oxidizing agent.
Hydrolysis of Organic Hazardous Wastes
Hydrolysis is the chemical process by which some functional group attached
to a molecule is replaced by an -OH functional group originating from a wat?r
molecule. Hydrolysis can be catalyzed by either an acid or a base, as defined
in chemistry for Lewis acids and bases.
Mabey and M1HS9 provide a good review of hydrolysis processes of organic
materials 1n the environment. Factors such as pHt temperature, and the
presence of other 1ons are known to affect the rate of hydrolysis. Depending
upon whether the pH is high or low, different mechanisms may apply. At low
pH, the hydronium ion (H30+) predominates in hydrolysis, while at high pH, the
hydroxide 1on (OH") predominates. Although the effect of temperature 1s
known, the magnitude of the Influence that temperature has on different
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compounds is not always known. The presence of certain alkaline earth and
heavy metal ions may catalyze hydrolysis for a variety of esters.
The effect of pH can be illustrated with aliphatic and allylic halides.
Hydrolysis may occur for these halides at neutral or basic conditions to give
alcohols but are not likely to undergo the same process at acidic
conditions. The type of halide being considered also affects the rate of
hydrolysis. The rate constant for phenyl dichloromethare is about five orders
of magnitude greater than that for dichloromethane. Chlorobenzene is
virtually resistant under normal circumstances to hydrolysis.
Most of the hazardous wastes studied that can potentially unaergo
hydrolysis reactions are halogenated hydrocarbons, such as carbon tetra-
chloride, ethylene dibromide, and chloroform. Most of the results to date are
derived from conditions most likely to occur near the surface of the earth.
For example, ethylene dibromide has a half-life of 5 to 10 days, whereas
carbon tetrachloride is much more resistant and has a half-life of 700 to 7000
years and that of chloroform is somewhere between these two ranges of
values. Subsurface environments may lead to shorter half-life times with
increased temperatures, pressures, and Eh. Since, most of these compounds are
not normally biodegradable, hydrolysis 1s expected to be the main mechanism of
transformation.
Half-life times can be estimated fairly accurately if rate constants are
known for the compound at the appropriate temperature, pH, ionic strength,
etc. However, the amount of data available is limited, and even though
extrapolations can be made from one temperature to another, such extra-
polations often introduce large errors.
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Microbiological Degradation
Biodegradation can result from a variety of processes.50"'2 These
processes include mineralization, detoxification, cometabolism, activation,
and defusing. Mineralization is the conversion of organic wastes to inorganic
wastes. Oetoxification is the conversion of toxic compounds to nontoxic
compounds. Cometabolism is the conversion of one organic compound to another
without the microorganism using this process as a nutrient. Activation is the
conversion of a nontoxic compound to a toxic compound. Defusing is the
process of converting a compound potentially capable of becoming hazardous to
another non-hazardous compound by circumventing the hazardous intermediate.
Although defusing has been confirmed in the laboratory, it has not been
identified in the environment.
The first question with respect to biodegradation most certainly is: When
do any microbes exist in the injection zone, or can microbes capable of
converting organic wastes to non-hazardous wastes exist at those conditions?
Several researchers have attempted to answer this question.
DiTommaso and Elkan63 analyzed a saline aquifer at the depths of 850 to
1000 ft. Much of the waste injected into this zone contained organic
compounds such as acetic acid, formic acid, and methanol. About 3000
organisms/ml were isolated from the unpolluted aquifer. Most of the organisms
identified were aerobes typically found 1n aquatic environments. The most
common genera include Aqrobacterium. Pseudomonas, Proteus, Bacillus.
Aerobacter, Coryne bactor, Arthobacter. and Micrococcus. Conversely, samples
taken after waste injection were found to contain primarily anaerobic
methanogenic bacteria.
Chr1stof1 et al.6* investigated several underground mines in Europe for
the presence of microbiological activity. The depth of mines from which
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samples were taken varied from 600 to more than 3000 ft below the ground
surface. Microorganisms were found in all wells, although the greatest
variety was found in the least saline aquifer. Salinity varied from less than
5.7xl02 mg/1 chloride to greater than 1.32x10s mg/1 chloride. The original
report should be consulted for more details.
Grula and Grula65 discussed the degradation of wastes in subsurface type
conditions. They noted that aerobic degradation usually is more efficient
than anaerobic degradation, that seme compounds such as aromatic chemicals can
be degraded only by aerobes, and that higher temperatures are not as limiting
for aerobes as for anaerobes. Grula and Grula65 studied various compounds to
determine which microorganisms and which supplemental nutrients would be
necessary.
Additional research has shown that once the injection of hazardous wastes
begins, other microorganisms that can ut111ze the wastes often appear and
remain in the reservoir while the wastes are being injected. Grula and
Grula65 evaluated a number of organic compounds including nltrlles, carboxylic
acids, alcohols, amines, benzoic acids, phenols, ketones, aldehydes, nitro-
aromatlc compounds, and others. These compounds were subjected to enriched
cultures to determine which organisms would be capable of incorporating and
modifying which compounds. The effect of temperature, pressure, and mixed
culture systems was also studied.
Elkan and Horvath*6"67 showed that upon injection of organic wastes the
injection wells became more anaerobic In nature. Unlike the biological system
of the unpolluted aquifer, the microorganisms 1n the injection zone during the
period of waste disposal was dominated by methanogenic and sulfate-reducing
bacteria. Additional laboratory model studies supported this conclusion.
Microbial populations increased by seven or more orders of magnitude when
39
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waste was introduced into the model. The effects of pressure varied.
Degradation rates of formic acid increased as pressure was increased to 500
psi, but the degradation rates decreased again when pressures were further
increased to 4,000 psi.
Wilson et al.°8 showed that certain chlorinated alkanes and alkenes were
not degraded in materials normally found in deep subsurface environments.
Other compounds, such as toluene and styrene, were readily degradable under
the same conditions, although not equally so in different environments. Thus,
Wilson et al.63 recommended that biodegradation should not be depended upon
for waste degradation unless the particular waste has been tested in the
materials encountered and at the likely downhole conditions.
Similarly, Rittman et al.69 conducted studies of biodegradation for
certain compounds. This study discussed the microorganism biofilm model that
presumably is formed to degrade the waste chemicals near the point of injec-
tion. Correlation of results with model predictions supported the formation
of a biofilm. Some Individual compounds, such as naphthalene and
heptaldehyde, were degraded, whereas others such as haloforms were not.
Horvath70 provides a good review of some of the studies conducted on
biodegradation of wastes 1n subsurface environments and summarizes some of the
processes Involved in the degradation of such compounds as acetate, formate,
methanol, formaldehyde, and aromatic acids. Horvath71 also developed a
laboratory model to evaluate these processes. These studies Indicated an
Interesting observation concerning methane and sulfate-reducing bacteria.
Apparently, even though the required nutrients were available, methanogenic
bacteria did not proliferate, whereas the sulfate-reducing bacteria did in the
zone studied. This behavior may have occurred because of the pH that
predominated for the test and supported work done by others who indicated that
40
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the two types of bacteria are mutually exclusive. Obviously, the degradation
of injected wastes will depend upon which type of bacteria prevails. Methane-
producing and sulfate-reducing bacteria do not degrade the same compounds.
Healy and Daughton71 provide a good literature review of biodegradation in
the groundwater. The authors concluded that even though several studies have
shown the existence of bacteria in the subsurface environment, other factors
necessary for fate prediction remain undetermined. The true origin of these
bacteria has not been established, the level of activity for these bacteria is
not always known, and the importance of other nonbiological processes already
discussed in microbial degradation are all important topics that need further
study.
Finally, although it is not of direct importance, the effect of pressure
on bacteria was studied by Zobell et al.72_7S For example, as pressures were
increased from 1 to 400 atmospheres, E. Coif growth and reproduction was
retarded, and above 400 atmospheres, the death rate was accelerated.70 A
number of other bacteria were also tested 1n this range, although the results
varied from one type to another.73 In general all growth and reproduction
processes decreased with Increasing pressures to 600 atmospheres.73 Bacteria
Isolated from the marine environment at depths normal to these same pressures
grew well in the laboratory studies and particularly at the slightly warmer
conditions.73 The effects such pressures have on the metabolic rates are
presently unknown.
In summary, microbial degradation often 1s a very important mechanism by
which certain hazardous wastes may be transformed to non-hazardous wastes.
Bacteria have been identified 1n the subsurface environment. Within certain
reasonable limits, bacteria are capable of surviving relatively hostile
environments. Studies have also shown that transformation processes via
41
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biological pathways can be very complicated and difficult to establish.
Therefore, this method should not be depended upon for waste detoxification in
the subsurface environment, unless pilot studies have establis-ed the
existence of these processes.
FIELD CASE STUDIES
Belle Glade, Florida
McKenzie75 discussed a case study concerning the upward migration and
geochemical interactions of an acidic industrial waste injected into a saline
aquifer near Belle Glade, Florida. The hot acidic liquid waste generated at a
furfural plant at Belle Glade was injected into the lower part of the aquifer
between depths of 1405-1939 ft. The injection of the waste began ;n 1966.
Within 27 months, effects of wastes were detected at a shallow monitoring well
in the upper part of the aquifer.
The analysis of the water samples indicated that the wastes wers trans-
ported upward and laterally. This migration was indicated by a decrease in
the sulfate/chloride ratio and a corresponding increase in the nydrogen
sulfide concentration in the observation well water.
Remedial actions were taken. The wastes were injected into a deeper
portion of the Injection zone (2200 ft). However, when the wastes continued
to migrate upward into the shallow well, the wastes were injected even deeper
(3000 ft). The effectiveness of this latest strategy is not known.
McKenzle76 concluded that the carbonate aquifer could not contain the hot
acidic wastes. No extensive work was performed to determine the area" extent
of the zone of contamination.
The first reaction Involving the waste with the limestone formation was
neutralization of the acids. As a result, the concentration of calcium,
42
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magnesium, and silica increased in the waste solution. Sulfate-reducing
bacteria present in the formation converted sulfates to sulfides. The
presence of hydrogen sulfide produced by the bacteria and the subsequent
decrease of sulfate/chloride ratio was one of the indicaters of fluid
migration.
Wilmington, North Carolina
From May 1968 to December 1972, an industrial organic waste derived from
the manufacture of dimethyl terephthalate was injected at a rate of about
300,000 gal/day into a sedimentary aquifer containing saline water at a site
near Wilmington, North Carolina. The injection zone consisted of multiple
zones ranging in depth from about 850 to 1,000 ft. The injection of waste was
started in May 1968 and was stopped in Oecember 1972. The injection was
discontinued after the operators determined that disposal of this waste into
the reservoir was not desirable. Even though injection of the waste was
discontinued, monitoring of the waste movement and subsurface environment were
continued Into the mid-1970s. Peek et al.77 reported the Initial results at
an international symposium on underground waste.' A final report documenting
the laboratory and field results of this project was presented by Leenheer et
al.78-79 The following paragraphs summarize this Investigation.
A site study was Initiated 1n June 1971 to Investigate the waste aquifer
Interactions. The first stage of the study Involved the characterization of
the industrial waste, the native ground water found in the injection zone, and
the site hydrogeologlc conditions. Sodium chloride was found to be the major
dissolved solid constituent of the native ground water. The average dissolved
solid concentration was estimated to be about 20,800 mg/1. The average
dissolved organic carbon of the industrial waste was determined to be about
43
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7,100 mg/1 and comprised acetic acid, formic acid, p-toluic acid, formal-
dehyde, methanol, terephthalic acid, phthalic aid, and benzoic acid. Before
injection, the organic waste was neutralized to a pH of 4 by adding lime.
Therefore, the major inorganic constituent of the waste was calcium (about
1,300 mg/1).
The second stage of the study determined the waste-aquifer interactions at
various observation wells. Water samples were taken from three observation
wells located 1,500 to 2,000 ft from injection wells. This second stage
revealed the following observations.
• The waste organic acids were responsible for the dissolution of
carbonate minerals, alumino-silicate minerals, and the sesquioxide
coatings on the primary minerals in the injection zone.
• The waste organic acids dissolved and formed complexes with iron and
manganese oxides. These dissolved complexes reprecipitated when the
pH increased to 5.5 or 6.0, due to neutralization of the waste by the
aquifer carbonates and oxides.
• The aquifer mineral constituents sorbed all waste organic compounds
except formaldehyde. The sorption of all organic acids except the
phthalic acid was increased with a decrease 1n waste pH.
• Phthalic acid was complexed with dissolved iron. The concentration
of this complex decreased as the pH Increased, because the complex
copreclpltated with the Iron oxide.
• Biochemical waste transformation occurred at low waste concen-
trations. This resulted 1n the production of methane. Additional
microbial degradation of the waste resulted in the reduction of
sulfates to sulfides, and the reduction of ferric 1ons to ferrous
44
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1ons. Additional biodegradation does occur slowly in this subsurface
environment.
The wells became plugged after a few months of injection because of the
reactive nature of the wastes. Thus, compatibility of wastes with fluids and
minerals in the injection zone should be considered before injecting these
types of wastes. The plugging resulted in this case from the precipitation of
the initially dissolved minerals, from the formation of gaseous products such
as carbon dioxide and methane, and from the dissolution of the bond between
the cement grout surrounding the well casing and confining beds by the organic
acids. As a result of the plugging 1n the formation, the waste leaked upward
into the shallower zones.
Pensacola. Florida (American Cyanaroid)
Vecch1ol1 et al. ®°"ai summarized the findings of an investigation on the
fate of an industrial waste liquid cqntalnlng organonltrlle compounds and
nitrate. These wastes were Injected Into the lower limestone formation of an
aquifer near Pensacola, Florida.
Chemical analyses of water from a monitor well and the backflow from the
injection well indicated that organic compounds were converted to carbon diox-
ide and the nitrate was reduced to elemental nitrogen. These microbiological
transformations were virtually complete within a short distance from the
Injection well.
Sodium thlocyanate contained 1n the waste remained unaltered during the
movement through the Injection zone. Thus, sodium thlocyanate was used to
detect the degree of mixing of waste liquid with native water at an obser-
vation well. Analysis of samples taken from the observation well indicated
45
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that the waste liquid was completely free of organonitriles and nitrate. An
80 percent reduction in chemical oxygen demand was also observed.
Pensacola. Florida (Monsanto)
Pascale et al.8"' discussed the hydraulic and chemical data collected at a
deep-well, waste-injection system near Pensacola, Florida. The industrial
liquid wastes generated at a Monsanto Company chemical plant consisted of
nitric acid, inorganic salts, and numerous organic compounds. The wastes were
injected into a saline water-filled limestone aquifer.
The report summarized the data collected between 1970-1977. These data
include injection rates, injection volumes, injection pressures, water levels,
and laboratory analyses of water samples taken from three monitor wells.
The wellhead pressure averaged 180 psi in March 1977, and the hydraulic
pressure gradient was 0.53 psi/ft of depth at the top of the injection zone.
While the chemical character of the water collected from the shallower obser-
vation well remained unchanged, the water samples from the deeper monitor well
to the south showed an increase in concentrations of bicarbonate, dissolved
organic carbon, and gas content. These observations Indicated that microbial
degradation of the wastes was occurring 1n the Injection zone.
CONCLUSIONS
Many conclusions were presented by the papers reviewed 1n this report;
some of the more significant ones are as follows:
• The basic compatabillty test conducted by mixing waste fluids and
reservoir fluids does not always give meaningful results. The test
must be conducted under reservoir conditions. Precipitates, if
formed in the compatlbll 1ty test, may or may not plug the well
depending upon the type of precipitate formed.
46
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For non-organic wastes, solution pH is critical for determining the
ultimate fate. The identity of soluble species, solubility products,
adsorption characteristics, and chemical interactions are seme of the
variables affected by pH.
The brine concentration, even though not listed as hazardous, is
important in affecting clay stability and adsorption characteristics.
The presence of organic complexing agents may or may not affect the
mobility of heavy metals in the reservoir.
Adsorption of non-organic wastes is dependent upon a number of
factors, such as Eh, pH, clay type, and the presence or absence of
iron oxides and hydroxides.
Mathematical models do successfully predict certain reaction pro-
cesses. However, some interactions have not been modeled yet.
Pentachlorophenols adsorb onto clays by a combination of ion exchange
and Van der WaaIs forces.
The major mechanism of degradation for certain halogenated hydro-
carbons is hydrolysis.
Microbial degradation of organic hazardous wastes has been shown to
be useful 1n decontamination after deep-well Injection. Wastes can
support growth of certain bacteria during the Injection process.
However, results are not always predictable, and studies suggest that
each case should be evaluated Individually to determine the
feasibility of the process.
Some case studies corroborate the interrelationships of degradation
processes discussed 1n this report.
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RECOMMENDATIONS
The authors of this report recognize that all areas discussed need to be
investigated further. Additional research in all areas will provide the
foundation needed for predicting the ultimate fate of hazardous wastes
disposed of by deep-well injection. However, the following areas are
considered more productive in the near-term and are recommended for Phase II
and Phase III of this project.
Phase II
Conduct dynamic coreflood studies of selected phenols to determine their
short-term fate (30 to 60 days) under typical reservoir conditions created in
the laboratory. Such parameters as solution pH, salt concentrations,
temperatures, clays, and waste concentration should be evaluated with respect
to precipitation, adsorption, permeability reduction, and thermal degradation.
Phase III
Conduct dynamic coreflood and/or related studies of selected hazardous
wastes to determine their fate 1n subsurface environments. Although the exact
scope has not been agreed upon, the following suggestions are possible.
Expand the work conducted 1n Phase II by doing similar experiments on other
cores or with other organic waste compounds. Investigate Interactions of the
phenols tested 1n Phase II with confining layer materials (this Investigation
probably should be done using hydrothermal reactors rather than corefloods).
Extend the work in Phase II to include the effects of microorganisms on the
degradation of phenols.
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