United States Office of Water and SW-873
Environmental Protection Waste Management September 1980
Agency Washington DC 20460 /i o.
vvEPA Closure of
Hazardous Waste
Surface
Impoundments
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SW-873
September 1980
CLOSURE OF HAZARDOUS WASTE SURFACE IMPOUNDMENTS
by
A. W. Wyss, H. K. Willard, and R. M. Evans
Acurex Corporation
Energy & Environmental Division
485 Clyde Avenue
Mountain View, California 94042
and
R. J. Schmitt, R. G. Sherman, D. H. Bruehl, and E. M. Greco
Metcalf and Eddy, Inc.
1029 Corporation Way
Palo Alto, California 94303
Contract No. 68-03-2567
Project Officer
John F. Martin
Energy Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
U.S. Environmental Protection Agency
Region V, Library
230 South Dearborn Street
Cx'^o, Wir.ois 60604
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, the Municipal Environmental Research Laboratory and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health and
welfare of the American people. Noxious air, foul water, and spoiled land
have occurred, giving testimony to the deterioration of our natural
environment. The complexity of that environment and the interplay between its
components and waste materials from our industrialized society require a
concentrated and integrated attack on the problems.
The Municipal Environmental Research Laboratory develops new and improved
technology and systems for the prevention, treatment, and management of
wastewater and solid and hazardous waste pollutant discharges from municipal
and community sources; for the preservation and treatment of public drinking
water supplies; and to minimize the adverse economic, social, health, and
aesthetic effects of pollution. This publication has been developed under a
fast tracking activity by the Office of Research and Development for the
Office of Solid Waste. Through this activity a series of technical manuals
have been prepared to assist in carrying out the current effort to implement
the Resource Conservation and Recovery Act.
This manual presents considerations that must be made to develop a plan
for closure of surface impoundments containing hazardous wastes. It provides
the current engineering judgement on closure operations that minimize the
possibility of adverse environmental impacts.
Francis T. Mayo, Director
Municipal Environmental Research Laboratory
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PREFACE
The land disposal of hazardous waste is subject to the requirements of
Subtitle C of the Resource Conservation and Recovery Act of 1976. This Act
requires that the treatment, storage, or disposal of hazardous wastes after
November 19, 1980 be carried out in accordance with a permit. The one
exception to this rule is that facilities in existence as of November 19, 1980
may continue operations until final administrative disposition is made of the
permit application (providing that the facility complies with the Interim
Status Standards for disposers of hazardous waste in 40 CFR Part 265). Owners
or operators of new facilities must apply for and receive a permit before
beginning operation of such a facility.
The Interim Status Standards (40 CFR Part 265) and some of the
administrative portions of the Permit Standards (40 CFR Part 264) were
published by the Environmental Protection Agency in the Federal Register on
May 19, 1980. The Environmental Protection Agency will soon publish technical
permit standards in Part 264 for hazardous waste disposal facilities. These
regulations will ensure the protection of human health and the environment by
requiring evaluations of hazardous waste management facilities in terms of
both site-specific factors and the nature of the waste the facility manages.
The permit official must review and evaluate permit applications to determine
whether the proposed objectives, design, and operation of a land disposal
facility will comply with all applicable provisions of the regulations
(40 CFR 264).
The Environmental Protection Agency is preparing two types of documents
for permit officials responsible for hazardous waste landfills, surface
impoundments, and land treatment facilities: Permit Writers Guidance Manuals
and Technical Resource Documents. The Permit Writers Guidance Manuals provide
guidance for conducting the review and evaluation of a permit application for
site-specific control objectives and designs. The Technical Resource
Documents support the Permit Writers Guidance Manuals in certain areas (i-e.,
liners, leachate management, closure, covers, water balance) by describing
current technologies and methods for evaluating the performance of the
applicant's design. The information and guidance presented in these manuals
constitute a suggested approach for review and evaluation based on best
engineering judgments. There may be alternative and equivalent methods for
conducting the review and evaluation. However, if the results of these
methods differ from those of the Environmental Protection Agency method, they
may have to be validated by the applicant.
In reviewing and evaluating the permit application, the permit official
must make all decisions in a well defined and well documented manner. Once an
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initial decision is made to issue or deny the permit, the Subtitle C
regulations (40 CFR 124.6, 124.7, and 124.8) require preparation of either a
statement of basis or a fact sheet that discusses the reasons behind the
decision. The statement of basis or fact sheet then becomes part of the
permit review process specified in 40 CFR 124.6 through 124.20.
These manuals are intended to assist the permit official in arriving at a
logical, well defined, and well documented decision. Checklists and logic
flow diagrams are provided throughout the manuals to ensure that necessary
factors are considered in the decision process. Technical data are presented
to enable the permit official to identify proposed designs that may require
more detailed analysis because of a deviation from suggested practices. The
technical data are not meant to provide rigid guidelines for arriving at a
decision. References are cited throughout the manuals to provide further
guidance for the permit official when necessary.
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CONTENTS
Foreword iii
Preface iv
Figures viii
Tables viii
1. Introduction 1
1.1 Purpose 1
1.2 Content Description 1
1.3 Related Topics Previously Covered 2
2. General Information on Surface Impoundments 5
2.1 Characteristics of Surface Impoundments 5
2.1.1 Definition of Surface Impoundments 5
2.1.2 Types and Construction of Surface Impoundments . . 5
2.1.3 Population of Surface Impoundments 6
2.1.4 Surface Impoundment Uses 6
2.1.5 Industrial Impoundment Practices 7
2.2 Methods of Closure 8
2.2.1 Waste Remains in Place 8
2.2.2 Waste Removed 9
2.3 Air and Water Impacts of Surface Impoundments 10
2.3.1 Surface Water 10
2.3.2 Ground Water 11
2.3.3 Air Emissions 12
2.4 Direct Public Exposure and Site Security 13
3. Environmental Considerations for Closure Plan Analysis .... 15
3.1 Leaching Potential of Wastes 15
3.1.1 Mechanisms of Leaching 15
3.1.2 Factors Affecting Leaching Rates 16
3.1.3 Methods to Quantify Leaching Rates 17
3.2 Containment System Performance 18
3.2.1 Factors Affecting Performance/Life 18
3.2.2 Assessment of Liner Condition and Effectiveness . . 21
3.3 Potential for Waste Migration 23
3.3.1 Water Balance 23
3.3.2 Attenuation Mechanisms 27
3.4 Cover Systems 31
3.5 Potential for Consolidation of Wastes 35
3.5.1 Stages of Consolidation 35
3.5.2 Impacts of Waste Consolidation 36
3.5.3 Mechanism of Consolidation 36
3.5.4 Timeframe of Consolidation 38
3.6 Post-Closure Use of the Surface Impoundment Site 39
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CONTENTS (Concluded)
3.6.1 Site Use Limitations for Impoundments Closed
as Landfills 41
3.6.2 Site Use Limitations for Impoundments Closed
with Hazardous Waste Components Removed 43
3.6.3 Considerations for Limiting Access 44
3.7 Air Emissions 44
3.7.1 Gases Emitted from Impounded Materials 44
3.7.2 Fugitive Dust Emissions 49
4. Technical Criteria for Implementation of Closure Procedures . . 56
4.1 Impoundment Dewatering 58
. 4.2 Waste Sediment and Soil Removal 59
4.2.1 Wet Methods for Sediment Removal 59
4.2.2 Dry Methods for Sediment Removal 60
4.2.3 Liner Preservation 61
4.2.4 Soil Removal 61
4.3 Sediment Dewatering 61
4.3.1 Passive Dewatering 62
4.3.2 Active Dewatering 63
4.4 Liner Removal/Repair 64
4.4.1 Reason for Removal 64
4.4.2 Liner Removal Methods 64
4.4.3 Reason for Liner Repair 65
4.4.4 Liner Repair Methods 65
4.5 Soil Contamination Testing 65
4.5.1 Surface Soils 66
4.5.2 Soils Adjacent to Impoundment 66
4.5.3 Soils Remote from Impoundment 66
4.5.4 Drilling and Sampling Programs 67
4.5.5 Ground Water Analysis 67
4.5.6 Soil Analysis 68
4.5.7 Interpretation of Results 68
4.6 Dike Stability 68
4.6.1 Inventory of Historical Information 69
4.6.2 Reconnaissance Investigations 70
4.6.3 Geotechnical Investigations 70
4.6.4 Engineering Criteria 71
4.6.5 Continued Surveillance 73
4.7 Consolidation and Stabilization of Wastes 73
4.7.1 Consolidation During the Dewatering Process .... 73
4.7.2 Determination of Consolidation Potential 75
4.7.3 Stabilization of Waste 76
4.8 Control of the Water Balance 78
4.8.1 Need for Control 78
4.8.2 Surface Water Controls 80
4.8.3 Ground Water Controls 81
4.8.4 Leachate Controls 81
4.8.5 Monitoring 81
4.9 Air Emission Control 83
4.9.1 Organic Gas Emission Reduction Procedures 83
4.9.2 Fugitive Dust Abatement 86
vii
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FIGURES
Number Page
3-1 Simplified water balance for open surface
impoundment 25
3-2 Moisture distribution during infiltration through
an unsaturated soil 27
3-3 Abandoned gravel pit with a clay layer at its base . . 28
3-4 Single aquifer with a deep water table 29
3-5 Breakthrough curve for bulk transport of solutes ... 30
3-6 Breakthrough curve for bulk transport and
diffusion/dispersion 32
3-7 Breakthrough curve with soil-solution interaction ... 32
3-8 Trace element controls in soils 34
4-1 Surface impoundment closure key steps 57
TABLES
Number Page
3-1 Liner and Industrial Waste Compatibilities 19
3-2 Types of Soil-Solute Interactions 33
3-3 Sources of Existing Information 40
3-4 Compatibility of Hazardous Waste Impoundment Features
and Various Site Uses 42
3-5 Compatibility of Various Site Uses and Impoundment
Features After Hazardous Waste Removal 43
3-6 Impounded Waste Gas Generation Rates 46
4-1 Evaporation Potential Variations 71
4-2 Hazardous Waste Consistency Classifications 74
viii
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SECTION 1
INTRODUCTION
In line with growing concern for the control of adverse impacts of wastes
on our environment, the 94th Congress passed the Resource Conservation and
Recovery Act (RCRA) of 1976, PL-94-580, in October 1976. This Act provided
for promulgation of "regulations establishing performance standards applicable
to owners and operators of facilities for the treatment, storage, or disposal
of hazardous wastes... as may be necessary to protect human health and the
environment." On May 19, 1980, the Environmental Protection Agency (EPA)
promulgated national standards that included closure and post-closure care of
such facilities, including surface impoundments (Si's). Manuals describing
best engineering judgment criteria for the management of hazardous wastes are
necessary to support these regulations.
1.1 PURPOSE
This manual presents a listing of closure plan and post-closure care
considerations and details for Si's containing hazardous wastes. It is
written primarily for staff members in EPA regional offices or state
regulatory offices who are charged with evaluating and approving closure plans
for Si's under these regulations. Methods of assessing site closure
considerations are documented.
1.2 CONTENT DESCRIPTION
This manual describes and references the methods, tests, and procedures
involved in closing a site in such a manner that (a) minimizes the need for
further maintenance, and (b) controls, minimizes, or eliminates, to the extent
necessary to protect human health and the environment, post-closure escape of
hazardous waste, hazardous waste constituents, leachate, contaminated
rainfall, or waste decomposition products to ground water, surface waters, or
the atmosphere. Problems that have been overlooked in abandoned impoundments
and have caused environmental degradation are discussed. The techniques
involved are pertinent to closing an impoundment either by removing the
hazardous wastes or by consolidating the waste onsite and securing the site as
a landfill. Technical criteria for implementing the closure, specifically
those regarding aspects substantially different from a landfill, are given.
Relevant literature or procedures are documented for more in-depth review as
necessary.
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1.3 RELATED TOPICS PREVIOUSLY COVERED
A large and useful group of support documents has been prepared by the
EPA that relates to SI closure plans. The basic manuals of concern to those
regulating the closure of impoundments are identified below as technical
resource documents. Other documents that further explain the subject
technical points are referenced in the appropriate sections of this manual.
Eight technical resource documents have been developed for support of the
recent RCRA rules. Since these documents will be published together, they
will be readily available to supplement one another. They include this manual
plus the following:
• "Landfill and Surface Impoundment Performance Evaluation"!
• "Evaluating Cover Systems for Solid and Hazardous Waste"2
• "Guide to the Disposal of Chemically Stabilized and Solidified
Wastes"3
• "Hydrologic Simulation on Solid Waste Disposal Sites'1^
• "Management of Hazardous Waste Leachate"^
• "Lining of Waste Impoundment and Disposal Facilities"^
t "Design and Management of Hazardous Waste Land Treatment
Facilities"7
The "Landfill and Surface Impoundment Performance Evaluation" manual is
intended to provide guidance in evaluating designs to predict the movement of
liquids through and out of an SI. It includes a discussion of acceptable
operating procedures, design configurations, analysis procedures, and
techniques for interpretation of results as they apply to impacts on ground
and surface water.
The manual "Evaluating Cover Systems for Solid and Hazardous Waste" is
intended for use by the regional offices in their evaluation of applications
from owners/operators of solid and hazardous waste disposal areas. More
specifically, it is a guide for evaluation of closure covers on solid and
hazardous wastes. The manual provides a guide to the examination of soil,
topographical, and climatological data, closure cover evaluation
recommendations, and a discussions of post-closure plans.
The "Guide to the Disposal of Chemically Stabilized and Solidified
Wastes" provides guidance to waste generators and regulatory officials in the
use of chemical stabilization/solidification techniques for limiting hazards
posed by toxic wastes in the environment. The current state and performance
of hazardous waste disposal and long-term storage techniques are discussed.
In addition to a discussion of major chemical and physical properties of
treated wastes, a list of major stabilization/solidification technology
suppliers and a summary of each process are provided.
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The document "Hydrologic Simulation on Solid Waste Disposal Sites"
presents an interactive computer program for simulating the hydrologic
characteristics of a solid hazardous waste disposal site operation. Using
minimal input data from the user, the model will simulate daily, monthly, and
annual runoff, deep percolation, temperature, soil-water, and
evapotranspiration. The manual provides sufficient information and commands
so that an inexperienced user may perform the operation. The model is
designed for conversational use, that is, interaction with the computer is
direct and output is received immediately.
The manual "Management of Hazardous Waste Leachate" presents management
options that a permit writer or hazardous waste landfill operator may consider
in controlling a leaching problem. The manual contains the following: a
general discussion of leachate generation; a section on leachate composition
providing the permit writer with possible guidelires for determining the
relative hazard of a particular leachate; a discussion of five potential
management options for the off-site treatment of leachate or the on-site
treatment of hazardous waste; and a discussion of treatment technologies that,
on a laboratory scale, have demonstrated reasonable success in treating
leachate.
"Lining of Waste Impoundment and Disposal Facilities" provides
information on performance, selection, and installation of specific liners and
cover materials for specific disposal situations, based upon the current state
of the art of liner technology and other pertinent technology. It contains
descriptions of wastes and their effects on linings; a full description of
various natural and artificial liners; liner service life and failure
mechanisms; installation problems and requirements of liner types; costs of
liners and installation; and tests that are necessary for preinstallation and
monitoring surveys.
The document entitled "The Design and Management of Hazardous Waste Land
Treatment Facilities" presents a dynamic design approach for land treatment
facilities. This design strategy is based upon sound environmental
considerations and is structured into a total system approach. The manual
discusses site assessment procedures aimed at selecting acceptable locations.
This site assessment procedure consists of (1) technical consideration of site
characteristics and (2) sociographical considerations of area land use. In
addition, the manual describes specific land treatment components and explains
why they are important to an effective design. These components include: the
land treatment medium, hazardous waste streams, preliminary tests and pilot
experiments on waste-soil interactions, facility design and management,
monitoring, changing wastes, contingency planning, and site closure.
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REFERENCES FOR SECTION 1
1, Moore, C. A., "Landfill and Surface Impoundment Performance Evaluation,"
U.S. Environmental Protection Agency, SW-869.
2. Lutton, R. J., "Evaluation Cover Systems for Solid and Hazardous Waste,"
U.S. Environmental Protection Agency, SW-867.
3. Malone, P. G., L. W. Jones, and R. J. Larson, "Guide to the Disposal of
Chemically Stabilized and Solidified Wastes," U.S. Environmental Protection,
Agency, SW-872.
4. Perrier, E. R. and A. C. Gibson, "Hydrologic Simulation of Solid Waste
Disposal Sites," U.S. Environmental Protection Agency, SW-868.
5. Monsanto Research Corporation, "Management of Hazardous Waste Leachate,"
U.S. Environmental Protection Agency, SW-872.
6. Matrecon, Inc., "Lining of Waste Impoundment and Disposal Sites," U.S.
Environmental Protection Agency, SW-870.
7. K. W. Brown & Associates, Inc., "Design and Management of Hazardous Waste
Land Treatment Facilities," U.S. Environmental Protection Agency, SW-874.
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SECTION 2
GENERAL INFORMATION ON SURFACE IMPOUNDMENTS
2.1 CHARACTERISTICS OF SURFACE IMPOUNDMENTS
2.1.1 Definition of Surface Impoundments
"Surface impoundment" or "impoundment" means a facility or part of a
facility that is a natural topographic depression, manmade excavation, or
diked area formed primarily of earthen materials designed to hold an
accumulation of liquid wastes or wastes containing free liquids. An
impoundment is not an injection well and may be lined with manmade materials.
Examples of Si's are holding, storage, settling, and aeration pits, ponds, and
lagoons.
Exceptions to the above definition include concrete-lined basins, which
are, by definition, considered tanks. Tanks are stationary devices designed
to contain an accumulation of hazardous waste. They are constructed primarily
of nonearthen materials (e.g., wood, concrete, steel or plastic) that provide
structural support.
2.1.2 Types and Construction of Surface Impoundments
Si's may be natural or manmade depressions lined or unlined and may range
in area from a few tenths of an acre to hundreds of acres. Manmade
impoundments range in depth from 2 to 3 feet to as much as 30 feet or more
below the land surface.' Impoundments are generally built above the
naturally occurring water table, and some may be constructed on the land
surface by using dikes or revetments. Sometimes diked impoundments are
designed to take advantage of natural topographical features such that valleys
or natural depressions are diked on one or more sides with the naturally
occurring slopes forming the remaining sides of the containment area. Dikes
may also be required for impoundments in areas of high water tables or to take
advantage of impermeable surface soils.
Impoundments may be operated individually or interconnected so that the
flow moves from one impoundment to another in series or parallel. Many
impoundments discharge, either continuously or periodically, while others lose
their fluids by evaporation or infiltration into the soil. Impoundments may
be unlined, permitting seepage of fluids into the soil for the purpose of
percolation or infiltration. For certain wastes, impoundments are lined to
prevent any seepage of fluid. Typical liner materials include clay, concrete,
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asphalt, soil sealants, and synthetic membranes. The actual type and
construction characteristics of an SI depend on many factors, including such
site-specific ones as:
• Physical properties and chemical composition of the wastes
• Soil permeability, and geological and geochemical characteristics of
the local and surrounding soil
t Depth to the water table
0 Rates of precipitation and evaporation (meteorology)
2.1.3 Population of Surface Impoundments
Existing inventory information for Si's containing hazardous wastes is
scant and inconsistant. A general survey estimated that there are nearly
133,000 SI sites in the U.S.; 75 percent are industrial waste sites,
15 percent are agricultural, and 10 percent are municipal, institutional, and
private/commercial (domestic or sanitary)J This survey includes surface
impoundments regardless of the waste type; therefore municipal, industrial,
and agricultural wastewater treatment facilities are included in the
quantitative information. The highest numbers of industrial impoundments are
as follows: oil and gas extraction industry, 71,832; agriculture (crops and
livestock) 19,363; and bituminous coal mining, 14,170.
In 1979, EPA estimates indicated that there were 96,800 SI sites with a
total of 160,000 individual impoundments.^ More recent EPA data
(August 1980) indicate that there are at least 26,000 industrial impoundments
(pits, ponds, and lagoons) covering 430,000 acres currently in use.3 The
majority of Si's are in the oil and gas extraction and mining industries,
while the largest impoundments are in the mining, paper and pulp, and
electrical utility industries.
2.1.4 Surface Impoundment Uses
Si's can be used for temporary holding of discharged wastes or spills or
for long-term dewatering. A very common impoundment is a settling pond for
separation of suspended solids from liquids. Chemical additives can be
introduced to accelerate solids coagulation and precipitation. A number of
existing Si's used as settling ponds are periodically dredged to restore them
to their original capacity.
Some impoundments are designed specifically to permit seepage of fluids
into underlying aquifers. These impoundments are unlined and situated on
permeable soils. Others are designed to prevent seepage and to serve as
temporary or permanent holding or evaporation impoundments. Disposal of waste
in these nondischarging impoundments is accomplished by a combination of
evaporation and infiltration. Evaporation is most effective in the arid parts
of the western states where climatic conditions favor losses by this mechanism.
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2.1.5 Industrial Impoundment Practices
Industrial wastes are highly variable in composition and flow, hence,
industry employs a wide variety of practices in treating and disposing these
fluids and sludges. Impoundments are used for the aeration, oxidation,
stabilization, settling, disposal, and storage of wastes.
Mining and milling operations produce various wastewaters such as acid
mine water, solvent wastes from solution mining, and wastes from dump
leaching. Waste streams may be treated and the resulting sludges stored in
impoundments. Settling for the separation, washing, and sorting of mineral
products from tailings and the concentration and recovery of valuable metals
(e.g.f copper by precipitation) can be carried out in impoundments.
The oil and gas industry is one of the largest users of Si's. Fluids
contained in these impoundments consist of salt water associated with oil
extraction and deep-well repressurizing operations, oil-water and gas-fluids
to be separated or stored during emergency conditions, and drill cuttings and
drilling mud. In many cases, these intermittent or continuously produced
wastes are treated in steel tanks or concrete basins with either the residuals
or the treated wastewater disposed via large earthen evaporation ponds.
Impoundments found in the textile and leather industries are primarily
used for wastewater treatment and sludge disposal. Textile sludges may
contain dye carriers such as halogenated hydrocarbons and phenols. Heavy
metals such as chromium, zinc, and copper may also be present. Leather
tanning and finishing wastes and wastewater sludges contain chromium,
sulfides, and nitrogenous compounds.
The chemical and allied products industry produces literally thousands of
products and many different waste streams, waste stream processing may
involve the use of impoundments for wastewater treatment, sludge disposal, and
residuals treatment and storage. Impounded waste constituents also vary
considerably and are related to the product produced, feedstock used, and the
production method employed. In the case of agricultural chemicals (i.e.,
fertilizers and pesticides), potential impounded wastes from phosphate
fertilizer production will contain phosphorous, fluoride, and nitrogen where
ammonia is used as a basic raw material. Also associated with the manufacture
of phosphate fertilizers are trace elements that may be extracted and
discarded in the waste stream such as cadmium, which is found in impounded
gypsum wastes.
Other examples of industrial SI uses that may result in the treatment,
storage, or disposal of hazardous wastes can be found in petroleum refining,
primary metals production, wood treating, and metal finishing. Impoundments
are also used for air pollution scrubber sludge and dredging spoils disposal.
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2.2 METHODS OF CLOSURE
The objective of implementing proper SI closure procedures is to control,
minimize, or eliminate adverse environmental and human health impacts. This
objective is accomplished only if the impoundment sites have been adequately
designed and constructed to contain hazardous wastes on a long-term basis.
Si's are generally constructed as temporary containment structures designed
for variable lengths of service life.
To alleviate adverse environmental impacts, SI closure plans must address
either of two means of SI closure. These are closure plans where the
hazardous wastes and hazardous waste residuals (including liners, soils, and
equipment contaminated with hazardous wastes) are either left to remain in the
impoundment after closure or removed from the impoundment site.
2.2.1 Waste Remains in Place
If hazardous wastes are to remain in the impoundment, the closure plan
must include the implementation of procedures that will: (1) prevent migration
of waste from the impoundment via ground water, surface water, and air,
(2) control surface water infiltration, and (3) prevent erosion after
closure. The remaining wastes should not contain free liquids and the closure
plan must meet, as a minimum, the same requirements as those for landfills.
Beyond these requirements, considerable flexibility is allowed in the final
plan so that site-specific characteristics can be considered. The following
factors must be considered in developing closure plans when an SI is closed as
a landfill:
• Type of waste and waste constituents in the impoundment
• The characteristics of the waste and waste constituents including
mobility, Teachability, reactions, degradation, and byproducts
• Potential intended use of the closed SI
• Site location and topography with respect to the potential impact
caused by pollutant migration; for example, proximity to population
centers, ground water, surface water, drinking water sources, soil
permeability, depth of watertable, and geological and geochemical
characteristics of surrounding soil
• Climate including amount, frequency, and pH of precipitation
• Cover material and its characteristics, such as porosity,
permeability, thickness, and final slope
• water balance control measures
• Amount and type of vegetation
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In addition to reducing the free liquids from Si's, other waste
preparatory procedures may be necessary prior to the construction of a
landfill cover. These procedures may consolidate and stabilize the wastes so
that the potential for leaching and differential settlement are minimized.
Such procedures are reviewed in Section 4.
2.2.2 Waste Removed
In some cases of SI closure, it may be necessary or advantageous to
remove the wastes and waste residuals. Instances where this may be required
include:
• Si's with irrepairable liners containing wastes with a high potential
for the generation of toxic leachate
• Impoundments with dikes in poor condition that may require extensive
and costly repair
• Cases where the type of waste or waste constituents generate gases
that cannot be controlled adequately or economically
• Sites where planned end uses require the least possible contamination
• Impoundments where free liquids cannot be removed to yield
consolidated wastes of sufficient density to support the cover and
associated construction vehicles
Closure of Si's by removing wastes would be typical for those
impoundments that are periodically dredged, as in the case of settling or
evaporation ponds. It should be noted, however, that contaminated liners and
underlying soils may also have to be removed. Such soil, particularly the
highly contaminated portions, could present a significant future danger to
public health and the environment if left in place. Movement of water through
the soil could cause leaching of contaminants and potential ground water or
surface water contamination. Therefore, the underlying soil must be
quantitatively analyzed for the hazardous constituents of the impounded
wastes. The dredged or excavated wastes and contaminated waste residuals from
an SI would need to undergo removal, transport, and disposal methods that meet
the regulations and procedures established for hazardous materials. This will
ensure that waste and waste residual can be removed without significant
environmental risk.
Upon removal of hazardous wastes and waste residuals, the impoundment
site itself may require some degree of reclamation. This may be necessary for
the following reasons:
• Erosion control
• Surface runoff control
• Water table restoration
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t Post-closure usage
• Dust control
Site reclamation may include filling an impoundment with native soils or
leveling the dikes to provide a graded elevation consistent with the
surrounding area. The nature and extent of site reclamation after hazardous
wastes have been removed is dependent on local or regional regulations and
site-specific factors.
In summary, specific SI closure procedures are quite varied and dependent
on individual site characteristics. This allows an owner or operator the
opportunity to present, in a closure plan, those procedures that will prevent
or minimize the migration of waste from the impoundment after closure. Each
facility needs to be considered on a case-by-case basis. Details of the
controls and effects of items mentioned in this section are given in Section 4.
2.3 WATER AND AIR IMPACTS OF SURFACE IMPOUNDMENTS
The adverse water and air impacts that can result from improperly closed
Si's are quite evident but frequently overlooked. Specific cases of pollution
of surface and ground waters or unhealthy ambient air have been reported.4
2.3.1 Surface Water
Public exposure to hazardous wastes contained in Si's can be quite sudden
and uncontrollable when dikes are breached or lagoons are washed out during
high surface runoff periods. General public awareness of impoundment hazards
has been heightened by news media reports of dike failures or waste slurry
pond spillage during heavy runoff. Most surface water contamination occurs
from impoundments where the waste containment system was unable to adequately
handle short-term unexpected events.
As explained in Section 2.1, Si's have an extremely wide variety of uses
and wastes. A pond's size or prominence often determines the attention its
closure and use are given by owners and regulatory authorities. Copper
tailings ponds in Arizona that are over 1 mile long and 100 feet high might be
closely observed and monitored. Such ponds are used for long periods of time
accepting slurry tailings for settling of the solids and evaporation or
decantation of the fluids. Seepage of impounded fluids into ground water
below the pond bottom or through a diked area can be anticipated. Conversely,
small onsite sludge disposal sites can be randomly used and easily overlooked
or neglected. Such impoundments have caused a large fraction of the surface
water contamination cited previously.
Although such inundations are apparent and alarming, equal concern is
merited for leached contaminants. A well engineered (as detailed in
references 5, 6, and 7) containment system is essential for public safety,
since liners and even fixed sludges can leak over a period of time.
10
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2.3.2 Ground Water
Contamination of underground waters from improperly closed Si's most
directly exposes the local population through well water withdrawals.
Exposure can also occur as a result of contaminated ground water seepage into
basements and subsequent volatilization of dissolved constituents.
Underground contamination of water can cover large areas traveling rapidly of
to 2 feet per day, although average rates are somewhat less.° Case history
studies generally show that water in shallow unconfined aquifers is the first
to be contaminated by seepage of wastes from impoundments. Such contaminated
waters may remain localized or extend considerable distances.^ Concerned
over public safety relating to the problem of seepage of wastes from
impoundments, the EPA initiated an assessment program to rate the contamination
potential of ground water from Si's and to develop practices for their
evaluation. A method of determining "potential endangerment" to current water
supplies as a function of waste and subsurface water characteristics has been
reported.^ This report developed an evaluation system based on ratings for:
• Ground water availability
• Ground water quality
t Waste hazard potential (determined by waste source or industry or
chemical content)
• Earth material characteristics (unsaturated zone beneath the
impoundment)
• Proximity to ground or surface source of drinking water
While this system provides methods for evaluating ground water contamination
potential from impoundment waste seepage, life characteristics of the waste
containment system must also be evaluated.
Most general literature does not present useful data for realistic
containment system life predictions. This is especially true for liner waste
compatibility where the wastes are industrial sludges (e.g., electroplating,
oily refinery, acid steel pickling, toxic pharmaceutical, and related
wastes). To contain these types of materials, the liner must resist attack
from chemicals (solvent, oils, greases), ozone, ultraviolet radiation, soil
bacteria, mold, fungus, and even vegetation.9 Weather resistance is
necessary to withstand stresses associated with wetting-drying,
freezing-thawing, or earth shifts at the site. They also must resist
laceration or puncture from cleaning or operating equipment or matter found in
the fluids or sludges contained. In impoundments with consolidated or fixed
contents, the potential for public exposure to hazardous materials may be
reduced but is not totally eliminated.
Comparative tests have been made on a variety of sludges using long-term
leaching or elutriation to determine the release of pollutants from sludges
that had been consolidated or untreated.10 Waste sludges from
11
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electroplating, chlorine production, inorganic pigment production, flue gas
desulfurization, and other industrial wastes were fixed with a variety of
additives and still exhibited high metal and organic constituent losses under
some leaching conditions.
Such elutriate tests do not simulate a disposal site since no provisions
are made for modeling the attenuation of pollutants by soil nor their dilution
by site ground water. But these tests are rapid and techniques are simple for
comparing the degree of fixation for sludges on the basis of pollutant
migration from the sludge to the elutriate. One use of these elutriate tests
is to compare the leaching of fixed and raw sludge under similar conditions.
Although by fixing a sludge it may become more highly consolidated, the
hazardous components may leach out at the same rate as without fixing.
Results of one elutriate study showed that metals were leached as rapidly from
chemically stabilized sludges as raw sludge.^
Although chemical fixation may provide only limited added control against
leaching,10 this procedure usually greatly controls the rate of air
emissions or surface losses of chemical constituents.
2.3.3 Air Emissions
When SI sites become inactive but remain unclosed, liquid waste may
volatilize organic compounds (e.g., benzene, chloroform, chlorinated
ethylenes) while bacterial activity and algal growth on sludges and liquid
wastes can produce gases. Such vapors and gases may be objectionable
(odorous) and unsafe (toxic gases).
Public exposure to materials thought to be safely contained is occurring
through air emissions at many locations. A typical example is emissions of
PCB in New York from contaminated material removed from direct water contact
but stored without adequate control of vapors. Annual losses of PCB to the
air from dredge spoil sites within the Hudson River Basin were reported at
205 Ib/year, while ground water transport was less than 1 lb/year.^
Erosion and physical removal at the same sites accounted for losses of about
90 Ib/year.
A well recognized characteristic of poorly closed waste impoundments is
the bare surface that often gives rise to excessive dust during winds or
vehicle use. Air emissions, such as decomposition gases, organic vapors, and
odors, affect more than aesthetics especially during subsequent site use.
Decomposition gases (e.g., hydrogen sulfide, methane, and carbon dioxide) and
organic vapors can diffuse upward affecting surface covers (killing grass and
plants, and bubbling up impermeable membranes) and buildings (due to
subsequent consolidation and settlement and toxic gas accumulation).
Volatilization of organic wastes from open or abandoned Si's involve
three different processes: (1) direct vaporization of the organic liquid or
mixtures, (2) volatilization of liquid chemical wastes from water, and
(3) volatilization of organics that have adsorbed onto soil or other solid
material. Decomposition gas formation is dependent on site temperature,
12
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organic waste character, lack of oxygen, and bactericidal constituents (high
pH and heavy metals).
2.4 DIRECT PUBLIC EXPOSURE AND SITE SECURITY
Hazardous materials that leach, diffuse, or are otherwise conveyed out of
a treatment, storage, or disposal site can and have caused public health and
environmental problems. Although environmental degradation from impoundment
pollution may not seem as hazardous as from landfills, typical incidents
confirm the severity of potential public exposure. In addition to emissions
listed here, direct contact of wastes at inactive but unclosed sites
frequently occurs. Abandoned coal cleaning and industrial sludge holding
sites that still contain contaminated runoff have been cited as a public
nuisance J '^ Such impoundments are both a physical safety hazard and
potential exposure hazard to an unsuspecting site user. Wind blown eroded
waste from dry impoundment surfaces and foam and aerosols from saturated and
inundated wastes can be carried considerable distance, thereby extending the
range of public exposure to abandoned hazardous waste impoundments.
An integral part of site maintenance is security against uncontrolled
access by the public. Improperly closed impoundment sites have had dikes
breached, unauthorized public dumping, rifle target practice ranges set up on
them, and unofficial testing grounds developed for offroad motorcycles and
four-wheel drive vehicles.^
Of utmost concern for site security is the preservation of hazardous
waste containment systems. Surface water diversion and cover systems may
rapidly deteriorate if disruptive surface activity and soil removal occurs
during unplanned site use. Fencing, policing, and site rezoning are necessary
site closure activities that can help preserve containment systems. These are
discussed in Section 3.
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REFERENCES FOR SECTION 2
1. Geraghty, J. J., et al., "Surface Impoundments and their Effects on
Groundwater Quality in the United States -- A Preliminary Survey," U.S.
Environmental Protection Agency, EPA-570/9-78-004, June 1978.
2. Air/Water Pollution Report, December 24, 1979.
3. Environmental Report, Trends Publishing Inc., August 4, 1980.
4. "Background Document -- Section 265.220," Final Interim Status Standards
for Surface Impoundments, Developed pursuant to Section 3004 of the
Resource Conservation and Recovery Act, U.S. Environmental Protection
Agency, Office of Solid Waste, April 28, 1980 (Available as part of the
RCRA docket).
5. Moore, C. and M. Roulier, "Landfill and Surface Impoundment Performance
Evaluation," U.S. Environmental Protection Agency, SW-869.
6. Lutton, R. and R. Landreth, "Evaluating Cover Systems for Solid and
Hazardous Wastes," U.S. Environmental Protection Agency, SW-867.
7. Lutton, R., et al., "Design and Construction of Covers for Solid Waste
Landfills," U.S. Environmental Protection Agency, EPA-600/2-79-165,
August 1979. PB 80-100381.
8. Silka, L. R. and T. L. Sieveringer, "A Manual for Evaluating
Contamination Potential of Surface Impoundments," U.S. Environmental
Protection Agency, EPA-570/9-78-003, June 1978.
9. Stewart, W. S., "State-of-the-Art Study of Land Impoundment Techniques,"
U.S. Environmental Protection Agency, EPA-600/2-78-196, December 1978.
PB 291-881/AS.
10. Thompson, D. W. "Elutriate Test Evaluation of Chemically Stabilized Waste
Materials," U.S. Environmental Protection Agency, EPA-600/2-79-154,
August 1979. PB 80-147069.
11. Tofflemire, T. J., et al., "PCB in the Upper Hudson River: Sediment
Distributions, Water Interactions, and Dredging," Technical Paper #55,
New York State Department of Environmental Conservation, Bureau of Water
Research, Albany, New York, January 1979.
12. Wilkey, M. and S. Zellmer, "Land Reclamation of Abandoned Deep Coal
Mine," Journal of the Environmental Engineering Division, American
Society of Civil Engineers, Vol. 105, No. EE5, Paper 14877, p. 843-53,
October 1979.
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N SECTIQH 3-
ENVIRONMENTAL CONSIDERATIONS FOR CLOSURE PLAN ANALYSIS
This section discusses environmental considerations that should be
addressed in a plan for SI closure. The closure of new and existing
impoundments by dewatering and residual solids removal or in situ
stabilization is also covered.
3.1 LEACHING POTENTIAL OF WASTES
Solids in impoundments may be leached by liquid added to the impoundment
by precipitation, by fluids already present in the waste, or by other flowing
or infiltrating fluids. If the impoundment is unlined or the liner is breached
and if an overflow from the impoundment occurs, leachate can seep into the
adjacent soil and eventually into ground water. This is of special concern if
the wastes contain hazardous materials. Mechanisms releasing the waste
constituents to the eluant are not fully characterized, and the methods to
quantify leaching rates are not well established. But a discussion of these
factors is certainly warranted, as considerable information exists from
specific cases of leaching.
Most of the current information on waste leaching was developed from
landfills holding either municipal or industrial waste. Even laboratory
studies have either selected actual leachate from such systems^ or set up
conditions to duplicate them.3»4 Leaching of materials from uncovered
impoundments is generally considered to more closely follow the release of
materials in pond or lake sediments for which a very large amount of
descriptive data exist. This similarity is closest for lake sediments exposed
to ground water seepage.5>6
3.1.1 Mechanisms of Leaching
When the leaching fluid (e.g., water) is absorbed into or passes through
a waste or impoundment sediment, various physical and chemical factors affect
the rate and extent to which contaminants in the waste diffuse into the liquid
medium. Leaching mechanisms and factors affecting these mechanisms are fairly
well established for certain specific nutrients used in agriculture and
forestry. These simplified systems have been examined for many types of soil
and moisture conditions.'>° Unfortunately, these results are only poorly
analogous to multiple constituent wastes. Many attempts have been made to
model the processes involved for complex wastes, but the actual mechanisms are
so complex in nature that these models, though quantitative in principle,
serve only as qualitative guides.
15
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One approach is to model the transport as an equilibrium phenomenon
(i.e., to assume that the driving forces for transport, the activity,
coefficients, and concentrations of all species are balanced among the solid,
liquid, and gaseous phases of the waste impoundment).9,10,11 Under these
conditions, liquids remain in contact with the waste long enough for chemical
exchange to attain equilibrium. Such an equilibrium model serves as a worst
case for concentration of contaminants in the leaching medium. Even such a
simple model in concept is difficult to apply in reality because of the
complex task of identifying and establishing the various equilibria involved.
A more elaborate approach is based on transport and mixing (convective
transport, diffusion, and gravitational transport) and the kinetics of
dissolution reactions as well as the kinetics of any chemical reactions
involved.n A further extension is to consider biological activity.^
Such an approach is not simple, thus, empirical tests and factors affecting
leaching are discussed below.
3.1.2 Factors Affecting Leaching Rates
The character and composition of leachate depends on the composition of
the waste material and environmental factors (e.g., meteorological
conditions)." > 12 Factors that exert a strong influence on the leaching
potential include:
• Chemical composition
• pH of the waste and eluant
• Oxidation and reduction conditions
• Buffer capacity
• Complexation capacity for organic compounds and metals
• Ionic strength
• Dielectric constant
• Temperature
Factors that primarily affect leachate transport include:
• Flowrate of eluant
• Specific surface area of waste material
• Porosity
• Permeability
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The effects of these factors have been discussed in detail by Lowenbach.11
Laboratory test data on a specific waste and site can be generated for these
parameters, and various leaching models can be applied.
Finally, meteorological conditions should be factored in. Precipitation
has a direct bearing on the quantity and flowrate of leaching water and,
hence, eluant. The distribution of precipitation with respect to time is also
significant. Several investigators have shown that liquid in contact with
metal bearing coal wastes contain constituents whose concentration is directly
related to the time of contact with the wasteJ3,14 jney reported that the
concentration of contaminants in the leachate initially increased significantly
with new precipitation but then decreased as existing fluid was replaced by
new liquid.
3.1.3 Methods to Quantify Leaching Rates
To assess the leaching potential of wastes and, hence, aid in evaluating
alternative SI closure plans, it is desirable to have quantitative,
standardized tests. These tests should be representative of the actual
impoundment situation, reproducible, conservative (worst case approach), and
capable of generating meaningful test data. They need to be standardized for
comparison of results and for comparison of the leaching potentials of different
wastes. Leaching tests fall into three categories: (1) batch (shake)
tests, (2) column tests, and (3) field cell tests.11 Shake tests involve
placing a sample of the waste material to be leached in a container with an
appropriate eluant, agitating the mixture for a specified period of time, and
analyzing the resulting leachate. This technique is a simple and rapid method
of generating a variety of equilibrium and kinetic data. However, the
technique is crude as conditions may not be representative or approximate
those of the actual environmental conditions. Column tests, involving flow of
the eluant through a column packed with the waste, may be a better simulation
of waste and liquid contact in an actual situation. The major disadvantage is
the great length of time needed to yield meaningful data, usually months to
years. Finally, actual field test sampling is even better, though test
conditions would be difficult to control and testing would involve great
expense and time. In fact, sampling and handling procedures are critical and
elaborate.!5 Current research emphasis is on the batch or shake test. EPA
has sponsored a study to compile and evaluate the various leaching methods now
available. Unfortunately, no single existing leachate test fulfills all the
desired needs.11
Over 30 shake tests were evaluated and compared by Lowenbach.11 The
study identified three shake tests for further investigation: the IU
Conversion Systems test,16 the State of Minnesota test,17 and the
University of Wisconsin testJ^ A subsequent EPA program investigated these
three tests further, and concluded the Wisconsin test was the only test able
to representatively leach each of 14 different industrial wastes supplied by
EPA, and also was the procedure with the most aggressive conditions.
In addition to data from specific leaching tests, information on site
soil and water balance characteristics must be compiled. These data may be
17
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utilized to evaluate potential contamination by a method described by Silka
and Swearingen.19 By developing a rating for the (1) waste hazard potential,
(2) ground water availability and quality, (3) soil zone, and (4) proximity of
water supplies, a net potential for drinking water contamination from leaching
can be determined. The latter three ratings must be determined for specific
sites as described in reference 19 or Section 3.3, Potential for Waste
Migration, of this manual. Waste hazard potential can be determined by waste
specific leaching tests or from general references.
The movement or attenuation of leached waste constituents and the
influence of various soil characteristics has been researched and
reported20,21,22 ancj -js discussed in Section 3.3.
3.2 CONTAINMENT SYSTEM PERFORMANCE
The function of the containment system for an SI is to prevent or
minimize escape of leachate, gases, solids, and bacteriological species from
the impoundment into the environment. The containment system may frequently
consist of a liner (for the bottom and sides), a cover (for the top), and any
leachate or gas collection equipment. This section examines liner
performance; covers are discussed in Section 3.4. The general intent of this
section is to provide an overview of factors that influence liner performance
and considerations for evaluating liner deterioration. A more detailed
discussion of liners for waste impoundments describing liner types, design
criteria, performance, and construction can be found in the document "Lining
of Waste Impoundment and Disposal Facilities."23
3.2.1 Factors Affecting Performance/Life
Numerous factors and historical events that can occur during the useful
life of an impoundment and effect liner performance should be considered in
developing and assessing closure plans. Liner damage can be caused by
interactions with the impounded waste, physical factors such as earth
movements or meteorological conditions, and improper installation, use, or
maintenance procedures.
Waste Composition
The single most critical factor affecting the performance of a liner is
the chemical composition of wastes. Liner materials should always be tested
for chemical resistance to wastes (e.g., ASTM Method D471). Such testing
should be part of the liner selection process and should precede addition of
any wastes with a composition different from that for which the liner was
designed. Examples of waste/liner compatibility test programs are described
in references 24 through 27. Observed impacts include chemical and biological
attack leading to a breech in the liner, dissolution of the liner, and an
increase in permeability of the liner.
The chemical compatibility of several liner materials with seven
different industrial wastes is shown in Table 3-1. Since liner material
composition, waste composition and concentration, and environmental conditions
vary considerably, the compatibility ratings provide only general guidelines.
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Table 3-1. Liner and Industrial Waste Compatibilities
28
Industrial waste3
Liner material
Flexible synthetic membranes
Polyvinylchloride
(oil resistant)
Polyethylene
Polypropylene
Butyl rubber
Chlorinated polyethylene
Ethylene
propylene rubber
Hypalon
Soil sealants
Soil cement
Admixed materials
Soil asphalt
Asphalt concrete
Asphalt membranes
Natural soils
Soil bentonite
(saline seal)
Compacted clays
Caustic
petroleum
sludge
G
G
G
G
G
G
G
F
f
f
F
P
P
Oily
refinery
sludge
G
F
G
P
P
P
P
G
P
P
P
G
G
Acidic
steel
pickling
waste
F
F
G
G
F
G
G
P
P
F
F
P
P
Electroplating
sludge
F
F
G
G
F
G
G
P
P
F
F
P
P
Toxic
pesticide
formulations
G
G
G
F
F
F
F
G
F
F
F
G
G
Toxic
pharmaceutical
waste
G
G
G
F
F
F
F
G
F
F
F
G
G
Rubber
and
plastic
G
G
G
G
G
G
G
G
G
G
G
G
G
aP » Poor, F = Fair, G = Good
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Briefly, rationales for the ratings are:
t Caustic petroleum sludge is alkaline and contains salt components;
therefore soil sealants, admixed materials, and natural soils would
be subject to attack. This waste may contain certain hydrocarbons
that could attack the asphalts and synthetics, with the possible
exception of polyethylene and polypropylene.
• Oily refinery sludge contains hydrocarbons, phenols, and heavy
metals, but has low salt and alkaline concentrations. Asphaltic and
synthetic liners (with the exception of oil resistant types) will not
perform well.
• Acidic steel pickling wastes (high acid and salt concentration) will
attack soil-based liners. If the waste is introduced to the pond at
an elevated temperature, asphaltic and synthetic liners may not be
suitable; however, rubber and some polyethylenes can be used.
• Electroplating sludges contain heavy metals and salts that attack
soil-based liners. Asphalt and thermoplastic membranes are rated
"fair" since these wastes may also contain organic additives.
• Toxic pesticides and pharmaceutical wastes are assumed to contain as
much as 25 percent organics; therefore, only natural soils, soil
cement, and the oil resistant membranes are considered suitable
• The primary pollutants in rubber and plastic wastes are oil, grease,
acids, bases, and suspended solids in concentrations sufficiently low
so that all liner materials could be suitable
It must be emphasized that the evaluation of liner performance or
assessment of an in-place liner should be based on directly related tests and
not general guidelines as given here.
Physical Factors
Physical factors such as earth movement, temperature variations,
rainfall, and sunlight can significantly degrade liner performance. Earth
movement can fracture the more rigid materials such as natural soils and
concretes. In some cases they may be self-sealing (i.e., bentonite can expand
to fill cracks); however, other physical and chemical factors can negate any
self-sealing capability.
Freeze/thaw cycles and freezing itself can seriously degrade liner
performance. Temperature-induced stress can cause fractures. Some of the
plastic materials become brittle at low temperatures and suffer property
degradation at high temperatures.
Some of the flexible polymeric membranes can be degraded to some extent
by exposure to sunlight (ultraviolet light) and ozone. These materials are
classed as exposable and unexposable. Those that are resistant to sunlight
and ozone, such as the synthetic rubbers, are termed exposable. A service
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life for most exposable liners of 20 to 25 years under normal atmospheric
conditions can be expected. Under similar conditions, unexposable materials
can be expected to perform 10 to 15 years.29 in both cases, however, it is
recommended that the liner be covered with earth.
Site Preparation/Installation
The performance and lifetime of the most carefully selected liners can be
severely degraded by improper construction/installation procedures. There are
three distinct phases of construction — subgrade preparation, liner
installation, and liner protection. General considerations are discussed in
the following paragraphs, while specific details are outlined in reference 23.
Any liner should be built on a firm base to prevent differential
settlement of the subgrade that can result in loss of liner integrity. The
soil should be well compacted and devoid of surface irregularities;
construction during wet or cold weather should be avoided. Foreign objects
such as rocks, roots, and stumps should be removed as should any nearby
vegetation that might root into the liner. A soil sterilant may be necessary
to inhibit plant growth.
Most liner materials require specific and unique installation procedures.
Soil bentonite may require prehydration and should be kept moist to maintain
stability. Hot sprayed asphalts must be applied in several thin coats to
prevent bubbles; drying times and application rates vary. Polymeric materials
must be carefully seamed and anchored.
In many cases, liners also require some sort of protection -- usually
provided by a layer of soil.23 Heavy equipment, particularly that with
crawler treads, should not be allowed directly on the liner. As previously
discussed, some polymeric liners must be protected from ozone and ultraviolet
attack.
3.2.2 Assessment of Liner Condition and Effectiveness
There are basically two approaches to evaluating the condition of a
liner. The first is an indirect approach and involves a review of the
original design considerations, construction technique, wastes stored, and
historical operational records. The second and direct approach is to test the
impoundment for leaks or deterioration of the liner. Both should be part of
closure plan development and evaluation.
The indirect approach includes activities such as:
• Reviewing operating records to determine the type and composition of
wastes
• Generalized waste/liner compatibility analysis
• Examining liner material/waste composition test results
• Examining construction and maintenance records
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• Reviewing any site problems that may indicate a leak
• Visually observing surrounding vegetation
• Comparing estimated lifetime of the liner with the containment
requirements of the wastes
• Assessing the degree of risk from breech of the liner
Consideration of these factors may be sufficient to conclude that it is not
reasonable or practical to close the impoundment without removing the
hazardous wastes. However, if closure as a landfill with the waste remaining
in place is a possibility, the direct assessment should be conducted.
There are several techniques for direct liner effectiveness testing.
Some or all of these techniques may be appropriate for individual site
specific closure considerations. These methods include using a leachate
detection system, extracting and examining a portion of the liner, and
monitoring the ground water in the vicinity of the impoundment.
Leachate Detection System
There are two basic types of SI leachate detection systems that can be
installed when the liner is constructed. The first consists of a series of
perforated pipes placed beneath the liner. Any leachate that may penetrate
the liner is collected in these pipes and can be withdrawn and tested.
However, the location of the leak cannot be determined with this method.
The second system consists of a series of metal pins driven into the
ground under the liner and interconnected so that electrical current can be
applied. The pins are used to take resistivity readings of the soil between
any two pins. To define a leachate plume, the method relies upon the fact
that the conductivity of the ground water is inversely proportional to the
resistivity measured in a section of earth containing that ground water.
Since the conductivity of a leachate is generally much higher than that of
fresh ground water, a sharp decrease in apparent resistivity will occur if
leachate is present in the measured section. However, resistivity is subject
to error in interpretation with many natural and manmade field conditions. In
addition, this method has been shown to have a limited life, which may be
significantly less than that of the impoundment.
Liner Examination
In some cases it may be desirable to directly examine the liner material
for chemical or biological attack by extracting a sample of the liner. This
may be particularly true of asphaltic and polymeric liners. A technical and
economic review of three techniques for this (the use of a dragline, backhoe,
and caisson) is given in reference 30. Tests of the liner may be used to
evaluate its deterioration and expected lifetime.
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Ground Water Monitoring
Leachate migration into ground water has a three-dimensional plume, the
exact location and extent of which is very difficult to predict. Therefore,
it is usually necessary to use wells at various locations within the aquifier
to extract samples. Contamination is detected by changes in ground water
composition that can be related to the wastes or by the presence of major
waste constituents in the ground water at levels in excess of background
concentrations. If the wells were not in place prior to construction of the
impoundment, samples of ground water "upstream" (hydraulically up-gradient) of
the impoundment may be used as reference samples.
3.3 POTENTIAL FOR WASTE MIGRATION
The potential for waste migration from an SI exists whenever residual
contaminants are in a liquid or water soluble form. Several processes control
the rate and extent of waste migration. They include:
• The solubility and rate of solution of the contaminant
t The balance between carrier fluid inputs and outputs from the SI
t The ability of the soil to restrict the movement of contaminants by
soil-solution interactions
The first process is the subject of Section 3.1 and is not discussed further.
The second and third processes are discussed in this section.
3.3.1 Water Balance
An estimate of leachate quantity generation at an SI facility is a
critical factor in the environmental assessment of the site. The water
balance is a quantitative statement of the relationship between the total
water gains and losses of an impoundment over a given period of time and is,
consequently, a tool for estimating leachate quantities and generation rates.
Several reports are available that document the use and application of
water balance theory to landfill sites.31>32>33 jhe manuai "Hydrologic
Simulation on Solid Waste Disposal Sites" 49 Provides computerized technique
for simulating the hydrologic characteristics of waste sites, therefore, the
following discussion is limited to a brief summary of general points to
consider.
Mathematically, the water balance may be expressed in terms of flow
continuity, for a given time interval, or
Onsite accumulation = £ inputs - £ outputs
If steady-state conditions are assumed to apply, the onsite accumulation
term becomes zero. Therefore,
S inputs = S outputs
23
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Seven principal input and output components of a hypothetical closed
surface impoundment include: (1) precipitation, (2) surface runoff onto the
impoundment, (3) surface runoff from the impoundment area,
(4) evapotranspiration, (5) ground water underflow in, (6) ground water
underflow out, and (7) infiltration or seepage. The illustration in
Figure 3-1 is general and assumes that the impoundment liner is leaking or
nonexistent. It is further assumed that surface runoff can enter the site
from uncontaminated areas. In practice, such runoff should be diverted away
from the site, eliminating this component. The illustration deals with a
closed SI; therefore, liquid waste has not been included as an input component.
As illustrated in Figure 3-1, inputs are limited to precipitation falling
directly on the site (including irrigation water if necessary) and surface
runoff onto the site. Outputs occur as evapotranspiration, surface runoff
from the site, and infiltration. Since the system has been defined to be in a
steady-state condition, infiltration of surface water may be assumed to move
down through the waste material and directly join the ground water underflow
or form a leachate plume. The factors that affect the magnitude of each term
are discussed in the following paragraphs.
Inputs
Except in cases where the SI is placed directly within a water table,
precipitation represents the principal source of water into an SI. The
frequency, amount, intensity, duration, and form of precipitation represent
important considerations for water balance calculations as they influence both
rainfall volume and runoff estimates. Precipitation varies considerably year
to year. Therefore, the use of mean precipitation data can be considered a
gross approximation at best. "Design" precipitation estimates can be generated
through statistical analysis of past precipitation events. Precipitation data
derived in such a fashion provide information on the percentage of time that
rainfall is equal to or greater than a given value. Thus, water balances can
be calculated for a given degree of risk. Historical precipitation data are
generally available from the U.S. Department of Commerce, National Oceanic and
Atmospheric Administration, Environmental Data Service, Asheville, North
Carolina. Precipitation intensity, duration, and physical form (i.e., rain,
sleet, and snow) are factors that affect runoff volume and are discussed in a
subsequent section.
Surface runoff represents a significant water input only where improper
design allows runoff to enter from upslope. This possibility exists for SI
facilities that have been constructed in hillsides or where they do not have
surrounding dikes.
Outputs
Evaporation reduces the total amount of water available for runoff and
infiltration and can occur from a free water surface, fallow soil, and snow.
Additionally, evaporative processes can transport soluble contaminants through
thin (approximately 1 foot) surface cover material, resulting in surface
contaminants amenable to resolution, runoff transport, and dust reentrainment
to the air. Surface containment accumulation can also damage vegetative cover.
24
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The rate of evaporation is directly proportional to atmospheric vapor
pressure that, in turn, is dependent on water and air temperature, wind speed,
atmospheric pressure, salinity, and the nature and shape of the evaporative
surface. Regional data on evaporation is generally available from the
Environmental Data Service or can be estimated from the above parameters.^
Transpiration processes remove water from soil moisture and from shallow
ground water via vegetational growth and, therefore, is significant only when
the surface soil cover is vegetated. Like evaporation, transpiration reduces
the total volume of water available to the site and can transport contaminants
upward, particularly if the root zone penetrates into the residual waste.
Temperature, solar radiation, windspeed, soil moisture, and type of vegetative
cover all affect the magnitude of transpiration. Often, the distinction
between evaporation and transpiration is unclear and the combined moisture
loss via these two processes (evapotranspiration) is estimated. Methods of
estimating evapotranspiration are straightforward and are discussed in
references 33 and 34.
Runoff from SI facilities can be a significant fraction of total offsite
migration volume. However, the interaction of runoff with waste contaminants
(and therefore offsite transport) is limited to the mass of contaminants
brought to the surface by capillary or evaporative processes. Runoff
transport of waste contaminants can also be significant when impoundments are
improperly covered or sealed.
The amount of surface runoff is dependent on many factors including
intensity, duration, and form of precipitation; antecedent soil moisture
conditions, permeability and infiltration capacity of the cover soil, slope,
and amount and type of vegetative cover. The use of "rational runoff
coefficients," as described in reference 34, generally provides a reasonable
estimate of surface runoff as a function of these parameters.
Infiltration represents the primary mechanism for the downward migration
of waste-derived constituents. Four processes are involved: (1) entry
through the cover soil (or residual waste strata, if no cover is present),
(2) storage within the soil, (3) transmission through the soil, and (4) deep
drainage through the residual waste strata and into the underlying soil. A
factor limiting any one of these processes (i.e., an impermeable soil cover)
can significantly reduce the net volume of vertical flow.
Rainfall characteristics (intensity, duration, and form), soil properties
(texture, structure, permeability), and vegetative cover all influence the
rate of infiltration. Fine textured soils (i.e., clays) generally have the
lowest infiltration rates and make excellent cover material. Methods used to
quantify infiltration are described in references 31, 35, and 36.
Once water enters the soil below residual waste strata, it advances as a
moisture front as illustrated in Figure 3-2. Water reaching a dry soil moves
slowly because the hydraulic conductivity of unsaturated soils is generally
low. The effective cross sectional area available for water transmission is
small in dry soils; adsorption and retention of water by the soil matrix is
also involved. However, water behind the wetting front flows quite rapidly
26
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Moisture content
Depth
Saturation zone I
Transition zone f
Transmission
zone
Figure 3-2.
Wetting front
Moisture Distribution During Infiltration Through an
Unsaturated Soil5
because the hydraulic conductivity is higher. Thus, water "piles up" at some
distance behind the wetting front until the soil is nearly saturated and then
moves onward. These processes take place in all soils; however, in very fine
grained soils, moisture migration is so slow as to be negligible. This
process of slow infiltration continues until the wetting front reaches a zone
of saturation or the ground water table.
Ground Water Underflow
Detailed field investigations are required to evaluate the volume of
ground water underflow. A complete ground water flow evaluation would provide
information on seasonal depths to ground water; rate and direction of ground
water flow; the location of ground water recharge and discharge areas; the
types of aquifers below the site; the rate of site infiltration relative to
total ground water underflow, the presence and location of fissures in
underlying bedrock, and specific gravity of the leachate and ground water
mass.31 Techniques described in reference 31 can be used to arrive at
reasonable approximations of both ground water inflow and outflow.
3.3.2 Attenuation Mechanisms
The simultaneous flow of water and solutes is a phenomena that is
associated with the leaching of hazardous wastes. The movement of solutes
through (and above) the soil profile depends on the combined action of bulk
transport, diffusion-dispersion, and soil-solute interactions. The number of
variations that can occur in aquifer pollution situations are virtually
limitless.38 Figures 3-3 and 3-4 represent two examples of hypothetical
27
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hydrogeologic pathways for aquifer contamination.
presented in references 31 and 38.
Additional pathways are
Bulk transport or mass flow represents that quantity of solute that is
transported at a rate and direction identical to that of the transporting
medium (usually water). Diffusion/dispersion describes the lateral flow of
solutes during transport. Diffusion is caused by random thermal motion of the
solute molecules, while dispersion describes mixing caused by the tortuous
flow of water around individual grains and through pores of various sizes.
Soil-solution interactions occur when the solute reacts with the soil, further
modifying the distribution of the solute between the solution and soil
phase.31,39
Mathematically, the movement of solute has been described in reference 40.
Simply stated, the rate of change of solute concentration C is a function of
diffusion/dispersion, bulk transport, and soil solution interactions. Three
cases are presented describing how each process effects the movement of
solutes. For each case, "C0" represents the initial solute concentration
entering the soil column and "C" represents the concentration of solute
leaving the column.
Solute Transport by Bulk Transport Only
Figure 3-5 shows a breakthrough curve for 100-percent bulk transport
through a soil profile of finite length. A sharp rise in the ratio C/Co is
noted because there is no opportunity for mixing. Solutes move at a rate
equivalent to that of the transporting fluid. This type of transport almost
never occurs in soils or streams.
1.0
o
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0.5
-------
Solute Transport by Diffusion-Dispersion and Bulk Transport
Figure 3-6 illustrates a series of breakthrough curves for bulk transport
combined with diffusion/dispersion. An instantaneous jump in C/Co is no
longer observed. Instead, C/Co rises gradually as effluent volume (or time)
increases. The combined effects of diffusion, viscous drag, and dispersion
result in a more complex flow pattern that changes as a function of pore size
distribution (curves A, B, C). This type of behavior is characteristic of
noninteracting solutes (chlorides, sulfates, nitrates, etc.).39
Solute Transport by Bulk Transport and Diffusion/Dispersion with Soil-Solution
Interaction
Figure 3-7 illustrates the effect of soil-solution interaction on solute
transport. In this case, the breakthrough curve shifts to the right
reflecting the longer time required for solute transport when soil-solution
interactions are present.41
The type of interactions that commonly occur in soil are presented in
Table 3-2. All listed mechanisms vary in magnitude as a function of waste and
soil characteristics. Soil pH, cation exchange capacity, organic matter
content, texture, and permeability are generally considered "master variables"
because they influence the rate and direction of interaction.
Several mechanisms are often associated with the removal of individual
waste components as illustrated in Figure 3-8. Detailed discussions of these
interactions are beyond the scope of this report, but can be found in
references 36, and 42 through 46.
3.4 COVER SYSTEMS
An integral step in the closure of an SI is the design and fabrication of
a cover. This is needed when the wastes are left in the impoundment after
closure and a closure plan similar to that required for a landfill is
implemented. In the case where wastes are removed from the impoundment, a
cover designed for purposes of waste isolation is not necessary. However,
some degree of site reclamation may be necessary for the control of erosion,
drainage, and wind blown dust as well as for safety, aesthetic, and end-use
considerations.
For an SI closed as a landfill, the cover must function primarily to:
• Control the migration of pollutants
• Control surface water infiltration
t Prevent erosion
t Control potentially harmful gas movement
• Support construction vehicles
31
-------
1.0
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Noninteracting
solute
Bulk
transport
Interacting
solute
0.5 1.0 1.5 2.0
Number of pore volumes collected
Figure 3-7. Breakthrough Curve with Soil-Solution Interactional
32
-------
Table 3-2. Types of Soil-Solute Interactions36.42-46
Biological
Chemical
Physical
Transformation
Degradation
Volatilization
Crop Uptake
Cation exchange
Am"on exchange
Cation-dipole interaction
Hydrogen bonding
Van der Waals attraction
Hydrophobic bonding
Specific ion sorption
Precipitation
Chelation
Filtration
Dilution
Decay
33
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In addition, the cover will function to meet aesthetic considerations by
controlling any noxious odors and providing a base for the establishment of
vegetation. The functions of a cover for a closed SI are usually complexly
interrelated. For example, a cover designed to impede infiltration and
percolation of surface water may call for a clay layer while dust control and
wind erosion considerations would best be met by a layer of coarse-grain-sized
sand. Where apparent conflicting functions exist, priorities must be
established on a site-specific basis.
In designing and specifying a cover to meet the established functional
objectives, reference 47 should be consulted. This design and construction
manual makes general recommendations with regard to covers, presents details
of each cover function, reviews pertinent characteristics of soils and other
materials, and proposes specific design methods taken from the present waste
disposal state of the art.
Upon development of a proposed design, reference 48 presents a procedure
for evaluating cover designs for closure impoundments. This manual outlines
guidelines to be used to evaluate the pertinent elements of the design. These
elements include: soil test data, site topography, climatological data, cover
composition, thickness, placement, cover configuration, site drainage,
vegetation, post-closure maintenance, and contingency plans. Persons involved
in assessing the adequacy of surface impoundment closure plans should refer to
this manual. One step in evaluating cover design involves an assessment of
cover thickness with respect to infiltration, surface runoff, and
evapotranspiration. The evaluator is referred to reference 40 where the
details of a recommended computerized water balance procedure are outlined.
3.5 POTENTIAL FOR CONSOLIDATION OF WASTES
Almost all Si's are intended for retention of aqueous wastes on either a
full- or part-time basis. These aqueous wastes contain solids (sludges and
slimes) or will produce solids by precipitation as a result of solar
evaporation and/or chemical reaction upon mixing of different aqueous wastes.
Consequently, dewatering of the SI prior to closure will result in a layer of
residual waste solids left on the bottom of the impoundment. These solids
will be saturated with water. If the impoundment has a soil bottom or a clay
liner or both, these soils will be saturated with water as well. If these
saturated or even partially saturated solids and soils are backfilled with an
earth or clay cover, the potential exists for significant consolidation of the
residual waste solids and, to a lesser degree, the clay liner and/or soil
beneath the waste solid sediment.
3.5.1 Stages of Consolidation
Consolidation is defined as the process of reducing the volume occupied
by a soil mass. This volume reduction occurs either at the expense of the
void volumes between the solid particles or by reduction of the volume of the
solid particles themselves. Consolidation occurs in stages: primary,
secondary, and tertiary.
35
-------
The initial step of the consolidation process (primary) is due to a
decrease in the water content of fully saturated waste. The rate of primary
consolidation is controlled by the rate at which water can be removed from the
waste either by overburden pressure forces or capillary forces. This rate is
of course controlled by the permeability or hydraulic conductivity of the
waste strata and the surrounding soils. The second step of the consolidation
process (secondary) results from compression of the constituent solid waste
itself. The third step of the consolidation process (tertiary) results from
reduction of the actual mass of the waste solid particles. This may occur as
a result of leaching (dissolution of waste solids in water); gasification by
chemical reaction; and biological oxidation, either aerobic or anaerobic.
Tertiary consolidation can occur in parallel with either primary or secondary
consolidation.
3.5.2 Impacts of Waste Consolidation
The primary impact of waste consolidation is a reduction in the surface
elevation of the covered site. When this reduction occurs to different
degrees at different points on the site it is called differential settlement.
If a covered impoundment site is to be used for either aesthetic or public
purposes, the surface subsidence from consolidation must be prevented. Severe
cases of subsidence result in very uneven ground contours and could even lead
to cracking of the surface and or fracture of the cover. Any type of
construction on the site would be endangered by subsidence, particularly
differential settling.
Serious subsidence problems can result in creation of one or more surface
depressions that will act as runoff catchment basins. This will result in
standing water on the cover, a condition that will significantly increase the
rate at which water can infiltrate a porous or semipermeable cover. Increased
infiltration will result in increased leaching that, in turn, can result in
tertiary consolidation due to dissolution of residual waste solids. The amount
of consolidation depends on the quantity of Teachable constituents. The weight
of the water impounded by surface depressions can also lead to additional
secondary consolidation of the residual waste solids. The overall result
would be additional subsidence and increased discharge of leachate. It must be
remembered that consolidation of an SI is a dynamic process and that
deformation of the cover surface will occur with time. Consequently,
regrading of the cover surface may be necessary to minimize the effects of
localized subsidence.
Perhaps the most serious consequence of differential consolidation is
that the cover may fracture. This could result in the production of a direct
channel to the residual waste solids that could allow direct access of surface
water to the residual wastes. The fracture would also act as a discharge
channel for gases and/or contaminated leachates.
3.5.3 Mechanism of Consolidation
The extent of consolidation primarily depends on the thickness of the
residual waste sediment layer. Differential settling will be a potential
problem when the thickness of the residual waste sediment varies within the
36
-------
site. The physical characteristics (grain size, pore volume, etc.) and the
chemical characteristics (solubility, gasification potential, organic content,
etc.) also affect the extent of consolidation.
Primary Consolidation
By definition, primary consolidation results from the drainage of
"connate water" from the voids between the waste solid particles. Thus, the
extent of primary consolidation will depend on the amount of connate water
left in the waste sediment layer at the time of backfill and cover. The rate
of primary consolidation will be controlled by the rate at which water can
drain from the sediment layer. The drainage can occur by several mechanisms:
• The primary mechanism is drainage through the liner and surrounding
soils. In the case of unlined impoundments, this drainage is
controlled by the permeability of the surrounding soils. In the case
of faulty liners, the size of the fault together with the
permeability of the waste sediment and the permeability of the soils
in the vicinity of the faults controls.
• A secondary mechanism is assimilation of moisture by the backfill/
cover material. If these materials are relatively dry at the time of
placement, capillary tension can move connate water upward into this
material. The extent to which this occurs will be controlled by the
particle size of the backfill/cover and the degree of compaction
achieved. In impoundments with an intact liner of low permeability,
this may be the primary mechanism for connate water removal from the
sediment layer.
• In some cases, when the liner is intact and connate water drainage is
expected to proceed slowly or not at all, it may be desirable to
"engineer" one or more drainage paths through the liner to a liquid
collection system.
Secondary Consolidation
By definition, secondary consolidation is due to plastic creep or
deformation of the residual sediment under the force of overburden stress.
Also, some solids undergo a volume shrinkage as the water content decreases
(clays are one example of the shrinkage phenomena). Clearly the extent of
secondary consolidation and the rate at which it occurs are very specific to
the physical characteristics of the sediment (rates of creep under specific
levels of overburden pressure).
A situation of particular concern is the case of a covered impoundment
hydraulically sealed to the extent that the residual waste solids cannot be
completely drained of connate water. In this case, the residual waste solid
will remain a flowable or plastic solid and, under the force of constant
overburden pressure, will remain in place in a more or less metastable
condition. If an unbalanced overburden stress is created (i.e., construction
of a structure on part of the cover), the residual waste can flow to the area
of lesser overburden stress. This results in settlement of the stressed
37
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overburden area (structure site) and rising of the unstressed overburden
area. If significant, this latter action could fracture the cover and exude
waste solids to the surface.
Tertiary Consolidation
Many mechanisms can contribute to reduction of the actual mass of
sediment solids. The most common include:
t Leaching -- Requires the supply and drainage of fresh (or at least
uncontaminated) water and soluble wastes and can be controlled by the
site water balance
t Gasification — Requires wastes capable of generating a gas by
chemical reaction (carbonates, sludges, etc.). The reactions are
generally pH controlled and are facilitated by water.
0 Biochemical degradation -- Requires organic wastes, a supply of
water, and either aerobic or anaerobic conditions. The reactions are
severely inhibited by toxic wastes.
The potential for tertiary consolidation is highly specific to the waste, type
of impoundment, method of closure, and site water balance.
3.5.4 Timeframe of Consolidation
Primary consolidation occurs relatively rapidly. Significant
consolidation has been observed over time periods ranging from several weeks
to several years in full-scale studies of soil. The timeframe is highly
dependent on the ability of the site to drain water and, consequently,
engineered drainage pathways can accelerate this otherwise slow process. Such
drainage systems may consist of infiltration trenches containing perforated
drainage or tiles backfilled with previous material such as sand. Another
means for shortening the timeframe would be to surcharge the cover with
surplus material to promote consolidation.
Secondary consolidation is relatively slow. In some cases, no effects
can be seen at all for many years until the imposition of an uneven surface
stress upsets the hydraulic equilibrium, and flow and/or deformation occur.
The rate of tertiary consolidation is highly specific to the operative
mechanism. No effect may be seen at all until local conditions occur that
activate one or more mechanisms. Leaching is clearly dependent on the water
throughput. Biological rates are relatively slow and environmentally
constrained. The presence of toxic materials may inhibit rates or prevent
activity entirely for many years. Chemical consolidation rates are dependent
on a supply of alkaline or acidic water and are constrained by the rates of
supply.
38
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3.6 POST-CLOSURE USE OF THE SURFACE IMPOUNDMENT SITE
Limitations of subsequent site uses should be considered prior to closure
of an SI. This section describes those site and waste characteristics that
will affect site uses and lists methods of controlling Site use. The
selection and design of a cover system for a closed SI should take into
account the post-closure land use. A planning study should identify uses that
will:
§ Control the migration of pollutants from the facility via ground
water, surface water, and air
• Control surface water infiltration including prevention of pooling
• Prevent erosion
In addition to the above regulatory requirements, land use plans should
promote the following objectives:
• Permanently upgrade the SI so that the land can be used in the most
advantageous manner
• Promote the permanent conversion of the impounded wastes to a stable
nonhazardous state
• Eliminate or minimize potential off-site conflicts with existing or
future development through the careful siting and maintenance of an
open space separation and utilization of natural buffers
• Be compatible with and complementary to existing natural conditions
and help meet the future needs of the community
The land use planning process should also be integrated with surrounding land
use and community needs. This process should be organized to provide
information that will aid in establishing the threat to human health and the
environment. A logical approach to site planning may include the following
steps:50
1. Perform site inventory. The existing land use must be identified,
and the impact of curtailment of current land use (whether it be
recreation, open space, etc.) must be determined. The inventory
might include topography, vegetation, water bodies, public
facilities, etc. Information can be obtained from aerial photos,
site visits, and review of public records. In addition, the sources
listed in Table 3-3 can be consulted.
2. Evaluation of needs. To assess future needs, an evaluation of local
plans for population, utility, and highway projections should be
attempted. Local planning offices should be contacted to determine
current land use policies for the area of consideration.
39
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3. Identify alternatives and select completed site use. Using the
information obtained above, an evaluation should be conducted noting
advantages and disadvantages of each potential use. If site
characteristics and constraints are known, alternative ultimate land
uses can be evaluated in terms of technical feasibility and costs.
The optimum site use can then be selected.
4. Select, design, and implement completed site use. After selecting
completed site use, a master plan should be prepared. It should
designate the scheme for cover soil stockpiling, maintaining positive
drainage by regrading, revegetation, sediment control, leachate
control, ground or surface water monitoring, and maintaining
acceptable environmental and aesthetic conditions.
3.6.1 Site Use Limitations for Impoundments Closed as Landfills
The first option for SI closure is to leave wastes in the impoundment,
dewater the solids, and close the site as a landfill. Under this option, the
owner must consider all problems of site maintenance and access that are
characteristics of landfills. A summary of major technological considerations
is presented in Table 3-4.
Closure plans for Si's differ most from those of landfills in the need of
solids dewatering and dike considerations. Neither of these items should
adversely affect post-closure use of the site if completed. Consolidation of
sludges to enable structural support of overlying building may require longer
periods of time than for landfills. Post-closure site uses may also be
limited due to closure cover (poor trafficability of soil, erosion by wind or
water), dikes and levees (side and mass instability), gas production (affects
on vegetation, safety to users, control devices), and surface water control
devices or other contour changes.
Detailed consideration for preclosure site surveys is given in
Section 4.6 for dike and levee stability and Section 3.7 for gas generation.
However, such a survey should collect information to evaluate other less
obvious site conditions that affect its subsequent usage. These include the
following:
• Trafficability characteristics — strength of site surface under
repeated traffic (these characteristics are often measured by the
rating cone index,^' soil moisture, and slope index^2)
t Construction support characteristics — wastes used in impoundments
exhibit both an enduring potential for serious pollution and
resistance to compaction. (Predictions on settlement can be made
that are adequately reliable for engineering construction design
use. Although the colloidal nature of sludges may keep them
water-saturated for years, the impoundment can be designed for more
rapid in situ stabilization if dewatering and drainage are
incorporated.)
41
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Table 3-4. Compatibility of Hazardous Waste Impoundment Features
and Various Site Uses
SI site uses upon closure
Design features
Parks,
playgrounds,
ballparks, Parking Open
Buildings golf courses areas Agriculture spaces
Subsurface water control
Extraction well
Well point system
Cut-off walls
Subsurface drainage
Surface water control
Cover
Grading
Diversion of surface
water
Levees/floodwalls
Drainage/erosion
control
Air factors
Passive gas control
Active gas control
Control of bird hazard
to aircraft
Surface area factors
Covers
Access
Land buffers
C
C
C
C
NC
NC
C
NC
RDA
NC
NC
C
C
C
NC
RDA
RDA
C
C
C
C, except
ballparks
C
NC
RDA
C
C
C
C
C
C for parks
and golf
courses
RDA
RDA
C
C
C
C
NC
NC
RDA
C
C
C
C
C
C
C
C
C
C
C, affects
techniques
C
C
NC
C, affects
techniques
C, affects
techniques
NC
C
C, affects
techniques
C
NC
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C = Compatible, NC = Not compatible, RDA = Requires design alteration
42
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• Vegetation growth characteristics — surface flooding, ground water
table, soil character, erosion by wind or water, and gas generation
each directly effect site vegetation
3.6.2 Site Use Limitations for Impoundments Closed with Hazardous Waste
Components Removed
Closed Si's that have insignificant remaining hazardous content are
essentially reclaimed areas in terms of contamination by hazardous wastes.
However, site changes that occurred during impoundment formation (i.e., dikes
or excavated depressions) or hazardous waste removal (channels, excavations,
treatment devices) should be reconditioned. Local regulations frequently
require that upon closure of industrial or commercial operations, equipment
and buildings be removed and the land be returned to its former natural
state. Under such regulations, the removal of dikes, waste flow controls, and
nonhazardous waste residuals would be completed and ground cover replanted.
If an alternative site use is planned, lesser refurbishing of the site may be
allowed. A listing of considerations limiting site post-closure use are
presented in Table 3-5.
Table 3-5. Compatibility of Various Site Uses and Impoundment Features
After Hazardous Waste Removal
SI site uses upon closure
Parks,
playgrounds,
ballparks, Parking Open
Design features Buildings golf courses areas Agriculture spaces
Subsurface water controls
Wells CIR CIR CIR CIR CIR
Subsurface drainage C C C C C
Surface water control
Cover
Diversion of surface
water
Levees/floodwalls
Air factors
Surface area factors
RDC
RDC
CIR
C
RDC
C
C
CIR
C
C
C
NC
CIR
C
C
C
C
CIR
C
C
C
C
CIR
C
C
C = Compatible, CIR = Compatible if removed/dismantled, RDC = Requires design
consideration
43
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3.6.3 Considerations for Limiting Access
Completion of impoundment site closure frequently requires access
restrictions. This is necessary to protect the site and both the general
public and maintenance personnel. During closure operations site access may
be limited by posting, entry controls, fencing, or other physical barriers.
Entry controls would typically include fencing with gates across the access
roads. Each entry gate should be well posted as should any readily accessible
periphery with incidental auto or foot traffic. Company personnel or law
enforcement officers should patrol sites on some periodic planned schedule.
Impoundments near population centers or frequently used company land may
require a chain-link fence or other secure access barrier. Subsequent to
closure, attention should be given to access control for gas, surface water,
or other pollutant control devices necessary to minimize nuisance or
environmental hazards. If cover grading, levees, dikes, buffer zones, or
floodwalls appear potentially inviting to users of recreational vehicles,
additional access control should be installed. Consideration should be given
to site uses compatible with cover maintenance, especially since use affects
vegetation established for cover protection and surface erosion control.
3.7 AIR EMISSIONS
The potential emission of organic gases and fugitive dust is a well
recognized impoundment problem that may appear or continue during and after
closure if preventive control measures are not taken. Generally, organic air
contaminants have not been measured in routine site surveys. Indeed, air
contaminants are often completely neglected in deference to water (leaching)
or solid (erosion, mass wastage) constituent losses during site survey
sampling and analysis. Air emission sampling and monitoring at hazardous
waste facilities has been carried out, and the results are described in
reference 53. Technical considerations of potential emissions of gases and
dust are "discussed in the following subsections.
3.7.1 Gases Emitted From Impounded Materials
Gases may be emitted from an impoundment due to the vaporization of
liquids, chemical reactions, or biological activity of the impounded solids
and liquids, or by venting of entrained gases. Emission of organic
decomposition gases (methane, hydrogen sulfide) from proteinaceous and
cellulosic wastes, radon gas from uranium mill tailings, and harmful gas
contaminants (chloroform, benzene, and trichloroethene) from chemical process
waste impoundments have been measured and reported.54 The emission of harmful
gases such as methane, methylmercaptan, dimethyl-disulfide, & hydrogen sulfide
from liquid and sludge industrial waste (notably sugar beet, pulp, and
chemical processing industries) have been the subject of public concern and
regulatory activity for many years. Various organic compounds may slowly but
continuously volatilize under improperly closed impoundment conditions. Low
boiling point organic materials including contaminated solvents, if improperly
impounded, will emit vapor that can be hazardous because of its toxicity or
ignitibility. Inorganic gases can also be emitted from impoundment surfaces.
Oxidant gases (Cl2 and 03) may react with polymeric liner materials and
organic materials. These gases either originate as entrained gases or as
44
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chemical reaction products. During closure of an active impoundment site,
consideration must be given to the possible release of impounded gases as a
result of closure operations or from biological or chemical activity.
Gases Entrained or Generated in Surface Impoundments
The traditional ponds, pits, lagoons, reservoirs, and other Sis used for
hazardous liquid and solid waste disposal, industrial waste storage, sludge,
or wastewater treatment prior to closure have exposed top surfaces. Both
liquid and sludge surfaces will vaporize solvent and related hazardous organic
compounds. Vaporized contaminants of greatest concern are the halogenated
organics and aromatic hydrocarbons because of their toxicity. Solvents and
inorganic fumes are also of major concern. The volatility of hydrocarbons are
reported in a series of Hydrocarbon Processing Journals,^ while information
on pesticides is available from Spencer and Cliath.56 Tne rate of waste
volatilization in soil or impoundments is dependent on physical and chemical
properties of the waste and the surrounding environment. Emissions into still
air are slower than evaporation into the wind. Characteristic maximum vapor
pressures increase with temperature. Vaporization of organics from water
surfaces is affected by Henry's law constant but wind speed, temperature, and
liquid turbulence also affect the rate.
Gases may be generated from chemical reaction of the impoundment contents
or by biological activity on the carbonaceous components. Upon closure of a
site, if existing organic and reactive constituents are not removed,
gas generation may continue or even increase.
The organic matter in impounded sludges, whether lying in a discrete
contained sludge layer or deposited within the subsoil in some distributed
concentration, will undergo decomposition. Such biological degradation will
change from aerobic to anaerobic, increasing especially after surface
closure. Organic constitutents are gradually oxidized to intermediate
products (organic acids and alcohols) and subsequently converted to gases and
organic residues. Unfortunately, many reduced sulfur and volatile intermediate
products may be vented before further stabilization.
The quantity of gaseous air emissions from impounded liquids or sludges
varies widely. Laboratory studies of gas production in covered wet solid
waste ranged from 22 to 45 ml/kg/day. The total amount varied between 2,600
to 183,000 ml/kg of waste.57 In closed systems, this gas can build up
pressure, break through cracks in the cover, and carry hazardous vapors, if
present, along with it to the surface. Some gas generation rates for several
industrial wastes impounded as liquids or covered are given in Table 3-6.
Impoundments containing hazardous components characterized by low boiling
points (<100°F and vapor density = 1.1) or low flashpoints must be assessed
for potential gas generation. Both potential direct venting and possible
reactions resulting in gas generation must be considered. Direct venting of
solvents in large quantities is prohibited, but small quantities mixed with
waste sludge are often held in outside open impoundments.
45
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Table 3-6. Impounded Waste Gas Generation Rates57
Gas generation rate
Waste (l/m2/day)
Methanol 8.8 x 105
PCB, aroclor 1242
liquid 2.1 x 104
6.4 ppm on sand 500
Paperwaste and radioactive solid 0.4
Hexachlorobenzene
no cover 2.9 x
1.9 cm cover 4.1 x
30 cm cover 900
Typical wet solid waste landfill 12.9 to 25.2
(70 lb/ft3)
Impounded solids may react with closure cover materials. A detailed
listing of the general types of materials that may produce gaseous emissions
upon impoundment closure are published in the Federal Register as EPA's
proposed rules (Vol. 43, No. 243, December 18, 1978, Appendix I).
Classifications of sludges that are acid-forming (i.e., sulfides), oxidizing
or reducing, fume or vapor forming, and exothermic have been listed by
Curry.$&
Impoundment operators must consider gas-forming reactions that may occur
either during or subsequent to site closure. This can best be identified by
impoundment content and subsoil characterization during a site survey or from
an inventory list. Cover materials can affect gas generation as well as
control its emission. This includes:
• Control of air transfer (causing less aerobic conditions)
• Possible reduction of infiltrate
t Affect on character of infiltrate
• Reactivity of the cover material (regulations specifically prohibit
adding wastes that react with cover material)
• Possible concentration of reactive gases produced beneath the cover
46
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The central consideration of whether to remove the residual waste
contents of the impoundment and to what depth or extent should be based
partially on probable gas problems. Therefore, a brief discussion of the
mechanisms of gas emission upon closure of impoundments is presented.
Gases Released from Surface Impoundments Upon Closure
The proper management of SI closure to minimize venting of toxic,
explosive, or reactive gases includes considerations to preclude further gas
generation and venting of existing gases. Such emissions will affect
subsequent site use especially for uses involving buildings and extended
exposure uses. Venting of gases can occur during three phases of the
impoundment closure:
• While the impoundment material remains uncovered and unremoved
• During the impoundment residue removal and cover placement
• After closure
While SI contents remain exposed, a continuous process of volatilization
and wetting and drying occurs. These events are affected by local
climatological factors such as insolation, precipitation, evaporation,
temperature, and surface air transfer (wind). With the site intact, an array
of conditions (dewatering, impoundment content fill or draw, chemical and
biological reactions, climatological variables) prevent chemical description
or prediction of impoundment gas emissions. The most apparent emissions will
be vaporization of solvents and volatile organics and venting of biologically
generated gases (mainly carbon dioxide, methane, and hydrogen sulfide). The
venting mechanism is dependent on vapor pressure and surface exposure and,
thus, is only indirectly controllable by impoundment operators.
When discharging, pumping, dredging, or removing impoundment residues, an
additional set of gas emission phenomena can occur:
t Liquid surfaces can be renewed and, thus, increase vaporization
• Dried surfaces or crusts can be removed thereby venting entrained
gases
• Pressures can be changed and residue components mixed, thereafter
affecting gas venting or production
Any decision to remove impoundment residual contents should be based on
consideration of gas emissions resulting from the removal process. The
natural readsorption or degradation processes of toxic and reactive gases
within impounded wastes has encouraged and justified allowing these residues
to stabilize and degrade onsite after impoundment use has ceased.59
As described in Section 2, the various site closure mechanisms basically
involve residue content removal to some depth or no removal, site covering,
47
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and protection. Upon impoundment site consolidation and cover placement, gas
emission may continue as a management problem requiring venting mechanisms.
Gases produced (or entrained and compressed) beneath covers on
impoundment sites will move in various directions due to pressure or by
dissolution into moving ground water (or other subsurface liquids). Although
diffusion is the most common gas flow factor, total pressure gradient may
become an overriding factor. The latter is often true where mechanical
pressure is purposefully applied to remove or disperse gases.
Gas flow within soil is dependent on porosity, free space diffusivity,
and the degree of saturation. The rate of diffusion through a porous soil
with a degree of saturation, S, is measured by the equation:
Dp = 0.66n D0 (1-S)
where
Dp = Diffusivity of wet soil
D0 = Diffusivity at 20°C of free air space
S = Degree of saturation (fraction of void space occupied by water)
n = Porosity of soil
Porosity of soils may vary by a factor of 2 from dense gravel to loose clay.
Saturation can vary from a low of 2 or 3 up to 100 percent, greatly affecting
gas venting. Diffusivity of individual gas, D0, is constant (21 ft^/day for
CH4, and 15 ft2/day for C02). Typical diffusivity values of a gas through a
wet covering soil have been demonstrated according to this formula in a study
of vaporization and flux of a nazardous chemical waste.4'
Such diffusivity can be used in the following equation to determine the
mass of gas emitted, Q, through a soil layer with time:
Q = Dp A Co/L
where
L = Soil layer thickness (feet)
A = Soil layer area (square feet)
Co = Gas concentration differences across the soil layer
This mass rate movement of gas is based on diffusion induced by gas
concentration. Any movement caused by external or internal induced pressure
would be additional.
48
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3.7.2 Fugitive Dust Emissions
Particulate air emissions can be generated during the operation, closure,
and post-closure use of Si's. The generation and dispersion of dust from a
hazardous waste disposal site is of concern because of its potential health
hazard characteristics as well as its adverse visibility effects. In recent
years, considerable attention has been focused on the problem of fugitive
dust, since many air quality control regions have not met the ambient air
standards for particulate matter. In many cases, the cause of nonattainment
has been identified as fugitive dust.
Causes and Sources of Dust
Fugitive dust emissions consist of particulate matter that may become
airborne due to the forces of wind, human activity, or both. During closure
and post-closure use of Si's, dust emissions may be caused by:
• Wind erosion of the waste materials
• Reentrainment of particulate matter by vehicular traffic on haul
roads and exposed surfaces
• Excavation of waste materials during closure
• Wind erosion of the cover soil
The fugitive emissions produced by wind erosion of SI stored wastes
depend on the waste type, moisture content, wind velocity, and surface
geometry. Although many equations have been developed by researchers in
estimating emissions generated from agricultural soils, there seems to be a
basic agreement that between 2.5 and 10 percent of all the soil eroded due to
wind becomes airborne as suspendable particulate matter.60 It can be
assumed that a similar value would be applicable to SI wastes.
Fugitive dust emissions from unpaved surfaces caused by vehicular traffic
on exposed waste surfaces and haul roads are affected by the surface texture
of the road, road material, surface moisture, vehicle speed, and type.
Fugitive emissions from unpaved surfaces can be estimated using emission
factors developed in EPA Publication AP-42, "Compilation of Emission Factors,"
if the silt content of the surface materials (percentage of weight of
particles smaller than 75 micrometers in diameter), average vehicle speed, and
average daily traffic are known. Dust emissions from unpaved surfaces
generally exhibit a particle size distribution of 60 percent of the particles
below 30 micrometers in diameter.61 Fugitive dust emissions from SI closure
operations involving waste removal are mainly due to excavation, vehicle and
equipment operation, and wind erosion of the exposed waste surfaces. Although
waste removal should be of a short duration, excavation activities can be a
major source of dust emissions. The exposed waste surfaces are susceptible to
wind erosion and to the mechanical movement processes of the excavation
equipment. Dust emissions are affected by the amount of excavation activity
and weather conditions. The dust generated from the mechanical movement
processes, as in the case of waste excavation, is .generally insensitive to the
49
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ambient wind speed. Wind speed does determine the drift distance of large
dust particles and, therefore, the localized impact of the fugitive dust
source.
Upon completion of the closure procedures, the SI site will be covered
with a soil layer that may act as a source of fugitive dust if not properly
constructed. Wind erosion of this soil will result in particulate emissions.
The quantity and characteristics of these emissions are dependent on soil
type, moisture content, wind velocity, and surface geometry. Cover design
features along with procedures that can be employed to minimize fugitive dust
emissions are discussed in Section 4.9.
50
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REFERENCES FOR SECTION 3
1. Ham, R., et al., "Comparison of Three Waste Leaching Tests," U.S.
Environmental Protection Agency, EPA-600/2-79-071, July 1979. PB 299-258.
2. Chian, E. S. K. and F. B. DeWalle, "Evaluation of Leachate Treatment
Volume I, Characterization of Leachate," U.S. Environmental Protection
Agency, EPA-600/2-77-186a, September 1977. pe 272-855/5BE.
3. Thompson, D. W., "Elutriate Test Evaluation of Chemically Stabilized
Waste Materials," U.S. Environmental Protection Agency, EPA 600/2-79-154,
August 1979. PB 80-147069.
4. Charlie, W. A., R. E. Wardwell, and 0. B. Andersland, "Leachate
Generation From Sludge Disposal Area," Journal of the Environmental
Engineering Division, American Society of Civil Engineers, Vol. 105,
No. EE5, p. 947, October 1979.
5. Fillos, J. and H. Biswas, "Phosphate Release and Sorption by Lake Mohegan
Sediments," Journal of the Environmental Engineering Division, American
Society of Civil Engineers, Vol. 102 No. EE2, p. 239, April 1976.
6. Lee, G. F., "Factors Affecting the Transfer of Materials Between Water
and Sediments," Literature Review #1 Water Resources Center, University
of Wisconsin, Madison, Wisconsin, 1970.
7. Fredriksen, R. L., "Nutrient Budget of a Douglas-Fir Forest on an
Experimental Watershed in Western Oregon," Proceeding -- Symposium in
Research on Coniferous Forest Ecosystems, Bellingham, Washington,
March 23, 1972.
8. McColl, J. G. and D. W. Cole, "A Mechanism of Cation Transport in a
Forest Soil," Northwest Science Vol. 42, p. 134, 1968.
9. Stumm, W. and J. Morgan, "Aquatic Chemistry," Wiley-Interscience, New
York, New York, 1970.
10. Morel, F. and J. Morgan, "A Numerical Solution for Solution of Chemical
Equilibria in Aqueous Systems," Aquatic Chemistry, Wiley-Interscience,
New York, New York, 1970.
11. Lowenbach, W., "Compilation and Evaluation of Leaching Test Methods,"
U.S. Environmental Protection Agency, EPA-600/2-78-095, May 1978.
PB 285-072/AS.
12. Ham, R., et al., "Background Study on the Development of a Standard
Leaching Test," U.S. Environmental Protection Agency, EPA-600/2-79-109,
May 1979. PB 298-280/9BE.
51
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13. Anderson, W. C. and M. P. Youngstrom, "Coal Pile Leachate — Quantity and
Quality Characteristics," Journal of the Environmental Engineering
Division, American Society of Civil Engineers, Vol. 102, No. EE6, p.
1239, December 1976.
14. Good, D. M., V. T. Ricca, and K. S. Shumate, "The Relation of Refuse Pile
Hydrology to Acid Production," Third Symposium on Coal Mine Drainage
Research Bituminious Coal Research Inc., Monroeville, Pennsylvania, 1970.
15. Chian, E. S. K. and F. B. DeWalle, "Compilation of Methodology Used for
Measuring Pollution Parameters of Sanitary Landfill Leachate," U.S.
Environmental Protection Agency, EPA-600/3-75-011, October 1975.
PB 248-602/AS.
16. IU Conversion Systems, Inc., "Shake Test for Evaluation of the Leaching
Potential from Land Disposal of Waste Materials," IU Conversion Systems,
Inc., Philadelphia, Pennsylvania, August"1977.
17. State of Minnesota, "Land Disposal Leach Test," Minnesota Pollution
Control Agency, Roseville, Minnesota, July 1977.
18. Ham, R., "Development of a Standard Leaching Test -- Second Progress
Report," EPA Grant No. R804773010, University of Wisconsin, January 1977.
19. Silka, L. R. and T. L. Swearingen, "A Manual for Evaluating Contamination
Potential of Surface Impoundments," U.S. Environmental Protection Agency,
EPA 570/9-78-003, June 1978.
20. Fuller, W. H., et al., "Influence of Leachate Quality on Soil Attenuation
of Metals," Proceeding of the Sixth Annual Research Symposium, U.S.
Environmental Protection Agency, EPA-600/9-80-010, March 1980. PB 800-175086.
21. Korte, N. E., et al., "A Baseline Study in Trace Metal Elution from
Diverse Soil Types," Water, Air, Soil Pollution No. 5, p. 149, 1975.
22. Fuller, W. H., "Movement of Selected Metals, Asbestos, and Cyanide in
Soil: Application to Waste Disposal Problems," Solid and-Hazardous Waste
Research, EPA 600/2-77-020, Cincinnati, Ohio, 1978. PB 266-905.
23. "Lining of Waste Impoundment and Disposal Facilities," U.S. Environmental
Protection Agency, SW-870.
24. Haxo, H. E., R. S. Haxo, and R. M. White, "Liner Materials Exposed to
Hazardous and Toxic Sludges — First Interim Report," U.S. Environmental
Protection Agency, EPA-600/2-77-081, June 1977. PB 271-013.
25. Haxo, H. E,, R. M, White, "Evaluation of Liner Materials Exposed to
Leachate — Second Interim Report," U.S. Environmental Protection Agency,
EPA-600/2-76-255, September 1976. PB 259-913.
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26. Haxo, H. E., R. S. Haxo, and T. F. Kellogg, "Liner Materials Exposed to
Municipal Solid Waste Leachate -- Third Interim Report," U.S.
Environmental Protection Agency, EPA-600/2-79-038, July 1979. PB 29-336/AS.
27. Styron, C. R., and Z. B. Fry. "Flue Gas Cleaning Sludge Leachate/Liner
Compatibility Investigation: Interim Report," U.S. Environmental
Protection Agency, EPA-600/2-79-136, August 1979. PB 80-100480.
28. Stewart, W. S., "State-of-the-Art Study of Land Impoundment Techniques,"
U.S. Environmental Protection Agency, EPA-600/2-78-196, December 1978.
PB 281-881/AS.
29. Kumar, J. and J. A. Jedlica, "Selecting and Installing Synthetic Pond
Linings," Chemical Engineering, Vol. 80, No. 3, February 5, 1973,
pp. 67-70.
30. Ware, S. A. and G. S. Jackson, "Liners for Sanitary Landfills and
Chemical and Hazardous Waste Disposal Sites," U.S. Environmental
Protection Agency, EPA-600/9-78-005. PB 293-335/AS.
31. "Procedures Manual for Ground Water Monitoring at Solid Waste Disposal
Facilities," U.S. Environmental Protection Agency, EPA 530/SW-611, 1977.
32. Renson, I., A. A. Fungaroli, and A. Lawrence, "Water Movement in an
Unsaturated Sanitary Landfill," J. ASCE, San. Eng. Div., 1968.
33. "Use of the Water Balance Method for Predicting Leachate Generation from
Solid Waste Disposal Sites," U.S. Environmental Protection Agency,
EPA 530/SW-168, 1975.
34. Chow, Ven Te, Handbook of Applied Hydrology, McGraw-Hill, New York, 1964.
35. "Alternatives for Small Wastewater Treatment Systems, Onsite
Disposal/Septage Treatment and Disposal," U.S. Environmental Protection
Agency, EPA-625/4-77-011, 1977. PB 299-609/8BE.
36. Keeney, D. R. and R. E. Wilding, "Chemical Properties of Soils, for:
Soils for Management of Organic Waste and Waste Waters," Soil Science
Society of America, Madison, Wisconsin, 1977.
37. "Process Design Manual for Land Treatment of Municipal Wastewater," U.S.
Environmental Protection Agency, EPA 625/1-77-008, 1977. PB 299-665/1BE.
38. Water Resources Engineering Educational Series, Program X, Groundwater
Pollution, Continuing Education Program, U.C. Berkeley, 1973.
39. Kirkham, D. and W. L. Powers, Advanced Soil Physics, Wiley-Interscience,
New York, 1972.
40. Goluber, V. S. and A. A. Gasibyants, "Heterogeneous Processes of
Geochemical Migration," Consultants Bureau, New York, 1971.
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41. Taylor, S. A. and G. L. Ashcroft, Physical Edaphology, W. H. Freeman and
Company, San Francisco, 1972.
42. Letey, J., "Physical Properties of Soils, In: Soils for Management of
Organic Wastes and Waste Waters," Soil Science Society of America,
Madison, Wisconsin, 1977.
43. Bohn, H., B. McWeel, and G. O'Connor, Soil Chemistry, Wiley Interscience,
New York, 1979.
44. Green, R. E., "Pesticide-Clay-Water Interactions," In: Pesticides in
Soil and Water, Soil Science Society of America, Madison, Wisconsin, 1974.
45. Overcash, M. R. and S. Pal, "Design of Land Treatment Systems for
Industrial Waste-Theory and Practice," Ann Arbor Science, 1979.
46. Griffin, R. A. and N. F. Shimp, "Attenuation of Pollutants in Municipal
Landfill Leachate by Clay Minerals," U.S. Environmental Protection
Agency, EPA-600/2-78-157, 1978. PB 287-140.
47. Lutton, R. J., et al., "Design and Construction of Covers for Solid Waste
Landfills," U.S. Environmental Protection Agency, EPA 600/2-79-165,
August 1979. PB 800-100381.
48. Lutton, R. J., "Evaluating Cover Systems for Solid Hazardous Waste," U.S.
Environmental Protection Agency, SW-867.
49. Perrier, E., "Hydrologic Simulation on Solid Waste Disposal Sites," U.S.
Environmental Protection Agency, SW-868.
50. "Process Design Manual for Municipal Sludge Landfills," U.S.
Environmental Protection Agency, Technology Transfer, EPA 625/1-78-010
(SW-705), October 1978.
51. "Sludge Treatment Disposal," U.S. Environmental Protection Agency,
Technology Transfer, EPA 625/4-78-012, October 1978. PB 299-593/4BE.
52. Meyer, M. P. and S. J. Knight, "Trafficability of Soils, Soil
Classification," U.S. Army Exp. Station, Technical Memorandum 3-240,
Supplement 16, Vicksburg, MS, 1961.
53. Ase, P., et al., "Air Pollution Sampling and Monitoring at Hazardous
Waste Facilities," U.S. Environmental Protection Agency, EPA Contract
No. 68-03-2654.
54. Cheremisihoff, N. P., et al., "Industrial and Hazardous Waste
) Impoundment," Ann Arbor Science, Ann Arbor, Michigan, 1979.
55. Gallant, R. W., "Physical Properties of Hydrocarbons," Hydrocarbon
Processing Journal, Vol. 44, No. 7-10; Vol. 46, No. 3, 6, 7, 10; Vol. 46,
No. 1-5, 7-10, 12; Vol. 47, No. 1-12, Vol. 48, No. 1-12, 1965-1969.
54
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56. Spencer, W. F. and M. M. Cliath, "Transfer of Organic Pollutants Between
the Solid-Air Interface," Fate of Pollutants in the Air and Water
Environments, Part 1, L. H. Saffet, ed. J. Wiley & Son, New York,
pp. 107-109, 1977.
57. Shen, T. T. and T. J. Tofflemire, "Air Pollution Aspects of Land Disposal
of Toxic Wastes," Journal of the Environmental Engineering Division,
American Society of Civil Engineers, Vol. 106, No. EE1, pp. 211-226,
February 1980.
58. Curry, N. A., "Philosophy and Methodology of Metallic Waste Treatment,"
Proceedings of the 27th Industrial Waste Conference, Purdue University,
Lafayette, Indiana, May 1972.
59. Willard, H. K., "Discussion of Lake Champlain-International Paper Sludge
Problem," Letter report to EPA Region I, September 28, 1972, and Region
II, August 2 & 19, 1976.
60. Evans, J., et al., "Setting Priorities for the Control of Particulate
Emissions from Open Sources," Presented at Symposium on the Transfer and
Utilization of Particulate Control Technology: Volume 4, U.S.
Environmental Protection Agency, EPA-600/7-79-044d, February 1979.
PB 259-229/9BE.
61. "Guideline for Development of Control Strategies in Areas with Fugitive
Dust Problems," Environmental Protection Agency, Office of Air Quality
Planning and Standards, Research Triangle Park, North Carolina,
EPA-450/2-77-029, October 1977. PB 275-474/5BE.
55
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SECTION 4
TECHNICAL CRITERIA FOR IMPLEMENTATION OF CLOSURE PROCEDURES
The alternatives that must be considered during closure of an SI are
shown schematically in Figure 4-1. The order of issues in Figure 4-1 may not
be completely correct for every situation. Furthermore, many issues are
interrelated to a degree that they cannot be accommodated in a generalized
procedure. Therefore, a thorough understanding of all technical criteria is
fundamental to selection of an environmentally sound closure procedure. This
section presents the detailed technical criteria for closure based on a
generalized procedure.
Dewatering of the impoundment is usually the first step in the procedure
to permanently close an SI. The next issue is whether the site will be
decontaminated by removal of residual waste sediments or whether the residual
waste sediments will be left onsite. In the extreme case, site
decontamination would involve removal and offsite disposal of all residual
waste sludges, liner materials, and any contaminated soils. Surface soils
contaminated by spillage must be considered as well as subsurface soils
contaminated by leakage. Partial decontamination is also possible. In this
case, portions of the sludge, liner, and underlying soils could be removed.
In the event that site geology and geography minimize waste migration,
leaving the residual waste solids onsite in an engineered closure may be the
most practical, cost-effective, and environmentally sound alternative
available. The physical and geohydrological integrity of the site combined
with the physical condition of any liners, dikes, or water balance controls
necessary to ensure the requisite integrity of the site must be considered in
detail. Methods of sludge consolidation, dike rehabilitation, backfill, and
cover are all crucial to the long-term stability of the surface of the closed
impoundment.
The choice of in situ versus offsite sediment disposal must be made after
careful consideration of the following criteria. If the SI was a technical
and environmental success and these conditions can be maintained after closure
with a minimum of facility maintenance, closure of the site with residual
sediments in place may be an acceptable alternative. If the waste sediments
are particularly hazardous, overall environmental impacts may be minimized by
in situ disposal in a properly engineered fill and closure operation.
Excavation of the sediment with transport to an active disposal site may
merely postpone the question of ultimate disposal of the waste sediment and
increase the risk of public exposure during excavation and transport. Unless
the waste can be destroyed or treated to render it chemically inert and/or
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nontoxic, in situ disposal should be fully evaluated. If the waste sediment
is extremely hazardous and of large volume, in situ disposal may be the only
feasible alternative.
Guidelines for selecting the method of site decontamination are
necessarily vague since many of the technical issues are waste specific and/or
site specific. However, some useful criteria are:
• Waste characteristics — Since the closure procedure is designed to
promote the safe and permanent containment of hazardous wastes, waste
characteristics are necessary criteria to consider. These
characteristics include the degree of hazard (i.e., corrosive,
reactive, ignitable, toxic, bioaccumulative, mutagenic) and the
potential for waste migration.
• Geohydrological characteristics -- A decision to leave either
residual waste sediments, contaminated soils, or any other source of
soluble contaminants onsite should not be made without a thorough
geohydrological field study. This investigation will reveal the site
geohydrological characteristics necessary to evaluate the potential
for ground water and surface water contamination.
§ Post-closure use -- The closure procedure should be designed to be
consistent with the proposed site end uses and promote the permanent
conversion of the wastes to a stable nonhazardous state.
• Minimum maintenance — The closure method should be designed to
minimize post-closure maintenance if at all possible. Such
maintenance would include collection, treatment, and disposal of
effluents from water balance control processes (runoff, leachates,
ground water, etc.) as well as the repair of cover, dikes, surface
drainage ditches, or other physical features.
• Environmental impacts -- Selection of a closure plan should take into
account the public health risks and environmental impacts (both
onsite and offsite) of each step of the closure process. These
evaluations should include the feasibility and impacts associated
with waste removal, transport, and final disposal.
More specific criteria regarding individual steps of the closure process are
discussed in the following sections.
4.1 IMPOUNDMENT DEWATERING
The first step in the closure procedure usually involves the removal and
disposal of standing liquid. This liquid generally occurs as a layer above
the waste solids and is comparatively free of suspended solids. Removal of
this liquid is necessary before the residual solids can be removed or before
sediments are dewatered. There are various methods for removing this aqueous
waste; several are described below. These liquids will probably be hazardous
and should be handled accordingly. Disposal should also be according to
appropriate federal, state, and local regulations.
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• Decanting — Liquids within or ponded on the surface of the
impoundment can be removed by gravity flow or pumping to a treatment
facility if there is not a large percentage of settlable solids.
t Pumping and settling -- Liquids or slurries composed of suspended or
partially suspended solids can be removed by pumping into a lined
settling pond and then decanting. Sludges are disposed in a dry
state, and either returned to the impoundment or disposed in another
contained site.
• Solar drying -- Disposal of the liquid in a climate suitable to
evaporation is another technique and could be subject to air emission
regulations. Sludges remaining after evaporation are left in the
impoundment or disposed in another contained site. Volatile organics
should not be handled in this manner.
• Infiltration — Certain aqueous waste can be handled by infiltration
through soil provided the hazardous substances are removed by either
soil attenuation or underdrain collection of the solute. Collected
solutes are usually treated.
• Process reuse — Some aqueous waste can be recycled in the
manufacturing process a number of times until the contaminants are at
a level requiring disposal by one of the methods previously
mentioned. Reuse does not dispose of the waste but can significantly
reduce the quantities to be disposed.
• Chemical neutralization — Aqueous waste with low levels of hazardous
constituents frequently lends itself to chemical neutralization and
subsequent normal discharge under NPDES permit requirements.
• Absorbants — Materials can be added to aqueous impounded wastes to
absorb free liquids. Absorbants include sawdust, wood shavings,
agricultural wastes such as straw, rice and peanut hulls, and
commercially available sorbents.
4.2 WASTE SEDIMENT AND SOIL REMOVAL
If it is determined that an SI will be best closed by removing the waste
residuals, the removal procedure must be selected so that adverse
environmental impacts are minimized. The alternate removal procedures fall
into two general categories — wet or dry method.
4.2.1 Wet Methods for Sediment Removal
These techniques are based on removing the sediment as a slurry. They
are convenient and inexpensive as long as the slurry produced can be
transported and disposed in slurry form. Removal of waste sediment under a
water blanket is an excellent way to minimize odor and/or waste oxidation
reactions that might occur upon contact with the atmosphere. Wet methods of
waste removal generally provide the fastest closure schedule since time for
sediment drying is not necessary prior to its removal from the impoundment.
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• Resuspension ~ Dewatering of the SI is stopped when the remaining
water volume is the minimum necessary to transport the sediment as a
pumpable slurry. Either an air jet or a water jet* can be used to
resuspend the sediment. A vacuum tank truck with internal mining
capability is recommended for pumping the slurry from the impoundment.
• Excavation — If the sediments have hardened or formed a plastic mass
that will not flow freely and resuspend, excavation is the only
alternative. Sediments that have solidified may be excavated with a
high-pressure water or air jet from a floating platform. However,
the simplest technique is to use a high-speed rotary cutter mounted
at the suction of a pump with the entire assembly hung from a
floating platform. Such devices are typically used to mine clays
underwater and are commercially available.
Plastic or semisolid sediments will probably have to be excavated by
clamshell bucket or some other mechanical digging operation. Unless a water
blanket is necessary for odor or gas control, this is best done with a minimum
of water remaining in the impoundment.
4.2.2 Dry Methods for Sediment Removal
These techniques require that the fill water in the sediment be removed
by evaporation. They have the advantage of no wastewater problem at the
disposal site, and the sediment can be disposed as a dry solid. The
disadvantage is that a long period of time may be required to air dry specific
sediments in certain climates. Thick sediment deposits may require removal in
layers. Environmental concerns are sediment exposure to the atmosphere and
sediment dusting during excavation. (See Section 3.7 for air emissions
considerations.)
• Vacuum transport -- This technique works only with powdery sediments
or sediments that can be converted to powder or granular form by
plowing, disking, or other techniques. Vacuum transport minimizes
dust problems; however, if sediment disking is necessary, the dust
problems are maximized.
• Excavation -- These techniques are best suited to hard, solidified
sediments that need some type of mechanical breakdown to produce
conveniently handled pieces. Frequently, the excavation process
produces severe dust problems that have to be controlled by water
sprays. Any dry excavation process will produce some dust and pose a
potential health hazard to excavation equipment operators. Samples
of the residual sediments should be subjected to chemical and
toxicology studies to determine potential health hazards before dry
excavation is selected. Excavation can be by drag line from the
perimeter of the impoundment or by front end loader or bulldozer
operations inside the impoundment. Covered conveyors can be used to
*If a water jet is used, impoundment water should be the water source.
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transport sediment from the impoundment bottom to truck loading
facilities outside the impoundment if truck access to the inside of
the impoundment is impractical or hazardous. Excavation operations
involving freefall of the sediments or extended airborne transfers
such as clamshell buckets, power shovels, etc. should be avoided
because of spill and dust problems. If possible, all operations
should be carried out inside the impoundment to minimize surface
contamination through spillage.
4.2.3 Liner Preservation
The impact of the waste removal process on the integrity of the
impoundment liner is of vital concern. If a wet excavation process is used,
liner integrity must be preserved throughout the entire sediment removal
process. Even if highly effective leachate collection systems are in
operation, major liner failures will result in large-scale contamination of
the surrounding soils and must be avoided.
Where dry excavation processes are used, the possibility of water
accumulation from rainfall exists and liner integrity must be maintained to
the greatest extent possible. Scheduling of the excavation process to confine
excavation operations to small areas that can be cleaned up and diked off to
prevent rainfall runoff from the remaining sediments to excavated areas is
recommended.
4.2.4 Soil Removal
Excavation of contaminated surface soils, soils underlying liners, and
dike soils is easily accomplished by normal excavation methods. Disposal of
the contaminated soils, however, is less straightforward and can be expensive
if disposal as a hazardous waste is required. Onsite disposal of all
contaminated soils within the impoundment site should be considered. Sealing
of contaminated soils in the impoundment via a landfill type closure process
may be a cost-effective and environmentally sound alternative to offsite
hauling and disposal. Excavation of deep soil strata is expensive and the
volumes of soil involved may be very large. Every consideration should be
given to soil decontamination by controlled leaching programs in preference to
excavation.
4.3 SEDIMENT DEWATERING
The reasons for dewatering the residual sediments are highly specific to
the site, the waste itself, and the method of ultimate disposal of the
solids. The feasible alternative methods of dewatering are specific to the
site, the sediment characteristics, and the degree of dryness required.
EPA guidelines for SI closure require that if residual wastes are left in
the impoundment, these wastes must have the consistency of nonflowable
solids. Generally, this must be done by removing water, although chemical
fixation (see Section 4.7.3) may also be required.
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If the sediments are to be transported offsite for ultimate disposal and
wet excavation methods are to be used, it may be cost effective to dewater the
solids prior to transport to reduce volume and/or produce a nonflowable solid
for land disposal at the new site.
Passive dewatering is confined to those methods where no mechanical
energy input is directly applied to the removal of water. In an SI, the only
operative passive methods are solar evaporation and drainage caused by gravity
or capillary forces. Active dewatering consists of those processes where
thermal energy (drying) and/or mechanical energy (filtration) is used to
remove water from the solids.
4.3.1 Passive Uewaterlng
The feasibility of passive dewatering is the evaporation potential at the
site. The evaporation potential is the maximum evaporation that can be
expected under ideal conditions and is defined as the difference between the
normal annual Class A pan evaporation rate and the average annual
precipitation. The evaporation potential is a very strong function of
regional climate and site exposure to wind and sun. Two extremes within the
continental U.S. are the Pacific Northwest Coast and the Sonora Desert as
shown in Table 4-1.° Similar calculations can be made for most locations in
the U.S., but local knowledge and/or data are required to adapt regional data
to specific sites since annual precipitation and sunshine days can vary widely
between areas only short distances apart.
It must be remembered that the evaporation potential is the maximum
evaporation that can be obtained from a liquid surface under ideal
conditions. It can be used to determine if solar evaporation is a significant
mechanism, but it is not the rate at which moist solids will dry. The drying
rate is controlled by the rate of moisture migration to the surface of the
sediment particles by diffusion from within the particles and capillary
i
Table 4-1. Evaporation Potential Variations^
Annual condition (inches of water)
Region
Class A Average Evaporation
pan evaporation precipitation potential
Pacific Northwest 30 100 -70
Coast
Sonora Desert 140 5 136
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tension from below the sediment surface layer. Therefore, only a function of
the Class A pan evaporation rate can be expected at an SI site.
The second passive dewatering mechanism is draining of water from the
voids between sediment particles. This mechanism is only significant if the
sediment is free-draining and there is a means of removing the drainage water
from the interface between the sediment and liner.
Both passive dewatering mechanisms can be significantly enhanced by
various forms of physical assistance. Evaporation can be significantly
accelerated by keeping the sediment layer thin and the waste solid surfaces at
maximum moisture content. This can be done by dividing the impoundment into
three areas: (1) sediment storage, (2) sediment drying, and (3) draining
water sump. Using this technique, the sediment is bulldozed or otherwise
transported to the storage area where it is stockpiled to a considerable
depth. The stockpile area should be drained to a sump so that the maximum
free drainage can be realized as a result of the depth of the sediment
stockpile. Sediment from the top of the stockpile should be placed in the
drying area in thin layers. When dry, the sediment can be either stockpiled
in a separate storage area or covered with another layer of sediment.
If the impoundment is too small in surface area to allow an in situ
drying program, sediment drying beds can be constructed outside the
impoundment. However, containment of all sediment drying operations within
the impoundment itself is highly recommended to minimize surface contamination
via spillage and wind drift.
If thin sediment layers cannot be provided, an alternative is to disk or
otherwise plow the sediment to break up the surface crust, turn under dried
material, and expose moist solids. This is not practical with a synthetic
film liner.
The evaporation of water requires a net heat input to the sediment.
Generally, solar radiation is the only cost-effective source of thermal
energy. Modifications of the adsorptivity of the sediment by addition of
carbon black is possible but has to be tested. Crushed coral and sawdust have
been used for restricted moisture adsorption. Protection of the sediment from
incident precipitation is desirable in areas where precipitation occurs on a
year-round basis and the evaporation potential is not high. Plastic films are
expedient for small surface areas but disposal of the contaminated plastic
film may be a serious problem.
4.3.2 Ac t i v e Dewater i ng
To implement either a mechanical dewatering or thermal drying operation,
it is necessary to remove the sediment from the impoundment or at least
stockpile the sediment in a diked storage area to clear a processing area
within the impoundment itself. The latter alternative is preferred to prevent
surface contamination around the impoundment.
Mechanical dewatering processes will produce a nonflowable filter cake
suitable for landfill disposal within the impoundment or at some other
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hazardous waste disposal site. The filter press is the most effective unit.
The filtrate may be disposed of in the same manner as the aqueous phase that
was removed when the impoundment was dewatered. However, the filtrate may be
of higher strength than the impoundment water and require special handling.
It also may be further contaminated by solids conditioning chemicals or oils
that do not completely remain with the solid fraction.
It must be remembered that not all sediment sludges can be filtered to
the extent necessary to produce a nonflowable solid. Chemical conditioners or
polymers may have to be added to the sediment sludge to obtain the desired
results. Uniform filter performance is unlikely if the impoundment was used
for the disposal of more than one waste since sediment properties and physical
characteristics will not be uniform.
Thermal drying has advantages; no filtrate is produced, and all of the
contaminants are converted to dry solids. However, there is a very high
probability that thermal drying will create a significant air emissions
problem. It is also energy intensive. Unless the sludge volumes are very
large, onsite thermal drying will not be cost effective if at all feasible.
The thermal stability of the sediments is the key to technical feasibility. A
reactive or easily decomposed material may produce a toxic or otherwise
hazardous gas.
4.4 LINER REMOVAL/REPAIR
Post-closure use of impoundment liners, whether of clay or artificial
material, is an integral part of site closure. The necessity of repair or
possibility of removal are dependent on waste disposal site, liner condition,
and site-specific factors.
4.4.1 Reason for Removal
The liner can be removed only if the waste sediments are removed for
offsite disposal, in which case the site can be backfilled and returned to any
suitable use. Removal of the liner is recommended under these conditions to
avoid creation of an artificial subsurface water reservoir that could affect
the surface load bearing capability of the soil.
If significant contamination of subsurface soils has occurred, an
argument can be made for leaving the liner in place to minimize leaching of
the contaminated strata by percolation of surface water that might eventually
reach the ground water system or surface water system. In the general case,
significant soil contamination would not be the rule with lined impoundments
unless the reason for closure was massive failure of the liner. Thus for the
case of permitted impoundments that will have residual sediments moved to
offsite disposal, liner removal is recommended.
4.4.2 Liner Removal Methods
Clay or other impermeable soil liners can be removed entirely by normal
excavation methods. Liner removal should follow and be separate from sediment
removal to minimize contamination of the underlying soils. If the clay or
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soil liner is relatively thick and it is possible to excavate only a few
inches off the surface of the liner, the remaining liner material could be
broken up and mixed with the underlying soil and/or backfill material to
minimize transport and offsite disposal.
Liners made of synthetic materials such as Hypalon, PVC, etc., should be
taken up in much the same manner as they were installed. Convenience of
handling and disposal should control the width of the individual sections.
Hard surface liners such as gunnite or concrete should be broken up by
normal mechanical means and, depending upon forecast post-closure use, either
removed or left in place in a rubble form.
4.4.3 Reason for Liner Repair
In the event that waste sediments are to be left in situ and the site
closed as a landfill, the physical condition of the liner is a significant
concern. The choice between liner repair or liner replacement depends on the
age and condition of the liner material, estimated service life of the liner
in contact with the waste sediment, the physical and chemical characteristics
of the sediment, and the probability of success of the water balance controls
(i.e., cover impermeability, ground water diversion, etc.).
In general, liners made of clay or impermeable soils are suitable for
buried service as long as ground fractures due to seismic activity are not a
problem. Synthetic liners provide flexibility for limited ground movement but
have unknown long-term service lives in a buried environment. Hard surface
liners such as gypsum or concrete may have problems due to ground movement or
excessive overburden stress.
4.4.4 Liner Repair Methods
Clay or soil liners are easily repaired but must be considered
contaminated and may pose health and safety hazards for workers. Synthetic
and hard surface liners may be washed clean prior to repair but repairs are
more difficult to effect. The strength and seal of repairs to hard surface
liners will always be questionable. Liner construction and repair methods are
described in references 1 and 2.
4.5 SOIL CONTAMINATION TESTING
In the event that contamination of the subsurface soils is suspected, a
field sampling program will be necessary to confirm the type and extent of
soil and ground water pollution. Fortunately, the same sampling and analysis
program will also provide supplemental data on soil strata by type and depth
and local data on ground water conditions.
If soil contamination is confined to local areas near liner failures,
soil excavation and offsite disposal may be feasible, cost effective, and
desirable. If soil contamination is general throughout the site and/or
extends offsite via a ground water plume, extensive water balance control
measures, as described in Section 4.8, may be necessary.
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4.5.1 Surface Soils
Contamination of surface soils surrounding the impoundment is a function
of past operating practices. Overfilling leads to wind driven waves
overflowing the edges of the impoundment. Spillage from waste discharge
operations, truck transport, sediment removal, etc., are all sources of
surface contamination in the general vicinity of the impoundment. Discolored
soils, lack of vegetation, dead vegetation, and discolored rainwater runoff
are all clues to surface and near surface contamination. Random samples of
surface soils (top 3 to 6 inches) should be taken in areas of suspected
contamination and analyzed for probable contaminant species.3 (See also
Section 4.5.6.)
4.5.2 Soils Adjacent to Impoundment
The soils that underlie the impoundment and line and form the dikes
generally will contain some small amount of contamination. The impoundment
that has never had a liner failure of any type is rare. Impoundments that
have a liner constructed of a low permeability soil or of a clay will, if the
impoundment is old enough, show some trace of contamination as a result of
slow seepage.
If the residual sediments are to be taken offsite for disposal and the
liner removed, random samples of the underlying soils should be taken and
analyzed for probable contaminant species. If the liner is to be left onsite
but not intact, the liner should be inspected for possible failure areas,
portions removed, and the underlying soils sampled. Dikes can be cored and
the samples analyzed.
4.5.3 Soils Remote from Impoundment
If a major failure of the liner occurs, large quantities of contaminated
water may infiltrate the underlying soils, reach a ground water aquifer, and
be transported away from the impoundment or at least away from the point of
liner failure. The areal extent of this large-scale contamination of
subsurface soils will be controlled by the rate of water transport and the
absorptive capacity of the soils for each of the contaminants.
If properly located, ground water monitoring wells will allow for the
detection of this contamination and these data may well be the reason for site
closure. However, definition of the areal extent, and depth and thickness of
the plume of contaminated ground water and soil generally require a relatively
detailed geohydrological field study.
If the contamination has significantly changed the electrical
conductivity of the contaminated ground water and soils, a surface resistivity
study provides a rapid and cost-effective semiquantitative determination of
the areal extent of the contaminant plume. Depth of contamination is less
precisely determined. The results of the surface resistivity study can be
used to plan the most cost-effective drilling and sampling program. Such a
program is essential to completely define the impacted areas, the type of
contamination, the concentrations, and the Teachability of the impacted soils.
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4.5.4 Drill ing and Sampling Programs
The objective of the geohydrological study is to identify the following
parameters:
• Extent of soil contamination
t Extent of ground water contamination
• Potential for contaminant migration
t Location of local ground water and surface water flows relative to
contaminant plume
A geotechnical consultant with prior experience in subsurface pollution
control should plan and direct the study. A key to identification of
contamination is to obtain background or reference samples of local soils and
ground waters known to be free from contamination. Soil and ground water
samples must be collected and stored to minimize contamination and physical
and chemical degradation of the samples.4"7
4.5.5 Ground Water Analysis
Water analyses can be divided into two types, screening and qualitative
identification. Certain basic parameters are indicative of contamination
without identifying the type and concentration of specific contaminants.
These parameters must be measured in uncontaminated samples and compared to
the results for suspected samples. Some of these parameters include:
t TOC ~ Indicator of organic chemicals
• Conductivity -- Indicator of soluble ions
t pH — Indicator of acidic or basic waters
• COD — Indicator of chemically oxidizable organic and inorganic
materials
• Oil and grease — Indicator of petroleum oils
Other indicators of groups and classes of contaminants exist but must be
detected by a component chemist on a case-by-case basis.
The standard methods of analytical chemistry are available for identifying
specific contaminant classes on a qualitative and quantitative basis.
Analytical procedures for quantitative determinations of specific organic and
inorganic materials is a rapidly evolving state of the art.8-10 Analytical
determinations are generally expensive, thus, the utility of such data and the
impact of the result on the decision making process must be carefully
considered during design of the sampling and analysis program.4^'>12
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4.5.6 Soil Analysis
There are three types of analyses of interest in soil characterization:
(1) soil properties, (2) leachable soil contaminants, and (3) exchangeable
soil contaminants. Soil property analyses should be performed only in the
event that geohydrological estimates of lateral and vertical migration of
contaminated water are necessary. Types of analyses, methods, etc. are
discussed in references 13, 14, and 15. Generally, the major variables such
as pH, cation exchange capacity, organic matter content, and permeability are
considered in this group of analyses.
Leachable soil contaminants analyses identify the types and amounts of
contaminants that can be released to uncontaminated ground water from the
soils. Types, methods, and interpretation are discussed in section 3.1.
Basically, extraction (or leaching) methodology is designed to determine the
potential mobility of specific compounds identified early in the investigation.
Exchangeable soil contaminants analyses identify the types and amounts of
contaminants that can be stored and/or released by soils via ion exchange
interactions with ions in ground water. Types, methods, and interpretation
are discussed in references 16 through 19. These analyses assist in detailing
the chemistry of specific solutes in the existing soil environment.
4.5.7 Interpretation of Results
The identification of one or more contaminants in either soil or ground
water is not conclusive evidence of a significant pollution problem. Results
of sampling and analysis programs must be interpreted from the geohydrological
point of view in terms of contaminant mobility, ultimate fate, long-term
soil-water interactions, etc. It is important, however, that the general
chemistry of the soil environment and of the contaminants in question be known
so that general conclusions regarding potential mobility can be made.
Given the rapidly developing state of the art in sampling and analyses
combined with the complexity of geohydrology, absolute conclusions are
difficult to prove. All results must be viewed from a soil-water systems
perspective.
4.6 DIKE STABILITY
Dikes are used as part of SI structures that are partially or completely
aboveground. A decision to close a diked impoundment as a landfill containing
water sediments is dependent upon an analysis of the structural integrity of
the dikes and the dike-soil system. Of particular interest is the ability of
the dike to withstand the loads imposed by the backfill and cover material,
particularly under conditions of water saturation of the backfill, cover, and
dikes.
Evaluation and surveillance of dike stability is necessary to avoid
environmental, property, and human damage due to failure of the impounding
structure. Elements to be considered in the evaluation of dike stability
include foundation conditions, embankment materials, liner type, and waste
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material, all of which are part of the dike system. The condition and
stability of the dike system is constantly changing. Long-term effects of
various external factors such as frost, wind, rain, and temperature as well as
man, animals, and vegetation should also be considered. Therefore, periodic
inspection and reevaluation is required to assure stability of the dike system
in the future.
Several phases are involved in the evaluation of dike stability. The
initial phase is a compilation and review of available geotechnical and
construction data. This is followed by a field reconnaisance of the site to
examine present conditions. Depending upon the results of these phases,
additional technical investigations may be necessary. An evaluation of the
stability of the dike system is then made from the compiled data. If the dike
is considered to be unstable, then recommendations should be made to either
repair or remove the structure. If the dike is considered to be stable, a
plan for future surveillance and monitoring should be recommended.
The following sections discuss more detailed guidelines for evaluating
the stability of the dike system. Rigid guidelines and standards cannot be
established for every conceivable site condition. The analysis of dike
stability must be site-specific and will require not only a systematic
technical approach but also considerable judgement by experienced engineers.
4.6.1 Inventory of Historical Information
The initial phase in investigating the stability of the dike system is an
inventory and compilation of all existing information. The purpose of the
inventory is to review what is known and to identify what is unknown about
factors that affect the stability of the dike system.
A location plan (i.e., USGS quadrangle sheet) should be obtained showing
the impoundment facility with respect to existing physical and topographical
features. Also, a failure impact zone can be shown on the location plan based
on an assumed failure of the dike. Next, an accurate site map needs to be
obtained (preferably 1 inch = 40-foot scale -- 2-foot contour interval)
showing specific site conditions including utilities, structures, wells,
geotechnical instrumentation, borings, test pits, bedrock outcrops, springs,
trees, and topographic features.
The as-built construction plans and specifications for the impoundment
facility can also be assembled together with all photographs, inspection
reports, and construction records. Quality control measurements such as
compaction tests, in-place density tests, moisture contents, grain size
analyses and soil test data should be compiled. In addition, all geotechnical
information such as geotechnical reports, logs of test borings and test pits,
soil test results, surficial and bedrock maps, aerial photographs, seismic
surveys, results of instrumentation, and related information should be
evaluated.
Based on the accumulated information, typical and critical cross sections
of the dike system can be developed showing soil and bedrock units, ground
water levels, and other geotechnical and construction information. Test
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results on the foundation soils and embankment materials should be catalogued
and cross-referenced to the soil profiles.
4.6.2 Reconnaissance Investigations
The reconnaissance investigation phase consists of a detailed site
inspection by a team of personnel experienced in the fields of engineering
geology, soils engineering, structural engineering, and dike design and
construction. The purpose of the field reconnaisance is to examine actual
conditions at the site, verify the existing data, and identify any signs of
dike instability.
A detailed visual inspection should be conducted preferably during times
when vegetation is minimal and snow cover is gone. The inspection will
identify features that indicate potential instability of the dike such as
seepage, settlement, cracking, bulging, sinkholes, surface erosion, growth of
vegetation, slumping or undercutting of the toe, and animal burrows. Typical
inspection checklists are shown in references 20 and 21. Photographs of all
pertinent features should be taken. The field inspection should also include
survey measurements to verify site and topographic data shown on the site
plan. Monitoring of all geotechnical instrumentation can also be completed
during the inspection. Areas of seepage and leakage should be carefully
examined, the flowrates recorded, and samples of the effluent obtained.
4.6.3 Geotechnical Investigations
Subsequent to the inventory and reconnaissance phases, the compiled data
can then be reviewed to determine whether additional geotechnical
investigations are needed to evaluate the stability of the dike system.
Further subsurface investigations may be necessary to determine types of
foundation and embankment materials, obtain soil and rock samples for
laboratory testing, install geotechnical instrumentation such as ground water
observation wells and piezometers, conduct in situ testing, and perform
laboratory tests. The scope of the investigation is dependent on the extent
of the available information, the size of the impoundment facility, and the
nature and variability of the subsurface conditions. All field and laboratory
investigations should be conducted under the supervision of registered
professional engineers.
Geophysical methods can be used to determine general subsurface
conditions and to determine optimum locations for further exploration.
Typical geophysical surveys include seismic refraction, cross-hole seismic
surveys, electrical resistivity, gravity, and acoustic monitoring. Direct
methods of subsurface exploration include soil and rock borings, auger
borings, probes, and test pits. Soil test borings in conjunction with
standard penetration tests (ASTM-D-1586) and undisturbed soil samples are the
most common procedures for determining subsurface conditions. Classification
of soil samples should be in accordance with the Unified Soil Classification
System. The spacing, depth, and sampling interval is dictated by the nature
and variability of geologic conditions.
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A profile of the ground water levels within and at the toe of the
embankment is necessary for stability analyses. Ground water observation
wells and/or piezometers should be installed and measured not only during the
exploration phase but also indefinitely thereafter. The elevation of the
observation wells and piezometers will depend on subsurface conditions,
present and future ground water levels, and the number of aquifers within
depths significant to the facility.
In situ field testing such as vane shear tests, cone penetrometor tests,
pressuremeter tests, and permeability or pumping tests may be used to further
define specific characteristics of the foundation or embankment materials.
Laboratory testing to determine engineering parameters of soil samples is
carried out for two purposes:
• Classification of the soil to identify the type and homogeneity of
the various earth materials making up the impounding structure. For
instance, these tests would determine whether the impoundment is made
of one uniform material or is a zoned embankment composed of two or
more different materials.
• Quantitative tests of the various soil types for their engineering
parameters. In this case, test results are used in the stability
analyses. These tests may include compaction tests, consolidation
tests, unconfined compression tests, direct shear tests, triaxial
tests, and cyclic-triaxial tests. For example, cyclic-triaxial tests
would be conducted to consider the effects of earthquakes on dike
stability.
Special soil tests are conducted to help analyze particular soil problems,
for example, to identify highly erodible soils known as dispersive clays."
These soils have a higher content of dissolved sodium in the pore water than
ordinary soils and erode when individual clay particles go into suspension in
practically still water. Severe erosion and failure of the embankment slope
may occur if saturation of those soils occurs because of leakage from the
impoundment facility.
4.6.4 Engineering Criteria
The analysis of stability for the dike system is dependent on numerous
variables and assumptions regarding stratification of soil and rock units,
physical properties of soil and rock materials, ground water elevations, and
predictions of external environmental factors. Accordingly, considerable
engineering judgement is required in selecting one of the methods of analysis
and factors of safety in the determiniation of dike stability.
Instability of the dike system occurs when a section of the dike mass
moves laterally by sliding or by rotation along a circular arc or curved
plane. Conventional methods of analysis are outlined in detail in
references 23, 24, and 25. The circular arc procedure is generally used for
analyzing homegeneous earth dikes founded on deposits of fine-grain material.
The sliding block or wedge method is more applicable to stratified deposits of
weak soils or inclined zones within the. dike section.
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Instability of the dike system can also be defined as deformation of the
embankment to such an extent that material seeps from the impoundment. This
may be due to failure of the lining or fracturing of the embankment
materials. Accordingly, the ability of the dike and the liner to yield
significantly without functional failure must be considered. Shear strains
and deformation of the embankment and foundation soils may develop as a result
of settlements caused by loadings due to closure fills and/or future
construction.
The analysis of the loading conditions for the dike system must include
not only present conditions, but predictions on future loading, ground water
elevations, and seepage conditions. The effect of these future conditions
must also be reflected in the selection of the shear strength parameters for
the soil and rock materials. Recommended minimum factors of safety and
corresponding shear strength tests relative to various design conditions are
given in reference 23. The final factor of safety to be selected by the
engineer should be based on completeness and uniformity of available data,
assumptions and predictions regarding future events and loading conditions,
and consequences of a failure relative to the environment, property damage,
and loss of life.
Seepage pressures as a result of present and future ground water levels
in the dike system should be analyzed to determine their effect on slope
stability and the potential for piping failures. Information from observation
wells and piezometers should be used to evaluate existing conditions.
Predictions on future ground water elevations should reflect the most severe
seepage conditions likely after closure of the impoundment.
Saturation of the downstream toe or slope may occur as a result of
inundation caused by flooding or overflow of nearby drainage facilities.
Instability due to saturation and/or sudden drawdown or receding of flood
levels must be examined. In addition, erosion and loss of toe support may
occur.
Seismic loading due to earthquakes must be included for all impoundment
facilities located in zones 1, 2, 3, and 4 as shown in Figures 1, 3, and 4 in
Appendix D of reference 20. The extent and type of the analysis will depend
on the foundation and embankment soils, location of the facility, and the
consequences of failure. Liquefaction of the foundation anch embankment soils
should be considered when these soils consist of loose to medium density fine
sands and silts below the ground water table. A procedure for evaluating the
potential for liquefaction is outlined in reference 26.
Certain types of soil, rock, or design conditions related to dike system
stability that may require special attention are: Sensitive clays, limestone
regions, mined out areas, hydraulic fracturing within the dikes, effect of
high temperatures on shear strength of foundation and embankment soils,
expansive clays or shales, collapsible soils such as loess, regional
settlement, dispersive or highly erodible soils, shrinkage cracks, and
formation of ice lenses.
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4.6.5 Continued Surveillance
The stability of the dike system is not a static condition. Future
loading conditions or environmental events may result in instability or
excessive deformation. It is essential that a continuing program of
maintenance and technical inspections be implemented immediately after closure
of the impoundment. Inspections shall be conducted on an annual basis.
Guidelines for periodic inspections are similar to those outlined for
reconnaissance investigations. The engineer responsible for the geotechnical
investigation and engineering evaluation should determine the inspection
program. During the inspections, the geotechnical instrumentation shall be
monitored and subsequently evaluated by the engineer.
All maintenance and repair work as recommended by the inspection team
shall be implemented immediately thereafter. Particular attention shall be
given to the elimination of growth of vegetation and trees on the dike and
burrowing animals in the area.
4.7 CONSOLIDATION AND STABILIZATION OF WASTES
A decision to use the impoundment for in situ disposal of the waste
sediments will require evaluation of the consolidation potential of the
sediments. The objective of this evaluation is to maximize consolidation
during the closure process so as to minimize any post-closure consolidation.
A decision to leave the sediments in the impoundment requires that the
sediments be dewatered to a nonflowable consistency and that the impoundment
be closed as a landfill. Consideration of sediment consolidation during the
closure process is necessarily closely coupled to the dewatering of the
sediment, and Section 4.3 should be reviewed prior to reading of this
section. This section will consider both consolidation of flowable sludges,
slurries, and solids during the closure process, and nonflowable solids during
the post-closure period. This section does not consider the consolidation of
either the base soils underlying the impoundment or consolidation of the
rockfill and cover material.
The consolidation problems anticipated during closure of an impoundment
will be highly specific to impoundment geometry, sediment depth, and the
physical and chemical properties of the sediment. These difficulties may be
compounded by the fact that more than one type of sediment may be present in
the impoundment. The problem of heterogeneous sediments can be handled by
area segregation within the impoundment or by sediment homogenization.
For discussion purposes, waste sediments will be classified in terms of
the consistency and bulk handling definitions of Table 4-2.
4.7.1 Consolidation During the Dewatering Process
The reduction of the water content of the sediment that will convert a
flowable sediment to a nonflowable solid will simultaneously implement primary
consolidation and, to a lesser extent, both secondary and tertiary
consolidation. The extent to which consolidation occurs will depend on the
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sediment properties and the residual moisture content after dewatering.
Indeed, the consolidation potential of the sediment as a function of moisture
content may be as critical to selection of a target residual moisture content
as the requirement to produce a nonflowable solid. Methods for such
determinations are discussed later in this section.
Primary Consolidation
It is expected that conversion of the sediment to a nonflowable solid
state will effectively eliminate any potential for the occurrence of primary
consolidation after closure. However, there are exceptions to every rule, and
definition of nonflowable solid is not rigorous. Sediments exhibiting
nonNewtonian properties (plasticity, thixotropy, etc.) may tend to entrap
water under extreme dewatering pressures and release water at conditions of
lower stress. Careful examination of the sediment behavior during exploratory
testing of dewatering alternatives is necessary to handle specific problems.
Secondary Consolidation
If the sediments are evaporated to dryness, any potential for secondary
consolidation should be eliminated. If evaporation to dryness is not feasible
or cost effective, or creates other problems such as a low density, fluffy
Table 4-2. Hazardous Waste Consistency Classifications
Consistency
category
Characteristics
1. Liquid waste
2. Pumpable waste
3. Flowable waste
4. Nonflowable
waste
<1% suspended solids,3 pumpable liquid,
generally too dilute for sludge dewatering
operation.
<10% suspended solids,a pumpable liquid,
generally suitable for sludge dewatering.
<10% suspended solids,3 not pumpable, will flow
or release free liquid, will not support heavy
equipment, may support high flotation
equipment, will undergo extensive primary
consolidation.
Solid characteristics, will not flow or release
free liquids, will support heavy equipment, may
be 100% saturated, may undergo primary and
secondary consolidation.
Suspended solids ranges are approximate.
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solid that must be moisturized and compacted in place to eliminate sediment
porosity (permeability), then the potential for volume reduction of solids
under expected overburden stress loads should be determined.
Tertiary Consolidation
The potential for reduction of solid mass by dissolution, biological
oxidation, and chemical reaction is unique to the sediment and the expected
environment in the closed impoundment. The ability to predict tertiary
consolidation will depend upon the degree of understanding of the chemical
composition of the sediments. Impoundments used for disposal of a limited
number of wastes, such as those in single product class industrial plants (oil
refineries, fertilizer plants, etc.), are more amenable to such analysis than
large, general use impoundments at commercial hazardous waste disposal sites.
4.7.2 Determination of Consolidation Potential
Primary and Secondary Consolidation
The consolidation behavior of a sediment during in situ dewatering by
drainage can be determined via a routine consolidation test (ASTM-D-2435).
Both the final consolidated volume and the rate of consolidation can be
determined. It is important to remember that the scaleup of test results to
full-scale operations is dependent on the ability to duplicate test conditions
in the field. In situ consolidation of deep sediment deposits will be
controlled by factors not measured in the simple consolidation test.
The consolidation behavior of a dewatered sediment experiencing secondary
consolidation under an applied overburden stress can also be estimated from
ASTM-D-2435 by beginning the test with a sample dried to the same moisture
content as proposed for the sediment. To estimate the consolidation behavior
of a compacted sediment, the sample should be compacted in the test column
before beginning the test.
Tertiary Consolidation
A number of independent mechanisms can contribute to tertiary
consolidation. Laboratory tests indicating biological activity and chemical
reactions leading to consolidation are discussed in the following paragraphs.
These tests will indicate maximum effects but not the rate at which they may
take place. The rates of tertiary consolidation are controlled by the
environment within the sealed impoundment. These environmental conditions
cannot be duplicated satisfactorily within the laboratory.
Biological
Biological activity is not a direct consolidation mechanism. However,
biological oxidation of organics can reduce the total mass of solids by
conversion to liquid and gaseous end products. Consolidation of the remaining
solids can then occur through conventional physical mechanisms.
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The total organic content of waste sediments can be measured by the TOC
test. However, this test measures all organics whether biodegradable or not.
Nevertheless, the TOC value can be used to estimate the maximum potential for
biological consolidation assuming that all the organics are biodegradable.
The ultimate biochemical oxygen demand (BOD) test can also be used to indicate
the maximum potential for biological consolidation.
A biological consolidation estimate can be calculated by assuming that
1 pound of organic matter will be destroyed for each 2 pounds of oxygen
consumed in the BOD test. An assumption regarding the density of the
consolidated waste must also be made. An assumption of no density change with
biological consolidation is not unreasonable. It must be emphasized that this
estimate is probably a maximum value.
Anaerobic conditions exist in many if not most post-closure Si's. The
potential for the reduction of the mass of organic matter through anaerobic
decomposition is about the same as aerobic decomposition. The potential for
generation of noxious odors, flammable gas, and toxic gas is associated with
anaerobic decomposition. The rate of anaerobic decomposition is perhaps more
sensitive to environmental factors than that of aerobic decomposition. The
nutrient balance, the presence of toxic compounds, pH, temperature, and
moisture content are some of the factors that can greatly reduce or stop the
rate of reaction.
Chemical
The only type of chemical consolidation considered here is chemical
conversion of a portion of the waste solids to a dissolved or gaseous product
followed by removal with the leachate or release to the atmosphere.
Additional chemical consolidation may occur by dissolving solids at one
location and reprecipitating them in voids between solid particles. This
mechanism is not expected to account for a significant amount of
consolidation, however. Testing of the chemical leaching of the waste can
indicate the potential for aqueous dissolution of the waste. Test methods are
outlined in Section 3.1.
4.7.3 Stabilization of Waste
A number of techniques have been developed for the stabilization of
wastes through solidification or encapsulation. The goal of these 'techniques
is to produce a solid, chemically nonreactive material. Some hazardous wastes
can be stabilized by these techniques.
Stabilization Technology
Seven major categories of industrial waste stabilization technology were
identified in one study.27 Six of these categories are based on the addition
of an agent for solidification or encapsulation. These techniques can produce
varying degrees of stabilization, but the volume of waste is increased from 5
to 100 percent. The major categories of waste stabilization are:
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• Portland cement-based processes
• Pozzolanic processes
• Thermoplastic techniques (including bitumen, paraffin, and
polyethylene incorporation)
• Organic polymer techniques
• Surface encapsulation techniques
• Self-cementing techniques
• Classification and production of synthetic minerals
Engineering Properties of Stabilized Waste
The available data on the engineering properties of stabilized hazardous
waste indicate a wide variation in properties depending upon waste type and
stabilization process. One study compared the engineering properties of raw
sludge to chemically fixed sludge for five different hazardous waste
sludges.28 One or more of seven different fixation processes were used to
fix the sludge.
Chemical fixation is the conversion of a nonsolid waste to a solid form.
Fixation is distinguished from stabilization in that stabilization produces a
chemically nonreactive waste in addition to one which is in a solid form.
Several chemical fixation processes are susceptible to leaching although they
may produce a solidified waste high in compressive strength.
Unconfined compressive strength test data indicate that the behavior of
fixed sludges in compression is highly process and material dependent. The
compressive strengths of sludges fixed by one process were comparable to those
of cohesive or cemented soils. Sludges fixed by other processes exhibited
compressive strengths resembling low strength soil-cement mixtures. The
highest compressive strengths, comparable to low strength concretes, were
obtained from four of the fixation processes. Compressive strengths ranged
from 0 to 4,500 psi for all tests.28
Fixed sludges were generally too hard to be compacted by conventional
methods. The 15-blow compaction test (ASTM-D-698) showed very little increase
in density with any fixed sludge including those of lowest compressive
strength. Results of this test suggest that multiple passes of heavy
compaction equipment will be required to achieve any significant increase in
density. Moderate compaction may produce a more homogeneous mass of fixed
sludge by reducing void space and honeycombing, but the density will not be
increased significantly.
The consolidation of fixed sludge is expected to be inversely proportional
to the compressive strength. Sludges fixed by most processes are considerably
stronger than most soils, and the settlement of the post-closure impoundment
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would be expected to be because of consolidation of compressive foundation
soils.
4.8 CONTROL OF THE WATER BALANCE
In the event that the residual sediments and any other contaminated
solids are removed to offsite disposal, closure as a landfill is not
required. For this case, water balance controls are generally not required as
pollution control measures. In some cases, runoff controls may be justified
for erosion control.
If any water soluble contaminants are left onsite or, more specifically,
in situ, water balance controls of some type are generally necessary. These
controls function to prevent the generation and migration of leachate as a
point or nonpoint source into ground water and/or adjacent surface water
supplies. Such controls are of two types:
• Water exclusion measures designed to minimize the infiltration of
water to the wastes
t Water collection measures designed to minimize the escape of leachate
to ground water and/or surface water
It is preferable to concentrate on water exclusion measures to prevent the
production of leachate. The incentives are twofold; collection systems
typically result in some leakage, therefore, an adverse environmental impact
may result. In addition, if leachate is generated and collected, it must
somehow be treated and/or disposed in an environmentally safe manner.
Treatment of leachate will generally be less cost effective than implementing
procedures to prevent its formation.
4.8.1 Need for Control
A systemwide appraisal of all environmental and geohydrological features
is required to identify the need for controls and the types of controls that
will be most cost effective. If the impoundment has been permitted and all
permitting requirements were fulfilled, a geotechnical and hydrological data
base adequate for evaluating the need for water balance controls should
exist. If this data base is inadequate, some additional field study may be
necessary to supplement existing data. This data base should include
information about the surface and ground water hydrology, site
characteristics, impoundment capacity, and dike characteristics.
Surface Water Hydrology
Factors affecting the occurrence and movement of surface water need to be
characterized. Existing data and field investigations should be used to
establish the following elements critical to water balance control measures:
• Drainage area
• Topography
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t Climatology ~ precipitation, temperature, evaporation
• Land use
t Runoff coefficient
• Stream geology — fluctuation, history, transport of suspended
materials, erosion rate
t Surface water quality
• Effect of SI on drainage area (quantity and quality)
Ground Water Hydrology
Factors affecting the occurrence and movement of ground water also need
to be characterized. Existing data and field investigations are used to
establish the following parameters needed for an understanding of the water
balance:
• Water table depth and seasonal fluctuations
t Thickness of aquifer(s)
• Ground water flow direction and rate
t Proximity of water supplies -- public and private
• Ground water quality — baseline data
• Infiltration rate -- recharge
• Ground water discharge area
• Effects of SI on ground water flow and quality — presence and
location of potential leachate plume
Site Factors
Specific site factors that affect the occurrence and movement of ground
and surface water need to be established. Existing data and field
investigations are used to study the following site factors as they relate to
the water balance:
• Site drainage
• Site soils
— Vertical and areal distribution
-- Permeability
— Attenuation capacity
— Extractable contaminants (Teachability)
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• Land use (site vicinity)
t Public safety and health hazards
• Relation of SI to drainage
Impoundment Capacity
Impoundment capacity must be known to estimate the retentive capacity of
the backfilled impoundment for infiltrating surface water. This allows
calculation of overburden stress on dikes and consolidating sediments and
estimation of the driving force for leachate migration from the impoundment.
Dike Stability
Water saturation of dikes or high ground water conditions under dikes are
two vital factors impacted by water balance controls. Dike stability may be a
major incentive for water table and runoff controls.
4.8.2 Surface Water Controls
The primary control measure for excluding water from most impoundments is
elimination or minimization of infiltration of surface water. This can be
done by a wide range of measures such as:
• Runoff diversion — Overland flow of runoff over the impoundment
cover must be minimized by diversion. This is the first line of
defense. The less water reaching the cover means the lower the
infiltration potential. In addition to drainage ditches and open
channels, structures such as berms, check dams, sedimentation ponds,
energy dissipators and dikes can be used to control runoff.
• Surface grading -- The cover itself should be constructed with
adequate slopes. This will assure maximum lateral surface runoff and
helps to minimize infiltration, which directly affects subsequent
enhancement for leachate generation.
• Cover construction ~ The cover should be constructed to minimize
infiltration
t Revegetation — Vegetation provides erosion control, and the root
system provides a consumptive use for infiltrated water
The importance of surface water controls cannot be overemphasized. Even if
the in-place residual sediments are covered by a clay seal, saturation of the
backfill above the clay seal must be prevented to minimize hydrostatic stress
on the cover and dikes. References 29, 30, 31, 32, and 33 should be consulted
for engineering details on the previously mentioned surface water control
measures.
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4.8.3 Ground Water Controls
Where local geological and hydrological conditions require it, various
types of ground water controls can be implemented. The following controls
function to prevent the subsurface flow of ground water into the impounded
waste.
• Diversion — Groundwater can be directed around an impoundment site
by several means. The effectiveness of diversion is controlled by
local soils and the volume of ground water flow'. Diversion dams of
polymer membranes or sheeting can be effective but will require
construction of a high permeability diversion path to guide the
accumulated ground water around the site. Slurry-trench cutoff walls
or grout curtains can also be used to divert ground water away from a
waste site.
• Interception — Ground water can be intercepted either by wells or
collector underdrain systems. Wells require pumping and a discharge
point. Depending on regional topography, collector underdrains may
also require pumping. Any system depending on pumping has an
inherent failure potential and an annual maintenance cost.
• Underdrain systems ~ If the impoundment was constructed with a
leachate control system, this series of underdrains and/or pump sumps
may be suitable for modification to peak shave an occasional high
water table. Again, the system will be pump dependent and have a
finite failure potential.
4.8.4 Leachate Controls
The last line of defense is to install and maintain a leachate control
system. If the impoundment site was originally equipped with leachate
controls, retention of this system is required. Special conditions requiring
leachate controls to protect ground water quality include:
• Significant soil contamination in and around the site
• Presence of a liner of unknown integrity
• Presence of a stationary reservoir of leachate below the liner
resulting from earlier liner failure
• Proximity of usable ground water or surface water resources
The design of leachate control systems is discussed in references 31 and
34. Again, such systems may require pump maintenance and have the additional
disadvantage of leachate collection and disposal.
4.8.5 Monitoring
The effectiveness of water balance control measures can be documented by
ground water monitoring. The need for a monitoring program would depend on
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the method of site closure, type of wastes, presence of a leachate plume,
presence of contaminated surface waters, proximity of water supplies, and
regulatory requirements. A careful analysis of the site hydrogeology should
precede the design of a monitoring program. The degree and areal extent of
soil, ground water, and surface water contamination must be established before
an effective monitoring program can be implemented. Once such investigations
have been completed, a site-specific program should be designed.
Monitoring may be either active or passive. Active monitoring systems
might consist of one or a series of pumping wells. They are best suited for
control of point source contamination to ground water from spills, impoundment
overflows, or dike leaks. Conversely, monitoring of leachate is well suited
to passive systems. A passive system consists of wells that are not connected
to pumps or other monitoring devices strategically located with reference to
ground water flow. These wells are sampled at regular intervals to determine
changes in concentrations of indicator chemical constituents.
A leachate monitoring system should be designed with the following
considerations:
• Monitoring stations — Wells and surface water points should be
established in sufficient number to adequately monitor the movement
of acceptable contaminants from an SI to the point of attenuation
t Multilevel monitoring stations — To sample various depths where
thick aquifers or multiple aquifers need to be monitored
• Sampling methods — May include pumping by suction, compressed gas,
submersible pump, or by bailing. Sample containers and preservation
techniques must be compatible with analytical goals, especially when
trace concentrations of constituents are to be determined.
a Monitoring indicators — Should be selected to determine the presence
and severity of contamination. A water quality baseline should be
established by using existing water quality data and/or new data for
nearby uncontaminated wells.
• Frequency of sampling -- Must be determined on a site-specific basis
and depend on the nature of contaminants and their threat to human
health and other environmental considerations
t Length of time — For monitoring, the flushing out of contamination
would depend on ground water flow rates and aquifer coefficients.
Monitoring should continue until the baseline condition is approached
or until EPA drinking water standards are met.
References 4 and 35, as well as applicable federal, state or local regulations,
should be consulted for detailed procedures on ground water monitoring.
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4.9 AIR EMISSION CONTROL
During the operation and closure of Si's for hazardous material,
emissions of gases and particulate matter may be minimized or eliminated by
properly engineered operations. Detailed technical criteria for controlling
emissions are presented in the following subsections.
4.9.1 Organic Gas Emission Reduction Procedures
Section 3.7 presented considerations for closure plans for impoundment
sites that would minimize the emission of organic gases. This section
discusses the control mechanisms available for gas emissions.
Surface drying beds and infiltration lagoons constitute the largest
segment of Si's, and these units have been widely used for the economical
dewatering of slurries and sludges. The practice of impoundment sludge drying
has decreased for large publicly owned treatment works but continues for large
industrial plants, especially for process (nonwastewater treatment) sludges.
Uncontrollable factors such as rainfall, temperature, drainage rates, and gas
(odorous) emissions have caused a decrease in the practice. Dewatering of
nonreactive (neither biologically nor chemically) slurries is quite widespread
and is not a significant source of gas emissions. Volatilization of materials
is dependent on surface exposure and the characteristics of any cover the
vapors may have to pass through.
Recognizing that the closure of operating sites, both new and long-used,
may produce gas emissions as varied as the impoundment content constituents,
controls under the following list of conditions are described:
• Impoundment loading discontinuation and site consolidation
• Emission control during removal for offsite treatment
• Emission control during open in situ stabilization
• Emission control after site covering
Impoundment Load Discontinuation
Upon discontinuation of impoundment loading, gas emissions can be
affected by the dewatering (or aging) of impoundment contents by both surface
phenomenon and biochemical activity. The preclosure site survey should
inventory impounded waste contents and sample liquids or sludge contents,
bottom residue, and underlying soil. Although this survey will be conducted
primarily for hazardous waste components, it should include sufficient
analysis to determine potential fume or gas generation by direct vaporization,
sublimation, or biological degradation.
Mechanisms of explosive and toxic gas emissions from covered impoundments
are similar to landfill gas transport mechanisms. Conversely, the mechanism
by which directly exposed surfaces of impounded liquids and sludges emit
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vapors and gases depends on properties of the liquids and gases themselves,
not on properties of a cover or surrounding soil.
While impoundments remain open, liquid wastes will continue to emit
available organic compounds (benzene, chloroform, chlorinated ethylenes)
depending on vapor pressure and exposed surface exchange rate. Temperature
and wind (or other mixing sources) increases will accelerate emission rates.
Upon consolidation, sludges that have a decreased movement of compounds to the
exposed surfaces will exhibit reduced vaporization but increased sublimation.
Control of surface emissions can best be accomplished by temporary impoundment
covers. Aluminum, glass, and synthetic fiber materials have all been used for
impoundment control either to prevent the loss of heat, rainwater input, or
gas. Such covers frequently are equipped with vents or exhaust gas treatment <•
facilities. Both supported fixed covers and floating materials are
available. The latter type of covers include liquids, foams, absorbant beads,,
and thin synthetic extruded products. Costs for these controls as well as
their handling and disposal must be considered.
In a laboratory study of the volatilization of hexachlorobenzene, waste
covered with various layers of material had the following flux rates:
HCB vapor flux
Cover (kg/hectare/year)
None 317
1.9 cm topsoil 4.56 r
0.15 rnn polyethylene film 201
1.43 cm water 0.38
120 cm topsoil 0.066
(silty clay loam)
The flux rates through soil were not attained readily as the soil adsorbed a
considerable amount of HCB. For the 1.9 cm soil, the maximum asmytotic flux
rate was attained at 50 days, while the 120 cm soil cover would have required
several years to reach a stable flux.36 Comparison of flux values for the
no cover and 120 cm topsoil conditions indicate excellent control of emitted
HCB from the waste material. This excellent vapor control is improved further
by increased soil compaction. The relative flux rates given above are also
typical of other compounds. Thus, the comparative control is indicative of
efficiency for other compounds as well.
Bacterial activity and algae growth on organic sludges and liquid wastes
can continue to produce gases during stabilization. Biologically generated
gas emission rates will decrease upon sludge consolidation. Control of
emissions from impoundments during exposed stabilization can be effected by
stripping existing gases in liquids through mixing and pH change. Biological
and chemical production of gases can be limited by rapid dewatering (employing
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absorbants ~ soil, cement, crushed coral, or draining) or chemically fixing
the waste.
Emission Controls During Removal for Offsite Treatment
Control of air emissions during the removal of accumulated impoundment
material may be necessary. Reduced sulfurous gases from processing wastes or
organic material decomposition can be emitted at unacceptable levels during
liquid or semisolid material removal. Likewise, losses of solvents may be
excessive during these operations. The following emission containment systems
use commercially available equipment and materials:
t Pressurized liquid pumping withdrawal and disposal (gases remain
entrained)
• Solidification and removal (employing fixation or water sorbtion)
• Gas adsorption, containment, or biological transformation (using
chemicals or barriers)
• Gas or vapor purging and residue removal (purging under pressure or
unpressurized)
As described above, a preclosure site survey should provide an inventory
of impoundment conditions that would indicate the probability of gas
generation. Control is most frequently accomplished to ensure worker safety
or surrounding environmental aesthetics.
Open stabilization of contents may be the most feasible closure operation
for an impoundment except for safety and air considerations. A plan that
covers such an operation should document the characterization of the site
(primarily through content inventory and sampling survey) and identify
probable air emissions. Emissions abatement procedures identified in the
previous sections are applicable to in situ stabilization.
Emission Control After Site Closure and Covering
Several devices are used to control gas emissions after impoundment
covering. However, proper cover construction after waste stabilization is a
preferred control of such emissions. Consideration of gas generation and
control is an integral part of site rehabilitation and greatly influences
post-closure uses. The listing of incompatible waste groups (Federal
Register, Vol. 43, No. 243, December 18, 1978) is an initial source listing
possible gas generating reactions for various groups of impoundment materials
and consolidating materials. By adding content inventories and sampling
surveys, the impoundment content characterization should be complete and
provide the basis for determination of air emission control needs
Common gas control devices used in landfills consist of trenches, piping
vents, and barriers. Trenches may be cut continuously around the reclaimed
deposit and backfilled with gravel. Such a trench will vent gases produced
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within the deposit area. Surface areas must have a more impervious cover of
saturated clay, artificial cover liner, or similar material. Piping vents are
usually constructed similarly to trenches but are placed at intervals around a
deposit area. Frequently the pipes are pumped out if used on high organic
content landfill areas.
To exclude gas, movement barriers are constructed of compacted clay or
other impervious liner material. Often such liners are placed in trenches or
as barrier walls underground. These operate in a similar manner to covers
except that gas accumulations are not expected to cause ballooning and rupture
due to gas entrapment. Placement of saturated cover soils or artificial cover
liners are useful for closed impoundment sites as they are for landfills. A
rather thorough discussion of such barriers is given in references 1, 37, and
38. The major gas control function of impervious covers is to keep those
gases within the closed impoundment site below the surface. By keeping the
gases submerged, three mechanisms will dilute their environmental effect:
t Gases that diffuse laterally out beyond the surface cover will be
distributed across a wider area and physically diluted
• Gases entrapped will undergo readsorption and chemical degradation by
soil components and microorganisms
• Gases that encounter moving ground water will be moved to areas where
they are vented or acted on by soil organisms
Surface barriers can effectively control direct vaporization and
sublimation. Biologically or chemically generated gases diffuse up through
any more permeable vent in the cover barrier. Such unplanned venting can
occur through drying cracks in clay, breaks in the cover (poor seals or
ruptures in artifical liners), or discontinuities in the barrier, such as rock
outcroppings in clay, incomplete compaction on various layers or abandoned
well vents as described previously.
A special case of application of surface cover material to impoundments
occurs for material addition to liquid or sludge contents for enhanced
consolidation or dewatering. Although these practices (fixation, absorption,
or material addition) are effective consolidating techniques, they do not
necessarily eliminate gases. Consideration should be given for delayed
release of gases associated with liquid waste consolidation or possible
generation of flammable or toxic gases.
4.9.2 Fugitive Dust Abatement
As discussed in Section 3.7, fugitive dust emissions may be generated
during closure and post-closure use of Si's. These emissions are generated
primarily from wind erosion of open areas, vehicle traffic on unpaved haul
roads, and excavation activities. Several options are available during
closure and post-closure use of impoundments for reducing the potential for
dust generation.
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Excavation Activities
Wetting and stabilizing are the common control techniques employed in
preventing and/or reducing fugitive dust emissions from excavating
activities. The effectiveness of these techniques are highly variable because
of the site specific characteristics of the emission sources. Generally,
surface impounded waste materials would posses sufficient moisture so that
wetting or application of soil stabilizers for dust abatement would be
infrequently required.
Unpaved Haul Roads
Fugitive dust emissions from unpaved haul roads can be reduced or
eliminated by using wet suppression, stabilization, or speed reduction
techniques. Wet suppression is a farily inexpensive short-term method of
controlling dust that can be used on a confined site. Dust emissions
reductions of 50 percent have been reported by wetting haul roads twice per
day with an application of 2 liters of water per square meter.40
Stabilization methods that isolate the dust sources from the traffic
disturbances can be used on haul roads. This can be done physically by adding
a layer of material on the exposed surfaces or chemically by using materials
that help to bind the dust to larger surface particles. Gravel added to the
haul road surface is used as a physical stabilizer. In a study comparing
various methods of controlling emission from unpaved roads in Arizona, gravel
paving had an annual control efficiency of 50 percent and a cost effectiveness
of $12/Mg of dust, while chip seal paving had air effectiveness of 100 percent
and a cost effectiveness of $11.9/Mg.39 Chemical stabilization involves the
use of binding materials that cause dust particles to adhere to larger surface
particles. The effectiveness of this method of dust supression on unpaved
haul roads is extremely variable primarily depending upon the amount of
traffic. Long-term effectiveness of various stabilization chemicals is also
quite variable since it is related to the amount of traffic, soil type, and
meteorological conditions. A recent study of various chemical stabilizers was
made for dust control on unpaved roads and is summarized in reference 39.
Speed reduction of vehicles traveling over unpaved haul roads has been
shown to reduce dust emissions because of diminished stirring effects.
Reductions of 62 percent can be achieved by lowering the average speed from
56 km/hr to 32 km/hr.40
Open Surfaces
Dust emissions caused by wind erosion of surface impounded waste
materials or soils covering an SI can be minimized by use of physical,
chemical, or vegetative stabilization. Physical stabilization methods
function to cover the exposed surfaces with a material that prevents the wind
from disturbing the surface particles. Common stabilizer materials include,
rock, soil, crushed or granulated slag, bark, and wood chips. The control
efficiency of this technqiue depends on the type of material and the type of
stabilizer. The primary drawback to physical covers is the high cost involved
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in their application, particularly when the cover materials are unavailable in
the immediate area.
Chemical stabilizers can be added to cover soils to reduce wind erosion.
Many types are available and are applied in conjunction with water or
separately. A listing of chemical soil stabilizing materials and their
recognized attributes are listed in references 41 and 42. Many of the
compounds are proprietary developments, and their properties are difficult to
evaluate without actual site-specific field testing. In selecting a soil
additive, one should consider effectiveness, stability, ease of application,
cost, safety, and environmental impact. Most chemical stabilizers only
provide dust suppression for a limited period of time, generally no more than
a few months; thereafter, a more permanent solution is needed. This solution
generally consists of the establishment of a vegetative cover.
Vegetation can be effectively used to stabilize a variety of exposed soil
surfaces. This method of stabilization not only provides permanent dust
suppression but makes the site more aesthetically acceptable. The control
efficiency of this method varies considerably with the amount and type of
cover established on the site. Control efficiencies of 50 to 80 percent have
been reported.40 Efficiencies of nearly 100 percent should be achieved with
complete vegetative covering on some sites.
Before an effective vegetative stabilization cover can be developed, many
of the cover soils must be prepared by the addition of fertilizers, organic
matter, pH neutralizers, and the establishment of proper slope and drainage.
The selection of the vegetative species to be planted should receive adequate
consideration. Plants compatible with the soil type, growing conditions,
climatic zone, and site end use should be chosen. In addition, the selected
species must be insensitive to gas contamination of their root systems by
decompositional gases that may be present in the closed site. References 43
and 44 should be consulted for listings of candidate species and planting
techniques.
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REFERENCES FOR SECTION 4
1. Haxo, H. E., Jr., et al., "Lining of Waste Impoundment and Disposal
Facilities," U.S. Environmental Protection Agency, SW-870.
2. Ware, S. A. and G. S. Jackson, "Liners for Sanitary Landfills and
Chemical and Hazardous Waste Disposal Sites," U.S. Environmental
Protection Agency, EPA-600/9-78-005, May 1978. PB 293-335/AS.
3. deVeru, E. R., et al., "Samplers and Sampling Procedures for Hazardous
Waste Streams," U.S. Environmental Protection Agency, EPA 600/2-80-018,
January 1980. PB 80-135353.
4. "Procedures Manual for Ground Water Monitoring at Solid Waste Disposal
Facilities," U.S. Environmental Protection Agency, Technology Transfer,
EPA/530/SW-611, 1977.
5. Dunlap, W. J., J. F. McNabb, M. R. Scalf, and R. L. Cosby, "Sampling for
Organic Chemicals and Microorganisms in the Subsurface," U.S.
Environmental Protection Agency, EPA-600/2-77-176, 1977. PB 272-679/2BE.
6. "Sampling and Analysis Procedures for Screening of Industrial Effluent
for Priority Pollutants," U.S. Environmental Protection Agency, April
1977.
7. Wood, W. W., "A Technique Using Porous Cups for Water Sampling at Any
Depth in the Unsaturated Zone," Water Resource Research, 9:486-488, 1973.
8. "Standard Methods in the Examination of Water and Wastewater," 14th Ed.,
American Public Health Assoc., New York, 1976.
9. Manual of Methods for Chemical Analysis of Waters and Wastes, U.S.
Environmental Protection Agency, Technology Transfer, EPA 625/6-7*>-003a,
1974. PB 259-973/6BA.
10. Chesters, G., H. P. Pionke, and T. C. Daniel, "Extraction and Analytical
Techniques for Pesticides in Soil, Sediments and Water." Pesticides in
Soil and Water, Richard C. Dinauer, ed., Soil Science Society of America,
Madison, Wisconsin, 1974.
11. Little, T. M. and F. J. Hills, "Agricultural Experimentation," John Wiley
& Sons, New York, 1978.
12. Petersen, R. G. and L. D. Calvin, "Sampling," In: Methods of Soil
Analysis, Part I, Agronomy No. 9, American Society of Agronomy, Madison,
Wisconsin, 1965.
13. Black, C. A., "Methods of Soil Analysis, Part I," Agronomy, No. 9,
American Society of Agronomy, Madison, Wisconsin, 1965.
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14. Chapman, H. D. and P. F. Pratt, "Methods of Analysis for Soils, Plants,
and Waters," University of California, 1961.
15. Olson, 6. W., "Significance of Soil Characteristics of Wastes or Land,"
In: Land as a Waste Management Alternative, edited by Raymond C.
Loehr, Ann Arbor Science, 1977.
16. Griffin, R. A. and N. F. Shimp, "Attenuation of Pollutants in Municipal
Landfill Leachate by Clay Minerals," U.S. Environmental Protection
Agency, EPA-600/2-78-157, 1978. PB 287-140.
17 Alesii, B. A., W. H. Fuller, and M. V. Boyle, "Effect of Leachate Flow
on Metal Migrates," J. Environ. Qual., 9:119-126, 1980.
18. Chan, K. Y., B. G. Davey, and H. R. Geering, "Interaction of Treated
Sanitatary Landfill Leachate with Soil," J. Environ. Qual., 7:300-310,
1978.
19. Sommers, L. E., D. W. Nelson, and D. J. Silviera, "Transformations of
Carbon, Nitrogen, and Metals in Soils Treated with Waste Materials," J.
Environ. Qual., 8:287-294, 1979.
20. "Recommended Guidelines for Safety Inspection of Dams," Department of
the Army, Corps of Engineers, ER 111-0-2-10, September 26, 1979.
21. "Preliminary Manual for Safety Evaluation of Existing Dams," Department
of the Interior, Bureau of Reclamation, August 1978.
22. "Identification and Nature of Dispersive Soils," Journal of the
Geotechnical Engineering Division, American Society of Civil Engineers,
April 1976.
23. "Engineering and Design Stability of Earth and Rock-Fil Dams,"
Department of the Army, Corps of Engineers, EM 1110-2-1902, April 1,
1970.
24. "Stability and Performance of Slopes and Embankments," Soil Mechanics
and Foundation Division, American Society of Civil Engineers, 1966.
25. "Soil Mechanics, Foundations, and Earth Structures," Department of the
Navy, NAVFAC DM-7, March 1971.
26. Seed, H. and I. Idriss, "A Simplified Procedure for Evaluating Soil
Liquefaction Potential," Earthquake Engineering Research Center,
University of California, EERC 70-9, November 1970.
27. "Guide to the Disposal of Chemically Stabilized and Solidified Wastes,"
U.S. Environmental Protection Agency, SW-872.
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28. Bartos, M. J., Jr. and Palermo, M. R., "Physical and Engineering
Properties of Hazardous Industrial Wastes and Sludges," U.S.
Environmental Protection Agency, EPA-600/2-77-139, Cincinnati, Ohio,
1977, 77 pp. PB 272-266.
29. Lutton, R. 0., et al., "Design and Construction of Covers for Solid
Waste Landfills," U.S. Environmental Protection Agency,
EPA-600/2-79-165, August 1975. PB 80-100381.
30. Lutton, R. J., "Evaluating Cover Systems for Solid and Hazardous
Waste," U.S. Environmental Protection Agency, SW-867.
31. Brunner, D. R. and Keller, D. J., "Sanitary Landfill Design and
Operation," U.S. Environmental Protection Agency, 1972. PB 227-565.
32. Flower, F. B., et al., "A Study of Vegetation Problems associated with
Refuse Landfills," U.S. Environmental Protection Agency, May 1978.
PB 285-228.
33. Tolman, A. L., et al., "Guidance Manual for Minimizing Pollution from
Waste Disposal Sites," U.S. Environmental Protection Agency,
EPA-600/2-78-142, August 1978. PB 286-905.
34. "Management of Hazardous Waste Leachate," U.S. Environmental Protection
Agency, SW-871.
35. Chain, E. S. and F. B. DeWalle, "Compilation of Methodology for
Measuring Pollution Parameters of Landfill Leachate," U.S.
Environmental Protection Agency, EPA 600/3-75-001, October 1975.
PB 248-102/AS.
36. Farmer, W. J., et al., "Land Disposal of Hexachlorobenzene Wastes,
Controlling Vapor Movement in Soils," Department of Soil and
Environmental Sciences, University of California, Riverside,
California, August 1978.
37. "Classifying Solid Waste Disposal Facilities, A Guidance Manual," U.S.
Environmental Protection Agency, SW-828, March 1980.
38. Ham, R. K., et al., "Recovery, Processing and Utilization of Gas from
Sanitary Landfills," U.S. Environmental Protection Agency,
EPA-600/2-79-001, February 1979. PB 299-258.
39. Sultan, H. A., "Soil Erosion and Dust Control of Arizona Highways, Part
IV, Final Report Field Testing Program," Arizona Department of
Transportation, November 1976.
40. Jutze, G. and K. Axtell, "Investigations of Fugitive Dust -- Volume I,"
U.S. Environmental Protection Agency, Office of Air Quality Planning
and Standards, Research Triangle Park, North Carolina,
EPA 450/3-74-036a, June 1974.
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41. Armbrust, D. V. and J. D. Dickerson, "Temporary Wind Erosion Control:
Cost and Effectiveness of 34 Commercial Materials," J. of Soil and
Water Conservation, pp. 154-157, July 1971.
42. Lutton, R. J., et al., "Design and Construction of Covers for Solid
Waste Landfills," U.S. Environmental Protection Agency,
EPA 600-12-79-165, August 1979. PB 80-100381.
43. Carpenter, B. H. and G. E. Weant, III, "Particulate Control for
Fugitive Dust," Environmental Protection Agency, EPA-600/7-78-071,
April 1978. PB 282-269/OBE.
44. Leone, I. A., et al., "Adapting Woody Species and Planting Techniques
for Landfill Conditions," U.S. Environmental Protection Agency,
EPA 600/2-79-128, August 1979. PB 80-122617.
Q9 * US GOVERNMENT PRINTING OFFICE 1981-757-064/0199
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U.S. Environmental Protection Agency
Region V, Library
230 South Dearborn Street
UVmois- 60604
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