United States
Environmental Protection
Office of Solid Waste
and Emergency Response
Washia^fon DC 20460
September 1982
Rfivised Edition
Closure of
Hazardous Waste
Surface  Impoundments


                                                 September 1982

         A.  W.  Wyss,  H.  K.  Willard,  and  R.  M.  Evans
                     Acurex Corporation
              Energy & Environmental Division
                      485  Clyde Avenue
              Mountain View, California 94042


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
                  CINCINNATI, OHIO 45268


    The information in this document has been funded wholly or in part by
the United States Environmental Protection Agency under assistance agreement
number 68-03-2567 to the Acurex Corporation, it has been subject to the
Agency's peer and administrative review, and it has been approved for
publication.  The contents reflect the views and policies of the Agency.


     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


     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 adminis-
trative 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 published interim final rules
in Part 264 for hazardous waste disposal facilities on July 26, 1982.
These regulations consist primarily of  two sets of performance standards.
One is a set of design and operating standards separately  tailored to each
of the four types of facilities covered by the regulations.  The other
(Subpart F) is a single set of ground-water monitoring and response require-
ments applicable to each of these facilities.  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, land treatment facilities and piles: Draft  RCRA Guidance
Documents and Technical Resource Documents.  The draft RCRA guidance
documents present design and operating specifications  which the Agency
believes comply with the requirements of Part 264, for the Design and
Operating Requirements and the Closure and Post-Closure Requirements
contained in these regulations.  'The Technical Resource Documents  support
the RCRA Guidance Documents in certain areas  (i.e., liners, leachate
management, closure, covers, water balance) by describing  current techno-
logies 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 good engineering
practices.  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 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 124.6-124.20.

     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.  The references  are  cited throughout the manuals
to provide further guidance for the permit officials when necessary.

     There was a previous version of this document dated  September  1980.
The new version supercedes the September 1980 version.

            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

                           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 . .  .  .  .	     54
         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	: .  V .  .  ;  ',  "„  .  .  .     65
         4.5.1   Surface Soils ..........  ., . ;.  .  .  "  ;  :]  *     55
         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   ......  	]        7]
         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



 3-1       Simplified water balance for open surface
             impoundment 	  „
 3-2       Moisture distribution during infiltration through
             an unsaturated soil	„
 3-3       Abandoned gravel pit with a clay layer at its base
 3-4       Single aquifer with a deep water table	
 3-5       Breakthrough curve for bulk transport of solutes
 3-6       Breakthrough curve for bulk transport and
             diffusion/dispersion  	  ,
 3-7       Breakthrough curve with soil-solution interaction  .
 3-8       Trace element controls in soils 	  ,
 4-1       Surface impoundment closure key steps .  	





Liner and Industrial Waste Compatibilities  .  . .  .  .
Types of Soil-Solute Interactions 	  .  .
Sources of Existing Information 	 ...
Compatibility of Hazardous Waste Impoundment Features
  and Various Site Uses	
Compatibility of Various Site Uses and Impoundment
  Features After Hazardous Waste Removal  ......
Impounded Waste Gas Generation Rates  	 ...
Evaporation Potential Variations  	 ...
Hazardous Waste Consistency Classifications .....



                                   SECTION 1

     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.


     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.


     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


     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

     •   "Hydrologic Simulation on Solid Waste Disposal Sites''^

     §   "Management of Hazardous Waste Leachate"^

     •   "Lining of Waste Impoundment and Disposal Facilities"^

     •   "Design and Management of Hazardous Waste Land Treatment

     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.

     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 guidelines 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

     "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.

                          REFERENCES FOR SECTION 1
1.  Moore, C. A., "Landfill and Surface Impoundment Performance Evaluation,"
    U.S.  Environmental Protection Agency, SW-869.

2.  Lutton, R. 0., "Evaluation Cover Systems for Solid and Hazardous Waste,"
    U.S,  Environmental Protection Agency, SW-867.

3.  Hal one, 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-871.

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.

                                  SECTION 2


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 with areas from  a few tenths
of an acre to hundreds of acres and depths from 2 to as much as 30 feet
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 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 liner.  In the
past, some impoundments were unlined, permitting seepage of fluids into the
soil for the purpose of percolation or infiltration.  All new impoundments
are lined to prevent any seepage of fluid.   Typical liner materials include
clay, 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:

    o    Physical properties and chemical  composition of the wastes

    o    Soil permeability,  and geological and geochemical  characteristics  of
         the local and surrounding soil

    o    Depth to the water table

    o    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 inconsistent.  A general survey of all impoundments whether
hazardous or non-hazardous, published in 1978, 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).'  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.2  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.-^  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

2.1.4    Surface  Impoundment Uses

     Si's can be  used for temporary  holding, treatment,  or disposal  of  wastes.
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 f;   •'
settling ponds  are periodically  dredged to  restore  them to  their original

     In the past,  some  impoundments  were designed specifically  to permit
seepage of fluids  into underlying aquifers.   These  impoundments were 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  air parts  of the western  states where climatic  conditions  favor losses by
this mechanism.

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., 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 v
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 bas-ins 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.


     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  minimize the release
of hazardous constituent-containing liquids into groundwater and surrounding
soils.   The remaining wastes must not contain  free  liquids  and  the  closure
plan  must  meet,  as a minimum, the requirements of 40 CFR 264.228.   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
         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

    In addition to eliminating 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 Haste 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:

    o    Impoundments with soil or clay liners

    o    Si's with irrepairable liners containing wastes with a high potential
         for the generation of toxic leachate

    o    Impoundments with dikes in poor condition that may require extensive
         and costly repair                                    .,  .......

    o    Cases where the type of waste or waste constituents generate gases
         that cannot be controlled adequately or economically

    o    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 will 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 groundwater or surface
water contamination.  Therefore, the underlying soil must be quantitatively
analyzed for the  hazardous constituents of the  impounded wastes.  Consult
current regulations and guidance documents for  appropriate analytical
procedures and requirements for dealing with contaminated soil,.  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:

    o    Erosion  control
    o    Surface  runoff control
    o    Water table  restoration

     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.


     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 Hater

     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.

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.1  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.8  This report developed an evaluation system based on ratings for:

     •   Ground water availability

     •   Ground water quality

     0   Waste hazard potential (determined by waste source or industry or
         chemical content)

     •   Earth material  characteristics (unsaturated zone beneath  the

     •   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

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.'0

     Although chemical fixation may provide only limited added control against
leachingJ° 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 Ib/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,

organic waste character, lack of oxygen, and bactericidal constituents (high
pH and heavy metals).


     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
nuisanceJ>'2  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 J^

     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.

                            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 p'ursuant 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.

                                   SECTION 3

     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.


     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.'»8  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.

     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.''  A further extension is to consider biological activity.11
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).1''^  Factors that exert a strong influence on the leaching
potential include:

     t   Chemical composition

     •   pH of the waste and eluant

     t   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

The effects of these factors have been discussed in detail by LowenbachJl
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 waste.'3» '4  They 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 quantify the leaching rates
of wastes and contaminated soils.  Tests for doing this are described below.
These tests are conducted to predict actual leaching behavior and performance
of lining systems.  They are different from and are employed for a different
purpose than the EP toxicity test that is used to establish if a waste is
hazardous.  Leaching tests fall into three categories:  (1) batch (shake)
tests, (2) column tests, and (3) field cell tests.^  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.'1

     Over 30 shake tests were evaluated and compared by LowenbachJl  The
study identified three shake tests for further investigation:   the IU
Conversion Systems test,"16 the State of Minnesota test,I7 and the
University of Wisconsin test.'8  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

utilized to evaluate potential contamination by a method described by Silka
and SwearingenJ^  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
reported*^»21,22 an(j -js discussed in Section 3.3.


     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.

Haste 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 v/astes 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.


            Table 3-1.  Liner and Industrial  Waste Compatibilities
Industrial waste3
Liner material
Flexible synthetic membranes
(oil resistant)
Butyl rubber
Chlorinated polyethylene
propylene rubber
Soil sealants
Soil cement
Admixed materials
Soil asphalt
Asphalt concrete
Asphalt membranes
Natural soils
Soil bentonite
(saline seal)
Compacted clays















. F




.. - F




F ,





aP = Poor, F = Fair, G = Good

            Briefly,  rationales  for  the  ratings  are:

                 •    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.

                 •    01ly  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
           llif     i^   ); £™ever'  other  Ph^sical  and chemical  factors  can negate any
           seir—seaiing capability.

                Freeze/thaw cycles and freezing itself can  seriously  degrade liner
           performance.  Jemperature-induced stress can cause fractures.  Some of the
           plastic materials  become brittle  at low temperatures and suffer property
           degradation at  high temperatures.                               re./

               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


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

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

     •   Generalized waste/liner compatibility analysis

     •   Examining liner material/waste composition test results

     t   Examining construction and maintenance records


     •   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 -V;' .•'_
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 conditions1.   In
addition, this method has been  shown to have a limited life, which may'bee^^
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.

 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.


      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:

      e   The  solubility and  rate of solution  of the contaminant

      c   The  balance  between carrier fluid  inputs  and outputs from the SI

      •   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  The manual "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

     Mathematically, the water balance may be expressed  in terms of flow
 continuity, for a given  time  interval, or

     Onsite accumulation = Sinputs - £ outputs

     If steady-state conditions are assumed to apply, the onsite accumulation
term becomes zero.  Therefore,

     Z, inputs = S outputs


     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.


     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.


      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.


                      + irrioation
Evapotranspi rati on
                  Ground water
                  underflow (out)
                                                                                     runoff (in)
                                            runoff (out)
                               Ground water
                               underflow  (in)
                                                          Sludge or fill
                                                          (filled impoundment)
                        Figure 3-1.  Simplified Water Balance for Filled Surface Impoundment

     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.4

     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


                          Moisture content
                             Saturation^ zone

                            Transition 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

                                                               Surface Impoundment
                               Figure 3-4.  Single Aquifer with a Deep Water Table

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

     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'
entering the soil column and
leaving the column.
                     "  represents  the  initial  solute  concentration
                      "C"  represents the  concentration  of  solute
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.

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

     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 caii be found in
references 36, and 42 through 46.                -            '   •


     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

Prevent erosion
Control potentially harmful gas movement

Support construction vehicles

                                   Concentration ratio,








2,   ro









                                                                          Concentration  ratio,


     Table 3-2.  Types of Soil-Solute Interactions36>42-46
Crop Uptake
Cation exchange
An ion exchange
Cation-dipole interaction
Hydrogen bonding
Van der Waals attraction
Hydrophobic bonding
Specific ion sorption

                                                trace  elements  (M)
                                                                                          Chelation and
                                                                                        complexation (C)
Insoluble MC
Soil solution
 M + C £ MC
   Exchange 5
surface sorption
                                               Crystalline mineral
                                 Figure 3-8.  Trace Element Controls in Soils

In addition,
wind erosion
sand.  Where
 the cover will  function to meet aesthetic considerations by
any noxious odors and providing a base for the establishment of
 The functions of a cover for a closed SI are usually complexly
.  For example,  a cover designed to impede infiltration and
of surface water may call for a clay layer while dust control and
 considerations  would best be met by a layer of coarse-grain-sized
 apparent conflicting functions exist, priorities must be
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.


      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.

      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

 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


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:

     i   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.                                                ,rr,..  .-_

     •   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


overburden area  (structure  site)  and rising of the  unstressed overburden
area.   If significant, this  latter  action could fracture the cover and exude
V/aste  solids to  the  surface.

Tertiary Consolidation

     Many mechanisms can contribute to reduction of the actual mass of
sediment solids.  The most  common include:

     •   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

     •   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.
         Biochemical degradation —• Requires organic wastes, a supply of
         water, and either aerobic or anaerobic conditions.  The reactions
         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


     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

     9   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

     t   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      '    -   ;
                                                    ;    -    ' •     '__      _. ' ->;-•  r; '
     •   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.

                             Table 3-3.   Sources  of Existing  Information2
 inform tion
Base map
               Topography and

               Land use

County road department
City, county, or regional  planning  department
U.S. Geological  Survey (USGS) office or  outlets for USGS map sales (such as
  engineering supply stores  and  sporting goods stores)
U.S. Department of Agriculture  (USDA), Agricultural Stabilization and Conservation
  Service (ASCS)
Local office of USGS
County Department of Agriculture, Soil Conservation Service (SCS)
Surveyors and aerial  photographers  in the area

USGS topographic maps
USDA, ARS, SCS aerial  photos

City, county, or regional  planning  agency

County agriculture department
Agriculture department at  local  university
USDA, SCS District Managers,  Local  Extension Service
USGS reports
Geology or agriculture  department of local university
USGS reports
State geological  survey  reports
Professional geologists  in  the area
Geology department of local  university
Ground water   General
                 Water  supply department
                 USGS water  supply papers
                 State  or regional water quality agencies
                 USDA,  SCS
                 State  or federal water resources agencies
                 Local  health department
Climatology    General
                 National  Oceanic and Atmospheric Administration
                 Nearby airports

     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 ,v er"osion 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 .;•,

     «   Trafficability characteristics -- strength of site surface under
         repeated traffic (these characteristics are often measured by.the
         rating cone index,47 soil  moisture, and slope index52)

     «   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

Table 3-4.   Compatibility  of Hazardous  Waste  Impoundment  Features
              and  Various Site Uses
                                    SI site uses upon closure
    Design features
           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


Diversion of surface
Air factors
Passive gas control

Active gas control
Control of bird hazard
to aircraft
Surface area factors

Land buffers












C, except





C for parks
and golf











C, affects


C, affects

C, affects

C, affects










C = Compatible,  NC = Not compatible,  RDA = Requires design  alteration

     •   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
     Design features
                  ballparks,   Parking              Open
       Buildings golf courses   areas  Agriculture spaces
  Subsurface water controls
   Wells                   CIR
   Subsurface drainage     C
Surface water control
Diversion of surface
Air factors
Surface area factors







	 c •'•'•'



 C =  Compatible,  CIR
= Compatible if removed/dismantled, RDC = Requires design

 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.


      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


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 Hydrocarbon1 Processing Journals,^ while information
on pesticides  is available from Spencer and Clia'th.56  jne 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 underg-o 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.

              Table 3-6.   Impounded Waste Gas Generation Rates57
Gas generation rate
     (l/m2/day.) . :•.

       PCB, aroclor  1242
          6.4 ppm on sand

       Paperwaste and radioactive solid

          no cover
          1.9 cm cover
          30 cm cover

       Typical wet solid waste landfill
          (70 Ib/ft3)
       8.8 x 105

       2.1 x 104

       2.9 x 105
       4.1 x 103

       12.9 to 25.2
     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

     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

     •   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

     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

     it   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 y,enting" 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:

     •   Liquid  surfaces can be renewed  and, thus, increase vaporization    :
                                     '"•"•' ' . "  • '     '.r* ;' '•"  t . •  " • "", • •" -    " .',-'' " '   -• . -. '.', ;
     •   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,

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)


     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  ?. o  to  mo  percent,  greatly  affectina
 qas venting.   Diffusivity of individual  gas, D0, is constant (21  fWday for
 CHd, and 15 ft2/day for C02).   Typical  diffusivity values of a gas tnrough a
 wet covering soil  have been demonstrated according to this formula in a study
 of vaporization and flux of a nazaraous chemical wasted'

     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/I

      L  = Soil  layer thickness  (feet)

      A  s 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.

 3.7.2  Fugitive Dust Emissions

      Participate  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

      t   Reentrainment  of particulate matter by vehicular traffic  on haul
         roads  and exposed surfaces                                '        :

      t   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  duetto
 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


            ambient wind speed.   Wind speed  does  determine  the drift  distance  of large
            dust particles  and,  therefore, the localized impact of the fugitive  dust

                 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.

                            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.   PB 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  298-280/9.BE.

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.  Ill 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 a!., "Influence of Leachate Quality on Soil Attenuation
     of Metals," Proceeding of the Sixth Annual Research Symposium, U.S.    ^rnnr
     Environmental Protection Agency,  EPA-600/9-80-010, March 1980.  PB 800-175086.

21.  Korte, N. E., et  a!., "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 gfid Hazardous Waste
     Research, EPA 600/2-77-020, Cincinnati,  Ohio, 1978.   HB 
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 6. 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.

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.  Bonn, H., B. McWeel, and 6. 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 arid 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.

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.

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.

Curry, N. A., "Philosophy and Methodology of Metallic Waste Treatment,"
Proceedings of the 27th Industrial Waste Conference, Purdue University,
Lafayette, Indiana, May 1972.

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.       .   • ;

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.
"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  2.75-474/5BE.

                                   SECTION 4

     The alternatives that must be considered during closure of an SI are
shorn 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

     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


Onsite sludge
sludge dewatering

•*• Dike re
":. i|r
-. ,..- Sludc

. '. r ;.'•



e . . ' '

Hastewater Wastew
treatment *" dispo
j i

\ r
•sludge disposal


Sludge ^ Sludge
removal dewatering
Liner _ , Liner
removal decontamination
Soil ^ Soil
removal decontamination

" ' . fc Water b
. - ,
ol s .
•' '
•;• - ' " monitoring system, . ' " . ,
---,- ;. ; •• f " - • • - - • - -
'. '.•' " '" Backf
'. "- • ,- ' ,. •'
., " •« 	 » • 	
iii- •• . . . .
f -

- Cover . . -
" " "" ,..„. 	 .._,,
f ' n ....

•Surface :_.- - - -
                                  Figure-4-1.; .Surface Impoundment  Closure Key Steps

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.

     e   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.

     c   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.

     0   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.

     e   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.


     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.


     •   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.

     •   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.

     t   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.


     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.
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.


      •   Resuspension — Dewaterlng 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 1s 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 semi'solid 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  -",* _.,f-
 conslderations.)                •                                        ,;;  '.
         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, solidifjiexf'«.
         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.


         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 arid 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

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.

     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 Dewatering

     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.
                                                                         Y ;
     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

                 Table 4-1. Evaporation Potential Variations^           ;
                                Annual condition (inches of water)
                             Class A           Average       Evaporation
                         pan evaporation    precipitation     potential
     Pacific Northwest

     Sonora Desert

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) draining1
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  Active Dewatering

     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 nonflowablo filter cake
suitable for landfill  disposal within  the impoundment or at some other


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.


     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


 son  Uner 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 offslte disposal.

      Liners made of synthetic materials such  as Hypalon, PVC, etc.,  should be
 taken up 1n 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
 1n 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.


      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.


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.


 4.5.4   Drilling  and  Sampling  Programs

     The objective of  the  geohydrological  study  is  to  identify  the  following

     9   Extent  of soil  contamination

     9   Extent  of ground  water contamination

     o   Potential for contaminant migration
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:

     «   TOC ~ Indicator of organic chemicals

     «   Conductivity — Indicator of soluble ions

     «   pH —Indicator of acidic or basic waters

     •   COD — Indicator of chemically oxidizable organic and inorganic

     •   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, "I"1,12

4.5.6  Soil Analysis

     There are three types of analyses of interest in soil characterization:
(1) soil properties, (2) Teachable 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 1n 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


     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

     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


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

     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


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.

     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:

     o   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 eyelic-triaxial tests.  For example, eyelic-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.22
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.


     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

     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 un.iformity 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

     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 and 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.

 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  geotechnlcal
 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 t9  the elimination of growth of  vegetation  and trees  on  the dike  and
 burrowing animals in the area.


      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  sedi.ment consolidation during  the
 closure process7 is necessarily  closely coup Ted  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 homogenlzation.

     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


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
   1.  Liquid waste
   2.  Pumpable waste
   3.  Flowable waste
   4.  Nonflowable
<1% suspended solids,a pumpable liquid,
  generally too dilute for sludge dewatering

<10% suspended solids,a pumpable liquid,
  generally suitable for sludge dewatering.

<10% suspended solids,a not pumpable, will flow
  or release free liquid, will not support heavy
  equipment, may support high flotation
  equipment, will undergo extensive primary

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.


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  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.

     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, arid
moisture content are some of the factors that can greatly reduce or stop the
rate of reaction.

     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.    ,jli','... ,
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       "V   -	
consolidation, however.  Testing of the chemical leaching of the waste dan
indicate the potential for aqueous dissolution of the waste.  Test methods.are
outlined in Section 3.1..  ,,           ,                                   :

4.7.3  Stabilization of Waste                                          '  "".
       •"'  ii i  ..-.—.-	 . .... i-.— i-... .-     _            ,         *       . •    i • ' *  • r s ' D
                                                             • •        ,"•< -.• ' -  r,' •  ';•
     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:

     o   Portland cement-based processes  •

     9   Pozzolanic processes

     9   Thermoplastic techniques (including bitumen, paraffin, and
         polyethylene incorporation)

     «   Organic polymer techniques

     o   Surface encapsulation techniques

     9   Self-cementing techniques

     9   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.^S  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

would be expected to be because of consolidation of compressive foundation


     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

     •   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


      •   Climatology --  precipitation,  temperature,  evaporation

      •   Land  use

      •   Runoff  coefficient

      •   Stream  geology  — fluctuation,  history,  transport  of  suspended
          materials,  erosion  rate

      •   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

      •   Water table depth and seasonal  fluctuations

     •  Thickness of aquifer(s)

     •   Ground water flow direction and rate

     •   Proximity of water supplies — public and private

     *   Ground water quality — baseline data

     •   Infiltration rate -- recharge

     t   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 area!  distribution
         --   Permeability
         —   Attenuation  capacity
         --   Extractable  contaminants  (Teachability)

     •   Land  use  (site vicinity)

     •   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 Hater 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
         enhancemeat for leachate generation.

     •   Cover construction — The cover should be constructed to minimize

     •   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

4.8.3  Ground Water Controls

     Where local geological and hydro.logical 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

     •   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.       •                ;       v

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 tie 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
                                                   f           '  /
                                       81 '

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

     •   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

     •   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.

     •   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

     •   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.


     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

     t   Emission control during removal for offsite treatment

     t   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


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, feams, 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:


                 1.9 cm topsoil

                 0.15 mm polyethylene film

                 1.43 cm water

                 120 cm topsoil
                    (silty clay  loam)
 HCB vapor flux





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

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:

     •   Pressurized liquid pumping withdrawal and disposal (gases remain

     «   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

     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

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.

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 •invdlves-Vh'e-
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, soiT 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 dimihished 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

 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 neutralizes, 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 listing's-of candidate species and planting

                             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-60Q/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.   Dun Tap, W. J., J. F. McNabb,  M. R.,Scalf,  andr'R.,L.  Cosby,  "Sampling for
      Organic Chemicals and Microorganisms in  the Subsurface," U.S.
   1   Environmental Protection Agency,  EPA-600/2-77-176,  1977.  PB 272-679/2BE1

 6.   "Sampling and Analysis  Procedures for Screening  of  Industrial Effluent
      for Priority  Pollutants," U.S. Environmental Protection  Agency,  April
 7.  Wood,'W. W., "A Technique Using Porousi. Cups for 'Water -'Samp 1 i fig" at' Afiy^'"'''''
     Depth in .the Unsaturated Zone," Water' Resource Research,  9;486r488i i;1973.

 8.  "Standard Methods in the Examination of Water rand Wastewater,":'l4th  Ed
     American Public Health Assoc., New York,. 1976, \   ; .'. '."..."  ,           "«   V

 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, 6., 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. 6. 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.

 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.  Qua!.,  9:119-126,  1980.

 18.     Chan, K.  Y., B. 6.  Davey, and H.  R.  Geering, "Interaction of Treated
        Sanitatary Landfill Leachate with Soil," G. Environ. Qua!., 7:300-310,

 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.  Qua!., 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,

 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.













 Bartos, M.  J.,  Jr.  and  Palermo,  M.  R.,  "Physical  and  Engineering
 Properties  of Hazardous Industrial  Wastes  and  Sludges,"  LUS.
 Environmental Protection Agency,  EPA-600/2-77-139,  Cincinnati,  Ohio,
 1977,  77  pp.  PB 272-266.

 Lutton, R.  J.,  et a!.,  "Design and  Construction of  Covers  for Solid
 Waste  Landfills," U.S.  Environmental  Protection Agency,
 EPA-600/2-79-165, August 1975.  PB 80-100381.

 Lutton, R.  J.,  "Evaluating Cover  Systems for Solid  and Hazardous
 Waste," U.S. Environmental Protection Agency,  SW-867.

 Brunner,  D. R.  and  Keller, D. J., "Sanitary Landfill  Design and
 Operation," U.S. Environmental Protection  Agency, 1972.  PB 227-565.

 Flower, F.  B.,  et al.,  "A Study of Vegetation  Problems associated with
 Refuse Landfills,"  U.S. Environmental Protection Agency, May 1978.
 Tblman, 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.

 "Management of  Hazardous Waste Leachate,"  U.S. Environmental Protection
 Agency, SW-871.

 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.
 Farmer, W. J.,  et al.,  "Land Disposal of Hexachlorobenzerie Wastes,
 Controlling Vapor Movement in Soils," Department of Soil and
 Environmental Sciences, University of California, Riverside,
 California, August  1978.

 "Classifying Solid Waste Disposal Facilities, A Guidance Manual," U.S.
 Environmental Protection Agency,  SW-828, March 1980.

 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.

 Sultan, H. A.,  "Soil Erosion and Dust Control of Arizona Highways, Part
 IV,  Final Report Field Testing Program," Arizona Department of
Transportation,  November 1976.

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.

41.    Armbrust, D. V.  and  G.  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.
   •U.S. GOVZSKHXKT PRIKTIMO OFFICE I   1982-0-361-032/321
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