OOOD82001
TD367
.R37
1982y
vol.1
DRAFT
RCRA GUIDANCE DOCUMENT
SURFACE IMPOUNDMENTS
LINER SYSTEMS, FINAL COVER, AND
FREEBOARD CONTROL
[TO BE USED WITH RCRA REGULATIONS
SECTIONS 264.221U) and
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TABLE OF CONTENTS
A. Purpose and Use
B. Liner System Function, Components, and Life
1. The Regulations
2. Guidance
3. Discussion
C. Leak Detection, Collection, and Removal Systems
1. The Regulations
2. Guidance
3. Discussion
D. Liner Specifications
1. The Regulations
2. Guidance
3. Discussion ,
*»
E. Cap (Final Cover) Design
1. The Regulations
2. Guidance
3, Discussion
F. Freeboard Control
1. The Regulations
2. Guidance
3. Discussion
Appendices
A. Hydraulic Conductivity Test Method
B. Compatibility Test Method
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A. Purpose and Use
This guidance document presents surface impoundment
design specifications which the Agency believes comply with
the Design and Operating Requirements of §§264.221(a) and (c),
and 264.222(a), and the Closure Requirements of §264.228(a) of
the RCRA surface impoundment regulations (40 CFR ).
These regulations have been formulated with the goal of elimia-
ting the escape of hazardous waste and hazardous constituents
from surface impoundments for all time to the extent practical.
Given that few things work perfectly, or work for all time,
absolute prevention of escape for all time is probably not
realistic. However, the regulations require surface impoundments
to come as close to the containment ideal as possible. In
actual practice, the Agency believes containment is practical
during the operating life of the impoundment in the absence of
damage to the containment system. In the long run, however,
in the distant years after closure of disposal impoundments,
minimization of leachate formation and escape is the best
that current technology can practically achieve.
For most impoundments, the regulations provide that liner
systems be installed that are capable of preventing release of
hazardous wastes and their derivatives during operating life. At
closure, the wastes and contaminated liners, equipment, and sub-
soils must either be removed or a cap must be installed that is
designed to minimize release of pollutants into the distant
future. To protect surface waters, a surface impoundment must
be designed, constructed, and operated so that it does not
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overflow. The closure rules essentially eliminate the potential
for significant overflow to surface waters after closure.
To provide flexibility, the design and operating character-
istics required are expressed in terms of performance standards
for system components as a whole. Optimally, these standards
would contain numeric limits to the performance required of
each system component, and most, but not all of the currently
promulgated standards are expressed in numeric terms. For
others, minimum specifications are not included. For example,
though a final cap must be incorporated, unless the waste is
removed at closure, the required capabilities of that system are
currently expressed in general terms, specifically "Provide
long-term minimization of the migration of liquids". The
Agency intends to augment the general statements currently in
the regulations by applying numeric limits to the performance
required of each component. But, there will still be substantial
flexibility in designing facilities to meet the standard and
substantial uncertainty involved in judging whether a given
design will, in fact, achieve the performance level prescribed.
This document is designed to provide specific guidance on
designs the Agency believes accomplish the performance state-
ments in the regulations. As a result, permit applicants
designing their facilities in accordance with the specifications
contained herein, will be considered in compliance with §§264.221(a)
and (c), 264.222(a)(3), and 264.228(a). This provides certainty
to the permitting process because, if these specifications and
procedures are followed, a draft permit will be issued. (Final
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permits cannot be issued until input from the public participa-
tion process is evaluated.)
The Agency wishes to emphasize that the specifications
contained herein are guidance/ not regulations. The Agency is
not requiring, and does not intend, that all facilities be built
in this way. On the contrary, the Agency believes there are
many designs which can be acceptably used, depending on waste
characteristics and location. Owners or operators wishing to
use a different design, but one that contains the basic design
components of §§264.221(a) and (c), 264.222(a), and 264.228(a),
i.e., liners, overtopping controls, and caps (if disposal
units),may demonstrate compliance with the performance require-
ments for the specific components, directly to the permitting
official. An easy way to demonstrate compliance with the
performance requirements would be to show that the specific
design incorporated at a particular unit provides the same
level of performance as would the design incorporated in this
guidance under similar circumstances (waste characteristics,
location, rainfall, etc.). For example, the specifications
for the final cover in this guidance call for a final slope of
between three and five percent to promote drainage without
causing erosion. To demonstrate the acceptability of a greater
slope, the applicant could attempt to show that because of the
materials used, perhaps in combination with other design
features, a greater slope will result in no more erosion than
would be the case utilizing the slope specifications contained
herein. The Agency will accept convincing demonstrations of
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equivalency of performance to the specifications in this
guidance as adequate demonstration of compliance with the
performance standards of §§264.221(a) and (c) and 264.228(a).
This document contains only initial guidance—it will be
significantly expanded over time to include additional designs
and specifications which the Agency believes acceptably comply
with the performance requirements of the regulations. Since
the Agency can only recommend the liner specifications contained
in this document for installation above the water table, it is
diligently working on similar specifications for location in
saturated soils. EPA hopes to issue this additional guidance
in the near future. This document will also be expanded by
incorporating the experience gained in implementing the
performance standards.
The document is arranged according to the section of the
regulation to which it corresponds. Those wishing to send
technical information or suggestions concerning this document
should address them to: Rod Jenkins, Chief, Land Disposal
Branch, Office of Solid Waste (WH-564), U.S. Environmental
Protection Agency, 401 M Street, S.W., Washington, D.C. 20460.
EPA is particularly interested in information and suggestions
concerning the usefulness of the document, expansion of it,
and the effectiveness of the guidance contained in ensuring
compliance with the performance requirements in the regulations.
EPA is also producing a series of Technical Resource
Documents (TRDs), two of which cover caps and liners, and a third
that covers surface impoundment closure. The TRDs are designed
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to comprehensively but concisely present the sum total of the
body of information and experience gained by the Agency over
the years on a given topic. As such, they contain factual
summaries concerning the experiences and effectiveness of
design alternatives, covering what has been found not to work
as well as what has been found to be effective. They contain
no policy-related direction. The TRDs can be considered as
technical background or development documents supporting these
guidance documents and the regulations. Based partially on
the information contained in the TRD's, the Ajency made the
policy decisions which resulted in the regulations and these
guidance documents. TRD's corresponding to the guidance in
this document are:
(1) Evaluating Cover Systems for Solid and Hazardous Waste
(SW-867) NTIS Publication No. PB-81-166-340.
(2) Lining of Waste Impoundment and Disposal Facilities
(SW-870) NTIS Publication No. PB-81-166-365.
(3) Closure of Hazardous Waste Surface Impoundments
(SW-873) NTIS Publication No. PB-81-166-894.
These documents can be obtained from the National Technical
Information Service, U.S. Department of Commerce, Springfield,
Virginia 22161. The Agency plans to publish amended versions
of these documents in the fall of 1982.
B. Liner System Function, Components, and Life
1. The Regulations
The regulations require the system to function through
scheduled closure and to consist of at least one liner designed
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and constructed to prevent transmission of liquids through it.
In the case of disposal impoundments (i.e., where the waste will
be left in place at closure), the liner must be essentially
impermeable to liquids, allowing no more than de minimum infiltration
of liquids into the liner itself.
2. Guidance
(a) Liner systems should be constructed wholly above the
seasonal high water table, i.e., in the unsaturated soil.
(b) Liner systems for storage or treatment impoundments
where the waste will be removed at closure should consist of
a single soil (clay) or synthetic liner, as a minimum.
(c) Liner systems for disposal impoundments where the
waste will remain at closure should consist of a single synthetic
liner, as a minimum.
(d) Where a synthetic liner is used in any surface impound-
ment which will not complete closure for 30 or more years
after first placement of wastes, the underliner system should
consist of the following as a minimum:
(i) A primary synthetic liner; and
(ii) A secondary soil liner (e.g., clay).
3. Discussion
In developing the designs contained in this guidance, the
Agency"has attempted to come as close as possible to complete
containment for as long as the impoundment is in operation.
However, the Agency also used, as an overriding criterion,
that the designs developed be based on conventional technology,
utilizing readily available equipment and materials, at practical
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Essentially complete but temporal containment is practical
using the synthetic liners developed over recent years. However,
experience with synthetic liners in contact with chemicals is
relatively recent. As a result, EPA has no experience base
from which to predict the life of these materials. However,
predictions based on chemistry, and limited recent real world
experience are sufficient to convince the Agency that with proper
selection for resistance to chemicals in the waste and proper
design and installation (tight seams and no tears), containment
for at least 30 years is practical, utilizing a single synthetic
liner (some believe that such liners will last in excess of
100 years). Therefore, a single synthetic liner system is
described for impoundments which will be closed in less than
30 years. Some surface impoundments, however, are designed
to function almost perpetually. While the regulations require
a prediction that the synthetic liner will last as long as the
projected life of the impoundment, regardless of how long that
is, there is no historic proof that such liners will, in fact,
function into the distant future. Therefore, if final closure
is not scheduled for 30 years or more, a double liner system
incorporating a top synthetic liner and a secondary clay liner
is recommended. The secondary soil liner functions as a backup
to the synthetic primary liner, taking over the task of minimizing
liquid transmission when and if the primary liner deteriorates.
Some soil materials, typically those classified as clays,
can be deposited and compacted to produce a liner system of very
low permeability. Movement of liquids through well constructed
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clay liners is very slow as long as the structure of the liner
is not affected by the waste materials or is not otherwise
damaged. As a result, when functioning properly, the release
of liquid-containing hazardous constituents to the ground water
and surrounding soils, is effectively minimized (but not pre-
vented) by the secondary clay liner. Thus, absolute preven-
tion of escape of liquid wastes and pollutants through the
liner system during the life of very long lived surface impound-
ments may not be fully achievable, in those cases where the
primary synthetic liner deteriorates, though the use of the
secondary clay liner should keep the rate of escape to very
low levels.
Storage impoundments are a special case, however. Storage
impoundments must be closed by removing the wastes, contaminated
liners, and equipment at closure. Should there be any leakage
through the liner during operation of a storage impoundment,
the contaminated soil must either be removed or decontaminated
as well. Since removing and decontaminating soil can be an
expensive process, it is important to owners and operators of
storage impoundments that liner systems not leak during the
life of the impoundment. The Agency is convinced that synthetic
liners will readily achieve this goal, assuming the liner is
not attacked chemically or damaged physically, and assuming
that site life is 30 years or less. The Agency also believes
that adequate protection can be achieved by use of a single
clay liner of sufficient thickness and impermeability to
ensure that no waste travels through the liner before closure
when both the waste and the saturated liner are removed.
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Thus, in the Agency's view, for storage impoundments, clay and
synthetic liners can be considered equally protective under most
circumstances.
For disposal impoundments, where the waste and contaminated
liners will remain after closure, the Agency believes that
synthetic liners are preferable because they constitute a more
efficient barrier to escape of liquid wastes. As long as they
are intact, they are essentially 100 percent effective as a
barrier. If the synthetic liner remains intact through closure,
when the cap functions to greatly reduce leachate generation,
then little, if any, pollutants should have exfiltrated to the
surrounding soil. (The Agency realizes that very small amounts
of liquids may enter the structure of synthetic membranes
causing them to swell, but the amount is truly negligible and
leads to no future ground water contamination.) Clay liners,
on the other hand, are somewhat permeable. Some of the liquid
waste will infiltrate the pore structure of the liner and will
be released over time. In the Agency's view, therefore, a
single clay liner in a disposal impoundment does not fully
prevent release of hazardous waste constituents reaching its
surface during operating life. It simply reduces the amount
that is released, retards release, and minimizes the rate of
release. EPA concludes, therefore, that clay liners are not
nearly so effective as synthetics in the near term (at least
30 years). The Ayency realizes, however, that there is disagree-
ment as to the relative effectiveness of various types of
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liners. The Agency is, therefore, seeking data and information
concerning:
(I) The relative efficiency of synthetic, soil, and other
liners in preventing and minimizing the transmission
of liquids and the release of pollutants;
(2) The effective life of various liner designs;
(3) The causes of physical and chemical damage to various
liners and how damage can be avoided;
(4) The potential for saturated soil liners to attenuate
pollutants;
(5) The potential for soil liners to release pollutants
after proper closure has removed liquids from the
impoundment and reduced the amount of leachate formed;
and
(6) The benefits to be realized and the risks posed by
various liner designs.
The designs suggested are specifically recommended for
installation in the unsaturated zone. The Agency views location
in the ground water as fraught with additional risks and design
difficulties. This does not mean, however, that the Agency frowns
on such locations; EPA is convinced that given certain hydrcgeo-
logical circumstances and accommodating designs, location in
saturated soils can be environmentally acceptable. In addition
to the potential for leak detection systems to fill with ground
water, the problems associated with location in the saturated
zone are primarily associated with the external pressure applied
by the saturated earth against the liner system. This can result
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in damage to the integrity of the liner system and to difficul-
ties in removing wastes at closure. The former is of real con-
cern to the Agency; the latter would be primarily a nuisance to
the operator at closure. Depending on the active earth pressure
and the way the surface impoundment is designed and operated,
the force exerted by the liquid contents of the impoundment
may offset the external force exerted by the saturated earth.
If so, no damage to the liner .system would be expected. Accord-
ingly, the Agency intends to expand the designs in this guidance
to include designs which will effectively minimize the rate of
pollutant release in saturated locations. In the interim,
those wishing to locate in the saturated zone and whose units
have the basic components specified in the regulations (i.e.,
at least one liner) may be able to readily show that the loca-
tion, design, and operating characteristics of the unit prevent
the migration of pollutants from the unit and that the surface
impoundment will function with an equivalent degree of certainty
(e.g., longevity, damage potential, etc.). The closer the
actual design is to those in this guidance document, the easier
that demonstration may be to make. In any event, for now, a
case-by-case demonstration of containment will be necessary
for impoundments located wholly or partially in the saturated
zone.
C. Leak Detection Systems
1. The Regulations
The regulations do not require a leak detection system.
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However, under the requirements of §264.222 (Double-lined surface
impoundments), owners or operators choosing to install a double
liner system with a leak detection system may be exempted from
the monitoring and other requirements of Subpart F unless and
until contaminated liquid is identified in the leak detection
system.
2. Guidance
Leak detection systems should have:
(a) At least a 30 centimeter (12-inch) drainage layer
with a hydraulic conductivity not less than 1 X 10~3 cm/sec
and a minimum slope of 2 percent;
(b) A drainage tile system of appropriate size and
spacing and a sump pump or other means to efficiently
conduct liquids.
3. Discussion
The leak detection system is the means by which one can
determine if the primary liner has failed or is leaking. Under
the operating requirements of §264.222(b), the owner or oper-
ator must then either repair the primary liner or institute
ground-water monitoring, if he is not already doing so.
There are, of course, many possible designs for detecting
leaks including the use of advanced instrumentation. The
system described here is essentially a gravity collection
system, very similar to the leachate collection system for
landfills and waste piles.
The minimum thickness (30 centimeters or 12 inches) of
the drainage layer is designed to allow sufficient head to
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promote drainage. The two percent minimum slope is also designed
to promote drainage. The hydraulic conductivity of not less
than 1 X 10~3 cm/sec was chosen because materials used widely
as drainage media are typically at least that coarse.
Drainage tile diameter and spacing are important because
they affect the removal of liquids. The closer the tiles are
together, the more quickly a leak is likely to be detected.
Unlike leachate collection systems for landfills and piles,
however, the primary purpose here is detection of leaks, not
removal. Thus, tile size and spacing need only be sufficient
for rapid detection of the initial leak and need not be designed
to remove some predetermined volume rate of flow. The Agency
is therefore not specifying minimum tile spacing or size in
this guidance. Nevertheless, a reasonably sized drainage system
coupled with an efficient means (such as a sump pump) for
removing collected liquids, will result in capacity to remove
leaking fluids except in the case of severe breaches of the
primary liner. By so doing, the liquid head on the bottom
liner will remain low providing an extra measure of protection.
EPA believes that a design incorporating 4 in. diameter tiles
on 50 to 200 foot (15 to 60 meter) centers will provide
efficient leak detection and capacity to remove leakage from
minor breaches of the primary liner.
D. Liner Specifications
1. The Regulations
As discussed in Section B of this guidance, the liner
system must be designed and built to achieve containment of
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fluids during the life of the site thus preventing the escape
of hazardous constituents to surrounding soils and ultimately
to the ground water. At least one liner must be installed and
the material used must be resistant to the chemicals it will
encounter in the wastes and in the leachate, and be of sufficient
strength to withstand the forces it will encounter during
installation and operation. In this regard, a base is required
which must provide sufficient support to the liner to prevent
failure. The liner system must, of course, cover all areas
likely to be exposed to waste and to leachate.
2. Guidance
In Section B of this guidance, the Agency identified the
conditions under which it believes single and double liner
systems are appropriate and the nature of the materials recom-
mended. Following are liner specifications which the Agency
believes will produce stable construction and which will prevent
the release of hazardous constituents.
(a) Synthetic liners should:
(1) Consist of at least a 30 mil membrane that is
chemically resistant to the waste managed at the unit. In
judging chemical compatibility of wastes and membranes, the
Agency will consider appropriate historical data, demonstrations
involving theoretical chemistry, and actual test data. Testing
of chemical resistance of liners should be performed using
either the EPA test method attached or an equivalent test
method.
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(2) Be protected from damage from below the membrane, by
at least 15 centimeters (6 inches) of bedding material no
coarser than Unified Soil Classification System (USCS) sand
(SP) and which is free of rock, fractured stone, debris, cobbles,
rubbish, roots, and sudden changes in grade. Leak detection
systems, soil (clay) liners, or natural, in situ soils may
serve as bedding materials when in direct contact with synthetic
liners if they meet the requirements specified herein.
(3) Be protected from damage when mechanical equipment
is used to remove sludge or for other reasons, by means of a
minimum of 45 centimeters (18 inches) of protective soil (or the
equivalent) above the top liner.
(4) Be protected from damage due to sunlight or wind, where
exposed to the elements, by means of a minimum of 15 centimeters
(6 inches) of protective soil (or the equivalent) over exposed
surfaces, unless it is known that the liner material used is not
physically or chemically impaired by exposure.
(b) Soil liners should:
(1) Consist of at least 60 centimeters (24 inches) of
natural or recompacted emplaced soil (e.g., clay) with a sat-
urated hydraulic conductivity not more than 1 X 10""^ cm/sec.
Saturated hydraulic conductivity testing should be conducted
using either the EPA test method attached or an equivalent.
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(2) Have a saturated hydraulic conductivity which is
not increased beyond 1 X 10~7 cm/sec as a result of contact
with the waste or leachate generated at the facility. Testing
of the effect of waste or leachate on soil liner hydraulic
conductivity should be performed using either the EPA test method
attached or an equivalent test method.
(3) Have no lenses, cracks, channels, root holes, or
other structural nonuniformities that can increase the nominal
hydraulic conductivity of the liner above 1 X 10~7 cm/sec; and
(4) Where recompacted emplaced soil liners are used, be
placed in lifts not exceeding 15 centimeters (6 inches) before
compaction to maximize the effectiveness of compaction.
(c) Single soil liners used in storage or treatment
impoundments from which wastes will be removed at closure should:
(1) Have a sufficient thickness of natural or recom-
pacted emplaced soil to provide containment of the waste in
the liner system (i.e., no fluid flow moves beyond the liner)
during the operating life of the unit; the necessary thickness
of soil should be determined by use of the following:
d = 0.5 I tk^ +j/(tk)2 + 4 itkh)
e
where:
J
d = necessary thickness of soil (feet)
3 = total porosity
k = hydraulic conductivity (ft/yr)
h - maximum fluid head on the liner (feet)
t = facility life from startup through closure (years);
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(2) Have a hydraulic conductivity which is not
increased beyond that used in the calculations as a result of
contact with the waste managed at the facility. Testing of
the effect of leachate on soil liner hydraulic conductivity
should be performed using either the EPA test method attached
or an equivalent test method.
(3) Have no lenses, cracks, channels, root holes or other
structural nonuniformities which can act to increase the nominal
hydraulic conductivity above that used in the calculations; and
(4) Where recompacted emplaced soil liners are used, be
placed in lifts not exceeding 15 centimeters (6 inches) before
compaction to maximize the effectiveness of compaction.
3. Discussion
EPA believes synthetic liners should be at least 30 mils
thick. Thinner synthetic membrane liners are known to be
readily damaged. One of the primary reasons for failure of
synthetic liners, is damage (i.e., punctures, rips, and tears).
Damage occurs during installation or during operation. With
surface impoundments, punctures occur as a result of the pressure
applied by liquid wastes forcing the membrane against sharp
objects below (rocks, sticks, debris, etc.). If the impoundment
is a double lined unit with a leak detection system, this is
not usually a problem because the leak detection system normally
provides protection. However, even leak detection systems are
sometimes constructed of coarse rock to promote drainage, but
which can damage the liner. To protect against this, EPA
recommends that a minimum six inch bedding layer be placed
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under the liner. The bedding layer should consist of materials
which are no coarser than sand (SP) as defined by the Uniform
Soil Classfication System (USCS). Use of a sand layer is
common practice for protection of membranes and other delicate
materials from damage due to contact with grading equipment and
materials, sharp materials in soil, etc. The bedding material
need not be a separate layer as natural soils or the leak detec-
tion, collection, and removal systems materials will often meet
the necessary criteria.
Bedding material is not usually necessary above the liner,
since direct contact is normally with the liquid waste contents
or material settling out of it. However, the liner can also be
damaged by sludge removal or other mechanical equipment used
in the impoundment. Where such equipment is used, EPA recommends
a minimum of 45 centimeters (18 inches) of protective soil, or
the equivalent covering the top liner. EPA believes this will
be sufficiently protective in most cases since sludge removal
equipment is usually carefully controlled. Additionally, some
liner materials are known to be degraded substantially by sun-
light. In some circumstances, wind can get under the edge of
exposed liners, causing flapping and whipping, which can lead to
tears. These problems have occurred most commonly above the
liquid level near the edge of the liner. As a result, it has
become common practice to cover exposed liner areas with six
inches or so of earth materials to hold the liner down and
prevent degradation. Of course, if the design is such that
wind creates no difficulties, and if it is known that the liner
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is not subject to solar degradation, then these precautions are
not necessary.
Chemical testing is prudent because synthetic liners are
degraded by certain species which may be present in the waste.
Because wastes and liner chemical characteristics are almost
infinitely variable, it is difficult to generalize concerning
incompatibility. The Agency therefore prefers test data as the
preferable way to demonstrate the compatibility of waste and
liner materials, but recognizes that historic data (results
elsewhere with similar wastes) or theoretical chemistry may
provide sufficient information in some cases. Data currently
available to EPA indicate the following combinations of waste
types and liner materials are often incompatible:
(a) Chlorinated solvents tend to dissolve polyvinyl
chloride (PVC)
(b) Chlorosulfonated polyethylene can be dissolved by
aromatic hydrocarbons.
(c) Clays may exhibit high permeability when exposed to
concentrated organics, especially organics of high
and low pH
(d) Asphaltic materials may dissolve in oily wastes
(e) Concrete and lime based materials are dissolved by
acids
The Agency is currently developing a more comprehensive summary
of waste/liner compatibility information which will be included
in a later edition of this document.
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An acceptable test method for evaluating waste/liner com-
patibility is included in the Appendix to this document. The
test method exposes a liner sample to the waste or leachate
encountered at the unit. After exposure, the liner sample
is tested for important characteristics—saturated hydraulic
conductivity in the case of soil liners; strength (tensile,
tear, and puncture) in the case of synthetics. The Agency
considers any significant deterioration in any of the measured
properties to be evidence of incompatibility unless a convincing
demonstration can be made that the deterioration exhibited
will not impair the integrity of the liner over the life of
the unit. Even though the tests may show the amount of deteri-
oration to be relatively small, the Agency is concerned about
the accumulative effects of exposure over very much longer
periods than those actually tested.
The Agency had intended to incorporate the National Sanita-
tion Foundation's (NSF) standard specifications for flexible
membrane liners as part of this guidance. This would have
provided minimum recommendations with regard to physical
properties, construction practices, seaming tests, etc. An
NSF committee has been studying the subject for some time, and
EPA believes that the specifications which are being developed
are reasonable and well thought out. However, at this point,
the NSF has not formally adopted the draft standards. Therefore,
given the possibility that they might still be changed, EPA
believes it prudent to wait for formal adoption by the NSF before
incorporating them into this guidance document. The NSF
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specifications are not intended to comprehensively cover the
myriad of hazardous waste applications, however. Therefore,
the Agency believes that some augmentation of the NSF specifica-
tions is appropriate. A few additions have been made (e.g.,
the 30 mil thickness requirement) and more may be incorporated
if experience warrants.
Once the NSF strength secifications have been published,
EPA plans to incorporate them in conjunction with the compatibility
test method for synthetic liners attached, in an improved method
of evaluating liner compatibility. While the Agency does not
want to prejudge how this may be done, one possible approach
might be to extrapolate the strength curves developed by the
test method to the expected life of the unit. The expected
strength at that'time could then be compared against minimally
acceptable strength levels, e.g., the NSF strength specifications
or some acceptable fraction of them. The Agency is interested
in comments, suggestions, and data on the subject of evaluating
strength loss on exposure to chemical leachates.
Soil liners will normally be of clay soils. They should
have a saturated hydraulic conductivity of not more than 1 X 10~7
cm/sec and be at least 60 centimeters (2 feet) thick. To
minimize the transmission of waste or leachate fluids, the
soil liner should be as tight as practical. Many clays can
readily be recompacted to meet the specified level. It is not
clear, however, that recompactiny to meet a tighter specifi-
cation can be routinely accomplished. In concert with the
philosophy of these designs, soil liners are usually incorporated
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as backup systems and are depended upon to minimize the rate
of liquid flow through them (except in the case of storage
impoundments to be discussed later). Thickness of the soil is
not as important as other factors in minimizing flow but a
minimum thickness is necessary to retain structural stability
(reduce cracking potential, etc.). Two feet is generally
accepted to be a minimum stable thickness for recompacted
clay.
When discussing the relative tightness of soils, the term
permeability is most often used. This is a generic term, refer-
ing to the property in general. In this guidance, EPA uses the
more specific term—"hydraulic conductivity". An acceptable
method for soil hydraulic conductivity has been included in the
Appendix to this document.
I_n situ soils can be considered acceptable as soil liner
material provided the specifications in this guidance are met.
Natural soil liners should be free of conduits and channels
which would convey liquids through the liner. This includes
root holes, sand lenses, cracks, fractures, etc.
In addition to meeting the other specifications specified for
clay liners, those wishing to use a single clay liner for storage
impoundments should be convinced that the liner system is capable of
retarding liquid flow through it to the extent that the liquid is
wholly contained within the liner through the life of the
unit. Ideally, one would calculate containment time on an
unsaturated basis, but the unsaturated flow equations are
difficult, complex, and controversial. As a surrogate which
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approximates the ideal and can be practically applied, the Agency
has chosen a transit time formula assuming saturated conditions.
The formula is based on the life of the facility through closure,
the porosity of the soil liner, the saturated hydraulic conducti-
vity, and the maximum fluid head in the surface impoundment.
The determination of the effective porosity of the soil is
difficult to do in practice. Because of the controversial nature
of the determination of effective porosity, the Agency believes
total porosity should be used in the calculation even though
in doing so the requirement is somewhat less protective. The
Agency is evaluating methods for determining effective porosity
and may change this guidance should confidence in a specific
method be established.
Use of the saturated flow equation is environmentally conser-
vative, and will result in a thicker soil liner than would abso-
lutely be necessary to assure containment in the liner system.
This is partially offset however by the use of total porosity
instead of effective porosity which causes the equation to be
somewhat less protective. Additionally, the saturated flow equa-
tion does not account for the effects of capillary tension which
will also cause the regulation to be somewhat less protective.
On balance, the use of total porosity and the lack of consi-
deration of capillary tension will somewhat offset the error
introduced by use of a saturated flow equation. While EPA
realizes that this formula is not perfect, it is the only
performance based approach which is practically implementable.
It is somewhat environmentally conservative; erring on the
23
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side of added protection. This is prudent, in the Agency's
opinion, given the uncertainties associated with prediction
of pollutant movement through soils.
Owners and operators choosing to incorporate a leak detec-
tion system between a double liner design as a means of qualify-
ing for exemption from the ground-water protection and associ-
ated monitoring requirements of Subpart F in accordance with
§264.222, must incorporate a secondary liner, under the leak
detection system, which meets the containment requirement for
liner systems under §264.221(a). For most surface impoundments,
this means that a synthetic secondary liner must be used as a
minimum. If the impoundment is being designed to operate for
more than 30 years, then the synthetic liner should be backed
up by a tertiary soil liner meeting the specifications discussed
herein. The regulations are written to require prevention of
release by the secondary liner in surface impoundments exempted
from Subpart F because the owner or operator may choose, upon
detection of a leak, to convert his unit to the same status
as other surface impoundments installing ground-water monitoring
facilities and becoming subject to the ground-water protection
standards of Subpart F. Most other surface impoundments must
have a liner system capable of preventing migration of liquids.
E. Cap (Final Cover) Design
1. The Regulation
The cap or final cover must be designed to minimize infil-
tration of precipitation into the surface impoundment after
closure. It must be no more permeable than the liner system.
24
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It must operate with minimum maintenance and promote drainage
from its surface while minimizing erosion. It must also be
designed so that settling and subsidence are accommodated to
minimize the potential for disruption of continuity and function
of the final cover.
2. Guidance
(a) The cap or final cover should be placed over the
surface impoundment after the waste has been solidified and
compacted enough to support it. Solidification and fixation
processes often take days or weeks to completely stabilize.
Final cover should not be applied before stabilization is nearly
complete.
(b) The cap (final cover) should consist of the following
as a minimum:
(1) A vegetated top cover, as described in paragraph (c)
of this section;
(2) A middle drainage layer as described in paragraph (d)
of this section; and
(3) A low permeability bottom layer as described in
paragraph (e) of this section.
(c) The vegetated top cover should:
(1) Be at least 60 centimeters (24 inches) thick;
(2) Support vegetation that will effectively minimize
erosion without need for continuing application of fertilizers,
irrigation, or other man-applied materials to ensure viability
and persistence (Fertilizers, water, and other materials may
be applied during the closure or post-closure period if necessary
to establish vegetation or to repair damage.);
25
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(3) Be planted with persistent species that will effect-
ively minimize erosion, and that do not have a root system
that will penetrate beyond the vegetative and drainage layer;
(4) Have a final top slope, after allowance for settling
and subsidence, of between three and five percent, unless the
owner or operator knows that an alternate slope will effectively
promote drainage and not subject the closed facility to erosion.
For slopes exceeding five percent, the maximum erosion rate
should not exceed 2.0 tons/acre using the USDA Universal Soil Loss
Equation (USLE); and
(5) Have a surface drainage system capable of conducting
run-off across the cap without forming erosion rills and gullies.
(d) The drainage layer should:
(1) Be at least 30 centimeters (12 inches) thick with a
saturated hydraulic conductivity not less than 1 X 10~3 cm/sec;
(2) Have a final bottom slope of at least two percent,
after allowance for settling and subsidence;
(3) To prevent clogging, be overlain by a graded granular
or synthetic fabric filter. Where a granular filter is used,
the grain size ratio should meet the following criteria:
D15 (filter soil) < 5
D85 (drainage layer) =
D50 (filter soil) < 25
D50 (drainage layer) =
and D15 (filter soil) = 5-20
D15 (drainage layer)
where:
D15 = grain size, in millimeters, at which 15% of
the filter soil used, by weight, is finer;
26
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D85 = grain size, in millimeters, at which
85% of the drainage layer media, by
weight, is finer;
D50 = grain size, in millimeters, at which
50% of the filter soil or drainage media,
by weight, is finer; and
(4) Be designed so that discharge flows freely in the
lateral direction to minimize head on and flow through the low
permeability layer.
(e) The low permeability layer should have two components:
(1) The upper component should:
(A) Consist of at least a 20 mil synthetic membrane;
(B) Be protected from damage below and above the membrane
by at least 15 centimeters (6 inches) of bedding material no
coarser than Unified Soil Classification System (USCS) sand (SP)
and which is free of rock, fractured stone, debris, cobbles,
rubbish, roots, and sudden changes in grade (slope). The
drainage layer and lower soil (clay) component may serve as
bedding materials when in direct contact with synthetic caps
if they meet the specifications contained herein;
(C) Have a final upper slope (in contact with the bedding.
material) of at least two percent after allowance for settling;
and
(D) Be located wholly below the average depth of frost pene-
tration in the area;
(2) The lower component should:
27
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(A) Include at least 60 centimeters (24 inches) of soil
recompacted to the maximum practical extent, but capable, if
placed on a firm base, of being recompacted to a saturated
hydraulic conductivity of not more than 1 X 10""7 cm/sec;
(B) Have the soil emplaced in lifts not exceeding 15
centimeters (6 inches) before compaction to maximize the
effectiveness of compaction;
(f) In designing the final cover, owners and operators
should estimate and accommodate the amount of settling and
subsidence expected as a result of degradation and long-term
consolidation of waste.
3. Discussion
The guidance calls for placing the final cover once the
waste remaining in the surface impoundment has been solidified
through sorption, fixation, or some other means and after it has
stabilized and been compacted sufficiently to support the final
cover. Some of the fixation processes take days or weeks to
stabilize and placement of final cover should not commence until
the process is nearly complete.
The Ajency believes that a three layer final cover (cap)
will adequately minimize infiltration of precipitation, which
is the primary purpose of the final cover. The final cover
acts to minimize infiltration by causing precipitation to run
off through use of slopes, drainage layers, and impermeable
and slightly permeable barriers. By minimizing infiltration,
the generation of leachate will also be minimized, thereby
reducing long-term discharge of pollutants to the ground water
28
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to a bare minimum. To prevent the "bathtub effect," i.e., to
prevent the landfill from filling with leachate after closure,
the final cover must be no more permeable than the most impermeable
component of the liner system (or of the underlying soils). In
this way, no more precipitation is allowed to infiltrate into
the closed impoundment than can escape through the bottom liner.
Prevention of the "bathtub effect" is important to eliminate the
possibility of surface overflow or migration through porous
surface strata. Other functions of the final cover include
prevention of contamination of surface run-off, prevention of
wind dispersal of hazardous wastes, and prevention of direct
contact with hazardous wastes by people and animals straying
onto the site.
The top layer should have at least two feet of soil capable
of sustaining plant species which will effectively minimize
erosion. Two feet was chosen because it will accommodate the
root systems of most nonwoody cover plantings and is typical
practice within the waste management industry today. Species
planted should not require continuing man-made applications of
water or fertilizers to sustain growth since such applications
cannot be guaranteed in the long term. Application of water and
fertilizer is, of course, acceptable during the early stages of
the post-closure care period as the plant growth is being
established. The plant species chosen should also not have
root systems which can be expected to penetrate beyond the
vegetated and drainage layers. If they penetrate deeper, they
can damage the integrity of the low permeability layer.
29
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After allowance for settling and subsidence, the final slope
should be at least three percent to prevent pooling due to
irregularities of the surface and vegetation but less than
five percent to prevent excessive erosion. Owners and operators
using different final slopes should determine that an alternate
slope will not be beset with erosion problems and that it will
promote efficient drainage.
The U.S. Department of Agriculture Universal Soil Loss
Equation (LISLE) is recommended as a tool for use in evaluating
erosion potential. The USLE predicts average annual soil loss
as the product of six quantifiable factors. The equation is:
A = RKLSCP
where R = rainfall and run-off erosivity index
K = soil erodibility factor, tons/acre
L = slope-length factor
S - slope-steepness factor
C = cover/management factor
P = practice factor
The data necessary as input to this equation are described in
Evaluating Cover Systems for Solid and Hazardous Waste (SW-867),
September 1980, U.S. EPA. The maximum rate of erosion for any
part of the cover should not exceed 2.0 tons/acre in order to
minimize the potential for gully development and future main-
tenance. The agricultural data base indicates that rates as low
as 1/3 ton per acre are achievable for a silt-loam soil, sloped
four percent with a blue grass vegetative cover. The Agency
believes that two tons per acre is more readily achieved and
30
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does not significantly increase cover maintenance. The top
layer should also have some means of conducting runoff (e.g.,
swales or conduits) to safely pass run-off velocities and
volumes without eroding the cover.
The second layer or drainage layer is analogous in function
to the leachate collection system over the liner of a landfill.
It should be at least 12 inches thick to provide capacity to
handle water from major sustained storm events, and should be
constructed of porous materials (at least 1 X 10~3 cm/sec
hydraulic conductivity). Drainage tiles or other collection
devices are not necessary. The Agency believes that the combin-
ation of very porous media, a final minimum two percent slope
after settling, and the impermeable nature of the layer beneath
will effectively conduct precipitation infiltrating the vegeta-
tive layer, off of the unit. As with the leak collection
system, the drainage layer should be overlain with a graduated
granular or synthetic fabric filter to prevent plugging of the
porous media with fine earth particles carried down from the
vegetated layer. To prevent fluid from backing up into the
drainage layer, the discharge at the side should flow freely.
The function of the low permeability layer is to reject
fluid transmission, thereby causing infiltrating precipitation
to exit through the drainage layer. It should consist of at
least two components. The upper component should be at least
a 20 mil thick synthetic membrane. While the regulations do
not specify that the cap prevent infiltration, the requirement
that it be no more permeable than the bottom liner, as a practical
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matter, necessitates the use of a synthetic membrane. This is
so because the regulatory requirement for the liner system
does specify that liquids be contained, and this will be trans-
lated, in most cases, into a very nearly impermeable synthetic
membrane liner.
The minimum thickness specified for the synthetic component
of the final cover (20 mil) is less than that recommended for
the liner (30 mil) because (1) the final cover is not expected
to come in contact with chemical wastes which will tend to
hasten failure, and (2) once placed, the potential for damage
is small as compared to the potential for underliner damage
where waste is in contact with the liner throughout the operating
life of the cell. While intact (30 + years in the absence of
damage), the synthetic component will essentially prevent
transfer of precipitation through it and leachate production
should be very nearly zero. As with underliners, synthetic
caps should be protected from from punture and tears by at
least six inches of bedding materials with the consistency of
sand or finer. In most cases, the drainage layer media above
the synthetic cap, together with the soil (clay) liner under
it, can effectively function as the bedding material.
Even with protection from damage, the synthetic cap will
not last forever. At some point, perhaps in the far distant
future, the synthetic membrane will degrade. At that time,
the function of minimizing infiltration will fall to the second
component, a 2-foot minimum clay soil cap with a maximum hydraulic
conductivity of 1 X 10~7 cm/sec. Although some small amount
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of precipitation will seep through this secondary cap, the
amount of leachate generated will be quite small and escape to
the ground water should be mimimal. Unless damaged or affected
by differential settling, the secondary soil liner should
remain intact and effective for all time. One source of damage
is frost heaving which can disrupt the continuity of the
impermeable layers. For this reason, the impermeable layer
should be wholly below the average depth of frost penetration
in the area. This may necessitate a thicker cover than would
otherwise be necessary.
One of the more difficult problems associated with de-
signing final cover is how to allow for settling and subsidence.
Settling occurs as a result of natural compaction and consoli-
dation and biological degradation of organics. It tends to be
relatively uniformly distributed and usually occurs shortly
after closure. Subsidence is a more difficult problem since
it tends to be unevenly distributed, resulting in differential
sinking which in turn can cause disruption in continuity of
the final cover. It most often occurs as the result of final
release of liquids from, and collapse of drums and is, therefore,
not normally a major problem with closed surface impoundments.
Settling on the other hand, may pose a significant problem if
remaining wastes are high in organic content or if organic
sorbants (e.g., sawdust or paper) are used to solidify the
wastes. Chemical fixation processes are usually inorganic in
nature and are not prone to significant settling once stabili-
zation is complete.
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EPA intends to develop specific design requirements which
will ensure adequate allowance for settling and subsidence. As
of this writing, however, the Agency lacks sufficient information
to judge the effectiveness of various design options. Therefore,
this guidance suggests simply that owners and operators estimate
the amount of subsidence and allow for it in the final cover
design as best they can. The final result should be a minimum
three percent final slope after settling and subsidence. During
the postclosure period, the regulations require that the
damaging effects of settling and subsidence (e.g., disruption
of the continuity and slope of the cap) be repaired. It thus
behooves the owner or operator to adequately allow for subsidence
and settling. As the Agency evaluates alternative methods of
designing final cover to effectively allow for settling and
subsidence, it will issue further guidance or perhaps even
additional regulations covering the subject.
One suggestion which owners and operators may consider as
a means of at least partially accomodating settling and sub-
sidence, is to stage final closure and the placement of the
final cover. Unsubstantiated information from the field leads
EPA to believe that the most severe subsidence and settling
problems occur rather soon after closure. It may be preferable
therefore, from both an environmental and cost standpoint, to
delay placement of the relatively expensive final cover for six
months or more in those cases where substantial subsidence or
settling are expected. By so doing, expensive repairs to the
final cover may be avoided. This would require an extension in
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the 180 day limit to the closure period imposed in Subpart G.
In deciding whether to grant such an extension, in accordance
with the rules of Subpart G, the permitting official will
normally require installation of an expendable interim cover,
capable of minimizing precipitation migration into the unit.
The Ayency solicits information on the effectiveness of this
and other approaches to dealing with the settling/subsidence
problem.
F. Freeboard Control
1. The Regulations
The regulations require simply that the owner or operator
prevent overtopping of his surface impoundment from virtually
any eventuality, including normal or abnormal operations, over-
filling, wind and wave action, rainfall, equipment malfunctions,
and human error.
To implement this requirement, the owner or operator must
demonstrate in his permit application that design features and
operating procedures at his operation will prevent overtopping.
If acceptable to the permitting official, these features and
procedures will be incorporated in the permit.
2. Guidance
(a) Where possible, surface impoundments should be designed
with outfall mechanisms such as weirs or spillways which are
relatively insensitive to inflow.
(b) Where outfalls are sensitive to inflow, i.e., where
adjustments must be made to maintain impoundment freeboard as
inflow increases, outfall devices (or inflow controls) should be
automaticaly controlled by signals from level-sensing instruments.
35
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(c) Except when equipped with inflow insensitive outfalls
as described in (a) above, surface impoundments should be
equipped with a high-level alarm based on a different level
sensor than that used for automatic control.
(d) Surface impoundments should be designed to maintain
at least 60 centimeters (two feet) of freeboard unless it is
known that normal fluctuations in level and maximum wave action
will not cause overtopping.
(e) A surface impoundment should be designed so that any
flow of waste into the impoundment can be immediately shut off
in the event of overtopping or liner failure.
(f) A surface impoundment should have a run-on control
system designed to prevent flow into the impoundment during the
peak discharge from a 100-year storm unless the impoundment is
designed to accommodate the extra flow without detrimental
effects to the impoundment or appreciable loss of freeboard.
3. Discussion
Preventing overtopping of surface impoundments is not
normally a difficult engineering problem. Many impoundments are
operated on a flow through basis. Typically, these are impound-
ments used for treatment of wastes; biological oxidation lagoons
are a common example, though not one normally associated with
hazardous wastes. Frequently, these impoundments are designed
with simple spillway or weir-type discharge structures which
maintain a constant freeboard level in the impoundment. With
this type of arrangement, the sensitivity of freeboard level is
dependent directly on the relative width of the spillway or weir,
36
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Normally, but not always, these structures are sufficiently wide
so that freeboard level is insensitive to normal changes in flow.
In these cases, all that is necessary is the provision of a
modest freeboard level sufficient to deal with wave action and
with the minor fluctuations which will occur as flow changes.
The Agency believes two feet will be sufficient in virtually
all cases where discharge structures of this type are used.
Some impoundments are designed with other discharge
arrangements. Some, such as circular weirs, operate on the same
principle as those discussed above, but because the effective
discharge width of the device is often narrow relative to
potential flow fluctuations, they may be overwhelmed by abnormal
rainfall events or malfunctions in the production equipment which
feeds wastes to the impoundment. Other arrangements require
adjustment to the discharge structures to maintain freeboard
level. A common design of this type incorporates underflow
pipes through a dike. Freeboard level in these designs is
usually controlled by a valve on the pipe. Others operate off
of a sump arrangement with the freeboard level controlled by
turning a pump on and off. Storage impoundments are often
constructed this way. Some other impoundments, usually those
operated as seepage or evaporation impoundments, have no dis-
charge arrangment. Obviously, with no discharge, the freeboard
level is very sensitive to substantial changes in inflow to
the impoundment.
Where freeboard level is sensitive to flow changes, there
are a number of design and operating alternatives which can be
37
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adopted to provide adequate protection against overtopping:
(1) Emergency spillways or overflow piping arrangements
can sometimes be provided which can be connected to holding
ponds or tanks to contain the overflow. If these latter units
are to be used only in the unlikely event of an emergency,
they need not be permitted. However, if they are to be used on
a statistically predictable recurring basis for surge capacity,
permitting is necessary. This will require exercise of some
judgment on the part of the permitting official.
(2) Another alternative is to control the discharge
device automatically based on freeboard level. The underflow
valve can be opened or closed automatically to maintain a set
freeboard level through signals from level-sensing instruments.
Reliable level sensing devices have been available for many
years and are usable in most situations. Discharge pumps can be
similarly controlled (turned on and off to maintain level with-
in a range). Where it can be accommodated from the point of
view of production or operation of the rest of the facility,
it may be possible to automatically control the amount of waste
flowing into the impoundment through valves or pumps based on
freeboard level.
(3) Outfall devices can also be controlled manually. In
these cases, the owner or operator must be prepared to demon-
strate that he either maintains sufficient freeboard to accom-
modate any reasonably possible increase in influent flow or that
the combination of the rate of possible flow increases coupled
with the frequency of operator inspections to control discharge
38
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will eliminate potential overtopping due to sudden unnoticed
increases in level. In these cases, the frequency of control
inspections must be specified in the inspection schedule and
thus in the permit.
(4) Some impoundments have no discharge devices. In these
cases, owners or operators must be able to demonstrate either
that the rate of seepage or evaporation is such that overflow
is not possible even under maximum possible inflow rates or,
more probably, that operating procedures are in effect which
will effectively control inflow so that overtopping conditions
will not occur. A convincing demonstration should be required
in any case.
Of the acceptable options discussed above, the Agency
clearly favors automatic controls and/ or provision of foolproof
arrangements such as weir discharges or emergency collection
devices (tanks or ponds). These are not as sensitive to human
error as are those arrangements requiring human inspection and
manual operation. Automatic control devices based on level
sensors are, however, subject to malfunctions. Because of
this, the .Agency recommends that any freeboard control arrange-
ment that is sensitive to inflow variations (i.e., all except
those using weirs, spillways, or similar devices, or where
possible inflow variations cannot cause overflow) be equipped
with an alarm to warn of loss of freeboard so emergency action
can be taken to prevent overtopping. Typically, these will also
be based on a level sensor device, and the Agency recommends
that a different sensing unit and different type of device be
39
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used than that used for automatic control. This will help
ensure that both do not fail at the same time.
EPA believes that two feet of freeboard will normally pro-
vide sufficient protection against overtopping due to inflow
fluctuations or wave action. However, where manual operation
is involved, freeboard levels substantially greater may be
necessary to assure adequate protection. Smaller freeboard
levels may be justified if the owner or operator can demonstrate
that level variations due to possible flow changes are very
small or that the automatic level control response is such
that level variations will be very small.
In the event overtopping does occur, in spite of the safe-
guards built into the system, or in the event of some other
catastrophic failure (e.g., dike failure), there must be some
way to quickly shut off inflow to the impoundment. The Agency
does not care how this is accomplished so long as it can be
done quickly and without causing significant environmental or
human health problems elsewhere. Possible options might include
provision of redundant units or immediate shutdown of production
operations feeding the impoundment.
Many ponds and lagoons are designed, either purposefully
or circumstantially, to collect run-off from adjacent plant
areas or even sometimes from whole watersheds. Depending on
the magnitude of rainfall events and the size of the drainage
area relative to the impoundment capacity, storm run-off can
provide an overwhelming inflow to the impoundment, causing
overtopping. Unless it can be shown at the time of permitting
40
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that the impoundment is designed to handle storm water without
appreciable loss of freeboard or other detrimental effects on
the impoundment, a run-on control system should be installed.
The Agency recommends that the capacity of the run-on control
system be designed to divert the maximum flow from a 100-year
storm event. This is the most severe storm event for which
historical meteorologic data is normally available. Choice of
this rather stringent storm event indicates the Agency's level
of concern over potential overtopping of surface impoundments
containing hazardous wastes. This level of concern steins not
only from the inherent threat posed by the uncontrolled escape
of hazardous wastes into the environment but also from the
potential for overtopping to threaten the very stability of the
dike itself; leading to a possible complete washout with
accompanying catastrophic results. Nevertheless, there are
some events, including storm events with greater than a 100
year severity, that separately or in combination can result in
overtopping, which must be ignored as a practical matter. Many
of these border on the absurd such as the remote possibility of
an airplance crash in the impoundment. Others are improbable
combinations of events such as the possibility that all liquid
containing storage tanks in a manufacturing operation will
break at once, releasing their contents to the sewer system
feeding the impoundment, causing it to overflow. EPA does
intend such events to be protected against. Judgement must be
exercised during the permit process in dealing with the more
remote possibilities.
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APPENDIX A
METHODS FOR DETERMINING SATURATED
HYDRAULIC CONDUCTIVITY, SATURATED
LEACHATE CONDUCTIVITY, AND
INTRINSIC PERMEABILITY
-------
TABLE OF CONTENTS
Page
1.0 INTRODUCTION 1-1
1.1 SCOPE AND APPLICATION 1-1
1.2 DEFINITIONS 1-5
1.2.1 Units 1-5
1.2.2 Fluid potential or head . 1-6
1.2.3 Hydraulic potential or head 1-6
1.2.4 Hydraulic conductivity 1-6
1.2.5 Fluid conductivity 1-7
1.2.6 Leachate conductivity 1-8
1.2.7 Aquifer 1-8
1.2.8 Confining layer 1-8
1.2.9 Transraissivity 1-8
1.3 TEMPERATURE AND VISCOSITY CORRECTIONS 1-9
1.4 INTRINSIC PERMEABILITY 1-10
1.5 RANGE OF VALIDITY OF DARCY'S LAW 1-10
1.6 METHOD CLASSIFICATION 1-12
2.0 LABORATORY METHODS 2-1
2.1 SAMPLE COLLECTION FOR LABORATORY METHODS . . . 2-1
2.2 CONSTANT-HEAD METHODS 2-1
2.3 FALLING-HEAD METHODS 2-3
2.4 GENERAL TEST CONSIDERATIONS 2-5
2.4.1 Fluid Supplies to be Used 2-5
2.4.2 Pressure and Fluid Potential Measurement 2-6
2.5 CONSTANT-HEAD TEST WITH CONVENTIONAL
PERMEAMETER 2-6
2.5.1 Applicability 2-6
2.5.2 Apparatus 2-7
2.5.3 Sample Preparation 2-7
2.5.4 Test Procedure 2-9
2.5.5 Calculations 2-10
-------
TABLE OF CONTENTS (Continued)
2.6 FALLING-HEAD TEST WITH CONVENTIONAL
PERMEAMETER 2-10
2.6.1 Applicability 2-10
2.6.2 Apparatus 2-10
2.6.3 Sample Preparation 2-11
2.6.4 Test Procedure 2-11
2.6.5 Calculations 2-11
2.7 MODIFIED COMPACTION PERMEAMETER METHOD .... 2-12
2.7.1 Applicability 2-12
2.7.2 Apparatus 2-12
2.7.3 Sample Preparation 2-12
2.7.4 Test Procedure 2-13
2.7.5 Calculations 2-13
2.8 TRIAXIAL-CELL METHOD WITH BACK PRESSURE .... 2-13
2.8.1 Applicability 2-13
2.8.2 Apparatus . '. 2-15
2.8.3 Sample Preparation 2-15
2.8.4 Test Procedure 2-15
2.8.5 Calculations 2-19
2.9 PRESSURE-CHAMBER PERMEAMETER METHOD 2-19
2.9.1 Applicability 2-19
2.9.2 Apparatus 2-19
2.9.3 Sample Preparation 2-19
2.9.4 Test Procedure 2-21
2.9.5 Calculations 2-21
2.10 SOURCES OF ERROR FOR LABORATORY TEST FOR
HYDRAULIC CONDUCTIVITY 2-21
2.11 LEACHATE CONDUCTIVITY USING LABORATORY METHODS 2-23
2.11.1 Applicability 2-23
2.11.2 Leachate Used 2-24
2.11.3 Safety 2-24
2.11.4 Procedures 2-25
2.11.5 Apparatus 2-25
2.11.6 Measurements 2-25
2.11.7 Calculations 2-26
ii
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TABLE OF CONTENTS (Continued)
Page
3.0 FIELD METHODS 3-1
3.1 WELL-CONSTRUCTION CONSIDERATIONS 3-2
3.1.1 Well Installation Methods 3-2
3.1.2 Wells Requiring Well Screens 3-3
3.1.3 Wells Not Requiring Well Screens .... 3-5
3.2 WELL DEVELOPMENT 3-5
3.3 DATA INTERPRETATION AND TEST SELECTION
CONSIDERATIONS 3-6
3.4 SINGLE WELL TESTS 3-8
3.4.1 Method for Moderately Permeable
Formations Under Confined Conditions . . 3-8
3.4.2 Methods for Extremely Tight Formations
Under Confined Conditions 3-13
3.4.3 Methods for Moderately Permeable
Materials Under Unconfined
Conditions 3-17
3.5 MULTIPLE WELL TESTS 3-22
3.6 ESTIMATES OF HYDRAULIC CONDUCTIVITY FOR
COARSE-GRAINED MATERIALS 3-22
3.7 CONSOLIDATION TESTS 3-25
3.8 FRACTURED MEDIA 3-26
4.0 CONCLUSION 4-1
5.0 REFERENCES 5-1
6.0 APPENDIX A 6-1
iii
-------
TABLE OF CONTENTS (Continued)
LIST OF TABLES
Table No. Page
A HYDRAULIC AND LINER CONDUCTIVITY
DETERMINATION REQUIREMENTS FOR SURFACE
IMPOUNDMENTS, WASTE PILES, AND LANDFILL
COMPONENTS, AS CITED IN RCRA GRUIDANCE
DOCUMENTS AND DESCRIBED IN SW-846 .... 1-2
B SUMMARY OF PUBLISHED DATA ON POTENTIAL
ERRORS IN USING DATA FROM LABORATORY
PERMEABILITY TESTS ON SATURATED SOILS . . . 2-22
C HYDRAULIC CONDUCTIVITIES ESTIMATED FROM
GRAIN-SIZE DESCRIPTIONS 3-24
LIST OF FIGURES
Figure No.
1 PRINCIPLE OF THE CONSTANT HEAD METHOD . . . 2-3
2 PRINCIPLE OF THE FALLING HEAD METHOD . . . 2-4
3 APPARATUS SETUP FOR THE CONSTANT HEAD
AND FALLING HEAD METHODS 2-8
4 MODIFIED COMPACTION PERMEAMETER 2-14
5 SCHEMATIC DIAGRAM OF TYPICAL TRIAXIAL
COMPRESSION APPARATUS FOR
HYDRAULIC CONDUCTIVITY TESTS WITH
BACK PRESSURE 2-15
6 PRESSURE CHAMBER FOR HYDRAULIC
CONDUCTIVITY 2-20
7 GEOMETRY AND VARIABLE DEFINITION FOR
SLUG TESTS IN CONFINED AQUIFERS 3-10
8 SCHEMATIC DIAGRAM FOR PRESSURIZED
SLUG TEST METHOD 3-15
9 VARIABLE DEFINITIONS FOR SLUG TESTS
IN UNCONFINED MATERIALS 3-18
10 CURVES DEFINING COEFFICIENTS A, B, AND C
to L/rw 3-21
iv
-------
METHOD SW-846
SATURATED HYDRAULIC CONDUCTIVITY,
SATURATED LEACHATE CONDUCTIVITY, AND
INTRINSIC PERMEABILITY
1.0 INTRODUCTION
1.1 SCOPE AND APPLICATION
This section presents methods available to hydrogeologists and
geotechnical engineers for determining the saturated hydraulic
conductivity of earth materials and conductivity of soil liners
to leachate, as outlined by the Part 264 permitting rules for
hazardous-waste disposal facilities. In addition, a general
technique to determine intrinsic permeability is provided. A
cross reference between the applicable parts of the RCRA
Guidance Documents and associated Part 264 Standards and these
test methods is provided by Table A.
Part 264 Subpart F establishes standards for ground-water
quality monitoring and environmental performance. To
demonstrate compliance with these standards, a permit applicant
must have knowledge of certain aspects of the hydrogeology
at the disposal facility, such as hydraulic conductivity, in
order to determine the compliance point and monitoring well
locations and in order to develop remedial action plans when
necessary.
In this report, the laboratory and field methods that are con-
sidered the most appropriate to meeting the requirements of
-------
1-2
TABLE A
HYDRAULIC AND LINER CONDUCTIVITY DETERMINATION
METHODS FOR SURFACE IMPOUNDMENT
WASTE PILE, AND LANDFILL COMPONENTS, AS CITED
IN RCRA GUIDANCE DOCUMENTS AND DESCRIBED IN SW-846
Surface Impoundments
Guidance
Associated Regulation
Corresponding
SW-846
Section
Soil liner hydraulic
conductivity
Guidance section D{2)(b)(1)
and D(2)(c)(1)/Section
264.221(a),(b)
2.0
Soil liner leachate
conductivity
Guidance section D(2) (b)(2)
and D(2)(c)(2)
-2.11
Leak detection system
Guidance section C(2)(a)/
Section 264.222
2.0
Final cover drain
layer
Final cover low
permeability layer
Guidance section E(2)(d)(I)/
Section 264.228
Guidance section E(2)(e)(2)(A)/
Section 264.228
2.0
2.0
General Hydrogeologic
site investigation
264 subpart F
3.0
RCRA Guidance Document: Surface Impoundments, Liner Systems,
Final Cover, and Freeboard Control. Issued July, 1982.
-------
1-3
Waste Piles
.„
Guidance Cite—'
Associated Regulation
Corresponding
SW-846
Section
Soil liner hydraulic
conductivity
Guidance section D(2)(b)(i)
and D(2)(c) (i)/
Section 264.251(a)(1)
2.0
Soil liner leachate
conductivity
Guidance section D(2)(b)(ii)
and D(2)(c)(ii)
2.11
Leak Detection
System
Guidance section C{2)(a)/
Section 264.252 (a)
2.0
Leachate collection
and renewal system
Guidance section C(2)(a)/
Section 264.251 (a) (2)
2.0
General hydrogeologic
site investigation
264 subpart F
3.0
-'RCRA Guidance Document: Waste Pile Design, Liner Systems.
Issued July»- 1982.
-------
1-4
Landfills
Guidance Cite—
Associated Regulation
Corresponding
SW-846
Section
Soil liner hydraulic
conductivity
Guidance section D(2)(b)(I)/
Section 264.301(a)(1)
2.0
Soil liner leachate
conductivity
Guidance section D(2) (b)(2)
2.11
Leak detection
system
Guidance section C(2) (a)/
Section 264.302(a)(3)
2.0
Leachate collection and Guidance section C(2)(a)/
removal system Section 264.301(a)(2)
2.0
Final cover drain
layer
Guidance section E(2)(d)(I)/
Section 264.310(a)(b)
2.0
Final cover low
permeability layer
Guidance section E(2)(e)(2)(A)
Section 264.310(a)(b)
2.0
General hydrogeologic
site investigation
264 subpart F
3.0
-/RCRA Guidance Document: Landfill Design, Liner Systems and
Final Cover. Issued July, 1982.
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1-5
Part 264 are given in sufficient detail to provide an
experienced hydrogeologist or geotechnical engineer with the
methodology required to conduct the tests. Additional labora-
tory and field methods that may be applicable under certain
conditions are included by providing reference to standard
texts and scientific journals.
Included in this report are descriptions of field methods con-
sidered appropriate for estimating saturated hydraulic conduc-
tivity by single well or borehole tests. The determination of
hydraulic conductivity by pumping or injection tests is not
included because the latter are considered appropriate for well
field design purposes but may not be appropriate for economi-
cally evaluating hydraulic conductivity for the purposes set
forth in part 264 Subpart F.
EPA is not including methods for determining unsaturated
hydraulic conductivity at this time because the Part 264 per-
mitting standards do not require such determinations.
1.2 DEFINITIONS
This section provides definitions of terms used in the remainder
of this report. These definitions are taken from U.S. Govern-
ment publications when possible.
1?2.1 Units; This report uses consistent units in all
equations. The symbols used are:
Length = L,
Mass = M, and
Time = T.
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1-6
1.2.2 Fluid Potential or head (h) is a measure of the poten-
tial energy required to move fluid from a point in the porous
medium to a reference point. For virtually all situations
expected to be found in disposal sites and in ground-water
systems, h is defined by the following equation:
h = hp + hz (1)
where
h is the total fluid potential, expressed as
a height of fluid above a reference datum, L;
hp is the pressure potential caused by the
weight of fluid above the point in question, L.
hp is defined by hp = P/pg,
where
P is the fluid pressure at the point in question,
ML-lT-2,
p is the fluid density at the prevailing tempera-
ture, ML" 3,
g is the acceleration of gravity, LT~2, and
hz is the height of the point in question above
the reference datum, L.
By knowing hp and hz at two points along a flow path
and by knowing the distance between these points,
the fluid potential gradient can be determined.
1.2.3 Hydraulic potential or head is the fluid potential when
water is the fluid.
1.2.4 Hydraulic conductivity is the fluid conductivity when
water is the fluid. The generic terra, fluid conductity, is
discussed below in 1.2.5.
-------
1-7
1.2.5 Fluid conductivity is defined as the volume of fluid at
the prevailing density and dynamic viscosity that will move in
a unit time under a unit fluid potential gradient through a
unit area measured at right angles to the direction of flow.
It is a property of both the fluid and the porous medium as
shown by the following equation:
(2)
where
K is the fluid conductivity,
k is the intrinsic permeability, a property of
the porous medium alone, L~2«
u is the dynamic viscosity of the fluid at the
prevailing temperature, ML~1 T~l.
The fluid conductivity of a porous material is also defined by
Darcy's law, which states that the fluid flux (q) through a
porous medium is proportional to the first power of the fluid
potential across the unit area:
q - - KI, (3)
A
where
q » the specific fluid flux, LT~1,
Q is the volumetric fluid flux, L3T-1,
A is the cross-sectional area, L2, and
I is the fluid potential gradient, L°.
-------
1-8
Darcy's law provides the basis for all methods used to deter-
mine hydraulic conductivity discussed in this report. The
range of validity of Darcy's law is discussed in Section 1.4
(Lohman, 1972).
1.2.6 Leachate conductivity is the fluid conductivity when
leachate is the fluid.
1.2.7 Aquifer is a geologic formation, group of formations, or
part of a formation capable of yielding a significant amount of
ground water to wells or springs (40 CFR 260.10).
1.2.8 Confining layer is a body of impermeable material stra-
tigraphically adjacent to one or more aquifers. In nature,
however, its hydraulic conductivity may range from nearly zero
to some value distinctly lower than that of the aquifer. Its '
conductivity relative to that of the aquifer it confines should
be specified or indicated by a suitable modifier, such as
slightly permeable or moderately permeable (Lohman, 1972).
1.2.9 Transmissivity, T [L^, T~l], is the rate at which water
of the prevailing kinematic viscosity is transmitted through a
unit width of the aquifer under a unit hydraulic gradient.
Although spoken of as a property of the aquifer, the term also
includes the saturated thickness of the aquifer and the proper-
ties of the fluid. It is equal to an integration of the
hydraulic conductivities across the saturated part of the
aquifer perpendicular to the flow paths (Lohman, 1972).
-------
1-9
1.3 TEMPERATURE AND VISCOSITY CORRECTIONS
By using Equation 2, corrections to conditions different from
those prevailing during the test can be made. Two types of
corrections can commonly be made: a correction for a tem-
perature that varies from the test temperature, and a correc-
tion for fluids other than that used for the test. The tem-
perature correction is defined by:
Kf
*t "t Pf , (4)
Wf Pt
where
the subscript f refers to field conditions, and
t refers to test conditions.
Most temperature corrections are necessary because of the
viscosity dependence on temperature. Fluid density variations
caused by temperature changes are usually very small for most
liquids. The temperature correction for water can be signifi-
cant. A temperature decrease from 75°C to 10°C results in a
68 percent reduction in viscosity and hence hydraulic conduc-
tivity. Equation 4 can also be used to determine hydraulic
conductivity if fluids other than water are used. It is
assumed, however, when using Equation 4 that the fluids used
do not alter the intrinsic permeability of the porous medium
during the test. Experimental evidence exists that shows that
this alteration occurs with a wide range of organic solvents
(Anderson and Brown, 1981). Consequently, it is recommended
-------
1-10
that tests be run using fluids, such as leachates, that might
occur at each particular disposal site. Special considerations
for using non-aqueous fluids are given in Section 3.3 of this
report.
1.4 INTRINSIC PERMEABILITY
Rearrangement of Equation 2 results in a definition of intrin-
sic permeability.
. (5)
pg
Since this is a property of the medium alone, if fluid proper-
ties change, the fluid conductivity must also change to keep
the intrinsic permeability a constant. By using measured fluid
conductivity, and values of viscosity and density for the fluid
at the test temperature, intrinsic permeability can be determined,
1.5 RANGE OF VALIDITY OF DARCY'S LAW
Determination of fluid conductivities using both laboratory and
field methods requires assuming the validity of Darcy's law.
Experimental evidence has shown that deviations from the linear
dependence of fluid flux on potential gradient exist for both
extremely low and extremely high gradients (Hillel, 1971;
Freeze and Cherry, 1979). The low gradient limits are the
result of the existence of threshold gradients required to ini-
tiate flow (Swartzendruber, 1962). The upper limits to the
validity of Darcy's law can be estimated by the requirements
-------
1-11
that the Reynolds number, Re, in most cases be kept below 10
(Bear, 1972). The Reynolds number is defined by:
Re=^, (6)
where
d is some characteristic dimension of the
system, often represented by the median grain
size diameter, DKQ, (Bouwer, 1978), and
q is the fluid flux per unit area, LT~1.
For most field situations, the Reynolds number is less than -
one, and Darcy's law is valid. However, for laboratory tests
it may be possible to exceed the range of validity by the impo-
sition of high potential gradients. A rough check on accep-
table gradients can be made by substituting Darcy's law in
Equation 6 and using an upper limit of 10 for Re:
, (7)
pKDso
where
K is the approximate value of fluid conductivity
determined at gradient I.
A more correct check on the validity of Darcy's law or the
range of gradients used to determine fluid conductivity would
be to measure the conductivity at three different gradients.
If a plot of fluid flux versus gradient is linear, Darcy's law
can be considered to be valid for the test conditions.
-------
1-12
1.6 METHOD CLASSIFICATION
This report classifies methods to determine fluid conductivity
into two divisions: laboratory and field methods. Ideally,
compliance with the Part 264 disposal facility requirements
should be evaluated by using field methods that test the
materials under in-situ conditions whenever possible. In
general, field methods can usually provide more representative
values than laboratory methods because they test a larger
volume of material, thus integrating the effects of macro-
structure and heterogeneities. However, field methods pre-
sently available to determine the conductivity of compacted -
fine-grained materials in reasonable times require the tested
interval to be below a water table, to be fairly thick, or to
require excavation of the material to be tested at some point
in the test. The integrity of liners and covers should not be
compromised by the installation of boreholes or piezometers
required for the tests. These restrictions generally result in
the requirement to determine the fluid conductivity of liner
and cover materials in the laboratory. The transfer value of
laboratory data to field conditions can be maximized for liners
and covers because it is possible to reconstruct relatively
accurately the desired field conditions in the laboratory.
However, field conditions that would alter the values deter-
mined in the laboratory need to be addressed in permit applica-
tions. These conditions include those that would increase con-
ductivity by the formation of microcracks and channels by
repeated wetting and drying, and by the penetration of roots.
-------
1-13
Laboratory methods are categorized in Section 2.0 by the
methods used to apply the fluid potential gradient across the
sample. The discussion of the theory, measurement, and com-
putations for tests run under constant and falling-head con-
ditions is followed by a detailed discussion of tests using
specific types of laboratory apparatus and the applicability of
these tests to remolded compacted, fine-grained uncompacted,
and coarse-grained porous media. Section 2.3 provides a
discussion of the special considerations for conducting
laboratory tests using non-aqueous permeants. Section 2.10
gives a discussion of the sources of error and guidance for -
establishing the precision of laboratory tests.
Field methods are discussed in Section 3.0 and are limited to
those requiring a single bore hole or piezometer. Methods
requiring multiple bore holes or piezometers and areal methods
are included by reference. Because of the difficulties in
determining fluid conductivity of in-place liner and cap
materials under field conditions without damaging their
integrity, the use of field methods for fine-grained materials
will be generally restricted to naturally occurring materials
that may serve as a barrier to fluid movement. Additional
field methods are referenced that allow determination of
saturated hydraulic conductivity of the unsaturated materials
above the shallowest water table. General methods for frac-
tured media are given in Section 3.8.
-------
1-14
A discussion of the important considerations in well installa-
tion, construction, and development is included as an introduc-
tion to Section 3.0.
-------
2-1
2.0 LABORATORY METHODS
2.1 SAMPLE COLLECTION FOR LABORATORY METHODS
To assure that a reasonable assessment is made of field con-
ditions at a disposal site, a site investigation plan should be
developed to direct sampling and analysis. This plan generally
requires the professional judgment of an experienced hydro-
geologist or geotechnical engineer. General guidance is pro-
vided for plan development in the Guidance Manual for
Preparation of a Part 264 Land Disposal Facility Permit
Application (EPA, in press). The points listed below should
be followed:
o The hydraulic conductivity of a soil liner should be deter-
mined either from samples that are processed to simulate
the actual liner, or from an undisturbed sample of the
complete liner.
To obtain undisturbed samples, the thin-walled tube sampling
method (ASTM Method f D1587-74) or a similar method may be
used. Samples representative of each lift of the liner
should be obtained, and used in the analyses. If actual
undisturbed samples are not used, the soil used in liner
construction must be processed to represent accurately
the liner's initial water content and bulk density. The
method described in Section 2.7.3 or ASTM Method ID698-70
(ASTM, 1978) can be used for this purpose.
o For purposes of the general site investigation, the general
techniques presented in ASTM method ID420-69 (ASTM, 1978)
should be followed. This reference establishes practices
for soil and rock investigation and sampling, and incorporates
various detailed ASTM procedures for investigations, sampling,
and material classification.
2.2 CONSTANT-HEAD METHODS
The constant-head method is the simplest method to determine
hydraulic conductivity of saturated soil samples. The concept
of the constant-head method is schematically illustrated in
-------
2-2
Figure 1. The inflow of fluid is maintained at a constant
head (h) above a datum and outflow (Q) is measured as a func-
tion of time (t). Using Darcy's law, the hydraulic conduc-
tivity can be determined using the following equation after the
outflow rate has become constant:
K = QL/hA, (8)
where
K = hydraulic conductivity, LT~1
L = length of sample, L
A = cross-sectional area of sample, L,2
Q = outflow rate, L^T1
h = fluid head difference across the sample, L
Constant-head methods should be restricted to tests on media
having high fluid conductivity.
2.3 FALLING-HEAD METHODS
A schematic diagram of the apparatus for the falling-head
method is shown in Figure 2. The head of inflow fluid
decreases from hj to h2 as a function of time (t) in a standpipe
directly connected to the specimen. The fluid head at the
outflow is maintained constant. The quantity of outflow can be
measured as well as the quantity of inflow. For the setup shown
in Figure 2a, the hydraulic conductivity can be determined
using the following equation:
^_
At -10 hi
-------
2-3
WATER SUPPLY
D
OVERFLOW
TO MAINTAIN
CONSTANT HEAD
T
L
— A-
SCR
EE N—'
GRADUATED
CYLINDER
Figure 1.—Principle of the constant head method
-------
2-4
STANDPIPE — »•
rT"
~ -^— "
*s
i
«<— d
^
v. D : :
: ; •"_•'.
i
i
h0
j
--!r=^j i
hl
1
L
OVERFLOW ^
' <^
J
r
ho
P
~=_=~ •=
7
'• o'-'
•V":v
__ ^^
(a)
(b)
A -
Figure 2.—Principle of the falling head method
using a small (a) and large (b) standpipe.
-------
2-5
where
a = the cross-sectional area of the standpipe, L2
A = the cross-sectional area of the specimen, L2
L = the length of the specimen, L
t = elapsed time from t^ to t2/ T.
For the setup shown in Figure 2b, the term a/A in Equation 9 is
replaced by 1.0. Generally, falling-head methods are applicable
to fine-grained soils because the testing time can be accelerated,
2.4 GENERAL TEST CONSIDERATIONS
2.4.1 Fluid Supplies to be Used
For determining hydraulic conductivity and leachate conduc-
tivity, the supplies of permeant fluid used should be de-aired.
Air coming out of solution in the sample can significantly
reduce the measured fluid conductivity. Deairing can be
achieved by boiling the water supply under a vacuum, bubbling
helium gas through the supply, or both.
Significant reductions in hydraulic conductivity can also occur
in the growth and multiplication of microorganisms present in
the sample. If it is desirable to prevent such growth, a bac-
tericide or fungicide, such as 2000 ppm formaldehyde or 1000 ppm
phenol (Olsen and Daniel, 1981), can be added to the fluid supply,
Fluid used for determining hydraulic conductivity in the labora-
tory should never be distilled water. Native ground water from
the aquifer underlying the sampled area or water prepared to
simulate the native ground-water chemistry should be used.
-------
2-6
2.4.2 Pressure and Fluid Potential Measurement
^
The equations in this report are all dimensionally correct;
that is, any consistent set of units may be used for length,
mass, and time. Consequently, measurements of pressure and/or
fluid potential using pressure gages and manometers must be
reduced to the consistent units used before applying either
Equation 8 or 9. Pressures or potentials should be measured
to within a few tenths of one percent of the gradient applied
across the sample.
2.5 CONSTANT-HEAD TEST WITH CONVENTIONAL PERMEAMETER
2.5.1 Applicability
This method covers the determination of the hydraulic conduc-
tivity of soils by a constant-head method using a conventional
permeameter. This method is recommended for disturbed coarse-
grained soils. If this method is to be used for fine-grained
soils, the testing time may be prohibitively long. This method
was taken from the Engineering and Design, Laboratory Soils
Testing Manual (U.S. Army, 1980). It parallels ASTM Method
D2434-68 (ASTM, 1978). The ASTM method gives extensive
discussion of sample preparation and applicability and should
be reviewed before conducting constant-head tests. Lambe (1951)
provides additional information on sample preparation and
equipment procedures.
-------
2-7
2.5.2 Apparatus
The apparatus is shown schematically in Figure 3. It consists
of the following:
a. A permeameter cylinder having a diameter at least
8 times the diameter of the largest particle of the
material to be tested,
b. Constant-head filter tank,
c. Perforated metal disks and circular wire to support
the sample,
d. Filter materials such as Ottawa sand, coarse sand, and
gravel of various gradations,
e. Manometers connected to the top and bottom of the sample,
f. Graduated cylinder, 100 ml capacity,
g. Thermometer,
h. Stop watch,
i. Deaired water,
j. Balance sensitive to 0.1 gram, and
k. Drying oven.
2.5.3 Sample Preparation
1. Oven-dry the specimen. Allow it to cool, and weigh to the
nearest 0.1 g. Record the oven-dry weight of material on a
data sheet as Ws. The amount of material should be sufficient
to provide a specimen in the permeameter having a minimum
length of about one to two times the diameter of the specimen.
2. Place a wire screen, with openings small enough to retain
the specimen, over a perforated disk near the bottom of the
permeameter above the inlet. The screen openings should be
approximately equal to the 10 percent size of the specimen.
3. Allow deaired water to enter the water inlet of the
permeameter to a height of about 1/2 in. above the bottom
of the screen, taking care that no air bubbles are trapped
under the screen.
-------
2-8
Conttant
Heed Tenk
Screen
Perforated
O Ite & Screen
-=• Cylinder
1
ted
r
;••-
1
•
V alve
A|-
=?>
Standplpe
C.^,
I1
If
e ]
.
^
S
•«
V
H
-
Fl
M t
creen.
live
B
De - Aired
Water Supply
Therm o- '
F liter [\ m eter
D Iteherge
A Level
Witt*
Perforated
O lie & Scraar
Ca)
constant head
Watte
(b)
falling head
Figure 3.— Apparatus setup for the constant head (a)
and falling head (b) methods.
-------
2-9
4. Mix the material thoroughly and place in the permeameter to
avoid segregation. The material should be dropped just at
the water surface/ keeping the water surface about 1/2 in.
above the top of the soil during placement. A funnel or a
spoon is convenient for this purpose.
5. The placement procedure outlined above will result in a
saturated specimen of uniform density although in a rela-
tively loose condition. To produce a higher density in the
specimen, the sides of the permeameter containing the soil
sample are tapped uniformly along its circumference and
length with a rubber mallet to produce an increase in
density; however, extreme caution should be exercised so
that fines are not put into suspension and segregated
within the sample. As an alternative to this procedure,
the specimen may be placed using an appropriate sized
funnel or spoon. Compacting the specimen in layers is
not recommended as a film of dust may be formed at the
surface of the compacted layer which might affect the
permeability results. After placement, apply a vacuum
to the top of the specimen and permit water to enter the
evacuated specimen through the base of the permeameter.
6. After the specimen has been placed, weigh the excess
material, if any, and the container. The specimen weight
is the difference between the original weight of sample and
the weight of the excess material. Care must be taken so
that no material is lost during placement of the specimen.
If there is evidence that material has been lost, oven-dry
the specimen and weigh after the test as a check.
7. -Level the top of the specimen, cover with a wire screen
similar to that used at the base, and fill the remainder of
the permeameter with a filter material.
8. Measure the length of the specimen, inside diameter of the
permeameter, and distance between the centers of the
manometer tubes (L) where they enter the permeameter.
2.5.4 Test Procedure
1. Adjust the height of the constant-head tank to obtain the
desired hydraulic gradient. The hydraulic gradient should
be selected so that the flow through the specimen is lami-
nar. Hydraulic gradients ranging from 0.2 to 0.5 are recom-
mended. Too high a hydraulic gradient may cause turbulent
flow and also result in piping of soils. In general,
coarser soils require lower hydraulic gradients. See
Section 1.5 for further discussion of excessive gradients.
2. Open valve A (see Figure 3a) and record the initial
piezometer readings after the flow has become stable.
Exercise care in building up heads in the permeameter
so that the specimen is not disturbed.
-------
2-10
3. After allowing a few minutes for equilibrium conditions to
be reached, measure by means of a graduated cylinder the
quantity of discharge corresponding to a given time inter-
val. Measure the piezometric heads (hi and h2) and the
water temperature in the permeameter.
4. Record the quantity of flow, piezometer readings, water
temperature, and the time interval during which the quan-
tity of flow was measured.
2.5.5 Calculations
By plotting the accumulated quantity of outflow versus time on
rectangular coordinate paper, the slope of the linear portion
of the curve can be determined, and the hydraulic conductivity
can be calculated using Equation (8). The value of h in
Equation 8 is the difference between hj and h2«
2.6 FALLING-HEAD TEST WITH CONVENTIONAL PERMEAMETER
2.6.1 Applicability
The falling-head test can be used for all soil types, but is
usually most widely applicable to materials having low per-
meability. Compacted, remolded, fine-grained soils can be tested
with this method. The method presented is taken from the
Engineering and Design, Laboratory Soils Testing Manual (U.S.
Army, 1980).
2.6.2 Apparatus
The schematic diagram of falling-head permeameter is shown in
Figure 3b. The permeameter consists of the following equipment:
(1) Permeameter cylinder - a transparent acrylic cylinder
having a diameter at least 8 times the diameter of the
largest particles,
(2) Porous disk,
-------
2-11
(3) Wire screen,
(4) Filter materials,
(5) Manometer,
(6) Timing device, and
(7) Thermometer.
2.6.3 Sample Preparation
Sample preparation for coarse-grained soils is similar to that
described previously in Section 2.4.3. For fine-grained
soils, samples are compacted to the desired density using
methods described in ASTM Method D698-70.
2.6.4 Test Procedure
1. Measure and record the height of the specimen, L, and the
cross-sectional area of the specimen, A.
2. With valve B open (see Figure 3b), crack valve A, and slowly
bring the water level up to the discharge level of the
permeameter.
3. Raise the head of water in the standpipe above the
discharge level of the permeameter. The difference in head
should not result in an excessively high hydraulic gradient
during the test. Close valves A and B.
4. Begin the test by opening valve B. Start the timer. As
the water flows through the specimen, measure and record
the height of water in the standpipe above the discharge
level, h]_, at time ti, and the height of water above the
discharge level, h£ at time t£.
5. Observe and record the temperature of the water in the
permeameter.
2.6.5 Calculations
From the test data, plot the logarithm of head versus time, on
rectangular coordinate paper or use semi-log paper. The slope
of the linear part of the- curve is used to determine
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2-12
Calculate the hydraulic conductivity using
Equation (9) .
2.7 MODIFIED COMPACTION PERMEAMETER METHOD
2.7.1 Applicability
This method can be used to determine the hydraulic conductivity
of a wide range of materials. The method is generally used for
remolded fine-grained soils. The method is generally used under
constant-head conditions. The method was taken from Anderson
and Brown, 1981, and EPA (1980).
2.7.2 Apparatus
The apparatus is shown in Figure 4 and consists of the equip-
ment and accessories as follows:
a. Soil Chamber - A compaction mold having a diameter
8 times larger than the diameter of the largest
particles. Typically, ASTM standard mold (Number CN405)
is used,
b. Fluid Chamber - A compaction mold sleeve having the
same diameter as the soil chamber,
c. 2 kg hammer,
d. Rubber rings used for sealing purposes,
e. A coarse porous stone having higher permeability than
the tested sample,
f. Regulated source of compressed air, and
g. Pressure gage or manometer to determine the pressure
on the fluid chamber.
2.7.3 Sample preparation
1. Obtain sufficient representative soil sample. Air dry the
sample at room temperature. Do not oven dry.
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(2). Thoroughly mix the selected representative sample with
water to obtain a desired moisture content.
(3). Compact the sample to the desired density within the
mold using the method described as part of ASTM Method
D698-70.
(4). Level the surface of the compacted sample with straight
edge, weigh and determine the density of the sample.
(5). Measure the length and diameter of the sample.
(6). Assemble the apparatus, make sure that there are no
leaks, then connect the pressure line to the apparatus.
2.7.4 Test Procedure
(1). Place sufficient volume of water in the fluid chamber
above the soil chamber.
(2). Air pressure must be applied gradually to flush water ,
through the sample until no air bubbles in the outflow
are observed. For fine-grained soils, the saturation
may take several hours to several days, depending on
the applied pressure.
(3). After the sample is saturated, measure and record the
quantity of outflow versus time.
(4). Record the pressure reading (h) on the top of the fluid
chamber when each reading is made.
(5). Plot the accumulated quantity of outflow versus time on
rectangular coordinate paper.
(6). Stop taking readings as soon as the linear portion of
the curve is defined.
2.7.5 Calculations
The hydraulic conductivity can be calculated using Equation 8.
2.8 TRIAXIAL-CELL METHOD WITH BACK PRESSURE
2.8.1 Applicability
This method is applicable for all soil types, but especially
for fine-grained, compacted, cohesive soils in which full fluid
saturation of the sample is difficult to achieve. Normally,
the test is run under, constant-head conditions.
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TO REGULATED PRESSURE SOURCE AND
PRESSURE GAGE OR MANOMETER USED TO
MEASURE H .
PRESSURE RELEASE VALVE
£* TOP PLATE
RUBBER "0" RING SEALS
BASE PLATE
OUTFLOW TO VOLUMETRIC MEASURING DEVICE.
PRESSURE SHOULD BE ATMOSPHERIC OR ZERO
GAGE PRESSURE
Figure 4.—Modified compaction permeameter.
Note: h in Equation 8 is the difference
between the regulated inflow pressure
and the outflow pressure. Source:
Anderson and Brown, 1981.
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2-15
2.8.2 Apparatus
The apparatus is similar to conventional triaxial apparatus.
The schematic diagram of this apparatus is shown in Figure 5.
2.8.3 Sample Preparation
Disturbed or undisturbed samples can be tested. Undisturbed
samples must be trimmed to the diameter of the top cap and
base of the triaxial cell. Disturbed samples should be prepared
in the mold using either kneading compaction for fine-grained
soils, or by the pouring and vibrating method for coarse-grained
soils, as discussed in Section 2.5.3.
2.8.4 Test Procedure
(1). Measure the dimensions and weight of the prepared sample.
(2). Place one of the prepared specimens on the base.
(3). Place a rubber membrane in a membrane stretcher, turn
both ends of the membrane over the ends of the stretcher,
and apply a vacuum to the stretcher. Carefully lower the
stretcher and membrane over the specimen as shown in
Figure 9. Place the specimen cap on the top of the
specimen and release the vacuum on the membrane stretcher.
Turn the ends of the membrane down around the base and
up around the specimen cap and fasten the ends with O-rings,
(4). Assemble the triaxial chamber and place it in position in
the loading device. Connect the tube from the pressure
reservoir to the base of the triaxial chamber. With
valve C (see Figure 5) on the pressure reservoir closed
and valves A and B open, increase the pressure inside the
reservoir, and allow the pressure fluid to fill the
triaxial chamber. Allow a few drops of the pressure fluid
to escape through the vent valve (valve B) to insure
complete filling of the chamber with fluid. Close valve A
and the vent valve.
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2-16
Figure 5.-
-Schematic diagram of typical triaxial compression
apparatus for hydraulic conductivity tests with
back pressure.
Source: U.S. Army Corps of Engineers, 1970
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2-17
(5). Place saturated filter paper disks having the same
diameter as that of the specimen between the specimen and
the base and cap; these disks will also facilitate remo-
val of the specimen after the test. The drainage lines
and the porous inserts should be completely saturated
with deaired water. The drainage lines should be as
short as possible and made of thick-walled, small-bore
tubing to insure minimum elastic changes in volume due to
changes in pressure. Valves in the drainage lines
(valves E, F, and G in Figure 5) should preferably be of
a type which will cause no discernible change of internal
volume when operated. While mounting the specimen in the
compression chamber, care should be exercised to avoid
entrapping any air beneath the membrane or between the
specimen and the base and cap.
(6). Specimens should be completely saturated before any
appreciable consolidation is permitted, for ease and
uniformity of saturation, as well as to allow volume
changes during consolidation to be measured with the
burette; therefore, the difference between the chamber
pressure and the back pressure should not exceed 5 psi -
during the saturation phase. To insure that a specimen
is not prestressed during the saturation phase, the back
pressure must be applied in small increments, with ade-
quate time between increments to permit equalization of
pore water pressure throughout the specimen.
(7). With all valves closed, adjust the pressure regulators to
a chamber pressure of about 7 psi and a back pressure of
about 2 psi. Now open valve A to apply the preset
pressure to the chamber fluid and simultaneously open
valve F to apply the back pressure through the specimen
cap. Immediately open valve G and read and record the
pore pressure at the specimen base. When the measured
pore pressure becomes essentially constant, close valves
F and G and record the burette reading.
(8). Using the technique described in step (3), increase the
chamber pressure and the back pressure in increments,
maintaining the back pressure at about 5 psi less than
the chamber pressure. The size of each increment might
be 5, 10, or even 20 psi, depending on the compressibi-
lity of the soil specimen and the magnitude of the
desired consolidation pressure. Open valve G and measure
the pore pressure at the base immediately upon applica-
tion of each increment of back pressure and observe the
pore pressure until it becomes essentially constant. The
time required for stabilization of the pore pressure may
range from a few minutes to several hours depending on
the permeability of the soil. Continue adding increments
of chamber pressure and back pressure until, under any
increment, the pore pressure reading equals the applied
back pressure immediately upon opening valve G.
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2-18
(9). Verify the completeness of saturation by closing valve
F and increasing the chamber pressure by about 5 psi.
The specimen shall not be considered completely
saturated unless the increase in pore pressure imme-
diately equals the increase in chamber pressure.
(10). When the specimen is completely saturated, increase the
chamber pressure with the drainage valves closed to
attain the desired effective consolidation pressure
(chamber pressure minus back pressure). At zero
elapsed time, open valves E and F.
(11). Record time, dial indicator reading, and burette
reading at elapsed times of 0, 15, and 30 sec, 1, 2, 4,
8, and 15 rain, and 1, 2, 4, and 8 hr, etc. Plot the
dial indicator readings and burette readings on an
arithmetic scale versus elapsed time on a log scale.
When the consolidation curves indicate that primary
consolidation is complete, close valves E and F.
(12). Apply a pressure to burette B greater than that in
burette A. The difference between the pressures in
burettes B and A is equal to the head loss (h); h divided
by the height of the specimen after consolidation (L)
is the hydraulic gradient. The difference between the
two pressures should be kept as small as practicable,
consistent with the requirement that the rate of flow
be large enough to make accurate measurements of the
quantity of flow within a reasonable period of time.
Because the difference in the two pressures may be very
small in comparison to the pressures at the ends of the
specimen, and because the head loss must be maintained
constant throughout the test, the difference between
the pressures within the burettes must be measured
accurately; a differential pressure gage is very useful
for this purpose. The difference between the eleva-
tions of the water within the burettes should also be
considered (1 in. of water = 0.036 psi of pressure).
(13). Open valves D and F. Record the burette readings at
any zero elapsed time. Make readings of burettes A and
B and of temperature at various elapsed times (the
interval between successive readings depends upon the
permeability of the soil and the dimensions of the
specimen). Plot arithmetically the change in readings
of both burettes versus time. Continue making readings
until the two curves become parallel and straight over
a sufficient length of time to determine accurately the
rate of flow as indicated by the slope of the curves.
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2.8.5 Calculations
The hydraulic conductivity can be calculated using Equation 8.
2.9 PRESSURE-CHAMBER PERMEAMETER METHOD
2.9.1 Applicability
This method can be used to determine hydraulic conductivity of
a wide range of soils. Undisturbed and disturbed samples can
be tested under falling-head conditions using this method.
This method is also applicable to both coarse- and fine-grained
soils, including remolded, fine-grained materials.
2.9.2 Apparatus
The apparatus, as shown in Figure 6, consists of
a. pressure chamber,
b. standpipe,
c. specimen cap and base, and
d. coarse porous plates.
The apparatus is capable of applying confining pressure to
simulate field stress conditions.
2.9.3 Sample Preparation
The sample preparation of disturbed and undisturbed conditions
can be prepared in the chamber and enclosed within the rubber
membrane, as discussed in Section 2.8.4.
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2-20
-HVtLIMC »ULi
mint*
NOTCCOWMCMIO AM U»€0
MICMtH LATIMAt
M M.ACI 0^ LCVtLINC «Uk»
Figure 6.-
-Pressure chamber for hydraulic
conductivity.
Source: U.S. Army Corps of Engineers,
1980.
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2-21
2.9.4 Test Procedure
(1). By adjusting the leveling bulb, a confining pressure is
applied to the sample such that the stress conditions
represent field conditions. For higher confining
pressure, compressed air may be used.
(2). Allow the sample to consolidate under the applied stress
until the end of primary consolidation.
(3). Flush water through the sample until no indication of
air bubbles is observed. For higher head of water,
compressed air may be used.
(4). Adjust the head of water to attain a desired hydraulic
gradient.
(5). Measure and record the head drop in the standpipe along
with elapsed time until the plot of logarithm of head
versus time is linear for more than three consecutive
readings.
2.9.5 Calculations
The hydraulic conductivity can be determined using Equation 9.
2.10 SOURCES OF ERROR FOR LABORATORY TEST FOR HYDRAULIC
CONDUCTIVITY
There are numerous potential sources of error in laboratory
tests for hydraulic conductivity. Table B summarizes some
potential errors that can occur. Olson and Daniel (1981) pro-
vide a more detailed explanation of sources of these errors and
methods to minimize them. If the hydraulic conductivity does
not fall within the expected range for the soil type, as given
in Table C, the measurement should be repeated after checking
the source of error in Table B.
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TABLE B
SUMMARY OF PUBLISHED DATA ON POTENTIAL ERRORS
IN USING DATA FROM
LABORATORY PERMEABILITY TESTS ON SATURATED SOILS
Source of Error and References
Measured K
Too Low or Too High?
1. Voids Formed in Sample Preparation
(Olson and Daniel, 1981).
2. Smear Zone Formed During Trimming
(Olson and Daniel, 1981).
3. Use of Distilled Water as a
Permeant (Fireman, 1944; and
Wilkinson, 1969).
4. Air in Sample (Johnson, 1954).
5. Growth of Micro-organisms
(Allison, 1947).
6. Use of Excessive Hydraulic
Gradient (Schwartzendruber, 1968;
and Mitchell and Younger, 1967).
7. Use of temperature other than the
test temperature.
8. Ignoring Volume Change Due to
Stress Change. (No confining
pressure used).
9. Performing Laboratory Rather
than In-Situ Tests (Olson and
Daniel, 1981).
10. Impedance caused by the test
apparatus, including the
resistance of the screen or
porous stone used to support
the sample.
High
Low
Low
Low
Low
Low or High
Varies
High
Usually low
Low
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2-23
2.11 LEACHATE CONDUCTIVITY USING LABORATORY METHODS
Many primary and secondary leachates found at disposal sites
may be nonaqueous liquids or aqueous fluids of high ionic
strength. These fluids may significantly alter the intrinsic
permeability of the porous medium. For example, Anderson and
Brown (1981) have demonstrated increases in hydraulic conduc-
tivity of compacted clays of as much as two orders of magnitude
after the passage of a few pore volumes of a wide range of
organic liquids. Consequently, the effects of leachate on these
materials should be evaluated by laboratory testing. The pre-
ceding laboratory methods can all be used to determine leachate
conductivity by using the following guidelines.
2.11.1 Applicability
The determination of leachate conductivity may be required for
both fine-grained and coarse-grained materials. Leachates may
either increase or decrease the hydraulic conductivity.
Increases are of concern for compacted clay liners, and
decreases are of concern for drain materials. The applicability
sections of the preceding methods should be used for selecting
an appropriate test for leachate conductivity. The use of the
modified compaction method (Section 2.7) for determining leachate
conductivity is discussed extensively in EPA Publication SW870
(EPA 1980).
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2-24
2.11.2 Leachate Used
A supply of leachate must be ootained that is as close in chemi-
cal and physical properties to the anticipated leachate at the
disposal site as possible. Methods for obtaining such leachate
are beyond the scope of this report. However, recent publications
by EPA (1980, SW-87U; 1982, SW-846) and Conway and Malloy (1981)
discuss methodologies for simulating the leaching environment
to obtain such leachate. Procedures for deairing the leachate
supply are given in Section 2.4. The importance of preventing
bacterial growth in leachate tests will depend on the expected
conditions at the disposal site. The chemical and physical
properties that may result in corrosion, dissolution, or
encrustation of laboratory hydraulic conductivity apparatus
should be determined prior to conducting a leachate conductivity
*- ~
test. Properties of particular importance are the pH and the
vapor pressure of the leachate. Both extremely acidic and
basic leachates may corrode materials. In general, apparatus
for leachate conductivity tests should be constructed of inert
materials, such as acrylic plastic, nylon, or teflon. Metal
parts that might come in contact with the leachate should be
avoided. Leachates with high vapor pressures may require
special treatment. Closed systems for fluid supply and pressure
measurement, such as those in the modified triaxial cell methods,
should be used.
2.11.3 Safety
Tests involving the use of leachates should be conducted under
a vented hood, and persons conducting the tests should wear
-------
2-25
appropriate protective clothing and eye protection. Standard
laboratory safety procedures such as those as given by
Manufacturing Chemists Association (1971) should be followed.
2.11.4 Procedures
The determination of leachate conductivity should be conducted
immediately following the determination of hydraulic conduc-
tivity (Anderson and Brown, 1981). This procedure maintains
fluid saturation of the sample, and allows a comparison of the
leachate and hydraulic conductivities under the same test
conditions. This procedure requires modifications of test
operations as described below.
2.11.5 Apparatus
In addition to a supply reservoir for water as shown in Figures
3 through 6, a supply reservoir for leachate is required.
Changing the inflow to the test cell from water to leachate can
be accomplished by providing a three-way valve in the inflow
line that is connected to each of the reservoirs.
2.11.6 Measurements
Measurements of fluid potential and outflow rates are the same
for leachate conductivity and hydraulic conductivity. If the
leachate does not alter the intrinsic permeability of the
sample, the criteria for the time required to take measurements
is the same for leachate conductivity tests as for hydraulic
conductivity tests. However, if significant changes occur in
the sample by the passage of leachate, measurements should be
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2-26
taken until either the shape of a conductivity versus pore
volume curve can be defined, or until the leachate conductivity
exceeds the applicable design value for hydraulic conductivity.
2.11.7 Calculations
If the leachate conductivity approaches a constant value,
Equations 8 and 9 can be used. If the conductivity changes con-
tinuously because of the action of the leachate, the following
modifications should be made. For constant-head tests, the
conductivity should be determined by continuing a plot of
outflow volume versus time for the constant rate part of the
test conducted with water. For falling-head tests/ the slope
of the logarithm of head versus time should be continued.
If the slope of either curve continues to change after the flow
of leachate begins, the leachate is altering the intrinsic per-
meability of the sample. The leachate conductivity in this
case is not a constant. In this case, values of the slope of
the outflow curve to use in Equation 8 or 9 must be taken as
the tangent to the appropriate outflow curve at the times of
measurement.
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3-1
3.0 FIELD METHODS
This section discusses methods available for the determination
of fluid conductivity under field conditions. As most of these
tests will use water as the testing fluid, either natural for-
mation water or water added to a borehole or piezometer, the
term hydraulic conductivity will be used for the remainder of
this section. However, if field tests are run with leachate or
other fluids, the methods are equally applicable.
The location of wells, selection of screened intervals, and the
appropriate tests that are to be conducted depend upon the spe-
cific site under investigation. The person responsible for
such selections should be a qualified hydrogeologist or
geotechnical engineer who is experienced in the application of
established principles of contaminant hydrogeology and ground
water hydraulics. The following are given as general guidelines.
(1). The bottom of the screened interval should be below the
lowest expected water level.
(2). Wells should be screened in the lithologic units that
have the highest probability of either receiving
contaminants or conveying them down gradient.
(3). Wells up gradient and down gradient of sites should be
screened in the same lithologic unit.
Standard reference texts on ground water hydraulics and con-
taminant hydrogeology that should be consulted include: Bear
(1972), Bouwer (1978), Freeze and Cherry (1979), Stallman
(1971), and Walton (1970).
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3-2
The success of field methods in determining hydraulic conduc-
tivity is often determined by the design, construction, and
development of the well or borehole used for the tests.
Details of these methods are beyond the scope of this report;
however, important considerations are given in Sections 3.1
and 3.2. Detailed discussions of well installation, construc-
tion, and development methods are given by Bouwer (1978),
pages 160-180, Acker (1974), and Johnson (1972).
The methods for field determination of hydraulic conductivity
are restricted to well or piezometer type tests applicable
below existing water tables. Determination of travel times of
leachate and dissolved solutes above the water table usually
require the application of unsaturated flow theory and methods
which are beyond the scope of this report.
3.1 WELL-CONSTRUCTION CONSIDERATIONS
The purpose of using properly constructed wells .for hydraulic
conductivity testing is to assure that test results reflect
conditions in the materials being tested, rather than the con-
ditions caused by well construction. In all cases, diagrams
showing all details of the actual well or borehole constructed
for the test should be made.
3.1.1 Well Installation Methods
Well installation methods are listed below in order of pre-
ference for ground-water testing and monitoring. The order was
determined by the need to minimize side-wall plugging by
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3-3
drilling fluids and to maximize the accurate detection of
saturated zones. This order should be used as a guide, com-
bined with the judgment of an experienced hydrogeologist in
selecting a drilling method. The combined uses of wells for
hydraulic conductivity testing, water-level monitoring, and
water-quality sampling for organic contaminants were considered
in arriving at the ranking.
a. Hollow-stem auger,
b. Cable tool,
c. Air rotary,
d. Rotary drilling with non-organic drilling fluids,
e. Air foam rotary, and
f. Rotary with organic based drilling fluids.
Although the hollow stem-auger method is usually preferred for
the installation of most shallow wells (less than 100 feet),
care must be taken if the tested zone is very fine. Smearing
of the borehole walls by drilling action can effectively seal
off the borehole from the adjacent formation. Scarification
can be used to remedy this.
3.1.2 Wells Requiring Well Screens
Well screens placed opposite the interval to be tested should
be constructed of materials that are compatible with the fluids
to be encountered. Generally an inert plastic such as PVC is
preferred for ground-water contamination studies. The screen
slot size should be determined to minimize the inflow of fine-
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3-4
grained material to the well during development and testing.
Bouwer (1978), and Johnson (1972) give a summary of guidelines
for sizing well screens.
The annulus between the well screen and the borehole should be
filled with an artificial gravel pack or sand filter.
Guidelines for sizing these materials are given by Johnson
(1972). For very coarse materials, it may be acceptable to
allow the materials from the tested zone to collapse around
the screen forming a natural gravel pack.
The screened interval should be isolated from overlying and -
underlying zones by materials of low hydraulic conductivity.
Generally, a short bentonite plug is placed on top of the
material surrounding the screen, and cement grout is placed in
the borehole to the next higher screened interval (in the case
of multiple screen wells), or to the land surface for single
screen wells.
Although considerations for sampling may dictate minimum casing
and screen diameters, the recommended guideline is that wells
to be tested by pumping, bailing, or injection in coarse-grained
materials should be at least 4-inches inside diameter. Wells
to be used for testing materials of low hydraulic conductivity
by sudden removal or injection of a known volume of fluid should
be constructed with as small a casing diameter as possible to
maximize measurement resolution of fluid level changes. Casing
sizes of 1.25 to 1.50 inches usually allow this resolution
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3-5
while enabling the efficient sudden withdrawal of water for
these tests.
3.1.3 Wells Not Requiring Well Screens
If the zone to be tested is sufficiently indurated that a well
screen and casing is not required to prevent caving then, it is
preferable to use a borehole open to the zone to be tested.
These materials generally are those having low to extremely low
hydraulic conductivities. Consolidated rocks having high
conductivity because of the presence of fractures and solution
openings may also be completed without the use of a screen and
gravel pack. Uncased wells may penetrate several zones for
which hydraulic conductivity tests are to be run. In these
cases, the zones of interest can be isolated by the use of
inflatable packers.
3.2 WELL DEVELOPMENT
For wells that are constructed with well screens and gravel
packs, and for all wells in which drilling fluids have been
used that may have penetrated the materials to be tested, ade-
quate development of the well is required to remove these
fluids and to remove the fine-grained materials from the zone
around the well screen. Development is carried out by methods
such as intermittent pumping, jetting with water, surging, and
bailing. Adequate development is required to assure maximum
communication between fluids in the borehole and the zone to be
tested. Results from tests run in wells that are inadequately
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3-6
developed will include an error caused by loss of fluid poten-
tial across the undeveloped zone, and computed hydraulic con-
ductivities will be lower than the actual value. Bouwer (1978)
and Johnson (1975) give further details on well development
including methods to determine when adequate development has
occurred.
3.3 DATA INTERPRETATION AND TEST SELECTION CONSIDERATIONS
Hydraulic conductivity may be determined in wells that are
either cased or uncased as described in Section 3.1. The tests
all involve disturbing the existing fluid potential in the
tested zone by withdrawal from or injection of fluid into a
well either as a slug over an extremely short period of time,
or by continuous withdrawal or injection of fluid. The
hydraulic conductivity is determined by measuring the response
of the water level or pressure in the well as a function of
time since the start of the test. Many excellent references
are available that give the derivation and use of the methods
that are outlined below, including Bouwer (1978), Walton
(1969), and Lohman (1972).
The selection of a particular test method and data analysis
technique requires the consideration of the purposes of the
test, and the geologic framework in which the test is to be
run. Knowledge of the stratigraphic relationships of the zone
to be tested and both overlying and underlying materials should
always be used to select appropriate test design and data
interpretation methods.
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3-7
The equations given for all computational methods given here
and in the above references are based on idealized models
comprising layers of materials of different hydraulic conduc-
tivities. The water-level response caused by disturbing the
system by the addition or removal of water can be similar for
quite different systems. For example, the response of a water-
table aquifer and a leaky, confined aquifer to pumping can be
very similar. Consequently, it is not considered acceptable
practice to obtain data from a hydraulic conductivity test and
interpret the type of hydraulic system present without sup-
porting geologic evidence.
The primary use of hydraulic conductivity data from tests
described subsequently will usually be to aid in siting moni-
toring wells for facility design as well as for compliance with
Subpart F of Part 264. As such, the methods are abbreviated to
provide guidance in determining hydraulic conductivity only.
Additional analyses that may be possible with some methods to
define the storage properties of the aquifer are not included.
The well test methods are discussed under the following two
categories: 1) methods applicable to coarse-grained materials
and tight to extremely tight materials under confined conditions;
and 2) methods applicable to unconfined materials of moderate
permeability. The single well tests integrate the effects of
heterogeneity and anisotropy. The effects of boundaries such
as streams or less permeable materials usually are not detec-
table with these methods because of the small portion of the
geologic unit that is tested.
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3-8
3.4 SINGLE WELL TESTS
The tests for determining hydraulic conductivity with a single
well are discussed below based on methods for confined and
unconfined conditions. The methods are usually called slug
tests because the test involves removing a slug of water
instantaneously from a well and measuring the recovery of water
in the well. The method was first developed by Hvorslev (1951),
whose analysis did not consider the effect of fluid stored in
the well. Cooper and others (1967) developed a method that
considers well bore storage. However, their method only
applies to wells that are open to the entire zone to be tested
and that tap confined aquifers. Because of the rapid water-
level response in coarse materials, the tests are generally
limited to zones with a transmissivity of less than about
70 cm2/sec (Lohman, 1972). The method has been extended to
allow testing of extremely tight formations by Bredehoeft and
papadopulos (1980). Bouwer and Rice (1976) developed a method
for analyzing slug tests for unconfined aquifers.
3.4.1 Method for Moderately Permeable Formations Under
Confined Conditions
3.4.1.1 Applicability. This method is applicable for testing
zones to which the entire zone is open to the well screen or
open borehole. The method usually is used in materials of
moderate hydraulic conductivity which allow measurement of
water-level response over a period of an hour to a few days.
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3-9
More permeable zones can be tested with rapid response water-
level recording equipment. The method assumes that the tested
zone is uniform in all radial directions from the test well.
Figure 7 illustrates the test geometry for this method.
3.4.1.2 Procedures. The slug test is run by utilizing some
method of removing a known volume of water from the well bore
in a very short time period and measuring the recovery of the
water level in the well. The procedures are the same for both
unconfined and confined aquifers. Water is most effectively
removed by using a bailer that has been allowed to fill and
stand in the well for a sufficiently long period of time so
that any water-level disturbance caused by the insertion of the
bailer will have reached equilibrium. In permeable materials,
this recovery time may be as little as a few minutes. An
alternate method of effecting a sudden change in water level is
the withdrawal of a weighted float. The volume of water
displaced can be computed using the known submersed volume of
the float and Archimedes' principle (Lehman, 1972).
Water-level changes are recorded using either a pressure trans-
ducer and a strip chart recorder, a weighted steel tape, or an
electric water-level probe. For testing permeable materials
that approach or exceed 70 cm2/sec, a rapid-response transducer/
recorder system is usually used because essentially full reco-
very may occur in a few minutes. Because the rate of water-
level response decays with .time, water-level or pressure
-------
3-10
Figure 7.—Geometry and variable definition for
slug tests in confined aquifers.
-------
3-11
changes should be taken at increments that are approximately
equally spaced in the logarithm of the time since fluid
withdrawal. The test should be continued until the water level
in the well has recovered to at least 85 percent of the initial
pre-test value.
3.1.1.3 Calculations. Calculations for determining hydraulic
conductivity for moderately permeable formations under confined
conditions can be made using the following:
a. Determine the transmissivity of the tested zone by
plotting the ratio h/ho on an arithmetic scale against
time since removal of water (t) on a logarithmic scale.
The observed fluid potential in the well during the test
as measured by water level or pressure is h, and ho is
the fluid potential before the instant of fluid
withdrawal." The data plot is superimposed on type
curves, such as those given by Lohman (1972)/ Plate 2
or plotted from Appendix A with the h/ho and time axes
coincident. The data plot is moved horizontally until
the data fits one of the type curves. A value of time
on the data plot corresponding to a dimensionless time
(0) on the type curve plot is chosen, and the transmis-
sivity is computed from the following:
(10)
where rc is the radius of the casing (Lohman, 1972, p. 29)
-------
3-12
The type curves plotted using data in Appendix A are not
to be confused with those commonly referred to as "Theis
Curves' which are used for pumping tests in confined
aquifers (Lohman, 1972). The type curve method is a
general technique of detemining aquifer parameters when
the solution to the descriptive flow equation involves
more than one unknown parameter. Although both the
storage coefficient and transmissivity of the tested
interval can be determined with the type curve method
for slug tests, determination of storage coefficients is
beyond the scope of this report. See Section 3.4.1.4 -
for further discussion of the storage coefficient.
If the data in Appendix A are used, a type curve for
each value of a is prepared by plotting F(a,6) on the
arithmetic scale and dimensionless time (3) on the
logarithmic scale of semi-log paper.
b. Determine the hydraulic conductivity by dividing the
transmissivity by the thickness of the tested zone.
3.4.1.4 Sources of Error. The errors that can arise in
conducting slug tests can be of three types: those resulting
from the well or borehole construction, measurement errors,
and data analysis error.
Well construction and development errors. This method assumes
that the entire thickness of the zone of interest is open to
-------
3-13
the well screen or boreholes and that flow is principally radial,
If this is not the case, the computed hydraulic conductivity
may be too high. If the well is not properly developed, the
computed conductivity will be too low.
Measurement errors can result from determining or recording the
fluid level in the borehole and the time of measurement
incorrectly. Water levels should be measured to an accuracy of
at least 1 percent of the initial water-level change. For
moderately permeable materials, time should be measured with an
accuracy of fractions of minutes, and for more permeable
materials, the time should be measured in terms of seconds or
fractions of seconds. The latter may require the use of a
rapid-response, pressure transducer and recorder system.
Data analysis errors. The type curve procedure requires
matching the data to one of a family of type curves, described
by the parameter a, which is a measure of the storage in the
well bore and aquifer. Papadopulos and others (1973) show that
an error of two orders of magnitude in the selection of o would
result in an error of less than 30 percent in the value of
transmissivity determined. Assuming no error in determining
the thickness of the zone tested, this is equivalent to a 30
percent error in the hydraulic conductivity.
3.4.2 Methods For Extremely Tight Formations Under
Confined Conditions
3.4.2.1 Applicability. This test is applicable to materials
that have low to extremely low permeability such as silts,
-------
3-14
clays, shales, and indurated lithologic units. The test has
been used to determine hydraulic conductivities of shales of as
low as 10-10 cm/sec.
3.4.2.2 Procedures. The test described by Bredehoeft and
Papadopulos (1980) and modified by Neuzil (1982) is conducted
by pressurizing suddenly a packed off zone in a portion of a
borehole or well. The test is conducted using a system such as
shown in Figure 8. The system is filled with water to a level
assumed to be equal to the prevailing water level. This step
is required if sufficiently large times have not elapsed since
the drilling of the well to allow full recovery of water
levels. A pressure transducer and recorder are used to monitor
pressure changes in the system for a period prior to the test
to obtain pressure trends preceding the test. The system is
pressurized by addition of a known volume of water with a
high-pressure pump. The valve is shut and the pressure decay
is monitored. Neuzil's modification uses two packers with a
pressure transducer below the bottom packer to measure the
pressure change in the cavity and one between the two packers
to monitor any pressure change caused by leakage around the
bottom" packer.
3.4.2.3 Calculations. The modified slug test as developed by
Bredehoeft and Papadopulos (1980) considered compressive
storage of water in the borehole. These authors considered
that the volume of the packed-off borehole did not change
-------
3-15
Pressure Gage
Valve
5=
V alve
System Filled
with Water -*.
- Pump
•Land Surface-
Initial Head
? ?-jn Testec
Casing Interval
_: Tight
?•*
r_-Well PointT
— ---___-—-]
T -
Tested -^-_
•ssure Gage(/)=
ad
? ? -
on._^.
System Filled
_with Water
_ -p _____ p
Open Hole
-"Packer-
._ .
. Interval to- —
"be Tested —
.J-.
Pump
(a)
(b)
Figure 8.—Schematic diagram for pressurized slug
test method in unconsolidated (a) and
consolidated (b) materials. Source:
Papadopulos and Bredehoeft, 1980.
-------
3-16
during the test and that all compressive storage resulted in
compression of water under the pressure pulse. Neuzil (1980)
demonstrated that under some test conditions this is not a
valid assumption. The computational procedure is the same in
either case. Data is plotted in the same manner as for the
conventional slug test and type curves are used from either
Lohman (1972, Plate 2) or plotted from data given in Appendix A
as described in Section 3.1.1.3. The value of time (t) and
dimensionless time, (3), are determined in the same manner as
for the conventional tests. If compression of water only is
considered, transmissivity is computed by replacing rc^ by the
quantity (Vy Crf> gA) in Equation 10:
= 3(VW Cw
where
Vw is the volume of water in the packed-off cavity, L3;
Cw is the compressibility of water, LT^M"!,
p is the density of water ML"3; and
g is the accleration of gravity, LT~2.
If the compressive storage is altered by changing the volume of
the packed-off cavity (V) , then the combined compressibility of
the water and the expansion of the cavity (Co) is used. Co is
computed by measuring the volume of water injected during
-------
3-17
pressurization (Av) and the pressure change AP for the
press urizat ion:
(Neuzil, 1982, page 440). Use of Co requires an accurate method
of metering the volume of water injected and the volume of the
cavity.
3.4.2.4 Sources of Error. The types of errors in this method
are the same as those for the conventional slug test. Errors
may also arise by inaccurate determination of the cavity volume
and volume of water injected. An additional assumption that is
required for this method is that the hydraulic properties of
the interval tested remain constant throughout the test. This
assumption can best be satisfied by limiting the initial
pressure change to a value only sufficiently large enough to
be measured (Bredehoeft and Papadopulos, 1980).
3.4.3 Methods for Moderately Permeable Materials Under
Unconfined Conditions
3.4.3.1 Applicability. This method is applicable to wells
that fully or partially penetrate the interval of interest
(Figure 9). The hydraulic conductivity determined will be
principally the value in the horizontal direction (Bouwer and
Rice, 1976.).
3.4.3.2 Procedures. A general method for testing cased wells
that partly or fully penetrate aquifers that have a water table
-------
3-18
WELL CASING
WELL SEAL
Lw
L«
-^
51 "iV
l>-1 ft!
i::--3
GRAVEL PACK
Lw
V
L«
Lw
STATIC WATER
LEVEL
IMPENETRABLE STRATUM ^'
(a) CASED WITH SCREEN
(b) CASED, NO SCREEN, NO
CAVITY ENLARGEMENT
(c) OPEN BOREHOLE
Figure 9.—Variable definitions for slug tests in
unconfined materials. Cased wells are
open at the bottom.
-------
3-19
as the upper boundary of the zone to be tested was developed by
Bouwer and Rice (1976). The geometry and dimensions that are
required to be known for the method are shown in Figure 9. The
test is accomplished by effecting a sudden change in fluid
potential in the well by withdrawal of either a bailer or sub-
mersed float as discussed in Section 4.4.1.2. Water-level
changes can be monitored with either a pressure transducer and
recorder, a wetted steel tape, or^an electric water-level
sounder. For highly permeable formations, a rapid-response
transducer and recorder system is required. The resolution of
the transducer should be about 0.01 m.
3.4.3.3 Calculations. The hydraulic conductivity is calcu-
lated using the following equation in the notation of this
report, taken from Bouwer and Rice (1976)
rc In R/r , y
2 Let~Y
where rc, rw, Le, t, Y, and K have been previously defined or
are defined in Figure 8a. Yo is the value of Y immediately
after withdrawal of the slug of water. The term R is an effec-
tive radius that is computed using the following equation given
by Bouwer and Rice (1976).
ln
rw In (Lw/rw
-------
3-20
for wells that do not fully penetrate the aquifer. If the quan-
tity (H0-Lw)/rw) is larger than 6, a value of 6 should be used.
For wells that completely penetrate the aquifer, the following
equation is used:
in*- =(_ I-* . + —-£_) , (14)
•w
In (Lw/rw) Le/rw
(Bouwer, 1976). The values of the constants A, B, and C are
given by Figure 10 (Bouwer and Rice, 1976).
For both cases, straight-line portions of plots of the
logarithm of Y or YO/Y against time should be used to determine
the slope, In Yo/Y
' " — ~- - •
t
Additional methods for tests under unconfined conditions are
summarized by Bower (1976) on pages 117-122. These methods are
modifications of the cased-well method described above that
apply either to an uncased borehole or to a well or piezometer
in which the diameter of the casing and the borehole are the
same (Figures 9b and 9c.)
3.4.3.4 Sources of Error. The method assumes that flow of
water from above is negligible. If this assumption cannot be
met, the conductivities may be in error. Sufficient flow from
the unsaturated zone by drainage would result in a high conduc-
tivity value. Errors caused by measuring water levels and
recording time are similar to those discussed in Sections
3.4.1.4 and 3.4.2.4.
-------
3-21
14
A
and
C
12
10
2-
10
50 100
500 IOOO
B
L/r.
5OOO
Figure 10.
—Curves defining coefficients A, B,
and C in equations 13 and 14 as
a function of the ratio L/rw.
Source: Bower and Rice/ 1976.
-------
3-22
3.5 MULTIPLE WELL TESTS
Hydraulic conductivity can also be determined by conventional
pumping tests in which water is continuously withdrawn or
injected using one well, and the water-level response is
measured over time in or near more observation wells. These
methods generally test larger portions of aquifers than the
single well tests discussed in Section 4.4. For some cir-
cumstances these tests may be appropriate in obtaining data to
use in satisfying requirements of part 264 Subpart F. However,
the large possibility for non-uniqueness in interpretation,
problems involved in pumping contaminated fluids, and the
expense of conducting such tests generally preclude their use
in problems of contaminant hydrogeology. The following
references give excellent discussions of the design and
interpretation of these tests: Lohman (1972), Stallman (1971),
and Walton (1970).
3.6 ESTIMATES OF HYDRAULIC CONDUCTIVITY FOR COARSE-GRAINED
MATERIALS
To characterize the ground-water flow system to satisfy the
intent of Part 264 Subpart F, estimates of the hydraulic con-
ductivity based on grain-size analyses or visual grain-size
classification may be appropriate. However, hydraulic conduc-
tivities determined by these methods are not to be used in per-
mit applications. Several theoretical models are available to
provide these estimates, with one of most widely used being
-------
3-23
Kozeny-Carmen equation which defines the intrinsic permeability,
as adapted from Bear (1972):
k . _!»L_ I^L. , (15)
(l-n)2 180
where n is the effective porosity, and all other terms are as
previously defined.
An empirical approach that has been used by the U.S. Geological
Survey (Lappala, 1978) in several studies relates conductivity
determined by aquifer testing to grain-size, degree of sorting,
and silt content. Table C provides the estimates of hydraulic
conductivity.
-------
3-24
TABLE C
HYDRAULIC CONDUCTIVITIES ESTIMATED PROM GRAIN-SIZE DESCRIPTIONS
(In Feet Per Day)
Grain-Size Class or Range
Prom Sample Description
I Degree of Sorting
f Poor
| Moderate
Well
Silt Content
Slight |
Moderate
High
Pine-Grained Materials
Clay
Silt, clayey
Silt, slightly sandy
Silt, moderately sandy
Silt, very sandy
Sandy silt
Silty sand
1. 1
Sands and Gravels
Very fine sand
Very fine to fine sand
Very fine to medium sand
Very fine to coarse sand
Very fine to very coarse sand
Very fine sand to fine gravel
Very fine sand to medium gravel
Very fine sand to coarse gravel
Fine sand
Fine to medium sand
Fine to coarse sand
Fine to very coarse sand
Fine sand to fine gravel
Fine sand to medium gravel
Fine sand to coarse gravel
Medium sand
Medium to coarse sand
Medium to very coarse sand
Medium sand to fine gravel
Medium sand to medium gravel
Medium sand to coarse gravel
Coarse sand
Coarse to very coarse sand
Coarse sand to fine gravel
Coarse sand to medium gravel
Coarse sand to coarse gravel
Very coarse sand
Very' coarse sand to fine gravel
Very coarse sand to medium gravel
Very coarse sand to coarse gravel
Pine gravel
Fine to medium gravel
Pine to coarse gravel
Medium gravel
Medium to coarse gravel
Coarse gravel
13
27
36
48
59
76
99
128
27
53
57
70
88
114
145
67
74
84
103
131
164
80
94
116
147
184
107
134
1270
207
160
201
245
241
294
334
I
I
Les
20
27
41-47
-
-
-
-
-
40
67
65-72
-
-
-
-
80
94
98-111
-
-
-
107
134
136-156
-
-
147
214
199-227
-
214
334
289-334
231
468
468
s than
1 - 4
5
7-8
9 - 1
11
13
27
-
-
-
-
-
-
-
53
-
-
-
-
-
94
-
-
-
-
-
134
-
-
-
-
187
-
-
-
267
-
-
401
-
602
.001
1
23
24
32
40
51
67
80
107
33
48
53
60
74
94
107
64
72
71
84
114
134
94
94
107
114
134
114
120
147
160
227
201
234
241
294
334
19
20
27 -
31
40
52
66
86
27
39
43
47
59
75
87
51
57
61
68
82
108
74
75
88
94
100
94
104
123
132
140
167
189
201
243
284
13
13
21
24
29
38
49
64
20
30
32
35
44
57
72
40
42
49
52
66
82
53
57
68
74
92
74
87
99
104
107
134
144
160
191
234
)Reduce by 10 percent if grains are subangular
-------
3-25
3.7 CONSOLIDATION TESTS
As originally defined by Terzagi (Terzaghi and Peck, 1967) the
coefficient of consolidation (Cv) of a saturated, compressible,
porous medium is related to the hydraulic conductivity by:
(16)
-v pga
where
K is the hydraulic conductivity, LT~1,
p is the fluid density, ML~3,
g is the gravitational constant, LT~2, and
a is the soil's compressibility, LM~lT2.
The compressibility can be determined in the laboratory with
several types of consolidometers, and is a function of the
applied stress and the previous loading history. Lambe (1951)
describes the testing procedure.
The transfer value of results from this testing procedure is
influenced by the extent to which the laboratory loading simu-
lates field conditions and by the consolidation rate. The
laboratory loadings will probably be less than the stress that
remolded clay liner will experience; therefore, the use of an
already remolded sample in the consolidometer will probably
produce no measurable results. This suggests that the test is
of little utility in determining the hydraulic conductivity of
remolded or compacted, fine-grained soils. Second, the con-
solidation rate determines the length of the testing period.
-------
3-26
For granular soils, this rate is fairly rapid. For fine-grained
soils, the rate may be sufficiently slow, so that the pre-
viously described methods will provide faster results.
Cohesive soils (clays) must be trimmed from undisturbed samples
to fit the mold, while cohesionless sands can be tested using
disturbed, repacked samples (Freeze and Cherry, 1979).
In general, EPA believes that consolidation tests can provide
useful information for some situations, but prefers the pre-
viously described methods because they are direct measurements
of hydraulic conductivity. Hydraulic conductivity values
determined using consolidation tests are not to be used in per-
mit applications.
3.8 FRACTURED MEDIA
Determining the hydraulic properties of fractured media is
always a difficult process. Unlike porous media, Darcy's Law
is not strictly applicable to flow through fractures, although
it often can be applied empirically to large bodies of frac-
tured rock that incorporate many fractures. Describing local
flow conditions in fractured rock often poses considerable dif-
ficulty. Sowers (1981) discusses determinations of hydraulic
conductivity in rock. This reference should be consulted for
guidance in analyzing flow through fractured media.
Fine-grained sediments, such as glacial tills, are commonly
fractured in both saturated and unsaturated settings. These
fractures may be sufficiently interconnected to have a significant
-------
3-27
influence on ground-water flow, or they may be of very limited
connection and be of little practical significance.
Frequently, a laboratory test of a small sample of clay will
determine hydraulic conductivity to be on the order of
10~8 cm/sec. A piezometer test of the same geologic unit over
an interval containing fractures may determine a hydraulic con-
ductivity on the order of perhaps 10~5 or 10~6 cm/sec. To
assess the extent of fracture interconnection, and hence the
overall hydraulic conductivity of the unit, several procedures
can be used. Closely spaced piezometers can be installed; one
can be used as an observation well while water is added to or
withdrawn from the other. Alternately, a tracer might be added
to one piezometer, and the second could be monitored. These,
and other techniques are discussed by Sowers (1981).
For situations that may involve flow through fractured media,
it is important to note in permit applications that an apparent
hydraulic conductivity determined by tests on wells that inter-
sect a small number of fractures may be several orders others
of magnitude lower or higher than the value required to
describe flow through parts of the ground-water system that
involve different fractures and different stress conditions
from those used during the test.
-------
4-1
4.0 CONCLUSION
By following laboratory and field methods discussed or
referenced in this report, the user should be able to determine
the fluid conductivity of materials used for liners, caps,
and drains at waste-disposal facilities, as well as materials
composing the local ground-water flow system. If fluid-
conductivity tests are conducted and interpreted properly, the
results obtained should provide the level of information
necessary to satisfy applicable requirements under Part 264.
-------
5-1
5.0 REFERENCES
Acker, W. L. , III, Basic procedures for soil sampling and core
drilling, Acker Drill Co., 246 p., 1974.
Allison, L. E., Soil Science, vol. 63, pp. 439-450, 1947.
American Society for Testing and Materials (ASTM), Annual Book
of ASTM Standards, part 19, 1978.
Anderson, D., and K. W. Brown, Organic leachate effects on the
permeability of clay liners, in Proceedings of Solid Waste
Symposium, U.S. EPA, p. 119-130, 1981.
Bear, J., Dynamics of fluids in porous media, American Elsevier,
764 p., 1972.
Bouwer, H., Groundwater hydrology, McGraw Hill, 480 p., 1978.
Bouwer, H., and R. C. Rice, A slug test for determining hydraulic
conductivity of unconfined aquifers with completely or
partially penetrating wells, Water Resources Research,
12, p. 423-428, 1976.
Bredehoeft, J. D., and S. S. Papadopulos, A method for deter-
mining the hydraulic properties of tight formations,
Water Resources Research, 16, p. 233-238, 1980.
Conway, R. A., and B. C. Malloy (eds.), Hazardous Solid Waste
Testing: first conference, ASTM Special Technical
Publication 760, 1981.
Cooper, H. H., J. D. Bredehoeft, and I. S. Papadopulos,
Response of a finite diameter well to an instantaneous
charge of water, Water Resources Research, 3, p. 263-269,
1967.
Fireman, M., Soil Science, vol. 58, pp. 337-355, 1944.
Freeze, R. A., and J. A. Cherry, Groundwater, Prentice Hall,
604 p., 1979.
Gordon, B. B., and M. Forrest, Permeability of soil using con-
taminated permeant, jLn Permeability and Groundwater
Contaminant Transport, ed. T. F. Zimmie and C. 0. Riggs,
ASTM Special Technical Publication 746, p. 101-120, 1981.
Hillel, D., Soil and Water, Academic Press, 288 p., 1971.
Hvorslev, M. J., Time lag and soil permeability in groundwater
observations, U.S. Army Corps of Engineers Waterways
Experiment Station Bull. 36, 1951.
-------
5-2
Johnson, A. I., Symposium on soil permeability, ASTM STP 163,
American Society of Testing and Materials, Philadelphia,
pp. 98-114, 1954.
Johnson, E. E., Inc., Groundwater and wells, Johnson Division,
UOP, 440 p., 1975.
Lappala, E. G., Quantitative hydrogeology of the Upper
Republican Natural Resources District, Southwest Nebraska,
U.S. Geological Survey Water Resources Investigations 78-38.
Lambe, T. W., Soil testing for engineers, John Wiley, N.Y.,
1951.
Lohman, S. W. , Groundwater hydraulics, U.S. Geological Survey
Professional Paper 708, 70 p., 1972.
Lohman, S. W., and others, Definitions of selected ground
water terms - revisions and conceptual refinements,
U.S. Geological Survey Water Supply Paper 1988, 1972.
Manufacturing Chemists Association, Guide for safety in the
chemical laboratory, Van Nostrand, Reinhold Co., N.Y.,
1971.
Mitchell, A. K., and J. S. Younger, Permeability and capillarity
of soils, ASTM STP 417, American Society for Testing and
Materials, Philadelphia,, pp. 106-139, 1967.
Neuzil, C. E., On conducting the modified 'slug' test in tight
formations, Water Resources Research, vol. 18, no. 2,
pp. 439-441, 1982.
Olsen, R. E., and D. E. Daniel, Measurement of the hydraulic
conductivity of fine-grained soils, in Permeability and
Groundwater Transport, ed. T. F. ZimmTe and C. 0. Riggs,
ASTM Special Publication 746, p. 18-64, 1981.
Papadopulos, S. S., J. D. Bredehoeft, and H. H. Cooper, Jr., On
the analysis of "slug test1 data, Water Resources Research,
9, p. 1087-1089, 1973.
Schwartzendruber, D., Soil Science Society of America Proceed-
ings, vol. 32, no. 1, pp. 11-18, 1968.
Sowers, G. P., Rock permeability or hydraulic conductivity - an
overview, in Permeability and Groundwater Transport, ed.
T. P. ZimroTe and Co. 0. Riggs, ASTM Special Technical
Publication 746, 1981.
Stallman, R. W., Aquifer-test design, observation and data
analysis, TWRI, Chap. Bl, Book 3, U.S. Geological Survey,
U.S. Govt. Printing Office, WAshington, D.C., 1971.
-------
5-3
Terzaghi, K.. , and R. B. Peck, Soil riechani.es in Engineering
Practice, 2nd Ed., John Wiley & Sons, N.Y., 729 p., 1967.
Walton, W. C. , Groundwater resource evaluation, McGraw Hill,
664 p., 1970.
Wilkinson, W. B., In situ investigation in soils and rocks,
British and Geotechnical Society, Institution of Civil
Engineers, London, pp. 311-313, 1969.
U.S. Army Corps of Engineers, Laboratory Soil Testing, Water-
ways Experiment Station Publication EMlllO-2-1906, 1970.
U.S. Environmental Protection Agency, Lining of waste impound-
ment and disposal facilities, Office of Solid Waste Report
SW-870, 1980.
U.S. Environmental Protection Agency, Hazardous waste guide-
lines and regulations (proposed), Federal Register,
Part IV, Dec. 18, 1978.
U.S. Environmental Protection Agency, Test Methods for Evaluating
Solid Waste, 2nd Edition, SW-846, Superintendent of Documents,
Government Printing Office, Washington, D.C., 1982.
-------
6-1
6.0 Appendix A
Values of the function F(a,B) for use in
the conventional and pressurized slug tests.
Source: Papadopulos et.al. (1973)
7Vr«»
0.001
0.002
0.004
0.006
0.008
0.01
0.02
0.04
0.06
0.08
0.1
0.2
0.4
0.6
0.8
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
20.0
30.0
40.0
50.0
60.0
80.0
100.0
200.0
a - 10-«
0.9994
0.9989
0.9980
0.9972
0.9984
0.9956
0.9919
0.9848
0.9782
0.9718
0.9655
0.9361
0.8828
0.8345
0.7901
0.7489
0.5800
0.4554
0.3613
0.2893
0.2337
0.1903
0.1562
0.1292
0.1078
0.02720
0.01286
0.008337
0.006209
0.004961
0.003547
0.002763
0.001313
a - 10-'
0.9996
0.9992
0.9985
0.9978
0.9971
0.9965
0.9934
0.9875
0.9819
0.9765
0.9712
0.9459
0.8995
0.8569
0.8173
0.7801
0.6235
0.5033
0.4093
0.3351
0.2759
0.2285
0.1903
0.1594
0.1343
0.03343
0.01448
0.008898
0.006470
0.005111
0.003617
0.002803
0.001322
a - 10-'
0.9996
0.9993
0.9987
0.9982
0.9976
0.9971
0.9944
0.9894
0.9846
0.9799
0.9753
0.9532
0.9122
0.8741
0.8383
0.8045
0.6591
0.5442
0.4517
0.3768
0.3157
0.2655
0.2243
0.1902
0.1620
0.04129
0.01667
0.009637
0.006789
0.005283
0.003691
0.002845
0.001330
a - 10-»
0.9997
0.9994
0.9989
0.9984
0.9980
0.9975
0.9952
0.9908
0.9866
0.9824
0.9784
0.&587
0.9220
0.8875
0.8550
0.8240
0.6889
0.5792
0.4891
0.4146
0.3525
0.3007
0.2573
0.2208
0.1900
0.05071
0.01956
0.01062
0.007192
0.005487
0.003773
0.002890
0.001339
o - 10-"
0.9997
0.9995
0.9991
0.9986
0.9982
0.9978
0.9958
0.9919
0.9881
0.9844
0.9807
0.9631
0.9298
0.8984
0.8686
0.8401
0.7139
0.6096
0.5222
0.4487
0.3865
0.3337
0.2888
0.2505
0.2178
0.06149
0.02320
0.01190
0.007709
0.005735
0.003863
0.002938
0.001348
-------
6.0 Appendix A (continued)
Extended values of F(a,6) for use in slug tests.
Source: Bredehoeft and Papadopulos (1980)
6-2
as 0.1
acO.2
a«0.5
a»2
a* 5
a* 10
C.OOC001
e.oocoo?
o.ontoo*
O.OOC006
O.OOC008
O.QBCO)
o.ooco?
O.AOCO*
o.ooco*
O.OPCOB
o.ooci
fl.Ont?
O.OOC*
o.ooc*
o.oncs
O.OPl
0.102
0.00*
o.ont
O.onf
0.01
O.OJ
0.04
o.oe
t .OP
0.1
e.2
0.4
O.f
0.8
u
2.
*•
e.
e.
10.
20.
40.
*0.
HC.
inc.
?no.
*nfl.
60C.
SAO.
1000.
0.9993
0.9990
0.94B6
0.99«2
1.99«0
0.9977
0.9966
3.9955
0.99*4
0.9936
0.9924
0.989H
0.9««55
0.9*22
1.9794
n.9769
0.9670
O.V52H
0.9417
0.93?2
0.9238
0.8904
1.8*?1
0.8t)4«>
n.773*
0.7459
0.641P
0.5095
0.4J27
0..159P
0.3117
0.17ftf
O.OP761
0.0?5?7
0.039*3
0.03065
0.01*0*
0,0<16680
0.00*167
0.003?*2
O.OC2577
0.001271
e.noo*307
0.0004141
P. 00031*0
0.0002510
0.99«0
0.99Cfi
0.99tO
0.947S
0.9971
0.99C6
0.99S5
0.993A
0.99Z2
0.9909
0.9»59
0.96S7
0.97S7
0.9752
O.S713
0.9«79
0.9S46
0.93S7
0.9211
0.9089
0.89*2
0.8S<2
0.7980
0.75*6
0.71SO
0.6865
C.577*
0.445*
0.36*?
0.307?
0.2%* e
0.1519
0.67*96
G.04f9C
0.03tS6
0.02670
O.OI3fl
o.nntsts
0.00*310
0.003214
0.00?5*9
o.oni?6'<
0.0006295
O.OOC41H«
C. 0003137
0.0002506
0.9964
0.9977
0.9968
0.9961
0.9955
0.9949
fl.<»92?
0.9^99
0.9877
0.98SA
0.9b<»l
0.977f
0.9685
0.9615
0.95S7
«.9505
0.9307
0.9031
0.8025
0.8654
0.8SQB
0.7947
0.7214
0.6697
A. 6289
O.SVS1
0.4799
0.3566
0.2«64
0.2397
0.206)
0.1202
0.06*20
0.0*331
0.0325*
fl.026no
0.012afl
0.006774
0.00*229
0.003163
0.002S2f>
O.OOl?5A
0.000*372
0.0004177
0.0003131
0.000250*
0.9977
0.9968
0.9955
0.9945
0.9936
0.9929
0.9900
0.9858
0.9827
0.9ROO
0.9777
0.9687
0.9560
0.9*65
0."3«5
0.9315
0.904A
0.66R6
O.«419
0.4202
C.8017
0.7336
0.6*89
0.5919
0.54H6
0.5137
0.4010
0.7902
0.2311
0.1931
0.1663
0.09912
0.05521
0.03830
0.02933
0.02376
0.01219
O.OOM71
0.00413?
0.00310*
0.00?*87
0.001247
0.00062*2
0.000*1*3
0.00031?3
o«noo?4«s
0.9968
0.9955
A. 9936
0.99?2
0.9910
0.9900
0.9H58
n.9»oi
0.*757
0.9720
0.9<,86
0.'S62
0.9389
O.V?5«
0.9151
fl.9057
0.0702
o.e?32
0.7896
0.7626
O.?*00
0.6595
0.5*5*
0.5055
0.4618
0.*276
0.3J3*
0.2?9Z
0.1P17
0.1521
0.1315
O.OaO**
0.0*660
0.0?32»i
0.0?S9«
0.02l3n
0.0]133
0.005*97
0.003994
0.0030??
0.002*^1
0.001230
O.OQ06195
0.000*1*1
0.00031 10
0.0002*90
0.9948
0.9927
0.9698
0.9876
0.9857
0.98*1
0.9776
0.9687
0.9619
0.9562
0.9512
0.9321
0.9061
0.0869
0.8711
0.8576
0.8075
0.7*39
0.7001
0.6662
0.638*
0.5*50
0.**S*
0.3872
0.3*69
0.3168
0.2313
0.1612
0.1280
0.1077
0.09375
0.05940
0.03621
0.02663
0.0212S
0.0177*
0.0099*3
0.005395
0.&03726
0.002853
0.002313
0.0(1119*
0.0006085
0.000*087
0.0003078
0.0002*69
0.9923
0.9894
0.9853
0.9822
0.9796
0.9773
0.9683
0.9SS8
0.9*6*
0.9387
0.9318
0.9059
0.8711
0.8*58
0.8253
Or8079
0.7*50
0.668*
0.6178
0.5797
0.5*92 "
0.4517
0.3556
0.3030
0.2682
0.2*28
0.17*0
0.1207
0.09616
0.0813*
0.07120
0.0*620
0.02908
0.02185
0.01771
0.01*99
0.008716
0.00*898
0.003«*5
0.002668
0.002181
0.0011*9
0.00059**
0.000*016
0.0003035
0.00024*0
-------
APPENDIX B
IMMERSION TEST OF MEMBRAWE
LINER MATERIALS FOR
COMPATIBILITY WITH WASTES
-------
-------
DRAFT
Method 9082
' IMMERSION TEST OF MEMBRANE LINER MATERIALS
FOR COMPATIBILITY WITH WASTES
1.0 Scope and Application
1.1 This'test method is for use in determining the effects
upon the physical properties of flexible ner.brane liner
materials intended to contain chemicals in a pit,
pond, lagoon or landfill-type installation, of the
chemical environment expected to be encountered. Data
s
from these tests will assist in deciding whether a
given liner material is acceptable for the intended
application.
1..2' This method is based on material resulting from wor>; by
the National Sanitation Foundation, Dr. Henry E. Haxo,
Dr. Robert Landrerh, ^acreccr., Inc. and Z?A:s .;ur.^c«ral
•Environmental Research Laboratory in Cincinnati, On.
2.0 Summary of Method
2.1 In order to estimate long term compatability, the
liner material is exposed to the expected chemical
environment for a period of 120 days at an elevated
temperature. A comparison of the membrane's physical
properties before and after this contact period is
used to estimate the properties of the liner at the
time of site closure.
3.0 Interferences
4.0 Apparatus and Materials
4.1 Exposure tank - A size sufficient to contain the sanoles
-------
they do not touch bottom or sides of the tank, or each
other; for stirring the liquid in the tank; and for
holding the specimens in such a manner that the liner
material contacts the test solution only on the surface
that would face the waste in an actual disposal site.
The tank shall be equipped with a means of maintaining
the solution at a temperature of 5CHh2°C and for prevent-
ing evaporation of the solution (e.g., cover equipped
with a reflux condenser). The Agency understands that
one such device is manufactured by A.ssociat.ec Design
and Manufacturing Company, 814 North Henry Street,
Alexandria, VA 22314, (703)549-5999.
4.2 Stress-strain machine suitable for measuring elongation,
tensile strength, tear and puncture resistance.
4.3 Jig for testing puncture resistance.
4.4 Labels and holders for specimens, of materials known to be
resistant to the specific wastes. Holders of stainless
steel, and tags made of 50 mil polypropylene, embossed
with machinist's numbering dies and fastened with stain-
*
less steel wire, are resistant to most wastes.
5.0 Reagents
6.0 Sample Collection Preservation and Handling
6.1 For information on what constitutes a representative
sample of the waste fluid to employ, refer to the
appropriate guidance document listed below:
1. RCRA Guidance Document: Surface Impoundments, Liner
Systems, Final Cover, and Freeboard Control. Issued
-------
July 1982 and used with 40 CFR 254. 221 (a) and (c),
and 264. 228 (a) .
2. RCRA Guidance Document: Waste Pile Design, Liner
Systems. Issued July 1982 and used with 40 CFR
264.251(a), 264.252, and 264.253.
3. RCRA Guidance Document: Landfill Design, Liner Systems
and Final Cover. Issued Julv 1982 and used with 40
CFR 264.301(a) and 264.310(a)~.
7 . 0 Procedure
7.1 Obtain a representative sample of. the waste fluid.
7.2 Perform the ^following tests on unexposed samples of the
polymeric membrane liner material:
7.2.2 Puncture resistance, three specimens
7.2.3 Tensile strength in two directions, three speci-
mens in each direction
7.2.4 Elongation at Break, (This test is only to be
performed on membrane material which does not
have a fabric or other non-elasrcmeric support
on its 'reverse [away from waste] i'uce.)
Tests are to be performed according to the protocols
referenced in Table 9082-1. See Figure 9082-1 for a
*
suggested cutting pattern.
7.3 Cut pieces of the lining material, "of a size to fit sample
holder, and of a sufficient number to permit at least
three samples for each test at each test period.
7.4 Label the test specimens with a plastic identification
tag and suspend in sample of the waste .fluid.
7.5 Expose the sample to the stirred waste fluid held at
-------
7.6 At the end of 30, 60, 90 and 120 days of exposure,
remove sufficient specimen from the waste fluid to
determine the membrane's physical properties (see 7.2).
Place wet specimen in a labelled container of fresh
waste fluid at room temperature for at' least one hour
to effect cooling prior to testing.
7.7 Tha sample should te tasted within 24 hours of removal
from the bath. Tc'test the immersed! sample, wipe off any
waste fluid, rinse with deioriizsd water, blot specimen
dry, and measure the physical properties listed in
7.2.
7.8 Results and Reporting
7.8.1 Plot the curve "for each property over the time
period 0 to 120 days.
7.8.2 Report all raw, tabulated, and plotted data. Evaluation
of the results is described "in the RCRA guidance
documents listed under 6.1.
8.0 Quality Control
8.1 Determine the mechanical properties of identical non-
immersed and"immersed specimens in accordance with the
standard methods for the specific physical property test.
Conduct mechanical property tests on nonimmersed and
immersed specimens prepared from the same sample or
lot of material in the same manner and run under identical
conditions. Test immersed specimens immediately after
they are removed from the room temperature test solution.
-------
DATE DUE
PVC(
.etic thermoplastic polymer made
Family of polymers produced by
on polyethylene. The resulting
tin 25 to 45% chlorine by weight
sed on isobuf/lene and a small
ites for vulcanization.
e for a synthetic rubber based
CM (Crosslinr.ed chlorinated polyethylene):
ethylene.
A polymer prepared by the low
•ylene as the sole monomer.
nsr): A synthetic elastomer
id a small amount of nonconju-
vulcaniz~tion.
Synthetic rubber including
ers which ar :• saturated, high
ers with :hloromethyl side
,»,*•*•»!»«•»•*• nopolymer (C" ) and a copolymer
oxide(SCO).
S3= cniorir.atea
PE.-EP-A (Polyethylene ethylene/propylene-alloy!: A blend of poly-
ethylene and "poly(ethylene/propylene).
HDPE-A (High density polyethylene / rubber alloy): A blend of
high density polyethylene and rubber.
CSPE (Chlorosulfonated polyethylene): Family of polymers that are
produced by polyethylene reacting with chlorine and sulfur
dioxide and usually containing 25 to 43% chlorine and 1.0 to
1.4% sulfur.
TN-PVC (Thermoplastic nitrile-polyvinyl chloride): An alloy of
thermoplastic unvulcanized nitrile rubber and polyvinyl
chloride.
T-EPDM (Thermoplastic EPDM): An ethylene-pro'-ylene diene monomer
blend resulting in a thermoplastic elastoncr.
EIA (Ethylene interpolymer alloy): A blend ^-f polyethylene and
polyvinyl chloride resulting in a thermoplastic elastomer.
.PVC-CPE (Polyyinvl chloride - Chlorosulfonated v-lvethvlene allov):
U L Env;rofimental Protection Agencv
f^ygJon V, Library
230 South Dearborn Street
6
-------
TABLE 9082-1
PHYSICAL PROPERTY TESTING PROCEDURES
[Appropriate ASTM or FTMS(*) Testing Method]
Polymer
FVC
CPE
Butyl rubber
CP
KDPE
E?DM
CO, ECO
CM
PE-EP-A
HDPE-A
CSPE
TN-PVC
T-EPDM
-
EIA
PVC-CPE
Tensile Strength
& Elongation at Break
D832
D882
D412
D.412
D63S
D412
D412
D412
D412
,
Do 38 Type IV Dunbeli
at 2 inches/second
,
D751 Method A
D751 Method A
•
•
D751 Method A
D751 Method A
D882 Method A
Tear
Resistance
D1C04 Dia C
D1004 Die C
C624 Die C
D624 Die C
-
D10C4 Die €
D624 Die C
D624 Die C
D624 Die C
D1004 Die C
DIOC4 Die C
D751 as
modified in
Appendix A
D751 as
modified in
Appendix A
D751 as
modified in
Appendix A
•
D751 as
modified in"
Appendix A
D1104 Die C
! Puncture
Resistance
"
1 *2065
*2065
.
.
*2065
•
*2065
'
*2065
*2065
*2C65
*2065
*2065
"2055
*206S
*2065
*2065
*2065
-*2065
Abbreviations:
ASTM: American Society for Testina and Materials
-------
•I***;
TEAR RESISTANCE.
TEST SPECIMENS
PUNCTURE RESISTANCE
SPECIMEN-"
^ -^ "^1,
Figure 9082-1. Suggested pattern for cutting test specimens
-------
------- |