EPA-660/2-74-065
June 1974
Environmental Protection Technology Series
An Evaluation of Tailings
Ponds Sealants
3D
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LU
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National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Corvallis, Oregon 97330
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RESEARCH REPORTING SERIES
Research reports of the Office ot Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five bread
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, eguipment and
methodology to repair or prevent environmental
degradation from point and -non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-660/2-74-065
June 1974
AN EVALUATION OF TAILINGS PONDS SEALANTS
Don A. Clark
James E. Moyer
Mining Wastes Section
Treatment and Control Technology Branch
Robert S. Kerr Environmental Research Laboratory
Post Office Box 1198
Ada, Oklahoma 74820
Project No. 21 AGF-16
Program Element IBB 040
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
For tale by the Superintendent of Documents, U.S. Qovernment Printing Office, Washington, D.C, 20402 - Price 70 cents
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ABSTRACT
This report presents a summary of the rather limited information
available in the literature pertaining to the use of sealants for mine
and mill tailings ponds. Included in the report is a discussion of
currently employed seepage detection methods, as well as the various
types of sealants currently in use—compacted earth, clays, chemicals,
waste tailings solids, asphalt, and synthetic membranes. Only properly
installed synthetic liners will prevent all seepage. Installation costs
of the sealants, including labor, are discussed and graphs for estimating
costs based on pond size are presented. Regulations governing the
amount of seepage allowed are ill-defined or non-existent in the
majority of States.
ii
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CONTENTS
Abstract ii
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Seepage Detection 5
V Compacted Earth 8
VI Clay Sealants 10
VII Chemical Sealants 12
VIII Waste Tailings Solids 16
IX Asphalt Sealants 17
X Synthetic Membrane Liners 19
XI Cost of Pond Liners 22
XII References 26
ill
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SECTION I
CONCLUSIONS
1. A literature search has not revealed data showing seepage rates
from mining and milling tailings ponds. Minimal data is available on
sealants for irrigation canals, brine ponds, and reservoirs; however,
satisfactory liners for these purposes might prove unsatisfactory for
mining wastes due to their chemical characteristics. The sealing method
most widely used is compacted earth, but the majority of tailings ponds
are not sealed prior to use.
2. To ascertain the continuing performance of a liner, a seepage
detection system should be operated continually. A water-budget
detection system would substantiate the volume of waste lost through
seepage within its limit of accuracy. Monitoring detection systems
will determine the type and concentration of pollutants seeping from
the pond.
3. Current seepage restrictions are non-existent or poorly defined.
The degree of seepage is unknown in almost all instances due to the
lack of detection systems. The fate of pollutants from mining wastes
that seep into the soil has not been investigated sufficiently. Increased
attention to environmental control of pollution will probably result in
seepage restrictions approaching zero.
4. Most liners allow seepage of one foot per year and often appre-
ciably more. Even in arid regions seepage losses of one foot per year
result in 25 percent of the total waste volume. "Zero" seepage is only
obtained from properly installed and maintained synthetic liners.
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SECTION II
RECOMMENDATIONS
1. Research should be conducted to determine effects of metal and
mineral mining wastes on pond sealants. Individual waste character-
istics will necessitate testing different lining materials to determine
maximum performance. Factors to be considered are liner deteriora-
tion upon prolonged contact with the waste and alterations in liner
permeability with time.
2. Research should be conducted to determine the movement of
mining and milling waste pollutants through the soil and groundwater
surrounding tailings ponds. The information would be beneficial in
planning more efficient seepage detection systems, and defining the
magnitude of seepage resulting from mine tailings ponds.
3. A comprehensive research study of all seepage detection systems
should be undertaken to determine their reliability. Efforts should be
made to improve the accuracy of the water-budget method. Improved
systems should be developed that allow the identification and quanti-
fication of seepage pollutants to be determined routinely.
4. Investigations should be conducted to determine the suitability
of waste slimes as pond sealants, since waste slimes gradually reduce
seepage from ponds. Slimes are readily available from old tailings
ponds and might serve to seal ponds in the same manner as clay
sealants.
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SECTION III
INTRODUCTION
Tailings ponds are utilized to contain both solid and liquid wastes for
recycle, treatment to remove contaminants prior to discharge, or disposal
by evaporation. Most industrial wastes contain pollutants that contami-
nate soil, surface and groundwater through seepage from inadequately
sealed tailings ponds. Factors that must be considered in the selection
of a sealant are as follows:
1. nature of pollutants in the waste
2. soil characteristics
3. geographical location
4. geological structure of the underlying strata
5. seepage restrictions set forth by regulating agencies
6. cost of sealant
Careful consideration of all factors will enable a proper sealant to be
chosen for testing prior to installation in the pond.
Soils of low permeability allow seepage of approximately one foot per
year. This amount of seepage accounts for 25 percent of the total loss
from ponds in an arid region where evaporation rates are high. At the
present time, most regulations governing the degree of seepage permitted
by the individual states are inadequate or non-existent. Current atten-
tion to environmental problems will probably result in the establishment
of seepage standards in all states. Seepage rates of one foot per year
or less have been considered satisfactory in sealant research studies
for brine ponds. * Some states have restrictions on seepage ranging
from 3.8 to 7.6 feet per year.2 Under these regulations, seepage
would contribute more to waste loss from ponds than evaporation, the
intended means of disposal. The trend in regulating seepage rates
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will be toward reduced seepage, thus greatly restricting the sealants
that may be employed. Only membrane liners can, at present, provide
"zero" seepage. The sealing proficiencies of other types of liners
fluctuate depending on the soil characteristics and uniformity of
their installation; hence, the method of seepage prevention chosen
will be dependent upon the degree of restrictiveness specified in
the regulations.
Most studies of sealants have dealt with their use for brine ponds,
irrigation canals, and reservoirs. In general, the sealing character-
istics for tailings ponds should be the same except for the effect of
chemical constituents in the tailings pond solutions on the sealant.
These effects should be studied for each type of tailings solution
before use of the sealant in the holding pond.
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SECTION IV
SEEPAGE DETECTION
While seepage at the ground surface is obvious, underground seepage
may go completely undetected unless observed through a monitoring
system. Though the geological structure of the area is well-known
and the directional flow of the groundwater previously determined,
monitoring wells may not detect a pollutant due to the slow band-like
dispersion of seepage liquid in the groundwater system. Faults and
fissures in the formation may allow the pollutants to travel to an un-
expected point; hence, the ultimate solution to the prevention of
pollution from seepage is complete elimination.
Two methods, the water-budget and a monitoring system, are presently
utilized to measure seepage rates. The water-budget method, with
a limit of accuracy of 12 to 30 percent, measures seepage by determina-
tion of the difference between all inputs and outputs to the pond. Many
variables are involved that may introduce errors into the calculation
of accurate seepage rates.
The following information must be known for a period of time to calcu-
late the amount of seepage:
1. evaporation rate
2. rainfall
3. area of water surface
4. gallons of solid and liquid waste discharged to pond
5. gallons of waste discharged from pond .
6. water level change in pond
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Seepage may be calculated from the following formulas:
(1)
E
En
Ct
Ca
= 0.
_ A
0
7 P
.13368
= G. + G + E
1 0
0.
[ x A
13368
S = C. - C0 (5)
I £1
where P = pan evaporation (ft)
E = pond evaporation (ft)
A = pond surface area (sq ft)
R = rainfall (ft)
0.13368 = conversion factor (cu ft/ gal.)
E = net evaporation corrected for rainfall (gal . )
G. = waste discharge to pond (gal.)
G = waste discharge from pond (gal . )
C. = theoretical change in pond volume (gal . )
H = pond waste level change (ft)
C = actual change in pond volume (gal.)
ol
S = seepage loss (gal.)
Note: The discharge and evaporation from the pond are entered into
the calculation as a negative value .
The 0 . 7 factor is an approximate correction for lake evaporation when
using a Class A Weather Bureau pan and may vary from 0. 60 to 0. 97
at different locations.3' 4 Rainfall introduces another source of error
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because of the difficulty in determining the surface area funneling run-
off into the pond. Additional errors are introduced in calculation due
to the masking effect of the larger inflow and outflow volumes of waste.
If two ponds are available for use, the inflow and outflow could be
transferred to one pond while seepage measurements are made on the
other pond, thus increasing the accuracy of the measurement by elimi-
nating GI and GQ. Seepage determination during periods of zero rain-
fall eliminate R and the associated error from the calculation.
Seepage may be monitored by a number of methods. The most common
involves the drilling of monitoring wells in the immediate vicinity to
detect contamination of the groundwater. The number, location, and
depth of the wells should be governed by prior knowledge of area geol-
ogy, direction and rate of groundwater movement. Routine analyses of
monitoring well samples will indicate fluctuations and trends of pollu-
tant concentrations. Monitoring of city, farm, and stock wells in the
tailings pond area may also be utilized to detect pollutants. A seepage
collection system may be installed under a tailings pond during con-
struction. Perforated or porous pipe installed under the lining material
drains seepage liquids into a collection basin located outside the pond
dikes. An electrical sensing system, employing a series of metal pins
inserted in the pond bottom prior to liner installation, has been used.
Waterproof cables connect the pins through a selector switch to a
resistivity meter. Resistance readings may be taken between selected
pins to detect leaks in the liner. The use of these methods to obtain
quantitative and qualitative information on seepage is desired. At
best, some seepage may go undetected because of deficiencies of the
methods; therefore, more accurate seepage detection methods are needed.
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SECTION V
COMPACTED EARTH
Compaction of the soil reduces the porosity, thus restricting the flow
of liquid through the soil. A soil suitable for compaction should have
low permeability, high stability, and good resistance to erosion. Soil
permeability is inversely proportional to the thickness of the compacted
layer. The soil is compacted in six-inch layers up to depths of three
feet.
Laboratory tests should be conducted on representative soil samples
to determine natural permeability and thickness of the compacted layer
that will reduce permeability to the desired level. Permeabilities of
soil for any combination of treated or compacted thickness and liquid
head may be calculated by the following formula developed by Casa-
grande.*
K = ^ (6)
h
where K = Casagrande permeability (cm/sec)
v = linear velocity of liquid (cm/sec)
AL = thickness of treated layer (cm)
h = liquid head (cm)
For the special case h = AL, then K = v. This condition does not
exist under normal pond conditions; therefore, K must not be con-
fused with actual seepage rates.
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The moisture level in the soil affects the degree of compaction and
thus the permeability.6 Soils from two different areas were tested
and showed maximum compaction and minimum permeability at 14
to 17 percent moisture respectively. An optimum moisture level
existed for maximum compaction after which an increase in perme-
ability occurred. Also, the optimum moisture level for maximum
compaction depended upon the type of soil; therefore, compaction
tests must be performed on each soil to determine optimum conditions.
When the moisture content of the soil is optimum, a compaction
greater than 95 percent of maximum density may be obtained by
approximately six passes with a tamping roller followed by four
passes with a rubber-tired roller.
Even under optimum conditions of compaction, soil permeabilities
may change over a period of time. Uncompacted soil becomes more
impermeable in ponds due to the filling of interstices by dispersed
fine solids; e.g., one uncompacted test pond seepage rate decreased
from 163 to 36 cubic feet per year over a one-year period.^ Com-
paction of a pond located on the same soil type resulted in a decreased
seepage rate from 35 to 6 cubic feet per year over the same period
of time. Although tests indicate that soil compaction reduces the
seepage rate, the permeability of the soil may remain too high for
some seepage requirements.
The seepage rate of compacted earth liners is often greater than the
evaporation rate from the pond. Should strict standards for seepage
be imposed, this method of pond sealing would be inadequate in many
cases.
The contained waste may have either detrimental or beneficial effects
on the permeability of the soil. Acid wastes may react with the soil
and destroy its expansion capabilities. Alkaline wastes may contain
compounds, such as sodium carbonate, that are beneficial in reducing
the soil permeability. Prior tests should be conducted to determine
the soil permeability effects of the waste to be contained.
Physical factors, including freezing, thawing, drying, and wetting,
may affect the lining. Cracking of the lining caused by one or more
of these factors results in large increases in permeability. If possible,
the lining should be kept moist to maintain stable conditions.
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SECTION VI
CLAY SEALANTS
High-swell clay minerals have been widely used to control excessive
seepage in soil by decreasing the permeability. Bentonite is a hetero-
geneous substance composed of mpntmorillonite and small amounts of
feldspar, gypsum, calcium carbonate, quartz, and traces of other
minerals. Bentonite has colloidal properties due to the small size
of the particles and negative charge. Seventy to ninety percent of
the particles are finer than 0.6 micron.7 Bentonite has the capa-
bility of absorbing approximately five times its weight in water and
occupies a volume 12 to 15 times its dry bulk at maximum saturation.8
The sodium content of the clay has a significant effect upon the
swelling characteristics of the clay.7* 9 In the presence of a high
ratio of sodium to calcium, much larger quantities of water are
sorbed and swelling increases. Clays with a low ratio have a
tendency to flocculate and settle from suspensions. The use of
chemicals to increase the sodium to calcium ratio in the clay min-
erals will be discussed in a later section of the report.
High-swell bentonites are found in Wyoming, South Dakota, Montana,
Utah, and California. An application rate of two pounds per square
foot is desirable. The cost including application is about $1.30 per
square yard for short transportation distances.
Various methods have been investigated for the application of bentonite
seals.10 Bentonite may be applied by mixing with soil in a ratio of
one to eight either in the surface or buried under a layer of soil.
Another method, buried membrane, involves placement of a layer of
bentonite one-half inch thick on the subsurface topped with six inches
10
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of soil. A bentonite suspension applied to the soil or a gravel
surface has proved unsuccessful. Large quantities of bentonite are
required to seal coarse soils; therefore, the method may be pro-
hibitive in cost. The buried mixture and the buried membrane
were found to be the most effective bentonite sealing methods.
Application of a buried mixture reduced the seepage rate of one
soil from 1.8 to 0.06 feet per day. The buried membrane reduced
the seepage rate of the same soil to 0.01 feet per day.
Low-swell clays have had limited use as sealants, but some research
has been conducted on their sealing characteristics.11 Low-swelling
clays, such as hydrated mica and kaolin, are located in Nevada and
other western states. These clays are economical and possibly more
stable than high-swell clays. Research has indicated that low-swell
clays are affected less by increased concentrations of magnesium or
calcium in water than high-swell clays, and damage from drying may
be less severe. Further investigations are warranted.
11
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SECTION VII
CHEMICAL SEALANTS
Under certain conditions soil permeability is reduced through the
application of chemicals. ^ • 6, 12, 13 chemical sealing agents
physically fill the interstices of the soil or chemically react with
the soil constituents to form a more impermeable membrane. Seal-
ant tests must be performed on each type of soil due to the highly
variable seepage rates that are obtained. No single chemical has
been found to effectively seal all soils. The life of the seal is
affected by freezing and thawing, wetting and drying, reaction
with constituents in the pond wastes, and leaching of the sealing
agent by waste liquid.
Chemical sealants are applied by surface spraying, mixing with
the soil, or as additions to the waste discharge to the pond. The
chemical is mixed with the soil to a depth of approximately six
inches followed by compaction or is sprayed on the previously
compacted surface.
Research investigations have established a relationship between
the sodium adsorption ratio (SAR) and soil permeability.7* 9
Several cations may be attached to a negatively charged clay soil
particle. The cations exchange with other cations contained in
liquid seeping through the soil. The exchange process alters
the soil characteristics, producing either a more dispersed or
flocculated soil aggregate. As the ionic ratio of sodium to calcium
and magnesium increases, the clay particles become more dispersed
and fill the pores of the soil. The ratio may be adjusted to obtain
minimum permeability. Too high a ratio will produce a liquid
state of the soil that increases the permeability and weakens the
12
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physical structure of the pond. Generally, laboratory tests indi-
cated the permeability decreased by a factor of ten as the sodium
adsorption ratio changed from 10 to 80. The formula used for calcu-
lating the ratio is as follows:
Na+
Note: Ionic concentrations expressed in milliequivalents per liter.
Sodium carbonate, sodium silicate, and sodium pyrophosphate were
the most effective sodium-bearing chemicals tested. Sodium carbonate
was the superior of the three, remaining an effective sealant after
five years. ^ Treated ponds that have become more permeable over
a period of years have been restored to their original state of imper-
meability by reapplication.
The effect of clay and sodium carbonate on sand may be seen in
Table 1. Each type of clay was added to three composites of sand
having natural permeabilities of 1,732, 713, and 135. The per-
centage of clay added was different for each sand composite. The
percentage of montmorillonite was low but resulted in reducing
permeabilities comparable to the other clays. Further investiga-
tions are needed to determine the sealing effects of higher percent-
ages of montmorillonite clay. Further reductions in permeabilities
ranging from 45 to 93 percent were obtained by adding sodium
carbonate to a sand-clay mixture. The wide range in permeabilities
after treatment indicates the effect of the individual soil character-
istics and proves the necessity of prior soil testing to determine
the benefits of clay and chemicals.
Sodium pyrophosphate and sodium silicate are also promising soil
sealants.51 15 The choice of these sealants was based on sealing
efficiency and costs. Soil treated with sulfuric acid and sodium
silicate prior to compaction resulted in significant seepage reduc-
tion. Ponds receiving sulfuric acid-bearing effluents should be
compatible with this sealant. Zeogel, an attapulgite clay drilling
mud, was a promising sealant used in another sealant study.6
Seepage was reduced to less than six inches per year by applica-
tion of a two percent solution.
13
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Table 1. PERMEABILITIES OF OTTAWA SAND COMPOSITE14
Hydraulic Conductivity, ft/yr
Clay type
Illite
fi
tt
Kaolinite
ti
»t
Percent
clay
7.5
4.0
3.0
10.0
5.0
5.0
Natural
composite
1,732
713
135
1,732
713
135
With clay
added
326
161
79
297
215
108
With Na2C03
added
0.4 Ib/sq yd
22
22
12
30
72
24
(Bentonite)
Mont morillonite
ti
ti
1.5
0.25
0.25
1,732
713
135
757
182
34
67
100
13
1 1 fi 17
Polymer compounds have also been investigated. ' 1D' In one
group of sealants studied, a sprayable, water soluble, liquid vinyl
polymer was utilized with success as a soil stabilizer and deserves
further study for use as a pond sealant. Polymer application re-
quires that the subsurface be smooth and firm; pre-wetting of the
soil prevents pinhole formation in the film.
Rubber latex has been used in sealant studies for control of acid
mine drainage.1** The seal penetrated the top ten inches of soil
which was unsatisfactory for the testing purposes; however, addi-
tional investigations might prove the suitability of latex as a pond
sealant.
Soil permeability tests are extremely time consuming; however, in-
vestigations have shown a relationship between permeability and liquid
limit.19 Liquid limit is the percent water content corresponding to
14
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the arbitrary limit between the liquid and plastic states of soil con-
sistency. Liquid limit measurements on soils may be made rapidly,
thus reducing the time required to select the most promising sealant
from a group of sealants. Final selection may be made on the basis
of permeability tests.
15
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SECTION VIII
WASTE TAILINGS SOLIDS
Mining industries discharge large quantities of sand and slimes
following extraction of the desired material. For example, uranium
ore is ground to a minimum size of 200 mesh; slimes, the finest
particles, represent 20 percent of the total waste. The fine solids
have a sealing effect on tailings ponds by reducing the seepage
rate as solids accumulate on the pond bottom.
Due to the sealing characteristics, ore wastes are beneficial in
reducing seepage in ponds. Covering a new pond bottom with
tailings solids should produce a condition similar to an old pond
with accumulated tailings, thereby eliminating initial high seepage
rates.
Research into the utilization of waste solids as sealants is needed
to prove their value. Advantages of using waste solids include
proximity to the site and negligible material cost.
16
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SECTION IX
ASPHALT SEALANTS
Asphalt for membrane liners is specially prepared at the refinery
by forcing air in the presence of a catalyst through the mixture to
produce characteristics of resistance to low temperatures, toughness,
and durability .2 Compaction of the top six inches of the subsurface
produces a firm smooth base for the liner. Soil sterilants are used
to prevent growth of vegetation on the subgrade that would puncture
the liner. The subsurface is sprinkled with water prior to asphalt
application to prevent small holes from occurring in the liner due
to dust. The asphalt is applied at 400° F under pressure of about
50 pounds per square inch through slot-type spray nozzles as used
in highway application. An application rate of 1.25 gallons per
square yard produces a suitable liner one-fourth inch thick. The
sections are joined by overlapping one to two feet. An earth cover
is added to protect the liner from puncture. Aging characteristics
have been investigated in the laboratory to provide a means of pre-
dicting the useful life of a liner.20 Penetration, ductility, and
softening point tests were performed on samples from asphalt liners
that had been in use for periods as long as 18 years to determine
an aging index. Laboratory accelerated aging methods were used
to predict the life expectancy of new asphalt liner material. A 14-
day oven exposure of asphalt to 140° F resulted in an aging index
similar to that obtained by 14-year field exposure. The asphalt
must exhibit a life expectancy of 14 years to qualify as a liner
material. Seepage losses have been 8.5 feet per year in one brine
test pond.*
Studies have shown that addition of rubber (three to five percent)
improves the properties of asphalt: greater resistance to flow,
increased elasticity and toughness, less brittleness at low tempera-
ture, and greater resistance to aging.^2
17
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Asphalt concrete linings are composed of a carefully controlled hot
mixture of asphalt and well-graded aggregate. The mixture is designed
for water tightness and an optimum degree of plasticity. Standard
road-paving equipment is used to apply a two to three inch layer.
Seepage losses have been reduced to 0.7 feet per year with this type
of liner.*> 2 A service life of 14 to 20 years can be expected and
the liner will support traffic without damage.
A cationic water-borne sealant has been developed by addition of a
cationic surfactant as an emulsifer to an asphalt base material.21
A cationic surfactant was chosen over an anionic and nonionic sur-
factant because it possessed a high degree of affinity for almost all
surfaces and adhered to soil particles in the presence of large volumes
of water. The flow of the seeping water carries the asphalt droplets
to the soil particles below the pond bottom. The asphalt droplets
are deposited on the soil and eventually adhere to form a membrane
that reduces seepage. Seepage reductions of 99 percent, or less
than one foot per year, have been obtained with application rates
of 0.75 gallons per square yard. The effect of waste constituents
on this sealant should be studied.
A new type of asphalt liner has been developed that uses a poly-
propylene fabric base followed by the application of two coats of
asphalt.22 The. liner panels are field-sewn by means of a portable
machine, and asbestos fibers are mixed with the second asphalt
application to prevent cold flow on pond slopes.
18
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SECTION X
SYNTHETIC MEMBRANE LINERS
Synthetic membrane liners are the only liners that prevent all seepage,
and have become increasingly popular since their introduction in 1953.
Synthetic liners may be broadly classified as latexes, plastics, and
fiberglass; the most widely used are polyvinyl chloride (PVC), butyl
rubber, and hypalon.^3. ^4 Polyethylene, chlorinated polyethylene
(CPE), neoprene, and ethylene propylene diene monomer (EPDM) are
used to a lesser extent. The liners range in thickness from 10 to 60
mils with life expectancies of 20 years.
Nylon reinforced liners are used on steep slopes where added strength
is required. The type of effluent to be contained, composition of the
subsurface, and nearness of earth cover must all be considered in
order to choose the best liner for the pond.
Available plastic liners include polyvinyl chloride (PVC), polyethylene,
and chlorinated polyethylene (CPE). The liners resist inorganic
chemicals but are attacked by organic substances. Polyethylene
liners are seldom used now because of the development of improved
plastics.25 Polyvinyl chloride is the most widely used because of
low installation cost, puncture resistance, and durability. Polyvinyl
chloride liners are subject to deterioration from sunlight; therefore,
the liner must be covered. An earth cover of six to twelve inches
will protect polyvinyl chloride from sunlight and from animal and
vehicle traffic. Chlorinated polyethylene is less affected by sunlight,
but is more expensive. A polyvinyl chloride bottom cemented to
chlorinated polyethylene sides has been used to prevent deteriora-
tion and reduce liner costs.
19
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Available rubber liners include butyl, ethylene propylene diene monomer
(EPDM), neoprene, and hypalon. Butyl rubber and hypalon are
the most widely used. The liners, although more costly than plastic,
may be more economical for some locations as the material does not
require an earth cover. Exposed butyl rubber was selected as the
most economical liner for a 110-acre reservoir.26 Butyl rubber is
durable, watertight, and flexible. One disadvantage of this liner
is that cemented seams have only 60 percent strength; therefore
seam separation is more likely, increasing the possibility of leakage.
Hypalon liners are inert and long lasting; however, shrinkage from
sunlight exposure poses a problem. Liners of EPDM material are
also susceptible to shrinkage from sunlight when not properly formu-
lated and cured, but are more resistant to ozone than butyl.^7
Fiberglass liners are newer than other types of synthetic liners and
have not been time tested for durability and seepage prevention.28
Composed of a fiberglass mat impregnated with epoxy resin, the liners
are thicker and stronger than other types (0.1 inch) and can support
traffic without puncturing. Although more expensive than other types
of liners, earth covers are not required. Some liners tested for perme-
ability showed flow areas of poorly impregnated mats which resulted
in a porous and structurally weak liner.
All synthetic liners are installed similarly and site preparation is
important to prevent punctures in the lining.29 The surface must
be graded smooth and sharp rocks, sticks, and vegetation removed.
Objects not removable are covered with a layer of earth. If air
bubbles are anticipated, the bottom should be sloped to allow the
bubbles to escape. Covering the liner after installation provides
weight to aid in gas removal.
An anchor trench for the liner is dug at the top of the berm. Liners,
in sheets as large as 60 feet by 700 feet, are unfolded on the pond
bottom with one end buried in the anchor trench. Sheets are over-
lapped two to four inches to allow bonding. A flat board may be
used under the liner to provide a smooth surface for cementing the
edges. The seam develops shear strength in about 15 minutes and
must be carefully inspected to detect and reseal any flaws in the
seam.
20
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The pond side slopes should not be steeper than 3:1 when an earth
cover is to be installed. A six to twelve inch cover is adequate
to protect the liner from traffic and exposure. Equipment must be
moved only on previously covered areas to prevent damage to the
liner.
21
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SECTION XI
COST OF POND LINERS
Approximate costs of installed liners, ranging from $0.02 to $0.55
per square foot, are shown in Table 2. The cost of earth cover
was included only for polyvinyl chloride. Esimated labor costs
included in Table 2 are as follows:
1. chemical application = $0.02/sq ft
2. uncovered synthetic liner = $0.04/sq ft
3. covered synthetic liner including cover costs = $0.07/sq ft
The installation and labor cost are identical for sodium carbonate
and sodium silicate because chemical costs are less than $0.005 per
square foot.
The total cost of a tailings pond liner may be approximated from
Table 2, Figure 1, and Figure 2 if the waste discharge rate,
evaporation rate, and annual rainfall are known. The pond size,
obtained from Figure 1, is used to determine the total cost from
Figure 2. For example:
1. 300 gal./min waste discharge to pond for disposal by
evaporation
2. Evaporation = 36 in./yr
3. Annual rainfall = 12 in./yr
4. Liner of 20 mil polyvinyl chloride with earth cover
The net annual waste loss is 24 inches after correcting the evapora-
tion for the rainfall. From Figure 1, a 243-acre pond is required
to contain a 300 gallon per minute waste discharge at the 24 inch
per year net annual waste loss. Table 2 shows an installation cost,
including labor and earth cover, of $0.18 per square foot for 20
mil polyvinyl chloride. From Figure 2, a cost of $1.8 million would
be incurred in lining a 243-acre pond at $0.18 per square foot.
22
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Table 2. COST OF INSTALLED LINER
Liner $/sq ft
Bentonite
2 Ib/sq ft 0.14
Chemical
Sodium Carbonate , 0.02
Sodium Silicate 0.02
Sodium Pyrophosphate 0.03
Zeogel 0.03
Coherex 0.03
Asphalt
Asphalt Membrane 0.14
Asphalt Concrete 0.20
Rubbera
Butyl
1/16" 0.42
3/64" 0,36
1/32" 0.30
EPDM
1/16" 0.41
3/64" 0.35
1/32" 0.29
Synthetic Membrane
PVC
10 mils 0.13
20 mils 0.18
30 mils 0.22
Chlorinated Polyethylene (CPE)
20 mils 0.26
30 mils 0.34
Hypalon
20 mils 0.26
30 mils 0.34
Fiberglass
1/8" 0.55
aNylon reinforced rubber costs an additional $0.10/sq ft.
23
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TOOh
50
100
ISO 2OO 250
POND SIZE (ACRES)
3OO
350
400
FIGURE I - TAILINGS POND SIZE
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50
IOO
150 200
POND SIZE (ACRES)
FIGURE 2 - LINING AND INSTALLATION COST
250
3OO
350
400
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SECTION XII
REFERENCES
1. Morrison, W. P.., R. A. Dodge, and J. Merriman. Pond Linings
for Desalting Plant Effluents. U.S. Bureau of Reclamation,
Engineering Research Center, Denver, Colo. Report Number
REC-ERC-71-25. May 1971. 51 p.
2. Day, M. E. and E. L. Armstrong. Brine Disposal Pond Manual.
U.S. Office of Saline Water, Washington, D.C. Research and
Development Progress Report Number 588. August 1970. 134 p.
3. Kohler, M. A., T. J. Nordenson, and W. E. Fox. Evaporation
from Pans and Lakes. U.S. Weather Bureau, Washington, D.C.
Research Paper Number 38. May 1955. 21 p.
4. Water-Loss Investigations: Lake-Hefner Studies, Technical
Report. U.S. Geological Survey, Washington, D.C. Profes-
sional Paper 269. 1954. 156 p.
5. Gooding, W. T., A. D. Bergmann, et al. Feasibility Study
of Chemical Sealing of Soils. U.S. Office of Saline Water,
Washington, D.C. Research and Development Progress Report
Number 266. June 1967. 31 p.
6. Mannion, J. J. and D. J. Porter. Soil Sealing Chemicals and
Techniques. U.S. Office of Saline Water, Washington, D.C.
Research and Development Progress Report Number 381. June
1968. 31 p.
26
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7. Dirmeyer, R. D. Report of Sediment Lining Investigations,
Fiscal Years 1954-55. Colorado A and M College, Fort Collins.
Report Number CER 55RDD7. June 1955. 120 p.
8. Dirmeyer, R. D. Report of Sediment Lining Investigations,
Fiscal Year 1956. Colorado A and M College, Fort Collins.
Report Number CER 56RDD17. August 1956. 34 p.
9. Matthew, F. L. and L. L. Harms. Sodium Adsorption Ratio
Influence on Stabilization Pond Sealing, J. Water Pollution
Control Federation. 41^383-391, Part 2, November 1969.
10. Rollins, M. B. and A. S. Dylla. Bentonite Sealing Methods
Compared in the Field. Journal of the Irrigation and Drainage
Division, Proc. Amer. Society of Civil Engineers. 96(IR2):
193-203, June 1970.
11. Rollins, M. B. Controlling Seepage with Playa Sediments.
Nevada Ranch and Home Review. 4(5): 14-15, Spring-Summer
1969.
12. Proceedings Second Seepage Symposium. U.S. Department of
Agriculture, Agricultural Research Service, Washington, D.C.
Report Number ARS 41-147. March 1968. 145 p.
13. Disposal of Brine Effluents from Desalting Plants. Review
and Bibliography. U.S. Bureau of Reclamation, Technical
Evaluation Branch, Denver, Colo. General Report Number
42. March 1969. 29 p.
14. Agey, W. W. and B. F. Andrews. Reduction of Seepage
Losses from Canals by Chemical Sealants. Part I - Laboratory
Research on Sodium Carbonate and Other Compounds. U.S.
Bureau of Mines, Washington, D.C. Report of Investigations
6584. 1965. 33 p.
15. Sewell, J.I. Laboratory and Field Tests of Pond Sealing
by Chemical Treatment. University of Tennessee, Agricultural
Experiment Station, Knoxville, Bulletin 437. March 1968.
25 p.
27
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16. Jones, C. W. Effect of a Polymer on the Properties of Soil-
Cement. U.S. Bureau of Reclamation, Office of Chief Engineer,
Denver, Colo. Report Number REC-OCE-70-18. May 1970.
9 p.
17. Morrison, W. R. Chemical Stabilization of Soils, U.S. Bureau
of Reclamation, Engineering and Research Center, Denver,
Colo. Report Number REC-ERC-71-30. June 1971. 39 p.
18. Use of Latex as a Soil Sealant to Control Acid Mine Drainage.
U.S. Environmental Protection Agency, Office of Research and
Monitoring, Washington, D.C. Report Number 14010 EFK 06/72.
June 1972. 84 p.
19. Sewell, J.I. and C. R. Mote. Liquid-Limit Determination for
Indicating Effectiveness of Chemicals in Pond Sealing. Trans.
of Amer. Society of Agricultural Engineers. 12(5):611-613,
Septembe r-Octobe r 1969.
20. Laboratory Investigation of Aging Characteristics of Asphalt
Cements Used in Membrane Lining Construction. U.S. Bureau
of Reclamation, Chemical Engineering Branch, Denver, Colo.
Report Number ChE-91. June 1969. 24 p.
21. Dybalski, J. N. A Cationic Water-Borne Soil Sealant. Armour
Industrial Chemical Company, Chicago, 111. (Presented at
Symposium on New Uses for Asphalt before the Division of
Petroleum Chemistry, Inc., American Chemical Society. Atlantic
City, N.J. September 8-13, 1968.) 4 p.
22. Field-Sewn Joints Make New Liner Tailored to Pit. Oil and
Gas Journal. 6JK6): 51-53, February 8, 1970.
23. Kumar, J. and J. A. Jedlicka. Selecting and Installing Synthetic
Pond-Linings. Chem. Eng. 8JK3):67-70, February 5, 1973.
24. Lee, J. Selecting Membrane Pond Liners. Pollution Engineering.
6:33-40, January 1974.
28
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25. Laboratory and Field Investigations of Plastic Films as Canal
Lining Materials—Open and Closed Conduits Systems Program.
U.S. Bureau of Reclamation, Chemical Engineering Branch,
Denver, Colo. Report Number ChE-82. September 1968. 46 p.
26. Chuck, R. T. Largest Butyl Rubber Lined Reservoir. Civil
Engineering. 40; 44-47, May 1970.
27. Hickey, M. E. Synthetic Rubber Canal Lining. U.S. Bureau
of Reclamation, Engineering and Research Center, Denver, Colo.
Report Number REC-ERC-71-22. April 1971. 43 p.
28. Hickey, M. E. Glass-Fiber Reinforced Polyester Lining. U.S.
Bureau of Reclamation, Office of Chief Engineer, Denver, Colo.
Report Number REC-OCE-70-36. August 1970. 19 p.
29. Staff, C. E. Seepage Prevention with Impermeable Membranes.
Civil Engineering. 37;44-46, February 1967.
29
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report No.
3. Accession No.
w
4. Title
AN EVALUATION OF TAILINGS PONDS SEALANTS,
7. Author(s)
Clark, D. A. and Moyer, J. E.
5. Report Date
6.' . -. . •
8. P.' rforming Organization
Report No..
9. Organization
United States Environmental Protection Agency
Robert S. Kerr Environmental Research Laboratory
P.O. Box 1198, Ada, Oklahoma 74820
10. Project No.
21AGF-16
11. Contract/Grant No.
13, Type of Report and
Period Coveted
12. Sponsorin- Organ.1 -at/on
15. Supplementary Notes
Environmental Protection Agency report number EPA-660/2-74-065, June 1974.
16.
Abstract
This report presents a summary of the rather limited information available in the
literature pertaining to the use of sealants for mine and mill tailings.ponds. Included
in the report is a discussion of currently employed seepage detection methods, as
well as the various types of sealants currently in use—compacted earth, clays,
chemicals, waste tailings solids, asphalt, and synthetic membranes. Only properly
installed synthetic liners will prevent all seepage. Installation costs of the sealants,
including labor, are discussed and graphs for estimating costs based on pond size
are presented. Regulations governing the amount of seepage allowed are ill-defined
or non-existent in the majority of States. (Clark - EPA)
17a. Descriptors
•"Linings, *Soil sealants, "Impervious membranes, Waste disposal, Liquid wastes,
Solid wastes, Permeability, Seepage, Monitoring, Liquid limits, Plastics.
17b. Identifiers
liner costs, Latexes, Fiberglass, Seepage detection.
17c. COWRR Field & Group
04A, 05A, 05E, 05G
18. Availability
'19. Security Class.
(Repoi.)
•>0. Ser
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