United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/124 July 1986
v>EPA Project Summary
In-Situ Methods to Control
Emissions from Surface
Impoundments and Landfills
Charles Springer, K. T. Valsaraj, and L. J. Thibodeaux
The full report presents the results of
a two-year study which included labo-
ratory investigations as well as a com-
prehensive literature review on meth-
ods of reducing the rate of emissions of
volatile chemicals from surface im-
poundments and landfills. It presents
information on the following in-situ
methods which may be employed to re-
duce emission rates: air supported
structures, floating solid objects, shape
modification, aerodynamic modifica-
tion, floating oil and/or surfactant cov-
ers and synthetic membranes over
landfills.
Conclusions are drawn with respect
to the suitability of each of the methods
under various circumstances and the
degree of control which might be ex-
pected.
The full report was submitted in ful-
fillment of Cooperative Agreement
No. 810856-01 -1 by the University of Ar-
kansas under the sponsorship of the
U.S. Environmental Protection Agency.
This report covers a period from Octo-
ber 1,1983 to September 30, 1985. The
full report is under CR710856.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The full document finalizes a study in-
volving laboratory and pilot scale inves-
tigations as well as a literature review
that was conducted to evaluate in-situ
control methods that might be readily
adopted for use at existing treatment,
storage, and disposal facilities (TSDF)
for reducing emissions of Volatile Or-
ganic Chemicals (VOC). Emissions of
VOC from TSDFs are a significant
source of contaminants entering the at-
mosphere. It has been reported that at
least one-third of the total emissions of
over 50 volatile, hazardous chemicals
are from TSDFs.
The main focus of federal and state
regulations of TSDFs in the past has
been to minimize contamination of sur-
face and ground water, to prevent air
contamination from incineration, and to
prevent accidental exposure. However,
more recently, attention has been di-
rected to direct emissions from TSDFs.
Much work had been done in quan-
tifying impoundment and landfill emis-
sions, and simplified models of the
mass-transfer processes had been de-
veloped and were shown to be gener-
ally valid. With that background, it was
possible to propose methods to reduce
the emissions. Some control methods
simply interpose a physical barrier be-
tween the impoundment and the atmo-
sphere, whereas others attempt to mod-
ify the mass transfer process in more
subtle ways to bring about reductions.
This work was undertaken to consider
all types of controls which might be
added to existing facilities in order to
reduce direct emissions from surface
impoundments and landfills.
The methods treated in this docu-
ment include: complete, positive con-
trol by use of an enclosure which pre-
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eludes loss of any vapor to the air, such
as a domed structure of synthetic mem-
brane covering the entire impound-
ment; floating solid objects which re-
strict the exposed surface area of the
impoundment; modification of the
shape of the impoundment; aerody-
namic modifications; the addition of
other materials, such as oils or surfac-
tants to the impoundment; and the use
of synthetic liner type membranes over
landfills.
To evaluate a control scheme and to
make a choice of control method, the
purpose of the impoundment and the
goals of the control strategy must be
considered. Frequently the reduction or
elimination of emissions may only
delay the process. To prevent volatile
emissions entirely there must be some
method of destruction of VOC, which
presumes some method of capture after
removal from water. If the goal is to re-
duce the rate of emission, thus to re-
duce the concentration of VOC at some
receptor location, then an absolute
elimination might not be necessary.
The parameters affecting the emis-
sion rate include the wind as well as the
size and orientation of the surface im-
poundment. The mass transfer process
which governs the volatilization of al-
most all the chemicals of interest is the
liquid phase process. Since this is so,
differing rates from one chemical to an-
other are largely a matter of liquid
phase diffusivity differences, and the
rates do not vary greatly from one
chemical to another, in the usual case,
due to vapor pressure variations. The
assumption in this instance is simply
that the volatility is high enough so that
it is not generally limiting. The tempera-
ture of the w^ter has a marked effect
upon the diffusivity; the diffusivity in-
creases approximately as the 1.8 power
of the absolute temperature. Thus, a
high liquid temperature favors more
rapid volatilization.
Control techniques that tend to
change the gas phase resistance will be
effective for only a few chemicals, those
with very low Henry's law constants.
Such materials will display very low
vapor pressure and/or higher solubility
in water.
When immiscible, volatile materials
float on the surface, the emission rate
will be greatly influenced by the gas
phase resistance, which is normally
quite low compared to the liquid phase
resistance. Such instances will be char-
acterized by extremely rapid volatiliza-
tion.
If an impoundment is being used to
carry out aerobic digestion, then a con-
tinual resupply of oxygen is necessary,
and devices such as aerators which are
intended to increase oxygen transfer
will simultaneously increase the
volatilization rate, whereas methods
which reduce volatilization will nor-
mally reduce oxygen transfer as well.
General Conclusions
A number of options are available to
reduce the rate of emissions from sur-
face impoundments. Choosing among
the options involves consideration of
the goals and circumstances surround-
ing the application. Each of the methods
considered was found to provide emis-
sion rate reductions.
In many cases it is impossible to pre-
dict the degree of control that might be
expected with a high degree of accu-
racy. This is perhaps not very signifi-
cant, because it is also impossible to
predict accurately the emissions with-
out controls.
Specific conclusions relating to the
various options considered or studied
in this work are given below.
Complete enclosure of an impound-
ment with an air supported structure
will provide nearly complete control if a
method of collecting the vapors such as
an adsorbent trap is available.
Floating covers will restrict the sur-
face area and thereby reduce emissions
accordingly. These include rafts, syn-
thetic membranes and hollow, inter-
locking spheres. Control of 90% or more
would be possible.
The shape of an impoundment and its
orientation with respect to the wind will
influence the emission rate. Reducing
the fetch (down-wind distance) will re-
duce the emission rate as will increas-
ing the depth.
Wind fences were found to be surpris-
ingly effective in reducing the emission
rate in a laboratory simulator. Reduc-
tions as high as 80% appear to be possi-
ble.
Laboratory simulations showed float-
ing oil layers to be effective in reducing
emissions. In the absence of wind, re-
ductions of over 90% were achieved. Al-
though wind tends to blow the oil cover
to one side, it may still be effective.
Laboratory measurements of perme-
ability of a polyvinylchloride membrane
indicated that such a membrane would
not provide significant protection
against vapor flow out of a landfill.
Study Results
Complete Enclosure by Air
Supported Structures
Complete enclosure of a surface im-
poundment by an air-supported struc-
ture is a feasible control method if a
suitable method is available either to
collect or dispose of generated vapors.
This is the only feasible method if a sur-
face aerator were to be used to improve
oxygen transfer. Air supported struc-
tures are susceptible to wind damage as
well as weathering. Some vapors may
be harmful to the polymeric materials.
The control effectiveness can approach
100%.
Vapors could be collected by con-
trolled venting into an adsorption trap,
or perhaps directly into an incinerator.
The vent gases will be nearly saturated
with water vapor which can interfere
with adsorption.
Floating Solid Objects
Floating solid objects include syn-
thetic membrane covers, rafts, and hol-
low plastic spheres.
Floating synthetic membrane covers
have been used successfully and are
feasible if oxygen transfer is unneces-
sary and if outgassing of the impound-
ment contents is not expected. Some
liner material may be highly permeable
to some organic vapors. The floating
membrane is subject to damage by
weathering and may also be damaged
by contact with the waste. The control
effectiveness can approach 100%.
Rafts and other such structures re-
strict the surface area of an impound-
ment which is exposed to the air and
reduce emissions and oxygen transfer
accordingly. Rafts generally have a
short lifetime because they are dam-
aged by contact with the waste water.
The maximum control effectiveness of
rafts is about 90%.
Floating hollow spheres have been
shown to reduce emissions by as much
as 80 to 90%. The most popular spheres
are made of polypropylene and have
projections to prevent rotation in the
wind. The spheres restrict oxygen ab-
sorption to the same degree that they
reduce emissions; they may be blown
away in a high wind.
Shape Modification of Surface
Impoundments
Shape modification is meant to in-
clude berm height, liquid depth, length
or width of the impoundment and direc-
tional orientation.
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Increasing berm height is an effective
method of emission reduction, al-
though its effectiveness cannot be accu-
rately predicted. This method is effec-
tive in reducing wind-enhanced
emissions, with emissions being ap-
proximately inversely proportional to
the square root of the berm height.
For a given impoundment volume, in-
creasing impoundment water depth will
cause emission reduction by reducing
the surface area. Wind-enhanced mass
transfer coefficients may also be re-
duced at the same time if the actual
water depth is increased.
Wind-enhanced emissions can be re-
duced if the fetch is reduced. Relatively
narrow impoundments will have lower
emissions if the wind is blowing normal
to the longer dimension of the im-
poundment.
Aerodynamic Modification
Laboratory investigations of wind
barriers show them to be quite effective
in reducing emissions under wind-
enhanced conditions. The performance
of perimeter and network fences were
found to be generally similar. The mass-
transfer coefficient was found to be ap-
proximately proportional to the square
root of the fetch to height ratio, up to a
maximum of 160. A commercial, porous
wind fence material commonly used for
dust control was found to be much su-
perior to solid fence material. Wind
fences can potentially achieve emission
reduction of up to 80%. Oxygen absorp-
tion will be affected similarly (Table 1).
Floating Oil Layers
A layer of immiscible liquid floating
on the surface of an impoundment was
found to be quite effective in reducing
emissions. Under conditions of little
wind, volatile materials with low solu-
bility in the oil cover material were con-
trolled more effectively than those
which are more soluble. However, an oil
covering of about one cm depth would
provide at least 90% emission reduction
for any volatile.
In the presence of wind, the covering
may be blown aside. Under windy con-
ditions, the effect of solubility is vari-
able; with low winds, a low solubility in
the oil is preferable, but with higher
winds a high solubility is preferable.
The mixing action of higher winds tends
to cause the volatile solute to transfer to
the oil phase, where emission mass
transfer coefficients are markedly
lower. For the windy conditions, emis-
sion reduction is greater than a simple
Apparent Diffusivities of Sev-
eral Chemical Vapors in a 20-
mil Sample of Polyvinylchloride
Film
ratio of exposed to covered area would Table 3.
predict. Emission reduction of 50 to 80%
may be expected for windy conditions,
depending upon the amount of oil used.
Oxygen absorption will be reduced in
accordance with the fraction of the sur-
face that remains covered by the oil
layer.
Results of pilot-scale measurements
of the effectiveness of oil layers are
shown in Table 2 for no-wind condi-
tions.
Synthetic Liner Covers for
Landfills
Laboratory measurements of the
vapor phase permeability of a 20-mil
polyvinylchloride (PVC) membrane
showed a high permeability for a num-
ber of volatile organic vapors as pre-
sented in Table 3.
The performance of a membrane as a
vapor barrier cannot generally be pre-
dicted and may be disappointing. Typi-
cal results of this work showed the PVC
Table 1. Fence Control Simulation Results at V = 3.9 m/s and V = 2.9 m/s
Results: Corrected to 293K
V (10 cm) =3.9 m/s
Fence height K, Reduction
(cm) (cm/hr) (%)
Diffusivity (at 30°C)
Chemical (cm2/s)
Methanol
Chloroform
Dichloromethane
Bromoform
Carbon tetrachloride
Benzene
Chlorobenzene
o-Dichlorobenzene
Toluene
m-Xylene
Acetone
Diethyl Ether
Octane
Dodecane
Cyclohexane
n-Hexane
n-Pentane
2.68 E-S
1.4 E-4
2.37 E-4
3.35 E-4
1.69 5-5
2.53 E-4
5.03 E-4
4.96 E-4
4. 12 E-4
4.73 E-4
2.17 E-4
1.79 E-4
7.05 E-5
1.06 E-3
2. 18 E-5
1.48 E-5
2.02 E-5
No Fence
Perimeter Fence
Solid:
90 deg.
80 deg.
45 deg.
Porous:
90 deg.
Solid Fence Networks
5 h
10 h
0.0
1.7
3.2
6.4
6.4
6.4
6.4
1.7
1.7
3.424
2.750
2.642
2.251
2.087
3.211
0.7445
0.7328
0.7540
0.0
19.7
22.8
34.3
39.1
6.2
78.3
78.6
78.0
V (10 cm) = 2.9 m/s
No Fence
Perimeter Fence
Solid:
90 deg.
0.0
1.7
3.2
2.375
1.403
1.893
0.0
40.9
20.3
Table 2. Fractional Reduction in Emissions Using Various Mineral Oil Layer Thicknesses
Oil
Thickness
(cm)
0.20
0.27
0.30
0.46
Temp. Ranges, °K
Air Water
303-309
300-306
303-304
303-304
320-318
321-318
319-317
319-317
Fractional Reduction
Benzene
0
0.10
0.32
0.53
Acetone
0.35
0.43
0.70
0.68
n-Propanol
0.38
0.60
0.58
0.69
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membrane to be the equivalent of only
a few inches of porous soil covering.
Little data on the permeability of vari-
ous polymers to vapors are available in
the public domain. However, simple
laboratory tests are available to mea-
sure the permeability of specific mem-
brane materials to specific vapors.
Charles Springer and Kalliat T. Valsaraj are with the University of Arkansas,
Fayetteville, AR 727O1; Louis J. Thibodeaux is with the Louisiana State
University, Baton Rouge. LA 70803-6421.
Paul R. dePercin is the EPA Project Officer (see below).
The complete report, entitled "In-Situ Methods to Control Emissions from Surface
Impoundments and Landfills," (Order No. PB 86-121 365/AS; Cost: $11.95.
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-85/124
0000329 PS
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CHICAGO
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