United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/2-84-050 Apr. 1984
r/r,o
Project Summary
Landfill Research at the Boone
County Field Site
Richard J. Wigh
From June 1971 until August 1980,
the Municipal Environmental Research
Laboratory constructed and monitored
five municipal waste landfill test cells in
Boone County, Kentucky. Primary
objectives were (1) to evaluate leachate
quantities and characteristics, gas
composition, temperature conditions,
and a soil liner for leachate control and
(2) to compare the performance of a
field-scale cell with smaller, similarly
constructed cells.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Five test cells containing municipal
solid waste were constructed at the
Municipal Environmental Research Labo-
ratory's Boone County Field site near
Walton, Kentucky, during 1971 and
1972. Cells 1 and 2D were constructed
similarly to normal landfill cells and
contained 286,000 and 72,450 kg of dry
refuse, respectively. The base of Cell 1
was lined with a 0.76-mm synthetic liner,
on top of which was placed a 45.7-cm-
thick, compacted, clayey silt liner. Both
the synthetic and soil liners were
provided with drains for leachate collec-
tion. A 0.6-m, compacted soil cover was
placed over the refuse in Cell 1. A
continuous synthetic liner was placed on
the sides and base of Cell 2D. Cover over
the .refuse consisted of 0.3-m of com-
pacted soil beneath a 0.3-m surficial layer
of pea gravel. A grid of 150-mm-high clay
dikes was constructed within the gravel
to promote uniform percolation into the
refuse. (See Figure 1).
Cells 2A, 2B, and 2C were constructed in
identical, cylindrical steel pipes, 1.83 m in
diameter by 3.66 m long. These small-
scale cells contained approximately 2100
kg of dry refuse each. These units were
constructed to compare performance of
small-scale systems with the field-scale
cell (2D) and to evaluate variations within
identical cells.
Cell construction data are summarized
in Table 1. All cells were monitored for
leachate quantity and characteristics, gas
composition, temperature, and settlement
until they were closed in August 1980.
Findings
Leachate Volume
Leachate was initiallly collected from
both the upper and lower pipes of Cell 1
approximately 2 months after construc-
tion. The observation unit adjacent to the
cell in which leachate was collected
collapsed in February 1979, and after
that, volume measurements were not
possible. At that time, 1.07 million liters
of leachate—representing 27.5% of the
precipitation recorded at the site—had
been collected.
The leachate volume predicted by using
the water balance method is shown
together with the cumulative leachate
volume in Figure 2. At the time leachate
volume measurements ceased, 1.07
million liters had been collected—only a
6% difference from the 991,600 liters
predicted by the water balance method. If
yearly average evapotranspiration values
had been used, rather than ones computed
from actual climatic conditions (precipita-
tion and temperature) experienced, the
difference would have been 33%. This
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To Equipment Storage Shed
and Site Office Trailer
Leachate
Spray Irrigation
Area
-N-
I
Observation
Gallery
Instrumentation
Shed
Weather Station
Leachate Holding Pond
Scale: 1"~ 50'
Figure 1. Site layout of Boone County test cells.
Table 1. Summary of Cell Data
Test Cell
Item
Cover soil classification
Depth of soil cover, m
Surface area of refuse, mz
Maximum depth of refuse, m
Mass of refuse, kg (dry)
Dry density of refuse, kg/m3
Moisture content of refuse.
% wet wt.
1
CL*
0.60
432.3
2.56
286,000
429
27.6
2A
CL
0.30
2.627
2.56
2,046
304.3
22.5
2B
CL
0.30
2.627
2.56
2,113
314. J
27.1
2C
CL
0.30
2.627
2.56
2,135
317.6
24.1
2D
CL
0.30
72.83
2.44
72,450
407.7
31.8
"USCS soil classification
large difference indicates that leachate
volume design calculations should be
based on extreme as well as average
values. Leachate was also collected during
the summer and fall, which is rarely
predicted by the water balance method.
One of the objectives of the Cell 1 tests
was to evaluate the effectiveness of the
soil liner in containing leachate. The
quantity of leachate from the pipe
beneath the soil liner was equal to or
greater than that volume from the upper
pipe untilJanuary 1972. This was caused
by leaving the valve closed on the upper
pipe except for weekly sampling, thereby
inducing sufficient head to cause leakage
into the lower pipe. Flow quantity
remained relatively constant after 1972
through a wide yearly variation in total
leachate flow; this indicated soil liner
saturation and relatively constant head
and soil permeability throughout the later
years of cell life. Tests of the soil liner at
closure showed reductions in permeabil-
ity of the soil of 2 to 3 orders of
magnitude, from the original 2x1 CT5 to 4
x 10~7to2x1CT8cm/sec.
Although greater than 99% of the total
leachate flow was collected from the
upper pipe, it appears that the Hypalon®*
liner and the soil liner were functioning
together and that the large percentage of
the leachate collected in the upper pipe
was not due to the soil alone. Apparently
the Hypalon® sheet blocked deep perco-
lation, forcing flow along the refuse-soil
interface, and resulted in the high
percentage of leachate being collected in
the upper pipe. If a free-draining granular
layer had been placed between the
Hypalon® and the base of the soil liner, a
more definitive evaluation of the soil liner
effectiveness could have been made.
The experimental design for Cells 2A-
2D called for the input of approximately
500 mm of precipitation each year into all
of the cells. Average annual rainfall at the
site exceeded 1,000 mm, so all.of the cells
were periodically covered—the cylinders
with caps, and 2D with nylon-reinforced
Hypalon®. Generally, about 100 mm of
precipitation fell on the cells before they
were covered for a 2- to 3-month period.
During the final year of the project, the
covers were left off. Evaporation and
transpiration losses were further reduced
by use of the 0.3-m gravel layer overlying
the soil cover; this layer prevented
vegetative growth and shielded the water
stored on top of the soil cover from direct
sunlight. Leachate volume collected
from the four cells is shown in Figure 3.
'Mention of trade names or commerical products
does not constitute endorsement or recommenda-
tion for use.
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n
O
I
•g
jmulative Lea
O
1.400
1,200
1,000
800
600
400
200
O - Leachate volume
A - Leachate volume estimated by water balance
L
A
O
O A
0 A
0 ° ° ° A
o A - -
O
o A
o
Q ^
1973 1974 1975 1976 1977 1978 1979
Time - years
Figure 2. Cumulative leachate volume for Cell 1.
Test Cell 2C produced very little
leachate during the reporting period in
comparison with that produced in Cells
2A and 2B. A test boring in the cell
showed no free water stored in the
cylinder. The assumption was that a leak
had developed at a welded joint near the
surface of the soil cover and very little of
the precipitation had actually entered the
refuse mass.
Leachate quantities collected from
Cells 2A and 2B at the end of the project
differed by only 5%. Leachate collected
from 2D began to exceed precipitation in
mid-1975. At project completion, leachate
equal to 7,000 mm of precipitation had
been collected, whereas the input was
only 4,570 mm. Possible causes of this
large difference might have been leakage
through the sidewalls and liner of the cell
or through the Hypalon® cover that was
periodically placed on the cell.
Graphic predictions of refuse field
capacity compared well with moisture
contents of refuse samples taken during
closure. Based on the experience with the
four cells, an appropriate design value for
field capacity would be 55% moisture on a
wet-weight basis.
Leachate Characteristics
Leachate samples from the test cells
were generally analyzed biweekly. A
summary of peak concentrations and
values recorded at closure is included in
Table 2. Many of the peaks occurred
within a relatively short time period,
during which the cells were reaching
field capacity. Apparently those peak
concentrations resulted during the initial
water contact, when the supply of
teachable substances and the contact
time were both high. Note that these
leachate concentrations were from
relatively shallow (2.5 m) batch cells in
which there was no daily or intermediate
cover soil.
Total solids concentration history and
mass removal curves for four of the test
cells are presented in Figures 4 and 5.
The concentration or cumulative mass
removal has been plotted against the
cumulative leachate volume rather than
time, since the leachate concentration
trends and subsequent mass removals
are more related to leachate volume than
to time. Leachate volume and mass
removal data are also normalized by
dividing by the dry weight of the refuse to
account for the different sizes of the cells.
Typical of many of the parameters was
a pattern of increasing concentration
until field capacity was reached, followed
by a gradual decline. Individual leachate
sample concentrations showed no dilu-
tion effects during periods of high flow.
This pattern was adequately described
with a simple exponential equation
developed by considering the cell as a
well-mixed reactor. The least squares fit
of the equation to the concentration
history of COD for Cell 2A is depicted in
Figure 6. Though such an equation was
useful in describing leachate character-
istics over the 9-year period of the
experiment, its accuracy for long-term
predictions remains uncertain. This
uncertainty is exemplified by the findings
that the total chloride remaining in
samples of 9-year-old refuse was 70
times greater than the leachate chloride
predicted by the equation. Since some of
the chloride remaining in the refuse may
not be teachable, verification of the
equation would require that studies be
conducted well beyond the amount of
leachate per unit of dry refuse reached in
this research program.
One of the primary objectives of Cell 1
was to evaluate the effectiveness of soil
6,000
5,OOO
4,000
3,000
•£ 2,000
-2
I
0 7,000
1.000
2,000
3,000
4.000
5,000
Cumulative Precipitation, mm
Figure 3. Leachate volumes for Cells 2A-2D.
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Table 2. Leachate Concentrations*
Parameter
Test Celt 1 Upper
Concentrations
Peak At Closure
Test Cell 2D
Concentrations
Peak At Closure
Test Cell 2A
Concentrations
Peak At Closure
Test Cell 2B
Concentrations
Peak At Closure
pH (lowest)
pH (highest)
COD
BOD5
Kjeldahl-N
Ammonia-N
Orthophosphate
Sulfate
Alkalinity
Acidity
Conductivity
Total Solids
Sodium
Potassium
Chloride
Iron
Magnesium
Manganese
Calcium
Zinc
Hardness
5.10
7.07
37,500
30.000
700
552
61
1.160
8.870
3.620
12.200
23.600
1.040
1.950
1.749
616
374
184
2.360
104
7,500
__
--
250
43
23
18
1.4
9
760
660
930
1.400
42
41
66
200
27
1.9
190
0.3
590
4.6
7.0
41.869
79. 120
1,413
947
82
1.280
8.963
5.057
16.OOO
36,252
1,375
1,893
2,940
1,492
411
58
2.300
67
6.713
__
--
600
4OO
14
10
1.6
23
460
560
87O
1,200
25
24
73
210
19
1.6
130
0.4
400
4.4
6.2
57.370
62,560
1.560
1.035
390
2,215
1 1.535
6,720
1 7,000
46,484
1.900
2,225
3,558
1,547
486
109
2.470
150
7.067
--
6.100
5.000
63
23
42
30
710
1,400
1.400
2,700
33
31
96
520
18
4.7
170
0.3
570
4.4
6.0
61.600
72.220
1.897
1.185
185
2.275
13,880
6.843
18.000
45.628
1.700
2.939
2.450
2.902
617
115
4.000
360
10.575
__
—
6,400
5,700
43
3O
31
41
830
1.30O
1,600
3,000
23
3O
99
480
22
5.1
290
1.4
8W
*Concentrations in mg/L, except for pH and conductivity (micromhos/cm).
liners for leachate control. Less than
9,000 liters of leachate was collected
from the drain pipe beneath the soil liner
during the first 7-1/2 years of the
project—a total that represented less
than a third of the soil pore volume. Even
after 9 years, iron and COD values were
only 50% of those for leachate that had
not passed through the soil liner. Total
solids attenuation averaged 31% over the
project. Desorption from the soil of
hardness, chloride, calcium, and sulfate
occurred during the later part of the
study. A complete evaluation of the soil
liner's efficiency in collecting and
attenuating leachate could not be per-
formed because of interference from an
underlying synthetic liner, variable soil
thickness, and a small hole discovered in
the soil liner during closure.
Leachate samples from Cell 1 were
used for bioassays during 1972. The 96-
hour LC5o was 2.5% and 2.1% for two
series of tests on fathead minnows.
o 2A
A 2B
O 2D
A— 1
Figure 4.
Cumulative Leachate Volume—L/kg of dry refuse
Total solids concentration history for Cells 1, 2A, 2B. 2D.
Microbiologic studies of leachate and
waste samples indicated that significant
numbers of fecal indicators had continued
to survive and reproduce for 9 years.
Pathogens were also identified in waste
sampled from Cell 1 at closure, even
though inoculated bags containing
poliovirus type 1 and Salmonella derby
indicated inactivation within 10 days of
the initial construction of Cell 1.
Gas, Temperature, and
Settlement
Gas samples were obtained from
various locations within the cells. Oxygen
was depleted quickly in all cells, and
thereafter it generally remained at less
than 3% at most probe locations for the
entire project. The characteristic early
carbon dioxide bloom appeared in all
cells. Within 2 weeks after cell construc-
tion, COz levels reached as high as 45% in
the center of Cell 1 and 38% in the center
of Cell 20. Levels in the small-scale cells
were slightly lower. Peak levels of CO2
were reached in all cells at aboutthe time
field capacity was achieved. Thereafter,
levels dropped slowly to 30% to 40% at
the conclusion of the project. Carbon
dioxide levels ranged from 5% to 20%
higher by volume in Cell 2D than in the
small-scale cells for the first 3 years, but
they were similar thereafter.
Very little methane was detected until
the cells reached field capacity. The
earliest appearance of methane in Cell 1
was at the base of the cell and beneath
the liner. Methane concentrations greater
than 10% were not detected in the small-
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scale cells until 2 years after similar
levels were reached in 2D. Peak methane
concentrations recorded in the small cells
were 25% in 2A, 20% in 2B, and 26% in
2C. The peak concentration detected in
20 was 57.9%. Though results were
erratic, methane levels in the small cells
appeared to be similar. Little similarity
existed between the methane history in
2D and in the small cells, 2A, 2B, and 2C.
60
350
Thermocouples and thermistors were
placed at various locations within the five
cells and in the surrounding soil. Peak
temperatures as high as 124°F were
recorded near the surface of 2A and 2B.
Peaks declined with depth in the small
cells, but they were similar at three levels
within 2D. After about 1-1/2 years, soil
and refuse temperatures at similar
depths were generally within a few
,40
\
o
I
30
20
-o
Figure 5.
50
12345
Cumulative Leachate Volume—L/kg of dry refuse
Total solid mass removal for Cells 7, 2A, 2B. 2D.
V
.0
I30
I
I 20
Figure 6.
12345
Cumulative Leachate Volume—L/kg of dry refuse
Comparison of COD concentration for Cell 2A. (*€q. 4 of full report)
degrees, indicating the end of active
aerobic decomposition. Except near the
surface of Cell 1, lower annual tempera-
tures were recorded in the soil, and the
highs were about the same in both the
refuse and the soil. Atime lag also existed
between soil and refuse peaks. This
amplitude difference and time lag was
thought to be due to specific heat
differences or perhaps minor residual
aerobic activity within the refuse.
Settlement in the small-scale cells was
quite similar, with more than half the
total recorded during the first 14 months
following cell construction. Final settle-
ment in these cells ranged from 15.2% to
17.1% of total cell refuse depth. Settle-
ment over the surface of 2D averaged
only 10.6% of refuse depth, probably
because of the 30% higher initial in-place
refuse density than in 2A, 2B, and 2C.
Estimated total settlement at the deepest
point in Cell 1 was 12% of the refuse
depth. The initial refuse density in Cell 1
was 35% higher than that in 2A, 2B, and
2C.
Performance Comparison
One of the primary objectives cf the
research was to compare the behavior of
a field-scale test cell (2D) with similarly
constructed small-scale cells. We hoped
to determine whether factors of scale
were involved or whether the small cells
produced duplicate results so that future
research efforts might use small, less
expensive cells to predict field behavior.
Composition and initial moisture
content were statistically similar, and
refuse depths varied only 5%. The in-
place wet refuse density in Cell 2D was
45% greater than the average refuse
density in the small cells. Leachate
collected from Cell 2C was so substantially
different from Cells 2A and 2B that the
leachate data were not used in any
comparative analysis. Leachate produc-
tion from Cell 2D was much greater than
that from the remaining small-scale cells
(2A and 2B), and it exceeded precipitation.
By the end of the project. Cell 2D had
produced nearly twice the leachate per
unit of collection surface area than had
Cells 2A and 2B.
Only minor differences in temperature,
settlement, and gas composition were
noted when comparing the performance
of the small-scale cells. Temperatures
were essentially the same in 2D as in the
small cells except for some surficial
heating as a result of the cover over 2D.
Settlement in the large cell was only two-
thirds of that in the small cells, perhaps
because of the initial 45% greater wet
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refuse density. Compared with Cell 2D,
the small-scale cells (2A, 2B, and 2C)
showed a substantial difference in
methane gas concentration, with delayed
production and lower concentrations.
Leachate concentration trends in Cell
2D were similar to those in the small-
scale cells, but typically the magnitude of
peak concentrations and mass removals
were lower—quite possibly because of
diluting sidewall leakage. Since this
leakage could have passed through a
portion of the refuse, it was impossible to
correct the concentration data simply on
the basis of excess water. This large
difference in leachate production from
Cell 2D was probably sufficient to
preclude comparisons of cell performance
based on leachate characterisitics.
Graphic comparisons of weighted
mean leachate concentration histories
and mass removals for Cells 2A and 2B
indicated that performances were gener-
ally similar. To compare concentrations
statistically, the Chow test for stability of
coefficients was used. Essentially, this
method compares the least squares fit of
two linear equations describing the data
from Cells 2A and 2B with the fit of a
single equation developed from the
combined set of data. The F statistic
calculated from a ratio of the residual
sum of the squares of the linear equations
is used as the measure of statistical
comparability. A log transform of the
exponential equation (Figure 5) was used
for the necessary linear equations and
least squares fitting. Results of this test
showed similarity for only 3 of 12
leachate parameters for Cells 2A and 2B
at the 0.05 level of significance. Compari-
son of Cell 2A with 2D indicated similarity
for only 1 of 12 parameters. Because of
the lack of statistical comparability, we
could not conclude that similarly con-
structed and operated cells would perform
similarly.
A 45% greater initial in-place wet
refuse density in Cell 2D than in the
smaller cells and the much greater
volume of leachate collected precluded
performance comparisons between the
different-sized cells. Differences in
settlement, gas composition with time,
peak leachate concentrations, and mass
removals were all apparent in the cell
data. Though we cannot conclude that 2D
would have performed differently if the
refuse density and leachate volume had
been the same, these operational problems
are only minor compared with the range
of conditions that may be encountered in
a field situation. Thus, it is doubtful that
small-scale, batch-type cells can provide
accurate predictions of sanitary landfill
behavior; but they may be useful in
describing performance ranges.
The full report was submitted in ful-
fillment of Purchase Order No. C3016NASX
by Regional Services Corporation, Inc.,
under the sponsorship of the U.S. Envi-
ronmental Protection Agency.
Richard Wigh is with Regional Services Corporation, Inc.. Columbus, IN 47201.
Dirk Brunner and Nor ma M. Lewis are the EPA Project Officers (see below).
The complete report, entitled "Landfill Research at the Boone County Field
Site," (Order No. PB 84-161 546; Cost: $14.50, 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 Officers can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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POSTAGE & FEES PAID
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PERMIT No. G-35
Official Business
Penalty for Private Use $300
ft U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/923
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