United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-058 Sept. 1983
v>EPA Project Summary
Field Assessment of Site
Closure, Boone County,
Kentucky
Landfill performance was investigated
before the closure of a 4-ha (10-acre)
experimental landfill site located in
Boone County, Kentucky. The site
contained a field-scale landfill and four
smaller test cells filled with compacted
municipal solid waste. From 1970 to
1980, the landfill was operated by the
U.S. Environmental Agency (EPA) to
monitor gas and leachate production.
The current project was undertaken
before the scheduled site closure to
obtain information useful to designers
of future landfill facilities.
Information was developed on cover
soils, refuse, leachate collection systems,
and lining materials from the test cells.
To examine and recover cell compon-
ents, exploratory excavations were
made through the refuse and base
liners. Each of the cell elements (cover,
refuse, liners, etc.) was thoroughly
documented, and samples underwent
extensive testing.
The project included the recovery and
detailed inspection of the cover soils
and of the clay and synthetic liners that
had been exposed to leachate for
approximately 9 years. Although the
cover soils were constructed to main-
tain tight permeabilities, a vertical
seepage plane did develop over the
project life. Both field and laboratory
testing showed little degradation of the
liners and no leachate migration through
these materials. The physical appearance
of the refuse was similar in all excavated
cells and showed little vertical difference.
Decomposition was limited primarily to
food wastes. Isolated incidences of
gravel cementation were found in the
upper leachate drain of one cell.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory 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
Landfill performance was investigated
just before the closure of an experimental
landfill site in Boone County, Kentucky.
The object was to obtain information
useful to designers of future landfill
facilities.
The 4-ha (10-acre) tract contained a
field-scale landfill (Test Cell 1) and four
smaller test cells filled with compacted
municipal solid wastes (see Figure 1).
Known as the Boone County Field Site, the
landfill is located at the top of a ridge 8 km
(5 miles) west of the City of Walton in
northern Kentucky. From 1970 to 1980,
the U.S. Environmental Protection Agency
(EPA) operated the site to monitor gas and
leachate production.
The present project examined the test
cells just before the site was closed to
develop information on cover soils,
refuse, leachate collection systems,
lining materials, and contaminant migra-
tion from the test cells. Exploratory
excavations were made through the
refuse and base liners to examine and
recover cell components. Each of the cell
elements (cover, refuse, liners, etc.) was
thoroughly documented, and samples
underwent extensive testing.
Description of Test Cells and
Conditions Immediately
Before Closure
Test Cell 1
The field-scale sanitary landfill (TC-1)
was constructed as a trench-type sanitary
landfill 45.4 m (149 ft) long, 9 m (30 ft)
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To Equipment Storage Shed
and Site Office Trailer
Leachate
Spray Irrigation
Area
Observation Gallery
Instrumentation Shed
Weather Station
Leachate Holding Pond
Scale Approx.: 1" = 50'
leachate to the lower pipe. The space
around both of the pipes was filled with
clean silica gravel. The test cell contained
94 m3 (869 yd3) of refuse.
The closure investigation was con-
ducted by means of seven exploratory
trenches constructed in the cell. Three of
these (B, E, and G) penetrated the refuse
pile and liners to the subsoil beneath the
landfill (Figure 2).
Cover Soils
TC-1 was capped with 60 to 90 cm (24
to 36 in.) of silty clay soil. Below a
surficial, root-weathered zone, this tan
clay layer became dense and difficult to
shovel. Permeability determinations
indicated that the cover at the BCFS was
constructed to maintain tight permeabil-
ities and thus minimize infiltration, but
this apparent tightness was offset by the
presence of a vertical seepage plane
penetrating the full depth of the cover.
This plane indicates that over an extended
period, soil structuring could increase
cover system permeability.
Refuse
Four test pits were excavated (Locations
AA, B, E, and G) to expose a cross-section
of the refuse. The reasonable well
preserved condition of the waste was
remarkable. Ten-year-old newspapers
were quite legible and slightly discolored.
Metal cans were only slightly.rusted, and
labels were only slightly discolored.
Grass clippings were bright green. Except
for corncobs, food material was reduced to
a brittle residue. Little odor was detected
from the excavated refuse. The most
extensive degradation occurred at Loca-
tion E, just above the clay liner. Here
refuse was saturated, and a malodorous,
black sludge covered the upper surface of
the clay liner. Newsprint was covered
with a black, gritty coating, and metal was
brittle and corroded.
Figure 1. Site layout plan.
wide, and about 3 m (10 ft) deep (Figure
2). The central portion of the base of the
cell was covered with a 0.76-mm (30-mil)
chlorosulfonated polyethylene (CSPE)
liner (Hypalon*), 9 by 15 m (30 by 50 ft)
long. A clay soil liner 45 cm (18 in.) thick
was placed directly above this synthetic
liner, and a two-layer drain system was
Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
constructed to collect leachate migrating
along the top of each liner (Figure 3). The
drain system consisted of a slotted
collection pipe along the transverse
center line of the cell directly above the
CSPE sheeting and a second pipe in a
trench installed in the top 32 cm (13 in.) of
the clay liner. The trench was lined with a
0.15-mm (6-mil), low-density polyethylene
(LDPE) strip. The purpose of this second
pipe was to prevent short circuiting of the
Moisture Content
The refuse was moist to the touch, and
laboratory tests showed fairly consistent
values of 43% to 63% moisture through-
out the refuse on a wet-weight basis.
Chemical Analysis
Attempts to determine whether chem-
ical composition varied vertically were
inconclusive. Concentrations of K, Ca,
and Mg tended to increase with depth,
and TKN showed the opposite trend.
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Limits of Synthetic Liner
X Approximate liner
sample location
Observation Unit
Test Cell I (TC-1)
figure 2. Sampling locations for TC-1.
, ^ *~ r'»» f f
fay As-Built construction details for cross section at observation bulkhead
x- t - < r"
s /- i - * ' f f y ^
i- ^
r ' " ^^r^ ^^
^-
I'/
\ ' s*. r-
i Refuse Penetration into
/ Gravel Drain
~-~~- ^- ' /v- ' y
{[
1
, /
^^l
Light Brown Clay. Gravel /
1 /2" to 1" Cemented Gravel
: Wypa/on Liner '//////
'//////'
(b) Cross section as exposed 8 ft. from observation bulkhead
Figure 3. Leachate collection system for TC-1.
Leachate Production
Nearly continuous leachate seepage
from refuse was encountered in a
saturated zone about 30cm (12 in.)above
the clay liner. Most leachate was light in
color and only moderately turbid, but two
or three zones of concentrated rust-
colored seepage were encountered in
each trench.
Density
A dramatic 70% increase in refuse
density was observed between time of
placement and site closure. This result
cannot be accounted for simply by volume
reductions that accompany decomposition.
The explanation is more likely to be that
no accurate, reproducible method exists
for determining in-place density at a
reasonable cost.
Permeability
The mean permeability of in-place
refuse ranged from 1 x 10~2 to 4 x 10~2
cm/sec when measured at seven locations
in the field. This value is somewhat
higher than the actual value because of
the difficulty in creating a complete seal
of the permeameters to the refuse. Also,
field permeameters yield values that are
about 50 times those measured in the
laboratory.
Pore Water
Chemical components were generally
higher in the refuse pore water than in
the leachate. Concentrations of constit-
uents in the pore water generally
increased with depth.
Microbial Assay
Soil samples of waste materials from
TC-1 were assayed for microbial content.
Levels of fecal conforms in the waste
were significant, indicating that the
waste represents a source of potential
disease transmission. Top soil was highly
contaminated, possibly as a result of
recent human or animal contact. The
isolation of Acinetobacter. Moraxella.
Salmonella, and Klebsiella pneumoniae
is significant since these organisms were
found only in the refuse samples.
Methane-producing bacteria were pre-
sent in greater numbers and at shallower
depths within the solid waste than in the
control soils.
Leachate Collection System
Leachate was drained from TC-1
through two collection pipes (Figure 3).
The area around both pipes was backfilled
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with washed silica gravel. Gray clay from
the liner and a light brown silty clay of
unknown origin partially covered the top
of the upper collector. The brown clay and
the gravel were both mixed with refuse.
The upper drain was typically 20 to 30cm
(8 to 12 in.) deep. The upper 10 cm (4 in.)
of gravel backfill was moist and natural in
color. The lower 10 cm (4 in.) was
saturated with an odorous, dark black
fluid. Gravel was stained with a thin, fine,
black and rust-colored coating. Tiny
particles of glass, metal, and sand part-
ially filled voids in the gravel, and the bot-
tom 0.3 cm (0.125 in.) contained a con-
tinuous gritty sand deposit. Gravel was
generally subrounded in shape and
accepted water at a rate greater than
could practicably be applied through
permeameters. A zone of cemented
gravel was found in the bottom 1.3 cm
(0.5 in.) of the upper collector. The ce-
menting material consisted of a fine-
grained mixture of quartz, rhodochrosite
with a minor iron component, gypsum,
and a small amount of illite. Evidence of
seepage appeared along the bulked-clay
interface and between drains. Gravel in
the lower collector was low in moisture
content and unstained throughout, re-
flecting minimal contact with leachate.
No free fluids were found in the lower col-
lector.
Liners
Chemical tests indicated that nearly all
of the leachate was contained above the
clay liner. No visual signs of cracking,
channeling, or unusual changes in
texture or consistency were noted in any
of the excavations.
CSPE li ner sa mples had been in contact
with dilute leachate for 9 years; they had
imprints of gravel and were swollen and
soft. Substantial amounts of leachate had
been absorbed by the CSPE samples. The
physical properties of all these samples
appeared to be approximately the same,
and values all appeared to be relatively
normal for a CSPE material. No significant
differences were noted in the data among
the different samples, indicating that
sample location in the cell did not affect
results and that all materials came from
the same lot.
The LDPE film was clear after the
surface stain was washed off, and it
appeared to be unaffected by its 9 years of
exposure to the full-strength leachate.
The sample showed little swelling, and its
properties were normal for a 6- to 7-mil
LDPE. No punctures or tears of the
material were observed during sample
removal.
Subsoils
The subsoil in TC-1 consisted of a thin
clay mantle overlying limestone bedrock.
Immediately below the CSPE liner, the
subsoil was a brown-gray for several
millimeters, grading to a natural orange
tan.
Test Cells 2A, 2B. and 2C
Test Cells 2A, 2B, and 2C consisted of
refuse enclosed in identical steel cylind-
rical pipes 1.83 m (6 ft) in diameter and
3.66 m (12 ft) high (Figure 4). Refuse was
placed in the pipes in 90 to 130-kg (200-
to 300-lb) increments and compacted.
Since all three cells were similar, TC-2B
was judged to be representative and was
excavated and examined in detail. The
cover soil and shallow refuse in TC-2C
were also investigated to confirm the
assumed similarity. No study was made
of TC-2A.
Soil Cover
Refuse in TC-2B was covered by a
surficial layer of clean pea gravel
underlain by a light brown clay of low
plasticity. The gravel layer was moist
below the upper few inches. No vegeta-
tion was established in the gravel or
underlying clay soil. The clay layer was 28
cm (11 in.) thick, becoming gray within 8
cm (3 in.) of the refuse. The cover soil was
very soft and moist to the touch.
Refuse
The physical appearance and composi-
tion of refuse in TC-2B after 9 years of
exposure was similar to that of the other
test cells. Newsprint was still quite
legible, cardboard was very soft, metal
cans were slightly rusty, painted labels
were discolored but legible, and plastics
were generally still pliable. A strong odor
occurred when the cover was penetrated,
6'
(0
(. Refuse Fill
- <
PVC Drain Pipe
to Collection Gallery '
r-
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a' >, -'.';' b '. .'« '- o.'. '.'
"'*<* »*.'*.* *.«*"
Pea Gravel
- e - o
Clay/Silt Soil
S r
/
Refuse Fill
/ <
. ^IJL^-IJV.'-' V'' /o.'Qf .:.. :''J,^i,'.
Medium Sand
- Gravel
30 m//. C/*£ i/ner
Medium Sand
Natural Clay
Figure 5. Test cell construction details for TC-2D.
but it quickly dissipated. The refuse was
very moist to the touch. No free fluids
were found anywhere in the refuse.
Chemical Analysis
Samples of refuse were obtained for
chemical assay to determine vertical
differentials in composition. Results
presented no clearly defined trends for
most assays, but potassium did exhibit a
weak trend of decreasing concentration
with depth.
Pore Water
The results for TC-2B contradict those
for all the other test cells. Contaminant
levels in the pore water were lower than
those in the leachate, except for total
solids, total volatile solids, TKN, Zn, As,
and Ba. Errors in sampling and analytical
procedures may account for these
results.
Test Cell 2D
TC-2D was constructed in an excavation
2.6 m2 (28 ft2) by 3 m (10 ft) deep to
provide a large-scale comparison for the
three smaller test cells. The base of the
cell was shaped with sand and a 7.6-mm
(0.30-in.) thick, reinforced chlorinated
polyethylene (CPE) liner was placed along
the cell sidewalls and over the base
(Figure 5). Refuse was added by a crane
and compacted by a bulldozer. The cell
was explored through three excavations
that penetrated through the cell into the
underlying subsoils.
Cover Soil
TC-2D was capped by a surficial layer of
clean pea gravel overlying a clay cover
soil. The gravel was dry near the surface,
but very moist below the upper 8 to 10 cm
(3 to 4 in.). No vegetation was established
in the gravel. The clay cover was easily
excavated by shovel and felt moist to the
touch, unlike the dry, hard texture of the
cover soil in TC-1. Permeabilities were
about one order of magnitude smaller
than in TC-1, reflecting an increased clay
content and greater plasticity.
Refuse
Three trenches were dug to expose a
cross section of the refuse pile in TC-2D.
The refuse was more odorous than in TC-
1, and it had a higher moisture content
throughout (49% to 65% on a wet-weight
basis). As in TC-1, the degree of refuse
degradation was low. Newsprint was very
legible, cardboard was still intact, metals
had little rust or corrosion, labels were
only slightly discolored, grass clippings
were bright green, and plastics were still
pliable. As with the other test cells, food
wastes were not observed except for
isolated bones, corn cobs, etc.
Chemical Analysis
Samples taken at two locations in TC-
2D generally showed a trend of decreasing
concentrations of chemical constituents
with increasing depth. The same trend
was found for S04, Na, K, and Mg. These
findings do not support the concepts
generally associated with single-pass
systems, but the mode of operation of
these test cells may have led to the
results.
Pore Water
Concentrations of most contaminants
were greater in pore water than in
leachate. Fe, Cl, K, and Ca were approxi-
mately equal in both, however. Contam-
inant concentrations generally increased
with depth, except for Ca and Fe. Such
exceptions may have been the result of
sampling errors
Moisture Content
The refuse pile was generally well
drained, and no zones of perched fluids
were encountered. Trenches remained
dry until saturated drain soils were ex-
posed.
Density
In-place mean wet density of the refuse
was 1,327 kg/m3 (2,237 Ib/yd3). Mean
dry density was 848 kg/m3 (1,430
Ib/yd3).
Permeability
The mean permeability determined in
the field was 5 x 10"2 cm/sec. These re-
sults are somewhat high because it was
impossible to seal the permeameters
completely within the refuse. Results
were comparable with those of TC-1.
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Drainage Soil
A sand collector blanket separating the
refuse from the CPE liner was very moist
to wet. The lower several inches of the
sand blanket were typically saturated and
black in scattered areas. A slotted PVC
pipe was placed along the transverse
center line of the cell for leachate
collection and gravity drainage. Silica
gravel was then placed on the top and
sides of the collection pipe. Some
staining of the gravel was noted. The
drain system was moist, but no free fluids
were encountered in Trench B, and only a
very slow seepage was noted in Trench A.
Liner
Analysis of the layers of sand above
and below the liner indicated that the
liner had contained the leachate. The
CPE liner samples were stiff and leathery
and showed significant adsorption of
leachate. Nonetheless, their properties
were relatively good. Two samples of CPE
liner that had been exposed only to
weather and not to leachate were
significantly higher in tensile strength,
moduli, and puncture resistance compared
with the leachate-exposed samples.
Subsoils
not completely block the leachate of the
upper gravel drains of TC-1.
Very little degradation had occurred in
the wastes uncovered during the investi-
gation. Newspapers buried for 10 years
were still legible, and grass clippings
were still green. Food wastes were
noticeably absent.
High microbial counts were found in
the landfill leachate, and high fecal-
indicator levels were present in the
refuse. Microbes apparently can survive
within a landfill for long periodsin this
case, more than 9 years.
Recommendations
Liners that have been exposed to solid
wastes over an extended period should be
examined to determine long-term expo-
sure effects. Determinations should also
be made of the origins of the pathogens
and fecal indicators, and of the mechan-
isms and dynamics of pathogen and fecal
indicator survival.
The full report was submitted in
fulfillment of Contract No. 68-03-2824/02
by EMCON Associates under the spon-
sorship of the U.S. Environmental Pro-
tection Agency.
This Project Summary was prepared by staff of EMCON Associates in San Jose,
CA 95112.
Dirk Brunner is the EPA Project Officer (see below).
The complete report, entitled "Field Assessment of Site Closure, Boone County,
Kentucky," (Order No. PB 83-251 629; Cost: $10.00, subject to change} will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
An excavation was made into a layer of
sand and a section of clay underlying the
CPE liner in TC-2D. Water beneath the
CPE liner contained no leachate and was
believed to be the surface runoff into the
sand surrounding the sides of the cell.
The upper 2.5 to 5 cm (1 to 2 in.) of the
clay layer had been reduced to a mottled
gray-green. The remainder of the exposed
clay was a natural orange-tan.
Conclusions
Soil structuring of cover soils are
subject to cracking, which can increase
cover permeabilities even though the
major portion re'mains tight
Both clay and synthetic liners in the
test cells examined provided effective
containment of leachate. Though many
synthetic liner samples were considerably
swollen, they retained reasonably good
physical properties after their 9 years of
leachate exposure. The leachate drain-
age system was still functional even
though there was minimal plugging of
gravel drains. One short section did
undergo cementation but apparently did
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