United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati, OH 45268
Research and Development
EPA-600/S2-83-028 June 1983
Project Summary
Impact of Coal Refuse
Disposal on Groundwater
Jacek Libicki, Stephen R. Wassersug, and Ronald D. Hill
This study examines the extent of
groundwater quality deterioration when
coal mine refuse is disposed of in open
pits. Disposal methods are also devel-
oped, and procedures for planning and
designing disposal sites are formulated.
The study was conducted from 1975
to 1979 at an abandoned sand pit near
Boguszowice, Poland. Groundwater
was monitored, and laboratory testing
was conducted on wastes and leach-
ates. These studies determined the
physical-chemical character of the
waste material and its susceptibility to
leaching of particular ions in a water
environment. Also examined were the
influence of precipitation on the migra-
tion of pollutants to the aquifer, and
the level of groundwater pollution in
the vicinity of disposal sites and its
dependence on local hydrogeological
conditions (particularly on hydraulic
gradients). Recommendations are
made for improving waste storage tech-
nology to limit the effect on ground-
water and for designing a monitoring
system.
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
The increased mining of coal and its
processing for combustion during the
1970's has resulted in large quantities of
coal solid waste. One common disposal
method for this waste is placement in
previously exploited open pit mines, but
this method creates potential hazards to
the groundwater.
The influence of coal waste and ash
disposal on groundwater quality was in-
vestigated between 1973 and 1976 by
the Central Research and Design Institute
for Open-Pit Mining (POLTEGOR) as part
of the U.S. Environmental Protection Agen-
cy's (EPA) overseas activities. A small test
disposal site with a capacity of 1,600 m3
was used to investigate the influence of
ash and refuse disposal on groundwater
quality. Similar tests were also conducted
for a short period on a large disposal site
with a total capacity of 2 million m3. Tests
were also performed on groundwater and
analog models to investigate pollutant
migration in groundwater.
Upon completion of the project EPA
published the final report in the Interagency
Energy-Environmental Research and De-
velopment Series (Effect of the Disposal of
Coal Waste Ashes in Open Pits; EPA-
600/7-78-067, NTIS No. PB 284-01 3).
This report presented a number of conclu-
sions relating to the pollution hazard and a
number of recommendations on methods
for reducing the hazard.
In 1976, EPA and POLTEGOR agreed
that it was important to verify the conclu-
sions of the report by further studies at the
large disposal site. A 5-year study was
undertaken from 1975 to 1979. This
report presents the results of the study on
the large refuse disposal site and its impact
on groundwater quality. Recommenda-
tions for groundwater monitoring and coal
waste disposal are included.
Disposal Site
The test disposal site was located in an
old sand pit situated in Boguszowice,
about 200 km southwest of Wroclaw,
Poland. The sand was exploited for back-
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filling of underground bituminous coal
mines until 1969. The site comprises
three pits that have a total capacity of
about 3 million m3. The main (central) pit
had a capacity of about 1.5 million m3 and
has been abandoned for nearly 6 years.
The western and eastern pits were smaller.
Beginning in 1975, coal wastes from a
bituminous coal mine located in the vicinity
was disposed of in the central and western
pits.
The disposal site is situated on a mor-
phological elevation. The natural surface
elevation varies from 275 to 280 m above
sea level, and the terrain slopes away in all
directions. The surrounding area is covered
with meadows and arable fields, and a
forest lies about 1 km to the east
The central pit, where wastes were
disposed first, was about 500 m long and
1 70 m wide, with an average depth of
16.5 m. The pit bottom and slopes were
sand, which sometimes contained clay
and silt The sand layer was about 7.5 m
thick in the northern part of the disposal
area and about 9 m in the southern part;
but in some places it decreased to zero.
ThegroundwatertablewasO'to2 m below
the pit bottom.
The western pit, planned as a reserve
disposal area, was about 580 m long and
about 150 m wide, with an average depth
of about 7 m. The bottom and sides were
sand, which sometimes contained clay
and silt The thickness of the sand layer in
the pit bottom varied from about 1 m in its
eastern end to about 6 m in the western
end. The groundwater table was 0.5 to 3
m below the pit bottom.
Climate
Since the disposal site was above the
groundwater table, the amount of precipi-
tation (which is the source of the aquifer
recharge as well as the medium for pol-
lutant leaching and transportation into
groundwater) was vital to the investigation.
These data should be helpful for applying
the research results to other regions of the
world.
The average precipitation for the region
during the investigated period was 788.0
mm per year, varying from 633.0 mm in
1979 to 958.6 mm in 1975. The highest
monthly precipitation was observed in
August 1977 (156.5 mm), and the lowest
was in February 1 976 (3.6 mm). The
maximum daily precipitation (62.5 mm)
occurred in August 1975. The average
temperature during the investigation was
+ 8.5c. The coldest month was- 4.2c and
the warmest + 19c.
Waste Characteristics
A total of 2.09 million m3 of waste was
deposited in the two pits. The central pit
received 1.51 million m3, and the western
pit 0.58 million m3. About 96 percent of
the waste consisted of coal refuse, and
about 4 percent was of power plant ash.
Between 1975 and 1977, the surface
area of the waste exposed to precipitation
and percolation gradually increased from
30,000 to 100,000 m2. Reclamation of
the disposal site began m 1978 and
decreased the exposed surface area in
1979 to about 78,000 m2, despite the
fact that the volume of wastes increased.
The surface area is an important factor in
determining the amount of water that can
contaminate the groundwater by percola-
tion.
To determine the leachability and pollu-
tion potential of the waste, representative
samples were taken every 4 to 6 months
from recently disposed material. About
10 kg of waste was delivered to the
laboratory for each leaching test.
Samples were placed in glass columns
100 cm high and 12 cm in diameter.
These were equipped with valves that
regulated the rate of water flow through
the waste. A sample was placed in the
column on a layer of sand taken from the
disposal area. The ratio of waste-to-sand
thickness was about 4:1. The material
was washed using a peristalic pump with
distilled water in a closed cycle.
Three successive teachings were per-
formed until 5 dm3 of water had been
used. Each leaching lasted 24 hours. For
the first test the leaching rate was 1
dm3/hr, and for the others it was 0.5
dm3/hr. These rates could theoretically
be compared with 88 and 44 mm of rain
per hour, respectively.
Leachates were analyzed from a total of
11 samples to determine the pollution
potential of the refuse (Table 1). The data
indicate that the contents of the samples
varied considerably but that the variations
were within acceptable limits.
Groundwater Monitoring
In March 1974, 14 monitoring wells
were installed to monitor the aquifer sur-
rounding the disposal area. All monitoring
wells were drilled by the dry method down
to the roof of the continuous clay layer. The
depths of the wells varied from 7 to 2 7 m.
The lithology of all layers found in each
well was described in detail, and samples
were taken for laboratory analysis to deter-
mine permeability and specific yield. In
1977, three additional monitoring wells
were drilled in the area northeast of the
disposal site because a model analysis of
the hydrodynamic network suggested that
the groundwater flow might run in that
direction.
Water samples for physico-chemical
analyses were taken from the monitoring
wells from 1974 (one year before disposal
Table 1. Summary of Leaching Tests
Designation Unit
pH
Conductivity jjs/cm2
TDS mg/dm3"
Cl
SO4
Na
K
Ca
Mg
Mn
Fe
NH4
P04
CN
Phenols
Al
Zn
Cu
Pb
Cr
As
Sr
Hg
Cd
Mo
B
of Coal Solid Waste
Maximum
9.9
2140
3372
479
230
357
48
355.9
21.85
2.995
75.8
4.46
3.140
0.066
0.088
38.5
3.085
0.925
0.271
0.089
0.133
2.050
10.9
0.056
0.029
3.600
Minimum
7.3
500
548
51
50
44.5
4.1
5.2
0.42
0.035
0.11
0.32
0.036
0.003
0.008
0.175
0.360
0.019
0.034
0.011
0.008
0.037
0.6
0.005
0.003
0.095
Average
8.4
1500
1600
209.2
164.6
243.7
26.3
75.9
7.3
0.729
24.65
1.733
0.522
0.0252
0.0282
11.71
0.883
0.1974
0.1956
0.0364
0.0581
0.406
5.17
0.024
0.017
0.855
* mg/dm3 = mg/L
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began) until the end of 1979. Sampling
was performed on a regular 3-week inter-
val. Until October 1976, every fourth
sample was taken for full analysis (42
parameters), whereas all others were taken
for simple analysis (14 parameters). After
October 1 976, every third sample was
taken for full analysis. A total of 85 sets of
water samples were taken for physico-
chemical analysis between 1975 and
1979; of these, 26 sets received full
analysis.
Results
The leachability of pollutants in the
column studies may be divided into three
groups: The components most easily
leached (Cl, S04, Na, K), the components
of medium leachability (Cu, Zn, Hg, Sr, Cd,
B, Mn, Mo, CN), and the components
characterized by the slowest leaching (Mg,
Al, Cr, As, Pb, NH4, Ca).
The glass column leaching experiments
showed that on the average, the following
masses of particular pollutants were leached
from 1 kg of coal wastes:
Table 2. Comparison of Actual Groundwater Pollution Versus Glass Columns Leachate
Ratio of Groundwater Values/Leachate Column Values
Item:
TDS
Cl
SO4
Na
K
Ca
Mg
Mn
Fe
NH4
P04
CN
Phenols
Al
Zn
Cu
Pb
Cr
As
Sr
Hg
Cd
Mo
B
Amount
(mg/kg)
320
41.8
32.9
48.74
5.26
15.18
1.46
0.146
4.93
0.347
0.104
0.005
0.0056
2.34
0.177
0.0395
0.0391
0.0073
0.0016
0.081
1.03
0.005
0.003
0.171
Data developed in this manner could be
used to forecast the amounts of teachable
pollutants contained in stored coal wastes
(see Table 2).
It was observed in the column studies
that colloidal sediments were flushed from
the coal waste and settled on the sand
layer. This material caused a gradual and
then complete sealing of the sand and
column.
Designation
pH
Conductivity
TDS
Cl
S04
Na
K
Ca
Mg
Mn
Fe total
NH4
P04
CN
Phenols
Al
Zn
Cu
Pb
Cr
As
Sr
Hg
Cd
Mo
B
Maximum
0.82
0.53
0.34
0.35
1.28
0.34
0.43
0.71
2.38
1.08
0.355
1.43
0.10
0.68
0.23
0.038
0.56
0.5
0.24
0.21
0.98
0.53
0.25
0.24
1.41
0.11
Average
0.75
0.307
0.20
0.19
0.72
0.14
0.21
0.45
1.40
0.36
0.152
0.705
0.047
0.23
0.13
0.02
0.19
0.16
0.13
0.15
0.47
0.36
0.12
0.15
0.49
0.08
Minimum
0.70
0.20
0.12
0.09
0.36
0.04
0.10
0.23
0.74
0.15
0.013
0.32
0.017
0.09
0.07
0.02
0.09
0.01
0.05
0.06
0.08
0.23
0.05
0.09
0.13
0.06
This research confirmed that coal refuse
disposal in an abandoned open pit in
which the refuse may have contact with an
underlaying aquifer deteriorates ground-
water quality. The level of groundwater
contamination depends first of all on the
leachability of the wastes. Other significant
factors include (1) the amount of precipi-
tation percolating into the disposal site
(which depends on the area of disposal
surface exposed to precipitation and the
amount of precipitation), and (2) the self-
sealing of the disposal site bottom by the
fine clays washed out from the waste that
settled at the aquifer roof. This process
was observed in the column studies, but
could not be proven at the field site because
the waste aquifer interface was not sam-
pled and water levels in the waste pile
were not measured.
The first indications of groundwater
pollution occurred in the form of singular
waves of pollution in specific wells in
19 7 6 (i. e., 12 to 18 months after disposal
operations had begun). But these devel-
opments were difficult to monitor. Con-
tinuous pollution began in early 1977, 2
years after the commencement of storage
operations (Table 3).
The waste caused significant pollution
of the aquifer only in the direction of the
greatest declination in the groundwater
table. The pollutants did not migrate in the
form of a wide, uniform front, as predicted
by hydrodynamic net analysis; rather, they
migrate in the form of narrow veins. This
finding has been proved by comparing
pollutant concentrations of particular wells
in the potentially polluted zone. Results
were not very uniform, demonstrating that
local differences in aquifer permeability
determine pollutant concentration (i.e., the
higher the permeability, the higher the
pollution), especially after 3 years.
Heavy pollution persisted for 2 n/2 years
and then decreased. This phenomenon
could be explained by two factors: First,
the surface area of the disposal site exposed
to rain infiltration was reduced by careful
reclamation of 30% to 40% of the total
disposal surface; and second, the inferred
self-sealing of the bottom of the disposal
site when the silty wastes were washed
from the disposal body and settled at the
bottom of the pit.
According to the model developed earlier,
the sequence and duration of pollutants
occuring in particular wells from the begin-
ning of storage could be predicted with 80
percent accuracy.
The system of monitoring wells in the
shape of five radial lines was sufficient to
monitor the aquifer for potential pollution.
In practice, however, a smaller number of
wells would be sufficient
Three-week intervals for groundwater
sampling and measurements were suffi-
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Table 3. Comparison of Groundwater Quality Before and After Waste Storage
Average Average Maximum
Concentration Concentration Concentration
Before During During
Designation Unit Disposal Disposal Disposal
PH
Conductivity
TDS
Cl
SO4
A/a
K
Ca
Mg
Mn
Fe total
NH4
P04
CN
Phenols
Al
Zn
Cu
Pb
Cr
As
Sr
Hg
Cd
Mo
B
6.66
its/ cm2 247.1
mg/dm3* 169.2
15.08
54. 1
7.84
2.77
16.26
4.95
0.24
4.60
0.43
0.014
0.0049
0.0034
0.16
0.360
0.023
0.0165
0.0064
0.0168
0. 130
0.630
0.0024
0.0148
0.032
6.25
460.72
329. 13
40.84
117.98
33.50
5.51
34.11
10.23
0.266
3.7433
1.22
0.0244
0.0059
0.0036
0.181
0.1672
0.0102
0.0246
0.0056
0.0274
0.1472
0.6294
0.0037
0.0083
0.0685
6.88
801.0
550.07
72.73
209.89
81.99
11.31
53.60
17.39
0.79
8.75
2.47
0.053
0.0172
0.0066
0.444
0.497
0.0313
0.047
0.075
0.057
0.216
1.300
0.0058
0.024
0.095
edge of the coal refuse characteristics
(including its leachability), detailed inves-
tigation of the hydrogeological conditions,
and assessment of aquifer use. The full
report discusses methods for surveying
the site and aquifer situation and the
design of a monitoring system.
The full report was submitted in fulfill-
ment of Contract No. J-5-537-1 , by Poltegor,
Powstancow SL95, Wroclaw, Poland,
under the sponsorship of the U.S. Environ-
mental Protection Agency.
"mg/dm3 = mg/L = ppm
cient, and in practice, measurements could
be reduced to once a month.
The schedule of physico-chemical anal-
yses (i.e., measuring 19 parameters for
every set of samples and 42 parameters
for every third set of samples) is appropriate.
Recommendations
The full report recommends methods
for the design and monitoring of coal
refuse disposal sites. Subject areas dis-
cussed are: (1) waste classification and
examination; (2) site classification; (3)
planning and designing disposal sites;
and (4) design of monitoring wells and
sampling systems.
Coal waste is divided into two subgroups
—dry and wet wastes. Of the two, the wet
waste has a greater potential for creating
groundwater pollution because of its fine
granulation. Disposal methods are thus
discussed in relation to this subgroup.
Chemical analysis of the refuse is not
recommended as means for character-
izing it Column leaching tests are preferred
because the results are more representative
of the chemical character of the leachate
that will be found at the disposal site.
The following criteria should be con-
sidered when classifying and evaluating
open pits for the storage of coal refuse and
the protection of groundwater:
1. The hydrogeological criteria based
on the relationship of the disposed
material and the threatened aquifer.
Two situations are recognized—the
dry disposal site, in which waste is
situated above the groundwater table,
and the wet site, in which waste is
situated below the groundwater table.
The four dry site subgroups discussed
are waste located within (a) the im-
permeable layer, (b) the permeable
layer, (c) the impermeable layer under-
lined with an unsaturated permeable
layer, and (d) the unsaturated per-
meable layer and underlined with an
impermeable layer. The four wet site
situations are waste located within
(a) the impermeable layer underlined
with an aquifer with hydrostatic pres-
sure, (b) the permeable layer under-
lined with impermeable layer, (c) the
impermeable layer directly underlined
with an aquifer with hydrostatic pres-
sure, and (d) the permeable layer.
2. Hydrogeological criteria based on the
relationship of the disposed material
and aquifer permeability.
3. Criteria for aquifer protection based
on aquifer use.
Planning the storage of refuse in an
open pit should be preceded by a knowl-
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Jacek Libickiis with POLTEGOR, Powstancow SL.95, Wroclaw, Poland; Stephen
Wassersug is also the EPA Project Officer (see below); and Ronald Hill is with
EPA, Cincinnati, OH 45268.
The complete report, entitled "Impact of Coal Refuse Disposal on Groundwater,"
(Order No. PB 83-193 649; Cost: $ 17.50, 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
-------
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
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