United States
Environmental Protection
Agency
Risk Reduction Engineering
Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-91/017 May 1991
& EPA Project Summary
Migration of Hazardous
Substances through Soils
G. Kenneth Dotson
Factorlally designed column and
batch leaching studies were conducted
on samples of various Industrial wastes,
flue gas desulfurlzatlon sludges, and
coal fly ash to determine the effect of
leaching solution composition on re-
lease of hazardous substances from
waste samples, and the effect of soil
properties and leaching solution com-
position on subsequent migration
through soils.
The wastes studied came from:
Electroplating
Secondary Zinc Refining
Inorganic Pigment
Zinc-Carbon Battery
Titanium Dioxide Pigment
Nickel-Cadmium Battery
Hydrofluoric Acid
Water-Based Paint
White Phosphorus
Chlorine Production
Oil Re-refining
Flue-Gas Desulfurlzatlon
Coal Fly Ash
Seven different soils and two leach-
Ing solutions (water and municipal land-
fill leachate) were used.
Waste characteristics, such as pH
and total metal content, were margin-
ally useful predictors of metal concen-
trations In water or municipal solid
waste (MSW) landfill leachate extracts
of the waste. However, no satisfactory
substitute for leaching tests, whether
by batch or column procedure, was
found. Waste and extract characteris-
tics such as pH, electrical conductivity,
and metal content were useful predic-
tors of metal movement in soils. Leach-
ing solution composition was highly
significant. MSW leachate solublllzed
greater amounts of metals from all
wastes than did distilled water, and met-
als contained In MSW leachate moved
more rapidly through soils than those
contained In water.
Serial batch extractions gave leach-
Ing data that were quite similar to data
obtained from the slower and less con-
venient column leaching procedure.
Both procedures require long-term ex-
traction because some waste do not
begin to release significant amounts of
metals until several void volumes of
leaching solution have been passed.
The results of the project have been
documented in three reports published
by the U.S. Army. These reports are
identified as Parts II, III, and IV. Part I
was an unpublished interim report that
was later incorporated Into the larger
Part II report. The complete citations
are given at the end of this Project
Summary.
This Project Summary was dew/oped
by EPA's Risk Reduction Engineering
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
Industrial processes and air and water
pollution abatement systems produce solid
wastes that, when placed in landfills, can
release hazardous substances that can
move through soils and find their way into
groundwater. Hazardous substances in the
wastes studied included elements such
as arsenic, beryllium, boron, cadmium,
chromium, copper, fluoride, lead, mercury,
nickel, selenium and zinc. Other elements
essential to plant growth, such as phos-
phorus, sodium, and magnesium may oc-
cur in toxic concentrations or may influ-
ence attenuation of toxic elements by soil.
Important factors to be weighed when con-
sidering land disposal are knowledge of
the way wastes behave in the disposal
Printed on Recycled Paper
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environment, and how hazardous materi-
als in leachates from landfills move in
soils. The broad objective of this study
was to answer such questions for selected
wastes. The study would serve as a guide
for future research and help to identify
wastes that may require special care in
disposal. Another objective for this study
was to develop techniques that would be
applied to the evaluation of leaching be-
havior of wastes at specific sites. This
work was conducted before final regula-
tions were issued under the Resource
Conservation and Recovery Act (RCRA).
Under current regulations many of the
wastes studied would be banned from land
disposal unless properly treated to reduce
their toxic'rty and mobility.
Determination of the
teachability of Metals from
Five Industrial Wastes and
their Movement Within Soil
The first phase of the study involved
sampling five different industrial wastes
and then determining composition and ten-
dency to solubilize when extracted with
distilled water or municipal landfill leachate.
The distilled water was used to simulate
rain or groundwater, and the landfill
leachate was used to simulate the leachate
produced when MSW and industrial wastes
are disposed of together. Samples of
wastes from industries such as electro-
plating, nickel-cadmium battery, inorganic
pigment, water-based paint, and chlorine
production, were studied using batch ex-
tractions and continuous flow columns.
The effect of pH on solubility of each of
the wastes was determined from single
batch studies with waste to distilled water
ratios of 40 g of dry waste/400 ml water
and 80 g dry waste/400 ml water. The
pH of each combination was adjusted to
5, 7, or 9. Alkaline conditions favored
immobilization of sample metals used, ex-
cept for chromium, which was mobilized
at alkaline and acid condition, but rela-
tively immobile at neutrality. The test indi-
cated that pH was the most important
factor in determining solubility of Cd. Cu,
Ni and Zn, which were about 100 times
more soluble at pH 5.0 than they were at
pH 7.0.
Serial batch extractions were conducted
by mixing waste with distilled water at a
ratio of 20 g waste/300 ml water and 1 kg
waste/2000 mL water and stirring for 72
hr. Samples were filtered, and the fil-
trates were analyzed for metals by Atomic
Absorption Spectrometry (AAS). The pro-
cess was then repeated by recovering the
residue, and adding 200 ml of water to it.
A total of seven extractions were con-
ducted at 20 g waste to 200 ml water.
Heavy metal solubilization remained rela-
tively uniform throughout the seven ex-
tractions. The first extractions removed
significant quantities of ions other than
heavy metals. But after four extractions
pH and conductivity became relatively
stable.
Serial batch extractions with landfill
leachate were conducted in a similar fash-
ion. All five of the wastes were subjected
to single batch extractions with water at 3
different pH levels and to serial batch ex-
tractions with both water and municipal
landfill leachates at (waste to water) ratios
of 20 g to 200 mL and 1 kg of waste to
2000 ml. Minor variations in procedure
were employed for different wastes. Land-
fill leachate solubilized more metals than
the distilled water did.
Columns of waste were leached to de-
termine solubilization rates by using six
columns with distilled water and six col-
umns with landfill leachate as solvents for
each waste. Wastes were packed into 37
ml mm glass tubing, that was equipped
for upflows of solvent at a flow rate of 0.5
to 1.5 soil pore volumes per day.
The waste leaching columns were con-
nected to soil columns to study the metal
migration through soils in a continuous
flow system. Samples of five soils were
collected and analyzed. They were:
• Kalkaska - a yellowish brown, rap-
idly permeable sandy Spodosol from
Michigan;
• Davidson - a reddish clayey, moder-
ately permeable Ultisol from North
Carolina;
• Anthony - a dark brown, permeable,
sandy Entisol from Arizona;
• Chalmers - a dark gray, fine, loamy,
slowly permeable Mollisol from Indi-
ana; and
• Nicholson - a yellowish brown, fine,
slowly permeable Alfisol from Ken-
tucky.
All five soils were tested in preliminary
batch attenuation studies to measure their
ability to remove metals from water and
landfill leachate that had been in contact
with wastes. Davidson soil, the most re-
tentive, and Kalkaska, the least retentive,
were selected for use in the column at-
tenuation studies.
An attempt was made to achieve a flow
rate of 0.5 to 1.5 pore volumes of leachate
through each soil column each day. It
was difficult to achieve similar flow rates
and contact times however because the
physical properties of the soils were differ-
ent. The soils were packed into columns
with an inside diameter of 3.3 cm but the
heights of the columns were varied from
10 cm for the Davidson to 21.4 cm for the
Kalkaska. Other aspects of column de-
sign such as the head (depth) of waste
leachate and the use of stop cocks were
varied in the attempt to equalize flow rates
and give each soil equivalent contact with
the waste leachate.
The solubilization studies showed that
substantial concentrations of cadmium and
copper were released by water from the
electroplating waste. In addition, chro-
mium was released by the landfill leachate.
Very high concentrations of nickel and
cadmium were released by water and
MSW leachate from nickel-cadmium bat-
tery waste. Nickel and Cd moved rapidly
in soils. The inorganic pigment waste
released only small quantities of cadmium,
chromium and lead for each solvent used,
but the concentration in the soil column
leachate exceeded drinking water stan-
dards. Water-base paint released only
mercury sporadically and at very low con-
centration. Mercury was also the only
metal found, though at low concentration,
in leachate from chlorine production brine
waste when landfill leachate was the sol-
vent. Although relative positions of the
soils in the ranking varied, depending on
which metals and extracts were exam-
ined, Kalkaska and Anthony were consis-
tently poor attenuators and Chalmers and
Davidson were consistently very good at-
tenuators. Davidson soil removed more
metals from the waste leachate than did
other soils with comparable pH even when
the other soils had higher clay contents,
cation exchange capacity, and surface ar-
eas per unit weight. The Davidson had a
high iron oxide content.
Flue-Gas Desulfurizatlon and
Fly-Ash Wastes
The second part of the study examined
the way that wastes from coal-burning
power plants react in the soil environ-
ment. Samples of flue-gas desulfurization
(FGD) sludge and/or fly-ash (FA) were
collected from nine power-generating
plants that burn coal from different sources
and/or use different scrubbing materials.
Six FGD wastes and three FA wastes
were characterized primarily by their heavy
metal, fluoride and boron content, as well
as their tendency to solubilize. They were
also analyzed for chloride, total residue,
volatile residue, filterable residue, and
nonfilterable residue in order to character-
ize the waste and help explain how waste
composition affects the migration of ele-
ments in soils. The FGD samples were
collected as liquid sludge with high solids
contents and FA was collected as a dry
powder. To determine the composition of
the waste, portions were dried, digested
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in aqua regia, the digestates filtered, di-
luted and then analyzed for arsenic, beryl-
lium, boron, cadmium, chromium, copper,
fluoride, lead, mercury, nickel, selenium,
and zinc. Iron was also determined to
further characterize the wastes. The FGD
waste contained high concentrations of
boron and fluoride, and moderate amounts
of arsenic, chromium, copper, lead, nickel,
and zinc. Concentrations of beryllium, cad-
mium, mercury, and selenium were low to
very tow. In addition to the elements in
the solid portion, the liquid portion was
found to contain a large amount of dis-
solved salts. A high concentration of cal-
cium, potassium, and sodium were found
in the supernatant liquor. This is signifi-
cant because these could interfere with
sort attenuation of metals.
The dry fly ash powder was mixed with
water at ratios of 20 g solids to 200 parts
water and 40 g solids to 200 ml water.
The slurries were stirred for 24 hr, filtered,
the pH measured, and the liquid analyzed
by atomic absorption spectrophometry and/
or argon plasma emission spectrophotom-
etry.
The pH was found to be an important
factor in determining the solubility of met-
als of interest. For instance, change in
pH between 5 and 9 did not change the
solubility of boron, but fluoride solubility
increased as pH increased.
Three of the soils used in previous batch
soil attenuation studies, Chalmers,
Davidson, and Nicholson, were used in
the soil column attenuation studies with
FGD and FA wastes. In addition to these,
a sample was collected from an unidenti-
fied clayey fill in Kentucky and from a
clayey, saline soil from the Dugway Prov-
ing Grounds in Utah. The Dugway sample
was chosen specifically to determine the
effect of salt accumulation on a soil's ca-
pacity to absorb metals from a percolating
liquid.
Solubilization and soil attenuation were
studied in continuous flow columns similar
to the column leaching procedure used in
studies of Solubilization of selected ele-
ments from industrial wastes with water
and landfill leachates as solvents, and the
attenuation of these elements from perco-
lating leachates by soil. Serial batch Solu-
bilization studies of FGD and FA wastes
were not conducted. It was concluded
that a highly soluble salt content could
diminish a soil's capacity to attenuate some
elements from waste leachates. It was
also shown that soils with the characteris-
tics of Chalmers, Nicholson, the Kentucky
soil, or the Dugway soil, would be rela-
, tively unchanged in permeability by FGD
and FA wastes similar to those used in
this study. Permeability of samples of
Davidson was increased significantly by
the waste leachates.
Boron and fluoride concentrations were
generally higher in the waste leachate than
were other elements of interest, but they
were successfully removed by the soils.
Significant concentrations of arsenic found
in waste leachates was effectively removed
by all soils except Dugway. The high
soluble salt content of Dugway apparently
interfered with adsorption of contaminants
by soil.
Development of a Serial Batch
Extraction Method and
Application to the Accelerated
Testing of Seven Industrial
Wastes
An important goal for conducting waste
leaching and soil adsorption tests in the
laboratory is to simulate field conditions.
While studying the teachability of indus-
trial wastes and the attenuation of ions
that occurred when the leachate passed
through soil, it was observed that serial
batch and continuous column studies gave
similar results. Column studies are slower
and more cumbersome. Some of the field
conditions to be simulated include the dy-
namic changes that occur in both leachate
and soils through the progression of leach-
ing and adsorption. Leaching of the most
soluble tons in the waste takes place first,
followed by other ions in order of their
solubility as leaching progresses. The
soils change chemically and physically as
tons are exchanged during the movement
of leachates through them.
The graded serial batch extraction pro-
cedure was developed. Seven industrial
wastes and three clayey soils were used
in this study. Seven extracts for each of
the 7 industrial wastes were applied to the
three soils. The three soils were Chalmers,
Davidson, and Nicholson. The industrial
wastes included the following: zinc-car-
bon battery manufacturing, titanium diox-
ide pigment production, hydrofluoric acid
manufacturing, white phosphorus produc-
tion, oil re-refining, and two from zinc sec-
ondary-refining (cinders and scrubber-
waste). The volume of extraction liquid
used was varied to simulate the variability
in time of leaching the waste under field
conditions. The soil batches were graded
in size to allow for analyzing samples of
the extracts after each step while main-
taining a constant ratio of waste extract to
soil.
Both before and after contact with the
soils, the resulting solutions were ana-
lyzed for pH, conductivity, and concentra-
tions of the elements of concern.
This analysis facilitated calculation of
distribution coefficients, penetration fac-
tors, the fraction of each ton retained on
the soils, the amount flushed off of a soil
by the passage of a later extract, and the
yield of an ion per unit weight of soil. The
effect of soil-to-waste ratio on these val-
ues and the limitations and applicability of
empirical equations and prediction mod-
els are discussed in the report. •
Conclusions
• Waste characteristics were only mar-
ginally useful as predictors of metals
concentrating in water or MSW ex-
tracts of the waste; leaching tests
are needed to predict characteristics
of leachate from MSW landfills con-
taining industrial wastes.
• Characteristics such as pH, electri-
cal conductivity, and metal content
of waste and extracts were useful
predictors of metal movement in
soils.
• MSW leachate solubilized greater
amounts of metals than water did
and the metals moved more readily
through soils.
• Of the soils used in absorption or
column studies, the Davidson re-
moved the greatest amount of met-
als, apparently because of its rela-
tively high iron oxide content.
• The FGD and FA waste contain toxic
elements that may sdubilize and cre-
ate adverse impacts on soil, and their
relatively high dissolved solids con-
tents in supernatents may cause min-
eralization of groundwater.
• The state-of-knowledge is inad-
equate to allow formulation of a pre-
diction model that would include all
of the factors that control movement
of metals in soil.
• The serial batch extraction proce-
dure provides a method for making
quick assessment of a site for dis-
posal of given wastes where soil
properties vary with depth, and where
alternative site management tech-
niques are to be considered.
This Project Summary is based on three
separate parts of a report submitted in
partial fulfillment of Interagency Agreement
EPA-IAG-D4-0443 between the U.S. En-
vironmental Protection Agency and the
U.S. Army Dugway Proving Ground. The
Principal Investigator was Martin J. Houle
of the Chemical Laboratory Division, U.S.
Army Dugway Proving Ground. Michael
H. Roulier was the EPA Project Officer.
•&U.S. GOVERNMENT PRINTING OFFICE: mi - SM-02I/40M7
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G. Kenneth Dotson is with the Risk Reduction Engineering Laboratory, Cincinnati,
OH 45268.
Michael H. Roulier is the EPA Project Officer (see below).
The titles for the complete report (except Part I) are listed below. Part I is an
unpublished interim report that was incorporated into the Part II report.
"Migration of Hazardous Substances through Soil: Part Il-Determination of the
Leachability of Metals from Five Industrial Wastes and their Movement within
Soil," (OrderNo. AD-A 158990; Cost: $31.00).
"Migration of Hazardous Substances through Soil: Part Ill-Flue-Gas Desulfurization
and Fly-Ash Wastes,"(Order No. AD-A 182108; Cost: $45.00).
"Migration of Hazardous Substances through Soil: PartlV-Devebpmentofa Serial
Batch Extraction Method and Application to the Accelerated Testing of Seven
Industrial Wastes," (Order No. AD-A 191856; Cost: $53.00).
The above reports are available (cost subject to change) 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:
Risk Reduction and Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-91/017
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