United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/108 Apr. 1987 '/I
&EPA Project Summary
Retention of Zinc, Cadmium,
Copper, and Lead by Geologic
Materials
J. P. Gibb and K. Cartwright
The vertical and horizontal migration
patterns of zinc, cadmium, copper, and
lead through the soil and shallow aquifer
systems at a secondary zinc smelter
were studied by the use of soil coring
and monitoring-well techniques. The
migration of metals that occurred was
limited to relatively shallow depths into
the soil profile by attenuation processes.
Cation exchange and precipitation of
insoluble metal compounds, as a result
of pH changes in the infiltrating solu-
tion, were determined to be the principal
mechanisms controlling the movement
of the metals through the soil. Increased
metals content in the shallow ground-
water systems was confined to the
immediate plant site.
Soil coring was an effective investi-
gation tool, but not suitable by itself for
routine monitoring of waste disposal
activities. However, it should be used
to gather preliminary information to aid
in determining the proper horizontal
and vertical locations for monitoring-
well design. The analysis of water
samples collected in this project gen-
erally did not provide an understandable
pattern of results. A brief experiment
on monitoring-well sampling indicated
the need to develop reproducible sam-
pling techniques to obtain representa-
tive water samples. The failure of some
well seals in a highly polluted environ-
ment also indicates the need for addi-
tional research in monitoring well
construction.
This Project Summary was developed
by EPA't Hazardous Watte Engineering
Research 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 primary purpose of this study was
to verify in the field the effectiveness of
glaciated region soils and associated sur-
face deposits in retaining specific haz-
ardous chemicals. The study also was
designed to develop effective investigative
and monitoring techniques for detecting
and quantitatively evaluating the extent
of groundwater pollution from surface
waste disposal activities.
Special emphasis was placed on defin-
ing: 1) the vertical and horizontal migra-
tion patterns of chemical pollutants
through the soil and shallow aquifer sys-
tems; and 2) the residual chemical buildup
in soils in the vicinity of pollution sources.
Four industrial complexes were select-
ed for study of the effects of their waste
disposal practices on the soils and shal-
low groundwater systems. Site Ar where
most of the time, money, and effort was
spent will be discussed.
Site A is a secondary zinc smelter
located in south-central Illinois. The plant
started operations between 1885 and
1890, initially processed zinc ore, and
was converted to a secondary zinc smelt-
ing facility about 1915. Waste from the
smelting operations during the first 85
years principally were heavy metals-rich
cinders and ashes. During the early years
large quantities of cinders were used as
road fill or surfacing in the plant area. As
a result of these disposal practices, there
now is a 1- to 10-foot thick layer of
metals-rich cinders covering about 12
acres of the plant property.
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In compliance with air pollution control
regulations, a scrubber was installed on
the plant stack in 1970. Prior to that time,
wind-blown ash, rich in zinc and other
heavy metals, was deposited on the plant
site and on the surrounding farmland.
This source of pollution has now been
minimized, but wastewater from the
scrubber is disposed of in a seepage pit
constructed on the cinder materials that
form the present-day land surfaces.
Several hundred tons of high zinc con-
tent sludge have accumulated from the
frequent cleaning of this pit and are being
reprocessed for zinc recovery. Most of
the water from the pit infiltrates into the
ground underlying the plant property.
The collection of continuous vertical
core samples for geologic study and
chemical analyses, and the construction
of piezometers or monitoring wells for
water level measurements and water
sampling were the principal field techni-
ques used in this study.
Water level measurements were made
and water samples were collected from
each well once a month. Water samples
were analysed for heavy metals at the
Environmental Research Analytical Labo-
ratory with zinc as the target element.
Two electrochemical methods, anodic
stripping voltammetry and pulse polaro-
graphy, proved to be most effective for
making zinc determinations and screen-
ing for the presence of other metals of
interest. Total mineral analyses were also
conducted.
Results
Altogether, 49 wells at 36 locations
were completed at Site A. Core samples
were taken at each of these locations and
at an additional 23 sites. Total well and
core sampling footages are about 1309
and 1454 feet respectively.
The glacial materials at the site range
in thickness from about 55 feet on the
east to about 75 feet on the west. The
stratigraphic units recognized are es-
sentially uniform in character and thick-
ness and generally flat lying across the
site. The elevation of the bedrock surface
dips from 449 feet above sea level on the
east to 432 feet on the west.
The expandable clay minerals, generally
referred to as montmorillonite, make up
more than 80 percent of the clay minerals
within the Peoria Loess, Roxana Silt, and
Berry Clay Member, thereby suggesting a
high base exchange potential in the upper
13 feet of the materials encountered. The
thin, continuous silty sand zone at the
top of the Vandalia Till would appear to
be the only permeable unit to allow
groundwater to travel laterally at any
moderate rate away from the site. Al-
though there is probably some downward
movement of groundwater through the
remainder of the Glasford Formation, it
would be expected to be extremely low.
On the basis of the geologic description
of this site, it is quite obvious that no
significant aquifer exists in the immediate
vicinity of the plant site. The Hagarstown
Member, a thin (1 to 2 feet thick) con-
tinuous silty sandy zone, appears to be
the only permeable zone that could allow
for significant lateral groundwater move-
ment away from the site. To develop even
a domestic water supply from this sand
unit probably would require the construc-
tion of two or more large-diameter bored
wells.
Water table contour maps show a water
table mound beneath the plant complex.
The relatively high permeability of the fill
materials at the plant site, its topographic
setting, and the liquid disposal activity at
the plant all contribute to the develop-
ment of this recharge mound.
No stabilized water levels were ob-
served in some of the deep wells for the
period of record. In general, water levels
in the deep wells are higher than those in
the shallow wells, indicating a probable
upward movement of water within the
glacial drift sequence. In the immediate
plant area, where the shallow water levels
are mounded, the movement of water in
the shallow deposits probably is down-
ward and horizontal. The average rates of
groundwater movement from the
mounded area were, for example, 0.17
ft/day in March 1976 and 0.19 ft/day in
November 1975.
Chemical analysis of the core samples
were conducted to define: 1) the vertical
and horizontal migration patterns of
chemical pollutants through the soil; and
2) the residual chemical buildup in soils
in the vicinity of the pollution source.
Preliminary analysis of core samples dur-
ing the early stages of the study indicated
that four elements (zinc, cadmium,
copper, and lead) were most likely to be
carried into the soils and groundwater
system beneath the plant property. As a
result these elements were selected for
routine analyses.
Results of chemical analysis of core
samples from the Site A control hole
located approximately 3 miles south-
southwest of the plant, and samples from
unaffected soil horizons beneath the plant
property suggest that background con-
centrations for the four elements tested
should be about 20 to 50 ppm for zinc,
0.04 to 1.5 ppm for cadmium, 10 to 30
ppm for copper, and 10 to 40 ppm for
lead. There appears to be no significant
chemical variation with depth or between
geologic unit boundaries. Some zinc levels
in isolated Pleistocene soils were higher.
A series of cross sections for zinc,
cadmium, copper, and lead concentra-
tions of the soil were prepared to outline
the limits of migration of these metals
beneath the plant and give an indication
of the effectiveness of the soils in retain-
ing these metals. Small quantities of zinc
were found in the upper 3 to 5 feet of the
soil profile outside of the plant property.
Most of the zinc introduced into this area
probably was wind blown dust and ashes
from the plant stack. The area of greatest
accumulation and deepest concentration
of zinc in the soil occurred immediately
beneath the plant property.
The general shapes of the cross sec-
tions for cadmium, copper, and lead were
similar to those for zinc. The depth of
penetration of cadmium is slightly less
than that of zinc but considerably greater
than that of copper and lead.
The very shallow depths of penetration
of these elements indicate the relative
immobility of these metals. In general,
the areas of greatest penetration of the
four elements occurred beneath the
scrubber wastewater pit. Here waste-
water is a significant source of the metals
and the recharge into the soil system is
greatest. In other areas removed from
the pit, the presence of the cinders be-
came the dominant source of metals, and
lowland areas where ponded water ac-
cumulates was the secondary source.
In addition to the direct percolation of
metals-rich waste at the plant site, a
significant amount of metals-rich surface
water runs off the plant property and
percolates into the stream beds draining
the plant to the southwest and southeast.
An accumulation of metals-rich cinder-
type sediments in the stream bed was
noted. The concentration of metal re-
tained and depth of penetration decreases
as the distance away from the plant site
increases.
The mechanisms retaining the metals
in the soil profile at Site A are pre-
dominantly cation exchange and precipi-
tation of insoluble metal compounds as a
result of pH change. Cation Exchange
Capacity data generated indicate little
variation in the retention capabilities of
the upper geologic units, the silts, clays,
and tills. Therefore, as metals-rich water
percolates downward through the soil
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profile, the metals are exchanged pre-
ferentially in reverse order of their
mobility.
Cation Exchange Capacities (CEC) of
soils measured at Site A range from
about 4 to 10 me/100 grams with the
larger values occurring in the shallower
soils. If zinc were transferred onto the
available exchange sites of the soil, cation
exchange could account for soil zinc con-
centrations up to about 3500 ppm. This
value could be higher, according to some
soil specialists, because the measured
CEC may be lower than the original
capacity of the soil. Some researchers
maintain that the soil becomes "poi-
soned" in the presence of pollutants and
true CEC values cannot be measured.
Aside from that possibility, three other
factors may explain the difference be-
tween the very high soil zinc concentra-
tions shown in the upper part of the soil
profiles and the values attributable to
cation exchange:
1) Some of the very high values obtained
for the surface and near surface
samples actually are chemical analy-
ses of cinder fill samples.
2) Immediately beneath the cinder fill,
fine-grained sediments from the
cinders have been illuviated (washed
down) into the underlying soil, also
resulting in high zinc values of those
samples.
3) Soluble and insoluble salts of zinc and
the other metals may be temporarily
stored in the aerated zone waiting for
eventual migration downward with
later recharge events. This also results
in higher zinc concentrations in soil
samples from this horizon.
As the Cation Exchange Capacity of the
soil is exhausted and sufficient depth is
reached to eliminate the three factors
just noted, the metals buildup in the soil
slowly continues to advance deeper into
the soil profile. As the exchange process
occurs, calcium and magnesium are re-
leased into the water from the soil and
the pH of the infiltrating fluid is lowered.
As the pH increases, the formation of
zinc precipitates results, and a sharp break
or decrease in soil zinc content is noted.
Samples of water collected after perco-
lating through the cinder fill materials
forming the sides of the disposal pit had
measured pH values near 5. It can be
assumed that the same pH was experi-
enced by water filtering downward
through the cinder fill covering the plant
surface. It is suspected that sulfur con-
tained in the cinders was dissolved to
form a weak sulfuric acid, thus creating
the low pH and increasing the mobility of
the zinc.
Conclusions pertaining to the mecha-
nism of zinc and other metals fixation
drawn from this field study indicated that
increased removal of metals from solution
occurs with increasing pH values and
with increasing concentrations of the
heavy metal in solution.
Chemical analysis of water collected
from deep wells at Site A showed less
than 0.5 mg/l zinc. The zinc contents of
water collected from the shallow wells
tapping the Hagarstown sand unit were
10,000 mg/l near the scrubber sludge
pit and decreased to 1 mg/l at the
boundary of the plant property. Because
the sampling procedure was not satisfac-
tory and the attempt to detect well seal
failures was unsuccessful, further analy-
sis of the water quality data generated
probably is not worthwhile. The sampling
procedure used in this study could ac-
count for as much as 40 to 80 percent of
the fluctuations noted between sampling
periods.
To better define the quality of water in
an affected and unaffected area, water
samples were collected from wells in
each area for total mineral analysis. The
results of the analysis of a water sample
from the shallow control hole well in-
dicated general agreement for the un-
affected area well. In the affected area
well, increases in mineral constituents
were observed. Also, the zinc concentra-
tion (750 mg/l) and pH (6.5) were in
excellent agreement with the solubility of
zinc (800 mg/l at 6.5pH). Evidence of ion
exchange was shown by the high con-
centrations of calcium (2400 mg/l) and
magnesium (893 mg/l). The cation ex-
change positions in soils in this region of
Illinois are principally filled with calcium
and lesser amounts of magnesium. Zinc
is higher in the montmorillonite exchange
series than Ca and Mg and thus will
replace these ions on the clay structure.
This process releases calcium and
magnesium to the environment, even
when these are not part of the original
waste stream.
Because of these phenomena, it is
recommended that total mineral analysis
be conducted on water samples from
monitoring wells where cation exchange
is likely to occur. Increases in one or
more of these constituents could be an
early warning of the eventual appearance
of more toxic metals. However, to in-
terpret a series of samples properly, the
problem associated with collecting com-
parative samples must be solved.
In attempting to evaluate the relative
merits of soil sampling versus well instal-
lation and water samplings, the costs of
analytical work and the results obtained
should be considered. Depending on the
type of waste to be disposed of or moni-
tored, soil sampling may prove to be
more effective even though more costly.
If a research project is being conducted,
coring would prove to be most useful.
The coring and analyses of the core
samples give a better understanding of
the phenomena taking place in the soil.
However, due to the costs, coring may
not be practical as a routine monitoring
technique.
Recommendations
On the basis of the results of this study
we recommend the following:
1) Coring and soil analysis should be
used in waste disposal research pro-
jects or in waste disposal operations
when the toxicity of a waste product
warrants the additional expenditure.
2) A limited number of core samples, soil
analyses, and geologic interpretations
are advisable for evaluating alternative
disposal sites. Soil analyses provide a
better understanding of soil interaction
with the waste product than is other-
wise possible, and geologic inter-
pretation of the core samples provides
better information for design and
location of monitoring wells.
3) Routine monitoring of most disposal
sites should be accomplished with
wells located and designed on the
basis of preliminary coring analysis.
Periodic coring and soil analysis may
be worthwhile to substantiate original
soil effectiveness assumptions.
The full report was submitted in partial
fulfillment of Grant No. R803216 by the
Illinois State Geological Survey and the
Illinois State Water Survey under the
sponsorship of the U.S. Environmental
Protection Agency. The report, entitled
"Retention of Zinc, Cadmium, Copper,
and Lead by Geologic Materials," was
published as Cooperative Groundwater
Report 9 by the Illinois State Water Survey
and the Illinois State Geological Survey.
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J. P. Gibb is with Illinois State Water Survey, Champaign, IL 61820; and K.
Cartwright is with Illinois State Geological Survey, Champaign, IL 61820.
Mike H. Roulier is the EPA Project Officer (see below).
The complete report, entitled "Retention of Zinc, Cadmium, Copper, and Lead
by Geologic Materials," (Order No. PB 83-232 819; Cost: $18.95, 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:
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 452G3
hi\ rV.' ,
Official Business
Penalty for Private Use $300
EPA/600/S2-86/108
0000329
U S ENVIR
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