United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV 89193-3478
Research and Development
EPA/600/S8-89/069 Sept. 1989
&EPA Project Summary
Bench Scale Fixation of
Soils from the Tacoma Tar Pits
Superfund Site
Gretchen Rupp
The full report documents the
results of Bench-scale soil fixation
study conducted with materials from
the Tacoma Tar Pits Superfund Site.
Chemical fixation (also called stabil-
ization/solidification) is a relatively
new technique for remediating con-
taminated soils. It entails both
immobilization of contaminants via
sorption or chemical reaction and
physical transformation of the soil
into a firm, impervious "monolith."
Fixation has been used for years to
immobilize metals in low-level radio-
active wastes and specialized
industrial wastes, such as baghouse
dusts. It has not been commonly
used at sites with organic contam-
ination, however. This study utilized
materials contaminated with metals
and several types of organic contam-
inants including benzene,- toluene,
xylene, polycyclic aromatic hydrocar-
bons, and poloychlorinated bi-
phenyls. Samples of heavily contami-
nated soils and wastes from the site
were chemically fixed using a
proprietary product, and the resulting
monoliths were subjected to various
physical, chemical, and leaching
tests. The purpose was to assess the
efficacy of fixation for a complicated
matrix, i.e., one that was physically
heterogeneous and contained several
classes of contaminants.
This Project Summary was devel-
oped by EPA's Environmental Monitor-
ing Systems Laboratory, Las Vegas,
NV, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report
ordering information at back).
In 1988, Region 10 of the U.S. EPA
conducted a soil-fixation treatability study
using materials from the Tacoma Tar Pits
Superfund site. The project involved
bench-scale stabilization/solidification of
mixed soil, coal tar, and automobile
shredder fluff. The objective was to test
fixation as a treatment technique for a
complicated waste matrix, i.e., a phys-
ically heterogeneous one containing
several classes of contaminants. The pro-
ject was part of a Region 10 program to
examine the efficacy of soil fixation under
varying conditions. EPA's Environmental
Monitoring Systems Laboratory at Las
Vegas provides overall direction for the
program.
The Tacoma Tar Pits site is an NPL
site in the industrial district of Tacoma
adjacent to the Puyallup River. The 30-
acre site lies atop coarse fill on what was
once the river delta. Between 1924 and
1956, a coal-gasification plant operated
on the site. Since 1967, a scrap-metal
recycling facility has occupied most of
the site.
Coal-gasification and metal-recycling
wastes are found over much of the site.
Coal tar (approximately 5,000 cubic
yards) is present in shallow pits and
within site soils. Tar-derived liquid ("non-
aqueous phase liquid," or NAPL) forms
lenses within the shallow fill over much of
the site. Several acres are covered 1-3
feet deep in decomposing "auto fluff,"
the rubber, foam, and non-ferrous metal
products of an automobile shredder.
Building rubble, metallic scrap, and
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miscellaneous debris are mixed with the
auto fluff.
The classes of contaminants derived
from these wastes include benzene,
toluene and xylene, polycyclic aromatic
hydrocarbons, polychlorinated biphenyls,
and metals (chiefly lead, arsenic, and
mercury). These are found in varying
concentrations within the auto fluff, the
soil, and a shallow aquifer that develops
on the site in the winter months.
The Record of Decision for the Tar Pits
Site establishes cleanup goals for lead,
benzene, PCBs, and PAHs in site soils
and waters. The ROD names on-site
stabilization/solidification as the principal
remedial technique. To remediate the
site, soils and auto fluff over 15 acres will
be excavated to a depth of about two
feet, mixed with a sorbing_ agent, water,
and a cementitious fixative, and replaced
in the excavation. The mixture will set up
as an impervious monolith. It will be
capped with asphalt and protected by
fencing and runoff-runon control
structures.
Site soil, coal tar, and auto fluff were
collected for the treatability study. Soil
and fluff sampling locations were chosen
on the basis of site contamination
information generated in the Rl. There
was deliberate bias towards sampling in
highly-contaminated areas, so as to
strongly challenge the fixatives. Seven
soil subsamples were collected by
digging shallow pits with hand tools. The
soil was screened through 3/8-inch
hardware cloth, composited, and mixed at
length on the site. Approximately 150 Ibs.
of field-moist soil were collected. Auto-
mobile fluff was sampled and handled
similarly. Sampling personnel dug to the
base of the fluff (about two feet) and
screened and composited four depth-
integrated subsamples in the field. About
100 Ibs. of fluff were collected. Two
gallons of coal tar were scooped from the
"tar pit" on the site.
Material mixing and fixation took place
at the Region 10 laboratory at Man-
chester, Washington. The materials fixed
were: pure soil; 1:1 soikauto fluff (w/w
mix): 3:1 soil:auto fluff; coal tar; 1:1
soihlar; and sand (a sample blank con-
sisting of clean commercial sand). As raw
materials were mixed, subsamples were
taken for chemical analysis; other sub-
samples were blended with fixation
reagents and poured into small cylindrical
molds. These monoliths were labelled,
stored at 100% relative humidity, and
allowed to cure for specified periods
before further testing.
The following tests of site materials
were conducted:
• analysis of contaminant concentrations
in raw and fixed materials;
• TCLP extraction of raw and fixed mate-
rials
• bulk density, apparent moisture con-
tent, permeability, compressive
strength, and wet/dry durability of fixed
materials;
• permeability and compressive strength
of fixed materials following wet/dry
stressing;
• ANS 16.1 sequential-batch leaching of
whole fixed monoliths, with and without
wet/dry stressing.
In each type of test, variability was
assessed by testing a triplicate set of the
3:1 soihfluff samples.
The. treatability^study-was designed-to-
ascertain whether or not fixation would be
effective for the highly-contaminated
materials from the Tar Pits Site;
therefore, very high reagent dosages
were used. This resulted in considerable
volume increases (45-95 percent) follow-
ing fixation. When the reagent mix is
optimized, lesser volume increases can
be expected.
Fixed soil and soil-fluff mixtures were
resilient to the wet/dry stressing (the
durability testing); they lost less than five
percent of their masses in these cyclic
tests. Tar and tar-soil cyclinders had
losses exceeding five percent; however,
this may have been caused by the high
temperature (60°C) used in the test.
Fixed cylinders gained compressive
strength throughout the 29-day testing
period. The standard 28-day test of
ultimate compressive strength of con-
crete may be inappropriate for hetero-
geneous fixed wastes. Later testing is
indicated. Fixed materials that included
auto fluff or tar developed less com-
pressive strength than fixed soil. Except
for tar, all-the^fixed'mateTials'could "be
expected to develop strength greater
than 50 psi, which is a potential
applicable standard. A full-scale monolith
two feet thick would be predicted to
support its own weight.
Permeabilities of fixed materials ranged
from 10'9 to 10-6 cm/sec. For every type
of material, wet/dry stressing increased
permeability by more than an order of
magnitude, probably through the creation
of micropores within the cylinders. Fixed
tar collapsed during these tests, and
would probably have insufficient physical
integrity to meet site-specific standards.
Contaminant concentration within site
samples fell within previously-reported
ranges. Although an effort was made to
collect highly-contaminated materials,
these samples fell within "typical" ranges
for this site for metals, PAHs, PCBs, and
the BTX compounds. Both raw and fixed
materials showed two exceedances of
site cleanup goals. All soil-containing
mixtures, raw or fixed, exceeded the soil
lead goal, and tar-containing mixtures
exceeded the PAH goal.
As measured by TCLP leaching,
fixation inhibited the release of the
various contaminant classes to different
degrees. Lead was strongly immobilized
by fixation: the maximum proportions
leached were 0.4 (from raw materials)
and 4x10-4 (fixed materials). Leaching of
the BTX compounds from tar-containing
cylinders was not curtailed by fixation.
PCBs and the PAHs of concern leached
from both raw and fixed materials at low
—levels-(less-than -5 -ng/l). TGLP leachates
of fixed materials met the PAH and PCB
goals for site cleanup. Tar-containing
monoliths leached excess benzene
relative to the goals, and soil and soil-fluff
monoliths released lead in concentrations
above the goal (3.2 pg/l) for surface
waters at the site boundary.
In the ANS 16.1 tests, cylinders of
fixed materials; were leached in seven
successive batches of deionized water
over a 90-day period. Leachate pH values
fell from 11.5 to 7.5-9.5 during the tests.
Metal levels were low (generally unde-
tectable) in these leachates; lead was
never detected (at 50 ng/l). At a detection
limit of 0.3 iig/l, PCBs were not found in
any leachate. PAH levels were generally
below 10 ng/l, although the lighter PAHs
leached from tar-containing cylinders at
levels up to 10 mg/l. The most readily-
extracted compounds were phenols;
about 14 percent of the phenols in the
tar-containing cylinders leached out
during these tests. Leachability indices
derived from the ANS 16.1 data ranged
from 9 to >15, 'ndiŁ5ting_jhatJM con-
taminants ^oftioncern^are relatively
immobile in these monoliths. Based on
the teachability indices, the proportions of
contaminants leached from a full-scale
monolith at various times in the future
were estimated. It was projected that less
than 10 percent of any contaminant of
concern would leach from a soil or
soihfluff monolith in 1000 years. Fifty
percent of the phenols, naphthalene, and
possibly other PAHs originally present in
a tar-containing monolith might leach out
over 1000 years.
The effects of cyclic wetting and drying
were assessed by coupling wet/dry
stress tests of different durations with
ANS 16.1 leaching. Leachate pH and
conductivity data indicated that the
wetting and drying accelerated cylinder
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weathering. However, contaminants were
so dilute in the leachates that effects on
their release could not be distinguished.
Where contaminants are effectively
immobilized, it may be appropriate to
spike them into raw materials before
attempting to distinguish among
treatments.
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Gretchen Rupp is with the University of Nevada - Las Vegas, Las Vegas, NV 89154.
The complete report, entitled "Bench Scale Fixation of Soils from the Tacoma Tar
Pits Superfund Site," (Order No. PB 89-224 950/AS; Cost: $21.95, 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:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Las Vegas, NV 89193-3478
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA,600'S8-89/069
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