United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada, OK 74820
Research and Development
EPA/600/S2-90/018 July 1990
4>EPA Project Summary
Mobility and Degradation of
Residues at Hazardous Waste
Land Treatment Sites at Closure
Raymond C. Loehr, David C. Erickson, Laura A Rogers, and Daniel M. Kelmar
The objectives of this study were to
determine: (a) the extent to which
organics remaining at hazardous
waste land treatment (HWLT) sites at
closure continue to degrade, (b) the
migration potential of the
accumulated waste residue
constituents, and (c) whether
available models (RITZ and MINTED)
are appropriate for closure decisions.
This was achieved by: (a) obtaining
representative soil samples from the
treatment zone of several HWLT sites,
(b) characterizing the residual
material in such samples, (c)
conducting laboratory studies to
determine the degradation and
potential mobility of the constituents
in the samples, and (d) using RITZ
and MINTED to evaluate the migration
potential of the residual constituents
under different closure options. Soils
used were obtained from three sites
to which listed refinery or wood
preserving wastes had been applied
and from a site which had soil
contaminated with coal tar.
In the surface soils of the HWLT
sites, the concentrations of the
organics and metals were greater
than in background soils. At depths
below 24-30" at the HWLT sites, the
concentrations of PAH compounds
were below detection limits and the
freon-extractable concentrations
were at background soil
concentrations or below detection
limits. At sites for which site soil
concentrations could be compared to
concentrations in background soils,
the concentrations of chromium and
nickel in site soils at depths below
24" appeared greater than
background soil concentrations,
whereas the concentrations of
copper, lead and zinc in site soils at
such depths appeared comparable to
those in background soils.
Analyses for organics in TCLP
extracts of the soils indicated that no
PAH compounds were extracted by
this procedure from either weathered
or non-weathered soils. Zinc was
found above detection limits in the
TCLP extracts of the site soils most
frequently. In most of the site soil
samples analyzed, the concentrations
of metals in the TCLP extracts were
close to or below detection limits of
0.1 mg/L.
The PAH and metal concentrations
measured in the TCLP extracts from
the site soils provided no reason to
conclude that these soils and
accumulated residues would fail to
pass a toxicity characteristic
determination using the TCLP test.
The aerobic and anaerobic
microcosm studies demonstrated
that there was no statistically
significant degradation of the PAH
and freon extractables in the zone of
incorporation (ZOI) samples over an
eight-month period. The data suggest
slow degradation of the accumulated
organics following closure of an
HWLT site.
MINTED is a predictive model that
estimates aqueous equilibrium
solubility concentrations for metals.
However, gaps in the MINTED
database do not allow it to identify
the relative solubility of many of the
metals of interest at HWLT sites.
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Thus, MINTEQ appears of limited
value for identifying the
environmental fate of metals under
different closure options.
When used with worst-case data for
a petroleum refinery HWLT site, the
modified RITZ model indicated major
differences in mobility and
persistence of PAH compounds
between capped and uncapped
closure scenarios. The closure
options in which the sites were
uncapped allowed for more rapid
degradation, but movement of the
constituents below the ZOI was
greater. For the clay or synthetic cap
option, the degradation of the organic
constituents was much slower, but
the movement below the ZOI
diminished. This simulation indicated
that the modified RITZ model can be
a useful tool for assessing the impact
of different closure options on
accumulated residuals at HWLT sites.
This Project Summary was
developed by EPA's Robert S. Kerr
Environmental Research Laboratory,
Ada, OK, 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
Land treatment has been used to treat
municipal wastes for centuries. In
addition, over the past thirty years there
has been increased use of land treatment
to treat industrial wastes, such as wastes
from the petroleum refining industry. With
the passage of the 1984 Hazardous Solid
Wastes Amendments (HSWA) to the
Resource Conservation and Recovery Act
(RCRA), many changes have occurred in
the regulatory framework with regard to
the use of land-based technologies for
disposal of hazardous wastes. Due to the
restrictions imposed by these regulations,
a number of hazardous waste land
treatment (HWLT) sites are, or soon will
be, undergoing closure. The organic and
inorganic waste constituents that have
accumulated at these sites can be of
concern due to: (a) potential mobility
during the post-closure period, which can
be as long as 30 years, and (b) the
human and environmental exposure that
might occur when the site is used after
the post-closure period.
There are several major options (Table
1) for the closure of a land treatment site
or a site with contaminated soils, all of
which involve the careful management of
the site over the post-closure period, as
defined by the regulations. Both direct
and indirect impacts on human health
and the environment are important in the
selection of the site-specific appropriate
closure options.
The purpose of this study was to
develop information pertaining to: (a) the
characteristics of the waste constituents
remaining at sites having long-term waste
application, such as HWLT sites, and (b)
the potential for subsequent degradation
and/or migration of the constituents at
such sites. Such information can help
regulatory agencies and industry identify
the most environmentally sound closure
and post-closure conditions for a specific
site and can help identify additional
research needs related to the closure of
HWLT sites.
Soil samples from four field sites were
obtained for project use. The sites were
chosen based on the following criteria: (a)
waste had been applied at the site for an
extended period of time, preferably at
least 10 years, or the waste treatment or
disposal site had been closed (unused)
for an extended period of time, (b) site
history and background information were
available, (c) the applied waste was
representative of listed refinery wastes
(K-048 to K-052) or of listed wood-
preserving wastes (K-001), and (d) the
site was available and accessible for
sampling. Four sites that most closely
met the criteria were chosen.
The soils evaluated were obtained froi
two operating HWLT sites, one close
land treatment site and a site which h«
soil contaminated with coal tar. The soi
were obtained from: (a) the Conoci
Ponca City, Oklahoma, closed oil refinei
research land treatment site, (b) th
Texaco, Anacortes, Washington, HWL
site which had been in operation sine
1958; (c) an HWLT facility at a woo
treating site (WTS) in Montana; and (d)
Niagara Mohawk Power Corporatio
(NMPC) site in New York. The NMPC sit
was not an HWLT site and the result
from samples obtained at this site shoul
not be construed to represent condition
at a managed HWLT site.
Two types of samples were obtaine
from the Texaco and the Conoco site:
(a) surface zone of incorporation (ZO
samples for a study to evaluate th
spatial distribution of residu
characteristics at such sites and (b) so
core samples taken as a function c
depth to determine whether the waste
which had been applied to the surfac
soils had migrated. Only core sample
were taken from the other two sites
Although different materials have bee
applied at these sites, similar constituent
were in the site soils - metals, long-chai
hydrocarbons, and polynuclear aromati
hydrocarbons (PAH).
Site Soil-Residue
Characteristics
Results from the Texaco site indicatee
that volatile and acid extractabl<
compounds were not found in the HWL"
soils but that PAH compounds wen
detected in concentrations considerably
above background. The soils from all fou
sites were evaluated for sixteen specifii
PAH compounds in the laboratory
studies.
The Texaco site had detectable
concentrations of most of the 16 PAr
compounds in the top (0-6" and 12-24"
soils of the site. The average
concentrations of these compound:
Table 1. Options for the Closure of an HWLT Site
Removal of the contaminated soil and subsequent disposal of such soil as a hazardous waste.
Placement of an impermeable cap over the site. The cap may consist of synthetic liners or clay.
The site is left alone with the only continued management being ground-water monitoring as well as run-
on and runoff control and a vegetative cover.
Continued managed in-situ treatment of the accumulated waste residues.
A combination of two or more of the above.
-------
found at increasing depths from the
urrent surface of the site are presented
in Table 2. The long-term application of
wastes and residues at this site has
raised the topographic surface of the soil
18-42 inches. At the plots sampled, the
surface was increased about 30 inches.
The absence of detectable
concentrations of PAH compounds in the
36-54" layer indicated that these
compounds had not migrated to this
depth.
Freon extractable determinations also
were done for the Anacortes samples.
This analysis is a relative measure of the
total oil and grease (0/G) residuals in a
sample. The 0/G concentration in the 0-
6" samples was 61,700 mg/kg and was
56,600 mg/kg in the 6-12" sample. The
0/G concentrations in soil samples taken
below 24" were: 24"-36" -- less than
1000 mg/kg; 36"-54" ~ 1680 mg/kg; and
54"-72" -- less than 1000 mg/kg. These
concentrations below 24" were about the
same as those in the site background
soils.
The concentrations of PAH at the
Conoco site were similar in type but
much lower in concentration than those
found at the Anacortes site. There has
been no application of wastes at this site
since 1978.
The PAH concentrations in the soil
cores from the plot receiving the largest
application at this site were 'determined.
Below the ZOI, the PAH concentrations
were close to or below analytical
detection limits. The data indicate that
there has been no migration of the PAH
from the surface soils to lower soils.
The wood-treating site soils had
detectable concentrations of all 16 PAH
compounds except acenaphthalene and
acenaphthene in the top layer (0-6") of
the soil. The concentrations of PAH
below the 0-6" layer were very low,
indicating that little or no migration had
occurred below this depth.
Sample Variability Studies
Separate surface soil samples were
taken from the Anacortes and the Conoco
sites to determine the variability in
characteristics that may exist in the
surface soils at a HWLT site. Knowledge
of this variability is important to
monitoring decisions, to closure
conditions and to an understanding of
whether the core samples taken from a
site were representative of the
characteristics throughout the site. The
ZOI samples were analyzed for organic
matter, dry weight, freon extractables,
ind three metals (copper, chromium and
iron). These parameters represent
compounds that are part of soil and of
the wastes that were applied and
accumulated in the surface soils. The
data from these analyses were compared
using standard statistical tests to
determine whether there was a difference
in chemical characteristics between the
sampling locations.
The statistical analyses indicated that
within the Texaco and Conoco plots,
consistent differences in constituent
concentrations at each site were not
observed. The analyses also indicated
that the residues that existed at the time
of sampling appeared to be uniformly
distributed at the site.
Based upon a comparison of core and
surface soil samples at the Conoco and
Texaco sites, it appeared that the core
samples were representative of the soils
at these sites.
Mobility and Weathering
Studies
These laboratory studies identified the
migration potential of constituents in the
site soils. The effects of simulated
weathering cycles on the quality of
potential leachate were determined using
the toxicity characteristic leaching
procedure (TCLP). The primary variables
were: (a) soil samples from six depth
intervals at each site, starting at the
surface and proceeding to six feet below
the soil surface; (b) two weathering
patterns, Freeze/Thaw and
Wetting/Drying cycles, and (c) analyses
of TCLP extracts from both weathered
and non-weathered samples of soil.
The methods used for the simulated
weathering cycles were adapted from
ASTM methods for tests of soil-cement
mixtures. These procedures were used
with the soil samples in their as-received
state, without the addition of cement.
During the gas chromatographic
analysis of the approximately 220
extracts analyzed for organics, eight
samples had some measurable peaks
that could be quantified. These samples
were analyzed on a mass spectrometer
and the peaks identified by a library
search of available chemicals. The results
indicated that six of the samples
contained phthalates, a common
laboratory contaminant, probably from
plastic containers used during the
methylene chloride extraction procedure.
The two remaining samples had peaks
which were identified as long-chain
hydrocarbon compounds.
The TCLP extract concentrations for
metals in soils at the Conoco site as a
function of depth were as indicated in
Table 3. These are illustrative of the
results obtained when the soils from the
other sites were evaluated. The pattern
was one of low concentrations, generally
about 0.1 mg/L, in the extract from the
surface soils and below detection limits in
extracts from the deeper soils. The one
exception was zinc, which in some
extracts was above a concentration of 1.0
mg/L.
The results of these laboratory studies
can be summarized as follows:
a)Analyses for organics in the TCLP
extracts indicated that no PAH
compounds were extracted by this
procedure from either the weathered or
non-weathered soils.
b)There was no difference in the
concentration of metals in the TCLP
extract of the non-weathered and the
weathered samples.
c)The PAH and metal concentrations
measured in the TCLP extracts from
the soil/residues from these four sites
provided no reason to conclude that
the soils and accumulated residues
would fail to pass a toxicity
characteristic determination using the
TCLP test and analysis of the TCLP
extract.
Degradation Studies
These laboratory studies were
undertaken to identify the extent to which
organics remaining at closure of a HWLT
or similar site will continue to degrade
under closure and post-closure
conditions. An impermeable cap will
reduce infiltration and leaching but also
will restrict oxygen transfer from the
atmosphere. Anoxic or anaerobic
conditions under this type of cover could
occur.
Because of the expected soil
conditions with these closure options,
degradation under both aerobic and
anaerobic conditions was evaluated and
microcosm studies were conducted over
an eight-month period. Only samples
from the Anacortes ZOI were used. Such
samples represent the accumulation of
residues over 30 years. The term
degradation is used to describe the
results, because it was expected that
microbial degradation would be the major
organic compound loss mechanism.
However, the actual loss mechanisms
were not investigated.
Three separate composites of four
different Texaco ZOI samples were
prepared for two aerobic and one
anaerobic degradation microcosm
studies. No uncontaminated soil was
added to these samples. The two aerobic
studies were: (a) the ZOI soils without
amendments or enhancements, and (b)
-------
Table 2. PAH Concentrations" at the Texaco Site as a Function of Depth
Sample Depth"
0-6"
Compound
naphthalene
acenaphthalene
acenaphthene
fluorene
phenanthrene
anthracene
fluoranthene
pyrene
benzo(a)anthracene
chrysene
benzo(b)fluoranthene
benzo(k)fluoranthene
benzo(a)pyrene
dibenzo(a,h)anthracene
benzo(g,h,i)perylene
indeno(i,2,3-c,d)pyrene
Ave.
1.8
BDL
BDL
6.8
5.9
BDL
30
21
BDL
100
130
BDL
204
340
82
38
Range
1-2
4-9
5-8
26-38
16-29
48-155
50-195
47-350
104-600
25-160
14-85
12-24"
Ave.
2.8
BDL
BDL
9.5
25
4.9
75
300
BDL
116
155
BDL
106
194
51
24
Range
2-5
_
6-12
3-39
2-6
19-100
37-432
60-146
31-220
62-136
47-300
8-85
6-40
24-36"
Ave.
1.5
BDL
BDL
0.7
6.7
BDL
BDL
BDL
7.9
4.2
BDL
BDL
1.5
4.1
BDL
BDL
Range
< 1-2.6
< 0.2-2
1-14
< 0.1 -20
2-9
<0.1-3
0.2-10
36-54" Detection
Ave.
2.0
BDL
BDL
BDL
1.4
BDL
BDL
4.0
BDL
0.9
BDL
BDL
BDL
0.8
BDL
BDL
Range Limit +
1.9-2.1 1.0
_ 2.0
_ 1.0
_ 0.2
<0.1-3 0.1
_ 0.1
_ 0.2
<0.1-7 0.1
_ 0.1
<0.1-2 0.1
_ 0.2
_ 0.1
_ 0.1
< 0.2-2 0.2
_ 0.2
0.1
* mg/kg dry weight of soil; average of three samples
BDL below detection limits
"" samples from the 6" to 12" depth were not analyzed
* detection limit of the analytical procedures used
Table 3. Average Metal Concentrations * in the TCLP Extracts from the Conoco, 10% Plot Site - Non-
Weathered Samples
Depth Cadmium Chromium Copper Lead Nickel Zinc
0-6" <0.
6-12" <0.
12-24" <0.
24-36" <0
36-54" <0
54-72" <0.
1 0-2 0.1 <03 .1 <0.1
U <0.7
mg/L in extract; detection limit was 0.1 mg/L
the ZOI soils with additional nitrogen and
phosphorus. The nutrients were added to
determine whether the addition of
nutrients to HWLT soils would increase
the loss of organics in these soils.
The results of these degradation
studies indicated that there was no
statistically significant degradation of
PAH and freon extractables in the ZOI
soils from the Texaco site over an eight-
month period. It was in these soils that
the residues from the applied wastes
accumulated. The data suggest that there
will be very slow degradation of the
accumulated organics at closed HWLT
sites.
Predictive Models for Closure
This modeling effort was conducted
simultaneously with the sample
characterization, spatial variability,
weathering and degradation studies that
were part of the project. Ideally, the
evaluation and use of the predictive
models should have occurred after data
were available from the various laboratory
studies. Such data could have been used
with the models for a more focused
evaluation of the models and more direct
comparison of site data to model results.
This could not be done in this project
because: (a) the respective models had
to be evaluated and modified for use
under closure and post-closure
conditions, since the models originall
had not been developed for that purposi
(b) the modified models had to b
checked to assure that results reasonab!
for closure conditions were bein
obtained, and (c) some of the laboratot
results, particularly from the degradatic
studies, were not available until very lal
in the project.
Thus, the input parameters to th
models used in this evaluation were m
those determined in the laborator
portion of this project. Rather, the inpi
parameters and site-specific scenario
used were those that were reasonable f<
petroleum refining and wood preservin
wastes and for the land treatment of sue
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wastes. The values for such parameters
were obtained from peer reviewed
literature and from studies in which land
treatment had been used for similar
wastes.
The Regulatory Investigative Treatment
Zone (RITZ) model was used to evaluate
the persistence and mobility of specific
organic constituents. The MINTEQ model
was used to evaluate the persistence and
mobility of metals. The initial version of
RITZ was obtained from the Robert S.
Kerr Environmental Research Laboratory
(RSKERL), U.S. EPA, Ada, Oklahoma
74820, and the initial version of MINTEQ
was obtained from the Center for Water
Quality Modeling, Environmental
Research Laboratory, U.S. EPA, Athens,
Georgia 30613.
The RITZ model was modified to: (a)
function with no waste input, (b) consider
variations in degradation rate as a
function of time, soil depth and aerobic
and anaerobic conditions, (c) include the
existence of a separate oil phase and the
separate degradation of the oil phase,
and (d) utilize different chemical partition
coefficients in the ZOI and LTZ. The
modified model was then used to
evaluate its use under conditions likely to
occur at HWLT and contaminated soil
sites. The sensitivity of MINTEQ was
examined for the three most important
parameters that are influenced by the
closure option, pH, the partial pressure of
carbon dioxide gas, and the redox state.
The modified versions of RITZ and
MINTEQ were used to evaluate HWLT
closure options. The modified models
were applied to conditions at the Texaco,
Anacortes refinery waste land treatment
site. Considerable data for this site were
available to understand and evaluate the
applicability of the models and to model
potential migration of constituents of the
accumulated residues. In addition,
conditions typical of other regions of the
country also were investigated.
When used with worst-case Texaco
Anacortes HWLT site data at three
different hypothetical locations, the
modified RITZ indicated major
differences between the capped and
uncapped scenarios. The closure options
in which the sites were uncapped allowed
for aerobic conditions, but the movement
of the constituents into the LTZ was
greater. For the clay or synthetic cap
option, reduced conditions should occur
and the movement into the LTZ was
greatly diminished, due to the lack of
infiltration created by the cap.
At the uncapped site, the persistence,
'.e., potential residence times, of organics
was estimated to be approximately 20
years for benzo(a)anthracene, and 1100
days for chrysene and pyrene. For the
capped site, 8 of the 12 PAH compounds
examined remained in the site for 1100
days or more, and 6 of the 12 remained
in the site for 15 years or more. The
sensitivity of the modified RITZ model to
the differences between the various
uncapped closure options was minimal,
since the bulk of the degradation took
place in the ZOI, and the depth constant
did not alter these results. These
differences are portrayed in Table 4.
The results obtained on the mobility
and persistence of organics at a HWLT
site under closure scenarios indicated
that the modified RITZ can be a useful
tool for assessing the impact of different
closure options on the migration potential
and persistence of residual organics at
such sites.
MINTEQ is able to estimate aqueous
equilibrium solubility concentrations for
metals but is unable to estimate the
actual mobility of metals. Gaps in the
MINTEQ database do not allow it to
identify the relative solubility of many of
the metals of interest at HWLT sites. This
evaluation indicated that MINTEQ is
useful to demonstrate the potential
mobility of metals as indicated by the
relative solubility of metal species and to
determine those most likely to migrate.
The results obtained as part of the
project provided insight into the
environmental effect of various closure
options. The most appropriate option
appears to be one in which the site is left
open to the atmosphere. The option of
continued treatment is beneficial because
the degradation rate of the organics will
be most rapid, and because the
conditions used during the active site life
to prevent metal migration will be
continued.
This was illustrated when the Texaco
Anacortes site was modeled. For the
organics, no leaching was predicted for
the uncapped site, and for the metals,
there was no significant increase in metal
solubility under oxidizing conditions. The
results for the capped site indicated that
the residual organics persisted for a long
time.
Two important results were generated
from this evaluation. One is that the
potential persistence and mobility of the
accumulated residue constituents are
affected by the closure option chosen.
Another is that RITZ and MINTEQ, when
modified to represent closure conditions,
can estimate the potential mobility and
persistence of metals and organics for
different closure options. The actual
choice of a closure option will depend on
such estimates as well as on operational
factors and regulatory concerns.
Conclusions
The major conclusions from this project
were:
1. Polynuclear Aromatic Hydrocarbons
(PAH), freon extractables, and metals
were determined in the site soil
samples. Except for the coal tar
disposal site, these chemicals
accumulated in the surface soils.
The difference in the coal tar site
data is due to the fact that the
applied residues were placed in a
trench rather than being incorporated
in surface soils.
2. In the surface soils of the HWLT
sites, the concentration of the
organics and metals were greater
than in background soils. At depths
below 24-30" at the HWLT sites, the
concentrations of PAH compounds
were below detection limits and the
freon extractable concentrations were
at background soil concentrations or
below detection limits. At the sites
for which soil concentrations could
be compared to concentrations in
background soils, the concentrations
of chromium and nickel in site soils
at depths below 24" appeared
greater than background soil
concentrations, whereas the
concentrations of copper, lead and
zinc in site soils at such depths
appeared comparable to those in
background soils.
3. A statistical analysis of sample
variability was conducted using
surface soils collected at the two
land treatment sites. There were no
consistent differences in chemical
concentrations of the surface soils.
The analysis also indicated that the
residues that existed at the time of
sampling appeared to be uniformly
distributed in the surface soils of
each site.
4. Analyses for organics in TCLP
extracts of site soils indicated that no
PAH compounds were extracted by
this procedure from either weathered
or non-weathered soils.
5. There was no difference in the
concentration of metals in the TCLP
extract of the weathered and the non-
weathered soil samples.
6. Zinc was found above detection
limits in the TCLP extracts of the site
soils most frequently. In most of the
site soil samples analyzed, the
concentrations of other metals in the
TCLP extracts were close to or below
detection limits of 0.1 mg/L.
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Table 4. Estimated Persistence and Mobility of Organics Present at the Texaco, Anacortes Site as
Influenced by the Closure Option
^ Leave-Alone Clay/Synthetic Cap
\JiQoiiiC ~ ~ '
Constituent
benzene
ethylbenzene
toluene
o-xylene
m, p-xylene
anthracene
benzo(a)anthracene
chrysene
1 -methylnaphthalene
naphthalene
phenanthrene
pyrene
% Leach
from ZOI
3.7
1.1
3.2
6.6
0.7
0.3
1.4
0.6
0.0
5.4
1.1
10
Time in
ZOI (days)
32
71
55
746
610
720
> 20 years
1100
240
450
720
1100
% Leach
from ZOI
01
0.0
0.0
7.2
0.0
0.0
0 1
0.0
0.0
0.1
01
0.1
Time in
ZOI (days)
100
200
200
> 15 years
720
15 years
> 30 years
30 years
1100
1100
20 years
20 years
7. The results suggest that the type of
weathering used in this study
(freeze/thaw and wet/dry) is not
expected to result in an increase in
organic or metal mobility in soils at
HWLT sites.
8. The PAH and metal concentrations
measured in the TCLP extracts from
the site soils provided no reason to
conclude that these soils and
accumulated residues would fail to
pass a toxicity characteristic
determination using the TCLP test.
9. The aerobic and anaerobic
microcosm studies demonstrated
that there was no statistically
significant degradation of the PAH
and freon extractables in the ZOI
samples over an eight-month period.
The data suggest, therefore, that
there will be slow degradation of the
accumulated organics at closed
HWLT sites.
10. The RITZ model, as modified for
HWLT site closure conditions,
indicated major differences in
mobility and persistence of PAH
compounds between capped and
uncapped closure scenarios. The
closure options in which the sites
were uncapped allowed for more
rapid degradation, but movement of
the constituents below the ZOI was
greater. For the clay or synthetic
cap option, the degradation of the
organic constituents was much
slower, but the movement below the
ZOI diminished.
11. The sensitivity of MINTEQ was
examined for parameters that are
influenced by the closure option:
pH, the partial pressure of carbon
dioxide and the redox state. It was
difficult to draw general conclusions
about the effects of these changes,
since different metals beha\
differently in solution. In gener;
most of the metals present
solution as cations became le;
soluble as the pH increased, and ;
the partial pressure of carbon dioxk
increased. No general statemen
could be made about rede
conditions, as the most soluble red<
state of a given metal varies fro
metal to metal.
12. Based on the low migration potent!
of PAH compounds, free
extractables and metals in the soi
at HWLT sites determined fro
laboratory and model simulatic
studies, it does not appear necessa
to cap such sites at closure. Both tt
leave-alone option, or the option
continue active site managemer
appear to be protective of hum;
health and the environment.
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R. C. Loehr, D. C. Erickson, L. A. Rogers, and D. M. Kelmar are with the
Environmental and Water Resources Engineering Program, The University of
Texas , Austin, TX 78712-1076.
Scott G. Huling is the EPA Project Officer (see below).
The complete report, entitled "Mobility and Degradation of Residues at
Hazardous Waste Land Treatment Sites at Closure," (Order No. PB 90-
212-564AS; Cost: $23.00, 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:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P. O. Box 1198
Ada, OK 74820
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
ICIAL MAIL"
U.S.POSTAGE
SO 35
EPA/600/S2-90/018
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