United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA/600/S2-89/039 Aug. 1989
&EPA Project Summary
Sensitive Parameter
Evaluation for a Vadose Zone
Fate and Transport Model
David K. Stevens, William J. Grenney, Zhao Van, and Ronald C. Sims
The full report presents information
pertaining to quantitative evaluation
of the potential impact of selected
parameters on output of vadose zone
transport and fate models used to
describe the behavior of hazardous
chemicals in soil. The Vadose Zone
Interactive Processes (VIP) model
was selected as the test model for
this study.
Laboratory and field experiments
were conducted to evaluate the effect
of sensitive soil and model param-
eters on the degradation and soil
partitioning of hazardous chemicals.
Laboratory experiments were con-
ducted to determine the effect of
temperature, soil moisture and soil
type on the degradation rate. Field-
scale experiments were conducted to
evaluate oxygen dynamics, through
depth and time, for petroleum waste
applied to soil.
Results of laboratory experiments
demonstrated that the sensitivity of
the degradation rate to changes in
temperature and soil moisture was
generally greater for low molecular
weight compounds and less for high
molecular weight compounds. For the
two soil types evaluated, soil type
was more significant with regard to
immobilization. Soil type was not
found to have an effect on degrada-
tion kinetics for the majority of chem-
icals evaluated.
The effect of oxygen concentration
on chemical degradation as pre-
dicted by the test model was found to
depend upon the magnitude of the
oxygen half-saturation constant.
Oxygen-limited degradation would be
anticipated to occur shortly after the
addition of chemicals to soil and
during active microbial metabolism of
chemicals.
Model output results for temper-
ature dependent reactions indicated
that depth-concentration profiles
would be sensitive to, and directly
related to the temperature correction
coefficient (0) for each chemical.
Model outputs would be very sensi-
tive to soil temperature when values
for 8 were 1.04 or greater.
Results from laboratory and short-
term field studies indicated that
sensitive model parameters-of a site-
specific nature need to be addressed
in modeling the fate and behavior of
hazardous chemicals in the unsatu-
rated zone of a soil system.
This Project Summary was devel-
oped by EPA's Robert S. Kerr Environ-
mental Research Laboratory, Ada, OK,
to announce key findings of the re-
search project that is fully docu-
mented in a separate report of the
same title (see Project Report order-
ing information at back).
Introduction
A mathematical description of the
soil/waste system establishes a unifying
framework for evaluation of laboratory
screening and field data that is useful for
determination of treatment potential for a
waste in soil. Mathematical models pro-
vide an approach for integration of the
simultaneous processes of degradation
and partitioning in soil systems so that an
assessment can be made of the pres-
ence of hazardous substances in leach-
-------
ate, soil and air. Models provide an
estimate of the potential for groundwater
and air contamination through a deter-
mination of the rate and extent of
contaminant transport and degradation in
soil as related to specific soil and
compound characteristics for a particular
site. Description of quantitative fate and
transport of chemicals in soil systems
also allows for identification of those
chemicals that require management
through control of mass transport and/or
treatment to reduce or eliminate their
hazardous potential. Thus, mathematical
models represent powerful tools for rank-
ing design, operation, and management
alternatives, as well as for the design of
monitoring programs for soil treatment
systems.
The Regulatory and Investigative Treat-
ment Zone (RITZ) model, was developed
at the Robert S. Kerr Environmental
Research Laboratory (RSKERL), Ada,
Oklahoma, for use in evaluating volatil-
ization-corrected degradation and parti-
tioning of organic constituents in land
treatment systems (USEPA, 1988). The
RITZ model incorporates factors involved
in soil treatment at a land treatment
facility, including site, soil, and waste
characteristics. The Vadose Zone Inter-
active £rocesses (VIP) model was
developed as an enhancement of the
RITZ model to allow for prediction of the
dynamic behavior of hazardous sub-
stances in unsaturated soil systems
under conditions of variable precipitation,
temperature, and waste application
(Grenney et a). 1987; Van 1988). These
models simulate vadose zone processes
including volatilization, degradation,
sorption/desorption.advection, and dis-
persion. The VIP model, Version 3.0
(Stevens et al., 1988) was used as the
test model in this study.
Rational mathematical models of soil
treatment are based upon conceptual
models of soil treatment processes. The
degradation process represents an
important destructive mechanism for
organic substances in soil systems.
Important variables that may affect the
degradation of organic chemicals in soil
include temperature, oxygen concentra-
tion, moisture, and soil type. Therefore,
these variables are anticipated to
influence the degradation rate of a
hazardous substance. Quantitative rela-
tionships for temperature and oxygen
concentration were incorporated into the
current version of the test model to allow
for determination of the effects of
sensitive parameters on model predic-
tions of chemical fate and transport.
The overall objective of this research
project was to determine the effect oi
sensitive model and soil parameters oh
soil treatment and on model outputs.
Specific objectives of this research
project were fo:
1. Select and modify a vadose zone
transport!and.fate model to simulate
the oxygen transport mechanism in
the unsaturated zone, including trans-
port in air, water, and free hydro-
carbon phases with exchange
between each phase and losses due
to degradation,
2. Evaluate j model output as a function
of soil oxygen tension,
3. Evaluate [ model output as a function
of soil temperature.
Evaluate the effect of soil moisture
and type on degradation rates of
organic substances, and
Compare model simulations with field
4.
5.
subsurface oxygen measurements.
Research Approach
Model modification — The selected
test model was modified and evaluated
with respect, to incorporation of oxygen
transport and oxygen-limited biodegra-
dation, and with respect to the effect of
temperature! on degradation rate. The
model describes a soil column 1.0 meter
square with pepth specified by the user.
The column( consists of a plow zone
(Zone of Incorporation, ZOI) and a lower
treatment zone (LTZ). The plow zone is
typically defined as the top 15 cm of soil
into which the substance is mixed during
application. The LTZ extends below the
ZOI to the bottom of the soil column and
may contain [substances which have been
mobilized and transported downward
from the ZOi.
The soil environment within the column
is made up, of four phases: soil grains;
pore water^ pore air, and pore oil.
Characteristics of the soil environment
may change with depth and/or time. An
organic contaminant being tracked by the
model mayi be a pure compound or a
mixture of several compounds as long as
the behavior of the mixture can be
adequately described by composite
constituent parameters. A waste can be
applied and incorporated into the plow
zone at loading rates and frequencies
specified by! the user.
These types of models simulate the
fate of hazardous organic substances in
unsaturated j soil systems. The fate of a
constituent in the soil is influenced by
mobilization' volatilization, and decompo-
sition processes. The test model also
simulates oxygen transport in the vadose
zone by air, water, and free hydrocarbon
phases with exchange between each
phase and losses due to degradation of
the hazardous waste constituents within
the soil column.
Once applied to the land and mixed
into the soil, the constituent and oxygen
may be mobilized by three mechanisms:
advection, dispersion, and migration
between phases.
Dispersion — Mobilization of the con-
stituent and oxygen by dispersion of the
phase within the soil column is only
included in the vapor phase.
Advection — The advection mecha-
nism for the constituent and oxygen is
used for the water and vapor phases
only. This version of the test model con-
strains the oil to the zone of application
and mixing.
Sorption/desorption — This term
represents migration of the constituent or
oxygen between phases. This mass flux
of the constituents or oxygen among
phases is modeled as a linear sorption
mechanism. This term is applied between
the water phase and each of the other
phases for the constituent, and between
the air phase and water or oil phases for
oxygen.
Volatilization is represented in the
model by two processes: mass flux into
the air phase and advection/dispersion.
The constituent is transported with the air
phase by advection and/or dispersion,
and may leave the system through the
top or bottom boundaries of the control
volume.
Degradation is represented by bio-
chemical, photochemical or hydrolytic
processes. Field and laboratory studies
have indicated that the use of first order
kinetics provides a reasonable approxi-
mation for the degradation of many
hazardous substances in soil systems.
Others have found that the microbial
metabolism can be limited by a lack of
either substrate (carbon and energy
source), oxygen (electron acceptor) or
both simultaneously. The degradation
expression in version 3.0 of the VIP
model combines the first order kinetics of
the previous version with a modified
Monod function. Because the constituent
may degrade at different rates in different
phases, separate rate and half-saturation
coefficients are provided for each phase
in the model. The apparent degradation
rate coefficients also are permitted to
vary with depth.
Effect of soil oxygen tension — The
effect of oxygen tension on constituent
-------
degradation was evaluated by conducting
a series of model simulations using
different values of the oxygen half-
saturation coefficient, Kq.
Effect of soil temperature -r Tempera-
ture is an important climatic factor
influencing rates of decomposition in
soils. Laboratory scale experiments using
glass beakers were conducted for 16
PAH compounds representative of
hazardous chemicals of concern to the
U.S. Environmental Protection Agency.
Experiments were conducted at three
temperatures (10°C, 20°C, and 30°C)
using a Kidman sandy loam soil. Details
of these experiments have been reported
by Coover. 1987.
A form of the Arrhenius expression, V.T
= IIT e(T~T°>, was used in the test model
to evaluate the effect of temperature on
the rate of degradation of several
hazardous constituents in the soil. Here
HT and HT are the first order rate .
constants at temperatures T and T0,
respectively, and 9 is the temperature
correction factor. The method of non-
linear least squares was used to establish
the degradation rate at 20 °C and the
temperature correction coefficient values
(9) for a subset of the hazardous sub-
stances given in Table 1, fluorene,
benzo[b]fluoranthene, and chrysene. The
parameter estimates were then used in
the VIP model to predict the degradation
of fluorene, benzo[b]fluoranthene, and
chrysene in a soil system at 10°, 20°,
and 30°C. The sensitivity of the output of
the model was evaluated with respect to
the effect of temperature on degradation
rate for these three PAH compounds.
Effect of soil moisture — Soil water
serves an important function as a trans-
port medium through which nutrients are
transported and through which waste
products are removed from the microbial
cell surface. Under saturation or near-
saturation conditions the diffusion of
gases through the soil is severely
restricted, oxygen is consumed and the
soil becomes-anaerobic, and major shifts
in microbial metabolic activity occur.
Experiments, were conducted to deter-
mine the effect of soil moisture on the
rate of apparent degradation of a subset
of hazardous substances. Soil moisture
levels of -0.33, -1.0, and -5.0 bars matric
potential were used. Temperature was
maintained at 20°C, and glass beaker
reactors containing 200 g sandy loam soil
were incubated in the dark to prevent
photodegradation. Periodically through
time triplicate sets of reactors containing
each soil type were- removed • .from
incubation, solvent extracted with dichlo-
romethane, and analyzed by HPLC
analysis of the soil extracts.
Effect of soil type — Soil texture and
clay mineralogy are also important
factors affecting soil microbial processes,
controlling factors such as swelling,
cation exchange capacity, buffer capac-
ity, and sorption of organic compounds
and inorganic ions. Soil organic matter
content plays an important role in
sorption as well as degradation, con-
trolling availability for microbial metabo-
lism and transformation. Soil pH is
important for controlling competition
between fungi, that are effective at pH <
5, and other microorganisms whose opti-
mum pH is between 6.5 and 8.5. The
effect of pH in soils is less clear than in
aqueous systems, however, because the
buffer capacity of clay and humic mate-
rials affects the concentration of protons
at the microsite scale.
Two soil types, a McLaurin sandy loam
and a Kidman sandy loam, were evalu-
ated with regard to degradation and
immobilization, or partitioning, of a subset
of hazardous substances. For biodegra-
dation rate determination, selected sub-
stances were mixed with the two soils
and incubated in glass beaker reactors at
20°C and constant -0.33 bar matric
potential in the dark. Periodically through
time triplicate sets of reactors containing
each soil type were removed from incu-
bation, solvent extracted with dichloro-
methane, and analyzed by HPLC analysis
of the .soil extracts.. Details of these
experiments have been reported by
Coover (1987) and Park (1987).
- Field verification of oxygen dynamics
— A field-scale experiment was -con-
ducted to evaluate the spatial and
temporal variability of oxygen in soil after
a petroleum waste was applied to the top
six inches of soil. Air phase oxygen
sensors were installed in the soil at 6
inches, 12 inches, and 24 inches below
the site, and a.continuous record of air
phase oxygen content was kept before,
during, and after waste application.
Measurements from the test plots were
compared with VIP model predictions.
Results and Discussion
Tesf model — the modular structure of
the VIP model, programmed in
FORTRAN and solved numerically, also
provides a convenient means for evalu-
ating the behavior of various processes
by isolating the modules for independent
analysis. The main solution algorithm is
divided into functional modules: loading
rates, degradation, oil decay, and phase
transport and sorption.
Effect of soil oxygen tension — Com-
parison of the test model results with and
without oxygen limits (Figure 1a) show no
discernible difference between the con-
stituent concentration profiles for the two
cases. Both constituent and oxygen
depth profiles are shown in Figure 1b.
The oxygen concentration decreases
over these depths due to the oxygen
demand imposed by microbial degra-
dation of the constituent. No microbial
activity has occurred below the constit-
uent wave front, therefore the oxygen
concentration is maintained at the satu-
ration concentration.
Breakthrough curves of the constituent
and oxygen concentration in the water
phase at a depth of 1.0 meter are shown
in Figure 1c. The oxygen concentration
decreases when the constituent passes
this depth due to microbial degradation of
the constituent. After the constituent slug
passes a particular depth, the oxygen
concentration is replenished due to the
advective transport mechanism in the air
and water phases. The effect of the half-
saturation constant for the same input
data set are shown in Figure 1d for a
range of KQ from 0.01 to 10 g/m3 in the
air, oil, and water phases. These simu-
lations demonstrate that, as the value of
this constant increases, the oxygen-
limitation of degradation increases, as
would be expected.
It is recognized that, under field condi-
tions, where 02 is replenished by dis-
persion/diffusion from the atmosphere,
this rate limitation will be less severe over
the long term, for slowly degradable sub-
strates. However, for short term dynam-
ics, such as immediately after a waste
application in land treatment of petroleum
sludges, 02 limits may be very important
and warrant inclusion in the model.
Effect of soil temperature — The per-
centages of each "compound remaining in
the soil at the end of the 240-day
incubation period are presented in Table
1. Also presented are the estimated half-
lives based on a first-order kinetic model
for degradation and representative half-
life values obtained from the literature.
The extent and rate of apparent loss
was much greater for PAHs of low
molecular weight and high aqueous
solubility. Substantial loss of three-ring
compounds acenapthene, fluorene, and
phenanthrene was observed at all tem-
peratures during the course of the study.
Four-ring compounds, including fluoran-
thene, pyrene, and benz[a]anthracene
demonstrated greatly reduced rates of
degradation. Loss of chrysene, a four-ring
compound, and the remaining five- and
-------
Table 1. Percentages
Compound
Acenapthene
Fluorone
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Bonzfajanthracent
Chrysene
Benzo[b]ftuoranthene
Benzo[k]fluoranthene
Benzofajpyrene
Dlberafahjanthracene
Benzo[g,h,i]perylene
lndeno[l,2,3-c,d]pyrene
of PAH Remaining at the End of the 240-Day Study Period and Estimatec
Percent of PAH Remaining , Estimated Half-Life (day)*
10°C 20°C 30°C 10°C
500, ,39l>,2-39°
69b,23l>,26°,9.7<',14<>
28b,17>>,108-175°,17,29>>,44-1S2<:,39d,34.27b,3-35°,58<',48<'
52>>,123b, 102-252°, 240*. 130*
7O»,42t>,5.5-10.5°,328,74t>
91",69l>,30-420,42t>, 100-1 90*
179b,70b
S7>>,42*>,200-600*
>>Sims [1986], r=20°C
cSims and Overcash [1983], T=15-25°C
"PACE [1985], T=20"C
'Sims [1982], r-20"C J
'Least squares slope (for calculation of t1tz) = zero with 95% \confidence
six-ring compounds was minimal at all
three temperatures.
A series of simulations using fluorene,
benzo[b]fluoranthene, and chrysene was
run to evaluate the effects of soil
temperature on the model prediction. The
0 values (± 95% confidence intervals)
were 1.04 ± 0.0075, 1.024 ± 0.012, and
1.003 t 0.016, for these compounds,
respectively. For this series of runs, a
high recharge rate 3.95 (cm3/day/cm3)
was used, the mass transfer rate
coefficients for the constituents and
oxygen were 1000 day1, assuming the
constituents and oxygen reached equi-
librium very rapidly.
A summary of degradation data of the
three compounds after a one year
simulation in the Kidman sandy loam is
presented in Table 2. The extent and rate
of apparent loss due to the biochemical
degradation for, the higher temperature
are greater than those for the lower
temperature for each of the three
compounds studied. However, the effect
of temperature on the apparent toss from
decay are quite different for each com-
pound. At 30°C'the apparent degradation
loss ranged from 20 percent for chrysene
to 100 percent for fluorene. Figure 2
demonstrates the depth profiles of chry-
sene, benzo[b]fluoranthene, and fluorene
in the water phase after one year in the
Kidman sandy loam. Compared to the
profiles for benzo[b]fluoranthene (Figure
2b) and fluorene (Figure 2c), the profile
for chrysene shows little apparent effect
of temperature. The plot for fluorene
(Figure 2c) shows the largest apparent
effect of temperature on the model output
profiles. The effect of temperature on the
degradation rate depends on the value of
9. Higher values of e (1.040 for fluorene),
show more sensitivity to temperature in
the model prediction than that for 9
values close to 1.0 (1.003 for chrysene).
Effect of soil moisture — Results for
the effects of soil moisture at 20°C on
-------
la
Ib
540
^ «0f A—,
360-
o
5 270-
180-
8 904
WITHOUT O-UM1TS
•—•
WITH 02-LIMITS
500
400 ••
300
§ 200
o
? 100-•
o.a
0.5 1.0
DEPTH (m)
t.5
0.0
E
10 ,2
0.5
1.0
1.5
DEPTH (m)
1C
Id
uw
"E
x.
«s
•i 400
w
§
8 200
t
\
0<
S \
* \
1
|
I
•u •
. . . A._. ..
0 30 60
l-rt..^^ m t
1 O
to~*
12 ^
a^
z
UJ
8 ^
X
o
•4
4 i
1
•4
n
9O 120
o
I
800
600
400
200
0
0
• — • Ko
»— *— » A . ..,
A A Ko
'-T-T
f'*3&-i
1
a — a KO
V T Ko
« * Ko
i • - ^ « a__j™_
0 0.4 0.8
= 0.0
= 0.01
= 0.1
= 1
= 10
Apt •• A
CJ ~ *
1.
TIME (DAYS)
DEPTH (m)
Figure 1. Effect of oxygen tension on VIP model simulation.
rat>/e 2. Degradation Summary from
Oufpuf R/es
Temp. %
Compound °C Decayed
Chrysene
Benzo[b]fluoranthene
Fluorene
10
20
30
10
20
30
10
20
30
18.6
19.2
19.7
37.9
45.5
53.4
98.3
99.8
100.0
the rate of degradation of a subset of
PAH compounds, expressed in terms of
the half-life values and their 95%
confidence intervals (Cl), are presented in
Table 3. Half-life values were calculated
based on a first-order model for PAH
disappearance.
Degradation rates were significantly
different at different soil moisture levels
for the three-ring anthracene and the
four-ring fluoranthene. No significant
effect of soil moisture was evident for the
naphthalene (two-ring), phenanthrene
(three-ring), and pyrene (four-ring).
Because of the lack of a rational
quantitative relationship between soil
moisture content and rate of degradation,
it was not possible to evaluate the mathe-
matical model VIP with regard to model
output as a function of soil moisture.
Effect of. soil type — Results for volatil-
ization-corrected degradation rates as a
function of soil type are presented in
Table 4 for a subset of PAH compounds
and pesticides incubated individually at
-0.33 bar soil moisture and 20°C. Half-life
values were calculated based on a first-
order kinetic model for degradation; 95%
confidence intervals (Cl) are also given.
There was no statistically significant
difference in degradation rate as a
function of soil type for the majority of
PAH compounds investigated. A statis-
tically significant difference was observed
for anthracene and phenanthrene; how-
ever, the difference was not consistent for
one soil type.
Eight pesticides were also evaluated
(Table 4). There were'statistically signif-
icant differences for degradation rates as
a function of soil type for only two,
aldicarb and pentachloronitrobenzene;
however the differences were not
consistent across the two soil types
investigated. Because of the lack of a
rational quantitative relationship between
soil type and rate of degradation, it Was
not possible to evaluate the VIP model
with regard to model output as a function
of soil type.
Field verification of oxygen dynamics
— The test model was run for the 5-day
period of the data record. Air phase 02
concentrations predicted by the model at
the 6-inch, 12-inch, and 24-inch depths
-------
2a
2b
0.600
o.4oo
0,200
0.000
Chrysene
10°C
20°C
30°C
0.0
0.5 1.0
DEPTH (m)
1.5
I
K)
o
0.600
0.400-
0.200--
0.000-1
O.O
Benzo[b]fluoranthene
— 10°C
20°C
30°C
0.5 1.0
DEPTH (m)
-1.5
2c
0.030
£ 0.020
1
UJ
o
0.010-
0.000-I
0.0
fluorene
10°C
20°C
30°C
^L
0.5 1.0
DEPTH (m)
1.5
figure 2. Simulated concentration profiles for chrysene, benzofblfluoranthene, and tiuorene, at W, 29", and 30°C.
were plotted alongside the field data.
Results are given in Figure 3 for 6-inch,
12-inch, and 24-inch depths. The solid
lines on the plots represent the model
simulation and the dashed lines represent
the field data.
The results for the 6-inch depth (Rgure
3a) showed quite good agreement be-
tween the model prediction and the field
data during the first 80 hours of the
simulation. The model was able to track
the descending leg of the data record but
was unable to simulate the recovery of
the O2 content at this level after 80 hours.
For the 12-inch depth (Figure 3b), the
model was able to predict the general
behavior of the data for 60 hours but was
unable to predict the recovery after this
time. At a depth of 24 inches (Figure 3c),
the model was able to predict the initial
drop in the 02 level, but continued to
descend while the field data leveled off.
However, at 60 hours, when the O2 had
decreased to about 25 g/m3, the model
and data agreed. The model failed to
predict the recovery after about 80 hours.
The inability of the test model to
predict the recovery of the O2 levels after
about 80 houh may be related to the
boundary conditions at the bottom of the
treatment zon6. For the simulations pre-
sented, the treatment zone was assumed
to extend to the 24-inch level. Below that
level, the soil'was assumed to be satu-
rated with water, and therefore no oxygen
could be transported from below. A more
realistic condition for this physical sys-
tem, in which: the groundwater was well
below the 24-inch level, is a boundary
that permits free transport of vapor. This
would provide an oxygen source from
below and would make the 02 drop more
slowly at this [level, and therefore would
provide an oxygen source for recovery.
Summary and Conclusions
The VIP model for simulating the fate
and transport |of organic contaminants in
the vadose Izone was enhanced to
include dynamics of oxygen transport
and oxygen-limited degradation. The
model was verified against an analytical
solution for a linear, two-phase case, and
used to evaluate the sensitivity of vadose
zone processes to temperature, subsur-
face oxygen tension, soil type and
moisture content. Specific conclusions
based on the objectives of this research
are:
1. Under field conditions with petroleum
waste addition, the model success-
fully predicted the depth location of
the decrease in the oxygen con-
centration in the air phase, and semi-
quantitatively predicted the oxygen
concentration. The model did not
predict the recovery of oxygen with
depth.
2. The effect of oxygen concentration
on chemical degradation predicted by
the test model was found to depend
upon the magnitude of the oxygen
half-saturation constant and the soil
oxygen concentrations. Low oxygen
concentrations in the soil would be
expected to occur shortly after waste
addition to soil and during active
microbial metabolism of waste.
-------
Table 3. The Effect of Soil Moisture on Degradation Rate of PAH Compounds in Sandy Loam
20-40% F.C.' 40-60% F.C. 60-80% F.C.
Compound
Naphthalene
Anthracene
Phenanthrene
Fluoranthene
Pyrene
tl/2
(days)
30
72
79
530
-
95% Cl
15-93 a +
50-128 a
53-154 a
462-578 a
-
(days)
28
46
-
200
7500
95% Cl
14-93 3
27-173 a
•
765-267 b*
877- oo a
fr/2
(days)
33
18
58
230
5300
95% Cl
18-23 a
7-46 b
72-147 a
193-289 b
2500- °o a
"F.C. = field capacity of the soil. , ,
* The same letter (a or b) for a compound at two moisture contents indicates no statistical
difference at the 95% level based on the t-test.
Table 4.
Degradation Rates Corrected for Volatilization for PAH Compounds and
Pesticides Applied to Two Soils
Kidman Sandy Loam
McLaurin Sandy Loam
Compound
PAHs:
Naphthalene
1 -Methyl-naphthalene
Anthracene
Phenanthrene
Fluoranthene
Pyrene
Chrysene
Benzfajanthracene
7, 12-Dimethyl-
benz[a]anthracene
Benzo[b]fluoranthene
Benzo[a]pyrene
Dibenz[a,h]anthracene
Dibenzo[a,i]pyrene
Pesticides:
Phorate
Aldicarb
Pentachloronitrobenzene
LJndane
Heptachlor
Famphur
Dinoseb
Pronamide
?1/2
(days)
2.1
1.7
134
16
377
260
371
261
20
294
309
361
371
32
385
17
: 61
58
53
103
96
95% Cl
1.7-2.7 a +
1.4-2.1 a
106-182 a
13-18 a
277-587 a
193-408 a
289-533 a
210-347 a
18-24 a
231-385 a
239-462 a
267-533 a
277-533 a
29-85 a
257-845 a
15-21 a
35-257 a
50-70 a
46-69 a
37-128 a
81-122 a
tin
(days)
2.2
2.2
50
35
268
199
387
162
28
211
229
420
232
24
30
51
65
63
69
92
94
95% Cl
1.7-3.4 a
1.6-3.2 a
42-61 b*
27-53 b
173-6303
131-4083
•257-866 a
131-217a
21-41 a
169-2773
178-31 5 a
267-990 a
178-330 a
19-35 a
27-35 b
38-74 b
39-204 a
58-76 a
58-98 a.
74-124 a
69-151 a
+ The same letter (a or b) for a compound at two soil types indicates no statistical
difference at the 95% level based on a t-test
-------
3a
ftf Phase O2 Simulalion — Depth - 6"
Air Phase Oj Simulation, Depth - 12"
40 50 M 70 H to 100 110 130 130
Time (hours)
VIP Simulation
Fi«ld Dolo
0 1O20304090M70AOMIOO 110 ISO 130
Time (hours)
3c
Air PHose <>2 Simulation Depth — 24"
I
u
ff
10 » » to 50 <0 70 M M 100 110 1» 130
Time (hours)
Figure 3. Field oxygen data from Nanticoke Refinery high load plot and VIP model predictions.
3. Model output results for temperature
dependent reactions indicated that
depth-concentration profiles were
sensitive to and were directly related
to the temperature correction coef-
ficient (0) for each chemical used in
the model. Model outputs were very
sensitive to soil temperature when
values for 0 were 1.04 or greater;
however, for chemicals with values
for 0»1.02 or less, there was little
sensitivity in the model output with
respect to temperature.
4. Results of laboratory experiments
demonstrated that the sensitivity of
degradation rate to changes in
temperature, soil moisture, and soil
type was generally greater for low
molecular weight compounds and
less for high molecular weight com-
pounds.
References
Copver, M. P. 1987.Studies of the per-
sistence of polycyclic aromatic hydro-
carbons in two acclimated agricultural
soils. Thesis, j Utah State University,
Logan, UT.
Grenney. W. J., [c. L. Caupp, R. C. Sims
and T. E. Short. 1987. A mathematical
model for the,fate of hazardous sub-
stances in soil: Model description and
experimental; results. Hazardous
Wastes and iHazardous Materials.
4(3):223-239. I
PACE (Petroleum Association for Con-
servation of the Canadian Environment).
1985. "The persistence of polynuclear
aromatic hydrocarbons in soil." Ottawa,
Ontario. Report No. 85-2,1985.1.
Park, K. S. 1987j Degradation and trans-
formation of polycyclic aromatic hydro-
carbons in soil;systems. PhD Disserta-
tion. Department of Civil and Environ-
mental Engineering, Utah State Univer-
sity, Logan, UT:
Sims, R. C. andlM. R. Overcash. 1983.
Fate of Polynuclear Aromatic Com-
pounds (PNAs) in Soil-Plant Systems.
Residue Reviews. 88:1 -68.
Sims, R. C. 1982. Land treatment of poly-
nuclear aromatic compounds. PhD dis-
sertation. North; Carolina State Univer-
sity, Raleigh, NC.
Sims, R. C., Loading rates and frequen-
cies for land treatment systems. 1986.
In: R.C. Loehr and J.F. Malina (Eds.).
Land treatment: A waste management
alternative. Water Resources Sympo-
sium No. 13. Center for Research in
Water Resources. University of Texas
at Austin, Austin, TX. pp. 151-170.
Stevens, D. K., W. J. Grenney and Z.
Van. 1988. User's Manual: Vadose zone
interactive processes model. Depart-
ment of Civil and Environmental Engi-
neering. Utah State University, Logan
UT 84322-4110.
USEPA. 1988. Interactive simulation of
the fate of hazardous chemicals during
land treatment of oily wastes: RITZ
user's guide. EPA/600/8-89-001. Robert
S. Kerr Environmental Research Labo-
ratory, Ada, OK.
Van, Z. 1988. Evaluation of the vadose
zone interactive processes (VIP) model
using nonequilibrium adsorption kinetics
and modification of VIP model. Thesis.
Department of Civil and Environmental
Engineering. Utah State University,
Logan, UT.
-------
David K. Stevens, William J. Grenney, Zhao Van, and Ronald C. Sims are with Utah
State University, Logan, Utah 84322-4110.
John E. Matthews is the EPA Project Officer (see below).
The complete report, entitled "Sensitive Parameter Evaluation for a Vadose Zone
Fate and Transport Model," (Order No. PB 89-213 987/AS; Cost: $15.95, 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
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada. OK 74820
-------
-------
-------
m
TO
I
o
o
3 3
Q) O
~* (O
'
•
CD
(A
£S-= ffg-2
^* iH rt
ar o
O —" r+
•** w o
Mi
-
_ o
= i5
SS
3.33
» 3
S-8
S5-
** 0}
0. O
S =
s i
3 01
3-g-
li
3 $5
(D 0)
T3
1
§
o
T' 3 (D
1.1 ill
oo
1
3
Tl
O
-n O)
™ ^
33 > CB
S1 O C
^~ rnr-
8 a'
CJ1 ^
D
------- |