United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S9-84-018 Sept. 1984
&ERA Project Summary
Conceptual Development of a
Toxic Screening Model
W. M. Grayman, J. E. Sarsenski, P. J. Wehrman, P. D. Koch
A project was conducted to determine
the utility of a model-based technology
for screening the types and concentra-
tions of contaminants that might exist at
any point along a stream system. The
project was conducted for the lower
Mississippi River in the vicinity of New
Orleans. A routing and graphical display
system (RGDS) was used for the
screening process. This system was
composed of an analytical reach file and
other data bases developed by the U.S.
Environmental Protection Agency
(EPA). Together these files can be used
to route pollutants along the stream
system represented in one of the data
files. Presently more than 68,000
stream reaches are represented in the
data base.
The technology represented by the
RGOS was appropriate to the task, but
results would have been better if more
specific information had been available
on the types and quantities of
contaminant actually discharged and if
specific disappearance rates had been
available for the selected contaminants.
Pilot-scale tests of this technology are
recommended for other locations
throughout the United States.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search 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
This project examines the utility of a
model-based technology for screening
the types and concentrations of
contaminants that might exist at any
point along a stream system. The specific
purpose of the project was to conduct this
screening process for the lower
Mississippi River in the vicinity of the City
of New Orleans and to determine the
feasibility of further developing it. A
routing and graphical display system
(RGDS) was selected to carry out the
screening process and to demonstrate
that this technology could be used for
similar purposes at other locations
through the United States.
Routing and Graphical
Display System
The RGDS is used in conjunction with
the analytical reach (AR) file system and
other data bases developed by the U.S.
Environmental Protection Agency (EPA).
Together they form a modular set of
computer-based data files and progams
that can be used to route pollutants along
the stream system represented in one of
the data files. At present, more than
68,000 stream reaches are represented
in the data base.
The central component in the RGDS is
the AR file. Information in the AR file is
organized by reach - that is, a stretch of
river uniquely defined by an upstream
and downstream point. The AR file
contains both base data on stream
reaches (length, flow, etc.) and a
description of the stream connecting the
reaches. In addition, the AR file can save
information generated by analysis
programs for further analysis and display.
Other information required for analysis
is stored in two other data base files: the
industrial facilities discharge file (IFD)
and the pollutant matrix file. The IFD file
contains discharge and discharger
information such as discharge flow, the
reach to which flow is discharged, and
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the industrial category or SIC number of
the discharger. Information on both
industrial and municipal dischargers is
included in the IFD. The pollutant matrix
file provides information on
representative concentrations of selected
pollutants under varying treatment
conditions for the various industrial
discharger categories as stored in the
IFD.
Two types of analysis programs are
available for estimating the impacts of
pollutants on receiving streams: the
downstream-directed influence line pro-
gram, and the upstream-directed influ-
ence line program. Both programs use
the same general modeling techniques,
which incorporate both dilution effects
and effects of decay (disappearance)of
certain constituents. The effect of dilution
is estimated by simple mass balance, as
represented by the equation:
Concentration = Load/Flow
A first-order, exponential decay func-
tion dependent upon travel time is used to
estimate disappearance of constituents
because of physical, chemical, and
biological processes. This disappearance
is represented mathematically as:
^ _ P -(t, -t0)/K
where
Ct, is the concentration of constituent
(n) at time t,,
Ct0 is the initial concentration of con-
stituent (n) at time t0, and
K is the disappearance coefficient (con-
stant).
In the downstream-directed influence
line approach, pollutant loadings
calculated by information stored in the
IFD and pollutant matrix file were applied
to a stream and the resulting pollutant
concentration at any downstream point
was calculated through dilution ratios
and first order kinetics. In the upstream-
directed influence line approach, the user
specified an in situ pollutant
concentration at any stream point and
dilution ratios, and first-order kinetics
were used to estimate the maximum
pollutant concentrations at upstream
points. Both programs store the pollutant
concentrations estimated for the
downstream end of each reach in the AR
file for further analysis or display or both.
The primary display module used in
this demonstration project was the profile
display software. This software produces
computer generated profile (influence
line) plots of any information stored in the
AR file. For example, it may produce a
profile of pollutant concentrations along
the Mississipi River from Memphis to
New Orleans as calculated by the
downstream-directed influence line
program.
The overall system is designed to
encourage the user to iteratively simulate
and display a wide range of alternatives.
Used in this context, the system can be a
powerful planning tool in the area of
water resources and water quality
analysis.
Study Area
The study area is composed of Hydro-
logic Region 8, the Lower Mississippi
River, as defined by the Water Resources
Council. This area encompasses the
mainstream of the Mississippi River, from
its confluence with the Ohio River to the
Gulf of Mexico and all the tributaries in
between that are represented in the AR
file data base. Hydrologic Region 8 is
represented by approximately 1800
reaches or stream segments in the AR file
data base. Primary emphasis is placed on
the highly industrialized mainstem of the
Mississippi River from the Baton Rouge
area to New Orleans.
Streamflow and suspended solids time
series data are available from the U.S.
Geological Survey (USGS) for a gaging
station at Tarbert Landing, Mississippi.
This gaging station is approximately 200
miles upstream of New Orleans and 8.2
miles downstream of the Old River
control structure, through which
approximately 30 percent of the
streamflow is diverted to the Atchafalaya
River Basin. Based on the gage data for
the period of record (water years 1973-
79), the average flow at this point on the
mainstem Mississippi River is approxi-
mately 540,000 cfs, and the range flow is
129,000 to 1.5 million cfs. Time-of-travel
(velocity) information based on dye
studies by USGS are available in the
RGDS. Average velocities for the
mainstem Lower Mississippi River are
2.6 fps and 1.5 fps'for average and low
flows respectively.
Water Quality
Water quality data for the Lower Mis-
sissippi River are extensive and available
from several sources. This study used
sampling data collected and analyzed at
the Jefferson Parish Water Treatment
Pleint just upstream of New Orleans. This
data base covered a 3-year period and
included analyses of nonspecific organics,
volatile organics, semivolatile organics,
physical and chemical constituents, and
microbiological parameters.
Various statistical and graphical anal-
yses were performed on the data set, and
the following observations were made.
Because the concentration and load-
ing of most contaminants vary
greatly, it is presumed that stream-
flow influences pollutant concentra
tion and that the discharge of tht
mass of contaminants varies greatly
Because streamflow and contami
nant concentration or load do no
correlate for most contaminants
very little relationship exist!
between river flow and the presenci
of contaminants.
A few contaminants appeared t
have a strong negative correlatioi
with streamflow (i.e., as streamflov
increased, contaminant concentra
tion decreased). This result suggest
that the contaminant mas
discharged is reasonably constar
for these contaminants.
A strong positive correlation appeal
to exist between streamflow an
contaminant concentration for a fe'
contaminants. This result is not £
easy to interpret, but it may t
caused by increased discharges
contaminants at higher flow
including contaminants contained
runoff or groundwater inflow.
Very little correlation appears to exi
between the concentration i
contaminants and suspended solid
This result is interpreted to met
that sediments do not appear to a
as a significant reservoir or transpc
mechanism for the contaminart
(assuming the analytical procedur
extract contaminants attached to tl
sediments). A few contaminants a
negatively correlated wi
suspended solids concentration; b
these may be spurious correlatio
given the apparent lack of correlati
between flow and contamin«
concentration and the stro
correlation between streamflow a
suspended solids. This result is to
expected given the severe eros
problems of the central Uni
States.
EPA has expressed an interest in the
contaminants listed in Table 1 becai
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.they were consistently present in water
quality samples and because there is
relatively more known about the
character of upstream discharges of
these contaminants. The means and
standard deviations of these
contaminants are presented in Table 1
together with the concentrations defining
the lower and upper 10 percent of the
distribution of values (i.e., limits within
which 80 percent of values were
observed).
Technology Application
The RGDS was applied to Hydrologic
Region 8 under varying hydrojogic condi-
tions Both the downstream-directed and
upstream-directed methods were used
The downstream-directed influence
line approach was applied for 12 different
contaminants at two different streamflow
regimes for three assumed disappear-
ance rates. The contaminants were
selected on the basis of the in situ water
quality data base at Jefferson Parish and
the availability of discharger data in the
pollutant/contaminant loading matrices.
The contaminants selected were those
given m Table 1 and phenol. The flow
regimes used for the analyses were
average and low streamflows contained
in the AR file data base. Low flow, as
defined in the file, is an estimate of the
minimum weekly flow that is expected to
occur once every 10 years (i e , the lowest
7-day flow m 10 years). The three
assumed disappearance rate coefficients
were 0, 0 05, and 0.2 days '. A value of
zero was selected to demonstrate the
effect of a conservative contaminant The
disappearance rate coefficient of 0.2
day ' results in a half-life of approxi-
mately 31/2 days, which corresponds
with the upper end of decay rates and was
selected to demonstrate the effect of
rapidly decaying contaminants. In all
cases, the concentration of pollutants in
water flowing into the study area
boundaries was assumed to be zero
Discharges of pollutants to the river
were estimated by using the IFD file and a
supplementary pollutant matrix file for
the selected organic constituents
provided by EPA This matrix used a
combination of (1) specific representative
information for industries on the Lower
Mississippi River, and (2) industry-wide
representative discharger data
The upstream-directed influence line
approach was applied under the same
streamflow and decay characteristics
assumed for the downstream-directed
influence line approach. For example, the
in situ concentration wasf ixed at 10/ug/L
at the end of the reach immediately
upstream of New Orleans for all flow and
decay conditions
Results
Based on the downstream-directed
approach, contaminant profiles were
produced for each of the selected
constituents for the selected streamflows
and decay rates The simulated
concentrations and actual in situ values
at Jefferson Parish are presented in Table
2 Except for nitrobenzene, bis (2 ethyl
hexyl) phthalate, and toluene, the
simulated values reasonably approximate
the range of in situ concentrations The
correspondence is best at average flow
The simulated concentrations at low flow
exceed the range of actual values for
some contaminants (e g , benzene) This
result might be expected because actual
streamflows during the monitoring pro-
gram were never as low as the low flow
used for simulation. An anomaly is appar-
ent in the case of carbon tetrachloride. For
this pollutant, the low flow simulated
values are within the range of actual
values, but the average-flow
concentrations are not. This result could
indicate an under loading of carbon tetra-
chloride in the simulation compared with
actual quantities discharged to river.
Conclusions
The technology represented by the
RGDS was appropriate to the task, but the
quality and specificity of the results
would have been considerably enhanced
if (1) more specific information had been
available on the types and quantities of
contaminants actually discharged
upstream, and (2) specific disappearance
rate had been available for the selected
contaminants
Results of downstream-directed and
upstream-directed analyses used in
conjunction with the results of a water
quality monitoring program, the IFD, and
the pollutant loading matrix provide a
method for comparing simulated and
observed concentrations. Thus, the types
and concentrations of contaminants
actually being discharge (as defined by
IFD and pollutant matrix) could be
compared with those that would have to
be discharged upstream to produce the
observed types and concentrations of
contaminants
Contaminant contributions from runoff
leachate, from contaminant disposal
sites, and from spills were not considered
in this project. If the contaminant
Table 1 Statistical Characteristics of Selected Pollutants in the Mississippi River at Jefferson Parish
Pollu-
tant
No
47
7
43
23
35
126
27
31
91
104
98
Pollutant
Dichloromethane
Chloroform
Carbon Tetrachlonde
1,2-Dichloroethane
Tnchloroethane
Tetrachloroethane
Benzene
Toluene
Bis (2-ethyl hexy/t phthalate
Fluorene
Nibrobenzene
No of
Samples
209
209
209
209
209
156
103
103
306
263
263
Mean
Cone
lug/Li
712
800
248
3585
188
746
299
455
168
1 72
282
Standard
Deviation
1824
633
1006
4889
396
170
526
100
97
46
377
Cone
Defining
Lower 10%
of Distr
Values
lug/U
0
200
0
480
0
0
0
0
1 1
0
0
Cone.
Defining
Upper 10%
of Distr
Values
tug/Li
1900
1660
250
8600
390
140
720
210
18.7
48
70
Mean
Cone.
f/jgSL)
1.34
1 80
0.50
730
0.53
0.20
0.56
0.11
005
0.006
0.06
Standard
Deviation
3.17
1.54
1.63
8.46
1.47
0.52
1.25
0,29
0.29
0.018
0.17
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contribution from such sources can be
quantified, however, the RGDS technol-
ogy can be used to simulate the resulting
downstream concentrations.
In summary, the RGDS is useful for
conducting model-based screening to
estimate the types and concentrations of
contaminants that might be expected to
occur at a specified location downstream
of discharges containing the contami-
nants. Of course, the stream reaches
involved must be part of the AR file
system data base. The quality of the
screening results will be largely deter-
mined by the quality of the input data on
the types and quantities of contaminants
being discharged and the specificity with
which the disappearance rate can be
defined for each contaminant.
The user's objectives would determine
which, of the dozens of available models,
would be selected. Models such as
EXAMS and TOXIWASP use a sophisti-
cated kinetic structure that allows the
study of different ionic forms of a
chemical, several ways to calculate
photolysis, etc. Although the EXAMS fate
module formulates a total transforma-
tion rate, the extensive data requirements
could be too costly and time-consuming
for preliminary water resource planning
strategies. As research advances on the
fate of chemicals in local environments, it
seems feasible that a refined overall
disappearance rate for the priority
pollutants will be available without
having to determine the individual data
necessary to operate EXAMS. If the user
requires different hydraulics or chemical
processes, other models should be
considered; but for this analysis, the
simple model presented can provide the
results desired given the resources
available.
Recommendations
To improve the quality of screening
results, users must understand the
limitations of the approach and be aware
of the latest discoveries about
relationships between contaminants and
the environment. Before implementing
the RGDS, or any model, the following
recommendations should be considered:
Reasonable, accuratedisappearance
coefficients should be developed for
either specific contaminants or spe-
cific classes of contaminants.
More specific and detailed discharge
contaminant loading data should be
incorporated into the pollutant
loading matrix (e.g., those available
from NPDES permit applications,
operating reports, and compliance
monitoring).
The technology should be applied on
a pilot scale to other situations
throughout the United States where
data similar to those from Jefferson
Parish are available.
The full report was submitted in
fulfillment of a purchase order contract by
W. E. Gates and Associates under the
sponsorship of the U.S. Environmental
Protection Agency.
Table 2. Comparison of Simulated and Observed Concentrations at Jefferson Parish
Simulated Concentrations
Pollutant
Dichloromethane
Chloroform
Carbon tetrachloride
1, 2 -Dichloroethane
Trichloroethane
Tetrachloroethane
Benzene
Toluene
Bis (2-ethyl hexyl)
phthalate
Fluorene
Phenol
Nitrobenzene
Pollutant
No.
47
7
43
23
35
126
27
31
91
104
NA
98
Average
Cone.
fag/L)
0.712
0.800
0.248
3.585
0.188
0.075
0.229
0.046
0.017
0.002
NA
0.028
Average Flows
K=0
0.093
0.562
0.007
7.412
1.061
0.065
1.764
1.417
0.066
0.009
7 135
5.631
K=0.05
0.076
0.445
0.006
6.116
0.846
0.045
1.456
1.169
0.048
0.007
5.708
4.649
K=0.2
O.044
O.242
0.004
3.507
0.464
0.024
0.835
0.670
0.028
0.004
3.140
2.664
K=0
0.408
2.541
0.033
33.635
4.781
0.454
7.767
6.238
0.472
0.038
31.581
24.794
Low Flows
K=O.05
0.291
1.656
0.023
23.318
3.150
0.189
5.550
4.459
0.213
0.028
21.196
17.716
K=O.2
0.113
0.604
0.009
9.080
1.159
0.069
2.161
1.736
0.094
0.011
7.804
6.899
NA - Not Available
*USGPO: 1984-759-102-10679
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W. M. Grayman, J. E. Sarsenski. P. J. Wehrman, and P. D. Koch are with W. E.
Gates and Associates. Batavia. OH 45103.
Richard G. Eilers is the EPA Project Officer (see below).
The complete report, entitled "Conceptual Development of a Toxic Screening
Model." (Order No. PB 84-223 494. Cost: $13.00, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protect/on Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES F
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PERMIT No. G-3
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Penalty for Private Use $300
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