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
        EPA
   PERMIT No. G-3
Official Business
Penalty for Private Use $300

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