ii/
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA/600/S3-88/013 Sept. 1988
Project Summary
CORMIX1, An Expert
System for Mixing Zone
Analysis of Toxic and
Conventional, Single Port
Aquatic Discharges
R. L. Doneker and G. H. Jirka
CORMIX1 predicts the dilution and tra-
jectory of a single buoyant discharge in-
to an unstratified ambient aquatic en-
vironment with or without crossflow.
CORMIX1 uses knowledge and inference
rules obtained from hydrodynamic ex-
perts to classify and predict buoyant jet
mixing. CORMIX1 gathers the necessary
data, checks for data consistency,
assembles and executes the appropriate
hydrodynamic simulation models, inter-
prets the results of the simulation in
terms of the legal requirements (in-
cluding toxic discharge criteria), and
suggests design alternatives to improve
dilution characteristics.
This Project Summary was developed
by EPA's Environmental Research
Laboratory, Athens, GA, to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
A mixing zone is defined as an "allocated
impact zone" where numeric water quality
criteria can be exceeded as long as acute-
ly toxic conditions are prevented. Water
quality regulations can prohibit lethal con-
centrations or require that a concentration
known as the criterion maximum concen-
tration (CMC) be met within a short distance
from the outfall. The CMC is a concentra-
tion that prevents lethality or acute effects
in tested species. If dilution of the toxic
discharge in the ambient environment is
allowed, this requirement (which is defin-
ed as a toxic dilution zone - TDZ), is more
restrictive than the legal mixing zone for
conventional and non-conventional
pollutants.
Any discharge into a navigable water-
course is regulated by a National Pollution
Discharge Elimination System (NPDES)
permit. The permit is designed to ensure
that the discharge meets all applicable
water quality standards. Implementation of
the mixing zone policy in the NPDES per-
mitting process requires that the applicants
and regulators predict the initial dilution of
the discharge and the charactistics of the
mixing zone. If the discharge is toxic, the
CMC value must be determined for the
discharge and special requirements for a
TDZ must be met within the mixing zone.
Given the large number of possible ambient
environments, discharge configurations,
and mixing zone definitions, the analyst
needs considerable training and ex-
perience to conduct accurate and reliable
effluent mixing analyses.
The most direct way of determining pollu-
tant concentration downstream is by
physical measurement. Non-polluting
tracers also can be injected to give indica-
tions of effluent dilution. Such field studies
require considerable time and effort, and
field personnel need specialized training to
perform studies reliably. Field studies are
in many cases impractical and expensive.
Because of the complexity of the physical
mixing process, permit writers are increas-
ingly relying on mathematical models to
-------
analyze the fate and transport of pollutants.
The difficulty with many present models is
that they tend to become specialized and
give accurate results only for a particular
type of outfall.
In determining the characteristics of the
mixing zone, the analyst may choose from
a wide variety of predictive models. The
models range in complexity from simple
analytical formulae to highly intricate
numerical solutions to differential equa-
tions. Although the USEPA has prepared
assessment manuals and actually endors-
ed certain models in specific situations, the
average user has little reliable guidance on
which model is appropriate for a particular
situation. Often, unnecessarily complicated
models are employed, creating a needless
burden for both regulators and dischargers.
Because of these difficulties, a large in-
vestment in time is required for the analyst
to become familiar and proficient with the
use of at least one model, or more likely,
a group of models. The analyst must
become highly skilled or an "expert" in the
use and interpretation of a number of
simulation models. Such expertise in model
use requires expensive training and is rare.
This is the reason for the development of
expert system tools for the analyst.
In essence, expert systems mimic the
way an expert or highly experienced per-
son would solve a problem. An expert
system is a structured computer program
that uses knowledge and inference pro-
cedures obtained from experts for solving
a particular type or class of problem call-
ed a "domain." This knowledge is encod-
ed into a "knowledge base" that enables
inexperienced personnel to solve complex
problems by using the same basic reason-
ing processes an expert would apply.
The development of an expert system for
mixing zone analysis promises significant
advantages when compared to existing
conventional simulation techniques for
water pollution control and management.
This type of expert system assures the pro-
per model choice for a given physical situa-
tion. It allows a flexible application of design
strategies for a given point source, screen-
ing of alternatives, and if necessary, swit-
ching to different predictive models, thus
avoiding rigid adherence to a single model.
It assures that the chosen model is applied
methodically without skipping essential
elements. It also provides a teaching en-
vironment whereby the initially inexperienc-
ed analyst can gain insight into and
understanding about initial mixing pro-
cesses. Expert systems are a technology
that has enormous potential for solving pro-
blems in environmental science.
The problem addressed was to develop
a tool for the analysis and design of
submerged, single port, continuous
buoyant discharges into a non-stratified
aqueous environment. The expert system
is labeled CORMIX1 for Cornell Mixing
Zone Expert System, Subsystem 1.
CORMIX1 is a subsystem of CORMIX,
which will include stratified environments,
negatively buoyant discharges, and bottom
attachments. CORMIX1 is primarily intend-
ed for applications to flowing ambient water
(such as rivers or estuaries), although the
limiting cases of non-buoyant discharges
and stagnant environments are included.
The emphasis of CORMIX1 is on discharge
geometry and characteristics of legal mix-
ing zone (LMZ) requirements, including the
toxic dilution zone (TDZ). CORMIX1 can
summarize dilution characteristics of the
proposed design, flag undesirable designs,
give dilution characteristics at legally impor-
tant regions if specified, and recommend
design alterations to improve dilution
characteristics.
Scope of Model
CORMIX1 (Figure 1) is a series of soft-
ware subsystems or elements for the
analysis and design of conventional or toxic
single port submerged buoyant or non-
buoyant pollutant discharges into
unstratified water sources, with emphasis
on the geometry and dilution characteristics
of the initial mixing zone. It is designed as
an analysis tool for regulators, dischargers,
and students of hydraulics.
The user supplies CORMIX1 with infor-
mation about the discharge and the am-
bient environment. CORMIX1 returns infor-
mation detailing the hydrodynamic
mechanisms controlling flow and dilution,
geometric information concerning the
shape of the pollutant plume or flow in the
ambient water body, and design recom-
mendations allowing the user to improve
the dilution characteristics of the flow. If
specified by the user, CORMIX1 also
presents information about the legal mix-
ing zone dimensions and dilution, toxic mix-
ing zone requirements, and zone of interest
characteristics for the flow.
CORMIX1 uses two programming
languages, M.1 and FORTRAN. M.1 is ef-
ficient in knowledge representation and
symbolic reasoning. It is, however, relatively
weak in numerical computational ability.
FORTRAN is ideal for computation of
mathematical functions but is poorly suited
for the tasks associated with symbolic
reasoning. Thus, M.1 is employed to imple-
ment the knowledge acquisition, model
selection, and hydrodynamic simulation
analysis portions of the expert system.
FORTRAN is used for the computation of
various length scales and in the
hydrodynamic flow simulation models.
The M.1 elements of CORMIX1 are
DATIN, CLASS, and SUM. M.1 is similar in
structure to PROLOG An M.1 program is
built from statements containing facts and
if-then rules about facts. This knowledge
base is supplied by the user corresponding
to a problem domain, in this case, buoyant
submerged jets and hydrodynamic mixing
processes. M.1 programs are driven by a
"goal" that the program tries to validate by
searching the knowledge base to construct
a "proof" using the facts and rules in the
knowledge base needed to deduce the goal
as a valid hypothesis
DATIN is an M.1 program for the entry of
relevant data and for the initialization of the
other program elements. The purpose of
DATIN is to specify completely the physical
environment of the discharge as well as
legal or regulatory specifications DATIN
tries to satisfy the goal by creating a valid
parameter input file for the other CORMIX1
elements. The goal is the statement that
drives the execution of DATIN
The knowledge base in DATIN is built
from rules that contain expressions that
force M.1 to seek valuations from other
rules. M.1 will never assign a valuation that
is a contracdiction within a rule, so the user
is assured that whatever valuations are con-
cluded are taken from a rule within the
knowledge base.
CLASS is an M.1 program that classifies
the given discharge into one of many possi-
ble flow configurations. The goal of CLASS
is to find a valuation for the expression
"flow class" from the flow classification
scheme. When the appropriate flow
classification rule fires, a detailed
hydrodynamic description of the flow is pro-
vided to the user. This detailed output in-
cludes a description of the significant near-
field mixing processes or the hydrodynamic
mixing zone (HMZ). The HMZ is defined to
give additional information as an aid to
understanding mixing processes and to
distinguish it from purely legal mixing zone
definitions. CLASS also creates a cache
output file that supplies the next CORMIX1
element, the FORTRAN hydrodynamic
simulation program HYDRO.
SUM is an M.1 program that summarizes
the hydrodynamic simulation results for the
case under consideration. SUM comments
on the mixing characteristics, evaluates
how applicable legal requirements are
satisfied, and suggests possible design
alternatives to improve dilution. Thus, SUM
may be used as an interactive loop to guide
-------
Ml
DA TIN
User Input
file CXD
Fortran
PA RAM
Parameter
Computation
file CXP
Ml
CLASS
Flow
Classification
file
CXC
Iteration
Alternatives
Corrections
file CXI
Fortran
HYDRO
Prediction/Simulation
Program
file CXO
Ml
SUM
Summary
Evaluation
Recommendations
(Legal/Engineering)
the tabular output file that gives detailed in-
formation on the trajectory and dilution of
the hydrodynamic flow simulation.
Conclusions and
Recommendations
In a test application, the results of the
hydrodynamic simulation agreed with field
and laboratory data. In particular, CORMIX1
correctly predicted highly complex
discharge situations involving boundary in-
teractions and buoyant intrusions, a result
not predicted by other existing initial mix-
ing models. What has been attempted here
is to place a modestly complex
hydrodynamic simulation methodology
within the framework of a rule-based expert
system. Many of the common pitfalls of
model use - incomplete or contradictory
data, choice of appropriate simulation
model, and faulty interpretation of results
- appear to be mitigated within the context
of an expert system methodology.
CORMIX1 facilitates the user's
understanding of important hydrodynamic
processes controlling the flow. It gives
three-dimensional discharge trajectory and
dilution. It alerts the user to where signifi-
cant legal criteria apply to the discharge.
CORMIX1 allows for rapid evaluation of
design alternatives and gives the user sug-
gestions for improving dilution
characteristics of the discharge. Overall,
CORMIX1 appears to be an excellent
analysis tool.
Although limited data are available for
both field and laboratory experiments, fur-
ther efforts will be made to compare model
predictions and adjust parameters in the
flow classification.
Figure 1. System elements of CORM/XJ
the user back to DATIN in order to alter
design variables. The output of SUM is ar-
ranged in four groups — site summary,
hydrodynamic simulation summary, data
analysis, and design recommendations.
The FORTRAN elements of CORMIX1
are PARAM and HYDRO. PARAM and
HYDRO are executed after the user has
successfully completed DATIN and CLASS.
PARAM is a FORTRAN program that com-
putes relevant physical parameters for the
given discharge situation. This includes the
various length scales, fluxes and other
values needed by the other CORMIX1
elements. PARAM also computes the max-
imum value for each specified mixing or in-
terest zone for each of the possible
hydrodynamic simulation termination
criteria.
HYDRO is a FORTRAN program that
runs the hydrodynamic simulation program
for the flow classification program specified
in CLASS. HYDRO consists of control pro-
grams or "protocols" for each hydro-
dynamic flow classification specified by
CLASS. HYDRO assembles the appro-
priate simulation from the modules.
HYDRO also creates a tabular output file
of the simulation containing information on
geometry (trajectory, width, etc.) and mix-
ing (dilution and concentration). After
HYDRO has executed, the user may view
-------
Robert L. Doneker and Gerhard H. Jirka are with Cornell University, Ithaca,
NY 14853.
Thomas O. Barn well. Jr., is the EPA Project Officer (see below).
The complete report, entitled "CORMIX1, An Expert System for Mixing Zone
Analysis of Toxic and Conventional, Single Port Aquatic Discharges," (Order
No. PB 88-220 504/AS; Cost: $32.95, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
College Station Road
Athens, GA 30613
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-88/013
0000329 PS
U S EWVIR PROTECTION *GE»CY
CMICA60
M
It 60604
liHiitliiiilliillimliililiill
------- |