United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA-600/S3-83-046 Sept. 1983
Project Summary
Analyzing Natural Systems:
Analysis for Regional Residuals
Environmental Quality
Management
Daniel J. Basta and Blair T. Bower
Information on approaches for ana-
lyzing natural systems for regional re-
siduals-environmental quality manage-
ment (REQM) was developed. The natu-
ral system components analyzed are
land surface runoff; surface receiving
water, and atmospheric systems. De-
tailed summaries of several operational
natural systems models are provided
along with a discussion of the factors
that must be considered in selecting a
model in a given REQM context. Infor-
mation is included on incorporating
modified and new models into an exist-
ing REQM framework
The report is intended for individuals
in government and private organiza-
tions who make the analyses necessary
to the development of strategies for
achieving and maintaining environ-
mental quality. The information is not
intended to replace other published
material on analyzing particular natural
systems. Rather, the purpose is to guide
the use of such material in a residuals
planning and management'context.
This Project Summary was developed
by EPA's Environmental Research Lab-
oratory, 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
ordering information at back).
Introduction
Over the past several decades, various
models have been developed to analyze
natural systems. The development and
use of these tools has greatly intensified,
primarily in response to the planning re-
quirements mandated in federal, state,
and local environmental legislation. The
various planning mandates have required
that parts of the natural system-for example,
surface water bodies, groundwater systems,
atmospheric systems--be analyzed to
evaluate the impacts of human activities
on the ambient quality of the respective
systems and to assess the effectiveness of
strategies for achieving and maintaining
an acceptable level of "quality." In other
words, the primary emphasis of natural
systems analysis has been within some
"management context," however that
context has been defined
A particularly useful framework for
describing this overall management con-
text is Residuals-Environmental Quality Man-
agement (REQM). The REQM framework
is well-suited to this purpose because it
explicitly incorporates all of the activities
required to achieve and maintain specified
levels of ambient environmental quality.
These activities and their residuals genera-
tion determine the natural systems anal-
yses that are to be undertaken.
The REQM Concept
"Residuals" are those materials and
energy flows that have no value in existing
markets or a value less than their costs of
collection, transportation, and use in the
same or another activity. Thus, a residual is
defined in an economic sense. Whether a
material or energy flow is a residual de-
pends on the relative costs of alternative
materials and energy for use in the same or
another activity. These costs in turn depend
on the level of technology in the society
and on various governmental policies, both
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of which change over time. The term
residual, then, is used rather than such
terms as waste, pollutant or contaminant
An unwanted material or energy flow may
or may not be characterized accurately by
any one of these terms, depending on the
specific material, the environment into
which it is discharged, and the effects on
environmental quality and subsequent
uses of the environment Not all discharges
of unwanted materials or energy into the
environment will have adverse impacts on
ambient environmental quality; some in
fact may have positive effects on receptors.
The analysis approach emphasizes (1) the
interrelationships among the three forms
of materials residuals-solid, liquid, and
gaseous-because one form of material
residual can be transformed into one or
more other forms by the addition of materials
or energy or both, and (2) the interrelated-
ness of the receiving natural systems or
environmental media For example, modifi-
cation of sewage in a sewage treatment
plant results in the generation of a semi-
solid residual, sludge, plus various types
of liquid residuals. If the sludge is in-
cinerated, gaseous residuals will be gene-
rated that may be deposited in surface
receiving waters. The material and energy
inputs required for the modification them-
selves become residuals. Modification is
undertaken under the assumption that the
discharge of the modified residual and the
discharge of residuals generated in its
modification will have fewer adverse im-
pacts than the discharge of the original
residual. This may not always be the case.
The natural systems analysis to be con-
ducted in any given context must be
devised with explicit recognition of these
interrelationships.
The concept of an REQM system is
illustrated in Figure 1. Within any given
region (however defined) at a given point
in time, there is a spatial distribution of
activities: industrial, mining, residential,
agricultural, commercial, transportation.
For each activity there are (1) alternative
combinations of factor inputs and related
production technologies to produce the
desired goods and services of specified
characteristics, with a set of types and
quantities of residuals associated with
each combination, and (2) alternative ways
of handling the residuals after generation.
Activities as sources of residuals can be
classified as point sources, such as a
power plant, a manufacturing plant, or a
residence; line sources, such as traffic
flow on a major street; and dispersed or
area sources, such as a logging or agri-
cultural operation.
From each activity some residuals are
directly or indirectly discharged into natural
systems-air, water, and land environmenta
In the natural environment these residuals
are affected by and may affect various
physical, chemical, and biological processes,
such as transport sedimentation, absorp-
tion, adsorption, volatilization, decom-
position, accumulation. These processes
transform the time and spatial patterns of
residuals discharged from the various ac-
tivities into the resulting short-run and
Goods and Services
Desired by Society
(Final Demand}
Residuals
Discharged to
Environment
Natural
Systems
Transformation
Processes
Spatial Pattern and
Levels of Production and
"Consumption" (Use)
Activities
Ambient
[ Environmental
\ Quality (AEQ1
REQM Strategy
• Physical Measures
• Implementation
Incentives
Final Protective
Measures
Institutional
Arrangement
Receptors
Humans
Plants
Animals
Inanimate Objects
Governmental
Structure
(Institutional
Arrangement)
and Responses
Figure 1. Concept of a residuals-environmental quality management (REQM) system.
2
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long-run time and spatial patterns of am-
bient environmental quality.
The resulting time and spatial pattern of
ambient environmental quality impinges
on receptors-humans, plants, animals,
and inanimate objects. The impacts on the
receptors, as perceived by humans, and the
responses of individuals and groups to the
perceived damages, provide the stimulus
for action. The extent and form of action,
as expressed in a selected management
strategy, depend on the institutional
structure, culture, and value system, and
on competing demands for scarce
resources for other desired goods and
services.
Developing an REQM strategy usually
involves (1) estimating residuals genera-
tion and modification activities, termed
"activity models"; (2) understanding the
processes that affect, and are affected by,
the residuals after their discharge into the
environmental media, termed "natural
systems models"; (3) specifying an ex-
plicit objective function, which includes
environmental quality indicators in the
function itself, or as constraints, or both;
(4) selecting a computational procedure;
and (5) developing and applying criteria
for evaluating strategies. This report pro-
vides guidelines and procedures for select-
ing one or more appropriate natural sys-
tems model.
Natural Systems Models
The types and quantities of residuals
discharged at specific locations and times
comprise the inputs into the natural sys-
tems models, along with the relevant hy-
drologic, geomorphologic, meteorologic,
and pedologic variables such as tempera-
tures, wind velocity, precipitation, soil
characteristics, topographic slope, stream
channel characteristics, and sunlight Major
types of natural systems models (NSMs)
include (1) physical dispersion models
such as for suspended participates, sulfur
dioxide, and total dissolved solids (salinity);
(2) physicochemical dispersion (or trans-
port) and fate models such as for photo-
chemical smog in air or pesticide move-
ment and modification in ground water
aquifers; and (3) biological systems models
such as terrestrial and aquatic ecosystem
models.
The time and resources available and
the relative importance of the environ-
mental media--in terms of the relevant
environmental quality problems-deter-
mine the degree of complexity necessary
for the NSMs. For example, a water quality
model may consist of a set of simple linear
transfer coefficients or it may be a multi-
compartment aquatic ecosystem model.
NSMs transform the time and spatial pat-
tern of residuals discharges into the en-
vironment into the resulting time and
spatial pattern of ambient environmental
quality as measured by whatever indicators
are of interest in the particular situation.
Selecting Natural Systems
Models
An approach was developed for selecting
NSMs in any given REQM context relative
to three environmental compartments--
land runoff (urban and rural), surface water,
and the atmosphere.
An NSM translates the time and spatial
pattern of residuals discharged into the
resulting time and spatial pattern of am-
bient environmental quality or delineates
the on-site changes in the state of a natural
system as a result of on-site production
processes and residuals discharged from
a source. The report (1) identifies and
describes the principal approaches and
associated analytical techniques presently
used to analyze natural systems, (2) pro-
vides detailed summaries of a number of
operational NSMs that are currently avail-
able, (3) indicates the factors which must
be taken into account in selecting a NSM
in a given REQM context, and (4) describes
how to select an appropriate operational
NSM.
Two attributes are necessary for a NSM
to be considered operational. The first is
that it has been successf u lly applied to and
verified for at least one natural system and
that it can be used to model another
different, but roughly similar, system
without extensive internal modification.
The second is that sufficient written doc-
umentation must be available about the
model to enable a potential user to apply
the model in a location other than that for
which it was verified.
The three basic analytical approaches to
analyzing natural systems, whether they
represent a surface water body, land area,
or atmospheric system, are physical mod-
eling, conservation of mass and energy,
and statistical. Three characteristics com-
mon to all NSMs are temporal variation,
averaging time and spatial dimensionality.
NSMs may be steady-state or nonsteady-
state depending on whether variables
change over time. Nonsteady-state models
may be characterized as either nonstochastic
(or deterministic) or stochastic.
The report discusses setting up the
natural systems analysis portion of an
REQM analysis. The factors determining
the scope and the type(s) of natural sys-
tems analysis include the questions to be
answered, the residuals of concern, the
conditions of relevant natural systems
measured in terms of ambient environ-
mental quality indicators, the available
analytical resources, and the relative im-
portance and characteristics of residuals-
generating activities. Figure 2 depicts the
NSM selection procedure.
Regardless of the category or type of
NSM, a number of common problems
exist with respect to adoption, operation,
and utility of models. The most important
problems relate to determining the ap-
propriate level of complexity necessary for
the analysis, calibrating and verifying the
candidate NSM, determining background
levels of residuals, linking NSMs and
residuals generating activities, and inter-
preting modeling results including the use
of sensitivity analysis.
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Given: Specification of Required Natural Systems
Analysis, as Specified in Step 3 of Steps
for Setting Up NSM Analysis
Search Problem Table
for Appropriate Models to
Address Defined Problems
Are There
Models with
Desired
Attributes?
Go to NSM
Summary Tables
Operational
Constraints
Can
Additional
Resources be
Obtained:'
Specify
Availability of.
data
personnel
time
computer
facilities
money
Are the
vailable Analytical
Resources Sufficient to
Implement Thes
Models?
Compare/Select Model
Based on
Evaluation Criteria
Evaluation
Criteria
Can
Additional
Resources be
Obtained?
Specify Model Modification or
New Model Development Options
and Required Resources
Are the
Available Analytical
Resources Sufficient to
Modify Existing or
Develop New
Model?
Complete Model within
Operational Constraints
Utilize NSM in
REOJM Analysis
\
Figure 2. Flow chart to NSM selection procedure.
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Daniel J. Basta and Blair T. Bower, editors, are with Resources for the Future,
Washington, DC 2O036.
T. E. Waddell is the EPA Project Officer (see below).
The complete report, entitled "Analyzing Natural Systems: Analysis for Regional
Residuals-Environmental Quality Management," (Order No. PB 83-223 321;
Cost: $38.50, 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
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