United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-124 Jan. 1984
SEPA Project Summary
Guidelines for the Monitoring of
Urban Runoff Quality
Michael B. Sonnen
This study was undertaken to define
adequate monitoring of urban runoff for
various objectives and to develop a
guidebook for those contemplating a
program of measuring urban runoff in
the field. Emphasis is placed on measur-
ing urban runoff while it is still flowing
on land and street surfaces rather than
after it has been integrated with other
waters in storm or combined sewers.
The study stresses the need to state
the exact objective of any field monitor-
ing program, since costs and require-
ments vary greatly depending on the
purpose of the monitoring. Six possible
objectives are identified for urban runoff
monitoring programs (scientific re-
search, problem identification, alterna-
tive solution monitoring, support of the
final design, regulatory compliance
monitoring, and operational perform-
ance monitoring).
The study also reviews current and
recent monitoring programs, literature
on monitoring program design, and
monitoring strategies for receiving
waters and best management practices.
Monitoring and protocols are developed
for satisfying various objectives, and a
set of guidelines is developed to assist
designers and planners of monitoring
programs for urban runoff.
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 reoort of the same title (see
Project Report ordering information at
back).
Introduction
Storm and snowmelt runoff from urban
lands contains constituents that can,
under certain circumstances, occur at
damaging, polluting levels. These circum-
stances and the phenomena and pro-
cesses that produce the runoff quality
levels are so poorly understood and so
inherently random and variable that only
field measurements can reliably charac-
terize them.
Sometimes it is necessary or desirable
to have extremely detailed information
about the processes that cause deterior-
ation in the quality of urban runoff. To get
such information, an expensive, compre-
hensive field monitoring program must
be launched. By contrast, a city planner or
engineer, for example, may simply need
information about the levels of one or
more constituents in local storm runoff.
Such a need can be met by a fairly cursory
or modest monitoring program. This study
defines what adequate monitoring is for
specific objectives and develops a guide-
book for those contemplating a field
measurement program.
Historically, runoff has generally been
sampled after it has entered storm or
combined sewers and been integrated
with waters from various sources. By
contrast, this study emphasizes the qual-
ity of runoff still flowing on the land and
street surfaces. Some discussion is also
presented of flows and qualities of runoff
in storm and combined sewers or at
points of combined sewer overflows.
This study especially concentrates on
statistical requirements and tests for
sufficiency or significance of data sets,
because these statistical considerations
affect the success of each monitoring
objective. Though insights to monitoring
program design can be gained through
the use of statistical inferences and
hypotheses, considerable art is required
in specifying sample numbers, levels of
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confidence, etc In particular, the investi-
gator should be able to anticipate the
general behavior of the phenomena being
sampled, or considerable sampling effort,
time, and money may be wasted. These
concepts are developed in detail through-
out the report.
Procedures
Developing Monitoring
Objectives
Since the requirements and costs of
monitoring urban runoff vary greatly
depending on the purpose of the monitor-
ing, this study stresses the need to state
the exact objective of the field monitoring
in each case. Six possible objectives were
identified: (1) Scientific research, (2) prob-
lem identification, (3) alternative solution
monitoring, (4) support of the final design,
(5) regulatory compliance monitoring, and
(6) operational performance monitoring.
Reviewing the Objectives and
Successes of Current and
Recent Monitoring Programs
Past monitoring programs reported in
the literature were reviewed, and the
results and conclusions were compared
with the originally stated objectives.
Reviewing Literature on
Monitoring Program Design
Past works on monitoring of urban
runoff were reviewed to indicate the
state-of-the-art in monitoring protocol
design.
Reviewing and Developing
Monitoring Strategies for
Receiving Waters and Best
Management Practices
Reviews were made of special-purpose
monitoring for characterizing impacts of
urban runoff on receiving waters and for
planning or monitoring performance of
certain runoff pollution control measures.
Guidance is given where weaknesses are
apparent.
Develop Monitoring
Protocols for Satisfying
Objectives
The study develops statistical infer-
ences of reliable numbers of sampling
sites and sample numbers for each of the
six monitoring objectives selected.
Designing and Producing a
Guidelines Report
A guidebook was developed to describe
all the foregoing material for those con-
templating a field measurement program.
Minimum measurements were described
for satisfying various objectives.
Summary Discussion
Storm and snowmelt runoff from urban
lands contains quality constituents which
under certain circumstances occur in
damaging, polluting levels. These circum-
stances, the phenomena and processes
making runoff quality levels what they
are, remain so poorly understood and are
so inherently random and variable that
only field measurements can be relied
upon to characterize their behavior.
Sometimes it is necessary or desirable
to learn in great spatial and temporal
detail what the processes are that cause
deterioration in the quality of urban
runoff. In these cases an expensive,
comprehensive field monitoring program
must be launched to learn the required
information. By contrast there are other
instances in which a planner or city
engineer, for example, may wish to learn
whether or not a particular constituent or
several constituents in storm runoff attain
potentially damaging levels in his or her
community. In this case, a fairly cursory
and modest monitoring program will
suffice to satisfy this objective.
Statistical theory provides some guid-
ance to the numbers of samples required
for satisfying various objectives for moni-
toring. Buta number of arbitrary variables,
such as the degree of confidence or
acceptable error must be specified by the
monitoring program designer. Moreover,
many statistical tests require that charac-
teristics of some sampled data already be
available, such as the sample standard
deviation in the t-test, before they can be
used to give guidance on the acceptability
of sample numbers for still further moni-
toring.
Numbers of samples for example pro-
grams specified for satisfaction of six
different monitoring objectives ranged
from 24 for a design objective to 54,000
for a comprehensive scientific, process-
monitoring objective. Costs for monitoring
varied proportionately, from about
$11,000 to $9,300,000, for the two
respective objectives.
Detailed sampling and laboratory anal-
yses are expensive. Sometimes the ex-
pense of sampling and analysis will prove
prohibitive. The major point of this work.
however, is that curtailment of monitoring
for reasons of expense or for any other
reason can mean that the original moni-
toring objective cannot be met. If one sets
out to elucidate runoff quality processes
or to build and verify a model of these
causative processes and finds that he can
afford only $75,000 per year to do the
indicated monitoring, then in fact he
cannot adequately define processes or
verify his model. The best he can hope for
is to monitor operational performance, to
gather information on what happened,
what the effects were, and not what
caused those effects to be realized. The
information gained is likely not to be
sufficient to allow prediction of what will
happen in other places or under changed
conditions.
Urban runoff quality in the early 1980's
is not considered a high priority item of
national environmental interest, except
in those instances where urban runoff is
conveyed and discharged through sys-
tems. Runoff quality control remains a
new field of engineering endeavor. It is
natural, therefore, that design criteria,
discharge standards and receiving water
criteria, and scientific knowledge about
this field are still preliminary, incomplete,
and rudimentary. For these same reasons,
however, it is virtually axiomatic that
mistakes may be made, monitoring and
construction monies may occasionally be
misspent on unnecessary or unsupported
or inadequate facilities or monitoring
programs. It is to be hoped that this
guidebook will assist in keeping straight
what is adequate monitoring for separate
objectives and what is not.
Conclusions
1. Urban runoff may be sampled for a
variety of reasons, i.e., to satisfy any
of a number of objectives. The ob-
jective in each case should be stated
explicitly and restated as necessary
in concrete, numerical terms so a
program of sampling can be devised
that will clearly satisfy that objective.
2. Sampling in the field is expensive.
Laboratory analyses are both expen-
sive and relatively inexpensive, de-
pending on which constituents are
being analyzed. But economies of
scale in laboratory analyses are
available, and opportunities should
be sought for learning more for the
same total budget by having more
analyses performed and sampling
fewer events in the field.
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3. Statistical theory that exists today is
somewhat useful in guiding decisions
about sampling program design. Cer-
tain concepts from statistics, such as
the existence of Type I and Type II
errors, should be appreciated since
they are axiomatic and unavoidable.
Statistical tests such as the t-test,
the F-test, and the chi-square test
are useful and instructive and worthy
of consideration, but they do not
function usefully in the absence of
any prior sample information. That is
very frustrating but inescapable.
Statistical theory on the whole is not
developed sufficiently to assist mean-
ingfully in multiple-site, multiple-
phenomena, multiple-constituent,
stochastic-process sampling.
4. Mathematical models existing today
for estimation of urban runoff quality
loads do not have a solid scientific
base. Some do not require or even
give regard to the satisfaction of
mass continuity. Directly as a result,
they are either difficult or impossible
to calibrate or they must be recali-
brated with practically every use.
Because they are so limited in trans-
ferability and even the most basic
level of scientific rigor, they cannot
be relied upon solely to replace or
obviate the need for local quality
sampling, regardless of the objective.
5. Research needs to be done to formu-
late the physics and chemistry of
urban runoff behavior at several
levels of sophistication and approxi-
mation. Just as it is not necessary to
monitor each drop of rainfall, each
clay particle, or each liter of runoff to
design a detention basin, it is not
necessary to model each of these
things rigorously to design the basin
without sample results. But design
"theory" does need to be developed
that is consistent with scientific
principles, that allows for variability
in behavior both chemically and
physically, both quality-wise and
hydraulically, and that approximates
at least the continuity of mass and
the processes of scour and deposition
and chemical equilibria and rates of
change of concentration with time
and with changes in chemistry of the
incoming and surrounding fluid.
Current models in wide use are
predicated on an assumed first-order
decay or wash-off or first-flush phe-
nomenon, which data frprn Denver
and other places have clearly indi-
cated does not always occur. Concen-
6.
trations or masses of pollutants in
runoff do not always decrease expo-
nentially or at all with time after the
onset of rainfall. Current theory on
the behavior of urban runoff and its
quality constituents is poor at best
and misleading or even wrong at
worst. Hydraulic behavior is much
better understood, and it is approxi-
mated adequately at various levels of
study detail, i.e., for use with varying
scientific, planning, design, or moni-
toring objectives. Quality theory
should be developed and advanced in
a commensurate fashion.
There is no guarantee that water
quality data, no matter how carefully
collected, will be transferable to other
areas and other circumstances. How-
ever, because data collection and
interpretation is so expensive and
time-consuming, EPA is encouraged
to maintain a data base, such as that
now started at the University of
Florida, wherein runoff quality data
from across the nation may be stored
and accessed by subsequent users.
But it is recommended that data so
stored be characterized by the con-
tributor as to their statistical proper-
ties (numbers of samples, variance,
and the like) and as to the conditions
and purposes under and for which
they were collected.
The full report was submitted in fulfill-
ment of Grant No. R-806704 by the
Denver Urban Drainage & Flood Control
District under the sponsorship of the U.S.
Environmental Protection Agency.
Michael B. Sonnen is with the M. B. Sonnen Co.. Inc., Walnut Creek, CA 94598.
Douglas Ammon is the EPA Project Officer {see below).
The complete report, entitled "Guidelines for the Monitoring of Urban Runoff
Quality." (Order No. PB 84-122 902; Cost: $14.50. 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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
*US. GOVERNMENT PRINTING OFFICE 1984-759-015/7267
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Environmental Protection
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Center for Environmental Research
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