EFA-60U/4-78-005
January 1978
WATER QUALITY INDICES: A SURVEY
OF INDICES USED IN THE UNITED STATES
by
Wayne R. Ott
Monitoring Technology Division
Office of Monitoring and Technical Support
Washington, D.C. 20460
OFFICE OF MONITORING AND TECHNICAL SUPPORT
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
U.S. Environmental Protection Agency,
Region V. ' u>f"!>y
230 Sci' ' 'n 5v!;;'jt
Chicago, ilnnois 60604
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DISCLAIMER
This report: has been reviewed by the Office of Research and Development,
U.S. Environmental Protection Agency, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement or
recommendation for use.
U.S. Environmental Prelection Agency
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FOREWORD
The U.S. Environmental Protection Agency was created because of
increasing public and governmental concern about the dangers of pollution
to the health and welfare of the American people. Polluted air, foul water,
and spoiled land are tragic testimony to the deterioration of our natural
environment. The complexity of that environment and the interplay between
its components require a concentrated and integrated attack on the problem.
Physical, chemical, and biological measurements of environmental quality
are the most important means available for determining the state-of-the-
environment. These monitoring data provide the basis for evaluating the
Nation's progress in improving environmental quality and are essential to
environmental managers and decision makers. Unfortunately, a gap often
exists between specialists who collect the data and managers who must
understand its implications. Environmental indices have been proposed as
one means for bridging this gap.
This report was prepared to provide the most comprehensive summary
currently available of the utilization of water quality indices throughout
the United States. We hope that the extensive data base assembled in this
effort will assist the Agency in establishing future policies in this area.
Albert C. Trakowski
Deputy Assistant Administrator
for Monitoring and Technical Support
111
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ABSTRACT
This study, conducted by the U.S. Environmental Protection Agency (EPA),
documents the extent to which water quality indices currently are being used
in the United States. It reviews the indices published in the literature and
surveys the States and interstate commissions to determine: (1) which
agencies are using indices, (2) the type of index being used, (3) the purpose
of its use, and (4) the attitudes of agency personnel toward indices.
Few of the more than 20 physical and chemical water quality indices pub-
lished in the literature are being used in practice. One-fifth of the State
and interstate agencies (12 out of 60 agencies) are classified as users of
water quality indices. An "index user" is defined as an agency that has used
an index in an official publication or large-scale study extending over a year
or more. Of the 51 State agencies (including the District of Columbia), 10
States (20 percent) are classified as index users. The National Sanitation
Foundation Index (NSFI) is the most commonly used index, accounting for 7 of
the 12 index users. The remaining agencies use Harkins' index or various
user-developed indices. A total of 16 additional States and 1 interstate
commission indicate that they are planning to evaluate indices for possible
future application, or are developing or evaluating indices at the present
time; these are classified as "potential users." Most of these agencies
indicate that they will be considering the NSFI.
Six new indices have been developed by water pollution control agencies,
four by the States, and two by the EPA Regional Offices. Three of the State-
developed indices are currently in use, and the remaining one has not reached
the stage of routine application. The mathematical structures of the new
indices are documented in this report.
The main purposes expressed by index users for applying their indices are
preparation of the annual reports required by Section 305 (b) of P.L. 92-500,
public information, and analysis of water quality trends. The majority of the
index users express satisfaction with their indices and rate them favorably.
Most users feel that EPA should have a suggested index available (or a set of
indices) for those agencies that wish to use a uniform index structure.
There is clear evidence of a trend toward increased utilization of water
quality indices in the United States. If the 17 agencies classified in this
study as potential users become users in the future, a total of 29 out 60
agencies (48 percent) will then be using water quality indices. Several
recommendations are included in this report for meeting the needs of index
users, attaining greater uniformity in water quality data analysis practices,
and identifying future research needs.
This report covers a period from October 1976 to June 1977 and work was
completed September 1977.
iv
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CONTENTS
FOREWORD iii
ABSTRACT iv
FIGURES vii
TABLES viii
ACKNOWLEDGMENTS x
I. INTRODUCTION 1
II. LITERATURE REVIEW 4
PHYSICAL AND CHEMICAL WATER QUALITY INDICES 4
Indices of General Water Quality 4
Indices for Specific Water Uses 1
Indices for Planning 9
Statistical Approaches 10
BIOLOGICAL WATER QUALITY INDICES 11
DISCUSSION 14
III. SURVEY DESIGN 15
SURVEY POPULATION 15
SURVEY APPROACH 15
CLASSIFICATION OF NONUSER AND USER AGENCIES 16
Nonuser Agency 16
User Agency 16
IV. SURVEY RESULTS 17
AGENCIES CURRENTLY NOT USING INDICES 17
Agencies Unfamiliar With Indices 17
Agencies That Have Previously Considered or
Evaluated Indices 17
Agencies Planning To Evaluate or Develop Indices .... 21
Agencies Currently Evaluating or Developing Indices . . 21
AGENCIES CURRENTLY USING INDICES ' . . 21
Indices in Current Use 21
Purposes of Index Applications 25
Attitudes of Users Toward Indices 30
DISCUSSION OF COMMENTS FROM EPA REGIONAL OFFICES 38
V. CASE STUDIES OF INDICES DEVELOPED BY WATER POLLUTION
CONTROL AGENCIES 40
STATE AGENCIES . * 40
Georgia 40
Illinois 42
Nevada 51
Oregon 52
EPA REGIONS 56
Region VIII 56
Region X 58
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VI. CRITERIA FOR AN IDEAL WATER QUALITY INDEX 61
VII. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS 63
SUMMARY 63
CONCLUSIONS 65
RECOMMENDATIONS „ 67
VIII. REVIEWERS' COMMENTS ,. 71
REFERENCES 76
APPENDICES
A. COMMENTS FROM NONUSERS OF WATER QUALITY INDICES ... 81
B. COMMENTS FROM USERS OF WATER QUALITY INDICES 88
C. QUALITY RATING CURVES FOR GEORGIA'S WATER QUALITY INDEX 95
D. QUALITY RATING CURVES FOR OREGON'S WATER QUALITY INDEX 104
E. QUALITY RATING CURVES FOR REGION X WATER QUALITY INDEX Ill
F. WATER QUALITY INDEX DATA SHEET 125
vx
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FIGURES
Number Page
1 Descriptive Language Suggested by Dinius to Enable a
Single Water Quality Index to be Applied to Different
Water Uses 6
2 Average Water Quality Conditions, As Indicated by the NSFI,
for the State of Michigan 28
3 Example of Water Quality Index Report Prepared by Michigan
for Selected Rivers 29
4 Example of Water Quality Trend Report Using the NSF Water
Quality Index on Michigan's Raisin River at Monroe
(Station 580046) 31
5 Example of Water Quality Trend Report Using the NSF Water
Quality Index on Michigan's Grand River at Grand Haven
(Station 700026) 32
6 Example of Water Quality Trend Report Using the NSF Water
Quality Index on Rivers in the State of New York 33
7 Descriptors and Ranges Used in Georgia's "Trend Monitoring
Index" 42
8 Water Quality Impact of Georgia's Urban and Industrial
Areas as Measured by Differences in Trend Monitoring
Index for Upstream and Downstream Locations 43
9 Comparison of Number of Fish Species and Pollution Index
Values for Illinois Water Quality Data 45
VII
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TABLES
Number Page
1 Comparison of Weights Used in Five Water Quality Indices .... 8
2 Overall Characteristics of Water Quality Indices Published
in the Literature 12
3 Status of Water Quality Index Utilization by States 18
4 Status of Water Quality Index Utilization by Interstate
Commissions 19
5 Summary of Water Quality Index Utilization by States and
Interstate Commissions 19
6 Nonusers Who Have Previously Considered or Evaluated
Indices 20
7 Nonusers Who Are Planning to Evaluate or Develop Indices .... 22
8 Nonusers Who Are Currently Evaluating or Developing Indices . . 22
9 Agencies Using Water Quality Indices, June 1977 23
10 Agencies Currently Using the National Sanitation Foundation
Index (NSFI) 25
11 Purposes for Which Indices Are Being Used 26
12 Comments from Personnel at EPA Regional Offices 39
13 Agencies Which Have Developed New or Substantially Modified
Water Quality Indices 40
14 Original Weights Used in Georgia's Water Quality Index 40
15 Ranges of Variables for the Water Pollution Index Proposed in
Illinois by Barker and Kramer 44
16 Descriptors for the Pollution Index Proposed in Illinois by
Barker and Kramer 44
17 Some Desirable Criteria for a Water Quality Index Suggested by
Schaeffer and Janardan 50
Vlll
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Number Page
18 Subindex Equations Used in Nevada's Water Quality Index .... 51
19 Oregon's Evaluation of 12 Water Quality Indices According to
CEQ Criteria 53
20 Weighting Factors Used in Oregon's Water Quality Index .... 54
21 Variable Groupings Used in Region VIII Water Quality
Index 56
22 Descriptive Categories Used for Reporting the Region VIII
Water Quality Index 58
23 Status of Water Quality Index Utilization in the United States,
March 1977 64
IX
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ACKNOWLEDGMENTS
Grateful appreciation is extended to Gary C. Thorn, for his assistance
in gathering information from water pollution control agencies, to
Irene Kiefer for editorial assistance, and to Gladys Bennie for typing the
final version of this report. Appreciation also is extended to James Ingram
for his art work and to John Holman and Company for composition of the tabular
information. Special thanks is extended to the technical reviewers of this
manuscript for their many thoughtful and excellent comments. The list of
reviewers includes Frederick Leutner, William Sayers, Lance Wallace,
Cornelius Weber, Ralph Harkins, Jurate Landwehr, John Ficke,
David Schaeffer, David Dunnette, Rolf Deininger, and James Reisa.6
Affiliations:
^.S. Environmental Protection Agency
2U.S. Geological Survey
3 Illinois Environmental Protection Agency
^Oregon Department of Environmental Quality
5University of Michigan
6 Council on Environmental Quality
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I. INTRODUCTION
In January 1959, the Committee on National Water Policy of the Conference
of State Sanitary Engineers (CSSE) proposed that a study be carried out to
develop a uniform indicator for reporting information on water quality. As a
result of this action, the CSSE Committee and the Conference of State and
Interstate Water Pollution Control Administrators (CSIWPCA) began developing
criteria for demonstrating the progress of water pollution control programs;
however, no further results emerged from this effort.1
In 1965, the Environmental Pollution Panel of the President's Science
Advisory Committee made the following recommendation:
We recommend that the Federal Government stimulate
development of a method for assigning a numerical
index of chemical pollution to water samples. The
method should be sensitive to most chemical pollutants,
and its results should be roughly proportional to the
unfavorable effects of the pollution on man or aquatic
life. Such an index will allow us to follow many
important changes in general water quality in a way
similar to that in which the coliform count has enabled
us to follow changes in pollution by untreated sewage.2
In that same year, Horton3 published a simple water quality index*
which he developed in conjunction with his activities with the Ohio River
Valley Water Sanitation Commission (ORSANCO). A great many different water
quality indices have appeared in the literature since that time. Among the
best known is the Water Quality Index (WQI) developed by the National
Sanitation Foundation (NSF) and originally proposed in 1970.^
Progress in developing and applying water quality indices generally has
paralleled similar efforts in air pollution. In air pollution, indices are
used to report air quality levels to the public on a daily basis in most
major U.S. cities. In May 1974, Thorn and Ott5 began a national survey of the
air pollution indices currently in existence, ultimately resulting in
publication of a compendium documenting the diversity of air pollution index
systems currently in use. The findings of this compendium contributed to a
decision by the U.S. Environmental Protection Agency (EPA) to recommend, in
conjunction with other Federal agencies, a nationally uniform air pollution
index, the Pollutant Standards Index (PSI), for reporting air quality levels
to the public on a daily basis.
*For purposes of this study, a "water quality index" was defined as any
mathematical approach which aggregates data on two or more water quality
variables to produce a single number.
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Although a uniform air pollution index has been recommended by the
Federal Government for voluntary use by State and local governments, similar
steps have not been taken in the water pollution area. One possible reason
is that the need to report water quality information to the public on a daily
or weekly basis may be less pressing than in the case of air pollution
information. In addition, the user community for a water pollution index
seems somewhat less clearly defined than in the case of the air pollution
index. The present study also reveals a somewhat greater uniformity in the
selection of water quality indices by environmental agencies than was true
for air pollution indices.
Another important difference between the data analysis activities of air
pollution control agencies and those of water pollution control agencies
stems from existing legislation. Section 305(b) of the Federal Water
Pollution Control Act Amendments of 19726 requires each State to prepare a.
report describing its water quality on an annual basis and to submit this
report to the EPA Administrator. In turn, the Administrator analyzes this
information and prepares a summary report. These Section 305(b) reports from
the States, with EPA's summary report, then are transmitted to Congress. Each
report includes a "... description of the water quality of all navigable waters
in such State during the preceding year, with appropriate supplemental
descriptions as shall be required to take into account seasonal, tidal, and
other variations ...."6 This information provides a yearly overview of
water quality trends throughout the Nation, and the impact of regulatory
activities upon water quality. Although EPA prepares annual trend reports
for air pollution, the States do not prepare individual air pollution reports
similar to the Section 305(b) water quality reports.
Despite the various air and water pollution indices that, have been
developed and published in the literature, a 1975 report by the National
Academy of Sciences (NAS) concluded that the Federal Government has made
insufficient progress in developing and utilizing environmental indices:
Environmental indices provide an important method for
evaluating the state of the environment. Despite
strong statements of need from all three branches of
Government, progress toward the development and use of
methods for evaluating environmental quality has not
been satisfactory.7
Specifically, the NAS report recommended development of a uniform air
pollution index, which has since been adopted by EPA, and increased emphasis
on development of water quality indices:
There have been fewer attempts to construct water
quality indices than air quality indices, despite the
importance of the Nation's water pollution control
program. There appear to be no insurmountable
obstacles to development of useful water quality
indices and the Committee recommends their prompt
construction and use.7
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In the past 2 years, considerable interest has focused on water quality
indices at the Federal level. The Council on Environmental Quality (CEQ), in
cooperation with the EPA and the U.S. Geological Survey (USGS), undertook an
extensive review of all the water pollution indices which had been
developed.8"11 This review included both indices reported in the literature
and those developed by EPA and other organizations. The study included a
computer comparison of the performance of a number of these indices on water
quality data.
Although the CEQ-EPA-USGS study provided a useful discussion of the
state-of-the-art for water pollution index development, it did not examine the
actual applications of these indices in the field. Who are the users of
water pollution indices? What indices are being used? What are they being
used for? What future applications will be undertaken? Is there a tendency
toward increased use of indices? What action, if any, should EPA take in
this area?
The present study was undertaken to answer these questions. Planning
for this study was coordinated with CEQ and with other interested organiza-
tional elements of EPA, such as the Monitoring and Data Support Division of
the Office of Water and Hazardous Materials. The study consists of a survey
of State water pollution control agencies, interstate water pollution control
commissions, and the EPA Regional Offices. The survey sought to determine:
(1) which agencies are using water indices, (2) the type of index being
used, (3) the purpose of its use, and (4) the attitudes of the agency
personnel toward indices. The survey was carried out by telephone calls to
individuals within each agency likely to be familiar with the agency's use
of indices.
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II. LITERATURE REVIEW
The first review of the literature on published water quality indices
appears in a doctoral thesis by Landwehr. The four-volume CEQ-EPA-USGS
study gives independent reviews of the literature on water quality indices in
Volume I8 and Volume II.9 Some of the material also appears in a recent
paper by Orlando, Wrightington, and Maxim.13 A book currently in preparation
by Ott11+ contains an extremely detailed literature review of this topic.
This chapter is intended, therefore, to provide only a brief overview of the
literature published on this topic. The primary emphasis is upon indices
that can be used with data on physical and chemical variables routinely
collected by water quality monitoring activities.
PHYSICAL AND CHEMICAL WATER QUALITY INDICES
The author has found it possible to classify the indices in the litera-
ture into four general categories: (1) indices of general water quality,
(2) indices for specific water uses, (3) indices for planning, and (4) statis-
tical approaches.
Indices of General Water Quality
Horton's index,3 published in 1965, uses 10 variables,* including
commonly monitored ones such as dissolved oxygen (DO), coliform count, pH,
specific conductance, alkalinity, chloride content, and temperature. Carbon
chloroform extract (CCE) is included to take into account the influence of
organic matter, and a unique variable, "percent of the population served" by
sewage treatment plants, is an attempt to assess the effectiveness of water
pollution abatement activities. Another unique variable, "obvious
pollution," is included to reflect the aesthetic characteristics of the
water. Horton's index is computed as the weighted sum of subindices. The
subindices are calculated using a table of specific subindex values
corresponding to ranges of each variable. Like many indices which came after
it, Horton's index ranges from 0 to 100, with "0" representing poor water
quality and "100" representing perfect water quality. It has a "decreasing
scale," because the index numbers decrease as pollution increases. With few
exceptions, the air pollution indices are just the opposite. They have
"increasing scales" in which the numbers increase as pollution increases.
In 1970, Brown, McClelland, Deininger, and Tozer* presented a water
quality index based upon a nationwide survey of water quality experts. In
*Although the water pollution community often uses the word "parameter ' to
denote a measured quantity, this usage is inconsistent with that found in
other scientific fields. To avoid confusion, we shall use the term
"variable" to denote any physical, chemical, or biological quantity.
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this work, which was supported by the NSF, a panel of 142 persons was polled
using mail questionnaires. In successive mailings, respondents were asked to
determine which variables should be included in a water quality index, the
importance (weighting) to be given to each variable, and the rating scales
(subindex relationships) to be used for each variable. In each successive
mailing, respondents were given a computer summary of the group responses and
were allowed to alter their replies. This approach, the Delphi technique
is intended to give greater convergence of opinion regarding the significance
of each variable for general water quality than would be possible without this
"feedback" of the group viewpoint. The resulting index, the National Sanita-
tion Foundation Index (NSFI), is based on 77 respondents who completed all
questionnaires. It includes nine variables: dissolved oxygen, fecal coliform,
pH, 5-day biological oxygen demand (BOD5), nitrates, phosphates, temperature
(i.e., deviation from equilibrium temperature), turbidity, and total solids.
One version of the NSFI, the sum (or additive) form is computed as the
weighted sum of nine subindices, each of which is read from a graph. In
another version, the product (or multiplicative) form, the weights are treated
as exponents of the subindices, and results are multiplied together. Toxic
substances and pesticides are included in both versions by setting the index
to zero whenever any of these substances exceeds its recommended limit.
McClelland16 applied the NSFI to water quality data in the Kansas River Basin.
With support from EPA's Region VII, the NSFI also has been applied in a
number of other geographical areas of the Nation.
In 1970, an index based on the water quality classification systems used
in a number of countries was proposed by Prati, Pavanello, and Pesarin."17 The
systems considered include ones from England, Germany, the Soviet Union,
Czechoslovakia, New Zealand, Poland, and some States of the United States. The
index includes 13 variables and is computed as the arithmetic mean of 13
subindices. Unlike the NSFI, which uses graphical subindex rating functions,
the index proposed by Prati et al.17 uses mathematical equations for each
subindex. Unlike Morton's index and the NSFI, it has an increasing scale and
ranges from "0", corresponding to good water quality (no pollution), to "15"
or more, corresponding to poor water quality.
McDuffie and HaneylS proposed an eight-variable water quality index, the
River Pollution Index (RPI), which has an increasing scale and is based on
the ratio of the observed value of each variable to its "natural" value. The
RPI varies from 100 ("natural" levels) to 1,000 ("highly polluted" levels).
The index can go below 100, making its overall range 0-1,000. The RPI was
applied on a test basis to stations on streams in New York State.
In 1972, Dinius proposed a water quality index as part of a larger
social accounting system designed to evaluate water pollution control
expenditures. This index includes 11 variables, and, like Prati's index, uses
explicit mathematical equations for the subindex functions. Like the NSFI, it
has a scale which decreases with increased pollution, ranging from 0 to 100.
The index is computed as the weighted sum of its subindices.
The indices discussed thus far assume that "general water quality" is a
concept which can be reported by a single numerical index, irrespective of
the use for which the water is intended. Many critics of indices designed to
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report general water quality argue that different variables must be weighted
differently if different water uses are to be taken into account. Dinius'
approach to the problem was to propose different descriptor language for
different index ranges, depending on the specific water use under considera-
tion (Figure 1).
PERCENT
M
H
7t
M
SB
W
M
21
11
1
PURIFI-
CATION
NOT
NECESSARY
MINOR
PURIFI-
CATION
REQUIRED
NECESSARY
TREATMENT
BECOMING
MORE
EXTENSIVE
DOUBTFUL
N
0
T
A
C
C
E
P
T
A
B
L
E
ACCEPT-
ABLE
FOR
ALL
WATER
SPORTS
BECOMING
POLLUTED
STILL
ACCEPT-
ABLE
BACTERIA
COUNT
DOUBTFUL
FOR
WATER
CONTACT
ONLY
BOATING
NO WATER
CONTACT
OBVIOUS
POLLUTION
APPEARING
OBVIOUS
POLLUTION
NOT
ACCEPT-
ABLE
ACCEPT
ABLE
FOR
ALL
FISH
MARGINAL
FOR
TROUT
DOUBTFUL
FOR
SENSITIVE
FISH
HAROY
FISH
ONLY
COARSE
FISH
ONLY
N
0
T
A
C
C
E
P
T
A
B
L
E
PURIFI-
CATION
NOT
NECESSARY
MINOR
PURIFI-
CATION
NECESSARY
FOR
INDUSTRY
REQUIRING
QUALITY
WATER
NO
TREATMENT
NECESSARY
FOR
NORMAL
INDUSTRY
EXTENSIVE
TREATMENT
FOR
MOST
INDUSTRY
ROUGH
INDUSTRY
USE
ONLY
NOT
ACCEPT-
ABLE
t
I
(
1
I
1
/
k
i
r
\
9
E
OBVIOUS
POLLUTION
APPEARING
OBVIOUS
POLLUTION
NOT
ACCEPT
ABLE
t
I
(
I
1
1
1
1
1
1
I
i
r
*
i
NOT
ACCEPT
ABLE
PUBLIC RECREATION FISH INDUSTRIAL NAVIGATION TREATED
WATER SHELLFISH AND WASTE
SUPPLY AND AGRI- TRANS
WILDLIFE CULTURAL PORTATION
FIGURE 1. DESCRIPTIVE LANGUAGE SUGGESTED BY DINIUS19 TO ENABLE A SINGLE
WATER QUALITY INDEX TO BE APPLIED TO DIFFERENT WATER USES.
Thus, 0 to 40 is designated as "not acceptable" if the water is to be used
for public water supplies, while Q to 20 is considered "not acceptable" if
the water is to be used for industry and agriculture.
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Indices for Specific Water Uses
Another approach for considering water uses is to develop specific-use
indices, or separate indices that are tailored to each water use. In 1971,
O'Connor2*^ developed two water quality indices, each designed for a very
different specific water use. One, the Fish and Wildlife index (FAWL), is
intended for water used to maintain fish and wildlife habitats; the other is
a Public Water Supply index (PWS). Each index was developed using the
Delphi technique in the same manner used by Brown et al.1*, but with a
much smaller panel of experts. O'Connor's purpose was to compare the
performance of the specific-use indices with each other and with the NSFI
using actual (and simulated) water quality data. He reasoned that if water
use is important enough to merit separate indices, then these two specific-use
indices should give very different results when applied to the same water
quality data. He found generally low correlations between the FAWL and the
PWS, but much higher correlations between either of these two specific-use
indices and NSFI. He concluded that FAWL and PWS may be reporting only a
subset of the information contained in NSFI. His finding apparently
strengthens the case both for specific-use indices and for general water
quality indices such as NSFI, since they serve different objectives.
n I
Deininger and Maciunas also have published a specific-use index for
public water supplies. It was developed by using the Delphi15 technique with
12 members of the original NSFI panel of 142. On the questionnaire, each
respondent was asked to keep in mind a "free flowing stream which will serve
as a source of raw water for a public water supply." Two basic index
structures were considered, a product form and a sum form; each has two
versions: an 11-variable version and a 13-variable version. The authors
compared the performance of these indices with the additive form of the NSFI
using actual water quality data. Even though the specific-use indices and
the nonspecific NSFI were developed from very different concepts, the authors
did not find marked differences between the two. They concluded that there
does not appear to be sufficient justification for developing specific-use
indices: "...Instead of developing a number of indices for the many water
uses, it appears more meaningful to further develop and refine a sensitive
and general water quality index."21
Comparing the weights of several of the (additive) specific-use-water
quality indices with NSFI reveals many differences (Table 1). However,
these weights generally lie in the range from 0.05 to 0.20, with most of
them close to 0.10 and more than half in the narrow range between 0.07 and
0.12.
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TABLE 1
COMPARISON OF WEIGHTS USED IN FIVE WATER QUALITY INDICES
Pollutant variable
Dissolved Oxygen
Fecal Coliform
pH
BOD5
Nitrates
Phosphates
Temperature
Turbidity
Total Solids
Phenols
Ammonia
Dissolved Solids
Color
Sulfates
Alkalinity
Hardness
Fluorides
Chlorides
Iron
Number of Variables
NSFI
(Brown et a/.4)
.17
.15
.12
.10
.10
.10
.10
.08
.08
9
FAWL
(O'Connor20)
.206
.142
.074
.064
.169
.088
.099
.084
.074
9
PWS
(O'Connor20)
.056
.171
.079
070
.058
.104
.084
.054
.050
.058
.077
.079
.060
13
PWS-1 1
(Deininger eta/.2 ' )
.06
.14
.08
.09
.10
.07
.09
.10
.10
.10
.08
11
PWS- 13
(Deininger et a/.2 ' )
.05
.12
.07
.08
.09
.06
.08
.08
.08
.08
.07
.07
.07
13
In 1974, Walski and Parker22 presented a water quality Lndex specifically
intended for recreational water use. The index includes 11 pollutant
variables grouped under four general headings (appearance; odor, and taste;
effect on aquatic life; and effect on health). The index, calculated as the
geometric mean of values obtained from subindex rating equations, varies from
0 (completely unacceptable water quality) to 1.0 (ideal water quality).
More recently, Stoner23 proposed a specific-use water quality index
designed to reflect two different water uses—public water supply and
irrigation—by changing the weights and equations embodied in the index.
This index incorporates recommended limits for certain toxic substances and
can vary from a large negative number (worst possible water quality) to 100
(best possible water quality). In general, the greater the negative number,
the higher the water treatment costs.
Nemerow and Sumitomo21* have proposed three specific-use water quality
indices which, when added together, give a general water quality index.
Their approach is unique in that each of the three specific-use indices
reflects both the mean value of its variables and the maximum value of any
variable. By this approach, the index reduces the tendency toward "eclipsing"
which Thorn and Ott5 discussed in connection with air pollution indices.
Eclipsing occurs when some event of importance occurs (such as violation of a
standard), but is not reflected in the overall index. The Nemerow and
Sumitomo index is an increasing scale form which varies from 0 (good water
quality) to values greater than 1.0, with 1.0 denoting pollution at the
recommended administrative limits.
-------
Indices for Planning
Another class of water quality indices is intended specifically for
administrative decision-making. These "planning indices" often incorporate
variables other than those routinely measured by water pollution monitoring
activities. The variables usually are suited to a particular decision under
consideration. For example, a planning index designed for allocating
pollution abatement funds might include factors such as the "number of people"
served by surface waters or the "cost of wastewater treatment."
Three different water quality indices proposed by Truett et al.25 are
intended for planning purposes. The first, the Prevalence Duration Intensity
Index (PDI) is computed as the product of three variables: (1) the number of
stream miles within an area which do not comply with established Federal or
State water quality standards (prevalence), (2) the number of quarter-year
periods for which violations of standards occur (duration), and (3) the
severity of pollution in terms of its effects on human welfare and ecology
(intensity). The second index, the National Planning Priorities Index,
is intended to help ensure that Federal funds for municipal wastewater
treatment projects are distributed in a cost-effective manner. It incorporates
the PDI in its formulation, but includes other factors such as the current
population of the area, the 1975-76 fiscal year investment, the "controlla-
bility" (a measure of the extent to which the pollution sources in the area
can be controlled), and per capita planning costs. The third index, the
Priority Action Index, is a simplified version of PDI. It incorporates
four components: the PDI, controllability, downstream affected population,
and current area pollution.
Dee et al.26 have proposed a general system for evaluating the impact of
large-scale water resource projects. Included in the system is a water
quality index which contains 12 water quality variables plus pesticides and
toxic substances. The overall system contains 78 variables, including such
factors as housing, land use, noise, and vegetation. Each variable is
represented in the system in Environmental Quality Units which vary from 0
(extremely poor quality) to 1 (extremely good quality). The sum of these 78
variables ranges from 0 to 1,000, with the water quality portions accounting
for about one-third of this total.
Inhaber27 proposed a water quality index intended as part of an overall
environmental quality index. The index combines 2 subindices: overall
effluent loading and ambient water quality. The overall effluent loading
subindex includes effluent data from five sources (municipal wastes and the
petroleum refining, chlor-alkali, fish-processing, and paper industries).
The ambient water quality subindex includes turbidity, trace metals (cadmium,
chromium, lithium, copper, and zinc), fish catch, and the mercury content of
fish. Although this index originally was intended for use as a Canadian
National Index, there is no evidence that it has been routinely applied in
Canada.
The Pollution Potential Index, developed by Zoeteman28 in 1973, is a
planning index designed to relate changes in river water quality to the human
activity responsible for these changes. It consists of the product of the
-------
number of people living in a drainage basin and the per capita Gross National
Product, divided by the average flow rate of the river. This index was
applied by the author to data on 160 river sites throughout the world.
Johanson and Johnson29 have developed a planning index specifically
designed for evaluating data on toxic pollutants built up in the sediments of
the U.S. ports, harbors, and waterways. The index was used to screen 652
data sets from locations throughout the United States to establish priorities
for removal or inactivation of these "in-place" pollutants, in accordance
with Section 115 of the Federal Water Pollution Control Act Amendments. The
index consists of the sum of the weighted maximum concentration of each toxic
pollutant.
Statistical Approaches
In addition to the above indices, a number of statistical approaches
have been suggested for evaluating water quality data. These approaches
usually employ some standard statistical procedures already available in the
literature. They have the advantage that they incorporate fewer subjective
assumptions, but the disadvantage that they are sometimes difficult to apply
and must be tailored to the data at hand.
One class of statistical approaches, correlation techniques, examines
the associations among variables to determine the importance of each as a
determinant of water quality. Shoji, Yamamoto, and Nakamura30 applied
"factor analysis" to the Yodo River System in Japan to examine the inter-
relationships among 20 variables. By comparing the correlation of each
variable, and selecting those variables with the highest correlations, they
identified three major factors: pollution, temperature, and rainfall. From
this procedure, the investigators also determined the weights for an
18-variable Composite Pollution Index which they applied to data from
each station on the Yodo River System.
In another correlation study, Coughlin, Hammer, Dickert, and Sheldon31
examined the relationship between a water quality index and the perception
and use of a stream made by nearby residents. The investigators used
"principal component analysis" to examine the relationships among individual
NSFI variables and such factors as distance of residence from the stream,
land values, and the tendency of residents to walk along the stream or to
wade or fish in it.
Another statistical approach involves ranking of water quality data. In
1974, Harkins32 proposed that a ranking approach originally suggested by
Kendall33 could be used to evaluate water quality data in a more objective
fashion than is possible with NSFI. In Harkins' approach, the values of each
variable are first ranked in decreasing order of magnitude. Then the rank
order numbers which result are used to calculate the index. A standard
transform based on the square of the difference between a control value and
the rank order number then is calculated. An index value for each group of
samples then is obtained by summing the transforms for the variables compris-
ing the group. This approach is "nonparametric"; the nature of underlying
probability distribution of the data does not affect any probability
10
-------
statements that might be derived from the results. However, because the index
is based on ranking of the values within a particular data set, the index
number generated from one data set cannot be directly compared with those
generated by a different data set.
Schaeffer and Janardan34 have extended Harkins1 approach by taking
advantage of the nonparametric nature of the ranked data. They observe that
the square root of the transform used in Harkins' index is normally distribu-
ted. Therefore, the transform itself is the square of a normally distributed
random variable and has a chi-square distribution. Using this argument, they
form an additional transform which has a beta distribution. Then they use
this transform to create an increasing scale index which varies from 0 to 1.
They examine the statistical properties of this index by means of simulation
and apply it to water quality data from the State of Illinois. They also
compare the index result with a biological water quality classification
system and find relatively good agreement.34 Unlike Harkins' approach, the
index numbers generated by this index can be compared with those generated
from a different data set.
Comparing the indices discussed shows a great many differences in the
number of variables, scales, and ranges (Table 2). The number of water
quality variables included in the 5 general and 6 snecific-use indices shown
ranges from 9 to 31. Most indices in these two groups (9 out of 11) have
decreasing scales, and the majority (6 out of 11) have ranges from 0 to 100.
Others have ranges of 0 to 1, 0 to 15, 0 to 1,000; and one can be negative.
When the seven planning indices and four statistical approaches are considered,
the variety among the different index types becomes much greater. Most of the
planning indices have increasing scales, and, by contrast, few have ranges
from 0 to 100. The overall picture that emerges is one of a great variety of
water quality indices, each structurally quite distinct and each having a
different interpretation.
Most of the above indices were designed for application to data from
free-flowing surface waters. However, special problems of eutrophication
(excessive plant and algal growth) can occur in nonflowing water bodies,
particularly in lakes. The National Eutrophication Survey carried out by EPA
in 197435 collected extensive data on the eutrophic conditions of over 800
U.S. lakes. Various statistical approaches were used to examine the relation-
ships among physical, chemical, and biological variables as indicators of
eutrophication, and these results were compared with field observations and
professional judgment of the condition of the surveyed lakes. As part of this
effort, EPA also developed a Trophic Index to rank the trophic condition of
lakes using six measures: total phosphorus, dissolved phosphorus, inorganic
nitrogen, Secchi disc, minimum dissolved oxygen, and chlorophyll-a. For the
lakes surveyed, EPA was able to relate index ranges to three trophic states
(oligotrophic, mesotrophic, and eutrophic).35
BIOLOGICAL WATER QUALITY INDICES
Although the principal emphasis of this report is on physical and chem-
ical water quality indices, many biological indices of water quality also
have been developed. In these systems, water quality is evaluated in terms
of its impact on aquatic life in some form. Three basic approaches have been
developed.
11
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TABLE 2
OVERALL CHARACTERISTICS OF WATER QUALITY INDICES PUBLISHED IN THE LITERATURE
Index Name3
Indices of General Water Quality
Quality Index
Water Quality Index
Implicit Index of Pollution
River Pollution Index
Social Accounting System
Indices for Specific Water Uses
Fish and Wildlife Index
Public Water Supply Index
Index for public water supply
Index for recreation
Index for dual uses
Index for three uses
Indices for Planning
Prevalence Duration Intensity Index
National Planning Priorities Index
Priority Action Index
Environmental Evaluation System
Canadian National Index
Potential Pollution Index
Pollution Index
Statistical Approaches
Composite Pollution Index
Principal Component Analysis
Kendall's ranking approach
Beta function index
Reference
Horton3
Brown eta/.4
Prati ef a/. ' 7
McDuffieef a/."
Dinius' '
O'Connor20
O'Connor20
Demmger ef a/. 2 '
Wai ski eta/.22
Stoner23
Nemerowet a/. 24
Truett ef a/. J5
Truett et al. 2 s
Truett ef a/.25
Dee eta/.26
Inhaber27
Zoeteman2 8
Johanson eta/.29
Shojiefa/.30
Coughlin et al.3 '
Harkins32
Schaefferef a/.14
No. of
Variables
10
9
13
8
11
9
13
11/13
12
31
14
d
d
d
78e
d
3
d
18
d
d
d
Scaleb
Decreasing
Decreasing
Increasing
Increasing
Decreasing
Decreasing
Decreasing
Decreasing
Decreasing
Decreasing
Increasing
Increasing
Increasing
Increasing
Decreasing
Increasing
Increasing
Increasing
Increasing
ISIA
Increasing
Increasing
Range
0 to 1 00
Oto 100
0 to 15+
Oto 1000
Oto 100
0 to 1 00
Oto 100
Oto 100
Oto 1
-100 to 100°
0 to 1 +
Oto 1
Oto 1
Oto 1
Oto 1000
Oto 1
0 to 1 000+
0 to 1 00+
-2 to 2
NA
0 to 100+
Oto 1
aWhere proper name for index is unavailable, index characteristic is listed.
^Increasing scale: index numbers increase with degree of pollution. Decreasing scale: index numbers
decrease with degree of pollution.
clndex can be less than -100 and can become a large negative number.
dAny number of variables can be included.
"Water quality variables account for 14 of the 78 variables used in this system
NA = not applicable.
The first approach focuses on the types and quantities of certain
organisms (indicator organisms) observed in the water. A simple example is
enteric bacteria such as fecal coliforms that are normal inhabitants of the
digestive tract of man and other warm-blooded animals. The presence of these
indicator organisms usually is taken as evidence of contamination with fecal
material. Another example consists of the saprobic classification systems
employed in environments rich in degradable organic matter. The saprobic
systems divide a stream into various zones of pollution depending principally
on the type of organisms present. The various saprobic systems that have been
developed are summarized by Orlando and Wrightington.9
The second approach concentrates on the mathematical properties of the
populations of organisms. For example, some techniques use information theory
12
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to describe the diversity of species within the community. Other species
diversity techniques employ various probabilistic models in their formulation.
Orlando and Wrightington9 observe that the theoretical development of some
species diversity indices seems far more advanced than their practical appli-
cation:
It must be stressed that the above mathematical
diversity index is highly theoretical and conceptual
even though Pielou applied it to communities of forest
trees. Whether or not some practical and useful infor-
mation can be generated from actual sampling of aquatic
environments remains to be seen. Any values developed
from the information-theory-based diversity index
should be correlated with some physical-chemical
measurements of water pollution to be useful as water
quality indicators.
The third biological approach examines biological responses such as the
physiological or behavioral changes of certain organisms as a result of
pollution. For example, pesticides are known to inhibit acetylcholinesterase
activity in the brains of fish, and fish-brain cholinesterase activity has
been used as a monitor for pesticide pollution. Behavioral changes of certain
species, such an increased activity and agitation of fish in response to toxic
substances, also have been studied as an indicator of environmental pollution.
One obvious biological indicator is the incidence of fish kills.36
Biological measures of pollution have the advantage that they have a
"pollution integrating" effect. Fish and other organisms tend to respond to
the entire historical record of water quality. Thus, if some toxic substances
are present on rare occasions and go undetected in routine water quality
monitoring activities, the presence of these pollutants would still be
reflected in terms of their effects on aquatic organisms. Orlando and
Wrightington observe that this integrating feature enables biological organ-
isms to monitor a number of pollutants at once:
Aquatic organisms respond to a number of chemical,
physical, and biological water quality variables in an
integrated manner. Thus, one or a few organisms can
do the work of several analysts in terms of demonstra-
ting that a large number of variables either are or are
not within the range of tolerance of aquatic life,
although they do not give specific numerical values for
each of the variables. A number of different industries
routinely pass their effluents through a fish pond
before discharge to demonstrate that the effluent is not
toxic to fish. Of course, by using tolerant species
such as goldfish or carp it is possible to greatly
reduce the chance that toxicity would be demonstrated.
In the past, data on biological measures of water quality have not been
collected as routinely as data on physical and chemical variables. However,
biological monitoring activities are expected to receive greater emphasis in
13
-------
the next few years. This survey is limited primarily to physical and chemical
water quality indices.
DISCUSSION
From the above literature review, it is clear that a great variety of
water quality indices have been published. These indices differ from each
other in terms of their fundamental structures and in terms of the number and
types of variables that have been selected for inclusion. Why have so many
different indices been developed? Is there evidence of an evolutionary
process that is moving toward a single preferred index structure for the
analysis of water quality data?
Scientific inquiry and development of scientific knowledge normally follow
a systematic pattern in which each study builds upon the knowledge gained in
the previous investigation. Usually each investigator begins by reviewing all
of the work of previous investigators to determine how to structure his own
study so that it will make a maximum contribution to knowledge. This process
helps assure that each study will tend to advance scientific knowledge in a
particular topic area.
However, the many water quality indices that have been developed in the
decade 1965-1975 give little evidence of the normal evolution that one would
expect to find in scientific inquiry. Rather, each index seems to emerge
"full blown" from the literature. Indeed, some of the authors do not cite the
work of previous authors, nor do they seem acquainted with other efforts in
this field. Thus, after reviewing the literature, one is left with the
impression that the authors seldom provide a sense of what has gone before.
What role does their index play in the scientific literature? What problem
does it solve that other indices before it have failed to solve?
The possible two exceptions to the above rule are the NSFI and the Harkins'
index. The NSFI was the first index to employ a systematic opinion research
procedure in its development. Follow-up studies by O'Connor20 and Landwehr12
have sought to answer additional questions of importance regarding character-
istics of NSFI, and a number of case studies have been carried out using this
index.16 Thus, an evolutionary process has occurred in this case. Harkins'
index32 also has evolved further in work carried out by Schaeffer and
Janardan.31* Except for these two cases, a proliferation of water quality
indices has occurred, each differing from the next, and each showing little
relationship to the one before it.
14
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III. SURVEY DESIGN
Our review of the literature indicates that the published articles
provide relatively little information about the routine use of indices by
water pollution control agencies. To learn which water pollution indices are
in common use and to gain insight into the experiences of water pollution
control agencies with these indices, an in-depth survey of these agencies was
necessary. In this survey, agencies throughout the United States were tele-
phoned and asked to provide information describing their experiences with
indices, if any. The data base in this investigation was assembled from notes
taken during the telephone conversations, from written materials received from
the agencies, and from the 1976 Section 305(b) reports from the States.
SURVEY POPULATION
The population surveyed in this investigation included: the 50 State
water pollution control agencies; the 9 interstate agencies having responsi-
bilities in the area of water quality; and the 10 EPA Regional Offices.
Information regarding the individual contact point in each agency was obtained
from several sources: The "1976 Environmental Program Administrators,"37 the
"Directory of State Agencies Engaged in Environmental Monitoring,"38 the
"Directory of Regional Water Pollution Control Agencies" published by
Water and Sewage Works,3 9 and a listing of the EPA Regional Office coordinators
for the Section 305(b) reports. Occasional difficulty was encountered in
identifying the individual within an agency who was knowledgeable about water
quality indices. However, in the State agencies, the proper individual was
usually involved in compilation of the State's Section 305(b) report; in the
EPA Regional Offices, the Section 305(b) report coordinator was contacted.
The smaller size of the interstate commissions facilitated contacting the
single individual who was familiar with water quality indices and data analy-
sis procedures.
Selection of the person "most knowledgeable" about an agency's use of
indices may have biased the survey so that it reflected less the view of
higher level managers and more the view of technical experts within the
agency. The bias appears to be inherent to the telephone survey approach.
Future surveys might utilize mail questionnaires so that the "official
position" of the agency may be ascertained more readily.
SURVEY APPROACH
The first step in assembling the type and quantity of information neces-
sary for this study was to develop a telephone survey data sheet
(Appendix F). Because there was considerable variation in the nature of the
questions asked during the interviews, the data sheet served only as a
guide. This was due partly to the wide range of respondents' experience and
15
-------
knowledge regarding water quality indices. In addition, as the survey pro-
gressed, the author learned more about which questions on the data sheet
obtained the greatest amount of information and what additional questions
were required to clarify particular points. In general, all respondents were
asked whether they used an index, and, if so, what type, how it was calculated,
its purpose, and its usefulness.
Telephone calls were made to the various agencies in the survey population
from October 1976 to February 1977. If an agency used an index or had evalua-
ted or developed one, the respondent was asked to supply information about the
index. All agencies also were asked what they felt the Federal Government
should be doing in the area of water quality indices and if they favored
development of a federally recommended water quality index. The responses
received to these and other questions form the basis for the brief comments
given in the tables in the next chapter. All comments are summarized in
Appendices A and B.
CLASSIFICATION OF NONUSER AND USER AGENCIES
Two definitions were used in classifying the agencies surveyed in this
study:
Nonuser Agency
Nonuser agencies were divided into four general categories: (1) agencies
unfamiliar with indices, (2) agencies that had considered or evaluated indices,
(3) agencies planning to evaluate or develop indices, or (4) agencies currently
evaluating or developing indices. Thus, the second category included those
agencies that had decided not to use an index after they had either briefly
considered various indices or had conducted a rather extensive evaluation to
determine their applicability to the agency's particular need. Agencies in
the third category were planning either to evaluate or to develop an index in
the near future; thus, this group includes "potential" index users. Agencies
in the fourth category are also potential index users, because, at the time of
this study, they were in the process of evaluating or developing an index for
use in the near future.
User Agency
To be classified as an "index user," the agency must have used an index
in an official capacity over an extended time period. Furthermore, the index
must have appeared in an official publication of the agency (for example, the
Section 305(b) report, State annual water quality report, or water quality
trends report) or be applied in a large-scale water quality study extending
over a year or more. However, if an agency had only carried out a small-
scale pilot project designed to test an index, it would not be classified as
an index user; rather, the agency would be considered an "index evaluator."
16
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IV. SURVEY RESULTS
A majority of the information gathered in this study was recorded on the
index questionnaire forms used during the telephone interviews; additional
information was obtained from material mailed on request. In either case,
this information has provided the basis for the following discussion of survey
results. This discussion is divided into two sections, nonuser and user
agencies, based on the definitions in the previous chapter. Tables 3 and 4
give the current status of water quality index utilization in the States, the
District of Columbia, and nine interstate commissions. Table 5 gives a summary
of index utilization of both of these groups. Comments from the index nonuser
and user community are recorded in Appendices A and B, respectively.
AGENCIES CURRENTLY NOT USING INDICES
Based on the comments received from the survey respondents, nonuser
agencies were divided into four categories. These categories were chosen to
form a continuum, beginning with agencies least familiar with indices and
ending with those most familiar, namely, agencies currently evaluating or
developing indices. Agencies in each of these categories are discussed in the
following sections. Comments from these agencies are summarized in Tables
6-8.
Agencies Unfamiliar With Indices
Respondents from 11 State agencies and 2 interstate commissions
indicated that they were, to a varying degree, unfamiliar with water quality
indices (Table 5). Actually, respondents from 7 of the 11 States and both of
the interstate commissions indicated that they were totally unfamiliar with
indices and/or their application to interpretation of water quality data.
Although respondents from two States were not familiar with either NSFI or the
Harkins-type index, they were acquainted with or had used one of the biological
indices.* Finally, the two other States simply stated that they were unfamil-
iar with water quality indices because they were opposed to use of any
qualitative or generalized techniques (for example, indices) for interpreting
water quality data.
Agencies That Have Previously Considered or Evaluated Indices
Most of the 18 agencies that have previously considered or evaluated
indices had unfavorable views toward indices. As can be seen by examining the
abbreviated comments from these agencies (Table 6), 10 of the 14 agencies felt
that indices were not really a very useful tool for presenting water
*For more information on biological indices, see Reference 9.
17
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TABLES
STATUS OF WATER QUALITY INDEX UTILIZATION BY STATES
Agency
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
District of Columbia
Florida
Georgia
Hawaii
Idaho
Illinois
1 ndiand
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Index Nonuser
Unfamiliar
with Indices
•
•
•
•
•
•
•
•
•
•
•
Considered
or Evaluated
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Planning to
Evaluate or
Develop
•
•
•
•
•
•
•
•
•
•
Currently
Evaluating
or Developing
•
•
•
•
•
•
Index
User
•
•
•
•
•
•
•
•
•
•
18
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TABLE 4
STATUS OF WATER QUALITY INDEX
UTILIZATION BY INTERSTATE COMMISSIONS
Commission
Delaware River Basin
Great Lakes
International Joint
Interstate (CN, NJ, NY)
Klamath River
New England Interstate
Ohio River
Potomac River Basin
Susquehanna River Basin
Index Nonuser
Unfamiliar
with Indices
•
•
Considered
or Evaluated
•
•
•
•
Planning to
Evaluate or
Develop
Currently
Evaluating
or Developing
•
Index
User
•
•
TABLE 5
SUMMARY OF WATER QUALITY INDEX UTILIZATION BY STATES
AND INTERSTATE COMMISSIONS
States
Commissions
Total
Index Nonusers
Unfamiliar
with Indices
11
2
13
Considered
or Evaluated
14
4
18
Planning to
Evaluate or
Develop
10
0
10
Currently
Evaluating or
Developing
6
1
7
Index
Users
10
2
12
Total
51
9
60
19
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TABLE 6
NONUSERS WHO HAVE PREVIOUSLY CONSIDERED OR EVALUATED INDICES
Agency
Alaska
California
Delaware
Florida
Hawaii
Maine
Massachusetts
Minnesota
New Hampshire
New Mexico
Pennsylvania
Texas
Utah
Washington
Index
-
NSFI
NSFI,
Harkins
Biological
Biological
-
-
NSFI
-
NSFI,
Harkins
NSFI,
Harkins
Harkins
NSFI
-
Comments
Insufficient data.
Indices very difficult to apply generally; we have a particular problem with
interface which indices cannot handle.
Used to calculate eutrophication index for lakes.
Used to indicate safety of public bathing areas.
Skeptical about applicability and understandability of indices.
Individual variables are satisfactory for our purposes.
tidal/fresh water
NSFI was not adequate for Section 305(b) report so individual variables are used.
Don't have a need for an index— it would just add another level of confusion
necessary.
None of the indices which have been developed are useful here because of high
levels.
Indices don't cover "special" situations; one really needs different indices
chemical and physical variables.
Water quality can be described more accurately without indices.
that is really not
stream sediment
for the different
Although there is some possibility of using an index in the future, we feel that indices in
general do not represent water quality; at the present time we don't have data on all nine NSFI
variables.
Evaluated several indices and found that, in general, they did not reflect the
water quality for our situation.
actual changes in
quality data. Several agencies felt that water quality could be described
more accurately without indices; others stated that indices would either
confuse the picture of water quality or would not be understood by the layman.
Similar comments were received from the interstate commissions, as seen
in Appendix A. The comments from the New York Interstate Commission generally
expressed the feelings of this group:
One is limited only by his ingenuity in the number
of ways the various water quality variables can be
put together. Thus, one comes up with a different
index number depending on the index used and what
weights are assigned to the variables. Although
the idea of a water quality index is great, water
quality indices oversimplify the picture of water
quality, and tend to get misused.
20
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Agencies Planning To Evaluate or Develop Indices
Of the 10 agencies planning to evaluate or develop indices (Table 5), 8
are including the NSFI in their plans for evaluation or development of a water
quality index (Table 7). In addition, most of the States indicated that one
of the major uses of the index would be in the Section 305(b) report. Since
these agencies were in a learning stage about indices, they yielded very little
other information. Consequently, it would be of interest to interview these
agencies again in the future to determine the status of their index evaluation
efforts or index development activities.
Agencies Currently Evaluating or Developing Indices
In mid-1977, six State agencies and one interstate commission were
evaluating or developing an index for possible use by their agencies (Table 8).
In most cases, these agencies planned to use the index in the State's Section
305(b) report. Four of the six State agencies were adapting the NSFI to fit
their particular data bases, and one, Nevada, was developing its own index.
Maryland, which has evaluated both the NSFI and the Harkins' index, was
developing a modified biological species diversity index instead of using one
of the existing water quality indices. Their reason for selecting this type of
index is their belief that biological communities provide a more valid measure
of water quality:
We feel that since aquatic species are subjected to
water pollution and tend to integrate effects over
time, biological indices are more descriptive of
water quality than chemical variables, which
give instantaneous values that are not necessarily
valid for a whole stream and do not reflect long-
term pollution. Furthermore, the layman does not
understand the significance of the various concentra-
tions of chemical variables and the statistical
methods used in computing a water quality index from
them. However, the average citizen can easily comprehend
the relationship between water quality and the type of
stream life.
AGENCIES CURRENTLY USING INDICES
To be classified as an index user, an agency must have used an index in a
large-scale water quality study extending over a year or more, or it must have
used one in an official agency publication.
Indices in Current Use
Of the 51 SJv3te agencies (including the District of Columbia) and 9
interstate agencies, 12 agencies (20 percent) have used a water quality index
(Table 9). However, one, the Interstate Commission on the Potomac River, used
an index in just one report and no longer can be classified as an index user.
Thus, a total of 11 agencies (18 percent of the State and interstate agencies)
is currently using a water quality index.
21
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TABLE 7
NONUSERS WHO ARE PLANNING TO EVALUATE OR DEVELOP INDICES
Agency
Index
Comments
Idaho
Iowa
Kentucky
Louisiana
Nebraska
North Dakota
Ohio
Rhode Island
South Dakota
Vermont
NSFI
NSFI
NSFI
NSFI
NSFI
NSFI
NSFI
NSFI
Planning to use a system similar to Region X water quality profiles.
Considering use as an indicator of water quality improvement.
Anticipate development of index within a year for use in Section 305(b) report.
Will develop index with fewer variables than NSFI for use in Section 305(b) report.
Want to develop for use in Section 305(b) report.
Now looking into possibility of using an index in the future.
Would like to use an index in our monthly water quality report.
Now in the process of looking into NSFI and other indices for possible use in the future.
Now looking at the possible use of NSFI in the future.
Will be using an unmodified NSFI in the 1977 Section 305(b) report.
TABLE 8
NONUSERS WHO ARE CURRENTLY EVALUATING OR DEVELOPING INDICES
Agency
Kansas
Maryland
Nevada
New Jersey
South Carolina
Wisconsin
Ohio Interstate
Index
NSFI
NSFI.
Harkins
-
NSFI
NSFI
NSFI
NSFI
Comments
Modified NSFI under development for use in Section 305(b) report.
Biological species diversity index now under development.
Fifteen variable "Combined Water Pollution Index" being evaluated.
Developing modified NSFI for use in Section 305(b) report and as a public information tool.
Developing modified NSFI for use in Section 305(b) report.
Developing modified NSFI for use in Section 305(b) report.
Evaluating NSFI for possible routine use.
22
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TABLES
AGENCIES USING WATER QUALITY INDICES, JUNE 1977
Agency
Colorado
Georgia
Illinois
Indiana
Michigan
Montana
New York
Oklahoma
Oregon
Wyoming
New England
Interstate
Potomac River
I nterstate
Index
Modified NSFI
Developed own index
Developed own index
Modified NSFI
Modified NSFI
Standard NSFI
Standard NSFI
Harkms' index
Developed own index
Modified NSFI
Standard NSFI
Harkins' index
Characteristics
8 variables (temperature deleted) ,
additive form.
8 variables Geometric mean of 8
submdices, with each subtndex
weighted according to its rank order
Rating curves similar to NSFI were
developed
Several indices developed by differ-
ent state agencies. One index includes
6 variables, and values 1 , 2,3, 4, and
5 are assigned to different variable
ranges. Current index includes 4 vari-
ables and is a statistically based rank-
ing formula.
7 variables (total solids and turbidity
deleted); additive form
8 variables (temperature deleted).
multiplicative form
9 variables; multiplicative form.
9 variables, not calculated if a varia-
ble is missing, multiplicative form
7 variables; three indices were com-
puted, a general index, a mineral
index, and a nutrient index. Cur-
rently using modified version of Mar-
kins' index with 10 variables.
6 variables; grouped into 5 impair-
ment categories
Usual ly 8 variables ( temperature
deleted, BOD sometimes deleted).
additive and multiplicative forms
9 variables, additive form, changing
to multiplicative form
4 variables total (usually 3 variables
at each station).
Length of Time
in Use
3 years
1 year
2 years
1 year
3 years
1 Vs years
1 year
1 72 years
1/2 year
2 years
1 year
Used for one
report only.
Application
Statewide application on an annual
basis; 13 stations in 1976, 27 stations
in 1977
Applied to 30 stations from state-
wide network of 105 stations for
use in 305(b) report. Calculated once
per year, applied to 5-year trends.
Statewide appl ication . A total of
300-600 stations.
Applied to 52 Indiana streams and
lakes where all 7 variables were avail-
able.
Statewide application to 85-100 sta-
tions on a monthly basts.
Applied to Yellowstone River on a
pilot basis with 8-10 runs using 18-25
stations
Applied to data from 162 stations
representing 17 major water basins.
Computed seasonally and applied to
11-year period 1964-1974.
Statewide application to 99 stations
having extensive variable coverage
Applied to stations m the Willamette
River Basin to give monthly water
quality reports. Statewide adoption
expected soon
Statewide application to 40 stations
covering 5 major basins.
Applied to 9 stations on the Nashua
River, 30 weeMy stations on Inter-
state waters.
Applied to 9 stations on the Potomac
River for the 1 0-year period
1962-1971
23
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Of the 51 State agencies, 10 agencies (20 percent), are classified as
index users. One additional State, Nevada, is developing its own index and may
become an index user in the immediate future.
Of the 11 current water quality index users, 7 agencies (6 States and one
interstate commission) have chosen to use the NSFI. Three states—Georgia,
Illinois, and Oregon—are using indices they have developed on their own. The
new indices developed by water pollution control agencies are discussed in
greater detail in Chapter V. One agency, Oklahoma, currently uses Harkins'
Index,* and the Interstate Commission on the Potomac River, which no longer is
an index user, previously used Harkins' index. In summary, the NSFI is the
most commonly used water quality index, accounting for 64 percent (7 out of 11)
of the agencies currently using indices.
The number of variables included in indices currently in use ranged from
four to nine (Table 9). The preferred numbers were nine variables (3 agen-
cies) , eight variables (3 agencies), and seven variables (2 agencies).
Most of the water quality indices have been adopted within the last 3 years,
and nearly half (45 percent of the users) were adopted within the previous
year. Thus, routine application of water quality indices is a relatively
recent phenomenon. This is not surprising when one considers that the first
formal physical/chemical water quality index, Horton's index , was published
in 1965, the NSFI was presented in 1970, and most of the other indices were
published in the period 1970-1975. However, probably the most important
reason for the recent growth in index utilization is the requirement imposed on
the States to prepare annual water quality reports under Section 305(b) of the
Federal Water Pollution Control Act. Although EPA guidance does not require
or encourage the use of indices in preparing these reports, it does not dis-
courage it either. It appears that a number of States have chosen to include
indices in these reports to facilitate reporting of water quality trends.
Most of the indices were applied on a Statewide basis, usually to those
monitoring stations with the most data available. In three cases, the index
was applied to a single river: in Montana, the NSFI was used on the
Yellowstone River; in New England, the NSFI was applied to the Nashua River;
and in the Virginia, Maryland, and the District of Columbia area, Harkins'
index was applied to the Potomac River.
Although the NSFI is the most widely used water quality index, a number
of the users tended to make minor modifications to this index, usually
deleting one or more variables due to data limitations (Table 10). The most
frequently deleted NSFI variable was (departure from equilibrium) temperature
(3 agencies), although total solids and turbidity were deleted in Indiana. In
Wyoming, BODg was deleted whenever it was missing, and the weights were
altered. With most deletions of variables, the user altered the weights so
that they retained the same ratios as before, but still added to 1.0. One
*Recent communication with Oklahoma suggests that a somewhat modified
version of Harkins' index will be used in the future.
24
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TABLE 10
AGENCIES CURRENTLY USING THE NATIONAL SANITATION FOUNDATION INDEX (NSFI)
Agency
Colorado
Indiana
Michigan
Montana
New York
Wyoming
New England
Interstate
Variables
DO
•
FC
•
pH
•
N03
•
P04
•
BODS
a
•
Temp
•
•
•
•
TS
•
•
•
•
.b
•
Turb
•
•
•
•
•
•
Additive
Additive
Multiplicative
Multiplicative
Multiplicative
Additive and
Multiplicative
Additive0
aFor stations with missing BOD5 data, this variable was dropped and weights were altered.
bTotal dissolved solids (TDS) was substituted for total solids (TS) when total suspended solids
(TSS) was missing.
cUsed additive form initially; currently changing to multiplicative form.
agency, the New England Interstate Water Pollution Control Commission,
deleted temperature from the NSFI and conducted a special study to examine
the effect of this deletion on the index values. The study usually found less
than 1/2-point difference between the modified and standard NSFI. This agency
concluded that the differences were negligible and, therefore, to achieve
greater uniformity with other agencies, decided to use the standard NSFI
rather than the modified version. No agency reported using toxic substances
in its NSFI application, although the original NSFI publication discussed ways
to include toxic substances.
Three agencies used the additive form of the NSFI, while three others
used the multiplicative form, and one agency used both. There was a trend
toward increased use of the multiplicative form of the NSFI. This trend is
consistent with the published literature on NSFI, which currently promotes the
multiplicative form, not the additive form of the index.
Purposes of Index Applications
In each telephone discussion with an index user, the author sought to
determine the nature of the index application. What are the agency's main
purposes for using the index? What needs does it serve? Can specific
examples be identified that show how the index was applied to solve a problem
or facilitate communication?
The primary purposes expressed by the index users for applying their
indices were quite varied (Table 11). Three purposes were mentioned most
frequently: preparation of the Section 305(b) annual report (9 agencies);
public information (8 agencies); and analysis of water quality trends
(8 agencies).
25
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TABLE 11
PURPOSES FOR WHICH INDICES ARE BEING USED
Agency
Colorado
Georgia
Illinois
Indiana
Michigan
Montana
New York
Oklahoma
Oregon
Wyoming
New England Interstate
Potomac River Interstate
Index type
Modified NSFI
Developed own index
Developed own index
Modified NSFI
Modified NSFI
Modified NSFI
Standard NSFI
Harkins' Index
Developed own index
Modified NSFI
Standard NSFI
Harkins' index3
Trend
Analysis
•
•
Intensive
Surveys
•
•
305(b)
Report
Other
Reports
•
•
•
•
Public
Hearings
•
Public
Information
•
•
Index usea for one report only.
Although preparation of the Section 305(b) reports was the most frequent-
ly cited purpose for applying a water quality index, examination of the 305(b)
reports reveals that the index results usually constituted only a small portion
of the overall report. For example, Michigan's Section 305(b) report40 uses
the result of a Statewide application of the NSFI to introduce the reader to
the "present state of Michigan's water quality," and the index discussion
occupies four or five pages in the overall report. The index is used to give
an overview of the status of Michigan's waters:
Michigan's abundant natural resources include over
36,000 miles of rivers and streams, more than 11,000
inland lakes, and 38,500 square miles of Great Lakes
waters. Michigan has selected the Water Quality
Index developed by the National Sanitation Foundation
to present a summary of stream quality. As shown In
Figure 2, most of Michigan's river basins rate good
to excellent on the water quality index scale for
water year 1975 (October 1974 through September 1975).
Generally, rivers in the basins shown as having medium
water quality flow through more populous areas and
receive waste loads from known point sources. Point
source pollution control programs are underway in these
26
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basins which should improve water quality. Any
problems that remain will have to be addressed
by nonpoint source programs. **®
The index results are illustrated in a map of the State in which areas are
shaded to depict three different water quality index values (Figure 2). To
deal with the problem of geographical differences in water quality between
Michigan and other States, the report1*0 redefines the normal range of the
NSFI:
The water quality index scale is designed to accom-
modate a wide range of water quality nationwide.
Because of weather and natural geological conditions,
it is unlikely that Michigan waters in even the most
remote and natural settings will reach 100 units on
the water quality index scale. By the same token,
values near 90 show that Michigan water quality is
within 10 units of a national ideal of the maximum
attainable limit.
The Michigan Section 305(b) report also shows the mean index values and the
high and low values observed in a number of selected streams around the State,
ranked in increasing order (Figure 3). This result illustrates that indivi-
dual streams can show great variability. For example, index values on the
Carp River vary from the "poor" to the "good" quality range.
The most commonly cited public information use of a water quality index
was for the purpose of communicating water quality information to the
"layman." A typical remark was, "We feel that the general public needed some-
thing more in keeping with the layman's knowledge than the raw data would
provide." It is not certain what form this communication took. One respon-
dent indicated that newspaper reporters had posed a number of questions about
water quality. He suggested that a typical question was, "Could you give us
an interpretation of water quality in the area for the past 3 years?" He felt
that a format more understandable than 10 or 25 variables was required for
presenting water quality information to the public. Another respondent
indicated that his agency intends to publish and distribute index reports
designed for various audiences throughout the State. These respondents
generally regarded their index as a useful public information tool, and they
sometimes mentioned actual instances in which it had been used to present
information to the public. However, documented examples of newspaper articles
in which an index had been used to report water quality data to the layman or
to members of the general public were not readily available. The audience of
many of the reports mentioned, such as the Section 305(b) annual water quality
reports, cannot be considered the "general public;" rather, judging by the
content of the reports, they seem to be informed professionals and water
pollution control officials. Thus, the present study was unable to find any
specific examples of cases where water quality index reports have appeared in
newspapers or on television. However, application of water quality indices is
a relatively new field, and possibly more direct public information uses will
emerge in the future.
27
-------
-------
90
80
70
WATER 60
DUALITY
INDEX 50
40
30
ts3
20
1C
|
T GOOD
(i o -L . .
^ T T I J "
,, 1 J- -1- ^
T ' 1 MEDIUM.
j HIGHEST WQ.I VALUE
1 MEAN W 0 1 VALUE
-1- LOWEST WO 1 VALUE
POOR
WOl VALUE RELATED WATER QUALITY
71-100 GOOD
51 - 70 MEDIUM
0-50 POOR
i i i i i i i i i i i
-
-
IVU
90
80
70
60
Cf\
4O
30
20
10
/i
Av* ^v- ^S* A** ^** ^** V^^ ^*" ^** ^"*" ^**
A ^ •& A >!$• X^ >V <
-------
The third major purpose cited for using a water quality index was to
present data on long-term trends:
If someone walked into my office and said,
"Damn, we're spending a lot of money in the State.
Are we improving water quality?" Right now I
can't really answer that question.
This respondent also indicated he would like to examine, on a long-term basis
of several years or more, the changes in the index in relation to the dollars
spent. Another respondent emphasized that the index used by his agency was
considered as a relative, rather than an absolute, measure of water quality.
Thus, its purpose was to display changes in water quality rather than the
status of water quality at any time. His agency's approach was to apply the
index at one time and then again 5 years later to observe relative changes
over the period. This agency referred to its index as a "trend monitoring
index" rather than a "true water quality index." Another NSF1 user, Wyoming,
also felt that the absolute value of the index was not too useful but that the
relative change provided insight into water pollution problems. Because
Wyoming's water quality is generally good, this respondent felt that the index
"really picks up the influences" of water pollution sources.
One specific trend application was to determine the changes in water
quality in response to specific pollution control efforts. For example, the
New England Interstate Water Pollution Control Commission has applied the NSFI
to the Nashua River to help assess the impact of $30 million in construction
of treatment facilities currently underway. This agency has applied the index
for about a year, and the staff will apply it again next summer after treat-
ment facilities are completed. Michigan also has applied the NSFI to examine
water quality trends on a number of streams (Figures 4 and 5). Similarly, the
New York State agency has used NSFI to display water quality trends (Figure 6).
Attitudes of Users Toward Indices
Although the survey of agencies was not designed to systematically assess
the attitudes of index users, some impressions have emerged. It is important
to discuss these impressions, even though it is occasionally necessary to draw
many inferences from respondent comments. We present these views in the
context of specific questions.
Were the index users satisfied with their indices? Nearly all users rated
their indices favorably. Typical comments were: "Overall, we are generally
very happy with the index," "We think it is a useful tool," and, "Thus, the
index appears useful, and we will keep using it." Some users seemed reluctant
to interpret indices as measures of "absolute" water quality, however, viewing
their indices as useful only for examining "relative" water quality changes.
Only one of the 11 agencies currently using an index indicated that it felt
"fairly neutral" about its index. This agency indicated that it might not
use the index again because it may not be "worth the effort."
How were the index users able to evaluate the validity of their indices?
The most common remarks about the validity of indices as true measures of water
quality were, "it correlated well with expert judgment," or "the water was
30
-------
0.
1969
1970
1975
1976
FIGURE 4. EXAMPLE OF WATER QUALITY TREND REPORT USING
THE NSF WATER QUALITY INDEX ON MICHIGAN'S RAISIN
RIVER AT MONROE (STATION 580046). "0
-------
X
UJ
O
z
O
DC
UJ
i
100.
90.
80.
70.
60.
50.
40.
30.
20.
10.
0.
1969
I
I
1970
1971 1972 1973
YEAR
1974
1975
1976
FIGURE 5,
EXAMPLE OF WATER QUALITY TREND REPORT USING
THE NSF WATER QUALITY INDEX ON MICHIGAN'S GRAND
RIVER AT GRAND HAVEN (STATION 700026).<*°
-------
SO
Nloooro Rivof ot LoH Ontario Inflow
50'-
i i i i i § i
Hudton Rivor btlow Capital OUtrlct
«.»*
*•*/••
sd- —\/- -
»»*
I i i i I i I i
Nloaoro Riv«r ot Late Ern Outflow
TO-
90
'.V.'i'sVs
i i i i i i i
^Otw/ooo Rivtr ot Otwoao
e s e
I Ii I i I i i IT
MoMwk Rivtr at Fonda
SO
30
I I i i i I s 5 I I
•o
so
Sutajionanno Ri»»f ot Smithbore
T'l , /_-^V
•o,
G«n*«M Riv«r btlow Eottmon-Kodak
TO
SO
?S & J S S s c C Z
_?l?*ee«ee
Hudwn River at Wat«rfor«
90
i f i i I I i M i
*0|
Rlvor at Corinth
SO
i I « i I ITT
Ch«m»ing »iv»r ot Chonuog
TO
SO
: i i I | i S
FIGURE 6. EXAMPLE OF WATER QUALITY TREND REPORT
USING THE NSF WATER QUALITY INDEX ON
RIVERS IN THE STATE OF NEW YORK*
*"New York State Water Quality Inventory Report," Department of Environmental
conservation, Division of Pure Waters [Section 305(b) Report], Albany, NY,
May 1976.
33
-------
improving in the places you would expect it to be," or "the index gave reason-
able results." One respondent viewed the impact of water pollution control
activities on the index as an important measure of its performance:
We initially applied this index to determine whether
it was usable to convey trends. We were very impressed
with its performance. It correlated well with what you
would intuitively expect. Water quality, as depicted
by the index, was improving at the places where we have
major investment in treatment facilities.
Another respondent indicated that his index "successfully showed distinct
changes in the river where you would expect them," and, "this result seemed
reasonable." Another respondent, to evaluate the validity of his index,
ranked the quality of streams using the raw data. Then he compared this
ranking with the values predicted by the index and found good agreement. The
dirtiest streams, according to the index, "came out on the bottom of the list"
and the cleanest streams "came out on the top of the list." One State agency
found good correlations between biological and chemical variables and felt
that its index had successfully passed this important test.
How were geographical differences in water quality handled by users?
Although many geographical differences in natural quality are encountered
across the Nation, most respondents (particularly NSFI users) felt that the
advantages of index uniformity outweighed the disadvantages of developing
customized indices for different geographical areas of the Nation. One NSFI
user placed "85" at the top of its water quality index graphs and dealt with
the problem of geographical differences by cautioning readers, "85 is the best
you can get in this State due to natural background conditions." This
respondent felt that the advantages of national index uniformity were very
important: "If you're going to accept the advantages of uniformity, you have
to accept the disadvantages." Typical of comments about the disadvantages was
a feeling that the variables contained in a particular index were not well-
suited to the respondent's geographical area. One respondent suggested that a
standardized way was needed to delete certain variables where natural condi-
tions make such deletions desirable:
While the concept of a water quality index is good,
I'm not sure that the NSFI is the best one. For
example, many of the variables in the index are not
as important here as they are in other areas of the
Country. The organic pollutants are not a serious
problem here, and the index does not place enough
emphasis on total dissolved solids and salinity.
We would like to add specific conductivity. We
don't have thermal discharges, so we would like to
omit temperature. We're thinking of a simplified
index. What is needed is a standardized way to
delete certain variables when they are not considered
a problem. Then, at least, if users drop a variable,
they'll all be doing it the same way.
34
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Several respondents felt that indices should be custom-tailored to each
specific geographical area and should be based on a detailed study of water
quality data in the area. One respondent, who had developed his own index,
felt that an index should evolve after many years of study of actual condi-
tions in the area:
We don't feel that an absolute type of index can
work; there are too many geographical differences,
even within a State. An index must be tailored to
the specific location and it must be empirically
based. We based our index on the data we have been
collecting in the State over a period of years. We
were able to assess the index performance in light
of our actual knowledge of the geographical varia-
tion of water quality and, thus, to come up with a
suitable means for detecting changes in water
quality over time.
Thus, a dichotomy of opinions emerges from these index user comments.
One viewpoint is that the many advantages of having a uniform index (that is
uniformly applied) outweigh the problems encountered by the geographical
variation in water quality. The other viewpoint is that geographical varia-
tion in natural conditions is so important that each index should evolve from,
and be adapted to, the specific characteristics of waters in the geographical
area where it will be used.
How are different water quality uses handled by index users? In general,
the index users did not seem seriously concerned about the problem of differ-
ent water uses. All of the indices currently in use were general water
quality indices rather than specific-use indices. For the common purposes for
which the indices were applied, such as public information and analysis of
water quality trends (see previous section), the users tended to prefer a
general water quality index. One respondent felt that the importance of water
uses, as it concerns indices, had been greatly exaggerated:
Many persons seem to be obsessed with "water use."
The public doesn't care about water use. The public
wants to know, "well, how do you rate the water?"
This limited concern expressed by the respondents toward water uses is consis-
tent with the contentions of O'Connor20 and Deininger and Landwehr that the
differences in performance and structure between general water quality indices
and a specific-use index are not sufficient to justify application of a
special class of specific-use indices.
Should EPA recommend a uniform water quality index, as the Agency has
done in the air pollution field? There was, as one might expect, a great
variety of views expressed about EPA's potential role. However, a majority of
the index users expressed views suggesting that EPA should recommend a uniform
water quality index. In fact, 8 out of 11 present index users expressed
positive views on this matter. Typical of their views were the following
comments, each from a different agency:
35
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Overall, we are generally very happy with the index.
It probably would be a good idea to have a uniform
national index. Yes, EPA should recommend a
standardized index.
It would be a good idea for EPA to recommend a
standardized index to avoid user "customizing."
The chief problem with customizing is that people
will say, "You customized just to make yourself look
good."
A uniform water quality index is a good idea if you
could come up with one. It would be advantageous
for us to have a proven index or a set of indices.
Possibly, indices should be applied on a region-by-
region basis.
An index like the NSFI would be better for national
use than an index based on water quality standards.
Violation of water quality standards is not a good
basis for an index for national use because each
State has different water quality standards.
I feel that a uniform index is a good concept. I
would support the idea that EPA should support a
uniform index. It would provide a basis to "educate
the public" that a certain number means a certain
quality. The standard NSFI appears to be a good
choice for a uniform index and would allow compari-
sons to be made of water quality in different States.
We favor the idea of EPA recommending a uniform water
quality index. We would like to see EPA come up with
a hierarchy of indices: (1) a "full-blown" index
covering all variables, (2) an intermediate index,
and (3) a very simple index. Each index would be
increasingly more complex than the next, but the more
complex indices would be applied to the more data-rich
situations.
A uniform index that could be recommended by the
Federal Government would be a good idea. One of the
best features of the NSFI is that already it has
received widespread application. Thus, a certain
amount of uniformity already has occurred. If EPA
were to recommend a uniform index, EPA should probably
first poll the users. It would not upset me greatly to
use a slightly different index, unless some new
variables were included. If the index software were
available, it would be very easy to recalculate the
values with the new index.
36
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Selection by EPA of a uniform national index probably
would be a good idea. If the structure of the index
were different than those in use, it probably would
be all right, just so the index is available on STORET.*
If a uniform index were to be recommended by EPA for those water pollu-
tion control agencies wishing to use indices, which index should it be? The
above comments indicated considerable support for the NSFI as the preferred
index structure. One important reason given was that the NSFI has received
such widespread application that considerable uniformity already has been
achieved. However, as the last two comments above indicate, the current
index users do not seem inflexibly wedded to one particular index. They
apparently would be willing to accept a different index structure than the
one they are using for the sake of uniformity, just so the new index is
supported by STORET and does not differ drastically from their present index.
One respondent's comment (third from the last above) suggests that EPA should
recommend three indices, each successively more complex, to accommodate the
problems encountered with missing data and geographical differences. Missing
data, which often occur because a variable is not considered a "problem" in
the area, constitute one of the more serious obstacles to adoption of a
uniform index. Thus, some respondents feel that EPA should develop uniform
criteria, or guidelines, on the manner in which deletions of variables should
be made from the uniform index. In effect, EPA would be proposing a uniform
approach for customizing the index.
By a "recommended uniform index" (or set of indices), the respondents
usually do not mean that EPA should promote the use of indices or attempt to
convert nonusers into users. However, for those agencies that choose, on
their own, to become index users, the suggested uniform structure would be
available. Presumably, it would be adequately documented by EPA, with
examples showing how to apply it and a discussion of its limitations.
Presumably, also, such a uniform index (or set of indices) would be supported
by STORET, and uniform procedures would be recommended for deleting missing
variables and for evaluating the performance of the index in a given area.
Only 2 of the 11 agencies which have actually used indices expressed
reseivations about the concept of a recommended uniform water quality index.
One of these agencies felt that uniformity on a regional basis might be
desirable, however, and the other felt that a uniform water quality classifi-
cation system might be worthwhile:
Rather than developing a uniform index, I think EPA
should develop a uniform variable-by-variable table
assigning "good," "fair," or "pass" to different ranges
of the variables. Such a listing would give more
useful guidance in interpreting water quality data
than indices.
*STORET stands for STOrage and RETrieval of water quality data and serves
as EPA's primary water quality data bank.
37
-------
The index really is too simplistic. It's useful
only when you understand its limitations. I would
not favor adoption by the Federal Government of a
uniform index, because the waters vary considerably
in different areas. Also, stream flow rates differ,
and different streams react differently to different
waste loads. Possibly, application of indices on a
regional basis would be useful, however.
It is possible that the latter respondent may have been considering
"adoption by the Federal Government of a uniform index" to mean an index that
would "be used by the Federal Government" to interpret the waters throughout
the Nation. The other respondents clearly were considering an index that
would be used by their own agencies for the data reporting purposes discussed
in the previous section (for example, public information).
In summary, a majority of the index users were satisfied with their own
indices and rated them favorably. Most of the users supported the idea that
EPA should have a suggested uniform index (or a set of indices) available for
those agencies that wish to avoid "index customizing." However, there was
some feeling that the suggested uniform structure also should include criteria
for deleting variables if such deletions prove necessary because of limited
data. Finally, there was a general feeling that the software for a suggested
uniform index (or set of indices) should be fully documented and available on
STORET, presumably as a utility program, and that EPA should support this
software by giving appropriate technical assistance to index users.
DISCUSSION OF COMMENTS FROM EPA REGIONAL OFFICES
Because the role of the EPA Regional Offices differs somewhat from that
of the State and interstate agencies, only limited information was assembled
on the views of the Regional Offices toward indices. Instead of following
the usual survey format (Appendix F), comments were obtained informally from
one or more persons in each Regional Office. Because a great: range of
opinions and views toward indices exist in any Regional Office, the comments
received are the views of the individual contacted and do not: necessarily
reflect the view of the entire Regional Office. The comments received were
classified into one of three categories: favorable, unfavorable, and neutral
toward water quality indices. A brief summary of the comments and their
classification are given in Table 12. Complete comments are listed in Appen-
dix A (nonusers of indices) and Appendix B (index users). Region VIII and X
Offices have developed indices of their own. These are available for use by
State agencies lying within their geographical jurisdiction.
The tabulation of opinions of the personnel contacted in the Regions is:
four favorable, four unfavorable, and four neutral toward indices. A signi-
ficant proportion of these respondents did not feel strongly about indices one
way or the other, the overall comments ranging from very unfavorable
(Region VII respondent) to very favorable (Region II respondent).
38
-------
TABLE 12
COMMENTS FROM PERSONNEL AT EPA REGIONAL OFFICES
Region
I
II
III
IV
V
VI
VII
VIM
IX
X
Opinion/Status*
N
F
U
N
U
N
U
F (Developer)
U,N,F
F (Developer)
Comments
The NSFI is now being evaluated by the New England Interstate Commission (See Appendix B);
however, indices in general do not adequately describe water quality.
The NSFI can be used to compare water quality on a nationwide basis.
Water systems are too complex to be described by a simplified index.
The Regional Administrator wants to use a water quality index as a part of a Region IV Environmental
Quality Profile.
Indices are subject to speculation.
Any index should be used in conjunction with other individual variables to pinpoint problem areas.
Water quality indices are an obsolete concept.
See Chapter V and Appendix B.
Three respondents with three opinions; see Appendix A.
See Chapter V and Appendix B.
*Key: U = Unfavorable; N = Neutral; F = Favorable.
39
-------
V. CASE STUDIES OF INDICES DEVELOPED BY WATER POLLUTION CONTROL AGENCIES
Among the ten State agencies classified as index users, three—Georgia,
Illinois, and Oregon—have developed new or substantially modified indices.
One additional State, Nevada, has developed its own index, but because the
index has not yet been implemented, Nevada is classified as a nonuser.
Finally, EPA Region VIII and X Offices have developed new water quality
indices. Thus, six new or substantially modified water quality indices have
been developed by governmental agencies (Table 13).
TABLE 13
AGENCIES WHICH HAVE DEVELOPED NEW
OR SUBSTANTIALLY MODIFIED WATER
QUALITY INDICES
Agency
States.
Georgia
Illinois
Oregon
Nevada
EPA Regions:
Region VIII
Region X
STATE AGENCIES
Index Status
In use
In use
In use
Developmental stage
Used for several reports
Modified and used
annually
ueorgla
Georgia's Department of Natural Resources (Environmental Protection Div-
ision) has evaluated two different water quality indices.1*1 The first, WQI1,
was similar to the multiplicative version of the NSFI, except that temperature
was deleted and the weights of the remaining eight variables were readjusted
(Table 14).
TABLE 14
ORIGINAL WEIGHTS USED IN
GEORGIA'S WATER QUALITY INDEX41
Variable
Dissolved Oxygen, % saturation
Fecal Cohform, MPN/100 ml
pH, units
BOD5, mg/l
NH3, total mg/l as N
NO2 + NO3, total mg/l as N
P, total mg/l
Turbidity, JTU
Total
Weight
0.185
0.170
0.120
0.120
0.120
0.110
0.110
0.075
1.0
40
-------
The second, WQI2, aggregated eight subindices using a novel method called
"variable weighting." This method was designed to give greatest emphasis to
the "worst" of the eight water quality variables. Each time the index was
calculated, the subindices were ranked in decreasing order of magnitude.
Subindices with the lowest values (worst water quality) were weighted more
heavily than those with the highest values (best water quality). This was
accomplished as follows:
The highest subindex is written down once, the second highest twice, the
third highest three times, and so on until the eighth highest subindex
(which is the lowest subindex) is written down eight times. This gives a
total of 36 numbers which are then multiplied together, and the 36th root is
taken of the product. The effect of these calculations is to substitute a
new set of weights for the subindices. The weight of the highest subindex
becomes 1/36 = 0.0278, and the weight of the lowest subindex becomes 8/36 =
0.2222. Thus, weights are no longer associated with a particular variable
but are applied in a way that always gives greatest weight to the variable
with the lowest subindex and least weight to the variable with the highest
subindex.
Mathematically, the index calculation can be described as follows:
• [i/36]
WQI = 1 1 I±
1=1
where I>I2>...>Ig
The sum of the weights w. = i/36 for 1=1, 2, ..., 8 is 1.0 and the water
quality index varies between 0 and 100.
The eight pollutant variables used in the index are given in Table 14,
but the weights in Table 14 were replaced by the variable weighting approach
just described. The quality rating curves for each subindex (Appendix C)
were independently developed by members of the Department of Natural Resources
using empirical data from Georgia's streams.
The index is viewed by its developers as a tool for examining changes in
water quality and is called the "Trend Monitoring Index" (TMI). It was
applied in Georgia's 1975 Section 305(b) report to "compare water quality
trends throughout the State on a common basis." In this report, the index was
computed for 2 years of data at most of the monitoring stations in Georgia and
for 5 years of data at selected stations. At the latter stations, the index
values were compared with expert evaluations of water quality based on both
chemical and biological data. From this evaluation evolved a qualitative
rating scale with four categories (Figure 7).
41
-------
QUALITATIVE DESCRIPTION
"POOR" "FAIR" "GOOD" "EXCELLENT"
40 60 80 100
TREND MONITORING INDEX VALUE
FIGURE 7. DESCRIPTORS AND RANGES USED IN
GEORGIA'S "TREND MONITORING INDEX." k2
To cope with the variation in the natural water quality from one Georgia
stream to another, different "natural trend monitoring index ranges" were
defined for different streams. When applied to Georgia streams, most
instances in which the index was in the "fair" or "poor" range could be
attributed to municipal or industrial wastewater problems. However, nonpoint
sources of pollution, such as urban run-off, could reduce the index to the
"fair" or even to the "poor" range for limited periods of time. Major urban
and industrial areas caused the most dramatic changes in the TM1. For example,
if the index is computed for sampling sites both upstream and downstream of
Georgia's urban and industrial areas, the difference in index values can be as
much as 50 points. Typical upstream/downstream differences have been calcula-
ted for a variety of stations (Figure 8).
Illinois
Governmental agencies within the State of Illinois have had considerable
experience in developing water quality indices. In 1972, Barker and Kramer1*3
of the Illinois Department of Transportation (Division of Water Resource
Management) developed a simple WQI. In the process, they identified six
criteria for a meaningful index:
• Water quality variables that are widely and
regularly measured.
• Variables that have clear effects on aquatic
life, recreational use, or both.
• Variables that have man-made sources as
opposed to natural sources.
• Variables that are amenable to control through
pollution abatement programs.
• Realistic ranges of each variable—from no
pollution to gross pollution.
• Sensitivity to reasonably small changes in water
quality.
42
-------
DIFFERENCE IN TREND
MONITORING INDEX
10
20
30
40
50 60
ATLANTA METRO
(CHATTAHOOCHEE R.)
ALBANY
(FLINT R.)
AUGUSTA
(SAVANNAH R.)
ATHENS
(OCONEE R.)
DALTON
(CONASAUGA R.)
COLUMBUS
(CHATTAHOOCHEE R.)
ROME
(COOSA R.)
WAYCROSS
(SATILLA R.)
SAVANNAH METRO
(SAVANNAH R.)
MACON
(OCMULGEE R.)
VALDOSTA
(WITHLACOOCHEE R.)
T
FIGURE 8. WATER QUALITY IMPACT OF
GEORGIA'S URBAN AND INDUSTRIAL
AREAS AS MEASURED BY DIFFERENCES
IN THE TREND MONITORING INDEX
FOR UPSTREAM AND DOWNSTREAM
LOCATIONS.42
43
-------
The resulting index has six ranges for five variables (Table 15). The index
TABLE 15
RANGES OF VARIABLES FOR THE WATER POLLUTION INDEX PROPOSED IN ILLINOIS BY BARKER
AND KRAMER43
Variable3
Dissolved Oxygen (mg/l)
Chemical Oxygen Demand (mg/l)
Ammonia, NH3 - N (mg/l)
Nutrients
P04 (mg/l)
NO2 + NO3 (mg/l)
Fecal Cohform (no. /100ml)
Index Value
1
>6.0
<19.0
<0.5
<1.0
<4.0
<20
2
5.0-5.9
19.0-22.9
0.5-1.4
1 .0-5,9
4.0-11.9
20-199
3
4.0-4.9
23.0-26.9
1.5-2.4
6.0-10.9
12.0-19.9
200-1 ,999
4
3.0-3.9
27.0-30.9
2.5-3.4
1 1 .0-1 5.9
20.0-27.9
2,000-19,999
5
2.0-2.9
31.0-34.9
3.5-4.4
16.0-20.9
28.0-35.9
20,000-199,999
6
<2.0
>35.0
>4.5
>21.0
>36.0
> 200,000
aAnnual maximum value, except for two variables; Dissolved Oxygen, which is annual minimum value and fecal
coliform, which is geometric mean.
bOnly the larger of the PO, or N02 + NO3 subindices is used.
uses the annual maximum value of each variable, or minimum value in the case
of dissolved oxygen, in its calculations. For fecal coliform, the annual
geometric mean is used. To apply the index, subindices for each variable are
read from the table. For the nutrient category, only the larger of the
subindices for PO. and N00 + NCL is used.
4 23
The Pollution Index (PI) is calculated as the sum of the five subindices:
PI
IX
1=1
1^ = subindex for variable i (from Table 15)
This index, which has an increasing scale, ranges from 0 to 30. The descrip-
tors reported with the index vary from "light" pollution to "gross" pollution
(Table 16).
TABLE 16
DESCRIPTORS FOR THE
POLLUTION INDEX PROPOSED
IN ILLINOIS BY BARKER
AND KRAMER43
Pollutant Index Range
0-7
8-9
10-11
12-15
16-25
Descriptor
Light
Moderate
Heavy
Severe
Gross
44
-------
The PI was applied on a pilot basis to monitoring stations in Illinois.
Lake Michigan stations had PI values in the range 0-3, while most waterways
in the Chicago area fell into the range 20-25. Barker and Kramer1*3 conclude:
This test confirms the range that knowledgeable people
believe water quality has in Illinois. That is, Lake
Michigan is the least polluted water and the Chicago
waterways are among the most polluted.
Index values also were compared with the number and kinds of fishes found in
Illinois stream surveys. Although the number of fish species generally de-
creased as the index increased, the overall correlation was relatively poor
(Figure 9).
V)
UJ
O
UJ
O.
C/3
I
V)
u.
u_
O
cc
UJ
CO
0
10 15
POLLUTION INDEX
20
FIGURE 9. COMPARISON OF NUMBER OF FISH
SPECIES AND POLLUTION INDEX
VALUES FOR ILLINOIS WATER
QUALITY DATA.4"4
45
-------
The authors'*3 attributed the poor correlation to a number of factors:
Fish sampling techniques were not always the same;
sampling results were not always reported the same
way; the date of fish sampling did not always cor-
respond to the period of water quality sampling;
the number of fish species is not solely a function
of pollution but also involves the nature of each
stream habitat.
Although this index was applied to water quality data throughout the State,
no subsequent applications of the index have been reported. A respondent
from the Illinois Environmental Protection Agency indicated that, as far as he
knew, PI was not being used at present. He felt that it was probably a
"one-shot" effort, and that no one in Illinois may have looked at it since it
was originally formulated. Barker and Kramer1*3 also proposed a Water
Treatment Index as a simplified first step toward computing the cost of
treating public water supplies.
More recently, the Illinois Environmental Protection Agency developed and
evaluated five statistically based water quality indices, and then selected
one for routine use. The five original indices, proposed in a paper by
Janardan and Schaeffer,**** include three based on a chi-square-like statistic
and two based on a ranking procedure similar to Harkins1 approach.32 The
chi-square-like statistic is a continuous analog of the discrete chi-square
statistic usually calculated for contingency tables. In the index, the
columns of the contingency table are variables and the rows are the successive
observations of these variables. The chi-square-like statistic is calculated
from the contingency table as the sum of the square of the difference between
the expected observation (E..) and the actual observation (0..) divided by
the expected observation: -*
P n (0 - E
X2= E E (°11
X = chi-square-like statistic
0. . = observed value
J
E.. = expected value of the ith observation of the jth
variable
n = population of values (number of sampling dates)
p = number of pollutant variables
46
-------
The three chi-square indices include the above chi-square-like statistic in a
mathematical relationship:
1/2
T + X
1/2
DF + X
I, =
X
1/2
T ( min |n-l,p-l|)
where T = sum of all observed values
DF = number of degrees of freedom
The investigators evaluated the performance of these three indices using real
data and computer simulation and, for various reasons, rejected them in favor
of indices based on ranked data. Both of the ranked data indices begin with
the Kendall transform33 originally proposed by Harkins32 for analysis of
water quality data. The data, including a control value (R ), are the first
ranked in order of magnitude. If the observations are repeated (tied), the
repeated observations are assigned the average rank of the observations assum-
ing no ties. If the jth value for the ith variable is better than or equal to
the control value (usually the water quality standard), then R-j^ is assigned
the same rank, R. , as the standard. The resulting transform is calculated
from the rank numbers:
R.
- R
ic
where R.. = rank of the jth observation of the
1J ith variable
R. = rank of the control value for the ith
variable
s. = standard deviation of the ranks for
the ith variable
47
-------
The standard deviation is calculated as follows:
Si =
m.
1 r 3
.[ni
- t)]
k=l
1/2
where n.
i
t =
m. =
number of values for each variable i
number of ties (repeated values)
number of separate occurrences of ties
for the ith variable
Two additional values are computed from the data, the sum of all the ranks
excluding the control value, and the sum of the square of the transform:
T =
R.
S =
n.
-------
Finally, the two indices, 1^ and 1^, were computed as follows
,1/2
I'
5 = antilog
"l-1
z
1=1 j=l
log
'id
+ 1
The investigators note that the sum of the z-values, in the limit as n
becomes large, is normally distributed by the Central Limit Theorem. There-
fore, S, the sum of the squares of a normally distributed variate, has a
chi-square distribution when n is large. They established the validity of
these assumptions about the distributions by using a computer simulation of
2,000 samples of sets of 12 observations for four variables.
From this analysis of five indices, Schaeffer and Janardan31* select I1
as the index of choice for analysis of Illinois water quality data. Because
of the inherent distribution of S (chi-squared) and T (approximately
constant), the investigators argue that the IzJ will have a beta distribution.
Thus, the index is nonparametric; it will be distributed in the same manner
regardless of the underlying distribution of the raw data. In applying the
index to actual data, they normalize it as follows so that its full range is
from 0 to 1:
where b =
1=1
1/2
=1
- 2p
1-1
n. = number of observations for the ith variable
i '
p = number of variables
49
-------
In evaluating this index, the investigators proposed 11 criteria that
they felt were desirable and necessary characteristics for a water quality
index (Table 17). They compared three other water quality indices published
in the literature (Harkins, NSFI, and Nemerow and Sumitomo) with this index
and concluded that it met the criteria better than any of the other three.*
TABLE 17
SOME DESIRABLE CRITERIA FOR A WATER QUALITY INDEX SUGGESTED
BY SCHAEFFER AND JANARDAN34
Criterion
1 . Definite range
2. Single valued and varies in
systematic manner
3. Responsive to changes in
data values
4. Statistical properties
5. Includes information about
standard
6. Dimensionless
7. Insensitive to the number of
variables employed
8. Insensitive to the number of
observations
9. Usable for all or selected
variables
10. Allows stations to be com-
bined
11. Insensitive to extreme values
Water Quality Index
Janardan
yes
yes
yes
yes
yes
yes
yes
b
b, c
yes
yes
yes
Harkins31
no
yes
a
yes
no
yes
yes
no
c
yes
yes
yes
NSFI4
yes
a
a
yes
no
yes
yes
no
c
yes
a
no
Nemerow24
no
a
a
yes
no
no
no
no
c
no
no
no
Response of the index to this property is not known.
If the number of observations for each variable is the same, this index is insensitive to
the number of variables used in the calculation. If the numbers of observations for the
variables differ, this is no longer true. The index is corrected for the number of
observations.
cThis criterion is not meaningful for real data, and can only be applied if the number
of observations is infinite.
*It should be noted that the technical reviewers of this report have raised
questions about the evaluations given in Table 17. For example, the NSFI is
listed by Schaeffer and Janardan34 as including information about water
quality standards, but the NSFI is based on subindex quality curves and not
on standards. Rather than addressing these issues, the author has chosen to
present this table exactly as it appears in the original literature reference.
50
-------
Its structure was derived from Harkins' index, but its statistical properties
enabled its values to be interpreted probabilistically.
This index was applied by the State of Illinois to examine water quality
data on over 500 stations using four variables in the index: dissolved oxygen,
fecal coliform, total dissolved solids, and ammonia nitrogen. The results are
included in the State's Section 305(b) report for 1976.**5 The numerical values
of the index over the 5-year period from 1971 to 1975 were compared for more
than 500 stations. Of the total, 93 stations had improved, 50 had deteriorated,
and 379 had remained the same. Based upon the index values, each water quality
monitoring station was assigned one of four ratings in each year: "good,"
"average," "semipolluted," and "polluted." The index appeared to perform
satisfactorily and will be used in subsequent annual water quality reports by
Illinois. The index also has been used to determine whether a statistically
significant difference in violations of water quality took place as a result
of mild drought during 1976.^6
Nevada
Nevada currently is in the initial stages of developing a simple water
quality index. The index has an increasing scale in which 1 or less consti-
tutes "good" water quality and 10 or more is "poor" water quality. The index
is calculated as 10 times the mean value of 15 mathematical subindex functions
(Table 18):
TABLE 18
SUBINDEX EQUATIONS USED IN NEVADA'S
WATER QUALITY INDEX
Variable
Temperature (°C)
Dissolved Oxygen (mg/l)
pH (standard units)
BOD5 (mg/l)
Chloride (mg/l)
Total PO, (mg/l)
Ortho P04 (mg/l)
N03 (mg/l)
Total Dissolved Solids (mg/l)
Alkalinity (mg/l CaCO3)
HC03 (mg/l)
CO3 (mg/l)
Total Coliform (no./100ml)
Fecal Coliform (no./100 ml)
Turbidity (JTU)
Equation
I = 0.0016 X2
I =0.0125 (X- 10)2
I =0.25 (X- 7)2 5« X <9
I = 0.125X
I = 0.140 X°-s
I = 0.33 X
I = 0.40 X
I = 0.20 X
I = 8 X 10~6 X2
I = 0.005 X
I = 0.0067 X
I = 0.20 X
I = 0.037 X0'333
I = 0.058 X0'333
I = 0.08 X
51
-------
T = -TlX.
n i=T
where I. = subindex for pollutant variable i
n = number of pollutant variables
The index is intended, in part, to meet a need to present information to the
layman in a simplified form. The index is relatively simple to apply, and its
developers feel it gives useful information when comparing water quality at
different locations on the same water monitoring network. As noted by Sheen49
of the Nevada Department of Human Resources (Environmental Protection Services):
In practice, this looks like a fairly simple tool and
quite useful for trend type analyses of water quality
at a set sampling point. However, again I point out
that all these relationships are purely empirical and
not very objective. In other words, they are subject
to change depending on the particular user's feel of
the actual water quality at a particular sampling
site. I feel that even in the seemingly infant stages
in developing these index programs, they hold a
certain degree of promise for making a complex list
of data a little easier to handle and understand
relative to points up or downstream in the same
analysis network.
At the present time, the index is being tested by Nevada officials but
has not been applied routinely.
Oregon
Oregon, through its Department of Environmental Quality (DEQ), has con-
ducted an extensive investigation over a period of several years to develop a
suitable water quality index. The index was developed in a manner similar to
the technique used by Brown et al.4 in developing the NSFI, but it was
carried out on a regional basis. Their approach also included additional steps
designed to remove redundant variables and to "custom fit" the index to
Oregon's Willamette River Basin. At the present time, the index is in use on
a monthly basis with waters in the Basin applied routinely and will ultimately
be applied to waters throughout the State.
As discussed in a draft manuscript by Dunnette,1*7 the evolution of this
index consisted of the four basic steps:
o Evaluation of water quality indices previously
proposed in the literature.
• Development of criteria for rejecting unsuitable
variables.
52
-------
• Survey of the DEQ staff using a modified Delphi
opinion assessment technique.
• Classification of variables into four general
"impairment" categories to eliminate redundancy.
Oregon's evaluation of water quality indices began by considering five
water quality index criteria that previously have been proposed by the Council
on Environmental Quality:^8
• Facilitate communication of environmental quality
information to the public.
• Be readily derived from available monitoring data.
• Strike a balance between oversimplification and
complex technical conceptualizations.
• Impart an understanding of the significance of
the data they represent.
• Be objectively designed but amenable to compari-
son with expert judgment so their validity can be
assessed.
A total of 12 published indices were evaluated according to these criteria
(Table 19). Except for the NSFI and Harkins' index, the other indices do not
TABLE 19
OREGON'S EVALUATION OF 12 WATER QUALITY INDICES ACCORDING TO CEO
CRITERIA47
Criterion*
1
2
3
4
5
Region X
X
X
O
X
O
Truett
X
X
X
O
O
Proposed Indices
NSFI
X
X
X
X
X
Nemerow
X
O
X
X
-o
Harkins
X
X
X
X
X
Dee
X
O
O
X
O
McDuffie
X
X
O
O
O
Inhaber
X
O
0
X
O
Dinius
X
X
X
X
O
Prati
X
O
X
X
0
Walksi
X
o
o
o
o
Morton
X
O
O
0
O
*Key to criteria: X - met; O - not met. The criteria, from the 1974 CEQ Annual Report,4' are as follows:
(1) Facilitate improved communication of environmental quality information to the public;
(2) Be readily derived from available monitoring data;
(3) Strike a balance between oversimplification and complex technical conceptualizations;
(4) Impart an understanding of the significance of data they represent;
(5) Be objectively designed but amenable to comparison with expert judgment in order that their validity can be assessed.
53
-------
meet all of the CEQ criteria as applied to use in Oregon. Because Harkins'
index uses a ranking procedure in which all previously calculated index values
must be recalculated to compare new data, it was eliminated from further
consideration. Oregon used some aspects of the remaining index, NSFI, in
developing the Willamette Basin water quality index (WBWQI).1*7
The process of selecting variables began with a list of 90 candidates.
This list was narrowed down to 30 by rejecting some because they were
(1) not present in harmful or significant amounts, (2) limited by
insufficient data, or (3) of questionable significance. This list of 30
variables then was sent to 22 professional members of the DEQ staff
involved in water quality work, and each member was asked to select 10
variables from the list and rate each one numerically (on a scale of one
to five) in terms of its reflection of general water quality on the
Willamette River Basin. A total of 15 rating forms was obtained from
this survey, and the results were tabulated and distributed to the
participants. After reviewing the group's ratings, each respondent was
allowed to change his original ratings. This reduced the list from 30
to 14 variables.^7
Finally, to further reduce the number of redundant variables, five
general "impairment categories" were identified: (1) oxygen status;
(2) eutrophication, or potential for excess algae and plant growth;
(3) physical characteristics; (4) dissolved substances; and (5) health
hazards. To the extent possible, the fewest possible variables were chosen
that would give suitable representation to each impairment category (Table 20)
TABLE 20
WEIGHTING FACTORS USED IN OREGON'S WATER
QUALITY INDEX47
Variable
Dissolved Oxygen
Fecal Coliform
pH
BOD
Total Solids
Nitrate + Ammonia
Impairment
Category3
1
5
4
1
3,4
2
Normalized
NSFI
Weight*5
0.24
0.21
0.17
0.14
0.10
0.14
Final
Variable
Weight
0.40
0.20
0.10
0.10
0.10
0.10
a1 = oxygen depletion; 2 = eutrophication; 3 = physical
characteristics; 4 = dissolved substances; 5 = health hazards.
bA normalized NSFI weight was obtained by deleting three
of the original NSFI variables and calculating new weights that
add to one and preserve the ratios among the remaining NSFI
weights.
54
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In some cases, a given variable was represented in more than one impairment
category. In summary, the choice of the variables was based on the importance
rating given to them by the DEQ staff, the desire to reduce redundancy in each
of the impairment categories, and the judgment of the investigator regarding
availability of data and significance of the variable for Oregon streams.
The overall index is computed as the weighted sum of n subindices:
n
WBWQI = / ; w. I.
1=1
where WBWQI = Willamette Basin Water Quality Index
w. = weight for variable i (from Table 20)
I. = subindex quality function for variable i
The subindex quality functions for each of the five subindices are
plotted on semilogarithmic paper (Appendix D). These functions were deter-
mined by examining historical records for six monitoring stations on the
Willamette River for the period of 1973-75. The mean values of data for
dissolved oxygen, BOD5, total solids, and nitrate-plus-nitrogen were assigned
subindex values of I = 80. For fecal coliform, the mean value was assigned a
subindex of 70. For pH, I = 60 was assigned to both pH = 6.0 and pH = 9.0.
The slopes of the subindex quality functions also were derived from historical
data.47
Correlations between several modified forms of the WBWQI and several
other indices also were examined. This comparison included a multiplicative
form of the WBWQI, Prati's Index, McDuffie's Index, and six- and eight-
variable versions of the NSFI and of Harkins' Index. Correlation coefficients
ranged from 0.76 to 0.99, with a mean of 0.89. The investigator attributes
these high correlations, in part, to the similar finding by O'Connor
(Chapter II) that selection of the variables which go into an index tends to
be more important than the particular shapes of subindex quality functions.47
This index, which may still undergo further evolution, was implemented
in 1977 as a monthly reporting system to provide information on water quality
conditions at each station. Oregon's approach is of particular interest
because it represents an example of a "case study procedure" in which existing
indices are systematically reviewed and adapted to the geographical area under
study. Thus, it gives a "custom fit," on an iterative basis, of the index to
the area. It is likely that other agencies following this same procedure
would develop indices with very different weights, variables, and subindex
quality functions. Presumably, this approach provides the best means poss-
ible for incorporating geographical differences of water quality into the
55
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resulting index. By using this approach, an agency can have greater assurance
that unique geographical characteristics of its waters will be properly
reflected in the index.
EPA REGIONS
Region VIII
In 1975, EPA's Region VIII in Denver, Colorado, developed an index based
upon the frequency of violation of water quality standards. The evaluation of
this index is described by Cogger, Payne, and Sprenger:50
Aided by fresh concepts and the need for a water
quality assessment required of each Region by Section
305 (b) of P.L. 92-500, an index was developed building
on experience earned in 1973. This index used some of
the conceptual ideas developed by the National Sanita-
tion Foundation (NSF) for its "Water Quality Index
Application in the Kansas River Basin" and those of
EPA's Region X in its "Water Quality Index." Temper-
ing these concepts with the experience and knowledge
of the kinds and characteristics of data in Region
VIII, an index emerged that was simple and had the
advantage of being reasonably unrestricted by the
extensive data requirements and one that was free of
statistical devices to supplement missing data.
In the index, pollutant variables were grouped into four general categor-
ies (Table 21).
TABLE 21
VARIABLE GROUPINGS USED IN REGION VIII WATER QUALITY INDEX50
Group 1
Dissolved Oxygen
Biological Oxygen Demand
Group 2
Bacteria (Total and Fecal Coliform)
Group 3
Nitrogen
Phosphorus
Group 4
Physical and Aesthetic
Factors (Salinity, Turbidity, etc.]
56
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Temperature and pH were not included because these pollutant variables are not
significant problems in the Region VIII geographical area, and violations are
infrequent. The index consists of the product of five subindices raised to
weights:
0.25 0.25 0.125 0.125 0.25
where Z = percent violation of DO and BOD standards
Z? = percent violation of fecal and total
coliform standards
Z., - percent violation of nitrogen standards
Z, = percent violation of phosphorus standards
Z = percent violation of criteria for physical
and aesthetic standards
The subindex weights were selected by reevaluating the weights used in NSFI in
light of water quality conditions in Region VIII. For example, NSFI weights
for DO (0.17) and BOD (0.11) had a combined weight of 0.28. This was cpnsi-
dered too high because few DO and BOD violations are measured on Region VIII
mainstreams by fixed stations; therefore the weight for this group was
reduced to 0.25. Similarly, fecal coliform has an NSFI weight of 0.16, and
total coliform is not normally included in the NSFI. This emphasis was
considered too low because total coliform (as a group) are somewhat more
resistant to chlorination and may indicate, at least for waters influenced by
sewage treatment plant wastewater, the presence of more tolerant and long-
lived pathogens. Thus, the weight for fecal and total coliform was raised to
0.25. Similarly, Group 3 pollutant variables, nitrogen and phosphorus, were
considered weighted too low by the NSFI; weights were increased from 0.10 to
0.125 for each, giving a combined weight of 0.25. Group 4 pollutant var-
iables, represented in the NSFI by total solids (0.07) and turbidity (0.08),
were considered as weighted too low in the NSFI. These variables are related
to irrigation and, therefore, relate to difficult land use problems which are
apparently worsening year by year. Toxic substances were not included in the
index but were treated in a separate fashion. The presence of toxic substan-
ces and pesticides was treated as a "severe event," and individual instances
were noted whenever they were observed. Because of the shortage of data on
toxic substances and pesticides at the various stations, the severe event
category proved a useful way to describe unusual or extremely hazardous
situations.
For each group, six observations was the smallest number that was
acceptable for index analysis. Unless each monitoring station had data in
all four groups, it was excluded from the index calculation. The index was
applied to the Region VIII area (Montana, North Dakota, South Dakota,
Wyoming, Utah, and Colorado), by comparing two 3-year time periods
57
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(July 1969-June 1972 and July 1971-June 1974). A total of 87 stations was
identified within the six States as having sufficient data for both periods.
Changes in water quality between the two periods were examined, and the status
of water quality (including data-deficient stream segments) in the July 1971-
June 1974 period was expressed on a map using a color-coded system. The index
ranges selected for the color coding scheme were based upon the empirical
judgment of the authors (Table 22).
TABLE 22
DESCRIPTIVE CATEGORIES USED FOR REPORTING THE REGION VIII
WATER QUALITY INDEX50
Index
>15
5-15
0-5
Insuff . Data
Color
red
yellow
blue
green
Significance
Waters or areas that have significant water quality problems
Waters or areas that have intermittent water quality problems
Waters that have infrequent water quality problems
Waters or areas requiring data for determination of status
The index reports were supplemented by a "severe events" list. This
qualitative information formed the basis for the 1975 Region VIII Section
305(b) report and will be used in subsequent reports. The index provided a
useful tool for evaluating water quality standards in different States and
for preparing "success story" reports for Region VIII.
Region X
An index developed by Beebe51"53 for EPA's Region X represents one of the
few attempts to incorporate both time and space into a water quality index.
Beebe5' notes that previous index development efforts have not emphasized
specific ways to handle time and space:
Other researchers in this area have proposed abstract
methods and formulae, but none has proposed a concrete
procedure for dealing with actual available data. For
example, when one talks about a water quality index,
what time period are we talking about? A day? A week?
Are we talking about the quality at a specific point on
a stream or lake? Or, are we talking about an entire
river basin? How does one evaluate the quality or
compare the quality of different waters? These and
other questions have not been answered before.
Inclusion of time (percent of time that criteria values were exceeded) and
space (length of stream affected by a given water quality) made the index seem
somewhat more complex than many of the other indices published in the litera-
ture. Tailored for use on a computer, this index employs both a set of quality
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rating curves and a set of recommended limits. The quality rating curves are
similar to those used in the NSFI, and Beebe51 notes, "Most of the quality
curves used in this procedure were borrowed from prior work done at the EPA
or from other researchers." Recommended limits were based on State and local
water quality standards and on values that appear in the National Academy of
Science's Water Quality Criteria.54
As originally developed, the index uses pollutant variables grouped into
10 different water quality categories. For each station j, a subindex
function is calculated for each category k. When data on more than one
pollutant variable are available within a category, the calculation uses the
maximum (or minimum) pollutant variable relative to the recommended limits.
Time is taken into account by computing the relative frequency that a
recommended limit is exceeded.
For each category k, a weighted quality value Z.= ^ is calculated by
multiplying the quality value (which is a measure of water quality impact) by
the product of the frequency of criterion violation times a weight:
where Q. , = quality rating for station j and
' category k (Appendix E)
F. = frequency of violation of recommended
' limit (proportion of time that recom-
mended limits were exceeded for jth
station and the kth category)
W. = weight for category k
K.
For any desired river reach, the subindex for category k is formed by
weighting the Z values by the distance in river miles between stations:
n-1
. , , , + Z . ) (d . , . - d . )
J+1»k J»k J+1 J
where 1, = water quality subindex for category k along
the reach
Z = water quality value of the kth category at the
jth station in the reach
d = river mile distance of the jth station (d.
-------
Finally, the index is formed by summing all the subindices for all reaches and
categories:
n
HQI = S \
1=1 k
In recent years, the index has been further simplified and refined so
that it could be used on water quality data from the various States within
Region X.55 The frequency term, for example, is no longer included in the
index calculation. The quality rating is now computed for each separate
observation, and the time-weighted average of quality ratings is computed.
The distance estimates are now based on the professional judgment of the user
regarding the representativeness of each station. These distance estimates
of the "affected river miles" also are used to weight the index computation.
This simplified version of the Region X index is now being used to prepare
annual environmental quality profiles for the States in Region X.
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VI. CRITERIA FOR AN IDEAL WATER QUALITY INDEX
Using this study as a basis, it was possible to identify criteria that
an "ideal" water quality index, if it could be developed, should possess.
These criteria have evolved from the survey data, comments from respondents,
comments from reviewers, and, particularly, from the criteria discussed by
Schaeffer and Janardan,34 Barker and Kramer j1*3 Dunnette,47 and the 1974 CEQ
annual report.^8 The criteria arising from these diverse sources have been
merged to form the following list of 20 characteristics that the ideal water
quality index should possess:
• Relatively easy to apply
• Strikes a reasonable balance between over-
simplification and technical complexity
• Imparts an understanding of the significance
of the data it represents
• Includes variables that are widely and
routinely measured
• Includes variables that have clear effects
on aquatic life, recreational use, or both
• Includes toxic substances
• Can easily accommodate new variables
• Based on recommended limits and water quality
standards
• Developed from a logical scientific rationale
or procedure
• Tested in a number of geographical areas
• Shows reasonable agreement with expert opinion
• Shows reasonable agreement with biological
measures of water quality
• Dimensionless
• Has a clearly defined range
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• Exhibits desirable statistical properties
permitting probabilistic interpretations to
be made
• Avoids eclipsing
• Shows sensitivity to small changes in water
quality
• Applicable for showing trends over time, for
comparisons of different locations, and for
public information purposes
• Includes guidance on how to handle missing
values
• Limitations of the index are clearly documented
No single index will completely meet all 20 criteria. However, different
candidate indices will vary in terms of their proximity to the ideal, and the
criteria are intended to provide a uniform system by which to judge indices.
Each criterion listed above varies, of course, in terms of its importance and
the significance that it should receive when evaluating indices. In addition,
because of many diverse attributes demanded of a water quality index, some
criteria may seem almost contradictory. When criteria conflict, such as the
need for simplicity and the need for technical completeness, it is necessary
to compromise.
By definition, a water quality index is a tool simplifying the presenta-
tion of data. In the process of simplification, some information inevitably
will be removed. Ideally, the removal of information will not be serious
enough to distort the meaning of the index to the audience for which it is
intended. Thus, the index, although imperfect, will still do its job of
communicating the proper information to its intended audience. If the
audience consists of members of the general public, considerable distortion
can occur in the interest of simplicity, and the index will still be of use.
The important point in evaluating indices is to determine the target audience
for which the index is intended and the ultimate context in which the index
results will be used.
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VII. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
SUMMARY
This study documents the extent to which water quality indices currently
are being used in the United States. It has sought to determine: (1) which
agencies were using water quality indices, (2) the types of indices being
used, (3) the purposes of their uses, and (4) the attitudes of agency personnel
toward indices. The study approach consisted of a review of the indices
published in the literature; a survey of 51 State agencies, 9 interstate
commissions, and 10 EPA Regional Offices; and brief case studies of agencies
that have developed their own water quality indices.
There is evidence of a proliferation of water quality indices in the
published literature. Over 20 physical and chemical water quality indices
have been published in journals, symposia proceedings, and technical reports.
A great many biological indices also have been developed and appear in the
literature. The present study has found it possible to classify the physical
and chemical indices into four general groups: (1) indices of general water
quality, (2) indices for specific water uses, (3) indices for planning, and
(4) statistical approaches. These published indices greatly differ in terms
of the numbers and types of variables included, mathematical structures,
scales (whether the numbers increase or decrease with pollution), and overall
index ranges. Rather than evolving toward a uniform structure, each published
index often shows little direct relationship to previously published indices.
The agencies surveyed were classified into five groups: (1) those unfam-
iliar with indices [11 States, 2 commissions]; (2) those that had previously
considered indices but were not interested in pursuing them further [14 States,
4 commissions]; (3) those planning to evaluate or develop indices in the near
future [10 States]; (4) those currently evaluating or developing indices
[6 States, 1 commission]; and (5) those agencies that were using (or 'previous-
ly had used) indices [10 States, 2 commissions].
These groups differed in terms of their familiarity with indices, with the
first group least familiar and the last group, the index users, most familiar.
The first group may or may not become index users in the future as their
knowledge about indices increases. The second group seems unlikely to become
index users, but Groups 3 and 4, when combined, constitute a class of
"potential" index users. When the 60 agencies are regrouped in this fashion,
the data can be summarized very compactly (Table 23).
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TABLE 23
STATUS OF WATER QUALITY INDEX UTILIZATION IN
THE UNITED STATES, MARCH 1977
Agency
States
Interstate Commissions
Total
Nonusers
25
6
31
Potential
Users
16
1
17
USING
10
2
12
Total
51
9
60
Of 51 States agencies (including the District of Columbia), 10 (20 per-
cent) are classified as index users. An "index user" is an agency that has
used an index in an official publication of the agency [for example, the
Section 305 (b) report] or has applied it in a large-scale study extending
over a year or more. Two interstate commissions also are classified as index
users, although one no longer uses an index. Of the 11 agencLes (10 States
and one interstate commission) that currently use indices, 7 (6 States and one
interstate commission) have chosen to use the NSFI. Three States are using
indices that they have developed on their own, and one State, Oklahoma, uses
Harkins' index. Despite the widespread use of the NSFI, many minor variations
occur in the way this index is applied.
Among potential users, the NSFI is the most frequently mentioned index,
with 14 of the 17 States and one interstate commission indicating that they
are currently considering the NSFI or will be considering it Ln their future
evaluations. If the 17 agencies now classified as potential users of a water
quality index were to become actual users in the future, 29 out of 60 agencies
(48 percent) then would be classified as index users. At that time, therefore,
roughly half of the United States water pollution control agencies would be
using water quality indices. Because nearly all of the present indices have
been adopted over the past 3 years, there is clear evidence of a trend toward
increased utilization of water quality indices in the United States.
Although a great many indices already appear in the literature, a number
of water pollution control agencies have developed new or substantially
modified indices. Some are empirically based systems uniquely designed to fit
the conditions and water quality of a particular locale. Others are statis-
tical procedures of considerable flexibility and sophistication. Six new
indices have been developed by the water pollution control agencies surveyed,
four by the States and two by the EPA Regional Offices (Regions VIII and X).
Three of the four State-developed indices are currently in use (these agencies
are classified above as index users), but one has not reached the stage of
routine application. The EPA-developed indices have been used for a variety
of reports and projects.
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Although the purposes expressed by index users for applying their indices
were quite varied, three purposes were mentioned most frequently:
(1) preparation of the Section 305(b) annual reports [9 agencies], (2) public
information [8 agencies], and (3) analysis of water quality trends [8 agencies].
Index results often appear in the Section 305(b) reports and are used to
describe water quality trends, but no specific examples could be found in which
any index results had appeared in newspapers, on television, or on the radio.
More often, the audience is a water quality specialist or government official
instead of a member of the general public. By contrast, air pollution indices
usually use the mass media to report air quality data to the public on a daily
basis.
The majority of the agencies currently using indices expressed satisfac-
tion with their own indices and rated them favorably. On the other hand, they
expressed a willingness to modify their indices, if necessary, in the interest
of uniformity. Most index users feel that EPA should make available a uniform
index, or set of indices, for use nationally by those agencies wishing to apply
indices. One reason given is that a uniform index would reduce the tendency
toward "index customizing," in which the user drops a variable, changes the
weights, or alters the mathematical structure of the index. Some respondents
feel that the suggested uniform structure also should include criteria for
deleting variables if such deletions prove necessary because of limited data.
Index users do not seem seriously concerned about the problem of differing
water uses and tend to prefer a general water quality index to a specific-use
index. Finally, there is agreement that computer software for such a sugges-
ted index (or set of indices or interpretive techniques) should be fully docu-
mented and available from EPA and fully supported on the EPA computer.
CONCLUSIONS
Water quality indices have proliferated
The literature reveals that a great number of different water quality
indices have been published. However, except in a few cases, these published
efforts do not reveal the normal evolution associated with scientific work.
That is, few of the authors cite previous indices or build upon the work of
previous authors. Rather, there is a tendency for each index to be a "new
start," emerging full blown with little relationship to previous index
development efforts. In addition, most of the indices in the literature,
although they have sometimes been applied to water quality data on a pilot
basis, have not been used routinely by water pollution control agencies or
officials.
A single index, the NSFI's Water Quality Index has gained wider acceptance
than any other index
Unlike the air pollution field, where nearly all of the indices were
developed by users,5 one index, the NSFI published in 1970 by Brown et al.,1*
has gained wider use in the water pollution field than any of its competitors.
Roughly, one-sixth (18%) of the State and interstate agencies (11 of 60
agencies) currently are using a water quality index, and 64 percent of these
(7 of 11 agencies) are using the NSFI. Thus, 7 of the 12 agencies (58%) that
have used a water quality index have selected the NSFI.
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Where it has been used, the NSFI seems to perform satisfactorily, meeting
users' needs without major complaint
Most index users do not seem very concerned that the NSFI is not a
specific-use index. In fact, some respondents feel that the problem of
different water uses had been exaggerated and that specific-use indices are
not necessary. The only complaint users have about NSFI is that the nine
variables contained in the index are not always well suited to their particu-
lar geographical areas. Nevertheless, most users feel that ttie need for
uniformity of an index outweighed the need to tailor it to individual geograph-
ical areas. Those index users who feel that an index should be tailored to
their individual situation generally have developed their own index.
The purposes for which water quality indices are being applied differ from
those for air pollution
Water quality indices, in the opinions of their users, are being applied
for three basic purposes: (1) Section 305(b) reports, (2) public information,
and (3) trend analyses. In the air pollution field, on the other hand, the
principal purpose is to report air quality levels directly to the public on a
daily basis. The air pollution field does not have legally required annual
reports from the States similar to Section 305(b) reports to Congress required
under the Federal Water Pollution Control Act,6 and air pollution indices
seldom are used in the analysis of air pollution trends. Although public
information is a major purpose cited for using a water quality index, this
purpose does not appear to be the same as reporting air quality data to the
public on a daily basis through radio, television, and the newspapers. In
fact, virtually no specific examples were found in which a water quality index
had been used to reach the general public directly through the mass media.
The audience usually consisted of water quality professionals or government
officials rather than general television viewers or newspaper readers.
Of course, many other differences exist between the air and water pollu-
tion fields. In air, nationally uniform air quality standards have been
adopted that greatly facilitate uniform air quality data reporting practices.
Also, where water has many uses, air has one primary use: it is consumed by
living systems to support life. This use is analogous to just one of the
uses in the water pollution field, the supply of public drinking water.
The need for a standardized water quality index, while it may exist, is much
less pressing in water pollution than it was in air pollution
Because the immediate audience of the results of water quality index
applications usually consists of informed professionals rather than members
of the general public, there is virtually no evidence of public confusion
over the different water quality indices that have been developed. Air
pollution changes occur on a daily basis, creating considerable public
interest in daily air quality index reports. Unlike air, however, water is
treated before it is consumed, and changes in raw water quality have less
direct and immediate impact upon the public. This does not mean that the
public has great interest in daily air quality levels and virtually no
interest in water quality levels. The public's interest in water quality
data simply appears less pressing than its interest in air quality data.
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The public's interest in water quality often becomes intense, however,
in situations that affect it immediately, such as a spill of toxic substances
upstream. Lack of public dissemination of water quality information (by means
of indices or any other approaches) also may be due partly to a lack of effort
on the part of agencies to interest the media (radio, television, and news-
papers) in presenting water quality data. Possibly, water quality information
could be reported on a monthly or seasonal basis in newspapers along with
coverage of the climate, the tides, and summary information on air quality.
This hypothesis needs further investigation.
Of course, an entirely different reason that the need for a standardized
index may be less pressing in water than in air is that the NSFI has been
adopted by more than half of the index users. Although the total number of
water quality index users is small, common use of a single index creates a
degree of standardization and uniformity that was not apparent among air
pollution control agencies. To achieve uniformity in the air pollution field,
EPA found it necessary to recommend a standardized national air pollution
index.56 In the water field, however, it may be possible to achieve national
uniformity simply by increasing the degree of communication among water
pollution control agencies. Probably the best means for doing so is for EPA
to establish a water quality data analysis user's group.
A number of new, and often very sophisticated, data analysis techniques and
indices have been developed by water pollution control agencies
Various water pollution control agencies across the Nation have pioneered
in development of new ways to interpret and analyze water quality data. Some
of these approaches, although they may be classified as indices, represent
initial applications of relatively sophisticated and powerful analytical
procedures. In general, most other water pollution control agencies are
unaware that data analysis procedures are available. This, in part, explains
why the indices developed by the agencies are so varied. The diversity of
these techniques, combined with the lack of knowledge of the agencies about
each other's data analysis activities, suggests there is a need for increased
communication among agency personnel engaged in analysis and interpretation of
water quality data. Such improved communication would reduce duplication of
effort and would allow agencies that have developed different data analysis
techniques to share their knowledge and experience, thereby helping to
standardize data analysis activities. Such communication would be assisted by
establishment of a centrally coordinated statistical data analysis support
group within EPA. Communication also would be enhanced by holding national
conferences and symposia dedicated to improving data analysis techniques.
RECOMMENDATIONS
The following recommendations represent the author's opinions and are
based on his review of the findings of this study and on his evaluation of
comments from the agencies and from the reviewers:
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The EPA should provide, technical support for two candidate uniform water
quality indices for those agencies wishing to use an index but should not at
the present time formally adopt an index in the Federal Register
Unlike the air pollution field, where indices are used to report air
quality data to millions of people on a daily basis, there appears to be
relatively limited dissemination of water quality information directly to the
general public. As with air, many different water quality indices exist, but,
because the information generated with these indices is seldom disseminated to
the general public through the mass media, there is little evidence of public
confusion. In water, indices appear to be used primarily as investigative
tools—techniques for studying trends and for reporting data in a simple
format to water quality professionals and managers. Without evidence of wide-
spread public confusion, the need for a formally adopted uniform national
index appears less pressing for water than it was for air. However, the
index users in this study generally feel that a recommended uniform index is
desirable for those agencies wishing to use indices. This does not imply that
use of such an index is encouraged or required; it implies merely that the
index, and the computer software for its support, are more readily available
than before. Adoption of an index in the Federal Register implies that EPA
officially endorses the index and encourages its use as a matter of policy.
Such encouragement would seem inappropriate at the present time when there
is serious disagreement among knowledgeable persons over the proper index to
use. Support of at least two candidate water quality indices, however, would
be a useful first step in attaining greater standardization in the application
of data analysis techniques to water quality data.
The EPA should take steps to increase communication among water quality
specialists and professionals throughout the Nation who must analyze and
interpret water quality data
A great variation is evident in the manner in which water pollution
control agencies approach indices: a number of agencies are unaware of
indices; some agencies are aware of indices but view them negatively; some
agencies are currently evaluating them for possible application; other
agencies are using them routinely; and still other agencies are developing
new and more advanced indices. In the author's view, this variation results,
in part, from an underlying lack of communication among specialists and
professionals engaged in water quality data analysis efforts. It also
suggests there may be fundamental differences of opinion regarding the way in
which water quality data should be analyzed and interpreted, along with
considerable nonuniformity in prevailing data analysis practices. Such non-
uniformity gives rise to potential duplication of effort, redundancy, and lack
of utilization of effective data analysis tools. These problems could be
corrected by increasing communication among water quality professionals and
specialists regarding data analysis techniques. The following steps should be
considered by EPA for increasing communication: (1) publishing more examples
of important applications of data analysis techniques; (2) holding data
analysis conferences, symposia, and seminars; (3) developing, maintaining, and
supporting special-purpose computer software of various data analysis tech-
niques for use by EPA and State agar.eles; and (4) encouraging greater direct
contact among data analysis specialists within EPA and the State agencies.
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CEQ appears to be the appropriate agency to play a lead role, along with EPA
and other interested agencies, in supporting a national data analysis
conference that could benefit specialists who analyze data in air, water, and
other environmental media.
The EPA should create a data analysis users' group to apply analytical
techniques to water quality data and to assist State agencies in developing
uniform data analysis procedures
Large sums of money are spent to collect environmental monitoring data,
and these data provide the most important quantitative measure available for
judging the effectiveness of pollution control efforts. However, the
resources spent to apply proper data analysis techniques to these data are
disproportionately low. Thus, maximum information on the state of environmen-
tal quality and on water quality trends is not being fully realized from
today's monitoring efforts. Development of a data analysis users' group is
viewed as necessary to increase the level and quality of data analysis efforts
in the Nation and to gain greater benefits from current expenditures on
monitoring activities. A small, centralized users' group is felt to be the
most efficient means for doing so. This group should consist of highly
qualified statisticians and other professionals thoroughly experienced in the
analysis and interpretation of environmental data. This group should serve as
a coordination point for EPA's environmental trends analyses and should carry
out studies to explore the application of new interpretive techniques to
environmental data. This group should have responsibility for developing and
supporting the necessary software for applying these techniques and should
serve as a general point of contact for assisting EPA and the State agencies
in their use. The group also should support the needs of other federal
agencies, such as the U.S. Geological Survey, the Council on Environmental
Quality, and others. Possible examples of these techniques include time series
analysis, computer programs to test for underlying probability distributions,
multivariate regression analysis, nonparametric statistical procedures,
quality control data screening models, simulation models, and other approaches.
It is estimated that 15 positions and $400,000 in contractual monies would be
adequate to maintain the environmental data analysis users' group.
In addition to its other statistical procedures, the EPA data analysis users'
group should support software for at least two different water quality indices
One of the most efficient means for attaining uniformity of water quality
index applications is central support of several carefully selected water
quality indices. The EPA data analysis users' group described above, there-
fore, should maintain at least two very different index types: an absolute
value index and a ranking inaex. A good example of an absolute value index
is the NSFI.14 It is relatively simple to apply, and a great degree of
uniformity already has been attained simply because of its widespread applica-
tion. A good example of a ranking index is the beta function index developed
and applied in Illinois.^ Based on the nonparametric procedures suggested by
Harkins,-"' this approach offers a potentially powerful statistical procedure
for comparing water quality data at different locations or over time.
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Future research studies should be undertaken by the EPA to gain better insight
into the relationship between candidate water quality indices and biological
measures of water quality
Two distinctly different ways to evaluate water quality appear to have
emerged: physical/chemical indices and biological systems for evaluating
water quality. An important way to evaluate water quality indices is to
compare them with the various biological measures. In such studies,
biological evaluation of various waters should be carried out alongside
water quality index calculations, and the results should be compared
statistically. An effort should be made to determine confidence intervals
for the indices, and the factors that affect the predictions should be
carefully examined. A simple example of such a comparative study was
performed by Schaeffer and Janardan using a biological classification
system to rate Illinois waters and comparing the rating with index
predictions.
The EPA should establish a statistical methods development program to conduct
research on techniques for analyzing environmental data
Many basic statistical techniques are available for data analysis, but
few of these have been applied to actual environmental data. Some techniques
are in their infancy and require future development. Other techniques imply
certain assumptions about underlying probability distributions or independence
that have not been tested or evaluated, even though the results of these tech-
niques are being used for Agency decision-making.
At present, EPA has no scientific program for developing and evaluating
statistical techniques to analyze environmental data, even though there is a
need to apply these techniques to the Agency's large data bases. Although a
central statistics unit will be established in Office of Planning and Manage-
ment, this unit will be located in an administrative part of the Agency which
does not conduct research.
There is need to establish, within the Office of Research and Development,
a statistical methods development program to evaluate and develop statistical
techniques, applying them to air, water, and other monitoring data to deter-
mine their statistical properties and to evaluate their potential use by the
Agency. This program should be organizationally linked to the monitoring and
quality assurance activities responsible for collecting the data. Its functions
should include not only development of practical tools for analyzing environ-
mental data, but also research on models to combine data from banks in dif-
ferent media (air, water, drinking water, disease variables), stochastic
models for decision-making, time series approaches for forecasting environ-
mental variables, techniques for making long-range projections, indices,
indicators, and other interpretive techniques. It is estimated that 5 posi-
tions and $550,000 in extramural funds would be sufficient to implement this
program.
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VIII. REVIEWER COMMENTS
When the first draft of this report was completed, it was circulated
to a select group of reviewers both within and without EPA. A number of
excellent comments were received from these reviewers, and most of these
resulted in changes to the original manuscript. It was not possible to
respond to all of the reviewer comments, however. Because of the contro-
versial nature of the topic and the relevance of many of the comments,
some of them are included here. Although these comments are taken from
written memoranda57"61 received from the reviewers, it was decided not to
identify each individual reviewer. Thus, the reviewers are identified
only as Reviewer A, Reviewer B, etc. Although the comments are taken out
of context from these materials, they give insight into the controversy
surrounding this topic and in the opinion of the author should be
presented as part of this report.
Overall, the reviewers seemed generally pleased with the contents of
this report and felt that the subject had been handled satisfactorily:
I am very impressed by the thoroughness, clarity, and
objectivity of your report. I believe it adds consider-
ably to the useful literature on the subject of water
quality indices. It performs an analysis which should
have been done a long time ago concerning the actual
use of indices, and it serves to put into perspective
the voluminous work which has been done in the past.
[Reviewer A]
... I have reviewed the manuscript of the report on
water quality indices, and am returning it with my
comments. The report is well-written and very infor-
mative. I think the inclusion of (positive and negative)
professional opinions expressed about the indices by the
regional and state program personnel is especially
useful. [Reviewer B]
Some reviewers felt, however, that the need for a nationally uniform
index was not given sufficient emphasis in the report:
I disagree that the need for standardizing a water
quality index is less pressing than that for air. It is
very difficult to undo "tradition" and "experience"; it
is much better to start cleanly. If everyone starts
using their own form then it will be impossible to undo
this state and the prime goal of national comparability
will be lost. [Reviewer C]
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Other reviewers, by contrast, disagreed with the concept presented in an
earlier draft of this report that EPA should formally adopt a uniform index:
... 1 tend to disagree with your first recommenda-
tion ... that we should support a uniform water
quality index. I believe that EPA should support
the development and use of more uniform analysis
techniques, and your recommendations two and three
would go a long way toward achieving this goal.
[Reviewer A]
This reviewer felt that the positive views expressed by respondents toward
water quality indices may stem more from their underlying need for improved
data analysis techniques than for indices themselves:
I suspect that many of the needs expressed by State
and Regional personnel for "indices" are really needs
for any kind of water quality analysis techniques
which will help them analyze trends and help make
decisions. The result is that your report may be
biased in the direction of encouraging usage of
indices, when the real needs for the water pollution
control program may be broader. [Reviewer A]
One reviewer, from the State of Oregon, disagreed with the concept of a
uniform water quality index because it would not permit the necessary
customizing which "is essential for a valid index." This reviewer felt
that an index should be custom-tailored to individual situations to best
reflect the "geographical, hydrological, and demographic characteristics" of
each araa. Such a customized index was developed for Oregon (Chapter V):
I believe EPA should support a general approach to
index design only. Of course, T believe my approach
is most suitable. I do not think EPA should or will
ever support a single WQI. The WOI must be based on
existing conditions. [Reviewer D]
Some reviewers felt that the report overemphasized the positive features
of the NSFI, and others felt that the NSFI received too little emphasis. One
reviewer felt that the popularity of the NSFI was not very surprising since
it exhibits a number of desirable features:
I think that you could stress that the popularity of the
NSF index is not too surprising since, (1) It is extremely
simple in construct; (2) It behaves in a very expectable
and understandable manner; (3) Among other indices, it has
had the most continuous level of development, study, and
application; (4) Computer packages for interface with
STORET are available; and (5) In the absence of any lead-
ing effort or guidelines by a federal agency, users have
chosen to use the form which suits their needs and for
which the most PR work has been done. [Reviewer C]
72
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Another reviewer felt that the report tended to overemphasize the widespread
usage of the NSFI, giving the impression that the NSFI is desirable simply
because it is widely used:
I think you make too much of the wide use of the
NSFI. It is used widely because it is easy to use
and has been widely promoted. To claim that it is
satisfactory or the best available because it is
widely used is parallel to claiming that the best
automobile made is a Ford because there are so many,
or the best food available is a McDonald's hamburger
because so many are sold. I realize that the
purpose of your report was to compile what people
are using, but I believe your recommendation goes
too far in suggesting that what is used most is the
best. [Reviewer E]
Some reviewers strongly objected to the concept of a "general" water
quality index; that is, one that does not report water quality in the context
of specific water uses:
I firmly believe that the opinion that a water
quality index should not be applied to a particular
use is erroneous .... Please note that ...
[criteria and standards for various trace metals] ...
in many cases range over two orders of magnitude or
more, and some are unclearly defined as a fraction
of the 96-hour LC50. It is erroneous to put on
blinders and ignore these differences and try to
melt them all into a single index that attempts to
consider all uses. The same error should be avoided
in selecting the particular constituents that go
into an index. Again, considering the metals, each
one of the eleven listed has some kind of a criteria
or limitations. In rivers the concentrations of the
metals vary as a function of the geology of the
terrain and individual pollutants. They do not
correlate well with each other or with other water
quality characteristics, and in order to judge the
suitability of a water through an index, that index
must consider every one of these metals. In order to
use the index it is necessary to have data for every
water quality characteristic for which there are
standards or criteria. It is just plain foolish to
narrow down to an index that considers only eight
variables and claim that people generally agree that
these are the important ones. If they were the only
important ones we wouldn't have the long lists of
standards and criteria that we now have. [Reviewer E]
73
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One reviewer noted that general water quality indices often have difficulties
with each individual subindex function;
A general use index concept is fine but as soon
as one is required to define the "subindex quality
function", he runs into trouble, e.g., the NSF and
Georgia oxygen curves (and most others) appear
adequate for general aquatic life but are not for
the capacity of natural waters to assimilate
wastes. Where significant quantities of oxygen-
demanding wastes are present, supersaturation may
be of benefit in reducing oxygen demand and
therefore protecting aquatic life from low oxygen
concentrations. Similar arguments may be made for
other parameters, i.e., pH, turbidity and nutrients.
Conditions have been documented in which increased
turbidity served to control algae growth by limit-
ing light penetration. These curves depict a
black and white situation. It is not black and
white. I would like to see you discuss some of
these problems in your paper so that the problem
and complexity of index development can be
appreciated. One can go through these recommended
curves and suggest literature supported reasons why
these curves are invalid for many situations.
These are some of the reasons why a valid uniform
and absolute index is not feasible. [Reviewer D]
It was noted that, although the report gives evidence of a trend toward
increased use of water quality indices, EPA is moving away from simple trend
analyses and toward more in-depth, problem-oriented studies:
The paper reports a trend in the direction of
increased use of indices by States, and implies that
the 305(b) report is a causal factor. While this may
be true, it should be pointed out that EPA is now
pushing the States to use the 305 (b) report as a more
integral part of the water quality management process.
One result of this effort will be to emphasize
analyses which are more specific with respect to
problem identification, including more use of inten-
sive surveys, or cause and effect relationships will
be required in order to make decisions and develop
strategies for cleanup. All of these factors suggest
that the emphasis will shift from simple trend
analyses, for which indices are potentially useful,
to more sophisticated problem oriented analyses, for
which a wider range of analytical techniques are
appropriate. [Reviewer A]
74
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Finally, the reviewers generally accepted the notion that additional research
on water quality indices would be desirable, as indicated by the following
comment:
The idea of doing further research on water quality
indices as expressed in recommendation five is a good
one, particularly in light of the objective of Public
Law 92-500. I would also suggest that indices need
to be further evaluated according to broader criteria
than simply technical adequacy. If they are to be
useful for decision makers, the entire process of
technical evaluation, management use, and public
reaction (if appropriate) must be evaluated. [Reviewer A]
75
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1. McClelland, Nina I., "Water Quality Index Application in the Kansas River
Basin," U.S. Environmental Protection Agency, Kansas City, MO,
EPA-907/9-74-001, February 1974.
2. "Restoring the Quality of Our Environment," a report of the Environmental
Pollution Panel of the President's Science Advisory Committee, the White
House, November 1965.
3. Horton, Robert K., "An Index-Number System for Rating Water Quality,"
Journal of the Water Pollution Control Federation, vol. 37, no. 3,
March 1965, pp. 300-306.
4. Brown, Robert M., Nina I. McClelland, Rolf A. Deininger, and Ronald G.
Tozer, "A Water Quality Index - Do We Dare?" Water and Sewage Works,
October 1970, pp. 339-343.
5. Thorn, Gary C., and Wayne R. Ott, "Air Pollution Indices: A Compendium
and Assessment of Indices Used in the United States and Canada,"
Ann Arbor Science Publishers, Ann Arbor, MI, 1976.
6. "Federal Water Pollution Control Act Amendments of 1972," Public Law
92-500.
7. "Planning for Environmental Indices," a report of the Planning Committee
on Environmental Indices, National Academy of Sciences, Washington, DC,
February 1975.
8. Rosen, Richard H., Ron Beck, Valerie P. Bennett, Joseph A. Orlando, and
Robert B. Wrightington, "A Review and Evaluation of Water Quality Indices
and Similar Indicators, Volume I: Summary and Users Guide," prepared for
the Council on Environmental Quality by Energy Resources Co., Inc.,
Cambridge, MA, and Mathematica, Inc., Philadelphia, PA, September 1976.
9. Orlando, Joseph A., and Robert B. Wrightington, "A Review and Evaluation
of Water Quality Indices and Similar Indicators, Volume II: A Review of
Available Indices," prepared for the Council on Environmental Quality by
Mathtech, Inc., a subsidiary of Mathematica, Inc., Cambridge, MA,
September 1976.
10. Rosen, Richard H., Ron Beck, Raymond T. Pierrehumbert, Jarre H. Harris,
and Gregg Heacock, "A Review and Evaluation of Water Quality Indices and
Similar Indicators, Volume III: Evaluation of Available Indices,"
prepared for the Council on Environmental Quality by Energy Resources
Co., Inc., Cambridge, MA, September 1976.
76
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11. Akeley, Roger P., Phillip E. Chase, Franz J. Mogdis, and James H.
Soalberg, "A Review and Evaluation of Water Quality Indices and Similar
Indicators, Volume IV: Nonpoint Sources and Indicators - a Special Case,"
prepared for the Council on Environmental Quality by the Bendix Corpora-
tion, Ann Arbor, MI, September 1976.
12. Landwehr, Jurate Maciunas, "Water Quality Indices - Construction and
Analysis," Ph.D. thesis, University of Michigan, 1974 (University
Microfilms 75-10,212).
13. Orlando, J. A., R. B. Wrightington, and L. D. Maxim, "Water Quality
Indices - A Review of Available Indicators," presented at the 171st
National Meeting of the American Chemical Society, New York, NY,
April 8, 1976.
14. Ott, Wayne R., Environmental Indices: Theory and Practice, to be
published by Ann Arbor Science Publishers, Inc., Ann Arbor, MI, in 1978.
15. Dalkey, Norman C. "Delphi," Report No. p-3704, The Rand Corporation,
Santa Monica, CA, October 1967.
16. McClelland, Nina I., "Water Quality Index Application in the Kansas River
Basin," U.S. Environmental Protection Agency, Kansas City, MO,
EPA-907/9-74-001, February 1974.
17. Prati, L., R. Pavanello, and F. Pesarin, "Assessment of Surface Water
Quality by a Single Index of Pollution," Water Research, vol. 5,
pp. 741-751, 1971.
18. McDuffie, Bruce, and Jonathan T. Haney, "A Proposed River Pollution
Index," presented at the spring 1973 meeting of the American Chemical
Society, Division of Water, Air, and Waste Chemistry, NY, April 13, 1973.
19. Dinius, S.H., "Social Accounting System for Evaluating Water Resources,"
Water Resources Research, vol. 8, no. 5, October 1972, pp. 1159-1177.
20. O'Connor, Michael Fredrick, "The Application of Multi-Attribute Scaling
Procedures to the Development of Indices of Water Quality," Ph.D.
Dissertation, University of Michigan, 1972 (University Microfilms No.
72-29,161).
21. Deininger, Rolf A., and Jurate Maciunas Landwehr, "A Water Quality Index
for Public Water Supplies," unpublished report, Department of Environmental
Health, School of Public Health, University of Michigan, Ann Arbor, MI,
July 1971.
22. Walski, Thomas M., and Frank L. Parker, "Consumers Water Quality Index,"
Journal of the Environmental Engineering Division, American Society for
Civil Engineering, June 1974. pp. 593-611.
23. Stoner, Jerry D., "Water Quality Indices for Specific Water Uses,"
unpublished report, U.S. Geological Survey, Oklahoma City, OK, 1976.
77
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24. Nemerow, Nelson L., and Hisashi Sumitomo, "Benefits of Water Quality
Enhancement," prepared for the U.S. Environmental Protection Agency by
Syracuse University, Syracuse, NY, Report 16110 DAJ, December 1970.
25. Truett, J. B., A. C. Johnson, W. D. Rowe, K. D. Feigner, and L. J. Manning,
"Development of Water Quality Management Indices," Water Resources
Bulletin, vol. 11, no. 3, June 1975, pp. 436-448.
26. Dee, Norbert, Janet Barker, Neil Drobny, Ken Duke, Ira Whitman, and Dave
Fahringer, "An Environmental Evaluation System for Water Resources
Planning," Water Resources Res, 9(3): 523-535, June 1973.
27. Inhaber, H., A National Environmental Quality Index for Canada, Technical
Edition, Internal Report to the Canadian Department of the Interior,
Ottawa, Ontario, 1974.
28. Zoeteman, B. C. J., "The Potential Pollution Index as a Tool for River
Water Quality Management," Technical Paper No. 6, World Health Organiza-
tion, International Reference Center for Community Water Supply, The
Netherlands, 1973, cited by Landwehr, Reference 12.
29. Johanson, Edward E., and Jaret C. Johnson, "Identifying and Prioritizing
Locations for the Removal of In-Place Pollutants," prepared for the
U.S. Environmental Protection Agency, Office of Water Planning and
Standards, Washington, DC, May 1976.
30. Shoji, Hikaru, Takeo Yamamoto, and Takakazu Nakamura, "Factor Analysis
on Stream Pollution of the Yodo River System," Air and Water Pollution
International Journal, vol. 10, 1966, pp. 291-299.
31. Coughlin, Robert E., Thomas R. Hammer, Thomas G. Dickert, and Sallie
Sheldon, "Perception and Use of Streams in Suburban Areas: Effects of
Water Quality and of Distance from Residence to Stream," Regional
Science Research Institute, Philadelphia, PA, Discussion Paper No. 53,
March 1972.
32. Harkins, Ralph D., "An Objective Water Quality Index," Journal of the
Water Pollution Control Federation, vol. 46, no. 3, March 1974, pp. 588-
59T~
33. Kendall, Maurice, Rank Correlation Methods, Charles Griffin & Co., Ltd.,
London, 1975.
34. Schaeffer, David J., and Konanur G. Janardan, "Communicating Environmen-
tal Information to the Public; A New Water Quality Index," Journal of
Environmental Education, vol. 8, no. 4, summer 1977, pp. 18-26.
35. "The Relationships of Phosphorus and Nitrogen to the Trophic State of
Northeast and Central Lakes and Reservoirs," U.S. Environmental
Protection Agency, Las Vegas, NV, Working Paper No. 23, 1974.
78
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36. Leutner, Frederick, "Sports Fishing Catch Data as a Water Quality
Indicator," U.S. Environmental Protection Agency, Office of Water Plan-
ning and Standards, Washington, DC, April 1975.
37. "Environmental Program Administrators," U.S. Environmental Protection
Agency, Office of Regional and Intergovernmental Operations, Washington,
DC, May 1976.
38. "Directory of State Agencies Engaged in Environmental Monitoring,"
U.S. Environmental Protection Agency, Office of Research and Development,
Washington, DC, December 1973.
39. "Directory of Regional Water Pollution Control Agencies," Water and
Sewage Works, 1976, pp. 232-251.
40. "Water Quality and Pollution Control in Michigan," Michigan Department of
Natural Resources, Bureau of Water Management [Section 305(b) Report],
Lansing, MI, April 1976.
41. Neal, Larry A., "A Water Quality Index for Georgia-Update of Technical
Memorandum of October 29, 1975," Technical Memorandum, Department of
Natural Resources, Environmental Protection Division, Atlanta, GA,
December 30, 1975.
42. "Water Quality Control in Georgia 1975," Georgia Department of Natural
Resources, Environmental Protection Division [Section 305(b) Report],
Atlanta, GA, 1975.
43. Barker, Bruce, and Paul Kramer, "Water Quality Conditions in Illinois,"
Appendix A to Chapter III, "Water Quality Management," Statewide Water
Resource Development Plan, Illinois Department of Transportation,
Division of Water Resource Management, 1972.
44. Janardan, Konanur G., and David J. Schaeffer, "Development and Applica-
tions of Five New Water Quality Indices," Illinois Environmental
Protection Agency, Springfield, IL, unpublished manuscript, February 1977.
45. "Illinois Water Quality Inventory Report 1976," Illinois Environmental
Protection Agency [Section 305(b) Report], Springfield, IL, 1976.
46. Hudson, LeVerne D., and David J. Schaeffer, "Effects of the 1976 Drought
on Illinois Water Quality," Illinois Environmental Protection Agency,
presented at the American Water Resources Association, Illinois Section,
Fifth Annual Water Resources Conference, June 10-11, Chicago, IL,
February 1977.
47. Dunnette, David A., "Water Quality Index Development and Application for
the Willamette Basin, Oregon," Department of Environmental Quality, Water
Quality Division, Portland, OR, unpublished manuscript, July 1976.
48. "Environmental Quality," Fifth Annual Report of the Council on Environmen-
tal Quality," Washington, DC, December 1974, pp. 333-334.
79
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49. Sheen, Jackson R. , letter to Wayne Ott, State of Nevada Department of
Human Resources, Environmental Protection Services, Carson City, NV,
January 19, 1977.
50. Cogger, William J., Marshall L. Payne, and Lester D. Sprenger, "Water
Quality Inventory," U.S. Environmental Protection Agency, Region VIII,
Surveillance and Analysis Division, Denver, CO, October 1975.
51. Beebe, James A., "WQI A Water Quality Analysis System," U.S. Environmental
Protection Agency, Region X, Seattle, WA, unpublished manuscript,
May 1, 1975.
52. Beebe, James A., "WQI A Water Quality Data Analysis System User Guide,"
U.S. Environmental Protection Agency, Region X, Seattle, WA, unpublished
manuscript, July 1975.
53. Beebe, James A., "WQI A Water Quality Data Analysis System Program
Documentation," U.S. Environmental Protection Agency, Region X, Seattle,
WA, unpublished manuscript, July 1975.
54. "Water Quality Criteria 1972," a report of the Committee on Water Quality
Criteria, National Academy of Sciences, Washington, DC, 1972.
55. Personal communication with Ray Peterson, Sanitary Engineer, U.S. Environ-
mental Protection Agency, Region X, Surveillance and Analysis Division,
Seattle, WA, August 1977.
56. "A Recommended Air Pollution Index," a report of the Federal Interagency
Task Force on Air Quality Indicators, Council on Environmental Quality,
U.S. Environmental Protection Agency, and Department of Commerce,
Washington, DC, December 1976.
57. Leutner, Frederick D. (Acting Director, EPA Monitoring arid Data Support
Division), "Comments on Water Quality Indices Report," m€>morandum to
Wayne Ott, dated August 1, 1977, Washington, DC.
58. Weber, Cornelius I. (Chief, Aquatic Biology Section, EPA Environmental
Monitoring and Support Laboratory), "Review of Report on a Survey of
Water Quality Indices Used in the United States," memorandum to
Wayne Ott dated June 17, 1977, Cincinnati, OH.
59. Landwehr, Jurate M. (U.S. Geological Survey), "Review of Report 'Water
Quality Indices': A Survey of Indices in the United States," memorandum
to Wayne Ott dated June 17, 1977, Reston, VA.
60. Dunnette, David A. (Special Projects Coordinator, Oregon Department of
Environmental Quality), letter to Wayne Ott dated June 24, 1977,
Portland, OR.
61. Ficke, John F. (Quality of Water Branch, U.S. Geological Survey), letter
to Wayne Ott dated June 28, 1977, Reston, VA.
80
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APPENDIX A
COMMENTS FROM NONUSERS
OF WATER QUALITY INDICES
81
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APPENDIX A. INFERRED COMMENTS FROM RESPONDENTS*
AGENCIES NOT USING INDICES
AGENCY NO. 1
We performed a preliminary analysis on several indices, including the
NSFI, and found all indices to be inadequate for use in the Section
305 (b) report. Therefore, we look at the values of specific variables
in evaluating water quality for the Section 305(b) report and for other
purposes.
AGENCY NO. 2
Several years ago we looked at the Harkins index and the NSFI, but
neither was useful for describing our waters. This is because of the
high amount of sediment and phosphate in our streams; thus, these
indices would have to be modified before we could use them. However,
we now use individual variables in determining water quality for our
Section 305(b) report and find this method more than satisfactory.
AGENCY NO. 3
Although they may be useful for administrators, water quality indices
really don't give a proper picture of water quality because there
exist many special stream situations. To describe water quality
adequately using an index, one would need to use different indices for
different variables; water quality indices also should distinguish
between the chemical and physical nature of water quality variables;
for example, salinity vs. conductivity.
AGENCY NO. 4
We are now evaluating the NSFI and hope to use it in our next Section
305(b) report. However, we do not have data for all of the NSFI
variables, but will obtain values for these by a correlation with other
variables. In our preliminary analysis of the NSFI, we found that the
NSFI curves are invalid in salt and coastal waters, and that different
indices will be required for lakes and streams.
*These are interpretations by the investigators of views expressed by
respondents during telephone conversations. They do not necessarily reflect
the official viewpoint of the agency contacted. Specific quotations of the
respondents are given in quotation marks.
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AGENCY NO. 5
Water quality indices are good for public relations purposes since they
give a "black and white" number which is easily understood by the layman.
However, indices really don't tell the quality of water because they
don't take all factors into account; for example, they often exclude
biological data. We looked at one index recently and found it unsatis-
factory for our purposes because it indicated only whether or not the
the water quality standards are being met. Thus, we have come to the
conclusion that, for our purposes, we are better off not using an index.
AGENCY NO. 6
We have looked briefly at several indices for possible use in monitor-
ing BOD reduction and several other problems. However, none of the
indices were able to adequately treat the waters in the tidal/fresh
water interface. As a result, we have not been able to utilize water
quality indices and feel that their general application would be very
difficult.
AGENCY NO. 7
We developed an index for use in our 1976 Section 305(b) report.
However, we were not very pleased with the performance of the index
for two reasons: First, some of the variable values which went into
the index calculation were arbitrary due to incomplete data on some
of our streams. Second, if one of the variable values is out of line,
then the index (i.e., stream) looks bad. We feel that indices are too
simplistic and are only useful when you completely understand the many
limitations of an index; some of the factors which must be taken into
consideration in interpreting index values are stream flow rates, the
fact that streams react differently to waste loads, and the fact that
water quality naturally varies as a function of geographical area.
AGENCY NO. 8
Water quality indices are of value in that they can be used: (1) to
reflect the attainment of water quality standards; (2) to rate the
priority of sewage treatment construction grants; and (3) to focus the
use of water resources in the proper areas. We anticipate developing
an index within a year or so to use in our Section 305(b) report. The
index will be based on a model developed at the University of Kentucky.
AGENCY NO. 9
We wanted to use the NSFI in the 1975 Section 305(b) report to indicate
the percent of water quality violations and give a graphical represen-
tation of stream water quality. However, we could not because, until
this year, we did not have the capability to collect data on all of the
NSFI variables. If we have insufficient data for the NSFI this year,
we will either use an index with fewer variables or develop an index of
our own.
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AGENCY NO. 10
One respondent: The specific water quality variables for each geograph-
ical area are more useful than the "mash number" given by an index.
Accordingly, we have divided our State into 200 water quality regions
and are mapping the streams within each region. These maps will
indicate the stream's problem pollutant, its concentration, and the
level above the corresponding water quality standard.
Second respondent: We have reviewed some of the more common water
quality indices to determine how they are used and which one might be
suitable for our use. After an extensive evaluation of several indices,
we have decided to use an index in our 1977 Section 305(b) report.
However, the index will not be a standard water quality index based on
chemical variables, but will be a modified biological species diversity
index. We feel that since aquatic species are subjected to water
pollution and tend to integrate effects over time, biological indices
are more descriptive of water quality than chemical variables, which
give instantaneous values that are not necessarily valid for a whole
stream and do not reflect long-term pollution. Furthermore, the layman
does not understand the significance of the various concentrations of
chemical variables and the statistical methods used in computing a
water quality index from them. However, the average citizen can easily
comprehend the relationship between water quality and the amount and
type of stream life. With regard to the NSFI, we feel that "the
National Sanitation Foundation has attempted to move its index to a
level of sophistication that it is not capable of meeting."
AGENCY NO. 11
We are now working on adapting the NSFI for use in our Section 305(b)
report. We may be able only to use an eight-variable modified version
of the NSFI because our coverage of turbidity is inadequate. In
general, indices are not universally applicable because there are
different water uses and characteristics.
AGENCY NO. 12
We have watched the development of water quality indices with interest
and would like to see a useful index developed. However, much more
work is needed before an adequate index can be developed because those
currently in existence have faults. There is obviously a need for a
straightforward method for comparing the water quality of two rivers or
the same river over time. Indices have a simplistic beauty which
fulfills this need; however, existing indices are deceptively beautiful,
creating, in some cases, illusions about true water quality.
AGENCY NO. 13
We have examined water quality indices in many different ways and have
found that "one is limited only by his ingenuity in the number of ways
that the various water quality variables can be put together." Thus,
84
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"one comes up with a different index number depending on the index used
and what weights are assigned to the variables." "Although the idea of
a water quality index is great, water quality indices oversimplify the
picture of water quality, and tend to get misused." This problem is
reflected in the fact that no single index can be used to characterize
water for different uses, since the required water quality is different
for each use. Of course, individual indices can be employed for each
use; but if this is done, one may as well use individual variables
instead of an index.
AGENCY NO. 14
Although no index can describe water quality completely, the NSFI appears
to be an adequate general indicator of water quality. We looked briefly
at the NSFI, but could not use it because we did not have data for all
nine variables. However, we feel that in the future the NSFI variables
will be of secondary importance when compared to toxic substances.
EPA Region A (Surveillance and Analysis Division)
The NSFI is currently being evaluated by the New England Interstate
Commission (see comments in Appendix B) to determine its applicability
to the Nashua River. After this evaluation is complete, we will decide
whether or not to use a modified NSFI in Regional Office evaluations of
all New England rivers. However, our general feeling toward indices is
that they do not adequately describe water quality, particularly in the
evaluation of short-term changes of water quality. Consequently, their
primary value appears to be in the evaluation of seasonal and long-term
trends.
EPA Region B (Management Division)
The NSFI has been used by New York in its Section 305(b) report for the
last three years; New Jersey is now modifying the NSFI for use in its
1977 Section 305(b) report. The NSFI is also being used by New York
City for the Section 208 planning and water quality assessment reports.
We think that the NSFI can be used to compare water quality on a
naf-ionwide basis; however, in tidal areas, some adjustment in the TDS
or salinity variable may be necessary.
EPA Region C (Water Division)
Although water quality indices were developed as public information
tools, they "don't serve the purpose for which they were intended."
This is primarily because water systems are too complex to be described
by a simplified index. As a result, we are not in favor of using
indices and feel that EPA should not spend time developing a water
quality index, and we further feel that it really can't be done.
85
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EPA Region F (Water Division)
Although we haven't used an index, we have looked at both the Harkins
and the Region X indices. In some situations, an index works well but,
since it does not take all things into consideration, any index should
be used in conjunction with other individual variables which pinpoint
problem areas. In this respect, any index developed or recommended by
EPA must be flexible enough to enable water quality from different types
of streams to be described.
EPA Region D (Surveillance and Analysis Division)
Our Regional Administrator wants to use some type of water quality index
in the development of a Region IV Environmental Quality Profile, similar
to the one developed in Region X. In fulfilling this request, we have
looked briefly at the NSFI, Harkins, Florida, and Georgia indices. We
feel that indices are useful in describing water quality to the public,
but they cannot be used as a substitute for the reports of individual
variable analyses required by technical people.
EPA Region E (Water Division)
Indices are subject to speculation because they are "based on varying
assumptions which do not accurately reflect water quality." Many States,
due to the fact that they conduct only random sampling and not intensive
surveys, take a lot of 'half data and establish an index. Thus, they
avoid the need for extensive monitoring programs.
EPA Region G (Water Division)
Water quality indices are an old concept developed by sanitary engineers.
Concepts have changed greatly since the NSF developed its index, and the
index has not responded to these changes. For example, PCB's and other
toxics have become increasingly important, but these are not handled by
the NSFI. In general, although water quality indices may be an easy way
to transmit information, they do not tell where or what pollution
problems are — is it an industrial, municipal, or nonpoint source
problem? For the Section 305(b) reports, we use specific variables and
"plain English," so that we can correctly respond to problems. Water
quality cannot be compared on a nationwide basis, and, although the use
of water quality indices by geographical area may not be a bad approach,
it only has marginal benefits.
EPA Region I (Water Division)
One respondent: Water quality indices are probably valuable ±f_ you use
them with extreme care. Although they are not absolute indicators of
water quality, they may be useful to show water quality trends.
Another respondent: We have not found water quality indices useful, but
maybe we haven't tried hard enough. Water quality indices do not
necessarily represent water quality and are generally not very revealing.
86
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For example, although an index might indicate good water quality,
potential or existing problems might not be clearly identified.
Specifically, water quality indices don't reflect the problems we have
and tend to be misleading when applied to our class of water. Our water
is now classified on the basis of indirect variables which may or may not
be a part of any index.
Third respondent: The NSFI is an excellent tool to indicate trends in
water quality and to display data to the uninitiated. We will hopefully
be using this index in conjunction with other individual water quality
variables.
87
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APPENDIX B
COMMENTS FROM USERS
OF WATER QUALITY INDICES
88
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APPENDIX B. INFERRED COMMENTS FROM RESPONDENTS*
AGENCIES USING INDICES
AGENCY NO. 1 INDEX TYPE: Modified NSFI
We threw out temperature and reweighted the index because temperature
was not a major problem here. The index was useful in comparing which
streams appeared dirty and which appeared clean. We looked at the raw
data for these streams and compared them with the index results. I
think the index gave a "reasonable result." You can look at those
streams which came out dirtiest, and, from the raw data, they came out
on the bottom of the list. Similarly, the cleanest streams, according
to the index, came out on the top of the list. Thus, the index
appears useful, and we will keep using it, probably increasing our
coverage from 13 stations to 27 stations. Selection by EPA of a uni-
form national index probably would be a good idea. If the structure
of the index were different than those in use, it probably would be
all right, just so the index is available on STORE!.
AGENCY NO. 2 INDEX TYPE: Developed own index
We developed two indices, evaluated them, and selected one for our use.
We used it in our Section 305(b) report. We do not consider it a "true
water quality index," but rather a "trend monitoring index." Our goal
is to apply it now and then again later to follow water quality changes
over a five-year basis. We don't feel that an absolute type of index
can work; there are too many geographical differences, even within a
State. An index must be tailored to the specific locale, and it must
be empirically based. We based our index on the data we have been
collecting in the State over a period of years. We were able to assess
the index performance in light of our actual knowledge of the geograph-
ical variation of water quality and thus to come up with a suitable
means for detecting changes in water quality. Even then, it is not
necessarily a finished technical product, and further refinement is
needed. However, "we feel that the general public needed something
more in keeping with the layman's knowledge" than the raw data would
provide. Unfortunately, an index is "like nuclear energy." It is
"extremely powerful or extremely dangerous, depending on how you use
it."
*These are interpretations by the investigators of views expressed by
respondents during telephone conversations.
89
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AGENCY NO. 3 INDEX TYPE: Developed own index
Some years ago, we developed five water quality indices. We selected
the best one of these and are now using it on a Statewide basis, par-
ticularly in the Section 305(b) report. Another agency in the State
also has developed and applied a water quality index, but that was
just a "one-shot" effort. Our current index is similar to the Harkins
index, but it overcomes some of the limitations of the Harkins index.
We have carried out comparisons between biological and chemical variables
and found good correlations. Our index varies from 0 to 1 and it
represents one of the few cases where an index matches up well with
biological variables.
AGENCY NO. 4 INDEX TYPE: Modified NSFI
We have used the index, but we feel fairly neutral about it. We included
it in our 305(b) report, but I'm not sure it will be used next year.
I'm not really sure it's worth the effort. Sometimes one variable may
be out of line, and the index makes the streams look bad, causing an
erroneous interpretation. The index really is too simplistic. It's
useful only when you understand its limitations. I would not favor
adoption by the Federal Government of a uniform index, because the
waters vary considerably in different areas. Also, stream flow rates
differ, and different streams react differently to different waste
loads. Possibly application of indices on a regional basis would be
useful.
AGENCY NO. 5 INDEX TYPE: Modified NSFI
In our index, we routinely ignore temperature, because we don't have
any power plants that are sources of thermal pollution. The water
quality index is just one part of our larger computerized water quality
display system. The Section 305(b) report was an important factor in
choosing to use an index, but not the only one. There were a number of
questions by newspaper reporters. For example, the newspaper and
television stations came to us and asked, "Could you give us an inter-
pretation of water quality in the area of this city for the past 3
years?" Their readers just were not able to understand 25 variables.
The technical people often don't realize that the public wants a simpler
result. The "Daily Gazette" requires a more understandable format for
presenting water quality information. We like the NSFI variables.
These can be controlled by waste treatment processes. We know,
however, that the index is designed to accommodate a nationwide
range of variables, and we solve the problem of geographical differ-
ences by simply cautioning readers, "85 is the best you can get in
this State due to natural background conditions." We just put "85"
at the top of all the graphs. We are very satisfied with the NSFI,
although we suggest that some research on biological variables would
be useful. A uniform index which could be recommended by the
Federal Government would be a good idea. One of the best features
of the NSFI is that it already has received widespread application.
90
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Thus, a certain amount of uniformity already has occurred. If EPA
were to recommend a uniform index, EPA should probably first poll the
users. It "would not upset me greatly to use a slightly different
index," unless some new variables were included. If the index soft-
ware were available, it would be very easy to recalculate the values
with the new index. Geographical differences can be handled by
redefining the range of the scale. "If you're going to accept the
advantages of uniformity, you have to accept the disadvantages."
Some technical people object to making the data easy to understand
through an index simply because they prefer keeping it as complex as
possible. Different water uses are not a problem with this index.
I would expect the index values to lie in certain ranges for certain
water uses. I suggest that this hypothesis be tested in a study.
AGENCY NO. 6 INDEX TYPE: Standard NSFI
We have been applying the index to one of our major rivers on a pilot
basis. We found that it successfully showed distinct changes in the
river where you would expect them. On the upper reaches, it was 85-90;
on the lower reaches, it was 50. This result seemed reasonable. We
are currently planning to use the index in our annual report on water
quality to the Department of Natural Resources. They will prepare a
series of reports for various audiences. The index results will be
published and distributed to "the citizens of the State." We applied
the index manually so far, but we are thinking about programming it on
a computer so that it can be applied to the entire State. We feel that
the index has been useful in our application to this river. We feel
very strongly that the index is an excellent idea. An index is
especially useful for assessing long-term trends where the layman needs
answers to obvious questions: "If someone walked into my office and
asked, 'Damn, we're spending a lot of money in the State. Are we
improving water quality?' Right now, I can't really answer that
question." I would like to examine, on a long-term basis of several
years or more, the change in the index for the dollars spent. While
the concept of a water quality index is good, I'm not sure this index is
the best one. For example, many of the variables in the index are not
as important here as they are in other areas of the Country. The
organic pollutants are not a serious problem here, and the index does
not place enough emphasis on total dissolved solids and salinity. We
would like to add specific conductivity. We don't have thermal dischar-
ges, so we would like to omit temperature. We're thinking of a
simplified index. What is needed is a standardized way to delete
certain variables when they are not considered a problem. Then, at
least, if users drop a variable, they'll all be doing it the same way.
We favor the idea of EPA recommending a uniform water quality index.
We would like to see EPA come up with a hierarchy of indices:
(1) a "full-blown" index covering all variables, (2) an intermediate
index, and (3) a very simple index. Each index would be increasingly
more complex than the next, but the more complex indices would be
applied to the more data-rich situations.
91
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AGENCY NO. 7 INDEX TYPE: Standard NSFI
We use the multiplicative form of the NSFI. It is exactly the same as
the published version which was applied to the Kansas River Basin. We
initially applied this index to determine whether it was usable to
convey trends. We were very impressed with its performance. It cor-
related well with what you would intuitively expect. Water quality, as
depicted by the index, was improving at the places where we have major
investments in treatment facilities.
I realize that there is much controversy surrounding water quality
indices. Many persons "seem to be obsessed with 'water quality use.1
The public wants to know, 'well, how do you rate the water?'" Probably
one or two or three variables will dominate the index, taut so what?
It would be a good idea for EPA to recommend a standardized index to
avoid user "customizing." The chief problem with customizing is that
people will say, "You customized just to make yourself Look good."
We have used results from the index in the Section 106 presentation, and
we have distributed the index results at public hearings. We also have
written several articles using the index in the Department's magazine
and in the Water Pollution Control Federation Journal. Overall, we are
generally very happy with the index. It probably would be a good idea
to have a uniform national index. "Yes, EPA should recommend a
standardized index."
AGENCY NO. 8 INDEX TYPE: Harkins
We used Harkins' approach in the Section 305(b) report to compute three
indices: (1) a general index with 7 variables; (2) a mineral index
using chloride, sulfate, and total alkalinity; and (3) a nutrient index
using pH, DO, nitrogen, and phosphate. We had originally attempted to
develop our own indices based on county data, but we were not able to do
what we had hoped because of lack of data and manpower restrictions.
This year we will be using a variation of Harkins' index, and the index
results will be used in the 1976 and 1977 Section 305(b) report. A
uniform water quality index is a good idea if you could come up with
one. It would be advantageous for us to have a proven index or a set of
indices. Possibly, indices should be applied on a region-by-region
basis.
AGENCY NO. 9 INDEX TYPE: Modified NSFI
We used an additive form of the NSFI last year; next year we will use
both the additive and multiplicative forms. We usually use just 8
variables, omitting temperature because our stations are so far apart
that we can't determine departure from equilibrium. For some stations,
we don't have BOD data, so we drop BOD and adjust the weights to add to
1.0. We also add total suspended solids and total dissolved solids;
where total suspended solids are missing, we use total dissolved solids.
92
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We feel very favorable about the index application; "We think it is a
useful tool." It helps explain the data to the Congressman and layman.
They can easily understand the concept that 100 = "good" water quality,
and 0 = "bad" water quality. It seems useful, and it gives reasonable
results. The absolute value of the index really is not too useful,
however, but the relative change really shows up pollution problems.
Because most of the State's water is generally good, the water quality
index "really picks up influences."
An index like the NSFI would be better for national use than an index
based on water quality standards. Violation of water quality standards
is not a good basis for an index for national use, because each State
has different water quality standards.
AGENCY NO. 10 INDEX TYPE: Standard NSFI
We originally applied the NSFI with one change: we deleted temperature
and modified the weights accordingly. We then did a study comparing the
modified NSFI with the standard version, and we usually found less than
1/2 point difference. Thus, we decided that modification was not
necessary, and we are now using the original version. Now we're
satisfied that the original weights are good.
We use the index primarily as a public information tool. It can be
used to show the people in the basin their water quality. The river
basin where we are applying the index is very polluted. We have
applied the index for about a year, and we will run it again next
summer after treatment facilities are completed to get before/after
results. It should help assess the impact of $30 million in construc-
tion of treatment facilities currently underway.
I feel that a uniform index is a good concept. "I would support the
idea that EPA should support a uniform index." It would provide a
basis to "educate the public" that a certain number means a certain
quality. The standard NSFI appears to be a good choice for a uniform
index and would allow comparisons to be made of water quality in
different States.
AGENCY NO. 11 INDEX TYPE: Harkins
We did use Harkins' index in our previous water quality report, but we
did not intend to use it again. I felt the results with Harkins' index
were very good. I think this index is one of the best I've seen.
However, like all the indices, it requires interpretation. This is the
problem with indices: they require interpretation, so why use them?
One problem with Harkins' approach is that it is a "ranking index."
Thus, depending on the other data in the set of observations, a pH of
6.0 may come out "good" or "bad." It may look good when it is not
really good. One advantage to this index, however, is that it is "open-
ended." You can easily add another variable; you're not locked in. Two
drawbacks to the NSFI are that (1) it is "closed" rather than open-ended,
93
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and (2) it contains subjective weights.
Indices attempt to simplify too complex a situation. It is like going
to the doctor and asking for an index of one's health. It probably
would be meaningless, because there are so many factors that affect
health. The same is true for streams. It depends whether you're deal-
ing with a stream or an estuary. Then it depends whether it is a fresh-
water or brackish estuary. Can your index tell you if you have algal
blooms or fish kills? Also, if you have different water uses, you have
to consider that.
Rather than developing a uniform index, I think EPA should develop a
uniform variable-by-variable table assigning "good," "fair," or "pass"
to different ranges of variable values. Such a listing would give more
useful guidance in interpreting water quality data than indices.
EPA Region H INDEX TYPE: Developed own index
We developed a water quality index based on the percent of the time that
different water quality standards are violated. We have applied the
index to the data from several of our States and have used the index in
a number of reports. The index is now available to any of the States
within the Region and they are welcome to use it.
EPA Region J INDEX TYPE: Developed own index
Our original water quality index developed by Beebe was based on the
incidence and location of violations of water quality standards. We
have since simplified the original Beebe index to make it more a
"production item than a research item." The new version is simpler and
uses a different approach for selecting the stations. Perhaps we have
retreated somewhat from the original Beebe index, which uses a better
calculation procedure, but the present version works well for our
purposes. We now use the index to prepare annual environmental quality
profiles for each State in the Region.
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APPENDIX C
QUALITY RATING CURVES FOR
GEORGIA'S WATER QUALITY INDEX
95
-------
100 -
vo
X
o>
c
15
CO
50
100
% Dissolved Oxygen
200
Figure 01. Subindex quality function for dissolved oxygen.
-------
100
10'
10
Fecal Coliform, mpn/100ml
Figure C2. Subindex quality function for fecal coliform.
-------
100
VO
00
80
60
X
0>
V)
40
20
12
Figure C3. Subindex quality function for pH.
-------
100
VO
X
CD
•
3
CO
50.0
100.0
Figure C4. Subindex quality function for B.O.D.
-------
100
o
o
x
-------
100
0.1
1.0 10.0
Nitrite + Nitrate, mg/l
100
1000
Figure C6. Subindex quality function for nitrite + nitrate.
-------
100
80
60
o
to
15
w
40
20
0.02
0.05
0.1
_J I [_
0.2 0.5 1.0
Total Phosphorous, mg/l
2.0
5.0
10.0
Figure C7. Subindex quality function for total phosphorous.
-------
100
o
OJ
•o
c
2
w
20 -
10
20
50 100
Turbidity, TU
200
1000
Figure C8. Subindex quality function for turbidity
-------
APPENDIX D
QUALITY RATING CURVES FOR
OREGON'S WATER QUALITY INDEX
104
-------
100
x
01
TJ
Mean = 94.3% for
6 stations, 1973-75
Used on WQIA B
Used on WQI Q (final version
to be used in Oregon)
10
60 100
Dissolved Oxygen, percent saturation
Figure D1. Subindex quality function for dissolved oxygen.
140
105
-------
100
Mean = 676 MPN per 100 ml for
, 6 stations during 1973—75
50
x
o>
•
5
CO
20
For fecal coliform greater than
3000MPN/100ml, the subindex is 10.
10,
_L
_L
1000 2000
Fecal Coliform Bacteria, MPN/100 ml
Figure D2. Subindex quality function for fecal coliform.
3000
106
-------
100
x
0)
•o
15
in
Mean = 7.03 for 6 stations
during 1973-75
Figure D3. Subindex quality function for pH.
107
-------
100
-Mean = 1.06 mg/l for 6 stations during 1973-75
50
•o
IE
V)
For B.O.D, greater than
6 mg/l, the subindex is 20.
20
10
_L
2 4
Biochemical Oxygen Demand, mg/l
Figure D4. Subindex quality function for B.O.D.
108
-------
100
Mean = 84.3 mg/l for
6 stations during 1973-75
For total solids greater than
280 mg/l, the subindex is 10
50
x
V)
20
10
_L
_L
40
120
200
280
Total Solids, mg/l
Figure D5. Subindex quality function for total solids.
109
-------
100
Mean = 0.42 mg/l for 6 stations during 1973-75
50
x
-------
APPENDIX E
QUALITY RATING CURVES FOR THE
REGION X WATER QUALITY INDEX
111
-------
Dissolved oxygen, mg/l
Figure E1. Subindex quality function for dissolved oxygen concentration.
-------
40
140
60 80 100 120
Dissolved oxygen, % saturation
Figure E2. Subindex quality function for dissolved oxygen saturation.
160
180
-------
1.0
0.8
0.6
x
0>
•
oo
0.4
0.2
J
10
20
Temperature, °C
Figure E3. Subindex quality function for temperature.
30
40
-------
15
00
0.2 -
6 8
pH, standard units
Figure E4. Subindex quality function for pH.
10
-------
1.0
0.8
0.6
x
0)
T3
3
C/J
0.4
0.2
10 20
Turbidity, JTU
Figure E5. Subindex quality function for turbidity
30
40
-------
X
tt
•o
!5
CO
0.2 —
4 6
Oil and Grease, mg/l
10
Figure E6. Subindex quality function for oil and grease.
-------
00
0.2 0.3
Chlorophyll -a
0.4
0.5
Figure E7. Subindex quality function for chlorophyll -a.
-------
C
in
0.2 —
a.4
0.8 1.2
Total phosphorus, mg/l
Figure E8. Subindex quality function for total phosphorus.
-------
N>
O
0.2 ~
100
110 120 130
Total dissolved gases (% saturation)
Figure E9. Subindex quality function for total dissolved gases.
140
-------
1000 2000 3000
Total dissolved solids, mg/l
Figure E10. Subindex quality function for total dissolved solids.
4000
5000
-------
X
03
T3
V)
0.2 -
Beta
Alpha
Radioactivity, pico curies/I
Figure E11. Subindex quality function for radioactivity.
-------
1.0
0.8
0.6
X
-------
1.0
0.8
0.6
X
0)
•a
c
5
C/3
0.4
0.2
0.01 0.1 1.0
Toxicants, toxicity units
Figure El3. Subindex quality function for organic and inorganic toxicants.
10.0
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APPENDIX F
WATER QUALITY INDEX DATA SHEET
125
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APPENDIX F
WATER QUALITY INDEX DATA SHEET
Agency Name:
Address:
Telephone:
1. Was the agency/office currently using water quality index?
(yes: see #2-9)
(nolsee #10)
IF YES:
2. What was the length of time the index had been used?
less than one year 1 year 2 years over 3 years
other:
3. What type of index was used?
NSF Walski
Modified NSF Harkins
PDI Other
Description:
Variables included:
4. How many stations were included in the calculation of the index?
5. For what specific purposes was the index intended?
Trend Analysis Intensive Surveys 305(b) report
Public Information Other:
Examples:
126
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6. What time interval was covered in the index calculation?
less than one year 1 year 2 years 3 years
4 years 5 years Other:
7. Was a literature write-up or other description of the index available?
Material:
(yes) (no)
8. How were the general success and usefulness of the index rated?
Very Unfavorable Unfavorable Favorable
Very Favorable Other:
Comments:
9. Were any future studies planned regarding the development, use and/or
application of indices?
IF NO;
10. What other means were used to display and report water quality data?
ALL RESPONDENTS;
11. Was the development of a uniform water quality index which might be
endorsed by the Federal Government favored?
(yes) (no)
If no, why? ^
127
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TECHNICAL REPORT DATA
[Please read Instructions on the reverse before completing)
1 REPORT NO.
EPA-600/4-78-005
3. RECIPIENT'S ACCESSION NO.
4 TITLE AND SUBTITLE
WATER QUALITY INDICES: A SURVEY OF INDICES USED
IN THE UNITED STATES
5. REPORT DATE
January 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Wayne R. Ott
8. PERFORMING ORGANIZATION REPORT NO.
9 PERFORMING ORGANIZATION NAM!- AND ADDRESS
SAME AS BELOW
10. PROGRAM ELEMENT NO.
1HD621
11. CONTRACT/GRANT NO.
In-house
12. SPONSCHING AGENCY NAME AND ADDRESS
Office of Monitoring and Technical Support
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
10/76 - 6/77
14. SPONSORING AGENCY CODE
EPA/600/19
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This study documents the extent to which water quality indices currently are
being used in the United States. It reviews the indices published in the literature
and surveys the States and interstate commissions to determine: (1) which agencies
are using indices, (2) the type of index being used, (3) the purpose of its use, and
(4) the attitudes of agency personnel toward indices. One-fifth of the State and
interstate agencies (12 out of 60 agencies) were classified as users of water quality
indices. Of the 51 State agencies (including the District of Columbia), 10 States
(20 percent) were classified as index users. The National Sanitation Foundation
Index was the most commonly used index, accounting for 7 of the 12 index users.
The remaining agencies use Harkins' index or various user-developed indices. A total
of 16 additional States and 1 interstate commission indicated that they are planning
to evaluate indices for possible future application, or are developing or evaluating
indices at the present time; these were classified as "potential users." Six new
indices have been developed by water pollution control agencies.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Mathematical, Computerized simulation,
Statistical, Pollution, Environmental
engineering, Civil engineering
Mathematical models,
Systems analysis, Data
analysis, Sanitary engin-
eering. Environmental
indices, Water quality
indices. Statistical
analysis. Environmental
decision making.
57 H 43 F
43 0
72 F
68 D
91 A
13 DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO OF PAGES
138
20. SECURITY CLASS (This page)
22. PRICE
"PA Form 2220-1 (9-73)
128
4US GOVERNMENT PRINTING OFFICE 1978— 757-140/6670
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