'ra»r*
United States
Environmental Protection
Agency
Office of Water (4204)
Washington DC 20460
www epa.gov/owm
EPA-832-R-00-008
June 2000
| irt i
An Evaluation of the National Investment
in Municipal Wastewater Treatment
Executive Summary
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Dedication
This effort to document the water quality benefits associated with the federal
funding provided through the Construction Grants Program and Clean Water
State Revolving Fund (SRF) Program to help plan, design and construct publicly
owned treatment works (POTWs) was initiated at the request of Michael J.
Quigley while he served as Director ofthe Office of Municipal Pollution Control.
It is dedicated to the many hardworking and conscientious individuals—
including the program advocates and critics alike—who help manage, direct
(or in some cases redirect), and implement the Construction Grants and SRF
Programs, which are among the Nations largest public works programs, in a
highly professional and effective manner. They include many EPA and state
program managers and staff and local wastewater authority managers and staff,
as well as the many highly qualified consultants and contractors who help the
local authorities conduct the necessary studies, develop the required facilities
plans and project design documents, and construct and operate the treatment
facilities that were established or upgraded with funding from these highly
successful public works programs.
The document could not have been written without the extensive water
quality monitoring efforts across the country undertaken by a legion of highly
qualified field staffand researchers for many local authorities, state and federal
agencies, and colleges and universities. Their efforts produced the extensive water
quality data available in the STORET system and local reports, as well as the
water quality models and local assessments that served as the basis for the analyses
undertaken and reported on in this document.
On The Cover
For four decades beginning in the 1920s the Lower Willamette River near Portland, Oregon, was considered
one of the most polluted urban-industrial rivers in the United States. In 1927 the Portland City Club
declared the Willamette River "ugly and filthy...with intolerable conditions." During the 1950s the Willamette
River was described as the "filthiest waterway in the Northwest and one of the most polluted in the
Nation." In 1967 the Izaak Walton League described the river as a "stinking slimy mess, a menace to
public health, aesthetically offensive and a biological cesspool."
Three decades after enactment of strict water pollution control regulations by the state of Oregon in the
late 1960s and the federal Clean Water Act in 1972, the remarkable improvements in water quality and
the ecological health of the river now provide important recreational and commercial benefits to the
citizens of the Willamette valley. Salmon and steelhead fisheries, once blocked by dams without fish
ladders and constrained by low dissolved oxygen conditions, are now sustained by migratory populations
that can safely reach upriver spawning grounds. The local economies of major cities on the Willamette
River are thriving, and upscale developments are attracted to riverfront locations by the aesthetics of a
clean river that was once considered noxious with an unsightly riverfront. Although the gross water pollution
problems of the first half of the 20th century have been eliminated, nutrient enrichment, sediment loading,
and the lingering presence of toxic chemicals in the river, sediment bed, and biota are ecological problems
that remain. Hopefully, they will be addressed in the early decades of the 21st century.
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A River Reborn
"Time has been good to the Potomac River—at least the
last 25 years have been . ... A generation ago (1960s and
1970), when we had gone to the Potomac for thrills, the river
was ugly and almost frightening in its decay. The water was an
opaque red-brown sludge, smelly and foaming with unknown
chemical pollutants. The shore was littered with the rotting
carcasses of carp and with slirne-covered tires, cans, glass and
other filth.
But as we sat talking this time, the water was clear—really
clear—as though we were in the countryside far from a big city.
We could see right to the sandy bottom. The shoreline was free
of debris, and the air smelled fresh.
Best of all were the birds. Mallards swooped overhead,
heading toward the water. Despite the season, some songbirds
still darted through the trees. And far out in the channel, close
to Virginia, a huge flock of birds circled round and round a
cluster of rocks. They seemed to be feeding out there (on what
type of freshwater creature?), and the sun glistened off their
wings....
Who are the stewards of the Potomac? Who is responsible
for the amazing rebirth of a beautifil river? To all, I extend a
hearty thanks..."
—Letter to the editor of The Washington Post,
January 15, 1995 (Chase, 1995)
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Progress in Water Quality:
An Evaluation of the National Investment in Municipal Wastewater Treatment
Executive Summary
The existence of serious water
pollution problems in the United
States, first recognized during the 1920s
and 1930s and increasingly well documented
during the 1940s through 1960s, led to the rec-
ognition that the practice of discharging raw
sewage and the use of only primary treatment
in publicly owned treatment works (POTWs)
were generally inadequate technologies for
wastewater disposal.
Excessive loading of organic
matter, nutrients, sediment,
pathogens, and other pollutants
into surface waters, combined
with natural hydrologic (low-
flow) conditions, frequently ac-
counted for incidences of dis-
solved oxygen (DO) depletion,
fish kills, nuisance algal blooms,
and bacterial contamination in
rivers, lakes, and estuaries.
Many of the United States' most
famous water bodies, including
Lake Erie, New York Harbor,
and the Hudson, Upper Mississippi, Potomac,
Chattahoochee, Delaware, and Ohio rivers fell
victim to these symptoms.
In 1948 the 80th Congress encapsulated its frus-
tration with the situation when it declared that
"... The pollution of our water resources by
domestic and industrial wastes has become
an increasingly serious problem for the rapid
growth of our cities and industries. ... Pol-
luted waters menace the public health through
the contamination of water and food sup-
plies, destroy fish and game life, and rob us
of other benefits of our natural resources."
- Senate Report No. 462, 1948
For the first half of
the 20th century,
pollution in the
Nation's urban
waterways resulted in
frequent occurrences
of low dissolved
oxygen, fish kills,
algal blooms,
and bacterial
contamination.
An Increased Federal
Policy Role In the Control
of Water Pollution
National policy for water pollution control has
been legislated primarily in the Federal Water
Pollution Control Act. First passed in 1948, the
act has been amended numerous times (in 1956,
1961,1965,1966,1970,1972,1977,1981 and
1987) to gradually expand the
authority of the federal govern-
ment in regulating pollutant
discharges from point sources
to surface waters. Until enact-
ment of the 1972 (PL 92-500)
and more recent amendments,
now known as the Clean Wa-
ter Act (CWA), the primary au-
thority and responsibility for
water pollution control was at
the state level.
Unfortunately, there was a great
diversity among the states in
terms of ability and willingness
to pay the costs of building and upgrading
POTWs and to enforce pollution control laws.
Lack of local water quality standards, monitor-
ing data, and penalties for violators exacerbated
the situation. Despite 49 joint state-federal en-
forcement conferences that were convened af-
ter the 1965 Amendments to abate critical water
pollution problems, national progress in im-
proving water quality was hindered, in part,
because unless a state formally requested inter-
vention by the federal government, federal au-
thority for regulating discharges was restricted
to interstate and coastal waters.
Public awareness of nationwide water pollution
problems served as a political catalyst to shift
increased authority and responsibility for the
regulation of water pollution control from the
The 1972 CWA
shifted primary
authority for
water pollution
controlfrom
the states to
the federal
government.
1
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From 1970 to 1995, USEPA distributed $61.1 billion
in grants for POTW upgrades to secondary treatment or
greater and, since 1988, over $16.1 billion in support
for state revolving loan funds for a wide range
of water quality improvement projects.
states to the federal government. Establishment
of a nationalpolicy requiring secondary treatment
of municipal wastewater as the minimum accept-
able technology supplemented by more stringent
water quality-based effluent controls on a site-spe-
cific, as-needed basis was a key provision of the
1972 act. This mandate, coupled with an in-
crease in funding assistance to municipalities
through the Construction Grants Program, led
to a dramatic increase in the number of POTWs
with secondary and advanced treatment capa-
bilities. Congress assumed that these actions
would directly support the long-term goal of
the CWA, the national attainment of "fishable
and swimmablc" waters.
Figure 1
Annual funding provided by USEPA's Construction Grants
and CWSRF Programs to local municipalities for improve-
ments in water pollution control infrastructure from 1970 to
1999. Costs reported in current year dollars. (Data from
USEPA GICS database and CWSRF Program.)
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Construction Grants
CWSRF
The National Investment In
Municipal Wastewater
Treatment
A total of $61.1 billion ($96.5 billion as con-
stant 1995 dollars) was distributed to munici-
palities through USEPA's Construction Grants
Program in the 25-year period from 1970 to
1995 in support of the CWA's municipal waste-
water treatment program (Figure 1). An addi-
tional $ 16.1 billion (capitalization) was also dis-
tributed to the states through the Clean Water
State Revolving Fund (CWSRF) Program from
1988 through 1999. Including the state contri-
butions and loan repayments, the CWSRF loan
program assets have grown to over $30 billion
since 1988 and are funding about $3 billion in
water quality projects each year.
In terms of promoting the minimum accept-
able technology-based standard of secondary
treatment nationwide, this investment was an
outstanding success. By 1996 the number of
POTWs offering less than secondary treatment
dwindled to less than 200 (down from 2,435 in
1968 and 4,278 in 1978). Correspondingly,
there was a dramatic increase in the number of
facilities offering secondary treatment or greater
(from 10,052 facilities in 1968 to 13,816 facili-
ties in 1996).
In 1968, 72 percent of the
Nation's POTWs were providing
secondary treatment and less than
1 percent were providing greater
than secondary treatment (out of
14,051 facilities). By 1996, 59
percent of the Nation's POTWs were
providing secondary treatment and
27 percent were providing greater
than secondary treatment (out of
16,024 facilities).
2
Executive Summary
-------
The number of people served by POTWs
with secondary or greater levels of
wastewater treatment almost doubled
between 1968 and 1996!
The success of these national investments is also
demonstrated by the increase in the number of
people served by POTWs, which shifted dra-
matically between 1968 (before-CWA) and
1996 (after-CWA), as shown in Figure 2. The
story told in Figure 2 is summarized below.
• The overall number of people served by
POTWs increased from 140.1 million in
1968 to 189.7 million in 1996 (a 35
percent increase).
• The number of people relying on POTWs
with less than secondary treatment
dropped rapidly after passage of the 1972
CWA. In 1968 about 39 percent (54.2
million) of the 140.1 million people
served by POTWs received less than
secondary treatment (raw and primary).
By 1996 this percentage was reduced to
about 9 percent (17.2 million) of the
189.7 million people served by POTWs.
This 9 percent includes approximately
5.1 million people currently served by
POTWs with CWA Section 301(h)
waivers allowing the discharge of less
than secondary treated effluent to deep,
well-mixed ocean waters.
• While the number of people served by
POTWs with secondary treatment
remained fairly constant between 1968
and 1996 (a slight decrease of 3.7
million people or about 4 percent of the
population), the number of people
provided with greater than secondary
treatment increased significantly (from
0.3 million people in 1968 to 82.9
million people in 1996). Stated another
way, the U.S. population served by
POTWs with secondary or greater
treatment almost doubled between 1968
and 1996from 85.9 million people in
1968 to 164.8 million people in 1996!
Figure 2
Population served by POTWs in 1968 (before the
CWA) and in 1996 (after the CWA) by treatment type.
CData from U.S. Public Health Service municipal
wastewater inventories; USEPA Clean Water Needs
Surveys; USDOI, 1970; USEPA, 1997.)
Raw1 ¦ < Secondary ¦ Secondary ~ > Secondary II i No Discharge:
2 160
6 140
Before the CWA (1968)
After the CWA (1996)
1 Raw discharges were eliminated by 1996.
2
Data for the "no-discharge" category were unavailable for 1968.
3
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Until now, no national-scale evaluation
of the effectiveness of the Cl/VA's
technology- and water quality-based control
policies has been accomplished.
Was the Public's Investment In POTWs Worth It?
Questions concerning the environmental ben-
efits, as well as the cost-effectiveness, of the na-
tional investment in municipal wastewater treat-
ment have been raised by Congress and by spe-
cial interest, environmental, and business ad-
vocacy groups. In the 25 years after the enact-
ment of the CWA, studies have attempted to
evaluate progress in achieving the goals of the
CWA by documenting (a) administrative ac-
tions (e.g., numbers of discharge permits and
enforcement actions) and programmatic evalu-
ations (see Adler et al., 1993); (b) trends in na-
tional wastewater infrastructure (e.g., popula-
tion served by secondary or greater treatment
levels, effluent loading rates); (c) state and na-
tional inventories of waterways meeting desig-
nated uses (e.g., 305(b) reports); and (d) changes
in water quality following wastewater treatment
plant upgrades for specific waterways.
Evaluations of water quality conditions in the
United States include a pre-CWA national water
quality analysis of conditions from the 1940s
through the 1960s (Wolman, 1971; USEPA,
1974) and post-CWA assessments of the national
effectiveness of the 1972 CWA (e.g., Smith et
al., 1987a, 1987b). Assessments of local (Isaac,
1991; GAO, 1986), regional (Patrick etal., 1992),
and national water quality conditions (Smith et
al., 1992) have demonstrated improvements in
some water quality constituents following up-
grades to secondary or greater levels of wastewa-
ter treatment at municipal facilities.
There is, however, no study that has attempted
a national-scale comprehensive evaluation of the
effectiveness of the CWA's technology- and wa-
ter quality-based effluent control policies in
achieving the "fishable and swimmable" goals
of the act (Mearns, 1995).
STUDY OVERVIEW: The "Three-Legged Stool" Approach
This study takes a unique,
three-pronged approach for an-
swering the prima facie ques-
tion—Has the Clean Water Act's
regulation of wastewater treat-
ment processes at POTWs been
a success? Or posed more di-
rectly, How have the Nation's
water quality conditions changed
since implementation of the
1972 CWA's mandate for sec-
ondary treatment as the mini-
mum acceptable technology for
POTWs?
This study takes a
unique three-pronged
approach to evaluate
nationwide progress
in water quality
conditions since
the enactment of
the 1972 CWA.
The three-pronged approach
described below (and presented
in the companion document,
USEPA, 2000) was developed
so that each study phase could
provide cumulative support
regarding the success, or failure,
of the CWA-mandated POTW
upgrades to secondary and
greater than secondary treat-
ment. Using the analogy of a
three-legged stool, the study
authors believed that each leg
must contribute support to the
premise of CWA success. If one
or more legs fail in this objec-
tive, the stool will be unable to
"stand up."
Executive Summary
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The First Leg: An
examination of BOD
loadings before and
after the CWA
As increasing numbers of people hooked into
more and upgraded POTWs, there was a corre-
sponding rise in influent BOD1 loading nation-
wide to these facilities. Figure 3 presents the
amount of influent BOD loading to "less than
secondary," secondary, and "greater than second-
ary" facilities for 1968 and 1996 (years repre-
senting before and after the CWA). BOD
loadings are shown both as BOD, (carbona-
ceous BOD, i.e., oxygen demand from the de-
composition of organic carbon) as well as BODL,
(ultimate BOD, which includes nitrogenous
BOD, i.e., oxygen demand from the decom-
position of ammonia and organic nitrogen, in
addition to carbonaceous BOD).
As shown, total influent loading of BOD, in-
creased by about 35 percent, from 18,814 to
25,476 metric tons per day. Similarly, total in-
fluent loading of BOD(I increased by about 35
percent, from 34,693 to 46,979 metric tons per
day. Fortunately, this situation was counteracted
by the CWA wastewater treatment mandates,
which resulted in rising BOD removal efficien-
cies (Figure 3).
In 1968 the national aggregate removal efficien-
cies stood at about 63 percent and 39 percent for
BOD5 and BOD{,, respectively. By 1996national
aggregate removal efficiencies had risen to nearly
85 percent and 65 percent, respectively!
1 BOD, or" biochemical oxygen demand" is a
measure of the oxygen-consuming organic
matter and ammonia-nitrogen in wastewater.
The higher the BOD loading, the greater the
depletion of oxygen in the waterway.
The amount of BOD, and BODu discharged
from POTWs to the Nation's waterways
declined by about 45 percent and 23 percent,
respectively, after the 1972 CWA, despite a 35
percent increase in influent loadings!
Figure 3
Influent and effluent loading of BOD to and from POTWs
in 1968 (before the CWA) and in 1996 (after the CWA)
by treatment type and associated BOD aggregate
removal efficiencies. (Data from U.S. Public Health
Service municipal wastewater inventories; USEPA Clean
Water Needs Surveys; USDOI, 1970; USEPA, 1997.)
I < Secondary K Secondary ~ > Secondary
I
I
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Without continued improvements in wastewater
treatment infrastructure, future population growth
will erode away many of the CWA achievements in
effluent loading reduction.
Figure 4
Projections of design-based, national effluent BODtJ loadings
through 2025 using middle-level U.S. population projections.
(Population projection data from U.S. Census, 1996.)
Assumptions:
Influent flow is a constant 165 gallon/capita-day1 with a B0Du of 396.5 mg/L
Projection Results:
1968 1972 1978 1996 2016 2025
Population served (millions) 140.1 141.7 155.2 189.7 275.0 295.0
Percent of total population 71% 69% 70% 72% 88% 88%
Design removal efficiency (BOD J 39% 41% 52% 65% 71% 71%
Effluent BOD„ (metric tons/day) 21,280 20,831 19,147 16,325 19,606 21,090
80,000
70,000
60,000
cjj
« 50,000 -
¦ Influent BODu
¦ Effluent BODu
O Removal Efficiency
40,000
P 30,000
d
Q
m 20,000
iiicr
10,000
1940 1950 1962 1968 1972 1978 1982 1988 1992 1996
Year
2016 2025
1 165 gal/capita-day is based on the mean of population served and wastewater flow
data in the Clean Water Needs Surveys for 1978 through 1986 and accounts for
residential, commercial, industrial, stormwater, and infiltration and inflow compo-
nents.
The dynamic
relationship be-
tween influent
BOD loading,
BOD design re-
moval efficien-
cy, and effluent
BOD loading creates an important model for
planning new investments in wastewater treat-
ment infrastructure (Figure 4). Based on the data
reported in the 1996 Clean Water Needs Sur-
vey Report to Congress (USEPA, 1997), the
overall design BOD removal efficiency is likely
to increase somewhat because there is an appar-
ent trend toward a higher proportion of ad-
vanced (greater than secondary) POTWs. In the
next 20 years, however, the proportion of the
U.S. population served by POTWs is also likely
to increase as the urban population of the na-
tion increases.
Using the assumptions listed in Figure 4, and
using middle-level population growth projec-
tions from the Census Bureau (U.S. Census,
1996), it was estimated that by 2016 nearly 275
million people will be served by POTWs that
discharge to surface waters. Assuming a 165 gal/
capita-day influent flow and 396.5 mg/L con-
centration of influent BODu, this growth
(1996-2016) would result in a 45 percent in-
crease in influent BODu loading to POTWs
(68,030 metric tons per day) and a 20 percent
increase in effluent BOD(l loading to surface
waters (19,606 metric tons per day). These pro-
jected 2016 effluent BOD(/ loadings are similar
to levels that existed in the mid-1970s, only a few
years after the CWA! Projecting further into the
future, effluent BODu loadings in 2025 (21,090
metric tons per day) would be similar to load-
ing rates experienced in 1968 (21,280 metric
tons per day), when they had reached a historic
maximum level!
Based on middle-level
population
projections, effluent
loading rates of
RODv in 2016 would
be similar to loading
rates experienced in
the mid-1970s, only a
few years after the
CWA!
6
Executive Summary
-------
These types of projections underscore the im-
portance of the need to continually invest in
improvements to wastewater treatment infra-
structure in order to maintain and improve pol-
lutant removal efficiencies. Without these im-
provements, many of today's achievements in wa-
ter pollution control will be overwhelmed by
tomorrow's demand from urban population
growth. A recent report by the Water Infrastruc-
ture Network (WIN, 2000) also documents the
risk of reversing the environmental gains of the
last three decades.
Although POTWs are often the dominant
source of BOD effluent loading in major urban
areas, other sources affect waterways on a na-
tional scale. To put POTW effluent loading in
perspective, USEPA's National Water Pollution
Control Assessment Model (NWPCAM) and
input data from USEPA's Permit Compliance
System (PCS) and the Clean Water Needs Sur-
vey (CWNS) were used to examine current
BOD., loading (ca. 1995) for several key point
and nonpoint sources (Bondelid et al., 1999).
From a national perspective, it was found that
currently (ca. 1995) POTW BOD5 loadings ac-
count for only about 38 percent of total point
source loadings and only 21 percent of total
loadings (point and nonpoint). Industrial fa-
cilities (major and minor) currently account for
about 62 percent of total point source BODs
loadings and 34 percent of total BODs load-
ings. Clearly, continued improvement in the
water quality conditions of the Nation's water-
ways will require an integrated strategy to ad-
dress all pollutant sources, including both point
and nonpoint sources.
The first leg of the three-legged stool approach
focused on the Nation's investment in building
and upgrading POTWs to achieve at least sec-
ondary treatment. Based on this historical BOD
Future water quality management strategies will
need to consider integrated point and nonpoint
source controls since POTWs account for only 21
percent of the total BOD5 loadings nationwide.
Figure 5
Percent changes in population served, influent BOD loading,
and effluent BODg and BODy loading before and after the
1972 CWA (1968 to 1996). (Data from U.S. Public Health
Service municipal wastewater inventories; USEPA Clean
Water Needs Surveys; USDOI, 1970; USEPA, 1997.)
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Served
35%
Influent
Load
35%
bod5
and
BODu
Effluent
Load
-45%
Effluent
Load
-23%
bod5
BODjj
loading analysis, it is clear that the CWA's
mandate for secondary treatment as the
minimum acceptable treatment technol-
ogy, supplemented by more stringent wa-
ter quality-based effluent controls on a site-
specific basis, combined with financial as-
sistance from the Construction Grants and
CWSRF Programs, resulted in a dramatic
nationwide decrease in effluent loading of
BOD from POTWs into the Nation's wa-
terways (see Figure 5).
The 45 percent nationwide reduction in
effluent BOD5 loading and the 23 percent
reduction in effluent BODu loading was
achieved during a period when total popu-
lation served and influent loading of BOD
both increased by 35 percent!
Conclusion
of the first leg
of the stool
There was a dramatic
nationwide decrease in
BOD effluent loading
from POTWs after the
1972 CWA despite a
significant increase in
population served!
7
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A systematic, peer-
reviewed approach was
developed to identify water
quality station records that
encode the "signal" related
to the water quality
impact of point source
discharges from the "noise"
of millions ofhistorical
records archived in
STORET.
The Second Leg: An
examination of "worst-
case" DO in waterways
below point sources before
and after the CWA
The second leg follows up on the first leg with
the question Has the CWA'spush to reduce BOD
loading resulted in improved water quality in the
Nation's waterways? And, if so, to what extent?
The key phrase in the question is "to what ex-
tent?" Earlier studies by Smith et al. (1987a,
1987b) and Knopman and Smith (1993) con-
clude that any improvements in DO conditions
in the Nation's waterways are detectable only
within relatively local spatial scales downstream
of wastewater discharges.
Because of the ecological significance of DO and
its well-known causal relationship with the de-
composition of organic carbon (car-
bonaceous BOD) and the decompo-
sition of organic nitrogen and ammo-
nia (nitrogenous BOD) from waste-
water discharges, historical DO
records provide an excellent environ-
mental indicator for characterizing
water quality responses to long-term
changes in wastewater loading. A con-
siderable amount of historical data is
archived, and readily accessible, in
STORET, USEPA's national water
quality database.
The inherent difficulty in evaluating
the effectiveness of reductions in point
source loading is the need to isolate
the water quality impact of discharges from the
impacts caused by other confounding factors
such as nonpoint sources, as well as the natural
influence of streamflow and water temperature.
In this assessment, a systematic, peer-reviewed
approach has been designed to identify water
quality station records that encode the "signal"
related to the water quality impact of point
source discharges from the overwhelming
"noise of millions of historical records archived
in STORET
With DO as the key water quality indicator, and
keeping in mind the need to evaluate the change
in the DO "signal" over time (before and after
CWA) as well as over different spatial scales (i.e.,
river reaches [which average 10 miles in length],
catalog units, and major river basins), the fol-
lowing "rules" for data analysis were used in a
six-step data mining process to create before-
and after-CWA data sets of "worst case" DO to
be used in an unbiased comparison analysis of
downstream water quality conditions. The
screening rules associated with each phase are
listed below:
Step 1—Data Selection Rules
• DO data were extracted only for
summer (July-September).
• Only surface DO data (within 2 meters
of the surface) were used.
Step 2—Data Aggregation Rules From a
Temporal Perspective
• 1961 -1965 served as the "time-block" to
represent persistent dry weather before
the CWA, and 1986-1990 served as the
time-block to represent persistent dry
weather after the CWA. These time-
blocks were selected based on an
analysis of long-term mean summer
streamflow.
• DO data must come from a station in a
catalog unit that had at least 1 dry year
out of the 5 years in each before- and
after-CWA time-block.
Executive Summary
-------
Worst case historical DO data were
aggregated by three scales of spatial
hydrologic units: reach, catalog unit,
and major river basin.
Step 3—Calculation of the Worst-case
DO Summary Statistic Rules
• For each water quality station, the 1 Oth
percentile of the DO data distribution
from the before-CWA time period (July
through September, 1961-1965) and the
10th percentile of the DO data distribu-
tion from the after-CWA time period
(July through September, 1986-1990)
were used as the DO "worst-case"
statistic for the comparison analysis.
• A station must have a minimum of
eight DO measurements within each of
the 5-year time-blocks.
Step 4—Spatial Assessment Rules
• Only water quality stations on streams
and rivers affected by point sources were
included in the before- and after-CWA
comparison analysis. Stations affected
only by nonpoint sources were ex-
cluded. Out of 64,902 river reaches in
the contiguous United States, 12,476
are downstream of a point source. Also,
out of 2,111 catalog units, 1,666 have
river reaches that are downstream of a
point source.
Step 5—Data Aggregation Rules From a
Spatial Perspective
• For each data set and time-block, the
1 Oth percentile value from each eligible
station was aggregated within the spatial
hydrologic unit. (Since the scales are
hierarchical, a station's summary
statistic was effectively assigned to a
reach and a catalog unit.) A summary
statistic was then calculated and as-
signed to the spatial unit for the
purpose of characterizing its worst-case
DO. If a spatial unit had only one
monitoring station within its borders
meeting the screening criteria, the 10th
percentile DO value from that station
simply served as the unit's worst-case
summary statistic. If, however, there
were two or more stations within a
spatial unit's borders, the 10th percen-
tile values for all the eligible stations
were averaged, and this value used to
characterize worst-case DO for the unit.
Step 6—Development of the Paired
Data Sets (at each spatial scale)
• To be eligible for the paired (before vs.
after) comparison analysis, a hydrologic
unit must have both a before-CWA and
an after-CWA summary statistic
assigned to it.
The comparative before- and after-CWA analy-
sis of worst-case DO data derived using the
screening criteria described above and aggregated
by three scales of spatial hydrologic units (reach,
catalog unit, and major river basin) yielded the
following results.
Only water quality
stations on streams
and rivers affected by
point sources were
included in the before-
and after-CWA
comparison analysis.
9
-------
The 311 evaluated reaches
represent a disproportionately
high amount of urban/industrial
population centers.
Reach Scale Analysis
• 69 percent of the reaches evaluated showed
improvements in worst-case DO after the
CWA (311 reaches [out of a possible
12,476 downstream of point sources]
survived the data screening process with
comparable before- and after-CWA DO
summary statistics. The number of
reaches available for the paired analysis
was limited by the historical data
archived for the 1961-1965 period).
• These 311 evaluated reaches represent
a disproportionately high amount of
urban/industrial population centers,
with approximately 13.7 million
people represented (7.2 percent of the
total population served by POTWs in
1996). As shown in Figure 6, the top 25
improving reaches saw their worst-case
DO concentrations increase by 4.1 to
7.2 mg/L!
• The number of evaluated reaches
characterized by worst-case DO below
5 mg/L was reduced from 167 to 97
(from 54 to 31 percent).
• The number of evaluated reaches
characterized by worst-case DO above
5 mg/L increased from 144 to 214
(from 46 to 69 percent).
Key finding at the
reach scale: 69
percent of the paired
reaches showed
worst-case DO
improvements after
the CWA!
10
Executive Summary
-------
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f
r
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[^uyahoga^ive^J
|_^Ocont^ive^l
I^Visconsir^Ri\^erJ
[ River Raisin |
Mahoning River
Manitowoc River
s_S\
Cattaraugus Creek
S
Root River
Sioux River
Milwaukee River
Casselman River
r
| DuPage River (E.B.)
IE
Neshaminy River |
| Pes Plains River |
Kanawha River |
naT
Before the CWA
After the CWA
Great Miami River
White River
a io.o
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Holston River-S Fk
Catawba River I
White River
Enid Lake
Grenada
Reed^Rive^^J
ID ,
Pascagoula River | j
2 3 4 5 6 7 8 9 10111213141516171819202122232425
River Reach Ranking
Figure 6
Location map and distribution chart of the 25 RF1 reaches identified with greatest after-CWA improvements in
10th percentile DO, 1961-1965 vs. 1986-1990. Reaches are ranked by greatest before- and after-CWA improvements.
-------
Key finding at the
catalog unit scale: 68
percent of the paired
catalog units showed
worst-case DO
improvements after
the CWA!
Catalog Unit Scale Analysis
• 68 percent of the catalog units evaluated
showed improvements in worst-case DO
after the CWA (246 catalog units [out of
a possible 1,666 downstream of point
sources] survived the data screening
process with comparable before- and
after-CWA DO summary statistics).
• The number of evaluated catalog units
characterized by worst-case DO below
5 mg/L was reduced from 115 to 65
(from 47 to 26 percent). The number of
evaluated catalog units characterized by
worst-case DO above 5 mg/L increased
from 131 to 181 (from 53 to 74 per-
cent).
As shown in Figure 7, 53 of the 167
improving catalog units (32 percent)
improved by 2 mg/L or more while only
10 of 79 degrading catalog units (13
percent) degraded by 2 mg/L or more.
These 246 evaluated catalog units
represent a disproportionately high
amount of urban/industrial population
centers (see Figure 8), with approxi-
mately 61.6 million people represented
(32.5 percent of the total population
served by POTWs in 1996).
Figure 7
Frequency distribution of the mean 10th percentile DO for 246 catalog units that
improved (n=167) and degraded (n=79) after the CWA. (Source: USEPA STORET.)
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(a) (b)
Magnitude of Decrease in 1 Magnitude of Increase in
Worst-Case DO (mg/L) after the CWA I Worst-Case DO (mg/L) after the CWA
I
12
Executive Summary
-------
owe^usquehannaj
[^owe^pokan^J
Lake Dubay | ^Ocont^^^J
Lower Fox
[^^attaraugu^^J
_^^Qjyahog^^|
Salinas
Coldwater
ower Great Miami
Before the CWA
After the CWA
|> 10.0
3 4 5 6 7 8
Catalog Unit Ranking
Catalog units with improved 10th percentile DO
Catalog units with degraded 10th percentile DO
Figure 8
Location map of the 246 catalog units that improved or degraded in terms of 10th percentile DO after the CWA, 1961-1965 vs. 1986-
1990. The 10 catalog units with the greatest after-CWA improvements are highlighted and presented in a distribution chart.
(Source: USEPA STORET.)
-------
Statistical tests run on the 311 paired
reaches aggregated as a national whole
revealed significant improvement in DO.
Major River Basin Scale Analysis
• A total of 11 out of 18 major river
basins had sufficient reach-aggregated
worst-case DO data for a before- and
after-CWA comparison.
• Based on two statistical tests, 8 of these 11
major river basins can be characterized as
having statistically significant improve-
ment in worst-case DO levels after the
CWA! The three basins that did not
statistically improve under either test
also did not have statistically significant
degradation (Table 1).
• When all the 311 paired (i.e., before vs.
after) reaches were aggregated and the
statistical tests run on the contiguous
states as a national whole, worst-case
DO also showed significant improve-
ment.
Key finding at the
hydrologic region scale:
8 of the 11 major river
basins with sufficient data
had statistically significant
improvement in worst-case
DO levels after the CWA!
Table 1: Statistical Significance of Trends in Mean 10th Percentile (Worst-Case) DO by Major River Basin
Before vs. After the CWA (1961-1965 vs. 1986-1990). (Source: USEPA STORET.)
Worst-
Worst-
No. of Paired
Kolmogorov
Case DO
Case DO
(before vs. after)
Paired
Smirnov
(mg/L)
(mg/L)
River Basin
Reaches
t-test
test
1961-65
1986-90
All USA (01-18)
311
Yes
Yes
4.56
5.53
01 - New England Basin
1
*
~
4.30
6.90
02 - Middle Atlantic Basin
17
Yes
Yes
2.80
4.94
03 - South Atlantic-Gulf
61
Yes
Yes
4.10
4.73
04 - Great Lakes Basin
26
Yes
Yes
3.85
6.06
05 - Ohio River Basin
66
Yes
Yes
5.40
6.04
06 - Tennessee River Basin
19
Yes
No
4.08
5.23
07 - Upper Mississippi Basin
48
Yes
Yes
3.80
5.31
08 - Lower Mississippi Basin
25
No
No
3.79
3.94
09 - Souris-Red Rainy Basin
2
*
*
5.65
6.75
10 - Missouri River Basin
10
No
No
5.76
6.53
11 - Arkansas-Red—White Basin
7
No
No
5.36
4.60
12 - Texas-Gulf Basin
2
*
*
5.77
4.37
13 - Rio Grande Basin
0
~
•*
—
-
14 - Upper Colorado River Basin
1
*
*
4.88
7.22
15 - Lower Colorado River Basin
0
~
*
—
—
16 - Great Basin
2
*
*
7.45
6.10
17 - Pacific Northwest Basin
17
Yes
No
7.61
8.21
18 - California Basin
7
Yes
Yes
5.61
7.58
Paired t-test: 95% confidence - 2-sided test. Kolmogorov Smirnov test: 90% confidence, 2-sided test
insufficient data for analysis
14
-------
Closer examination of urban
Conclusion of
the second leg
of the stool
There were significant
after-CWA improvements
in worst-case summer DO
conditions in two-thirds
of the hydrologic units at
all three spatial scales!
waterways helps identify; quantify;
and document specific causes of
water quality improvements.
The second leg of the three-legged stool ap-
proach focused on assessing the change in the
point source discharge/downstream worst-case
DO signal over progressively larger spatial scales.
The results of this analysis show that there were
significant after-CWA improvements in worst-
case summer DO conditions in two-thirds of
the hydrologic units at all three spatial data ag-
gregation scales, from the small subwatersheds
of Reach File Version 1 river reaches (mean
drainage area of 115 mi2) to the very large wa-
tersheds of major river basins (mean area of
434,759 mi2).
These results provide strong evidence that the
CWA's requirements for municipal wastewater
treatment using secondary treatment as the
minimum acceptable technology, supplemented
by more stringent water quality-based effluent
controls on a site-specific basis, yielded broad
as well as localized benefits!
The Third Leg: Case
Study Assessments of
Water Quality
The national-scale evaluation of long-term
trends in water quality conditions associated
with the second leg of the three-legged stool
identified numerous waterways characterized
by substantial improvements in DO after the
CWA. The uniqueness of each waterway and
the activities surrounding it requires an inves-
tigation to go beyond STORET to identify,
quantify, and document in detail the specific
actions that have resulted in water quality im-
provements and associated benefits to water
resource users.
Nine urban waterways were selected for closer
examination of the factors that caused improve-
ment in local water quality and environmental
resources (Figure 9). Note that the case study
site selection was made prior to completion of
the DO trend analysis described in the second
study leg.
Most of the case study waterways were sites
of interstate enforcement cases from 1957 to
1972, were listed as potential waterways to con-
vene state-federal enforcement conferences in
1963, or were subjects of water quality evalua-
tion reports prepared for the National Com-
mission on Water Quality. Two sites (Ohio
River and tributaries to the Hudson-Raritan
estuary) were on a 1970 list of the top 10 most
polluted rivers. Yet, interestingly, these case
study waterways included none of the 25 river
reaches with the greatest before- versus after-
CWA improvements in DO found in the sec-
ond leg of this study (see Figure 6).
These case study waterways represent heavily ur-
banized areas with historically documented wa-
ter pollution problems. A variety of data sources,
including the scientific literature, USEPA's na-
15
-------
Figure 9
Location map of case study waterways and distribution chart of their before- and after-CWA mean 10th
percentile DO for case study RF1 reaches: 1961-1970 vs. 1986-1995. (Source: USEPA STORET.)
2. Hudson-Raritan
estuary
3. Delaware estuary
J
1. Connecticut River
9. Willamette River
4. Potomac estuary
8. Upper Mississippi River
7. Ohio River
5. James estuary
10.0---
Before the CWA
After the CWA
7.5
2 3 4 5 6 7
Case Study Waterway Number
6. Chattahoochee River
12.5-1-
tional water quality database, and federal, state,
and local agency reports, were used to character-
ize long-term trends in population, point source
effluent loading rates, ambient water quality, en-
vironmental resources, and recreational uses. Ad-
ditional information was obtained from validated
water quality models for the Delaware, Potomac,
and James estuaries and Upper Mississippi River
case studies to quantify the water quality improve-
ments achieved by upgrading municipal facili-
ties to secondary and greater levels of treatment
as mandated by the 1972 CWA.
16
Executive Summary
-------
Key findings from the nine case studies are high-
lighted below.
• In each of the case study urban areas,
significant investments were made in
expansions and upgrades to POTWs
with commensurate increases in popula-
tion served.
• Before the CWA, during the 10-year
period from 1961 to 1970, "worst-case"
DO levels fell in the range of 1 to
4 mg/L for most of the case study sites;
after the CWA, during the 10-year
period from 1986 to 1995, worst-case
DO levels improved to levels of almost
5 to 8 mg/L.
• Water quality improvements associated
with BOD,., suspended solids, coliform
bacteria, heavy metals, nutrients, and
algal biomass have been linked to
reductions in municipal and industrial
point source loads for many of the case
study waterways.
• Tremendous progress has been made in
improving water quality, restoring
valuable fisheries and other biological
resources, and creating extensive water-
based recreational opportunities (an-
gling, hunting, boating, bird-watching,
etc.) in all case study waterways.
The results of the third leg of the three-legged
stool approach revealed that the significant in-
vestments made in municipal wastewater treat-
ment resulted in dramatic improvements in re-
storing water quality and biological resources and
in supporting thriving water-based recreational
uses in all the case study areas.
Although significant progress has been achieved
in eliminating noxious water pollution condi-
tions, remaining problems with nutrient enrich-
ment, sediment contamination, heavy metals,
and toxic organic chemicals continue to pose
threats to human health and aquatic organisms
for these case study waterways. Serious ecologi-
cal problems remain to be solved for many of the
Nations waterways, including the sites of these
case studies.
Conclusion of
the third leg
of the stool
Tremendous progress
has been achieved in
improving water quality,
restoring valuable
biological resources,
and creating recre-
ational opportunities in
all the case study areas!
Progress in Water Quality: An Evaluation of the National Investment in Municipal Wastewater Treatment
-------
Conclusion
The three-legged stool approach to answering
the question Has the Clean Water Act's regula-
tion of wastewater treatment processes at POTWs
been a success? was developed
so that each of the legs could
provide cumulative support
regarding the success or fail-
ure of the CWA-mandated
POTW upgrades to at least
secondary treatment. Exam-
ining the results of each of
the study legs, the conclu-
sion is overwhelming that
the stool does indeed "stand
Conclusion of
the three-legged
stool approach
up
At both broad and local
scales, the water pollution
control policy decisions
of the 1972 CWA have
achieved significant suc-
cesses nationwide in terms
of reduction of effluent
BOD from POTWs,
worst-case (summertime,
low-flow) DO improve-
ment in waterways, and overall water quality
improvements in urban case study areas.
Each leg of the stool
cumulatively and quantita-
tively supports the theory
that the 1972 CWA's regula-
tion of wastewater treat-
ment processes at POTWs
has been a significant
success!
long-term trends in signals for water quality
parameters other than DO (e.g., suspended
solids, nutrients, toxic chemicals, pathogens) to
develop new performance
measures to track the effec-
tiveness of watershed-based
point source and nonpoint
source controls.
As new monitoring data are
collected, it is crucial for the
success of future perfor-
mance measure evaluations
of pollution control policies
that the data be submitted,
with appropriate QA/QC
safeguards, to accessible
databases. If the millions
of records archived in
STORET had not been
readily accessible, it would
have been impossible to
conduct this national analy-
sis of DO changes over the
last quarter century.
Manij challenges
remain. We must maintain
and enhance the progress already
achieved in municipal wastewater
llution control as well as address
The data mining and statisti-
cal methodologies de-
signed for this study
can potentially be
used to detect
po
other pollution
and problems
pollution sources and pro
in the Nation's waterways.
Importantly, this study
provides the first national-scale comprehensive
evaluation of the effectiveness of the CWA's
technology- and water quality-based effluent
control policies in achieving the "fishable and
swimmable" goals of the act. Population
growth and expansion of urban development,
however, threaten to erase these achievements
unless improvement in wastewater treatment
and pollution control continues.
With the newer watershed-based strategies
for managing pollutant loading from point
and nonpoint sources detailed in USEPA's
Clean Water Action Plan (USEPA, 1998),
the Nation's state-local-private partner-
ships will continue to work to attain the
original "fishable and swimmable" goals
of the 1972 CWA for all surface waters
of the United States.
18
Executive Summary
-------
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Progress in Water Quality: An Evaluation of the National Investment in Municipal Wastewater Treatment
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