United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
March 1980
?XEPA QECHNOLOGY
QRANSFER
The Bridge Between
Research and Use
Hydraulic Considerations That Affect Secondary
Clarifier Performance
Robert M. Crosby and Jon H. Bender
Introduction
Properly designed and operated clarif iers are essential to the overall performance of
virtually every municipal wastewater treatment process. Present design guidance for
clarifiers is generally incomplete because it is based on idealized hydraulic and
process conditions that do not exist in most clarifiers. In many cases, clarifier design
has been reduced to specifications of size without consideration of the internal and
external factors which affect the process.
Concern about clarifier design prompted the initiation of a research project to define
flow regimes by adapting existing and developing new measurement and analytical
techniques.
The project involved a study of eight full-scale units, including both center- and
peripheral-feed circular and rectangular clarifiers, where problems were thought to
exist. With the problems identified, modifications were to be attempted and any
performance improvements documented.
This article presents the preliminary conclusions of the investigators, based on a
mixture of the data collected and other observations, though all of the observations
are not completely quantified. It is the intent of the authors to generate feedback from
other members of the profession with knowledge and experience in clarifier design.
Analytical Procedures
The facilities listed in Table 1 were selected for study: Historically, settling basin
hydraulic characteristics have been examined by measuring the dispersion of a slug of
tracer as it moves from inlet to point of discharge. From a plot of tracer concentration
versus time at the discharge one can infer the flow regime within the basin. However,
these results give no indication of the fluid movements within the clarifier.
One analytical tool adapted for this study is a boundary- and time-limited version of a
technique more commonly used by oceanographers to trace the source and fate of
pollutants in estuarine and coastal waters. Its purpose here was to acquire a series of
"snapshots" of the dye plume's progress in a representative radial or longitudinal
section of the tank.
The tests began with continuous injection of RhodamineWT dye just upstream of the
clarifier inlet. Subsequently, samples for dye concentration measurement were taken
within several sequential 3- to 5-minute periods at 25 predetermined points in the
tank. Usually three or four sets of 25 samples were taken at about 30-minute
intervals. The complete test series took from 11/2 to 2 hours. For this study, each
sample included sufficient fluid volume for total suspended solids (TSS)
measurement, after removal of the small quantity needed to determine the dye
concentration.
-------
TABLE 1. PROJECT FACILITIES
Location
Albuquerque, NM
Dallas, TX -Ten Mile
Creek Regional Waste
Treatment Plant
Holly Hill, FL
Morganton, NC
Process Design Clanfier
Type (mVd x 103)Type
Air Activated 148.00 CFPO
Sludge
Air Activated 25.50 CFPO
Sludge
Mechanical 4.54 R
Activated
Sludge
Pure O2 30.30 CFPO
Activated
Sludge
Design Surface Sludge
Dimensions Depth Overflow Rate Removal
(m) (m) (mVmVd) Mechanism
41
32
20
4
24
(diam) 4.0 27.8
(diam) 3.7 32.1
(L) 2.7 23.5
9(W)
(diam) 4.9 32.6
Siphon
Siphon
Chain & Flight
Siphon
Oakland, CA - East Bay
Municipal Utility
District
Main Plant
Process Water
Orange County, FL
Sand Lake Waste Water
Treatment Plant
Stamford, CT
Pure O2 636.00 PFPO
Activated
Sludge
Air 3.78 CFPO
Activated
Sludge
Air Activated 114.00 R
Sludge
Mechanical 75.70 CFPO
Activated
Sludge
43
14
63
23
40
(diam) 4.3 26.5
(diam) 3.0 25.6
(L) 4.0 19.7
(W)
(diam) 4.0 30.6
Siphon
Siphon
Traveling
Bridge Siphon
Siphon
CFPO - center feed, peripheral overflow
PFPO - peripheral feed, peripheral overflow
R - rectangular
The "snapshot" was produced by drawing the contours, or
lines of equal tracer or TSS concentration, on a scaled
sectional drawing of the clarifier. The timed series of
contour drawings provided a clear picture of the fluid's
path. Figure 1 is a plot of the flow pattern test of a 20-m
rectangular secondary clarifier.
A second adaptation of traditional dye tracer methodology
was the test to measure dispersion. After release of a dye
slug upstream of the inlet, frequent samples were taken at
three to six widely separate weir locations rather than at
the point of discharge. This technique provided information
on direction preferences, often showing peaks which
correlated closely with physical disturbances such as
those created by sludge removal mechanisms.
The third test, "solids wave," was developed for this study
to determine the effect of sludge removal mechanisms on
clarifier performance. This involved frequent vertical
profiles of TSS concentration at one location near the
effluent weirs. The "solids wave" is depicted by a plot of
solids concentration versus time at each depth in the
vertical profile.
Figure 1. Typical results of flow pattern test showing dye concentra-
tions in a longitudinal section of clarifier after 15 minutes of
continuous dye release. (Note: vertical scale exaggerated)
Results and Preliminary Conclusions
Influence of System Physical Features on Process
Performance
Balance Between Parallel Clarifiers—\\ seems axiomatic
that the best use of available hydraulic capacity, when two
-------
or more clarifiers operate in parallel, is when both receive
the same influent flow rate and solids loadings and have
equal amounts of sludge removal. In five of the six plants
included in this study with two or more parallel clarifiers,
adequate means for either measuring or adjusting t'he
overflow rate of individual clarifiers was not available.
Flow measurements by dye dilution techniques or newly
installed flow measurement weirs revealed imbalances of
5 to 20% during normal peak flow hours.
Gate valves on the influent lines were commonly used to
control flow. The hydraulic characteristics of gate valves
are nonlinear, requiring in some cases almost complete
closure to balance flows at one rate. In situations where
one valve is partially closed to balance flows, variations in
flow rate will be greater through the open valve and make
manual balancing of diurnal flows difficult.
A satisfactory design solution would be to provide equal
distribution by means of hydraulic drops across equivalent
weirs exiting a level head channel or basin upstream of the
clarifiers. Regardless of head loss downstream of the drop,
each unit would then receive equivalent flows. Additional
head (<.3m) may be necessary for this flow splitting
scheme to be implemented. To assure flow balance,
operators must have some means to measure flows. This
usually can be accomplished at low cost by providing flow
measurement weirs and staff gauges at each clarifier's
discharge.
Inlet-To-lnlet Balance—A gross imbalance between inlet
port flows was observed (but not measured) at one of the
rectangular clarifiers studied. Downstream ports received
a majority of the mixed liquor flow, as shown in Figure 2.
A similar phenomenon, but on a larger scale, resulted in
imbalance between several parallel rectangular clarifiers
on a common mixed liquor channel. Obviously, inadequate
r
ML
Figure 2. Inlet imbalance observed in one rectangular clarifier with a
4.9-m long mixed liquor channel.
consideration had been given to influent flow distribution
during the design of these clarifiers. It is also possible that
the algorithms commonly used for head calculations and
channel design do not adequately address the dynamic
effects of flow variations.
Inlet Design—Clarifier theory and common design
standards suggest that inlet velocities should be
minimized, flows distributed equally, both horizontally and
vertically in the inlet zone, and short circuiting prevented.
Though this guidance appears rational, it is actually
difficult to implement in practical design. This general type
of guidance has resulted in the use of solid skirted baffles
in most common designs to direct the influent flows
towards the bottom of the clarifier. Rationale for this
practice is not consistent but is generally based upon a
belief that short circuiting in the basin will be minimized
and flow brought in contact with the sludge blanket will
enhance solids capture.
Typical results from the flow pattern shown in Figure 3
indicate that a dead or back-eddy region is developed by the
solid skirt baffle and good vertical distribution of the
incoming mixed liquid is prevented. This is shown by the
large areas of low dye concentration directly in front of the
baffle. Instead of good vertical distribution, the flow
proceeds along the sludge blanket in a relatively narrow
path until it strikes the far wall and flows toward the
effluent weirs. These data substantiate the presence of
density currents which are generally accepted as existing
in secondary clarifiers.
It is interesting to note that for each of the three center-
feed circular clarifiers in Figure 3, the height of the flow
layer between the sludge blanket and the dead region
(density current) varied. At Albuquerque, the flow layer
utilized approximately 70% of the tank's depth; Stamford's
and Morganton's utilized substantially less, 45 and 25%,
respectively. Intuitively, the Albuquerque clarifier would
appear to have superior hydraulic characteristics. Effluent
TSS data substantiated this, with Morganton, Stamford
and Albuquerque each having successively better
performance.
Presently, it is not known why the depth of the flow layers
of these clarifiers differed so greatly. There were physical
differences and also differences in the mixed liquor quality
among the three clarifiers. It is interesting to note that
Albuquerque had the highest Sludge Volume Index (SVI =
110), while Stamford and Morganton had SVI's of 82 and
47, respectively. These data suggest that settling
properties of sludge may have an impact on the flow layer
in the clarifier. A more closely controlled experiment at one
site would be required to substantiate any relationship.
At Holly Hill, Florida, inlet baffles were modified to provide
better vertical distribution of the mixed liquor. Flow pattern
tests performed after modification showed that most of the
liquor above the sludge blanket was included in the flow
-------
Albuquerque #1
Morganton #1
.0
Figure 3. Flow pattern results for center-feed circular clarifiers
19 minutes after start of continuous tracer release.
(Note: vertical scale exaggerated)
layer. Even with dramatic improvements in flow patterns,
only small improvements in performance were seen.
Additional modification of the inlet baffles further
eliminated downward flows. After these modifications, the
flow pattern was almost identical to that seen before the
clarifier was modified. Small performance improvements
still were seen over the unmodified clarifier, but clarifier
hydraulics appeared to be controlled by other factors in
addition to the inlet configuration.
It is obvious from this study that hydraulic conditions
recommended by classical theory or current design
standards are difficult to achieve through design of inlet
structures. At this ti me no definitive recommendations can
be made regarding inlet design since its impact on clarifier
hydraulics is not completely understood.
Outlets—The usual clarifier outlet is a length of overflow
weir placed at the surface in a region believed to be most
distant, in terms of fluid movement, from the inlet region.
Current design standards suggest that weirs should be
adjustable for leveling; located to optimize hydraulic
detention time and minimize short circuiting, and related,
in terms of length, to the rate of discharge of the basin.
There is no question about the value of weir adjustability.
The rationale for standards of weir length appears to be
related to predicted upward velocities of particle-
entraining fluid However, upward velocities are seldom
uniformly distributed. In seven of the eight cases studied,
highest upward velocities were found at end or
circumferential walls where weirs are generally placed to
meet length requirements. Thus, selection of weir location
is typically not given adequate consideration.
Weir Leveling—There is direct evidence from this study
that weir height adjustment is critical for good horizontal
distribution of flow. A good example of this is in the center-
feed, peripheral-overflow unit at Morganton, where there
is direct correlation of weir elevation with total flow in
various directions. The nondimensional dispersion curves
from three weir locations on the periphery of Morganton's
test clarifier were integrated. The area under the curves is
proportional to the inventory of tracer dye which
overflowed the weir at each location. This is interpreted as
the relative flow in each direction as shown in Table 2.
Subsequent measurements of weir elevations and
calculations of flow rates from weir formulas confirmed
that lower elevations coincided with greater flow rates as
shown by the tracer. It was possible to calculate that, at the
existing flow rate, a variation in elevation of i 3.0mm
would result in a flow direction preference of ± 20%. This
is, in effect, a short circuit by direction preference.
TABLE 2 TOTAL RELATIVE DYE INVENTORY AT THREE WEIR
LOCATIONS (MORGANTON DISPERSION
APRIL 29, 1979)
Area Under Curve Expected Flow
Weir Station (Nondimensional) Variability (%)
1
2
3
Average
05063
06608
07474
0.6382
-207
+ 35
+ 17 1
A frustration faced during this study was the tedious
nature of weir leveling in order to minimize direction
preference. Weir leveling using common surveying
instruments may not be accurate enough. Leveling on the
surface of a shut-down clarifier is the easiest, most
accurate method, but is sometimes difficult if weirs are
sealed in place by a mastic compound.
Weir Length—Results of this study have shown that the
influent flow in a clarifier is across the top of the sludge
blanket then upward on the peripheral or end wall.
-------
Momentum of the through-flowing liquor often carries
particulates directly to the weirs, especially if they are
located on end or peripheral walls. However, since the
greatest weir length can be achieved at the peripheral wall
of a circular clarifier, this is where weirs are usually placed.
This is also the simplest and cheapest structural
alternative. It is suggested that the mere specification of
weir length per unit overflow may be counter-productive
since the alternative may be to place weirs in the path of
the higher solids concentrations. Longer weir lengths also
make leveling more difficult.
Weir Position—Flow patterns in clarifiers at Holly Hill,
Morganton and Stamford indicate that weir locations are
far from optimum under the initial conditions measured.
Figure 1 illustrates the progression of tracer dye in the
Holly Hill clarifier 15 minutes after start of the continuous
release. The higher value contours outline the major
horizontal through-flow route. Upturn of fluid near the
weirs is just apparent in the 10 ppb contour, but frequent
solids clouds could be observed at the end wall. The
distribution of TSS in a radial section at Stamford, Figure 4,
offers more direct evidence. Rising solids at the peripheral
wall seem common in center-feed circular units. In
selecting a location for clarified liquid overflow,
consideration should be given to evidence showing that a
flow layer is developed by some combination of inlet
configuration and mixed liquor character, which may
persist to the outlet wall. Unless a structural means is
provided to prevent it, the overflow path will follow a
relatively thin pathway atop the sludge blanket,
undergoing only minimal vertical dispersion. A
modification now being evaluated at Stamford is intended
to interrupt the layer of upflow on the peripheral wall. From
initial observations, with only one-fourth of the tank's
circumference baffled, it appears that significant
improvement in effluent quality might result if the baffle
were extended the full circumference of the tank.
This study has not fully answered the question of where
to locate weirs. Given an "ideal settling zone" immediately
upstream, the optimum location for overflow is predictably
as far downstream as possible. The flow regimes
measured in this study indicate the point of discharge
should not be adjacent to the outer (or far) walls.
Sludge Arm Induced Solids Waves—This study included an
evaluation of the solids disturbing effects of rotating
continuous suction sludge removal devices in five circular
tanks and the hydraulic implications of intermittent sludge
removal in a large rectangulartank with a traveling bridge.
Only the circular tank devices are discussed in this
subsection; intermittent sludge removal is covered later.
It is evident from the five circular clarifiers examined that
settling performance is adversely affected by rotational
speeds commonly specified. A time-varying velocity
increase (time-varying directional short circuit) is induced
by the rotation of the mechanisms. This is evident in the
individual weir station dispersion curves. At a given weir
location, solids overflow also correlates well with
rotational period.
The phenomenon was first noted in this study at one weir
location on Oakland's peripheral-feed clarifier #11. The
overall dispersion curve for the unit, measured at the point
of discharge, presented no evidence of disturbance.
However, weir sampling station #1, which produced the
partial dispersion curve shown in Figure 5, displayed peaks
which closely correlated with time of passage of the single
arm sludge collector, every 35.5 minutes. (In
nondimensional terms, plotted in these dispersion figures,
35.5 minutes is equivalent to 0.162 T/To units.) Similar
effects were noted in Oakland's small process water
secondary at Morganton, Stamford and, to a lesser degree,
at Albuquerque. These last four clarifiers are all center-
feed circular units.
The influence of the trailing "solids waves" is clearly
illustrated by measurements from one depth of the time
series of solids profiles at Stamford, Figure 6. Here peaks
occurred about 90 degrees behind the sludge header.
The data collected are strong evidence of excessive sludge
header rotational speeds in the units studied. At
Morganton, the sludge header on the test clarifier was
Figure 4. Distribution of TSS in a radial cross-section of Stamford's
clarifier #1. The effects of localized upflow are apparent.
(Note: vertical scale exaggerated)
u
1 5
1.0
05
0
-
_
A
\\
IV
0
>, /
j*l Jf
I\A_ /
IV ^
1 '
J
05
T/To
^*" s
\
\
\
\
1 1
1 0
Figure 5. Dispersion curve from one of six individual weir sampling
stations on the periphery of Oakland's clarifier #11.
-------
150
100
TSS,
mg/l
50
0.
1 —
- A
i v.
*~^' 1 1
0 10
A
-^ ^ V
i i i i — r
20 30
Time, mm.
Figure 6. Solids wave at depth of 1.4 m near the peripheral wall of
Stamford's clarifier #1.
slowed to 56% of design rate in order to evaluate the
implications of header speed. Because of a persistent
imbalance in flows between the test and control clarifiers,
data comparing their performance, Table 3, are presented
in terms of normalized values of TSS or performance
expected if flows were equal.
Influence of Hydraulic and Flow Phenomenon on Process
Performance
Subordinate Influences on Flow—The first four factors to
be discussed (wind, temperature, seiche, and speed of
hydraulic response) are termed "subordinate influences"
because they may be implicated in flow disturbance to
some degree. The primary concern is the effect these
factors have on flow and its variability. In itself, flow is
subordinate to velocity which is, in its turn, the closest we
can now come to a definition of the mechanism by which
solids are transported to the clarifier's discharge point.
Wind—The effects of wind on the surface of a clarifier
are often apparent only by the position or distribution of
scum. Casual observation of subsurface particles leads to
the conclusion that the fluid a few millimeters beneath the
surface is not affected. Yet, it is well known from analysis
of ocean currents and lake levels that wind effects are not
negligible.
It is useful to examine a simplified analogy between lakes
and clarifiers. By assuming a linear water surface slope, no
water loss over the weirs, and a rectangular basin, it can be
shown (Table 4) that a 2.0-mm difference in end-to-end
water elevation can result from commonly observed steady
wind speeds. On typical clarifiers with V-notch weirs, a
3.0-mm difference in elevation is equivalent to a 20%
difference in flow. Thus, though the effects of wind are not
readily observed (unless waves are present) results in
flow-distribution may be significant.
Temperature—Inlet and overflow temperatures were
measured at most sites during this study. At no time during
the moderate weather encountered was there any
temperature difference greater than 0.06°C. In the
commonly measured case, in which flow is along the tank
TABLE 4. APPROXIMATE WIND SPEEDS CAPABLE OF CAUSING
SURFACE ELEVATION DIFFERENCES OF 2mm IN A
RECTANGULAR BASIN
Water Depth Basin Length Wind Speed Wind Speed
(m) (m) (m/sec) (miles/hr)
2
2
2
4
4
4
10
30
50
10
30
50
15.4
5.1
3.1
30.8
102
6.2
34
11
7
69
23
14
TABLE 3. COMPARISON OF EFFLUENT TSS VALUES IN MORGANTON'S TEST AND
CONTROL CLARIFIERS*
Test Clarifier
(header slowed to 56%)
Control Clarifier
(normal header speed)
Week of
Average
1
2
3
4
5
% of Total
Flow
55.1
50.7
48.0
529
53.1
Actual TSS
(mg/l)
22.8
244
34.0
27.3
22.9
TSS
Adjusted for
Flow Split
(mg/l)
20.7
24 1
35.4
258
21.6
% of Total
Flow
44.9
49.3
520
47 1
46.9
Actual TSS
(mg/l)
23.4
43.3
61 0
26.3
24.6
TSS
Adjusted for
Flow Split
(mg/l)
26.1
43.9
58.7
27.9
26.3
Average 25 5
Average 36.6
'Normalization of TSS valves were accomplished by dividing measured values of the
composite samples by two times the flow fraction
-------
bottom, there would seem to be only one condition under
which differential temperatures could conceivably result in
flow disturbance: in the case of a heated influent
accompanied by a surface temperature approaching the
maximum water density value of 4°C. In a still-lake,
overturn from this cause may occur once or twice a year. In
clarif iers, nearly complete mixing occurs in an hour or two.
The mechanism of overturn is not well known. One theory
involves the formation of small cold-water cells at the
surface; these cells gradually assume a pendulous shape
and greater density which carries them downward through
the underlying fluid. The phenomenon, if real, is not easy to
measure.
Seiche— In larger water bodies, on the scale of the Great
Lakes, surface level oscillation due to wind or other
atmospheric disturbances is well documented. It is
instructive to examine whether this type of oscillation
(seiching) can occur in a basin the size of a clarifier.
The period of the fundamental oscillation is related to the
horizontal and vertical scale of a rect angular water body, as
follows:
2L
TABLE 5 PERIODS OF NATURAL (HARMONIC) SURFACE OSCILLA-
TION FOR SEVERAL CLARIFIER SCALE RECTANGULAR
BASINS
where T = period (seconds)
h = basin depth
L = basin length
g = acceleration of gravity.
In a clarifier, however, there are often two "free" surfaces:
the visible water surface and the sludge blanket surface.
An approximation of the period of the first harmonic of
sludge blanket seiches can be made by the following
related expression:
2L
Ti =
where T, = period of sludge blanket surface (seconds)
L = basin length
g = acceleration of gravity
S.G. = specific gravity of the sludge
h = overall basin depth
he = depth of clarified liquor above the blanket
hn = thickness of the blanket.
Calculations for surface seiche periods of representative
clarifier scales are presented in Table 5. Oscillation periods
for the blanket may be double the time shown.
For a circular basin, two types of seiching can occur. One
type, which is symmetric about the vertical centerline of
the tank, produces wave periods of approximately
Water Depth
(m)
2
2
4
4
Basin Length
(m)
10
50
10
50
Time
(sec)
4 5
250
32
160
T= 1.64
where R = the tank radius.
For a 3.0-m deep circular clarifier with a 20-m radius, a
seiche period of about 6 seconds would be characteristic. A
second type of seiche, called "sloshing," is asymmetric
about the centerline, extending across the diameter of the
basin. This type of seiche has a characteristic period of
R
gh
For the same clarifier described above, the sloshing period
would be about 12.6 seconds.
The major concern about seiche is the possibility thatsuch
disturbances may be caused by wind gusts or transient
flow phenomena, such as those induced by lift stations or
in-plant process pumps. Because of the enormous
variation in tank sizes and the frequencies and amplitudes
of seiche, a quantitative assessment of the potential
impact of this form of motion has not been attempted.
Speed of Hydraulic Response — The majority of waste
treatment plants utilize gravity to move fluids from the
front end to the point of discharge. Since "retention time"
is such an important part of the design language, there is a
tendency to overlook the fact that a level (or pressure)
change at the influent point will be followed very quickly by
a level change downstream at approximately the small
amplitude wave speed c = Vgh. In a 3.0-m deep tank, for
example, c = 5.5 m/sec. Thus, a rapid change in influent
flow rate will cause nearly as rapid a change in flow rate in
a secondary clarifier, often within seconds.
Rapid flow rate changes, which can be important
disturbing influences, can be caused by intermittent lift
station or internal process pump operation or simply from
severe sewer system inflow. Figure 7 is a plot of secondary
clarifier discharge rate at Holly Hill. Measurements were
taken at 12-second intervals during a period of high flow.
The rate of discharge from Orange County's clarifier #1,
the result of on-off operation of return sludge collectors, is
-------
S\
45
Q 30
| 1.5
/\
10 15 20
Time, mm
25
30
Figure 7. Short-term record of Holly Hill's clarifier discharge during a
period of high plant flow.
shown in Figure 8. Several pertinent features of the
system's flow regime can be derived from this plot. At
times A and C, intermittent sludge return pumps were
started. At B, pumps were shut off. This is the normal cycle.
The periods A-D and C-l represent the time required for the
leading edge of the return sludge wave to have travelled
throughout the plant complex and back to the point of
clarifier discharge, all by gravity. The two humps between
E and G are believed to result from whole plant seiche.
Average Horizontal Flow Velocity Toward Weirs—As
discussed previously, regardless of tank slope and
dimension, or inlet configurations, all measured flow
patterns appeared to assume parabolic profiles of various
thicknesses on top of the sludge blanket. This flow layer or
density current, flowing horizontally, persisted to the
peripheral wall, where it turned upward toward the weirs.
Although this article has not provided sufficient data for a
complete explanation of this phenomena, preliminary
results indicate that the depth of the flow layer associated
with the horizontal flow toward the weirs may be related to
inlet configuration and mixed liquor quality.
The unsealed velocity profiles, presented in Figure 9, have
been estimated from the flow pattern measurements at
Albuquerque, Stamford and Morganton. Albuquerque's
effluent quality was excellent; Stamford's and
Morganton's were successively poorer. It should be noted,
50
O 40
X
Q
\
E
o
30
20
10
0
~\ /"
- V
I
0 10
•-^_/ A " ',
* G \ /
F i f
\ /
V
I
! I I
20 30 40
Time, mm.
'•*
J
|
50
Figure 8. Short-term record of the discharge of Orange County's
clarifier #1.
Blanket
Blanket
Blanket
Time,
mm
0
5
10
15
20
30
60
MLTSS
SVI
Settled Sludge Volume
Albuquerque
1000
550
450
380
340
270
240
2450 mg/l
110
Stamford
1000
350
260
230
210
200
180
2430 mg/l
82
Morganton
1000
300
225
195
185
170
150
3600 mg/l
47
Figure 9. Velocity profiles derived from flow-pattern tests in three
center-feed circular clarifiers.
that all three plants had relatively steady flow rates during
test times. Transient peak flows at any of the sites may
have seriously degraded effluent quality, especially at
Albuquerque. The depth utilized for forward flow must, by
physical necessity, be inversely related to the velocities of
horizontal throughflow. Higher velocity is associated with
higher levels of turbulence, which is in turn suspected as a
prime mover of solids toward the weirs. Table 6 presents a
set of velocity calculations based on the three velocity
profiles of Figure 9.
Increased So/ids Transport Induced by Amplitude Variation
of Flow—By any reasonable estimate, horizontal clarifier
flows are turbulent, not laminar. Thus, we are confronted
with eddies which move particles upward while horizontal
transport is occurring. By use of some simplifying
assumptions, including a uniform eddy viscosity and
reasonable values of particle settling velocity, a diffusion
model can be solved to provide a factor by which increased
TABLE 6. CALCULATED MEAN FORWARD FLUID VELOCITIES AT MID-
RADIUS FROM THREE CENTER-FEED CIRCULAR CLARIFIERS
Site
% Depth
Utilized
Tank Radius
(m)
Mean Forward Velocity at
Mid-Radius*
(m/sec)
Albuquerque 70
Stamford 45
Morganton 25
2057
1981
12 19
0.00323
0 00436
0 00489
"Based on total overflow plus one half underflow rate
-------
transport of solids within the clarifier, resulting from
amplitude variations of plant flow, can be predicted:
TR
where TR = solids transport relative to that expected in
steady flow
T_= total period of measured values
u = Spatial average instantaneous forward velocity in
some cross-section (say at mid-radius)
v = time average of all 0" values.
A simple example of an evaluation of this equation is
presented in Table 7 This evaluation indicates that a plant
flow variation of ± 10% would result in an increase in
solids transport in the clarifier of 5%. Application of the
same equation to normal, dry weather diurnal flow
variations in five small Texas cities resulted in predicted
increased solids transport of 46 to 123%. This turbulent
diffusion model predicts flow-induced solids transport in
secondary clarifiers, but does not determine amounts of
solids escaping the clarifier. If it is assumed that effluent
solids are proportional to the solids transported, then flow
variability could have significant impact on clarifier
performance.
TABLE 7 HYPOTHETICAL FLOW VARIATIONS EVALUATED FOR
INCREASE IN EFFLUENT TSS
Tj
1 8
20
22
u/v
09
1 0
1 1
Average
(u/v)3
0729
1 000
1 331
1 05
At Holly Hill, an attempt was made to explain
improvements in effluent TSS performance, which
apparently resulted from attempting to equalize flows by
using the channel ahead of the aeration basin. These
improvements are listed in the preliminary data
compilation, Table 8.
At moderate flows, illustrated in Figure 10, the amplitude
equation predicts only 9.6% improvement in TSS
performance where all flow variations have been removed.
It was apparent that yet another phenomenon was
operating, as shown by the consistently better
performance of both the test and control clarifiers when
the small storage channel is in use.
Frequency of Flow Variation—The turbulent diffusion
model predicts higher concentrations of transportable
solids above the blanket at higher velocities of horizontal
flow. Three representative solids profiles may be similar to
those shown in Figure 11, which correspond to increasing
velocity and turbulence levels.
Turbulence is quickly generated by higher velocity, but is
very slow to die off as velocity decreases. Theoretical
o 45
x
Q
30
I 15
I
10 15 20
Time, mm.
25
30
Figure 10. Measured discharge ratefromthe Holly Hill clarifier during
a 30-minute period.
TABLE 8 EFFLUENT TSS AVERAGES IN TEST AND CONTROL CLARIFIERS (HOLLY HILL) AT FLOWS EQUAL TO OR
LESS THAN DESIGN RATES OF 1.2 MGD
Number of Days
in Sample
25
23
20
Test Condition*
First trial of new reaction baffles, 1000 gallon
storage not in use. March 12 — June 1, 1979
First trial of new reaction baffles, 1000 gallon
storage in use March 12 — June 1, 1979
Second baffle revision, 1000 gallon storage not
Test (South) Clarifier
Effluent TSS (mg/l)
25.6
15 5
160
Control (North) Clarifier
Effluent TSS (mg/l)
25 2
207
196
13
in use June 1—August 18, 1979
Second baffle revision, 1000 gallon storage
in use June 1—August 18, 1979
11 5
17.2
'Storage was utilized on a week-on, week-off basis to separate hydraulic improvement phenomena from the possible
effects of long-term process changes.
-------
Blanket Blanket
Figure 11. Concentration profile at a) low horizontal velocity, b) moderate horizontal velocity, c) high horizontal velocity.
analysis has shown that die-off time is on the order of the
retention time of the basin, or longer.
Since the decrease in turbulence is so much slower than
its onset, it can be seen that rapid changes in flow rate will
result in concentrations of suspended and transportable
solids which are much nearer high velocity values than
average velocity values. As a first approximation, transport
varies as the frequency of flow rate changes. This estimate
helps to explain the discrepancy in modest predicted
improvement versus actual significant improvement in
effluent TSS at Holly Hill by use of a small equalization
basin. This phenomenon, as well as several other
observations and calculations mentioned in this article,
will be further verified during research planned for 1980.
This study was completed by Robert Crosby of Crosby,
Young and Associates, underthe direction of Jon Bender of
Urban Systems Management Section, Municipal
Environmental Research Laboratory, U.S. EPA. All
requests for additional information should be directed to
Crosby, Young and Associates, 1201 E. 15th Street, Piano,
Texas 75074.
Symposium Announcement: Health
Risks Associated with Land Application
of Municipal Sludges
An international symposium on "Evaluation of Health
Risks Associated with Feeding and/or Land Application of
Municipal Sludges" will be held in Tampa, Florida, on April
29-May 1, 1980. This symposium is sponsored jointly by
EPA's Office of Research & Development and the Institute
of Food and Agricultural Sciences of the University of
Florida. The program will feature invited papers delivered
by authorities in the field. These speakers will cover major
aspects of health significance as they relate to sludge
application to land. Two sessions will be devoted to
contributed papers based on original research. Major
findings of a number of research projects deal ing with land
application of sludge will also be discussed. Information
concerning presentation of papers, registration and
accommodations can be obtained form E. M. Hoffmann,
1059 McCarty Hall, University of Florida, Gainesville,
Florida 32611.
Seminar Series Ends—Wastewater
Treatment Facialities for Small
Communities
The last two in the series of Technology Transfer Municipal
Design Seminars on Wastewater Treatment Facilities for
Small Communities were held November 5-7, in Orlando,
Florida and December 4-6, 1979 in Philadelphia,
Pennsylvania.
Completion of these seminars brings to an end almost
three years' work and 22 seminar presentations by the
Technology Transfer Environmental Control Systems Staff
and the seminar speakers. The series, which began in
March 1977, has been continually updated to include the
latest design information and research results for handling
waste from individual residences and small communities,
as well as changes in federal legislation (P.L. 95-217). Over
4,000 engineers and pollution control officials attended
these seminars.
-------
EPA Plans International Seminar on
Control Technology for Nutrients in
Municipal Wastewater Effluents
The Municipal Environmental Research Laboratory will
sponsor a seminar to disseminate information by
worldwide experts in the field of full-scale municipal
nutrient control systems. This seminar is scheduled to be
held September 9-11,1980, in San Diego, California atthe
Hotel del Coronado.
In the past ten years, nutrient control technology has
advanced from the pilot plant and prototype stage to
hundreds of full-scale installations. The purpose of this
seminar is to review the design, operating, and economic
characteristics of successful full-scale systems. The
material presented will benefit environmental personnel
involved in designing second generation systems to meet
stringent water quality requirements.
Case histories will be presented by over 20 invited
speakers from the United States, Canada, Japan, Sweden,
Austria, Australia, England, and South Africa. A wide
range of nutrient control approaches will be discussed,
including chemical-physical, biochemical, chemical
supplementation, batch process, and land application. The
seminar will be divided into three one-day sessions:
phosphorus control, nitrogen control, and combined
phosphorus and nitrogen control. A block of rooms has
been reserved for conference attendees; no registration
fee is required. To obtain more information about the
seminar, contact:
Norm Kulujian
USEPA
Cincinnati, OH 45268
Telephone (513) 684-7394
New Capsule Report on Acoustic
Monitoring
There are as many as 500,000 earthen diked areas in the
United States containing hazardous wastes which if spilled
or leaked to the environment could have long-lasting
impact. EPA's Office of Research and Development has
long been aware of the potential hazard posed by these
earthen impoundments and the need for an inexpensive
and simple technique to monitor their stability. Under this
impetus, a system—acoustic emission monitoring—was
developed through the Industrial Environmental Research
Laboratory in Cincinnati. This system is based on the
phenomenon that soils emit sounds under stress and,
when properly amplified and quantified, can be a valuable
guide in evaluating the stability of the hazardous waste
dams.
A new Technology Transfer Capsule Report, "Acoustic
Monitoring to Determine the Integrity of Hazardous Waste
Dams," describes the theory, installation and costs of this
system.
To order the report, check box #2024 and return the order
form at the back of this Newsletter.
Earthen dams containing hazardous wastes
are potential danger to the environment.
New Seminar Publication on Forest
Products
"Pollution Control in the Forest Products Industry" is a
compilation of the presentations of seminars held in
Portland, Oregon and Dallas, Texas. This publication deals
with both air and water pollution control problems in the
forest products industry and briefly reviews the Clean Air
and Clean Water Acts as they apply to this industry.
Examples of the kinds of research and technologies being
applied by the industry to meet its air and water pollution
control responsibilities are described. Several case studies
are also included in the report. To order a copy of this
Seminar Publication, check box #3010 and return the
form at the back of this Newsletter.
-------
New TT Publication on Diesel
Emissions Research
Because of the fuel efficiency of diesel engines, the
number of diesel-powered passenger cars on U.S.
roadways is expected to increase substantially during the
next decade. Concern aboutthe human health implications
of this change has prompted EPA's Office of Research and
Development (ORD) to launch a major research effort to
assess the potential human health impacts from diesel
emissions.
The Center for Environmental Research Information
(CERI), in cooperation with ORD's Mobile Sources
Research Committee, has recently generated a new
publication describing this research effort. The report,
entitled "The Diesel Emissions Research Program,"
highlights the work that is being done by seven ORD
components to determine the health effects of diesel
emissions. Research includes: human population studies,
animal and cellular studies, chemical characterization of
diesel particles, pollutant monitoring, control technology
development and pollutant level and human population
exposure estimations.
In addition, the report explains how the information
generated from this research will be used to assess the
public health risk associated with increased use of the
diesel engine. The estimated risk along with other
important factors then will be used by EPA to determine
whether additional regulation is required for diesel
emissions.
A copy of this report can be ordered by checking box
#9004 and returning the order form at the back of this
Newsletter.
Potential health effects by diesel emissions is
currently being researched.
1979 Bibliography of Small
Wastewater Flows
"The 1979 Bibliography of Small Wastewater Flows,"
compiled by the U.S. EPA National Small Wastewater
Flows Clearinghouse has been published and is now
available.
The Clearinghouse is administered by the West Virginia
University Energy Research Center, under a grant funded
by EPA's Center for Environmental Research Information
(Office of Research and Development) under the authority
of and as provided for by the 1977 Clean Water Act.
Included in the bibliography are indexes by accession
number and title, toxonomy index, an author index, a state
index and a glossary of descriptive words. Information is
included on the following topics:
• septic tanks and subsurface disposal systems;
• other on-site systems, including dual systems;
• cluster systems serving a small number of households
or commercial users, with average annual dry weather
flows of under 25,000 gallons per day;
six-inch and smaller gravity sewers carrying partially
or fully treated wastewater or carrying raw wastewater
as part of limited conveyance systems which serve
clusters of households and small commercial
establishments;
pressure and vacuum sewers;
the above and other alternative sewers that are
specifically exempted from the collector sewer
interceptor designations and that are not the subject of
EPA collection system policy; and
other treatment or conveyance works that employ
alternative technologies and that serve communities
with populations of 3,500 or less or the sparsely
populated areas of larger communities.
Copies of the 1979 Bibliography of Small Wastewater
Flows, at a cost of $7 per copy (including postage and
handling), are available from:
West Virginia Bookstore
Mountain Lair
West Virginia University
Morgantown, WV 26506
-------
Seminar Announcement: Water and
Wastes Management in the Arctic
Environment
Two Technology Transfer seminars on "Water and Wastes
Management in the Arctic Environment" will be held in
March. The Center for Environmental Research
Information (CERI), in association with the Environmental
Research Laboratory at Corvallis, Oregon, is sponsoring
the series to be held March 27-28 in Anchorage, Alaska,
and March 31-April 1 in Seattle, Washington.
The seminar series is intended for consulting engineers,
municipal and industrial design engineers, and federal,
state and local officials who are involved in planning,
construction and operation of utility facilities in an arctic-
type environment.
These seminars are based on a new Process Design
Manual, "Cold Climate Utilities Delivery," which was
prepared by a group of U.S. and Canadian experts who
have extensive field experience in this area. Presentations
will include: planning for design and construction of cold
region facilities; water supply systems—storage and
treatment; drinking water distribution and wastewater
collection; wastewater treatment and disposal; thermal
consideration for design and construction; energy
considerations in design of utilities; solid waste
management; and design of central facilities and water
conservation.
For additional information on this seminar series, contact
Dr. J. E. Smith, Jr., USEPA—CERI, Cincinnati, Ohio45268,
(5I3) 684-7394.
New Capsule Report: Physical Coal
Cleaning Demonstration at Homer City,
Pennsylvania
The Center for Environmental Research Information
recently published a Technology Transfer Capsule Report
entitled, "First Progress Report: Physical Coal Cleaning
Demonstration at Homer City, Pennsylvania." Under the
1 977 Clean Air Act, as amended, specific standards have
been established to limit sulfur dioxide (SCh) emissions
from large stationary sources, such as coal-burning
boilers. In addition, new sources may emit only a limited
percentage of the sulfur and other pollutants present in the
raw coal. This cleaning process allows the use of raw coals
with a pyritic to organic sulfur content of 2:1 to 4:1, by
removing enough pyrite sulfur to permit the cleaned coal to
be burned while still meeting the SCh standards. An
advantage of this process is that other SOa emission
control devices are rarely needed. This publication
describes the theory, the current testing program at Homer
Magnetic separators used in the physical coal-
cleaning method.
City and other applications of the PCC process, such as its
use in combination with flue gas desulfurization to
minimize costs. To order this publication, check (#2023)
and return the order form at the back of this Newsletter.
Seminar Series Ends
Approximately 1500 engineers, municipal officials,
government engineers, and other interested individuals
attended the series of ten seminars held in 1979 dealing
with EPA's new Innovative and Alternative (I/A)
Technology Program. The "Innovative and Alternative
Technology Assessment Manual," EPA-430/9-78-009,
MCD-53, a draft of which was handed out at the seminars,
is currently under revision. To obtain a copy of the final
edition, write:
U.S. Environmental Protection Agency
WH-547
401 M Street, S.W.
Washington, DC 20460
-------
ERRATA SHEET
Sulfur Oxides Control Technology Series:
Flue Gas Desulfurization
Wellman-Lord Process
EPA 625/8-79-001 (February 1979)
The second paragraph on page 5 reads (in part) "All
equations are in the un-iomzed form to simplify the
presentation." However, throughout the report, the
equations are shown in the ionized form The fol-
lowing corrections are required to change the chem-
ical reactions to the un-iomzed form
Page No.
From
To
(D
Na2S03 + S02 + H20
2NaHSO,
(11
Na0C07 + SO,
23 *
(2)
2C03 + SO2 —
Na2S03 + C02
(2)
8,15
Na0S07+ '/20,-
* *> *
32SOT (3)
1/20
(3)
12
6NaHSO~ _ >2Na2S07 (5)
+ Na2S2Og + 2SO2+ 3H20
6NaHSO3-
-2Na2SO4 (5)
12
* 2Na2SO7
(6)
2NaHSO3+
2Na2SO4+Na2S203+H2O
(6)
15
SO3 + H20
(7)
2Na2S03
H20
Na SO + 2Na HSO
24 23
(7)
-------
REQUEST FOR TECHNOLOGY TRANSFER MATERIAL
The publications listed on this form are the only ones available through the Office of Technology Transfer.
(Check appropriate boxes)
PROCESS DESIGN MANUALS
Phosphorus Removal (April 1976) 100lD
Carbon Adsorption (Oct 1973) 1002 D
Suspended Solids Removal (Jan 1975) 1003D
Upgrading Existing Wastewater Treatment Plants (Oct 1974| 1004 D
Sulf ide Control in Sanitary Sewerage Systems (Oct 1974) 1005 D
Nitrogen Control (Oct 1975) 1007 D
Land Treatment of Municipal Wastewater (Oct 1977) 1008 D
Wastewater Treatment Facilities for Sewered Small Communities
(Oct 1977) 1009D
Municipal Sludge Landfills (Oct 1978) 1010 D
Sludge Treatment and Disposal (Oct 1979) 1011 D
TECHNICAL CAPSULE REPORTS
Recycling Zinc in Viscose Rayon Plants by Two Stage Precipitation 2001 D
Color Removal from Kraft Pulping Effluent by Lime Addition 2002 D
Pollution Abatement in a Copper Wire Mill 2003 D
First Progress Report Limestone Wet-Scrubbing Test Results at the
EPA Alkali Scrubbing Test Facility 2004 D
Pollution Abatement in a Brewing Facility 2006 D
Flue Gas Desulfunzation and Sulfunc Acid Production via
Magnesia Scrubbing 2007 D
Second Progress Report Lime/Limestone Wet-Scrubbing Test
Results at the EPA Alkali Scrubbing Test Facility 2008 D
Magnesium Carbonate Process for Water Treatment 2009 CD
Third Progress Report Lime/Limestone Wet-Scrubbing Test
Results at the EPA Alkali Scrubbing Test Facility 2010 D
First Progress Report Wellman-Lord S02 Recovery Process — Flue
Gas Desulfunzation Plant 2011 D
Swirl Device for Regulating and Treating Combined
Sewer Overflows 2012 D
Fabric Filter Particulate Control on Coal-Fired Utility Boilers
Nucla, CO and Sunbury, PA 2013 D
First Progress Report Static Pile Composting of Wastewater Sludge .... 2014 CD
Efficient Treatment of Small Municipal Flows at Dawson, MN 2015 ID
Double Alkali Flue Gas Desulfunzation System Applied at the
General Motors Parma, OH Facility 2016 D
Recovery of Spent Sulfunc Acid from Steel Pickling Operations 2017 CD
Fourth Progress Report1 Forced-Oxidation Test Results at the
EPA Alkali Scrubbing Test Facility 2018 D
Control of Acidic Air Pollutants by Coated Baghouses 2020 CD
Paniculate Control by Fabric Filtration on Coal-Fired Industrial Boilers . .2021 CD
Bahco Flue Gas Desulfunzation and Particulate Removal System 2022 D
• First Progress Report Physical Coal Cleaning Demonstration at
Homer City, PA 2023 D
• Acoustic Monitoring to Determine the Integrity of Hazardous
Waste Dams 2024 D
INDUSTRIAL SEMINAR PUBLICATIONS
Upgrading Poultry Processing Facilities to Reduce Pollution (3 Vols)... .3001 D
Upgrading Metal Finishing Facilities to Reduce Pollution (2 Vols.) 3002 CD
Upgrading Meat Packing Facilities to Reduce Pollution (3 Vols ) 3003 CD
Upgrading Textile Operations to Reduce Pollution (2 Vols ) 3004 CD
Choosing the Optimum Financial Strategies for Pollution Control
Systems 3005 D
Erosion and Sediment Control — Surface Mining in the
Eastern U S (2 Vols ) 3006 D
Pollution Abatement in the Fruit and Vegetable Industry (3 Vols ) 3007 D
Choosing Optimum Management Strategies 3008 CD
Controlling Pollution from the Manufacturing and Coating of
Metal Products (3 Vols ) 3009 CD
• Pollution Control in the Forest Products Industry 3010 CD
MUNICIPAL SEMINAR PUBLICATIONS
Upgrading Lagoons 4001 D
Status of Oxygen/Activated Sludge Wastewater Treatment 4003 D
Nitrification and Denitnfication Facilities 4004 D
Upgrading Existing Wastewater Treatment Plants — Case Histories 4005 CD
Flow Equalization 4006 CD
Wastewater Filtration 4007 CD
Physical-Chemical Nitrogen Removal 4008 CD
Air Pollution Aspects of Sludge Incineration 4009 D
Land Treatment of Municipal Wastewater Effluents (3 Vols ) 4010 CD
Alternatives for Small Wastewater Treatment Systems (3 Vols ) 4011 CD
Sludge Treatment and Disposal (2 Vols ) 4012 D
Benefit Analysis for Combined Sewer Overflow Control 4013 D
BROCHURES
Logging Roads and Water Quality 5011 CD
Environmental Pollution Control Alternatives Municipal Wastewater... .5012 CD
Forest Harvesting and Water Quality 5013 CD
Irrigated Agriculture and Water Quality Management 5014 CD
Forest Chemicals and Water Quality 5015 CD
Environmental Pollution Control Alternatives Economics of Wastewater
Alternatives for the Electroplating Industry 5016 CD
HANDBOOKS
Monitoring Industrial Wastewater (1973) 6002 CD
Industrial Guide for Air Pollution Control (June 1978) 6004 CD
Continuous Air Pollution Source Monitoring Systems (June 1979) 6005 D
INDUSTRIAL ENVIRONMENTAL
POLLUTION CONTROL MANUALS
Pulp and Paper Industry — Part 1 /Air (Oct 1976) 7001 CD
Textile Processing Industry (Oct 1978) 7002 CD
SUMMARY REPORTS
Sulfur Oxides Control Technology Series FGD Wellman-Lord Process ..8011 CD
Control Technology for the Metal-Finishing Industry Series'
Evaporators 8002 CD
EXECUTIVE BRIEFINGS
Environmental Considerations of Energy — Conserving Industrial
Process Changes 9001 CD
Environmental Sampling of Paraho Oil Shale Retort Process 9002 CD
Short-Term Tests for Carcinogens, Mutagens and Other Genotoxic
Agents 9003 CD
• Diesel Emissions Research Report 9004 CD
ATTENTION PUBLICATION USERS
Due to the increasing costs of printing and mailing, it has become necessary to institute positive management controls over distribution of Technology Transfer
publications Although these publications will be distributed on a no-cost basis, any request for more than five documents total, or for more than one copy of a
single document must be accompanied by written justification, preferably on organization letterhead In the event your order cannot be filled as requested, you
will be contacted and so advised
If you are not currently on the mailing list for the Technology Transfer Newsletter, do you want to be added? Yes CD No CD
•Name
Employer
Street
City, State, Zip C.nde
*lt is not necessary to fill in this block if your name and address on reverse are correct.
• Publication listed for the first time.
Note. Forward to CERI, Technology Transfer, U.S Environmental Protection Agency, Cincinnati, OH 45268
-------
Where to Get Further Information
In order get details on items appearing in this publication, or any other aspects of the
Technology Transfer Program, contact the following individual in your region
REGION CHAIRMAN
1 Allyn Richardson
ADDRESS
Environmental Protection Agency
John f Kennedy Federal Building
Room 2313
Boston, Massachusetts 02203
617 223-2226
(Maine, N H , Vt , Mass , R I , Conn )
Robert Bongiovanni Environmental Protection Agency
26 Federal Plaza, Room 907
New York, New York 10007
212 264-1867
(NY,NJ,PR,VI)
REGION CHAIRMAN
ADDRESS
3 Albert Montague
Asa B Foster, Jr
Clifford Risley
Environmental Protection Agency
6th & Walnut Streets
Philadephia, Pennsylvania 191O6
215 597-9856
(Pa , W Va , Md, Del D C , Va )
Environmental Protection Agency
345 Courtland Street, N E
Atlanta, Georgia 30308
404 881-4450
(N C S C , Ky , Tenn , Ga , Ala , Miss ,
Fla )
Environmental Protection Agency
536 South Clark Street
Chicago, Illlmois 60604
312 353-3805
(Mich , Wis , Minn , II! , Ind , Ohio)
Information Center Environmental Protection Agency
Office of Public Awareness
1201 Elm Street
First International Building
Dallas, Texas 75270
214 767-2697
(Texas, Okla , Ark , La , N Mex )
Charles Hajiman
8 Roger Dean
Chuck Flippo
10 John Osborn
Environmental Protection Agency
324 East 11th Street
Kansas, Missouri 64106
816 374-2921
(Kansas, Nebr, Iowa, Mo )
Environmental Protection Agency
1860 Lincoln Street
Denver, Colorado 80203
303 837-2277
(Colo , Mont, Wyo , Utah, N D , S D )
Environmental Protection Agency
215 Fremont Street
San Francisco, California 94105
415 556-7858
(Calif, Ariz, Nev , Hawaii)
Environmental Protection Agency
1200 Sixth Avenue
Seattle, Washington 98101
206 442-1296
(Wash , Ore, Idaho, Alaska)
USEPA - ORD
Center for Environmental Research Information
Cincinnati, Ohio 45268
513 684-7394 - 98 (Inc.)
•it U S GOVERNMENT PRINTING OFFICE 1980-660-330
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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