EPA-600/2-76-272
December 1976
Environmental Protection Technology Series
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EPA-600/2-76-272
December 1976
DEMONSTRATION OF VOID SPACE STORAGE
WITH
TREATMENT AND FLOW REGULATION
by
Karl R. Rohrer Associates, Inc.
Akron, Ohio 44321
Project No. 11020 DXH
Project Officer
Alfred Smith
U.S. Environmental Protection Agency
Ohio District Office
Cleveland, Ohio 44126
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND 'DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
-------
FOREWORD
The Environmental Protection Agency was created because of in-.
creasing public and government concern about the dangers of
pollution to the health and welfare of the American people.
Noxious air, foul water, and spoiled land are tragic testimony
to the deterioration of our natural environment. The complexity
of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step ,in problem
solution and it involves defining the problem, measuring its
impact, and searching for solutions. The Municipal .Environmental
Research Laboratory develops new and improved technology and
systems for the prevention, treatment, and management of waste-
water and solid and hazardous waste pollutant discharges from
municipal and community sources, for the preservation and
treatment of public drinking water supplies, and to minimize
the adverse economic, social, health, and aesthetic effects of.
pollution. This publication is one of the products of that
research; a most vital communications link between the
researcher and the user community.
This report describes one method of prevention of combined sewer
overflows by storing potential overflows in an underground void
space retention tank. The collected wastewater is discharged,
at a regulated rate, to the treatment plant during non-peak hours
to prevent overloading of the treatment plant facilities.
Francis T. Mayo
Director
Municipal Environmental Research Laboratory
1X1
-------
ABSTRACT
The purpose of this project was to demonstrate and evaluate the
feasibility of an underground void space storage tank, in con-
taining and regulating storm overflows from a combined sewer
thus reducing the pollution loads discharged to the receiving
water body. System design, construction, and two years
operation were conducted under the study.
The prototype facility was constructed in Akron, Ohio with a
combined sewer drainage area of 76.3 hectare (188.5 acres).
The excess combined sewer flows were fed by gravity into the_
3.8 x 106 liter (1 MG) void space retention tank. The tank is
of an excavated hopper shape, lined with an impermeable membrane
and filled with an inert media. Storage of the wastewater is in
the void space of the media. After the storm event, the stored
stormwater was gravity fed into the interceptor sewer for
subsequent treatment. The underground facility was a dual usage
concept. In addition to collecting, chlorinating, and detaining
potential combined sewer overflows, the facility's top surface
could be made usable as a park or recreational grounds.
This report was submitted in fulfillment of Project No. 11020
DXH between the United States Environmental Protection Agency
(U.S.EPA) and the City of Akron, Ohio
IV
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TABLE OF CONTENTS
Title Page
Disclaimer
Foreward '
Abstract
Figures
Tables
Abbreviations
Acknowledgements
SECTION I
SECTION II
SECTION III
SECTION IV
SECTION V
SECTION VI
SECTION VII
SECTION VIII -
SECTION IX
INTRODUCTION
CONCLUSIONS
RECOMMENDATIONS
TEMPORARY STORAGE FOR POLLUTION
REDUCTION
RAINFALL AND SITE CONDITIONS
SYSTEM DESIGN
SYSTEM COMPONENTS
Diversion Manhole
Influent Pipe
General Tank Configuration
Clarifier
Tank Level Indicator
Ground Water Monitor
Rain Guage
TOP ACTIVITY
CONSTRUCTION AND EVALUATION
Clarifier Level Indicator
Automatic Samplers
Tube Settlers
Chlorination System
Page
i
ii
iii
iv
vii
viii
ix
x
1
3
5
7
11
24
28
28
28
32
38
49
49
49
50
51
58
58
60
61
v
-------
SECTION X
SECTION XI
SECTION XII
Contained Solids Within Media Storage
Area
Cost
Aesthetics
- BIBLIOGRAPHY
PATENTS
APPENDICES
Appendix A
Appendix B
Appendix C
Appendix D
Head Loss Through Media
Overflow System
Reduction of Void Space
Volume
Operations Manual
Data Tables
Page
62
65
68
69
71
72
72
78
79
91
VI
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FIGURES
No. Page
1 Intensity-Duration-Frequency Curves for Akron 13
2 Monthly Rainfall Probability Curves 14
3 Yearly Rainfall Probability Curve 15
4 Monthly Maximum Daily Precipitation 16
5 Yearly Maximum Daily Precipitation 17
6 Drainage Area Location 19
7 Topographic Drawing of Drainage Area 20
8 Intensity-Duration-Flow Rate-Volume Relationships 22
9 Block Diagram of System Components . 25
10 Aerial Cut-Away Perspective of System . 26
11 Diversion Manhole 29
12 Theoretical Influent Rates 30
13 Retention Tank Site 31
14 Void Space Volume 37
15 Flow Rate from 0.46 Meter Outlet 40
16 Flow Rate from 1.52 Meter Outlet 41
17 Cut-Out View of Settling Tube Module 42
18 Representative Component Elevations 44
19 Volume in Clarifier 46
20 Isometric of Automatic Samplers 48
21a Installation of Asphalt Side Liner 52
21b Installation of Bottom Liner (West) 52
22a Installation of Bottom Liner (South) 53
22b Backfill with Media 53
23a Top Liner Material 54
23b Clarifier and Exposed Media 54
A-l Overflow System Analysis 73
A-2 Velocity of Flow vs. Effective Diameter 75
C-l Annunciator Panel Lights and Recorders 80
C-2 Instrument Mounting Board 85
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TABLES
NO.
1
2
3
4
5
6
D-l
D-2
D-3
D-4
D-5
Rainfall Stations
Maximum Recorded Rainfall-Akron Area
Sizes of Coarse Aggregates
Solids Contained Within Media
Construction Costs
Construction Cost Comparison
Precipitation Events
Sampling Data
Sampling Data Supplement
Grab Sampling Data
Grab Sampling Data Supplement
Page
11
18
35
63
65
67
91
97
107
113
114
Vlll
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ABBREVIATIONS
BOD
C
of s
cm
COD
CY
DO
DWF
DIG
fps
ft.
gal.
GPM
HP
hr
i
in.
k
km
1
I/sec
LP
LS
m
mg
MG
MGD
N.D.
psi
P.V.C.
Q
SS
SY
t
U.S. EPA
biochemical oxygen demand
coefficient of runoff
cubic feet per second
centimeter
chemical oxygen demand
cubic yard
dissolved oxygen
dry weather flow
stone size of which 10% is finer
feet per second
feet
gallons
gallons per minute
horse power
hour
rainfall intensity
inch
permeability of stone
kilometer
liter
liter per second
lineal feet
lump sum
meter
milligram
million gallons
million gallons per day
not detectable
pounds per square inch
polyvinyl chloride
flow rate
suspended solids
square yard
rainfall duration
United States Environmental Protection Agency
ix
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ACKNOWLEDGEMENTS
It has required the support and kind assistance of many
individuals and organizations to make this project possible.
The following acknowledgements are only a few of those to
whom we are sincerely grateful.
Assistance and direction were provided by the U.S. EPA Storm
and Combined Sewer Pollution Control Research and Development
Program through Messrs. William A. Rosenkranz and Farancis J.
Condon. Mr. Alfred C. Smith, Project Officer of the U.S. EPA
Region V, Ohio District Office also deserves recognition.
The support of the Mayor of Akron, Ohio, the Honorable
John Ballard, Mr. David Zimmer, Service Director, and the
entire City Council is acknowledged with sincere thanks,
along with the Bureau of Engineering, Mr. James E. Watson,
Project Engineer, Mr. C.E. Susong, Municipal Engineer and
Project Director, and Mr. Lewis Debevec, Division Manager of
Water Pollution Control for Akron, Ohio.
Bay Construction, Inc., of Sandusky, Ohio is acknowledged
for the competent construction of the facilities.
Acknowledgement is made for the assistance provided by various
members of the consulting engineering firm of Karl R. Rohrer
Associates, Inc., throughout the project:
To Mr. Karl R. Rohrer who conceived the project and gave
counsel and direction throughout' its development;
To Mr. Harold L. Laurila whose able assistance in the
planning, construction, operation and evaluation phases
was invaluable;
To Mr. Terrence Gerson who provided supervision as the
Project Engineer;
To Mr. John Hollis who was in charge of the daily operation
of the facility and the laboratory; and
To Mr. Bryan Ashman who provided assistance in preparation
and assembly of the final report.
x
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SECTION I
INTRODUCTION
PURPOSE OF THE PROJECT
Combined sewer systems, which make provision to overflow excess
amounts of stormwater during precipitation events, were adopted
by many cities throughout the United States due to the economic
savings incurred when compared to separate storm and sanitary
sewers. Untreated combined sewer overflows have high concentra-
tions of 5-day Biochemical Oxygen Demand (BOD) and suspended
solids (SS). The average BOD concentrations in combined sewer
overflows are approximately one-half that of raw sanitary
sewage; the average SS concentrations are approximately twice
that of the raw sanitary sewage.
Methods are being studied on the elimination of the pollution
problem associated with combined sewer overflows. In addition
to being a costly alternative, sewer separation does not
necessarily alleviate the problem. Even separate storm waste-
waters are significant sources of pollution, typically
characterized with SS concentrations equal to or greater than
thQse of untreated sanitary wastewater and BOD concentrations
approximately equal to those of secondary effluent.
This project demonstrates and evaluates the feasibility of an
underground void space temporary storage tank, as one solution
to the pollution problem presented by combined or storm sewer
overflows. By intercepting the combined sewer overflows, storing
them in the void space retention tank, and regulating the dis-
charge of the detained stormwater to the treatment facility
during nonpeak hours, a significant degree of pollution reduction
at the outfall can be attained. All stormwater which would exceed
the storage capacity of the facility, would be chlorinated before
being discharged into the receiving waterbody.
The_underground storage facility is a dual usage concept. In
addition to collecting, storing, and regulating potential com-
bined sewer overflows, the facility's top surface could be made
usable as a park or recreation grounds. This dual usage concept
establishes an aesthetically pleasing and socially acceptable
storage facility.
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SCOPE OF PROJECT
The scope of the project can be divided into three distinct
areas. The first area of work consisted of:
1. site investigation and acquisition of property
2. topographic and hydrographic surveys
3. hydraulic studies
4. structural and instrumentation design
5. specifications and construction drawings.
The second area of work consisted of:
1. construction of the prototype facility.
The third area of work consisted of:
1. operation of the prototype facility for two years
2. evaluation of the operational period
3. continued operation of the facility by the city.
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SECTION II
CONCLUSIONS
Much emphasis has been placed on the pollution load to receiving
water bodies caused by combined sewer overflows, and many methods
have been studied on controlling and preventing these overflows.
Determination of the most economical approach must consider the
available methods: sewer separation, storage, treatment, and
storage with treatment. The underground void space storage con-
cept can be one economically feasible and aesthetically appealing
solution to the abatement of combined sewer overflows.
1. The total capital cost of the 3.8 million liter (1 MG)
demonstration project was $750,000. Of this amount,
$471,000 was used in the construction and instrumentation
of the prototype facility. It is anticipated that future
facilities, with limited instrumentation for storm evalua-
tion, could be constructed for $0.079 to $0.092 per liter
($0.30 to $0.35 per gal.).
2. The underground void space storage concept allows for dual
land usage. This versatility permits adaptation of the
surface for recreational ground, parking, open-air storage,
or other facilities which make it compatible with its
surrounding areas.
3. No detectable offensive odors or flammable gases were
generated in the storage facility during the two year
operational period. A combination of factors was re-
sponsible for this: the storm flow from this steeply
sloped combined sewer system r.onsisted mainlv of suspendp-.rl
inorganic solids rather than putrescible organic materials,
chlorination of the flow entering the media prevented the
wastewater from going septic, and the detention times of
the stored overflows were relatively short. Slime and algal
growth within the media were not detected, and there were
no rodent or insect infestations.
4. The first flush concept, produced by settleable material
being deposited within the combined sewers during dry-
weather flow, was not evident for the Tallmadge Memorial
Parkway drainage area. The high dry-weather flow velocities
associated with the steep sloped (9%) drainage area,
-------
prevented material from settling in the sewers. At the
onset of a storm, however, there are high initial, concentra-
tions of suspended solids due to the sediment which is
carried into the inlet basins as runoff from the drainage
area.
5. Based on the calculated volume reduction due to contained
solids, and an average of 10 complete fillings per year,
over 65 percent of the void space volume would remain after
25 years of use. These calculations assume that all of the
suspended solids which enter the media would be contained.
6. The prototype facility was not designed to operate auto-
matically, hands-off, thus many storms had ceased before
an operator arrived at the facility. Due to the drainage
area's short initial time of concentration (20 min.), the
variable nature of storms, and the difficulties experienced
with the storm notification system, many precipitation
events were not stored in the facility and operational data
was not collected.
Although the prototype facility experienced some opercitional
difficulties and several design changes are recommended, the
void space storage concept could be a practical and economical
solution to the pollution problems associated with combined
sewer overflows.
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SECTION III
RECOMMENDATIONS
The primary purpose of the two-year study and evaluation period
of the Tallmadge Memorial Parkway Storm Water Retention Tank #1,
was to determine the feasibility of the underground void space
storage concept (Geo-Cel) in the reduction of pollutant loads
from combined sewer overflows on receiving water bodies. Based
on the results obtained from the prototype facility, several
design alterations are presented which would increase the
potential and cost-effectiveness of the void space storage
concept.
1. Due to the insufficient data obtained from the influent
sampler, the effectiveness of the settling tube modules
could not be completely evaluated, however, because of the
high and variable flow rates of stormwater entering the
system (greater than those recommended by the manufacturer),
they did not prevent the carryover of suspended solids onto
the exposed media surface. For systems involving flow
rates greater than the tube settler's design rate, the
modules, should not be incorporated into the facility design.
2. If the settling tube modules would be eliminated from the
system design, the clarifier, which comprised nearly one-
fourth of the total construction costs, could be drastically
reduced in size. This, however, would require an alterna-
tive means of solids removal or a redesigned storage cell
feed system to prevent the detrimental effects of solids
reducing the infiltration rate into the exposed media
surface.
Where natural media (stone) is used, the storage cell
should have a bottom or well feed system which would be
partially self-flushing after each storage event. If an
economical artificial inert media could be obtained, which
would have greater void space and less surface contact
points, any feed system would be adequate since the
suspended solids would not be captured on the exposed media
surface.
3. The present 1.22 meter (48 in.) riser overflow system and
the 1.52 meter (60 in.) emergency pressure relief gate
valve could be redesigned to allow a more economic and
-------
automatic operation. If and when the suspended solids
would reduce the infiltration rate into the media, the
overflow system should automatically provide pressure
alleviation.
4. The combined sewer influent flow should be monitored with a
direct readout flow meter. In addition to giving instan-
taneous influent rates, the flow meter signal (electrical
or pressure) could be used to provide a precise automatic
chlorination input system.
5. Due to the turbidity and color of the combined sewer flows,
a non-colorimetric chlorine analyzer is suggested if an
analyzer is to be used in the facility.
6. Future study of detention time of combined sewer overflows
should be conducted to determine the deleterious effects of
odor and combustible gas as a function of time.
7. Both liner materials tested proved effective for the dura-
tion of the prototype facility's evaluation period. Con-
tinued use of the facility by the City will provide
additional information on the life expectancy of the two
liners. Where good slite conditions prevail, future in-
stallations could use the more economical liner.
Future studies should be performed which would focus on analyzing
a series of void space retention tanks at combined sewer outfalls
for their joint effects on the water quality of the receiving
watercourse. The sampling program should include both a pre-
and post-installation evaluation of the receiving river or stream
water quality, in addition to the monitoring and sampling of the
stored combined sewer overflows.
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SECTION IV
TEMPORARY STORAGE FOR POLLUTION REDUCTION
Within the past decade increasing awareness and concern of the
pollution factors in the environment have focused attention on
the pollution load contributed to the nation's water resources
by combined sewer systems. Many cities adopted the combined
manner of sewer construction due to economic savings when
compared to separate storm and sanitary sewers.
Methods are constantly being studied on how to eliminate the
pollution problem presented by combined sewer overflows.
Separation of sewers is not only economically unfeasible but
also does not allow treatment of the storm runoff which is
recognized as a major contributor of pollutants to the receiving
water body. The U.S. EPA report 11022 ECV 09/71 entitled
"Underwater Storage of Combined Sewer Overflows" states:
"Separation of sewers may not be the economical
answer for elimination of combined sewer pollution
load. From studies conducted during the past decade,
evidence is that the total pollution load from storm
overflow from combined sewer systems is not from
sanitary flow only. About 80% of the pollution load
is due to the sanitary wastes. The other 20% of the
pollution load is entirely due to storm runoff."
Both the quantity and quality of stormwater runoff from an urban
area are highly variable and transient in nature, being dependent
upon meteorological and climatological factors, hydraulic
characteristics of the surface and underground conduits, and on
the nature of the antecedant period. The pollutants contained
in urban stormwater runoff and drainage include street litter,
leaves, grass clippings, dust and debris of airborne fallout,
eroded soil, animal excreta, fertilizer, insecticides, road salt
and other chemicals.
Combination sewer systems have three major drawbacks:
1. The increased flow during storms may overload the hydraulic
capacity of the sewage treatment plant.
-------
2. Low velocities of dry-weather flow promote high loadings
of solids and BOD to settle in the sewers, promoting a
septic condition.
3. The "first flush" of stormwater including these solids may
be discharged directly into the receiving body of water
through the regulating device, or may be flushed to the
treatment plant where it upsets the biological balance.
Although combined sewers may provide adequate capacity to carry
peak storm flows, sewage treatment facilities do not have the
same hydraulic capacity. During periods of precipitation, the
sewage treatment facility may be unable to cope with the combined
flows; the excess is diverted from the treatment plant and dis-
charged directly to a receiving water or water course. These
combined sewer overflows are of particular concern because they
result in the bypass to the environment of untreated sewage and
present a potential public health hazard.
Advocates of partial storage systems point out that the major
pollutant load encountered in storm overflow from combined
sewers occurs during the first flushing action of a storm. If
storage can be provided to accommodate this first flush of
water, a high degree of pollution control will be accomplished
at much less capital investment than with sewer separation or
total storage systems.
Due to the nature of combined sewer overflow, that is, a short
duration, high flow volume discharge, it appears that, in many
cases, a storage cell could be incorporated into the overall
system or scheme to control pollution from combined sewer
overflows.
For those treatment facilities containing high-rate processes
such as mechanical screening and dissolved air flotation, the
least costly facility always resulted when the treatment process
was combined with a holding pond whose capacity was matched with
that of the process to provide a facility of optimum size. The
holding pond provides mainly peak flow attenuation, but also
some pollutant removal capability as well. Reduction of instan-
taneous peak flows results in both smaller downstream treatment
facilities with improved utilization factors, and lesser instan-
taneous pollutant loadings and effects on receiving waters. For
example, if an appropriately sized storage facility was placed
strategically at the point of overflow, ahead of a municipal
water pollution control plant, it may be possible to accommodate
the combined sewer overflow discharge over an extended period of
time. The storage facility would return the storm drainage,
which would have otherwise overflowed, to the municipal treatment
plant some time after the storm overflow had ceased. The storage
treatment facility would be sized to treat a certain peak volume
of combined sewer overflow, which can be determined from an
8
-------
analysis of the combined sewer overflow hydrographs for a defined
drainage area. All overflows in volume equal to or less than the
design capacity of the storage-treatment facility would be
handled without any untreated pollutant discharge to the receiving
waterbody. Determination of the required capacities of a storage
facility to contain stormwater runoff and combined sewer over-
flows associated with specific storm recurrence intervals must
be based upon the treatment facility's hydraulic capabilities,
drainage area topography, rainfall intensity probabilities, and
future runoff coefficient projections.
The appropriate location for future overflow storage-treatment
facilities would be in the vicinity of the present overflows or
diversion structures and, in certain locations, where large trunk
sewers meet the interceptor, even though an overflow structure
does not now exist. The facility is used as an interim storage
device to stop overflows, hence possibly alleviating the need
for an expensive program to meet current effluent standards.
This project demonstrates and evaluates one method for the re-
duction of combined sewer pollution. Excess stormwater is
chlorinated, clarified and flows into a large, underground, lined
tank filled with "media" (in this case gravel) which holds up the
roof. The water is stored in the void space of the media until
the storm subsides. This concept of void space storage in an
underground, lined tank filled with inert media is called a
Geo-Cel.
Pollution reduction is accomplished by containment and delay
with chlorination in the Geo-Cel. Combined sewage, which would
normally flow into the receiving waterbody, is contained within
the storage facility until the sewage treatment plant has the
capacity to process the Geo-Cel effluent. The facility effluent
can be delayed and regulated by manipulation of the effluent
slide gates.
The storage holding basin concept will work on both combined and
storm sewers should there be sewer separation.
Void space storage, where applicable, offers low land costs
through dual land usage, an aesthetically pleasing and compatible
installation, and an economical method of elimination of combined
sewer pollution.
By dual use of the top surface, it is possible to incorporate
aesthetically appealing landscaping, and possibly recreational
facilities, such as playgrounds or tennis courts. The added
cost of landscaping or recreational facilities would not be high
from the standpoint of the project, but would substantially
increase the social acceptance and social value of the project.
Parking space is also another potential usage.
-------
Geo-Cel temporary holding tanks should be considered as one of
the alternative approaches to regaining system storage in the
future, when population and industrial growth have, encroached
upon the current excess capacity (if any) built into the
collection system.
10
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SECTION V
RAINFALL AND SITE CONDITIONS
RAINFALL AND PRECIPITATION
Prior to construction of the test facility, available recorded
rain data for the area was investigated. Four different sources
were available from the National Weather Records Center in
Asheville, North Carolina. Table 1 lists the four sources, their
respective length of record, and their location with respect to
the site.
Source
1. Akron Water
Pollution Con-
trol Station
TABLE 1. RAINFALL STATIONS
Data From- To
4-13-1957 Present
Location
4.55 km (4.16
miles) N.N.W.
of the site
Elev = 232
meters (760
feet)
2. Cuyahoga Falls 10-2-1939
12/1941
4.55 km (4.16
miles) N.N.W.
of the site
3. Akron Municipal
Airport
1946
1952
4.62 km (4.22
miles) S.E.
of site
4. Akron-Canton
Airport
1948
Present
15.26 km
(4.22 miles)
S.E. of site
Elev = 369
meters (1209
feet)
11
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The existing data was used in the analysis of storm events for
the Akron, Ohio area. The City of Akron, Bureau of Rnaineering
has previously analyzed recorded rainfall data and formulated
intensity - duration - frequency relationships for the Akron area,
The intensity formula is of the form:
I = cTm/ 2.54 (t+d)
n
Where:
and:
I is the intensity in centimeters per hour
t is the duration in minutes
T is the frequency of occurrence in years
c,d,m, and n are regional constants
These curves are represented in Figure 1 for recurrence intervals
Of 1,3,5,10,15,25,50 and 100 years and durations from 5 to 180
minutes. These relationships are less accurate for durations
less than 5 minutes or greater than 180 minutes.
Also useful in the analysis of precipitation are two reports.
The first report, by Marvin E. Miller, State Climatolqgist, and
C.R. Weaver, was Monthly and Annual Probabilities for Selected
Locations in Ohio published in March, 1969, by the Ohio Agricul-
tural Research and Development Center in Wooster, Ohio. Curves
were prepared for finding the probability of receiving a depth
of precipitation for a given return period for any given month
and annually for the Akron area. These curves are represented
in Figures 2 and 3.
The second report contains the results of a study conducted by
Marvin E. Miller. Curves were prepared for finding the maximum
daily precipitation of a given return period for any given month
and annually for the Akron area. These curves are represented
in Figures 4 and 5.
The yearly maximum 24-hour precipitation for the 1887 to 1974
period for the Akron area are listed in Table 2.
DRAINAGE AREA AND SITE CONDITIONS
Within the lower, eastern, portion of the Tallmadge Memorial
Parkway drainage area (Figure 6), bounded by the B & 0 Railroad
on the west, Tallmadge Memorial Parkway on the south, and the
Little Cuyahoga River on the east is a sector of land owned by
the City of Akron. This land, which was in part used for
sanitary landfill started in 1963, was allocated by the City of
Akron for the construction and evaluation of the project:
"Demonstration of Void Space Storage with Treatment and Flow
Regulation". A topographical drawing of the drainage area is
included as Figure 7.
12
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8
O
fa
t/3
1
CD
U
O
D
C
fa
I
6
H
EH
Q
I
H
EH
S
H
w
O
H
fa
o
13
-------
MONTH
FIGURE 2. MONTHLY RAINFALL PROBABILITY CURVES
14
-------
m~~
5-
0_
r $•
zi10
-
o
m
o-
-8
O
8
0
S
o
o
J I I 1 I I I »
O 5 IO -ZO 3O4OEOGOTO SO
PEOBAE>\UTV OF REC&1V\MG EQUAL. ~TO
OR ~
FIGURE 3. YEARLY RAINFALL PROBABILITY CURVE
15
-------
0
MONTH
FIGURE 4. MONTHLY MAXIMUM DAILY PRECIPITATION
16
-------
c
J
4
a
2
-------
TABLE 2. MAXIMUM RECORDED RAINFALL - AKRON AREA
Precipitation
Year Month 24 Hour Period
(cm)
Precipitation
Year Month 24 Hour Period
(cm)
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
Aug. 6
Aug. 4
June 28
Spet. 11
June 18
June 19
Oct. 13
Sept. 8
Aug. 6
June 7
July 5
Nov. 5
May 27
July 25
Aug. 19
July 18
Aug. 27
April 1
May 25
July 5
Jan. 4
May 20
Aug. 15
Oct. 6
Sept. 15
July 14
March 25
March 24
June 15
May 29
June 1
May 13
June 26
June 17
March 28
May 19
May 12
June 29
July 10
Sept. 2
Dec. 1
July 20
April 5
Jan. 8
4.24
4.24
4.98
7.75
2.95
4.14
4.64
4.17
4.50
9.14
5.21
4.62
6.07
5.84
4.78
5.28
7.92
4.87
4.17
3.07
3.73
4.22
4.32
6.10
8.18
7.85
12.07
4.70
3.66
13.03
2.74
3.94
4.17
6.73
5.16
3.73
4.60
10.92
4.37
11.81
5.26
7.16
6.48
2.74
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
•Sept. 26
Aug. 18
March 13 ',
Sept. 15 :
Aug. 2
July 24
January
Sept. 12
Oct. 27
Aug. 27 :
July 7
May 15
July 7
Aug. 23
May 17
July 21
Aug. 25
Sept. 19
July 9-10
July 9-10
Sept. 13
Sept. 18-19
June 16-17
March 1
Nov. 15
May 26-27
Feb. 24-25
July 15
July 18
June 12-13
July 19
July 3
Aug . 6
July 21
Aug. 25
Nov. 2
Sept. 27
July 17
July 5
June 14-15
Aug. 26-27
July 15-16
July 20-21
Aug. 3-4
2.95
4.57
7.11
5.56
4.83
6.10
4.75
11.05
4.98
4.88
7.92
3.91
15.14
4.09
7.24
3.43
5.44
6.12
4.83
5.64
3.86
5.56
6.32
2.44
5.08
6.86
5.70
4.27
4.52
5.79
8.15
3.91
3.48
7.75
3.81
4.37
3.89
3.48
6.10
9.17
7.29
8.33
4.17
5.84
18
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CUYAHOGA
TAUI_MAO©& AVE.
RETENTION
CITY L1M
Q 1NJTEESWE EDUTE
O STATE: ROUTE
O
FIGURE 6.
DRAINAGE AREA LOCATION
19
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The drainage area, which is generally an older but above average
income neighborhood, is characterized by large lawn areas and
steep slopes. Over 91 meters (300 ft.) of elevation difference
are encountered between the area's highest point and the headwall
at_the Little Cuyahoga River. There are several apartment
buildings and one primary school within the area. No commercial
establishments, not even gasoline stations, are contributory to
the drainage area.
The landfill, which was started in 1963 on the area adjacent to
the retention tank, is approximately 2 km (1-1/4 mi.) long and
an average of 0.4 km (1/4 mi.) wide. The depth of fill adjacent
to the tank was 1.2 to 1.5 meters (4 to 5 ft.) and increased in
depth to approximately 3 meters (10 ft.) near the Little Cuyahoga
River. The area in which the retention tank is located was
filled with a clean fill since some housing previously existed
nearby. The intention was to keep the organic material further
away from the housed area to reduce complaints of odors and
pests. These houses have since been removed. In the area near
the retention tank, all debris was covered with a minimum of
0.91 meters (3 ft.) of cover.
One of the reasons the City of Akron selected this area as a
land fill was the fact that a blue clay stratum underlies the
entire landfill, thereby reducing the leaching and pollution of
ground water. The generalized stratigraphic sequence of rock in
the area of the tank shows a Pleistocene series of till with a
heterogeneous mixture of clay, sand and gravel with a predomi-
nance of clay. Previous to construction, it was anticipated that
the ground water table at the tank was 6.1 meters (20 ft.) below
the ground surface. The last fill dumped on the area adjacent
to the retention tank was land filled in 1964.
Runoff coefficients for the 76.28 hectare (188.5 acre) residen-
tial drainage area vary from approximately 0.40 to 0.70 with a
weighted average estimated at 0.60. This weighted coefficient
was used to predict anticipated flow rates into the system for
any intensity rainfall.
Based on the intensity-duration-frequency relationships for
Akron, and the Rational Method of drainage computation, Figure 8
represents the intensity-duration-flow rate-and volume relation-
ships for the Tallmadge Memorial Parkway drainage area. The
weighted coefficient of discharge, c, for the drainage area of
76.28 hectares (188.5 acres) was assumed to be 0.6.
The Tallmadge Memorial Parkway area is one of 35 combined sewer
drainage areas in Akron, Ohio. Most of the present combined
sewer collection system was built during 1929 and 1930, with
additional areas being added as necessary. The existing
Tallmadge Memorial Parkway drainage area system consists of 0.20
21
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meter (8 in.) to 1.37 meter (54 in.) diameter sewers and a 1.37
meter x 1.37 meter (54 in. x 54 in.) rectangular storm overflow
outlet.
The major trunk sewer through the drainage area varies from 0.38
meter (15 in.) to 1.37 meter (54 in.) diameter culverts.
Vitrified clay tile is used for the small pipe diameters with
brick and reinforced concrete being used for the larger sizes.
At the time of construction, the maxinum dry-weather flow from
the Tallmadge Memorial Parkway drainage area was estimated at
1.987 million liters per day (0.525 MGD) or 22.94 liters per
second (0.81 cfs). The maximum flow from the drainage area to
the Little Cuyahoga Interceptor was limited by a 0.305 meter
(12 in.) pipe from the trunk sewer drop inlet to the interceptor.
The 0.305 meter (12 in.) pipe had a capacity of 278 liters per
second (9.8 cfs). All flow in excess of 278 liters per second
(9.8 cfs) was discharged directly into the Little Cuyahoga River.
Overflow into the river, therefore, could have been expected for
any storm with rainfall intensities greater than 0.23 centimeters
(0.09 in.) per hour.
23
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SECTION VI
SYSTEM DESIGN
The "Demonstration of Void Space Storage with Treatment and Flow
Regulation" consisted of construction, operation, and evaluation
of an underground storage and treatment facility for combined
sanitary and storm flows. The primary project facilities in-
cluded a diversion manhole, a clarifier, and a 3.8 million liter
(1 MG) temporary storage space. The wastewater was intercepted
from the existing combined sewer system at the diversion manhole
and was directed to the clarifier chamber of the retention cell
by the 1.22 meter (48 in.) influent pipe. (Figures 9, 10, 13 and
A-l visually aid in the explanation of the system.) The clari-
fier was a large volume tank 379,000 liters (100,000 gal.)
designed to reduce the high entrance pipe velocities and aid in
the settling out of suspended sediment. Within the clarifier
were tube settlers which increased the settling rate of suspended
matter. The wastewater entered into the void space retention
area by passing over the clarifier weir (above the tube settlers)
and infiltrating into the exposed media surface (Figure A-l).
The temporary storage tank included novel concepts in design
and operation. It was a 60.96 meter x 60.96 meter x 3.05 meter-
deep (200 ft. x 200 ft. x 10 ft. deep) excavated hopper, lined
with an impermeable membrane, filled with an inert media, covered
with another impermeable membrane and soil, and the surface media
made usable. The Tallmadge Retention Tank #1 used na.tural, non-
fractured rock as the media with a void space of approximately
40 percent of the total volume..
With the occurrence of a storm, the flow rate into the facility
increased in proportion to the rainfall intensity. If the flow
rate of stormwater entering the clarifier was greater than the
effluent rate, storage of excess stormwater automatically
commenced. So long as the influent rate exceeded the effluent
rate, regulated by the 0.46 meter (18 in.) and 1.52 meter
(60 in.) slide gates, the volume stored within the clarifier
increased until the water level reached the level of the weir.
All additional flow caused overflow of the weir and sank into
the 60.96 meter x 2.59 meter (200 ft. x 8.5 ft.) exposed media
surface. The maximum storage space within the media was
approximately 3.8 million liters (1 MG). If the volume of flow
which passed over the clarifier weir exceeded 3.8 million liters,
the chlorinated stormwater overflowed into the 1.22 meter (48 in.)
24
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LITTLE
CUVAHOSA.
R.IVER
m. X 3.OS m. TO
PAVED DITCH
OVEUPLOW TO RIVER
CLARIFIED, CWLORIMATED
IKi
OP
3, -res, .4.1 z J2.
|O6
STORED.
SAKAPLEU.
GRAVEL
MEDIA
WEIR SAMPLER
DlVERSlOW MANHOLE
FIGURE 9. BLOCK DIAGRAM OF SYSTEM COMPONENTS
25
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risers and was transported to the Little Cuyahoga River. (The
chlorinator was triggered when the water surface elevation
reached that of the clarifier weir.) After the storm, the flow
entering the clarifier gradually subsided to the dry-weather flow
rate. That stormwater which was contained within the facility
was gravity discharged, at a regulated rate, to the Akron Treat-
ment Plant through the 0.46 meter (18 in.) effluent gate.
A more detailed analysis of each of the system components is
presented in the following section, "System Components".
27
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SECTION VII
SYSTEM COMPONENTS
Studies have been conducted on the various individual components
of the facility to evaluate their operational feasibility and
design. The basic project facilities included a diversion man-
hole, a clarifier, and a 3.8 million liter (1 MG) temporary
storage space.
DIVERSION MANHOLE
The diversion manhole regulated, by means of an orifice and
diversion wall (added during the operational phase of the pro-
ject) , the allowable flow rate into the clarifier. It was
located at the point of connection to the existing sewer
approximately 76 meters (250 ft.) west of the B & O Railroad.
At this location, the combined sewer was outside the edge of the
Tallmadge Memorial Parkway pavement which eliminated construction
in the street and allowed for periodic visual inspections.
The diversion chamber, which was 2.74 meters x 3.96 meters
(9 ft. x 13 ft.) rectangular and 4.27 meters (14 ft.) deep
(Figure 11), diverted combined sanitary and storm flow to the
storage facility. The maximum influent flow rate to the
clarifier was controlled by means of the orifice and diversion
wall. The height of the orifice opening and diversion wall
were controlled by 8.9 centimeter (3-1/2 in.) planks of
appropriate lengths. The orifice opening was adjustable from
0 to 1.22 meters (0-48 in.); the diversion wall height was
adjustable from 0 to 1.83 meters (0-72 in.). A minimum height
of 1.22 meters (4 ft.) was recommended for the diversion wall.
This allowed for all dry-weather flow and low storm flow rates
to be directed into the clarifier. During larger storm flow
rates, part of the flow was bypassed into the original sewer.
Figure 12 lists the theoretical total and influent flow rates
expected for various orifice openings with the diversion wall
height equal to 1.22 meters (4 ft.).
INFLUENT PIPE
The 1.22 meter (48 in.) diameter system influent pipe (refer to
Figure 13) connected the clarifier with the diversion manhole.
The culvert passed beneath the B & O Railroad tracks and was
28
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PLAN
••'• •• *•:•?•; \ ••«' .;> •;•••>
i-r.:>.•>• \ ;-P .: * : >•- • .>
SE.CT1ON B-E>
WALL-
SECTION A -A,
FIGURE 11.
DIVERSION MANHOLE
29
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31
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divided into two sections, each with different slopes. The first
section, from the diversion manhole to the manhole approximately
21 meters (70 ft.) west of the B & O tracks, was 76 meters
(250 ft.) in length with a 3.2 percent slope: the second section,
which entered into the clarifier, was 40 meters (132 ft.) in
length with a 10 percent slope. Given the maximum orifice flow
conditions produced at the diversion manhole, the influent pipe
had an ultimate theoretical capacity approaching 6510 liters per
second (230 cfs).
GENERAL TANK CONFIGURATION
The general tank configuration and location was partially dic-
tated by the site conditions. A limited land area was "available
due to the old sanitary landfill which borders the site to the
north and east. In addition, a grey silty clay lay under the
site along with a high water table above the clay. Construction
in the clay strata to any appreciable depth would have required
considerably greater installation costs. The allowable depth of
the retention tank was, therefore, limited to 3.05 meters (10 ft.).
Optimum conditions for tank depth versus cost would have required
the tank to exceed 5.5 meters (18 ft.) in depth assuming
acceptable soil conditions.
Figures 7 and 13 show the retention tank location and shape.
The tank was a truncated pyramid with bottom dimensions of
42.67 meters x 51.82 meters (140 ft. x 170 ft.). The top
dimensions were 60.96 meters x 60.96 meters (200 ft. x 200 ft.)
The side slopes were constructed at a 3:1 slope due to the
existing soil conditions and the bottom slope constructed at
0.25 percent slope toward the clarifier to aid in draining the
cell. The south side of the retention cell consisted of, and
was formed by, the sidewall of the clarifier.
Within the confines of the storage cell were three observation
manholes equally spaced on a diagonal line from the southeast
to the northwest corner of the site. In addition to providing
observation points, the manholes housed the pressure transducers
which recorded the water depth in the tank and transmitted this
data to the control building. The pressure transducers were
secured at a height of 7.6 centimeters (3 in.) above the bottom
liner material.
The following sections describe the individual components of
the retention cell and discuss their affect on the flow pro-
perties and storage capacity of the cell: liner materials,
storage media, feed-overflow-draining systems.
Membrane
One of the important considerations for the storage tank to
function properly was the tank liner. The following properties
32
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of liners were compared:
1. Relative cost of liner per square meter,
2. Relative cost of construction due to the number of days
required for fabrication, the size of sheet available to
reduce the number of field seams and to reduce potential
leakage, and the ability to bond the liner to itself and
dissimilar materials in the field,
3. Physical properties of elongation, puncture resistance,
tear resistance, specific gravity, and flexibility,
4. Chemical resistance to environment and chemical properties
of the liner material,
5. Biological resistance,
6. Maximum allowable slopes and padding requirements,
7. Relative availability, and
8. Expected life of the liner.
The types of liners studied were:
1. Natural and synthetic rubber such as (Hypalon),
2. H.C. Vinyl, pure vinyl, and P.V.C. sheet, and
3. Asphalt.
Although the asphalt concrete was the most economical liner
material, the bottom tank area soil conditions (silty clay with a
high water table) prohibited laying asphalt directly on the soil.
An engineering study was made by the City of Akron and their con-
sultants to determine the most feasible and least expensive liner
design. The following methods were considered:
1. Placing a 15 centimeter (6 in.) concrete pad on the bottom
of the tank instead of asphalt at an additional cost of
$20,000.
2. Placing a 762 micron (30 mil) P.V.C. liner under the whole
tank. This would have, cost an additional $12,000.
3. Placing a slag base 0.30 meters (12 in.) thick over the
bottom area then laying the asphalt. This would have cost
an additional $20,000.
4. Placing a 762 micron (30 mil) P.V.C. liner on the bottom
only, and retaining the asphalt side slopes at an additional
cost of $7,148.18.
In addition to being more economical, there was the feature of
testing both the P.V.C. and asphalt liner in this installation.
The original construction design of a 5 centimeter (2 in.) thick
asphalt top liner material was not practical due to climatic
conditions. Delays in the project, initiated by rain, postponed
placing of the top liner until December, 1972. Because of the
cold weather a substitution was made to a 254 micron (10 mil.)
P.V.C. liner.
The recommendation for the choice of P.V.C. sheet as compared to
Hypalon was made due to the following:
33
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1. Hypalon is laid in an uncured state and gains strength
during curing. Hypalon strength in a cured state is higher
than P.V.C. but, maximum strength was required during con-
struction and the Hypalon would have been at a lesser
strength at this point.
2. Hypalon cures to full strength only after several months of
exposure in normal use of the material. In this application,
full strength may have never been realized due to the moist
underground environment.
3. Hypalon could be supplied only in 18.29 meters x 69.96
meters (60 ft. x 200 ft.) sheets; thus the field seams
required would have been more numerous. A P.V.C. liner
could be supplied in two pieces.
The stormwater which would be stored in the tank was from a
residential drainage area, therefore, the chemical properties of
the effluent were not expected to promote excessive deterioration
of the liner materials. The liners installed have sufficient
strength to withstand the static loads and hydrostatic pressures
to be encountered.
Two hundred fifty four micron (10 mil.) P.V.C. buried membranes
have a twenty-five year life expectancy according to the Bureau
of Reclamation.
Media
The tank media was one of the more important items studied for
use in "Demonstration of Void Space Storage with Treatment and
Flow Regulation". Some of the factors considered in the media
study were:.
1. Void space available,
2. Physical and chemical resistence,
3. Plow of stored liquid through the media,
4. Availability in the local area,
5. Method of installation,
6. Cost per ton.
The void space available from a given media has a direct effect
on tank size for a given volume, and thus, a direct bearing on
all tank costs. Optimum conditions for tank costs are reached
at a maximum of void space for a given media. However, maximum
void space and strength to carry the load to be expected limited
the type of media which could be used.
Both artificial and natural media were considered. Artificial
media were (1) artificial trickling filter media, (2) tower park-
ing media and filter blocks, (3) manufactured ceramic shapes and
(4) industrial wastes or scrap.
34
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The artificial trickling filter media did not possess sufficient
structural strength for this application. The tower parking
media and filter blocks were not available in the quantity
necessary nor at a competitive price.
No industrial wastes or scrap were available in the area for use
as media at the time of construction.
Natural media, such as bank run gravel and stone, was studied and
found to be the only choice economically available in the Akron
area at the present time.
The manufacture of ceramic shapes remains a possibility for
future designs. The possibility of an 80 percent void space
would allow the cost to be competitive even if the cost per cubic
meter were twice as high as natural media. The ceramic media can
be manufactured with sufficient strength for the tank media;
however, installation might pose a problem.
Determination of the type of natural media to be used posed
several problems:
1. What void space was available, with required washing.
2. Physical and chemical properties necessary,
3. Quantities and types of media available, and
4. Method of installation.
The specifications for the natural media chosen stated that the
bulk of the media be comprised of AASHO #1 or #2 size stones with
0.102 meters to 0.152 meters (4 in. to 6 in.) of #46 stone placed
on the exposed media surface. The AASHO specifications for these
stone sizes are given in Table 3.
TABLE 3.
SIZES OF COARSE AGGREGATES
Size
No.
Amounts Finer Than Each Laboratory Sieve (Square Openings)
Percentage By Weight
.089m
3.Sin.
.076 .064
3.0 2.5
.051
2.0
.038
1.5
.025 .019
1.0 .75
.013 .010
.50 .38 NO.
1
2
46
90-100
100
25-60
90-100
35-70
100
0-15
0-15
95-100 -
0-5
0-5
35-70
10-30 0-5
The specifications for stone sizes #1 and #2 limited the percen-
tages of material less than 3.8 centimeters (1.5 in.) in diameter
to a negligible amount. The specific weight of the stone ranged
35
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between 1560 to 1430 kilograms per cubic meter (2630 to 2410
pounds per cubic yard).
To obtain a maximum void space, the graded material was
thoroughly washed prior to placement. The porosity of the media
was estimated at 40 percent, yielding a cell storage capacity
approaching 3.8 million liters (1 MG). Figure 14 represents the
void space volume as a' function of the water surface depth in
the retention tank. Solids which are deposited in the storage
area during filling will reduce the porosity of the media. The
extent of this problem is related to the efficiency of the
clarifier, and to the amount of total solids in storm overflow.
This is analyzed in the evaluation section of the report.
The chemical and physical characteristics of the media were such
that the bank run type material was desirable from a void space
aspect for media shape as well as strength and chemical inertness.
Specifications similar to those used for trickling filter media
were required to enable the media to withstand the environmental
conditions to which it would be subjected.
Natural media as recommended for this system was available in
the Akron, Ohio area.
Feed-Overflow-Draining System
The flow hydraulics of the storage cell are dependent upon the
concepts and design of the feed, overflow, and draining systems.
The feed system describes that method by which flow entered the
media storage area. The overflow system describes that method
by which flow exited the storage area and discharged into the
Little Cuyahoga River. The draining system describes that
method by which flow exited the storage area and discharged
back into the clarifier.
Stormwater could enter into the media storage area by passing
over the clarifier weir or by seepage through the flap gates.
The rate of seepage through the flap .gates, however, was deter-
mined to be minimal 28.3 liters per second (1 cfs) maximum and
can be neglected. The flow over the clarifier weir and the in-
filtration rate into the media were a function of the developed
headwater and the characteristics of the exposed media. The
media characteristics of median size, gradation, porosity, and
permeability were all interrelated and influenced both the in-
filtration and overflow flow rates. So long as fine material did
not accumulate on the exposed media surface, the theoretical
infiltration rate varied from 42,500 to 255,000 liters per second
(1500 to 9400 cfs) depending upon the developed headwater. (Cal-
culations for infiltration rates are presented in Appendix A.)
Small sediment particles could be trapped on the exposed media
surface and could drastically reduce the permeability of, and
infiltration rate into, the media.
36
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10 IS ZO ZE> 30
I (£.MOS)
O \
IO
FIGURE 14. VOID SPACE VOLUME
37
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If and when the entire media storage space was filled with
stormwater, flow may exit the system by means of the 1.22 meter
(48 in.) overflow risers which empty into the 1.52 meter (60 in.)
overflow pipe. The overflow riser system extended from the
clarifier for 32 meters (106 ft.) along the east side of the
storage retention area (Figures 9 and 13). There were 12 risers
protruding from the 1.52 meter (60 in.) corrugated metal pipe,
one of which was located within the exposed media. The overflow
pipe sloped (1/2 percent) toward a metal tee section which
joined the 1.52 meter (60 in.) pipe with a 1.37 meter (54 in.)
pipe. The 1.37 meter (54 in.) pipe, which had a 2 percent slope
and was 15.24 meters (50 ft.) long, discharged into a concrete,
trapezoidal channel. This channel, with a 1.83 meter (6 ft.)
bottom width and 3:1 side slopes, directed overflow to the Little
Cuyahoga River.
The overflow into the 1.22 meter (48 in.) risers occurred when
the storage area was full and sufficient headwater developed on
the exposed media surface. (Overflow claculations are also
presented in Appendix A.) Assuming no significant accumulation
of fines on the exposed media, the overflow risers could dis-
charge approximately 4248 liters per second (150 cfs) for the
maximum headwater depth of 0.91 meters (3 ft.). The overflow
rate, however, was dependent upon, and limited to, the infiltra-
tion rate, therefore, accumulation of fines on the exposed media
surface seriously reduced both the infiltration and overflow
rates.
The draining system describes the method by which stormwater
exited the storage cell and discharged through the flap gates
and into the clarifier. The 1.83 meter x 1.22 meter (72 in. x
48 in.) cast iron flap gates, which were hinged to the clarifier
wall, had a bottom elevation equal to that of the retention cell
to allow for complete draining. There were four flap gates
joining the two system components.
When a positive water surface elevation difference existed
between the retention cell and the clarifier, the flap gates
opened, due to the hydraulic force, and allowed storrawater
to exit the storage cell. The rate of flow was dependent upon
many variables; however, it was considerably greater than the
maximum effluent rate of the 0.46 meter (18 in.) culvert
exiting from the clarifier.
CLARIFIER
The most complex of the system components was the cla.rifier
chamber. Within the clarifier, regulation and treatment of the
stormwater was performed.
Some clarification was desirable before the combination storm
and sanitary flow was diverted into the storage tank. This
38
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rectangular chamber, 60.96 meter x 1.83 x 4.72 meter high (200ft
x 6 ft. x 15.5 ft. high), was a large volume tank 379,000 liters
(100,000 gal.) designed to reduce the high influent pipe velo-
cities and aid in the settling out of the suspended sediment.
The clarifier floor was sloped at 2 percent, toward the effluent
gate, to promote cleansing of the chamber during draining.
At the east end of the clarifier were two sluice gates which
regulated the rate of flow exiting from the system. The flow
rates from the openings were dependent upon the height of the
sluice gates and the water surface elevation in the clarifier
(Figures 15 and 16). The 0.46 meter (18 in.) effluent culvert
directed flow to the Little Cuyahoga interceptor, whereas that
of the 1.52 meter (60 in.) culvert was discharged directly into
the Little Cuyahoga River. The 1.52 meter (60 in.) gate, which
was designed as an emergency outlet, had a maximum opening of
0.56 meters (22 in.) allowing an overflow rate up to 2550 liters
per second (90 cfs). The 0.46 meter (18 in.) culvert had a
maximum flow rate of 850 liters per second (30 cfs) at 4.57
meters (15 ft.) of headwater.
Stormwater could also flow out of the clarifier by passing over
the 48.77 meter (160 ft.) long weir and into the retention tank
media. The flow over the clarifier weir was dependent upon the
infiltration rate into the media. If sediment would accumulate
on the exposed media surface, the infiltration rate and weir
overflow would be drastically reduced. The overflow weir
elevation was 246.26 meters (807.94 ft.) above seal level, and
was 87 percent of the clarifier full level. There was 0.55
meters (1.8 ft.) of available freeboard between the weir and the
cover tees. The double tees, which enclosed the top of the
clarifier and the exposed media surface, were precast and were
5.11 meters x 2.44 meters (16.75 ft. x 8 ft.) with 0.05 meter
(2 in.) thick flanges.
Within the clarifier were a number of subsystems which treated
and evaluated the storm and sanitary flow: tube settlers,
level indicator, chlorinator and samplers.
Tube Settlers
It was determined that before flow could enter the storage media,
high rate clarification was needed to settle out particles from
a combination sewer, given relatively short detention periods.
Inclined tube settlers were designed to function as a high rate
settler. A cut-out view of a settling tube module is given in
Figure 17. By reducing the width of the flow paths, the wetted
perimeter increases, the Reynolds number decreases, and the
distance a particle is required to settle before encountering
the tube wall reduces. The discrete particles which settle to
the lower tube wall should agglomerate thus reducing the drag
39
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resistance exerted against them. This reduced drag resistance
may allow the agglomerated particles to slide down the tube wall
and settle to the bottom of the clarifier, thus reducing the
carryover of settleable material from the flow passing over the
clarifier weir and onto the exposed media surface. The settling
tube modules may, incidentally, reduce the carryover of
suspended solids.
The manufacturer's operating instructions manual commented that
the installation of settling tube modules would not automatically
improve the performance of the settling basin. The performance
of the tube modules is a function of the following parameters;
basin inlet hydraulics, basin effluent collection hydraulics,
water temperature, chemical feed and coagulation, flocculation,
influent characteristics and range of variations, floe settling
rate, sludge removal capability and effectiveness, flow rate
change frequency and duration, filter design, maintenance and
cleaning, and operator ability and dedication. Many of these
parameters apply to the retention tank system.
Approximately 85.47 square meters (920 sq. ft.) of settling tube
modules were installed in the clarifier to reduce the carryover
of settleable material. The 0.05 meter (2 in.) square tubes
were inclined at a 60° angle from the horizontal and had a flow
length of nearly 0.61 meters (24 in.). The tube modules were
installed at a bottom elevation of 245.4 meters (805.1 ft.)
above sea level (69% of clarifier height).
Clarifier Level Indicator
The clarifier influent flow rate and water level were measured
by evaluating the recorded data of the purge air bubbler type
depth measurement system. Elevations of important structural
components can be represented as corresponding percent of
clarifier full height (Figure 18). Air was forced, by a 5.07
HP (5 HP, U.S. ) air compressor, through the 0.64 centimeter
(1/4 in.) piping of the bubbler mechanism which extended
vertically to the clarifier bottom near the 0.46 meter (18 in.)
gate valve. The compressed air was discharged into the line at
a slow constant rate which, by eliminating silt buildup, was
self-cleansing.
When the water level in the clarifier exceeded the elevation of
the outlet of the 0.64 centimeter (1/4 in.) line, (7.6 centi-
meters or 3 in.), the static pressure produced by the water
elevation resisted the flow of air in the pipe. Measurement of
the pneumatic pressure was analogous to the water level in the
clarifier and was converted by an electronic differential
pressure transmitter to give a specific chart recorder pen
response.
43
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44
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The single purge air bubbler had three pressure transmitters
which yielded water level recordings from 0 to 0.508, 0 to 4.78,
and 4.22 to 4.78 meters (0-20, 0-188, and 166-188 inches). The
bubbler mechanism and the 0 to 0.51 and the 0 to 4.78 meter
(0-20 and 0-188 in.) level recorders operated continuously. The
4.22 to 4.78 meter (166-188 in.) level recorder was energized
when the clarifier level reached 4.22 meters (166 in.). Relays
on the different transmitters controlled the annunciator alarm
lights, sampler operation, chlorine pump, and colorimetric
chlorine analyzers.
The system's average influent and effluent flow rates could be
calculated through the integration of the clarifier water level
with respect to time and gate openings. The volume of stormwater
contained within the clarifier was dependent upon the water
surface level as represented in Figure 19.
Chlorinator
The Tallmadge Memorial Parkway Retention Tank #1 was designed
not only to detain and regulate the peak storm flows but also to
chlorinate that flow which was stored in the media or was over-
flowed to the Little Cuyahoga River. A proportional volume of
15 percent sodium hypochlorite solution was used to disinfect
the stored combined sanitary and stormwater. Chlorine was added
to the stormwater entering the system at the influent pipe when
the water surface elevation equaled that of the clarifier weir.
Three 5678 liter (1500 gallon) subsurface storage tanks were
located near the southwest corner of the clarifier. A 190 liter
per minute (50 GPM) pump drew the sodium hypochlorite solution
from the tanks and discharged a portion of it into the clarifier
at the outlet of the 1.22 meter (48 in.) influent pipe. The
remainder was pumped back into the storage tanks. The quantity
of the solution pumped to the clarifier was regulated by a
manually preset ratio controller.
Both the sodium hypochlorite pump and the ratio controller were
dependent upon the water surface level in the clarifier. At a
clarifier water level of 85 percent of full (4.06 meters or
160 in.) the sodium hypochlorite pump was triggered and began to
prime. At 87 percent of full (4.22 meters or 166 in.) the pre-
set ratio controller was activated. The ratio controller could
be preset between 0.3 to 3.0 which, in conjunction with the
clarifier water level, regulated a 4 to 20 ma B.C. output signal.
Given any preset ratio value, the output signal increased
lineally with increasing clarifier water levels above 4.22 meters
(166 in.). The 4 to 20 ma B.C. output signal was converted into
an 0.21 to 1.06 kilogram per square centimeter (3 to 15 psi) air
signal by an electric pneumatic transducer . The air signal
adjusted the diaphram controlled pinch valve located directly
45
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after the 190 liter per minute (50 GPM) pump, which regulated
the flow of hypochlorite solution to the clarifier.
The chlorine residual of the stormwater was monitored at the
tank influent, within the tank, and the tank overflow by
analyzing an aliquot obtained by the automatic samplers. The
chlorine residual was measured colorimetrically by two Each
CR2 automatic chlorine residual analyzers. The data from the
analyzers was relayed to the control panel recording charts. If
the detected chlorine residual was improper, the ratio controller
could be adjusted accordingly. The ratio controller was housed
in the analog control center cabinet. (Refer to Figure C-l).
Samplers
Three automatic samplers were incorporated into the project to
analyze the combined sanitary and stormwater flow. The samplers
could also be operated manually. The inputs for the samplers
were installed at four locations: adjacent to the outlet of
the 1.22 meter (48 in.) influent pipe, above the tube settlers
prior to flow over the weir, within the 1.52 meter (60 in.)
overflow pipe, and in the retention tank observation manhole #1.
Sampler #1, which collected from the influent flow, activated
when the clarifier water level reached 87 percent of full (4.22
meters or 166 in.). The sampler turned off when the water level
dropped below 4.22 meters (166 in.). Sampler #2 collected
samples from both the flow above the tube settlers and from
observation manhole #1. Within the control building, on the
north wall, were two gate valves which had to be manually
regulated to obtain the desired sampling location. The sampler
automatically started when the flow exceeded 4.22 meters (166
in.) in the clarifier and stopped when the water level in man-
hole #1 dropped below 7.6 centimeters (3 in.) in depth. Sampler
#3, which collected from the 1.52 meter (60 in.) overflow pipe,
activated when the depth of flow in the 1.52 meter (60 in.) pipe
reached 7.6 centimeter (3 in.) and turned off when the depth of
flow dropped below 7.6 centimeter (3 in.).
When activated the samplers (Rohrer Model 2) ran continuously.
An isometric representation of the automatic sampler is shown in
Figure 20. Cam timers were incorporated into each sampler and
were adjusted to discharge one 1.9 liter (1/2 gal.) sample every
5 minutes. A stepping motor rotated the funnel feed system to
another sample bottle after each 5 minute interval. The auto-
matic samplers had a capacity of 24 samples. After filling all
24 bottles, the sampler automatically stopped. If additional
samples were required, the bottles were changed and the sampler
reactivated. A small composite sample was also taken every
interval and stored in an 18.9 liter (5 gal.) capacity jug. All
additional flow from the samplers was drained back into the
clarifier.
47
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TANK LEVEL INDICATORS
The water surface elevation in the media storage area, retention
tank, was monitored by three differential pressure diaphrams,
one in each of the three observation manholes. The pressure
diaphrams were secured to the side of the manhole approximately
7.6 centimeters (3 in.) from the bottom liner material.
When the water level in the retention tank exceeded the elevation
of the bottom of the diaphram the static water pressure signal
was transmitted from the diaphram to a differential pressure
transducer. The transducer output a 4 to 20 ma B.C. signal which
initiated a chart recorder pen response.
Each of the three pressure diaphrams had a separate chart
recording. The retention tank water level chart recorders
ran continuously.
GROUND WATER MONITOR
On the east side of, and adjacent to, the retention tank was a
purge air bubbler device installed in a well casing to monitor ,
the ground water level. Similar to the purge air bubbler in
the clarifier, the pressure signal was converted to an electrical
signal which was transmitted to the control center recorder.
The bubbler measured the ground water level from an elevation
0.61 meters (2 ft.) below the bottom of the retention tank to
an elevation equal to that of the exposed media. The continuous
chart recorder measured the 0 to 5.08 meter (200 in.) range on
a 0 to 100 percent full scale readout. The ground water meter
was installed to check the condition of the retention tank media.
If a rupture in the liner material would occur during filling,
a sharp rise of the ground water level would occur.
RAIN GAUGE
Due to isolated thunderstorms and the variability of rainstorms
over large areas, it was deemed necessary to incorporate a rain
gauge at the testing facility. A Belfort Instruments (5915
series) recording rain gauge was installed within the control
building. Precipitation was collected from a funnel on the roof
and transferred to a galvanized bucket mounted on a weighing
mechanism. The deflection of the weighing mechanism produced by
the weight of the precipitation was transferred through a gear
and lever mechanism to a low torque, 25,000 ohm precision
potentiometer.
The rain gauge mechanism had an accuracy to 0.13 centimeters
(0.05 in.) and the data was plotted on a continuous chart re-
corder which measured 0 to 0.25 meters (0 to 100%) full scale.
49
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SECTION VIII
TOP ACTIVITY
The Tallmadge Memorial Parkway Stormwater Retention Tank #1 is
a novel concept in underground storage and provides a top sur-
face usable for other purposes. Possible usages would include
parking areas, sporting facilities or playgrounds which could be
accommodated.
Future plans for the city property at the site area were for
recreation or park land along the Little Cuyahoga River Valley.
In order that the finished tank area may be compatible with its
location, the Akron Parks and Planning Departments were consulted
about the Project. No specific plans had been completed for the
immediate site area.
The neighborhood west of the site area is generally above average
in income levels, while the neighborhood to the east is below
average. To the north is additional city owned property and to
the south is a sparsely developed are in the valley.
Both neighborhoods, east and west would require a travel distance
of at least one-half mile to reach the site. The Tallmadge
Memorial Parkway is a busy thoroughfare which presently has no
sidewalks along the steep grades up both sides of the valley.
Therefore, it was felt that an adult type playfieId would be
most compatible with the conditions.
As in most cities today, Akron is deficient in recreation areas
and is in a program to improve this condition. Additional
baseball and Softball facilities are needed at present, which
would be compatible with the underground tank facilities.
50
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SECTION IX
CONSTRUCTION AND EVALUATION
Construction of the prototype facility was begun in July 1972 by
the Bay Construction Inc., of Sandusky, Ohio. Photographs of
the construction of the prototype facility are presented in
Figures 21 through 23. Figure 21a is a view looking north at the
installation of the asphalt side liner. In the foreground is
the overflow riser system. Figures 21b and 22a show the place-
ment of the P.V.C. bottom liner material. In the background of
Figure 21b is the clarifier's north wall with openings for the
flap gates. Figure 22b shows the backfilling of the storage
cell with media. A close-up of the AASHO #1 and #2 size aggre-
gate is in the foreground. The square perforated concrete
columns in photograph 22b, are the observation manhole casings.
Figure 23a is a view looking west at the corner of the control
building and the top 254 micron (10 mil) P.V.C. liner. Figure
23b looks east at the clarifier and exposed media surface. Note
the placement of the precast concrete cover tee sections.
At the bottom excavation grade for the retention tank, saturated
grey silty clay was encountered as indicated by the soil borings.
Four French drains were installed in the bottom of the tank
excavation to drain away ground water and dry the grey silty
clay material. The French drains partially aided in dewatering
the silty clay, however, the existing soil condition was not
suitable for the placement of asphalt directly on the soil. An
engineering and economic study was made, and a 762 micron
(30 mil) P.V.C. liner was substituted as the bottom material.
Excessive rain throughout October and November caused consider-
able delays in construction. These delays necessitated the
redesign of two system components. The approaching cold
weather made the asphalt top liner material impractical, there-
fore, a substitution was made to a 254 micron (10 mil) P.V.C.
liner. The overflow ditch, which was originally to be paved
with asphalt, was instead paved with reinforced concrete.
Delays in the shipment of vital equipment needed in the opera-
tion of the clarifier section postponed the completion date of
the facility. The Armco flap gates and sluice gates for the
clarifier were not received until the end of December 1972. In
addition, the 84 square meters (900 sq. ft.) of clarifier tube
51
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FIGURE 21a. INSTALLATION OF ASPHALT SIDE LINER
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FIGURE 21b. INSTALLATION OF BOTTOM LINER (WEST)
52
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FIGURE 22a. INSTALLATION OF BOTTOM LINER (SOUTH)
FIGURE 22b. BACKFILL WITH MEDIA
53
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FIGURE 23a. TOP LINER MATERIAL
FIGURE 23b. CLARIFIER AND EXPOSED MEDIA
54
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settlers, when delivered to the site, were inspected and found to
be unacceptable. Field repairs to the modules would have been
insufficient, therefore, these modules were not used. A new
supplier was chosen and their tube settlers were installed in
the clarifier.
A problem developed during construction with sewer gas backing
up through the 0.46 meter (18 in.) effluent pipe from the Little
Cuyahoga Interceptor to the clarifier. A one-way gas valve was
installed in the first manhole above the interceptor sewer which
eliminated the problem.
On January 1, 1974, the operational phase of "Demonstration of
Void Space Storage with Treatment and Flow Regulation" was
initiated. The two year operational period of the prototype
facility tested the applicability of the void space storage
"Geo-Cel" concept.
The existing combined sewer system for the Tallmadge Memorial
Parkway drainage area was designed to overflow into the Little
Cuyahoga River when the flow at the interceptor exceeded 278
I/sec (9.8 cfs). Based on the Rational Formula for flow compu-
tation, a rainfall with an intensity greater than or equal to
0.08 cm (0.033 in.) per 20 minute duration would be sufficient
to cause overflow to the river. Approximately one hundred and
fifty (150) precipitation events, exceeding the minimum intensity
promoting overflow, occurred during the two year operational
period. These precipitation occurrences, with related opera-
tional data, are listed in Appendix D, Table D-l. Of the 150
events that would have promoted overflow at the original inter-
ceptor device (9.8 cfs) ,_ twelve selected storms filled the
clarifier to the weir level. Automatic and grab sampling data
was obtained during these storms and is presented in Appendix D
Tables D-2 and D-3.
During the operational period, several unusually severe storms,
in addition to mechanical malfunctions, prevented acquisition of
a considerable amount of data. One of the first significant
storms occurred on April 1, 1974, when a seventy-five year
intensity downpour beset the retention tank. The recording
rain gauge, which collects rainfall through a funnel on the
control building's roof, indicated a rainfall of 5 cm (2 in.) in
a duration of 25 minutes. The deluge caused considerable
erosion of the steeply sloped (9%) drainage area and carried
heavy concentrations of inorganic solids into the system.
The flow in the original combined sewer was intercepted at the
diversion manhole and a majority of the storm flow was diverted
into the clarifier. The clarifier filled to capacity in 20
minutes at an average flow rate of 935 I/sec (33 cfs). The
clarifier filling rate (33 cfs) was determined through the
55
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integration of the clarifier water level surface with respect
to time. It was anticipated that the flow entering the clarifier
increased with time up to maximum flow rate of 6230 I/sec (220
cfs) as calculated by a combination of the Rational Formula and
Figure 12.
Due to the high flow rates entering the system, the large con-
centration of solids produced by the eroded slopes was not
reduced by the tube settlers and was partially deposited on the
surface of the exposed media. When solids are trapped on the
exposed media surface the infiltration rate into the media can
be reduced. (Calculations are presented in Appendix A.) The
stormwater that could not enter the void space storage cell
moved several of the clarifier cover sections (a few inches) and
flowed overland to Memorial Parkway. The precast concrete cover
sections, which were not anchored down, were designed as an
emergency overflow to provide water pressure relief during
extreme flow conditions.
The storm flow notification system malfunctioned, therefore,
personnel were not at the site in time to manipulate the gate
valves, which would have alleviated the extreme buildup_of
pressure in the clarifier. The notification system, which
consisted of a copper pronged probe suspended inside the
clarifier at a specified elevation, sent a signal to the Akron
Sewer Maintenance Building when the clarifier water level
reached the probe elevation. The signal illuminated a red light
on their control panel, and the dispatcher, upon recognition of
the illuminated light, notified personnel from Karl R. Rohrer
Associates, Inc. When notified, between 20 to 30 minutes travel
time was required for personnel to arrive at the site. For high
intensity, short duration storms, the notification system was not
adequate since the time of concentration (that time required for
water from the most remote point in the drainage area to reach
the facility) for the drainage area was only approximately 20
minutes.
Full operation of the prototype facility was not resumed until
October 1974, when repairs and re-evaluation studies were
completed. After removing the cover tee sections, a layer of
sand was observed ranging from 15 cm (6 in.) in depth at the
point of flow over the weir, to 2.5 cm (1 in.) at the north edge
of the exposed media (8.25 ft. width), and extending for the
entire exposed media length (200 ft.). The surface silt, sand,
and grit deposits were removed from the exposed media surface,
two masonry seals in the clarifier entrance chamber were re-
placed, the clarifier cover sections were reset, and a manually
preset throttle orifice in the diversion manhole was designed
and installed. Particular attention was given to the design_of
the diversion manhole throttle orifice which limited the maximum
flow rate allowed to enter the clarifier. The orifice opening
56
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was adjusted to allow only that flow rate into the system which
could be drained out through the overflow and effluent gates.
All additional flow was diverted back into the original sewer.
Reassessment of the physical limitations of the system, combined
with the critical drainage area conditions, dictated a conser-
vative approach in the testing of the retention tank. To pre-
vent any excessive storm flow from entering and possibly re-
stricting the infiltration rate into the exposed media, the
overflow and effluent slide gates were adjusted to allow all dry
weather and stormwater flow to pass through the clarifier with-
out causing flow over the weir until an observer arrived on the
site. The observer, upon notification or anticipation of a
precipitation event, would travel to the site and make the
appropriate gate adjustments to allow storm flow to enter the
media. This testing procedure was deemed necessary to prevent
events similar to that of the April 1, 1974 storm from
occurring. The detrimental effects produced by sediment re-
ducing the infiltration rate into the exposed media surface
illustrates the necessity of a fail-safe storage cell feed
system in future installations. This could possibly be
accomplished with one or more of the following: an automatic
overflow system which would prevent excessive pressure buildup
given a reduction in the infiltration rate, a well feed system
which would be partially self-cleaning during draining of the
cell, or a media with greater void space and less surface to
surface contact points (possibly an artificial media) which
trap sediment and reduce infiltration rates.
A general investigation of the prototype facility indicates
that with these and other minor design changes, the void space
storage concept could be a practical means for the prevention of
untreated combined, or storm, sewer overflows to receiving
water bodies.
It is also envisioned that future installations would be de-
signed to operate automatically (unattended) and without the
sophisticated instrumentation which was incorporated in the
prototype facility.
No noticeable offensive odors or flammable gases (detected by
the combustible gas monitors) were generated in the storage area
during the two year operational period. A combination of
factors were responsible for this: the storm flow from this
steeply sloped combined sewer system consisted mainly of
suspended inorganic solids rather than putrescible organic
materials, chlorination of the flow entering the media prevented
the wastewater from going septic, and the detention times of the
stored stormwater were relatively short. Slime and algal growth
within the media were not visually detected, and there were no
rodent or insect infestations.
57
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The four clarifier flap gates, which allowed the stored storm-
water to flush by gravity back into the clarifier, did_not
completely seal and permitted minor seepage (1 cfs maximum)
to circumvent the tube settlers and enter the void space storage
tank during filling. The effluent and overflow slide gates were
also observed not to seal as tightly as expected, allowing minor
quantities of flow to escape the clarifier during filling events.
The underground P.V.C. and asphalt lined storage tank "Geo-Cel"
performed satisfactorily. No membrane ruptures or surface in-
filtrations were detected. No subsidence of the ground surface
level above the tank, which would indicate a rupture of the top
P.V.C. liner, was observed. Also, no unusual increased ground-
water " levels occurred on the groundwater chart recorder during
filling of the retention tank, which may have indicated a side
or bottom membrane rupture.
CLARIFIER WATER LEVEL INDICATOR
nucleus of the testing and evaluation of the facility was the
The
single purge air
bubbler which was located adjacent to the 0.46
meter (18 in.) effluent gate. Measurement of the pneumatic
pressure in the bubbler was analogous to the water level in the
clarifier and was converted by an electronic differential
pressure transmitter to give a specific chart recorder pen
response. Activation of the annunciator alarm lights, automatic
samplers, chlorine pump
and colorimetric chlorine analyzers
were dependent upon the electronic relays of the single purge
air bubbler. In addition, approximate influent and effluent
flow ratew were calculated through the integration of the
clarifier water level with respect to time and gate openings
(Figures 15 and 16). These calculations gave only the average
flow rate for a specific time interval, based on the recorded
data of the single purge air bubbler. Malfunctions of the air
compressor, used to supply air to the bubbler mechanism,
electronic drift in the switch relays, and loss of inking in the
chart recorders caused minor loss of operational data.
The evaluation of the automatic samplers, tube settlers, and
chlorination system will be discussed individually, although
they are interrelated and dependent upon the purge air bubbler
for activation.
AUTOMATIC SAMPLERS
The feasibility evaluations of two system components were
primarily dependent upon the data obtained by the three automatic
sampling devices which were incorporated into the system. Cor-
relation and comparison of the sampling data was to be used for
a general evaluation of the tube settlers and the media void
space storage concept. The effectiveness of the tube settlers
58
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was to be predicted by the differences in solids between the
samples taken with the influent sampler and the weir sampler.
The weir sampler data was to be used to estimate the volume of
solids carried into the retention media, while the observation
manhole sampler data, combined with that obtained with the weir
sampler, was to be used to analyze the leaching of solids
through the media.
Although a number of grab samples were taken during dry-weather
flows and precipitation events, the bulk of the sampling data
was from the automatic samplers. The collection pipes for the
three automatic samplers were installed at four locations:
adjacent to the outlet of 1.22 meter (48 in.) influent pipe,
above the tube settlers prior to flow over the clarifier weir,
in the retention tank observation manhole #1, and within the
1.52 meter (60 in.) overflow pipe. A detailed description of
the sampler operation is presented in Section VII of this
report.
The twelve precipitation events which activated the influent
and weir samplers were analyzed by some or all of the following
tests: total solids, suspended solids, volatile solids,
settleable solids, BOD, COD, pH, ammonia, nitrite, nitrate, and
phosphorous. The results from these tests are presented in
Appendix D, Tables D-2 and D-3.
Correlation of the sampling data was difficult to access since
the influent sampler activated only after the clarifier had
filled with stormwater to the point of flow over the wier and
into the exposed media surface. The influent sampler did not
collect the anticipated first flush of suspended solids or BOD.
The first flush concept associated with combined sewers is
generally characterized as the large concentrations of SS and
BOD which are collected at the inception of a storm, due to the
settleable material which had been deposited within the sewer
during the dry-weather period prior to the storm. Due to the
activation relay of the influent sampler, any first flush of
solids or BOD had already passed the sampler's collection
point and was contained within the clarifier. It was
impractical, however, to change the influent sampler's activa-
tion relay point since an evaluation of the first flush concept
at the clarifier entrance would have required the sampler to run
continuously. Analysis of the weir sampler data does indicate
high initial concentrations of suspended solids, however, it is
predicted that this was due to that sediment which was carried
into the inlet basins as runoff from the steep drainage area
(Refer to Table D-2 in Appendix D). From the sampling data
obtained, the concentration of suspended solids ranged from a
high of 9,800 mg/1, to a low of 13 mg/1, and with an average of
510 mg/1. Decreasing concentrations of suspended solids were
evident with increasing durations of time from the initiation of
59
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a storm. The weir sampler data does not indicate a severe first
flush of BOD which would be produced by the buildup of organic
solids within the sewer during dry-weather flows. Since the
Tallmadge Memorial Parkway drainage area is steeply sloped (9%),
the organic material does not settle out within the sewers
during dry-weather flows, therefore the first flush concept for
this particular drainage area was not evident and thus may not
be representative of a typical combined sewer system.
The automatic tank sampler activated on only four precipitation
events and the overflow sampler activated only once., Some of
the sampling data was lost due to compressor and sampler
malfunctions.
TUBE SETTLERS
An in-depth evaluation of the tube settler efficiency is not
possible based on the data obtained by the automatic samplers.
The direct reduction of suspended solids by the tube settlers
cannot be calculated because of the influent sampler's location
and activation relay point within the purge air bubbler (level
indicator). Upon initiation of a storm a high initial concen-
tration of suspended solids was carried into the system from
the streets and catch basins. (This is not assumed to be a first
flush concept.) The concentration of solids decreased with
increasing time intervals from the start of the storm. Since the
influent and weir samplers did not activate until the water level
in the clarifier reached the level of the weir, the high initial
concentration of suspended solids was missed by the influent
sampler but collected by the weir sampler.
The manufacturer1s operating instructions manual commented that
the performance of the tube settlers was a function of many
parameters and that the installation of the modules would not
automatically improve the performance of the settling basin.
Two of the performance parameters were the rate of flow through
the modules and the variability of the flow rate. The manu-
facturer also commented that the tube settlers are most
efficient with a constant flow, rate not exceeding 4 GPM per
square foot of surface area (8 cfs for the Tallmadge Memorial
Parkway facility).
The Tallmadge Memorial Parkway retention tank system, however,
had varying rates of flow, dependent upon the storm intensity,
and generally had flow rates in excess of 223 I/sec (8 cfs).
When the actual flow rate was greater than the recommended
design flow rate, the efficiency of the tube settlers was not
sufficient to prevent the carryover of suspended solids onto
the exposed media surface. Three precipitation events which
had high flow rates and significantly large concentrations of
suspended solids, resulted in a reduction of the infiltration
rate into the media. (See recommendations for design
60
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modifications to alleviate this condition.) This possibility of
a reduction of the media infiltration rate, combined with the
rapid runoff from the drainage area and the time involved for
personnel to arrive at the site, necessitated the conservative
testing procedure which was adopted after the April 1, 1974
storm.
Leaves and other floating debris were not a problem as speculated
During the initial stages of the clarifier filling process, the
floating debris which entered the clarifier was transported by
the flow toward the effluent end. When the clarifier became 50
percent full, the debris was trapped in a chamber isolated from
the tube settlers by the clarifier's transverse structural
supports. During the two year operation period, the tube
settlers never clogged.
CHLORINATION SYSTEM
Fifteen percent sodium hypochlorite solution was automatically
added to the combined sewer flow when the water exceeded the
level of the clarifier weir and entered into the tank media. A
total of approximately 8350 liters (2200 gal.) of solution was
used during the operational period of the prototype facility.
The sodium hypochlorite solution was added to retard the BOD
requirement of the water and prevent the accumulation of odors
and gases during the detention time. During the two-year
evaluation period, no significant odors or gases developed.
Sodium hypochlorite was not added to those flows which did not
exceed the level of the clarifier weir. Many of the precipita-
tion events did not promote flow over the clarifier weir and
were drained, after a short detention period, to the Akron
sewage treatment plant.
The evaluation of the chlorination system is difficult to
access because of the inconclusive sampling and the poor
results generated from the colorimetric chlorine analyzers. A
small quantity of stormwater from each sample of the weir, tank,
and overflow samplers was colorimetrically analyzed for chlorine.
However, due to the high turbidity of .the stormwater the line
feeding the water to the analyzer often clogged and the chlorine
readouts which were obtained were inaccurate and inconclusive.
Filters were installed in the line prior to the analyzer;
however, they did not remedy the situation.
The samples taken from the postchlorination sampling location,
above the tube settlers, had average BOD concentrations slightly
higher than the prechlorination influent values. Although
opposite of that originally anticipated because of the chlorina-
tion, these results are understandable. Both the samplers and
the chlorinator were activated by the electronic relays in the
purge air bubbler (level indicator) only when the water level in
61
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the clarifier reached the level of the weir. Therefore, the
initial samples collected by the weir sampler were unchlorinated
and had slightly higher concentrations of BOD as compared to
the influent samples. This was due to any organic material which
may have entered into the system at the initiation of a storm as
runoff from the drainage area. On seven of the ten events for
which BOD data was obtained, the BOD levels of the weir samples
were greater than those of the influent samples. Disregarding
the data for the April 1, 1974 storm, the average BOD levels
obtained by the influent and weir samplers were 33.8 mg/1 and
36.5 mg/1 respectively. The storm of April 1, 1974 was heavily
chlorinated with BOD levels of 119.3 mg/1 and 8.2 mg/1 for the
influent and weir samplers respectively. On this;occasion,
activation of the samplers was delayed due to a malfunction,
therefore, when the weir sampler activated it was collecting
chlorinated stormwater. Between the weir and tank seimplers
there was an average BOD reduction of approximately 30 percent.
CONTAINED SOLIDS WITHIN MEDIA STORAGE AREA
One of the primary objectives of the "Demonstration of Void
Space Storage with Treatment and Flow Regulation" was the evalu-
ation of the applicability of inert media, void space storage,
"Geo-Cel", for combined sanitary and stormwater flows;. The
feasibility of the concept was dependent upon the loss of
storage volume due to the entrapment of solids within the
retention area.
The solids which are encountered in combined sewer systems are
classified either as inorganic (sand and silt) or organic
matter. The percentages of each are highly variable and are
dependent upon the site characteristics, intensity and duration
of rainfall, time of year, time interval between storm events,
and the time the sample was taken with respect to the initiation
of the storm. Dry-weather flows consist of sanitary wastes,
the solids of which are primarily organic material. During a
precipitation event, however, the storm flow generally reduces
the average percentage of organic material and increeises the
average percentage of inorganic material.
Within the two year operation and evaluation period, twelve
selected storm events caused flow to pass over the clarifier
weir and into the media storage area. Sampling data was
obtained for eleven of the twelve events.
Primarily, equipment malfunctions prevented additioneil sampling
data from being obtained. Based on the sampling data for the
eleven storm events, general trends were analyzed to predict the
volume of solids which would enter into the media void space for
the Tallmadge Memorial Parkway tank. The volume of solids re-
tained in the void space is based on the difference between the
62
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solids' mass entering the media during filling of the tank and
the solids' mass existing during draining of the tank. With the
sampling data that was obtained during the operational period,
it was not possible to determine the concentration of suspended
solids removed with the effluent from the media.
Table 4 lists all the available significant data for the
determination of the volume of solids entering into the media
storage area. The values given are averages for each specific
storm.
Total solids is defined as the sum of the dissolved and un-
dissolved constituents in the wastewater. Suspended solids
are those that float on the surface of, or are in suspension in
wastewater, and which are largely removable by laboratory
filtering. Volatile solids are those which are lost on ignition
of the dry solids at 600°C.
TABLE 4. SOLIDS CONTAINED WITHIN MEDIA
Date
Weir Sample Averages
# Of Solids mg/1
Tank Manhole Sample Averages
# OF Solids mg/1
Samples Total SS Volatile Samples Total SS Volatile
4-01-74
11-04-74
11-20-74
1-08-75
2-23-75
5-21-75
5-31-75
6-22-75
9-05-75
9-18-75
10-17-75
17
3
4
12
12
5
12
5
2
3
7
16256
611
378
314
332
908
1066
1185
551
185
233
2469
259
95
194
172
842
477
839
199
17
42
103
40*
15*
45
20
176
101
105
31*
3*
6*
9
10
12
5
3
8
236
223
686
292
168
208
71
,53
173
144
46
30
27
7
56
60
14*
9*
*based on an average between
volatile and suspended
Generally, the organic solids can be considered as volatile
solids. The bulk of the volume associated with organic matter
consists of water which naturally comprises about 95 percent of
its weight. The values (mg/1) given in Table 4 refer to the dry
solids weight. The reduction of retention tank volume, however,
was determined by the solids' wet volume. Based on the average
concentration of volatile solids in the flow over the weir, an
associated wet volume of 1,110 liters of sediment was obtained
per million liters of wastewater entering the media. Calcula-
tions are presented in Appendix B.
63
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The volume associated with inorganic matter, however, is com-
prised primarily of solids. The concentration of the inorganic
solids (sand and silt) was assumed to be the concentration of
the suspended solids minus that of the volatile solids. Based
on the average concentration of inorganic solids in the flow
over the weir, an associated wet volume of 283 liters of sediment
was obtained per million liters of wastewater entering the media.
Calculations are also presented in Appendix B.
Comparison of the dissolved solids (total solids minus suspended
solids) of the weir samples with those of the manhole; samples
revealed that only a minor reduction of concentration occurs.
Therefore, it was assumed that the dissolved solids will pass
through the retention tank with only minor volumetric:
accumulation within the media.
The total decrease of void space within the media wasi estimated
by the summation of the organic and inorganic volume reductions.
Representing the data obtained during the operational period, a
total volume reduction of 1393 liters of sediment can. be
expected per million liters of wastewater passed through the
media. This approximation assumes that all the suspended solids
which entered the media are trapped within the void space. In
reality, however, many of the solids which are contained in the
media will exit through the clarifier flap gates upon draining
of the retention tank. It was not possible to analyze the con-
centrations of solids removed from the tank media, and any solids
which are present in the media effluent will increase the
remaining void space volume. Based on the calculated volume re-
duction due to solids entering the media, and an average of ten
complete fillings per year, over 65 percent of the void space
volume would remain after the system life expectancy of 25 years.
(The P.V.C. liner has a designed life expectancy of 25 years.)
The leaching of the total solids through the media void space
was analyzed by comparing the weir sampler data to that of the
tank manhole sampler. Manhole #1, where the sample collection
pipe was located, was approximately 30 feet from the exposed
media surface. Both the weir samples and the manhole samples
are collected by one sampler, sampler #2. Manipulation of the
valves for the sampler collection pipes determined which
sampling location was being used. During general operation,
sampler #2 collected stormwater from the flow over the weir
while the media retention tank "Geo-Cel" was being filled. After
subsidence of the storm, when flow was no longer passing over the
weir, the valves were adjusted to collect samples from manhole
$1 of the stored wastewater during drainage of the tank.
Although a substantial time lag between the collection of
samples from the two locations was apparent, the data was
reasonable in approximating the initial leaching of solids
64
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through the media void space. Between the two sampling locations
there was an 82 percent average reduction of the suspended solids
(refer to Table D-2). The reduction for any specific event may
vary from the average and it is anticipated that with continued
use of the facility, the leeching effect would become less
pronounced due to the filling of the media with sediment.
The reduction of suspended solids, between the samples of the
weir and tank manhole #1, was comprised of a 51 percent decrease
of the volatile solids and an 86 percent decrease of the in-
organic solids. This is a logical distribution since the
volatile matter, which is 95 percent water, has a low specific
gravity causing it to remain in suspension for longer periods of
time as compared to the inorganic matter , which is nearly 100
percent solids and has a higher specific gravity.
Due to the 82 percent decrease in the suspended solids from the
weir to manhole #1, it can be predicted that a majority of the
solids passing over the weir are trapped by the media near the
north wall of the clarifier. A parabolically decreasing con-
centration of solids retained in the media would be expected
with increasing distances from the clarifier. The concentration
of solids nearest the clarifier, however, may be reduced during
draining of the retention tank since some of the suspended matter
will exit the media with the wastewater effluent.
COSTS
The total cost for the experimental demonstration project was
$750,000. Of this amount, approximately $471,000 was used for
construction of the prototype facility. An itemized breakdown
of the construction costs, based on 1972 prices, is given in
Table 5.
TABLE 5.
CONSTRUCTION COSTS
Description
General
Site preparation
Excavation, backfill
and embankments
Driveway
Rip rap
Effluent pipe bedding
Clarifier
Bottom PVC liner
Asphalt side liner
Top PVC liner
Est. Quant.
LS
9300 CY
520 SY
200 SY
325 CY
LS
2894 SY
1797 SY
4144 SY
Unit Price
3,000.00
5.00
2.50
10.00
13.00
110,937.50
5.47
3.
.00
2.75
Total
3,000.00
46,500.00
1,300.00
2,000.00
4,225.00
110,937.50
15,830.00
5,391.00
11,396.00
(continued)
65
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TABLE 5.
(continued)
Description Est. Quant.
Geo-Cel media 11,300 CY
Overflow ditch 550 LF
Control building LS
Influent pipe 410 LF
Overflow pipe LS
Effluent pipe 465 LF
Diversion chamber LS
Manholes 2 Ea
Instrumentation LS
Misc. tools LS
Automatic samplers 3 Ea
Project signs 2 Ea
Mechanical
Heating & ventilating LS
Plumbing LS
Sodium Hypochlorite sys. LS
Compressed air sys. LS
Sampler piping LS
Plumbing LS
Electrical
Power S lighting LS
Instrumentation LS
Miscellaneous LS
Unit Price
7.25
11.88
6,535.00
72.00
12,500.00
21.50
16,000.00
900.00
2,750.00
1,200.00
5,225.00
250.00
800.00
3,000.00
6,000.00
1,000.00'
1,624.00
700.00
5,750.00
34,300.00
32,710.00
TOTAL
Total
81,925.00
6,534.00
6,535.00
29,520.00
12,500.00
9,997.50
16,000.00
1,800.00
2,750.00
1,200.00
15,675.00
500.00
800.00
3,000.00
6,000.00
1,000.00
1,624.00
700.00
5,750.00
34,300.00
32,710.00
471,400.00
Much of the cost which was required in the construction and
evaluation of the "Geo-Cel" prototype facility would not be
necessary for the installation of a second retention tank. Many
of the system components could be simplified thus promoting a
reduction of the construction and operating costs. The clarifier
could be reduced in size and the tube settlers could be elimi-
nated. The overflow and void space storage feed systems could
be redesigned to provide automatic system operation during a
storm. Except where restricted by soil conditions, asphalt
could be used to completely line the tank. Where site condi-
tions allow, reduced lengths of the influent and effluent pipes
and the overflow ditch would be desirable. Other cost reduc-
tions could be achieved in future non-research installations by
reducing or eliminating the instrumentation and recording
equipment. The three observation manholes, control building,
and all associated heating, wiring, and plumbing could be
eliminated.
The actual cost of future retention tank systems would depend
primarily on total volumetric storage capability, type of void
space media used, application, and design requirements.
66
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Depending upon the desired use of the facility for combined
sewer overflow storage or other uses such as consumer fuels
storage, flood control, or industrial chemical and water storage,
the design restrictions, inert material used, and resultant
costs would vary. Based on the 1972 costs for the Tallmadge
Memorial Parkway retention tank, and a combined sewer overflow
storage capacity of 3.8 million liters (1 MG.)/ the total cost
of the facility as built was $0.124 per liter of storage. By
limiting instrumentation, eliminating the tube settling modules,
and redesigning the clarifier section a cost of $0.079 to
$0.092 per liter of storage capacity could be expected. Land
costs are not included in the figures given. Where any
appreciable amount of land must be purchased, the cost per unit
of storage would reflect this cost.
Table 6 shows a comparison of the cost of storage capacity for
the void space storage concept as compared to underwater storage
tanks, underground concrete tanks, and lagoons. The projected
cost does not include preliminary studies for each site, extra
costs encountered due to specific site conditions, land
acquisition, acquisition of all permits, and major alterations
to existing structures. Operational costs are also not
included.
TABLE 6 CONSTRUCTION COST COMPARISON
Storage Method
Void space storage
(Geo-Cel)
Underwater tank
Reinforced concrete
tank
Lagoons
Storage Capacity
liters (MG)
3,800,000 (1.0)
3,800,000 (1.0)
3,800,000 (1.0)
3,800,000 (1.0)
Cost
7.9-9.2 30-35
12.7 (48)
12.2 (47)
3.5
(13)
Estimated minimum operational costs for the Akron, Ohio prototype
facility as constructed were about $3,000 per year. The power
requirements for the facility were minimal since filling and
draining of the retention tank was not by electrical pumps but
by gravity. With minor design changes and minimal funds, the
facility could be operated automatically thus drastically re-
ducing the projected yearly operational costs.
67
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AESTHETICS
The underground temporary void space storage concept,, "Geo-Cel",
with its unique design capabilities incorporating ducil land
usage, provides a storage facility which is compatible with the
surrounding area. This versatility permits adaptation of surfcice
usage to such facilities as recreation, parking, open-air storage,
scenic reservation, farming or grazing land, and even the
possibility of minor structures.
The nature of the "Geo-Cel" construction offers a safety advan-
tage as a built-in factor. There are no vaults; therefore, no
possibility that a gaping surface hole could suddenly form.
This is of particular concern where surface dual-usage is a
playground, and consideration for the safety of small children
paramount.
The Tallmadge Memorial Parkway facility was originally designed
to incorporate top surface usage as an adult recreational area,,
Limited available city funds, however, prevented the grounds
from being developed and the area has become an informal trail
bike course.
68
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SECTION X
BIBLIOGRAPHY
American Public Works Association, Problems of Combined Sewer
Facilities, U.S. EPA Report No. 11020 12/67,
NTIS-PB 214 469, December 1967.
Anderson, R.J.; Weibel, S.R.; and Woodward, R.L. "Urban Land
Runoff As A Factor In Stream Pollution." Water Pollution
Control Federation Journal, Volume 36, No. 7.July,1964.
Bauer, William; Dalton; Frank; and Koelzer, Victor.
The Chicagoland Deep Tunnel Project. The Metropolitan
Sanitary District of Greater Chicago. September, 1968.
Benzie, W.J. and Courchaine, R.J. "Discharges From Separate
Storm Sewers and Combined Sewers." Water Pollution Control
Federation Journal, Volume 38, No. 3 March, 1966.
Cedergen, H.R. Seepage, Drainage and Flow Nets. John Wiley
and Sons, Inc. New York 1967.
Envirogenics Co., Division of Aerojet General Corporation,
Urban Storm Runoff and Combined Sewer Overflow Pollution,
Sacramento, CA; U.S. EPA Report No. 11024 FKM 12/71,
NTIS-PB 208 989, December 1971.
Fair, G.M; Geyer J.C.; and Okum, D.A. Water and Wastewater
Engineering. John Wiley and Sons Inc. New York 1968
Fair, G.M. and Imhoff, K. Sewage Treatment 2nd ed., John
Wiley and Sons, Inc. New York 1966.
Field, R., Tafuri, A.N., and Masters H.E., Urban Runoff Pollution
Control Program Overview FY '76, U.S. EPA Report No.
EPA-600/2-76-095, Edison, N.J., February 1976.
Hittman Associates, Inc. The Beneficial Use of Storm Water
Final Report. U.S. EPA Report No.11030 DNK 08/68
NTIS-PB 195 160, August 1968. '
King, H.W.; Wisler, C.O.; and Woodburn, J.G. Hydraulics
5th ed. John Wiley and Sons, Inc. New York 1956
69
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Klashman, Lester M. and Romer, Harold. U.S. Department of
Health, Education, and Welfare, Public Heather Service.
"How Combined Sewers Affect Water Pollution, Public
Works Magazine. March and April, 1963.
Miller, E.M. and Weaver, C.R. Monthly and Annual Prescipitation
Probabilities for Selected Locations in Ohio, Bull. No. 1012
Ohio Agricultural Research and Development Center, Wooster,
Ohio, 1969.
Miller, E.M., and Weaver, C.R., Mean Recurrence Tables of Daily
Precipitation Amounts for Selected Locations in Ohio,
Bull. No. 1034, Ohio Agricultural Research and Development
Center, Wooster, Ohio, 1970.
Morris, H.M. and Wiggert, J.M. Applied Hydraulics in Engineering
2nd ed. The Ronald Press Company. New York 1972.
Ohio Department of Health, Division of Engineering. Summary
of Municipal Sewage Treatment Works In Ohio. '• January,
1968.
Peck, R.B. and Terzaghik. Soil Mechanics in Engineering
Practice 2nd ed. John Wiley and Sons Inc. New York
1967.
Rohrer Associates, Inc., Karl R., Underwater Storage of Combined
Sewer Overflows, U.S. EPA Report No. 11022 ECV 09/71,
NTIS-PB 208 346, September, 1971.
Standard Methods for the Examination of Water and Wastewater
13th edition^American Public Health Association,
New York, 1971.
U.S. Department of Health, Education, and Welfare, Public Health
Service. A Preliminary Appraisal - Pollutional Effects of
Stormwater and Overflow from Combined Sewer Systems. Public
Health Service Publication No. 1246. November, 1964.
U.S. Department of the Interior, Federal Water Pollution Control
Administration. Great Lakes Region. Lake Erie Report, A
Plan for Water Pollution Control. August, 1968,,
U.S. Department of the Interior, Federal Water Pollution Control
Administration. Water Pollution Aspects of Urban Runoff
Water Pollution Control Research Series No. WP--20-15
January, 1969.
70
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SECTION XI
PATENTS
The Underground Fluid Storage Tank patent was issued on
December 23, 1969, numbered U.S. Patent No. 3,485,049.
The Automatic Sampling Device patent was issued on June 28,
1971 as U.S. Patent No. 3,587,324.
71
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SECTION XII
APPENDIX A
HEAD LOSS THROUGH MEDIA OVERFLOW SYSTEM
When the void space retention area "Geo-Cel" is completely full
and stormwater is exiting the 1.22 meter (48 in.) overflow
risers, the overflow flow lines are assumed to resemble those
presented in Figure A-l. The accuracy of the calculations are
dependent upon the "in-situ" characteristics of the media and
the precision of the flow analysis. Since the media specifica-
tions are vague, an in depth flow analysis would be unwarranted.
The overflow system was divided into five approximate flow
channels (Figure A-l) and these channels evaluated for their
maximum potential flow rate.
The flow through a porous media can be determined by Darcy's
equation:
Q = kiA (A-l)
where Q is the flow rate through the media, k is the permeability
of the media, i is the'hydraulic gradient, and A is the cross-
sectional flow area.
The permeability of the porous media is a significant factor in
the determination of the rate of flow through the media. Per-
meability is highly variable and dependent upon many media
characteristics, however, as an approximation, Cedergren states
that permeability is a function of the "effective" diameter of
the pore spaces in the media. The "effective" pore diameter is:
deff = 1/5 (D1Q)
(A-2)
where D,Q is the stone diameter of which 10 percent is finer by
weight.
According to specifications, the bulk of the aggregate placed
within the retention tank is AASHO #1 or #2 size with 10 to 15 cm
(4 to 6 in.) of AASHO #46 size covering the exposed media surface.
The bulk of the media, therefore, has an "effective" pore
diameter of approximately 7.62 mm (0.3 in.). The cover stone
72
-------
max
FIGURE A-l.
OVERFLOW SYSTEM ANALYSIS
73
-------
has an "effective" pore diameter of approximately 1.91 mm
(0.075 in.). Cedergren also presented a chart, Figure A-2,
which correlates the "effective" diameter with the velocity
of flow given that the hydraulic gradient, i, equals 0.01.
From Figure A-2 we obtain:
vcover = 0.0027 m/sec (0.009 fps) for deff equal to
691 mm (0.075 in.)
and
Vbulk = °-0122 m/sec (0.04 fps) for deff equal to
7.62 mm (0.03 in.)
However, since the hydraulic gradient was 0.01, the per-
meabilities of the two aggregates are:
kcover =0-27 m/sec (0.90 fps)
and
kbulk = 1- 22 m/sec (4- °
(A-3)
(A~4)
The head loss through two permeabilities can be calculated on
the basis that the rate of flow which passes through the cover-
aggregate will also pass through the rest of the, media:
= Q2
(A'5
where the subscripts 1 and 2 refer to cover the bulk re-
spectively. Based on equation (A-l) and rearranging the
variables:
ko Ao ALn
The maximum allowable headwater is equal to the elevation _ of
the bottom of the cover tee's minus the elevation of the rim of
the 1.21 meter (48 inch) risers. Therefore:
Ahx = Ah2 = 0.96 m (3.15 ft) .................. - - -• (A-7)
The flow lengths, AL, can be determined by analyzing Figure A-l,
ALn is equal to the thickness of the cover material. AL2 is
equal to the average flow length for each of the flow channels
involved:
74
-------
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/ SOURX1E : CEOEC2<=iREKl
x tf^2.
5«IO-* 2.5
»«\o-* .0
25 2.
5 2?
55 Z5
,450
("O
1*10-^
EFFECTIVE
|K|O
-3
O.I
IO
IOOO
PIAMETER OF FLOW CHANNELS,
FIGURE A-2.
VELOCITY OF FLOW VS. EFFECTIVE DIAMETER
75
-------
* 0.15 m (0.5 ft)
AL2_i = 9
m
( 30 ft)
21 m ( 70 ft)
AL2_5 - 38 m (125 ft)
AL2_4 = 55 m (180 ft)
AL2-5 = 70 m (230 ft)
w/
14
22
28
28
28
(150
(240
(300
(300
(300
ft2)
ft2)
ft2)
ft2)
ft2)
Substitution into equation (A-6) gives:
Ah]_ = .022(A2/AL2) (0.06-Ah-j) ....... . . (A-8)
Trial and error solution of equation A-8 yields:
Ahl-l = -03 m (>1° ft)
Ahl-2 = -02 m (-07 ft)
i.hi_3 = .015m (.05 ft)
Ahi_4 = .01 m (.03 ft)
Ahl-5 = -01 m ('
ft)
Ah2_i
Ah2-2
Ah2_3
Ah2-4
Ah2-5
=
=
=
=
=
.93
.94
.945
.95
.95
m
m
m
m
m
(3.
(3.
(3.
(3.
(3.
05
08
10
12
12
ft)
ft)
ft)
ft)
ft)
Substitution back into equation A-l gives:
On = 1730 I/sec
Q2 = 1190 I/sec
Qo = 850 I/sec
Q4 = 590 I/sec
Qc = 450 I/sec
( 61 cfs)
( 42 cfs)
( 30 cfs.)
( 21 cfs)
( 16 cfs)
The total maximum overflow rate is equal to the sura of the
individual channel flows therefore at maximum allowable
headwater:
Qoverflow a 481° I/sec (170 cfs)
INFILTRATION RATE INTO EXPOSED MEDIA
When the void space retention area "Geo-Cel" is only partially
full the infiltration rate, or filling rate, is controlled by
the permeability of the exposed media. According to the
specifications the exposed media consists of AASHO #46 size
stone. The permeability of the stone is approximately 0.27
m/sec (0.90 fps). An infiltration rate, calculated by equation
A-l, of nearly 42,500 I/sec (1500 cfs) could be obtained without
any pooling of stormwater on the exposed media surface.
The media, however, can trap the suspended solids that are
carried over the clarifier weir. If a significant quantity of
solids would be retained on the exposed media surface, the
infiltration rate into the media would be reduced. On April 1,
1974 a severe storm, 75 year recurrence interval, deposited
fine sand on the exposed media surface. Assuming that a fine
silty-sand, with a permeability of 0.0001 cm/sec (3.3 x 10~b fps),
76
-------
was deposited at an average depth of 5 cm (2 in.)/ the infil-
tration rate into the media would be drastically reduced. Based
on a_maximum allowable headwater of 0.96m(3.15 ft.), the infil-
tration rate into the media is approximately 3 I/sec (0.1 cfs).
Since the allowable infiltration rate (0.1 cfs) was considerably
less than the influent flow rate, three cover sections were
lifted_slightly out of place by the forces developed within the
clarifier. The clarifier cover tees were designed to alleviate
the pressures developed during extreme flow conditions. The
tee sections were easily moved into place after the April 1st
storm repairs were completed.
77
-------
APPENDIX B
REDUCTION OF VOID SPACE VOLUME
Based on the weir sampling data obtained for eleven precipitation
events (Table 7), the reduction of void space volume can be
estimated assuming that the suspended solids which flow over the
clarifier weir are trapped within the media. The suspended
solids are composed of both organic and inorganic solids. The
average concentration of organic solids is assumed to equal the
average concentration of volatile solids. The average concen-
tration of inorganic solids is equal to the average of the
suspended minus the volatile solids.
Avg. organic concentration 59 mg/1
Avg. inorganic concentration 451 mg/1
Organic sludge is comprised primarily of water, 95 percent,
with a specific gravity approximately equal to 1.06. The volume
reduction due to organic solids is based on the wet weight,
therefore:
Organic Volume
Organic Volume
59 ppm x 8.34 Ib/gal x
(100/5)x[7.48 gal/cf/(1.06x62.4 Ib/cfI]
1110 liters wet organics per million
liters of stormwater
Inorganic material is comprised primarily of solids (estimated
at 75 percent) with a specific gravity approximately equal to
2.i25. The volume reduction due to 'inorganic solids is also
based on the wet weight, therefore*
Inorganic Volume
Inorganic Volume
451 ppm x 8.34 Ib/gal x
(100/75)x[7.48 gal/cf/(2.:125x62.4 Ib/cf) ]
283 liters wet inorganics per million
liters of stormwater
78
-------
APPENDIX
OPERATIONS MANUAL
An operations manual for the pilot facility in Akron, Ohio was
prepared and submitted to the City of Akron Sewer Maintenance
Division upon turnover of the facility at the completion of the
two year operational period. The operations manual provided a
detailed description of the system components and design and
their function in the operation of the facility. Some of the
major items included were:
1. Analysis of the drainage area and anticipated runoff,
2. Plow regulation and control devices,
a. Diversion manhole baffle wall and orifice
b. Effluent slide gate and theoretical flow rates
c. Overflow slide gate and theoretical flow rates
3. Detailed description of the control building instrumenta-
tion, their operation, maintenance, test checks, and
adjustments,
4. Facility storage operations,
a. Prior to a storm
b. During a storm
c. After a storm
Selected portions of items 3 and 4 of the operations manual are
presented to familiarize the reader with some of the precision
equipment which was incorporated in the prototype facility.
Annunciator Lights
The annunciator panel lights located at the top of the control
cabinet (Figure C-l) provide a visual alarm indication of sig-
nificant conditions. There are 7 messages. When activated the
appropriate panel light will blink until the acknowledge button
is pushed. The "ACK" button is on the right side adjacent to
the lights. If the condition is true, the appropriate light
will remain lit when acknowledged, if the condition is false
or has already passed, the light will go out.
Combustible Gas Alarm —
This light will activate if there is an accumulation of flammable
gases in the clarifier section. Sewage can potentially give off
methane. To date, over the two year operation period, there
have been no such accumulations. One of the monitor detection
79
-------
ANNUNCIATOR.
«.Eo-creu.
I-!—+.
FIGURE C-l. ANNUNCIATOR PANEL LIGHTS AND RECORDERS
80
-------
head devices is located under the control building and access is
via the external hatchway. If activated, the clarifier gas
monitor will trigger the annunciator panel light "Combustible
Gas Alarm" . A second detection head is located at the base of
the plywood instrument mounting board. This monitor covers the
region inside the control building. Should combustible gas be
detected in the control building a loud audible horn alarm will
sound and a red globe warning light, mounted outside the control
building over the entrance doorway, will activate. In the event
of a positive alarm condition personnel should notify their
supervisors, turn off unnecessary electrical devices to eliminate
sources of ignition, open all hatchways, and provide ventilation
for dilution of concentrations of hazardous gases.
Clarifier Over 20" —
This signal light provides the first indication that the water
level in the clarifier is rising, and is above the top of the
effluent slide gate.
Clarifier Over 160" Storm Flow —
This signal light indicates the level is almost to the point of
flow over the weir. The chlorine pump should automatically
energize at this time. The chlorine pump is located in a pump
pit at the influent end of the clarifier.
Flow Over Weir 166" —
This signal light indicates that the clarifier is full and
stormwater should flow over the weir elevation and begin to fill
the tank. The chlorine ratio controller located on the lower
right side of the control cabinet should activate at this time
indicated by deflection of the green needle pointer in the ratio
controller. This annunciator light (and ratio controller) is
activated by a relay from the air pressure bubbler located
beneath the control building hatchway. The air bubbler gives a
pressure reading produced by the clarifier water level.
Geo-Cel Overflow --
This device operates via a pressure diaphram located in the
overflow pipe. This signal light is activated when the level
of flow in the pipe exceeds 7.6 centimeters (3 in.) which in-
dicates that either the tank has reached capacity, or the 1.52
meter (60 in.) gate is open to bypass.
Clarifier High Level 180" —
This signal light indicates that the freeboard above the weir is
being exceeded. Flow over the weir is at 4.22 meters (166 in.),
at 4.78 meters (188 in.) flow will exceed the clarifier tee
sections. The slide gates should be adjusted to prevent a high
level overflow condition.
81
-------
Geo-Cel Filling —
This signal light activates when the water level in the storage
tank exceeds 7.6 centimeters (3 in.) in depth. The sensor,
located in depth manhole #1 nearest the control building, cannot
respond to water levels less than 7.6 centimeters. Geo-Cel
filling will occur when there is flow over the clarifier weir or
infiltration through the flap gates.
Monitoring Devices
Also located on the annunciator panel are a number.of items
(ten chart recorders, one chlorine ratio controller, and two
combustible gas monitors) which monitor and record the flow
through the prototype facility.
Function #la: Rain Gauge —
A Belfort rainfall gauge is located in the control building
behind the annunciator panel. The collection funnel is located
on the roof with a rubber hose transferring the rainfall. The
gauge was calibrated to a 25.4 centimeter (10 in.) full scale to
provide a direct chart scale reading. A set of weights is
provided to check the device. The chart is changed at the end
of each month and the collection bucket emptied. The rain chart
records in red ink. A potentiometer is mounted on the concrete
wall by the rain gauge which is used to zero and span the chart
recorder.
Function fib: Ground Water Level Monitor —
The blue pen of the two pen chart recorder indicates the ground
water level in relation to the Geo-Cel tank. There is a bubble
level device inside a 10 centimeter (4 in.) well casing located
6 meters (20 ft.) NE of the control building which measures
ground water level. Typically the dry-weather ground water
level is 5 percent of full scale on the recorder chart, rises to
10 percent within twenty minutes after a storm, and falls slowly
over several hours. This recorder measures a depth of 0 to 5.1
meters (200 in.) of ground water with respect to the bottom
elevation of 240.8 meters (790.0 ft). The ground water level
also rises in relation to spring thaw conditions. A sharp rise
during a tank filling or emptying operation may indicate a rup-
ture in the tank membrane liner.
Function #2: Clarifier Level —
The level of combined sewage flow in the rectangular clarifier
section is recorded on a two pen chart recorder in the annuncia-
tor cabinet. The red pen records from 0 to 51 centimeters
(20 in.) of flow. When twenty inches is exceeded a light
"Clarifier Over 20 inches" in the annunciator alarm panel will
begin to blink. The blue pen measures water level from 0 to
4.78 meters (188 in.). When the water level in the clarifier
reaches 4.22 meters (166 in.), water should flow over the weir
and into the tank. The remaining 0.56 meters (22 in.) between
82
-------
the top of weir and the bottom of the concrete tees is freeboard.
If it appears that the clarifier level of 4.78 meters will be
reached the slide gate valves should be manipulated to relieve
the excess flows. This will normally occur only when flows
received exceed the acceptance rate of the Geo-Cel media. This
condition can be caused by fine particles or debris which may
reduce the infiltration rate into the media (Appendix A).
Table C-l lists significant clarifier levels.
TABLE C-l. SIGNIFICANT CLARIFIER LEVELS
Item
20 inch alarm light
Bottom of flap gates
Alarm probe
Bottom of 1.52 meter
(60 in.) bypass
Top of 1.52 meter (60 in.)
gate opening
Weir
High Water Level
Maximum Water Level
Meters
0.51
0.69
0.61 to 1.
1.85
2.41
4.22
4.57
4.78
22
Inches
20
27
24 to 48
73
95
166
180
188
% Full
11
14
12 to 25
39
51
88
96
100%
Function #3 —
This records the clarifier level between 4.22 meters, the point
of flow over the weir, to 4.78 meters, the point of overflow of
the concrete clarifier tees.
Function #4 —
This records the flow exiting the 1.52 meter bypass pipe for
depths between 7.6 centimeters (3 in.) to 1.52 meters (60 in.)
(The sensor cannot respond to levels less than 7.6 centimeters).
The red pen charts the depth on a scale from 0 to 100 percent.
Function #5 —
This records water depth in the tank manhole nearest the control
building from 0 to 3.05 meters (0 to 100%) with a bottom
elevation of 242.9 meters (797.1 ft.).
Function #6 —
This records water level in the middle tank manhole from 0 to
3.05 meters (0 to 100%) with a bottom elevation of 243.0
meters (797.34 ft.)
Function #7 —
This records water level in the northwest tank manhole from 0 to
3.05 meters (0 to 100%) with a bottom elevation of 243.3 meters
(798.23 ft.)
83
-------
Function #8 —
This records the chlorine residual in the water flowing over the
weir as indicated by the Hach Chlorine Residual Analyzer, 0 to
5 PPM full scale.
Function §9 —
This records the chlorine residual in the overflow effluent
should the Geo-Cel overflow.
Function #10 —
This is an extra blank channel. Should one of the recorders
in this section malfunction, its function could be transferred
to this station.
Function #11: Chlorine Ratio Control Station —
This device operates via the bubbler air pressure to control
the valve regulating the position of the chlorine feed valve
from a .3 to 3.0 ratio. The setting can be changed by
adjusting the scale pointer slide. The chlorine is added as a
15 percent sodium hypochlorite solution by a 190 liter per
minute (50 GPM) pump.
Function §12: Clarifier Combustible Gas Monitor —
This indicates that the combustible gas in the clarifier_has
reached 40 percent of the lower explosive level. This -will
trigger both the alarm light in the annunciator panel and an
audible horn. The meter is located on the lower left side of
the control panel.
Function #13: Control Building Combustible Gas Monitor —
This indicates percentage of lower explosive level of combustible
gas in the control building. If activated this will trigger the
external red globe over the entrance doorway. This is located
on the lower right of the control cabinet.
Mounting Board Instrumentation
Adjacent to the control panel is the instrument board which
houses the interface devices that convert the pneumatic pressure
signals to electrical signals. Figure C-2 shows the instrument
mounting board and the locations of the various controls.
A items -
are electric-pressure transmitters for the depth
recording devices: Al is for the overflow pipe;
A2, A7, and A8 are for the three tank depth
monitors; A3, A4, and A5 are for the clarifier
level monitor; and A6 is for the water table
monitor.
B items - are the filter type pressure regulators.
84
-------
"TO O-U-ORIXJE COWIT*CO_
FIGURE C-2. INSTRUHEIIT MOUNTING BOARD
85
-------
C items
D items -
E items -
are the site feed bubblers. These are for the
visual confirmation of air pressure in the lines.
is an electro-pneumatic transducer for the chlorine
control valve.
are high pressure air valves for blowing out the
air lines and performing test checks on the
recording instruments.
Instrumentation Test Checks
The annunciator panel warning lights and chart ink pen response
can be tested by regulating the appropriate air pressure knobs
located on the plywood instrument mounting board (Figure C-2).
Each blowdown control has a function:
El
E2
E3
E4
E5
E6
triggers a test signal to the pressure diaphram in the
overflow pipe. Upon triggering a signal, the "Geo-Cel
Overflow" annunciator panel light should blink. The
overflow sampler motor will start, the overflow chlorine
analyzer needle will deflect and the; tank overflow
recorder #4 pen should also deflect.,-
triggers a test signal to the pressure diaphram located in
tank depth well #1 (nearest control building). The test
signal should cause the "Geo-Cel Filling" annunciator
panel light to blink. The weir chlorine analyzer needle
and the tank depth well #1 pen (recorder #5, channel #1,
should respond by deflecting.
triggers a test signal to the pressure diaphram located in
tank depth well #3. The test signal should initiate a pen
deflection from the tank depth well #3 pen (recorder #5,
channel #3).
triggers a test signal to the pressure diaphram located in
tank depth well #2. The test signal should initiate a pen
deflection from the tank depth well #2 pen (recorder #5,
channel #2).
triggers a test signal to the ground water table bubbler.
(Close E8) This signal should cause the ground water table
recorder pen (recorder #1, pen #2 (blue)) to deflect.
triggers a test signal to the clarifier level bubbler.
Regulation of this blowdown control should trigger (close
E7) the following annunciator panel lights: Clarifier
over 20", Clarifier over 160", Clarifier over 180", and
Clarifier over 166". The Clarifier 0-20", Clarifier 0-188
and Clarifier 166-188" recorder pens (recorder #2 pen #1,
recorder #2 pen |2, and recorder #3 respectively) should
86
-------
E7
E8
respond by deflecting. The signal should also activate
the relay xn the chlorine fuse box; an audible click can
be heard.
is an isolation valve which protects the clarifier bubbler
and regulator. Before opening the E6 blowdown control knob,
the E7 knob must be closed. Otherwise E7 should remain
open.
is an isolation valve which protects the ground water
bubbler and regulator. Before opening the E5 blowdown
control knob, the E8 knob must be closed. Otherwise E8
should remain open.
Required Maintenance
1. Drain compressor of condensed moisture by opening the
bottom drain. The manufacturer's manual suggests doing
this once per week.
2. Test the clarifier water probe monthly, by immersing in
water and checking with the Sewer Maintenance Division
to determine if the alarm light functions. The copper
prongs of the probe should be cleaned with emery cloth to
a bright surface once a month.
3.
4.
5.
7
8,
9.
Change rain gauge, clarifier depth and tank depth charts
once per month.
Change ink cartridges on the rain gauge and clarifier level
every four months.
Check annunciator panel lights by pressing "Test" button
Press the "Acknowledge" button to stop.
Check the various control functions by individually opening
(and then closing) the air pressure valves located on the
plywood panel.
Grease the gears on the slide gate pedestals.
Oil various door and hatch hinges as needed.
Verify setting of chlorine ratio controller and auto button
on samplers.
10. Inspect diversion manhole monthly for integrity of the
orifice. The orifice limits the stormflow to the clarifier.
11. Check fuse box and chlorine fuse box. This is located on
the south wall adjacent to the plywood instrument mounting
board.
87
-------
12. Check calibration of rain gauge with weights provided.
Empty bucket at end of month and reset. This is explained
under the section on test checks and adjustments.
13. Check remaining amount of chlorine monthly, by opening the
underground holding tank bolted coverlid and measuring
manually with a dip rod. The chlorine is in the form of a
15 percent liquid sodium hypochlorite solution.
Caution: Chlorine is caustic to the skin and eyes. The
tank holds a maximum of 5700 liters (1500 gal.),. A 5.1
centimeter (2 in.) filler pipe is located adjacent to the
clarifier south wall approximately 7.6 meters (25 ft.)
east of the chlorine tank.
Operations Prior To A Storm
1. Preadjust and check periodically the influent pipe orifice
opening within the diversion manhole to obtain a maximum
desirable flow rate. Upon turnover of the system to the
City of Akron, the orifice opening was 25.4 centimeters
(10 in.) which allows a maximum influent flow rate of
approximately 990 liters per second (Figure 12). The
diversion wall height is equal to 1.22 meters (4 ft.)
2. The probe alarm, which signals upon filling of the
clarifier, can be adjusted to any height. The probe,
however, should be set at a height greater than 0.6
meters (2 ft.) to reduce triggering of the signal by
slight increases of the dry-weather flow, yet less than
1.22 meters (4 ft.) to allow a maximum personnel response
time.
3. The 46 and 152 centimeter (18 and 60 in.) gate valves
control the flow exiting from the clarifier and can be
adjusted in anticipation of a storm. The 46 centimeter
gate should remain at least 10 centimeters (40 turns)
high to allow dry-weather flow, up to 71 liters per
second (2.5 cfs), to pass through the clarifier without
triggering the probe alarm. The 152 centimeter gate can
be regulated between 0 and 56 centimeters high, allowing
up to 2550 liters per second (90 cfs) to exit from the
system. If the orifice opening within the diversion
manhole is less than 51 centimeters (20 in.), and the 1.52
meter gate is open 56 centimeters then no flow will pass
over the clarifier weir and into the storage media. This
flow, however, is discharged directly into the river and
defeats the purpose of the retention tank. When the 1.52
meter gate is closed, the clarifier filling rate is
dependent upon the intensity of the rainfall; however, the
allowable response time for personnel to get to the site
is short. Personnel should be on the site for observation
88
-------
4.
and regulation of the storm flow. There have been instances
in the past (4-1-74) where the infiltration rate into the
exposed media was reduced by sand and silt being deposited
on the media surface.
Check functioning of various devices (clarifier charts,
samplers, etc.) by using the blowdown controls. This is
explained under the section on test checks and adjustments.
Operations During A Storm
1. When the probe alarm signals, personnel should be dis-
patched to the retention tank site to monitor and regulate
the 0.46 meter (18 in.) and 1.52 meter (60 in.) slide
gates.
2. If the 1.52 meter gate valve is open, it should be closed
to prevent any overflow into the river. The 0.46 meter
gate can remain at the dry-weather flow height.
3. Careful observation of the clarifier filling chart is
necessary to assure that flow is infiltrating into the
media. At 87 percent, flow is passing over the weir and
into the media. If the clarifier level exceeds 90 percent,
check the retention tank depth recordings. If the reten-
tion tank is not full, the water is not infiltrating
properly. Visual observation through the hatch gate
outside the building should be made to check pooling on
the exposed media surface. If pooling on the media is
occurring, the 1.52 meter gate should be opened immediately
to prevent excessive pressure buildup within the clarifier.
4. Sampling: Check to make sure the samplers activate at the
proper_times, otherwise regulate manually. Label samples
according to time and location. Take grab samples as
needed. Reload sample jugs and change valving to take
samples from tank as it drains. Regulate valve opening to
get bottle filled in the required amount of time.
5. Chlorination: Observe the Hach Chlorine Analyzer for
priming and operation: Adjust the chlorine ratio control
as needed.
Operations After A Storm
1. After the storm has subsided, the retention tank and
clarifier should be drained through the 0.46 meter
effluent gate opening. The 1.52 meter gate should remain
closed to prevent discharging storm flow directly into
the river.
89
-------
2.
3.
4.
The 0.46 and 1.52 meter gate valves should be adjusted to
the desired dry-weather flow openings.
The clarifier filling actuator probe should be cleaned with
emery cloth or steel wool and adjusted to the proper
elevation. This should be done after each storm.
The sample bottles should be replaced. The sampler valve
should be reset to take the next sample from the clarifier.
The check valve on the pumps should be opened and closed
to drain residual stormwater in the pickup lines. The
filling nozzle should be reset at the beginning bottle.
5. Turn off potable water, heat, lights and secure door.
The operations which were presented are those that were required
for the prototype facility. The City of Akron, however, has
planned for minor alterations to the prototype facility to
provide for a more automatic system operation with less data
evaluation.
90
-------
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2. '" "
EPA-600/2-76-272
4. TITLE AND SUBTITLE
DEMONSTRATION OF VOID SPACE STORAGE WITH TREATMENT
AND FLOW REGULATION
7. AUTHOR(S)
KARL R. ROHRER ASSOCIATES, INC.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
KARL R. ROHRER ASSOCIATES, INC.
3810 Ridgewood Road
Akron, Ohio 44321
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
December 1976 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
1O. PROGRAM ELEMENT NO.
1BC611
11. CONTn ACT/GRANT NO.
Project 11020 DXH
13. TYPE OF REPORT AND PERIOD COVERED
Final 1/74 to 1/76
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES ~
The purpose of this project was to demonstrate and evaluate the feasibility of an
underground void space storage tank, in containing and regulating storm overflows
from a combined sewer thus reducing the pollution loads discharged to the receiving
water body. System design, construction, and two years operation were conducted
under the study.
The prototype facility was constructed in Akron, Ohio with a combined sewer drainage
area of 76.3 hectare (188.5 acres). The excess combined sewer flows were fed by
gravity into the 3.8 x 10 liter (1 MG) void space retention tank. The tank is of
an excavated hopper shape, lined with an impermeable membrane and filled with an
inert media. Storage of the waste water is in the void space of the media. After
the storm event, the stored stormwater was gravity fed into the interceptor sewer
for subsequent treatment. The underground facility was a dual usage concept. In
addition to collecting, chlorinating, and detaining potential combined sewer
overflows, the facility's top surface could be made usable as a park or recreational
grounds.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Underground storage, Combined sewers.
Overflows, Water pollution. Waste
treatment, Runoff, Waste water, Flow
regulators, Containment
b.IDENTIFIERS/OPEN ENDED TERMS
Void space storage,
Geo-Cel, Combined sewer
overflow, Pollution
abatement
c. COSATI Field/Group
13B
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
- UNCLASSIFIED
21. NO. OF PAGES
125
lEPA Form 2220-1 (9-73)
>0. SECURITY CLASS (Thispage)
UNCLASSIFIED
115
U.S. GOVERNMENT PRINTING OFFICE: 1377-757-056/5^9 Region No. 5-M
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