WATER POLLUTION CONTROL RESEARCH SERIES
ORD-4
Combined Sewer Separation
Using Pressure Sewers
U.S. DEPARTMENT OF THE INTERIOR • FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports describe the results and
progress in the control and abatement of pollution of our Nation's
Waters. They provide a central source of information on the research,
development and demonstration activities of the Federal Water Pollution
Control Administration, Department of the Interior, through inhouse
research and grants and contracts with Federal, State, and local agen-
cies, research institutions, and industrial organizations.
Triplicate tear-out abstract cards are placed inside the back cover to
facilitate information retrieval. Space is provided on the card for
the user's accession number and for additional keywords. The abstracts
utilize the WRSIC system.
Water Pollution Control Research Reports will be distributed to
requesters as supplies permit. Requests should be sent to the Publica-
tions Office, Department of the Interior, Federal Water Pollution
Control Administration, Washington, D.C. 20242.
Previously issued reports on the Storm & Combined Sewer Pollution Control
Program;
WP-20-11 Problems of Combined Sewer Facilities and Overflows-
1967.
WP-20-15 Water Pollution Aspects of Urban Runoff.
WP-20-16 Strainer/Filter Treatment of Combined Sewer Overflows.
WP-20-17 Dissolved-Air Flotation Treatment of Combined Sewer
Overflows.
WP-20-18 Improved Sealants for Infiltration Control.
WP-20-21 Selected Urban Storm Water Runoff Abstracts.
WP-20-22 Polymers for Sewer Flow Control.
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Combined Sewer Separation Using Pressure Sewers
Feasibility and Development of a New Method
for Separating Wastewater from
Combined Sewer Systems
Federal Water Pollution Control Administration. Department of the Interior
by
American Society of Civil Engineers
345 E. 47th. Street
New York, N.Y. 10017
Program No. 11020 EKO
Contract No. 14-12-29
October, 1969
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FWPCA Review Notice
This report has been reviewed by the Federal
Water Pollution Control Administration and
approved for publication. Approval does not
signify that the contents necessarily reflect
the views and policies of the Federal Water
Pollution Control Administration.
ii
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ABSTRACT
This report is concerned with the separation of community waste-
waters and runoff from rainfall and snowmelt in areas presently served
by combined and intercepting sewers. Separation is accomplished by
withdrawing the wastewater fraction of flows from existing plumbing
systems and passing it through a sequence of added systems components
as follows: (1) a storage, grinding and pumping unit within each
building; (2) pressure tubing fished from the unit through each existing
building sewer into the existing combined sewer; and (3) pressure piping
inserted in that sewer and extending to the existing intercepting sewers
that carry the wastewaters to treatment and disposal works. Runoff from
rainfall and snowmelt, thus unencumbered by wastewaters, is removed from
the community through the residual passageways of the one-time combined
sewer system, which has thus become a combination of a new pressure
conduit system within an old gravity conduit system.
The feasibility of this scheme of separation, the selection of
available systems components and the development of required new systems
components are described in this report on the basis of information
drawn from 25 project reports and technical memoranda.
The feasibility of storing, grinding and pumping sewage from
individual residences has been established; and standard comminuting and
pumping equipment will be satisfactory for serving larger buildings.
Acceptable types of pressure tubing are available that can be pushed and
pulled through existing building drains and sewers. Pressure conduits
can be suspended inside combined sewers that can be entered by workmen.
There are combined sewer areas that can be separated most effectively by
a version of the method investigated, but generally pressure systems
will cost more than new gravity systems. New capabilities developed
appear to be of potentially greater use for applications other than
separation, such as new construction including utility corridors, and
introduce viable alternatives for design of wastewater sewerage.
This report was submitted in fulfillment of Contract Number
14-12-29 between the Federal Water Pollution Control Administration and
the American Society of Civil Engineers.
111
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CONTENTS
Section Title
ABSTRACT 11L
LIST OF TABLES viii
LIST OF FIGURES x
I SUMMARY, FINDINGS AND CONCLUSIONS
Summary
Findings and Conclusions
II INTRODUCTION
What Is Combined Sewerage? 8
Extent of Combined Sewerage in the United States . . 11
The Proposed Project of Study 12
Authorization, Scope and Content of the Report ... 15
Opinion Survey
Ill ALTERNATIVE METHODS OF REDUCING POLLUTION FROM
COMBINED SEWER OVERFLOWS
19
Introduction
Complete Separation of Existing Combined Systems . . 19
Partial Separation of Existing Combined Systems . . 20
Retardation or Storage of Interceptor Overflows . . 21
Treatment of Overflowing Waters
Other Alternatives for Reducing Pollution by
Overflows
ASCE Combined Sewer Separation Project 23
IV RESIDENTIAL AND COMMERCIAL SEWAGE FLOWS
27
Introduction
Information from Earlier Studies
28
Project Studies •
Results of Project Studies 2°
Flow Rates in Collection System 33
Comparison of Per Capita Flows with Flows Based
on Water Demand Ratios ~
Design Curves
Flows from Commercial Buildings
Comparison of Observed Sewage Discharges with
Water Demands
Unit Fixture Discharge Rates 7
Storage Volume and Minimum Required Pump Rate ... 47
Suggested Measurements
xv
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CONTENTS (Continued)
Section Title FaSe
V EQUIPMENT FOR STORING, GRINDING AND PUMPING SEWAGE
FROM RESIDENTIAL AND OTHER SMALL SOURCES
Introduction 50
Performance Requirements 50
The General Electric Household SGP Unit 51
Equipment Installation and Operating Costs 51
Alternative Equipment 59
VI CONVENTIONAL EQUIPMENT AND CONTROLS FOR STORING,
COMMINUTING, AND PUMPING SEWAGE FROM COMMERCIAL
BUILDINGS AND OTHER LARGE SOURCES
Introduction 60
Comminuting and Pumping Equipment 60
Combined Grinders and Pumps 61
Non-Clog Centrifugal Pumps 61
Pneumatic Ejectors 61
Cost of Comminutor-Pump Installations 63
VII PRESSURE SEWER SYSTEMS
Introduction 64
Tubing and Conduit Defined 64
Materials 65
Insertion of Tubing 65
Tubing and Conduit Installation 65
Ranges of Combined Sewer Sizes 71
Suspension of Conduits within Existing Sewers ... 72
Burial of Tubing and Conduit by Plowing 72
Other Installation and Maintenance Considerations . 73
Pressurized Sewerage Collection System Layouts ... 73
Conduit Sizing 82
System Hydraulics and Controls 84
VIII INSTALLATION OF THE PROJECT SCHEME IN EXISTING SEWERS
Introduction "0
Relative Cost and Reliability of Pressure System . . 90
Effect of Inserted Pipes on Hydraulic Capacity
of Sewers 90
Maintenance and Operation of Pressure System .... 94
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CONTENTS (Continued)
Section Title Pafie
IX INTRODUCING PRESSURE SEWER SYSTEMS INTO EXISTING
COMBINED SEWER DISTRICTS
Introduction 96
Study Areas 97
Separation of Building Plumbing 97
San Francisco 97
Milwaukee 1°7
Boston 1°7
Summary of Plumbing Separation Studies 110
Storage-Grinder-Pump Units HO
Building Service Connections 113
Pressure Sewer Systems 113
Sewage Flow Rates H3
Conduit Materials H4
Hydraulic Criteria H4
Service Districts and Pressure Zones 114
Alternative Arrangements of Collection Systems . . . 114
Layout Studies H5
San Francisco H^
Milwaukee H9
Boston
Estimates of Annual Costs, Milwaukee Study Area . . 124
Summary and Comparison of Estimated Costs,
Three Study Areas 129
Evaluations and Conclusions of Engineering
Consultants I32
X BROADER ASPECTS OF PLUMBING SEPARATION
Introduction 136
Summary
XI NON -TECHNICAL CONSIDERATIONS RELATED TO PRESSURE
SEWER SYSTEMS
Introduction ....................
Public Acceptance and Financial Support ...... 143
Direct Precedents ................. 143
Sampling Public Attitudes ............. 144
XII BENEFITS AND DISADVANTAGES OF THE ASCE PROJECT SCHEME
Adjunct Applications ................
vi
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CONTENTS (Continued)
Section Title
XIII APPLICATION OF ASCE PRESSURIZED SEWERAGE SCHEME
TO DISPOSAL OF SOLID WASTES FROM HOUSEHOLDS AND
INDUSTRY
Page
Introduction 151
Solid Wastes to Be Considered 151
Carrying Capacity of Sewers and Loads of Refuse
Solids to Be Transported 152
Separation and Grinding of Solid Wastes 153
Treatment of Combined Solid Wastes 154
Costs and Benefits of Collecting and Treating
Solid Wastes with Sewage 154
Conclusion 157
XIV FOLLOW-ON FIELD TESTING
Introduction 158
Field Testing of Household Units 158
Field Demonstration in an Entire Service District . 161
XV ACKNOWLEDGEMENTS I64
XVI BIBLIOGRAPHY i69
XVII PATENT NO. 3,366,339 178
XVIII GLOSSARY I82
APPENDICES
A ABSTRACTS OF PROJECT TECHNICAL MEMORANDA 186
B ABSTRACTS OF PROJECT SUBCONTRACTORS' REPORTS 193
vii
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TABLES
Table
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
iLCJ-e J
Ratios of Household Water Demand Rates for Various
Periods to Mean Daily Household Water Demand Rates . . .
Northeastern U.S. Variations in Domestic Water Demand .
Determination of Storage, for Synthetic Hydrographs,
Mean Rates of Discharge of Individual Fixtures and
Synthetic "Minimum" Discharge Rates for Fixture
Specifications for Prototype Storage -Grinder-Pump Unit .
Tubing Less than 2 Inches in Diameter Considered for
Pipe Materials \\ Inches through 16 Inches in
Summary of Conduit Layout Lnaracceri&uiLt.
Summary — Building Plumbing £>epar«*Liuu
Annual Cost of Sewer Separation, Prospect Avenue
Comparison of Annual Costs for Milwaukee Study Area . .
31
36
38
39
46
48
48
58
66
67
68
69
75
98
128
130
131
Vlll
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Fable
TABLES (Continued)
Title
19 Summary of Information on Costs of Building
Plumbing Separation
20 Attitudes of Occupants of Twenty-Five Buildings to
Experience with Pumping Units, Radcliff , Kentucky ... 145
21 Evaluation of ASCE Combined Sewer Separation
Project Scheme .....................
22 Typical Quantities of Community Refuse and of
Sewage Solids .....................
IX
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FIGURES
Number Title Page
1 Diagrammatic Example of Normal Functioning of
Typical Combined Sewer System under Dry-Weather
10
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Pressure Sewerage Research Plan for ASCE Combined
Sewer Separation Project
Variation in Daily Water Use
Variation in Peak Hour Water Use
Variation in Peak Hour Water Use, Combination of
Sources
Mass Curve of Water Usage, Single Home
Water Demand Variations, Northeastern U.S
Water Demand Variations, California
Relation of Extreme Discharges on Maximum and Minimum
Days to the Average Daily Discharge of Domestic Sewage .
Comparison of Discharge from First Part of Test # 8,
Station A, with Composite Discharge Curve
Storage-Pump Combinations to Accommodate Synthetic
Inflows
Cut-Away Sketch of Household Storage -Grinder -Pump Unit .
Completed Prototype of Household Storage-Grinder-Pump
Unit
Grinder Mechanism Viewed from Below through Pump
Suction Bell
Close-Up View of Components above Mounting Flange . . .
Characteristic Curves, Prototype SGP Unit
Tanks for SGP Prototype
Effect of Comminutor and Garbage Grinder on Sewage
Particle Sizes
14
29
30
32
34
40
41
43
45
49
52
53
54
55
56
57
62
X
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FIGURES (Continued)
Number Title
19 Alternative Methods of Installing and Connecting
Pressure Tubing and Conduit (One Side of Street,
only, Shown) 70
20 Layout A 76
21 Layout A, Details for Fig. 20 Sector 77
22 Layout A, Arrangement for Manhole "W" in Figure 21 ... 78
23 Example of Layout B 80
24 Layouts C, D and E 81
25 National Sanitation Foundation Pressure Sewer Layout . . 83
26 Example of Minimum and Maximum Hydraulic Grade Lines . . 86
27 Example of Pressure Zone Control 87
28 Example of In-Line Pumping 88
29 Turbulent-Flow Friction Factor for Concentric
Annulus as a Function of Diameter Ratio 92
30 Deviation of Friction Factors for Conduits of
Annular Cross-Section Based on Hydraulic Radius
Concept 93
31 Location of Laguna Street Study Area, San Francisco . . 99
32 Basic Land Uses in the San Francisco Study Area .... 100
33 Location Map Milwaukee Study Area 101
34 Present Population, Present and Future Estimated
Flow and Number of Dwelling Units 102
35 Location of Summer Street Sewer Separation Area,
Boston, Mass., and Typical Building Selected for
Study 103
36 Summer Street Sewer Separation Study Area,
Boston, Mass
XI
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FIGURES (Continued)
Number Title Page
37 Typical In-House Wastewater and Rainwater Plumbing
Systems, San Francisco Study Area 105
38 Piping Requirements and Estimated Costs for
In-House Separation of Selected Structures,
San Francisco Study Area 106
39 Downspout Connection Groups Milwaukee Study Area .... 108
40 Plan of Basement Plumbing in 55 Summer Street 109
41 Section of Proposed Pit and Plumbing,Pressure System . . Ill
42 Pressure Sewer System Layout — Alternative A,
San Francisco Study Area 116
43 Details of Trunk System — Alternative A,
San Francisco Study Area 117
44 Profile of Pressure Sewer System — Alternative A,
San Francisco Study Area 118
45 Gravity Sewer System Layout, San Francisco Study Area . 120
46 Hypothetical Pressure Sewer System Layout M-l,
Milwaukee Study Area 121
47 Hypothetical Pressure Sewer System Layout M-2,
Milwaukee Study Area 122
48 Gravity Sewer System Layout M-Gr, Milwaukee Study Area . 123
49 Pressure Sewer System Design I, Boston Study Area . . . 125
50 Design II (Differences from Design I),
Boston Study Area 126
51 Design III (Differences from Design I),
Boston Study Area 127
52 Schematic Diagram of Systems for Disposal of Sewage
and Solid Wastes 155
xii
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SECTION I
SUMMARY, FINDINGS AND CONCLUSIONS
Summary
1. Introduction. Effective water pollution control may require
separate or separated collection systems, viz., wastewater systems that
collect and deliver to treatment works the water-carried wastes of
household and industry and storm water systems that collect and deliver
to nearby watercourses the runoff from rainfall and snowmelt. Waste-
water treatment works remove or modify waste substances in the carrying
water to a required degree before discharging the effluent to receiving
waters within or not far from the communities in which the waste matters
are generated.
For historical reasons, about a fifth of the nation's population
is presently served by combined systems of sewerage (Ref. 27) that
collect both wastewater and storm runoff in a single set of sewers. To
keep the wastewater component carried by combined collecting systems out
of rivers, lakes, and tidal estuaries, the dry-weather flows of combined
sewers are intercepted before they reach the terminals of the sewer
system and are diverted to treatment works. Only during rainstorms and
snowmelts that swell the flows of combined sewers beyond the capacity
of the interceptors is a mixture of wastewater and runoff from rainfall
and snowmelt discharged into the bodies of water that are otherwise
protected by the intercepting system. In the Northern United States
about 3% of the total annual volume of sewage and substantial volumes of
wastewater solids are scoured from the sewer system during heavy runoff
and are discharged to receiving watercourses through storm water over-
flows. The nature and extent of combined sewerage in the United States
are discussed in Section II.
After the turn of the last century the danger and nuisance of
combined-sewer overflows were abated in many new municipal sewerage
schemes by the construction of two separate systems of sewers: a waste-
water system and a storm water system. However, most of the existing
combined systems were continued in service together with their inter-
ceptors except that in some instances additions to these systems were
built as separate systems in which the sanitary sewers alone were
connected to the existing combined sewers.
In recent years, a greater public awareness of the value of a
clean environment and unpolluted natural waters, together with a desire
to eliminate urban blight, has focused interest on the prevention,
storage, and treatment of overflows from combined sewers. In most
cases, overflows can be prevented by restricting the use of the existing
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combined sewers to the removal of storm water alone, or to the removal
of wastewater alone. Whichever is done, it is necessary to carry the
physical separation of the two systems into tributary private properties.
What is often referred to as conventional separation therefore
normally involves considerable inconvenience to and disruption of normal
community life by construction activities on private properties as well
as on public thoroughfares. The estimated construction cost for con-
ventional separation of the combined sewer systems in the United States
that serve about 36 million people is $48 billion (Ref. 27), averaging
close to $1,300 per person served. Because it recognized the high cost
and disruptive nature of conventional separation, the U.S. Congress
provided funds for the development of alternatives as part of the scope
of the "Clean Water Restoration Act of 1966" (P.L. 89-753). Methods of
reducing pollution from combined sewers other than by sewer separation
are discussed in Section III.
2. Project Concept. As conceived by Professor Gordon M. Fair of
Harvard University, the method of sewer separation with which the
present report is concerned (Section II) would incorporate into existing
combined sewer systems relatively small-diameter pipes which would
convey the wastewater fraction under pressure to existing interceptors.
The one-time combined sewers would be retained as the conveyors of storm
water that would discharge to receiving bodies of water either directly
through existing outlets or indirectly after passage through storm water
retention or treatment tanks or underground facilities of a similar
nature.
Structurally, the proposed system would begin at a grinding and
pumping unit within each building served by the system. Where possible,
the unit would prepare the wastewaters for delivery to the system
through small-diameter tubing inserted in the building sewer and con-
nected to a conduit inserted in and attached to the interior of the
existing combined sewer. The main trunks of the branching network of
pressure conduits would discharge into the existing interceptor which
thus would convey only wastewaters to treatment works. The existing
building sewers and combined sewers would deliver to receiving water
bodies only storm water runoff from rainfall and snowmelt, together
with such groundwater as entered the system from the soil.
In the creation of the proposed separate wastewater system, con-
struction activity and traffic disruption would be greatly reduced by
using the pipe-within-a-pipe concept or, where necessary, by installing
the relatively small-bore piping in shallow trenches exterior to the
combined sewers. If total costs were less than for conventional separa-
tion, the scheme would constitute a viable alternative to conventional
separation. By excluding seepage waters from pressurized reaches the
hydraulic loads on interceptors and treatment works would be reduced
accordingly. In addition, an inherent potential advantage of pressure
sewerage is that the piping is free from the limitations of gravity
systems which must constantly slope downward no matter what the surface
topography.
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To minimize and, in so far as possible, prevent the clogging of
tubing, conduits and auxiliary fittings, Professor Fair's concept
included the grinding of sewage solids and pressurization in a single
assembly at each building in which surges of peak flows would be atten-
uated by storage of incoming flows from the building served. Each
residential building or structure with similar flows, therefore, would
have a "storage-grinder-pump" unit.
3. Project Scope. With the support of an FWPCA contract, the
American Society of Civil Engineers (ASCE) conducted an investigation
of the feasibility of Professor Fair's concept. The present report
contains the results of that investigation, which had the benefit of the
counsel of an advisory committee called the Project Steering Committee.
The principal project concerns were: (1), the development of an assembly
of workable and dependable systems components; (2), a study of the
physical feasibility of hypothetical pressure systems introduced into
existing combined sewerage districts; and (3), a cost analysis of the
hypothetical systems.
Because there was little, if any, direct information on pressurized
sewer systems of this kind, it was necessary to develop required design
criteria and procedures, construction methods and installation techniques,
workable systems devices and parts, general system designs and other sup-
porting information. The following example illustrates one of the
required developments. Although engineering interest in pressure sewer-
age for a variety of applications is by no means new, lack of a suitable
household storage-grinder-pump unit stood in the way of the effective
utilization of pressure systems in residential areas. Accordingly, the
development of a suitable storage-grinder-pump unit became a focal point
of interest of the project.
Assistance was sought from organizations and individuals that were
experienced in related fields. In the course of the work assistance was
received from over a hundred individuals in almost fifty organizations
(Section XV).
The Project Steering Committee recognized the principle that
research findings should be useful for future pressure sewer applications
both within and beyond the immediate Project concept and that, to this
end, the Project studies should be as broad as time and funds would
permit. The studies accomplished in this spirit are documented in detail
in a series of twenty-five technical memoranda and reports (see Section
XVI and Appendices) totaling close to 1,500 pages.
Findings and Conclusions
1. Findings and Conclusions on the Feasibility of Grinding,
Storing and Pumping Domestic Sewage. The feasibility of storing,
grinding and pumping sewage from individual residences has been estab-
lished. The final phase of development of the household storage-grinder-
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pump unit and its associated field testing is in progress in a follow-
on project by the New York State Department of Health under an FWPCA
grant (Section XIV).
In reference to the operation of comminuting and pumping installa-
tions serving commercial buildings, multiple dwellings, and other large
sources it is concluded that the use of standard equipment on services
of this scale in pressurized systems will be satisfactory.
It is recognized that there is still room for the development of
suitable storage, grinding and pumping equipment for duties lying
between those of individual households and large sources. However, some
recently introduced assemblages appear to be suitable.
2. Findings and Conclusions on Systems of Pipes Inserted in
Existing Conduits. The question of inserting and securing tubing and
piping in combined sewers required evaluation of: methods of threading
tubing through building drains and sewers and suspending conduit in
street sewers (Section VII); and the effect of inserted conduits and
their hangers on the hydraulic capacity of intruded combined sewers
(Section VIII).
The Project studies and demonstrations showed that pressure tubing
can be pushed and pulled through existing building drains and sewers,
and that acceptable types of tubing are available.
A single-piece molded plastic hanger was developed for suspending
pressure conduits inside combined sewers and found to be structurally
adequate. However, it was discovered that field-insertion of conduits
in hangers bonded in place was an awkward and complicated task. In this
connection, furthermore, laboratory flow tests demonstrated that within
a certain range of ratios of the conduit diameter to the sewer diameter,
the protrusion of the portion of the hanger adjacent to the conduit
unduly decreased the hydraulic capacity of intruded combined sewers.
It is concluded that since the main feature of the hanger is its bonding
system, a conventional metal-strap loop and suspension rod can be used
satisfactorily in conjunction with the original plastic hanger seat,
which will facilitate installation and minimize the diminution of
intruded combined sewer hydraulic capacity.
Hanger installation was found to require direct access to the
interior of combined sewers, thus limiting the installation of conduits
to sewers that can be entered by workmen. This conclusion restricts the
pipe insertion concept to about one-seventh of the total length of
combined sewers in major cities and to a still lower proportion of such
sewers in smaller communities. However, there are sectors of communities
with large combined sewers and so much congestion of underground util-
ities and street traffic that installation of an additional system of
sewers is not economically feasible unless the required piping is
installed in the existing sewers. This is not to say that separation is
the only way to reduce pollution from overflows. Alternatives do exist
and are being investigated currently (Section III).
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3. Findings and Conclusions on the Cost of Separation by the
Project Scheme Versus Conventional Means. The feasibility and cost of
the Project scheme were investigated by designing pressurized sewer
systems for three areas of reasonable size (Section IX) that are repre-
sentative of many existing combined sewer systems, as follows: (1) a
53-acre commercial downtown area in Boston, Mass.; (2) a 157-acre mainly
residential area in Milwaukee, Wis.; and (3) a 323-acre predominantly
residential area in San Francisco, Cal. For purposes of comparison,
conventional separation of the test areas was studied by consultants in
the cases of Boston and Milwaukee and by the Department of Public Works
in the case of San Francisco.
Much background information had to be collected or developed
before suitable designs could be prepared. Examples of required infor-
mation are: expected residential and commercial sewage flows (Section
IV); conventional equipment and controls for storing, grinding, and
pumping sewage from commercial buildings and other large sources
(Section VI); search for and testing of suitable tubing, piping and
fittings, and methods for their installation (Section VII); identifica-
tion of the configurations of collection systems amenable to proper
operation and maintenance (Section VII); satisfaction of requirements
for overall system pressure controls and pumps (Section VII); and
determination of minimum solids transport velocities (Section VII).
It is estimated that construction costs for separation of these
three test areas by the ASCE Project method might cost about 50% more
than their separation by the conventional method of laying a second
system of gravity conduits. These estimates did not take into account
the inconvenience and loss of business that would be associated with
conventional separation.
Whereas the unit cost of separating the plumbing systems of
buildings might be lowered by including all conversions in a single
contract, the structurally variegated requirements and special situa-
tions bound to be encountered in such work (Section X) would probably
operate against a substantial cost reduction. This is an important
consideration because this work represents some 407,, to 60% of the total
cost of conventional separation of the three study areas. Because the
cost of building separation was quite similar for the two methods in
these instances, the net competition in construction costs between
pressure and gravity systems was thereby restricted to the remaining
60% to 40% of the total cost of conventional separation.
Operation and maintenance would presumably be more expensive for
a pressure system. Estimates of annual costs for the Milwaukee study
area, including operating costs and amortization of construction costs,
were about 85% higher for the pressure scheme than for conventional
separation.
It is not possible without further study to determine the typi-
cality of the cost estimates for the three study areas on a national
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basis. Because much care was exercised in selecting these areas as
reasonably typical, the results obtained suggest that the Project scheme
will generally cost more than conventional separation. However, although
the Project scheme was not found to offer a general and direct means to
lower the cost of sewer separation, it was recognized that there are
special situations in which existing systems or parts of systems can be
separated most effectively by the ASCE Project method or a suitable
modification of that method (Section XII).
4. Findings and Conclusions on the Physical Feasibility of the
Project Scheme for Other Applications. Inherent in the successful
first-phase development of the household storage-grinder-pump unit is
the promise of the technological feasibility of pressurized sewer systems
for residential areas. Completion of this development in the field in
the near future, coupled with information on materials, procedures and
design criteria collected or developed in the ASCE Project, provides a
further degree of freedom in the design of sewer systems. Uses for this
new knowledge appear to be potentially greater for applications to
purposes other than the separation of existing combined sewer systems.
There is good reason to believe that many residential communities
or subdivisions of communities will eventually have to replace septic
tanks with public sewerage. Some of them will find that pressure
systems meet their needs best. Typical examples are: residences on
steeply sloping shores; areas encumbered by physical barriers such as
escarpments and swamps; isolated pockets of low land; areas of undulant
terrain; buildings from which wastewaters must be lifted to the level of
existing gravity sewers; and areas of dispersed occupancy such as semi-
rural areas.
Most of the examples cited have some bearing on new sewerage
construction. In the leap-frog development of suburban areas, for
instance, installation of light-weight pressure conduit by plowing
techniques at shallow depth becomes relatively inexpensive and easy.
Such pressure systems can then serve isolated new developments and
subsequently be linked into the community system, whether it be a
gravity or a pressure system.
A promising future use of pressure systems is the full exploita-
tion of utility corridors, called "utilidors." These corridors beneath
city streets conserve and make efficient use of underground space partic-
ularly where streets are burdened with heavy traffic, both vehicular and
pedestrian. They also simplify maintenance, repair and replacement of
the utilities they shelter. Inclusion of gravity sanitary sewers in
utilidors would force the placing of the utilidors at the grades
required for the sewers. This is a profoundly restrictive requirement
except where needed sewer slopes and ground-surface slopes happen to be
reasonably parallel. The use of pressure sewers would lift this con-
straint from utilidors in the same way as it commonly does from water
mains. Utilidors, incidently, are important features of cities in the
far north where perma-frost otherwise imposes severe restrictions on
water supply and sewerage.
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Lastly, some thought has been given in the Project study to the
potential of extending the Project concept to the selective isolation,
grinding, and wastewater transport of essentially all readily decom-
posable organic waste substances from households and industries to
existing, enlarged, or integrated new waste treatment works (Section XIII)
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SECTION II
INTRODUCTION
What Is Combined Sewerage?
Combined sewer systems that collected sanitary sewage flows
together with storm water flows and dry-weather infiltration were
constructed in Europe during the first half of the 19th century and
somewhat later in the United States. Responsible for this action was
the rapid growth of cities during the industrial revolution and the
consequent overtaxing of arrangements for removal of night-soil and
other wastes. Existing storm or surface water drains were pressed into
service to carry off both liquid and solid waste matters to nearby
streams, lakes and coastal waters. When the receiving waters were no
longer able to accept the waste matters -without nuisance, they them-
selves were either converted into underground drainage canals or other-
wise protected by the introduction of marginal intercepting drains or
interceptors.
The first municipal combined system of sewerage was designed and
built for this purpose "from the ground, up," at Hamburg, Germany, in
1843. The first such system in the United States was completed at
Brooklyn, N.Y., in 1857. About ten cities were served in this manner
before the Civil War, and about 200 more systems were built in the next
twenty years.
The first intercepting system of sewers was introduced into the
Boston main drainage scheme in 1877-1884. It intercepted flow from
combined sewers emptying into Boston Harbor and adjacent waters along
the periphery of the peninsula on which much of the city was situated.
Fecal matter had been excluded from existing drains by city ordinances
until thirty-five years earlier. The Main Drainage scheme still serves
the core city which, incidentally, includes the Summer Street district
studied for separation by the A.SCE Project scheme. (See Section IX).
Many engineers hold that the present public concept of the nature
of overflows from combined sewers is incorrect and that the inherent
purpose of such systems to discharge sewage to watercourses by design
is not understood. The true nature of combined sewer systems is masked
by the use of euphemistic terms that seem to subscribe to the accidental
and infrequent nature of overflows of mixed sewage and storm water.
Terms such as "overflow" and "spill," "bypassing of excess flows" and
"relief outlets," tend to give the impression that discharges are
infrequent and of an unusual or emergency character.
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The definitions of intercepting sewers and regulators in the Water
Pollution Control Federation (WPCF) glossary also imply the casualness
of such discharges, thus:
INTERCEPTING SEWER — "A sewer which receives dry-
weather flow from a number of transverse sewers or
outlets and frequently additional predetermined
quantities of storm water (if from a combined
system), and conducts such waters to a point for
treatment or disposal."
(This implies that the intercepting sewer receives
all the sanitary sewage plus some storm water.)
REGULATOR — "A device or appratus for controlling
the quantity of sewage admitted to an intercepting
sewer or a unit of a sewage treatment plant."
(This suggests that the regulator passes only a
portion of the flow of mixed sanitary sewage and
storm water. The balance, large or small, must
discharge to the local watercourse.)
The importance of possible discharges of mixed sewage and storm
water flow to receiving streams is illustrated diagrammatically in
Fig. 1. As there shown, almost all the sanitary sewage is discharged
to the watercourse rather than to the intercepting sewer when rainstorms
are heavy and prolonged. At the same time, sludge and debris that have
been deposited or stranded in combined sewers during relatively low
rates of flow in preceding dry-weather periods are scoured from the
laterals and trunk sewers of combined systems and are lifted or other-
wise transported by the augmented flows and eventually discharged to
the receiving waters. It is estimated that, in consequence, as much as
5 per cent of the annual flow of sewage, and 20 to 30 per cent of the
annual volume of solids, are discharged to receiving watercourses from
combined systems.
Runoff rates of about 1/2 inch per hour or more are estimated to
occur in the northeastern United States about 2% to 3% of the time in
the critical six-month period of June-November inclusive, for a medium
sized district of about 200 to 500 acres in which roofs and pavements
constitute about 80 to 90% of the area.
Ejection of mixed flows does not occur at a single level of storm
runoff. It depends instead on the specific characteristics of indi-
vidual overflow structures or regulators and on circumstances such as:
(1) the capacities of upstream combined sewers and downstream inter-
cepting sewers relative to runoff rates; (2) the behavior of regulating
devices relative to the elevation of overflow weirs or their settings;
(3) existence and state of repair of backflow gates; (4) types of control
devices and their actuation relative to water levels in the combined
sewers and interceptors; and (5) distribution of excess rainfall over
significant or different subdistricts of tributary drainage areas.
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1CFS
REGULATOR OR
INTERCEPTING-7
CHAMBER /
DAM
SEWAGE
OflRllflRl aCHftbC /
(DRY-WEATHER FLOW) \
COMBINED SEWER-*
DRY-WEATHER FLOW CONDITION
SANITARY SEWAGE FLOW IN COMBINED SEWER.
ALL FLOW DIVERTED TO INTERCEPTING SEWER
IN DRY-WEATHER.
SANITARY
SEWAGE FLOW,
REGULATOR OR
INTERCEPTING CHAMBER
50 CFS ^^^gf^ r^^^l^=~
STORM FLOW CONDITION
SAME CONCENTRATION OF SEWAGE AND
STORM WATER IN PORTION OF DISCHARGE
TO WATERCOURSE AS TO INTERCEPTOR,DURING
AND FOR SOME TIME AFTER END OF RAINSTORM
OR SNOW MELT.
<=>
<->
oe
FIGURE 1
DIAGRAMMATIC EXAMPLE OF NORMAL FUNCTIONING OF
TYPICAL COMBINED SEWER SYSTEM UNDER DRY-WEATHER
AND STORM FLOW CONDITIONS
-10-
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Generally speaking, the quantities of biochemical oxygen demand
(BOD) and suspended solids (SS) in the storm water runoff are normally
overshadowed by the BOD and SS in the dry-weather sludge accumulations
scoured from combined sewers by higher velocities of flow during rain-
storms or other flood flows. Consequent ejection to watercourses of
this sludge, equivalent to about one third of the untreated, partially
digested, and possibly septic sanitary sewage solids, is the real objec-
tion to combined sewers.
Spills from combined sewer systems of mixed sanitary sewage and
storm water, as well as scourings from sewer deposits accumulating
between storm rainfalls, have long been recognized as major sources of
pollution of inland watercourses and lakes, and of estuaries and bays
of the oceans.
Extent of Combined Sewerage in the United States
The 1967 report, "Problems of Combined Sewer Facilities and Over-
flows," by the American Public Works Association, (Ref. 27), estimates
that more than 1,300 jurisdictions in the United States, with a total
population of about 54 million and an area of more than 3 million acres,
are served in whole or in part by combined sewer systems and that the
households of at least 36 million people are connected exclusively to
combined sewers.
No less than 14,212 points of discharge to watercourses, lakes and
coastal waters were identified in the 641 jurisdictions surveyed in the
APWA study. Of these, 9,860 were outlets from combined sewers in 493
jurisdictions. Noted, too, were 759 outlets from combined-sewer pumping
stations. The balance was made up of sanitary sewage overflows from
pumping stations, treatment plant bypasses and miscellaneous sources.
The report places the estimated construction cost of providing
existing combined sewer systems with the additional conduits needed for
the creation of separate systems for (1) sanitary and industrial wastes
and (2) storm water at about $30 billion and suggests a further cost
figure of $18 billion for the associated separation of plumbing systems
on private properties. Alternative means of control with or without
treatment facilities were estimated to cost $15 billion, without the
need for plumbing separation. (Alternative control measures are
enumerated in a succeeding paragraph and some of these alternatives are
discussed in the next section) .
For historic reasons, combined sewer systems are concentrated
mostly in four regions of the United States: the Northeast States, the
Great Lakes Region, the Ohio River Basin and the North Pacific Coast
area.
All too few of the systems studied had monitored the quantity and
quality of their combined sewer overflows.
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Excerpts from the conclusions of a report issued by the U.S. Public
Health Service in 1964, (Ref. 28), provide the following additional
information:
"Existing sewer systems are inadequate to handle water
and stormwater without creating excessive overloads at
treatment plants and throughout the sewer systems, and
as a result these overloads are discharged to the avail-
able water courses.
Stormwater and combined sewer overflows are responsible
for major amounts of polluting material in the Nation's
receiving waters and the tendency with growing urbani-
zation is for these amounts to increase.
Both combined overflows and stormwater contribute sig-
nificant amounts of pollutional materials to watercourses.
These discharges affect all known water uses adversely
in the receiving watercourses.
Significant economic loss results from the damages
caused by these discharges although precise levels of
these damages remain to be determined.
Damages occur more frequently during the summer storm
season but many systems are so overloaded that overflow
occurs during dry weather throughout the year.
Infiltration is a major problem contributing to hydraulic
overloading of sanitary, combined and storm sewers.
Complete separation of stormwater from sanitary sewers
and treatment of all waste is the ultimate control measure
to provide maximum protection to receiving waters.
Other solutions which have been considered, separately
or in combination, include: (a) partial separation of
roof, yard, areaway, foundation, and catch basin drains
from sanitary and combined sewers; (b) expanded or new
treatment facilities; (c) holding tanks, with or without
chlorination; (d) disinfection; (e) storage using lagoons,
lakes, quarries and other depressions; (f) storage using
guttering, streets and roadways, and inlets; (g) additional
sewer capacity; (h) regulation and control of flow through
the sewer system; and (i) improved planning and zoning.
Evaluation of the effectiveness of all methods except
complete separation is unavailable because of the lack of
installations to study."
The Proposed Project of Study
The underlying concept of the sewage separation scheme using pres-
sure tubing was originated by Gordon M. Fair, Professor of Sanitary
Engineering at Harvard University, and made public in mid-summer of 1965.
Professor Fair filed a patent application through the Harvard Corporation
in November 1965 for a "Converted Sewer System." Patent No. 3,366,339
was granted in January 1968, and assigned to the public by the inventor.
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Section XVII is a facsimile of the patent text and drawing. Patent
No. 3,211,167 for "Apparatus for Transporting Sewage and Waste Liquids"
(via pressure sewerage) was granted to M.A. Clift, e_t al_ on October 12,
1965.
The immediate objective of the project was to examine and evaluate
the feasibility and probable cost of the separation systems suggested
by Professor Fair. This objective was pursued from the standpoint of
applied research. Modifications and alternative schemes were introduced
in the course of the studies.
Study and expansion of the concept was undertaken by the American
Society of Civil Engineers (Ref. 1), acting through its Executive
Secretary, Mr. W.H. Wisely, and its Research Manager, Mr. B.C. Taylor.
General overview of the project was provided by the Urban Hydrology
Research Council of the ASCE Hydraulics Division, and immediate and
overall guidance was assumed by a Steering Committee of seven members of
the Society under the Chairmanship of Professor Fair. The membership of
the Committee is listed in Section XV of this report. Steering Committee
liason was maintained with the Water Quality Research Council of the ASCE
Sanitary Engineering Division by a contact member, Mr. Richard Hazen.
The Project was directed by Mr. M.B. McPherson, assisted by Messrs.
L.S. Tucker and D.H. Waller.
The plan of research is outlined diagrammatically in Fig. 2. As
shown, component elements of the problem were categorized as (1) develop-
ment of devices for storage, grinding and pumping at buildings,
(2) provision of design criteria for street pressure sewerage, (3) ways
and means for inserting tubing in building service connections and in
conduits suspended in street sewers, and (4) ancillary considerations.
From the outset, the project management approach was to maximize
assistance from knowledgeable organizations and individuals experienced
in the specialized subjects relating to the project. In the course of
the work, various levels of assistance were provided by over a hundred
individuals from almost fifty organizations, including officials of
municipal water pollution control agencies, representatives of manufac-
turers, members of firms of consulting engineers, and staff members of
trade and professional associations.
Because of the paucity of immediately helpful precedent, equipment
assemblage of compatible materials, methods of installation and main-
tenance and establishment of design criteria founded on fundamental data
were based on experiment and trial.
In evaluating the feasibility and general acceptability of the
methods for pollution abatement studied in the ASCE Project it was
assumed that the following criteria for judgment should be applied:
(1) the merits of the system in terms of physical capability of con-
struction and operation of the system to accomplish the desired results;
and (2) the relative economy of the construction effort compared with
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STORAGE,
GRINDING,
PUMPING AT '
BUILDINGS
STREET
PRESSURE
SEWERAGE .
SYSTEM
CRITERIA
STREET
PRESSURE
CONDUIT
IN COMBINED
SEWER
CONCEPT
ANCILLARY
CONSIDERA-'
TIONS
COMPONENT
ASSEMBLY
FIELD
TEST
INDIVIDUAL
BUILDING
FLOW
VARIATIONS
SOLIDS
TRANSPORT
VELOCITY
CRITERIA
PUMPING
REQUIREMENTS
HEAD
LOSS
CRITERIA
HANGER
SYSTEM
DEVELOPMENT,
FIELD TEST
NON-
MECHANICAL
CONSIDERATIONS
SOLID
WASTES
ASPECT
HOUSEHOLD
UNIT
DEVELOPMENT
SYSTEM
FLOW
VARIATIONS
PUMPS FOR
LARGER
BUILDINGS
COMMINUTOR
SERVICE,
LARGER
BUILDINGS
SYSTEM
__ PIPING
LAYOUTS,
APPURTENANCES
1
SYSTEM
CONTROL
DEVICES
SYSTEM
nrri/^MC
.„..,...,_..-— AND COSTS
TUBING
THREADING
FIELD
TESTS
1
EXTENT OF
WALK-THROUGH
SIZES
SURVEY
* FUNCTIONS TO BE PER
BY OTHERS
'MODULE \
OF UNITS I
FIELD TEST)
h.
FEASIBILITY
CONCLUSIONS
j
(VuLL-SCALE
- FIELD
^ DEMONSTRATION^
OPERATING
UNKNOWNS,
FULL- SCALE
CONDITIONS
R^ J
GENERAL I
APPLICATION 1
FIGURE 2
PRESSURE SEWERAGE RESEARCH PLAN FOR ASCE COMBINED SEWER SEPARATION PROJECT
-------
that of alternative methods. Physical capability was understood to
include the hydraulic design of the system, the construction of the
pressure tubing and conduit system, the manufacturing and installation
of appropriate grinding and pumping equipment, and the establishment of
suitable maintenance facilities and staff.
The source of funds, local, State and Federal, was not considered
to be a factor in the evaluation of economic feasibility.
Authorization, Scope, and Content of the Report
The studies of sewer separation covered in the present report were
undertaken with the support of a contract with the Federal Water Pollu-
tion Control Administration of the Department of the Interior acting
through the Storm and Combined Sewer Pollution Control Branch, Division
of Applied Science and Technology, of its Office of Research and Develop-
ment. The work was performed under the legal authorization of Section 6
of the Federal Water Pollution Control Act ("Clean Water Restoration Act
of 1966," PL-89-753). The project, numbered 14-12-29 and titled
"Feasibility and Development of New Methods of Separating Sanitary Sewage
from Combined Sewerage Systems," was funded by a contract in the sum of
$343,210 awarded to the American Society of Civil Engineers on February
15, 1967, following an earlier and initial study under Demonstration
Grant WPD 104-01-66 dating back to February 1, 1966.
The project scope is indicated by the quotation below from the
FWPCA public information release.
"The project will determine the feasibility and applicability
of installing small pressure conduits within combined (storm-
sanitary) sewers as a means of separating sanitary sewage from
storm water. The conduits will be used to transport finely
ground sewage under pressure to interceptor sewers for con-
veyance to municipal treatment plants. It is anticipated that
the separation of sanitary sewage from storm water will reduce
the pollution load discharged to surface waters at system over-
flow points.
Combination grinder-pump units will be developed for both
household and some commercial uses to pre-condition wastes for
discharge into the pressure conduits "
The ultimate goal of the project was to develop feasible designs
and operations for the separation of combined systems of sewerage that
would abate the pollution of receiving waters from overflows of mixed
sewage and storm water, and to put those measures to test by converting
existing combined systems, or suitable portions of existing combined
systems, into completely separated systems.
The present extent of combined sewerage and conditions requiring
remedial action have been discussed herein. Alternative methods to
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accomplish the separation of combined systems are briefly summarized in
the following section.
As described in Section III, the ASCE "Combined Sewer Separation
Project" for the removal of sanitary sewage from combined sewers, was
based on pumping domestic sewage from all generating sources to inter-
cepting sewers through an independent system of tubing and pressurized
sanitary sewers while retaining the existing combined sewers as separate
storm drainage conduits that discharge only storm water to receiving
watercourses.
The details of grinding or comminution, storage and pumping are
explained in Sections IV through VII.
Sections VIII and IX contain the results of studies on the effects
of installing pressure tubing in existing building connections and
larger pressure conduits in street sewers; feasibility studies based on
introducing the proposed system into three existing combined sewer
districts, including required separation of existing building plumbing;
and pertinent non-technical considerations.
The advantages and disadvantages of the ASCE Project system are
evaluated in Section XII, together with the application of devices and
techniques developed under Project sponsorship to sewerage purposes
other than those of separation of combined sewers; possible application
of project equipment and techniques to sewers for the transportation of
solid wastes is discussed in Section XIII; and proposed tests of house-
hold storage-grinder-pump units in an installation involving a dozen
homes, and a projected large-scale field demonstration are described in
Section XIV.
The information from the study was reported initially in a series
of ASCE Combined Sewer Separation Project Technical Memoranda, and in
eleven technical reports, submitted to and approved for distribution by
the Project Officer, Contract No. 14-12-29, for the Federal Water Pollu-
tion Control Administration. These memoranda and reports are listed by
title in the Bibliography (Section XVI) as References 1 through 26,
inclusive. Appendix A contains abstracts of the technical memoranda and
Appendix B contains abstracts of the reports.
Opinion Survey
A survey of the eleven largest cities of the United States equipped
with fully-combined or partly-combined sewer systems was made in 1966 by
ASCE project staff engineers (Ref. 15) in consultation with city water
pollution control officials. The most frequent comments of these
officials can be summarized as follows:
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Complete, conventional separation of a combined sewer
system is a clearly definable objective only when the
combined sewers are of adequate capacity for at least con-
temporary storm drainage requirements. In several cities
extensive areas are served by combined sewers with inade-
quate storm drainage capacity. In many cases inadequacy
is based, in some degree, on the upgrading of design
standards since World War II. Land-use practices, not
anticipated when these sewers were designed, are major
contributing factors. In these instances the separation
of sanitary sewage is inextricably tied to storm-water
flooding relief.
Virtually all officials noted that, like conventional separation,
the ASCE Project scheme would not change the quality of storm water
discharged directly to receiving watercourses except for the non-
inclusion of bottom deposits traceable to the previous transport of
solids of domestic and industrial origin. It was noted that current
national interest in pollution abatement had extended from concern for
diversion of all sanitary sewage to treatment plants to include reduc-
tion in pollution from storm drainage.
The reservations of city officials about the efficacy of conven-
tional separation and directly comparable alternatives are echoed as
follows in Reference 35: "The separation of storm and sanitary sewers
has been recommended but recent evidence indicates that the contamina-
tion from streets, sidewalks, and city surfaces would make the runoff
from rains quite a pollutant to receiving waters, even if it did not
contain sewage. Therefore, the very expensive reconstruction of city
sewer systems would not yield comparable increases in quality in the
receiving water Evidence is now accumulating that the separation
approach would have very little benefit for the quality of receiving
waters even if it could be accomplished." Detention and treatment
basins for combined-sewer overflows are of paramount current interest
because they have the potential of reducing the pollution from overflows
at possibly much less attendant costs than the separation of existing
sewer systems.
Officials in one city were of the opinion that, little by little,
major cities are being rebuilt, separate sewers are becoming part of
nearly all new construction, and in another 50 years or so existing
combined sewer systems will have been largely eliminated. The virtue of
a crash program of sewer separation under the constraints of prevailing
and foreseeable land-use was therefore questioned.
Several officials recognized that the problems for which solutions
are being sought have not been adequately defined, that "more research
is needed to develop understanding of the whole storm water pollution
problem," and that "this research should cover the hydrology, the
hydraulics, the treatment, the effects on recovery waters, and related
factors." (Ref. 36).
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Although some officials conceded that feasible and acceptable
methods and devices might be developed for introducing pressure conduits
into walk-through size combined sewers (about 54 in. in height or larger),
firm reservations were expressed on the introduction of pressure conduits
into smaller sewers. Development of suitable installation techniques was
considered a formidable problem, but objections were directed more specif-
ically to difficulties of maintenance, repair, and replacement of such
systems. Included in particular, was the possibility that inserted
conduits or tubing would aggravate the accumulation of debris; that the
intruding services would interfere with free movement of sewer cleaning
devices; and that conduits, tubing, and connections would not be conve-
niently accessible for repair, for the connection of new building services
and for the inevitable long-term replacement of necessary parts of pres-
surized systems. Although major skepticism was voiced in regard to
pressure conduits in non walk-through sewers, there was opposition also
to the presence of 3/4-in. to 1 1/4-in. I.D. plastic tubing in a building
sewer because it would accentuate clogging by roof debris and interfere
with the operation of cleaning devices and the cutting of tree roots.
There was concern about ownership of necessary storage-grinder-pump
units, the relative merits of municipal versus private ownership, the
attainability of adequate home-owner acceptability and related aspects of
equipment maintenance and necessary provisions for overloading conditions.
Prevention of backflow into buildings and protection against overflow from
household storage-grinder-pump units during power outages was a major
consideration.
On the basis of cost estimates covering ten of the cities, projected
to the requirements of the United States as a whole, tentative estimates
for conventional separation of combined sewer systems were as high as $100
billion, including allowance for debt service.
Accounts of other surveys are contained in Ref. 37 by Gannon and
Streck, 1967.
An indication of the relative length of various combined sewer size
ranges is given in Technical Memorandum No. 4, 1967, Ref. 4. An average
of about 15% of the total combined sewer mileage in major cities is
54-in. in height or larger, generally -considered to be the walk-through
size range. This percentage is apparently even smaller for cities with
a population of 100,000 or less.
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SECTION III
ALTERNATIVE METHODS OF REDUCING POLLUTION
FROM COMBINED SEWER OVERFLOWS
Introduction
That plans for protecting receiving waters against pollution by
overflows from combined sewers connected to interceptors take many
forms, is shown by the extensive bibliography included in this report.
The currently most promising measures of control are discussed
briefly in the present section. Some of them are complete within
themselves; and others must be fitted into related schemes. In many
instances, moreover, different measures may be most suitable for indi-
vidual sub-areas of existing sewer systems, the choice of measures
depending on the type of development, the topography of the community
and the many other factors entering into the design of effective drain-
age schemes.
Complete Separation of Existing Combined Systems
The designer is offered the following two choices for the separa-
tion of existing fully combined sewer systems that are connected to
interceptors:
1. Conversion of all or part of the existing scheme into a storm
water system and addition in toto or in part of a complementary system of
sanitary sewers. Normally this will require the retention of existing
catchbasins as storm water inlets and the separation of existing roof and
yard drains from house drainage piping and their connection to the storm
water system.
2. Conversion of all or part of the existing scheme into a sani-
tary sewer system and addition in toto or in part of a complementary
system of storm water sewers. Normally this will require the retention
of existing house sewers and the separation of roof and yard drains from
the house drainage piping and their connection as well as that of catch-
basins or street inlets to the storm water system.
Choice will be determined by the projected relative effectiveness
and cost (1) of the existing system as a storm water or a sanitary sewer
system and (2) of the added complementary sanitary sewer or storm water
system. Either choice is referred to as traditional, common or conven-
tional separation.
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Many existing systems are composed of (1) combined systems gener-
ally constructed before the turn of the century and serving the older,
downtown, or core areas of the community and (2) separate systems
generally constructed after the turn of the century and serving the
newer, peripheral, or suburban areas of the community. In partially
separated systems of this kind, the sanitary sewers are normally con-
nected to regional or zonal mains that terminate in the interceptors or
outfalls of the existing combined but intercepting system.
Construction of the separate portions of sanitary or storm water
sewers (1) would entail excavation and repaving in nearly every street
and circumvention of existing utilities and subways, and (2) would
result in massive interference with traffic and the movement of pedes-
trians and often, too, in substantial business losses.
If it is completely accomplished, either method of separation of
existing combined systems or combined portions of existing systems
would eliminate, within the limits of the capacity of the intercepting
system, all overflows of municipal and industrial wastewaters to
receiving waters. Estimated costs of separation are given in Section IX
for three comparative studies of conventional separation on the one hand
and the ASCE project scheme on the other hand.
Partial Separation of Existing Combined Systems
Partial separation of storm water flows from combined systems by
the addition of a storm water system to the existing combined sewer
system which is retained in operation, is a less expensive but under-
standably also less effective alternative to complete separation.
Auxiliary storm water conduits are built to intercept storm runoff from
street and large paved surfaces, such as parking lots, before the run-
off can reach the inlets to the existing combined system. The demand
on the combined system is thereby reduced by diversion of readily
separable surface runoff to local watercourses and lowers the frequency
of occurrence and duration of flow rates in excess of interceptor capa-
city. Partial separation is sometimes employed as a means of enlarging
the storm flow capacity of sewers in areas where existing combined
sewers have proved inadequate for rainfalls of frequent occurrence.
How beneficial partial separation of this kind can be is deter-
mined by the capacity of existing components of combined and intercepting
sewers. The supplemental storm water system normally relegates con-
struction of large-sized additional pipes to busy downtown streets, and
incurs the associated difficulties of construction, disruption of normal
community life, and possible financial losses. At the penalty of
reduced effectiveness, building plumbing is not separated from the
remaining combined system in this scheme of partial separation.
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Retardation or Storage of Interceptor Overflows
The provision of off-system and intra-system storage reservoirs,
holding tanks, or retardation basins that reduce peak rates of runoff
to acceptable values in conjunction with existing capacities of inter-
cepting sewers creates another method of overflow control. Storage may
be provided (1) in upstream reservoirs, including temporary ponds within
playgrounds or other open areas that withhold storm waters from the
combined system, (2) in oversized conduits within the combined sewer
system, and in retention, detention, or retarding reservoirs or tanks
towards the downstream end of the system, often preferably near existing
storm water outlets.
Downstream storage lying between low- and high-water levels of the
combined sewers, is normally intended to return accumulating volumes of
wastewater to the combined sewer system or to the interceptors after the
rate of runoff has diminished to a level at which stored volumes can be
released in gravity flow from the tanks. Waters stored below the water
levels of the combined sewer system or interceptors must be returned by
pumps to the system for treatment. Necessary storage tanks are useful
only when available treatment facilities are large enough, or when they
can be enlarged to provide required treatment of the accumulated masses
of water between storms, in addition to the normal dry-weather flows of
sewage.
Holding or standby tanks have been in use for many years at
Columbus, Ohio, and are being built in New York City and elsewhere. At
Detroit, Michigan, stormflows being metered and dispatched within large-
sized pipes offer an example of the utilization of intra-system storage.
The so-called deep tunnel systems being studied and cautiously imple-
mented at Chicago, and being recommended for the Boston area, provide
very large volumes of storage.
As an alternative or augmentation to the kinds of storage cited,
storm water can be diverted to groundwater by means of various land
treatment methods and by groundwater disposal wells and basins.
Treatment of Overflowing Waters
Overflow discharges can be treated partially or completely before
they are ejected to receiving waterways. Treatment can be provided at
individual outlets, at interconnected groups of outlets, or at central
locations. The number of treatment plants will vary accordingly.
Depending upon the required degree of treatment, overflows might be
screened for the removal of coarse and unsightly particles, disinfected
for the destruction of pathogens, settled for the removal of fine sus-
pended solids, etc. Required treatment facilities would often lie in
heavily built-up high-value areas, historically located near water-
courses. Plant capacities must be large enough to receive and treat
the flows at expected and definable peak rates of outflow in concordance
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with flood-routing procedures, taking into account the attenuation of
peak flows afforded by storage.
The capacities of the combined sewers must be inherently suffi-
cient, or rendered so by the provision of adequate relief capacity.
Practically all the mixed sewage and storm runoff must normally be
carried to the points of treatment. Upstream overflows can normally
not be tolerated. Crews and equipment must generally be on stand-by,
and maintenance is normally a routine item of continuing expense.
Required conduits as well as treatment works must be capable of con-
veying storm flows from the collection system at peak rates of discharge,
They, too, may be in the high-value congested areas of municipalities.
Planned or inadvertent interconnections between district sewer systems
may add to difficulties of design and operation.
Other Alternatives for Reducing Pollution by Overflows
Among other alternatives of reducing the pollution of watercourses
that are the recipients of overflows are: (1) segregation of trunk
sewer flows by construction of pipes within pipes as has been done
experimentally at Minneapolis, where large combined sewers provided
excess storm water capacity; (2) reduction of sludge volumes subject to
scour by storm water flows through the systematic flushing of combined
sewers in dry weather, provided that interceptor capacity is large
enough to transport the scourings to the treatment works; (3) addition
of coagulating polyelectrolytes to mixed flows and disinfection within
combined sewers; (4) separate treatment of domestic and industrial
sewage flows at the source, followed by discharge of treated effluents
to the combined sewers; and (5) reduction of friction losses in inter-
ceptors by the addition of polymers, thereby increasing their flow
capacity.
Other provisions include: (1) the storage of wastewater flows in
large combination rubberized fabric and steel tanks submerged in
receiving waters at shoreline outlets as at Washington, D.C., and
Cambridge, Maryland; (2) the storage of flows in enclosed portions of
lakes, as at Cleveland, Ohio, and Syracuse, New York; (3) reduction of
dry-weather as well as wet-weather overflows from combined sewers by
better organization for efficient and effective maintenance of existing
sewage regulators, design of improved regulators for more effective
action and easier maintenance, and monitored and remote operation and
control of regulators, as at Minneapolis and St. Paul, Minnesota; and
(4) elimination of discharge of mixed flow of sewage and storm water
from combined systems to local receiving waters by relocation of over-.
flow outlets, involving their extension to points where large volumes
of diluting water are available, as at Boston, Massachusetts, where an
off-shore outlet beyond the limits of the outer harbor is under study.
- 22 -
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ASCE Combined Sewer Separation Project
The foregoing discussion of separation methods currently under
investigation have been presented as background information on the need
and urgency of developing economical and effective methods for preventing
the pollution of local watercourses and other receiving bodies of water
by overflow discharges from existing combined sewers.
To these methods the present section adds a discussion of the ASCE
Project, which is examined with a view to its ability to effect the same
degree of separation as the conventional method without the construction
of the new pipes and attendant trenching of streets of the cities and
other disruptions, as well as costs.
The ASCE Combined Sewer Separation Project to study and make
recommendations to the Federal Water Pollution Control Administration
"on the feasibility and development of new methods of separating sani-
tary sewage from combined sewer systems," looks to complete separation
of sanitary sewage and storm water at their sources by the use of
storage-grinder-pump equipment in advance of discharging the ground and
pressurized building flows through pressure tubing and conduits, where
possible within existing building and street sewers.
The general concept of the Project is to pump minutely subdivided
sanitary sewage from individual buildings and building groups through
relatively small tubing inserted into existing building drains and
sewers (the pipe within a pipe system) or laid parallel to building
drains and in separate trenches adjacent to building sewers. The tubing
connects to pressure conduits suspended in or laid parallel to existing
street sewers, and thence into existing intercepting sewers that convey
the separated sanitary sewage to treatment works.
Storm water alone is carried in the system of pipes that originally
served as combined sewers and is discharged as such into available water-
courses. Existing gravity building sewers remain available for transport
of roof and similar storm and subdrainage flows to the street sewer (now
a storm water drain) in the cross-sectional area of the gravity building
drain and building sewer not occupied by the pressure tubing.
The ASCE Project scheme is based on Professor Fair's concept of a
system composed of: (1) individual building tanks, grinders and pumps;
(2) pressure tubing inserted in building drains and sewers; and (3)
pressure piping laid within the street sewers and leading to the
existing interceptors of the drainage system.
Because of the difficulty of inserting tubing through building
traps where these are required; through sharp bends where they exist;
and through cracked and offset pipe lengths and other possible obstruc-
tions in existing building drains and sewers; and because no methods
were developed for joining tubing and conduits within small-sized
combined sewers without extensive excavation, alternatives to the
- 23 -
-------
original concept were studied. To this purpose small combined sewers
were taken to be those of less than walk-through height which was
assumed to be 54-in. Alternative piping consisted of (1) tubing in-
serted in a building sewer as far as an obstruction and laid thence in
a trench to the street main; (2) tubing laid all the way from a building
to the existing street main in a trench; or (3) tubing extending from a
building to a pressure conduit in the street independent of any existing
sewer. Such independent conduits might be laid in trench beneath the
sidewalk or at the gutter line on one or both sides of the street.
It was considered that the following functions should be accom-
plished:
1. Interception of domestic or industrial wastewaters at the
source to remove them from combined piping. This would be effected by
excluding storm or related runoff from the building plumbing system.
Generally this would be effected at the principal horizontal run of
pipe or pipes in the building basement.
2. Discharge of the intercepted flow from the building to the
street pressure sewer through pressure tubing. This would be effected
by storage-grinder-pump (SGP) household units for domestic flow rates
from individual dwelling units and by comminutor-pump installations for
larger installations. Solids must be reduced in size and stringy and
rubbery materials must be chopped up to permit their passage through
pumps, valves and tubing and to prevent the accumulation of deposits in
storage tanks, and in tubing and other pressure conduits.
3. Collection of the sewage flows in a separate street pressure
sewer system, and transmission to the existing intercepting sewer. This
can be effected by the pressure conduit system studied if pressure-
control valves are installed at the interceptors and perhaps at other
points within the system. Collection may require auxiliary lift
stations and control valves.
If the pressure system is to function reliably its piping must
remain free of stoppages and its mechanical and electrical components
in terms of pumps, grinders or comminutors, and valves must operate
without trouble. The household unit must be provided (1) with a device
that will prevent back-flow from the pressure system when the pump is
not operating or is out of service, and (2) with an overflow outlet to
the existing building drain or sewer or with an adequate alternative
appurtenance for the emergency discharge of sewage to the storm water
system. To safeguard the storm system against sewage entering the
system because of equipment failure, and to give warning of failure, an
economical signal device of some sort would be of advantage. The system
must be easily maintained and repaired and its parts must be rapidly
replaced.
Separation of plumbing systems is discussed in Section X.
Grinding, storage, and pumping for small residential and commercial flow
- 24 -
-------
rates are discussed in Section V and for larger residential, commercial
and industrial flows in Section VI. The insertion of pressure tubing,
installation and suspension of conduits, and general arrangement of
collection systems are discussed in Section VII.
Because of the lack of experience with pressure systems and limited
precedent for accomplishing needed functions, other than the grinding of
garbage in kitchen units, research was undertaken in the following areas:
1. Grinding and pumping domestic sewage at low rates of production.
2. Threading tubing into and through small-sized pipes such as
building drains and sewers.
3. Suspending pressure conduits in sewers during times of low flow
or temporary periods of removal from service.
4. Determining the magnitude of maximum and minimum rates of flow
from households and groups of households.
5. Solving hydraulic problems associated with pumping liquids
containing sewage solids in a collection system, as contrasted to clear
water in a water distribution system.
The Project staff conducted research on all phases of the project,
with the assistance of interested engineers and others, many of whom
were not reimbursed. Specific examples of non-reimbursed assistance are
as follows:
1. Comminuting and pumping: FMC Corporation, Chicago Pump-
Hydrodynamics Division, Chicago, 111.
2. Hypothetical applications to existing sewer systems: Public
Works Departments of San Francisco, Cal., Milwaukee, Wis., and Boston,
Mass.
3. Plans and arrangements for pressure tubing insertion and
connection to pressure conduit in field trials: Department of Sanitary
Engineering, Washington, D.C.
4. Flow and pressure control valves: BIF Division of the General
Signal Corporation, Providence, R.I.
5. Plans and arrangements for field suspension of pressure conduit
in walk-through sewer: The Metropolitan Sanitary District of Greater
Chicago, 111.
6. Distribution of combined sewer size categories in major cities:
Portland Cement Association, Chicago, 111.
- 25 -
-------
7. Magnitude and range of variations in rates of sewage flow.
Department of Environmental Engineering Science, The Johns Hopkins
University, Baltimore, Md.
Research was also conducted under contract with equipment manu-
facturers, research organizations, and consultants in specific phases
of the project, as follows:
1. Grinding, storing and pumping, and back-flow prevention:
General Electric Company, Water Management Laboratory and Major
Appliance Laboratories, Louisville, Ky., and Research and Development
Center, Schenectady, N.Y.
2. Hypothetical applications to existing sewer systems: Brown
and Caldwell, San Francisco, Cal., Greeley and Hansen, Chicago, 111.,
and Camp, Dresser and McKee, Boston, Mass.
3. Pressure tubing insertion, connection to pressure conduit and
overall conduit system: National Sanitation Foundation, Ann Arbor,
Mich.
4. Minimum solids transport velocities in pressure conduits:
FMC Corporation, Central Engineering Laboratories, Santa Clara, Cal.
5. Hydraulics of flow in eccentric annular conduits: Department
of Theoretical and Applied Mechanics, University of Illinois, Urbana,
111.
6. Magnitude and range of variation in rates of sewage flow:
Water Management Laboratory, General Electric Company, Louisville, Ky.
7. Pressure conduit hanger system for walk-through sewers:
Research and Engineering Center, Johns Manville Corporation, Manville,
N.J.
- 26 -
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SECTION IV
RESIDENTIAL AND COMMERCIAL SEWAGE FLOWS*
Introduction
Fundamental to the design of pressure house-connections and
pressure street sewer conduits for the ASCE Combined Sewer Separation
Project is reliable information on (1) rates of discharge of sewage
from individual households, small groups of households, and commercial
and individual sources in pressure-sewer laterals; and (2) concurrent
aggregate rates of flow from pressure-sewer laterals to pressure-sewer
branches and mains.
Data of this nature must be known with greater precision than for
gravity piping systems because velocities in the pressure piping must
(1) be above the minimum velocities at which excessive deposition of
solids takes place at least part of each day and (2) not be excessive at
peak flows if pressure-loss gradients and pumping heads within the
capabilities of the units selected are to be maintained. By contrast,
gravity sewers, which are commonly designed to flow at maximum design
rates at 0.5 to 0.9 full depth, will accept higher flow rates without
being surcharged.
There is little information on rates of sewage flow from individual
households and commercial buildings, particularly for time intervals on
the order of a minute. As a substitute, practically all of the data
recorded and studied were water-supply demand-rates, based on the assump-
tion that departures from true rates of discharge because of storage
effects in household supply and drainage systems are minor and can be
neglected, provided no substantial amount of water is diverted from the
drainage system. This is generally true in winter in northern latitudes
because little water is then used for watering growing plants, washing
automobiles, and air conditioning.
Information from Earlier Studies
Staff research engineers prepared a review of published and un-
published information on flows to or from households and small commercial
buildings. Special emphasis was placed on (1) information on water
demands observed for groups of up to 400 households and reported by the
Residential Water Use Research Project of the Johns Hopkins University
(Ref. 29), (2) winter quarter-year flows in ten county areas compiled
* Refs. 2, 8, 9, 19 and 20.
- 27 -
-------
by the U.S. Public Health Service Taft Center (Ref. 30), and (3) the
Farmstead Water Study of the U.S. Department of Agriculture for 11
individual households in the English Manor subdivision near Wheaton,
Maryland, north of Washington, D.C., covering about a month in 1964
(Ref. 31). English Manor data had been reduced to successive minutes
of use, from which peak flow demands were determined for two seven-day
periods in 6 of the 11 households.
Project Studies
A search for flow rates to be used in systems design was made by
the ASCE Project staff assisted by records of individual household water
demands monitored in 1966 and 1967 by the Water Management Laboratory of
the Major Appliance and Hotpoint Division, General Electric Company,
Appliance Park, Louisville, Ky. (Refs. 19 and 20). This investigation
was based on observations of water supply demand during a 4-week period
at 2 households in Louisville, Kentucky. Peak water demands for various
durations were determined.
Results of Project Studies
Fig. 3 shows for the USDA and G.E. observations the ratios of
daily household demands to mean daily household demands plotted against
the percentage of time a specific ratio was equalled or exceeded. From
extrapolation of an auxiliary semi-logarithmic data plot it was found
that the ratio of the daily to the mean daily demands would be on the
order of 2.4 an average of twice per year compared to a ratio of 2.0
for the recorded maximum value for both sets of observations. The ratio
of minimum daily demand to mean daily demand determined from the plot
was about 0.7 compared to recorded minimum values of about 0.4 for both
sets of observations.
For the USDA and G.E. observations Fig. 4 shows the ratios of
daily peak 60-minute household demands, to mean daily household demands
plotted against the percentage of time the ratio was equalled or
exceeded. From extrapolation of an auxiliary semi-logarithmic data
plot it was found that the ratio of daily 60-minute peak to the mean
daily demand would be on the order of 13 an average of twice per year,
a value in the neighborhood of the recorded maximum values for both sets
of observations.
Ratios of peak daily household demands to mean daily household
demands for shorter periods of flow were developed. The results for
daily, 60-minute, 15-minute and 4-minute periods are shown in Table 1.
To augment data for the design of pressure sewer laterals serving
more than a single household source, demands for groups of three and six
houses were analyzed using the USDA data. The results of these analyses
are shown in Fig. 5 and Table 1. Typical attenuation of peak ratios
with increase in number of services is evident.
- 28 -
-------
2.1
9
''**
•
I
i
Q
Q
O
I
7l-| RATIOS ARE FOR SAMPLE OF
en
*' GE DATA
>-
CURVE FOR RATIOS
< J5 1 * FROM INDIVIDUAL HOMES,
USDA DATA
j -*
1.3
<
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UJ
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cr
0.3
I
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X.
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g
bO.5
\
\
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«-
I I I i L
0 20 40 60 80 100
PER CENT OF TIME RATIO IS EQUALLED
OR EXCEEDED
FIGURE 3
VARIATION IN DAILY WATER USE (Modified from Fig. 2, Ref. 2)
- 29-
-------
(,i
17.0 •
16.0
oo
oV
12.0
10.0
• tn
13
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era
GE DATA
FIT TO USDA DATA
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6.0
4.0
2.0
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10
20 30 40 50 60 70 80
PER CENT OF TIME RATIO IS EQUALLED OR EXCEEDED
FIGURE 4
VARIATION IN PEAK HOUR WATER USE (Modified from Fig. 4,Ref. 2)
90
100
-------
TABLE 1
RATIOS OF HOUSEHOLD WATER DEMAND RATES FOR VARIOUS
PERIODS TO MEAN DAILY HOUSEHOLD WATER DEMAND RATES
Source
Individual
Households,
USDA & GE
Data
Groups of
Three Houses,
USDA Data
Group of
Six Houses,
USDA Data
Ratios for
Daily Demands
Maximum
Expected
an Average
of Twice
Observed Per Year
2.0 2.4
1.5 1.9
1.2 1.5
Minimum
Expected
an Average
of Twice
Observed Per Year
0.4 0.7
0.7 0.8
0.9 0.9
Ratios for
Peak 60-Min. Demands
Max imum
Expected
an Average
of Twice
Observed Per Year
11-17 13
5.8 7.9
3.9 5.5
Min imum
Expected
an Average
of Twice
Observed Per Year
2.0 4.0
2.0 2.8
2.0 2.6
Ratios for
Other Peak Demands
Peak Peak
15-min. 4-min.
Maximum Maximum
Observed Observed
22-24 31-46
"
-------
I
C.J
ro
i
12.0
Q
2 11.0
o
X
LU
I
o
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9.0
o 8.0
£ 7-o
o 6.0
5 5.0
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LU
a- z 4.0
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INDIVIDUAL HOME DATA - 84 OCCURRENCES
+ + + +3-HOME COMBINATIONS -28 OCCURRENCES
xxxxe-HOME COMBINATION • 14 OCCURRENCES
1
1
1
1
1
10
20 30 40 50 60 70 80
PER CENT OF TIME RATIO IS EQUALLED OR EXCEEDED
FIGURE 5
VARIATION IN PEAK HOUR WATER USE, COMBINATION OF SOURCES
(Reproduced from Fig. 3, Ref. 2)
90
100
-------
A typical or representative day of water usage data for one home
was selected. Average annual energy for pumping and grinding by a
household storage-grinder-pump (SGP) unit was estimated using this data
sample. The mass curve of inflow for the 24 hours of the selected
typical day is shown in Fig. 6 together with that for a critical day
that would place a severe loading on an SGP unit.
Combinations of storage volumes ranging from 20 to 30 gallons and
pump capacities from 6 to 10 gallons per minute (gpm) were tested for
adequacy against the most severe usage record, Fig. 6. Specifications
thereby tentatively selected for a household unit were a 10 gpm nominal
pumping rate and a storage of 30 gallons (Ref. 2). As the result of
later studies (Ref. 9) this nominal pumping rate specification was
increased to 12 gpm with 30 gallons of storage, and the unit finally
developed by the General Electric Company (Section V) had a usable
capacity range of 11 to 15 gpm with a tank of 44 gallons effective
volume, a more desirable combination than the minimum capability sought.
Flow Rates in Collection System
The design of pressure laterals and smaller branch pressure sewers
can be based on an analysis of cumulative rates from individual house-
hold units if suitable allowances are made for differences in time of
outflow from the individual units and time of flow from the sources to
the outlet. Outflows from storage-grinder-pump units for a group of six
households were routed through street sewers using as inflows the peak
demand day of the USDA data. Applying the principle of superposition,
routed flows summed over time at the outlet point of a hypothetical
pressurized lateral sewer serving six houses resulted in the following
values:
Gallons
per
Gallons Minute
Maximum rate -- 20
4-minute peak volume and rate 60 15
15-nvinute peak volume and rate 120 8
60-minute peak volume and rate 330 5%
Each household unit was assumed to have a constant pumping rate of 10
gpm, or a combined capacity for the six units of 60 gpm. In contrast,
above, the maximum rate at the outlet point was only 20 gpm. The
attenuation of peaks diminished with increase in duration, becoming
imperceptible for the 60-minute peak.
- 33 -
-------
400 i-
401
NOTE: CURVES BASED ON USDA
WATER USAGE DATA
WATER USAGE RECORD FOR "TYPICAL" DAY
300
CO
3
8
CO
200
I
UJ
1
Z>
^
100
WATER USAGE RECORD FOR DAY WITH
MOST SEVERE PERIOD WITH RESPECT
TO STORAGE-GRINDER-PUMP UNITS
1
12M
6 8 10 12N 2
HOUR OF DAY
FIGURE 6
MASS CURVES OF WATER USAGE
J
10 12M
SINGLE HOME
-34-
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Comparison of Per Capita Flows with Flows Based on Water Demand Ratios
Per capita water discharges were determined from an analysis of
Taft Center and Johns Hopkins University reports and are presented in
Table 2.
Assuming that the results are reasonably representative of pre-
vailing demand variations in different communities, estimated mean
winter water demands for up to 500 homes and estimated winter per
capita demands in terms of number of occupants per home may be in error
by + 30%. To be noted is that the entries in Table 2 are themselves
averages of a number of observations and thus obscure further variations
for individual homes and for year to year changes. For Santa Clara,
California, (Ref. 30), the following results were obtained;
No. Occupants Item Jan. Feb. Mar.
3 No. of Home-Months 35 35 35
Mean Use, gpcd 52 54 63
Standard Deviation, gpcd 20 17 30
5 No. of Home-Months 31 32 32
Mean Use, gpcd 41 44 45
Standard Deviation, gpcd 24 14 15
Changes in building occupancy over the projected design period of
sewer systems can be anticipated only subjectively. Mean annual domestic
demands might be projected with a reasonable degree of confidence for
expected future land-use, but the projections could be made realistically
only for whole blocks or sub-areas in a given system. Hence, it is
reasonable to conclude (1) that refinements in projections to account for
differences in demand related to expected numbers of occupants per home
would not be realistic, (2) that estimates of mean annual domestic
demands based on data from other communities would contain considerable
errors, and (3) that projection of such mean annual domestic demands to
the end of the design period would require acceptance of rather specious
criteria. Instead, it would appear preferable to project observed mean
annual domestic demands for the drainage area of the system to be analysed,
with the details available governing the attainable degree of refinement.
If the sewer system is served by a fully metered water system and meter
readings are suitable for direct use, acceptable estimates of mean annual
sanitary sewage flows can be obtained by employing water-demand meter-
readings for non-lawn-sprinkling months. Even though these may be
fairly reliable indicators of present sewage flows, their projection will
be subjective, and use of refinements, such as allowances for differences
in the number of occupants per dwelling, does not appear to be justified.
- 35 -
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TABLE 2
WINTER WATER DEMAND
(Reproduced from Table 1, Ref. 8)
Month*
State
(County)
2 persons
gpcd
gpcd**
3 persons
gpcd
gpcd**
4 persons
SPd
gpcd
gpcd**
5 persons
gpcd
gpcd**
6 persons
gpcd
gpcd**
Total No.
Homes:
Total
Record:
Taft Center Report
J-F-M
N.J.
(Bergen)
83
42
(61)
158
53
(52)
210
53
(48)
210
42
(45)
278
46
(44)
97
1955-60
J-F-M
Texas
(Dallas)
180
90
(100)
251
84
(81)
286
72
(71)
314
63
(65)
348
58
(61)
495
1955-59
J-F-M
Tenn.
(Knox)
102
51
(54)
133
44
(44)
152
38
(39)
169
34
(36)
191
32
(33)
90
1947-58
J-F-M
Calif.
(Santa Clara)
81
40
(60)
169
56
(54)
228
57
(50)
216
43
(48)
304
51
(47)
21
1949-57
J-F-M
N.C.
(Mecklenberg)
120
60
(62)
149
30
(49)
172
43
(43)
200
40
(39)
217
36
(37)
207
1950-58
J-F-M
Texas
(Nueces)
178
89
(74)
186
62
(54)
201
50
(44)
218
44
(38)
234
39
(34)
56
1948-53
Winter
Ten
Areas
142
71
(71)
178
59
(60)
232
58
(55)
262
66
(51)
292
49
(49)
21-495
Varies
Johns Hopkins
Winter Fit,
Pine Valley Five Areas
(Md.) (Md.)
70
(80)
72
(61)
52
(51)
39
(44)
(39)
120
1959-62 Varies
* : J-F-M = January, February and March.
**: From statistical fits to data by Taft Center.
-------
It was assumed for the ASCE Project that presentation and usage
of data on residential demand variability from diverse communities
should preferably be in terms of variations about their respective
winter average domestic water demands.
Design Curves
Based (1) on data in a Johns Hopkins University report (Ref. 32)
for cities in the northeastern quadrant of the continental United States
and northern California and (2) on the data discussed earlier in this
section, curves for Northeastern United States and California were
derived from Tables 3 and 4 and are presented in Figs. 7 and 8. These
curves were used in the preliminary design of pressure sewers in studies
of hypothetical combined-sewer separation systems in two cities
(Section IX). (For further discussion of the application of these
curves see Section VII and Ref. 8).
USDA data (Ref. 2) for individual household winter water demands
were utilized as inflows to various sized tributary portions of the
hypothetical pressure sewer system for the Milwaukee Study Area (Ref. 17)
in an exploratory wastewater routing study (Ref. 14). The results
indicate: that the rate of attenuation with number of dwelling units of
the upper curve in Fig. 7 is reasonably realistic; and that although
this curve was drawn as an envelope of the available data it lies defi-
nitely below a comparable curve for peaks of a few minutes duration
obtained from the routing study, and its use for determining expected
maximum hydraulic gradients in the Milwaukee Study Area system was
therefore not particularly conservative.
Flows from Commercial Buildings
There is little information other than that in Refs. 18 and 33 on
flows from commercial buildings, such.as hotels and restaurants. The
Commercial Water Use Research Project, (Ref. 33), provides some data on
flows from individual buildings for 42 business establishments in
Baltimore. However, there would be considerable difficulty in inte-
grating this information into the use of Figs. 7 and 8 for areas of
mixed residential and commercial development.
Design ratios for peak hour demands proposed in the Commercial
Water Use Report are as follows:
- 37 -
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TABLE 3
NORTHEASTERN U.S. VARIATIONS
IN DOMESTIC WATER DEMAND
(Reproduced from Table 2, Ref. 8)
Northeastern U.S.,
Location/Area
Des Moines, la.
Patricia Park
Clive
Wash. Sub. San Dist.
Palmer Park
Glenmont
English Manor
N.W. Branch Est.
Baltimore, Md.
Country Club Park
Pine Valley
Campus Hills
Hampton
Philadelphia, Pa.
Normandy
Benton St.
Phila. Suburban
Downeast
St. Albans
Dogwood Lane
English Manor-U.S.D.A.
(From Ref. 2)
No. of
Dwelling
Units
325
307
395
129
309
124
289
210
179
44
410
200
287
137
113
(1)
(3)
(6)
Winter Rates (Dec., Jan. and Feb.)
Gal. /Day /Dwell ing Unit
(a) (b) (c) (d) (e)
Avg. Min. Max. Peak Peak
Hr. of
Min.
Annual Daily Daily Hourly Day
182 (167) 242 425 (354)
165 (162) 195 405 (275)
175 (171) 219 431 (273)
173 (176) 216 409 (298)
224 (190) 276 536 (482)
262 (274) 290 542 (542)
189 (154) 243 442 (367)
204 (148) 272 555 (326)
251 (249) 323 602 (471)
157 (133) 216 457 (277)
220 (262) 331 595 (407)
252 (182) 303 565 (413)
m__ O f. O /. *7 -7
ZOZ *f / /
195 (166) 242 596 (356)
228 (188) 322 713 (380)
Ratios
(b) (c) (d) (e)
* • • •
(a) (a) (a) (a)
(0.92) 1.33 2.34 (1.95)
(0.98) 1.18 2.45 (1.67)
(0.98) 1.25 2.46 (1.56)
(1.01) 1.25 2.36 (1.72)
(0.85) 1.23 2.39 (2.15)
(1.04) 1.11 2.07 (2.05)
(0.82) 1.29 2.34 (1.94)
(0.73) 1.33 2.72 (1.59)
(0.99) 1.29 2.40 (1.87)
(0.85) 1.38 2.91 (1.76)
(1.19) 1.50 2.70 (1.85)
(0.72) 1.20 2.24 (1.64)
(0.85) 1.24 3.06 (1.82)
(0.82) 1.41 3.13 (1.66)
0.40 2.40 13.0 2.0
0.70 1.85 7.9 2.0
0.87 1.45 5.5 2.0
No.
Full
Days
of
Data
106
33
13
11
28
2
39
225
163
90
53
32
(0)
44
131
- 38 -
-------
TABLE 4
CALIFORNIA VARIATIONS IN DOMESTIC WATER DEMAND
(Reproduced from Table 3, Ref. 8)
California,
Location/Area
East Bay
San Lorenzo
Creekside Acres
Burton Valley
Chabot Park
San Diego
( Rancho Hills
| R.H. Sewage
Ruff in Road
j Muirlands
( Muir. Sewage
Helix Irrig. Dist.
El Cajon
Lemon Grove
Cal. Water and Tel.
Minot Ave
Sacramento
Golf Course Terr.
.
No. of
Dwelling
Units
81
143
137
295
112
(110)
259
66
(71)
187
235
63
134
Winter Rates (Dec., Jan. and Feb.)
Gal. /Day /Owe 11 ing Unit
(a) (b) (c) (d) (e)
Avg. Min. Max. Peak Peak
Hr. of
Min.
Annual Daily Daily Hourly Day
233 (210) 452 1227 (386)
295 (214) 610 1635 (377)
282 (269) 474 1242 (559)
297 (253) 700 1665 (562)
215 (176) 294 705 (337)
(239) (135) (376) (754) (273)
234 (199) 377 1338 (374)
344 (265) 598 1547 (558)
(336) (243) (467) (846) (549)
194 (177) 322 912 (317)
223 (173) 379 924 (374)
150 (126) 335 940 (256)
248 (285) 559 1090 (479)
Ratios
(b) (c) (d) (e)
(a) (a) (a) (a)
(0.90) 1.94 5.27 (1.66)
(0.73) 2.07 5.54 (1.28)
(0.96) 1.68 4.40 (1.98)
(0.85) 2.36 5.61 (1.89)
(0.82) 1.37 3.28 (1.57)
(0.59)(1. 64)(3.28) (1.19)
(0.85) 1.61 5.72 (1.62)
(0.77) 1.74 4.50 (1.62)
(0.72)(1.3S)(2.52)(1.64)
(0.91) 1.66 4.70 (1.63)
(0.78) 1.70 4.14 (1.68)
(0.84) 2.23 6.27 (1.71)
(1.15) 2.25 4.40 (1.93)
No.
Full
Days
of
Data
180
151
88
76
151
171
75
168
80
35
166
77
15
__^_
- 39 -
-------
LU
Q
cr ^
LU
CJ
LU
^
O
Q
< 5
j
§4
cr
LU
o
Q_
O
+
A
+
-
O
o
o
^A^ "A^
O
O
CP
NORTHEASTERN U.S.
MIDDLE CURVE:
ASSUMED LOWEST PEAK HOURLY
MULTIPLE ON ANY DAY
UPPER CURVE:
ASSUMED MAXIMUM PEAK HOURLY
MULTIPLE ON ANY DAY
0Q0
A
fi
O
MAX. PEAK HOUR OF
ANY DAY(O)
o
PEAK HR. OF MIN. DAY_(jl-]_
~MA"X. "24~HR" (A") "
MIN. 24 HR. (O)
0
1
;
i
0
100 200 300 400 500 600
NUMBER OF DWELLING UNITS (SERVICES)
700
FIGURE 7
WATER DEMAND VARIATIONS, NORTHEASTERN U.S.
(Reproduced from Fig. 1, Ret.8)
-40-
-------
8
Q
LJ
Q
7
_
o
/
0
0
i
CALIFORNIA
MIDDLE CURVE:
ASSUMED LOWEST PEAK HOURLY
MULTIPLE ON ANY DAY.
UPPER CURVEl
ASSUMED MAXIMUM PEAK HOURLY
MULTIPLE ON ANY DAY.
cr
w
o ' °
\- 5
UJ
V y^»
O
. 4
<
UJ
<
cc
UJ
MAX. PEAK HOUR OF ANY DAY(O
A
PEAK HR. OF MIN. DAY(
V4..4- A A
MAX. 24 HR. (A)
A ? +
'I— r
_n _ (-
r> ^^^_ . MLN._24J1R.JUJ
J L
0 100 200 3OO 400 500 600 700
NUMBER OF DWELLING UNITS (SERVICES)
FIGURE 8
WATER DEMAND VARIATIONS, CALIFORNIA
(Reproduced from Fig.2,Ref.8)
-------
Type of Establishment Ratio of Peak-Hour
or Institution to Annual Water Use
High-rise apartments 2.6
Office buildings, general
offices less than 10 yr. old 3.6
Department stores 2.9
Commercial laundries and
dry cleaners 3.1
Conventional restaurants 3.6
Barber shops 4.4
Beauty salons 2.5
Compared with the upper curve of Fig. 7 for groups of homes, most
of these ratios are not particularly high. In a study of demands for a
hypothetical community of 100,000 persons with 28,000 dwellings, synthe-
sized from demand hydrographs in the Commercial Water Use Report,
including those for a representative number of institutions and commer-
cial establishments, the commercial demands for a typical winter day
(no lawn sprinkling) during the peak hour constituted only a fifth of
the total demands. Presumably the same relative magnitude would be
maintained approximately also for the peak hour of a year, provided
lawn sprinkling is discounted.
A copy of Fig. III-l from Ref. 18, "Relation of Extreme Discharges
on Maximum and Minimum Days to the Average Daily Discharge of Domestic
Sewage," similar to Fig. 5 in Ref. 34, is presented as Fig. 9 together
with Curve B from Fig. Ill-7 of Ref. 18, "Peak on Maximum Day" which was
used in the Summer Street Separation Study for Boston (Section IX).
Fig. 9 is based on observed sewer flows, corrected for infiltration, and
on water records, for municipalities and sectors of municipalities in
New England with mean domestic sewage flows of about 0.1 mgd or greater.
Fig. 7 does not include data for New England, Fig. 9 is for heterogeneous
land-occupancy and not for household flows alone, and hence Fig. 9 rather
than Fig. 7 was deemed appropriate for application to mixed-occupancy
areas in New England and was used in a study of a hypothetical combined-
sewer separation system in Boston (Section IX).
Comparison of Observed Sewage Discharges with Water Demands
Data on sewage flows from two household observation stations in
Louisville, Kentucky were obtained for the ASCE project by the Water
Management Laboratory of the General Electric Company. Discharges were
- 42 -
-------
CO TO *O «OKX>
I
<•
: ,1
:!
5
1
o
Q
5
1J
o
LEGEND
Rtloition of peak to average flow*
PEAK ON MAXIMUM
USED IN SUMMER
STREET SEPARATION
STUDY (REF. 18)
O Sewage flows of gaging points
Q Sewage flows at Nut Island Sewage Treatment Plant, Boston
A Sewage flows at seven MewYorhCily sewage treatment plants
+ Wafer consumption atJofcn Hancock Buildings ft the Prudential Plaza, Boston
MAXIMUM DAY
MAXIMUM 24 HR
AVERAGE DAILY DISCHARGE
MINIMUM 24 HR
r- -EXTREME MINIMUM ON
MINIMUM DAY
O.I .IS .2 .23 .3
Note: Infiltration not Included
.9 .« .7 .• .• 1.0 1.3 2 Z-3 » 4 3 « T • • 10
AVC1A6C DAILY DISCH«N«! OF OOMCSTIC SCWACC-MCO
TO 8090KX)
FIGURE 9
RELATION OF EXTREME DISCHARGES ON MAXIMUM AND MINIMUM DAYS TO THE AVERAGE
DAILY DISCHARGE OF DOMESTIC SEWAGE (Reproduced from Fig. HI-1 of Ref. 18)
-------
measured at the individual pump installations by observing displacement
in the wet well and length of operation of the constant discharge pump.
Allowances were made for periods during which flows were bypassed. The
observations covered a period of about two months.
Comparisons of sewage discharged with water supplied, due allow-
ance being made for storage in the system and the pump wet well, agree
closely, indicating that water demand rates can be safely substituted
for rates of sewage outflow.
Unit Fixture Discharge Rates
The ASCE Project staff studied unit fixture discharge rates
obtained from the G.E., Louisville data (Ref. 19), in order to synthe-
size composite hydrographs for refinement of pump capacities and
associated storage requirements. Fig. 10 shows a composite hydrograph
based on superposition of component 1-minute flows in comparison with
a mass curve of observed flows for fixtures including a toilet, a shower,
and a washing machine. The synthesized composite discharge pattern
appears to represent reasonably the household sewage discharge, and it
seems that the method of superposition of flows can be applied safely.
Table 5 indicates the volumes of storage used in a storage-pump-
grinder unit for synthesized hydrographs of flow from three combinations
of fixtures and a constant pump discharge of 13 gallons per minute (gpm).
The fixture combinations are as follows:
Combination Fixtures included
I Toilet, washbasin, bathtub, kitchen
sink, dishwasher, and clothes washer
II Same as I, plus a second toilet and
washbasin
III Same as II, plus a third toilet and
washbasin.
Table 5 shows that storage capacity needed to accommodate flows
from the assumed combinations of fixtures is determined by sewage flows
that would occur during the first three minutes or so of the maximum
flow period. According to similar synthetic hydrograph calculations,
for pump capacities of 10 and 15 gpm, 26 and 18 gallons respectively
would have to be stored to accommodate the simultaneous flow of about
46 gallons in a 2-minute period from a bathtub and an automatic clothes
washer. The probability of simultaneous discharge of fixtures of this
kind is high.
- 44 -
-------
I
CJl
50
en 40
z
O
<
O
LJ
O
>
30
20
3 10
o,
NOTE: Composite curve constructed by addition of
individual fixture curves. Fixture curves
assume uniform rates of discharge
over 1 minute periods.
COMPOSITE
MASS CURVE
MASS CURVE OF FIRST 14 MINS.
OF TEST #8
WASHER-12.9 G.RM. x 2 MINS.
^SHOWER-1.25 G.PM.XI4MINS.
TOILET-4.5 G.PM. x | MIN.
TIME —
MINUTES
15
20
FIGURE 10
COMPARISON OF DISCHARGE FROM FIRST PART OF TEST *8, STATION A
WITH COMPOSITE DISCHARGE CURVE (DATA FROM REFS. 9 AND 19).
(Reproduced from Fig. 17, Ref. 9)
-------
TABLE 5
DETERMINATION OF STORAGE, FOR SYNTHETIC HYDROGRAPHS,
PUMP DISCHARGE RATE OF 13 GPM
(Reproduced from Table 16, Ref. 9)
Volume, Gallons
Time (minutes):
Combination I
inflow
Into storage,
inflow less
pump discharge
Total in storage
Combination II
inflow
Into storage,
inflow less
pump discharge
Total in storage
Combination III
inflow
Into storage,
inflow less
pump discharge
Total in storage
123
45.5 14 5
4
8.
32.5 1 -8 -4.
32.5 33.5* 25.5 21
(* Maximum
50.5 15 10
37.5 2 -3
37.5 39.5* 36
9.
-3.
.5 33
(* Maximum
55.5 16 15
42.5 3 2
42.5 45.5 47
10.
-2.
.5* 45
5
5 5
5 -8
13
Storage
5 10
5 -3
30
Storage
5 15
5 2
47
6
1
-12
1
Used
2
-11
19
Used
3
-10
37
(* Maximum Storage
7
10.5
-2.5
-33.5
15.5
2.5
21.5
- 39.5
20.5
7.5
44.5
Used
8 9 10 11
35 6.5 5
-10 -8 -6.5 -8
gallons)
4 10 7.5 10
-9 -3 -5.5 -3
12.5 9.5 5 1
gallons)
5 15 8.5 15
-8 2 -4.5 2
36.5 38.5 34 36
- 47.5 gallons)
12 13
1 10.5
-12 -2.5
2 15.5
-11 2.5
2.5
3 20.5
-10 7.5
26 33.5
I
•p-
-------
Storage Volume and Minimum Required Pump Rate
Table 6 lists the rates of fixture discharge and synthesized rates
of flow for Combinations I, II, and III and Table 7 gives the storage
volumes computed for the three synthesized household loading conditions
for pumping rates from 8% to 16 gpm. The relation between required
storage and pump capacity for the synthesized inflow sequences is shown
in Fig. 11.
The storage volumes and minimum pump discharge rates in Fig. 11
should be considered extreme upper limits. Underlying frequencies,
durations, and rates of fixture use are deliberately conservative. The
only ordinary discharges that the given storage volumes are not designed
to accommodate are those of the second bathtub in a two-bathroom house
or those of the second and third bathtubs in a three-bathroom house
during the first 5 minutes of the maximum discharge period. Storage
requirements for Combinations II and III are not affected by the dis-
charge of one extra bathtub after 6 minutes or more from the beginning
of the maximum flow period. However, the associated available storage
at the end of the maximum discharge period is significantly reduced.
The hydrographs do not include flows caused by extraordinary discharges
of fixtures such as (1) leakage from a defective toilet-tank outlet-
valve assembly, and (2) discharge of a hose into a basement floor drain.
The possibility of such flows during a period of maximum discharge is
discounted because a toilet discharging in this manner would not operate
also as asuumed in the fixture combinations; and because the occupants
of a house containing a storage-pump combination would presumably be
aware of the need to exercise some control over extraordinary discharges,
Suggested Measurements
Future tests should include the measurement of flows from individual
households, groups of households served by single laterals, and pressure
sewers in districts serving many contributors. The measurements should
be made in as much detail as possible, in order to serve as sources of
information for the modification of design data. The characteristics of
sewage entering and discharged from the pressure system should be deter-
mined to ascertain the effect of the system on the sewage discharged to
the intercepting sewer system for treatment, permitting further refinement
of pressure-sewer design.
- 47 -
-------
TABLE 6
MEAN RATES OF DISCHARGE OF INDIVIDUAL FIXTURES
AND SYNTHETIC "MINIMUM" DISCHARGE RATES
FOR FIXTURE COMBINATIONS
(Reproduced from Table 17, Ref. 9)
Fixture or Combination
Toilet
Basin
Bathtub
Sink
Clothes Washer
Dishwasher
Combination I
Combination II
Combination III
Rate
GPM
5
1
20
5.5
13
12
--
—
--
Duration
minutes
1
1
1
1
2
over
--
—
••—
Frequency
minutes
2
2
15
3
13
33 mins .
--
—
" ™
Mean
Discharge
GPM
2.5
0.5
1.3
1.8
2.0
0.4
8.4
11.4
14.4
TABLE 7
SYNTHESIZED STORAGE-PUMP COMBINATIONS
(Reproduced from Table 18, Ref. 9)
Pump Discharge Rate (GPM) :
1 Bathroom House
1^ or 2 Bathroom House
2% or 3 Bathroom House
Storage Volume in Gallons
for Given Pump Discharge Rate
8.5 10 11.5 13
42.5 39.5 36.5 33.
42.5 39.
14.5
5 31.0
5 36.5
43
16
29.5
34.5
39.5
- 48 -
-------
70
60
CO
2
O
_J
_J
o
50
40
30
LU
O
or
P
CO
Q
LU
or
Z)
S 20
or
10
0
0
--3 BATHROOMS
^-2 BATHROOMS
1 BATHROOM
__Min_imum Pump Capacities Required
to Accomodate Recurrence of Peak Flow
X Reference 2
® Station B
® Station A
1
5 10
GALLONS/MINUTE
PUMP DISCHARGE RATE
15
FIGURE 11
STORAGE-PUMP COMBINATIONS TO ACCOMMODATE SYNTHETIC INFLOWS
(Reproduced from Fig. 21, Ref. 9)
-49-
-------
SECTION V
EQUIPMENT FOR STORING, GRINDING AND PUMPING SEWAGE
FROM RESIDENTIAL AND OTHER SMALL SOURCES*
Introduction
A prototype of the storage-grinder-pump household unit (SGP) was
developed in 1967-1968 by the Research and Development Center of the
General Electric Company, at Schenectady, N.Y. under subcontract with
ASCE as part of the Combined Sewer Separation Project.
Performance Requirements
Initial requirements, modified somewhat during the period of
development, were based on: experience with mock-up units at observa-
tion stations at two households in Louisville, Ky., Refs. 19 and 20;
and research reported by the ASCE Project staff, especially Refs. 2, 6,
8 and 9. The established requirements follow.
For a storage-grinder-pump unit serving a single residence, the
probable required effective volume of the receiving tank lies between
30 and 45 gallons and the pump discharge rate between 10 and 15 gallons
per minute (gpm), as is explained in the previous section.
The target range of pump discharge head was 0 to 35 pounds per
square inch above atmospheric pressure (psig). In order to maintain
pressurization of the sewerage system at all times, the minimum curb
pressure criterion was set at 0 psi, requiring a typical minimum SGP
unit discharge pressure of approximately 0 to 5 psig. The maximum
economical curb pressure was initially assumed to be 30 psi, requiring
a typical maximum SGP unit discharge pressure of 30-35 psi.
The grinder should be capable of reducing solids introduced through
household plumbing fixtures to sizes clearing the pump spaces, the check
and pressure control valves, and the pressure tubing. Controls and
mechanical equipment should be completely reliable, need little mainte-
nance and repair, and be low in purchase price and cost of installation.
For household flows beyond the capacity of a single SGP unit, it
was assumed that two or more units would be installed in parallel and
provided with a larger discharge line to the pressure sewer in the street.
As an alternative, an enlarged unit might be developed with a greater
capacity if the 11 to 15-gpm prototype is found to work well in practice.
* Ref. 21.
- 50 -
-------
The General Electric Household SGP Unit
The SGP unit developed by the General Electric Company is shown
in a cut-away sketch in Fig. 12; and is pictured in Figs. 13, 14 and 15
(Figs. 1, 6 and 20 of Ref. 21). The characteristic curves of the
progressing-cavity type pump (Moyno, Model FS-44, Robbins & Myers) are
shown in Fig. 16 (Fig. 15 of Ref. 21), and dimensions of the reinforced
concrete or steel receiving and storage tank are shown on Fig. 17
(Fig. 19 of Ref. 21). Specifications for the prototype storage-grinder-
pump unit are given in Table 8 (Table 5 of Ref. 21).
The SGP unit functions as a grinder, pump, and backflow preventer
in an integral assembly that can be installed in a receiving tank below
the basement floor or otherwise in line with the house drain. The inlet
connection attaches to standard 3-in. or 4-in. drain-waste-vent piping
in the plumbing system. Discharge piping is 1%-in. copper tubing con-
nected to polyethylene or other acceptable tubing outside the foundation
wall.
The single-phase electric wiring is designed to carry 230 volts
and 10 amperes or 115 volts and 20 amperes at 60 Hz. The pump and
grinder are driven by a 1 horsepower capacitor-start motor. The unit
delivers between 11 and 15 gallons per minute of finely ground sewage
slurry to the discharge tubing at pressures from zero to 35 psig. The
effective storage of the tank is 44 gallons.
Backflow is prevented by a special check valve, designed for
reliable operation in sewage containing ground solids such as bits of
string and fabric, small blocks of wood, gritty substances and fruit
rinds and pulps. The check valve has a low head-loss characteristic of
about 0.8-in. Hg (0.4 psi) for flows between 10 and 13 gpm.
Equipment Installation and Operating Costs
The General Electric Company estimates that without the receiving
tank the SGP unit can be manufactured in quantity at a wholesale price
of between $309 and $412 and a most probable price of $343 (December,
1968 price level). The Company estimates the cost of the installed SGP
unit locally purchased receiving tank and plumbing and electrical labor
based on prevailing price levels, at about $550 for new work and about
$650 for work requiring cutting and remodeling of existing house drainage
piping.
Operating costs of the SGP for a year, not including service
charges for maintenance and repair or replacement of parts, are estimated
by General Electric at $2 for energy costs of 1%-cents per K.W.H. and
power consumption of about 1-kw for a family of five and an average
sewage flow of 60 gallons per capita per day.
- 51 -
-------
Backflow
prevention
valve-
Electric
/"connection
Housing
Motor
Pump suction
pipe
Grinder
FIGURE 12
CUT-AWAY SKETCH OF HOUSEHOLD
STORAGE-GRINDER-PUMP UNIT
(Adapted from Fig. 5-1, Ret. 16)
-52-
-------
FIGURE 13
COMPLETED PROTOTYPE OF HOUSEHOLD
STORAGE-GRINDER-PUMP UNIT
(Reproduced from Fig. 1, Ret. 21 )
-53-
-------
FIGURE 14
GRINDER MECHANISM VIEWED FROM
BELOW THROUGH PUMP SUCTION BELL
(Reproduced from Fig.6, Ref. 21)
-54-
-------
FIGURE 15
CLOSE-UP VIEW OF COMPONENTS
ABOVE MOUNTING FLANGE
(From Fig. 20, Ret. 21)
-55-
-------
40
CD
CO
Q_
35
30
§ 25
UJ
I 20
<
z
>-
Q 15
10
0
56 7 8 9 10 11 12 13 14 15 16
Q-GPM, Pj-WATTS x 10~2, I-AMPERES AT 110 VAC
FIGURE 16
CHARACTERISTIC CURVES, PROTOTYPE SGP UNIT
(Reproduced from Fig. 15,Ref. 21)
- 56-
-------
T
5"
3"PVC-IDWV
90°STREET EL
(CAST IN PLACE WITH
HUB FLUSH AND
SPIGOT TURNED DOWN
-6 THREADED INSERTS
-| -18 x|i" DEEP, EQUALLY
SPACED ON 26"D BOLT CIRCLE
I'D-
CO
r n
o
c •
. o
3"F.PT. STAINLESS
COUPLING-WELDED
6 HOLES -^0 EQUALLY SPACED
ON26"D BOLT CIRCLE I
•ffi-
MATERIAL-PRECAST REINFORCED
CONCRETE
-24"0-
CO
ro
J
MATERIAL-14 GA. MILD STEEL
FINISH-PRIMER AND TWO FINISH
COATS EPOXY PAINT INSIDE AND OUT
FIGURE 17
TANKS FOR SGP PROTOTYPE
(Reproduced from Fig. 19,Ref. 21 )
-------
TABLE 8
SPECIFICATIONS FOR PROTOTYPE
STORAGE-GRINDER-PUMP UNIT
(Reproduced from Table 5, Ref. 21)
Motor: 1-HP, 1,725-rpm, capacitor start, thermally protected.
Electrical supply requirement: 230-v, 10-amp, 60-Hz (fused 10-amp);
or 115-v, 20-amp, 60-Hz (fused 20-amp).
Electrical Name Plate Rating:
115/230 volts, 13.8/6.9 amp, 60 Hertz, 1 phase, 1,725 rpm,
Rise 40° C, Service Continuous, General Electric Mod. 5KC47RG913U.
Inlet Connection: 3" or 4" C.I., copper, or non-metallic DWV may be
adapted at tank entrance fitting.
Discharge Connection: 1%" copper tube (hard drawn) adaptable to 1%"
polyethylene tube outside foundation.
Net weight (not including tank): 150 Ib.
Maximum Discharge Pressure: 35 psig.
Discharge: 15 gpm @ 0 psig; 11 gpm @ 35 psig. (Discharge data include
losses through check valve which are minimal).
- 58 -
-------
Alternative Equipment
Alternative pumping equipment, including centrifugal, turbine, and
positive displacement pumps, and pneumatic ejectors were considered, but
it was decided that the need for a steep head-discharge characteristic,
freedom from clogging by sewage solids, and good economy of operation
could be met best by the progressing-cavity type pump in combination
with a separate grinder unit.
Alternatives are discussed in Refs. 3 and 21.
- 59 -
-------
SECTION VI
CONVENTIONAL EQUIPMENT AND CONTROLS FOR STORING,
COMMINUTING, AND PUMPING SEWAGE FROM COMMERCIAL
BUILDINGS AND OTHER LARGE SOURCES*
Introduction
The ASCE Project requirements for equipment to grind and discharge
sewage from sources larger than single and possibly two-family residen-
tial buildings (Section V) are based on flow rates developed in Section IV
and given in Fig. 9.
The maximum pumping head would be the same at the curb line as for
the smaller SGP unit, assumed to be about 30-psig from the hydraulic
analysis of the pressure collection system piping in the next section of
this report.
Comminuting and Pumping Equipment
To grind and pump discharges above those of single or double instal-
lations of the SGP unit (Section V), namely above about 15 or 30 gpm,
conventional comminutors and non-clog centrifugal pumps were selected.
Comminutor-pump installations have long been in service in sewage works,
produced satisfactory records of operation, and provided capacities up to
many hundreds of gallons per minute.
The Project staff began a comminutor monitoring program in mid-1966
and pursued it until the end of November 1967 in cooperation with opera-
tors of installations. Day-to-day records were kept by the operators and
sent monthly to the staff for compilation and analysis.
The installations ranged in size from 4-in. (1,000 gallons per day)
to 15-in. (300,000 gpd) and were situated in New York, Florida and Nova
Scotia. A summary of the frequency and extent of their maintenance is
given in Ref. 3.
Of the 30 installations for which adequate records of past expe-
rience were obtained, 16 required no repair or replacements. All but one
were less than four years old. Repairs to 7 of the others involved the
cutting elements, 3 suffered breakage of gears by stresses incidental to
jamming, 1 shaft failed from corrosion and 1 motor burned out. Most of
the 30 machines had jammed occasionally or frequently, stopping the
machines until the causes of jamming had been removed.
* Ref. 3.
- 60 -
-------
Descriptions of comminutor equipment produced by three manufac-
turers are given also in Ref. 3.
Figure 18 shows the particle size reduction obtained in a single
test of a comminutor for raw sewage in comparison with the result
obtained in passing sewage through a %-hp. commercial garbage grinder.
The conclusion reached was that commercially produced comminutors
would be adequate for larger buildings in the use of the project scheme.
Comminutors were, therefore, included in the hypothetical designs of
pressure sewer systems for San Francisco, Milwaukee, and Boston, reviewed
and evaluated by consultants, as reported in Section IX.
Combined Grinders and Pumps
The possible use of commercial grinder-pump devices, among them
the Gorator (Dorr-Oliver, Inc., Stamford, Conn.), the Stereophagus and
Disintegrator pumps (Sigmund Pulsometer Pumps, Ltd., Reading, England)
and the Mazorator (Moyno Pump Division, Robbins & Myers, Inc.,
Springfield, Ohio) was reviewed. Because they require a substantial
motor horsepower and have capacities greater than the range considered
for household application and for all but the larger commercial applica-
tions it was concluded that they might be considered only for larger
commercial and industrial uses.
Non-Clog Centrifugal Pumps
Non-clog centrifugal pumps have commonly been used for pumping
sewage. They usually have capacities greater than about 10 gpm. Dual
installations and pumps of the wet-pit or submerged type in the capacity
ranges considered in the ASCE Project appear to be satisfactory.
Because of their general acceptance for sewage pumping, non-clog
pumps were included in the comminutor-pump installations for sewage
sources larger than those to be handled by single or double SGP unit
installations, and they have been included in the designs of hypothetical
systems reported in Section IX.
Pneumatic Ejectors
Pneumatic ejectors for sewage are available in capacities of 30 to
1 000 gpm and have been generally accepted for locations where low effi-
ciency can be offset by relative freedom from clogging and complete
enclosure of the sewage. Pneumatic ejectors, including air compressors
and controls, cost more and require greater 8Pac« ^"^iafe^Se fs
equal capacity. The ability to handle sewage solids of moderate size is
of no advantage in their possible application to the ASCE Project,
- 61 -
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CD
ro
i
UNGROUND SEWAGE
COMMINUTED SEWAGE
GROUND SEWAGE
> 0 —
to 0.0017
0.05
0.10 0.15
SIEVE OPENING-INCHES
0.20
0.25
FIGURE 18
EFFECT OF COMMINUTOR AND GARBAGE GRINDER
ON SEWAGE PARTICLE SIZES
(Reproduced from Fig.3,Ref. 3)
-------
because the solids must be reduced in size for passage through the
pressure tubing and valves.
For these reasons, and because of the difficulty of matching the
discharge characteristics of pneumatic ejectors with those of the pres-
sure sewer system, they have not been considered for adoption under the
ASCE Project scheme.
Cost of Comminutor-Pump Installations
The estimated cost of equipment and installation of a comminutor-
pump unit for large buildings in the Milwaukee area was about $2,600:
$1,700 for the equipment and $900 for installation. The receiving wet
well (Ref. 17) was included, but no allowance was made for contingencies
and engineering.
- 63 -
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SECTION VII
PRESSURE SEWER SYSTEMS*
Introduction
Design and implementation of the ASCE Project scheme of pressur-
ized sewerage required the following information: present and future
maximum, average, and minimum discharge rates of sewage from sources of
all sizes; equipment for grinding sewage solids and storing and pumping
sewage, together with consideration of head and capacity limitations;
available tubing and conduit materials and appropriate methods for their
installation and repair; emergency or alternative avenues for routing
flows; minimum transport velocities for conveying sewage solids in
conduits flowing full; and methods and devices for the control of pres-
sure and rate of flow and the prevention of backflow.
Rates and volumes of sewage generated over short periods of time
have been discussed in Section IV. The use of rate of flow curves
outlined in Section IV for design of street sewers is detailed and
exemplified fully in Refs. 16, 17 and 18. Application of flow data to
the selection of pump capacities and storage volumes has been discussed
in Section V for small sewage sources and in Section VI for large sewage
sources.
Equipment for grinding sewage solids and storing and pumping
sewage is described in Section V for small wastewater sources (the
household storage-grinder-pump unit) and in Section VI for large sources
(comminutor-pump and wet-well installations).
Tubing and Conduit Defined
The term "tubing" as used in this report applies to flexible
tubing of relatively small diameter that can be inserted in existing
building drains and sewers or buried in a separate trench extending
from a building to the street. The term "conduit" is applied to rigid
or semi-rigid pipe larger than tubing that can be suspended in existing
street sewers of walk-through size or laid in a separate trench.
* Refs. 4, 5, 6, 7, 11, 22, 23 and 24,
- 64 -
-------
Materials
The materials considered for pressure tubing and conduit in the
ASCE Project scheme are identified respectively in Tables 9 and 10 (from
Ref. 23).
The requirements for tubing that is to be pushed or pulled through
existing 4-in. and larger inside diameter building service connections
were: flexibility and ease of manipulation; resistance to external and
internal scoring and abrasion; resistance to structural collapse or
flattening; freedom from chemical attack by sewage constituents or
trench backfill; freedom from damage by electrolysis; strength equiva-
lent to a bursting pressure at least three times the maximum expected
system pressure in order to compensate for the possible corrosive
effects of sewage; and commercial availability and economical cost.
The materials considered and recommended for pressure conduit in
Table 10 include those commonly used in sewage force mains and meeting
the normal requirements of force mains and possessing, in addition,
adequate stiffness and beam strength between supports for suspension in
existing street sewers.
Insertion of Tubing
The results of field trials of inserting tubing in a building
sewer in Washington, B.C., performed by the District Department of
Sanitary Engineering in 1967 (Ref. 5) are summarized in Tables 11 and
12. As there shown, 3/4, 1 and 1%-in. diameter polyethylene tubing was
successfully pushed through the building sewer, whereas 3/4 and 1-in.
polybutylene and 3/4-in. copper tubing were not. Moreover, polyethylene
tubing of all three sizes and 3/4 and 1-in. diameter polybutylene tubing
were successfully pulled through the building sewer whereas 3/4-in.
copper tubing was not.
Special tools and methods for inserting and connecting tubing to
pressure conduits are described in detail in Ref. 23. Included are a
leading roller-guide for pushing tubing and special grips for pulling
tubing.
Tubing and Conduit Installation
Three alternative methods for installing tubing and conduit are
outlined in Fig. 19. In Method A, tubing is inserted in the existing
building sewer and connected to a pressure conduit suspended in the
existing street sewer. This method can be used only where building
sewers are free from obstructions and where street sewers are large
enough to install conduit and connect tubing to it. Method A embodies
the original pipe-within-a-pipe ASCE Project concept, which is conceded
- 65 -
-------
TABLE 9
TUBING LESS THAN 2 INCHES IN DIAMETER
CONSIDERED FOR PRESSURE BUILDING CONNECTIONS
(Ref. 23)
Material and Type
Polyethylene WST
type 3, grade 2
3206
Polyethylene WST
type 3, grade 3
3306
Polybutylene WST
type 2, grade 1
2110
Type L Soft Copper
Tubing
Nominal
Size,
Inches
3/4
1
1 1/4
3/4
1
1 1/4
3/4
1
1 1/4
3/4
1
Ave. Type of Working
Weight, Fitting Pressure,
#/ft. psi
0.05 flared 160
0.22 " "
0.5 "
0.05 flared 160
0.22
0.5
0.05 flared 160
0.1 "
_ n ii
0.41 flared 510
" 450
ID,
Minimum,
Inches
0.764
0.983
1.202
0.764
0.983
1.202
0.796
1.027
1.258
0.785
1.015
- 66 -
-------
TABLE 10
PIPE MATERIALS 1% INCHES THROUGH 16 INCHES IN DIAMETER
CONSIDERED FOR PRESSURE CONDUITS (Ref. 23).
Type and Grade
of Material
PVC 1120
(solvent
veld
connection)
Asbestos
Cement
Class 150
(compression
gasket
coupling
connection)
Ductile Iron**
Pushon Joint
(compression
gasket bell
and spiggot
connection)
Cast Iron
Class 150
Pushon Joint
(compression
gasket bell
and spiggot
connection)
Nominal
Size,
inches
1 1/2
2
2 1/2
3
3 1/2
4
5
6
8
10
12
3
4
6
8
10
12
14
16
yadt
fyfrfak
6
8
10
12
14
16
2
2 1/4
3
4
6
8
10
12
JL &~
14
16
Ave.
Weight,
*/ft.*
0.25
0.39
0.57
0.85
--
1.41
—
3.10
_ _
_ _
__
5.6
7.0
11.7
18.2
30.0
40.8
52.1
64.8
10.5
13.4
21.0
29.7
38.9
49.0
55.9
65.8
6.2
6.8
12.4
16.5
25.9
37.0
49.0
63.4
78.2
94.5
Working
Pressure
(psi)
160
ii
II
II
II
II
II
II
II
II
II
150
II
II
11
1 1
1 1
II
II
350
ii
ii
ii
200
ii
M
ii
150
ii
ii
ti
n
ii
n
ii
it
n
S tandard
Lengths ,
Feet
20
ii
n
n
ii
ii
n
n
n
n
n
13
II
If
H
ll
1 1
f 1
12/18/20
18/20
18/20
18/20
20
n
n
"
20
n
12/16
12/16
12/16
12/16
18/20
18/20
18/20
18
ID,
minimum,
inches
1.708
2.147
2.608
3.182
3.644
4.103
5.071
6.042
7.866
9.924
11.770
mandrel
sized
""•
~
3.68
4.51
6.59
8.72
10.40
12.48
14.58
16.66
2.0
2.25
3.32
4.10
6.14
8.23
10.22
12.24
14.28
16.32
* Includes fittings
** Assuming wall thickness for 5 foot cover
*** 3 and 4 inch size limited to 1 inch tap
- 67 -
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TABLE 11
RESULTS AND OBSERVATIONS OF PUSHING TESTS
(Ref. 5)
Tubing
Material
Polyethylene
Polyethylene
Polyethylene
Polybutylene
Polybutylene
Type L
Soft Copper
Nominal
Internal
Diameter
of Tubing
(inches)
3/4
1
1 1/4
3/4
1
3/4
Calculated
Working
Pressure of
Token Length
(psi)
146
165
159
154
154
Manufacturer ' s
Rated Working
Pressure
(psi)
160
160
160
160
160
510
Actual
Inside
Diameter
(inches)
.681
.875
1.069
.745
.957
.785
Wall
Thickness
(inches)
.097
.125
.153
.065
.084
.045
Results
Successfully pushed
from upper building
pit to combined sewer.
Successfully pushed
from upper building
pit to combined sewer.
Successfully pushed
from upper building
pit to combined sewer.
Could not be pushed
from upper or lower
building pit to
combined sewer.
Could not be pushed
from upper or lower
building pit to
combined sewer.
Could not be pushed
from upper or lower
building pit to
combined sewer.
Remarks
One man was able to
push tubing through
lateral.
One man was able to
push tubing through
lateral.
Two men were required
to push as hard as
possible to get tubing
through lateral.
Tubing buckled very
easily under a pushing
force .
Tubing buckled very
easily under a pushing
force .
Tubing was very hard
to work with . It
would tend to buckle
instead of bend.
When in lateral it
tended to buckle and
coil up in lateral.
oo
i
-------
TABLE 12
RESULTS AND OBSERVATIONS OF PULLING TESTS
(Ref. 5)
Kind of
Tubing
Nominal
Internal
Diameter
of Tubing
(inches)
Calculated
Working
Pressure of
Token Length
(psi)
Results
Remarks
Polyethylene
3/4
146
Successfully pulled from
combined sewer to the
upper building pit.
Pulled through by one man.
Pulling was more difficult
than pushing 3/4" polyethylene.
Polyethylene
165
Successfully pulled from
combined sewer to the
upper building pit.
Pulled through by four men.
Pulling was more difficult
than pushing 1" polyethylene.
Polyethylene
1 1/4
159
Successfully pulled from
combined sewer to the
upper building pit.
Pulled through by four men.
Pulling was more difficult
than pushing 1 1/4" polyethylene,
Polybutylene
3/4
154
Successfully pulled from
combined sewer to the
upper building pit.
Pulled through by one man.
It was easier to pull than the
3/4" polyethylene.
Polybutylene
154
Successfully pulled from
combined sewer to the
upper building pit.
Pulled through by one man.
It was easier to pull than the
1" Polyethylene but harder to pull
than the 3/4" Polybutylene.
Type L
Soft Copper
3/4
Could not be pulled from
combined sewer to either
the upper or lower
building pit.
Five men were pulling at the upper
building pit. It was apparently
stuck between the two 45° bends.
-------
A. PRESSURE TUBING INSTALLED ENTIRELY IN EXISTING
HOUSE SEWER AND CONNECTED TO PUBLIC PRESSURE
CONDUIT INSTALLED IN EXISTING MAN-SIZED STREET SEWER
STREET
NEW PRESSURIZED
CONDUIT FOR PUBLIC
SANITARY SEWER
EXISTING
COM8NED MAN-
SIZED PUBLIC
SEWER
GRINDER, PUMP,
STORAGE UNIT
EXISTING HOUSE
SEWER LATERAL
NEW PRESSURIZED
TUBING FOR HOUSE
SANITARY SEWER
PRESSURE TUBING INSTALLED PARTLY IN EXISTING HOUSE
SEWER AND CONNECTED TO PUBLIC PRESSURE CONDUIT
INSTALLED IN TRENCH DUG PARALLEL TO STREET.
EXISTING
COMBINED
PUBLIC SEWER
PIT TO EXPOSE
EXISTING HOUSE SEWER
LATERAL
TRENCH FOR
PUBLIC PRESSURE
CONDUIT
C. PRESSURE TUBING INSTALLED ENTIRELY IN A TRENCH
DUG FROM HOUSE TO PRESSURE CONDUIT AND CONNECTED
TO PUBLIC PRESSURE CONDUIT INSTALLED IN TRENCH
DUG PARALLEL TO STREET.
EXISTING
COMBINED
PUBLIC SEWER
FIGURE 19
ALTERNATIVE METHODS OF INSTALLING AND CONNECTING
PRESSURE TUBING AND CONDUIT (ONE SIDE OF
STREET, ONLY, SHOWN) (Modified from Fig. 1, Ref.5)
-70-
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to be feasible only when street sewers are of adequate size for direct
internal access. There appears to be no feasible method for installing
pressure conduit in combined sewers smaller in height than about 54-in.
without excavating access pits.
In Method C, tubing and conduit are buried in trenches. The
existing combined sewer becomes the storm sewer. The trenches are
excavated to a depth just below frost penetration. They parallel the
ground surface irrespective of its slope. The conduit trench can be
placed inside the curb line, or in the street cartway, so as to reduce
interference with traffic to a minimum. All four types of tubing in
Table 9 are suitable for individual homes.
Method B combines the features of Methods A and C, and might be
useful in special circumstances. This method was also demonstrated in
the Washington, D.C., field tests (Ref. 5). A building sewer no-hub
wye branch was developed especially for this purpose (Ref. 23).
In all three methods, the smaller sizes of conduit in Table 10
can carry the sewage normally discharged through much larger sewers.
Construction of the pressure system would closely conform to that of
traditional water distribution systems. For these there is abundant
precedent.
For Method C in Fig. 19, dual parallel street sewers would be
laid in each block, one on either side of the street. It is important
to note that this method is applicable to combined sewer separation and
for sewering established communities or new developments.
Ranges of Combined Sewer Sizes
A voluntary study of major American cities made for the ASCE
Project by the Portland Cement Association (Ref. 4) showed that on an
average about 85% of the total length of their combined sewers has an
interior clear height of 48-in. or less, and that on an average about
72% of their total length has an interior clear height of 24-in. or
less. Supplementary information from the American Public Works Associa-
tion places the proportion of the larger sizes still lower for cities
with under 100,000 inhabitants.
The accepted minimum walk-through size is 54-in. clear interior
height. Although the Project staff enjoyed the benefit of much outside
advice and assistance, it was unable to devise practicable methods for
inserting and securing conduits in sewers smaller than 54-in. and maki-ng
tubing connections to them without resorting to extensive and expensive
street excavations. It must be assumed, therefore, that the pipe-
within-a-pipe concept (Method A of Fig. 19) is restricted to about one-
seventh the total length of combined sewers in major U.S. cities and to
less than this in U.S. communities as a whole.
- 71 -
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Suspension of Conduits within Existing Sewers
A hanger system for suspending pressure conduits for sanitary
sewage within existing sewers was developed for the ASCE Project by the
Research and Engineering Center of the Johns-Manvilie Products Corpora-
tion, Manville, New Jersey, Ref. 24. Single-piece molded polyester
hangers were designed for this purpose and epoxy adhesives were used to
secure the hangers to the crowns of combined sewers. The basic hanger
design was suitable for PVC, ABS, steel, cast iron and asbestos-cement
conduits 2 to 12-in. in diameter. The required hanger spacing was based
on their ability to support the filled conduits without structural
damage to the sewer under a limited conduit deflection.
A trial installation by Johns-Manville was made in an existing
7-ft. diameter concrete intercepting sewer in Evanston, Illinois, in
cooperation with The Metropolitan Sanitary District of Greater Chicago
in July, 1968. The test section consisted of 100-ft. of 3-in. PVC pipe
in 10-ft. pipelengths, supported by 13 polyester pipe hangers. Instal-
lation was completed in three nights at times of low sewage flows. The
sewer crown surface was cleaned and scored to assure a good bond. The
installation was tested structurally. Inspection of the installation
after four and one-half months of exposure in the active sewer showed
no signs of deterioration of pipe, hanger or epoxy adhesive. Three
hangers were later tested to failure in tension at loads of about 2,500
pounds. Failure was by fracture that left the top half of the hanger
connected to the sewer crown. In accordance with Ref. 24, the materials
and basic method of suspension used are satisfactory for sewers at least
about 5-ft. in height provided the sewer itself is structurally capable
of sustaining the added distributed load at the crown.
The effect of conduit hangers on the hydraulic capacity of
intruded combined sewers is discussed in the next section of this report.
For better intruded combined sewer flow capacity and easier conduit
installation, a two-part hanger would be preferred. The basic distributed
polyester crown seat would be preserved. However, the thick polyester
section around the conduit would be replaced by a corrosion-proof thin
metal strap and support anchored to the plastic crown seat via an
imbedded end plate.
Burial of Tubing and Conduit by Plowing
Field experience with laying conduit by plowing instead of by
trenching and burial or jacking is documented in Reference 23. It was
concluded that plowing-in 4-in. or smaller pressure conduit (or tubing)
is worth investigation, particularly for new subdivisions or for estab-
lished areas in which driveways are not paved with concrete and there
are few buried utilities to be crossed. Plowing is potentially a
superior means for burying tubing and/or conduit for Method C of Fig. 19
under the prescribed restrictions. After the National Sanitation
- 72 -
-------
Foundation report (Ref. 23) was completed a more comprehensive survey
of plowing methods has been published (Ref. 38).
Other Installation and Maintenance Considerations
Reference 23 also contains information and recommendations on
devices for cleaning pressure tubing in the field; tapping procedures
and fittings for connecting tubing to conduits, including corporation
and curb stops and access manholes; classes of pipe to withstand
specific overburden loading conditions; and jacking and tunneling
methods for placing tubing and conduit under streets and driveways.
The difficulty of maintenance and repair of street pressure sewers
is a direct function of the type of piping layout and the number of
valve and clean-out fittings provided. Of considerable concern is the
minimization of the number of services that must be interrupted when a
section of street sewer is closed off for cleaning, repair, replacement,
or other purposes. Six collection system layouts with various advan-
tages and degrees of flexibility for operation and maintenance are dis-
cussed immediately below.
Pressurized Sewerage Collection System Layouts
Pressurized sewer systems may be arranged in two basic configura-
tions, dendriform (branched) and reticulate (latticed or looped). In the
dendriform arrangement several lateral sewers are connected to a sub-main
sewer which, together with other sub-main sewers, is connected to a main
conduit serving the pressure-sewer district. The district main dis-
charges into a gravity (open-channel) flow interceptor. Laterals in the
reticulate system (single or dual) are connected to sub-main conduits at
both ends, and the sub-mains are joined to main conduits that discharge
to the interceptor.
For the purpose of providing continuous service to a maximum number
of buildings during periods of routine maintenance or in an emergency,
and to remove stoppages or replace segments of conduit, systems should
be arranged so that portions can be shut down and drained without inter-
ruption of service in other portions of the system. For this reason a
dendriform arrangement with long single conduits throughout is undesirable
and, in the opinion of one consultant, "totally unacceptable." However,
in some instances a single conduit might be adequate and less expensive.
The report by the National Sanitation Foundation (Ref. 23) presents
six layouts which provide for "routine re-routing without widespread
shutdown by virtue of a dual configuration for all or practically all
conduits." The first five arrangements were developed by the ASCE
Project staff and the sixth was added by the Foundation.
- 73 -
-------
Table 13 outlines the characteristics of the six alternative
layouts and comments on their relative merits. Of the six, the nSf
Layout (bottom of the table) is the only true reticulate or looped
system. Each layout is discussed separately in the remainder of this
section, the illustrations used being noted in Table 13.
1. Layout A — The conduit configuration for Layout A is shown in
Fig. 20. Flow directions are indicated by arrowheads. Layout A incor-
porates dual pressure conduits placed in shallow trenches (dug below
frost line), one on each side of the street and parallel to it as for
Method C, Fig. 19. A portion of the conduit system of Fig. 20 is
enlarged in Fig. 21. The dashed lines denote street curbs and the
solid lines denote pressure conduits.
Referring to Fig. 21, a portion of the system, say line a. between
manholes W and X, is isolated by closing the valves on line a_ in man-
holes W and X. Flow from line c_ into manhole X is then diverted across
the street to manhole Z where it joins the flow from lines d_, £ and f_
and is directed thence through line b_ to manhole Y. Flow then continues
in the direction shown by the arrows. While the flow is being diverted
around line a_, flows from buildings directly tributary to line a_ are
interrupted. If the shut-down lasts only a short time, say two or three
hours during the night, there is little hardship. If the shut-down
lasts much longer, however, sewage flows from the buildings must be
accommodated in some manner. One possibility is to lay a temporary
by-pass conduit on the ground between manholes W and X and to connect
the tubing from tributary buildings to the by-pass as in "high-lining"
a water main.
It should be noted that for Layout A (Figs. 20 and 21) flow in
each line can move in one direction only, except in some of the short
sections across streets between dual conduits, such as the sections
between manholes X and Z. One of the objectives of this layout and the
next four layouts to be discussed is to permit as little looping as
possible in order to minimize the residence time of sanitary sewage in
the pressure-conduit system.
Each intersection has four manholes and various arrangements of
clean-out fittings and valves. Manhole diameter depends on the size of
the entering and leaving conduits and the arrangement of valves and
clean-out fittings. Figure 22 shows the valves and clean-out fittings
for manhole W of Fig. 21.
The layout shown in Fig. 21 permits isolating and cleaning the
conduits along each block. This is the most elaborate and hence most
expensive layout. It is assumed that the greatest reach of pressure
sewer that can be cleaned between two access points is one block long
(approximately 500 feet). If the length can be increased to two blocks,
the valving and clean-out arrangement can be simplified somewhat with a
consequent reduction in cost.
- 74 -
-------
TABLE 13
SUMMARY OF CONDUIT LAYOUT CHARACTERISTICS
Ref. 23 Text Dual Dual
Layout Figure Lateral Main
Designation Number Sewers Sewers
"A" 20, 21 Yes Yes
and 22
"B" 23 Yes Yes
"C" 24 Yes Yes
"D" 24 Yes Dual
and
Single
"E" 24 Yes Dual
and
Single
"nSf" 25 Yes Yes
Conduits Inserted
A True in Walk-Through
Network Combined Sewers
No No
No Yes, dual without
building connec-
tions.
No Yes, dual with
building connec-
tions .
No Yes, single
without building
connections.
No Yes, single with
building connec-
tions.
Yes No
Auxiliary
Conduits Outside Comments
Main Sewer
No Most flexible
of non-network
arrangements .
Yes Less flexible
than "A".
No Less flexible
than "A" or "B".
Yes Less flexible
than "A", "B" or
"C"; must bypass
to storm sewer.
No Least flexible;
must bypass to
storm sewer.
No Must close 6
valves to clean
main; longest
sewage residence
time.
-------
STREET BOUNDARY (CURB LINE)
PRESSURE CONDUIT
MAIN LINE PRESSURE CONDUIT
• PRESSURE CONTROL VALVE
• ARROWS INDICATE FLOW DIRECTION
PRESSURE CONTROL VALVE(S)
AT INTERCEPTOR
1
1
1
*
1
1 1
' L
1 1
| '
1 1
1
1
J j
. .
J
I
i
7 " " 7. "
f!
,
i
i
t
'
_"
' '
' '
1
5
'
'
-r
,
3
{
M
~
J L- -
M =— ^ jl
1 ll
H — • — =1
i
i
M — "* n
L-[ -_ ,
FIGURE 20
LAYOUT A
(Reproduced from Fig. 9, Ref. 23)
J
SEE FIG. 21
FOR"TYPICAL"
DETAILS OF
THIS SECTOR
-76-
-------
I
- STREET BOUNDARY (CURB LINE)
° CLEANING TEE
« SHUT OFF VALVE
— • ARROWS INDICATE FLOW DIRECTION
O MANHOLE FOR HOUSING VALVES AND TEES
• PRESSURE CONTROL VALVE
NOTE: FITTINGS, VALVES AND MANHOLES NOT TO SCALE
/-G
^^-^^
s^**^
/
1 r
* — — ^dw
si
•Q
\
\__
^ — — .
€
i
i
B •" li
r?
1
B "' C
1
1
!
'1
1
I
i « \
3 I"
i
i
^ ^~^^~^ —-^1
J
^ - d
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FIGURE 21
LAYOUT A, DETAILS FOR FIG. 20 SECTOR
(Reproduced from Fig. 10, Ref. 23)
-------
-,
:
CLEAN-OUT
FITTINGS
PLAN VIEW (INSIDE MANHOLE)
MANHOLE
COVER
SIDEWALK
WATER-TIGHT
MANHOLE
CLEAN-OUT
FITTINGS
VALVES
NOTE: D WOULD VARY DEPENDING
ON SIZE OF INCOMING AND
OUTGOING CONDUITS.
MINIMUM H WOULD BE
DEPTH TO FROST LINE .
LINE a
SECTION A-A
FIGURE 22
LAYOUT A, ARRANGEMENT FOR MANHOLE "w" IN FIGURE 21
(Reproduced from Fig. 11, Ret. 23)
-78-
-------
Reference 23 reports on available types of clean-out fittings and
established methods of cleaning that might be applied.
2. Layout B — As shown in Fig. 23 the main pressure conduits shown as
dual lines in Layout B, as lines j* and b_, for example, are placed in
walk-through combined sewers, but the building tubing is not connected
directly to them but to auxiliary dual conduits shown as single lines
in shallow trenches on either side of the block. Main conduits along
reaches of combined sewers too small to accommodate them, lines £ and d_,
for example, would be placed in shallow trenches as for Layout A.
To isolate a portion of conduit, say line a. between manholes R and
S in Fig. 23, the same steps are taken as for line a_ of Layout A in
Fig. 21. To isolate a portion of conduit inside a combined sewer, say
line b_ between manholes P and Q, similar steps are taken. The valves in
manholes P and Q on line b_ are closed; the flow entering manhole Q
through lines £, d_, e_, and £_ then passes through line j* to manhole P
where it is distributed to the two dual conduits inside the combined
sewer.
Layout B requires large vaults for valves and clean-outs in man-
holes P and Q, for example. However, the provision of auxiliary dual
laterals makes this arrangement the most flexible and probably most
expensive way of inserting main conduits in combined sewers.
3. Layout C — As shown in Fig. 24, Layout C connects household tubing
to the dual main conduits inside the combined sewer and eliminates the
shallow-trench conduits on the route of the walk-through combined sewers
in Layout B. The connections of tubing to conduits are made inside the
combined sewer and the tubing is normally fished through the building
sewer as in Method A of Figure 19.
From the standpoint of maintenance and operation, this makes for
less flexibility than Layout B. Valves and clean-outs in vaults above
the combined sewer are the same for Layouts B and C. Only the arrange-
ments in manholes through which auxiliary conduits otherwise pass are
changed. Lines are isolated in essentially the same manner in both
layouts.
4. Layout D — Layout D in Fig. 24 is the same as Layout B, except that
dual pressure conduits inside the combined sewer are replaced by a
single conduit.
Isolation of a section of the single pressure conduit for mainte-
nance or repair is accomplished by temporary diversion of sanitary
sewage flow to the storm sewer (former combined sewer). This was antici-
pated by Professor Fair in the original Project scheme. For example, if
a blockage occurs in line b of Layout D, Fig. 24, tributary flow is
diverted temporarily to the storm sewer by an automatic relief valve
located in manhole M. Shut-off valves on line b in manholes L and M are
- 79 -
-------
o
STREET BOUNDARY (CURB LINE)
PRESSURE CONDUIT
CLEAN-OUT FITTING
SHUT OFF VALVE
MANHOLE FOR HOUSING VALVES AND FITTINGS
ARROWS INDICATE FLOW DIRECTION
\
i
I1:
FIGURE 23
EXAMPLE OF LAYOUT B
(Reproduced from Fig. 13, Ref.23)
NOTE: A PORTION OF THIS SYSTEM
CONTAINS WALK-THROUGH SIZE
COMBINED SEWERS. WHERE
THEY EXIST THE MAIN PRESSURE
CONDUIT IS INSTALLED INSIDE
OF THEM. CONSEQUENTLY,
WALK-THROUGH COMBINED SEWERS
EXIST WHERE THE MAIN PRESSURE
CONDUITS LIE BETWEEN CURB
LINES.
BUILDING CONNECTIONS ARE NOT
MADE TO THE SEWER-INSIDE-THE-
SEWER, BUT INSTEAD TO CONDUITS
IN SHALLOW TRENCHES ON EACH
SIDE OF THE STREET. THESE
CONDUITS IN TURN CONNECT TO
THE SEWER-INSIDE-THE-SEWER,
AT EACH INTERSECTION.
THE FITTINGS, VALVES AND MAN-
HOLES ARE MOT TO SCALE.
-------
o
STREET BOUNDARY (CURB LINE)
PRESSURE CONDUIT
ARTERIAL PRESSURE CONDUIT
CLEAN-OUT FITTING
SHUT-OFF VALVE
RELIEF VALVE
MANHOLE FOR HOUSING VALVES
AND FITTINGS
ARROWS INDICATE FLOW DIRECTION
NOTE: FITTINGS, VALVES AND
MANHOLES ARE NOT TO SCALE
rn
LAYOUT C
LAYOUT D
FIGURE 24
LAYOUTS C, D AND E
(Reproduced from Fig. 15, Ref. 23)
LAYOUT E
-------
closed to isolate line b_ for cleaning or repair. While line b_ is out
of service the sewage flows by gravity from the point of diversion
through the storm sewer to the interceptor.
5. Layout E — Layout E in Fig. 24 creates the least flexible scheme by
combining the less flexible features of Layouts C and D, using Method A
in Fig. 19.
Line b_ in Layout E is isolated in the same way as line b_ in
Layout D, except that flows from buildings tributary to line b_ must
either be interrupted or disconnected, flow being diverted into the
storm sewer or elsewhere during maintenance or repair.
6. National Sanitation Foundation Layout — In the pressure-sewer layout
shown in Fig. 25, a valve and a tee are installed for cleaning purposes
at intervals of about 600 feet or at the ends of each block. After a
blockage has been located, up to six valves must be closed before a
section of main sewer can be cleaned. The valves are situated at oppo-
site ends of a two-block main sewer and at the end of each tributary
lateral sewer. To clean a lateral sewer only two valves must be turned.
The flow pattern in this layout is such that when a line is shut down a
maximum number of alternative routes are opened up to tributary flows.
This advantage is offset in part by the disadvantage of encouraging a
longer sewage residence time in the system than in Layouts A through E.
Moreover, it is difficult to adapt the nSf Layout to irregularly-shaped
pressure districts of varying block size.
Conduit Sizing
Pressurized sanitary sewers must be sized to ensure the creation
of minimum scouring velocities often enough to prevent stoppages.
Wastewater flows are bound to be low in the course of each day, and
solids are bound to be deposited at such times. The longer the time of
non-deposition provided for, the smaller must the conduit be. The
smaller the conduit is, the steeper does the hydraulic gradient become
for all flows. Peak rates of flow produce maximum hydraulic gradients,
and these in turn determine pressure requirements within the system, for
all pumping and pressure control. Thus, a compromise must be reached
between the degree of solids transport effected and system pressure
levels deemed tolerable from the standpoint of other hydraulic criteria
or as imposed by economic considerations.
Because design criteria for minimum transport velocities of
sewage solids in pressure pipes were not available, special research was
conducted at the Central Engineering Laboratories of the FMC Corporation
in Santa Clara, California (Ref. 22). Raw sewage, with and without
reduction of the size of its particulates by comminution was passed
through smooth 2-in., 3-in., 4-in., 6-in., and 8-in. I.D. pipe. (A few
tests were also run with an 8-in. spiral corrugated pipe and exploratory
open-channel tests were made with the smooth 8-in. pipe).
- 82 -
-------
—=-— Flow direction
Valve
Cleanout tee
Manhole
I | Underground
structure
Typical for all
FIGURE 25
NATIONAL SANITATION FOUNDATION PRESSURE SEWER LAYOUT
(Reproduced from Fig. 17, Ref. 23)
-83-
-------
Extensive observation showed that sand was predominantly the
sewage constituent that was scoured last and deposited first. In all
tests the sewage was "salted" with ground egg shells, but these were
always moved at lower mean velocities of flow than the sand, which was
present only in low concentrations, viz., 8 to 78 ppm. There was no
discernable difference between minimum transport velocities for flows
with and without particle-size reduction, because the weight of sand
was not affected. The minimum scouring velocities tended to be greater
than the maximum depositing velocities, but the difference was small.
The minimum mean transport velocity in feet per second was found to
approximate /D/2, where D is the interior pipe diameter in inches, e.g.,
the minimum velocity for a 4-in. pipe is approximately 1.0 fps. More
precise values (Ref. 7) require accounting for sand concentration.
Data on minimum transport velocity of sanitary sewage were combined with
other data on sand transport. The unified results are given in detail
in Reference 7.
For the design of hypothetical pressure-sewer systems in the
Milwaukee and San Francisco study areas (Section IX) the lowest peak
hour rate of any day for the given number of tributary residences was
combined with the minimum transport criteria to size the street pressure-
conduits. The highest peak hour rate of any day for the given number of
tributary residences was then used to estimate the maximum hydraulic
gradients for the size of conduit selected. As explained in Section IV,
highest peak-hour flow rates were estimated by applying to metered mean-
annual winter-quarter water-demands projected into the future the ratios
indicated by the curves in Fig. 7 for the Milwaukee study area and Fig. 8
for the San Francisco study area. With minor modification, essentially
the same procedure was followed in connection with the Boston study area
using Fig. 9. In all three cases the lowest peak-hour was similarly
determined, but beginning-of-design-period demands were used instead.
These are normally the lowest and hence the most critical flow rates in
terms of solids transport.
System Hydraulics and Controls
The operating pressure ranges of pressurized systems are determined
by the hydraulics of a given reach and its domination by hydraulic regime
controls at either end of the reach. In the ASCE Project scheme, sewage
from a pressure-sewerage area ultimately discharges into an intercepting
sewer. It would be difficult to develop a pressurized interceptor and
sewer system in which the sole control was a valve at the downstream end
of the interceptor. Pressure ranges in the interceptor and throughout
the connected sewerage districts would then be dominated by a single
control point. More importantly, a large pressure system would generally
be constructed in stages, and each stage would require the use of at
least temporary controls befitting that stage. Consequently, each pres-
sure service district should be hydraulically independent of the pressure
magnitudes and variations in the interceptor to which it is tributary.
- 84 -
-------
This calls for a regulating valve wherever a trunk pressure sewer joins
an interceptor.
As flow in a pressure district approaches zero, the hydraulic
gradients for all branches approach the horizontal. To maintain a
positive conduit pressure during extremely low flows, therefore, the
associated flat hydraulic gradient must be artificially raised and held
above the highest ground elevation in the district, as illustrated
schematically by the ground profile, conduit profile and minimum-flow
hydraulic grade-line in Fig. 26.
Assuming that at least some of the buildings are served by house-
hold storage-grinder-pump units, the upper pressure range is limited by
the maximum total dynamic head of 35-psi for which the units are designed
(Section V), or by a maximum curb pressure of 30-psi if 5-psi is allowed
for friction and elevation pressure attrition in transmitting the sewage
from the household unit to the street sewer. The limiting level for
hydraulic grade lines equal to ground elevation plus 30-psi is also
shown in Fig. 26.
A constant-pressure valve and a flow-responsive valve are the two
basic types of pressure control valves. If case "A" in Fig. 26 depicts
the hydraulic grade line for maximum flow, a control valve set to hold
a constant pressure head at about 75-ft. will restrict all hydraulic
gradients to the range between that maximum and the minimum hydraulic
grade line. If the hydraulic grade line for maximum flow was depicted
by case "B" in Fig. 26, it becomes necessary to use a flow-responsive
control valve that will provide pressure heads of about 75-ft. at minimum
flow, of about 40-ft. at maximum flow, and meet all intermediate flows
without letting the hydraulic grade line pass above the ground line level
plus 30-psi or below the ground line level itself.
Where the topography is steep, a service district may have to be
subdivided into pressure zones in which the hydraulic gradients are
regulated by separate zonal control valves as shown in Fig. 27. Where
the topography is flat or adverse, in-line booster pumping stations will
usually be required as well as interceptor and perhaps zonal control
valves as shown in Fig. 28.
Major system-pressure transients can originate at the system
control valves but such pressure rises can be constrained by proper
valve-stroking design. For a street sewer system maintained under
pressure at all times, the extent of over-pressure and under-pressure
can therefore be regulated by proper valve actuation. Even though
large air pockets would not usually be created in a continuously pres-
surized system, it will still be necessary to provide air release-air
inlet valves at the summits of the system.
Because the total dynamic head of centrifugal pumps declines with
flow through-put and the opposite characteristic is desired for the type
- 85 -
-------
00
en
i
INTERCEPTOR
GROUND LINE
PLUS 30 PSI
(30PSICURB PRESSURE)
HYDRAULIC GRADE LINE
FOR MAXIMUM FLOW
HYDRAULIC GRADE LINE
FOR MINIMUM FLOW
PRESSURIZED
PUBLIC CONDUIT
2000 3000 4000
HORIZONTAL DISTANCE IN FEET
FIGURE 26
EXAMPLE OF MINIMUM AND MAXIMUM HYDRAULIC GRADE LINES
(Adapted from Ref.6)
5000
-------
CD
-^
I
2IOr
180
150
120
90
60
30
INTERCEPTOR
Mf.-C.R- CURB PRESSURE
H.G.L = HYDRAULIC GRADE LINE
*
H.G.L.AT
FLOW
-nH.Gl.AT
/JMIN_FLO
H.G.L.AT
MIN. FLOW
'C.R = 66'
^HCONTROL VALVE
ItCONSTANT PRESSURE)
•CONTROL VALVE (CONSTANT PRESSURE)
1000
2000 3000 4000
HORIZONTAL DISTANCE IN FEET
FIGURE 27
EXAMPLE OF PRESSURE ZONE CONTROL
(Reproduced from Fig.8,Ref. 6)
5000
-------
100
80
60
00
CO
40
FLOW-
RESPONSIVE
CONTROL
VALVE
INTERCEPTOR^1'
L
HOTE\ C.P. • CURB PRESSURE
H.G.L. = HYDRAULIC GRADE LINE
GROUND LINE
PLUS 30 PSI
(30PSI CURB PRESSURE)
H.G1. AT
MIN. FLOW
C.P. = 61'
H.G.L. AT
. FLOW
H.6.L AT
MAX. FLOW
H.6.L. AT
MIN. FLOW
C. P. • 21'
0
1000
2000 3000
HORIZONTAL DISTANCE IN FEET
FIGURE 28
EXAMPLE OF IN-LINE PUMPING
(Reproduced from Fig.7, Ref.6)
4000
5000
-------
of system at issue, pumps must be selected with great care for large
sewage sources in pressurized sewer systems in order to insure meeting
the full range of required operation.
Reference 6 contains a comprehensive summary of hydraulic consid-
erations in pressure sewerage including those for source and in-line
pumping as well as district and zone pressure control. Devices and
techniques for controlling pressurized sewer systems are covered in
Reference 11. Both references deal with readily available equipment
and techniques already developed for water works service. Their full
applicability to the handling of wastewater that has been passed through
a grinder must be determined in future field demonstrations (Section XIV).
Reference 11 discusses devices for back-flow prevention in comminutor-
pump installations in large buildings. The check valve developed for the
prevention of back-flow in household storage-grinder-pump units is
described in Reference 21.
- 89 -
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SECTION VIII
INSTALLATION OF THE PROJECT SCHEME
IN EXISTING SEWERS*
Introduction
Important in the evaluation of the ASCE scheme of inserting small-
diameter tubing into existing building drains and sewers and introducing
suspended conduits into existing street sewers is (1) the associated
reduction in the capacity of the building drains and sewers that convey
roof and yard drainage to street sewers and of the sewers to convey
storm water flows to receiving waters, (2) the increased danger of stop-
pages by debris caught between the tubing and the pipe walls, and
(3) the increased difficulty of cleaning and repairing both building and
street sewers.
Relative Cost and Reliability of Pressure System
Studies made by consultants for ASCE on hypothetical pressure
systems for San Francisco, Milwaukee and Boston (Section IX) agree
(1) that the costs of such systems will be greater than those of conven-
tional combined-sewer separation; (2) that the service reliability of
the pressure system will be less than that of separated gravity systems;
and (3) that pressurized systems will be subject to more outages and
stoppages than the gravity systems.
Effect of Inserted Pipes on Hydraulic Capacity of Sewers
Under a subcontract with the ASCE Project, the Department of
Theoretical and Applied Mechanics of the University of Illinois prepared
two reports on the "Effect of Inserted Pipe on Flow Capacity of Sewers,
References 25 and 26. Investigated was the hydraulic behavior of conduit
sections within which the insertion of circular sections leaves ring-
shaped flow areas. Much pertinent information was available in published
studies on heat transfer tubing in boilers and other heat exchangers and
in theoretical fluid dynamics. Pertinent references are included in the
University of Illinois reports.
In the Illinois experiments, turbulent flow was studied in a
100-ft. long, 6-in. diameter, pressure line in which 3/4-in. and 1 1/2-in.
pipes could be inserted in critical positions. Maximum velocities of
* Refs. 24, 25 and 26.
- 90 -
-------
flow were over 20-ft. per second and minimum velocities were about 2-ft.
per second. The pipe walls were hydraulically "rough."
The ratio of the inside diameter, Do, of the outside pipe to the
outside diameter, D^, of the inside or inserted pipe, designated by the
symbol £ = D /D-, and the eccentricity of the insertion, given the symbol
6 = AcA(D0 - D^), where AC is the offset of the center of the inserted
pipe from the center of the outside pipe, were varied. Observed flow
resistance coefficients or friction factors were related to the hydraulic
radius interpreted as the ratio of the area of flow to the total wetted
perimeter.
Experimental results for concentric annalus friction-factor ratios
associated with different pipe-diameter ratios are plotted in Fig. 29,
together with values obtained by others in earlier studies. The Univer-
sity of Illinois results are shown as double circles. Although there is
considerable scatter in the results obtained by different experimenters,
it appears that the following conclusions can be drawn: (1) at a dia-
meter ratio near unity (DQ/DJ^ = 1), the friction factor for concentric
annular conduits is about 10% less than that of an unobstructed pipe;
(2) the friction factor ratio increases thence rapidly with increasing
diameter ratios to a maximum value about 107<> above the reference value
fa/f = 1 up to a diameter ratio of about two; and (3) after that the
friction factor ratio drops off slowly towards unity as the diameter
ratio increases further and lies only slightly above that for an unob-
structed pipe at a diameter ratio of six.
Fig. 30 identifies as curve A from Fig. 29 the ratios of friction
factors for the concentric annulus, and as curves B, C and D the ratios
of friction factors for annular eccentricities e equalling 0.667, 0.90
and 1.00, that obtain at diameter ratios a ranging from 1 to 8. The
effect of eccentricity is seen to be considerable when the inserted pipe
is nearly of the same diameter as the outer pipe (£ = 1.2) and is placed
against the inner wall of the larger pipe at maximum eccentricity. The
friction factor is then reduced to 64% of its concentric value. This
reduction decreases as the relative size of the inserted pipe becomes
smaller and reaches 82% when the diameter of the inserted pipe is one
fifth that of the outer pipe, i.e., when a = 5.0. The mode of friction
reduction at eccentricities between zero and one is suggested in Fig. 30,
but it is based on limited data.
Flow capacity is a function of friction factor and cross-sectional
area of flow for a given hydraulic gradient. For a diameter ratio, a,
close to 6, with the inserted pipe suspended by slender rods spread
about 14 D0 apart and held in place by thin wires in tension, the flow
capacity is reduced by 12.7 per cent at zero eccentricity (concentric
pipes). At full eccentricity, i.e., when the inner pipe rests against
the outer pipe, on the other hand, the reduction is only 4.5%, probably
because the inserted pipe is within a region of lower intruded pipe
velocities.
- 91 -
-------
cr
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§
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cr
CO
If
Z O
z —
zt
95
Ol*J
GTO
1.5
1 A
I.*T
1.3
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1.0
0.9
r\ o
A
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0.8-
2
©
•O
0?^
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1
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x
X
1
SYMBOLS
I BECKER 1907 v ROTHFUS 1950
+ WINKEL1923 * STEIN 1954
O LONSDALE1923 ® DEISSLER1955
A ATHERTON 1926 -OBARROW 1955
T CALDWELL1930 <|) OLSON 1963
X KRATZ 1931 $ BRIGHTON 1964
• LORENZ 1932 BRIGHTON 1964
0 PIERCY 1933 J JONSSON 1966
A
CARPENTER 1946 t> QUARMBY 1967
l FRAZIER 1948 <=" OKIISHI 1967
a OWEN 1951 O ROBERTSON 1968
D OWEN (BR) 1951
A
a «c
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2 3
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V
CURVE A
/
^
•
^*
^B
4 5678
D
RATIO OF DIAMETERS, a=
(LOGARITHMIC SCALE)
FIGURE 29
TURBULENT- FLOW FRICTION FACTOR FOR CONCENTRIC
ANNULUS AS A FUNCTION OF DIAMETER RATIO
(Modified from Fig. 1, Ref. 25)
- 92
-------
CURVE A, e = 0, (CONCENTRIC ANNULUS)
v-CURVE B, € 0.667
CURVE C, e = 0.90
CURVE D,e- 1.00
1/2 (Dn-DO
DEFINITION SKETCH
4.0 5.0 6.0 7.0 8.0
DO
RATIO OF DIAMETERS, 9 = 1^"
(LOGARITHMIC SCALE)
FIGURE 30
DEVIATION OF FRICTION FACTORS FOR CONDUITS OF ANNULAR
CROSS-SECTION BASED ON HYDRAULIC RADIUS CONCEPT
(Modified from Fig. 10, Ref. 25)
-93-
-------
Flow capacity will be further reduced if the type of pipe hanger
employed offers a significant additional obstruction to the flow. The
Johns-Manville Company developed a special single-piece molded plastic
hanger for the Project (Ref. 24) dimensioned for adequate structural
strength with a resultant fairly thick profile at the periphery of the
supported pipe. In a hydraulic test of this design at laboratory scale
for a pipe diameter ratio, £, of 5.8, flow capacity was 407, less than
that for an outer pipe without an inserted smaller pipe. In a trial
installation in a combined sewer the field insertion of pipe in this
type hanger, subsequent to bonding the hangers in place (Section VII),
was found to be awkward and complicated. The main feature of the hanger
is its bonding system, and the disadvantages of the original design
would be mostly overcome by using an ordinary thin metal strap loop
around the inserted pipe, suspended by a rod or rods connected to a
molded plastic seat of the original design bonded against the street
sewer. That is, installation would be facilitated and hangers would not
have an appreciable deleterious effect on flow capacity, over and above
that for the inserted pipe. Thus, the indications of the previous para-
graph would be reasonably applicable to the revised hanger design.
Maintenance and Operation of Pressure System
As stated in Reference 17, the principal difficulty in a pressure
system is believed to be routine maintenance of piping and individual
storage-grinder-pump units. Although the anticipated ASCE scheme pres-
surized sewerage layouts have been provided with a liberal number of
cleanout tees, depressuring and cleaning may be attended by numerous
difficulties. A gravity sewer can be rodded at any time and still
provide service during the cleaning operation. By contrast, a pressure
sewer must be closed down during cleaning. All affected storage-grinder-
pump units must be turned off, the main must be valved shut, the cleanout
tees must be unbolted, and the main must be dewatered. After it has been
rodded by conventional means the main must then be resealed and the
storage-grinder-pump units must be turned on again.
The required cleaning frequency of pressure sewers cannot be fore-
told. Because provision would be made in their design for the occurrence
of self-cleaning velocities at least once a day, they should need no
routine cleaning. However, this surmise will have to be confirmed in
practice.
Dewatering a pressure sewer might be a messy and arduous task.
A hose valve will conceivably have to be attached to half of the clean-
out tees if the pipe is to be dewatered between manholes.
To prevent willful overflows, storage-grinder-pump units will
probably not be equipped with an external off-on switch. Some other
provision will have to be made to turn the units off for cleaning,
repair and maintenance. Night maintenance might be successful.
- 94 -
-------
Cleaning building sewers containing inserted tubing will offer
some difficulties. Conventional rodding and root-cutting equipment may
be inadequate. Even the larger sized walk-through street sewers in
which conduits are suspended at the crown may be difficult to clean with
bucket-type drag-through equipment. Pressure water-jet cleaners may
work better.
The designer of pressure sewerage must keep in mind the mainte-
nance, repair and replacement of all system components. It may be
necessary to provide temporary bypass piping and connections. To speed
and simplify the repair of storage-grinder-pump units, they might be
replaced in much the same way as water meters have been for many years.
Control valve maintenance will include resetting the valves to function
within the pressure and flow regime of each particular portion of the
system. Careful and complete records of settings would therefore have
to be kept. Systems maintenance and repair would probably have to be
followed by confirming the operation characteristics of all working
parts.
- 95 -
-------
SECTION IX
INTRODUCING PRESSURE SEWER SYSTEMS INTO
EXISTING COMBINED SEWER DISTRICTS*
Introduc tion
The feasibility and cost of the Project scheme were tested for
three areas representative of existing combined sewer systems: (1) a
central downtown commercial area in Boston, Mass., (2) a mainly resi-
dential area in Milwaukee, Wis., and (3) a predominantly residential
area in San Francisco, Cal.
Using data supplied by municipal officials and design criteria
developed by the ASCE Project, designs of pressurized sewer systems
were prepared for the three areas by the Project staff. Under sub-
contract with ASCE, the three designs were reviewed and evaluated
independently by consulting engineers familiar with the study areas.
For comparison of the Project scheme with conventional gravity sewer
separation, moreover, conventional separation was studied by the
consultants for the Boston and Milwaukee study areas and by the San
Francisco Department of Public Works for the study area in its juris-
diction.
Brown and Caldwell studied the 323-acre Laguna Street Sewer
Service District of San Francisco, Cal. This area is predominantly
residential in character with some commercial and a few industrial
properties. Most of the structures were built after the 1906 fire.
Exclusive of streets, 80% of the area is occupied by buildings. The
sanitary sewage is carried to the city's North Point Treatment Plant.
Overflows from the combined sewers discharge to San Francisco Bay.
Greeley and Hansen gave their attention to the 157-acre Prospect
Avenue Study Area of Milwaukee, Wis. This area is mainly residential
but contains scattered institutional or public buildings and small
commercial establishments. Originally the area was occupied very
densely by small residential structures. Of the single-family residen-
tial buildings most were constructed before the late 1930's and a large
number even before 1900. Many of them have since been converted to
multiple-family use. The dry-weather flow is carried to interceptors
near the Milwaukee River and in Brady Street. These discharge to the
city's Jones Island Treatment Works. Overflows from the combined sewers
discharge to the river.
* References 16, 17 and 18.
- 96 -
-------
Camp, Dresser & McKee studied the 53-acre Summer Street Separation
Study Area of Boston, Mass. This is a heterogeneous commercial district
with closely spaced multi-story office buildings, department stores, and
theaters. Many of the buildings date back to the late 1800's. However,
a major department store has been added in the last twenty years, and a
large apartment and parking-garage building is of recent construction.
Dry-weather flow enters the East Side Interceptor of the 1884 Boston
Main Drainage System, which has recently been connected to the Deer
Island Treatment Plant. Overflows from the combined sewers and the
interceptor empty into the Fort Point Channel of Boston Harbor.
Study Areas
Other pertinent characteristics of the three study areas are
summarized in Table 14. Location maps and general plans for San
Francisco are shown in Figs. 31 and 32, for Milwaukee in Figs. 33 and
34, and for Boston in Figs. 35 and 36.
Separation of Building Plumbing
With the help of plumbing consultants and plumbing and mechanical
contractors, the engineering consultants developed the measures needed
to separate the sanitary and roof-water drainage piping in the different
kinds of buildings of the study areas. Restructuring was based on
building surveys and upon data provided by the municipal departments of
public works.
Piping to connect the restructured system to gravity and pressure
sanitary sewers and to storm drains was identified and cost estimates
were made for the different types of plumbing separation required in
each class of structure. Layouts were based as closely as possible on
local plumbing codes.
The separation of building plumbing is discussed in general in
Section X.
San Francisco
As shown in Fig. 37, soil and drain stacks rise separately through
the building from the main horizontal building drain in the basement.
Traps and vents are required.
Designs and cost estimates were made for separating piping in
single-family dwellings, apartment buildings and commercial buildings,
as shown in Fig. 38. The principal requirement was an additional main
drain and the reconnection of the soil and drain stacks. The cost asso-
ciated with disruption of normal use of the buildings during their
reconstruction was allowed for. The costs of connecting piping to
- 97 -
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TABLE 14
CHARACTERISTICS OF STUDY AREAS
HYPOTHETICAL APPLICATIONS OF ASCE COMBINED SEWER SEPARATION PROJECT
Study Area Designation
Consultant making evaluation
Year for Design
Extent of gross area (ac.)
Type of development:
present -
projected -
Length of combined sewers (ft.)
Topography
Population
San Francisco. Cal.
Laguna Street
Brown and Caldwell
1993 (25-yrs)
323
Milwaukee, Wis.
Prospect Avenue
Greeley and Hansen
1993 (25-yrs)
157
Predominantly residential Mainly residential
Residential, including
highrise
66,000
Steeply sloping
(El. 10 to El. 340)
(1960) 21,800
Dwelling units ("Housing units") (1960) 10,900
Annual (winter rate) water use:
metered -
future
Number of structures
Number of service connections
Special difficulties
(1966) 2.97 cfs
(1993) 4.78 cfs
(1963) 2,773
Steep slopes
Primarily residential
with large apartment
complexes
33,000
Gently sloping
(El. 30 to El. 80)
(1966) 11,300
(1993) 14,000
(1966)
(1993)
3,500 (est.)
5,800
(1968) 1.15 cfs
(1993) 1.76 cfs
(1996) 843
Boston, Mass.
Summer Street
Camp, Dresser and McKee
2020
53
Heterogeneous commercial
High-rise commercial
13,000
Gently sloping
(El. 21 to El. 85)
(1968) 1.54 cfs
(2020) 3.41 cfs
(1968) 600 (200 to be
separated)
Closely spaced buildings Narrow streets, subways,
crowded utility piping,
surcharging at high tide.
-------
G*ldw> Got*
YocM ChA
A
INTERCEPTOR
FIGURE 31
LOCATION OF LACUNA STREET
STUDY AREA, SAN FRANCISCO
(Reproduced from Fig. 2-1, Ref. 16)
-99-
-------
STUDY AREA BOUNDARY—7
fe
>
'I I <<
m m t ?\
\
H
LAND USE CATEGORIES
PUBLIC USE OR
PRIVATE INSTITUTION
RESIDENTIAL
COMMERCIAL
\
BOUNDARY
FIGURE 32
BASIC LAND USES IN THE SAN FRANCISCO STUDY AREA
(Adapted from Fig.2-5, Ref. 16
-100-
-------
MILWAUKEE
STUDY AREA
SCALE : 0.5 0 0.5 I MILE
I. ,1 I I
FIGURE 33
LOCATION MAP, MILWAUKEE STUDY AREA
(Reproduced from Fig. 1, Ref. 17)
-101 -
-------
,
N ASTOH |T. '
ii il\
, ^
iil [01 tel \i i
"
j, , ^
Sl/'tS* 104 \ i 5 j
V . *v . U '
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"nafTn' ' ; >2?™.Li^;e£r'!i0!2as/>^!yjr?1^i i -j
ii! /i,, lii xltv|E^iHipif^|^
\l L/(.o««it«ij]\U" i/t^wmi^iMiM j |_ (£i«^C££««i 3J i^o3ii[.oijj| " ^oa^i^oitflj " j£ip»i[^Ji]j u [_ («>roi(.<>ii£j IJjX'
TT •/> \/ w HUMAOLOT AVI ^ / / C^" ^
XXX
I xxxx)
I.XXXX)
I XXX I
100 0 100 200 JOO 400 500 600 TOO BOO 900 1,000 FEET
I i I I I I I I I I I I I
LEGEND
POPULATION PER BLOCK
PRESENT FLOW (C.F.S.)
FUTURE FLOW (C.F.S.)
PRESENT NUMBER OF DWELLING UNITS
FUTURE NUMBER OF DWELLING UNITS
CONTOUR LINES
FIGURE 34
PRESENT POPULATION, PRESENT AND FUTURE
ESTIMATED FLOW AND NUMBER OF DWELLING UNITS
MILWAUKEE STUDY AREA
(Reproduced from Fig. 3, Ref. 17)
-------
TYPICAL
BUILDING AT
55 SUMMER
STREET
LIMIT OF
STUDY AREA
FIGURE 35
LOCATION OF SUMMER STREET SEWER SEPARATION AREA, BOSTON,
MASS.,AND TYPICAL BUILDING SELECTED FOR STUDY
(Adapted from Fig-lZ-1, Ref. 18)
SCALE :l"= 100O'
- 103-
-------
3£
0
4*7
39
IT*.
£to
:-LEV.25
BOSTON
COMMON
SUBWAY
TUNNEL
^,
^>
,ELEV. 85
-3
^<**.
^
L^J^.
VI
^
>^
^
*?//
A^
^LEV6O
LELEV. 35
&
tu
M
01
m
'//
ELEV. 40
• SUBWAY
TUNNEL
^
TYPICAL COMMERCIAL
BUILDING AT
55 SUMMER
-SUBWAY TUNNEL
40" COMBINED
SEWER
fa
I BOUNDARY OF SUMMER
STREET SEWER SEPARATION
STUDY AREA
REFERENCE ELEVATION*
MEAN HIGH WATER
10.23 FEET
ELEV. 25
c
c
\
^
v>
v>
X
C1'
>,
*
A>
FIGURE 36
SUMMER STREET SEWER
SEPARATION STUDY AREA
BOSTON, MASS
(Reproduced from Fig-31-1 Ref.18)
^Overflow •
.<>»/.
V>,
»'ro.
TO BOSTON
HAMOM
Scale: |" =400'
- 104-
-------
S1MGLE FAMILY DWELLING
vent line
— — — roof leoder or
roinwoter line
——— wastewofer or
combined line
roof-
roof leader
i i—ouTstoe i
I / with tr
Ctf"
c.o.
(cleanout, typical)
area drain
op
-boundary trap
APARTMENT BUILDING
(6 STORY)
fresh air inlet
to surface
curb
,— outside
ff area droi
floor drain
-boundary trap
COMMERCIAL BUILDING
soil stacks
;.:::;;" "•_-.:,., c.o,
; ::/-^ iT /—porting areo
\ il "T^^-C. Jroin
roof leader-
c.o.
T
-boundary trap
FIGURE 37
TYPICAL IN-HOUSE WASTEWATER AND RAINWATER
PLUMBING SYSTEMS, SAN FRANCISCO STUDY AREA
(Reproduced from Fig. 3-1, Ret. 16)
- 105-
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STRUCTURE A^
Victorion-Type residence
3 story, incl. ground level garage
Estimated cost of in-house
separation - $ 1,487
lOO1 - new 4" C. I. main
building drain for rainwater
property
3" roof leader
Detail I , Fig. 9
intercept existing 4
main building drain
3" area drain
-3" area drain
- 3" roof leader
(Detail 2, Fig. 9)
STRUCTURE B
New two family residence
3 story, incl. ground level garage
Estimated cost of in-house
separation - $ 569
existing
main drgir
I
property
line -*]
(^intercept existing
" 3" outside roof
leader (Details 3
and 4, Fig. 9)
35'- new 3" C. I. main
building drain for
rainwater
STRUCTURE C
New multiple family residence
3 story, incl ground level garage
Estimated cost of in-house
separation - $ 633
property
intercept exist.
3" outside roof
leader
6'off set to place
new line in
garage area
30'-new 3"C.I. main
building drain for
rainwater
STRUCTURE D
New commercial building
ground floor restaurant
2nd floor office space
Estimated cost of
in-house separation
$1,180
exist ing main drain
I ---"
intercept exist
4"roof leader
in wall
property
-55'-new 4" C.I-main
building drain for
rainwater
FIGURE 38
PIPING REQUIREMENTS AND ESTIMATED COSTS FOR IN-HOUSE
SEPARATION OF SELECTED STRUCTURES,
SAN FRANCISCO STUDY AREA
(Reproduced from Fig. 3-3, Ref. 16)
- 106 -
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gravity sewers was found to be slightly higher than that for pressure
sewers. It was assumed that the conventional building sewer would
extend to the front property line, whereas for a pressure sewer system
it would terminate at the inlet to the storage tank of the household
storage-grinder-pump unit.
Milwaukee
Because the Milwaukee plumbing code formerly allowed all struc-
tures on a single building lot to be connected through a single pipe to
the combined sewer, separation called for the installation of new
sanitary and storm sewers to the street where single pipes had been
employed before. Roof drains were generally connected to the main
building drain beneath the basement floor. There were no building
footing drains in the study area.
For purposes of design the structures were classified by use,
number of floors, type of construction, number of dwelling units and
location on the lot. Typical separations were designed for each class,
as shown in Fig. 39. It was assumed that new storm drains would have
to be laid outside the structures for the collection of roof water but
that basement floor drains would not be separated from the existing
plumbing.
It was assumed further that the separation of plumbing in the
larger buildings would be adapted to their specific requirements and
that new storm drains would be laid either along the inside or outside
faces of basement walls, whichever was simpler.
Included in the cost of separation for connection to an ASCE
pressure system was the line to the street sewer. The cost of the
storage-grinder-pump unit itself was made a separate item.
Boston
In the largely commercial Boston study area, where residential
structures were restricted to a few buildings with apartments in upper
stories, the cost of plumbing separation was estimated for a typical
building for which structural and piping plans were available. This
five story commercial building, Fig. 40, was constructed in 1892.
Connection of the plumbing system to a gravity sanitary sewer lateral
and to pressure sewers of the ASCE Project was studied. Typical of
Boston buildings is the extension of their basements beneath the sidewalk
to the curb line. This reduces the length of the building sewers to the
street sewer and storm drain. As shown in Fig. 40, moreover, for a
typical building the waste or soil stacks and the roof-water drain
stacks extend separately to a junction in the building drain close to
the basement wall. The building chosen for study had two service connec-
tions to public sewers on intersecting streets, and it was estimated that
- 107 -
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Connecting drain „
L
VI
Downspout
r
i_
s s / s
_ — .
/
* , * * .
rT
w
i
i
i
L_
' y / /
._.__
y
/ / / /
n~
i
1
J
GROUP "A"
t
A
r f S /
T7
GROUP "B"
T
1
T
L.
r . .
— — -
-
t^* y •"
:^—
i
1
1
1
I
j
GROUP "C"
p-
l_
— -<
/
1
>' r f
* s s
••=v-
i
1
1
1
|
^
t
GROUP "D"
GROUP"E"
NOTE =
Downspouts show
minimum number
required per group
FIGURE 39
DOWNSPOUT CONNECTION GROUPS
MILWAUKEE STUDY AREA
(Reproduced from Fig.4, Ref. 17)
-108 -
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8" PIPE TO
EXISTING I8'XI8"
COMBINED SEWER
STREET
EXISTING
EXTERIOR WALL
I
i ;
I
FIGURE 40
SUMMER STREET SEPARATION AREA
BOSTON,MASSACHUSETTS.
PLAN OF BASEMENT PLUMBING
IN 55 SUMMER STREET
(Reproduced from Fig."21- 2 , Ref. 18 )
SIDEWALK ABOVE
(TYPICAL ALL AROUND)
9" STORM
4' SANITARY
W 4'
SANITARY
5'COMBINED
8" PIPE TO
EXISTING 36 X3I
COMBINED SEWER _
-00-
LEOEND
EXISTING HORIZONTAL
WASTE WATER PLUMBING
EXISTING VERTICAL
WASTEWATER PLUMBING
EXISTING RUNNING TRAP
NEW 4" SANITARY
SCALE IN FEET
-------
only 200 of the approximately 600 recorded building connections to
street sewers would require separation. The estimated cost of con-
structing pits below basement floors and installing comminutors and
duplicate pumps was added to that of connections in the item for
plumbing separation. A sketch of the suggested pit and pressure piping
is shown in Fig. 41.
Summary of Plumbing Separation Studies
A summary of the consultants' information on plumbing separation
is presented in Table 15. Estimated costs are given at the bottom of
the table.
For San Francisco and Milwaukee, in which the cost of separation
does not include the cost of the storage-grinder-pump unit or a func-
tionally equivalent comminutor wet-well pump unit, the cost of building
plumbing* separation is about the same for the gravity street system
and the pressure sewer system.
Storage-Grinder-Pump Units
The requirements for household and commercial-sized grinding and
pumping units, needed volumes of storage, development of the storage-
grinder-pump (SGP) unit by the General Electric Company, and the use of
comminutors and non-clog sewage pumps are stated in Sections V and VI
of this report. It was assumed that the SGP equipment would be appli-
cable to the residential and smaller commercial installations in San
Francisco and Milwaukee and that comminutor and non-clog pumps would be
installed in the wet-wells of large installations in San Francisco and
Milwaukee and of all installations in Boston.
In the Milwaukee study, it was assumed that single-family houses
would be served by single SGP units, multi-family houses and small com-
mercial buildings by modified (enlarged) SGP units and larger commercial
and industrial buildings by comminutor-pump installations.
In the San Francisco study, the assumption included the use of
single SGP units in single- and two-family dwellings; single modified
SGP units in small multi-family (3-4 dwelling units) buildings; two or
more modified units in large apartment buildings, hotels, and public
buildings; and comminutor-pump installations in large commercial and
industrial buildings.
* With allowance for different lengths of building drains and sewers
in San Francisco.
- 110 -
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BOSTON STUDY AREA
RUN NEW 4" CHAMBER
VENT TO ATMOSPHERE
EXISTING 4"
SANITARY
SANITARY
NEW PIT
WALL -
-MOTOR
SUPPORT
PLATFORM
\
^—ALTERNATE
LOCATION
OF PLASTIC
TUBING
\
N,
\ N..N N,
EXISTING 5 COMBINED
TO BE 5" STORM DRAIN
AIR 8 WATER TIGHT SLEEVE
THRU COVER.
NEW AIR 8 WATER TIGHT
COVER 8 FRAME WITH
HATCH , LADDER 8
LIGHTS
EXISTING
PIT WALL
NEW PLASTIC TUBING
CONTROL VALVE
NEW COMBINATION GATE 8
BACK WATER VALVE
5" OPENING TO RECEIVE
PLASTIC TUBING. MAKE
TIGHT JOINT
REMOVABLE
GRATING
EXISTING 4
SANITARY
COMMINUTOR
WITH BYPASS
AND SCREEN
NEW 5
SANITARY
COMBINED TO BE
STORM DRAIN
OPEN END IN 8" LINE
FOR EMERGENCY GRAVITY FLOW
IN CASE OF ELECTRICAL
FAILURE
4'x 4'x 4' WET WELL
FIGURE 41
SECTION OF PROPOSED PIT AND PLUMBING, PRESSURE SYSTEM
(Reproduced from Fig. 12-5, Ref. 18)
NOT TO SCALE
- in -
-------
TABLE 15
SUMMARY - BUILDING PLUMBING SEPARATION
HYPOTHETICAL APPLICATION OF ASCE COMBINED SEWER SEPARATION PROJECT
Typical structure
Age of structure
Number of building service connections
Plumbing code controls
Roof drains connected separately to
junction in basement
San Francisco, Cal.
Residential
Since 1906
2773
Yes
Yes
Milwaukee, Wis,
Residential
Prior to 1930
843
Yes
Yes
Boston, Mass,
Commercial
Late 1800's
200
Yes
Yes
Average cost of plumbing separation
including engineering and contingencies
Per building, not including SGP unit
Per building, including SGP and connections
Pressure Gravity Pressure Gravity Pressure Gravity
$1,590(1) $1,950(2) $1,440(3) $1,350(3)
#3,500 $2,300 $3,100 $1,350 $20,000 $10,000
(1) Connection as far as SGP unit
(2) Connection as far as front property line
(3) Connection to lateral
-------
Building Service Connections
Two principal alternative arrangements of building service connec-
tions were studied. In one of them, as in Professor Fair's original
scheme, the pressure tubing was inserted in the existing building drain
and sewer for the full distance to the existing street sewer. In the
other arrangement, pressure tubing was laid below frost depth in a
trench leading from the building to a pressure conduit in trench near
the sidewalk. These alternative schemes are described and summarized
in Section VII.
Because of the difficulty of inserting pressure conduits in small
combined sewers, which predominated in the study areas, cost estimates
were based on adoption of the second scheme.
Pressure Sewer Systems
The ASCE Project method for separation by pressure pipes leading
from storage-grinder-pump units to pressure conduits in the street was
applied by the ASCE Project staff to each study area and the resulting
designs were reviewed and accepted as reasonable by the consultants.
Sewage Flow Rates
Design criteria for pressure sewer systems are reported in some
of the Technical Memoranda prepared by the ASCE Project staff. Flow
rates are summarized in Section IV.
For maximum and minimum conduit sizing, rates of flow are gener-
ally based on the average annual domestic water demand, multiplied by
a factor reflecting the number of dwelling units or services tributary
to the reach of conduit under consideration. The factors are shown in
Figs. 6 and 7. Those in Fig. 6 are for the northeastern United States
and were assumed to be applicable to the Milwaukee study area, and
those in Fig. 7 were assumed to be applicable to the San Francisco
study area.
Annual domestic water demands considered representative of sewage
flows were taken from records of measured winter water use for the San
Francisco and Milwaukee study areas.
Design periods assumed for San Francisco and Milwaukee are
25-years, and for Boston 50-years.
- 113 -
-------
Conduit Materials
Suitable pipe-within-a-pipe tubing for building drains and sewers
and for pipe conduits in street sewers were identified by the National
Sanitation Foundation (Ref. 23). Tubing could be copper, or polyethylene
or polybutylene plastic such as that employed in domestic water service-
connections 1%-in. to 2-in. in diameter. Conduits could be asbestos-
cement, cast iron, ductile iron, coated steel, or plastic pipes, 2-in.
through 18-in. in diameter.
Hydraulic Criteria
Basic hydraulic criteria for the design of piping systems, including
the choice of pipe sizes for different ranges of flow and the preserva-
tion of reasonable hydraulic gradients within available pumping heads and
horsepower ratings are discussed and illustrated in Section VII.
Service Districts and Pressure Zones
A service district is defined as a section of a pressurized
sanitary sewer system that is hydraulically independent of an interceptor
and adjacent service districts. Such a district has definable boundaries
and discharges its sanitary sewage into an interceptor for transport to
a treatment plant. It would necessarily be treated as a complete unit
and provide for the separation of all the combined sewers it contains.
A pressure zone is defined as a subdivision of a service district sepa-
rated from the remainder of the district by a pressure-control valve.
Alternative Arrangements of Collection Systems
Six alternative arrangements of pressurized sewerage schemes were
presented in the report of the National Sanitation Foundation (Ref. 23).
They are summarized and discussed in Section VII. Of these arrangements,
three were used in alternative designs reviewed by the engineering con-
sultants to establish the probable cost of constructing pressurized
systems. These three are identified as Layouts A, D and nSf in Figs. 20,
24, and 25, respectively.
Layouts A and nSf are relatively conservative in nature. Each
includes dual-main pressure conduits as well as dual laterals. Street
valves isolate block-long runs of mains to permit maintenance and repair
without shutting down large portions of the system. Although the resul-
tant partially duplicative piping might appear extravagant, it was the
opinion of the engineering consultants that this made for a reasonable
and safe substitute for gravity separation of sewers.
If methods of cleaning pressure conduits in lengths greater than
about 500-ft. can be developed and confirmed, fewer street valves and
- 114 -
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valve manholes would be required than assumed in the cost estimates,
which should substantially reduce the costs for these components.
Layout Studies
As explained earlier in this section, alternative systems designed
by the ASCE Project staff were reviewed and their costs estimated by
engineering consultants. These studies are summarized immediately below.
San Francisco
For the San Francisco study area, two alternative arrangements of
pressurized sewers were chosen. Alternative A established an essentially
dendriform (branching) pattern of sewerage in which individual branches
consist of parallel conduits on the sides of each street. Interconnec-
tions at street intersections would provide some manifolding and duplex
available paths. Alternative A, based on Layout A in Section VII
(Fig. 20), is shown in Figs. 42 and 43. Pressure conduits were not
placed inside existing combined sewers.
As shown in Fig. 44, a profile with hydraulic gradients for the
main sewer, five pressure zones separated by pressure control valves were
necessary to care for existing differences in ground elevation.
Alternative B would be similar in design except that pressure
conduits would be suspended from the crown of combined sewers of walk-
through size. Use of pressure conduits suspended in existing sewers
would thereby be restricted to the reach of trunk sewers downstream from
Broadway and Franklin Streets, Fig. 42. The resulting layout would be
similar to Layout D of Section VII (Fig. 24).
Although field tests have shown that in the absence of obstructions
tubing can be inserted in building drains and sewers as far as the street
sewers, where the tubing could be connected to a pressure conduit within
the street sewer if it is of working height, this would be complicated in
San Francisco by the presence of a plumbing trap located in each building
service connection at the line of curb or sidewalk or immediately inside
the wall under the sidewalk, as called for in the plumbing code. With
separation via a pressure system there would no longer be a need for the
trap and it could be removed and replaced by a straight section if the
plumbing code was amended accordingly. Tubing could then be inserted in
building drains and sewers as far as the street sewer. However, for
study purposes it was assumed that the trap would not be removed and that
tubing would be installed in a trench leading from the basement to small
auxiliary conduits in trenches on each side of the street, which in turn
would be connected to the conduit within the existing sewer at street
intersections.
- 115 -
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£
I
o
2
UJ
•z.
o
-J
CHESTNUT ST.
LOMBARD ST.
GREENWICH ST.
FILBERT ST.
UNION ST.
^e
WASHINGTON ST.
PRESSURE CONDUITS
PRESSURIZED TRUNK SEWERS
STUDY AREA BOUNDARY
PRESSURE ZONE BOUNDARY
^4) NODES ON PIPELINE NETWORK
^
SACRAMENTO ST.
FIGURE 42
PRESSURE SEWER SYSTEM LAYOUT-ALTERNATIVE A,
SAN FRANCISCO STUDY AREA
(Reproduced from Fig. 5-4, Ref. 16)
-116-
-------
-INTERCEPTOR
FRANCISCO ST
CHESTNUT ST
LOMBARD ST.
GREENWICH ST.
FILBERT ST
GREEK ST
SCALE IN FEET
200 400 600 800
o
CURB LINE
PRESSURE CONDUIT (SIZES SHOWN
FOR TRUNK CONDUITS ONLY)
CLEANOUT
SHUTOFF VALVE
MANHOLE FOR HOUSING VALVES ft FITTINGS
PRESSURE CONTROL DEVICE
SEWERAGE FACILITIES ARE SHOWN SCHEMATICALLY
FIGURE 43
DETAILS OF TRUNK SYSTEM - ALTERNATIVE A, SAN FRANCISCO STUDY AREA
(Reproduced from Fig. 5-5 of Ref 16)
- 117-
-------
PRESSURE ZONE
PRESSURE ZONE I
PRESSURE ZONE H
HGL AT MIN
FLOW (370')
HGL AT MIN
FLOWI3OO')
X
CONTROL, PCV-5
HGL AT MIN FLOW (230)
CONTROL,PCV-4
HGL AT MIN.
FLOW Il60')x
GROUND PLUS 30 PSI
^CONTROL. PCV-3
HGL AT MAX FLOW
_ HGL AT MlN FLOW [_90_
HGL HYDRAULIC GRADE LINE
H8L FOR MAXIMUM SIZED CONDUIT
HSL FOR ADJUSTED SIZE CONDUIT
'-CONTROL, PCV-2
CONT|ROL.PCV-I| | | | |
IOOO
-INTERCEPTOR
4OOO SOOO fOOO
HORIZONTAL DISTAMCC IH FCCT
FIGURE 44
PROFILE OF PRESSURE SEWER SYSTEM-ALTERNATIVE A, SAN FRANCISCO STUDY AREA
(Reproduced from Fig.5-7, Ref. 16)
- ISO
IOJOOO
-------
A drawing of Alternative B would be similar to that of Alternative
A in the arrangement of conduits, cleanouts and valves. The nSf Layout
(Fig. 25 of Section VII) was considered but not used because of marginal
applicability.
A design of gravity sewers by the San Francisco Department of
Public Works for the conventional separation of sewers in the combined-
sewer area is shown in Fig. 45. The engineering consultants accepted
this design for their cost estimates.
Milwaukee
At Milwaukee, two alternative pressure systems of separation were
studied along with a conventional gravity scheme. Milwaukee pressure
sewerage Layout M-l based on Layout A of Section VII is shown in Fig. 46
as a dendriform system in which dual pressure lines are placed on the
sides of each street. The dual conduits in each street are cross-
connected at every street intersection. The study area is flat enough
to lie in a single pressure zone.
Milwaukee Layout M-2, Fig. 47, is based on the nSf Layout,
Section VII. As stated there, the nSf Layout is the most flexible one.
It comprises a reticular or latticed network structure, including dual
conduits cross-connected at each cross-street. The resulting parallel
grid allows the sewage to bypass a blockage or a valved-off zone of the
system. However, it might increase the residence time of the sewage
within the system and cause some stagnation because flows would be free
to follow paths of least resistance and cause some elements of the
system to carry little sewage. The service district lies in a single
pressure zone, upstream of pressure control valves at the interceptor.
The two alternative arrangements call for placing conduits in
separate shallow trenches. None would be inserted in existing sewers.
Less than 6% of the length of the combined sewers in the study area is
composed of 54-in. or larger sewers and only 8.6% of 48-in. or larger
sewers. The ASCE Project staff considers a 54-in. sewer the smallest
suitable as a walk-through structure in accordance with the 1967 report
of the Portland Cement Association to the Project (Ref. 4). The lack
of long runs of walk-through sewers in suitable locations precluded the
use of inserted conduits in the Milwaukee study.
A conventional gravity alternative arrangement, Layout M-Gr,
which is shown in Fig. 48, was used as a basis of cost estimate for
comparison with cost estimates for Layouts M-l and M-2.
- 119 -
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, GRAVITY SEWERS 18" UNLESS O1_M 1
-------
"IT "TftT-
100 0 100 200 300 400 500 600 700 600 900 1.000 FEET
I , I I I I I I I I I I '
LEGEND
— PRESSURE CONDUIT
—— SHUT-OFF VALVE
—— CLEANOUT TEE
STREET CURBLINE
PRESSURE SERVICE DISTRICT BOUNDARY
NUMBERS AT INTERSECTIONS INDICATE NODES
WHERE CONDUITS ARE INDICATES 48"
OR GREATER COMBINED SEWER
AIR RELIEF VALVE
- PRESSURE CONTROL VALVES
FIGURE 46
HYPOTHETICAL PRESSURE SEWER
SYSTEM LAYOUT M-l
MILWAUKEE STUDY AREA
(Reproduced from Fig. 9, Ref. 17)
-------
i i
J L_ J L
I
I
•'],)•" I, i •
PRESSURE CONDUIT
SHUT-OFF VALVE
CLEANOUT TEE
STREET CURBLINE
PRESSURE SERVICE DISTRICT BOUNDARY
NUMBERS AT INTERSECTIONS INDICATE NODES
AIR RELIEF VALVE
PRESSURE CONTROL VALVE
FIGURE 47
HYPOTHETICAL PRESSURE SEWER
SYSTEM LAYOUT M-2
MILWAUKEE STUDY AREA
(Reproduced from Fig. 11, Ref. 17 )
-------
I
100 0 100 200 300 400 500 600 700 BOO 900 1,000 FEET
LEGEND
8" SEWER
LARGER THAN 8"
MANHOLE
JUNCTION CHAMBER
FIGURE 48
GRAVITY SEWER SYSTEM LAYOUT M-GR
MILWAUKEE STUDY AREA
(Reproduced from Fig. 12, Ref. 17 )
-------
Boston
At Boston, the physical arrangement of the pressure sewer system
was studied in terms of Layout A of Section VII because this layout
seemed to fit the branching pattern of existing streets better than the
nSf Layout. The three alternative designs developed differed only in
the extent to which in-line pumps and controls were assumed to be incor-
porated in the scheme.
Design I, Fig. 49, employs no pumps other than those in the
building basements. The system lies within two pressure zones and is
controlled by pressure valves, one pair at the interceptor and two
pairs at Winter and Washington Streets. This arrangement is possible
because the area is fairly flat. Requisite pipe sizes are indicated in
Fig. 49.
Alternative designs were prepared to evaluate the advantages of
in-line pumping to produce steeper hydraulic gradients and permit use
of correspondingly smaller pipes and higher minimum velocities. The
minimum velocity downstream of an in-line lift-station pump is fixed by
the discharge rate of the smallest station pump operating alone. As
shown in Design II, Fig. 50, which includes a single in-line lift-
station, most of the pressure trunk conduits could be reduced by one
pipe size below those in Design I, were it not for the fact that the
elevated hydraulic grade line of the trunk sewer requires the allowable
gradients of branches within the reach downstream of the pumping station
to be flatter. In some instances, larger pipes might be required for
such branches.
Design III, Fig. 51, incorporates three lift-stations on the trunk
conduit in order to reduce the elevation of the hydraulic grade line
downstream of the single-lift pumping station of Design II. Design III
requires pipes of smaller diameter than many of the corresponding pipes
in Design I and does not require branch pipes as large as those in
Design II. However, Design III requires more pumping stations and more
complex pump and pressure controls.
Conventional gravity separation of the combined sewers in the
Boston study area had been studied by the engineering consultants prior
to their being engaged for the ASCE Project. Associated cost estimates
were available for comparison with those of the pressure scheme. No
illustration of the gravity separation is included in this report.
Estimates of Annual Costs, Milwaukee Study Area
Annual costs, including operating cost and amortization of the
cost of construction, were evaluated for the three alternative Milwaukee
designs by the engineering consultants and are presented for comparison
in Table 16.
- 124 -
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MAMHQLt TYPES
FIGURE 49
SUMMER STREET SEPARATION AREA
BOSTON, MASSACHUSETTS
PRESSURE SEWERAGE SYSTEM - DESIGN I
(Reproduced from Fig. Y-6, Ref. 18)
ALTERNATIVE LAXOUTI
FOft PRESSURE SEWERS FROM POINT 1 TO POINT *» -
IMSIOE EXISTIN* COMBINED SEWERS
SHALLOW SERVICE PRESSURE SEWERS RECEIVE
DISCHARGE FDOM BULGING CONNCCTIOWS TRUNK PKES8UM
SEWERS INSTALLED INSIDE EXISTING COM6INED SEWFRS
PURCHASE STREET
OMNECTIONS THREADED THROUGH EXISTING CONNECTIONS
CROSS-OVER WE (FLOW EITHER WAT 1
MANHOLE
PRESSURE CONTROL VALVE. IN MANHOLE
PREISURE-FLOW CONTROL. >N MANHOLE
AIR RELIEF VALVt. IN MANHOLE
CLEANOUT TCC (SEE MANHOLE TYPES)
SHUTOFF VALVE " "
SCALE IN PtET
-------
^t
LEGEND
BOUNDARY OF SUMMER
STREET SEWER SEPARATION
STUDY AREA
PRESURE CONTROL
PRESURE FLOW CONTROL
El LIFT STATION
PRESSURE SEWER
FIGURE 50
DESIGN H
(DIFFERENCES FROM
DESIGN I)
(Reproduced from
Fig.¥-8,Ref.l8)
Scale: I" =400
-126-
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BOUNDARY OF SUMMER
STREET SEWER SEPARATION
STUDY AREA
PRESURE CONTROL
PRESURE FLOW CONTROL
PI LIFT STATION
PRESSURE SEWER
FIGURE 51
DESIGN HI
(DIFFERENCES FROM
DESIGN I)
(Reproduced from
Fig. Y-10,Ref.l8)
Scale'I " = 400'
- 127-
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TABLE 16
ANNUAL COST OF SEWER SEPARATION, PROSPECT AVENUE STUDY AREA, MILWAUKEE, WISCONSIN
HYPOTHETICAL APPLICATION OF ASCE COMBINED SEWER SEPARATION PROJECT
(Reproduced from Ref. 17)
Proiect M-l
PRESSURE SYSTEM Construction
Cost
IN-HOUSE COST
Total $2,630,000
Minus S tor. -Grind. -Pump Cost (519,000)
Subtotal $2,111,000
S tor. -Grind. -Pump Cost 519,000
Power
S tor .-Grind. -Pump Maintenance
SUBTOTAL
AREA COLLECTION COST (All Public
Financing}
Constr. Cost Amortization $ 595,000
Op. & Main., Adm. & Gen. @ 1.25%
TOTAL COST $3,225,000
GRAVITY SYSTEM
IN-HOUSE COST
AREA COLLECTION (All Public Financing)
Constr. Cost Amortization
Op. & Main., Adm. & Gen. @ 0.5%
TOTAL COST
Annual Cost
Project M-2
Public Private Construction
Financing Financing Cost
$150,000 $181,000
67,000 74,000
1,700 1,700
16,900 16,900
$235,600 $273,600
42,000 42,000
7,500 7,500
$285,100 $323,100
Proiect M-Gr
Annual
Construction Public
Cost Financing
$1,114,000 $ 79,000
1,081,000 74,000
5,300
$2,195,000 $158,300
$2,630,000
(519,000)
$2,111,000
$ 630,000
$3,260,000
Cost
Private
Financing
$ 95,000
74 , 000
5,300
$174,800
Annual Cost
Public Private
Financing Financing
$150,000 $181,000
67,000 74,000
1,700 1,700
16,900 16,900
$235,600 $273,600
45,000 45,000
7,900 7,900
$288,500 $326,500
-------
In-house plumbing changes would probably be made by the property
owner and their cost was assumed to be amortized at 7 per cent in 25
years. The cost of the storage-grinder-pump unit itself was assumed
to be amortized over a 10-year period. For distribution of the total
construction cost to the taxpayers through general obligation or
revenue bonds, it was assumed that necessary funds could be borrowed
at 5 per cent for 25 years for construction work and 5 per cent for
10 years for the storage-grinder-pump unit.
The cost of work done in the public right-of-way is normally
financed by the municipality, and it can be assumed that the construc-
tion cost of an area collection system can be amortized at 5 per cent
in 25 years.
In Table 16, costs related to operation for the alternative
schemes are based on the following prices:
1. Power: $0.030/Kwh, paid by individual property owners.
2. Storage-grinder-pump Unit: Estimated as one maintenance
call per year per unit, at $20/visit.
3. Routine Operation and Maintenance: Estimated at 1 per cent
of the construction cost for pressure systems, and at 0.257.,
for gravity systems.
4. Administration and General: Estimated as 0.25% of the
construction cost.
Estimated annual costs for a conventional gravity system are from
7.2 to 8.0% of the estimated construction cost for a gravity system,
Table 17. In comparison, estimated annual costs for the two alternative
pressure systems range from 13.0 to 14.97, of the estimated construction
cost for a gravity system, Table 17.
Summary and Comparison of Estimated Costs, Three Study Areas
Table 18 summarizes the estimates of construction costs for the
three studies. The engineering consultants estimated (1) construction
costs for capital investment in round numbers, and (2) ratios of costs
between pressure and gravity designs as follows:
Pressure Gravity
San Francisco $13,000,000 $8,800,000
Milwaukee 3,200,000 2,200,000
Boston 6,400,000 4,700,000
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TABLE 17
COMPARISON OF ANNUAL COSTS
FOR MILWAUKEE STUDY AREA
Project
Gravity System
M-Gr
All public funds*
Public & private
Pressure Systems
M-l
All public funds*
Public & private
M-2
All public funds*
Public & private
Estimated Estimated
Project Annual
Construction Cost
Cost
(1) (2)
$2,195,000 $158,300
2,195,000 174,800
3,225,000 285,100
3,225,000 323,100
3,260,000 285,500
3,260,000 326,000
Estimated Annual Cost As
A Percentage
Relative to Relative to
Construction Gravity System
Cost of Given Construction
Alternative** Cost***
(3) (4)
7.2 7.2
8.0 8.0
8.8 13.0
10.1 14.7
8.7 13.0
10.0 14.9
* Except cost of electric energy.
** Column (2) -r Column (1), in per cent.
*** Column (2) + $2,195,000, in per cent.
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TABLE 18
ESTIMATES OF CAPITAL COST
HYPOTHETICAL APPLICATION OF ASCE COMBINED SEWER SEPARATION PROJECT
Engineering News Record
Construction Cost Index
Capital Costs
Plumbing Separation and
Connection to SGP Units
Connection as far as
property lines
Connection to laterals
SGP -Units (or comminutor-
pump equivalent)
Alone
And connection to laterals
Connection, property lines
to laterals
Subtotals
Area collection systems
TOTALS
Unit Costs
Per gross acre
Per connection
San Francisco, Cal . Milwaukee, Wis. Boston, Mass.
1320 1200 1250
(if mid-1968)
Pressure (Alt. B) Gravity Pressure (M-l) Gravity Pressure (Des.I) Gravity
$4,416,000
5,413,000
1,214,000 1,140,000
1,417,000
5,304,358
1,003,075
9,720,000 6,416,075 2,631,000 1,140,000 4,000,000 2,000,000
3,313,626 2,374,848 594,000 1,055,000 2,400,000 2,700,000
$13,033,984 8,790,923 3,225,000 2,195,000 6,400,000 4,700,000
$40,350 27,220 20,600 14,000 128,000 94,000
$ 4,700 3,170 3,830 2,610 32,000 23,500
-------
It would appear, therefore, that including changes in building
plumbing the separation of a combined sewer system by the method studied
for the ASCE Project might cost about half again as much as separation
by the conventional method of laying a second system of gravity conduits.
In terms of total costs for building plumbing changes and connec-
tions to street laterals shown in Table 18, neglecting street sewers:
Pressure
System,
Including
SGP Unit Gravity
San Francisco $9,720,000 $6,420,000
Milwaukee 2,630,000 1,140,000
Boston 4,000,000 2,000,000
The ratios of cost are shown to vary from 2.5 to 1.5.
Evaluations and Conclusions of Engineering Consultants
Some principal evaluations and conclusions of the engineering
consultants, extracted from various parts of their reports, are quoted
as follows:
San Francisco Study Area (from Brown and Caldwell report, Ref. 16)
"Factors which would tend to lend an economic advantage to pres-
sure systems are high density of existing development, complexity of
existing substructures, and inadequate ground slope. The latter factor
results in large diameter gravity sewers and a greater number of sewage
pumping stations. It appears from the cost data developed in this
report that a net capital cost advantage would accrue to the pressure
sewerage scheme only if all of the above factors were favorable, in the
extreme, to the pressurized system design. It is unlikely that such an
area exists in San Francisco.
"Components of the pressure sewerage system which hold most
promise for cost reduction are fittings, control appurtenances, and the
grinder-pump assemblies. Fittings, manholes, and special appurtenances
account for about 40 percent of the total cost of the pressure conduit
network. Development of special fabricated fittings to perform the
several functions of main-to-trunk connections, cleanouts, and pressure
control might save as much as one-third of the cost of the piping
appurtenances. Experience with freely discharging conduits may indicate
that pressure control works are unnecessary. This modification would
reduce total costs by a few percent. A reduction in the number of
cleanouts and by-pass connections might be made if operating and mainte-
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nance experience with pressure sewer networks is found to be very
favorable. The potential cost reduction in this case is limited to a
few percent of total system cost. The estimated cost of the grinder-
pump equipment modules represents about one-fourth of the total cost of
the pressure sewerage system. If the advent of pressure sewer systems
develops a mass market for grinder-pump equipment it seems likely that
major cost reductions will be achieved.
"This study does not include any estimates of operating and
maintenance expenses. Clearly, these costs would be greater for a
pressure system in every instance. Relative importance of comparative
operational costs and capital costs should be evaluated for some
specific cases.
"Service reliability of a conventional gravity sewage collection
system is excellent. Pressure system components would be designed with
great care to enhance their reliability and serviceability. Neverthe-
less, it is certain that a pressurized system would suffer more outages
and cause more resident inconvenience than a conventional gravity system.
"Disruption of normal street and property usage can be held to a
minimum during construction of pressure pipeline systems. This is an
advantage of the pressure sewer scheme which will obtain in all cases.
In an area such as a downtown shopping district, this factor could be
of considerable importance.
"In total, it appears that, for the San Francisco study area, the
favorable features of a pressurized wastewater collection system cannot
compensate for its economic disadvantages. The pressure system design
is believed to hold little promise for wastewater and storm drainage
separation in areas such as the one studied here."
"In sum, it is felt that the pressure system design for wastewater
and storm drainage separation holds little promise in areas similar to
the San Francisco study area."
Milwaukee Study Area (from Greeley and Hansen report, Ref. 17)
"Aside from cost considerations, in our opinion it would be unwise
to embark upon major pressure system projects until experience with
pilot installations has demonstrated that operation and maintenance
difficulties are not of serious consequence. Although for the Milwaukee
test area the pressure system is estimated to cost much more than the
gravity system, it is possible that in other situations the cost rela-
tionship will be different."
"The cost of in-house plumbing changes would be only slightly
higher for a pressure system. The collection system cost for the pres-
sure system would be only about 9/16 that for a gravity system, but this
is much more than offset by the added cost of providing and installing
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grinder-pump units. Even though pressure system components were devel-
oped to lesser unit cost levels as a consequence of market demand, it
is likely that the costs for pressure systems would significantly exceed
the costs for gravity systems.
"The pressure systems have, in addition to higher costs, the draw-
back of being dependent on electrical power for their operation. In
addition, grinder-pump units in each house require that construction be
done in each home, possibly damaging the basement as a dwelling unit.
"Engineering and construction of a pressure system can be accom-
plished. However, in view of the economic disadvantages and intangible
problems such as public relations, it seems unlikely that a pressure
system used for separation of combined sewage would be found advantageous
in the Milwaukee test area."
Boston Study Area (from Camp, Dresser and McKee report, Ref. 18)
"All of the above costs are for construction (including engineering
and contingencies) only. While the gravity separation system would have
minimum annual maintenance cost, the pressure systems would require con-
siderable operating and maintenance cost because the flows from each
building would have to be pumped into the street force mains. Based on
reports and data furnished by the ASCE Project, appreciable annual main-
tenance costs also would be required for pressure systems.
"The concept of hanging pressure force mains inside large existing
combined sewers has been investigated. Estimates indicate that construc-
tion of pipes inside combined sewers would be more costly than the con-
struction of a two-pipe system of comparable size located in the same
streets. In addition, the capacity of the existing combined sewer would
be considerably reduced, and maintenance difficulties of both the com-
bined sewer and the hanging pipe system would be severe."
"While these estimated construction costs are preliminary only, it
is our opinion that they are sufficient to show that there is no economic
advantage in constructing pressure sewer systems over a conventional
gravity system. In addition, the pressure sewer systems have the further
disadvantage that they would have significant annual operation and main-
tenance costs. The annual operating costs have not been estimated, but
it is evident that they would be major. Pumps and control equipment have
an expected design life of about 20 years, whereas gravity connections
should have a life of about 100 years. Therefore, there would be a
recurring capital outlay to keep the pressure system in operation.
"An additional factor which must enter into any comparison of sewer
systems is the likelihood of failure or improper operation. A gravity
system properly designed is essentially free of the significant possi-
bility of failure by its very nature. On the other hand, a pressure
system with its numerous mechanical equipment and control features, is
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subject to regular though unpredictable failures. At any given time
during the life of such a system (composed of pumping, grinding, pump
control, pressure control and back-flow prevention equipment), jamming,
clogging, power failure or equipment failure can be. expected. The
possible flooding damage and inconvenience which may occur during a
period of repairs may also involve considerable additional costs.
"It is evident that to keep a pressure system in 100 per cent
satisfactory operation is almost impossible. A frequent maintenance
schedule for the many building units and main pumping and pressure
control equipment is required.
"In our opinion, the problems of operation and maintenance of a
pressure system together with higher estimated construction costs indi-
cate that such a system is not a feasible solution to the problem of
separation in large cities."
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SECTION X
BROADER ASPECTS OF PLUMBING SEPARATION*
Introduction
Separation of private building plumbing systems is an important
element in the separation of combined systems of sewerage for both con-
ventional and ASCE Project schemes. It represents a substantial portion
of the total construction costs in either case. Cost estimates for
street sewerage are made reliable by the accumulated and accessible
information on such undertakings. By contrast, there are few public
records on the nature and cost of plumbing modifications on private
property. Moreover, costs fluctuate widely because of the particular-
ized requirements of individual buildings.
Separation of private plumbing systems has been reviewed in
Section IX for the study areas of San Francisco, Milwaukee, and Boston,
and cost estimates by the three consulting engineering firms connected
with these studies are included in Table 15. In order to augment and
categorize costs for these three cases a survey was made of seven other
large cities (Ref. 13): Cleveland, St. Louis, Detroit, New York City,
Washington, Chicago and Philadelphia. Wanted information was supplied
by city officials and local plumbing contractors, and additional infor-
mation was obtained from Charles A. Maguire and Associates for a 430-acre
urban-renewal area in Boston and from the findings of the American Public
Works Association Research Foundation in its recent study of combined
sewer systems (Ref. 27).
Details for typical piping arrangements and auxiliary data are
given in the appendix of Reference 13.
Summary
A summary of information on the separation of plumbing systems in
the ten cities follows:
(1) Differences in the nature and scale of the plumbing-system work
required for the conventional and ASCE Project schemes can be summarized
as follows for most private residences:
a. The ASCE Project scheme requires the installation of a
storage-grinder-pump unit in the building drain down-
stream from existing fixture connections.
* Ref. 13.
- 136 -
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b. Instead of requiring a new gravity building sewer leading
to a public gravity sewer, the ASCE Project scheme calls
for the installation of pressure tubing between the
storage-grinder-pump unit and a proposed public pressure
sewer. In most ASCE Project scheme applications, the
associated difficulties and costs for typical plumbing
arrangements would, at worst, not exceed those for con-
ventional building separation; in some cases they would
be simpler and/or less expensive. However, the ASCE
Project scheme is more likely to entail the correction
of plumbing inside buildings, with attendant difficulties
and costs.
c. If the existing building system is not completely separate
(i.e., if illegal balcony drains, deep window-wells,
foundation drains, and the like are connected to the system)
the additional hydraulic load placed on the pressure piping
may exceed the normal design capacity of the storage-grinder-
pump units for sanitary flows.
(2) In the five cities for which data were available:
a. 50% to 6070 of the total land area is occupied; streets,
vacant properties, and open areas such as parks and
cemeteries being excluded.
b. 5070 to 707o of the occupied land area is residential.
c. 807, to 907o of the individual properties are residential.
d. Only a small proportion of the residential properties
house more than four or five families.
(3) Row housing is common in Philadelphia, Boston, Washington, and some
parts of New York City. It is uncommon in the other seven cities.
(4) In Washington, St. Louis and Detroit, most residential sewers are
located in alleys at the back of the houses. The other seven cities are
provided mainly with street sewers.
(5) The plumbing codes of all ten cities require storm drainage from
buildings to be piped to existing storm or combined sewers. In smaller
communities such connections are normally prohibited.
(6) Washington and Philadelphia require rear yard drains on each
property, and Chicago requires catchbasins for kitchen-sink wastes.
(7) It is expected that the plumbing systems in the ten cities can be
separated before they reach the building drain. Balcony drains connected
to such systems in violation of the plumbing code are possible exceptions,
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(8) Separation of plumbing systems in residential buildings, exclusive
of those in Detroit and about half those in Cleveland, involves discon-
nection of existing roof leaders at the front and rear of each house.
About half the houses in Cleveland have separate plumbing systems. In
Detroit most buildings are provided with separate drains as far as their
junction at the building sewer in the vicinity of the foundation footing.
(9) Only in Detroit would separation generally not involve reconstruc-
ting the existing storm drainage system. However, work to be done would
usually extend into the buildings only in row houses or non-residential
buildings.
(10) Foundation drains are uncommon in most of the ten cities. In
Chicago they are used only for larger houses. In Detroit and about half
the houses in Cleveland, the foundation drains are connected to storm
drains and intercept roof water. Other Cleveland houses could install
a shallow storm drain to intercept roof water alone or a deep drain to
accept both roof water and foundation drainage.
(11) Most large buildings have interior downspouts.
(12) Records of plumbing layouts and modifications are not available
for many older buildings.
(13) In many downtown buildings, basement floors lie below sewer level
and drains are suspended from basement walls or ceilings. Therefore
separation could be effected without excavating below basement floors.
(14) In some of the ten cities, the drainage systems of significant
numbers of large buildings had been separated at the time of construction
up to the building front or the street sewer, either to reduce flooding
or costs.
(15) In four of the ten cities, separation of plumbing systems in new
buildings is required by regulations introduced during the past ten
years. This has resulted in a significant number of structures with
separate systems in downtown areas.
(16) Most of the following alternatives to piped roof-water connections
have been used where storm sewers were not available:
a. Installing splash blocks or providing piped connections
to pervious areas or streams on private properties, as
in Washington, D.C. Discharging roof water directly onto
the ground in designated areas now being considered in
Chicago and already allowed in some Detroit suburbs.
b. Regrading surfaces to divert storm water from deep window
wells, for instance, where area drainage can not be
economically separated from the sanitary system.
- 138 -
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c. Roofing or enclosing small areas originally drained to
the system when the drains can not be economically
disconnected from the sanitary system.
d. Installing curb drains to conduct roof or surface water
under a sidewalk to a street gutter.
e. Diverting roof water to more convenient collection
points. Introduction of horizontal drains into the
attics of large buildings has been suggested as a way
of bringing roof water to the front of buildings. New
roof gutters have been provided here and there in
Washington.
(17) In Washington it was found that separation of the drainage systems
of some buildings was impractical or uneconomical.
Building owners cannot be depended upon to separate existing
plumbing systems fully. Financing extensive plumbing changes, especially
in older buildings of marginal economical value, may be difficult and
may impose a hardship on some owners. Compliance, even by financially
capable owners, might be difficult to enforce unless strict ordinances
were enacted. Teams of inspectors would be required to ensure full
compliance with the ordinances. It would seem better for municipalities
to provide crews to do the work in all buildings. However, making neces-
sary political, financial, and legal arrangements to do this might be
intricate and controversial. Many buildings would have to be renovated
extensively to permit separation.
Table 19 gives the estimated costs of plumbing separation on
private property based on the data obtained for the ten cities; 1968
prices are used. They include normal allowances for contractors' over-
head and profit and contingencies,
a. For the San Francisco study area allowances were made
for disruption of normal property use. They ranged
from $100 per structure for one- and two-family resi-
dential buildings to $400 for commercial, industrial,
and similar buildings. The mean value was $2,100 per
acre.
b. At Washington, costs of public relations and planning
for separation varied from $140 to $250 per residential
building or from $260 to $1,950 per acre.
c. Cleveland estimates provided for a cost escalation of
14 per cent, or about $1,500 to $2,000 per acre, for
anticipated cost increases over a seven-year construc-
tion period.
- 139 -
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TABLE 19
SUMMARY OF INFORMATION ON COSTS OF BUILDING PLUMBING SEPARATION (1968 LOCAL COST LEVELS;
INCLUDES ALLOWANCES FOR CONTRACTORS' OVERHEAD AND PROFIT)
(Table J-l of Ref. 13)
City
Boston
-Urban Renewal
Area
-Study Area
Cleveland
New York
Washington, D.C.
Chicago
St. Louis
Detroit
Philadelphia
San Francisco
-Study Area'3)
Milwaukee .
-Study Area*-3'
Row Houses
$ per
building
700
750
$/occu-
pied
acre
15,000
Detached Houses
$ per
building
2,024
1,750
to . .
3,230*- ;
1,030
5,000
1,650
600
l,720
l,650
$ /occu-
pied
acre
12,900
to ...
'
11,300
47,000
15,900
17,300
20,700(e)
12,SOO«>
$ per
gross
acre
9,000
to
3,280
6,600
26,000
9,300
9,700
Industrial
$ per
building
4,300
$ /occu-
pied
acre
9,000(b)
Office Buildings,
Large Apts . , etc.
$ per
building
\ Q J
J_ \j \j\j\j
13,000
/ 1 \
6,189(h)
2,120(d)
2,'lOO(^
$ /occu-
pied
acre
43,600^
25,000
7,500
11,300
Housing
Project
$ per
building
23,600
$ /occu-
pied
acre
1,510
o
I
(a) Refs. 16, 17 and 18. (f) Based on 606 residences, 94 stores and stores with
(b) Area includes street areas. houses over.
(c) Estate-type houses on large properties. (g) Based on study of one 10,000 sq. ft.commercial bldg.
(d) Cost includes work to property line only. (h) Mean for 41 buildings.
(e) Residential-commercial area: residential, 2,434 bldgs.; (i) Apartment buildings.
commercial and other, 339 bldgs. (j) Office and institutional buildings.
-------
d. Cost of repair or renovation of finished basement areas
was not allowed for.
e. Recorded per acre costs for Washington assumed that all
buildings are provided with combined systems. No allow-
ance was made for buildings that might be partially or
completely separated.
The costs in Table 19 expressed in terms of cost per occupied acre
are probably most useful, because they are based in so far as possible
on the areas occupied by buildings in which plumbing would be separated.
Vacant land, parks, cemeteries, streets and alleys were excluded.
Although some of the costs in Table 19 vary widely, it is possible
to say that the estimated cost per occupied acre for residential housing
(with the exception of data from St. Louis) lies between $11,000 and
$17,000 per acre. The only available estimate for industrial buildings
of $9,000 per acre is based on a unit area including streets. If the
street area is assumed to be 25 per cent the cost would be $12,000 per
occupied acre. Data for large buildings range from $7,500 to $43,600
per occupied acre. The cost for a mixed residential-commercial area in
San Francisco was placed at $20,700 per occupied acre.
Table 19 supports the American Public Works Association's estimate
for nation-wide building separation of $18.4 billion (Ref. 27), if that
cost is not taken to include supplementary costs such as disruption of
use. Because the estimated total area served by combined sewers in the
United States is 3,029,000 acres, the approximate cost of building sepa-
ration is about $6,100 per gross acre. Assuming that 5570 of the total
acreage is occupied, the unit cost becomes $11,100 per occupied acre.
This value lies at the low end of the range shown in Table 19, but it
appears to become an average figure if small cities and suburban areas
with relatively few buildings per acre are included. The APWA estimate
is based on less information than that provided in Table 19, but the
values used are reasonably consistent with those in the table.
Taken as a whole, the data summarized here are considered to offer
a suitable basis for valid generalizations about costs of separation of
building plumbing systems on private property. Where reliable estimates
of the cost of building separation are required, on-site studies should
be made of a sufficient number of buildings to identify existing
problems and costs. Such studies would constitute a necessary prelimi-
nary step in a full-scale field demonstration of the ASCE Project scheme.
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SECTION XI
NON-TECHNICAL CONSIDERATIONS RELATED
TO PRESSURE SEWER SYSTEMS*
Introduction
One of the objectives of the ASCE Project study was to evaluate
the importance of related non-technical matters such as home-owner
acceptability and ownership and maintenance of system components. It
was assumed that proof of the physical and economic feasibility of the
ASCE Project method of combined sewer separation would otherwise resolve
questions normally related to the construction of sewer systems such as
public financing, establishment of an administrative and operational
organization, and necessary legal and legislative decisions. Accordingly
the problems uniquely related to the project are of primary interest in
this section. Among them, in particular, are the need to separate
building plumbing, to install storage-grinder-pump (SGP) units in private
as well as public properties and to convince property owners that these
changes will be made to their profit in spite of some inconvenience and
possible out of pocket expenses to themselves. This might not be an
easy task.
Convincing the public and their elected representatives of the
advantages of sewer separation by a scheme of the ASCE Project type
other non-technical considerations include study and determination of:
(1) who should purchase, install, replace and hold title to SGP units
and tubing inserted in building drains and sewers and who should pay for
the amortization of the capital cost and interest on investment;
(2) whether the community as a whole or the individual property-owner
should pay for operation, including cost of electric energy (a minor
annual cost), and routine servicing, emergency repairs, and parts
replacement; (3) what agency should actually perform the maintenance
repairs, and periodic inspections; (4) where the responsibility should
lie for damages from malfunction of an SGP unit, or stoppage in a pres-
sure service connection; and (5) who or what agency should pay the costs
for required plumbing changes within private properties.
Specific answers to such questions of public policy are hard to
find However, there are some records of what has been done before in
the development of sewer systems, and parallels can be drawn also from
policies adopted by public utilities. These are examined in the next
two parts of this section. Additionally, the essence is presented of
* Ref. 12.
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interviews conducted by ASCE Project staff at Louisville and Radcliff,
Ky., and with three consulting engineering firms that have been inte-
rested in sewerage schemes involving sewage pumping equipment on private
property. Interviews are reported in Ref. 12, and comments on how to
obtain the cooperation of building owners are given in Ref. 13.
Public Acceptance and Financial Support
Existing building plumbing must be restructured in conventional
separation as well as in the ASCE Project scheme. However, the addition
of the SGP equipment within the building or adjacent to it is a unique
requirement of the ASCE scheme alone. The associated benefits and dis-
advantages of the ASCE Project scheme to the individual householder are
discussed in Section XII.
Most important is the cooperation and consent of building owners,
individually and as voters. Engineers suggest that opinion and, to a
limited extent also, practice would be in favor of installing and main-
taining the SGP equipment and tubing as a public purpose.
To be considered, too, are: the direct burden of temporary dis-
ruption of normal activity while piping is being changed and equipment
installed; the loss of space occupied by the SGP unit; and such incon-
venience and minor nuisance as the unit may create.
In general and as well as in situations where one drainage district
is served by gravity sewers and another by pressure sewers it would
appear desirable to equalize the financial burden of sewerage: (1) by
reimbursement of the cost of minimum plumbing changes; (2) by furnishing,
installing, and maintaining the SGP unit as a public responsibility of
the community; and (3) by providing a fast and responsive repair service
as well as adequate maintenance and inspection. Damage by flooding
caused by unit malfunction should be paid for from public funds or by
insurance with premiums paid by the community.
Common precedents for outside ownership and maintenance of service
and metering equipment on private property are set by telephone services
(equipment), water companies and departments (meters), gas and electric
power companies (meters) and, in some parts of the country, heating
appliances. Where sewer service charges are imposed, rate differentials
could offset the cost of electric energy for operating the SGP unit.
Even though it would be a minor cost, public acceptance might be encour-
aged by taking it into account.
Direct Precedents
A precedent for also separating combined sewers on private property
at public expense has been set in Washington, D.C. There it was reasoned
that: "Since the separation of plumbing on any single premise is of no
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specific benefit to the owner, but rather is an incremental part of a
larger and general public benefit, the municipality is standing the
entire cost of such piping changes. ... It is recognized that the
combined plumbing systems were installed according to city codes and
that property owners are not obliged to change them." An extensive
public relations program has thus far induced all but 470 of the building
owners to agree to the alteration of their systems. (Ref. 39).
Well known is the fact that in 1953 the village of Shorewood Hills,
Wis., introduced community-wide installation of garbage grinders that
were purchased, installed, and owned and maintained by the community.
All property owners accepted their grinders, and it was agreed that
because the grinders were a clean and convenient means of disposing of
garbage they eliminated the nuisance associated with the storage and
hauling of garbage through the streets of the community, a practice that
could, therefore, be prohibited by ordinance. (Ref. 40).
Sampling Public Attitudes
To obtain the response of individuals acquainted with the behavior
of pumping equipment on private property, householders and the super-
intendent of the sewer system in Radcliff, Ky., and representatives of
three consulting-engineering firms were interviewed (Ref. 12).
At Radcliff (Refs. 12 and 41), small portions of an otherwise
gravity system are served by pressure sewers through which domestic
sewage is lifted to the gravity mains by pneumatic ejectors. Almost all
the pumping units are in pits outside single-family houses. The ejectors
were purchased and installed under public contract, as appurtenances to
the community system, and they are maintained by a public agency.
Property owners pay about 10 cents a month for the electric power con-
sumed. Construction costs were financed publicly, partly with Federal
aid. A connection charge and a sewer-use charge pay for operating the
units and amortizing the system. Costs of pressure as well as gravity
connections to the premises served were borne by the property owners.
Most of the ejectors have required frequent repair and maintenance,
generally in response to telephone requests for assistance to a repair-
man on call.
Twenty-five households were asked about the pressure facilities,
most of which were installed in 1964. Responses with regard to pumping
units are summarized in Table 20. Noise and vibration led the list of
complaints about the pneumatic ejectors. Eight inside and 3 outside
installations bothered the householders greatly. Odors, frequency of
interruption, and limitation of fixture use were other grounds for com-
plaint. Possible flooding was a source of worry in 15 responses. A
majority of the people questioned were not pleased with the ejectors.
The poor performance of the pumping system employed at Radcliff may have
depreciated the value of the properties served.
- 144 -
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TABLE 2O
ATTITUDES OF OCCUPANTS OF TWENTY-FIVE BUILDINGS TO EXPERIENCE WITH PUMPING UNITS,
RADCLIFF, KENTUCKY
(Reproduced from Table I of Ref. 12).
(a) Number responding to question: "To what extent do each of the following bother you?"
Not at all Slightly Somewhat Greatly
Units Units Units Units Units Units Units Units
Inside Outside Inside Outside Inside Outside Inside Outside
Noise -12- 1- 18 3
Odor 3 12 2 1- 23 2
Expense 6111 3- -1 3
Appearance 6 8 - 41 11 4
Loss of Space 6 10- 41 -1 3
Limitations on
Fixture Use 6 11- 2- 22 2
Interruptions
of Service 1 52 3.2 23 4
Source of Worry 1 5 - 43 44 4
(b) Relative preference for pumping unit versus previous system
Previous System Preferred Pumping Unit Preferred
Previous System Slightly Definitely Slightly Definitely
Public System 2 10 - 1
Septic Tank - 622
(c) Response to question: "In view of your experience with the pumping unit,
would you make the same choice again?"
(i) Converted from septic tank or constructed new house, and no choice
was available regarding adoption of unit
(ii) Bought or rented house: would make same choice
would not make same choice
Not applicable
in view of
other answers
-
-
-
-
-
_
3
-
No
Preference
-
2
14
2
9
-p-
Ui
-------
At Lousville, 5 householders, all General Electric Co. employees,
agreed to the temporary installation of sewage sampling units in their
yards. Equipment and operation were paid for by the company. The
stations consisted of field-assembled grinders and pumps set in small
vaults at or just below ground level outside the houses. Although none
of the householders questioned were particularly bothered by the units,
3 did report noticing slight noises at night when bedroom windows were
open and one said he had occasionally noted a brief odor.
Representatives of Sieco, Inc., Consulting Engineers, Columbus,
Ind., have become interested in the possibilities of rural pressurized
sewer systems employing a storage-grinder-pump unit and plastic dis-
charge tubing. In their opinion, pumping units for individual buildings
provided, installed, and serviced by the community would have greater
acceptance than private installations and would be better serviced.
Moreover, there would be better acceptance of such installations for new
rather than existing systems where pressure systems offered a practicable
and economical solution of a sewerage problem.
The cost of gravity sanitary sewers is a function of trenching
depth which, in turn, depends on the elevation of the lowest plumbing
fixture in the building served. A representative of Williams and Works,
Consulting Engineers of Grand Rapids, Mich., has long considered the
merits of a system in which domestic sewage would be lifted by storage-
grinder-pump installations in individual basements into conventional
gravity sewers laid at less than normal depth. Duplicate units might
be installed to increase reliability of operation.
A representative of Prince William Engineering Company, Woodbridge,
Va., stated that his firm believed that pumping units for new housing
developments should be purchased and installed by the property owner and
that contracts for maintenance and repair should be made with commercial
agencies. Moreover, that pumping unit installations should generally be
located outside the dwelling.
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SECTION XII
BENEFITS AND DISADVANTAGES
OF THE ASCE PROJECT SCHEME
In this study and report, the advantages of combined sewer separa-
tion by the ASCE Project scheme have been compared mainly with conven-
tional sewer separation by construction of a second system of conduits
for sanitary sewage or for storm drainage. Other methods of accom-
plishing abatement of pollution of receiving waters from overflows from
combined sewers have also been pointed out, and their relative advan-
tages have been compared with conventional separation (Section III).
Benefits to householders would chiefly be a generally improved
environment through the regional abatement of pollution of receiving
bodies of water. On the other hand, household storage-grinder-pump
units may be a direct cost to the houseowner who may furthermore face a
loss of space in his basement or yard and a risk of flooding in the
event of the malfunctioning of the pertinent equipment (grinders, pumps,
and valves).
Advantages and disadvantages of the ASCE Project scheme are summa-
rized in Table 21. Major advantages over conventional separation are:
(1) the elimination of all seepage waters from all pressurized reaches,
and a consequent reduction in the hydraulic loads placed on treatment
plants; and (2) reduced interference with commerce and traffic at con-
struction sites. Most important, however, is the fact that pressurized
systems are a viable alternative to gravity systems and that necessary
technical information has been assembled by the ASCE Project to identify
the relative merits of pressure versus gravity systems. There will be
sectors and service districts of existing combined systems and of new
separate systems where the pressure sewer system will prove to be the
superior alternative. However, it is expected that there will be few
major cities where pressurized sanitary sewerage will be the exclusive
superior alternative.
Adjunct Applications
Adjunct applications of pressure-sewer concepts developed under the
auspices of the ASCE Project are important and may be of benefit in many
locations. The core equipment consisting of a household storage-grinder-
pump unit, pressure tubing and conduits, and control valves may be suit-
able where conditions are unfavorable for the economical installation of
gravity systems. Examples are: (1) an area of ridges and valleys through
which a main sewer can not be extended within the lowest valley for
political or other reasons; (2) steeply sloping shores of lakes where
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TABLE 21
EVALUATION OF ASCE COMBINED SEWER SEPARATION PROJECT SCHEME
Factors for Consideration
Benefits and Advantages
Disadvantages
Planning and design;
Effect on quality of
receiving water:
Effect on groundwater
infiltration flows on
capacity of sewage
treatment plants:
Effect on hydraulic
capacity of combined
sewer converted to a
separate storm drain
if pressure conduit
is suspended in sewer:
Effect on capacity of
building drain and
sewer if tubing is
inserted in them:
Construction costs,
ratio to cost of
conventional sewer
separation:
Construction activities:
Annual cost, ratio to
cost for conventional
separation:
Anticipated public
response to introduc-
tion of untried system,
disrupting households
for installation:
An alternative to gravity
systems, offering an
additional degree of
freedom in design.
Improvement by eliminating
sanitary sewage.
Eliminate, reduce plant
hydraulic load.
Could minimize inter-
ference with commerce
and traffic.
Reduce as much as
407o, depending on
location and type
of hanger system.
Reduced capacity
and contribution
to stoppages.
(a)
As much as 1.5,
depending on
specific situations,
As much as about 1.8,
depending on specific
situations.
General public would
need to be persuaded
of the value to abate
water pollution.
(b)
- 148 -
(Continued)
-------
TABLE 21 (Continued)
Factors for Consideration
Benefits and Advantages
Disadvantages
Anticipated homeowner
response:
Availability of Equipment -
Household storage-
grinder-pump unit^c':
Comminutor and pump:
Tubing and conduit:
Control valves:
Operation of System -
Routine inspection:
Repair and maintenance:
Valves for control:
Prototype unit
developed.
Commercially available.
Commercially available.
Commercially available.
Possible concern for
flooding in event of
a malfunction, and
for payment for
electrical energy.
Untested in field
service.
Required.
Difficult in some
situations.
Adjustment delicate
and complex.
Reliability -
Household storage-
grinder-pump unit:
Tubing and conduit:
Subject to tampering:
Untested, and subject
to shutdown with
electric power failure.
Occasional stoppages
to be expected.
Possible.
(a): Data from estimates for three studies, Refs. 16, 17 and 18 (see
Section IX).
(b): Estimated for Milwaukee study area, Ref. 17 (see Section IX).
(c): Including backflow prevention valve.
- 149 -
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individual or small groups of houses and cottages then can pump their
wastewaters either to a pressure sewer at or near the shore line or to
a higher-lying gravity sewer; (3) fixtures in basements or subbasements
from which sewage must be lifted to the level of the street sewer;
(4) introduction of pressurized sewers into utility conduits in common
pipe tunnels or utility corridors for which gravity sewers cannot nor-
mally be employed; and (5) the isolation, comminution and selective
water transport of essentially all readily decomposable organic waste
substances from households and industries to existing, enlarged, or new
waste treatment works (see Section XIII).
Hydraulic characteristics of pressure systems are explained at
length in Refs. 6, 11, 16, 17 and 18.
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SECTION XIII
APPLICATION OF ASCE PRESSURIZED SEWERAGE
SCHEME TO DISPOSAL OF SOLID WASTES
FROM HOUSEHOLDS AND INDUSTRY*
Introduction
The efficient and economical transportation, treatment, and dis-
posal of solid wastes from households, industry and from the community
at large without unwanted pollution of the urban environment has been
recognized as a major need of our present and future cities and towns.
Because it seemed that the pressure pipeline scheme for the separation
of combined sewers might be expanded to this use, the possibilities of
applying it also to the selective water transport of a wider range of
household and industrial solids were given some study (Ref. 10).
As is well known, sewage collection and disposal systems have
already been pressed into service to include ground garbage as well as
normal sewage solids, and the question is whether pressurized systems
can be employed effectively also for the transport of a wider variety
of solid wastes. To be noted is that research on or development of
suitable methods as such did not lie within the scope of the ASCE
Project and that what is said in this section is only ancillary to the
central project itself.
Available information on the collection and disposal of solid
wastes by water carriage systems including the use of proprietary
systems under study (as of 1968) is summarized in Reference 10. Alterna-
tive methods of collection and disposal are under intensive study in
projects sponsored by the Federal Solid Wastes Program of the Environ-
mental Control Administration within the Department of Health, Education
and Welfare, under provisions of the Solid Waste Disposal Act of 1965.
Solid Wastes to Be Considered
Solid wastes comprised in the term municipal refuse are classified
as garbage, rubbish, ashes, street sweepings, dead animals, abandoned
automobiles, solid industrial wastes, demolition materials, sewage solids,
and hazardous and special wastes. Garbage and rubbish are the most
common components and are considered as such for discharge with sewage
in the present section.
* Ref. 10.
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For comparison with sewage of normal strength, Table 22 lists the
loads that garbage and rubbish would add to sewage collection systems
in general.
TABLE 22
TYPICAL QUANTITIES OF COMMUNITY REFUSE AND OF SEWAGE SOLIDS
(Ref. 10)
Type of Refuse
Gross weight
(Ibs/capita/day)
Dry weight Concentration
(Ibs/capita/day) in sewage flow
of 80 gcpd
(ing/liter)
Municipal Refuse
(20% moisture),
total solids: 4 to 8
Residential Refuse
(207» moisture),
total solids: 2.0
Residential Garbage
(72% moisture),
total solids: 0.5
Municipal Sewage,
Total solids:
Suspended solids:
Biochemical oxygen
demand (BOD):
3.2 to 6.4
1.6
0.14
0.55
0.2
0.12
4800 to 9600
2400
214
825
295
180
Carrying Capacity of Sewers and Loads of Refuse Solids to Be Transported
The primary function of sanitary sewers, and combined sewers during
dry weather, is to transport the solid matter in the sewage. So-called
"minimum self-cleaning velocities" have been suggested for normal and
some abnormal sewage solids, but, except for ground garbage, there has
been little study of velocities needed to transport the heavier elements
in other ground or pulped refuse.
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Ground refuse from which glass and metals have been removed has
been transported successfully in large-sized pipe lines for many miles.
Ground solid wastes up to 1-in. in particle size have been transported
in pressure pipe lines at concentrations up to 12% (Ref. 45). For con-
centrations up to 470, observed head losses have not perceptibly exceeded
those for water alone. At concentrations as low as 2%, solid waste
slurries formed a colloidal matrix that tended to hold heavier materials
in suspension, and minimum velocities required to sustain such suspen-
sions have been found to be lower than those for lower concentrations of
component solids dispersed in the transporting water.
Although mean flow velocities vary directly with rates of flow in
pressure pipe lines and pipe sizes must be large enough to accommodate
peak flows within reasonable hydraulic gradients, it is generally pos-
sible to maintain velocities that will transport some types of community
waste solids during at least part of each day of the year. Pressure
sewer laterals and mains could be sized to insure the occurrence of self-
cleansing velocities with sufficient frequency to remove deposited solids
before clogging or other objectionable conditions are created. Thus, the
introduction into suitably-dimensioned pressure pipes of suitably well-
ground solid wastes should be feasible although deposits might on occasion
be somewhat greater in quantity.
The dimensions of sewage solids successfully transported in pres-
surized pipes are measures of the allowable sizes also of other waste
matters that can flow through pipe and valve passages of pressurized sewer
systems. Still to be considered, however, is the development of econom-
ical grinding and pumping devices for water-borne wastes other than sewage
and garbage solids and, in addition, the determination of how much water
is needed to create effective suspension of ground particles of different
kinds. Clean water might be added if necessary, as in the use of garbage
grinders, or specific solid wastes might be discharged into the system
only when adequate volumes of water have accumulated in the storage-
grinder-pump unit.
Separation and Grinding of Solid Wastes
As has been true for domestic garbage grinders now on the market,
there are some solid wastes that are not suitable for grinding by the
moderate-duty equipment so far developed for use in household and related
building installations (Sections V and VI). Some large1 and hard-to-grind
solid wastes would have to be disposed of in other ways. Some of them
might be transported separately and in a dry state to central grinding
stations capable of preparing them for transport through larger-sized
downstream pressure sewers. The remainder might be collected and disposed
of separately as is now the practice with bulky wastes. Common examples
of such wastes are discarded major appliances, bed springs and automobile
tires. However, the sorting and separate disposal of some of the solid
waste components would presumably work against the acceptance of grinding
- 153 -
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units for processing waste solids in advance of their discharge of such
solids either to pressure or gravity sewers.
Discharge to sewers of solid wastes not presently admissible to
them would probably call for heavier duty equipment. This equipment
might nevertheless be subjected to more frequent breakage than conven-
tional sewage comminutors and the household sewage grinders developed
in connection with the ASCE Project.
To reduce solid waste materials, such as bundled paper, rags,
towels, corrugated boxes, tin cans, and bottles to acceptable size in
advance of available household grinders, auxiliary "pulping" devices
might have to be provided. Although these can presumably be developed,
the economy of small-scale installations and their public acceptance
are uncertain.
Treatment of Combined Solid Wastes
Sewage-carried solid wastes can be treated and disposed of by
enlarging treatment and disposal units and mechanizing grit-handling,
screening, sludge collection and sludge disposal. After grit removal,
most of the ground solids would settle with the primary tank sludge.
Available information suggests that the per capita sludge production
might be increased 13 to 25 times, and that digester capacity might have
to be enlarged even more than this because refuse solids have been shown
to digest less readily than normal sewage solids. Gas production per
pound of volatile solids added would presumably be reduced and the
removal of accumulating solids would be more cumbersome. The organic
loading of secondary treatment units is expected to be about two-thirds
greater, whereas the organic constituents of ground garbage are known
to respond well to normal sewage treatment processes. However, much
remains to be learned about the response of other solid waste consti-
tuents. Processes designed for the treatment of normal sewage may have
to be modified and new processes may have to be introduced to care for
such solids.
Costs and Benefits of Collecting and Treating Solid Wastes with Sewage
Water carriage of a significant portion of community refuse and
its effective disposal with sewage could add to the amenity and economy
of community living. Potential net benefits and costs to the community
should take into account the construction and operation of all of the
structures required.
Figure 52 is a simplified schematic diagram of possible community
systems for the disposal of municipal refuse with sewage. It illustrates
ways in which solid wastes might be diverted to sewer systems from con-
ventional disposal systems or from alternatives to conventional systems.
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INPUTS
TRANSPORT I TREATMENT
DISPOSAL
en
ui
i
TRANSPORT CENTRAL
PROCESSING
ON-SITE
PROCESSING
Solid
Wastes
LAND
Land f i
Dumping
Burial
Biological
Processes;
New or
Improved
Methods
Separation
Processes
FIGURE 52
SCHEMATIC DIAGRAM OF SYSTEMS FOR DISPOSAL OF SEWAGE AND SOLID WASTES
(Reproduced from Fig. 1, Ref. 10)
-------
Necessary operations have already been discussed and are assumed to be
economically, technically and socially beneficial. Alternatives to
vehicular transport are seen to include: (1) the immediate segregation,
grinding, and discharge of solid wastes by the use of garbage grinders
in the household or building in which the wastes originate; (2) central
garbage grinding and sewer transport; (3) use of truck mounted grinders
at convenient points in the sewer system, as suggested in Reference 43;
and (4) introduction of a dry vacuum system for transport of solid
wastes from buildings to central stations, as discussed in Reference 45.
Whether the integrated costs of collection of combined refuse and sewage
solids would be less than the sum of the costs of separate collection as
at present is the decisive question.
A study of the costs of vehicular collection and sewer transport
of garbage in 1966 (Ref. 44) led to the conclusion that handling garbage
with sewage would cost one quarter to one half that of vehicular collec-
tion of garbage if householders are required to purchase and install
kitchen garbage grinders.
A comparison of presently conventional collection at Philadelphia,
Penna., versus pneumatic transport through a dry vacuum system to four
central grinding stations where the wastes would be mixed with sewage,
ground, and pumped into a solid-wastes pipeline for transport to a dis-
posal point, led to the following conclusions: (1) based on a comparison
of direct costs projected for a 50-year period and on construction of
necessary works by present technology, the proposed system would be
competitive if the distance to the disposal site were about 50 miles;
(2) with assumed moderate improvements in costs and technology, the
proposed system would be only slightly more expensive if the distance to
the disposal point was short. Not taken into account were the indirect
benefits of the proposed system or possible increases in disposal costs
by the delivery of a sewage-solid wastes slurry. (Ref. 45).
Mr. John D. Parkhurst, Chief Engineer and General Manager of the
County Sanitation Districts of Los Angeles County, replied to an inquiry
from the ASCE Project as follows:
"The addition of refuse to the sewers is not now being
practiced nor do we anticipate doing so in the near future.
It is doubtful that the handling of ground refuse as sewage
sludge will ever be a major factor in the disposal of refuse
in Los Angeles County, but it might find some small applica-
tion in the southernmost areas of the County where landfills
are scarce and where sewage will probably continue to receive
only primary treatment before discharge to the ocean. Even
this is doubtful, however, as more and more effort is devoted
to curtailing the discharge of solids to the natural receiving
waters."
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Conclusion
Based on the available evidence, it would appear that the ASCE
Project scheme of grinding and pumping sewage through pressure tubing
and conduits could become a physically feasible system of transporting
finely ground refuse waste solids provided that suitable heavy-duty
grinding devices can be developed and glass and metals are removed from
or by-passed within the system; but that the economic feasibility and
desirability in terms of costs and benefits remain to be determined.
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SECTION XIV
FOLLOW-ON FIELD TESTING
Introduction
The household storage-grinder-pump unit (SGP) developed by the
General Electric Company and described in Section V has been tested in
the laboratory in relatively short test-runs with what may be considered
troublesome constituents of domestic sewage and with sanitary sewage
from an industrial plant including cafeteria wastes. The test demon-
strated as well as possible the ability of the unit to grind and pump
domestic sewage at rates between 15 gpm at atmospheric pressure and
11 gpm at the maximum planned service pressure of 35 psig at the outlet
of the unit. The unit has also been tested to insure tentative general
compliance with anticipated Underwriters' Laboratories requirements for
electrical safety.
Needless to say, responsible manufacturers will submit new products
such as the SGP unit to field tests before placing them on the market.
Originally the ASCE Project planned to include a field test of the
proposed system in an existing combined sewer district. About a dozen
SGP units were to be manifolded via tubing from each household to a
common street pressure sewer. Limitations in time and funds were respon-
sible for the omission of this advanced testing program. However,
because the SGP unit is the heart of pressurized sewerage physical
feasibility for residential service, the New York State Department of
Health enthusiastically assumed responsibility for follow-on development
(Ref. 47) in a Facilities Demonstration Grant awarded the Department by
FWPCA in 1969. Such a follow-on is crucial because all previous attempts
to exploit the pressure sewerage principle have been frustrated by the
absence of a reliable, thoroughly developed, reasonable unit-cost house-
hold storage-grinder-pump unit.
Field Testing of Household Units
The main purposes of "A Pressure System Demonstration" by the New
York State Department of Health are to:
(1) provide opportunity for modification of the initial household unit
design, as indicated by unexpected field requirements, or by malfunction
or by premature wearing out of parts; (2) provide a test of the rugged-
ness and reliability of the units operating singly and in concert (mani-
folded to a common street sanitary pressure sewer); (3) provide proof of
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the field suitability of the assemblage, which should be regarded as
essentially a module of a much larger pressure system; and (4) provide
new data which would be invaluable in subsequent pressure system appli-
cations .
Specific objectives will include measures to: (1) document the
effectiveness of small-diameter non-metallic pressure sewers in carrying
routinely the wastewater from a number of residential buildings over an
extended period of time, including seasonal changes and prolonged periods
of disuse (long weekends, vacations and the like); (2) obtain the oper-
ating experience necessary for an evaluation of the effectiveness of
individual storage-grinder-pump units by subjecting these prototypes to
an extended period of actual use in a significant number of homes where
the mechanical performance, use patterns, operating costs and maintenance
requirements would be completely monitored; (3) determine through a
monitoring program the occurrences and durations of any overflows, either
confirming the initial choice of SGP unit pumping rates and storage
capacity or showing the need for modification; (4) determine whether or
not there is an optimum operating pressure range for this type system
which is within or outside the range under consideration (such results
would also supply design inputs for the future design of a working
system); and (5) characterize by physical and chemical analyses the
quality of wastewater produced by such a pressure system and draw
conclusions on what, if any, difference would result from transporting
such wastewater through a gravity sewer system with disposal in a con-
ventional treatment plant over similar handling of conventional unground
wastewater.
The demonstration proposed in the approved Grant Application will
include installation of storage-grinder-pump units in twelve residences
of close proximity. The pressure tubing from each unit will be connected
to a common pressure street sewer. A conventional gravity building
service connection will also be installed in each house, to accommodate
any overflows that might occur, for example during brief periods when
the pressure system might be taken out of service for modification of
components. When the demonstration has been completed the residential
plumbing will be permanently connected to the gravity building sewer and
the pressure system connections will be removed.
The street pressure conduit into which the twelve pressure tubing
lines will be joined will discharge at a manhole into the gravity sewer-
age of the subdivision. An automatic sampling device will be provided
at the pressure system outlet to permit characterization of the waste-
water. The type of analytical work contemplated includes:
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(1) analytical determinations of —
pH Ammonia Nitrogen
Suspended Solids Total Phosphate
Total Solids Chloride
Total Volatile Solids Grease
Settleable Solids Sulfide
(Relative to time)
BQD5 Relative Stability
COD Hardness
Total Nitrogen Detergent (LAS);
(2) a particle size distribution study;
(3) a benchtop study for evaluation of the treatability
of ground wastewater; and
(4) a settleability study.
Instantaneously available intelligence will be continuously
provided on the operating status of each household unit, e.g., on the
incidence and duration of pump operation, and on the occurrence of
power outages. It is anticipated that sensors for six such parameters
would be connected to each household unit, feeding data through an
underground system of control wiring into a central data collection
facility installed in a small building or vault at a convenient on-site
location. At this center, data are to be recorded automatically on
magnetic tape for periodic collection. Subsequent translation and
printout of the data in response to a computer program will accomplish
the bulk of data reduction, thereby minimizing engineering involvement
in routine aspects of the project while assuring that all pertinent data
will be systematically and reliably accumulated.
By means of a single leased line, the over-all system status will
be continuously displayed at a manned, remote surveillance station,
while the individual status of each household unit will be continuously
displayed via auxiliary visual indicators at the on-site data center.
It is planned to conduct the demonstration over a period of at
least twelve months in order to develop adequate, significant operating
data and experience. Including time for final planning and for instal-
lation of the SGP units and tubing while the houses are being built, the
total time required for the demonstration is estimated at about twenty-
one months. The demonstration will take place in the Albany, N.Y. area.
(Ref. 48).
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Field Demonstration in an Entire Service District
There is widespread conviction that the intensive 12-home module
field demonstration under way by the New York State Department of Health
should be completed before a full-scale pressure sewer system demonstra-
tion is undertaken in a combined sewer service district of several
hundred buildings. The probability of a successful large-scale demon-
stration would thereby be maximized. As implied in Fig. 2 in Section II,
experience with a successful full-scale field demonstration will be
necessary before the ASCE Project scheme will achieve acceptance for
general application by the civil engineering profession at large.
The text of Reference 13 is essentially an ASCE Project annotated
check list of matters that should be taken into account in planning a
full-scale field demonstration. Its purposes are: to delineate problems
that might be encountered in planning, constructing and operating a
pressure sewer system; to indicate unknowns and effects currently subject
to question; and to suggest minimum required or desirable field measure-
ments, observations, and sampling for an adequate demonstration of the
scheme. The major points raised in Reference 13 are summarized in the
remainder of this section.
In the implementation of a demonstration project every available
means should be exploited to assure that as many buildings as possible
in the project area are connected to the demonstration system. Means
recommended include an extensive public relations program, public owner-
ship and management of building storage-grinder-pump and comminutor-
storage-pump installations, preventive maintenance and inspection by a
public agency, adequate stocking of spare parts to minimize down time,
and availability of repair service around the clock. Special legal
agreements must be effectuated which include consideration of: right of
access for inspection and maintenance of building units; allocation of
costs; liability for flooding or other damage that might result as a
consequence of the demonstration; and restoration of private property
should reversion to a gravity system become necessary or desirable.
Means should be provided to detect inadvertent and deliberate by-passing
of building units, which might defeat the purpose of the scheme.
The demonstration project would provide an opportunity for evalua-
ting the degree of satisfaction of beneficial objectives, particularly
improved receiving water quality and elimination of groundwater and
surface water from the isolated sanitary sewage. Required are measure-
ments of quality and quantity of combined sewage before separation and
of both storm water and sanitary sewage after separation, together with
receiving water quality determinations before and after separation.
Several monitoring locations will be needed for adequate evaluations.
There will be opportunities for careful accounting of construction,
operating and all other costs, and of intangible disbenefits such as
nuisance and inconvenience.
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There has been universal agreement on the need for solids-size
reduction prior to pressurization of domestic sewage, to assure a mini-
mization of obstruction and blockage. Despite this precaution and
although the criteria for design of street collection systems developed
by the ASCE Project are generally considered to be on the safe side,
their collective adequacy can be ascertained only in the field. There-
fore, means should be incorporated for detecting obstructions so that
design criteria and operating procedures can be modified, if necessary,
to reduce their occurrence. On the other hand, techniques should be
investigated to determine the greatest practicable reach of pressure
sewer that can be cleaned because the number and cost of street valves
and fittings might be significantly decreased the greater the reach.
Field measurements should be made to assess the adequacy of other design
criteria, such as minimum solids transport velocity requirements.
Alternative conduit layouts should be provided in portions of the demon-
stration system for evaluation of configuration options. There would
also be opportunities for testing the effectiveness of polymer additives
in reducing resistance to pipe flow as an alternative to routine solids
accumulation removal, or to accommodate individual larger-than-anticipated
building loads in lieu of new larger or paralleling mains. A demonstra-
tion project would provide a unique opportunity for determining the
relative extent of blockage with and without solids-size reduction:
grinding could be deferred until the sewage reached the remainder of the
system served by grinders or comminutors in individual buildings.
One of the effects on which a demonstration project could provide
new information is that of the anaerobic environment that is expected to
exist in a pressure sewer system. Some force main failures due to
sulfuric acid attacks have occurred. Other effects might be restriction
of flow at high system points by accumulated gas despite the presence of
air-relief valves or at other interior pipe locations by accumulations
of bacterial growths. A major reason for maintaining a system under
pressure at all times that would be pressurized at least part of the
time is to avoid air entrapment and/or aggravation of liquid-column
separation because of resultant amplifications of water-hammer pressures
during rapid changes in flow rates. Despite continuous pressurization,
gas accumulations might nevertheless aggravate liquid-column separation.
Extensive measurements of flow and pressure will play an important
role in the operation and evaluation of a demonstration project pressure
sewer system. Additionally, measurements of flows at various points in
the system would provide valuable design data presently unavailable and
bases for verifying or correcting assumptions on flows used in designing
the demonstration system. If water demands and wastewater flows could
be measured simultaneously in individual buildings and for groups of
buildings, invaluable information would be obtained on relationships
between water demand and wastewater production patterns.
One of the objectives of a demonstration project should be to
establish procedures for dealing with interruptions of service in a
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pressure sewer system in a manner that would result in a minimum duration
of interruption, minimum property damage and minimum health hazard in the
event of sewage flooding.
One version of the ASCE Project scheme included the installation of
pressure conduits inside existing combined sewers. It might be possible
in a demonstration project to utilize walk-through size combined sewers
for field test installations of some of the pressure conduits. Questions
that would be investigated are: structural problems encountered in
fastening pressure conduits inside sewers of various materials and
varying physical condition; problems of installing pressure sewers inside
existing combined sewers of various heights; structural integrity of
hangers and adjacent sewer walls when exposed to the thrust of storm
flows; effect of accumulated debris on the collective hydraulic capacity
of the former combined sewer and its inserted conduit; and suitable
methods for cleaning former combined sewers containing inserted pressure
conduits. Adoption of the pipe-in-a-pipe concept, however, might intro-
duce problems of legal responsibility for damage to sewered structures,
for possible flooding and related property damage, and for restoration
of property at the termination of the demonstration.
Possibilities for obtaining synergistic benefits by carrying ground
solid wastes in pressurized sewer systems have been outlined in Section
XIII. Part of the sewerage demonstration project under discussion might
be extended to incorporate an investigation of this multiple-purpose
service.
It should be noted in closing that the project for field testing
of a dozen household units by the New York State Department of Health
will yield important initial information on several of the questions that
have been raised here, even though their comprehensive resolution will
not be possible until a field demonstration is undertaken in a complete
combined sewer service district.
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SECTION XV
ACKNOWLEDGEMENTS
The American Society of Civil Engineers is greatly indebted to
the following organizations and individuals for their assistance and
cooperation in pursuit of project studies. Affiliations given were
in effect at the time assistance was rendered.
*******
Federal Water Pollution Control Administration
Mr. Allen Cywin
Dr. R.N. Kinman
Mr. G.A. Kirkpatrick
Mr. W.A. Rosenkranz
Municipalities and Other Governmental Jurisdictions
Baltimore DPW:
Boston DPW:
Chicago DPW:
Cleveland Department of Public
Service:
Department of Housing and
Urban Development:
Detroit Department of Water
Supply:
District of Columbia, Department
Sanitary Engineering:
Mr. B. Suwall.
Deputy Commissioner E.G.A. Powers;
Mr. J.J. Devlin.
Mr. C.J. Keifer.
Commissioner J.R. Wolfs;
Assistant Commissioner P.F. Nuhn;
Mr. G. Newell.
Dr. R.M. Michaels.
Mr. A.C. Michael';
Mr. D.G. Suhre;
Mr. J.W. Brown.
Director (Retired) R.L. Orndorff;
Director N.E. Jackson;
Mr. G.J. Moorehead.
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Metropolitan Sanitary District
of Greater Chicago:
Milwaukee DPW:
Minneapolis-St. Paul Sanitary
District:
New York City DPW:
New York State Department of
Health:
Philadelphia Water Department:
Pittsburgh DPW:
San Francisco DPW:
St. Louis Metropolitan Sewer
District:
Mr. F. Dalton;
Mr. F. Neill.
Commissioner H.A. Goetsch;
Mr. H. McCullough;
Mr. E. Hirsch;
Mr. T. Prawdzik.
Mr. J.J. Anderson.
Mr. M. Lang;
Mr. W. Stampe.
Mr. Dwight F. Metzler;
Dr. Leo J. Hetling.
Commissioner S.S. Baxter;
Mr. C.F. Guarino;
Mr. J.V. Radziul.
Director B. deMelker.
Director S.M. Tatarian;
Mr. A.O. Friedland;
Mr. L.A. Vagadori.
Executive Director P.F. Mattei;
Mr. E.J.A. Gain.
Consulting Engineers
Black and Veatch:
Brown and Caldwell:
Camp, Dresser and McKee:
Chas. A. Maguire and Associates:
Greeley and Hansen:
Metcalf and Eddy:
Parsons Corporation:
Prince Williams Engineering Co.
Seico, Inc.:
Williams and Works:
Mr.
Mr.
Mr.
Mr.
Mr.
Mr.
Mr.
Mr.
Mr.
Mr.
Mr.
R.E.
F.J.
C.A.
D.R.
K.P.
T.M.
E.B.
G.E.
B.C.
G.F.
T.C.
Lawrence .
Kersnar .
Parthum;
Horsef ield
Devenis.
Niles.
Cobb.
Arnold.
Burns .
Hendricks .
Williams.
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Universities and Research Organizations
Aerojet-General:
APWA Research Foundation:
Battelle Memorial Institute:
Cast Iron Pipe Research
Association:
Central Engineering
Laboratories, FMC:
Mr. F. Bowerman.
Mr. H.G. Poertner.
Mr. J.A. Eibling;
Mr. R.B. Engdahl.
Mr. R.G. Dittig.
Mr. M.F. Hobbs.
General Electric R. and D. Center: Mr. K.S. Watson;
Mr. R.P. Farrell;
Dr. J.S. Anderson;
Harvard University:
Hittman Associates, Inc.:
National Sanitation Foundation:
Portland Cement Association:
The Johns Hopkins University:
The Pennsylvania State
University:
Travelers Research Center:
University of Illinois:
University of Pennsylvania:
Dr. R. Brooks.
Dr. H.A. Thomas, Jr.;
Dr. G.M. Fair.
Mr. J. Rosenblatt.
Mr. R.M. Brown;
Mr. C.A. Parish.
Mr. J. Hendrickson.
Dr. J.C. Geyer;
Dr. F.P. Linaweaver, Jr,
Prof. E.R. Mclaughlin.
Dr. P. Bock.
Dr. J.M. Robertson.
Dr. I. Zandi.
Manufacturers
American-Standard:
BIF, A Unit of General Signal
Corporation:
Carlson and Son:
Mr. J.W. Schellinkhout.
Mr. J.R. Daneker.
Mr. K. Roach.
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Chicago Pump, Hydrodynamics
Division, FMC:
Crane Company:
Dorr-Oliver:
Fairbanks-Morse:
Hays Manufacturing Company:
Interpace:
Johns-Manville:
Kaiser Aluminum:
Liljendahl System:
M.A. Clift and Associates:
Mueller Company:
Westinghouse Electric:
Worthington Corporation:
Final Report Typing
Mrs. Jan Donker.
Mr. M.A. Lamb;
Mr. D. Hallmark.
Mr. John H. Redmond.
Mr. R.P. Borden.
Mr. R.R. Bridge.
Mr. L.L. Buzzard.
Dr. J.T. McCall.
Mr. J.E. Parkinson;
Mr. H.J. Kazienko.
Mr. R.H. Vaterlaus.
Mr. B.C. Hryniewicz,
Mr. M.A. Clift.
Mr. H.T. Huffine.
Mr. G.S. McCloy.
Mr. D.L. Gallagher.
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ASCE COMBINED SEWER SEPARATION PROJECT
ASCE URBAN HYDROLOGY RESEARCH COUNCIL
Stifel W. Jens, Chairman
PROJECT STEERING COMMITTEE
Vinton W. Bacon
Dr. Morris M. Cohn
Dr. Gordon M. Fair, Chairman
Dr. John C. Geyer
Richard Hazen
Martin Lang
S.W. Steffensen
AMERICAN SOCIETY OF CIVIL ENGINEERS
Dr. William H. Wisely, Executive Secretary
PROJECT STAFF
Murray B. McPherson, Project Director
Lincoln W. Ryder, Consulting Editor
Donald C. Taylor, Project Administration
L. Scott Tucker, Deputy Project Director
Donald H. Waller, Deputy Project Director
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SECTION XVI
BIBLIOGRAPHY
Text References
Ref. No. Title
1. "Outline Description of ASCE Project on Separation of
Sanitary Sewage from Combined Systems of Sewerage,"
Tech. Memo. No. 1, ASCE Project, Feb., 1966.
2. Tucker, L.S. "Sewage Flow Variations in Individual Homes,"
Tech. Memo. No. 2, ASCE Project, Feb., 1967.
3. Waller, D.H., "Experience with Grinding and Pumping of
Sewage from Buildings," Tech. Memo. Nos. 3 and 3A, ASCE
Project, May, 1967 and March, 1968.
4. Hallmark, D.E., and Hendrickson, J.G., Jr., "Study of
Approximate Lengths and Sizes of Combined Sewers in Major
Metropolitan Centers," Tech. Memo. No. 4, ASCE Project,
May, 1967.
5. Tucker, L.S., "Pressure Tubing Field Investigation,"
Tech. Memo. No. 5, ASCE Project, Aug., 1967.
6. Tucker, L.S. "Hydraulics of a Pressurized Sewerage System
and Use of Centrifugal Pumps," Tech. Memo No. 6, ASCE
Project, Nov., 1967.
7. McPherson, M.B., Tucker, L.S., and Hobbs, M.F., "Minimum
Transport Velocity for Pressurized Sanitary Sewers,"
Tech. Memo. No. 7, ASCE Project, Nov., 1967.
8. McPherson, M.B., "Domestic Sewage Flow Criteria for
Evaluation of Application of Project Scheme to Actual
Combined Sewer Drainage Areas," Tech. Memo.'No. 8, ASCE
Project, Nov., 1967.
9. Waller, D.H., "Peak Flows of Sewage from Individual Houses,"
Tech. Memo. No. 9, ASCE Project, Jan., 1968.
10. Waller, D.H., "An Examination of the Benefits and
Disadvantages of the Project Scheme with Respect to the
Disposal of Solid Wastes," Tech. Memo. No. 10, ASCE Project,
Feb., 1968.
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Text Reference^ (continued)
Ref. No. Title
11. Daneker, J.R., and Frazel, W.H., "Control Techniques for
Pressurized Sewerage Systems," Tech. Memo. No. 11, ASCE
Project, March, 1968.
12. Waller, D.H. "Non-Mechanical Considerations Involved in
Implementing Pressurized Sewerage Systems," Tech. Memo.
No. 12, ASCE Project, May, 1968.
13. Waller, D.H., "Special Requirements for a Full Scale Field
Demonstration of the ASCE Combined Sewer Separation Project
Scheme," and Appendix "Combined Sewer Separation on Private
Property," Tech. Memo. No. 13 with Appendix, ASCE Project,
June, 1968.
14. Tucker, L.S., "Routing of Flows in Sanitary Sewerage
Systems," Tech. Memo. No. 14, ASCE Project, July, 1969.
15. McPherson, M.B., "ASCE Combined Sewer Separation Project
Progress," Conference Preprint 548, ASCE National Meeting
on Water Resources Engineering, New York, N.Y., Oct., 1967;
and Civil Engineering, Dec., 1967.
16. "Separation of Combined Wastewater and Storm Drainage
Systems, San Francisco Study Area," (Task 4), Brown and
Caldwell, Consulting Engineers, San Francisco, Cal.,
Sept., 1968.
17. "Combined Sewer Separation Project Report on Milwaukee
Study Area," (Task 4), Greeley and Hansen, Consulting
Engineers, Chicago, 111., Dec., 1968.
18. "Report on Pressure Sewerage System, Summer Street
Separation Study Area, Boston, Mass.," (Task 4), Camp,
Dresser & McKee, Consulting Engineers, Boston, Mass.,
Sept., 1968.
19. Farrell, R.P., Anderson, J.S., and Setser, J.L., "Sampling
and Analysis of Wastewater from Individual Homes," (Task 2),
67-MAL-3, General Electric Co., Water Management Laboratory,
Major Appliance and Hotpoint Division, Appliance Park,
Louisville, Ky., March, 1967.
20. Farrell, R.P., "Long-Term Operation of Wastewater Observation
Stations," (Task 2), S-68-1064, General Electric Co.,
Research and Development Center, Schenectady, N.Y., Apr.,
1968.
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Text References (continued)
Ref. No. Title
21. Farrell, R.P., "Advanced Development of Household
Pump-Storage-Grinder Unit," (Task 6), S-69-1038,
General Electric Co., Research and Development Center,
Schenectady, N.Y., Dec., 1968.
22. Hobbs, M.F., "Relationship of Sewage Characteristics to
Carrying Velocity for Pressure Sewers," (Task 5), R-2598,
Environmental Engineering Department, Central Engineering
Laboratories, FMC Corporation, Santa Clara, Cal., Aug.,
1967.
23. Bowen, R.N., and Havens, J.G., "Report to ASCE Combined
Sewer Separation Project on FWPCA Contract No. 14-12-29,"
(Tasks 7 and 9), National Sanitation Foundation, Ann Arbor,
Michigan, Dec., 1967.
24. Kazienko, H.J., "Report to ASCE Combined Sewer Separation
Project on FWPCA Contract No. 14-12-29, Develop and Field
Test Method of Installing Pressure Conduits in Combined
Sewers," (Task 7), Johns-Manville Products Corporation,
Research and Engineering Center, Manville, New Jersey,
Dec., 1968.
25. Robertson, J.M., "Turbulent Friction in Eccentric Annular
Conduits-Effect of Inserted Pipe on Flow Capacity of Sewers,"
(Task 12), Report No. 310, Dept. of Theoretical and Applied
Mechanics, University of Illinois, Urbana, 111., March, 1968.
26. Nelson, A.R. and Robertson, J.M., "Analytical Studies of
Turbulent Friction in Annular Conduits-Effect of Inserted
Pipe on Flow Capacity of Sewers," (Task 12), Report No. 321,
Dept. of Theoretical and Applied Mechanics, University of
Illinois, Urbana, 111., Nov., 1968.
27. Problems of Combined Sewer Facilities and Overflows,
WP-20-11, by The American Public Works Association, Project
123, for the U.S. Dept. of the Interior, Federal Water
Pollution Control Administration, Dec., 1967.
28. Pollutional Effects of Stormwater and Overflows from
Combined Sewer Systems, Publication No. 1246. Information
Branch, Div. of Water Supply and Pollution Control,
U.S. Public Health Service, Washington, D.C., Nov., 1964.
29. "Report on Phase One, Residential Water Use Project,"
Dept. of Environmental Engineering Science, The Johns
Hopkins Univ., Baltimore, Md., Oct., 1963.
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Text References (continued)
Ref. No. Title
30. Thomas, R.E. and Bendixen, T.W., "Domestic Water Use in
Suburban Homes," Final Report to the F.H.A., from U.S.
Public Health Service Taft Sanitary Engineering Center,
Cincinnati, Ohio, June, 1962.
31. Orndorff, J.R., "Domestic Water Use Differences in
Individual Well and Public Water Supplies," Report III,
Phase 2 of the Residential Water Use Research Project,
Dept. of Environmental Engineering Science, The Johns
Hopkins Univ., Baltimore, Md., June, 1966.
32. Linaweaver, F.P., Jr., Geyer, J.C., and Wolff, J.B.,
"Report V, Phase 2, Final and Summary Report on the
Residential Water Use Project," Dept. of Environmental
Engineering Science, The Johns Hopkins Univ., Baltimore,
Md., June, 1966.
33. Wolff, J.B., Linaweaver, F.P., Jr., and Geyer, J.C.,
"Water Use in Selected Commercial and Institutional
Establishments in the Baltimore Metropolitan Area,"
Dept. of Environmental Engineering Science, The Johns
Hopkins Univ., Baltimore, Md., June, 1966.
34. Design and Construction of Sanitary and Storm Sewers,
ASCE Manuals of Engineering Practice No. 37, WPCF Manual
of Practice No. 9, Prepared by a joint Committee of the
American Society of Civil Engineers and the Water Pollution
Control Federation, New York, N.Y., 1969.
35. Environmental Pollution, A Challenge to Science and
Technology, Report of the Subcommittee on Science, Research
and Development to the Committee on Science and Astronautics,
U.S. House of Representatives, 89th Congress, Second Session,
1966.
36. Waste Management and Control, National Academy of Sciences,
National Research Council, Publication 1400, Washington,
D.C., 1966.
37. Gannon, J.J., and Streck, L., "Current Developments in
Separate versus Combined Storm and Sanitary Sewage Collection
and Treatment," School of Public Health, Univ. of Michigan,
Ann Arbor, Mich., June, 1967.
- 172 -
-------
Text References (continued)
Ref. No. Title
38. Paone, J., Bruce, W.E. and Morrell, R.J., Horizontal
Boring Technology; a State-of-the-Art Study, Bureau of
Mines Information Circular 8392, U.S. Dept. of the Interior,
Bureau of Mines, Washington, D.C., Sept. 1968.
39. Auld, D.V., "Protecting the Potomac at Washington," J.WPCF,
Vol. 37, No. 3, Mar., 1965.
40. Tooley, L.J., "All Homes in Shorewood Hills Village Will
Grind Their Garbage," The American City, Feb., 1953.
41. Clift, M.A., "Experience with Pressure Sewerage," J. San.
Eng. Div., ASCE Proc., SA5, No. 6150, Oct., 1968.
42. Refuse Disposal, American Public Works Ass'n., 1966
(Chapt. 7 - "Grinding Food Wastes.").
43. Golueke, C.G., and McGauhey, P.H., "Comprehensive Studies
of Solid Wastes Management," Univ. of California, Berkeley,
Cal., 1967.
44. Clark, C.M., Stroud, L.H., and Watson, K.S., "Home Disposers
versus Surface Collection — a Comparative Cost Analysis,"
Water and Wastes Engineering, Sept., 1966.
45. Zandi, I., and Hayden, J.A., "Collection of Municipal Solid
Wastes in Pipelines," Presented at ASCE Transportation
Conference, San Diego, Cal., Feb., 1968.
46. Wolfe, H.B., and Zinn, R.E., "Systems Analysis of Solid
Waste Disposal Problems," Public Works, Sept., 1967.
47. "Metzler Leads a Pure Water War," Engineering News-Record,
Sept. 11, 1969.
48. Cywin, Allen, and Rosenkranz, W.A., "Storm and Combined
Sewer Research and Development," Meeting Preprint 1039,
ASCE Annual and Environmental Meeting, Chicago, 111., Oct.,
1969.
- 173 -
-------
General References
Federal Government
A National Policy for the Environment. Senate Interior and Insular
Affairs Committee, and Committee on Science and Astronautics of House
of Representatives, Ninetieth Congress, Oct., 1968; and Colloquium,
July, 1968.
"Pertinent Areas for Research and Development, Storm and Combined
Sewer Pollution Control," FWPCA, U.S. Dept. of Interior, Washington,
D.C., July, 1968 (mimeo).
"Research, Development and Demonstration Projects," Vol. 1, Div. of
Applied Science and Technology, FWPCA, U.S. Dept. of Interior,
Washington, D.C., Jan., 1969.
"Selected Urban Stormwater Runoff Abstracts," for FWPCA, U.S. Dept. of
Interior, Washington, D.C., by the Franklin Institute Research
Laboratories, Science Information Services, Contract 14-12-467,
Jan., 1969.
Reed, P.W., "Control of Pollution from Combined Sewer Systems,"
Division of Water Supply and Pollution Control, U.S. Dept. of Health,
Education and Welfare, Washington, D.C., Aug., 1965.
National Professional Society Reports
"A Study of Sewage Collection and Disposal in Fringe Areas," Progress
Report from Committee on Public Health Activities of the Sanitary
Engineering Division, J. San. Eng. Div., ASCE Proc., 84: SA2, Paper
No. 1613, 1958.
"Background on Water Pollution, Manual for Municipal, State and Federal
Planners," National Water Institute, Water and Wastewater Equipment
Manufacturers Association, New York, N.Y., Feb., 1968.
"Minimum Velocities for Sewers," J. BSCE. 29:286, 1942.
Individual Authors
Akerlindh, G., "Permissible Water Pollution at Combined Sewer Overflows,"
Sewage Works Journal, 21:6, June, 1949.
Anderson, J.S., and Watson, K.S., "Patterns of Household Water Usage,"
J. AWWA, Oct., 1967.
- 174 -
-------
General References (continued)
Bacon, V., Leland, R., and Sosewitz, B., "Separation of Sewage from
Storm Water," Paper No. 12, Inst. of Civil Engineers, England, May, 1967.
Baker, R.J., "Package Aeration Plants in Florida," J. San. Eng. Div.
ASCE Proc., 88:SA6, Nov., 1962.
Burm, R.J., Krawczyk, D.F., and Harlow, G.L., "Chemical and Physical
Comparison of Combined and Separate Sewer Discharges." J. WPCF, 40:1,
Jan., 1968.
Burm, R.J., and Vaughn, R.D., "Bacteriological Comparison Between
Combined and Separate Sewer Discharges," J. WPCF, 38:3, Mar., 1966.
Camp, T.R., "Overflows of Sanitary Sewage from Combined Sewerage
Systems," Sew, and Ind. Wastes, Apr., 1959.
Camp, T.R., "The Problem of Separation in Planning Sewer Systems,"
J. WPCF, Vol. 38, No. 12, Dec., 1966.
Clark, C.M., Stroud, L.H., and Watson, K.S., "Home Disposers versus
Surface Collection," Water and Wastes Engineering, Sept., 1966.
Cohn, M.M., "The Disposal of Sewage and Garbage — Related Municipal
Functions," Sew. Wks. Journal. 10:1, 1938.
Cosens, K.W., "Design Factors in Dual Disposal," Sew, and Ind. Wastes
Eng., Jan., 1950.
Cosens, K.W., "Household Garbage Grinders — How They Affect Sewers,"
American City, Sept., 1949.
Cosens, K.W., and Hanemann, E.J., "Sewer Velocity Required for Kitchen
— Ground Waste," American City, Jan., 1949.
Davidson, R.N., and Gameson, A.L.H., "Field Studies on the Flow and
Composition of Storm Sewage," Water Pollution Research Laboratory,
(British, undated, about 1965).
Dobbins, W.E., "Quantity and Composition of Sewage Overflows," N.Y. ASCE
Met. Sect. Symposium, Apr., 1962.
Dunbar, D.D., and Henry, J.G.F., "Pollution Control Measures for Storm-
waters and Combined Sewer Overflows," J. WPCF, Vol. 38, No. 1, Jan., 1966.
Fair, G.M., Geyer, J.C., and Okum, D.A., Water Supply and Wastewater
Removal. Water and Wastewater Engineering, Vol. 1, John Wiley and Sons,
New York, N.Y., 1966.
- 175 -
-------
General References (continued)
Firstman, S.I., "Advanced Sewage Systems for Housing Cost Reduction,"
Rand Corporation, #D-17170-PR, May, 1968.
Hunter, R.B., Methods of Estimating Loads in Plumbing Systems,
N. Bu. Stds., BMS Report 65, 1940.
Linaweaver, F.P., Jr., and Geyer, J.C., "Use of Peak Demands in
Determination of Residential Rates," J. AWWA. Vol. 56, No. 4, Apr.,
1964.
McKee, J.C., "Loss of Sanitary Sewage Through Storm Water Overflows,"
J. BSCE, 34, Apr., 1947.
Palmer, C.L., "The Pollutional Effects of Storm-Water Overflows from
Combined Sewers," Sew, and Ind. W., Vol. 22, No. 2, Feb., 1950.
Poertner, H.G., Anderson, R.L., and Wolf, K.W., Urban Drainage
Practices. Procedures and Needs, American Public Works Assn., Proj. 119,
APWA Research Fdn., Spec. Rep. 31, Dec., 1966.
Rawn, A.M., "Some Effects of Home Garbage Grinding Upon Domestic Sewage,"
American City, Mar., 1951.
Rath, C.A., and McCauley, R.F., "Deposition in a Sanitary Sewer,"
Water and Sewage Works, May, 1962.
Riis-Carstensen, E., "System Design and Operation to Minimize Pollution,
(Buffalo)," Art. 6, "Treatment of Storm Sewage Overflow," N.Y. ASCE
Met. Sect. Symposium, Apr., 1962.
Romer, H., and Klashman, L.M., "Influence of Combined Sewers on
Pollution Control," Public Works, Oct.; 1961.
Romer, H., and Klashman, L.M., "How Combined Sewers Affect Water
Pollution," Public Works, Mar., 1963.
Rousculp, J.A., "Storage Basins as a Supplement to Storm Sewer Capacity,"
Civil Engineering, Nov., 1940.
Shifrin, W.G., and Homer, W.W., "Effectiveness of the Interception of -
Sewage-Storm Water Mixtures," J. WPCF. Vol. 38, No. 6, June, 1961.
Stegmaier, R.B., "Storm-water Overflows," Sewage Works Journal, 14:6,
June, 1942.
Symonds, G.E., "Pumps and Pumping," Water and Wastes Engineering,
Sept., 1966.
- 176 -
-------
General References (continued)
Thomas, H.A., Jr., Coulter, J.B., Bendixen, T.W., and Edwards, A.B.,
"Technology and Economics of Household Sewage Disposal Systems,"
J. WPCF, 22:2, Feb., 1960.
Watson, K.S., "Water Requirements of Dishwashers and Food Waste
Disposers," J. AWWA, 55:5, May, 1963.
Watson, K.S., Farrell, R.P., and Anderson, J.S., "The Contribution from
the Individual Home to the Sewer System," J. WPCF, Sept., 1966.
Weller, L.W., and Nelson, M.K., "Diversion and Treatment of Extraneous
Flows in Sanitary Sewers," J. WPCF, 37:3, Mar., 1965.
Wolff, J.B., Linaweaver, F.P., Jr., and Geyer, J.C., "Water Use in
Selected Commercial and Institutional Establishments in the Baltimore
Metropolitan Area," Dept. of Environmental Engineering Science, The
Johns Hopkins Univ., Baltimore, Md., June, 1966.
Wolff, J.B., "Peak Demands in Residential Areas," J. AWWA, Vol. 53,
No. 10, Oct., 1961.
Wraight, F.D., "Garbage Grinder Experiences, Jasper, Indiana,"
Sew, and Ind. Wastes, Jan., 1956.
- 177 -
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Jan. 30, 1968
SECTION XVII
PATENT
G. M. FAIR
CONVERTED SEWER SYSTEM
Filed Nov. 26. 1965
3,366,339
77
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- 178 -
-------
United States Patent Office
3,366,339
Patented Jan. 30, 1968
3,366,339
CONVERTED SEWER SYSTEM
Gordon M. Fair, 29 Robinson St.,
Cambridge, Mass. 02138
Filed Nov. 26, 1965, Ser. No. 509,711
The entire term of the patent has been
dedicated to the public
6 Claims. (CI. 241—101)
This invention relates to sewage systems and particu-
larly to a novel system for separating sanitary sewage (do-
mestic, mercantile, industrial) from stormwater in pre-
viously combined systems of sewerage. The term "sani-
tary sewage" is used to designate water discharged from
water fixtures and collected as wastewater after serving
its primary purpose, as well as water serving the purpose
of carrying away waste matters from households, mer-
cantile, commercial and industrial establishments.
The U.S. Department of Health. Education, and Wel-
fare, in its recent publicarion, "Pollutional Effects of
Stormwater and Overflow from Combined Sewer Systems,"
November 1964, estimates that 59 million people in the
United States live in communities with combined systems
of sewerage. The main and branch sewers of such systems
are usually designed to accommodate not only sanitary
sewage but also the runoff from rainstorms. Because it is
impractical to carry the occasional stormwater-swollen
flows, which are a great many times the volume of sani-
tary sewage, to treatment plants and treat them before
discharging them into nearby watercourses such as rivers,
lakes, and tidal estuaries, intercepting sewers built to
intercept sanitary sewage flows before they can spill into
water courses are seldom designed for a flow capacity
much beyond the maximum dry weather flow. This dry
weather flow normally consists only of the sanitary sew-
age and water leaching into sewers from wet ground, or
coming from street-washing, lawn-sprinkling, and other
dry-weather operations. Intercepters are seldom given a
flow capacity in excess of 3 times the dry-weather flow in
United Stales practice. At times of storms, the excess flow
above the intercepter capacity is overflowed, usually di-
rectly to a watercourse. This overflow contains raw sew-
age and the amount of raw sewage discharged in this man-
ner into the streams may, in the course of a year, amount
to as much as or more than 5% of the total annual sani-
tary sewage.
The extensive pollution of waters from this source is
a serious problem to which, the above publication con-
cludes, the ultimate answer is complete separation of sani-
tary sewage flow from stormwater flow. When new sew-
age disposal systems are being installed the provisions of
completely separate lines for sanitary sewage leading to
the treatment or disposal works and for stormwater lead-
ing to the watercourse is economically feasible and mod-
ern systems are normally of this type. However, the provi-
sion of a conventional separate sanitary sewage system in
communities presently employing a combined system
would be tremendously expensive, estimated in the above
publication to cost the nation 20 to 30 billion dollars.
The object of this invention is to provide a novel ap-
paratus system by which combined sewage systems may
be converted to separate sanitary sewage and stormwater
disposal systems at greatly reduced cost and without the
inconvenient and costly opening up of streets and side-
walks as required by prior proposals.
In accordance with the invention, each building hav-
ing an existing sanitary sewage connection to a combined
sewer is provided with a tank, usually in the basement,
in which all sanitary sewage from the building is received.
The tank is provided with a pump or pumping system,
preferably including or preceded or followed by a shred-
der or system of shredding. The pump or pumping system
forces the sewage through a pipe which extends through
the existing house or other building sewer conduit which
is connected to the combined sewer, and is of substantially
5 smaller diameter than such conduit. This pipe is preferably
made of flexible plastic or otherwise so constructed that
it may be fished through the existing conduit to the sewer
and will accommodate the pressurized flow of sewage from
th: pump. Within the combined sewer there is laid a
10 sa.ititary sewage receiving pipe to which the sanitary sew-
age discharge pipe from the pump of each unit served by
the sewer pipe is connected. This receiving pipe is of a
construction such as asbestos cement suitable for con-
taining pressurized flow of sewage and of sufficient diam-
15 eter to contain the sanitary sewage flow from all sources
connected thereto, but of substantially smaller diameter
than the existing combined sewer pipe or conduit within
which it is laid. The sanitary sewage receiving pipe with-
in the existing combined sewer extends to the nearest
20 intrecepter leading to the sewage treatment or disposal
works and preferably discharges into such intercepter,
although it may, if desired, be continued through such
intercepter to the works. Such receiving pipe may be laid,
hung or otherwise supported within the existing combined
25 sewer readily and without the necessity of opening up the
streets or sidewalks above the sewer. If the sewer at the
point at which the existing sewage conduit discharges to
it is too small to permit access of a workman to connect
the sanitary sewage discharge pipe from the unit to the
30 receiving pipe within the sewer, the discharge pipe is con-
tinued within the sewer and fished to the nearest man-
hole, normally not more than 200 feet away, where the
connection may be readily made.
It will be seen that the invention makes possible a
35 completely separate sanitary sewage disposal system which
may be provided within an existing combined sewer sys-
tem without opening up the ground over the existing sys-
tem. This is accomplished without the necessity of new
piping other than a single, relatively small sewer pipe in
40 each existing combined sewer line for receiving the sani-
tary sewage from each source discharging to said line
and which need extend only to the nearest intercepter
leading to the sewage treatment plant, and the relatively
small pipe extending from each source through the exist-
45 ing building sewer conduit to the sanitary (small) sewer
pipe in each existing combined sewer. The saving in cost
thereby effected, as compared with laying a new sani-
tary sewer system in the conventional way from each
unit to the treatment plant, far exceeds the cost of the
50 additional equipment which such a conventional sepa-
rate gravity flow system would not require, such as the
receiving tank, pump and shredder. In addition, the pres-
surized system which the invention provides at much
lower cost, has distinct advantages over a gravity flow
55 system.
To the cost saving above mentioned should be added
the smaller diameter of piping required as compared
with a separate gravity system and the fact that, due to
its protection by housing within an existing sewer sys-
60 tem, it can be of less costly construction than that of
piping which is laid directly under ground. For exam-
ple, the sanitary sewage piping according to this inven-
tion may be of the order of V6 to V* the diameter of
the existing sewer connections and much of it may be
made of inexpensive plastic material.
At times of storms my system disposes of the storm-
water to the watercourses as before but free of sanitary
sewage or with not more than a trace thereof which may
be occasioned by overflow from safety valves or other
control outlets provided in the pressurized sanitary sew-
age system or from overflow devices provided in the
tank within the premises.
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3,366,339
The invention will be further described in connection
with the accompanying drawing wherein:
FIG. 1 illustrates in vertical cross-seclion a portion of
a house or similar unit and sewer connections to it which
have been modified according to the invention to con-
vert the system from combined to separated sanitary sew-
age and stormwater disposal; and
FIG. 2 is a view similar to FIG. 1 of the existing com-
bined sewer now serving as a storm sewer and the sani-
tary sewer showing a junction with an intercepter leading
to the sewage treatment or disposal works, and also show-
ing a safety valve in the pressurized line.
Referring to FIG. 1 of the drawing, the sewer con-
nections for only one house or similar unit are shown, it
being understood that such connections are essentially
duplicated for each unit served by the sewer pipe up
to the nearest intercepter leading to the sewage treat-
ment plant.
Referring to the drawing, the sanitary sewage collecting
tank for the house or other unit is shown at 10 located at
a low level such as on or below the basement floor, hav-
ing an inlet 12 to the existing sewage outflow pipe from
the unit and an overflow outlet 14 connected to the usual-
ly underground conduit 16 which connects the unit to the
existing combined sewer pipe 30. Inlet 12 is shown as
preceded by a shredder 13 provided with a cutting screen
15 which discharges the shredded sewage through elbow
17 to inlet 12. Above tank 10 is located a pump 18, dia-
grammatically indicated as a gear pump, the motor for
which is not shown. The pressure required of the pump
is not great, and may be such as to produce a flow rate
of the order of six feet per second as compared with the
normal gravity flow rate of the order of one to four feet
per second.
10
it m.iy have shielded exposure to the atmosphere. Pipe 26
may also have a branch connection to the inlet side of
comminuter 13 in order to insure complete venting of
the system.
Tank 10 will usually be equipped with controls (not
shown) for governing the operation of the pump, such as
one or more float valves or sensors for starting the unit
when the contents of the tank reach a desired maximum
storage level and stopping it when the tank is emptied to
a desired minimum level. Controls for operating the
shredder during times of flow, also not shown, will also
normally be provided. There may also be included time
controls which permit the pump to operate only at certain
times unless an emergency love! is renched in the mean-
13 lime. By staggering operating times of the various units
served by m:iin scwcr pipe 30 the daily sewnpe flow to
the treatment plant can be regularized and overloads pre-
vented. If the pump 18 is a gear pump ns shown, it will
prevent backflow from pipe 22. If another type of pump
20 is used which does not prevent backflow, a backflow con-
trol device such as a check valve will ordinarily be pro-
vided for the purpose.
It should be noted that conduit 16. except for the small
volume thereof occupied by pipe 22, is now available to
conduct to sewer p'Pe 30 waste water from roofs and
Slitters, and from area and cellar drains and the like. These
may now be safely connected to this conduit whereas in
the former combined
-------
3,366,339
vided at suitable intervals with emergency overload re-
lief valves which will discharge into sewer pipe 30 to such
extent as necessary to remove temporary overloads. Such
a valve is shown at the right in FIG. 2 in the form of a
to said works, said second system being connected to re-
ceive pressurized sanitary sew;ige flow from said sources
of sanitary sewage by means of pipe connections extend-
ing through said pipe connections of said first piping sys-
vertically dispose pipe 50 opening at its base into pros- 5 tern, said sources of sanitary sewage including a storage
sure pipe 32 nnd closed at the top by a hinged cover 52. tank for the sewage and pump means connected to with-
draw sewage from said tank and to discharge it under
pressure through said pipe connections of said second
The upper part of pipe 58 extends into a compartment 54
which rises above the main sewer pipe 30 and may con-
veniently be a manhole. Under normal pressure and flow
the sanitary sewage in pipe 32 will not rise to the top of
pipe 50 and cover 52 will remain closed. If sufficient
back pressure should develop in the pressure system due
to overload or plugging, the sanitary sewage will rise to
the top of pipe 50 and force open cover 52, escaping into
piping system.
10
2. A sewage system according to claim 1 wherein said
first system of piping includes intercepters leading !o said
works and said second system of piping discharges to said
intercepters.
^ ^ 3. A sewage system according to claim 1 which in-
compartment 54 and to main sewer pipe 30 until the 15 eludes means for shredding the sewage before it is dis-
condition is relieved, whereupon the cover 52 again closes charged into said second piping system.
under its weight. At times of storms the stormwater will 4. A sewage system according to claim 1 wherein said
not ordinarily rise above the cover 52 and so the relief pipe connections of said second piping system from said
system remains operable at such times. sources of sanitary sewage are of flexible material such
While it will usually be satisfactory and less expensive 20 that they may be readily fished through the piping of said
to permit the sanitary sewage to discharge from the pres- first piping system.
5. A sewage system according to claim 1 wherein said
tank is provided with means permitting emergency over-
flow to said pipe connections of said first piping system.
6. A sewage system according to claim 1 wherein said
second piping system is provided with means permitting
emergency overflow from said second piping system to
25
sure pipe system into the existing intercepter system as
shown, it may be desirable in some instances to continue
the pressure system within the intercepters to the sewage
treatment or disposal works.
I claim:
1. A sewage system for separately conducting storm-
water to an outfall and sanitary sewage to a sewage treat-
ment or disposal works comprising a first system of pip-
ing leading to an outfall, having inlets for stormwater 30
and also having pipe connections from sources of sanitary
sewage such as buildings, a second system of piping of
substantially smaller diameter (han the piping of said
first system and housed within it for receiving pressurized
sanitary sewage flow, said second system being normally 35
closed to said outfall and having connections leading
said first piping system.
References Cited
UNITED STATES PATENTS
2,852,313 9/1958 Mickel 302—14
3,239,849 3/1966 Liljendahl 302—14
i A. DOST, Primary Examiner.
- 181 -
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SECTION XVIII
GLOSSARY*
BOD — (1) The quantity of oxygen used in the biochemical oxidation of
organic matter in a specified time, at a specified temperature,
and under specified conditions. (2) A standard test used in
assessing wastewater strength.
branch sewer — A sewer that receives wastewater from a relatively small
area and discharges into a main sewer serving more than one
branch-sewer area.
building sewer — In plumbing, the extension from the building drain to
the public sewer or other place of disposal.
coliform-group bacteria — A group of bacteria predominantly inhabiting
the intestines of man or animals but also occasionally found
elsewhere.
combined sewer — A sewer intended to receive both wastewater and storm
or surface water.
combined wastewater — A mixture of surface runoff and other wastewater
such as domestic or industrial wastewater.
comminuted solids — Solids which have been divided into fine particles.
contamination — Any introduction into water of microorganisms, chemicals,
wastes, or wastewater in a concentration that makes the water unfit
for its intended use.
diverting weir — A weir placed in a combined sewer to divert storm flow
from the normal dry-weather direction.
dry-weather flow — The flow of wastewater in a combined sewer during dry
weather. Such flow consists mainly of wastewater, with no storm
water included.
force main — A pressure pipe joining the pump discharge at a wastewater
pumping station with a point of gravity flow.
hydraulic grade line — A hydraulic profile of the piezometric level of
water at all points along a line. In an open channel, it is the
free water surface.
(*: From Glossary; Water and Wastewater Control Engineering, ASCE,
WPCF, AWWA, APHA, In Press)
- 182 -
-------
industrial wastes - The liquid wastes from industrial processes, as
distinct from domestic or sanitary wastes.
infiltration — The quantity of groundwater that leaks into a pipe
through joints, porous walls, or breaks.
intercepting sewer - A sewer that receives dry-weather flow from a
number of transverse sewers or outlets and frequently additional
predetermined quantities of storm water (if from a combined
system), and conducts such waters to a point for treatment or
disposal.
lateral sewer — A sewer that discharges into a branch or other sewer
and has no other common sewer tributary to it.
main sewer - (1) In larger systems, the principal sewer to which branch
sewers and submains are tributary; also called trunk sewer. In
small systems, a sewer to which one or more branch sewers are
tributary. (2) In plumbing, the public sewer to which the house
or building sewer is connected.
outfall sewer - A sewer that receives wastewater from a collecting
system or from a treatment plant and carries it to a point of
final discharge.
outlet — Downstream opening or discharge end of a pipe.
overflow weir - Any device or structure over which an excess wastewater
beyond the capacity of the conduit is allowed to flow or waste.
pollution - A condition created by the presence of harmful or objection-
able material in water. Also see contamination.
regulator - A device for regulating the diversion of flow in combined
sewers.
sanitary sewer - A sewer that carries liquid and water-carried wastes
from residences, commercial buildings, industrial plants, and
institutions, together with minor quantities of ground-, storm,
and surface waters that are not admitted intentionally. See
wastewater.
sanitary wastewater - (1) Domestic wastewater with storm and surface
water excluded. (2) Wastewater discharging from the sanitary
conveniences of dwellings (including apartment houses and hotels),
office buildings, industrial plants, or institutions.
sewage - This term is no longer in common use. See wastewater.
sewer - A pipe or conduit that carries wastewater or drainage water.
- 183 -
-------
sewer outfall - The structure through which wastewater is finally
discharged.
sewer outlet — The point of final discharge of wastewater or treatment
plant effluent.
sewer system — Collectively, all of the property involved in the
operation of a sewer utility. It includes land, wastewater
lines and appurtenances, pumping stations, treatment works,
and general property. Occasionally referred to as a sewerage
system.
**storage-grinder-pump (sgp) — An assembly or unit for preparing and
pressurizing wastewater from individual homes; a major component
of the ASCE Project system (See Section V).
storm sewer — A sewer that carries storm water and surface water,
street wash and other wash waters, or drainage, but excludes
domestic wastewater and industrial wastes. Also called storm
drain.
suspended solids — Solids that either float on the surface of, or are
in suspension in, water, wastewater, or other liquids, and which
are largely removable by laboratory filtering.
trunk sewer - A sewer that receives many tributary branches and serves
a large territory. See main sewer.
wastewater — The spent water of a community. From the standpoint of
source, it may be a combination of the liquid and water-carried
wastes from residences, commercial buildings, industrial plants,
and institutions, together with any groundwater, surface water,
and storm water that may be present. In recent years, the word
wastewater has taken precedence over the word sewage.
wastewater facilities - The structures, equipment, and processes
required to collect, carry away, and treat domestic and industrial
wastes, and dispose of the effluent.
wastewater outfall - The structure through which wastewater is finally
discharged.
wastewater outlet - The point of final discharge of wastewater or
treatment plant effluent.
(**: Not included in Glossary: Water and Wastewater Control
Engineering. ASCE, WPCF, AWWA, APHA, In Press)
- 184 -
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APPENDICES
Appendix A — Abstracts of Project Technical Memoranda
Appendix B — Abstracts of Project Subcontractors' Reports
NOTE — Copies of technical memoranda and subcontractors' reports are
available at $3.00 per copy from the Clearinghouse for Federal
Scientific and Technical Information, U.S. Department of
Commerce, Springfield, Va. 22151. Orders should specify item
title and the Clearinghouse identifying number.
Clearinghouse Identifying Numbers
Technical Memoranda Subcontractors' Reports
No. 1 PB 185 995 Brown & Caldwell PB 186 001
No. 2 PB 185 996 Greeley & Hansen PB 186 003
No. 3 PB 185 997 Camp, Dresser & McKee PB 186 000
No. 3A PB 185 998 General Electric, March, 1967 PB 185 990
No. 4 PB 185 999 General Electric, April, 1968 PB 185 994
No. 5 PB 186 Oil General Electric, Dec., 1968 PB 186 004
No. 6 PB 186 012 FMC Corporation PB 185 991
No. 7 PB 186 013 National Sanitation Foundation PB 185 992
No. 8 PB 186 014 Johns-Manville PB 186 005
No. 9 PB 186 015 Univ. of Illinois, March, 1968 PB 185 993
No. 10 PB 186 006 Univ. of Illinois, Nov., 1968 PB 186 002
No. 11 PB 186 007
No. 12 PB 186 008
No. 13 PB 186 009
No. 14 PB 186 010
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APPENDIX A
ABSTRACTS OF PROJECT TECHNICAL MEMORANDA
"OUTLINE DESCRIPTION OF ASCE PROJECT ON
SEPARATION OF SANITARY SEWAGE FROM COMBINED SYSTEMS
OF SEWERAGE"
Technical Memorandum No. 1
February 21, 1966
(Reference 1, Section XVI, "Bibliography")
The general concept of the ASCE Project scheme is to discharge
comminuted sanitary sewage from individual buildings and building
complexes through relatively small pressure tubing laid in existing
building connections and thence into new pressure conduits suspended
in existing street sewers. Potential advantages of the scheme are
discussed. The ultimate goal of the Project is to develop feasible
designs and operations and to put them to test in actual systems. The
immediate objective is to examine and evaluate both the feasibility
and probable cost. The background of the project is reviewed.
Dr. Gordon M. Fair conceived the scheme on which the Project is based.
An appendix summarizes the need for separation of combined sewerage
systems and the national scope of the problem. (9 pp.)
"SEWAGE FLOW VARIATIONS IN INDIVIDUAL HOMES"
Technical Memorandum No. 2
by L.S. Tucker
February 24, 1967
(Reference 2, Section XVI, "Bibliography")
Winter water demands are assumed to represent sewage flows in the
absence of sewage flow data. Two sets of 1-minute interval household
water demand data are used: from six homes in Maryland for two weeks,
and from two homes in Louisville for four weeks. Maximum and minimum
24-hour and 60-, 15-, and 4-minute demands for each day are given for
each home. Frequency distributions of 24-hour and 60-minute flows for
each sample are compared with each other and with distributions of total
flows from groups of 3 houses and 6 houses. Based on routing of peak
flows from nearly five hundred home-days of data through various storage-
pump combinations, a pump capacity of 10 GPM and a usable storage capacity
of 30 gal. are indicated for initial sizing of household storage-grinder-
pump units. Pressure discharge tubing for pressure building services to
handle expected flows at reasonable head losses would be 3/4 to 1 1/4 inch
I.D. (70 pp.)
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"EXPERIENCE WITH GRINDING AND PUMPING
OF SEWAGE FROM BUILDINGS"
Technical Memoranda Nos. 3 and 3A
by D.H. Waller
May 1, 1967 and March 1, 1968
(Reference 3, Section XVI, "Bibliography")
In T.M. 3, a typical garbage grinder is described and use of
grinders for toilet wastes is reviewed. Two wet process building-waste
pulping systems and two machines that combine the functions of grinding
and pumping are described. Practice in the use of pumps, piping and
backflow valves for sewage in buildings is reviewed. An appendix
describes the Liljendahl vacuum sewerage system. (102 pp.)
Results of monitoring the operation of thirty-six comminutor
installations that serve individual buildings are reported in T.M. 3A.
The monitoring program, which covered periods of up to sixteen months,
is described. Descriptions and prior operating histories of the instal-
lations are included. Frequency of attention and maintenance is recorded
and compared with manufacturers' recommendations. Twenty-five of the
machines were inspected at least five times each week. Twenty-four of
the installations include sewage pumps following the comminutors with
discharge mains 3 to 6 inches in diameter. An appendix contains a sum-
mary description of a system developed at Pennsylvania State University
for conservation of water in residences by recycling. (47 pp.)
"STUDY OF APPROXIMATE LENGTHS AND SIZES OF
COMBINED SEWERS IN MAJOR METROPOLITAN CENTERS"
Technical Memorandum No. 4
by Dasel E. Hallmark and John G. Hendrickson, Jr.
May 1, 1967
(Reference 4, Section XVI, "Bibliography")
A tabulation is given for five major cities of mileage and percent-
age of combined sewers with heights: greater than 48 inches; equal to
or less than 48 inches; and equal to or less than 24 inches. An average
of 72 per cent of the sewers are smaller than 24 inches. Heights of 54
inches and larger, classified as walk-through sewers, account for an
average of about 15 per cent of the total combined sewer mileage. (9 pp.)
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"PRESSURE TUBING FIELD INVESTIGATION"
Technical Memorandum No. 5
by L.S. Tucker
August 15, 1967
(Reference 5, Section XVI,"Bibliography")
Three methods of installing pressure tubing from houses or small
buildings, and of connecting the tubing with street pressure conduits,
are described and discussed. One would be the installation and connec-
tion of pressure tubing and conduit in trenches by traditional water
distribution methods. Field trials were conducted to indicate the
feasibility of inserting tubing in building sewers. Tubing was pushed
through an 86 foot long 4 and 5 inch diameter building lateral, which
included three 45° bends, from a specially dug pit at the upstream end
into a 4 foot diameter combined sewer. The forward end of the tubing
was guided by a special leader device. 3/4, 1, and 1% inch polyethylene
tubing could be pushed. Polybutylene and copper tubes could not be
pushed because they buckled or crimped. A Kellems grip and swivel on
the end of a rope were used to pull tubing from the combined sewer to
the upstream pit. 3/4, 1, and 1% inch polyethylene and 3/4 and 1 inch
polybutylene could be pulled. 3/4 inch copper tubing could not be
pulled because of its stiffness. The third method, tested in the field,
combined the insertion of tubing with a street main in trench. (29 pp.)
"HYDRAULICS OF A PRESSURIZED SEWERAGE SYSTEM
AND USE OF CENTRIFUGAL PUMPS"
Technical Memorandum No. 6
by L.S. Tucker
November 15, 1967
(Reference 6, Section XVI, "Bibliography")
Hydraulic gradients for high and low flows and the use of pressure
control devices for service zones and at the interceptor are illustrated
and discussed. For some flat drainage areas sewage pumping would be
necessary; a pressure control assembly would be needed immediately
upstream and a surge control valve would be used immediately downstream
of a lift station. For steep drainage areas, pressure control assemblies
would be needed to limit maximum pressures. Centrifugal pump character-
istics are discussed and information on thirty-two classes of sewage and
solids handling pumps is tabulated. Sewage pump characteristics are such
that maximum reasonable limits on discharge rates would be greatly
exceeded if variations in total dynamic head were allowed to equal curb
pressure variations that are expected in some parts of a pressure sewer
system. Ordinary use of centrifugal pumps in these cases would be
precluded. A possible modification of building pumping systems with a
valve controlled to maintain a constant discharge pressure is discussed
together with the use of variable speed drivers. (35 pp.)
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"MINIMUM TRANSPORT VELOCITY FOR PRESSURIZED
SANITARY SEWERS"
Technical Memorandum No. 7
by M.B. McPherson, L.S. Tucker and M.F. Hobbs
November 16, 1967
(Reference 7, Section XVI, "Bibliography")
Raw sewage, with and without particle-size reduction by comminu-
tion, was pumped through 2-in. to 8-in. clear plastic pipe. Extensive
observation indicated rather conclusively that the material last to be
scoured and first to be deposited was predominantly sand. For all
tests, the sewage was salted with ground egg shells but these were
always moved at lower mean flow velocities than the sand, which was in
low concentrations, viz., 8 to 78 ppm. No discernable difference was
noted in the minimum transport velocities for comminuted and uncomminuted
sewage, and the difference between minimum scouring velocities and
maximum depositing velocities was small. Test results were blended with
those from sand transport experiments elsewhere for general representa-
tion. Exploratory open channel tests were made with the 8-in. pipe for
a firmer correlation with sand tests. Results are presented in terms of
ditnensionless parameters. Limited tests were made on an 8-in. spiral
corrugated pipe. (23 pp.)
"DOMESTIC SEWAGE FLOW CRITERIA FOR EVALUATION OF APPLICATION
OF PROJECT SCHEME TO ACTUAL COMBINED SEWER DRAINAGE AREAS"
Technical Memorandum No. 8
by M.B. McPherson
November 17, 1967
(Reference 8, Section XVI, "Bibliography")
Residential sewage flow criteria are developed for use in design
of pressurized sanitary sewers for hypothetical applications of the ASCE
Project scheme. In a typical combined sewer area, data on domestic water
demands is the most that can be expected to be available. On the basis
of a study of winter water demand data it is concluded that projection of
such observed demands for a service area to the end of the design period
is the preferred basis of design. Data for California and the north-
eastern United States are presented separately. For each region, design
curves represent the variation, as a function of the number of dwelling
units served, of flows for the minimum 24 hours, for the peak hour of the
minimum day, and for the maximum peak hour of any day, expressed as
ratios to the annual average rate. (19 pp.)
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"PEAK FLOWS OF SEWAGE FROM INDIVIDUAL HOUSES"
Technical Memorandum No. 9
by D.H. Waller
January 1, 1968
(Reference 9, Section XVI, "Bibliography")
Sewage flows and water demands measured at two household observa-
tion stations, as well as water and wastewater flows from individual
fixtures and appliances is used to estimate upper limits of pump and
storage capacities for a storage-grinder-pump unit for individual homes
and to examine the relationship between peak rates of sewage flow and
corresponding water demand rates. For individual fixtures, combinations
of rate, duration and frequency of discharge that will produce maximum
hydraulic loading conditions are selected. Single-fixture hydrographs
are combined to produce synthetic hydrographs of peak period sewage
discharge, from which combinations of storage and pump capacities are
derived. Peak sewage flows and simultaneous water demands for a
fourteen day period at one house are presented and analysed. (117 pp.)
"AN EXAMINATION OF THE BENEFITS AND DISADVANTAGES
WITH RESPECT TO THE DISPOSAL OF SOLID WASTES"
Technical Memorandum No. 10
by D.H. Waller
February 1, 1968
(Reference 10, Section XVI, "Bibliography")
Important considerations in an evaluation of the feasibility and
benefits of adapting any sewerage system to solid wastes disposal are:
the extra solids load that community refuse could add to a sewage
disposal system; velocities required to move solid wastes and the effect
of flow variations on sewer velocities; solid wastes separation practices
and attitudes toward separation of household refuse; the need for
grinding, and considerations involved in the development of a household
refuse grinding device; the effects of solid wastes on sewage treatment
processes; and costs and benefits involved in evaluation of alternative
systems for disposal of sewage and solid wastes. Considerations
peculiar to the ASCE Project scheme are: the possibility of adapting
building sewage storage-grinder-pump units for handling solid wastes;_
the need to discharge solid wastes into the system under pressure;
reduced clearances in the small pipes of a pressure system; and the
possibility of greater solids deposition at low flows. Appendices
include information on: composition and characteristics of solid wastes;
pertinent solid wastes research and development; and results of research
on transport and treatment of solid wastes in sewage disposal systems.
(54 PP.)
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"CONTROL TECHNIQUES FOR PRESSURIZED SEWERAGE SYSTEMS"
Technical Memorandum No. 11
by James R. Daneker and William H. Frazel
March 4, 1968
(Reference 11, Section XVI, "Bibliography")
Instrumentation and control of a pressurized sewerage system can
be attained with current technology, and special designs are foreseen
that can approach zero maintenance. A rubber-seated butterfly valve is
recommended. A venturi type element or a magnetic meter could be used
in flow control. For control of pressure in response to flow changes,
a transducer will be required to generate some characterized signal that
will be the set point for a pressure controller. The transducer should
incorporate a cam that can be cut in the field. "System No. 1" maintains
a fixed pressure upstream of the control element by modulation of the
valve to correct or reduce any deviation of measured pressure from a
selected set point. "System No. 2" modulates the valve to maintain a
specific upstream pressure corresponding to every rate of flow measured
at the flow element. "System No. 3" would control the start-stop
sequence of a booster or lift station centrifugal pump to permit starting
without surge and maintain a constant discharge pressure. For a booster
station this system would vary pump speed in response to suction pressure.
For nearly fool-proof fail-safe control, an all-hydraulic control system
is recommended in preference to pneumatic, hydro-pneumatic, or electronic
systems. (27 pp.)
"NON-MECHANICAL CONSIDERATIONS INVOLVED IN
IMPLEMENTING PRESSURIZED SEWERAGE SYSTEMS"
Technical Memorandum No. 12
by D.H. Waller
May 31, 1968 :
(Reference 12, Section XVI,"Bibliography")
Installation of a storage-grinder-pump unit in every home raises
questions regarding: allocation of costs of the units; responsibility
for malfunction of the units; arrangements for service of the units; and
willingness of owners to accept the presence of units in their buildings.
Twenty-five householders in Radcliff, Kentucky, whose houses are served by
sewage ejector units were interviewed to obtain opinions about features
of the units that appeared to represent potential sources of nuisance,
inconvenience, or other liabilities. Also interviewed were the super-
intendent of the utility operating the Radcliff sewerage system, owners
of five houses in Louisville, Kentucky, at which sewage sampling stations
were located, and three consulting engineering firms who have considered
schemes involving the installation of sewage pumping equipment on private
properties. Opinions and practices reported reflect the view that sewage
pumping equipment placed on private property as part of a public project
should be purchased, installed, and serviced at public expense, (27 pp.)
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"SPECIAL REQUIREMENTS FOR A FULL SCALE FIELD DEMONSTRATION
OF THE ASCE COMBINED SEWER SEPARATION PROJECT SCHEME"
Technical Memorandum No. 13
by D.H. Waller
June 3, 1968
(Reference 13, Section XVI, "Bibliography")
Matters that should be considered in planning a field demonstra-
tion of the ASCE Project pressure sewerage scheme are summarized. These
include: importance of connecting as many buildings as possible in the
demonstration project area; need for protection from overflows of
building storage-grinder-pump units; relationship between occurrence of
overflows from buildings and given levels of public inspection, detection
and control; effectiveness of alarms on SGP units; legal agreements with
property owners; importance of complete records of project costs; effec-
tiveness of the project as a pollution control measure; possible benefits
of elimination of infiltration from interceptors and treatment plants;
detection and clearing of obstructions; use of polymer additives to
reduce fluid friction; behavior of unground sewage including anaerobic
decomposition; self-cleansing characteristics of flow; rate and extent
of deterioration of friction factors; sewage flow variations and their
relationship to water demands; handling of interruptions of service; and
field tests on installations in walk-through combined sewers. The
appendix is an assessment of the physical problems to be overcome in
separation of plumbing on private property, with estimates of cost, based
on information from officials in seven large cities having combined
sewers, and from a consulting engineer and a recent American Public Works
Association survey. (84 pp.)
"ROUTING OF FLOWS IN SANITARY SEWERAGE SYSTEMS"
Technical Memorandum No. 14
by L.S. Tucker
July 18, 1969
(Reference 14, Section XVI, "Bibliography")
Water demand data from individual homes, assumed to represent sewage
flows, are combined by routing into a 10-home input unit. These input
units are then routed through a collection system via a hydrograph super-
position procedure. The hypothetical pressure system serves 3,270 dwelling
units. The ratio of peak flow to the two-week average flow is 2.7 at the
outlet. Similar analyses of portions of the pressure system consisting of
1,000 and 250 dwelling units are made. The ratio of peak to the two-week
average for the 1,000 dwelling unit portion of the system is 3.5, and for
the 250 dwelling unit portion of the system is 4.0.
A method of analysis based on notes and calculations of Professor
H.A. Thomas of Harvard U. involving theoretical moments of frequency
distributions is presented. The method is explained by applying it to a
simple example of a sewage collection system. The method provides an
estimate of peak flows and time of occurrence, and has a potential for
examining parameter sensitivity. (39 pp.)
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APPENDIX B
ABSTRACTS OF PROJECT SUBCONTRACTORS' REPORTS
"SEPARATION OF COMBINED WASTEWATER AND STORM DRAINAGE SYSTEMS,
SAN FRANCISCO STUDY AREA" (TASK 4)
Brown and Caldwell, Consulting Engineers
San Francisco, California
September, 1968
(Reference 16, Section XVI, "Bibliography")
The report is one of three by consultants to study the design,
estimate costs and evaluate the feasibility of the hypothetical appli-
cation of the ASCE Project scheme of pressure sewers for separation in
representative combined sewer areas from layouts by the Project staff.
The San Francisco study considered the 323 acre predominantly
residential, steeply sloping Laguna Street Sewer Service District,
rebuilt since the 1906 fire. The report describes methods of building
plumbing separation and indicates two alternative arrangements of pres-
sure sewers, with plans and profiles. Estimates of construction cost of
each ($13,000,000 and $13,350,000) are compared with that of a conven-
tional gravity system of separation designed earlier by the City
($8,800,000). Plumbing separation, included in the above, is estimated
to cost about $5,400,000 for the gravity method and about $4,400,000 for
the pressure method, not including storage-grinder-pump units. (81 pp.)
"COMBINED SEWER SEPARATION PROJECT, REPORT ON
MILWAUKEE STUDY AREA" (TASK 4)
Greeley and Hansen, Consulting Engineers
Chicago, Illinois
December, 1968
(Reference 17, Section XVI, "Bibliography")
The report is one of three by consultants to study the design,
estimate costs and evaluate the feasibility of the hypothetical applica-
tion of the ASCE Project scheme of pressure sewers for separation in
representative combined sewer areas from layouts by the Project staff.
The Milwaukee study considered the 157-acre mainly dense residen-
tial, moderately sloping Prospect Avenue Study Area essentially built
prior to 1930 with many buildings dating from before 1900. The report
describes methods of building plumbing separation and indicates two
alternative arrangements of pressure sewers with plans and a profile.
Estimates of construction cost of each ($3,225,000 and $3,260,000) are
compared with that of a conventional gravity system of separation
designed by the consultant ($2,195,000). Plumbing separation, included
in the above, is estimated to cost $912,000 for the gravity alternative
and $971,000 for the pressure alternatives, not including storage-
grinder-pump units. (84 pp.)
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"REPORT ON PRESSURE SEWERAGE SYSTEM, SUMMER STREET SEPARATION
STUDY AREA, BOSTON, MASSACHUSETTS" (TASK 4)
Camp, Dresser & McKee, Consulting Engineers
Boston, Massachusetts
September, 1968
(Reference 18, Section XVI, "Bibliography")
The report is one of three by consultants to study the design,
estimate costs and evaluate the feasibility of the hypothetical appli-
cation of the ASCE Project scheme of pressure sewers for separation in
representative combined sewer areas from layouts by the Project staff.
The Boston study considered the 53-acre gently sloping, hetero-
geneous commercial Summer Street Separation Study Area, including many
buildings built in the late 1800's. The report describes the separa-
tion of building plumbing in detail in a typical three-quarter century
old five story and basement commercial building 65-ft. by 145-ft. in
plan, and estimates the cost of plumbing separation. Four alternative
pressure sewer collection systems are indicated with plans and hydraulic
profiles. Some systems included in-line main pumping stations. The
least expensive complete pressure system, which did not include a main
pumping station, is estimated to cost $6,400,000 compared to the cost
of a gravity separation system designed by the consultants, estimated
to cost $4,700,000. Both costs include costs of building plumbing
separation, $4,000,000 for the pressure system including communitors,
wet wells and non-clog pumps, and $2,000,000 for the gravity system.
(82 pp.)
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"SAMPLING AND ANALYSIS OF WASTEWATER FROM
INDIVIDUAL HOMES" (TASK 2)
by R.P. Farrell, J.S. Anderson, and J.L. Setser
General Electric Company
Appliance Park, Louisville, Kentucky
March 24, 1967
(Reference 19, Section XVI, "Bibliography")
The results of the initial phase of operation of two household
wastewater observation stations are described. During a three month
period household wastewater was sampled for analysis, wastewater flow
rates were measured, and the behavior of components when handling
wastewater under actual conditions of use was observed. Each station
included a garbage grinder for reduction of incoming sewage solids
sizes, a float well and level recorder, a pump and pump operation time
recorder, a check valve on the pump discharge line, and fifty feet of
clear plastic discharge tubing. An extensive program of sampling and
analysis was carried out to characterize completely the wastewater from
each home. Particulate matter in the wastewater was analyzed over an
intensive seven-day period to determine its exact nature in terms of
particle size, density and microscopic appearance. Analyses were made
of water demand data obtained from measurements at one gallon intervals
at each house telemetered to recording equipment. A set of fixture
tests, during which fixtures were discharged singly and in combinations
in preplanned sequences, was run at both stations to obtain information
on water and sewage flow patterns for fixtures. (79 pp.)
"LONG-TERM OPERATION OF WASTEWATER OBSERVATION
STATIONS" (TASK 2)
by R.P. Farrell
General Electric Company
R. and D. Center, Schenectady, N.Y.
April 24, 1968
(Reference 20, Section XVI, "Bibliography")
In the terminal phase of operation of two household wastewater
observation stations (see preceding abstract), the stations were operated
for seven months during which the principal objective was collection of^
usage experience. The two garbage grinders were never a source of diffi-
culty. The 3/4 inch check valves regularly trapped fibrous or stringy
materials. A significant increase in head loss in the 3/4 inch discharge
tubing in the last month of operation at one station is attributed to a
thick coating of anaerobic slime on the interior walls, attributed to
low inflow rates and extended periods of disuse. The 1-inch tubing at
the other station was essentially clean throughout the tests. Results
of fixture flow tests, and information on overflows from the station
wet-wells, was obtained to supplement results of the earlier studies.
(48 pp.)
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"ADVANCED DEVELOPMENT OF HOUSEHOLD
PUMP-STORAGE-GRINDER UNIT" (TASK 6)
by R.P. Farrell
General Electric Company
R. and D. Center, Schenectady, N.Y.
December, 1968
(Reference 21, Section XVI, "Bibliography")
This report describes the development, by the General Electric
Company for the ASCE Project, of a 150-pound household SGP unit
comprising a domestic sewage grinder and progressing-cavity pump driven
by a 1-h.p., 1725-r.p.m. motor, and mounted on a 58-gallon receiver
tank, meeting criteria established by the Project investigation. The
unit is capable of discharging through a backflow valve and 1%-in.
outlet at 15-gpm at atmospheric pressure and 11-gpm at 35 psig pressure,
The estimated cost of the unit without tank is $343, and estimated
total installed costs are $548 for new work and $648 where cutting and
patching are involved. Cost of energy for operation is about $2 per
year. (74 pp.)
"RELATIONSHIP OF SEWAGE CHARACTERISTICS TO CARRYING
VELOCITY FOR PRESSURE SEWERS" (TASK 5)
by M.F. Hobbs
Central Engineering Laboratories
FMC Corporation, Santa Clara, California
August, 1967
(Reference 22, Section XVI, "Bibliography")
Minimum carrying velocities for solid phase matter in smooth
plastic 2", 3", 4", 6", and 8" pressure pipes were measured using
comminuted and uncomminuted raw sewage. The minimum velocity for
scouring and the maximum velocity for depositing were essentially the
same. Velocities appeared to be independent of: the concentration
magnitudes of suspended solids, fixed suspended solids, sand concentra-
tion, and the size distribution of suspended matter and sand for the
sewages studied. Velocities appeared to be dependent on the fixed
solids content. Egg shells that had been passed through a garbage
grinder were carried at lower flow rates than required for moving the
bottom sediments. Carrying velocities were investigated in an 8" spiral
pressure pipe but the results obtained were very erratic. Tests were
also made on the 8" plain plastic pipe with open channel flow. All data
acquired are reported. (96 pp.)
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"REPORT TO ASCE COMBINED SEWER SEPARATION PROJECT
ON FWPCA CONTRACT NO. 14-12-29" (TASKS 7 AND 9)
by Robert N. Bowen and John G. Havens
National Sanitation Foundation, Ann Arbor, Mich.
December, 1967
(Reference 23, Section XVI, "Bibliography")
Assistance was provided in connection with special field trial
installations of flexible tubing inserted in building sewers. Materials
were proposed for pushing or pulling through a building sewer and a
methodology and necessary attachments and tools were recommended.
Polyethylene and polybutylene tubing are recommended for use inside
building sewers and copper tubing for use in open trenches. A saddle
type of connection is recommended for connection of pressure tubing to
street pressure conduits. Cast iron, PVC, asbestos cement, or ductile
iron are recommended for pressure conduits. Experience with plowing of
pressure pipe is reviewed. Reference is made to standard practice for
trench installations, street crossings and thrust blocking. Two methods
of cleaning house pressure tubing are proposed. Six possible layouts of
pressure conduits are discussed in terms of operation and maintenance.
All six arrangements provide for routine rerouting of flow by exploiting
a dual conduit configuration. (55 pp.)
"DEVELOP AND FIELD TEST METHOD OF INSTALLING
PRESSURE CONDUITS IN COMBINED SEWERS" (TASK 7)
by H.J. Kazienko
Research and Engineering Center
Johns-Manville Products Corporation, Manville, N.J.
December 30, 1968
(Reference 24, Section XVI,"Bibliography")
This report describes the development and testing in the laboratory
of polyester molded hangers cemented to the sewer pipe crown. Polyester
hanger material formulations, epoxy cement, and hanger dimensions are
specified, and methods of installation given in detail. Test of the
hanger to failure in the laboratory showed fracture in tension through
the conduit ring, leaving the upper part bonded to the concrete sewer
crown. The field installation of 100-ft. of 3-in. diameter PVC pipe
filled with water was made in a 7-ft. sewer in Evanstan, 111., in
cooperation with the Metropolitan Sanitary District of Greater Chicago.
The installation was sound and unaffected when removed after 4% months.
(38 PP.)
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"TURBULENT FRICTION IN ECCENTRIC ANNULAR CONDUITS" (TASK 12)
by James M. Robertson
Department of Theoretical and Applied Mechanics
Report No. 310
University of Illinois, Urbana, 111.
March, 1968
(Reference 25, Section XVI, "Bibliography")
Following a general review of the analytical and experimental
information on the friction loss encountered by fluids flowing in
annular pipes, with particular regard to the influence of eccentricity
of the inner member, experiments are described on an evaluation of the
friction of water in a steel annular pipe of diameter ratios 5.8 and
3.2 in the Reynolds number range of 105 to 106. It is found that on a
discharge basis, for the same head loss in a given length, with the
diameter ratio of 5.8 the flow capacity of the pipe line is decreased
12.7% in the concentric situation but only 4.57,, with full eccentricity.
The latter decrease is not greatly different from the 3% reduction in
area due to the inserted smaller pipe. An analysis is included showing
that for the simple insert at full eccentricity the near-full-flow
capacity of a sewer is little affected. The effects of hangers such as
might be employed to support inserts in sewers is found to have an
appreciable effect on the flow capacity of a full-flowing sewer. (63 pp.)
"ANALYTICAL STUDIES OF TURBULENT FRICTION IN ANNULAR CONDUITS,
EFFECT OF INSERTED PIPE ON FLOW CAPACITY OF SEWERS" (TASK 12)
by Alan R. Nelson and J.M. Robertson
Department of Theoretical and Applied Mechanics
Report No. 321
University of Illinois, Urbana, 111.
November, 1968
(Reference 26, Section XVI, "Bibliography")
An analytical solution for fully developed turbulent flow in an
annular conduit is presented, performed with the aid of a digital
computer. To account for the observed divergence of the velocity traverses
of recent investigations with increasing ratio of radius of inside wall
of outside pipe to radius of outside of inserted pipe, a modified wall
law-core law velocity formulation is adopted. The effect of variations
in radius ratio, eccentricity, and roughness upon the location of maximum
velocity, velocity distribution, and friction are discussed. The radius
of maximum velocity is found to be nearer the wall of the inserted pipe
for smooth annuli and is independent of Reynolds number for values greater
than 40,000. Friction decreases with increased eccentricity but is
considerably less affected by changes in the radius ratio. Variations in
wall roughness cause the greatest alteration in the flow occurrences in
annular conduits. Using the modified two-law velocity distribution, a
new prediction of friction is given for the limiting case of radius ratio
approaching unity. Even though equivalent magnitudes were not achieved
for experimental and analytical results, the trends are similar. (81 pp.)
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BIBLIOGRAPHIC: American Society of Civil Engineers. Combined Sewer Separation
Using Pressure Sewers. FWPCA Publication No. ORD-4, 1969.
ABSTRACT: The feasibility and development of a new method for separating
wastewater from combined sewer systems are reported on the basis of informa-
tion drawn from 25 project reports and technical memoranda. The general
concept Involves pumping ground wastewater from buildings through pressure
tubing connected to street pressure conduits discharging in turn into inter-
ceptors. The tubing and conduits would be contained within existing combined
sewers. The feasibility of storing, grinding and pumping sewage from Indi-
vidual residences has been established; and standard comminuting and pumping
equipment will be satisfactory for serving larger buildings. Acceptable
types of pressure tubing are available that can be pushed and pulled through
existing building drains and sewers. Pressure conduits can be suspended
Inside combined sewers that can be entered by workman. There are combined
sewer areas that can be separated most effectively by a version of the method
Investigated, but generally pressure systems will cost more than new gravity
systems. New capabilities developed appear to be of potentially greater use
for applications other than separation, such as new construction including
utility corridors, and introduce viable alternatives for design of wastewater
sewerage,
I
r -
ACCESSION NO:
KEY WORDS:
Pressure Sewers
Sewer Design
Pumping Sewage
Grinding Sewage
Combined Sewers
Sewer Separation
Sewer-Hithin-Sewer
BIBLIOGRAPHIC: American Society of Civil Engineers. Combined Sewer Separation
Using Pressure Sewers. FWPCA Publication No. ORD-4, 1969.
ABSTRACT: The feasibility and development of
ACCESSION NO:
KEY WORDS:
Pressure Sewers
Sewer Design
Pumping Sewage
Grinding Sewage
Combined Sewers
Sewer Separation
Sewer-Within-Sewer
BIBLIOGRAPHIC: American Society of Civil Engineers. Combined Sewer Separation
Using Pressure Sewers. FWPCA Publication No. ORD-4, 1969.
ABSTRACT: The feasibility and development of a new method for separating
wastewater from combined sewer systems are reported on the basis of Informa-
tion drawn from 25 project reports and technical memoranda. The general
concept involves pumping ground wastewater from buildings through pressure
tubing connected to street pressure conduits discharging In turn into inter-
ceptors. The tubing and conduits would be contained within existing combined
sewers. The feasibility of storing, grinding and pumping sewage from Indi-
vidual residences has been established; and standard comminuting and pumping
equipment will be satisfactory for serving larger buildings. Acceptable
types of pressure tubing are available that can be pushed and pulled through
existing building drains and sewers. Pressure conduits can be suspended
Inside combined sewers that can be entered by workmen. There are combined
sewer areas that can be separated most effectively by a version of the method
investigated, but generally pressure systems will cost more than new gravity
systems. New capabilities developed appear to be of potentially greater use
for applications other than separation, such as new construction includina
utility corridors, and introduce viable alternatives for design bf wastewater
L.
ACCESSION NO:
KEY WORDS:
Pressure Sewers
Sewer Design
Pumping Sewage
Grinding Sewage
Combined Sewers
Sewer Separation
Sewer-Within-Sewer
. J
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