WATER POLLUTION CONTROL RESEARCH SERIES • 11022 DMU 07J70
         Combined Sewer
  Regulator Overflow  Facilities
DEPARTMENT OF THE INTERIOR • FEDERAL WATER QUALITY ADMINISTRATION

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1 .iijiii''. hid. i; '.',„['•!!. .:,,'!, i'l'V  • , "' |i';!iWater Pollution Control Research Reports  will  be distributed to requesters as
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                               supplies permit. Requests should  be sent to  the Project Reports System, Office of
                             ;J  Research and Development, Department of the Interior, Federal Water Quality
                               Administration, Washington, D. C. 20242.
                                 ''Previously issued reports on  the Storm  & Combined Sewer Pollution Control
                               Program:
                               11020
12/67
11030
11020
11020
11020
11020
11020
11020
11 Q20
11023
H02b
11020
11023
11020
11020
11024
11034
11024
1102-1
'llOOC)
DNS
EXV
FKI
DIH
DBS
DIG
EKO
-
FDD
-
DGZ
DPI
DWF
FKL
FKN
DMS
—
01/69
07/69
01/70
06/69
06/69
08/69
10/69
10/69
03/70
06/69
10/69
08/69
03/70
12/69
06/70
07/70
1 1/6.9
05/70
01/70
Problems of Combined Sewer Facilities and Overflows,
1967.(WP-20-11)
Water Pollution Aspects of Urban Runoff. (WP-20-15)
Strainer/Filter Treatment of Combined Sewer Overflows.
(WP-20-16)  	  '	
Dissolved Air Flotation Treatment of Combined Sewer
Overflows. (WP-20-17)
Improved Sealants for Infiltration Control. (WP-20-18)
Selected Urban Storm Water Runoff Abstracts.
(WP-20-21)
Polymers for Sewer Flow Control. (WP-20-22)
Combined Sewer Separation Using Pressure Sewers.
(ORD-4)
Crazed Resin Filtration of Combined Sewer Overflows.
(DAST-4)
Rotary Vibratory Fine Screening of Combined Sewer
Overflows. (DAST-5)
Sewer Infiltration Reduction by Zone Pumping.
(DAST-9)
Design of a Combined Sewer Fluidic Regulator.
(DAST-13)
Rapid-Flow Filter for Sewer Overflows.
Combined Sewer Overflow Seminar Papers.
Control of Pollution by Underwater Storage.
Combined Sewer Overflow Abatement Technology.
Storm Water Pollution.
Storm Pollution & Abatement from Combined Sewer
Overflows-Bucyrus, Ohio. (DAST-32)
Engineering Investigation of Sewer Overflow
prpt>leni—Rpanoke, Virginia.
Storm & Combined Sewer Demonstration Projects-
January 1970.

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COMBINED SEWER REGULATOR OVERFLOW FACILITIES

                      REPORT
                       by the

             American Public Works Association
                      for the

       FEDERAL WATER QUALITY ADMINISTRATION

            DEPARTMENT OF THE INTERIOR

                       and

   TWENTY-FIVE LOCAL GOVERNMENTAL JURISDICTIONS
               Program No, 11022 DMU a, 3(

                  Contract 14-12-456  :

                     July, 1970
   For sale by the Superintendent of Documents, U. S. Government Printing Office
              Washington, D.C., 20402 - Price $1.50
                 EERU-TIX
RECEIVED
 APR   51989
 EERU-TiX

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          SPONSORING LOCAL AGENCIES
                   City of Akron, Ohio
                City of Alexandria, Virginia
                 City of Atlanta, Georgia
               City of Boston, Massachusetts
   Metropolitan District Commission, Boston, Massachusetts
            City of Charlottetown, PEI, Canada
   Metropolitan Sanitary District of Greater Chicago, Illinois
                  Gity of Cleveland, Ohio
                  City of Eugene, Oregon
                City of Fort Wayne, Indiana
               City of Kansas City, Missouri
                 City of Middletown, Ohio
             City of Montreal, Quebec, Canada
                  City of Muncie, Indiana
 Metropolitan Government of Nashville and Davidson County
                 City of Omaha, Nebraska
               City of Owensboro, Kentucky
Allegheny County Sanitary Authority, Pittsburgh, Pennsylvania
                City of Richmond, Virginia
       Metropolitan St. Louis Sewer District, Missouri
                City of St. Paul, Minnesota
      Municipality of Metropolitan Seattle, Washington
                City of Syracuse, New York
             City of Toronto, Ontario, Canada
             Washington, District of Columbia
                 FWQA Review Notice

   This report has been reviewed by the Federal Water
   Quality Administration and approved for publication.
   Approval does  not  signify  that the  contents
   necessarily reflect the  views and policies  of the
   Federal Water Quality Administration.
                             111

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\
i.
V
\
                                                     ABSTRACT

                                       Current  design,  operation  and  maintenance
                                     practices  used by local jurisdictions in the United
                                     States  and  Canada  were  determined  by  personal
                                     interviews and compiled  in  this report. Particular
                                     attention was given  to  the performance of various
                                     types of regulators, the use of tide gates, new designs,
                                     European  practices  and  the systems  concept  of
                                     combined  sewer  regulation.  Thirty-seven drawings
                                     and  photographs   of  regulators are included.
                                     Seventeen recommendations are made, the adoption
                                     of which would upgrade regulator facilities and tend
                                     to reduce receiving water pollution from combined
                                     sewer overflows.
                                      This  report  and  accompanying manual  were
                                     submitted in  fulfillment  of Contract  14-12-456
                                     between the  Federal Water Quality Administration,
                                     twenty-five  local jurisdictions and the American
                                     Public Works Research Foundation.
                                                          111

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          APWA RESEARCH FOUNDATION
                      Project 68-la


                STEERING COMMITTEE

                Peter F. Mattel, Chairman
      Arthur D. Caster           Walter A. Hurtley
      William Dobbins           Ed Susong
      George T. Gray          •••  Harvey Wilke
      Carmen Guarino'         >
            Richard H. Sullivan, Project Director
           J. Peter Coombes; Principal Investigator

                SPECIAL CONSULTANTS
                    James J. Anderson
                   Dr. Morris M. Cohh
                   Morris H. Klegerman
                    Ray E. Lawrence
                    M. D. R. Riddell
APWA Staff*
R.D. Bugher
R.Bf.Ball
Leo Weaver
Lois V. Borton
Marilyn L. Boyd
Kathryn D. Priestley
Patricia Twist
Violet Perlman
Katherine Manolis
Ellen M. Pillar
Maxine Coop
Mary J.Webb
Sheila J. Chasseur
Oleta Ward
*Personnel utilized on a full-time or part-time basis on this project

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        AMERICAN PUBLIC WORKS ASSOCIATION
                        Board of Directors

                      Ross L. Clark, President
                 Myron D. Calkins, Vice President
              John A. Lambie, Immediate Past President
Timothy J. O'Leary
Frederick R. Rundle
Donald S. Frady   .
William W. Fagan
Herbert Goetsch
Leo L. Johnson
Erwin F. Hensch
Lyall A. Pardee
Gilbert M. Schuster
                Robert D. Bugher, Executive Director
                APWA RESEARCH FOUNDATION
                        Board of Trustees
                    Samuel S. Baxter, Chairman
                    W. D. Hurst, Vice Chairman
     Fred J. Benson
     John F. Collins
     James V. Fitzpatrick
                         Milton Pikarsky
               Robert D. Bugher, Secretary-Treasurer
                Richard H. Sullivan, General Manager
                    William S. Foster
                    D. Grant Mickle
                    Milton Offner

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                                    CONTENTS
                                                                                Page
           Abstract	i
Section 1   Findings and Recommendations of the Study	1
Section 2   Definitions of the Overflow Problem
           As a Source of Pollution	5
Sections   Scope of the Study Project: Plan of Action	9
Section 4   Types and Applicability of Regulators
           In Use in Combined Sewer Systems    	23
Section 5   Performance of Regulator Facilities in Service	51
Section 6   Maintenance of Regulators	71
Section 7   Tide Gates: Applications, Design
           and Performance	87
Section 8   European Regulator Practices	-95
Section 9   Role of Products, Processes  and Future Regulator
           Progress in Improved Control of Overflows	103
Section 10  The "Systems Concept" of Combined Sewer
           Regulation: An Overview	109
Section 11  Summation of the State of the Art of
           Combined Sewer Management   .  .	121
Section 12  Acknowledgements	 123
Section 13  Glossary	125
Section 14  Appendices   	127
   Appendix 1  Report of the Subcommittee on Most Effective Materials
               to Meet Specific Regulator Conditions and Functions   	127
   Appendix 2  Report of Subcommittee on Sewer Regulation Systems    	129
   Appendix 3  Report of the Subcommittee on the Systems Concept of
               Combined Sewer System Regulation and Control	133
   Appendix 4  Report on Diversion Screening	137
                                      vn

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                                     TABLES
                                                                                Page
  1.   Number of Regulators Actually Surveyed in
      Each Jurisdiction and Relationship to
      Jurisdictions Interviewed in 1967  ...........	11
  2.   Supplementary Survey, Operation and
      Maintenance Evaluation:
        2 (a) Orifices	  14
        2(b) Weirs   ..-...'	,	  15
        2 (c) Manually Operated Gates ->	16
        2 (d) Float-Operated Gates	  16
        2 (e) Tipping Gates	•,	17
        2 (f) Cylinder Gates	17
  3.   Opinion Survey on Existence of First Flush Phenomenon	  18
  4.   Are Solids Deposited During Dry-Weather Flow, Which
      Are Flushed Out During Storm, Producing Overflows
      of Greater Pollution Strength?	19
  5.   Are Solids Flushed Out of Combined Sewer Systems
      During early Part of Storm or Continuously Over
      Long Period of Storm Flows?    	19
  6.   Does Solid Material Settle Out During Dry-Weather
      Flow Periods and Debris From Wet-Weather Flows
      Cause Blockages at Regulator Chambers?   	21
  7.   1964 Cost of Regulator, Structure and
      Tide Gates-New York City   	26
  8.   Locations of Regulators on Systems	'	52
  9.   Relationship Between Precipitation Events
      and Numbers of Overflows for Six-Month
      Period—Allegheny County Sanitary Authority   	53
10.   Evaluation of Performance and Operation of
      Regulators by Types, as Reported by Surveyed
      Jurisdiction Personnel   	*	55
11.   Relationship Between Types of Regulators and
      Annual Precipitation	56
12.   Relationship Between Types of Regulators and
      Maximum Rainfall	57
13.   Summary of Regulator Function
      Experiences, by Type	53
14.   Performance and Operation of Orifice Regulator   	64
                                        IX

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Tables (Continued)
Page
15.   Performance and Operation of Leaping Weirs	66
16.   Performance and Operation of Side-Spill Weirs   	66
17.   Performance and Operation of Float-Operated Gates	67
18.,  Performance and Operation of Manually Operated Gates	67
19.   Performance and Operation of Siphons   	69
20.   Performance and Operation of Cylinder-Operated Gates   	69
21.   Performance and Operation of Tipping Gates	70
22.   Performance and Operation of Motor-Operated Gates   	70
23.   Performance and Operation of Cylindrical Gates    	70
24.   Frequency of Regulator Maintenance-Inspection—By Type	72
25.   Summary of Annual Unit Maintenance Costs—By Type    	72
26.   Allowable Working Stresses of Timber-	89
27.   Field Survey Findings on Tide Gate Practices	92
28.   Technical Catalogs and Bulletins Relating to
      Products and Processes of Primary and Secondary
      Applicability to the Regulation and Control of
      Overflows from Combined  Sewer Systems	104
29.   Number of Measurement and Control Functions—
      Minneapolis-St. Paul Sanitary District	114

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FIGURES
1.
2.

3.
4.
5.
6.
7.
8.
9.
10.

11.

12.
13.
14.

15.
16.

17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
Rainfall-Overflow Characteristics 	 	
Typical Interception System— The Metropolitan
Corporation of Greater Winnipeg 	 	 	
Orifice with Perpendicular Weir 	
Typical Manually Operated Gate Regulator— Philadelphia . .
Orifice with Manually Operated Shear Gate 	
Side-Overflow Weir for Small Overflow 	 	
Siphon Overflow— Omaha 	 	
Isometric View— Float Controlled Sewer Regulator 	
View of Float Operated Chamber 	
Tipping Gate— Used by Allegheny County
Sanitary Authority 	
Photograph of Three Tipping Gates— Allegheny
County Sanitary Authority 	
Cylindrical Gate 	
Motor-Operated Tainter Gate 	
Motor-Operated Gate— Municipality of
Metropolitan Seattle 	
Cylinder Operated Gate Regulator— Philadelphia 	
Schematic Arrangement— Fluidic Interceptor
Sewer Flow Control 	
External Self-Priming Siphon 	
Clogging of Orifice 	
Overflow Screens 	
Derrick Barge and Boat 	
Loaded Derrick Barge 	
Swamp Buggy 	
Hinged-Type Tide Gate 	 	 .
Timber-Type Tide Gate 	
Sluice-Type Tide Gate 	
Tandem Tide Gate Installation 	
Storm Overflow in the Form of a Side-Spill Weir . . .
Possible Application Stilling Pond Regulator 	
Vortex Regulator 	
Spiral Flow (Helical) Regulator 	
	 20

	 21
	 25
	 30
	 31
	 32
	 34
	 35
	 36

	 39

	 40
	 41
	 42

	 44
	 48

	 59
	 62
	 73
	 74
	 78
	 79
	 79
	 87
	 88
	 90
	 91
	 96
	 99
	 100
	 101
   XI

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Figures (Continued)

31.   Mechanical Screens    	
32.   Artist's Drawing, Inflatable Control Gate System   .  .
33.   Upstream View of Inflatable Fabric Dam in Use    .  .
34.   Typical Level Cell Installation in Sewer ,
      Manhole—Detroit   	
35.   Flushing Installation	
36.   Storm Sewer Interceptor Screen—Reciprocating Rack
37.   Storm Sewer Interceptor Screen-Bar Rack   . .  .  .
38.   Storm Sewer Interceptor Screen-Curved Bar Screen
 Page

. 102
. 115
. 116

. 118
. 119
. 137
. 138
. 139
                                       xn

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                    FOREWORD

    The  report which follows gives the  result  of  an
extensive  study  conducted by   the  APWA  Research
Foundation concerning the design, operation, maintenance,
and  application of combined sewer  overflow regulators.
Publication  is in  two  parts,   this  report  and  the
accompanying manual of practice.
    The American Public Works Association because of its
close association with operating  officials  and its  extensive
work in the field of combined sewers and of pollution of
urban storm waters  has responded to the needs of local
public agencies  for  a source of information concerning
combined sewer overflow regulators.  We wish to express
our  appreciation to the 25 local agencies and the Federal
Water Quality  Administration for  jointly  financing  this
project.
    The Association is quite aware  that the solution of our
combined sewer overflow problem is  not the only  step in
the control of pollution of our receiving waters. We are very
much aware, however, that as other sources of pollution are
removed through existing programs, that combined sewer
overflows and  related  sources of  pollution will remain,
unless local agencies have done adequate  planning to treat
or prevent such pollution. The overflow regulator is one of
the keys to minimizing pollution. It is not the only means
and  this  is recognized.  However, it  is  apparent that
treatment or control facilities cannot function effectively
without adequate and effective regulation.
    The findings and recommendations of this report point
to the need for the development of devices which will allow
control of both the quantity  and quality  of the overflows.
As regulators are rebuilt to effect control and incorporated
into overall systems, there will be  many  opportunities for
upgrading regulators. We hope that this report and  manual
of practice  will  be helpful to those who must design  and
operate combined sewer systems.

                            Samuel  S. Baxter, Chairman
                            APWA Research Foundation
                           xin

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                                              SECTION 1
                          FINDINGS AND RECOMMENDATIONS OF THE STUDY
    An in-depth investigation  of combined  sewer
regulator practices—in terms of design, application of
types of  devices,  performance,  and operation and
maintenance experiences has been carried out by the
American Public Works Association in the  United
States  and Canada and in selected foreign countries.
The study was sponsored by 25 local agencies and the
Federal Water Quality Administration, Department of
the Interior.
    The  studies brought to light information upon
which  to  base  recommendations  on  the  more
effective use and management of existing regulator
faculties for the  purpose of minimizing overflow
quantities  and maximizing the  quality  of wastes
discharged to receiving waters.
    The  findings and recommendations concern the
regulator facilities and not the entire combined sewer
system. A report  entitled "Problems  of  Combined
Sewer  Facilities and Overflows—1967," prepared by
the American Public Works Association, highlighted
many  of the overall problems  of combined sewer
systems. Among the 14 findings were included such
items as insufficient  sewer capacity, local flooding,
inadequate  manpower  as well  as  a  finding that
regulator  facilities should  be improved and  better
maintained. Deficiencies in the sewer system may be
such that improvement of the regulator facility alone
will not significantly reduce pollution. However, few
systems  will  function  effectively with  minimum
pollution impact, if the regulator facilities have not
been properly chosen and adequately maintained.
    The findings and major recommendations of the
study include,  but are not limited to, the  following:
     1. A proliferation of overflow points has led to
the frequent use of insensitive regulator devices. This
has been necessary in many cases, because of small
flows  handled  by  each  station.  It  has  been
economically  infeasible  to apply  expensive and
sophisticated facilities in small  regulator  structures
which handle  flows  of 2 cfs or  less. These multiple
retaliations are subject to infrequent maintenance
iervice; are equipped with insensitive static devices;
ind  experience frequent malfunctions  and resultant
 mnecessary wet-weather  overflows and undetected
 Iry-weather discharges.  Consolidation of these small
 egulator-overfiow locations into fewer larger stations
 rould make it feasible to provide more effective
 ontrol facilities and perhaps eliminate a  significant
percentage of the present deterioration of water and
land resources.
    Efforts should be made by local jurisdictions to
consolidate  minor  overflow  points  into  fewer
locations, in which the installation and maintenance
of sophisticated regulator devices and controls will be
economically and physically justified.
     2. Common practice in North America has been
to  emphasize  the  quantity-control  function  of
regulators. Little consideration has been given to the
importance  of controlling  the quality of  overflow
wastes simultaneously with quantity regulation. The
new definition of regulator functions propounded in
this  project  emphasizes the  control  of both the
quantity and  quality  of  overflow  wastes  from
combined sewer systems.
    Regulators and their appurtenant facilities should
be  recognized  as  devices  which  have  the  dual
responsibility  of  controlling  both  quantity and
quality of overflows to  receiving  waters,  in the
interest of more effective pollution control.
    Further research  should be  sponsored by the
FWQA to determine  the ability  of new devices to
induce separation  and interception of concentrated
pollutional solids and  liquors, and the decantation of
dilute  storm water—sewage  admixtures to  receiving
waters; to determine  practical  applications  of such
devices and systems; to demonstrate their potentiality
by  means  of  mathematical modelling;  and  to
determine their cost-benefit relationships.
     3. Combined  sewer regulation has been based
on the principle of each-regulator-for-itself. There has
been' little effort to tie each regulator into a complete
system. Management of the entire sewer system as a
total  network could  result  in  the  reduction  of
discharges of storm flows to receiving waters.
    "Total systems"  management of sewer  system
regulator-overflow  facilities should  be  instituted
wherever this procedure can be shown to be feasible
and  economical. 'This  will  involve the  use  of
dynamic-type regulator devices and the application of
instrumentation  and  automatic-automation control
methods which will be expedited by a reduction in
the number of overflow points.
     4. In current practice, overflows occur at points
of  surcharge in collector-interceptor sewers.  Other
parts of the same sewer system may be under-loaded
because  of variations  in precipitation and runoff in

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 various parts of a community and its drainage area.
 The  full use  of  the transportation and  retention
 capacity of such a total system is not utilized by this
 practice.  Overflows which could be  prevented
 continue to occur.
     Dynamic-type regulators should be used wherever
 possible  and feasible  for "traffic  control"  of
 combined sewer flows. This could shunt surcharges of
 portions of such  a system into sections of sewers
 which  are  not  simultaneously  so  affected.  This
 approach could be  enhanced by the monitoring of
 precipitation and  sewer  flows through an adequate
 network of stations, in communication with a central
 control point from whence flow routing decisions can
 emanate.
      5.  The choice and application of  types  of
 regulators in many  cases has been  dictated by the
 desire to minimize the first cost of installation and
 the  effort of maintenance work. This has led to the
 use  of static  or insensitive  devices. Dynamic-type
 regulators may be  more costly to build and maintain,
 however they may  reduce pollution by reacting to
 sewer system hydraulic needs.
     The type of regulator used should be determined
 on  the basis  of  its performance  and  potential
 reduction in overflow polhitional effects.
      6. Many  dynamic-type regulators  have  been
 removed, or have been made inoperative, to overcome
 the  frequency  and cost  of  maintenance and repair
 work. These modifications  have reduced  the  true
 regulating function of these installations.
     Maintenance  schedules and  budgetary
 appropriations should be planned on the basis of the
 specific needs of static,  dynamic and instrumented
 units in service. Each type of regulator should be
 given the attention it requires to achieve maximum
 performance.
     7. Inaccessible regulator stations and chambers
 which do not provide adequate space for maintenance
 and  repair  operations  tend,  to  discourage  the
 frequency  and  effectiveness  of  inspections  and
 attention.
    Regulator  facilities should  be  situated in
 accessible  locations,   provided  with  safe  and
 dependable  access  facilities, be free  of other safety
 hazards, have  adequate  space  for  necessary
 maintenance work and, when possible, be accessible
 from locations other than  the street  or  highway
 right-of-way.
     8. The proper  functioning  of overflow control
 devices depends, in great measure, on the capabilities
 of sewer system orews and the equipment and tools
with which  they are supplied. On-the-job training is
 necessary  to  keep maintenance personnel aware of
 the importance of their work and its relation to the
 water pollution contr'ol effort.
     Maintenance crews should be adequately staffed
 and  crews should be  provided  with all  necessary
 service equipment and tools for their work and for
 their  protection.  In-service training  should  be
 provided  and  preventive  maintenance  schedules
 should be established. Records of maintenance work
 must  be accurate and complete hi order to assess
 properly the effectiveness of regulator operations and
 to allocate budget costs for each specific maintenance
 and operation procedure.
      9.  Regulator  devices and  appurtenant
 equipment  and  control facilities  are exposed  to
 extremely  deleterious  atmospheric  and  fluid
 conditions in  combined sewer installations. Corrosion
 and wear  can shorten the  economic life of such
 equipment  and facilities and adversely affect their
 efficiency of operation.
     Specifications must require the use of the most
 serviceable  corrosion-resistant and  moisture and
 explosion-proof  materials hi  the  fabrication and
 installation of regulator devices and control facilities.
 The number  of  movable  parts and  appurtenances
 should be reduced as much as possible, commensurate
 with efforts  to  provide greater  sophistication  of
 regulator facilities.
     10.  Tide  gates, or backwater  gates, are often
 located at locations which are remotely situated from
 regulator chambers.  These  locations tend  to be
 inaccessible and inconvenient for maintenance crews
 while  attending regulator devices.  Malfunctions and
 failures  may  result,  permitting the  entry of tide
 waters or high river stages into regulator chambers.
    Where possible,  tide gates  should  be located hi
 adequate chambers. In cases where system control of
 regulator-overflow  networks  is  provided  by
 automatic-automated  means, the  proximity of tide
 gates with regulator chambers will facilitate the tie-in
 of backwater control with overflow control.
    11. State  and provincial water pollution control
 agencies have  maintained very  limited control over
 the design,   installation  and  performance  of
 regulator-overflow  devices. The  quality  of the
 receiving  waters .into  which  combined  sewers
 overflow is generally the responsibility of the state.
    State and provincial  water  pollution control
agencies should increase  their regulatory control of
this  source  of  pollution and  provide  standard
requirements and  the engineering personnel necessary
for enforcing the control of overflows from combined
sewer systems. Further, such agencies must recognize

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the fact  that existing combined sewer systems must
be upgraded if pollution levels are to be reduced.
    12. This  research  study,  for  the first  time,
established a technical liaison between manufacturers
in the  regulator field, and governmental officials and
designers  who  utilize these manufacturing services.
This  relationship  can  open  up  new  avenues of
regulator  research  and development, and induce
better  application of existing facilities.
    This type of producer-consumer relations should
be continued as a workable means of advancing the
state of the art of combined sewer management and
control.  The FWQA  should consider appointing an
advisory  committee  consisting  of  public  officials,
consulting  engineers,  and   manufacturing
representatives to  aid  in  developing  workable
guidelines and criteria in this field.
    13. A Manual of Practice has been developed on
the design, operation and maintenance of combined
sewer  overflow regulator and tide gate facilities, as a
part of this study.
    Federal, state, and local agencies, and consulting
engineers should be encouraged to adopt the Manual
of Practice  as  a technical guide  for  the  improved
application, design,  operation  and  maintenance of
regulator and tide gate facilities.
    14. Clogging is  the  most  prevalent  cause of
regulator  malfunctions.  This  type  of difficulty  is
particularly experienced in horizontal orifices or drop
inlets,  where  protective  gratings  tend  to clog so
rapidly  that  they  may  require   almost   constant
attention to prevent excessive wet-weather and even
dry-weather overflows of volumes which "jump over"
plugged entries to interceptor lines.
    Efforts should  be made to design regulators to
minimize  clogging  and  consequent  pollutional
overflows. Where clogging is inevitable, maintenance
schedules should be adapted to correct this condition
as expeditiously as possible.
     15.  Few  local jurisdictions have established
programs to determine the  frequency and extent of
overflow  events.  Such  information,  however,  is
necessary  in  the  design  of  improved  facilities.
Detection  of dry-weather overflows is also possible
with monitoring.
     As a design tool, pollution control measure, and
the  initial  step in developing a controlled system of
regulators, a monitoring system to  determine the
occurrence,  time and volume of  overflows  is
desirable.
     16. The supplementary survey  carried  out in
European  countries disclosed the use of regulator
stations  and  devices  which  tend  to  reduce the
concentration  of  wastes  discharged  to  receiving
waters. These included a demonstration installation
of a vortex device  which has  the ability to separate
waterborne pollutants from the conveyed fluid flows
and, thereby, to enable the diversion of heavier or
more concentrated liquors to interceptor systems and
treatment  work and to  spill relatively more dilute
waste waters into receiving watercourses. Laboratory
studies  have  indicated  that  similar  separable
solids-liquid interface phenomena may be achieved by
inducing  secondary motions   or helical  hydraulic
patterns  by means of structural  configurations  along
the line of flow in the  sewer conduits themselves. In
European countries, devices such as screens, baffles or
scumboards are used to  improve the quality of the
overflows.
    Adaptation of such devices to American practice
could  serve to reduce the pollutional  character of
overflow  wastes and  improve  the  appearance  of
receiving waters and waterways. Their applicability to
the regulation and control of overflow quality in the
United States and Canada should be determined by
appropriate research procedures.

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                                              SECTION!

                DEFINITION OF THE OVERFLOW PROBLEM AS A SOURCE OF POLLUTION
    Combined sewer systems,  by deliberate design
 and  construction,  are  intended  to  overflow
 periodically.  Overflows relieve  severe  and  often
 dangerous  overloading  of  local collection  lines,
 interceptors,  and sewage  pumping  and  treatment
 works.  The discharge of such overflows into nearby
 receiving waters creates pollution in receiving waters.
 Such  pollution  is  of growing concern  to  water
 pollution control authorities.
    The importance of this source of pollution was
 brought to  light in 1967 in a report on a study of
 "Problems  of  Combined Sewer Facilities and
 Overflows,"  hereafter  referred  to  as  the  1967
 investigation,  conducted by the  American  Public
 Works Association and co-sponsored by the Federal
 Water Quality Administration, Department of the
 Interior. The current investigation has taken the form
 of "second generation," in-depth  research into the
 design, application, performance and maintenance of
 regulator devices which are intended to  control
 combined sewer overflows.  Its practical goal has been
 to indicate  changes in practices which will improve
 regulator performance and, thereby, minimize or even
 eliminate such overflows and their pollutional effects.
 Federal, state and  local  officials  and engineering
 authorities are exploring the physical and economic
 feasibility  of various  solutions for the  combined
 sewer overflow problem. Among such solutions is the
 improvement and upgrading of regulator facilities and
 practices. Such action should minimize the frequency
.and  duration  of overflow incidents which  occur
 during both wet and dry weather.
    If this  solution can be achieved, hard-pressed
 communities could reduce  pollution from combined
 sewer systems more rapidly and more economically
 than  would otherwise be possible by procedures such
 as sewer  separation  or overflow treatment and
 holding facilities. The application of new  and more
 sophisticated regulator hardware and methods, such
 as the "systems  concept" of  combined  sewer
 management described later in this report, holds out
 hope that more effective overflow control is feasible,
 both with  regard to the  volume of waste,waters
 spilled and  to the pollutional concentration of these
 discharges.
 Extent of the Regulator Problem:
 Findings of the 1967 Investigation
    Achievement of the goal of improving regulator
 facilities  and  practices will not  be  simple  or
inexpensive. The 1967 national survey and inventory
disclosed the vast scope  of the  overflow problem:
1,329  governmental  jurisdictions utilize  combined
sewers and approximately  36 million  persons  are
served by such facilities.
    The major  findings of  the 1967 inventory and
investigation  emphasized  the  extent  of  the
overflow-regulator problem  and  disclosed the need
for, and means of, providing  actions.
    1. A  total of 10,025  regulators at  combined
    sewer overflow  structures and  other locations
    were used by the 641 jurisdictions  surveyed, to
    serve 34  million  people. The most commonly
    used  types  were perpendicular weirs, side weirs,
    and other "static" devices non-responsive to flow
    conditions.  The  least   commonly used  were
    "dynamic"  types, that are  responsive to flow
    conditions,  such  as  hydraulic  cylinders,
    float-operated gates, and tipping gates.
    2. A  total of  14,212 overflow  points were
    reported; all were not  equipped with regulator
    devices.
    3. Dry  weather overflows from  combined
    sewers  were reported by 96 jurisdictions. The
    cause  of  such  overflows   was described  by
    one-half of  those  reporting  as  troublesome
    regulators, and  the other  half  reported
    insufficient  sewer capacities.
    4. Many regulator devices were reported to be
    inadequate,  unreliable  or insensitive  to flow
    variations; they were inadequately inspected and
    maintained; and they produced unnecessary and
    extended overflows.  Better  regulator  devices
    coupled with  more  effective  maintenance
    practices, offered  a  means  of reducing" the
    overflow problem.
    5. Better guidelines for the  choice of facilities
    to meet specific  flow  control  conditions and
    improved devices  for such applications,  would
   .pay dividends in  the  form of reduced overflow
    pollution.
    6.  Improved  maintenance  and  management
    practices  would  result  in better operation of
    existing regulator installations.
    7. The numerous  instances of  dry weather
    overflows,   occurring  because of  troublesome
    regulators  and  insufficient sewer  capacity,
    constituted  a continuing source of  pollution.
    Since such  overflows  were seldom monitored, it

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    was assumed that many more occurred than were
    actually reported.
    8.  In one  representative community, overflow
    of a combined sewer system into a watershed was
    estimated to have lowered the potential value of
    abutting land more  than $5 million, representing
    an annual revenue loss of $70,000 in city taxes.
    These  findings  and  conclusions  led to  the
following significant recommendations:
    "It is recommended that programs  to monitor
combined sewer overflow events be initiated, and that
remedial steps be taken to prevent or  reduce  this'
source of pollution as soon as practical."
    "It is recommended that a  thorough  study be
instituted on regulator facilities, aimed at developing
better application engineering, improved devices and
more effective maintenance practices."
    The latter recommendation emphasized the need
for this in-depth study of regulator practices, relating
to  design,  application,  construction,  control,
operation  and maintenance; and for the development
of guidelines  for improved designs and  procedures.
This  recommendation  was  implemented  by  the
contractual  agreement  between  the  Federal  Water
Quality Administration and  the APWA  Research
Foundation. This report documents the investigations
carried out pursuant to  the terms of this contractual
agreement.
    This current project offers a two-faceted concept
of regulation  and the function of a regulator. This
may be referred to as the "Two Q's" concept—that is,
control of the quantity and the quality  of overflow
waste waters.
Effective Regulator—Overflow Facilities as a Means of
Pollution Control
    As has been stated, a combined sewer system is
basically designed and built to permit a portion of
wet-weather   flow  to  overflow.  Thus,  the
regulator-overflow facility  acts as a safety valve to
protect the interceptor and the treatment works from
overload and surcharge.  It is equally evident that any
spills not actually required  to protect the interceptor
and treatment facility, or to eliminate any hazard of
overloading or flooding of combined sewer systems,
and unnecessary and unjustified loadings of pollution
to receiving waters. Any means which will reduce the
quantity  of  spill  will  automatically   reduce  the
pollutional effect of combined sewer overflows.
    While the volume of flows can be imposed and
controlled  in  and within  sewer systems, to varying
degrees by  present regulator and control devices,
there are few, if any, installations which attempt or
accomplish  quality  improvement of  the  overflow
waste waters. If there were some means for reducing
the concentration  of pollutional constituents of the
sanitary   sewage-storm  water  admixture  at  the
regulator-overflow  structure, the result could be  a
marked improvement in  the  characteristics  of  the
overflow,  and a reduction in pollutional loading on
receiving  waters.  Means  for quality  control  are
discussed later in this report.
    Both  the  1967  investigation and the  current
study demonstrate  that four factors relating to  the
type  and  operation of  regulators  contribute  to
excessive  and  unnecessary pollution  of receiving
waters:
    1.  Regulators  which  permit overflow  during
    dry-weather flow periods, or during periods of
    minimal  runoff resulting   from  minor
    precipitation   events,  before  the volume  of
    sanitary and storm flows reaches a predetermined
    designed wet-weather:dry-weather carrying ratio;
    2.  Regulators  which continue 'to overflow for
    durations  considerably longer than: required  to
    protect the  interceptor  system  or  treatment
    facility;
    3.  Regulator-overflow structures  which' fail to
    remove contaminating constituents in the flow,
    such as coarse  trash and organic solids and grit,
    and to direct  these wastes to  the interceptor
    instead of to overflow points; and
    4.  Tide  gates  or  backwater  control  devices
    which fail to protect interceptors from the inflow
    of receiving waters  into the sewer system, and
    this eventually  produces surcharges which result
    in unnecessary spillage  of combined  flow into
    these receiving waters.
    These  conditions  result  from  improper
application  of types  of regulators  or tide gates at
specific  overflow  points,  malfunctioning  of  the
existing facilities, an'd lack of coordinated preventive
and periodic maintenance of the regulating devices.
    The  importance  of improving  regulator
performance  is proved  by the projected estimated
cost  of  pollution  control from  combined  sewer
sources. The  fact   that  corrective measures  are  so
fiscally  costly  and  physically inconvenient  makes
their  application as practical  solutions unattainable
and unrealistic under present  conditions. The 1967
investigation estimated a cost  of $48 billion for the
separation  of public sewer systems  and necessary
plumbing   and drainage  separation  procedures  in
private structures;  and $15 billion for such alternate
pollution control facilities as retention and treatment
works for handling overflow wastes.
    The- 1967 investigation concluded that improved

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regulator practices would pay dividends in the form
of  reduced  pollution  contributions  at  points  of
overflow at lower costs than the extensive procedures
outlined above. However, this is  only a first step in
controlling pollution from combined sewers.
How Improved Regulator
Practices Can Reduce Pollution
    What,  then, are the available practical solutions
for this  problem,  in  terms  of improvement  of
regulator  practices? The current investigation has
demonstrated that these benefits might be achieved
by:
    1.  Better application of regulators, by  way of
    appropriate choice of types and locations of such
    installations;
    2.  Extensive  use  of  regulators which are
    sensitive  to variations in hydraulic patterns, to
    replace existing ineffective installations;
    3.  Better operation  and maintenance practices
    which will result  in improved  performance of
    existing facilities and  would, in the future, insure
    the  realization  of the  full  potential  of new
    developments  and devices in the regulator field;
    4.  Utilization  of the  "total system concept"
    approach  to  the  integration  of individual
    regulators into  a complete management of the
    total  regulator  problem and of the complete
    combined sewer  collection, interception  and
    treatment  system,  rather than, considering each
    individual regulator as an unrelated device;
    5.  The use of instrumentation for the purpose
    of implementing this "total systems" approach,
    by taking  full advantage of the available storage
    capacity of the total  combined sewer system
    upstream of the regulating devices or by means of
    "traffic routing" of wet-weather flow  volumes
    within the system;
    6.  Development  and   application  of new
    regulator devices and techniques, not yet used in
    current combined sewer practices, for controlling
    both the quantity and quality of overflow spills;
    and
    7.  Provision  of  trained  and better-equipped
    personnel  to  administer and maintain regulating
    systems,  backed  up  by  adequate  budgetary
    appropriations for these purposes.
    It  must not be assumed from this evaluation of
the corrective  measures available for reducing the
pollution  impact stemming from better control of
sewer  overflows that these corrective measures are
applicable to all systems. These are merely suggested
guidelines.   A  complete  engineering  study  and
evaluation of the problems and solutions applicable
to each particular combined sewer system is the only
way to assure improved regulator practices at the
lowest possible cost.

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                                              SECTION 3
                           SCOPE OF THE STUDY PROJECT: PLAN OF ACTION
    The problems of regulator design, applicability,
construction,  operation  and maintenance were
ascertained and evaluated by the following research
approaches:
1.  A survey  of  representative  existing regulator
installations, referred to  as the National Survey, for
the  purpose  /of ascertaining  their capabilities  to
perform the function of regulators as  described in
Section 2 of this report;
2. An evaluation of current practices for the purpose
of showing designers, municipal officials and state
water  pollution  control agencies  how to  provide
better  management and utilization  of  existing
facilities, and to replace ineffective or malfunctioning
regulator devices with more efficient equipment;
3.  The   establishment  of  criteria  for improved
regulator  facilities,  followed  by explorations with
manufacturers which could lead to the  development
and  production  of such improved equipment and
systems,  and  to  the  evolution  of  overflow
management methods and techniques not now being
employed in the regulator field; and
4. Application of instrumentation for total systems
control  of  complete  sewer  networks  and  all
regulators, wherever  this type of combined sewer
system  management can  result in more effective
utilization of the storage capacities of sewer systems
by  "traffic routing" procedures and  for  reduced
pollution impacts caused by overflows.
     The  research  project  provided  for  further
investigations  by  a  three-member Consulting
Engineering Panel, leading to:
     "Basic design criteria for regulator  facilities; the
exploration of  design theories and applicability of
regulators; the determination  of the need for new
methods of regulation, and the principles on which
they would  function; all  to  be  incorporated in a
Manual of Practice."
     In order to create a fruitful climate in which an
evaluation of existing regulator facilities could be
achieved, and the development of new techniques and
equipment  could  be stimulated,  discussions  were
instituted  with  a Manufacturers' Advisory Panel on
available  regulator  devices  and  appurtenant
equipment; applicability of such facilities; choice of
materials   to  withstand  deleterious conditions  in
sewers and regulator chambers; new products  and
processes applicable  to  regulator  installations;
improved maintenance procedures; and other phases
of regulator practices. The functioning and findings
of this manufacturers' group are discussed in Section
9 of this report.
Survey of Eighteen Representative
Combined Sewer Systems
    Evaluation of the applicability, performance, and
effectiveness  of maintenance  of  presently installed
regulators  was  accomplished by  detailed  on-site
investigations of eighteen combined sewer systems in
the United States and Canada. These field surveys
were conducted by trained and experienced sanitary
and municipal engineers engaged  in private practice,
public  service  and  universities. This  staff  of
investigators was chosen to utilize the knowledge and
experience of persons indigenous to the particular
regions being investigated. These investigators  were
carefully briefed in the purposes of the study.
    The systems included in the survey were:
     1. Akron, Ohio
     2. Allegheny County Sanitary Authority, Pa.
        (ALCOSAN)
     3. Metropolitan  District Commission,  Mass.
        (MDC)
     4. Metropolitan Sanitary District  of Greater
        Chicago, 111. (MSB)
     5. Metropolitan Sanitary District  of Greater
        Cincinnati, Ohio
     6. Cleveland, Ohio
     7. Detroit  Metropolitan  Water Services, Mich.
     8. District of Columbia
     9. Milwaukee Sewerage Commission, Wis.
    10. Minneapolis-St Paul Sanitary District, Minn.
        (MSSD)
    11. Montreal, Quebec, Canada
    12. New York City, N. Y.
    13. Omaha, Nebr.
    14. Philadelphia, Pa.
    15. San Francisco, Calif.
    16. St. Louis, Mo.
    17. St. Paul, Minn.
    18. Municipality of Metropolitan Seattle, Wash.
    These jurisdictional entities were chosen on the
basis  of data developed in the  1967  investigation,
including such  factors  as population;  geographical
location;  regulator  types;  specific  maintenance
procedures; existence  of special problems such as
discontinuance  of the  use  of  specific  types  of
regulators; application of instrumentation techniques
and use of instrumentation methods to effect total

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 systems  control;  and  the  existence  of  FWQA
 combined sewer  demonstration projects of  various
 types.
     Tide gates, or backwater gates, were included in
 the survey because  they  were deemed to be  part of
 the overall regulation control of flows out of, or into
 combined sewer interceptor systems.
     The  18  surveyed systems provided  a  highly
 representative  cross section of the  regulator facilities
 in  use in the United States and Canada. Investigation
 revealed  that  this  choice  of only 18 jurisdictions
 would  encompass almost 25 percent of  the  total
 regulators  found by  interviews  in  the  641
 jurisdictions  included in the 1967 Inventory. The
 survey  of the  18  jurisdictions covered  15 percent of
 the float-operated gates; 46  percent  of the  tipping
 gates; 16 percent  of the leaping weirs;  19 percent of
 the side-jpill weirs;  29  percent of the fixed orifices;
 87  percent  of  the manually  operated gates; 26
 percent of the horizontal orifices or drop inlets; and
 16  percent of the  other regulator types inventoried in
 1967.
     Table  1,  Number  of  Regulators  Actually
 Surveyed in  Each Jurisdiction and Relationship  to
 Jurisdictions  Interviewed in  1967,  indicates  the
 number of regulators, by type, surveyed in each of
 the jurisdictions and compares these totals  to those
 determined in the  1967 investigation.
     Each of the  18 investigations ascertained  the
 types  of regulators  in  service;  the  number  of
 regulators out  of service or inoperative; dates  the
 regulators were installed; their locations along  the
 interceptor  system, at  the  collector-interceptor
junction, at pumping stations, at treatment  facilities,
 at junctions with  other jurisdiction's systems, or at
 other points.
    The  local  interviews  covered  details of
 construction of regulator devices and reasons for the
 choice of specific  regulators. An effort was  made to
 obtain data on the capital costs of integral parts or
 elements  of regulator  stations; details  on  design
 criteria  relating to wet-weather to  dry-weather flow
 ratios  (WWFrDWF)  for  discharge in interceptor
systems; precipitation records and intensity data; and
overflow connection layouts.
    Operation and  maintenance practices  were
investigated  in  terms  of  types  of  malfunctions;
reasons  for malfunctions; frequency and duration of
overflows; variations in performance;  frequency of
maintenance,  by   regulator  type;  repairs  and
adjustments required, by regulator type; the  makeup
and  numbers of maintenance  crews;  and  the
maintenance tools  and equipment used fw this work,
 by regulator type.
     The investigation provided  the relatively limited
 amount of information available on the utilization of
 automatic  devices,  automation  facilities and
 instrumentation  practices in collection systems,  in
 whole or in part.
     Data  concerning  special  control  methods,
 including automatic-automation  devices and
 instrumentation  facilities, were obtained wherever
 available in the surveyed communities.
     The .correlation between FWQA demonstration
 projects  and  existing regulator practices was
 investigated in  those  systems where such federally
 sponsored  studies were underway.
 ~   In'depth surveys were carried out in 12 of the  18
 jurisdictions. The remaining six were investigated for
 the  purpose  of disclosing specific points  of interest
 including:  Total systems control of entire combined
 sewer systems,  such  as those  being developed  in
 Seattle  and  Minneapolis—St. Paul; use  of special
 structures  housing  tide  gates and  regulators in San
 Francisco;  use of inflatable dams for flow regulation
 purposes  in a  FWQA  demonstration program  in
 Minneapolis-St.  Paul; and the conditions which led
 to the abandonment of certain types of regulators in
 the  Boston  metropolitan area  served  by the
 Metropolitan District Commission.
 Result of Survey of Practices of
 State Water Pollution Control Agencies
    Over and above the field surveys of reprrsentative
jurisdictional  entities,  an  effort was  made   to
 investigate  and evaluate present and future policies
 and practices of state water pollution control agencies
 in regulating the design, construction, operation and
maintenance of overflow facilities. Agencies in the 50
 states and  the 10 Canadian provinces were surveyed.
The survey asked for information on  the following
questions:
    1.  What  are the  existing   practices regarding
    combined sewer overflow regulator facilities?
    2.  What types of regulatory devices are used?
    3.  Have  design criteria  been  established for
    regulator installations?
    4.  Are regular  reports made by state engineers
    concerning the operation, field conditions, and
    maintenance  practices of  regulator devices in
    community sewer systems?
    All but one state responded to the questionnaire;
the results may be summarized as follows:
    1.  In  states where few combined sewer systems
    exist, i.e., where the ratio  of  combined  sewer
    systems to  separate  systems is  less  than 25
    percent, little interest in combined sewers was
                                                  10

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    indicated. No state regulations or legislation were
    mentioned  and  few  records  were  kept.  The
    standard  comment from  state authorities was
    that where combined  sewer systems exist in the
    state they are being systematically separated as
    quickly   and  as  economically  as  possible.
    Twenty-eight states were included in this group.
    Only one indicated an interest in the problem.
    2.  In states where the ratio of combined sewer
    systems to separate sewer systems is between 25
    and 50 percent, the response to the questionnaire
    by state water pollution control authorities was
    evenly divided. One-half of the group recognized
    that combined sewer overflows were a problem.
    They  indicated  that they lacked  legislation,
    manpower, and necessary design criteria to meet
    the need  for state control.  Their comments
    indicated interest in the results  produced by the
    APWA-FWQA  regulator  study;  this  interest
    indicated  that  the problem was  of sufficient
    magnitude to warrant some type of action. The
    other half of these agencies demonstrated only a
    limited concern over the importance of overflows
    in  terms of water pollution problems in their
    states.
    3.   In states where more than  50 percent of the
    sewer systems are  combined, all but one of the
    agencies indicated  concern over the  problem.
    Five states were in this category.
    States that expressed the most specific interest in
the problem were Georgia, Indiana, Massachusetts,
Maine, New Jersey,  New York, Ohio, Pennsylvania
and Wisconsin. Each  recognized the pollution caused
by  combined  sewer  overflows and said it would
welcome guidelines for the application of regulatory
devices. Their answers indicated that states have little
or no legislation upon which to base overflow control
and  regulator  practices.  They lack  information
concerning  regulator  facilities  in service;  proper
applications  and standard practices;  and operating
and  maintenance needs. Most states reported that
they have insufficient personnel to approve or inspect
regulator  installations  and,  consequently, there is
little follow-up of operating conditions and practices
by agency personnel.
    The State of New York reported that its policy
is:  to eliminate  overflows  where  possible and
feasible;  and  to reduce  overflows to  a  practical
minimum.
    Technical  Bulletin No.  20 of the  New York
Department  of Health outlines that  department's
attitude concerning  combined sewer overflows, as
follows:
    (A) Evaluate overflows by surveillance-measuring
        the quantity, the frequency, arid the quality
        of the overflow.
    (B) Measure the effectiveness of existing control
        devices at  overflow locations. These include
        regulatory  devices and tide gates.
    (C) Monitor  overflow  locations,  providing
        instrumented  information  at  central
        locations where possible.
    Special attention  is called  to the fact that the
present State policy is to approve new sanitary sewer
projects only. Old  combined sewers may be replaced
or repaired, but they  should be separated at such
times—if possible—in conformity with master plans
for sewage and drainage services. The bulletin lists the
following  methods  and  procedures to  minimize
combined sewer overflows:
    (A) Utilize maximum  storage capacity  in
        combined  sewers without backflooding.
    (B) Disinfect along the interceptor immediately
        prior to overflow points to reduce bacterial
        loading.
    (C) Eliminate  separate  storm water connections
        to interceptors and collector sewers.
    (D) Separate storm water from sanitary sewage as
        quickly and as economically as possible.
    (E) Locate   and  eliminate  illegal
        cross-connections of local storm sewers.
    (F) Utilize the maximum storage capacity in the
        interceptor in order to reduce shock loading
        on the treatment facilities.
    New York  State was not alone in stressing'the
fact that new combined sewer systems are no longer
permitted. A number of states referred to this policy
in explaining the absence of supervision of regulator
design,  construction  and  performance,  and the
absence of any plans to modify this procedure in the
foreseeable future.  The following states reported that
they  do  not  allow  combined  sewers:  Arkansas,
Florida,  Georgia,  Hawaii, Kentucky,  Mississippi,
Missouri,  Nevada,  Nebraska,  New Mexico,  North
Dakota, Oklahoma, Rhode  Island,  Texas,  Utah,
Virginia, and Wyoming.  The following  states
indicated  that they seldom permit or are reducing the
number  of  combined  sewer systems:  Alaska,
Alabama,  Arizona, Colorado,  Louisiana, Montana,
North  Carolina, New  Jersey, South Carolina,
Tennessee, and Washington.
    Combined sewer systems are prohibited in many
states  and existing systems  are  being phased  out.
Since  overflows are not recognized  as a problem,
however,  little  control  is provided  by  the state
agencies and contact  with the  immediate authority
                                                  12

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utilizing regulator devices is minimal. In states where
combined sewers form a large percent of the total
sewer  installations, the  importance of control of
overflows  by  means  of regulators  is  generally
acknowledged.
Special Survey on Operation
and Maintenance Practices
    Because of  the effect of the  performance of
regulator  devices,  in  terms  of operation  and
maintenance  experiences,  on  pollution  control
conditions, and the influence of the choice of various
types of regulator  devices  for specific  control
functions on operation and maintenance practices, it
was  deemed  advisable to -augment  the  18
jurisdictional surveys by carrying out an investigation
in  a  number  of additional  communities.  The
communities where operation and maintenance data
were  solicited  were chosen  on  the basis of data
obtained during the 1967 investigation.
    The   items  investigated  included:  types  and
frequency of  'regulator malfunctions;  operation
experiences, including abandonment,  modification,
dangerous  or inaccessible  installations,  excessive
corrosion, and other conditions; devices used for the
protection  of regulator equipment; types  and
numbers  of maintenance  experiences,  including
maintenance crews and  equipment;  and cost of
maintenance service. Responses were received from
15 jurisdictions. The results of the survey are shown
in Table  2, Supplementary Survey—Operation and
Maintenance Evaluation.  The data show that static
regulators are being inspected an average of 43 times
per  year  by  three-man  crews.   This compares to
dynamic regulators .which are  inspected an average of
49 times per year by three-man crews.
    The  most common malfunction experienced  is
clogging,  as  reported by 60 percent  of the
respondents.  Operational  problems  relating to
corrosion  of mechanical  components were reported
by  40  percent  of the respondents.  Some  of the
regulators have been abandoned or  require changes.
The survey demonstrated that the principal  reasons
for abandoning or modifying regulator units were the
lack  of  well-organized,  preventive  maintenance
programs,  shortage of funds to carry  out  these
programs, and the age of the regulators which caused
problems, many of which were installed more  than 30
years ago.                   ,
    None  of  the  15  jurisdictions reporting in the
supplementary  survey  had  any experience with
instrumentation, automation or automatic devices.
Special Survey of Overflow
Quality Control Practices
    The project stressed the importance of improving
the quality  of the  combined sewage  discharged to
overflow,  as outlined in the "Two Q" concept in
Section 2  of this report. In order to learn more about
national practice of overflow quality control, a mail
questionnaire  was  sent to  115 jurisdictions using
combined sewer systems, chosen on the basis of data
obtained  in the 1967 investigation. These systems
reported the use of some form of screens to improve
overflow quality.
    The  information  requested included:  type  of
regulators and locations where overflows resulted; the
types of  devices used to protect regulators or to
improve the quality of overflows, including screens,
comminutors,  baffles or skimmers,  modified weir
crest configurations, special orifices or other devices;
the  benefits  of   quality  control,  as shown  by
monitoring data on overflow liquids before and after
the installation of quality improvement devices.
    Twenty-five   percent  of  the  jurisdictions
responded to the mail survey. Of these, only Muncie,
Indiana used  screens, and none  used  baffles  or
skimmers  or other  quality improvement devices. In
30 percent  of  the jurisdictions equipped  with
side-spill weir regulators, modifications of some type
have been made to weir crests.
    This  special  survey  attempted  to obtain
information  not   only  on  improvements within
regulator overflow stations, but  also on improvement
of overflow  liquids  by  means  of  in-system  or
off-system  retention  tanks,  storm  water holding
tanks,  and  disinfection installations.  Terre Haute,
Indiana,   and  Ontonagon;  Michigan,  of the  eight
jurisdictions which reported  on quality  control of
overflows, used in-system storm water holding tanks;
none used off-system holding tanks.
    Greenfield, Indiana, reported the use of settling
tanks and overflow chlorination;  it was  the  only
jurisdiction  reporting  this form of overflow quality
control.
    The   results   of this  supplementary survey
indicated  very  limited  use   of  waste  water
improvement procedures in combined sewer regulator
chambers  or  in  overflow  treatment or  retention
facilities  installed  between overflow chambers and
receiving waters.
Special Survey on Overflow Monitoring
    Limited information concerning monitoring of
the quality  and quantity of overflow  wastes  was
                                                  13

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obtained as a result of surveys carried out in the 1967
investigation. Similarly,  a  lack of basic monitoring
information   was  evident in  the  field surveys
conducted  in  the 18 communities  in the current
project. In order to focus more definite attention on
the importance of monitoring data  upon  which to
base decisions on  the pollutional effects of overflows
and  justification  of  expenditures  for  overflow
control, inquiries  were addressed to  54 jurisdictions
which,  in  the  1967 investigation,  reported  some
method  of monitoring  overflows.  The  letter of
inquiry  to  these jurisdictions  requested  a  brief
synopsis of any  monitoring studies, together with
pertinent findings on the quantity  and quality of
overflows, their frequency, and the pollutional effect
on  receiving waters. Data pertaining  to statistical
evaluation of the monitoring were solicited. Of the 15
communities «which  replied, only  San Francisco,
Philadelphia, Detroit, and  Wilmington, Delaware,
actually  had carried  out some  form  of  overflow
monitoring.  Of these, two measured  the quantity of
overflow. The monitoring of overflows for quality
determination in the remaining two jurisdictions was
carried  out  on a momentary  or "catch sampling"
basis. There  were no reports of overflows having been
monitored consistently over long periods.
Special Survey on  the Impact of First-Fluush
Phenomena on Regulator Practices
    The  common opinion  among  many  persons
associated with the field of waste water collection
and  disposal has  been that, with the  advent of a
storm,  peak flows  in  combined sewers  tend to
dislodge  solids  deposited in the conduits during
dry-weather  flow  periods. In accordance with  this
concept, solids tend to move along the sewer barrel as
    a concentrated  "slug"  and  to  produce a  sudden
    heavily polluted  discharge of waste water  through
    regulator-overflow installations and into  receiving
    waters. On the basis of the occurrence of first-flush
    phenomena, some designers have attempted to retain
    this brief peak flow in the system and prevent its
    discharge to receiving waters, on the assumption that
    subsequent overflows would be diluted with relatively
    cleaner  storm  water  which would reduce  the
    pollutional impact on receiving waters.
       To obtain information concerning the  actual
    existence  of these phenomena in practice, letters of
    inquiry were addressed  to the 19 members of the
    project's  Advisory Committee.  The  communities
    which these  members  represent were  financial
    participants  in   the  project  and, as such, have
    experienced overflow-regulator operational problems.
    The general findings of this supplementary survey can
    be summarized as follows.
       1.  Is there  a first-flush condition  in combined
       sewers which produces a peak of high-strength
       condition in overflows when storm  flows occur?
       Table 3  evaluates  opinions  concerning  the
       existence   of the  first-flush phenomenon.
       Fifty-eight percent  of those reporting believed
       that a first-flush condition  exists within  the
       entire  combined   sewer  system;  79  percent
       expressed the belief that the phenomenon exists
       in their local collector sewers.               .
       2.  Are  solids deposited in  your combined
       sewers during dry-weather flows, which are then
       flushed  from the  lines  during  storms, thus
       producing  overflows of greater  pollutional
       strength in receiving waters? Table 4 shows no
       clear concensus on this question.
                                              TABLE 3
                                OPINION SURVEY ON EXISTENCE
                                 OF FIRST-FLUSH PHENOMENON
(A) In Total Combined Sewer Systems
No. of Jurisdictions Reporting
Percent of Jurisdictions Reporting

(B) In Local Collector Sewers
No. of Jurisdictions Reporting
Percent of Jurisdictions Reporting
                                                 Yes
 8
58
11
79
                No
 2
14
 2
14
                 In
               Part
 3
21
               Don't
               Know
1
7
                 1
                 7
                                                 18

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                                             TABLE 4
                   ARE SOLIDS DEPOSITED DURING DRY-WEATHER FLOW,
                         WHICH ARE FLUSHED OUT DURING STORMS,
             PRODUCING OVERFLOWS OF GREATER POLLUTIONAL STRENGTH?
  No. of Jurisdictions Reporting
  Percent of Jurisdictions Reporting
                                                Yes
   5
  37
                 No
 4
28
 In
Part

  1
  7
Don't
Know

  4
 28
     3.  Do all solids flushed along sewers under such
     flow  conditions, scour out of combined sewers
     during the  early stages of storms, or are they
     moved  slowly along the  barrel  of sewers and
     leached out over a long period of storm flow?
        Table  5  indicates  that  58 percent of  the
        jurisdictions  surveyed  believe  that  solids  are
        flushed out of the combined sewer system during
        the entire period of the storm.
                                             TABLES
                      ARE SOLIDS FLUSHED OUT OF COMBINED SEWER
                           SYSTEM DURING EARLY PART OF STORM
                OR CONTINUOUSLY OVER LONG PERIOD OF STORM FLOWS?
 No. of Jurisdictions Reporting
 Percent of Jurisdictions Reporting
Early Part
of Storm

     4
   28
    During Entire
        Storm

           8
         58
              Don't
              Know

                 2
               14
    4.  Does the coarse trash material in combined
    sewers during dry-weather flows, as well as debris
    contained in storm runoff flows', cause trouble at
    regulator chambers? Only  14 percent reported
    having  this problem  under dry-weather flow
    conditions, as indicated in Table 6.
    This survey indicated that although personnel
from  several reporting  jurisdictions believe  the
phenomenon of first-flush  does  exist, none produced
evidence to  support-the theory. Opinions  indicated
that in small sectors of the .drainage basin and their
local  combined sewers,  there  may  be  a  higher
concentration of pollutant loads coincident with  the
first peak of storm water flow; however, in major
elements of the combined sewer system, it is more
likely that the pollution load during  periods of
wet-weather flow varies in direct proportion  to  the
intensity and duration  of the particular storm. The
concentration of pollutants, the quantity  of
suspended solids, solids in  the sewer invert, volatile
matter and floating debris  in the wet-weather flow,
    will increase with the length of time between storms.
        The  Metropolitan  Corporation  of Greater
    Winnipeg  has established .that the pollution load in
    the  overflow  varies  in  direct proportion to  the
    intensity of  the  particular  storm.  Figure  1,
   , Rainfall-Overflow Characteristics,  presents  these
    findings graphically for one facility at an overflow of
    2.75 x Dry Weather Flow (DWF). Similar results were
    obtained for 5 x DWF.
       To  improve the  quality of  overflow during a
    storm, jurisdictions surveyed recommended  the
    following  procedures: Maintenance  of self-cleansing
    velocities  in combined  sewers during dry-weather
    flow conditions by using 'vertically-oriented,
    elliptical-sewer cross sections,  or by providing
    dry-weather flow channels; use of side inlets instead
    of catch basins; initiation of thorough street sweeping
    programs in order to reduce the volume of street dirt
    and  debris flushed into the combined sewer system;
    inauguration of  a combined sewer flushing program,
    particularly during prolonged periods of dry weather,
                                              19

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                            FIGURE 1
 OVERFLOW - HOURS
20

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and reduction in the number of overflow locations
within the jursidiction so that, within the economies
of  the  system,  retention,  sedimentation, and
disinfection of the overflow will be feasible.
    The presence of concentrated amounts of solids
in the flow to the interceptor tends to cause pump
    malfunctions. Figure  2,  Typical  Interception
    System—the Metropolitan Corporation  of  Greater
    Winnipeg, illustrates that area's use of comminutors
    to reduce  the size of solids  in the flow to the
    treatment plant prior to pumping.
                                      TABLE 6
          DOES SOLID MATERIAL SETTLED OUT DURING DRY-WEATHER
             FLOW PERIODS AND DEBRIS FROM WET-WEATHER FLOWS
                 CAUSE BLOCKAGES AT REGULATOR CHAMBERS?
 (A) Under Wet-Weather Conditions
No. Of Jurisdictions Reporting
Percent of Jurisdictions Reporting
(B) Under Dry-Weather Conditions
No. of Jurisdictions Reporting
Percent of Jurisdictions Reporting
                                               Yes
       8
      58
                                        Yes
 2
14
            No
 8
58
                         No
 4
28

Don't
Know

    2
   14
                              Don't
                              Know
                                 2
                                14
                      Occasionally
 2
14
                                                                         FIGURE  2
            •TRUNK SEWER
  tWEIR(FIXED HEIGHT)
       (2.75X D.W.F.)
                                  HYDRAULIC
                                  GATE VALVE FOR
                                 /FLOW CONTROL
         COMMINUTOR
                                                  DOWNSTREAM WEIR

           TYPICAL  INTERCEPTION  SYSTEM
           THE  METRO. CORP.  OF GREATER  WINIPEG
                                        21

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                                              SECTION 4
         TYPES AND APPLICABILITY OF REGULATORS IN USE IN COMBINED SEWER SYSTEMS
    Regulator devices serving systems in the United
States  and Canada 'have been developed  to divert
waste water flows from one flow system to another
and to control the quantity diverted. The regulator is
generally sized to intercept peak dry-weather flow
and  a  portion of the wet-weather flow.  Excessive
wet-weather flow is bypassed to receiving waters, or
to holding tanks or treatment facilities which prevent
overflow of these waters or provide some degree of
treatment prior to discharge.
    Regulators  may  also  operate  as emergency
overflow devices. A typical application is protection
of pumping stations and waste water treatment plants
where excessive flow is diverted to an outfall, in order
to prevent overloading of  mechanical  facilities and
treatment processes.  A common application  is in
upstream  areas of collection  systems  where
surcharging of local combined sewers may be relieved
by overflow regulators which divert wet-weather flow
to nearby receiving waters or a dry watercourse.
    When regulators  are used to direct waste water
into an interceptor system  which delivers  flow  to a
treatment plant, three distinct methods are used to
control the  quantity of combined flow intercepted:
    1.   Control of flow by its upstream depth in the
   ' collector. This method  results in little control of
    the amount of flow to the interceptor and the
    treatment plant.             .
    2.   Control of quantity by depth of'flow in the
    interceptor. This method exercises  accurate
    control  of  the diverted  water  up  to  the
    interceptor's maximum designed capacity. This
    method produces more uniform conditions of
    flow in the interceptor and at  the  treatment
    facility;  it  makes maximum  use  of both,
    providing  a reduction in overflow quantity but
    not necessarily making any attempt to improve
    the quality of the overflow.   • ' • •
    3.   Control of quantity by depth of flow, both
    in   the  interceptor and  the  collector  sewer.
    Actuated  by remote control, and in sequence
    with other  similar  diversion  structures,  this
    method  can vary  flow  conditions   in  both
    systems. The flexibility  of the  total system
    produces a  more accurately controlled  flow in
    the  interceptor,  and   at  the  treatment plant,
    reducing' flow peaks by retaining  runoff volumes
    in  collector mains.  This insures  maximum
    utilization  of interceptor and treatment  plant
    capacities. Reduction of the number of Overflow
    points and quantity of overflow is possible. The
    quality of overflow may also be improved.
    For the  purpose of this report, regulators are
described as  either "static", or "dynamic." A static
regulator cannot be adjusted without manual changes
or structural modification. Flow rates over or through
the regulator  increase as the hydraulic head upstream
increases. These devices operate primarily on the basis
of pre-installation design criteria; they include  fixed
orifices, side-spill weirs, simple siphons, .and leaping
weirs.
    A  dynamic  regulating device is  one which
functions  semi-automatically  or  automatically  to
adjust  the  quantity of flow introduced into the
interceptor and, consequently, the volume diverted to
overflow. Dynamic regulators include  tipping gates;
cylinder-operated  gates; cylindrical  float-operated
gates,  motor-operated   gates,  and some  types  of
siphons^ The  mechanical devices,  by design, have a
range of settings which permits varying volumes  to be
intercepted  and  diverted  in  response  to  flow
conditions  upstream, downstream,  or  both,-in
accordance with pre-established design criteria.
    The principal application of regulators presently
in use in North America has been to control the  flows
entering  the   interceptor system  and  to protect
pumping and waste water treatment plant facilities.
Thus, control of the pollution effect of combined
sewer overflows plays  only a secondary role. The'
quantity, duration  and quality of overflow  waste
discharges have  been neglected and, in many cases,
they have been disregarded.
    The  ideal  combined  sewer  regulator  should
perform the following functions:
    1.  Divert  peak  dry-weather  flow to the
    interceptor system;
    2.  Cause street, gutter  inlet and  sewer-scour
    debris  to be  retained and  intercepted   when
    interceptor capacity permits;
    3.  Minimize   frequency:  of  combined  sewer
    overflows;
    4.  Provide  optimum utilization of the storage
    capability of collector sewer lines;
    5.  Permit  utilization  of  potential storage
    capability of interceptor sewers in separate  areas
    under  varying  storm  and runoff  conditions,
    making available the maximum capacity of the
    interceptor;
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     6.  Permit overflows when necessary at selected
     locations,  where  the effects  of pollution  on
     receiving waters will be minimized, and where it
     may be possible to construct overflow treatment
     facilities; and
     7.  Reduce the concentration of overflow waste
     water in order to minimize the pollutional effect
     of these spills.
     Most devices investigated in the study, more or
 less,  meet  the  first  requirement.  The  second
 requirement may,  to a large degree, be accomplished
 by .retaining the heavy  debris which arrives at the
 regulator staiton  in the form  of a  first-flush,  an
 extended period of scour flow, or in some other form
 or time interval. This can be accomplished either by
 providing retention tanks or by remotely regulating
 the flow in the collection and interception system in
, order to provide more effective utilization of system
 storage capacity.  Frequency of  combined  sewage
 overflows may be  reduced by remotely controlling
 regulator  actuation  to fully  utilize system  storage
 capacity.  Other means of splitting storm flows to
 divert  concentrated  liquids to the interceptor may
 include use  of such means as scum or baffle boards,
 screens,  vortex solid-liquid  separators  and  helical
 separation devices.
     There are eleven existing major types of regulator
 devices  presently  in use in North America. Their
 functions,  applicability  and  performance  were
 investigated during the national survey conducted for
 this  research project. These factors are discussed in
 this section of the project report.
     For ease of reference, regulator descriptions have
 been grouped into three major groups.
     1.   Static Regulators
         (a)  Fixed orifices (vertical)
         (b)  Fixed orifices (horizontal)
             (the drop inlet)
         (c)  Leaping weirs
         (d)  Manually operated gates
         (e)  Side-spill weirs (side-flow weirs)
         (f)  Siphons (internal self-priming)
     2.   Dynamic Regulators—Semi-Automatic
         (a)  Float-operated gates
         (b)  Tipping gates
         (c)  Cylindrical gates
     3.   Dynamic Regulators—Automatic
         (a)  Motor-operated gates
         (b)  Cylinder-operated gates

                I.  Static Regulators
 A. Fixed Orifices
 Function
     The fixed orifice diversion regulator consists of a
 perpendicular weir constructed across a combined
 sewer, which dam diverts  peak dry-weather flows
 through  an opening or orifice into the interceptor.
 During   a storm, the  excess  wet-weather  flow
 discharges over the weir to overflow.
    The  principal   advantages   of  fixed  orifice
 regulators are:
    1.  Maintenance  is usually limited to periodic
    inspection by unskilled labor, as malfunctions are
    ordinarily confined to clogging,
    2.  The structure  and housing are  small  and
    inexpensive,
    3.  Standard construction materials are used,
    4.  Few, if any, metal components are required,
    5.  They operate effectively  under  minimum
    head,
    6.  They operate  in a  stable, predescribable
    manner when submerged, and
    7.  They may be adapted to shear or  sluice gate
    control.
    The  orifice may be rectangular or circular. The
 circular units may be fitted with rings or sleeves, i.e.,
 the flow can be  adjusted to meet the interceptor
 conditions. Rectangular orifices, when gate-regulated,
 present a uniform  aperture which  does not  clog as
 readily as the crescent-shaped opening produced by a
 gate-controlled circular orifice.
    The  minimum opening of orifices encountered in
 the national survey was  8 inches. The  consensus,
 however,  indicated that  a more desirable minimum
 would be in the order of 12 to 15 inches. Because of
 the size  of the opening, flow control is sacrificed in
 order to reduce maintenance problems.  Although
 design diversion  capacity may  be  based on a  2:1
 wet-weather: average dry-weather ratio, it actually
 may be as high as 6:1 during periods of rainfall.
    The  fixed orifice was undoubtedly one  of the
 first types of regulators  used to  divert  combined
 sewer flows  and  to prevent  surcharge   of  the
 interceptors and  overload of  downstream pumping
 and treatment facilities.
    Today, the simple orifice is applicable principally
 for diverting relatively small flows where, because of
 pipe sizes, space is limited. They are applicable where
mechanical regulating devices would be uneconomical
 to  install  and  difficult  to  maintain,  or  where
 flow-responsive  regulators  would   function
intermittently due to low head.
    In its vertical  application, an  orifice regulator
 consists of two components: a diversion chamber and
an orifice chamber. When a -tide gate is required to
 protect  the interceptor from high  water levels in
 receiving  waters,  this  third  regulating appurtenance
is also housed in  a chamber. The diversion chamber
                                                   24

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contains a dam or perpendicular weir, which diverts
normal dry-weather flow into the orifice chamber. In
flat regions and/or where combined sewer slopes are
less than 1 percent, the height of this weir is generally
restricted in order to minimize backwater effects in
the upstream collection system during storm flows.
With this height limitation, it is sometimes necessary
to depress  the invert of the upstream sewer in  the
diversion chamber, so that the peak dry-weather flow
can be diverted.  In hilly  regions, or where head is
available, this limitation need not be imposed.
    Flow through the orifice may occur as in an open
channel, as through an orifice with free discharge, or
as through a submerged orifice, depending on  the
water surface elevations upstream and downstream of
trie orifice. During  a storm the orifice will discharge
quantities greater than the peak dry-weather flow, or
the design discharge  rate. This may  surcharge  the
interceptor and/or the branch interceptor connecting
the orifice chamber to the intercepted. If the latter is
surcharged,  the  hydraulic  grade  line  may  rise
sufficiently to submerge the orifice, thus reducing the
flow to the interceptor. This is the basis of the claim
that,  with vertical  orifices, the  flow  entering the
interceptor under storm conditions will automatically
adjust itself to the capacity of the interceptor.
    Figure 3, Orifice with Perpendicular Weir, shows
a simple diversion  device. In this structure the  weir
was poured in the sewer invert and some dry-weather
flow continues to the receiving waters.
Application
    The fixed orifice is used to advantage where the
intercepted  .flow is  to  be  further  regulated
downstream  by a  more  sophisticated  regulating
device.  The  fact that excess flow may be discharged
to the interceptor through the orifice during periods
of rain, is not significant  because of the downstream
regulation.
    The national survey disclosed that New York
City employed fixed orifices for stormrwater flows

                                   FIGURES
                       r
        .ifffiffifai* .......I... * (r*l&r 9
                            ORIFICE WITH PERPENDICULAR WEIR
                                                25

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 less  than  4 cfs.  The  Allegheny County Sanitary
 Authority (ALCOSAN) has applied them when flows
 are less than 2 cfs. Such use reflects the practice of
 other  surveyed  systems.
 Practices  in Surveyed  Jurisdictions
     ALCOSAN uses a  total of  116 vertical fixed
 orifice regulators. The intercepted flow is diverted to
 a  large  system  of  intercepting  sewers,  which
 principally carry sanitary sewage and industrial flows
 to the Authority's treatment works. At the time of
 design the orifice  regulators were considered to be
 more applicable than mechanical  regulating devices
 when  used to divert  relatively  small  amounts  of
 sewage, for the following reasons:
     1.  Construction cost  is  low  due  to  small
     structures  and elimination  of mechanical
     equipment  except  for  floodgates (tide  gates)
     when required,
     2. Maintenance   is  confined  to  cleaning
     chambers  and  occasional  lubrication   of
     backwater gate hinges,
     3. Maintenance can be carried out by unskilled
     labor,
     4. Considering the small flow,  the  orifice
     aperture  is relatively large, resulting in  fewer
     incidences of clogging, and
     5. It  functions as  a relief for a  surcharged
    interceptor.
    A regulator using two vertical fixed orifices was
 also reported by ALCOSAN. An engineering report
 prepared by consulting engineers to the Authority
 stated  that, ideally,  the  regulator structure  should
 offer  minimum  resistance  to  small  flows  being
 diverted, and maximum  resistance to large flows to
 the  interceptor.  Since  these ideals  are  somewhat
 contradictory, a compromise structure was developed
 which provided:
    1.  A   rectangular  orifice  mounted in  the
    common wall between the diversion chamber and
    the orifice chamber: and
    2.  An  orifice  chamber having  a dry-weather
    flow channel directed to a circular orifice and
    outlet  pipe, with the outlet pipe having a slope
    which will generate self-cleansing velocities.
    Nine  other  surveyed  jurisdictions  reported
 utilizing 470 fixed orifice regulators. In Detroit, three
 orifice regulator stations were installed to restrict the
 flow from  the combined sewer to the interceptor.
 They permit the passage of all dry-weather flow, but
 restrict excessive amounts of storm flow entering the
 interceptor. The WWF:DWF design ratio was 1.5:1.
 The  orifices are used on  sewers carrying a minimum
 amount of dry-weather flow.
    Officials  in Cleveland reported  that the 221
 orifices in their interceptor-collector system are very
effective. The major reasons for this opinion were low
  capital and maintenance cost, reliability, and absence
  of major backwater flooding problems.
      Milwaukee  Sewerage  Commission  personnel
  reported  that  4-inch  orifices or  larger  are  less
  troublesome than mechanical devices, indicating their
  concern over the clogging problem.
      In New  York  City,  104  orifice  units are in
  operation, installed  at collectors, branch interceptor
  junctions,  interceptors, and at junctions with other
  systems. They are used to advantage where a number
  of parallel combined sewers  must  be intercepted.
  Instead of installing  a complex and costly mechanical
  regulator on each combined sewer, fixed orifices are
  used and  the intercepted flows from several sewers
  are  conveyed , through a  branch intercept&f to  a
  downstream mechanically controlled  regulator. Table
  7,  1964 Cost  of Regulator, Structure and Tide
  Gates-New York City, indicates a total cost for this
  type  of regulator  facility  of from  $10,300  to
  $22,800.
                      TABLE 7
              1964 COST OF REGULATOR,
            STRUCTURE AND TIDE GATES
                  NEW YORK CITY
  Orifice Diam.

      12"
      15"
      18"
      24"
No. of Regulator
   Structures

      1
      1
      2
      4
  Total Cost

$12,700
 11,200
 16,200-22,800
 10,300-22,400
    Forty vertical orifices have been installed in San
 Francisco. These are located on collector-interceptor
 junctions, in locations where the collector continues
 to the outfall. They are used as part of a structure
 designed   to  reduce  the backwater effects  of
 tidewater. The regulator chamber is depressed and a
 channel with a weir diverts flow to the interceptor. A
 low-profiled, perpendicular weir is placed across the
 collector invert downstream from  the  regulator to
 prevent  discharge of  dry-weather flows.  Past the
 perpendicular weir, the gradient rises to the outfall.
 The outfall is protected by a tide gate, which is only
 submerged when a 7.5-foot tide occurs. In this event,
 backflow  of saline water into the interceptor was
 reported to cause sludge  digestion problems in the
 waste water treatment facility downstream.
    The device, as applied in San Francisco, does not
regulate or control the  overflow. Its primary purpose
is  to reduce tidewater backflow into the interceptor
system.
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B. Fixed Orifice Regulators—Horizontal
(The Drop Met)
Function
    The  drop  inlet  is  a static  regulator that is
analagous to the leaping weir, in that it is a horizontal
orifice located at the invert of the combined sewer. It
is  designed to  allow  at  least the peak dry-weather
flow to be delivered via a connecting conduit to the
interceptor  sewer. Sometimes  the  drop  inlet is
referred to as a slot regulator.
Description
    Drop inlets  are   usually housed  in  a  single
regulating chamber.  However, in  the  case of small
 sized collector  sewers,  manhole  access  may be
 sufficient.
    Under dry-weather conditions, the peak flow is
 intercepted.  During  periods of  wet-weather  flow,
 most of the combined wastes pass over the opening
 and continue to overflow. The  positive interception
 of peak dry-weather flows and  the  prevention of
 "jumping over" the inlet without interception during
 periods  of  storm flow is  induced  by  placing  a
 low-profiled,  perpendicular weir at the  downstream
 lip of the orifice.
    The national  survey indicated that in almost all
 cases,  the  inlet  to  the connecting  conduit  was
 protected from clogging by  a grating. These gratings
 have the added purpose of protecting maintenance
.crews from the hazard of falling into  the downdraft
 opening.
Applicability
    The drop inlet is used when diverting low flows
 iri the order of 2 cfs or less. The interceptor system
 should be  protected  by  further  automatic
 downstream regulation to prevent surcharging of the
 interceptor.
     The advantages of the drop inlet are:
     1.  Low initial cost;
     2.  Simple  construction  with no  mechanical
     parts; and
     3.  Simple maintenance by unskilled labor.
     When considering the installation  and use of the
 drop  inlets,  the  following  problems  should be
 considered:
     1.  Continuous  maintenance of the  grates  is
     required.  Some  surveyed communities reported
     such  maintenance   as  a  7-day-per-week,
     24-hour-per-day problem.
     2.  Blockage   of  grates  is inevitable  during
      periods of wet-weather  flow. In the case  of large
      sewers  and  large  flows,  the  high volume  of
      combined  wastes   prevents  clearance  of the
      blockage by  maintenance personnel during storm
      flows,  with  the result that  for  at  least the
    duration of the storm all suspended and floating
    solids are permitted to discharge to the receiving
    stream.
    3.   Unless a large  maintenance staff is available
    to  remove  the debris from the  orifice grating
    immediately after  the storm, dry-weather flow,
    i.e., raw sanitary sewage, will pass over the inlet
    and overflow into the receiving stream.
Practices in Surveyed Jurisdictions
    Drop inlets are in  use in five surveyed systems.
The design criteria established  for the interception,
pumping and. sewage  treatment  system for Akron
provide diversion  facilities handling two times  the
estimated water consumption in the  tributary area,
plus an allowance for  infiltration and for  increased
future  waste water flows. The inlet  is  satisfactory
when   diverting  peak  sanitary  flows  which
approximate one-fifth of the pipe capacity. However,
when operating under wet-weather .flow conditions,
from 2.75  to  5  times  dry-weather  flow will be
intercepted unless  the inlet connection pipe from the
orifice to the interceptor is restricted so as to throttle
this excess  flow. Such  a design modification  is
presently being considered.
     Studies to determine the  performance of inlet
gratings indicate that  for  36-inch and 48-inch
diameter combined sewers, gratings may be suitably
selected without inhibiting the delivery of flow to the
interceptor. Inlet  gratings were standardized in two
basic sizes and frames  of different sizes are used with
combinations of these standard gratings.
     The cost of these  regulators ranged from $1,500
to $2,000 each.
     Because the drop  inlets with gratings are subject
 to a large amount of maintenance to keep them clear
 of refuse, a monitoring system has been established in
 Akron. Sensors   monitor  flow conditions  in  .the
 interceptor and  the collector. These serve to  alert
 maintenance personnel when gratings^re blocked.
     In Omaha, 25 units of this type  are in use. They
 were chosen many years  ago when limited sewer size
 and flexibility of control were factors. At that  time,
 treatment of waste water was, not required and the
 prime consideration  was  relief of surcharge  in
 combined  sewer  mains  due  to lack  of capacity.
 Present plans  call for the elimination of at least half
 of these units.
     In Cincinnati MSD, 141  grated drop inlets  are
 utilized to avoid overloading of the interceptor sewer.
 A telemetering system is used to monitor overflows
 and  advise personnel  where  and  when  overflows
 occur, and to record  how often overflows take place.
 The monitoring system alerts  maintenance personnel
 when clogging at  the inlet grate occurs.
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C. Leaping Weirs
Function
    Leaping weirs are located at the invert of the
combined sewer and are designed to allow at least the
peak  dry-weather flow  to drop through it via a
connecting pipe to  the  interceptor sewer. Under
wet-weather flow  conditions the increased velocity
and depth cause most of the flow to leap over the
opening and continue to the outfall.
    An adjustable orifice plate may be an integral
part of the design.  Installed over the opening, this
plate  can be adjusted as part of the field operation, so
that the quantities  of sewage  to be intercepted or
diverted  to  overflow  may  be varied  to  satisfy
downstream interceptor conditions.
Description
    Two  types  of leaping weirs were found in use
during the national survey:
    1.  The  continuous invert  leaping weir, as the
    name implies, is a horizontal orifice placed at the
    invert of the combined sewer  with  no special
    modifications to the  conduit configuration; and
    2.  The  stepped invert leaping weir has a raised
    upstream lip, the downstream lip being the invert
    of the combined sewer. This raised lip may be a
    part  of  the  regulator  chamber design  and
    constructed of  concrete for a new installation;
    alternatively,  in  the  case of existing  combined
    sewers, a plate may be installed.
    During dry-weather flow conditions,  the orifice
of the leaping weir intercepts all  sanitary  sewage.
During wet-weather  flow, much of this excess flow is
presumed to leap over the weir to  discharge at  the
overflow. In  practice, however, these  devices  are
subject to "jumping  over," with the result that almost
all of the combined sewage will overflow. In an
attempt to insure  that dry-weather flow volumes will
be intercepted at all times, some leaping weirs have
been  designed  so  that the orifice is  tipped up at the
•downstream  lip, usually  by means  of a low profile
perpendicular weir.  This  has the effect of arresting
and intercepting a portion of the flow. By using the
dam, heavier solids in the stream flow are intercepted
for conveyance to the treatment facility.
Applicability
    The  leaping  weir  is  usually applied  when
intercepting small flows. As in the case of the vertical
orifice, design capacities have been limited in practice
to a maximum of 4 cfs. On the average, the national
survey indicated that interception of a maximum of 2
cfs was most  acceptable. They therefore are  used
frequently in local  drainage basins  where flows are
low  and  mechanical  equipment for  regulating
purposes might not  be economically justified. Being a
compact unit, the leaping weir is well suited for the
space  limitations  generally  associated  with  small
capacity sewer main installations. In this application,
a special regulator chamber may not be  required and
manhole access may suffice.
    The advantages of this device are as follows:
    1.   Low capital cost;
    2.   Useful for interception of small flows in local
    drainage areas; and
    3.   Simplicity of the device, permitting routine
    maintenance by unskilled labor.
    Disadvantages included:
    1.   Control  of the  amount of   flow to  be
    intercepted is difficult to regulate;
    2.   Under  wet-weather flow  conditions,  all or
    most of the combined sewage may pass over the
    opening, and no flow will be intercepted; and
    3.   Without  a  regular  preventive-maintenance
    type of operation, blocking or  bridging of the
    orifice will result in the  overflow of sanitary
    sewage and storm flows.
Practices in Surveyed Jurisdictions:
    A  total of 189 leaping weir units are being used
in the surveyed jurisdictions. Philadelphia utilizes 73
leaping weirs. The branch conduit from the weir to
the interceptor is terra-cotta.  Under present  traffic
wheel  loadings this material has  in many instances
failed, blocking off the regulator chamber from the
interceptor. It was also  reported that blockage was
more of a problem in industrial areas.
    Itemized  below is the  cost  of a leaping weir
regulator installation in Philadelphia, including special
structures, built in 1963. The regulator was designed
for an ultimate flow of 1.35 cfs.
      1. Excavation — General                $1,500
                  - Interceptor             8,000
                  - Drop Manhole           2,100
      2. Intercepting chamber                 1,708
      3. Drop manhole                      1,580
      4. Tide gate chamber                   3,360
      5. Tide gate                          1,900
                               Total:      $20,148
     In Cleveland, 103 units are used to divert excess
 flows   from  the collectors and interceptors.  The
 interception  ratio  is  being  modified for  a 4:1
 WWF:DWF  ratio.  Investigations  are now  being
 conducted  for  improvement of  the system  by
 centrally controlling and monitoring the operation of
 regulators. The purpose is to make additional use of
 in-system  storage, thereby  reducing overflows. This
 will render larger leaping weirs obsolete. Cost of these
 units, when built in 1964, was $1,500 to $3,200.
     Six leaping weirs are used  on the collector sewers
 at  the  interceptor junction in  the Milwaukee
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Sewerage Commission system.
D. Manually Operated Gates
Function
    The purpose. of a manually operated gate  is to
permit flow through a vertical orifice, the opening of
which may be varied by manual adjustment. As in the
case of the fixed orifice, this regulator consists of a
perpendicular weir constructed across the channel of
a combined sewer, which  directs  peak dry-weather
flow to the interceptor through an orifice. The size of
the   orifice and,  consequently,   the  amount  of
combined sewage intercepted,  is a function of the
position  of the  gate. During a  storm,  additional
wet-weather  flow  discharges over  the  weir  to
overflow.  Figure 4, Typical Manually Operated  Gate
Regulator—Philadelphia,  illustrates  a  typical
installation. Figure  5 is  a  photograph of  a  typical
orifice with a manually o'perated shear gate.
Description
    The manually operated gate regulator consists of
two  chambers.  The  first,  for diversion  purposes,
consists.of a perpendicular  weir positioned across the
combined  sewer   channel,  which  diverts  normal
dry-weather flow into the second or orifice chamber.
The  height of  the dam  is  restricted in  order to
minimize  backwater  effects  in the  upstream
collection system during storm flows.
    The orifice chamber  consists of a channel with a
gate seated on the outlet orifice, which is preferably
located on the common wall between the orifice and
diversion chambers. A branch, sewer conveys the flow
from the  orifice  chamber to the interceptor. The
manual unit may be a shear or sluice gate. Slide gates
are used in open flumes and are not tight enough for
this purpose. Openings in shear gates are adjusted by
raising and lowering the gate  by  means of a lifting
handle  generally two feet long and held open by
attaching the handle to a  hook on the  wall. Sluice
gates may be self-contained gates  with the operating
mechanism attached to the top of the frame, or may
have a bench stand mounted on a wall bracket or  a
floor stand mounted on the  floor above the gate. In
either case the  gate is operated by  manually turning a
wheel or crank which may or may not be connected
to reduction gears.
Applicability
    The major advantages  of the  manually operated
gate regulator are:
     1.  It provides greater  control than an orifice;
     2.  It  is  simple to  adjust   to meet  desired
     operating conditions;
     3.  Capital and maintenance  costs are low; and
     4.  It may  be  possible to  adapt it for motorized
     and remote control.
    Manually operated gates are subject to clogging,
particularly if circular orifices and gates are used, .as
debris has a tendency to jam in the two sides of the
crescent-shaped  opening formed when the  gate  is
partially closed.
    The setting  of the gate  should be calculated on a
conservative design  flow,  as excessive amounts of
water may be diverted to the interceptor under storm
conditions, due to upstream surcharging  and the
subsequent pressure  head  which  is developed. In
applications in New York City, as much as six  times
the dry-weather flow has been diverted for a system
" designed to intercept a WWF :DWF ratio of 2:1.
    Some  surveyed jurisdictions reported the use of
manually  operated  gates   to  throttle  wet-weather
flows and  protect pumping stations and waste water
treatment  facilities  from  surcharging.   In  this
application, the regulating  station  was between the
interceptor and  the plant facility.
    Manually operated gates have been used in several
jurisdictions as a temporary  substitute  for  more
sophisticated equipment. One inherent  advantage of
this   type  of regulator,  whether  temporary  or
permanent,  is  that  it  is  adaptable  to  automatic
operation and remote control.
Practices in Surveyed Jurisdictions:
    In Chicago  MSB,  a  total of 328 such regulating
stations are in use. The design criteria for the system
provide for  twice  the dry-weather  flow to  be
intercepted, with manually operated gates being fixed
to accept  1.5 times peak dry-weather flow, and the
remaining  wet-weather  flow  being discharged to
outfail.  Shear  gates  are   used  at  260 regulating
stations.  One   hundred  and twenty-five  units  are
replacements  for  float-operated gates, which  were
found to  be   unsatisfactory because  of excessive
clogging, corrosion of shafts and jamming  of float
mechanisms.
     For installations requiring more than three square
feet  of orifice  opening, sluice gates are used in the
Chicago system and 23  regulating  structures of this
 type  are presently  in service. They were  selected
because of ease  of operation in larger sizes.
    The cost of the regulator installation  in Chicago,
 including  special  structures and equipment, ranged
 from $6,000 to $200,000, depending on the size and
complexity  of  the  regulator structures  and their
location.
     In New York City, 62 manually operated gate
 regulators  are  in use. Their choice was based on
 simplicity   and  economy,   and the fact  that  more
 accurate control  of flows  less than 4 cfs.  was not
 required. The  gate  is usually set  with a minimum
 opening of 4 inches and is operated on a regular basis
                                                   29

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                         FIGURE 4
xxxxxx
 TYPICAL MANUALLY OPERATED
     GATE REGULATOR
       PH ILADE LPHIA
         30

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                                                             FIGURES
ORIFICE WITH MANUALLY OPERATED SHEAR GATE
                  NEW YORK CITY
              Typical dam and backwater gate.
              Orifices are to right of gate.
                 Typical orifice with shear gate.
                            31

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 to ^prevent freezing or jamming. The minimum size of
 gate is 8 x 8 inches, or 12 inches diameter, for flows
 less than .4 cfs. Because a certain minimum opening
 must be maintained, the diverted flow during storms
 may exceed  the desired interceptor WWFrDWF ratio.

     In the future, New York City intends to use cast
 iron shear gates, instead of the present sluice  gates,
 with  provisions for  setting  the  gates  at  various
 openings.
     In Philadelphia, five manually operated gates are
 utilized at a particular group of collector-interceptor
 junctions   as a  temporary expedient, pending
 motorization and an overall systems program in that
 area.
 E. Side-Spfll Weirs
 Function
     The side-spill weir is  a static regulator  which
 consists of a standard weir constructed parallel to, or
 at a  slight  angle  to  the  flowline  or axis  of the
 combined  sewer.  As flow  in  the combined sewer
 increases, the  weir is  crested  and overflows to the
 side, to be discharged into the  receiving stream. Peak
 dry-weather  flow  and   some  portion of the
 wet-weather  flow  continues past  the  weir,  to  be
 further  regulated  downstream.   Figure  6,
 Side-Overflow Weir for Small Overflow, illustrates an
"example of tliis device for small flows.
Description
    Side-spill regulators are  used principally to divert
 relatively small flows where, because of pipe sizes,
 space  is limited and mechanical  regulating devices
would  be uneconomical and difficult  to  maintain.
Two types of side-spill weirs are in use:  low side-spill
weirs; and high  side-spill weirs.
    Low side-spill weirs consist virtually of side weirs
formed along  the length of a combined  sewer by
cutting away the sides of the conduit. They are
located below  the horizontal diameter  of  the pipe.
They  are  economical, easy to  operate,  easy  to
maintain, and they function with negligible head loss
in the main channel. However, they do present several
basic problems. Their hydraulic behavior is difficult
to  analyze  and  large errors  in  calculating  flows
overflowing  the weir or continuing downstream are
probable. Any downstream problem or slight increase
in combined  sewer flow rate results in  a premature
overflow, discharging sanitary sewage to the receiving
stream. This poor control of discharge over the weir is
undesirable for three reasons:
    1.   The overflow spills  too much of the highly
    polluting first-flush, if this occurs, and spills too
    frequently in small storms;
    2.   In larger storms, too much flow is passed on
    to treatment; and
     3.  Floating solids  easily  pass over the weir  to
     outfall  during periods  of slight  increase  in
     combined, sewer flow.
     The weir crest in high side-spill weir applications

                                       FIGURES
              SIDE-OVERFLOW WEIR
             FOR SMALL OVERFLOW
      DAM
 "A" i
  A 4—
                                     PLAN
         SECTIONAL  PLAN
                    STANDARD MANHOLE
                    FRAME AND COVER
                        BRICK
        SECTION  "A"-'A"
SECTION  "B"-"B"
is  above the horizontal diameter of the pipe and
preferably near the sewer crest elevation. The amount
of flow continuing down the combined sewer past the
overflow is not as variable as with the low side-spill
weir.  The  degree of control of the volume which
overflows is dependent  on the  length of weir used.
Rule-of-thumb design indicates  that, on the  average,
the successfully operating high  side-spill weir length
equals 20 times the  diameter of the inlet sewer. In
England, because of unsatisfactory experience with
conventional side-spill weirs, this type of regulator is
in  frequent use. Unlike  the  conventional weir, the
flow continuing downstream  is  controlled either by
                                                  32

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an orifice or a  "throttle pipe." A single regulating
chamber is required.  Access  should be  provided
through the roof  of the chamber to a platform at
both ends of the weir.
Application
    The side-spill weir is used  in upstream parts of
the sewer system to prevent surcharge of combined
sewers. As  an area becomes developed, these existing
combined  sewers  may  become overloaded so that
relief storm sewers  are  constructed,  carrying storm
water  directly to overflow. Many years  ago,  this
device was used on  large collectors and interceptors
where they functioned  as surcharge relief units. The
principal advantage of the side-spill weir regulator is
its low capital cost  and the fact that it rarely needs
maintenance, and that maintenance which is required
may be carried out by unskilled labor.

Practices in Surveyed Jurisdictions
     The New York City, Cincinnati and Cleveland
 systems are using  side-spill  weirs  on  small local
 combined  sewers to serve as  relief  overflows. The
 policy in  New York   City is to  further  control
 diversion downstream by means of an automatic or
 semi-automatic regulator station.
     The Metropolitan  District Commission  (MDC),
 Boston, indicated  that 111  side-spill weirs were
 installed  during  the   period  1893  to  1936. The
 elevation of the crest of the weir in the original design
 provided  for  overtopping  of the  weir  when
 experiencing  a rainfall rate  that  represents  a
 WWF:DWF ratio  of 2:1. These units were located
 principally at junctions with other systems. However,
 10  were located  on the interceptor  and one at the
 treatment plant.
     Because  of tide gate   operation  problems,
 backflow  into  the  collector and  interceptor system
 caused  damage  to   the  downstream  system.
 Consequently, the MDC had side-spill weirs raised and
 blocked  off with  timber in  a  majority  of their
 installations. The MDC reported that, for all practical
 purposes,  they had discontinued overflow operations,
 since this timber shoring had  raised the crest of the
 weir to such a height that overflows take place only
 under  rainfalls of  hurricane  proportion.
 Discontinuance  of regulation  has   the  effect of
 surcharging the interceptor and requiring control by
 other collector-interceptor facilities.
     In Cleveland, where 234 siderspill weirs are in
 service, the design WWF:DWF ratio is 2:1. However,
 tests have indicated that interception volumes may be
 as  high as 9:1. Cincinnati MSD  plans  to reduce its
 ratio to  4:1.  Installation costs  in  Cleveland were
 reported to be between $750 and  $21,000 each.
F. Siphons
Function
    Siphons  of  the internal,  self-priming type are
static devices which may be used to regulate flows
from the collection system to the interceptor, or they
may function as overflow units, thereby controlling
the amount of flow discharged to the overflow.
     If the combined sewer  does not have sufficient
depth,  a  chamber may be required  at the diversion
point.  This  chamber acts  as a  stilling  basin  by
constricting  the downstream  outlet, throttling the
flow and creating sufficient  head  to  activate the
siphon.
Description
     The siphon  regulator is used where obstruction or
 elevation problems do not permit the use of a vertical
 fixed orifice with branch interceptor. In the case of
 dry-weather  flows, it may be used to control  the
 water level in a conduit leading to treatment facilities
 or pumping stations by  discharging excess flows to
 receiving waters when the  water  level  rises above  a
 certain maximum.
     To control overflows,  one or more siphons are
 used to discharge excess wet-weather flow from the
 collector. In this  case, a large chamber is required.
 The downstream  outlet is constructed to carry peak
 dry-weather  flow and  some  portion  of  the
 wet-weather  flow.  The  remainder  of the flow is
 collected in  the chamber and discharged through the
 siphons.
     The  inlet to the siphons is set  well above invert
 level and below top water level  to avoid, as far as
 possible, the carry-over  of either heavy or floating
 debris. Use of a scum board or vertical baffle ahead of
 the entrance to the siphon  will reduce the amount of
 floating material discharged to overflow.
     Maximum  operating  sewage  level  in  the
 interception  chamber  at Omaha  is  normally
 established  at from 160 to 185  percent of the inlet
 sewer diameter.
 Applicability
     Clogging  is  a  prime  consideration in  siphon
  design. The positioning of the orifice in the diversion
  chamber is  of  major importance in  preventing
  clogging. Furthermore, a minimum diameter of 12
  inches  is   recommended.  Siphon  velocities are
  considerably higher than  normal   combined sewer
  flow rates  and the operating head on a siphon  is
  considerably greater than  the allowable head above'
  other  static  devices. Consequently,  the diversion
  chamber may be quite compact, reducing capital cost.
      During periods of overflow, the upstream level'
  entering the diversion chamber does not rise above
  priming level. Consequently, the   available storage
                                                     33

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                                                                                            FIGURE?
                                   SIPHON OVERFLOW - OMAHA

                                                                SCUM  BOARD
MAX.FLOW LEVElTp)

     INLET
                                                                  i-J
                                                                               SIPHON  INLET
                                                                                  THROTTLED
                                                                                    OUTLET
                                                                            SIPHON SPILL
   *Maximum flow level set by design. Standard depth is 1.6-1.85 x
    inlet diameter.
 capacity of the sewer and the diversion chamber may
 be used to advantage.
     The principal advantages of the siphon overflow
 are:
     1.   Capital cost is low;
     2.   Materials used are not  subject to corrosion;
     3.   Maintenance may be performed by unskilled
    labor; and
    4.  Quality  of  overflow can be better than in
    other regulator devices.
    The principle disadvantages are created when the
 device clogs. If the clogging takes place in the siphon
 tube  itself,  all  flows must  be  diverted in  another
 manner, and  the  removal  of  the obstruction is
 arduous. To prevent this clogging, it may be desirable
 to protect the opening to the siphon with a grating
 similar  to that  used with drop inlets. This would
 protect  the  siphon  and as the  opening is vertical,
 there would not be as great a degree of plugging as
 the horizontal drop  inlet grating. In congested areas,
 odor may be emitted to the atmosphere, as venting is
 generally required to reduce  turbulence and prevent
 air lock  for proper siphon operation.
Practices in Surveyed Jurisdictions
    Omaha,  Nebraska,  was  the only  community
interviewed  in  the national survey  which  used
                                               siphons. The 26 units in service were installed prior to
                                               1940. Because of the difficulty in restoring these
                                               regulators to operation  once they  become clogged,
                                               the community is considering replacing siphons with
                                               another  type  of  regulator. Figure  7,  Siphon
                                               Overflow-Omaha,  is  a  cross section  of a typical
                                               siphon overflow.

                                                     Dynamic Regulators-Semi-Automatic

                                               A. Float-Operated Gates
                                              Function
                                                  Float-operated gates regulate the flow through an
                                               orifice. In its common application,  a predetermined
                                              maximum flow  of  sewage  is  diverted from the
                                              collector sewer into the regulator chamber by means
                                              of a  perpendicular  weir placed across  the sewer
                                              channel. The  gate is  directly controlled  by a float
                                              placed in a separate well, with the water levels in this
                                              float well being determined by the flow level in either
                                              the  collector  or the interceptor,  depending upon
                                              where the regulation is desired.
                                                 This is a semi-automatic  device, which does not
                                              require any external  energy  source  for  operation.
                                              Figure 8  is an isometric view of a  float  controlled
                                              regulator as installed in Detroit. Figure 9 is a detailed
                                                 34

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                                                                                             FIGURES
  transmission shaft
  regulating chambw
         cabl*
    counterweights
  regulator gat*
  trw**miteUn chain
  to treatment plant
                            outfaH to river
                            ISOMETRIC  VIEW
                            FLOAT  CONTROLLED
SEWER  REGULATOR
Courtesy Detroit Metropolitan Water Service


 view of the regulator chamber.
 Description                          ;•'-'.
     The regulator will  consist of two, and in some
 instances three,  chambers. The first, or diversion
 chamber, consists of a perpendicular weir with its
 crest a maximum of 6 inches above the invert of the
 combined collector sewer. The 6-inch crest height is
 usually chosen in flat  areas to minimize backwater
 effects. The sewer invert may be depressed to increase
 the  flow  velocity to  the interceptor. The  6-inch
 height is measured from the normal invert elevation.
 Peak dry:weather flow is diverted into the second, or
 regulating  chamber  by means of this weir which is
 low profiled, so as to reduce the hazard of backwater
 damage  upstream. The collector  channel may be
 depressed at the face of the weir, in order that peak
 dry-weather  flow  may  be diverted without
 overtopping the dam. During periods  of storm flow,
 quantities  in excess of the desired WWF:DWF  ratio
 are  carried  over  the  perpendicular  weir and are
 discharged to overflow.
      The second, or regulating chamber is subdivided
 into a float compartment and a gate compartment. If
     more than one regulator is used at the station, each
     should have its own float chamber. In most instances,
     the regulating equipment consists of: (1) A gate unit
     with a built-in wall casting leading from the combined
     sewer;- (2) A float unit, including a float and float
     guides with collars for limiting float travel; and (3) A
     transmission unit, including a shaft with wheels and
     universal pillow blocks, supporting beams with wall
     brackets,   adjustable  transmission  chains  and
     counterweights, so  positioned  that  the float itself
     overbalances the  gate shutter when it  is buoyed a
      predetermined distance. The  gate shutter  is  a sector
      gate, facing upstream.
          The  float  well  is  directly  connected  to  the
      interceptor or the collector, i.e., the downstream flow
      or the  upstream flow is connected to the well, thus
      determining the  height  of  water in the  well. In
      Detroit,  each flow  chamber  is  connected to the
      interceptor  by a  small-diameter  pipe.  This pipe is
      tapped into the interceptor near the bottom but high
      enough so  that  it will  not be  blocked by  debris
      carried along the  invert of the interceptor. The water
      level in the float chamber, therefore, is the same as
                                                     35

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that in the interceptor. The gate is held open by the
float  as  long  as  the  water  level is less   than
seven-tenths of the diameter of the interceptor pipe.
As the level rises above seven-tenths, the gate begins
to  close and when eight-tenths of the  diameter  is
reached, it is in its closed position.
    A third chamber may be employed if a  tide gate
is required.
Applicability
    The orifice plate opening and the float travel  is
set so that  all dry-weather flow  and a portion of the
wet-weather flow can be diverted to the interceptor.
    During storm flow periods, the velocity  and
depth of flow increase in the combined sewer, with a
corresponding  increase in flow  into the regulating
chamber. As the float rises, the transmission shaft
begins to turn, causing the shutter gate to close. Since
the travel of the float is limited by the top float stops
on  the guide pipes, the shutter  gate will always be
partly open when the float stops  rising.
    Depending on  the  purpose  for  which  the
regulator was installed, control of the regulator may
be actuated in several ways:
    1.   If it is desired to  restrict the  flow to the
    interceptor  when  the  downstream  flow  has
    reached   a  predetermined  volume,   the
    interconnection or telltale pipe connects the float
    chamber compartment directly to the combined
    sewer. This applieation is designed to control the
    volume of collector sewer flow delivered to the
    treatment plant facility. Usually, adjustments are
    made, so that a small  opening will remain at the
    regulator  gate, permitting  partial  flow to  the
    interceptor at all times.
    2.  If  control  of  intercepted  volume  is
    paramount, the type of control,  such as  in
    Detroit,  connects the float  well with a telltale
    pipe to the interceptor. Overflows do not occur
    until  the  interceptor  has  loaded to a
    predetermined limit.
                                                                                      FIGURE 9
          VIEW OF FLOAT OPERATED REGULATOR CHAMBER
       Courtesy Brown & Brown Inc.
                                                    36

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    3.   If it is required to pass a specific quantity
    through  the  gate  to the  interceptor or  the
    collector,  the arrangement is similar to type 2,
    except that an orifice is  installed between the
    regulator gate and the outfall pipe. The regulator
    is,  therefore, acting  as a governor, the float being
    actuated by the level in the regulator  chamber,
    permitting the desired quantity to be controlled
    with ± 7 percent accuracy. This quantity control
    is most desirable.
    4.   The same purpose as described in (3) may
    also  be  accomplished by means  of headwater
    actuation. In this instance, the float is retarded
    by weights which are  automatically picked up at
    predetermined intervals.  However,  this control
    requires a float of such depth that it will not be
    submerged under maximum storm conditions.
    Float-actuated regulators have been used for the
following reasons:
    1.   No outside energy source is required;
    2.   Accurate flow control over  a wide range of
    flow conditions on a presetting or semi-automatic
    basis can be obtained;
    3.   A wide range of sizes is available. One  firm
    produces more than 30 different models; and
    4.   Replacement parts are readily available.
    The  principal disadvantage of the float-operated
gate is  that  it  requires  a continuous preventive
maintenance program in order to function properly.
In Chicago, this problem was considered to be of such
magnitude  that all  127  float-operated gates were
removed in order to reduce maintenance costs.
Practices in Surveyed Jurisdictions
    A  total of 216 operating units are presently in
use in seven of the jurisdictions surveyed. Many of
these units  were installed more than 20 years  ago.
They  were  probably  applied  because  designers
favored regulators which operated without external
energy  requirements. These  units were considered
semi-automatic and capable of always  diverting a
portion  of  the  flow  to  the  interceptor.  The
mechanical  operation of the   regulator  was
intentionally  kept  simple in  an attempt to reduce
maintenance  problems  generated  by the  corrosive
sewer atmosphere.
    As the interception and overflow of sewage from
a combined sewer is controlled at individual locations
with this type of regulator, without regard to what
may be happening in  the rest of  the system, the
following  problem  occurred  in  one   surveyed
community where the  regulators  are actuated by
interceptor flow.
    A storm in the west part of the drainage basin
caused a  rise  in  the  liquid  level  in the  entire
interceptor system. This caused regulator gates in the
east part of the area to close and divert flow to the
river.  Thus, the treatment plant  was treating  storm
water from the west side, while sanitary sewage from
the east was being bypassed. It is recognized that this
condition existed because the regulator was operated
by conditions in the interceptor, but as these units
are now of an age to be replaced, that community is
studying the  feasibility  of replacing   them  with
remote-controlled, motor-operated gates.
    Originally,   float-operated  units  were supplied
with cast iron floats. These were so heavy that the
shutter side  of  the  pulley  system required
counterweights in order to operate effectively, and
the bulky system required considerable maintenance.
Such  floats are  now being manufactured of stainless
steel and counterweights have been removed from the
shutter side of the  system and placed  on the float
side, producing a substantial increase in  sensitivity of
gate operation together with a significant reduction in
weight of the apparatus.
    The  collection  of debris  in the float chamber
results in the buildup of material beneath the float. In
some  cases,  this  has  prevented  the   float  from
dropping to its seat, with the result  that  the regulator
gate remained partly closed and needless overflow of
sanitary  or  dry-weather flow occurred. To combat
this problem inexpensively, regulator stations in some
jurisdictions have  had asphalt and tar placed on top
of the float to  add  to its weight. In some cases, the
regulator has  been wired open, thus permitting the
unit to operate as a restricted vertical  orifice. This
problem  was  especially prevalent  in  large-size
regulators where float diameters were as much as five
feet.
    If the units are not, properly greased, an increased
depth of sewage  is needed to overcome the initial
inertia of the  float system, resulting in early overflow
of high-strength wastes. When the gate does move, it
moves very quickly, causing a quick reaction in the
regulator chamber  and,  to  some extent,  in the
upstream sewer system.
Costs
    In  1937,  Detroit installed  two  No.  12
float-operated  gates at  a cost of $41,300. In 1967,
two No. 12  float-operated  gates  and  their  special
structures were installed at a cost of $168,000.
    A regulator designed for an ultimate flow of 5 cfs
was installed  in an eastern city  in 1964. The costs
were  as follows:
      Excavation                    $34,200
      Chamber and regulator          23,000
      Tide gates                       12,000
      Total Cost                    $69,200
                                                    37

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 B. Tipping Gates
 Function
     The purpose of a tipping gate is to regulate flow
 through a  fixed vertical orifice.  Usually, the peak
 dry-weather flow is diverted from a collector sewer
 into a regulator chamber by means of a perpendicular
 weir placed across  the  collector sewer channel. The
 quantity  of sewage passing through the regulating
 chamber, it$ outlet orifice and connecting conduit to
 the interceptor is determined by the position of the
 tipping gate. During periods of wet-weather flow, the
 surcharge is carried over the dam and permitted to
 overflow to receiving waters.
 Description
     The  tipping  gate  regulator  consists  of  two
 chambers. The first, or diversion chamber, consists of
 a perpendicular weir,  the  crest  of which,  where
 combined sewer gradients are less than 1 percent, is
 often a maximum of 6 inches above the invert of the
 combined collector sewer. Peak dry-weather flow is
 thus diverted into the second chamber.  The weir is
 low-profiled  so as  to reduce   the  problems  of
 backwater damage  upstream. The collector channel
 may be depressed at the face of the weir, so that peak
 dry-weather  flow will  be  diverted  without
 overtopping the dam.
    The second chamber houses the regulator. The
 tipping gate consists of a  rectangular metal plate
 mounted  on  a horizontal axis and enclosed  in a
 casting so that the flow diverted to the interceptor
 must  pass  under  the  plate. Stops  on  the  casting
 permit manual adjustment of  the maximum  and
 minimum  opening. In  dry weather  periods  the
 resultant pressure of the water on the upstream side
 of the gate is below the horizontal pivot of the gate,
 thus keeping the gate in its maximum open  position
 and permitting all flow to  pass through the gate. In
 storm  periods  the  increase in water level in the
 combined sewer raises  the resultant pressure above
 the horizontal pivot of the gate, causing the gate to
 partially close  and limiting the  quantity  of flow
 diverted to  the interceptor. The gate opening is thus
 reduced but  due  to the greater head  on the gate
 opening the discharge  to  the  interceptor  may  be
 greater than  when the gate  is  at  its  maximum
 opening. The gate  is  set to remain slightly open,
 permitting  a  reduced but  continuous  amount  of
 combined sewage to be diverted to the interceptor.
    Following the storm, as  the flow rate diminishes,
 the  water level in  a diversion  chamber lowers, the
 force  against the  tipping  gate decreases and  the
 unbalanced gate reopens. The tipping gate regulator is
 a semi-automatic device requiring no floats, pulleys or
 outside energy source for proper operation.
Applicability
    Tipping gates have  been used to advantage for
flows greater than 4 cfs, where variable flow control
is required without instrumentation or automation.
The  regulator may be adjusted easily in the field by
adjusting  the gate  stop  disk  which  controls the
tailgate  opening.  This adjustment  may accomodate
diversion of increasing peak dry-weather flow in areas
where additional  domestic, commercial or industrial
sewage is being generated, without increasing the rate
of wet-weather flow diversion.
    In order to function as designed, the tipping gate
requires continual preventive maintenance, since the
gates are  located in  a highly corrosive atmosphere
which may cause  deterioration of metal components.
The  pivot shaft  must be lubricated, frequently to
prevent  tightening or freezing.  The device is also
subject  to clogging. The gate  faces  upstream. Its
component parts are, therefore, on the dry side of the
regulator chamber, facilitating maintenance.
    In summary, the  principal advantages of the
tipping gate regulator are:
    1.   Moving parts are simple;
    2.   It is  adjustable so that  flows to be diverted
    may be altered to fit changing conditions;
    3.   Extraneous power source is not required; and
    4.   Maintenance  can  be  performed on the dry
    side of the regulator.
    The principal disadvantages of this device are:
    1.  The gate and orifice may frequently clog;
    2.  Maintenance costs may be high; and
    3.  The pivot shaft may be subject to sticking,
    and surcharging of  the  interceptor or excessive
    overflows to receiving waters may result.

Practices in Surveyed Jurisdictions
     In  1959, ALCOSAN installed 147 tipping gate
regulators  at  major  collector-interceptor  sewer
junctions. These were designed to divert 2.5 times
dry-weather flow to the interceptor during periods of
wet-weather flow. Under  heavier wet-weather flows,
the gates  close, allowing 1.5 times dry-weather flow
to be intercepted. The orifice height when opened is
3 to 9  inches and when  closed  is 1 to 3 inches. The
latter restricted  opening may cause these units to
clog.
    ALCOSAN reported  the following reasons for
choosing this  type  of  regulator:  simplicity of
operation; adjustability  of maximum and minimum
discharge  to the  interceptor; servicing possible from
the  dry  side; hydraulic  application suitable  for
industrial development areas.
    Experience has shown that  debris collects in the
side clearances between  the tipping gate and  the
housing casting,  although this does not prevent the
gate from assuming a closed position. In some cases it
would not open automatically as the flow decreased.
In  the  original application, lubrication of the pivot
                                                   38

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                                                               FIGURE 10
                                                   STOP DISC BOLT
                                                              STOP LINK
                                TIPPING GATE



           USED BY ALLEGHENY COUNTY SANITARY AUTHORITY
Courtesy Rodney Hunt Co.
                                      39

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                                                                                         FIGURE 11
                            PHOTOGRAPH OF THREE TIPPING GATES,

                         ALLEGHENY COUNTY SANITARY AUTHORITY
 shaft did not prevent it from corroding and impeding
 the operation  of the gate. This problem has been
 diminished  by using bronze, bushings and stainless
 steel shafts.  Figure   10,  Tipping  Gate  Used  by-
 Allegheny County Sanitary Authority, shows a cross
 section of a typical gate. Figure 11 is a photograph of
 the gates.
    Milwaukee Sewerage  Commission  has  used  85
 modified tilting  gate  regulating stations,  but has
 found their maintenance so expensive that they are
 now replacing them with vertical fixed orifices. These
 regulators are not true tipping gates but function  on
 the tipping gate principle  and have historically been
 referred  to as "The Milwaukee  Regulator." In place
 of a sector gate, a leaf gate is used. Adjustment of the
 orifice may be accomplished by repositioning the
lower plate stop or by adjusting the bottom plate
Costs
    The  most  recently installed  tipping gates are
those used by ALCOSAN. The following 1959 costs
were reported by the Authority:
                    Gate
Chamber
                    $1,000     $ 20,000-50,000
                     2,500
  75,000
                     7,500      170,000
  Tipping gates—
   12 inch
  Tipping gates—
   24 inches
  Two 24-inch &
   one 36-inch
C. Cylindrical Gates
Function
    Cylindrical gate-type regulators consist of a dam
placed perpendicularly across the  channel at  the
invert  of a combined sewer, which diverts peak
dry-weather flow through a horizontal orifice located
above  the  interceptor.  The  flow  through  the
horizontal orifice may be varied by fully or partially
closing^ a  vertically  oriented,  cylindrical  gate
positioned  above  the  orifice.  During periods of
                                                 40

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                                    FIGURE 12
           CYLINDRICAL GATE
Courtesy Neyrpic Canada Ltd.

wet-weather flow, the surcharge is carried over the
dam to the outfall.
Description
    The  cylindrical gate  regulator  normally consists
of  two  chambers. The  first  houses the  diversion
equipment; the  second,  the cylindrical  gate and its
appurtenances. A third chamber may be used when a
tide gate is required to protect the interceptor from
in-flow from rising water  levels in the receiving waters
at the outfall. All chambers  should have separate
access points.
    The  diversion  chamber   contains  a  through
channel  and an  overflow  dam which diverts peak
dry-weather flow to the  adjacent regulator chamber.
    The  regulator  chamber contains  a vertical
hydraulic cylinder, the diameter of which is slightly
larger than the orifice below it.  The orifice is an
inverted truncated cone,  which may be protected by
a cast iron or stainless steel sleeve. The shape of the
orifice permits closure of the  gate, if required. The
cylinder is connected to a  stem and is controlled by
two guide  arms to a vertical fixed support. The upper
guide  arm  continues  past   the support  and  a
counterweight is suspended from  its end.  Neoprene
pinions  connect the guide arms  to the  cylindrical
gate, the fixed support and the counterpoise, so that
unrestricted movement is possible. Neoprene has been
used because  of its corrosion-resistant character. The
gate is sensitive  to variations in flow. Stop bars at the
orifice  will  prevent total  closure of  the gate,
permitting a  predetermined flow  to be intercepted
under wet-weather conditions. Figure 12, Cylindrical
Gate,   illustrates the  basic components  of  the
 regulator.
     Gate closure has a  tendency  to be sudden and
design modifications call for shock absorbers to be
installed from the fixed support to the cylindrical
gate to dampen the closure action.
Applicability
    The cylindrical  gate  may be  adjusted to be
sensitive to upstream or downstream flow conditions.
Upstream control is effected when the flow into the
regulator chamber exceeds the rate exiting  through
the orifice.  In this case, the sewage backs up in the
chamber. As the water rises above the cylindrical gate
head, its weight  and the velocity of water rushing
through the orifice overcomes the counterweight and
the gate  descends.  The volume of flow diverted is
controEed in design by the size  of the orifice used
and the weight of the counterpoise.
    When in the  closed position,  the remaining
wet-weather flow is  permitted  to   flow  over the
diversion dam and discharge to the outfall. When the
inflow  recedes and the head of water above the
cylinder  diminishes,  the counterweight opens the
gate.
    The interceptor flow may also be used to control
the operation of the cylindrical gate. In this instance,
an aspirator is linked between the cylinder gate in the
regulator chamber and the interceptor, with the open
end of the aspirator being located a predetermined
 distance below the crest of the interceptor sewer. The
 remaining configuration in the regulator chamber is as
 previously described. The gate is opened and balanced
 as long as the pipe to the interceptor can "breathe."
 When  the  flow  level in the  interceptor increases,
 covering the mouth of the aspirator, a partial vacuum
 occurs, pulling the cylinder down to close the orifice.
 In this application,  the  cylinder head is  partially
 submerged under peak dry-weather  flow conditions.
     Some of the advantages of the  cylindrical gate
 regulator are:
     1.  No mechanical moving parts-are submerged;
     2.  No  gear  or  chain-driven  mechanical
     components are required;                    \
     3.  Appurtenances are kept to a minimum and
     no floats  or float chambers, and their required
     maintenance are needed;
     4.   Capital cost  is  low for  an  adjustable
     mechanical device; and
      5.   Maintenance  costs are low, when compared
      to other mechanical gates.
      The  principal  difficulties encountered  in the
  application of these gates are:
      1.   Closure, unless  restricted,  can be violent,
      causing damage to the regulator, its components,
      or the orifice; and
      2.  The cylinder is very large in relation to other
                                                   41

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     mechanical devices. Adequate provision must be
     made  for  access from the surface in case the
     cylinder has to be removed or replaced.
 Practices in Surveyed Jurisdictions
     This is a newly developed regulator and presently
 is used only in Montreal on  this continent. Four
 regulator  stations each  house from one  to three
 cylinder gates in that city. They have been in  use for
 three  to   four -years  and  cost  from  $20,000  to
 $75,000,  including  all  structures  and  special
 appurtenances.  The units have  been  relatively
 maintenance-free.

        3. Dynamic Regulators-Automatic

 A. Motor-Operated Gates
 Function
    The regulator consists  of a perpendicular weii
 constructed across the channel of a combined  sewer,
 which  permits  peak  dry-weather  flow  to  be
 intercepted through an orifice. The orifice is sized to
 accept the maximum amount of combined sewage to
 be   intercepted.  Variations in  this  quantity   are
achieved by operating a motor-driven gate. During a
storm, quantities of  combined  sewage  greater than
that  acceptable  to the regulator are discharged over
the weir to the overflow. Figure 13, Motor-Operated
 Tainter  Gate,  is  a photograph of  a typical gate,
 usually constructed in a sewer to obtain the desired
 interception capacity.
 Description
    The motor-operated gate regulator  consists of
 three  chambers: one  for  diversion  purposes; the
 second for housing the gate and the orifice; the third,
 vertically mounted above the  regulator chamber for
 housing  the  energy sources.  A fourth chamber  is
 needed when tide gates are used.
    The  diversion  chamber contains a perpendicular
 vveir  placed  across the  combined  sewer  channel,
 which is used to divert the flow into the regulating
 chamber. The  height  of this weir  is  restricted to
 prevent backflooding of the upstream system.
    The  regulator,  or  gate chamber,  consists of  a
 channel with a  gate seated on the outlet orifice. The
 outlet orifice is connected by a branch conduit to the
 interceptor. The gate may be a sluice gate, connected
 by  a  stem through the roof of the chamber,to -the
 operating chamber.
    The   operating chamber  contains  a gearing
 assembly, an electrical impulse motor, such electrical
hardware as is required, and a gas or diesel standby
energy source. Corrosion can  be troublesome in the
humid, acid atmosphere of a combined sewer system.
                                                                                        FIGURE  13
                              MOTOR-OPERATED TAINTER GATE.
                                      •NEW YORK CITY
                                                 42

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When  this  chamber is located below ground,  it is
forced-air ventilated. The use  of dehumidifiers  may
also be a requirement. When possible, the chamber is
located above grade. Since the motor mechanisms are
separately housed apart from the regulator chamber,
the regulator gate functions even if submerged. Figure
14, Motor-Operated  Gate,  Municipality of
Metropolitan Seattle, is a detailed plan of a typical
installation as used in Seattle.
    The electric motor-driven gear assembly is of
heavy  cast iron mounted on a cast iron pedestal. The
assembly system is so set that the motor will attain
full-rated rpm before stem loading commences. Each
gear assembly may also be provided with a handwheel
or  crank of manufacturer's specification relative to
gate size, so that manual operation of the regulator is
possible.
    Limit switches  are provided  as an upper-limit
torque-governor, to protect the stem and gate against
damage  if  any obstruction is encountered  during
opening or closing operations of the regulator.
    Originally, motor-operated  gates were used where
maintenance  personnel  had  difficulty  manually
operating gates because of their size. More recently,
they have been  used as part of a system controlling
flows by remote control monitoring.
    The motor, and consequently  the regulator, is
activated by  a sensing probe, which records the
sewage level  in  the  control  section. When  a
predetermined maximum sewage level in the control
section is reached, the  sensor transmits a signal which
excites the  electric motor. The probe  may  also
transmit a continuous signal to  a remote location and
provide a record of flow levels and  gate operations.
Indications of operating problems, thereby, may be
transmitted  to maintenance  personnel as they occur.
Applicability
    Operation  of the gate may be controlled by
downstream or upstream flow levels, the former being
most commonly used. Under dry-weather flow, the
gate is fully opened and peak dry-weather flow is
intercepted. During periods of storm, additional flow
passes  through the openiqg to the interceptor and the
sewage level rises. At a preset level, the sending probe
signals  to, and activates the electric motor. The gate
then gradually  closes off a  portion  of the opening,
limiting the  flow to the interceptor. If the water level
in the  interceptor continues to  rise, the gate is closed
further.  This  procedure  continues  until a  stable
condition exists in the  interceptor. As the liquid level
in the  interceptor recedes below the previous level,
the process is  reversed  and the  gate  is gradually
opened. This  operation  is fully  automatic,
 consequently the gate will continuously "hunt" for
 the  most  advantageous position with  respect  to
 interceptor flow  conditions unless a time delay is
 imposed on the operating controls. Delays of three to
 five minutes have been used to decrease wear.
    The motor-operated gate  is  used where large
 quantities of combined  sewage are to be handled. It
.permits variation  in interceptor flows and overflows
 depending on the particular operating condition, and
 is readily adaptable to remote control. It is used for
 flows greater than 4 cfs, where automatic  regulation
 of intercepted flow is desired.
     The ability to remotely control  the interceptor
 system  flows and the flows to pumping  or  sewage
 treatment  facilities,  through  impulse  sensitive
 regulators, permits  maximum  utilization  of  the
 interceptor and collection  system storage capacity.
 This results  in  as full use  of  sewage  treatment
 facilities  as  possible  while  reducing,  within  the
 absolute  limits of the  system,  the  quantity, and
 improving the  quality  of overflow  discharged  to
 receiving watercourses.
     The benefit  of this  type  of  control  is  best
 exemplified in a test carried out by  Seattle (Metro)
 where  several motor-operated  gate   regulators  are
 installed. Recently, an overflow was monitored at an
 existing side-spill regulator for a period of one month.
 The  flow  exceeds the   downstream  interceptor
 capacity leight times in fiffe days during this period.
 The resultant overflow amounted  to  6.4  million
 gallons. A  mass  hydrograph was prepared  which.
 revealed that if motorized gates had been installed,
 overflows would have been reduced to one occasion,
 with a 2.7-million-gallon discharge.
     For small, locally concentrated  storms of high
 intensity,   overloading of  the  interceptor may be
 prevented  by temporarily restraining downstream
 flows by  remote  control and by fully utilizing any
 available storage capacity in adjacent  collectors. In a
 typical  installation there are two gates—one  to the
 interceptor and one to the overflow which will act as
 a tide gate. With both gates closed, collector storage
 capacity can  be  utilized. A weir  at  an  appropriate
 elevation is used to prevent backflooding. The  stored
 water can be bled into the interceptor as capacity in
 that main becomes available; when there is sufficient
 head differential the tide  gate is activated.
    Further advantages of the motor-operated gate
 are:
     1.   It offers ease of-operation for  large gates.
    2.   All major elements of  the  regulator are
    standard  manufactured  products, readily
    available from several sources.
                                                  43

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                                                                    FIGURE 14
                                  7 AND
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                                              U -'**-.'• -- •••	:
 C£U£KA~CK SET
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 couc PAD.
                                   MJUUAL

                                   6A T£
                                   Of£KA TO (A
  DRAI/J
BASC OF OUC T.
                                -40* CIA. 1UFLUEUT
                                 SLUICE GATE.
                               S4 X54' OUTFALL
                               5LU/C£ SATE
                                                                      •54" KCP
                      Motor Operated Gate
          MUNICIPALITY OF METROPOLITAN SEATTLE
                                 44

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    3.  Component parts for maintenance purposes
    are available from local stock supplies.
    The disadvantages include:
    1.  The opening is subject to clogging.
    2.  Electrical circuitry will fail from time  to
    time, consequently a standby generator must be
    provided.
    3.  Relatively high capital cost is involved.
    4.  Skilled technicians are  required to perform
    maintenance functions.
    5.  Preventive  maintenance programs  must  be
    established  to   insure continuing  operation  of
    sensory probes and their telemetric system.
    6.Special additional structures are required.
Practices in Surveyed Jurisdictions
    In Seattle (Metro), the regulator station at each
collector sewer to be intercepted is provided with two
automatically operated  sluice  gates. The  regulator
gate is  located in a chamber on an orifice  to the
interceptor. The gate is controlled by a downstream _
sensor in the interceptor. A tide gate  is located in
either  a  separate'  chamber  downstream  of  the
regulator diversion chamber or in the main chamber.
A sensory probe is located upstream of the gate in the
interceptor  and actuates  the motor drive when a
predetermined flow level is reached. Air bubblers are
used as sensory devices in the Seattle system.
    Under dry-weather flow conditions, the regulator
gate is  fully open and.  all sanitary sewage flow is
diverted into the  interceptor.  Under storm "flow
conditions,  the regulator gate  is closed a sufficient
amount to maintain a preset maximum flow level in
the interceptor. As the level in the collector rises due
to the flow restrictions through the  regulator  gate, a
preset liquid level may be reached downstream of the
diversion chamber, causing the  tide gate to open. If
the tide level is above  the gate face, an override
control  is  employed,  preventing  the gate  from
opening until the tide elevation has been exceeded by
the head in the collector.
    The  Seattle  (Metro)  system is not  yet fully
operational. Some of the interceptors being used are
part of an  older  system and are scheduled  for
replacement because they lack sufficient capacity.
This has resulted in the  regulator gate functioning
several hundred times per day, constantly  hunting to
relieve surcharging  on the interceptor and storing
some of the flow in the collector until the interceptor
flow subsides.
    Seattle  (Metro)  has  experienced  difficulty  in
stations where tide gates  are situated some distance
from the regulator station. Air bubbler sensors could
not function satisfactorily over the distance involved
 and,  consequently,  gates  were  not  actuated.  In
 addition, only one air line was provided and in the
 event  it became  clogged  or ruptured,  a  total
 shutdown in  the  regulator station'or  the  tide gate
 station resulted. Seattle officials recommended that
 operational units and gates be located as near to one
 another as possible,  and that a standby air line  be
 provided  between sensory devices and the operation
 chamber as an operational fail-safe procedure.
    Information about the system (power failures,
 high  wet  well,  open overflow  gates,  telemetry
 failures) is now telemetered to a receiving-recording
 unit at a  sewage treatment plant which is manned  24
 hours  per day. The  system  is  being expanded  to
 include much more  data and  future control by a
 process  control computer  at  a  different site  as
 described in Section 10.
    Chicago (MSD) operates 45 motor-operated gate
 regulator  stations, six of which house  tainter gates.
 The 39 remaining structures contain from one to four
 sluice gates. Eighteen  of these regulator stations are
 remotely  controlled.  Local officials  feel the  use  of
 remotely controlled  gates  provides  considerable
 flexibility to  the system  and  additional  units are
 being planned. The remaining 21 regulator stations use
 motor-operated  gates  because the  size of the gates
 involved  precluded  manual operation.  The  design
 criteria of the interceptor system are based  on
 handling two times the average dry-weather flow.
    Electrical failures  at  motor-operated regulator
 stations have been estimated to increase the incidence
 of malfunctions and  to require expenditure of five
 percent of the general maintenance budget.
 Costs
    Cost estimates are inconclusive because of limited
 experience and  the use of different cost bases for
 different  systems.  For example,  Chicago (MSD)
 reported  that regulator stations, including sensory
 devices  but excluding monitoring and remote control,
 cost between  $50,000 and  $200,000 each.  The
 estimate for  a regulator station built in Seattle  in
 1968  indicated  that the gate and frame,  including
 labor, materials, and installation, cost $17,800. The
 substructures  and  the   superstructure,  including
 mechanical and electrical installations, plus normal
 overhead, profit and  engineering costs, raised the
 total cost  of a regulator station to $142,000.
 B. Cylinder-Operated Gates
Function
    This regulator device consists of a perpendicular
weir constructed across a  combined sewer invert,
which  diverts  peak  dry-weather  flow through  a
vertical, fixed orifice with a variable opening to  an
                                                   45

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intermediate  conduit and  a collector sewer or an
interceptor. The dam is the diversionary device and
the variable orifice controls the volume of combined
sewage to be intercepted. During a storm, the excess
wet-weather flow  discharges  over the  weir  to
overflow.
Description
    This  regulator  may  consist  of two to  four
chambers: one for diversion purposes; the second for
regulation, containing a sluice gate, cylinder and float
or bubbler tube; the third for an equipment chamber
when electrical equipment is required; and the fourth
for a flap gate or tide gate chamber. On some deep
and large  chambers the  diversion and tide  gate
chambers may be combined, but the other  chambers
should  remain separate.  If possible, the equipment
chamber should be located above ground.
    The diversion chamber contains an overflow dam
to  divert the dry-weather flow by a 90-degree bend
through an  opening  into the  adjacent  regulator
chamber. The top of the diversion dam is usually set
not more than 6 inches above the invert of the inlet
sewer   to minimize  the  raising of  the flow  line
upstream of the regulator during storm flows. Other
design considerations, however, may require the dam
to  be  higher than this elevation  if no damage  will
result  upstream  from  raising the  flow line.  The
diversion channel invert  is established  so that the
peak  dry-weather  flow will  be diverted without
overtopping  the  dam. During wet-weather periods,
the excess  flow  goes over the  dam  through the
opening in  the  wall to  the flap  gate chamber and
thence into the  receiving  waters.  The  opening
between the diversion chamber and flap gate chamber
is equipped with one or more flap gates.
    The  regulator  chamber  contains  a
cylinder-operated  sluice  gate  which  governs  the
amount of flow to the branch interceptor. The action
of the  cylinder  is related to the sewage level in the
sewer by a sensing device which can be used either
upstream or downstream of the sluice gate. The latter
location is used if the main objective of the regulator
is to avoid overloading the interceptor and treatment
plant.  Generally,  the  sensing device is  a  float  or a
bubbler-tube  through  which  compressed  air  is
continually  pumped.  The  cylinder is  operated by
pressure from either water, air or oil. Floats are used
in  conjunction  with  cylinders  operated  by water
pressure  to  avoid the addition of compressed air
equipment.  During dry-weather periods,  the sluice
gate is wide open. In wet-weather periods, the rising
sewage level will raise the float or  pressure in the
 bubbler tube so that the gate will partially close. The
float  or bubbler  tube is  located  in  a float  well
connected to the flow channel by a telltale passage.
    When the sensing device is located downstream of
the gate it is generally necessary to install a control
device to maintain subcritical flow in  the regulator
chamber. One type of control which is found to be
satisfactory is the  use of vertical timber stop logs to
decrease the channel width. A vertical slide gate can
also be  used as a control to act either as a weir or an
orifice on the  bottom  of the  channel. The  use of
vertical wood stop logs has the following advantages:
The width of channel opening can be adjusted in the
field; and there is nothing to impede the discharge of
debris which may be carried along the bottom of the
channel or may be  floating on the flow.
    While the  hydraulics of the  regulator  can be
computed, adjustments are  usually required  in the
field to suit actual flow conditions.  Usually the  float
or bubbler-tube is set  to act when the flow  level is
about one inch above  the  actual peak dry-weather
flow  line to make sure that all dry-weather sanitary
flow will be diverted to the interceptor.
    Water used as a medium is usually obtained by
connection to a public water supply. Some engineers
frown on such a  connection even  though provided
with  backflow preventive devices. Since the pressure
in the water system may vary, the hydraulic cylinder
is usually designed to operate on a minimum pressure
of 25 psi. For small gates this pressure is adequate but
for  large  gates this  would  require  a very  large
hydraulic cylinder. None of the commercial hydraulic
cylinder manufacturers will guarantee  cylinders for
water operation.  Therefore, the gate  manufacturer
either  builds  the cylinder or goes to  a specialty
manufacturer.  The chief advantage of  the  use of
water is that no electrical power is required and hence
the regulator will not stop functioning  due to power
failure;  and  a separate chamber is not needed for
installation  of  air compressors  or  electrical
equipment. The chief disadvantage is  the required
connection to  a public water- supply, the possibility
of  contaminating the system  by  such  physical
cross-connection and the possibility that the regulator
will not function  due to insufficient water pressure.
    Tightening of the  packings around  the piston rod
and tail rod, if overdone,  may increase the  friction
forces. Sometimes valves become inoperative due to
rust or  scale in the water supply. To prevent this, a
strainer should be  installed  in   the  supply  line;
however,  clogging   of  the  strainer  may  cause
malfunction of the gate.
     When air is used as a medium for operating the
 gate, a separate chamber should be provided for the
                                                   46

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air compressors  and electrical  equipment. Air has
been used at  pressures of  90  to 100 psi.  The
disadvantages of this system are that electrical power
is required which  is subject to failure; a separate
chamber must be provided to house the electrical and
compressed air  equipment; and difficulty may be
encountered in  maintaining electrical equipment  in
subsurface chambers. Recently some cities using air
pressure for cylinder operation have converted to oil
pressure.                      . .. .'
   , Recent practice in  cylinder-operated gates tends
to favor, oil as a medium rather than air or water. Oil
has been used at pressures of 350,750, and 3,000 psi
but pressures from 600 to 750 psi seem to be favored.
To avoid corrosion, a  separate chamber, preferably
above ground, should be provided  for electrical and
pumping  equipment.  The use of oil results in less
corrosion of valves and cylinders than the use of air
or water. Smaller cylinders are needed to operate the
gate due  to  the  higher   pressures  used.  The
disadvantages are the same as  those for air cylinders.
Applicability
    The hydraulically operated gate  is used for flows
greater  than 4  cfs, where  automatic regulation of
intercepted flows is 'desired. Since it is a self-enclosed
system, it continues to  operate even if submerged. In
addition,  in  areas  where  peak  sanitary  flow  is
increasing  due to  additional  domestic,  commercial
and  industrial  development,  the  regulator may be
adjusted  easily  in  the  field  by  varying the float
setting.  The units have the additional advantage of
operating automatically or being controlled remotely
if  the  water-cylinder  types are  replaced  with
oil-cylinder units. This indicates a ready  adaptability
to total systems control.
    The disadvantages  of this  type of installation
center around the  water requirement for operation
purposes. The hazard  of cross-connection  to the
public water supply system has been pointed out.
Proper  design of water actuating facilities can and
must  provide  fail-safe  protection  against  such
cross-connection hazards. In many locations, making
water available  is  a problem due to  the remote
location of the  regulator unit. Since water supply
systems also may be subject to breakdown^ there will
be times when adequate  pressure may not be available
for operation purposes. Problems of incrustation of
cylinders may be experienced  where water is used as
the medium.
Practices In Surveyed Jurisdictions:
    New  York  City operates  126 float-actuated,
hydraulically operated cylinder gates  for flows greater
than  4  cfs.  Usually,  the structure consists  of  a
 diversion  chamber; regulating chamber; and  a  tide
 gate chamber, if necessary. In some deeper and larger
 chambers, the diversion and tide gate chambers are
 combined. The regulator,  however, is always housed
 separately.
     The  crest of the diversion  dam  is set 6  inches
 above the  invert  of  the  combined  sewer.  The
 regulator  is  designed  to   intercept two  times  the
 average  dry-weather  flow. .After  completion,  the
 regulator is adjusted so that it .will start to close the
 gate when the flow level in the regulator chamber is
 one  inch above  the  peak dry-weather flow.  The
 'hydraulic cylinder is operated by use of city water at
 a minimum  pressure of  25 psi. Check valves  and
 vacuum breakers provide adequate protection against
 any possible  cross-connection hazard, in the opinion
 of the city's engineering personnel.
     New York City is presently considering the use of
 telemetric monitoring equipment for  central control
 of the interceptor system. Separate  chambers at each
 regulator  site will permit operator surveillance  and
 control of gate positions, continuous monitoring and
 consequently, maximum  utilization of the  sewage
 treatment  capacities.  City  officials  oppose  the
 housing  of  electrical  equipment  in the  regulator
 chamber  because it cannot be maintained  in  the
 corrosive atmosphere.                    '
     In Philadelphia,  a  number  of units  are  in
 operation which have dual hydraulic cylinders for the
 operation of both sluice gates and tide gates. This use
 is shown  in  detail in Figure 15, Cylinder Operated
 Gate  Regulator,  Philadelphia.  Under normal
 conditions, the small gate is open  and the tide gate
 closed. With the rise in elevation of combined sewage
 in the float-controlled  chamber during a storm, the
 float rises, allowing water  pressure  to  be transmitted
'through the four-way valve to, the top of the cylinder
 controlling the sluice gate, thus causing it to close.
 Simultaneously, water pressure is exerted on the head
' of the large cylinder, the  stem of which is attached
 through the sewer wall  to  a tide  gate. When pressure
 is exerted, the tide  gate opens, causing an overflow.
 The procedure reverses as the flow rate decreases.
     Eight modified float-operated hydraulic cylinders
 are  also used in Philadelphia. These consist of a cast
 iron stand on which is mounted a four-way valve; on
 top  of the stand is a counterweight arm attached to a
 float rod, and on the bottom of the stand another
 arm  is attached  to the  float rod. Travel can be
 adjusted by a stem  on the base  of the stand. Water
 supply is connected to  the four-way valve. A second
 line  from the valve  is  attached to the top  of  the
.hydraulic  cylinder,  the third to the bottom of the
                                                  47

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                                                   FIGURE 15
 VITRIFIED PLATE LINING
                                     6-6" X7-0"
                                     TIDE GATE
   GALV. PIPE
TO FLOAT WELL
                             PLAN VIEW


CYLINDER-OPERATED GATE  REGULATOR
           PHILADELPHIA
                         48

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hydraulic cylinder, and the fourth acts as an exhaust,
discharging to the regulator chamber channel. In the
chamber, this unit is  mounted on a bench alongside
the float well. The float well is open. At the discharge
end  of the  chamber,  an adjustable orifice plate
protects the fixed vertical orifice, controlling flows to
the  conduit connecting  the   chamber  and  the
interceptor.  This  orifice  plate   may be  manually
adjusted to control the amount of combined sewage
to be intercepted. When the inflow to the regulating
chamber exceeds the  outflow capacity, as restricted
by the orifice plate, the water level in the  float well
rises, operating the float and actuating the hydraulic
cylinders.
    In Omaha, 28 oil-operated hydraulic gates are in
service; 25  of these  are  at collector-interceptor
junctions and three protect pumping stations. These
bypass flows  in excess of 3:1 WWF:DWF ratio are
centrally controlled.  It is the opinion  of the city
officials  in Omaha  that  one dynamic, automatic
regulating unit such as this can equal the performance
of  many   static  devices  due to its flexibility.  In
addition,  it  utilizes  the  storage capacity  of  the
system, with a resultant reduction in overflows and
their pollutional effect on the receiving waters.
Costs
    Capital costs of  these devices in  1964 ranged
from $25,000 for 4-cfs units, to $70,000  for 50-cfs
units in  the New York area. Omaha reported costs
varying from $10,000 to $120,000, with the  average
cost in the $10,000 to $20,000 range. Costs for units
associated  with pumping  facilities  in  that city
averaged approximately $50,000.
Why Were Particular Regulators Selected?
    Static devices were generally selected on the basis
of their economy and on the presumption that they
would be maintenance-free.
    Semi-automatic, dynamic  regulators  were
selected because they offered greater'protection to
the downstream interceptor system and the pumping
stations  at  waste  water  treatment  facilities  by
automatic partial  closure  of  the  gate, thereby
restricting  the orifice and reducing the effect of
upstream head increases. Settings for gate positions
could  be  adjusted  by  maintenance  personnel to
accomodate variations in sanitary sewage flows.
    Remotely controlled automatic regulators were
selected to provide flexibility in the system, positive
control  of  intercepted  flow and  reduction  of
overflows.
What Were the Results of These Selections?
    Static devices, on the whole,  function best as
overflow  regulators  in  the  upper regions  of  a
collection system.  They may be used economically to
prevent surcharging  of  existing combined sewers.
Dynamic  regulators at  these locations  may  be
economically unjustifiable, and, generally, they are
too space-consuming  to be practical.
    On the collector or interceptor system, static
regulators  may  be  used  as  overflow  diversion
structures, where backwater from the receiving body
is. not a problem. Best  suited  for  this application
would be siphons.  They should be located well above
invert level and below top water level to avoid, as far
as possible, the carry-over of either  heavy or floating
solid  matter.  Use  of a  scum board could further
reduce the carry-over of floating matter.
    Semi-automatic regulators are true regulators, in
that they  can control  the  maximum amount of
combined sewage  being  intercepted under low and
high  upstream head conditions by automatically
assuming one of two gate positions without requiring
external energy for operation.
    Remo'te  controlled  automatic regulators  can
effectively utilize the full capacity of the interceptor
and treatment facility while making use of the storage
capacity  of the collection  system and  reducing the
quantity of  overflow. Used with  retention  tanks,
storage of first-flush  flows for pumping back into the
interception system when the storm flow recedes is
also  feasible. Fully automatic gates are  also used on
inlets  to  pumping  stations  and sewage treatment
plants. In this case, they  act not as  regulators, but as
protective overflow devices.
                                                  49

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                                              SECTION 5
                       PERFORMANCE OF REGULATOR FACILITIES IN SERVICE
    A  regulator should make as much use  of the
capacity  of  the interceptor  as  possible without
surcharging  it or  causing  dangerous  hydraulic
conditions  in  upstream  collecting  sewers.  Flow
variations through the interceptor should be as small
as possible to prevent operational fluctuations at the
treatment  facility.  Undiluted  sewage should be
delivered to  the interceptor and sewage  treatment
facility. The  regulator device should be  sized and
located to  minimize malfunctions,  such as clogging
and jamming  with the solids and debris indigenous to
combined sewer flows. Frequent malfunctions can
result  in backflooding  of  collector  sewers,
dry-weather  overflows,  excessively  long and
over-frequent  wet-weather  spills  and subsequent
unnecessary  pollution loading on  the  receiving
stream.
    A well-designed regulator station could make use
of scum boards or overflow baffles or other facilities
designed  to  prevent  floating  materials  from
discharging to the receiving stream during  periods of
overflow, and to improve the quality of waste waters
discharged to receiving waters. Automatic regulators,
such as motor-operated gates, have  the advantage of
being operated  in  the  fully closed or fully open
positions  or  at intermediate  points  depending on
upstream  and  downstream  flow  conditions.  By
varying the orifice,  any available storage capacity in
the  upstream collector  system  can  be  used
temporarily   until   the  flow  level recedes  in  the
interceptor.  This type of  operation, with central
monitoring control, lends itself to "total systems"
control of the collector-interceptor sewer network as
a whole. This  temporary  storage has the effect of
reducing the  quantity of overflow and consequently
reducing the pollution loading on the receiving waters
at the outfall.
Location of Regulators
    More than two-thirds  of  the regulator  sites
investigated in the  National Survey were  located at
collector-interceptor junctions. Table 8, Locations of
Regulators  on Systems,  indicates the locations of
regulators on combined sewer systems. A total of 639
of 678 or 94 percent of  the  semi-automatic and
automatic   regulators,  were located  at  the
collector-interceptor junction points. Other regulator
locations, such as on the collector, on the interceptor,
at pumping  stations, and at  the treatment  plant,
demonstrate the use of these devices as an emergency
measure to prevent local surcharging or overloading
of treatment facilities. It is significant that 636  of
664, or 95.8 percent of the  emergency diversion
structures, located  on  the  collector  or  on the
interceptor,  were inexpensive, non-controlled, static
devices.
    The National survey indicates that only 2 percent
of  the  regulator  devices are  located at pumping
stations or treatment facilities. It is probable that this
percentage would be somewhat higher, if cognizance
is taken of the existence of some form of emergency
overflow protection at these, locations.  Since such
devices  at  these  locations  were  acting solely  as
diversion structures and not as  regulators, they have
only indirect bearing on the findings of the study  of
regulator practices.
Wet-Weather and Dry-Weather
Design Factors and Performance
    Table  9, Relationships  Between  Precipitation
Events  and   Number of  Overflows  for  Six-month
Period,  Allegheny  County Sewage , Authority,
indicates that, although intensity and total rainfall are
important factors, they are  not the total cause  of
overflow events. Other factors, such as ground slope,
elevation of the water table, length of time between
rainfalls, the effect of freezing or near-freezing soil
temperatures, the amount of impervious  area in the
collection  basin and the characteristics and direction
of the particular rainstorm, will all have an effect on
the  amount of  wet-weather flow reaching the
combined  sewer system and, consequently, on the
incidence of overflows. The accepted generality that a
precipitation  rate  of 0.04  inch  per  hour  will
universally result in overflow spills can no longer be
accepted,  as  evidenced by  the  Table  and  as
corroborated in other sewer monitoring experiences
investigated in the  National Survey. For example, the
Metropolitan Corporation  of  Greater Winnipeg
reported that the critical precipitation rate was 0.08
inch per hour.
    Each system and, in fact, each subsystem has its
own individual characteristics. The condition which
will  prompt functioning of overflow devices  requires
individual  engineered investigation.
    The survey shows that ratios of wet-weather flow
to average dry-weather flow were determined on the
basis of hydraulic conditions for each system, rather
than  by  regulator types.  Design  criteria for
interceptor system and 'pumping station or treatment
                                                   51

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                             TABLE 9
                RELATIONSHIP BETWEEN PRECIPITATION
                 EVENTS AND NUMBER OF OVERFLOWS
                      FOR SIX-lViONTH PERIOD-
               ALLEGHENY COUNTY SEWAGE AUTHORITY
Precipitation
Total
Rainfall
(in.)
.03"
.05"
.07"
.07"
.09"
.11"
.12"
.13"
.14"
.15"
.17"
.19"
.21"
.21"
.25"
.27"
.28"
.31"
.49"
.51"
.53"
.60"
.64"
.64"
.66"
.73"
1.13"
1.35"
1.76"
Maximum
Intensity
(in/hr.)
.01"
.02"
.03"
.07"
.05"
.11"
.08"
.11"
.14"
.08"
.17"
.05"
.13"
.08"
.14"
.13"
.05"
.14"
.32"
.09"
.25"
.47"
.12"
.11"
.52"
.57"
.55"
.61"
.29"
Number of
Structures
Inspected
10
42
37
37
39
20
33
65
37
83
58
59
67
58
26
37
45
22
55
57
82
57
86
87
40
57
51
85
80
Number That
Did Not
Overflow
8
13
29
10
22
8
19
24
14
47
37
31
28
12
3
20
19
10
13
31
18
4
30
31
3
12
0
8
2

Percent Not
Overflowing
80
30
78
27
57
40
58
37
38
56
64
53
42
20
12
54
42
45
24
54
22
7
35
36
7.5
21.5
0
10
2.5
                               53

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 plant capacity were determined without respect to
 the  type of regulator  being  used. For example,
 ALCOSAN  uses  tipping gates  and vertical orifices.
 Tipping  gates are designed to  deliver 2.5  times the
 ultimate design average dry-weather flow during peak
 flow periods. Orifices intercept 2.5 times the average
 dry-weather  flow to  the interceptor  and throttle
 down to 1.5 times the dry-weather flow during peak
 runoff periods.
    The  City of New York utilizes cylinder-operated
 gates, manually-operated  gates and vertical orifices.
 All are designed to divert two times dry-weather flow
 to the interceptor system. Detroit uses float-operated
 gates,   orifices,  cylinder-operated  gates,  and
 manually-operated gates. All are designed to intercept
 1.5 DWF. The determination of WWF:DWF ratio by
 system rather than by  regulator type was common to
 each surveyed community.
    Characteristically, the volume of flow diverted by
 a static  regulator is a function of the  head on the
 device. As the surcharge on  the regulator increases,
 the  flow increases  at the treatment  facility:  For
 example, New  York  has found that  its  vertical
 orifices,  although designed to  intercept 2 x DWF,
 actually intercept five to 6 x DWF during periods of
 runoff. Cleveland designed its side-spill weirs to divert
 2.5 x  DWF, but recent measurements indicate that
 flows of 9  x  DWF have been  intercepted during
 wet-weather  periods.  This type  of experience is
 typical for  the static  regulators encountered in the
 survey.
    Semi-automatic regulators are set for dry-weather
 and  wet-weather flow  conditions,  and  will
 automatically hunt  for either position depending on
 the flow rate. As stated, at ALCOSAN, tipping gates
 are set to divert 2.5 x DWF to  the interceptor; when
wet-weather flows exceed this  design limit, the gate
automatically "tips," partly  closing  the orifice  and
 throttling the flow to 1.5 x DWF. As the  surcharge on
 the  upstream side  of the regulator increases,  the
added head may increase the WWFrDWF ratio above
 1.5, but the interceptor system design  rate is  not
exceeded.
    Cylinder-operated gates used in New York City
similarly   throttle the  regulator  gates. These  are
actuated  automatically  by a float control upstream of
the regulator gate in order to prevent surcharge of the
downstream system.
    Automatic  regulators  which  are  remotely
controlled and equipped with level sensors upstream
and  downstream  of the  regulator station may  be
paced or actuated by  flow levels in  the interceptor
and in the collector system.
      To varying degrees, all regulators are capable of
  dividing the flow between the interceptor and the
  receiving waters,  but  none  has the capability as
\ presently  designed  and operated  to   divert only
  sanitary sewage, suspended solids, and floating solids
  to the interceptor system and permit clearer, more
  dilute liquids to overflow. An engineering approach
  to  this  type of  separation  has  been  tried  in
  Minneapolis. It involves the installation  of  a "sewer
  within a sewer," with the sanitary flow carried in a
  lower quadrant of the dual line and the higher flows
  of the storm water  runoff jumping vertically to the
  upper sewer section.
  Evaluation of Regulator Performance
  by Jurisdictional Personnel
      Information obtained from surveyed jurisdictions
  concerning  the performance  and  operation  of
  regulators indicates the inadequacy of attention given
  to this service problem. A total of 414 questions were
  asked of respondents concerning performance at the
  local government level.  .These inquiries  could have
  been  answered if observations  and measurements
  were being made on such systems. Less  than  50
  percent  (187) of these  queries were answered and
  many of the  responses were of such general nature
  that they were neither qualitative nor quantitative in
  character. Table 10, Evaluation of Performance and
  Operations of Regulators by  Types, as reported by
  Surveyed  Jurisdiction  Personnel,  presents  the
  expressed opinions by surveyed system personnel on
  the performance of regulators currently in use. It
.: represents  their satisfaction or dissatisfaction with
  their maintenance  practices  and  the   ability  of
  regulators to effect control of the flows- intercepted
  and the flows diverted to receiving waters.       :
     The findings indicate that static  regulators give
  limited satisfaction, that semi-automatic regulators
  give average performance, and that automatic devices
  perform most satisfactorily.
  Relationship between Types of
  Regulators and Precipitation
     Table   11,  Relationship Between  Types  of
  Regulators and Annual Precipitation, and Table 12,
  Relationship  Between  Types  of Regulators and
  Maximum  Rainfall,  represent  an effort to correlate
  the selection and performance of regulators, by types,
  with  average  annual  precipitation  and maximum
  rainfall rates.
     The  total  annual  rainfall  in  the  surveyed
 jurisdictions varied from 20 to 60 inches per year.
  However, no  indications were given that regulator
  selection  was  made on the basis  of  expected
  precipitation  experiences.  Comparison  of  data  in
                                                   54

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Table  11  with  the  'evaluation  of  regulator
performance in Table  10 indicates that total annual
rainfall in the ranges experienced does not, in itself,
influence the performance of the  different types of
regulators used.
    Table  12  demonstrates no apparent selectivity
pattern for a  particular type of regulator to  meet
rainfall rate conditions. Furthermore, no reactions
were  expressed  by  the  personnel of surveyed
jurisdictions as to the  performance of devices under
different rainfall intensities.
Effect of Infiltration on Regulator Performance
    The report  on  "Problems of Combined  Sewer
Facilities  and  Overflows,  1967," indicated  that
infiltration in excess of design,criteria is  widespread,
but follows no particular pattern. In 85 communities,
representing 14 percent  of the total respondents,
ground water infiltration was listed as a problem in
dry-weather flow periods. Wet-weather ground water
infiltration  was  reported  as  a  problem by  331
jurisdictions,  representing  53  percent  of those
responding  to  the query. Twenty-nine  percent of
those  reporting  indicated that infiltration exceeded
code  or design limits; 36 percent stated that it did
not; and 35 percent had not established the degree of
infiltration and were unable to evaluate the effect of
infiltration  on the frequency or period of duration of
overflows.
    By accepted definition, ground water infiltration
does  not include water entry into the  collection
system via  actual sewer connections, such as  roof
leaders and basement  and foundation drains, or
through manhole covers.
    If  infiltration  is  occurring during  dry-weather
flow  periods,  dilution  of sewage  directed  to the
interceptor  system  will occur,  sewage 'treatment
operation costs  will  .increase,   and  dry-weather
overflows may  occur  during  peak-flow  hours.
Infiltration  occurring  during  wet-weather flow will
increase the volume of overflows and produce further
dilution in the flow to  the treatment facility.
    In summary, reduction of infiltration by better
sewer design   and construction  methods,  better
jointing practices,  and  other  efforts to  create :
watertight  sewers in modern  design would result in
fewer overflow incidents, and of lesser duration.
Role of Regulators in Projects Sponsored  by FWPQA
    The  Federal Water  Quality  Administration,
(FWQA), in recognition of the pollution problem
caused by  untreated waste waters  discharged from
combined sewers, has  provided financial aid through
grants and contracts to stimulate the development of
projects which  will demonstrate  new or improved
methods of controlling the discharge of untreated or
inadequately  treated  sewage or other wastes from
sewers which carry storm water. The main thrust of
this research and development program to resolve the
combined sewer problem has been  the development
and  demonstration of techniques  and hardware  to
improve system efficiency  and minimize,  if not
completely control, overflow discharges.
    The demonstration projects being carried out
involve  the application of two new regulating devices.
Fluidic Devices
    A  study  is presently  being  carried  out  on
development  of a flow separator  operating  on the
fluidic principle that a jet stream attaches itself to the
wall of a flat nozzle and remains there because of the
stable,  dynamically formed  and sustained pressure
gradient across the fluid stream.
    The three basic elements of a fluidic device are:
    1.  The bi-stable diverter, basically a Y-shaped
    element, the throat of which by design acts as the
    nozzle and the legs  of which enable a single
    stream to be diverted to either or to variations
    thereof;
    2.  The control ports, one on either side of the
    throat,  and immediately  in   front   of  the  Y
    diversion.  Fluid from the nozzle is diverted into
    either  of  the two output legs by varying the
    atmospheric pressure at either control port; and
    3.  The discharge weirs, which  are located at the
    end of the legs of the Y and  dampen the  flow
    from critical to normal velocity.  '
    Figure  16,  Schematic Arrangement—Fluidic
Interceptor  Sewer  Flow  Control—Single  Sensor,
illustrates a possible configuration for the  use of this
device.
    The principal  identifying  characteristic of a
fluidic device is the elimination or great reduction in
the number of moving mechanical parts.  Given the
proper  natural fluid-dynamic  conditions,  physical
phenomena perform  functions normally  requiring
moving parts. Preliminary investigations indicate that
the physical operating principles of a fluidic system
are  not size-limited;  in  fact, some become more
effective as size increases.  Consequently,  there may
be  a particular advantage to  the  application  of a
fluidic  device  to  separate normal combined sewer
flows, particularly with respect to  materials  used in
construction, size of apertures, omission  of
mechanical parts,  and suitability for replacement of
existing regulator devices.
Inflatable Fabric Dams
    A demonstration grant project is being carried
out  by the  Minneapolis-St. Paul  Sanitary  District
                                                   58

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                                                                           FIGURE 16
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                                       59

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providing for the use  of inflatable and deflatable
dams of rubberized fabric which, by remote control,
can  utilize  the  storage capacity  of  the  collector
system as a direct means of controlling the amounts
of  wet-weather  flows  to  regulator structures and
thereby limit the volumes overflowing to receiving
waters. By coordinating the operation of these fabric
dams, the maximum in-system storage possible may
be  utilized  by  taking  advantage  of the hydraulic
capacity in the "total" system.
Demonstrating Improvement in Overflow Quality
    Demonstration grant  projects also  are  being
sponsored by FWQA to ascertain the feasibility  of
processes for improving the quality of the overflows
from combined sewers. These projects include the
following:
Retention Tanks
    Projects involving  retention  or  storage  of
combined sewer  overflows are located at Chippewa
Falls  and  Milwaukee, Wisconsin,  Boston,
Massachusetts,  and  Shelbyville, Illinois.  In-system
storage in deep tunnels  in Chicago will accomplish a
reduction in receiving water pollution while reducing
local flooding.
Microscreening
    Microscreening,  using a nominal  23-micron
aperture screen, is reported to have removed up to 98
percent of the  suspended solids from a combined
sewer overflow.  The sewer,  which  has  an average
sanitary sewage flow of 1,000 gph, serves a residential
area of, 11 acres in the City of Philadelphia, Pa. The
maximum  combined sewer  flow  recorded  during
rainstorms in one year of operation has  been 305,000
gph. Volatile suspended  solid removals have averaged
68 and 71 percent during different test periods. BOD
removals and coliform bacteria concentrations in the
microstrained  effluent  have varied widely  and
chlorination  of  the  effluent  appears necessary for
disinfection. First costs indicate this technique will be
approximately  50 percent  cheaper  than  sewer
separation in the 11-acre district studied.
Void Space Storage
    The  City of Akron recently has  been granted
funds  for  a  demonstration  project  to  install  a
gravel-filled, rubber-lined retention tank. The rubber
lining at  the base and over  the  gravel  acts as a
membrane seal, forming an enclosed filter bed tank.
Tank capacities are created in the  interstices  of the
aggregate particles. The necessary intakes, outlets and
valving  are  provided within  the  tank. The  upper
membrane is covered with soil; the surface  of the
underground  facility  may be used for  park and
recreational areas.
    These  efforts  to  develop and demonstrate
workable  methods  for  the  improvement  of the
quality  of waste  waters which  overflow  from
combined  sewer  systems  indicate  the  growing
realization of the need to incorporate quality control
with  the  quantity  control provided  by regulator
devices. This concept has been outlined in Section 2
of the report and described as the "Two Q" concept.
They also have indicated the important role that the
regulator must perform to assure proper functioning
of the combined sewer overflow treatment facilities.
Automatic-Automation Instrumentation Applications
    To reduce  backwater flooding of  building
basements and surcharging  of pumping stations and
treatment  facilities,  and  to  prevent unnecessary
overflows,  centrally  monitored  information  is
required concerning  precipitation events  within the
natural drainage basin of a combined sewer system, as
well as flow conditions at critical points within the
collector-interceptor  system. This  information,
coupled with  the ability to regulate  the combined
sewer  flow by  remote control,  could offer the
greatest possible  utilization  of the  combined sewer
collection-interception system. Some of the potential
benefits derived  from the application and use of
automatic-automation-instrumentation  procedures
and devices are:
    1.  Malfunctioning regulators may be  detected
    quickly  and repaired.
    2.  Regulator  gate ports may  be  adjusted
    remotely,  providing  optimum  utilization of
    interceptor and treatment plant capacities.
    3.  The flow to the interceptor from various
    collection  system locations can be coordinated to
    fully use interceptor capacity and thereby limit
    surcharging downstream.
    4.  The first-flush phenomenon,  if present, or
    some variation of the solid-slugging phenomenon,
    can be delayed in the collector, with heavy solids
    diverted to treatment when interceptor capacity
    is available.
    5.  In-sewer  flow  routing is possible to divert
    runoff from  overloaded  sewer sections to
    conduits  simultaneously experiencing  less
    loading. This  would minimize  local surcharges
    due to small spot storms which may not affect
    the system's entire contributary  area, and would
    prevent pollutional impacts of overflows.
    Instrumentation   and remote  control  of  a
combined sewer  regulator  system could  lead to
greater utilization of each  part  of  the system, and
result in fewer overflows, better and more economical
sewage  treatment plant operation,  and a general
                                                  60

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reduction in pollution loading of receiving waters, all
at costs far below that of sewer separation.
    An engineering study of each  combined sewer
system would be required to  indicate the equipment
and operating procedures  which are most applicable
to that particular system.
    The elements of total system control are:
    1.  Measurement—A probe or sensor is used to
    gather specific information such as water levels in
    collectors or interceptors, flow rates,  regulator
    gate position, and rainfall intensity.
    2.  Data  Communication-Ths specific system
    information is  transmitted over  some  type of
    communication channel; the telephone system is
    most  frequently  the  most  available   and
    economical medium of communication.
    3.  Data Collection-lbs specific information-is
    received by recorders or computers so that it may
    be  summarized  and  collated.  Emergency
    information is often translated to some form of
    alarm system to institute immediate attention.
    4.  Decision-On  the   basis  of  the   collated
    information, a reaction decision is necessary. This
    may  be made manually  by  the  operating
    personnel;  or  by means of  computer program
    control  of such functions as the  activation of
    pumps,  the chlorination  of  the  overflow,  the
    utilization  of the interceptor  capacity, or the
    opening  or  closing of tide gates  by operating
    personnel or remote control means.
    5.  Evalwtion-On  the  basis  of  the  revised
    information,  conditions  are  deemed  to be
    satisfactory  or the data show that further control
    is required.
    6.  Feed-Back-The  system  probes or sensors
    measure the changes that have taken place due to
    the above corrective action.
Ponsar Siphon
    The Ponsar Siphon was developed in France and
is named for its inventor.  It operates on the principle
that flows through the  siphon are controlled by the
presence or  absence of air  pressure  at the siphon
head.  The  Ponsar  regulator  is  essentially  a
vacuum-operated, balanced air valve, which responds
to the vacuum intensity and liquid level in the siphon
chamber. The air valve is  normally  closed and opens
only  in response to siphon conditions as required to
maintain the design flow-through by admitting air,
thereby  preventing  vacuum  intensity  in  excess of
desired design conditions. It consists  of two basic
elements: a  regulator valve which has a floater at the
top of the valve immersed in oil over a mercury seal,
with  a connecting shaft to an air inlet valve at the
bottom;  and a level-sensing pipe assembly with its
lower  end  inside the  separate chamber where  a
water-filled  plastic bag is attached at the bottom. A
level-sensing tube is installed inside the level-sensing
pipe. The water-filled bag is sensitive to variations in
air  pressure and the level  tube rises  or falls  with
similar changes in liquid level. Figure  17, External
Self-Priming  Siphon,  indicates   the various
components of this type of regulator.
    This regulator  is  in  use  in   France  and
Switzerland. Construction of a demonstration unit in
this country has not been undertaken.

                 Existing Practices
    Caught and  ever-increasing   demands  for
controlling pollution iri  receiving waters, a number of
jurisdictions  have either  installed, or are  in  the
process of installing, some  type of remote control
system.

    In Akron, all the interceptor inlet  locations and
pumping stations which serve the  sewer system are
monitored  by  a  supervisory system  comprised
essentially of sensing probes set  at predetermined
high-water level;  remote transmission  units to  send
signals over telephone lines to the central station; and
a central receiving station.
    Incoming signals are indicated on a graphic panel
equipped with audible alarms and  recorders. By this
means maintenance department  personnel can be
made aware that the flow depth has come up to the
level of the probe, that overflows are occurring, and
corrective action may be required.
    In Detroit, a monitoring and reporting system  is
being constructed in order that information will be
made available on what is occurring in the system,
and sewer system personnel will be able, on the basis
of such knowledge, to control the system as a whole.
    This system  will monitor the rainfall  and its
intensity at a number of points throughout the city;
monitor  the depth of flow in all the major combined
sewers at various points; measure the,depth of flow
along the interceptors, and  control pumping stations.
    This information will be transmitted to a central
station, along with continuous data on  the condition
and operation of the various pumping stations. The
system  has been designed  so  that reports, will be
transmitted normally on an hourly basis, but this will
be increased to  15-minute intervals when the rain at
any station  exceeds 0.03 inch per hour. If the  flow in
any combined  sewer exceeds the dry-weather flow,
the interval will be  reduced to five  minutes. The
controller will then be  able to follow  the course of
                                                  61

-------
the storm  across an  area and determine  how the
various  collectors  and  interceptors  react  to  this
condition. On the basis of this information, decisions
can then be made concerning system changes. Further
reference  to  the Detroit system  is contained  in
Section  10 of this report.
    A   total  system  control  program  is being
developed  by  the Municipality  of  Metropolitan
Seattle.  The  Minneapolis-StPaul Sanitary  District
control program has already been placed in operation.
These are also discussed in Section 10.

               Field Survey Results
           Performance and Operation
    Questions  asked  in the  National  Survey  on
regulator  performance  were  concerned with
malfunctions  and  overflow  durations and
characteristics. Many  of the responses  were of a
general  nature, based only  on  estimates  by the
personnel  of the surveyed jurisdictions, rather than
on actual operation records.
    The type and frequency of a malfunction of the
various types of regulators is an important indication
of their performance capability. Malfunctions were,
in the majority of cases, due to clogging. Table 13,
Summary of Regulator Malfunction Experiences, by
Types, summarizes the frequency of malfunctions per
year for the various types of regulators. The findings
by regulator type were erratic and in 42.7 percent of
the  regulator  installations  the  frequency of
malfunctioning was unknown.
    Tables 14  through 22  summarize performance
and  operation  data obtained for various  types of
regulators in the jurisdictions surveyed during the
course of the project.
Perpendicular Weirs, Orifices and Drop Inlets
       Due to the similarity of operation of drop
inlets,  perpendicular  weirs,  and  vertical  and
horizontal orifices, they have been grouped together
for the purposes of evaluation. Although all of these
regulating devices are  susceptible  to  the problem of
clogging,  the field results  indicated  that the vertical
orifices were deemed to perform more  effectively
than the  drop inlet type of regulator. In part, this
may be due to the increased frequency of drop inlet
malfunctions.
    The  information  as  tabulated in Table  14,
Performance  and Operation  of  Orifice  Regulator,
covering  the surveys  concerning  the frequency and
duration of overflows, indicated a range of 30 to 100
                                                                                          FIGURE 17
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                                                 62

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occurrences per year, some of these overflows lasting
as long as several days. In one instance, a 170-hour
wet-weather overflow was,recorded. In the majority
of cases, duration and frequency were determined by
means of inspection, although an alarm system was in
use in one of the  surveyed  systems. The  National
Survey  disclosed the  limited  information  that, is
available on this subject. Although 11 of the surveyed
jurisdictions had one or more of these alarm devices
in  use,  only  five  of  these  communities had
information concerning the duration and frequency
of  overflows  during  dry-weather and  wet-weather
periods. Even in some of these limited cases, the data
that were provided by the local personnel were based
solely on estimates. Better record keeping practices
are needed.
Leaping Weirs
    Leaping weirs  were  rated  satisfactory,  within
certain limitations, in the  surveyed systems although
one community  reported this type of regulating
device to be unsatisfactory.
    Since the  information pertaining  to  the
performance  of this type of regulator  was available
from only one of the  five communities  in which it
was used, the results must be considered to be of only
limited value and dependability. As indicated in Table
15,  Performance  and Operation  of Leaping
Weirs—Cleveland, malfunctions occurred 40 to  50
times per year  and  were  attributed  mainly  to
clogging,  a  problem  that  was  common  to  all
jurisdictions surveyed.
Side-Spill Weirs
    With regard to performance, the side—spill weir
was regarded  as similar to the leaping weir in the
surveyed communities. In no case, however, was this
regulator felt to be unsatisfactory.
    There  was  a wide  variation  in frequency of
malfunction of this type of device,  ranging from
"rarely" in one  case, to  90 incidents per year in
another community  as  indicated in  Table  16,
Performance  and  Operation  of  Side-Spill  weirs.
Similarly, a wide discrepancy was  reported, ranging
from "never"  to daily  during periods of dry-weather,
and "seldom" to  150 per year during wet-weather.
Duration of overflows ranged from several hours to
several days. Because of the wide differences in local
condition and the limited data, the information is of
limited value.
Float-Operated Gates
    Generally,  float-operated  gates  were  not
considered to perform satisfactorily. Three of the
seven surveyed  jurisdictions regarded  this  type of
regulator to be in the category of "unsatisfactory."
One jurisdiction has replaced these units, due to the
frequency of malfunction, and in others the gates
have been wired open so that they  perform like
vertical orifices.
    The most common complaint, once again, was
clogging;  the  frequency of this  problem  averaged
approximately once per week as shown in Table 17,
Performance and Operation of Float-Operated Gates.
    Wet-weather overflows varied from 15 per year in
Montreal to a maximum of 150 per year in Cleveland.
The validity of national conclusions is doubtful, since
few surveyed jurisdictions had information available
on  this phase of regulator practice. The information
that was gathered in the field surveys was the result
of a combination of both inspection and estimation.
No automatic recording devices were reported to be
in use  in the surveyed communities. The duration  of
both  the dry-weather  and wet-weather overflows
ranged from a fraction of an hour  to several days, an
experience quite similar to that reported for the trther
types of regulators.
Manually Operated Gates
    The  five surveyed jurisdictions that utilize this
type of  regulator considered it to be satisfactory,
although several did express the opinion that it has
certain limitations with regard to performance.  In
rating  the various regulators surveyed in the cities,
this  device  was  generally  considered to  be  as
acceptable as fully automatic devices.
    Table  18,  Performance  and  Operation  of
Manually Operated Gates, indicates that malfunctions
due to clogging were reported to be once or twice per
year by  two  of  the surveyed jurisdictions.  This
estimate  was assumed  to  be • a   reasonable
approximation for malfunction expectation of this
device.   The   lack   of dependable  information
concerning  frequency  and duration  of overflows
makes any more definitive evaluation unwarranted.
Siphons (Internal Self-Priming)
    The  single surveyed jurisdiction  which
commented on siphon regulators reported that they
were   an  unsatisfactory  means for  diversion and
regulation. The survey data  indicated that clogging
problems  were responsible for malfunctions, but no
data   were  available  on the  frequency  of this
condition, nor was any information disclosed on the
duration or  frequency  of  overflows  during
dry-weather and wet-weather periods.
Cylindrical Gates
    This type  of regulator has  been in service for
approximately four years, and has been tested in only
one   surveyed  community.   Consequently,
performance  evaluations  must be considered  only
                                                   65

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preliminary in  nature.  Because  of the  size  and
shearing force of the gate, and because  of the shape
of the opening to the interceptor sewer, few problems
have been experienced  in  relation  to  regulator
clogging.  Infrequently, these regulators have  been
jammed open  by  a large obstruction,  permitting
excessive diversion to the interceptor.

    At the WWFrDWF settings currently employed in
Montreal, as indicated in Table 19, Performance and
Operation  of Cylindrical Gates, approximately  five
overflow  events have occurred  per year  at  each
installation. These  events  are split evenly between
summer rainfall, and spring thaws accompanied by
rainfall.

    To date, no dry-weather overflows have occurred
there. Monitoring  reveals if the regulator has been
actuated.
Tipping Gates
    Table 20, Performance  and Operation of Tipping
Gates, indicates that  the two surveyed  jurisdictions
utilizing tipping  gate regulators  regard  them  as
satisfactory. Clogging was  reported to be  the most
common cause  of malfunction, the frequency being
reported as an  average of five instances per year.
Additional information concerning overflows was not
available,  although one  jurisdiction  reported that
overflows during  dry-weather periods seldom
occurred and were of limited duration.
Motor-Operated Gates
    The two jurisdictions which -utilized this type of
regulator  considered  it to  be  satisfactory.  The
frequency  of malfunction  was reported to vary as
indicated in Table 21, Performance and Operations of
Motor-Operated Gates. One system reported only one
to two occurrences per year, and the third reported
the frequency of malfunction  to  be approximately
three times per month. In one jurisdiction an alarm
system was  utilized to  record the frequency and
duration of wet-weather overflows. Records indicated
that the duration ranged between 6 and 15 hours.
Cylinder Gates
    This fully automatic device was, on the average,
considered satisfactory in performance by  the five
surveyed jurisdictions  in which it  was used.  One
jurisdiction reported  it  to  be   quite  effective.
Malfunctions, due to clogging,  lack of water supply
and mechanical breakdown, were considered possible.
Although  little information was available regarding
frequency of malfunctions, as indicated in Table 22,
Performance and Operations  of Cylinder-Operated
Gates, the  satisfaction  with which these units are
viewed would seem to indicate that such difficulties
are relatively infrequent. Two Jurisdictions reported
malfunctions once or twice per year. Two reported
that overflows occurred during wet-weather periods,
but additional information concerning duration and
frequency of overflows for other installations was not
available.
                                                  68

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                                              SECTION 6
                                   MAINTENANCE OF REGULATORS
    To the extent that maintenance determines the
capabilities of its  performance,  no device is better
than  its  maintenance. In  the  case of  regulators
installed  in  combined  sewer systems, the nature of
their location, the characteristics of the liquids they
handle,  the  conditions under  which  they  must
bperate and other factors make maintenance practices
of  great  importance.  One of  the  determining
factors—but not  the  only  factor—in the  choice of
regulator equipment must be the anticipated nature,
frequency and cost of maintenance, and the resulting
performance  of the chosen device: For this reason,
the  National  Survey  placed great emphasis on
national maintenance experiences and practices.
    One  of the findings of the survey was that few
jurisdictions  vary  their maintenance practices for
different  types  of  regulating  devices.  Rather,
maintenance  policies for all regulators,  regardless of
type,  have been arbitrarily  established.  Maintenance
costs,  when reported, were frequently  given  in
lump-sum amounts. Unit   costs  related to specific
functions were unavailable or undependable.
    As a rule a specific number of work  crews follow
a routine maintenance  performance check for each
regulator  and  its  appurtenances. Preventive
maintenance  programs were reported by  several
surveyed jurisdictions, but  this  was not a universal
practice.  The  value  of preventive  scheduling  of
regulator inspections and attention, and sewer system
cleaning and maintenance work was demonstrated by
the national survey.
    The  number of visits per year to each regulator
station depends' upon the community's policy for
inspecting its system;  this policy rarely  bases its
inspection requirements on  the types of regulators in
service. Frequency of maintenance  varies widely. For
example, two jurisdictions  surveyed, located within
three  hundred miles of each other and having similar
climatological  conditions,  utilize similar  design
criteria for combined sewers and their appurtenances.
A particular  regulator type is common to the two
communities,  both  maintained  with  two-  or
three-man crews; and both express satisfaction with
the total performance of the  regulator. However, the
policy of one jurisdiction is  to inspect  its regulator
sites on  the  average of seventy-five times per year,
regardless of regulator type,  while the policy of the
other is to check each regulator  site from twenty to
thirty-five times per year.
    As a  consequence of  these  differences  in
maintenance procedures, annual cost  of maintenance
by  regulator  type  and  scheduled  number  of
maintenance  visits  per  year  by regulator  type is
difficult to analyze and evaluate. The national survey
brought to  light many  weaknesses in maintenance'
procedures and a significant lack of authentic data on
costs,  practices and  results.   Actual  maintenance
practices, by regulator types, are summarized in Table
24,  Frequency  of  Regulator Maintenance-inspec-
tion—by  Types. The annual  maintenance cost  per
regulator unit, by  types, is  reported in Table 25
Summary  of  Annual  Unit Maintenance  Costs—by
Types. The  data on costs contained in this section
have  been  derived in many  cases,  from  .local
operational and manpower estimates.

               A. Static Regulators
Vertical Fixed Orifices and Siphons
Reasons for Malfunctions
    The  principal  problem  encountered with both .
vertical fixed  orifices and siphons is the clogging of
their openings. This is particularly serious within the
curved throat of a siphon, since clearing of debris is
often difficult and time-consuming and it cannot be
carried out  during wet-weather flow  conditions.
During periods of malfunction little or no combined
sewage can be  discharged  to the interceptor  and
excessive  overflows  result.  Figure  18, Clogging of
Orifice, illustrates  a typical situation where a grate
became clogged and a dry-weather overflow occurred.
Figure 19, Overflow Screens, shows the clogging of an
open wire mesh placed to attempt to catch debris on
the overflow.
Maintenance Requirements
    These  types   of  static regulators  may  be
effectively maintained by a crew of two or three men
who visit each regulator site  30 to 35 times per year
on a regular basis, and  following  each storm. Hooks
may be  used to advantage to  remove  debris  and
unblock the  orifice. The regulator chamber usually
requires  cleaning  after a   storm.  Three  effective
cleaning  procedures  encountered in  the national
survey are: washing down  the chamber with-water
from the  city supply;  using  a compressor  and air
nozzles to blow small  debris  into the dry-weather
channel; and using a vacuum tank truck of the type
used to remove debris from catch basins.
                                                  71

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                                      TABLE 24
            FREQUENCY OF REGULATOR MAINTENANCE-INSPECTION, BY TYPES
  Type of Regulator
Maintenance Insp./yr.
                                                                                    Total

Static
Orifice
Drop Inlet
Leaping Weir
Manually Oper. Gate
Side-Spill Weir
Siphon
Sub-total
Semi-Automatic
Float-Oper. Gate
Tipping Gate
Cylindrical Gate
Automatic
Cylinder-Oper. Gate
Motor-Oper. Gate
Sub-total
Total Regulators
Percent of Total
0-15 16-30 31-45 46-60

129 (2)

7 (2)
345 (2)
11 32 (2)

11 513

56 (3)

7

126
45
108 126 -
11 621 126
.4 24.8 5.0
61-75

150 (2)





150

44
147




191
341
13.6
>75


38
73

14

125

13



6
8
27
152
6.1
Unknown

338 (6)
242 (4)
109 (2)
15 (3)
302 (2)
26
1032

97 (2)
85


44 (3)

226
1258
50.1


617
280
189
360
359
26
1831

210
232
7

176
53
678
2509
100
                                      TABLE 25
               SUMMARY OF ANNUAL UNIT MAINTENANCE COSTS, BY TYPES
                              Annual Maintenance Cost Unit
  Type of Regulator   0-$200 $201-$400 $401-$600 $601-$800 $801-$1000 >$1000  Unknown
NOTE: Number of Reporting Jurisdictions Shown in Brackets

                                          72
                                     Total
Static
Orifice
Drop Inlet
Leaping Weir
Manually Oper. Gate
Side-Spill Weir
Siphon
Setni-A utomatic
Float-Operated
Tipping Gate
Cylindrical Gate
Automatic
Cylinder-Open Gate
Motor-Oper. Gate
Total Regulators —
Percent of Total —

67
58
6

14



85




230
9.2

254 (3)


3
79 (2)


44
147


1

528
21.0


141
73
288 (2)



129 (2)



21
53 (2)
705
28.1

296 (6)
38 43 (2)
110 (3)
62 7
266 (3)
26

17 (2) 20 (2)

7

126 28

243 803
9.7 32.0

617
280
189
360
359
26

210
232
7

176
53
2509
100

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                                                                                 FIGURE 18
                                      CLOGGING OF ORIFICE
Cost of Maintenance
    The annual maintenance cost for these regulators
was  consistently  reported in the order of $700 to
$900 per unit per year.
Horizontal Fixed Orifices (Drop Inlets)
    In all  applications surveyed where drop inlets
were  used, except  at  the  Minneapolis-St.  Paul
Sanitary District, the orifice was protected by a grate.
Comments hereafter, take that fact into consideration.
Reasons for Malfunctions
    The drop inlet regulator grating is particularly
susceptible to  frequent  clogging with  leaves, rags,
plastics, sticks and other debris.
Maintenance Requirements
    Operating personnel reported that drop  inlets
require almost constant maintenance. In Akron, each
unit  is serviced daily and some large drop  inlets
require cleaning even more frequently. Maintenance
personnel  reported  that they had no assurance that
clogging would not  recur immediately after cleaning.
    Two-  to  three-man crews are used to maintain
these regulators.  A two-man crew consists of two
laborers, while  a  three-man crew  consists of two
laborers and a technician. Their principal function is
to scrape the grates clean. In this case, the debris
must be lifted to the surface for final disposal. As a
minimum, grills  and chambers must be cleaned on a
weekly or bi-weekly basis.
Cost of Maintenance
    Because of the need  for regular maintenance, the
annual service cost is relatively high. Cost estimates in
the order of $1,200 to $1,500 per unit per year were
reported to be not unusual.
Recent and Proposed Changes
    In order to  reduce the maintenance burden and
to  improve  operating  characteristics,  two  recent
proposals  should  be  considered:  that  the  space
between bars of the grating be increased, so that at
least smaller objects will not cause malfunction; and
that   flow levels  in  the  regulator  chamber • be
monitored  so that maintenance  personnel may be
alerted  in  case  of blockage  during  periods  of
dry-weather flow,  thus  eliminating prolonged
overflows of sanitary sewage.
                                                   73

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                              FIGURE 19
OVERFLOW SCREENS
                 Debris Captured
                 from Overflow
    74

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 Side-Spill Weirs
 Reasons for Malfunctions
     Side-spill weirs are subject to an accumulation of
 trash on the upstream face  and on the downstream
 end  at  the toe.  Since these  regulators are usually
 equipped with an outlet pipe, clogging of this conduit
 is also a problem. The weir crest must be rebuilt from
 time to  time  and can be damaged by large heavy
 objects carried in wet-weather flows.
 Maintenance Requirements
     The  side-spill  weir  regulator  is . relatively
 maintenance-free, requiring  only  periodic  cleaning
 and removal of accumulated debris. When the crest of
 the weir is damaged, reconstruction of the brick
 course or other material is necessary. The procedures
 may be performed by a two-man labor crew.
 Cost of Maintenance
     On the average, side-spill weirs cost $400 to $500
 per annum to maintain.
 Manually Operated Gates
     The principal maintenance problem encountered
 with manually operated gates  is clogging  of the
 orifice.
 Maintenance Requirements
     This  regulator may be  adequately maintained
 with a two-man  labor crew,  or a three-man  crew
 consisting of two laborers and one technician. Repairs
 and adjustments to the device are minimal, although
 the  gearing and  gate  stem  must  be kept  weE
 lubricated. Wall brackets are particularly susceptible
 to corrosion and require frequent attention. Clearing
 of blockages in the orifice can often be accomplished
 by  raising the gate. If this is not successful,  a hook
 may  be  used to dislodge  the  blockage.  General
 cleaning of the regulator chamber is usually required
 following every storm.
    Inspections are carried out  on a regular basis, on
 the order of 15 to 30 times per year.
 Cost of Maintenance
    The  average  cost  of  maintaining  a manually
 operated gate regulator and chamber was reported to
 be from $900 to $1,000 per year.

     B. Dynamic Regulators-Semi-Automatic
 Float-Operated Gates
Reasons for Malfunctions
    Float-operated   gate-regulators  have  many
components and consequently  require a preventive
maintenance program carried out on a regular basis in
order to assure proper functioning. Some of the.types
of malfunctions common to this device are: blockage
of the gate with wood; accumulations of rags or other
storm debris; clogging of the float well, causing the
 gate  to rest  continuously in its  closed position;
 accumulation  of sludge on the float, preventing the
 float from rising and resulting in the gate remaining in
 its open position at all times; guide chains slipping off
 gear  wheels;  breakage  of the chain; corrosion  or
 incrustation between  moving and stationary parts of
 the gate; rusting of chains and .pinions, causing gear
 wheels to jam; and clogging in the telltale pipe.
     With the exception of clogging in the float well
 or  at  the gate,   these  problems  do  not  occur
 frequently, provided maintenance is carried out on a
 regular or preventive basis.
 Maintenance Requirements
     Float-operated  gates  can be maintained  by  a
 three-man  crew, consisting of two  laborers and  a
 technician, plus a  supervisor who  oversees several
 similar operations.  The additional technical assistance
 is required due to the complexity of the regulator.
 Typical maintenance  operations include  removal of
 blockage and debris; cleaning  of grit and grease from
 the float well;  lubricating of metal parts, particularly
 friction areas;  repairing  or replacing chain links; and
 general  cleaning of the  regulator  chamber. Large
 gates, because  of their weight, should provide clear
 access directly  above the gate so that adequate rigging
 or a truck-mounted crane can  operate  the  gate or
 remove it if this is required.
    Regular inspections should follow each rainstorm
 because clogging and  debris problems will be  most
 common  at  those times. Detroit- reported  that
 approximately  five percent of their units  require
 servicing   after  each  rainfall.  Regular  weekly
 inspections  should also be made, to serve as the basis
 for a preventive maintenance program.
 Cost of Maintenance
    The annual maintenance cost for a float-operated
 gate was reported  to  be  approximately  $1,000  to
 $ 1,200 per station.
 General Comments
    Local  authorities  stressed  the   degree  of
 maintenance required  to keep these units in good
 functioning  condition,  and  the  cost  of this
 maintenance.  Three jurisdictions,  in   particular,
 expressed concern  over  this type of regulator. The
 first estimated  an annual maintenance cost of $350
 per float-operated gate unit. The second community
 had operated these  regulator units for 50 years and
 for the past ten has wired them open. In the third
jurisdiction, the units were more than 30 years old
 and were given only sporadic maintenance.
    The  national  survey  indicated  that
 semi-automatic  or  automatic regulators  are  not
 successfully  maintained for less than $800 per year,
                                                  75

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as compared with successful maintenance programs
on static devices at a cost of approximately $350 per
year.
    The  effective life  expectancy  of mechanical
equipment housed  within  a  sewer system  and
subjected to its  corrosive  atmosphere may not be
more  than  25  years. However, 80  percent of the
float-operated  gates in  service in  the surveyed
communities were reported to be more than 30 years
old.  These devices may  not be   in  serviceable
condition. Approximately 50 percent were described
as more than 40 years old.
Tipping Gates
Reasons for Malfunctions
    The  most  common  maintenance  problem
associated with this  type of  regulator is blocking of
the gate orifice. This occurs  most frequently during
and  after  heavy storms.  In addition,  debris  may
collect between  the tipping gate and its side wall
casting. This is difficult to remove by hand. Friction
on the leaf pivot shaft due to lack of lubrication is a
problem peculiar to  the  tipping  gate  regulator.
Although lubrication may be carried out frequently,
the pivot shaft is alternately submerged and exposed
to  the air. Alternate wetting  and  drying in this
particularly  corrosive  atmosphere damages  the
lubricant and results in deterioration of the shaft and
the potential freezing of the gate. Malfunctions occur
most frequently after heavy rains.
Maintenance Requirements
    The most  successful  tipping gate  application
surveyed is at ALCOSAN, where the maintenance
program requires that each regulator structure be
visited  at   least  every   other week. The  average
frequency  of servicing is 75  to  100  times per year.
Authority  representatives reported that maintenance
work was required to restore operation on an average
of 10 percent of the maintenance visits. The crew was
reported to have removed  large pieces of wood, tin
cans, and other debris in front  of the gate opening.
Some debris which had become jammed between the
gate and the sidewall casting required compressed air
jetting  for removal.  Removal of  other debris was
carried out with a rodding tool or hook. The pivot
shaft was greased regularly.
    The maintenance crew  used  for all regulator
installations at  ALCOSAN  is  comprised  of one
maintenance   superintendent, one maintenance
foreman and 18 maintenance men.
    Because of  the corrosion problem  of the leaf
(gate)  pivot shaft,  ALCOSAN specifications  have
provided for the  use of bronze brushings on stainless
steel  shafts. This has  corrected  the  problem
effectively.
Cylindrical Gates
    Cylindrical gates  are  recent  developments and
have  only  lately been  used  on  the  American
continent.  Experience is  limited to six  units  in
Montreal which have been in operation less than three
years.  As a  consequence,  insufficient maintenance
data upon which to base  a valid  assessment of this
type of regulator are available at this time.
    To date, clogging of the  orifice has not been as
great a problem  as experienced  in that  city with
float-operated gates. This is probably due to the fact
that the orifice is  circular and the gate is poised a
minimum of  5 inches above  it.  With the cylinder
restriction at the centre of the orifice, its diameter is
large in relation to the flow-through. Consequently,
partial blockage may occur but complete blockage is
rare. The weight of the cylinder makes it possible to
shear off any partial obstruction  when closing, or if
further opened, the size of the orifice can usually pass
all  but larger timbers. No  instance  of complete
blockage  was  reported at any  Montreal  regulator
station.
    The gate  cylinder is  particulary  heavy and
cumbersome, and consequently, special trap doors are
required at the roof of the chamber for removal of
the equipment or  for special maintenance purposes.

        C. Dynamic Regulators-Automatic
Motor Operated Gates
Reasons for Malfunctions
    The most common causes of malfunction of this
device is  clogging or blocking at the gate opening,
electrical failure due to corrosion  on circuit contacts,
partial blockage or collapse of compressed air lines,
and power failure where standby generators have not
been provided.
Maintenance Requirements
     One  community  is   working  with  the
motor-operated gate  on  a systems  control  basis;
another is using motor-operated gates in another form
of control. Maintenance practices on both systems are
described here.
     At Metropolitan Seattle, gate operation is fully
checked once a week and  emergency power is  tested
for  a one-hour period.  Originally, the emergency
power was set by a time  clock to operate one hour
per week. However, this system did not test the gate
operation under  hydraulic loading. This has been
rectified. The telemetry system is checked every three
weeks and  the drive  gears on the Limitorque are
                                                   76

-------
 checked  on  a  six-month preventive maintenance
 schedule.
     Potential problems with the air compressor used
 as  part  of  the  air-bubbler  sensing  system  are
 anticipated by determining if there is an increase in
 the hours of compressor operation per day.
     At the Metropolitan Sanitary District of Greater
 Chicago,  the  motor-operated  gates  are  remotely
 and/or locally controlled. Remote control permits the
 treatment plant or pumping station operator to limit
 the amount of combined flow to be intercepted. Each
 installation is checked monthly  and following all
 major storms. Additionally, overflows are checked by
 boat and helicopter to disclose regulator malfunctions
 and improper discharges.
     Regular maintenance visits require the testing of
 dehumidifiers,  heaters,  water level  recorders,
 telemetry  equipment, and other  facilities.  Gate
 openings  are  reset at design requirements on an
 annual basis.
 Cost of Maintenance
     The devices reported  in the Chicago and Seattle
 systems are relatively new and, consequently, annual
 cost of maintenance as reported is probably lower
 than will be  the case after several years of service.
 Seattle reported five hours of maintenance work per
 month per regulator station and Chicago reported a
 cost of $60,000 per year to maintain a total of 660
 regulator  stations,  328  of which  are  tide  gate
 installations.
 Cylinder-Operated Gates
 Reasons for Malfunctions
    The types of malfunctions encountered with the
 cylinder-operated gates are: clogging of the  orifice;
 clogging of the float control, preventing the gate  from
 closing; excess weight from accumulations  of grease,
 rags and other debris which  prevent the float  from
 rising, thus keeping  the   gate  in  closed position;
 clogging of the strainer on the water supply line to
 the  four-way  valve; breaks or  leaks  in  the water
 supply line; wear and leaking of the four-way valve
 and its appurtenant items; leakage of the  hydraulic
 cylinder;and insufficient water pressure—less than 25
 psi-from the public water supply. Such conditions as
 accumulations of debris on floats can be minimized
 by proper design and effective maintenance.
    The sensing devices and their electronic or  air
 compressor  systems are  subject to corrosion and
 clogging of bubbler-tubes.
Maintenance Requirements
    Cylinder-operated gates are maintained by a four
 or five-man crew: a foreman, technician and laborers.
    In New York City, each crew uses a specially
 designed truck with winch, generator, blowers, pumps
 and safety equipment. They spend approximately 85
 percent of their time on regulator maintenance.
     Special inspections follow each rainstorm when
 the  regulator  and its appurtenances are checked for
 damage. A general check of all sensing equipment,
 cleaning of gate orifice of any clogging, and general
 cleaning of the regulator structure are required. Twice
 a month, preventive maintenance is carried out on the
 operating devices.
 Cost of Maintenance
     New York City's  budget  appropriation in  1969
 for  operation  and maintenance of regulators was
 $300,000.  Of this amount, $159,000 was provided to
 maintain 126 float-operated gates.
 Proposed Changes
     New York  City is  considering installation  of
 telemetering in  connection with  one  regulator  in
 which the water cylinder layout will be replaced with
 oil-cylinders. Since the city feels electrical equipment
 cannot be  maintained in a regulator chamber, this
 equipment  will be separately housed. If below grade,
 the  chamber requires heating and  forced ventilation
 and  dehumidification  equipment.  Because  of  this,
 some communities locate the chamber above grade,
 wherever possible.
    Maintenance  personnel  have  suggested  that
 operating pressures of no more than 600 psi be  used
 to facilitate maintenance procedures.
 Equipment Used for Maintenance Work
    Although  regulator maintenance  practices  and
 policies  vary  from  city to  city, the  equipment
 supplied  to maintenance  crews  follows  a  common
pattern. The  following  items are  typical of a
well-equipped maintenance program:
    •  A specially designed 1%-ton panel truck with
    winch and A-frame
    •   110-220-volt portable generator
    •   1 or 2-hp blower unit
    •  Various  chains, ropes,  hoses, ladders,  pike
    poles, sewer hooks, sewer rods, chain jacks,  tool
    kits, and related items
    •  An  oxygen deficiency  meter,  an explosive
    and toxic  gas meter, safety equipment, helmets,
    harnesses,  first  aid  kits,  danger  flags, signs,
    barricades, life jackets, flares, gas masks, gas
    detector lamps,  fire extinguishers, extension
    cords, rubber jackets, pants, boots,  and waders.
    •  Equipment  such as air  compressors, truck
    pumps,  diagraph pumps bucket  sewer  cleaning
 .   machines,  and chain saws may be available from
    an equipment pool.
    Some jurisdictions also provide their maintenance
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crews with air packs.
    Figure 20, Derrick Barge and Boat for Regulator
Maintenance, is a photograph of equipment used by
ALCOSAN  to  maintain  regulators  which  are
accessible only from the river. Figure  21, Loaded
Derrick Barge, shows the variety of equipment used
for  maintenance,  including  a bucket-cleaning
maqhine.
    Figure 22, Swamp Buggy, is a photograph  of a
vehicle  used by the Metropolitan  Sewer District of
Greater  Cincinnati  to  maintain  structures  located
along  streams: The wheels of  the  Buggy are the
flotation units. A small  crane is mounted on the rear
and a large pump is mounted on the frame.
Structural Design to Facilitate Maintenance
    Maintenance personnel  are critical  of regulator
structures  which provide inadequate space for safe
 and effective maintenance work. The survey disclosed
 that, too frequently, capital cost economies are  given
 major  priority  and  the  cost  of maintenance and
 operation  is left to  the maintenance superintendent
 to work out as best he can once the installation has
 been  completed. This  was  characterized by
 respondents to  the survey as an expensive and  futile
 procedure. As an example, the use of stairways or
 portable  ladders  should  be  considered  wherever
 possible, instead of manhole steps.
    A  significant  number  of regulator  stations
observed in the  18  interviewed jurisdictions were
inaccessible, could only.be reached by boat, or could
be entered only by descending 30 feet into a 30-inch
diameter manhole section. It is obvious that regulator
devices in these difficult locations suffer from lack of
maintenance.
    The following conclusions can be drawn from the
evaluation  of  the regulator  maintenance practices
disclosed in the national survey.
     1.      Components of regulator stations should
    be housed in separate chambers. For example, a
    float-operated  gate  regulator  station  should
    consist  of a chamber for  the  regulator, with
    separate housing for its float control;  a diversion
    chamber for directing the combined sewer flow
    to the  regulator; and  a tide gate chamber,  if
    required.  All  chambers   should  be  readily
    accessible.
     2.      Access  to  the  chambers   should  be
    unobstructed. There should  be adequate space to
    admit personnel freely while carrying  equipment
    they may require  to perform their  duties. An
    access  opening should  be   located  above  any
    heavy  or  bulky mechanical device,  so that,  if
    necessary,  it  can  be removed and  replaced
    without excavation, or so that it may  be repaired
                                 DERRICK  BARGE AND BOAT

                        ALLEGHENY COUNTY SANITARY AUTHORITY
                                                                                         FIGURE 20
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                                                        FIGURE 21
                LOADED DERRICK BARGE
      ALLEGHENY COUNTY SANITARY AUTHORITY
                                                FIGURE 22
Courtesy Metropolitan-Seiver District of Greater Cincinnati'
                      SWAMP BUGGY
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 in  the  relative  comfort  and  security  of an
 above-grade location.
  3.    The  environment  of an  overflow
 chamber is likely to be damp and corrosive, so
 mechanical equipment should  be fabricated of
 corrosion-resistant materials. Special care should
 be paid to bearings and other friction or contact
 surfaces. In this respect, the use of neoprene may
 be of benefit. Electrical gear should be housed in
 a  separate chamber,  situated above  grade,  if
 possible. If it is absolutely necessary to install
 electrical  equipment  in  conjunction  with the,
 regulator chamber,  it  should  comply  with
 National  Board  of Fire   Underwriters
 specifications  for  hazardous  locations.  The
 chamber  should be   protected  by forced-air
 ventilation.
  4.    All  chambers  associated  with  sewer
 systems  should  have   ample  ventilation
 capabilities, preferably at two points, to provide
 cross ventilation.
  5.    Convenient and non-corrosive  ladders
 and steps should be provided.
  6.    Reasonable headroom is  essential within
 the chamber.
  7.    A well-defined, adequate, large landing
 area should be provided in the chamber. Where
 possible,  it should be so located as to  give
 convenient access to all key maintenance points
 and  allow inspection of  the  incoming  and
 outflowing combined sewage.
  8.     If at all possible, the chamber should be
 lighted. Only explosion-proof fixtures should be
 used.
  9.     Guard  rails  should  be provided.
 However,  New York City, for example, does not
• favor railings in regulator stations, since they feel
 that reliance on a railing which may fail due to
 corrosion  is more hazardous than the omission of
 the  railing. Where conditions  are particularly
 hazardous and where  a fall might mean death or
 serious injury, railings have been constructed of
 structural steel encased in concrete.
  10.     A ceiling hook over  float gates,  small
 gate assemblies, and screens is a simple but  often
 useful facility.
  11.     Simplicity- in cleanability and design are
  essential.  Projections  and small  gaps where rags,
  sticks and floating material can collect, should be
  carefully avoided.
  12.     Adequate size in the  regulator chamber
  must be provided to prevent blockage by deposits
    of sewage solids, and  oddities  such as  bicycle
    frames  or  long  timbers,  which are  not
    infrequently found in combined sewers.
    Provision  of  such  structural  and  equipment
facilities will enable the maintenance department to
maintain regulator facilities in a manner that will
assure effective performance.
Preparing a Regulator Chamber for Inspection
    There  are  dangers  associated with  sewer
maintenance procedures, both in the sewers and their
access  chambers  below grade, and from the traffic
above grade.  Basic safety precautions  are applicable
to  maintenance  crews  across  the  country.  The
instructions given  to  maintenance crews in
Philadelphia  are  an  example  of  standard  safety
practice:
    1.   Truck should be parked so as not to obstruct
    traffic  but,  if possible, it should be  used to
    protect men working near  open manholes. If a
    truck is used for this purpose, suitable flashing
    lights must be used on the truck.
    2.   Warning cones, flags, signs, and lights should
    be used to make areas safe for both vehicles and
    pedestrians.
    3.  A  manhole cover should be raised with a.safe
    and proper tool and a bar placed under it, so that
    it can be rolled to one side.
    4   A  manhole  guard  should be  placed around
    the open manhole.
    5.  A  chamber  or  sewer should be  given
    adequate ventilation before entry is made.
    6.  The  air in both sewer and chamber should be
    checked  for  explosive mixtures,  oxygen
    deficiency, and hydrogen sulfide content.
    7.  If there is an indication of gases, a portable
    blower should be used to clear the area.
 Effect of Automatic-Automation
 Systems on Maintenance Procedures
    The  experience reported by  one  jurisdiction
 indicates that overflow of dry-weather sanitary flow
 has been  reduced by 50  to 75 percent because of
 improved  use of manpower and methods, without.
 taking  into   consideration   the
 instrumented-automated system. A  study made of
 1962 raw-waste data compared the average plant load
 received on dry days versus runoff days. This study
 concluded that,  "The average annual  BPD  would
 .possibly be 15 percent greater, the suspended solids 6
 to 10 percent higher, and the total solids 3 to 6
 percent greater if the sewer system were not affected
 by runoff."1 Since improved manual surveillance
 methods  were implemented and revisions  made to
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 regulators  utilizing the  automated  system, average
 annual plant  load  has  increased  markedly.  The
 increases are due, in part, to a number of factors, but
. a substantial portion of the increased load is due to
 better regulator performance. The added increase in
 plant load has been from 5 to 15 percent above past
 growth projection curves.2 '3
     An instrumented  or  automated  regulator
 maintenance system may be  defined as one  which
 provides continuous information at a central location
 concerning status and performance of the combined
 sewer   overflow  regulators.  The  information may
 include rain gauge readings,  trunk  and interceptor
 sewer  flow  or level, regulator gate position,  and
 possibly robot water quality  monitoring data, or it
 may be limited to  on-off, yes-no  information as to
 whether or not a regulator is overflowing. To date,
 there  have  been  only a  few  installations  using
 instrumented  systems.  Among  these,  few  have
 provided  for  remote control of  the regulators. In
 some cases, the surveillance system  causes an alarm
 indication so  that  a crew may  be dispatched to
 correct the  malfunction. The systems installed at
 Minneapolis—Saint Paul Sanitary District and Detroit,
 and now  being finalized at  the Municipality of
 Metropolitan Seattle, provide  for remote control of
 regulator  devices so that overflows can  be corrected
 immediately from the central location.
     Also, for the purposes of this report, a definition
 of regulator maintenance is necessary. There are two
 kinds of maintenance which  will be  described here.
 Normal maintenance is inspection and servicing of the
 regulator equipment to  correct unnecessary overflow
 due  to  blockage,  stoppage,  and equipment
 malfunction. This kind of regulator maintenance in a
 sense is a part of operation of the system.
     The second kind of maintenance is equipment
 1  Anderson, J. J., "Analysis of Operating Data from
 a  Full-Scale Primary  Sedimentation Plant  at  the
 Minneapolis-Saint Paul  Sanitary District," A Thesis
 Submitted to the Faculty of the Graduate School of
 the University of Minnesota, April 1967.
 2  Toltz, King, Duvall, Anderson and Associates, Inc.,
 St. Paul, Minnesota, "Report on the Expansion of the
 Sewage  Treatment  Plant-Minneapolis-Saint Paul
 Sanitary District."
 3  Anderson, J. J., "Computer Control of Combined
 Sewers," Presented  at  American Society of Civil
 Engineers  Annual and Environmental  Engineering
 Meeting, October 13-17,1968.
maintenance or repair maintenance required because
of wear, deterioration, and equipment failures which
require a rebuilding or repairing of the equipment.
This kind of maintenance normally requires shop
facilities and tools and equipment such as welding
devices. For the purposes of this report the latter will
be designated as repair maintenance, and the former
as routine maintenance.
    One of the functions of routine maintenance is
the  regular  inspection  of regulators  on  either  a
periodic basis or following each use of the regulator
system by storm flow. With an instrumented system,
the number  of routine  inspections required can be
reduced significantly.   For  example,  in  one
jurisdiction, inspection  of  125 miles of river front,
required two and  a half days' time for a four-man
crew to complete.  Of these regulators, approximately
20  percent  caused  most   of  the operational
difficulties.  Routine  inspection  of regulators  was
reduced substantially and almost eliminated when the
major—and  the most troublesome  ones—could be
continuously monitored. By providing remote control
of these troublesome regulators, corrections could be
made  from a  central location  within a matter of
minutes, compared with hours when a crew had to be
dispatched to the site.
    Not all  of  the savings from routine maintenance
can be credited to  the use of an instrumented system.
In  exchange  for  reduced routine  maintenance,
additional control facility  maintenance is  required.
After the original problems in  the instrumentation
system are  eliminated,  this maintenance  is rather
minimal, requiring only  a fraction of one man's time
for 40 instrumented locations.
Manpower Requirements
    Manpower requirements  for  automated,
combined  sewer,  overflow-regulator  facilities
maintenance differ considerably from those for static
systems,  both  in  kinds and numbers  of personnel
required.
    For  static  regulators,  maintenance requires at
least one man  for each 10 to  20 regulators. These
men must be willing to spend  a good  deal of their
time   in the  sewers,  working  under  unpleasant
conditions with their main duty consisting of clearing .
clogged facilities. Periodically, they may be required
to adjust weir levels and gate settings.  The cleaning
work will require removal of debris an'd shoveling or
flushing grit and heavy sediment. Typically, the worst
conditions are in the larger  regulators carrying heavy
flow, usually containing industrial wastes. Typically,
these large regulators cause the  most overflow, and
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should be given the closest checking and most prompt
attention. Much of the sewer crew's time is spent in
travel between locations looking for problems and in
setup and cleanup  operations if proper safety and
work methods are used.
    At the opposite extreme, modern, well-designed
remote-controlled regulators can substantially reduce
the amount of unappealing and hazardous work in
sewers. Inspection is done remotely by an operator or
instrument at  the  central  location.  Repair
maintenance  will  be  of  a different  nature and
somewhat increased. Various types of equipment will
require   such crafts  as  electricians,  electronic
technicians,  pipe  fitters, mechanics,  and possibly
computer specialists. In most major jurisdictions the
work load in each specialty will  not require full time
attention, particularly after any faults in the system
have been corrected.
    Primary coordination must be effected between
central regulator operations, routine  maintenance,
and repair maintenance. Maintenance personnel must
make known to central operations their presence in
areas where the activation of operations might cause
injury or death to such personnel. At the  same time
there  should be  a  "lockout"  of such equipment.
Frequently,  the  three  functions must  provide  a
coordinated  effort. Thus,  the  maintenance  crew
might provide the safety equipment, hoisting facilities
and  other paraphernalia for the  repair crew while
they are in the sewer or control chamber.
     Subsequent  to repair and prior to  departure
from  a  particular site,  the  central  operations
personnel will make tests to insure that a return trip
will not be necessary. Operating personnel can inform
maintenance  personnel  of problems whether at  an
automated location or other location, by  inferential
judgment. Maintenance personnel can assist operating
and  maintenance personnel in checking calibrations
of systems and  preventive testing.
    The  maintenance personnel  should be given the
most extensive safety training and equipment, since
they  will spend the  most  time under  hazardous
conditions.   They  should also  be given  prime
responsibility  for protecting other personnel who
infrequently  will be  in hazardous   locations.
Cooperation  with sewer  cleaning and maintenance
crews will also be necessary.
    Effective utilization of personnel in a remotely
controlled system  is essential.  Because  of  wide
geographic distribution  of  equipment  and  the
interconnection  • of  mechanical, electrical,  and
electronic systems, considerable time  can be spent
diagnosing problems and  removing,  repairing,  and
replacing  defective  equipment. For example, it is
conceivable that several days might elapse before it is
determined whether a defect is in the telemetry, the
electrical or mechanical system, if a craftsman of each
class was sent sequentially to investigate. Sending all
three craftsmen to each trouble area is also wasteful.
    Several solutions of this problem are available.'In
the design of a system, modular plug-in units can be
used for easy replacement by the maintenance men.
For  example, small air compressors can be installed
using plug-in power cords and quick-disconnects  on
air, lines.   Similar  techniques  are  available  for
telemetry, power units,  and  instruments. Judicious
inclusion  of  test points, gauges, and indicating lights
also  can be of benefit as a repairing aid.
    In order  to avoid excessive travel-and-turnaround
time by  repair crews to  obtain parts, equipment or
additional aid,  a  support  team  with a  suitably
equipped and stocked vehicle should be provided to
serve such crews when required. Since manholes and
underground structures are not easily identifiable on
the  ground,  adequate maps and location drawings
must be readily available for the crews.
     In  some cases, it  is  not  practicable  for the
operating agency to provide  the depth and range of
skills in-house for maintaining an automated system.
Increasingly,  therefore, use  has  been made  of
contractual services on a yearly, or on-call basis when
required.
     The   management of  an  automated  regulator
control  system  requires  cooperation  with other
organizations. A partial list of these for a typical
system might include the: telephone company; power
company;  gas  company; weather  bureau; street
department;  engineering department; water
department;  and fire department.
     It is advisable to have a key person for contact
with all  of these  agencies. Normal contact  will be
minimal  with some agencies and  continuous  with
others. The  Weather  Bureau will  usually  be  very
cooperative   in  providing  information  on  rainfall
conditions. This information will be helpful in the
planning  of  operations. Troubles  with telemetry
systems will  be minimal  if the proper person is found
within the local telephone company. A number of the
other  organizations will assist in spotting overflows
arid also can provide  significant data and technical
assistance. Equipment used by other utilities can be
examined for possible use  in regulator management.
     Fixed equipment  required at a central  site  for
maintenance of an automated system will generally
be electric  or electronic in  nature. A number of
sophisticated test instruments are  available  for
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checking leased telephone lines. Shop facilities may
or may not be required depending on the equipment
and methods used. Replacement of defective modules
with  substitutes makes it possible  to  send  the
defective unit to the factory or depot for repair.
Good truck  and equipment washing  facilities are
desirable, and periodically all portable and central site
equipment  should  be  inspected, inventoried,  and
cleaned.
    Communication is  needed between the  central
dispatcher and all  field units, as well as between
personnel working in regulator chambers, sewers and
vaults and those remaining outside. For calibration
purposes,  the telemetry  system  can  be  used for
communications  but two-way radio is more useful.
Speaker and microphone extensions can be used to
allow personnel to  use  the radio while in  a shallow
chamber or in a field  structure.  Where this  is not
possible, hand-held transceivers can be used to relay
messages between the site and the vehicle and thence
to  the  central  site. Communications between
underground  personnel and those remaining  at the
surface can be   by  sound-powered  telephones,
switchless   intercoms,  or  by  transistorized
megaphones. Revisions to the equipment can be made
for use in the sewers. A  direct outside  telephone
should be provided  at the central control site, in
addition to the normal business extension telephones.
The  central site should also have means  for direct
radio communication with the field.
    The organization and administration of regulator
maintenance  operations obviously should be tailored
to  the  operating agency's  needs.   Typically,
maintenance  has  been largely  ignored,  with
dependence on random complaints for determination
of unnecessary overflow. With  or  without  the
automated system, the  maintenance function should
be given prime consideration. Separating the regulator
maintenance from sewer maintenance  facilitates the
development of the specialized capability needed for
reduction of  pollution  from  overflows  and
development  of the information and technology
necessary to improve the operation of the  regulators
and thus the entire sewer system.

Example of Maintenance Practices
in an Advanced System
    The  Minneapolis-Saint  Paul  Sanitary District
maintains approximately  150  regulators  which
discharge  to   about  80 river  outlets.  Automated
regulator equipment is provided at 15 locations which
control about 80 percent of the system's dry-weather
flow. In addition, there are approximately 25 other
locations  where equipment has been placed  to
    The following is a suggested organizational chart
for regulator maintenance.
      SUGGESTED ORGANIZATION CHART
          REGULATOR MAINTENANCE
                 MANAGEMENT

                   ENGINEER
                  (PART TIME)


                                         OTHER
                              ADMINISTRATIVE
                            AND MANAGEMENT
                                    FUNCTIONS

              ROUTINE       REPAIR
 OPERATION MAINTENANCE MAINTENANCE
 Records      Field Crew       (Part Time)
 Calibration                   Electrician
                              Fitter
                              Electronics
                               Technician
                              Instrument
                               Repair
measure  interceptor sewer levels, rainfall, and river
quality. About 140 measurements are telemetered to
a central location; 34 gates and 15 inflatable fabric
dams are subject to control.
    An engineer is responsible for the maintenance of
the  system, which was placed in operation in the
spring of 1969.   Under  his  supervision,  the
maintenance crew consists of  five men. Prior to the
District's assumption of maintenance,  18  sewer
workers from the two cities worked part-time on the
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 regulators.
     Computer  equipment  is  maintained  under
 contract by the contractor who installed the system.
 The  telemetry  system  is maintained  by  a plant
 electrician who is assigned to work part-time on the
 system.  Mechanical  repairs have  been minimal  and
 have been  performed part-time  by help from  the
 plant machine shop. In-sewer replacements of bubbler
 tubes have been accomplished by  the  maintenance
 crew. The maintenance function at major automated
 regulators is performed by the computer at variable
 time intervals. Typically,  each  of the 40  gates is
 checked  every 4  hours  during  dry-weather  to
 determine gate  position. The measured position is
 compared with the desired position and, if necessary,
 the  gates are  readjusted.  A complete  report is
 automatically typed  showing initial and  final gate
 positions, as well as notations of inoperative gates or
 telemetry  system failures. During storm  flows  the
 gates can be adjusted individually by remote control
 or by establishing new gate settings in the computer
 system. In the latter case, the gates will be reset to
 the  new positions when  the periodic check is made.
 In addition to the periodic check of gates, a complete
 computer check  of all gates  can  be initiated at  the
 central site by operation of a single select button.
     The  remaining   overflows are  given  periodic
 routine checks by the maintenance crew. A very  few
 locations known to be troublesome, are  visited more
 frequently. Depending on the work load of the crew,
 the periodic checks are made once or twice monthly
 during dry weather.  A full check of outlets requires
 2H days on the ground. The same information can be
 obtained in a little more than one hour by helicopter.
 Before a helicopter trip is ordered after a rainfall, the
 local weather bureau is asked for a current weather
 prediction. A checkoff sheet of overflowing locations
 is prepared and usually all overflow can be stopped in
 one  shift. Helicopter flights -are  only ordered if a
 detectable increase in flow due to runoff is observed
 on  one of a number of sewer level or flow meter
 charts.
    Thunderstorm activity occurs  frequently at night
 in the Twin Cities. By using the helicopter flight and
 based on information from the instrumented system,
 all overflows are cleared by the end of the normal
 working day. By comparison, using  old methods,
 overflow often continued for several days after such
 storms.
Regulator Maintenance as a Specialty
    In  many jurisdictions there is a  division  of
responsibility for collection and treatment of sewage.
In some  of  the  larger jurisdictions, the collection
 system frequently is under the control of the sewer
 division in  the public works  department.  The
 responsibility  for interception  of the  dry-weather
 flow in the combined sewers often rests with a larger
 agency, such as a countywide sanitary district, which
 also has responsibility for treatment of the conveyed
 wastes  before disposal to the receiving stream. The
 exact point where each agency's responsibility begins
 and ends is often not clearly defined. Traditionally,'
 cities have performed minimal regulator maintenance,
 with the main emphasis  on getting rid of the waste
 water and avoiding local  area and basement flooding.
 Often   the  cities  are charged  for operation and
 maintenance of a more comprehensive district, based
 on flow volume  delivered to  it, and there  is little
 incentive for the contributing communities to capture
 the maximum flow. In such cases excessive overflows
 from collector lines, prior to their junction with the
 interceptors of  the agency  which serves  multiple
 jurisdictions, is encouraged. Engineering departments
 usually  are  not  anxious  to raise  the  height of
 permanent weirs or dams to increase the capture of
 runoff since this may affect the hydraulic functioning
 of the combined trunk sewer system during times of
 peak  flows.  The  impediment  of  flow by  high
 permanent dams  may cause  serious backups and
 health hazards in basements.
    In   order to satisfy  the  often  conflicting
 requirements  of maximum diversion to interceptors
 and protection of upstream sewers from discharge,
 regulators in  which a weir or  dam height  can be
 adjusted with complete  reliability is  required. The
 adjustments  must  be  made frequently, based upon
 knowledge  of  the  capacity  of  the   interceptor
 downstream from the  regulator, upon flow depths in
 the combined  sewer leading into the regulator and on
 comparisons of strength  and quantities intercepted
 and  spilled  at   other  regulators  in  the  system.
 Knowledge of reserve  treatment plant capacity for
 quantities  of  polluted storm  runoff must  be
 considered.
    In  most  operations,  sewer  maintenance crews
 spend their time  immediately after a storm answering
complaints of flooded basements and plugged catch
basins.  After  the  majority   of the  post-storm
complaint work  is completed,  the regulators are
visited.  In some cases, due to the large  number of
regulators, the last regulator may not-be cleared for as
long as two weeks after a storm.
    Because  of these  difficulties, a dedicated crew
that is  committed totally to a  routine and regular
surveillance program is a must to  improve operations.
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The logical agency to handle this function is usually a
larger .or regional multi-community agency. With the
many limitations on local budgets, the larger district
responsible for treatment and  pollution abatement
may be able to more easily obtain funds for manning
and equipping the regulator crew and operating the
instrumented systems. If this assignment of authority
is to be provided by a local community  to a regional
agency, it must be  clearly defined by agreement  or
regulations.
    Most of the employees on an average sewer crew
are laborers with limited knowledge or experience in
the   functioning  of  the  hydraulic,  electrical,
mechanical, and  pneumatic equipment  that is now
being used  on  more sophisticated regulators. The
most efficient  use of manpower is to  assign to the
regulator crew those men having some of the training
and skills necessary  to ensure the routine continuous
maintenance  of the control equipment  in service  in
the system.
    The ideal, situation would be for the supervisor to
assign to the  sewer  crew a  man  or  men  with a
knowledge  of electrical and  mechanical  systems
where they are in use. The men should be able to read
and  understand instruction  manuals, drawings, and
other written materials. They should also be able  to
maintain necessary records and to prepare reports and
written memoranda.  They  should be  required  to
maintain  an  inventory to  requisition  necessary
supplies and replacements, and to recommend field
revisions.
    Improvement  of regulator maintenance
procedures requires the proper manpower selection
and  training; establishment of standards of manual
surveillance methods, accurate record-keeping; and
availability of certain special equipment.
    The  critera  for  selecting  manpower  for a
regulator crew are important. The men should have
considerable  agility  to enable  them to  climb in and
out  of manholes and small spaces without physical
injury.  The men selected should be willing to enter
the   sewer  when  assured  that  adequate   safety
precautions have been satisfied, and they  should  be
sufficiently intelligent to understand the dangers  of
the work.
    Regulator crews, like other skilled team workers,
should  be constantly  trained to carry out their jobs
effectively. They must have the essential elements of
their jobs clearly identified to carry out  their mission
in the  most efficient manner. Knowing the general
objectives  of their  jobs,  they must  be carefully
trained to realize these goals with ease and safety.
Their training should be adequate to ensure that  all
reasonable precautions for their safety and the safety
of others are being  provided. They must  be  well
trained in the use of hazard detection equipment and
capable of developing needed contingent plans for
unexpected situations.
    Training  should be sufficiently complete to allow
them to perform simple tests of  any mechanical,
pneumatic,  or electrical equipment  used  in  the
operation of .the regulator devices. A contingent plan
should be developed for any anticipated malfunctions
to  assure  the  least possible damage  while   the
malfunction  is occurring and to  provide  for  the
speedy correction of any difficulties. The crew must
understand fail-safe systems employed to provide for
the least serious consequences, in  the several options
of operation, coincident with power failures. In some
instances,  fail-safe  operation would  require   the
lowering of adjustable dams during power failure and
the  crew must  be  able, at  the  more  important
regulators,  to  provide  emergency  power by
connecting  portable  power   units  to  enable   the
regulator to  return it, to operation at the earliest
possible time.
    By using improved manual surveillance methods,
a  more  effective  policing job can be  done  with
reduced manpower. A number of jurisdictions hire
helicopters to expedite the location  and reporting of
overflows and malfunctions.  By  reviewing  existing
manual inspection methods,  an  improved program
can usually be established to improve response  time
and utilize manpower more effectively. The improved
program  may require minor  system  modifications,
such as installation of new manholes  or ladders for
inspection or access.  In  areas where  many  outfalls
exist, those which are connected to regulators should
be  easily identified  from air, ground or water by
adequate  marking  and  numbering.  An  outfall
checkoff list can be  prepared, referring  to nearby
landmarks and  including a  list  of  contributing
regulators if more than one is tributary.
    Record-keeping  in  any  successful regulator
maintenance  program should be simple, yet contain
the essential  information that  would be required for
improved management.  In  establishing a new  or
revised  regulator maintenance program,  the  usual
first-step requirement is  generation of, or updating
the  inventory  of regulators and assembling  all
pertinent  drawings  and  records.  All  drawings  and
records should be field-checked by the regulator
crew. New drawings  and records  should be made
where necessary. A duplicate file system, one for  field
use and one  for office use, should be made  with all
information for  each  regulator  assembled  and
                                                  85

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grouped by regulator location.
    Standard forms should be developed for routine
record-keeping. Preferably, these should be  arranged
in  a manner suitable  for  later  analysis  by data
processing methods. The best  approach is  to use a
simple form for making the  notations, with  boxes to
check, requiring a minimum of writing by  the field
crews. However, there should be room on the form
for  remarks  to  permit  the  field men  to  make
notations not covered in the standard form. Some of
the simple data to be included on the form are: (a)
Location  of  the  regulator;  (b) identification  of
regulator; (c) time of day, (d) day of week; (e) date;
(f) condition—working or clogged; (g) if clogged, how
many inches  going  over  the  dam  spilling into
waterway; (h) condition of the orifice—any blockage,
hangings, etc.; (i)  anything  unusual  about  the
quantity or quality of flow  coming to the regulator;
and  (j) any  unusual  odors  or discoloration in  the
flow.
    In  order  to  implement improved  methods  of
regulator  maintenance,  special equipment  must  be
provided. The current  high  cost of  labor  easily
justifies  the  purchase of all  tools  and equipment
needed  to expedite the work and minimize working
time. A complete list  of all equipment needed is
rather extensive. Items of major  significance can be
grouped  in three  categories—safety,  descent and
ascent, and working equipment.
    All  equipment must be  evaluated from a  safety
standpoint. Special safety equipment should include
sophisticated electronic and  chemical testing devices
for explosive or noxious gas, for oxygen deficiency,
and for  toxic  fumes.  Testing  equipment  should
include battery-operated sampling pumps to insure
reliable  results.  Duplicate  equipment  should  be
provided for oxygen deficiency and explosive gases.
Nylon parachute harnesses should be furnished for all
personnel, with sufficient spares, and it should be the
established rule  that  a harness is worn at all times
below  ground to facilitate rescue in case of accident.
Special rescue devices should also be available at the
surface.  A  small portable self-contained breathing
apparatus, usually with a 10 capacity, is available and
should be provided. Standard procedure should be to
have at least one breathing apparatus available at all
times  when  the  men are underground.  Procedure
should also require  that a breathing  apparatus  be
lowered into a hole before a man enters.
    Equipment for ascent or descent should include
hoists, one powered  and one manual. During ascent
and descent in deep manholes,  a safety  harness
connected to a nylon safety line should be used. This
safety line can be snubbed around an appropriate part
of the  truck and attended by a person on the ground.
    Working  equipment should include  temporary
working platforms and supports, flushing equipment,
tools for cutting and removing clogged  materials and
numerous other items. Modern self-contained blower
generators  can be used for  power  and  ventilation
when  maintenance   work  other   than short time
inspection  or the  clearing  of debris is  being
performed. Battery-operated tools  are now available
for use in hazardous locations to eliminate shock and
explosion hazards. Non-sparking tools and equipment
will reduce explosion hazards.
                                                 86

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                                              SECTION 7
                       TIDE GATES: APPLICATIONS, DESIGN AND PERFORMANCE
    Tide,  or  backwater  gates,  or  flap  gates  are
employed to protect collector sewers and interceptor
systems from the inflow of tidal or high  river-stage
waters.  Without  such  control devices,  backflows
would 'surcharge interceptors, pumping stations  and
treatment  plants  and  adversely  affect  treatment
processes. The  inflow of such  receiving waters into
combined  sewer  systems  at  some  points would
ultimately result in uncontrollable overflows and the
bypassing of excessive volumes of waste waters to
receiving waters at treatment plants.
    Tide  gates are  intended to open and permit
discharge  at the  outfall  when  the  flow line in the
sewer system  regulator  chamber  produces a small
differential head  on the upstream face of the gate.
Conversely,  backwater gates are designed  to close
when the stage or tide level in the receiving waters
produces a small differential head on the downstream
side of the gate. Some types of gates are sufficiently
heavy to close automatically, ahead of any water level
rise in the receiving body. With careful installation
and balancing,  coupled with an effective  preventive
maintenance program, the ability of the gate to open
during overflow periods is not impaired because of
this additional weight.
Types and Sizes of Tide Gates
    Tide gates are available in a wide variety of sizes;
they may be rectangular, square or circular in shape,
depending on the  requirement.
    Tide gates are manufactured in three basic types,
depending on the construction of the flap, as follows:
    1. Cast iron,
    2. Sheet metal plates, and
    3. Timber.
    Cast iron Agates are available in sizes varying from
4 to 96 inches in diameter, when circular, and 8x8
inches to 96 x 96 inches when square, or variations in
rectangular shapes within these limits.
    Sheet metal is used to fabricate a lightweight tide
gate shutter, which is a double-walled structure with
interior air cells. This lightweight application offers a
more positive opening response to  small differential
outfall  heads.  This  is of particular advantage over
heavier cast  iron models, which may, particularly
with age,  require  a significant upstream head to swing
open. When the waste water flows on  the  receiving
water courses are corrosive, pontoon tide gates have
had.a life expectancy of only  10 to 12 years unless
carefully  protected  with inert, corrosion-resistant
coatings  or  constructed  of  corrosion-resistant
materials. These "pontoon" shutters of sheet metal
are available in circular style from 48 to 120 inches in
diameter. Square and rectangular gates are available in
dimensions from 48 to 120 inches.
    An important  feature of such metal tide gates is
their hinge arrangement. Except for very large sizes,
instead of hinging the shutter at  the top only,  a
second set of hinges of a linkage type are attached at
the sides of the shutter. -This  linkage is devised in a
way that will  permit  it to open at the top if its
bottom has become jammed in the closed position by
the weight of debris deposited at the downstream side
during periods of high river levels or high tides. Figure
23,  Hinged-Type  Tide Gate,  illustrates a  typical
hinging configuration.
                                FIGURE 23
                           POSITION B
                HINGED TYPE
        TIDE OR BACKWATER GATE

    Position A  shows  the  normal  full  opening
attained  when  the outlet  channel is unobstructed.
Position  B indicates the advantage of the second set
of hinges, which permits the shutter to open at the
top when the lower body  of the gate is blocked by
debris. The resulting outflow may then wash away
the debris and permit the gate to function fully, as in
Position A.
    Early tide gates were made of timber or wooden
planks,   and were either  hinged  at the  top  or
double-leafed with hinges  at the side  similar  to  a
double barn door, with the gate frame inclined at the
top. Gates of this latter type  were installed in the
                                                   87

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  Boston area.
     Timber tide gates suffered a decline in popularity
  during the early  part of the century. However, they
  are again being used in large  sizes. Such gates are
  economical in sizes larger than 7x7 feet or in odd
  dimensions. A typical timber tide gate is shown in
  Figure 24, Timber-Type Tide Gate.
     The construction  features of this gate are  as
  follows:
     1.  A gate frame made pf cast iron in securely
     bolted sections;
     2.  Shutter,  with timbers laid in the vertical
     position;
     3.  Carrying bars inserted between particular
     timbers to act as reinforcement or stiffeners for
     the shutter and for connection with the hinge
     blocks;
     4.  Horizontal stiffeners and tie rods provided to
     prevent warping,  to structurally stabilize  the
     shutter, and to prevent flotation;
     5.   Hinge arrangement to permit the attachment
     of the gate to the gate frame and structure;
     6.   Hinge bracket anchor bolts  set in oversize
     pipe sleeves to provide slight adjustment; and
     7.   Lifting bolts  provided at the base of the
     shutter  to enable  the  gate  to be  operated
     manually when required.
     The tide gate  should be cured before machine
 fitting.
     Use of timber gates which  are alternately wetted
 and dried may accelerate deterioration.
     Dense  structural  Southern yellow pine is the
 most common timber material used  for such gates.
 Cypress and Douglas fir have also been used. These
 woods  require creosote treatment to prevent  rapid
 deterioration.
     In  New York, greenheart  timber is now being
 used.  This structural  timber  requires no

                                     FIGURE 24
                                   TIMBER-TYPE TIDE GATE
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                                                     88

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wood-preservative  treatment,  and is  resistant  to
marine  borers  and  wood-destroying fungi.  It is
extremely dense (approximately 70 pounds per cubic
foot so that little additional weight  is required to
offset buoyancy. It is resistant to seasoning splits and
checks that are common to other structural wood, it
machines well, and has a high resistance to warping or
distortion. Table 26, Allowable Working Stresses for
Timber, compares the working stresses for greenheart
and other structural woods.
                    TABLE 26
    ALLOWABLE WORKING STRESSES OF TIMBER
  Timber
Yellow Pine
Cypress
Douglas Fir
Greenheart
                Parallel to Grain-PSI
                                       Perpendicular
                                       to Grain-PSI
            Compression  Tension Shear  Compression
1550
1466
1100
3000
2000
1733
1450
3300
135
133
 95
400
 455
 300
 390
1500
     In  some of the jurisdictions surveyed, tide gates
 are  of  shear or sluice  gate type, motor-operated  or
 hydraulically actuated. This type of application lends
 itself to  remote  control  of the  rate  of tide gate
 operation, as required. Information is transmitted  to
 the  central monitoring station by bubbler-type level
 sensors located upstream and downstream of the tide
 gate in order to  provide regulator control  of the
 interceptor system.
 Installation of Tide Gates
     Tide gates usually are installed at the head of the
 outfall  sewer line,  as part  of the regulator station, or
 in series, at a selected site within the  outfall sewer
 line, at a point between the Outfall discharge and the
 regulator  station.  Installation  of  the  tide  gate
 structure at the outfall discharge point may have the
 advantage of lower capital cost, and the availability of
 sufficient space to  permit  the construction  of  an
 outfall structure protected by several small gates, as
 opposed to one large control unit. The  use of several
 smaller parallel tide gates  permits the opening of the
 gate flap under a relatively small head differential.
 Because  of their  smaller individual bulk,  they are
 more   readily  operated  by  maintenance  personnel
 when jammed with debris.
     The  disadvantages of  tide gate installation at the
 outfall discharge point are:
     1.   Boats and boat  crews will be required  to
     effect maintenance, since the gates may be partly
     or fully submerged  during high river  stages  or
     high tides.
     2.   In tidal  waters,  severe  wave action may
    overbalance the pressure behind the gate shutter,
    thereby forcing the gate to close abruptly with
    considerable force. Repetition of this cycle  at
    short intervals. may produce objectionable noise
    levels, especially in residential areas.
    3.   During periods of high river stages, or high
    tides in coastal  or estuary waters, the trapped
    sewage in the barrel of the outfall sewer between
    the regulator  station  and the tide gate may
    become septic. This pollution load eventually will
    be discharged into the receiving stream.
    4.   In the "total systems" concept of combined
    sewer interceptor operation, the tide gate  should
    function in  a  coordinated  manner  with the
    operations of its upstream regulator, a condition
    which  may not be attainable  if the tide  gate is
    located at a distance from the regulator structure.
        Tide gates that are installed within the barrel
of the outfall, in tandem, at a predetermined point
between the outfall and the regulator station, provide
an  additional safeguard to the interceptor system,
particularly when the  crest of the diversion dam at
the regulator station is only slightly higher than the
normal water level at the point of outfall. This point
of installation also may be used in locations where
very high tides or severe variations in river stages are
experienced for extended periods of  time.  Where
wave action causes  slapping of the flap  against the
gate seat, tide gates have been installed upstream in
the barrel  of the overflow pipe at a point where the
wave energy will have been dissipated.
    Figure 25, Sluice  Gate-Type Tide Gate, shows a
typical  installation  for  a/,slmce  type-gate in  a
two-chamber facility.  Figure 26', Tandem Tide Gate
Installation, shows a tandem  tide gate installation,
with a stop-plank arrangement for shutting off the
outfall line at the downstream face of the gates to
permit servicing of the gates.
    Tide gates have been installed to advantage at the
outfall connection of a regulator station at the head
of the overflow pipe, as was shown in Figure 15. This
type of installation has the following advantages:
    1.  Routine  preventive  maintenance and
    inspection can be carried out in conjunction with
    regular visits to the regulator chamber.
    2.  Major  repairs, such as shutter removal for
    hinge  replacement  and  shutter  repair  or
    replacement, are facilitated because of increased
    accessibility.
    3.  Motorized equipment, such as hoists, can be
    located vertically above the  gate  for more
    efficient maintenance.
                                                     89

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                                                                                    FIGURE 25
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                               TANDEM TIDE GATE INSTALLATION
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    4.   Stop-planks  may  be placed in a preformed
    channel in the' tide gate chamber, so that major
    repairs and inspections can be carried out under
    dry conditions.
    5.   Remote control  in conjunction with  the
    adjacent regulator operation may be used.
    The capital  cost of a tide  gate installation at a
regulator station will frequently be higher than at the
outfall discharge point, particularly if the regulator is
located in a congested area of the community. If the
flow being discharged to the outfall is large, sufficient
space may not be available to install smaller and more
sensitive tide gates in parallel. In such cases, the larger
single gate installation wiE often require an auxiliary
power source to operate effectively.
Operation and Maintenance of Tide Gates
    To  evaluate the  operation  and maintenance
characteristics  of tide gate facilities,  the  project
survey investigators made  an effort to obtain specific
information from  personnel experienced with these
devices. The  following  design,  application  and
operation guidelines were obtained:
    1.   Periodic inspections are necessary to insure
    free rotational movement  at the pivot points;
    lubrication is a regular requirement. Permanently
    lubricated  bushings  are  now  available  which
    greatly reduce this lubrication requirement.
    2.   Hinge  arms  and  gate openings  must  be
    checked regularly to be sure that they are free of
    trash, timber, or other obstructions which lock
    the shutter in the partly open position, allowing
    inflow.
    3.  Metal  seating  surfaces should  be  scoured
    regularly if  evidence of surface Corrosion exists.
    This will enable tight closure of the shutter.
    4.  Neoprene gaskets  or buta-N rubber gaskets
                     improve  the sealing  characteristics  of the  seat
                     between the shutter and its frame. These are inert
                     and not subject to corrosion.
                     5.  In locations where tide gate installations are
                     subjected to particularly corrosive waters, brass
                     fittings will require periodic  replacement. Some
                     systems use stainless steel fittings in  this kind of
                     service.
                     6.  New  York  City's experience demonstrated
                     that wrought iron pontoon -tide gates had a life
                     expectancy of only  10 to 12 years because of
                     rapid corrosion.  The metal  pitted through and
                     the air cells  subsequently filled with water. The
                     loss  of  buoyancy affected gate  operation.
                     Redesign  of the gates in terms of material and
                     buoyancy  characteristics  has  corrected  this
                     condition.
                     7.  The base of the gate should be equipped with
                     one or more lifting eyes, depending on gate size.
                     A chain should be attached through the lifting
                     eye to a  readily accessible maintenance area, so
                     that the  gate can be lifted with comparative ease.
                     8.  A careful selection of the tide gate  site or
                     structural modification of the site and the tide
                     gate,  can facilitate maintenance  and  reduce its
                     cost.
                  Field Survey Results
                     Activation of tide gates is most commonly set to
                  occur  at approximately  a   6-inch  hydraulic
                  differential. The information  on tide gates obtained
                  from- the  surveys is summarized in Table No.  27,
                  Field Survey  Findings  on  Tide  Gate  Practices.
                  Although the data obtained were relatively meager, a
                  number of important points were disclosed in some
                  of the surveyed jurisdictions. These merit  special
                  attention.
                                                    91

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    In New York City, although some outlets in the
higher areas are not provided with  tide gates, the
proximity of the city to the tidal waters of New York
Harbor and tributary  rivers  makes the  use  of tide
gates   essential  at   the  majority  of  the  regulator
chamber overflows. Selection is on the basis of 10.to
15 percent greater area of opening than the combined
sewer, to reduce the head loss and to compensate for
the fact that the perpendicular dam in the sewer is six
inches higher than the invert of the inlet  sewer to the
diversion chamber.  Because  of the relatively low
elevation of the combined sewer,  there are several
locations in the city where tide gates  are used in
series; a chamber in one instance contained two banks
in series, each bank with eight gates.
    The  present practice in New York City is to use
cast iron gates with neoprene gaskets for sizes up to 4
x 4 feet and greenheart timber  from British Guiana
for the larger gates. Timber gates are reinforced with
steel rails to prevent warping, and they are furnished
with  lifting chains which are accessible  from above
the structure for lifting the device.
    In Detroit,  timber gates  are mounted  in walls
which are battered % inch per foot. Variations in the
design of these  units  include frame  castings which
have been made in a single piece, and frames with an
inclined  seating  face, made for mounting on walls
with vertical faces.
    In Washington,  D.C., planned maintenance of
tide gates  is carried out  by a special  crew, on a
schedule of once a year at the treatment plant and
twice a year where the units are in service on the
interceptor system.
    In Philadelphia, two horizontally-operated tide
gates are  in use. A large hydraulic cylinder, with
cylinder stem in a separate chamber, is used to power
the gates. Activation of the cylinder is by means of
water pressure. Under normal dry-weather conditions,
the small regulator gate is opened and the tide gate is
closed,  with  all  sewage  passing  through  to the
operating chamber and ultimately to the interceptor.
Under wet-weather  conditions, the water elevation
rises and, by means of the interconnecting telltale
pipe, the float commences to  rise. As the float rises,
the regulating collar on  the float stem contacts the
pilot arm and raises it, changing the position of the
four-way valve. This changes the position of the port
and  allows the water to pass onto the top of the small
cylinder and commence closing the regulating gate.
At the same time, the water passes through the front
of the large  cylinder and the tide gate starts to open.
With the small gate closed and the tide  gate now
open, the combined sewer overflow is diverted to the
river via the outfall sewer.
    When the period of wet-weather flow is rver, or
the  elevation  in  the  main  sewer  drops,  a
corresponding drop occurs in  the float well, and the
reverse procedure closes the tide gate and the small
gate  opening.
                                                 93

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                                               SECTION 8
                                  EUROPEAN REGULATOR PRACTICES
    The use of combined sewers in urban areas is not
peculiar to the United States and Canada. Combined
sewers  are in general  use  in many other countries.
Those nations with older communities make greater
use of such combined facilities, just as the older cities
on the American continent are served by combined
systems.
    The technical literature on this subject indicates
that only a limited number of cities  have advanced
their  water pollution control programs to the point
where sewer  separation,  or the control or treatment
of overflows  has become essential. However, in some
cases  efforts  have been made-to reduce the strength
of the overflow waste water, and to retain and treat
flows which are carried in interceptor systems.
    As part of the present study, an investigation was
made of conditions and practices in specific areas of
Great  Britain, France,  Switzerland  and  Germany.
These countries were chosen on the basis of regulator.
and control practices disclosed in literature reviews;
on the  personal knowledge of the project staff and
advisory members; and on information contained in
replies  to  letters  of inquiry on  regulator practices
which were sent  to governmental agencies in several
countries.
    In   general,  the. study  of foreign  practices
indicated the following general policies and practices
which   are  at  variance with  recent  trends and
developments in the United States and  Canada:
    1.  The  number  of combined sewer overflow
    regulator  facilities are  limited to  restrict  the
    number of overflow points.
    2.  Standards of  practice require  the  use  of
    storm water detention tanks in conjunction with
    regulator  devices  to minimize the  pollutional
    impact of overflows on  receiving waters.
    3.  There has been  somewhat  greater effort in
    some foreign areas to control the quality, as well
    as the quantity, of overflow wastes, by means of
    in-sewer  design  features and devices. (This is
    referred to in the current project as the "Two Q"
    concept—control of both quantity and quality of
    overflow  wastes.)
    European practice  is  generally based upon lower
per capita sanitary sewage flows and somewhat lower
rainfall intensities  than  those  experienced  in
American  communities.  Local  officials  during
personal  interviews in  European  cities  did  not
indicate  any  problems with oversize  debris such  as
 timbers, automobiles, etc., such as have been reported
 in several major jurisdictions of this country.
    The following abstracts of European survey data
 are  intended  to illustrate  some  of  the  foreign
 regulator overflow practices which will be of interest
 to  officials and engineers  in  the United States and
 Canada.

                1. German Practices
    Each state within the German Republic is almost
 completely  autonomous with  regard   to  water
 pollution control practices. Secondary treatment of
 sanitary sewage  and industrial wastes is  generally
 specified. Mechanical devices are not widely used in
 conjunction  with  combined  sewer  overflow
 regulation.
    General criteria4 require that:
      1. Storm overflow structures in combined sewer
    systems should be applied  if this seems  to be
    useful  under technical and economical aspects.
    Generally, this would be the case for sewers with
    a  large  cross  section area,  from  a nominal
    diameter of 60 cm. (24 in.) upwards,
     2. If  it can be  avoided, several sewers should
    not be tributary to one storm overflow structure.
    If necessary, a connecting  structure should be
    inserted ahead of the overflow structure and the
    conduit leading to the storm overflow structure
    should be  designed -as a region of steady flow.
    The length of the calm region should be at least
    20 times the nominal diameter of the sewer.
     3. Nominal width and slope of invert  of the
    calm  region should be  selected so  that  the
    conduit is completely filled for the design storm
    and that the velocity of flow does not exceed 1.0
    to 1.5 m/sec (3-4.5 ft/sec).
     4. The  contraction   of  the  through-trough
    should be continuous from approach conduit to
    discharge conduit.
     5. It  may  become necessary  to design  the
    discharge conduit as a throttling pipe. In this case.
    its nominal diameter shall be at least 20 cm. (16
    in)  in  order to avoid  clogging. If possible, the
    invert  slope of  the  throttling  pipe  should be
    selected to allow  twice the dry-weather flow to
    be discharged into the continuing conduit so that
    open-channel flow conditions will  be maintained
    in  the  discharge conduit. The minimum velocity
    of flow should be 0.5 m/sec (approximately 1.5
4 Note:  Edited general translation
                                                   95

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   ft/sec).
     6. The  weir  crest  should  be  constructed
   horizontally  over its (active)  length.  The
   elevation of the weir crest should be high enough
   to avoid backwater from the discharge channel to
   the receiving water. The weir height should be at
   least  25  cm.  (8 in)  above the  invert of  the
   through-trough.
     7. A service  platform should be constructed
   along the through-trough. Clearance between the
   floor of the service platform  and the ceiling of
   the structure should be not less than 1.80 m (5&
   ft). A sufficient number of manholes should be
   provided  in order that all parts  of  the sewer
   system can be maintained and cleaned. In larger
   storm overflow  structures,  lighting facilities of
   moisture-proof type should be provided.
     8. Generally, it is recommended that the storm
   overflow  be constructed as a side-spill weir-on
   one side. If local conditions require a shortened
   length of the structure, this can be achieved by
   constructing side-spill weirs on both sides.
     9. Within  fenced-in areas  of treatment  plants,
   storm overflow facilities can be designed as open
   structures.
    10. When  double side-spill weirs are used, only
   75  percent   of the  weir  length  should be
   considered usable. A minimum depth of 20 cm (6
   in) should be maintained under the through-pipe.
                                    FIGURE 27
                       To Receiving Water
      STORM OVERFLOW IN THE
       FORM OF A SIDE WEIR

    Figure 27, Storm Overflow  in the  Form  of a
Side-Spill  Weir, is a sketch  of  a typical  German
installation. The   flow  to  the  treatment plant is
usually  controlled by the  use of a "throttle pipe"
which, under overflow conditions, acts as a pressure
system. With this type of control, excellent gauging
of flows to the treatment, plant is reported. As with
any system which is dependent  upon the inherent
hydraulic characteristics of the system, it is important
that approach grades to  the facility be such that a
hydraulic jump does not occur in the chamber. This
would make part  of the weir length unusable and
raise the water elevation in the facility.
    Regulator installations were  visited  by project
personnel- in  Mainz, Rhineland-Platz. All  were  of
single high side-spill weir overflow design. The design
of access and maintenance facilities  was excellent.
For  one  large facility under an arterial  street, a
stairway has been constructed with its entrance from
the parkway. This  provided ease of entrance, without
any restriction to street traffic.

                2. Swiss Practices
    The national policy  in Switzerland-permits  the
continued construction of combined sewer systems.
The usual design is to carry two times DWF to the
treatment plant and to store the remaining flow in
storm water retention tanks for eventual pump-back
to treatment processes, or to storm water clarification
tanks for partial treatment of flows in excess of the
available storage capacity.
    Water quality  rules have been established which
specify the settleable solids, BOD, and nitrogen to be
removed  from  the  combined sewer overflow.
Research has  been  carried out to ascertain  the
retention .time required in. clarification tanks  to
achieve the desired degree of removal.
    The economics  of  constructing  and operating
either retention or clarification tanks requires that
the regulator and  tank be  placed on the interceptor
sewer at a point  where sufficient  flow occurs to
justify the  facility,  rather   than  increase  the
interceptor size and carry the entire flow to the waste
water treatment works.
    In  Geneva, all of the combined sewer flow is
taken to a central  waste  water treatment plant which
provides the following facilities:
    1.  Screens and detritors are designed to receive
    up  to  90,000  cu  m/hr,  or  570  mgd;  this
    represents the total  summer sanitary flow, plus
    storm water runoff.
    2.  Siphons automatically distribute half of this
    flow (45,000  cu m/hr  or 285 mgd) equally to
    eight primary  tanks  in parallel, or equally up to
    this rate to any other  number which happen to
    be in operation. The flow of 285 mgd is 4.9 times
    the average annual daily water consumption and
                                                  96

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    three  times the  average  daily summer  water
    consumption.
    3.  When  flows  exceed 285 mgd (3 times the
    summer average DWF) the siphons automatically
    and equally distribute 285 mgd to six of the eight
    primary tanks and the flow in excess of this rate,
    up to an additional 285 mgd is diverted to the
    remaining  primary tanks. This provides from 10-
    to  15-minute detention time for this additional
    flow.
    4.  After  leaving the primary tanks, the flow is
    distributed automatically and equally by means
    of Ponsar  siphons,  up  to  a rate of 127 mgd
    (20,000 cu m/hr) 2.25 times the average annual
    daily  water consumption and  1.34 times the
    average daily summer water consumption), to the
    secondary^ units .which consist  of eight aerators
    and eight final clarifiers. All flow in excess of 127
    mgd  (20,000 cu- m/hr) is automatically diverted
    to  the River Rhone, ahead of the secondary
    facilities. In all, 49 automatic Ponsar siphons are
    utilized in  this plant.

               3. French Practices
    The practice in Paris and environs indicates that
very few  automatic  regulators  or other mechanical
devices are currently utilized for control of overflows
from  combined sewers. Fixed  weir overflows have
been used most commonly for this purpose. In a very
few cases, these are  manually adjustable. Automatic
regulation by  adaptation of the Ponsar siphon  is
provided  at Clichy,  a major screening  and control
station  on the  Paris  sewer  system.  At  several
treatment plants outside  of Paris, such as at Calais,
the Ponsar siphon is used at the plant inlet to limit
flows  entering  the plant  from  combined  sewer
interceptors to a fixed rate.

               4. English Practices
    The Minister of Housing and Local Government
appointed  a Technical  Committee  on Storm
Overflows and the Disposal of Storm Water in 1955.
Since  that time   the  committee  has conducted
extensive  research into the design and operation of
several types of combined  sewer overflow regulator
devices, described in an  interim report  in 1963. In
1969'the committee was continuing preparation of its
final report.  The  preliminary conclusions  of the
committee, as  expressed in the interim report,were as
follows:
    1.  There is  a  better  method than  that
    traditionally used for determining the setting for
    overflows. Instead of setting them at a multiple
    rate, usually six times the dry-weather flow, it is
    better to set them  so  that  a  fixed volume  of
    surface water will be  retained in the sewer in
    addition to  the dry-weather flow. This allows for
    the  variations in dry-weather flow from place to
    place, and  for the fact that  surface water does
    not vary proportionately.
    2.   Many overflows  are set at levels far less than
    six  times  the  dry-weather  flow.  Unnecessary
    pollution could be  prevented in many  places
    without the need for new sewers by raising the
    overflow setting; where this is possible it should
    be donejmmediately.
    3."New sewer systems are  usually planned to
    provide for expected increases in sewage flow as a
    result of growing population, industrial demands
    and water consumption, and full use should  be
    made  of spare sewer  capacity as long as it is
    available, for  the retention of additional surface
    water.
    4.   Some  types of overflow (specified in the
    report) are unsatisfactory in themselves, and their
    use should be discontinued.
    5.   The practicability,  of incorporating storage
    in new systems to contain as much as possible of
    the  "first  flush"  of  storm sewage should  be
    considered.
    6.   Sewer system authorities should assess the
    performance of their present overflow systems as
    a basis for  deciding  what  improvements are
    necessary and economically practicable. What is
    needed for  this assessment is an examination of
    the  existing  sewers and  sewage  treatment
    facilities, an evaluation of the population that is
    served and  expected to be served; of the sewage
    flow, and of the local rainfall. The impact on the
    water courses into  which overflows  discharge
    must also be considered.
    The  results  of the model and field  studies
conducted  for  the  committee  were,  published,
following a Symposium on Storm Sewage Overflows,
conducted by the Institution of Civil  Engineers, May
4, 1967. This excellent set of 11 papers described:
     1.  Field studies on the flow and composition of
    storm  sewage (Northampton,  Bradford  and
    Brighouse)
     2.  Effect of storm overflow  on river quality
     3,  The treatment of storm sewage
     4.Laboratory studies of storm  overflows with
    unsteady flow
     5.  The performance  of stilling ponds  in
    handling solids
     6.  Storm  overflow performance studies  using
                                                  97

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    crude sewage
     7. Secondary motions applied to storm sewage
    overflows
     8. Design,  construction and  performance  of
    vortex overflows
     9. Reconstruction of overflows
    10. Practical design of storm sewage overflows,
    and
    11. The storage and discharge capacities of sewer
    systems and the  operating frequency of storm
    overflows: Dutch methods of calculation.
    The laboratory experiments (No. 4) were used to
determine  the   operating  characteristics  of: low
side-weirs;  stilling  ponds; vortex;  and  storage
overflow.  The  models apparently  had  many
limitations  and  in  some  cases   they  did  not
incorporate  provisions  found desirable in existing
field installations. Both the Storage-type Regulator,
and the Stilling Pond  Regulator, Figure 28, exhibited
good operating characteristics. The Vortex Regulator,
Figure 29, had inconsistent characteristics.
    Field  experiments (No. 6) were conducted using
crude  sewage and a  low double side-spill weir, a
stilling pond, a  vortex overflow, and a high level
side-spill weir with position flow control.  The low
side-spill  weir  was found  to  be  generally
unacceptable. The other three types exhibited various
favorable  qualities. The high side-spill weir and vortex
overflows, both with  outlet  control, gave good
control of flow to treatment facilities.
    The field tests, in contrast to the model tests,
gave little indication of pollution improvement of the
overflow  by type of regulator, except for the vortex
at  high  flows. This  lack  of  overflow  quality
enhancement was thought to be a characteristic of
the constraints at the  testing facility inasmuch as the
results of actual test installations indicated overflow
quality improvement.
    Of particular interest is the work which was done
involving  secondary motions (No.7)  with regard to
liquid  flow.  Research was  carried  out  with  the
development of helical flow. It was found that a short
bend,  or  a series of short  bends can  be used  to
separate the  solids from the flow discharging to the
overflow.  The formation  of a helix or a system of
helices exist in any  flow of liquid within curved
boundaries.  Solids are concentrated on  the inside of
the bend.  The flow with the concentrated solids load
can be bled off with siphons or slots, or the overflow
can be permitted to take place along a high side-spill
weir on the outside  of the  bend. Figure 30 Spiral
Flow   Helical Regulator,  illustrates   a  typical unit
configuration.
    The  circular vortex overflow is another form of
secondary motion device. Two such regulator devices
have been constructed at Bristol. The results obtained
with full-scale units were reported to be far superior
to the  results  obtained from  the model and  test
facilities.
    Interviews were conducted in England with both
national and local officials. These interviews revealed
that:
    1.  Stilling ponds  and  high side-spill  weir
    overflows are the two general types of overflows
    now being constructed. Many of these regulators
    use a penstock control (mechanical sluice gate) to
    control discharge to the interceptor.
    2.  Mechanical screens  are  in general use,  (see
    Fig.  31) to screen solids from the overflow and
    return solids to the interceptor sewer.
    3.  The number of  overflow  points is  being
    reduced  in  order  that  detention  or treatment
    facilities can economically be constructed for the
    overflows.
    Regulator installation  in Coventry,  Manchester
and  Bristol  were  visited by project  personnel.
Highlights of practices at each jurisdiction follow:
Coventry:  Coventry has recently established three
storm water stations. All of the combined sewage is
taken into  one of the three stations where the flow in
excess of the sewage treatment facilities is overflowed
to a series of three storm water tanks, with a capacity
of approximately 20 times the  dry-weather flow. At
the regulator facility, "Parkwood" screens are used to
minimize the amount of floating solids overflowing to
the tanks.
    Figure  31, Mechanical Screens,  illustrates  a
typical installation  on  a side-spill weir. The  storm
water  tanks  overflow  approximately three times  a
year. They provide good primary settling. Solids are
removed in a  conventional manner. The overflow
weirs  have  penstock controls to limit the outflow to
the treatment facility;  however,  this is  based on a
calculated rate and is controlled  only by the incoming
flow. The tanks are pumped back into the interceptor
line whenever the flow to the treatment plant  is less
than the plant capacity.
    The  storm water  stations  are  landscaped  and
located adjacent to new developments.  In one case, a
golf course  abuts the facility and  another station is
adjacent to a university housing project.
    Along the orifice outlet of the regulator an  access
chamber is  provided for a  considerable distance in
order  to  facilitate  measurement  of the flow  and
maintenance operations.
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                                                                        FIGURE 28
                                               X3.s«"      END  ELEVATION
     COMBINED  SEWER
                                        SCALE OF FEET
                                        "B"
                           I: 4
                                                    le - II
                                                     A
                                                         TO PLANT
                                                         TO  RIVER
                     PLAN
                  SECTION  "A"-"A1
SECTION"B"-"B"
                       POSSIBLE  APPLICATION

                  STILLING   POND  REGULATOR
Courtesy Institution of Civil Engineers
                                          99

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                                                                      FIGURE 29
                       COMBINED  SEWER
    STORM SEWER
 B
                                                INLET 36"OIA.
                                                     AFFLE


                                                   BRANCH INTERCEPTOR


                                                   TO TREATMENT PLANT
                         SECTION  "A"-"A"
                   WHITE   LADIES   ROAD
                COMBINED SEWER
             INLET 4'X3'
                                                   SCUM BOARD
                          BRANCH.
                          INTERCEPTOR
         SCALE OF FEET
        5     IO      15
ALMA  ROAD
                                                     VORTEX  REGULATORS
Courtesy Institution of Civil Engineers
                                      100

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                                                                        FIGURE 30
             CROSS  CONNECTION FOR OVERFLOW..
                            CONTROL
,FLUME INVERT
                                                                  TO PLANT
                   PIPE FOR NORMAL FLOW --^

                       PROFILE  ALONG CENTER LINE
                                                      OVERFLOW WEIRS
                                                      WITH DIP PLATES
                     CHANNEL  FOR NORMAL
                     FLOW 8 HEAVY SOLIDS
           FLUME FOR
           FLOATING
           MATERIAL
                                    PIPE FOR NORMAL
                                    FLOW a SOLIDS
           "A1-"A"
                                  CONTROL PIPE  FOR
                                   OVERFLOW CHAMBER
                                                       TO INTERCEPTOR
  SECTION "B"-"B'
                                    SPIRAL  FLOW  (HELICAL)
                                            REGULATOR
Courtesy Institution of Civil Engineers
                                           101

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                                    FIGURE 31
Courtesy The Longwood Engineering Co. Ltd.
Manchester:  The  City  of Manchester is rebuilding
portions of its combined sewer system to eliminate
overflows and to increase capacity. The new regulator
facilities are basically of the long weir type with large
stilling  basins; a  scum board is  used to minimize
overflow of floating debris. Storm water in excess of
the sewage treatment plant capacity is taken to the
treatment plant where the flow is screened and then
run through long grit chambers prior to  entry into
storm water holding tanks. The stilling basin serves to
reduce  the  number   of  overflows  and  to  return
non-floating  solids  to the  foul sewer.  Penstock
controls are used to control flows.
Bristol: The City of Bristol is rebuilding much of its
storm  water  combined  sewer  system, using high
side-spill weir overflows and taking six times DWF to
the treatment facility.
    During  the investigation of possible  design for
regulators  to  be  used on a major relief sewer to
protect the business area of the city, the  concept of
using a circular vortex regulator was  evolved in order
to obtain adequate weir length without the expense
of  constructing  a long  side-spill  weir   structure.
Laboratory studies of the vortex configuration were
carried out  and  eventually two  regulators were
constructed jn 1964.
    The  facility which was inspected by  the project
personnel had a diameter of approximately 16 feet.
Retention  time is approximately 11  seconds; tests
indicate that 70 percent of the solids are  diverted to
the interceptor.
    A scum board is used to retain floating solids.
Clogging of the outlet has occurred only three times
in  six years—caused  each  time by  bricks from
deteriorated sewers.
    The  City  of  Bristol  is continuing   its  work,
utilizing  the vortex principle with  an experimental
primary  settling tank  for a flow rate of 3,000 gpm.
Results to date are very satisfactory.

         Summary of European Experience
    Although hydraulic  conditions  in Europe  and
England  vary from American conditions, there are
several practices  which should be  considered for
adoption  or adaptation in  the  United  States  and
Canada:
    1.  Limit the number of overflow points.
    2.  Improve  the quality of overflow by screening
    or applying secondary flow motions.
    3.  Consider  utilization of stilling ponds, high
    side-spill weirs, and circular vortex regulators—all
    with controlled outlet controls.
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                                             SECTION 9
                     ROLE OF PRODUCTS, PROCESSES, AND FUTURE REGULATOR
                         PROGRESS IN IMPROVED CONTROL OF OVERFLOWS
    The  investigation  of problems  relating  to
combined sewer overflows,  carried  out under  the
1967  Investigation disclosed the numbers, locations,
and types of regulator  devices  in use in the United
States. These devices may be categorized, basically, as
static  and dynamic regulators.
    Devices  in  the  static  class,  such as weirs and
orifices, have been fabricated locally by either small
foundries or machine shops or installed or built in
place  by the sewer system jurisdiction or contractors
serving them. Other so-called static devices, such as
manually  operated  gates  and siphons, have been
supplied by companies in the national field. Dynamic
regulator  devices,   including  semi-automatic  and
automatic units, have  been built and  supplied by
manufacturers for the national market and are usually
listed in   catalogs  and  technical brochures.
Instrumentation facilities  for application to  the
regulator field have been manufactured by companies
experienced in  the  electronic-electrical
recording-controlling-automation field.
    Potential developments and future progress will
depend  in  great   measure  on  the  desires  and
capabilities of experienced  manufacturers to research ~
and  create improved  processes,  products  and
materials for primary applications to combined sewer
service and for other related functions.   '
    The  interrelationship  between  the equipment
manufacturers  and  the development  of improved
regulator  practices  for the  improved  control  of
overflows is  very important.  It  was  decided  that
evaluations of available  devices and facilities and the
prospect for future developments must be determined
directly with manufacturers. The purpose of such
contacts  between producers and  users  of  regulator
devices and systems was to ascertain the need for, and
means of,  developing  new  regulator  practices  to
eliminate unnecessary  overflows; to provide  better
guidelines for  the application and  adaptation  of
existing and proposed  regulator  facilities; and  to
catalyze  the development  and  use  of new  and
improved technologies, and materials.
Developing a Relationship With  Manufacturers
    This  type of  coordinated  effort can  be
accomplished in two ways: by individual contacts
with all such manufacturers; or by collective group
discussions with'  interested  and  concerned
manufacturers and suppliers.
    The second procedure was adopted on the basis
that better  exchange of information would result
from such group contacts and that a broadening and
cross-fertilization  of  interests  between  all such
manufacturers and suppliers would result from this
procedure.  To expedite this  decision, a one-day
exploratory  conference  on regulator problems was
convened by the American Public Works Association,
with   a  representative  of FWQA  participating.
Approximately 50 manufacturers of various types of
regulator equipment  and appurtenant facilities were
invited to attend the  session. Eighteen manufacturers
sent representatives  and approximately  ten  more
expressed interest  in the project and  asked to  be
advised of  further  developments  and to receive
information  on the findings and conclusions of  the
exploratory meeting.
Creation of the Manufacturers' Advisory Panel
    During  the  exploratory  conference,  the
manufacturers'  representatives  recommended  the
creation of a smaller working panel to  serve as  the
liaison between  the  manufacturing  field and  the
FWQA-APWA research project. This subgroup was
created  and  designated  as  the  Manufacturers'
Advisory Panel. Members of the panel  are listed in
Section 11 of this report, in  acknowledgement  of
their invaluable services and the importance of  the
information which they supplied to the project.
    At the  first organizational meeting,  the panel
decided that  its  operations could be  expedited and
the performance  of its  functions  improved,  by
designating  subcommittees  to  carry  out  specific
phases  of   its  responsibilities.  The  following
subcommittees were created:
    1.  A  subcommittee  on  the  most  effective
    materials for regulator facilities;
    2.  A subcommittee on improved operation and
    maintenance practices;
    3.  A subcommittee  on  instrumentation  and
    control; and                     •
    4.  A subcommittee  on the  "total systems"
    concept of sewer management and control
    Pertinent excerpts from 'preliminary reports  of
panel  subcommittees  are included in Section 14  of
this report.
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Survey of Existing Products and Processes and Stimu-
lation of Future Developments in Regulator Practices
    Over and  above the  functions assigned to the
Manufacturers' Advisory Panel, an attempt was made
to contact all known manufacturers of products and
processes directly  or indirectly  applicable  to the
regulator field. A communication was addressed to all
such  companies  requesting  them  to  supply  the
following information:
    •   A full catalog listing of all equipment now
    offered,  such as:  regulators,  gates,  valves,
    standard  actuating  devices,  direct controls,
    instrumentation, automatic-automation systems,
    sensing devices, remote  control and telemetry
    facilities,  and  any other related  products or
    processes.
    •   Other  technical literature  on  regulator
    equipment,  materials and  methods, such as
    brochures, engineering reports, technical papers,
    cost data, and application data.
    •   Forecasts  covering important  trends  and
    developments  in improved  regulator methods,
    materials and mechanisms, all within the limits of
    proper protection of any and all proprietary and
    patent rights  to their products and processes.
    Catalog material was received from a number of
manufacturers, partially  serving  the  purpose of
inventorying  available hardware  and  auxiliary
equipment related to the regulator field. A limited
number of replies  gave  some indication of future
trends  and .developments and  showed limited
manufacturers  interest in  the  improvement  and
enhancement of regulator practices  by means of new
products and technologies and better application of
existing facilities and equipment.  In a number of
cases, manufacturers who  do  not  now market
products in the regulator field, but  whose equipment
could have  such  applicability,  expressed minimal
interest in the utilization  of  their products and
processes for regulator-control purposes.
    In addition to the catalogs and technical bulletins
received from manufacturers, other sources of such
information  were utilized to partially augment these
basic data. In keeping with the broader definition of
regulation  to  encompass  the  control  of both the
quality  and  quantity of overflow waste waters (the
"Two  Q"  concept  outlined in  Section 2 of this
report), a  search was made for catalog and bulletin
data which  might  have  a  direct bearing on this
two-phase  principle of overflow regulation, either
directly or  in a secondary manner. Table No. 28
contains collated data on products and processes.
                                            TABLE NO. 28
                        TECHNICAL CATALOGS AND BULLETINS RELATING TO
                     PRODUCTS AND PROCESSES OF PRIMARY AND SECONDARY
                       APPLICABILITY TO THE REGULATION AND CONTROL OF
                           OVERFLOWS FROM COMBINED SEWER SYSTEMS
    ADis Chalmers  Manufacturing  Corp.—Butterfly
valves; fabricated valves; water control gates
    Armco Steel Corp.—Sluice gates; flap gates
    Autocon Industries,  Inc.-Supervisory  control
equipment; remote control; telemetry; panels
    Badger  Meter  Mfg.  Co.,   Instrument
Division —Flow   tubes;  Parshall flumes;
transmitters/receivers
    Bailey  Meter Co.—Pneumatic and  electric level
transmitters; computer control systems; orifices; flow
nozzles
    BIF—Application data  on electronic  control
systems; telemetry; weirs; orifices; valves
    Bird Machine Co.—Aeration process
    Bowles  Fluidic  Corp.—Technical  bulletins/data
on fluidic/technology and water management; FWQA
report on fiuidic interceptor control
    Bristol  Co.—Liquid level measurement  and
control  equipment; telemetering;  pneumatic  and
electric transmitters and controls
    Brown  &  Brown  Inc.—Automatic  sewage
regulators; tide gates; engineering data
    Chicago  Pump,  FMC  Corp.—Barminutors;
Comminutors; screening machines; grit removal
    Cla-Val Co.-Valves
    Clow—Comminutors
    Coldwell-Wil cox  Co . —Hy dr aulic
cylinder-operated sluice gates; flap gates; tide gates;
backwater  gates;  fabricated diverter  gates;  gate
operators
    Crane,  Cochrane  Division—Microstrainers;
ozonators for storm water overflows; waste water
treatment equipment
    Delta Scientific Corp.—Analytical equipment for
monitoring and control of waste water
    DeZurik Corp.—Eccentric valves
    Dorr Oliver—Grit  removal  equipment; waste
water treatment equipment
    Firestone  Coated   Fabrics  Co.—Fabricated
plastics; Fabri tanks; Fabridams
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    Fischer &  Porter  Co.—Time  pulse  receivers;
chlorinators; meters
    Flomatcher Co.—Sewage pump control systems;
fluid  start-stop  sequencers;  pneumatic  control
systems
    Foxboro Co.,—Liquid  level measurement  and
control equipment; telemetering; receiver-recorders;
transmitters;  pneumatic  and  electronic  controls;
analog computing stations
    General Electric Co.—Integrated circuitry; remote
station operators; digital coding systems; supervisory
systems for automatic variable-speed pumps
    Glenfield  &  Kennedy,  Ltd.—Microstraining
equipment
    Golden  Anderson  Valve  Specialty
Co.—Solenoid-operated valve systems
    Healy-Ruff Co.—Telemetry  equipment;
pressure-operated controls; float operated controls
    Henry Pratt Co.-Butterfly valves; controls
    KDI  Poly-Technic, Inc.-Water quality monitors
    Leopold  &  Stevens,  Inc.—Flow  meters;
telemetering systems
    Link—Belt, FMC—Screens;  grit  removal
equipment
    Minneapolis Honeywell Regulator Co.—Flow and
The Potential Market For
Regulators and Appurtenant Devices
    The contacts with the manufacturer were made
for the purpose of stimulating new research  and
development  efforts. At the exploratory conference,
manufacturers expressed concern over the required
expenditure of industry's time and money for the
development  of materials, methods and mechanisms
which  would have  limited use and sales  potential.
Reference was  made  to  the general  lack  of action
against combined sewer overflows on the part of
pollution  control regulatory agencies, and to  the
hesitancy  of  municipal officials to expend  the funds
necessary  for the improvement of regulator facilities
and systems.  This concern was based on these above
factors, and on  the fact that the construction of new
combined  sewer   systems  will be  of limited
significance in  sewer practice  in  the  future, hence
limiting the market for new regulator stations.
    Manufacturers were advised that  the market lay
not necessarily  in the area of new regulator station
installations but, rather, in  the  modernization  and
upgrading of regulator facilities  in existing systems
and stations,  in order to facilitate the reduction of
the frequency and period of duration of overflows.
liquid  level meters; telemetry;  industrial controls;
graphic panels
    National  Sonics  Corp.-Water-solids interface
sensors
    Neptune  Meter  Co.,   Neptune  MicroFloc,
Inc.—Microfloc equipment
    Phipps & Bird, Inc.—Sewage sampling equipment
    Rex Chainbelt,  Inc:—Trash racks; water screens;
grit collectors
    Rockwell  Mfg.   Co., Republic  Div.-Pneumatic
transmitters; pneumatic relays; pneumatic controllers,
positioners; electronic transmitters; final drives
    Rodney Hunt  Co.—Sluice gates; gate hoisting
equipment; fabricated  slide gates; fabricated timber
gates; flap valves; tide gates
    Rohrer Associates Inc.—Underground  storage
faculties for storm water,
    Waco,  Products Div.—Stop gates; slide gates; bar
screens; weir plates,-aluminum products
    Wallace & Tiernan  Co.—Chlorinators; residual
chlorine  analyzers; controls
    Western Machinery Co.—Grit removal  equipment
    Yeomans-Clow—Pneumatic  pump-ejectors;
aeration equipment; clarifiers
    Zurn Industries, Inc.—Microstrainers; waste water
treatment equipment
Upgrading  of regulator  facilities  may  also  be
necessary  when facilities  are  constructed  to  treat
overflows.
    While the project survey of the policies of state
water  pollution  control  agencies  gave no  great
assurance that any intensive drive for  the betterment
of regulator facilities was imminent at the state level,
a  subsequent investigation  of  Federal  policies
indicated that a tangible market for the improvement
of regulator practices could be anticipated. A partial
listing was obtained of recent Federal water pollution
control enforcement conferences with state agencies,
where Federal recommendations had  been made  on
combined sewer problems. Excerpts from this record
of  enforcement conferences  are  included  here  to
indicate that there  is a new interest in the prevention
of pollution caused by ineffective regulator devices.
This interest indicates a reasonably important market
for new regulator  devices, and  the  application  of
automatic-automation-instrumentation practices
which  will  result  from research  and development
efforts by manufacturers.
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 SUMMARY OF SPECIFIC RECOMMENDATIONS
 CONCERNING STORM WATER OVERFLOWS IN
   RECENT FEDERAL-STATE ENFORCEMENT
                 CONFERENCES
    The following are  excerpts  from enforcement
conferences  where recommendations were made on
the combined sewer problem.

   Pollution of Boston Harbor and Its Tributaries
                 April 30,1969
    1.  A report, by a consulting engineering firm,
    calls  for  the  most  practical  and economical
    solution for abatement of the  pollution effects
    from  tributary streams  and combined sewer
    overflows  in  Boston  Harbor  which  will  be
    completed by the winter of 1970-71. The report
    is to be  followed by an implementation schedule
    which  will  incorporate  the  approved
    recommendations.

     Pollution of Lake Erie and Its Tributaries
 (Michigan, Indiana, Ohio, Pennsylvania, New York)
          Second Session, August,  1965
    1.  All new sewerage facilities are to be designed
    to  prevent the necessity of bypassing untreated
    wastes.
    2.  Combined sewers are to be prohibited in all
    newly developed urban areas and eliminated in
    existing  areas  wherever  feasible.  Existing
    combined  systems  are to  be  patrolled  and
    flow-regulating structures adjusted to convey the
    maximum  practicable amount of combined flows
    to and through treatment plants.
    While the  dates for completion  of various stages
of the other requirements for municipal treatment,
etc., have extended, it is to be noted that the above
requirement  of patrolling combined  sewer systems
was to start immediately.

        Pollution of the Inter-State Waters
      Of the Hudson River and Its Tributaries
             (New York, New Jersey)
                September, 1965
    1.  The pollution  problem caused by discharges
    from  combined  sewer  overflows is to  be
    reviewed,  and a program  for  action is  to be
    developed  for  consideration by  the  Federal
    government,  the  states, and the Interstate
    Sanitation  Commission, by December 31, 1968.
    2.  Programs shall be established for surveillance
    of existing combined sewer  systems and flow
    regulatory  structures to convey  the maximum
    practicable  amount  of  combined flows to and
    through treatment plants.

 Pollution of Lake Michigan and Its Tributary Basin
       (Wisconsin, Illinois, Indiana, Michigan)
              January-March, 1968
    1.  Unified collection systems serving contiguous
    urban areas are to be encouraged.
    2.  Adjustable overflow regulating devices are to
    be installed on existing combined sewer systems,
    so designed  and operated as to utilize to the
    fullest extent possible the capacity of interceptor
    sewers for conveying combined flow to treatment
    facilities.
   -The -treatment facilities shall be modified where
necessary to minimize bypassing. This action is to be
taken as soon as possible and not later than December
1970;  pollution from  combined  sewers  is  to  be
controlled by July, 1977.

   Pollution of the Interstate and Intrastate Waters
  of the Upper Mississippi River and Its Tributaries
             (Wisconsin, Minnesota)
             February-March, 1967
    1.  Present  combined   sewers  should  be
    continuously  monitored and  operated  so  as to
    convey the maximum  possible  amount  of
    combined  flows  to  and  through the  waste
    treatment plant. Methods  to be used to control
    waste from combined sewers and a time schedule
    for their accomplishment should be reported to
    the conferees within two years.

       Pollution of Interstate Waters of the
         Potomac River and Its Tributaries
          Washington Metropolitan Area
     (District of Columbia, Maryland, Virginia)
                 April-May, 1969
    1.  Detailed analyses of  alternate methods of
    meeting future water quality requirements and
    sewerage needs  in the Metropolitan Area shall
    include fail-safe  sewer systems to prevent raw
    sewage  discharges; possibilities for load  transfers
    to other sewage treatment plants, etc.
    2.  The conferees, at six-month intervals, shall
    review  plans for elimination  of pollution from
    combined  sewer  overflows  and  establish  a
    timetable for the control of such pollution.
    3.  The State of Maryland shall take action to
    control • sewage overflows  from  sources  in
    Maryland.  Alexandria, Virginia,  shall  complete
    plans by December 31, 1971, for elimination of
    pollution from combined sewer overflows.
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 Functional Gaps in Regulator Practices
    One of the major goals of the research study, in
 terms of contacts with manufacturers, was to create a
 recognition of the functional gaps which  now exist
 between present products and practices,  and those
 which hold promise  to provide new  sophisticated
 improvements in  regulator control facilities.  The
 challenge  is to  fill these gaps with new products,
 processes and procedures.
    As  has  been  stated,  the problem  of
 regulator-overflow improvements must be solved by a
 two-pronged  approach to  quality and  quantity
 control of waste waters discharged from  combined
 sewer systems to receiving waters, either directly or
 following some form of treatment, or quasi-treatment
 processing.
    Two things are apparent from a listing of "gaps"
 in combined  sewer system  operation  and control.
 Reduction  in the quantity of overflow wastes from
 combined  sewers  must be  combined  with  the
 improvement of the quality of overflow  wastes which
 reach receiving waters.  The "Two Q"  definition of
 regulator functions and overflow- control must be
 accepted in all future work in this field.
    Study  of foreign and current North  American
 trends has served to emphasize the challenges that lie
 ahead. These  include, but are not limited  to, the
 following procedures:
A. Control of Overflow Quality
    1.  Use of  screens, present  or  new  types, to
    protect  regulator  devices  from  clogging,
    deterioration or other physical damage, and to
    intercept  waterborne waste  substances  which
    might otherwise add to the pollutional impact of
    overflows;
    2.   Utilization of skimming-baffling  devices to
    improve the quality of overflow waters;
    3.   Utilization  of  fluid  secondary-motion
    configuration devices to concentrate  solids in
    sewer flows and to thus enable the withdrawal of
    the solids to the interceptor sewers and treatment
    works;
    4.   Utilization of fiuidics-principle devices for
    better  and more sensitive- regulation  of
    intercepted  and  wasted  flows, and for  the
    possible improvement of the quality  of waste
    waters allowed to overflow to receiving waters;
    5.   Use  of  retention  facilities  to  intercept
    combined  sewer overflows and  return them to
    the  treatment plant  during nprmal flow periods;
    and
    6.   Treatment facilities such  as microstraining,
    dissolved air-flotation, and high-rate filtration.
 B. Control of Overflow Quantities
     1.  Application of new siphonic principles for
     better regulation of  overflows from combined
     sewers, and for prevention of backflow into
     collector and interceptor sewers by tidal and high
     river-stage waters;
     2.  Application of  inflatable  fabric dams  to
     provide  effective   and sensitive   control  of
     overflows by storing combined flows upstream in
     sewer systems;
     3.  Adaptation of  valves,  pumps  and  other
     available equipment  to the  specific  purpose  of
     combined sewer regulation and overflow control;
     4.  Maximizing  application of  all  feasible
     methods of in-system or off-system retention  of
     surplus flows to reduce or eliminate discharges of
     overflows to receiving waters; and
     5.  Monitoring of overflow incidents and periods
     of duration, for the  purpose  of evaluating the
     feasibility of quantity control of overflows.
C. Total Systems Management of Combined Sewer
Systems
    1.  Application  of  more  effective  and
    sophisticated  instrumentation  and
    automatic-automation facilities for the purpose
    of achieving "total  systems" management of
    combined sewer networks;
    2.  Development of new hardware and auxiliary
    equipment to implement systems management of
    combined sewers and to utilize the full potential
    carrying and retention capacities of all parts of a
    total sewer system;
    3.  Integration of urban area precipitation and
    runoff rates by means of rain gauge monitoring
    circuitry  which will alert control centers and
    automated  overflow-regulator stations to
    anticipated excess flow conditions;
    4.  Total  systems  analysis of combined sewer
    networks  for  the  purpose of ascertaining the
    potential benefits of more sophisticated overflow
    control;
    5.  Utilization  of the  knowledge and skills of
    local utilities  in the communication field, in
    exploring the feasibility and workability of total
    systems management techniques; and
    6.  Consolidation of overflow points  into fewer
    locations which can then be equipped with more
    effective  regulator  facilities  and geared into  a
    total systems control and management program
    by means of automatic-automation-instrumenta-
    tion procedures.
    The necessary improvements in equipment and
systems is dependent on the manufacturing industry.
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This cooperation must  be nurtured and guided by
means of a continuing liaison between suppliers and
users  of the kind of equipment and apparatus upon
which improved regulator-overflow practices must
depend.
    Some of the goals set forth above are being met,
in whole or in part, in combined sewer practices in
demonstration  projects  in  the  United States and
Canada,  and in actual  field installations  in other
countries.  Current  developments in regulator and
control  facilities and  methodologies offer tangible
proof that the scientific knowledge of the 1960's will
be better utilized for the control of the quantity and
quality of overflows from combined sewer systems in
the 1970's. Of  special significance is the application
of the  "total  systems"  management concept  in
demonstration projects stimulated by FWQA grants
to various governmental jurisdictions. The possibility
of "making two blades of grass grow where one grew
before"—utilizing not only the transporting capacity
of sewer  systems but their retention capacity—by
means of "total systems" control is worthy of serious
consideration  by  the  governmental  field and  the
industries which serve it.
    References to actual in-system applications of
combined sewer  management in this report of the
study project, and in the Manual of Practice which is
an integral portion of the project, add pertinence and
practicality  to the  use  of improved  quality  and
quantity control  of  overflows to alleviate the water
pollution  problems besetting the water  resources of
the American continent.
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                                               SECTION 10
             THE "SYSTEMS CONCEPT" OF COMBINED SEWER REGULATION: AN OVERVIEW
     Combined sewer-systems have been designed and
 constructed  on  the  principle  that  overflows  at
 frequent locations could be used most effectively  to
 provide prompt and local relief of collector sewers
 and interceptor lines. This proliferation of overflows
 and  regulators  also  served  to reduce the size  of
 interceptors required in various sections of the total
 sewer system.
     This  principle may  have been pertinent  and
 permissible when the amount  of combined  sewer
 overflow  and  the actual location of the discharge
 were not  considered  significant in the  control  of
 water pollution. However, if pollution control is to be
 achieved,  there must be  a reduction in  volume  of
 overflows, in terms of frequency and duration, and  in
 the pollutional strength of the waste water discharged
 to receiving waters. Improved regulator practices and
 facilities can play a major role in achieving this goal.
 In addition, treatment facilities for  combined sewer
 overflows  can be more  effectively  operated if the
 flow to the faculties is controlled by a well designed
 and operated regulator.
    The  major  imperfection  of combined  sewer
 overflow regulation stems from the  proliferation of
 individual  facilities,  designed to  perform: the
 elementary function  of  relieving  the sewer system
 without  any  consideration  to  the  effect of each
 individual  discharge  point  upon the  total  sewer
 system, as well  as  on the  waters  into  which  the
 overflows spill.  This each-unit-of-a-sewer-system-for-
 itself concept  fails to integrate the various facilities
 into  a master management plan. Specifically,  it  is
 based on  the  principle  that,  in  substance, each
 regulatorTOverflow installation is a separate entity not
 related to the rest of the total  system. If this principle
 prevails, little  can be done to alleviate the  frequency
 and  duration  of the total system's overflows. Even
 with  better control obtained at each overflow point,
 for example, by converting static regulator devices
which are  insensitive to in-sewer conditions to
 dynamic systems which react to collector  sewer and
interceptor levels and capacities; such regulators will
tend to maintain desired hydraulic conditions in the
restricted  area where the  unit is installed, but no
major benefits are likely  to occur in the overall
system.
    The   defects  of single-unit control   are: (1)
multiplicity of  overflow  points; (2) inability to
establish a priority sequence of locations to minimize
 environmental harm and hazard; (3) failure to achieve
 the full hydraulic capabilities of each section of a
 total sewer  system; and (4) lack of opportunity  to
 utilize  the whole sewer system in direct  relation  to
 the patterns of storm and runoff in various areas of a
 community, particularly. those  with large areas and
 variable topographic characteristics.
     This unintegrated condition can be likened to an
 automobile  traffic  control system  which  relieves,
 congestion at a specific intersection and blinds itself
 to the  fact  that in so  doing it affects the flow of
 traffic in all other parts  of the system.
     The value of improving each regulator device to
 the highest level  of effectiveness, to sense and do
 something about local  conditions at a local point
 must not be minimized; however, maximum benefits
 of regulator control and combined sewer management
 cannot  be achieved until the perspective is broadened
 into the  full function  of a combined sewer system
 control program.  This latter procedure involves the
 "systems concept;"
    The  systems concept in' its   simplest  form
 envisions  the  management or control of all elements
 or facilities which are parts .of the sewer system to:
     1.  Make  maximum utilization  of interceptor
    sewer capacity to carry combined sewage to the
    waste water treatment plant;
    2.  Make  maximum utilization  of in-system
    storage;'
    3.  Give  priority  in the interceptor sewer to
    those flows which have a higher  pollutional load
    and which, if they overflow, would result in
    adverse conditions in receiving waters; and
    4.  Integrated use of combined sewer overflow
    storage or treatment facilities.
    Effects  of systems  control  on the waste  water
 treatment plant must be considered and modification
 in facilities and procedures provided.
    The systems concept envisions  that means are
 available to control the operation of elements of the
 system  and  that  there  is  available  adequate
 information  as  to flow  volumes   and  pollution
 characteristics to allow decisions to be made.
    In the newly recognized "traffic routing" system
 of combined sewer operation,  applicable  for  large,
interconnected systems, the  capability of  an overall
systems management program is applied to the task
of shunting flows from surcharged conduits to those
with surplus  flow and storage capacities and could,
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thereby,  eliminate or at least reduce the need for
overflows  from  the  total  system.   Large-sized
combined  sewer  networks have  large  storage
potential.
    Communication is the key to a systems approach.
Lack  of  such communication  between  individual
regulator  installations  is the  weakness  of  the
each-regulator-for-itself procedure. The effective use
of modem communication methods is the basis for
"tying together" all the individual units into a master
system.
    The  fact  that water seeks its  own level  offers
possibilities  for  intercommunication between
individual  control-overflow  points by  means  of
transferred hydraulic levels. This means of integrating
operation procedures, however,  is not  sufficiently
dynamic  to  provide  sensitive  control.  The  same
hydraulic conditions which might be depended upon
to actuate unified regulator operations, of themselves,
may cause  the type of local hydraulic  overloads in
sewer  systems which  individual regulation stations
were intended to prevent
    Over simplification  of the  systems concept of
combined sewer  system management and overflow
control must  be avoided. First of all, fixed or static
regulator devices  will be  of limited value  in  any
sophisticated,  integrated system. Thus,  systems
control  dictates conversion from static to dynamic
facilities in a majority of regulator installations. For
this reason, the  feasibility of  converting multiple
chamber  locations  into a  single,   sophisticated
regulator-overflow  station is a key part of a total
systems management plan.
    The  adoption of dynamic  regulators,  or the
adaptation  of existing devices into facilities  having
adequate regulating capabilities, is only  the first step
in weaving a system of regulators into a total  master
plan. The problem requirement is to develop facilities
and techniques  that  will efficiently  route,  limit,
divert, transfer, and store waste waters  within the
sewer  system according  to  a. planned  scheme of
action. This will involve elements for measurement or
registering hydraulic conditions  at a wide range of
locations; for status determination in  terms of the
 rest of the  system; for gathering information or data
 at a systems  control station; for using  these data to
 provide  the basis for decision-making; for execution
 of  the control  plan;  for  verification that the
 instructions have been executed, by feedback; and for
 correction and evaluation  of the results of the master
 control  system. The fact  that conditions in a sewer
 system are constantly changing makes prompt control
 and correction essential.
    Measurement and  status determination can be
accomplished  by various types  of sensors  which
utilize electrical or electronic signals to represent such
conditions as flow, head, differences in pressure, gate
position, and level in receiving waters. Data gathering
can be achieved by equipment which conditions or
codes  signals  over  prearranged   communication
channels. Correlation of data is the role of indicators,
recorders, loggers,  alarm systems,  and  computers.
Decision-making becomes the function of supervisory
personnel or of computer programs prepared by such
persons.  Execution of decisions is assigned to field
crews  or to  remote  control automation  facilities
capable of  receiving instructions  and carrying them
out.  Verification  can  'be  accomplished  through
communications  with  field  crews  or playback  of
automated data by way of communication  channels.
Verification can be accompanied by any corrections
required to achieve the  desired regulator control.
Examples of Total System Management
    The total systems concept is in use in  several
jurisdictions with combined sewer  systems,  as the
result  of demonstration grants  from  the Federal
Water Quality Administration.
    Three  systems  are  a matter  of  record: (1) The
Minneapolis-Saint Paul  Sanitary  District; (2)  the
Municipality of Metropolitan Seattle; and (3) the City
of Detroit.
The Municipality of Metropolitan
Seattle, Washington
    A total systems concept plan has been  described
in reports  and  technical  papers  prepared  by
Metropolitan  Engineers, Consulting Engineers. The
following information  on studies  of the feasibility of
such a system for Metropolitan Seattle are  excerpted
from these documents.
    The  Municipality  of Metropolitan  Seattle
("Metro") has awarded a contract to the Philco-Ford
Company  for over  $1,200,000  for furnishing and
installing a Computer  Augmented Treatment  and
Disposal System ("CATAD  System").  The primary
 objective   of the  CATAD  System is  to   permit
 optimum   utilization   of  available storage   within
 existing combined sewers  in regulating  storm water
 flows to minimize the frequency and magnitude of
 sewage overflows  into Puget  Sound. Successful
 implementation of the CATAD System will serve the
 immediate  and  urgent  need for abatement  of the
 pollution of Puget Sound by sewage overflows and
 postpone   the multi-million  dollar separation of
 combined sewers which can thereby be accomplished
 by an' orderly construction program as funds become
 available. Further, it is  expected that the  degree of
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 separation required will be substantially lessened by
 the CATAD System, thus saving many millions of
 dollars.                                      .
     To minimize the volume and duration of these
 overflows, motor-operated gate regulator stations are
 being built  wherever major trunk sewers cross  the
 main interceptor sewer. FWQA demonstration grant
 funds have  partially contributed to construction of
 some of the regulator stations and all of the CATAD
 System controls. Ten regulator stations are now in
 operation and nine more are planned or are under
 construction.                  .   >
     The primary function of the Metro system is the
 interception of sewage from the collector sewers of
 the various  cities and sewer  districts in the Metro
 service area and conveying the sewage to a treatment
 plant.
     A significant portion of the Seattle Metropolitan
 area, including the downtown  area and the major
 industrial  area along the lower Duwamish River, is
 presently  served by combined  sanitary  and storm
 sewers. All of these  combined sewers are tributary to
 the West  Point System.  Economic  considerations
 dictated that neither the interception system nor the
 treatment  plant be designed to handle storm flows in
 addition  to ultimate  sanitary flows.  Thus, during
 some, storms, it may  be necessary  to overflow
 untreated combined sewage  into the Duwamish River
 and into Puget Sound.
 Existing Local Station Controls
    Each regulator-outfall station has been provided
 with local automatic  controls which use  operating
 conditions  at the  station  as  control references.
 Diversion  of flows  from  trunk lines  into  the
 interceptor sewer is controlled by a regulator gate
 which  is modulated to maintain a preset maximum
 level in the interceptor sewer. When the interceptor
 level is above the control set-point, sewage is stored in
 the trunk sewer up to a preset maximum level. When
 this level is exceeded, the outfall gate is opened in
 steps to maintain the level at the overflow set point.
 The maximum tidal range in Puget Sound is about 16
 feet and many of the  outfalls are below high tide
 levels.  Therefore outfall  gate  controls have been
 provided  with  tidal  override  features  which
 automatically maintain the  trunk level  control set
 point 6  inches  above the tide  level.  The existing
controls are of the pneumatic type, water levels being
sensed through bubbler devices.
Objectives of Controls
    The principal objectives of the CATAD System
controls are as follows:
    1.   To provide optimum trunk sewer lines;
     2.  To  permit utilization  of potential storage
     capability of collector and interceptor sewers in
     separated areas under storm conditions and to
     make available the maximum  capacity of the
     interceptor  for  combined  storm  and sanitary
     flows in unseparated areas; and
 ,    3.  When overflows  are necessary,  to  control
     such discharges  at  selected locations so  as  to
     obtain minimum harmful effects on  marine life
     or public, beaches.
 Control Procedures
     The regulation of storage in  the sewage collection
 system  will  be  accomplished  by  controlling  the
 operation   of regulator  stations  and  of  sewage
 pumping stations.
     Since  the  primary objective of  the  CATAD
 System controls  is  to   reduce  the  number  of
 occurrences  of sewage overflows, it was  considered
 essential that a high degree of reliability be built into
 the  design.  Therefore,  an  overflow  occurrence
 directly  attributable to any  failure of the  remote
 control  equipment including  the  communications
 channel  could not be tolerated and the  criterion was
 established that upon failure of the remote control
 equipment,  the station would be restored to  local
 automatic controls in an orderly procedure.
     Storage  control  at  regulator stations  is
 accomplished through direct control of the position
 of the regulator gates which control the  volume of
 sewage being  discharged into the interceptor, sewers
 and consequently the volume .of sewage being stored
 in  the trunk  sewers. The regulator  gate will be
 returned to local control only on loss of the remote
 signal.
   , The  storage of sewage in the trunk  lines, with
 overflow provisions is  limited to a preset maximum
 level by a local outfall gate controller.  If sewage  is
 stored above the set point level  the outfall gate will
 open, resulting in an,overflow. In establishing the set
 point level for .the outfall  gate controller, the most
 unfavorable tidal condition has been considered since
 the local station controller  does not include logic for
 determining either the direction of tidal movement or
 the  maximum  level  -of, the  next  high   tide.
 Consequently,, the trunk level set point  has been set
 low enough so that peak flows can be stored for the
 maximum duration of the high tide condition, which
 imposes a severe limitation on the use  of potential
 storage in trunk lines.          .   .  .
    In order  to  .overcome this  limitation  when
 operating under remote control, it is necessary for the
CATAD  System to include  remote controls for the
outfall gates. Two,procedures were investigated for
                                                 111

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these controls, as follows:
    1.   Direct  control through the  gate motor
    controller, and
    2.   Indirect control by varying  the outfall gate
    controller set point.
    Direct control of the outfall gate position from
the central terminal would result in potential backup
of sewage in the trunk if telemetry to the station
failed while a storage operation was in progress. This
problem cannot be resolved by restoring the station
to local controls since this procedure would result in
an unnecessary overflow if the level of sewage in the
trunk was above the local set point.
    Indirect control of  the  outfall gate through
control of the set point provided a more satisfactory
solution.
    As in the first alternative, loss of the telemetry
signal  could result in a potential sewage backup if the
set point had been moved above the normal level for
local control  or  in  a potential  overflow  if the set
point  was abruptly lowered from the abnormal high
level  on  the  loss  of signal.  To  prevent  either
occurrence, electronic circuitry was installed at  each
outfall gate controller which will cause  the  outfall
gate set point to be restored  to the normal level for
local control over a selected period of time. The time
interval will be sufficient to  allow sewage stored in
 the trunk sewer to be discharged into the interceptor
 through the regulator gate.
     Remote control of the set point is accomplished
by transmission  of a contact command signal to the
 remote terminal  which opens or closes a contact in a
 circuit from  a  variable-rate  pulse  generator  to a
 stepping  motor.  The   stepping  motor drives  a
 potentiometer which produces a proportional voltage
 output signal. The potentiometer signal is converted
 to a  digital  quantity  through an analog to digital
 converter and  transmitted  back  to  the  central
 terminal. When the desired set point has been reached
 a  contact command  signal  is transmitted  to the
 remote terminal  which opens  the contact.
     A  loss  of  signal  from  the   remote  control
 equipment will  initiate  a  local  control restoring
 sequence. The restoring  circuit  equalizes  the remote
 controlled set point with a  constant signal from a
 manual set point device at a prescribed rate through a
 closed-loop balancing circuit.
 Pumping Station Control
     Sewage  pumping stations in  Metro's  system
 contain  from  three  to  six  variable speed  pumps.
 Existing pneumatic  controls at these stations  use a
 pressure signal which senses the influent sump level as
 a  control reference. In  response to changes in  the
influent level,  the  controller  varies  the  pump
operating speed and at designated levels changes the
pump  operating  mode.  The  operating  mode
determines the number of operating pumps or, where
the station  contains pumps of more than one size,
determines the specific combination of pumps.
    The  alternatives for remote control of the pump
stations were similar in principle to those investigated
for control of the outfall gates. These  alternatives
were as follows;
    1.  Direct control, overriding local controls, and
    2.  Indirect  control, overriding the  pressure
    signal  from  the  influent  level  sensor  with a
    computer  directed  control  signal.  The direct
    control  procedure would  have  required
    substantial modifications  and extensions to the
existing local  controls  which, in the case of the larger
stations, were already quite complex. Direct control
also  introduced major  problems of  designing and
installing the  necessary  circuitry  for effecting an
orderly  transfer from remote to local control upon
failure of the remote equipment.
    As in the case of the regulator stations, indirect
control provided the most satisfactory procedure. No
modifications  to  existing  local   controls were
necessary  and  relatively  simple  methods were
available for  controlling the  set  point  and  for
restoring the  station to local control. These methods
and the control circuitry used for implementation are
 similar to those used for restoration of the outfall
 gate  set  point.  The  computer-directed   control
 reference is varied by positioning a stepping motor
 connected  to  a  potentiometer  which  provides ,a
 proportional  current  signal.  The current signal  is
 converted to  a pneumatic signal through  a current to
 a pressure transducer  as the input to the local control
 equipment.
     Loss of remote signal will initiate a sequence for
 restoring  control  to the influent level pneumatic
 signal which  is equalized with the influent level signal
 through an electronic balancing  circuit. Equalization
 takes place over a sufficiently long  time interval to
 permit  the local controller to settle  into the control
 mode which  is appropriate to the inflow rate without
 overshooting.                           •
 CATAD Equipment
     The CATAD  System  includes the  following
 principal items of equipment:
      1.  A computer central processor with input and
      output terminal equipment;       ,
      2.  Peripheral input and output devices;  :
      3.  A digital transmission system; and.
      4.  An operator's;console. -      ;,    '>
                                                   112

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     The computer central processor is a Xerox Data
 Systems  XD5  Sigma 2  Computer  which  is  a
 high-speed  unit  with  an  access  time  of 920
 nanoseconds to each 16-bit word of core memory and
 a maximum channel  input-output transfer rate  of
 400,000 8-bit bytes per  second. The initial system
 will  provide  32,768  words  of  core memory
 expandable to   65,536  words  which  will  be
 supplemented by a fixed  head disk memory with a
 capacity of  1,474,560 16-bit  words and an average
 access time of 17 milliseconds.
     In addition to  its data gathering and control
 functions,  the  computer  will  be  time-shared by
 background  data  processing  operations.  For this
 purpose the system includes  such peripheral input
 and output devices as  a line printer, card punch and
 reader, and a  paper  tape  punch and reader,  in
 addition to the customary programmer's console.
 Operator's Console
    ,An operator's console and wall map  display  at
 the  central  terminal  will  serve  as  the  interface
 between the operator  and the control system. The
 console will incorporate light panels for  displaying
 the  operating status and alarm conditions at any
 remote terminal, and push-button arrays for selecting
 point locations for the execution of control functions
 and for data entry. A  major feature of the console
 will be a bank of seven cathode ray tubes for display
 of quantitative  operating  data  from selected
 groupings of pump and regulator stations which are
 located within a common area and are related from
 an  operating standpoint. The  operating data to be
 displayed  will include  both observed data^  such  as
 water .levels, and computed data, such as sewage flow
 rates and storage volumes.      .  •     •  ',
    The wall map  will supplement the operator's
console by associating each cathode ray tube display
and each  alarm  with its geographic  location. - Four
lights will be .situated adjacent to the location of each
station  to  indicate one  or all  of .the  following
conditions:            .                 ,
   •t   The  station • is one  of the- group 'being
    displayed on   the  cathode  ray  tubes, or  a
    supervisory control command is being 'executed
    at the station.                   ..-- . .-:..-
    2.  The  station  is  operating  under .remote
 -   control .from the  central  terminal or is  under
    local control.                      •
    3.   An overflow, is taking place at a regulator
    station or a  high influent level is .occuring at  a
    pump stations -,.-i  >•,,_  .      ..-,..  •-
    4.  Alarm condition is i present  at, the  station
    (light blinks until the situation is corrected).
 Telemetering
     All  data  from  regulator-outfall  and  sewage
 pumping stations will be telemetered  to a central
 location in Metro's offices over leased telephone lines.
 At the central terminal these data will be entered in a
 process control computer which will also direct the
 data  gathering.  Control signals  from  the  central
 terminal  will  be  transmitted  as contact operate
 commands.
 Monitoring
     A two-phase monitoring  program has  been
 implemented to evaluate the effect and eventually to
 provide input data for control of the CAT AD System.
 Half  of  the  monitoring  program  examines  the
 receiving  water quality; the  other half checks on
 overflow strength and volumes.
     The Duwamish River is monitored automatically
 by  five robot instruments that telemeter dissolved
 oxygen, temperature, pH, conductivity, turbidity and
 solar  radiation information  hourly to  a  central
 recording station.  This information is supplemented
 by  manually collected  receiving  water  samples  at
 some  55 locations  in  the  immediate  study area
 (nearly  300  points  in the  entire  Seattle  area).
 Bacteriological and additional chemical tests are run
 on the manually-collected samples.
     A second study centers on  the overflow utfalls
 themselves.  Refrigerated automatic samplers  have
 been installed  at  nine overflow sites and  will be
 installed at four more when the adjacent gate control
 structures are completed in  1970. These automatic
 samplers also are supplemented by a manual sampling
 program which  adds bacteriological analyses to the
 chemical  tests  run  on  automatically collected
 overflow samplers.
    The  monitoring  program:  (1)  provides
 information on amounts and variation of loading to
 receiving  water  caused  by  combined seweage
 overflows, (2)  establishes  relationships  between
 overflows and  rainfall  characteristics, (3) provides
 information to determine the benefits of converting
 from locally controlled regulators to total system
 control, (4) locates critical  overflow sites or  other
 pollutants-should  be  programmed to be the last
 overflow point  under total system management, (5)
 assists  in locating  sources/of undersirable industrial
 wastes within the city,  and (6) allows evaluation of
 the effects of Seattle's combined sewer separation
 program and  other  sewer   construction; activities
 within the collection-system.     .  '.   ,  ;
 System Operation                     .  .,:
    It  is planned' that the central: terminal initially
will  be attended by  an operator  only  during the
                                                 113

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normal 40-hour work week. While this operator is on
duty, the  system initially  will be  operated in a
supervisory  control  mode.  During  the remaining
hours, control will be returned to the local stations,
but data gathering and alarm monitoring from the
central terminal will be continued.
    When a mathematical model of  the system has
been  developed  and  adequately reconciled with
observed operating characteristics, the system  will be
put under program control by the computer.
      Minneapolis-Saint Paul Sanitary District
    A  system of computer control of its  combined
sewers has been developed for this important District,
to  "maximize capture  of urban  runoff by  the
combined sewer system." Its purpose is  to eliminate
"past methodologies (which) assume the 'worst case',
establishing the limiting threshold at  the peak design
conditions, necessarily requiring a low threshold limit
to  avoid damage  due to  flooding  during extreme
runoff. This  method  allowed  overflows to  occur
during light, frequent runoff even though the  system
was not being used to fullest capacity or .advantage."
    It  is   evident  from  this  statement   by  a
representative of the Sanitary District that the new
computer-controlled  system will make fuller use of
the in-sewer system capacity and markedly reduce the
pollutional overflow waste waters discharged into the
upper Mississippi River.
    The following  excerpts  have been taken from
reports covering the new system.
Project Objectives
    The ^pfoject objectives,  as outlined  in  the
Minneapolis-Saint Paul Sanitary District (MSSD)
grant  application to  the  Federal   Water  Quality
Administration, were as follows:
     "The proposed project will demonstrate a new
 technique  of instantaneous observation and  control
 of  interceptor system  performance,  based  on
 adequate information, to drastically  reduce losses of
 combined wastes. Information gathered will provide a
 basis for further reduction  of Ipsses by using trunk
 sewers for  storage and the facilities  constructed will
 allow such  a  measure  to  be  attempted.
 Post-construction evaluation will provide information
 which  will  allow the method to be adapted to other
 large  combined  sewer systems  of differing
 configuration and climatology.
     Since  the majority of losses of wastes occurs
 during the recreational season, considerable benefit to
 the Mississippi River,  where it passes through the
 populated area, will accrue."
 Regulator Modifications
     Modification of regulators and installation of the
data acquisition and control system (DACS) were the
largest of  the  tasks  required  for  the  physical
installation.  Regulators  were typically modified to
meet the needs. Existing floats on gates were removed
and  replaced by  hydraulic  cylinder  operators.
Inflatable  dams were installed in the trunk sewer
outlet to the river. Level sensing bubbler tubes with
transducers and gate position slidewires were installed
to  provide  sewer level  and regulator  status
.information. The control and telemetry equipment
was installed in underground vaults.
    Figure  32, Artist's Drawing, Inflatable Control
Gate System, indicates the typical arrangement that is
used  in Minneapolis-St. Paul. Figure  33,  Upstream
View of Inflatable Fabric Dam, shows a dam in use.
Leased Telephone Lines
    The leased line communications system utilized
eight pairs, each connected in party-line fashion to a
number of individual remote stations.  Connection in
this   fashion  minimizes  line rental  costs  and
substantially  reduces equipment costs  and
maintenance  problems. A slight sacrifice in access
time and system redundancy  and reliability occurs.
Access time  for any  data  point is  less  than two
seconds. The  system  uses  random  access and by
proper selection of sampling  frequency,  adequate
system response is obtained.
Data Acquisition and Control System
     The data acquisition and control system provides
both manual remote, as well as automatic, control of
the system by  the  central  computer. The interface
equipment uses multiplexed parallel tones to connect
the manual controls and the computer to the leased
communications lines. Table  No.  29  shows  the
number of  measurements  and control  functions
provided by the system. In addition to the out-plant
functions  shown,  equipment  was  provided  and
interfaced  to  the treatment plant  process  to log
 approximately 250 points of plant process data.
                  Table No. 29
 NUMBER  OF  MEASUREMENT AND CONTROL
 FUNCTIONS-MINNEAPOLIS-ST. PAUL
 SANITARY DISTRICT
FUNCTION
Level Measurement —
Level Measurement —
Level Measurement —
Gate Positions and Controls .


(a) Total number of locati
NUMBER OF NUMBER OF
LOCATIONS POINTS
12 12
. . . 15
14
17
8
... 5
	 19
(a)
ions of telemetry
16
14
34
8
30
19
133
equipment
                                                      is 37 due to overlapping functions at certain stations.
                                                   114

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                                                                                         FIGURE 32
                            Artist's Drawing, Inflatable Control Gate System
                                                     TO INTERCEPTOR
Courtesy Firestone Coated Fabrics Co.     "•-'..

River Quality Monitors
    Five river quality monitor stations were installed/
one in a permanent location and four in semi-portable
trailers. The units measure chlorides, conductivity,
dissolved oxygen, oxidation reduction potential, pH,
and  temperature.  The  units  are  installed  in the
21-mile stretch of river  in  the urban area. They are
intended  to be  used  to  -measure  the  effect of
combined sewer overflows on the river.
Sampling and Analytical  Program
    An extensive sampling and analytical program
was  undertaken and  operated for various  periods
during  two years of  the  project.  Approximately
25,000  hourly  grab  samples of waste  water were
obtained and analyzed, using automated sampling and
automated  chemistry techniques. Determinations of
chemical oxygen demand, kjeldahl nitrogen, ammonia
nitrogen,  dissolved  phosphate, and chloride ion
concentration were made.
Data Reduction and Analysis
    These  data,   and  data  obtained  by  manual
sampling of the  river, and from automatic composited
plant influent samples  have  all :been  stored using
electronic data processing techniques. The purpose of
the sampling and /analytical program .and the placing
of these data in ADP form were:               ,
    1.  To  facilitate  an  attempt  to  produce
    approximate chemical mass balances: across the
    entire system;             :                ,
    2.  To  evaluate the pollutional losses from the
    combined sewer system to the river before  and
    after modifications;                        '
    3.  To  possibly  define'the  character  and
    quantity • of urban  runoff in  comparison, with
    waste water; and                ,"•<      , •':•:.
    4.  To provide a  basis for priorities of point of
    discharges at regulators, based on pollutional load
    at cpntrolled'locations.                   ''..'•'
Mathematical Model
    The original  purpose of preparing a mathemetical
model of storm runoff, regulator  performance  and
interceptor  routing was to provide a guide ;.to the
operator and assist him in making changes in gate
settings  during  runoff  events.  In addition,  as
                                                   115

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                                                                            FIGURE 33
                      Upstream View of Inflatable Fabric Dam
Courtesy Firestone Coated Fabrics Co.
                                           116

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secondary objectives, the model preparation also was
intended to be  useful as a research tool  and as a
planning and design tool.
    The mathematical model, using rain guage data as
input,  generates  a  runoff  hydrograph   at  each
regulator, calculates the quantity of flow diverted by
the regulators, and routes the diverted flow through
the interceptor  sewer  system. The entire operation
requires about 10 minutes to do all calculations and
to communicate output information  to the operator.

        Detroit  Metropolitan Water Services
    Faced with  the problem of preventing pollution
in the Detroit and Rouge Rivers and in Lake Erie,
Detroit  has evaluated  what  it characterizes  as a
"dubiously effective sewer separation program" at a
cost of  $2 billion, in  comparison with  a sewer
monitoring and remote control system for controlling
the pollution from overflows during  numerous small
storms at a cost of $2 million.
    The total system would involve rain gauges which
will be telemeter-connected to a control center; sewer
level sensor systems; overflow detection facilities; a
central computer; master data logging equipment; and
a central control  console for remote activation  of
pumping stations and  selected regulating gates. The
instrumentation  system will enable the  operators to
anticipate storm flows; intercept "first-flush" flows;
selectively retain storm flows; and selectively regulate
overflows.
    The following excerpts have been taken from a
report on the Detroit system made  by, personnel of
the Detroit Metropolitan Water Services.
    The Detroit Metropolitan Water Services has been
monitoring water  pressures  and,remotely operating
water pumping  stations and valves  throughout the
metropolitan area  for eight years.: Utilizing this
experience, DMWS  studied, the  possibilities,  of
installing a  sewer monitoring system with .remote
control of sanitary sewage and storm water pumping:
stations and regulating gates.,The following factors
relate to the installation of a monitoring and remote
control system.'                                 ;
    1.  There are  large areas served by  pumping
    stations whose tributary lines could be used as
    storage areas during small storms.           '."..-.
    2.  The grades of the sewers,  either rectangular
    or cylindrical types,  are  relatively  flat, which
    would  permit  substantial  storage  under  level
    conditions near the outfalls.
    3.;  Interceptors  along the Detroit  and Rouge
    Rivers are fed through float-controlled regulators
    equipped with sluice  gates which appear to  be
    adaptable  to  conversion  to  remote-controlled,
    power actuated regulators.
    4.   Interceptors  along the Detroit  and Rouge
    Rivers are fed through float-controlled regulators
    equipped with sluice  gates which appear to  be
    adaptable  to  conversion  to  remote-controlled,
    power actuated regulators.
    5.   Most of the  71 outfall points are equipped
    with backwater gates and/or dams which serve as
    automatic retention devices.
    6.   Interconnections  exist  throughout  the
    system which could be used  for flow routing if
    remote controlled gates are added.
    7.   From knowledge  of the particular industrial
    plants  connected   to  certain  sewers,  there
    apparently would be a  wide variation in  the
    quality of dry-weather effluent.    :
    8.   In  order  to  utilize  the potential of  the
    system, it is necessary  to  have instantaneous
    synchronized information about the behavior of
    the  system, including  rainfall,  sewer and
    interceptor levels, and the status of pumps, valves
    and  backwater gates, as  well as the ability  to
    remotely operate the pumps and valves.
    9.   To  later determine   the  improvements
    achieved through monitoring and remote control,
    it  is first necessary  to establish  a  base by
    monitoring the  system  as  it  would naturally
    behave.
Potential Benefits
    With  central  system  monitoring and remote
control, the following benefits appeared possible: !
    1.   The  sewer .system  could  be operated  to
    contain completely a small spot storm."
   '2.   Runoff could be anticipated, sewers could be
    emptied  and  in  readiness,  and  grossly
    contaminated "first flushes" in areas  adjacent to
    the  interceptor  selectively could  be captured,
    especially during large storms.                '
 :   3.   All flow near the  end of a large storm could
    be held in the system for subsequent treatment.
    4.   Regulators could be adjusted to get the most
    efficient use  of the interceptor and to favor the
    most grossly contaminated inlets.            vV
    5.   Backwater from  floods in the Rouge River
    Valley could be selectively controlled.   '
    6.   Pumps   could  be  operated  to tnihimize
    basement  flooding" in the east side, areas  which
    have no gravity relief outlets, r     ,   ,  ;  :   :
    7.   The  flow to the waste  Water "plaiit, from
    various segments of  the  city could be  better
    balanced.
                                                     117

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                                                                                         FIGURE 34
 SAW
3/4" CONDUIT
   • I/4"NYLON TUBING
'** '*,*.-»" ""*•*'••'' **• ."*.*"' */-'
i^
c
.^"-
                                                                   POWER 8 TELEPHONE -
                                                                      CIRCUITS
                            -CONCRETE
          SECTION "A"-"A"
                                                            LEVEL INDICATOR
                                                             S TRANSMITTER -^2^*"
                                                                       BURIED CABLE'
                                                                       (CARRYING POWER.  I
                                                                       a TONE SIGNAL)   L
                                                                                            UTILITY POLE
                                                           TYPICAL   LEVEL  CELL
                                                         INSTALLATION  IN SEWER MANHOLE
                                                                 DETROIT,  MICH.
                                                                  Courtesy Detroit Metropolitan Water Services
Special Equipment
    The  recent  Detroit  installation  includes  the
following equipment:
    (a)  14 telemetering rain gauges;
    (b)  89  telemetering  sewer  level  sensors,  41
    telemetering  interceptor  level  sensors  and 4
    telemetering river level sensors;
    (c)  30  telemetering proximity  sensors  on
    backwater gates;
    (d)  38  telemetering probe-type dam overflow
    sensors;
    (e)  3  event recorders for storm water pumping
    stations discharging direct to river;
    (f)  1  central digital computer with drum and
    disc memory;
    (g)  3 data loggers with 30-inch platens;
    (h)  1 teletypewriter for input, output and alarm;
    (i)  1 central operator console;
    (j)  8  sets of equipment for the remote control
    and monitoring of pumping stations; and
    (k)  5  sets of equipment for the remote control
                                               and monitoring of sluice and flushing gates.
                                           Anticipating Small Storms
                                               In order to safely practice storm water storage in
                                           the sewer barrels, it is  necessary to determine the
                                           correlation between  the various storm intensities and
                                           the  recorded  downstream  storm  flow.  From
                                           precipitation and flow data, the sewer hydrographs of
                                           the maximum amount of storm water  that can be
                                           stored in  the various combined systems  are being
                                           developed for each area.
                                               The present level  sensors on 25 of the larger
                                           outfalls  in Detroit permit calculating the runoff from
                                           86 percent of the area of the city. Measurement of
                                           the flow from the remainder of the smaller outfalls
                                           has been  deferred  because  of the capital cost  for
                                           equipment. However, some very reasonable estimates
                                           of the overflow can  be secured since elapsed time of
                                           spilling is known, plus average runoff per square mile
                                           from  other comparable areas.  Figure  34, Typical
                                           Level Cell  Installation in Sewer Manhole—Detroit.
                                                  118

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                                                                                       FIGURE 35
                     TYPICAL TRANSMITTER

                       COMBINED
                LEVEL SENSOR
                   -OVER OPENINGS
                                                  ^•«*.

                                                     ^7

                        FLUSHING  GATES  CLOSED
                                                                            SECTION
                                 FLUSHING INSTALLATION
Courtesy Detroit Metropolitan Water Services
  Small Storm Water Storage
     The  storage of flows from small storms within
  the barrels of sewers is dependent upon the following
  factors:
     1.  Size of box  or parallel,
     2.  Slope of the conduit,
     3.  Imperviousness of tributary area,
     4.  Time elapsed since previous rain,
     5.  Available height in sewer before gates open,
     6.  Intensity of length of storm,
     7.  The level of the receiving water, and
     8.  Available capacity in the interceptor.
     Available storage at  the various  outfalls either
  upstream  of pumps or backwater gates, must be
  calculated  and tabulated for  use by  the  system
control operators.
    Any storage of runoff in larger trunk line sewers
results in  reduced  velocity. Velocities below. 2 feet
per second usually cause graded sedimentation, with
coarse  deposits  occurring  upstream  where  the
velocities are still relatively high and finer deposits
downstream where the velocities approach zero. This
is another problem which must be considered in the
operation of a system with in-system storage.
    Figure  35,  Flushing Arrangement,  Detroit,
incicates the physical location of a system of gates
which has  been  installed  in  a  three-barreled
interceptor sewer. Dry-weather flow will be passed
through only one barrel at a time in order to flush
deposited solids to the treatment facility.
                                                  119

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                                             SECTION 11
                               SUMMATION OF THE STATE OF THE ART
                                 OF COMBINED SEWER MANAGEMENT
    The combined sewer systems which now serve all
or parts of more than 1,300 municipal jurisdictions in
the  United  States,  and the  larger  Canadian
communities are not the product  of today's sewage
works needs and practices. Their use in local areas in
the  older  sections  of the  continent  labels  this
combined method  of collection  of both sanitary
sewage  and  storm  drainage runoff  waters as  a
sanitation solution  which predates the  intensified
water pollution  control efforts  of the sixth  and
seventh decade of the 1900's.
    The need for new methods and new techniques in
the management of these combined  sewer systems is
brought  into sharp  focus by advancements in  the
treatment of sanitary sewage and industrial waste. As
long as  the  periodic  and  repetitive  overflows of
admixtures of sewage  and other wastes with storm
runoffs  continue to pollute rivers, lakes and coastal
waters,  the  maximum  value  of urban liquid wastes
treatment cannot be achieved. This  fact makes it
mandatory  that  new concepts  and  methods  of
combined sewer  management be evolved to prevent
spoiling the water and land resources  which treatment
works are intended to protect.
    This need led in 1966 and 1967, to a study of the
"Problems  of  Combined  Sewer Facilities  and
Overflows" sponsored by FWQA, and carried out by
the  APWA. From  the  study came findings  which
stressed the generally unsatisfactory application  and
condition of many overflow regulators, as well as the
inadequate methods used by some local jurisdictions
in operating arid maintaining these devices and their
appurtenant facilities. A recommendation was made
in 1967 that an in-depth investigation of design,
application, operation, performance and maintenance
of regulators was needed, to  serve as the basis for a
new approach to combined sewer management.  The
project upon which this current report is based  was
the outcome of that recommendation.
    The  vast numbers of overflow points, with  and
without  regulator  devices to  "split" total  storm
period flows  into  portions  to be transported .to
treatment plants and surplus volumes to be wasted
into nearby receiving waters are the product of an era
when the  main  thrust was  to  prevent  local sewer
flooding and interceptor system surcharging and to be
less  concerned with the pollutional effect of such
spills on these receiving waters.
    The  great numbers  of  overflow-regulator
locations pose the challenges which pollution control
authorities, governmental sewer system owners and
the  design  engineering profession now face.  An
important factor in corrective programs is  the fact
that practices  in  the  design, choice  of overflow
locations, applications of types of available regulator
devices,  and operation and maintenance  practices
were, and continue to be  inexact and inadequate.
Those who will innovate better combined sewer and
regulator management   techniques  now  have  the
opportunity  to reduce  the  pollution  effects  of
unnecessary  overflows  at  far  lower cost than
equivalent improvements in receiving waters could be
accomplished by  partial  separation  of combined
sewer  systems  and/or  the  treatment  of overflow
wastes by partial purification  means. The fact that.
better combined sewer  management methods will be
aimed  at  utilizing the  relatively  large  internal
capacities of  combined  sewer  networks  for  the
retention of significant amounts  of  storm runoff
flows adds incentive to  the methods set forth in this
report.
    The further fact that this project has spotlighted
the new  concept that regulator installations can and
must be charged  with the dual  responsibility  of
controlling  the  quality as  well as the quantity  of
overflow wastes, is a challenge that offers new goals
in performance  and economics  for regulator facilities
and systems.
    These   new   techniques  cannot  be  achieved
without more advanced knowledge than was available
to previous designers and administrators of combined
sewer systems and regulator installations. Regulator
control must be based on new and specific guidelines
of design, facility choices and  operational practices.
    For  this  reason the  project  involved  the
preparation of two documents: This report  contains
the actual study methods used, the findings of the
in-depth  research   work,  and the  specific
recommendations which reflect the findings and the
means by which  combined  sewer  practices can  be
achieved. The second volume,  a Manual of Practice,
provides guidelines for the actual accomplishment of
better system management methods.
    The research project took  on greater depth and
dimension under  the guidance of advisory groups
which  represented  the  many facets   of  the
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government, engineering and industrial life involved
in the  combined  sewer problem. To provide the
understanding  and concern  of  local government
operations, a broad-based Advisory Committee was
created, composed of representatives of jurisdictions
which contributed funds to assist in financing the
studies.  A more  specialized Steering Committee was
created  to guide the details  of the research program
and  to  help interpret  and evaluate the  findings.
Representatives  of the  American Society of Civil
Engineers and the Water Pollution Control Federation
were included in this steering group for greater depth.
A Consulting  Panel  was retained  to   add the
knowledge and experience of planners and designers
of sewer systems.  A  Manufacturers Advisory  Panel
was set  up to enlist the advice and guidance of the
industrial organization which serves the sewer system
field.
    These advisory bodies had a greater purpose than
the mere charting  of research goals and procedures.
Behind  their service in this connection was the hope
that  by creating a team effort, the findings and
recommendations emanating from the research and
investigative work  would be converted into tangible
accomplishments.
    The 1967 Investigation of overflow  problems
resulted in "price  tags"  of an extrapolated nature
which estimated  the cost of such corrective actions as
separation of public  sewer  systems;  separation of
facilities  in private structures  and  on  private
properties;  and/or  the  construction  of   treatment
facilities to handle overflow wastes.
    The current project has turned its attention to
the ability  of improved sewer  system management
and combined sewer regulator practices to minimize
or correct  overflow problems.  Efforts to  arrive at
rational cost  estimates  for construction of  new
regulator improvement  programs,   and  for
maintenance practices, were not fruitful because of
the paucity of such information in the governmental
field. There is need for such fiscal data to serve as the
basis  for  comparisons  of  costs  and benefits of
regulator  modernization  and  "total  systems"
management practices with the multi-billion-dollar
price tags of the corrective procedures to which the
1967 investigation addressed itself.
The Impact of Combined Sewer Overflow
Control  on National Water Resources
    Regardless of how effectively a combined sewer
system  is managed and its admixed sanitary and
storm water flows  controlled by means of the most
sophisticated   total  systems  techniques,  some
overflows will occur. The system concept is designed
to  reduce these  overflows  to  the irreducible
minimum. It can do this if the parts of the system are
coordinated into a planned master control network.
The  impact of these  waste  discharges  on receiving
waters will be markedly  reduced by  the  type of
practices described, and defined in the three specific
system  examples previously  outlined.  The greatest
reduction of the pollutional  effect will result from
the ability  of  a monitored and controlled system to
retain flows during precipitation and runoff incidents
of less  than maximum amounts. However,  unless
provision  is  made for  the   further  retention of
maximum storm runoff and the return of the  stored
waste water  back  to the interceptor system and
thence to the treatment plant during  periodsfrom of
non-peak  flows,  or  unless  some form of  initial
treatment is provided for  overflow waste discharges
from combined  sewers  such  overflows will impose
pollutional  loads on receiving waters.  If discharges of
combined sanitary  sewage  and storm water flows are
limited  to periods of high  runoff, there  is the
possibility that the spills will benefit from the high
dilution afforded by such high runoff volumes.
    This  point  is  stressed here  to avoid  any
impression  that even  the most efficient  systems
management program can be expected to eliminate all
overflow incidents.
    Regulator  practice improvement can accomplish
a  partial, perhaps  a  significant  correction  of the
pollution  effects  of overflows.  The  regulator
problems and palliatives outlined in this report must
be placed  in  focus with the total problem, and
evaluated to determine what they can accomplish in
partially solving the water  pollution control problem
now facing the American continent.
    This will  take  a  full   understanding of the
potentialities  of  the  total  systems  management
concept as well as the  improvements  which  better
individual regulator  units  can  accomplish.
Instrumentation, telemetry and centralized control of
total systems management should be  adapted  to the
combined sewer field if the full potentials of overflow
control  are  to be  achieved.  Dependable cost  data
must be  evolved   to  make   it   possible  to  make
comparable  economic  evaluation  on  such  new
techniques.
    The complexity  of such  new  technologies
emphasizes   the   need  for experienced  and
knowledgeable   personnel  for every phase of
combined  sewer   practices—from  conception, to
consummation to  operation and  maintenance.  The
era of "buried and forgotten" is  gone  in combined
sewer service.  The problems  caused by combined
sewer overflows must be brought to light and  solved
by effective and economical means.
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                                             SECTION 12
                                        ACKNOWLEDGEMENTS

The American Public Works Association is deeply indebted to the following persons and their organizations for the
services they rendered to the APWA Research Foundation in carrying out this study for the 25 local governmental
jurisdictions and the Federal Water Quality Administration who co-sponsored the study. Without their cooperation
and  assistance  the study  would no't  have  been possible. The  cooperation of the American Society of Civil
Engineering (ASCE) and the Water Pollution Control Federation (WPCF) is acknowledged for their participation on
the project Steering Committee.
                                          Steering Committee
                          Arthur D. Caster (WPCF)
                          William Dobbins (ASCE)
                          George T-. Gray
                          Carmen Guarino (WPCF)
 Walter A. Hartley
 Peter F. Mattei, Chairman
 Ed Susong
 Harvey Wilke (ASCE)
                                              Consultants

                                 Dr. Morris M. Cohn, Consulting Engineer
                           Ray Lawrence, Black & Veatch, Consulting Engineers
                         M. D. R. Riddell, Greeley and Hansen, Consulting Engineers
                   Morris H. Klegerman, Alexander Potter Associates, Consulting Engineers
                              James J. Anderson, Watermation, Incorporated

                                  Federal Water Quality Administration

                                    Darwin R. Wright, Project Officer
                           William A. Rosenkranz, Chief, Storm and Combined
                           Sewer Pollution Control Branch, Division of Applied
                                        Science and Technology.
                                      Manufacturers Advisory Panel
                          Vernon F. Brown
                          Peter A. Freeman
                          R. E. Gerhard
                          R. W. Henderson
                          Karl E. Jasper
                          Louis F. Lemond
                          Charles Prange
                          Milton Spiegel, Chairman
                          Jack D. Stickley
                          E. P. Webb
                          Leon W. Weinberger
Badger Meter Manufacturing Co.
Bowles Fluidics Corporation
AUis-Chalmers Company
Rodney Hunt Company
American Chain & Cable Co., Inc.
Coldwell-Wilcox Company
Rockwell Manufacturing Co.
FMC Corporation
Honeywell, Inc.
Firestone Coated Fabrics Co.
Zurn Industries, Inc.
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ACKNOWLEDGEMENTS (Continued)
                                          Advisory Committee
                        Vinton Bacon

                        Donald Bee
                        Philip Blunck

                        C. A. Boeke
                        C. A. Boileau
                        Ron Bonar
                        Richard J. Durgin
                        Paul Ehrenfest
                        John F. Flaherty
                        George T. Gray

                        Allison C. Hayes

                        Robert S. Hopson
                        Walter A. Hurtley
                        Roy L. Jackson
                        Gene E. Jordan
                        Robert E. Lawrence

                        O. H. Manuel
                        Peter F. Mattel

                        Hugh McKinley
                        George J. Moorehead
                        J. D. Near
                        Richard W. Respress
                        Max N. Rhoads
                        Harry E. Rook
                        Ben Sosowitz

                        Ed Susong
The Metropolitan Sanitary District
of Greater Chicago, Illinois
City of Muncie, Indiana
Municipality of Metropolitan
Seattle, Washington
City of Middletown, Ohio
City of Montreal, Quebec, Canada
City of Fort Wayne, Indiana
City of Alexandria, Virginia
City of Cleveland, Ohio
City of Boston, Massachusetts
Allegheny County Sanitary Authority,
Pittsburgh, Pennsylvania
Metropolitan District Commission,
Boston, Massachusetts
City of Richmond, Virginia
City of St. Paul, Minnesota
City of Kansas City, Missouri
City of Omaha, Nebraska
Metropolitan Government
of Nashville & Davidson County
City of Charlottetown, P.E.I., Canada
Metropolitan St. Louis
Sewer District, Missouri
City of Eugene, Oregon
Washington, District of Columbia
City of Toronto, Ontario, Canada
City of Atlanta, Georgia
City of Owensboro, Kentucky
City of Syracuse, New York
The Metropolitan Sanitary District
of Greater Chicago, Illinois
City of Akron, Ohio
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                                             SECTION 13
                                GLOSSARY OF PERTINENT TERMS
                           (as applied to this report on the regulator stuUy project)
    Collector  Sewer—A.  pipe  or  conduit  which
collects sewage, other waste water, and storm wate'r
runoff from their points of origin and conveys these
flows by means of other collecting sewers to points of
discharge, or by means of interceptor sewers to points
of treatment.
    Combined Sewer-A sewer which carries sanitary
sewage with its component commercial and industrial
wastes at all times, and which during storm or thaw
periods serves as the  collector  and transporter of
storm water from streets or other points of origin,
thus serving a "combined" purpose. Combined sewers
make provision for the overflow of excessive amounts
of flow, over and above the volumes to be carried by
interceptor sewers  and handled by  treatment  or
pumping facilities, from the combined sewer system
at  predetermined points  where  some  form  of
regulator devices are located.
    Dynamic  Regulator—A  semi-automatic  or
automatic regulator device  which may or may not
have moveable parts that are  sensitive to hydraulic
conditions  at  their points of installation  and are
capable of adjusting themselves to variations in such
conditions, or  of being adjusted by remote control to
meet hydraulic conditions at points of installation or
at other points in  the total combined sewer  system.
    Helical Motion—The inducement  of secondary
motion,  over  and above  the  normal  pattern  of
hydraulic  flow, in  a stream of  flowing sewage by
configurations  in the structure of the sewer conduit
itself,  thus  producing a physical separation of  a
portion of the suspended, floating or settleable solids
contained in the flow at predetermined points, from
which  the  more  concentrated liquors  can be
discharged  to  an interceptor  sewer  and the more
dilute liquids can be wasted to overflow points.
    Interceptor  Sewer—A  sewer  that  receives
dry-weather flow from  a number  of transverse sewers
or outlets, and frequently additional predetermined
quantities of  storm water  admixed  with  sanitary
flows, and conducts such waste waters to a point for
treatment or  disposal  point between the collector
sewer and the interceptor sewer.
    Jurisdiction—Any  unit of  local  government,
including a  county, city,  town  or  village,  or
multi-county agency or a duly constituted district or
authority, which has responsibility for one  or more
phases of sewer system service in the area served.
    Overflow Facility—A weir, orifice or other device
or  structure  which  permits  the  discharge from a
combined sewer system of that portion of sewage and
storm, water flow which is in excess of the amounts
allowed to enter the interceptor sewer and which
must, therefore, be discharged to receiving waters or
to some form of retention or treatment facility.
    Regulator—A  device or  apparatus for controlling
the quantity and quality of admixtures of sewage and
storm  water admitted  from  a combined  sewer
collector sewer into an interceptor sewer or pumping
or  treatment facility,  thereby determining  the
amount and quality of the flows discharged through
an overflow device to receiving waters, or to retention
or treatment facilities.
    Static Regulator—A regulator device which has
no  moving parts, or has moveable  parts which are
insensitive to  hydraulic conditions at the point of
installation and which are  not  capable of adjusting
themselves to meet varying flow  or level conditions in
the regulator-overflow structure.
    Storm Water—Waste water  flow  hi  a combined
sewer  system,  resulting  from  the  runoff  of
precipitation from any part of the urban area or from
the thawing or draining of previous precipitation.
    Tide Gate (Backwater Gate; Flap Gate)—A gate
generally with a flap suspended  from a free-swinging
horizontal hinge,  normally  placed at the  end  of a
conduit discharging into  a  body of water having a
fluctuating surface elevation. During high water stages
in the receiving waters the  gate is closed because of
external hydraulic pressure, but it opens when the
internal head is sufficient to  overcome the external
pressure, the  weight  of the flap, and the friction of
the hinge.
    "Total   Systems" Concept—Total  systems
includes any and all control and treatment needed to
fully  control   combined  sewer   overflows.  AE
regulator-overflow operations  in an entire combined
sewer system must be coordinated by means of some
type of central information and control point which
integrates climatological data and sewage  flow  and
the  operation of  individual control  stations  or
overflow points into conditions existing in the entire
sewer network. This coordination serves to reduce the
frequency and duration  of overflow incidents  by
utilizing the  retention and transporting capacities of
the entire system. The "total systems" management
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plan  is  adaptable  to automatic-automation
instrumentation control of a complete sewer system
by  means  of predetermined  operational  and
maintenance procedures.
    The  "Two-Q" Principle-Assignment  of  two
distinct and related functions to a regulator device:
The  control  of overflow  quantities,  and  the
improvement of the quality of the overflow waste
waters by some  means  which  will  result in  the
entrainment or concentration  of pollutional solids
and their  diversion into the interceptor system, and
the consequent improvement of the liquids which are
to be discharged into  receiving waters or overflow
retention or treatment facilities.
    Vortex Separator—A  device which, by structural
configuration, kinetically  induces a rotary motion to
the flow  of waste  waters  in a combined sewer,
resulting  in secondary motion  phenomena which
cause a concentration of solid pollutional materials at
a predetermined point from which it can be diverted
into the interceptor sewer,  thereby producing a less
concentrated waste liquor for discharge or overflow
into receiving waters.
    Wet-Weather to Dry-Weather  Flow  Ratio
(WWF:DWF)  -The  numerical  ratio  between  the
wet-weather flow of sanitary sewage and storm water
runoff in a combined sewer system and the average
dry-weather flow  of  sanitary  sewage  and other
extraneous  waste waters. The ratio is dictated by the
design  capacity  of  the  interceptor sewer  and
treatment plant to handle predetermined amounts of
the  admixtures of  sewage and storm water.  For
example, a  WWF:DWF ratio of 3 to 1 represents the
ability of  the  interceptor  to  carry three  times  the
average  dry-weather  flow  during  periods of storm
runoff.
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                                              SECTION 14
                                              APPENDIX 1
                  REPORT OF THE SUBCOMMITTEE ON MOST EFFECTIVE MATERIALS
                    TO MEET SPECIFIC REGULATOR CONDITIONS AND FUNCTIONS
Durability
    Sewage regulator equipment should be designed
for a minimum useful service life of 20 to 30 years.
This period approximates the time that a properly
designed  treatment plant  will  operate  without
extensive  redesign  and  refurbishing  of its  major
equipment.
Service Conditions
    Although the environment in a sewer can have a
fairly wide  chemical  range, extreme conditions are
usuaEy short-lived; and it is not normally necessary or
desirable to"design" for them. Fresh sewage is slightly
alkaline; but as it becomes septic, it becomes acid.
Dry spells  coupled  with  over-capacity  sewers, will
result in acid semi-septic  or septic  sewage  which is
more inimical to treatment, than fresh sewage. Small
amounts of hydrogen  sulfide,  ammonia,  carbon
dioxide  and sometimes methane will be present in the
sewer atmosphere.  Temperature variations are not
extreme,   but  the   humidity  can  be  very  high.
Condensation  conditions  necessitate  the use of
corrosion  resistant materials  for  equipment.
Regulator facilities in coastal cities usually overflow
into salt water  basins  and  must  have tide  gates
constructed of a material  that will  stand up in salt
water.
Metals
    The best of the bronzes for corrosion resistance
and strength seems to be silicon bronze. This is a very
high copper, zinc-free bronze.  Manganese  bronze
castings  and extrusions  wear well.  For this reason
they are used for valve seats and operator stem nuts.
    Among  the  stainless  steels,  the   18-8
(chromium-nickel  content  percent,  respectively)
series wears best.  Types 303, 304, and 305 are used
for valve stems, studs,  nuts and  bolts. Type  316
stainless steel is especially good in sea water and less
costly than Monel metal, which also gives excellent
service in salt water. Heavy body castings are usually
grey  iron  complying  with ASTM A-126  Class B.
However, in highly corrosive applications, Ni-Resist
Type 1A, or equal, can be used successfully. This is a
trade name of International Nickel Company for an
iron casting with the folowing alloys: 14% nickel, 6%
copper, 2%% chromium.
    Cast iron is customarily coated with a hot tar
enamel,  in accordance  with  AWWA  Specification
C203-62.  Bronze,  stainless steel and Monel are not
usually coated.
Elastomers and Gasket Materials
    The most commonly used elastomer is Neoprene.
Neoprene is  a copolymer  of butadiene and acrylic
nitrile. It has good resistance to hydrocarbons and
ozone and  resists air-hardening. Nitrile and a blend of
nitrile  and polyvinyl  chloride  also have  good
resistance  to  sewer  atmospheres. Natural rubber
deteriorates  in  sewer  applications  and  is  not
recommended. Gaskets and packing should be made
of  asbestos,  teflon coated  asbestos  or  tallow
lubricated flax.
Electrical Equipment
    Certain municipalities  allow electric lines to be
run in sewers. Motors  must be explosion-proof and
water  proof. All wires  must  be  run  in  solid
corrosion-resistant  conduits. No exposed wires are
allowed because of the possibility of rats chewing off
insulation and causing an explosion.
Plastics
    Although plastics  and plastic-coated metals have
not been used to  any appreciable  extent in sewer
regulator systems, they offer considerable promise for
the future.  Coatings such as epoxy, vinyl, nylon, and
cellulosic applied by  the fluidized bed process all
endure  well   in sewers.  They  are quite  abrasion
resistant, which is necessary because grit has not been
removed from the sewer flow. These coatings applied
to  steel or  aluminum  offer  maximum corrosion
resistance, coupled with good strength characteristics.
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                                            APPENDIX 2
                   REPORT OF SUBCOMMITTEE ON SEWER REGULATION SYSTEMS
    A  typical  sewer  regulator,  as viewed  from a
control system  standpoint,  is shown in the block
diagram.  Typical  in-loop functions  noted  in  this
diagram are the error sensor, control logic, and main
flow  actuator-modulator. Typical out-of-loop
functions are  the  command  and monitoring
instrumentation  equipment. The  error  sensing
equipment is  often  considered  part  of the
instrumentation equipment. The result of the in-loop
functions is the modulation of flow into the normal
channel in accordance  with a preset, or remotely
commanded, flow  requirement.  The out-of-loop
functions serve to relay commands to the regulator
from a remote command location, and to monitor the
operation  of the  error sensor,  control logic, or
actuator-flow modulator; and to either generate time
records of these functions for later review, or to relay
the performance  of  these  functions to a remote
command location for  real-time monitoring at that
location.
                              Each principal block is discussed below.
                          Error Sensor
                              The error sensor provides the remainder of the
                          regulator loop with intelligence  as to whether the
                          flow output is in conformance with the desired value.
                          This intelligence is in the  form of an error signal
                          whose  sense and magnitude are  interpreted by the
                          control logic block in determining the degree of main
                          flow  modulation  necessary to  satisfy  the flow
                          demands desired in the normal  channel.  In most
                          current installations, the error signal represents the
                          difference  between  the actual  water level  in the
                          normal channel and a preset reference level. In a few
                          modern sewer systems,  where  flows are remotely
                          commanded,  the command control  input  directly
                          establishes the reference level.
                              In some sewer installations, flow into the normal
                          channel is sensed,  or measured  directly, instead  of
                          being derived through the sensing of another variable,
                          such as the water level. Again, an error signal is
                           SCHEMATIC BLOCK DIAGRAM
                           SEWER REGULATOR
          r
          i
                         Recording
                         or Remote
                         Monitor
    Remote
   Command
      or
   Present Level
   Reference
Error
Sensor
Control
Logic
Actuator/
  Flow
Modulator
                                                    Sewer
                                                     Flow
                                                    Dynamics
                                          Modulated Sewer Flow
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generated when  the  actual flow  differs  from  the
preset,  or  commanded reference  flow.  As  the
requirements  for sewer regulation  systems have
become  more  sophisticated,  variables other than
water level or flow are being sensed. For example, in
addition  to flow magnitude it is sometimes desirable
to modulate the flow into the main  channel as  a
function  of sewage quality, such as, concentration of
pollutants, acidity, alkalinity and temperature.
    The  error  sensor may use a wide variety  of
communication means to transmit error information
to the control logic  equipment. These can include
many forms  of electrical energy such as DC ,or  AC
voltage, current, pulse width and pulse  frequency; as
well as mechanical motion, gas or liquid pressure or
flow, acoustics,  or various combinations  of these.
These instruments can be energized directly by  the
flow  stream  from  appropriate  auxiliary  energy
sources,  such as electric service or water  power, or
locally installed pumps, compressors or generators.
    Several of the most  used types of error sensors
are described in greater detail below.
Flow Meters
    Partially Filled Sewers: The Parshall flume is the
most commonly used metering device.  It lends itself
to this type  of service since it is self-cleaning and
relatively maintenance-free, inexpensive and durable.
Sizes 36 inches and  under  (throat  width),  are
frequently  fabricated  from   fiberglass  reinforced
plastic. Larger sizes can be formed easily in concrete
to adequate tolerances.
    There is  one major  consideration  that must be
given to  this device.  Generally, in new installations
sewer  grades are such as  to provide  free flow
conditions. However,  where these flumes are installed
in existing sewers there is usually not sufficient grade
to provide the free-flow conditions,  thus  producing
submerged  flow  conditions  and  erroneous flow
measurements.
    The  secondary instrumentation for this device is
usually a transmitter and  flow recorder, the most
popular  of which  is the  in-stream type,  since it
eliminates  most  of  the maintenance  and  cleaning
problems. The  secondary  instrumentation can be
equipped with electrical  and pneumatic transmitters
for control functions, the scope of which is limited
only by the imagination of the design engineer.
    Sewers Flowing Full: The Venturi  tube has long
been used as  a primary  device  for  sewage flow
measurement. Its major limitation is that  it requires
continuous  purge  water and  periodic  cleaning.
However, under  normal maintenance, the  venturi
tube and secondary  instrumentation  will give long
dependable service.
    Secondary  instrumentation  is  usually  a  main
meter or D/P sensor, transmitting to a recorder. Here
again the  instrumentation  can  be  equipped with
electrical  and  pneumatic transmitters  for  control
purposes.
Level Sensors
    Quite frequently flow measurement is important
in the overall control of combined sewer regulation.
However,  level measurement  is  a  basic  control
parameter.
    Bubbler Systems consist of a tube extending to
the bottom area of the sewer, through which air flows
at a fixed supply pressure. As the level increases, the
back pressure increases  accordingly. This pressure is
then converted to a usable signal for overall system
control.
    Capacitance is measured by means  of a coated
probe immersed in the fluid  to form one plate of the
capacitor. The  second plate is formed by the fluid
level around the outside of the probe. The changing
level causes a corresponding change in capacitance
which is converted to a usable signal for control.
    Floats are  mechanical devices that float on  the
surface of the  water and move  with level changes.
This motion is converted  to  a usable signal  for
control.
Analytical Sensors
    Various sensors  are  available for analyzing pH,
conductivity,  dissolved' oxygen,  oxygen-reduction
potential, and  dissolved chlorides and other sewage
components which would provide  readout for  the
amount  of pollution  that  would  be bypassed to
receiving  waters in  the event of high  storm  flow.
These can be provided with usable signals for control.
Control Logic
    It is the function of the control logic equipment
to  ascertain  the  degree, or extent  to  which  the
actuation-flow  modulation  equipment  should  be
operated in order  to produce  the desired flow .into
the normal channel. Its  operation in  many  respects
resembles  that of a computer,  in that  the  basic
proportions,  thresholds,  limits,  operating points,
operating  modes,  specialized  mathematical or
time-dependent  functions,  and   other  factors  are
programmed while real-time  data are fed in from the
error sensor equipment.  The control logic equipment
then computes  an input  to  the  actuator-flow
modulator directing it when, in which direction, and
how far to operate.
    As its likeness to a computer suggests, the control
logic function can be implemented in a wide variety
of ways,  using many forms of  mathematical logic.
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Two  commonly  used  types  of logic for control
systems  are analog  and  digital.  Analog  logic is
characterized  by  smooth,  continuous  outputs,
generally in proportion to the inputs. Digital logic is
characterized by discontinuous, or on-off outputs, in
response to changes in the state of input  conditions
or to the exceeding of certain magnitudes by input
conditions.
    In addition to the basic logic arrangement of the
controller, certain time-dependent characteristics may
be required in order that the system operate properly.
For example, a "lead" or anticipation function may
be useful to prevent or minimize excessive oscillation
or "hunting" of a  sewer .regulator  during rapidly
varying,  or surging flow occurring as a result  of
violent thunderstorms. In another situation, it may be
desirable   to  add  a  smoothing,  or  delaying
characteristic  to  the control action in order  to
prevent excess  operating wear on the actuator-flow
modulator  when  small fluctuations in water  level
produce a "noisy"  error signal input from the error
sensing equipment.
    Sewer control logic equipment may require two
or more modes of operating logic, depending on the
general weather conditions or water usage by the area
being serviced. For example  during storm  periods,
dry-weather flow  peaks, or emergency situations such
as water main breaks, a high-speed mode of analog
operation of the sewer regulator may be required. In
periods  of low, or slowly changing flow, a simpler
digital operation  mode may prove useful to prolong
the operating life of the regulator.
    As  in   the  case  of  the  sensor, the  detailed
mechanization  of  the control  logic  can  be
accomplished in a multitude of ways, available to the
system designer to best match the  local situation.
Available  approaches include   electronic,
electromechanical, pure  mechanical,  hydraulic,
pneumatic, fluidic, or various hybrids of two or more
of these. The control logic unit may also require one
or more  transducers, depending on  the mechanical
choice, to  properly  interpret information  being
received from the error sensor, or to properly have its
outputs interpreted by the actuator-flow modulator.
It is obviously desirable to select a type of mechanism
that  uses  the minimum number of  such interface
devices, to reduce costs and to achieve the maximum
operating reliability. A good example of this is shown
by the simple mechanical float-operated regulators in
current use. In this case, the error sensor, the float,
drives the controller,  the linkage which operates the
actuator-flow modulator,  and the gate.  In larger
installations, the operating forces for flow modulating
 are beyond the practical capabilities of float linkages,
 and a source of externally supplied energy is required.
 Again, to minimize interface equipment, all-electric,
 or all-hydraulic mechanism could be selected. Further
 details  of  control  logic   mechanization follow:
 Electronic Equipment
    A very  broad base  of electronic technology,
 engendered by  recent aerospace advances, is available
 to  mechanize  any  desired  degree  of  sewer
 regulator-logic  complexity. The  initial cost  of
 electronic control equipment is fairly reasonable; its
 basic operating reliability  is  fair,  however service,
 other than  through  the  manufacturer,  may  be
 difficult to obtain since municipal maintenance crews
 usually are not trained for electronic repair work. Its
 capability  to  operate  when needed  most may  be
jeopardized by power failures often accompanying
 storms, unless emergency standby power is available.
 An electronic control logic  unit requires a relatively
 expensive  interface  arrangement, usually  involving
 either electrical switchgear,  or  electro-hydraulic
 valving.  Both  of  these   devices  have, involved
 maintenance  and reliability  problems in  the  sewer
 environment.  This  type  of equipment  can  be
 procured  from many  electronics or  computer
 manufacturers,  usually on a special  order basis. An
 off-the-shelf product status undoubtedly will occur if
 demand warrants.
 Mechanical Equipment
    Mechanical  systems have been successful  in
 smaller regulator installations. They are relatively
 simple and inexpensive.  They  are  susceptible  to
 environmental  corrosion  and fouling by sewage
 debris, particularly  if the mechanism is submerged.
 Municipal experience has shown that frequent (once a
 week in  some  cases)  inspection and servicing, are
 required to keep such systems operating.
 Hydraulic Equipment
    Hydraulic systems are  finding acceptance in a
number of jurisdictions. A basic version of hydraulic
 control logic consists of a  3-or 4-way  spool  valve,
using  potable  water  as  a  source  of pressurized
hydraulic fluid. The valve outputs are connected to
large  hydraulic cylinders, which operate  the  flow
modulation  structure. The  spool  valve can  be
 operated  either by a small  hydraulic valve on the
error  sensor, or  positioned  directly by the sensor.
This system  is comparatively expensive to install,
however,  it  is  fairly  reliable  when  frequently
inspected  and  maintained.  The  regulation
performance  is  quite good.  Adequate  design
precautions are required to prevent cross-connection
of sewage into the water system in the event of a loss
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of water pressure.
Electro-mechanical Equipment
    A typical electro-mechanical version of a control
logic unit is a switch-gear installation containing a
power  relay train and starting circuitry for a large
electric motor drive.  This  type  of equipment  is
generally used for a digital system. It is moderately
expensive to  install, and is subject to corrosion
problems  in  the  sewer environment.  Elaborate
protection must  be installed  to protect  against
spark-triggered  explosions, a danger  which has led
many  jurisdictions  to  ban   the  use of  electrical
equipment in sewers.
Pneumatic Equipment
    The pneumatic  approach to  a  sewer  regulator
control logic unit is generally similar to that of a
high-pressure  hydraulic  unit, and  has  the  same
advantages and disadvantages.
Fluidic Equipment
    The  fluidic  approach is  currently  in the
experimental stage. It has  been  investigated under a
FWQA  research  contract. Basic  characteristics  of
fluidic devices  are no moving mechanical parts and
ability to be used to  implement  a wide variety of
system  approaches.  The  working fluid  can be the
sewage stream itself, and no outside source of control
energy need be supplied. Fluidic control logic units
may be  constructed  with  any corrosion resistant
material including concrete, and the interface devices
are simple, low cost, and flexible in construction.
Instrumentation Equipment
    This  equipment may be provided when it is
desirable  to secure data on the  total system and to
control the collection  of  sewage in  various parts
thereof. Communication equipment  is required at
sampling  stations  to  provide  data  to  a  central
location.
Complete Sewer Regulator Systems
    The   foregoing   has  dealt  with  equipment
conforming  to individual functions. In surveying the
available equipment that conforms to these functions,
it has been found that very few manufacturers supply
equipment  for  more  than  one  of the  indicated
functions. This situation sometimes requires that the
sewer  system designer piece together a  complete
system from a large assortment of components and,
in the process, consider all the interface requirements
that arise in integrating many dissimilar elements into
an operating system.
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                                             APPENDIX 3
                   REPORT OF THE SUBCOMMITTEE ON THE SYSTEMS CONCEPT OF
                       COMBINED SEWER SYSTEM REGULATION AND CONTROL
    The role of regulators and control facilities in use
today makes it  imperative that they  be designed,
equipped, and maintained on  the basis of a total
systems concept. This is necessary just to meet the
standards  of combined  sewer  control  already in
existence today, and to prepare  for those  of the
future. They can no longer  be simple "either—or"
devices, left all alone to function or not, as the case
may be, in  any  storm,  flood,  or other emergency.
Each  regulator and its associated control is not an
isolated  entity,  affecting  only its  immediate
environment. Rather, it is a part, however small, of a
total water-flow  pattern and,  as such, can  be
compared to the individual link in a chain, the  proper
functioning  of each being required to  obtain the
desired result from the total system.
    There are many  factors and parameters  that
influence the total combined  sewer system; these
must  be considered by  those involved  in planning
design,  construction and  operation. They can be
catergorized as follows:
    1.  Function and type of unit—overflow, bypass,
    fixed, variable,  temporary, permanent;
    2.  Flow handled—minimum, maximum  and
    variation, high or low pressure;
    3.  Area  served—minimum, maximum  and
    variation due to inter-regional operation;
    4.  Quality  of  wastes—normal,   abnormal,
    organic, chemical; upstream and downstream;
    5.  Treatment  of wastes—normal,  minimum
        desired, future requirements;
    6.  Instrumentation and  control—gravity,
    manual, electric, automatic, automated;
    7.  Communications—normal,  emergency,
    manual, electronic, automated;
    8.  Authority  responsibility—public, private,
    individual, group, legal entity; and
    9.  Responsibility—public,  private, 'individual,
    group, legal entity.
    The effectiveness and subsequent sucess of each
regulator, each group, each system, and finally each
total watershed regulatory system, will depend  on the
amount of forethought,  planning,  design and,
ultimately,  the  implementation  of  the
aforementioned  factors.  Where shortsightedness  is
combined with limited funds, the system fia'ally put
into service will be inadequate to perform ffee task
expected of it, let  alone meet the required tegional
and  sectional  environmental and  performance
standards.
    A further detailed analysis of each main factor
must cover the following criteria:
    1.   Function and type:
        a.  Is there a current method  for using any
        or all of the existing or proposed regulators
        in series?-in parallel?
        b.  How  does  operational  failure  of a
        regulator affect other regulators in its flow
        pattern, both upstream and downstream?
    2.   Flow:
        a.  What  is   the  sanitary,  flow
        variation—hourly  through yearly; minimum
        through maximum?
        b.  What  is  the   storm  water  flow
        variation—hourly  through yearly; minimum
        through maximum?
        c.  On  what  basis  does  overflow  from
        combined flow (untreated) occur?
        d.  Will gravity handling be sufficient,?
        e.  If gravity flow is not sufficient,  what
        total  pumping system will be required?
        f.  Can the current or proposed system
        sense  upstream  and  downstream  flow
        variation?
    3.   Area:
        a.  What is the specific area affecting each
        individual regulator?
        b.  What is the specific area affecting each
        series of regulators?
        c.  Into  what receiving  waters  does  the
        effluent  from  sanitary  flow,  treatment
        discharge?
        d.  Into  what receiving  waters  does  the
        effluent  from combined  flow  treatment
        discharge?
        e.  Into  what receiving  waters  does  the
        overflow  from  combined  flow (untreated)
        discharge?
        f.  What failure of any group of regulators
        can  the  total  system tolerate  and  still
        maintain 50 percent or higher effectiveness?
    4.   Treatment:
        a.  What degree of sanitary  flow treatment
        is currently maintained?
        b.  What degree of sanitary  flow treatment
        do regulatory agencies now require?
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    c.  What degree of combined flow treatment
    is currently maintained?
    d.  What degree of combined flow treatment
    do regulatory agencies now require?
    e.  What degree of storm flow treatment is
    currently provided?
    f.  What  degree  of combined storm  flow
    treatment will regulatory agencies require?
    g.  What degree of combined flow treatment
    can be provided while  still in  the retention
    area awaiting regular treatment?
5.  Instrumentation and control:
    a.  How is  control of flow and quality of
    sanitary flow obtained?
    b.  How is  control of flow and quality of
    combined flow obtained?
    c.  How is  control of flow and quality of
    storm flow obtained?
    d.  How is control of  flow  and  quality
    measured?
    e.  How are variations of flow and quality
    ,measured?
    f.  How are failures  of regulatory devices
    detected?
    g.  If control is by gravity, what limitations
    apply as to flexibility?
    h.  If control  is manual, what limitations
    apply on flexibility?
    i.   If control is automatic, what system is
    used and what is its reliability.
    j.   If control is  automatic, can  it be
    automated; and to what extent?
6.  Communications:
    a.  What system is  used to  communicate
    data on the treatment process?
    b.  What system is  used to  communicate
    data on the operation of regulators?
    c.  What system is  used to  communicate
    failure  or malfunction  of individual
    regulators?
    d.  What   is  the  reliability  of  the
    communication system during storms?
    e.  What backup system  is available in case
    of power failures?
    f.   What is the extent of the communication
    network as  compared  to the total regional
    watershed area?
7.  Authority:
    a.  In whom  is  the  regulatory  authority
    vested—individual or agency?
    b.  In what   agency  is  the regulatory
    authority vested—private or public?
    c.  How  is the regulatory authority
        vested—legal: assumed?
        d.  How widespread is the authority in the
        watershed area?
        e.  Who has master control authority in the
        watershed area?
        f.   Who  has  authority  to  recommend
        changes, additions and expansions?
    8.  Responsibility:
        a.  To whom is the individual or agency
        having authority accountable?
        b.  How is  this  responsibility  assigned or
        designated?
        c.  If involved with more than one private
        or public body, how is cooperation obtained
        and maintained?
        d.  Who or what entity has responsibility to
        initiate  or  approve  changes,  additions or
        expansions?
        e.  Who or what entity has responsibility to
        finance the total system?
    Many more problems arise when the scope of the
regulatory system is expanded  beyond the individual
or localized area.  These intensify and multiply as the
regulatory system expands from the unit to the area;
to  the municipality;  to  multiple—community; to
sanitary district; to intrastate regional watershed area;
to  national  levels;  and  finally  to  international
watersheds.  The more significant problems include,
but are not limited to:
    1.  From the individual municipality standpoint,
    what effect on its total combined flow problem
    does the following have:
        a.   Intensity  and duration of the individual
        storm?
        b.  Intensity  and  duration of a  series of
        storms over  a day, several days,  weeks or
        months?
        c.   Failure  of one  or several  regulatory
        devices?
        d.  Upstream  conditions, if located on
        stream or river?
        e.   Tidal conditions, if located on ocean or
        estuary?
        f.   Sudden thaw conditions, if located in
        heavy snow areas?
        g.   Effect of  its  overflow  on downstream
        communities?
        h.   Effect of its  overflow  on the  total
        watershed?
        i.    Effect of its, overflow on its own potable
        raw water supply?
        j.   Effect of its  overflow  on downstream
        potable raw water supply?

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2.  From  the  multiple-community or  area
sanitary district standpoint, what effects do the
following factors have:
    a.   What is the primary responsibility of the
    district, by law?
    b.   What  are the secondary responsibilities
    of the district, by law?
    c.   What  is the  moral responsibility of the
    district,   based on  public  opinion  and
    accentuated by local news media?
    d.   In case of failure of primary  regulatory
    functions,  what determines the  choice  of
    area to be flooded,  polluted,  or  otherwise
    affected?
    e.   What  relationship  exists  between  the
    sanitary  district and  the  potable water
    authority, if they are separate entities?
    f.   Can one legally restrain the other if they
    are separate entities?
    g.   What is most important to  overall health
    of the total area?
3.  From   the  newly  established regional
watershed pollution  control district standpoint,
additional requirements are:
    a.   Establishment of priorities of need  for
    regulating  devices and systems during storms.
    b.   Maintenance  of  potable raw water
   - supplies in the total watershed.
    c.   Alternative sources of potable  raw water
    supplies in case of pollution.
    d.   Maintenance  of  total   watershed
    conservation  and recreation capabilities  at
    highest level appropos to storm emergencies.
    e.   Maintenance  of  total   agricultural
    endeavor  in  the  watershed area, with
    minimum interference due  to  flooding
    and/or pollution.
    f.   Maintenance  of total  industrial
    endeavors in  the  watershed area, with
    minimum  interference  due to  flooding or
    contamination of  potable  and/or  process
    water.
    g.   Maintenance  of total residential facilities
    in   watershed  area, with minimum
    interference  and  inconvenience due  to
    flooding, sewer backup, potable water  supply
    contamination, or other conditions.
    h.  Maintenance  of  marine facilities and
    endeavors, such as fisheries,  oyster and clam
    beds  and shipping, with minimum
    interference due  to flooding, pollution and
    actual destruction of facilities  in  estuaries,
   harbors, and tidal areas.
     4.  In regional  watershed  pollution  control
     districts  which  cross  state boundaries,  the
     environmental factors include:
        a.  How is the regional  district comprised
        and made up politically?
        b.  Which  state or states, if any, are most
        influential?
        c.  Which  state or states have most urgent
        needs during storms?
        d.  Where  and  how  is recourse  action
        located and accomplished when states object
        or  disagree with actions of the  regional
        district?
        e.  What are the arbitration procedures  and
        in what agency are they vested?
        f.  What agency has ultimate authority over
        district actions?
     In view of the  extreme complexity of the total
 systems described above, and the human as well as
 the  purely mechanical  factors, the most important
 parameter of all involves communication. This must,
 of necessity, involve the following aspects:
        a.  It  must  be  vertical, horizontal   and
        diagonal.
        b.  It  must  be accurate, especially as regards
        objective data.
        c.  It  must  be timely, or fast enough so that
        decisions  made  therefrom  can  be
        implemented in time to be effective.
        d.  It  must  be aimed primarily at preventive
        rather  than corrective analysis, diagnosis  and
        action.
        e.  It  should have as its ultimate goal  the
        maintenance of the current level of control,
        as a minimum.
        f.   It  should have as its final ultimate goal
        the establishment of  a  regulator  control
        system that will actually  enhance the total
        environmental  and  ecological state  of
        existence for all living things.
    To  accomplish  this  desired  level  of
communication, there is no satisfactory substitute for
a completely automated system of environmental and
ecological data  sensing,  transmission,  collection,
analysis,   evaluation,  action  based  thereon,  and
feed-back  to indicate results as soon as possible. The
basic advantages of automation include but  are not
limited to:
    1.   Capability to communicate almost instantly
    throughout the system.
    2.   Awareness of systemic water quality at any
    given time.
    3.   Awareness of systemic water quantity at any
                                            135

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given time.
4.  Awareness of localized water quality at any
given time.
5.  Awareness of localized water quantity at any
given time.
7.  Awareness  of  the  effect  of any  specific
external environmental change.
8.  Awareness of the effect of a combination of
external  environmental changes  occurring
simultaneously or sequentially.
9.  Awareness  of  the  effect  of any  specific
regulatory control procedure.
10. Awareness of the effect of any combination
    of regulatory control procedures.
    11.  Awareness  of the effect  of any specific
    treatment process during a crisis.
    12.  Awareness of the effect of any combination
    of treatment processes during crisis.
    Failure to consider all of the foregoing factors, as
a minimum, will result in a regulatory system that is
inadequate or incapable of responding to the current
combined sewer overflow requirements and problems.
Such a system would be completely helpless to meet
new water quality standards and make  impotent any
attempt  to meet  the  even  more   stringent
requirements of the future.
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                                                   APPENDIX 4
                                                   REPORT ON
                                             DIVERSION SCREENING
         Diversion  screening  comprises  screening
     equipment wherein  the  trash  removed  by  the
     screening rake is discharged into the interceptor sewer
     to the plant for centralized removal or handling.
         Diversion  screening is  recommended  to avoid
     clogging of regulators  and to remove floatable trash
     from  the overflow to  the  receiving  waters  thus
     improving the quality of the storm water overflow.
         Generally, bar rack screen openings of 1-inch are
     satisfactory.  However,  for outfalls into the ocean or
     lakes drum screens are available having 1A inch circular
     openings  which will remove ten to twenty times the
     trash removed by a 1-inch screen opening including
     cigarette filter tips which otherwise  float and cause
     unsightly litter on beaches or shore banks.
         The bar racks shown in Figs. 1,2, and 3 have 3/4
inch or 1 inch openings with reciprocating rakes that
can  be driven  by  water or oil-operated hydraulic
pressure systems used for some regulators, or electric
motors,  totally  enclosed for  explosion-proof and
water-proof application.
    The rakes  are actuated by water  levels  that
indicate  overflow  conditions for  flow-through
regulators and outfalls where layouts are generally as
shown in Figs. 35, 36, and 37.
    Otherwise where  dry-weather flow is directed
through a regulator to the interceptor sewer, such as
through a Fluidic Y-Branch Diverter, screening rakes
operate continuously. The revolving drum screen for
fine, 1/4-inch screening can  be  applied to discharge
screenings directly into the interceptor sewer from a
discharge chute or by means of a conveyor driven by
a screen drive take-off.
                                                                                              FIGURE 36
                 Arrangement, Storm Sewer Interceptor Screen—Reciprocating Rack
Courtesy FMC Corp.
                                                     137

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                                                                                 FIGURES?
                    Arrangement, Storm Sewer Interceptor Screen—Bar Rack
                                               ro
                                                             I  I
                                                           -  I   I
                                                           -  I   I
                                                           ;  i   !
Courtesy KMC Corp.
                                              138

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                                                                                  FIGURE 38
                  Arrangement, Storm Sewer Interceptor Screen—Curved Bar Screen
                                            To
  DKY VieaTHEK I=L£>W
Courtesy FMC Corp.
                                                139

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                                                         BIBLIOGRAPHIC:   American  Public Works  Association,
                                                            Research Foundation. Combined  Sewer Regulator Overflow
                                                            Facilities FWQA Publication No. 11022DMU07/70

                                                         ABSTRACT:   Current  design,  operation  and maintenance
                                                            practices used by local jurisdictions in the United State's and
                                                            Canada were determined by personal interviews and compiled
                                                            in  this  report.  Particular  attention  was  given  to  the
                                                            performance of various types of  regulators, the  use of tide
                                                            gates,  new  designs,  European practices and the systems
                                                            concept of combined sewer regulation. Thirty-seven drawings
                                                            and photographs of regulators  are  included.  Seventeen
                                                            recommendations  are made, the  adoption of which would
                                                            upgrade regulator facilities and tend  to reduce receiving water
                                                            pollution from combined sewer overflows.
                                                            This report  and accompanying manual were submitted in
                                                            fulfillment of Contract 14-12-456 between the Federal  Water
                                                            Quality  Administration,  twenty-five local jurisdictions and
                                                            the APWA Research Foundation.
                                                         BIBLIOGRAPHIC:   American  Public Works  Association,
                                                            Research Foundation.  Combined  Sewer Regulator Overflow
                                                            Facilities FWQA Publication No. 11022DMU07/70

                                                         ABSTRACT:   Current  design,  operation  and  maintenance
                                                            practices used by local jurisdictions in the United States and
                                                            Canada were determined by personal interviews and compiled
                                                            in  this  report.  Particular  attention  was  given  to the
                                                            performance of various types of regulators, the use of tide
                                                            gates,  new  designs, European practices  and the systems
                                                            concept of combined sewer regulation. Thirty-seven drawings
                                                            and photographs of  regulators  are  included. Seventeen
                                                            recommendations  are made,  the  adoption of which would
                                                            upgrade regulator facilities and tend to reduce receiving water
                                                            pollution from combined sewer overflows.
                                                            This report  and accompanying manual were submitted  in
                                                            fulfillment of Contract 14-12-456 between the Federal Water
                                                            Quality  Administration,  twenty-five local jurisdictions and
                                                            the APWA Research Foundation.
                                                         BIBLIOGRAPHIC:   American  Public  Works Association,
                                                            Research  Foundation.  Combined  Sewer Regulator Overflow
                                                            Facilities  FWQA Publication No. 11022DMU07/70

                                                         ABSTRACT:   Current  design,  operation  and  maintenance
                                                            practices used by local jurisdictions in the United States and
                                                            Canada were determined by personal interviews and compiled
                                                            in  this  report.  Particular  attention  was  given  to the
                                                            performance of various types of  regulators, the  use of tide
                                                            gates,  new designs, European practices  and the systems
                                                            concept of combined sewer regulation. Thirty-seven drawings
                                                            and photographs  of  regulators   are  included.  Seventeen
                                                            recommendations  are  made,  the  adoption of which would
                                                            upgrade regulator facilities and tend to reduce receiving water
                                                            pollution from combined sewer overflows.
                                                            This report  and accompanying manual were submitted  in
                                                            fulfillment of Contract 14-12-456 between the Federal  Water
                                                            Quality Administration,  twenty-five local jurisdictions and
                                                            the APWA Research Foundation.
                                                 KEY WORDS


                                                    Combined Sewers
                                                    Overflows
                                                    Regulators
                                                    Design
                                                    Operation
                                                    Maintenance
                                                    System Control
                                                    Quantity of Overflow
                                                    Quality of Overflow
                                                    Tide Gates
                                                  KEY WORDS


                                                    Combined Sewers
                                                    Overflows
                                                    Regulators
                                                    Design
                                                    Operation
                                                    Maintenance
                                                    System Control
                                                    Quantity of Overflow
                                                    Quality of Overflow
                                                    Tide Gates
                                                  KEY WORDS


                                                    Combined Sewers
                                                    Overflows
                                                    Regulators
                                                    Design
                                                    Operation
                                                    Maintenance
                                                    System Control
                                                    Quantity of Overflow
                                                    Quality of Overflow
                                                    Tide Gates
     jurisdictions  and  the American Public Works  Research  Foundation.
                                                           Abstractor
                                                                        Richard  H.  Sullivan
                                                            institution
                                                                               Research Foundation
WR;I02 (REV. OCT. 18«B>
WRS1C
SEND TO! WATER RESOURCES SCIENTIFIC INFORMATION CENTER
          U S. DEPARTMENT OF THE INTERIOR
          WASHINGTON, D.C. 20240
                                                                                                                               819—718

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