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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

-------
                                      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.
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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,
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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
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 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
                                                 77

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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
                                                    78

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                                                        FIGURE 21
                LOADED DERRICK BARGE
      ALLEGHENY COUNTY SANITARY AUTHORITY
                                                FIGURE 22
Courtesy Metropolitan-Seiver District of Greater Cincinnati'
                      SWAMP BUGGY
                           79

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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
                                                   81

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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
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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.
                                                   98
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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.
                                                    102
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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.
                                                103
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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
                                                104
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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.
                                                 105
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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.
                                                 106
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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
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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. -      ;,    '>
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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
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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
                                                 121
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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.
                                                 122
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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.
                                               123
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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
                                              124
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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.
                                             136
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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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