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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
-------
FIGURE 18
CLOGGING OF ORIFICE
Cost of Maintenance
The annual maintenance cost for these regulators
was consistently reported in the order of $700 to
$900 per unit per year.
Horizontal Fixed Orifices (Drop Inlets)
In all applications surveyed where drop inlets
were used, except at the Minneapolis-St. Paul
Sanitary District, the orifice was protected by a grate.
Comments hereafter, take that fact into consideration.
Reasons for Malfunctions
The drop inlet regulator grating is particularly
susceptible to frequent clogging with leaves, rags,
plastics, sticks and other debris.
Maintenance Requirements
Operating personnel reported that drop inlets
require almost constant maintenance. In Akron, each
unit is serviced daily and some large drop inlets
require cleaning even more frequently. Maintenance
personnel reported that they had no assurance that
clogging would not recur immediately after cleaning.
Two- to three-man crews are used to maintain
these regulators. A two-man crew consists of two
laborers, while a three-man crew consists of two
laborers and a technician. Their principal function is
to scrape the grates clean. In this case, the debris
must be lifted to the surface for final disposal. As a
minimum, grills and chambers must be cleaned on a
weekly or bi-weekly basis.
Cost of Maintenance
Because of the need for regular maintenance, the
annual service cost is relatively high. Cost estimates in
the order of $1,200 to $1,500 per unit per year were
reported to be not unusual.
Recent and Proposed Changes
In order to reduce the maintenance burden and
to improve operating characteristics, two recent
proposals should be considered: that the space
between bars of the grating be increased, so that at
least smaller objects will not cause malfunction; and
that flow levels in the regulator chamber • be
monitored so that maintenance personnel may be
alerted in case of blockage during periods of
dry-weather flow, thus eliminating prolonged
overflows of sanitary sewage.
73
-------
FIGURE 19
OVERFLOW SCREENS
Debris Captured
from Overflow
74
-------
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
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crews with air packs.
Figure 20, Derrick Barge and Boat for Regulator
Maintenance, is a photograph of equipment used by
ALCOSAN to maintain regulators which are
accessible only from the river. Figure 21, Loaded
Derrick Barge, shows the variety of equipment used
for maintenance, including a bucket-cleaning
maqhine.
Figure 22, Swamp Buggy, is a photograph of a
vehicle used by the Metropolitan Sewer District of
Greater Cincinnati to maintain structures located
along streams: The wheels of the Buggy are the
flotation units. A small crane is mounted on the rear
and a large pump is mounted on the frame.
Structural Design to Facilitate Maintenance
Maintenance personnel are critical of regulator
structures which provide inadequate space for safe
and effective maintenance work. The survey disclosed
that, too frequently, capital cost economies are given
major priority and the cost of maintenance and
operation is left to the maintenance superintendent
to work out as best he can once the installation has
been completed. This was characterized by
respondents to the survey as an expensive and futile
procedure. As an example, the use of stairways or
portable ladders should be considered wherever
possible, instead of manhole steps.
A significant number of regulator stations
observed in the 18 interviewed jurisdictions were
inaccessible, could only.be reached by boat, or could
be entered only by descending 30 feet into a 30-inch
diameter manhole section. It is obvious that regulator
devices in these difficult locations suffer from lack of
maintenance.
The following conclusions can be drawn from the
evaluation of the regulator maintenance practices
disclosed in the national survey.
1. Components of regulator stations should
be housed in separate chambers. For example, a
float-operated gate regulator station should
consist of a chamber for the regulator, with
separate housing for its float control; a diversion
chamber for directing the combined sewer flow
to the regulator; and a tide gate chamber, if
required. All chambers should be readily
accessible.
2. Access to the chambers should be
unobstructed. There should be adequate space to
admit personnel freely while carrying equipment
they may require to perform their duties. An
access opening should be located above any
heavy or bulky mechanical device, so that, if
necessary, it can be removed and replaced
without excavation, or so that it may be repaired
DERRICK BARGE AND BOAT
ALLEGHENY COUNTY SANITARY AUTHORITY
FIGURE 20
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FIGURE 21
LOADED DERRICK BARGE
ALLEGHENY COUNTY SANITARY AUTHORITY
FIGURE 22
Courtesy Metropolitan-Seiver District of Greater Cincinnati'
SWAMP BUGGY
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in the relative comfort and security of an
above-grade location.
3. The environment of an overflow
chamber is likely to be damp and corrosive, so
mechanical equipment should be fabricated of
corrosion-resistant materials. Special care should
be paid to bearings and other friction or contact
surfaces. In this respect, the use of neoprene may
be of benefit. Electrical gear should be housed in
a separate chamber, situated above grade, if
possible. If it is absolutely necessary to install
electrical equipment in conjunction with the,
regulator chamber, it should comply with
National Board of Fire Underwriters
specifications for hazardous locations. The
chamber should be protected by forced-air
ventilation.
4. All chambers associated with sewer
systems should have ample ventilation
capabilities, preferably at two points, to provide
cross ventilation.
5. Convenient and non-corrosive ladders
and steps should be provided.
6. Reasonable headroom is essential within
the chamber.
7. A well-defined, adequate, large landing
area should be provided in the chamber. Where
possible, it should be so located as to give
convenient access to all key maintenance points
and allow inspection of the incoming and
outflowing combined sewage.
8. If at all possible, the chamber should be
lighted. Only explosion-proof fixtures should be
used.
9. Guard rails should be provided.
However, New York City, for example, does not
• favor railings in regulator stations, since they feel
that reliance on a railing which may fail due to
corrosion is more hazardous than the omission of
the railing. Where conditions are particularly
hazardous and where a fall might mean death or
serious injury, railings have been constructed of
structural steel encased in concrete.
10. A ceiling hook over float gates, small
gate assemblies, and screens is a simple but often
useful facility.
11. Simplicity- in cleanability and design are
essential. Projections and small gaps where rags,
sticks and floating material can collect, should be
carefully avoided.
12. Adequate size in the regulator chamber
must be provided to prevent blockage by deposits
of sewage solids, and oddities such as bicycle
frames or long timbers, which are not
infrequently found in combined sewers.
Provision of such structural and equipment
facilities will enable the maintenance department to
maintain regulator facilities in a manner that will
assure effective performance.
Preparing a Regulator Chamber for Inspection
There are dangers associated with sewer
maintenance procedures, both in the sewers and their
access chambers below grade, and from the traffic
above grade. Basic safety precautions are applicable
to maintenance crews across the country. The
instructions given to maintenance crews in
Philadelphia are an example of standard safety
practice:
1. Truck should be parked so as not to obstruct
traffic but, if possible, it should be used to
protect men working near open manholes. If a
truck is used for this purpose, suitable flashing
lights must be used on the truck.
2. Warning cones, flags, signs, and lights should
be used to make areas safe for both vehicles and
pedestrians.
3. A manhole cover should be raised with a.safe
and proper tool and a bar placed under it, so that
it can be rolled to one side.
4 A manhole guard should be placed around
the open manhole.
5. A chamber or sewer should be given
adequate ventilation before entry is made.
6. The air in both sewer and chamber should be
checked for explosive mixtures, oxygen
deficiency, and hydrogen sulfide content.
7. If there is an indication of gases, a portable
blower should be used to clear the area.
Effect of Automatic-Automation
Systems on Maintenance Procedures
The experience reported by one jurisdiction
indicates that overflow of dry-weather sanitary flow
has been reduced by 50 to 75 percent because of
improved use of manpower and methods, without.
taking into consideration the
instrumented-automated system. A study made of
1962 raw-waste data compared the average plant load
received on dry days versus runoff days. This study
concluded that, "The average annual BPD would
.possibly be 15 percent greater, the suspended solids 6
to 10 percent higher, and the total solids 3 to 6
percent greater if the sewer system were not affected
by runoff."1 Since improved manual surveillance
methods were implemented and revisions made to
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regulators utilizing the automated system, average
annual plant load has increased markedly. The
increases are due, in part, to a number of factors, but
. a substantial portion of the increased load is due to
better regulator performance. The added increase in
plant load has been from 5 to 15 percent above past
growth projection curves.2 '3
An instrumented or automated regulator
maintenance system may be defined as one which
provides continuous information at a central location
concerning status and performance of the combined
sewer overflow regulators. The information may
include rain gauge readings, trunk and interceptor
sewer flow or level, regulator gate position, and
possibly robot water quality monitoring data, or it
may be limited to on-off, yes-no information as to
whether or not a regulator is overflowing. To date,
there have been only a few installations using
instrumented systems. Among these, few have
provided for remote control of the regulators. In
some cases, the surveillance system causes an alarm
indication so that a crew may be dispatched to
correct the malfunction. The systems installed at
Minneapolis—Saint Paul Sanitary District and Detroit,
and now being finalized at the Municipality of
Metropolitan Seattle, provide for remote control of
regulator devices so that overflows can be corrected
immediately from the central location.
Also, for the purposes of this report, a definition
of regulator maintenance is necessary. There are two
kinds of maintenance which will be described here.
Normal maintenance is inspection and servicing of the
regulator equipment to correct unnecessary overflow
due to blockage, stoppage, and equipment
malfunction. This kind of regulator maintenance in a
sense is a part of operation of the system.
The second kind of maintenance is equipment
1 Anderson, J. J., "Analysis of Operating Data from
a Full-Scale Primary Sedimentation Plant at the
Minneapolis-Saint Paul Sanitary District," A Thesis
Submitted to the Faculty of the Graduate School of
the University of Minnesota, April 1967.
2 Toltz, King, Duvall, Anderson and Associates, Inc.,
St. Paul, Minnesota, "Report on the Expansion of the
Sewage Treatment Plant-Minneapolis-Saint Paul
Sanitary District."
3 Anderson, J. J., "Computer Control of Combined
Sewers," Presented at American Society of Civil
Engineers Annual and Environmental Engineering
Meeting, October 13-17,1968.
maintenance or repair maintenance required because
of wear, deterioration, and equipment failures which
require a rebuilding or repairing of the equipment.
This kind of maintenance normally requires shop
facilities and tools and equipment such as welding
devices. For the purposes of this report the latter will
be designated as repair maintenance, and the former
as routine maintenance.
One of the functions of routine maintenance is
the regular inspection of regulators on either a
periodic basis or following each use of the regulator
system by storm flow. With an instrumented system,
the number of routine inspections required can be
reduced significantly. For example, in one
jurisdiction, inspection of 125 miles of river front,
required two and a half days' time for a four-man
crew to complete. Of these regulators, approximately
20 percent caused most of the operational
difficulties. Routine inspection of regulators was
reduced substantially and almost eliminated when the
major—and the most troublesome ones—could be
continuously monitored. By providing remote control
of these troublesome regulators, corrections could be
made from a central location within a matter of
minutes, compared with hours when a crew had to be
dispatched to the site.
Not all of the savings from routine maintenance
can be credited to the use of an instrumented system.
In exchange for reduced routine maintenance,
additional control facility maintenance is required.
After the original problems in the instrumentation
system are eliminated, this maintenance is rather
minimal, requiring only a fraction of one man's time
for 40 instrumented locations.
Manpower Requirements
Manpower requirements for automated,
combined sewer, overflow-regulator facilities
maintenance differ considerably from those for static
systems, both in kinds and numbers of personnel
required.
For static regulators, maintenance requires at
least one man for each 10 to 20 regulators. These
men must be willing to spend a good deal of their
time in the sewers, working under unpleasant
conditions with their main duty consisting of clearing .
clogged facilities. Periodically, they may be required
to adjust weir levels and gate settings. The cleaning
work will require removal of debris an'd shoveling or
flushing grit and heavy sediment. Typically, the worst
conditions are in the larger regulators carrying heavy
flow, usually containing industrial wastes. Typically,
these large regulators cause the most overflow, and
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should be given the closest checking and most prompt
attention. Much of the sewer crew's time is spent in
travel between locations looking for problems and in
setup and cleanup operations if proper safety and
work methods are used.
At the opposite extreme, modern, well-designed
remote-controlled regulators can substantially reduce
the amount of unappealing and hazardous work in
sewers. Inspection is done remotely by an operator or
instrument at the central location. Repair
maintenance will be of a different nature and
somewhat increased. Various types of equipment will
require such crafts as electricians, electronic
technicians, pipe fitters, mechanics, and possibly
computer specialists. In most major jurisdictions the
work load in each specialty will not require full time
attention, particularly after any faults in the system
have been corrected.
Primary coordination must be effected between
central regulator operations, routine maintenance,
and repair maintenance. Maintenance personnel must
make known to central operations their presence in
areas where the activation of operations might cause
injury or death to such personnel. At the same time
there should be a "lockout" of such equipment.
Frequently, the three functions must provide a
coordinated effort. Thus, the maintenance crew
might provide the safety equipment, hoisting facilities
and other paraphernalia for the repair crew while
they are in the sewer or control chamber.
Subsequent to repair and prior to departure
from a particular site, the central operations
personnel will make tests to insure that a return trip
will not be necessary. Operating personnel can inform
maintenance personnel of problems whether at an
automated location or other location, by inferential
judgment. Maintenance personnel can assist operating
and maintenance personnel in checking calibrations
of systems and preventive testing.
The maintenance personnel should be given the
most extensive safety training and equipment, since
they will spend the most time under hazardous
conditions. They should also be given prime
responsibility for protecting other personnel who
infrequently will be in hazardous locations.
Cooperation with sewer cleaning and maintenance
crews will also be necessary.
Effective utilization of personnel in a remotely
controlled system is essential. Because of wide
geographic distribution of equipment and the
interconnection • of mechanical, electrical, and
electronic systems, considerable time can be spent
diagnosing problems and removing, repairing, and
replacing defective equipment. For example, it is
conceivable that several days might elapse before it is
determined whether a defect is in the telemetry, the
electrical or mechanical system, if a craftsman of each
class was sent sequentially to investigate. Sending all
three craftsmen to each trouble area is also wasteful.
Several solutions of this problem are available.'In
the design of a system, modular plug-in units can be
used for easy replacement by the maintenance men.
For example, small air compressors can be installed
using plug-in power cords and quick-disconnects on
air, lines. Similar techniques are available for
telemetry, power units, and instruments. Judicious
inclusion of test points, gauges, and indicating lights
also can be of benefit as a repairing aid.
In order to avoid excessive travel-and-turnaround
time by repair crews to obtain parts, equipment or
additional aid, a support team with a suitably
equipped and stocked vehicle should be provided to
serve such crews when required. Since manholes and
underground structures are not easily identifiable on
the ground, adequate maps and location drawings
must be readily available for the crews.
In some cases, it is not practicable for the
operating agency to provide the depth and range of
skills in-house for maintaining an automated system.
Increasingly, therefore, use has been made of
contractual services on a yearly, or on-call basis when
required.
The management of an automated regulator
control system requires cooperation with other
organizations. A partial list of these for a typical
system might include the: telephone company; power
company; gas company; weather bureau; street
department; engineering department; water
department; and fire department.
It is advisable to have a key person for contact
with all of these agencies. Normal contact will be
minimal with some agencies and continuous with
others. The Weather Bureau will usually be very
cooperative in providing information on rainfall
conditions. This information will be helpful in the
planning of operations. Troubles with telemetry
systems will be minimal if the proper person is found
within the local telephone company. A number of the
other organizations will assist in spotting overflows
arid also can provide significant data and technical
assistance. Equipment used by other utilities can be
examined for possible use in regulator management.
Fixed equipment required at a central site for
maintenance of an automated system will generally
be electric or electronic in nature. A number of
sophisticated test instruments are available for
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checking leased telephone lines. Shop facilities may
or may not be required depending on the equipment
and methods used. Replacement of defective modules
with substitutes makes it possible to send the
defective unit to the factory or depot for repair.
Good truck and equipment washing facilities are
desirable, and periodically all portable and central site
equipment should be inspected, inventoried, and
cleaned.
Communication is needed between the central
dispatcher and all field units, as well as between
personnel working in regulator chambers, sewers and
vaults and those remaining outside. For calibration
purposes, the telemetry system can be used for
communications but two-way radio is more useful.
Speaker and microphone extensions can be used to
allow personnel to use the radio while in a shallow
chamber or in a field structure. Where this is not
possible, hand-held transceivers can be used to relay
messages between the site and the vehicle and thence
to the central site. Communications between
underground personnel and those remaining at the
surface can be by sound-powered telephones,
switchless intercoms, or by transistorized
megaphones. Revisions to the equipment can be made
for use in the sewers. A direct outside telephone
should be provided at the central control site, in
addition to the normal business extension telephones.
The central site should also have means for direct
radio communication with the field.
The organization and administration of regulator
maintenance operations obviously should be tailored
to the operating agency's needs. Typically,
maintenance has been largely ignored, with
dependence on random complaints for determination
of unnecessary overflow. With or without the
automated system, the maintenance function should
be given prime consideration. Separating the regulator
maintenance from sewer maintenance facilitates the
development of the specialized capability needed for
reduction of pollution from overflows and
development of the information and technology
necessary to improve the operation of the regulators
and thus the entire sewer system.
Example of Maintenance Practices
in an Advanced System
The Minneapolis-Saint Paul Sanitary District
maintains approximately 150 regulators which
discharge to about 80 river outlets. Automated
regulator equipment is provided at 15 locations which
control about 80 percent of the system's dry-weather
flow. In addition, there are approximately 25 other
locations where equipment has been placed to
The following is a suggested organizational chart
for regulator maintenance.
SUGGESTED ORGANIZATION CHART
REGULATOR MAINTENANCE
MANAGEMENT
ENGINEER
(PART TIME)
OTHER
ADMINISTRATIVE
AND MANAGEMENT
FUNCTIONS
ROUTINE REPAIR
OPERATION MAINTENANCE MAINTENANCE
Records Field Crew (Part Time)
Calibration Electrician
Fitter
Electronics
Technician
Instrument
Repair
measure interceptor sewer levels, rainfall, and river
quality. About 140 measurements are telemetered to
a central location; 34 gates and 15 inflatable fabric
dams are subject to control.
An engineer is responsible for the maintenance of
the system, which was placed in operation in the
spring of 1969. Under his supervision, the
maintenance crew consists of five men. Prior to the
District's assumption of maintenance, 18 sewer
workers from the two cities worked part-time on the
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regulators.
Computer equipment is maintained under
contract by the contractor who installed the system.
The telemetry system is maintained by a plant
electrician who is assigned to work part-time on the
system. Mechanical repairs have been minimal and
have been performed part-time by help from the
plant machine shop. In-sewer replacements of bubbler
tubes have been accomplished by the maintenance
crew. The maintenance function at major automated
regulators is performed by the computer at variable
time intervals. Typically, each of the 40 gates is
checked every 4 hours during dry-weather to
determine gate position. The measured position is
compared with the desired position and, if necessary,
the gates are readjusted. A complete report is
automatically typed showing initial and final gate
positions, as well as notations of inoperative gates or
telemetry system failures. During storm flows the
gates can be adjusted individually by remote control
or by establishing new gate settings in the computer
system. In the latter case, the gates will be reset to
the new positions when the periodic check is made.
In addition to the periodic check of gates, a complete
computer check of all gates can be initiated at the
central site by operation of a single select button.
The remaining overflows are given periodic
routine checks by the maintenance crew. A very few
locations known to be troublesome, are visited more
frequently. Depending on the work load of the crew,
the periodic checks are made once or twice monthly
during dry weather. A full check of outlets requires
2H days on the ground. The same information can be
obtained in a little more than one hour by helicopter.
Before a helicopter trip is ordered after a rainfall, the
local weather bureau is asked for a current weather
prediction. A checkoff sheet of overflowing locations
is prepared and usually all overflow can be stopped in
one shift. Helicopter flights -are only ordered if a
detectable increase in flow due to runoff is observed
on one of a number of sewer level or flow meter
charts.
Thunderstorm activity occurs frequently at night
in the Twin Cities. By using the helicopter flight and
based on information from the instrumented system,
all overflows are cleared by the end of the normal
working day. By comparison, using old methods,
overflow often continued for several days after such
storms.
Regulator Maintenance as a Specialty
In many jurisdictions there is a division of
responsibility for collection and treatment of sewage.
In some of the larger jurisdictions, the collection
system frequently is under the control of the sewer
division in the public works department. The
responsibility for interception of the dry-weather
flow in the combined sewers often rests with a larger
agency, such as a countywide sanitary district, which
also has responsibility for treatment of the conveyed
wastes before disposal to the receiving stream. The
exact point where each agency's responsibility begins
and ends is often not clearly defined. Traditionally,'
cities have performed minimal regulator maintenance,
with the main emphasis on getting rid of the waste
water and avoiding local area and basement flooding.
Often the cities are charged for operation and
maintenance of a more comprehensive district, based
on flow volume delivered to it, and there is little
incentive for the contributing communities to capture
the maximum flow. In such cases excessive overflows
from collector lines, prior to their junction with the
interceptors of the agency which serves multiple
jurisdictions, is encouraged. Engineering departments
usually are not anxious to raise the height of
permanent weirs or dams to increase the capture of
runoff since this may affect the hydraulic functioning
of the combined trunk sewer system during times of
peak flows. The impediment of flow by high
permanent dams may cause serious backups and
health hazards in basements.
In order to satisfy the often conflicting
requirements of maximum diversion to interceptors
and protection of upstream sewers from discharge,
regulators in which a weir or dam height can be
adjusted with complete reliability is required. The
adjustments must be made frequently, based upon
knowledge of the capacity of the interceptor
downstream from the regulator, upon flow depths in
the combined sewer leading into the regulator and on
comparisons of strength and quantities intercepted
and spilled at other regulators in the system.
Knowledge of reserve treatment plant capacity for
quantities of polluted storm runoff must be
considered.
In most operations, sewer maintenance crews
spend their time immediately after a storm answering
complaints of flooded basements and plugged catch
basins. After the majority of the post-storm
complaint work is completed, the regulators are
visited. In some cases, due to the large number of
regulators, the last regulator may not-be cleared for as
long as two weeks after a storm.
Because of these difficulties, a dedicated crew
that is committed totally to a routine and regular
surveillance program is a must to improve operations.
84
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The logical agency to handle this function is usually a
larger .or regional multi-community agency. With the
many limitations on local budgets, the larger district
responsible for treatment and pollution abatement
may be able to more easily obtain funds for manning
and equipping the regulator crew and operating the
instrumented systems. If this assignment of authority
is to be provided by a local community to a regional
agency, it must be clearly defined by agreement or
regulations.
Most of the employees on an average sewer crew
are laborers with limited knowledge or experience in
the functioning of the hydraulic, electrical,
mechanical, and pneumatic equipment that is now
being used on more sophisticated regulators. The
most efficient use of manpower is to assign to the
regulator crew those men having some of the training
and skills necessary to ensure the routine continuous
maintenance of the control equipment in service in
the system.
The ideal, situation would be for the supervisor to
assign to the sewer crew a man or men with a
knowledge of electrical and mechanical systems
where they are in use. The men should be able to read
and understand instruction manuals, drawings, and
other written materials. They should also be able to
maintain necessary records and to prepare reports and
written memoranda. They should be required to
maintain an inventory to requisition necessary
supplies and replacements, and to recommend field
revisions.
Improvement of regulator maintenance
procedures requires the proper manpower selection
and training; establishment of standards of manual
surveillance methods, accurate record-keeping; and
availability of certain special equipment.
The critera for selecting manpower for a
regulator crew are important. The men should have
considerable agility to enable them to climb in and
out of manholes and small spaces without physical
injury. The men selected should be willing to enter
the sewer when assured that adequate safety
precautions have been satisfied, and they should be
sufficiently intelligent to understand the dangers of
the work.
Regulator crews, like other skilled team workers,
should be constantly trained to carry out their jobs
effectively. They must have the essential elements of
their jobs clearly identified to carry out their mission
in the most efficient manner. Knowing the general
objectives of their jobs, they must be carefully
trained to realize these goals with ease and safety.
Their training should be adequate to ensure that all
reasonable precautions for their safety and the safety
of others are being provided. They must be well
trained in the use of hazard detection equipment and
capable of developing needed contingent plans for
unexpected situations.
Training should be sufficiently complete to allow
them to perform simple tests of any mechanical,
pneumatic, or electrical equipment used in the
operation of .the regulator devices. A contingent plan
should be developed for any anticipated malfunctions
to assure the least possible damage while the
malfunction is occurring and to provide for the
speedy correction of any difficulties. The crew must
understand fail-safe systems employed to provide for
the least serious consequences, in the several options
of operation, coincident with power failures. In some
instances, fail-safe operation would require the
lowering of adjustable dams during power failure and
the crew must be able, at the more important
regulators, to provide emergency power by
connecting portable power units to enable the
regulator to return it, to operation at the earliest
possible time.
By using improved manual surveillance methods,
a more effective policing job can be done with
reduced manpower. A number of jurisdictions hire
helicopters to expedite the location and reporting of
overflows and malfunctions. By reviewing existing
manual inspection methods, an improved program
can usually be established to improve response time
and utilize manpower more effectively. The improved
program may require minor system modifications,
such as installation of new manholes or ladders for
inspection or access. In areas where many outfalls
exist, those which are connected to regulators should
be easily identified from air, ground or water by
adequate marking and numbering. An outfall
checkoff list can be prepared, referring to nearby
landmarks and including a list of contributing
regulators if more than one is tributary.
Record-keeping in any successful regulator
maintenance program should be simple, yet contain
the essential information that would be required for
improved management. In establishing a new or
revised regulator maintenance program, the usual
first-step requirement is generation of, or updating
the inventory of regulators and assembling all
pertinent drawings and records. All drawings and
records should be field-checked by the regulator
crew. New drawings and records should be made
where necessary. A duplicate file system, one for field
use and one for office use, should be made with all
information for each regulator assembled and
85
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grouped by regulator location.
Standard forms should be developed for routine
record-keeping. Preferably, these should be arranged
in a manner suitable for later analysis by data
processing methods. The best approach is to use a
simple form for making the notations, with boxes to
check, requiring a minimum of writing by the field
crews. However, there should be room on the form
for remarks to permit the field men to make
notations not covered in the standard form. Some of
the simple data to be included on the form are: (a)
Location of the regulator; (b) identification of
regulator; (c) time of day, (d) day of week; (e) date;
(f) condition—working or clogged; (g) if clogged, how
many inches going over the dam spilling into
waterway; (h) condition of the orifice—any blockage,
hangings, etc.; (i) anything unusual about the
quantity or quality of flow coming to the regulator;
and (j) any unusual odors or discoloration in the
flow.
In order to implement improved methods of
regulator maintenance, special equipment must be
provided. The current high cost of labor easily
justifies the purchase of all tools and equipment
needed to expedite the work and minimize working
time. A complete list of all equipment needed is
rather extensive. Items of major significance can be
grouped in three categories—safety, descent and
ascent, and working equipment.
All equipment must be evaluated from a safety
standpoint. Special safety equipment should include
sophisticated electronic and chemical testing devices
for explosive or noxious gas, for oxygen deficiency,
and for toxic fumes. Testing equipment should
include battery-operated sampling pumps to insure
reliable results. Duplicate equipment should be
provided for oxygen deficiency and explosive gases.
Nylon parachute harnesses should be furnished for all
personnel, with sufficient spares, and it should be the
established rule that a harness is worn at all times
below ground to facilitate rescue in case of accident.
Special rescue devices should also be available at the
surface. A small portable self-contained breathing
apparatus, usually with a 10 capacity, is available and
should be provided. Standard procedure should be to
have at least one breathing apparatus available at all
times when the men are underground. Procedure
should also require that a breathing apparatus be
lowered into a hole before a man enters.
Equipment for ascent or descent should include
hoists, one powered and one manual. During ascent
and descent in deep manholes, a safety harness
connected to a nylon safety line should be used. This
safety line can be snubbed around an appropriate part
of the truck and attended by a person on the ground.
Working equipment should include temporary
working platforms and supports, flushing equipment,
tools for cutting and removing clogged materials and
numerous other items. Modern self-contained blower
generators can be used for power and ventilation
when maintenance work other than short time
inspection or the clearing of debris is being
performed. Battery-operated tools are now available
for use in hazardous locations to eliminate shock and
explosion hazards. Non-sparking tools and equipment
will reduce explosion hazards.
86
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SECTION 7
TIDE GATES: APPLICATIONS, DESIGN AND PERFORMANCE
Tide, or backwater gates, or flap gates are
employed to protect collector sewers and interceptor
systems from the inflow of tidal or high river-stage
waters. Without such control devices, backflows
would 'surcharge interceptors, pumping stations and
treatment plants and adversely affect treatment
processes. The inflow of such receiving waters into
combined sewer systems at some points would
ultimately result in uncontrollable overflows and the
bypassing of excessive volumes of waste waters to
receiving waters at treatment plants.
Tide gates are intended to open and permit
discharge at the outfall when the flow line in the
sewer system regulator chamber produces a small
differential head on the upstream face of the gate.
Conversely, backwater gates are designed to close
when the stage or tide level in the receiving waters
produces a small differential head on the downstream
side of the gate. Some types of gates are sufficiently
heavy to close automatically, ahead of any water level
rise in the receiving body. With careful installation
and balancing, coupled with an effective preventive
maintenance program, the ability of the gate to open
during overflow periods is not impaired because of
this additional weight.
Types and Sizes of Tide Gates
Tide gates are available in a wide variety of sizes;
they may be rectangular, square or circular in shape,
depending on the requirement.
Tide gates are manufactured in three basic types,
depending on the construction of the flap, as follows:
1. Cast iron,
2. Sheet metal plates, and
3. Timber.
Cast iron Agates are available in sizes varying from
4 to 96 inches in diameter, when circular, and 8x8
inches to 96 x 96 inches when square, or variations in
rectangular shapes within these limits.
Sheet metal is used to fabricate a lightweight tide
gate shutter, which is a double-walled structure with
interior air cells. This lightweight application offers a
more positive opening response to small differential
outfall heads. This is of particular advantage over
heavier cast iron models, which may, particularly
with age, require a significant upstream head to swing
open. When the waste water flows on the receiving
water courses are corrosive, pontoon tide gates have
had.a life expectancy of only 10 to 12 years unless
carefully protected with inert, corrosion-resistant
coatings or constructed of corrosion-resistant
materials. These "pontoon" shutters of sheet metal
are available in circular style from 48 to 120 inches in
diameter. Square and rectangular gates are available in
dimensions from 48 to 120 inches.
An important feature of such metal tide gates is
their hinge arrangement. Except for very large sizes,
instead of hinging the shutter at the top only, a
second set of hinges of a linkage type are attached at
the sides of the shutter. -This linkage is devised in a
way that will permit it to open at the top if its
bottom has become jammed in the closed position by
the weight of debris deposited at the downstream side
during periods of high river levels or high tides. Figure
23, Hinged-Type Tide Gate, illustrates a typical
hinging configuration.
FIGURE 23
POSITION B
HINGED TYPE
TIDE OR BACKWATER GATE
Position A shows the normal full opening
attained when the outlet channel is unobstructed.
Position B indicates the advantage of the second set
of hinges, which permits the shutter to open at the
top when the lower body of the gate is blocked by
debris. The resulting outflow may then wash away
the debris and permit the gate to function fully, as in
Position A.
Early tide gates were made of timber or wooden
planks, and were either hinged at the top or
double-leafed with hinges at the side similar to a
double barn door, with the gate frame inclined at the
top. Gates of this latter type were installed in the
87
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Boston area.
Timber tide gates suffered a decline in popularity
during the early part of the century. However, they
are again being used in large sizes. Such gates are
economical in sizes larger than 7x7 feet or in odd
dimensions. A typical timber tide gate is shown in
Figure 24, Timber-Type Tide Gate.
The construction features of this gate are as
follows:
1. A gate frame made pf cast iron in securely
bolted sections;
2. Shutter, with timbers laid in the vertical
position;
3. Carrying bars inserted between particular
timbers to act as reinforcement or stiffeners for
the shutter and for connection with the hinge
blocks;
4. Horizontal stiffeners and tie rods provided to
prevent warping, to structurally stabilize the
shutter, and to prevent flotation;
5. Hinge arrangement to permit the attachment
of the gate to the gate frame and structure;
6. Hinge bracket anchor bolts set in oversize
pipe sleeves to provide slight adjustment; and
7. Lifting bolts provided at the base of the
shutter to enable the gate to be operated
manually when required.
The tide gate should be cured before machine
fitting.
Use of timber gates which are alternately wetted
and dried may accelerate deterioration.
Dense structural Southern yellow pine is the
most common timber material used for such gates.
Cypress and Douglas fir have also been used. These
woods require creosote treatment to prevent rapid
deterioration.
In New York, greenheart timber is now being
used. This structural timber requires no
FIGURE 24
TIMBER-TYPE TIDE GATE
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88
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wood-preservative treatment, and is resistant to
marine borers and wood-destroying fungi. It is
extremely dense (approximately 70 pounds per cubic
foot so that little additional weight is required to
offset buoyancy. It is resistant to seasoning splits and
checks that are common to other structural wood, it
machines well, and has a high resistance to warping or
distortion. Table 26, Allowable Working Stresses for
Timber, compares the working stresses for greenheart
and other structural woods.
TABLE 26
ALLOWABLE WORKING STRESSES OF TIMBER
Timber
Yellow Pine
Cypress
Douglas Fir
Greenheart
Parallel to Grain-PSI
Perpendicular
to Grain-PSI
Compression Tension Shear Compression
1550
1466
1100
3000
2000
1733
1450
3300
135
133
95
400
455
300
390
1500
In some of the jurisdictions surveyed, tide gates
are of shear or sluice gate type, motor-operated or
hydraulically actuated. This type of application lends
itself to remote control of the rate of tide gate
operation, as required. Information is transmitted to
the central monitoring station by bubbler-type level
sensors located upstream and downstream of the tide
gate in order to provide regulator control of the
interceptor system.
Installation of Tide Gates
Tide gates usually are installed at the head of the
outfall sewer line, as part of the regulator station, or
in series, at a selected site within the outfall sewer
line, at a point between the Outfall discharge and the
regulator station. Installation of the tide gate
structure at the outfall discharge point may have the
advantage of lower capital cost, and the availability of
sufficient space to permit the construction of an
outfall structure protected by several small gates, as
opposed to one large control unit. The use of several
smaller parallel tide gates permits the opening of the
gate flap under a relatively small head differential.
Because of their smaller individual bulk, they are
more readily operated by maintenance personnel
when jammed with debris.
The disadvantages of tide gate installation at the
outfall discharge point are:
1. Boats and boat crews will be required to
effect maintenance, since the gates may be partly
or fully submerged during high river stages or
high tides.
2. In tidal waters, severe wave action may
overbalance the pressure behind the gate shutter,
thereby forcing the gate to close abruptly with
considerable force. Repetition of this cycle at
short intervals. may produce objectionable noise
levels, especially in residential areas.
3. During periods of high river stages, or high
tides in coastal or estuary waters, the trapped
sewage in the barrel of the outfall sewer between
the regulator station and the tide gate may
become septic. This pollution load eventually will
be discharged into the receiving stream.
4. In the "total systems" concept of combined
sewer interceptor operation, the tide gate should
function in a coordinated manner with the
operations of its upstream regulator, a condition
which may not be attainable if the tide gate is
located at a distance from the regulator structure.
Tide gates that are installed within the barrel
of the outfall, in tandem, at a predetermined point
between the outfall and the regulator station, provide
an additional safeguard to the interceptor system,
particularly when the crest of the diversion dam at
the regulator station is only slightly higher than the
normal water level at the point of outfall. This point
of installation also may be used in locations where
very high tides or severe variations in river stages are
experienced for extended periods of time. Where
wave action causes slapping of the flap against the
gate seat, tide gates have been installed upstream in
the barrel of the overflow pipe at a point where the
wave energy will have been dissipated.
Figure 25, Sluice Gate-Type Tide Gate, shows a
typical installation for a/,slmce type-gate in a
two-chamber facility. Figure 26', Tandem Tide Gate
Installation, shows a tandem tide gate installation,
with a stop-plank arrangement for shutting off the
outfall line at the downstream face of the gates to
permit servicing of the gates.
Tide gates have been installed to advantage at the
outfall connection of a regulator station at the head
of the overflow pipe, as was shown in Figure 15. This
type of installation has the following advantages:
1. Routine preventive maintenance and
inspection can be carried out in conjunction with
regular visits to the regulator chamber.
2. Major repairs, such as shutter removal for
hinge replacement and shutter repair or
replacement, are facilitated because of increased
accessibility.
3. Motorized equipment, such as hoists, can be
located vertically above the gate for more
efficient maintenance.
89
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FIGURE 25
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TANDEM TIDE GATE INSTALLATION
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Outfall flow
Stop-Plank Niche
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
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crude sewage
7. Secondary motions applied to storm sewage
overflows
8. Design, construction and performance of
vortex overflows
9. Reconstruction of overflows
10. Practical design of storm sewage overflows,
and
11. The storage and discharge capacities of sewer
systems and the operating frequency of storm
overflows: Dutch methods of calculation.
The laboratory experiments (No. 4) were used to
determine the operating characteristics of: low
side-weirs; stilling ponds; vortex; and storage
overflow. The models apparently had many
limitations and in some cases they did not
incorporate provisions found desirable in existing
field installations. Both the Storage-type Regulator,
and the Stilling Pond Regulator, Figure 28, exhibited
good operating characteristics. The Vortex Regulator,
Figure 29, had inconsistent characteristics.
Field experiments (No. 6) were conducted using
crude sewage and a low double side-spill weir, a
stilling pond, a vortex overflow, and a high level
side-spill weir with position flow control. The low
side-spill weir was found to be generally
unacceptable. The other three types exhibited various
favorable qualities. The high side-spill weir and vortex
overflows, both with outlet control, gave good
control of flow to treatment facilities.
The field tests, in contrast to the model tests,
gave little indication of pollution improvement of the
overflow by type of regulator, except for the vortex
at high flows. This lack of overflow quality
enhancement was thought to be a characteristic of
the constraints at the testing facility inasmuch as the
results of actual test installations indicated overflow
quality improvement.
Of particular interest is the work which was done
involving secondary motions (No.7) with regard to
liquid flow. Research was carried out with the
development of helical flow. It was found that a short
bend, or a series of short bends can be used to
separate the solids from the flow discharging to the
overflow. The formation of a helix or a system of
helices exist in any flow of liquid within curved
boundaries. Solids are concentrated on the inside of
the bend. The flow with the concentrated solids load
can be bled off with siphons or slots, or the overflow
can be permitted to take place along a high side-spill
weir on the outside of the bend. Figure 30 Spiral
Flow Helical Regulator, illustrates a typical unit
configuration.
The circular vortex overflow is another form of
secondary motion device. Two such regulator devices
have been constructed at Bristol. The results obtained
with full-scale units were reported to be far superior
to the results obtained from the model and test
facilities.
Interviews were conducted in England with both
national and local officials. These interviews revealed
that:
1. Stilling ponds and high side-spill weir
overflows are the two general types of overflows
now being constructed. Many of these regulators
use a penstock control (mechanical sluice gate) to
control discharge to the interceptor.
2. Mechanical screens are in general use, (see
Fig. 31) to screen solids from the overflow and
return solids to the interceptor sewer.
3. The number of overflow points is being
reduced in order that detention or treatment
facilities can economically be constructed for the
overflows.
Regulator installation in Coventry, Manchester
and Bristol were visited by project personnel.
Highlights of practices at each jurisdiction follow:
Coventry: Coventry has recently established three
storm water stations. All of the combined sewage is
taken into one of the three stations where the flow in
excess of the sewage treatment facilities is overflowed
to a series of three storm water tanks, with a capacity
of approximately 20 times the dry-weather flow. At
the regulator facility, "Parkwood" screens are used to
minimize the amount of floating solids overflowing to
the tanks.
Figure 31, Mechanical Screens, illustrates a
typical installation on a side-spill weir. The storm
water tanks overflow approximately three times a
year. They provide good primary settling. Solids are
removed in a conventional manner. The overflow
weirs have penstock controls to limit the outflow to
the treatment facility; however, this is based on a
calculated rate and is controlled only by the incoming
flow. The tanks are pumped back into the interceptor
line whenever the flow to the treatment plant is less
than the plant capacity.
The storm water stations are landscaped and
located adjacent to new developments. In one case, a
golf course abuts the facility and another station is
adjacent to a university housing project.
Along the orifice outlet of the regulator an access
chamber is provided for a considerable distance in
order to facilitate measurement of the flow and
maintenance operations.
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FIGURE 28
X3.s«" END ELEVATION
COMBINED SEWER
SCALE OF FEET
"B"
I: 4
le - II
A
TO PLANT
TO RIVER
PLAN
SECTION "A"-"A1
SECTION"B"-"B"
POSSIBLE APPLICATION
STILLING POND REGULATOR
Courtesy Institution of Civil Engineers
99
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FIGURE 29
COMBINED SEWER
STORM SEWER
B
INLET 36"OIA.
AFFLE
BRANCH INTERCEPTOR
TO TREATMENT PLANT
SECTION "A"-"A"
WHITE LADIES ROAD
COMBINED SEWER
INLET 4'X3'
SCUM BOARD
BRANCH.
INTERCEPTOR
SCALE OF FEET
5 IO 15
ALMA ROAD
VORTEX REGULATORS
Courtesy Institution of Civil Engineers
100
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FIGURE 30
CROSS CONNECTION FOR OVERFLOW..
CONTROL
,FLUME INVERT
TO PLANT
PIPE FOR NORMAL FLOW --^
PROFILE ALONG CENTER LINE
OVERFLOW WEIRS
WITH DIP PLATES
CHANNEL FOR NORMAL
FLOW 8 HEAVY SOLIDS
FLUME FOR
FLOATING
MATERIAL
PIPE FOR NORMAL
FLOW a SOLIDS
"A1-"A"
CONTROL PIPE FOR
OVERFLOW CHAMBER
TO INTERCEPTOR
SECTION "B"-"B'
SPIRAL FLOW (HELICAL)
REGULATOR
Courtesy Institution of Civil Engineers
101
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FIGURE 31
Courtesy The Longwood Engineering Co. Ltd.
Manchester: The City of Manchester is rebuilding
portions of its combined sewer system to eliminate
overflows and to increase capacity. The new regulator
facilities are basically of the long weir type with large
stilling basins; a scum board is used to minimize
overflow of floating debris. Storm water in excess of
the sewage treatment plant capacity is taken to the
treatment plant where the flow is screened and then
run through long grit chambers prior to entry into
storm water holding tanks. The stilling basin serves to
reduce the number of overflows and to return
non-floating solids to the foul sewer. Penstock
controls are used to control flows.
Bristol: The City of Bristol is rebuilding much of its
storm water combined sewer system, using high
side-spill weir overflows and taking six times DWF to
the treatment facility.
During the investigation of possible design for
regulators to be used on a major relief sewer to
protect the business area of the city, the concept of
using a circular vortex regulator was evolved in order
to obtain adequate weir length without the expense
of constructing a long side-spill weir structure.
Laboratory studies of the vortex configuration were
carried out and eventually two regulators were
constructed jn 1964.
The facility which was inspected by the project
personnel had a diameter of approximately 16 feet.
Retention time is approximately 11 seconds; tests
indicate that 70 percent of the solids are diverted to
the interceptor.
A scum board is used to retain floating solids.
Clogging of the outlet has occurred only three times
in six years—caused each time by bricks from
deteriorated sewers.
The City of Bristol is continuing its work,
utilizing the vortex principle with an experimental
primary settling tank for a flow rate of 3,000 gpm.
Results to date are very satisfactory.
Summary of European Experience
Although hydraulic conditions in Europe and
England vary from American conditions, there are
several practices which should be considered for
adoption or adaptation in the United States and
Canada:
1. Limit the number of overflow points.
2. Improve the quality of overflow by screening
or applying secondary flow motions.
3. Consider utilization of stilling ponds, high
side-spill weirs, and circular vortex regulators—all
with controlled outlet controls.
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SECTION 9
ROLE OF PRODUCTS, PROCESSES, AND FUTURE REGULATOR
PROGRESS IN IMPROVED CONTROL OF OVERFLOWS
The investigation of problems relating to
combined sewer overflows, carried out under the
1967 Investigation disclosed the numbers, locations,
and types of regulator devices in use in the United
States. These devices may be categorized, basically, as
static and dynamic regulators.
Devices in the static class, such as weirs and
orifices, have been fabricated locally by either small
foundries or machine shops or installed or built in
place by the sewer system jurisdiction or contractors
serving them. Other so-called static devices, such as
manually operated gates and siphons, have been
supplied by companies in the national field. Dynamic
regulator devices, including semi-automatic and
automatic units, have been built and supplied by
manufacturers for the national market and are usually
listed in catalogs and technical brochures.
Instrumentation facilities for application to the
regulator field have been manufactured by companies
experienced in the electronic-electrical
recording-controlling-automation field.
Potential developments and future progress will
depend in great measure on the desires and
capabilities of experienced manufacturers to research ~
and create improved processes, products and
materials for primary applications to combined sewer
service and for other related functions. '
The interrelationship between the equipment
manufacturers and the development of improved
regulator practices for the improved control of
overflows is very important. It was decided that
evaluations of available devices and facilities and the
prospect for future developments must be determined
directly with manufacturers. The purpose of such
contacts between producers and users of regulator
devices and systems was to ascertain the need for, and
means of, developing new regulator practices to
eliminate unnecessary overflows; to provide better
guidelines for the application and adaptation of
existing and proposed regulator facilities; and to
catalyze the development and use of new and
improved technologies, and materials.
Developing a Relationship With Manufacturers
This type of coordinated effort can be
accomplished in two ways: by individual contacts
with all such manufacturers; or by collective group
discussions with' interested and concerned
manufacturers and suppliers.
The second procedure was adopted on the basis
that better exchange of information would result
from such group contacts and that a broadening and
cross-fertilization of interests between all such
manufacturers and suppliers would result from this
procedure. To expedite this decision, a one-day
exploratory conference on regulator problems was
convened by the American Public Works Association,
with a representative of FWQA participating.
Approximately 50 manufacturers of various types of
regulator equipment and appurtenant facilities were
invited to attend the session. Eighteen manufacturers
sent representatives and approximately ten more
expressed interest in the project and asked to be
advised of further developments and to receive
information on the findings and conclusions of the
exploratory meeting.
Creation of the Manufacturers' Advisory Panel
During the exploratory conference, the
manufacturers' representatives recommended the
creation of a smaller working panel to serve as the
liaison between the manufacturing field and the
FWQA-APWA research project. This subgroup was
created and designated as the Manufacturers'
Advisory Panel. Members of the panel are listed in
Section 11 of this report, in acknowledgement of
their invaluable services and the importance of the
information which they supplied to the project.
At the first organizational meeting, the panel
decided that its operations could be expedited and
the performance of its functions improved, by
designating subcommittees to carry out specific
phases of its responsibilities. The following
subcommittees were created:
1. A subcommittee on the most effective
materials for regulator facilities;
2. A subcommittee on improved operation and
maintenance practices;
3. A subcommittee on instrumentation and
control; and •
4. A subcommittee on the "total systems"
concept of sewer management and control
Pertinent excerpts from 'preliminary reports of
panel subcommittees are included in Section 14 of
this report.
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Survey of Existing Products and Processes and Stimu-
lation of Future Developments in Regulator Practices
Over and above the functions assigned to the
Manufacturers' Advisory Panel, an attempt was made
to contact all known manufacturers of products and
processes directly or indirectly applicable to the
regulator field. A communication was addressed to all
such companies requesting them to supply the
following information:
• A full catalog listing of all equipment now
offered, such as: regulators, gates, valves,
standard actuating devices, direct controls,
instrumentation, automatic-automation systems,
sensing devices, remote control and telemetry
facilities, and any other related products or
processes.
• Other technical literature on regulator
equipment, materials and methods, such as
brochures, engineering reports, technical papers,
cost data, and application data.
• Forecasts covering important trends and
developments in improved regulator methods,
materials and mechanisms, all within the limits of
proper protection of any and all proprietary and
patent rights to their products and processes.
Catalog material was received from a number of
manufacturers, partially serving the purpose of
inventorying available hardware and auxiliary
equipment related to the regulator field. A limited
number of replies gave some indication of future
trends and .developments and showed limited
manufacturers interest in the improvement and
enhancement of regulator practices by means of new
products and technologies and better application of
existing facilities and equipment. In a number of
cases, manufacturers who do not now market
products in the regulator field, but whose equipment
could have such applicability, expressed minimal
interest in the utilization of their products and
processes for regulator-control purposes.
In addition to the catalogs and technical bulletins
received from manufacturers, other sources of such
information were utilized to partially augment these
basic data. In keeping with the broader definition of
regulation to encompass the control of both the
quality and quantity of overflow waste waters (the
"Two Q" concept outlined in Section 2 of this
report), a search was made for catalog and bulletin
data which might have a direct bearing on this
two-phase principle of overflow regulation, either
directly or in a secondary manner. Table No. 28
contains collated data on products and processes.
TABLE NO. 28
TECHNICAL CATALOGS AND BULLETINS RELATING TO
PRODUCTS AND PROCESSES OF PRIMARY AND SECONDARY
APPLICABILITY TO THE REGULATION AND CONTROL OF
OVERFLOWS FROM COMBINED SEWER SYSTEMS
ADis Chalmers Manufacturing Corp.—Butterfly
valves; fabricated valves; water control gates
Armco Steel Corp.—Sluice gates; flap gates
Autocon Industries, Inc.-Supervisory control
equipment; remote control; telemetry; panels
Badger Meter Mfg. Co., Instrument
Division —Flow tubes; Parshall flumes;
transmitters/receivers
Bailey Meter Co.—Pneumatic and electric level
transmitters; computer control systems; orifices; flow
nozzles
BIF—Application data on electronic control
systems; telemetry; weirs; orifices; valves
Bird Machine Co.—Aeration process
Bowles Fluidic Corp.—Technical bulletins/data
on fluidic/technology and water management; FWQA
report on fiuidic interceptor control
Bristol Co.—Liquid level measurement and
control equipment; telemetering; pneumatic and
electric transmitters and controls
Brown & Brown Inc.—Automatic sewage
regulators; tide gates; engineering data
Chicago Pump, FMC Corp.—Barminutors;
Comminutors; screening machines; grit removal
Cla-Val Co.-Valves
Clow—Comminutors
Coldwell-Wil cox Co . —Hy dr aulic
cylinder-operated sluice gates; flap gates; tide gates;
backwater gates; fabricated diverter gates; gate
operators
Crane, Cochrane Division—Microstrainers;
ozonators for storm water overflows; waste water
treatment equipment
Delta Scientific Corp.—Analytical equipment for
monitoring and control of waste water
DeZurik Corp.—Eccentric valves
Dorr Oliver—Grit removal equipment; waste
water treatment equipment
Firestone Coated Fabrics Co.—Fabricated
plastics; Fabri tanks; Fabridams
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Fischer & Porter Co.—Time pulse receivers;
chlorinators; meters
Flomatcher Co.—Sewage pump control systems;
fluid start-stop sequencers; pneumatic control
systems
Foxboro Co.,—Liquid level measurement and
control equipment; telemetering; receiver-recorders;
transmitters; pneumatic and electronic controls;
analog computing stations
General Electric Co.—Integrated circuitry; remote
station operators; digital coding systems; supervisory
systems for automatic variable-speed pumps
Glenfield & Kennedy, Ltd.—Microstraining
equipment
Golden Anderson Valve Specialty
Co.—Solenoid-operated valve systems
Healy-Ruff Co.—Telemetry equipment;
pressure-operated controls; float operated controls
Henry Pratt Co.-Butterfly valves; controls
KDI Poly-Technic, Inc.-Water quality monitors
Leopold & Stevens, Inc.—Flow meters;
telemetering systems
Link—Belt, FMC—Screens; grit removal
equipment
Minneapolis Honeywell Regulator Co.—Flow and
The Potential Market For
Regulators and Appurtenant Devices
The contacts with the manufacturer were made
for the purpose of stimulating new research and
development efforts. At the exploratory conference,
manufacturers expressed concern over the required
expenditure of industry's time and money for the
development of materials, methods and mechanisms
which would have limited use and sales potential.
Reference was made to the general lack of action
against combined sewer overflows on the part of
pollution control regulatory agencies, and to the
hesitancy of municipal officials to expend the funds
necessary for the improvement of regulator facilities
and systems. This concern was based on these above
factors, and on the fact that the construction of new
combined sewer systems will be of limited
significance in sewer practice in the future, hence
limiting the market for new regulator stations.
Manufacturers were advised that the market lay
not necessarily in the area of new regulator station
installations but, rather, in the modernization and
upgrading of regulator facilities in existing systems
and stations, in order to facilitate the reduction of
the frequency and period of duration of overflows.
liquid level meters; telemetry; industrial controls;
graphic panels
National Sonics Corp.-Water-solids interface
sensors
Neptune Meter Co., Neptune MicroFloc,
Inc.—Microfloc equipment
Phipps & Bird, Inc.—Sewage sampling equipment
Rex Chainbelt, Inc:—Trash racks; water screens;
grit collectors
Rockwell Mfg. Co., Republic Div.-Pneumatic
transmitters; pneumatic relays; pneumatic controllers,
positioners; electronic transmitters; final drives
Rodney Hunt Co.—Sluice gates; gate hoisting
equipment; fabricated slide gates; fabricated timber
gates; flap valves; tide gates
Rohrer Associates Inc.—Underground storage
faculties for storm water,
Waco, Products Div.—Stop gates; slide gates; bar
screens; weir plates,-aluminum products
Wallace & Tiernan Co.—Chlorinators; residual
chlorine analyzers; controls
Western Machinery Co.—Grit removal equipment
Yeomans-Clow—Pneumatic pump-ejectors;
aeration equipment; clarifiers
Zurn Industries, Inc.—Microstrainers; waste water
treatment equipment
Upgrading of regulator facilities may also be
necessary when facilities are constructed to treat
overflows.
While the project survey of the policies of state
water pollution control agencies gave no great
assurance that any intensive drive for the betterment
of regulator facilities was imminent at the state level,
a subsequent investigation of Federal policies
indicated that a tangible market for the improvement
of regulator practices could be anticipated. A partial
listing was obtained of recent Federal water pollution
control enforcement conferences with state agencies,
where Federal recommendations had been made on
combined sewer problems. Excerpts from this record
of enforcement conferences are included here to
indicate that there is a new interest in the prevention
of pollution caused by ineffective regulator devices.
This interest indicates a reasonably important market
for new regulator devices, and the application of
automatic-automation-instrumentation practices
which will result from research and development
efforts by manufacturers.
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SUMMARY OF SPECIFIC RECOMMENDATIONS
CONCERNING STORM WATER OVERFLOWS IN
RECENT FEDERAL-STATE ENFORCEMENT
CONFERENCES
The following are excerpts from enforcement
conferences where recommendations were made on
the combined sewer problem.
Pollution of Boston Harbor and Its Tributaries
April 30,1969
1. A report, by a consulting engineering firm,
calls for the most practical and economical
solution for abatement of the pollution effects
from tributary streams and combined sewer
overflows in Boston Harbor which will be
completed by the winter of 1970-71. The report
is to be followed by an implementation schedule
which will incorporate the approved
recommendations.
Pollution of Lake Erie and Its Tributaries
(Michigan, Indiana, Ohio, Pennsylvania, New York)
Second Session, August, 1965
1. All new sewerage facilities are to be designed
to prevent the necessity of bypassing untreated
wastes.
2. Combined sewers are to be prohibited in all
newly developed urban areas and eliminated in
existing areas wherever feasible. Existing
combined systems are to be patrolled and
flow-regulating structures adjusted to convey the
maximum practicable amount of combined flows
to and through treatment plants.
While the dates for completion of various stages
of the other requirements for municipal treatment,
etc., have extended, it is to be noted that the above
requirement of patrolling combined sewer systems
was to start immediately.
Pollution of the Inter-State Waters
Of the Hudson River and Its Tributaries
(New York, New Jersey)
September, 1965
1. The pollution problem caused by discharges
from combined sewer overflows is to be
reviewed, and a program for action is to be
developed for consideration by the Federal
government, the states, and the Interstate
Sanitation Commission, by December 31, 1968.
2. Programs shall be established for surveillance
of existing combined sewer systems and flow
regulatory structures to convey the maximum
practicable amount of combined flows to and
through treatment plants.
Pollution of Lake Michigan and Its Tributary Basin
(Wisconsin, Illinois, Indiana, Michigan)
January-March, 1968
1. Unified collection systems serving contiguous
urban areas are to be encouraged.
2. Adjustable overflow regulating devices are to
be installed on existing combined sewer systems,
so designed and operated as to utilize to the
fullest extent possible the capacity of interceptor
sewers for conveying combined flow to treatment
facilities.
-The -treatment facilities shall be modified where
necessary to minimize bypassing. This action is to be
taken as soon as possible and not later than December
1970; pollution from combined sewers is to be
controlled by July, 1977.
Pollution of the Interstate and Intrastate Waters
of the Upper Mississippi River and Its Tributaries
(Wisconsin, Minnesota)
February-March, 1967
1. Present combined sewers should be
continuously monitored and operated so as to
convey the maximum possible amount of
combined flows to and through the waste
treatment plant. Methods to be used to control
waste from combined sewers and a time schedule
for their accomplishment should be reported to
the conferees within two years.
Pollution of Interstate Waters of the
Potomac River and Its Tributaries
Washington Metropolitan Area
(District of Columbia, Maryland, Virginia)
April-May, 1969
1. Detailed analyses of alternate methods of
meeting future water quality requirements and
sewerage needs in the Metropolitan Area shall
include fail-safe sewer systems to prevent raw
sewage discharges; possibilities for load transfers
to other sewage treatment plants, etc.
2. The conferees, at six-month intervals, shall
review plans for elimination of pollution from
combined sewer overflows and establish a
timetable for the control of such pollution.
3. The State of Maryland shall take action to
control • sewage overflows from sources in
Maryland. Alexandria, Virginia, shall complete
plans by December 31, 1971, for elimination of
pollution from combined sewer overflows.
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Functional Gaps in Regulator Practices
One of the major goals of the research study, in
terms of contacts with manufacturers, was to create a
recognition of the functional gaps which now exist
between present products and practices, and those
which hold promise to provide new sophisticated
improvements in regulator control facilities. The
challenge is to fill these gaps with new products,
processes and procedures.
As has been stated, the problem of
regulator-overflow improvements must be solved by a
two-pronged approach to quality and quantity
control of waste waters discharged from combined
sewer systems to receiving waters, either directly or
following some form of treatment, or quasi-treatment
processing.
Two things are apparent from a listing of "gaps"
in combined sewer system operation and control.
Reduction in the quantity of overflow wastes from
combined sewers must be combined with the
improvement of the quality of overflow wastes which
reach receiving waters. The "Two Q" definition of
regulator functions and overflow- control must be
accepted in all future work in this field.
Study of foreign and current North American
trends has served to emphasize the challenges that lie
ahead. These include, but are not limited to, the
following procedures:
A. Control of Overflow Quality
1. Use of screens, present or new types, to
protect regulator devices from clogging,
deterioration or other physical damage, and to
intercept waterborne waste substances which
might otherwise add to the pollutional impact of
overflows;
2. Utilization of skimming-baffling devices to
improve the quality of overflow waters;
3. Utilization of fluid secondary-motion
configuration devices to concentrate solids in
sewer flows and to thus enable the withdrawal of
the solids to the interceptor sewers and treatment
works;
4. Utilization of fiuidics-principle devices for
better and more sensitive- regulation of
intercepted and wasted flows, and for the
possible improvement of the quality of waste
waters allowed to overflow to receiving waters;
5. Use of retention facilities to intercept
combined sewer overflows and return them to
the treatment plant during nprmal flow periods;
and
6. Treatment facilities such as microstraining,
dissolved air-flotation, and high-rate filtration.
B. Control of Overflow Quantities
1. Application of new siphonic principles for
better regulation of overflows from combined
sewers, and for prevention of backflow into
collector and interceptor sewers by tidal and high
river-stage waters;
2. Application of inflatable fabric dams to
provide effective and sensitive control of
overflows by storing combined flows upstream in
sewer systems;
3. Adaptation of valves, pumps and other
available equipment to the specific purpose of
combined sewer regulation and overflow control;
4. Maximizing application of all feasible
methods of in-system or off-system retention of
surplus flows to reduce or eliminate discharges of
overflows to receiving waters; and
5. Monitoring of overflow incidents and periods
of duration, for the purpose of evaluating the
feasibility of quantity control of overflows.
C. Total Systems Management of Combined Sewer
Systems
1. Application of more effective and
sophisticated instrumentation and
automatic-automation facilities for the purpose
of achieving "total systems" management of
combined sewer networks;
2. Development of new hardware and auxiliary
equipment to implement systems management of
combined sewers and to utilize the full potential
carrying and retention capacities of all parts of a
total sewer system;
3. Integration of urban area precipitation and
runoff rates by means of rain gauge monitoring
circuitry which will alert control centers and
automated overflow-regulator stations to
anticipated excess flow conditions;
4. Total systems analysis of combined sewer
networks for the purpose of ascertaining the
potential benefits of more sophisticated overflow
control;
5. Utilization of the knowledge and skills of
local utilities in the communication field, in
exploring the feasibility and workability of total
systems management techniques; and
6. Consolidation of overflow points into fewer
locations which can then be equipped with more
effective regulator facilities and geared into a
total systems control and management program
by means of automatic-automation-instrumenta-
tion procedures.
The necessary improvements in equipment and
systems is dependent on the manufacturing industry.
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This cooperation must be nurtured and guided by
means of a continuing liaison between suppliers and
users of the kind of equipment and apparatus upon
which improved regulator-overflow practices must
depend.
Some of the goals set forth above are being met,
in whole or in part, in combined sewer practices in
demonstration projects in the United States and
Canada, and in actual field installations in other
countries. Current developments in regulator and
control facilities and methodologies offer tangible
proof that the scientific knowledge of the 1960's will
be better utilized for the control of the quantity and
quality of overflows from combined sewer systems in
the 1970's. Of special significance is the application
of the "total systems" management concept in
demonstration projects stimulated by FWQA grants
to various governmental jurisdictions. The possibility
of "making two blades of grass grow where one grew
before"—utilizing not only the transporting capacity
of sewer systems but their retention capacity—by
means of "total systems" control is worthy of serious
consideration by the governmental field and the
industries which serve it.
References to actual in-system applications of
combined sewer management in this report of the
study project, and in the Manual of Practice which is
an integral portion of the project, add pertinence and
practicality to the use of improved quality and
quantity control of overflows to alleviate the water
pollution problems besetting the water resources of
the American continent.
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SECTION 10
THE "SYSTEMS CONCEPT" OF COMBINED SEWER REGULATION: AN OVERVIEW
Combined sewer-systems have been designed and
constructed on the principle that overflows at
frequent locations could be used most effectively to
provide prompt and local relief of collector sewers
and interceptor lines. This proliferation of overflows
and regulators also served to reduce the size of
interceptors required in various sections of the total
sewer system.
This principle may have been pertinent and
permissible when the amount of combined sewer
overflow and the actual location of the discharge
were not considered significant in the control of
water pollution. However, if pollution control is to be
achieved, there must be a reduction in volume of
overflows, in terms of frequency and duration, and in
the pollutional strength of the waste water discharged
to receiving waters. Improved regulator practices and
facilities can play a major role in achieving this goal.
In addition, treatment facilities for combined sewer
overflows can be more effectively operated if the
flow to the faculties is controlled by a well designed
and operated regulator.
The major imperfection of combined sewer
overflow regulation stems from the proliferation of
individual facilities, designed to perform: the
elementary function of relieving the sewer system
without any consideration to the effect of each
individual discharge point upon the total sewer
system, as well as on the waters into which the
overflows spill. This each-unit-of-a-sewer-system-for-
itself concept fails to integrate the various facilities
into a master management plan. Specifically, it is
based on the principle that, in substance, each
regulatorTOverflow installation is a separate entity not
related to the rest of the total system. If this principle
prevails, little can be done to alleviate the frequency
and duration of the total system's overflows. Even
with better control obtained at each overflow point,
for example, by converting static regulator devices
which are insensitive to in-sewer conditions to
dynamic systems which react to collector sewer and
interceptor levels and capacities; such regulators will
tend to maintain desired hydraulic conditions in the
restricted area where the unit is installed, but no
major benefits are likely to occur in the overall
system.
The defects of single-unit control are: (1)
multiplicity of overflow points; (2) inability to
establish a priority sequence of locations to minimize
environmental harm and hazard; (3) failure to achieve
the full hydraulic capabilities of each section of a
total sewer system; and (4) lack of opportunity to
utilize the whole sewer system in direct relation to
the patterns of storm and runoff in various areas of a
community, particularly. those with large areas and
variable topographic characteristics.
This unintegrated condition can be likened to an
automobile traffic control system which relieves,
congestion at a specific intersection and blinds itself
to the fact that in so doing it affects the flow of
traffic in all other parts of the system.
The value of improving each regulator device to
the highest level of effectiveness, to sense and do
something about local conditions at a local point
must not be minimized; however, maximum benefits
of regulator control and combined sewer management
cannot be achieved until the perspective is broadened
into the full function of a combined sewer system
control program. This latter procedure involves the
"systems concept;"
The systems concept in' its simplest form
envisions the management or control of all elements
or facilities which are parts .of the sewer system to:
1. Make maximum utilization of interceptor
sewer capacity to carry combined sewage to the
waste water treatment plant;
2. Make maximum utilization of in-system
storage;'
3. Give priority in the interceptor sewer to
those flows which have a higher pollutional load
and which, if they overflow, would result in
adverse conditions in receiving waters; and
4. Integrated use of combined sewer overflow
storage or treatment facilities.
Effects of systems control on the waste water
treatment plant must be considered and modification
in facilities and procedures provided.
The systems concept envisions that means are
available to control the operation of elements of the
system and that there is available adequate
information as to flow volumes and pollution
characteristics to allow decisions to be made.
In the newly recognized "traffic routing" system
of combined sewer operation, applicable for large,
interconnected systems, the capability of an overall
systems management program is applied to the task
of shunting flows from surcharged conduits to those
with surplus flow and storage capacities and could,
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thereby, eliminate or at least reduce the need for
overflows from the total system. Large-sized
combined sewer networks have large storage
potential.
Communication is the key to a systems approach.
Lack of such communication between individual
regulator installations is the weakness of the
each-regulator-for-itself procedure. The effective use
of modem communication methods is the basis for
"tying together" all the individual units into a master
system.
The fact that water seeks its own level offers
possibilities for intercommunication between
individual control-overflow points by means of
transferred hydraulic levels. This means of integrating
operation procedures, however, is not sufficiently
dynamic to provide sensitive control. The same
hydraulic conditions which might be depended upon
to actuate unified regulator operations, of themselves,
may cause the type of local hydraulic overloads in
sewer systems which individual regulation stations
were intended to prevent
Over simplification of the systems concept of
combined sewer system management and overflow
control must be avoided. First of all, fixed or static
regulator devices will be of limited value in any
sophisticated, integrated system. Thus, systems
control dictates conversion from static to dynamic
facilities in a majority of regulator installations. For
this reason, the feasibility of converting multiple
chamber locations into a single, sophisticated
regulator-overflow station is a key part of a total
systems management plan.
The adoption of dynamic regulators, or the
adaptation of existing devices into facilities having
adequate regulating capabilities, is only the first step
in weaving a system of regulators into a total master
plan. The problem requirement is to develop facilities
and techniques that will efficiently route, limit,
divert, transfer, and store waste waters within the
sewer system according to a. planned scheme of
action. This will involve elements for measurement or
registering hydraulic conditions at a wide range of
locations; for status determination in terms of the
rest of the system; for gathering information or data
at a systems control station; for using these data to
provide the basis for decision-making; for execution
of the control plan; for verification that the
instructions have been executed, by feedback; and for
correction and evaluation of the results of the master
control system. The fact that conditions in a sewer
system are constantly changing makes prompt control
and correction essential.
Measurement and status determination can be
accomplished by various types of sensors which
utilize electrical or electronic signals to represent such
conditions as flow, head, differences in pressure, gate
position, and level in receiving waters. Data gathering
can be achieved by equipment which conditions or
codes signals over prearranged communication
channels. Correlation of data is the role of indicators,
recorders, loggers, alarm systems, and computers.
Decision-making becomes the function of supervisory
personnel or of computer programs prepared by such
persons. Execution of decisions is assigned to field
crews or to remote control automation facilities
capable of receiving instructions and carrying them
out. Verification can 'be accomplished through
communications with field crews or playback of
automated data by way of communication channels.
Verification can be accompanied by any corrections
required to achieve the desired regulator control.
Examples of Total System Management
The total systems concept is in use in several
jurisdictions with combined sewer systems, as the
result of demonstration grants from the Federal
Water Quality Administration.
Three systems are a matter of record: (1) The
Minneapolis-Saint Paul Sanitary District; (2) the
Municipality of Metropolitan Seattle; and (3) the City
of Detroit.
The Municipality of Metropolitan
Seattle, Washington
A total systems concept plan has been described
in reports and technical papers prepared by
Metropolitan Engineers, Consulting Engineers. The
following information on studies of the feasibility of
such a system for Metropolitan Seattle are excerpted
from these documents.
The Municipality of Metropolitan Seattle
("Metro") has awarded a contract to the Philco-Ford
Company for over $1,200,000 for furnishing and
installing a Computer Augmented Treatment and
Disposal System ("CATAD System"). The primary
objective of the CATAD System is to permit
optimum utilization of available storage within
existing combined sewers in regulating storm water
flows to minimize the frequency and magnitude of
sewage overflows into Puget Sound. Successful
implementation of the CATAD System will serve the
immediate and urgent need for abatement of the
pollution of Puget Sound by sewage overflows and
postpone the multi-million dollar separation of
combined sewers which can thereby be accomplished
by an' orderly construction program as funds become
available. Further, it is expected that the degree of
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separation required will be substantially lessened by
the CATAD System, thus saving many millions of
dollars. .
To minimize the volume and duration of these
overflows, motor-operated gate regulator stations are
being built wherever major trunk sewers cross the
main interceptor sewer. FWQA demonstration grant
funds have partially contributed to construction of
some of the regulator stations and all of the CATAD
System controls. Ten regulator stations are now in
operation and nine more are planned or are under
construction. . >
The primary function of the Metro system is the
interception of sewage from the collector sewers of
the various cities and sewer districts in the Metro
service area and conveying the sewage to a treatment
plant.
A significant portion of the Seattle Metropolitan
area, including the downtown area and the major
industrial area along the lower Duwamish River, is
presently served by combined sanitary and storm
sewers. All of these combined sewers are tributary to
the West Point System. Economic considerations
dictated that neither the interception system nor the
treatment plant be designed to handle storm flows in
addition to ultimate sanitary flows. Thus, during
some, storms, it may be necessary to overflow
untreated combined sewage into the Duwamish River
and into Puget Sound.
Existing Local Station Controls
Each regulator-outfall station has been provided
with local automatic controls which use operating
conditions at the station as control references.
Diversion of flows from trunk lines into the
interceptor sewer is controlled by a regulator gate
which is modulated to maintain a preset maximum
level in the interceptor sewer. When the interceptor
level is above the control set-point, sewage is stored in
the trunk sewer up to a preset maximum level. When
this level is exceeded, the outfall gate is opened in
steps to maintain the level at the overflow set point.
The maximum tidal range in Puget Sound is about 16
feet and many of the outfalls are below high tide
levels. Therefore outfall gate controls have been
provided with tidal override features which
automatically maintain the trunk level control set
point 6 inches above the tide level. The existing
controls are of the pneumatic type, water levels being
sensed through bubbler devices.
Objectives of Controls
The principal objectives of the CATAD System
controls are as follows:
1. To provide optimum trunk sewer lines;
2. To permit utilization of potential storage
capability of collector and interceptor sewers in
separated areas under storm conditions and to
make available the maximum capacity of the
interceptor for combined storm and sanitary
flows in unseparated areas; and
, 3. When overflows are necessary, to control
such discharges at selected locations so as to
obtain minimum harmful effects on marine life
or public, beaches.
Control Procedures
The regulation of storage in the sewage collection
system will be accomplished by controlling the
operation of regulator stations and of sewage
pumping stations.
Since the primary objective of the CATAD
System controls is to reduce the number of
occurrences of sewage overflows, it was considered
essential that a high degree of reliability be built into
the design. Therefore, an overflow occurrence
directly attributable to any failure of the remote
control equipment including the communications
channel could not be tolerated and the criterion was
established that upon failure of the remote control
equipment, the station would be restored to local
automatic controls in an orderly procedure.
Storage control at regulator stations is
accomplished through direct control of the position
of the regulator gates which control the volume of
sewage being discharged into the interceptor, sewers
and consequently the volume .of sewage being stored
in the trunk sewers. The regulator gate will be
returned to local control only on loss of the remote
signal.
, The storage of sewage in the trunk lines, with
overflow provisions is limited to a preset maximum
level by a local outfall gate controller. If sewage is
stored above the set point level the outfall gate will
open, resulting in an,overflow. In establishing the set
point level for .the outfall gate controller, the most
unfavorable tidal condition has been considered since
the local station controller does not include logic for
determining either the direction of tidal movement or
the maximum level -of, the next high tide.
Consequently,, the trunk level set point has been set
low enough so that peak flows can be stored for the
maximum duration of the high tide condition, which
imposes a severe limitation on the use of potential
storage in trunk lines. . . .
In order to .overcome this limitation when
operating under remote control, it is necessary for the
CATAD System to include remote controls for the
outfall gates. Two,procedures were investigated for
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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.
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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.
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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.
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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.
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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
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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
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given time.
4. Awareness of localized water quality at any
given time.
5. Awareness of localized water quantity at any
given time.
7. Awareness of the effect of any specific
external environmental change.
8. Awareness of the effect of a combination of
external environmental changes occurring
simultaneously or sequentially.
9. Awareness of the effect of any specific
regulatory control procedure.
10. Awareness of the effect of any combination
of regulatory control procedures.
11. Awareness of the effect of any specific
treatment process during a crisis.
12. Awareness of the effect of any combination
of treatment processes during crisis.
Failure to consider all of the foregoing factors, as
a minimum, will result in a regulatory system that is
inadequate or incapable of responding to the current
combined sewer overflow requirements and problems.
Such a system would be completely helpless to meet
new water quality standards and make impotent any
attempt to meet the even more stringent
requirements of the future.
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APPENDIX 4
REPORT ON
DIVERSION SCREENING
Diversion screening comprises screening
equipment wherein the trash removed by the
screening rake is discharged into the interceptor sewer
to the plant for centralized removal or handling.
Diversion screening is recommended to avoid
clogging of regulators and to remove floatable trash
from the overflow to the receiving waters thus
improving the quality of the storm water overflow.
Generally, bar rack screen openings of 1-inch are
satisfactory. However, for outfalls into the ocean or
lakes drum screens are available having 1A inch circular
openings which will remove ten to twenty times the
trash removed by a 1-inch screen opening including
cigarette filter tips which otherwise float and cause
unsightly litter on beaches or shore banks.
The bar racks shown in Figs. 1,2, and 3 have 3/4
inch or 1 inch openings with reciprocating rakes that
can be driven by water or oil-operated hydraulic
pressure systems used for some regulators, or electric
motors, totally enclosed for explosion-proof and
water-proof application.
The rakes are actuated by water levels that
indicate overflow conditions for flow-through
regulators and outfalls where layouts are generally as
shown in Figs. 35, 36, and 37.
Otherwise where dry-weather flow is directed
through a regulator to the interceptor sewer, such as
through a Fluidic Y-Branch Diverter, screening rakes
operate continuously. The revolving drum screen for
fine, 1/4-inch screening can be applied to discharge
screenings directly into the interceptor sewer from a
discharge chute or by means of a conveyor driven by
a screen drive take-off.
FIGURE 36
Arrangement, Storm Sewer Interceptor Screen—Reciprocating Rack
Courtesy FMC Corp.
137
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FIGURES?
Arrangement, Storm Sewer Interceptor Screen—Bar Rack
ro
I I
- I I
- I I
; i !
Courtesy KMC Corp.
138
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FIGURE 38
Arrangement, Storm Sewer Interceptor Screen—Curved Bar Screen
To
DKY VieaTHEK I=L£>W
Courtesy FMC Corp.
139
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BIBLIOGRAPHIC: American Public Works Association,
Research Foundation. Combined Sewer Regulator Overflow
Facilities FWQA Publication No. 11022DMU07/70
ABSTRACT: Current design, operation and maintenance
practices used by local jurisdictions in the United State's and
Canada were determined by personal interviews and compiled
in this report. Particular attention was given to the
performance of various types of regulators, the use of tide
gates, new designs, European practices and the systems
concept of combined sewer regulation. Thirty-seven drawings
and photographs of regulators are included. Seventeen
recommendations are made, the adoption of which would
upgrade regulator facilities and tend to reduce receiving water
pollution from combined sewer overflows.
This report and accompanying manual were submitted in
fulfillment of Contract 14-12-456 between the Federal Water
Quality Administration, twenty-five local jurisdictions and
the APWA Research Foundation.
BIBLIOGRAPHIC: American Public Works Association,
Research Foundation. Combined Sewer Regulator Overflow
Facilities FWQA Publication No. 11022DMU07/70
ABSTRACT: Current design, operation and maintenance
practices used by local jurisdictions in the United States and
Canada were determined by personal interviews and compiled
in this report. Particular attention was given to the
performance of various types of regulators, the use of tide
gates, new designs, European practices and the systems
concept of combined sewer regulation. Thirty-seven drawings
and photographs of regulators are included. Seventeen
recommendations are made, the adoption of which would
upgrade regulator facilities and tend to reduce receiving water
pollution from combined sewer overflows.
This report and accompanying manual were submitted in
fulfillment of Contract 14-12-456 between the Federal Water
Quality Administration, twenty-five local jurisdictions and
the APWA Research Foundation.
BIBLIOGRAPHIC: American Public Works Association,
Research Foundation. Combined Sewer Regulator Overflow
Facilities FWQA Publication No. 11022DMU07/70
ABSTRACT: Current design, operation and maintenance
practices used by local jurisdictions in the United States and
Canada were determined by personal interviews and compiled
in this report. Particular attention was given to the
performance of various types of regulators, the use of tide
gates, new designs, European practices and the systems
concept of combined sewer regulation. Thirty-seven drawings
and photographs of regulators are included. Seventeen
recommendations are made, the adoption of which would
upgrade regulator facilities and tend to reduce receiving water
pollution from combined sewer overflows.
This report and accompanying manual were submitted in
fulfillment of Contract 14-12-456 between the Federal Water
Quality Administration, twenty-five local jurisdictions and
the APWA Research Foundation.
KEY WORDS
Combined Sewers
Overflows
Regulators
Design
Operation
Maintenance
System Control
Quantity of Overflow
Quality of Overflow
Tide Gates
KEY WORDS
Combined Sewers
Overflows
Regulators
Design
Operation
Maintenance
System Control
Quantity of Overflow
Quality of Overflow
Tide Gates
KEY WORDS
Combined Sewers
Overflows
Regulators
Design
Operation
Maintenance
System Control
Quantity of Overflow
Quality of Overflow
Tide Gates
jurisdictions and the American Public Works Research Foundation.
Abstractor
Richard H. Sullivan
institution
Research Foundation
WR;I02 (REV. OCT. 18«B>
WRS1C
SEND TO! WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U S. DEPARTMENT OF THE INTERIOR
WASHINGTON, D.C. 20240
819—718
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