EFA-670/2-73-077 <*
NOVEMBER 1973
                            Environmental Protection Technology Series
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      Combined Sewer Overflow

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                                       National Environmental Research Center
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                                       U.S. Environmental Protection  Agency
                                       Cincinnati,  Ohio 45268

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                                             EPA 670/2-73-077
                                             November  1973
     COMBINED SEWER OVERFLOW SEMINAR PAPERS
       A compilation of technical papers
       and discussions presented at three
       seminars in New York State given
       jointly by the U. S. Environmental
       Protection Agency and New York
       State Department of Environmental
       Conservation.
            November 29, 1972

            January   3, 1973

            February  1, 1973
     Edison Water Quality  Research Laboratory
        Office of Research and Development
National Environmental Research Center—Cincinnati
      U. S. Environmental  Protection Agency
           Edison, New Jersey 08817
               EERU-TIX
RECEIVED
 APR  51989
 EERU-TIX

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                  FORWARD
The.U.S. Environmental Protection Agency
in conjunction with the New York State
Department of Environmental Conservation
conducted three one-day seminars on the
problem of wet-weather flow pollution
abatement.  Many facets of the problem
were considered including a brief over-
view of its magnitude and what the
federal government is doing to manage
and control this source of pollution.
Various management, control and treat-
ment techniques were described and the
most up-to-date information on design
and economics was presented.  The audi-
ience consisted of consulting and muni-
cipal engineers from all areas of New
York State.

It is hoped that these seminars and this
compilation of papers will help solve
community problems or at least stimulate
new ideas as to how storm and combined
sewer overflow pollution abatement might
be approached.

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                           CONTENTS
SECTION
                                             PAGE
   I

  II
STORMFLOW POLLUTION CONTROL U.S.

PREVENTION AND CONTROL OF INFILTRATION
AND INFLOW.   '               •
  1

 49
 III  :      COMBINED SEWER OVERFLOW REGULATOR
            FACILITIES
                                              57
  IV


   V
PRESSURE.SEWERS
APPLICATION OF MICROSTRAINING TO
COMBINED SEWER OVERFLOW
 65


 89
 VI


 VII
HIGH-RATE MULTI-MEDIA FILTRATION
SCREENING/DISSOLVED-AIR FLOTATION
TREATMENT OF COMBINED SEWER OVERFLOW
115


129
VIII
HIGH-RATE DISINFECTION OF COMBINED
SEWER OVERFLOW   .
153
   IX
THE SWIRL CONCENTRATOR AS A COMBINED
SEWER  OVERFLOW REGULATOR
171
             THE  EPA STORMWATER MANAGEMENT MODEL:
             A CURRENT  OVERVIEW
                                             181

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                     SECTION I
       STORMFLQW POLLUTION CONTROL IN THE U.S.
                        by
               Richard Field, Chief
         Anthony N; Tafuri, Staff Engineer
     Storm & Combined Sewer Technology Branch
     Edison Water Quality Research Laboratory
National Environmental Research Center - Cincinnati
        Office of Research and Development
     U. S. Environmental Protection Agency
            Edison, New Jersey 08817

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I.   PREFACE

In an effort to introduce this seminar and tie the various dis-
cussions you'll be hearing today together, I thought it would be
appropriate to discuss the problem of stormwater discharges and
combined sewer overflows from the Federal Government's involvement.

The nation-wide significance of pollution caused by storm generated
discharges was first identified in a U.S. Public Health Service re-
port published in 1964.  Congress, in recognizing this problem,
authorized funds under the FWPC Act of 1965 for the research, de-
velopment and demonstration of techniques for controlling this
source of pollution.  Further authorization has been provided by
the 1972 Amendments to the Act.

Hence, the Storm and Combined Sewer Overflow Pollution Control Pro-
gram was originated and the problem of wet-weather flow pollution
was classified into three categories:
     1.  Combined Sewer Overflows
     2.  Stormwater Discharges
     3.  Non-Sewered Runoff

To date over 116 grants and contracts totalling over $82,000,000
have been awarded,  the Federal Government's share being in the
neighborhood of $40,000,000 or 47.5%.

II.  INTRODUCTION
The earliest sewers were built for the collection and disposal  of
stormwaters, and for convenience emptied into the nearest water-
course.  In later years, house sewage was discharged into these

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large storm drains, automatically converting them into "combined"
sewers.  Subsequently, combined sewers came into widespread use
in communities because they represented a lower investment than
the construction of separate storm and sanitary sewers.   (Fig,  1)

When the problem of pollution caused by sanitary or dry-weather
discharges became recognized, the engineer was confronted with
how to best separate the wet from the dry-weather flows to enable
proper treatment of the sanitary sewage portion.  This was over-
come by designing overflow structures at selected points in the
sewerage system, so that combined sewage flows greater than a pre-
determined multiple of mean dry-weather flow were discharged
directly into the receiving stream.  The diversion points were
usually chosen close to the receiving water for economy, and new
sewers were installed for intercepting and conveying the dry-
weather flows to the sewage works for treatment.

These  overflow or relief points may also be integral to separate
sanitary systems.   Initially, nominal allowances were made for in-
filtration and with pipe age this became more of a problem.  Unauth-
orized connections  compounded the problem, and reliefs in the "so
called" separate sanitary system were used as an immediate and low
cost solution.  Studies conducted for the USEPA found that .separate
systems, with excessive infiltration and other  inflows, act essent-
ially  as combined  sewer systems.

III.   COMBINED  SEWER  OVERFLOW  PROBLEMS

The basic  difficulty  with combined and  "nominal" sanitary  sewers
involves  their  "built-in"  inefficiencies,  i.e.,  their overflow
points.

Untreated overflows from  combined sewers,  particularly  during  wet-

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Figure   1.   SCHEMATIC SYSTEM DRAWING RAINFALL THROUGH OVERFLOW

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weather, has proven to be a substantial  pollution source in terms
of impact upon receiving stream water quality—even though the
percentage of sanitary sewage lost from the system by overflow is
small, that is, in the order of 3 to 5 percent.

Pollution problems stemming from combined sewer overflows are
widely distributed through the United States; the Northeast, Mid-
west, and Far-West being the principal areas .of concentration.  In
a nation-wide survey performed by the APWA it was found that there
are over 3,000,000 acres of combined sewer drainage area contained
in more than 1,300 municipalities with a population of 54 million
served by some 55,000 miles of combined sewers.  Of 641 jurisdictions
surveyed,
     - 493 reported some 14,200 combined sewer overflow points,
     - 340 reported infiltration problems during wet-weather and
     - 96 indicated combined sewer overflows during dry-weather.

The magnitude of the overflow problem was exemplified by a 2-year
study conducted on a 229 acre combined sewer watershed in North-
hampton, England.  This study showed that the  cumulative yearly
biochemical oxygen demand  (BOD) load in the combined sewer over-.
flows nearly equaled the BOD load contained in the effluent of the
local secondary treatment  plant. .Suspended solids within the  ." -/•..
overflows were three times the load contributed by the treatment
works effluent.

The  relatively poor flow characteristics of combined sewers during
dry-weather when sanitary  wastes alone are carried, encourages
settling and build-up of solids in the lines until a surge of flow
caused  by a rainstorm purges the system.  Studies  in Buffalo, New
York  have shown that 20 to 30 percent of the annual collection of
domestic sewage solids are settled and eventually  discharged during
storms.  As a  result, a large residual sanitary pollution  load,

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  over and  above  that  normally  carried  is discharged over a relatively
 short interval of  time,  oftentimes  resulting  in what is Known as a
 "first flush" phenomenon.  This  can produce shock loadings detri-
 mental  to  receiving water  life.

 Aside from the raw domestic  and  industrial sewage carried in the
 overflow,  non-sanitary urban runoff in  itself is a significant con-
 tributor to the  overflow pollution  load.  As  the storm runoff drains
 from  urban land  areas, it  picks  up  accumulated debris, animal drop-
 pings,  eroded soil, tire and vehicular  exhaust residue, air pollu-
 tion  fallout, heavy metals,  deicing compounds, pesticides and PCB's,
 fertilizers and  other chemical additives, decayed vegetation, haz-
 ardous  material  spills,  together with many other known and unknown
 pollutants.  A study  on  a  1,067  acre drainage basin in Durham,
 North  Carolina has shown that  the annual BOD  contribution attrib-
 utable  to  surface wash from  storms  is approximately equal to that
 contribution of  the secondary  treated sanitary effluent and the
 total organic matter  exhibited by chemical oxygen demand was est-
 imated  to  exceed the  amount  in the raw  sanitary sewage from a res-

 idential area of the  same  size.
 It is important to note  that there is no apt description of
 "typical"  combined sewage  or stormwater runoff characteristics due
 to the  variable nature of  the rainfafll-runoff patterns.  Figure
 2 illustrates some general  concentration ranges of the wastewater
 constituents listed.   The major characteristic,  i.e.,  qualitative
 variability, is shown by these data.  Quality may range from super-
 strong sanitary sewage during the "first flush"  to very diluted
 sewage later in the storm.   The composition is dependent on  a
number of factors,  including:  length  of antecedent dry weather,
 local  climatic conditions,  condition of the sewerage system  and
the nature of the drainage  area.

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 *               FIGURE  2
 GHARACTERISTICS  OF COMBINED SEWER WERFLDWS
               (SELECTED DATA)
   '5
TSS
TOT, SOL,
VOL, Tor, SOL,
pH
SETTL, SOL,
OKG, N
Tor, €OLI,
PEG, COLI,
PEC, STREP,
30
20
 3
 5
 ,
 2
TO
TO
TO
TO
TO
TO
TO
TO
TO
TO
TO
TO
600
1,700
2,300
820
8,7
1,53)
33,1
-12.5
6,2
goxio6/:
MG/L
MG/L
MG/L
MG/L

ML/L
MG/L
MG/L
MG/L
Id) ML
17X106/1GO ML
MO6/:
ICO ML

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As mentipned, urban stormwater in itself is a significant contri-
butor to the problem since it picks up a variety of known and
unknown pollutants as it drains from urban land area.   Figure 3
illustrates some selective data on urban stormwater characteristics.
As noted, the extremely high chlorides concentrations  have been
attributed to deicing salts.  Our program has done some work in
this area resulting in the following conclusions:
     1.  Highway salts can cause injury and damage across a wide
         environmental spectrum.
     2.  Practically all  highway authorities in the U.S.  believe
         that ice and snow must be removed quickly from roads and
         highways and that "bare pavement" conditions  are necessary,
         often resulting  in excessive salt application.
     3.  Salt storage sites are persistent and frequent sources of
         ground and 'surface water contamination and vegetation
         damage.
     4.   The special  additives,  e.g.,  chromates and cyanides,  found
         in  road  deicers  provoke great concern because  of their
         severe latent toxic properties  and other potential  side
         effects.
     5.   A sufficient number of incidents  and  detailed  studies  have
         been  described to  show adverse  impact of deicing  salts  to
         water supplies and receiving  waters.
     6.   In  less  severe cases as  salt  intrusion  into public water
         supplies—salt free  patients  have  been  cautioned  to change
         their potable water  source.
     7.   Deicing  salts are  found  in high concentrations in highway
         runoff.
         Surveillance data  is needed to clearly  define the many  in-
         fluences of deicing salts upon the environment.
        The majority of in-depth studies support the finding that
        deicing salts are  a major factor in vehicular corrosion and
        roadway damage.  The literature also indicates that rust
8.

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                FIGURE  3
     CmRACERISTICS OF URBAN STOfWATER
               (SELECTED DATA)
 GOD
 TSS    ;       '
 TOT,  SOL,
 VOL,  TOT, SOL,
 SETTL, SOL,
'Ore',  N    .
 9m   PO,
 OUL, ru/i
 TOT, P0i|
 CHLORIDES
 OILS
 PhENOLS
 LEAD
 TOT, OoLi'i
 FEC, COLI,
 FEC, STREP,
  1
  5
  2
TO
TO
TO
450   TO
 12   TO
 0,5  TO
 0,1  TO
 0,1  TO
 0,1  TO
 0,1  TO
  2   TO
  0   TO
  0   TO
  0   TO
 200   TO
  55   TO
 200   TO
                                >700  MG/L
                               3,10)  MG/L
                              11,300  MG/L
                              14,600  MG/L
                               L6QO  MG/L
                               5,TO  ML/L
                                  16  MG/L
                                  2,5 MG/L
                                  10  MG/L
                                 125  MG/L
                              25,0X3  MG/L*
                                 110  MG/L
                                  0.2MG/L
                                  1,9 MG/L
                               MMO^/lOO ML
                               112xl06/100 ML
                               L2X105/10Q ML
*WlTH HIGHWAY DEICING

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          inhibiting additives do not produce results  to justify
          their continued use.  It is further noted that deicers may
          attack and cause damage to telephone cables,  water distri-
          bution lines and other utilities  adjacent to  streets  and
          highways.
      10.  There is little doubt that road deicers  can  disturb a
          healthy balance in  soils,  trees and other vegetation  com-
          prising the roadside environment.

 Sewer Separation

 Hhen  considering combined sewer overflow problems,  first attention
 is  generally  given  to the construction of  separate  sanitary  and
 storm sewer systems.   In  contrast,  the 1964  PHS study  stipulated
 that  alternative solutions be investigated to  determine if means
 other than sewer separation  could be  found at  lower cost.

 The previously mentioned  APWA study of combined sewer  problems  in-
 dicated that  if  all  communities  with  combined  sewers in this country
 were  to effect sewer separation, they would  face an expenditure of
 approximately 85  billion  dollars at today's  cost.   Of  this amount
 New York State's  share would  roughly come to $18 billion, the
 highest figure for any state  in  the nation.  It was further esti-
 mated that the use of alternate measures could reduce  the national
 figure to about 25-30 billion dollars.

 It is again emphasized that urban stormwater runoff itself can  be
a significant source of stream pollution.  Sewer separation would
not cope with this pollution load.  An EPA study revealed that  if
separation were used, the reduction in wet-weather pollution would
be only 50 percent.   The other 50 percent would remain in the un-
treated urban storm runoff.
                              10

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IV.   CORRECTIVE METHODS

Program research, development and demonstration projects have pro-
vided significant results, and have illustrated that sewer separa-
tion in most cases is not the logical  course of action.   We.have
categorized three basic approaches other than separation:  control,
treatment and combinations of the two.
Control

Control of combined sewer overflows can be obtained byreduction
or equalization of peak stormwater flows,  increasing the effective
capacity of the sewerage system, minimizing infiltration and by
source prevention techniques.

For existing system control, the operator can attempt to maximize
wastewater treatment at the sanitary plant during wet-weather by
trying to contain as much flow or treat as much sewage as possible
during a storm flow occurrence.  This would serve to reduce wet-
weather by-passing which at the beginning of storm flow can have
a high pollutant concentration, as previously described.  It is
recognized this extra plant burden may decrease treatment effi-
ciencies somewhat, and create added sludge or solids handling
problems; however, these practices for only short periods during
storm  flows are well worth the effort.   If the operator deter-
mines  that hydraulic loading will cause a serious upset of a unit
process then primary treatment plus disinfection should be con-
sidered as a minimum measure.

In, Detroit, where the prevailing direction of storms is known, ;the
operator receives advanced information on storms from a remotely
stationed rain gauge.  The treatment plant pumping is increased,
thus lowering the surcharged interceptor gradient, allowing for
greater interceptor storage capacity and conveyance.  This practice
                               11 '

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 has enabled the city to  entirely  contain  and  treat many intense
 spot storms plus many scattered city-wide rains.

 The operator should  also concern  himself  with  improved regulator
 inspection  and maintenance,  and preventive schedules to minimize
 the occurrence of overflows.   Overflows during dry as well as wet-
 weather due to malfunctioning  devices and clogged orifices can
 thus be alleviated.   Tide gate conditions allowing backwater in-
 trusion can be corrected,  and  diversion structure settings can
 be  raised to obtain  more interceptor carrying capacity.

 Municipalities  can also  control combined  sewer overflows without
 large and costly modifications by concerning themselves with,in-
 filtration  and  extraneous  inflow.  Excess  flow caused by infil-
 tration is  a major thief of  capacity that would otherwise be avail-
 able to transport wastewater and can thereby affect proper operation
 of  sewerage systems  and,  consequently, the quality of streams.
 Other adverse impacts caused by infiltration include:  (a) sur-
 charging and back-flooding into streets and private areas and need
 for relief  sewers ahead  of schedule; (b)  surcharging of treatment
 plants  and  pumping stations, causing flow by-passing, decrease
 in  treatment efficiency, and higher treatment costs; and (c) diver-
 sion of raw wastewater and greater incidence and duration of over-
 flows.  The  APWA  has reported that infiltration was a pronounced
 problem during dry weather in 14 percent of communities surveyed and
 in  53 percent of the communities during wet weather.   The APWA also
 indicates that other sources of extraneous inflow compounding the
 problem include roof leaders; depressed manholes  covers;  cellar,
 foundation,   and yard drains; air conditioning and industrial  cooling
waters;  and other connections.

 Control  of infiltration should first take  place during sewer pipe
 installation.  Better construction materials  and  proper installation
                               12

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techniques are necessary.   The new methods of sewer-sealing and
lining should be fully evaluated before major rehabilitation or
replacement is undertaken.

Infiltration surveys should be undertaken when extraneous inflows
are suspected.  Such surveys may use television and other visual
pipeline inspection, smoke tests, air and water pressure tests* and
various flow techniques.  Undue deposits, partial  blockages and
cave-ins causing premature surcharging and dry- and wet-weather
overflows (usually in older sewer systems) will   also be pin-
pointed for subsequent corrective action.

Building connections to street sewers are a major source of infil-
tration.  As much as 70 to 80 percent of the infiltration load can
occur in these lines.  Accordingly, the aforementioned infiltration
control practices should be strictly followed here.

Before a municipality considers removing extraneous inflows, the
following basic factors should be considered:
     1.  Determination of what a "clean" or unpolluted inflow really
         is.  For instance, subsurface drainage may be contaminated
         leachate or contain toxic material washed from basement
         floors.
     2.  Sewer septicity and odor conditions that may arise because
         of lowered flow from the elimination of long-standing in-
         flow sources.                                      .
     3.  Effect on the public of any sudden decision to eliminate
         inflow sources and the associated problems of enforcement.
     4.  The strong possibility that communities will be forced tb
         treat separate urban runoff sometime in the future .indicates
         that the reconnection of certain so-called "clean" waters
         from sanitary to storm drains may be done,in vain.
                              13

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Studies have indicated that it may be cheaper to remove solids from
the street surfaces by sweeping than by eliminating them via the
sewer system.  One set of figures showed that street sweeping
costs $24 to $30/ton of solids removed as compared to $60 to $70/
ton of solids removed via the sewerage system.  What may be even
more important is that the wet-weather overflow polluting potential
of these solids is eliminated by the urban surface removal practice.

Aside from abating the usual contaminants, a particular advantage
of effectively removing the dust and dirt fractions prior to sewer
entry would come from the reduction of major amounts of the more
exotic pollutants which include heavy metals (lead, zinc, cadmium,
mercury, copper, chromium), pesticides and PCB's, and nutrients
that commonly adhere to the surfaces of solids.   Because of the
potential  land and groundwater contamination, care should be given
to the solids disposal site selection and the fate and effects of
these pollutants.  At this juncture it is appropriate to mention
that greater efforts should be applied in the area of non-routine
stormwater constituents.  Their impacts and abatement measures must
be further researched, whether they be by surface "housekeeping" at
the source, or treatment of the storm flow  itself.

It is recommended that the newer and more promising street clean-
ing equipment such as vacuum sweepers, air brooms and wet scrubbers
be further evaluated and employed as opposed to  conventional
sweeping and flushing methods.  The newer devices offer benefits
in picking up the dust and dirt particles rather than redistributing
them for aesthetic purposes as the conventional  devices do.

Certain land use, zoning, and construction site  erosion control
practices  are other ways of alleviating the solids burde/i to 'the
receiving  streams or treatment plants by surface source prevention.
                              14

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 Cleansing  of  catch  basins,  sewer  Tines, wet .wells and other appur-
^tenances^by flushing  or  dry mechanical means may reduce  solid
 loadings in wet-weather  discharges  and alleviate premature over-
 flows  during  dry or wet  periods due to partial  or complete sewer
 obstructions.-  But  here  we  must weigh the  benefits  of system
 cleaning against "closing, the  loop" by the installation  of wet-
 weather flow  control  and/or treatment facilities.

 It is  emphasized that before  a community considers  the establish-
 .ment or continuation  of  the household garbage  grinding practice,
 it must be realized that increased  solids  deposition in  both
 combined and  sanitary sewer lines will occur at times of low  flow -
 during dry weather  which will  be  scoured put by the high storm flow
 conditions.  As a result, the overflows will create more severe
 stream impacts.  The jurisdiction's plans  regarding future overflow
 control and treatment will  be an  important consideration since
 again the  "loop" will be closed.

 If there  is insufficient carrying capacity in  the "sewer  lines,
 polymer addition may serve to measurably  reduce fluid friction.
 Research  has  shown  that polymeric injection can increase flow
 capacity as much as 2.4 times at  a  constant head.   This  method can
 be used as a measure to correct troublesome pollution-causing con-
 ditions such as localized flooding  and  excessive overflows.   Pre-
 liminary cost comparisons have shown this  procedure to  be feasible.
 ', .   , '"$ ' •• " - ','', •'"' :   .  ,-':'•',.  .'    -   '    .''-"-,-      L  - '      f " .
 Advanced Control /Systems

 In this segment of the talk,  some of the newer and more advanced
 technology being developed by our  Program will be described.
                               15

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  Flow Regulation

 .Several  methods have been used to reduce operation problems  asso-
 tciated with the conventional  regulator devices.   Cincinnati  utilizes
  telemetered monitoring to detect unusual  or improper dry-weather
  overflows.   More sophisticated approaches are being applied  by the
  Minneapolis-St. Paul Sanitary District and the Cities of Detroit,
 'and Seattle.   All  three jurisdictions  are making use of unused
  storage capacity within the existing sewerage system for the purpose
Vpf reducing the frequency and volumes  of overflows.   For instance,
 ""in the period from 1969 to 1970, Minneapolis was able to reduce
  overflow occurrences by 55% and the volume of overflow by B5%.  The
  general  approach comprises remote monitoring of rainfall, flow levels,
 'and sometimes quality, at selected locations in  the network, together
  with a centrally computerized control  console for positive regulation
  of the overflow structures.   Figure 4  depicts the computer console
  and strategy  room in Seattle, and is a preview of what the operator
  in 1980  may be contending with.
  New types  of regulators  such  as  positive  control  gates  and  in-
  flated  rubberized-fabric dams (Figure  5)  have  been  demonstrated
  successfully.   Another unique overflow device  which has  been
  constructed  for full-scale  demonstration  utilizes fluidic technology;
  and requires no moving parts  or  external  power since operation is
 '.^entirely dependent  upon  motion of  the  wastewater.   Improved regulator
  capability and  reduced operation and maintenance  costs  are  anticipated.
  Additional improvement in regulators is now  in progress.
 t

  Storage

 'Storage  offers  direct  control  by containing  the wastewaters pro-
  duced during wet-weather periods.  The  use of  storage facilities
  for controlling combined sewer overflows  has been convincingly
  demonstrated.   The  general  procedure involves  the return of re-

                                16

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Figure 4. Computer console for augmented flow
control system, Seattle, Washington.. ; .. •  .
                        17

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                            t   r s   ft at
Figure 5. Inflatable Control  Gate  System
                    18

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tained overflows to the conventional  treatment works for subsequent
treatment during low flow, dry-weather periods.

Concrete holding tanks are the most commonly used type of storage
facility.  The storm stand-by tanks at Columbus, Ohio, shown in
Figure 6, constructed as early as 1932, were recently modernized by
installation of sludge collection and automatic flow control equip-
ment.  The City of Boston has commenced operation of overflow hold-
ing tanks designed to provide 10-minute settling plus chlorination
for treating excess overflows of 233 million .gallons per day.  New
York City and Milwaukee have similar facilities in operation.  The
New York City plant has four storage, tanks which have a combined
capacity of 9.7 million gallons.  Intercepted storm flow is stored,
degritted, and pumped, along with the sludge back to a nearby
Municipal Treatment Plant.  Excessive overflows receive treatment by
sedimentation through the tank and are chlorinated and discharged.
The objective of the facility is to reduce coliform and solids
contamination of Jamaica Bay.

Chippewa Falls, Wisconsin has constructed an asphalt-lined  basin
providing storage  for up to 3.5 million gallons of overflow.
(Figure  7)  During the 1969 - 1970 evaluation  period, 50 river
discharges out of  62 storm overflows were eliminated.

Two  basic problems encountered by conventionally-designed storage
facilities in urban areas are land cost and availability, and
adverse  aesthetic  impacts.   In this regard, we are  seeking  new
concepts.  A major demonstration in Chicago involves  the-new
concept  of "deep tunnels".  The  cost of the Metropolitan Chicago
tunnel  storage  system  is  estimated at  over one billion  dollars  as
contrasted to over four  billion  for sewer separation.   Additional
benefits of turtnel (or  in-sewer) storage are  a result of coverage
of an expanded  area or  length.   Thus,  storage  is  more readily  avail-
                              19

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                                                  2S&BI
Figure 6. Storm Stand-by tank with  upper  portion
of sludge collection mechanism visible, Columbus,
Ohio.
Figure 7.  Asphalt-lined basin providing storage
for up to 3.5 MG, Chippewa Falls, Wisconsin.
                        20

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able to remote areas, hydrographs may be smoothed or reduced for
treatment facility design because intense storms often are quite
localized, and overflows greater than storage capacity can be select-
ively and automatically'discharged!to the most suitable stream loca-
tions.  Another subsurface storage idea, to be demonstrated in
Lancaster, Pa., is the underground "silo".  The use of a 50-foot
diameter, 100-foot deep silo could afford over 1 million gallons of
storage.  The preliminary design is shown in Figure 8.

Other designs requiring little or no urban land include offshore
storage and the use of natural underground formations.  Two demon-
stration projects have evaluated the use of flexible neoprene-coated
nylon fabric material as underwater containers, for the temporary
storage of combined sewer overflows.  Figure 9 presents a drawing
of such an installation.                                             :

The engineer and operator will be interested in the sludge-handling
aspects of temporary storage.  Two possibilities are the re-suspension
of solids by agitators and settling prior to pump-back.  Re-suspension
can provide easier draw-off and is being evaluated.  However, if
sludge  is settled, on-site sludge disposal in lieu of solids pumped
back  in stored flow should be considered.

Design  criteria should be based on the pollution abatement results
expected.  For example, Milwaukee used a mathematical model to
determine size and projected efficiency of its holding tanks.

Wherever possible, design of full-scale facilities should consider
the total environmental impact, including aesthetics.  Figure 10 is
a conceptual drawing showing an off-shore site in Lake Erie at
Cleveland, Ohio

A concept worthy of note, which was successfully demonstrated in
                              21

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                             SCUM RING   VORTEX fOUi. OUTLET
           Preliminary Drawing — Elevation View of System,  Lancaster,  Pa.
                                            PLAN AT EUVATJON 256'-0"
Figure 8.  Preliminary Drawing  - Plan View of  System, Lancaster, Pa.
                                   22

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                   FIGURE  9
               UNDERWATER   TANK
                 INTERIOR SECTIONED VIEWS
         COATED FABRIC
                                     STEEL FRAME-
FLUSHING JETS
                       23

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Figure 10. Conceptual design of combined sewage
retention-stabilization basin, Cleveland, Ohio
                     24

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London, England and Decatur, Illinois, is the conversion of existing
or abandoned sanitary treatment units, in this case sedimentation
tanks, to storm holding facilities as part of a plant expansion.
Also, plans have been proposed to use an abandoned trickling filter
as a  storage tank for stormwater infiltration.
Porous Pavement           •

Another feasible method to attenuate flows is the installation of
porous pavement;  This pavement'is made of asphaltic-concrete and has
been developed for an ability .to, allow 60. or more inches per hour of
rainfall to permeate, through its. depth ^(Fjgure;OJ)vVri|;^$e^.|or
major highway, street, and parking lot paving-projects, it would have
the potential for reducing capacity and associated costs for both
sewer and wet-weather flow treatment systems, a feature attributable
to the porous pavement's ability to equalize flows entering or divert
flows away from the  sewerage system.  This type of pavement install-
ation can;lal so offer a'substantial benefit by recharging::water supplies.
Even more important  are the safety 'features :whleft-could be-realized,  .
i.e., an increased coefficient of friction which will  help prevent
wet skidding or hydroplaning accidents, and enhanced visibility of
pavement markings due to more rapid removal of'rainwater and rougher
surfaces.  However,  when porous pavement  is considered, we must real-
ize that such features as geographical area, temperature, subsurface
soil  condition, and  the possibility of groundwater contamination may
play  an  important part in design-and site selection.

New Sewer  Systems

New types  of sewer  systems  being  demonstrated,  based on  vacuum and  pres-
sure  operation  for  the collection  and  conveyance of sanitary  sewage,
can  reduce the  waste volume generated,  reduce  conduit  sizes,  eliminate
 infiltration, minimize associated  installation  and treatment  costs,
                               25

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Treatment methods which have been evaluated or are currently under
investigation by the Storm and Combined Sewer Pollution Control  Pro-
gram include:

      1.  Fine-mesh screening and microscreening
      2.  Dissolved-air flotation
      3.  Rotating biological contactors
      4.  High-rate plastic and rock media trickling filters '*'"
      5.  High-rate, single, dual and tri-media filtration
      6.  Swirl and helical separators"
      7.  Advanced disinfection methods, e.g., high-rate application,
          on-site generation, automated operation, ozonation, and use
          of combined halogens (chlorine and iodine) and chlorine di-
          oxide
      8.  Tube settlers
      9.  Powdered and granular activated carbon adsorption
     10.  Polymer and other chemical additives for improved settling,
          microscreening, filtration and flotation
     11.  Chemical oxidation                                       -
     12.  In-line or in-sewer treatment
     13.  Sludge handling and treatment
     14.  Regeneration of carbon and coagulants, and
     15.  Reclamation and reuse.

Time does not allow a detailed discussion of each of these methods
Some of the more promising treatment techniques will be discussed.

Since high throughput rates, are necessary for combined sewer over-
flows, the sanitary treatment processes are being studied for poss-
ible modifications.  For example, the microstrainer is conventionally
designed for polishing secondary sewage plant effluent at an optimum
rate of around 10 gallons per minute per square foot,  tests on a
                             28

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pilot microscreening unit in Philadelphia, Pa.  have shown that, at
                                  2
high flux rates of 35 to 45 gpm/ft , suspended solids removals in
combined overflows exceeding 99 percent can be achieved.  Mr. George
Glover will speak about this in more detail this afternoon.

Increased flow rates greatly reduce capital costs and space require-
ments.  Increased throughputs have also been obtained with other
fine-mesh screening processes, for example, fiberglass filtration
and dissolved-air flotation.

An EPA study in Cleveland showed high potential for treating com-
bined sewer overflows by contact coagulation and ultra high-rate
filtration.  Figure 12 depicts the process flow diagram.  With the
                                2
high loadings of 16 to 32 gpm/ft  surface area, removal of solids
is effectively accomplished throughout the entire depth of filter
column.  Test work showed suspended solids removal up to and
exceeding 90 percent and BOD removals in the range of 60 to 80 per-
cent.  Substantial reductions, in the order of 30 to 80 percent of
phosphates, can also be obtained.  Mr. Pat Harvey will discuss this
at length later on today.

Results from a 5.0 MGD screening and dissolved-air flotation demon-
stration pilot plant, in Milwaukee, indicate that greater than 70
percent removals of BOD and suspended solids are possible.  Find-
ings also revealed 85 to 97 percent reduction in suspended,sol ids,
and better than 90 percent reduction in phosphate can be achieved
as an additional benefit, by employing chemical coagulants.  Mr.
Gupta will give his presentation on this topic this afternoon.

A unique variation of the usual coagulation-adsorption, physical-
chemical treatment process has been demonstrated in Albany.  This
                             29

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system, shown schematically in Figure 13, is comprised of a 100,000
GPD trailer mounted pilot plant where both powdered carbon and coag-
ulants are added in a static mixing-reaction pipeline, and the result-
ant coagulated matter is flocculated downstream,  separated by tube-
settlers and polished by multi-media filtration.   The project also
demonstrated regeneration of alum and activated carbon by fluidized-
bed incineration.             ,

At this point it is appropriate to bring out an important fact of
which future designers of storm overflow treatment facilities must be
cognizant--process efficiency should not be considered in the usual
terms of percent removal used in municipal treatment.  It was found
during the microstrainer and dissolved-air flotation operation that,
due to extreme variation of the influent suspended solids concentra-
tion, removal efficiency would also vary while the more desirable
effluent concentration remained relatively constant.  For example,
a typical effluent concentration of 10 mg/1 suspended solids would
yield a reduction of 99 percent for an influent concentration of
1,000 mg/1, whereas the suspended solids reduction would be only
50 percent if the influent concentration were 20 mg/1.  This pheno-
menon is apt to reoccur in other physical-chemical stormwater treat-
ment operations.

Another project has studied a new biological process, described as
the rotating biological contactor consisting of a series of shaft-
mounted rotating disks.  Similar in principle to trickling filtration,
a biological growth attaches onto the disks.  Under steady loading
rates, efficiencies exceeding those of the trickling filter have been
attained, but a surge tank appears essential.  Figures 14 and 15
give a close-up of the rotating disks and an overall view of the
pilot facility, respectively.

Another approach in overcoming the extreme variation in overflow rates
is to provide surge facilities prior to the storm treatment plant or
                               31

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32

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Figure 14. Close-up view of rotating biological
disks, Milwaukee, Wisconsin.
Figure 15. Overall' view of rotating
biological, disks, Milwaukee, Wisconsin,
                     33

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 the  municipal  plant.  The  surge  basin(s)  (or existing combined sewers)
 could  furthermore  serve  a  dual function in equalizing not only wet-
 weather  flows  but  dry-weather flows as well.   In this way, a single
 future treatment system  can  readily be designed for storm and sanitary
 flow conditions.   This could also assist  presently overloaded sani-
 tary plants  in obtaining more uniform operation.  Short-term storage
 incorporated into  the treatment  plant would even out the daily cycle
 of dry-weather flows allowing for more efficient use of the treatment
 process  over the entire  24 hours.  Equalization would permit reduced
 treatment process  design capacity.  Further analysis is necessary to
 determine the most economical break-even  point between the amount of
 storage  versus the treatment capacity.  The designer should recognize
 the  wet-weather treatment plant's capability to draft stored flow con-
 tinuously while it is raining in his evaluation of the optimum surge-
 treatment system.

 New  Orleans  has demonstrated the use of sodium hypochlorite for dis-
 infection of storm flows as  high as 11,000 cfs, to both reclaim and
 protect  public bathing beaches.  In order to economically provide the
 large  quantities of disinfectant required, an on-site hypochlorite
 batching plant was constructed (Figure 16).  Figure 17 gives a view
 of the massive-size chlorine contact basin in operation.

The  disinfection of combined sewage entails certain differences,
which make the design and operation of facilities difficult when com-
 pared to sanitary  sewage.  The highly varying qualitative and quan-
titative character of the storm generated inflows require disinfectant
dosages to be based on a predicted rather than an established tech-
nique.   A decrease in temperature decreases disinfectant kill  power.
This points to the importance of temperature in additon to the usual
 (time and dosage) control parameters.   As temperature is apt to have a
much wider range for runoff waters than it does for domestic sewage
flows,  combined sewage may require disinfectant dosage to vary season-
                              34

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Figure 16. Stormwater disinfection project -
hypochlorite batching plant, New Orleans, Louisiana.
Figure 17. Stormwater disinfection project - chlorine
contact basin, New Orleans, Louisiana^
                       35

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 ally  or  as  effected  by ambient  temperature.

 The Storm and Combined Sewer Overflow Technology Program is also
 searching for high-rate disinfection systems to save on large
 tankage  requirements for the high storm flow rates encountered,
 with  the help of more rapid oxidants e.g. chlorine-dioxide, and, •
 by imparting greater turbulence to the flow.  Successful attempts
 toward high-rate disinfection are being noticed at our Phila-   !
 delphia, Pa. and Onondaga County, New York demonstration sites.•••.>
 The Philadelphia project also made an evaluation of ozone,  gener-
 ated on-site for disinfection purposes.   Another study proposes .
 the use of combined halogens (chlorine and iodine)  to provide
 more effective disinfection of viruses as well  as  bacteria  in a
 swimming lake.   This study also supports  dechlorination by.acti-
 vated carbon or use of ozone,  with a relatively short half  life,
 in lieu of chlorine to alleviate residual  toxicity  problems  to fish
 life.   Mr.  George Glover  will  present more on this  subject.

 Combinations
 When  a  single  method  is  not  likely  to  produce  the  best  possible ans-
 wers  to a  given  pollution  situation, various treatment  and control
 measures—as previously  described—may be combined for  maximum flex-
 ibility and efficiency.  One  such combination  might be:  in-sewer
 or off-system  storage  for  subsequent overflow  treatment in specifi-
 cally designed facilities, followed by groundwater recharge or
 recovery for water sports  and aesthetic purposes.  Another combin-
 ation might be flow retention with pump or gravity feed-back to the
 sanitary sewerage system.

 In all  cases.the optimum abatement plan for stormwater overflow
 pollution will  have to be evaluated separately for the geographical
area in consideration.,  Aside from climatological conditions,  terrain,
and land uses,  choice of control and treatment will depend  on  the
                              36

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 existing sewerage  system configuration.   For  example,  systems  with
 large contributory areas and .few overflow points  present problems
 and require design philosophies which differ  from those in  systems
 divided into many  subdrainage  areas with individual  combined waste-
 water outfalls.

 The temporary storage concept, previously discussed  as a control  pro-
 cess, also provides for a certain degree of treatment by settling,  for
 excessive overflows greater than the design storage  capacity dis-
 charging directly to the receiving stream.  Likewise, this  settling
 potential for flows less than  design capacity, together with on-site
 solids disposal  usually overlooked, should be definitely considered.
 The proposed prototype demonstration for Lancaster,  Pennsylvania,
 previously cited and shown schematically in Figure 18, will pre-treat
 by a swirl device and microstrain and disinfect discharges greater
 than the storage capacity of the "silo" structure.

 Mr. Clemens, Michigan installed a system involving discharge of
 combined sewage overflows into a series of three  "lakelets" each
 equipped with surface aerators.  Effluents pass from  one pond to the
 next through microstrainers and filters, and  the  final  effluent is
 .chlorinated.  This, control  and treatment scheme is designed to have
 no adverse aesthetic impacts,  and  the possibility of  reusing  these
 waters for recreational  purposes is  being  explored.   Figure 19 shows
 a  schematic of  the  Mt.  Clemens  facility.

 A  conceptual engineering study for the  Washington, D. C. area (Figure
 20) has shown that it would be feasible to construct a control-treatment
 facility to handle combined sewer  overflows  up to 3,000 cfs.   A  175
 million gallon  storage  facility is tentatively planned with an over-
  head parking garage,  coupled  with  a 50  MGD high  rate filtration-
-.. adsorption-disinfection plant.  This treatment complex is  intended
  to produce reclaimed waters suitable for swimming,  boating, and  fishing.

                               37

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Our Program, in conjunction with APWA, has refined and is demonstra-
ting the swir.l flow regulator/solids-liquid separator (Figure 21).
The device is;of simple annular-shaped construction requiring no
moving parts.  It provides a dual function, regulating flow by a
central circular weir, while simultaneously treating combined sewage
by swirl action which imparts liquid-solids separation.  The low-
flow concentrate is diverted to the sanitary sewerage system, and
the relatively clear liquid overflows the weir into a downshaft and
receives further treatment or is discharged to the stream.  This
device is capable of functioning effectively over a wide range of
combined sewer overflow rates having the ability to effectively
separate settleable and light-weight organic suspended matter at a
small fraction of the detention time required for conventional sedi-
mentation.  For these reasons serious.thought is now being given to
the use of swirl units in series and in parallel solely as wet-,
weather treatment plant systems.  A helical or spiral type regulator/
separator has also been developed based on similar principles "as the
swirl device, and .we are looking for further refinement.  Mr,. Richard
Sullivan will speak on this subject following my presentation.

Flow Measurement

The quantitative %and qualitative measurement of storm overflows .is
essential for process design, control, and evaluation.  The  "urban
intelligence  systems" previously mentioned require real-time  data
from rapid,  remote sensors  in order to achieve remote control of a
sewerage network.  Conventional  flow meters have not been developed
for the highly-varying surges encountered  in combined sewers.  Here,
a  measuring  device may be subjected to very low flow rates,  submer-
gence,  reverse  flow, and surcharge, all during a single  rainstorm.
These  severe  flow conditions rule out the  reliable and accurate app-
lication of  conventional devices, such as  weirs and flumes at many
                               41 •

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                                                                                      inflow
foul
sewer
  overflow
a
b
c
d
e
f
g
h
  Legend
Inlcl Ramp
Flow Deflector
Scum Ring
Overflow Weir and Weir Plate
Spoilers
Floatables Trap
Foul Sewer Outlet
Floor Gutters
                                  Figure 21
            Isometric View of Swirl Regulator/Concentrator
                                      42

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locations.  Consequently, we are deeply Involved in the development
and demonstration of sophisticated and new flow measuring equipment
utilizing the various principles of:  hot-film anemometers, concen-
tration of induced foreign matter, ultrasound, and electromagnetics
as applied to open channel flow.

Our Program has also contributed towards the development of a pro-
totype monitor capable of instantaneous, in-situ measurement of sus-
pended solids based on the optical principle of light depolarization.

USEPA Stormwater Management Model (SWMM)

The capability to analyse various component flows and pollution loads
throughout a sewerage system is one of the keys to better design of
control and treatment systems.  Due to complexities of the rainfall-
runoff- flow phenomena past analyses have been less than adequate,
resulting in poor estimates of  flow and predicted system responses to
a storm.  By virtue of previous undertakings, we now have available
an operational "descriptive" mathematical model which can overcome
former analytical deficiencies.   Figure 22 depicts a schematic over-
view of the model.

We are now in the initial phase of demonstrating the application of
this method for  "decision-making", that is, its ability to analyse a
major combined sewer system to  s.elect and to  design control and treat-
ment approaches  based on  cost/effectiveness and to eventually design
a computerized means of  overall management of the system during storm
flows.  The model will be fully explained later on today by Dr. Wayne
Huber.

PROGRAM PROJECT  NEEDS

Looking ahead, the  Storm and  Combined  Sewer Pollution  Control Program
                              43

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RUNOFF
(RUNOFF)
  DECAY
  (QUAD
                   INFILTRATION
                      (INFIL)
TRANSPORT
  (TRANS)
                    EXTERNAL
                    STORAGE
                    (STORAG)
                RECEIVING WATER
                     (RECEIV)
                    DRY WEATHER
                        FLOW
                        (FILTH)
INTERNAL
STORAGE
(TSTRDT)
 COST
(TSTCST)
                    TREATMENT
                      (TREAT)
     Note:  Subroutine nalnes are" shown in parentheses,
                                     I

           Figure 22,   OVERVIEW OF MODEL STRUCTURE
                          44

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needs are vast and numerous.
to the following:
At present, we are directing our efforts
     1.  A nation-wide assessment of sewered and non-sewered straight
         urban runoff impacts, not combined sewage - a consideration
         which has been stressed by the 1972 Amendments to the FWPC    :
         Act.'' '	"""""         '" ' '  '•'   ';"'-"  •'       	;;"  ;  	
     2.  Dual  use facilities for wet-weather and dry-weather treat-
         ment.  Wet-weather facilities built in conjunction with new
         or existing sanitary.pi ants can  demonstrate their synergistic
         benefit by being  utilized to take  over during repairs,  polish-
         ing secondary effluents, or increasing dry-weather treatment
         capacity during the vast majority  of the time, i.e.,  when
         it is not raining.                             . -.      '
     3.  Land  development  making full use of runoff and natural  drain-
         age - aesthetically blending into  the surrounding environment
         rather than upsetting it.
     4.  Wet-weather facilities for treatment of dry-weather creek flow,
         again making full  use of these.facilities during  otherwise
         downtime.
     5.  A stormwater model  monitoring/management system for dissemin-
         ation, updating,  and instructions  on model  application.
     6.  A functional  evaluation of the need for catch basins  today -
         and development of new alternatives.
     7.  Establishment of  uniform techniques for sampling  and  analysis
        .of storm flow and  for determining  design volumes  and  flowrates.
     8.  Further development of flow measuring devices.
     9.  Fostering a stormwater survey course at the  university  grad-
         uate  level.   Storm generated pollution ranks high along  with
         domestic and industrial  sources  and yet remains unstressed in
         the schools.   With  wet-weather control  requirements evident,
         now is the time to  encourage universities to cover the  concepts
         of stormwater runoff and combined  sewer overflow  pollution
         in proper perspective in their graduate school water  pollution
                              45

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         control curriculum.
     10. The swirl device applied for grit removal  and primary separa-
         tion of solids from combined sewage, stormwater, erosion run-
         off, along with the optimization of its sister device, the
         helical flow regulator/solids separator.

There are also certain major control methods requiring further.develop-
ment.  "Upstream" storage or other control processes to decrease the
stormwater runoff effect on lower portions of the system is one case
in point.  Aside from the main objective of controlling storm-generated
pollution, upstream control can preclude the need for additional down-,
stream sewer line capacity and associated construct!'o.n requirements,
alleviate shock loadings due to scouring velocities, relieve the often
occurring expense of constructing facilities downstream near water-
courses in unstable soil with high water table, while offering greater
flexibility for control and treatment.  An example of this would be
the temporary storage or attenuation of stormwater at the building or
immediate area through the use of holding tanks, seepage pits  (possibly
for recharge), rooftops, parks and playgrounds, backyard detention
facilities, porous pavement (previously discussed) or neighborhood
decentralized stormwater collection sumps including storage facilities
under streets.  Upstream control systems should automatically regulate
discharge from storage to the groundwater, a watercourse, or a sewer
system.  Plans for reuse of stored water for irrigation, street clean-
ing, sewer flushing, aesthetic and recreational ponds, potable supply,
and other purposes is also encouraged.

Many more ideas and concepts could be added - some may be more sig-
nificant than those discussed.  Submission of ideas, project proposals
or grant applications to the USEPA is strongly encouraged.
                              46

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 CONCLUSION   .-• .  •  -. •  •. • .-.. •-•        •-

 All  facts point-to a  real  requirement for treating and controlling
 stormwater runoff and combined sewer overflows.   In view of the tre-
 mendous quantities,,of pollutants bypassed during rainfall, from the
 combined sewer,system, it  does not seem reasonable to debate whether
.secondary treatment plants should be designed for 80, 85, or 901 BOD
 or suspended solids removal,  when in fact the small increments .gained
 in this,range are completely  overshadowed by the;bypassing occurring
 at regulators, during  wet-weather flow.

 The multirbillion dollar treatment plant upgrading and expansion
 .program now going on  throughout the country-will do much to alle-
 viate pollution of our waters.  However, means of mitigating the
 effects of combined sewers must also be found if we hope to abate'
 the pollution in an optimal manner.  Wet-weather standards are al-
 ready being instituted by the federal government and, some states and
 localities.  Recognizing this, our Program will  strive to be a prime
 support for this real world application.
                               47

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                   SECTION II
PREVENTION AND CONTROL OF INFILTRATION AND INFLOW
                        by

               Richard H. Sullivan
          Assistant Executive Director
         American Public Works Association
                         49

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     The American Public Works Association has had an active program
of research in the field of storm water pollution.  Its program has
investigated such fields as the pollution of storm water, the extent
of combined sewer facilities, the design, operation and maintenance
of combined sewer overflow regulators and the prevention and correc-
tion of excessive infiltration and inflow into sewers.   These pro-
jects were either conducted under contract with the U.  S. Federal
Governement or as cost-sharing projects jointly financed by local
public agencies and the federal government.  My remarks today will
be based upon the research findings of our Foundation.

     I will briefly review some of the major findings of our report,
"Prevention and Control of Infiltration and Inflow".   I will also
review with you guidelines for the establishment of a survey to
determine the nature and extent of infiltration, and some of the
factors to be used in making an economic analysis of desirable
corrective actions.

     In our study of the problems of combined sewer facilities it
                             50

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 became evident that infiltration plays a major role in many facil-
 ities by either causing more frequent or prolonged overflow events.
 With the assistance of some 34 local  agencies and the Water Quality,
 Office, we undertook a study of the prevention and correction of
 infiltration.   For ease of discussion we decided to consider the
 "Two I's" of infiltration.  The first "I" - infiltration - is in
 the classic sense, that flow which enters the sewer through pipe
 and joint defects and manhole covers, etc., and - inflow - is
 surface water  which is deliberately introduced into the system
'through footing drains, downspouts, area-way drains,  and .such.
 Infiltration and inflow both take up  capacity within  the'collection
 system.  However, the two have entirely different characteristics
 as  to time of  occurrence, and means of correction and prevention.

      If infiltration and inflow exist,  why should we  be concerned?
 One of the most common problems associated with excessive  infil-
 tration or inflow is backups into basements,  flooding of manholes,
 treatment plant overloads, pavement and sewer failures;  all  are
 common problems.   Exfiltration may result in  pollution of  the
 groundwater table.

      When we look at the extent of infiltration,  we can  conclude
 that all  sewers  are combined,  it is all  a matter  of degree.   Where
 even minimal amounts of infiltration  and inflow are present,  a
 regulator device  of some type  will  be used on  the  sanitary  sewer
 system to relieve the  excess  flow condition.   Quite often this
 is  only a leader  from  a  sanitary sewer  to  a storm  sewer, or a
 hole in the side  of a  sanitary sewer  manhole which, under sur-
 charge  conditions,  will  allow  excess  flow to enter a  creek or stream
 bed.   For such systems  to  be described  as  "separate"  is  ironic,
 inasmuch  as  its volume of  non-sanitary  flow may reach  40 to 1, as
 contrasted  to the strict  combined  system where  this could be  90
 to  100  to  1.                            •
                              51

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     Correction of infiltration problems can ,be categorized under
the dual headings of prevention of infiltration and inflow in new
systems and the correction of existing conditions.           :;

     With regard to new construction; tremendous advances have been
made in pipe and joint materials.  Contractors;and pipe suppliers
who worked with the APWA in the preparation of-the report were
agreed that a construction standard of 200 gallons per inch-mile
per day was reasonable and could be met without additional cost to
the local agency.  In practice we found that consulting engineers
had, in effect, an extremely wide array of,construction standards
.which they regularly cite for new construction.  There was,little
agreement as far as to the unit of measure or how the standard
would be applied.  In this regard I think it is important to :remember
the effects of a low standard for gallons per inch per mile applied
to lengths of 200, 300 and 500 feet.  Allowable infiltration may be.
almost impossible to measure.  Specifications using low infiltration
rates should spell out how compliance is to be measured.  For example:
200 gallons per inch per mile per day allows 4.4 gallons in an 8-inch
pipe an hour between manholes 350 feet apart.

     The detection of infiltration is a time consuming and generally
expensive process.  I am not aware of any short cuts to the prepar-
ation of a comprehensive survey.  Our report contains an outline of
a ten-point program as developed by the American Pipe Services Co.
of Minneapolis, Minnesota. . For purposes of our discussion.today I
have expanded this to twelve points, and would like to consider: ...
these steps briefly with you.                  , .           . ••  ,,

     The steps involved in a complete infiltration-inflow.analysis
include:
     1.  SET OBJECTIVES:  detemine what is the apparent problem,
         .in what condition is the sewer system, is there an adequate
                              52

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         maintenance program, how can sources of infiltration/
     •    inflow be determined, and at what cost.           :
     2,  IDENTIFY SYSTEM:  prepare plot plan of entire system,
         identifying component drainage systems and key manholes
         within the system.                           '
     3.  IDENTIFY SCOPE'OF INFILTRATION:  make flow measurement,
         install ground water gauges in manholes, and'meter flows
    '- •••'<'• at lift-pumps.      ;  '"••'  •"•"        ' •'•• •
    4.  ^RAINFALL SIMULATION:  flood the storm sewer and determine
    •'  " rif flowerite'rs the sanitary system - use when infiltration/
    "'  :inflow problems are identified as rain-connected.
    : 5:  .DETERMINE EXTENT OF SEWER CLEANING NEEDED:  a TV camera is
       'not effective unless a sewer Tine is very clean.
     6,  MAKE'-AN ECONOMIC & FEASIBILITY STUDY to determine which
         portions of the system will be cleaned and physically
    : ,    inspected.    •'        -•••"•' "-'•.'••'•''
     7.  CLEAN SEWERS'to be inspected.  ;
     8.  MAKE TELEVISION INSPECTION.  '
     9.  DETERMINE EXTENT & LOCATION OF,INFLOW.
    10.  MAKE ECONOMIC ANALYSIS:   where should rehabilitation or
         replacement work be conducted.
    11.  RESTORE AND REPAIR SYSTEM.
    12.  ESTABLISH TREATMENT PLANT DESIGN CRITERIA on basis.of
         reduced flows.
I
   '  One of the important points that must be stressed again and
again is that if we are going to look for infiltration we must
look when it logically will be present.  Thus, the use of ground-
water gauges to determine whether or not the individual pipe sec-
tions are belpw the groundwater table is a necessity.  Second, the
sewer lines must be clean if they are to be inspected.  By clean,
I mean that a full gauge tool must be passed through the line.  This
is generally more than?the normal cleaning procedure of most agen-
                               53

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cies.  The cleaning procedure will  be expensive and time consuming.
Therefore, careful analysis must be made as to the capability of
the agency to clean sewers and this must be attached with the plan-
ned progress of the survey.  Cleaning may be a deciding factor in
determining how much of a system may be actually investigated.  It
may be necessary to contract for cleaning.

     Properly timed television inspection in a well-cleaned sewer
is extremely helpful in analyzing the location and amount of infil-
tration waters entering the sewer line.  Data obtained will include
an indication as to locations of many sources of inflow and build-
ing sewer infiltration.  The latter, building sewer infiltration, is
a hard problem to approach, inasmuch as it is very difficult to
gain access to that portion of the sewer system.  A rough analysis
of a community's total sewer system may indicate as much as half
of the total sewer system is building sewers.  Should the ground-
water table be high, and the building sewers under the groundwater
table, a substantial portion of the total load may come from this
portion of the sewer system.  Again, such lines if they are shallow
may be an important source of infiltration and inflow during periods
of precipitation.  One community which experienced severe overload-
ing and basement backups during periods of rainfall found that roof
leaders discharged adjacent to a building allowed almost a direct
connection of the water from the roof into the building sewer.
This community required that roof  leaders be discharged five feet
from the foundation, and the problem was corrected.  In other
communities official practice may  have allowed foundations drains
to be connected to the sanitary sewer.  This again leads to a tre-
mendous increase  in the flow.   In  a like manner, sump pumps,  if
allowed to discharge into  the sewer system, quickly cause over-
loading.  Yet another  source of inflow water is from manholes.
There are many conflicting opinions, however, with regard to  using
watertight covers  on manholes because of the buildup of  gas within
                                54

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 the  system.  However, if the manhole is to be located'in an area  .-
 where  storm water may enter the system, many communities have gone
 to watertight covers or have added plugs to the openings to keep
 storm  water out.

     Detection  of the location of inflow is perhaps the easiest
 part of the battle.  The real test is  to attempt  to change or
 correct the conditions within private  property.   Residents of
 built-up areas  without storm drains  in many areas are loathe to
 have sump pumps discharge  onto lawn  areas.  In  fact,  in many areas
-there  may not  be sufficient lawn area  to take the flow.   In like
 manner, foundation  drains  must have  a  location  and a  way  of carrying
 off the flow  or there will be backup into  the basement.   To reduce
 erosion, roof leaders.may  be discharged  into the  sanitary sewer.

      The APWA report has  recommended that  agencies prior  to fund-
 ing reconstruction  of paralleling  of their interceptor  sewer  or
 relief sewer and construction or additional treatment facilities,
 make a .thorough infiltration  study to determine the amount of flow
 which might be eliminated by correction  of inflow conditions  or
 improvements of the sewer line  to  eliminate infiltration.

      From a dollars and cents  point.of. view,  this seems appropriate.
 From a standpoint of controlling pollution, we are generally  further
 ahead  in eliminating pollution  if we clean up the source rather than
 if we  build additional  facilities and then have continuing opera-
 tional cost.                    _

       For this  reason, in  our Manual of Practice, we attempted to
 develop  an outline of an  economic analysis in order that the cost of
 infiltration and inflow waters might  be determined and so that an
 agency could determine how much it  could afford  to spend for the
                                 55

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control of infiltration and inflow.  Very few examples were found
where such an economic evaluation had been made.   While many of the
tools that are available at this time are not exact,  because of
lack of adequate record systems by local  agencies, we must have the
economic justification of our pollution control  activities.
                              56

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               SECTION' III
COMBINED SEWER OVERFLOW REGULATOR FACILITIES
                    by
           Richard H. Sullivan
       Assistant Executive Director
     American Public Works Association
                      57

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     There is a broad cross-sectional interest in the proper
design and operation of combined sewer overflow regulators.
Consulting engineers - general design of facilities; pollution
control personnel - monitoring facilities to determine the
nature and extent of the pollutional load to receiving waters;
industrial representatives - to design and build the actual
regulator; and local governmental officials - to bridge between
these three groups and to pay for the facilities.  Payment is very
important inasmuch as for this portion of the pollution control
program, federal and state aid is not generally available to
assist local government in financing the construction and recon-
struction of facilities that will lead to a reduction of this
source of the pollutional load.  Lack of such aid is somewhat
unique and, undoubtedly, is directly responsible for the fact
that relatively little work has been accomplished at the local
level to implement the types of pollution control programs which
have been advocated and demonstrated by the Water Quality Office
in the field of storm and combined sewers,.  Construction grant
funds from EPA have been available for only a handful of facilities,
                              58

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where  essentially  primary treatment will be accomplished.

      It  is  appropriate  to consider the  "of.ficial policy" re-
garding  combtned sewers.  For many years it appeared that the
official  policy of the  federal government was that combined
sewers would  be separated.   In 1967 the APWA completed  its report
on  the extent of combined sewer facilities with a cost  estimate
of  $48 billion in  1967  dollars to separating systems involving
some  36  million persons.  It appears  that generally the Washington
officials are now  convinced  that separation alone is not the
solution, though the word has not necessarily been reached, or
been  adopted  by the regional offices, as we still see results of
conferences which  will  require separation of combined sewers on a
wholesale basis.   Other federal agencies such as DOT and HUD have
also  geared their  programs to further the separation of combined
sewers.   This becomes particularly ironic as the extent of storm-
water pollution becomes evident and in  some areas we begin to talk
or  require  treatment facilities for stormwater.  A great deal of
rethinking  appears warranted at this  time before actually establ-
ishing a national  policy.  From the work that the APWA  has accom-
plished, it has been shown that storm waters are polluted whether
or  not they are carried in separate or  combined sewers  and that
to  meet  receiving  water quality standards, treatment or control
facilities  may be  necessary.

      Consulting engineers and local government officials in consid-
'ering the combined sewer overflow regulator facility problems
should begin  by defining their needs, particularly in measurable
terms.  For instance, a general need  is to either reduce or elim-
inate pollution from combined sewer overflows.  The need might be
based upon  a  requirement to  improve receiving water quality, to
improve  the value  of land adjacent to the overflow, to  improve or
make  possible operation of treatment  or control facilities, or to
                             59

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improve operation of the treatment plant.  The need, then, must
be defined in terms of how much or the extent of actual improve-
ment required.  Means must be available to determine whether or
not the desired goal has been achieved.

     If our desire is to reduce pollution, we should determine
whether or not the economical solution is to reduce flow in the
combined sewer by a system of surface storage, in-system storage
or treatment of the overflow.  The type and size of the regulator
will vary considerably depending upon the nature of the treatment
or control device.

     Criteria for the operation of the regulator traditionally has
been to limit flow to the interceptor.  I would like for you to
consider, however, the concept of the Two Q's, control  of quality
and quantity of the overflow.  Regulators can be classified as
either static or dynamic.  If they are static, they perform in a
determined manner, and are unresponsive to changes in control  levels
in the interceptor or changes in the quality of the sewage.  Dynamic
regulators, on the other hand, can be designed to be responsive to
a variety of flow conditions and flow characteristics.   The reg-
ulator must be responsive to flow both in the interceptor and
collector sewer, the maximum pollutional  load should be diverted
to the interceptor sewer, there should be no dry weather overflows,
there should be low maintenance cost, and a low initial cost is
desirable.  Operation of the regulator must be responsive to
changing conditions.  Quality of overflow may be improved by
screening, use of secondary motion, or the mode of operation.
Choice of the individual  regulating device to be used will  be influ-
enced by space required,  availability of access, outflow conditions,
head-loss within the regulator, and exterior power requirements.
All must be evaluated and considered.
                               60

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The major findings and recommendations of the APWA study were:
                     .'       .     •                ..ซ,'.:.i ,

Efforts should be made by local jurisdictions to consolidate
minor overflow points into fewer locations, in which the
installation and maintenance of sophisticated regulator
devices and controls will be economically and physically
justified.

"Total systems" management of sewer system regulator-overflow
facilities should be instituted wherever this procedure can be
shown to be feasible and economical.  This will involve the
use of dynamic-type regulator devices and the application of
instrumentation and automatic-automation control methods
which will be expedited by a reduction in the number of over-
flow points.

Dynamic-type regulators should be used wherever possible and
feasible for "traffic control" of combined sewer flows.  This
could shunt surcharges of.portions of such a system into sec-
tions of sewers which are not simultaneously so affected.  This
approach could be enhanced by the monitoring of precipitation
and sewer flows through an adequate network of stations, in
communication with a central control point from whence flow
routing decisions can emanate.

The type of regulator used should be determined on the basis
of its performance and potential reduction in overflow pol-
lutional effects.

Maintenance schedules and budgetary appropriations should be
planned on the basis of the specific need's of static, dynamic
and instrumented units in service.  Each type of regulator
should be given the attention it requires to achieve maximum
                       61

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performance.

Regulator facilities should be situated in accessible locations,
provided with safe and dependable access facilities, be free of
other safety hazards, have adequate space for necessary mainte-
nance work and, when possible, be accessible from locations
other than the street or highway right-of-way.

Maintenance crews should be adequately staffed and crews should
be provided with all necessary service equipment and tools for
their work and for their protection.  In-service training should
be provided and preventive maintenance schedules should be estab-
lished.  Records of maintenance work must be accurate and com-
plete in order to assess properly the effectiveness of regulator
operations and to allocate budget costs for each specific main-
tenance and operation procedure.

Specifications must require the use of the most servicable
corrosion-resistant and moisture and explosion-proof materials
in the fabrication and installation of regulator devices and
control facilities."  The number of movable parts and appur-
tenances should be reduced as much as possible, commensurate
with efforts to provide greater sophistication of regulator
facilities.

Where possible, tide gates should be located in adequate cham-
bers.  In cases where system control of regulator-overflow
networks is  provided by automatic-automated means, the prox-
imity of tide gates with regulator chambers will  facilitate
the tie-in of backwater control with overflow control.   State
and provincial  water pollution control  agencies should incr-
ease their regulatory control  of this source of pollution and
provide standard requirements and the engineering personnel
                        62

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     necessary for enforcing the control  of overflows from combined
     sewer systems.  Further, such agencies must recognize the fact
     that existing combined sewer systems must be upgraded if pol-
     lution levels are to be reduced.

     Efforts should be made to design  regulators to minimize .clog-
     ging and consequent pollutional  overflows.  Where clogging is
     inevitable, maintenance schedules should be adapted to correct
     this condition as expeditiously as possible.

     As indicated, interest by various states in regulators and
overflow pollutional problems vary considerably.  Few states have a
staff knowledgeable enough to give much guidance to local officials
or to even review plans.  Many states  appear to want to believe
th'at if they do not get too concerned about the problem, it will
go away.  Many seem to be taking the textbook advice that combined
sewers are a thing of the past.  Inasmuch as over 30 million people
are directly served by combined sewers with some 18,000 overflow
points, I doubt that this represents much more than wishful thinking.

     At the close of the research project the APWA developed a
Manual of Practice.  There is a great deal of heretofore unpublished
work in it, which represents good practice in the field.  Certainly
you and the public agency which you serve should review the Manual
for information regarding requirements for the design, operation
and maintenance of facilities, as well as a description of'some
of the newer types of regulating devices.  Many of you will have  a
very difficult time convincing an agency that they should pay more
than the $2,000 to $4,000 cost of a static regulator device.  How-
ever, if pollution is to be  reduced, time and money  spent on the
design and  construction of adequate regulator facilities will do
much to enhance the local program.
                               6.3

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                     SECTION IV
                   PRESSURE SEWERS
                         by
                 Italo 6. Carcich
             Senior Sanitary Engineer
New York State Dept. of Environmental Conservation
        Environmental Quality Research Unit
                 Albany, New'York.    .
                           65

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Introduction



          The pressure sewer concept has been around for a number of years.



When referring to pressure sewers, we are dealing with a wastewater collection



system that utilizes a newly developed Grinder Pump Unit and small diameter



plastic or metallic piping systems.  It is by no means intended to replace



gravity sewers but only to supplement the wastewater collection system.



          With financial assistance from both the State and Federal governments,



a 13 month study was completed in Albany, New York for the purpose of evaluating



the functional specifications of the GP Units and to gain first hand operating



experience on the mechanical performance, use pattern, operating cost, main-



tenance requirements, etc. on these units.  The final report is available from



the U. S. Government Printing Office^ '.  A full description of the installations, .



the monitoring equipment, the piping system, etc. was published previously^2'.



          Therefore, it is not necessary to go into a detailed description of



the installation, with the exception of stating that the pressure sewer system



was very simple in design.  The wastewater was diverted to the Grinder Pump



Unit's tank from which point it was discharged by means of a 1-4" plastic pipe



pressure lateral to an outside 1-j*' to 3" plastic pressure main.  The pressure



main at a 4 foot depth received the macerated wastewater from all 12 houses



and simply discharged it into a gravity system within the city of Albany (Figure l).





Grinder-Pump Units



          The GP Unit consists of the following mechanical components (Figure 2):



(a) Grinder, placed in an inverted position and operating at 1725 ppm with the



capability of handling foreign objects without jamming;  (b) Pump, positive dis-



placement, progressing cavity type with an almost vertical H-Q curve and proven
                                   66

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-------
                   FIGURE 2
CROSS   SECTION   OF   GP  WITH   LOCATION   OF
 LEVEL  AND   OVERFLOW  RECORDING   FLOATS

                                   STEEL TANK-
                      	BELL SHAPE
                       PRESSURE SENSING
                          TUBE
     GRINDER MECHANISM
                                                 DISCHARGE PIPE
                                               ISULATED HOOD
                  3.8* O...IA.T.*
                                                  OVERFLOW  RECORDING
                                                          FLOAT .:
                     68

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solids handling ability;  (c) Motor, 1.0- horsepower, operating at 1725 RPM,



capacitor start, 'high : torque, '-squirrel cage induction motor with a 'built-in



thermal overload protector;  (d) Check Valve^ swing check type with passageways



smooth .and free from roughness, and obstructions, and a unique flexible hinge



c-f small section without mechanical pins, rivets, .screws, .etc;  (e) Controls,



an inverted diving bell system  to -turn the motor on and off.


                                                                   (3)
          A li inch discharge pipe was selected as the optimum size    capable



of not only handling the macerated wastewater without clogging but also



minimizing the frictional head losses (Figure 3).





Results • .  • .        ,  ,   /.     ..                       •; . .  ,  . . ' ; •  .  •   ,



          Thirty nine out of the 44 recorded malfunctions were contributed by



the Prototype GP Units.  Nine of these Prototype units were replaced by



Modified GP Units (Figure 4) after only 6 months because of the large  number



of malfunctions.  The newer units performed .satisfactorily for the remaining of



the project.  Loss of prime by pump and grease  clogging  of the 1" opening



within the bell-shaped pressure sensing tube was the major cause  of the mal-



functions experienced by the Prototype Units.   Corrective modifications were



incorporated  in  the manufacturing  of  the  modified GP Units with considerable im-



provements  in the daily operation.



          One of the primary interests of  this  project was to extensively  test



the reliability of  the mechanical  components in an  actual field  installation.



Pre-installation testing and post-installation Resting  (Table l)  was performed



in order to determine marked deterioration if any, in. the physical  structure  arid



performance of  the  GP  Unit's  components.
           In addition to  the 6282 'operations ^occurred during the so-called
                                   69

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          V-V = 4.5 f ps
to 3
O ฐ
o
cc
u_
     V=2.5fps
   -  ^=1.8
            GP Units  NORMAL OPERATING RANGE
                      J.
         10    II      12     13     14    15
           DISCHARGE- GALLONS PER MINUTE
            FRICTION LOSS vs DISCHARGE
               FOR THREE  SIZES OF
               POLYETHYENE PIPE

                 FIGURE  3
                   70

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4" INLET
I . H-P MOTOR
PRESSURE
SENSING TUBE
                      FIBERGLASS   TANK
                      	 24.00" DIA. 	
             CROSS-SECTIONAL   VIEW
              OF  MODIFIED  GP  UNIT
                     FIGURE  4
                         71

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to  3
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de-bugging period, a total of 73,458 GP Units operations were recorded during


the remainder of the demonstration project  (Table 2).


          Even though the operating cycle varied greatly for the prototype


units, the modified units operated on a cycle between 57 and 74 seconds (Figure 5),


with the average operating time of 11^5 minutes -to . 27.5; minutes per day.  Further-


more, based on the occupancy rate of 75 persons for the 12 town houses, a value


of 2.6 operating cycles per capita per day was calculated for-this particular


single family residential development.          .


          The documentation of the .operating cost was of prime interest, since


it was essential to verify the theoretical cost value of $2.12/year for a

           (34)                      ,
family of 5V '  .  Two watt-hour meters were installed to register only the


total power consumption of two individual GP Units.  Based on the monthly oper-


ating time, proportional monthly power consumption values of 10.2 and 5.3 KW


were calculated.  Applying an average incremental power consumption rate of


2.3$ per kilowatt hour (KWH), the monthly operational cost for Unit No. 1


amounted to $0.24 and $0.12 for Unit No. 2 (Figure 5), which is equivalent to


$1.18 for a family,of 3,up to $3.50 for a family of 9.


          The GP Unit's usage varied greatly from day to day for any given unit.


An even greater variation was documented when comparing weekday versus weekend


usage.  This is graphically illustrated in Figure 6 for two given units.  The


total weekend daily usage exceeded ::,the weekday total .daily usage by 50-60


operations (an;increase of 35% over the weekday total).


          As an indication of the improved performance record of Modified Units


versus the Prototype Units,; a value, known as;the, "downrtime", was computed for


each of the GP Units.  The "down-time" value is based on the amount of time a


unit was non-operational over the total amount of time of possible operation.
                                   73

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                      76

-------
The Prototype GP Units produced a "down-time" of 2.69% for the first six

months in comparison to; only 0.27% for the Modified Units over the last ?•ฃ

month period.


Discussion.

          The pressure sewer system pipe sizing was based on the ASCE minimum
                                    (5,6)
scouring velocity criteria of V  =ฃ•ฃ     and on certain engineering assumptions
      i    ••••;'             .2
regarding the estimated wastewateir flows from the 12 GP Units.

          It must be understood that the flows in the different portions of the

pressure main were based strictly on an engineering estimate.  There was no

data available on the frequency of GP operations for a multiple units system.

It wasi'possible to predict the peak usage hours of the GP Units, but since the

operating cycle per GP Unit is very small,: 57 sees, to 74 sees., it was almost

impossible to predict the number of units working simultaneously during this

peak period.  It was, therefore, assumed that a maximum flow of 90 gpm would

flush regularly that portion of the pressure main serving all 12 GP Units.  It

must be understood that the hydraulic characteristics of the pressure sewer

system is dependent greatly on the varying wastewater flows within that system.

           Information on simultaneous occurrences was an essential phase of

the project.  This type of data is critical for the design of future pressure

sewer systems.  The maximum anticipated flows will dictate the size of pipe

within the pressure system.  At the same time, the hydraulic gradient will

reach its peak slope.  The engineer, therefore, must design a system optimizing

the sizes  and scouring velocities and be certain that the upper recommended

working pressure of the GP Unit is not exceeded.
          v                   •'              - ,'        . •   '   '  '
          During the last ten (10) months of5' the demonstration project, during

which time the 12 channel event recorder was in operation, a total of 58,823


                                   77

-------
 operations were recorded, which represent approximately 191 operations per day.



 Therefore, in order to obtain a picture of the minimum and maximum flows within



 the pressure system, the above mentioned data indicated that  (a) on the average,



 2 GP units ran simultaneously 20 times per day • (b) 3 GP units operated simul-



 taneously slightly more than once per day, and  (c) 4 GP units ran simultaneously



 on the average of once every 14 days.




           Also, by using all the automatically recorded data,  total wastewater



 flows were calculated, which ranged between 95 and 100 percent of the actual



 water consumption (Figure 7).




           The close relationship between the water and calculated wastewater



 flow is a highly reliable indicator of the corresponding wastewater discharges.



 Also,  winter water flow records  can be used  to.estimate accurately expected



 wastewater flows.




           Pressure gages were installed in each basement so  that  the  maximum



 and  minimum pressures  occurring  during any fifteen minute  period  might  be



 recorded.   These pressure readings  were indicative of  the  varying hydraulic



 gradient  line  for  each of the twelve  GP units  (Figure  8).  The  computerized



 data indicate  that pressures  in  excess of  30 psi were  reached by  a  few  GP



 Units.




           Once  the  demonstration phase of  the project  was  completed, portions



 of the pressure main and  the  1^-  in. pressure laterals  were carefully excavated



 and  removed.  Grease accumulation within most sections was evident.  Reductions



 of up to 40$ occurred  in  the pressure  main.




          The system was  simply overdesigned.  Where flows were expected to



reach 90 gpm regularly, flows of only  45 gpm were recorded (Figure 9).  Therefore,



instead of a 3" pressure main, a 2" main would have been sufficient for the 12



town houses.




                                  78                    .       .

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         80

-------
                             FIGURE 9         ;

     ASSUMED AND ACTUAL FLOWS FOR THE PRESSURE MAIN
          "  :   1, V    _    '"	     PROP. LINE
                         _ .    -—
TRLRi
      726 728 730 732
         SAMPLING a
^^^ SECTION NUMBERS
'"72 II 10 9 B'l ~ 7 65 4 3 2 1 _
' II 1 1
12
1 1
IO
' 9. .;,

Ill 1
'•-••'•
7
,.6;
5

4

1
3
2

I
         CONTROL BOX
734  736 738  740 742
STREET ft  PROPERTY LINE
                                                  744 746 748
    M.H.i
SECTION
NUMBER
1
2
3
4
5
6
7
8
9
!0
II
12
PVC-DWV
PIPE SIZE
1.25"
2.0"


,


1
3.0"




•







LENGTH OF
SECTION
(FT)'
19.7
20.0
59.2
19.2
19.5
19.6
1.9
58.5
1 7.4
" 19.5
2.7
81.0
ASSUMED
MAX.
FLOW
(GPM)
15
30
45




60

1


75




90
MAX.
FLOW
RECORDED
(GPM)
15
30
45





'
60









f
ASSUMED
MIN.FLOW
IN 24hrs
(GPM)
15
- |
\
30




45




60



f
DAILY FLOWS (GPM)
MAXIMUM
15
30
*
45
















AVERAGE
15
30




















MINIMUM
15









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.

                           81

-------
                                 TABLE g

              SUMMARY OF COMPOSITE SAMPLE ANALYTICAL RESULTS
Parameter
5 Day Biochemical Oxygen Demand
Chemical Oxygen Damand
Soluble Total Organic Carbon
Total Solids
Total Volatile Solids
Total Fixed Solids
Total Suspended Solids
Volatile Suspended Solids
Fixed Suspended Solids
Total Dissolved Solids
Volatile Dissolved Solids
Fixed Dissolved Solids
Organic Nitrogen**
Ammonia Nitrogen**
Nitrate Nitrogen**
Total Phosphate***
Particulate Phosphate***
Filterable Phosphate***
Total Ortho Phosphate***
Methylene Blue-Active Substances
Grease
Settleable Matter & Hr.
Settleable Matter 1 hr. '
Chlorides
Hardness
Alkalinity
PH
Number
of
Samples
• 57
56
6
55
56
56
56
56
56
55
55
55
53
54
38
63
50
51
32
39
9
56
56
38
55
9
54
.. Mean*
330
855
140
681
476
205
310
274
36
372
201
171
29
51
0.1
15.9
2.8
13.1
8.7
12.4
81
14.5
15.0
52
65
198
7.8
Standard
Deviation
53
158
49
87
84
63
77
84
48
90
62
58
12
9
-
6.3
0.9
6.5
3.9
4.5
12.3
6.1
6.2 '
4
7.4
8.1
.3
Minimum
Value
216
570
21
526
336
57
130
78
0
195
22
27
7
34
—
7.2
0.4
5.2
1.3
4
31
4
4.5
41
46
185
7.1
Maximum
Value
504
1450
225
928
706
355
468
440
268
637
372 ;
353
76
68
	
49.3
4.2
47.9
17.9
24
140
37
38
61
90
209
8.7
*     All values expressed as mg/1 except pH
**    As nitrogen
***   As phosphorus
****  As linear alkylate sulfonate
                              82

-------
          There are no existing standards for velocities dealing with the




grease accumulation problem, even though velocities in the range of 2 fps to



8 fps have been used by some in designing wastewater pressure conduits.  However,




for a pressurized sewer system utilizing GP Units, a velocity range of 2 fps to




5 fps is hydraulically and economically preferable.             =     .



          Extensive chemical analysis were performed (Table 3).  The concentra-



tion of various pollutants in a pressure sewer system was found to be approxi-



mately 100% greater than those found -in conventional systems.  On a gm/capita/day




basis the pressure sewer waste contained approximately 50% less contaminants




than reported for conventional domestic sewage.   Settleability tests show no




significant differences when compared with conventional wastewater.



          Therefore, the difference in the strength must be taken 'into account




in designing treatment facilities for a pressure  system.






Conclusions



          The pressure sewer system, which included the .usage of PVC Schedule




40 pipes  and PVC-DWV fittings, functioned well for the duration of the demon-



stration  project.  Careful  considerations must be given to the material used



in backfilling pressure main trenches.  A good engineering practice is to en-




case  the  plastic pipe in sand.



          As for the GP Units, the 'functional specifications have proven to



be appropriate.  Even though the Prototype Unit  exhibited low mechanical



reliability, the Modified GP Unit operated to its expectations.  Pesign mpdi-



ficationS virtually eliminated all major malfunctions; that  is, the 1" opening




of the pressure  sensing tube was increased to 3"  and  the pump was relocated  so




 as to be  positively primed.
                                  83

-------
          The service record  coupled with the "down-time" performance of the



Modified Units was  impressive, a 0.27% "down-time" value versus a 2.69%




"down-time" value for the Prototype GP Units.



          Both the  pump size  and tank volume were more than adequate to handle



peak wastewater flows, so that no further design modifications are necessary



in this area.



          Therefore, in order to summarize the operational performance of the



GP Units, a brief review of previously presented facts has been tabulated;



          (l)  Total Number of GP Operations for the duration of the project -



               73,740 operations



          (2)  Average Operations per capita per day - 2.6



          (3)  Average Length of operating cycle - 57-74 sec.



          (4)  Electrical power consumption cost - 34
-------
































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85

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-------
           SECTION V
APPLICATION OF MICROSTRAINING TO
    COMBINED SEWER OVERFLOW
     George E. Glover, P.E.
        Research Engineer
  Cochrane Division-Crane Co.
                 89

-------
       Combined sewer overflow is a mixture of stormwater and sanitary flow.




The special problems of dealing with this flow are due   almost exclusively




to the stormwater component.  Thus, these remarks should apply equally well




to overflow of separate storm sewers.




       The two components - stormwater and sanitary waste - are somewhat




similar in composition.  Both contain suspended solids, BOD, and coliform




concentrations equal to many times the usual secondary effluent standards.




On an annual basis our eleven acre drainage area produces some 9,000,000




gallons  of sanitary flow and about 3,000,000 gallons of storm runoff.




       The flow rate of stormwater runoff,  however, is very high and widely




variable.  At our site, we have monitored several storms a year where the runoff




rate is over 400 times the mean dry weather sanitary flow.  It is the flow rate




aspect of combined (and separate) sewer overflow that requires a totally




different approach when treatment is considered.




        Only recently have we become aware of the magnitude of the possible




pollutional load from stormwater runoff and have considered treating it.  It is




not surprising that there is a considerable difference in opinion as to what a




stormwater treatment facility should be able to do.  The two basic dimensions




of a combined sewer (or separate storm sewer) overflow treatment facility are:




        (a)   The  instantaneous flow  rate it can handle,  and




        (b)   the amount of each type of pollutant it can remove.
                                90

-------
        In our studies we have used a flow rate of 2.0 cfs/acre (1.34 mgd/acre)




as the required instantaneous capacity of the treatment facility. This runoff




rate would require (at a runoff coefficient of 0.4) 4.5 inches per hour rain




intensity.  At our site we have this intensity sustained for about 15 minutes




every 10 years. Analyses  of very large drainage areas such as the Boston and




Chicago stormwater tunnels where rainfall does  not occur over the entire  area




simultaneously, and where there is tremendous surge volume within the sewer




(tunnel), have led to the adoption of a flow rate of.0.2 cfs/acre (0.13 mgd/acre)




based on the area  of the entire basin.  Less understandable is the adoption of




low (0.2 -0.3 cfs/acre) instantaneous design rate for the treatment of combined




sewer overflow from small drainage areas of 100 acres or so.  Additional




experience will permit the  selection of realistic design rates for each  situation.




        It has been suggested that flow equalization basins  be included above




ground as part of the overflow treatment facility to reduce the peak instantaneous




flow rate.  Above ground, flow rate equalization basins by themselves may be




an attractive scheme of treating overflows, providing space at low cost is




available.  In this scheme, the  peak overflow rate is reduced to a rate where




the existing interceptor sewer and sewage plant can handle  it as an alternative




to an on-site combined  sewer treatment facility.  Although the annual  stormwater




volume  is some 35% of the sanitary volume,  only some 15%  additional flow rate




capacity would be required.




        Flow equalization is most attractive where the subsequent treatment




techniques are very expensive on a dollar/cfs peak capacity basis.  Flow
                                91

-------
equalization is essential where the subsequent treatment techniques cannot


accept sudden starts and stops or rapid changes in flow rate of several


hundred times the dry weather flow variation.


       The extent of treatment to be required on combined sewer overflow is


at present not standardized.  It is  not certain what form regulations will take.


As will be seen later the familiar "percentage removal" type regulation would


be most inappropriate for this  problem.  Much more work and study must be


completed before it can be decided whether it is necessary or consistent with


the cost to design overflow treatment facilities for a 25, year return storm or a


5 year return storm.


       With current practice,  the combined sewer overflow regulator is adjusted
                               !                 '                   •'

to overflow when the rate exceeds  perhaps 3-5 times the mean dry weather flow.


Thus, the composition of the combined sewer overflow is 1 part sewage to at


least 1-1/2 parts of storm runoff.  Frequently the composition is over 100 parts


of storm runoff to 1 part of sanitary flow.   In any event, when significant  over-
                                                                *
flows occur,  the composition of the overflow water is determined almost


exclusively by the composition of the storm runoff.


       The wide range of contaminant  levels in the combined sewer overflow


reflect the breadth of the range in the storm runoff.


       The contaminant level  in the combined sewer overflow observed in our


site is shown in Table 1.
                                    92

-------
                                    Table 1
Contaminant

Suspended solids mg/1

BOD5            mg/1

Total coliform
cells/100 ml
.Minimum

  . 15

    8


1,000
  Mean

    100

    800
Maximum

  ' 700

  3,000
1,000,000    3,000,000
       Previously we had found (during the fall and winter storms) that,  in

general,  the contaminant concentrations were higher on the bigger-storms

particularly in the case of the suspended solids.  Recently, however,  (during

spring and summer storms) we found little relation between storm intensity and

contaminant levels.  The BOD and coliform content of overflow do not seem to

have any relation to storm intensity but do seem to have an annual variation.

Each drainage area has no doubt a unique combination of features which will

influence the character of the stormwater overflows.  Our experience, however,

has been paralleled by the reported observations of others.'    They find that

sustained higher contaminant concentration levels are as likely if not more

likely to occur in large overflows from the bigger storms as from the smaller

overflows from less intense  storms.

             Thus, the treatment design criteria and the regulations  must, for

the present, assume that maximum overflow contamination concentration will
                                    93

-------
 exist at design peak flow rate.  More work is needed on this aspect.




 To attack a given combined sewer overflow situation, the first step is to predict




 the peak rate-duration and frequency of the actual overflows.  With these




 predictions at hand a decision to treat all storms of less than a certain return




 frequency must be made more or'less arbitrarily. One method of arranging the




 storm flow data is that  used by Dow (2).  See Figure 2 from that report.  Note




 that treating about one-third of the peak,flow observed  over an 8 year study




 would treat some 98% the total annual flow.




        The benefit of flow equalization can be evaluated for the "storms to be




 treated. That is, the relation between equalization basin volume and the reduced




 peak rate can be ascertained.  This work  might be extended to, say, 60  minutes,




 which will be the residence time of some  of the  actual treatment techniques. We




 will return to this flow rate consideration after we look at the degree of treatment




 needed.




        There is paucity of information regarding the impact of combined  sewer




 overflow contaminants on the receiving  stream.  It seems that the pounds of




 suspended  solids discharged per year would be an important criterion.




        It is not  known how much greater impact these solids would have when




 they are discharged in slugs  of approximately 40-60 hours annual  duration.




 If it  is found that the instantaneous rate of solids discharge is significant, the  "




regulations may be phrased in terms of maximum pounds per hour.  This ;is a,




very complex problem and the methods of considering it have not been developed.
                                    94

-------
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                                                5
96

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       The potential pollutant load of untreated combined sewer overflow during




a big storm is:  (Overflow Rate) x (Pollutant Concentration; e.g. , S.S.).




       The potential load can be reduced by treatment to a lower level, depending




upon the design of the treatment facility as follows:               •




       (Overflow Rate-Peak Capacity) x (Pollutant Concentration) plus




       (Peak Capacity) x (Pollutant Leakage).




       Figure 1 is a preliminary attempt to illustrate this relationship in a




stylized manner. The  bars represent overflows in increments of magnitude.  The




height  of the bar represents the magnitude of the flow (the left of the pair) and




of the instantaneous contaminant flow; e.g.,  pounds of  suspended solids per




second.  The width of  the bar represents the duration of flow of the indicated




magnitude in minutes per year.  The area of the bars  then represent overflow




volume per year at indicated rate  (left of pair) and the pounds of contaminant




per year/.; The  shaded  area at the bottom of the solids bar represents the solids




leaking through treatment facility and entering the stream.  An arbitrarily selected




design peak flow rate for a treatment facility  is shown.  The  shaded area on the




solids  bars representing the biggest storms shows the additional solids,entering




the stream by direct bypass of the facility.




      The amount of the annual contaminant load to  the river of the design




parameters - peak flow capability of the facility and the leakage through the




facility can be seen.  Also, the instantaneous rate of contaminant discharge can




be seen.
data.
       Figure 2 shows another way to consider the overflow rate-annual duration
                                    97

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       In the previous application section, I have attempted to show the


importance of Peak Flow Rate Capability of a combined sewer overflow treatment


technique  (s). Also I tried to show the importance of Contaminant Level Removal


Capability of treatment techniques at design (peak) rate and below design rates.


       The announced subject of this paper is  a description of the capability


of the Microstraining technique  in this service.

                                     of
       Figure 3 is an isometric  drawing^a  micros trainer.  A microstrainer is a
                                     A

rotating drum fitted with fine screen. For  stormwater the screen used is what


we call Mark 0, a stainless steel Dutch twill screen with 600 x 125 wires per


inch yielding about 23 micron (1-1/2 millions of an inch) apertures.


       The stormwater enters the  open end of the  drum and passes through the


screen into the outlet chamber and then to waste.   The suspended solids are


retained  by the screen.  As the drum rotates, the  screen with a mat of retained


solids on the inside is brought up and under a row of backwash jets which wash


the solids  off into a hopper and  thence to disposal. The backwash water


requirement is about 1-1/2 gpm  per foot  of drum length which is a fraction of


a per cent  of the thruput capability. The solids-rich backwash water stream


is small  -  less than the  DWMF - and can easily be sent via the interceptor


to the sewage plant, for smaller CSO facilities, or disposed of locally. The

                                                                      "•"lyj'
backwash water source can be re pumped microstrained CSO or preferably city


water on small unattended satellite facilities.


       The flow of water through the screen is motivated by the difference in


level inside the drum over the level outside the drum.  In conventional applica-


tions of Microstraining this differential is about  6 inches. At this differential


                                    98

-------
              .Figure'3



Isometric Drawing of a~ Microstrainer
                  99

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the Mark 0 screen will pass only about 6-8 gpm/ft2 of gross submerged screen




area.  It might be noted here that the flow capability is not based upon the gross




area of the drum but rather upon the open submerged area.  That is, that area of




screen unimpeded by hold-down straps which lie below the liquid level inside




the drum. There is considerable difference in the per cent submergence attained ,




and the per cent unimpeded area in currently available micros trainers and the




percentages vary a little from size to size.  In the Current Crane design for a




10' dia x 10' long drum, the per cent submergence is 83% and the per cent




unimpeded area is 94%.  The'Glenfield-Crane (older) design we are using has




only 83% unimpeded area and was adapted to achieve  83% submergence.   Some




competitive designs have lower percentage submergence and unimpeded area.




       For stormwater service we use much higher differentials,  up to 24", and




have achieved flow rates of up to 45  gpm/ft2 of gross  submerged  area (i.e. ,




54 gpm/ft^ of unimpeded submerged area) with very high removals.




       The following remarks will be based upon 35 gpm/ft2 of gross submerged




area (42 gpm/ft2 of unimpeded submerged area).  Also, these remarks will be




based primarily on the use  of a  microstrainer as a satellite station for treatment




of CSO; i.e., located at the point of  overflow so that  no additional sewerage




is required.




       Perhaps the best way to describe a microstrainer CSO facility is by an




example.




       A present-day Crane 10  x  10 has  314 gross sq  ft of screen area of which




245 sq ft is unimpeded and  submergible.  Such a machine can treat some
                                   100

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 10,500 gpm or 23 cu ft/sec of any of the combined sewer overflows we have


 seen in 16 months of study.  Our example will be a facility with two such


 machines in parallel.   (As previously mentioned,  the 46 cfs  (30 mgd) flow


 capability of these two machines would be required by a drainage area of from


 24 to 240 acres depending on many factors unrelated to the microstrainer.)


        Any CSO treatment facility will require a coarse bar screen.  The space


 for and the cost of a travelling bar screen have been included in this example

                                                              ซL
 facility. Almost certainly any CSO'treatment facility will be sizeAto treat


 something less than the peak storm that will occur in the life of the equipment.


 Thus/ a bypass  arrangement is. required to divert  the flow in excess, of the peak   • •


 capacity of the treatment equipment without interfering with the capability of


 the equipment to treat its peak flow.  This consideration may be less important


 with Microstraining than with other techniques .     A microstrainer will flood;


 i.e., untreated water will  overflow the washwater hopper at inlet  levels 3" or


 so above the design level at peak design flow rate.  The microstrainer cannot,however,


 dump previously removed solids into the effluent under excess flow conditions.


 The  space for and the  cost of a bypass  weir and channel suitable to divert


 excess flow equal to  the design flow have been included in this facility.


 That is, this facility  can accept 92 cfs, treat 46 cfs without hinderance, and


' bypass the reaminder to the receiving  stream, or rather to the disinfection


 chamber, and then to the stream.   ,          -               ,


        ;The  bar :screen-microstrainer facility with flumes and chambers for bar


 screening of 92 cfs,  Microstraining of 46 cfs, and bypass of 46 cfs will occupy


 a ground area of 30 x 40 ft x 10 ft deep.  The facility area of 1200 sq ft of ground


                                     101

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  area is 1/35 acre cr about 1/1.000 to 1/10,000 of the drainage basin. The liquid




  volume of the facility is about 9,200 ft3, or 200 sec residence, at peak flow.




  The head loss through the facility is about 3 ft during peak flow.  While 3 ft  -,




  is the minimum head required during a storm, ideally there should be 10 ft of   ~




  head available so that the facility can be drained by gravity  after the storm.




  Otherwise, a small (3 hp) sump pump will be required.                    '




         The chamber will be comprised of about 2,500 sq ft of concrete walls




  and  1,200 sq ft of floor, and to put it below ground will require about 600 yards



  of excavation.                                        ...





        The microstrainer section should be housed  and kept above freezing.




 The recommended building then would be about 16' x 40' x  18' high.  The




 individual microstrainer units weigh about 13,000 pounds and an I beam




 craneway should be provided for installation and maintenance.  An insulated




 Butler Building of this size is included in the cost data.




        To keep the microscreen in condition to operate when  needed it must not




 be allowed to become dry while soiled.  The recommended procedure for




 combined sewer overflow service then is following a storm to  drain the chamber,




 continue the backwash of the slowly rotating drum using city water as washwater



 for several hours and then stop the  drum and the backwash water/




        Also, for sustained dry periods the drum can be rotated slowly for short




 periods at intervals under backwash jets and the  UV lights. The program controls




for carrying out this maintenance operation automatically are included in the



cost data.                                                            .     ,  .
                                    102

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     '- The'• cost of a complete facility installed, le'ss land and engineering, was

estimated to  be $195,000 in 1969 dollars* This investment represents an annual

capital "charge  of about $19 ,500/year ,to be "applied to the facility. •• This  annual

capital charge  is^,,-by far, the major.cost for Microstraining (or^ other techniques)  -

for combined sewer overflow.  This cost applied to the drainage area represents '

about $80 to  $800 per acre at peak design rating of .0.2 and 2.0 cfs/acre respectively.

       The effect of scale on the cost of a facility can be seen in. Figure 4.

       The utilities required for the two machine facility include about 50 gpm of ;

city water. The electrical power demand is for two 5 hp drum drive motors,, a

3 hp sump pump, if required, a 5 hp drive for the automatic bar screen rake, and

for lighting and controls - about 25 kilowatt connected load in all.  With 50 over-

flow events a year (we see only 40) ,  and several hundred short, dry weather

periods of operation, the running time then will be 280 hours  a year so that the

annual power consumption will be 7,000 kwh/year or abour $140/year.  Similarily,

the city water consumption will be about 14,000 gallons/year most of which is

consumed during rainy weather.                  '

    '  '' The microstrainer is  automated.  At onset  of storm overflow the liquid
                                            ,.',...    .        . .    _       ..jTi'... .•
level in the inlet channel rises and actuates a level switch which starts  the

microstrainer drum motor, -the backwash jets, turns on the UV lights, and the

bar'screen-rake drive.

.,, ~    The'microstrainer drum speed controls regulate the speed of the drum in

accordance, with the difference in liquid level across the screen which is roughly

proportional  to the flow rate.  All of the combined sewer overflow passes through
                                     103 :;

-------
               •  MICROSTRAINER a CONTROLS
               o  MICROSTRAINER  INSTALLATION a BLDG.
               O  MICROSTRAINER  INSTALLED
                    (LESS ENGR,,  LAND, PROFIT)
               O  120 SEC. CHLORINATION FACILITY
                    (LESS ENGR.,  LAND, PROFIT)
0               50               100
 CAPACITY OF FACILITY- CU. FT. PER  SEC.

                    FIGURE 4
                104

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 the drum.  If the storm flow should exceed the peak'design rate of the machines


ซ(i.e., cause a differential in excess of 24,") the excess water overflows the


 bypass weirs and flows directly to the receiving stream or to the disinfection


 facility and  then to the stream.  At the end of the storm, the program controls


 continue the operation of the microstrainer, sump pumps, etc. , until the chamber
                                                        '

 is drained and the screen is clean and then shut them down.  The instant


 readiness  and the very low residence volume of the Microstraining technique '


 permits unattended operation with very simple controls.  Our equipment ran on


 all storms under automatic controls.. It was unattended  during the first:part of


 all storms.  No trouble was observed.


        The  labor required for a facility would be weekly inspection and routine


 maintenance visits (i.e.,, lubrication, etc..) and it is believed that a two man


 crew could accomplish this in 2 hours.  The labor cost would be the cost of


 104 hours, or at $2.50/hour, $260/year.


        Maintenance supplies,  replacement parts, and maintenance labor (in


 addition to operation-routine maintenance labor) should, not exceed  1% of the


 facility cost per year.  We have no long-term experience on the screen life


 at high differentials/  however, it is believed that the original screen will serve


 for  10  or more years in stormwater sen/ice. The cost of re screening a  10 x 10


 is about $5,000.  Our experience over a 3 year period has indicated a  maintenance


 cost of less than 1% of facility cost, even if a screen change every 10 years is


 anticipated.           ,
                                     105

-------
        In summary, the annual cost of a facility having 490 sq ft of open

 submersible area (capable of treating 45 cfs) would be:
        Capital charge @ 10% of installed facility cost
        (less land and engineering)

        Utilities - electric power and city water

        Routine labor

        Maintenance and supplies @ 1% of installed
        facility cost
$19,500

     200

     250


  1.950
                                                               $21,900

        The annual cost of installing and operating a dual 10 x 10 microstrainer

 facility is -$22,000/year.  Such a facility will accept 92 cfs and treat 46 ,cfs .

 Depending on conditions previously discussed, such a facility would serve a

 drainage area of from 24 to 240 acres.

        The suspended  solids removal performance of a microstrainer on  storm-

 water follows a pattern that will seem strange to engineers  accustomed to other

 liquid-solid  separation techniques such as settling or granular bed filtration.

        A large portion  of the first increment of solids applied to the screen leak

 through before the mat  is established.  Most of subsequently applied solids are

 retained as shown in Figure 5.  Thus, those conditions that contribute to high

 solids loading; i.e., high potential pollution make for high  removals.  These

 conditions are high flow rate, high stormwater solids concentration and low drum

 speed.  It  may be repeated that the higher the flow rate and the higher the

influent solids, the  lower the effluent solids.  This latter relation is shown in

Figure 6 and  Figure 7.

       The suspended solids in the  stormwater at our site exhibited a surprising

                                    106

-------
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                    10              20

             APPLIED SOLIDS LBS. / IOOO FT. 2

                      FIGURE 5

          STORM WATER SOLIDS APPLIED VS.

          STORM WATER SOLIDS  RETAINED
                       107

-------



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109

-------
 characteristic.  The greater the concentration of solids the easier they were




 strained out. The permeability parameter is the flow rate possible at unit head




 loss; i.e., one inch of water head loss per inch of mat thickness.   The units




 of this parameter, borrowed from oil well practice, are inconvenient for




 Microstraining since buildup consists of mats of a few thousandths  of an inch.




 In any event, this permeability is a measure of the flow capacity of the machine




 within the differential limitation imposed by the  screen strength.




        In summary, we have found in two studies totaling about 22'months of




 operation at one site that the microstrainer will  reduce suspended solids from




 50-700 mg/1 down to 40-50 mg/1 at flow rates of 35 to 45 gpm/ft2 of gross




 submerged screen area; i.e.,  42-54 gpm of unimpeded submerged area.  These




 flow rates have been routinely achieved within an arbitrary  limiation of 24"



 of water differential between inlet and outlet liquid levels.




        The  removal of organic  and other oxygen demanding  material is shown




 on Table 2 to be 25-40%.   This removal is confirmed by BOD5, COD and TOG




 measurements performed by the Standards  Methods with and without  a maceration




 pretreatment in a Waring Blender.  The advantage of this pretreatment is covered



in the  formal report on this work.




       The  Microstraining had little or no effect  on the coliform  content of the



 stormwater.
                                    110

-------
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       The advantages of the Microstrai-ning technique for suspended solids




removal are:




       1.   Instant readiness and low residence volume permit simple




            automation for unattended facilities at remote locations.    :  ,",




       2.   Instant readiness and very high flow   rate capability/unit




            equipment cost permits installation without flow equalization



            basins.




       3.  The low head loss - 3 ft - through the entire Microstraining




           facility will generally eliminate the need for re pumping.




       4. • The removal performance of Microstraining, where highest




           removals,  both absolute and percentage-wise, are achieved




           at highest  flow rates and highest suspended solids loadings',




           is particularly suitable for the conditions  existing in combined




           sewer overflow servi ce.




       5.  The excess flow bypass is an integral part of a microstrainer




           facility and eliminates the need for this necessary feature




           as an appendage.




       6.  The very high flow rate capability and  low residence volume




           permit Microstraining to be the lowest cost solids removal




           technique - less than $500/year per cfs capacity.
                                   112

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  -' •    •                .  ACKNOWLEDGEMENT









        This work was conducted with the City of Philadelphia in two phases,




 (l) Under a contract from the Environmental'Protection Agency to the Cochrane




 Division of the Crane Co., and (2) under an EPA grant-to the City of




 Philadelphia.  The efforts Of City personnel were under the general direction




 of  Carmen Guarino, Water Commissioner,  with William Wankoff and M.




 Lazanoff,  serving,as Project  Director and Laboratory Director. -J. Radzuil




headed the .City's R and D Department who also lent valuable' assistance.




       The assistance and guidance of  these people are gratefully acknowledged.




       The overall guidance  and helpful advice of Richard Field/ Project Officer,




EPA, Edison, New Jersey, were  most valuable.               "
                                   113

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             SECTION VI
 HIGH-RATE MULTI-MEDIA FILTRATION
           Patrick Harvey
       Environmental Engineer
U.S. Environmental Protection Agency
     Region II, 26 Federal Plaza
        .New York, New York
                  115

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GENERAL

     The nature of combined sewer overflow, i.e., a highly pollut-
ional, high volume discharge, requires a relatively high rate treat-
ment process for economical pollution control.  Deep bed, high rate
filtration, a new development in the field of industrial wastewater
treatment, has demonstrated favorable cost-efficiency, factors when
dealing with high volume wastewater discharges/ especially where •
suspended solids comprise one of the principal contaminants.  Thus,
it was felt that such a process, which currently has significant
applicability and usage in the steel industry, might prove an effect-1
ive. and efficient solution to the treatment of combined sewer over-
flows .

     To evaluate the applicability and effectiveness of the high rate
filtration process in removing contaminants from combined sewer over-
flows, a testing program was undertaken at Cleveland's Southerly
Wastewater Treatment Plant, beginning in 1970.  The work was under-
taken by Hydrotechnic Corporation, Consulting Engineers, New York,
New York, under the sponsorship of the Office of Research and Monitor-
ing, USEPA.

     The City of Cleveland ranks seventh in the nation in total area
served by combined sewers ,(44,000 acres), and is fourth in pppulation
served by combined sewer systems  (1,000,000 persons).  As can be
expected, Cleveland has a, very serious problem of combined sewer over-
flows .
                                 ,116

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TESTING PROGRAM                                              '•••.'.'•-"•'

  ;'.,• The two major  process units or equipment units in the proposed
treatment  system are  the drum screen'and the deep,bed, high rate  .
filter.• The function of the -screen is to remove coarser material •
 (fibrous type,  etc.)  that would impede the filtration operation.
Construction of a full scale treatment plant employing the, process-'
sequence under  study  would require design parameters for the screen
and for the filtration process.  'The major criteria,for the screen
are screen type,  screen mesh,  and hydraulic loading.           "

  ,   The filtration system,  which is the heart of the overall process
sequence,  can be characterized and described by the following para-
meters :
-    ; Media'Composition  •  ,   .      Length of filter run  ,
 •'..•.' ' .Media. depth   •<,•':    ......   , Head loss      -•    ,  .•-..
   •: .Filtration rate       ,         Backwash water volume ' .    • '  ',•-•
  ,   Coagulant  -addition  ;        .  Backwash procedure         . ,  ,. ,

 ,    A definition of  these elements allows the construction,of a
full scale facility.                                      .-•.-,

     Testing'equipment at Southerly included a drum screen, two 5,000
gallon storage  tanks, lucite filter columns of four (4) and six;'(6)
inch internal diameter,  and chemical and polyelectrolyte feed equip-
ment.  .(Figures 1 and ,2)  . ••    ,       , ,  - -     ,-••-.    -.- • • - •

     The testing program evaluating the filtration components of the
proposed system was conducted primarily in two phases:  'first, evalu-
ation and  selection of system media and filtration rates, and secondly,
optimization of the filtration process via coagulants and polyelec-
trolyte addition prior to filtration.
                                117

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           Figure 1
       Lucite Filter Columns
          Figure 2
Drum Screen and Storage Tanks

             118

-------
filter run, and backwash procedure.

TEST RESULTS

     The recommended system is a drum screen  (No. 40 mesh screen
element) followed By a deep bed, dual media filter  (five feet of
No;.3 anthracite over three feet .of No. 612 sand).  Sixty-nine
pilot filtration runs were performed in 1970 and 1971 utilizing
this system.  Polyelectrolyte feed is an essential and critical
part of the system to achieve optimum treatment efficiencies.
Data utilizing coagulants ahead of filtration showed inconsistency
in treatment efficiencies and at the present stage of development,
polyelectrolyte feed alone appears optimum.

     The proposed system,, with addition of appropriate polyelec--
trolyte, achieved t;he following treatment performance:
     Filtration Rate                 Average Removals(%)      .
     (gpm.sq ft)           Suspended Solids    BOD    Phosphorous
          8
         16
         24
96
95.
93
43
40
40
66
57
46
         average influent suspended solids concentration ranged
from 50 to 500 mg/1 and the average influent BOD concentration
ranged from 30 to 300 mg/1.  Effluent 'levels at 24 gpm/s^ ft with
polyelectrolyte addition were 15 mg/1 suspended solids and 22 mg/1
BOD, respectively. '(Figures 3, 4, and 5)
HIgH RATE. FILTRATION -INSTALLATION  - "   -  ,           '\

     Combined sewer overflows would be conveyed from an automated
overflow chamber, or chambers (in case the centralized filtration
system is for many overflow points) , to a low lift pump station.
                               119

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     Filtration media evaluated included:  four or five feet of
anthracite over three feet of sand.  The characteristics of the
media are indicated as follows:
Media Effective Size Uniformity Coefficient
No. 4 Anthracite 7.15 mm.
No. 3 Anthracite 4.0 mm.
No. 2 Anthracite 1.78 mm.
No. 612 Sand 2.0
No. 48 Sand 3.15 mm.
Screen meshes tested included:
Mesh Screen Screen Opening Tyler Screen
Designation microns/inches Scale Equivalent
(mesh)
No. 3 6350 0.025 3
No. 20 841 0.0331 20
No. 40 420 0.0165 35
1.42
1.5
1.63
1.32
1.27
Open Area
(%)
57.6
43.6
43.6
     The filter tests were directed to determine the degree of
treatment that could be achieved by using different depths and
composition of filter media when operating at different flux rates,
with and without the application of coagulants and polyelectrolytes.
Using the results of the tests, criteria could be established to
determine design parameters of full scale installations.

     The principal water quality parameters carefully observed and
recorded were:  suspended solids, BOD, and COD.  Measurements were
also made on pH, temperature, total solids, settleable solids, coli-
forms, and total organic, carbon.  The laboratory analyses were per-
formed by a local laboratory in Cleveland.

     Filtration operational factors measured and recorded were:
media depth and composition.,' flux rate, head loss, length of
                               120

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               fc&UTofi
                                            Figure  3
                                            Filtration•System
                                            Performance—
                                            Suspended Solids
                                            Removal
Figure 4
Filtration 'System'
Performance  - ,-..-.
B.O.D. Removal
                         121

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           |l^^

 a	;v;yg:,: • ;,.i:. 10       3O      50

                             "''11"*

tiy!*'^
           Figure 5

Filtration System Performance

Effluent  Suspended Solids  Quality
                      '•  TOSEWSGE:
                        TREATMENT
                          PLANT
          Figure 6

 High-Rate Filtration Plant

      Flow Diagram
            122

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                Figure 7
     High Rate Filtration Installation
                 .-PLAN
              Figure 8
Plan - High Rate Filtration Installation
                (100 MGD)
                123

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                    . fV'tts ."••!" I..- - .•. • ' i  ' .  •
          Figure  9
Longitudinal Section High Rate
Filtration Installation (100 MGD)
              Figure 10
        Cross Section - High Rate
        Filtration Installation  (100 MGD)
                124

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Before entering the pumping station, the combined sewer overflow
would pass through a bar rack  (screen) for removal of coarse mater-
ials which might cause problems in the operation, maintenance or
wear of the low lift pumps.  In certain locations, where consistent
with local topography and sewer invert, a low lift pumping facility
may not be required.,,  ,

     The combined sewer overflow from the low lift pump station
would enter a treatment building and be delivered to drum type
screening units.  The wastewater would be introduced into the center
of the drum type screen and would pass through the screening mesh
into the influent channel to the filters.  A gravity type design,
i.e., open filtration units, is proposed.  The water would be intro-
duced at the top of the filter and flow downward through the filter
bed.  The plant effluent could be discharged by gravity to the respec-
tive receiving water body.

     Filtered wastewater would serve as a source of water for back-
washing filters after the overflow has attenuated to a sufficient
degree.  The filtration building would be provided with low pressure
air blowers as a source of" backwash air.  Backwash pumps would be
located in the filtration facilities to deliver water to the filters
for backwashing.  The treatment building would also include a con-
trol area, office space, a polyelectrolyte feeding set-up, and a
system for adding hypochlorite to ^filter backwash water for the
prevention of slime growth on the filter media.  The operation of the
high rate filtration facility would be completely automated, and could
be left unattended, except for routine maintenance and periodic de-
livery of chemicals.  In full size .treatment systems, chlorine feed
for disinfection could be incorporated into the filtration facilities.

     Dirty backwash effluent from the filtration facilities and       /
                               125

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screenings would be directed into the interceptor running to the sani-
tary sewage treatment facility.  The concentrated solids from the
drum screening units would be passed first through a grinder, and
then through a trash basket or classification device to insure that
very coarse, settleable material is not returned to the sewer system.
Sludge handling facilities should not be located at the filtration
site, as this would prove very costly.  Centralization of material
handling facilities has always proved most economical; as an example,
the Southerly Wastewater Treatment receives sludge from another plant
in Cleveland.

     For filter backwashing, two types of process control should be
considered:  the first parameter would be total head loss through
filter bed, and the second would be effluent suspended solids con-
centration .

     For measuring the filter head loss, each filter would be equipped
with a differential pressure transmitter to continuously sense the
loss of head across the filter and transmit a pneumatic signal line-
arly proportionate to this head loss  to a central control panel.
When the filter head loss would reach a preset value, the differential
pressure switch associated with the  filter would be actuated.  A
contact in  this switch would open a  stepping switch circuit  and the
filter would start to backwash.

     An alternate, filter backwash  control could be achieved with  an
effluent suspended solids monitor.   A continuous reading, light
scatter type suspended  solids  meter would be installed  in each
filter effluent pipe to  continuously measure the suspended  solids
concentration  and transmit  the reading  to a recorder  at a central
control panel. When the filter breakthrough would suddenly take
place  and the  suspended solids concentration indicator  would reach a
preset level,  then a micro  switch would be activated  and an alarm
                                126

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would be initiated.  The operator would check the filter performance
condition and start to backwash the filter.
                                        1
     Principal advantages of the proposed system are:  high treat-
ment efficiencies, automated operation, and limited space require-
ments as compared with alternate flotation or sedimentation systems.

COST DATA

 ' •          '   '      '     ',,•'•   '  v-   -"'••.'   -  *
     Estimated total construction costs (ENR=1470) of a filtration
plant for treating combined sewer overflows range from $830,000
for the 25 MGD capacity to $3,754,000 for 200 MGD capacity at design
rate of 24 gpm/sq ft.

     Estimated annual cost data ranges from $97,270 per year for a
25 MGD capacity plant to $388,210 per year for a 200 MGD capacity
plant.  Annual treatment costs utilizing the high rate filtration
process are due primarily to interest and amoritzation charges, and
are less affected vby the volume of combined sewer overflow to be
treated annually.

     These .costs do not include disposal of waste screenings and
filter backwash since the proposed system would discharge these to
the municipal sewage treatment plant.  Assuming an average of 200
mg/1 of solids removed and a combined sewer overflow treatment plant
operation of 300 hours per year, solids processing and disposal
costs incurred by the municipal, sewage treatment plant could range
from 3 to 35 percent of the total annual' charges for the combined
sewer overflow treatment facility.

DUAL PURPOSE OF UTILIZATION OF HIGH RATE FILTRATION PROCESS

     The selected media for combined sewer overflow treatment was
                                127

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also evaluated in terms of its capacity for polishing secondary
effluent under another research contract.  Test data has confirmed
the applicability of this combined sewer overflow media to reducing
suspended solids, BOD, and phosphate to low residuals.

     In Cleveland, the total duration of the overflows from the
combined sewer system is approximately 300 hours per annum.  This
indicates the possibility of utilizing dual purpose treatment plants
based on the high rate filtration process.  Such installations
would treat combined sewer overflows when they occur, and in be-
tween such periods, for over 95 percent of the time, the filtration
process would treat other wastewaters depending on the location of
the process.

     For a high rate filtration process for combined sewer overflow
treatment located in the area of the domestic wastewater treatment
plant, the filtration process can be utilized for polishing the treat-
ment plant effluent as well as to protect the effluent quality
during plant overloading or process malfunction.

     The economical benefits of such dual purpose utilization of
the high rate filtration process should not be overlooked.
                               128

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            SECTION VII
 SCREENING/DISSOLVED - AIR FLOTATION
TREATMENT OF COMBINED SEWER OVERFLOWS
               by
       Mahendra K. Gupta
        Robert W. Agnew
 Environmental Sciences Division
  Envirex, Inc. (A Rexnord Co.)
       Milwaukee, Wisconsin
                  129

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Introduction

The problem of combined sewer overflows (CSO) has been recognized
as a significant pollution problem in recent years (1).  Large
amounts of untreated pollutants find their way into our water
courses through this route.  The abatement methods dealing with
this problem are sewer separation, storage, treatment, or a
combination of these.  The cost of separating the sewers is
prohibitive and this method is not considered as an economical
solution to the problem.  A great deal of literature has been
published since 1964 which describes the characteristics of (CSO)
(2).  Based on the data published, it has now been established
that a major portion .of the pollutional substances in CSO is
particulate in nature.  This indicates that an efficient solid/
liquid separation process can be expected,to provide an effective
treatment of CSO.  It was the mission of the Environmental Sciences
Division of Rexnord Inc. to develop an effective and economical
solid/liquid separation process under a program sponsored by the
U.S.Environmental Protection Agency.

A combined sewer outfall near Haw!ey Road in the west-central
portion of Milwaukee, Wisconsin was selected as a source of
combined sewer overflow for the bench scale studies.  This
outfall services a 495 acre residential area.  It was determined
that approximately 42% of the area was impervious, i.e. streets
and parking areas, house roofs etc.  The calculated value of the
runoff coefficient was 0.40 and it compares well with the values
reported in the literature (3).  The drainage area comprises of
mostly one and two family dwellings with an estimated density of
35 people per acre.  No manufacturing industries are located
within the drainage-area except some small business shops.
Bench scale tests were conducted on 14 separate overflow samples
                             130

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to define the quality of the Haw!ey Road outfall and to evaluate
the various potential treatment proces$es.  The evaluatory tests
included screening with various sized media, chemical oxidation,
flotation and disinfection.  It was 'determined from tHese tests
that chemical oxidation of the raw CSO did not appear technically
and economically' feasible (4).  However, the results of the
screening and dissolved-air flotation tests were encouraging.
These tests served as the design basis of a 5 MGD test facility
at the Hawley Road outfall utilizing screening and dissolved
air flotation.                 '        •        '

Design of the Treatment System   i ':1>""\

The process "schematic of the proposed treatment system is shown
in Figure 1.  The raw overf1ow is pumped from the sewer to a
half inch manually cleaned bar rack..  The purpose of the bar
rack is to remove large objects which may clog or damage the
finer screen downstream.  The flow then enters a 50 mesh
(approximately 300 micron) drum screen.  The basic screen is
fabricated from mild carbon steel while the screening media is
a 304 stainless steel.  The screen is an octagonal shaped drum
with an effective diameter of 7.5 ft', arid 6 ft. length.  The
total screen area is 144 sq. ft. with wetted screen area rang-
ing between 72 and 90 sq. ft. depending'upon'the head loss
across the screen.  The design hydraulic loading for the screen
is 50 gpm/sq. ft. and a maximum head loss capacity of 14 inches.
The drum speed can be varied in the range of 0:5 to 5.0 rpm.

Screened water is used to backwash' the screen.  The solids
which are removed from the screen 'are collected in a hopper and
are then routed to1 the sanitary sewer.  The screened effluent
is split into-two portions. ' A major portion of the flow goes
directly to the flotatipn tank while the.remainder of the flow
                            131

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CSO SOURCE
   EFFLUENT tO
 RECEIVING STREAM
                                   CHEMICAL ADDITION
                                                                               SCREEN BACKWASH SYSTEM
DRUM SCREEN
  50 MESH
                         Vi" BAR RACK
                                   TO INTERCEPTOR SEWER
                                                                                      SCREENED EFFLUENT
                                                                    SCREENED
                                                                 SOLIDS DISCHARGE
                                                                    FLOATED
                                                                 SCUM DISCHARGE
                        FLOTATION ZONE AND CHLORINE CONTACT
                                                                      MIXING ZONE
                                                                                         AIR SOLUTION SYSTEM
                                             CHLORINE AND CHEMICAL
                                              FLOCCULANT ADDITION
                                                                            PRESSURE
                                                                            REDUCTION
                                                                                   AIR DISSOLVING TANK
                                                           c
                                                               AIR COMPRESSOR
                                 SCREENING/FLOTATION FLOW DIAGRAM
                                                    FIGURE 1
                                                     132

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(approx. 20%) goes to a pressure tank where it is mixed with
air under pressure (approx, 50 psi).  The pressurized air-
water "stream is then brought into contact with the bulk of the
raw flow at atmospheric pressure in a mixing zone.  The dissolved
air comes out of solution in the form of tiny bubbles (50-100
micron size) in the mixing zone and these bubbles attach them-
selves to the suspended matter in the waste water.  The mixed
flow then passes through a distribution baffle and into the
flotation tank where solid/liquid separation occurs.  The scum
which floats to the top is then scraped into a trough via skim-
mers and is routed to the sanitary sewer.  The treated effluent
is discharged to the Menomonee River.

The main details of the treatment system are shown in Figure 2.
Flexibility was,provided in the design so that the flotation
zone could be segmented for evaluating various hydraulic over-
flow rates.  Chemical flocculants when utilized were added to
the raw waste as it enterad the drum screen or in the pressurized
flow stream after the pressure reduction valve.  Chlorine was
also added in the pressurized flow stream for disinfection of the
CSO. '"Th'e entire system was automated and .was put,into operation
by sensing a pre-set level of the waste water in the sewer.

Operation of the Demonstration System

The system was operated on 55 separate combined sewer overflows
during 1969 and 1970.  The quality characteristics of these over-
flows are seen, in Table 1.  About 20 percent of the overflows exhi-
bited the first flush phenomenon, which was either caused by high
rainfall intensity or a length of time greater than four days
between overflows.  After the first flush diminished, the quality
of the overflow was remarkably constant for each storm.   The 95%
confidence ranges for the extended overflows were only about 10-
                            133

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                                        PLAN VIEW
 PRESSURE TANK
RAW
FLOW
       •*- 5'-
                FLOTATION ZONE
                                      ELEVATION VIEW
   BAR SCREEN
                         MIXING ZONE
               DRUM SCREEN
     CL^^:
                                               SCUM COUECTOR
                                                                           EFFLUENT WEIR
   rr
^k
                                               8.S' WATER DEPTH
     PRESSURIZED FLOW HEADER '
                                              PERFORATED BAFFLE
                            DEMONSTRATION SYSTEM DETAILS
                                     FIGURE 2
                                       134

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                           TABLE 1
    COMBINED SEWER OVERFLOW CHARACTERISTICS AT HAWLEY ROAD3
         Analysis
Total Solids (tng/1)
Total Volatile Solids (mg/1)
SS (mg/1)
VSS (mg/1)
COD (mg/1)
BOD (mg/1)
Total Kjeldahl Nitrogen  (mg/1)
pH
First Flushes'1
 861 ฑ 117
 489 + 83'
 522 + 150
 308 18.3
 581 + 92
 186 + 40
 17.6 + 3.1
 7.0 + 0.1
         3
Total Coliform  (individuals/ml)  142  x
Dissolved COD/Total COD4
           +_ 108
            0.34 + 0.04
Extended
        3
Overf1ow
378 + 46
185 +_ 23
166+26
90 +_ 14
161 ฑ 19
44 +_ 10
5.5+0.8
7.2 +_0.1
62.5 x 103 + 27
1
  Ranges shown at 95 percent  confidence  level.
  Represents  12 overflows.
  Represents  44 overflows.
  Represents  34 overflows.
                             135

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15% of the mean value as compared with 20-25% for the first flush
data.  The dissolved organic fraction (measured as chemical oxy-'
gen demand) was approximately one third of the total organic load
in the raw combined sewer overflow.  This. showed that a large por-
tion (2/3 of the total) of the organic pollutants was of a parti cu-
late nature which would be amenable to treatment via screening/
dissolved-air flotation.
The variables evaluated during operation included hydraulic load-
ing and drum speed for the screening operation, and surface over-
flow rate, pressurized flow rate, operating pressure, and floccu-
lant dosages for the flotation system.  The optimum operating con-
ditions based on the treatment of 55 CSO are given in Table 2.  The
optimum solids loading rate at a drum speed of 4.7 rpm and a head
loss of 12" was 1.2 pounds of dry solids removed per 100 sq. ft.
of screen area.  This loading could possibly be increased by incr-
easing the allowable head loss differential.  The hydraulic through-
put rate was in the range of 40-45 gpm/sq.ft.  This rate again can
probably be increased depending upon solids loading.  It was found
that no statistical difference could be shown in the removal effi-
ciencies by increasing the pressurized flow rate up to 45 percent
of the raw flow, or by increasing the operating pressure to 60 psi.
A pressurized flow rate of 20% of the raw flow at 50 psi was recom-
mended for future designs.  The air usage was approximately one
cfm per 100 gpm of pressurized flow.  The overflow rate at
which removal efficiencies were satisfactory and the capital
cost still reasonable was 3.3 gpm/sq.ft.  Floated scum con-
centrations generally ranged between 0.7 and 1.4% of the raw
flow.  The chemical flocculants utilized during this study were
FeClo and a cationic polymer (C-31, Dow Chemical Co.).  The
selection of these chemicals was based on the results of a series
of bench scale jar tests.  The optimum chemical dosages were
found to be 20 mg/1 FeClg and 4 mg/1 of C-31.
                            136 .

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                          .TABLE 2
                OPTIMUM OPERATIONAL CONDITIONS
Characteristics
                      Screening
Operational Condition
Backwash
Head Loss
Rotation Speed
Submergence
Hydraulic Throughput Rate
0.7 - 1.0% raw flow
12 in. water
4.7 rpm
50 - 63%
40 - 45 gpm/sq. ft.
                      Flotation
Floated Scum
Pressurized Flow
Operation Pressure
Overflow Rate
Chemical Dosage
0.75 - 1.41% raw flow
20% raw flow
50 psi
3.3 gpm/sq. ft.
20 mg/1 Fed*
            O
4 mg/1 cationic polyelectrolyte
                             137

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 The performance of the 50 mesh screen alone is summarized in
 Table 3.  The pollutant removals (measured in terms of suspended
 solids, volatile suspended solids, COD and BOD) ranged between
 33-39% for the first flushes and between 26-34% for the extended
 overflows.  The slightly higher removal efficiencies for the first
 flush overflows is probably a result of the screening-filtration
 phenomenon that occurs during these high pollutant loading periods.

 The total  removal  efficiencies for the combined screening/flota-
 tion system are shown in Table 4.   The pollutant removals ranged
 between 35-48% without flocculating chemicals.   However,  the
 removal  efficiencies  were significantly enhanced on the,addition
 of flocculating chemicals and ranged between  57-71%.   Removals  during
 the first  flushes  were similar to  the results  for extended over-
 flows  with chemical addition.   The  average  effluent quality  exper-
 ienced with  chemical  addition  and  that can  be  expected  via
 screening/flotation treatment  is shown in Table  5.  These values
 compare  favorably  with  many  secondary sewage treatment  efflu-
 ents.

 Future Design  Considerations

 The data presented so far had  been  based on the results of two
 operational seasons,  1969 and  1970.   Research was continued on
 this treatment facility during  1971 to obtain additional  design
 data for the optimization of the screening and dissolved-air
 flotation  processes in order to improve upon the effluent water
 quality of the treated combined sewer overflows.

 Laboratory bench scale tests have indicated that changing the
 split flow mode of dissolved-air flotation to effluent recycle
mode of operation may enhance the effluent water quality signi-
 ficantly.  This change may require the operation of the flotation
                            138

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                           TABLE 3
            PERCENT POLLUTANT REMOVALS BY SCREENING*
Characteristics
                       First Flushes
   Extended Overflow
ss • ' '"
VSS
• COD
BOD '
36 + 16
37 i 18
39 +,15
33+17
27 + 5
34 + 5
26 +_ 5
27 + 5
* Values given at the 95 percent confidence level.
                           TABLE 4
PERCENT POLLUTANTS REMOVALS BY SCREENING/FLOTATION TREATMENT*

                                                 Extended Overflows

Characteristic ,
SS .
VSS
'COD
BOD
First
Flushes
72 +_ 6
75 +_6
64 + 6
55 + 8
Without
Chetoicals
43 + 7
48 +_ 11
41 + 8
35 + 8
With
Chemicals
71 + 9
71 +_ 9
57 + 11
60 + 11
Nitrogen (total
    Kjeldahl)
                      46 + 7
29 + 8
24 + 9
* Values shown in a 95 percent confidence range.
                          v 139

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                    TABLE 5
EXPECTED AVERAGE EFFLUENT QUALITY AT HAWLEY ROAD
    Analysis


      SS


      VSS


      COD


      BOD


      Nitrogen (total  Kjeldahl)
Value
"(mg/1)


 48


 26


 69


 20


 4.2
                    140

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  system at reduced overflow rates and could therefore increase the
  flotation area requirements by approximately.20%...

  Also, several  other chemical  flocculant combinations have shown
  promise over the ferric chloride - C-31 polymer combination uti-
  lized during the 1969 and 1970 operational seasons.   Use.of pow-
  der activated  carbon along with screening/dissolved-air flotation
  has also shown some merit.  The economics of these concepts for  ,
  an optimum cost benefit relationship still, need evaluation.  These
  evaluations are a part of the proposed modifications to the Hawley
  Road treatment facility.   It  is anticipated that these  consider-
  ations will be evaluated on the modified Hawley Road treatment
  facility during the 1973 operational  season..

  Racine Root River Project

  Encouraged by  the promising results  of the Hawley Road  demonstration
  facility,  a search was made to find  a site where the feasibility
  of utilizing screening/dissolved-air flotation  could be demonstrated
  on a full  scale for the treatment  of combined sewer  overflows.   The
  City of Racine, Wisconsin was  indicated.to be an ideal  site for
  such a project.   Racine is a  city  of approximately 100,000  people
  located on Lake Michigan,  approximately 30 miles south  of Milwaukee.
  The Root River,  a stream  having a  mean  annual discharge of  approxi-
  mately 100 cfs  flows  through  the city and  serves as  a receiving body
  for runoff from much  of the northern  half  of the city.   There  are
  approximately  700-acres of land having  combined  sewer systems  in  this
  area.   In  the  3.7 miles of Root River through the  city,  there  are
  36 combined sewer overflow points  and 17 storm water discharges  to
  the river.   It  was  estimated that  the cost of separation of the
  existing combined sewer areas  in Racine would be  10-13  million
  dollars.   The  estimated cost of installing  the screening/dissolved-
  air flotation  treatment plants  at  the various outfalls  was  4
                             141
Two full scale SDAF systems have bieen. installed in Racine for
treatment of combined sewer overflow.  The design criteria for
each of the various elements is shown, in Table,6.  The systems
have been designed for completely automatic startup, operation
and shutdown.

The two systems are similar in function.and differ only in
design capacity.   A schematic diagram of the larger system is
                            143  ,

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million dollars.  Thus significant savings were evident in going
for the screening/dissolved-air flotation route for the treatment
of combined sewer overflow problem in the City of Racine.

In April of 1970 a grant application was submitted to the U.S.
Environmental Protection Agency.  Under the terms of this proposal
the funds would be rendered by the federal government, State of
Wisconsin, and the City of Racine.  The technical approach proposed
for meeting the project objectives includes the following elements:
     1.  Quantitativ_e_measurement^of^ the.
                              TABLE 6
   DESIGN CRITERIA - SCREENING/AIR FLOTATION TREATMENT SYSTEM
                         RACINE, WISCONSIN
    Item

    Contributing  area  (acres)
    Design  Storm  Intensity  (inch/hour)
    In-Sewer  Storage  (gallons)
    Design  Flow for Treatment  System (MGD)
Site .#1     Site #2
82.5
0.5

14.13
364.2
0.5
600,000
44.4
    Bar  Screens

        Mechanically cleaned and located
        Just Upstream of Pump Sump
Yes
Yes
    Drum Screens

        Parallel  Operation,  automatic
        bypass to flotation  tanks should all
        screens clog

        Number of screens                        2
        Length (feet)                            7
        Diameter (feet)                          8
        Filter Media Stainless Steel -
          50 mesh, .009 inch wire
          Screen Backwash flow gpm
          (when operating)                       210
            4
            10
             675
                                 144

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                       TABLE.6 CONTINUED  .
 Item                                         Site #1     Site #2

 Flotation System

     Operation-Each tank reaches 701  •  :        .-  .,,.-•  ... ;, ?, <
•   ,  maximum flow before the next tank is
  ,   put into use.       -;                   ."  ,.• ,-      ?

     Number of tanks                          3         -8
     Surface overflow rate - gpm/ft           3.5         3.5
  ,-..•'. Pressurized flow - gpm/tank  ;     :.   ,  650         770
     Scum Removal  - timer controlled
       Surface skimmer to scum trough -            •          •
       Screw conveyed to sludge holding  tank

 Chemicals
     Chlorine  -  maximum concentration  mg/1     20
     Fed g  - maximum  concentration  mg/1        25

     Polyelectrolyte  -  concentration
   •Dependent on  specific  polyelectrolyte

Sludge Storage                        ..•--;     ,

   ..1.5% of design flow for 3 hour duration
     Volume -  cubic feet                     3,500

     Disposal  to sanitary sewer by  gravity
     Drain following  storm
20
25
11,030'
                             145

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shown in Figure 3.  Upon sensing a high level in the overflow
sewer, the system is placed into operation.  Raw overflow enters
the plant through a mechanically cleaned bar screen located in
the wet well.  A by-pass weir is provided for storm flows in
excess of the design capacity.  Flow entering the wet well is
pumped by means of a spiral screw pump through a Parshall flume
and into the screening chamber.  The output of the flow recorder/
totalizers are used to provide a proportional signal for pacing
the chemical feed equipment.  Ferric chloride is added to the
wastewater upstream of the screens.  Chlorine and polyelectrolyte
are added downstream of the screens.

Each of the drum screens is equipped with 50 mesh stainless steel
screens.  The screens are backwashed at a preset headless level.
Solids removed on the screen are conveyed to a sludge holding tank
by means of a screw conveyor which runs along the head end of the
flotation tanks.

Effluent from the drum screens is diverted to the flotation tanks
by means of a series of weirs and orifices.  The inlet system is
designed so that the tanks are filled in series.  This enables the
utilization of only as much tankage as is actually required by the
storm flow.  Screened effluent is used as the source of pressurized
flow.

Scum produced in the air flotation tanks is skimmed to the head
end of the tanks where it is conveyed to the sludge holding tanks
by means of a screw conveyor.  All sludge generated during a
storm is held in the holding tanks until after the storm subsides
and then is discharged to the interceptor sewer.  At some future
date it may prove fruitful to provide onsite dewatering facili-
ties rather than return the concentrated sludge to the sewer
system.
                             146

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              o
             •ง•
                     o
                   z
                   =>

                   z

                   2
SCHEMATIC LAYOUT OF THE TREATMENT SYSTEM FOR SITE NO. 1

                           FIGURE 3
                     147

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The flotation tank effluent which has been chlorinated will be
discharged directly to the Root River.

Following a storm all of the sludge, as well as the contents of
the flotation tanks will be discharged to the adjacent sanitary
interceptor sewer.  The system will then be ready for the next
storm.                      .

Special Considerations

Certain special considerations have been made in order to insure
optimum use of the system.  A floodgate was installed in one of
the overflow sewers to provide approximately 600,000 gallons of
in-system storage.  This storage capacity will be utilized when
the treatment facility reaches full capacity.

In addition, the  system has been equipped to be completely self-
draining.  This will enable use of  the system during peripds of
snow  melt and cold weather.  A roof has also been provided to
prevent floe breakup during heavy rains..
 Costs
 The cost for the  Racine  SDAF system is  $30,000  per  mgd  installed
 capacity.   A detailed cost breakdown is given in  Table  7.

 Racine Program

 A two year system evaluation and optimization is  scheduled to
 begin on April 1, 1973.   The intent of  this program is  to  fully
 evaluate the installed facility, validate the EPA Stormwater
 Management Model  and determine the effect of the  system on water
 quality in the Root River.
                             148

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                        TABLE 7    : -
       COST OF SCREENING/DISSOLVED AIR FLOTATION
                     Capital Costs
Cost per MGD Capacity
Cost per Acre*
$30,000
$ 3,900
   * Based on 0.5"/hour runoff rate
                    Operating Costs
Power
Chemicals
Maintenance
                                     TOTAL
Based on plant capacity .of more than 30 MGD
and 40 hours per month operation.
<ฃ/1000 gallons
  0.54  :•:
  2.51  ...
  0.04  :
  3.09^/1000 gallons
                          149

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Acknowledgement

The work in this paper for the Hawley Road Demonstration Facility
was sponsored by the U.S. Environmental Protection Agency.  The
implementation of the findings of the Hawley Road project as
applied to the Racine Root River Project were undertaken through
the joint sponsorship of the U.S.E.P.A., State of Wisconsin and
the City of Racine.  Portions of this paper have been derived from
two publications:  1)  Screening/Flotation Treatment of Combined
Sewer Overflows, EPA Project Report by Ecology Division, Rex
Chainbelt Inc., WPCR Series 11020 FDC, January, 1972, and 2) Treat-
ment of Combined Sewer Overflows by D.G.Mason, JWPCF, December,
1972.
                             150

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                         REFERENCES
 1.  Pollution of Stormwater;and Overflows from Combined Sewer
    Systems - A Preliminary Appraisal,1 USPHS  (November 1964).

 2.  .Combined Sewer Overflow Abatement Technology, U.S. Depart-
  ;.^ment of .the Interior, FWQA (June 1970).

 3.  Fair, G. and Geyer, 0., Water Supply and Waste Disposal,
    John Wiley & Sons, N.Y, (1961).     ;

4. • Screening/Flotation Treatment of Combined Sewer Overflows,
    Ecology Division, Rex Chainbelt' Inc.,  Contract 14-12-40,
    11020 FDC (January 1972),
                              151

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           SECTION  VIII
    HIGH-RATE  DISINFECTION  OF
    COMBINED SEWER OVERFLOW
              by
    George E. Glover, P.E,
       Research Engineer
Cochrane Division-Crane Co.
               153

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       The bacteria content of combined sewer overflow has been reported to




be as high as  30 million total coliform/100 ml and 3 million fecal coliform.




These levels are 1,000 to 10,000 times the allowable concentration in




secondary effluents and similar restrictions have been considered for combined




sewer overflows.  The techniques used to remove suspended solids have




in themselves no ability to remove or kill coliform.  Thus bacteria kills  of




3 to 4 logs (that is, 99.9% to 99.99%) are required as a separate operation for




combined and separate sewer overflows.




       As reported by others  (1)  (previous speakers) it may be possible to




achieve a suitable bacteria kill with high.chlorine dosages within certain types




of solids  removal devices so that no separate contact chamber will be required.




Considerable more work needs to be done over a broad range of flow rates before




the proposed advantage of dual use of this volume can be utilized on full scale




plants.  It is anticipated that required bacteria kills may not be obtained at.




low flow  rates.



        The special design considerations required to cope with the very high




instantaneous overflow rates previously mentioned  (this  morning) for removal




 of suspended solids and organic matter hold for the disinfection equipment




 as well.



        Conventional  chlorine contact chambers installed at sewage plants




 are sized to provide  15 to 30 minutes detention which would require considerable




 area (about 1 acre per 250 acres drained at 1.0 of s/acre).  Operating close to







                                   154

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 their design rate as determined by'the 2 to 1 diurnal flow variation, these basins,




 as often as not,  fail to achieve the required bacteria kills.  During the initial




 filling, these sewage  contact chambers do not, and are not expected to, perform.




 A contact chamber,sized to'provide  15 minutes residence for a peak stormwater




 overflow rate would never be filled to its operating level during most storms.




 The operation of  conventional 15-30 minute contact chambers in combined




 sewer overflow would  be  uncertain at best.                             •




        Our work on disinfection as well as the work of others (2) (3) was




 performed in pilot size contact chambers at a constant flow rate.  That is,  these




 chambers have not been tested at the wide  (20 to 1) variations in overflow rate




 anticipated for-a full scale chamber  in stormwater service.   As will be seen




 later, the assumption  that performance of a contact chamber will be as good,




If not better, at lower flow rates as it is at the higher rates is questionable




even though the contact time is  longer.




       We have  made, five disinfections of combined sewer overflow while  the




 storm was in progress. We achieved 99 .99% kill (4  logs) with chlorine




 dosages (10 ppm) in 120 seconds.  The flow rate through our units -we have




 two identical units - was 20 gpm.'  In every case, both total and fecal coliform




were reduced to below 10 cells/100 ml.  This performance was obtained on both




the raw overflow  before Microstraining and the micros trained effluent.  The




 3 minute chlorine demand-was surprisingly uniform at about 3 ppm for the




microstrained effluent  and somewhat higher for the raw stormwater.




        One of these chambers is shown in Figure 1.  They were designed to
                                 155

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               Figure 1
Intensely Mixed Chlorine Contact Chamber
               156

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ensure that the hypochlorite was promptly and well mixed with the stormwater.




More important, or equally important, they were designed to ensure a high




degree of small eddy turbulence in the passages of the contact chamber.




       We attribute the extraordinarily high kill rate of these chambers to




the turbulence during contact  time.




       The  very recent literature  (Collins et al (2), Kruse et al (3) and




the Dow  work (4)  ) reports several instances of laboratory studies on sewage




and stormwater disinfection where similar extraordinary kill  rates have been




observed.  Examination of the apparatus and the procedure used in these




studies reveals that very  high turbulence existed during these studies as well.




       In one case - a beaker study by Kruse et al (3), a high stirring rate was




used to demonstrate the advantage of prompt and thorough dispersion of the




chlorine. Very high (4 - 5 logs) kill rate of bacteria was observed in




2 minutes when the fast s'tirring rate (i.e., "fast mix") condition was sustained




throughout the whole study.   Much poorer performance  (only 1-2 logs in




2 minutes) was obtained at the same dosage when the more normal mixing




regime of a few seconds fast mix followed by 15 minutes slow mix was used.




It is of great importance that,in this study,virus were killed  at high rate under




the sustained fast mix condition for a few minutes  whereas there was minimal




virus kill even with prolonged slow mixing.




       In the case of the  Dow EPA (4) study, a long 1,500 ft  tube was selected




as a flow thru contact chamber. This configuration was apparently selected




to permit precise collection of samples after a specified contact time and to
                                157

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a collision during the operation.




       Several studies (7) (8) have shown that the reduction of the number of




particles (I.e., the formation of a single particle  from two colliding particles)




is proportional to the GT product in secondary effluent flocculation. Special




hardware has been developed to enhance the flocculation of sewage-like




solids (9).  -Design and calculation methods have  been developed so that the




mixing intensities as measured by velocity  gradient can be controlled in the




laboratory  (1'P) (11) and also reproduced in full scale equipment (12).




       The application of this already developed  mixing intensity technology




to disinfection has been proposed by the writer (13).




       The following will be a description  of (a)  the performance of the pilot




units, (b) the preliminary design scheme, and (c)  of a 92 cfs chamber designed




according to this scheme.



        Figure  2  shows the results of our disinfection studies to date  on




combined sewer  overflow in an intensely mixed chlorine contact chamber.




The kill is shown as the surviving fraction  of,the  total coliform on a log scale.




Note that almost 4 logs (99.99%) are obtained with  10 ppm'dosage at  GT of




5,000 (2 minutes at G = 40). The contact time-mixing intensity scale is




dimensionless.  It is  based on the nominal contact time; that is, the  volume




of the chamber divided by the thruput rate and is  not corrected for short




circuiting. The  value of 9,500, for example,  is the product  of the G =  40 sec




velocity gradient times 240  seconds  (4 minutes) nominal contact time.




        For comparison, the velocity gradient in the contact chamber  of a local
-1
                                 160

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                   161

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sewage plant was calculated from observed velocity and head loss and found

to be about 6 sec   .  The nominal residence time in this chamber was 1,800

seconds (30 minutes)  and the GT product then was 10,000.   It might be noted

here that the nominal residence time is used although it has been shown (2)

(14)  thatthe true residence time is often considerably less  due to short

circuiting.  Preliminary studies have indicated that the use of a true residence

time would improve this scheme but this  refinement has not been incorporated

yet.

        The design objective for our pilot chambers was to achieve a GT of

10,000. We arbitrarily selected 240 seconds (4 minutes)  as the  residence

time T so that we needed a G of about 40 sec"1.  The velocity gradient is

defined (G) as:
       G =
     Energy Dissipation Rate/Volume
                                            1/2
                        Viscosity
For open channel flow, it has been shown (12) that:
G =  1730         \   Velocity-fps x Channel Slope ft/ft
    V viscosity-cp \
                                                                   (Eq.  1)
The viscosity is known from the towest temperature to be considered in the

design; e.g., 1. 4 centipoise at 45ฐ F.

        The velocity can be arbitrarily selected at some level between 0.25

and  1.5 ft/sec, or possibly higher.  The volume of the chamber has already

been determined by the selected nominal residence time so that now the

velocity selection also fixes the path cross-sectional area and path length.


                               162

-------
        The depth of the chamber can now be selected based upon usual


 considerations of soil condition, and land cost, etc., although, as-will be


 seen later, shallower depths than usual are preferable.  The remaining problem


 is to ensure that the required slope is obtained.  The required slope is


 calculated from Equation 1.  The slope in open channel flow can be calculated


 by Mannings' equation:
                            I"    T  I"T  /

        Slope = (Velocity)2  j^J  ||4, 3                            (Eq<
      where  "n" is a factor relating to the obstruction to flow of obstacles at


walls and within the channel.  This factor is historically called a : "roughness


factor" and the numerical value found in hydraulics handbooks is 0.011 for


steel or neat concrete and 0.03 for the situati6n where corrugated metal:froms


the wall of a channel whose width is several hundred times the corrugation


height.  For our purpose, this could be considered a turbulence promotion


factor.   Work  is in progress to determine the effective turbulence promotion


effect of corrugated baffles in narrow passages where we believe it to be at


least twice the 0.03 value given above.  The effect for other.configurations


is being studied as well.  The term "roughness factor" will be used until a more


appropriate term is coined.


        The hydraulic radius "R" is the ratio of the cross-sectional area of


the passage in ft2 to the wetted perimeter in feet.


        Since the velocity has been fixed and the required slope calculated,


only the roughness factor relating to-iie type of wall and/or baffle surface


and the hydraulic radius relating to the wall area parallel to the flow path
                                 163

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can be governed by the designer.




       The combined effect of these two variables is calculated from




Equation 2.




       For illustration in Figure 3, corrugated baffles parallel to the path are




shown.  In this simplified sketch, the significant dimensions are shown.




The passage xvidth is fixed by the selected velocity and channel depth.  The




number of the  parallel baffles inserted determines the hydraulic radius.  The




roughness factor is determined primarily by the surface of the baffle  material




selected.




       In spite of the undeveloped state of this  design scheme, we Were  able




to produce a chamber within  6% (9,400) of the design target  (10,000), on our




first attempt.   Also, additional baffles can be easily inserted at a later date




if required.




       This design scheme yields considerable insight to the evaluation of




the performance of existing and future contact chambers. The disinfection




performance has been shown to be a function  of the GT parameter.. In




conventional chambers the outlet weir is located near the design rate water,




level so  that the water volume is nearly constant at all flow rates.  As can be




seen by Equations 1 and 2, the G varies as the (velocity) *5.  With constant




liquid level, the T varies as  (I/velocity), thus the GT parameter will vary




as the (velocity) •5  or with (flow rate) • 5.   This poorer performance at reduced




flow rate would escape attention under relatively constant rate conditions in




a sewage plant.  However, under the widely variable rate conditions met in
                                  164

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                           165

-------
 combined sewer overflow service, it must be considered.  The use of a Sutro

 weir has been proposed to maintain  a constant velocity at all flow rates .

        A 92 cfs (60 mgd) Intensity Mixed Chlorine Contact Chamber has been

 designed.  This chamber was designed to follow a microstrainer facility with

 46 cfs treatment capacity and an additional 46 cfs bypass capacity.  The

 chlorine contact chamber was designed to have 120 seconds residence time at

 the 92 cfs rate and,since a Sutro weir is used the residence time at less than

 the 92 cfs rate will be about 120 seconds also.  The velocity is 1.5 ft/sec and the

 amount of baffling and its configuration is such to yield a velocity gradient

 G of 40,as in our pilot plant.

        The chamber is 40' by 40' and has an average liquid depth of 7' at

 maximum flow.  Internal walls form  a labyrinthine-like passage of 8' in width

 and produce a velocity of 1.5 ft/sec.  The internal walls are faced with a

 commercially available corrugated asbestos siding having 1-1/2" deep

 corrugations.

        Two additional corrugated panels are mounted as parallel baffles in the

 channels forming 32 inch wide passages.  The  baffles extend from liquid level

 to within a foot of the floor. Ideally the floor would be similiarly corrugated*

 but this is not necessary.  The head loss through the chamber at peak flow

is about 8 inches.   (See Figure 3)

       The  inlet to the chamber is equipped with a 3 hp mixer sweeping an

 8' x 81 section of the channel  (about 5 sec residence time). A mixer of this
                                                                        ••*
horsepower  should be able to impart   1 hydraulic horsepower to the water to
                                166

-------
 enduce a mixing intensity of about 200 sec"1 in this 450 ft3 volume, which
 should be adequate for thoroughly mixing the chlorine chemicals.  Such a
 provision for mixing of chemicals is incomparably superior to the methods
 usually used in sewage plants.  The mixer should be of such a type that it
 can operate at varying water levels from 7* down to 1'.
       . The outlet of the chamber should be fitted with a relatively narrow
 outlet weir placed as low as the available outfall head will allow, preferably
 at the bottom.  Further, the outlet weir should be of the Sutro type to maintain
 the velocity in the  chamber, at less than peak rate, as near the  peak rate
 velocity as possible.  A Sutro weir at the bottom will maintain peak rate
 velocity at all  flow-thru rates.  In the event the allowable  outfall head will
 not permit placing the weir at the bottom,  a small pump must be provided to
 empty the chamber  at the  end of the  storm.                                 ' .   '
        The installed cost of such a  chamber has been calculated to be  about
 $53,000 (in 1969 dollars) less  the cost of  land, engineering and  profit  (1).   It
 is difficult to compare costs developed by different estimators. However, this
 cost can be compared to the data developed by Smith (15) of $25,000 for an
 $11, 000 ft3 basin, which is the volume of the basin described above.  Also,
 it can be compared  to Smith's estimate of $90,000 for the 8Z,000 ft3 chamber
 required to provide  15 minutes  residence for 60 mgd in a conventional chamber.
        The inherent advantage of increased turbulence  economically induced in
 this type of installation to enhance reaction rates can be used in many  situations.
An obvious example would be to use  it in chlorine contact chambers at sewage
 plants with savings in construction cost,  land,  and the advantage of high
virus kill.and reliable bacteria kill.
                                 167

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                          ACKNOWLEDGEMENT









       This work was conducted with the City of Philadelphia in two phases,




(I) under a contract from the Environmental Protection Agency to the Cochrane




Division of the Crane Co.,  and (2) under an EPA grant to the City of




Philadelphia,  The efforts of City personnel were under the general direction




of Carmen Guarino, Water Commissioner, with William Wankoff and M.




Lazanoff, serving as Project Director and Laboratory Director.  J. Radzuil




headed the City's R and D Department who also lent valuable assistance.




       The assistance and guidance of these  people are gratefully acknowledged.




       The overall guidance and helpful advice of Richard Field, Project Officer,




EPA, Edision, New Jersey, were most valuable.
                                 168

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                                  REFERENCES
   1.  Mason, D.G and Gupta, M.K. ,: (Rex Chainbelt Co.),  "Screening/
       Flotation Treatment of Combined Sewer Overflows ", Water Pollution
       Control Research Series &lln?.n.Fnr; m /79              ;      :

   2. Collins, H.F., Selleck, R.E.y and White G.C., "Problems in Obtaining
      Adequate Sewage Disinfection", Proc.  Sanitary Engineering nป,i a,™
      ASCE, October 1971.  ,                           -      -  ..

   3. Kruse, C.W.., 'Olivieri, V. , and Katvata, K.,  "The Enhancement of
      Viral Inactivation by Halogens ", Water and Sewage Works . June 1971.

   4. The Dow Chemical Company (Daniels, S.L.),  "Chemical Treatment
      of Combined Sewer Overflows", Water Pollution  Control R^^rr-.h
      Series fl 1023 FDB 09/70.      "'      ~~      '-  :      : - ~

   5. Cochrane Division-Crane Co.  (Glover G.E. and Yatsuk'-P.), "Microstraining
      and Disinfection of Combined Sewer Overflows (Phase I) ", Water Pollution
      Control Research Series ftlln?.3 -pun ns/yn                 ~     ;

   6. Camp, T. R. ..and. Stein,  P.C,, 'Velocity Gradient and Internal Work in
      Fluid Motion", -Journal, of the Boston Society of Civil Engineers r 30 219
                             '                     j
  7.  Parker, D.S., Kaufman, W.J., and Jenins, D., "Physical Conditioning
      of Activated Sludge Floe", Journal of the Water Pollution Control
      Federation . September 19.71.

  8.  Argaman, Y. ,  and Kaufman W.J., "Turbulence and Flocculation",
      Proc. Sanitary Engineering Division ASCE .  April 1970.

  9.  Cochrane Division -Crane 'Co. (Glover, G.E.),  Patent Application for
      Liquid Agitator to  Produce Uniform Velocity Gradient.

10.    Camp/ T.R. , and Conklin, G.F. ;  "Towards  a Rational Jar Test for
      Coagulation", Journal of Boston Society of  Civil Engineers. March 1970.

11.    Camp, T.R., "Floe Volume Concentration", Journal of American Watsr
     Works Association 6Q:Sfi.S (1968).                  ~    ~~~~ - -
                                169

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12.   Cochrane Division-Crane Co. (Glover,  G.E.), Series of Internal Studies
      "Calculation of Velocity Gradient in Mechanically Activated Chambers "
      in Open Channel Flow, in Pipeline Flow, in Flowthru Granular Beds, etc.,
      (1964-67).

13.   Glover, G.E., Discussion of Collins et al (Reference 2, herein), Journal
      of Sanitary Engineering Division ASCE.  August 1972.

14.   Louie,  D.S. and Fohrman, C.H.,  "Hydraulic Model Studies of Chlorine
      Mixing And Contact Chamber", Tournal  of Water Pollution Control
      Federation, February 1968.

15.   Smith,  R.,  Private communication - Preliminary Results of Cost of
      Wastewater Treatment Equipment (1969).
                                 170

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             SECTION IX
    THE  SWIRL  CONCENTRATOR  AS  A
 COMBINED  SEWER  OVERFLOW  REGULATOR
                by
      Richard H. Sullivan
 Assistant Executive Director
American Public Works Association
                171

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         A report by the American Public Works Association published
in 1970 gave the results of a study of combined sewer overflow regulator
facilities.  Design, performance and operation and maintenance experiences
from the United States and Canada, and in s.elected foreign countries
were reported.  It was evident that North American practice has
emphasized the design of regulators simply as flow splitters, dividing
the quantity of combined sewage to be directed to the treatment
facitilities, and the overflow to receiving waters.  Little consideration
was given to improving the quality of the overflow wastewater.
         Using hydraulic laboratory tests and mathematical modeling
strongly we have determined that it is possible to remove significant
portions of settleable and floatable solids from combined sewage overflows
by using a swirl concentrator.  The practical, simple structure has"
the advantages of low capital cost; absence of primary mechanical parts
should reduce maintenance-problems; and construction largely with inert
material should minimize corrosion.  Operation of the facility is      . :  •
automatically induced by the inflowing combined sewage so that operating
problems normal to dynamic regulators such as clogging will be very    . ;
infrequent.                                                       ,
         The device, as developed, consists of a circular channel in
which rotary,motion of the sewage is induced by the kinetic energy of.
the sewage entering the chamber.  Flow to the treatment.plant is deflected
and discharges through an orifice called the foul sewer outlet, located
at the bottom and near the center of the chamber.  Excess flow in storm
periods discharges over a circular weir around the center of the tank
and is conveyed to storage treatment devices as required or to receiving
waters.  The concept is that the rotary motion causes the sewage to ,
follow along a spiral path through the circular chamber.
                           172

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           A free surface vortex was eliminated by using a flow deflector,
  preventing flow completing-'its'first'revolution in the chamber from
  merging with inlet flow.   Some rotational movement remains,  but in
  the form of a gentle swirl,  so that water entering the chamber from the
  inlet  pipe is slowed down and  diffused  with very little turbulence.   The
  particles entering the  basin spread over  the full cross.'section, of the
  channel-and settle rapidly.  Solids are entrained along' the.bottom,
  around the chamber,  and are  concentrated  at the  foul sewer outlet.
           Figure  1,  Isometric View  of Swirl  Concentrator; depicts the
  final  hydraulic model layout showing details  such as the floatables
  trap,  foul outlet  and floor gutters.
           The  swirl concentrator may  have practical applications as a
 degritter, or grit-removal device  for sanitary sewage flows or separate
 storm water discharges of urban runoff waters.   It may have capabilities
 for the clarification of sanitary  sewage in treatment plants, in the
 form of primary settling or, possibly,  final settling chambers.  It
 might be used for concentrating, thickening, or elutriating sewage
 sludges.  It may be serviceable in the  separation, concentration and
 recycling of certain industrial waste waters, such as pulp and paper
 wastes  or food processing wastes,  with  reuse of concentrated  solids and
 recirculation of clarified overflow waters in industrial processing
 closed  circuit systems.
          In water purification  practices,  it may find feasible
 applications in chemical mixing, coagulation and clarification of
 raw water.  Other uses may prove to be realistic .and  workable.
          Complete reports  describing the hydraulic laboratory study
 and the mathematical  modeling are  included in the report EPA  R2-72-008,
 September  1972, published  by USEPA.   The body  of  the  report details the
 basis of the assumptions used to establish the character and  amount of
 flow to be treated  and the design of  a swirl concentrator based upon
 the  hydraulic  and mathematical  studies.
         Although the study was performed for the  City of Lancaster,
Pennsylvania, with a specific point of'application  defined, all work
was  accomplished in a manner which  allows'ready translation
                          173

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                                                                                  inflow
overflow
Inlet Ramp
Flow Deflector
Scum Ring
Overflow Weir and Weir Plate
Spoilers
Floatables Trap
Foul Sewer Outlet
Floor Gutters
                                       FIGURE 1
                     ISOMETRIC VIEW OF SWIRL CONCENTRATOR
                                    174

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3.
4.
5.
 application of the results to conditions which might be found at other
 installations and for other purposes.
          Consideration of the use of- a swirl concentrator as a combined
 sewer overflow regulator facility requires an evaluation of many factors
 which include:
          1.  hydraulic head differential between the collector
              and interceptor sewers and head available in collector
              sewer to allow insystem storage;
          2.  .hydraulic capacity of collector sewer;
              design flow;
              dry-weather flow and capacity of interceptor sewer;  and
              amount and character of settleable solids.
          Although many of  these items  have been mentioned in the
 preceding sections of the  report,  the  importance of  each  will be
 highlighted in order  to emphasize the  importance of.  each  point in a
 preliminary evaluation of  the use of the  swirl  concentrator.
          Hydraulic Head Differential.   There must be sufficient
 hydraulic head available to allow dry-weather flows  to pass  through the
 facility  and  remain in the channel.  The  total  head  required  for
 operation is  shown in Figure  2, Hydraulic  Head  Requirements.   Determination
 of the maximum elevation in the collector  sewer that  can be utilized for
 insystem  storage  and  the differential  elevation between the collector
 and interceptor sewers  is the  total  available head.
          The head  required will vary directly with flow and the outlet
 losses in  the  foul  sewer.
          If sufficient head is not available to operate the foul sewer
discharge by gravity, an economic evaluation would be necessary to
determine the value of either pumping the foul sewer outflow continuously,
or pumping the foul flow during storm conditions and bypassing the swirl
concentrator during'dry-weather conditions, perhaps with a fluidic
regulator.
                  175

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      Maximum elevation-
      of flooding in
      collector sewer
      Overflow weir (side)_
                        height of flow
                        over weir
      Overflow weir (central)
      Collector sewer
      invert            —
      Foul outlet
I   chamber depth
                         losses due to outlet,
                      J  gate, connecting
                     \  sewer and flow
Interceptor                through chamber
sewer inlet   	          1—
                       FIGURE 2
             HYDRAULIC  HEAD REQUIREMENTS
                                                 hydraulic
                                                 head required
         Hydraulic Capacity  of  Collector Sewer'System.   The facility
must be designed  to handle the  total flow which might be delivered by '
the collector system.   Thus  a study of the drainage area must be made
to determine the  limiting grade and pipe sizes which control the quantity
of flow.  Solids  removal from a peak flowrate may not be required.
If the chamber is not  designed  for such maximum flows, however, velocity
energies which could be developed at such full flow conditions should
be avoided by providing a bypass in the form of a side overflow weir.
         Design Flow.     Selection of the design flow for sizing the
chamber should be accomplished  on the basis of a complete hydrological
study to determine frequency and amount of precipitation which can be
anticipated as well as runoff hydrographs.  Computer models such as
developed by the  University  of  Florida for USEPA can be of assistance
in determining the solids load  which may be associated with various amounts
and intensity of  precipitation.  Provision of maximum solids removal for
a two-year frequency storm for  the Lancaster, Pennsylvania, project was
made on the basis of engineering judgment and an evaluation of local
receiving water conditions.  As the cost of construction will increase
in direct proportion .to design  flow, an economical evaluation should
generally be used to select  the flow capacity.  The efficiency curve
                           176

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 for the facility 'is rather flat over a wide range of ;flow^v resulting
 in perhaps large increases in cost for marginal improvements in'
 efficiency.
          A major constraint in selecting large design flows is the
 anticipated shoaling problems of solids at low flow rates in large
 facilities.   Self cleaning is enhanced by reduced diameters. 'This
 consideration may make it desirable to design for lower flows,'
 particularly where some form of overflow treatment is to be provided.
 Again the computer model can be used to determine the magnitude .of
 the solids carry-over problem to the-secondary device.      ->•'-..
          A third consideration is, the maintenance of   low-inflow        •
 velocities,  with turbulence minimized.   At the design flow the inflow
 velocity  should  be in' the range of three to five fps.  The inflow  ' """""
 velocity  may require reduction by enlarged pipe sections or other
 means  to  achieve this rate.  ..".-.••-.,_-      '    "  .   :'''::
         ,Dry Weather Flow and Capacity  of  Interceptor Sewer.  '.Sizing
.of  the  foul  sewer,  the foul outlet and the gutter .depend upon  a
 de-termination of the dry-weather, flow in addition,  the capacity of the
 interceptor  sewer- to handle the foul flow.must be .known.  , The .fbul ,sewer
 must be large enough to maintain and not be subject to blockage—
 usually a minimum 12-inch diamter.   however,  the head on the outlet
 during  overflow  conditions  will allow considerable  variations  in  the
 foul discharge if  it is not  controlled.
          The efficiency of  the  chamber  is  affected  by the ratio of
 foul flow to  overflow	although there  appears to be  a broad  operating
 range over which reasonable  removal  efficiencies can  be  maintained.
         Maximum advantage  should  be taken of  capacity in the interceptor
 system, particularly during  the period  when the  chamber  is  being'drawn
down.   Thus,  sensing of the  flow in  the interceptor and  the use of a
control gate  on  the  foul  sewer  appear desirable  to  obtain maximum  results
 from the use 'of  the  chamber.    '   "  "  '      ' "            '        ' :
                           177

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         Amount of Character of Settleable Solids.  The sewer system
must provide capacity to handle the increase in settleable solids which
will be captured from the combined sewer overflow and discharged to
the  treatment plant.  In the case of Lancaster, Pennsylvania, this
could amount to mote than a ton  of solids from one device in a very
short period of time.  Additional grit removal and sludge processing
equipment may be necessary.  Should the foul flow be pumped, sumps and
pumps should be designed to handle the anticipated high solids content.
         If the settleable solids which can be anticipated in the
combined sewer overflow can be defined by the amount, specific gravity,
and particle size, the mathematical and the hydraulic model may be
used to determine the size of the chamber required to achieve desired
levels of solids removal*  Ordinarily this will not be feasible and
the flow criteria developed by the hydraulic model will be used to
design the facility and predict removal efficiencies.
         In order to evaluate the efficiency of the chamber, facilities
should be provided for sampling the .inflow, foul sewer flow and overflow.
Settleable solids should be delineated in all of these flows.  The
quantity of inflow and foul sewer flow should also be measured.
Difficulties in obtaining representative samples from any of the flows
may make evaluation difficult.  However, the treatment plant or
combined sewer overflow treatment facility  , if used, should provide an
excellent means of making a gross evaluation into the effectiveness
of the chamber.
         Provision of a means to measure the depth of flow over the
weir should act to give a reliable measurement of the flow when added
to the quantity of flow to the foul sewer.
         Data from many full-scale operations, operating with various
flow conditions and  solid loadings will be  necessary to properly
evaluate the usefulness of the swirl  concentrator as a combined sewer
overflow regulator.
                            178

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          Cost of Facility.   The cost of construction of the swirl
 concentrator will vary with the length of inlet pipe which must be  •
 reconstructed, the depth of the chamber and the nature of the material
 to be excavated, the need for a roof, and the'general site conditions
 under which the work will be conducted.  The materials of construction
 will usually be concrete and steel and elaborate form work will not
 be required.
          For the Lancaster,  Pennsylvania, application where a
 36 foot diameter chamber in limestone is contemplated, the preliminary
 estimate of cost was $100,000 in 1972 costs.   This cost estimate included
 a roof,  foul sewer outlet control and a wash-down system.   Site
 construction problems are minimized in as much  as the construction will
.be off of the street right-of-way.
                             179

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                    SECTION X
     THE  EPA  STORMWATER  MANAGEMENT  MODEL
              A CURRENT OVERVIEW
                       by
  Wayne C. Huber, James P. Heaney, Hasan Sheikh
Department of Environmental Engineering Sciences
            University of Florida
          Gainesville, Florida 32611
                        181

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                        1,  INTRODUCTION






              A,  COMBINED AND STORM SEWER OVERFLOWS



     An enormous pollution load is placed on streams and other




receiving waters by combined and separate storm sewer overflows.




It has been estimated that the total pounds of pollutants (BOD




and suspended solids) contributed yearly to receiving waters by




such overflows is of the same order of magnitude as that released




by all secondary sewage treatment facilities (Gameson and Davidson,




1964; Field and Struzeski, 1972).  The Environmental Protection




Agency (EPA) has recognized this problem and led and coordinated




efforts to develop and demonstrate pollution abatement -procedures




(Field and Struzeski, 1972).  These procedures include not only




improved treatment and storage  facilities, but also possibilities




for upstream abatement alternatives such as rooftops and parking




lot retention,  increased infiltration, improved street sweeping,




retention basins and catchbasin cleaning or removal.  The com-



plexities and costs  of proposed abatement  procedures require  that




 care and effort be expended by municipalities  and  others charged




 with, decision making for the  solution of these problems.






                B,   THE STORM  WATER MANAGEMENT  MODEL



      It  was  recognized that an invaluable tool to  decision  makers




would be a  comprehensive mathematical computer simulation program




 that would  accurately model quantity (flow)  and quality (concen-




 trations)  during the total urban rainfall-runoff process.   This model
                              182

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  woyld not only provide an accurate representation of the physical




  system,  but also provide an opportunity to determine the effect  of




  proposed pollution abatement procedures.   Alternatives-could  then




  be  tested on the model and least  cost  solutions  could be developed.




       As  a result,  the  University  of Florida (UF), Metcalf and Eddy,




  Inc.,  Engineers  (ME) and Water Resources Engineers  (WRE)  were




  awarded  a joint  contract for the  development, demonstration and




  verification of  the Storm Water Management Model  (SWMM).  The re-




  sulting  model, completed in  Ociober> 1970, has been  documented




  (EPA,  1971a,  b,  c, d)  and  is presently being used by a variety




  of consulting firms and  universities.




 :     The present SWMM  is descriptive in nature and will model most




 urban configurations encompassing rainfall, runoff, drainage,




 storage-treatment, and receiving waters.  The major components of




 the SWMM are illustrated in Figure 1-1.  However, it does not




 define nor determine any decisions for the system or consider alter-




 native methods for efficient economic comparisons.







                         C, 'DECISION MAKING



      In recognition of  the need  for improved decision making




 capabilities, the University of  Florida submitted a proposal to EPA




 titled "A Decision Making Model  for the Management  of Storm Water .




 Pollution Control" in which it was intended to provide a  sys-




 tematic   procedure which, could be applied  to a wide  variety of




.specific  circumstances  in support  of intelligent management decisions,




 The work  required to obtain a least  cost solution would be considerably
                            183

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 RUNOFF.
(RUNOFF)
    DECAY'
    (QUAL)
                     INFILTRATION
JFILTRAT
 (INFIL)
 TRANSPORT
  (TRANS)
                        EXTERNAL
                        STORAGE.
                        {STORAG)
                     RECEIVING WATER
                        (RECEIV)
                     DRY WEATHER
                        FLOW
                        (FILTH)
INTERNAL
S"TORAGEV
(TSTROT)
                      TREATMENT
                        (TREAT)
  COST
(TSTCST)
                    COST
                  (TRCOST)
        Note:  Subroutine names  are  shown  in parentheses.


                          Figure 1-1
                  Overview of Model,Structure
                             184

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  reduced by means of  determining  the  origin  of  the most severe 	••"—




  pollution load, consideration  of all upstream  and downstream"pol-




  lution abatement procedures and  associated  costs, and through the




  possible use of mathematical optimization techniques.        ;,




      The project was funded as part  of an EPA Demonstration




  Grant to Lancaster,,,. Pennsylvania (Federal Grant No.. 11023GSC)-,




  in which an underground "silo,"1  a swirl concentrator and a micro-




  strainer were to be installed at the outfall of the Stevens Avenue




 Drainage District to control overflow into the Conestoga Creek    *




  (details are presented in the next section).                      ',




      Results of the decision-making methodology and other aspects




 of the research have recently been formulated .(Heaney and Huber,




 1973).   Decision-making for urban storm water management is




 presented  in the broader context  of urban water resources management.




 Pollution  sources and control options are inventoried and accompanied




 by economic  data.   Performance standards  are considered  and the




 importance of automobile-related  facilities  (e..^.., streets,  parking




 lots, curbs and  gutters) as  contributors'to  storm water pollution




 and quantity is  emphasized.  Finally, a,linear  programming  and game




 theory approach  is  used  to develop efficient  and equitable  control



 strategies.




     This paper presents an overview  of the SWMM by illustrating  its




use in Lancaster; the following section is "taken from the Final




Report (Heaney and Huber, 1973) from which other details are available.




Major revisions to the Model have been made to include urban erosion
                               185

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prediction, modeling of new treatment devices and'biological treat-




ment facilities, monitoring of significant pollution sources,




flexibility in modeling new areas, new and improved cost functions




for treatment and storage options and a modest hydraulic design




capability as well as minor programming changes and slight format




revisions.  The SWMM has proven to be a useful and economical




tool in the assessment of urban storm water problems.  Incjividual




runs described in the following section,  for instance, could be




accomplished using less than  three minutes of CPU time on the




IBM 370/165 at the University of  Florida  Computing Center, for a



Runoff-Transport-Storage/Treatment-Receiving simulation.  Although




computational  changes vary,  they  are well within reasonable bounds.
                               186

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                2,  TESTING IN LTOSTER,  PENNSYLVANIA




      The/City of Lancaster, Pennsylvania, population 79,500, is



 .situated in a drainage area of about 8.24 square miles (5,274 acres),



 The receiving stream in the Lancaster area is the Conestoga Creek



 which drains an area of approximately 473 square miles into the




 Susquehanna River.   The average flow is 387 cubic feet per second



 with a maximum recorded flow of 22,800 cubic feet per second.




      There are two  sewage treatment  plants within the city,  both of



 which discharge into the Conestoga Creek.   The North Plant with a



 capacity of 10 mgd  serves a population of  36,000 people, and  the



 South Plant recently expanded  from 6 mgd to 12 mgd and is  designed to




 serve 69,000 people.   Both plants provide  secondary  treatment.   About



 one  third of the flow to  the North Plant is derived  from areas with



 separate sewers outside  the city serving an estimated  population of



 17,500 people  and some industries.   The remaining  two  thirds of  the



 sewage flow to  the North  Plant is derived  from the combined sewers



 serving  the north part of  the city plus about  250 suburban acres



 estimated  to have 18,500 people.and many water-using industries.  In



 addition, most of the year  the water table  is high resulting in con-



 siderable infiltration.  An overflow line diverts excess flow to the



 Conestoga during wet weather.  The North Plant drainage,area is esti-



mated at 3.72 square miles,




     The South Plant is designed to handle a population of 34,500



served by combined sewers and,in addition,up to an approximately equal
                             187

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amount from separated sewers throughout the surrounding area.   The




South Plant drainage area encompasses 4.52 square miles and is




comprised of four districts.  Stevens Avenue district which is the




subject of EPA  demonstration grant is one of the four districts




connected to the South Plant,  Three of the districts, including




Stevens Avenue, pump the sewage from a receiving station within the




district to the South Plant.  All locations have overflow arrange-




ments  that discharge into  the Conestoga Creek when the capacity of




the system is  exceeded.



      The  total drainage  area of  the Stevens Avenue district is 227




acres which, while only  about 4.3%  of  the total Lancaster



 drainage area served by  North  and South treatment plants,  is  17%  of




 the drainage area designed to  flow into the South Plant from  combined




 sewers.  The population within the Stevens Avenue district is esti-




 mated at 3,900.  Figure 2-1  illustrates various drainage districts




 within the city.






 1.  DEMONSTRATION GRANT DESCRIPTION



       In order to  remedy the situation resulting from combined sewer




 overflows, the City of Lancaster decided to explore means other  than




 sewer separation. Construction  of several underground  silos at




 various  locations within  the  city  is  contemplated for retention  of




 overflow during wet periods and subsequent pumping  to  the treatment




 plants during low flow  periods,



       Stevens Avenue district  was selected as the demonstration site




  for evaluation of the effectiveness of a silo in combating combined
                              188

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                         189

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sewer overflows.  The sewer layout for Stevens Avenue district is

shown in Figure 2-2.   During normal dry weather periods, the dry

weather flow is pumped to the South treatment plant.  During wet

periods, when the incoming flow to the pump station exceeds the

capacity of the station, the overflow discharges directly into the

Conestoga Creek through a 60 inch sewer located at point 6 on

Figure  2-1.

     The City of Lancaster also authorized APWA to develop design

parameters for   a  full-scale swirl concentrator for removal of

solids  prior *to the retention of flow in  the underground silo.

Location of the demonstration site is shown in Figure.2-2.  A

flow diagram of the proposed swirl concentrator-silo treatment is

presented  in Figure 2-3.   In order to  fully evaluate this treatment

the city decided  to include chlorination  and microstraining as a

part of this demonstration project.  The  capacity  of the silo is

expected  to be 160,000 cf.

      The  tasks assigned to  the  University of Florida were  as  follows;

      1)  Conduct  further verification and testing  of the Storm
          Water Management Model based on active overflow
          measurements on selected storm events and to make
          refinements to the Model;

      2)  Provide results of simulations to the APWA in  order
          for it to develop design criteria and sizing of the
          swirl concentrator;

      3)  Simulate,  the effect of the swirl concentrator-under-
          ground silo treatment; and

      4)  Simulate  the effect of combined sewer overflow from
          the entire city to the Conestoga Creek.
                              190

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         CONDUIT USED IN STUDY

     ฉ  SUBCATCHMENT MANHOLE
      9)  MANHOLE

     ——	CONDUIT NOT USED IN STUDY
    STEVENS AVENUE  DRAINAGE AREA
           LANCASTER,PA.
                                                             SCALE  IN FEET
                                                       0           500

_„       A                     Figure 2-2
Stevens Avenue  Drainage  Area with Runoff-Transport  Numbering System.
1000
                               191

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192

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  2.   DESCRIPTION OF> THE STEVENS  AVENUE  RUNS




      A total  of  four studies  comprising nine  storms were  simulated.




  The  city and its engineers provided input data as well as two overall




  measurements.   The Stevens Avenue district was subdivided into 41




  subcatchments.  A  description of each  study and its results are given



  below:





      Study No.  2.—The first study was based on a/series of storms




 between July 29 and August 3, 1971.  This six-day period deposited




 a record amount of precipitation throughout the Lancaster area        -




  (variously measured between 7.3 and 9.46 inches);  During;four of the




 six days,  the storms were very,intense over short periods;  in one case,




 being'the  second heaviest of record!   For purposes of simulation,




 Study No.  1 was  divided into six storms.   The amount  and times of




 precipitation assumed for each of these six storms are shown in




 Figures 2-4  through 2-9   and results of  computer simulations  for




 each  of these storms are  shown in;the same  figures.   These figures




 show  the expected quantity and quality  of the overflow from  the




 Stevens Avenue district for a given rainfall.  These  runs indicate




 that  an overflow/as high  as 400  cfs may be expected for a storm event



 similar to  Storm No.  6.               ,-•-,.




\.     These  computer runs  also indicate  that .total suspended solids and




 BOD discharges expected in the overflow aay be on the order of magnitude




 of 778  pounds and 635 pounds respectively for Storm No. 5 and 849 pounds"




 and 768 pounds respectively for Storm No. 6.  Unfortunately,  since'




 actual  flow measurements were not taken during this study, it was not pos-




 sible to determine the actual overflow quantity and quality.   However,
                            193

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.S
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           ^COMPUTED  FLOW  FROM  TRANSPORT
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   CO
        300"4locTsoo6=00     7=00
                      TIME, HOUR  OF  DAY
       CM
             .COMPUTED  BOD  FROM TRANSPORT
        3=00
                                                  8=00
                                           700     8--00
                       TIME,  HOUR  OF  DAY
                 COMPUTED  SS  FROM   TRANSPORT
         3:00
                  4:00
                           5=00
                                   6:00
                                            7=00
                       TIME,  HOUR  OF DAY
                                                    8--00
                            Figure 2-4
           Runoff-Transport Simulation for Stevens Avenue.
                          Study 1, Storm 1.
                          194

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.5




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111
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               RAINFALL
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                    TIME,  HOUR  OF DAY
             • COMPUTED  BOD  FROM  TRANSPORT
                    5=00         7=00



                   TIME,   HOUR  OF  DAY
                          9=00.
               COMPUTED   SS  FROM   TRANSPORT
5=00
                                 7:00
                    TIME*  HOUR OF DAY
          •              Figure 2-5

        Runoff -Transport Simulation .for Stevens Avenue.

                     Study 1, Storm 2.
                      195

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       3:00
       1:00
                                 RAINFALL
                              COMPUTED  FLOW  FROM  TRANSPORT
                   4:00        5=00       5=00
                       TIME ,  HOUR OF DAY
 7:00
                         COMPUTED  BOD  FROM  TRANSPORT
                   4:00 .       5'00        6=00 .

                        ,TlME,  HOUR  OF DAY
7=00
                           COMPUTED   SS   FROM  TRANSPORT
                   4=00       5=00       6=00
                        TIME, HOUR  OF  DAY
7=00
           Runoffs-Transport  Simulation, for Stevens Avenue.
                         Study 1, Storm 4.
                             197

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 results of subsequent studies indicate that  actual  overflows  are




 generally predicted adequately by computer runs.  Quality  predictions



 are more variable.




      Results of this study were used by'APWA in sizing the swirl  con-




 centrator.  A design flow of this device was established at 150 cfs.




      Computer simulation studies were also conducted  for all  six




 storms  to evaluate  the effect of the swirl concentrator-underground




 silo facilities on  the combined overflow quality.   The results of




 Storm Nos. 5 and 6  are shown on Figures  2-8   and 2-9   respectively.




 As  illustrated in these figures,  the quality of the overflow  is




 significantly improved through the installation of  the swirl  concen-



 trator-underground  silo.




     Study No.  2.—This  study consisted  of a storm  that began in the




 morning of August 27,  1971  and continued almost 30  hours to the




 morning of the next day.  It  resulted  in varying amounts of rainfall




 throughout the city averaging more than  3.5  inches.  The results of




 the  computer simulation were  similar to  those obtained from Study No. 1,




 and  for this  reason are not included herein.  Again, no measurements



were taken during this study.




     Study No.  3.—This study is-based on  a  relatively minor rainfall




event of March 22,  1972.  This  study is  of special  importance, however,




because it  is  one of the types most frequently experienced in terms of




intensity of rainfall.  It is also one for which relatively complete




verification data such as rainfall, flow readings and samples were




collected.  The rainfall is shown in Figure 2-10 along with results




of the  computer simulation showing overflow quantity and quality.
                                   198

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         \
         .S
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               ro
              
              •So
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              "c\r
 ^-RAINFALL

•COMPUTED  FLOW  FROM  TRANSPORT


  -SILO  STORAGE

      COMPUTED  FLOW  TO  RIVER
               ^COMPUTED   FLOW  TO   SOUTH
                PLANT   WITH  SILO
                3=00
                                     4:00


                            TIME,  HOUR  OF  DAY
                                      5=00
               u>
                        -COMPUTED   BOD   FROM   TRANSPORT

                         -SILO STORAGE

                         ^COMPUTED  BOD  TO   RIVER
                              COMPUTED  BOD   TO  SOUTH  PLANT  WITH,
               3;00                  4:00                  5:00
                      *,"..'     '       .,     '     '        •

                          TIME,   HOUR  OF  DAY






                         COMPUTED  SS  FROM  TRANSPORT


                         'SILO STORAGE


                           :OMPUTED SS  TO RIVER
                           /COMPUTED   SS  TO  SOUTH  PLANT WITH.
                           / SILO

                          > ^-~^
               3:00
                                     4=00
                                                          5:00
                         TIME,  HOUR   OF  DAY                        ..  '.

    ,.,.                           Figure 2-8                     \
Runoff-Transport  Simulation for Stevens Avenue with Silo an4 Swirl Concentrator,
                             Study 1, Storm 5.      .

-------
        O-,
        CO
     55
     LJ
     z
     < CM
        CM
        CO
  RAINFALL
  -COMPUTED  FLOW  FROM  TRANSPORT


        COMPUTED   FLOW TO   RIVER
                                    •COMPUTED FLOW  TO  SOUTH  PLANT
                                    WITH  SILO
              3=00
             to-
              4!00

     TIME,  HOUR  OF DAY


-SILO  STORAGE


    COMPUTED BOD  TO  RIVER
                                                         5=00
                    /!.__ y	
             3=00
                         /COMPUTED  BOD   FROM  TRANSPORT

                          /COMPUTED  BOD  TO SOUTH PLANT  WITH  SILO
              4iOO                  5:00

     TIME, 'HOUR  OF  DAY


 IOMPUTED   SS    FROM  TRANSPORT.


    •COMPUTED  SS  TO  RIVER


      SILO STORAGE


       COMPUTED SS  TO SOUTH  PLANT WITH  SILO
              3:00                  4=00

                        TIME,  HOUR  OF  DAY
                                    5=OO
                               Figure 2-9
Runoff-Transport  Simulation for Stevens Avenue with Silo and Swirl Concentrator.
                             Study 1, Storm 6.
                                 200

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 Shown in the same illustration are the actual quantity and quality




 measurements of the overflow.  It can be seen that agreement between




 the computer simulation and the actual measurements of flow is fairly




 good considering the degree of accuracy of the input data as well




 as that of the measurements.  The agreement between the computed and




 measured quality parameters is not as good as for flows.




      Computer simulations were also conducted on this study to deter-




 mine the effect of the swirl concentrator-underground silo system.




 These results are also shown in Figure 2-10.   With the silo system,  the




 Model indicates no overflow in the Conestoga .Creek.




      Study  No.  4.— This study is  based on a storm that occured on




 November 29,  1971.   This study is also of importance  from the  stand-




 point of Model  verification as overflow measurements  were conducted




 during this storm.   The rainfall  and  results  of  the computer simu-




 lation for  this storm  are  presented in Figure 2-11 along  with  the




 actual measurements  for comparison.   Again, it/can be seen that




 agreement between the  actual measurements and predicted results is




 fairly good.  The predicted results of  the swirl  concentrator-under-



 ground silo system are  also shown in  Figure 2-11.






 3.' RUNS  IN THE NORTH AND  SOUTH DISTRICT




   _  Limited computer simulations were also conducted for the North




and South drainage districts.  The North district was subdivided




into 66 catchments and the South district into 104 catchments.   The




sewer layouts for the North and South districts are shown in Figures




2-12 and  2-13.
                             201

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                             OMPUTED, FLOW
                                SOUTH  PLANT
                            WITH  SILO
                                                           EASURED  FLOW
                        -COMPUTED  FLOW  FROM
                         TRANSPORT
                 11:20
                                                             4:20
I2':20      1:20     2i20      3=20

      TIME, HOUR  OF  DAY


  /MEASURED BOD


              BOD  FROM  TRANSPORT
                                                  •COMPUTED  BOD TO
                                                  SOUTH  PLANT WITH  SILO
                 11:20
12=20
                                                             4=20
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               •r CM
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                : co
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   |:20     2=20     3:20

TIME,  HOUR  OF  DAY
MEASURED  SS
                                COMPUTED  SS  FROM  TRANSPORT
           MEASURED  SS
                                                      .COMPUTED  SS  TO
                                                      SOUTH  PLANT  WITH  SILO
                  11=20
12=20
   1:20
                                            2:20
                           3'20
                             4:20
                                TIME,  HOUR  OF  DAY

                                     Figure 2-10                  .-,.'•,.•
Runoff-Transport Simulation for Stevens Avenue with Silo and Swirl Concentrator .
            Study 3.  No Overflow to River Since Silo Capacity not Exceeded.
                                202

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           .ฃ
           I-?
           I
           i
                RAINFALL

               COMPUTED  FLOW  FROM  TRANSPORT

               cฐMPUTED  FLOW  TO RIVER

               MEASURED  FLOW

               /COMPUTED  FLOW  TO  SOUTH
         j   \\(   PLANT WITH  SILO
         I    * ป\\i  •    •       '
        ,}...„ ..\%VP... - ... ^. ..........
                                            5;I5       T^Ii"

                               HOUR,  TIME  OF  DAY


                       ^COMPUTED BOD  FROM TRANSPORT
                          9=15
                                                   o- MEASURED BOD
                        /•COMPUTED BOD TO  SOUTH  PLANT WITH  SILO

                                                 -COMPUTED  BOD  TO  RIVER
                          IMS      3'!5     5:15     TI59=15

                                HOUR,  TIME  OF  DAY


                          -COMPUTED   SS   FROM  TRANSPORT


                                                  o-MEASURED  SS
                                      COMPUTED SS  TO SOUTH   PLANT
                                      WITH  SILO
                                            IMPUTED  SS TO   RIVER
                          1=15
3:I5
5=15
                               HOUR,   TIMS  OF DAY
,                                    Figure 2-11
Runoff-Transport Simulation for Stevens  Avenue with Silo and Swirl Concentrator.
               •  '  '  -  .               Study 4.

                      '                 203      ;'

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             204

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205

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     Results of computer simulation for Study No.  3 for the North




district are presented,in Figure 2-14 and for the South .district




in'Figure 2-15.  The North district outfall is located at point 1




while the South district outfall is located at point 12 as shown




in Figure 2-11.



     An examination of these figures shows that for a rainfall event




equivalent to Study No. 3, overflow from the North district would




be about 100 cfs and from the South district, 160 cfs.  The BOD




and SS discharged to the river would be 7,075 pounds and 9,696




pounds from the North District and 4,468 pounds and 10,006 pounds




respectively for the South district..






4.  EFFECT ON RECEIVING WATER



    To simulate the effect of the  overflow  on the  Conestoga Creek,




Receiving Water Model was run on the  entire city for  the  Study  No. 3.




The manner in which various  districts were  combined is shown  on




Figure  2-16^  In  conducting  this run, the swirl concentrator




was  used at  Stevens Avenue while Refined Storage and



Treatment Model,  as described  elsewhere*  was utilized to simulate




 the  existing biological treatment  at the North and South plants.  The




 silo was deleted in order to have  an overflow at Stevens Avenue




 outfall since the installation of  the silo prevents any overflow for




 rainfall event equivalent to Study No. 3.



      The reaeration coefficient for the.Conestoga Creek was computed




 from a formula by O'Connor and Dobbins (1958).  Results of the Receiving




 Water Model are shown in Figures  2-17 through 2-20.  Figure 2-17 shows
                                     206

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              COMPUTED  FLOW
               FROM TRANSPORT
11=20
          I2:20      |i20      2=20     3-:20

                TIME,  HOUR  OF  DAY
              IMPUTED  BOD FROM TRANSPORT
                                           4:20
                                   COMPUTED BOD
                                    FROM  TREATMENT
 12:20
        1=20     2=20     3=20      4=20     5=20

              TIME,  HOUR  OF  DAY



        ^COMPUTED SS FROM TRANSPORT

                -COMPUTED  SS  FROM TREATMENT
12:20
                                   4:20
              TIME,  HOUR   OF  DAY

                .  Figure 2-14
     Simulation of North Drainage District.
                   Study 3.
                   207
                                          5=20

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  SOUTH
    A
 RUNOFF  a
  TRANSPORT
          SOUTH
            B
        RUNOFF  a
STEVENS
  AVE.
RUNOFF  8r
TRANSPORT
                                        RUNOFF
                                        TRANSPORT
TRANSPORT
                                 STEVENS
                                    AVE.
                               TREATMENT
COMBJNE
  SOUTH
                     SOUTH  a
                     STEVENS
                       SILO
                     SOUTH
                    TREATMENT
                       PLANT
                                        NORTH
                                      TREATMENT
                                        PLANT
                                COLLATE
                               SOUTH, NORTH
                                &  STEVENS
                                 OVERFLOW
                          RECEIVING
                     ' Figure 2-16
Combination of SWMM Runs for Overall 'Lancaster Simulation.
                          209

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DO profiles 24 and 48 hours after the storm inception, while

Figure 4-28 shows the BOD profile for the same period.  Suspended

solids and coliform are shown in Figures 2-19 and 2-20 respectively.

Initial values used to simulate the Receiving Water Model are listed

in Table  2-1:

                             TABLE 2-1
       PARAMETERS USED FOR SIMULATING RECEIVING WATER MODEL
Dissolved  Oxygen in  Conestoga  Creek  (all junctions)

BOD  in Conestoga Creek (all junctions)

Suspendid  Solids in  Conestoga  Creek  (all junctions)

Coliform in Conestoga Creek (all junctions)

Decay Coefficient (BOD)

Reaeration Coefficient

Flow in Conestoga Creek (entering junction 1)
 10.0 mg/1

  5.0 mg/1

 10.0 mg/1

 50/100 ml

  0.20/day

  1.50/day

700 cfs
 5.  SUMMARY

      The above discussion can be summarized as follows:

      1)  The SWMM was able to predict fairly accurately
          the quantity as well as quality of the combined
          overflow for the Stevens Avenue district in
          Lancaster.

      2)  The installation of the swirl concentrator and
          the silo will result in substantial improvement
          in the quality of the overflow at Stevens Avenue,
          provided the full-scale performance of the swirl
          concentrator is comparible  to the results obtained
          in laboratory studies by APWA.
                               210

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                          3,
American Public Works Association, "Water Pollution Aspects
   of Urban Runoff,"• Federal Water Pollution Control Admini-
   .stration Contract WP-20-15, 1969.

Environmental Protection Agency, "Storm Water Management Model,"
   Water Pollution Control Research Series, Washington, DC, 1971:

   a.  "Volume I, Final Report,"  Rept. No. 11024DOC07/71
   b.  "Volume II, Verification and Testing,"  Rept. No. 11024DOC08/71
   c.  "Volume III, User's Manual,"  Rept. No. 11024DOC09/71
   d.  "Volume IV, Program Listing,"  Rept. No. 11024DOC10/71

Field R., and E. J. Struzeski, Jr., "Management and Control
   of Combined Sewer Overflows,"  J.  Water Pollution Control
   Federation., Vol. 44, No. 7, 1972.

Gameson, A. L., and R. N. Davidson, "Storm Water Investi-
   gations at Northhampton,"  Institute of Sewage Purification,
   Conference Paper Np. 5, Annual Conference, Leandudno,
   England, 1962.

Heaney, J. P., and W. C. Huber, "A Decision-Making Model for the
   Management of Urban Storm Water Pollution,"  Final Report to
   Lancaster, Pennsylvania and Environmental Protection Agency,
   Department of Environmental Engineering Sciences, Gainesville,
   Florida, June, 1973.

O'Connor, P.  J., and W. E. Dobbins, "Mechanism of Reaeration
   in Natural Streams,"  Trans. ASCE3  Vol. 123, 1958.
                             215

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                Simulation results presented herein were  performed for the




           City of Lancaster, Pennsylvania as part of  Demonstration Grant




           No. 11023GSC from the Environmental  Protection Agency.  We are




           grateful to many people in Lancaster,  EPA,  Meridian Engineering,




           Inc. (consultants to Lancaster), and APWA for  their cooperation




           and suggestions.  Our systems  analyst, Mr.  W.  Alan Peltz "bore the




           brunt of the computational effort.   Computations were performed




           on the IBM 370/165 at the Northeast  Regional Data Center at the




           University of Florida.
*US. GOVERNMENT PRINTING OFFICE: 1974 546-317/Z96 1-3
                                           216

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   SELECTED WATER
   RESOURCES ABSTRACTS
   INPUT TRANSACTION FORM
*31 3.  AccessionNo.
   4.  Title
                 Combined Sewer Overflow Seminar Papers
   7.  Authors)
                 USEPA Storm &  Combined Sewer technology Branch
   9.  Organization  jj.g. Environmental Protection Agency
                 Edison Water Quality Research Laboratory
               ,  National Environmental Research Center- Cinn.
 	Edison, New Jersey

                                                                    10. Project No.
  11.  Contract/'Grant No.
   IS. Supplementary Notes
                          U.S. Environmental Protection Agency Report No.  EPA-670/2-73-077
                          November 1973.
   16. Abstract
                      The U.S. Environmental Protection Agency in  conjunction
                 with the New York State Department of Environmental  Conser-
                 vation conducted three  one-day seminars on the problem of wet-
                 weather flow pollution  abatement.  Many facets of the  problem
                , were considered including a brief overview of its magnitude
                 and what the federal government is doing to manage and control
                 this source of pollution.   Various management, control,  and
                 treatment techniques were described and the most  up-to-date
                 information on design and economics was presented.   The  audi-
                 ence consisted of consulting and municipal engineers from all
                 areas of New York State.

                      This publication is  a compilation of the papers presented
                 at  the seminar.
   17a. Descriptors
                Combined sewer overflow management and control
      Identifiers
                Infiltration/Inflow,  Regulation, Pressure Sewers,  Microstraining,
                Filtration, Dissolved Air Flotation, Disinfection, Storm Water
                Management Model.
  I7c. CO WRR Field & Group
  18.  Availability
                                     aifc
                               B,2^V-*yP .%?>•; ^t*"1 -W-Tis;-;  U.S. DEPARTMENT OF THE I
                               KfJjifeiiitpVito: ;,';i%,^;.;::-,:-•;-!ซ':  WASHINGTON. D. c. 20240
                                                        Send To:
  Abstractor USEPA Storm and Combined  I Institution U.S. Environmental Protection Agency
WRSIC 102 (REV. JUNE i97ป Sewer T.eclinolagy Brantsh

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