EPA-600/2-76-271
December 1976
Environmental Protection Technology Series


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                 RESEARCH REPORTING SERIES

 Research reports of the Office of Research and Development, U.S. Environmental
 Protection Agency, have  been grouped  into five series. These  five broad
 categories were established to facilitate further development and application of
 environmental technology. Elimination of traditional grouping was consciously
 planned to foster technology transfer and a maximum interface in related fields.
 The five series are:

      1,    Environmental Health Effects Research
      2.    Environmental Protection Technology
      3.    Ecological Research
      4,    Environmental Monitoring
      5.    Socioeconomic Environmental Studies

 This report has been assigned to the  ENVIRONMENTAL PROTECTION
 TECHNOLOGY series. This series describes research performed to develop and
 demonstrate instrumentation,  equipment, and methodology to repair or prevent
 environmental degradation from point and  non-point sources of pollution. This
 work provides the new or improved technology  required for the control and
 treatment of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

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                                        EPA-600/2-76-271
                                        December  1976
THE SWIRL CONCENTRATOR FOR EROSION RUNOFF TREATMENT
                             By
       Richard H. Sullivan, American Public Works Association
                   Morris M. Cohn, Consultant
             James E. Ure, Alexander Potter Associates
         F. E. Parkinson, LaSalle Hydraulic Laboratory, Ltd.
               Paul E. Zielinski, Clemson University
                  Contract Number 68-03-0272
                        Project Officer

                        Richard Field
               Storm and Combined Sewer Section
                  Wastewater Research Division
      Municipal Environmental Research Laboratory (Cincinnati)
                  Edison, New Jersey  08817
    MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
          OFFICE OF RESEARCH AND DEVELOPMENT
         U.S.ENVIRONMENTAL PROTECTION AGENCY
                  CINCINNATI, OHIO 45268

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                     DISCLAIMER

    The Municipal  Environmental  Research  Laboratory  —
Cincinnati, has  reviewed  this report  and  approved  its
publication.  Approval does  not signify that the contents
necessarily  reflect  the  views  and policies  of the U.S.
Environmental Protection Agency, nor does mention of trade
names  or  commercial products constitute endorsement or
recommendation for use.
                         11

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                          FOREWORD

    The Environmental Protection Agency  was created because of
increasing public and government concern about  the  dangers  of
pollution  to the  health  and  welfare  of  the American  people.
Noxious air, foul water, and spoiled land are tragic testimony to the
deterioration of our natural environment. The complexity of that
environment  and the interplay between its components require a
concentrated and integrated attack on the problem.
    Research and  development is that necessary first step  in
problem solution and it involves defining the problem, measuring its
impact, and searching for solutions. The Municipal Environmental
Research Laboratory develops new and improved technology and
systems  for  the  prevention, treatment,  and management  of
wastewater and solid and hazardous waste pollutant discharges from
municipal  and  community  sources,   for  the  preservation  and
treatment of public  drinking water supplies, and to minimize the
adverse economic, social, health, and aesthetic effects of pollution.
This publication is  one of the products of that research; a most vital
communications  link between  the   researcher  and  the  user
community.
    As part of these  activities, the study described here investigated
the applicability of  a swirl concentrator chamber to perform the
function of concentrating erosion products from stormwater runoff.

                                     Francis T. Mayo
                                     Director
                                     Municipal Environmental
                                     Research Laboratory

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                  ABSTRACT
    A  device  for  the  partial  removal of erosion
products in stormwater runoff has been developed.
The swirl concentrator as an erosion control device
has been designed to concentrate the heavier soils
from large flows. The  concentrated  underflow  of
up  to  14 percent of the flow can be directed to a
forebay or settling basin.
    The device is circular and for small watersheds
a simple stock watering tank  could  be used  with
only minor modifications.
    The design  of  the swirl  concentrator as  an
erosion control  device is based  upon a hydraulic
model  study and research previously sponsored by
the City of Lancaster, Pennsylvania  and  the  U.S.
Environmental  Protection   Agency  into  the
mechanics  of  secondary  motion  flow-fields  as
developed in the swirl concentrator.
    This  report  is  submitted by the American
Public  Works Association in partial fulfillment  of
the  contract  68-03-0272 between  USEPA  and
APWA Research Foundation.
                     iv

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                                      CONTENTS

                                                                               Page No.
Chapter I    Overview, Conclusions and Recommendations	1
Chapter II   The Study  	6
Chapter III  Design Factors for Swirl Erosion Runoff Treatment Prototypes	13
Chapter IV  Glossary of Pertinent Terms	31
Chapter V   Appendix — LaSalle Hydraulic Laboratory Report	32
                                       TABLES

 1  Sieve Analysis    	24
 2  Swirl Efficiency Analysis   	26
 3  Modifications Tested in Model and Results  	45
 4  Comparable Recovery Rates for Sloping and Horizontal
    Chamber Floors	62
 5  Percent Suggested Recovery in Model	69
                                       FIGURES

  1  Schematic View, Swirl Concentrator as an Erosion
    Runoff Treatment Facility	3
  2  Flow Diagram	4
  3  Model  Layout   	9
  4  Original Layout for Test No.  1	10
    a  Plan and Elevation	10
    b  Photos,  Original Layout and Original Layout with Inlet Baffle	11
  5  Prototype Particle Sizes Represented by Gilsonite — 1.06       	14
  6  Recovery Rates on Model as Function of Particle  Settling
    Velocity and Discharge with 5 Percent Draw-off	15
  7  Recovery Rates on Model as Function of Particle  Settling
    Velocity and Discharge with 10 Percent Draw-off	16
  8  Recovery Rates on Model as Function of Particle  Settling
    Velocity and Discharge with 14 Percent Draw-off  .	17
  9  Predicted Prototype Recovery Rates with 5 Percent Draw-off   	18
 10  Predicted Prototype Recovery Rates with 10 Percent Draw-off	19
 1.1  Predicted Prototype Recovery Rates with 14 Percent Draw-off	20
 12  General Design Dimensions, Scale — 1:4	  .21
 13  Prototype Particle Sizes Represented by Petrothene — SG 1.01	25
 14  Standard Stock Watering Tank	29
 15  Gradation Curve for Gilsonite Used in Model   	34

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                                   FIGURES (Continued)
                                                                               Page No.

16  Prototype Settling Velocities Simulated by Gilsonite - SG 1.06   	35
17  Gradation Curve for Petrothene Used in Model   	37
18  Prototype Settling Velocities Simulated by Petrothene-SG 1.01    	38
19  Prototype Particle Sizes Represented by Petrothene - SG 1.01  .	39
20  Range of Prototype Grit Particle Sizes (SG 2.65) Simulated,
    Respectively, by Gilsonite, Petrothene and Petrothene Dust   	40
21  Settling Velocity Distributions for Petrothene Dust and
    Stormwater Runoff	41

22  Settling Velocity Distributions for Shredded Petrothene X
    and Stormwater Runoff	42
23  Settling Velocity Distribution for Gilsonite and
    Stormwater Runoff	43
24  Model Layout for Tests 2 to 13, Modification 1	47
    a  Plan and Elevation   . .		47
    b  Photos, Uneven Flow Spoilers Stuck on the 50.8 cm (20 in.)
       Weir Disk and Modification 1, Tested with a 3 I/sec
       (0.8 gal/sec) Discharge	  .	48
25  Photos, Deposit of Petrothene Found After 3 I/sec (0.8 gal/sec) Test	49
26  Influence of Inlet Deflector on Recovery Rate 0.50 m (20 in.) $
    Weir Disk 5 Percent Draw-off, Modification 11   	50
27  Model Layout for Tests 14 to 16, Modification 2   	'51
28  Model Layout for Tests 17 to 19, Modifications   	53
29  Photos, Inlet Baffle, Modification 3   	54
30  Model Layout for Tests 20 to 22, Modification 4   	55
31  Photos, Details, Modification 4	56
32  Model Layout for Tests 23 to 3 ^Modifications 5, 6, and 7   	57
33  Model Layout for Tests 3 2 to 3 5, Modifications   	58
34  Model Layout for Tests 36 to 38, Modification 9   	59
35  Photos, Details, Modification 7	60
36  Influence of Weir — Chamber Diameter Ratio	61
37  Model Layout for Tests 39 to 41, Modification  10	63
38  Model Layout for Tests 42 to 59 and 69 to 107, Modification 11	64
39  Influence of Chamber Floor Slope   	65
40  Influence of Continuous Underflow Draw-off, Modification 11	66
41  Model Layout for Tests 60 to 68, Modification  12	67
42  Influence of Inlet Size	68
43  Suggested Recovery Curves for Gilsonite and Petrothene in
    Model with 5 Percent Draw-off	70
44  Suggested Recover Curves for Gilsonite and Petrothene in
    Model with 10 Percent Draw-off	71
45  Suggested Recovery Curves for Gilsonite and Petrothene in
    Model with 14 Percent Draw-off	72
46  Retention Times for Prototype	73
                                         VI

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                ACKNOWLEDGEMENTS

         The American  Public Works  Association  is
     deeply indebted to the following persons and their
     organizations for the services they have rendered to
     the APWA  Research Foundation in carrying out
     this study for the U. S. Environmental Protection
     Agency.
                  PROJECT DIRECTOR
                   Richard H. Sullivan
                    CONSULTANTS
        Dr. Morris M. Cohn, P.E., Consulting Engineer
                  Paul B. Zielinski, P.E.
ALEXANDER POTTER ASSOCIATES, CONSULTING ENGINEERS
                  Morris H. Klegerman, P.E.
                     James E. Ure, P.E.
       LA SALLE HYDRAULIC LABORATORY, LTD.
                     F. E. Parkinson
                     George Galina
     U. S. ENVIRONMENTAL PROTECTION AGENCY
  Richard Field, P.E., Project Officer, Chief, Storm & Combined
            Sewer Section (Edison, New Jersey)
                          VII

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      AMERICAN PUBLIC WORKS ASSOCIATION
                   Board of Directors


                 Ray W. Burgess, President
               John J. Roark, Vice President
        Herbert A. Goetsch, Immediate Past President
           Robert D. Bugher, Executive Director
Joseph F. Casazza
John T. Carroll
William B. Drake
Lambert C. Minis
James J. McDonough
Robert D. Obering
Robert C. Esterbrooks
James E. McCarty
Kenneth A. Meng
Frank R. Bowerman
N. W. Diakiw
Rear Admiral A. R. Marschall
         APWA RESEARCH FOUNDATION
                 Board of Trustees
            Samuel S, Baxter, Chairman
            Ross L. Clark, Vice Chairman
        Robert D. Bugher, Secretary-Treasurer
         Richard H. Sullivan, General Manager
     John F. Collins
     Jean L. DeSpain
     William B. Drake
     Richard Fenton
     William C. Gribble, Jr.
     Erwin F. Hensch
     John A. Lambie
     Harold L. Michael
                        vm

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                                      CHAPTER I
                 OVERVIEW, CONCLUSIONS AND RECOMMENDATIONS
 Overview of the Study Project
     The discharge of erosion runoff solids and
 other debris into receiving waters represents a
 source  of  water  pollution of  significant
 proportion. Numerous points of construction
 and reconstruction which involve disturbance
 of the native soil and earth-moving operations
 make control  of erosion  and treatment of
 such runoff stormwaters an important factor
 in protecting  the  nation's  water resources,
 eliminating damage to reservoirs and other
 water areas, and preventing impairment of the
 natural beauty  of the land.
     The recent level of such construction as
 subdivision housing and highway projects may
 continue  and increase in the future, adding
 further reason  for invoking  the principle of
 control and treatment of erosion wastewaters.
     Study of  the application of the swirl
 solids-liquid  separator  for  the removal  of
 suspended solids  contained in  stonnwater
 erosion flows is a natural consequence of the
 proven   ability  of  such  secondary-flow
 patterns  in  similar  hydraulic  devices  to
 remove substantial  amounts of solids from
 combined sewer overflows during wet-weather
 flow incidents; to classify and separate  grit
 from  sanitary  and  combined  sewer
 wastewaters; and to achieve  clarification, or
 primary   treatment,  of   wastewaters  in
 treatment plants. These solids-removal uses of
 swirl chambers  have been demonstrated in a
 series  of  sequential  hydraulic  and
 mathematical model studies  carried out  as
 parts of previous  investigations  by  the
 American Public Works Association (APWA)
 Research  Foundation for, and on behalf of,
 the  U.S.Environmental Protection  Agency
 (USEPA)  and  other involved entities. These
 reports include:
 •   The Swirl Concentrator as a Combined
    Sewer  Overflow  Regulator  Facility,
    EPA-R2-72-008
 •   Relationship  Between  Diameter  and
    Height for   the  Design  of  a  Swirl
    Concentrator  as  a  Combined  Sewer
    Overflow Regulator, EPA-670/2-74-039
•   The   Swirl  Concentrator as  a  Grit
    Separator Device, EPA-670/2-74-026
«   Helical Bend Combined Sewer Overflow
    Regulator, EPA-600/2-7 5-062
These  studies  were,  in  particular,  directed
toward  solution of point pollution problems.
    In addition, studies are being conducted
by  Onondaga County, Syracuse, New York,
USEPA Grant No. S-802400 - swirl overflow
regulator, full-scale  prototype; Metropolitan
Toronto,  Ontario,  USEPA  Grant  No.
S-803157; -  swn-i  primary separator, pilot;
Metropolitan Sewer District No.  1, Denver,
Colorado, USEPA  Grant No. S-803157  -
swirl  degritter,  pilot; Monroe County Pure
Waters  Agency,  Rochester, New  York,
USEPA Grant No.  Y-005141, swirl primary
separator and degritter, pilots; The University
of  Wisconsin, Milwaukee, project, grit  and
floatables;  and  Clemson  University,  South
Carolina, project, aquiculture wastes.
    The  study of  the  applicability  and
capability  of  modified  swirl concentrator
chamber  facilities  to  serve a  related
solids-removal function  for  nonpoint
pollution control resulted from the successful
demonstrations of these  direct uses in sewer
systems.  The  utilization  of the  swirl
secondary-flow pattern to alleviate a nonpoint
drainage pollution  problem is, therefore, a
"fourth-generation"  approach to a  related
resources protection need. The simplicity  of
the model swirl device  studied, and of the
proposed prototype  units for actual  field
installations,  should  offer a  workable
opportunity to apply  this hydraulic principle
for the  correction of a major source of water
and land resources despoilation.
    The final result  of  the  model erosion
treatment studies undertaken  by  the APWA
Research Foundation at the LaSalle Hydraulic
Laboratoiy at LaSalle, Quebec, has been  to
provide the basis of an economical, effective
swirl  device  which can  utilize  a relatively
inexpensive  standard  cattle watering tank,
properly modified, fitted, and equipped, for
the purpose of removing adequate amounts  of
earthen   material  contained   in
nonpoint-stormwater  erosion  runoff  flows.
The use  of a conventional, purchasable basin

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or tank which  can  be installed at a point to
intercept and treat erosion  waters offers the
added  advantage  that  this  unit  can  be
removed with minimum effort and  expense,
transferred to another location and reinstalled
to handle  such flows at  any other  point of
erosion. This flexibility makes the swirl device
useful  during  construction  work,  and
removable  and reusable in connection with
other similar projects. It,  therefore, falls into
the category of a construction "tool" which
contractors or  governmental or private field
crews can use to meet temporary needs.
    The  development and  demonstration of
the performance of the model swirl erosion
runoff treatment unit involved the  use of  a
0.9-m (3  ft)  scaled -laboratory  hydraulic
model made of Plexiglas®  fitted with a pipe
inlet, a   15.24-cm  (6 in)  control  circular
overflow  pipe  and  spill  weir  for clarified
storm erosion water,  a foul sewer outlet, and
other investigative internal  appurtenances.
Facilities  were provided  for  the  measured
introduction of small particles of Petrothene®
and Gilsonite® specific gravity 1.01  and 1.06
respectively, into the  incoming water stream
to simulate grit and  other  solids material in
erosion  runoff,  and  for  collection  and
evaluation of  solids  discharged  through  the
foul  sewer  outlet  and  contained  in  the
clarified overflow.
    A series  of twelve  modifications were
made in the internal structure of the swirl
model. A cycle of  62 exhaustive performance
tests  was  carried in the swirl  chamber,
covering  liquid  flow and solids separation
phenomena under  these modifications. After
investigation of all of the variations in  the
model,  the studies were finalized in terms of
the optimum configuration and ratio of sizes
and  locations  of  the  variable components.
Original studies of performance with a sloping
bottom   floor  were   discontinued and
subsequent findings were based on a flat-floor
configuration. This made  it  possible  to
translate  design  criteria  in terms  of use of
standard cattle watering  tanks as the "shell"
of prototype  swirl   chambers  for  treating
erosion storm flows.
    The  effect  of continuous  draw-off of
collected grit   material,  via  the swirl
concentrator chamber foul sewer  outlet, on
solids recovery  demonstrated the beneficial
effects of such  removal on entrained  solids.
The hydraulic studies served as  the basis for
the evolvement  of suggested recovery rate or
performance  curves,  influenced  by  foul
material  draw-off  and  particle  settling
velocities.  General  design dimensions were
ascertained for actual prototype installations;
designing engineers  will be provided with the
structural, and appurtenant design criteria and
step-by-step instructions on how to utilize the
study curves to determine and  predict swirl
removal performance levels.
    Figure  1,   Schematic View,   Swirl
Concentrator as  an Erosion Runoff Treatment
Facility, shows  the essential features  of the
device.                     ;
    The essential features, as indicated on
Figure 1 include:
a)  a round outer shell
b)  a flat floor
c)  an   internally supported  clear   water
    overflow weir with a bottom discharge
d)  a  concentrate  discharge take-off to  a
    settling basin
e)  a baffled inlet to insure the development
    of the swirl  flow field
f)  flow spoilers to improve the efficiency of
    the circular  discharge weir.
    Figure  2, Flow  Diagram, indicates  the
basic assumptions concerning the use  of the
device.  A permanent installation will require a
flow-splitting diversion device, where multiple
units are used, and bar screens to protect the
units from  coarse debris. A  settling pond or
other facility will be required to handle the  5
to  14 percent concentrated' underflow from
the swirl assembly. The clarified flow may be
run  into a detention  pond  or  directly into
receiving water, based  upon the degree of
protection against  erosion solids required by
receiving water quality standards.

Conclusions
    The following  conclusions can be drawn
from the studies carried out at the LaSalle
Hydraulic  Laboratory,  LaSalle,  Quebec, on
the  applicability and  capability of the swirl
concentrator  for  the  treatment  of  surface
erosion runoff.
    •  A properly designed and proportioned
swirl concentrator chamber can perform an

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                                                                     LEGEND
                                                                  a — Inlet
                                                                  b — Flow Deflector
                                                                  c — Spoilers
                                                                  d—Overflow Weir
                                                                  e-Weir Plate
                                                                  f — Overflow (clear)
                                                                  g — Underflow (solids)
                                                                  h —Floor
            FIGURE 1    SCHEMATIC VIEW, SWIRL CONCENTRATOR AS
                          AN EROSION  RUNOFF  TREATMENT  FACILITY
effective job of removing erosion  particles
from  stormwater  runoff, and  thereby
markedly  reduce  the  effects of soil erosion
and  the  impact  of  such  earth solids on
contiguous land and surface  waters which are
the recipients of the erosion materials.
    • Such a swirl device can be rapidly and
economically installed at points of erosion
runoff by use of a standard or conventional
cattle watering tank having  a 3.66-m (12 ft)
diameter and a 0.9-m (3 ft)  depth, fitted and
equipped with a suitable inlet line, a circular
overflow weir,  a foul  sewer outlet,  and
necessary  interior  appurtenances.  Such a
chamber  could be  readily  disassembled,
moved to another site, and reinstalled for the
treatment of erosion runoff flows.
    • The  desilted, or clarified effluent could
be  discharged  to  drainage  facilities  and
disposed of into receiving  waters  or other
points of disposal or use. The collected matter
could be discharged through the foul sewer

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                        UNDERFLOW
     DRAINAGE
       AREA
                                                 SOLIDS
                                                LAGOON
                                                    OR
                                                FOREBAY
                    RETENTION POND
                            OR
                   RECEIVING WATER
                                                  OVERFLOW
                                         SWIRL
                                    CONCENTRATOR
                                  PIPE
                               OR  DITCH
                              FIGURE 2  FLOW DIAGRAM
outlet and entrained  or collected at suitable
points for return to  the  point or  points of
erosion or for use for other predetermined
purposes.
    •  An  inlet baffle, extending  from the
inlet to a point tangent to the overflow weir,
can double the solids  removal effectiveness' of
the swirl chamber.
    •  The retention of floatable materials in
the chamber, by  means of a concentric skirt,
is not feasible;  however, floatables  from
nonpoint runoff  are not anticipated to be a
problem.
    •  A  weir-to-chamber  diameter ratio ,of
2:3  will produce the optimum clarification
efficiency in the swirl  clarification device.
    •  Continuous draw-off of the collected
erosion  material  through  the foul  sewer
opening in the bottom of the swirl chamber
enhances  the solids removal efficiency  of the
unit.
    •  An  inlet   pipe-to-chamber  diameter
ratio of  1:6 will  produce  effective grit solids
removal  efficiencies  for  low,  intermediate,
and high rates of erosion runoff discharges.
    •  Use of standard cattle watering tanks
for the swirl chamber will be simplified if the
chamber bottom is left flat, rather than being
sloped to the point of foul sewer  outlet. If
higher degrees of erosion  runoff clarification
are desired, and  if the  cost of installing  a
sloping  floor  in  the  swirl cattle  watering
chamber is  merited,  increases  in  efficiency
may be achieved,  ranging  from  10  to 25
percent  for maximum and minimum discharge
rates, respectively.
    • Based on the hydraulic;model studies,
practicable  prototype design:  criteria  have
been  developed and  a  step-by-step  design
procedure utilizing rational design curves and
detailed sketches has evolved.

Recommendations
    The erosion of soil  and other native  or
indigenous materials at points ;of unprotected
land areas,  such  as at general construction
sites,  housing  developments,1  and  highway
location  and   relocation projects,  can be
damaging to  the  nation's  land  and  water
resources. Various means should be instituted
to prevent the washing  or  scouring of such
materials and the disturbance of sites, and the
damaging of environmental  aesthetics.  When
erosion  has occurred, or is occurring, it  is
beneficial to  intercept  the disturbed soil
material and to make provision  for its return
to the eroded  areas, or to make provision for
its  use  for other  purposes. Treatment  of
erosion  runoff waters will  prevent obvious
and  visible  water  pollution conditions and

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prevent heavy siltation of reservoirs, streams,
and lake areas.
    The ability of  a  simple swirl  chamber
constructed of a standard cattle watering tank
to be moved and reinstalled at other sites — as
demonstrated   by hydraulic  model studies
carried  out under this investigation project at
the LaSalle Hydraulic Laboratory — should
promote its utilization  for  erosion runoff
treatment.
    « It is recommended that erosion runoff
treatment units of the swirl type be installed
at a  number  of sites  in accordance  with
prototype  design  recommendations.  These
prototype  units  should  be  placed  under
technical  study  to  ascertain their  solids
removal   efficiency  under  practical  field
conditions.
    • Any modifications in basic design,  or
in the size and location of appurtenant parts
of the swirl  device, should be researched  to
compare findings  with other installations  in
the first prototype group  and to  establish
standards for future utilization of this  simple
treatment device.

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                                     CHAPTER II
                                     THE STUDY
    Because  of the  potential  impact  of
erosion  runoff  on  water  quality  and soil
conservation  and  current  concern  over
corrective  actions  that  will  prevent  such
conditions,  APWA,  under contract  to the
US EPA,  has conducted  a  study  of the
applicability of the  simple, economical swirl
concentrator  principle  to  the  problem  of
removing erosion products from stormwater
runoff.
    The  hydraulic  model studies1'4  were
carried  out at  the  LaSalle  Hydraulic
Laboratory, where  all  of the  previous
investigations of the swirl concentrator were
performed  for APWA-USEPA research
projects.  The research swirl  facilities which
were  utilized in the previous  studies  of
combined  sewer overflow  regulation  and
clarification,1-2  removal  of grit  from
wastewater flows,3 and the primary treatment
of wastewaters4  were modified for this study.
    Full  utilization  was  made  of the
principles that  were  developed during the
preceding  swirl   chamber  investigations.1"4
Background data  developed  by  Beak
Consultants, Ltd., Rexdale, Ontario, Canada,
on  the nature of wastewater solids and the
choice of solids materials that will simulate
field  conditions  in  laboratory studies, were
the basis for  the choice of Petrothene and
Gilsonite for the  erosion solids studies.
    The  principle involved in the swirl unit
for the erosion runoff studies was to produce
swirl-action  secondary-flow  patterns  in  a
rotational-velocity  chamber  which  will
separate solids from liquids in erosion runoff
wastewaters.  The deposited solids would  be
removed  from the  bottom of the chamber
through a foul sewer connection; the clarified
liquid  would  be discharged  over a  central
weir,  through a shaft. Monitoring of the solids
contained in the bottom draw-off and in the
clarified  effluent would  be  performed by
trapping  and measuring  these  solids; the
recovery  efficiency  would be determined by
comparing the bottom material with the total
solids injected into the inflow to  the swirl
concentration  chambers  by  means  of  a
feeding device.
    The model previously fabricated for other
swirl  studies was  used; it was modified  to
simulate,  by  scale-up  procedures,   a
commercial cattle watering tank which would
constitute  the  proposed  field   prototype
installation. The 0.9-m (3 ft) diameter model
was,  therefore, on  a scale of 1:4 with the
3.66-m (12 ft) cattle watering tanks available
in  the  commercial  market.  Inlet facilities,
interior appurtenant  units, a bottom  solids
draw-off connection, and an overflow weir
and downdraft effluent pipe were installed.
The bottom of the model was first  tested with
a  1:15 concrete floor slope. The floor was
later  made flat, to represent the  bottom  of
the commercial cattle watering tank proposed
as a prototype unit that would be 0.9 m (3 ft)
deep.
    The  Plexiglas  outer  shell  of the swirl
chamber  was 13  mm  (0.5 in) thick.  In the
center of the cylinder, an imbedded polyvinyl
chloride  (PVC) pipe, 15.2-cm (6  in)  inside
diameter,  was  installed  to  serve  as the
downdraft  outlet  for the clarified erosion
water that would spill over the circular weir
supported by the vertical pipe structure. The
weir was maintained at a height of 0.61 m  (2
ft) over  the   swirl  concentrator  chamber
bottom  during  the  entire  series  of tests
performed with the unit.
    The inlet pipe for the chamber was 15.2
cm (6 in) in  diameter, set at a slope  of
1:1,000. The test solids introduced into the
swirl  concentrator  chamber,  with   water
supplied  from  a  constant-level tank  in the
laboratory's supply system, were injected into
the inlet  pipe by means of a vibrating  feeder
upstream from  the  swirl chamber. The rates
of flow tested during the course of the studies
of chamber  modifications were 3, 5,  and 7
I/sec  (0.8, 1.3,  and 1.8 gal/sec). These flows,
respectively,  represented  the  following
erosion   water  flows  in  the  proposed
prototype:

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3
0.8
96
25
0.096
3.39
1289.2
2.19
5
1.3
160
42
0.160
5.65
13815.3
3.65
7
1.8)
224
59)
0.224
7.91)
19341.4
5.11)
3
0.8
96
2.19
54.2
5
1.3
160
3.85
32.5
7
1.8)
224
5.11)
23.2
Model Q     I/sec
(Model Q     gal/sec
Prototype Q  I/sec
(Prototype Q  gal/sec
Prototype Q  m3/sec
(Prototype Q  ft3/sec
Prototype Q  m3/day
(Prototype Q  mgd

    The prototype unit,  3.66 m (12 ft) in
diameter,  with an effective depth of 61 cm
(24 in) from the floor to the crest or lip of-
the  overflow  weir,  will  serve as  a "flash"
solids separator. The  overflow pipe would be
0.67 m (2.2 ft)  in  diameter. The  overflow
liquid would experience short detention times
in the chamber,  as  shown by the following
data:
Model Q     I/sec
(Model Q     gal/sec
Prototype Q  I/sec
(Prototype Q  mgd
Prototype    sec
   detention

Grit Simulation in the Model Studies
    To carry out meaningful studies of  swirl
concentrator  chamber  efficiencies in  the
removal ;of the type of soil solids contained in
erosion runoff wastewaters, it was necessary
to  determine  the  type  of  laboratory  test
materials  which  would best  simulate actual
field conditions.
    Gilsonite  was   chosen  for  laboratory
studies because it simulated the  major range
of grit material that  would be encountered in
prototype  operation.  The Gilsonite had  a
specific gravity of 1.06. Its gradation sizes, or
particle sizes, were  determined  and settling
velocities corresponding to these  sizes for the
model  and prototype  at  1:4  scale  were
ascertained  in accordance with  techniques
described  in  the literature,  and  based  on
irregularly shaped particles. For the range of
prototype settling velocities simulated by the
Gilsonite test  material, the study was able to
determine the particle  sizes for  the type of
grit that would be contained in actual erosion
runoff, with  a  specific  gravity   of  2.65.
Because of  the  relatively  large particle  sizes
which the  Gilsonite  simulated, it   was
determined that shredded Petrothene, with a
specific gravity of 1.01, would best represent
actual prototype grit in the laboratory model
studies, and that Petrothene dust, which had a
grain size range of 0.5 to  3 mm (.02 to .12
in),  should  be studied because it had lower
settling velocities  than shredded Petrothene.
    Because  of  the   ease  in handling  the
Petrothene,  this material was chosen as the
simulating material in subsequent tests carried
out  for the  purpose  of exploring modified
swirl chamber configurations and appurtenant
structural formats that would achieve the best
possible solids  recovery performance. The
same type of settling velocity studies made
with  Gilsonite   were  repeated   for  the
Petrothene particles.  Families of curves  to
define these characteristics were evolved from'
these study procedures. The work carried out
by  Beak  Consultants,  Ltd.,5  in  connection
with previous studies of swirl units for other
applications  was  utilized  in the  erosion
clarification studies. The final result was the
development  of settling velocity distribution
curves   that  would predict  the ability  of
prototype  installations  to  recover  erosion
solids,  based  on extrapolation  of model tests
solids  at  a  1:4  scale,  when  scaled  in
accordance with Froude's Law.
    Some of the laboratory Petrothene dust
particles, and the  silts and  clays that will be
contained in  erosion runoff waters in actual
field  operations  were  found  to lie  in  the
general range  of  colloids. The short-time
detention  of  erosion runoff  in  a swirl
concentrator  could  not  possibly  achieve
removal of such fine  solids and  the studies
made   no  pretention  of  being   able  to
accomplish their removal.

Model Test Procedures
    The tests of  solids separation  in  the
model  were  carried out under  steady-state
flows,  despite  the  fact that  any  field
prototype would be subjected to a wide range
of flow rates during the course of any storm
event.  A liter (0.26 gal)  of the test solids was
added  to the incoming flow over a 5 minute
period  and  the model was operated for  10
minutes after the cessation of the injection
period.  The  solids  retained  in  the  swirl
chamber, the amount collected in the settling

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basin used to capture and gauge the effluent
overflow,  and the material  entrained in the
foul  sewer settling tower  were  measured.
Efficiencies of  solids  recovery  were
computed.
    These  efficiency determinations made it
necessary   to  provide  wells  or basins for
collecting  the slurry discharge from the foul
sewer and  the clear water overflow from the
swirl  chamber. Flow was gauged in the clear
effluent overflow collecting basin by means of
a calibrated  V-notch weir.  The foul sewer
settling tower was equipped with a discharge
line  that   could  be adjusted  in  height  to
modify the withdrawal of underflow from the
swirl  chamber at predetermined rates. Figure
3, Model Layout, shows the details of the test
unit and its gauging and control facilities.
    Brief tests of solids recoveries under three
variations  of flow rates, utilizing the original
model layout, as shown in Figure 4, Original
Layout for Test  No. 1, with a flat  disc weir,
showed that  the  flow pattern induced in the
unit was an unstable vortex, rather than a true
swirl, at even the lowest flow rate. A baffle
was installed to  overcome this vortex action,
extending from the inlet pipe to the  periphery
of the  overflow weir,  but  the vortex flow
pattern persisted. Flow spoilers were installed
on  the flat disc  weir, shaped irregularly to
produce  better   flow  distribution  in  four
quadrants  of  the weir.  Solids recovery rates
were  uniformly  high  - approximately  95
percent — with Gilsonite. The use of the flow
deflector  or  baffle was found to  enhance
solids recovery.  This  baffle was used in  all
subsequent model tests.
    Extended series  of twelve   structural
modifications   were  made  in  the  swirl
chamber's internal facilities,  and a total of 62
specific   tests  were  conducted,  involving
different  flow rates,  changes in foul sewer
draw-off  rates,  and  the  use  of  different
laboratory model solids  — Gilsonite, shredded
Petrothene and Petrothene dust. The various
structural  changes or configurations, the type
of solids injected into the incoming flow, the
rate  of draw-off, and  the  solids recoveries
achieved are tabulated in the full report of the
LaSalle Hydraulic Laboratory, contained in
Chapter V.
    Various modifications were tested in the
model.  In all of the modifications, except
one, the inlet size was 15.2 cm x 15.2 cm (6
in  x  6  in).  The modifications produced
varying solids recovery efficiencies,  ranging
from a high of 99.5 percent to a low of 42
percent for a model flow rate of 3 I/sec (0.78
gal/sec); from 95 percent to 25  percent for
model flows of 5 I/sec (1.3 gal/sec); and from
95 percent to 12 percent under flows of 7 I/sec
(1.8 gal/sec). The highest consistency  in solids
recovery  occurred  at  the lowest hydraulic
loading rate. Gilsonite recoveries were generally
higher than for the smaller and lighter Petro-
thene materials. The use of an inlet baffle and
flow  spoilers was found  to improve solids
recovery.
    Chapter V  describes  the  model  test
procedures,  the nature  of  the model
modifications  and  the  recovery levels. It
explains the influence of the  weir crest and
the spiral  flow.guide on shredded Petrothene
recovery;  the effect of a concentric  skirt for
collecting  floatable solids in the swirl chamber
on  solids  separation;  the influence  of weir
diameter  on solids recovery;  the effect of
chamber floor slope  on  chamber efficiency;
the  influence  of  continuous  underflow
draw-off on  solids separation;  and  the
influence  of inlet size  on  swirl  chamber
performance. Similar studies were carried out
with Petrothene  dust, used to simulate the
smaller solids particles which will  enter actual
prototype  swirl  chambers  in  the form  of
native  silts  and  clays carried with  heavier
eroded materials by storm runoff waters.
    As  a  result  of  the  complex series  of
studies  with model structural  modifications,
while handling  the three  types of simulated
test solids at the three rates of flow applied to
the laboratory model, the LaSalle Laboratory
evolved rational estimates  of solids recoveries
in  the  model  and developed a design
procedure.  Two  examples of  the design
procedure are contained in Chapter III.

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                                                                            Foul outflow    Foul  solids
                                                                            settling  tower    rscovery screen
                                                   Chamber cylinder 13 mm (O.S in.)
                                                   plexiglass -914 mm (36 in ) dia
              Clear outflow settling basin


P 1'Vi H V f h












i /


/I

                               Clear water overflow outlet
                               pipe  102 mm  (4 in ) plexiglass
      Discharge returned to
      pumping station
r\
      Calibrated V-notch weir
////////A/////////////////////////////

     Clear  outflow settling  basin
                                                                   Foul outlet
                                                                   discharge
                                                                   control
                                      Butterfly control
                                          valve
                  PVC Supply pipe
                                                                                  Small water supply
                                                                                  for solids injection
                                                                                  Water supply from
                                                                                  pumping station
                                                                         Foul Outlet
                                                                         discharge control
                                             Chamber cylinder 13 mm (0.5 in )
                                             plexiglass - 914 mm (36 in.) dia
                                                                                                   PVC
                                                                                                   Supply
                                                                                                   pipe
                                                                                              Foul  outflow
                                                                                              settling tower
                                          Butterfly
                                          control valve
Clear water overflow pipe
102  mm (4 in)  plexiglass
Foul solids
recovery screen
                                               ELEVATION
                                               Section  A-A
                                   FIGURE 3   MODEL LAYOUT

-------
0.91 m  0 Chamber
(36 in)	
            INLET
           15.2 cm x 15.2 cm
            (6 in x 6 in)
                                             270
                                             FOUL OUTLET

                                             320°
0.50 m Weir
(20 In)
         PLAN
To Overflow Tank
FOUL OUTLET

        ELEVATION
        Section A-A
        FIGURE 4a ORIGINAL LAYOUT FOR TEST NO. 1
                            10

-------
            ORIGINAL LAYOUT
     ORIGINAL LAYOUT WITH INLET BAFFLE
FIGURE 4b  ORIGINAL LAYOUT FOR TEST NO. 1
                   11

-------
                                   REFERENCES
    1. The Swirl Concentrator as a Combined
Sewer    Overflow    Regulator    Facility,
EPA-R2-72-008, September 1972.
    2.  Relationship Between Diameter and
Height for the Design of a Swirl Concentrator
as a Combined Sewer Overflow Regulator,
EPA-670/2-74-039, July 1974.
    3.  The  Swirl  Concentrator as a  Grit
Separator Device,  EPA-670/2-74-026, June
1974.
    4.  Swirl  Concentrator  as  a   Primary
Treatment Facility, Draft Report, 1976, EPA
Grant No. 803157.
    5. Physical and Settling Characteristics of
Particles  in Storm  and Sanitary Wastewater,
EPA-670/2-75-011, April 1975.
                                         12

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                                      CHAPTER III
                                DESIGN FACTORS FOR
                 SWIRL EROSION RUNOFF TREATMENT PROTOTYPES
    This section  on  design makes frequent
reference to the following listed Figures:

     5  Prototype Particle Sizes Represented
        by Gilsonite - SG 1.06
     6  Recovery Rates in Model as Function
        of  Particle  Settling  Velocity  and
        Discharge with 5 percent Draw-off
     7  Recovery Rates in Model as Function
        of  Particle  Settling  Velocity  and
        Discharge  with 10 percent Draw-off
     8  Recovery Rates in Model as Function
        of  Particle  Settling  Velocity  and
        Discharge  with 14 percent Draw-off
     9  Predicted Prototype Recovery Rates
        with 5 percent Draw-off
    10  Predicted Prototype Recovery Rates
        with 10 percent Draw-off
    11  Predicted Prototype Recovery Rates
        with 14 percent Draw-off
    12  General Design Dimensions
    The procedure described in this section is
relevant to a  fixed prototype size whose scale
is  imposed by  the  use  of  a  standard or
conventional  3.66-m  (12 ft) diameter cattle
watering tank as the swirl chamber. The fixed
scale of 1:4 determines the dimensions of the
whole structure as they appear in Figure 12,
General Design Dimensions.
    Under  operating conditions, it is assumed
that the user has a  situation  in which the
prototype discharge, Qp, is known,  as well as
the prototype particle settling velocity v  , of
the materials to be removed from the flow.
 1. Enter  Figure  9  (5  percent   draw-off)
    where  the expected discharge appears on
    the abscissa
 2. Move  up in  the  graph until  the given
    particle settling velocity curve (or particle
    size) is found
 3. Check  whether or not  this intersection
    gives an acceptable rate of recovery
 4. If  the  recovery is not high enough, try
    Figures 10 or  11 in  which draw-off is
    increased,  respectively,  to  10 and  14
    percent of the inflow
 5. If conditions are still not acceptable, even
    with   the  larger  draw-off rates,  then
    reduce the expected discharge per unit by
5/2
    providing multiple swirl chambers
 6. If this gives  too many standard 3.66-m
    (12 ft) units, try larger chambers, making
    reference directly to Figures 6, 7, and 8,
    the recovery curves for the 0.914-m (3 ft)
    diameter model
 7. Select  an  approximate  new  chamber
    diameter,  Dn  and  divide this  by  the
    model diameter to find the new scale:
    l/\n = 0.9l4/Dn  m = 3/Dn ft
Where:
    Xra = scale factor
Next, calculate:
    new discharge scale = l/Xn"
    new settling velocity scale = 1 /\n n
 8. Multiply:
    2pxl/A,j5/2  =  Qm  model discharge
    vsp x \l\n '/2   =  vsm  model particle
                        settling velocity
 9. Go into Figures 6,  7,  or 8  with these
    model values, interpolating as necessary
    between the discharge curves, to find the
    corresponding recovery
10. If  the  recovery   is   too   low,  try
    progressively  larger  chambers, each time
    following the procedure in steps 7,8, and
    9 above until a satisfactory recovery rate
    is obtained
11. Use Figure 12 to find the dimensions of
    the new  chamber.  Since  the  chamber
    shown  on  the  figure  is  the  standard
    3.66-m  (12 ft)  unit studied at scale 1:4,
    each dimension must be multiplied by the
    factor Xn/4

    For purposes of illustrating the procedure
for the application of this swirl unit to the
problem of soil erosion, two examples will be
given. The first is based upon an  engineering
approach  where a permanent facility is to be
designed  for a required level  of  efficiency.
The  second example is for the case where a
developer must provide temporary facilities at
a construction site.

Permanent Erosion Control Facility
    For a permanent erosion control facility
the  use  of the swirl concentrator may  be
envisioned as  an auxiliary treatment device
                                           13

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7.0 (2.76) ^
6.0 (2.36) ..
5.0 (1.97) -

 4.0 (1.57)

 3.0(1.18)


 2.0 (.787)




    1.0
         RANGE OF PROTOTYPE
         GRIT SETTLING VELOCITY
         REPRESENTED BY
         GILSONITEAT
         SCALE 1/4
    0.5
 | (.20)
  E
  o

 f:
 O
 LU

 o
    0.1
    (.04)
                                                   PROTOTYPE
                                                   "GRIT PARTICLE
                                                   SIZES
                                                   SIMULATED
                                                   BY GILSONITE
0.01
(.004)
    0.01 (.0004)
                                                          1.2 (.05)
                                         PARTICLE DIAMETER, mm (in )
      FIGURE 5 PROTOTYPE PARTICLE SIZES REPRESENTED BY
                GILSONITE-SG 1.06
                                 14

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 100
 90
      0.07
      (.03)
             PARTICLE SETTLING VELOCITY, cm/sec (in/sec)
FIGURE 6 RECOVERY RATES ON MODEL AS FUNCTION OF PARTICLE SETTLING
         VELOCITY AND DISCHARGE WlTH 5 PERCENT DRAW-OFF
                                15

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100
10
 0
     0.07
     (.03)
                  PARTICLE SETTLING VELOCITY, cm/sec (in/sec)
FIGURE 7  RECOVERY RATES ON MODEL AS FUNCTION OF PARTICLE SETTLING
          VELOCITY AND DISCHARGE WITH 10 PERCENT DRAW-OFF
                                16

-------
                           Qm  = 3 I/sec
                                (0.79 gal/sec)
                             Qm  = 5 I/sec
                                  (1.3 gal/sec)
      0.07
      (0.03)
   0.2             0.5
  (.08)             (2.0)
PARTICLE SETTLING VELOCITY, cm/sec (in/sec)
FIGURE 8    RECOVERY RATES ON MODEL AS FUNCTION OF PARTICLE SETTLING
            VELOCITY AND DISCHARGE WITH 14 PERCENT DRAW-OFF
                                    17

-------
o
DC
HI
a.
>
cc
\u
O
o
ui
cc
     100
      so
      60
      40
  CL
    0
    I/sec
      (gal/sec)
Qpm3/sec   _l
 (ft3/sec)
                 I        n
              PARTICLE SETTLING VELOCITY
                                                  PROTOTYPE  GRIT PARTICLE
Qpm3/day
  (mgd)
                          _L
                                       PROTOTYPE DISCHARGE
                                      	I	I	I	L_
                                         _L
 2.5'
(.07)

	L
  3
 (.08)

	1_
                          3.5
                          (.10)
                              4
                            (.11)
              5
             (.14)
  6
 (.17)

	l_
 7
(.2)
 8    9
(.23)  (.25)

   	[_
                                                            _L
          1.7      2
        (6,435)  (7,570)
 2.5      3     3.5     4
(9,463)  (11,355)  (13,248) (15,140)
     5       6
  (18,925) (22,710)
         FIGURE 9    PREDICTED PROTOTYPE RECOVERY RATES
                      WITH 5 PERCENT DRAW-OFF
                                      18

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   100
I-
Z
LU
o
cc
LU
a.

>
CC
LU


o
o
LU
DC
                                              PROTOTYPE GRIT PARTICLE
 Qp I/sec

   (gal/sec!
                                           >
200  jSf^ 250

(52.8) -  (66)
                                        PROTOTYPE DISCHARGE
Q m3/sec
{ft3 /sec)

Qp m3/day
(mgd)

1 1
2.5 3
(.07) (.08)
, ,
1.7 2
(6.435) (7,57).
1 1
3.5 4
(.10) (.11)
I
2.5
(9,463)



5
(.14)
I
3
(11,355)


I
3.5
I.
6
(.17)
1
4
(13,248X15,140)
1 I
7 8
(.2) (.23)
I
5
(18,925)
I
9
(.25)
I
6
(22,710)
          FIGURE 10 PREDICTED PROTOTYPE RECOVERY RATES

                     WITH 10 PERCENT DRAW-OFF

                     3.6 m (12 ft) Diameter Chamber
                                 19

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100
          I	r-|
         PARTICLE SETTLING VELOCITY
                                        PROTOTYPE GRIT PARTICLE
(gal/sec)
 200  ^ 250
(52.8) 
-------
Four Flow  Spoilers
     0.86 m (34 in ) long
        -PIPE
        0.61 m (2 ft)


         INLET
                                                         0.61 m x 0.61 m
                                                          (2 ft x 2 ft)
                                                                      A

                                                                J
ELEVATION
Section A-A
        TO DISCHARGE
           TANK
OUTLET  °-10 •" W in )

   Foul Outlet discharge
   adjusting device
           FIGURE 12   GENERAL  DESIGN DIMENSIONS
                        SCALE: 1/4
                                  21

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installed  ahead  of  a  stormwater
retention-detention  facility.  The  primary
purpose of the unit would be to concentrate
the larger soil particles in order to retard the
siltation  of  the  retention facility or
downstream receiving waters. To this end, the
concentrated underflow  could be directed to
a  readily  cleaned auxiliary  sediment  trap
where  conventional  equipment, such  as  a
backhoe, Gradall,® or even a bucket loader —
assuming that the area could be dewatered  —
could be used to remove the collected soil.
    Such a facility would minimize the total
maintenance  cost and improve the efficiency
of  the  major  storage  facility  or receiving
waters.
    The design  procedure  is  developed in
accordance  with  the  various  elements
normally required for  a  complete system.
These   elements are:
    Hydrological Considerations
    Solids Analysis
    Swirl Unit Design
    Efficiency Computation
    Assessment of Retention Volumes
    Other Design Considerations and Details
    A typical site situation is shown in Figure
2, Flow Diagram. This plan shows a large drain-
age area with a stormwater retention facility.
The  swirl  unit  and  soil  collection  pond
intercept this flow ahead  of  the  retention
facility ponds.  It is assumed that all runoff
from the basin is detained on the property and
passed through the swirl unit or units.
    For purposes of determining the quantity
of runoff to  be expected from the drainage
area,  any of a number  of  methods, can be
used.   In  references to  a  recent  survey
conducted  by   APWA6   rainfall  runoff
predictions in practice are based primarily on
unit hydrographs and the Rational Method. In
general,  maximum erosion will occur under
conditions  of peak runoff.  The peak storm
which   may  cause maximum  erosion  may
never occur during a given interval of interest
in design for erosion runoff control. Common
design practice for drainage structures is based
on  a   rainfall  intensity which  occurs
frequently.   A   commonly  used rainfall
intensity is  a  10-year  recurrence interval,
although in many  cases the choice of a design
rainfall is determined for a specific project by
the requirements of the local or state public
agency having jurisdiction.
    As an example, let it be  assumed that a
80.9  hectare (200  acre)  drainage  basin  is
selected.  For this  watershed,  the  time of
concentration is found to be  45 minutes.
Assuming that it is  desired  to find the peak
runoff at a time when equilibrium conditions
are established for this site, the duration of
the   storm  is  taken  as  the  time  of
concentration.  From  a  duration-intensity
relation established  for  this site,  it  is
determined  that the intensity is 1.27 cm/hr
(0.5  in/hr). Further information on the site
indicates  that  20  percent  of  the  basin  is
occupied  by buildings for which a runoff
coefficient of 0.9 is selected; 15 percent  is
roadways with a runoff coefficient of 0.9; and
the remainder is grassed yard areas for which
a  runoff coefficient of 0.3 is assumed. An
average   coefficient  for  this site  can be
calculated as:
          (40 ac + 30 ac) x 0.9 + 130 ac x 0.3
Cave  •=                200    ;

Cave  =0.51
    The peak runoff calculated for this storm,
using the Rational Method, is:
    Q  =   CiA
    Q  =   0.51 (1.27 cm/hr) 80.9 ha - 52.4
            cm-ha/hr
        -52.4x27.8= 1,460  I/sec
    Q  =0.51  (0.5 in/hr) (200 ac) = 51
        ft3 /sec
    This flow will  be used later as the inflow
to the  swirl erosion control  facility. More
accurate predictions of the proper intensity of
rainfall upon which to predict the most severe
eroding rainfall to  be handled  by this erosion
control device  can  only  be  obtained  after
several field experiences have been evaluated.
Any  method used  prior  to  the time  of
verification  can  only  be subjective  and is
highly dependent  upon local  conditions. In
many  areas  of the  country,  more accurate
information is available for the prediction of
times  of concentration  and peak  rainfall
intensities.
    A second part of the hydrologic analysis
required  to design an erosion control  facility
involves an  estimate of the peak volume of
                                          22

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runoff for a given storm. This volume will be
used to size the retention pond and the soil
collector pond. Obviously, the high-intensity,
short-duration storm  may  contribute a high
flow rate for a short period, but  it would
represent only a portion of the total volume
of runoff  that  could be expected from  a
storm of longer duration. With reference to a
set  of  intensity-duration  curves, it was
observed  that  for  the  same  recurrence
frequency that was used in the determination
of the. peak flow rates, a  storm of longer
duration of 4 hours would yield an intensity
of 1.02 cm/hr (0.4 in/hr).  The peak rate of
flow for this storm can be  estimated in the
same manner as previously:
Q   =   0.51 (1.02 cm/hr)  80.9 ha = 42.1
        cm-ha/hr
    =   42.1 x27.8 = 1170  I/sec
<2   =   CiA = 0.51 (0.4 in/hr) 200 ac
    =   40.8 ft3 /sec
    The use of the Rational Method C factor
will result in an estimate of a larger flow than
would  ordinarily be anticipated for all but the
most intense storms.
    Perhaps the most accurate method for
determining the volume of runoff would be to
integrate   the  area  on   a  hydrograph
determined  for this watershed.  For  the
determination of this volume,  the  use of a
unit hydrograph would be advantageous.
    Various other methods  are also available
for computing the storage volume necessary
to hold the total runoff. Using one of these
methods,  assume  the  resultant volume  is
8,420  m3 (297,226  ft3). This yields a larger
volume than  that associated  with  the
short-duration, higher-intensity storm.
    The final hydrologic determination deals
with an annual estimate of the total quantity
of sediment to be expected. This volume will
be  used to  estimate the  total  amount of
settleable solids to be collected  in the two
ponds.  Reference to a chart of  expected
annual rainfall in the project area, will provide
the annual  precipitation rate. It is  probably
not  necessary  to reduce  these  values  for
precipitation occurring as  snowfall for  the
purpose of this estimate.  Assume  that  this
value is 76.2 cm (30 in) per year.  It is also
assumed that  the  area of the two  retention
ponds  is small compared to the total area,
although this  fact may not  always be  true.
The runoff volume per year is then:
V = 0.51 (76.2    ) x
                              x 80.9 ha
               10,000m2
             x— - - - 3 14,000 m3/yr
                 ha
                        1 ft
  V=  0.51 (30in/yr)x -
                      12 in
                     ft2
    x 200 ac x 43,500 —
                     ac

       = 11,1 00,000 ft3 /yr = 4 1 1 ,000 yd3 /yr

    In  summary,  these  three  calculated
quantities will  be used in  the following
manner:
a.   The peak runoff rate will be used to size
    the swirl concentrator  erosion  control
    device  or  devices,  the main drainage
    trench conducting flow to the device and
    any inlet conduit that must be used.
b.   The single storm  volume will be used to
    size the two retention basins.
c.   The annual storm runoff volume will be
    used  to estimate the quantity  of
    settleable material which will accumulate
    in  the retention  basins. This represents
    material for which storage capacity  must
    be  provided  within  the  pond,  or the
    volume  of  material  which  must  be
    removed.

Solids Analysis
    The next step in  the design procedure is
to determine the quantity,  type  and size of
material  that  is  likely to  be  found  in
stormwater runoff at  this site. Table 1 ,  Sieve
Analysis, presents  an  analysis  of a sample of
storm runoff from an erosion  site which was
sieved  and  separated  into groups  having
similar specific gravities. Such an analysis is
used  to  determine  the  type and  specific
gravities of the material present, thus enabling
a  reasonable  estimate  of the  type and
quantity of material that can be removed in a
swirl  erosion control  unit.  This example
should be viewed as merely an indication of
the  type  of investigation  that  should  be
conducted.  There  may  be many sites for
                                           23

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                                         TABLE 1
                                     SIEVE ANALYSIS
Sieve Size

10
20
60
100
120
200
PAN

Size
mm (in)
2.00 (.08 )
0.84 (.03 }
0.25 ( .01)
0.149(.006)
0.125(.005)
0.074(.003)
	

Material
Retained
gm (oz)
4.0(0.14)
6.5(0.23)
39.0(1.4 )
100.5(3.5 )
77.0(2.7 )
44.0(1.5 )
79.0(2.8 )

Percent
Retained

1.14
1.86
11.14
28.71
22.00
12.57
22.57
TOTAL
Percent Retained
According to SG
SG/2.65 SG/1,20 SG/1.01

1.04
1.06
8.64
23.61
21.00
12.07
22.57
90.59



2.0
5.0
# * * #
1.0
0.5

8.5

0.1
0.2
# * * #
0.5
0.1
_ _ _


0.9
 which more elaborate and complete analyses
 may be desirable.
    Assuming that it is desirable to remove as
 much settleable material as  possible  in the
 swirl  unit,  the   smallest  particle  that is
 predicted  from the  model  studies  to be
 removed  is  a grit  particle,  specific  gravity
 2.65, 43 microns in diameter, having a settling
 velocity of  0.14  cm/sec (0.055  in/sec) as
 shown  in  Figure  11. A design  incorporating
 the removal of this size of grit particle  will
 also  remove larger size  particles  of  lighter
 weight. For example, with reference to Figure
 5, a  particle  of specific gravity 2.65 and  a
 settling velocity of 0.14 cm/sec (0.055 in/sec)
 is 0.045 mm (.002 in) in diameter. For the
 same  settling velocity a particle of SG  1.20
 with  a diameter of 0.14 mm (0.006 in) will
 settle at the same rate as a particle having a
 SG of 1.01 (organic material)  with a diameter
 of 0.6 mm (0.02 in). Similar settling velocities
 can be  obtained from  Figure 13, Prototype
 Particle Sizes Represented by Petrothene —
 SG. 1.01. Particle sizes larger in diameter than
 those quoted are expected to  be removed. In
 the sieve  analysis  shown  in Table  1,  the
 material expected  to be removed in part by
 the swirl concentrator is shown in the specific
 gravity columns at the right side of the table
 above the asterisk  marks, considering that the
 settling velocity is 0.14 cm/sec (0.055 in/sec)
 for a particle having an SG of 2.65.
    Hydrometer analysis using pan material,
or 22.5 percent of the total sample, showed:
    Percent particle size greater than 0.052
mm (0.002 in)- 16.0%
     Percent particle size less than 0.052 mm
 (0.002 in) - 6.57 %
     From design data, using a particle settling
 velocity of 0.14 cm/sec (0.055 in/sec) it was
 determined that  the  following percent  of
 material will be subject to removal in the swirl
 chamber:
     SG2.65  90.59-6.57 = 84.02%
     SG 1.20    8.5 - 1.5  =  7.0 %
     SG 1.01    0.9 -0.6  =  0.3 %

 (These quantities are shown in the table as the
 percent in each SG column  above the asterisk)
     Total material subject to removal by swirl
 concentrator - 91.33%
     Total material  not  subject  to removal —
 8.67%
     The removable  material percent shown
 here will  be  multiplied  by  the  recovery
 efficiencies  of the  chamber from the design
 curves, Figures 9, 10, or 11.

 Swirl Unit Design
     From  an   earlier  section  it  had  been
 determined that the peak design runoff flow
 rate is  1,460 I/sec (51 ft3/sec). With reference
 to   Figure  11,  it is  seen  that for  a
 12-foot-diameter  chamber,  the highest
 efficiency is obtained when the flow rate does
not exceed 96 I/sec (3.4 ft3/sec). Dividing the
 flow by  a factor of 15 would give  97  I/sec
(3.4 ft3/sec) as the design flow for each of the
 chambers, and this flow in  Figure 11 is at the
left  end  of the curve, at the highest possible
removal efficiency for this particle size. The
 use  of 15 chambers would also mean that
                                           24

-------
1 !
I SETTLING VELOCITY, cm/sec (in./sec) 1

—

2.5 (1)
,




—


0.2 ^
1
0.1
—



.0121
t
RANGE OF PROTO-
TYPE GRIT SET-
TLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
' (.08)
i
(.04)
RANGE OF PROTO-
TYPE GRIT SET-
TLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
(.0047)
£L (.004)



PROTOTYPE
PARTICLE SIZES
SIMULATED BY
— PETROTHENE DUST
0.12 mm < d < 0.5 mm
— (.008in
-------
higher intensity storms could still be handled
by  these  chambers  with  only  a  small
reduction in efficiency. In fact,  the  design
runoff could be more than doubled in each
chamber.  It should  be  noted that  if  the
14-percent draw-off rate is excessive  for  the
volume of storage desired, Figures 9 and 10
should  be used with smaller draw-off rates
and corresponding reductions in efficiencies.

Efficiency Computation
    Using the efficiencies given in Figure 11
and the percent of each size material given in
Table  1, the efficiency of the 3.65-m (12 ft)
diameter  chamber  can  be determined,  as
shown in Table 2, Swirl Efficiency Analysis.
    For specific gravities less  than 2.65, an
equivalent particle size for that particle can be
obtained  from  Figure 5. As an example with
reference to Table 2, a particle for  specific
gravity of 1.20 is taken as 0.25 mm (0.01  in).
In Figure 5, find this size along the abscissa;
go vertically upward to the curve marked SG
1.20, then left  or horizontally  to  the curve
marked SG  2.65,  then  downward  to   the
abscissa. The values  read, settling velocity is
0.5 cm/sec (0.19 in/sec)  for a  SG 1.20 and
particle size 0.25 mm (0.01 in); an equivalent
particle  of  SG  2.65  having  this  settling
velocity is a particle  of 0.082 mm (0.003 in).
Refer back to Figure 11 for  this size  particle
of 82 microns  and  settling  velocity of  0.5
cm/sec (0.019 in/sec). For a flow rate of 97
I/sec (3.4 ft3/sec), this yields an efficiency of
69 percent. This procedure is continued  for
other particle  sizes.  It  is seen  that  an
efficiency of 68.76  percent  is predicted  for
this material if a set  of 15 swirl concentrators
were used.

Alternate Chamber Design Investigation
    The design discharge, Q is 1,460 I/sec (51
ft3/sec).  With  reference to   Figure  8,   the
smallest particle shown is one  having a settling
                                        TABLE 2
                               SWIRL EFFICIENCY ANALYSIS



Sieve
Size
10
20
60
100
120
200
HYD
COL. 1


Particle
Size mm(in)
2.00 (.08 )
0.84 (.03 )
0.25 (.01 )
0.149(.006)
0.125(.005)
0.074(.003)
0.052(.002)
COL. 2

Percent
Retained
SG 2.65
1.04
1.66
8.64
23.61
21.00
12.07
16.00
COL. 3

Percent
Eff. from
Fig. 11
100
100
92
82
79
69
59
COL. 3
= 1 x2
100


1.04
1.66
7.95
19.36
16.59
8.32
9.44
COL. 4

Percent
Retained
SG 1 .20
	
	
2.0
5.0
1.0
0.5

COL. 5

Percent
Eff. from
Fig. 11 &5
— .—
	
69
56
	
	

COL. 6
= 4x5



	
	
1.38
2.8
	
	

                                                  64.36
                                     4.18


Sieve
Size
10
20
60
100
120
200
HYD
COL. 7
Percent
Retained
SG1.01
0.1
0.2
0.5
0.1
	
	
	
COL. 8
Percent
Eff. from
Fig. 5 & 11

60
	
	
	
	
	
COL. 9
= 7X8


0.1
0.12
	 '.,
	 •
	
	 '
	 .
                                                Total percent of removal material removed in
                                                swirl unit = 64.36% + 4.18% + 0.22%
                                                         = 68.76%

                                                Total percent of settleable material removed
                                                by swirl concentrator
                                                         = 68.76% x 91.3% = 62.7%
                                       0.22
                                            26

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velocity  of 0.07  cm/sec (0.03 in/sec). For
other draw-off rates, Figure  6  or 7 could be
used  for  5  percent or 10 percent draw-off,
respectively.  Figure 8 was selected since the
best recovery occurred with a draw-off of 14
percent.  Assume  that  four  prototype
chambers will be used, each having a diameter
of 6.4 m  (21 ft). This sets the model scale at:
 X = Lp/Lm = 6.4 m/0.914 m (21 ft/3ft) = 7

From  the  Froude  Law  the  velocities of
settlement can be related as:
   vsp/vsm  = VLjT^ = ^fT  =  2-65
The  model  discharge  is  also found  from
the Froude Law as:
                              = 129.64
                               1
                            1.29.64
                                   = 2.811/s
    Referring now to Figure 8, the discharge
line  for 2.81  I/sec  (0.74 gal/sec) must be
interpolated  between  the  3  I/sec   (0.80
gal/sec) line and zero at 100 percent recovery.
Assume  it  crosses the  0.07  cm/sec (0.03
in/sec)  settling velocity  line  at  about  60
percent recovery.
    This model settling velocity corresponds
to a prototype settling velocity of:

0.07 cm/sec x 2.65 =  0.185 cm/sec (0.073
in/sec)
    From Figure 5, this gives a particle size of
0.05 mm (0.002 in) for SG = 2.65 material.
    Another  approach  to  selecting  the
chamber size would be to decide to use 3 I/sec
(.106 ft3/sec) in either Figures 6, 7,  or 8 as
the required rate of recovery curve. Working
with Froude's Law, the scale can be found:
      • O  IO  = i''4OU  x -— =1217
      - Upl
-------
 the firm of Beak Consultants, Ltd.5 Among
 figures  quoted  for  suspended  solids  in
 stormwater, these settleable solids vary from
 0 to 7,640 mg/1, with an average of 687 mg/1.
 The concentration of solids can vary widely
 and is depending upon the character and the
 use of the land from which the storm flow is
 generated. Using an average value of 700 mg/1,
 an estimate of the settleable solids per storm
 is:
                      1
                              mg
 V = 8,420 m3 x 1,000 — x 700 -~
      kg
             x
•= 3.68m3 (130ft3)
   1,000,000   1,600kg

    On  an  annual  basis  the  volume  of
 settleable solids is:

 V = 314,000 m3xl, 000-^r x  700 —
               kg
                        m
  m
           1,000,000 g  1,600kg

      = 137m3  (4,841ft3)

    Assume that 100 percent of all settleable
solids will be retained in the ponds.

Temporary Facility at Construction Site
    Another application of the swirl separator
is  as a temporary facility for erosion control
at a construction site.  For  this purpose the
foul sewer underflow, conveying most of the
settleable  solids, would discharge into a soil
collector  pond  and  the  overflow  would
discharge into a drainage ditch or channel or
flow directly  into a watercourse.  For  this
purpose, the  conventional  cattle  watering
tank, with a diameter of 3.65 m (12 ft) and
height of 0.91 m (3.0 ft), could be used after
modification to meet the design details shown
in  Figure  12.  Figure  14,  Standard  Stock
Watering Tank, shows a typical unit.
    The riser pipe, shown in Figure 12 as 0.67
m (2.2 ft), could be changed to 0.61 m (2.0
ft)  to utilize standard size pipe. The clarified
overflow outlet could be attached directly to
the underside  of the chamber  and  could be
made rectangular in shape. Dimensions of
0.61 m (2.0 ft)  wide and 0.22 m  (0.75  ft)
 high would provide a waterway having an area
 equivalent to the riser pipe. The underflow or
 foul   outlet  could likewise  be  made in
 rectangular or square shape,  attached to  the
 bottom  of the  box.  The  outlet  should
 probably  be at least 0.15 cm (0.06 in) square
 to prevent problems with clogging. The outlet
 could  terminate  at  the  outside wall of  the
 chamber,  with  a  0.15 cm (0.06 in) standard
 pipe flange for attaching the pipe to convey
 flow to the soil collection pond.
    Assume the following conditions:
 Site area  tributary  to chamber is 3.12 ha (8
 ac)
 Runoff coefficient C is 0.4
 Time of concentration is  15 min
 Rainfall intensity  is 6.35 cm/hr (2.5 in/hr)
 For
 Q = CiA:
    = 0.4 x 6.35 cm/hr  x  3.12 ha
    = 8 cm-ha/hr
    = 8 x  27.8 = 222.4 I/sec
 Q  = 0.4 x 2.5 in/hr x 8.0 ac
    = 8 ft3/sec
    From Figures 9, 10, and 11, it is apparent
 that the largest allowable flow through  one
chamber  is   222.4   I/sec  (8.0  ft3/sec).
Therefore,  under  the  above  assumed
conditions the largest site that can be served
by one  chamber is 3.12 hectares (8.0 ac). The
greatest recovery of solids will  occur  if a
 14-percent draw-off (Figure 11) is used rather
than  10-percent  (Figure 10)  or 5-percent
(Figure  9).
    From Figure   11,  the  percentage  of
 various  size solids to be  recovered will be as
 follows:
                             Size Solids
                        mm
                        0.35
                        0.30
                        0.25
                        0.18
                        0.16
                                        in
              0.014
              0.012
              0.009
              0.007
              0.006
Percentage
 Recovery
    85
    73
    53
    37
    31
                           A  14-percent draw-off means that this
                        percentage of the peak flow will pass through
                        the  underflow outlet to the soil collection
                        pond. This amounts to 0.14 x 222.4 I/sec (8
                        ft3/sec) = 32 I/sec (1.1 ft3/sec). The head or
                        depth of water above the underflow outlet
                        will  be 0.61  m (2.0 ft) when the outlet weir
                                           28

-------
                FIGURE 14   STANDARD STOCK WATERING TANK
starts overflowing.  At peak flow this head
may increase to 0.76 m (2.5 ft). Approximate
hydraulic  computations  indicate  that  this
head is  too  small to permit use of a 0.10-m,
(0.33 ft)  diameter underflow  outlet.  If an
outlet  pipe  0.15 m (0.5 ft) in diameter is
used, the  head is sufficient to force the flow
through about 15 m (50 ft)  of outlet.
    To meet the recovery performance shown
in  Figure  11 it is necessary  to keep  the
underflow to about 32 I/sec (1.1 ft3/sec). To
prevent decreasing the rate of underflow due
to backwater, the maximum water level in the
soil collection pond should be below the top
of  the  underflow pipe.  The most practical
way of regulating the underflow rate would
be to provide a shear gate  at the outlet pipe
and to determine the actual setting of the gate
from measurements  of  the volume in  the
collection   pond  during actual  storm
conditions.
    A  further design consideration  is  the
volume  of the soil erosion collection pond.
Obviously, the foul sewer discharge from the
swirl chamber underflow will outlet into the
pond, and clear effluent will overflow to the
selected  drainage  ditch   or  the designated
watercourse during a storm period. However,
whenever the rate of flow into the swirl
chamber is not sufficient  to fill the chamber
to the overflow weir crest, all of the storm
runoff will discharge  through the foul sewer
into the soil collection pond. Thus, the rate of
flow into the pond will vary from 0 to 32
I/sec (1.1 ft3/sec). Hence, if it is desired to
provide storage for all underflow in a 4-hr
storm the required storage would be 32 I/sec
(1.1 ft3/sec)  x  4  x  60  x 60,  or 447  m3
(15,800 cu ft). This would require a pond 1.2
m (4 ft) deep and 18.9 m (62 ft) square. If a
2-hr detention time is considered adequate to
settle  out the  suspended  solids,  then  the
                                           29

-------
depth could be reduced to 0.61 m  (2 ft) or
the surface dimensions of the pond  reduced.
An overflow weir should be provided to pass
32 I/sec (1.1 ft3/sec) when the pond becomes
filled to the designed depth.
    The chief advantage of such a temporary
construction  swirl  separator  is  that  it  is
portable and has no mechanical parts. Thus,
the chamber  could be moved about on the
construction site, as required, or moved to
other sites. Multiple units could be used to
meet requirements of larger sites or to remove
higher percentages of suspended solids.
              REFERENCES

    6.  Practices  in  Detention  of  Urban
Stormwater Runoff, APWA Special Report
No. 43, Table 8, p. 33.
                                          30

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                                     CHAPTER IV
                         GLOSSARY OF PERTINENT TERMS
    Cattle  Watering  Tank  —  A standard,
commercially available tank or tub used on
farms,  ranches and stock feeding lots for
dispensing drinking water for cattle and other
livestock.
    Concentric  Skirt  — A vertical sheet  or
panel, constructed in circular form concentric
with the  outer  diameter  and  the  overflow
downdraft  pipe in a  swirl chamber for the
purpose of separating flow zones and acting as
a suppressant of any short-circuiting of flow
patterns  or the overflow  of floating solids
with the effluent.
    Depth  of  Chamber —  The  vertical
distance  between  the  bottom  of the  swirl
chamber and the crest or lip of the overflow
weir, or  the level of the flat weir disc; the
depth of the chamber to the overflow level.
    Erosion — The washing or scouring action
of stormwater on the land, resulting in the
displacement and movement of grit, silt and
other indigenous  solids with the  wastewater
flow; the type of solids which are  intended to
be  removed from the flow  by the  swirl
concentrator chamber.
    Flat Weir Disk  - The flat circular  plate
that extends around the overflow pipe in the
swirl chamber, to  a predetermined diameter,
over which  the clarified effluent flows on its
way to the overflow opening.
    Flow   Spoiler  —   Vertical  energy
dissipating baffle or plate installed on the weir
disc or elsewhere  in  the  swirl concentrator
chamber  for  the  purpose of  preventing
excessive  flow  disturbances and  dampening
the development of free vortex  flow patterns
and other  undesired flow conditions in the
chamber.
    Foul Sewer — A sewer line, from the
bottom of the swirl concentrator  chamber to
some point of discharge  to an  interceptor
sewer,  a catchment basin  or other point of
solids disposal, installed for the  purpose of
drawing off the solids slurry  retained in the
swirl chamber due to the  recovery efficiency
of the device.
    Gilsonite® —  A test material  used in the
swirl studies to simulate the grit material that
will be contained in erosion runoff flows into
prototype units in the field; solids having  a
specific gravity of  1.06 and a size range of 0.5
to 3 mm.
    Grit — Solids carried by erosion runoff
waters which, because of their size, >0.2 mm
(0.008 in), and specific gravity, 2.65, settle
readily in a swirl concentrator chamber.
    Inlet Baffle — A structural plate installed
from  the inlet to  the overflow weir for the
purpose of producing or inducing the desired
flow pattern  in  a swirl  chamber; a device to
serve  as a guide for the  incoming flow and to
place  it in circulatory  action to take  full
advantage of  the swirl secondary flow pattern
in the chamber.
    Petrothene®  —   A  synthetic  plastic
material which, in shredded or dust form, has
a specific gravity of 1.01 and was used in the
study to simulate the lighter silts and clays
which may be. contained in erosion runoff
wastewater to be treated by  prototype field
units.
    Prototype — A  full-scale  version of the
laboratory  test  model,  designed  to  handle
erosion  runoff  in  actual  practice;  in  this
study, a scaled-up replica of the  laboratory
model of  a  size that  would  be  four times
larger than the model itself; in this study, one
prototype proposed  for actual field use on a
temporary  basis would be a  conventional,
commercial cattle or stock watering tank.
    Recovery  — The  percentage of  solids
introduced into a swirl concentrator chamber
that will be retained as settled material in the
bottom  of  the chamber  and  drawn  off
through  the  foul  sewer; solids carried over
with the clarified effluent are not  considered
as part of the recovery in the current studies.
    Swirl  Concentrator  Chamber  —  A
cylindrical  tank or  chamber, in  which the
shape, method of inflow and overflow,  and
internal  appurtenant   structures  induce  a
swirl-type flow  pattern  which  produces the
desired  separation of solids from the  liquid
flow.
    Underflow  — The slurry,  containing the
recovered solids, which is withdrawn from the
bottom of the  swirl concentrator chamber;
the converse of the clarified overflow; the
erosion  solids  which   the  prototype  swirl
chamber is intended to recover  and, thus,
prevent from causing environmental pollution,
loss of soil cover, and downstream siltation.
                                           31

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                                      CHAPTER V
                                       APPENDIX
                           (LaSalle Hydraulic Laboratory Report)
    Previous research has been carried out on
the  Swirl  Concentrator,  covering  its
application  as a stormwater regulator, a grit
separation  device,  and  a primary settling
chamber. The present study was undertaken
to investigate the  application  of  the  swirl
solids separation principle to the treatment of
erosion runoff.  The same model  used in
previous   studies  was  utilized,  with
modifications that would accommodate larger
flows and  demonstrate  the capabilities of a
prototype   device  that  would  be simple,
sturdy, moveable, and easy to operate.
    Since the object of the  study was to
develop  a  design that would  remove  grit
particles whose   size and  gradation would
depend on  the nature of the watershed area
and its indigenous soils, three kinds of solid
materials were used in  the model to allow
interpretation and  interpolation of results.
Scaling up was accomplished   to  provide
recovery rates for various sizes of prototype
particles as a function of discharge rates.
    The principle in the swirl separation of
erosion soil solids from runoff waters covered
a controlled combination  of solids settling
with rotational  liquid velocity, induced  by
means  of spill over an overflow weir, the slope
of the  chamber floor and a bottom foul draw-
off.  Modifications  were  innovated  and
investigated in  order  to  obtain  optimum
removal  of the  solids. The foul outlet  was
provided during  construction of the model
and a  continuous underflow was drawn off
during all tests at predetermined rates.
    The basic layout was  evolved  from the
laboratory's  previous  experience with  the
swirl  combined sewer  overflow  regulator
configuration and based on the desire to use
standard cattle watering tanks in actual field
installations. These commercial tanks are 3.66
m (12  ft) diameter and 0.91 m (3  ft) deep;
they would  provide  the  basic  shell of  an
economical swirl chamber. The inlet, circular
weir, clear  effluent  overflow, and foul outlet
could be added at moderate cost.
Description of the Model
    The  central part of  the  hydraulic test
model was  the separation  chamber, which
took  the form of a vertical Plexiglas cylinder
with  1:15 cement floor slope in the first stage
of the tests, as shown on Figure 3 and Figure
4, contained in Chapter II of this report. The
floor   slope  was later  eliminated  and  the
chamber floor was  made flat,  level with  the
inlet  floor  elevation.  A  spiral flow  guide
encircling the foul  outlet was embedded in
the floor for some tests of the  research series.
    In  the  center  of  the cylinder   an
embedded  poly vinyl chloride (PVC) pipe,
15.2  cm (6  in) inside diameter, provided  the
support for the circular weir  and the outlet
which discharges the clear effluent overflow
spilling over  the weir. The elevation of  the
weir was maintained constant  at 15.2 cm (6
in) above the inlet floor level during the entire
series of tests.
    Inflow  to  the  chamber  was  supplied
through PVC pipe,  15.2-cm (6 in) diameter
set at a slope of 1:1,000. A vibrating solids
injection system was placed  in this supply
line, 2:14 m (9 ft) upstream of the  chamber.
Water supply for the model  was  obtained
through  a pipe  directly  connected  to  the
constant level tank in one of the laboratory's
permanent pumping stations.
    The overflow effluent through the central
outlet pipe was conducted to  a large settling
basin   equipped with  a calibrated V-notch
weir.  A point gauge in a manometer pot was
used   to  read  the  level  in the basin,
determining  the discharge  going  over  the
V-notch weir.
    A flexible 2.5 cm- (1  in) diameter tygon
tube  was placed inside the cylinder beneath
the floor of the test chamber  to collect  the
foul flow. The foul  flow was withdrawn from
the bottom of the cylinder, and conducted to
a  solids  settling  tower  fitted   with   an
adjustable level  outlet  pipe which could  be
raised or lowered at will to control the rate of
discharge drawn off through the foul outlet.
                                           32

-------
    The suggested use of a conventional cattle
watering tank as the prototype swirl chamber
established the model scale of 1:4. This meant
that the  prototype unit would have  to  be
operating with a 61 cm (24 in) square duct
entering a 3.66-m (12 ft) diameter chamber,
based on the first step of the study. Later, the
square  duct inlet  was reduced  to  0.40 cm
(0.16  in)  while  the  chamber remained
unchanged.
    The selected discharges (Qm) to be tested
were respectively, 3, 5, and 7 I/sec (0.8, 1.3,
and  1.8  gal/sec)  in  the  model.  When
transposed at the prototype scale  (Qp), these
values represented the following flows:
QP
QP
QP
I/sec
I/sec
m3/sec
ft3/sec
mgd
3
96
0.1
3.4
2.2
5
160
0.16
5.6
3.6
7
224
0.2
7.9
5.1
    The  3.66  m  (12  ft)  prototype  size
chamber, with the weir crest or lip 61 cm (24
in)  above the horizontal floor and a central
overflow pipe of 67.3 cm-(26.5 in) diameter,
would  give,  respectively, the  following
detention times:
Qm I/sec
(ft3 /sec)
Qp I/sec
(ft3 /sec)
Detention (sec)
Prototype
3
(0.1)
96
(3.4)

54.2
5
(0.2)
160
(5.6)

32.5
7
(0.2)
224
(7.9)

23.2
Grit Simulation in the Model
    The  amount  and  composition of  the
erosion  runoff  depends  essentially  on
topography and the nature of the soil of the
watershed  area.  The  nature  of  the  soil
particles which are to be  removed  from  the
runoff flow in a proposed prototype structure
is not precisely known.
    According  to  their  grain  sizes,  soil
particles are classified as sand, silt,  and clay.
Following  is a list of the  generally  accepted
soil classifications, according to grain size:
Coarse Sand
Medium Sand
Fine
Silt
     4.8-2.0 mm
     2.0-0.4 mm
     0.4-0.05 mm
     0.05-0.005 mm
       (0.19-0.08 in)
       (0.08 - 0.02 in)
       (0.02-0.002 in)
       (0.002 - 0.0002 in)
Clay          Smaller than
                0.005 mm    (0.0002 in)
Colloidal clay   Smaller than
                0.001 mm or M (0.00004 in)

    To ascertain the range of simulation used
in  the  model,   the  approach  involved
determination of  the kind  of solids which
could  be  represented  by  the materials
commonly used in  the  laboratory  for  such
solids simulation.

Gilsonite - SG 1.06

    0.5 mm (0.02 in) > d > 3 mm (0.12 in)
    The Gilsonite used  in these  tests had a
gradation curve  as  shown in   Figure  15,
Gradation Curve for Gilsonite Used in Model.
Figure  16,    Prototype   Settling Velocities
Simulated by Gilsonite — SG 1.06, shows the
settling  velocity  corresponding  to  various
particle sizes for the model and prototype at
scale   1:4,  determined   according  to  the
approach described by Larras.7 This work is
based  on irregularly shaped  particles such as
were used in the model studies.
    A  family of curves for different specific
gravities was presented in  Figure 5. For the
range  of  prototype  settling velocities
simulated by the Gilsonite in Figure  15, it is
possible, in Figure 5, to find the particle sizes
for specific  gravity  2.65  corresponding  to
erosion runoff components.
    As an example, in Figure  16 the  finest
Gilsonite particle of 0.5 mm (0.02 in) (No.  35
sieve)   simulates,  at  1:4   scale,  a  settling
velocity of 1 cm/sec (0.4  in/sec). Using this
value  in  Figure 5,  grit solids  with  specific
gravity 2.65 would have a particle  size of 0.14
mm (0.0055 in). However,  given the relatively
large  particle  sizes represented  by  the
Gilsonite, shredded Petrothene X - SG 1.01
was judged  more  adequate for testing  of
further improvements in  the swirl  chamber
structure.

Shredded Petrothene X -  SG 1.01

    0.5 mm (0.02 in) > d > 3.0 mm (0.12 in)
    Gilsonite, at prototype  scale 1:4,  left a
zone of fine  grit not represented. Petrothene
X,  with particle sizes  ranging from  0.5  to 3
                                             33

-------
            3 4
    U.S. STANDARD  SIEVE  NUMBERS

6    8  10     16   20  30   40 50   70  100  140
       100
       90
            6     4
            (.24)  (.16)
                         0.6   0.4
                         .02) (.01)
 0.2
(.008)
 0.1
(.004)

Fine
GRAVEL

Coarse
UI-SMIIM ii^-c uu mm \in
Medium
;
Fine
SAND



    FIGURE 15   GRADATION CURVE FOR GILSONITE USED  IN MODEL1


1Tho Helical Bend Combined Sewer Overflow Regulator, USEPA Report, EPA-600/2-75-062, December 1975,
 Figure 8, p. 18.
                                      34

-------

10 (3.9)
7.2 (2.8)
5(2)
4(1.6)
3 (1.2)
2 (.8)
o
< 1 (.4)
c
u
=l/4

1.06




























I.03 0.1 0.2 0.3 0.5 1.0 2.0. 3.0 5 10
012) (.04) (.08) (.12) .2) U) (.8) (1,2) (2) (4)
PARTICLE SIZE, mm (in)
FIGURE 16  PROTOTYPE SETTLING VELOCITIES SIMULATED BY
           GILSONITE - SG 1.06
                            35

-------
mm (0.02 to 0.12 in), was selected to fill this
void;  its gradation curve is shown in  Figure
17, Gradation Curve  for Petrothene Used in
Model.
    The  same procedure described earlier for
Gilsonite was followed to define the settling
velocities  of  the  particles  simulated by
Petrothene X at scale 1:4 as shown in Figure
18, Prototype  Settling Velocities  Simulated
by  Petrothene  -  SG  1.01.  Similarly,  the
prototype  particle sizes can  be  found  in
Figure  19,  Prototype  Particle  Sizes
Represented by Petrothene.
    Following  an  example  through  this
procedure  again,  the  finest particle  in  the
model, 0.5 mm (0.02 in) at scale 1:4,  gives a
prototype settling velocity of 0.2 cm/sec (0.4
in/sec) in Figure 7. Using this value in Figure
8, it  can  be determined  that the smallest
particle simulated at specific gravity 2.65 is
0.052 mm (0.004 in), or down to the lower
end of the fine sand range.
    Due to its relative ease of handling and
the wide range of recovery rates it simulated,
this  material was selected  for  testing  of
improvements in the swirl chamber structure.

Petrothene Dust - SG 1.01
    d< 1.0 mm (0.04 in)
    As  shown  in  Figure 8, Petrothene  with
grain size 0.5 - 3.0 mm (0.02 - 0.12 in) does
not cover  the prototype  silt  range.  It was
therefore evident that a new kind  of material
with lower settling velocity had to be  found:.
    Settling column tests performed by T. W;.
Beak  Consultants,  in  connection  with
previous swirl studies,2 defined the size of the
dust particles in  the range of 120  to 500
microns. Use of these values in Figures  18 and
19,  and  utilizing  the  same   procedure
described earlier,  indicates  that  the finest
prototype size  represented at specific  gravity
2.65 is  0.012 mm (12 microns), covering 95
percent of the silt range (50 to 0.5 microns),
    Since only  one scale for  the  prototype
was being considered (X = 1:4),  all  results
could be presented more simply as shown in
Figure 20, Range of Prototype Grit Particle
Sizes  (SG 2.65) Simulated, Respectively, by
Gilsonite, Petrothene, and  Petrothene Dust.
The   figure  shows  directly  the   prototype
particle  sizes   at  specific  gravity  2.65
(ordinate) as a function of the model particle
sizes  (abscissa).  This  figure  also  has the
advantage of showing either overlaps or gaps,
if any, existing in the simulation.

Settling Velocity Distributions for Gilsonite,
Petrothene,  Petrothene Dust, and Stormwater
Runoff
    Settling velocity  distribution for
Petrothene  dust, carried  out by T.W.  Beak
Consultants, is   represented  in   Figure 21,
Settling Velocity Distributions for Petrothene
Dust and Stormwater Runoff. Also delineated
in Figure 21 is the curve  for the  settling
velocity distribution  of solids in Stormwater
runoff. Both of these  curves were taken
directly from the Beak report.
    Above  the  model  curve for Petrothene
dust in Figure 21, a second curve has been
drawn, giving the settling velocity distribution
at prototype scale  1:4 represented  by the
model material, when transposed according to
Froude's  Law.   The  same   procedure  was
followed for Petrothene [0.5 - 3 mm (0.02 -
0.12 in)]  and Gilsonite [0.5  - 3 mm (0.02 -
0.12  in)]   and  the  results are  plotted
respectively  in Figure 22,  Settling  Velocity
Distributions for Shredded Petrothene X and
Stormwater Runoff,  and  in  Figure 23,
Settling Velocity Distributions for Gilsonite
and  Stormwater Runoff. The extrapolated
Stormwater  runoff curve  from Beak was also
traced in the figure.

Model Simulation of Prototype Runoff
    Examination of  Figures  21, 22, and 23
shows clearly that  the   model  particle
simulation  is several orders of  magnitude
away from  the settling velocities given in the
Beak  Consultants,  Ltd.,  runoff  sample.
Further analysis  .of the curve for  runoff in
Figure 21, shows it to have a median settling
velocity considerably less than 0.01 cm/sec
(0.004 in/sec),  meaning that the  particles
were  at least  as fine  as silt, and probably in
the clay sizes range.
    Samples like these fall into the  class of
colloidal turbid water which might  require at
least days of quiescent settling to be clarified.
It is evident,  therefore, that there  should be
no pretention of trying to remove  these fine
particles  in  the  swirl  concentrator.
                                            36

-------
              U.S. STANDARD  SIEVE NUMBERS
  6    4
(.24) (.016)
 0.6   0.4
(.02)  (.02)
 0.2
(.008)
      GRAIN  SIZE IN mm (in )
                                                             100
  34    6   8  tO     /6   2O   3O   4O  SO    7O  IOO  140
 0.1
(.004)

Fine
GRAVEL

Coarse

Medium

Fine
SAND

FIGURE 17 GRADATION CURVE FOR PETROTHEIS1E USED  IN MODEL
                               37

-------




1b0 SETTLING VELOCITY, cm/sec (in /sec)



2.5(1)
t
_i.
(.4)
75
(.2)
.2 ^
1
J
1




























RANGE OF PROTOTYPE
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE AT
SCALE I/4
(.08)
I
(.04)
RANGE OF PROTOTYPE
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE DUST
AT SCALE I/4
'0.012 (.0047)
.01 (.004)







.001 (.OC







103)








>







/
'







/

/





/

/





/

/




/
t

>
f

0




















/
//
7 /
/ /
/
/
/

PETR

















/
/
/
' /
/




















1
1
t
/
/






















/
I
'











OTHENE
DUST
12 (.0047) |













/
/
























/

/























/

1























J


'






















/


/



















/

/
/

/
/
f



















/

.
S
f





















/

Jr
r



















SHREDDED
PETROTHENE











X




























/

/


























'



























s




























s

s

























,»


t

























1/4


1.01

























01 0.1 0.5 1 3 10
03) (.004) (.02) (.04) (.12) (.4)
PARTICLE SIZE IN mm (in,)
FIGURE 18   PROTOTYPE SETTLING VELOCITIES SIMULATED BY
           PETROTHEIME-SG 1.01
                         38

-------
"o
c
SETTLING VELOCITY, cm/sec (





2.5 (1)



0.2
0.1

0121
L
RANGE OF
PROTOTYPE GRIT
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
'(.08)
(.04)
RANGE OF
PROTOTYPE GRIT
SETTLING VELOCITY
REPRESENTED BY
PETROTHENE
AT SCALE 1/4
(.0047)
ML (.004)

C
.(
001
PROTOTYPE
PARTICLE SIZES
SIMULATED BY
PETROTHENE DUST
).12 mm < :d < 0.5 mm
D08in

'/

/ /
^ — f
r~/~?
//
/
/
~-L 	







PROTOTYPE
PARTICLE SIZEJ
SIMULATED BY
^ PETROTHENE
).5 mm 
-------

l.U.d'H
0.5 (.02)
0.4 (.016;
0.3 (.012)
0.2 (.008)
¥
J 0.1 (.004)
N 0.08 (.0031)
W
ill
> 0.06 (.0024)
H
|2 0.05 (.002)
O
0- 0.04 (.0016)
0.03 (.001 2)
0.02 (.0008)
0.012 (.0005
0.01 (.0004
j
t


•\
0.57


RANGE OF
PARTICLES
GILSONITE
0.22 (.009)
; ,
r i

RANGE



PROT
REP
SG
3 mrr
l-\7

OF PR



OTYF
RESE
1.06
. <
in E
:NTED
rf<0.5r
^<.02i

TYPE
Y
UPMFi^

/
y^
/
/
f


•'RANGE OF
/PROTOTYPE
/PARTICLES REPRE-
SENTED BY i y
PETROTHENE ]/
DUST y/|
0.5 mm 
IE D



/

UST




3Y
nm
n)


/





S
/




/



J
/










/



/















/





PE





/


/






TR







l/







OT





N?
<£s
<£s

^








SILSONITE
HENE X in


cp








mm (in)


b/


0Y










I

/



.S













I .12 .15 .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.5 2 2.5 3
^v ^5 ^^ ^^ *^ ^3 £)f ^i ^^ ^3 ^^ ^^ ^^ ^— ^^
^s ^^ ^5 ^5 ^5 v:* ^* ^^ Cl?' ^S N^J x^ ' ^^J ^^
MODEL SIZE IN mm (in)
FIGURE 20 RANGE OF PROTOTYPE GRIT PARTICLE SIZES (SG 2.65) SIMULATED,
       RESPECTIVELY, BY GILSONITE, PETROTHENE and PETROTHENE DUST
                              40

-------
      0.3
     (.12)
      0.2
     (.08)
 8    0-1
 IE   (>04)
 ~^   0.08
 JB  (.031)
 "E
 o
 O
 o
 Ul
 0.06
(.024)

 0.05
 (.02)

 0.04
 (M6)
a
<=   0.03
H  (.012)
LU
CO
    0.02
    (.008)
    0.01
    (.004)
                                       .Median, settling Velocity
                                        for Petrothene  Dust
                                               SG  I.Ot
Model Petrothene Dust1
  d < 1 mm
                                                           Velocity distribution of
                                                           Solids in Stormwater
                                                           Runoff2
         10      2O        4O   50  60        80       90    95
                        PERCENT  LESS THAN OR  EQUAL TO
                                                                     98  99  99.5
          nd Settling Characteristics of Particulates in Storm and Sanitary Wastewater. USEPA Report
      -670/2-75-011 April 1975 — Figure 12, p. 21

  Physical and Settling Characteristics of Particulates in Storm and Sanitary Wastewater. USEPA Reoort
  ErA-670/2-7 5-011 April 1975 — Figure 3, p. 9!                                          '
FIGURE 21   SETTLING VELOCITY DISTRIBUTIONS FOR PETROTHENE DUST
               AND STORMWATER RUNOFF
                                         41

-------
   4.0
   (1.6)

   3.0
   (1.2)
    2.0
    (.8)
u
o
o
tu
    1.0
    (.4)

    0.8
   (.31)
 *  0.6
§ (.24)
UJ  0.4
w (.16)
    0.3
   (.12)
   0.02
   (.08)
                 Median .Settling Velocity,
                 for Shredded  Petrpthene
                SG-1.011
                                                                  Model   :
                                                            shredded
                                                        Petrotihene SG l.0;l
                                                         0.5-3mm(.02-.12in.)2>.
                                                       Stormwater Runoff.
         10      20   30   40   50   60  70   80      90    95
                          PERCENT  LESS  THAN  OR  EQUAL TO
                                                                     98  99  99.5
    1  Physical and Settling Characteristics of Participates in Storm and Sanitary Wastewater, EPA 670/2-75-011
      April 1975 - Figure 7, p. 16'
      Physical and Settling Characteristics of Particulates in Storm and Sanitary Wastewater, EPA 670/2-75-011
      April 1975 — Figure 3, p. 9


              FIGURE 22  SETTLING VELOCITY DISTRIBUTIONS FOR

                            SHREDDED PETROTHENE X®  AND

                            STORMWATER RUNOFF
                                        42

-------
 o
-I
 u
 8.0
(3.1)

 6.0
(2.4)

 5.0
 (2)

 4.0
(1.6)


 3.0
(1.2)
    2.0
    (.8)
o
o
111

e>
i?  1.0
jJ  (.4)

III  0.8
 (.31)

    0.6
   (.24)

    0.5
    (.2)
    0.4
   (.16)

    0.3
   (.12)
                    Median-.
           Settling, .yeto
-------
Model-to-prototype  particle  transposition
will, therefore,  be based  on the individual
particle sizes as portrayed in Figure 20.
Testing Procedure
    Although use of the swirl  concentrator
for  erosion  runoff  clarification  would
normally  involve a  continuously  varying
discharge  over  a  storm  hydrograph,
steady-state discharges were used  for testing
purposes.   For  each  individual test  a
steady-state discharge was set running in the
model until  equilibrium  conditions  were
established. A mixture  containing one liter
(0.26  gal) of Gilsonite  or Petrothene  was
injected into the supply pipe,  using the same
vibrating rate for all tests. The full liter (0.26
gal) was added over a period of 5 minutes and
the model was allowed to run 10 minutes
after the end of soils injection.
    The amount  of material found on the
bottom  of  the chamber  was  measured
separately. The same procedure  was  followed
for material  floating in the effluent  overflow
settling  basin.  The  remaining  portion
deposited in  the settling basin was found by
subtraction, assuming no material was lost.
    The recovery rate was  taken  as the
percentage  represented by  the  amount
measured on  the  bottom of the chamber,  as
compared to  the  total found  in the chamber
and deposited in the effluent overflow settling
basin.
Settleable Solids Recovery Results
    In  discussing settleable solids  for the
purpose  of this study, reference is made to
the recovery rates for Gilsonite and shredded
Petrothene X, both with a particle size range of
0.5 mm < d < 3 mm (0.02 in < d < 0.12 in)
and Petrothene dust with a size range of 0.12
mm < d < 0.5 mm (0.005 in < d < 0.02 in).
As described,  Gilsonite and Petrothene, both
shredded  or  dust,  were  considered as
representing grit  material  over  the ranges
defined  in Figure  19.  The different  steps
followed in the model testing are recorded in
Table  3, Modifications Tested in. Model and
Results.
Tests Carried Out With Gilsonite - SG 1.06
    Brief tests  carried out with the original
model  layout, including a flatwise weir 0.50
m (11.6 ft) diameter, as shown in  Figure 4,
Original Layout for Test No. 1, covered three
selected discharges.  They  showed  that  the
flow pattern established in the swirl chamber
was an unstable vortex even when the smallest
discharge 3 I/sec (0.8 gal./sec) ;was used. Due
to these  special conditions prevailing in the
chamber, no solids injection was made; hence,
no volumetric measurement was taken.
    To eliminate the vortex flow pattern,  a
baffle extending  from  the  inlet to  the
periphery of the weir was tested, as shown in
Figure 4b,  Original Layout With-Inlet Baffle.
This did not completely still  the vortex, so
flow spoilers were  installed on the flat disc
weir. These flow spoilers were cut unevenly to
obtain a better distribution of flow over the
four quadrants of  the weir.  This format  is
shown in Figure 24a, Model Layout for Tests
2 to 13 - Modification 1.
    Tests carried out with Gilsonite and the
deflector were unable to show any further
improvements  since  recovery  rates  were
almost constant  around  95  percent. They
proved, however,  that  the  presence of  a
deflector at the inlet end was very useful in
increasing the efficiency rate, particularly for
high-flow  conditions. After the  model  had
been improved using Petrothene X, 0.5 —  3
mm (0.02  —  0.12 in), Gilsonite tests were
resumed  with  different rates of  draw-off.
Table  3, Modifications Tested in Model and
Results, shows quantitative results  for those
tests. Slight deposits of Petrothene  remained
in the chamber after the tests, as  shown in
Figure 25, Deposit of Petrothene Found After
3 I/sec (0.8 gal/sec) Test.

Tests Carried out with Shredded Petrothene X
SG 1.01  - 0.5 mm < d <3 mm (0.02 in 
-------
                                  TABLE 3
           MODIFICATIONS TESTED  IN MODEL AND RESULTS
Mod.
No.
Fig. Weir
No. 6
cm (in)
Inlet
Baffle
Draw-off
(Percent)
Percent Recovery vs Discharge Recovery
3 I/sec ... 5 I/sec 7 I/sec Fig.
(0.8 aal/sec) (1.3 aal/sec) (1.8 aal/sec)
18   20
            Flat weir disc; 4 uneven flow spoilers; 1/15 floor slope;
            15.2 cm x 15.2  cm  (6  in  x 6 in) inlet size;
            material used  —
            Gilsonite 0.5 mm <  d< 3  mm (.02 in < d < .12 in)  SG  1.06
1 13 20
1 13 20
No
Yes
5
5
95
96
90
95
76
95
            Flat weir disc; 4 uneven flow spoilers; 1/15 floor slope;
            15.2 cm x 15.2  cm  (6  in  x 6 in) inlet size;
            material used  - shredded  Petrothene X 0.5 mm < d <3 mm
            (.02  in  < d  < .12  in)  SG  1.01
1 13
1 13

20
20

No
Yes

5
5

42
86

17
52

8
22

14
14
21
            Circular weir with  lip 5.1 cm (2 in) high;  4 even flow  spoilers;
            1/15 floor slope;  15.2 cm x 15.2 cm (6  in  x  6 in)  inlet size;
            shredded Petrothene X 0.5 mm < d <  3 mm  (.02 in  < d <  .12 in)  SG  1.01;
            spiral flow guide 2.5 cm (1 in) high encircling foul outlet
2

3

4
15

16

17
20

20

20
Yes
Spiral flow
Yes
Spiral flow
Yes
5
guide
5
guide
5

0.87 m (2

7.6 cm (3

71
.85
76
in)
79

ft)



high

high.



43
, open
42
open at

48
23
at oul inlet
23
foul outlet
25
            Circular weir with lip 5.1  cm (2 in)  high;  4 even flow spoilers;
            1/15 floor slope; shredded Petrothene 0.5 mm < d < 3 mm
            (.02  in < d <  .12 in) SG 1.01; concentric skirt 60.5 cm (24  in) 0
            immerse 0.5 m  (1.64  in)  no  spiral  flow guide; 15.2 cm  x 15.2 cm
            (6  in  x 6 in)  inlet size
Yes
65
35
18
            Circular weir with lip 5.7 cm (2.25 in)  high; 4 even low  spoilers; flat
            floor; shredded Petrothene 0.5  mm < d < 3 mm (.02 in  < d < .12 in)
            SG  1.01; no skirt,  no spiral  low guide;
            15.2 x 15.2  cm  (6  in x  6 in)  inlet size.
                                        45

-------
TABLE 3   (Continued)
Mod. Fig.
No. No.
11
11
23
23
Weir
e
cm(in)
24
24
Inlet
Baffle
Yes
Yes
Draw-off Percent Recovery vs Discharge Recovery
(Percent)
3 I/sec 5 I/sec 7 I/sec Fig.
(0.8 gal/sec) (1.3 gal/sec) (1.8 gal/sec)
14
20
81 54 31
84 56
25
25
12
26   24
                   Circular weir with lip 5.7 cm (2.25 in) high; 4 even flow spoilers;
                   horizontal floor; 10.2 cm x 10.2 cm (4 in x 4 in) inlet size;
                   shredded Petrothene 0.5 mm 
-------
Four  Flow Spoilers
of  uneven length
             INLET
             15.24 a 15.24cm
              (6inx 6in)
Four Flow Spoilers
of uneven length
 To Overflow Tank
FOUL OUTLET
        ELEVATION
         Section A-A
           FIGURE 24 a MODEL LAYOUT FOR TESTS 2 to 13
                      MODIFICATION 1
                              47

-------
  UNEVEN FLOW SPOILERS STUCK ON THE 50.8 cm (20 in )  WEIR DISK
                     (Modification 1)
MODIFICATION 1 TESTED WITH A 3 I/sec (0.8 gal/sec) DISCHARGE
       FIGURE 24 b MODEL LAYOUT FOR TESTS 2 to 13
                   MODIFICATION 1
                            48

-------
DEPOSIT OF PETROTHENE FOUND AT INLET AFTER 3 I/sec (0.8 gps)
  DEPOSIT OF PETROTHENE FOUND IN THE CHAMBER BOTTOM
          AFTER 3 I/sec (0.8 gal/sec) TEST
 FIGURE 25   DEPOSIT OF PETROTHENE FOUND AFTER
              3 I/sec (0.8 gal/sec) TEST
                          49

-------
    Qm I/sec    0
      (gal/sec)
   Qp  I/sec     L_
       gal/sec
°P
Q
       ft3/sec

       mgd
                                     DISCHARGE
                                    J_
                      50
                      (13.2)
 100
(2.64)
 150
(39.6)
 200
(52.8)
250
(66)
                	 Tests carried out with Inlet Deflector
                —	Tests carried out without  Inlet Deflector
                MATERIAL USED : Ground Petrothene X-nominal  SG 1.01
                                Grain sizes  0.5 - 3 mm irregular shapes
FIGURE 26   INFLUENCE OF INLET DEFLECTOR ON RECOVERY RATE
             0.50 m (20 in.) 0 WEIR DISK, 5 PERCENT DRAW-OFF - MODIFICATION 11
                                      50

-------
                                                        15.24 cm x 15.24cm
                                                          (6inx 6 in)
                                             (1 in)

                                            FOUL OUTLET
TO OVERFLOW TANK
                                                                INLET
                                                                BAFFLE
FLOW SPOILERS
OF SAME LENGTH
BOTTOM
SPIRAL
FLOW
GUIDE
         FIGURE 27   MODEL LAYOUT FOR TESTS  14 to 16
                      MODIFICATION 2
                                  51

-------
    the foul outlet, also shown in Figure 27,
    Modification  2.  The  purpose  of  this
    device was to help concentrate a part of
    the flow around the central overflow pipe
    where weak  velocities prevailed, and to
    reduce the solids deposits on the chamber
    bottom during normal  operation of the
    model.
    Results as  shown  in  Table  3,  when
    compared to previous values for Stage  1,
    indicated  an  18-percent  drop  of
    efficiency for small 3 I/sec (0.8 gal/sec)
    and  intermediate  5  I/sec (1.3 gal/sec)
    flows. Values for  the high flow 7 I/sec
    (1.8 gal/sec) remained unchanged.
    Modifications 3 and 4 included the same
    spiral flow guide with different heights;
    both  were open at  the four  outlet. As
    shown in  Figure  28, Model  Layout for
    Tests  17  to  19,  Modifications  3,  the
    height of the spiral flow guide was 2.2 cm
    (0.87 in) above the chamber floor at the
    foul outlet.  This is shown in Figure 29,
    Inlet Baffle, Modification 3. It was raised
    to 7.6 cm (3.0 in)  as shown in Figure 30,
    Model Layout for Tests 20  to  22,
    Modification 4; and in Figure 31, Details,
    Modification 4.  Results showed a slight
    improvement  with   respect  to
    Modification 2, but the best efficiency
    rate was still 8 percent  below the values
    obtained in Stage 1, with no special flow
    guide, and deposits of solids at the small
    flow were still not eliminated. This device
    was discarded in the ensuing tests for this
    reason.
2. Influence of a Concentric Skirt
for Collecting Floatables —
Modifications 5, 6, and 7
    The configuration for these tests is shown
in Figure  32, Model Layout for Tests 23 to
31, Modifications  5,  6,  and 7. These  stages
dealt with the influence of a concentric skirt,
61.0 cm (24.0 in) in  diameter, designed to
retain  floatables when  set at  different
immersion depths.
    The bottom of the skirt was successively
placed 1.25 cm (0.5 in)  Modification 5; 2.5
cm (1.0 in) Modification 6; and 5.0 cm (2^0
in) Modification 7; below the water level in
the chamber. Weir diameter and inlet  baffle"
conditions  were similar to those • previously
used in Modifications-2, 3, and 4.
    Addition  of  the skirt  resulted  in •  a
decrease of about 30 percent in the recovery
rate. The  reduction  in efficiency seemed to
increase with  the immersion depth, but the
scattered results obtained failed to define  a
specific trend. The poorest results were those
obtained with the 5.0 cm  (2.0 in) immersion
depth,  Modification  7,  and  intermediate
discharge 5 I/sec (1.3 gal/sec).
    Therefore,  the  use   of  the  skirt  was
discarded  in subsequent  tests and floatables
were allowed to discharge with the overflow
effluent.

3. Influence of Weir Diameter —
Modifications 8 and 9
    These modifications are shown in Figures
24a and 24b, Model Layout for tests 2  to 13;
Figure 33, Model Layout  for Tests 32  to 35,
Modification 8; and Figure 34, Model Layout
for Tests 36 to 38, Modification 9.
    Smaller diameter weirs  provide a  wider
area between  the  weir lip and the chamber
wall than  do  larger  weirs. This reduces the
upward velocity component, giving a  better
opportunity for the simulated erosion runoff
particles in suspension to settle.
    On the other hand, the distance from the
central overflow pipe to the weir lip or crest  is
reduced in proportion when smaller weirs are
used and,  consequently, the time  allowed for
particles in suspension under the weir to settle
is shortened. On the  basis that an  optimum
size must exist, decision was made to test two
additional weirs: one had a weir with a 61 cm-
(24 in) diameter,  Modification 8,  shown in
Figure 33, Model Layout  for Tests 32  to 35.
The  other  provided a weir with a 71 cm-(28
in) diameter.  Figure  34,  Model  Layout for
Tests 36 to 38, Modification 9; and Figure 35,
Details - Modification 7; show this change.
    Results, as plotted in Figure 36,  Influence
of Weir-Chamber Diameter Ratio, show that
the  differences  in   efficiency  are smaller
between  the  small  and  intermediate  weirs
than when the largest weir is utilized. They
show also  that  the  maximum was reached
when a weir of 61 cm (24 in) was used.
    Subsequent  tests  were, therefore, carried
out  with  a weir-chamber diameter  ratio of
2:3.
                                            52

-------
                                                        15.24 cm x 15.24cm
                                                           (6 in x 6 in)
                                             2.54 cm
                                              (1 in.)
                                            FOUL,  OUTLET
TO OVERFLOW TANK
                                                                INLET
                                                                BAFFLE
FLOW SPOILERS
OF SAME LENGTH
BOTTOM
SPIRAL
FLOW
GUIDE
              FIGURE 28   MODEL LAYOUT FOR TESTS 17-19
                           MODIFICATIONS
                                  53

-------
Modification 2:   50.3 cm (20 in ) diameter weir.  Inlet Baffle and bottom.
                Spiral Flow Guide 2.5 cm (1 in } high closed at foul outlet.
Modification 3:  50.3 cm (20 in ) diameter weir. Inlet Baffle and bottom.
                Spiral Flow Guide 2.2 cm (0.87 in ) high open at foul
                outlet.
           FIGURE 29   INLET BAFFLE, MODIFICATION 3
                                 54

-------
                                                        15.24 cm x 15.24 cm
                                                           (6 in x 6 in) ,
                                            FOUL OUTLET
TO OVERFLOW TANK
                                                                INLET
                                                                BAFFLE
FLOW SPOILERS
OF SAME LENGTH
                                              2.54cm
                                              (1 in)
BOTTOM
SPIRAL
FLOW
GUIDE
               FIGURE 30  MODEL LAYOUT FOR TESTS 20 to 22
                          MODIFICATION 4
                                   55

-------
                                                          .^____i^H
 Modification 4:  View of the bottom spiral. Flow Guide 7.5 cm (3 in
                 high at foul outlet.
Modification 4:  50.3 cm (20 in ) diameter weir.  Inlet Baffle and bottom.
                Spiral Flow Guide 7.5 cm (3 in ) high open at foul outlet.
            FIGURE 31    DETAILS, MODIFICATION 4
                                56

-------
                                                               INLET
                                                            15.24 cm x 15.24cm
                                                               (6 in x 6 in)
     FOUR  FLOW SPOILERS
     OF SAME LENGTH
Variable immersion
  of Skirt End
                                                   FOUL OUTLET
                                                   54 cm (1 in.)
      TO OVERFLOW TANK
      ELEVATION
       Section A-A
                  FIGURE 32  MODEL LAYOUT FOR TESTS 23 to 31
                              MODIFICATIONS 5, 6 and 7
                                    57

-------
FOUR FLOW SPOILERS
OF SAME LENGTH
 INLET

15.24 cm x 15.24cm
   (6 in x 6 in)
 TO OVERFLOW TANK
                                           FOUL OUTLET
                                           2.54 cm   (1 in )
 Section A-A
            FIGURE 33  MODEL LAYOUT FOR TESTS 32 to 35
                       MODIFICATION 8
                                58

-------
FOUR FLOW SPOILERS
OF SAME LENGTH
 INLET
15.24 cm x 15.24cm
  (6 in x 6 in)
                                         FOUL OUTLET
                                         2.54 cm (1 in )
 TO OVERFLOW  TANK

 ELEVATION
 Section A-A
            FIGURE 34  MODEL LAYOUT FOR TESTS 36 to 38
                       MODIFICATION 9
                               59

-------
61 cm (24 in.) diameter weir and inlet baffle
71 cm (28 in ) diameter weir and inlet baffle
FIGURE 35   DETAILS, MODIFICATION 7
                   60

-------
   Q
   Op
            90
            80
            70
         g  60
         cc
         LLJ

         >  50
         UJ

         8  40
         UJ
         CC

            30
           20  -
            10
I/sec
(gal/sec)

I/sec
 _
O
   Op   ft3 /sec
        mgd
                           \
                            \
                               \
                                 \
                                     \
                                       \
                                                        \
                                                          \
  1
(.26)
                             2
                           (.53)
                                      Discharge
                                   -i	:	1	L
                     3
                    (.8)
              5
            (1.3)
          6
        (1.6)
       7
     (1.8)
  8
(2.1)
          50
IOO
150
200
 i
                                                                     250
           0 = 0.51 m  (20in)D3/D =0.555  Mod.  I   •   	—•
           0 = 0.61 m  (24ln)  D3/D = 0.667 Mod.  8   Q—	D
           0 = 0.71 m  (28in)  Dg/D = 0.78   Mod.  9   O	-•——O

               Material  Used = Ground Petrothene X nominal SG 1.01
                           Grain Sizes 0.5-3 mm (0.2-12 in ) irregular shapes
FIGURE 36     INFLUENCE OF WEIR - CHAMBER DIAMETER RATIO
                         (All tests carried out with inlet baffle)
                1:15 CHAMBER FLOOR SLOPE AND 5 PERCENT DRAW-OFF
                                     61

-------
4. Influence of the Chamber Floor Slope —
Modification 10
    These modifications  are shown in Figure
37,  Model  Layout for  Tests  39  to  4,1,
Modification  10; and  in Figure 38, Model
Layout for Tests 42 to 59 and 69  to 107,
Modification 11.
    Since cattle watering tanks are suggested
as an economical way to construct these swirl
chamber units,  studies were  undertaken to
test the effect on the recovery rate produced
by a flat chamber floor. Both the 51 cm- (20
in) and 61 cm- (24 in) diameter weirs wete
tested with 5 percent  draw-off.  Only results
relevant to the second weir are  presented in
Figure 3 9, Influence of Chamber Floor Slope.
It shows that a flat floor is not as efficient.
Recovery  rates decreased,  as  indicated by
Table  4,  Comparable Recovery Rates  for
Sloping and Horizontal Chamber  Floors.
    Table 4 indicates that the  61 cm- (24 in)
diameter weir had smaller losses, and yielded
better recovery rates  for  intermediate  and
high  discharges when  the  floor slope  was
eliminated.  Therefore,  this weir  diameter
should be considered for design purposes with
either a flat chamber bottom or with the 1:15
sloping floor.
                 TABLE 4
   COMPARABLE RECOVERY RATES
    FOR SLOPING AND HORIZONTAL
           CHAMBER FLOORS

                   Recovery Rates (Percent)
                       at Rate of Flow
Model discharge
I/sec {ft3/sec)     3(0.11)   5(0.18)     7(0.25)
A. Tests of recovery rates performed with a 51 cm
   (20 in) <£ Weir:
slope of 1/15       86       52         22
horizontal floor      66       37         15
absolute loss         20       15          7
relative loss         23       29         31
B. Tests of recovery rates performed with a 61 cm
   (24 in)  Weir:
slope of 1/15       87       54         20
horizontal floor      66       44         23
absolute loss         21       10          3'
relative loss         24       19         11
5. Influence of Continuous Underflow
Draw-Off, Modification 11
    This configuration is shown in Figure 38,
Model Layout for Tests 42  to  59 and 69 to
107,  Modification   11.  Although  the
preceeding tests were all carried out with a 5
percent  continuous  underflow, additional
tests  were performed  at  increased  draw-off
rates.  The rates selected were  10  and  20
percent of the discharge.
    The foul outlet pipe was unable  to pass
the-l,400-cm3/sec (85.4 in3/sec) required for
the 7  I/sec (1.8 gal/sec)  discharge at  the  20
percent  draw-off  rate.  The maximum rate
evacuated was 14 percent; therefore, the same
rate was applied respectively to 3 and 5 I/sec
(0.8 and 1.3 gal/sec) discharges.
    Results, as plotted in Figure 40, Influence
of  Continuous Underflow  Draw-off,
Modification 11,  show  that  the efficiency
increased  with  the draw-off. This
phenomenon seemed more  pronounced for
small discharges 3,I/sec (0.8 gal/sec) than for a
high 7 I/sec (1.8 gal/sec) rate.
    Of importance is the fact that deposits of
solids  on the bottom of the  swirl chamber
disappeared  gradually  as  the underflow
draw-off rate was increased.

6. Influence of Inlet Size Modification 12
    Conditions  represented  by  Figure .41,
Model  Layout  for  Tests  60   to  68,
Modification 12, were  similar to those for
Modification 11, except that the  square inlet
pipe was reduced to  10.1 cm (4 in) instead of
the 15.2 cm (6 in) previously used. Trie same
draw-off, representing 5 percent  of the total
discharge,  was  maintained so  the  results
would be directly comparable.
    The recovery rate for the two  sizes  of
pipe inlets are shown in Figure 42, Influence
of Inlet Size. Although the  same inlet baffle
was used, Figure 41  shows that efficiency of
the swirl chamber dropped significantly when
the  inlet  velocity  was   increased.
Consequently, the 15.2 cm x 15.2 cm (6 in x
6 in)  inlet was  installed in! the model for
further tests.

Tests Carried Out with Petrothene
'Dust - SG 1.01
 0.12 mm < d < 0.5 mm (0.005 < d < 0.2 in)
    After the  model had been  set  up for
                                            62

-------
FLOW SPOILERS
OF SAME LENGTH
                                                          INLET
                                                      15.24 cm x 15.24cm
                                                       (6 in x 6in)
                                                        270  —

                                                         FOUL OUTLET
                                                              INLET
                                                              BAFFLE
WEIR UP 5cm
        (2 in )'
ELEVATION
 Section A-A
TO OVERFLOW TANK
                                            2.54 cm
                                            (1 in)
                                           FOUL OUTLET
          FIGURE 37  MODEL LAYOUT FOR TESTS 39 TO 41
                      MODIFICATION 10
                                 63

-------
FOUR  FLOW SPOILERS
OF SAME LENGTH
 INLET
15.24 cm x 15.24cm
 (6 in x6in)
TO OVERFLOW TANK
                                            FOUL OUTLET
                                            2.54cm (1 in.)
 Section A-A
           FIGURE 38  MODEL LAYOUT FOR TESTS 42 TO 59
                      AND 69 TO 107
                      MODIFICATION  11
                               64

-------
100
90
80
70
60
50
40
30
20
10
Qm I/sec C
(gal/sec)
Q I/sec
Q ft3 /sec
P
Q mgd


\
\
\ \
\ \
\ \
\ \
\ ~
\ *
\ \
\ \
\ \
\ \
\ \
\ \
\ \
\ ^
n\
i







D123456789
(.26) (.53) (.8) (1.1) (1.3) (1.6) (1.8) (2.1) (2.4)
DISCHARGE
i i i i i
0 50 IOO I50 200 250
I i i i i i ill
0123456789
1 | l 1 1 1
01 23456
0.61 m (24 in) Weir Diameter
n— • 	 •— D Horizontal Chamber floor Mod. II


Material used - Shredded Petrothene X nominal SG = 1.01
Grain Size 0.5 - 3mm irregular slopes
FIGURE 39  INFLUENCE OF CHAMBER FLOOR SLOPE
                (All tests carried out with inlet baffle
                and 5 percent Draw-off)
                       65

-------
















80


70
H-
0 60
•CC
LU
CL
> 50
LU
8 40
LU
CC
30
20
i r\
IU

\"
-.
~ .'.
- < . \\
•v \ •'•-
\. \\-.
\. \ o
\y ^ \~|
N. \ M^
\\\
\.NN\
^V » \
>VX\
\>°\
*\
Discharge
i i i i i i i
















Q,,, I/sec 0 1 23 4 5 6 7 8


°P

Qp

Qp






(gal/sec) (.26) (.53) (.8) (1.1) (1.3) (1.6) (1.8) (2.1)
I I I i I
I/sec 0 50 100 150 200 250
1 1 1 I I i i 1 1
cfs 0 1 2 34 5 6 7 89
1 1 | 1 II
mgdO 1 2 3 4 5 6


A— —A 1 n °/ " " / d U/nir ^



0 	 d 14% " " ( 15.2 x 15.2 cm (6x6 in))

Material Used: Shredded Petrothene X nominal SG 1.01
Grain Sizes 0.5 - 3 mm irregular shapes
FIGURE 40   INFLUENCE OF CONTINUOUS
           UNDERFLOW DRAW-OFF
           MODIFICATION 11
               66

-------
FOUR  FLOW SPOILERS
OF SAME LENGTH
- INLET

10.2 cm x 10.2 cm
   (4 in x4 in)
 TO OVERFLOW TANK
                                            FOUL OUTLET
                                              2.54cm (1 in )
  Section A-A
             FIGURE 41   MODEL LAYOUT FOR TESTS 60 to 68
                        MODIFICATION 12 - SG 2.65
                                67

-------









80
70

2 60
01
O
DC
uj 50
cc
% 40
O
0
LU
cc 30
20
10
0
I/sec
(gal/sec)



N •.
X°N\
x x\
NNN *\
N ^S.
"^^
I
1 | , i | i | 1
1 234 5678
(.26) (.53) (.8) (1.1) (1.3) (1.6) (1.8) (2.1)
Discharge
i ill i









0 I/sec 0 50 100 150 200 250
QP
QP

ft3/sec 0 ',2 3, 4 ,5 6, 7 |8 9|
mgd c

) 1 2 3 4 5 6
15.2 cm x 15.2 cm (6 in x 6 in) INLET SIZE. Mod. 11-5% Draw off

O-„.-._._o 10.1 cm x 10.1 cm (4 in x 4 in) INLET SIZE. Mod. 12-5% Draw off

           Material used: shredded Petrothene x nominal SG — 1.01
                       Grain sizes: 0.5 - 3 mm  (.02- .12 in)
                        irregular shapes
                FIGURE 42   INFLUENCE OF INLET SIZE
                                    68

-------
optimum  recovery, a new series of tests was
carried   out  with  Petrothene  dust.  The
configuration  corresponding to Modification
1, Figure  23,  was used, namely a 15.2 cm x
15.2 cm (6 in x 6 in) square inlet, and a 0.61
m (2 ft) diameter weir with 5.7 cm (2.25 in)
lip. The crest of the lip was  set at the same
elevation as the inlet crown; the flat chamber
floor was retained.
    The series of tests involved  the use of the
three respective discharges — 3,5, and 7 I/sec
(0.8,  1.3, and 1.8 gal/sec) in the model  with
varying draw-off rates (5, 10, and 14 percent).
This total of nine additional tests completed
the data necessary  to  prepare  the curves in
Figures 43, 44,  and 45, Suggested Recovery
Curves for Gilsonite and Petrothene in Model
with 5  percent,  10 percent, and  14 percent
Draw-off, respectively.

Predicted Prototype Grit Recovery
    As  mentioned,  the recovery  curves
attained for the Gilsonite  and Petrothene in
the model studies are as shown in Figures 43,
44, and 45.
    For the  three  model  discharges used in
the tests, the corresponding recovery rates are
given in Table 5, Percent Suggested Recovery
in Model.
    The recovery rates have been expressed as,
a function of the particle settling velocity, to
provide for more  effective use of the curves.
Plotting according to this method  gave the
curves represented  in  Figures  6,  7, and 8.
    The  advantage  of  this  method  of
presentation  is   that  it  allows  a  precise
interpolation  for  particle settling velocities
lying within the range  of  the materials used.
For example, to   find  the recovery  rate
corresponding  to   a  particle  whose  settling
velocity is 0.5 cm/sec (0.2 in/sec) with  10
percent draw-off, the values can be found in
Figure  33 on the  vertical  0.5  cm/sec (0.2
in/sec) at the respective intersections with the
3,  5, and 7 I/sec (0.8,  1.3, and  1.8 gal/sec)
discharges. Results are 66, 42, and 21 percent,
respectively.
    The  final  steps  in   calculating  the
predicted prototype recoveries are as follows:
a.  For  a  given  model  particle settling
    velocity  in either Figure 6, 7, or 8.  To
    find  the  recovery  rate  for  a  given
    discharge.
b.  Multiply  the particle_settling velocity by
    the velocity  scale, ^/ 4 = 2,   to find the
    particle settling velocity in the prototype.
c.  Use Figure 5 with this prototype particle
    settling  velocity  and  find  the
    corresponding grit size for SG 2.65.
d.  Multiply the given discharge in (a), above,
    by  the discharge scale 4s/2 = 32 to find
    the prototype discharge.
e.  Plot the  grit  particle size (c) as a function
    of discharge  (d)  and recovery rate (a) in
    Figures 9, 10, or 11.
    An example can be followed through this
procedure: in  Figure 8,  take the particle
settling velocity  of 0.8 cm/sec  (0.3  in/sec)
with a model discharge of 5 I/sec (1.3 gal/sec).
This  shows  a recovery  rate of  54 percent.
These particles in the prototype would have a
settling velocity of 2 x 0.8 =1.6 cm/sec (0.63
in/sec). In Figure 5, this gives a grit particle
size  of  0.16  mm  (0.006 in)  or  160/u.
Multiplying the  model  discharge of 5  I/sec
(1.3  gal/sec)  by  32  gives  160  I/sec  (42.2
gal/sec).  The  particle size,  discharge,  and
recovery rate  then define one point in Figure
.11, as shown.
    A network of points  was calculated for
each  of the draw-off rates  to give the families
of curves in Figures 9, 10, 11.
                                        TABLE 5
                      PERCENT SUGGESTED RECOVERY IN MODEL
Discharge
model
I/sec qal/sec
3 (0.8)
5 (1.3)
7 (1.8)
Gilsonite
Draw-off
5% 10% 14%
99.5 99.5 99.5
89 93 95
67 75 84
Shredded Petrothene
Draw-off
5% 10% 14%
66 73 81
44 50 54
23 27 31
Petrothene Dust
Draw-off
5% 10% 14%
46 52 56
25 28.5 33
12 14 18
                                            69

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     100


      90


      80


      70
  Z   60
  LU
  O
  DC
  S   50

  cc
  LU
  >   40
  o
  LU
  or
      30
      20
      10
Q_
 p
QL
    I/sec  0
    gal/sec
    I/sec
ft3/sec o

mcjd  o
                       Model
                      J	I
                           Discharge
                                                           Gilsonite
                                                           0.5 - 3 mm
                                                           (.02-.12 in)
                                                       Petrothene x
                                                       0.5 - 3 mm
                                                       .02 -.12 in)
                                                         Petrothene Dust
                                                         0.12 — 0.5 mm

                                                         (.005 - .02 in)
            1
           (.26)
 2
(.53)
 3
(.8)
 4
(1.1)
 5
(1.3)
 6
(1.6)
  7
(1.8)
 8
(2.1)
               50
        100
           150
               200
                I
                                                       250
                                                      	I
                                            PROTOTYPE
                                            ' DISCHARGE

                                            (SCALE 1/4)
            15.2 cm x 15.2 cm (6 in x 6 in ) INLET SIZE - INLET DEFLECTOR
             FIGURE 43   SUGGESTED RECOVERY CURVES FOR
                          GILSONITE AND PETROTHENE IN MODEL
                          WITH 5 PERCENT DRAW-OFF
                                    70

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      o
      cc
      8
      m
        100
         90
         80
         70
         60
         50
         40
         30
         20
         10
              felLSONITE
               0.5-3 mm
              (.02-.12 in)
SHREDDED
PETROTHENE 'X
  0.5-3 mm
 (.02-.12 in)

PETROTHENE
    DUST
 0.12-0.5 mm
 (.005 - .02 in)
Qm  I/sec
    (gal/sec)
                    I
                                                         I
                                                                I
     1
    (.26)
 2
(.53)
 3
(.8)
 4
(1.1)
                       5
                      (1.3)
 6
(1.6)
 7
(1.8)
 8
(2.1)
 9
(2.4)
                                DISCHARGE MODEL

                     DISCHARGE  PROTOTYPE  SCALE  I/4
   Qp  I/sec   0

   2p  ft3/sec
             1_
   T>  mgd   0
                                 I
                   I
 50
	I
                  IOO
                  150
                                                    _L
                    200
                              I
                                   I
                                         I
                                            I
     I
                         _L
                       J_
                         I
                                 8
                        250
                        	L_
        123456

 15.2 cm x 15.2 cm (6 in x 6 in.) INLET SIZE - INLET DEFLECTOR
          FIGURE 44   SUGGESTED RECOVERY CURVES FOR
                      GILSONITE AND PETROTHENE IN MODEL
                      WITH 10 PERCENT DRAW-OFF
                                   71

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   100
    90
    80
    70
Z  60
in
o
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a.  5O
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ui
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    20
    10
     0
I/sec    0
(gal/sec)
              I
                    I
             I
                    I
                          j_
 1
,26)
 2
(.53)
 3
(.8)
 4
(1.1)
                                          5
                                        (1.3)
 6
(1.6)
                                        GILSONITE
                                         0.5-3 mm
                                       (.02-.12 in)
                                       SHREDDED
                                       PETROTHENE
                                          0.5-3 mm
                                        (.02-.12 in)
                                       PETROTHENE
                                          DUST
                                        0.12-0.5 mm
                                        (.005 - .02 in)
 7
(1.8)
 8
(2.1)
                        DISCHARGE MODEL
               DISCHARGE PROTOTYPE SCALE
 9
(2.4)
                                    I/4
Qp  I/sec   0

Qp  ft3/sec  0
Q p  m g d
             I
                50
                          JL
              IOO
                 ISO
                                 _L
                        I
                             I
                                   I
                    200
                     I
                                                    I
                                 _L
                                     _L
                                                   8
                        250
                          I
        0123456

          15.2 cm x 15.2 cm (6 in. x 6 in ) INLET SIZE - INLET DEFLECTOR
        FIGURE 45   SUGGESTED RECOVERY CURVES FOR
                    GILSONITE AND PETROTHENE IN MODEL
                    WITH 14 PERCENT DRAW-OFF
                             72

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    After the range  of discharge of normal
operation  for  the  prototype  had  been
determined, computations were carried out to
determine the corresponding retention time.
The approach followed was to take the whole
volume of the chamber up to the circular weir
lip rest  level  and to  subtract  the volume of
                  both the weir and central overflow pipe. The
                  results of this computation are presented in
                  Figure 46, Retention Times for Prototype.

                                REFERENCES
                      7.  Hydraulique et Granulats,  Jean Larras,
                  Eurolles, Paris, 1972, 256 pp.
  
-------
                                      TECHNICAL REPORT DATA
                              (Please read Instructions on the reverse before completing)
 REPORT NO.
 EPA-600/2-76-271
                                                                3. RECIPIENT'S ACCESSION- NO.
 . TITLE AND SUBTITLE
 THE SWIRL CONCENTRATOR FOR EROSION
             RUNOFF TREATMENT
              5. REPORT DATE
               December 1976  (Issuing Date)
              6. PERFORMING ORGANIZATION CODE
 , AUTHOR(S)
 Richard H. Sullivan, Morris M. Cohn, James E. Ure,
 F. E. Parkinson, and Paul  E. Zielinski
                                                                 8. PERFORMING ORGANIZATI
                                                                                          REPOR
 PERFORMING ORG'VNIZATION NAME AND ADDRESS
 American Public Works Association
 1313 East 60th Street
 Chicago, Illinois 60637
              10. PROGRAM ELEMENT NO.

                       1BC611
              11. CONTRACT/GRANT NO.


                       68-03-0272
12. SPONSORING AGENCY NAME AND ADDRESS
 Municipal Environmental Research Laboratory - cin.,
 Office of Research and Development
 U.S. Environmental Protection Agency        \
 Cincinnati, Ohio 45268	
  OH
              13. TYPE OF REPORT AND PERIOD COVERED
                       FINAL
              14. SPONSORING AGENCY CODE
                   EPA/600/14
15. SUPPLEMENTARY NOTES                        i
 Supplement to "The Swirl Concentrator as a Combined Sewer Overflow Regulator Facility,"
 EPA-R2-72-008, September 1972 (NTIS PB-214 687). USEPA Project Officer: Richard Field,
16. ABSTRACT                                                           Telephone: 201-548-3347.
        A device for the partial removal of erosion products in stormwater runoff has been developed. The
    swirl concentrator as an erosion control device has been designed to concentrate the heavier soils from
    large flows. The concentrated underflow of up to 14 percent of the flow can be directed to a forebay
    or settling basin.
        The device is circular and for small watersheds a simple stock watering tank could be used with
    only minor modifications.
        The design of the swirl concentrator as an erosion control device is based upon a hydraulic model
    study and  research  previously sponsored by  the  City of Lancaster, Pennsylvania and  the U.S.
    Environmental Protection Agency into the mechanics of secondary motion flow^fields as developed in
    the swirl concentrator.
        This  report is submitted by the American Public Works Association in partial fulfillment of the
    contract 68-03-0272 between USEPA and APWA Research Foundation.
17.
                                   KEY WORDS AND DOCUMENT ANALYSIS
                    DESCRIPTORS
                                                   b.IDENTIFIERS/OPEN ENDED TERMS , C.  COS AT I Field/Group
  Overflows
  Design
  Flow rate
  Swirling—separation
  Waste treatment
 *Erosion control
  Soil  erosion
 *Solids separation
 * Swirl concentrator
  Overflow quantity
  Overflow quality
  Stormwaterl runoff
      13b
18. DISTRIBUTION STATEMENT

                  RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
  Unclassified
21. NO. OF PAGES
       82
                                                   20. SECURITY CLASS (Thispage)
                                                     Unclassified
                                                                                22. PRICE
EPA Form 2220-1 (9-73)
                                                 74
                         
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